Cascade Electrocatalytic and Thermocatalytic Reduction of CO 2 to Propionaldehyde.

Electrochemical CO 2 reduction can convert CO 2 to value-added chemicals, but its selectivity toward C 3+ products are very limited. One possible solution is to run the reactions in hybrid processes by coupling electrocatalysis with other catalytic routes. In this contribution, we report the cascade electrocatalytic and thermocatalytic reduction of CO 2 to propionaldehyde. Using Cu(OH) 2 nanowires as the precatalyst, CO 2 /H 2 O is reduced to concentrated C 2 H 4 , CO, and H 2 gases in a zero-gap membrane electrode assembly (MEA) reactor. The thermochemical hydroformylation reaction is separately investigated with a series of rhodium-phosphine complexes. The best candidate is identified to be the one with the 1,4-bis(diphenylphosphino)butane diphosphine ligand, which exhibits a propionaldehyde turnover number of 1148 under a mild temperature and close-to-atmospheric pressure. By coupling and optimizing the upstream CO 2 electroreduction and downstream hydroformylation reaction, we achieve a propionaldehyde selectivity of ~38 % and a total C 3 oxygenate selectivity of 44 % based on reduced CO 2 . These values represent a more than seven times improvement over the best prior electrochemical system alone or over two times improvement over other hybrid systems.