Mixed Metal Oxides for NO2 Generation to Enhance SCRoF

Robert  Henderson, Southwest Research Institute

As emissions regulations become more stringent for mobile applications, aftertreatment systems become larger and increasingly complex. In particular, oxides of nitrogen (NOX) and particulate matter (PM) have been controlled by using two separate systems, selective catalytic reduction (SCR) and the catalyze diesel particulate filter (CDPF), or the functionality has been combined into a single device producing the SCR on filter (SCRoF).  The SCRoF forgoes beneficial NO2 production present in the CDPF to avoid NH3 oxidation which occurs when using platinum group metals (PGM) for oxidation. In this study mixed-metal oxides are shown to oxidize NO to NO2 without appreciable NH3 oxidation. Ce was co-precipitated with Zr, La and Pr at different ratios and doped with Cu or Fe. 0.5% Fe on Ce0.8Zr0.2OX and Ce0.75Pr0.25OX oxidized 30% of incoming NO at 350 °C while oxidizing < 5% of the NH3 in a synthetic exhaust environment, demonstrating possible formulations that allow enhanced NO2 derived soot oxidation compatible with an SCRoF.