Cellulose-to-HMF conversion using crystalline mesoporous titania and zirconia nanocatalysts in ionic liquid systems

Abstract

Mesoporous titania and zirconia nanoparticles (MTN and MZrN, respectively) exhibiting a desired specific surface area and porous structure, different acidity, and different crystallinity were successfully synthesized through a controlled hydrolysis method and different post-treatments without the utilization of surfactants. The catalytic activities of the synthesized MTN and MZrN were investigated for the conversion of cellulose to glucose and 5-hydroxymethylfurfural (HMF) in an ionic liquid (i.e., 1-ethyl-3-methylimidazolium chloride, [EMIM]Cl) system. The amount of the catalyst (4.0 mg) and reaction time (3 h) were optimized for cellulosic conversion over the HT-MTN catalyst, resulting in maximum 12.9% glucose and 18.2% HMF yields at 120 °C reaction temperature. HT-MZrN exhibited superior HMF yield (i.e., 29.2%) to HT-MTN (i.e., 18.2%) because of the appearance of relatively strong acidity at 450 °C. In addition, we studied the effect of different crystallinity (i.e., amorphous, tetragonal, and monoclinic phases) of the same MZrN material on the conversion yields of glucose and HMF. Crystalline MZrN materials (i.e., either tetragonal or monoclinic phase) exhibited higher HMF yields than amorphous MZrN because of the existence of relatively strong acidity. The tetragonal MZrN catalyst presented better performance than monoclinic and amorphous MZrN catalysts because its acidity at higher temperature (i.e., over 450 °C) was higher than that of the other two, which shows great potential in one-pot cellulose-to-HMF conversion.