The microstructure and catalytic behavior of M1 and M2 phases with bulk Mo-V-M-O compositions (M= combination of Sb, Nb, Te and Ta) in propane ammoxidation to acrylonitrile

Acrylonitrile, ACN, is a top 50 chemical produced globally. The bulk mixed metal Mo-V-M oxides (M= combination of Nb, Te, Sb, and Ta) consisting of so-called "M1" and "M2" phases are highly promising catalysts for a one-step propane ammoxidation to ACN. The M1 phase has been proposed to be responsible for propane activation and its selective transformation to ACN. The ab planes [001] in M1 phase have been proposed to contain the active and selective sites for propane ammoxidation. However, the structure-directing (in a sense of the Mo/V distribution in surface ab planes) and catalytic roles of these M substituents in the ab planes are poorly understood. Specifically, there is a lack of the fundamental understanding of the Sb functions in the Mo-V-Sb-O, Mo-V-Sb-Nb-O, and Mo-VSb-Ta-O catalysts. Moreover, the M2 phase has not been studied as extensively as the M1 phase, whereas this phase was found to play a role in the ammoxidation of the propylene intermediate. The synergy between the Mo-V-Te-Nb-O M1 and M2 phases was reported previously. However, very little is known about synergistic effects for the Mo-VSb-O, Mo-V-Sb-Nb-O, and Mo-V-Sb-Ta-O compositions, which are also active and selective for propane ammoxidation to ACN.