Synergistic Catalysis of Brønsted Acid, Al-Lewis Acid, and Zn-Lewis Acid on Steam-Treated Zn/ZSM-5 for Highly Stable Conversion of Methanol to Aromatics

Abstract

The development of stable and selective ZSM-5 catalysts for methanol aromatization remains an ongoing challenge. Here, we demonstrate highly stable aromatization on ZSM-5 by preliminary steam treatment before Zn introduction. Steam treatment destroyed part of frameworks, which decreased acid density from 0.5 to 0.25 mmol g −1 and increased Al-Lewis acid sites (Al-LAS) at the expense of Brønsted acid sites (BAS). However, aromatization activity was further increased and the lifetime was still kept at 100 h. A comparative experiment found that increasing the SiO 2 /Al 2 O 3 ratio from 60 to 240 also decreased acid density to 0.25 mmol g −1 , but BAS-based acid sites aggravated coke formation and reduced lifetime to 50 h. This reflected that Al-LAS and BAS on steam-treated ZSM-5 provided synergistic catalysis for stable aromatization. Introducing Zn into steamtreated ZSM-5 further transformed part of BAS to Zn-LAS but not changed acid density, which determined increased aromatics selectivity and a quite different well-maintained stability.

Catalytic performance and mechanism study of the isomerization of 2,5-dichlorotoluene to 2,4-dichlorotoluene

“…39,40 A paired aluminium atom signal (Al pairs ) at around 55.8 ppm was tted, which is located in straight and sinusoidal pores within the zeolite. Additionally, an isolated aluminium atom signal peak (Al single ) at approximately 65.8 ppm was tted, representing aluminium species situated at pore intersections, 41,42 Fig. 2e.…”

“…The acidity of zeolite catalysts primarily depends on the coordination state and distribution of aluminium species, including framework Al and extra-framework Al. 2 Various posttreatment methods, such as acid treatment, 3,4 alkali treatment, 5 and hydrothermal treatment, [6][7][8] can modify the catalyst's acidity. Among these techniques, hydrothermal treatment has garnered signicant research attention owing to its convenience, cost-effectiveness, and substantial potential for industrial applications.…”

“…Zhao et al , 14 reported that hydrothermal treatment could effectively reduce the acidity of the zeolite. Moreover, hydrothermal treatment results in varying degrees of dealumination, as studied by Zhang et al , 15 and Fu et al , 8 who examined the effects of hydrothermal treatment on the structure and acidity of ZSM-5 zeolite.…”

Synergistic Catalysts of Lewis Acid and Brønsted Acid for Highly Efficient Preparation of Bisphenol Compounds

“…Lewis acids, commonly used as efficient catalysts, have been applied in various reactions, including methanol aromatization, 16 γ-valerolactone decarboxylation, 17 and indole cycloaddition. 18 involving alkenes with trifluoropyruvates, 19 pyrroles with 2enoyl-pyridine N-oxides, 20 and ferrocene with allylchlorosilanes.…”

“…Lewis acids, commonly used as efficient catalysts, have been applied in various reactions, including methanol aromatization, γ-valerolactone decarboxylation, and indole cycloaddition . Additionally, Lewis acids such as Ni­(ClO 4 ) 2 ·6H 2 O, Zn­(OTf) 2 , AlCl 3 , and ZnCl 2 have been demonstrated to be effective in catalyzing Friedel–Crafts alkylation reactions involving alkenes with trifluoropyruvates, pyrroles with 2-enoyl-pyridine N -oxides, and ferrocene with allylchlorosilanes .…”