Modeling and flow reactor experiments were used to study the kinetics of NO x storage/release on a Pt/BaO/Al2O3 model catalyst. The mechanism for this concept can be divided into four steps:  (i) NO to NO2 oxidation on Pt, (ii) NO2 storage on BaO, (iii) NO x release, and (iv) NO x reduction to N2. In this paper, we have focused on the first three steps. From the NO oxidation study on Pt/Al2O3 compared to Pt/BaO/Al2O3, we observed that the presence of BaO decreases the formation of NO2. To test the importance of this step for effective storage, experiments were performed with a Pt/Al2O3 catalyst placed before the Pt/BaO/Al2O3 catalyst. This resulted in increased NO x storage for the combined system compared to the Pt/BaO/Al2O3 case. To resolve the second and third steps, an experimental investigation of NO x storage/release on BaO/Al2O3 was performed using only NO2 and N2 in the gas feed. We propose a kinetic model, which first includes adsorption of NO2, which oxidizes the surface, followed by nitrate formation. Finally, NO3 -BaO−NO2, i.e., Ba(NO3)2, is formed. By using the kinetic parameters from the NO oxidation on Pt/BaO/Al2O3 and the NO x storage on BaO/Al2O3, a kinetic model was constructed to describe NO x storage/release experiments on Pt/BaO/Al2O3. However, the rate for NO x release was increased when Pt was present, and the kinetic model could not accurately describe this phenomenon. Therefore, the mechanism was modified by including a reversible surface spillover step of NO2 between Pt sites and BaO sites. Further, experiments with NO2 exposure followed by a temperature ramp with NO/N2 showed that the desorption behaviors from the BaO/Al2O3 and Pt/BaO/Al2O3 were significantly different, which further supports the spillover mechanism. Finally, the models describing NO x storage on BaO/Al2O3 and on Pt/BaO/Al2O3 were successfully validated with independent experiments.

NO 2 adsorption at a BaO(100) surface is investigated by means of spin polarized GGA density functional theory. A periodic supercell procedure is employed, and two redox reaction channels are mapped out, involving two chemisorbed NO 2 molecules per supercell. The chemisorption is studied in two subsequent steps. The reaction paths are initiated by NO 2 adsorption in the form of a nitrite over a Ba 2+ site. This generates an electron hole among the surrounding surface oxygen atoms. A reaction path branching occurs as the second NO 2 either (a) acts as surface oxidant, forming a surface nitrite-peroxide pair by releasing NO(g), or (b) binds to an Osurf site to form a formal surface nitrate. A redox reaction involving surface nitrite-nitrate interconversion is also addressed. The computed results are employed to interpret experimental observations of surface nitrites, peroxides, NO(g) desorption, and surface Ba(NO 3 ) 2 formation. The understandings are discussed in the context of the NO x storage concept of lean-burn catalysis.

We present a detailed theoretical evaluation for the g j factor of a bound electron in hydrogenlike ions up to Zϭ94. All quantum electrodynamical corrections of order (␣/) are evaluated in detail and various other contributions to the g j factor are computed and listed for 61 Z. A comparison with all existing experiments is carried out and excellent agreement is found. The present uncertainty in our calculations is discussed. It is not possible to improve this precision with only minor effort since two-photon bound-state QED terms are uncalculated up to now.

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