Challenges and Opportunities for Platinum in the Modern Three-Way Catalyst : Flexibility and performance in gasoline emissions control

Abstract

Gasoline vehicles have generally relied upon a combination of palladium and rhodium for more than 25 years to facilitate the required oxidative and reductive reactions of carbon monoxide (CO), hydrocarbons (HCs), and nitrogen oxides (NOx). Recently, steady increases in the price of palladium relative to platinum have fuelled demand to reincorporate platinum into three-way catalysts (TWCs). However, the fundamental properties of platinum, including susceptibility toward sintering and inhibition under typical gasoline operating conditions, present significant challenges. This article presents an overview of the origins for these challenges, as well as select strategies for maximising platinum’s contribution to modern-day TWCs. Optimisation of ceria-zirconia supports is one route by which platinum’s performance can be significantly improved through tuning of the ceria-to-zirconia ratio. Additionally, alloying platinum with a secondary platinum group metal (pgm), such as rhodium, leverages complimentary properties of both metals, imparting stability and overall activity enhancements. Such routes not only enable pgm flexibility, but also provide opportunities to further improve TWC performance.