Hiroshi Hirabayashi

Iron ion-exchanged zeolite: the most active catalyst at 473 K for selective reduction of nitrogen monoxide by ethene in oxidizing atmosphere

Among various metal ion-exchanged zeolites, metal loading alumina, and oxides, iron ion-exchanged mordenite was the most active for the selective reduction of nitrogen monoxide to nitrogen by ethene in the presence of oxygen at the temperature as low as 473 K. The catalytic activities of iron ion-exchanged zeolites depended on the zeolite structure and the iron ion exchange level. The effects of the zeolite structure are in the order of MOR > FER > MFI > Y > LTL at 473 K. The activity of iron ion-exchanged mordenite increased with the increment in the exchange level and levelled off above about 60%.

Selective catalytic reduction of no by ethene in excess oxygen over platinum ion-exchanged MFI zeolites

Abstract 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 N2. 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.

Selective catalytic reduction of nitrogen monoxide by hydrocarbon on platinum-zeolite

The catalytic activity for the title reaction was examined over noble metal (Ru, Rh, Pd, Ir, Pt) ion-exchanged zeolites using ethene as a reductant. Among the catalysts employed, Pt-ZSM-5 catalyst showed the highest activity at the temperature as low as 485 K. The order of the catalytic activities was Pt>Rh>Pd≫Ru ≈ Ir and the active temperature region was dependent on the kind of metal ion. The activity of Pt-ZSM-5, -mordenite, and -ferrierite was almost the same, indicating little effect of zeolite structure on the catalytic activity. On these catalysts much amount of N2O was formed as by-product. The conversion of NO into N2 over Pt-ZSM-5 was little affected by the introduction of water vapor or SO2.