A facile and large-scale synthesis of Co3O4/N-doped graphene for CO oxidation: Low-temperature catalytic activity and the role of nitrogen states

Abstract Co3O4/N-doped graphene is synthesized with a one-pot and low-cost thermal decomposition in air. N-doped graphene improves their reductivity and their low-temperature catalytic performance of CO oxidation. After the treatment with dry reaction gases, the treated composites show the changed chemical structure of nitrogen species from N-(C)3 structure to C=N-C structure. After the treatment with wet reaction gases, nitrogen species on N-doped graphene are decomposed and the anchored sites of Co3O4 nanoparticles are converted into oxygenated groups. The nitrogen sites of N-(C)3 structure are beneficial to promote the reversible conversion between the reduced Co2+ ions and active Co3+ ions on Co3O4 nanoparticles at low temperature, but Co3+ ions can irreversibly be converted into the reduced Co2+ ions on Co3O4 nanoparticles anchored at the nitrogen sites of C=N-C structure and it is more difficult to reduce Co3O4 nanoparticles anchored at oxygenated groups from the converted nitrogen species. Since CO oxidation is promoted by the reversible conversion between Co2+ ions and Co3+ ions on Co3O4 nanoparticles, Co3O4/N-doped graphene has low-temperature catalytic activity, but the composites treated with dry reaction gases require higher temperature to show catalytic activity and the composites treated with wet reaction gases show lower catalytic performance.