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 H2/CO ratio would favor methane, the kinetic studies in the literature, and our results reported here, show that the point selectivity for ethanol (S=rEtOH/rCH4)(S=rEtOH/rCH4) actually increases with increasing H2/CO ratio on Rh-based catalysts. This may be attributed to the increased hydrogenation of the surface acetaldehyde intermediate to ethanol.