Dehydration of D-xylose into furfural over H-zeolites

The liquid-phase dehydration of D-xylose into furfural was carried out over various H-zeolites-H-ferrierite, H-beta, H-ZSM-5, H-Y and H-mordenite-with various SiO2/Al2O3 molar ratios in different solvent systems: water, dimethyl sulfoxide (DMSO) and a mixture of water and toluene (water/toluene). For comparison, gamma-Al2O3 and silica-alumina were also examined. FT-IR spectroscopy after pyridine adsorption was conducted to probe the acidity of the H-zeolites. The D-xylose conversion and furfural yield generally decreased with increasing SiO2/Al2O3 molar ratio over the H-zeolites having the same crystal structure irrespective of the kind of solvent system. This is closely related to the accessible acid sites. In a comparison study using the three different solvent systems, the D-xylose conversion and furfural selectivity generally decreased in the following order: water/toluene > DMSO > water. In water and water/toluene, H-beta (25) showed the highest furfural selectivity at a similar D-xylose conversion among the tested zeolites. On the other hand, H-mordenite (20) showed the highest furfural selectivity at a similar D-xylose conversion in DMSO.