Patent ID: 7638457

Claim:
A process for the preparation of a modified vanadium/phosphorus mixed oxide catalyst comprising vanadyl pyrophosphate as main component and niobium as a promoter element in an amount corresponding to an atomic ratio of vanadium to niobium in the range of 250:1 to 60:1, said process comprising the steps of (i) providing a reaction mixture comprising a vanadium source, a niobium source, a phosphorus source, an organic medium capable of acting as a solvent and a reducing agent, and an additive selected from the group consisting of benzyl alcohol and polyols, (ii) heating said reaction mixture to form a modified vanadyl acid orthophosphate catalyst precursor, (iii) isolating and drying said vanadyl acid orthophosphate catalyst precursor, (iv) precalcining said dried vanadyl acid orthophosphate catalyst precursor at a temperature of 200 to 330° C., (v) optionally shaping said vanadyl acid orthophosphate catalyst precursor into a shape suitable for the bed and reactor type wherein the finished catalyst is to be used, and (vi) calcining and activating said vanadyl acid orthophosphate catalyst precursor by (a) heating under superatmospheric pressure and in a steam-containing atmosphere to a temperature of 380 to 600° C., (b) maintaining the temperature reached in step (a) under superatmospheric pressure and (c) cooling the activated catalyst.