Formation of Active Sites on WO₃ Catalysts: A Density Functional Theory Study of Olefin Metathesis

Industrial demand for poly(propene) has spurred research on improved catalysts and mechanisms for propene production. Recently, tungsten trioxide (WO 3 ) was reported to exhibit high activity for the metathesis of ethene and 2-butene to form propene. The whole process is divided into two stages: (1) Initiation (i.e., formation of W-carbene active sites on WO 3 surfaces), and (2) Propagation (i.e., metathesis reaction on these active sites to yield propene). This study investigates the mechanism of W-carbene active site formation, using first-principles calculations based on density functional theory. For the WO 3 orthorhombic crystal, the (001) surface has been found to be the most stable, since it contains four chemically distinguishable types of surface atoms: 5-fold coordinate W 5 c, 6-fold coordinate W 6 c, 2-fold bridging oxygen O 2 c, and singly coordinated oxygen O 1 c . Because of the different energies of adsorption for ethene and 2-butene at these four types of active sites, we find that 2-butene forms W-carbene active sites more readily, with lower activation energies, than ethene, because of a combination of electrophilic and steric effects. These results reveal the relationship between WO 3 catalyst surface structure and activity for metathesis, which ultimately will guide the development of more active and selective catalysts for propene production.