CO2 reduction by H2 to CHO on Ru(0001): DFT evaluation of three pathways

Abstract

Using a DFT approach, we explored three pathways to formyl, HCO, starting from CO2, on a Ru(0001) model catalyst. Previously the direct CO scission has been discussed as preferential which we confirmed in this study. CO formation is both kinetically and thermodynamically the most preferred reaction of CO2 conversion on bare Ru(0001). The most favorable reaction of CO* is desorption; only in the next favorable channel, CO* is converted to formyl via a (calculated) absolute free energy barrier of 63 kJ/mol. We also show that formate HCOO* is formed with an absolute free energy barrier of 73 kJ/mol; it may dissociate directly to formyl HCO* via an absolute barrier of 80 kJ/mol. The carboxylate path has an even higher crucial barrier right in the first transformation step on the surface, 97 kJ/mol. At a higher coverage of 1/4 we determined that the CO scission path and the formate route become more similar, with the former being preferred by 8 kJ/mol only.