Production of 5-HMF from glucose using TiO2-ZrO2 catalysts: Effect of the sol-gel synthesis additive

Abstract

Different TiO2-ZrO2 (50/50 wt%) mixed metal oxide catalysts were synthesized by the sol-gel method after varying the synthesis additive (e.g., CH3COOH, HNO3, NH4OH and NaOH) to study its effect on the production yield of 5-HMF from the conversion of glucose at 175 °C and 30 bar (Ar) (batch reaction system). Various characterization techniques such as BET, XRD, FTIR, 1HNMR, NH3-TPD, TPO, SEM and TEM were employed to study the physicochemical properties of the synthesized materials and to correlate them with the reaction product yields. Highest HMF yield (76%) was obtained over the TiO2-ZrO2-C2H4O2 catalyst in a biphasic reaction system with a glucose concentration of 2 wt% and a glucose/catalyst mass ratio of 2.5. From the NH3-TPD results, highest amount of total acid sites was observed for the TiO2-ZrO2 (50/50 wt%) prepared by the sol-gel method using the acetic acid additive, and acidity value was 3 and 2.5 times higher than that of TiO2 and ZrO2 alone, respectively. It was concluded that total acid sites density is an important parameter to obtain high 5-HMF product yields. A higher number density of sites can be obtained using the complexing additive of acetic acid in the Sol-Gel method among the other additives investigated.