Mechanism study on catalytic oxidation of chlorobenzene over MnxCe1-xO2/H-ZSM5 catalysts under dry and humid conditions

Abstract

Developments on advanced catalysts for catalytic oxidation of chlorinated hydrocarbons still encounter bottlenecks in Cl deactivation, low HCl and CO2 selectivity, toxic by-products generation, etc. In this paper, a well-reported MnxCe1-xO2 catalyst was selected as active phase to access the role of H-ZSM5 in catalytic oxidation of chlorobenzene (CB) under both dry and humid conditions. The HCl and CO2 production, by-products generation and CB oxidation routes variation were evaluated by using a range of analytical techniques including XRD, BET, GC/MS, in situ DRIFT, Ion Chromatography, etc. It was noted that the presence of H-ZSM5 could induce ca. 90% CB conversion at ca. 230°C. However, only 20% CB was converted into CO2. There were nearly 25 by-products being detected in the off-gas. In situ DRIFT analyses revealed that under dry condition, the H-ZSM5 could promote Cl dissociation from the aromatic ring of CB, which transferred the CB into cyclohexanone or benzoquinone species, hence facilitating CB ring-opening process. Under humid condition, the presence of H2O could not only protect the active sites of Mn0.8Ce0.2O2 from accumulated chlorine poisoning but also act as H and OH radical source to deeply oxidize CB, promoting the HCl and CO2 production over the MnxCe1-xO2/H-ZSM5 catalyst.