The reactivity of adsorbed NO and the nature of Cu sites on under-, over-exchanged, and silane-treated Cu-ZSM-5 have been probed by the CO and H-2 pulse during NO decomposition at 673 K. Cu+(NO) was identified to be the active adsorbate responsible for NO decomposition to N2O and O-2 as well as to N-2 and O-2. Pulsing CO and H-2 into the NO flow facilitates the reduction of Cu2+ to Cu+ and increases Cu+(NO) concentration, resulting in an enhancement of N2O formation rate on under-exchanged Cu-ZSM-5-83/silane-treated Cu-ZSM-5-523 and an acceleration of N-2 and O-2 formation rates on over-exchanged Cu-ZSM-5-127 and -523. The difference in the product formation among these catalysts is attributed to the isolation of Cu sites on the silane-treated Cu-ZSM-5-527 and under-exchanged Cu-ZSM-5-83 catalyst as well as the presence of Cu-dimer sites (Cu-O-Cu) on the over-exchange Cu-ZSM-5 catalyst. In contrast to the widely postulated steps for N-2 formation via N2O, the profiles of N-2, N2O, O-2, and IR observable adsorbates during the CO and H-2 Pulse suggest that N-2 can be formed without involvement of N2O during NO decomposition.