The importance of site isolation and phase cooperation in propane ammoxidation on rutile-type vanadia catalysts

Abstract

Propane ammoxidation to acrylonitrile over rutile-type vanadia catalysts is discussed regarding phase cooperation and site isolation effects. Compared with the pure phases, biphasic catalysts with both ∼SbVO₄and α-Sb₂O₄are considerably more selective to the formation of acrylonitrile. It is demonstrated that cooperation between the phases during the calcination of the catalyst and the use in propane ammoxidation results in spreading of antimony species from free antimony oxide to the surface of ∼SbVO₄, forming Sb⁵⁺–V³⁺/V⁴⁺supra-surface sites being involved in the formation of acrylonitrile. Dilution and isolation of the vanadium centers in ∼SbVO₄through the partial replacement with, e.g., Al, Ti and W improves the catalytic properties. Structure–reactivity correlations using data for a nominal Sb_0.9V_0.9-x Ti _x O _y series indicate that the activation of propane occurs on a V³⁺site and the activation of ammonia requires an Sb⁵⁺site.