Catalysts For Meeting Vehicles EU Ⅲ Emission Standards

In recent years, more and more attention has been paid to the air pollution result from the automobile exhaust gas. The exhaust catalysts can remove the harmful hydrocarbons (HC), nitrogen oxides (NOx) and carbon monoxide (CO). Along with the strict emission standards, more and more requests for the performance of the catalysts are put forward. A rare earth oxygen storage material (Ce_0.45Zr_0.45La_0.05Y_0.05O₂) with excellent performance and the thermal-resistant materials (stabilized Al₂O₃) with high specific surface area were prepared in this paper. Many kinds of exhaust catalyst were prepared using the two kinds of support material. The catalytic activity, durability, fast light-off performance and precious metals distribution of the catalysts, etc. were investigated in detail. Many researchs in the application of motorcycle exhaust catalysts were carried out. The main contents and results in this thesis can be summarized as follow:(1) Stabilized Al₂O₃ (La-Al₂O₃, La-Ba-Al₂O₃ and Ce-Zr-Al₂O₃) prepared with Gel-Solution method has excellent performance in textural structure and thermal stability, so as the oxygen storage material (OSM, Ceo.45Zro.45Lao.05Yo.05Ox). In addition, the OSM has good oxygen storage capacity (OSC). After aged at 1050℃, the specific surface area (S_BET) is up to120 m².g^-1 for stabilized Al₂O₃, the OSC is up to 284.3μmol.g^-1 for OSM. Two kinds of material still keep single phase. Two kinds of support material can satisfy completely the request of preparing exhaust catalysts.(2) After the investigation of Pd only catalysts, some results are obtained. The common usage of the La and Ce additives is the best way to promote the catalytic activity of Pd only catalyst. The OSM is an indispensable composition to Pd only catalyst, the best content is within 35 wt% and 65 wt%. Ba additive can enhance NOx conversion, but has a disadvantage influence to HC conversion.(3) The optimal ratio between the precious metals (PM) content and the coating weight is obtained after the investigation of low precious metals content Pt-Rh catalyst. This result is advantageous to the economical usage of the precious metals in preparing catalysts.(4) Pd-Rh catalyst with double coating layers was prepared elaborately. The catalyst possesses excellent catalytic activity, durability and fast light-off performance. It shows better performance than that of the three foreign catalyst samples, especially the high thermal stability. (5)Medium-Coupled Catalysts (MCC) meeting gasoline vehicles EU III emission standards were prepared elaborately. The encapsulated MCC was tested in a JETTA-MT gasoline vehicle according to the LDECE2000 test recycle. The values of HC, CO and NOx given by the results are only 65.5 %, 61.8 % and 38 % of the value of the EU III emission standards, which shows that the MCC not only has good low temperature activity but also has high thermal stability. The high performance MCC will help to bring the EU III emission standards into effect on time in China.(6) The MCC meeting CNG vehicles EU III emission standards was prepared elaborately also. It was tested in a JETTA-MT CNG vehicle according to the LDECE2000 test recycle. The test value of CH₄, CO and NOx given by the results are only about 50% of the value of the EU III emission standards. The MCC for CNG vehicles will help to bring the EU III emission standards into effect in China.(7) According to the characteristics of motorcycle exhaust gas, various types and specifications of catalysts were designed and prepared elaborately. The results of evaluation that the catalysts have low light-off temperature, fast light-off performance, high thermal stability and a wider A/F window. Pd only catalyst shows good oxidizing performance. Pd-Rh catalyst shows good performance for oxidizing CO and reducing NOx. Pt-Rh catalyst shows excellent catalytic activity at low temperature and wide A/F window. Pt-Pd-Rh catalyst possesses excellent qualities of the three catalysts mentioned above and shows the price advantage.(8) Compared with other catalysts, the motorcycle exhaust catalysts prepared in this thesis show the the best performance in the recycle test, which will help to bring the motorcycle EU III emission standards into effect on time in our country.(9) The excellent performance of all kinds of catalyst prepared is based specially on the excellent textural structure and stability of support materials.