Ca-doped chromium oxide catalysts supported on alumina for the oxidative dehydrogenation of isobutane

The oxidative dehydrogenation (ODH) of isobutane has been investigated on Ca-doped chromium oxide catalysts supported on ?-Al2O3. The effect of Ca loading on the micro-structural properties of chromia catalysts was investigated by chemical analysis, X-ray diffraction (XRD), scanning electron microscopy with elemental mapping (SEM-EDX), UV-Vis diffuse reflectance spectroscopy (DRS), temperature programmed reduction (TPR), and micro-calorimetry of adsorbed NH3. Cr3+ and Cr6+ species dispersed on alumina, as well as ?-Cr2O3 and CaCrO4 crystallites, were found on the catalysts surface. The relative amount of the chromium species depends on the Ca loading. The Cr3+/Cr6+ ratio decreases on increasing the Ca loading due to the preferred formation of bulk chromate species. The Ca loading affects the reducibility of the Cr6+ species and the acid sites strength distribution of the catalysts. ... ... ...