Abstract: A series of MnO_x/Ce_0.7Zr_0.2La_0.1O₂-Al₂O₃ supported catalysts with the Ce_0.7Zr_0.2La_0.1O₂:Al₂O₃ mass ratio of 1:1 and different MnO_x loadings were prepared by the incipient wetness method. The catalysts were characterized by X-ray diffraction, low temperature N₂ adsorption-desorption, X-ray photoelectron spectroscopy, O₂ temperature-programmed desorption, and H₂ temperature-programmed reduction. The catalytic performance of these catalysts for the combustion of diesel soot was investigated. It is found that surface-adsorbed active oxygen species and low-temperature reducibility of MnO_x are the determinants of catalytic activity. When the MnO_x loading is 5%, the catalyst activity decreases owing to the loss of active oxygen species, which are necessary for the catalytic combustion. When the MnO_x loading is increased to 10%, the catalyst activity is dramatically increased because of the enhanced reducible manganese species. Interestingly, the optimal values for reducible manganese species and surface-adsorbed oxygen species can be achieved in the catalyst with 20% MnO_x, and so the catalyst exhibits the best catalytic activity, giving a light-off temperature about 179 ^oC lower than that of the non-catalytic soot combustion. With a further addition of MnO_x species up to 30%, its catalytic activity is deteriorated mainly due to the decrease in surface-trapped oxygen species and upper shift of the reduction temperature.

Key words: manganese oxide, loading amount, soot, catalytic combustion, ceria, zirconia, lanthana, alumina