Comparative analysis of the mechanism and selectivity of CO2 hydrogenation on undoped and Fe-doped Rh(111) surfaces.

CO2 hydrogenation can yield both CO and methane as products on the undoped Rh surface, while the addition of Fe can promote the formation of alcohols. Density functional theory (DFT) calculations were used to investigate the effect of the Fe promoter on the reaction mechanism of CO2 hydrogenation to single-carbon and ethanol products. We observe that the HCO species is a key intermediate on the Fe-doped Rh surface, involved in the favourable pathways towards all products. The presence of Fe has a promoting effect, facilitating the formation of HCO, with the Rh site promoting HCO coupling with CH2 species to produce ethanol via a bifunctional mechanism. Consequently, methane formation is suppressed owing to HCO coupling with CH2 competing against further hydrogenation of CH2 to methane. This article is part of the theme issue 'Surfaces, interfaces and heterogeneous catalysis'.