Process for preparing acrylic acid and oxidation catalyst

Claim 1

In the continuous process for preparing acrylic acid by vapor phase oxidation of propylene wherein acrolein is mainly prepared in the first oxidation step and oxidized in the second oxidation step without separating acrolein from by-products or off gas, the improvement which comprises carrying out said second oxidation step with molecular oxygen in the presence of an oxidation catalyst of the empirical formula: Mo.sub.a v.sub.b T.sub.c A.sub.d O.sub.e wherein Mo, V and O represent molybdenum, vanadium and oxygen, respectively, T represents tungsten or antimony, A represents an alkali metal, and a, b, c, d and e represent number of atoms of Mo, V, T, A and O, respectively, and when a is 12, b is 0.5 to 6, c is 0 to 6, d is 0.01 to 1.5 and e is a number naturally determined by the valence requirements of the other elements present, said catalyst being prepared by mixing a water-soluble molybdate, a water-soluble vanadate, a water-soluble salt of an alkali metal and, optionally, tungsten or antimony compound all in the form of aqueous solution or powder, adding, if necessary, a suitable carrier, evaporating the mixture to dryness and calcining the dried mixture at a temperature of from 300° to 500°C.