NOVELTY - An improved process for the calcination and activation of a catalyst containing mixed oxides of vanadium and phosphorus (V/ P/ O) useful in the preparation of maleic anhydride from n-butane.    USE - The catalyst is used in the oxidation of n-butane to maleic anhydride.    ADVANTAGE - The catalyst exhibits enhanced activity for the oxidation.    DETAILED DESCRIPTION - A process for the selective vapor phase oxidation of n-butane to maleic anhydride using a recirculating solids reactor comprising a reaction zone and a catalyst regeneration zone. N-butane is converted to maleic anhydride in the reaction zone of the recirculating solids reactor by vanadium / phosphorus oxide (V/P/O) catalyst in oxidized form and the reduced V/P/O catalyst is regenerated by contact with oxygen in the reactor. The specific improvement comprises:    (i) adding catalyst precursor to the regeneration zone maintained at 380-400degreesC;    (ii) maintaining the catalyst precursor in a fluidised state within the regeneration zone by use of air or oxygen containing gas for a sufficient time and pressure to remove entrained organics and to partially dehydrate the catalyst precursor;    (iii) transferring calcined catalyst precursor from the regeneration zone to the reaction zone such as to maintain an average residence time for catalyst precursor in the regeneration zone resulting in an average Vox of 4.55 or less; and    (iv) maintaining the calcined catalyst precursor in a fluidised state within the reaction zone near operating temperature using a substantially non-oxidising gas until catalyst circulation is commenced.    An INDEPENDENT CLAIM is also included for the process for calcining V/P/O catalyst comprising:    (a) establishing a gas flow within a fluidised bed reactor using air or oxygen containing gas at 370-420degreesC;    (b) adding to the fluidised bed reactor of step (a) a hydrated V/ P/O or V/P/O-SiO2 catalyst precursor at a rate such that the catalyst precursor experiences a rapid temperature rise in a fluidised bed state at 370-420degreesC;    (c) maintaining the catalyst precursor from (b) in a fluidised state at the temperature range for a sufficient time and pressure to remove entrained organics and to dehydrate the catalyst while simultaneously achieving an average Vox in excess of 4.05 but not in excess of 4.55; and    (d) recovering and storing the calcined V/ P/O catalyst produced in a non-oxidising gas.