Construction of ZIF-derived CoCrOx/HZSM5 catalysts for deep catalytic oxidation of dichloromethane: Synergistic of B acid, L acid, and redox sites

Abstract

The acidic and oxidizing properties of the catalyst are critical for the removal of chlorinated volatile organic compounds (CVOCs). An excellent catalyst often requires outstanding chlorine resistance and byproduct inhibition. In this study, CoOx, which is widely used for the removal of volatile organic compounds (VOCs) because of its outstanding activity was chosen to provide oxidizing properties. To address the potential for chlorination byproducts and the lack of activity, we loaded CoOx on the acidic carrier HZSM-5 by ZIF-derived method, then doped CrOx using impregnation method to enhance both oxidation and acidity. It was found that ZIF-derived method disperse CoOx nicely thus providing more oxidation sites. Besides, CrOx effectively increases the superficial lattice oxygen of the catalyst to compensate for the loss of sites due to the occupation of oxygen vacancies by DCM during the oxidation process. This contributes to the superior oxidizability of the modified catalysts, which explains the high CO2 selectivity. Invigoratingly, CrOx can increase the ratio of Lewis acid to Brønsted acid to completely break the C–Cl bond, hence eliminating the possibility of chlorine-containing byproducts and accomplishing a deeper degradation of CVOCs. The bimetallic catalysts we prepared have high activity and can achieve very low or even zero byproduct generation. In addition, the catalyst shows outstanding stability and water resistance, which is quite meaningful in the field of catalytic oxidation of CVOCs.