Solid micellar Ru single-atom catalysts for the water-free hydrogenation of CO2 to formic acid

The catalytic hydrogenation of CO2 to formic acid is one of the most promising pathways towards a renewable hydrogen-storage system. The reaction is usually performed in aqueous phase in the presence of basic molecules over homogeneous or heterogeneous catalysts, generating relatively dilute formate solutions (<1 M). The newly designed solid micellar Ru single-atom catalyst enables efficient and stable water-free CO2 hydrogenation to formate under mild reaction conditions. Concentrated formate solutions (up to 4 M) are produced directly from the hydrogenation of carbon dioxide in water-free tertiary amine. In the catalyst, Ru(III) single sites are incorporated into the walls of MCM-41 during hydrolysis creating a solid micelle structure. The presence of the CTA(+) surfactant in the pores of MCM-41 stabilizes the Ru sites and prevents catalyst deactivation. DFT modelling suggests that the reaction proceeds via heterolytic hydrogen splitting, forming a Ru-H species and subsequent hydride transfer to CO2.