Catalytic ozonation of chlorinated VOCs on ZSM-5 zeolites and alumina: formation of chlorides

This study aims to understand the mechanisms and kinetics of chlorinated volatile organic chemicals (VOCs) removal during the catalytic ozonation process on γ-alumina and ZSM-5 zeolites. Both the H-ZSM-5 and Na-ZSM-5 types with different SiO₂/Al₂O₃ ratios and counter ions (Z1000H:SiO₂/Al₂O₃ = 1000, Z900Na:SiO₂/Al₂O₃ = 900, Z25H:SiO₂/Al₂O₃ = 25 and Z25Na:SiO₂/Al₂O₃ = 25) were studied. In order to fully understand the mechanisms behind the catalytic processes, degradation of VOCs and chlorides formation were investigated during both ozonation alone and catalytic ozonation on alumina and zeolites. The effects of pH and hydroxyl radical scavengers on the efficiency of catalytic ozonation on alumina and zeolites were also studied. The results revealed that, as opposed to alumina, zeolites promoted decomposition of VOCs. Furthermore, the decomposition of chlorinated VOCs resulted in the generation of chlorides at significantly higher levels when compared with ozonation alone. The presence of hydroxyl radical scavengers had no significant effect on the removal rates of VOCs and the generation of chlorides in the presence of zeolites. It is therefore suggested that catalytic ozonation of organic VOCs on zeolites proceeds via a non-radical mechanism that involves reactions of molecular ozone with pollutants adsorbed on the surface of zeolites.