Fundamental science on oxygen storage capacity of cerium complex oxides for advanced on-board diagnostics (2) Quantitative observation of oxygen released from cerium complex oxides

In recent years, increasingly stringent emissions regulations have forced automakers to further improve emission control catalysts and to upgrade on-board diagnostics (OBD). For gasoline-powered vehicles, OBD detects the degradation of the oxygen storage capacity (OSC) of the automotive catalysts over time, but the detection limits are becoming stricter. Therefore, we conducted research to gain a deeper understanding of OSC in catalysts. In general, cerium complex oxides (ceria) releases oxygen from the crystal lattice into the gas phase due to the change in valence in oxidizing and reducing atmospheres, as shown in the following formula. (formula) Ce^(4+) O_2 ⇄〖Ce^(4+)〗_(1-x) 〖Ce^(3+)〗_x O_(2-x/2) + (x/4) O_2 In this study, we directly quantified the amount of oxygen released from the ceria crystal lattice under various reducing gas conditions and temperatures using a micro thermogravimetric analyzer (μ-TG) that can measure as small as 1 μg (1 × 10^-6 g). In addition to ceria, precious metals such as palladium also release oxygen when switching from an oxidizing atmosphere to a reducing atmosphere. In this study, we prepared ceria with various compositions and compared the amount of oxygen released by ceria with different precious metals supported, Pt, Pd, and Rh, as well as ceria without precious metals. In addition, a detailed analysis was conducted on how differences in boundary conditions such as reduction depth (H2 concentration), ambient temperature, and aging (simulated mileage deterioration) affect the amount of OSC in a fluctuating redox atmosphere. The results of this study not only provide guidance for more accurate OBD methods, but also provide fundamental scientific knowledge on catalytic emissions control.