Acid–base synergistic catalysis of biochar sulfonic acid bearing polyamide for microwave-assisted hydrolysis of cellulose in water

The development of a highly efficient heterogeneous catalysis process for the hydrolysis of cellulose to reducing sugars (RSs) and especially 5-hydroxymethylfurfural (HMF) in water is highly anticipated for large-scale use of cellulosic biomass in the future. Herein, a bamboo-derived biochar sulfonic acid bearing polyamide (BCSA-PA) designed by us was found to show much higher catalytic activity, better repeatability and especially HMF yield for microwave-assisted such hydrolysis compared to the PA-free BCSA, achieving 25.60% RSs and 23.10% HMF yields with 4.71 turnover number (TON) under optimal conditions. Also, its TON value (2.58) for the conversion of cellulose into HMF was much higher than those obtained from it-catalyzed transformation of glucose (TON, 1.44) and especially fructose (TON, 0.79). The BCSA-PA showing an excellent catalysis performance in cellulose hydrolysis is likely due to the following two reasons: (1) the BCSA and especially BCSA-PA, as supported by glucose and cellobiose adsorption experiments, have a stronger affinity to β-1,4-glycosidic bonds of cellulose than two monosaccharides, thereby leading to the highly-efficient hydrolysis of cellulose on the SO3H groups. (2) The acid–base synergistic catalysis between the SO3H and PA groups of BCSA-PA may be responsible for its higher HMF selectivity and excellent repeatability in water medium. The current work highlights new opportunities for the direct production of 5-HMF from glucose and especially cellulose.