Characterization of the local structure of the vanadium silicalite (VS-2) catalyst and its photocatalytic reactivity for the decomposition of NO intoN-2 and O-2

The vanadium silicalite (VS-2) catalyst was hydrothermally synthesized, and a molecular level characterization was carried out by means of in situ pho toluminescence, XAFS, ESR, FT-IR, UV-vis, solid-state wide-line V-51 NMR, a nd XRD in the presence or absence of reactant molecules. These spectroscopi c investigations of the VS-2 catalyst clearly show that the vanadium oxide moieties are incorporated within the zeolite framework as tetrahedrally coo rdinated vanadium oxide species having a terminal vanadyl group (V=O) with a bond distance of 1.64 Angstrom and three V-O bonds with a bond distance o f 1.73 Angstrom. VS-2 catalyst also exhibits a charge-transfer absorption b and at around 270-340 nm and an intense phosphorescence spectrum as a radia tive decay from the charge-transfer excited triplet state at around 450-550 nm with a vibrational fine structure at 77 K, UV irradiation of the cataly st in the presence of NO was found to lead to the efficient photocatalytic decomposition of NO into N-2 and O-2 at 295 K. Dynamic studies of the phosp horescence in the presence of NO clearly indicate that the charge-transfer excited triplet state of the terahedrally coordinated vanadium oxide specie s plays a vital role in the photocatalytic decomposition of NO into N-2 and O-2. The results Obtained by these spectroscopic measurements and photocat alytic reactions provide important information on the local structure of th e vanadium oxide moieties incorporated within the zeolite framework and on the photocatalytic reactivity of the charge-transfer excited triplet state of the vanadium oxide species at the molecular level.