Reaction of NO{sub 2} with Zn and ZnO: Photoemission, XANES, and density functional studies on the formation of NO{sub 3}
Synchrotron-based high-resolution photoemission and X-ray absorption near-edge spectroscopy (XANES) have been used to study the interaction of NO{sub 2} with polycrystalline surfaces of metallic zinc and zinc oxide. NO{sub 2} exhibits a complex chemistry on metallic zinc. After absorbing nitrogen dioxide, N, O, NO, NO{sub 2}, and NO{sub 3} are present on the surface of the metal. At room temperature the NO{sub 2} molecule mainly dissociates into O adatoms and gaseous NO, whereas at low temperatures (<250 K) chemisorbed NO{sub 2} and NO{sub 3} dominate on the surface. NO{sub 2} is a very good oxidizing agent for preparing ZnO from metallic zinc. Zn reacts more vigorously with NO{sub 2} than metals, such as Rh, Pd, or Pt which are typical catalysts for the removal of NO{sub x} molecules (DeNO{sub x} process). At 300 K, the main product of the reaction of NO{sub 2} with polycrystalline ZnO is adsorbed NO{sub 3} with little NO{sub 2} or NO present on the surface of the oxide. No evidence was found for the full decomposition of the NO{sub 2} molecule (i.e., no NO{sub 2} {r{underscore}arrow} N + 20). The results of density functional (DF-GGA) calculations for the adsorption of NO{sub 2} on a six-layer slab of ZnO, or INDO/S calculations for NO{sub 2} on a Zn{sub 37}O{sub 37} cluster, show stronger chemisorption bonds on (0001) Zn-terminated terraces than on (000{bar 1}) O-terminated terraces. The Zn {leftrightarrow} NO{sub 2} interactions on ZnO are strong and the Zn sites probably get oxidized and nitrated as a result of them. It appears that NO{sub 2} is very efficient for fully oxidizing metal centers that are missing O neighbors in oxide surfaces. On zinc oxide, the nitrate species are stable up to temperatures near 700 K. ZnO can be useful as a sorbent in DeNO{sub x} operations.
- Research Organization:
- Brookhaven National Lab., Upton, NY (US)
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 20017484
- Journal Information:
- Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical, Vol. 104, Issue 2; Other Information: PBD: 20 Jan 2000; ISSN 1089-5647
- Country of Publication:
- United States
- Language:
- English
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