Spectroscopic Investigation of Vanadium-Phosphorus Catalysts

Article abstract of DOI:10.1021/j100206a020

The structural and surface changes occurring in vanadium-phosphorus mixed oxides with P/V atomic ratios in the 1.0 - 1.8 range prepared by reducing the V(V) with oxalic acid were investigated by ESR, diffuse reflectance spectroscopy, X-ray diffraction, and redox titrimetry.Poorly crystallized α-VOPO4 was formed for a P/V ratio of 1.0, and new phases containing V(IV) were found as the P/V ratio increased.The V(IV) centers changed progressively from isolated, dispersed ions in a α-VOPO4 matrix into a V(IV) phosphate phase, as revealed by ESR and diffuse reflectance spectra.These results are compared with catalytic activity data for the 1-butene oxidation in a pulse reactor.The highest yield of maleic anhydride was given by the samples with a 1.0 - 1.2 P/V ratio, indicating that VOPO4 with dispersed V(IV) ions is the active phase.