초록 ▼

This invention provides polyfunctional catalysts comprising a composite of platinum and one or more of rhodium, ruthenium and iridium, a substantially larger quantity of one or more base metal oxides in which the metal is selected from the group consisting of metals having an atomic number from 25 t

This invention provides polyfunctional catalysts comprising a composite of platinum and one or more of rhodium, ruthenium and iridium, a substantially larger quantity of one or more base metal oxides in which the metal is selected from the group consisting of metals having an atomic number from 25 to 28 and rhenium, and an alumina support, which composite is made and then deposited on a suitable carrier. In a preferred embodiment, the catalysts contain 1-20 weight percent of said base metal oxide, typically nickel oxide; 0.05-0.5 weight percent platinum; and 0.002-0.3 weight percent rhodium, and an alumina support deposited on a monolith or other carrier. The improved catalysts are especially applicable for purifying exhaust gases from combustion processes, and in particular those from internal combustion engines. These polyfunctional catalysts have in a single formulation, the ability to accomplish four objectives--to oxidize carbon monoxide and unburned hydrocarbons while reducing nitrogen oxides, thereby converting those contaminants found in the exhaust of internal combustion engines into carbon dioxide, water and elemental nitrogen, but without producing significant amounts of hydrogen sulfide, sulfur trioxide or sulfuric acid. Such chemical conversions take place over the catalyst when the ratio of air to fuel supplied to the catalyst is controlled to nearly stoichiometric conditions, thereby maintaining the exhaust feed gases within a narrow compositional range, sometimes called a "window", in which the catalyst can substantially convert the contaminants.

대표청구항 ▼

1. A method of reacting contaminants in combustion exhaust gases to substantially simultaneously oxidize gaseous hydrocarbons and carbon monoxide and reduce nitrogen oxides therein, comprising reacting said gases with a controlled approximately stoichiometric amount of oxygen under conditions which

1. A method of reacting contaminants in combustion exhaust gases to substantially simultaneously oxidize gaseous hydrocarbons and carbon monoxide and reduce nitrogen oxides therein, comprising reacting said gases with a controlled approximately stoichiometric amount of oxygen under conditions which convert said contaminants to carbon dioxide, water and nitrogen, by contacting said gases with a catalyst consisting essentially of: (a) an alumina support selected from the group consisting of alumina and alumina stabilized with one or more rare earth oxides; (b) a platinum group metal component dispersed on the support and selected from the group consisting of (i) to (iv), as follows: (i) platinum plus at least one of rhodium, ruthenium and iridium; (ii) platinum plus palladium plus at least one of rhodium, ruthenium and iridium; (iii) the metals of each combination of (i) as an alloy with each other; and (iv) the metals of each combination of (ii) as an alloy with each other; (c) a base metal oxide component, the base metal thereof being selected from metals having atomic numbers from 25 to 28 and rhenium, and mixtures thereof, said base metal oxide component being present in a weight ratio to said platinum group metal component of at least 2 to 1; and (d) a carrier on which said support, said platinum group metal component and said base metal oxide component are deposited. 2. The method of claim 1 wherein a combination of all of said support, all of said platinum group metal component and all of said base metal oxide component is coated on the surfaces of said carrier. 3. The method of claim 1 wherein said platinum group metal component is selected from the group consisting of (v)-(viii), as follows: (v) platinum plus rhodium; (vi) platinum plus rhodium plus palladium; (vii) an alloy of platinum with rhodium; and (viii) an alloy of platinum, rhodium and palladium with each other. 4. The method of claim 1 wherein the carrier of said catalyst consists essentially of a refractory oxide monolith. 5. The method of claim 1 wherein the carrier of said catalyst consists essentially of cordierite-mullite. 6. The method of claim 1 wherein the base metal oxide component consists essentially of iron oxide. 7. The method of claim 1 wherein the catalyst is made by impregnating said support with respective compounds in aqueous solution of the metals of at least one of the combinations defined in step (b). 8. The method of claim 1 wherein the catalyst is made by impregnating said support with respective compounds in aqueous solutions of the metals of at least one of the combinations defined in step (c). 9. The method of claim 1 wherein the catalyst is made by depositing the support on the surface of the carrier by contacting said carrier with an aqueous dispersion of the support particles. 10. The method of claim 1 wherein the base metal oxide component consists essentially of nickel oxide. 11. The method of claim 10 wherein said platinum group metal component is selected from the group consisting of (v)-(viii), as follows: (v) platinum plus rhodium; (vi) platinum plus rhodium plus palladium; (vii) an alloy of platinum with rhodium; and (viii) an alloy of platinum, rhodium and palladium with each other. 12. The method of claim 11 wherein platinum is 0.05 to 0.5 weight percent and rhodium is 0.002 to 0.3 weight percent of the catalyst, the amount of platinum is at least equal to the amount of rhodium, and the nickel oxide is 1 to 20% of the catalyst. 13. The method of claim 12 wherein the carrier comprises a monolithic structure having channel walls and a combination of all of said support, all of said platinum group metal component and all of said base metal oxide component is coated on the surfaces of the channel walls. 14. The method of claim 13 wherein the support consists essentially of alumina stabilized by ceria. 15. The method of claim 1 wherein the catalyst is made by contacting the support in particulate form with, respectively, the platinum group metal component and the base metal oxide component in the form of separate aqueous solutions of soluble platinum group metal and base metal compounds and in relative proportions such that essentially all of each aqueous solution is absorbed by the support, and said components are separately fixed on said support. 16. The method of claim 15 in which the separate fixings of said platinum group metal component and said base metal oxide component are conducted in the absence of unabsorbed aqueous medium. 17. The method of claim 15 wherein the platinum group metal component is selected from the group consisting of (v) platinum and rhodium and (vi) an alloy of platinum with rhodium and comprises about 0.05 to 0.8 weight percent of said catalyst, the amount of platinum being at least equal to the amount of rhodium, and the base metal oxide component is nickel oxide and comprises about 1 to 20 weight percent of the catalyst. 18. A method of reacting contaminants in combustion exhaust gases to simultaneously oxidize gaseous hydrocarbons and carbon monoxide and reduce nitrogen oxides therein, comprising reacting said gases with a controlled approximately stoichiometric amount of oxygen under conditions which convert said contaminants to carbon dioxide, water and nitrogen, by contacting said gases with a catalyst consisting essentially of (a) a support consisting essentially of alumina; (b) a platinum group metal component selected from the group consisting of (i) to (iv), as follows: (i) platinum plus at least one of rhodium, ruthenium and iridium; (ii) platinum plus palladium plus at least one of rhodium; ruthenium and iridium; (iii) the metals of each combination of (i) as an alloy with each other; and (iv) the metals of each combination of (ii) as an alloy with each other; (c) a base metal oxide component, the base metal thereof being selected from metals having atomic numbers from 25 to 28 and rhenium, and mixtures thereof, said base metal oxide component being present in a weight ratio to said platinum group metal component of at least 2 to 1; and (d) a carrier on which said support, said platinum group metal component and said base metal oxide component are deposited; (e) said catalyst being made by combining the platinum group metal component, the base metal component, and said support, and depositing the resulting composite on said carrier and heating the thus combined support at a temperature sufficiently high to provide said platinum group metal component and base metal oxide component on said support. 19. The method of claim 18 wherein said platinum group metal component is selected from the group consisting of (v)-(viii), as follows: (v) platinum plus rhodium; (vi) platinum plus rhodium plus palladium; (vii) an alloy of platinum with rhodium; and (viii) an alloy of platinum, rhodium and palladium with each other. 20. The method of claim 18 wherein the carrier of said catalyst is monolithic. 21. The method of claim 18 wherein the base metal oxide component consists essentially of iron oxide. 22. The method of claim 18 wherein the combining of step (e) is carried out by impregnating said support in particulate form with respective compounds in aqueous solution of the metals of at least one of the combinations defined in step (b), and the depositing of step (e) is carried out by contacting said carrier with an aqueous dispersion of the resulting impregnated support particles. 23. The method of claim 18 wherein the combining of step (e) is carried out by impregnating said support in particulate form with respective compounds in aqueous solution of the metals of at least one of the combinations defined in step (b), and with respective compounds in aqueous solution of at least one of the combinations defined in step (c). 24. The method of claim 18 wherein the depositing step (e) is carried out by contacting said carrier with an aqueous dispersion of the combined support particles. 25. The method of claim 18 wherein the base metal oxide component consists essentially of nickel oxide. 26. The method of claim 25 wherein said platinum group metal component is selected from the group consisting of (v)-(viii), as follows: (v) platinum plus rhodium; (vi) platinum plus rhodium plus palladium; (vii) an alloy of platinum with rhodium; and (viii) an alloy of platinum, rhodium and palladium with each other. 27. The method of claim 26 wherein platinum is 0.05 to 0.5 weight percent and rhodium is 0.002 to 0.3 weight percent of the catalyst, the amount of platinum is at least equal to the amount of rhodium, and the nickel oxide is 1 to 20% of the catalyst. 28. The method of claim 27 wherein the carrier of said catalyst is monolithic. 29. The method of claims 18, 19, 25 or 26 wherein the catalyst is made by contacting the support in particulate form with, respectively, the platinum group metal component and the base metal oxide component in the form of separate aqueous solutions of soluble platinum group metal and base metal compounds and in relative proportions such that essentially all of each aqueous solution is absorbed by the support, and said components are separately fixed on said support. 30. The method of claim 29 in which the separate fixings of said platinum group metal component and said base metal oxide component are conducted in the absence of unabsorbed aqueous medium. 31. The method of claim 29 wherein the platinum group metal component is selected from the group consisting of (v) platinum and rhodium and (vi) an alloy of platinum with rhodium and comprises about 0.05 to 0.8 weight percent of said catalyst, the amount of platinum being at least equal to the amount of rhodium, and the base metal oxide component is nickel oxide and comprises about 1 to 20 weight percent of the catalyst.