C2 oxygenates formation from syngas over the promoter M(M = Rh, Co) monolayer-modified Cu(111) surface: Probing into the role of monolayer promoter on the selectivity

Abstract

Abstract The promoter metal monolayer deposited over other metal substrate exhibits excellent catalytic performance, in this study, the mechanism of syngas conversion to C2 oxygenates over the promoter M(M = Rh, Co) monolayer-modified Cu catalysts have been systematically investigated to identify the role of monolayer promoter M and its effect on the selectivity using density functional theory calculations. Here, two key steps are examined, including the formation of key CHx intermediates and the C C bond formation of C2 oxygenates. The results show that compared to the pure Cu catalyst, the promoter Co monolayer-modified Cu catalyst exhibits higher selectivity towards CHx(x = 1–3) formation instead of methanol, the most favored CHx monomer is CH2; whereas CHx(x = 1,2) is the most favored CHx monomer on the promoter Rh monolayer-modified Cu(111), which is competitive with methanol formation. The favored CHx monomer originates from the C O bond cleavage of CHxO(x = 1,2) and CHxOH(x = 1,2) species formed by CO hydrogenation. Starting from the favored CHx monomer, compared to the pure Cu catalyst, C2 oxygenates formed by CHO insertion into CHx is the most favorable over the promoter Rh and Co monolayer-modified Cu catalysts. In general, the promoter Co monolayer-modified Cu catalyst exhibits higher selectivity towards syngas conversion to C2 oxygenates than the promoter Rh monolayer-modified Cu, as well as the pure Cu, Rh and Co catalysts, the reasons is attributed to that the d-band center of Co monolayer-modified Cu is the closest to Fermi level leading to the enhancement of adsorption capacity of the intermediates, and promoting the C O bond activation as well as reducing the repulsion interaction between CHx and CHO to facilitate the formation of C2 oxygenates. The present study provides useful information for the design of highly efficient catalysts with the metal promoter monolayer-modified metal substrate in syngas conversion to C2 oxygenates.