An Investigation on the Promoting Effect of Pr Modification on SO2 Resistance Over MnOx Catalysts for Selective Reduction of NO with NH3

Abstract

Manganese oxides (MnOx) exhibit excellent low-temperature activities in SCR reaction of NO with NH3, and they are considered as a promising catalyst for future application. However, MnOx still suffer from poor resistance to SO2 and H2O. In this work, Pr was used to modify MnOx catalysts via co-precipitation process, and MnPrOx catalyst exhibited superior SO2 resistance over pure MnOx catalyst. A series of characterization techniques, such as XRD, BET, H2-TPR, XPS, TG and in-situ DRIFTS, were adopted to explore the promoting effect of Pr modification on SO2 resistance over MnOx catalyst in detail. The results indicated that, in the presence of SO2 in feed gas, it seemed that PrOx rather than MnOx were apt to react with SO2, which was favorable to protect Mn active sites on the catalyst surface to some extent. It was known that there was strong competitive adsorption between SO2 and NH3/NO species on SCR catalyst surface. In-situ DRIFTS results revealed that the adsorption of NH3 and NO on MnOx catalyst had been severely suppressed after the introduction of SO2, resulting in the relevant SCR reactions following either L-H or E-R mechanisms would be inhibited obviously. But for Pr-modified MnOx catalyst, the introduction of SO2 almost had no effect on the adsorption of NH3 on catalyst surface, while it exerted a relatively noticeable impact on the adsorption of NO. As a result, SCR reactions occurred on Pr-modified MnOx catalyst surface could still proceed in a near-normal way through E-R rather than L-H mechanisms. Therefore, Pr modification on MnOx catalyst exhibited a distinctively promoting effect on SO2 resistance performance in SCR process.