Higher oxygenate formation from ethanol on Cu/ZnO catalysts: Synergism and reaction mechanism

A remarkable synergism was observed in the higher oxygenate formation from ethanol on Cu/ZnO catalysts compared to one component catalyst of Cu or ZnO, The reaction mechanism was examined by C-13 labelling studies and selective feeding methods. A C-13 NMR and a GC/MS were used to determine the structure of the labelled products, A mass spectrometer was used to trace the dynamic change of the product distribution. A comprehensive reaction mechanism for the carbon chain growth on Cu/ZnO catalysts was proposed. The synergism could be explained by different intrinsic characteristics of copper and ZnO in the dehydrogenation of ethanol. Nucleophiles are produced preferentially on ZnO and electrophiles are produced preferentially on copper, and they would associate to form dioxygenated C-4 intermediates, which are converted to various higher chain products. A stabilization of ethoxy carbanion on ZnO was suggested, which would participate in the chain growing reaction.