Catalytic reduction of NO over the modified MFI metallosilicalites
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Catalysis Letters Vol. 112, Nos. 1–2, November 2006 (Ó 2006) DOI: 10.1007/s10562-006-0170-3
Catalytic reduction of NO over the modified MFI metallosilicalites Ewa Janiszewska,* Stanisław Kowalak, Monika Gierczyn´ska, Violetta Dolata, Michał Zielin´ski, and Maria Wojciechowska Faculty of Chemistry, A. Mickiewicz University, Grunwaldzka 6, 60-780 Poznan, Poland
Received 6 August 2006; accepted 30 August 2006
The metallosilicalites (MFI) containing copper ([Cu,Si]), zinc ([Zn,Si]) or both elements ([Cu,Zn,Si]) were prepared and modified as potential catalysts for the NO reduction with propene. The H-[Cu,Si] samples showed the highest activity, which was initially comparable to that of Cu-ZSM-5, but contrary to the latter, it increased with time. The framework Cu or Cu released from the framework probably act as active sites. KEY WORDS: metallosilicalites; [Cu,Zn,Si]; [Zn,Si] MFI; synthesis; characterization; catalysts for NO reduction.
1. Introduction Zeolites ZSM-5 belong to a group of zeolites of great industrial importance and they are applied as very efficient and selective catalysts. The MFI structure can be attained not only as aluminosilicate with very broad Si/ Al ratio (including pure silica silicalite-1) but also as metallosilicalites with various kind of metals. The isomorphous substitution of the framework aluminum for other metals results in substantial changes in the properties of internal surface and subsequently in the nature, concentration and strength of catalytic active sites generated in obtained MFI metallosilicates [1]. The nitrogen oxide abatement has been one of the most challenging environmental problems in recent decades. The selective catalytic reduction of NOx [2–4] is considered the most promising approach to this problem. The works of Iwamoto [5] evoked a great hope that the catalytic decomposition of nitrogen oxides over CuZSM-5 could be the easiest way to eliminate these air pollutants. The high activity and selectivity of Cu-ZSM5 appeared, however, not stable, and therefore this catalyst never attained any industrial application. The Cu modified zeolites are still investigated as catalysts for selective catalytic reduction of NOx. The role of MFI structure as well as that of Cu cations seems to be crucial, although the details remain still not quite clear. It is interesting to study, whether the copper atoms introduced into the framework of the MFI metallosilicalite could also result in catalytic activity for NOx reduction, and whether a potential activity would be more stable than that of Cu cation modified aluminosilicate ZSM-5. The following study presents the synthesis of [Zn,Si] MFI, [Cu,Si] MFI and [Cu,Zn,Si]MFI and their cation *To whom correspondence should be addressed.
modifications with Cu2+ and H+. The resulting metallosilicalites were characterized with physicochemical methods. Their catalytic activity was first examined for the propan-2-ol decomposition in order to assess the presence and the efficiency of acid and red-ox active sites. The selected samples presenting both acti
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