INSITU OBSERVATION OF OXIDATION AND REDUCTION OF SMALL SUPPORTED COPPER PARTICLES USING OPTICAL-ABSORPTION AND X-RAY-DIFFRACTION

Oxidation and reduction of small copper particles on supports has been studied at temperatures between 298 and 673 K, using in situ observation of optical absorption and X-ray diffraction. The change in chemical composition with time was traced by observing the change in optical absorption spectra at wavelengths between 300 and 800 nm and in X-ray diffraction peak intensity for Cu(111), Cu2O(111) and CuO(1BAR11) when the ambient gas was alternated between 5% H2/He and 1% O2/He. We found that the oxidation of small supported copper particles involves a fast reaction of Cu to CuO(x) (x approximately 0.67) with Cu2O structure and a slow reaction of CuO(x) (x approximately 0.67) to CuO(x) (x approximately 1). The activation energy of the CuO(x) (x approximately 0.67) to CuO(x) (x approximately 1) reaction is found to be 69 kJ/mol.