Discerning and modulating critical surface active sites for propane and CO oxidation over Co3O4 based catalyst

Identifying active sites is critical for rational catalyst design. We clarified the surface active sites for propane and CO oxidation over Co3O4-based catalysts using probe reactions of propane and CO oxidation, respectively. In comparison to Co3O4/ZSM-5, Co3O4/CeO2 has superior CO oxidation activity but inferior propane oxidation activity. CeO2 oxygen vacancies promote O2 activation, the rate-determined step (RSD) for CO oxidation, and avoid competitive adsorption of O2 and CO on Co3O4 species, resulting in superior CO oxidation activity on Co3O4/CeO2. Whereas the RSD for propane oxidation is synergistic catalysis of Co3O4 species and acid sites, Co3O4/ZSM-5 exhibits improved propane oxidation activity as a result of the abundant acid sites from ZSM-5. Due to a lack of oxygen vacancies for O2 activation, competitive adsorption of O2 with propane or CO on Co3O4 species is observed on Co3O4/ZSM-5. Furthermore, surface Co3+ species in Co3O4 are discovered to be active sites for both CO and propane activation. As a result of the increased surface Co3+ species, the pre-reduced and post-oxidized Co3O4 catalysts (Co3O4/ZSM-5-A and Co3O4/CeO2-A) exhibit improved activity for both propane and CO oxidation.