Fe-exchanged zeolites as materials for catalytic wet peroxide oxidation. Degradation of Rodamine G dye

The effect of surface acidity, nature, and dispersion of iron species, controlled by the catalyst preparation techniques and parent zeolite Si/Al ratio, on the catalytic wet peroxide oxidation of Rodamine G dye over the Fe-ZSM-5 materials has been studied. Fe-ZSM-5 and Fe-USY have been prepared using two techniques: improved aqueous ion exchange (IE) and conventional aqueous ion exchange (CE). The former procedure causes some rearrangement of the coordination sphere of four-fold coordinated Al3+, accompanied by formation of a small amount of octahedrally coordinated non-framework aluminium species. In case of Fe-ZSM-5(IE), iron is predominantly present in the form of well-dispersed Fe2+ ions, while Fe-ZSM-5(CE) and Fe-USY(CE) contain small aggregated oligonuclear (FeO)(n) clusters formed by Fe3+. In both cases, iron species are mainly located inside the zeolite pore system. The contribution of the zeolite is a controlling factor in enhancing the Rhodamine G dye degradation activity of the Fe-ZSM-5 catalysts, which is influenced by the specific procedure used for preparation of these materials. The catalytic wet peroxide oxidation (CWPO) behaviours of the materials prepared via the (IE) and (CE) procedures differ due to different nature of the iron species involved. The non-framework Al3+ species present in both the Fe-exchanged ZSM-5 and USY zeolites may participate in formation of the active sites responsible for CWPO of Rhodamine G dye over these catalysts. At near ambient temperature (323 K), quasi-neutral pH (4.9), short reaction time (around 150 min), catalyst concentration of 1.0 g L-1, and H2O2 addition rate of 41.2-82.3 mmol h(-1), the (IE)-prepared Fe-ZSM-5 catalyst enables the total degradation of the dye, accompanied by removal of ca. 80% of TOC without notable leaching of the Fe ions. (C) 2011 Elsevier B.V. All rights reserved.