Fe-clay catalysts have been prepared and tested for Orange II oxidation with H2O2 in aqueous solution. The reaction is carried out in a batch reactor, using different hydrogen peroxide concentrations, and in a wide range of temperature and pH values. Twelve samples were prepared, with three different iron loads (7.5, 13.0 and 17.0 %, w/w), and using four iron salts as precursors, namely Fe(II) acetate, Fe(II) oxalate, Fe(II) acetylacetonate and Fe(III) acetylacetonate. The samples were characterized using X-ray diffraction, thermal analysis, infrared spectroscopy and adsorption of nitrogen at 77K. The catalytic results show that these solids present good catalytic properties for the degradation and mineralization of Orange II solutions, allowing to reach, in the best conditions and after 4h of oxidation, 99% of dye degradation with 91% of TOC (Total Organic Carbon) reduction (at 70ºC), using only ca. 90 mg of clay catalyst per litre of solution. Nevertheless, 96% of dye removal with 82% of mineralization were also reached at 30ºC. Besides, the amount of iron released into the final solution is lower than 1 ppm, in the worst of the cases, and 0.09 ppm in the best case.

Chromium-saponite catalysts have been prepared by two synthesis procedures. The first method consisted in the intercalation of the saponite with solutions containing aluminium and chromium oligomers with various molar ratios, while the second one consisted in the incipient wetness impregnation of alumina-pillared saponite with several chromium salts, ammonium chromate, Cr(II) acetate and Cr(III) nitrate. Several techniques, X-ray diffraction, nitrogen physisorption at À196 8C, thermogravimetric and differential thermal analysis, infrared and DR-UV-vis spectroscopies, temperature-programmed reduction and electron paramagnetic resonance spectroscopy at À196 8C, have been used to characterize and to compare the properties of the materials synthesized. The results show that the solids obtained combine the layered structure of the clay and the thermal stability given by the alumina pillars. The catalysts have been tested in the oxidation of propene, showing a catalytic behaviour according to the Mars-van Krevelen mechanism, the performance not depending on the method in which chromium was incorporated to the clay.

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