Halloysite-supported silicotungstic acid as an efficient catalyst for dehydration of fructose to 5-hydroxymethylfurfural

Abstract

Three Keggin-type heteropolyacids were impregnated upon halloysite to produce heterogeneous acidic catalysts for synthesizing 5-hydroxymethylfurfural (5-HMF). Comparing the effectiveness of variously prepared catalysts in producing 5-HMF from fructose revealed the important role of halloysite in the final catalyst's acidic properties and performance in the reaction of halloysite-supported silicotungstic acid. Adjusting the reaction parameters for obtaining optimal results for the catalyst of choice was conducted via Response Surface Methodology and it was found that use of catalyst with 11 wt% active ingredient at 125 °C in DMSO solvent yielded the target compound with 99.5% after 43 min. Moreover, immobilization of silicotungstic acid upon halloysite suppressed its leaching-out remarkably, and the catalyst had 12.5% loss of activity when reused in five consecutive reaction cycles. The activity of the catalyst was also examined to convert several other carbohydrates to 5-HMF amongst which glucose feed displayed the best product yield of 64.24%. According to the chemical kinetic investigations performed, converting fructose to 5-HMF through dehydration, the activation energy and reaction rate constants were determined to be 85.26 kJ/mol and 11.94 h−1, respectively. Additionally, the thermodynamic parameters of ΔH≠, ΔS≠ and Gibbs free energy were measured to be 80.77 kJ/mol, −61.10 J/mol and 105.09 kJ/mol, respectively.