(583ao) Density Functional Theory and Microkinetic Based Analysis of CO2 Reduction Reactions On Ru Surfaces

With CO₂ emissions still on the rise and the level of atmospheric CO₂ reaching the highest level in human history, the significance of CO₂ reduction methods becomes ever more apparent. One of the more promising ways for CO₂ reduction is the catalytic hydrogenation of CO₂ to higher value hydrocarbon fuels as a potential route to achieve environmental and energy sustainability. In this work a thorough mechanistic study has been performed for CO₂ methanation on Ru catalyst surfaces as a model reaction, to address fundamental mechanistic questions and existing debates in literature regarding the CO₂ hydrogenation mechanism. Ab-initio density functional theory (DFT) computational methods are utilized for geometry optimization and binding energy calculations for adsorbed species. The complete reaction pathway is mapped out using the energy levels of the intermediates and CI-NEB calculated energy barriers. The possible reaction paths and probability of competing reactions such as reverse water gas shift reaction are analyzed by comparison of the energetic levels of elementary steps. The results of DFT calculated energetics and vibrational frequency analysis are used to perform a microkinetic analysis of the reaction which helps us identify active surface sites, stable surface species, the performance limiting and selectivity controlling steps. The results of our study will provide a molecular level understanding of the hydrogenation reaction mechanism which is essential in the search of optimal catalytic materials for CO₂ methanation.