Redox State Dynamics at the Surface of MoVTe(Sb)NbO M1 Phase in Selective Oxidation of Light Alkanes

The influence of Te or Sb on the catalytic properties of the M1 phase of MoVTe(Sb)NbO catalysts in the oxidation of propane or oxidative dehydrogenation of ethane has been investigated. The results show that Te and Sb affect the intrinsic activity of the catalyst for ethane and propane oxidation in the same way and that the Te-containing M1 phase was significantly more active than the Sb-containing phase, even when they contained the same amount of vanadium, which is known to be the active species for the reactions. This feature has been explained by a strong modification of the relative number of available V⁵⁺ sites, which is related to the fact that Sb tend to stabilize vanadium in active site, in a reduced state. Sb and Te were also shown to affect the selectivity in the case of propane oxidation but not in the case of ethane oxidative dehydrogenation. This demonstrated that they should be involved directly in the further transformation of the alkene molecules that are formed as an intermediate and presumably play a role in the α-hydrogen abstraction from these molecules, as proposed earlier. Blocking problems related to the substitution of Te by Sb in view of industrialization are also discussed.