Studies on CO Oxidation over Nanocrystalline Pd-doped CeO2 Catalysts

• Main Authors: Wen-Yu Pong, 彭文郁
• Other Authors: Huey-Ing Chen
• Format: Others
• Language: en_US
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/31911941343507314098

碩士 === 國立成功大學 === 化學工程學系碩博士班 === 95 === Palladium-doped CeO2 (Pd/CeO2) nanoparticles as well as the needle-like(N-) and particulate(P-) CeO2 nanoparticles synthesized in this work were used as oxidation catalysts. Experimentally, the oxidation of carbon monoxide was employed as the model reaction for this purpose. The influences of particle shape, calcination temperature, palladium impregnation procedure on the activities of catalysts were investigated. Besides, the reactions with different feed compositions were carried out under various temperatures for the kinetic study. Then, the catalysts were further characterized by using TPR and FTIR analyses in order to elucidate the activity of catalysts in the CO oxidation. From the experimental results, as compared with P-CeO2 nanoparticles, N-CeO2 was found to have larger surface area with a large portion of relatively higher-energy facets, i.e., {100} and {110} planes exposed on the outer surface. Therefore, higher activity for CO oxidation was obtained for the N-CeO2 nanoparticles. The result of TPR revealed that the N-CeO2 nanoparticles showed a relatively lower reduction temperature due to the easier release of oxygens from N-CeO2 surface. Besides, owing to the reduction of surface area, the activities of catalysts were decreased as the calcination temperature increased. Subsequently, high-temperature and low-temperature processes were employed for preparation of Pd/CeO2 catalysts, respectively. From the results of activity tests, it was found that the Pd/CeO2 catalyst prepared by low-temperature process had higher activity than that prepared at high temperature. To further compare the activities of CeO2 and Pd/CeO2, it showed that the activity of Pd/CeO2 was largely promoted with the presence of Pd. This was attributed from the interaction between Pd and CeO2 which would therefore obviously lower the reduction temperature as seen in TPR analysis. Furthermore, four kinds of catalysts, i.e., CN3, CP3, Pd/CN3 and Pd/CP3, were used for the kinetic study. The results showed that the activity of catalyst on CO oxidation was in the order as Pd/CN3 > Pd/CP3 > CN3 > CP3. By using the regression analysis, the activation energies for CN3, CP3, Pd/CN3 and Pd/CP3 catalysts were estimated as 16, 27, 7.4 and 11.3 kJ/mol, respectively. It is worthy to note that activation energies of needle-like catalysts were smaller than those of corresponding particulate ones, which was in a good agreement with the result of exposed facets for different catalysts.