Patent ID: 7060649

Claim:
A process for preparing a vanadium, phosphorus, and oxygen containing catalyst suitable for heterogeneously catalyzed gas-phase oxidation of a hydrocarbon having at least four carbon atoms to maleic anhydride, in which a corresponding vanadium, phosphorus, and oxygen containing catalyst precursor containing particles having an averaged diameter of at least 2 mm is converted into a catalytically active form by calcining, which comprises passing a stream of the catalyst precursor for calcining at substantially constant speed through at least one calcining zone n of length 1 n on a conveyor belt, the fluctuation in the gas temperature from a setpoint value over time at each point in the region of the stream of the catalyst precursor after half the length of the calcining zone, 1 n /2, being in each case≦5° C. and the local difference in gas temperature between any two points in the region of the stream of the catalyst precursor after half the length of the calcining zone, 1 n /2, being in each case≦5° C.