Sulphated zirconia on cyclodextrin nanosponge: A carbohydrate-based catalyst for conversion of mono-saccharides to 5-hydroxymethylfurfural

To expand the utility of cyclodextrin nanosponges for catalytic purpose, β-cyclodextrin nanosponge was prepared via melting method and then utilized as a catalyst support for the stabilization of sulphated zirconia_. The resulting catalyst, denoted as CDNS-SO₄²⁻/ZrO₂, was then applied as a heterogeneous acidic catalyst for conversion of fructose to 5-hydroxymethylfurfural. The results, underpinned that the catalytic activity of CDNS-SO₄²⁻/ZrO₂, was superior to that of ZrO₂ and SO₄²⁻/ZrO₂, confirming the role of sulfonation of ZrO₂ and immobilization of SO₄²⁻/ZrO₂ on CDNS in catalysis. To optimize the reaction parameters and achieve maximum yield of the desired product, Response Surface Method that is an accurate procedure for appraising the impacts of the reaction variables was employed and it was found that using 35 wt% CDNS-SO₄²⁻/ZrO₂ at 80 °C, HMF in 93 % yield was achieved in 45 min. Kinetic study also showed that the activation energy was 13.28 kJ/mol. Furthermore, thermodynamic parameters, i.e. enthalpy, entropy and Gibbs free energy were estimated as 10.46 kJ/mol, −150.40 J/mol and 63.58 kJ/mol respectively. Noteworthy, the catalysis was true heterogeneous, as confirmed by Hot filtration test and the catalyst could be recycled several times with low leaching of SO₄²⁻/ZrO₂.