화학공학소재연구정보센터
Journal of Catalysis, Vol.201, No.1, 89-99, 2001
Reduction of NOx with ammonia over Fe/MFI: Reaction mechanism based on isotopic labeling
The selective catalytic reduction of nitrogen oxides has been studied in the presence of O-2 over Fe/MFI catalysts with Fe/Al similar to 1, prepared by sublimation of FeCl3 vapor onto HMFI. Reduction of NOx is much faster with NH3 than with isobutane. A 100% NOx reduction to N-2 is observed for an NH3/NO ratio above unity and 90% for a 1/1 dosage, The catalyst is very active and stable in the presence of water vapor. Isotopic labeling with (NO)-N-15 shows that the preferred path for the reduction of NOx with NH3 is via NH4NO2. This nitrite decomposes to N-2 + 2H(2)O. A 100% pure (NN)-N-15-N-14 product is obtained by circulating a 1/1 mixture of (SNO)-S-15 and (NO2)-N-15 over a catalyst covered with adsorbed (NH3)-N-14. In contrast, N-14(2) is formed by oxidation of (NH3)-N-14 With O-2 or N2Ox with x > 3. The high efficiency of this catalyst is due to the fact that ammonia swiftly intercepts the oxidation of NO when the value of x = 3 is reached. At high temperature when little adsorbed water is present, water vapor promotes activity because it is needed for the formation of ammonium nitrite. At low temperature it acts kinetically as a mere competitor for the active sites.