Effective Utilization of Pt Catalyst in Three-Way Catalytic System by Employing Calcined Ceria with Alumina

To satisfy the stringent regulations for exhaust gas emissions from gasoline-powered vehicles, large amounts of Rh and Pd have often been employed in three-way catalysts (TWCs) as the main active components. On the other hand, Pt-based TWCs are not often used in gasoline vehicles because Pt is readily sintered by its exhaust gases at approximately 1000 °C [1, 2]. In general, Pt-based TWCs must be located away from large thermal loads to maintain the active sites for gas purification. Based on this background, we previously reported that employing a small amount of CeO₂ calcined at 1000 °C (cal-CeO₂) in Pt-based TWCs was one of the most effective approaches for improving the catalytic activity without increasing the amount of Rh and Pd [3]. The effect of cal-CeO₂ was attributed to the higher redox performance and Pt dispersion derived from the strong interactions between Ce and Pt. Therefore, the resulting Pt-based TWCs exhibited high catalytic performance, despite the low specific surface area (SSA) of cal-CeO₂ due to high temperature calcination. In this study, we demonstrated that the low SSA of cal-CeO₂ can be easily improved by adding Al₂O₃. The SSA of Al₂O₃-modified CeO₂ calcined at 1000 °C (Al₂O₃-CeO₂) was 45% higher than that of cal-CeO₂ owing to the inhibition of CeO₂ sintering by Al₂O₃. In addition, the interactions with Pt were significantly improved, leading to higher redox performance and Pt dispersion compared to the corresponding Pt catalyst supported on cal-CeO₂. To determine the effects on the catalytic performance, vehicle evaluations were performed after aging treatment by gasoline-powered engine. Al₂O₃-CeO₂ was employed in a Rh/Pt double-layered TWC placed at the rear bed in a close-coupled system. The results of the FTP mode test cycles on a dynamometer indicate that the addition of Al₂O₃-CeO₂ to Rh/Pt double-layered TWCs is clearly more effective for suppressing exhaust gas emissions than the addition of cal-CeO₂.