PREPARATION AND CHARACTERIZATION OF BIMETALLIC OXIDES OF CHROMIUM AND TITANIUM

Mixed oxides of Cr(III) and Ti(IV) were prepared by the hydrothermal method in basic solutions (pH > 12). With NaOH as base, the resultant materials had a layered structure. After exchange with NH4+ ions and calcination at 623 K, the layered structure was converted to the anatase phase. When the calcination temperature was raised to 723 K and higher, a portion of the anatase phase was converted to the rutile phase for samples of high Cr(III) content. The latter also contained a small amount of Cr2O3 structure. When the 2-propanol decomposition reaction was carried out, the mixed oxides demonstrated both acidic and basic sites on the surfaces. Furthermore, both Brønsted and Lewis acid sites were found on the surface of the bimetallic oxides, based on IR spectra of the adsorbed pyridine. The Brønsted acid sites were identified as CrOH groups. When the bimetallic oxides were used as catalysts in oxidative dehydrogenation of ethane, activity was found to be a function of Cr content. The CrO species were proposed to be the active sites for formation of both ethylene and CO2. Titanium served as a diluent. © 1990.