Promotional effect of Mn on Pt/Al2O3 catalysts in HC, CO, and NOx oxidation for controlling diesel emission

Emissions from diesel engines, including hydrocarbons (HCs), carbon monoxide (CO), and nitric oxide (NO), cause serious environmental and human health problems. Diesel oxidation catalysts (DOCs) are drawing attention for their ability to eliminate such harmful exhausts effectively. Here, we report significantly improved activities of Pt-based catalysts, which are widely used as DOCs, in the oxidation of HC, CO, and NOx after Mn addition. Mn-doped Pt/Al2O3 showed significantly lower light-off temperatures in the oxidation of HC, CO, and NOx than those of the unmodified Pt/Al2O3 catalysts, by as much as 30 °C. The size of Pt particles was reduced from 71 nm to 33 nm after Mn addition, as evidenced by X-ray diffraction analysis and transmittance electron microscopy. Additionally, the interaction between CO and Pt on Mn-doped catalysts was weakened, and the CO adsorbed on Pt was readily oxidized even at room temperature, as confirmed by diffuse reflectance infrared Fourier-transform spectroscopy and CO temperature-programmed desorption experiments. The results of this study provide insights towards the improvement of the activity of Pt-based DOCs used for HC, CO, and NOx oxidation, by enhancing the fundamental understanding of the Pt nature promoted with Mn.