A theoretical and experimental XAS study of monolayer dispersive supported CuO/γ-Al2O3 catalysts

The local structures of supported CuO/γ-Al2O3 monolayer dispersive catalysts with different CuO loadings have been investigated by EXAFS and multiple scattering XANES simulations. The EXAFS results show that the first nearest neighbors around the Cu atoms in the CuO/γ-Al2O3 catalysts are similar to that of the polycrystalline CuO powder, which is independent of the CuO loadings. Moreover, the Cu K-XANES FEFF8 calculations for CuO reveal that the monolayer-dispersed CuO species are of small distorted (CuO4)mn+ clusters, which is mainly composed of a distorted CuO6 octahedron incorporated in the surface octahedral vacant sites of the γ-Al2O3 support. We consider that the CuO species for the CuO/γ-Al2O3 catalysts with loadings of 0.4 and 0.8 mmol/100 m2 are distorted (CuO4)mn+ clusters composed mainly of a distorted CuO6 octahedron incorporated in the surface octahedral vacant sites of the γ-Al2O3 support after calcinations at high temperature in air for a few hours. On the contrary, for the CuO/γ-Al2O3 with loading of 1.2 mmol/100 m2, the local structure of Cu atoms in CuO/γ-Al2O3 is similar to that of polycrystalline CuO powder.