Cobalt-Molybdenum Oxides for Effective Coupling of Ethane Activation and Carbon Dioxide Reduction Catalysis

Abstract

This study reports the discovery of CoMoOx moieties with synergistic catalytic roles in C2H6–CO2 catalysis. C2H6–CO2 catalysis occurs through multiple, concomitant catalytic cycles, initiated by the dual cycles of C2H6 activation and CO2 activation, together with an undesired coke deposition cycle. C2H6 activation requires reactive oxygen species that assist with the kinetically relevant C–H bond activation; these oxygen species are generated from the CO2 activation cycle within the reverse water-gas shift (RWGS) reaction. An efficient CO2 activation in the RWGS reaction would retain higher O contents in CoMoOx moieties, leading to more effective kinetically relevant C–H bond activation of C2H6 and oxidation of coke precursors and thus increasing turnovers while mitigating deactivation. This mechanistic insight led us to design CoMoOx moieties, where the Co cation acts as a Lewis acid. Together with a vicinal oxygen vacancy, the Co cation activates CO2 via a Vacancy route through the formation of a kinetically relevant [Co···C(O) ═ O··· □vacancy···Mo]‡ transition state, at which the Co interacts with the C and the oxygen vacancy (□vacancy) abstracts the leaving O of CO2. The kinetically coupled cycles lead the ethane conversion rates in dehydrogenation and reforming reactions to both depend directly on the RWGS reaction rates. This mechanistic understanding of rate coupling has led to the design of CoMoOx moieties with dual functionality for effective C2H6–CO2 catalysis.