| abstract |
A process for preparing a vanadium, phosphorus, and oxygen comprising catalyst precursor for preparing maleic anhydride by heterogeneously catalyzed gas-phase oxidation of a hydrocarbon having at least four carbon atoms, which comprisesn (a) reacting vanadium pentoxide with 102% to 110% strength phosphoric acid in the presence of isobutanol and optionally of a primary or secondary, noncyclic or cyclic, unbranched or branched, saturated alcohol having 3 to 6 carbon atoms in a temperature range from 80 to 160° C.; (b) isolating the precipitate formed; (c) (i) drying the isolated precipitate down to a residual isobutanol content of less than 5% by weight;n (ii) then passing a gas which in addition to one or more inert gases comprises 0.1% to 9% by volume of oxygen through the dried precipitate, directly or after isolation, in the temperature range from 130° C. to 200° C. |