【作者】 朱凌云；

【导师】 沈美庆；

【作者基本信息】 天津大学 ， 化学工艺， 2006， 硕士

【摘要】 近年来各国科学家开发了能够同时转化CO、HC和NOx的贵金属三效催化剂,以Pt、Rh、Pd等贵金属为活性组分的催化剂不仅有合适的烃类吸附位,还有大量的氧吸附位。随着表面反应的进行,能快速的发生氧活化和烃类的吸附。但贵金属资源有限,价格昂贵,这类催化剂的成本较高。铈锆固溶体以其高的热稳定性、良好的储放氧能力使催化剂最大限度的发挥三效作用,尤其是汽车刚启动时的低温过程。系统而深入地研究铈锆固溶体与贵金属之间相互作用,对于汽车尾气净化催化剂的发展会起到宏观指导作用。本文以溶胶凝胶法制备锶掺杂的铈锆固溶体,以锶掺杂的铈锆固溶体为载体采用浸渍法制备贵金属负载的催化剂,并对新鲜样品进行水热老化处理。采用动态储放氧测试和模拟配气催化剂评价手段,研究PM和CZS之间的相互作用。考察PM对CZS的OSC性能和高温热稳定性的影响及CZS对PM催化性能的作用效果。利用XRD,HRTEM,BET和XPS对样品的结构、晶相、比表面积和表面元素组成进行研究。通过动态储放氧测试,发现锶掺杂可以提高铈锆固溶体的OSC性能,但是PM负载后,纯的铈锆固溶体显示出最佳的储放氧性能。这可能是由PM与载体之间的强相互作用所导致。通过CO脉冲实验,可以得出锶掺杂有助于提高体相氧的迁移,Pd和Rh对CZS所表现的不同的促进作用,可以归结为Pd和Rh与载体发生的不同的SMSI。CZS能够提高PM的催化活性,特别是老化载体上负载PM的催化剂,同时表明载体的比表面积对活性的影响不大。更多还原

【Abstract】 Automotive exhaust is the main source of air pollution now. Generally engine modification and after-treatment control technique are used for this problem, and setting three-way-catalyst, one of after-treatment control, is the most effective solution. At present, the hot issues about three-way-catalyst include improving cold-start performance, reducing noble metal dosage and prolonging the used life.Pd, Pt and Rh played the important role in TWC application; Pd and Pt have influence on HC and CO oxidation, whereas Rh has effects on NOx reduction. As we known, HC, CO and NOx can reach the best conversion around the A/F=14.6. For the redox couple of Ce³⁺/Ce⁴⁺, Ceria-zirconia mixed oxides was used to accommodate the fluctuation of A/F around the 14.6 which storage oxygen when lean fuel condition and release oxygen when rich fuel condition, resulting in best conversion efficiency of HC, CO and NOx. The research of the interaction between the PM and CZ in application, resulting in changing in catalytic activity and OSC performance is ofimportant influence. In this paper, Sr doping samples Ce_0.67Zr_0.33Sr_xO_2+x （CZS_x） were prepared by sol-gel method and aged under H2O/air condition as the aged samples. PM （Pd, Rh） loaded on fresh and aged CZS samples were prepared by impregnation. Both fresh and aged samples were characterized on home-made dynamic OSC measure instrument and TWC measure equipment for their dynamic OSC and TWC performance. Structure analysis were also done by Brunnauer-Emmett-Teller （BET）, X-ray diffraction （XRD）,X-ray photoelectron spectroscopy （XPS）and high resolution transmission electron microscopy（HRTEM）.OSC results show that the oxygen storage capacity is enhanced by Sr²⁺ doping. However, after supporting Pd or Rh, undoped CZ shows higher dynamic OSC of CZ than Sr-doped samples, which may be ascribed to the SMSI effect. Sr doping can efficiently promote the catalytic activities, especially for PM supported on aged samples.Pd/aged CZS5 and Rh/aged CZS5 exhibit good performance indicating potential in practical applications.更多还原