Development of noble metal catalysts and detailed kinetic models for CO oxidation and water gas shift reactions

Abstract

Noble metal (Pt, Pd, Rh) based catalysts have been highly effective for CO abatement applications such as CO oxidation and the water gas shift reaction (WGS). In the venture for development of novel catalysts, noble metal supported catalysts have been developed with support materials ranging from inert metal oxides such as ZrO2, SiO2, carbonaceous graphene oxide and reducible supports such as CeO2, TiO2 and cobalt oxide. In contrast to the impregnated catalysts, monometallic and bimetallic noble metal substituted ionic catalysts have been developed and were demonstrated to have superior catalytic activity for CO oxidation and WGS. However, despite abundant experimental data and spectroscopic insights, the reaction mechanisms, kinetic models and the rate expressions developed for gas phase reactions over noble metal based catalysts are still points of debate with no consensus. This is particularly evident for bimetallic catalysts and noble metal based reducible catalysts. This lack of comprehensive kinetic models can be attributed to the deficiency of intuitive understanding of reaction mechanisms and Name Mandapaka Ravikiran Sr No 05-04-00-10-12-13-1-10418 Department Chemical Engineering Advisor Prof. Giridhar Madras (Dept. of Chemical Engg) Title Development of noble metal catalysts and detailed kinetic models for CO oxidation and water gas shift reactions. robust modeling procedures accounting for the contribution of the support materials in the reaction mechanisms. With the advent of robust simulation protocols, and spectroscopy based instrumentation it has now been possible to investigate the energetics of complex reaction mechanisms involving gas-phase reactions through DFT calculations and probe the mechanistic insights using FTIR based experiments. These advancements can be decisive in developing detailed kinetic models or microkinetic models for various gas phase reactions over reducible oxides. In order to address the aforementioned issues, this thesis emphasizes on the comprehensive development and application of novel noble metal based catalysts for CO oxidation and WGS starting from the catalyst synthesis, characterizations, activity testing and detailed kinetic model development. Chapter 1 of the thesis presents the need for development of efficient catalyst for CO abatement applications. It presents the literature background on the usage of noble metal based catalysts and their application in conjunction with different support materials. The chapter also presents various synthesis procedures, experimental protocols, drawbacks and complications involved in the synthetic procedures. This chapter also illustrates various reaction mechanisms, rate expressions developed in the literature for CO oxidation and WGS reaction catalyzed by noble metals. Chapter 2 of the thesis presents the synthesis protocols implemented in this thesis to synthesize various noble metal ionic catalysts i.e. palladium doped, platinum co-doped and rhodium co-doped ceria catalysts. The chapter presents the XRD, XPS, TEM characterizations, of the catalysts presenting the crystal structure, surface morphology, structural parameters and ionic state of the respective consistent elements of the catalysts. The chapter also presents the BET surface area of the catalysts and H2-TPR profiles of the catalysts illustrating the oxygen storage capacity of the catalysts. Chapter 3 of the thesis discusses the development of kinetic models and rate expressions for different noble metal based catalysts involving single site and dual site mechanisms. This chapter gives a brief overview of the methodology followed to obtain and design rate expressions for microkinetic models for CO oxidation and WGS over various noble metal based catalysts. Chapters 4, 5 and 6 of the thesis present the experimental protocols, catalytic activity and reaction mechanisms of various noble metal catalysts i.e. palladium doped, platinum co-doped, rhodium co-doped ceria, Fe-Pt/GO and Pd/SiO2 for WGS reaction and CO oxidation, respectively. These chapters illustrate the application of differential reactor proximity approach followed for obtaining the intrinsic rate of reactions, comparison of activity of the catalyst using apparent activation energies for noble metal ionic catalysts and Fe-Pt bi metallic catalysts. Chapter 6 also presents the development and validation of the microkinetic models developed for CO oxidation using isothermal plug flow approach for bi-metallic Fe-Pt/GO catalysts and palladium impregnated silica catalyst. Chapter 7 of the thesis presents the conclusions of the various applications of the ionic catalysts for CO abatement reactions illustrating the activity of the developed catalysts. The chapter also illustrates the validity and robustness of the kinetic modeling procedures implemented in the above studies to understand the intrinsic kinetics of the reactions. Chapter 7 of the thesis also presents the scope and orientation for future work in the field of catalyst development and kinetic modeling for various gas phase reactions such as preferential oxidation and reforming reactions with applications involving various side reactions.