Surface chemistry and catalytic performance of chromia/alumina catalysts derived from different potassium impregnation sequences

Chromia/alumina catalysts prepared with different K impregnation sequences were compared in the dehydrogenation of propane. The materials were characterized by a variety of techniques. The catalyst with K impregnated prior to Cr loading (sample Cr/K/Al2O3) exhibited higher propene selectivity than that prepared with the reverse impregnation sequence (sample K/Cr/Al2O3). Catalyst Cr/K/Al2O3 possesses a higher amount of surface acid sites and more readily reducible chromium species compared with catalyst K/Cr/Al2O3. The majority of chromium species were observed to exist as polymeric species on catalyst Cr/K/Al2O3, while isolated and oligomeric chromium species were mainly found on catalyst K/Cr/Al2O3. A detailed correlation between catalytic performance and characterization results demonstrated that isolated and oligomeric species possessed higher cracking and coking activities than polymeric chromium species, which may account for the difference in the propene selectivity of catalysts.