Mesoporous silica-supported 12-tungstophosphoric acid catalysts for the liquid phase dehydration of d-xylose

Hybrid composites comprising 12-tungstophosphoric acid (PW) immobilized in micelle-templated silicas have been prepared and characterized by several techniques, and were shown to possess dehydration activity for the conversion of xylose to furfural in liquid phase. These catalysts exhibit higher activity for xylose dehydration than non-supported PW, and are comparable with H2SO4 in terms of furfural yield achieved after 4 h, under similar reaction conditions (58%). The catalytic performance of the PW-supported catalysts depends on the interplay of several variables, such as the catalyst preparation method, type of support (purely siliceous or aminopropyl-functionalized silicas with different pore sizes), PW loading (15–34 wt.%), and the reaction conditions (temperature 140–160 °C, type of solvent – toluene/water (T/W) or dimethylsulfoxide (DMSO)). The stability and reusability of the catalysts was also studied and the best results were obtained in DMSO using either the 15 wt.% PW inorganic composites, or PW immobilized in the aminopropyl-functionalized silicas. Strong host–guest interactions and active site isolation appear to benefit catalytic activity and stability when DMSO is used as the solvent. Catalyst surface passivation plays a significant role.