A process for preparation of a catalyst, said catalyst consisting of a complex of metal oxides wherein the relative ratios of the elements in said catalyst are represented by the following formula: Mo 12 Bi a Fe b A c D d E e F f G g Ce h O x wherein A is at least one element selected from the group consisting of sodium, potassium, rubidium and cesium; and D is at least one element selected from the group consisting of nickel, cobalt, manganese, zinc, magnesium, calcium, strontium, cadmium and barium; E is at least one element selected from the group consisting of chromium, tungsten, boron, aluminum, gallium, indium, phosphorus, arsenic, and vanadium; F is at least one element selected from the group consisting of lanthanum, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, scandium, yttrium, titanium, zirconium, hafnium, niobium, tantalum, aluminum, gallium, indium, thallium, silicon, germanium, and lead; G is at least one element selected from the group consisting of silver, gold, ruthenium, rhodium, palladium, osmium, iridium, platinum and mercury; and a is from 0.05 to 7, b is from 0.1 to 7, c is from 0.01 to 5, d is from 0.1 to 12, e is from 0 to 5, f is from 0 to 5, g is from 0 to 0.2, h is from 0.01 to 5, and x is the number of oxygen atoms required to satisfy the valence requirements of the other component elements present; characterised in that the catalyst is a catalyst for the catalytic ammoxidation of propylene, isobutylene or mixtures thereof, to acrylonitrile, methacrylonitrile and mixtures thereof, respectively, in a fluid bed reactor, and that the process for the preparation of the catalyst comprises: (a) combining source compounds of the metals which comprise the metal oxide catalyst to form a catalyst precursor, (b) spray drying the catalyst precursor to form microspheroidal catalyst particles, and (c) calcining the microspheroidal catalyst particles to yield the catalyst, and where at least one heat-decomposable nitrogen containing compound is added during the preparation of the catalyst, wherein the heat-decomposable nitrogen containing compound is ammonium nitrate. wherein A is at least one element selected from the group consisting of sodium, potassium, rubidium and cesium; and D is at least one element selected from the group consisting of nickel, cobalt, manganese, zinc, magnesium, calcium, strontium, cadmium and barium; E is at least one element selected from the group consisting of chromium, tungsten, boron, aluminum, gallium, indium, phosphorus, arsenic, and vanadium; F is at least one element selected from the group consisting of lanthanum, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, scandium, yttrium, titanium, zirconium, hafnium, niobium, tantalum, aluminum, gallium, indium, thallium, silicon, germanium, and lead; G is at least one element selected from the group consisting of silver, gold, ruthenium, rhodium, palladium, osmium, iridium, platinum and mercury; and a is from 0.05 to 7, b is from 0.1 to 7, c is from 0.01 to 5, d is from 0.1 to 12, e is from 0 to 5, f is from 0 to 5, g is from 0 to 0.2, h is from 0.01 to 5, and x is the number of oxygen atoms required to satisfy the valence requirements of the other component elements present; (a) combining source compounds of the metals which comprise the metal oxide catalyst to form a catalyst precursor, (b) spray drying the catalyst precursor to form microspheroidal catalyst particles, and (c) calcining the microspheroidal catalyst particles to yield the catalyst,