A combined bond-valence and periodic DFT study of the active sites in M1 phase of MoVTeNbO composite oxide catalyst

A combined bond-valence and periodic DFT study was carried out to interpret the nature of the d electrons in the active sites of the MoVTeNbO composite oxide catalyst (M1 phase). On investigating all the possible distribution of the coupled d electrons and oxygen vacancies, the most efficient combination of M-M-Te (M = Mo or V) active sites for propane selective oxidation has been argued. Besides, MoO₆ octahedra primarily stabilizes the crystal structure of M1 phase by attaining strong covalent Mo-O bonding in the equatorial plane, while VO₆ octahedra plays a minor role. Nb species that has been considered to stabilize the M1 phase was found to have mainly ionic interactions with the framework and act as a structure-directing agent in forming the pentagonal channels in the M1 phase.