Add-Functionalized SBA-15-Type Silica Catalysts for Carbohydrate Dehydration

A bifunctional silane, 3-((3-(trimethoxysilyl)-propyl)thio)propane-1-sulfonic acid (TESAS), was designed for incorporation into SBA-15-type silica by co-condensation. To achieve mesopore ordering in the functionalized silica, the standard SBA-15 synthetic protocol was modified, resulting in well-formed hexagonal particles. In a variation, the thioether group of TESAS was oxidized by H2O2 to the sulfone during the synthesis of the modified SBA-15. The presence, concentration, and location of functional groups were assessed by elemental analysis, potentiometric titration, and C-13 and Si-29 CP/MAS NMR spectroscopy. Pore structure and particle morphology were observed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and powder X-ray diffraction (XRD). The materials were studied and compared in the selective dehydration of fructose to 5-hydroxymethylfurfural (HMF). Interestingly, the thioether-containing TESAS-SBA-15 shows higher activity in the dehydration of aqueous fructose, as well as higher selectivity toward HMT (71%. at 84% conversion) than its sulfone derivative, possibly because of its more hydrophobic nature.