A process for the preparation of molybdenum-containing mixed oxide

The invention relates to a process for preparing a compound oxide containing the elements molybdenum, vanadium, niobium and tellurium, comprising the steps of: a) preparing a mixture of starting compounds containing molybdenum, vanadium, niobium and tellurium-containing starting compound is present in the tellurium in the +4 oxidation state, b) hydrothermally treating the mixture of starting compounds at a temperature of 100 ° C to 300 ° C, to obtain a product suspension, c) separating and drying the solid resulting from step b) product suspension, d) activating the solid in inert gas to obtain the mixed oxide, characterized in that the output tellurium-containing compound having a particle size D