Structure and stability during the catalytic reaction of unsupported V-antimonate catalysts for the direct selective ammoxidation of propane to acrylonitrile

V-antimonate catalysts prepd. by redox reaction in a soln. contg. both V5+ and Sb3+ and heat treated in air or under vacuum were characterized by chem. analyses of the V and Sb valence state and IR spectroscopy, X-ray diffraction anal. and SEM before and after the catalytic tests. The V-antimonate rutile phase is a mixed valence oxide contg. V3+ and V4+ with a relative ratio that depends on the prepn. conditions, but which evolves to a similar situation (characterized by a V3+:V4+ ratio of around 1:3) after the catalytic tests of propane ammoxidn. Some aspects of the stability of this phase during the catalytic reaction are also discussed. [on SciFinder(R)]