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

Authors: 
Rasmus Brogaard, Bert M. Weckhuysen, Jens K. Nørskov
Year of publication: 
2013
Journal: 
Journal of Catalysis

The acidic zeolite H-ZSM-5 is a widely used catalyst in industrial methanol-to-hydrocarbons (MTH) con- version, 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 func- tional. 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 deac- tivation of H-ZSM-5 during MTH conversion is caused by polycyclic arenes growing in the straight chan- nels near the outer surface of the zeolite crystal on which they join to form graphitic layers.