N2O and NO decomposition pathways on Cu-ZSM-5 have been investigated by monitoring the adsorbate dynamics and changes in reactant and product concentrations using infrared spectroscopy (TR) and mass spectrometry (MS) under transient reducing and oxidizing conditions. Transient reducing and oxidizing conditions were produced by the H-2, CO, and O-2 pulses into either N2O or NO streams. IR and MS studies under the transient conditions revealed that adsorbed O produced from N2O exhibited different reactivity and dynamics from the adsorbed O produced during NO decomposition. The differences in reactivity and dynamics of the adsorbed O were evidenced by the fact that (i) adsorbed O from N2O interacted with CO/H-2 to produce two humps in the H2O and O-2 concentration profiles; adsorbed O from NO reacted with CO/H-2 that led to only one hump in the H2O and O-2 concentration profile, and (ii) addition of the O-2 pulse led to reaction of O-2 With adsorbed O from NO, resulting in oxidation of Cu+ in Cu+(NO) to Cu2+ in Cu2+(NO3-); addition of O-2 did not lead to any reaction with adsorbed O from N2O decomposition. N2O decomposition is proposed to proceed via Cu+-ON2, Cu2+O-, and Cu2+O--ON2 with Cu+-ON2 serving as a precursor for N-2 formation and Cu2+O- as a precursor for O-2 formation. NO decomposition proceeds via Cu+(NO), Cu2+O-, and Cu2+(NO3-) with Cu+(NO) serving as a precursor for NO dissociation. Cu+ in Cu+(NO) is different from that of Cu+ in Cu+-ON2. The former may be associated with Al(OH)(4)(-) of the zeolite, the latter with Si(OH)(4)(-). (C) 2000 Academic Press.