Two-stage catalyst system for lean burn engines
AssigneeFord Motor Company
InventorsSomasundaram Subramanian, Robert J. Kudla, Mohinder S. Chattha
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Abstract
The present invention broadly relates to a catalyst system for promoting oxidation-reduction reactions of the exhaust gases produced by an internal combustion engine wherein the catalyst comprises a two-stage system of a first-stage nitric oxide removal (by reduction) catalyst and a second-stage carbon monoxide and hydrocarbon removal (by oxidation) catalyst. The first-stage catalyst comprises between about 0.1 and 3% by weight tungsten carried on a support material comprising mostly .gamma.-alumina. The second-stage catalyst is an oxidation catalyst such as platinum on alumina.
Claims10
A two-stage catalyst system comprising a first-stage catalyst and a second-stage catalyst for promoting oxidation-reduction reactions of exhaust gases containing nitrogen oxides, carbon monoxide, and hydrocarbons, the system comprising:
- a first-stage catalyst comprising between about 0.1 and 3% by weight tungsten carried on a support material consisting of more than about 50% by weight .gamma.-alumina and, optionally, materials selected from the group consisting of cerium oxide, barium oxide, zirconium oxide, lanthanum oxide, .alpha.-alumina, and titanium oxide;
- and
- a second-stage catalyst comprising noble metal, said first-stage catalyst and said second-stage catalyst being in fluid communication, and
- said exhaust gas being exposed to said second-stage catalyst after being exposed to said first-stage catalyst.
A method of making a two-stage catalyst system comprising a first-stage catalyst and a second-stage catalyst for promoting oxidation-reduction reactions of exhaust gases containing nitrogen oxides, carbon monoxide, and hydrocarbons, the first-stage catalyst comprising between about 0.1 and 3% by weight tungsten carried on a support material;
- and the second-stage catalyst comprising noble metal, wherein the first-stage catalyst is made by impregnating said support material consisting of more than about 50% by weight .gamma.-alumina and, optionally, materials selected from the group consisting of cerium oxide, barium oxide, zirconium oxide, lanthanum oxide, .alpha.-alumina, and titanium oxide with a solution of a tungsten containing compound in an aqueous or organic solvent, subsequently drying the impregnated support material, and then calcining it to leave a coating of tungsten or tungsten oxide on the support material.
A method for the conversion of exhaust gases containing nitrogen oxides, carbon monoxide, and hydrocarbons which comprises sequentially exposing said exhaust gases to a first-stage catalyst comprising between about 0.1 and 3% by weight tungsten carried on a support material consisting of more than about 50% by weight .gamma.-alumina and, optionally, materials selected from the group consisting of cerium oxide, barium oxide, zirconium oxide, lanthanum oxide, .alpha.-alumina, and titanium oxide and then a second-stage catalyst comprising a noble metal.
Dependencies are inferred from the claim text.