Janus Pd/Al2O3&P/CeO2 Dual-Bed Catalysts: Synergistic mechanism and chlorine resistance in mixed VOCs oxidation

The emission of volatile organic compounds (VOCs) from industries such as coatings and pharmaceuticals typically involves complex mixtures of aromatic hydrocarbons ( e.g. , toluene) and chlorinated compounds ( e.g. , dichloromethane, DCM), posing significant threats to environmental safety and human health. A central challenge in their catalytic elimination is achieving both high activity and robust chlorine resistance. This study introduces a tandem catalytic system labeled Pd/Al 2 O 3 &P/CeO 2 for the synergistic degradation of toluene-DCM mixtures. The system employs a sequential reactor design with Pd/Al 2 O 3 in the front bed and P/CeO 2 in the rear. Compared to physically mixed catalysts, this configuration demonstrated superior low-temperature activity, achieving 90% conversion of 800 ppm toluene and 200 ppm DCM at 314 °C, while effectively suppressing the formation of toxic byproducts like chlorobenzene and chloromethane. Characterization revealed that the spatially decoupled design creates a distinct distribution of active sites. The front bed is rich in surface-adsorbed oxygen and PdO species, while the rear bed possesses enhanced acidity. This arrangement enables active oxygen in the front zone to initiate the oxidation of toluene and DCM, while the acidic sites in the rear facilitate the transfer and deep mineralization of chlorinated intermediates. Operando studies confirmed this cooperative mechanism, showing that Pd/Al 2 O 3 preferentially oxidizes toluene to CO 2 , and the adjacent P/CeO 2 subsequently ensures the deep oxidation of chlorine-containing intermediates. Consequently, Pd/Al 2 O 3 &P/CeO 2 tandem catalyst not only delivers high oxidation activity with minimal byproducts but also exhibits exceptional stability during a 36 h prolonged test and under humid conditions. This work showcases a novel tandem design strategy for the efficient purification of multi-component VOCs, offering a promising pathway for industrial waste gas treatment that integrates high activity with chlorine resistance.