Abstract: The invention relates to a catalyst system for producing maleic anhydride by means of the catalytic oxidation of n-butane, comprising at least one reactor tube, which has two catalyst layers consisting of different catalyst particles, characterized in that the geometric surface area per catalyst particle is greater in the catalyst layer that is first in the gas flow direction than in the second catalyst layer. The invention further relates to a process for producing maleic anhydride by means of the catalytic oxidation of n-butane, wherein a mixture of oxygen and n-butane is fed through the catalyst system according to the invention and the at least one reactor tube is at elevated temperature.

Abstract: The disclosure relates to a process for producing a VPO catalyst containing molybdenum and a vanadyl pyrophosphate phase, which comprises the steps: a) provision of a reaction mixture comprising a V(V) compound, a P(V) compound, an Mo compound, a reducing agent and a solvent, b) reduction of the V(V) compound by means of the reducing agent at least in parts to give vanadyl hydrogenphosphate in order to obtain an intermediate suspension, c) filtration of the intermediate suspension from step b) in order to obtain an intermediate, d) drying of the intermediate at a temperature of not more than 350° C. in order to obtain a dried intermediate and e) activation of the dried intermediate at a temperature above 200° C., characterized in that not more than 0.2% by weight of water, based on the weight of the reaction mixture, is present in step a) and no water is withdrawn during the reduction in step b).

Abstract: The disclosure relates to a process for producing a VPO catalyst containing molybdenum and a vanadyl pyrophosphate phase, which comprises the steps: a) provision of a reaction mixture comprising a V(V) compound, a P(V) compound, an Mo compound, a reducing agent and a solvent, b) reduction of the V(V) compound by means of the reducing agent at least in parts to give vanadyl hydrogenphosphate in order to obtain an intermediate suspension, c) filtration of the intermediate suspension from step b) in order to obtain an intermediate, d) drying of the intermediate at a temperature of not more than 350° C. in order to obtain a dried intermediate and e) activation of the dried intermediate at a temperature above 200° C., characterized in that not more than 0.2% by weight of water, based on the weight of the reaction mixture, is present in step a) and no water is withdrawn during the reduction in step b).