Microwave assisted rapid conversion of carbohydrates into 5-hydroxymethylfurfural catalyzed by mesoporous TiO2 nanoparticles

Energy efficient and sustainable process for the production of 5-hydroxymethylfurfural (HMF) from carbohydrates is highly demanding. Here, direct conversion of carbohydrates into HMF has been investigated over self-assembled mesoporous TiO2 nanoparticles (NPs) catalyst. Monosachharides d-fructose and d-glucose, disaccharides sucrose, maltose, cellobiose were successfully converted into HMF with variable yields in both aqueous and organic mediums under microwave-assisted heating conditions. The effects of solvent polarity, microwave absorbing ability, catalyst loading, reaction time, and substrate variations on the HMF yields have been studied. Pyridine-IR and NH3-TPD analyses confirmed the presence of Lewis acidic sites, whereas N2 sorption analysis revealed high BET surface area for the self-assembled mesoporous TiO2 nanomaterials synthesized by using sodium salicylate as template. High surface area, Lewis acidity and uniform nanosphere-like particle morphology are responsible for high catalytic activity in the dehydration of carbohydrate substrates over this mesoporous TiO2 nanomaterial, whereas commercially available TiO2 is almost inactive for this dehydration reaction under similar conditions. The higher microwave energy absorbing ability (tan δ) of the DMSO and NMP resulted in higher HMF yield in organic solvents than water. Catalyst life-time analysis suggested that mesoporous TiO2 NPs catalysts can be recycled for four catalytic cycles without appreciable loss of its catalytic activity.

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► Self-assembled mesoporous TiO2: high surface area, Lewis acidity.
► Conversion of carbohydrates into liquid transportation fuels.
► 5-Hydroxymethylfurfural (HMF) production.
► Microwave assisted nanocatalysis.
► Sustainable chemistry: high catalytic efficiency.