Utilization of biodiesel byproduct glycerol: Production of methyl lactate over Au/CuO and Sn-Beta binary catalyst under mild reaction conditions

Highlights: • Glycerol was converted to methyl lactate directly over binary Au/CuO and Sn-Beta catalyst. • 86% glycerol conversion and 60% methyl lactate yield can be obtained at 90 °C. • CuO precursors have great influence on the oxidative catalytic activity of Au/CuO. • Oxygen mobility of CuO prepared from copper acetate is the highest. • Au particles on CuO from copper acetate are small (2–4 nm) and uniform. -- Abstract: Utilization of glycerol is important for the sustainable development of biodiesel industry. In this study, green conversion of glycerol to methyl lactate was realized over Au/CuO and Sn-Beta binary catalyst at low temperature in base-free methanol, 86% glycerol conversion and 60% methyl lactate yield can be obtained at 90 °C. Precursors for preparation of CuO have significant influence on the catalytic oxidative activity of Au/CuO. Oxygen mobility of CuO prepared from copper acetate (CuO-CA) is the highest compared to CuO materials prepared from copper nitrate (CuO-CN) and commercial CuO (CuO-Commercial). Meanwhile, dispersion of Au particles is significantly affected by the precursor for synthesis of CuO. Au particles on CuO-CA are small (2–4 nm) and uniform. Accordingly, Au/CuO-CA shows the best catalytic activity for the oxidation of glycerol. Synergism of oxidative active sites on Au/CuO-CA and Lewis acid sites on Sn-Beta facilitates the production of methyl lactate from glycerol. Meanwhile, the catalysts are recyclable and can be reused easily without any treatment.