Download or read book Characterization of Alumina and Titania supported Iridium Catalysts Using Temperature programmed Reduction CO Chemisorption and Propane Hydrogenolysis Reaction written by Olt Emil Geiculescu and published by . This book was released on 1996 with total page 950 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Masters Theses in the Pure and Applied Sciences Accepted by Colleges and Universities of the United States and Canada written by and published by . This book was released on 1996 with total page 442 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Reactivity and Characterization of Supported Noble Metal Catalysts written by Keishla R. Rivera-Dones and published by . This book was released on 2020 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Catalytically driven processes account for over ninety percent of industrial chemical manufacturing today. Developments in manufacturing processes are largely driven by continued improvements in catalytic materials, which aim to increase production volumes while minimizing costs along with safety and environmental hazards. In order to achieve these goals, however, a rational approach in catalyst design must be pursued that aims to understand and build upon the fundamental structural, electronic, and chemical properties governing catalytic performance. To that purpose, the work presented in this dissertation makes use of kinetic experiments, theoretical models, and advanced characterization techniques to generate a fundamental understanding of noble metal surfaces employed in a variety of catalytic reaction systems. In Chapter 2, we discuss the use of N2 physisorption, CO chemisorption, and NH3 temperature programed desorption to evaluate the effect of support acidity on the reactivity profiles of various zeolite-supported Pt and Pt-Sn catalysts for the non-oxidative coupling of methane to ethylene and aromatics. Reactivity studies for Pt-Sn/H-ZSM-5 catalysts at 973 K showed that, while all catalysts produced ethylene as the primary product, increasing support acidity led to an increase in naphthalene selectivity at the expense of benzene selectivity. Volcano-shaped profiles observed for the generation of aromatic products suggest that the formation of a reactive hydrocarbon pool on acidic support surfaces could be responsible for the oligomerization of ethylene. Notably, the Pt-Sn/H-ZSM-5 (SiO2:Al2O3 = 50) catalyst was found to be comparable to the state-of-the-art Mo/H-ZSM-5 catalysts in terms of carbon product generation and resistance to coke formation. In Chapter 3, x-ray absorption spectroscopy (XAS) was used to highlight the effect of local electronic and structural environments in specially synthesized metallic catalysts. The local coordination and nearest-neighbor distance of Pd species were evaluated to understand metal dispersion and the effect of catalyst support on the extent of bimetallic particle formation in Pd, AgPd, CuPd, and AuPd catalysts synthesized by controlled surface reactions (CSR) for a variety of amination, hydrodechlorination, and hydrogenation reactions. Near-edge structure analyses were also used on these Pd catalysts, as well as on a set of Mo-containing multi-metallic catalysts prepared by atomic layer deposition (ALD) for synthesis gas conversion, to understand catalyst reducibility along with potential support and hydrogen spillover effects on the extent of metal reduction. Chapter 4 evaluates the effects of catalyst support and pretreatment conditions on the hydrogenation of acetone over SiO2-, Al2O3-, and ZSM-5-supported platinum catalysts. Pt/ZSM-5 catalysts were found to have specific conversion rates and turnover frequencies that were 2 - 3 orders of magnitude higher than those observed over Pt/SiO2 and Pt/Al2O3 catalysts, regardless of zeolite acidity or pretreatment conditions. For Pt/ZSM-5 catalysts, the higher activity was achieved by increasing calcination and decreasing reduction temperatures, likely due to the effects of these treatments on the morphology of the platinum particles. CO-FTIR measurements showed a shift to higher frequencies of the Pt-CO band in Pt/ZSM-5 catalysts compared to Pt/SiO2, which alluded to the interactions between Pt and the porous zeolite structure as a source of the activity enhancements observed. Chapter 5 introduces the use of transient kinetics studies and theoretical modeling to explore the importance of surface coverage effects in the hydrogenation of acetone over platinum. Transient models based on steady-state microkinetics using static and dynamic inclusion of surface coverage via the Langmuir and Bragg-Williams approximations, respectively, predicted notable differences in the decay profiles of the most abundant reactive intermediate (MARI) from the catalytic surface. Experimental studies using steady-state isotopic transient kinetic analysis (SSITKA) methods served to validate the theoretical predictions for transients induced by complete acetone removal from or its substitution in the reactant feed and provided tangible evidence for the importance of surface coverage effects in understanding the reactivity of platinum catalysts for acetone hydrogenation. Lastly, Chapter 6 addresses possible future research directions in the field of transient kinetics studies.

Download or read book Physical and Chemical Characterization of Iron titania Model Supported Catalysts written by Bruce John Tatarchuk and published by . This book was released on 1981 with total page 336 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Effect of Alumina Support Modification on Performance of Cobalt and Iron Catalysts in Fischer tropsch Reaction written by and published by . This book was released on 2006 with total page 252 pages. Available in PDF, EPUB and Kindle. Book excerpt: Effect of alumina support modification for applications as cobalt and iron catalyst supports in Fischer-Tropsch reaction were studied. Alumina supports consisting of various gamma to chi ratios were prepared using solvothermal method and employed as supports for cobalt catalysts. In order to identify the characteristics, all the catalysts were characterized using surface area analysis, X-ray diffraction (XRD), Scanning electron microscopy2Energy dispersive X-ray (SEM/EDX), Transmission electron microscopy (TEM), Fourier transform Infrared Spectroscopy (FT-IR), Temperature programmed reduction (TPR), and hydrogen and carbon monoxide chemisorption. CO hydrogenation (H 2CO = 10/1) was also performed to determine the overall activity and selectivity of the Co/AL O catalysts containing various gamma to chi ratios. It was found that both activity and selectivity were increased with increasing the chi to gamma ratios of the alumina supports. It is suggested that the spherical;-shape like morphology of the -phase AL O provide better stability and dispersion of the Co particles. In addition, the effect of Cu-modification of alumina support for applications as iron catalyst supports in Fischer-Tropsch reaction (H 2CO - 2/1) was also investigated. It was found that the use of copper-modified alumina supports enhanced both reducibilities and the overall activities of Fe/AL O catalysts. However, Cu-modification of alumina support appeared to have no effect on selectivity of the F-T products.

Download or read book Characterization of the Structure Bonding Uniformity and Catalytic Properties of Supported Molecular Iridium Catalysts written by Adam Scott Hoffman and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Supported metal catalysts are widely applied in technology, and a class of such catalysts, supported single-site metal catalysts, is drawing increasing attention because of prospects for increased application and the opportunities for fundamental understanding afforded by such catalysts made to have nearly uniform structures. Elucidation of structure-catalytic activity relationships of supported metals is complicated by the heterogeneity of the metal bonding sites on almost all support surfaces, especially those that are amorphous or incorporate multiple phases. The research summarized in this dissertation was carried out with the goal of fundamental understanding of the structures, reactivities, and catalytic properties of supported single-site catalysts with relatively well-defined structures. The catalyst samples consisted of Ir(C2H4) 2 or Ir(CO)2 supported on MgO or HY zeolite. The catalysts were synthesized by chemisorbing Ir(C2H4)2(acac) or Ir(CO)2(acac) (acac is acetylacetonate) on the above-mentioned supports that had been treated at elevated temperatures to remove water, or, in the case of MgO, to generate unique surface sites for bonding of the metal. The samples were characterized by infrared spectroscopy, X-ray absorption spectroscopy (including X-ray absorption near edge structure and extended X-ray absorption fine structure (EXAFS) analysis), scanning transmission electron microscopy, X-ray diffraction, N2 adsorption, and thermogravimetric analysis. The samples were tested as catalysts for the ethylene hydrogenation reaction. The research yielded four main results. First, a spectroscopic cell was developed for characterization of supported ultra-low loading metal catalyst, second, infrared spectroscopy characterizing metal carbonyls elucidated the uniformity of the metal-support interaction, third, high-energy-resolution X-ray absorption spectroscopy was used to identify ligands not detectable with infrared, and finally a limiting case of the metal-support interaction is identified and characterized. A specific goal was to generate unique surface sites on MgO as a support for samples with iridium loadings as low as 0.01 wt%, to determine sites for preferential bonding of iridium to the support. For characterization of samples with low iridium loadings using X-ray absorption spectroscopy, a novel experimental X-ray absorption spectroscopy cell was designed and fabricated; it allows for investigation of samples in transmission or fluorescence detection modes at temperatures up to 300°C under flow or vacuum conditions. Infrared characterization of the [nu][subscript CO] bands of supported Ir(CO)2 showed that narrower full bands corresponded to higher degrees of uniformity of the supported metal species, with the most uniform being those on zeolites, as a consequence of high degree of crystallinity and uniformity of bonding sites. The results also include new synthesis techniques, such as those involving low synthesis temperatures, high Si:Al ration in the zeolites, and high degrees of support crystallinity resulting from treatments that lead to high degrees of bonding site uniformity. High-energy-resolution fluorescence detection X-ray absorption spectroscopy was used to detect the dynamic exchange of C2H4 and CO ligands on the single-site Ir under conditions for which the sensitivity of conventional infrared spectroscopy was insufficient. The improved resolution in the XANES region also identified specific, assignable, features to C2H4 and CO ligands making it a valuable technique for catalyst characterization. EXAFS analysis of samples consisting of Ir(C2H4)2 supported on MgO demonstrated a change in coordination with decreasing loading and a limiting case of tripodal iridium on the MgO surface. The tripodal species have low initial activity for ethylene hydrogenation relative to the corresponding bipodal species, but they are characterized by greater thermal stability and can be used stably as catalysts at temperatures as high as at least to 300°C in reductive atmospheres. The results show that various surface sites can be involved in the bonding metals to MgO and that these sites exhibit distinct properties.

Download or read book Iridium Catalysis written by Pher G. Andersson and published by Springer Science & Business Media. This book was released on 2011-01-05 with total page 244 pages. Available in PDF, EPUB and Kindle. Book excerpt: From the contents: Robert H Crabtree: Introduction and History. - Montserrat Diéguez, Oscar Pàmies and Carmen Claver: Iridium-catalysed hydrogenation using phosphorous ligands. - David H. Woodmansee and Andreas Pfaltz: Iridium Catalyzed Asymmetric Hydrogenation of Olefins with Chiral N,P and C,N Ligands. - Ourida Saidi and Jonathan M J Williams: Iridium-catalyzed Hydrogen Transfer Reactions. - John F. Bower and Michael J. Krische: Formation of C-C Bonds via Iridium Catalyzed Hydrogenation and Transfer Hydrogenation. - Jongwook Choi, Alan S. Goldman: Ir-Catalyzed Functionalization of CH Bonds. - Mark P. Pouy and John F. Hartwig: Iridium-Catalyzed Allylic Substitution. - Daniel Carmona and Luis A. Oro: Iridium-catalyzed 1.3-dipolar cycloadditions.

Download or read book Design Synthesis and Mechanistic Evaluation of Iron Based Catalysis for Synthesis Gas Conversion to Fuels and Chemicals written by and published by . This book was released on 2007 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This project extends previously discovered Fe-based catalysts to hydrogen-poor synthesis gas streams derived from coal and biomass sources. These catalysts have shown unprecedented Fischer-Tropsch synthesis rates and selectivities for synthesis gas derived from methane. During the first reporting period, we certified a microreactor, installed required analytical equipment, and reproduced synthetic protocols and catalytic results previously reported. During the second reporting period, we prepared several Fe-based compositions for Fischer-Tropsch Synthesis and tested the effects of product recycle under both subcritical and supercritical conditions. During the third and fourth reporting periods, we improved the catalysts preparation method, which led to Fe-based materials with the highest FTS reaction rates and selectivities so far reported, a finding that allowed their operation at lower temperatures and pressures with high selectivity to desired products (C{sub 5+}, olefins). During the fifth and sixth reporting period, we studied the effects of different promoters on catalytic performance, specifically how their sequence of addition dramatically influenced the performance of these materials in the Fischer-Tropsch synthesis. We also continued our studies of the kinetic behavior of these materials during the sixth reporting period. Specifically, the effects of H2, CO, and CO2 on the rates and selectivities of Fischer-Tropsch Synthesis reactions led us to propose a new sequence of elementary steps on Fe and Co Fischer-Tropsch catalysts. Finally, we also started a study of the use of colloidal precipitation methods for the synthesis small Co clusters using recently developed methods to explore possible further improvements in FTS rates and selectivities. We found that colloidal synthesis makes possible the preparation of small cobalt particles, although large amount of cobalt silicate species, which are difficult to reduce, were formed. During this seventh reporting period, we have explored several methods to modify the silanol groups on SiO2 by using either a homogeneous deposition-precipitation method or surface titration of Si-OH on SiO2 with zirconium (IV) ethoxide to prevent the formation of unreducible and unreactive CoO(subscript x) species during synthesis and FTS catalysis. We have synthesized monometallic Co/ZrO2/SiO2 catalysts with different Co loadings (11-20 wt%) by incipient wetness impregnation methods and characterized the prepared Co supported catalysts by H2 temperature-programmed reduction (H2-TPR) and H2-chemisorption. We have measured the catalytic performance in FTS reactions and shown that although the hydroxyl groups on the SiO2 surface are difficult to be fully titrated by ZrO2, modification of ZrO2 on SiO2 surface can improve the Co clusters dispersion and lead to a larger number of exposed Co surface atoms after reduction and during FTS reactions. During this seventh reporting period, we have also advanced our development of the reaction mechanism proposed in the previous reporting period. Specifically, we have shown that our novel proposal for the pathways involved in CO activation on Fe and Co catalysts is consistent with state-of-the-art theoretical calculations carried out in collaboration with Prof. Manos Mavrikakis (University of Wisconsin-Madison). Finally, we have also worked on the preparation of several manuscripts describing our findings about the preparation, activation and mechanism of the FTS with Fe-based catalysts and we have started redacting the final report for this project.

Download or read book Structurally Well defined Supported Iridium Cluster Catalysts written by Ailian Zhao and published by . This book was released on 1996 with total page 436 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Study of Metal Catalysts by Temperature Programmed Desorption 1 Chemisorption of Ethylene on Silica supported Platinum written by R. Komers and published by . This book was released on 1969 with total page 8 pages. Available in PDF, EPUB and Kindle. Book excerpt: An attempt was made to extend the temperature programmed desorption (TPD) technique to the study of metal catalysts by investigating the chemisorption and surface reactions of ethylene on silica-supported platinum. Self-hydrogenation was observed at room temperature as an important part of the process. In addition, a large fraction of ethylene remained irreversibly adsorbed, undergoing farther self-hydrogenation at about 100C and decomposition to methane at around 220C as the temperature was raised during the subsequent TPD. A second decomposition, observed at temperatures higher than 500C, is probably due to the formation of methane from the fragmental surface residue left after the first (lower temperature) decomposition. The temperature programmed desorption technique was applied in this instance not only to the simple desorption processes but also to the surface reactions which give desorbed material different from the initially chemisorbed species. (Author).

Download or read book Exchange and Hydrogenolysis Reactions of Hydrocarbons on Rhodium titania and Platinum iridium alumina Catalysts written by Arnaldo da Costa.Jr Faro and published by . This book was released on 1984 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book The Preparation and Characterization of Highly Dispersed Supported Bimetallic Catalysts from Inorganic and Organometallic Molecular Precursors written by Bert Donald Chandler and published by . This book was released on 1999 with total page 576 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Synthesis and Characterization of Pt and Pd Overlayer Catalysts for Aqueous Phase Reforming of Lactose and Hydrodeoygenation of Guaiacol and Anisole written by Qinghua Lai and published by . This book was released on 2016 with total page 157 pages. Available in PDF, EPUB and Kindle. Book excerpt: Supported bimetallic overlayer catalysts, Ni@Pt, Co@Pt, Ni@Pd, and Mo@Pt have been prepared by the directed deposition synthesis technique. The single crystal and computational studies have predicted that formation of Pd or Pt overlayer on Ni, Co or Mo base metal would cause a negative shift of d-band center of surface Pd or Pt, resulting in reduced binding strength for adsorbed species. The hydrogen chemisorption, ethylene hydrogenation descriptor reaction, XRD, H2-TPR, XAS and TEM studies were employed to characterize the catalysts. The alumina supported Ni@Pt and Co@Pt overlayer catalysts have been studied for aqueous phase reforming (APR) of lactose. Silica alumina supported Ni@Pt, Ni@Pd, and Mo@Pt catalysts have been investigated for hydrodeoxygenation (HDO) of lignin derived bio-oils. The H2 chemisorption and ethylene hydrogenation descriptor showed that alumina supported Ni@Pt and Co@Pt overlayer catalysts had reduced adsorption strength compared to a Pt only catalyst, which agrees with the computational prediction. XAS results showed that overlayer catalysts exhibited higher white line intensity than Pt catalyst, indicating a negative d-band shift for the Pt overlayer. Lactose APR studies showed that lactose could be used as feedstock to produce H2 and CO under desirable reaction condition. The Pt active sites of alumina supported Ni@Pt and Co@Pt overlayer catalysts showed significantly enhanced H2 production selectivity and activity when compared with that of a Pt only catalyst. The single deposition overlayer with the largest d-band shift showed the highest H2 activity. Silica alumina supported Ni@Pd, Ni@Pt, and Mo@Pt overlayer catalysts also showed the reduced adsorption strength compared to the Pd or Pt only catalyst. The TEM images of Ni@Pd overlayer catalyst provided evidence for a core/shell type structure. The H2-TPR results demonstrated the close interaction between Pt and Mo species for Mo@Pt overlayer catalysts. Guaiacol and anisole hydrodeoxygenation results showed that Pd and Pt active sites of overlayer catalysts showed significantly enhanced deoxygenation activity compared with that of Pd or Pt only catalyst. Further studies showed that guaiacol and anisole could be completely deoxygenated over the silica alumina supported metal catalysts at high W/F, yielding benzene, toluene, and xylenes as major products.

Download or read book Exchange and Hydrogenolysis Reactions of Hydrocarbons on Rhodium Titania and Platinum Iridium Alumina Catalysts written by A. C. Faro and published by . This book was released on 1984 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Surface Organometallic Chemistry Molecular Approaches to Surface Catalysis written by Jean-Marie Basset and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 340 pages. Available in PDF, EPUB and Kindle. Book excerpt: Surface organometallic chemistry is a new field bringing together researchers from organometallic, inorganic, and surface chemistry and catalysis. Topics ranging from reaction mechanisms to catalyst preparation are considered from a molecular basis, according to which the "active site" on a catalyst surface has a supra-molecular character. This. the first book on the subject, is the outcome of a NATO Workshop held in Le Rouret. France, in May. 1986. It is our hope that the following chapters and the concluding summary of recommendations for research may help to provide a definition of surface organometallic chemistry. Besides catalysis. the central theme of the Workshop, four main topics are considered: 1) Reactions of organometallics with surfaces of metal oxides, metals. and zeolites; 2) Molecular models of surfaces, metal oxides, and metals; 3) Molecular approaches to the mechanisms of surface reactions; 4) Synthesis and modification of zeolites and related microporous solids. Most surface organometallic chemistry has been carried out on amorphous high-surf ace-area metal oxides such as silica. alumina. magnesia, and titania. The first chapter. contributed by KNOZINGER. gives a short summary of the structure and reactivity of metal oxide surfaces. Most of our understanding of these surfaces is based on acid base and redox chemistry; this chemistry has developed from X-ray and spectroscopic data, and much has been inferred from the structures and reactivities of adsorbed organic probe molecules. There are major opportunities for extending this understanding by use of well-defined (single crystal) oxide surfaces and organometallic probe molecules.

Download or read book Characterization of Platinum molybdenum Catalysts Supported on Alumina and Titania written by Jae-Soon Shin and published by . This book was released on 1991 with total page 428 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Catalyst Characterization Using Thermal Conductivity Detector written by The Open The Open Courses Library and published by . This book was released on 2019-12-04 with total page 25 pages. Available in PDF, EPUB and Kindle. Book excerpt: Catalyst Characterization Using Thermal Conductivity Detector Physical Methods in Chemistry and Nano Science A thermal conductivity detector has four filaments that change resistance according to the thermal conductivity of the gas flowing over it. Two filaments meassure the reference gas and the other two measures the sample gas. The detector is isothermal; it will increase or decrease the voltage in each of the resistors in order to maintain a constant temperature. The temperature of the detector is 125 °C. When both the reference and samples gas have the same composition and same flow rate, the resistors are balanced and the detector will zero the signal. If there is a change in flow rate or in the gas composition the detector will react to maintain the constant temperature. The detector circuitry can be described using a Wheatstone bridge configuration. Chapter Outline: Principles of thermal conductivity Thermal conductivity detector Temperature programmed reduction (TPR) Pulse chemisorption Data collection for hydrogen pulse chemisorption Pulse chemisorption data analysis The Open Courses Library introduces you to the best Open Source Courses.