Conversion of xylose to levulinic acid over modified acid functions of alkaline-treated zeolite Y in hot-compressed water

• Levulinic acid is produced from xylose over alkaline-treated zeolite in hot water.
• Realumination on the zeolite’s external surface forms new strong acid sites.
• The strong acid site is the key factor for enhancing selectivity to levulinic acid.

Levulinic acid (LA) was effectively synthesized from xylose conversion under hot-compressed water using alkaline-treated zeolite catalysts. Zeolite Y was treated in alkaline solution to modify its acid-sites and physical properties. After NaOH treatment, the surface area markedly decreased due to collapses of crystal structure, while the pore size and pore volume increased. Interestingly, new strong acid sites were formed in the catalyst treated in 0.25 M NaOH, while the Si/Al ratio did not change significantly due to the realumination of aluminum species on the external surface of zeolite. The higher concentration of NaOH gave rise to higher amount of new strong acid sites, improving LA yield. The maximum LA yield of 30% was achieved from the treated zeolite in 0.25 M NaOH. The roles of reaction time and temperature as well as the effect of pressurized gases on the catalytic activity and selectivity were studied.

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