초록

A system for NOx reduction in combustion gases, especially from diesel engines, incorporates an oxidation catalyst to convert at least a portion of NO to NO2, a particulate filter, a source of reductant such as NH3 and an SCR catalyst. Considerable improvements in NOx conversion are observed.

대표청구항 ▼

What is claimed: 1. A method of reducing pollutants, including particulates and NOx, in a gas stream, comprising passing said gas stream over an oxidation catalyst under conditions effective to convert a portion of NO in the gas stream to NO2 to produce a gas mixture comprising a mixture of NO and

What is claimed: 1. A method of reducing pollutants, including particulates and NOx, in a gas stream, comprising passing said gas stream over an oxidation catalyst under conditions effective to convert a portion of NO in the gas stream to NO2 to produce a gas mixture comprising a mixture of NO and NO2, wherein the gas mixture has an enhanced NO2 content relative to the gas stream entering the oxidation catalyst, removing at least a portion of said particulates in a particulate trap located downstream of the oxidation catalyst, reacting trapped particulate with NO2, adding reductant fluid to the gas stream to form a gas mixture downstream of said trap, and passing the gas mixture over an SCR catalyst under NOx reduction conditions. 2. A method according to claim 1, wherein said gas stream is the exhaust from a diesel, GDI or DNG engine. 3. A method according to claim 1, wherein the gas stream is cooled before reaching the SCR catalyst. 4. A method according to claim 1, wherein the NO to NO2 ratio of the gas mixture is adjusted to a level pre-determined to be optimum for the SCR catalyst, by oxidation of NO over said oxidation catalyst. 5. A method according to claim 1, wherein the SCR catalyst is maintained at a temperature from 160�� C. to 450�� C. 6. A method according to claim 1, wherein the SCR catalyst includes a component selected from the group consisting of a transition metal and a rare-earth metal. 7. A method according to claim 1, wherein the SCR catalyst includes a component selected from the group consisting of copper and vanadium. 8. A method according to claim 1, wherein the SCR catalyst is V2O5/WO3/TiO2. 9. A method according to claim 4, wherein the ratio of NO:NO2 leaving the oxidation catalyst is adjusted to about 4:3. 10. A method according to claim 1, wherein the reductant fluid is a hydrocarbon. 11. A method according to claim 1, wherein the reductant fluid is selected from the group consisting of ammonia, ammonium carbamate and urea. 12. A method according to claim 10, further comprising the step of contacting the gas mixture leaving the SCR catalyst with a clean-up catalyst to remove NH3 or derivatives thereof. 13. A method according to claim 1, wherein the space velocity of the exhaust gas over the SCR catalyst is in the range 40,000 to 70,000 h-1.