Mononuclear pseudo-tetrahedral V species of VSiBEA zeolite as the active sites of the selective oxidative dehydrogenation of propane

This work reports on the investigation of the influence of the nature of the V species in the ODH of propane. For this purpose, VSiBEA catalysts, including framework and/or extra-framework V species, were synthesized via the two-step method by controlling the speciation of the V species of the aqueous NH4VO3 solutions (via the pH of the corresponding solutions) to which the SiBEA zeolite was contacted with. The samples were characterized by N2 physisorption, XRD, FT-IR, 27Al, 29Si and 57V NMR, DR UV–vis and EPR. The TOF of the C3H8 ODH reaction of the samples exhibiting framework V species were found to be in good agreement with those reported in earlier works for which V species were highly dispersed on various silica supports and one order of magnitude higher than those of the samples exhibiting extra-framework V species, suggesting that isolated pseudo-tetrahedral framework V species would be the active sites of the C3H8 ODH catalytic reaction. EPR measurements of the spent catalysts indicated that these pseudo-tetrahedral framework V species were stable under the C3H8 ODH reaction conditions and were much more abundant in the V0.70SiBEA sample (for which incorporation of V in the SiBEA framework was targeted) than in the V1.00SiBEA sample (for which deposition of V occurred both in framework and extra-framework positions of SiBEA).