Unraveling the role of the Mn–[Ox]–Ce structure in MnOx/CeO2 catalysts for the catalytic oxidation of VOCs: resistance to sintering, increasing oxygen vacancies and activation of lattice oxygen

Abstract

The preparation of a catalyst with high activity and sintering resistance remains a great challenge. In this study, a series of MnO_x/CeO₂ catalysts denoted as 5-M-Y (Mn loading of 5 wt% and calcination temperature of Y) were prepared through the modified impregnation (MI) method for the catalytic oxidation of volatile organic compounds (VOCs). Among the synthesized catalysts, the 5-M-500 catalyst demonstrated superior catalytic performance, achieving complete oxidation of both ethyl acetate (EA) and toluene at 230 °C (T₁₀₀ value is operationally defined as the minimum temperature required to attain 100% conversion of VOCs). More importantly, the 5-M-800 catalyst exhibited excellent sintering resistance, and the T₁₀₀ value only slightly increased to 250 °C. However, the 5-AO-800 and 5-O-800 catalysts prepared by the conventional impregnation on cerium oxides from cerium acetate decomposition and commercial product exhibited high T₁₀₀ values of 320 °C and 400 °C, respectively. The exceptionally high activities and sintering resistances of the 5-M-Y catalysts are attributed to the high contents of the Mn–[O_x]–Ce structure. The Mn–[O_x]–Ce structure anchored the Mn species in the CeO₂ crystals through their strong interactions. Meanwhile, the robust Mn–[O_x]–Ce structure inhibited the ordered growth of CeO₂ crystallites during the calcination process. Thus, the aggregation and sintering of MnO_x and CeO₂ particles at high temperatures were limited. In addition, the Mn–[O_x]–Ce structure promoted the formation of multisite oxygen vacancies and enhanced the adsorption and activation of VOCs and oxygen. On the other hand, the Mn–[O_x]–Ce structure weakened the Ce–O bond to increase the content of surface lattice oxygen and boost the lattice oxygen migration and activation ability. This study emphasizes the important role of the Mn–[O_x]–Ce structure in the high activities and sintering resistances of the catalysts, and it illustrates the possible reaction mechanism for the simultaneous oxidation of EA and toluene.