Deep oxidation of CH2Cl2 over Mo-doped CoAl2O4 spinel oxides: Unravelling the promoting roles of Brønsted acidity and H2O

A series of Mo-doped CoAl2O4 spinel oxides were prepared and tested for deep oxidation of dichloromethane (CH2Cl2). The Mo-doping resulted in much improved surface acidity of the catalyst, and thus significantly enhanced the catalytic activity. The best performance was obtained on a CoAl1.7Mo0.3O4 catalyst, which gave a nearly 3-fold higher reaction rate than the pristine CoAl2O4 (26.5 x 10-8 versus 10.5 x 10-8 mol g−1 s−1 at 230 °C). Moreover, the Mo-doped catalyst remarkably suppressed the formation of organic byproduct of CH3Cl. The good catalytic performance of the catalysts was ascribed to the fact that abundant Brønsted acid sites derived from Mo5+–OH in the Mo-doped catalysts facilitated the C-Cl bond cleavage of the CH2Cl2 and CH3Cl reactants and their further oxidation. Water in the reaction feed was found to enhance the activity, due to its dissociation on the catalyst surface to hydroxyl groups that could react with CH2Cl2. Therefore, our findings revealed the vital roles of surface Brønsted acidity and H2O in the catalytic combustion of chlorinated volatile organic compounds.