oa Migration of Pt Nanoparticles via Volatile PtO2 during Lean High-Temperature Aging of Diesel Oxidation Catalysts

When Pt containing diesel oxidation catalysts (DOC) are exposed to high temperatures under lean conditions, the Pt nanoparticles form volatile PtO2 on the catalyst surface. The exhaust flow carries the volatile PtO2 to the downstream aftertreatment catalyst, such as the selective catalytic reduction (SCR) catalyst, that is responsible for reducing the NOx emissions, and can negatively impact its performance. Here we investigate the factors such as exposure time, temperature and DOC design characteristics for their impact on the PtO2 migration, by characterizing the amount of Pt deposited on the SCR catalyst at very low levels (< 5ppm), using ICP-OES (Inductively coupled plasma optical emission spectroscopy) fire assay technique. Our results indicate that well-dispersed Pt, not associated with Pd, is most prone to PtO2 migration. We also compare several methods to suppress the PtO2 migration from the DOC, such as sintering of the Pt nanoparticles, stabilizing the Pt nanoparticles via interaction with Pd or covering the Pt nanoparticles with a high surface area capture layer to trap the volatile PtO2.