Highly active SO2-resistant ex-framework FeMFI catalysts for direct N2O decomposition

Ex-framework FeFI catalysts, prepared by isomorphous substitution of iron in the aluminosilicate or gallosilicate MFI-type framework and activation by calcination at 823 K and steaming (300 mbar H2O in N-2) at 873 K, show high activity and stability in N2O decomposition in the presence of O-2, CO2, H2O, and SO2. The N2O conversion of the ex-framework catalysts in simulated tail-gas mixtures was >80% at 800K and 75,000 h(-1). The specific activity per mole of Fe (turnover frequency, TOF) of the ex-framework catalysts in N2O-He is four to nine times higher than observed for catalysts prepared by conventional solid and liquid-ion exchange, and sublimation methods. The stability of ex-framework catalysts for the direct N2O decomposition, in the absence of any reductant, is remarkable, showing no significant deactivation (at N2O conversion levels ranging from 20 to 65%) after 600h on stream. Sublimed and especially ion-exchanged FeZSM-5 catalysts show a strong irreversible deactivation in feed mixtures containing H2O and SO2. The effect of SO2 on the catalytic performance of FeMFI catalysts is discussed, as well as the applicability of the ex-framework FeMFI catalysts in fluid-bed combustion facilities. (C) 2002 Elsevier Science B.V. All rights reserved.