以奈米鈦管及二氧化鈦為擔體製備低溫SCR觸媒處理NOx之SO2毒化影響研究

Abstract

選擇性觸媒還原法(Selective catalytic reduction，簡稱SCR) 廣泛用於處理氮氧化物(NOx)。傳統上以WO3/V2O5/ TiO2或是MoO3/V2O5/ TiO2觸媒為主要使用觸媒，然而其操作溫度過於狹窄(300~ 400℃)，若煙道廢氣經除塵及脫硫設備處理後，則SCR入口端之廢氣溫度勢必降至150~160℃，故欲行 SCR處理，則須消耗大量能源，且煙道廢氣經脫硫設備處理後尚存有低濃度之SO2，倘若能發展低溫SCR 觸媒且具有良好之抗硫化能力，可顯著降低 SCR之耗能與操作成本。本研究利用共沉澱法製備低溫SCR觸媒，活性金屬方面選擇Mn、Fe過渡金屬，製備出三種MnFe/TiO2觸媒與三種MnFe/TNT觸媒，其前驅物分別來自於TiO(OH)、P25及ST01，本研究於低溫SCR系統下探討各觸媒其NO轉化率與受SO2毒化之影響，反應溫度為150℃，空間流速為20,000h-1。研究成果顯示，在無SO2影響下，各觸媒於低溫脫硝方面可達90%以上之NO轉化率；於系統內加入100 ppm SO2，5小時後其NO轉化率由90%衰退至32~76%，其中以MnFe/TNT觸媒抗SO2毒化能力較Mn/TiO2觸媒佳。根據BET分析結果顯示，觸媒比表面積小於150m2/g時，對於NO轉化率有顯著之影響，然而當觸媒比表面積大於150m2/g時，對於NO轉化率則影響不大。另外，由NH3-TPD分析結果顯示，觸媒活性與Bronsted酸性基具有正相關性。因MnFe/TNT觸媒其比表面積與Bronsted酸性基皆高於Mn/TiO2觸媒，故MnFe/TNT具有較佳之觸媒活性且對於SO2具有較佳之抗硫能力。

The selective catalytic reduction (SCR) is one of the major technologies for reducing NOx emission from flue gas streams. The WO3 or MoO3 with V2O5 supported on TiO2 are currently the most widely employed SCR catalysts. However, it is active within a narrow and higher temperature window of 300~400℃. For some processes which emit NOx at lower temperatures, this would lead to high energy consumption upon heating up the flue gas to above 300℃. On the other hand, operating the SCR at temperatures lower than 280℃ tends to be suffered from SO2 poisoning effect. Therefore, the development of a superior low temperature SCR catalyst which can have high catalytic activity and good resistance to SO2 poisoning would significantly improve the cost-effectiveness of the SCR process. In this study, MnFe/TiO2 and MnFe/TNT catalysts from different precursors of TiO(OH), P25 and ST01 were prepared by the hydrothermal method and co-precipitation method and then tested for their NO removals under simulated flue gas system at low temperatures as low as 150℃. The experimental results showed higher than 90% NO conversion in the absence of SO2. However, the NO conversion tends to be decreased from 90 to 76-32% in the presence of SO2. The MnFe/TNT catalysts showed better resistance to SO2 than that of MnFe/TiO2 catalysts. The BET result showed that NO conversion was correlated with surface area of catalysts when surface area was lower than 150m2/g. In addition, the NH3-TPD results indicate that the NO conversion was highly correlated with the Bronsted acid site of catalysts. MnFe/TNT catalysts have high NO conversion in the presence of SO2 due to their high surface area and Bronsted acid site. Therefore, it could be considered as potential catalyst for low temperature SCR.