초록 ▼

Ag/Al2O3 materials may be packaged in a suitable flow-through reactor, close coupled to the exhaust manifold of a diesel engine, and upstream of other exhaust gas treatment devices, such as a diesel oxidation catalyst and a selective reduction catalyst for NOx. The silver/alumina catalyst material u

Ag/Al2O3 materials may be packaged in a suitable flow-through reactor, close coupled to the exhaust manifold of a diesel engine, and upstream of other exhaust gas treatment devices, such as a diesel oxidation catalyst and a selective reduction catalyst for NOx. The silver/alumina catalyst material uses hydrogen in a cold-start engine exhaust and serves to oxidize NO to NO2 in the relatively low temperature, hydrocarbon-containing, exhaust during a short period following the engine cold start, and to temporarily store NOx during the start-up period. After the exhaust has heated downstream catalytic devices, the silver yields its nitrogen oxides for conversion to nitrogen by the then-operating devices before NOx is discharged to the atmosphere.

대표청구항 ▼

1. A method of treating the exhaust gas stream flowing from a vehicle internal combustion engine during a period following a cold-start of the engine, the exhaust gas stream comprising a mixture of nitric oxide, carbon monoxide, hydrocarbons, hydrogen, water, carbon dioxide, oxygen, and nitrogen, th

1. A method of treating the exhaust gas stream flowing from a vehicle internal combustion engine during a period following a cold-start of the engine, the exhaust gas stream comprising a mixture of nitric oxide, carbon monoxide, hydrocarbons, hydrogen, water, carbon dioxide, oxygen, and nitrogen, the exhaust gas stream being at an initial temperature below 100° C. and progressively warming during further engine operation, the method comprising; continually passing the hydrogen, oxygen, and nitric oxide-containing exhaust gas stream in contact with a silver/alumina particulate catalyst to oxidize at least a portion of the nitric oxide to nitrogen dioxide and to temporarily store some of the nitrogen oxide and nitrogen dioxide product on the particulate catalyst material, the silver/alumina particulate catalyst consisting of particles of silver or silver oxide deposited on carrier particles of alumina, the silver/alumina particulate catalyst oxidizing nitric oxide to nitrogen dioxide in the presence of hydrogen and temporarily storing nitrogen oxide and nitrogen dioxide product as the exhaust gas temperature range is progressively warmed from 100° C. to 190° C.; then, continuallypassing the exhaust gas stream into contact with at least one downstream catalytic material for further oxidation of nitric oxide or for reduction of nitric oxide and nitrogen dioxide as the exhaust gas increases in temperature and heats each such downstream reactor to an operating temperature; andcontinuing the passage of the exhaust gas through each reactor during the duration of engine operation, while stored material is removed from the silver/alumina particulate catalyst and the silver/alumina particulate catalyst ceases its affect on the warmed exhaust gas stream until the engine is stopped and started again, following an engine cool-down period. 2. A method of treating the exhaust from a vehicle internal combustion engine as recited in claim 1 in which the silver/alumina catalyst consists of particles of silver or a silver oxide deposited on carrier particles of alumina and the silver content is in the range of 0.5% to 10% of the total of the particles of silver or silver oxide and alumina. 3. A method of treating the exhaust from a vehicle internal combustion engine as recited in claim 1 in which the hydrogen and nitric oxide-containing exhaust is passed in contact with the silver/alumina particulate catalyst and then with a different oxidation catalyst for NO, which oxidation catalyst is composed to commence oxidation of NO at temperatures of about 190° C. or higher. 4. A method of treating the exhaust from a vehicle internal combustion engine as recited in claim 3 in which the different oxidation catalyst for NO comprises a platinum group metal. 5. A method of treating the exhaust from a vehicle internal combustion engine as recited in claim 1 in which the silver/alumina particulate catalyst is located so that exhaust gas exits an exhaust manifold of the engine in a defined exhaust gas flow path and flows into contact with the silver/alumina catalyst after flowing no more than about fifty centimeters distance along the flow path after leaving the exhaust manifold. 6. A method of treating the exhaust from a vehicle internal combustion engine as recited in claim 1 in which the vehicle internal combustion engine is a diesel engine which is controlled to operate at an air-to-fuel ratio of about 17:1 during a major portion of its operation. 7. A method of treating the exhaust from a vehicle internal combustion engine as recited in claim 1 in which the silver/alumina particulate catalyst is deposited as wash coat layers on the wall surfaces of parallel open-ended channels in an monolithic body, the parallel open-ended channels extending from an exhaust gas flow inlet to an exhaust gas flow outlet of the monolithic body. 8. A method of treating the exhaust from a vehicle internal combustion engine as recited in claim 7 in which the silver/alumina particulate catalyst is deposited as wash coat layers on the wall surfaces of parallel open-ended channels in an monolithic body at the gas flow inlet end of the body and particles of an oxidation catalyst comprising particles of a platinum group metal are deposited as a wash coat on the wall surfaces of parallel open-ended channels at the gas flow outlet end of the body. 9. A method of treating the exhaust from a vehicle internal combustion engine as recited in claim 7 in which particles of an oxidation catalyst comprising particles of a platinum group metal are deposited as a wash coat on the wall surfaces of parallel open-ended channels, the wash coat of platinum group metal extending on the wall surfaces from the exhaust gas flow inlet of the body to its exhaust gas flow outlet, and in which particles of the silver/alumina particulate catalyst are deposited as a wash coat overlying the wash coat particles of the platinum group metal. 10. A method of treating the exhaust from a vehicle internal combustion engine as recited in claim 1 in which the hydrogen content of the total exhaust gas stream is in the range of about 100 ppm to about 1000 ppm during a period following the cold start of the engine. 11. A method of treating the exhaust gas stream flowing from a vehicle internal combustion engine during a period following a cold-start of the engine, the engine being operated in a lean-burn mode during the cold start, the exhaust gas stream comprising a mixture of nitric oxide, carbon monoxide, hydrocarbons, hydrogen, water, carbon dioxide, oxygen, and nitrogen, the exhaust gas stream being at an initial temperature below 100° C. and progressively warming during further engine operation, the method comprising; continually passing the hydrogen, oxygen, and nitric oxide-containing exhaust gas stream in contact with a silver/alumina particulate catalyst to oxidize at least a portion of the nitric oxide to nitrogen dioxide and to temporarily store some of the nitrogen oxide and nitrogen dioxide product on the particulate catalyst material, the silver/alumina particulate catalyst being the first catalyst material contacted by the flowing exhaust gas stream, the silver/alumina catalyst consisting of particles of silver or a silver oxide deposited on carrier particles of alumina, the silver content being in the range of 0.5% to 10% of the total of the particles of silver or silver oxide and alumina, the silver/alumina particulate catalyst oxidizing nitric oxide to nitrogen dioxide in the presence of hydrogen and temporarily storing nitrogen oxide and nitrogen dioxide product as the exhaust gas is progressively warmed from 100° C. to 190 ° C.; then, immediately andcontinually passing the exhaust gas stream into contact with a catalytic material comprising particles of one or more platinum group metals for oxidation of nitric oxide as the exhaust gas increases in temperature and heats the platinum group metal catalyst to an operating temperature; andcontinuing the passage of the exhaust gas into contact with each of the silver/alumina catalyst and the particles of platinum group metal for the duration of engine operation, while stored material is removed from the silver/alumina particulate catalyst and the silver/alumina particulate catalyst ceases its affect on the warmed exhaust gas stream when it has reached at temperature of about 190° C. or lower and until the engine is stopped and started again, following an engine cool-down period. 12. A method of treating the exhaust from a vehicle internal combustion engine as recited in claim 11 in which the silver/alumina particulate catalyst is located so that exhaust gas exits an exhaust manifold of the engine in a defined exhaust gas flow path and flows into contact with the silver/alumina catalyst after flowing no more than about fifty centimeters distance along the flow path after leaving the exhaust manifold. 13. A method of treating the exhaust from a vehicle internal combustion engine as recited in claim 11 in which the hydrogen content of the total exhaust gas stream is in the range of about 100 ppm to about 1000 ppm during a period following the cold start of the engine. 14. A method of treating the exhaust from a vehicle internal combustion engine as recited in claim 11 in which the vehicle internal combustion engine is a diesel engine which is controlled to operate at an air-to-fuel ratio of about 17:1 during a major portion of its operation. 15. A method of treating the exhaust from a vehicle internal combustion engine as recited in claim 11 in which the silver/alumina particulate catalyst is deposited as wash coat layers on the wall surfaces of parallel open-ended channels in an monolithic body, the parallel open-ended channels extending from an exhaust gas flow inlet to an exhaust gas flow outlet of the monolithic body. 16. A method of treating the exhaust gas stream as recited in claim 11 in which the exhaust gas stream passing from the particles of platinum group metal catalyst particles is then subjected to a catalyzed reduction reaction to reduce nitrogen oxides to nitrogen. 17. A method of treating the exhaust from a vehicle internal combustion engine as recited in claim 15 in which the silver/alumina particulate catalyst is deposited as wash coat layers on the wall surfaces of parallel open-ended channels in an monolithic body at the gas flow inlet end of the body and particles of an oxidation catalyst comprising particles of a platinum group metal are deposited as a wash coat on the wall surfaces of parallel open-ended channels at the gas flow outlet end of the body. 18. A method of treating the exhaust from a vehicle internal combustion engine as recited in claim 15 in which particles of an oxidation catalyst comprising particles of a platinum group metal are deposited as a wash coat on the wall surfaces of parallel open-ended channels, the wash coat of platinum group metal extending on the wall surfaces from the exhaust gas flow inlet of the body to its exhaust gas flow outlet, and in which particles of the silver/alumina particulate catalyst are deposited as a wash coat overlying the wash coat particles of the platinum group metal.