CATALYST FOR NITROGEN OXIDE DECOMPOSITION AND METHOD OF CLEANING NITROGEN OXIDE-CONTAINING EXHAUST GAS.

摘要

A catalyst for decomposing N oxides (NOx) comprises a crystalline silicate containing Cu. The crystalline silicate (1) is represented, in the dehydrate state, by general formula (I) which specifies the mole ratio of the oxides, ( 1.0(+/-)0.4)R2O.a M2O3.b.Al2O3!y SiO2 (I) where R is an alkaline metal ion and/or H atom; M is an ion of an element of gp. VIII of the periodic table, or of Ti, Cr, Nb, or Sb; a+b=1, a greater than 0, b greater than 0, y greater than 12. M is pref. a combination of Fe and Cr or of Fe and Co. Cleaning of an exhaust gas containing NOx, CO and hydrocarbons is carried out by bringing the gas and catalyst into contact at 300 - 800 deg.C. The crystalline silicate (1) can not be obtained naturally, but is synthesised as in the following examples: (i) A mixt. of a substance contg. silica, a substance contg. oxides of some elements of gp. VIII of the periodic table, or of Ti, Vn, Cr, Nb or Sb, substances contg. l2O3, alkaline substances, water and organic cpds. contg. nitrogen, is heated to produce the crystalline silicate. (ii) A reaction mixt. in which the following mole ratios pertain: SiO2/(M2O3 + Al2O3) = 12 - 3000 (pref. 20 - 200), OH/SiO2 = 0 - 1.0 (pref. 0.2 - 0.8), H2SiO2 = 2 - 1000 (pref. 0 - 200), organic cpds/(M2O3 + Al2O3)=5 - 50, is heated at 30 - 300 deg.C (pref. 130 - 200 deg.C) for 0.5 - 14 days (pref. 1 - 10 days). A crystalline silicate containing Cu (120%) has the following mole ratios of oxides: (H. Na)2 O (0.1 Fe2O3 0.9 Al2O3) 80 SiO2. It achieves an NO removal of 85 %, a C3H6 removal of 95 % and a CO removal of 97 %.