Effects of dealumination and desilication of H-ZSM-5 on xylose dehydration

• The dehydration of d-xylose was examined over dealuminated and desilicated H-ZSM-5.
• The total amount of acid sites decreased significantly for desilicated H-ZSM-5.
• The fraction of Brønsted acid sites increased after dealumination of H-ZSM-5.
• The fraction of Brønsted acid sites decreased after desilication of H-ZSM-5.
• The furfural selectivity increased with increasing dealumination in H-ZSM-5.

The continuous liquid-phase dehydration of d-xylose into furfural was examined over various zeolites (H-ferrierite, H-ZSM-5, H-mordenite, H-β, and H-Y) having a similar surface area, external surface area, and amount of acid sites to determine the effects of zeolite structure on catalytic performance. Xylose conversion was proportional to the zeolite channel size, whereas the H-ZSM-5 zeolite showed the highest furfural selectivity due to shape-selectivity. In order to improve the catalytic activity, H-ZSM-5 zeolite was dealuminated or desilicated using an aqueous solution of HCl or NaOH, respectively. The prepared catalysts were characterized using N2 physisorption, X-ray diffraction (XRD), solid-state 27Al and 29Si magic-angle spinning nuclear magnetic resonance (MAS/NMR) spectroscopy, temperature-programmed desorption of ammonia (NH3-TPD) and isopropylamine (IPA-TPD). Dealumination of H-ZSM-5 appeared to remove extra-framework Al species without a collapse of the crystalline zeolite framework, while desilication generated extra-framework Al species accompanied by destruction of the zeolite framework. Among the tested catalysts, dealuminated H-ZSM-5 showed the highest furfural selectivity.

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