IR INVESTIGATION OF SELECTIVE REDUCTION OF NO BY ETHENE ON CU-ZSM-5

Adsorbed species during the reaction of selective catalytic reduction of NOx by hydrocarbons (HC-SCR) on Cu ion-exchanged ZSM-5 (Cu-ZSM-5) were investigated by in situ FT-IR using isotopes as well as gas phase analysis. No oxygen-containing species was observed by IR and no reaction proceeded in the presence of gaseous O-2 and C2H4 below 473 K, at which HC-SCR occurs. However, an extra NOx species (tentatively assigned to organic nitrite or nitrate species), other than inorganic NOx species derived from O-2 and NO, appeared very rapidly in IR at 1670 cm(-1) at room temperature, in the presence of adsorbed NO2 species, gaseous C2H4 and NO. Afterwards, a carbonyl species (1677 cm(-1)) was formed gradually at room temperature. When the extra NOx species was observed, N-2 and N2O evolved even at room temperature, therefore, the extra NOx species is considered to be related to HC-SCR. In the O-2+C2H4+NO reaction at 473 K, no nitrogen-containing species, except for quite a small amount of nitrile (2168 cm(-1)), was observed in IR. At 473 K, N-2, and CO evolved very rapidly with a steep increase in the IR intensity of carboxylate (1574 and 1375 cm(-1)), while CO2 and carbonyl species increased more slowly.