Dehydration of glucose/fructose to 5-hydroxymethylfurfural (5-HMF) over an easily recyclable sulfated titania (SO42−/TiO2) catalyst

Abstract

A new SO₄²⁻/TiO₂ catalyst was developed via sol–gel hydrolysis followed by the wetness impregnation method. The Lewis (L) and Brønsted (B) site proportion in the catalyst was tuned by variation of the sulfate ion concentration in the catalyst. The dehydration of glucose/fructose to 5-hydroxymethylfurfural (5-HMF) was evaluated in a batch reactor in the presence of organic and/or aqueous medium at different temperatures (100–180 °C) and reaction times (1–8 h). The 0.5 M SO₄²⁻/TiO₂ catalyst was found to be very efficient, which demonstrated 100% conversion of glucose/fructose with a maximum 5-HMF yield of ∼37%, and ∼75%, respectively, at 150 °C and after 6 h of reaction. Results showed that the proportion of Lewis and/or Brønsted acidic strength of the catalyst played a crucial role in the yield of 5-HMF. The presence of water in the reaction medium demonstrates a negative effect on the 5-HMF yield and glucose/fructose conversion. Further, a new catalyst regeneration strategy was developed and it has been established that the 0.5 M SO₄²⁻/TiO₂ catalyst can be regenerated completely and can be reused several times with constant activity and 5-HMF yield. A kinetic study of the glucose dehydration reaction over a 0.5 M SO₄²⁻/TiO₂ catalyst suggested a second-order kinetic model with an activation energy of 195.4 kJ mol⁻¹.