Insights into synergistic oxidation mechanism of Hg0 and chlorobenzene over MnCo2O4 microsphere with oxygen vacancy and acidic site.

The simultaneous control of Hg0 and chlorinated organics has become the frontier of environmental engineering but still lacks the understanding of synergistic oxidation mechanism. Herein, we designed a Mn-Co catalyst with abundant oxygen vacancies and acidities, which delivered more than 90 % oxidation performance of Hg0 within 100-325 °C and achieved 90 % conversion of chlorobenzene at 220 °C. A synergistic effect was observed in the oxidation of Hg0 and chlorobenzene. Experimental and computational results revealed that Lewis acid over Mn site weakened C-Cl bands of chlorobenzene by electronic traction. The strong interaction between adsorbed mercury and Cl further promoted dechlorination process to generate HgCl2 gas, while accelerating the nucleophilic substitution of Brønsted acid attacking the benzene ring over Co site, consequently triggering synergistic oxidation of Hg0 and chlorobenzene. Oxygen vacancies enhanced the initial adsorption of Hg0 and chlorobenzene. Meanwhile, the interfacial charge-transfer from Hg-d to Cl-p orbitals alleviated deactivation of Lewis acid and slowed down the consumption of Brønsted acid, which accelerated the conversion of intermediates to CO2/H2O and promoted deep oxidation of chlorobenzene. This work provides a unique insight into the promotion of the synergistic oxidation of Hg0 and chlorobenzene and is expected to guide the industrial applications.