Catalysts having the general formula:V.sub.1 Bi.sub.a Sb.sub.b Fe.sub.c X.sub.d Y.sub.c Z.sub.f O.sub.gwherein,X=Mo, Cu, W, Nb, Te, P, Sn, Ge, AsY=Co, Ni, Ce, La, Mn, CrZ=Alkali, alkaline earth, B, Tl and,a=0.1-10,b=0.01-20,c=0.01-5,d=0-5,e=o-3,f=0-1, and g is determined by the valance requirements of the elements present,are produced by first forming and calcining an iron-antimony oxide composition which is subsequently combined with compounds of vanadium, bismuth and other elements. The catalysts are useful in the formation of phthalonitriles from the reaction of xylenes with oxygen and ammonia at elevated temperatures.