A process for preparing a vanadium, phosphorus and oxygen-containing catalyst

A method for producing a to maleic anhydride suitable for the heterogeneously catalyzed gas-phase oxidation of a hydrocarbon having at least four carbon atoms, containing vanadium, phosphorus, and oxygen catalyst, in which containing a corresponding vanadium, phosphorus, and oxygen catalyst precursor having wherein particles with an average diameter of at least 2 mm , converted by calcination into a catalytically active form, in which l¶n¶ carries a current of the catalyst precursor for calcining at substantially constant speed on a conveyor belt through at least one calcining zone of length n, wherein the temporal variation of the gas temperature from the setpoint value on each site in the region of the stream of the catalyst precursor after half the length of the calcining l¶n¶ / 2 every 5 DEG C and the local difference in gas temperature between any point in the region of the stream of the catalyst l¶n¶ precursor after half the length of the calcining / 2 each 5 ° C.