On the Role of a Cobalt Promoter in a Water-Gas-Shift Reaction on Co-MoS2

The role of a Co promoter in a water-gas-shift reaction on Co-MoS2 has been investigated on the basis of density functional theory computation. On the basis of the computed adsorption energy of the reaction intermediates and H2O dissociation barriers, the active catalyst is the Mo edge with 25% Co substitution and 25% sulfur coverage, while the S edge with 25% Co substitution and 50% sulfur coverage is not active. On the basis of the computed reaction barriers, the redox mechanism (CO + H2O → CO + O + 2H; CO + O + 2H → CO2 + H2) is the preferable reaction path, and the rate-determining step is the second step dissociation of OH into surface O and H, while the reaction path from carboxy (CO + OH → COOH; COOH → CO2 + H) is not favored due to its high dissociation barrier. In addition, formate (HCOO) is a side product from gas phase CO2 and surface H and does not participate directly in the reaction mechanism. Detailed comparisons reveal that the Co promoter is not an active center in H2O dissociation and CO oxidation but changes the adsorption configuration of the reaction intermediates and reduces the reaction barriers. The Co promoter plays the role of a textual promoter in creating more active sites and accelerating the reaction rate.