Versatile CO2 hydrogenation-dehydrogenation catalysis with Ru-PNP/ionic liquid system

Abstract

High catalytic activities of Ru-PNP complexes in ionic liquid (IL) were obtained for the reversible hydrogenation of CO2 and dehydrogenation of formic acid (FA) under exceedingly mild conditions. The novel catalytic system relies on an unprecedented IL-promoted activation of CO2 and proceeds already at 25 ⁰C under a continuous flow of 1 bar of CO2/H2, leading to 14 mol% FA with respect to the IL, whereas a pressure of 40 bar of CO2/H2 (1:1) provides 126 mol% of FA/IL. The conversion of CO2 contained in imitated biogas was also achieved at 25 ⁰C. Furthermore, the Ru-PNP/IL system catalyzes FA dehydrogenation with turnover frequencies (TOF) up to 11,000 h-1 under heat-integrated conditions for proton-exchange membrane (PEM) fuel cell applications (<100 ⁰C). Thus, 4 mL of a 0.005 M Ru-PNP/IL system converted 14.5 L FA over four months with a turnover number (TON) exceeding 18,000,000. Finally, 13 hydrogenation/dehydrogenation cycles were achieved with no sign of deactivation. These results demonstrate the potential of the Ru-PNP/IL system as a Liquid Organic Hydrogen Carrier (LOHC) battery, LOHC H2 releaser, and hydrogenative CO2 converter.