Cu-based catalysts are often used for the production of C-2 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 C-C chain formation of C-2 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 C-2 oxygenates. However, promoters Rh and Ni-doped Cu(2 1 1) surfaces show a better activity and selectivity to C-2 oxygenates rather than hydrocarbons, in which CH2 species is responsible for C-2 oxygenates formation by CHO insertion. In addition, the difference between CO and CHO insertion into CHx (x= 1-3) to form C-2 oxygenates is mainly attributed to the HOMO-LUMO gap of CHx-CHO and CHx-CO, the smaller HOMO-LUMO gap greatly facilitates the charge transfer and hybridization between adsorbed species and catalysts. (C) 2013 Elsevier B.V. All rights reserved.