Lean-burn nox catalyst/nox trap system

A catalyst system, located in the exhaust gas passage of a lean-burn internal combustion engine, useful for converting carbon monoxide, nitrogen oxides, and hydrocarbons present in the exhaust gas, said catalyst system comprising two-components:

• (1) lean-burn nitrogen oxide catalyst being a transition metal selected from the group consisting of copper, chromium, iron, cobalt, nickel, iridium, cadmium, silver, gold, platinum, manganese, and mixtures thereof (i) loaded on a refractory oxide or (ii) exchanged into zeolite, wherein said transition metal exchanged zeolite comprises 20 to 200% based upon the cation content of the zeolite;
• and
• (2) a nitrogen oxide (NOx) trap material which absorbs NOx when the exhaust gas flowing into said trap material is lean and releases the absorbed NOx when the concentration of oxygen in the inflowing exhaust gas is lowered;
• said nitrogen oxide trap material being located downstream of said lean-burn nitrogen oxide catalyst in said exhaust gas passage such that said exhaust gases are exposed to said lean-burn catalyst prior to being exposed to said nitrogen oxide trap material.

A catalyst system, located in the exhaust gas passage of a lean-burn internal combustion engine, useful for converting carbon monoxide, nitrogen oxides, and hydrocarbons present in the exhaust gas, said catalyst system comprising two-components:

• (1) lean-burn nitrogen oxide catalyst;
• and
• (2) a nitrogen oxide (NOx) trap material which absorbs NOx when the exhaust gas flowing into said trap material is lean and releases the absorbed NOx when the concentration of oxygen in the inflowing exhaust gas is lowered;
• wherein said nitrogen oxide trap material comprises (i) at least one precious metal selected from the group consisting of platinum and palladium loaded on a porous support;
• and (ii) at least one alkali metal or alkaline earth metal either (a) loaded on a porous support or (b) present as a bulk oxide thereof, wherein said least one alkali metal or alkaline earth metal is present in an amount of about 2 to 30 weight percent on said porous support;
• said nitrogen oxide trap material being located downstream of said lean-burn nitrogen oxide catalyst in said exhaust gas passage such that said exhaust gases are exposed to said lean-burn catalyst prior to being exposed to said nitrogen oxide trap material.

A catalyst system, located in the exhaust gas passage of a lean-burn internal combustion engine, useful for converting carbon monoxide, nitrogen oxides, and hydrocarbons present in the exhaust gas, said catalyst system comprising two-components:

• (1) lean-burn nitrogen oxide catalyst being a transition metal selected from the group consisting of copper, chromium, iron, cobalt, nickel, iridium, cadmium, silver, gold, platinum, manganese, and mixtures thereof (i) loaded on a refractory oxide or (ii) exchanged into zeolite, wherein said refractory oxide comprises alumina;
• and
• (2) a nitrogen oxide (NOx) trap material which absorbs NOx when the exhaust Gas flowing into said trap material is lean and releases the absorbed NOx when the concentration of oxygen in the inflowing exhaust Gas is lowered;
• said nitrogen oxide tram material being located downstream of said lean-burn nitrogen oxide catalyst in said exhaust gas passage such that said exhaust gases are exposed to said lean-burn catalyst prior to being exposed to said nitrogen oxide trap material.

A catalyst system, located in the exhaust gas passage of a lean-burn internal combustion engine, useful for converting carbon monoxide, nitrogen oxides, and hydrocarbons present in the exhaust gas, said catalyst system comprising two-components:

• (1) lean-burn nitrogen oxide catalyst;
• and
• (2) a nitrogen oxide (NOx) trap material which absorbs NOx when the exhaust gas flowing into said tram material is lean and releases the absorbed NOx when the concentration of oxygen in the inflowing exhaust gas is lowered;
• wherein said nitrogen oxide tram material comprises (i) at least one precious metal selected from the group consisting of platinum and palladium loaded on a porous support;
• and (ii) at least one alkali metal or alkaline earth metal either (a) loaded on a porous support or (b) present as a bulk oxide thereof, wherein said porous support is selected from alumina, zirconia, titania, or silica;
• said nitrogen oxide tram material being located downstream of said lean-burn nitrogen oxide catalyst in said exhaust gas passage such that said exhaust gases are exposed to said lean-burn catalyst prior to being exposed to said nitrogen oxide trap material.

A method for conversion of nitrogen oxides, carbon monoxide and hydrocarbons present in exhaust gases produced by an internal combustion engine operated under lean-burn conditions, which comprises the steps of:

• exposing said exhaust gases to a catalyst system comprising:
• (1) a lean-burn nitrogen oxide catalyst being a transition metal selected from the group consisting of copper, chromium, iron, cobalt, nickel, iridium, cadmium, silver, gold, platinum, manganese, and mixtures thereof (i) loaded on a refractory oxide or (ii) exchanged into zeolite, wherein said transition metal is loaded on said refractory oxide in an amount of about 0.1 to 10 weight percent based on the weight of said refractory oxide;
• and
• (2) a nitrogen oxide (NOx) trap material which absorbs NOx when the exhaust gas flowing into said trap material is lean and releases the absorbed NOx when the concentration of oxygen in the inflowing exhaust gas is lowered;
• such that said exhaust gases are exposed to said lean-burn catalyst prior to being exposed to said nitrogen oxide trap.

A method for conversion of nitrogen oxides, carbon monoxide and hydrocarbons present in exhaust gases produced by an internal combustion engine operated under lean-burn conditions, which comprises the steps of:

• exposing said exhaust gases to a catalyst system comprising:
• (1) lean-burn nitrogen oxide catalyst being a transition metal selected from the group consisting of copper, chromium, iron, cobalt, nickel, iridium, cadmium, silver, gold, platinum, manganese, and mixtures thereof (i) loaded on a refractory oxide or (ii) exchanged into zeolite, wherein said transition metal exchanged zeolite comprises 20 to 200% based upon the cation content of the zeolite;
• and
• (2) a nitrogen oxide (NOx) trap material which absorbs NOx when the exhaust gas flowing into said tram material is lean and releases the absorbed NOx when the concentration of oxygen in the inflowing exhaust gas is lowered;
• said nitrogen oxide trap material being located downstream of said lean-burn nitrogen oxide catalyst in said exhaust gas passage such that said exhaust gases are exposed to said lean-burn catalyst prior to being exposed to said nitrogen oxide trap material.

A method for conversion of nitrogen oxides, carbon monoxide and hydrocarbons present in exhaust gases produced by an internal combustion engine operated under lean-burn conditions, which comprises the steps of:

• exposing said exhaust gases to a catalyst system comprising:
• (1) lean-burn nitrogen oxide catalyst;
• and
• (2) a nitrogen oxide (NOx) trap material which absorbs NOx when the exhaust gas flowing into said trap material is lean and releases the absorbed NOx when the concentration of oxygen in the inflowing exhaust gas is lowered, wherein said nitrogen oxide trap material comprises (i) at least one precious metal selected from the group consisting of platinum and palladium loaded on a porous support;
• and (ii) at least one alkali metal or alkaline earth metal either (a) loaded on a porous support or (b) present as a bulk oxide thereof, wherein said least one alkali metal or alkaline earth metal is present in an amount of about 2 to 30 weight percent on said porous support;
• said nitrogen oxide trap material being located downstream of said lean-burn nitrogen oxide catalyst in said exhaust gas passage such that said exhaust gases are exposed to said lean-burn catalyst prior to being exposed to said nitrogen oxide trap material.

A method for conversion of nitrogen oxides, carbon monoxide and hydrocarbons present in exhaust gases produced by an internal combustion engine operated under lean-burn conditions, which comprises the steps of:

• exposing said exhaust gases to a catalyst system comprising:
• (1) lean-burn nitrogen oxide catalyst being a transition metal selected from the group consisting of copper, chromium, iron, cobalt, nickel, iridium, cadmium, silver, gold, platinum, manganese, and mixtures thereof (i) loaded on a refractory oxide or (ii) exchanged into zeolite, wherein said refractory oxide comprises alumina;
• and
• (2) a nitrogen oxide (NOx) trap material which absorbs NOx when the exhaust gas flowing into said trap material is lean and releases the absorbed NOx when the concentration of oxygen in the inflowing exhaust gas is lowered;
• said nitrogen oxide trap material being located downstream of said lean-burn nitrogen oxide catalyst in said exhaust gas passage such that said exhaust gases are exposed to said lean-burn catalyst prior to being exposed to said nitrogen oxide trap material.

A method for conversion of nitrogen oxides, carbon monoxide and hydrocarbons present in exhaust gases produced by an internal combustion engine operated under lean-burn conditions, which comprises the steps of:

• exposing said exhaust gases to a catalyst system comprising:
• (1) lean-burn nitrogen oxide catalyst;
• and
• (2) a nitrogen oxide (NOx) trap material which absorbs NOx when the exhaust gas flowing into said trap material is lean and releases the absorbed NOx when the concentration of oxygen in the inflowing exhaust gas is lowered, wherein said nitrogen oxide trap material comprises (i) at least one precious metal selected from the group consisting of platinum and palladium loaded on a porous support;
• and (ii) at least one alkali metal or alkaline earth metal either (a) loaded on a porous support or (b) present as a bulk oxide thereof, wherein said porous support is selected from alumina, zirconia, titania, or silica;
• said nitrogen oxide trap material being located downstream of said lean-burn nitrogen oxide catalyst in said exhaust gas passage such that said exhaust gases are exposed to said lean-burn catalyst prior to being exposed to said nitrogen oxide trap material.