CO hydrogenation on M1/W6S8 (M = Co and Ni) single-atom catalysts: Competition between C2 hydrocarbons and methanol synthesis pathways

Abstract

Comprehensive density functional theory (DFT) calculation of methanol synthesis and C2 hydrocarbons formation in Fischer-Tropsch synthesis (FTS) on M1/W6S8 (M = Co and Ni) Single-Atom Catalysts have been carried out. The activation barriers and reaction energies for CO dissociation, CHx hydrogenation, CHx + CHy coupling and C(HO) insertion into CHx, and CHxCHy-O bond scission involved in C2 hydrocarbons formation have been examined. Methanol production (CO* + 4H* → CHO* + 3H* → CH2O* + 3H* → CH3O*+ H* → CH3OH*) is highly favored by Ni1/W6S8 catalysts. In contrast, Co1/W6S8 catalysts strongly favor C2 hydrocarbons production. The rate constant of the step for the subsequent transformation of CH3O* species on the Co1/W6S8 and Ni1/W6S8 was determined with the harmonic transition state theory (TST). The results of rate constant are in line with our kinetic results. Simultaneously, we use the d-band center to prove the correctness of the previous steps, the d-band center value of Co1/W6S8 is closer to EF than that of Ni1/W6S8; the result indicates that the catalytic activity of Co1/W6S8 is the best. The present study provides the basis to understand and develop novel M1/W6S8 (M = Co and Ni) single-atom catalysts for C2 hydrocarbons and methanol synthesis.