Hydrogenation of CO2 to Formate over Ruthenium Immobilized on Solid Molecular Phosphines

Formic acid is a promising hydrogen storage medium and can be produced by catalytic hydrogenation of CO2. Molecular ruthenium complexes immobilized on phosphine polymers have been found to exhibit excellent productivity and selectivity in the catalytic hydrogenation of CO2 under mild conditions. The polymeric analog of 1,2-bis(diphenylphosphino)ethane exhibited the highest activity and turnover numbers up to 13170 were obtained in a single run. This catalyst was already active at 40 degrees C and with a catalyst loading of only 0.0006 mol%. Recycling experiments revealed a loss of activity after the first run, followed by a gradual decrease during the subsequent runs. This is attributed to a change in the catalytically active complex during the hydrogenation reaction. High selectivity towards formate and low leaching were maintained in the absence of CO formation. Based on the catalyst characterization, a mechanism for the CO2 hydrogenation is proposed.