Preparation And Oxygen Storage Properties Of CLA Intergrowth Mixed Oxides

As air pollution has posed a more and more urgent threat to the health of human beings, the demand for better catalytic performance to purify automotive exhaust gas is higher and higher. The catalytic conversion is regarded as one of the most popular and efficient solution for engine pollution control. Three-way catalyst (TWC) has been used as a suitable alternative to reduce pollution from gasoline engine powered vehicles by converting basic pollutants like CO, HC and NOx to their inactive products CO2, N2 and H2O simultaneously. However active component of three-way catalyst Pt, Pd, Rh and so on, only near the theory air-fuel ratio can play a maximum effect, therefore, need to use the ceria-based oxides to reduce the oscillation of the air-fuel ratio engine operation process. In this paper, a serious of La3+-doped CeO2-γ-Al2O3 intergrowth mixed oxide powders were synthesized by an improved amorphous citric precursor (IACP) method and then steam-aged with 90% steam and 10% air for 12 h at 788℃. The synthesized materials were characterized by a lot of measurements and the results clearly indicated that La3+ was successfully doped into the CeO2-γ-Al2O3 lattice to form an intergrowth system. Strong intergrowth interactions were observed between CeO2, La2O3, and the γ-Al2O3 crystallites.La3+ ions in the binary CeO2-γ-Al2O3 system were investigated using multiple analytical techniques, and the following effects were observed:(a) marked decreases in average particle size, (b) effective stabilization of the defective structure, and (c) considerable enhancement of the OSC. Incorporation of La3+ ions into the ceria lattice to form a CeO2-La2O3 solid solution as well as intergrowth effects between the CeO2-La2O3 solid solution and γ-Al2O3,which influence structural homogeneity, oxygen vacancy formation and inhibit the CLA particles sintering in the steam-aging process, which leads to enhancements in OSC and hydrothermal stability.In CLA intergrowth mixed oxides, La3+ ions are successfully incorporated into the ceria lattice to form a solid solution, such that the CeO2-La2O3 solid solution and γ-Al2O3 form an intergrowth system. Because of the intergrowth effects, the average particle sizes of all CLA samples are much smaller than those of the CL samples. There has a strong interactions between CeO2-La2O3 and γ-Al2O3 and γ-Al2O3 3 induces CeO2 lattice distortions so that more lattice defects and oxygen vacancies are produced. The OSC value of the samples was about three times that of mechanical mixture samples.The sample (Ce0.92La0.08)0.4Al0.602-z showed a maximum OSC of 979 μmol·g-1; by contrast, the pure ceria sample showed an OSC of only 315 μmol·g-1. The CLA samples maintained a relatively high OSC of 880 μmol·g-1 even after hydrothermal treatment. These results may be explained by taking into account the incorporation of La3+ ions into the ceria lattice to form a CeO2-La2O3 solid solution as well as intergrowth effects between the CeO2-La2O3 solid solution and γ-Al2O3, which influence structural homogeneity, oxygen vacancy formation and inhibit the CLA particles sintering in the steam-aging process.