Integrated CO2 Capture and Conversion to Formate with a Molecular Platinum Bis(diphosphine) Electrocatalyst.

Carbon dioxide is a potentially valuable feedstock for carbon-based fuels or commodities but is only available in dilute streams. Many studies have focused on either the capture and concentration of CO2 or the reduction of pure CO2 streams. The direct reduction of sorbent-captured CO2 in an integrated process would skip the energy-intensive CO2 concentration and sorbent regeneration step. Herein, we report the electrocatalytic reduction of 1,3-bis-(2,6-diisopropylphenyl)-imidazolium-2-carboxylate (IPr·CO2), which forms quantitatively from the reaction of sorbent 1,3-bis-(2,6-diisopropylphenyl)-imidazol-2-ylidene (IPr) with 10% and 0.04% CO2 streams, by catalyst [Pt-(dmpe)2]-(PF6)2 (dmpe = 1,2-bis-(dimethylphosphino)-ethane) to formate with >70% Faradaic efficiencies. Unexpectedly, experimental studies indicate that the proton source phenol facilitates rapid decarboxylation of IPr·CO2 to release CO2, which is the substrate for reduction. Kinetic studies determined the rate of hydride transfer from a catalytic intermediate [HPt-(dmpe)2]-(PF6) to form the C-H bond in formate to be 0.22 M-1s-1. Further details on the mechanism, transition state energy, and structure for hydride transfer to CO2, a common step in CO2 reduction, were explored using computational methods.