Activity and durability of Fe/ZSM-5 catalysts for lean burn NOx reduction in the presence of water vapor

A novel method for the preparation of superior Fe/ZSM-5 catalysts is described. FeCl3 is sublimed into the cavities of H/ZSM-5, where it reacts chemically with the acid sites of the zeolite. With this method, Fe/ZSM-5 with an iron loading as high as Fe/Al=1 can be easily achieved. This preparation method is less sensitive to the origin of the zeolite and its synthesis history than the conventional ion-exchange method. HRAEM, FTIR, H-2-TPR and CO-TPR results show that iron is located at the exchange sites of the zeolite. An oxygen bridged binuclear iron complex is a plausible prototype for the active iron species. The iron is reduced from +3 to +2 below 800 degrees C. These catalysts are very active and selective in the catalytic reduction of NO, with iso-butane; they have a high durability under conditions simulating vehicular emission. A conversion of NO to N-2 Of about 76% was observed near 350 degrees C. Remarkably and in contrast to most other M/ZSM-5 catalysts, the performance of the new catalysts was not impaired when 10% H2O was added to the feed. H2O actually enhances the NOx conversion at low temperatures. CO and CO2 are both true primary products of NOx SCR over Fe/ZSM-5 catalysts. (C) 1998 Elsevier Science B.V. All rights reserved.