摘 要
本研究旨在探討近紫外光(λ=365nm)激發自行製備之奈米級二氧化鈦(TiO2)光觸媒，進行光催化還原氣相二氧化碳之批次反應研究，並進一步探討不同操作參數對光催化還原反應效率之影響。
本研究採用自行設計之批次式光催化還原反應系統，觸媒則選擇商業型 TiO2(Degussa P-25)及溶膠凝膠法製備之光觸媒（包含NO3-/TiO2、SO42-/TiO2），進行光催化還原二氧化碳之實驗。實驗探討之操作參數包括二氧化碳初始濃度(0.5%~7.5%)、還原劑種類(氫氣、水氣、水氣和氫氣)、反應溫度(35℃~85℃)及水氣含量([H2O]/[CO2]=1~4)。反應器上方置放三支15W近紫外光燈管為光源，內部則放置披覆TiO2薄膜之載體，反應氣體則以氣密式注射針筒(gasket syringe)置入，進行光催化還原反應實驗。產物分析係以氣相層析儀/火燄離子偵測器（Gas Chromatography/Flame Ionization Detector；GC/FID）配合甲烷轉換器（Methaneizer）偵測並定量之。
由光觸媒篩選之結果得知，本研究所採用之商業型TiO2(Degussa P-25)、NO3-/TiO2、SO42-/TiO2等三種光觸媒中，以SO42-/TiO2光觸媒之光還原活性最佳，主要還原反應產物為CO、CH4及微量C2H4、C2H6等產物；而載體篩選方面則以金屬載體(不鏽鋼網)較石英玻璃之光還原效果為佳。操作參數實驗結果顯示，光催化反應速率隨著二氧化碳初始濃度提高，其光還原產物累積總產量愈高；還原劑種類方面，氫氣呈現最佳還原效率，若以水氣為還原劑時，水氣分子可能會抑制SO42-/TiO2光觸媒之還原活性，而降低光還原效果；反應溫度方面，提高反應溫度顯然加速反應速率，對於產物生成有促進效果；水氣含量方面，適當之水氣分子為還原劑時，水氣分子濃度愈高，光還原效果愈佳，但達到趨近飽和的水氣濃度(相對濕度=75%~100%)時，將造成水氣分子過多而抑制觸媒活性，降低光催化還原效率。
本研究結果與相關文獻比較得知，本研究以SO42-/TiO2為光觸媒之主要還原產物（CO、CH4）產率較文獻為高。另外，本研究亦提出以SO42-/TiO2為光觸媒反應產生CO、CH4、C2H4和C2H6之反應路徑，同時亦嘗試以單分子吸附之L-H反應動力模式模擬光催化還原CO2之情形，模式模擬結果良好。

ABSTRACT
The increase of carbon dioxide (CO2) concentration in the atmosphere has become a severe environmental problem, since it could cause global warming due to greenhouse effects. Thus, the reduction of CO2 emission to tackle the greenhouse effect has become one of the most important tasks for sustainable development. The outcomes of this study would be valuable to evaluate the feasibility of applying photocatalytic reduction process to remove CO2 from the atmosphere as well as the flue gas.
This study investigated the photocatalytic reduction of CO2 in a self-designed batch UV/TiO2 photocatalytic reactor. The photocatalysts tested included commercial TiO2 (Degussa P-25) and synthesized TiO2 via modified sol-gel process (i.e. NO3-/TiO2 and SO42-/TiO2). Stainless steel supports coated with TiO2 were packed in the batch reactor. The initial concentrations of CO2 ranged from 0.5% to 7.5%. The reductants investigated included hydrogen (H2), water vapor (H2O), and hydrogen with water vapor (H2+H2O). The incident UV light with wavelength of 365 nm was irradiated by a 15-watt low-pressure mercury lamp. The photocatalytic reaction was conducted continuously for approximately 48 hours. Reactants and products were analyzed quantitatively by a gas chromatography with a flame ionization detector followed by a methaneizer (GC/FID-Methaneizer).
Experimental results indicated that stainless steel coated with TiO2 had better photoreduction efficiency than that of quartz glass. The optimal operating conditions of CO2 photoreduction were observed by using H2 over SO42-/TiO2, which could produce major products of CO and CH4 and minor products of C2H4 and C2H6. Sulfuric acid used as a stabilizer in the sol-gel process could produce TiO2 of high specific surface area. Results obtained from the operating parameter tests showed that the photoreduction rate increased with the initial concentration of carbon dioxide and resulted in more product accumulation. Higher photoreduction efficiency of carbon dioxide was observed by using the hydrogen (H2) than water vapor (H2O). The photoreduction rate of carbon dioxide increased with reaction temperature, which promoted the formation of products. In addition, proper water vapor (ie. relative humidity of water vapor =25%~75%) could increase the photoreduction efficiency. However, the photoreduction efficiency decreased white it was close to (ie. relative humidity of water vapor =75%~100%).
Concurred with previous researches, the reaction rate of major products over SO42-/TiO2 were higher than previous investigations of CO2 photoreduction. This study proposed the reaction pathway using hydrogen and/or water vapor as the reductants. Moreover, a one-site Langmiur-Hinshewood kinetic model (L-H model) was successfully applied to simulate the reaction rate of CO2 during the photoreduction reaction process.

目 錄
中文摘要….................….................….................….......................... Ⅰ
英文摘要….................….................….................…......................... Ⅲ
目錄….................….................….................….................................. Ⅴ
表目錄….................….................….................….............................. Ⅸ
圖目錄….................….................….................….............................. Ⅹ
第一章 前言….................….................….................….................... 1-1
1-1 研究緣起............….................….................….................... 1-1
1-2 研究目的............….................….................….................... 1-2
1-3 研究範圍............….................….................….................... 1-2
第二章 文獻回顧............….................….................…..................... 2-1
2-1 光觸煤之應用及發展趨勢...….................…...................... 2-1
2-2 二氧化鈦光觸煤….................….................…............ 2-4
2-2-1 二氧化鈦結構特性....….................…...................... 2-4
2-2-2 二氧化鈦之製備方法................….......................... 2-6
2-2-3 二氧化鈦之光催化反應............…........................... 2-13
2-3 二氧化碳之光催化反應.......…........................................... 2-15
2-3-1 二氧化碳之來源與性質........................................... 2-17
2-3-2 異相光催化反應....................................................... 2-17
2-3-3 光觸媒表面之吸附現象........................................... 2-19
2-3-4 光催化反應機制....................................................... 2-26
2-4 光催化還原效率之影響因子.............................................. 2-28
2-4-1 觸媒晶型與量子尺寸效應之影響........................... 2-28
2-4-2 觸媒與載體之影響................................................... 2-30
2-4-3 還原劑種類之影響................................................... 2-31
2-4-4 反應溫度及水氣含量之影響................................... 2-33
第三章 研究方法............................................................................... 3-1
3-1 實驗材料.............................................................................. 3-1
3-1-1 光觸媒製備方法………………………………....... 3-3
3-1-2 溶膠凝膠法製備二氧化鈦溶液…………………... 3-3
3-1-3 浸漬覆膜法製備二氧化鈦薄膜............................... 3-5
3-2 光催化還原實驗設計........................................................ 3-6
3-2-1 批次式光催化還原系統.......................................... 3-6
3-2-2 操作參數及範圍..................................................... 3-8
3-2-3 採樣與分析系統...................................................... 3-8
3-2-4 品保與品管............................................................. 3-10
3-3 光催化還原反應實驗......................................................... 3-12
3-3-1 反應器測漏試驗....................................................... 3-12
3-3-2 載體吸附測試.......................................................... 3-12
3-3-3 均相光反應測試...................................................... 3-13
3-3-4 異相光反應測試...................................................... 3-13
3-4 產物分析方法..................................................................... 3-13
第四章 結果與討論.......................................................................... 4-1
4-1 光觸媒及載體之篩選.......................................................... 4-1
4-2 光觸媒基本特性分析.......................................................... 4-2
4-2-1 比表面積................................................................... 4-2
4-2-2 表面特性及粒徑大小……………........................... 4-7
4-2-3 表面化學成份……………..………………………. 4-9
4-3 光催化還原反應測試結果................................................. 4-12
4-3-1 系統測試結果.......................................................... 4-12
4-3-2 載體吸附測試結果.................................................. 4-12
4-3-3 均相光解反應測試結果.......................................... 4-13
4-4光催化反應測試結果........................................................... 4-17
4-4-1 操作參數對還原效率之影響.................................. 4-17
4-4-2 反應速率常數.......................................................... 4-17
4-5 產物分析結果...................................................................... 4-18
4-6操作因子對光催化還原反應………................................... 4-24
4-6-1 二氧化碳初始濃度對光催化還原反應之影響….. 4-24
4-6-2 還原劑種類對光催化還原反應之影響………….. 4-30
4-6-3 反應溫度對光催化還原反應之影響…………….. 4-31
4-6-4 水氣含量對光催化還原反應之影響…………….. 4-36
4-7 與其他文獻比較.................................................................. 4-47
第五章 結論與建議.......................................................................... 5-1
5-1 結論....................................................................................... 5-1
5-2 建議....................................................................................... 5-2
參考文獻............................................................................................ R-1
附錄A CO2、CO、CH4之檢量線................................................. A-1
附錄B 光觸媒之XRD 分析結果................................................. B-1
附錄C 遠紅外線光譜儀化合物鑑定表…………………………. C-1
附錄D 各組實驗數據之整理……………………………………. D-1

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