Catalytic Performance of Ag2O and Ag Doped CeO2 Prepared by Atomic Layer Deposition for Diesel Soot Oxidation

The catalytic behaviour of Ag2O and Ag doped CeO2 thin films, deposited by atomic layer deposition (ALD), was investigated for diesel soot oxidation. The silver oxide was deposited from pulses of the organometallic precursor (hfac)Ag(PMe3) and ozone at 200 degrees C with growth rate of 0.28 A/cycle. Thickness, crystallinity, elemental composition, and morphology of the Ag2O and Ag doped Ce-2 films deposited on Si (100) were characterized by ellipsometry, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and field emission scanning electron microscopy (FESEM), respectively. The catalytic effect on diesel soot combustion of pure Ag2O, CeO2 and Ag doped CeO2 films grown on stainless steel foil supports was measured with oxidation tests. Nominally CeO2:Ag 10:1 doped CeO2 films were most effective and oxidized 100% of soot at 390 degrees C, while the Ag2O films were 100% effective at 410 degrees C. The doped films also showed much higher stability; their performance remained stable after five tests with only a 10% initial reduction in efficiency whereas the performance of the Ag2O films reduced by 50% after the first test. It was concluded that the presence of Ag+ sites on the catalyst is responsible for the high soot oxidation activity.