Dehydration of xylose into furfural over micro-mesoporous sulfonic acid catalysts

Surfactant-templated micro-mesoporous silicas possessing sulfonic acid groups (SAGs) have been prepared, characterized, and tested as catalysts in the dehydration of d-xylose to furfural. All of the materials possessed catalytic activity. In general, selectivity to furfural was lower for a poorly ordered microporous hybrid material, prepared via the co-condensation of (3-mercaptopropyl)trimethoxysilane with bis(trimethoxysilylethyl)benzene, than for mesoporous MCM-41 silica anchored with SAGs via postsynthesis modification. The MCM-41 material with the highest loading of SAGs (0.7 meq g−1) displayed fairly high selectivity for furfural (ca. 82% in DMSO or water/toluene mixture) at high xylose conversion (>90% within 24 h, at 140 °C). Xylose conversion increased significantly with reaction temperature. At 170 °C, more than 85% conversion was achieved within 4 h with any of the sulfonic acid-functionalized catalysts. Furfural yield tended to increase with temperature. Xylose conversion increased with increasing amount of catalyst, and for a xylose/MCM-41-SO3H ratio of 0.5, 76% conversion was achieved within 4 h, at 140 °C. Catalyst deactivation was observed after long residence times, possibly because of the interaction of reaction products with the acid sites, leading to surface loading.