Patent ID: 7208636

Claim:
A process for preparing acrolein by heterogeneously catalyzed partial gas phase oxidation, comprising: passing a starting reaction gas mixture which comprises propene, molecular oxygen and at least one inert gas, in which the molecular oxygen to propene (O 2 :C 3 H 6 ) mole ratio is ≧1, and carbon dioxide and saturated hydrocarbons together in a total amount of at most 15 mol % over a fixed catalyst bed; and oxidizing the propene component of the reaction gas at elevated temperature and at an hourly space velocity on the fixed catalyst bed of propene present in the starting reaction gas mixture of ≧120 l(STP)/l·h wherein the catalysts are comprised of annular unsupported catalysts whose active component is at least one multimetal oxide of formula I, Mo 12 W a Co b Fe c Bi d Si e K f O n (I) where a=from ≧1 to ≦3, b=from ≧3 to ≦8, c=from ≧1 to ≦4, d=from ≧0.5 to ≦1.5, e=from ≧0 to ≦10, f=from ≧0 to ≦0.2 and n=a number which is determined by the valency and frequency of the elements in the composition of formula I other than oxygen, in such a way that the propene conversion in single pass is ≧90 mol % and the associated selectivity of acrolein formation is ≧80 mol %, wherein, in the multimetal oxide composition of formula I, the following mole ratios are: Co/Fe=from 2 to 4 and Co/Mo=from 0.3 to 0.7.