Single-crystalline mesoporous CaO supported Cr–V binary oxides: Highly active catalysts for the oxidative dehydrogenation of isobutane

The three-dimensional mesoporous calcium oxide (meso-CaO) supported chromium–vanadium binary oxide catalysts yCrOx/10 wt.% VOx/meso-CaO (i.e., yCr/10V/meso-CaO, y = 0–4 wt.%; the VOx and CrOx weight percentages referred to the mass contents of V2O5 and Cr2O3 in the catalysts, respectively) were prepared via an incipient wetness impregnation route and characterized by means of XRD, BET, SEM, TEM/SAED (selected-area electron diffraction), Raman, and H2-TPR (temperature-programmed reduction) techniques. The catalytic performance of the materials was evaluated for the oxidative dehydrogenation (ODH) of isobutane. It is found that the meso-CaO and yCr/10V/meso-CaO displayed wormhole-like mesoporous structures, VOx and/or CrOx were highly dispersed in the form of mono- and polyvanadate or polychromate on the surface of the meso-CaO support. The H2-TPR results indicate that 2Cr/10V/meso-CaO exhibited the best low-temperature reducibility among the as-prepared catalysts. Under the conditions of isobutane/oxygen molar ratio = 1/2, space velocity = 30,000 mL/(g h), and temperature = 540 °C, a maximal C4-olefins yield of 15% with the corresponding C4-olefins selectivity of 79% was achieved over the 2Cr/10V/meso-CaO catalyst. It is concluded that the good dispersion of CrOx and VOx domains and low-temperature reducibility of the catalyst as well as the strong basicity and three-dimensional wormhole-like mesoporosity of the CaO support were responsible for the excellent catalytic performance of 2Cr/10V/meso-CaO for the ODH of isobutane.