Design And Study Of Three-Way Catalysts Modified By Ce-Zr-Ln Solid Solutions

In this paper, we have mainly studied and prepared three-way catalysts improved by adding rich-Ce and rich-Zr solid solutions to the washcoats. The idea is to form the cubic phase with defect and increase the oxygen mobility in the crystal lattice of solid solutions by introducing trivalent rare earth cation into Ce-Zr-Ln solid solutions so that oxygen storage materials with high performance can be obtained, and then add this kind of solid solutions to the washcoats of three-way catalysts in order to enhance their redox properties and high temperature stability.First, by using ethanol as solvent, two groups of Ce-Zr-Ln (Ln=La, Y, Yb, Gd, Sm, Pr, Dy, Nd) solid solutions with high specific surface areas were prepared by sol-gel method at 600℃ and 900℃respectively. And the characterization, specific surface areas test and oxygen storage capacities (OSC) test of these solid solutions have been made by means of X-ray diffraction analyses, BET method and gas chromatogram. The results show that both of them present the cubic phase of fluorite-structured, the crystal particles of solid solutions prepared at 600℃ are more tiny, because of calcinations the crystallization degree of solid solutions prepared at 900℃ increase but no second phase is found, which indicating a good thermal stability. Based on XRD diagrams, the average sizes of crystallite grains of the two groups of solid solutions have been calculated as 6-8nm and 15-18nm respectively. The specific surface areas of solid solutions prepared at 600℃ and at 900℃ is about 60 m2/g and 40 m2/g, respectively increasing by 300% and 170% than that of CeO2. Oxygen storage capacities(OSC) of two groups solid solutions are respectively 0.26-0.28 mmol/g and 0.22-0.25mmol/g, especially the OSC at 900℃ increase by 140% than that of CeO2 at 900℃, which meaning that these solid solutions havehigher OSC at high temperature. Then, two groups of three-way catalysts were prepared through adding rich-Ce and rich-Zr solid solutions to the washcoats. And the activities of these three-way catalysts were evaluated. The results show that the addition of the solid solutions can promote the catalysis activities of three-way catalysts to the three pollutants of CO, HC and NO; the catalysis activities of C group catalysts are mostly higher than those of Z group three-way catalysts; as compared with the three-way catalyst without adding the solid solutions, the ignition temperatures of C group catalysts for CO, HC and NO have been separately decreased by 25-70℃, 50-137℃ and 0-42℃. As to Z group catalysts, the ignition temperatures for CO, HC and NO have been separately decreased by 25-35℃, 20-30℃ and 12-20℃. Among C group catalysts, the catalyst C5 of adding Ce-Zr-Sm solid solution has the best catalysis activity and the catalyst C3 of adding Ce-Zr-Gd solid solution takes the second place. The ignition temperatures of C5 and C3 for CO, HC, NO are separately 198℃,248℃,195℃ and 205℃, 255℃, 205℃。...