X.A.F.S. study of model vanadium sulphide phases suspected to form on HDM catalyst surfaces

Abstract This paper reports on structural investigations of the vanadium and sulphur environments in vanadium sulphide phases incorporated in a calcined δ-Al 2 O 3 support. Evidence is produced showing the formation of V=O entities coordinated to additional oxygen and sulphur ligands. Striking analogies are found with the XAFS spectra of a vanadyl hydroxythiolate species [(OH)(SH):V=O]. Combining the structural information gained from both the V * K-edge and the S * K-edge EXAFS spectra of the latter compound, we have been led to propose for it a dimeric (or even polymeric) structure with disulphide bridges. The paper also includes a report of preliminary results relative to a real NiOMoO 3 Al 2 O 3 HDM catalyst after completion of a full catalytic cycle including presulphidation, hydrogenation of toluene (HYD) and hydrodemetallation.