| The key fundamentals of Density Functional Theory (DFT) and Microkinetic Modeling are introduced and a combination of theory and modeling coupled with experiments is used for understanding the water gas shift reaction (WGSR). Self-consistent periodic DFT-GGA calculations are used to investigate the low temperature WGSR on the close packed surfaces of 10 late transition metals and based on these calculations thermodynamic potential energy surfaces are generated. A new mechanism involving the formation of carboxyl species from CO and OH is outlined and it is shown that on metals such as Cu, Ag, Au, and Pt, the carboxyl mechanism is the dominant reaction pathway. Since copper-based catalysts are the catalysts of choice for this reaction, detailed minimum energy paths are computed for all elementary steps on the Cu(111) surface. Using the DFT-derived parameters such as activation energies, thermochemistries, and frequency factors, a detailed mean-field microkinetic model is developed. This model is employed to predict experimental reactions rates on commercial Cu/ZnO/Al2O3 catalyst under a variety of different experimental conditions and important reaction parameters such as orders of the reaction, apparent activation energy and the rate controlling steps are determined.; Detailed mechanisms of early Fischer Tropsch Synthesis (FTS) steps are also studied using DFT on the most close-packed surfaces of Fe and Co. Furthermore, the effect of carbide phase on the reactivity of Fe catalysts is probed using a subsurface-carbon-modified Fe(110) surface. The thermochemistry and activation energies for the various elementary steps such as CO dissociation, methanation, C-C coupling, C2 hydrogenation, internal H-transfer, water formation, and CO oxidation are studied. These studies are used to predict the most favorable C-C coupling steps on Fe and Co surfaces. |
