Distribution and formation mechanisms of polychlorinated organic by-products upon the catalytic oxidation of 1,2-dichlorobenzene with palladium-loaded catalysts

Clarifying the oxidative products and their formation mechanisms in the catalytic oxidation of chlorinated volatile organic compounds is important to provide detailed understanding of the degradation of pollutants with the simultaneous removal of secondary pollutants. In this study, catalytic oxidation of 1,2-dichlorobenzene (1,2-DCB) using commonly commercial catalysts (Pd/γ-Al 2 O 3 , Pd/ZSM-5, and Pd/SiO 2 ) was investigated. During the oxidation processes, substantial amounts of polychlorinated organic by-products, such as trichlorobenzene, tetrachlorobenzene and pentachlorobenzene, were detected. The reaction temperature and types of supports played a vital role in the formation of chlorinated organic by-products. With an increase of the reaction temperature, the degree of chlorination of the organic by-products increased gradually, and the concentration of polychlorinated organic by-products was increased sharply at low temperatures and then decreased when the reaction temperature was above 450 °C. Meanwhile, the amounts of polychlorinated organic by-products increased with an increasing silicate-to-aluminium ratio. Furthermore, based on the distribution of chlorinated organic by-products and characterization results of pyridine from FTIR, XPS, UV–vis-DRs, and in situ FTIR, the formation mechanisms of the polychlorinated organic compounds were proposed.