Electrochemical Oxidative Carbonylation: Strong CO Binding Suppresses C-C Coupling and Steers Selectivity to Organic Carbonates.

Electrochemical oxidative carbonylation offers a route to the synthesis of organic carbonates such as dimethyl carbonate (DMC), but its practical implementation is hindered by a competing C-C coupling pathway to dimethyl oxalate (DMO), the origins of which remain poorly understood. Here we study how selectivity in methanol carbonylation is influenced by tuning the adsorption of key surface intermediates. We find, by modulating the interfacial environment using ionomers and isotopically substituted solvents, that strong CO adsorption suppresses C-C coupling and directs the reaction toward carbonate formation. Enhancing methoxy binding promotes deep methoxylation that benefits the overall methanol carbonylation reaction and DMC production. We propose that adsorbed methoxycarbonyl, once viewed as an undesired intermediate, in fact serves as a branching point from which the carbonate and oxalate pathways diverge. Guided by knowledge of these descriptors, we develop a composite catalyst that leverages metal-support interactions, strengthening CO binding and simultaneously accelerating alcohol dissociation, thereby increasing selectivity by 3 orders of magnitude relative to a benchmark Pd catalyst and achieving a Faradaic efficiency of 98% for DMC production.