Surface species structure and activity in NO decomposition of an anatase-supported V–O–Mo catalyst

The paper concerns the evolution of surface species of a V–O–Mo/anatase catalyst in the course of its thermal treatment in oxidising and/or reducing conditions. The catalyst was obtained by the sol–gel method. The structure of its surface was investigated by XPS and Raman spectroscopy. The fresh catalyst consists of anatase nanocrystallites with some vanadium and molybdenum ions substituted for titanium ones and molybdenum oxide islands on their surfaces. A V/Mo₅O₁₄ solid solution-containing V atoms in its channels, as well as MoO₃ and anatase with some surface vanadia species are present on the catalyst surface.The reduction of anatase to TiO_2−x and of MoO₃ to Mo₅O₁₄, accompanied by inward vanadium diffusion occurs during the catalyst interaction with ammonia at 523 K. The oxidation of the TiO_2−x but not Mo₅O₁₄ and V reappearance in the surface channels take place during the interaction of the reduced catalyst with molecular oxygen.However, the oxidation of Mo₅O₁₄ to MoO₃ occurs under the influence of atomic oxygen, formed by NO decomposition at 423 K. It is accompanied by the surface vanadia species formation. The activity of V ions of these species in NO decomposition is lower than of the surface interstitial ones.