Guest–host interactions of arenes in H-ZSM-5 and their impact on methanol-to-hydrocarbons deactivation processes

The acidic zeolite H-ZSM-5 is a widely used catalyst in industrial methanol-to-hydrocarbons (MTH) conversion, due to its pronounced stability to the formation of unreactive arenes that degrade the catalyst. In the present work, adsorption of a series of mono- and polycyclic arenes in H-ZSM-5 is modeled through periodic density functional theory calculations on the complete unit cell employing the BEEF-vdW functional. Polycyclic arenes are predicted to fit in the zeolite framework, the preferred adsorption site being the intersection region between the straight and sinusoidal channels. Supporting recent experimental results, an adsorbate orientation along the straight channel is predicted. A pronounced confinement of the arenes governs their directional interaction with acid sites. From the findings, it is plausible that deactivation of H-ZSM-5 during MTH conversion is caused by polycyclic arenes growing in the straight channels near the outer surface of the zeolite crystal on which they join to form graphitic layers.

Graphical abstractAdsorption of mono- and polycyclic arenes in the H-ZSM-5 zeolite has been modeled with density functional theory. The preferred adsorption site is the intersection region between the channels. Confinement governs the interaction with acid sites; the arene shape and size determine whether stabilization is possible.Figure optionsDownload full-size imageDownload high-quality image (96 K)Download as PowerPoint slideHighlights► Adsorption of mono- and polycyclic arenes at multiple sites in H-ZSM-5 was modeled. ► Periodic DFT were employed on the complete MFI unit cell. ► Long- and short-range interactions were simultaneously described with BEEF-vdw functional. ► Arenes prefer adsorption in channel intersection and orient along straight channel. ► Interaction with acid sites is governed by confinement of the rigid arenes.