US 5,670,444 A · Exhaust gas cleaner and method for cleaning same

Abstract

Nitrogen oxides are efficiently removed from an exhaust gas containing nitrogen oxides and an excess amount of oxygen, by (i) disposing an exhaust gas cleaner in a flow path of the exhaust gas, the exhaust gas cleaner comprising a first catalyst comprising 0.2-15 weight % (on a metal basis) of at least one silver salt selected from the group consisting of silver halides, silver sulfate and silver phosphate supported on a porous inorganic oxide on an inlet side and a second catalyst comprising (a) 0.2-15 weight % (on a metal basis) of at least one silver salt selected from the group consisting of silver halides, silver sulfate and silver phosphate and (b) up to 2 weight % (on a metal basis) of copper or copper oxide supported on a porous inorganic oxide on an outlet side; (ii) introducing at least one reducing agent selected from hydrocarbons and oxygen-containing organic compounds into the exhaust gas on an upstream side of the exhaust gas cleaner; and (iii) bringing the exhaust gas into contact with the exhaust gas cleaner at a temperature of 200.degree.-600.degree. C.

Claims17

Dependent claims

An exhaust gas cleaner for removing nitrogen oxides from an exhaust gas containing nitrogen oxides and oxygen in an amount larger than its stoichiometric amount relative to unburned components in said exhaust gas, which consists essentially of

a first catalyst on an inlet side of said exhaust gas cleaner and a second catalyst on an outlet side of said exhaust gas cleaner,
said first catalyst consisting essentially of 0.2-15 weight % (on a metal basis) of at least one silver salt supported on a porous inorganic oxide, and
said second catalyst consisting essentially of (a) 0.2-15 weight % (on a metal basis) of at least one silver salt and (b) up to 2 weight % (on a metal basis) of copper or copper oxide supported on a porous inorganic oxide,
said silver salt for each catalyst being selected from the group consisting of silver halides silver sulfate and silver phosphate.

1 more element

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

first, second and third catalysts in this order from an inlet side to an outlet side of said exhaust gas cleaner,
said first catalyst consisting essentially of 0.2-15 weight % (on a metal basis) of at least one silver salt supported on a porous inorganic oxide,
said second catalyst consisting essentially of (a) 0.2-15 weight % (on a metal basis) of at least one silver salt and (b) up to 2 weight % (on a metal basis) of copper or copper oxide supported on a porous inorganic oxide, and
said third catalyst consisting essentially of up to 2 weight % (on a metal basis) of at least one element selected from the group consisting of Pt, Pd, Ru, Rh, Ir and Au supported on a porous inorganic oxide,
said silver salt for each catalyst being selected from the group consisting of silver halides, silver sulfate and silver phosphate.

2 more elements

Dependencies are inferred from the claim text.

Exhaust gas cleaner and method for cleaning same

Life of this patent

Exhaust gas cleaner and method for cleaning same

Life of this patent

Abstract

Claims17