Facile synthesis of SAPO-34 nanocrystallites with excellent performance for the dehydration of carbohydrates to 5-hydroxymethylfurfural

Abstract

The conversion of biomass resources into 5-hydroxymethylfurfural (5-HMF) is of great significance for the valorization of biomass into key chemicals and fuels. However, designing heterogeneous catalysts with controllable Brønsted and Lewis acid sites for achieving high yields of 5-HMF remains a challenge. Herein, a highly efficient SAPO-34 nanocrystallites catalyst has been synthesized by a facile strategy, employing commercial low-cost organosilane [3-glycidoxypropyltrimethoxysilane (AC-230)] together with seeds and microporous template triethylamine. The complex functionalities of AC-230 were investigated by conditional experiments and systematic characterizations. The resultant SAPO-34 nanocrystallites (SP-MS) have an ultra-high external surface area (180 m² g⁻¹), large mesopore volume (0.51 cm³ g⁻¹), a high amount of accessible Brønsted/Lewis acid, and good hydrophilicity. For the conversion of mono-, di-and poly-saccharides into 5-HMF, SP-MS exhibited remarkable activity. Typically, an 81% yield of 5-HMF with a complete glucose conversion was achieved in a biphasic NaCl–H₂O/methyl isobutyl ketone solvent system at 170 °C within 45 min, obviously better than other heterogeneous acid catalysts. According to the kinetic study, the Lewis acid sites over SP-MS decreased the apparent activation energy (85 kJ mol⁻¹) of glucose isomerization, and then the abundant Brønsted acid sites boosted the 5-HMF yields. More attractively, the catalytic activity can be restored after at least four cycles. This work is anticipated to provide insights into designing efficient and robust SAPO catalysts for 5-HMF production.