Isobutane dehydrogenation over chromia alumina catalysts prepared from MIL-101: Insight into chromium species on activity and selectivity

Various mesoporous chromia alumina catalysts were prepared by five different methods based on a metal-organic framework MIL-101 and their catalytic performances over isobutane dehydrogenation were investigated. The highly dispersed chromium species were produced on catalyst KCrAl-I-1 with largest specific surface area of 198 m(2).g(-1) prepared with aluminium isopropoxide (Al(i-OC3H7)(3)) by ultrasonic impregnation method. "However, the catalyst KCrAl-I-2 synthesized by stirring impregnation possessed crystalline alpha-Cr2O3 phase, which was poorly dispersed. Two types of Cr-rich and Al-rich CrxAl2-xO3 solid solutions, designated as CrAl-I and CrAl-II phase, were formed over the catalysts KCrAl-I-3 (prepared by Al(i-OC3H7)(3) with nitric acid regulation), KCrAl-C-4 (prepared by aluminium chloride hexahydrate) and KCrAl-N-5 (prepared by aluminium nitrate nonahydrate). Catalytic evaluation results revealed that KCrAl-I-1 exhibited the high isobutane conversion due to its highly dispersed chromium species. However, KCrAl-I-3, KCrAl-C-4 and KCrAl-N-5 showed the higher isobutene selectivity (95.2%-96.4%) on account of the formation of chromia alumina solid solutions in the catalysts. Moreover, the solid solution over the chromia alumina catalysts could greatly suppress the coke formation.