초록 ▼

The invention is a catalyst system for purifying exhaust gases generated by a lean-burn internal combustion engine, particularly automotive engines. The catalyst system comprises two separate components located in the exhaust gas passage, the first being a lean-burn nitrogen oxide catalyst and the s

The invention is a catalyst system for purifying exhaust gases generated by a lean-burn internal combustion engine, particularly automotive engines. The catalyst system comprises two separate components located in the exhaust gas passage, the first being a lean-burn nitrogen oxide catalyst and the second being a nitrogen oxide trap material, where the lean-burn NOx catalyst is located upstream of the NOx trap material in the exhaust gas passage. Preferably the catalyst comprises a transition metal such as copper, chromium, iron, cobalt, or manganese loaded on a refractory oxide or exchanged into a zeolite. The NOx trap preferably comprises (i) at least one precious metal selected from platinum and palladium loaded on a porous support; and (ii) at least one alkali metal or alkaline earth metal (a) loaded on a porous support or (b) present as an oxide thereof. Optionally the catalyst system may further comprise a three-way catalyst located either between the two-components or after the NO.sub.x trap material.

대표청구항 ▼

[ We claim:] [1.] 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

[ We claim:] [1.] 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 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;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 tram material.