A First Principles Mechanistic Study of Higher Alcohol Synthesis from Syngas on a Stepped Rhodium Surface.

The mechanism of higher alcohol synthesis (HAS) from syngas on a stepped Rhodium surface was explored using first principles calculations based on density functional theory. Results showed that the activation of CO proceeds most energetically feasible via a sequential hydrogenation towards CH2OH, followed by the C–OH bond cleavage yielding CHx species. Because the initial CO hydrogenation step is highly activated, the cascade of elementary steps toward methane formation is highly favored. The formation of C2 oxygenates toward ethanol production is kinetically favored by CO insertion to CH2, or alternatively, by a lower activation barrier CHO insertion to CH3. On the other hand, the C3 species is formed more preferably by CO rather than CHO insertion to a CH3CH2 fragment, indicating the effect of a more extended carbon structure on the reaction mechanism. The overall reaction mechanism for HAS points to a cycle of CO insertion, hydrogenation, and OH elimination steps. [ABSTRACT FROM AUTHOR]