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Abstract

A process for preparing a vanadium, phosphorus, and oxygen catalyst precursor for preparing maleic anhydride by heterogeneously catalyzed gas-phase oxidation of a hydrocarbon having at least four carbon atoms, which comprises (a) reacting vanadium pentoxide with from 102 to 110% strength phosphoric acid in the presence of a primary or secondary, noncyclic or cyclic, unbranched or branched, saturated alcohol having from 3 to 6 carbon atoms in a temperature range from 80 to 160.degree. C.; (b) isolating the precipitate formed; (c) setting an organic carbon content of .ltoreq.1.1% by weight in the isolated precipitate by heat treatment in a temperature range from 250 to 350.degree. C., the heat-treated product, following the addition of 3.0% by weight of graphite, giving a powder X-ray diffraction diagram which in the 2.theta. region features a ratio of the height of the peak of any pyrophosphate phase present at 28.5.degree. to the height of the peak due to the graphite at 26.6.degree. of .ltoreq.0.1; and (d) shaping the heat-treated product obtained from step (c) into particles having an averaged diameter of at least 2 mm; a catalyst precursor obtainable from this process; a process for preparing a catalyst from the catalyst precursor; a catalyst obtainable from that process; and also a process for preparing maleic anhydride over that catalyst.

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