Active centers in Mo–V–Nb–Te–Ox (amm)oxidation catalysts

The catalytically active centers of the MoVNbTeOx system for propane ammoxidation to acrylonitrile have been identified. The catalytic system is comprised of three crystalline phases: orthorhombic Mo7.8V1.2NbTe0.94O28.9 (M1) (Pba2: a=21.1337 Å; b=26.6440 Å; c=4.01415 Å; z=4), pseudo-hexagonal Mo4.67V1.33Te1.82O19.82 (M2) (Pmm2: a=12.6294 Å; b=7.29156 Å; c=4.02010 Å; z=4) and a trace of monoclinic TeMo5O16 (P21/C: a=10.0349 Å; b=14.430 Å; c=8.1599 Å; β=90.781°; z=1). The catalytically active and selective centers reside on the surface of the basal plane of the M1 phase and are comprised of an assembly of five metal oxide octahedra (2V0.325+/Mo0.686+, 1V0.624+/Mo0.385+, 2Mo0.56+/Mo0.55+) and two tellurium–oxygen sites (2Te0.944+), which are stabilized and structurally isolated from each other (site isolation) by four Nb5+ centers, each surrounded by five molybdenum–oxygen octahedra. The V5+ surface sites, distinguished through their (V5+O↔4+Vradical dotOradical dot) resonance structure, are the paraffin activating sites capable of methylene-H abstraction; the Te4+ sites (lone pair of electrons) for the α-H abstraction of the chemisorbed propylene molecule, once formed; and the adjacent Mo6+ sites for the NH insertion into the π-allylic surface intermediate. Herewith, all key catalytic elements needed to transform propane directly to acrylonitrile are contained, strategically arranged and within bonding distance of each other, at the active center of the M1 phase.