(600e) Reaction Dynamics of Alkene Methylation in H-MFI

The Methanol-to-Olefins (MTO) and related processes are prominent technologies for the incorporation of a variety of non-crude based feedstocks in the production of transportation fuel.  Methylation of various hydrocarbons catalyzed by acidic zeolites has been shown to be a key reaction pathway in the MTO process.  A fundamental understanding of the reaction pathway can provide insight on how to tune performance and product distribution of these catalysts.  Density functional theory is used to analyze the reaction pathways of acid-catalzed alkene methylation in the zeolite H-MFI.  Apparent activation barriers found with the computationally efficient QM(T5)/MM method agree well with experimental measurements.  Intrinsic reaction coordinate analysis reveals the existence of a stable, carbocation intermediate post-rate limiting step.  The final product distribution is determined by dynamics of this intermediate.  Ab initio molecular dynamics simulations are performed to sample reaction pathways post-rate limiting step and to gain insight on the underlying potential energy surface.  The carbocation lifetimes and their influence on product selectivity are discussed.