Tailoring hierarchical ZSM-5 with water-soluble polymers templates for BTX production in methanol-to-aromatics.

Abstract

Hierarchical ZSM-5 zeolites were synthesized by one-pot methods utilizing water-soluble polymers-polyvinylpyrrolidone (PVP) and polyethylene glycol (PEG)-and were compared with a desilicated (DS/ZC) typical microporous ZSM-5 (ZC). Thorough evaluation utilizing XRD, FT-IR, NH₃ physisorption, SEM and TEM, ICP-OES, NH₃-TPD, and TGA demonstrated that PVP-templated ZSM-5 (PVP/ZC) displayed distinct mesoporosity while maintaining its inherent microporous structure, resulting in a balanced allocation of weak and strong acid sites. All catalysts were assessed in the methanol-to-aromatics (MTA) reaction at 400 °C, with a weight hourly space velocity (WHSV) of 5 h^-1 and atmospheric pressure (time on stream = 3 h), resulting in over 99.5% methanol conversion. PVP/ZC attained the highest BTX selectivity of 51.3% and an overall aromatic selectivity of 60.1%, due to its uniform mesoporosity, reduced diffusion pathways along the <i>b</i>-axis, and optimized distribution of acid sites, which collectively minimized secondary C₉₊ formation (8.8%) and coke deposition (3.27 wt%). The findings indicate that water-soluble polymer templates, specifically PVP, facilitate the customized synthesis of hierarchical ZSM-5 catalysts, which improve BTX production and stability in the MTA process, providing a cost-effective and environmentally friendly alternative to conventional templating and post-synthetic treatments.