CATALYST COMPOSITION AND OXIDIE METHOD FOR PREPARING UNSATURATED ALDEHYDE BY GASEOUS OXIDATION OF OLEFINE

New catalyst composition for the preparation of alpha , beta -unsaturated aldehydes by gas phase oxidation of olefins; the invention also relates to the process for the preparation of alpha , beta -unsaturated aldehydes using this catalyst composition. This catalyst composition, which comprises a support in the form of full and solid beads with a diameter of between 0.5 and 6 mm and a catalytically active phase based on iron and bismuth molybdate, doped with potassium and phosphorus and, if appropriate, with one or a number of other metallic or nonmetallic elements, the said support being uniformly covered with an adherent layer of the said catalytically active phase, is characterised in that a) the phosphorus and the potassium are each present in an atomic quantity of between 0.005 and 0.06 per 12 atoms of molybdenum or of molybdenum and tungsten in the said phase, and in that b) the said catalytically active phase represents from 15 to 33 % by weight of the catalyst composition.