Process for the transformation of vanadium/phosphorus mixed oxide catalyst precursors into active catalysts for the production of maleic anhydride

A process for the transformation of a catalyst precursor represented by the formula

• VO(M).sub.m HPO.sub.4.aH.sub.2 O.b(P.sub.2/c O).n(organics)
• wherein M is at least one promoter element selected from the group consisting elements from Groups IA, IB, IIA, IIB, IIIA, IIIB, IVA, IVB, VA, VB, VIA, VIB, and VIIIA of the Periodic Table of the Elements, and mixtures thereof, m is a number from 0.0001 to about 0.2, a is a number of at least about 0.5, b is a number from taken to provide a P/V atom ratio of from about 1.0 to about 1.3, c is a number representing the oxidation number of phosphorus and has a value of 5, and n is a number taken to represent the weight % of intercalated organics component, into an active catalyst represented by the formula
• (VO).sub.2 (M).sub.m P.sub.2 O.sub.7.b(P.sub.2/c O)
• wherein M, m, b, and c are as defined above, which process comprises:
• (a) heating the catalyst precursor in an atmosphere selected from the group consisting of air, steam, inert gas, and mixtures thereof to a temperature not to exceed about 300.degree. C.;
• (b) maintaining the catalyst precursor at the temperature of Step (a) and providing an atmosphere containing molecular oxygen, steam, and optionally an inert gas, the atmosphere being represented by the formula
• (O.sub.2).sub.x (H.sub.2 O).sub.y (IG).sub.z
• wherein IG is an inert gas and x, y, and z represent mol percent of the O.sub.2, H.sub.2 O, and IG components, respectively, in the molecular oxygen/steam containing atmosphere, with x having a value greater than zero (0) mol %, but less than 100 mol %, y having a value greater than zero (0) mol %, but less than 100 mol %, and z having a value representing the balance of the molecular oxygen/steam-containing atmosphere;
• (c) increasing the temperature at a programmed rate of from about 2.degree. C./min to about 12.degree. C./min to a value effective to eliminate the water of hydration from the catalyst precursor;
• (d) adjusting the temperature from Step (c) to a value greater than 350.degree. C., but less than 550.degree. C., and maintaining the adjusted temperature in the molecular oxygen/steam-containing atmosphere for a time effective to provide a vanadium oxidation state of from about +4.0 to about +4.5;
• and
• (e) continuing to maintain the adjusted temperature in a nonoxidizing, steam-containing atmosphere for a time effective to complete the catalyst precursor-to-active catalyst transformation to yield the active catalyst.