Methods for reprocessing used catalysts

A method for reprocessing a used catalyst including an oxygen-containing compound of titanium, vanadium, and at least one of the elements molybdenum or tungsten, comprising at least step (T4):

• (T4) heating of a solid fraction comprising an oxygen-containing compound of titanium and at least one of the elements tungsten or molybdenum in the presence of a vanadium compound at a temperature ≧200° C.,
• and further comprising steps (T1) through (T3) prior to step (T4):
• (T1) bringing into contact of the used catalyst with an aqueous base, thus obtaining a water-containing mass, which comprises:
• a liquid fraction comprising a water-soluble material, and
• a solid fraction, which comprises a water-insoluble material;
• (T2) separation of the solid fraction from the liquid fraction of step (T1);
• (T3) bringing into contact of the separated solid fraction of step (T2) with a vanadium compound;
• wherein the aqueous base of step (T1) is selected from the group composed of an aqueous alkali hydroxide, an aqueous alkaline earth hydroxide, an aqueous alkali hydrogen carbonate, an aqueous alkali carbonate, an aqueous alkaline earth carbonate, an aqueous C1-C4 alkylamine, an aqueous amino alcohol, and a mixture of at least two of the aqueous bases thereof.