Probing the Structural Changes and Redox Behavior of Mixed Molybdate Catalysts under Ammoxidation Conditions: An Operando Raman Spectroscopy Study

Mixed model molybdate catalysts that contain CoMoO4, Bi2Mo3O12, and Fe2Mo3O12 were investigated in the ammoxidation reaction of propene to acrylonitrile to study the redox behavior of the iron molybdate component. The flexible changes of the oxidation state of the Fe component during ammoxidation were followed by examining the intensity changes of the characteristic bands of Fe2Mo3O12 and FeMoO4 in the Raman spectra and could be correlated with the catalyst performance examined by simultaneous MS analysis. Depending on the catalyst composition and the oxygen content in the feed, Fe2Mo3O12 is reduced to a different extent, and consequently, FeMoO4 is formed, which is accompanied by a restructuring of the catalyst and the formation of nanostructured MoOx species. In accordance with previous investigations, operando Raman studies revealed that CoMoO4 and Bi2Mo3O12 influence the redox behavior of Fe2Mo3O12 in different ways.