The chemical state of copper during methanol synthesis: Reply to Chinchen and Waugh

Abstract

X-ray diffraction (XRD), temperature-programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS) were employed to investigate the dispersion of copper oxide in CuO/TiO2 samples prepared by one and double-step impregnations and the NO + CO activities of CuO/TiO2 samples were also tested. The results indicate that the dispersion capacity of copper oxide in CuO/TiO2 samples with one-step impregnation and double impregnations are about 0.52 and 0.98 mmol/100 m2 TiO2, respectively, which should be related to the shielding effect of accompanying NO3− anions during the impregnations. Therefore, the dispersion capacity of copper oxide on anatase with double impregnations could approach to 1.16 mmol/100 m2 TiO2, i.e. a value corresponding to the density of vacant sites on the (0 0 1) surface of TiO2. The NO + CO activities of CuO/TiO2 samples suggest that dispersed copper oxide species in these catalysts is the mainly active species and the increasing amount of dispersed copper oxide would enhance their activities. It seems to suggest that, for the supported catalysts, double or multiple impregnations would result in better activity than those prepared by one-step impregnation. In addition, the coordination environment of the dispersed copper oxide species existed on the anatase surface has been discussed by the incorporation model [Y. Chen, L.F. Zhang, Catal. Lett. 12 (1992) 51].