Characterization of the Local Structure of the Vanadium Silicalite (VS-2) Catalyst and Its Photocatalytic Reactivity for the Decomposition of NO into N₂ and O₂

The vanadium silicalite (VS-2) catalyst was hydrothermally synthesized, and a molecular level characterization was carried out by means of in situ photoluminescence, XAFS, ESR, FT-IR, UV−vis, solid-state wide-line ⁵¹V NMR, and XRD in the presence or absence of reactant molecules. These spectroscopic investigations of the VS-2 catalyst clearly show that the vanadium oxide moieties are incorporated within the zeolite framework as tetrahedrally coordinated vanadium oxide species having a terminal vanadyl group (VO) with a bond distance of 1.64 Å and three VO bonds with a bond distance of 1.73 Å. VS-2 catalyst also exhibits a charge-transfer absorption band at around 270−340 nm and an intense phosphorescence spectrum as a radiative 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 catalyst in the presence of NO was found to lead to the efficient photocatalytic decomposition of NO into N₂ and O₂ at 295 K. Dynamic studies of the phosphorescence in the presence of NO clearly indicate that the charge-transfer excited triplet state of the terahedrally coordinated vanadium oxide species plays a vital role in the photocatalytic decomposition of NO into N₂ and O₂. The results obtained by these spectroscopic measurements and photocatalytic reactions provide important information on the local structure of the 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.