Mechanistic studies of methanol-to-hydrocarbons conversion on diffusion-free MFI samples

Abstract Self-pillared pentasil MFI (∼1 nm diffusion length) exhibited low ethene selectivity (1.1%) at p -xylene with DME increased the number of chain carriers of the aromatics-based cycle, thereby enhancing its propagation and resulting in a 2–3-fold increase in ethene selectivity. Co-feeding propene or 1-hexene, however, did not have an effect on the product distribution, suggesting that the olefins-based hydrocarbon pool is saturated in the pores of MFI. At high temperature (723 K) and low DME space velocity (⩽2.5 mol C [mol Al-s] −1 ), conditions resulting in complete DME/methanol conversion, the catalyst bed comprises two stages: The first stage performs methanol-to-hydrocarbons chemistry in the presence of DME/methanol; the second stage begins after 100% DME conversion is achieved and is characterized by the absence of DME/methanol. The aromatics-based methylation/cracking cycle is absent in the second stage as methylbenzenes cannot dealkylate in the absence of DME/methanol, and the dominant pathway to ethene formation under these reaction conditions is olefin inter-conversion.