Identifying surface species by vibrational spectroscopy: Bridging vs monodentate nitrates

Interaction of NO2 with Model NSR Catalysts: Metal–Oxide Interaction Controls Initial NOx Storage Mechanism

“…Selected IR spectra of the NO stretching region for the different NSR model systems and selected NO 2 exposures are displayed in Figure 2 [1 L (Langmuir) corresponds to a gas dose of 10 À6 Torr s]. The assignment of the spectral features was discussed in detail in recent publications, with systematic comparison with DFT calculations [39] and X-ray photoelectron spectra. [18] Briefly, the feature at 1250 cm À1 is assigned to flat-lying surface nitrite (NO 2 À ), the intensity of which is low due to orientation of the dynamic dipole moment nearly parallel to the surface.…”

“…Pioneering work on the interaction of NO 2 with model BaO surfaces was published by Bowker and co-workers, [16,32,33] Szanyi and co-workers [23,[34][35][36][37] and recently by us. [18,[38][39][40] Here we present the first model study on a "complete" NSR model system, involving the Ba storage compound and co-deposited noble metal nanoparticles on an alumina model support. By taking advantage of the full spectrum of surface-science methods, the structural and chemical properties of the model system were characterized and the degree of metal-oxide interaction controlled in great detail.…”

Model NOx Storage Materials at Realistic NO2 Pressures

“…[26][27][28] Based on density functional theory (DFT) calculations [28] and XPS, [27] absorption features at 1245 cm À1 were attributed to surface nitrites and bands at 1332 and 1468 cm À1 were assigned to the split asymmetric stretching vibrations of surface nitrates on Ba 2 + [n as A C H T U N G T R E N N U N G (NO 3 À )], in monodentate and bridging configurations, respectively. [26][27][28] The low intensity of the nitrite band was associated with a flatlying geometry, giving rise to an orientation of the dynamic dipole moment largely parallel to the surface. Note that, due to the metal surface selection rule, only the perpendicular component of the dynamic dipole gives rise to absorption features in IRAS.…”

“…[16][17][18][19][20] More recently, the reaction of NO 2 with BaO deposits on Al 2 O 3 / NiAlA C H T U N G T R E N N U N G (110) were studied by Szanyi et al [21][22][23][24] and our group. [25][26][27][28][29][30][31] Some of the key results of these studies may be summarized as follows: A strong interaction with the support gave rise to interdiffusion of Al 3 + and Ba 2 + ions, resulting in the formation of barium aluminate-like nanoparticles. [29] As the exact stoichiometry was not established, we denoted these particles BaAl 2x O 1 + 3x .…”

“…[27] To some extent, the assignment of the observed bands has been controversial and we refer to the literature for a more detailed discussion. [23,24,28,31] Herein, we address the issue of the pressure gap in the above-described model studies. [32] Typical UHV-based experiments are limited due to the high-vacuum regime.…”