Methanol conversion over TiO2-anatase supported oxomolybdate catalysts: an integrated operando – DFT modeling approach

Abstract

TiO2-supported molybdenum oxide has been studied through a combination of X-ray absorption near edge structure (XANES) and Raman operando spectroscopy. XANES gives insights on the electronic structure of the molybdenum embedded in the active phase, while Raman spectroscopy probes the structure of the oxomolybdate phase at the molecular level. These paired experiments have also been complemented by density functional theory calculations to better refine the resulting structure and make it possible to further understand the structure–activity correlations. In line with the approach, we show that the reactivity of the supported oxomolybdate phase is strongly dependent on the molybdenum loading of the catalyst. Indeed, low molybdenum content catalysts exhibit isolated tetrahedrally coordinated molybdenum centers that are not reducible and show a very low activity in methanol conversion. On the other hand, high molybdenum loading catalysts present reducible molybdenum centers that are rather active in methanol conversion. This change in the behavior of the supported phase is found to be related to a change in the oxygen coordination spheres: high loading induces molybdenum oxide clusters of higher nuclearity where the molybdenum atoms are surrounded by five or six oxygen atoms.