Efficient transformation of 5-hydroxymethylfurfural to ethyl levulinate over the Brønsted acidic ionic liquid functionalized dendritic fibrous nanosilica spheres

Abstract

Brønsted acidic ionic liquid (BAIL) functionalized dendritic fibrous nanosilica sphere catalysts, [C 3 PrIm][SO 3 CF 3 ]-DFNS (C 3 = PrSO 3 H), are prepared via a hexadecylpyridinium bromide reverse micelle-directed co-condensation of tetraethoxysilane and 3-chloropropyltriethoxysilane in a water-in-oil emulsion system followed by successive chemical modification with imidazole, 1,3-propanesultone and trifluoromethane sulfonic acid, and the particle diameter, fiber thickness and fiber density of the catalysts are well-adjusted by changing the composition of the starting materials. The [C 3 PrIm][SO 3 CF 3 ]-DFNS catalysts are successfully applied in transformation of 5-hydroxymethylfurfural (HMF) to ethyl levulinate (EL). Combination of superstrong Brønsted acidity and unique open three-dimensional dendritic fibrous nanostructures, the [C 3 PrIm][SO 3 CF 3 ]-DFNS can transform HMF in ethanol media rapidly and completely; nevertheless, the selectivity to EL remarkably depends on the fiber thickness and fiber density, which affect diffusion and mass transfer of the reactants and products as well as the accessibility to the acid sites. Among the tested [C 3 PrIm][SO 3 CF 3 ]-DFNS catalysts, the [C 3 PrIm][SO 3 CF 3 ]-DFNS- 1 with the thinnest fiber sheet and considerably high fiber density exhibits the highest selectivity to EL (93.0%). The [C 3 PrIm][SO 3 CF 3 ]-DFNS catalysts also show good reusability, and they can be reused at least for five times without obvious changes of the reactivity, total selectivity, morphology, textural properties and chemical structure. • The [C 3 PrIm][SO 3 CF 3 ]-DFNS are prepared by CPB reverse micelle-directed co-condensation route. • Particle diameter, fiber thickness and fiber density of the catalysts can be well-regulated. • The catalysts with thin fiber thickness and high fiber density exhibit high ethanolysis activity. • The [C 3 PrIm][SO 3 CF 3 ]-DFNS exhibit excellent reusability and stability in the target reaction.