Mn-Ce solid solution growth on Mn2O3 surface to form heterostructure catalysts with multiple active sites for toluene degradation

Abstract

A solid solution-heterostructure catalyst with abundant active sites was successfully constructed in this study by in situ growth of Mn-Ce solid solution on the surface of Mn2O3. The solid solution structures with optimum physical and chemical properties were synthesized initially by controlling the Mn-Ce ratios. Subsequently, the reaction time was controlled to realize the orderly growth of the solid solution on the Mn2O3 surface. The catalyst (M−CeMn0.5) with solid solution-heterostructure formed by the reaction of Ce3Mn1 and Mn2O3 for 0.5 h could reach more than 90 % toluene degradation rate at 183 °C and was operated continuously for 15 h without deactivation. XRD showed that the appropriate reaction time resulted in the active components on the catalyst surface exhibiting lower crystallinity and reduced grain size. The reduction capacity (2.28 → 10.47 mmol/g) and the mobility of lattice oxygen were significantly enhanced in the M−CeMn0.5 catalyst compared to the Mn-Ce solid solution. Meanwhile, a high content of low valent metal ions (Ce3+/Ce4+ 0.33, Mn3+/Mn4+ 1.64) and reactive oxygen species (Oads/Olatt 0.53) were also present on the catalyst surface. The DFT demonstrated that the Mn atoms and Mn-O bridge sites on the solid solution surface exhibited high adsorption energy values for toluene (−0.8402/-0.8406 eV) and oxygen (−1.6546/-1.661 eV) molecules. The TEM indicated that lattice distortion and oxygen vacancies were formed at the interface between the solid solution and Mn2O3 at the interface. The synergy of multiple active sites favors the generation of reactive oxygen species and thus promotes p-methyl dehydrogenation. Meanwhile, the high mobility of lattice oxygen facilitates the breakage of benzene ring. This study provides a new strategy for the synthesis of efficient Mn-Ce-based catalysts.