Mechanistic insights into the role of Co in the activity and stability of sulfide CoMo/Al2O3 catalysts for Water Gas Shift reaction

Cobalt promotion of Mo/Al 2 O 3 markedly enhances water‑gas shift (WGS) activity. This work elucidates the mechanistic origin of this promotional effect. Specifically, CO/IR technique provides the direct evidence of water-induced oxysulfide sites unable to be reduced by CO over CoMo/Al 2 O 3 catalyst, and thereby allowing us to exclude the conventional redox mechanism in which direct water dissociation is followed by CO reduction of the active site. Operando spectroscopy detects both formate and carbonyl sulfur intermediates, revealing that the reaction proceeds via coexisting formate and COS‑mediated redox pathways. Comparative experiments on unpromoted Mo/Al 2 O 3 and CoMo/Al 2 O 3 catalysts further show that the edge sites of the CoMoS phase are intrinsically more active toward COS formation. Moreover, the oxysulfide species formed in-situ by water can be completely restored to their original state by H 2 S treatment, implying that the presence of cobalt also improves the regenerability of the sulfide phase.