Conversion of Furfuryl Alcohol to Levulinic Acid in Aqueous Solution Catalyzed by Shell Thickness-Controlled Arenesulfonic Acid-Functionalized Ethyl-Bridged Organosilica Hollow Nanospheres

A series of arenesulfonic acid functionalized ethyl-bridged organosilica hollow nanospheres, ArSO3H-Et-HNS, with different shell thicknesses (2-6 nm) were successfully fabricated by P123 and/or F127-directed sol-gel cocondensation route and carefully controlled molar composition of the starting materials in the synthetic gel. The ArSO3H-Et-HNS were applied in the synthesis of levulinic acid (LA) from the hydrolysis of furfuryl alcohol (FAL), and the influence of experimental parameters including solvent nature, volume ratio of FAL-to-solvent-to-water, shell thickness of hollow nanospheres, and reaction temperature were considered. The hydrolysis activity of the ArSO3H-Et-HNS outperformed commercially available HY-zeolite, Amberlyst-15, and p-toluenesulfonic acid, regardless of the shell thickness of the hollow nanospheres; additionally, P123-directed ArSO3H-Et-HNS with the thinnest shell (2 nm) and the largest BET surface area (529 m(2) g(-1)) exhibited the highest hydrolysis activity among various ArSO3H-Et-HNS nanohybrids, and under the conditions of 0.72 mol L-1 FAL in 4:1 acetone-H2O, 3 wt % catalyst, and 120 degrees C, the yield of LA reached 83.1% after the reaction proceeded for 120 min. The excellent hydrolysis activity of the ArSO3H-Et-HNS was explained in terms of the strong Bronsted acid nature and unique hollow spherical nanostructures with opening shell and hydrophobic surface. Based on the catalytic test results and the identified intermediates, the reaction mechanism of the ArSO3H-Et-HNS-catalyzed hydrolysis of FAL to LA was tentatively revealed. Finally, the reusability of the ArSO3H-Et-HNS was studied through three consecutive catalytic cycles.