Synthesis and spectroscopic characterization of microporous VAPO-5

A microporous VAPO-5 catalyst; was prepared by hydrothermal synthesis starting from a vanadyl sulfate precursor. The sample shows the expected AFI phase, high crystallinity and high surface area, The homogeneous distribution of vanadium in the sample crystallites was checked by EDS. Nature and reactivity of the inserted vanadium ions were studied by spectroscopic analysis. UV-Vis mainly showed features related to monomeric species: two tetrahedral V5+ ions with different symmetry were, found in the oxidized sample, forming two distinct V4+ species upon reduction. These reduced ions were studied by FTIR, spectra, of adsorbed CO. showing that. they can form stable complexes at, low temperature. Two bands at 2192 and 2184 cm(-1) were assigned to two distinct V4+/CO adducts, based on their stability upon outgassing and on the fact that they both form after reduction at 673 K. The vanadium sites distribution looks more homogeneous with respect to literature reports, suggesting that, vanadyl sulfate is more effective than V2O5 as Metal source to obtain "single site" catalysts.