Modification of the surface reactivity of vanadium antimonate catalysts during catalytic propane ammoxidation

The changes that take place in a vanadium antimonate catalyst during catalytic propane (I) ammoxidn. were studied by transient reactivity expts. and IR spectroscopy. The investigation was focused on both the change in catalytic behavior of a fresh sample and the change in reactivity with stepwise increases in the concn. of one or more reagents while maintaining the concn. of the other reactants const. Two main types of modifications are present. A change in the reactivity from the fresh to the activated samples due to the surface formation of a VSbO4 phase by reaction of vanadium and antimony oxides that have not reacted during calcination leads to the formation of carbon oxides and a decrease in the rate of I depletion as well as a considerable increase in the rate of acrylonitrile (II) formation. A change in the reactivity of the activated sample which is a function of the redox characteristics of the reagent mixt. does not change the rate of I depletion, but rather only results in differences in the relative selectivity to products. In the steady state, the activated catalyst is partially reduced in comparison with the same sample after treatment with oxygen and the rate of II formation is lower. IR results confirm the formation of oxygen vacancies in the catalyst upon interaction with ammonia and propene as well as the presence of these defects in the sample after the catalytic tests. [on SciFinder(R)]