Integrated CO2Capture and Conversion to Formate with a Molecular Platinum Bis(diphosphine) Electrocatalyst

Abstract

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 CO2or the reduction of pure CO2streams. The direct reduction of sorbent-captured CO2in an integrated process would skip the energy-intensive CO2concentration 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% CO2streams, 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·CO2to 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 CO2reduction, were explored using computational methods.