Efficient conversion of cellulose to 5-hydroxymethylfurfural using a bifunctional hydrophobic SBA-15 catalyst: The effects of hydrophobicity, morphology and acidity.

Owing to the negative impact of water on catalyst activity, and the consequent side reactions, the hydrophobicity and acidity of the catalyst are important factors in the conversion of cellulose to 5-hydroxymethylfurfural in an aqueous solvent. In the present study, we prepared SBA-15 catalysts comprising hydrophobic methoxy groups, phosphotungstic acid as Lewis acid groups, and -SO 3 H Brønsted acid groups. The introduction of methoxy groups increased the contact angle of the catalyst from 57.42 to 87.80° and changed its morphology from stubby short rods to long curved sticks. The maximum 5-hydroxymethylfurfural yield (61.24%) was obtained using 2SBA-15-SO 3 H, which comprised 237.31 μmol·g−1 of the Brønsted acid and 14.44 μmol·g−1 of the Lewis acid and had a contact angle of 75.93°. The low yields of levulinic acid and formic acid (below 10%) confirmed the resistance of such SBA-15 catalysts to water. Furthermore, adequate hydrophobicity facilitated glucose isomerization, whereas the catalyst morphology, which tended to comprise short rods, improved the fructose dehydration rate. Density functional theory analysis of the acidity sites route revealed a 3-DG pathway for 1,4,5,6-tetrahydroxy-hexan-2-one generation with Lewis acid sites, and a free energy of 0.13 eV, paralleled by glucose isomerization to fructose through a 1,2-enediol. [Display omitted] • Introduction of methoxy groups changes water-tolerance and morphology of catalyst. • Adequate hydrophobicity of the SBA-15 catalysts facilitated glucose isomerization. • Short rod morphology of the SBA-15 catalysts improved fructose dehydration rate. • 5-HMF yield was reached as 61.24% and <10% of LA and FA was obtained using 2SBA-15-SO 3 H. • 1,4,5,6-tetrahydroxy-hexanone generated by Lewis acid sites through 3-DG pathway. [ABSTRACT FROM AUTHOR]