Zirconia on acid-treated halloysite as an efficient catalyst for conversion of mono-saccharides to 5-hydroxymethylfurfural

An acidic catalyst was designed for catalyzing conversion of fructose into 5-hydroxymethylfurfural through a two-step approach. First, the textural features and acidity of halloysite nano clay were improved via acid-treatment. Secondly, zirconia, an acidic catalytic species, was synthesized through a simple procedure and immobilized on the acid-treated halloysite, resulting in an effective catalyst with increased acidity. Analysis of the catalyst confirmed that both acid-treatment and the incorporation of zirconia enhanced the acidity of the catalyst and improved its activity. To optimize the yield of the product, Response Surface Method was used and the effects of various reaction variables were studied. According to the results, yield of 93 % of the product was achieved within 60 min at 80 °C by using 25 wt% of the catalyst. The kinetic study showed that the activation energy was 61.6 kJ/mol. Thermodynamic parameters were determined to be 70 kJ/mol for enthalpy, −60 J/mol for entropy, and 91.5 kJ/mol for Gibbs free energy, respectively. Notably, the catalyst demonstrated high recyclability with minimal leaching of zirconia. In addition to its effectiveness in catalyzing the conversion of fructose, the catalyst exhibited efficient performance in the conversion of other monosaccharides.