Download or read book The Structure and Activity of Supported Metal Catalysts I Crystallite Size and Specific Activity for Benzene Hydrogenation of Platinum silica Catalysts Reprinted from Journal of Catalysts Vol 5 No 1 February 1966 written by T. A. Dorling and published by . This book was released on 1966 with total page 5 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Structure and Activity of Supported Metal Catalysts II Crystallite Size and CO Chemisorption on Platinum silica Catalysts Reprinted from Journal of Catalysis Vol 7 No 4 April 1967 written by T. A. Dorling and published by . This book was released on 1967 with total page 8 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 Catalytic Hydrogenation Over Platinum Metals written by Paul Nels Rylander and published by . This book was released on 1967 with total page 576 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Supported Metal Catalysts written by J. Hartley and published by . This book was released on 1969 with total page 25 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Relative Activity of Impregnated and Mixed Molybdenum Catalysts for Coal Hydrogenation written by Martin D. Schlesinger and published by . This book was released on 1962 with total page 20 pages. Available in PDF, EPUB and Kindle. Book excerpt: Experimental data for coal hydrogenation are presented to show that when a vehicle oil produced from coal is present, coal is hydrogenated to the same conversion whether molybdenum catalyst is impregnated on the coal or intimately mixed with the slurry. Differences in product distribution could be related to the severity of operating conditions. No minimum mixing time was established, but 2 hours was sufficient. Longer periods of mixing, to 14.75 hours, had no effect on the results. The hydrogenation conditions were in the pressure range of 8,500 to 10,000 p.s.i. at 400° to 500° C. Most of the experiments were made in duplicate.
Download or read book Reaction Kinetics Over Supported Metal Catalysts written by William Francis Taylor and published by . This book was released on 1967 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Effect of Crystallite Size on the Activity and Selectivity of Silver Catalysts written by James Chien-hsing Wu and published by . This book was released on 1973 with total page 364 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Catalytic Hydrogenation written by L. Cervený and published by Elsevier. This book was released on 1986-08-01 with total page 705 pages. Available in PDF, EPUB and Kindle. Book excerpt: The collection of contributions in this volume presents the most up-to-date findings in catalytic hydrogenation. The individual chapters have been written by 36 top specialists each of whom has achieved a remarkable depth of coverage when dealing with his particular topic. In addition to detailed treatment of the most recent problems connected with catalytic hydrogenations, the book also contains a number of previously unpublished results obtained either by the authors themselves or within the organizations to which they are affiliated.Because of its topical and original character, the book provides a wealth of information which will be invaluable not only to researchers and technicians dealing with hydrogenation, but also to all those concerned with homogeneous and heterogeneous catalysis, organic technology, petrochemistry and chemical engineering.
Download or read book Structure reactivity Relationships Characterizing Hydrogen Transfer and Hydrogenation in Trisubstituted Tetrairidium Silica supported Cluster Catalysts Modified by Choice of Ligands written by Andrew Philip Palermo and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Catalysts are used in nearly ninety percent of large-scale chemical manufacturing process. Eighty percent of these catalysts are solids, almost all discovered empirically, one application at a time. The design of catalysts for whole classes of reactions through understanding of relationships between structure and catalyst performance is most readily realized when the catalysts are molecular. Such a catalyst was investigated in the work described in this dissertation, made by the stabilization of a tetrairidium dodecacarbonyl cluster with three bulky calixarene phosphine ligands: Ir4L3(CO)9, where L = tert-butyl-calix[4]arene(OPr)3(OCH2PPh2) (Ph = phenyl and Pr = propyl). The substitution of calixarenes on the Ir4 framework produced two distinct Ir sites: those on the basal plane of the tetrahedral metal frame, where three of the four Ir atoms are bonded to a calixarene phosphine ligand, and an apical Ir site. This cluster was supported on dehydroxylated silica and, after various modifications of the ligands, investigated as a catalyst for reactions involving hydrogen transfer. The Ir4L3(CO)9 cluster provided a well-defined structure allowing experiments with the goal of answering questions that have captivated researchers for 200 years. These questions include: 1) what is a physical model that would account for a modified Horiuti-Polanyi mechanism involving two distinct sites for ethylene hydrogenation (one where both olefin and hydrogen bond and react, and one where only hydrogen bonds); 2) how does oxygen influence hydrogen-transfer-related reactions; and 3) how does the cooperativity of organic and inorganic ligands distant from an active site, tune hydrogen transfer. The answers to these questions provide fundamental understanding of the hydrogen transfer in industrially relevant reactions: hydrodesulfurization, Fischer-Tropsch synthesis, olefin hydroformylation, naphtha reforming, hydroisomerization, and hydrocracking. The number of catalytically active iridium sites was controlled by selectively decarbonylating apical sites by removing carbonyl ligands from them by reaction with a mild oxidant, trimethylamine N-oxide (TMAO). The reaction with TMAO in an inert atmosphere resulted in the removal of 0.48 of the 6 terminal carbonyl ligands per cluster (quantified by the integration of carbonyl band areas from infrared (IR) spectra), engendering a supported cluster catalyst with an ethylene hydrogenation activity of 2.12 (mol of ethane formed)/(mol of Ir4 cluster ∙ h), measured in a flow reactor with 250 mg of catalyst (1 wt.% Ir) at 313 K and 1 bar. When the same decarbonylation was done in an atmosphere of ethylene under otherwise identical conditions, 1.1 of the 6 terminal carbonyl ligands per cluster were removed, and the hydrogenation activity approximately doubled. Further changes in the cluster leading to increased catalytic activity were achieved by substituting 2 bridging carbonyl ligands with 2 bridging peroxo ligands, which were characterized by IR, Raman, and X-ray absorption spectroscopies. The peroxo ligands reduced the activation energy for the catalytic ethylene hydrogenation reaction from 15.3 to 10.5 kcal/mol by opening up a new reaction mechanism that was determined by electronic structure calculations. This mechanism involves a hydride ligand bridging the basal plane of the tetrahedral iridium cluster and the active iridium atom, which is an apical site. This new mechanism did not occur when the number of peroxo ligands present on the cluster was 1 or 0. Additional modifications of the tetrairidium cluster’s ligand sphere were carried out by replacing the calixarene phosphine ligands with other, analogous ligands, both in the presence and absence of bridging peroxo ligands. These were: 5,11,17,23-tetra-tert-butyl-26,27,28-tripropoxy-calix[4]arene-25-X, where X = diphenylphosphinite, diphenylphosphonite, and diphenylphosphite. Upon reaction with TMAO in an atmosphere of ethylene, these variously ligated clusters supported on silica demonstrated an activity that was 3-fold greater than that of the cluster with three phosphine ligands; however, a lack of variance in ethylene hydrogenation activity was observed between the clusters containing a phosphinite, phosphonite, or phosphite ligand. By replacing TMAO treatment with a treatment with flowing dioxygen to synthesize catalytically active Ir4 clusters with 2 peroxo ligands (except for a triply bound phosphite Ir4 cluster), the activity ranged from 12.8 to 556 (mol of ethane formed)/(mol of Ir4 cluster ∙ h).
Download or read book The Structure and Activity of Supported Metal Catalysts written by and published by . This book was released on 1967 with total page 19 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Microcalorimetric Spectroscopic and Kinetic Studies of Supported Platinum Reforming Catalysts written by Sanjay Bhardwaj Sharma and published by . This book was released on 1993 with total page 438 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Structure of Metallic Catalysts written by John Russell Anderson and published by . This book was released on 1975 with total page 488 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Evaluation of Catalysts for Hydrogenating Shale Oil written by H. C. Carpenter and published by . This book was released on 1959 with total page 38 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Transition metal graphite catalysts for production of light hydrocarbons from synthesis gas written by Texas A & M University. Department of Chemistry and published by . This book was released on 1976 with total page 32 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Effect of Crystallite Size on Kinetics of Exchange of Neopentane and Benzene with Deuterium Over Supported Platinum Catalysts written by Gunseli Sagun and published by . This book was released on 1982 with total page 900 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Studies of Immobilized Homogeneous Metal Catalysts on Silica Supports written by Keith James Stanger and published by . This book was released on 2003 with total page 322 pages. Available in PDF, EPUB and Kindle. Book excerpt: Rhodium complexes of the chiral, chelating diphosphine (2S,4S)-4-(diphenylphosphino)-2-(diphenylphosphinomethyl)pyrrolidine tethered on silica were characterized by 31P NMR and IR. The tethered complex catalyzes the enantioselective hydrogenation of methyl-[alpha]-acetamidocinnamate (MAC). Spectral and catalytic investigations indicate that the tethered complex reacts by the same mechanism as the untethered complex in solution. The rhodium complexes, [Rh(COD)H]4, [Rh(COD)2]BF4−, [Rh(COD)Cl]2, and RhCl3·3H2O, adsorbed on SiO2 are optimally activated for toluene hydrogenation by pretreatment with H2 at 200°C. The same complexes on Pd-SiO2 are equally active without pretreatments. The active species in all cases is rhodium metal. The catalysts were characterized by XPS, TEM, DRIFTS, and mercury poisoning experiments. Rhodium on silica catalyzes the hydrogenation of fluorobenzene to produce predominately fluorocyclohexane in heptane and 1,2-dichloroethane (DCE) solvents. In heptane/methanol and heptane/water solvents, hydrodefluorination to benzene and subsequent hydrogenation to cyclohexane occurs exclusively. Benzene inhibits the hydrodefluorination of fluorobenzene. In DCE or heptane solvents, fluorocyclohexane reacts with hydrogen fluoride to form cyclohexene. Reaction conditions can be chosen to selectively yield fluorocyclohexane, cyclohexene, benzene, or cyclohexane. The oxorhenium(V) dithiolate catalyst [-S(CH2)3S-]Re(O)(Me)(PPh3) was modified by linking it to a tether that could be attached to a silica support. Spectroscopic investigation and catalytic oxidation reactivity showed the heterogenized catalyst's structure and reactivity to be similar to its homogeneous analog. However, the immobilized catalyst offered additional advantages of recycleability, extended stability, and increased resistance to deactivation.
