Interfacial and Surface Structures of CeO₂−TiO₂ Mixed Oxides

Abstract

The interfacial and surface structures of CeO2−TiO2 mixed oxides prepared by the sol−gel method have been investigated in detail by means of X-ray diffraction (XRD), BET surface area measurement, X-ray absorption spectroscopy (XAS), high-resolution transmission electron microscope (HRTEM), and selective chemisorption of methyl orange. TiO2 and CeO2 are in the anatase phase and the cubic fluorite phase in CeO2−TiO2 mixed oxides, respectively. The mixed oxides exhibit much higher surface areas than the individual oxides and are with both mesopores and micropores. XAS results suggest that Ce atoms nucleate as cubic [CeO8] polyhedrons with the formation of a Ce−O−Ti interface in mixed oxides. With the increasing Ce/TiO2 weight ratio, the cubic fluorite CeO2 crystallites gradually develop. TiO2 anatase forms ultrafine particles in mixed oxides, whose local structure is stabilized by the presence of CeO2. HRTEM results reveal that the exposed surfaces of mixed oxides depend on the Ce concentration. Chemisorption results of methyl orange that was found to adsorb profoundly on CeO2 but little on TiO2 demonstrate that CeO2 in mixed oxides exhibits much lower adsorption capacity toward methyl orange than pure CeO2. Our results demonstrate an approach to characterize interfacial and surface structures of complex mixed oxides, which are of great importance in understanding their properties.