The role of low-coordinate oxygen on Co3O4(110) in catalytic CO oxidation

A complete catalytic cycle for carbon monoxide (CO) oxidation to carbon dioxide (CO2) by molecular oxygen on the Co3O4(110) surface was obtained by density functional theory plus the on-site Coulomb repulsion (DFT + U). Previously observed high activity of Co3O4 to catalytically oxidize CO at very low temperatures is explained by a unique twofold-coordinate oxygen site on Co3O4(110). The CO molecule extracts this oxygen with a computed barrier of 27 kJ/mol. The extraction leads to CO2 formation and an oxygen vacancy on Co3O4(110). Then, the O-2 molecule dissociates without a barrier between two neighboring oxygen vacancies (which are shown to have high surface mobility), thereby replenishing the twofold-coordinate oxygen sites on the surface and enabling the catalytic cycle. In contrast, extracting the threefold-coordinate oxygen site on Co3O4(110) has a higher barrier. Our work furnishes a molecular-level mechanism of Co3O4's catalytic power, which may help understand previous experimental results and oxidation catalysis by transition metal oxides.