Fine-Tuning Texture of Highly Acidic HZSM-5 Zeolite for Efficient Ethanol Dehydration

Achieving high and stable ethylene yield from (bio)ethanol dehydration over highly active acidic zeolite remains challenging due to undesired side-reactions. To overcome this issue, the fine-tuned textural property of the HZSM-5 catalyst with a hierarchical structure is crucial to overcome diffusion restrictions and limit undesired side-reactions. Herein, the texture of high acid catalysts obtained via hydrothermal synthesis was simply tuned in the presence of tetrabutylammonium hydroxide as a meso- and micropore directing agent and the controlled molar ratio of NaF-to-Al2O3. The hierarchically designed HZSM-5 with the small nanosheet size of 6.5 nm exhibits a high external surface area and mesopores, largely enhancing the catalytic performance of ethanol dehydration up to 95 % ethylene yield as well as preventing the formation of heavy hydrocarbons. To gain insights into the mechanistic points of view, the in situ DRIFTS study revealed that ethylene could form through ethoxy-mediated mechanism or decomposition of diethyl ether (DEE). The catalyst deactivation caused by polyaromatics obtained from side-reactions is the reason for low ethanol conversion and high DEE selectivity. Reducing the crystal size of highly acidic zeolite to ultra-thin nanosheet can shorten the residence time of ethanol, intermediates, and products in porous structures, substantially suppressing the transformation of coke precursors into heavy hydrocarbons to achieve high and stable ethylene yield.

Automated summary

By fine-tuning the texture of HZSM-5 catalysts and reducing the crystal size to ultra-thin nanosheet, high and stable ethylene yield can be achieved from ethanol dehydration.