Mechanistic Aspect of NO-NH3-O2 Reacting System

In this chapter, the reaction mechanisms of the standard SCR reaction are discussed from various perspectives including steady-state kinetics, the relations with NH3/NO oxidation ability and acid site amount, the effect of coexisting gases, and transient reaction behavior. Through these comprehensive analyses, some similarities and differences of the reaction mechanism among the conventional SCR catalysts could be extracted. Also, new perspectives on standard SCR mechanism could be suggested. 

To have a grasp of basic reaction behaviors, standard SCR as well as NH3/NO oxidation reactions were investigated under steady-state condition. For the samples, three conventional SCR catalysts, V-WATi02, Fe/ZSM-5, and Cu/ZSM-5, 

Toyota Central R D Laboratories, Inc., 41-1 Yokomichi, Nagakute, Aichi 480-1192, Japan e-mail iwasaki mosk.tytlabs.co.jp 

Nova and E. Tronconi (eds.), Urea-SCR Technology for deNOx After Treatment cf Diesel Exhausts, Fundamental and Applied Catalysis, 

From Fig. 8.1b, NH3 oxidation without inlet NO started above 300 °C for all the catalysts, which is much higher onset temperature than the SCR reaction. As by-products, N2O was not detected for all the catalysts, and NOx was produced only for H-ZSM-5 above 300 °C (Fig. 8.1c). It indicates that NH3 oxidation reaction to N2 (2NH3 + N2 + 3H2O) mainly proceeds for the three SCR 

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