Fructose conversion to 5-ethoxymethylfurfural takes place in Lewis acidity provided by the partial reduction of TiS₂ catalyst. The reduction of TiS₂ catalyst generates S-vacancies and formation of TiS_2−x structure, which interacts with protic solvent for propagation of reaction. The reaction provides a faster heating rate and lower reaction time in a microwave reactor providing green process for biofeedstock upgradation.

Abstract

In this study, TiS₂ catalyst was synthesized, which was partially reduced at 500 °C, 600 °C, 700 °C, and 800 °C to generate the active sites which resulted in enhanced catalysts’ performance for transforming fructose to 5-ethoxymethylfurfural (EMF). The partial reduction resulted in the formation of TiS_2-x giving rise to Lewis acid centers. The Lewis centers interact with the polar protic solvent in the reaction medium, forming H⁺ moieties which facilitated the dehydration of fructose. The catalysts TiS₂, TiS₂500, TiS₂600, TiS₂700, and TiS₂800 showed acid strengths of 1.08, 1.44, 1.69, 1.27, and 1.36 mmol/g, respectively. The prepared catalysts were tested for successive dehydration of fructose and etherification of 5-hydroxymethylfurfural (HMF) resulting in an efficient 63% EMF yield at 160 °C in 30 min. The relationship between S vacancies, acidity and activity of the catalyst is well established in the study. The activation energies (140–160 °C) for fructose dehydration and HMF etherification were 44.67 kJ/mol and 20.86 kJ/mol respectively, which were comparable to other Brønsted acid catalysts. Additionally, rate constants indicates that HMF etherification (k ₂ = 5.77 to 7.8 min⁻¹) is faster than fructose dehydration (k ₁ = 2.93 to 5.6 min⁻¹) reaction showcasing an ideal green chemical process by integrating bio-renewable feedstock, catalyst, and green protic solvent.