Identifying the active sites and their interaction mechanism in the CO catalytic combustion process over Co3O4

Co3O4 is one of the most promising catalysts for CO catalytic combustion. Nevertheless, the roles of Co2+ and Co3+ in the catalytic combustion process are still incompletely explored. Existing studies mostly focused on the role of Co3+, but the role of Co2+, and the interactions between the Co3+ and Co2+ are ignored. The catalytic activity of different Co sites is always affected by the electronic structure and the adsorption ability towards gas molecule, but clarifying the role of a single site is difficult due to the coexistence of Co2+ and Co3+. Herein, for exploring the role of single Co2+ or Co3+ site and their interaction, the Co2+ and Co3+ sites were replaced by Zn2+ and Al3+, respectively, which are more inert in CO catalytic combustion. According to catalytic activity measurement, the catalytic performance follows the order that: Co3O4(T-90 = 153 degrees C) > ZnCo2O4(T-90 = 189 degrees C) > CoAl2O4(T-90 = 292 degree celsius). The experimental and calculation results showed that both Co2+ and Co3+ could act as active sites for CO catalytic combustion. CO and O-2 are more prone to be absorbed over Co3+ and Co2+ sites, respectively. Co2+ and Co3+ make adsorbed oxygen and surface lattice oxygen highly reactive, respectively. The interaction between Co3+ and Co2+ is also important. The coexistence of Co2+ and Co3+ could increase the ratio of lattice oxygen and avoid the competitive adsorption between CO and O-2, thereby Co3O4 showed the excellent catalytic performance.