Investigation of zeolites by photoelectron and ion scattering spectroscopy Part IV XPS studies of vanadium-modified zeolites

Abstract

Vanadium was introduced into zeolites in different amounts (0.36–3.3 wt.%) and chemical states and was investigated by XPS, UV–VIS and EPR spectroscopies. The vanadium zeolites studied were vanadium silicalites, vanadyl ion (VO²⁺)-exchanged ZSM-5, MOR, Y, X and vanadium oxide aggregates deposited in/on ZSM-5 via chemical vapour deposition of VOCl₃ with subsequent hydrolysis and calcination. By careful treatment of the X-ray satellite subtraction, reliable XPS analyses were obtained for all samples. Four types of vanadium species (intra-framework V, VO²⁺ ions, intra-zeolite V^V oxide clusters and extra-zeolite V₂O₅ aggregates) could be discerned by their differing V 2p binding energies. The assignment of their signals was supported by UV–VIS and EPR spectroscopical evidence. It was thus shown that combination of XPS with UV–VIS and EPR provides a useful method for the analysis of vanadium-containing zeolites.