BACKGROUND The zirconium-containing metal-organic framework (MOF) UiO-66 was used as a cell to synthesize SO42-/ZrO2@Al2O3, a high-density superacid with relatively strong Bronsted acidity. The UiO-66 MOF was first coated with alumina to form ZrO2@Al2O3. Impregnation with ammonium sulfate and calcination at 500 degrees C afforded the bimetallic composite solid superacid SO42-/ZrO2@Al2O3. RESULTS Scanning and transmission electron microscopy images confirmed that UiO-66 was successfully coated with aluminium oxide, and its octahedral structure and uniform size (400-600 nm) were retained. SO42-/ZrO2@Al2O3 had a Brunauer-Emmett-Teller specific surface area of 301-330 m(2) g(-1) and average pore diameter of 9.6-10.7 nm. X-ray photoelectron spectroscopy and Fourier transform infrared analysis showed that SO42-/ZrO2@Al2O3 contained S6+ and Al3+. Temperature-programmed ammonia desorption analysis showed that SO42-/ZrO2@Al2O3 contained super-strong acid sites. The total volume of desorbed ammonia reached 90-109 cm(3) g(-1). Infrared spectra of adsorbed pyridine indicated that SO42-/ZrO2@Al2O3 contained mainly Lewis acid sites and was relatively rich in Bronsted acid sites. Thermogravimetric analysis showed that the thermal stability of SO42-/ZrO2@Al2O3 was high. CONCLUSIONS SO42-/ZrO2@Al2O3-3M (the impregnation concentration of ammonium sulfate was 3 mol L-1) and glucose were used to synthesize ethyl levulinate (EL) in ethanol. The highest EL yield of 37.5 mol% was obtained after reacting the mixture at 200 degrees C for 5 h. An EL yield of 28.8 mol% was obtained after four consecutive reuses of the SO42-/ZrO2@Al2O3-3M catalyst. (c) 2020 Society of Chemical Industry