Catalytic Activity of Phenol Oxidation over Iron and Cooper-Exchanged Pillared Bentonite

Abstract

Al, mixed Al–Fe and Al–Cu pillared clays were prepared by the conventional method in a diluted medium with two additional parameters for the synthesis; the first one is the cooling of the clay suspension and the second is the exchange between the clay and metal solutions before pillaring with the polymeric mixed solution. The solids were characterized by X-ray diffraction (XRD), N2 adsorption and H2-TPR. The effects of the atomic ratio (M/Al + M) and hydrolysis molar ratio (OH/M), on the basal spacing and/or the specific surface were examined. The exchange does not seem to fix more Cu as in the case of Fe. The dispersion of the cold clay suspension, before pillaring, leads to a greater basal spacing of the solid at room temperature. In the case of mixed Al–Fe exchanged and/or pillared clays calcined at 350 °C, the cold dispersion of the clay suspension increases the basal spacing from 15.89 to 17.44 Å and from 15.32 to 16.07 Å for MR-AlFe (10) and Fe/MR-AlFe (10) respectively. Catalytic Wet Peroxide Oxidation (CWPO) of phenol under mild conditions (25 °C, 1 atm) was carried out without correction of pH. Mixed Al–Fe and Al–Cu pillared clays have comparable performances, although they showed some differences in the H2O2 decomposition kinetics. A total conversion of H2O2 is obtained without the complete phenol conversion over mixed Al–Fe pillared clays suggesting the presence of active species in these catalysts. In a slight excess of H2O2, the activity increases for all Fe-based clays catalysts with increasing the Fe content. A total conversion of phenol was obtained within 15 h of reaction over Fe/MR-AlFe (10) and after extending the reaction time to 30 h in the presence of Fe/MR-Al. On the contrary, MR-AlFe (10) only converted 57.12% under the same conditions. MR-AlFe (10) has the greater basal space (17.44 Å) and is more active for H2O2 decomposition than Fe/MR-Al, which certainly allowed greater accessibility of the reactant to the Fe-species. Fe exchanged and post-pillared clay with mixed (Al–Fe) solution containing 10% Fe expressed as molar percentage {Fe/MR-AlFe (10)} was the most efficient for this reaction combining good catalytic activity with high stability against iron leaching (0.02%). It showed a total phenol degradation, the highest H2O2 decomposition (85.7%) and more than 80% of TOC removal after 15 h of reaction.