SELECTIVE REDUCTION OF NO BY HYDROCARBON IN O2 ON METAL ION-EXCHANGED ZEOLITE CATALYSTS

Abstract

The title reaction by ethene has been studied on 13 kinds of cation-exchanged ZSM-5 zeolites. Both the maximum activity and the active temperature have depended on the cation introduced into the zeolite. The maximum activities changed as follows; Ag (the maximum conversion into N2, 47%) ≃ Co (45%) ≃ Zn (44%) ≃ Cu (41%) > H (39%) ≃ Ni (38%) > Mn (27%) > Fe (12%) ≃ Ca (12%) ≃ La (11%) ≃ Pd (10%) > Cr (3%) > Na (≃0%). The order of active temperature region of the most active ZSM-5 zeolites was Cu (the most active temperature, 523 K) < Co (623 K) < H (673 K) < Ag (723 − 873 K) ≃ Zn (873 K). The conversion into N2 upon Cu-MFI-105 did not decrease even at 48000 h-1 of GHSV. The activity of copper ion-exchanged zeolite depended on the zeolite structures and the exchange level of copper ion. It follows that 80-100% copper ion-exchanged zeolite with ZSM-5 structure is the most active for the selective reduction of NO by ethene in the presence of O2 at the temperatures as low as 523-573 K among cation-exchanged zeolites. The reaction mechanism of selective reduction on copper ion-exchanged ZSM-5 zeolite has also been investigated and the presence of some reactive intermediate which selectively reduces NO has been proposed.