| 摘要 |
PROBLEM TO BE SOLVED: To maintain a high NOx purification rate in a practical temp. range in a lean atmosphere even after the catalyst is used at high temp. for a long time by trapping Pt in an apatite crystal structure of an apatite compd. expressed by a specified formula. SOLUTION: The apatite compd. is expressed by the formula, Ca10-z(HPO4)z(PO4)6-zX2-znH2O (wherein (z) ranges 0 to 1, (n) ranges 0 to 1 and X represents OH or halogen elements), and for example. hydroxyapatite is used. In the apatite compd., Pt is trapped in the apatite crystal structure to prepare a catalyst having selective reducing activity of nitrogen oxides. The Pt element added is trapped by exchanging with Ca ions which constitute the apatite or by possessing lattice points of Ca defects. Thereby, the Pt added strongly interacts with the apatite and gives the NOx purification activity in a lean atmosphere. |
