One-pot sol-gel synthesis of a phosphated TiO₂ catalyst for conversion of monosaccharide, disaccharides, and polysaccharides to 5-hydroxymethylfurfural

Catalytic conversion of biomass or biomass-derived carbohydrates into 5-hydroxymethylfurfural (HMF) is an important reaction for the synthesis of bio-based polymers, fuels, and other industrially useful products. In this study, phosphated titania (P-TiO₂) catalysts with different phosphoric acid content were prepared through a simple one-pot sol-gel method and characterized by BET, XRD, FT-IR, NH₃-TPD, py-FT-IR, and XPS techniques. The catalyst characterization results revealed the incorporation of phosphorus into the TiO₂ framework in the form of a Ti-O-P bond. The P-TiO₂ catalysts were applied to the conversion of glucose (≥10 wt%) into HMF in a biphasic water/THF reaction medium at 175 °C. Under optimized reaction conditions, 98% glucose conversion and 53% HMF yield were obtained over a 15P-TiO₂ catalyst, and the catalyst was reused for several cycles with consistent activity and selectivity. The presence of both Brønsted and Lewis acid sites, high BET surface area and pore volume, and high acidity could account for the high catalytic activity and selectivity. Besides, the 15P-TiO₂ catalyst was also demonstrated to be active for the conversion of disaccharides (sucrose and cellobiose), polysaccharides (starch and microcrystalline cellulose) and industrial grade sugar syrups into HMF with reasonable yield. © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019.