Fabrication of hydrophobic polymer foams with double acid sites on surface of macropore for conversion of carbohydrate

• Two kinds of hydrophobic polymer foam catalysts were prepared by HIPEs.
• Cr3+-HPFs-1-H+ and HPFs-1-H+ possess Lewis–Brønsted double acid sites.
• Lewis and Brønsted acid sites could be adjusted.
• This work opens up a simple route to synthesis catalysts with double acid sites.

Herein we reported a simple and novel synthetic strategy for the fabrication of two kinds of hydrophobic polymer foam catalysts (i.e. Cr3+-HPFs-1-H+ and HPFs-1-H+) with hierarchical porous structure, inhomogeneous acidic composition and Lewis–Brønsted double acid sites distributed on the surface, which was used to one-pot conversion of carbohydrate (such as cellulose, glucose and fructose) to a key chemical platform (i.e. 5-hydroxymethylfurfural, HMF). The water-in-oil (W/O) high internal phase emulsions (HIPEs), stabilized by both Span 80 and acidic prepolymers as analogous particles offered the acidic actives, were used as the template for simultaneous polymerization of oil phase in the presence of divinylbenzene (DVB) and styrene (St). After subsequent ion-exchange process, Lewis and Brønsted acid sites derived from exchanged Cr3+ and H+ ion were both fixed on the surface of cell of the catalysts. The HPFs-1-H+ and Cr3+-HPFs-1-H+ had similar hierarchical porous, hydrophobic surface and acid sites (HPFs-1-H+ with macropores ranging from 0.1 μm to 20 μm, uniform mesopores in 14.4 nm, water contact angle of 122° and 0.614 mmol g−1 of Brønsted acid sites, as well as Cr3+-HPFs-1-H+ with macropores ranging from 0.1 μm to 20 μm, uniform mesopores in 13.3 nm, water contact angle of 136° and 0.638 mmol g−1 of Lewis–Brønsted acid sites). It was confirmed that Lewis acid sites of catalyst had a slight influence on the HMF yield of fructose came from the function of Brønsted acid sites, and Lewis acid sites were in favor of improving the HMF yield from cellulose and glucose. This work opens up a simple and novel route to synthesize multifunctional polymeric catalysts for efficient one-pot conversion of carbohydrate to HMF.