Catalytic Oxidation of Chlorobenzene over Mn_<i>x</i>Ce_1–<i>x</i>O₂/HZSM-5 Catalysts: A Study with Practical Implications

Abstract

Industrial-use catalysts usually encounter severe deactivation after long-term operation for catalytic oxidation of chlorinate volatile organic compounds (CVOCs), which becomes a "bottleneck" for large-scale application of catalytic combustion technology. In this work, typical acidic solid-supported catalysts of Mn_xCe_1-xO₂/HZSM-5 were investigated for the catalytic oxidation of chlorobenzene (CB). The activation energy (E_a), Brønsted and Lewis acidities, CB adsorption and activation behaviors, long-term stabilities, and surficial accumulation compounds (after aging) were studied using a range of analytical techniques, including XPS, H₂-TPR, pyridine-IR, DRIFT, and O₂-TP-Ms. Experimental results revealed that the Brønsted/Lewis (B/L) ratio of Mn_xCe_1-xO₂/HZSM-5 catalysts could be adjusted by ion exchange of H• (in HZSM-5) with Mnⁿ⁺ (where the exchange with Ce⁴⁺ did not distinctly affect the acidity); the long-term aged catalysts could accumulate ca. 14 organic compounds at surface, including highly toxic tetrachloromethane, trichloroethylene, tetrachloroethylene, o-dichlorobenzene, etc.; high humid operational environment could ensure a stable performance for Mn_xCe_1-xO₂/HZSM-5 catalysts; this was due to the effective removal of Cl• and coke accumulations by H₂O washing, and the distinct increase of Lewis acidity by the interaction of H₂O with HZSM-5. This work gives an in-depth view into the CB oxidation over acidic solid-supported catalysts and could provide practical guidelines for the rational design of reliable catalysts for industrial applications.