PREPARATION AND CHARACTERIZATION OF VANADIUM-PHOSPHORUS OXIDATION CATALYSTS

Precursor phases of the maleic anhydride vanadium phosphate catalysts (atomic P/V ratios from 0. 8 to 1. 3) were prepared by reduction of V//2O//5 with N//2H//4, followed by reaction with H//3PO//4. The precipitates and products of evaporation to dryness were examined by chemical and thermal analysis, XRD, IRS, DRS and XPS. Five phases were formed, namely VO(H//2PO//4)//2 and the new phases VO(HPO//4) multiplied by (times) 3H//2O, (VO)//2P//2O//7 multiplied by (times) 6H//2O, (VO)//2P//2P//7 multiplied by (times) 9H//2O and an unidentified compound. Intermediate and final activated pohases consist of (JVO)//2P//2O//7 multiplied by (times) 3H//2O, alpha - and beta -VOPO//4 and the beta * phase. At intermediate temperatures (423-553 K) and P/V greater than 1 the phases are stabilized in the V(IV) state.