Insights into the effects of zeolite structural confinement on pentene catalytic cracking to light olefins

It has long been known that the structural and topological diversity of microporous voids confer significant catalytic diversity to zeolites. What is less understood, however, is the insights into the role of confinement on reactivity of important reactions such as alkene cracking and hydrogen transfer. The influence of confinement environment toward the reaction process on conversion of pentene is the focus of this study. Pentene is mainly converted through the reaction of hydrogen transfer, dimerization cracking and monomolecular cracking. The more effective van der Waals stabilization within smaller voids leads to lower enthalpies, and the transition state of monomolecular cracking retain higher entropies, which makes monomolecular cracking dominant in F-ZSM-5 at high temperature. It is therefore favorable for the enhancement of ethene selectivity in the cracking products. Furthermore, the tighter confinement could strengthen the adsorption ability and weaken the CC bonds of pentene, which results in prominently enhanced rate of pentene monomolecular cracking, as suggested by the kinetic analysis and density functional theory (DFT) simulation.