Direct conversion of cellulose to ethyl levulinate catalysed by modified fibrous mesoporous silica nanospheres in a co-solvent system

Abstract

KCC-1/Al–SO₃H solid acids with different Si/Al molar ratios were prepared by sulphonic acid functionalisation using fibrous nanoporous silica particles (KCC-1/Al) as carriers. Field emission scanning electron and transmission electron microscopy measurements revealed that the sulphonation did not change the spherical morphology and fibrous structure of KCC-1/Al. The Brunauer–Emmett–Teller (BET) analysis indicated that the BET surface area of KCC-1/Al–SO₃H could reach 293–372 m² g⁻¹, while the average pore size was 7.31–7.43 nm. In addition, pyridine adsorption infrared profiles showed that KCC-1/Al–SO₃H contained abundant Lewis–Brønsted acid sites, while based on ammonia temperature-programmed desorption characterisation, a total ammonia desorption quantity of 91 cm³ g⁻¹ could be achieved using a Si/Al molar ratio equal to 5. The efficiency of the prepared KCC-1/Al–SO₃H was examined in the synthesis of ethyl levulinate (EL) from cellulose in a mixture of ethanol and toluene. Among them, 5KCC-1/Al–SO₃H exhibited superior performance, affording EL in 28.8 mol% yield under the optimal reaction conditions (200 °C, 6 h). Furthermore, a mechanism demonstrating the synergistic effect of the Lewis–Brønsted acid sites was proposed based on the reaction activity of different biomass sugars at the acidic sites.