Download or read book The Catalysis of Uniform Metal Nanoparticles Deposited Onto Oxide Supports written by Nathan Musselwhite and published by . This book was released on 2015 with total page 135 pages. Available in PDF, EPUB and Kindle. Book excerpt: Model materials consisting of metal nanoparticles loaded onto oxide supports were synthesized, characterized, and investigated in a number of catalytic chemical reactions. By varying the size, shape, and composition of nanoparticle, as well as the material used to support the nanoparticles, it was found that small changes to the catalyst can have enormous changes to the reaction activity and selectivity. Investigation of these carefully synthesized catalysts via in situ characterization, and reaction studies, leads to a deeper understanding of the molecular level parameters that govern catalysis. Through study of the properties of the nanoparticles it was discovered that nanoparticle size and shape have a dominant role in the chemoselective catalysis of furfural over platinum nanoparticles. When vapor phase furfural and hydrogen gas were passed over Pt nanoparticles ranging in size from 1.5 to 7.1 nm, the catalytic selectivity was found to be dominated by the size of the nanoparticle. Large nanoparticles promoted hydrogenation of furfural to furfuryl alcohol, while smaller nanoparticles favored decarbonylation to furan. The same size specific selectivity was found in the hydrogenative reforming (the transformation of hydrocarbons to branched isomers) of C6 hydrocarbons, in which Pt nanoparticle size controls isomerization selectivity. Methylcyclopentane was found to be extremely size dependent at lower temperatures (553 K). It was found that smaller sized nanoparticles favored isomer formation, while larger sizes catalyzed the aromatization reaction more efficiently. n-hexane was found to be much less dependent on particle size, but still showed an increase in isomerization with small particles over larger sized Pt nanoparticles. The composition of PtxRh1-x bimetallic nanoparticles was also studied. These catalysts were characterized under hexane reforming conditions with Ambient Pressure X-ray Photoelectron Spectroscopy (AP-XPS), in order to find the actual surface atomic composition under real catalytic working conditions. By using AP-XPS and catalytic data in tandem, it was found that an optimum Rh loading occurred when the surface ensemble statistically favored one Rh atom surrounded by Pt atoms. By utilizing different oxide materials for catalytic supports the flow of charge can play a role in the reaction at the surface or interface in a phenomenon known as the strong metal-support interaction (SMSI). When Pt nanoparticles were loaded onto mesoporous supports made of Co3O4, NiO, MnO2, Fe2O3, and CeO2 it was found that their activity for carbon monoxide oxidation was greatly enhanced relative to the support alone or Pt loaded onto inert mesoporous silica. This finding demonstrates that the interface of the metallic Pt nanoparticle and the oxide support is able to produce turnovers that are orders of magnitude higher than the two materials separately. When the same type of experiments were investigated with n-hexane as the reactant and macroporous Al2O3, TiO2, Nb2O5, Ta2O5, and ZrO2 were utilized as supports, it was found that the reaction selectivity was greatly altered depending on the catalytic support material. TiO2, Nb2O5, and Ta2O5 (all of which are strong Lewis acids) were found to be much more selective for isomer production than the standard SiO2 mesoporous silica supported Pt nanoparticle catalyst. Finally, an acidified mesoporous silica material was utilized as the support. This material was synthesized by using AlCl3 to modify the surface of mesoporous silica. This support was found to have no activity for hexane isomerization alone. However, when Pt nanoparticles were supported on the material, the activity and isomer selectivity in hexane reforming was increased several orders of magnitude as compared to the same nanoparticles supported on unmodified mesoporous silica. This dissertation builds on the existing knowledge of known concepts in catalysis science such as structure sensitive reactions, the metal-support interaction, and acid-base chemistry. The results show how small changes in the active sites of a catalyst can create large changes in the catalytic chemistry. This research demonstrates how careful material control, characterization and reaction study can help to elucidate the molecular level components necessary to design efficient catalysts.

Download or read book Metal Nanoparticles written by Daniel L. Fedlheim and published by CRC Press. This book was released on 2001-10-26 with total page 348 pages. Available in PDF, EPUB and Kindle. Book excerpt: A state-of-the-art reference, Metal Nanoparticles offers the latest research on the synthesis, characterization, and applications of nanoparticles. Following an introduction of structural, optical, electronic, and electrochemical properties of nanoparticles, the book elaborates on nanoclusters, hyper-Raleigh scattering, nanoarrays, and several applications including single electron devices, chemical sensors, biomolecule sensors, and DNA detection. The text emphasizes how size, shape, and surface chemistry affect particle performance throughout. Topics include synthesis and formation of nanoclusters, nanosphere lithography, modeling of nanoparticle optical properties, and biomolecule sensors.

Download or read book Novel Photodeposited Catalysts for Carbon Monoxide Oxidation and Preferential Oxidation of Carbon Monoxide in the Presence of Hydrogen PROX written by Sze Chi Chan and published by ProQuest. This book was released on 2008 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: It has been shown that gold nanoparticles supported on metal oxides with sizes below 5 nm exhibit unique catalytic properties for CO oxidation, water-gas shift, and epoxidation of propylene. In particular, Au/TiO 2 exhibits CO oxidation activity at temperature as low as 90 K. Recent research reported that silver nanoparticles supported on TiO 2 are similar to Au nanoparticles supported on TiO 2 . Conventional methods for preparing Ag/TiO 2 and Au/TiO 2 supported catalysts include deposition-precipitation, wet impregnation and co-precipitation. Among these methods deposition-precipitation has shown the best results for these reactions due to the narrow size distribution of Ag and Au. The major disadvantage of the deposition-precipitation method is that Au and Ag particle sizes are very sensitive to precursor concentration. Preparation of Au particles less than 5 nm requires a low precursor concentration and low Au loading. In this work, a different approach, photodeposition, was used to prepare Ag and Au nanoparticles supported on TiO 2 . The main shortcoming of photodeposition is that its efficiency is very sensitive to both bulk and surface structural features. However, such problems can be overcome by reducing the size of TiO 2 particles to the nanoscale. Photodeposition of Ag nanoparticles on commercial TiO 2 particles and nanoparticles was performed on microscope grid-supported samples in order to provide direct visualization of the spatial distribution of photoactive sites on sub-micron-scale and nanoscale TiO 2 particle surfaces and to create materials for potential catalytic applications. HRTEM (high-resolution transmission electron microscopy) and HAADF-STEM (high-angle annular dark-field scanning transmission electron microscopy) were used to characterize these materials. The size and spatial distributions of the Ag nanoparticles on the commercial TiO 2 were not uniform; the concentration of Ag was higher on grain boundaries and at the edges of these submicrometer particles. In the case of TiO 2 nanoparticles, the size distribution of the Ag nanoparticles deposited was relatively uniform and independent of irradiation time and photon energy. The amount of Ag deposited on TiO 2 nanoparticles was at least 6 times higher than that on commercial samples for comparable irradiation conditions. Compared to the case of Ag photodeposition, the difference in the amount of Au photodeposited on TiO 2 particles and nanoparticles was even greater, especially at low precursor concentration. Photodeposition on TiO 2 nanoparticles is suggested as a potential method for the preparation of Ag/TiO 2 and Au/TiO 2 catalysts. The high photoreactivity of TiO 2 nanoparticles makes them an ideal material for preparation of supported metal catalysts when highly uniform nanoscale particle size is required. Extending the previous work, the Ag and Au photodeposition on TiO 2 nanoparticles were scaled-up from micro scale to laboratory scale to generate sample powders in sufficient quantity to be utilized in catalytic reactor. Most of the methods published for the preparation of metal-decorated TiO 2 by photodeposition involve suspended particles in a aqueous media. Our approach for the scale-up process was different, and was developed based on the sample preparation for metal photodeposition on microscope grids. A thin film of TiO 2 nanoparticle powders coated on a glass plate was obtained by using a spin-coating technique before metal photodeposition. Several commercial TiO 2 nanoparticles were used in this study, in order to choose appropriate samples for the scale-up experiments. Preliminary studies of the photoreactivity of commercial TiO 2 nanoparticles for Ag photodeposition on a microscope grid were carried out prior to the scale-up process. The effects of Ag photoreduction conditions, in particular the radiation source and the metal precursor solution concentration, on Ag photodeposition were investigated to determine the optimum conditions for the scale-up process. The size and spatial distribution of Ag nanoparticles, as well as the Ag loading on commercial TiO 2 nanoparticles for the scale up process under various conditions were determined using TEM and HAADF-STEM techniques. After the optimal conditions for the scale-up process were established, Ag/TiO 2 and Au/TiO 2 nanoparticles obtained from the scaled-up process were characterized by atomic absorption spectroscopy (AAS), X-ray diffraction (XRD), Xray photoelectron spectroscopy (XPS) and HAADF. In addition, Ag/TiO 2 and Au/TiO 2 nanoparticles were also prepared using traditional deposition-precipitation methods. The catalytic performance of Ag/TiO 2 and Au/TiO 2 nanoparticles prepared using two different methods for CO oxidation and preferential oxidation of CO in the presence of H 2 (PROX) were investigated using a high-throughput reactor. Results obtained from this study showed that the size of Ag particles, Ag loading, as well as preparation method contributed to the difference in activity of Ag/TiO 2 for CO oxidation and PROX. In the case of Au/TiO 2 the difference in activity for CO oxidation and PROX is mainly due to the preparation method and Au loading.

Download or read book Nanoparticles in Catalysis written by Karine Philippot and published by John Wiley & Sons. This book was released on 2021-04-29 with total page 384 pages. Available in PDF, EPUB and Kindle. Book excerpt: Nanoparticles in Catalysis Discover an essential overview of recent advances and trends in nanoparticle catalysis Catalysis in the presence of metal nanoparticles is an important and rapidly developing research field at the frontier of homogeneous and heterogeneous catalysis. In Nanoparticles in Catalysis, accomplished chemists and authors Karine Philippot and Alain Roucoux deliver a comprehensive guide to the key aspects of nanoparticle catalysis, ranging from synthesis, activation methodology, characterization, and theoretical modeling, to application in important catalytic reactions, like hydrogen production and biomass conversion. The book offers readers a review of modern and efficient tools for the synthesis of nanoparticles in solution or onto supports. It emphasizes the application of metal nanoparticles in important catalytic reactions and includes chapters on activation methodology and supported nanoclusters. Written by an international team of leading voices in the field, Nanoparticles in Catalysis is an indispensable resource for researchers and professionals in academia and industry alike. Readers will also benefit from the inclusion of: A thorough introduction to New Trends in the Design of Metal Nanoparticles and Derived Nanomaterials for Catalysis An exploration of Dynamic Catalysis and the Interface Between Molecular and Heterogeneous Catalysts A practical discussion of Metal Nanoparticles in Water: A Relevant Toolbox for Green Catalysis Organometallic Metal Nanoparticles for Catalysis A concise treatment of the opportunities and challenges of CO2 Hydrogenation to Oxygenated Chemicals Over Supported Nanoparticle Catalysts Perfect for catalytic, organic, inorganic, and physical chemists, Nanoparticles in Catalysis will also earn a place in the libraries of chemists working with organometallics and materials scientists seeking a one-stop resource with expert knowledge on the synthesis and characterization of nanoparticle catalysis.

Download or read book In situ Gas Phase Catalytic Properties of Metal Nanoparticles written by Luis Katsuya Ono and published by . This book was released on 2009 with total page 385 pages. Available in PDF, EPUB and Kindle. Book excerpt: Recent advances in surface science technology have opened new opportunities for atomic-scale studies in the field of nanoparticle (NP) catalysis (1, 2). The 2007 Nobel Prize of Chemistry awarded to Prof. G. Ertl, a pioneer in introducing surface science techniques to the field of heterogeneous catalysis (3-16), shows the importance of the field and revealed some of the fundamental processes of how chemical reactions take place at extended surfaces. However, after several decades of intense research, fundamental understanding on the factors that dominate the activity, selectivity, and stability (life-time) of nanoscale catalysts are still not well understood. This dissertation aims to explore the basic processes taking place in NP catalyzed chemical reactions by systematically changing their size, shape, oxide support, and composition, one factor at a time. Low temperature oxidation of CO over gold NPs supported on different metal oxides and carbides (SiO2, TiO2, TiC, etc.) has been used as a model reaction. The fabrication of nanocatalysts with a narrow size and shape distribution is essential for the microscopic understanding of reaction kinetics on complex catalyst systems ("real-world" systems). Our NP synthesis tools are based on self-assembly techniques such as diblock-copolymer encapsulation and nanosphere lithography. The morphological, electronic and chemical properties of these nanocatalysts have been investigated by atomic force microscopy (AFM), scanning tunneling microscopy (STM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and temperature-programmed desorption (TPD). Chapter 1 describes briefly the basic principles of the instrumentation used within this experimental dissertation. Since most of the state-of-art surface science characterization tools provide ensemble-averaged information, catalyst samples with well defined morphology and structure must be available to be able to extract meaningful information on how size and shape affect the physical and chemical properties of these structures. In chapter 2, the inverse-micelle encapsulation and nanosphere lithography methods used in this dissertation for synthesizing uniformly arranged and narrow size- and shape-selected spherical and triangular NPs are described. Chapter 3 describes morphological changes on individual Au NPs supported on SiO2 as function of the annealing temperature and gaseous environment. In addition, NP mobility is monitored. Chapter 4 explores size-effects on the electronic and catalytic properties of size-selected Au NPs supported on a transition metal carbide, TiC. The effect of interparticle interactions on the reactivity and stability (catalyst lifetime) of Au NPs deposited on TiC is discussed in chapter 5. Size and support effects on the formation and thermal stability of Au2O3, PtO and PtO2 on Au and Pt NPs supported on SiO2, TiO2 and ZrO2 is investigated in chapter 6. Emphasis is given to gaining insight into the role of the NP/support interface and that played by oxygen vacancies on the stability of the above metal oxides. Chapter 7 reports on the formation, thermal stability, and vibrational properties of mono- and bimetallic Au[subscript x]Fe[subscript 1-x] (x = 1, 0.8, 0.5, 0.2, 0) NPs supported on TiO2(110). At the end of the thesis, a brief summary describes the main highlights of this 5-year research program.

Download or read book Strong Metal support Interactions written by R. T. K. Baker and published by . This book was released on 1986 with total page 258 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Metal Nanoclusters in Catalysis and Materials Science The Issue of Size Control written by Benedetto Corain and published by Elsevier. This book was released on 2011-08-11 with total page 471 pages. Available in PDF, EPUB and Kindle. Book excerpt: Metal Nanoclusters in Catalysis and Materials Science: The Issue of Size Control deals with the synthesis of metal nanoclusters along all known methodologies. Physical and chemical properties of metal nanoclusters relevant to their applications in chemical processing and materials science are covered thoroughly. Special attention is given to the role of metal nanoclusters size and shape in catalytic processes and catalytic applications relevant to industrial chemical processing.An excellent text for expanding the knowledge on the chemistry and physics of metal nanoclusters. Divided in two parts; Part I deals with general aspects of the matter and Part II has to be considered a useful handbook dealing with the production of metal nanoclusters, especially from their size-control point of view. * Divided into two parts for ease of reference: general and operational * Separation of synthetic aspects, physical properties and applications* Specific attention is given to the task of metal nanoclusters size-control

Download or read book Metal Nanoparticles for Catalysis written by Franklin Tao and published by Royal Society of Chemistry. This book was released on 2014-06-12 with total page 285 pages. Available in PDF, EPUB and Kindle. Book excerpt: Catalysis is a central topic in chemical transformation and energy conversion. Thanks to the spectacular achievements of colloidal chemistry and the synthesis of nanomaterials over the last two decades, there have also been significant advances in nanoparticle catalysis. Catalysis on different metal nanostructures with well-defined structures and composition has been extensively studied. Metal nanocrystals synthesized with colloidal chemistry exhibit different catalytic performances in contrast to metal nanoparticles prepared with impregnation or deposition precipitation. Additionally, theoretical approaches in predicting catalysis performance and understanding catalytic mechanism on these metal nanocatalysts have made significant progress. Metal Nanoparticles for Catalysis is a comprehensive text on catalysis on Nanoparticles, looking at both their synthesis and applications. Chapter topics include nanoreactor catalysis; Pd nanoparticles in C-C coupling reactions; metal salt-based gold nanocatalysts; theoretical insights into metal nanocatalysts; and nanoparticle mediated clock reaction. This book bridges the gap between nanomaterials synthesis and characterization, and catalysis. As such, this text will be a valuable resource for postgraduate students and researchers in these exciting fields.

Download or read book Metal catalyzed Cross coupling Reactions written by François Diederich and published by John Wiley & Sons. This book was released on 2008-07-11 with total page 540 pages. Available in PDF, EPUB and Kindle. Book excerpt: Carbon-carbon bond forming reactions are arguably the most important processes in chemistry, as they represent key steps in the building of complex molecules from simple precursors. Among these reactions, metal-catalyzed cross-coupling reactions are extensively employed in a wide range of areas of preparative organic chemistry, ranging from the synthesis of complex natural products, to supramolecular chemistry, and materials science. In this work, a dozen internationally renowned experts and leaders in the field bring the reader up to date by documenting and critically analyzing current developments and uses of metal-catalyzed cross-coupling reactions. A particularly attractive and useful feature, that enhances the practical value of this monograph, is the inclusion of key synthetic protocols, in experimental format, chosen for broad utility and application. This practice-oriented book can offer the practitioner short cuts to ensure they remain up-to-date with the latest developments.

Download or read book Monodispersed Particles written by Tadao Sugimoto and published by Elsevier. This book was released on 2019-11-16 with total page 852 pages. Available in PDF, EPUB and Kindle. Book excerpt: Monodispersed Particles, Second Edition, covers all aspects of monodispersed particles, including inorganic and polymer particles and their composites. The book consists of four parts: fundamentals, preparation, analyses, and applications. Specifically, the fundamental part covers the theoretical insight into the surface energy of particles and its application to the formulation of the new theories of nucleation, growth and habit formation of monodispersed particles. In addition, the theories of recrystallization and solid-solution formation are introduced. These fundamental theories are applied to the precise control of their size, size distribution, shape, internal structure, and composition, leading to the design of diverse monodispersed functional particles widely used in basic science and modern industry.This second edition is fully updated and revised, detailing new theories and recent progress in the field of nanoparticles, including advanced nucleation theory, arrested growth mechanism for monodispersed nanoparticles, and energetics of habit formation. Additionally, the text covers in-depth insights into the anisotropic growth of Au and Ag nanoparticles, the formation mechanisms of polycrystalline Au spheres, iron oxide nanoparticles in heat-up and hot-injection processes, amorphous TiO2 spheres in a sol-gel system, anatase TiO2 in a gel-sol system and their shape control, AgCl nanoparticles in a reverse micelle system, organic-inorganic hybrid liquid crystals, and extensive biomedical applications. Covers most of the known uniform particles, including inorganic and polymer particles and their composites Includes development of novel fundamental theories of formation mechanisms, full of the author's own original ideas, and detailed background discussion on recent progress in the feild of nanoparticles and the latest advances in their applications Features 2000 bibliographic references, providing a comprehensive guide to related study

Download or read book PEM Fuel Cell Failure Mode Analysis written by Haijiang Wang and published by CRC Press. This book was released on 2011-08-25 with total page 366 pages. Available in PDF, EPUB and Kindle. Book excerpt: PEM Fuel Cell Failure Mode Analysis presents a systematic analysis of PEM fuel cell durability and failure modes. It provides readers with a fundamental understanding of insufficient fuel cell durability, identification of failure modes and failure mechanisms of PEM fuel cells, fuel cell component degradation testing, and mitigation strategies against degradation. The first several chapters of the book examine the degradation of various fuel cell components, including degradation mechanisms, the effects of operating conditions, mitigation strategies, and testing protocols. The book then discusses the effects of different contamination sources on the degradation of fuel cell components and explores the relationship between external environment and the degradation of fuel cell components and systems. It also reviews the correlation between operational mode, such as start-up and shut-down, and the degradation of fuel cell components and systems. The last chapter explains how the design of fuel cell hardware relates to failure modes. Written by international scientists active in PEM fuel cell research, this volume is enriched with practical information on various failure modes analysis for diagnosing cell performance and identifying failure modes of degradation. This in turn helps in the development of mitigation strategies and the increasing commercialization of PEM fuel cells.

Download or read book Advanced Nanomaterials for Catalysis and Energy written by Vladislav A. Sadykov and published by Elsevier. This book was released on 2018-08-27 with total page 590 pages. Available in PDF, EPUB and Kindle. Book excerpt: Advanced Nanomaterials for Catalysis and Energy: Synthesis, Characterization and Applications outlines new approaches to the synthesis of nanomaterials (synthesis in flow conditions, laser electrodispersion of single metals or alloys on carbon or oxide supports, mechanochemistry, sol-gel routes, etc.) to provide systems with a narrow particle size distribution, controlled metal-support interaction and nanocomposites with uniform spatial distribution of domains of different phases, even in dense sintered materials. Methods for characterization of real structure and surface properties of nanomaterials are discussed, including synchrotron radiation diffraction and X-ray photoelectron spectroscopy studies, neutronography, transmission/scanning electron microscopy with elemental analysis, and more. The book covers the effect of nanosystems' composition, bulk and surface properties, metal-support interaction, particle size and morphology, deposition density, etc. on their functional properties (transport features, catalytic activity and reaction mechanism). Finally, it includes examples of various developed nanostructured solid electrolytes and mixed ionic-electronic conductors as materials in solid oxide fuel cells and asymmetric supported membranes for oxygen and hydrogen separation. Outlines synthetic and characterization methods for nanocatalysts Relates nanocatalysts' properties to their specific applications Proposes optimization methods aiming at specific applications

Download or read book Nanotechnology in Catalysis 3 written by Bing Zhou and published by Springer Science & Business Media. This book was released on 2007-09-05 with total page 342 pages. Available in PDF, EPUB and Kindle. Book excerpt: This volume continues the tradition formed in Nanotechnology in Catalysis 1 and 2. As with those books, this one is based upon an ACS symposium. Some of the most illustrious names in heterogeneous catalysis are among the contributors. The book covers: Design, synthesis, and control of catalysts at nanoscale; understanding of catalytic reaction at nanometer scale; characterization of nanomaterials as catalysts; nanoparticle metal or metal oxides catalysts; nanomaterials as catalyst supports; new catalytic applications of nanomaterials.

Download or read book Novel Preparation and Magneto Chemical Characterization of Nanoparticle Mixed Alcohol Catalysts written by and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: We have developed and streamlined the experimental systems: (a) Laser-induced solution deposition (LISD) photosynthesis, ball-milling, and chemical synthesis of Fe, Co, and Cu nanoparticle catalysts; (b) Sol-gel method for mesoporous [gamma]-Al2O3, SiO2, hybrid alumina/silica granular supports; (c) Three sol-gel/oil-drop catalyst preparation methods to incorporate metal nanoparticles into mesoporous 1 mm granular supports; (d) Low-cost GC-TCD system with hydrogen as carrier gas for the determination of wide spectrum of alkanes produced during the F-T reactions; and (e) Gas-flow reactor and microchannel reactor for fast screening of catalysts. The LISD method could produce Co, Cu, and Fe (5 nm) nanoparticles, but in milligram quantities. We could produce nanoparticles in gram quantities using high-energy ball milling and chemical synthesis methods. Ball milling gave wide particle size distribution compared to the chemical synthesis method that gave almost uniform size (≈5 nm) particles. Metal nanoparticles Cu, Co, Fe, Cu/Co, Cu/Fe and Co/Fe were loaded (2-12 wt%) uniformly into [gamma]-Al2O3, SiO2, or alumina/silica hybrid supports by combined sol-gel/oil-drop methods followed by calcination and hydrogenation steps, prior to syngas FT reaction studies. The properties of metal loaded [gamma]-Al2O3 granules were compared for the two precursors: aluminum tri-sec-butoxide (ALTSB) and aluminum tri-iso-propoxide (ALTIP). The effect of solgel supports alumina, silica, and alumina/silica hybrid were examined on catalytic properties. Metal loading efficiencies for pure metal catalysts increased in the order Co, Cu and Fe in agreement with solubility of metal hydroxides. In case of mixed metals, Co and Cu seams to interfere and reduce Fe metal loading when metal nitrate solutions are used. The solubility differences of metal hydroxides would not allow precise control of metal loading. We have overcome this problem by introducing a novel method of nanoparticle metal oxide co-entrapped sol-gel that gave the highest metal loading with precise control and reproducibility, and greater mechanical strength of granules than the metal nitrate solution co-entrapping and wet impregnation methods. Both, slurry-phase-batch and gas-phase-continuous-flow, reactors were used for syngas conversion reactions. Our investigations of Co and Fe thin film deposited micro-reactors showed higher CO/H2 conversion for Fe compared to Co. The catalytic activity for CO/H2 conversion was observed in the increasing order for the nanocatalysts Cu, Co, Fe, Co/Fe, Cu/Co and Cu/Fe in alumina sol-gel support, and Co/Fe showed the highest yield for methane. The optimization of CO/H2 ratio indicated that 1:1 ratio gave more alkanes distribution in F-T process with Co/Fe (6% each) impregnated on alumina. We could estimate the activity of catalysts (involving Co, Fe) during hydrogenation and after catalytic reaction using magnetization studies. In summary our accomplishments are: (1) Novel chemical methods for the synthesis of (5 nm) Fe, Co, Cu nanoparticles with narrow size distribution. (2) Developing a method of metal oxide nanoparticles addition to alumina/silica sol-gel to control metal loading of pure and mixed metal catalysts compositions in high yields. (3) A low-cost GC-TCD system to analyze wide spectrum of alkanes (F-T reaction products). (4) Fe/Co mixed metal alumina/silica mesoporous catalysts with higher FT activity. (5) Characterizing nanoparticle catalysts and supports for detail understanding of FT-process.

Download or read book Exploring the Chemistry of Metal metal Oxide Catalysts written by Carly Byron and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The work outlined in this dissertation is dedicated to the surface chemistry of promoted metal nanoparticle catalysts for dry reforming of methane (DRM). The main part of this work focuses on the effect of promoters on platinum and nickel active catalysts and understanding how the change in surface chemistry affects the mechanism of the DRM reaction. We have identified several promoters that improve the DRM activity by tuning the surface chemistry; boron promoter with platinum catalyst and transition metal promoters with nickel catalyst. The addition of promoter sites led to the migration of coke deposits away from active sites, improved surface activation of CO2, and morphological control over the coke deposits. This work is necessary because growing concern over the effects of climate change has necessitated research into potential fossil fuel replacements. The current energy infrastructure already supports hydrocarbon fuel sources. However, researchers' current challenge is the ability to produce fuel in a carbon-neutral process using inexpensive catalytic materials. Heterogeneous catalysis is paramount to solving the energy problem, and the chemistry of catalytic surfaces must be optimized to achieve carbon-based fuel production that can replace fossil fuels long term. Noble metals and transition metals are highly active to hydrocarbon conversion. The dry reforming of methane (DRM) is a promising reaction because it converts methane and carbon dioxide into a "synthesis gas", or syngas, which can be processed to produce fuels and other value-added chemicals. When in the form of a nanoparticle supported on metal oxide, the active surface area of the metal is maximized, and less metal is required for catalysis. However, nanoparticle catalysts are readily deactivated by coking (carbon deposits) and sintering (nanoparticle agglomeration). Noble metals are highly active to DRM due to their high selectivity and resistance to deactivation, but they are typically too costly for practical use. Nickel is a promising DRM catalyst because of its low cost and high activity but is more susceptible to deactivation, therefore nickel is often paired with a second "promoter" metal to optimize the material and prevent deactivation. The development of active, stable bimetallic catalysts requires a detailed understanding of the chemistry at the surface during the reaction. In this work, we have identified the role of promoter sites using surface characterization techniques which provide better understanding of the catalytic mechanism.

Download or read book The Synthesis of Solid Supported Palladium Nanoparticles written by Kendra W. Brinkley and published by . This book was released on 2015 with total page 272 pages. Available in PDF, EPUB and Kindle. Book excerpt: Catalysis is one of the pillars of the chemical industry. While the use of catalyst is typically recognized in the automobile industry, their impact is more widespread as; catalysts are used in the synthesis of 80% of the US commercial chemicals. Despite the improved selectivity provided by catalyst, process inefficiencies still threaten the sustainability of a number of synthesis methods, especially in the pharmaceutical industry. Recyclable solid supported catalysts offer a unique opportunity to address these inefficiencies. Such systems coupled with continuous synthesis techniques, have the potential to significantly reduce the waste to desired product ratio (E-factor) of the production techniques. This research focuses developing sustainable processes to synthesize organic molecules by using continuous synthesis methods. In doing so, solid supported metal catalyst systems were identified, developed, and implemented to assist in the formation of carbon-carbon bonds. Newly developed systems, which utilized metal nanoparticles, showed reactivity and recyclability, comparable to commercially available catalyst. Nanoparticles are emerging as useful materials in a wide variety of applications including catalysis. These applications include pharmaceutical processes by which complex and useful organic molecules can be prepared. As such, an effective and scalable synthesis method is required for the preparation of nanoparticle catalysts with significant control of the particle size, uniform dispersion, and even distribution of nanoparticles when deposited on the surface of a solid support. This project describes the production of palladium nanoparticles on a variety of solid supports and the evaluation of these nanoparticles for cross coupling reactions. This report highlights novel synthesis techniques used in the formation of palladium nanoparticles using traditional batch reactions. The procedures developed for the batch formation of palladium nanoparticles on different solid supports, such as graphene and carbon nanotubes, are initially described. The major drawbacks of these methods are discussed, including limited scalability, variation of nanoparticle characteristics from batch to batch, and technical challenges associated with efficient heating of samples. Furthermore, the necessary conditions and critical parameters to convert the batch synthesis of solid supported palladium nanoparticles to a continuous flow process are presented. This strategy not only alleviates the challenges associated with the robust preparation of the material and the limitations of scalability, but also showcases a new continuous reactor capable of efficient and direct heating of the reaction mixture under microwave irradiation. This strategy was further used in the synthesis of zinc oxide nanoparticles. Particles synthesized using this strategy as well as traditional synthesis methods, were evaluated in the context industrially relevant applications.

Download or read book Metal Metal Oxide Nanoparticles Supported on Nanostructured Carbons for Electrochemical Applications written by 杨纯臻 and published by . This book was released on 2017-01-26 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation, "Metal/metal oxide nanoparticles supported on nanostructured carbons for electrochemical applications" by 杨纯臻, Chunzhen, Yang, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Among various electrochemical devices that have been developed for energy storage and conversion, electric double layer capacitors (EDLCs) and direct methanol fuel cells (DMFC) have received much research attention. Nanostructured carbon materials have been playing an important role in the development of these devices, due to such characteristics as good electrical conductivity, high chemical stability, high surface area and large pore volumes and etc. In an EDLC, nanostructured carbon electrodes, possessing pores of varied length scales, can deliver electric energy at high current loadings. This kind of pore structure also benefits the deposition of metal catalysts and the transport of reactants and products in the methanol oxidation reaction. In order to systematically study the structural effects on the electrochemical capacitance and ionic transport, a series of three-dimensional hierarchical carbons with hollow core-mesoporous shell (HCMS) structure were template-synthesized. Periodically ordered macroscopic hollow cores of 330 nm in diameter were surrounded by a mesoporous shell containing uniform pores of 3.9 nm. The shell thickness was stepwise increased from 0, 25, 50 to 100 nm. The HCMS structure was modeled by a 5-level transmission line model to study the capacitance contribution from the pores at different length scale. Results revealed that the HCMS carbon with thicker mesoporous shells can provide high capacitance, while thinner shells could deliver high power output. A series of HCMS carbon sphere supported Pt nanoparticles were synthesized via the "Carbonization over Protected and Dispersed Metal" (CPDM) method. Contrary to the conventional "polyol" synthetic method, whereas most of Pt nanoparticles were deposited on the external surface of carbon spheres; the Pt nanoparticles synthesized via the CPDM method were found encapsulated in the mesoporous carbon shells and highly dispersed throughout the carbon texture. "Accelerated stress tests‟ (ASTs) were conducted to investigate the nanopores confinement effect toward the electrochemical stability of these Pt catalysts. Results revealed that (1) the nanopores confined Pt nanoparticles on HCMS carbon spheres exhibited a stable electrochemical active surface area (ECSA) and catalytic activity; and (2) thick mesoporous carbon shells could provide better protection over the Pt nanoparticles. This "CPDM" method was further extended to synthesize highly alloyed PtRu nanoparticles supported electrocatalysts. It is expected that this CPDM method can also be applied to synthesize other metal/metal oxide supported catalysts with stable electrochemical performance. WO3 has been demonstrated as a promsing co-catalyst for Pt in the methanol oxidation reaction (MOR). The synthesis of Pt-WO3/C catalyst with well-controlled nanoparticle size (2.5 nm) and composition was achieved via a microwave-assisted water-oil microemulsion reaction. Hydrogen adsorption, CO-stripping and Cu- stripping methods were used to estimate the ECSA of Pt in the Pt-WO3/C catalysts. Among these, Cu-stripping method was relatively more reliable due to the overlapping involvement of the WO3 component in the other methods. The methanol oxidation measurement shows that a 1:1 Pt: W ratio catalyst exhibits the highest Pt-mass current density of 271 mA mg-1-Pt, 1.4 times higher than that of commercial E-TEK catalyst.