Catalytic oxidation of chlorinated aromatics over Fe-based oxide catalysts modified by Mn

Abstract

FexMny mixed oxide catalysts prepared by co-precipitation method are applied in catalytic combustion of chlorobenzene (CB) and 1,2-dichlorobenzene (1,2-DCB). Characterization shows that Mn species of Fe9Mn1highly disperse into α-Fe2O3 as Fe-O-Mn structure. With the increase in Mn content, a part of Mn is separated as MnO2 and α-Mn2O3. Fe-O-Mn structure greatly increases the acidity (especially for strong acid) and reducibility of α-Fe2O3. In CB and 1,2-DCB oxidations, FexMny catalysts are active, of which Fe9Mn1 catalyst presents the highest activity. At 5% – 20% O2 and 500 – 2000 ppm 1,2-DCB at space velocity of 15,000 mL g-1h−1, the apparent rates at 300 °C over Fe9Mn1 are estimated to be 0.056 – 0.112 μmol min−1 m−2, and the temperatures needed for 50% and 90% conversions are 294 – 342 °C and 346 – 375 °C, respectively. High availabilities of surface oxygen and acid sites are related to effective Cl removal in aid of active hydroxyls produced during the reaction (confirmed by in situ FT-IR tests), which are responsible for high activity of Fe9Mn1 catalyst. For the catalysts with MnO2 and Mn2O3 domains on the surface, Cl strong adsorption results in their deactivation. Moreover, Fe9Mn1 catalyst shows high stability at 350 °C on feed stream containing 1000 ppm 1,2-DCB within 600 min duration or for five runs. The selectivity for CO/CO2 approaches 98% or higher and no chlorination products are detected within FID limitation (1 ppm) under the above mentioned broad reaction conditions, which are highly desirable for industrial application.