(600bq) Computational Study On Olefin Metathesis of Ethene and 2-Butene On WO3 Surfaces

Industrial demand for poly(propene) has spurred research on improved catalysts and mechanisms for propene production. Recently, tungsten trioxide (WO₃) was reported to exhibit high activity for the metathesis of ethane and 2-butene to form propene. In this work, we employ first-principles calculations based on density functional theory to explore the energetics and kinetics of W-carbene active site formation on WO₃ surfaces, and of propagation reaction on these active sites. For the WO₃ orthorhombic crystal, the (001) surface has been found to be the most stable, which contains four chemically distinguishable types of surface atoms: 5-fold coordinate W_5c, 6-fold coordinate W_6c, 2-fold bridging oxygen O_2c, and singly coordinated oxygen O_1c. We find that the formation of initial W–carbene occurs via the [2+2] cycloaddition reaction following the break of four membered ring. We also find 2-butene preferentially forms W-carbene active sites, compared to ethene, because of the presence of electrophilic and steric effects that destabilize the intermediates.  In the propagating step, ethene and 2-butene would further react with W-carbene to yield propene molecule which also interacts with the active site to affect the rate of metathesis reaction. These results reveal the relationship between WO₃ catalyst surface structure and activity for metathesis, which ultimately will guide the development of more active and selective catalysts for propene production.