Revealing the effects of preparation methods over Ce-MnOx catalysts for soot combustion: Physicochemical properties and catalytic performance

Abstract

Catalytic oxidation for soot emissions from diesel engines is a major post-processing technology, but limited by the lack of efficient catalysts. Herein, a series of MnCeOx catalysts with different Mn/Ce molar ratios were prepared by the traditional hydrothermal (tr-MnCeOx) and MOFs derivatization method (M-MnCeOx), and mechanism behind for soot combustion were investigated by several techniques and density functional theory (DFT) calculations. Encouragingly, N2 adsorption–desorption result demonstrates M-MnCeOx has a larger specific surface area, thus increasing the number of active sites and contact efficiency between soot and catalysts. Further, XPS, H2-TPR observations manifest the appropriate Ce doping would promote the generation of oxygen vacancy through the redox cycle of Ce4+ + Mn3+ ↔ Mn4+ + Ce3+, thereby improving the catalytic performance for soot combustion. More importantly, the DFT calculations indicate that MOFs-derived 2Mn1Ce-200 possesses the lowest oxygen vacancy formation energy and stronger affinity for both O2 and H2O, which is favorable for the generation of active oxygen species. Among all catalysts, the 2Mn1Ce (Mn/Ce molar ratio of 2:1) exhibited the highest catalytic activity under tight contact with T90 value of 360 °C, and maintained good stability. Our work provides guidance for developing catalysts with tunable physicochemical properties.