Condensed-Phase Ethanol Conversion to Higher Alcohols over Bimetallic Catalysts

The catalytic condensation of ethanol to n-butanol and higher alcohols, known collectively as Guerbet reactions, has attracted attention in recent years as ethanol becomes increasingly available as a biorenewable feedstock. Results are presented here for the continuous, condensed-phase conversion of ethanol to higher alcohols using Ni/La2O3/gamma-Al2O3 catalysts and for catalysts containing a second metal (Cu, Co, Pd, Pt, Fe, Mo) in addition to nickel. Detailed characterization of the catalyst surface and bulk properties has been carried out and is correlated to catalyst activity and selectivity. The best results obtained for nickel catalysts are a selectivity to higher alcohols of 75-80% and a turnover frequency of 200 mol ethanol/mol Ni site/h at 230 degrees C. The addition of cobalt nearly doubles the ethanol conversion rate relative to Ni alone, with only a slight reduction in higher alcohol selectivity. Results of catalyst characterization, a simple kinetic model, and experiments with reaction intermediates support the initial dehydrogenation of ethanol as the rate-limiting step of the condensed-phase reaction.