Abstract: The invention relates to supported catalysts consisting of an active material on an inert support in the shape of rings, wherein the rings have one or more notches in the upper and/or lower flat side of the ring.

Abstract: A method is provided for producing catalysts useful for synthesizing maleic anhydride by oxidizing saturated and/or unsaturated C4 hydrocarbons. A vanadium (V) compound is reacted with a mixture of phosphorous and phosphoric acids in a particular ratio, in a solvent mixture containing a structure former, and an entrainer and where the water of reaction together with entrainer is distilled off and the resulting precursor is subjected to calcination.

Abstract: There is a process for producing coated catalysts for the gas-phase oxidation of C.sub.4 hydrocarbons to maleic anhydride. A vanadyl phosphate catalyst precursor is prepared having a V/P ratio of from 1:0.5 to 1:2 and a mean vanadium oxidation state of from 3.9 to 4.5. The vanadyl phosphate precursor is then calcined by heating for a several hours at a temperature of from 200.degree. C. to 500.degree. C. before being applied, in an aqueous suspension to the support bodies. Furthermore, there is the use of these coated catalysts in processes for the gas-phase oxidation of saturated or unsaturated C.sub.4 -hydrocarbons to maleic anhydride.