New requirements for catalyst resulting from changes in FTP modes are discussed in this study.
Air conditioner(AC) operation results in dramatic changes in both engine-out and tailpipe emissions, especially NOx emission. Even though NOx emission limits will be loosened by 15% in the proposed regulations, the effect of AC operation is much greater than that. Prolonging the intermediate soak time would result in lower catalyst bed temperatures for both the close-coupled and underfloor positions. This results in a delay in light-off by 15 to 35 seconds. Tightening the A/F control under aggressive driving results in an increase in catalyst bed temperature of approximately 150°C. Also, CO and NOx emission breakthroughs are found in high space velocity(SV) operation.
Addressing this situation requires improvements in catalyst performance: 1)increase in activity, 2)lower light-off, 3)higher thermal stability and 4)increase in reactivity under extreme A/F and flow rate conditions.
Among catalysts with advanced washcoat technologies, Pd-based catalyst systems such as Pd-only and trimetal formulations help to meet these requirements.