Abstract
The catalytic activity of vanadium−phosphorus oxide (VPO) catalysts for the oxidative dehydrogenation of propane is analyzed. Two series of catalysts were synthesized in an organic medium with P/V molar ratios of 0.9 and 1.1. These materials were characterized by X-ray diffraction, N2 physisorption, NH3 adsorption microcalorimetry, decomposition of 2-propanol, and redox titration. The crystalline phase (VO)2P2O7, with a tetravalent vanadium oxidation state, was observed in all the catalysts. As a result of thermal treatment, their crystal size increased, which suggests more crystallinity, and a slight increment in the surface area (31−39 m2/g) also was observed. The microcalorimetry studies of the vanadium phosphates showed heats of adsorption for NH3 between 260 and 60 kJ/mol that can be associated with strong and medium strength acid sites, which are responsible for promoting the selectivity toward oxygenated products and COx; furthermore, it was found that larger crystallographic disorder favors the selectivity to propylene up to an 8.82% over a VPO that has been calcined at 673 K and has a P/V molar ratio of 1.1.
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