Isomerization and metathesis of 2-methyl-1-alkenes over Re 2O 7—Al 2O 3 catalysts

Abstract

The double-bond shift isomerization and the metathesis of 2-methyl-1-alkenes were investigated over Re 2O 7-Al 2O 3 catalysts in the liquid phase at atmospheric pressure using a continuous-flow system. When the amount of rhenia was increased, both isomerization and metathesis activity increased in a similar manner. Over a wide range of reaction temperatures ( −35 °C to 60 °C), activation temperatures (50 °C to 500 °C) and reduction temperatures (100 °C to 500 °C), isomerization occurred very readily and seemed to reach equilibrium. In contrast, the metathesis activity was greatly affected by the reaction conditions: it was very low at reaction temperatures lower than 0 °C and at activation temperatures lower than 150 °C, and was destroyed at reduction temperatures higher than 200 °C. This indicates that the active sites of double-bond isomerization are not necessarily directly associated with those for metathesis. As skeletal isomerization and polymerization did not occur, the acid strength is probably fairly weak. The active sites for the double-bond isomerization are thought to be both Brønsted and Lewis acid sites, but Brønsted acidity is more important than Lewis acidity for isomerization.