Effect of H2O on the Morphological Changes of KNO3 Formed on K2O/Al2O3 NOx Storage Materials: Fourier Transform Infrared and Time-Resolved X-ray Diffraction Studies

Based on the combined FTIR and XRD studies, we report here that H 2 O induces a morphological change of KNO 3 species formed on model K 2 O/Al 2 O 3 NOx storage-reduction catalysts. Specifically as evidenced by FTIR, the contact of H 2 O with NO 2 preadsorbed on K 2 O/Al 2 O 3 promotes the transformation from bidentate (surface-like) KNO 3 species to ionic (bulk-like) ones irrespective of K loadings. Once H 2 O is removed from the sample, a reversible transformation into bidentate KNO 3 is observed, demonstrating a significant dependence of H 2 O on such morphological change. TR-XRD results show the formation of two different types of bulk KNO 3 phases (orthorhomobic and rhombohedral) in an as-impregnated sample. Once H 2 O begins to desorb above 400 K, the former is transformed into the latter, resulting in the existence of rhombohedral KNO 3 phase only. On the basis of consistent FTIR …