Probing the Reactivity of Adsorbed NO Species by the CO and H₂ Pulse during NO Decomposition on Cu-ZSM-5

Abstract

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 H2 pulse during NO decomposition at 673 K. Cu+(NO) was identified to be the active adsorbate responsible for NO decomposition to N2O and O2 as well as to N2 and O2. Pulsing CO and H2 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 N2 and O2 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 N2 formation via N2O, the profiles of N2, N2O, O2, and IR observable adsorbates during the CO and H2 pulse suggest that N2 can be formed without involvement of N2O during NO decomposition.