Investigation of adsorbate reactivity during NO decomposition over different levels of copper ion-exchanged ZSM-5 using in situ IR technique

In situ infrared (LR) and mass spectroscopy (MS) coupled with temperature-p rogrammed reaction (TPR), isotopic temperature-programmed desorption (TPD), step transient, and pulse transient techniques have been used to study the dynamic behavior of adsorbed species in the NO decomposition reaction on o ver- and underexchanged Cu-ZSM-5. Overexchanged Cu-ZSM-5 showed higher NO d ecomposition activity and produced more Cu+ sites at lower temperatures tha n the underexchanged sample during the TPR study. Furthermore, overexchange d Cu-ZSM-5 allows rapid equilibrium between gaseous NO and Cu+(NO)/Cu2+ (NO 3-) during NO decomposition. N-2 formation accompanied by the presence of C u+(NO) suggests that Cu+ initiates the NO decomposition process. However, n o direct correlation between Cu+(NO)/Cu+(NO)(2) intensity and N-2 formation was observed. Adsorbed oxygen from dissociated NO changes the oxidation st ate of Cu+ ion, causing the formation of Cu2+(NO3-). While Cu2+(NO3-) decom poses to N-2, N2O, NO2, and O-2 during TPD, it is only partially responsibl e for the formation of O-2 during NO decomposition. Isotopic study shows th at adsorbed oxygen on Cu-ZSM-5 desorbs during the pulse NO reaction. These results demonstrate the presence of two pathways for O-2 formation: oxygen produced from the decomposition of Cu2+(NO3-) and oxygen from the desorptio n of adsorbed oxygen on Cu-ZSM-5.