The adsorption of NO and reaction of NO with O{sub 2} on H-, NaH-, CuH-, and Cu-ZSM-5: An in situ FTIR investigation
- Los Alamos National Lab., NM (United States)
The adsorption of NO and the reaction of NO with O{sub 2} on H-, NaH-, CuH-, and Cu-ZSM-5 zeolites were studied at 300 K using in situ Fourier transform infrared spectroscopy (FTIR). At this temperature, NO readily adsorbs on the Cu{sup +} sites of CuH- and Cu-ZSM-5 catalysts and decomposition of NO is observed for all catalysts, although the rate of decomposition is vastly different on these materials. In comparison, this reaction is negligible over the H- and NaH-ZSM-5 samples. The time evolution of several nitrogen-containing molecules after controlled O{sub 2} exposure to the NO/ZSM-5 systems has allowed the spectral correlation of these species. These nitrogen-containing species can interact with either the protonic sites of bridging hydroxyls forming hydrogen bonding complexes or the metal cations producing primarily surface nitrates and nitrites. The hydrogen bonded N{sub x}O{sub y} complexes were characterized with their IR absorption features: (1) NO{sub 2}, 2133 cm{sup {minus}1}; (b) N{sub 2}O{sub 3}, 1875 and 1587 cm{sup {minus}1}; and (c) N{sub 2}O{sub 4}, 2185 and 1745 cm{sup {minus}1}. The stretching vibrational frequency of the acidic OH groups of ZSM-5 red-shifts due to the interaction with nitrogen-containing molecules and forms {open_quotes}ABC{close_quotes} band structures characteristic of medium and strong hydrogen bonding complexes. Although the adsorbed N{sub x}O{sub y} species (N{sub 2}O{sub 3}, N{sub 2}O{sub 4}) interacting with the Bronsted protons exhibit characteristics of a strong Lewis base, adsorption enthalpies are sufficiently weak that their existence is not observed even after brief evacuation. Nitric oxide, oxygen coadsorption produces metal cation (Na{sup +} and Cu{sup n+}) bonded surface species possessing IR absorption bands between 1400 and 1650 cm{sup {minus}1} characteristic of nitrite and nitrate species. 46 refs., 9 figs.
- OSTI ID:
- 486391
- Journal Information:
- Journal of Catalysis, Vol. 164, Issue 1; Other Information: PBD: Nov 1996
- Country of Publication:
- United States
- Language:
- English
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