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 NO_x storage capacity of ceria is reduced from 0.27 to 0.16 mmol g⁻¹ CeO₂.