TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: The rate of addition of catalyst precursor is co-ordinated simultaneously with the transferring of calcined catalyst precursor from the regeneration zone to the reaction zone such as to maintain the temperature within the regeneration zone until the entire charge of catalyst is calcined. The charge of calcined catalyst precursor is activated, in situ, under operating conditions with introduction of n-butane to the reaction zone and catalyst recirculation between the reaction zone and the regeneration zone. The regeneration zone is maintained at 390 +/- 5degreesC at a pressure of up to 3.5 atmosphere and the average residence time for catalyst precursor in the regeneration zone is maintained at 4 hours or less. The average range of residence time for catalyst precursor in the regeneration zone is less than 4 hours at 3.5 atmosphere of air or above and up to 20 hours at 1 atmosphere of air. The temperature range of 380-400degreesC is achieved by direct fire heating using n-butane resulting in a water vapor content in the air or oxygen containing gas of up to 3 mol %. EXAMPLE - A commercial scale fluidised transfer bed plant for direct oxidation of n-butane to maleic anhydride involving a riser reactor for n-butane oxidation and a separate fluidised bed reactor for regeneration of catalyst was started up by continuously added spray dried V/ P/O catalyst precursor at a nominal rate of 10 thousand pounds per hour to the regeneration zone. During catalyst addition the calcining fluidised bed of catalyst precursor within the regeneration reactor was maintained at 390degreesC and 2.7 atmosphere using hot air which contain    19% oxygen after direct fire heating using n-butane as fuel. The calcining catalyst precursor was periodically removed from the regenerator reactor and transferred to the riser reactor of the plant at a rate such as to have an average residence time in the regenerator under oxidative calcination conditions of 3.25-3.5 hours. The calcined catalyst precursor transferred to the riser reactor was maintained at an operating temperature not more than 50degreesC less than the calcination temperature by use of recirculating nitrogen until the entire charge of catalyst had been added and calcined. Upon commencement of circulating the fluidised catalyst charge and introduction of n-butane to the riser reactor, the catalyst quickly reached a maleic production rate 25% greater than that previously experienced for such V/ P/ O catalyst.