In situ characterization of the vanadium silicalite catalyst (VS-2) and its photocatalytic reactivity

The in situ characterization of the vanadium silicalite catalyst (VS-2) and its photocatalytic reactivity have been investigated using dynamic photoluminescence, XAFS (XANES, EXAFS), ESR, FT-IR, UV-VIS, solid-state wide-line V-51-NMR and XRD techniques along with an analysis of the reaction products. Results obtained with the VS-2 catalyst showed that vanadium oxide moieties are present within the zeolite framework as a 4-fold tetrahedrally coordinated V oxide species having a terminal monoxovanadyl group (V=O). This VS-2 catalyst exhibited an absorption band at around 270-340 nm and an intense phosphorescence at around 450-550 nm with a vibrational fine structure and both are attributed to the charge-transfer processes. UV irradiation of the VS-2 catalyst in the presence of NO and cis-2-butene at 295 K led to the photocatalytic decomposition of NO to form N-2, O-2 and N2O while the photocatalytic isomerization of cis-2-butene produced 1-butene and trans-2-butene, respectively. Dynamic studies of the excited state of the catalyst and its photocatalytic reactions showed that the charge transfer excited state of the vanadium oxide species incorporated into the zeolite framework plays a vital role in these reactions.