SELECTIVE CATALYTIC REDUCTION OF NO BY ETHENE IN EXCESS OXYGEN OVER PLATINUM ION-EXCHANGED MFI ZEOLITES

Various noble metal ion-exchanged MFI zeolites have been examined as catalysts for the selective reduction of NO by ethene in the presence of excess oxygen. Of the catalysts ion-exchanged for Ru, Rh, Pd, Ir, and Pt, Pt-MFI zeolite showed the highest catalytic activity for the conversion of NO into N-2. The catalytic activity was not reduced upon the addition of 8.6 vol.-% water vapor or 300 ppm sulfur dioxide in the reactant stream. It was hardly changed during the continuous experiment of 1000 h except for the initial period of use, indicating the high durability of Pt-MFI. Temperature-programmed decomposition and dynamic XRD measurements over Pt-MFI revealed that metallic platinum particles were formed through the decomposition of tetraammineplatinum ion during the pre-treatment around 673 K in helium atmosphere. The sizes of platinum particles were confirmed by TEM to be about 3 and 13 nm and did not change after use in the catalytic run.