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Author : Michael Edward Grass
Publisher :
ISBN 13 :
Total Pages : 416 pages
Book Rating : 4.:/5 (34 download)
Download or read book Monodisperse Platinum and Rhodium Nanoparticles as Model Heterogeneous Catalysts written by Michael Edward Grass and published by . This book was released on 2008 with total page 416 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author :
Publisher :
ISBN 13 :
Total Pages : 204 pages
Book Rating : 4.:/5 (16 download)
Download or read book Monodisperse Platinum and Rhodium Nanoparticles as Model Heterogeneous Catalysts written by and published by . This book was released on 2008 with total page 204 pages. Available in PDF, EPUB and Kindle. Book excerpt: Model heterogeneous catalysts have been synthesized and studied to better understand how the surface structure of noble metal nanoparticles affects catalytic performance. In this project, monodisperse rhodium and platinum nanoparticles of controlled size and shape have been synthesized by solution phase polyol reduction, stabilized by polyvinylpyrrolidone (PVP). Model catalysts have been developed using these nanoparticles by two methods: synthesis of mesoporous silica (SBA-15) in the presence of nanoparticles (nanoparticle encapsulation, NE) to form a composite of metal nanoparticles supported on SBA-15 and by deposition of the particles onto a silicon wafer using Langmuir-Blodgett (LB) monolayer deposition. The particle shapes were analyzed by transmission electron microscopy (TEM) and high resolution TEM (HRTEM) and the sizes were determined by TEM, X-ray diffraction (XRD), and in the case of NE samples, room temperature H2 and CO adsorption isotherms. Catalytic studies were carried out in homebuilt gas-phase reactors. For the nanoparticles supported on SBA-15, the catalysts are in powder form and were studied using the homebuilt systems as plug-flow reactors. In the case of nanoparticles deposited on silicon wafers, the same systems were operated as batch reactors. This dissertation has focused on the synthesis, characterization, and reaction studies of model noble metal heterogeneous catalysts. Careful control of particle size and shape has been accomplished though solution phase synthesis of Pt and Rh nanoparticles in order to elucidate further structure-reactivity relationships in noble metal catalysis.
Download or read book Converting Homogeneous to Heterogeneous in Electrophilic Catalysis Using Monodisperse Metal Nanoparticles written by and published by . This book was released on 2009 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A continuing goal in catalysis is the transformation of processes from homogeneous to heterogeneous. To this end, nanoparticles represent a new frontier in heterogeneous catalysis, where this conversion is supplemented by the ability to obtain new or divergent reactivity and selectivity. We report a novel method for applying heterogeneous catalysts to known homogeneous catalytic reactions through the design and synthesis of electrophilic platinum nanoparticles. These nanoparticles are selectively oxidized by the hypervalent iodine species PhICl2, and catalyze a range of [pi]-bond activation reactions previously only homogeneously catalyzed. Multiple experimental methods are utilized to unambiguously verify the heterogeneity of the catalytic process. The discovery of treatments for nanoparticles that induce the desired homogeneous catalytic activity should lead to the further development of reactions previously inaccessible in heterogeneous catalysis. Furthermore, our size and capping agent study revealed that Pt PAMAM dendrimer-capped nanoparticles demonstrate superior activity and recyclability compared to larger, polymer-capped analogues.
Author : Matthew James Lundwall
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (78 download)
Download or read book Characterization and Reaction Studies of Silica Supported Platinum and Rhodium Model Catalysts written by Matthew James Lundwall and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The physical and catalytic properties of silica supported platinum or rhodium model catalysts are studied under both ultra high vacuum (UHV) and elevated pressure reaction conditions (>1torr). Platinum or rhodium nanoparticles are vapor deposited onto a SiO2/Mo(112) surface and characterized using various surface analytical methods. CO chemisorption is utilized as a surface probe to estimate the concentration of various sites on the nanoparticles through thermal desorption spectroscopy (TDS) and infrared reflection absorption spectroscopy (IRAS) along with microscopy techniques to estimate particle size. The results are compared with hard sphere models of face centered cubic metals described as truncated cubo-octahedron. Results demonstrate the excellent agreement between chemisorption and hard sphere models in estimating the concentration of undercoordinated atoms on the nanoparticle surface. Surfaces are then subjected to high pressure reaction conditions to test the efficacy of utilizing the rate of a chemical reaction to obtain structural information about the surface. The surfaces are translated in-situ to a high pressure reaction cell where both structure insensitive and sensitive reactions are performed. Structure insensitive reactions (e.g. CO oxidation) allow a method to calculate the total active area on a per atom basis for silica supported platinum and rhodium model catalysts under reaction conditions. While structure sensitive reactions allow an estimate of the types of reaction sites, such as step sites ([less than or equal to]C7) under reaction conditions (e.g. n-heptane dehydrocyclization). High pressure structure sensitive reactions (e.g. ethylene hydroformylation) are also shown to drastically alter the morphology of the surface by dispersing nanoparticles leading to inhibition of catalytic pathways. Moreover, the relationships between high index single crystals, oxide supported nanoparticles, and high surface area technical catalysts are established. Overall, the results demonstrate the utility of model catalysts in understanding the structure-activity relationships in heterogeneous catalytic reactions and the usefulness of high pressure reactions as an analytical probe of surface morphology.
Author : Robert M. Rioux
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (316 download)
Download or read book The Synthesis, Characterization and Catalytic Reaction Studies OfMonodisperse Platinum Nanoparticles in Mesoporous Oxide Materials written by Robert M. Rioux and published by . This book was released on 2006 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Monodisperse Metal Nanoparticle Catalysts on Silica Mesoporous Supports written by and published by . This book was released on 2009 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The design of high performance catalyst achieving near 100% product selectivity at maximum activity is one of the most important goals in the modern catalytic science research. To this end, the preparation of model catalysts whose catalytic performances can be predicted in a systematic and rational manner is of significant importance, which thereby allows understanding of the molecular ingredients affecting the catalytic performances. We have designed novel 3-dimensional (3D) high surface area model catalysts by the integration of colloidal metal nanoparticles and mesoporous silica supports. Monodisperse colloidal metal NPs with controllable size and shape were synthesized using dendrimers, polymers, or surfactants as the surface stabilizers. The size of Pt, and Rh nanoparticles can be varied from sub 1 nm to 15 nm, while the shape of Pt can be controlled to cube, cuboctahedron, and octahedron. The 3D model catalysts were generated by the incorporation of metal nanoparticles into the pores of mesoporous silica supports via two methods: capillary inclusion (CI) and nanoparticle encapsulation (NE). The former method relies on the sonication-induced inclusion of metal nanoparticles into the pores of mesoporous silica, whereas the latter is performed by the encapsulation of metal nanoparticles during the hydrothermal synthesis of mesoporous silica. The 3D model catalysts were comprehensively characterized by a variety of physical and chemical methods. These catalysts were found to show structure sensitivity in hydrocarbon conversion reactions. The Pt NPs supported on mesoporous SBA-15 silica (Pt/SBA-15) displayed significant particle size sensitivity in ethane hydrogenolysis over the size range of 1-7 nm. The Pt/SBA-15 catalysts also exhibited particle size dependent product selectivity in cyclohexene hydrogenation, crotonaldehyde hydrogenation, and pyrrole hydrogenation. The Rh loaded SBA-15 silica catalyst showed structure sensitivity in CO oxidation reaction. In addition, Pt-mesoporous silica core-shell structured NPs (Pt@mSiO2) were prepared, where the individual Pt NP is encapsulated by the mesoporous silica layer. The Pt@mSiO2 catalysts showed promising catalytic activity in high temperature CO oxidation. The design of catalytic structures with tunable parameters by rational synthetic methods presents a major advance in the field of catalyst synthesis, which would lead to uncover the structure-function relationships in heterogeneous catalytic reactions.
Author : Jonathan E. Sutton
Publisher :
ISBN 13 :
Total Pages : 112 pages
Book Rating : 4.:/5 (212 download)
Download or read book Synthesis of Platinum Nanoparticles and Their Use in Novel Heterogeneous Catalysts written by Jonathan E. Sutton and published by . This book was released on 2007 with total page 112 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : Robert Martin Rioux
Publisher :
ISBN 13 : 9780542826405
Total Pages : 760 pages
Book Rating : 4.8/5 (264 download)
Download or read book The Synthesis, Characterization and Catalytic Reaction Studies of Monodisperse Platinum Nanoparticles in Mesoporous Oxide Materials written by Robert Martin Rioux and published by . This book was released on 2006 with total page 760 pages. Available in PDF, EPUB and Kindle. Book excerpt: A catalyst design program was implemented in which Pt nanoparticles, either of monodisperse size and/or shape were synthesized, characterized and studied in a number of hydrocarbon conversion reactions. The novel preparation of these materials enables exquisite control over their physical and chemical properties that could be controlled (and therefore rationally tuned) during synthesis. The ability to synthesize rather than prepare catalysts followed by thorough characterization enable accurate structure-function relationships to be elucidated. Pt nanoparticles (1.7--7.1 nm) are synthesized by solution phase reduction methods in which Pt precursors are reduced in protic solvents in the presence of a surface templating polymer, which serves to stabilize the metal nanoparticles in solution. Particle size can be controlled during synthesis by altering either the PVP: Pt salt ratio, reaction media and by seeded growth methods. After Pt nanoparticles are synthesized, their size and morphology are confirmed with transmission electron microscopy and x-ray diffraction. Low power sonication in either aqueous or organic solvent was utilized to disperse Pt nanoparticles within the mesoporous metal oxide matrix. This method of catalyst synthesis is named capillary inclusion (CI). An alternative approach to catalyst synthesis combines the hydrothermal synthesis of mesoporous silica with Pt nanoparticle synthesis in the same solution. Synthesis under neutral conditions led to a catalyst in which the nanoparticles were highly dispersed throughout the catalyst matrix. This method of catalyst synthesis called nanoparticle encapsulation (NE) ensured that Pt nanoparticles were located on the internal pore surface of the mesoporous silica. Catalysts were characterized by transmission electron microscopy (TEM), x-ray diffraction (XRD), small angle x-ray scattering (SAXS) and physical adsorption to determine metal particle size and mesoporous structure. The surface chemistry of the nanoparticle surface was studied by infrared spectroscopy, selective gas adsorption (chemisorption) and catalytic reactivity studies. During nanoparticle synthesis, PVP is added to the solution to stabilize the platinum nanoparticles against aggregation. This polymer remains bound to the nanoparticle surface after catalyst synthesis and must be removed before catalytic reactions. Calcination of the catalyst at high temperature (623--723 K) for long time periods (24--36 hours) followed by reduction was initially used to clean the Pt surface. (Abstract shortened by UMI.)
Download or read book Structure Sensitivity of Carbon-Nitrogen Ring Opening written by and published by . This book was released on 2008 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The ability to control fundamental properties (e.g., particle size, surface structure, and metal-oxide interface) in order to design highly selective heterogeneous catalysts would greatly reduce energy intensive separations. Particle size dependence (i.e., structure sensitivity) upon selectivity can now be examined with well defined nanoparticles (NPs) because of advances in synthetic chemistry. Colloidal chemistry has provided means for synthesizing monodisperse Pt NPs as small as (almost equal to)2 nm. Using a dendrimer templated approach, Pt NPs smaller than 1 nm--a new size regime for studying size induced effects in heterogeneous catalysis--can be synthesized (Scheme 1). In this contribution, we report that ring opening for pyrrole hydrogenation is distinctly different for Pt NPs smaller than 2 nm. This insight has not been demonstrated for hydrogenation of cyclic heteroatom bonds to the best of our knowledge. This finding adds fundamental insight into hydrodenitrogenation (HDN) chemistry, which is important for fuel processing and involves removal of N-containing organics. Advances in HDN catalysis are needed to meet new fuel quality regulations because N-containing organics inhibit hydrodesulfurization (HDS) through competitive adsorption and poison acid catalysts, which are used for downstream processing and as supports for HDS catalysts. Pyrrole was selected as the reactant because organics with 5-member N-containing rings are the most common components in fuel.
Author : Simon Armando Mostafa Covone
Publisher :
ISBN 13 :
Total Pages : 92 pages
Book Rating : 4.:/5 (688 download)
Download or read book Synthesis, Structure, and Catalytic Properties of Size-selected Platinum Nanoparticles written by Simon Armando Mostafa Covone and published by . This book was released on 2010 with total page 92 pages. Available in PDF, EPUB and Kindle. Book excerpt: The use of heterogeneous catalysis is well established in chemical synthesis, energy, and environmental engineering applications. Supported Pt nanoparticles have been widely reported to act as catalysts in a vast number of chemical reactions. In this report, the performance of Pt/ZrO2 nanocatalyst for the decomposition of methanol, ethanol, 2-propanol, and 2-butanol is investigated. The potential of each alcohol for the production of H2 and other relevant products in the presence of a catalyst is studied. All the alcohols studied show some decomposition activity below 200°C which increased with increasing temperature. In all cases, high selectivity towards H2 formation is observed. With the exception of methanol, all alcohol conversion reactions lead to catalyst deactivation at high temperatures (T [greater than]250°C for 2-propanol and 2-butanol, T [greater than]325°C for ethanol) due to carbon poisoning. However, long-term catalyst deactivation can be avoided by optimizing reaction conditions such as operating temperature. In addition, the performance of Pt/[gamma]-Al2O3 is evaluated in the oxidation of 2-propanol. Pt nanoclusters of similar size (~1 nm diameter) but different structure (shape) were found to display distinctively different catalytic properties. All the systems studied achieve high conversion (~ 90%) below 100°C. However, flatter particles display a lower reaction onset temperature, demonstrating superior catalytic performance. Acetone, CO2, and water are generated as products indicating that both partial and complete oxidation are taking place. A number of techniques including AFM, XPS, TEM, HAADF-TEM, XAFS as well as packed-bed reactor experiments were used for sample characterization and evaluation of catalytic performance.
Author :
Publisher :
ISBN 13 :
Total Pages : 208 pages
Book Rating : 4.:/5 (684 download)
Download or read book Reaction Selectivity Studies on Nanolithographically-fabricated Platinum Model Catalyst Arrays written by and published by . This book was released on 2004 with total page 208 pages. Available in PDF, EPUB and Kindle. Book excerpt: In an effort to understand the molecular ingredients of catalytic activity and selectivity toward the end of tuning a catalyst for 100% selectivity, advanced nanolithography techniques were developed and utilized to fabricate well-ordered two-dimensional model catalyst arrays of metal nanostructures on an oxide support for the investigation of reaction selectivity. In-situ and ex-situ surface science techniques were coupled with catalytic reaction data to characterize the molecular structure of the catalyst systems and gain insight into hydrocarbon conversion in heterogeneous catalysis. Through systematic variation of catalyst parameters (size, spacing, structure, and oxide support) and catalytic reaction conditions (hydrocarbon chain length, temperature, pressures, and gas composition), the data presented in this dissertation demonstrate the ability to direct a reaction by rationally adjusting, through precise control, the design of the catalyst system. Electron beam lithography (EBL) was employed to create platinum nanoparticles on an alumina (Al2O3) support. The Pt nanoparticle spacing (100-150-nm interparticle distance) was varied in these samples, and they were characterized using x-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM), both before and after reactions. The TEM studies showed the 28-nm Pt nanoparticles with 100 and 150-nm interparticle spacing on alumina to be polycrystalline in nature, with crystalline sizes of 3-5 nm. The nanoparticle crystallites increased significantly after heat treatment. The nanoparticles were still mostly polycrystalline in nature, with 2-3 domains. The 28-nm Pt nanoparticles deposited on alumina were removed by the AFM tip in contact mode with a normal force of approximately 30 nN. After heat treatment at 500 C in vacuum for 3 hours, the AFM tip, even at 4000 nN, could not remove the platinum nanoparticles. The increase of adhesion upon heat treatment indicates stronger bonding between the Pt and the support at the metal-oxide interface.
Author : Yuen Wu
Publisher : Springer
ISBN 13 : 3662498472
Total Pages : 119 pages
Book Rating : 4.6/5 (624 download)
Download or read book Controlled Synthesis of Pt-Ni Bimetallic Catalysts and Study of Their Catalytic Properties written by Yuen Wu and published by Springer. This book was released on 2016-05-14 with total page 119 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis focuses on the controlled synthesis of Pt–Ni bimetallic nanoparticles and the study of their catalytic properties. It discusses in detail the nucleation mechanism and the growth process of bimetallic systems, which is vital for a deeper understanding of the design of bimetallic catalysts. The author presents four pioneering studies: (1) syntheses of water-soluble octahedral, truncated octahedral, and cubic Pt–Ni nanocrystals and the study of their structure-activity relationship in model hydrogenation reactions; (2) a strategy for designing a concave Pt–Ni alloy using controllable chemical etching; (3) defect-dominated shape recovery of nanocrystals, which is a new synthesis strategy for trimetallic catalysts; (4) a sophisticated construction of Au islands on Pt−Ni, which is an ideal trimetallic nanoframe catalyst. This thesis inspires researchers working in materials, catalysis as well as other interdisciplinary areas.
Author : Aaron Scott Eppler
Publisher :
ISBN 13 :
Total Pages : 242 pages
Book Rating : 4.:/5 (482 download)
Download or read book Platinum Nanoparticle Model Catalysts written by Aaron Scott Eppler and published by . This book was released on 1995 with total page 242 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : Konrad Koszinowski
Publisher :
ISBN 13 : 9783832504137
Total Pages : 0 pages
Book Rating : 4.5/5 (41 download)
Download or read book Gaseous Platinum Clusters written by Konrad Koszinowski and published by . This book was released on 2003 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Cationic platinum clusters are proposed as models for heterogeneous catalysts. In the gas phase, the intrinsic reactivities of the cluster ions can be thoroughly investigated by means of Fourier-transform ion-cyclotron-resonance mass spectrometry. The reactions probed in these experiments indeed closely resemble various industrially important processes and contribute to a better understanding of the metal's catalytic activity.
Download or read book Rhodium Catalysts in the Oxidation of CO by O2 and NO written by and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: It is well known that the activity, selectivity, and deactivation behavior of heterogeneous catalysts are strongly affected by a wide variety of parameters, including but not limited to nanoparticle size, shape, composition, support, pretreatment conditions, oxidation state, and electronic state. Enormous effort has been expended in an attempt to understand the role of these factors on catalytic behavior, but much still remains to be discovered. In this work, we have focused on deepening the present understanding of the role of nanoparticle shape, nanoparticle composition, and hot electrons on heterogeneous catalysis in the oxidation of carbon monoxide by molecular oxygen and nitric oxide. These reactions were chosen because they are important for environmental applications, such as in the catalytic converter, and because there is a wide range of experimental and theoretical insight from previous single crystal work as well as experimental data on nanoparticles obtained using new state-of-the-art techniques that aid greatly in the interpretation of results on complex nanoparticle systems. In particular, the studies presented in this work involve three types of samples: (almost equal to) 6.5 nm Rh nanoparticles of different shapes, (almost equal to) 15 nm Rh1-xPdx core-shell bimetallic polyhedra nanoparticles, and Rh ultra-thin film ((almost equal to) 5 nm) catalytic nanodiodes. The colloidal nanoparticle samples were synthesized using a co-reduction of metal salts in alcohol and supported on silicon wafers using the Langmuir-Blodgett technique. This synthetic strategy enables tremendous control of nanoparticle size, shape, and composition. Nanoparticle shape was controlled through the use of different organic polymer capping layers. Bimetallic core-shell nanoparticles were synthesized by careful choice of metal salt precursors. Rh/TiO(subscript x) and Rh/GaN catalytic nanodiodes were fabricated using a variety of thin film device fabrication techniques, including reactive DC magnetron sputtering, electron beam evaporation, and rapid thermal annealing. The combination of these techniques enabled control of catalytic nanodiode morphology, geometry, and electrical properties.
Author : Eric Courtland Taylor
Publisher :
ISBN 13 : 9781303173189
Total Pages : 92 pages
Book Rating : 4.1/5 (731 download)
Download or read book Synthesis of Platinum and Platinum-copper Branches Nanoparticles for Electrooxidation of Methanol written by Eric Courtland Taylor and published by . This book was released on 2013 with total page 92 pages. Available in PDF, EPUB and Kindle. Book excerpt: Platinum and Pt alloys are among the most important heterogeneous catalysts for many organic reactions and electrochemical reactions associated with the fuel cell technologies. How to reduce Pt usage while maintaining the performance of the catalysts becomes a subject for intensive research in materials chemistry. For heterogeneous catalysis, the catalytic reactivity and selectivity are strongly correlated with different crystallographic facets exposed on the surface. The facets with high-index planes whose Miller indices with at one is larger than unity are generally more active than those with low-index planes (e.g., {100}, {111}, and {110}). Tuning the morphology of the nanoparticles to expose more high-index planes on the surface can improve the catalytic activity of the nanoparticles. As compared to isotropic nanoparticles, the branched nanostructures are the promising morphology that can improve both the activity and stability of the catalysts. In this work, a two-step polyol synthesis has been developed to synthesize the branched nanostructures of Pt at high-yield. This two-step process involves a slow reduction using ethylene glycol in the presence of oxidative etchants, following by a fast reduction using ascorbic acid. The slow reduction kinetics facilitates the formation of cubooctahedral single-crystal seeds while the fast reduction kinetics allows for the overgrowth of nanocrystals along the {111} facets in a short period of time, resulting in the branched nanostructures. By co-reducing Pt and Cu precursors, this approach has been demonstrated to synthesize the Pt-Cu dendritic nanostructures for the first time. The catalytic activity of these Pt and Pt-Cu nanostructures has been studied for MOR. It was found that Pt branched nanostructures reduced the CO-poisoning as compared to the Pt/C and the dendritic Pt-Cu nanostructures showed both enhanced resistance of CO-poisoning and improved efficiency of ethanol oxidation.
Author : Mark E. Davis
Publisher :
ISBN 13 :
Total Pages : 432 pages
Book Rating : 4.:/5 (44 download)
Download or read book Selectivity in Catalysis written by Mark E. Davis and published by . This book was released on 1993 with total page 432 pages. Available in PDF, EPUB and Kindle. Book excerpt: Discusses recent research and provides tutorial chapters on enhancing selectivity in catalysis through stereoselectivity, reaction pathway control, shape selectivity, and alloys and clusters. Presents an interdisciplinary approach to increasing selectivity in homogeneous and heterogeneous catalysis research. Includes an overview chapter that discusses the current state of the field and offers a perspective on future directions.
