Origin of Efficient Catalytic Combustion of Methane over Co₃O₄(110): Active Low-Coordination Lattice Oxygen and Cooperation of Multiple Active Sites 

A complete catalytic cycle for methane combustion on the Co₃O₄(110) surface was investigated and compared with that on the Co₃O₄(100) surface on the basis of first-principles calculations. It is found that the 2-fold coordinated lattice oxygen (O_2c) would be of vital importance for methane combustion over Co₃O₄ surfaces, especially for the first two C-H bond activations and the C-O bond coupling. It could explain the reason the Co₃O₄(110) surface significantly outperforms the Co₃O₄(100) surface without exposed O_2c for methane combustion. More importantly, it is found that the cooperation of homogeneous multiple sites for multiple elementary steps would be indispensable. It not only facilitates the hydrogen transfer between different sites for the swift formation of H₂O to effectively avoid the passivation of the active low-coordinated O_2c site but also stabilizes surface intermediates during the methane oxidation, optimizing the reaction channel. An understanding of this cooperation of multiple active sites not only might be beneficial in developing improved catalysts for methane combustion but also might shed light on one advantage of heterogeneous catalysts with multiple sites in comparison to single-site catalysts for catalytic activity.