ZSM-5沸石擔載鐵基雙金屬觸媒在一氧化氮選擇性催化還原活性：酸性及金屬負載量效應研究

Abstract

氮氧化物去除(DeNOx)技術的研發深受日益嚴重的空氣污染以及更嚴格的環保規範而更受重視。本研究針對一系列鐵基雙金屬負載Fe-Z-M2 (Z = ZSM-5沸石；矽/鋁比值= 25)觸媒在氨氣選擇性催化還原(NH3-SCR)反應之催化效能進行系統性的探討。吾人利用各種分析及光譜實驗技術，對各DeNOx觸媒樣品進行物化特性鑑定，特別是利用本實驗室所開發之31P-TMPO MAS NMR酸性鑑定技術，深入探討各觸媒的酸種類、強度、酸量分佈等特性與SCR反應效能的關聯性。此外，本論文亦著重在探討金屬負載量及反應溫度對SCR效能的影響。在固定觸媒第一金屬(Fe)及其負載量下，隨第二金屬負載量(M2 = Cu、Ce、Pr、Cr)的增加，更多的超強路易士(L)酸亦隨之產生，並引發B/L酸協同效應而助長SCR反應效能。最後，吾人亦針對各系列觸媒在SCR反應前後之酸性特性變化及其對SCR反應活性進行研究。研究結果顯示，鐵基雙金屬負載Fe-Z-M2觸媒在適當的反應溫度區間(200 ~ 450 oC)有極佳的NH3-SCR效能，其NO轉化率可高達90%，故具備實際工業應用潛力。Owing to the increasing severity in air pollution and stringent environment specifications, the R&D of nitrogen oxides removal (DeNOx) technology have drawn considerable attention. The present study aims at the syntheses of various iron-based Fe-Z-M2 (Z = ZSM-5 zeolite; Si/Al = 25) catalysts and their catalytic performances during selective catalytic reduction of ammonia (NH3-SCR).。The physicochemical properties of these DeNOx catalysts were characterized by a variety of different techniques. Their acid features (type, strength, and concentration and distribution) were probed by 31P-TMPO MAS NMR technique developed in this laboraty. In particular, the effects of primary and secondary metal loadings and reaction temperature on SCR activity were investigated. For a given priminary metal (Fe) loading, an increasing dosage of the secondary metal (M2 = Cu、Ce、Pr、Cr) tends to provoke formation of strong Lewis acid sites, which are favorable fot the Brønsted-Lewis acid synergy during the SCR reaction. Furthermore, correlations between the acid features of various catalysts with SCR activity were also investigated. It is found that, the Fe-based bimettalic Fe-Z-M2 catalysts exhibit superior NH3-SCR performance over the desirable temperature range of 200450 oC, leading to a NO conversion of 90%, rendering perspective and practical industrial applications for DeNOx.