Mechanistic exploration of syngas conversion at the interface of graphene/Cu(111): identifying the effect of promoted electron transfer on the product selectivity

Abstract

Syngas conversion into ethanol is a promising pathway to obtain an attractive alternative fuel, but its selectivity is not ideal. Here, we used a combination of density functional theory calculations and microkinetic modeling to study the reaction mechanism of syngas conversion at the confined graphene/Cu(111) interface. It was found that the confinement using a 2D graphene cover promotes the formation of the key intermediate CH₃ through H-assisted CH₃O dissociation and the production of CH₄, but suppresses the formation of CH₃OH. Moreover, C₂H₅OH is the most competitive product with CH₄ through CHO insertion into the easily generated CH₃ species to complete the carbon chain growth. Detailed DOS and Bader charge results revealed that covering with 2D graphene promotes the electron transfer along the direction vertical to the Cu(111) surface, leads to the charge redistribution of the confined space, and eventually affects the product selectivity of syngas conversion. The corresponding degree of rate control analysis showed that the final hydrogenation step of CH₃ and CH₃CHOH limits the rate of the production of CH₄ and C₂H₅OH, respectively. Furthermore, the adsorbed hydroxyl is identified as the rate controlling intermediate. Our findings provide a useful guide for further modification of Cu-based catalysts for syngas to ethanol conversion.