Sustainable and selective production of aromatics from bio-oil model compounds over Zn/ZSM-5 zeolites

The sustainable production of green aromatics is of great importance for industry due to the growing demand for these compounds. In this work, we investigated Zn/ZSM-5 zeolites synthesized by evaporation-impregnation and ion-exchange methods for the conversion of n-octane and methylcyclohexane, two model compounds of a hydrotreated bio-oil, into valuable aromatics, such as benzene, toluene, and xylenes (BTX). The introduction of Zn into the zeolite framework altered its acidic properties by creating new Lewis acid sites at the expense of Brønsted acid sites. A balanced distribution of Lewis and Brønsted acid sites, along with an optimal SiO₂/Al₂O₃ ratio, are crucial parameters governing the zeolite performance towards the desired BTX products. Thus, it was found that catalysts with a higher Brønsted-to-Lewis acidity ratio (based on the number of acid sites) are more selective towards xylenes, while lower ratios favor the selective production of toluene. Ion-exchanged Zn-zeolites outperformed impregnated ones, promoting higher conversion and xylene yield due to increased Brønsted acidity, which favored cyclization pathways.