銅負載二氧化鈦在雙胞反應器進行光催化還原二氧化碳

Abstract

目前二氧化碳光催還原之研究中，效率並不高且再現性不佳。本研究利用添加氫氣於反應器中，可得較高產率，且提升反應結果的穩定性。並探討不同重量及價態的銅負載觸媒對二氧化碳還原效率的影響。 利用溶膠凝膠法製備二氧化鈦，並使用初濕含浸法將銅負載於其上，利用不同氣體環境鍛燒使其擁有不同價態：由氧氣鍛燒成CuO而由氫氣還原成Cu。並以UV-Vis、SEM、EDS、XRD、XPS等檢測方法，鑑定觸媒對光的吸收、表面狀況、晶相等性質，另外也偵測到反應前後銅的價態有變化，由氧化態向還原態偏移。並使用254nm的UV燈進行氣相反應，其光強度約為12mW/cm2，並提高溫度至約90oC，在0.01atm分壓的氫氣中照射TiO2、1%CuO/TiO2、2%CuO/TiO2、1%Cu/TiO2及2%Cu/TiO2。結果顯示在此實驗條件中還原價態銅具有較高活性，1%Cu/TiO2及2%Cu/TiO2之產量並沒有太大分別。最高產量分別可達28.72μmol/g甲烷和5.74μmol/g一氧化碳，及26.13μmol/g甲烷和7.23μmol/g一氧化碳。 因此利用1%Cu/TiO2放入雙胞反應器中，使用Fe2+/Fe3+為電子傳遞媒介，在AM1.5G模擬太陽光氙燈照射，並利用預處理過的Nafion薄膜分隔兩邊半反應器，分別為產氧端及還原端。在產氧端中放入Pt/WO3；在還原端水溶液中則放入產氫觸媒Pt/SrTiO3:Rh，利用其產生的氫氣做為二氧化碳之氫源。還原端最高產量分別為1.6556μmol/g氫氣、0.2005μmol/g甲烷及1.3008μmol/g一氧化碳。

Currently in the carbon dioxide photocatalytic reduction, the efficiency is not high and is not always reproducible. In this thesis, we got high amount of products and increased the stability by adding hydrogen into the photoreactor. We studied the effects of the weight loadings and the valance states of copper on the efficiency of carbon dioxide reduction. Sol-gel method was used to synthesize titanium dioxide. Copper was loaded on titanium dioxide by incipient-wetness impregnation method. The variations of copper valence state were obtained under different calcination atmospheres. CuO was formed under air calcination while Cu was formed under H2 reduction. Several instruments, UV-Vis, SEM, EDS, XRD and XPS were applied to measure the light absorption, surface morphology, crystalline phase and chemical status. The valence change of copper was found from the oxidation to reduction states before and after the reaction. In the vapor-phase photoreaction, an UVC lamp was used as the light source 254 nm and the light intensity 12 mW/cm2. The temperature was raised up to 90oC. The reaction were carried out by using TiO2, 1%CuO/TiO2, 2%CuO/TiO2, 1%Cu/TiO2 and 2%Cu/TiO2 under 0.01 atm hydrogen. The results revealed that the reduced copper had higher activity for the CO2 reduction under these conditions. There was not much difference in yields between 1%Cu/TiO2 and 2%Cu/TiO2. For these two catalysts, the highest yields were 28.72μmol/g methane, 5.74μmol/g CO and 26.13μmol/g methane, 7.23μmol/g CO, respectively, in 8 hours. Thus, the 1%Cu/TiO2 was used in the twin reactor with Fe2+/Fe3+ as electron mediator. We used artificial sunlight, AM1.5G Xenon lamp, to irradiate the catalysts. Pre-treated Nation cation-exchanged membrane was used for separating two different solutions that were called oxygen side and reduction side. Pt/WO3 was put into the oxygen side solution. In the reduction side, hydrogen catalyst Pt/SrTiO3:Rh, was put into the solution. The hydrogen generated by the catalyst can be used as the hydrogen source of carbon dioxide reduction. 1%Cu/TiO2 was put on the quartz plate in the reduction side to contact with the carbon dioxide in the gas phase. The highest yields in reduction side are 0.5863μmol/g hydrogen, 0.2005μmol/g methane and 1.3008μmol/g CO.