Propagation of Olefin Metathesis to Propene on WO3 Catalysts: A Mechanistic and Kinetic Study

Abstract

The production of propene (H2C═CH–CH3) has attracted widespread interest due to industrial demand, and an intriguing route involves the metathesis of ethene (H2C═CH2) and trans-2-butene (H3C–CH═CH–CH3). We recently investigated the initiation of olefin metathesis on tungsten trioxide (WO3) catalysts, by showing that trans-2-butene more readily forms W-carbene active sites on the surface, compared to ethene. We now present our analysis of the propagation steps at these active sites. We have computed optimized structures and energetics of the reaction intermediates and products of propagation. We have also computed the rate constants for the elementary steps comprising the reaction mechanism. These results are used to elucidate a complete mechanistic description of the metathesis of ethene and trans-2-butene. We find that W═CH2 sites are less active in the propagation process compared to W═CHCH3. Furthermore, [2 + 2] cycloaddition of trans-2-butene to form the six-membered (oxa)metallacycle ring is the rate...