Complementary Physicochemical Characterization by SAXS and 129Xe NMR Spectroscopy of Fe-ZSM-5: Influence of Morphology in the Selective Catalytic Reduction of NO

Fe-ZSM-5 catalysts were prepared by FeCl3 sublimation (CVD method) and impregnation in aqueous media. To describe the morphology of the iron species, the materials were characterized by XRD, SAXS, and 27Al and 129Xe NMR spectroscopy. In the catalysts prepared by impregnation, XRD detected large hematite particles at the external surface of the zeolite. In contrast, the Fe2O3 phase was not detectable by XRD in the materials prepared by CVD, indicating much smaller species. The 129Xe NMR results show that, in the CVDprepared materials, the amount of free space inside the zeolite cavities was decreased appreciably by the presence of the Fe oxo species. Furthermore, 129Xe NMR spectroscopy reveals a sharp peak for the CVD-prepared material with Fe (3.8 wt %), indicating that this catalyst exhibits strong adsorption sites that are not detectable in the sample of similar Fe content that was prepared by impregnation. Morphology appears to be strongly affected by the method of preparation of the catalyst. The fractal dimension of the metal phase was associated with the catalytic activity in the selective catalytic reduction (SCR) of NO using ammonia and n-decane as reducing agents.