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 IR, XAFS, and near-ambient-pressure XPS (NAP-XPS), in combination with 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 been evaluated on a practical driving mode test cycle (LA-4; city cycle of US 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.