Enhanced Monoaromatic Formation via Hydropyrolysis of Torrefied Chilean Oak over Metal (Ga, Zn) Supported on Modified Natural Zeolite

Biomass pyrolysis stands out among biomass recovery technologies due to its potential to obtain value-added compounds. However, its liquid product presents many oxygenated compounds that reduce its chemical stability. This study aimed to evaluate zinc and gallium supported on Chilean natural zeolite (NZ) as a catalyst in the hydropyrolysis of lignocellulosic biomass to drive the formation of monoaromatic (MAH) compounds through hydrodeoxygenation reactions (HDO). The biomass to be recovered was Chilean Oak, which was subjected to torrefaction treatments and characterized through various analyses. The natural zeolite was modified using ion exchange treatments to (i) remove its compensating cations and increase acidity, and (ii) load Ga and Zn at 2% and 5%. Catalytic hydropyrolysis tests were performed in an analytical pyrolysis system (Py-GC/MS). The fiber analysis of the biomass revealed that hemicellulose content decreased while lignin content increased, resulting in higher energy density and lower oxygen levels. The proximate and ultimate analyses confirmed these findings. On the other hand, natural zeolite maintained its crystalline properties even after modification, and the metal nanoparticles were smaller than 5 nm. The supported metals were in their oxidized state to promote surface acidity. The Ga3+ catalysts were able to form up to 35% phenols, 27% ketones, and 10% MAH, while the Zn2+ catalysts formed up to 34% MAH, 24% ketones, 17% furans, and 13% phenols. The key factors behind Zn’s effectiveness were the Lewis acid sites that could activate C–O bonds and encourage HDO reactions, making it a promising catalyst.