Cr2O3 is a major component in commercial supported CrOx/alumina catalysts for commercial C3-C4 dehydrogenation uses. The study investigates the nature, activity, and stability of chromium (Cr) species on un-supported Cr2O3 catalysts for isobutane dehydrogenation using a combined analytic technique. The findings reveal that Cr species identified include predominant Cr3+ on α-Cr2O3, Cr3+ on amorphous Cr2O3, and small amounts of CrO3 on Cr2O3 surface. Cr3+ species (both crystalline and amorphous) are the predominant active sites. Reduction treatment at 600°C significantly decreased Cr6+ content from 1000 ppm to 30 ppm while preserving Cr3+, resulting in improved catalyst performance. The reduction treatment primarily affected the CrO3 species while maintaining the Cr3+ species in both crystalline and amorphous forms. Reduced Cr2O3 showed higher relative activity and isobutylene selectivity compared to the fresh sample. Aging tests suggested that Cr3+ species are both more active and stable than Cr6+, providing insights relevant to industrial CrOx/alumina catalyst development.
