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 KCr Al-I1 with largest specific surface area of 198 m2 g-1prepared with aluminium isopropoxide(Al(i-OC3H7)3) by ultrasonic impregnation method. However, the catalyst KCr Al-I2 synthesized by stirring impregnation possessed crystalline α-Cr2O3 phase, which was poorly dispersed. Two types of Cr-rich and Al-rich Crx Al2-xO3 solid solutions, designated as Cr Al-I and Cr Al-II phase, were formed over the catalysts KCr Al-I3(prepared by Al(i-OC3H7)3with nitric acid regulation), KCr Al-C4(prepared by aluminium chloride hexahydrate) and KCr Al-N5(prepared by aluminium nitrate nonahydrate). Catalytic evaluation results revealed that KCr Al-I1 exhibited the high isobutane conversion due to its highly dispersed chromium species. However, KCr Al-I3, KCr Al-C4 and KCr Al-N5 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.