A convenient synthesis of core-shell Co3O4@ZSM-5 catalysts for the total oxidation of dichloromethane (CH2Cl2)

Abstract

Core-shell structured Co3O4@ZSM-5 catalysts were successfully synthesized by a simple two-step microwave hydrothermal method and used for the catalytic oxidation of dichloromethane (DCM). Co3O4@ZSM-5 catalysts exhibited better CO2 yield and lower byproduct yield than pristine Co3O4 and ZSM-5. For pure ZSM-5 and Co3O4, dechlorinated byproducts CH3Cl formed more readily over ZSM-5 due to its higher acidity and lower redox property, while polychlorinated byproducts (CHCl3 and CCl4) formed more readily over Co3O4 due to its lower acidity and higher redox property. Thanks to its core-shell structure, Co3O4@ZSM-5 exhibited appropriate redox ability and a suitable distribution of acid sites, possibly explaining its lower byproduct yields and more efficient formation and desorption of HCl and Cl2. In situ Fourier transform infrared (FTIR) spectra analysis indicated that formaldehyde, formate and methoxy species were the main intermediates of the catalytic oxidation reaction. A pathway for the catalytic oxidation of DCM on 1.5-Co3O4@ZSM-5 was proposed based on the DCM degradation performance and physicochemical property analysis. The addition of water vapor to the DCM degradation process on core-shell structure Co3O4@ZSM-5 was shown to promote DCM conversion and CO2 yield. In addition, we concluded that core-shell catalysts exhibited good thermal stability and durability for DCM oxidation.