Effect of coexchanging with a second metal upon the interaction of nitric oxide with Cu-ZSM-5

The effect of coexchanging of Cu-M-ZSM-5 zeolites (M = Ce, Sn, Sm) upon the interaction with nitric oxide was investigated by FT-IR. Spectra recorded on Cu-ZSM-5, in the presence of NO and at room temperature, exhibit typical features, very well reported in the literature. During NO decomposition at 673 K in the presence of 50 mbar NO, the band assigned to (NO)(delta+) species exhibits both a splitting and a shift. This behavior was attributed both to some modification in the copper(II) state during the reaction and to the formation of N2O3 species, active in NO decomposition. The presence of a second metal influences this process, and the intensity of the effect depends both on the chemical nature of the second metal and on its loading. It was also found that in the presence of Ce or Sm, the bands assigned to gem-dinitrosyl and to Cu+-NO as well as those of the N2O3 species are more intense. These effects were correlated with a more intense activity of Ce or Sm-promoted zeolites compared to pure Cu-ZSM-5. It is noteworthy that this increase occurs simultaneously with a diminution of the intensity of the nitrate-nitrite species bands.