Acid etching-induced Ce3+−O − Mn4+ active sites of SmCe0.1Mn1.9O5 mullite for enhanced elimination of Hg0 and chlorobenzene

Abstract

The efficient control of co-existing Hg⁰ and chlorobenzene in flue gas through catalytic oxidation is a major challenge in the field of energy-intensive industry. In this study, a porous SmCe_0.1Mn_1.9O₅ catalyst is prepared via a sol–gel method followed with acid etching for the synergistic elimination of Hg⁰ and chlorobenzene. The optimized Ce-SM-E exhibits near 100% removal efficiency of Hg⁰ within 100–400 °C and 90% chlorobenzene conversion above 275 °C as well as excellent performance under complex flue gas conditions. The Ce substituting Mn³⁺ in the mullite structure enables favorable electron transfers from SmMn₂O₅ to CeO₂ while causing more active defects. Subsequent acid etching removes the surface Sm species and modulates the electronic state of Mn atoms, inducing formation of more Ce³⁺-O-Mn⁴⁺ active sites, consequently enhancing the redox cycle. Especially, the generation of aldehydes, aromatic rings, maleate species and monodentate carbonate species are considered as the main rate-limiting steps in the chlorobenzene degradation path. The influence of complex flue gas components (SO₂, NO, H₂O, etc) on the distribution of reaction by-products is analyzed. The sulfation poisoning from SO₂ consumes reactive oxygen species and promotes more dichlorobenzenes through electrophilic reactions. The presence of NH₃/NO and H₂O are found to promote the generation of NH₄Cl and HCl, respectively, but the addition of which also generates much oxygen-containing byproducts such as acetophenone, benzoyl chloride and benzenecarboxylic acid via the Friedel-Crafts reaction. These results provide a promising approach for engineering efficient catalysts and benefit the evaluation of environmental risk under industrial conditions.