Propane Oxidative Dehydrogenation on BiP1-XVXO4 Supported Silica Catalysts

The molecularly dispersed BiP1-xVxO4/SiO2 supported oxides, with x varying from 0 to 1, were prepared by impregnation of Bismuth, Phosphorus, and Vanadium on silica. Their structures have been characterized by different techniques: X-ray diffraction, Raman spectroscopy, Temperature-Programmed Reduction of catalysts in H2 (H2-TPR), and methanol oxidation reaction. This very sensitive technique provided us with relevant information on the nature of the active sites (acid-base and redox) on the surface of the catalysts. The results of the characterization show the structural evolution of the vanadium species of the isolated crystallites from V2O5 for x =0.3 and x =0.5, to BiVO4, with the disappearance of BiPO4, with the increase of the vanadium content from x=0.5 to x = 1. The oxidation of methanol showed the basic properties of the BiPO4/SiO2 catalyst, by the formation of carbon dioxide as the major product of the reaction. The substitution of phosphorus with vanadium promotes the formation of formaldehyde, confirming the presence of redox sites on these substituted catalysts. These catalysts were examined in the Oxidative dehydrogenation (ODH) of propane. For x ≥ 0.5, the dispersed BiVO4 exhibited significant activity in propane ODH than the BiPO4 and V2O5 crystallites, with good selectivity to propylene and acrolein, consistent with their high reducibility confirmed by H2-TPR, and the presence of redox sites shown by the oxidation of methanol. The catalyst with x = 0 was less selective for propylene due to the favorable combustion of propylene during its formation. Such an understanding of the intrinsic catalytic properties of the BiP1-xVxO4/SiO2 oxides and in particular, the BiPO4 and BiVO4 crystallites provides new information on the structural requirements of the propane ODH reaction, beneficial for the design of more efficient Bi-P-V-O based catalysts for propylene and acrolein production.