臺灣博碩士論文加值系統

本研究中，首先製備鈀摻雜CeO2、針狀及顆粒狀CeO2奈米微粉以作為氧化觸媒。實驗中係以一氧化碳之氧化反應為模式反應，探討CeO2晶形、鍛燒溫度及鈀含浸步驟對觸媒催化活性之影響。另外，改變反應進料氣體組成進行動力學研究，並輔以TPR、FTIR等特性分析，以解析各式觸媒之催化行為。
實驗結果顯示，針狀粉體比顆粒狀擁有較大比表面積，且外露較高能之(100)與(110)面，故其活性較高。TPR結果亦顯示，針狀粉體具有較低之還原溫度，易於釋出晶格氧來進行反應。另外，隨著鍛燒溫度上升，觸媒之催化活性降低，此係因比表面積減小之故。
在Pd/CeO2觸媒之製備中，採用高溫、低溫兩種鍛燒製程來進行。實驗結果顯示，低溫製備之觸媒擁有較高之催化活性。比較CeO2與Pd/CeO2觸媒發現，含浸鈀金屬可明顯提高反應性。由TPR分析結果顯示，鈀與CeO2間存在一相互作用力，故可大幅降低反應溫度。
進一步，以四種觸媒(CN3, CP3, Pd/CN3及Pd/CP3)來進行動力學研究。各觸媒一氧化碳之催化氧化反應活性依序為Pd/CN3 > Pd/CP3 > CN3 > CP3。利用回歸分析可求出此四種觸媒之反應活化能分別為16, 27, 7.4 與 11.3 kJ/mol。值得一提的是，針狀觸媒之活化能較顆粒狀觸媒為低，此與觸媒外露之晶面之分析結果相吻合。

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.

誌謝………………………………………………………………………….... I
摘要…………………………………………………………………………… II
Abstract……………………………………………………………………….. III
各章概要……………………………………………………………………... V
List of Contents………………………………………………………………. XII
List of Tables…………………………………………………………………. XV
List of Figures………………………………………………………………… XVI

Chap 1 Introduction………………………………………………………… 1
1.1 Properties of CeO2……………………………………………... 1
1.1.1 Physical properties………………………………………. 1
1.1.2 Chemical properties……………………………………… 1
1.1.3 Optical properties………………………………………... 2
1.2 Preparation method of CeO2 and Pd/CeO2…………………….. 2
1.2.1 Preparation methods…………………………………….. 2
1.2.2 Precipitation method for preparing CeO2………………... 3
1.2.3 Wetness Impregnation for preparing Pd/CeO2…………... 4
1.3 Application of CeO2……………………………………………. 4
1.3.1 Ultraviolet (UV) absorbents……………………………… 4
1.3.2 Buffer layer with silicon wafer…………………………… 4
1.3.3 Gas sensors……………………………………………… 5
1.3.4 Photocatalytic oxidation of water………………………... 5
1.3.5 Water-gas-shift catalysts…………………………………. 5
1.4 Motivation and objectives………………………………………. 6
1.5 Organization……………………………………………………. 6

Chap 2 Theoretical………………………………………………………..... 14
2.1 Formation of CeO2 nanoparticles by precipitation……………... 14
2.1.1 Nucleation……………………………………………….. 14
2.1.2 Growth…………………………………………………... 15
2.2 CO Oxidation over CeO2 nanoparticles………………………… 17
2.2.1 Adsorption of CO on CeO2…………………………....... 17
2.2.2 Adsorption of O2 on CeO2………………………………. 18
2.2.3 Effect of exposed CeO2 surface…………………………. 19
2.3 CO Oxidation over Pt/CeO2 nanoparticles……………………... 20
2.3.1 Eley-Rideal mechanism…………………………………... 20
2.3.2 Langmnir-Hinselwood mechanism………………………. 20
2.3.3 Strong Metal-supported interaction(SMSI)………………. 21

Chap 3 Experimental Details……………………………………………….. 26
3.1 Chemicals and materials………………………………………… 26
3.1.1 Chemicals………………………………………………... 26
3.1.2 Gas………………………………………………………. 26
3.2 Instruments and measurements…………………………………. 26
3.2.1 Instruments………………………………………………. 26
3.2.2 Instruments for analysis...…………...…………………… 27
3.3 Preparation of catalysts………………………………………… 28
3.3.1 Preparation of CeO2……………………………………... 28
3.3.2 Preparation of Pd/CeO2………………………………….. 28
3.4 Characterization of catalysts……………………………………. 29
3.4.1 BET analysis…………………………………………….. 29
3.4.2 TEM and HRTEM analysis……………………………… 29
3.4.3 TPR analysis…………………………………………….. 29
3.4.4 XRD analysis…………………………………………….. 30
3.4.5 FT-IR analysis…………………………………………… 30
3.4.6 AA analysis……………………………………………… 31
3.5 Activity test of catalysts………………………………………... 31
3.5.1 Intrinsic reaction setup…………………………………... 31
3.5.2 CO oxidation reaction…………………………………… 31
3.5.3 Kinetic model of CO oxidation reaction…………………. 33

Chap 4 CO Oxidation over CeO2 Catalysts……………………………….. 42
4.1 Objective……………………………………………………….. 42
4.2 Characterization of CeO2 catalysts……………………………... 42
4.2.1 BET analysis…………………………………………….. 42
4.2.2 XRD analysis…………………………………………….. 43
4.2.3 TEM analysis…………………………………………….. 44
4.3 CO oxidation…………………………………………………… 45
4.4 Interpretation by TPR analysis…………………………………. 46

Chap 5 CO Oxidation over Pd/CeO2 Catalysts…………………………… 57
5.1 Objectives………………………………………………………. 57
5.2 Characterization of Pd/CeO2 catalysts………………………….. 57
5.2.1 BET analysis…………………………………………...... 57
5.2.2 XRD analysis…………………………………………….. 58
5.2.3 CO oxidation…………………………………………….. 58
5.3 Comparison of activity between Pd/CeO2 and CeO2 catalysts…. 59
5.3.1 Properties of catalysts…………………………………… 59
5.3.2 CO oxidation…………………………………………….. 60
5.3.3 Interpretation by TPR analysis…………………………... 61

Chap 6 Oxidation Kinetics………………………………………………….. 68
6.1 Objectives……………………………………………………….. 68
6.2 Reaction kinetics for CO oxidation…………………………….. 68
6.3 FTIR analysis…………………………………………………... 72
6.3.1 CO adsorbed on CeO2…………………………………... 72
6.3.2 CO adsorbed on Pd/CeO2………………………………. 73

Chap 7 Conclusions and Propective……………………………………….. 90
7.1 Conclusions…………………………………………………….. 90
7.2 Propective……………………………………………………… 91

References…………………………………………………………………….. 92

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