Ethanol Synthesis from Syngas on the Stepped Rh(211) Surface: Effect of Surface Structure and Composition

The mechanisms of ethanol synthesis from syngas including CHx (x = 13) species and C-2 oxygenates on the stepped Rh(211) surface have been systematically investigated by using density functional theory together with a periodic slab model. Our results show that among all CHx (x = 13) species, CH3 is the most favorable monomer, which is more favorable than CH3OH formation; this result is quite different from that on the flat Rh(111). Beginning with CH3 species, CH3 + CHO -> CH3CHO dominantly contributes to the formation of C-2 oxygenates; subsequently, CH3CHO is successively hydrogenated to ethanol via CH3CH2O intermediate. Meanwhile, CH4 formation by CH3 hydrogenation is energetically compatible with CH3CHO formation; that is, the productivity and selectivity of ethanol is determined by the formations of CH3CHO and CH4. As a result, the strategy of improving the Rh-based catalyst with the help from the promoter Mn is employed to tune the relative activity of CH3CHO and CH4 formations that control the productivity and selectivity of ethanol from syngas. Our results show that the productivity and selectivity of ethanol from syngas can be improved by introducing promoter Mn into the Rh catalyst.