LHCII修飾光觸媒與光催氫化觸媒還原二氧化碳

Light-harvesting complex promoted photocatalyst and photo hydrogenation of CO2

李健瑋(Chien-Wei Lee)

指導教授 ： 吳紀聖

國立臺灣大學/工學院/化學工程學研究所/碩士(2012年)

https://doi.org/10.6342/NTU.2012.02094

摘要

Light harvesting complex (LHCⅡ)葉綠素蛋白質複合體是一種有助於光吸收的複合物，其包含了chlorophyll a 和chlorophyll b。從活體菠菜植物體中萃取出來並修飾於二氧化鈦光觸媒表面，並將其運用在液相反應氣中以300W氙燈進行光催化還原二氧化碳反應。反應六小時後，CO產量可到達3.43 μmol/g，Acetaldehyde 產量可到達19.2 μmol/g，Methyl formate 產量1.53 μmol/g。相較於其他使用二氧化鈦做光觸媒團隊，本研究有更多種的二氧化碳還原產物，而且有更高的還原產量。本研究以實驗證實LHCⅡ物質本身具有光穩定與熱穩定性，不會在反應過程中受光照或受熱而變性或分解。
以氫氣的添加提升二氧化碳還原的效果是第二部分研究。氫氣的添加有利於反應平衡向產物，由理論推測較小自由能的反應平衡常數較高，使反應較容易平衡向產物移動。本研究終極目標是要利用太陽光水分解反應產生的氫氣進行二氧化碳還原，然而在目前產氫效果不佳情形下以額外添加氫氣當作氫能量的來源。本研究以固態熔融法合成CuAlGaO4光觸媒，為了增加對氫氣的吸附以及減緩電子電洞再結合的速度，以初濕含浸法負載銠金屬，另外再以光沉積法負載白金金屬。以添加氫氣的光催化還原反應為實驗組，未添加氫氣做對照組。在液相反應器中進行六小時的還原反應，結果發現以銠金屬作為共觸媒可以得到一氧化碳、甲醇、乙醇等產物，加氫氣未能改變其產物的類型但提升了反應的產率。於反應一開始測得的一氧化碳中間產物說明了反應方向是二氧化碳的還原而非可能的有機物降解反應。氫氣的添加反應六小時後可以讓甲醇產率達到7.38 μmol/g。乙醇產率達到9.36 μmol/g。對比白金金屬於光催化還原二氧化碳僅能得到CO和甲醇兩種產物，而添加氫氣僅在CO中間產物的部分有一倍提升，甲醇則沒有明顯產率的提升。而還原二氧化碳除了期望做到二氧化碳減量以外，進一步要將其轉成有用的能源，因此選銠觸媒作為氫化反應的共觸媒。為了確認反應的準確度，本研究除了參考文獻，確定以銠金屬作共觸媒能藉由氫化反應將二氧化碳轉成醇類外，也做了原位傅利葉轉換紅外線偵測，除了與GC偵測結果相互印證外，也希望進一步了解可能的反應過程。

關鍵字

氫化觸媒 ； 葉綠素蛋白質複合物 ； 光催化還原二氧化碳反應

並列摘要

Light harvesting complex (LHCⅡ) which was extracted from green plants could enhance the visible light absorbance. It gave an idea that attaching the LHCⅡmaterial to the surface of TiO2 series catalysts might get a good efficiency in reducing CO2. In this research, we prove the concept with following experiments. Two kinds of photo catalysts, TiO2:Rh and TiO2:Rh-LHCⅡwere used to reducing CO2 in slurry system. After six hours reaction, the yield of CO could reach 3.43 μmol/g, acetaldehyde could reach 19.2μmol/g and methyl formate could reach 1.53μmol/g with TiO2:Rh-LHCⅡcatalysts which was nine to ten times enhancement in acetaldehyde. Four times increase in methyl formate compared to TiO2:Rh. Use FTIR and APCI/MS analysis to investigate the mechanism of the photo reaction.
The second part of the research was to enhance the efficiency of CO2 reduction with hydrogen. Hydrogen involving in the photo reaction could give a smaller ΔG value comparing to which was without hydrogen. In the research, we dedicated ourselves to finding a catalyst which could utilize hydrogen to reduce CO2 efficiently. We loaded rhodium and platinum by impregnation and photodeposition method on CuAlGaO4 respectively. Some groups prove that the two kinds of cocatalyst have better efficiency in utilizing hydrogen. CuAlGaO4 was chosen as the photocatalyst which was synthesized by solid state method. The result showed that the yield of methanol could reach 7.38μmol/g and the yield of ethanol could reach 9.36μmol/g after six hours photo reaction. What we expect was not only to reduce CO2 but also to transform it to useful fuels. FT-IR analysis was to check the result of the photoreaction and gave a possible reaction mechanism.

並列關鍵字

CO2 reduction ； Photocatalysis ； Light-harvesting complex ； TiO2:Rh- LHCII ； Renewable

參考文獻

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