Insight into the Surface-Tuned Activity and Cl2/HCl Selectivity in the Catalytic Oxidation of Vinyl Chloride over Co3O4(110) versus (001): A DFT Study

Abstract

Co3O4 has received tremendous attention in the oxidation of chlorinated volatile organic compounds (CVOCs) for its general catalytic oxidation ability. However, to rationally optimize the Co3O4-based catalysts, ascertaining the reaction mechanism and active-site-specific activity variation at the molecular level remains an open issue. Herein, we performed the first-principles calculations to systematically explore the catalytic oxidation process of vinyl chloride (VC) on two representative (110) and (001) surfaces of Co3O4. The reaction pathways of VC oxidation are thoroughly calculated, mainly consisting of three subprocesses, namely, the C–Cl bond scission, CH2CH oxidation, and the elimination of Cl species. Results show that the oxygen vacancy is indispensable to break the C–Cl bond on Co3O4(110), whereas the C–Cl bond cleavage can be achieved by the collaboration of two adjacent Co5c sites at a lower barrier on Co3O4(001). Both surfaces are reactive for the oxidation of the CH2CH group, indicative of the excellent oxidative ability of the Co3O4 catalyst. More importantly, we identify the rate-determining step in the overall VC oxidation as the elimination of Cl species, and HCl is the preferential chlorine-containing product rather than Cl2. In comparison with Co3O4(110), the Co3O4(001) surface gives a lower energy barrier for Cl elimination and indicates its potentially superior performance for VC oxidation. Finally, some propositions are made for how to improve the VC oxidation on Co3O4 catalysts. These fundamental insights identified in this work may provide a theoretical basis for the design and synthesis of Co3O4-based catalysts in CVOC oxidation.