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標題: | 以錳鈰氧化物與石墨烯複合材於不同反應環境進行低溫脫硝 Low-temperature NOx removal under different atmospheres over cerium and manganese oxide supported graphene-based materials |
作者: | An-Chun Chu 諸安均 |
指導教授: | 席行正(Hsing-Cheng Hsi) |
關鍵字: | 氮氧化物,選擇性催化還原,催化氧化,錳鈰氧化物,氧化石墨烯, nitrogen oxides,selective catalytic reduction,catalytic oxidation,Mn-Ce oxides,graphene oxide, |
出版年 : | 2020 |
學位: | 碩士 |
摘要: | 鍋爐燃燒產生之氣狀汙染物包含會導致酸雨及次級污染物形成的氮氧化物,故須加處理。現行主要移除方法之一為以氨氣或尿素為還原劑,金屬氧化物做為觸媒的選擇性觸媒還原法(selectivity catalytic reduction,SCR)。該法常用觸媒為釩鎢鈦複合氧化物觸媒。該法缺點包括所需溫度較高、氨氣為一工安上的可能危險來源,以及廢棄觸媒中的釩具有毒性等。故大量團隊投入以其他金屬複合物於更低溫度進行不同程序之氮氧化物移除研究。本研究以超音波震盪含浸法合成數種不同氧化石墨烯添加量、錳鈰比例不同 (錳鈰比: 4:1或8:1)的錳鈰氧化物與石墨烯複合材 (MnOx-CeOx-GO)觸媒,並探討了數種MnOx-CeOx-GO觸媒於添加氨氣的還原條件與不添加的氧化條件,不同溫度下對氮氧化物以還原或氧化來進行移除之結果,並以二氧化錳、錳鈰氧化物(MnO2-CeOx)與錳氧化物與石墨烯複合材(MnOx-GO) 觸媒比較。實驗結果發現不同GO添加量的MnOx-CeOx-GO觸媒於60oC到120oC於NH3-SCR條件進行脫硝時具有至少50%的NO轉化率。最佳者於150oC即具有95% 轉化率,但在更高的溫度其NO2產生量較多。該類觸媒亦能促進NO之氧化。於240oC到270oC具有80%以上的轉化率。物化分析結果顯示,MnOx-CeOx-GO觸媒具有較多的路易士酸吸附位、較高的氧物種移動活性,且金屬活性物較分散,這些特性的協同作用使得MnOx-CeOx-GO觸媒具有好的low temperature SCR活性。 對於水氣、二氧化硫等致毒化物種的耐性測試,結果顯示於180oC時進行含水氣的low temperature SCR,MnOx-CeOx-GO觸媒具有優異的抗水氣能力,轉化率的恢復也極優異。於二氧化硫的影響下,雖180oC時NH3-SCR轉化率會降低到40%到60%,但270oC可保有70%到90%的轉化率,代表於含硫煙氣下,發生於MnOx-CeOx-GO觸媒表面的毒化大部分為硫酸銨鹽造成,可藉由高溫分解。 The gaseous pollutants caused by boiler combustion include different amounts of NOx, which cause the irritation of the respiratory tract and also lead to the formation of acid rain and secondary pollutants. Therefore, the control of these pollutants must be implemented. One of the conventional pollution control methods, selective catalytic reduction, abbreviated as “SCR”, is a universal used process that uses ammonia or urea as reducing agents to reduce NOx with the help of specific catalysts. Vanadium/tungsten/titanium oxide catalysts are popular for the SCR process. The disadvantages of SCR process include high temperature requirement, potential industrial safety concerns due to ammonium storage, and the toxicity of vanadium in waste catalysts. Therefore, studies pertaining to using different types of catalysts to remove NOx at lower temperatures in different processes have been extensively studied. In this study, several kinds of manganese-cerium oxides and graphene composites (MnOx-CeOx-GO) catalysts with different amounts of GO and two Mn/Ce ratios (8 and 4) were synthesized by the ultrasonication impregnation method. NO removal efficiency of those catalysts in different temperatures by NH3-SCR and NO oxidation were investigated. MnO2, MnO2-CeOx, and MnOx-GO catalysts were also used to compare with the MnOx-CeOx-GO catalysts. The result showed that MnOx-CeOx-GO catalysts with different GO loading exhibited at least 50% conversion activity for low-temperature NH3-SCR reaction condition over 60oC to 120oC. The best NO conversion was found to be 95% at 150oC, but they would generate a large amount of NO2 at higher temperatures. MnOx-CeOx-GO catalysts also possessed excellent catalytic activity for NO oxidation, which could achieve up to 80% oxidation activity around 240oC to 270oC. The results of physicochemical characterization indicate that MnOx-CeOx-GO exhibits better low-temperature NH3-SCR activity due to the synergistic effect of more Lewis acid sites, higher oxygen species mobility, and higher dispersion of metal oxides. For the reactive species tolerance, MnOx-CeOx-GO catalysts showed outstanding water tolerance when NH3-SCR was operated at 180oC. For the sulfur tolerance, although the NO conversion of NH3-SCR at 180oC in the presence of SO2 decreased to about 40% to 60%, it could still maintain 70% to 90% NO conversion when NH3-SCR was 270oC, which implies that the main cause of the SO2 poisoning effect is the formation of ammonium sulfate species that could decompose at a higher temperature. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/8258 |
DOI: | 10.6342/NTU202002987 |
全文授權: | 同意授權(全球公開) |
顯示於系所單位: | 環境工程學研究所 |
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