Partial oxidation of propene on MoPrO catalysts

Abstract

A study of the propene mild oxidation on MoPrO catalysts and the characterization of catalysts (with Mo (Mo + Pr) atomic ratios ranging from 0 to 1) has been carried out. The yield of CO + CO 2 decreased and the selectivity to acrolein and acetaldehyde + acetic acid increased significantly with increasing MoO 3 content up to atomic ratios Mo (Mo + Pr) = 0.80–0.88 . Afterward, the selectivity decreased. The samples are composed of crystalline needles of MoO 3 and agglomerates where Mo and Pr were detected. Pr is present as Pr 6O 11 in catalysts with low Mo content, this oxide being gradually converted to Pr 2O 3 with increasing MoO 3 loading. It appears that the presence of MoO 3 also has the effect of dispersing the praseodymium oxide. In the catalysts with high Pr content, the reduction rate decreases continuously with time indicating that this process takes place according to the contracting sphere model. However, the catalysts with high Mo content present sigmoidal reduction curves; i.e., they reduce according to the nucleation model. The extent of reduction, for reduction times lower than 0.5 h, decreased with increasing MoO 3 content in the samples. The observed maxima in selectivity for partial oxidation products seem to be due to the higher structural stability of highly disperse Pr 2O 3 relative to Pr 6O 11 when the latter oxide is mixed with MoO 3 in the above atomic ratios.