Promotional Effect of La in the Three-Way Catalysis of La-Loaded Al 2 O 3 -Supported Pd Catalysts (Pd/La/Al 2 O 3 )

La-loaded Al 2 O 3 (La/Al 2 O 3 ) is a practical support for three-way catalysis (TWC) reactions. Although it has been reported that the addition of La to Al 2 O 3 results in improved thermal stability to retain high specific surface areas, its effect on the catalytic reduction of NO x (DeNO x ) has not been studied systematically. Herein, we describe the role of La in La/Al 2 O 3 -supported Pd catalysts (Pd/La/Al 2 O 3 ) for TWC reactions. For that purpose, we employed various in situ spectroscopic studies, including infrared (IR), X-ray absorption fine structure (XAFS), and near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS) in combination with density functional theory (DFT) calculations. The obtained results revealed that Pd 0 species supported on La/Al 2 O 3 are more electron-deficient compared to those on pristine Al 2 O 3 without La(Pd/Al 2 O 3 ). Kinetic studies using powdered catalysts revealed that the addition of La suppresses the poisoning effect by CO during the DeNO x reactions. In addition to the catalytic tests with powdered catalysts, monolithic honeycomb forms of the catalysts were prepared and employed for TWC reactions, which showed that Pd/La/Al 2 O 3 exhibits higher DeNO x activity than Pd/Al 2 O 3 . In this study, we also reexamined the effective loading amount of La, which has traditionally been ∼3–5 wt % of La for TWC processes in order to retain the high specific surface area of the La/Al 2 O 3 supports. Our investigations showed that an increased La loading (15 wt %) is even more effective for the DeNO x reactions tested in this study due to the higher reactivity toward NO and the greater suppression of the poisoning effect of CO. The developed catalyst Pd/La(15)/Al 2 O 3 has also been tested in a commercial vehicle and has been evaluated on a practical driving mode test cycle (LA-4; city cycle of U.S. Federal and California), where it showed a better catalytic performance than the conventionally used Pd/La(3–5)/Al 2 O 3 catalysts. Our study suggests that the loading amount of La in Pd/La/Al 2 O 3 catalysts needs to be adjusted depending on the application systems, considering not only the support stability (surface areas) but also the promotional effect in the TWC process.