Mechanistic Insight into the C2 Hydrocarbons Formation from Syngas on fcc-Co(111) Surface: A DFT Study

Abstract

A comprehensive density functional theory (DFT) calculation of C2 hydrocarbons formation in Fischer–Tropsch synthesis (FTS) on the close-packed fcc-Co(111) surface has been carried out. The activation barriers and reaction energies for CO dissociation, CHx hydrogenation, CHx + CHy coupling and C(HO) insertion into CHx, CHxCHy–O bond scission, and successive hydrogenation reactions involved in C2 hydrocarbons formation have been examined, and the following conclusions could be concluded: (i) CH is the dominant monomer, which is formed via CO + H → CHO → CH + O; (ii) CHO insertion is more plausible for C–C chain formation compared with CO insertion and CHx–CHy coupling. The rate-determining steps for C2 hydrocarbons are CO + H → CHO and CHCH + H → CH2CH. Meanwhile, CH3 hydrogenation to form CH4 is more facile than C2 hydrocarbons, which will lead to the low productivity and selectivity to C2 hydrocarbons. (iii) Stepped-Co(111) surface has been modeled to clarify the role of defects during C2 hydrocarbons fo...