Influence of cerium on the performance of LaMO3+λ (M = Mn or Mn–Cu) perovskite-type catalyst

The influence of cerium (Ce) on the structure and properties of automotive catalyst LaMO3 (M=Mn or Mn–Cu) and washcoat materials γ-Al2O3 has been analyzed by a combination of scanning electron microscopy (SEM), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), and catalytic test studies. The results showed that the thermostability of the washcoat was positively improved by adding Ce into γ-Al2O3. The temperature of phase transformation from γ- to α-Al2O3 was modified from 800 to 1150 °C with 6% ceria. At the same time, the washcoat of γ-Al2O3 still presented the maximum surface area. On the other hand, by adding Ce into the perovskite-type catalyst LaMn0.7Cu0.3O3+λ, the oxidation ability of active materials had a little decrease due to the conversion of hydrocarbon (HC). However, the oxidation ability of carbon monoxide (CO) and the reduction ability of nitrogen monoxide (NO) using the catalyst LaMn0.7Cu0.3O3, were greatly modified. In the oxygen-rich gas with 10% O2, the conversion rate of NOx was greatly increased to over 40%, using the catalyst LaMnO3/Au doped with Ce. Not only were the formation and separation of perovskite crystals restrained by Ce additive, but the crystal size also decreased, so as to make a better distribution of active component on the surface.