| abstract |
β as a crystalline silicate having the iron in the skeleton structure, SiO 2 / Fe 2 O 3 molar ratio is 20 to 300, and more than 80% of the contained iron isolated iron ions (Fe 3 +) of the first nitrogen oxide purification catalyst, and A crystalline silicate having iron in the β-skeletal structure, wherein the second nitrogen oxide purification catalyst has a molar ratio of SiO 2 / Fe 2 O 3 of 20 to 300 and a log (SiO 2 / Al 2 O 3 ) of 2 or more. In these catalysts, it is preferable that most of the contained iron is lone iron ions, and at least some of the lone iron ions have a symmetric tetrahedral structure. These catalysts have high hydrothermal durability, and in the presence thereof, the nitrogen oxides can be efficiently purified in a wide temperature range from low to high temperatures by reacting nitrogen oxides with reducing agents such as ammonia, urea, and organic amines. |