Catalytic ozonation of CH2Cl2 over hollow urchin-like MnO2 with regulation of active oxygen by catalyst modification and ozone promotion

This paper firstly reported efficient catalytic ozonation of CH2Cl2 (dichloromethane, DCM) at low temperature over hollow urchin-like MnO2 with high chlorine resistance. Regulations on morphologies and Cu doping, as well as ozone promotion were conducted to optimize active oxygen of MnO2 catalysts, contributing to excellent catalytic behaviors. Cu doping MnO2 with hollow urchin-like morphology attained a stable 100% DCM conversion with O3/DCM molar ratio of 10 at 120 °C. The ozone utilization rate, final products, and byproducts distribution were discussed. Abundant crystal defects, low-valance Mn/Cu, Oads, and weak acidity, as well as better low temperature reducibility contributed to its superior performance. During DCM catalytic ozonation, DCM oxidation exhibited competitive effect on O3 decomposition due to the occupation of intermediates (CH2ClO3·, O-CH2Cl, and O-CH2 -O) over active sites that should belong to O3 originally. Nevertheless, O3 decomposition exhibited synergistic effects on DCM oxidation with promotion on active oxygen. Density functional theory (DFT) calculations confirmed the positive effect on oxygen vacancy formation and O3/DCM adsorption from Cu doping. The possible mechanism for DCM catalytic ozonation included four parts, including O3/DCM adsorption, O3 activation, DCM oxidation, and electron replenishment. This paper provides new insight for catalytic elimination of chlorinated alkanes at mild conditions.