Eco-Friendly Synthesis of SO<sub>3</sub>H-Containing Solid Acid via Mechanochemistry for the Conversion of Carbohydrates to 5-Hydroxymethylfurfural
Shuang Sun, Lijie Zhao, Jirui Yang, Xiaoqi Wang, Xiaoya Qin, Xinhua Qi, Feng Shen
Abstract
A green, efficient, and facile ball-milling-assisted strategy was proposed to design an SO3H-containing solid acid for biomass valorization, where −SH groups were grafted on a natural clay attapulgite by wet ball milling with 3-mercaptopropyltrimethoxysilane (MTPS), followed by the oxidation of −SH to −SO3H with H2O2 at room temperature. The mechanism of the −SO3H functionalization by the ball-milling process was investigated, and the investigation indicated that the MTPS was grafted on the attapulgite through hydrolysis and condensation, which was induced by the mechanical forces of ball milling. Characterization, including SEM, EDX (energy-dispersive X-ray spectrometry), NH3-TPD, TGA, FT-IR, elemental analysis, and XPS, confirmed the success of −SO3H modification on attapulgite with a total acidity of 1.81 mmol/g. Harsh conditions involving a corrosive sulfonating agent, organic solvent, or high temperature in traditional methods are avoided in the developed approach. The prepared catalyst displayed a high activity toward the transformation of biomass-derived carbohydrates (glucose, fructose, cellobiose, sucrose, starch, and cellulose) into the more valuable chemical 5-hydroxymethylfurfural due to the synergy effect of MgO and −SO3H sites on the catalyst. Moreover, the catalyst showed excellent stability and recyclability for five recycles without loss of activity. This study provides a novel green method for the preparation of an SO3H-containing heterogeneous catalyst, which should have great application potential in other processes of biomass valorization.