鑒於現今工業Haber-Bosch氨氣製程所需操作環境嚴峻(高溫450-500 °C及高壓30 MPa)，導致能源消耗占比過高及溫室氣體排放量過大。釕(Ru)基觸媒材料在產氨反應中最接近活化能-反應速率火山圖之頂點，亦即為一極有潛力於高活性觸媒，因此本研究之一將針對釕觸媒於製氨反應之主要速率決定步驟 - 氮氣活化進行原子尺度下之密度泛函理論(DFT)計算模擬，欲了解降低氮氣斷鍵活化能之主因，並探討釕觸媒中一特殊反應活性位點B5對活化反應之作用，比較一般表面與活性位點上氮氣活化機制的不同，於此此結果可提供實驗團隊於產氨之方向。此外，基於先前研究發現釕觸媒搭載於氧化鎂(111) ((Ru/MgO(111))之系統可有效解決氨氣製程中解離氫原子毒化觸媒材料表面之問題，本次研究也欲探討此Ru/MgO(111)觸媒於氮氣活化之效應，同時在Ru8觸媒團簇上結合B5活性位點，建構了類B5之Ru8，一來以檢測基載及氧溢流機制對於整體氮氣吸脫附行為的影響，二來測試基載對於團簇形成之活性位點有無效益，進而完善氮氣活化機制之探討及證明強金屬-載體相互作用(SMSI)對於催化反應的貢獻性。此DFT結果發現結合SMSI及類B5活性位點之Ru8MgO(111)觸媒對於氮氣活化有顯著降低N-N斷鍵活化能。

The capital and energy-intensive ammonia synthesis industry by the application of conventional iron-based catalysts prompts the tryout and the selection of ruthenium (Ru). Experiments on the corresponding employment had shown that the higher activity of Ru in the current Haber-Bosch process could be achieved with even milder operation conditions, which is beneficial for the development of minor-scale intermittent-operation-capability hardware units. Therefore, the study of the nitrogen activation, the rate-limiting step of the overall ammonia synthesis, on Ru is of all prominence. The comparison of the activation mechanism between the Ru terrace site and the B5 active site, the specific structure discovered in the synthesis, could give detailed insights into the catalysis, which could be exploited in future catalyst design and composite.
The preliminary data has further shown that the application of Ru catalyst on the MgO(111) system has demonstrated significant impacts on solving hydrogen poisoning, which could inhibit the subsequent synthesis of Ru. The extending study on the nitrogen activation by the system is the other goal of the work for a better understanding of the support and the oxygen spillover effect on the nitrogen sorption and activation behavior, and the investigation of B5-like structure construction on the system could determine the influence of the metal-support interaction on the active site, as well as the activity dependence of active site toward the support.

摘要 1
Abstract 2
Acknowledgment 3
Table of Contents 4
List of Figures 6
List of Tables 10
Chapter 1 Introduction 11
1.1 Current State of Ammonia Synthesis and Challenges 11
1.2 Objectives and Experiments Design 13
Chapter 2 Literature Review 16
2.1 Background of N2 activation in NH3 production 16
2.2 Selection of Ru Catalysts and Sabatier Principle 19
2.3 N2 Activation by Ru Catalysts 23
2.4 Alleviated Nitrogen Activation by B5 site 24
2.4.1 Discovery and Definition of B5 site 24
2.4.2 Effect of B5 Site on N2 Activation 30
2.5 Effect of Support on Assisting in N2 activation 31
Chapter 3 Methodology 35
3.1 Related Theory Introduction 35
3.1.1 First-Principles Calculations 35
3.1.2 Density Functional Theory (DFT) 37
3.1.3 Transition State Search 43
3.1.4 Bader Charge Analysis 46
3.2 Calculation Details 47
3.2.1 Convergence Test 47
3.2.2 Lattice Constant Optimization 50
3.2.3 Cohesive Energy, Binding Energy, and Adsorption Energy 52
3.2.4 Thickness Test For Surface Slab Model and Vacuum Layer 54
Chapter 4 Results and Discussion 57
4.1 Ru(0001) Terrace Model 57
4.1.1 N2 Dissociation 57
4.1.2 Coverage and Layer-Thickness Effects 62
4.2 Ru B5 Model 65
4.2.1 N2 Dissociation 65
4.2.2 DOS Analysis 69
4.3 Ru Clusters on MgO(111) 70
4.3.1 Ru1/MgO(111) 71
4.3.2 Ru4/MgO(111) 74
4.3.3 RuB5*/MgO(111) 79
4.4 Comparison of Ru(0001), B5, and Ru/MgO(111) Models 86
Chapter 5 Conclusions 89
Chapter 6 Prospect, Research, and Future works 90
Reference 91
Appendix 96
Appendix I : Detailed Introduction of Input and Output Files for VASP 96
Input Files 96
Output Files 98
INCAR Tag Setting 99
Appendix II : Interpretation of the Convergence Test 100

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