Effective catalytic elimination of dichloromethane under humid environment over Co-based oxides†

Abstract

Chlorinated volatile organic compounds (CVOCs) emitted during waste incineration are major precursors of dioxins. Effective elimination of CVOCs at low temperatures from complex flue gas still has challenges from water resistance. This paper reported a type of cobalt-based catalyst that attained effective catalytic elimination of dichloromethane (DCM) with water-promotive effect. The NH₄F-modified CoO_x catalyst achieved a DCM conversion of 90% by catalytic ozonation at 120 °C with an O₃/DCM ratio of 10.0. Interestingly, water addition facilitated DCM transformation and mineralization while suppressed by-products formation, which could endure a high-water content of 12.5 vol%. Similar results were also observed for catalytic oxidation with the same catalyst at higher temperatures. Additionally, synergistic catalytic ozonation of DCM and NO was successfully validated under humid conditions, in which water produced hydroxyl radicals to save O₃ and attain enhanced oxidation efficiency. Catalyst characterization revealed that the superior performance of CoO_x-UF10 arose from its high reducibility and acidity. The template agent urea and NH₄F were responsible for the crystallization and morphological modification of Co, as well as the generation of oxygen vacancies. CoO_x inherently possessed excellent H₂O activation capabilities, and NH₄F modification further enhanced its reducibility and H₂O activation properties. The strongly oxidizing O₂²⁻ and O₂⁻ were enriched by water to replenish lattice oxygen and foster the generation of active hydroxyl groups. In situ DRIFTS analysis demonstrated the formation of active OH and OOH groups with the assistance of water, thereby facilitating the complete oxidation of DCM. These findings have significant implications for elimination of CVOCs in industrial flue gas treatment with the co-existence of NO and water vapor.