Insight into the preference mechanism for CC chain formation of C2 oxygenates and the effect of promoters in syngas conversion over Cu-based catalysts

• CH2 coupling to C2H4 is a spontaneous reaction on Cu(2 1 1) in syngas conversion.
• Cu catalyst favors hydrocarbons formation rather than C2 oxygenates.
• M-doped Cu(2 1 1) (M = Rh, Ni) shows a better catalytic activity to C2 oxygenates.
• C2 oxygenates is formed via CHO insertion into CH2 on M-doped Cu(2 1 1) (M = Rh, Ni).
• The HOMO–LUMO gap is responsible for the difference between CO and CHO insertion.

Cu-based catalysts are often used for the production of C2 oxygenates or hydrocarbons from syngas, although numerous studies have been reported, the exact mechanism remains in debate, and presents a major challenge in catalysis. In this study, the preference mechanism for CC chain formation of C2 oxygenates and the role of promoters in syngas conversion on Cu(2 1 1) and metal-doped MCu(2 1 1) (M = Rh, Ni) surfaces, including CHx (x = 1–3) hydrogenation, dissociation and coupling, as well as CO or CHO insertion into CHx (x = 1–3), have been systematically investigated by using density functional theory method. Our results show that pure Cu(2 1 1) surface shows a better catalytic activity to C2H4 formation rather than C2 oxygenates. However, promoters Rh and Ni-doped Cu(2 1 1) surfaces show a better activity and selectivity to C2 oxygenates rather than hydrocarbons, in which CH2 species is responsible for C2 oxygenates formation by CHO insertion. In addition, the difference between CO and CHO insertion into CHx (x = 1–3) to form C2 oxygenates is mainly attributed to the HOMO–LUMO gap of CHxCHO and CHxCO, the smaller HOMO–LUMO gap greatly facilitates the charge transfer and hybridization between adsorbed species and catalysts.

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