以La(1-x)Sr(x)Mn(1-y)Co(y)O3波洛斯凱特型觸媒用於低溫SCR處理NOx之研究

Abstract

The selective catalytic reduction (SCR) has been applied for several decades to reduce NOx emissions with ammonia from stationary sources. The MoO3 or V2O5 supported on TiO2 are the most commonly employed SCR catalysts. However, it is limited to a narrow and relatively higher temperature window (300~400℃). This limits the application of SCR to many other industrial processes such as the steel manufacture industry which has high NOx emissions at relatively lower temperatures of around 150℃. Perovskite-type oxides, with the characteristics of low-cost materials and high structural stability even at above 1000℃, could be the potential candidate for industrial NO removal catalysts at low temperatures. In this study, the reactivity of perovskite-type mixed oxides for low temperature SCR of NO with NH3 is investigated. The general formula of perovskite oxide is ABO3, the B-site cations could also be substituted by another one without changing the material structure and the oxidation state of B cations could be modified. A series of La(1-x)Sr¬(x)Mn(1-y)Co(y)O3 perovskite-type oxide catalysts were prepared by the co-precipitation method and they were divided into four groups of ABO3, AA'BO3, ABB'O3 and AA'BB'O3. The SCR tests were carried out under the typical reaction condition of 200 ppm NO, 200 ppm NH3, 150℃ and GHSV of 70,000 h-1. The experimental results showed that the highest NO conversion of 95% was observed by using LaCo0.2Mn0.8CoO3 when the reaction temperature was 150℃. The NO conversion declined to below 65% at 350℃. And as GHSV was 100,000 h-1, the NO conversion decreased to 64%. The BET results revealed that the specific surface area was highly correlated to the NO conversion. The XRD results showed that poor crystallinity correlated to a higher NO conversion. The TPD results revealed that the amount of adsorbed NO played an important role in the SCR reaction at 150℃. As the NO desorption amount was larger, the catalyst activity was higher. The TPR results indicated that as the reduction peak appeared at a lower temperature the NO conversion was higher, which is due to the lower energy was being consumed.