Monolithic Diesel Particulate Filters (DPF) Substrate Coated with CeO ₂ -MnO _x Nanorods Catalysts for Soot Oxidation

Noble metal based Diesel Particulate Filters (DPF) are efficient aftertreatment devices to reduce the PM emissions of diesel engine at present. Because of the high cost of noble metal, it is necessary to develop base metal soot combustion catalyst.

In this work, CeO₂-MnO_x nanoparticles and nanorods catalysts were prepared by coprecipitation method using different precipitants. The crystal morphology of CeO₂-MnO_x nanomaterials was identified by a scanning electron microscope. The nitrogen physisorption and hydrogen temperature-programmed reduction results suggest that CeO₂-MnO_x nanorods have smaller specific surface area and greater redox capacity than CeO₂-MnO_x nanoparticles. The temperature programmed oxidation (TPO) tests were performed to evaluate the catalytic activity of the catalysts for soot oxidation. Results show that the CeO₂-MnO_x nanorods catalyst exhibit higher soot oxidation activity than CeO₂-MnO_x nanoparticles.

Afterwards, the prepared CeO₂-MnO_x materials were loaded on wall-flow Diesel Particulate Filters (DPF) substrates using a proprietary preparation method. The determination of Balanced Point Temperature (BPT) which is representative of the DPF regeneration equilibrium temperature was carried out on a diesel-powered engine for the CeO₂-MnO_x or Pt based catalysts. The results have shown that the BPT of CeO₂-MnO_x nanorods based DPF and Pt based DPF is ∼ 264 °C and 267 °C respectively, which is substantially lower than ∼ 309 °C of the CeO₂-MnO_x nanoparticles based DPF. Then the three DPF catalysts were aged at 750 °C for 20 h on a combustor. The results indicate that DPF-CeO₂-MnO_x (NR)-Aged has the best soot oxidation performance among the three aged DPF catalysts. Overall the low-cost CeO₂-MnO_x nanorods based catalyst we prepared is superior to Pt based catalysts on soot oxidation.