Direct propane ammoxidation to acrylonitrile: kinetics and nature of the active phase

Acrylonitrile (I) formation from propane on V-Sb-Al-(W) mixed oxides proceeds by two parallel pathways, directly from propane and, predominantly, via the intermediate propylene formation. The limiting step in the I formation is allylic oxidn. of the propylene intermediate. Propylene oxidn. to I is controlled by the surface availability of NH3 which, in turn, depends considerably on the undesirable NH3 oxidn. to N2. The catalytic behavior of different modified V-Sb-(Al)-O systems was studied by x-ray diffraction anal. and by Raman, IR, and x-ray photoelectron spectroscopies. In the course of the catalytic reaction, a redn. of both V and Sb occurs. The presence of V not stabilized in the rutile-like phase is responsible for the NH3 oxidn. and decreasing selectivity. Alumina reacts with Sb forming AlSbO4 in the rutile phase which could be epitaxially intergrown or in the solid soln. state with the VSbO4/Sb2O4 system, which, in turn, limits the presence of not stabilized (unselective) V species. The doping with V of this sample increases slightly the activity, but esp. gives rise to the formation of I instead of acetonitrile. [on SciFinder(R)]