Study on New Characteristic CeO ₂ -ZrO ₂ Based Material for Advanced TWC 2009-01-1078

Performance improvements resulting from the adoption of a new type CeO₂-ZrO₂-based material were found using a two-brick three way catalyst (TWC) system. Compared to a conventional CeO₂-ZrO₂-based material, this new type CeO₂-ZrO₂ has both a larger oxygen storage capacity and a slower oxygen release rate. Such characteristics were confirmed by fundamental studies. Vehicle evaluations showed this material was most effective for hot NO_x control when used in the rear catalyst, especially after fuel cuts. The improvement in NOx was thought to be caused by the increased oxygen storage capacity (OSC), which effectively stored excess oxygen during fuel cuts. As a result, the air-to-fuel ratio (A/F) surrounding the active sites could be kept at stoichiometry even if the engine control shifted to a lean setting.