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標題: | 銅鈰氧化物負載在SBA-15介孔材料中及其在富氫氣氛中對一氧化碳的選擇性氧化 CuO/CeO2 supported on SBA-15 for Preferential Oxidation of CO in Hydrogen Rich Environment |
作者: | Chen-Yu Wu 吳鎮宇 |
指導教授: | 鄭淑芬(Soofin Cheng) |
關鍵字: | 銅鈰氧化物,選擇性氧化,質子交換膜燃料電池,SBA-15, PROX,PEMFC,CuO,CeO2,SBA-15, |
出版年 : | 2012 |
學位: | 碩士 |
摘要: | 質子交換膜燃料電池使用之燃料為氫氣,是具有高能量密度且低污染的能源。但在製備氫氣過程中殘餘0.25%~0.5%的一氧化碳會吸附在白金電極上造成電池效率降低。目前白金電極所能容忍的一氧化碳濃度約為10-100 ppm,現今最有效降低氫氣中之一氧化碳濃度的方法是使用觸媒在富氫環境下進行一氧化碳的選擇性氧化。
銅鈰氧化物對於一氧化碳之氧化具有高度轉化率以及選擇率,而介孔洞材料SBA-15具有高表面積、均勻六方角柱規則孔洞、良好的水熱穩定性之性質,使其成為極具潛力的觸媒載體。本論文利用含浸法將銅鈰氧化物負載在SBA-15介孔材料之孔道中,期望增加銅鈰氧化物之表面積,提升觸媒對一氧化碳的轉化率及選擇率。藉由改變不同的含浸順序、負載金屬比例、重量、煆燒溫度、以及不同的形態之二氧化矽載體以得到最佳化之觸媒。利用XRD、氮氣吸附儀、SEM、TEM、XANES以及H2-TPR 對觸媒進行分析。實驗的反應氣體組成成分為He : CO : O2 :H2 = 48.4 : 0.8 : 0.8 : 50,流速為每分鐘100毫升,並探討添加水氣與二氧化碳對觸媒活性的影響。由 XRD 與 TEM 發現金屬氧化物成功含浸至SBA-15 孔洞中,且形成分散性良好的小顆粒。由 TPR 發現形成較大的CeO2 顆粒有助於增加其與 CuO 顆粒的接觸介面,使得還原溫度降低。活性結果指出SBA-15載體經由900 oC煆燒處理去除表面 OH 基後,可提升其CO 轉化率及對水氣的容忍度,顯示表面的 OH 基對於反應有不利的影響。所合成之觸媒中,以0.1CuO-0.9CeO2/ 2SBA-15-p-900具有最高的活性,在140oC時可達到100 %的轉化率與70%選擇率。 Proton exchange membrane fuel cell (PEMFC) has been a powerful energy source due to several advantages such as high energy density, low emission of pollutants and low operation temperature. However, there are still some challenges needed to overcome. For example, the CO impurity in H2 fuel may poison the Pt electrode. During the hydrogen production by steam reforming and water-gas shift, there are still 0.25 %~0.5% CO in flowing gas, and the tolerance limit of Pt alloy anode for CO concentration is around 10-100 ppm. Therefore, it is necessary to eliminate 99% of the CO present in the H2 fuel, and the most effective way has been by preferential oxidation (PROX). Copper and cerium mixed oxide has been found as a promising catalyst for PROX duo to its high conversion and relative cheap price. Mesoporous silica SBA-15 with uniform 2 D hexagonal arrays of pores and high surface area is a promising support to increase CuO/CeO2 surface area and dispersion. Various amounts of copper oxide were impregnated onto SBA-15.The catalysts were characterized by XRD, N2 sorption isotherm, SEM, TEM, XANES, TPR. The activities of the catalysts were tested in PROX reaction under 0.8 % CO, 0.8 % O2, 50 % H2, and 48.4 % He with a total flow rate of 100 mL/min. XRD patterns showed that copper oxide formed small particles and well dispersed when the mixed oxide was supported on SBA-15. TPR showed that the formation of large CeO2 can enhance the reducibility of catalyst, The reason may due to the particle size of cerium oxide in the high surface silica support is too small, and it would lower the interface of CuO contact with CeO2 .CuO-CeO2 supported on SBA-15 dehydrated at 900oC gave higher catalytic activity than that supported on 500oC calcined SBA-15, probably due to hydroxyl groups on the surface hinder the active site. The activities of the catalysts were significantly decreased in the presence of H2O, especially the silica supported catalysts. This negative effect may be attributed to the hydrophilic surfaces of silica. Among the supported catalysts, 0.1CuO-0.9CeO2/ 2SBA-15-p-900 catalyst could reach 100% CO conversion at 140oC with O2 selectivity around 70%. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/63969 |
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