| abstract |
An exhaust gas cleaner for removing nitrogen oxides by reduction from an exhaust gas containing nitrogen oxides, sulfur oxides, moisture, unburned or partially burned components and oxygen, a content of oxygen in the exhaust gas being larger than a stoichiometric amount required for completely oxidizing or burning the unburned or partially burned components, wherein the exhaust gas cleaner consists essentially of a first catalyst consisting essentially of a first porous inorganic oxide carrying at least one silver component, and at least one transition metal component selected from the group consisting of copper, iron, cobalt, nickel and compounds thereof; and a second catalyst selected from the group consisting of (a) a catalyst consisting essentially of a porous titania, (b) a catalyst consisting essentially of a second porous inorganic oxide carrying a titanium component, (c) a catalyst consisting essentially of the second porous inorganic oxide carrying at least one first component selected from the group consisting of copper, nickel, silver, cobalt and compounds thereof, at least one second component selected from the group consisting of titanium, zirconium and compounds thereof, and at least one third component selected from the group consisting of alkali metal elements and rare earth elements, and (d) a catalyst consisting essentially of the second porous inorganic oxide carrying a titanium component and at least one noble metal component selected from the group consisting of platinum, palladium, ruthenium, rhodium, iridium and gold. |