Formation of Mo-carbene active sites in Mo/Beta zeolite catalysts with different olefins: Theoretical exploration of possible reaction pathways and substituent effects

Metal-carbenes act as the active sites in varieties of important reactions, and in this work, the possible pathways of Mo-carbene formation in Mo/Beta zeolite were explored by density functional calculations. Four chiral oxametallacyclobutane intermediates of different energies were determined for either propylene or 2-butylene, corresponding to the four independent reaction pathways. The main products were Mo-methylidene for propylene and syn-Mo-ethylidene for 2-butylene, respectively. On the basis of energy profiles, the activities of producing the Mo-carbene species were found to decrease in the order of propylene > 2-butylene > ethylene, which were the compromising results of electrophilic and steric effects.