常溫常壓下可見光光催氫化二氧化碳

Abstract

氣候變遷與能源危機的問題提升了對於溫室氣體的減量與開發能源的研究動力， 由於目前二氧化碳氫化的效率並不高，在本實驗加入氫氣進行二氧化碳還原。氫氣的添加有助於反應平衡向右。因此在本篇研究當中欲得知加入氫氣是否有助於二氧化碳還原為碳氫化合物，並進行了在各種不同氫氣分壓下光催氫化二氧化碳還原，找到最適合的氫量應用於二氧化碳還原。若能找到最佳氫氣分壓於二氧化碳還原實驗中，應用於本研究的最終目標利用水分解產氫結合二氧化碳還原，以期提升二氧化碳還原效率。 本研究利用前人比較後最有效率之光觸媒Pt/CuAlGaO4作為二氧化碳還原觸媒，分別使用了三種反應器，氣相反應器、液相反應器、gas-liquid反應器。比較後發現gas-liquid反應器效果最佳，利用AM1.5 G模擬太陽光於常溫下在通入CO2與不同氫氣分壓0atm、0.01atm、0.05atm、0.2atm下於gas-liquid反應器中，證實適量的氫氣加入有助於二氧化碳還原，然而過多的氫氣參與二氧化碳還原反應並不會使效率上升，其中在0.01atm的氫氣分壓下有最好之二氧化碳還原效率，主要產物為甲烷、甲醇與甲酸等產物。最高產量分別可達0.85μmol/g、7.35μmol/g、2.27μmol/g。當反應器轉換為氣相反應器時，在0.1atm氫氣分壓下會有最好的甲烷產量1.58μmol/g。 比較三種不同反應器的效率後，應用gas-liquid反應器於雙反應器進行可見光光催氫化水分解產氫結合二氧化碳還原的實驗，利用300W 氙燈作為可見光來源，並利用Nafion薄膜分隔兩邊半反應器分為產氧端與產氫端，在產氧端使用產氧觸媒WO3、在產氫端使用產氫觸媒Pt/SrTiO3:Rh以及還原觸媒Pt/CuAlGaO4。也同樣得到氫、甲烷、甲醇與甲酸產物。最高產量分別可達0.74μmol/g，0.20μmol/g、0.035μmol/g、0.07μmol/g。

Global warming and energy crisis are our motivation to reduce CO2 and develop renewable energy. However, the reduction of carbon dioxide by photocatalyst is still low efficient for converting carbon dioxide into useful chemicals (hydrocarbons) by sunlight. The objective is to study the enhancement reduction of CO2 with H2. Various partial pressures of H2 was added and expected to maximize the CO2 photo hydrogenation under an optimal H2 pressure. After the optimal photo hydrogenation of CO2 was found, the final goal was that the reaction was performed by the combination of the water-splitting H2 and CO2 photoreduction. Thus the overall CO2 reduction can be significantly increased. In this study, the efficient Pt/CuAlGaO4 was used as CO2 reduction catalyst. The CO2 photo hydrogenation was carried out in three different reactor, gas reactor, liquid reactor and gas-liquid reactor, respectively. The gas-liquid reactor gave the highest yields. The results indicated that H2 would enhance the CO2 reduction at H2 partial pressures, 0.01atm、0.05atm、0.2atm under irradiation by AM 1.5G sunlight on gas-liquid reactor at ambient temperature. However, increasing H2 pressure did not enhance CO reduction. An optimal H2 pressure, 0.01atm, was observed with main products, methane, methanol and formic acid. The maximum yields of methane, methanol and formic acid were, 0.85, 7.35 and 2.27 μmol/g, respectively. When the reactor changed to gas reactor, the major product became methane and the maximum yields are 1.58μmol/g under 0.1atm H2 pressure Based on the results of three different reactors, the CO2 photoreduction was then carried out in a twin reactor using visible light. A 300W xenon lamp was used as the visible-light source and a Nafion membrane was applied to divide two sides of the twin reactor for H2 and O2 separately evolution. WO3 was used as oxygen catalyst into the oxidation-side half reactor. Pt/SrTiO3:Rh was used as hydrogen catalyst and Pt/CuAlGaO4 was used as reduction catalyst into the reduction-side half reactor. The yields of H2, methane, methanol and formic acid were 0.74 μmol/g, 0.20 μmol/g, 0.035 μmol/g and 0.07 μmol/g, respectively.