Oxide supported metal catalysts for the aldehyde water shift reaction: Elucidating roles of the admetal, support, and synergies

There is significant interest in the use of H2O as a reactant for production of commodity chemicals and fuels, in particular from water-laden biomass-derived feedstocks. In this paper, we describe results for the aldehyde water shift (AWS), a reaction where aldehydes are partially oxidized by water to produce the corresponding carboxylic acid and H-2, over a series of CeO2-, Al2O3-, and SiO2-supported Cu, PL and Au catalysts. The effects of support were further investigated by evaluating the performances of a Cu-Zn-Al water gas shift catalyst and bulk Cu nanoparticles. The supported Cu catalysts were more active than the supported Pt and Au catalysts, and the reducible oxide (CeO2) supported Cu catalyst had the highest AWS activity. The high activity of the Cu/CeO2 catalyst is believed to derive from coupling H2O dissociation and aldehyde oxidation. The two major side reactions, aldol condensation and aldehyde disproportionation, appeared to be catalyzed by acid and Cu sites, respectively. The results indicate that both the admetal and support play critical roles in catalyzing the AWS reaction and provide guidance for the design of highly active AWS catalysts.