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However, for example, when ceria-zirconia composite oxide is used as an OSC material, cerium contained in the composite oxide exhibits OSC performance, but reduces exhaust gas purification performance.
Therefore, if the amount of OSC material is increased in order to improve OSC performance, exhaust gas purification performance may decrease
In addition, if the amount of OSC material is increased in order to improve OSC performance, the pressure loss deteriorates
Therefore, in a catalyst for exhaust gas purification using an OSC material, OSC performance and exhaust gas purification performance are in conflict, and OSC performance and pressure loss are also in conflict. Improve OSC performance under conditions
[0008] In the catalysts for exhaust gas purification described in Patent Documents 1 to 4, pressure loss was not studied, and all of exhaust gas purification performance, OSC performance, and pressure loss were not presented at a high level.
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[0070] Hereinafter, the present invention will be described in more detail using examples. However, the technical scope of the present invention is not limited by these examples.
[0071] 1. OSC material
[0072] As the OSC material, ceria-zirconia (CeO 2 -ZrO 2 ) composite oxides.
[0073] Preparation of Ceria-Zirconia Composite Oxide (Pyrochlore ZC) with Pyrochlore Structure
[0074] will be CeO 2 49.1 g of a 28% by weight aqueous cerium nitrate solution in terms of ZrO 2 After dissolving 54.7 g of an aqueous zirconyl nitrate solution of 18% by weight in conversion and a commercially available surfactant in 90 mL of ion-exchanged water, 1.2 times the equivalent of NH was added to the anion. 3 In 25% by weight of ammonia water, a coprecipitate was generated, and the obtained coprecipitate was filtered and washed. Next, the obtained coprecipitate was dried at 110° C., and then fired at 500° C. in the air for 5 hours to obtain a solid solution of cerium and zirconium. T...
Embodiment 1、2 and comparative example 5
[0092] In Examples 1, 2, and Comparative Example 5, pyrochlore ZC was added to the slurry 2 for forming the upper layer of the catalyst coating so that the capacity relative to the substrate was 30 g / L, 50 g / L, and 70 g / L, respectively. Each catalyst was obtained in the same manner as in Comparative Example 4 except for the amount of L.
Embodiment 3、4 and comparative example 7
[0094] In Examples 3, 4, and Comparative Example 7, pyrochlore ZC was added to the slurry 2 for forming the catalyst coating layer of the upper layer, so that the capacity relative to the base material became 30 g / L, 50 g / L, and 70 g / L, respectively. Each catalyst was obtained in the same manner as in Comparative Example 6 except for the amount of L.
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Abstract
The present invention relates to a catalyst for exhaust gas purification. [Problem] An object of the present invention is to provide a catalyst for exhaust gas purification which optimizes OSC performance and pressure loss. [Solution] A catalyst for exhaust gas purification, which has a substrate and two or more catalyst coatings formed on the substrate, wherein the uppermost catalyst coating contains: an OSC material having a pyrochlore structure, oxygen An OSC material whose absorption and emission rate is faster than that of an OSC material having a pyrochlore structure, and a noble metal catalyst containing at least Rh; The material capacity is 30g / L-50g / L, and the content of the OSC material whose oxygen absorption and release rate is faster than the OSC material having a pyrochlore structure is 36g / L-72g / L relative to the above-mentioned base material capacity.
Description
technical field [0001] The present invention relates to a catalyst for exhaust gas purification. Background technique [0002] Exhaust gas from internal combustion engines such as automobiles contains harmful components such as carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx), and these harmful components are released into the atmosphere after being purified by exhaust gas purification catalysts. Conventionally, as the catalyst for purifying exhaust gas, a three-way catalyst that simultaneously oxidizes CO and HC and reduces NOx has been used. As the three-way catalyst, noble metals such as platinum (Pt), palladium (Pd), and rhodium (Rh) have been widely used. supported on alumina (Al 2 o 3 ), silicon oxide (SiO 2 ), zirconia (ZrO 2 ), titanium oxide (TiO 2 ) and other porous oxide carriers. [0003] In order to use such a three-way catalyst to effectively purify the above-mentioned harmful components in exhaust gas, the air-fuel ratio (A / F) of the ai...
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