Monodisperse Platinum and Rhodium Nanoparticles as Model Heterogeneous Catalysts PDF Download
Are you looking for read ebook online? Search for your book and save it on your Kindle device, PC, phones or tablets. Download Monodisperse Platinum and Rhodium Nanoparticles as Model Heterogeneous Catalysts PDF full book. Access full book title Monodisperse Platinum and Rhodium Nanoparticles as Model Heterogeneous Catalysts by Michael Edward Grass. Download full books in PDF and EPUB format.
Author: Michael Edward Grass
Publisher:
ISBN:
Category :
Languages : en
Pages : 416
Get Book Here
Book Description
Author: Michael Edward Grass
Publisher:
ISBN:
Category :
Languages : en
Pages : 416
Get Book Here
Book Description
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 203
Get Book Here
Book Description
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.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
Get Book Here
Book Description
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:
Category :
Languages : en
Pages :
Get Book Here
Book Description
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:
Category :
Languages : en
Pages :
Get Book Here
Book Description
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
Get Book Here
Book Description
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:
Category : Environmental management
Languages : en
Pages : 112
Get Book Here
Book Description
Author: Robert Martin Rioux
Publisher:
ISBN: 9780542826405
Category :
Languages : en
Pages : 760
Get Book Here
Book Description
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.)
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
Get Book Here
Book Description
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:
Category : Alcohols
Languages : en
Pages : 92
Get Book Here
Book Description
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.
