Correlation between the Oxidation State of Copper and the Photocatalytic Activity of Cu/Nb2O5

A structural analysis of the reduction oxidation process of copper loaded on Cu/Nb2O5 has been performed using Cu K-edge XAFS spectroscopy to reveal the correlation between the oxidation state of copper and the catalytic activity of alcohol photooxidation. On the basis of the simulation of the XANES spectra of Cu/Nb2O5, the superposition of Cu metal (Cu(0)), Cu2O (Cu(I)), and CuO (Cu(II)) is observed, and, furthermore, the concentration of these three phases was evaluated. XANES and EXAFS analyses revealed the following reduction-oxidation process. Cu metal particles with a diameter of approximately 4 nm were formed after reductions at 673 K. Cu2O and CuO phases were formed in the surface layers at low oxidation temperature. The process of formation was followed by phase growth both in the surface layers and in the bulk Cu particle with increasing oxidation temperature. The change in photocatalytic activity well correlated with the fraction of Cu2O (Cu(I)).