Patent ID: 7026506

Claim:
A process, comprising: preparing acrylic acid by heterogeneously oxidizing propene to acrylic acid in the gas phase with molecular oxygen over at least one multimetal oxide catalyst material present in a reaction zone, wherein the multimetal oxide catalyst material has a stoichiometry I Mo 1 V b M c 1 M d 2 O n (I), where M 1 is Te and/or Sb, M 2 is at least one element from the group consisting of Nb, Ta, W, Ti, Al, Zr, Cr, Mn, Ga, Fe, Ru, Co, Rh, Ni, Pd, Pt, La, Bi, B, Ce, Sn, Zn, Si and In, b is from 0.01 to 1, c is from>0 to 1, d is from>0 to 1 and n is a number which is determined by the valency and frequency of the elements other than oxygen in (I), wherein the X-ray diffraction pattern of the at least one multimetal oxide active material (I) has reflections h, i and k whose peaks are at the diffraction angles (2θ) 22.2±0.4° (h), 27.3±0.4° (i) and 28.2±0.4° (k), the reflection h being the one with the strongest intensity within the X-ray diffraction pattern and having a half-width of not more than 0.5°, the intensity P i of the reflection i and the intensity P k of the reflection k fulfills the relationship 0.65≦R≦0.85, where R is the intensity ratio defined by the formula R=P i /( P i +P k ) and the half-width of the reflection i and that of the reflection k are each ≦1°.