Fructose dehydration to 5-HMF over three sulfonated carbons: effect of different pore structures

BACKGROUND: To invesigate the effect of pore structure on catalysis behavior, three sulfonated carbons with hierarchically ordered pores (SCHOP), mesopores (SMC), or micropores (SAC) were compared in conversion of fructose with 5-hydroxymethyl furfural (5-HMF). Fructose and 5-HMF adsorption by three carbons with different pore structures were also measured. Kinetic modeling was employed to correlate the reaction and the adsorption data. RESULTS: SEM characterization showed that SCHOP has hierarchical ordered macropores (about 220 nm in pore diameter) and mesopores (4.81 nm), whereas N-2 adsorption desorption, EDS and -SO3H group determination suggested both its specific surface area and -SO3H group content were close to those of SMC but quite distinct in comparison with SAC. The fitted active energies of fructose dehydration over SCHOP, SMC and SAC by a pseudo-first-order kinetic model were 84.54, 62.88, and 61.42 kJ mol-1, respectively. CONCLUSION: It was found that pore structure has a significant effect on catalytic activity and 5-HMF selectivity. SCHOP was a highly efficient catalyst for fructose dehydration to 5-HMF. Adsorption capacity measurement confirmed SCHOP favored the internal diffusion of both fructose and 5-HMF due to its hierarchical ordered porous structure, and possessed more effective specific area for fructose but less for 5-HMF. In the presence of SCHOP the rate-determining step was chemical reaction, whereas in the case of SMC or SAC the effects of molecular internal diffusion were not negligible. As a result, SCHOP was superior to both SMC and SAC for fructose conversion and 5-HMF selectivity. (C) 2016 Society of Chemical Industry