Multifunctional Heterogeneous Catalysts for the Selective Conversion of Glycerol into Methyl Lactate

Multifunctional catalytic systems consisting of physical mixtures of Au nanoparticles (2-3 nm) supported on metal oxides and Sn-MCM-41 nanoparticles (50-120 nm) were synthesized and investigated for the selective conversion of glycerol to methyl lactate. The Au catalyst promotes the oxidation of glycerol to trioses, whereas the solid acid Sn-MCM-41 catalyzes the rearrangement of the intermediate trioses to methyl lactate. Among the supported Au nanoparticles, Au/CuO led to the highest yield and selectivity toward methyl lactate, while the Sn-MCM-41 nanoparticles showed much better catalytic performance than a benchmark solid acid catalyst (USY zeolite). The activity of the multifunctional catalytic system was further optimized by tuning the calcination temperature, the gold loading in the Au/CuO catalyst, and the Au/Sn molar ratio, reaching 63% yield of methyl lactate (ML) at 95% glycerol conversion. This catalytic system also showed excellent reusability. The catalytic results were rationalized on the basis of a detailed characterization by means of TEM, N₂-physisorption, UV-vis spectroscopy, and by FT-IR using probe molecules (CO and ethanol).