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| - FTIR Spectroscopic Characterization of NOx Species Adsorbed on ZrO2 and ZrO2−SO42-
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| - The nature of the NOx species produced during the adsorption of NO at room temperature and during itscoadsorption with oxygen on pure and sulfated zirconia has been investigated by means of in situ FTIRspectroscopy. The adsorption of NO on both samples occurs through disproportionation leading to the formationof nitrous acid; water molecules; nitro species; and anionic nitrosyls, NO-. A mechanism for the formationof these adsorption forms is proposed. The NO- species are stable on the surface of zirconia, whereas on thesulfated sample, they are readily oxidized by the SO42- groups. The process of NO disproportionation isfavored by wet surfaces and occurs with participation of the tribridged (ZrO2) and terminal (ZrO2−SO42-)hydroxyl groups. Coadsorption of NO and O2 on pure zirconia leads to the formation of various kinds ofnitrate species. The presence of sulfate ions reduces the amount of surface nitrates and decreases their thermalstability. An analysis of the combination bands of the nitrate species shows that this spectral region can beused for structural identification of bidentate and bridged nitrates.
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