Abstract
Chromium dioxide, CrO2, supported on titania was prepared by impregnation of the carrier with chromium(III) nitrate (10 wt% Cr2O3 on TiO2) followed by its thermal decomposition and calcination under oxygen at 573 K, X-ray amorphous CrO2 (ca, 95%) was found to be present after calcination. The chemical and structural changes of the supported CrO2 phase during thermal treatment in hydrogen, oxygen, air, argon, and ammonia, and under SCR conditions (selective catalytic reduction of NO by NH3 in excess oxygen) were investigated by thermoanalytical methods, (ferro)magnetic resonance, XRD, and UV-visible and IR spectroscopy. Supported CrO2 is reversibly reduced under hydrogen, producing antiferromagnetic CrOOH on titania. Reoxidation to CrO2 occurs at temperatures above 520 K in air, under oxygen, and under SCR conditions (NO + NH3 + O2) CrOOH and CrO2 were decomposed at T ≍ 770 K under argon to antiferromagnetic Cr2O3; the decomposition is complete only at T > 1000 K. The composition and thermal stability of the supported oxides are compared to the corresponding bulk phases CrOx.
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