Efficient conversion of carbohydrates and biomass into furan compounds by chitin/Ag co-modified H3PW12O40 catalysts

The development of heterogeneously functional catalysts is of great significance in selective catalysis for biomass valorization. Herein, we report for the first time the applicability of chitin/Ag co-modified HPWO composites (Chx-AgPW) as catalysts for producing valuable furans from carbohydrates and biomass. The as-prepared Ch15-AgPW catalyst exhibited the best catalytic performance, due to the dual Brǿnsted-Lewis acidity and appropriate chitin content. When the amount of Ch15-AgPW catalyst was 0.25 mmol, an excellent 5-hydroxymethylfurfural (HMF) yield of 78.3% could be achieved at 150 °C for 3 h with nearly 100% glucose conversion in the HO/MIBK (V = 4:6) solvent system. Furthermore, high-yield HMF could also be obtained from other carbohydrates such as fructose (85.3%), sucrose (72.3%), cellobiose (65.6%), starch (52.7%) and inulin (43.5%). Additionally, corn stover, rice straw and sugarcane bagasse under typical reaction conditions simultaneously produced furfural and HMF in yields of 64.6%–72.2% and 18.5%–25.6%, respectively. Combined with the characterization, mechanism study demonstrated that the surface functional groups in chitin were conductive to rapid absorption of the substrates; the Brǿnsted acid sites from heteropoly anion (H[PWO]) promoted the initial depolymerization of biomass and the final dehydration to furans; the introduction of Ag favored the isomerization of intermediates. After reaction finished, the Ch15-AgPW catalyst could be easily recovered by filtration and effectively reused at least eight cycles without substantial loss in catalytic activity. This work provides a novel strategy to synthesize stable heterogeneous catalysts with tunable acidity for producing bio-based fuels and chemicals from renewable resources.