ABSTRACT
Owing to strengthened regulations toward vehicle emissions, the use of diesel particulate filter technology to reduce particulate matter emissions has attracted significant attention. To achieve low temperature oxidation of particulate matter, numerous studies on Ag/CeO2 catalysts for soot oxidation have been reported. Herein, Ag/La-CeO2 catalysts with different La contents are synthesized and compared to analyze the effect of La. Hydrogen temperature programmed reduction analysis confirms that the reducibility increases with an increase in the La content in La-CeO2. X-ray photoelectron spectroscopy and Raman analysis confirm an increase of oxygen vacancies with La doping. Accordingly, the soot oxidation performances estimated by temperature programmed oxidation experiments increase with La doping. However, the catalytic activity of Ag/La-CeO2 exhibits a volcano trend. When an appropriate amount of La is incorporated in Ag/CeO2, peroxide generation and reducibility improve, thereby enhancing the soot oxidation performance. Conversely, the catalytic activities gradually decrease with excess La-doping. Scanning transmission electron microscopy analysis and density functional theory calculations confirm that excess amounts of La induce the sintering of Ag particles, which lead to the degradation of peroxide generation and reducibility of the catalysts. Consequently, an optimal amount of La incorporation on Ag/La-CeO2 results in the best soot oxidation performance.
ABSTRACT
To evaluate the usability of TiO2 support for silver in soot oxidation, Ag/TiO2 and Ag/CeO2 catalysts were prepared and soot oxidation experiment was performed. The catalytic activity of silver was more enhanced on P25 and rutile than on anatase and CeO2 in tight contact, as evidenced from comparing the activities of supports and silver impregnated catalysts. The reasons for the difference in active metal enhancement were elucidated by various characterization methods (TEM, H2 TPR, and XPS), and it is verified that it resulted not from dispersion of silver but from oxidation ability. On the other hand, Ag/P25 showed poor activity in loose contact because of low contact between silver and soot. To improve the loose contact activity of the Ag/P25 catalyst, CeO2 was introduced for active oxygen delivery. The synthesized CeO2-Ag/P25 catalyst showed enhanced loose contact activity when compared with Ag/P25 and Ag/CeO2 due to synergistic effects from the active oxygen supply ability of silver on P25 and the oxygen transfer ability of loaded CeO2. Thermal stability of the catalyst was identified by recycling test to 800â, and the maintained T20 and T50 demonstrated its durability for practical use in automobile exhaust removal.
