PURPOSE: To efficiently remove nitrogen oxides in exhaust gas containing oxygen and sulfur oxide in a theoretical reaction amt. or more by combining a first catalyst obtained by supporting a silver component on alumina composite inorg. oxide containing a specific amt. of inorg. oxide with a second catalyst obtained by supporting a component such as W or the like on a porous inorg. oxide.
CONSTITUTION: A first catalyst is obtained by supporting 0.2-15wt.% of silver and/or a silver compd. or a mixture of them on alumina composite oxide containing 50wt.% or less of the oxides of silica, titania and the like other than alumina and a second catalyst is obtained by supporting 0.5-30wt.% of W, V or the like being an active seed on titania alone or titania composite oxide containing oxide such as alumina. When both of them are combined, ammonia is formed on the first catalyst as a reaction byproduct of an oxygen- containing org. compd., oxygen and nitrogen oxides and is used as a reducing agent to reduce and purify nitrogen oxides by the W/V type catalyst.
SAITOU MIKA
YOSHIDA KIYOHIDE
