New insights into the effect of morphology on catalytic properties of MnOx–CeO2 mixed oxides for chlorobenzene degradation

Abstract

We synthesized four CeO₂–MnO_x mixed oxides with different morphologies using simple hydrothermal methods. The catalytic activity for chlorobenzene (CB) degradation decreases in the following order: rod-CeO₂–MnO_x > plate-CeO₂–MnO_x > polyhedra-CeO₂–MnO_x > cube-CeO₂–MnO_x. CeO₂ and MnO_x in the mixed oxides are highly dispersed and two new phases of both todorokite (S.G.: P2/m:b) and vernadite (S.G.: I4/m) with a special tunnel-like structure are found. Both rod-CeO₂–MnO_x and plate-CeO₂–MnO_x exhibit increased lattice microstrains generated from lattice distortion and defects; further, there are more oxygen vacancies and more MnO_x (Mn⁴⁺ and Mn²⁺) species on the surface, particularly when compared to cube-CeO₂–MnO_x. Therefore, this promotes deeper oxidation activity for CB. Moreover, the strong interaction between CeO₂ and MnO_x also promotes the redox ability of CeO₂–MnO_x mixed oxides, while their oxygen storage capacity (OSC) properties are not only intrinsic to their structures but also limited to their surfaces and by their particle sizes.