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

Abstract

<div class="section abstract"><div class="htmlview paragraph">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 [<span class="xref">1</span>, <span class="xref">2</span>]. 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 CeO<sub>2</sub> calcined at 1000 °C (cal-CeO<sub>2</sub>) in Pt-based TWCs was one of the most effective approaches for improving the catalytic activity without increasing the amount of Rh and Pd [<span class="xref">3</span>]. The effect of cal-CeO<sub>2</sub> 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-CeO<sub>2</sub> due to high temperature calcination. In this study, we demonstrated that the low SSA of cal-CeO<sub>2</sub> can be easily improved by adding Al<sub>2</sub>O<sub>3</sub>. The SSA of Al<sub>2</sub>O<sub>3</sub>-modified CeO<sub>2</sub> calcined at 1000 °C (Al<sub>2</sub>O<sub>3</sub>-CeO<sub>2</sub>) was 45% higher than that of cal-CeO<sub>2</sub> owing to the inhibition of CeO<sub>2</sub> sintering by Al<sub>2</sub>O<sub>3</sub>. 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-CeO<sub>2</sub>. To determine the effects on the catalytic performance, vehicle evaluations were performed after aging treatment by gasoline-powered engine. Al<sub>2</sub>O<sub>3</sub>-CeO<sub>2</sub> 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 Al<sub>2</sub>O<sub>3</sub>-CeO<sub>2</sub> to Rh/Pt double-layered TWCs is clearly more effective for suppressing exhaust gas emissions than the addition of cal-CeO<sub>2</sub>.</div></div>