Modification of ZSM-23 zeolite via vapor-phase transport method: Reducing the length along the unidimensional channels for enhanced catalytic performances in methanol-to-hydrocarbons

Abstract

ZSM-23, a unidimensional zeolite, finds application in the methanol-to-hydrocarbons (MTH) reaction, but commonly suffers from rapid deactivation due to diffusion hindrances. Given the challenges of reducing the length along the a-axis of ZSM-23 zeolite while preserving its catalytic functions using conventional methods, this study introduces a post-modification approach inspired by the vapor-phase transport (VPT) method, wherein ZSM-23 is subjected to the vapor of an iso-propylamine (IPA) solution. The results demonstrated that the crystal lengths aligned with the micropores can be effectively reduced to less than half of the original material (115 nm vs. 289 nm), while preserving much of the microstructure and acidity. Insights into the post-treatment mechanism unveiled a coexistence of etching and re-crystallization processes during the procedure, with conditions finely adjustable by varying the concentrations of the IPA solution. The optimized modification procedure resulted in ZSM-23 zeolite demonstrating an increased C2–C4 olefin yield (62.2 % vs. 53.2 %) and enhanced stability (22 h vs. 5 h) in MTH reaction compared to the untreated sample, which can be attributed to the enhanced diffusion properties of the modified zeolite. This vapor-assisted modification protocol successfully expands the toolkit for synthesizing efficient one-dimensional zeolite for catalytic purposes.