Download or read book Understanding Catalytic Activity Trends for NO Decomposition and CO Oxidation Using Density Functional Theory and Microkinetic Modeling written by Hanne Falsig and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Catalytic Activity Trends of CO Oxidation written by Tao Jiang and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book The Microkinetics of Heterogeneous Catalysis written by J. A. Dumesic and published by Wiley-VCH. This book was released on 1993-04-20 with total page 340 pages. Available in PDF, EPUB and Kindle. Book excerpt: Defines the emerging field of catalytic reaction synthesis in the search for new catalysts and catalytic processes. Illustrates how experimental data from diverse sources can be consolidated to form a quantitative description of the essential chemistry taking place on the catalyst surface. Elucidates the possible relationships between catalyst kinetic properties and surface chemical bonding properties. Offers examples of microkinetic analysis and catalytic reaction synthesis for a variety of catalytic reactions over metals, oxides, and zeolite catalysts. Illustrates the underlying strategy used to formulate a microkinetic model, calibrate the model to the existing experimental data, and assess the critical aspects of the essential surface chemistry involved in the catalytic process.

Download or read book Fundamental Mechanistic Studies of Formic Acid Decomposition on Transition Metals written by Sha Li and published by . This book was released on 2018 with total page 191 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book New Theoretical Insights for Oxygen Electrocatalysis written by Sara Rois Kelly and published by . This book was released on 2021 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Oxygen electrocatalysis, defined here as the study of electrocatalytic reactions consisting of O2, H2O, H2O2, has applications in a wide variety of industries from clean transportation to water purification. By utilizing electrochemical synthesis via either the 2-electron water oxidation reaction (2e-WOR) or the 2-electron oxygen reduction reaction (2e-ORR), we can produce hydrogen peroxide remotely for use as a water disinfectant in places with limited access to clean drinking water. By reducing oxygen to water in fuel cells, we can produce electricity to propel vehicles and power cities. In this work, we use a combination of density functional theory (DFT), microkinetic modelling, and ab initio molecular dynamics (AIMD), to develop new understanding of catalysts for these reactions.Specifically, we show that binding energies can help us understand and predict catalysts for the2e-WOR and 2e- and 4e-ORR, as well as predict more general electrochemical behavior of transition metal surfaces. First we use limiting potential analysis to predict ZnO as an active and selective catalyst for the 2e-WOR. We demonstrate that ZnO is not only the most active catalyst for this reaction known to date, but is also remarkably stable in reaction conditions. This result demonstrates the power of simple tools like limiting potential analysis in predicting catalysts for electrochemical reactions. Next, we demonstrate some of the limitations of limiting potential analysis in the ORR in two specific scenarios. First, we show that on transition metals, incorporating electric field ejects into microkinetic modeling allows us to accurately predict varying pH dependencies on several model catalysts. We use this newly developed model to create activity volcanoes which help us understand how and why electric field affects different catalysts in different ways in both the 2e- and 4e-ORR. We extend this understanding to transition metal oxides, where the intercept of the O-OH scaling relation is much higher than in metals. We show that by applying a similar microkinetic model to these new scaling relations, we can explain the relative inactivity of oxides in the 4e-ORR. Finally, we demonstrate that using similar principles as used in oxygen electrocatalysis, we can predict trends in work function reduction, and consequently, potential of zero charge (PZC), across transition metal surfaces. We connect work function reduction directly to water coverage using AIMD, and show that even simple vacuum binding energy calculations have predictive power for PZC. Throughout this thesis we attempt to show that by using simple descriptors to explain binding energies, reaction rates, and other electrochemical properties, we are not only able to predict new catalysts, but also better understand the physical phenomena which govern the way existing catalysts behave.

Download or read book A Mechanistic Study of Redox Pathway in Iron ZSM 5 written by and published by . This book was released on 2006 with total page 137 pages. Available in PDF, EPUB and Kindle. Book excerpt: Experiments and computational chemistry have been used to explore the identity of the active Fe/ZSM-5 surface oxygen which participates in redox reactions and the possible kinetics pathways involving it. The experiments entail monitoring the mass of the catalyst during reactions using a Tapered Element Oscillating Microbalance (TEOM), measuring kinetics in a tubular reactor as well as in the TEOM, and characterizing the catalysts using Fourier Transform Infrared (FTIR) spectroscopy, X-ray Diffraction (XRD) and Temperature Programmed Reduction (TPR). Computer studies involve kinetics modeling using microkinetic modeling theory, and probing the structures and thermochemistry of possible catalytic intermediate species using Density Functional Theory (DFT). In-situ gravimetry results show that the redox capacity of Fe/ZSM-5 using H 2 /O 2 probe is high (0.6 ~1.25), additionally two peaks are observed in H2-TPR. This indicates that following reduction, some of the iron may exist in an oxidation state lower than +2. However, for the redox reactions studied herein, the working state of the catalyst is fully oxidized and corresponds to ferric cations. The catalyst mass was monitored while making step changes in the gas phase composition at N 2 O decomposition conditions. The results suggest that NOx surface species do not form in N 2 O/He, and if they form in N 2 O/NO/He, their surface concentration is exceedingly small. A single mechanistic framework was proposed and used to model a variety of redox reactions; the microkinetic model is consistent with experimental observations of conversion and catalyst mass change as well as DFT calculations. Water Gas Shift (WGS) can not proceed over Fe/ZSM-5 up to 500°C. Unlike NO, trace CO and H 2 don't have a promotional effect beyond stoichiometric reaction when introduced at trace levels into N 2 O decomposition. Similarly, trace NO does not promote CO/H 2 oxidation. It appears that NO produces nitrite/nitrate intermediates and creates a fast pathway for O 2 desorption. The latter species' coverage is under 1% both in modeling as well as experimental results. However, the modeling was successful only if the surface bond energy of oxygen on the active site is different, when generated from N 2 O decomposition than when generated from oxygen. Density functional calculations were performed on the surface species involved. The computational chemistry shows that when this site is reduced, one of the terminal hydroxyl groups moves into a bridging position. In this way there exists a pool of 1.5 oxygen atoms per iron cation which participate in the N 2 O decomposition reaction whereas the redox capacity of the catalyst is only 0.5 oxygen atoms per iron cation.

Download or read book Catalytic Kinetics and Thermal Management in Microchemical Systems for Distributed Energy and Portable Power Generation written by and published by . This book was released on 2009 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Catalytic kinetics and thermal management in fabricated microreactors were studied for the design of distributed energy and portable power production systems. Specifically, kinetically relevant experimental data was generated for the following chemistries: preferential oxidation (PROX) of CO in excess H 2, water-gas shift (WGS), reverse water-gas shift (RWGS), and H 2, CO, syngas, CH 4, C 2 H 6, and C 3 H 8 oxidation over a supported Pt/Al 2 O 3 catalyst. The effect of wall material properties and reactor configuration was also determined through the modeling, design, fabrication, and experimentation of microcombustors for integration with thermoelectrics and enhancement of thermal stability from heat recirculation. CO oxidation over Pt was found to be structure sensitive, as the observed turnover frequency (TOF) rate increased with larger Pt crystallite sizes. A multisite, microkinetic model (containing reaction and diffusion steps) developed using density functional theory (DFT) energy barriers and thermodynamically consistent preexponentials for terraces (Pt(111)) and steps (Pt(211)) also predicts this trend. An excessive fraction of H 2 was shown to enhance and inhibit CO oxidation at low and high temperature, respectively. By increasing the CO:O 2 ratio in the presence of excess H 2, CO conversions above the equilibrium value were observed and rationalized with a microkinetic model. WGS and RWGS experiments were performed at high temperatures (where RWGS is favorable) and positive order kinetics were observed for H 2 O and H 2 in WGS and RWGS, respectively. In the catalytic combustion of syngas mixtures (1:1 and 1:3 for coal gas and methane reformate, respectively), high CO selectivities were observed at low temperatures. CO and H 2 catalytic combustion experiments were also performed for comparison purposes. H 2 catalytic oxidation was strongly inhibited by the presence of CO. Hysteresis was also observed at high H 2 conversions and is discussed. Kinetic parameters were estimated for lean CH 4, C 2 H 6, and C 3 H 8 catalytic combustion. The relative activity was observed to be C 3 H 8> C 2 H 6> CH 4 and the catalytic combustion of small alkanes over Pt/Al 2 O 3 was found to follow a homologous series. Thermal management of an integrated thermoelectric/single channel, catalytic microcombustor was studied using H 2, CH 3 OH, and C 3 H 8 fuels. Electrical power generation (maximum 0.65 W) with a thermal efficiency up to ~ 1.1% was measured. Thermal management strategies, such as heat recirculation, were exploited with fabricated microreactors designed via computational fluid dynamics (CFD) for C 3 H 8 combustion. It was shown through both experiments and simulation that catalytic heat recirculation burners have similar stability to single channel burners in the limit of highly conductive walls. In contrast, for low conductivity walls, heat recirculation proved to be effective at increasing combustion stability relative to single channel burners.

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 Material and Composition Screening Approaches in Electrocatalysis and Battery Research written by Kai S. Exner and published by Frontiers Media SA. This book was released on 2021-07-08 with total page 133 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Toward a Molecular Level Understanding of Mixed Metal Oxide Oxidation Catalysts written by Andrew Getsoian and published by . This book was released on 2013 with total page 150 pages. Available in PDF, EPUB and Kindle. Book excerpt: The selective oxidation and ammoxidation of light olefins comprises a 5 million ton per year industry, and is responsible for making possible products from nitrile rubber to Plexiglas to acrylic paint. The industrial catalyst of choice for such reactions is based on bismuth molybdate, and was first patented in the 1950s. In the intervening decades, a significant body of research has been done on bismuth molybdate-based catalysts, and yet a surprising amount is still not known about how these catalysts work. This Thesis has focused primarily on developing new methods for studying bismuth molybdates and related catalysts in order to gain new insight into the means by which the physical and electronic structures of the active sites in these catalysts give rise to their catalytic activity. The mechanism by which propene is oxidized on the (010) surface of Bi2Mo3O12 has been investigated using the RPBE+U variety of density functional theory (DFT). The location of the active site was determined, and the calculated barrier for the rate-determining step at this site found to be in good agreement with experimental results. Calculations revealed the essential roles of bismuth and molybdenum in providing the geometric and electronic structure responsible for catalytic activity at the active site, and suggested that catalytic activity could be further enhanced by substitution with a more reducible element. In order to accurately model substitution of an additional reducible element in to Bi2Mo3O12 using DFT, more sophisticated approaches than RPBE+U were required. Two more advanced density functionals, M06-L and HSE, were examined. The HSE functional was found to be too expensive for practical use on extended systems like bismuth molybdate catalysts. The accuracy of the M06-L functional for lattice constants and geometries, reaction energies and barriers, electronic structures, and non-covalent interactions was investigated, and compared results from the RPBE+U method. The M06-L functional was found to be superior to RPBE+U for lattice constants, reaction energies, and non-covalent interactions, and as good as or better than RPBE+U for electronic structures. Use of the M06-L functional was therefore determined to be preferable to use of RPBE+U for use in the study of substituted bismuth molybdate catalysts. Calculations employing the M06-L functional were combined with physical characterization using diffuse reflectance UV-VIS, x-ray photoelectron, and x-ray near edge absorption spectroscopies in order to understand the effect of substitution of vanadium for molybdenum on the activation energy for propene oxidation in catalysts of formula Bi1-x/3V1-xMoxO4. In these catalysts, substitution of vanadium for molybdenum has been observed to lower the apparent activation barrier for propene oxidation. It was found that the lower activation barrier for propene oxidation over mixed vanadate-molybdate catalysts is a consequence of the smaller difference between the catalyst conduction band edge energy and the energy level of the highest occupied molecular orbital in propene. The lower conduction band edge energy in mixed vanadate-molybdate catalysts is related to the energies of and degrees of mixing between the V 3d and Mo 4d orbitals comprising the conduction band. Both of these observations suggest general principles that may be of relevance to a variety of mixed metal oxide catalyst systems. An improved procedure for synthesizing bismuth molybdate and bismuth vanadate catalysts was also developed. This procedure involved a two step templating process: a structured mesoporous carbon was templated from KIT-6 or MCM-48 mesoporous silica, and the structured mesoporous carbon in turn used as a template during synthesis of the metal oxide catalyst. Catalysts produced by the double templating process had surface areas of 14-17 m2/g, a large improvement on the

Download or read book Density Functional Theory Study on Catalytic Activity of Single Atom Electrocatalysts for Oxygen Reduction Reaction written by Hong Zhong and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Single transition metal (TM) and nitrogen-coordinated carbon materials (M0́3N0́3C) have been extensively studied as promising electrocatalysts due to their excellent catalytic activity towards oxygen reduction reaction (ORR). However, the ORR catalytic activity of these single-atom electrocatalysts (SACs) is normally not as good as Pt-based electrocatalysts, especially, in acidic media. In this project, the first-principles density functional theory (DFT) methods are used to study the ORR catalytic activity of single-atom iron/cobalt electrocatalysts (Fe/Co SACs) in acidic media. The ORR catalytic performance of Fe SAC can be improved by doping N atoms around the Fe0́3N4 moiety through replacing C atom with N atom. For the Co SAC, the ORR catalytic activity is improved by reducing the number of Co-coordinated N atoms through replacing the N atom with C atom. The electronic occupancy of metal dz2 orbital in pristine SACs can be used as a descriptor of ORR catalytic activity.

Download or read book Computational Modeling of Heterogeneous Catalysis for Molecular and Kinetic Understanding of Aerobic Oxidation and Electrocatalytic Oxygen Reduction written by Aurora Naomi Janes and published by . This book was released on 2021 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Rational design of heterogeneous catalysts is of utmost importance to improve the efficiency of industrial chemical synthesis. In this thesis, we investigate two chemical reactions catalyzed by heterogeneous catalysts through theoretical modeling, the aerobic esterification of primary alcohols and the two electron oxygen reduction reaction. First, we develop a microkinetic modeling code, Micki, that both provides an easy-to-use interface for standard statistical mechanical methods for microkinetic modeling as well as novel ways to incorporate complex physics that influence the liquid-solid interface. Then we use Micki to determine the role of P block promoters for the aerobic esterification of alcohols. Tellurium atoms modify the electronic structure of the catalyst which reduces the barrier of the rate limiting step, C-H bond scission, as well as providing lower energy pathways for O2 reduction. Next, we develop a theoretical framework to evaluate the performance of cobalt dichalcogenides based on density functional theory calculations. Together with experimental collaborators, we discover the best 2e? ORR catalysts in acidic media to date as well as transferable physical principles. We apply these physical principles to nickel dichalcogenides and cobalt nickel dichalcogen alloys. We conclude that while nickel dichalcogenides show great promise for 2e? ORR, the alloy does not as neighboring metal centers have little electronic influence on each other. Finally we use Micki to develop an electrochemical microkinetic model of 2e? ORR on cobalt dichalcogenide catalysts and compare results to bulk electrolysis experiments. While significant work must be done to reach quantitative accuracy for electrochemical kinetic models, our results indicate qualitative trends are properly modeled and electrochemical kinetic models can be used to predict catalyst performance.

Download or read book Operando Research in Heterogeneous Catalysis written by Joost Frenken and published by Springer. This book was released on 2016-12-26 with total page 232 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book is devoted to the emerging field of techniques for visualizing atomic-scale properties of active catalysts under actual working conditions, i.e. high gas pressures and high temperatures. It explains how to understand these observations in terms of the surface structures and dynamics and their detailed interplay with the gas phase. This provides an important new link between fundamental surface physics and chemistry, and applied catalysis. The book explains the motivation and the necessity of operando studies, and positions these with respect to the more traditional low-pressure investigations on the one hand and the reality of industrial catalysis on the other. The last decade has witnessed a rapid development of new experimental and theoretical tools for operando studies of heterogeneous catalysis. The book has a strong emphasis on the new techniques and illustrates how the challenges introduced by the harsh, operando conditions are faced for each of these new tools. Therefore, one can also read this book as a collection of recipes for the development of operando instruments. At present, the number of scientific results obtained under operando conditions is still limited and mostly focused on a simple test reaction, the catalytic oxidation of CO. This reaction thus forms a natural binding element between the chapters, linking the demonstrations of new techniques, and also connecting the theoretical and experimental studies. Some first results on other reactions are also presented. If there is one thing that can be concluded already in this early stage, it is that the catalytic conditions themselves can have dramatic effects on the structure and composition of the surfaces of catalysts, which, in turn can greatly affect the mechanisms, the activity, and the selectivity of the chemical reactions that they catalyze.

Download or read book Methanol Synthesis written by Jerzy Skrzypek and published by . This book was released on 1994 with total page 174 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Plasma Catalysis written by Annemie Bogaerts and published by MDPI. This book was released on 2019-04-02 with total page 248 pages. Available in PDF, EPUB and Kindle. Book excerpt: Plasma catalysis is gaining increasing interest for various gas conversion applications, such as CO2 conversion into value-added chemicals and fuels, N2 fixation for the synthesis of NH3 or NOx, methane conversion into higher hydrocarbons or oxygenates. It is also widely used for air pollution control (e.g., VOC remediation). Plasma catalysis allows thermodynamically difficult reactions to proceed at ambient pressure and temperature, due to activation of the gas molecules by energetic electrons created in the plasma. However, plasma is very reactive but not selective, and thus a catalyst is needed to improve the selectivity. In spite of the growing interest in plasma catalysis, the underlying mechanisms of the (possible) synergy between plasma and catalyst are not yet fully understood. Indeed, plasma catalysis is quite complicated, as the plasma will affect the catalyst and vice versa. Moreover, due to the reactive plasma environment, the most suitable catalysts will probably be different from thermal catalysts. More research is needed to better understand the plasma–catalyst interactions, in order to further improve the applications.

Download or read book Mechanistic Studies for Catalytic Transformation of Small Oxygenates on Transition Metals written by Suyash Singh and published by . This book was released on 2014 with total page 178 pages. Available in PDF, EPUB and Kindle. Book excerpt: Over the past century, heterogeneous catalysis has played a central role in the development of efficient chemical processes for the conversion of fossil resources to fuels and chemicals, and identification of new, sustainable routes to upgrade renewable carbon sources that minimize the ecological footprint. More recently, unprecedented advances in electronic structure theory and related computational methods have provided a major thrust to the efforts that utilize density function theory (DFT) calculations for developing fundamental atomic-level understanding of these processes, and subsequently designing new and improved catalysts. In this dissertation, a combined theoretical and experimental approach is presented to study the reaction mechanisms for the catalytic conversion of formic acid (FA) and propylene oxide on transition metals. An iterative methodology comprising of DFT calculations, reaction kinetics measurements, and mean-field microkinetic modeling is employed to determine the nature of active sites on supported catalysts, explain the experimentally observed trends, and obtain predictions for the surface environment under reaction conditions. A detailed analysis of the DFT derived thermochemistry and kinetics parameters over a wide range of transition metal surfaces is performed to identify the key reactivity descriptors for FA decomposition on transition metal catalysts, and develop semi-empirical linear correlations that are then used to develop a microkinetic modeling based framework for the identification and design of improved (active and selective) bimetallic alloy catalysts. Finally, the possible utilization and applications of these methods and ideas in other key chemical transformations are proposed, and suggestions for future work are included.

Download or read book Classical And Quantum Dynamics In Condensed Phase Simulations Proceedings Of The International School Of Physics written by Bruce J Berne and published by World Scientific. This book was released on 1998-06-17 with total page 881 pages. Available in PDF, EPUB and Kindle. Book excerpt: The school held at Villa Marigola, Lerici, Italy, in July 1997 was very much an educational experiment aimed not just at teaching a new generation of students the latest developments in computer simulation methods and theory, but also at bringing together researchers from the condensed matter computer simulation community, the biophysical chemistry community and the quantum dynamics community to confront the shared problem: the development of methods to treat the dynamics of quantum condensed phase systems.This volume collects the lectures delivered there. Due to the focus of the school, the contributions divide along natural lines into two broad groups: (1) the most sophisticated forms of the art of computer simulation, including biased phase space sampling schemes, methods which address the multiplicity of time scales in condensed phase problems, and static equilibrium methods for treating quantum systems; (2) the contributions on quantum dynamics, including methods for mixing quantum and classical dynamics in condensed phase simulations and methods capable of treating all degrees of freedom quantum-mechanically.