ANATASE CRYSTAL-GROWTH AND PHASE-TRANSFORMATION TO RUTILE IN HIGH-AREA TIO2, MOO3-TIO2 AND OTHER TIO2-SUPPORTED OXIDE CATALYTIC-SYSTEMS

Anatase-to-rutile phase transition has been studied on high-area TiO2-anatase and bicomponent systems containing molybdena and, for comparison, cobalt oxide, copper oxide, vanadia and corresponding TiO2-rutile based systems, using TG-DTA, XRD and surface-area measurements. These materials were prepared by impregnation and (co)precipitation methods. Conversion to rutile and crystal size growth strongly depend on the minority phase oxide. It is found that, while Cu and V oxides speed up both phase transition and particle sintering, Mo and Co oxides inhibit them. Moreover, the rutile particles obtained by phase transition are always much larger than both the starting and residual anatase particles. A mechanism of rutile formation by coalescence and phase transformation of anatase particles is proposed.