SOLID-STATE AND SURFACE-CHEMISTRY OF CUO-TIO2 (ANATASE) POWDERS

CuO-TiO2 samples have been prepared by impregnation of two different p reformed TiO2 supports with copper nitrate, and have been characterize d by X-ray diffraction (XRD), thermogravimetry-differential thermal an alysis (TG-DTA), Fourier-transform infrared (FTIR), Fourier-transform far-infrared (FT-FIR) and ultraviolet-visible (UV-VIS) spectroscopies. The surface properties have been investigated through surface area an d porosity measurements, and FTIR spectra of surface OH groups and of adsorbed carbon monoxide at low temperature. The surface is thought to consist of complexes of Cu2+ and Cu+, involving surface Ti-O groups o f the support as the ligands. These complexes can be reduced by CO und er very mild conditions with the appearance of small Cu metal clusters . Ti4+ centres are also in part exposed on the surface, but their elec tron-withdrawing effect is weakened by the surface copper complexes. S urface copper ions act as electron-donor centres, giving rise to absor ption over in the entire visible range, with a parallel weakening of t he TiO2 absorption edge. Surface copper complexes have a pronounced ac celerating effect on the anatase-to-rutile phase transition. A paralle lism between the CuO-TiO2 and the V2O5-TiO2 systems is proposed.