| Abstract
| - Synchrotron-based high-resolution photoemission and X-ray absorption near-edge spectroscopy (XANES)have been used to study the interaction of NO2 with polycrystalline surfaces of metallic zinc and zinc oxide.NO2 exhibits a complex chemistry on metallic zinc. After adsorbing nitrogen dioxide, N, O, NO, NO2, andNO3 are present on the surface of the metal. At room temperature the NO2 molecule mainly dissociates intoO adatoms and gaseous NO, whereas at low temperatures (<250 K) chemisorbed NO2 and NO3 dominate onthe surface. NO2 is a very good oxidizing agent for preparing ZnO from metallic zinc. Zn reacts more vigorouslywith NO2 than metals, such as Rh, Pd, or Pt which are typical catalysts for the removal of NOx molecules(DeNOx process). At 300 K, the main product of the reaction of NO2 with polycrystalline ZnO is adsorbedNO3 with little NO2 or NO present on the surface of the oxide. No evidence was found for the full decompositionof the NO2 molecule (i.e., no NO2 → N + 2O). The results of density functional (DF-GGA) calculations forthe adsorption of NO2 on a six-layer slab of ZnO, or INDO/S calculations for NO2 on a Zn37O37 cluster, showstronger chemisorption bonds on (0001) Zn-terminated terraces than on (0001̄) O-terminated terraces. TheZn ↔ NO2 interactions on ZnO are strong and the Zn sites probably get oxidized and nitrated as a result ofthem. It appears that NO2 is very efficient for fully oxidizing metal centers that are missing O neighbors inoxide surfaces. On zinc oxide, the nitrate species are stable up to temperatures near 700 K. ZnO can beuseful as a sorbent in DeNOx operations.
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