Disproportionation of Propylene over Supported Metal Oxide Catalysts

Abstract

Disproportionation of propylene on several metal oxide catalysts was studied by means of a flow method. The effects of pretreatment of catalyst with various gases and of various supports on the reaction were investigated in order to clearify the formation of active centers of catalyst. The reaction was carried out at the temperature range from 100°C to 200°C on each catalyst activated 'previously with dry nitrogen gas, dry oxygen or dry hydrogen at 500°C.It was found that WO3-γ-Al2O3 was the most active catalyst for this reaction, but selectivity was rather small. On the other hand, the activity of MoO8-γ-Al2O3 was very high at the beginning of the reaction, but the activity decreased gradually with the reaction time. When the catalyst was pretreated with nitrogen, the activity was greatly different with the various supports, that is, MoO3-SiO2.Al2O3 was most active, and both MoO2-SiO, and MoO3-α-Al2O3 had no activity for this reaction. From these results, it seems that the activity of several supported MoO3 was correlated with the acidity of these carriers.By reducing all these catalysts with hydrogen before the reaction, the activity prominently increased, especially the activity of both MoO3-SiO2 and MoO3-α-Al2O3 became almost equivalent to that of MoO3-γ-Al2O3.From these phenomena, it is concluded that the active center of these catalyst is slightly reduced molybdenum oxide, and the acidic carrier plays a role in forming the active center during the pretreatment of catalyst, without directly participating in the reaction.