Structural and spectroscopic characterisation of CeO2-TiO2 mixed oxides.

Mixed CeO2-TiO2 systems have been synthesized using the sol-gel technique in a symmetric range of nominal compositions (0.1, 0.5, 0.9 CeO2 molar fraction respectively). The solid materials have been 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, beside the two individual oxide phases, of a mixed phase of a cerium titanate (Ce2Ti2O7, pyrochlore structure) which contains Ce3+ ions imparting particular optical properties to the solid (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 in 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.