Electrified Hydrogenation of Aliphatic Ketones in a Palladium Membrane Reactor.

Thermochemical hydrogenation of crude oil is a key step in biofuel production. This process is CO2-intensive because (i) H2 is derived from fossil fuels, and (ii) the reactions require high temperatures and pressures. We identified that electrocatalytic hydrogenation in a membrane reactor could lower the CO2 intensity by deriving hydrogen from H2O and driving the reactions under ambient conditions. In this work, we demonstrate the electrocatalytic hydrogenation of 2-butanone to 2-butanol, a model bio-oil reaction, in a palladium membrane reactor. This reaction was observed when we added a Ru/C catalyst layer on the face of the palladium foil facing the chemical chamber and by operating in either acidic or basic media. We systematically investigated the effects of counterions, acid/base concentrations, and pH to determine that the reaction is catalyzed by either H3O+ or OH-. In the acid-catalyzed reaction at pH < 5, ketone hydrogenation proceeds either directly or through an enol intermediate. In the base-catalyzed reaction at pH ≥ 12, the ketone is hydrogenated directly, and no other intermediates are observed. We also demonstrate that these reaction conditions can be translated to other model crude bio-oil compounds such as acetone, 2-butanone, cyclohexanone, 2,3-butanedione, and 2,4-pentanedione. This study expands the scope of chemistry that can be accessed in a palladium membrane reactor to aliphatic carbonyls and teaches how reaction media can influence hydrogenation chemistry.