Isobutane dehydrogenation over the mesoporous Cr2O3/Al2O3 catalysts synthesized from a metal-organic framework MIL-101

The reactivity of isobutane dehydrogenation over a series of non-ordered mesoporous chromia/alumina (Cr2O3/Al2O3) catalysts with large specific surface area (149.4-381.6 m(2) g(-1)) and high pore volume (0.77-1.24 cm(3) g(-1)), synthesized using a metal-organic framework MIL-101 as a molecular host and chromium precursor, aluminium isopropoxide (Al(i-OC3H7)(3)) as the aluminium precursor, were studied in detail. The chromium species were highly dispersed over the catalyst with chromia loading up to 10 wt.%. The specific surface area of the catalyst decreased, whereas the amount of surface Cr3+ species and the mole ratio of Cr3+ and Cr6+ species (Cr3+/Cr6+) increased with the increasing chromia loadings (5-25 wt.%) and calcination temperature (500-900 degrees C), respectively. The addition of potassium to the catalyst system greatly promoted isobutene selectivity and catalyst stability. The catalyst with 1.5 wt.% K2O and 10 wt.% Cr2O3 loadings calcined at 800 degrees C was found to exhibit the highest isobutane conversion 60.1% with the isobutene selectivity up to 93.2% among all the catalysts. The maintainable catalytic reactivity demonstrated the high stability of the catalyst in ten dehydrogenation-regeneration cycles. Moreover, it was proposed that the Cr3+ species was mainly the active site and catalytic selectivity was depended on the surface Cr3+/Cr6+ value over the catalyst. The catalyst presented much more stable dehydrogenation activity compared with the conventional catalyst. Consequently, this study presents a feasible way to facile synthesis of the mesoporous MOF-derived Cr2O3/Al2O3 catalysts with high stability and good catalytic reactivity over isobutane dehydrogenation. (C) 2013 Elsevier B.V. All rights reserved.