Добірка наукової літератури з теми "Nanostructured catalytic supports"

Carbon deposition from catalytic methane decomposition has drawn increasing interest recently. Previously, we have found the carbon formation depends on the crystalline structure of the support, following the trend of Ni/CeO2 > Ni/CaO > Ni/MgO, because Ni supported on MgO is uniformly dispersed and can stabilize high-x CH x intermediates. We have also found that the addition of Pt can inhibit the carbon deposition on Co/Al2O3 because the alloying between Pt and Co results in the better dispersion of Co on the support. Furthermore, it was revealed that by judging the Ni/Mg molar ratio from 1 to 0.25 we could reduce the diameter of deposited carbon nanotubes from 20 to 12 nm, with substantially smaller production rate. All of these previous studies indicated that better dispersion of the supported metal would benefit the decreasing of carbon deposition. Here we present our recent investigation of the effect of support particle size on the carbon deposition. Three different types of 10 wt% Co/Al2O3 catalysts were prepared: Co on commercial Al2O3 (Cat 1), Co on sol-gel-processed Al2O3 (Cat 2), and sol-gel-made homogeneous Co-in-Al2O3 (Cat 3). TEM showed that the diameter of the Co3O4 particles in sol-gel Al2O3 is only around 6 nm, while it is 20-40 nm in the commercial catalyst. By using XRD and FTIR, Co was identified as crystalline Co3O4 in the as-prepared Cat 1 sample, CoAl2O4 in Cat 2, and amorphous Al2O3 in Cat 3, indicating the best dispersion in Cat 3. Methane CO2 reforming was studied on the three catalysts. Longer lifetime was measured for Cat 3 as compared to those on Cat 1 and Cat 2 (>20 h vs. 1 h). The support size effect is discussed.

Mesoporous and silica-based SBA-15 and SBA-16 materials were used as supports of novel nanostructured ternary Co(Ni)-Mo-W hydrodesulphurization (HDS) catalysts. These materials have shown a high catalytic activity in HDS of dibenzothiophene (DBT) reactions, even much higher compared with commercial catalysts. An exploration was made on the structure of both the supports as well as on tri-metallic sulfide HDS catalysts. The sulfided catalysts were tested in the HDS of DBT performed in a batch reactor at 623 K and total pressure of 3.1 MPa. The calcined and fresh sulfide catalysts were characterized by a variety of techniques, such as N2 adsorption-desorption isotherms, Temperature-Programmed Desorption (TPD) of NH3, X-ray Diffraction (XRD) and High Resolution Transmission Electron Microscopy (HRTEM). It has been found that both the morphology of the supports as its modification with varying amounts of phosphorus affect the catalytic activity of these nanostructured materials in HDS of DBT reactions. Furthermore, the nanostructures which correspond to the tri-metallic sulfided catalysts exhibit a typical morphology of MoS2 – 2H structure. The present work shows the microstructural study of these nanostructured materials, carried out from HRTEM images and XRD analysis. Both techniques, X–ray Diffractometry and High Resolution Transmission Electron Microscopy, play a fundamental role in the characterization of the microstructure of HDS catalytic nanomaterials, as well as in understanding the various phenomena involved, starting from the synthesis process unto the final performance of those materials.

In present work, a new technique to prepare alumina nanoparticles and nanofibers using a sol-gel method was proposed. A solution combustion method was applied to form a nanostructured catalytically active layer of CuO–Co3O4–CeO2 on the surface of the alumina. The uniform distribution and fine dispersion of active components provide the appropriate activity of the catalysts obtained in a model reaction of CO oxidation. The morphology of nanostructured alumina was found to affect the catalytic behavior. Carbon monoxide conversion was observed at lower temperatures when alumina nanofibers were used as a catalyst support.

Abstract In the present study, we present nanostructured bimetallic Cu/CuCl/Cu2S/Au(Ag) supports that exhibit plasmonic electromagnetic field enhancement and peroxidase-like catalytic activity. The Cu2S component acts as the peroxidase-like catalyst, while the Au or Ag component provides the necessary light enhancement for surface enhanced Raman spectroscopic (SERS) studies of surface bound molecular reactants. As a test reaction the catalytic oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) in presence of H2O2 was investigated. The comparison of product evolution in solution measured by UV-Vis spectroscopy and on the surface measured via SERS is able to give more insight into the different steps involved in the overall catalysis.

Nanobiocatalysts, i.e., enzymes immobilized on nanostructured supports, received considerable attention because they are potential remedies to overcome shortcomings of traditional biocatalysts, such as low efficiency of mass transfer, instability during catalytic reactions, and possible deactivation. In this short review, we will analyze major aspects of immobilization of cellulase—an enzyme for cellulosic biomass waste processing—on nanostructured supports. Such supports provide high surface areas, increased enzyme loading, and a beneficial environment to enhance cellulase performance and its stability, leading to nanobiocatalysts for obtaining biofuels and value-added chemicals. Here, we will discuss such nanostructured supports as carbon nanotubes, polymer nanoparticles (NPs), nanohydrogels, nanofibers, silica NPs, hierarchical porous materials, magnetic NPs and their nanohybrids, based on publications of the last five years. The use of magnetic NPs is especially favorable due to easy separation and the nanobiocatalyst recovery for a repeated use. This review will discuss methods for cellulase immobilization, morphology of nanostructured supports, multienzyme systems as well as factors influencing the enzyme activity to achieve the highest conversion of cellulosic biowaste into fermentable sugars. We believe this review will allow for an enhanced understanding of such nanobiocatalysts and processes, allowing for the best solutions to major problems of sustainable biorefinery.

Recent works in the development of nanostructured catalysts for bromate reduction in drinking water under hydrogen have highlighted the importance of the properties of the metallic phase support in their overall performance. Since most works in catalyst development are carried out in powder form, there is an overlooked gap in the correlation between catalyst support properties and performance in typical continuous applications such as fixed bed reactors. In this work, it is shown that the mechanical modification of commercially available carbon nanotubes, one of the most promising supports, can significantly enhance the activity of the catalytic system when tested in a stirred tank reactor, but upon transition to a fixed bed reactor, the formation of preferential pathways for the liquid flow and high pressure drops were observed. This effect could be minimized by the addition of an inert filler to increase the bed porosity; however, the improvement in catalytic performance when compared with the as-received support material was not retained. The operation of the continuous catalytic system was then optimized using a 1 wt.% Pd catalyst supported on the as-received carbon nanotubes. Effluent and hydrogen flow rates as well as catalyst loadings were systematically optimized to find an efficient set of parameters for the operation of the system, regarding its catalytic performance, capacity to treat large effluent flows, and minimization of catalyst and hydrogen requirements. Experiments carried out in the presence of distilled water as a reaction medium demonstrate that bromate can be efficiently removed from the liquid phase, whereas when using a real water matrix, a tendency for the deactivation of the catalyst over time was more apparent throughout 200 flow passages over the catalytic bed, which was mostly attributed to the competitive adsorption of inorganic matter on the catalyst active centers, or the formation of mineral deposits blocking access to the catalyst.

The mesoporous CeO2were prepared via a surfactant-assisted method of nanoparticle assembly, CTAB was used as surfactant. The mesoporous CeO2were used as the supports for preparingxAu/CeO2catalysts by the chemical reduction method, and the catalytic activities of the total oxidation of propane were studied. The prepared catalysts were characterized by XRD, TEM and N2adsorption techniques. The content of Au can affect the catalytic properties of thexAu/CeO2catalysts. 4Au/CeO2exhibited the highest catalytic activity in propane complete oxidation with theT100of 420 °C.

Novel nanostructured catalytic membranes (NCMs) have been prepared by ruthenium deposition (Ru3(CO)12 wet-impregnation) within the porous framework of different tubular porous supports modified and unmodified with microporous glassy-carbon (GC) material. The aim of this work is to investigate the influence of the transport mechanism, layer distribution, textural properties, surface composition and metallic phase distribution of each type of NCMs on the partial benzene hydrogenation to cyclohexene performance in gas phase, operating under through-flow mode in a membrane reactor. Two types of glass (Vycor®) and ceramic (Cordierite-Alumina) supports with different layer distribution, have been used to prepared the NCMs. The modified and unmodified with GC membranes have been characterised by gas permeability measurements. High resolution-scanning electron microscopy (HR-SEM) and energy dispersive X-ray spectroscopy (EDS) have been realised to evidence GC deposition and to analyse the ruthenium nanoparticles distribution along the porous membranes section, respectively. An attempt to correlate the membrane characterization results and the catalytic results has been carried out.

La catalisi ha profondamento modificato la nostra società e giocherà un ruolo chiave nella risoluzione della crisi energetica ed ambientale che stiamo affrontando in questo secolo. Il grande vantaggio nello sviluppo dei nanomateriali nel regno della nanotecnologia ha portato a possibilità impreviste anche per la progettazione di nuovi catalizzatori. La produzione e la comprensione del funzionamento di catalizzatori ad alta efficienza basati su materiali nanostrutturati è lo sforzo del campo emergente della nanocatalisi. Negli ultimi anni, i nanocatalizzatori sono stati ampiamente studiati e si è registrato un costante progresso nella loro produzione su larga scala. La tecnologia è tuttora in evoluzione ed ulteriore ricerca è necessaria per capitalizzare appieno il suo potenziale. I metodi computazionali sono molto adatti a studiare il funzionamento dei nanocatalizzatori e a fornire importanti informazioni da un punto di vista atomistico. Un accurato ed efficiente metodo è rappresentato dalla teoria del funzionale della densità (DFT). In questa tesi, abbiamo esplorato le caratteristiche chimiche e fisiche di clusters metallici supportati e di film sottili di ossidi utilizzando principalmente il metodo basato su DFT. Questi materiali sono di particolare interesse nella catalisi e in molte altre applicazioni, a causa delle loro caratteristiche uniche che derivano dalla nanostrutturazione. In particolare, abbiamo studiato la geometria, lo stato di carica, l’interazione cluster-supporto, e la reattività di clusters metallici sub-nanometrici supportati su ossidi. In un caso particolare abbiamo inoltre affrontato il ruolo della dimensione in nanoparticelle metalliche più grandi. Per quanto riguarda i clusters supportati, abbiamo verificato che le forze di dispersione di van-der-Waals sono molto importanti per la corretta descrizione dell’interazione cluster-supporto. Inoltre, abbiamo stabilito che difetti e dopanti presenti sulla superfice del supporto ossido hanno un'influenza determinante sui cluster, determinandone intrinsecamente la reattività. Anche la modifica dei cluster attraverso la formazione di leghe altera l’interazione metallo-supporto, e può essere sfruttata per evitare l’agglomerazione dei clusters. La nanostrutturazione del supporto a base di ossido può generare nuove proprietà del materiale e in questo contesto abbiamo esaminato le caratteristiche di un film ultrasottile di ossido supportato su metallo. Infine, abbiamo eseguito studi meccanicistici che hanno contribuito a chiarire il meccanismo di reazione dell’ossidazione di CO su catalizzatori a base di Au/TiO2 e dell’idrogenazione di CO2 su catalizzatori a base di Ru/TiO2 and Cu/TiO2.
Catalysis has largely shaped society and will play a key part in the resolution of the energy and environment crisis we are facing in this century. The great advancements in the development of nanomaterials in the realm of nanotechnology have brought forth unforeseen possibilities also for the design of novel catalysts. The production and understanding of highly efficient catalysts based on nanostructured materials is the endeavor of the emerging field of nanocatalysis. In the last years, nanocatalysts have been studied extensively and progress in their large-scale fabrication has been demonstrated. Still, the technology is immature and further research is necessary to capitalize its full potential. Computational approaches are well suited to investigate the functioning of nanocatalysts and provide valuable atomistic insights. An accurate and efficient method is density functional theory (DFT). In this thesis, we explored the physical and chemical characteristics of supported metal clusters and oxide thin films using mainly DFT. These materials are of special interest in catalysis and many other applications, because of their unique features emerging from the nanostructuring. In particular, we investigated the geometry, the charge state, the cluster-support interaction, and the reactivity of sub-nanometer metal clusters supported on oxides. In a case study, we also addressed size-effects on larger metal nanoparticles. Regarding the supported clusters, we find that van-der-Waals dispersion forces are important for the correct description of the cluster-support interaction. Furthermore, we establish that defects and dopants present on the supporting oxide surface have a determining influence on the clusters, inherently affecting their reactivity. Also the modification of the clusters via alloying alters the metal-support interaction which can be exploited against cluster agglomeration. Nanostructuring of the oxide support engenders new material properties and in this context we examined the features of metal-supported oxide ultrathin films. Finally, we performed mechanistic studies contributing to elucidate the reaction mechanism of CO oxidation on Au/TiO2, as well as CO2 hydrogenation on Ru/TiO2 and Cu/TiO2.

Recent advances in nanoscience and nanotechnology have provided the scientific community with exciting new opportunities to rationally design and fabricate materials at the nanometer scale with drastically different properties as compared to their bulk counterparts. In this dissertation, several challenges have been tackled in aspects related to nanoparticle (NP) synthesis and characterization, allowing us to make homogenous, size- and shape-selected NPs via the use of colloidal chemistry, and to gain in depth understanding of their distinct physical and chemical properties via the synergistic use of a variety of ex situ, in situ, and operando experimental tools. A variety of phenomena relevant to nanosized materials were investigated, including the role of the NP size and shape in the thermodynamic and electronic properties of NPs, their thermal stability, NP-support interactions, coarsening phenomena, and the evolution of the NP structure and chemical state under different environments and reaction conditions.
Ph.D.
Doctorate
Physics
Sciences
Physics

Transition metal oxides are functional materials that have advanced applications in many areas, because of their diverse properties (optical, electrical, magnetic, etc.), hardness, thermal stability and chemical resistance. Novel applications of the nanostructures of these oxides are attracting significant interest as new synthesis methods are developed and new structures are reported. Hydrothermal synthesis is an effective process to prepare various delicate structures of metal oxides on the scales from a few to tens of nanometres, specifically, the highly dispersed intermediate structures which are hardly obtained through pyro-synthesis. In this thesis, a range of new metal oxide (stable and metastable titanate, niobate) nanostructures, namely nanotubes and nanofibres, were synthesised via a hydrothermal process. Further structure modifications were conducted and potential applications in catalysis, photocatalysis, adsorption and construction of ceramic membrane were studied. The morphology evolution during the hydrothermal reaction between Nb2O5 particles and concentrated NaOH was monitored. The study demonstrates that by optimising the reaction parameters (temperature, amount of reactants), one can obtain a variety of nanostructured solids, from intermediate phases niobate bars and fibres to the stable phase cubes. Trititanate (Na2Ti3O7) nanofibres and nanotubes were obtained by the hydrothermal reaction between TiO2 powders or a titanium compound (e.g. TiOSO4·xH2O) and concentrated NaOH solution by controlling the reaction temperature and NaOH concentration. The trititanate possesses a layered structure, and the Na ions that exist between the negative charged titanate layers are exchangeable with other metal ions or H+ ions. The ion-exchange has crucial influence on the phase transition of the exchanged products. The exchange of the sodium ions in the titanate with H+ ions yields protonated titanate (H-titanate) and subsequent phase transformation of the H-titanate enable various TiO2 structures with retained morphology. H-titanate, either nanofibres or tubes, can be converted to pure TiO2(B), pure anatase, mixed TiO2(B) and anatase phases by controlled calcination and by a two-step process of acid-treatment and subsequent calcination. While the controlled calcination of the sodium titanate yield new titanate structures (metastable titanate with formula Na1.5H0.5Ti3O7, with retained fibril morphology) that can be used for removal of radioactive ions and heavy metal ions from water. The structures and morphologies of the metal oxides were characterised by advanced techniques. Titania nanofibres of mixed anatase and TiO2(B) phases, pure anatase and pure TiO2(B) were obtained by calcining H-titanate nanofibres at different temperatures between 300 and 700 °C. The fibril morphology was retained after calcination, which is suitable for transmission electron microscopy (TEM) analysis. It has been found by TEM analysis that in mixed-phase structure the interfaces between anatase and TiO2(B) phases are not random contacts between the engaged crystals of the two phases, but form from the well matched lattice planes of the two phases. For instance, (101) planes in anatase and (101) planes of TiO2(B) are similar in d spaces (~0.18 nm), and they join together to form a stable interface. The interfaces between the two phases act as an one-way valve that permit the transfer of photogenerated charge from anatase to TiO2(B). This reduces the recombination of photogenerated electrons and holes in anatase, enhancing the activity for photocatalytic oxidation. Therefore, the mixed-phase nanofibres exhibited higher photocatalytic activity for degradation of sulforhodamine B (SRB) dye under ultraviolet (UV) light than the nanofibres of either pure phase alone, or the mechanical mixtures (which have no interfaces) of the two pure phase nanofibres with a similar phase composition. This verifies the theory that the difference between the conduction band edges of the two phases may result in charge transfer from one phase to the other, which results in effectively the photogenerated charge separation and thus facilitates the redox reaction involving these charges. Such an interface structure facilitates charge transfer crossing the interfaces. The knowledge acquired in this study is important not only for design of efficient TiO2 photocatalysts but also for understanding the photocatalysis process. Moreover, the fibril titania photocatalysts are of great advantage when they are separated from a liquid for reuse by filtration, sedimentation, or centrifugation, compared to nanoparticles of the same scale. The surface structure of TiO2 also plays a significant role in catalysis and photocatalysis. Four types of large surface area TiO2 nanotubes with different phase compositions (labelled as NTA, NTBA, NTMA and NTM) were synthesised from calcination and acid treatment of the H-titanate nanotubes. Using the in situ FTIR emission spectrescopy (IES), desorption and re-adsorption process of surface OH-groups on oxide surface can be trailed. In this work, the surface OH-group regeneration ability of the TiO2 nanotubes was investigated. The ability of the four samples distinctively different, having the order: NTA > NTBA > NTMA > NTM. The same order was observed for the catalytic when the samples served as photocatalysts for the decomposition of synthetic dye SRB under UV light, as the supports of gold (Au) catalysts (where gold particles were loaded by a colloid-based method) for photodecomposition of formaldehyde under visible light and for catalytic oxidation of CO at low temperatures. Therefore, the ability of TiO2 nanotubes to generate surface OH-groups is an indicator of the catalytic activity. The reason behind the correlation is that the oxygen vacancies at bridging O2- sites of TiO2 surface can generate surface OH-groups and these groups facilitate adsorption and activation of O2 molecules, which is the key step of the oxidation reactions. The structure of the oxygen vacancies at bridging O2- sites is proposed. Also a new mechanism for the photocatalytic formaldehyde decomposition with the Au-TiO2 catalysts is proposed: The visible light absorbed by the gold nanoparticles, due to surface plasmon resonance effect, induces transition of the 6sp electrons of gold to high energy levels. These energetic electrons can migrate to the conduction band of TiO2 and are seized by oxygen molecules. Meanwhile, the gold nanoparticles capture electrons from the formaldehyde molecules adsorbed on them because of gold’s high electronegativity. O2 adsorbed on the TiO2 supports surface are the major electron acceptor. The more O2 adsorbed, the higher the oxidation activity of the photocatalyst will exhibit. The last part of this thesis demonstrates two innovative applications of the titanate nanostructures. Firstly, trititanate and metastable titanate (Na1.5H0.5Ti3O7) nanofibres are used as intelligent absorbents for removal of radioactive cations and heavy metal ions, utilizing the properties of the ion exchange ability, deformable layered structure, and fibril morphology. Environmental contamination with radioactive ions and heavy metal ions can cause a serious threat to the health of a large part of the population. Treatment of the wastes is needed to produce a waste product suitable for long-term storage and disposal. The ion-exchange ability of layered titanate structure permitted adsorption of bivalence toxic cations (Sr2+, Ra2+, Pb2+) from aqueous solution. More importantly, the adsorption is irreversible, due to the deformation of the structure induced by the strong interaction between the adsorbed bivalent cations and negatively charged TiO6 octahedra, and results in permanent entrapment of the toxic bivalent cations in the fibres so that the toxic ions can be safely deposited. Compared to conventional clay and zeolite sorbents, the fibril absorbents are of great advantage as they can be readily dispersed into and separated from a liquid. Secondly, new generation membranes were constructed by using large titanate and small ã-alumina nanofibres as intermediate and top layers, respectively, on a porous alumina substrate via a spin-coating process. Compared to conventional ceramic membranes constructed by spherical particles, the ceramic membrane constructed by the fibres permits high flux because of the large porosity of their separation layers. The voids in the separation layer determine the selectivity and flux of a separation membrane. When the sizes of the voids are similar (which means a similar selectivity of the separation layer), the flux passing through the membrane increases with the volume of the voids which are filtration passages. For the ideal and simplest texture, a mesh constructed with the nanofibres 10 nm thick and having a uniform pore size of 60 nm, the porosity is greater than 73.5 %. In contrast, the porosity of the separation layer that possesses the same pore size but is constructed with metal oxide spherical particles, as in conventional ceramic membranes, is 36% or less. The membrane constructed by titanate nanofibres and a layer of randomly oriented alumina nanofibres was able to filter out 96.8% of latex spheres of 60 nm size, while maintaining a high flux rate between 600 and 900 Lm–2 h–1, more than 15 times higher than the conventional membrane reported in the most recent study.

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 distance
Poly(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

This dissertation demonstrates the application of a vapor phase method to synthesize supported and unsupported nanoparticle catalysts for CO oxidation. The method is based on the Laser Vaporization/Controlled Condensation (LVCC) technique. The first part of this dissertation presents the vapor phase synthesis and characterization of gold nanoparticles supported on a variety of oxide supports such as CeO2, TiO2, CuO and MgO.The results indicate that Au nanoparticles supported on CeO2 exhibit higher catalytic activity than Au supported on other oxides. The high activity of the Au/CeO2 catalyst is attributed to the strong interaction of Au with CeO2. The results also indicate that 5% Au loading on CeO2 has higher activity than 2% Au or 10% Au. When comparing the catalytic activity of Au/CeO2 prepared by physical (LVCC) and chemical (deposition-precipitation)methods, it was found that the catalytic activity is higher for Au/CeO2 prepared by the deposition-precipitation method.The effect of alloying Au and Cu nanoparticles on the catalytic activity for low temperature CO oxidation was also investigated. The unsupported Au-Cu alloy nanoparticle catalyst exhibits higher catalytic activity than the activities of the individualcomponents and their physical mixtures. The XRD data of Au-Cu alloy taken after the catalysis test indicates the formation of CuO within the bimetallic nanoparticles, whichimproves the catalytic activity of Au-Cu alloy nanoparticle.The second part of this dissertation investigates the gas phase reactions of Au+ and Cu+ with CO, O2 and H2O molecules using the Laser Vaporization ionization, High-Pressure Mass Spectrometry (LVI-HPMS) technique. The gas phase reactions resulting from the interactions of Au+ with CO and O2 molecules are investigated. Although multiple additions of CO and O2 molecules on Au+ have been observed at room temperature, no evidence was found of the production of CO2. This is attributed to the presence of water molecules which effectively replace the oxygen molecules on Au+ at room temperature.Finally, the role of the metal cations Au+ and Cu+ in initiating the gas phase polymerization of butadiene and isoprene vapors was investigated.

Dans ce travail, nous décrivons la méthode de synthèse, la structure, les propriétés et quelques applications en catalyse de différentes formes du carbone, en particulier les nanostructures carbonées (Chapitre I). La technique de dépôt chimique en phase vapeur en réacteur à lit fluidisé a été utilisée pour le dépôt de métaux ou d’oxydes de métaux sur des supports comme l’alumine ou la silice. Le matériau résultant est utilisé comme catalyseur pour la synthèse de diverses nanostructures carbones par dépôt chimique en phase vapeur catalytique : nanotubes de carbone mono- et multi-feuillets (SWCNTs, MWCNTs), nanofibres de carbone (CNFs), et des nanotubes de carbone (N-MWCNTs) ou nanofibres (N-CNFs) dopés en azote (Chapitre II). Après dissolution du catalyseur par un traitement a l'acide sulfurique ou par la soude, suivit dans le cas des MWCNTs et CNFs, par un traitement à l'acide nitrique pour générer des fonctions carboxyliques de surface, les nanostructures carbonées ont été utilisées comme supports de catalyseurs. L’hydrogénation du cinnamaldehyde a été choisit comme réaction modèle pour comparer les performances de différents catalyseurs bimétalliques de Pt-Ru en fonction de la nature du support. Une étude paramétrique détaillée ainsi que l'étude de l'effet d'un traitement thermique sur l'amélioration des performances du catalyseur de Pt-Ru/MWCNT sont présentes. Une explication de l'augmentation des performances catalytiques sera proposée après analyses du catalyseur par HREM, EDX, EXAFS et WAXS (Chapitre III). Les nanostructures carbonées préparées seront également testées comme supports conducteurs d'électrocatalyseurs pour l'élaboration d'électrodes de "polyelectrolyte membrane fuel cells" (PEMFC)
In this work, we describe the synthesis, structure, physical properties and some applications in catalysis of previously known carbon allotropes, and recently discovered carbon nanostructure (Chapter I). First, FB-OM-CVD deposition was used for metal or metal oxide deposition on metal oxide supports like alumina or silica, leading to the production of supported catalysts. The resulting material was used as catalyst for catalytic chemical vapor deposition of carbonaceous nanostructures i.e single- and multi-walled carbon nanotubes (SWCNTs, MWCNTs), carbon nanofibers (CNFs), and nitrogen doped carbon nanotubes (N-MWCNTs) and nanofibers (N-CNFs) (Chapter II). After catalyst removal by a H2SO4 or NaOH treatments and carboxylic surface group generation by a HNO3 treatment in the case of MWCNTs and CNFs, the carbon nanostructures were used as supports for heterogeneous catalysis. The hydrogenation of cinnamaldehyde was used as a model reaction to compare the performance of different bimetallic Pt-Ru catalysts as a function of the nature of the support. Detailed parametric studies as well as the effect of a heat treatment on the performance improvement of the Pt-Ru/MWCNT catalyst are presented. An explanation for the increase of performances upon heat treatment will be proposed after HREM, EDX, EXAFS and WAXS characterization of the catalyst (Chapter III). The prepared carbon nanostructures were also tested as supports for Pd based electrocatalysts for direct alkaline fuel cells applications in both cathodes for the ORR reaction and anodes for alcohols oxidation

Abstract: The aim of the present thesis work is the development of methodologies for the synthesis and functionalization of nanostructured silicon-based mesoporous materials. By coupling innovative synthesis approaches such as microwaves irradiation for thermal activation, ultrasounds for micromixing and the use of a non-conventional silicon source as building block, the overall synthesis time was reduced, the dispersion of the functionalizing agent was enhanced and a synthesis procedure for the preparation of hexagonally ordered silica sieves using a geothermal waste was disclosed. The time reduction and the decrease in the number of synthesis steps poses signicant advantages from an economic point of view and favors the development of green chemical processes. The prepared materials were used as catalytic supports to produce sustainable energy sources and to valorize glycerol as potential raw material for the synthesis of value-added chemical reagents. Cerium promoted mesoporous silica supports were prepared following two different methodologies: I) Direct in situ modication of hexagonally ordered MCM-41 under solvothermal synthesis, using a cationic surfactant as structure-directing agent and II) Post synthesis cerium oxide grafting of mesoporous SBA-15, prepared with a non-ionic triblock poloxamer and a swelling agent to control the pore diameter and surface area. Direct synthesis of MCM-41 silica sieves was achieved by ultrasound-assisted solvothermal synthesis to obtain highly dispersed Ce into the silica framework. The explored Ce/Si molar ratios for the synthesis of the mesoporous materials ranged from 0.02 to 0.08. Microwave irradiation applied by a coaxial antenna was used for thermal activation to reduce the overall hydrothermal synthesis time. The hexagonal ordering of the materials decreased by Ce direct incorporation in the structure. As the amount of Ce/Si increased, two different mechanisms of Ce incorporation were observed: isomorphic substitution and ceria particles deposition outside the silica framework. The mesoporous sieves were used as catalytic supports for a Ni active phase (10 wt.% of metal loading). Their catalytic activity was evaluated in the ethanol steam reforming reaction to produce hydrogen. The new catalysts featured complete ethanol conversion, and higher H2 selectivity (compared to the same Ni catalyst over bare silica) ranging from 60 to 65%. The main product distribution was not dependent on Ce content, these materials did not exhibit catalyst deactivation after 6h on stream and were selective towards H2, CO2, CO and CH4 as sole reaction products. Post synthesis modication of silicon-based SBA-15 was performed over large pore mesoporous sieves, prepared by solvothermal methodology using a non-ionic triblock copolymer as structure directing agent. By modifying the 1,3,5 trimethylbenze/Pluronic 123 mass ratio and the solvothermal ageing temperature, it is possible to obtain hexagonally ordered mesophases in the pore size interval from 4 to 20nm. Selected samples of variable pore diameter were selected as support for the preparation of CeO2/SiO2 composites. The surface grafting methodology enabled the formation of well-dispersed ceria particles that do not match the pore size and therefore do not produce pore blocking. Finally, a green methodology for the preparation of mesoporous silica was developed using a non-conventional silicon-source. A series of template-based mesoporous molecular silicas were prepared using a geothermal waste. Microwaves irradiation was provided by the coaxial applicator for thermal activation. All prepared materials feature hexagonal ordering, narrow pore size distribution and high surface areas (over 500m2/g). By changing the parameters of the solvothermal synthesis, it is possible to tune the ordering and textural properties of the mesophases and reduce the reaction time. These materials were successfully used as a Zn catalytic support for the solventless MW-assisted conversion of glycerol to glycerol carbonate.

Nanostructured oxide materials ultra-thin films, nanoparticles and other nanometer-scale objects play prominent roles in many aspects of our every-day life, in nature and in technological applications, among which is the all-oxide electronics of tomorrow. Due to their reduced dimensions and dimensionality, they strongly interact with their environment gaseous atmosphere, water or support. Their novel physical and chemical properties are the subject of this book from both a fundamental and an applied perspective. It reviews and illustrates the various methodologies for their growth, fabrication, experimental and theoretical characterization. The role of key parameters such as film thickness, nanoparticle size and support interactions in driving their fundamental properties is underlined. At the ultimate thickness limit, two-dimensional oxide materials are generated, whose functionalities and potential applications are described. The emerging field of cation mixing is mentioned, which opens new avenues for engineering many oxide properties, as witnessed by natural oxide nanomaterials such as clay minerals, which, beyond their role at the Earth surface, are now widely used in a whole range of human activities. Oxide nanomaterials are involved in many interdisciplinary fields of advanced nanotechnologies: catalysis, photocatalysis, solar energy materials, fuel cells, corrosion protection, and biotechnological applications are amongst the areas where they are making an impact; prototypical examples are outlined. A cautious glimpse into future developments of scientific activity is finally ventured to round off the treatise.

Ultrasound (US) technology is already into the research field providing a powerful tool of producing nanomaterials or being implicated in decoration procedures of catalyst supports for energy applications and material production. Toward this concept, low or/and high-frequency USs are used for the production of nanoparticles, the decoration of catalytic supported powders (carbon-based, titania, and alumina) with nanoparticles, and the production of metal-organic frameworks (MOFs). MOFs are porous, crystalline materials, which consist of metal centers and organic linkers. Those structures demonstrate high surface area, open metal sites, and large void space. All the above produced materials are used in heterogeneous catalysis, electrocatalysis, photocatalysis, and energy storage. Batteries and fuel cells are popular systems for electrochemical energy storage, and significant progress has been made in nanostructured energy materials in order to improve these storage devices. Nanomaterials have shown favorable properties, such as enhanced kinetics and better efficiency as catalysts for the oxygen reduction reaction (ORR).

This chapter described the advancements in the development of nanostructured supported material and enzyme immobilization techniques. The functionalized nanomaterials extremely affect the inherent mechanical properties and provide the highest biocompatibility and specific nano-environment surrounding the enzymes for improving enzymes stability, catalytic performance, and reaction’s activities. The enzyme immobilization on nanomaterials considerably enhances the robustness and durability of the enzyme for its frequent applications, which reduces the overall expenses of the bio-catalytic process. There are various types of nanomaterials i.e. metal nanoparticles, metal oxide, carbonaceous materials (carbon nanotubes, graphene, and activated carbon), that have been used for the immobilization of the enzyme. So that durability, catalytic activity, leaching of the enzyme, and mechanical steadiness are evaluated for their continual operation.

Natural enzymes perform pivotal role in all biological reactions in living things. But their practical operations are restricted due to difficulty in synthesis, reprocessing, cost, and easy denaturation. To combat these hurdles, blistering exertion is dedicated for improving these enzymes to other enzymes known “artificial enzymes.” The man-made enzymes, which possess enzyme mimicking properties, have fascinated researchers’ attentions. From last decade, nanozymes have attained tremendous progression. Nanomaterials-based enzyme elucidates expressive features like distinct preparative protocols, low cost, long duration for storage, and high stability towards environment than natural enzymes. This draft carries survey on 1) nanozymes literature, which is considerably explored by a diverse class of nanocomposites such as composites of halogens, carbon-based nanostructured materials etc.; 2) the recent progresses made in the fabrication of nanozymes for enzyme mimicking activity; 3) the mechanism of action, schemes to increase enzymatic activities, catalytic property and recent trends of using nanomaterials-based enzymes in the food industries.

Aluminum is the third most abundant element in Earth’s crust (8.3% in mass), behind oxygen (45.5%) and silicon (27.2%). It forms in nature various oxygenated mineral phases: hydroxides Al(OH)3, oxyhydroxides AlOOH, of which bauxite is the main ore, and oxides, Al2O3, alumina. Corundum, α- Al2O3, is the component of many gems: sapphire (pure Al2O3, perfectly colorless), ruby (red colored due to the presence of Cr3+ ions), and blue sapphire (blue colored by the presence of Ti4+ and Fe2+ ions), among many others. The content of foreign elements substituted for Al3+ ions in these phases accounts for only a small percentage of the total. Aluminum also forms many natural phases in combination with various elements, especially silicon in aluminosilicates, such as feldspars, clays, zeolites, allophanes, and imogolites. The biochemical cycling of the elements involves many soluble complexes of aluminum in natural waters [1, 2]. Aluminum oxides and oxy(hydroxi)des are important materials and nanomaterials used in many fields: for instance, as active phase for adsorption in water treatment; as inert support and active phase in catalysis; as active phase in flame-retardant polymers; as refractory material for laboratory tools and in the ceramics industry; and as abrasives [3, 4]. Alumina Al2O3 is produced in various forms (tubes, balls, fibers, and powders) for numerous industrial uses (laboratory tools, filtration membranes, ball bearings, fine powders as catalysis supports, etc.). The structural chemistry of aluminum oxy(hydroxi)des is rich. There are various hydroxides, Al(OH)3 (gibbsite, also named hydrargillite, bayerite, and some other polytypes such as nordstrandite and doyleite), oxyhydroxides, AlOOH (boehmite and diaspore), and a series of oxides, Al2O3, so-called transition aluminas. These last phases have different degrees of hydration and different degrees of order of the Al3+ cations within the cubic close packing of oxygen atoms according to the temperature at which they have been submitted. They belong to various structural types (γ, δ, θ, η, κ, etc.). These aluminas of huge specific surface areas are usually used in catalysis, especially γ-alumina of spinel crystal structure.

There is an urgent need in surface mount technology (SMT) for a nontoxic, reusable and low temperature bonding technique which can afford good mechanical support as well as electrical contact. Meanwhile in the nanotechnology, many excellent and unique structure-related properties such as the high mechanical strength, the high conductivity and the adhesion ability of gecko feet have been studied. Our lab proposes a new patterned structure of Au nanowire array named nanowire surface fastener (NSF), which cold bonding for surface mount technology can be realized at room temperature. Then various methods have been developed to fabricate nanowire, such as arc discharge, catalytic CVD growth and template synthesis, and so on. Among these methods, the template method has been widely used for preparing one-dimensional nanostructures such as metals, semiconductors, polymers, and other materials by electrochemical, electroless deposition or sol-gel technique. Especially anodic aluminum oxide template assisted way has attached considerable attention due to its unique structure properties, such as controllable pore diameter, extremely narrow pore size distribution with high densities, high aspect ratios, and ideally cylindrical pore shape. The well arranged porous anodic aluminum oxide membrane is fabricated from aluminum film by two steps zM oxalic acid electrolytes. The anodic aluminum oxide membrane was investigated for features such as pore size, interpore distance, and thickness by 40 V. It is important for fabrication of porous anodic aluminum oxide template to find out elimination of the barrier layer of oxide and the pore extending rate by 0.5 M phosphoric acid. Morphologies of surface of aluminum film between anodization process and the anodic aluminum oxide barrier layer was researched by using atomic force microscope and scanning electron microscope. Results showed that the anodic aluminum oxide having the same diameter of the pore and the well arranged pore array without branching channel was obtained. The diameter of the pore before the pore extending treatment is 42 nm and the diameter of the pore after the pore extending treatment for 30 minutes is 86 nm. It was found that the diameter of the pore increased per 15 nm by the pore extending treatment for 10 minutes. We fabricated the through-hole anodic aluminum oxide template and made Cu nanowire by the template of our own making. By using Cu nanowire, we try to produce nanowire surface fastener and evaluate its properties.