Effect of Additives on a Catalytic Converter for Removing CO and HC Emissions from a Two-sroke Motorcycle

• Main Authors: Lee, Chiou-Hwang, 李秋煌
• Other Authors: Chen Yu-Wen
• Format: Others
• Language: zh-TW
• Published: 1997
• Online Access: http://ndltd.ncl.edu.tw/handle/09018997831353390452

博士 === 國立中央大學 === 化學工程學系 === 85 === The effects of additives (Na2O, K2O, CeO2, and SiO2) on Pd/ Al2O3 and Pt/Al2O3 for CO and HC oxidation were studied in this work. The objectivesof this work are (1) to improve the CO conversion on the existing commercialcatalytic converter for a two-stroke motorcycle and (2) to pursue a methodto improving the CO conversion on the Pd-containing catalytic converter. The characterization of the catalysts includes BET surface area, pore volume, temperature-programmed reduction of hydrogen, temperature-programmeddesorption of carbon dioxide, and CO chemisorption. The reactions were performedunder the stoichiometric and oxygen-deficient conditions. In addition, theactual performances of the catalytic converters were verified by the ECE-40 mode driving cycle test. From the experimental results, one finds that the addition of promoteron Pt/Al2O3 or Pd/Al2O3 catalyst slightly decreases the surface area and porevolume of the catalyat but does not markedly change the Pt dispersion. TheCO2-TPD results reveal that the basicity of the Pt powder catalyst is in the order: Pt/K2O/Al2O3 ≒ Pt/K2O/CeO2/ Al2O3 > Pt/Na2O/Al2O3 > Pt/K2O/Al2O3-SiO2 > Pt/Al2O3 > Pt/Al2 O3-SiO2. The basicity of Pt/CeO2/Al2O3 or Pt/Al2O3-SiO2 can be increased by the addition of K2O. In addition, the basicity of Pt/K2O/Al2O3 added amount of K2O. The order of basicity of the Pt catalysts can also be applied to the Pd catalysts. Under the stoichiometric point, the activities of the Pt powder catalystsfor CO and C3H6 oxidation follow the order: Pt/K2O/Al2 O3 > Pt/Na2O/Al2O3 > Pt/Al2O3 > Pt/Al2O3-SiO2,that is the same as the order of basicity of these catalysts. The activity of Pt/ K2O/Al2O3 is even higher than Pt/CeO2/Al2O3. Inaddition, the effect of K2O on activities of Pt/Al2O3 for CO and C3H6 oxidation is affected by the added amount of K2O. In addition, Pd catalysts exhibit a higher activity than Pt catalysts for CO and C3H6 oxidation when they are supported on the same support. Under an oxygen-deficient condition and in the absence of water, C3H6 conversionson all powder catalysts studied in this work always increase with increasing reaction temperature. Nevertheless, the CO conversion shows the reverse trend once oxygen is completely reacted. Pt/Al2O3 and Pt/Al2O3-SiO2 exhibit higher C3H6 conversions and lower CO conversions, that is contrary to Pt/K2O/Al2O3. Moreover, the CO conversion on Pt/Al2 O3 can be promoted by addition of CeO2, Na2O, and K2O. Under an oxygen-deficient condition and in the presence of water, CO and C3H6 conversions can be increased by the water-gas shift (WGS) and steam reforming reactions. Pt/Al2O3 and Pt/Al2O3-SiO2 exhibit higher activities for the steamreforming reaction, while they exhibit lower activities for the WGS reaction. The addition of Na2O or K2O on Pt/Al2O3 catalyst can significantly enhance the WGS reaction. The activities of the catalysts for the WGS reaction also followthe order of basicity of these powder catalysts,i.e., Pt/K2O/Al2O3>Pt/Na2O2/Al2O3>> Pt/Al2O3 > Pt/Al2 O3-SiO2. In addition, the promotional effect of Na2O or K2Oon the Pt/Al2O3 for the WGS reaction is better than that of CeO2. When Pt and Pdare supported on the same support, CO conversions on Pd-containing catalystsare significantly lower than those on Pt-containing catalysts under an oxygen- deficient condition. Nevertheless, the CO conversion on Pd/Al2O3 can be significantlyincreased by the simultaneous addition of K2O and CeO2. The effect od air/fuel ratio on the CO conversion of the monolithic catalystis significantly greater than that on the HC conversion. The experimental results reveal that the HC conversions on PtRh-containing monolithic catalysts follow the order: PtRh/Al2O3-SiO2 >= PtRh/Al2O3 > PtRh/Al2O3-CeO2 > PtRh/K2 O/Al2O3-SiO2 >PtRh/K2O/Al2O3 > Pt/K2O/Al2O3-CeO2, that is contrary to the order of the CO conversion.On the other hand, the CO conversion on the PdRh-containing monolithic catalystis significantly lower than that of the PtRh-containibg catalyst. Nevertheless,the difference in CO conversions between PdRh/Al2 O3-CeO2 and PtRh/Al2O3-CeO2 canbe significantly lessened by adding K2O on the Pd catalyst. The experimental results verifiy that K2O is a promising additve to the catalyticconverter for a two-stroke motorcycle. The test results of the ECE-40 mode drivingcycle reveal that the CO conversions on PdRh/Al2O3-CeO2 and PtRh/Al2O3-CeO2 can be significantly promoted by the addition of K2O. The CO conversion PdRh/K2O/Al2 O3-CeO2is close to that PtRh/Al2O3-CeO2 (the existing commercial catalytic converter for a two-stroke motorcycle). Therefore, PtRh/K2O/Al2O3-CeO2 can be applied to a two-stroke motorcycle with the higher CO emission. PdRh/K2O/Al2O3-CeO2 might substitute PtRh/Al2O3-CeO2 to be used in a two-stroke motorcycle with the lower CO emission.