Strategies for immobilization of manganese on expanded natural clays: Catalytic activity in the CWPO of methyl orange

The efficiency of the immobilization of manganese on natural bentonite has been studied by the comparison of three methods: (i) pillaring with Al13 followed by wet impregnation with aqueous manganese nitrate, (ii) pillaring with a mixed Al/Mn oligomeric solution and thermal treatment, and (iii) Mn2+-homoionization of the starting clay and subsequent in situ generation of MnS clusters by H2S gas treatment. The resulting solids were characterized by atomic absorption spectroscopy (AAS), cationic exchange capacity (CEC), powder X-ray diffraction (XRD), scanning electron microscopy/energy dispersive X-ray analysis (SEM-EDX), nitrogen adsorption at −196 °C and thermal analysis (DSC/TGA). Catalytic assessment of the materials was made in the Wet Peroxide Oxidation (CWPO) of the azo-dye methyl orange in aqueous solution at room temperature and atmospheric pressure. The in situ generation of the intercalated MnS clusters was shown to be the most efficient method for the metal incorporation in the interlayer of the hosting aluminosilicate. The solids obtained by this method resulted to be stable against the chemical leaching of the metal as well as the most active to catalyze the CWPO reaction under very mild conditions of temperature, pressure and pH (18 °C, 0.7 atm and 7.5).

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► A novel procedure for the preparation of Mn-pillared like clays is presented.
► Mn incorporation competitive to wet impregnation is achieved on expanded clay.
► Mn-expanded clay shows interesting catalytic behaviour in CWPO reaction at pH 7.5.