TPR, ESR, AND XPS STUDY OF CU2-GEL-DERIVED TIO2( IONS IN SOL)

Fine titanium(IV) oxide amorphous powders containing two different amo unts of CuO were prepared by the sol-gel process. The samples were cry stallized to anatase by heating. The reduction of CuO-TiO2 samples was investigated by temperature-programmed reduction (TPR). Three types o f signals were detected: Two of them are strong and were assigned to t wo different types of copper ions distributed on the surface, The thir d kind was a weak broad signal and was ascribed to the simultaneous re duction of titanium and a third type of copper ion incorporated into t he TiO2 network. This was confirmed by electron spin resonance measure ments of the samples before and after programmed reductions at various temperatures selected from the TPR profiles. The results showed that the lowest reduction temperature is due to the existence of isolated c opper ions distributed on the surface. The second TPR peak was due to a CuO phase with small particle size. These results were consistent wi th X-ray photoelectron spectroscopy studies, which showed two signals assigned to-Cu-O-Ti-O- and CuO species. (C) 1998 Academic Press.