In situ observation of oxidation and reduction of small supported copper particles using optical absorption and X-ray diffraction

Abstract

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), Cu 2O(111) and CuO(1̄11) when the ambient gas was alternated between 5% H 2/He and 1% O 2/He. We found that the oxidation of small supported copper particles involves a fast reaction of Cu to CuO x ( x ~ 0.67) with Cu 2O structure and a slow reaction of CuO x ( x ~ 0.67) to CuO x ( x ~ 1). The activation energy of the CuO x ( x ~ 0.67) to CuO x ( x ~ 1) reaction is found to b