Rational Design of Oxidation Catalysts for Diesel Emission Control 2008-01-0070
Euro IV-V and US 2007-2010 emission control regulations, combined with changing engine-out emission characteristics of advanced diesel combustion systems result in different performance and durability requirements for diesel oxidation catalysts depending upon specific platforms and regulation levels. A rational catalyst design approach has been utilized to develop a series of catalysts with performance, durability, and PGM utilization characteristics to meet different system requirements. Promoted-Pt catalysts with 40 °C lower CO light-off temperatures and improved thermal durability compared to Pt-only formulations have been developed for use in applications with low exhaust temperatures. The promoted-Pt catalysts also provide tunable NO oxidation activity, which is important for NO/NO2 control (SCR) and areas where excessive NO2 emissions are of concern. Results are presented for a Pt/Pd formulation that provides major improvements in thermal durability compared to Pt-only formulations for use in high temperature environments (e.g., active regeneration systems). Data are also presented for Pt/Pd/Au formulations with equal or better performance and durability compared to Pt/Pd formulations. The Pt/Pd/Au systems provide alternative PGM utilization strategies that can act as a buffer from PGM price fluctuations, allowing more stable system cost.