CHEMISTRY OF VANADIUM PHOSPHORUS OXIDE CATALYST PREPARATION

The chemistry of the reduction process of V2O5 with mixtures of aliphatic and benzyl alcohols was studied using several analytical techniques. The aromatic alcohol, which acted as the reducing agent, was invariably oxidized to benzaldehyde while further oxidation to benzoic acid often occurred. The presence of soluble vanadium (V) alkoxides was detected through IR spectroscopy. At the higher reduction temperatures, which varied between 353 and 393 K, V2O4 appeared in the solid residue. In no case, however, was the vanadium pentoxide completely reduced with the alcohol mixture. The nature and proportion of the aliphatic alcohol defines the reflux temperature and therefore the rate of the kinetically controlled redox process. The reduction of V2O5 is completed upon addition of H3PO4 (100%). The precursors obtained invariably showed the X-ray diffraction pattern of VOHPO4 . 1/2H2O. The extent of disorder of the lattice in the direction perpendicular to the (010) plane increased with a higher proportion of benzyl alcohol in the reduction mixture. The oxidation of n-butane to maleic anhydride was studied using a plug flow reactor. The equilibrated catalysts display very similar X-ray diffraction patterns characteristic of (VO)2P2O7. No correlation was found between the extent of disorder of the precursors prepared in organic medium and the catalytic performance of the equilibrated solids.