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

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 prop-erties and performance in the reaction of halloysite-supported silicotungstic acid. Adjusting the reaction pa-rameters 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 degrees 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 Delta H/=, Delta S/= and Gibbs free energy were measured to be 80.77 kJ/mol,-61.10 J/ mol and 105.09 kJ/mol, respectively.

Automated summary

In this study, three Keggin-type heteropolyacids were impregnated on halloysite to produce heterogeneous acidic catalysts for synthesizing 5-HMF. The role of halloysite in the catalyst's acidic properties and performance was found to be important. The reaction parameters for the optimal catalyst were adjusted using Response Surface Methodology, resulting in a 99.5% yield of the target compound after 43 minutes at 125 degrees C in DMSO solvent. Immobilization of silicotungstic acid on halloysite significantly reduced leaching-out, with only a 12.5% loss of activity in five consecutive reaction cycles. The catalyst's activity was also tested on converting different carbohydrates to 5-HMF, with glucose showing the highest product yield of 64.24%. Furthermore, the kinetic and thermodynamic parameters of the conversion of fructose to 5-HMF were determined.