OXIDATION-STATES OF VANADIUM IN V-P-O OXIDATION CATALYSTS - P-31-NMR BY SPIN-ECHO MAPPING

The oxidation state of vanadium in V-P-O catalysts before and after use has been examined using P-31 NMR spin echo mapping. The presence of V4+ and V5+ species could be detected for beta-VOPO4, (VO)2P2O7 and industrially-related materials with P/V = 0.9, 1.0, and 1.1. Magnetic susceptibility measurements were used to confirm the presence of para-magnetic vanadium in most catalysts which had been exposed to n-butane or 1-butene. Several models of active V-P-O catalysts have been offered previously which can be related to the NMR results.