The CO oxidation performance of the Au/Co3O4 catalyst on the micro gas sensor device with different treatment conditions has been investigated. The CO oxidation performance of the Au/Co3O4 catalyst on the micro device has been improved by the H2 combustion treatment under the flow of H2 in air and the reduction treatment under the flow of H2 in N2. The H2 combustion treatment of the Au/Co3O4 catalyst on the micro device prevented the degradation of the CO oxidation performance. To investigate the chemical states and microstructures of Au and Co in the Au/Co3O 4 catalysts after the reduction and H2 combustion treatments, transmission X-ray absorption fine structure (XAFS) measurement and X-ray photoelectron spectroscopy (XPS) have been performed. Au particles of Au/Co3O4 were found to be metallic Au regardless of the treatment conditions. However, a hydroxyl group bonded to the transition metal Co as a form of Co(OH)2 was found on the catalyst surface after the H2 combustion treatment. The H2 combustion treatment of Au/Co3O4 results in the formation of OH- in the metal-support interface, which is considered to be an origin of the improvement of the CO oxidation performance of the Au/Co3O4 catalyst.
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