Catalytic ozonation of toluene using zeolite and MCM-41 materials.

The effects of passing ozone over different zeolite and MCM-41 materials to remove toluene were investigated. Different ozone-to-toluene ratios were used to evaluate the catalytic performance during ozonation. The micro- and meso-porous materials removed about 50% of the toluene via adsorption and another 20-40% was decomposed by ozonation, which was catalytically enhanced by the zeolite and MCM-41 materials. The catalytic reaction portion increased by using a higher ozone inlet concentration and it was further enhanced to around 50% with the use of more adsorbents or with longer residence times. Inside the porous structure of the material, ozone was either decomposed into active atomic oxygen for reactions or converted into oxygen for active site regeneration. The number of Lewis acid sites in the adsorbents for ozone decomposition and byproduct generation during the reactions limit the catalytic activities. Trace amounts of intermediates including aldehydes and organic acids were quantified in the ozonation process. A higher ozone inlet concentration helped to reduce intermediate species formation but it led to more residual ozone in the exhaust. The high adsorption capability of the zeolite and MCM-41 adsorbents could serve as reservoirs for suppressing the release of intermediate species to the exhaust.