One-Pot Microwave Assisted Etherification of Fructose to Sustainable Liquid Fuel Over TiS2 Catalyst

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 TiS2-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 (k2 = 5.77 to 7.8 min−1) is faster than fructose dehydration (k1 = 2.93 to 5.6 min−1) reaction showcasing an ideal green chemical process by integrating bio-renewable feedstock, catalyst, and green protic solvent.