Suppressing Dormant Ru States in the Presence of Conventional Metal Oxides Promotes the Ru-MACHO-BH-Catalyzed Integration of CO₂ Capture and Hydrogenation to Methanol

Abstract

Integrated CO2 capture and hydrogenation to methanol may replace fossil resources for production of clean fuels, chemicals, and materials. As opposed to the classic concept of lowering the transition state barriers in the rate determination step, here we demonstrate that suppression of a resting state species can also be a viable approach to accomplish catalytic improvement. As a promising NH/M bifunctional molecular catalyst for integrated CO2 capture and conversion to methanol, Ru-MACHO-BH in the presence of amine additives was evaluated in the presence of a second catalyst, preferably ZnO. The latter is capable of suppressing the Ru-formate resting state intermediate by accelerating formate to formamide formation. This strategy is capable of advancing methanol formation and CO2 conversion, adding up to 100 and 294 turnover numbers, respectively, under mild operational conditions. Operando high-pressure ATR-IR spectroscopy evidenced the existence of such Ru-formate resting state species in the presence of amine additives and its disappearance upon addition of ZnO under catalytic conditions. Given that metal oxide enhances the amide bond formation rate, but has insignificant activity in catalytic hydrogenation of CO2 and the formamide intermediate, its promoting effect can be fully ascribed to an increased availability of the active Ru-dihydride species upon suppressing the dormant Ru-formate catalyst intermediate