Study on olefin oxidation by periodic-pulse technique: I. Propylene oxidation into acrolein using various oxide catalysts

Abstract

By the periodic-pulse technique, distinguished from the conventional continuous-flow reaction by the alternate feeding of oxygen and hydrocarbon, the oxidation of propylene was investigated over various oxide catalysts. It is shown that the reaction takes place according to the same mechanism, i.e., the reoxidation-reduction mechanism, irrespective of the reaction technique. We attempted to characterize various oxide catalysts by the periodic-pulse technique and by electrical-conductivity measurements. The speculations regarding surface oxidation states on the basis of a separative analysis of the combustion reaction and the electrical conductivity during the reaction are consistent. Combustion is found to take place at the oxygen-regeneration pulse (O-pulse) over the Sn-P, Bi-W, and Bi-Mo oxide catalysts, which are severely reduced, while at the propylene-reaction pulse (R-pulse) over the Sn-Sb and Sb-Mo oxide catalysts, the catalysts maintain higher oxidation states. The catalysts can also be classified into three groups on the basis of the period dependence; (a) Bi-Mo, B-iW (b) Sn-Sb, Sb-Mo (c) MoO 3, Sn-P The catalysts are divided into Group (b) and Groups (a) and (c) on the basis of the results of the combustion reaction; these results are correlated with the characterization of the separative analysis and electrical-conductivity measurements. On the basis of these findings, some discussions are made of the catalyst properties controlling their surface oxidation states. Furthermore, the roles of bismuth and antimony are speculated on.