Effect of Ba/Ce Ratio on the Structure and Performance of Pt-Based Catalysts: Correlation Between Physicochemical Properties and NOx Storage–Reduction Activity

The continuous tightening of emission regulations and the escalating costs of palladium (Pd) and rhodium (Rh) have renewed interest in platinum (Pt)-based three-way catalysts (TWCs) as cost-effective alternatives for gasoline aftertreatment. However, despite extensive studies on Pt/CeO₂ and Pt/Ba-based formulations, the cooperative roles of Ba and Ce and, in particular, the fundamental influence of the Ba/Ce ratio on oxygen mobility, NO_x storage behavior, and Pt–support interactions remain poorly understood. In this work, we address this gap by systematically tuning the Ba/Ce molar ratio in a series of Pt–Ba–Ce/Al₂O₃ catalysts prepared from Ba(CH₃COO)₂ and CeO₂ precursors, and evaluating their structure–function relationships in both fresh and hydrothermally aged states. Through comprehensive characterization (N₂ physisorption, XRD, XPS, H₂-TPR, NO_x-TPD, SEM, CO pulse adsorption, and dynamic light-off testing), we establish previously unrecognized correlations between Ba/Ce ratio–dependent structural evolution and TWC performance. The results reveal that the Ba/Ce ratio exerts a decisive control over catalyst textural properties, Pt dispersion, and interfacial Pt–CeO₂ oxygen species. Low Ba/Ce ratios uniquely promote Pt–Ce interfacial oxygen and O₂ spillover—providing a new mechanistic basis for enhanced low-temperature oxidation and reduction reactions—while higher Ba loading selectively drives BaCO₃ formation and boosts NO_x storage capacity. A clear volcano-type dependence of NO_x storage on the Ba/Ce ratio is demonstrated for the first time. Hydrothermal aging at 850 °C induces PtO_x decomposition, BaCO₃–Al₂O₃ solid-state reactions forming inactive BaAl₂O₄, and Pt sintering, collectively suppressing Pt–Ce interactions and reducing TWC activity. Importantly, an optimized Ba/Ce ratio is shown to mitigate these degradation pathways, offering a new design principle for thermally durable Pt-based TWCs. Overall, this study provides new mechanistic insight into Ba–Ce cooperative effects, establishes the Ba/Ce ratio as a critical and previously overlooked parameter governing Pt–support interactions and NO_x storage, and presents a rational strategy for designing cost-effective, hydrothermally robust Pt-based alternatives to Pd/Rh commercial TWCs.