Evaluation of Fe-zeolite catalysts prepared by different methods for the decomposition of N2O

Zeolite supported iron catalysts were prepared by different methods and their catalytic performance was studied in the N2O decomposition reaction. Iron-zeolite was prepared in accordance with the best-known recipes described in literature, not only at Energy research Centre of the Netherlands (ECN), but also at other independent institutes to ensure that the best available expertise in the field was applied for each method. The preparation methods subject to investigation were the wet ion-exchange (WIE), chemical vapour deposition/sublimation and ex-framework method. All catalysts were subjected to similar reaction conditions representative of exhaust emissions from nitric acid factories and the total conversion of N2O by decomposition reaction were compared. With respect to the catalytic activity and ease of catalyst manufacture, the wet ion-exchange based preparation method to prepare iron-zeolite is slightly favoured over alternative methods. WIE based Fe-zeolite catalysts combine high N2O decomposition (and selective catalytic reduction, SCR) activity with good hydro-thermal stability. The pH of the suspension of the iron salt and the zeolite during WIE is a key factor in achieving catalysts with high activity in NO decomposition. The topology of the zeolite is also a key factor for both activity and stability under realistic practical conditions. However, over-exchange (Fe/Al ratio = 1), which can be achieved with the chemical vapour deposition (CVD) method, but which is also a goal in studies on WIE preparation, is not a key factor in gaining high activity. Wet ion-exchange yields a catalyst with less than 50% of the exchange sites occupied by Fe. (C) 2004 Elsevier B.V. All rights reserved.