A process for the preparation of a promoted VSbOx catalyst comprising mixing a vanadium compound, at least a first portion of an antimony compound, and at least a portion of the support material to form a slurry, heating the slurry to remove the water, calcining the dried slurry to form a catalyst precursor, combining the catalyst precursor with a second aqueous sol containing the remaining portion of the support material and the remaining portion of the antimony compound to form a second slurry, drying the second slurry to remove the water and calcining the dried mixture to form the finished catalyst.