Surface vanadium compounds in supported vanadium-magnesium catalysts for ethylene polymerization: X-ray photoelectron and infrared diffusion reflectance spectroscopy studies

Adsorption of NO as a probe molecule in infrared diffusion reflectance spectroscopy (DRIFTS) and X-ray photoelectron spectroscopy (XPS) have been used in order to identify surface vanadium species in vanadium-magnesium catalysts (VMC). The presence of V3+ and V4+ in VCl4/MgCl2, and V4+ in VOCl3/MgCl2 was shown by XPS and DRIFTS. However, DRIFTS has some limitations due to oxidation of V3+ by the reaction with NO; moreover, apparently ions V5+ and V2+ do not adsorb NO. We have also demonstrated the possible identification of Surface ions V5+ and V2+ in VMC using XPS. Practically in all cases (VCl2/MgCl2, VCl4/MgCl2 and VOCl3/MgCl2) one can see a mixture of vanadium ions in different oxidation and coordination states. (C) 2000 Elsevier Science B.V. All rights reserved.