Insight into the Selection of the Post-Treatment Strategy for ZSM-5 Zeolites for the Improvement of Catalytic Stability in the Conversion of Methanol to Hydrocarbons

Abstract

Desilication and dealumination are two common strategies to modify acidity and porosity of the ZSM-5 catalyst to enhance catalytic stability. However, the applicability of these strategies on the post treatment of specific ZSM-5 remains to be investigated. In this paper, a series of post-treated nano-ZSM-5 was prepared using single dealumination and desilication or combining two strategies and the effects of the silicon–aluminum structure, porosity, and acidity on catalytic stability of methanol to hydrocarbons (MTH) have been comparatively studied. This study found that for nano-ZSM-5 whose diffusion limitation is not the main cause of deactivation, dealumination should be considered to optimize acidity and silicon–aluminum structure on the surface for the improvement of catalytic stability, while for micro-ZSM-5, desilication should be first applied to construct mesopores to reduce diffusion constraints, followed by dealumination to optimize acidity and surface silicon–aluminum structure to improve the catalytic stability.

Rapid solvent-free synthesis of nano-sized ZSM-5 with a low Si/Al ratio at 90 °C

“…Z4: it is a conventional hydrothermal synthesis method, according to the literature 36 crystallizing a gel with a molar composition of 36SiO 2 : NaAlO 2 : 9.0TPAOH : 5.0NaOH : 144EtOH : 300H 2 O at 170 °C for 48 h, which was used for comparison with our protocol.…”

“…35 Then sodium aluminate, sodium hydroxide, and fumed silica were added to the liquid seed in the same way as that of Z1 but retaining the final molar ratio of the solid mixture. Finally, the solid mixture was crystallized at 90 °C for b h. Z4: it is a conventional hydrothermal synthesis method, according to the literature 36 crystallizing a gel with a molar composition of 36SiO 2 : NaAlO 2 : 9.0TPAOH : 5.0NaOH : 144EtOH : 300H 2 O at 170 °C for 48 h, which was used for comparison with our protocol.…”

Design of a Compact Microreactor/Heat-Exchanger for a Distributed Production of Liquid Hydrocarbons from Methanol

“…It can be concluded that the H-ZSM-5 catalyst is preferred for both reaction zones. The activity and selectivity over H-ZSM-5 zeolite further depends on its acidity (the Si/Al ratio), which can be varied by partial ion-exchange with Ca [17] or via postsynthesis treatments [18]. Yet the internal diffusion of bulky molecules is hindered in microporous zeolites; therefore, only active sites located in the channels close to the crystal outer surface are accessible for the reactants.…”

Improving the Hydrothermal Stability of ZSM-5 Zeolites in 1-Octene Aromatization by Sequential Alkali Treatment and Phosphorus Modification

“…It is generally accepted that Brønsted acid sites of zeolites are the active centers for the conversion of olefins to aromatics. However, this type of catalyst suffers from rapid deactivation during the aromatization reaction [9].…”