AThe infrared and Raman spectra of N2 matrix-isolated silicon oxides o were investigated. The vibrational frequencies of SiO, Si 20 2 , and S303°'4 U were identified and assigned on the basis of normal coordinate analyses. a 'u Heating the solid to -,50: (evaporating the matrix) leaves a residue whose =wz\ O H o infrared spectrum is identical to that of a smoke condensed at ambient c> o ' temperatures. Further heating of the sample to s500K leads to significant rtaU M4 E-4 m x changes in the band shapes. Investigations of the infrared spectra at L) 7 H several stages of the diffusion process enabled us to propose a mechanism 0w>eCO H A 04^' for the transition from molecular properties to those of the residue (bulk)
In situ Raman spectroscopy combined with quantitative FT-IR gas phase analysis was used to elucidate the mechanism of NO2 storage in ceria. At room temperature, NO2 exposure induces an immediate increase in the degree of ceria reduction accompanying nitrate formation. Two parallel reaction pathways for nitrate formation are identified. The presence of steam strongly influences the storage behavior by favoring the formation of free nitrates over bidentate/bridging nitrates. At 200°, faster free nitrate formation and gas phase NO formation is observed, while the NOx storage capacity of ceria is reduced from 0.27 to 0.16 mmol g(-1) CeO2.
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