A DFT Study of Tungsten–Methylidene Formation on a W/ZSM‐5 Zeolite: The Metathesis Active Site

Tungsten–methylidene formation from ethene on either the W IV , W V , or W VI active sites of a W/ZSM‐5 zeolite is investigated by using the M06‐L functional. The reaction is assumed to proceed in two steps; the first step is the [2+2] cycloaddition between ethene and the W−O active site to form an oxametallacycle intermediate. The intermediate is then decomposed to produce the W–methylidene active site from the metathesis reaction. The overall activation barrier of the reaction on W VI (27.3 kcal mol −1 ) is considerably lower than the ones for W IV and W V (69.4 and 37.1 kcal mol −1 , respectively). Moreover, the reaction involving the W VI site also stabilizes intermediates and products to a larger extent than the ones on the W IV and W V sites. As a result, we have demonstrated that the reaction of the W–methylidene metathesis active site is both kinetically and thermodynamically favored to occur on the W VI active site of the zeolite.