Gold nanoparticles supported on modified red mud for biphasic oxidation of sulfur compounds: A synergistic effect

• Preparation of Au catalysts supported on different matrixes of red mud waste.
• Pure red mud, reduced red mud and carbon coated red mud supports were studied.
• The catalysts were tested in biphasic oxidations of sulfur contaminants.
• Catalyst with carbon coated red mud showed different behavior and higher efficiency.
• A synergistic effect occurs between Au that adsorbs S and Fe that forms OH radicals.

Gold nanoparticles were supported on the surface of three different matrixes based on red mud waste: (i) pure red mud, (ii) reduced red mud and (iii) partially carbon coated red mud, in order to produce different catalysts for desulfurization reactions. The catalysts were extensively characterized by X-ray diffraction, Mössbauer spectroscopy, thermogravimetric analyses, electron microscopies (SEM and TEM), energy dispersive spectroscopy (EDS) and BET surface area. Results showed that gold was successfully supported and distributed on the surface of red mud based materials as nanoparticles with diameters around 30 nm. The catalyst prepared with carbon coated red mud has shown to be twice more efficient than others for biphasic desulfurization reactions. This result can be associated with its amphiphilicity, which allows the catalyst to be located on the interface of biphasic systems. In this position a synergistic effect occurs between gold nanoparticles that adsorb S containing molecules and red mud Fe sites that promote the formation of OH radicals. The same effect is not observed for catalyst with hydrophilic supports.

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