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

Abstract

The reactivity of isobutane dehydrogenation over a series of non-ordered mesoporous chromia/alumina (Cr2O3/Al2O3) catalysts with large specific surface area (149.4–381.6m2g−1) and high pore volume (0.77–1.24cm3g−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 10wt.%. 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 (5–25wt.%) and calcination temperature (500–900°C), respectively. The addition of potassium to the catalyst system greatly promoted isobutene selectivity and catalyst stability. The catalyst with 1.5wt.% K2O and 10wt.% Cr2O3 loadings calcined at 800°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.