(448e) Theoretical Insights into Catalytic Upgrading of Ethanol over 2D MFI Zeolite

The acid-catalyzed conversion of ethanol over zeolite has been considered as one of the promising routes for producing desirable liquid hydrocarbons. In particular, the reaction pathway near Brønsted acid site (BAS) proceeds via multiple mechanisms, including dehydration of ethanol to ethene with subsequent dimerization to butene or higher olefins. Changing the zeolite morphology from 3D framework to 2D lamella has been known to impact such Brønsted acid chemistry, ultimately affecting the product reactivity/activity of zeolite catalyst. As our first step to understanding the effects of zeolite morphology, we have examined the mechanistic steps of ethanol conversion at the interior and exterior of 2D MFI-based zeolite model. Using density functional theory (DFT) calculations, the relative binding energetic of reaction intermediates were computed at BAS. Our DFT calculations showed that the binding energies of intermediates are similar at the interior and exterior sites. The reaction pathway and free energy profile were further investigated by performing ab initio molecular dynamics (AIMD) simulations at experimental conditions (T ~ 425 °C). The enthalpic and entropic contribution to the free energy at the interior and exterior sites will be discussed in this work. We will show that the rate-determining steps and product selectivity towards higher hydrocarbons are significantly affected by the morphology of zeolite pores.