A new NOx storage-reduction electrochemical catalyst has been prepared from a polycrystalline Pt film deposited on 8 mol% Y2O3- stabilized ZrO2 (YSZ) solid electrolyte. BaO has been added onto the Pt film by impregnation method. The NOx storage capacity of Pt-BaO/ YSZ system was investigated at 350℃ and 400℃ under lean conditions. Results have shown that the electrochemical catalyst was effective for NOx storage. When nitric oxides are fully stored, the catalyst potential is high and reaches its maximum. On the other hand, when a part of NO and also NO2 desorb to the gas phase, the catalyst potential remarkably drops and finally stabilizes when no more NOx storage occurs but only the reaction of NO oxidation into NO2. Furthermore, the investigation has clearly demonstrated that the catalyst potential variation versus temperature or chemical composition is an effective indicator for in situ following the NOx storage-reduction process, i.e. the storage as well as the regeneration phase. The catalyst potential variations during NOx storage process was explained in terms of oxygen coverage modifications on the Pt.

The complex oxide Ba–Fe–O catalysts were prepared by sol–gel method. The XRD, DTA, NO-TPD, XPS and NSC measurements were used to characterize the structures, NOx storage property and sulfur resistance ability. It is concluded that when coadsorption of NO and O2 at 400 C, the sample calcined at 750℃ possesses high NOx storage capacity and sulfur resistance. The perovskite type BaFeO3 and BaFeO3-x phases are the active centers in the catalyst for NOx storage.

The NOx storage catalyst Pt/BaAl2O4–Al2O3 was prepared by a coprecipitation–impregnation method. For fresh sample, the barium mainly exists as the BaAl2O4 phase except for some BaCO3 phase. The BaAl2O4 phase is the primary NOx storage phase of the sample. EXAFS and TPD were used for investigating the mechanism of NOx storage. It is found that two kinds of Pt sites are likely to operate. Site 1 is responsible for NO chemisorption and site 2 for oxidizing NO to nitrates and nitrites. When NO adsorbs on the sample below 200℃, it mainly chemisorbs in the form of molecular states. Such adsorption results in an increase of the coordination magnitude of Pt–O, and a decrease of that of Pt–Pt and Pt–Cl. The coordination distance of Pt–Pt, Pt–Cl and Pt–O also increases. When the adsorption occurs above 200℃, NO can be easily oxidized by O2, and stored as nitrites or nitrates at the basic BaAl2O4. Site 2 is regenerated quickly. A high adsorption temperature is favorable for nitrate formation.

This study deals with the relationship between open-circuit potential and catalytic activity of the system Pt/YSZ. Temperature-programmed desorption (TPD) of oxygen was carried out in order to investigate the link between the oxygen coverage and the potential. Then, catalytic activity in parallel with the potential value was measured between 200℃ and 500℃ for NO oxidation, C3H8 combustion, C3H6 combustion and the selective catalytic reduction (SCR) of NO by C3H6 in the presence of oxygen. It was found that potential measurement can give precious information on the competitive adsorption between oxygen and other reactants. Finally, it seems to be also a good way to anticipate the NEMCA behavior for reactions, which involve oxygen.

Aseries of Pt/BaAl2O4-Al2O3 NOx storage catalysts were prepared using the coprecipitation-impregnation method. XRD, XANES and EXAFS were used to characterize the microstructure of barium and platinum species in the samples. Barium exists in the forms of BaAl2O4 and BaCO3 crystallites. With the decreasing of calcination-temperature and barium content, the dispersion of BaAl2O4 phases becomes higher in the samples. In comparison with platinum standard compounds, the magnitude of the Pt-Pt coordination is significantly decreased, and the coordination distance is also shortened by about 0.01 nm. Platinum mainly exists as small atomic clusters, which possess a high dispersion, while some Pt (+4) species still present in the samples. A high dispersion of platinum and barium can greatly enhance the catalyst to store NOx.