Download or read book Metal metal Oxide Interactions in a Supported Platinum Catalyst Containing Europium Oxide written by Beth Ann Milligan and published by . This book was released on 1987 with total page 270 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Strong Metal support Interactions in Supported Platinum and Palladium Catalysts written by Abdulaziz A. Al-Dosari and published by . This book was released on 1997 with total page 154 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Syntheses Structures and Support Interactions of Potential Metal Oxide Catalyst Precursors written by Margaret Hamm Venable and published by . This book was released on 1990 with total page 122 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Strong metal support interaction of Pt based electrocatalysts with transition metal oxides nitrides carbides for oxygen reduction reaction written by Min Chen and published by OAE Publishing Inc.. This book was released on 2023-06-06 with total page 31 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Tuning Metal support Interaction for Catalysis at Multi component Interfaces written by Shyam Deo and published by . This book was released on 2021 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The enhancement of catalytic activity is often attributed to special sites along a metal-oxide boundary, where an adsorbed species interacts with both the metal and the support. Indeed, such "dual" reaction sites often with emergent chemical properties have been implicated as the active sites for many chemical reactions, whether it be simpler molecular reactions such as CO oxidation and water-gas shift or far more complex reaction pathways such as de-oxygenation of multi-oxygenated reactants like furfuryl alcohol, m-cresol etc. Moreover, close connections of synthesis, characterization, kinetic testing, and computational modeling can enable researchers to tailor metal/metal-oxide catalytic systems towards such complex catalytic requirements. In this thesis, computational catalysis techniques are integrated with experimental efforts of collaborators to investigate two catalytic reactions: furfural hydrodeoxygenation (HDO) to methyl furan and CO oxidation. Experimental works motivate a series of research questions and hypotheses, towards connecting multi-component (oxide-metal) catalytic site properties to catalytic performance. In particular, Density Functional Theory (DFT) has been used in combination with experimental characterization and reactivity studies to underline the principles governing the potentials and design of multi-component catalytic systems. HDO of furfuryl alcohol was examined using a DFT model of a metal/TiO2 nanowire interface. Redox functionality of the metal oxide aids in breaking the C-O bond of the alcohol, while the metal facilitates C-H formation to the final product, 2-methylfuran. In addition to this "bifunctionality", electron transfer between the oxide and the metal alters reactivity, suggesting emergent chemical properties unique to the interface. Our DFT results were used to explain experimental observations of enhanced selectivity for TiO2-coated Pd nanoparticles. We have also successfully extended our TiO2/Pd interface model, altering the composition of this interface to develop a set of descriptors that predict optimal HDO activity at the metal oxide/metal interface. Low-temperature CO oxidation was examined over CeO2 supported single atoms, a probe for determining the synergetic roles of single metal atom catalysts (SACs) and redox active supports. The redox states involved in catalytic oxidation cycles on SACs are not well-determined and limit rational design of these catalytic systems. Experimental characterization observes only "resting states" of SACs, whereas DFT and microkinetic studies can be used to reconcile a full redox cycle. We addressed these challenges by developing a first principles microkinetic model and reconciling elementary step reaction kinetics with experimentally measured reaction orders and activation barriers. We calibrated the microkinetic model through Bayesian statistical inference approach to include the error in both DFT calculated energetics and experimental measurements in mechanism determination. This approach successfully elucidated reaction mechanisms and identified dominant reaction networks to directly match experimental reaction orders and barriers. Combining experiment and modeling, we demonstrated role of metal oxidation states with their reactivity for oxidation catalysis, indicating that the unique oxidation activity of these catalysts arises from the relatively close stability of the wide range of oxidation states achieved through synergistic interaction with metal oxides. In addition, to achieve proper active site environment over the oxide supports, a careful and controlled adsorption of ionic and/or hydrated metal precursors over the surface is essential during synthesis, therefore we also briefly examine synthesis rules for catalysts with precise control over size and uniformity in dispersion with specific potential to generate singly adsorbed metal catalysts over oxides. In short, these works combinedly demonstrate how metal/metal oxide catalytic systems can be used to improve heterogeneous catalytic activity and selectivity for important energy conversion processes, and further on, the broader perspective of active sites design along the metal and oxide boundaries for oxidation and reduction catalysis.

Download or read book Influence of Metal support Interactions on the Reduction of Nitric Oxide Over Rhodium Catalysts written by Nutan Kumari Pande and published by . This book was released on 1985 with total page 432 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Utilizing Metal oxide and Oxide oxide Interactions for Improved Automotive Emissions Control Catalysts Final Report written by and published by . This book was released on 2003 with total page 5 pages. Available in PDF, EPUB and Kindle. Book excerpt: The goal of this research program was to elucidate the structure-activity relationships associated with metal-metal oxide and metal oxide-metal oxide interfaces of relevance in automotive emissions control catalysts. Particular emphasis was placed on explaining the mechanism by which ceria (CeO2) acts as an oxygen storage medium, oxygen transport on the surface and in the bulk of ceria, and how the ceria-zirconia interaction affects oxygen storage capacity and reactivity. These properties were studied using x-ray surface scattering, pulsed neutron scattering, termperature programmed desorption, x-ray photoelectron spectroscopy, and high-resolution electron energy loss spectroscopy. The overall research program was composed of two primary thrust areas: (1) detailed studies of the lattice and defect structures of ceria and mixed ceria-zirconias, and (2) surface science studies of the reactivity of ceria single crystals and ceria thin films supported on zirconia. A brief overview of the significant contribution made in each of these areas is given.

Download or read book Metal Oxide Promotion of Cobalt Based Fischer Tropsch Synthesis Catalysts written by Gregory Robert Johnson and published by . This book was released on 2015 with total page 196 pages. Available in PDF, EPUB and Kindle. Book excerpt: Synthetic fuel production by means of Fischer-Tropsch synthesis (FTS) involves the catalytic hydrogenation of CO over Co-based catalysts. Often, these catalysts incorporate performance-enhancing additives known as promoters. Although not catalytically active for FTS by themselves, promoters can alter the structural and electronic properties of the active Co metal so as to improve catalyst activity, selectivity, or stability. Elements that form metal oxides have been studied for their ability to increase CO consumption rates and shift the product distribution toward higher molecular weight. Despite several decades of study of such elements, there remains limited understanding of the connections between these promotional effects and element properties. Accordingly, this dissertation focuses on clarifying the chemical basis for the effects of metal oxide promotion and making connections to periodic trends. To understand the importance of physical contact between the promoter and the Co, the influence of Co-Mn spatial association on the magnitude of Mn promotional effects was investigated. Elemental maps obtained by STEM-EDS revealed that different catalyst pretreatment methods could control how closely associated the promoter and Co were at the nanoscale. By relating these results to catalytic reaction data, it was determined that higher extents of contact between the two elements were correlated with higher selectivities toward C5+ hydrocarbons. This work was extended to the elements Ce, Gd, La, and Zr, which are among the most commonly studied metal oxide-forming promoters. The presence of the promoter element suppressed methane formation and increased the FTS chain propagation probability, but the sensitivity of these effects toward promoter loading was different for each element. Elements that deposited preferentially onto the Co nanoparticles led to rapid shifts in the product distribution as the promoter loading increased, whereas elements that dispersed over the entire catalyst surface resulted in more gradual changes. For all promoters, the product selectivities became insensitive to loading when the loading reached a quantity nearly equivalent to that which would form a half monolayer of the promoter on the Co nanoparticle surface. These trends are characteristic of the formation of active sites along the interface between the Co and the promoter that exhibit improved product selectivity. Structurally, the oxidation states and local coordination environments of the promoters were consistent with highly dispersed oxides. No evidence for the formation of bimetallic alloys or large promoter-containing crystallites was detected by either X-ray absorption spectroscopy or X-ray diffraction. These data suggest that small promoter oxide moieties decorate the surface of the Co metal nanoparticles so as to form metal-metal oxide interfaces. Under this model, the promotional effects increase in magnitude as the fraction of Co active sites that are adjacent to the promoter increases. When the Co surface is sufficiently covered by the promoter so that the fraction of active sites that are along the perimeter of the promoter moieties is nearly unity, the catalyst performance ceases to improve as a function of promoter loading. Guided by this reasoning, the catalytic properties of the promoted catalysts were investigated using samples in which the fraction of sites that were promoted was near unity. Measurements of reaction kinetics were conducted to assess the impact of metal oxide promotion on the rate parameters governing FTS. The rates of CO consumption for both unpromoted and metal oxide-promoted catalysts followed a Langmuir-Hinshelwood rate law for which H-assisted CO dissociation is assumed to be the rate determining step. Each promoter increased the apparent rate constant and the CO adsorption constant that appear within the rate law. Thus, metal oxide promotion appears both to facilitate the cleavage of the C-O bond and to enhance the extent of CO adsorption onto the catalyst. This finding was reinforced by CO temperature programmed desorption experiments and an evaluation of the effects of Mn promotion on the rate of CO disproportionation. Owing to the appearance of the CO adsorption constant in the numerator and denominator of the rate law, it is possible for promoted catalysts to have both higher and lower turnover frequencies than unpromoted catalysts depending on the chosen operating pressure. As a consequence, an optimal promoter can be found for maximizing the turnover frequency at a given operating pressure. However, product selectivity, which is largely determined by the availability of adsorbed H, is invariably improved by a higher CO adsorption constant because it decreases the ratio of adsorbed H to CO on the Co surface. Strong correlations between catalyst performance and the Lewis acidity of the promoter oxide suggest that Lewis acid-base interactions between the promoter and the adsorbed CO are the cause for the observed metal oxide promotional effects. Much of the experimental data presented in this work favors the hypothesis that CO can interact simultaneously with Co through the C atom and with the promoter cation through the O atom. These chemical interactions, in which the promoter serves as a Lewis acid, weaken the bond between C and O. Experimental evidence for this effect was observed in the lower activation barrier for CO hydrogenation over the ZrO2-promoted catalysts and the appearance of adsorbed carbonyl species on the MnO-promoted catalyst with severely redshifted C-O stretching frequencies measured by in situ infrared spectroscopy. These results provide insight into the chemical mechanism by which metal oxides affect the reaction and identify Lewis acidity of the promoter as the relevant descriptor for quantitatively predicting metal oxide-based promotional effects over Co FTS catalysts.

Download or read book Metal support Interactions in Zeolite Supported Platinum Catalysts written by Paul Vincent Menacherry and published by . This book was released on 1997 with total page 426 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Heterogeneous Catalysis of Mixed Oxides written by Makoto Misono and published by Elsevier Inc. Chapters. This book was released on 2013-02-28 with total page 42 pages. Available in PDF, EPUB and Kindle. Book excerpt: Several substantial examples of mixed oxide supports that show unique and interesting roles as catalyst supports are described. The examples are perovskites and heteropoly compounds as supports for finely dispersed metals, ceria–zirconia related mixed oxides as supports for noble metals in automobile catalysts, and zeolites for atomically dispersed noble metals. In addition, the general roles of catalyst supports are briefly summarized. Among the different roles of supports, the most important are dispersing the catalytically active components and increasing their surface area, and improving the catalytic performance through chemical interactions between the active component and the support.

Download or read book Metal support Interactions in Hydrogenation and Oligomerization of Acetone Over Oxide supported Copper Catalysts written by James Neal Hickey and published by . This book was released on 1992 with total page 134 pages. Available in PDF, EPUB and Kindle. Book excerpt:

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 Fundamental Studies of the Reforming of Oxygenated Compounds Over Supported Metal Catalysts written by and published by . This book was released on 2016 with total page 28 pages. Available in PDF, EPUB and Kindle. Book excerpt: The main objective of our research has been to elucidate fundamental concepts associated with controlling the activity, selectivity, and stability of bifunctional, metal-based heterogeneous catalysts for tandem reactions, such as liquid-phase conversion of oxygenated hydrocarbons derived from biomass. We have shown that bimetallic catalysts that combine a highly-reducible metal (e.g., platinum) with an oxygen-containing metal promoter (e.g., molybdenum) are promising materials for conversion of oxygenated hydrocarbons because of their high activity for selective cleavage for carbon-oxygen bonds. We have developed methods to stabilize metal nanoparticles against leaching and sintering under liquid-phase reaction conditions by using atomic layer deposition (ALD) to apply oxide overcoat layers. We have used controlled surface reactions to produce bimetallic catalysts with controlled particle size and controlled composition, with an important application being the selective conversion of biomass-derived molecules. The synthesis of catalysts by traditional methods may produce a wide distribution of metal particle sizes and compositions; and thus, results from spectroscopic and reactions kinetics measurements have contributions from a distribution of active sites, making it difficult to assess how the size and composition of the metal particles affect the nature of the surface, the active sites, and the catalytic behavior. Thus, we have developed methods to synthesize bimetallic nanoparticles with controlled particle size and controlled composition to achieve an effective link between characterization and reactivity, and between theory and experiment. We have also used ALD to modify supported metal catalysts by addition of promoters with atomic-level precision, to produce new bifunctional sites for selective catalytic transformations. We have used a variety of techniques to characterize the metal nanoparticles in our catalysts, including scanning transmission electron microcopy (STEM) to measure size and structure, energy dispersive X-ray spectroscopy (EDS) to measure atomic composition, X-ray absorption spectroscopy (XAS) to measure oxidation state and metal coordination, Fourier transform infrared spectroscopy (FTIR) to study adsorbed species, laser Raman spectroscopy to probe metal oxide promoters, and temperature programmed reaction/desorption to study the energetics of adsorption and desorption processes. We have studied our bimetallic catalysts for the selective cleavage of carbon-oxygen bonds, and we have studied the effects of adding metal oxide promoters to supported platinum and gold catalysts for water-gas shift (i.e., the production of hydrogen by reaction of carbon monoxide with water). We anticipate that the knowledge obtained from our studies will allow us to identify promising directions for new catalysts that show high activity, selectivity, and stability for important reactions, such as the conversion of biomass-derived oxygenated hydrocarbons to fuels and chemicals.

Download or read book Electrocatalyst support Interactions written by and published by . This book was released on 1978 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The maximum utilization of noble metals as heterogeneous catalysts is achieved by dispersing the noble metals as small particles supported on a porous, high surface area powder. In some studies with supported noble metal catalysts, it has been reported that the metal particle interacts with the support material and that the interaction affects the catalytic properties of the metal. Experimental studies on metal-support interactions that are pertinent to electrocatalysis will be discussed. Platinum supported on carbon black is one of the most active electrocatalysts for oxygen reduction in phosphoric acid fuel cells. In the acid environment at 100 to 200/sup 0/C, the Pt surface area decreases with time due to the growth of the supported Pt particles. The effects of a liquid-phase environment on the particle growth mechanism of supported Pt catalysts is discussed. 60 references.

Download or read book Spectroscopic Characterization of Supported Metal Oxide Catalysts written by Michael Andrew Vuurman and published by . This book was released on 1992 with total page 167 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Preparation and Characterization of Vanadium Oxide aluminum Antimonate and Supported Antimony Oxide Catalysts written by Thomas John Curtis and published by . This book was released on 1993 with total page 218 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Structure and Reactivity in Catalytic Systems Involving Metal Oxides and Electrode Surfaces written by John M. White and published by . This book was released on 1986 with total page 3 pages. Available in PDF, EPUB and Kindle. Book excerpt: Secondary ion mass spectrometry as a kinetic tool was developed was used to characterize a number of interesting metal-metal oxides and metal-adsorbate systems. The most significant of these include the behavior of rhodium and platinum on titanium dioxide thin films. We showed conclusively that the rhodium and platinum on titanium dioxide thin films. We showed conclusively that the rhodium and platinum overlayers become encapsulated with TiO when these metals on metal oxides are heated. This is the most direct evidence of longstanding interest in strong metal support interactions for the mechanism by which the interaction occurs. We have also characterized carefully the role of small amounts of impurities in noble metals and their influence on catalysis . These levels are established by secondary ion mass spectroscopy and lie below the detectability limits of Auger electron spectroscopy. Finally, we have established the kinetics of surface decomposition of species like methoxide on platinum using SIMS to monitor the decomposition channels directly.