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1
Ben, Salem Roua. „Catalyseurs à base d'oxydes métalliques fluorés : synthèse, caractérisations et applications catalytiques“. Electronic Thesis or Diss., Lyon 1, 2023. https://n2t.net/ark:/47881/m6c53kx4.
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Ces travaux de thèse portent sur la synthèse de nouveaux catalyseurs fluorés, utilisant d’acide trifluoroacétique (TFAH) comme précurseur de Fluor, leurs caractérisations physico-chimiques et l’étude de leurs propriétés acido-basiques en phases gazeuse et aqueuse. Une première méthode consiste en l’échange anionique entre des supports oxo/hydroxo de titane, de niobium ou de zirconium, de surfaces spécifiques élevées, et une solution de TFAH. La rétention du fluor, avant et après calcination, est plus importante au contact du support à base de zirconium. La présence de fluor inhibe la basicité de la zircone et génère une acidité de Brønsted expliqué par l’effet électroattracteur de fluor et rend la surface du catalyseur plus hydrophobe. La zircone fluorée convertit sélectivement l’isopropanol en propène en phase gazeuse et la dihydroxyacétone en pyruvaldéhyde dans l’eau. La deuxième synthèse est une nouvelle approche multi-étape couplant la décomposition d’un précurseur de fluor à base d’yttrium Y(TFA)3(H2O)3 en NPs de YF3 et leur incorporation dans un gel de TiO2. Différentes techniques de caractérisations physico-chimique (XPS, DRX, RMN 19F) indiquent que le fluor existe sous la forme YF3 dans la matrice de TiO2, stable après une calcination à 500°C. YF3 dispersé dans TiO2 de surface spécifique élevée catalyse efficacement la conversion de la dihydroxyacetone (DHA) dans l’eauThis thesis work focuses on the synthesis of new fluorinated metal catalysts, using trifluoroacetic acid (TFAH) as fluorine precursor, their physico-chemical characterizations and the study of their acid-base properties in the gas and aqueous phases. The first synthesis is the anionic exchange between oxo/hydroxo supports of titanium, of niobium and of zirconium, with high specific areas, and a solution of TFAH. The fluorine retention, before and after calcination, is greater using the zirconium support. The presence of fluorine inhibits the basicity of the zirconia and generates Brønsted acidity due to the electron-withdrawing effect of fluorine and makes the catalyst’s surface more hydrophobic. Fluorinated zirconia produces selectively propene from isopropanol in gas phase and pyruvaldehyde from dihydroxyacetone in water. The second synthesis is new multi-step approach coupling the decomposition of an yttrium-based fluorine precursor Y(TFA)3(H2O)3 into YF3 NPs and their incorporation into TiO2. Various physico-chemical characterization techniques (XPS, XRD, 19F NMR) indicate that fluorine exists in the form of YF3 in the TiO2 matrix, stable at after calcination at 500°C. YF3 dispersed in TiO2 of high surface area catalyzes efficiently the conversion of dihydroxyacetone (DHA) in water
2
Ren, Xiaolin. „Synthesis and characterisation of metal oxides and fluorinated perovskite-related oxides“. Thesis, Open University, 2005. http://oro.open.ac.uk/54200/.
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Perovskite-related materials of composition LaFe1-xCoxO3 prepared by conventional calcination methods and mechanical milling are shown by temperature programmed reduction to be more susceptible to reduction in a flowing mixture of hydrogen and nitrogen by the incorporation of cobalt. X-ray powder diffraction and Mossbauer spectroscopy show that in iron-rich systems the limited reduction of iron and cobalt leads to the segregation of discrete metallic phases without destruction of the perovskite structure. In cobalt-rich systems, the reduction of Co3+ to Coo precedes complete reduction of Fe3+ and the segregation of alloy and metal phases is accompanied by destruction of the perovskite structure. Phases made by milling techniques were of smaller particle size and are more susceptible to hydrogen reduction than their counterparts made by conventional techniques. Materials of the type La0.5Sr0.5MO3 (M= Fe, Co) made by calcination methods are more susceptible to reduction when the transition metal M is cobalt as compared to iron. Perovskite-related oxides of composition La1-xSrxFe1-yCoyO3 have been fluorinated by reaction with poly(vinylidene fluoride). The materials have been characterised by X-ray powder diffraction and Mossbauer spectroscopy. Fluorination induces a reduction in the oxidation state of iron from Fe4+ to Fe3+. The fluorinated materials were magnetically ordered at 298 K. Compounds of the type SrFe1-xSnxO3 were found to contain Fe5+ and Fe3+. Fluorination resulted in reduction of the transition metal to Fe3+ and, in iron-rich systems, magnetic order. The compound Ba2SnO4 which adopts the K2NiF4-type structure has also been fluorinated by reaction with zinc fluoride. X-ray powder diffraction shows an enlargement of the unit cell of the fluorinated phase along the c-axis. Small particle iron- and vanadium- antimonate have been prepared by mechanical milling methods. The phases have been examined by M6ssbauer spectroscopy and can be formulated M3+Sb5+O4 (M = Fe, V). Thermal analysis suggests that the vanadium animonate formed by milling V2O5 and Sb2O3 in an inert atmosphere may be oxygen deficient. X-ray powder diffraction shows that milling also induces the phase transformation of the cubic senarmontite Sb2O3 form to the orthorhombic valentinite Sb2O3 form and of a-Sb2O4 to B-Sb2O4.
3
Abdoullah, Mohamad. „Supported transition metal oxides as solid base catalysts“. Thesis, University of Huddersfield, 2016. http://eprints.hud.ac.uk/id/eprint/28325/.
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The initial objective of the work studied here was to investigate the effects of isomorphously-substituted transition metals in lattice sites in Layered Double Hydroxides (LDHs) in terms of basicity and catalytic activity in base-catalysed reactions and oxidation reactions. Experiments in which copper(II), nickel(II), cobalt(II), zinc(II) and iron(III) were substituted in the lattice of synthetic hydrotalcites showed that, on calcination, the resultant mixed oxides arising from hydrotalcites containing copper(II) exhibited the greatest enhancement of catalytic activity. Test reactions were the conversion of 4-methylpentan-2-ol to methylisobutylketone, the oxidation of benzyl alcohol and the Henry reaction between benzaldehyde and nitromethane. Results showed conclusively that copper(II) imparted base catalytic activity to the mixed metal oxides formed on calcination of the LDHs. This was confirmed through an extension to the study in which the copper(II) content in the LDHs was varied. It was shown that there is an optimum copper(II) loading, above which additional copper(II) is not effectively incorporated in the LDH lattice. Other supports for copper(II) as an oxide were investigated, on the basis that activity was linked to effective dispersion of copper(II) oxide. A series of copper(II) dispersions on zirconia, on silica and on magnesium oxide were prepared and tested. The zirconia-supported catalysts were the most active so work was concentrated on these. Two methods for preparing copper(II) oxide/zirconia were investigated, using a solid state reaction and using a sol-gel process. Catalysts were prepared with molar copper contents of from 2 to 60 mol%. It was possible to see from powder X-ray diffraction that copper(II) was dispersed in the zirconia matrix at levels up to about 20% depending on the synthetic method. And it was shown that base-catalytic activity of these materials correlated with the amount of fully incorporated copper(II). Activities of these were generally higher than the mixed metal oxides made from the LDHs. For comparison, another, different, approach to incorporating basicity in oxide supports was examined, in which alkylamino groups were tethered to silica supports, specifically a mesoporous molecular sieve form of silica, SBA-15. The activity of these materials were compared with those of the copper(II) based catalysts in the Henry reaction between nitromethane and benzaldehyde. An advantage of these catalysts was exploited by coordinating palladium(II) to the amine groups at different levels to impart oxidation catalytic activity. The resultant materials, in which only part of the amine functionality was coordinated by palladium(II), were tested as bifunctional catalysts, for combined oxidation and base catalytic activity, in the two step reaction between benzyl alcohol and nitromethane, which proceeds via an oxidation step to benzaldehyde followed by a base-catalysed step. The overall conclusion was that copper(II) is effective at imparting base catalytic activity to a range of support oxides, and that it does not have significant activity towards oxidation reactions., contrary to some claims in the literature. Oxidation activity can be obtained alongside base activity by preparing bifunctional catalysts but only through a different approach.
4
Popa, Tiberiu. „Metal oxide catalysts for green applications“. Laramie, Wyo. : University of Wyoming, 2009. http://proquest.umi.com/pqdweb?did=1955861591&sid=1&Fmt=2&clientId=18949&RQT=309&VName=PQD.
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5
Gonçalves, Alexandre Amormino Dos Santos. „Development of Nanostructured Ceramic Catalysts Based on Mixed Metal Oxides“. Kent State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=kent1543412496976455.
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6
Han, Binghong. „Activating oxygen chemistry on metal and metal oxides: design principles of electrochemical catalysts“. Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/104100.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2016.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 93-98).
Electrochemical energy storage and conversion devices are important for the application of sustainable clean energies in the next decades. However, the slow kinetics of oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) lead to great energy loss in many electrochemical energy devices, including polymer electrolyte membrane fuel cells (PEMFCs), water splitting electrolyzers, and rechargeable metal-air batteries, which hampers the development of new-energy applications such as electric vehicles. To increase the energy efficiency of ORR and OER processes, various catalysts have been studied for oxygen electrocatalysis, but they are still not active enough or not stable enough in developing commercial friendly electrochemical devices. In this work, systematic studies have been applied on two catalyst systems: Pt-metal (Pt-M) alloys for ORR and perovskite oxides for OER. The combination of electrochemical characterizations with transmission electron microscopy (TEM) techniques provides deeper insights on how the basic physical and chemical properties could influence the stability and activity of the catalysts. For Pt-M ORR catalysts, it is found that using transition metal with more positive dissolution potential or forming protective Pt-rich shell by mild acid treatment can improve their stability in acid electrolyte. While for perovskite oxide OER catalysts, it is found that a closer distance between O 2p-band and Fermi level leads to higher activity but lower stability at pH 7, due to the activation of lattice oxygen sites. Moreover, with the help of environmental TEM techniques, structural oscillations are observed on perovskite oxides in the presence of water and electron radiation, caused by the oxygen evolution after water uptake into the oxide lattice. Such structural oscillation is greatly suppressed if the formation and mobility of lattice oxygen vacancy is hampered. The various new activity and stability descriptors for oxygen electrocatalysis found in this work not only provided practical guidelines for designing new ORR or OER catalysts, but also improved our fundamental understandings of the interactions between catalysts and electrolyte.
by Binghong Han.
Ph. D.
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Motshweni, Jim Sipho. „Synthesis of mixed metal oxides for use as selective oxidation catalysts“. Thesis, Link to the online version, 2007. http://hdl.handle.net/10019/445.
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8
Brown, Adrian St Clair. „The application of superacidic materials for the oxidation of methane“. Thesis, Nottingham Trent University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.312315.
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9
Kotbagi, T. V. „Synthesis of fine chemicals from renewables using supported metal oxides as catalysts“. Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 2013. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/2170.
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10
Messi, C. „Nanostructured catalytic metal oxides supported over oxide supports of various nature : the iron oxide system“. Doctoral thesis, Università degli Studi di Milano, 2008. http://hdl.handle.net/2434/57081.
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11
Ngo, Lien Thuy. „Sintering and reactivity of model oxide-supported catalysts : Pt/ZnO(000-1)-O and Pd/[alpha]-Al₂O₃(0001) /“. Thesis, Connect to this title online; UW restricted, 2004. http://hdl.handle.net/1773/8543.
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12
Beyer, Hans [Verfasser]. „Activation of nitrogen oxides by supported noble metal catalysts: Structure-activity relationships / Hans Beyer“. München : Verlag Dr. Hut, 2010. http://d-nb.info/1009095641/34.
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13
Bruce, David Alan. „Synthesis and characterization of heterogeneous metal oxide catalysts on amorphous and molecular sieve supports“. Diss., Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/30409.
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14
Hewa, Dewage Amendra Fernando. „Theoretical investigation of the water splitting mechanism on transition metal oxide catalysts“. Diss., Kansas State University, 2016. http://hdl.handle.net/2097/32148.
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Doctor of PhilosophyDepartment of Chemistry
Christine M. Aikens
Water oxidation can be considered as the ‘holy grail’ of renewable energy research, where water is split into constituent molecular hydrogen and oxygen. Hydrogen is a very efficient energy source that is both clean and sustainable. The byproduct of hydrogen combustion is water, which in turn can be reused as the source for hydrogen generation. Natural water splitting is observed during photosynthesis in the oxygen-evolving complex of photosystem II, which consists of a CaMn₄O₄ cubane core. Herein, we report in silico approaches to understand bottom up catalytic design of model transition metal oxide complexes for water splitting. We have employed density functional theory to investigate model ligand-free architectures of cobalt and manganese oxide dimer (Mn₂(μ-OH)(μ-O)(H₂O)₃(OH)₅, Mn₂(μ-OH)₂(H₂O)₄(OH)₄, Mn₂(μ-OH)₂(H₂O)₂(OH)₂(O(CH)₃O)₂, Co₂(μ-OH)₂(H₂O)₄(OH)₄ and cubane (Co₄O₄(H₂O)₈(OH)₄, Mn₄O₄(H₂O)[subscript]x(OH)[subscript]y x = 4-8, y = 8-4) complexes. The thermodynamically lowest energy pathway on the cobalt dimer catalyst proceeds through a nucleophilic attack of a solvent water molecule to a Co(V)-O radical moiety whereas the pathway on the cubane catalyst involves a geminal coupling of a Co(V)-O radical oxo group with bridging oxo sites. The lowest energy pathway for the fully saturated Mn₂O₄•6H₂O (Mn₂(μ-OH)(μ-O)(H₂O)₃(OH)₅) and Mn₂O₃•7H₂O (Mn₂(μ-OH)₂(H₂O)₄(OH)₄) complexes occur through a nucleophilic attack of a solvent water molecule to Mn(IV½)O and Mn(V)O oxo moieties respectively. Out of all the oxidation state configurations studied for the manganese cubane, we observed that Mn₄(IV IV IV IV), Mn₄(III IV IV IV), and Mn₄(III III IV V) configurations are thermodynamically viable for water oxidation. All three of these reaction pathways proceed via nucleophilic attack of solvent water molecule to the manganese oxo species. The highest thermodynamic energy step in manganese dimer and cubane complexes corresponds to the formation of the manganese oxo species, which is a significant feature that reoccurred in all these reaction pathways. We have also employed multireference and multiconfigurational calculations to investigate the Mn₂(μ-OH)₂(H₂O)₂(OH)₂(O(CH)₃O)₂ system. The presence of Mn(IV)O[superscript]• radical moieties has been observed in this catalytic pathway. These simplest models of cobalt and manganese with water-derived ligands are essential to understand microscopic properties that can be used as descriptors in designing future catalysts.
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Romano, Esteban Javier. „In-situ surface science studies of the interaction between sulfur dioxide and two-dimensional palladium loaded-cerium/zirconium mixed metal oxide model catalysts“. Diss., Mississippi State : Mississippi State University, 2005. http://library.msstate.edu/etd/show.asp?etd=etd-04062005-093500.
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16
Shang, Hongyu SHANG. „Investigating Electronic Structure Effects in Transition Metal Oxides Used as Catalysts for Water Oxidation and CO2 Reduction“. The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1525451894252362.
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17
SCELFO, SIMONE. „Metal oxides catalysts for the synthesis of value-added chemicals from 2nd generation sugars and sugar derivatives“. Doctoral thesis, Politecnico di Torino, 2017. http://hdl.handle.net/11583/2675152.
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The present Ph.D. thesis provides some examples of innovative 2nd generation catalytic processes for the conversion of renewable raw materials into green value-added chemicals. In particular, D-glucose and some its derivatives, all ideally representing waste materials of dedicated biomasses, agricultural residues, or solid organic urban waste exploitation in the biorefinery plant, were converted into useful chemical building-blocks.
After a brief introduction to the topic and the description of the experimental method, each chapter of the work is based on one or more scientific articles either published or submitted. Among the possible catalytic reactions, the hydrogenation, oxidation and hydrodeoxygenation were investigated: for this purpose, several novel catalysts were synthetized, tested and characterized. The catalysts were made from precursor solutions with the incipient wet impregnation method or with the solution combustion synthesis, depending by the catalyst type. The conversion of glucose and some glucose-derivatives was typically performed under gentle operative conditions and in aqueous mean.
Pt-based catalysts were tested for glucose conversion to adipic acid in a two-step process carried out in water solution without any pH control by investigating the effect of a series of supporting materials (active carbon, alumina, silica and ceria). The process consisted in the D-saccharic acid (SacA) production by D-glucose catalytic wet air oxidation followed by a hydrodeoxygenation treatment of SacA to adipic acid (AA) with the same catalyst. The main limit of using Pt for D-glucose oxidation is represented by the catalyst inhibition operated by the first product of the reaction, the gluconic acid (GluA), which prevents the consecutive reaction of SacA formation, but a deeper investigation of the reaction scheme allowed us to assess that over Pt/alumina the consecutive oxidation of gluconic acid to SacA is slightly favored under uncontrolled pH too.We have demonstrated that a 5.2 wt.% Pt on γ-alumina sample, the catalysts presenting the larger amount of strong Brønsted acid sites, was the best material for obtaining SacA (with a molar yield of about 13.5%); afterward, by performing the halogen-promoted hydrodeoxygenation of the resulting solution, the SacA was quantitatively converted into AA (and thus the overall adipic acid molar yield from glucose was about 13.0%).
Effectively, The efficient conversion of common biomass derivatives, as D-glucose, into value-added chemicals has received a great deal of attention in the last few years. Several heterogeneous catalytic systems, characterized by noble metals, have already been investigated for the Catalytic Wet Air Oxidation (CWAO) of derived biomass. Nevertheless, the redox effect of such catalysts on biobased compounds has not been described in detail. In the present thesis, some perovskite type oxides (Fe, Co, Mn) that present high redox properties and stability under hydrothermal conditions have been tested to establish their ability to convert D-glucose into C6 aldaric acid, lactic acid (LacA) and levulinic acid (LevA). The influence of the reaction temperature, and the affinity of the catalysts to hydrogen and oxygen on the distribution of the liquid products have been investigated. In the best conditions, 50.3 mol.% and 69.5 mol.% of lactic and levulinic acid have been obtained by employing LaCoO3 and LaMnO3, respectively. Apart from the oxidative effect, which has led to several oxidation products, a high reductive effect of the catalysts has enabled the conversion of some key intermediates, such as pyruvic acid (PyrA) and hydroxymethylfurfural (HMF), into the desired products. LaMnO3, which has resulted to be the most oxidizable/reducible catalyst over a low temperature range, has shown the best performance of the studied perovskite type oxides; it has been found to promote the conversion of hydroxymethylfurfural to levulinic acid and to give the highest overall molar yield.
Moreover, performing catalysts have been synthetized through incipient wet impregnation and tested for cis,cis-muconic acid (ccMA) hydrogenation to adipic acid.
Before the hydrogenation, the investigation on the solubility of ccMA dissolution in different polar solvents has been carried out by characterizing and modelling the dissolution as a function of temperature. Water, ethanol, 2-propanol and acetic acid have been investigated as solvents in the range temperatures from a 298.15 to 348.15 K. Owing to the absence of ccMA solubility data, the reliability of the adopted experimental set-up was validated comparing published and experimental solubility data of a similar compound, that is, AA. From the results, it has emerged that the employed system is appropriate for the determination of molar fractions of an organic compound dissolved in polar solvents. The molar fraction and temperature were correlated using the Apelblat equation model, which is applied for the mathematic fitting of experimental data.
A total relative average deviation of 3.54% was obtained for the experimental results and the solubility data obtained with the model, thus attesting the adequacy for this study. The use of Apelblat equation also allowed to determine the apparent molar enthalpy and molar entropy of dissolution. The dissolution of ccMA in water, ethanol, 2-propanol and acetic acid, over temperatures ranging from 298.15 to 348.15 K, has been shown to be endothermic.
The activity of Pt-based catalysts has been compared with a Ni-based catalyst at a gentle condition. A supported 14.2 wt.% Ni on γ-alumina converted 100% of muconic acid, yielding 99.4 mol.% of AA.
Finally, the oxidative cracking of 5-keto-L-aldonic acids to tartaric acid (TarA) was successfully performed at room temperature and atmospheric pressure in a carbonate buffer (pH = 10.34), by employing various V-based catalysts. The performance of the novel heterogeneous V-based catalysts was compared with the one of a conventional homogeneous system.
The effect of the catalysts was obvious and 2%VOx/ZrO2 was found to be the best catalyst for the 5-keto-aldonic acids conversion to tartaric acid. The tartaric acid selectivity was equal to 74.5% and 44.3% starting from the 5-keto-D-gluconic acid (5kGl) and 5-keto-L-galactonic acid (5kGa), respectively. The best performances in terms of tartaric acid selectivity were obtained at the beginning of reaction, and about one fourth of the carbon moles were converted into tartaric acid after 24 h of reaction. The substrate was entirely converted after 24 h indicating that several by-products were also produced during the reaction. So, an overall reaction pathway was supposed and the effect of the vanadium structure to the catalytic activity was hypothesized. Moreover, the reaction mechanism of the 5-keto-aldonic acids conversion to tartaric acid promoted by the anchoring VOx-support bond was described.
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Ren, Yu. „Applications of ordered mesoporous metal oxides : energy storage, adsorption, and catalysis“. Thesis, University of St Andrews, 2010. http://hdl.handle.net/10023/1705.
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The experimental data and results demonstrated here illustrate the preparation and application of mesoporous metal oxides in energy storage, adsorption, and catalysis. First, a new method of controlling the pore size and wall thickness of mesoporous silica was developed by controlling the calcination temperature. A series of such silica were used as hard templates to prepare the mesoporous metal oxide Co₃O₄. Using other methods, such as varying the silica template hydrothermal treatment temperature, using colloid silica, varying the materials ratio etc., a series of mesoporous β-MnO₂ with different pore size and wall thickness were prepared. By using these materials it has been possible to explore the influence of pore size and wall thickness on the rate of lithium intercalation into mesoporous electrode. There is intense interest in lithium intercalation into titanates due to their potential advantages (safety, rate) replacing graphite for new generation Li-ion battery. After the preparation of an ordered 3D mesoporous anatase the lithium intercalation as anode material has been investigated. To the best of our knowledge, there are no reports of ordered crystalline mesoporous metal oxides with microporous walls. Here, for the first time, the preparation and characterization of three dimensional ordered crystalline mesoporous α-MnO₂ with microporous wall was described, in which K+ and KIT-6 mesoporous silica act to template the micropores and mesopores, respectively. It was used as a cathode material for Li-ion battery. Its adsorption behavior and magnetic property was also surveyed. Following this we described the preparation and characterization of mesoporous CuO and reduced Cu[subscript(x)]O, and demonstrated their application in NO adsorption and delivery. Finally a series of crystalline mesoporous metal oxides were prepared and evaluated as catalysts for the CO oxidation.
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Buselli, Lorenzo. „Study of Co-based hydrotalcite-derived mixed metal oxides partially modified with silver as potential catalysts for N2O decomposition“. Master's thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amslaurea.unibo.it/11930/.
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Co-Al-Ox mixed metal oxides partially modified with Cu or Mg, as well as Ag were successfully prepared, characterized and evaluated as potential catalysts for the N2O decomposition. The materials were characterized by the following techniques: X-Ray Diffraction, Thermogravimetric Analysis (TGA), N2 Physisorption, Hydrogen Temperature-Programmed Reduction (H2-TPR), and X-ray photoelectron spectroscopy (XPS). Ag-modified HT-derived mixed oxides showed enhanced activity compared to the undoped materials, the optimum composition was found for (1 wt.% Ag)CHT-Co3Al. The catalyst characterization studies suggested that the improved catalytic activity of Ag-promoted catalysts were mainly because of the altered redox properties of the materials.
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Fu, Qi. „Activity and stability of nanostructured gold-cerium oxide catalysts for the water-gas shift reaction /“. Thesis, Connect to Dissertations & Theses @ Tufts University, 2004.
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21
Biswas, Somnath. „Watching Electrons Move in Metal Oxide Catalysts : Probing Ultrafast Electron Dynamics by Femtosecond Extreme Ultraviolet Reflection-Absorption Spectroscopy“. The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1586375150350782.
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22
Popa, Adriana. „Study of the Effect of Nanostructuring on the Magnetic and Electrocatalytic Properties of Metals and Metal Oxides“. Case Western Reserve University School of Graduate Studies / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=case1427735465.
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Baktash, Elham Verfasser], Arne [Akademischer Betreuer] Thomas, Matthias [Akademischer Betreuer] Driess und Holger [Akademischer Betreuer] [Dau. „Porous metal oxides : catalysts for activation of small molecules / Elham Baktash. Gutachter: Arne Thomas ; Holger Dau. Betreuer: Arne Thomas ; Matthias Driess“. Berlin : Technische Universität Berlin, 2014. http://d-nb.info/106655062X/34.
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Patil, Aniket. „Simultaneous Fixed Bed Removal of Nitrogen Oxides and Mercury Using Manganese and Cerium Mixed Metal Oxide Catalysts at Low Temperature SCR“. University of Cincinnati / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1530266242697853.
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Baktash, Elham [Verfasser], Arne Akademischer Betreuer] Thomas, Matthias [Akademischer Betreuer] Driess und Holger [Akademischer Betreuer] [Dau. „Porous metal oxides : catalysts for activation of small molecules / Elham Baktash. Gutachter: Arne Thomas ; Holger Dau. Betreuer: Arne Thomas ; Matthias Driess“. Berlin : Technische Universität Berlin, 2014. http://d-nb.info/106655062X/34.
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AL-SAEEDI, JAMAL N. „MOLECULAR STRUCTURE-REACTIVITY RELATIONSHIPS FOR PROPANE OXIDATION OVER MODEL MIXED OXIDE CATALYSTS“. University of Cincinnati / OhioLINK, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1053698262.
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Ahmed, Shibbir. „Micro-wave synthesis of co-doped transition metal oxides anchored on reduced graphene oxide and their implementation as catalysts for water oxidation“. Thesis, Umeå universitet, Institutionen för fysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-104909.
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Abstract: Artificial photosynthesis is a very attractive and a desirable way to solve the rising energy demand. In order to harvest energy directly from sunlight catalyst for oxygen reduction and evolution reaction are at the core of key renewable-energy technologies including fuel cells and water splitting. Herein, tungsten oxide-reduced graphene oxide (WO3-rGO), cobalt oxide-reduced graphene oxide (Co3O4-rGO) and tungsten oxide-cobalt oxide-reduced graphene oxide (WO3-Co3O4-rGO) nano-composites were synthesized via a facile, efficient, one-pot microwave assisted method as an efficient electro-catalyst for water oxidation. The structural and chemical compositions of the produced nano-structures were investigated by Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS), Raman Spectroscopy as well as thremogravimetric analysis. Catalytic performances of the engineered nano hybrids for the oxygen evolution reaction (OER) were evaluated using a standard three electrode system in 0.1 M KOH aqueous solution, with a coiled Pt wire as the counter electrode and an Ag/AgCl as the reference electrode. In the produced nano-composites, WO3 and Co3O4 nano-particles are uniformly decorated on the reduced graphene oxide sheets without any agglomeration. The WO3-Co3O4-rGO hybrids afforded current density 1 mA/cm2 at 1.693 V vs RHE and the Co3O4-rGO reached the current density 1 mA/cm2 at 1.769 V vs RHE regarding the catalytic performance for OER in alkaline solution. The over potential was significantly reduced by 76 mV after co-doping of WO3 with Co3O4-rGO nano hybrids. The WO3-Co3O4-rGO gives current density 1 mA/cm2 at 1.658 V vs RHE. We also show that the over potential for oxygen evolution of the WO3-Co3O4-rGO was further reduced by illuminating the catalyst to visible light thus manifesting the photo-catalytic properties of the hybrid catalyst.
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Bobin, Alexey. „Methane reforming by carbon dioxide over metal supported on nanocrystalline mixed oxides : mechanism and transient kinetics for relating catalysts structure and performance“. Thesis, Lyon 1, 2014. http://www.theses.fr/2014LYO10164/document.
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L'énergie de liaison, la mobilité et la réactivité de l'oxygène dans des matériaux nanocristallins de type cérine-zircone dopée aux terres rares (La, Gd, Pr, Sm) supportant des métaux (Pt, Ni, Ru) ont été étudiées par échange isotopique en réacteurs statiques et traversés (18O2 and C18O2), DTP d'O2, RTP d'H2 et CH4, microcalorimétrie pulsée et réacteur TAP. La mobilité d'oxygène de coeur apparait comme contrôlée par le réarrangement des sphères de coordination des cations Ce et Zr et par des chemins préférentiels le long de chaines Pr3+/Pr4+. En surface et subsurface, ce contrôle se ferait par des interactions fortes métal/support avec l'incorporation de cations métalliques. Cette mobilité de l'oxygène limiterait le vieillissement et le frittage en conditions réalistes de reformage par le gaz carbonique. Des études cinétiques non stationnaires et par marquage isotopique ont permis de proposer un mécanisme bi-fonctionnel fondé sur des étapes rédox indépendantes pour l'activation du méthane et du dioxyde de carbone. L'étape limitante serait l'activation du méthane tandis que l'activation du gaz carbonique s'opérerait plus rapidement sur des sites réduits du support, générant de l'oxygène diffusant aisément vers l'interface métal/support (enthalpie de désorption 600-650 kJ/mol) pour oxyder les fragments du méthane en CO et H2. Dans les meilleures formulations catalytiques, des agrégats Ni-Ru faciliteraient l'activation du CO2 dans son état de transition, en marge de carbonates stables qui restent "spectateurs" de la réaction. Pour le Pt/PrCeZrO, il existerait une autre voie d'activation de carbonates faiblement adsorbés sur des ions Pt+ stabilisés par des cations Pr4+. Cette spécificité confère à cette formulation des perspectives très intéressantes en reformage à sec, notamment sur des supports structurés de type alumine corindon, bien adaptés à des réacteurs compacts à temps courts pour des ressources en gaz dispersées et de capacité limitéeOxygen bonding strength, mobility and reactivity in nanocrystalline Ln-doped ceria-zirconia (Ln=La, Gd, Pr, Sm) with supported Pt, Ni, Ru were studied by state-of-the-art techniques such as isotopic exchange in static and flow reactors with 18O2 and C18O2, O2 TPD, H2 and CH4 TPR, pulse microcalorimetry and TAP reactor. Bulk oxygen mobility is found controlled by a rearrangement of Ce and Zr cations coordination sphere with doping as well as by fast oxygen migration along Pr3+/Pr4+ cationic chains. Surface and near-surface oxygen mobility appears controlled by a strong metal-support interaction with incorporation of metallic ions into surface layers and domain boundaries. In realistic feeds, the catalytic activity in dry reforming of methane correlates with oxygen mobility, required to prevent coking and metal sintering.Transient kinetic studies (non steady-state and SSITKA) allowed us to propose a bi-functional reaction mechanism corresponding to independent redox steps of CH4 and CO2 activation. The rate- limiting step is shown to be the irreversible activation of CH4 on metal sites, while CO2 dissociation on reduced sites of oxide supports proceeds much faster (being reversible for the steady-state surface) followed by a fast oxygen transfer along the surface/domain boundaries to metal sites where CH4 molecules are transformed to CO and H2. The CH4 selective conversion into syngas would involve strongly bound bridging oxygen species with heat of desorption ::600-650 kJ/mol O2. For optimized formulations, Ni+Ru clusters could be involved in CO2 activation via facilitating C-O bond breaking in the transition state, thus increasing the rate constant of the surface reoxidation by CO2, while strongly bound carbonates behave as spectators. For Pt/PrCeZrO, an additional fast route to syngas would occur on Pt ions with participation of weakly bound carbonates stabilized by neighboring Pr4+ ions. Such specificity makes this system highly promising for methane oxi-dry reforming, especially on structured corundum supports for short contact time compact reactors, well adapted to stranded and limited gas resources
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Kapustin, Yaroslav A. „Forcefield-Based Simulations of Bulk Structure of Mo-V-(Te, Nb)-O M1 Phase Catalysts for Selective Propane Ammoxidation to Acrylonitrile“. University of Cincinnati / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1296848202.
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Eckhardt, Björn [Verfasser], Ralph [Akademischer Betreuer] Krähnert, Peter [Akademischer Betreuer] Strasser und Michael [Akademischer Betreuer] Wark. „Synthesis of micelle-templated metal oxides as catalysts for the oxidative coupling of methane / Björn Eckhardt. Gutachter: Peter Strasser ; Michael Wark ; Ralph Krähnert. Betreuer: Ralph Krähnert“. Berlin : Technische Universität Berlin, 2014. http://d-nb.info/1066161658/34.
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Sandra, Fabien. „Elaboration de matériaux céramiques poreux à base de SiC pour la filtration et la dépollution“. Thesis, Montpellier 2, 2014. http://www.theses.fr/2014MON20015.
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En 1920, le moteur Diesel marque l'histoire en se faisant une place dans le milieu de l'automobile. Toutefois, malgré la révolution que représente le moteur Diesel notamment en terme de technologie (moteur à combustion interne dont l'allumage n'est pas commandé mais spontané par phénomène d'auto-inflammation (absence de bougie d'allumage)), des inconvénients majeurs subsistent, tout particulièrement au niveau environnemental et sanitaire (émission de gaz à effet de serre, prélèvement accru d'énergie fossile, impact direct sur la santé). Afin de lutter contre ces émissions, l'Union Européen à mit en place les normes EURO (depuis 1993) incitant les constructeurs automobiles à concevoir des procédés d'élimination des particules carbonées et à apporter des évolutions au niveau des motorisations. C'est dans ce contexte qu'a vu le jour la technologie Filtre à Particules initié par Peugeot en 1999 pour évoluer d'années en années jusqu'à être considérées aujourd'hui comme une avancée majeur en terme de traitement des particules Diesel. Encore aujourd'hui les problèmes d'émanations demeurent en raison des imbrûlés générés par le moteur diesel (suies, HC aromatiques polycycliques, d'oxyde de soufre, d'oxyde d'azote…). Les dégagements de particules de suies fines demeurant un problème particulièrement important au niveau de la santé. Cette thèse s'inscrit dans l'optique d'optimisation du procédé FàP en proposant l'élaboration de membrane à base de SiC supportée. Plus généralement, notre étude concerne l'élaboration de céramiques poreuses (membranes supportées et mousses) à base de silicium pour application environnementale et sanitaire (Filtration des particules fines, dépollution et séquestration de CO2).Le Chapitre I traite du contexte général de l'étude. La problématique des émissions de particules est abordée d'un point de vue sanitaire et environnemental en précisant les normes en vigueurs pour leur contrôle. La technologie FàP est décrite avant d'introduire le SiC et la voie dite des « polymères précéramiques » (PDCs). L'aspect catalytique est ensuite abordé avant de développer le principe d'élaboration de membrane SiC et leur intérêt pour une application de dépollution automobile.Le Chapitre II traite de l'élaboration de membranes SiC supportées. L'étude concerne l'élaboration d'un procédé optimale pour déposer une membrane au sein de la porosité du FàP qui modifierait les caractéristiques de porosité de ce dernier sans pour autant engendrer des répercussions néfastes sur la filtration. Le polymère précéramique, précurseur de SiC, sera alors décrit et nous étudierons sa mise en forme par la technique dite de « trempage-tirage » (dip-coating) afin d'élaborer, après pyrolyse, une membrane SiC. Cette dernière sera caractérisée par de nombreux outils expérimentaux.Le Chapitre III reprend le procédé d'élaboration des membranes de SiC élaboré dans le Chapitre II mais il proposera d'aller plus loin avec la réalisation et l'étude de catalyseurs pour la combustion des suies, et leur intégration au sein d'une microémulsion de type SiC-MxOy utilisée pour revêtir les FàP.Le Chapitre IV propose une étude sur la préparation de mousses à base de SiC. Ce chapitre d'aspect plus fondamental consistera à développer des mousses cellulaires et à porosité hiérarchisée à base des éléments silicium (Si), bore (B), carbone (C) et azote (N). Cette phase de carbonitrure de silicium et de bore (Si/B/C/N) sera élaborée par couplage de la voie PDCs avec soit des agents sacrificiels soit par réplication. Une étude préliminaire sur la séquestration de CO2 sera alors décrite pour finirSince the 90's, Diesel engines are widely used though they are criticized because of the pollution emitted. The constant updates of the Europeans norms (since 1993) concerning the diesel emissions imply a perpetual improvement of filtration techniques. The Diesel Particles Filter (DPF) technology used by the car manufacturer PSA Peugeot Citroën is one of the best ways to fulfill the limitation for diesel emissions. However, particles emission issue is still a problem and future legislations more and stricter, so an improvement of the DPF process is required to respect them. In this context, we have considered the elaboration of two different types of porous membranes on the DPF channels. The first one was in SiC, and had the aim to enhance the filtration efficiency. In this way, the smallest particles matter could be locked in the filter. The second kind of membrane integrates a catalytic phase inside the ceramic matrix, so in addition to the filtration aspect, it could improve soot combustion during the regeneration step of the DPF.The first chapter of my thesis deals with the literature corresponding to the subject, i.e. the DPF technology, non-oxides Si-based ceramics, and in particular those obtained through polymer-derived ceramics route (also called PDCs route). Then, ceramic coatings and catalytic phases are also treated. In the second chapter, we have considered the PDCs route and preceramic polymers to elaborate a SiC coating inside the DPF channels. We employed the dip-coating technique to overlay the channel surface with the AHPCS precursor of SiC (allylhydridopolycarbosilane), then, a pyrolysis under argon allows obtaining a SiC coating, in order to decrease the average pore diameter of the DPF (keeping an efficient filtration while avoiding overpressure) to catch soot nanoparticles evolving from Diesel engine.The third part of my PhD deals with the elaboration of another kind of coating for the DPF channels including a catalytic phase in the ceramic membrane. For this purpose, the microemulsion synthesis has been considered to prepare SiC-MxOy membrane. Further, we incorporated various catalytic phases based on Ce, Fe and Pt as activators of soot combustion. By employing the dip-coating technique, we successfully covered the DPF channels of our monoliths with the aforementioned microemulsion and after a heat treatment under controlled atmosphere; a porous coating consisting of the catalytic phase and the ceramic matrix was obtained. From this film, the porosity has been modified by lowering the diameter of the initial pores, but also by getting an additional porosity due to the polymer conversion and the surfactant decomposition. Catalytic sites in the ceramic have improved the soot combustion by lowering the temperature of the combustion.The fourth chapter introduces the elaboration of porous SiBCN materials through two approaches, replication and warm-pressing with sacrificial template (polymethylmethacrylate, PMMA). The SiBCN ceramic is a promising material due to its high mechanical properties and its stability at high temperature (1700-1800°C). By coupling the PDCs way with those two techniques, we are able to elaborate SiBCN porous materials which features can be tuned according to the technological application envisaged
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Coulibaly, Gnougon Nina. „Élimination des antibiotiques quinolones sur des catalyseurs supportés : Applications sur des effluents hospitaliers“. Thesis, Rennes, Ecole nationale supérieure de chimie, 2019. https://www.ensc-rennes.fr/formations/doctorats.
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L'usage excessif des antibiotiques en médecine humaine et animale pose de graves problèmes environnementaux et de santé publique. L’objectif de cette thèse était d’éliminer deux types d’antibiotiques quinolones pouvant être détectés dans des eaux usées ou effluents hospitaliers. Dans un premier temps, nous avons évalué la réactivité d’oxydes métalliques (fer ou zinc) pour promouvoir des réactions d’oxydation avancée, en présence d’oxydants comme le peroxyde d’hydrogène, le persulfate ou le peroxymonosulfate, et sous irradiation (UVA ou visible). Les oxydes réactifs étaient supportés sur des membranes en acétate de cellulose ou polyester, peu coûteux, respectueux de l’environnement, ce qui permet de fonctionner dans des réacteurs en flux continu à recirculation. L’influence des différents paramètres opératoires (type et quantité de catalyseur, type et quantité d’oxydant, pH, etc.) a été étudiée. L’impact de mélange avec d’autres antibiotiques sur la performance d’élimination a été évalué vis-à-vis de la réactivité de chaque composé avec les espèces radicalaires. Les essais menés sur des effluents hospitaliers ont permis d’identifier des effets compétitifs voir inhibitifs provenant des composants principaux des eaux usées comme les matières organiques, les phosphates et les sulfates ou les chlorures. Les performances observées dans les eaux réelles usées ainsi que les résultats d’évaluation de la réutilisation des solides supportés sont encourageants. Cette étude ouvre la voie à l’application de ce type de réacteur à recirculation intégrant de catalyseurs supportés dans des technologies de traitement des effluents contaminésThe excessive use of antibiotics in human and animal medicine poses serious environmental and public healthissues. The aim of this thesis was to remove two types of quinolone antibiotics that can be detected in wastewater or hospital effluents. Initially, we evaluated the reactivity of metal oxides (iron or zinc) to promote advanced oxidation reactions, in the presence of oxidants such as hydrogen peroxide, persulfate or peroxymonosulfate, and under irradiation (UVA or visible ). The reactive oxides were supported on inexpensive, environmentally friendly cellulose acetate membranes or polyester, which made it possible to operate on a recirculating continuous flow reactor. The influence of the various operating parameters (type and concentration of catalyst, type and concentration of oxidant, pH, etc.) was studied. The impact of mixing with other antibiotics on the removal performance was evaluated with respect to the reactivity of each compound with the radical species. The tests carried out on hospital effluents made it possible to identify competitive or even inhibitory effects coming from the main components of wastewater such as organic matter, phosphates and sulphates or chlorides. The observed performance in the real wastewater as well as the evaluation results of the reuse of the supported solids are encouraging. This study has important implications for possible application of recirculation reactor with supported catalysts in wastewater treatment technologies
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Gao, Xingtao. „Molecular engineering of multilayered surface metal oxide catalysts /“. Diss., 1998. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:9914427.
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Makhanya, Nokubonga Prudence. „Solvent-free Knoevenagel condensation over supported mixed metal oxides catalysts“. Thesis, 2017. http://hdl.handle.net/10321/2667.
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Submitted in the fulfillment of the requirement for the Master's Degree in Chemistry,Durban University of Technology, 2017.Knoevenagel condensation reaction is a useful protocol for the formation of C=C bond in organic synthesis. This protocol is extensively utilized by synthetic chemist to generate dynamic intermediates or end-products such as perfumes, polymers, pharmaceuticals and calcium antagonists. The reaction is catalyzed by bases such as ammonia, primary and secondary amines, quaternary ammonium salts, Lewis acids, catalysts containing acid-base sites, which are carried out under homogeneous conditions. This necessitates the use of organic solvent which generate the large volumes of solvent waste. From green chemistry perspective, solvent free heterogeneous catalysts have received considerable attention. Since, these heterogeneous catalysts not only avoid the use of organic solvents but also suppress side reactions such as self-condensation and oligomerisation leading in better selectivity and product yield. In recent years, therefore, the use of heterogeneous catalyst, their recovery and reusability are in demand in industry. The use of cobalt, iridium and platinum hydroxyapatites, MgO/ZrO2, MgO/HMCM- earlier been reported in the literature, and used as heterogeneous catalysts for the Knoevenagel condensation of aldehydes and esters. Based on these evidences, we envisioned that MgO and VMgO could also be used as heterogeneous catalysts for this reaction. Magnesium oxide was synthesized from three precursors, viz. magnesium nitrate, magnesium carbonate and magnesium acetate. Magnesium oxide prepared from magnesium nitrate precursor was found to be the optimum giving an 81 % product yield. Vanadium-magnesium oxide catalysts with different vanadium loadings; 1.5, 3.5 and 5.5 wt. %, were synthesized by wet impregnation of magnesium oxide with aqueous ammonium metavanadate solution. The synthesized catalysts were characterized by ICP-AES, FTIR, Powder XRD, SEM-EDX and TEM. The Knoevenagel condensation reactions between benzaldehyde and ethyl cyanoacetate were carried out in a 100 mL two-necked round bottom flask equipped with a reflux condenser, magnetic stirrer and a CaCl2 guard tube. An equimolar quantity (10 mmol) of substrates and 0.05g of catalyst were added to the flask and heated at 60 °C, stirred vigorously for the required time. The yields were determined using GC-FID equipped with a capillary column. Elemental composition of the catalysts (vanadium and MgO) was determined by ICP-AES. IR spectra of MgO showed that magnesium oxide was the only phase present in the catalysts prepared from different precursors. The 1.5 and 5.5 wt. % VMgO showed weak bands attributed to pyrovanadate and orthovanadate phases present in small quantities. The phases manifested more with the increase in the vanadium concentration (3.5 and 5.5 wt. % VMgO). The diffraction patterns of all the catalysts showed the existence of MgO and magnesium orthovanadate. The morphology of the catalysts with increasing vanadium was more affected by precursor treatment rather than chemical differences. Electron microscopy showed that the VMgO surface is only sparingly covered with vanadium and MgO showed stacked with large rounded particles. Good to excellent yields were obtained for the MgO catalysts: MgO(1) 68 %, MgO(2) 65 %, MgO(3) 72 %, MgO(P) 73 % and MgO(DP) 82 %. Excellent yields were obtained for the VMgO catalysts: 1.5VMgO 83 %, 3.5VMgO 91 % and 5.5VMgO 97 %. The 5.5VMgO catalyst was found to be the optimum catalyst and was further tested for it activity using different aldehyde substrates. Excellent yields of the products were obtained for benzaldehyde 97 %, nitrobenzaldehyde 94 %, bromobenzaldehyde 96 %, chlorobenzaldehyde 93 % and methoxybenzaldehyde 95%.
M
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Lin, Wan-Ying, und 林宛穎. „Nitrogen-graphitized metal oxides as support for methanol oxidation catalysts“. Thesis, 2013. http://ndltd.ncl.edu.tw/handle/22559806127932972683.
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碩士國立中央大學
化學學系
101
Direct methanol fuel cell (DMFC) has the advantages of higher energy conversion rate less air pollution. However, its high cost becomes a major challenge for large-scale commercialization. The development of highly effective catalyst support to reduce the amount of platinum while increasing the activity of the catalyst has become the major goal in fuel cell technology. In recent years, the attempt of treating metal oxide material as catalyst support has drawn increasing attentions. This is primary due to high inherent dimensional and electrochemical stability enhance the interaction between the metal and the support, which help stabilize metal particles with improved fuel reaction and raised proton conductivity. However, limited by the low surface area and low electronic conductivity, metal oxide material inhibits catalytic activity. Purpose of this study is to modify the metal oxide with thin layer of conducting carbon in order to circumvent this deficiency. The first part of this research examines the activity of such surface functionalized metal oxides (titanium dioxide, silicon dioxide and zirconium dioxide). The nitrogen-graphitized metal oxide (NG-MO) were prepared by first coating a thin layer of conducting polymer (e.g. polyaniline) on ceramic metal oxides (TiO2, SiO2, and ZrO2) followed by graphitization at 900℃under N2 atmosphere. The thin layer of N-containing graphite coated on the ceramics served as electron conductor. Furthermore, it served as stable anchorage for metal nano-catalysts. Surface topography mapping showed that Pt nanoparticle with stable size of 3~4 nm was homogeneously dispersed on NG-MO compared to that on XC-72 or on the other graphite-based carbons. The current density derived from cyclo voltametry suggested that Pt/NG-MO exhibits distinctively higher methanol catalytic performance compared to those at XC-72 supports. The topology of the Pt nanoparticle on NG-MO and its methanol oxidation activity depends heavily on the type of the ceramic metal oxide with SiO2 appeared to give the best results. However, all the Pt/NG-MO system displayed lower life-time durability compared to that of commercial catalyst (E-TEK). The second part of the research studied the polyaniline content on catalytic behavior. Three supports with polyaniline to metal oxide ratio of 1:1、1:5、1:10 are prepared. In TiO2 system, higher content of metal oxide lead to higher methanol oxidation activity; however, in SiO2 and ZrO2 system, lower content of metal oxide lead to higher methanol oxidation activity .The results showed that metal oxide may be involved in the oxidation reaction of methanol. TiO2 performed better adsorption of OH group, enhancing the methanol oxidation reaction. Better methanol oxidation reaction activity is observed with higher TiO2 . In contrast, SiO2 and ZrO2 served as dormant substrate that the MOR only increases with increasing polyaniline coating. Finally, the third part of the study explored the effect of NG-MO support on alloy system. We compared the activity and stability of alloy metal catalyst with that on carbon support. Since the platinum-rhodium alloy system displayed the best MOR in the research, we supported the platinum-rhodium alloy on graphite metal oxides containing nitrogen in the proportions of 1:1. The results showed that platinum-rhodium alloy catalyst displayed higher catalytic activity and stability than single-platinum metal. SiO2 and TiO2 system performed better stability than the commercial catalyst (E-TEK), but ZrO2 is much worse. Further work is required to verify such difference.
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Thangaraju, Mahadevan. „Study of precious metal-oxide based electrocatalysts for the oxidation of methanol“. Thesis, 1996. http://hdl.handle.net/1957/34264.
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„Water-gas shift reaction over supported metal oxides with special reference to the cobalt manganese oxide system“. Thesis, 2015. http://hdl.handle.net/10539/16690.
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Almukhlifi, Hanadi. „The effects of gold nanoparticles on isobutane oxidation by phosphopolyoxomolybdates and metal oxides“. Thesis, 2012. http://hdl.handle.net/1959.13/933148.
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Masters Research - Master of Philopophy (MPhil)This thesis describes a new approach for the preparation of oxidation catalysts that contain pure gold nanoparticles on their surfaces and within their pore structures. The prepared gold nanoparticles were loaded onto phosphopolyoxomolybdate and metal oxide surfaces and the resulting catalysts were used for the partial and complete oxidation of isobutane. The process involved the initial formation of n-hexanethiol-stabilised gold nanoparticles, followed by addition of a solution of the stabilised gold nanoparticles in n-hexane to the solid catalyst and allowing adsorption to occur. Following this, thermolysis converted the n-hexanethiolate-stabilised gold nanoparticles to pure gold nanoparticles loaded on the catalyst surface by decomposition of the thiolate ligand from the gold nanoparticle surface.
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Mhlaba, Reineck. „Preferential oxidation of carbon monoxide over cobalt and palladium based catalysts supported on various metal oxides“. Thesis, 2020. http://hdl.handle.net/10386/3365.
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Thesis (Ph.D.(Chemistry)) -- University of Limpopo, 2020The interest on the use of proton exchange membrane (PEM) fuel cells for vehicle application has increase due to its efficiency, high power density and rapid start up. The on-board reforming process is used to generate hydrogen; however, this process simultaneously produces 1% CO which poisons Pt-based anode catalyst. Previous studies have shown that supported Pd-based catalysts have very good stability on preferential oxidation (PROX) of CO, but these catalysts suffer from lower selectivity. Metal oxides such as Co3O4 and CeO2 are known to have high oxygen vacancy which promotes CO oxidation. Furthermore, the pre-treatment of the catalysts by hydrazine as well as the addition of MnOx species have been shown to improve the surface properties of metal/metal oxides catalysts. The study envisages that the modification of PROX catalysts will improve the CO conversion and its selectivity while maintaining higher stability. In this work, as-prepared (Co3O4) and hydrazine treated cobalt (Co3O4(H)) based catalysts were prepared by precipitation method and investigated at temperature range of 40-220 oC for preferential oxidation (PROX) of CO in excess hydrogen. The FTIR and XPS data of hydrazine treated Co3O4 does not show peak ratio differences, indicating that usual amounts of Co3+ and Co2+ were formed. An improved surface reducibility with smaller crystallite size was noted on Co3O4(H) catalyst, which indicate some surface transformation. Interestingly, the in-situ treatment of standalone Co3O4(H) decreased the maximum CO conversion temperature (T100%) from 160 oC (over Co3O4) to 100 oC. The Co3O4(H) catalyst showed good stability, with approximately 85% CO conversion at 100 oC for 21 h, as compared to fast deactivation of the Co3O4 catalyst. However, the Co3O4(H) catalyst was unstable in both CO2 and the moisture environment. Based on the spent hydrazine treated (CoO(H)) cobalt catalyst, the high PROX is associated with the formation of Co3+ species as confirmed by XRD, XPS, and TPR data. The Pd species was incorporated on different Co3O4 by improved wet impregnation method and this has improved the surface area of the overall catalysts. However, the presence of Pd species on Co3O4(H) catalyst decreased the CO conversion due to formation of moisture. Although, the Pd on Co3O4(H) had lower activity, the catalyst showed better stability under both moisture and CO2 conditions at 100 oC for 21 h. vi The 2wt.% metal oxides (MnO2, CeO2, Cr3O4, TiO2, MgO) on cobalt, and Pd on CeO2- Co3O4 and MnO2-Co3O4 were prepared by co-precipitation method and the structural composition was confirmed by XRD, FTIR, XPS and TPR data. Although, 2wt.%MnO2 on Co3O4(H) showed higher activity at 80 oC, both MnO2 and CeO2 improved the activity of Co3O4(H) at 100 oC. The higher activity of MnO2 is attributed to the higher surface area of the composite catalyst, in relation to ceria composite catalyst. Although the MnO2 species transformed the structure of Co3O4 by lowering the oxidation state to Co2+, the spent catalyst showed transformation from Co2+ to Co3+ during PROX, as confirmed by TPR data. Studies on the effects of CeO2 loading on Co3O4 catalysts, showed an optimum activity over 2wt.%CeO2-Co3O4 as compared to other ceria loadings (i.e., 3, 5, 8, 10, 15, 30wt.%CeO2). However, upon addition of 0.5wt.%Pd species on 2wt.%CeO2- Co3O4(H) composite, the activity of the catalyst decreased slightly at 100 oC, which could be due to a decreased surface area. Although its activity is lower, the catalyst has shown good stability in dry, moisture and CO2 conditions at 100 oC for 21 h. In addition, studies were also undertaken on the effect of MnO2 concentration on Co3O4 catalysts. The data shows that 7wt.%MnO2 species improved the activity of Co3O4 catalyst at 60 oC, however, the catalyst could not improve the activities at higher temperatures. This low activity is associated with a decrease in surface area as concentration increases. The presence of 0.5wt.%Pd species on 7wt.%MnO2-Co3O4 increased the activity at 60 and 80 oC, which could be due to reduction of Co3+ to Co2+ in the presence of Pd, as confirmed by XPS data. The catalyst has shown good stability in dry, moisture, and CO2 conditions at 100 oC for 21 h. The hydrazine treated cobalt-based catalysts in the presence of palladium and manganese oxide is the promising catalysts for proton exchange membrane fuel cells technology.
National Research Foundation (NRF) , Faculty of Science and Agriculture University of Limpopo and School of Physical and Mineral Sciences
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Roy, Sounak. „Noble Metal And Base Metal Ion Substituted Ceo2 And Tio2 : Efficient Catalysts For Nox Abatement“. Thesis, 2007. https://etd.iisc.ac.in/handle/2005/584.
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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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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.
Der volle Inhalt der QuelleAnnotation:
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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Ching, Chang Jyh, und 張志清. „Effect of Transition Metal Oxides Modifying .gamma.-Alumina on Carbon Monoxide Hydrogenation over .gamma.-Alumina-Supported Cobalt Catalysts“. Thesis, 1993. http://ndltd.ncl.edu.tw/handle/56141106923164554766.
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碩士國立中央大學
化學工程研究所
81
The cobalt supported catalysts were prepared in impreg- nation. The supports used were modified by tungsten oxide or molybdie oxide in methods of solid reaction or impregnation in advance. From X-ray diffraction、temperature programmed reduction、temperature programmed surface reaction and reaction of car- bon monoxide hydrogenation ,we suggest tungsten oxide or moly- bdie oxide may disperse onto the surface of .gamma.- alumina. The presence of tungsten oxide or molybdie oxide as a monolay- er may reduce interaction between cobalt and alumina besides promoting activity of carbon monoxide hydrogenation. We favor interpreting the increase of activity by tungst- en oxide or molybdie oxide promoting in side-bond model.
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„Preparation and characterization of nanocrystalline cerium-based oxides as a carbon monoxide oxidation catalyst“. 2005. http://library.cuhk.edu.hk/record=b5892607.
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Ho Chun Man.Thesis (M.Phil.)--Chinese University of Hong Kong, 2005.
Includes bibliographical references.
Abstracts in English and Chinese.
ABSTRACT --- p.iv
DECLARATION --- p.vi
ACKNOWLEDGEMENT --- p.vii
TABLE OF CONTENTS --- p.viii
LIST OF TABLES --- p.xi
LIST OF FIGURES --- p.xii
Chapter Chapter One: --- Introduction --- p.1
Chapter 1.1 --- Overview --- p.1
Chapter 1.2 --- Fundamental of CeO2 --- p.2
Chapter 1.3.1 --- Synthesis and Modification of Ceria-based Materials --- p.5
Chapter 1.3.1 --- Synthetic Method --- p.5
Chapter 1.3.2 --- "Mesoporous Structure of Ce02, CexZr1-x02" --- p.6
Chapter 1.3.3 --- Doped Ce02 Materials --- p.6
Chapter 1.3.4 --- Fabrication of Ceria and Cerium-based Nanoparticles --- p.7
Chapter 1.4 --- Scope of work --- p.8
Chapter 1.5 --- References --- p.11
Chapter Chapter Two: --- Meso- and Macro-porous Pd/CexZr1-x02 as Carbon Monoxide Oxidation Catalysts --- p.16
Chapter 2.1 --- Introduction --- p.16
Chapter 2.2 --- Experimental Section --- p.18
Chapter 2.2.1 --- Sample Preparation - Synthesis of the Catalyst Support --- p.18
Chapter 2.2.2 --- Addition of Pd to the Catalyst Support --- p.19
Chapter 2.2.3 --- Characterization --- p.20
Chapter 2.2.4 --- Carbon monoxide oxidation measurement --- p.21
Chapter 2.3 --- Results and Discussion --- p.22
Chapter 2.3.1 --- XRD analysis --- p.22
Chapter 2.3.2 --- SEM and TEM --- p.25
Chapter 2.3.3 --- N2-Soprtion --- p.32
Chapter 2.3.4 --- X-ray Photoelectron Spectroscopy --- p.40
Chapter 2.3.5 --- Thermal Catalysis Study --- p.45
Chapter 2.4 --- Conclusion --- p.52
Chapter 2.5 --- References --- p.54
Chapter Chapter Three: --- Morphology-Controllable Synthesis of Ce02 Nano and Meso-structures --- p.60
Chapter 3.1 --- Introduction --- p.60
Chapter 3.2 --- Experimental Section --- p.62
Chapter 3.2.1 --- Materials and Experimental Conditions --- p.62
Chapter 3.2.2 --- Characterization --- p.64
Chapter 3.3 --- Results and Discussion --- p.67
Chapter 3.3.1 --- SEM and TEM Analysis --- p.67
Chapter 3.3.2 --- XRD Analysis --- p.75
Chapter 3.3.3 --- N2-Soprtion --- p.78
Chapter 3.3.4 --- X-ray Photoelectron Spectroscopy --- p.84
Chapter 3.3.5 --- FT-IR Analysis --- p.87
Chapter 3.3.6 --- GC-MS Analysis --- p.89
Chapter 3.3.7 --- Proposed Formation of Ce02 nanospheres and their transformation to microrods --- p.95
Chapter 3.3.8 --- UV absorption spectra and band gap energies --- p.97
Chapter 3.3.9 --- Thermal Catalysis Study --- p.100
Chapter 3.4 --- Conclusion --- p.103
Chapter 3.5 --- References --- p.105
Chapter Chapter Four: --- Conclusion --- p.110
LIST OF PUBLICATIONS --- p.112
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Ruz, Sichem Guerrero. „Activity in-situ IR and EXAFS spectroscopy studies, and Monte Carlo simulation of the preferential oxidation of carbon monoxide on Nb-promoted Pt/A12O3 catalysts and Pt-free metal oxides catalysts“. 2007. http://etd.nd.edu/ETD-db/theses/available/etd-12202007-161930/.
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Thesis (Ph. D.)--University of Notre Dame, 2007.Thesis directed by E. E. Wolf for the Department of Chemical and Biomolecular Engineering. "December 2007." Includes bibliographical references (leaves 196-214).
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Bauer, John C. „Nanoparticles as Reactive Precursors: Synthesis of Alloys, Intermetallic Compounds, and Multi-Metal Oxides Through Low-Temperature Annealing and Conversion Chemistry“. 2009. http://hdl.handle.net/1969.1/ETD-TAMU-2009-05-642.
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Alloys, intermetallic compounds and multi-metal oxides are generally made by
traditional solid-state methods that often require melting or grinding/pressing powders
followed by high temperature annealing (> 1000 degrees C) for days or weeks. The research
presented here takes advantage of the fact that nanoparticles have a large fraction of their
atoms on the surface making them highly reactive and their small size virtually
eliminates the solid-solid diffusion process as the rate limiting step. Materials that
normally require high temperatures and long annealing times become more accessible at
relatively low-temperatures because of the increased interfacial contact between the
nanoparticle reactants.
Metal nanoparticles, formed via reduction of metal salts in an aqueous solution
and stabilized by PVP (polyvinylpyrrolidone), were mixed into nanoparticle composites
in stoichometric proportions. The composite mixtures were then annealed at relatively
low temperatures to form alloy and intermetallic compounds at or below 600 degrees C. This
method was further extended to synthesizing multi-metal oxide systems by annealing metal oxide nanoparticle composites hundreds of degrees lower than more traditional
methods.
Nanoparticles of Pt (supported or unsupported) were added to a metal salt
solution of tetraethylene glycol and heated to obtain alloy and intermetallic
nanoparticles. The supported intermetallic nanoparticles were tested as catalysts and
PtPb/Vulcan XC-72 showed enhanced catalytic activity for formic acid oxidation while
Pt3Sn/Vulcan XC-72 and Cu3Pt/y-Al2O3 catalyzed CO oxidiation at lower temperatures
than supported Pt.
Intermetallic nanoparticles of Pd were synthesized by conversion chemistry
methods previously mentioned and were supported on carbon and alumina. These
nanoparticles were tested for Suzuki cross-coupling reactions. However; the
homocoupled product was generally favored. The catalytic activity of Pd3Pb/y-Al2O3
was tested for the Heck reaction and gave results comparable to Pd/y-Al2O3 with a
slightly better selectivity.
Conversion chemistry techniques were used to convert Pt nanocubes into Ptbased
intermetallic nanocrystals in solution. It was discovered that aggregated clusters
of Pt nanoparticles were capable of converting to FePt3; however, when Pt nanocubes
were used the intermetallic phase did not form. Alternatively, it was possible to form
PtSn nanocubes by a conversion reaction with SnCl2.
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Li, Jerry Pui Ho. „Characterisation of heterogeneous acid/base catalysts and their application in the synthesis of fine and intermediate chemicals“. Thesis, 2014. http://hdl.handle.net/1959.13/1049156.
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Research Doctorate - Doctor of Philosophy (PhD)The catalytic treatment of volatile organic compounds in the form of aliphatic and aromatic hydrocarbons was investigated on different heterogeneous catalysts. With the aliphatic hydrocarbons, a transesterification reaction between methanol and ethyl acetate was conducted using an MgO-BaO composite catalyst. The catalyst was catalysing the reaction but the work highlighted a knowledge gap regarding the mechanistic pathway. The study was extended to the catalytic treatment of an aromatic hydrocarbon, benzaldehyde, applying the Knoevenagel condensation reaction. SiO₂, γ-Al₂O₃, ZnO, Fe₂O₃ supports impregnated with Mg and Ba were used as catalysts Based on the TOF of the reaction, catalysts with the high TOF values had fewer base sites, showing high catalytic activity per site, but also high rate of deactivation. Most interestingly, over ZnO modest TOF values were obtained but the highest concentration of base sites per area was found. ZnO as a catalyst was further investigated, using in situ FTIR and TPD-MS to observe benzaldehyde and ethyl cyanoacetate adsorption and desorption on the surface. Most interestingly, benzaldehyde and ethyl cyanoacetate form intermediate species that are stabilised on the surface, which play an important role in the reaction mechanism. TPD-MS showed the intermediates are thermally stable on the catalyst surface. Finally the catalytic treatment of phenol through a hydroxylation reaction with H2O2 as oxidant over-MFI, Fe-MFI, H-BEA, Fe-BEA and TS-1 zeolite catalysts was investigated. Over H-BEA, biphenyl product was observed. It is suggested, that the larger pore size of H-BEA facilitates coupling of two phenol molecules. Two distinct mechanistic pathways are proposed for acid and redox catalysts.