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 KCrAI-I1 with largest specific surface area of 198 m2-g-1 prepared with aluminium isopropoxide （Al（i-OC3HT）3） by ultrasonic im- pregnation method. However, the catalyst KCrAI-I2 synthesized by stirring impregnation possessed crystalline a-Cr203 phase, which was poorly dispersed. Two types of Cr-rich and Al-rich CrzA12_zO3 solid solutions, designated as CrAI-I and CrAI-II phase, were formed over the catalysts KCrAI-I3 （prepared by Al（i-OC3HT）3 with nitric acid regulation）, KCrA1-C4 （prepared by aluminium chloride hexahydrate） and KCrA1-N5 （prepared by aluminium nitrate nonahydrate）. Catalytic evaluation results revealed that KCrAI-I1 exhibited the high isobutane con- version due to its highly dispersed chromium species. However, KCrAI-I3, KCrA1-C4 and KCrA1-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.     

The effect of encapsulated Zn-POM on the catalytic activity of MIL-101 in the oxidation of alkenes with hydrogen peroxide

Zinc monosubstituted Keggin heteropolyanion [PZnMo₂W₉O₃₉]^5? was electrostatically bound to nanocages of MIL-101 polymer matrix. The Zn-POM@MIL-101 catalyst was characterized by XRD, N₂ adsorption, atomic absorption (AAS), and FT-IR spectroscopic methods. The catalytic activity of the new composite material, Zn-POM@MIL-101, was assessed in the oxidation of alkenes using aqueous hydrogen peroxide as oxidant. Zn-POM@MIL-101/H₂O₂ catalytic system demonstrated good catalytic activity in the oxidation reactions. Zn-POM@MIL-101 was reusable for three catalytic cycles. While the MIL-101 matrix is an active catalyst in these oxidation reactions, the presence of Zn-POM significantly changed the selectivity and reaction times.