Exhaust gas cleaner and method for cleaning exhaust gas

An exhaust gas cleaner for removing nitrogen oxides by reduction and unburned components of carbon monoxide and hydrocarbons by oxidation from an exhaust gas containing nitrogen oxides and oxygen in an amount larger than its stoichiometric amount relative to said unburned components in said exhaust gas, wherein said exhaust gas cleaner consists essentially of

• a first catalyst disposed on an inlet side of said exhaust gas cleaner and consisting essentially of a first porous inorganic oxide supporting 0.2-15 weight % of an Ag component, 0.01-10 weight % of a base metal component and 1 weight % or less of a platinum-group metal component and
• optionally a second catalyst disposed on an outlet side of said exhaust gas cleaner and consisting essentially of a second porous inorganic oxide supporting 5 weight % or less of a platinum-group metal component alone or in combination with 10 weight % or less of a base metal component,
• said weight percentages being expressed by metal basis, said Ag component consisting essentially of at least one of Ag and compounds thereof, said platinum-group metal component of said first and second catalysts consisting essentially of at least one of Pt, Pd, Ru, Rh and Ir, and said base metal component of said first and second catalysts consisting essentially of at least one of W, V, Mn, Mo, Nb and Ta.