Mechanism of NO2 storage in ceria studied using combined in situ Raman/FT-IR spectroscopy

Abstract

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.

FTIR and density functional study of NO interaction with reduced ceria: Identification of N3− and NO2− as new intermediates in NO conversion

“…Initial stages of 14 NO/ 15 NO interaction with reduced ceria. It is also seen that with the two samples the bands appear with strongly different relative intensities.…”

“…It was demonstrated [21] that bands at 1270 and 1160 cm -1 (assigned to chelating nitrites) and a band at 1090 cm -1 (attributed to trans-hyponitrites) were due to N-O modes because were accordingly shifted after adsorption of 15 NO. Szanyi and Kwak [50] recently reported that 15 nitrite species (1153 and 815 cm -1 ) absorb at 1137 and 798 cm -1 after substitution of one of the 16 O atoms by 18 O. It is established that the deNO x activity of ceria correlates with the number of oxygen vacancies [17].…”

“…Many catalysts for NO x conversion, e.g., three-way [13], storage reduction [14,15], selective catalytic reduction [16,17] and soot oxidation (by NO x ) catalysts [18] contain ceria. Important peculiarities of CeO 2 are its high oxygen storage capacity and easy reducibility [05].…”

“…NO,15 NO, and14 NO + 15 NO isotopic mixtures and periodic density transition band of Ce 3+ , was used to follow the reduction degree of ceria[51]. The significant difference between the 15 N/ 14 N isotopic shift factors for N-N and N-O bonds[52] allowed unambiguous assignments of particular IR bands to N-N or N-O modes.…”

Impedance and Raman Spectroscopy Study of Effect of H2S on Ni‐YSZ SOFC Anodes

“…Moreover, we have shown that nickel sulfides can be formed during cooling at the end of the experiment. Since in situ Raman spectroscopy has proved to be able to characterize electrode reactions in SOFCs and H 2 S reaction products , , , as well as adsorbed species , we combined electrochemical measurements with in situ Raman spectroscopy to monitor cell evolutions under open circuit and polarizing conditions at 500 °C.…”