Synthesis and characterization of Au supported on carbonaceous material-based catalysts for the selective oxidation of glycerol

Catalysts supported on carbon materials, with different structures: activated carbon (AC), graphite (G) and three types of carbon nanofibers (CNF) with different structures with respect to the arrangement of the graphitic planes (platelet (CNF-P), fishbone (CNF-F) and ribbon (CNF-R)) were prepared by the following methods: impregnation and gold–sol. CNF were synthesized by a chemical vapour deposition (CVD) method using C2H4 as the carbon precursor and Ni/SiO2 as the catalyst. Different techniques were employed to characterize both the supports and the final Au catalysts: atomic absorption spectrometry, transmission electron microscopy (TEM), temperature-programmed oxidation (TPO), X-ray diffraction (XRD), Raman spectroscopy, elemental analyses (CNH), N2 adsorption–desorption analysis, temperature-programmed reduction (TPR) and temperature-programmed decomposition (TPD), which have established distinct morphological, graphitic and porous characteristics. Both the crystalline nature of the carbon supports and the preparation method had a strong influence on the way in which Au particles were deposited on the carbonaceous supports. The higher the crystallinity and the smaller the particle size, the higher the activity and selectivity of the catalysts in the liquid-phase oxidation of glycerol. The following sequence in the catalytic activity was observed in terms of TOF (min−1): Au/G-SGT (0.07) > Au/CNF-R-SGT (0.067) > Au/G-IMP (0.053) > Au/CNF-F-SGT (0.052) > Au/CNF-P-SGT (0.051) > Au/AC-SGT (0.049) > Au/CNF-R-IMP (0.047) > Au/AC-IMP (0.045) > Au/CNF-F-IMP (0.040) > Au/CNF-P-IMP (0.036).

► The graphitic nature of the supports obtained was AC < CNF-P < CNF-F < CNF-R < G. ► The high graphitic character of the supports generated a greater anchorage of small, thin and dispersed Au particles. ► Catalysts, where gold was supported by the gold–sol method, were more active and selective than those prepared by the precipitation method. ► Both high crystalline supports and the gold–sol method to introduce gold lead to a better dispersed metal and to the highest catalytic activity.