Method for producing shell catalysts for catalytic gas-phase oxidation of aromatic hydrocarbons

A process for producing coated catalysts for the catalytic gas-phase oxidation of aromatic hydrocarbons to give carboxylic acids and/or carboxylic anhydrides, on the support material of which a layer comprising catalytically active metal oxides is applied in the form of a shell, wherein a powder is first produced, by spray drying or freeze drying, from a solution and/or a suspension of the catalytically active metal oxides and their precursor compounds or these precursor compounds alone in the presence or absence of auxiliaries for catalyst production, the powder is subsequently applied as a paste in the form of a shell in the presence or absence of auxiliaries for catalyst production to the support after or without prior conditioning, without prior heat treatment to generate the catalytically active metal oxides and the support coated in this way is subjected to a heat treatment to generate the catalytically active metal oxides, the average layer thickness of the active composition of the coated catalysts produced in this way being from 10 to 250 μm.