A process for the preparation of a catalyst 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 Gg Ce h O n 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, antimony, vanadium and tellurium; F is at least one element selected from the group consisting of a rare earth element, 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, b, c, d, e, f, g, h and n are, respectively, the atomic ratios of bismuth (Bi), iron (Fe), A, D, E, F, cerium (Ce) and oxygen, relative to 12 atoms of molybdenum (Mo), wherein 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 n is the number of oxygen atoms required to satisfy the valence requirements of the other component elements present; and wherein the elements in said catalyst are combined together in an aqueous catalyst precursor slurry, the aqueous precursor slurry so obtained is dried to form a catalyst precursor, and the catalyst precursor is calcined to form said catalyst, the process comprising: (i) combining, in an aqueous solution, source compounds of Bi and Ce, and optionally one or more of Na, K, Rb, Cs, Ca, a rare earth element, Pb and W, to form a mixture, (ii) adding a source compound of molybdenum to the mixture of (i) to react with the mixture and form a precipitate slurry, and (iii) combining the precipitate slurry with source compounds of the remaining elements and of the remaining molybdenum in the catalyst to form the aqueous catalyst precursor slurry. 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, antimony, vanadium and tellurium; F is at least one element selected from the group consisting of a rare earth element, 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, b, c, d, e, f, g, h and n are, respectively, the atomic ratios of bismuth (Bi), iron (Fe), A, D, E, F, cerium (Ce) and oxygen, relative to 12 atoms of molybdenum (Mo), wherein 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 n is the number of oxygen atoms required to satisfy the valence requirements of the other component elements present; and wherein the elements in said catalyst are combined together in an aqueous catalyst precursor slurry, the aqueous precursor slurry so obtained is dried to form a catalyst precursor, and the catalyst precursor is calcined to form said catalyst, the process comprising: (i) combining, in an aqueous solution, source compounds of Bi and Ce, and optionally one or more of Na, K, Rb, Cs, Ca, a rare earth element, Pb and W, to form a mixture, (ii) adding a source compound of molybdenum to the mixture of (i) to react with the mixture and form a precipitate slurry, and (iii) combining the precipitate slurry with source compounds of the remaining elements and of the remaining molybdenum in the catalyst to form the aqueous catalyst precursor slurry. (i) combining, in an aqueous solution, source compounds of Bi and Ce, and optionally one or more of Na, K, Rb, Cs, Ca, a rare earth element, Pb and W, to form a mixture, (ii) adding a source compound of molybdenum to the mixture of (i) to react with the mixture and form a precipitate slurry, and (iii) combining the precipitate slurry with source compounds of the remaining elements and of the remaining molybdenum in the catalyst to form the aqueous catalyst precursor slurry.