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This investigation focused on the study of formation mechanism for highly mesoporous ZSM-5 under the introduction of tetrapropylammonium hydroxide (TPAOH) during NaOH treatment. Determined based on N 2 sorption, transmission electron spectroscopy, scanning electron spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, inductively coupled plasma atomic emission spectroscopy, and 29 Si magic-angle spinning nuclear magnetic resonance characterizations, increased mesoporosity, crystallinity, and surface integrity for the desilicated ZSM-5 were found after TPAOH introduction. This protective effect of tetrapropylammonium (TPA + ) on desilication was reflected by increased surface SiO 2 /Al 2 O 3 ratios with increased concentrations of TPA + . TPA + was first confirmed to be mainly adsorbed on the Si(4Si, 0Al) sites to provide a protective effect. Na + played an indispensable role in the induced desilication during alkali treatment. The co-effect of protective desilication from TPA + and preferential desilication near Na + on the surface accounts for the formation of ZSM-5 with high mesoporosity. Contributing to larger external surfaces, the TPAOH-aided desilicated sample possessed a longer methanol-to-hydrocarbons lifetime of 102 h, twice that of ZSM-5 treated by traditional NaOH treatment.

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Supporting informationand the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.org/10. 1002/cctc.201700925. This work aims to improve the catalystl ifetime of ZSM-5 for the methanol-to-hydrocarbons conversion by tuning the pore structurea nd external surface area on nano-ZSM-5 (100 nm). Severald ifferently pore-structured samples were synthesized based on the controllable desilicationo fn ano-ZSM-5 by prolongingt he alkali-treatment time and introducingt etrapropylammonium hydroxide (TPAOH) into NaOH solution. 2h NaOH treatment produced mesoporous ZSM-5 with well-maintained interior,a nd the catalytic lifetime was prolonged from 60 to 127 ha longw ith increased isoparaffins selectivity owing to improvedd iffusion and accessibility of internal weak acid sites. If prolonging the treating time to 15 h, nano-ZSM-5 with initially formed hollow structure (HI-Z5) was achieved, which shows relativelys hort lifetimeo f8 5h and high aromaticss electivity. After as econdary treatment of HI-Z5w ith fresh NaOH solution for 5h,the formed thin shell and clean interior significantly improvedd iffusion, and the lifetime increased from 85 to 115h. The aromatics selectivity was also increased by the enhanced acidity.Mesopores were introduced into the shell of HI-Z5 after treatingi tw ith af reshly mixed solutiono fN aOH andT PAOH. The external surfacearea exhibited a9 4% increase, resulting in ah igh isoparaffins selectivity and al ong lifetimeof149 h.

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