Hydrogen Production via Aqueous-Phase Reforming of Ethanol Catalyzed by Ruthenium Alkylidene Complexes

A series of ruthenium alkylidene complexes were adopted to catalyze aqueous-phase reforming of ethanol for H2 production at readily achievable temperatures (<100 °C). The best results were obtained using (SIMes)Ru(PCy3)(3-methyl-2-butenylidene)Cl2 (SIMes, 1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene; PCy3, tricyclohexylphosphine) with a five-day reaction producing a maximum turnover number (TON) of 47,295; this value is the second-largest one known for homogeneously catalyzed ethanol dehydrogenation. Kinetic experiments confirmed that the reforming process undergoes a second-order reaction kinetics, with both ethanol and water contributing to H2 production. Analyses of the reaction mixture using an in situ 1H NMR experiment revealed a possible intermediate coordinated with a hydride ligand, based on which and previous work a plausible mechanism was proposed.