To support a noble metal easily up to the inside of a coating layer and to make the increase of the NOx storage quantity at the time of a lean state and the high efficient reduction and purification of the storage NOx by a short rich spike time compatible by diffusing a reaction gas in a gas phase up to the inside of the coating layer to increase the reaction probability.
The coating layer, in which the pore volume of fine pore having 0.1-20 μm pore diameter occupies ≥50% of the pore volume of fine pore having ≤50 μm pore diameter and the pore volume of fin pore having 0.5-10 μm pore diameter occupies ≥20% of the pore volume of fine pore having ≤50 μm pore diameter, is formed. The coating layer has the pore diameter 10-2000 times of that of the conventional coating layer, in which the fine pore having 0.01 μm pore diameter occupies the majority, and the rate of diffusing gas into the fine pore is 10-2000 times of that of the conventional coating layer. Since the noble metal is supported up to the inside of the coating layer along the fine pore, the grain growth of the noble metal is suppressed and the utilization efficiency of the NOx storage material in the inside of the coating layer is increased.
MATSUNAGA SHINICHI
TSUJI RYUSUKE
SUDA AKIHIKO
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