Effect of Crystalline Phases for VPO Catalysts on the Oxidation of Butane: Thermodynamics and Kinetics

Serial VPO catalysts with different compositions of crystalline phases were prepared at various activation temperatures. The characterization results revealed that the proportion of V5+ species, the acidity levels, and the surface P/V ratios of VPO catalysts showed an increasing tendency with activation temperature. The performances of n-butane oxidation for serial VPO catalysts were tested at different conditions. It was shown that the S-405 catalyst (activated at 405 degrees C) presented the highest conversion of n-butane (75.2%) at a GHSV of 1000 h(-1) and the highest selectivity for maleic anhydride (MA) (68.9%) at a GHSV of 1800 h(-1), which were attributed to S-405's high intensities at different crystalline faces, the highest amount of acidity (5.52 mL/g), the highest number of total removed oxygen atoms (2.88 x 10(21) atom g(-1)), and the best reducibility. In addition, the kinetic and thermodynamic analyses confirmed that the S-405 catalyst possessed the best activity and selectivity of n-butane oxidation, and the effects of Lat-O and Sur-O on the selectivity for MA were also disclosed.