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 (CO(2)) by molecular oxygen on the Co(3)O(4)(110) surface was obtained by density functional theory plus the on-site Coulomb repulsion (DFT + U). Previously observed high activity of Co(3)O(4) to catalytically oxidize CO at very low temperatures is explained by a unique twofold-coordinate oxygen site on Co(3)O(4)(110). The CO molecule extracts this oxygen with a computed barrier of 27 kJ/mol. The extraction leads to CO(2) formation and an oxygen vacancy on Co(3)O(4)(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 Co(3)O(4)(110) has a higher barrier. Our work furnishes a molecular-level mechanism of Co(3)O(4)'s catalytic power, which may help understand previous experimental results and oxidation catalysis by transition metal oxides.
Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA. jiangd@ornl.gov
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