Analysis of active oxygen species generated during the catalytic ozonation using various zeolite powders

Abstract

The advanced oxidation process (AOP), chemical oxidation using aqueous ozone in the presence of appropriate catalysts to generate highly reactive oxygen species, offers an attractive option for removing poorly biodegradable pollutants. Active oxygen species generated during the catalytic ozonation using various zeolite powders as heterogeneous catalysts were analyzed by the spin-trapping/ESR technique using DMPO as a spin-trapping agent. Direct evidence has been obtained for the generation of active oxygen species during the catalytic ozonation using zeolite powder as heterogeneous catalysts. It was found that hydrophilic zeolites with high alkali cation contents in the crystal structures that possessed high catalytic activity for decomposing aqueous ozone also acted as the heterogeneous catalyst for converting aqueous ozone to hydroxyl radicals. The catalytic activities of hydrophilic zeolites for converting aqueous ozone to hydroxyl radicals were deteriorated by removing metal cations in the crystal structures. In the case of hydrophobic zeolites, there was a general trend that the less cation content the zeolite powder possessed, the less the catalytic activities for decomposing aqueous ozone became, which resulted in the less catalytic activities for converting aqueous ozone to hydroxy radical. However, some protonated Y type zeolite powders with low catalytic activity for decomposing aqueous ozone showed the highest catalytic activities for converting aqueous ozone to hydroxy radical, which might relate to the Brønsted and/or Lewis acid sites in the crystal structure of protonated Y type zeolites.