Catalytic oxidation of crude glycerol using catalysts based on Au supported on carbonaceous materials

Au catalysts supported on different carbon materials, such as graphite (G, 10 m2 g−1), ribbon-type carbon nanofibers (CNF-R, 109 m2 g−1), and carbon nanospheres (CNS, 3 m2 g−1), were prepared by the sol–gold method using tetrahydroxymethyl phosphonium chloride as the reducing agent. Different techniques were employed to characterize both the supports and the final Au catalysts: atomic absorption spectrometry, transmission electron microscopy, thermogravimetric analysis, X-ray diffraction, elemental analyses, N2 adsorption–desorption analysis, temperature-programmed reduction, and temperature-programmed decomposition. Au catalysts were tested in the liquid phase by selective oxidation of both commercial and crude glycerol, the latter obtained from the manufacture of biodiesel. Catalytic results obtained with commercial glycerol showed that the product distribution was dependent on the nature of the support and consequently on the Au particle size. The highest catalyst activity was achieved using highly crystalline carbon supports, supporting small-size (highly dispersed) Au particles. Accordingly the graphite-based catalyst exhibited higher catalytic activity than the CNF-R-based one. Catalytic results similar to those obtained with commercial glycerol were obtained when testing the stream resulting from a low cost neutralization procedure of the crude glycerol.

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► Au/G catalyst showed higher catalytic activity than Au/CNF-R catalyst.
► CNS-based catalyst was the most active due to the presence of many open edges in the CNS.
► The liquid phase oxidation of glycerol catalyzed by carbon-supported Au is structure sensitive.
► Catalytic activity decreased with crude glycerol in reason of the presence of impurities.
► Catalytic activity with neutralized glycerol is comparable to that with commercial glycerol.