The effect of temperature and phase state on the infrared spectrum of Ba(NO3)2

Taha, S.; Tosson, M.

doi:10.1016/0040-6031(94)80270-x

Cited by 12 publications

(9 citation statements)

References 10 publications

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“…These changes in the IR spectrum can be attributed to the amorphous-to-crystalline phase transformation of Ba(NO 3 ) 2 , as reported on NO 2 -exposed BaO (Y BaO 4 1 MLE)/Al 2 O 3 /NiAl(110), and high surface area BaCl 2 /SiO 2 , and BaO powders. 15,37,38 It should be noted that the IR peak positions presented here for crystalline Ba-nitrate are not identical to that of crystalline bulk Ba(NO 3 ) 2 reported previously, [39][40][41] due, most probably, to the presence of nanoclusters supported on a metal single crystal. In addition to the sharp peaks, a broad peak is present at 1310 cm À1 in Fig.…”

Section: Resultscontrasting

confidence: 71%

Reactions of NO2 with BaO/Pt(111) model catalysts: the effects of BaO film thickness and NO2 pressure on the formation of Ba(NOx)2 species

Mudiyanselage

Szanyi

2011

Phys. Chem. Chem. Phys.

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The adsorption and reaction of NO(2) on BaO (<1, ∼3, and >20 monolayer equivalent (MLE))/Pt(111) model systems were studied with temperature programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), and infrared reflection absorption spectroscopy (IRAS) under ultra-high vacuum (UHV) as well as elevated pressure conditions. NO(2) reacts with sub-monolayer BaO (<1 MLE) to form nitrites only, whereas the reaction of NO(2) with BaO (∼3 MLE)/Pt(111) produces mainly nitrites and a small amount of nitrates under UHV conditions (P(NO(2))≈ 1.0 × 10(-9) Torr) at 300 K. In contrast, a thick BaO (>20 MLE) layer on Pt(111) reacts with NO(2) to form nitrite-nitrate ion pairs under the same conditions. At elevated NO(2) pressures (≥1.0 × 10(-5) Torr), however, BaO layers at all these three coverages convert to amorphous barium nitrates at 300 K. Upon annealing to 500 K, these amorphous barium nitrate layers transform into crystalline phases. The thermal decomposition of the thus-formed Ba(NO(x))(2) species is also influenced by the coverage of BaO on the Pt(111) substrate: at low BaO coverages, these species decompose at significantly lower temperatures in comparison with those formed on thick BaO films due to the presence of a Ba(NO(x))(2)/Pt interface where the decomposition can proceed at lower temperatures. However, the thermal decomposition of the thick Ba(NO(3))(2) films follows that of bulk nitrates. Results obtained from these BaO/Pt(111) model systems under UHV and elevated pressure conditions clearly demonstrate that both the BaO film thickness and the applied NO(2) pressure are critical in the Ba(NO(x))(2) formation and subsequent thermal decomposition processes.

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Section: Resultscontrasting

confidence: 71%

Reactions of NO2 with BaO/Pt(111) model catalysts: the effects of BaO film thickness and NO2 pressure on the formation of Ba(NOx)2 species

Mudiyanselage

Szanyi

2011

Phys. Chem. Chem. Phys.

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“…The number of bands observed in the four IR spectra differs strongly, even though the same reference powder was used for all investigations. Ba(NO 3 ) 2 has a characteristic band pattern with a small sharp band around 1775 cm À1 assigned to the combination mode n 1 + n 4 of nitrate, 32,33 a minor sharp band in between 1423-1408 cm À1 assigned to the 2n 4 vibrational mode and a major broad band around 1375-1329 cm À1 assigned to the splitted n 3 asymmetric stretching of nitrate. [32][33][34] In addition, the n 2 band is observed around 817 cm À1 and the n 4 around 730 cm À1 .…”

Section: Resultsmentioning

confidence: 99%

On the local sensitivity of different IR techniques: Ba species relevant in NOx storage-reduction

Roedel

Urakawa

Kureti

et al. 2008

Phys. Chem. Chem. Phys.

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IR spectroscopy is widely used to elucidate reaction mechanisms in NO(x) storage and reduction (NSR). Observed band positions and assignments of vibrational modes, however, differ remarkably among the various investigations. We report an IR study of barium species relevant in NSR, aiming to clarify the source of the reported discrepancies and different surface and bulk sensitivity of various IR measurement configurations. Four IR techniques, namely, transmission IR spectroscopy (TIRS), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), attenuated total reflection infrared spectroscopy (ATR-IRS), polarization-modulation infrared reflection-absorption spectroscopy (PM-IRRAS), all suitable for in situ studies of the reaction system, were used. Depending on the IR technique certain bands undergo a clear band shift or disappearance, evidently showing different surface and bulk sensitivity. In spectra of barium nitrate recorded by the more bulk sensitive IR techniques, i.e. TIRS, ATR-IRS, and PM-IRRAS, fewer bands appeared than in the more surface sensitive DRIFTS spectra. This work constitutes a collection of IR spectra of reference barium compounds for the clarification of species present in the NSR catalyst system. The band position or the presence of certain bands assigned to the same chemical species may deviate if the spectra were measured by different IR techniques, especially if the compared IR techniques differ in surface/bulk sensitivity. This implies that the band assignment valid for spectra measured by DRIFTS can be transferred to TIRS, ATR-IRS, and PM-IRRAS only with precautions.

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“…The other bands are assigned to nitrates; the combination mode of m 1 ? m 4 of ionic type nitrate at 1,770 cm -1 [23,26], adsorbed bidentate nitrate species [10,27,28] at around 1,585 cm -1 , and symmetric stretching mode of nitrate [27] at 1,028 cm -1 , which is normally infrared inactive unless its structure is distorted. This band is, therefore, assigned to surface nitrates.…”

Section: Resultsmentioning

confidence: 99%

Influence of Pt–Ba Proximity on NO x Storage–Reduction Mechanisms: A Space- and Time-Resolved In Situ Infrared Spectroscopic Study

2009

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The influence of Pt-Ba proximity on the performance and mechanism of NO x storage-reduction (NSR) was investigated by a comparative study of Pt-Ba/CeO 2 , Pt/CeO 2 and mechanically mixed Pt/CeO 2 -Ba/CeO 2 . NO x storage capacity, regeneration activity and selectivity to nitrogen and ammonia during periodic lean (NO ? O 2 )-rich (H 2 ) cycles were evaluated and the chemical gradients along the axial direction of the catalyst beds were monitored by space-and time-resolved in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The presence of Ba and its proximity to Pt greatly influenced the NSR process. In particular, the proximity was crucial to achieve better utilization of bulk Ba components as well as enhancing selectivity to N 2 . The space-resolved approach is shown to be a powerful tool to understand the impact of the proximity of Pt and Ba constituents on the final NSR performance.

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The effect of temperature and phase state on the infrared spectrum of Ba(NO3)2

Cited by 12 publications

References 10 publications

Reactions of NO2 with BaO/Pt(111) model catalysts: the effects of BaO film thickness and NO2 pressure on the formation of Ba(NOx)2 species

Reactions of NO2 with BaO/Pt(111) model catalysts: the effects of BaO film thickness and NO2 pressure on the formation of Ba(NOx)2 species

On the local sensitivity of different IR techniques: Ba species relevant in NOx storage-reduction

Influence of Pt–Ba Proximity on NO x Storage–Reduction Mechanisms: A Space- and Time-Resolved In Situ Infrared Spectroscopic Study

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