IRIDIUM CATALYST FOR PURIFYING NITROGEN OXIDES IN EXHAUST SYSTEMS

摘要

A catalyst for clarification of nitrogen oxides which comprises (A) a catalytically active substance comprising (A-a) iridium and (A-b) at least one element selected from the group consisting of the elements belonging to Groups IIIB and IVB of the periodic table and, formed thereon, (B) a refractory inorganic compound covering the substance; or a catalyst for clarification of nitrogen oxides which comprises (A) a catalytically active substance comprising (A-a) iridium and (A-b) at least one element selected from the group consisting of the elements belonging to Groups IIIB and IVB of the periodic table and (C) at least one element selected from the group consisting of the elements belonging to Grou p IIIA of the periodic table. The catalyst is capable of decomposing NO x in an exhaust gas with good efficiency in an oxygen excess atmosphere, and is excellent in thermal resistance and in durability in a high temperature region, under a high temperature oxydizi ng atmosphere, and under the co-presence of moisture and SO x, and further exhibits good catalytic activity in a wide temperature region.