Abstract CrO x /SiO 2 catalysts were characterized and their activity in the dehydrogenation of i-butane was measured. Cr loading of the catalysts was between 1.1 and 11 wt% and preparation was by impregnation. The consumption of isolated OH groups of SiO 2 upon deposition of CrO x was followed by DRIFT-IR. The presence of unreacted OH groups in the calcined catalyst at high loadings of Cr and the formation of α-Cr 2O 3 (XRD) showed, however, the tendency of CrO x to form clusters rather than a well-dispersed phase on SiO 2. After calcination, 0.8–1.0 wt% Cr was stabilized in 6+ oxidation state (UV-VIS). On the basis of H 2-TPR measurements it was suggested that these Cr 6+ were stabilized by anchoring on SiO 2 or on the α-Cr 2O 3/SiO 2 formed with increasing Cr loading. The activities of the CrO x /SiO 2 catalysts were studied in the dehydrogenation of i-butane at 540°C by monitoring the product distributions with a rapid FT-IR gas analyzer. The dehydrogenation activity is attributed to redox Cr in 3+ and 2+ oxidation states and tentatively to part of the nonredox Cr 3+. The relatively low selectivity of CrO x /SiO 2 at low loadings of Cr was evidently due to the presence of Cr 2+ directly anchored to SiO 2.