Electron paramagnetic resonance study of vanadium exchanged H-ZSM5 prepared by vapor reaction of VCl4. The role of 17O isotope labelling in the characterisation of the metal oxide interaction

Site isolated vanadium ions supported on zeolites are central in many catalytic processes. However, an atomistic description of the species formed is often hampered by the heterogeneous nature of zeolites and the random distribution of active species. In this contribution we applied pulsed electron paramagnetic resonance spectroscopy on 17O exchanged ZSM-5 zeolite loaded with V4+ ions, via gas phase reaction with VCl4 vapors. From the magnetic parameters relative to 1H, 17O, 27Al and 51V isotopes we prove that a single, structurally well-defined VO(OH)+ species is formed at zeolite Al framework sites and derive a detailed atomistic model inclusive of bond lengths and angles. Comparison is set to vanadyl aquo complexes, highlighting analogies between surface and solution coordination chemistry. The results showcase the power of EPR spectroscopy and 17O isotopic labelling in the geometrical and electronic characterisation of inorganic complexes formed at the surface of oxide materials. Pulsed EPR on disorder systems can therefore compete in structural insight with more well-established X-ray techniques.