TiO2-CeO2 prepared by using pressurized and supercritical fluids: effect of processing parameters and cerium amount on (micro)structural and morphological properties
Abstract
Ce (x) Ti1-x O (n) composites with different Ti:Ce molar ratios (from 95:05 up to 70:30) were prepared unconventionally, via the sol-gel process controlled within reverse micelles of nonionic surfactant and processing by pressurized hot and supercritical fluids in a flow regime as an alternative to common thermal treatment. Nitrogen physisorption, powder X-ray diffraction (XRD) combined with Rietveld/whole powder pattern modeling (WPPM) and organic elemental analysis (OEA) were used as tools for characterization of the porous structure morphology, structural and microstructural properties, and purity of the prepared composites.
All prepared Ce (x) Ti1-x O (n) composites possessed well-developed mesoporous structure with minimum portion of micropores, showing specific surface area in the range of 203-256 m(2)/g. The experimental conditions during pressurized hot and supercritical processing as well as the Ce loading played a key role in crystallization of individual Ce (x) Ti1-x O (n) composites.
With increasing Ce loading, crystallization of anatase at the expense of brookite was promoted, accompanied with decreasing microstrain in anatase crystallites. The elevated processing temperature (250 A degrees C) led to crystallization of CeO2 cubic beside TiO2 anatase.
As a consequence of the different solubility of the used surfactant in pressurized hot and supercritical solvents under pressures of 10 and 30 MPa, cubic CeO2 crystallites of different sizes were formed. This property of CeO2 crystallites crucially affected the recrystallization of Ce0.30Ti0.70O (n) -S composites at elevated temperatures; small and uniform CeO2 crystallites stabilized the anatase-cerianite phase mixture, giving rise to minor brookite phase.