Molecular Dynamics Simulations of Methanol to Olefin Reactions in HZSM-5 Zeolite Using a ReaxFF Force Field

A ReaxFF force field has been extended and used in the present work to simulate methanol to olefin (MTO) reactions in H-ZSM-5 zeolite. By explicitly considering multibody interactions and thermodynamic conditions, the initial reaction network of MTO in acidic zeolite has been obtained. New reaction mechanisms are proposed based on the simulations. For the activation of methanol, a less possible but very important CH3 radical mechanism is identified in addition to the commonly accepted methoxyl mechanism. The commonly accepted chain-growth mechanism, in which ethene interacts with methyloxide, has been observed. However, it is a small contribution to the total production. The more popular route for the chain growth is attributed to the presence of deprotonated Bronsted sites, which are produced via the activation of methanol molecules. Therefore, the hydrocarbon pool is working with the methanol molecules involved. With the hydrocarbon pool, the chain growth is significantly accelerated. Considering the collision probability, the rate-determining step for MTO is not the activation of methanol as suggested by static calculations but the C-C chain formation. The simulation data are consistent with previously reported experimental observations.