Isolation of Active Adsorbates for the NO–CO Reaction on Pd/Al2O3by Selective Enhancement and Selective Poisoning

Abstract A novel experimental approach which couples in situ infrared (IR) with selective enhancement and poisoning has been developed to identify the active adsorbate for the NO–CO reaction on Pd/Al 2 O 3 . In situ IR studies of the steady-state NO–CO reaction show that NO adsorbs as Pd–N≡O δ+ , Pd–N=O, and Pd–N //Oδ− ; CO adsorbs as Pd–C≡O and Pd Pd >C=O. Addition of H 2 to the NO–CO flow as a reaction enhancer which reacts with adsorbed nitrogen and oxygen results in depletion of Pd–N=O, while addition of O 2 to the NO–CO flow as a reaction poison leads to accumulation of Pd–N=O on the Pd surface. These observations suggest that Pd–N=O is the active adsorbate involved in NO dissociation. The observed variation in the concentrations of CO 2 and Pd–C≡O suggests that Pd–C≡O is the active adsorbate leading to CO 2 . This study demonstrates that combined in situ IR with careful selection of enhancing and poisoning reagents allows unambiguous identification of active adsorbates under reaction conditions.