A Silica-Supported Iron Oxide Catalyst Capable of Activating Hydrogen Peroxide at Neutral pH Values

摘要

Iron oxides catalyze the conversion of hydrogen peroxide (H_2O_2) into oxidants capable of transforming recalcitrant contaminants. Unfortunately, the process is relatively inefficient at circircumneutral pH values because of competing reactions that decompose H_2O_2 without producing oxidants. Silica- and alumina-containing iron oxides prepared by sol-gel processing of aqueous solutions containing Fe(Cl_4)_3, AICI_3, and tetraethyl orthosilicate efficiently catalyzed the decomposition of H_2O_2 into oxidants capable of transforming phenol at circumneutral pH values. Relative to hematite, goethite, and amorphous FeOOH, the silica-iron oxide catalyst exhibited a stoichiometric efficiency, defined as the number of moles of phenol transformed per mole of H_2O_2 consumed, which was 10-40 times higherthanthatofthe iron oxides. The silica-alumina-iron oxide catalyst had a stoichiometric efficiency that was 50-80 times higher than that of the iron oxides. The significant enhancement in oxidant production is attributable to the interaction of Fe with Al and Si in the mixed oxides, which alters the surface redox processes, favoring the production of strong oxidants during H_2O_2 decomposition.