Distribution of polychlorinated organic by-products during the hydrolytic oxidation of chlorinated volatile organic pollutants over Pd–Ni-based catalysts

Abstract

Hydrolytic oxidation has been proven to effectively minimize the formation of polychlorinated organic by-products during the catalytic degradation of chlorinated volatile organic pollutants (CVOCs). In this study, we delved into the distribution characteristics of chlorinated organic by-products that occur during the hydrolytic oxidation of chlorobenzene, 1,2-dichlorobenzene, and o-chlorophenol. When it came to the catalytic degradation of chlorobenzene and 1,2-dichlorobenzene, we detected a small quantity of chlorinated organic by-products. Notably, both the types and concentrations of these by-products exhibited a volcano-type trend with increasing temperature, which was attributed to the competition between CVOC degradation and by-product formation at different temperature stages. On the other hand, during the catalytic degradation of o-chlorophenol, no aromatic chlorinated organic by-products were found at all. The 0.5% Pd–10% Ni/ZSM-5(25) catalyst stood out with the best hydrolytic oxidation activity. Specifically, the complete conversion temperatures for o-chlorophenol, chlorobenzene, and 1,2-dichlorobenzene were 250 °C, 375 °C, and 425 °C respectively. We employed various analytical techniques such as XRD, XPS, FTIR, H₂O-TPD, and pyridine-FTIR to explore the impact of the structure and surface properties of modified ZSM-5 zeolites on catalytic activity. The study revealed that the catalytic activity mainly stems from the surface acidity, active protons and the redox properties of the catalyst.