Synthesis of Acrylonitrile from Propane on V-Sb-based Mixed Oxides

The catalytic behavior of propane ammoxidation to acrylonitrile of pure VSbO 4 + Sb 2 O 4 (VSbO) samples (V:Sb atomic ratio in the range 0.2-1), of modified VSbO samples with Al 2 O 3 , TiO 2 or SiO 2 and of further promoted systems with W or Mo is analyzed. V-Sb-Al 2 O 3 based systems show an interesting potential for the development of a new process of acrylonitrile formation directly from propane. Al-oxide does not act merely as a support for the VSbO phase, but has a specific structural effect and greatly promotes the formation of propylene from propane. Catalytic and characterization results suggest that the active phase in propane ammoxidation is not a pure VSbO 4 rutile phase plus Sb 2 O 4 , but rather an amorphous VSbO 4 /Sb 2 O 4 system epitaxially intergrown with AlSbO 4 rutile phase whose formation is catalyzed by the presence of V. This system may be further promoted by the addition of W or Mo. Kinetic analysis of the propane ammoxidation shows that acrylonitrile forms by two parallel pathways, one directly from propane and the second through the intermediate formation of propylene, the latter being the prevalent path. In all cases propylene is the main reaction product observed, especially at low conversion, with selectivities up to about 80%.