| 摘要: | 本研究以共沉澱法將不等量MnOx引入CeO2製備具良好redox特性的共溶性氧化物Ce1-xMnxO2作為觸媒擔體，再以含浸法製備7%CuO /Ce1-xMnxO2觸媒進行揮發性有機物苯的全氧化反應，探討煅燒溫度、Mn引入量及CuO負載量對反應的影響。反應測試是利用空氣進入飽和蒸氣瓶內帶出定量(500~1500 ppm)的苯蒸氣於F/W = 6000~24,000 ml h-1 gcat-1條件下進行苯的全氧化反應，並採BET、TPR、Raman、XPS及H2-TPR等分析方法探討觸媒之物理特性與表面性質。 本研究發現Ce1-xMnxO2擔體與CuO/Ce1-xMnxO2觸媒的最佳煅燒溫度為500°C，Mn引入量為x = 0.3~0.4時，Ce1-xMnxO2擔體具有最好的固溶性，CuO負載量5~10%時有最佳活性。本研究發現Ce0.7Mn0.3O2擔體本身對苯就有不錯的反應活性，於300°C下可將苯完全轉化，負載CuO後可明顯提升反應活性，使苯的完全轉化溫度降至265°C。CuO/Ce1-xMnxO2觸媒於PROX反應中，Cu+為吸附CO的活性基，Ce1-xMnxO2擔體本身對CO無明顯活性。然而，在苯的全氧化反應中，具良好redox特性的Ce1-xMnxO2擔體本身就有吸附苯進行氧化反應的不錯能力，引入CuO能增加苯的吸附量，單獨CuO進行苯氧化反應的能力並不佳，顯示CuO/Ce1-xMnxO2觸媒於苯的氧化反應機制不同於PROX反應，CuO並不是苯全氧化反應主要的活性中心，而Ce1-xMnxO2的redox作用可提供晶格氧復原CuO氧化過程中所消耗的氧或直接提供晶格氧進行苯的全氧化反應。因此，Ce1-xMnxO2擔體不論是自身進行反應或釋出晶格氧進行氧化反應的協同角色在苯的全氧化反應中皆非常重要，是影響活性的關鍵。CuO/Ce1-xMnxO2觸媒進行苯的全氧化反應有相當不錯的活性表現，能處理的苯濃度範圍相當廣且有相當高的穩定性，經過200小時反應仍能維持活性，應用於揮發性有機物苯的去除是一相當不錯的觸媒選擇。 In order to promote the redox properties of the support CeO2, Mnn+ was incorporated into CeO2 by co-precipitation method to prepare good solid solution Ce1-xMnxO2 mixed oxides. Ce1-xMnxO2 mixed oxides were prepared as supports of 7% CuO/Ce1-xMnxO2 catalysts, which prepared by impregnation method. Then CuO/Ce1-xMnxO2 catalysts were used in the complete oxidation reaction of volatile organic compound benzene. Besides the effects of calcinations temperature, MnOx doping amount, and CuO loading amount were examined, the roles of Ce1-xMnxO2 mixed oxides and CuO were also discussed. The benzene vapor feed was diluted with air into the reactor at the flow rate of 100 ml/min (F/W = 6000~24,000 ml h-1gcat-1). The physical and surface properties of catalysts were determined by BET, XRD, Raman, XPS and H2-TPR. First, the catalyst optimum calcinations temperature was 500°C. When the Mnn+ doped amount at x = 0.3~0.4, the Ce1-xMnxO2 supports could achieve the best solid solution state. Then loading CuO amount 5~10% exhibited the best activity. Even though only Ce1-xMnxO2 supports could have high oxidation ability toward benzene, the temperature (T100) for complete conversion was about 300oC. After adding CuO, T100 of 7%CuO/Ce1-xMnxO2 catalysts decreased to 265oC. In the CO PROX reaction, Cu+ was the active site adsorbing CO, though Ce1-xMnxO2 supports were not active with CO but benzene. Only Ce1-xMnxO2 supports could adsorb and oxidize benzene. Adding CuO could further increase benzene adsorption and CuO didn’t show good oxidation ability toward benzene alone, so the mechanism of CuO/Ce1-xMnxO2 catalysts for complete oxidation of benzene is quite different from PROX reaction. CuO is not the active site in the complete oxidation reaction of benzene and Ce1-xMnxO2 supports could offer lattice oxygen for the complete oxidation reaction of benzene. Therefore, the key points of Ce1-xMnxO2 supports for complete oxidation reaction of benzene are very important, not only because of itself oxidation, but also because of the synergetic role of offering lattice oxygen to CuO. CuO/Ce1-xMnxO2 catalysts exhibited good activity and stability toward benzene, and could eliminate a wide range of benzene gas. Even after 200hr of complete oxidation reaction of benzene, it also showed 100% conversion. It is a very practical and ideal catalyst for complete oxidation reaction of benzene. |
