Benzene methylation by methanol is studied on acidic zeolites H-ZSM-5 (MFI) and H-beta (BEA) to investigate the influence of the catalyst topology on the reaction rate. Experimental kinetic measurements at 350 °C using extremely high feed rates to suppress side reactions show that methylation occurs considerably faster on H-ZSM-5 than on H-beta. Theoretical rate constants, obtained from first-principles simulations on extended zeolite clusters, reproduce a higher methylation rate on H-ZSM-5 and provide additional insight into the various molecular effects that contribute to the overall differences between the two catalysts. The calculations indicate this higher methylation rate is primarily due to an optimal confinement of the reacting species in the medium pore material. Co-adsorption of methanol and benzene is energetically favored in H-ZSM-5 compared with H-beta, to the extent that the stabilizing host-guest interactions outweigh the greater entropy loss upon benzene adsorption in H-ZSM-5 vs. in Hbeta.

Alkylation and methylation are important reactions in industrial zeolite catalyzed hydrocarbon transformation processes. This contribution compiles the present knowledge concerning the reaction mechanism of zeolite catalyzed methylation of alkenes and aromatics, based on insights obtained using spectroscopy, quantum chemistry, and kinetic measurements. A central issue is to discuss the potential role surface bound methoxy group intermediates.

The methylation of aromatics is a reaction step that occurs in several petrochemical processes. Here, we have investigated the methylation of benzene by methanol over H-ZSM-5 and H-beta catalysts by conducting kinetic measurements and in situ FT-IR spectroscopy at comparable reaction conditions. A lower rate of methylation per Brønsted acid site is seen for H-beta, and this is linked to the formation of fairly persistent cationic species, as observed with FT-IR.