Selective conversion of furfuryl alcohol to levulinic acid by SO3H-containing silica nanoflower in GVL/H2O system

Levulinic acid in high yields (90%) was produced from hemicellulose-derived furfuryl alcohol catalyzed by a uniform, dandelion-like, SO3H-modified silica nanoflower solid acid (SiNF–SO3H). The SiNF–SO3H catalyst was prepared by soft template method in microemulsion system, followed by grafting of –SH and oxidation of –SH to –SO3H at room temperature to avoid use of corrosive sulfonating agents such as concentrated H2SO4. Dandelion-like porous structures of the SiNF–SO3H catalyst provided accessible and abundant catalytic sites ensuring high activity for furfuryl alcohol conversion (100%). Mixed-solvent γ-valerolactone-water (GVL-H2O) inhibited undesirable furfuryl alcohol polymerization reactions ensuring highly selective conversion of furfuryl alcohol to levulinic acid. Combination of catalyst and solvent system allowed achievement of the highest levulinic acid yields that have been reported to date. Both the catalyst synthesis protocol and reaction solvent (GVL-H2O) are green and sustainable. The SiNF–SO3H/(GVL-H2O) catalytic system has application to many acid catalyzed schemes for lignocellulosic biomass conversion.