Dissertations / Theses on the topic 'Nano-catalysis'
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Elrabei, Abubakar Osman Zina <1994>. "Supramolecular Catalysis in Confined Nano-space." Master's Degree Thesis, Università Ca' Foscari Venezia, 2022. http://hdl.handle.net/10579/20687.
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Supramolecular structures have emerged as a promising enzyme mimetic. In this study we focused on the resorcinarene hexamer which is a self assembled capsule that have been studied intensively due to it’s ready availability. The hexameric capsule shows some catalytic features reminiscent of natural enzymes include; substrate selectivity , stabilization of transition state and intermediate through secondary interactions, an inherent Bronsted acidity and it’s ability to act as a hydrogen bond catalyst.
Inside the cavity of the capsule reagents are confined in a restricted space in close proximity, such that they react faster .
Here in, It was shown how the catalytic activity of the capsule can be modulated in the presence of competitive alkyl ammonium guests in the profile of conversion of tri alkyl phosphite substrate to it’s corresponding di alkyl phosphite product.
The profile of the reaction was monitored using GC and NMR spectroscopy.
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Ahn, Sun Yhik. "Carbon based nano-composite interfaces for electro-catalysis." Thesis, University of Bath, 2016. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.698985.
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Electrochemical processes suffer from a number of challenges that needs to be overcome for widespread industrial adaptation. The need for an excess amount of inert supporting electrolyte in conventional three electrode set-ups with a single electrolyte medium makes synthetic applications uneconomical in both resource and sustainability aspects, and adds further complexities when the resulting product needs to be purified from the mixture which may also include the electro-catalyst. From an electro-analytical stand-point, altering the sample with the addition of high concentrations of electrolyte salt can have unpredictable chemical effects which may be difficult to account for in the analysis. The following results of the thesis addresses these issues by i) utilising triple-phase boundary systems where the electro-active species are kept in a separate phase from the source of electrons and ions, ii) introducing methods of heterogenising the electro-catalyst from the reaction mixture by immobilising in immiscible oils or polymers of intrinsic microporosity, and iii) offer practical application of such systems through the use of economical and technically unsophisticated methodologies. In the introduction the concept of an Integrated Chemical System is introduced where components with different functions can be synergistically combined and arranged to achieve a more complex output. In the context of electrochemistry, modifying electrodes with materials to add or improve activity, stabilise performance and to substitute more expensive materials, is desirable for enhanced control over the activity of an electrode. The first chapter begins with a general overview of various electrode modification strategies pioneered throughout the last few decades as an introductory narrative for the approach taken in the thesis. Integrated Chemical Systems synthesized and investigated in the thesis are as follows. In chapter 3, electrospun carbon nanofiber based triple-phase boundary systems are utilised for ion-transfer voltammetry across the liquid-liquid interface. Chapter 4 introduces a more conveniently prepared carbon microsphere-polystyrene composite, where the carbon is mechanically held together into a porous structure by an electrically insulating polymer binder. The porous carbon structure is demonstrated to be an effective host for organic oil analysis, under a triple-phase boundary set-up. Chapter 5 is also a study of a carbon-polymer of intrinsic microporosity composite, the polymer functions as a binder as well as a porous host for electrocatalytic guest molecules. Chapters 6 and 7 presents a novel hydrodynamic technique and its use in modulating mass transport in solution, which can be used as a diagnostic tool to study electrode processes at both modified and unmodified electrodes. Chapter 7 demonstrates the method’s utility through a mechanistic analysis of the organic free radical catalyst utilised in chapter 5. It is the hoped that the series of studies presented in the thesis addresses the issues with electrochemical processes at least in part through utilising economic materials and simple methodologies. Whilst the final outcome and devices presented are not fully optimised, they demonstrate a proof-of-principle of the main advantages of employing the modified electrodes. In future, better materials are needed to address the weaknesses of the composites investigated in the thesis to extract the full benefits offered by the electrochemical approach of chemical synthesis and analysis.
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Xu, Jiahui. "Catalytic properties of nano ceria in heterogeneous catalysis." Thesis, University of Oxford, 2010. http://ora.ox.ac.uk/objects/uuid:02e68ff9-ce28-475a-bd08-6b60bcda64e7.
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There have been many applications of cerium oxide in oxidation catalysis but the understanding of its role in catalysis is rather limited. This research is concerned with the use of nano-size cerium oxide in methane steam reforming reaction. It is found that addition of cerium oxide to the commercial supported Ni catalysts can dramatically reduce the undesirable carbon deposition (through surface oxidation), which is thermodynamically favorable under low steam conditions. In order to understanding the fundamental role of oxidation activity of the cerium oxide, different sizes of nano-crystallined cerium oxides have been carefully prepared by micro-emulsion technique. Their reactivity is clearly shown to be size dependent. We found that ceria particle sizes of lower than 5.1 nm are able to activate molecular oxygen, which accounts for the unprecedentedly reported critical size effect on oxidation. Characterizations by EPR, XPS, TPR suggest that a substantially large quantity of adsorbed oxygen species (O2 -) is preferentially formed in the small size ceria from air. Also, it is found that the oxygen vacancies are formed in the interface of metal and oxide, and the strength of the metal oxide interaction may influence the formation of the efficient oxygen vacancies, which are responsible for the adsorbed surface oxygen.
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Jegadeesan, Gautham. "Environmental catalysis using nano-sized bimetallic particles : selenium remediation /." Available to subscribers only, 2005. http://proquest.umi.com/pqdweb?did=1068236761&sid=29&Fmt=2&clientId=1509&RQT=309&VName=PQD.
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Zhang, Yeshui. "Hydrogen and carbon nano-materials from the pyrolysis-catalysis of wastes." Thesis, University of Leeds, 2017. http://etheses.whiterose.ac.uk/18509/.
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In this work, a two-stage fixed-bed reaction system was used for the production of carbon nanotubes along with hydrogen production from waste tyres and plastics from a pyrolysis-catalysis/catalytic-reforming process. The preliminary investigations concerned different metal catalysts (Ni/Al2O3, Co/Al2O3/ Fe/Al2O3 and Cu/Al2O3), which were investigated to determine the effects on carbon nanotube and hydrogen production by pyrolysis-catalysis of waste truck tyres. The results showed catalyst addition in the pyrolysis-catalysis of waste tyre process can increase hydrogen production. The Ni/Al2O3 catalyst gave the highest hydrogen production at 18.14 mmol g-1 along with production of relatively high quality carbon nanotubes which were homogenous. The influence of catalyst support was investigated with different SiO2:Al2O3 ratios (3:5, 1:1, 3:2, 2:1) with nickel. The results showed that the Ni-based SiO2:Al2O3 supported catalyst at a 1:1 ratio at 900 oC with sample to catalyst ratios at 1:2 gave the highest hydrogen production at 27.41 mmol g-1, and the 1:1 ratio gave the highest filamentous carbon production at 201.5 mg g-1. The influence of process parameters on hydrogen and CNTs production were investigated with the Ni/Al2O3 catalyst. Hydrogen production reached the highest amount which was 27.41 mmol g-1 at 900 oC with sample to catalyst ratio was 1:2. The highest filamentous carbon production was produced with the sample to catalyst ratio at 1:1 at 900 oC catalyst temperature. The water injection rates were also investigated, the results showed that water introduction inhibited filamentous carbon production but increased the hydrogen production. An in-depth study to better understand the process involved investigation of three different tyre rubbers and five tyre pyrolysis oil model compounds to understand the mechanism of carbon nanotubes formation in waste tyres by the pyrolysis-catalysis process. The results showed that natural rubber which is the main component of tyre samples which used for this thesis, dominated hydrogen production at 25 mmol g-1 and SBR gave the highest carbon formation which was 40 wt. %. The aliphatic model compounds (hexadecane and decane) favoured gaseous hydrocarbons formation instead of solid carbon formation, but the aromatic model compounds (styrene, naphthalene and phenanthrene) favour solid carbon formation where the majority of carbon formation was filamentous carbon. The study was extended to investigate waste plastics and different types of waste plastic feedstock used in the pyrolysis catalysis/catalytic reforming process to produce hydrogen and carbon nanotubes. As carbon nanotubes separation from the catalyst is a challenge for this project, the nickel metal catalyst was loaded on stainless steel mesh and applied in the high-density polyethylene pyrolysis-catalysis process. The benefit of this catalyst has been shown in that the carbon formation could be easily separated by physical shaking from the stainless steel-nickel mesh catalyst. However, further investigation on waste plastics was concentrated on hydrogen production and where carbon nanotubes were the by-product from the process. Fe-based and Ni-based catalysts as bimetallic catalysts supported by MCM-41 with different Fe:Ni ratios were investigated using simulated mixed waste plastics. A synergistic effect of the iron and nickel was observed, particularly for the (10:10) Fe/Ni/MCM-41 catalyst where the highest gas yield (95 wt.%) and highest H2 production (46.1 mmol g-1plastic) have been achieved. Along with lowest carbon deposition which was 6 wt.% with carbon nanotubes formation. Seven real world waste plastics were used to produce hydrogen and carbon nanotubes in the presence of a Fe:Ni at 10:10 ratio catalyst with an MCM-41 support. The results showed that the agricultural waste plastic gave the highest hydrogen production that was 55.99 mmol g-1 with carbon nanotubes formation. The calorific values of the produced gases from different plastic samples were in the range of 12.13 - 24.06 MJ m-3, which could provide the process fuel that shows the possibility to apply the technology for further larger scale of research.
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Kim, Kyungduk. "Novel Nanocatalyst for the Selective Hydrogenation of Bio-Oil Model Compounds." Thesis, The University of Sydney, 2016. http://hdl.handle.net/2123/16353.
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This thesis focuses on the understanding the effect of various factors, such as physical structures of metal particles, chemical composition of supports and metal-support interactions, on the catalytic performance of Pd or Pt nanocatalysts for hydrodeoxygenation (HDO) of bio-oil model compounds. The first part of the thesis addressed the alternative catalyst synthesis strategy based on emerging double-flame spray pyrolysis method (FSP), which was able to tune the catalytic properties of nanocatalysts without changing their precursors and chemical compositions during the synthesis. A series of Pd catalysts on the silica-alumina supports, SiO2- , and Al2O3 supports have been synthesized with the tunable surface properties within micro-seconds. The characterization results showed that various flow rates of precursors and gases used for the synthesis of catalysts influenced the formation of the catalyst structures and further change the surface acidity of catalysts due to the correlation between acidity and structure, but, the flow rates did not influence the electronic properties of Pd particles. Therefore, the higher conversion but the similar chemoselectivity have been reached in the hydrogenation of the bio-oil model ketone compound-acetophenone The second part is to identify the dominant effects from size of metal catalysts (under uniform shape and face) or the support acidity in the hydrodeoxygenation of the bio-oil model compounds of acetophenone, benzaldehyde, and butyrophenone. The uniform cubic Pd particles with different size (8, 13, and 21 nm) have been synthesized and loaded on the most popular supports (SiO2-, Al2O3-, and silica-alumina) with various functional groups and acidity. The results showed different acidities on the supports (Brønsted acidic site for Silica-alumina, Lewis acidic site for Al2O3-, and non/weak silanol OH group for SiO2- support) could not influence the chemoselectivity of the reaction but effected the conversion obviously. The particle size has more significant influence than the acidity. The smallest (8nm) Pd particle catalysts regardless of kinds of supports revealed the highest conversion for the hydrogenation the bio-oil model compounds. The third part focused on the influence of various types of catalysts with different acidities, chemical composition, and metal-support interaction on enantioselective hydrogenation of several model compounds in two reaction systems: 1). Pt-cinchrona modified system, and 2). Pd-(S) proline modified system. The result indicated acidic supports promoted the both conversion and enantioselectivity. Specially, Pd/SA made by double-FSP method, which has the highest Brønsted acid sites, showed 100 % conversion of isopherone on 60 min with 99% ee values.
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Garrido, Torres José A. "Density functional theory investigations of molecules on surfaces : from nano-electronics to catalysis." Thesis, University of St Andrews, 2017. http://hdl.handle.net/10023/15618.
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In this thesis, a wide breadth of topics related to the field of surface science are addressed using density functional theory (DFT). Specifically, five studies with relevance to molecular electronics and heterogeneous catalysis are presented, with a particular focus on interadsorbate interactions, reactivity and characterisation of molecules on transition metal surfaces. The first part of this work focuses on giving strong theoretical underpinning to the atomic-scale observations provided by scanning tunnelling microscopy (STM) experiments conducted by my group colleagues. The theoretical calculations presented here provide support to the experimental evidences but also serve to unravel information that is inaccessible from the experiments. On the one hand, the variety of results obtained in this thesis using standard DFT methods serve to highlight the capabilities of the computationally low-demanding methods for modelling processes occurring on metal surfaces. On the other hand, we notice that these workhorse methods in DFT have inherent limitations for providing an accurate description of some properties, in particular binding energies. This, further improvements in the level of theory are necessary for advancing the computational accuracy of standard DFT methods in materials science. The second part of this thesis is devoted to highlight the high level of accuracy obtained by the new theoretical approaches in the field of materials science. Due to the recent implementation of new algorithms combined with the increasing computer power that is available to the scientific community, these sophisticated methods are becoming more accessible for modelling solid-state systems. Here, the recent implementation of the random-phase approximation (RPA) for solids is employed to perform to benchmark study on the adsorption of benzene on different close-packed transition metal surfaces. The development of new theoretical tools is also essential to improve our predictive capabilities in surface science. A novel approach to correct vibrational intensities by including anharmonicities using density functional perturbation theory (DFPT) is proposed. The new method is tested for the adsorption of different organic molecules on various transition metal surfaces. The results obtained by this implementation demonstrate excellent improvements for predicting accurate spectra of molecules on surfaces.
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Snyder, Brian. "An investigation into bimetallic hollow nanoparticles in catalysis." Thesis, Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/47614.
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Nanocatalysis, catalysis using particles on the nanoscale, is an emerging field that has tremendous potential. Nanoparticles have different properties than bulk material and can be used in different roles. Macro sized precious metals, for example, are inert, but nanoparticles of them are becoming more widely used as catalysts. Understanding the manner in which these particles work is vital to improving their efficacy.
This thesis focuses on two aspects of nanocatalysis. Chapter 1 begins with a brief introduction into nanotechnology and some of the areas in which nanoparticles are different than bulk particles. It then proceeds into an overview of catalysis and nanocatalysis more specifically. Focus is brought to the definitions of the different types of catalysis and how those definitions differ when applied to nanoparticles. Chapter 2 is in finding an inert support structure to more easily assist in recycling the nanoparticles. Polystyrene microspheres were studied and found to prevent platinum nanoparticles from aggregating in solution and possibly aid in recycling of the nanoparticles. These nanoparticles were used in catalysis, aiding in the reduction of 4-nitrophenol in the presence of sodium borohydride. While the rate decreased by a factor of ~ 7 when using the polystyrene, the activation energy of the reaction was unaltered, thus confirming the inactivity of the polystyrene in the reaction.
In Chapter 3, nanocatalysis was studied by examining bimetallic hollow nanoparticles with specific attention to the effect of altering the ratios of the two metals. Ten different bimetallic nanocages were tested in an electron transfer reaction between hexacyanoferrate and thiosulfate. Five PtAg nanocages and five PdAg with varying metal ratios were prepared and studied. It was found that while silver cubes immediately precipitate out of solution when combined with thiosulfate, a small amount of either platinum or palladium allows the particles to remain in solution and function as a substantially more effective catalyst. However, as additional Pt was added the activation energy increased. To obtain a better understanding of the catalysis using bimetallic cages, the evolution of these cages was studied as the 2nd metal was added. Initially the particle edge length increased and then slowly decreased back to the size of the template cubes. The increase in edge length suggests of addition of material to the nanoparticles. This indicated the 2nd metal is on the outside of the cage, which was confirmed using UV-Vis spectroscopy and EDS mapping. By understanding how these bimetallic particles evolve, we may be able to manipulate these synthetic methods to more precisely design nanoparticles for catalysis.
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Duanmu, Chuansong. "Expanding applications of iron oxide nanoparticles by surface functionalization : from magnetic resonance imaging to nano-catalysis /." Available to subscribers only, 2009. http://proquest.umi.com/pqdweb?did=1967917191&sid=4&Fmt=2&clientId=1509&RQT=309&VName=PQD.
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Li, Richard Ph D. Massachusetts Institute of Technology. "Catalysis and manufacturing of two-scale hierarchical nano- and microfiber advanced aerospace fiber-reinforced plastic composites." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/120419.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2018.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 195-210).
The development of hierarchical nanoengineered "fuzzy fiber" aerospace fiber-reinforced plastic (FRP) composite laminates holds the potential for enabling future generations of lightweight, durable, and multifunctional vehicle structures. By reinforcing the weak matrix-rich regions between individual fibers and plies, the circumferential growth of aligned carbon nanotubes (A-CNTs) on carbon microfibers (CFs) enables new composites with improved strength, toughness, electrical and thermal properties. While these improvements have been empirically demonstrated on alumina fiber FRPs, CNT growth degrades the CFs and sacrifices in-plane FRP properties for the benefits of CNT reinforcement. This thesis presents novel and scalable methods for realizing advanced fuzzy carbon fiber reinforced plastic (fuzzy CFRP) composite laminates with retained CF and interlaminar strength properties. Earth-abundant sodium (Na) is revealed as a new facile catalyst for CNT growth that allows for direct deposition of the catalyst precursor on carbon fabrics without any fiber pretreatments. This new catalyst discovery also enables high-yield CNT growth on a variety of low-temperature substrates. Simultaneously, this finding has led to other novel findings in carbon nanostructure catalysis including a core-shell morphology and the use of other alkali metals (e.g., potassium) for CNT growth. Towards the development of advanced composites, vacuum-assisted resin infusion processes are studied and refined, resulting in high-quality woven and unidirectional fuzzy (via Na-catalysis of CNTs) CFRP laminates. Growth uniformity improvement studies yielded strategies for increasing the quantity of CNT reinforcement within matrix-rich regions. Moreover, a new commercial unidirectional fabric enables the first retention of CF properties concomitant with interlaminar shear strength retention in the fuzzy CFRP architecture. The contributions of this thesis extend beyond CF composites: techniques developed for improving fuzzy CF synthesis were applied towards demonstrating A-CNT growth on SiC woven fabric, desired for creating damage tolerant and multifunctional lightweight vehicle systems. These advances pave the way for improvements in catalysis of nanostructures, electronics interfaces, energy storage devices, and advanced composite materials.
by Richard Li.
Ph. D.
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Duanmu, Chuansong. "EXPANDING APPLICATIONS OF IRON OXIDE NANOPARTICLES BY SURFACE FUCNTIONALIZATION: FROM MAGNETIC RESONANCE IMAGING TO NANO-CATALYSIS." OpenSIUC, 2009. https://opensiuc.lib.siu.edu/dissertations/110.
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In this dissertation, research efforts mainly focused on exploring the applications of superparamagnetic iron oxide nanoparticles (SPIONs) in MR imaging and nanocatalysis via surface functionalization. A dopamine-based surface-functionalization strategy was established. The Simanek dendrons (G1 to G3), oligonucleotides and amino acids were loaded onto SPION surfaces via this approach to develop pH-sensitive MRI contrast agents, specific-DNA MR probes and a biomimetic hydrolysis catalyst. Dendron-SPION conjugates (G1 to G3) have good aqueous solubilities and high transverse relaxivities (>300 s-1*mM-1). They also showed interesting strong pH-sensitive R2 and R2* relaxivities, which were governed by the clustering states of dendron-SPIONs in different pH environments. Values of R2m and R2* m/R2m varied by over an order of magnitude around pH 5. The efficient cell-uptake (~3 million/cell) and low cytotoxicity of G1 to G3-SPIONs were demonstrated on HeLa cell cultures. The strong R2* effects were observed indicating the SPION clustering in HeLa cells. Two SPION-oligonuleotide conjugates were synthesized by coupling two half-match oligonucleotides onto domapine-capped SPIONs via SPDP linkers. They served as MR probes to detect a single-strand DNA with the same sequence to miRNA-21 based on the change of R2 values due to the DNA-bridged SPION clustering. The detection limit of the DNA could reach to 16.5 nM. A biomimetic hydrolysis nanocatalyst (i.e., Fe2O3-Asp-His complex) was developed by loading Asp and His-dopamine derivatives onto SPIONs. Paraoxon and nitrophenyl acetate were hydrolyzed under a mild condition (neutral pH, 37 °C) catalyzed by the Fe2O3-Asp-His complex. The two amino acids Asp and His cooperated with each other on the SPION surfaces to catalyze hydrolysis reactions. This catalyst could be recycled by a magnet and reused for four times without a significant loss of catalytic activity.
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Li, Wai Chung. "Preparation and characterization of noble metal-magnetite hybrid nano/micro composites towards drug delivery and heterogeneous catalysis." HKBU Institutional Repository, 2019. https://repository.hkbu.edu.hk/etd_oa/668.
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This thesis describes the preparation and characterization of core-shell noble metal-magnetite hybrid hollow nanocomposites utilizing hierarchical architecture. The hollow magnetite (hFe3O4) nanoparticles were prepared by hydrothermal method, forming the cavity via Oswald ripening. Further surface modifications involved both inorganic and organic coatings, conferring the intracellular drug delivery ability and the catalytic enhancement. In the first part, a series of hierarchical core-shell nanostructures flower-like hFe3O4@AlOOH was synthesized through solvothermal method and sol-gel process. The formation of cavity accessible hFe3O4@γ-AlOOH was achieved using silica-templated solvothermal treatment where the Kirkendall effect was observed. The morphologies of the as-prepared nanocomposites were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), dynamic light scattering (DLS), thermogravimetric analysis (TGA) and Fourier-transform infrared spectroscopy (FTIR). Then, the nano-encapsulation of platinum drug using hollow magnetite and its derivatives, has been developed with improved loading efficiency via co-solvent system. A dimethylformamide/water co-solvent system was found to be the most efficient system to encapsulate water-insoluble cisplatin. The platinum content was further quantitatively and qualitatively analyzed by inductively coupled plasma mass spectrometry (ICP-MS) and FTIR spectroscopy. The enhancement of loading efficiency could be driven by emulsification due to the diffusion of hydrophobic cisplatin into the hollow cavity of iron oxide nanoparticles. By incorporating water, the loading efficiency of hFe3O4 and hFe3O4@γ-AlOOH increased from 1-2% to 27% and from 6% to 54%, respectively. The grafting of cisplatin on AlOOH nanoflakes might account for the high loading efficiency of flower-like hFe3O4@AlOOH. As a complement to naked hFe3O4, a cell-penetrating poly(disulfide)s (CPD)-decorated hollow iron oxide nanoparticle was synthesized by immobilizing both cysteine and MPTMS as an initiator, followed by in situ polymerization to form hFe3O4-Cys-CPD-CONH2 and hFe3O4-MPS-CPD-CONH2. The morphologies were characterized by TEM/energy-dispersive X-ray spectroscopy (TEM/EDX) and the compositions of the as-prepared iron oxide nanocomposites were characterized by TGA, FTIR and X-ray photoelectron spectroscopy (XPS) and ICP-MS. The CPD coating not only serve as a protective layer, but also prevent the encapsulated cisplatin from a premature release. The hFe3O4-MPS-CPD-CONH2 exhibit promising features for the intracellular delivery of cisplatin, demonstrating a glutathione (GSH)-responsive drug release. Comparing with other hFe3O4 nanoparticles, an enhancement of cellular uptake of hFe3O4-MPS-CPD-CONH2 could be observed by optical microscope, showing rapid accumulation of the hFe3O4-MPS-CPD-CONH2 nanocomposites in the primary human renal proximal tubular epithelial cells (HRPTEpiCs) cell in 2 h. At 24 h, hFe3O4 (F), hFe3O4-MPS (FS) and hFe3O4-MPS-CPD-CONH2 (FSC) together with cisplatin treatment did not cause any significant cytotoxicity to the cells when the particle concentration is less than 10 µg/mL. Interestingly, FSCC showed a certain extent of toxicity with increasing Fe and Pt concentration along with the treated time. It may suggest that the hFe3O4-MPS-CPD-CONH2 nanoparticle, as a cisplatin carrier, could enhance the drug efficiency by increasing cellular uptake of the nanoparticles in HRPTEpiCs together with the boosted cytotoxicity. Based on these data, cisplatin- hFe3O4-MPS-CPD-CONH2 (FSCC) treatments with the concentration less than 20 µg/mL and duration no more than 24 h could maintain around 70% of the cell viability of the HRPTEpiCs. The hypothesis, at which CPD serves as an efficient carrier for intracellular cisplatin delivery, could be confirmed by both microscopic images and the cell viability test. In the second part, a series of Au/Fe3O4 hybrid nanocomposites was prepared to investigate their catalytic efficiencies using 4-nitrophenol reduction as a model system. The flower-like hFe3O4@γ-AlOOH@SiO2-NH2@Au was prepared by using protonated ammonium on hFe3O4@γ-AlOOH@SiO2-NH2 to entangle gold nanoparticles (AuNPs) via electrostatic attraction. In comparison to numerous of catalytic studies, the turnover frequency (TOF) of hFe3O4@γ-AlOOH@SiO2-NH2@Au shows a superior conversion rate up to 7.57 min-1 (4-nitrophenol per Au per min) for the 4-nitrophenol using sodium borohydride as a reductant. A rapid conversion of 4-nitrohpenol was observed using flower like composites that converted the 4-nitrophenol within 2 min. Our result suggests that silica residue hinders the reduction rate of the 4-nitrophenol. A significant deviation from pseudo first order was observed for densely AuNPs-functionalized nanoflower system, hFe3O4@γ-AlOOH@SiO2-NH2@Au2X, which is different from most of the 4-nitrophenol reductions reported in literature. The hFe3O4@γ-AlOOH@SiO2-NH2@Au also demonstrates catalytic activity when heated up to 800 °C before reduction. The recyclability was examined using magnetically recycled hFe3O4@γ-AlOOH@SiO2-NH2@Au, which showed insignificant decrease in the catalytic efficiency. To prove the concept, platinum nanoparticles (PtNPs) immobilized hFe3O4@γ-AlOOH@SiO2-NH2@Pt and hFe3O4@γ-AlOOH@SiO2-NH2@Pt/Au were also prepared via electrostatic attraction to verify the feasibility of endowing modular functionality via post modification.
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Kisurin, Vitaly Mr. "Laser Vaporization Controlled Condensation and Laser Irradiation in Solution for the Synthesis of Supported Nanoparticle Catalysts." VCU Scholars Compass, 2016. http://scholarscompass.vcu.edu/etd/4636.
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Solid catalyst supports of SiOx-RGO (Reduced Graphene Oxide) and UiO-67 (Universitet i Oslo) have been successfully synthesized and were loaded with palladium nanoparticles to test for a series of heterogeneous reactions. The SiOx/RGO catalysts were synthesized through laser ablation of silicon and graphite oxide micron powder and UiO-67 metal-organic framework (MOF) was synthesized through mixing of precursors with DMF/HCl solution and washing the resultant powder from impurities. The SiOx/RGO supports were later impregnated with palladium precursors which were then subject to Microwave Irradiation (MWI). The UiO-67 framework was impregnated with palladium precursors and was irradiated with pulsed Nd:YAG 532 nm laser and was purified through washing and centrifugation. The resulting catalyst supports were characterized with UV-Vis, FTIR, Raman, XRD and XPS techniques and the UiO-67 framework was subject to Brunauer-Emmet-Teller (BET) surface area measurements before and after the catalytic reactions. The catalytic activity of palladium nanoparticles supported on SiOx/RGO and UiO-67 framework was tested in carbon cross-coupling reactions of Suzuki-Miyaura, Sonogashira reactions and oxidation of benzyl alcohol respectively. The catalysts have demonstrated excellent performance and have yielded a promising future for the catalytic supports in the previously stated reactions.
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Hajar, Yasmine. "Effect of Electrochemical Promotion and Metal-Support Interaction on Catalytic Performance of Nano-catalysts." Thesis, Université d'Ottawa / University of Ottawa, 2019. http://hdl.handle.net/10393/39701.
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In heterogeneous catalysis, promoting the activity of the catalytic metals is long known as an important method to make a process more efficient and viable. Noble metals have been promoted classically by a chemical coverage of an ionic solution on the surface of the catalyst or using inert support, e.g., silica or alumina, allowing an increase of the dispersion of the catalyst. Therefore, new methods of promotion needed to be better explored to improve the efficiency of metal and metal oxide catalysts. One way of enhancing the catalyst’s activity is to disperse the noble metal at the nanoscale using an active type of support that is ion-conducting. Not only lattice ions can be exchanged with the surface of the nanoparticles but it can also engage in the oxidation reaction on the surface, resulting in what is known as metal-support interaction (MSI). Another method of improving the catalytic activity is to polarize the catalyst, allowing ions to migrate from a solid electrolyte to the gas-exposed surface, in a phenomenon known as electrochemical promotion of catalysis (EPOC). The change in the ions concentration on the surface would change the adsorption energy of the gaseous reactants and enhance or supress the catalytic rate.
In this thesis, the effect of supporting nanoparticles of noble and non-noble metal (oxides) (Pt, Ru, Ir, Ni) was studied for the case of ionic and ionic-electronic conducting supports (CeO2, TiO2, YSZ). The enhancement in their catalytic rate was found and correlated to an electrochemical property, the exchange current density. Then, using isotopically-labeled oxygen, the oxygen exchange ability of the conductive oxides was evaluated when supporting Ir and Ru nanoparticles and correlated with the results from C3H8 isotopic oxidation reaction, which showed the extent of involvement of oxygen from the support as carried by the isotopically-labeled CO2 produced.
Following this, electrochemical promotion of catalysis experiments were performed for different reactant/catalyst systems (C2H4 - Pt, Ru; C3H8 - Pt; CH4 - Pd, Ni9Pd). In the first system, the main outcome was the functional equivalence found for the MSI and EPOC effect in promoting the catalysts as experiments were performed at different temperatures, reactants partial pressures and polarization values. In the case of C3H8/Pt, the novel dispersion of Pt on an intermediate supporting layer (LSM/GDC) was found as a feasible method to obtain long stability of the catalyst while electrochemically promoting the rate of reaction. For CH4 oxidation, the polarization of the Pd nanoparticles showed continuous oxidation of the bulk of the catalyst resulting in a continuous increase of the catalytic rate. The Ni9Pd synthesized in a way to form a core/double-shell layer of Ni/Pd resulted in an enhanced catalytic rate and enhanced stability compared to stand-alone Pd.
And lastly, to comprehend the ions’ effect in the electrochemical promotion and the non-Faradaic nature of the phenomena, density-functional theory (DFT) modeling was used to demonstrate the increase of the heat of adsorption of reactants depending on their electronegative/positive nature.
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Harmel, Justine. "Synthèse de nano-catalyseurs hybrides à base de cobalt pour la catalyse Fischer-Tropsch." Thesis, Toulouse, INSA, 2016. http://www.theses.fr/2016ISAT0035/document.
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En raison de la raréfaction des ressources de pétrole et des variations des prix avec le contexte géopolitique, la réaction de catalyse de Fischer-Tropsch qui permet la production d’hydrocarbures à partir du mélange syngas des gaz CO et H2 en présence d’un catalyseur à base de fer ou de cobalt, présente aujourd’hui un regain d’intérêt tant de la part des industriels que des académiques. Bien que découverte en 1923 par les allemands Franz Fischer et Hans Tropsch, les mécanismes qui entrent en jeu lors de cette réaction et les paramètres importants des propriétés des catalyseurs demeurent encore incertains. Dans ce contexte, les travaux présentés dans cette thèse visent à étudier l’impact de paramètres tels que la structure cristallographique et la forme de nano-objets de cobalt, phase active du catalyseur pour cette réaction. Ceci passe par la synthèse de catalyseurs modèles à base de nano-objets de cobalt et l’étude de leurs propriétés catalytiques. Dans un premier temps, la préparation d’un catalyseur à base de cobalt présentant une structure cristallographique hcp et une morphologie anisotrope a été réalisée, via une voie de synthèse par décomposition d’un précurseur organométallique de cobalt, conduisant à la formation de nano-objets de cobalt anisotropes. Puis, des tests catalytiques ont été réalisés en réacteur slurry, en collaboration avec un partenaire industriel, l’IFP-EN. Cela a permis la réalisation de tests Fischer-Tropsch en conditions proches des conditions industrielles réelles. Ces études ont permis de mettre en évidence la très grande stabilité de ces catalyseurs en comparaison à des catalyseurs de référence.Enfin, différents catalyseurs à base de cobalt, supportés sur des supports originaux de type macrostructurés permettant une meilleure gestion des échanges thermiques de la réaction, ont été préparés et leurs propriétés catalytiques étudiées sur un réacteur de type lit-fixe, mis en œuvre durant cette thèseDue to the decreasing the oil resources, and because of the the fluctuations of the price as a result of the geopolitical context, the Fischer-Tropsch synthesis, that enables the production of hydrocarbons form the syngas mixture (CO and H2) in the presence of a catalyst based on cobalt or iron, has recently gained a renewed interest from industrial as well as form the academic communities. Although this reaction was discovered in 1923 by the Germans Franz Fischer and Hans Tropsch, the mechanisms that come into play during this reaction and the crucial properties of the catalyst properties remain uncertain. In this context, the work presented in this thesis, aims to investigate the impact of parameters such as the crystallographic structure and the shape of the cobalt nano-objects, which is the active phase of the catalyst for this reaction. For this purpose, model cobalt nano-objects were synthetized and their catalytic properties were studied. As a first step, a cobalt based catalyst exhibiting an hcp crystallographic structure and an anisotropic shape was prepared via a synthetic route involving the decomposition of an organometallic precursor of cobalt and leading to the formation of anisotropic cobalt nano-objects. Catalytic tests were then conducted in a slurry reactor, in collaboration with an industrial partner, IFP-EN. This collaboration allowed performing catalytic studies under conditions that are very close to the actual industrial conditions. These studies revealed an increased stability of these catalysts compared to reference catalysts that deactivate with time. Finally, several cobalt-based catalysts, supported on innovative supports, such as macrostuctured supports, allowing a better control of the exothermicity, were prepared and their catalytic properties studied on a fixed-bed reactor that was set up during the course of this thesis work
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Wierzbicki, Dominik. "New nano-oxide catalysts for CO2 hydrogenation reaction." Thesis, Sorbonne université, 2019. http://www.theses.fr/2019SORUS420.
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L’augmentation de la concentration de CO2 dans l'atmosphère, considérée comme l'une des sources anthropiques du réchauffement de la planète, suscite de plus en plus d'inquiétudes et une prise de conscience sociale face au changement climatique. Les stratégies de réduction des émissions de CO2 peuvent être divisées en deux groupes (i) capture et stockage du carbone (CCS) et (ii) capture et utilisation du carbone (CCU). En comparaison avec le CCS, les technologies CCU permettent de convertir le dioxyde de carbone en un produit valorisé. Ainsi, les méthodes CCU traitent le CO2 en tant que matière première et non en tant que polluant. Parmi les processus convertissant le CO2 en un composé valorisé, on trouve la méthanation du dioxyde de carbone. Dans ce processus, le dioxyde de carbone est hydrogéné en méthane à l’aide de l'hydrogène provenant de l’électrolyse de l'eau en utilisant par exemple des excès d'énergie. Il convient de mentionner qu’une installation à l’échelle industrielle existe déjà (jusqu’à 10 MW). La littérature suggère que le nickel est le métal actif le plus approprié dans ce procédé en raison de (i) sa très bonne activité catalytique (comparable aux métaux nobles), (ii) un faible coût et (iii) une grande disponibilité. Dans la littérature, différentes stratégies ont déjà été mises en œuvre afin d'accroître l'activité des catalyseurs à base de Ni lors de la méthanation du CO2. Les plus courants incluent l’utilisation de divers supports, la modification de la teneur en nickel ou l’introduction de promoteurs. De telles stratégies modifient les propriétés physicochimiques telles que l'interaction entre la phase active au nickel et le support, ce qui inhibe le frittage et augmente la capacité d'adsorption du CO2. Ces deux propriétés sont essentielles afin d’obtenir un catalyseur à la fois actif et sélectif pour la méthanation du CO2. L’application d’oxydes mixtes de magnésie et d’alumine permet d’introduire ces propriétés car le MgO possède un caractère basique et est fortement lié au NiO en raison de la formation d’une solution solide de NiO-MgO. Les hydrotalcites semblent être les matériaux les plus prometteurs pour une telle application car NiO, MgO et Al2O3 peuvent être facilement introduits dans ceux-ci. La littérature a confirmé que les hydrotalcites contenant du Ni sont très actifs dans cette réaction. L'objectif de cette thèse était donc d'évaluer les propriétés catalytiques d'oxydes mixtes dérivés d'hydrotalcite contenant du Ni lors de la méthanation du CO2. Comme la revue de littérature a montré qu'il y avait peu d'études sur de tels matériaux pour cette réaction, ces travaux ont servi à combler ces lacunes. Ces travaux peuvent être divisé en quatre parties : (i) évaluation des propriétés catalytiques d’hydrotalcites contenant diverses quantités de nickel dans des couches de type brucite, (ii) évaluation des propriétés catalytiques d’hydrotalcites contenant du nickel activées à l'aide de Fe ou de La, (iii) évaluation de l'effet de la méthode d'introduction de La sur les propriétés catalytiques des Ni-hydrotalcites et (iv) optimisation des catalyseurs et examen de l'effet promoteur de La. Afin de corréler les modifications des propriétés physico-chimiques des matériaux préparés par co-précipitation, les catalyseurs ont été caractérisés par analyse élémentaire (ICP-MS ou XRF), DRX, IRTF, sorption de l’azote à basse température, H2-TPR et CO2-TPD. De plus, les catalyseurs sélectionnés ont été caractérisés par TEM, XANES et XES. Les tests catalytiques ont été effectués dans une plage de températures allant de 250°C à 450°C. Afin d'examiner l'effet de promotion de l'introduction du lanthane, les méthodes XANES et XES dans diverses conditions de réaction ont été mises en œuvre. (...)The increasing concentration of CO2 in the atmosphere, which is considered to be one of the anthropogenic sources of global warming, increased concerns and social awareness about the climate change. The strategies for CO2 emissions reduction may be divided into (i) carbon capture and storage (CCS) and (ii) carbon capture and utilization (CCU) groups. In comparison to CCS, the CCU technologies allow to convert carbon dioxide into a valuable product. Thus, CCU methods are treating CO2 as raw material and not as pollutant. Among the processes that convert CO2 into a valuable compound is carbon dioxide methanation. In this process carbon dioxide is hydrogenated to methane with hydrogen supplied via water electrolysis using e.g. excess energy. It should be mentioned that some industrial scale installation already exists (up to 10MW). The literature study suggests that the most appropriate active metal in this process is nickel due to (i) very good catalytic activity (comparable to noble metals), (ii) low cost and (iii) availability. As reported in literature, different strategies were implemented in order to increase the activity of Ni-based catalysts in CO2 methanation. The most common ones include using various supports, changing the content of nickel or introduction of promoters. These strategies change the physicochemical properties, such as interaction of nickel active phase with the support, which inhibits sintering and increases the CO2 adsorption capacity. The latter property , as well as stability towards sintering, are crucial in order to obtain an active, selective and stable catalyst for CO2 methanation reaction. The application of mixed oxides of magnesia and alumina allows to introduce these properties, as MgO possesses basic character and is strongly bonded with NiO due to the formation of a solid solution of NiO-MgO. Hydrotalcites seem to be the highly promising materials for such application, because NiO, MgO and Al2O3 may be easily introduced into such materials. Literature studies confirmed that Ni-containing hydrotalcites are very active in CO2 methanation. Therefore, the goal of this PhD thesis was to evaluate the catalytic properties of Ni-containing hydrotalcite-derived mixed oxide materials in CO2 methanation. As the literature review showed that there are not many studies focused on such materials in the mentioned field, this work was focused on filling these gaps. The work was divided into four parts: (i) evaluation of catalytic properties of hydrotalcites containing various amounts of nickel in brucite-like layers, (ii) evaluation of catalytic properties of nickel-containing hydrotalcites promoted with Fe or La, (iii) evaluation of the effect of different methods of introduction of La on catalytic properties of Ni-hydrotalcites, and (iv) optimization of the catalysts and examination of promoting effect of La. In order to correlate the changes of physico-chemical properties, of the materials prepared by co-precipitation, the catalysts were characterized by means of elemental analysis (ICP-MS or XRF), XRD, FTIR, low temperature nitrogen sorption, H2-TPR and CO2-TPD. Additionally, selected catalysts were characterized using TEM, XANES and XES. The catalytic tests were carried out in the temperature range from 250°C to 450°C. In order to elucidate the promoting effect of lanthanum introduction operando XANES and XES under various reaction conditions were implemented. (...)
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Assaud, Loic. "Fonctionnalisation de substrats nano-structurés pour la conversion et le stockage de l'énergie." Thesis, Aix-Marseille, 2013. http://www.theses.fr/2013AIXM4049.
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Afin de répondre au besoin de la société actuelle qui utilise toujours plus de moyens de transport et de dispositifs portables, les modes de production, de conversion et de stockage de l'énergie, sont en train de connaître de véritables mutations. Afin de créer des systèmes capables de générer une énergie maîtrisée et renouvelable, les nanosciences et nanotechnologies sont des domaines de premier plan. Le travail présenté dans ce manuscrit décrit la fabrication de structures, de taille nanométrique, organisées à grande échelle. La fonctionnalisation se fait par synthèse de films ou de particules par ALD. Des systèmes MIM sont synthétisés sur des structures ordonnées d'alumine poreuse. Les matériaux déposés en couches minces sont TiN, Al2O3 et HfO2. L'objectif est de fabriquer des nano-condensateurs à hautes performances pouvant être utilisés pour des applications de stockage de données, de mémoire ou pour le stockage d'énergie dans des petits dispositifs comme la technologie RFID.Dans une deuxième partie, des catalyseurs métalliques Pd/Ni sont déposés sur des membranes d'alumine pour l'électro-oxydation de l'acide formique. De la même manière, des nano-tubes de TiO2 fabriqués par oxydation anodique sont fonctionnalisés par des nano-particules de Pd pour l'électrooxydation de l'éthanol. Ces deux études systèmes peuvent conduire à leur utilisation comme catalyseurs au niveau de l'anode des piles à combustible liquide à combustion directe. Enfin, la dernière partie de ce travail consiste au dépôt par voie électrochimique de Cu2O, sur des nano-tubes de TiO2 qui servent de support. La jonction p/n ainsi fabriquée pourra servir pour la photo-conversion de l'énergie solaireIn order to meet the growing needs in today's society that requests more transportation and portable devices, energy production, conversion and storage systems are now experiencing real changes. To fabricate systems able to generate a controlled and renewable energy, nanoscience and nanotechnology are leading research fields. The work presented in this manuscript describes the fabrication of nanosized, large-scale organized structures. These nanostructures have been functionalized through film and particle synthesis using a chemical vapor deposition method: the Atomic Layer Deposition (ALD).Thus, metal/insulator/metal (MIM) systems are fabricated on highly-ordered high-aspect ratio porous alumina. The materials that have been deposited are TiN, Al2O3 and HfO2. The aim is to produce high performance nanocapacitors that can be used for data storage (DRAM) application or for energy storage in small devices such as RFID.In a second part, metallic catalysts such as Pd/Ni have been deposited on alumina membranes for formic acid electro-oxidation. Similarly, TiO2 nanotubes have been fabricated by anodic oxidation and they have been functionalized with Pd nanoparticles for ethanol electro-oxidation. Both studied systems can be used as anode catalysts in direct liquid fuel cells.Finally, the last part of this work has consisted in the study of Cu2O, as a p-type semiconductor, that has been electrochemically deposited onto TiO2 nanotubes (n-type semiconductor). The resulting p/n junction can be interesting for solar energy photoconversion
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Mongin, Cédric. "Synthèse et étude de cages moléculaires photo-modulables et génération de nano-cristaux d’or par photo-catalyse supramoléculaire." Thesis, Bordeaux 1, 2013. http://www.theses.fr/2013BOR14996/document.
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Les objectifs de cette thèse sont articulés autour de deux axes principaux : la synthèse et l’étude de cages moléculaires photo-modulables, et la génération de nano-cristaux d’or par photo-catalyse supramoléculaire. Ces deux thématiques sont reliées entre elles par l’exploitation des propriétés photophysiques et photochimiques d’un motif commun, le 9,10-diphénylanthracène (DPA). Dans un premier temps, de nouvelles architectures tridimensionnelles photo-modulables de type cage moléculaire ont été conçues et étudiées. En présence d’oxygène, l’irradiation directe ou sensibilisée du DPA permet de former réversiblement le dérivé endoperoxyde et ainsi moduler les propriétés de complexation de la cage. Les différentes stratégies de synthèse mises en place reposent sur l’exploitation conjuguée de la réactivité de la 2,4,6-trichloro-1,3,5-triazine, et de réactions de chimie « click » (métathèse des oléfines, cycloaddition de Huisgen). L’étude et la modulation des propriétés des reconnaissances ont été effectuées sur des sels de cations alcalins (sodium et césium) et suivies par émission de fluorescence et spectroscopie d’absorption UV-visible. Les résultats obtenus avec deux cages possédant des constantes d'associations élevées (logK = 8,7 pour le cation sodium) montrent une augmentation de la constante d’association d’un facteur 10 et 20 pour respectivement le sodium et le césium entre la forme DPA et la forme endoperoxyde. Dans un second temps, des photocatalyseurs supramoléculaires basés sur le chromophore DPA ont été étudiés en vue de la synthèse de nano-cristaux d’or nus. L’association du chromophore avec des thioéthers permet de former un complexe en phase organique par extraction de sels d’or(III) depuis une phase aqueuse. L’irradiation à 400nm permet la réduction de l’or(III) par transfert d’énergie depuis le 9,10-diphénylanthracène. Les atomes d’or sont ensuite relargués en phase aqueuse pour former des nano-cristaux nus qui ont pu être caractérisés par MET, XPS, AFM et DLS. Par ailleurs, ce procédé est catalytique dans le toluène et un système de réduction en flux continu a été mis au point permettant un turnover moyen de 150The goals of this thesis are organized around two major axes: the synthesis and study of photo-gated molecular cages, and the generation of gold nanocrystals by supramolecular photocatalysis. These two themes are connected by the use of the photochemical and photophysical properties of a common chromophore, 9,10-diphenylanthracene (DPA). Three-dimensional photo-gated cage-like architectures were designed and synthesized. Various synthetic strategies based on the combined use of the 2,4,6-trichloro-1,3,5-triazine unit and "click" chemistry reactions (olefin metathesis, Huisgen cycloaddition) were employed for the synthesis. In the presence of oxygen, sensitized or direct irradiation of the DPA chromophore forms the corresponding endoperoxide derivative, thereby modulating the binding properties of the cage. The study and the modulation of the recognition properties were performed on various alkali metal cations and a strong binding of sodium and cesium was evidenced by fluorescence emission and UV-visible absorption spectroscopy. The cages investigated possessed high association constants towards sodium and cesium cations (logK = 8.7 for the sodium cation) which could be reversibly increased by a factor 10 and 20 for sodium and cesium, respectively, upon formation of the endoperoxide. Supramolecular photocatalysis of gold(III) reduction based on the DPA chromophore was also studied for the preparation of uncapped gold nanocrystals. The combination of the DPA chromophore with thioether chains allows the formation of a complex in the organic phase by extraction of gold(III) chloride from an aqueous phase. Irradiation at 400 nm enables the reduction gold(III) by energy transfer from the 9,10-diphenylanthracene followed by oxidation of the solvent. The gold atoms are subsequently released in the aqueous phase to form uncapped nanocrystals characterized using TEM, XPS, AFM, and DLS techniques. Furthermore, the process is catalytic in toluene, where a continuous flow reactor was developed. The latter allowed an average catalytic turnover of 150 to be determined
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Souza, Edith Marie Malateaux de. "Adesivo de contato de policloropreno base aquosa nanoaditivado e condicionado magneticamente." Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/3/3133/tde-21062016-113107/.
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Atualmente, os adesivos de contato de policloropreno base aquosa, possuem capacidade de adesão, variando entre 1,15 até 2,75 kgf/cm2. Em contrapartida, os adesivos de policloropreno base solvente, suportam tensões médias de cisalhamento de 3,8 kgf/cm2. Esta pesquisa apresenta uma proposta inovadora de condicionamento magnético do adesivo de contato de policloropreno base aquosa com o objetivo de aumentar a capacidade de aderência entre o adesivo e o substrato. Para promover um incremento na capacidade de adesão do adesivo de policloropreno base aquosa, formulou-se um adesivo utilizando um nanoaditivo, o gás carbônico como catalisador e um processo de condicionamento magnético precedente à etapa de aplicação sobre os substratos. Os resultados obtidos demonstraram aumento médio de 292 % na tensão de cisalhamento do adesivo condicionado magneticamente quando comparado com o adesivo de mesma formulação sem o condicionamento magnético, e quando comparado com um adesivo comercial de policloropreno base aquosa, o aumento foi de 122 %.Currently, the aqueous based polychloroprene contact adhesive presents an adhesion capacity variation between 1,15 and up to 2,75 kgf/cm2. However, the solvent based polychloroprene adhesives support average tensions of shearing of 3,8 kgf/cm2. This research is an innovative proposal for magnetic conditioning of the aqueous based polychloroprene contact adhesive with the purpose of increasing the adherence capacity between the adhesive and the substrate. To promote an increase of adhesion to the aqueous based polychloroprene contact adhesive, we formulated one adhesive using a nano-additive, carbon dioxide as catalyst, and a magnetic conditioning process before the phase of application on the substrates. The results obtained show an average increase of 292 % in the shearing tension of the adhesive magnetically conditioned when compared with an adhesive of the same formulation without the magnetic conditioning and 122 % increase when compared to the commercial aqueous based polichloroprene adhesive.
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Parulkar, Aamena. "Developing Synthesis and Characterization Methods for Enhancing Material Performance." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1542739064703435.
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Lambert, Romain. "Nouveaux copolymères et nanostructures dérivés de liquides ioniques à base d'imidazoliums : applications en catalyse et comme additifs conducteurs ioniques." Thesis, Bordeaux, 2016. http://www.theses.fr/2016BORD0306/document.
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Des poly(liquides ioniques) (PILs) arrangés sous la forme de copolymères statistiques,de nanoparticules à chaine unique ou bien sous la forme de copolymères à blocs autoassemblés ont été employés comme précurseurs de carbènes N-hétérocycliques (NHC)s à des fins de catalyses organiques ou organométalliques. L’introduction d’anions acétate dans des unités PIL dérivés d’imidazolium permet la génération in situ de NHCs actifs en catalyse. Les nanoparticules composées d’une chaine unique polymère repliée sur elle-même (SCNP) ont été spécialement conçues selon deux stratégies impliquant, d’une part, une réaction d’autoquaternisation entre groupements fonctionnels antagonistes portés par la chaine et, d’autre part, une réaction de complexation organométallique à l’aide d’un sel de palladium. Dans lesdeux cas, les chaines polymères ont été obtenues par polymérisation contrôlée (méthode RAFT). Les copolymères à blocs amphiphiles comportant un bloc PIL fonctionnalisé par du palladium ont été synthétisés par polymérisation RAFT et auto-assemblés dans l’eau sous forme de micelles.Un effet de confinement des sites catalytiques a clairement été démontré à travers des réactions de catalyse pour les couplages de Suzuki et de Heck dans l’eau, avec un gain cinétique très net par rapport à des homologues non micellisés, en plus d’une grande facilité de recyclage de ces supports micellaires.Enfin, des copolymères à blocs à base de PIL-benzimidazolium à contre anion bis(trifluoromethane)-sulfonylimide de lithium ont été développés comme agents dopants conducteurs ioniques de matrices structurantes PS-b-PEO. Des mélanges configurés en films minces avec une quantité minimale d’agent dopant ont conduit dans certaines conditions à des valeurs optimales de conductivité ionique grâce à une nano structuration des films à longue distancePoly(ionic liquid)s (PILs) in the form of random copolymers, single chain nanoparticles(SCNPs), or self assembled block copolymers have been used as N-heterocyclic carbenes(NHCs) precursors for the purpose of organic and organometallic catalysis. Introducing acetate derivative counter anion in imidazolium based PIL units enable in situ generation of catalyticallyactive NHC. SCNPs have been specially designed along two strategies including, firstly, a self quaternization reaction involving two antagonists groups supported on to the polymer chain and,secondly, an organometallic complexation featuring palladium salt. Both polymeric precursors were obtained using RAFT as controlled polymerization method. Amphiphilic block copolymers composed of a PIL block functionalized by palladium have been synthesized by RAFT and self-assembled in water, leading to micellar structures. Confinement effect has been demonstrated through Suzuki and Heck coupling in water showing kinetic gain compared to molecular homologue in addition to an easier recycling method.Finally, PIL-benzimidazolium based block copolymers with lithium bis(trifluoromethane)-sulfonylimide anion have been developed as ionic conductor doping agent for PS-PEO matrix. Thin films blends with minimum doping agent amount led to optimum ionic conductivity owing tolong range order
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Zhang, Yan. "SURFACE AND STRUCTURAL MODIFICATION OF CARBON ELECTRODES FOR ELECTROANALYSIS AND ELECTROCHEMICAL CONVERSION." UKnowledge, 2018. https://uknowledge.uky.edu/chemistry_etds/96.
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Electrocatalysis is key to both sensitive electrochemical sensing and efficient electrochemical energy conversion. Despite high catalytic activity, traditional metal catalysts have poor stability, low selectivity, and high cost. Metal-free, carbon-based materials are emerging as alternatives to metal-based catalysts because of their attractive features including natural abundance, environmental friendliness, high electrical conductivity, and large surface area. Altering surface functionalities and heteroatom doping are effective ways to promote catalytic performance of carbon-based catalysts. The first chapter of this dissertation focuses on developing electrode modification methods for electrochemical sensing of biomolecules. After electrochemical pretreatment, glassy carbon demonstrates impressive figures-of-merit in detecting small, redox-active biomolecules such as DNA bases and neurotransmitters. The results highlight a simplified surface modification procedure for producing efficient and highly selective electrocatalysts. The next four chapters focus on evaluating nitrogen-doped carbon nano-onions (𝑛-CNOs) as electrocatalysts for oxygen reduction and CO2 reduction. 𝑛-CNOs exhibit excellent electrocatalytic performance toward O2 to H2O reduction, which is a pivotal process in fuel cells. 𝑛-CNOs demonstrate excellent resistance against CO poisoning and long-term stability compared to state-of-the-art Pt/C catalysts. In CO2 electrochemical conversion, 𝑛-CNOs demonstrate significant improvement in catalytic performance toward reduction of CO2 to CO with a low overpotential and high selectivity. The outstanding catalytic performance of 𝑛-CNOs originates from the asymmetric charge distribution and creation of catalytic sites during incorporation of nitrogen atoms. High contents of pyridinic and graphitic N are critical for high catalytic performance. This work suggests that carbon-based materials can be outstanding alternatives to traditional metal-based electrocatalysts when their microstructures and surface chemistries are properly tailored.
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Zhao, Jinhui. "Novel Nano-catalysts for Sustainable Processes." Thesis, The University of Sydney, 2019. https://hdl.handle.net/2123/21523.
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The key aim of this thesis was to develop suitable catalysts for sustainable processes and investigate the potential reaction mechanism. Characterizations were conducted to investigate the morphology and properties of the synthesized catalysts. The first part of this thesis is employing synthesized Au, Pt and AuPt loaded N-doped mesoporous carbon nanosphere catalysts for the photocatalytic oxidation of alcohols. Several characterizations and finite-difference time-domain (FDTD) simulation were conducted to study the intrinsic properties of the catalysts. AuPt bimetallic catalysts performed overwhelming higher catalytic activity and > 99 % selectivity to the corresponding aldehyde was detected. The Pt electronic sink effect and the co-catalyst effect were considered to enhance the catalytic activity. Moreover, reactant polarity and support conductivity influence on the catalytic performance had also been studied and a charge transfer reaction mechanism was proposed. The second part of this thesis focused on the application of Ni loaded three-dimensionally ordered macroporous (3DOM) CeO2 with different metal loading amount on CO2 conversion. The catalysts were synthesized by loading Ni nanoparticles by the wet impregnation method on 3DOM CeO2, which was pre-synthesized by sol-gel method with poly(methyl methacrylate) PMMA sphere substrate. All four catalysts with Ni loading amount from 2.5 % to 10 % showed great catalytic activity to CH4 and CO. The concentration of metallic Ni, oxygen vacancy and the macroporous structure of the catalysts played an important role during the catalytic reaction. The relatively smaller Ni nanoparticles in 2.5 % Ni loaded catalysts is proposed to result in the selectivity shift to CO. The reaction mechanism was studied and a reaction pathway demonstration diagram is depicted.
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O'Connor, Timothy F. III. "Synthesis and Dynamics of Photocatalytic Type-II ZnSe/CdS/Pt Metal-Semiconductor Heteronanostructures." Bowling Green State University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1340038781.
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Wang, Lizhuo. "Nano Catalyst Design and Application in Sustainable Chemistry." Thesis, The University of Sydney, 2022. https://hdl.handle.net/2123/29570.
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Heterogenous catalytic process is a complex art of surface, the surface properties, especially the properties of active sites such as geometric structure and chemical environment would drastically influence the reaction performance. Traditionally, most studies for catalyst surface properties rely on the ex situ characterisation which examines catalysts out of reaction condition. However, considering most of the heterogenous catalytic reactions are carried out under a harsh condition, i.e. elevated temperatures and pressures, the surface dynamic change over catalyst under reaction condition is generally not negligible and dominating the reaction performance. Thus, for understanding the real catalyst surface behaviour, we must observe the catalyst during reaction condition. Three different catalytic systems were selected in this research and the combined in situ microscopy and spectroscopy techniques, including in situ TEM, in situ EELS spectroscopy and in situ DRIFTS spectroscopy, were implemented to investigate the catalyst behaviour during the reactions. The first reaction is the oxidative methane coupling reaction over Li/MgO. Then followed by the oxidative methane coupling over La/MgO and ammonia synthesis over Ru/MgO. The in situ TEM provides the information of surface geometric change while the in situ EELS and DRIFTS give the chemical information of catalyst surface as well as adsorbed intermediates. Combined with ex situ characterisation results, the more comprehensive pictures for the mechanism of the investigated reactions can be depicted. The outcome of this thesis bridged the gap between surface geometric-chemical change over catalysts active sites and the reaction performance over heterogenous catalyst, which might even be the guidance for heterogenous catalyst development in the similar systems.
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Düskünkorur, Hale. "Biopolyester synthesis by enzymatic catalysis and development of nanohybrid systems." Phd thesis, Université de Strasbourg, 2012. http://tel.archives-ouvertes.fr/tel-00864276.
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This thesis aims at presenting the use and development of original catalytic systems based on lipases immobilized on clays which are efficient for the synthesis of biopolyesters and allowing the preparation of organic/inorganic nanohybrids based on clay nanoparticles (sepiolite and montmorillonite) grafted with such polyesters. These nanoclays were used as lipase supports and the clay-immobilized forms of Candida antarctica lipase B (CALB) were tested for ε-caprolactone and lactide isomers polymerization. Polymerization kinetics and characterization of resulting materials have shown that lipases immobilized on montmorillonite show better performances compared to the ones immobilized on sepiolite. Clay surface organo-modification has proved to greatly enhance the catalytic activity of the corresponding systems. CALB immobilized on montmorillonite allowed the elaboration of organic/inorganic nanohybrids as evidenced by the effective grafting of polyester chains from the clay surface. Finally, random PCL/PLA copolyesters were successfully obtained by lipase-catalyzed copolymerization of D-lactide with ε-caprolactone.
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Dole, Holly. "Connecting Metal-Support Interaction and Electrochemical Promotion Phenomena for Nano-structured Catalysts." Thesis, Université d'Ottawa / University of Ottawa, 2016. http://hdl.handle.net/10393/34610.
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Air pollutants can cause poor air quality; however, the use of heterogeneous catalytic oxidation has been shown to be an efficient and cost-effective removal method. Some examples of commercial application of such catalysts include catalytic convertors in automobiles and industrial process exhausts. Research with regards to improving these technologies has included using less-expensive catalyst materials, increasing catalytic performance, and achieving higher efficiency.
The concept of metal-support interaction (MSI) is one method of altering catalytic performance through changing the properties of the metal catalyst due to the interaction with the support material. Similarly, the phenomenon of electrochemical promotion of catalysis (EPOC) has also been shown to enhance the catalytic activity, however, through the application of a small electrical stimulus to a catalyst-working electrode deposited on a solid electrolyte (e.g. yttria-stablized zirconia). The properties of the metal catalyst are altered due to the movement of ions (in this case, O2-) from the electrolyte. Since its discovery, several factors were identified that are preventing EPOC from being commercialized, including the use of thick film catalysts. Implementing nano-catalysts makes this method competitive with typical heterogeneous catalysts; however, it has not been studied by many research groups. Furthermore, many heterogeneous catalytic studies have been performed separately for each of these phenomena; however, a connection between EPOC and MSI has yet to be fully understood.
The overall objective of this project is to study the concept of EPOC over highly-dispersed nano-catalysts and determine how MSI relates to the change in catalytic activity. Supported nano-catalysts were synthesized, characterized, and evaluated for catalytic performance using model reactions. A reactor was designed to carry out the electrochemical studies, where the EPOC concept was successfully implemented and a relationship with MSI established. Furthermore, additional studies were conducted to determine the role of the O2- in the catalyst support and its relationship to MSI.
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You, Sheng Mu. "Metal organic frameworks as efficient photosensitizer for TiO₂ nanoarray anode and application to water splitting in PEC cells Fe/Ni Bimetallic organic framework deposited on TiO₂ nanotube array for enhancing higher and stable activity of oxygen evolution reaction Novel nano-architectured water splitting photoanodes based on TiO₂-nanorod mats surface sensitized by ZIF-67 coatings Surface sensitization of TiO₂ nanorod mats by electrodeposition of ZIF-67 for water photo-oxidation Electrochemically capacitive deionization of copper (II) using 3D hierarchically reduced graphene oxide architectures." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASF015.
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Les réserves de combustibles fossiles diminuent et leur utilisation illimitée depuis la révolution industrielle a généré de profonds changements du climat, notamment des cycles de la température atmosphérique. Stocker l'énergie solaire sous forme d'hydrogène produit par dissociation de l'eau est un moyen idéal pour combattre le réchauffement climatique. Les matériaux de la famille des «metal organic framework» (MOF) commencent à être utilisés comme photo-électrocatalyseurs, notamment pour la photo-dissociation de l'eau. Leur porosité extrêmement élevée et leur grande polyvalence, tant chimique que structurelle, les désignent comme des candidats potentiels pour faciliter l'absorption du rayonnement solaire et catalyser la dissociation de l'eau dans les cellules photoélectrochimiques. En contrôlant la composition chimique et le dopage du linker utilisé dans le MOF, il est possible d'ajuster l'énergie de la bande interdite, de favoriser la fonctionnalisation sur des substrats très variés ou encore d'ajuster leur résistance à la corrosion dans divers environnements chimiques. Ce sont donc des matériaux d'un grand intérêt pour la catalyse, l'électrocatalyse ou la photo-électro-catalyse. D'autre part, le TiO₂ nano-structuré, par exemple sous forme de tapis d’épaisseur micrométrique de nanotubes ou de nanofils, parfois appelé TNA, est un matériau bien adapté à la construction de photoanodes pour le dégagement d'oxygène en milieu aqueux. Il a déjà été largement étudié et décrit dans la littérature. Au cours de notre thèse, nous avons fabriqué des matériaux composites constitués de MOF de métaux de transition (Ni, Co, Fe) déposés sur TNA (TDNR et TNTA). Pour cela, nous avons utilisé une méthode électrochimique d'électrodéposition. Cela nous a permis de déposer des nanoparticules métalliques sur du TNA à potentiel fixe - 1,0 V puis de les transformer par réaction chimique avec des ligands organiques (BTC, BDC, et 2MZ) par voie thermo-thermique. Les matériaux obtenus présentent une activité électrocatalytique significative et une excellente durabilité photoélectrochimique. Ces matériaux composites ont été utilisés avec succès comme phase active dans des photo-électrodes pour la réaction de dégagement d'oxygène moléculaire (OER)The fossil fuel reserves are dwindling and their unrestricted use has generated profound changes in Earth's surface temperature and climate. Storing solar energy in the form of hydrogen produced by dissociation of water is an ideal way to mitigate global warming. Materials from the “metal organic framework” (MOF) family are starting to be used as photo-electrocatalysts, especially for photo-dissociation of water. Their extremely high porosity and their great versatility, both chemical and structural, designate them as potential candidates to facilitate the absorption of solar radiation and catalyze the dissociation of water in photoelectrochemical cells. By controlling the chemical composition and doping of the linker used in the MOF, it is possible to adjust the band gap energy, to favor the functionalization on very varied substrates or even to adjust their resistance to corrosion in various chemical environments. They are therefore materials of great interest for catalysis, electrocatalysis or photo-electro-catalysis. On the other hand, nano-structured TiO₂, for example in the form of nanotube or nanowire mats, sometimes called TiO₂ nanoarray (TNA), is a material very suitable for the construction of photoanodes for the evolution of oxygen in aqueous medium. It has already been extensively studied and described in the literature. During our thesis, we manufactured composite materials made up of MOFs of transition metals (Ni, Co, Fe) deposited on TNA (network of nanotubes or nanowires). For this we used an electrochemical method of electrodeposition (cyclic voltammetry). This allowed us to deposit metallic nanoparticles on TNA with fixed potential - 1.0 V and then transform them by chemical reaction with organic ligands (1,3,5-benzenetricarboxylic acid, BTC, 1,4-benzenedicarboxylic acid, BDC and imidazole, 2MZ) by thermal-thermal route. The materials obtained exhibit significant electrocatalytic activity and excellent photoelectrochemical durability. These composite materials have been successfully used as an active phase in photo-electrodes for the oxygen release reaction (OER)
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PRADA, STEFANO. "Enhancing oxide surface reactivity by doping or nano-structuring." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2014. http://hdl.handle.net/10281/50011.
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Wide band-gap simple oxides are rather inert materials, which found applications in heterogeneous catalysis mainly as supports for active metal nanoparticles. This thesis investigates tailored modifications of the oxide characteristics aimed at making these substrates more reactive in catalytic processes. In particular we are interested in engineering the charge transfer with supported metal catalysts in order to enhance their activity and selectivity. By using first principles calculations in the framework of the density functional theory, we have explored two main routes in this field: 1) nanostructuring, in particular nanothick oxide films supported on metals, and 2) doping of oxides with substitutional metal ions. After addressing methodological aspects related to the theoretical simulations of these materials, we have considered the role of oxide doping in optimizing the structural and electronic properties of supported gold adparticles; we have shown that depending on the dopant and the nature of the oxide it is possible to finely tune the shape and the charge state of adsorbed metal particle. Moreover we have combined oxide doping and nanostructuring in modifying the work function of metal substrates. By varying parameters like nature, position, and concentration of dopants within the metal-supported oxide films, it is possible in principle to modify the work function of the metallic support in a desired way.
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Belarbi, Hichem. "Élaboration des zéolithes nano-structurées M-ZSM-5 (M=Cu, Cr et Fe) : Etude comparée des solides poreux minéraux et organométalliques MOFs dans l’oxydation de méthylènes benzyliques." Thesis, Montpellier 2, 2014. http://www.theses.fr/2014MON20192.
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L'énergie, le développement durable et la santé sont au cœur des préoccupations actuelles de la planète. La disparition inéluctable des énergies fossiles, les conséquences graves des émissions de gaz carbonique sur l'environnement et la santé appellent des solutions rapides et efficaces pour suppléer aux premières et minimiser les autres.Parmi les solutions envisagées la catalyse hétérogènes représentés par les matériaux poreux, ces derniers ont prouvé leur efficacité, néanmoins des obstacles sont à corriger ou à contourner tel que le problème d'inaccessibilité des molécules encombrantes dans sites des micropores de ce matériau. Dans cette thèse nous avons essayé de trouver la solution à ce problème en travaillant sur des nanostructures ZSM-5.Dans une première étape, nous avons optimisé ce matériau en l'occurrence ZSM-5, avec une réduction de la taille des particules, d'une échelle microscopique vers une autre nanométrique, ce qui nous a permis d'augmenter la surface externe après une modification de certains paramètres. Dans la deuxième étape, et afin de donner une entité catalytique à notre support (la zéolithe), nous avons activé ce matériau par l'incorporation des cations, choisis en fonction d'une réaction bien spécifique, qui est celle d'oxydation des méthylènes benzéniques. Pour ce fait nous avons élaboré différents catalyseurs pour nos réactions.Nous avons conclu cette thèse par la catalyse avec la M-ZSM-5 (M = Cu, Cr et Fe) et une étude comparative est faite avec les MOFs qui portent les mêmes cations actifs dans leur partie minéraleEnergy, sustainable development, and health are at the heart of contemporary concerns of the planet. The inevitable disappearance of fossil fuels, the severe consequences of carbon emissions on the environment and health require quick and effective solutions to supplement the first and minimize others. Among the solutions proposed, there are porous materials which have proven their effectiveness; however, there are still obstacles to be corrected or circumvented. In this thesis, we focus on the problem of bulky molecules' inaccessibility in micro pores of the materials we wish to study. In the first part, we optimize the material in this case, ZSM-5, with a reduction in particle size to a microscopic scale to another nano, which allows us to increase the external surface after changing certain parameters. In the second step, in order to give a catalytic entity to our support (zeolite), we activate with this material incorporating cations selected according to a specific property of the benzyl methylenes oxidation reaction. For this reason we developed different method of preparation. We conclude this thesis by catalysis with M-ZSM-5 (M = Cu, Cr and Fe) and a comparative study on the method of preparation and the MOFs that bears the same cations as mineral part which constitutes the materials
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Panaritis, Christopher. "Metal-Support Interaction and Electrochemical Promotion of Nano-Structured Catalysts for the Reverse Water Gas Shift Reaction." Thesis, Université d'Ottawa / University of Ottawa, 2021. http://hdl.handle.net/10393/41963.
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The continued release of fossil-fuel derived carbon dioxide (CO₂) emissions into our atmosphere led humanity into a climate and ecological crisis. Converting CO₂ into valuable chemicals and fuels will replace and diminish the need for fossil fuel-derived products. Through the use of a catalyst, CO₂ can be transformed into a commodity chemical by the reverse water gas shift (RWGS) reaction, where CO₂ reacts with renewable hydrogen (H₂) to form carbon monoxide (CO). CO then acts as the source molecule in the Fischer-Tropsch (FT) synthesis to form a range of hydrocarbons to manufacture chemicals and fuels. While the FT synthesis is a mature process, the conversion of CO₂ into CO has yet to be made commercially available due to the constraints associated with high reaction temperature and catalytic stability.
Noble metal ruthenium (Ru) has been widely used for the RWGS reaction due to its high catalytic activity, however, several constraints hinder its practical use, associated with its high cost and its susceptibility to deactivation. The doping or bimetallic use of non-noble metals iron (Fe) and cobalt (Co) is an attractive option to lower material cost and tailor the selectivity of the CO₂ conversion towards the RWGS reaction without compromising catalytic activity. Furthermore, employing nanostructured catalysts as nanoparticles is a viable solution to further lower the amount of metal used and utilize the highly active surface area of the catalyst. Dispersing nanoparticles on ionically conductive supports/solid electrolytes which contain species like O²⁻, H⁺, Na⁺, and K⁺, provide an approach to further enhance the reaction. This phenomenon is referred to as metal-support interaction (MSI), allowing for the ions to back spillover from the support and onto the catalyst surface. An in-situ approach referred to as Non-Faradaic Modification of catalytic activity (NEMCA), also known as electrochemical promotion of catalysis (EPOC) is used to in-situ control the movement of ionic species from the solid electrolyte to and away from the catalyst. Both the MSI and EPOC phenomena have been shown to be functionally equivalent, meaning the ionic species act to alter the work function of the catalyst by forming an effective neutral double layer on the surface, which in turn alters the binding energy of the reactant and intermediate species to promote the reaction.
The main objective of this work is to develop a catalyst that is highly active and selective to the RWGS reaction at low temperatures (< 400 °C) by employing the MSI and EPOC phenomena to enhance the catalytic conversion. The electrochemical enhancement effect will lower energy requirements and allow the RWGS reaction to take place at moderate temperatures. Catalysts composed of Ru, Fe and Co were synthesized through the polyol synthesis technique and deposited on mixed-ionically conductive and ionically conductive supports to evaluate their performance towards the RWGS reaction and the MSI effect. The nano-structured catalysts are deposited as free-standing nanoparticles on solid electrolytes to in-situ promote the catalytic rate through the EPOC phenomenon. Furthermore, Density Functional Theory (DFT) calculations were performed to correlate theory with experiment and elucidate the role polarization has on the binding energy of reactant and intermediate species.
The high dispersion of RuFe nanoparticles on ion-containing supports like samarium-doped ceria (SDC) and yttria-stabilized zirconia (YSZ) led to an increase in the RWGS activity due to the MSI effect. A direct correlation between experimental and DFT modeling was established signifying that polarization affected the binding energy of the CO molecule on the surface of Ru regardless of the type of ionic species in the solid electrolyte. The electrochemical enhancement towards the RWGS reaction has been achieved with iron-oxide (FeOₓ) nanowires on YSZ. The in-situ application of O²⁻ ions from YSZ maintained the most active state of Fe₃O₄ and FeO towards the RWGS reaction and allowed for persistent-promoted state that lasted long after potential application. Finally, the deposition of FeOₓ nanowires on Co₃O₄ resulted in the highest CO₂ conversion towards the RWGS reaction due to the metal-oxide interaction between both metals, signifying a self-sustained electro-promoted state.
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M'Nasri, Najib. "Elaboration de nanomatériaux composites métal@nanoparticules de silice mésoporeuses (MSN) : étude des performances catalytiques en phase aqueuse et des propriétés d'adsorption sélective du diiode en phase gaz." Thesis, Montpellier 2, 2014. http://www.theses.fr/2014MON20199.
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Ce travail a concerné l'étude de la fonctionnalisation métallique et du contrôle morphologique de nanoparticules de silice mésoporeuse appelées MSN. La voie de fonctionnalisation par synthèse directe a été privilégiée et a consisté en une encapsulation des précurseurs métalliques dans la phase porogène. L'insertion de cuivre, palladium, platine, argent or et de bimétalliques Cu/Pd et Pd/Pt a été réalisée. Il résulte de cette approche une localisation des nanoparticules métalliques dans les pores et d'une grande accessibilité des fonctionnalités à l'origine des excellentes performances catalytiques mesurées. Ces performances et le recyclage du catalyseur Cu@MSN ont été démontrés pour des réactions de Huisgen et de Sonogashira. Il a également été étudié l'adsorption de l'iode moléculaire en phase gaz sur des MSN fonctionnalisées par des nanoparticules d'argent avec d'excellentes capacités de rétentionThe objective of this thesis was to develop efficient synthesis routes to prepare mesoporous silica-based nano-sized particles, designated as MSN, with controllable morphology and derivatised with selected transition metals. One-pot preparation and surface functionalisation procedures based on the insertion of the metal-phase precursor into the porogen aggregates were thoroughly optimised leading to silica particles containing such single metals as copper, palladium, platinum, silver or gold, as well as a two-metal phase of copper and palladium or that of palladium and platinum. It was demonstrated that the highly dispersed metal phase was localised on the pore surface and therefore it was readily accessible to the target chemicals on which to base the catalytic performance of the resulting materials. Among others, the remarkable catalytic performance of the Cu@MSN material in Huisgen and Sonogashira reactions and its propensity to undergo efficient recycling were proven through laboratory-scale testing. Experimental study of the selective adsorption of iodine vapour onto MSN supports functionalised with silver nanoparticles indicated an excellent retention capacity of such materials
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Genuzio, Francesca. "Spectro-microscopic investigation of Fe-oxide based model catalysts and instrumental development." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2016. http://dx.doi.org/10.18452/17526.
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Diese Arbeit untersucht Fe-Oxid-Systeme mit Hilfe einer Kombination aus Mikroskopie (LEEM, Röntgen PEEMs), Beugung (LEED) und Spektroskopie (XPS) und berichtet über die elektronenoptische Entwicklung adaptiver Optiken und Aberrationskorrekturen für einen elektrostatischen abbildenden Energieanalysator. Experimentell untersuchten wir Magnetit und Hämatit Dünnschichten. Ihre Kristallstruktur, Stöchiometrie sowie deren Oberflächenterminierung können durch spezielle Herstellungsverfahren eingestellt werden. Unter Ausnutzung der Echtzeit-Beobachtung mit Mikroskopie, Beugung und Spektroskopie untersuchten wir (a) die Oberflächenmodifikationen von Fe3O4 und α-Fe2O3-Dünnschichten durch Fe Ablagerung; (b) die reversible Phasenumwandlung Fe3O4 ↔ α-Fe2O3 unter verschiedenen Oxidationsbedingungen; (c) die Bildung der metastabilen γ-Fe2O3-Phase und (d) die Wechselwirkung von Fe3O4 und α-Fe2O3 Oberflächen mit unterstützten Pt-Nanopartikeln. Es wurde ein Algorithmus entwickelt, um den LEEM Bildkontrast für inhomogene 2D Oberflächen zu simulieren. Abschließend wird das Design eines Energiefilter-System vorgestellt, das in ein PEEM/LEEM Mikroskop der neuen Generation eingebaut werden wird. Das System basiert auf dem gleichen Abbildungsprinzip wie der magnetische Ω-Filter, der erfolgreich im aktuellen SMART Mikroskop eingesetzt wird. Das neue Instrument zielt auf die Verbesserung der Orts- und Energieauflösung im XPEEM (5 nm und 70 meV). Die Mehrzahl der möglichen Aberrationen zweiter Ordnung wird durch die intrinsische Symmetrie selbstkompensiert. Die Wirkung der anderen Aberrationen wird durch ein geeignetes Design der Verzögerungs- und Beschleunigungsoptiken kombiniert mit einer optimierten Passenergie reduziert. Darüber hinaus kompensieren zusätzliche Hexapole die restlichen dominierenden Aberrationen, wodurch eine Orts- und Energieauflösung besser als 2 nm bzw. 75 meV erreicht wird.This work presents the investigation of Fe-oxide systems, combining microscopy (LEEM, X-PEEM), diffraction (LEED) and spectroscopy (XPS), and the electron-optical development of adaptive optics and aberration corrections for an electrostatic imaging energy analyzer. Experimentally, we studied magnetite (Fe3O4) and hematite (α-Fe2O3) thin films. Their crystal structure, stoichiometry as well as their surface termination can be tuned by special preparation procedures. Taking advantage of real time observation with microscopy, diffraction and spectroscopy, we investigated (a) the surface modifications of Fe3O4 and α-Fe2O3 thin films by Fe deposition; (b) the reversible phase transformation Fe3O4 ↔ α-Fe2O3 under different oxidation conditions; (c) the formation of the metastable γ-Fe2O3 phase and (d) the interaction of Fe3O4 and α-Fe2O3 surfaces with supported Pt nanoparticles . An algorithm was developed to simulate the LEEM image contrast for inhomogeneous 2D surfaces. The possible application to experimental data and the limitation will be discussed. Finally, the design of an energy filtering system is presented, which will be implemented in a new generation PEEM/LEEM microscope. The system bases on the same imaging principle as the magnetic Ω-filter, successfully implemented in the actual SMART microscope. The new instrument aims for the improvement of lateral and energy resolution in X-PEEM (5 nm and 70 meV, respectively). The majority of the possible second order aberrations are self-compensated by intrinsic symmetry. The effect of the other aberrations is reduced by an adequate design for the deceleration-acceleration optics in combination with optimized pass energy. Furthermore, additional hexapole multipoles compensate for the residual dominating aberrations, yielding in the lateral resolution and energy resolution better than 2 nm and 75 meV, respectively.
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Kane, Kenneth. "Metallic systems at the nano and micro scale: Bimetallic nanoparticles as catalysts and MCrAlY bond coats in thermal barrier coatings." VCU Scholars Compass, 2019. https://scholarscompass.vcu.edu/etd/5732.
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The dissertation is split into two parts. The first part will be focused on changes in material properties found at the nanoscale, as miscibility and electronic structure can change significantly with size. The formation of classically-immiscible bimetallic nanoparticles (BNPs) becomes favorable at the nanoscale and novel catalytic properties can emerge from the bimetallic alloying. The formation of alloyed and non-alloyed BNPs is achieved through pulse laser ablation (PLA) and a significant increase in catalytic activity is observed for both. Recently discovered, the increased activity in the non-alloyed BNPs, deemed multicomponent photocatalysis, is examined and the proposed mechanism discussed. The second part of the talk will focus on thermal barrier coatings (TBCs), which are advanced, multi-layered coatings used to protect materials in high temperature environments. MCrAlY (M=Ni, Co) bond coats deposited via atmospheric plasma spray (APS) are intrinsically rough and initially the roughness provides a high surface area platform for the mechanical interlocking of the yttria stabilized zirconia (YSZ) top coat, which provides the bulk of the thermal insulation. After high temperature exposure, a protective oxide scale forms at the top coat/bond coat interface however the convex asperities of the bond coat can grow non-α-Al2O3 type oxides that can be detrimental for coating lifetime. A surface modification technique that removes the asperities while leaving intact the concavities is used to examine the role that roughness distribution has on 1100°C APS coating lifetime. Lastly, recent work validating a modelling strategy for evaluating 900°C TBC lifetimes, which can typically surpass 25 kh, is presented. Differences in coating-substrate
interdiffusion behavior over 5-20 kh of 900°C exposure are discussed and reproduced with Thermo- Calc/DICTRA for three superalloys (1483, 247, X4) deposited with high velocity oxy fuel (HVOF)
NiCoCrAlY coatings.
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Bordet, Alexis. "Une nouvelle génération de nano-catalyseurs à base de carbure de fer pour le stockage chimique de l'énergie." Thesis, Toulouse, INSA, 2016. http://www.theses.fr/2016ISAT0017/document.
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Après plusieurs décennies de consommation insouciante et inconsidérée des ressources d’origine fossile, l’humanité doit aujourd’hui faire face à une crise sans précédent concernant le réchauffement climatique global et la production et le stockage de l’énergie. Dans le double contexte de stockage des énergies renouvelables intermittentes et de valorisation du dioxyde de carbone, l’approche power-to-gas (conversion de l’énergie électrique en énergie chimique), et plus précisément la réaction de Sabatier (hydrogénation catalytique du dioxyde de carbone en méthane), apparait comme une stratégie attractive. Dans cette thèse, nous cherchons en particulier à réaliser la réaction de Sabatier en utilisant des nano-catalyseurs chauffés par induction magnétique. L’utilisation de nanoparticules magnétiques pour convertir l’énergie électromagnétique en chaleur – hyperthermie magnétique – est une approche d’intérêt grandissant dans le domaine de la catalyse, même si le domaine biomédical concentre évidemment la grande majorité des applications (hyperthermie magnétique, drug delivery, etc.). L’intérêt biomédical des nanoparticules synthétisées est d’ailleurs étudié et discuté. Dans ce contexte hautement pluridisciplinaire, nous décrivons la synthèse de nanoparticules magnétiques à base de carbure de fer dédiées à la catalyse par induction magnétique et à l’hyperthermie magnétique médicale. Nous montrons que la puissance de chauffe des nanoparticules de carbure de fer sous excitation magnétique est grandement influencée par leur teneur en carbone et leur cristallinité. En particulier, il apparait que lorsque la phase cristalline de carbure de fer Fe2.2C est largement majoritaire au sein des nanoparticules (> 80%), ces dernières possèdent des débits d’absorptions spécifiques (Specific Absorption Rate SAR) remarquablement élevés. Ces propriétés singulières nous ont permis de réaliser la réaction de Sabatier dans un réacteur à flux continu et d’obtenir des résultats extrêmement prometteurs. Nous avons ainsi été en mesure de démontrer que l’association du concept de catalyse par induction magnétique à la réaction de méthanation du CO2 représente une approche à la fois innovante et attractive dans le double contexte de stockage des énergies intermittentes et de valorisation du CO2. Pour finir, les nanoparticules de carbure de fer ont été fonctionnalisées avec des ligands dérivés de la dopamine, les rendant ainsi dispersables et stables en milieux aqueux pendant plusieurs semaines. La toxicité et l’internalisation cellulaire des systèmes [nanoparticules-ligands] ont été étudiées, et se révèlent grandement dépendantes de la nature des ligands utilisésAfter several decades of oblivious fossil resources consumption, humanity is now facing major issues regarding global warming and energy production and storage. In the double context of intermittent renewable energy storage and CO2 recovery, the power-to-gas approach, and especially the Sabatier reaction (catalytic hydrogenation of carbon dioxide to methane + water) is of special interest. The main goal of this thesis is to perform the Sabatier reaction using magnetically activated nano-catalysts. The use of magnetic nanoparticles to convert electromagnetic energy into heat is indeed an approach of growing interest in catalysis, even if the field of biomedicine obviously concentrate most of the applications (magnetic hyperthermia, drug delivery, etc.). In this respect, the interest of the synthesized nanoparticles for biomedical applications is studied and discussed. We describe herein a pathway to iron carbide nanoparticles allowing a fine tuning of their carbon content and magnetic properties. We show that the carbon content and the crystallinity of the synthesized nanoparticles greatly impact their magnetic heating efficiency. The Fe2.2C crystallographic phase especially appears to be the key to highly enhanced specific absorption rates (SARs). We took advantage of these exceptional heating properties to investigate the Sabatier reaction in a continuous flow reactor, the catalyst being activated through magnetic induction. The SAR of synthesized iron carbide nanoparticles appeared to be sufficient to reach the temperature required for the activation of the Sabatier reaction (typically > 250°C), and promising results were obtained in a continuous flow reactor. We were thus able to demonstrate that the concept of magnetically induced catalysis can be successfully applied to the CO2 methanation reaction and represents an approach of strategic interest in the double context of intermittent energy storage and CO2 valorization
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Koneti, Siddardha. "In situ and 3D environmental transmission electron microscopy of Pd-Al2O3 nano catalysts : Fast tomography with applications to other catalytic systems in operando conditions and to electron beam sensitive nanomaterials." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEI123/document.
Full textAbstract:
Au début du XXIème siècle, la Microscopie Electronique à Transmission en mode Environnemental (ETEM) est devenue l’une des techniques les plus fiables de caractérisation de nanomatériaux dans des conditions simulant leur vie réelle. L’ETEM est maintenant en mesure de suivre l’évolution dynamique des nanomatériaux dans des conditions variables comme l’exposition à des températures élevées, l’observation en milieux liquide ou gazeux à diverses pressions. Parmi différents domaines de recherche et développement concernés, la catalyse peut bénéficier de manière significative des avancées permises par la microscopie électronique environnementale. Cette thèse, dédiée au développement de l’ETEM au laboratoire MATEIS, a commencé avec l’étude du système catalytique Pd-alumine. Les nanoparticules de Pd déposées sur alpha -Al2O3 et delta-Al2O3 sont très utilisées en physicochimie avec un impact environnemental important : en particulier dans le domaine de l’hydrogénation sélective, pour la synthèse de polymères ou l’hydrogénation de CO2 pour la production de méthane. Nous avons tout d’abord effectué des analyses 2D aux différentes étapes du processus de synthèse du catalyseur : imprégnation du précurseur, séchage et chauffage pour la calcination dans l’air à la pression atmosphérique. La motivation de cette approche a été de comparer des analyses post mortem avec des traitements en ETEM où l’évolution des nanoparticules peut être mesurée in situ et pas seulement « avant » et « après ». De manière générale, les études faites en ETEM en 2D donnent un aperçu limité sur la morphologie des objets et la distribution spatiale des nanoparticules supportées. Nous avons développé une nouvelle approche d’acquisition rapide pour collecter dans des temps très courts des séries d’images sous différents angles de vue pour la tomographie électronique, la rapidité de cette acquisition étant un prérequis pour appréhender correctement la morphologie d’un nano-système au cours de son évolution dynamique in situ. La technique a ensuite été utilisée pour l’étude de plusieurs systèmes où une acquisition tridimensionnelle rapide est indispensable, notamment sur un sujet concernant un enjeu sociétal important, la dépollution des moteurs diesel : l’oxydation de la suie a été étudiée in situ sur des supports à base de zircone entre 400 et 600°C et une pression de 2 mbar d’oxygène à différents degrés de combustion, ce qui a permis d’extraire des données cinétiques telle que l’énergie d’activation du processus. La tomographie électronique rapide a été également appliquée à des matériaux sensibles au faisceau électronique, comme des nanocomposites polymères et des objets biologiques, montrant le large spectre d’applications possibles pour cette technique, qui constitue un pas important vers la caractérisation operando 3D de nanomatériaux en temps réelIn the beginning of the XXIst century, Environmental Transmission Electron Microscopy has become one of the reliable characterization techniques of nanomaterials in conditions mimicking their real life. ETEM is now able to follow the dynamic evolution of nanomaterials under various conditions like high temperature, liquid or various gas pressures. Among various fields of research, catalysis can benefit significantly from Environmental Microscopy. This contribution starts with the study of the Palladium-Alumina catalytic system. Pd nanoparticles supported by α-Al2O3 and δ-Al2O3 are of an important physicochemical and environmental interest, particularly in the field of selective hydrogenation in petrochemistry, for the synthesis of polymers or CO2 hydrogenation for methane production. We first performed 2D analyses at different steps of the synthesis process, then the same synthesis steps were performed under in situ conditions. The motivation of this approach was to compare post mortem treatments with ETEM observations. In general, 2D data provide limited insights on, for example, the morphology and position of supported nanoparticles. We have then developed a new fast acquisition approach to collect tomographic tilt series in very short times, enabling to reconstruct nano-systems in 3D during their dynamical evolution. Taking advantage of this approach, we have determined the activation energy for soot combustion on YSZ oxidation catalysts for diesel motors from volumetric data extracted from in situ experiments. Fast electron tomography was also applied to electron beam sensitive materials, like polymer nanocomposites and biological materials, showing the wide spectrum of possible applications for rapid 3D characterization of nanomaterials
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Nowakowski, Pawel. "Systèmes micro-nano-structurés et couches minces multifonctionnels, à base de dioxyde de ruthénium : élaborations et propriétés catalytiques et électriques." Phd thesis, Université du Sud Toulon Var, 2008. http://tel.archives-ouvertes.fr/tel-00343499.
Full textAbstract:
Le présent travail porte sur l'étude de nanomatériaux et couches minces élaborés à base d'oxydes de ruthénium, à finalités catalytiques et électriques. Ces matériaux sont multifonctionnels et pourraient être destinés à des applications variées aussi bien dans le domaine de la microélectronique et des microcapteurs, que dans l'industrie chimique (catalyse, conversion du méthane). L'étude développe les relations entre élaborations, microstructures et propriétés catalytiques et électriques. Les nanopoudres de RuO2 élaborées par voie sol gel présentent des propriétés catalytiques intéressantes vis-à-vis de CH4 et CO. Des affinements structuraux (méthode Rietveld) ont montré une légère modification des mailles cristallines lorsque les tailles de cristallites étaient nanométriques (10 à 20 nm). La microscopie électronique en transmission a permis de préciser les résultats obtenus par diffraction de rayons X sur les tailles de cristallites. L'efficacité catalytique a été mesurée par spectroscopie infrarouge à transformée de Fourier en fonction de la température et du temps d'exposition au flux gazeux (air-méthane ou air-monoxyde de carbone). Les conversions de CH4 et de CO en CO2 ont été observées au-dessus de 200°C pour CH4, et à partir de la température ambiante (25°C) pour CO. Un modèle semi-empirique permettant de simuler le taux de conversion a été proposé et a permis de reproduire des comportements très différents pour la conversion de CH4 ou CO en fonction du temps. Des études de couches minces à base de RuO2 et de composites RuO2-CeO2 ont été entreprises, soit par spin-coating, soit par pulvérisation cathodique. Les couches obtenues par spin-coating manifestent une certaine activité catalytique liée à leur porosité. Les couches obtenues par pulvérisation cathodique sont des couches mixtes RuO2-CeO2. Elles n'ont aucune activité catalytique notable. Elles ont un comportement électrique non linéaire fortement lié à la microstructure et à la composition. Un modèle en loi de puissance a été appliqué avec succès pour décrire l'évolution de la conductivité en fonction de la composition en RuO2. Ces couches pourraient être utilisées dans des dispositifs piézorésistifs. En parallèle à ces études, un dispositif préfigurant un multicapteur de gaz a été mis au point.
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Nguyen, Tao-Nhân V. "Theoretical studies of solvation and catalysis : clusters as chemical nano-reactors." Thesis, 2005. http://spectrum.library.concordia.ca/8643/1/NR09951.pdf.
Full textAbstract:
In this work, computational studies of clusters were performed to understand solvent effects on chemical reactivity (Part A), and assess their potential use as micro-reactors to catalyze reactions not usually possible (Part B). In Part A, a comparative investigation of the structural and energetic properties of ions and ion pairs in polar solvent clusters of acetonitrile, ammonia and water is undertaken by means of Monte Carlo simulations with custom-built model potentials. Quantum chemistry calculations demonstrate the presence of nonlinear hydrogen-bonded I-(CH3CN)2 isomers, which leads to a reinterpretation of previous experimental work. In addition, our work has some implications for the strong solvent selectivity observed experimentally for the NaI photoionization in polar clusters. Equilibrium constant calculations of the NaI ion pair in clusters suggest that the lack of large ionized product fragments observed experimentally in acetonitrile is not due to solvent-induced charge separation (as suggested previously in analogy with water clusters), but could be attributed either to differential solvation effects or to solvent evaporation on the ionized state. On the other hand, the lack of large product signal in NaI(NH3)n multi-photon ionization experiments might be connected to the low evaporation temperature of ammonia, which may prevent production of large parent ground-state NaI(NH3)n clusters, and result in massive solvent evaporation on the excited states. In Part B, the dynamics of energy transfer in (O2)n cluster-surface scattering is characterized by means of classical molecular dynamics simulations, providing insights for several experiments, such as the cluster-catalyzed oxidation of a silicon surface. Simulations of the cluster scattering process reveals that the oxidation mechanism cannot occur through molecular dissociation nor by direct molecular reaction. Molecular dynamics simulations of (O2)n cluster-surface scattering, along with high-level quantum chemistry calculations of the (O2) 2 cluster model, suggested a novel 'ladder climbing' mechanism, involving curve-crossing and spin orbit coupling, for the efficient mechanically-induced formation of highly reactive singlet O2 molecules. Such a process may also be responsible for the presence of a 'dark channel' in the enhanced vibrational relaxation of highly excited O2 molecules, and shows that the Born-Oppenheimer approximation breaks down in the 'chemistry with a hammer'
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Lin, Jiunn-Nan, and 林俊男. "Development of Supported Gold Nano-Particles and Their Applications in Combustion Catalysis." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/53122831542945342811.
Full textAbstract:
博士國立臺灣大學
化學工程學研究所
90
The development of highly active supported gold nano-particles for catalysis application was studied in this dissertation. The effects of supports, surface acidity modification, and gold solution on the supported gold nano-particles were investigated. The characterization of the catalysts, the examination of catalytic activities, and the discussion of the effects of preparation conditions were presented. The mechanisms of gold loading were also built. It was found that the catalytic activity of supported gold nano-particles was related to the dispersion, supports, and preparation conditions, which control the sizes of the gold particles on selected supports. For zeolites as supports, it was found that the gold loading didn’t depend on the IEPs of the the zeolites and was related to the structures and the amount of ion-exchange sites of the zeolites. It was also found that the protons in zeolites can catalyze the condensation of gold precursors to form the larger gold particles. Thus, decreasing the amount of protons in zeolites before loading gold was effective to prepare highly active Au/zeolite catalysts for low temperature CO oxidation. The gold particles on acidity modified Y-type zeolite were 2.5 times more active and stable than those on proton-rich Y-type zeolite for CO oxidation at 0℃. From the TEM results, it was found that most of the gold particles on the acidity modified Y-type zeolite were smaller than 2nm and were more uniformly dispersed. The catalytic activities and stability of Au/zeolites for CO oxidation were also affected by the structures of the zeolites and Au/Y catalyst was the best among them.. From the study of gold precursors in the solution, it was found that different species and sizes of gold precursors were formed in the solution at different preparation conditions, which affected the gold particle sizes and catalytic activity. The gold precursors were affected by the gold concentrations, pH values, preparation temperature, and time. Therefore, it was concluded from this research that for the preparation of Au/Y with high CO oxidation activity, a gold solution with surface acidity modified Y-type zeolite (1 g of zeolite per 125 ml solution) and with initial gold concentration around 1.46×10-3 M, solution pH at 6, a solution temperature around 80 ℃ and stirring for 1h were recommended. γ-Al2O3, SiO2 and TiO2 were also used as supports to investigate the effects of these oxides on the preparation of gold catalysts. Forγ-Al2O3 and SiO2, it was found that the mechanism of gold loading was via electrostatic deposition, which depended on the IEPs of the supports. It was observed that the gold particles supported onγ-Al2O3 and SiO2 from gold solutions with pH value of 6.0 were not active for CO oxidation at 0℃. High temperature reduction was needed to activate these supported gold particles for CO oxidation. This was due to the formation of large gold particles and small gold particles with residual chlorides on the supports. Different fromγ-Al2O3 and SiO2, the mechanism of gold loading on TiO2 was via adsorption-reduction model, which resulted in higher gold loading and less residual chlorides. Thus, the Au/TiO2 were very active for CO oxidation as Au/Y at 0℃. It was inevitable to have an inlet gas stream with moisture for the application of CO oxidation. It was found that moisture showed little effect on CO oxidation over as-prepared Au/TiO2 catalysts; however, the catalytic activity of as-prepared Au/Y can be enhanced over 20% of CO conversion by the presence of water vapor. The activity of Au/Y was superior to that of Au/TiO2 in wet reaction conditions. In addition to the application for low temperature CO oxidation, Au/Cr/γ-Al2O3 was also prepared in this study to test the complete oxidation of C3H8 for the application in VOCs removal and compared with Cr/γ-Al2O3. It was found that the oxidation of C3H8 over Cr/γ-Al2O3 was via reduction-oxidation mechanism, which was also named as Mar-van Krevelen mechanism, and the existence of gold can increase the reduction-oxidation rate, therefore, the activity of Cr/γ-Al2O3 was enhanced by gold. However, the catalytic activity of Au/Cr/γ-Al2O3 decayed during reaction. After the regeneration process, the activity of Au/Cr/γ-Al2O3 couldn’t be recovered to its initial conversion. The deactivation was the formation of coke and the gold particles sintered during reaction and/or the regeneration process. According to these research results, Au/Y catalyst prepared in this study can be as active and stable as Au/TiO2 at 0℃ for CO oxidation. Moreover, the presence of 3 % water vapor in the feed stream can enhance the catalytic activity of Au/Y and the performance was even superior to Au/TiO2 at 25℃. Furthermore, gold particles were not capable of high temperature catalytic reaction in the view of application because the gold particles sintered more easily. It was suggested that it was better to make use of these supported gold nano-particles in catalysis at lower temperature, such as the removal of CO from our surroundings at room temperature.
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Roy, Sounak. "Noble Metal And Base Metal Ion Substituted Ceo2 And Tio2 : Efficient Catalysts For Nox Abatement." Thesis, 2007. http://hdl.handle.net/2005/584.
Full textAbstract:
In recent times, as regulations and legislations for exhaust treatment have become more stringent, a major concern in the arena of environmental catalysis is to find new efficient and economical exhaust treatment catalysts. Chapter 1 is a review of the current status of various NOx abatement techniques and understanding the role of “auto-exhaust catalysts” involved therein. Chapter 2 presents the studies on synthesis of ionically substituted precious metal ions like Pd2+, Pt2+ and Rh3+ in CeO2 matrix and their comparative three-way catalytic performances for NO reduction by CO, as well as CO and hydrocarbon oxidation. Ce0.98Pd0.02O2- showed better catalytic activity than ionically dispersed Pt or Rh in CeO2. The study in Chapter 3 aims at synthesizing 1 atom% Pd2+ ion in TiO2 in the form of Ti0.99Pd0.01O2- with oxide ion vacancy. A bi-functional reaction mechanism for CO oxidation by O2 and NO reduction by CO was proposed. For NO reduction in presence of CO, the model based on competitive adsorption of NO and CO on Pd2+, NO chemisorption and dissociation on oxide ion vacancy fits the experimental data. The rate parameters obtained from the model indicates that the reactions are much faster over this catalyst compared to other catalysts reported in the literature. In Chapter 4 we present catalytic reduction of NO by H2 over precious metal substituted TiO2 (Ti0.99M0.01O2-, where M = Ru, Rh, Pd, Pt) catalysts. The rate of NO reduction by H2 depends on the reducibility of the catalysts. Chapter 5 presents the studies on reduction of NO by NH3 in presence of excess oxygen. 10 atom % of first row transition metal ions (Ti0.9M0.1O2-, where M = Cr, Mn, Fe, Co and Cu) were substituted in anatase TiO2 and TPD study showed that the Lewis and Bronsted acid sites are adsorption sites for NH3, whereas NO is found to dissociatively chemisorbed in oxide ion vacancies. The mechanism of the low temperature catalytic activity of the SCR and the selectivity of the products were studied to understand the mechanism by studying the by-reactions like ammonia oxidation by oxygen. A new catalyst Ti0.9Mn0.05Fe0.05O2- has shown low temperature activity with a broad SCR window from 200 to 400 °C and more selectivity than commercial vanadium-oxides catalysts. We attempted NO dissociation by a photochemical route with remarkable success. In Chapter 6 we report room temperature photocatalytic activity of Ti0.99Pd0.01O2- for NO reduction and CO oxidation by creating redox adsorption sites and utilizing oxide ion vacancy in the catalyst. The reduction of NO is carried out both in the presence and in the absence of CO. Despite competitive adsorption of NO and CO on the Pd2+ sites, the rate of reduction of NO is two orders of magnitude higher than unsubstituted TiO2. High rates of photo-oxidation of CO with O2 over Ti0.99Pd0.01O2- were observed at room temperature. In Chapter 7 the results are summarized and critical issues are addressed. Novel idea in this thesis was to see if both noble metal ions and base metal ions substituted in TiO2 and CeO2 reducible supports can act as better active sites than the corresponding metal atoms in their zero valent state.
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Barrett, Dean Howard. "A stable high temperature gold nano-catalyst: synthesis, characterization and application." Thesis, 2013. http://hdl.handle.net/10539/12346.
Full textAbstract:
A stable high temperature gold nano-catalyst:
synthesis, characterization and application
The ability of supported gold nanoparticles to catalyse many reactions even
at very low temperatures has spurred a great deal of research into the eld.
Reactions such as CO oxidation and NOx reduction have many industrial applications
as well as uses in the motor industry for catalytic converters. The
interest is both for scienti c as well as economic reasons as gold supplies far
exceed all PGM supplies. Scienti cally gold catalysts are able to catalyze reactions
from below 0°C, a feat that no PGM catalyst can achieve. The low
temperature activity of gold catalysts will reduce the emission of pollutants
during start up. Since the discovery and development of gold catalysts one of
the most researched topics has been nding ways to stabilise the gold nanoparticles
on the support surface. The importance of gold nanoparticle stability
is crucial as the catalysts are only highly active if the gold nanoparticles are
less than 5 nm in size. A number of companies have worked to develop gold
catalysts that are stable for long durations at temperatures over 450°C with
no signi cant progress made over the last two decades other than a catalyst
produced by Toyota.
In this thesis, literature reviews of current support materials as well as synthesis
methods are investigated in order to determine reasons for the instability
of current gold catalysts. Further, the Mintek Aurolite catalyst is tested and
its deactivation mechanisms probed using in-situ VT-PXRD, Rietveld re nement,
TEM, HR-TEM, as well as CO oxidation tests. Testing revealed aws in
the support structure of the catalyst which resulted in dramatic deactivation.
As titania is such a common support material for many reactions in industry
as well as being known to be one of the best supports for gold it was chosen
as a support material. However, as is revealed, in its current forms and
morphologies it is unable to provide the thermodynamically stable and high
surface areas that are required for a stable catalyst After the development of a
robust and reproducible synthesis method for the deposition of gold and other
PGM's a number of supports were tested. These include silica and zirconia as well as titania derivatives such as Degussa P25 and commercial anatase. Initially
these supports o er high usable surface areas but after a relatively small
amount of time complete deactivation occurs. Reasons for this deactivation
are determined and the information gained is used to develop supports that
can combat these deactivation processes. Phase pure nano anatase is synthesised
which produced a support with an incredibly large surface area compared
to the aforementioned supports. The catalyst was able to withstand temperatures
over 450°C for longer durations compared to other catalysts exposed
to the same conditions. However, the phase conversion of the anatase to its
thermodynamically stable form rutile once again deactivated the catalyst with
time. Finally a rutile nanosupport is developed with the desired morphology
and thermodynamic stability needed for high temperature applications. The
catalyst is able to withstand temperatures over 550°C for more than 200 hours
as well as still being active after exposure to 810°C. The industrial Aurolite
catalyst showed complete deactivation after just 12 hours at 500°C. The catalyst
produced in this thesis has been shown to be one of the most stable and
thermally resistant gold catalysts in the world.
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Shodiya, Titilayo. "Utilization of Nano-Catalysts for Green Electric Power Generation." Diss., 2015. http://hdl.handle.net/10161/9817.
Full textAbstract:
Nano-structures were investigated for the advancement of energy conversion technology because of their enhanced catalytic, thermal, and physiochemical interfacial properties and increased solar absorption. Hydrogen is a widely investigated and proven fuel and energy carrier for promising "green" technologies such as fuel cells. Difficulties involving storage, transport, and availability remain challenges that inhibit the widespread use of hydrogen fuel. For these reasons, in-situ hydrogen production has been at the forefront of research in the renewable and sustainable energy field. A common approach for hydrogen generation is the reforming of alcoholic and hydrocarbon fuels from fossil and renewable sources to a hydrogen-rich gas mixture.
Unfortunately, an intrinsic byproduct of any fuel reforming reaction is toxic and highly reactive CO, which has to be removed before the hydrogen gas can be used in fuel cells or delicate chemical processes. In this work, Au/alpha-Fe2O3 catalyst was synthesized using a modified co-precipitation method to generate an inverse catalyst model. The effects of introducing CO2 and H2O during preferential oxidation (PROX) of CO were investigated. For realistic conditions of (bio-)fuel reforming, 24% CO2 and 10% water the highest document conversion, 99.85% was achieved. The mechanism for PROX is not known definitively, however, current literature believes the gold particle size is the key. In contrast, we emphasize the tremendous role of the support particle size. A particle size study was performed to have in depth analysis of the catalysts morphology during synthesis. With this study we were also able to modify how the catalyst was made to further reduce the particle size of the support material leading to ~99.9% conversion. We also showed that the resulting PROX output gas could power a PEM fuel cell with only a 4% drop in power without poisoning the membrane electrode assembly.
The second major aim of this study is to develop an energy-efficient technology that fuses photothermal catalysis and plasmonic phenomena. Although current literature has claimed that the coupling of these technologies is impossible, here we demonstrate the fabrication of reaction cells for plasmon-induced photo-catalytic hydrogen production. The localized nature of the plasmon resonance allows the entire system to remain at ambient temperatures while a high-temperature methanol reformation reaction occurs at the plasmonic sites. Employing a nanostructured plasmonic substrate, we have successfully achieved sufficient thermal excitement (via localized surface plasmon resonance (LSPR)) to facilitate a heterogeneous chemical reaction. The experimental tests demonstrate that hydrogen gas can indeed be generated in a cold reactor, which has never been done before. Additionally, the proposed method has the highest solar absorption out of several variations and significantly reduces the cost, while increasing the efficiency of solar fuels.
Dissertation
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Ruderman, Andrés. "Electrocatálisis en electrodos nano estructurados de plata." Doctoral thesis, 2016. http://hdl.handle.net/11086/5468.
Full textAbstract:
Tesis (Doctor en Física)--Universidad Nacional de Córdoba, Facultad de Matemática, Astronomía, Física y Computación, 2016.Los estudios realizados en este trabajo abarcan diferentes aspectos de la cinética de la reacción de desprendimiento de hidrógeno (her). Esto tiene como finalidad la obtención de nuevos conocimientos que permitan comprender la actividad electrocatalítica en diversas superficies monocristalinas de plata. De esta manera, las investigaciones realizadas se enmarcan en la búsqueda de un catalizador eficiente y a un costo razonable para la her. El trabajo desarrollado se divide en dos áreas: comprender la cinética de la her en diferentes superficies monocristalinas escalonadas de Ag(11n) y estudiar el mecanismo de deposición de Rh sobre Ag, el cuál puede ser un electrocatalizador bimetálico eficiente para la her.
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"The Effects of Different Particle Size of Nano-ZnO and Alumina-based Catalysts on Removal of Atrazine from Water with Ozone." Thesis, 2015. http://hdl.handle.net/10388/ETD-2015-12-2380.
Full textAbstract:
Due to the widespread application of pesticides and herbicides in agricultural industries, these substances have been highlighted as emerging contamination of natural ground and surface water resources. Conventional water treatment processes are only effective in removing emerging contaminants in water.
The mechanism of degradation of organic impurities present in water using ozone is known to either directly involve the ozone molecule or to occur by the indirect effect of free hydroxyl radicals (•OH). The latter are produced in the radical chain reaction of ozone decomposition.
A series of experiments were carried out to investigate the effects of particle sizes of nano-ZnO catalysts on removal of atrazine (ATZ). Nano-ZnO catalysts increase the rate of ozone decomposition and atrazine removal by production of hydroxyl radicals as oxidative intermediates. However, different particle sizes have a minimal effect on the rate of ozone decomposition and atrazine removal. It is believed that molecular ozone is adsorbed on the surface of nano-ZnO followed by the oxidation of the ozone molecule. This leads to the production of OH radicals. Therefore, it is reasonable to assume that reaction is carried out in the bulk of the solution and the rate is independent of catalyst’s surface area. This is probably the reason for similar reaction rates of different particle sizes of nano-Zno catalysts.
Additionally three different metal oxides (ZnO, Mn2O3 and Fe2O3) loaded on ƴ-alumina and ƴ-alumina (metal oxide-free) were used in catalytic ozonation of aquatic atrazine samples. The findings substantiate the strong influence of molecular ozone on degradation of ATZ and the partial involvement of hydroxyl radicals in the mechanism. Based on adsorption studies, atrazine has a low affinity towards adsorption on the surface of the catalysts. It is logical to assume that ozone reacts with the hydroxyl groups of the catalyst to form a highly reactive metal-ozone complex. This layer could react with a molecule of atrazine through an electron-transfer mechanism.
The residual concentration of ATZ and total organic carbon (TOC) were determined by High Performance Liquid Chromatography (HPLC) and Total Organic Carbon (TOC) analyses.
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Goislard, De Monsabert Thomas. "Couches de Nanotubes et Filaments de Carbone pour l'Emission Froide d'Electrons -Intégration aux Ecrans Plats à Emission de Champ." Phd thesis, 2006. http://tel.archives-ouvertes.fr/tel-00090016.
Full textAbstract:
Ce travail concerne l'élaboration in situ, par CVD catalytique, de couches de nanotubes et filaments de carbone pour leur intégration en tant que couches émissives d'électrons dans les écrans plats à émission de champ. Les paramètres clés, avantages et limitations de plusieurs techniques de préparation et d'intégration de nano particules catalytiques ont d'abord été analysés : le démouillage d'un film continu, la gravure humide post-démouillage, le dépôt de nano agrégats et la lithographie électronique. Trois techniques de croissance de couches carbonées ont ensuite été étudiées dans le même réacteur : la CVD thermique simple, la CVD en présence d'un champ électrique et la CVD avec assistance plasma à partir d'une source de carbone solide. Enfin, les propriétés émissives des diverses couches carbonées élaborées ont été mesurées, en mode diode pour les couches synthétisées sur échantillon plan et en mode triode pour les couches intégrées sur structure cathodique d'écran.
L'analyse de ces résultats a permis de clarifier les liens entre paramètres technologiques d'élaboration, morphologie et performances émissives des films de nanotubes et filaments de carbone.