Mechanochemical Synthesis of Sulfonated Palygorskite Solid Acid Catalysts for Selective Catalytic Conversion of Xylose to Furfural

A green, safe, and easy-operation method for the preparation of sulfonated palygorskite solid acid catalyst (PAL-SO₃H) was developed by a mechanochemical process, where thiol groups (−SH) were grafted onto natural palygorskite by a high-speed shearing process with 3-mercaptopropyltrimethoxysilane in aqueous solution under mild conditions, followed by the oxidation of −SH to −SO₃H groups. The as-prepared PAL-SO₃H catalyst was applied in the catalytic conversion of biomass-derived xylose into furfural, and it showed excellent catalytic activity, and as high as 87% of furfural yield with 96% selectivity was achieved at 180 °C in 60 min reaction time in the γ-valerolactone–water mixture (95:5 v/v %). The PAL-SO₃H catalyst was tolerant of high initial xylose loading concentration up to 120 g/L and exhibited good recyclability. This study provides a green and mild process for the synthesis of a sulfonated solid acid catalyst, which should have potential applications in many fields such as catalysis and adsorption.