Removing harmful pollutants in automotive exhaust has been a focus of the automotive industry over the last several decades. In particular, the emissions regulations for fuel-efficient diesel engines that were implemented in 2007 and 2010 have resulted in a new generation of emissions control technologies. These catalysts usually reach 90% conversion of pollutants between 200 °C and 350 °C, but below these temperatures, the catalysts are relatively inactive. Thus, as emissions regulations become more stringent and improved fuel efficiency is required, resulting in lower exhaust temperatures, the need for increased emissions control activity at low temperatures is necessary. This project focuses on developing new catalytic materials and approaches that reduce emissions at lower temperatures. We have recently reported that Pd dispersed on ZrO2-coated SiO2 supports are excellent CO oxidation catalysts with good hydrothermal stability and sulfur tolerance. In this work, we extended this approach through advanced metal-oxide support modifications combined with HC and NO trap materials. The oxidation catalyst supports were prepared using a core@shell approach with a synthesized SiO2 core sphere and a ZrO2 shell (SiO2@ZrO2). The catalysts were dispersed on these supports by impregnating Pd or Pt with the targeted location on the ZrO2 shell using strong electrostatic adsorption techniques. Catalytic performance was measured under guidelines relevant to diesel combustion provided by industry. The performance was evaluated in degreened and hydrothermally aged states up to 900°C. Additionally, ion-exchanged Pd/zeolite was employed as a HC/NO trap in front of or as a physical mixture with the oxidation catalyst. The impact of hydrothermal aging and sulfur was also evaluated. Modifying the support as described above led to significant gains in the low temperature activity of the oxidation catalysts. The best overall reactivity was observed when combining the Pt/SiO2@ZrO2 and Pd/SiO2@ZrO2 catalysts in a physical mixture. In a follow-up study, a DOC consisting of a physical mixture of high-performing Pt/ZrO2@SiO2 and Pd/ZrO2@SiO2 was placed after a bed of Pd/ZSM-5 trapping material and in another physical mixture with all three components. The trap/DOC system showed significantly reduced emissions below 200C, including direct conversion of NO.

Catalytic approaches to reducing automotive exhaust emissions at low temperatures

2019 Spring National Meeting

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