Effect of H2/CO ratio and temperature on methane selectivity in the synthesis of ethanol on Rh-based catalysts

The hydrogenation of CO to form ethanol is thermodynamically limited if methane is allowed as a reaction product. The literature confirms this - selectivity to ethanol versus methane is limited even on Rh-based catalysts, which are the most selective for ethanol. Although it might be anticipated that increasing H-2/CO ratio would favor methane, the kinetic studies in the literature. and our results reported here, show that the point selectivity for ethanol (S = r(EtoH)/r(CH4)) actually increases with increasing H-2/CO ratio on Rh-based catalysts. This may be attributed to the increased hydrogenation of the surface acetaldehyde intermediate to ethanol. (C) 2008 Elsevier B.V. All rights reserved.