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

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 similar to SbVO4 and al pha -Sb2O4 are considerably more selective to the formation of acrylonitril e. It is demonstrated that cooperation between the phases during the calcin ation of the catalyst and the use in propane ammoxidation results in spread ing of antimony species from free antimony oxide to the surface of similar to SbVO4, forming Sb5+-V3+/V4+ supra-surface sites being involved in the fo rmation of acrylonitrile. Dilution and isolation of the vanadium centers in similar to SbVO4 through the partial replacement with, e.g., Al, Ti and W improves the catalytic properties. Structure-reactivity correlations using data for a nominal Sb0.9V0.9,TixOy series indicate that the activation of p ropane occurs on a V3+ site and the activation of ammonia requires an Sb5site.