以低溫SCR觸媒同時處理2-氯酚及NOx之研究

Abstract

SCR技術在處理NOx時，需在反應溫度約250℃~300℃才能有效進行反應，但大多數的工業製程如鋼鐵廠而言，所排放之廢氣溫度多在150□C以下，且廢氣中往往同時含有NOx、戴奧辛或其前驅物如2-氯酚等，因而必須將SCR入口之煙道廢氣預熱，造成能源之大量消耗。 本研究旨在開發能在反應溫度150□C及空間速度5000h-1下，其NO及2-氯酚個別的催化效率達80%以上之低溫SCR觸媒，研究成果顯示以10wt%錳(Mn)加上4wt%鈰(Ce)擔持在TiO(OH)2所製備的TiO2擔體經過450℃煅燒及使用商用褐煤擔體搭配10wt%錳(Mn)和5wt%鈰(Ce)在氮氣下310℃煅燒，此兩種觸媒其NO及2-氯酚催化效率皆可達80%。將TiO(OH)2所製備的TiO2擔體進行XRD分析，其結晶相以銳鈦礦(Anatase)為主，而金屬氧化物為無晶相存在。其TiO2擔體為非孔洞材，顆粒大小介於10~20nm，經由錳與鈰改質後，其金屬氧化物大小約在5nm以下。在2-氯酚及NO長效性催化效率測試中，一開始可維持在80%以上的去除效率，但隨著時間增加去除效率亦下降。 另一方面，具有高比表面積及均勻孔洞排列的中孔洞材亦可作為觸媒擔體，經由金屬改質後亦具有催化NO及2-氯酚之功能，故本研究以簡易省時的氣膠自我組裝排列(aerosol-assisted self-assembly, AASA)一步合成製程，利用噴霧乾燥器(spray dryer)為主要設備，製備中孔洞矽材(Mesoporous Silica Particle, MSP)為觸媒擔體，由金屬錳(Mn)和鈰(Ce)改質，在不同金屬含量下所製備之中孔洞材觸媒，低溫150℃下處理2-氯酚的催化效率最高可達80%，但NO催化效率只有20%，長效性測試結果顯示兩者之催化效率均會隨著時間增加而減少。

Selective Catalysis Reduction (SCR) is one of the best techniques for NOx removal efficiency at temperature of 250℃~300℃. However the temperature of waste gas for steal manufactory is always below 150℃ and the content of waste gas includes NOx and the precursor of dioxin such as 2-Chlorophenol. The waste gas has to be reheated before entering the SCR reactor, which increases the energy cost. In this study, catalysts which can reach 80% removal efficiencies for NO and 2-Chlorophenol at temperature as low as 150℃ are investigated. It was found that using the 10wt%Mn and 4wt%Ce doped on the TiO2 support, then calcined at 450℃, and using the 10wt%Mn and 5wt%Ce doped on lignite then calcined at 310℃ with nitrogen can both reach 80% NO and 2-Chlorophenol removal efficiencies. After doped the TiO2 or lignite with Mn and Ce metals, the metal oxides are amorphous and the particle sizes are below 5nm. However, the long-time tests of NO and 2-Chlorophenol removal efficiencies would decrease with time. On the other hand, the mesoporous material has high surface area and well order pore structure that might increase the catalyst activity after modifing with metals. In this study, AASA one-step method was used to synthesize Mn and Ce doped Mesoporous Silica Particles (MSP) by a spray dryer. It was demonstrated that the 2-Chlorophenol removal efficiency can reach 80% at 150℃ while the NO removal efficiency is only 20%. The long time tests showed that both NO and 2-Chlorophenol removal efficiencies decrease with time.