Catalyst for purifying exhaust gas from internal combustion engine and process for purifying exhaust gas using the same
View Patent ↗An Object of the patent is to remove highly reducing hydrocarbon exhausted during acceleration period, and to remove efficiently hydrocarbon even after contacting with highly reducing hydrocarbon. By using a catalyst having a higher proportion of palladium having surface charge of 2-valence or 4-valence supported than that of 0-valence by supporting palladium together with magnesium oxide, hydrocarbon exhausted from an internal combustion engine especially during acceleration period can be efficiently removed.
1. A catalyst for treating an exhaust gas from an internal combustion engine, which comprises a catalyst active component comprising at least both palladium and magnesium, wherein said palladium includes palladium that has a surface charge of 2-valence, 4-valence, or both, and the proportion of the palladium that has a surface charge of 0-valence is less than 0.5, said proportion being calculated by 0-valence/(0-valence+2-valence+4-valence), and said catalyst active component is supported on a refractory inorganic oxide powder that comprises activated alumina, zeolite, titania, zirconia, silicon oxide, or a composite oxide thereof and, optionally, further comprises a rare-earth metal other than cerium.
2. The catalyst according to claim 1 , wherein said catalyst active component is supported on a three-dimensional structure.
3. The catalyst according to claim 2 , wherein the amounts of palladium (in terms of Pd) and magnesium (in terms of MgO) supported on 1 L of the three-dimensional structure are 0.05 to 20 g and 0.1 to 40 g, respectively.
4. The catalyst according to claim 3 , further comprising platinum and/or rhodium.
5. The catalyst according to claim 2 , further comprising platinum and/or rhodium.
6. The catalyst according to claim 1 , further comprising platinum and/or rhodium.
7. The catalyst according to claim 6 , wherein the amount of platinum supported on 1 L of the three-dimensional structure is 10 g or less, and the amount of rhodium supported on 1 L of the three-dimensional structure is 5 g or less.
8. The catalyst according to claim 1 , wherein the amount of refractory inorganic oxide powder supported on 1 L of the three-dimensional structure is 10 to 300 g.
9. The catalyst according to claim 1 , further comprising cerium oxide and/or ceria-zirconia composite oxide.
10. A process for purifying an exhaust gas, which comprises treating hydrocarbon in the exhaust gas from an internal combustion engine including a reducing gas in the presence of the catalyst as set forth in claim 1 .
11. A process for removing hydrocarbon, which comprises treating an exhaust gas having an A/F ratio less than 14.7 from an internal combustion engine in the presence of the catalyst as set forth in claim 1 .
12. The process according to claim 11 , wherein an exhaust gas emitted from an internal combustion engine in an acceleration state is treated.
13. The process according to claim 12 , wherein an acceleration speed in the acceleration state is less than 10 km/s 2 .
14. The process according to claim 13 , wherein a speed in the acceleration state is less than 300 km/h.