Effect of Ba and La Additives to the Pd layer of a Pd:Rh TWC

Paper #:
  • 2017-01-0922

Published:
  • 2017-03-28
Abstract:
New Pd-Rh type CC-TWC (three way catalysts in CC (close-coupled) position) has been developed to improve low-temperature gas activity. In this study Pd top and Rh bottom layered TWC was used, and Ba and La were tested as an additive to Pd, respectively. Alumina was used for Pd support and La or Ba was co-supported to Pd. The catalysts were aged at 950C for 200hrs and CO, HC and NOx performance were evaluated. As a result, Pd-La catalyst showed higher gas performance than Pd-Ba catalyst. The reason and mechanism of this phenomenon were investigated by three points. First one is Pd activation by the additives, second one is Pd particle size by increasing thermal durability of alumina support, and third one is specific NOx adsorption and desorption by the additives. Pd activity seemed to be increased by La addition but details of activation energy analysis and characterization of Pd by XPS, etc. are under investigation. By STEM observation, slightly smaller Pd particle size was observed in Pd-La catalyst compared to Pd-Ba catalyst. NOx adsorption and desorption was evaluated by TPD. Pd-La and Pd-Ba catalysts showed some amount of NOx adsorption, but Pd-La showed desorption at lower temp. (ca. 300C) than Pd-Ba (ca. 500C). Low temp. CO-NOx reaction in Pd-La catalyst might be promoted by the pre-adsorpted NOx. Details of results and mechanism investigation will be reported in the manuscript.
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