Abstract: The local structures of monolayer dispersive CuO/γ-Al2O3 catalysts prepared by means of impregnation have been investigated by XAFS technique.For the CuO/γ-Al2O3 sample with CuO loading 0.4 mmol/100 m2 lower than the monolayer dispersion threshold,the XAFS results indicate that only the first coordination shell appears in the radial distribution function of Cu atoms,and that the RCu－O and coordination number in the first shell are 0.195 nm and 4,respectively.Hence,we consider that the CuO active species on the surface of γ-Al2O3 are in the form of isolated atomic cluster ().Small amount of CuO nano-grains is formed onto the surface of γ-Al2O3 while the CuO loading is just equal to the threshold 0.8 mmol/100 m2.For sample with CuO loading of 1.2 mmol/100 m2,the local structure of Cu atom in CuO/γ-Al2O3 is similar to that of CuO powder.On the basis of the XAFS results,a monolayer dispersion model of CuO/γ-Al2O3 catalysts has been proposed.

Key words: Monolayer dispersion, CuO, XAFS(X-ray adsorption fine structure)