Structural and spectroscopic characterization of CeO2–TiO2 mixed oxides

Abstract

Mixed CeO₂–TiO₂ systems have been synthesized using the sol–gel technique in a symmetric range of nominal compositions (10, 50 and 90 mol% CeO₂). The solid materials were characterised using a variety of diffractometric and spectroscopic techniques. The intimate contact between the two components during the synthesis leads to heterogeneous systems which are based on the presence, besides the two individual oxide phases, of a mixed phase of a cerium titanate (Ce₂Ti₂O₇, pyrochlore structure) which contains Ce³⁺ ions that impart particular optical properties to the solid (a pronounced red shift with respect to the band gap transition of the two oxides). Ce³⁺ ions are present at the surface of the systems together with tetravalent Ce and Ti ions. The mixed solids can be reduced by annealing under vacuum and, upon reoxidation under mild conditions with O₂, form superoxide species adsorbed on Ce⁴⁺ which have, as already reported for low loading CeO₂–TiO₂ systems, peculiar spectroscopic properties with respect to superoxide adsorbed on bare cerium dioxide.