以燒綠石結構的Y2Ce2O7為主體在低起始溫度下進行乙醇氧化蒸氣重組反應

Abstract

根據本實驗室之前在乙醇氧化蒸氣重組反應的研究，具燒綠石結構的La2Ce2-xRuxO7和La2Ce2-x-NixO7-0.5x-固溶體皆分別能在400oC及500oC起始乙醇氧化蒸氣重組反應並有良好的催化效果，在此研究中，我們利用降低晶胞常數的概念，合成出能在低起始溫度下進行乙醇氧化蒸氣重組反應的觸媒。 首先，我們成功地使用溶膠凝膠法合成出Y2Ce2-xRuxO7(x=0~0.4)固溶體。在Ｘ光光電子能譜(XPS)中我們發現隨著Ru參雜比例的上升，Ce的環境也隨之改變；Ru的氧化態也從原本的4+部分提升至5+以上；Ce4+的比例同時隨Ru參雜比例上升而上升。程式控制溫度還原系統(TPR)顯示有Ru4+與Ru2+/Ru3+的還原峰，且表面Ce4+的還原溫度隨著Ru參雜比例上升而下降。觸媒活性的測試上，我們可發現反應的最低起始溫度可降低至300oC，最佳的觸媒活性表現為Y2Ce1.6Ru0.4O7觸媒，在300oC及C/O為0.5下其乙醇轉換率可達100(2)%，氫氣選擇率有80(2)%。長時間穩定測試48小時其活性僅衰退5%且反應後經粉末X光繞射儀測試無雜相產生，且其元素的分散性皆很好。接著我們以Y2Ce2O7主體在Ce位置參雜Ni，成功合成出Y2Ce2-xNixO7 (x=0~1.0)，其反應起始溫度能降低至400oC，溫度低於La2Ce2-x-NixO7-0.5x-的500oC，Y2Ce1.4Ni0.6O7觸媒的活性在400oC之乙醇轉換率90(2)%，氫氣選擇率64(4)%。 經過此研究我們能證明經由主體晶胞常數的下降，在乙醇氧化蒸氣重組反應中能得到更低的起始溫度。第二部分之材料尚待更完整的研究，例如特性鑑定與長時間穩定性測試方面。

In our previous research in Oxidative Steam Reforming of Ethanol (OSRE), catalysts of pyrochlore phases La2Ce2-xRuxO7 and La2Ce2-x-NixO7-0.5x- exhibit activating temperature of 400oC and 500oC, respectively. In this work, we successfully synthesized pyrochlore phase solid solutions with reduced cell dimension that lead to decreased activating temperature of OSRE reaction. The first part of this thesis contains pyrochlore phases of Y2Ce2-xRuxO7 (x=0~0.4) that were synthesized by the sol-gel process, and the influence of doped Ru on the catalytic activity for OSRE reaction was investigated. The temperature-programmed reduction revealed the decrease reduction peak of surface Ce4+. The oxidation states of each ion were confirmed by XPS measurements. The catalytic performances were tested with varied temperature, Ru ion content, carbon-to-oxygen ratio and long-term stability. The OSRE reaction with the prepared catalyst began at 300oC, which is significantly lower than that of ~300 oC to La2Ce2-xRuxO7 catalyst (400oC). The catalyst Y2Ce1.6Ru0.4O7 exhibited optimized selectivity of hydrogen SH2 = 80(1)% (T = 300oC, XEtOH = 100(1)% ethanol conversion, with C/O = 0.5). The synthesized catalyst showed stable performance over a time-on-stream of 48 h, and the ethanol conversion rate remained at 100(1)%, while the hydrogen selectivity remained at 84(4)% under the operating conditions. The second part of thesis is focused on and the solid solutions Y2Ce2-xNixO7 (x=0~1.0). The activating temperature for OSRE is 400oC, which is lower than that of La2Ce2-x-NixO7-0.5x- (500oC). It revealed good activity in OSRE with the Xethanol = 90(2)% and SH2 = 64(4)% at 400oC.