Research On The Synergistic Effects Between MnO_x And CeO₂and NO Oxidation Activities Of MnO_x-CeO₂Catalysts

MnOx-CeO2catalysts were prepared by two physical mixing methods. MnO andCeO2powders were mechanically mixed by a spatula and by milling to obtainloose–contact and tight–contact mixed oxides, respectively. The monoxides and theirphysical mixtures were characterized by X–ray diffraction (XRD),Brunauer–Emmett–Teller (BET), X–ray photoelectron spectroscopy (XPS), Raman, O2temperature–programmed desorption (O2–TPD), H2temperature–programmed reduction(H2–TPR) and NO temperature–programmed oxidation (NO–TPO). The MnOx–CeO2solid solutions do not form without any calcination process. The oxidation state ofmanganese tends to increase while the ionic valence of cerium decreases in the mixedoxides, accompanied with the formation of oxygen vacancies. This long–rangedelectronic interaction occurs more significantly in the tight–contact mixture of MnO andCeO2. The tight–contact mixed oxides present better redox property and NO oxidationactivity, which are mainly associated with the formation of more Mn4+and oxygenvacancies.Two Mn0.15Ce0.85O2-δmixed oxides were synthesized by co-precipitation withdifferent manganese precursors (Mn(NO3)2vs. KMnO4). No diffraction peaks ofmanganese oxides could be detected by XRD due to the formation of MnOx–CeO2solidsolutions. Structure analyses revealed that there are more Mn4+species and adsorbedoxygen on the surface of the mixed oxides using KMnO4as the precursor, resulting inhigher catalytic activity for NO oxidation.Some manganese-cerium interaction exists on both MnOx-CeO2catalysts preparedby means of mechanical mixing and co-precipitation, although the mechanically mixedcatalysts do not form a solid solution. The increase in the oxidation state of manganeseions and the amount of oxygen vacancies promote the redox property and catalyticactivity of the catalyst in the NO-O2reaction.