Finding the Compromise between Bronsted Acidity and Mesoporosity in Hierarchical ZSM-5 Zeolites

Mesoporous ZSM-5 catalysts were prepared from a commercial ZSM-5 (Si/Al=15), using a 2-step micelle-templating procedure. By varying the NaOH/Si synthesis ratio in the range of 0.3-0.7, ZSM-5 catalysts with different textural and acidic properties were obtained. Increasing the NaOH/Si ratio in the synthesis gel leads to zeolites that feature reduced number of Bronsted acid sites, but higher mesopore volume, which allows for reducing the diffusion path length. In order to assess the best compromise between Bronsted acidity and mesopore volume two test reactions were run. The alkylation of phenol with tert-butyl alcohol allowed to evidence the accessibility of bulky molecules to active sites. The esterification of benzyl alcohol with hexanoic acid allowed to probe the specificity of Bronsted acid sites in ZSM-5. The best compromise was found for micro-/mesoporous ZSM-5 catalysts prepared with the ratio 0.38

Automated summary

This study prepared mesoporous ZSM-5 catalysts using a 2-step micelle-templating procedure and varying the NaOH/Si synthesis ratio. The catalysts obtained showed different textural and acidic properties, with reduced acidity but higher mesopore volume. By testing two reactions, the best compromise was found for micro-/mesoporous ZSM-5 catalysts prepared with the ratio 0.38, which showed good accessibility for bulky molecules and specificity for Bronsted acid sites.