Search

Two samples of TiO2/Cr2O3 composites are synthesized in the form of spherical grains via the stagewise thermal treatment of ion-exchange resins preliminarily saturated with chromium Cr3+ cations and dichromate anions, and then coated with a film-forming titania-based solution. Calcination temperature regimes are set on the basis of a thermal analysis and determined by the type of ion-exchange resin selected as a template. The synthesized composites are generally composed of the α-Cr2O3 phase, and the content of the TiO2 phase is less than 4%. The composites replicate the spherical shape of grains for the initial ion-exchange resins with sizes of 370 to 660 µm. The grains of the sample based on kaolinite adsorbing Cr3+ ions have a porous structure with bulbs and cavities. The anion-exchange resin-based sample grains have kinks and cracks over their surfaces due to a nonuniform distribution of adsorbed anions in the initial anion-exchange resin. The composites exhibit catalytic activity in the deep p-xylene oxidation reaction. The cation-exchange resin-based sample is more active, due apparently to the smaller accessible titania surfaces in the anion-exchange resin-based sample as a result of the formation of a solid Ti3+ solution in α-Cr2O3. [ABSTRACT FROM AUTHOR]

A method for the preparation of a SiO2–TiO2/Cr2O3(840) porous composite material in a block form with walls made of a silicate matrix and the interconnected channels of the matrix containing TiO2/Cr2O3(840) spherical hollow oxide composites was proposed. The specific surface area (Ssp) of the block composites was 212.2 m2/g, which is 20 times greater than the value of Ssp for spherical composites not fixed in the silicon(IV) oxide matrix. The composition of the TiO2/Cr2O3(840) and SiO2–TiO2/Cr2O3(840) samples was studied by X-ray diffractometry and X-ray microanalysis, which indicated the presence of chromium(III) oxide, titanium(IV) oxide, and an amorphous silicon(IV) oxide phase in the latter. The SiO2–TiO2/Cr2O3(840) block composite material exhibited catalytic activity in the deep oxidation reaction of para-xylene: a 100% conversion of the organic substance was achieved at a temperature of 350°C. [ABSTRACT FROM AUTHOR]