JP4698505B2 - Exhaust gas purification catalyst - Google Patents
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- JP4698505B2 JP4698505B2 JP2006177042A JP2006177042A JP4698505B2 JP 4698505 B2 JP4698505 B2 JP 4698505B2 JP 2006177042 A JP2006177042 A JP 2006177042A JP 2006177042 A JP2006177042 A JP 2006177042A JP 4698505 B2 JP4698505 B2 JP 4698505B2
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- 238000000746 purification Methods 0.000 title claims description 39
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- RKTYLMNFRDHKIL-UHFFFAOYSA-N copper;5,10,15,20-tetraphenylporphyrin-22,24-diide Chemical compound [Cu+2].C1=CC(C(=C2C=CC([N-]2)=C(C=2C=CC=CC=2)C=2C=CC(N=2)=C(C=2C=CC=CC=2)C2=CC=C3[N-]2)C=2C=CC=CC=2)=NC1=C3C1=CC=CC=C1 RKTYLMNFRDHKIL-UHFFFAOYSA-N 0.000 claims description 14
- 229910052684 Cerium Inorganic materials 0.000 claims description 8
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- 239000002994 raw material Substances 0.000 description 3
- 229910004625 Ce—Zr Inorganic materials 0.000 description 2
- NIPNSKYNPDTRPC-UHFFFAOYSA-N N-[2-oxo-2-(2,4,6,7-tetrahydrotriazolo[4,5-c]pyridin-5-yl)ethyl]-2-[[3-(trifluoromethoxy)phenyl]methylamino]pyrimidine-5-carboxamide Chemical compound O=C(CNC(=O)C=1C=NC(=NC=1)NCC1=CC(=CC=C1)OC(F)(F)F)N1CC2=C(CC1)NN=N2 NIPNSKYNPDTRPC-UHFFFAOYSA-N 0.000 description 2
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- HSJPMRKMPBAUAU-UHFFFAOYSA-N cerium(3+);trinitrate Chemical compound [Ce+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O HSJPMRKMPBAUAU-UHFFFAOYSA-N 0.000 description 2
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- JSKIRARMQDRGJZ-UHFFFAOYSA-N dimagnesium dioxido-bis[(1-oxido-3-oxo-2,4,6,8,9-pentaoxa-1,3-disila-5,7-dialuminabicyclo[3.3.1]nonan-7-yl)oxy]silane Chemical compound [Mg++].[Mg++].[O-][Si]([O-])(O[Al]1O[Al]2O[Si](=O)O[Si]([O-])(O1)O2)O[Al]1O[Al]2O[Si](=O)O[Si]([O-])(O1)O2 JSKIRARMQDRGJZ-UHFFFAOYSA-N 0.000 description 2
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- ITHZDDVSAWDQPZ-UHFFFAOYSA-L barium acetate Chemical compound [Ba+2].CC([O-])=O.CC([O-])=O ITHZDDVSAWDQPZ-UHFFFAOYSA-L 0.000 description 1
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- UJVRJBAUJYZFIX-UHFFFAOYSA-N nitric acid;oxozirconium Chemical compound [Zr]=O.O[N+]([O-])=O.O[N+]([O-])=O UJVRJBAUJYZFIX-UHFFFAOYSA-N 0.000 description 1
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- 229910052697 platinum Inorganic materials 0.000 description 1
- NWAHZABTSDUXMJ-UHFFFAOYSA-N platinum(2+);dinitrate Chemical compound [Pt+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O NWAHZABTSDUXMJ-UHFFFAOYSA-N 0.000 description 1
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- 238000009849 vacuum degassing Methods 0.000 description 1
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Description
本発明は、排気ガス浄化用触媒に関する。 The present invention relates to an exhaust gas purification catalyst.
自動車の排気ガス中のＨＣ（炭化水素）、ＣＯ（一酸化炭素）及びＮＯｘ（窒素酸化物）を同時に浄化する三元触媒に関し、担体上の触媒層にＣｅとＺｒとを含有する中空状複酸化物粒子を含ませることは知られている（特許文献１参照）。その中空状複酸化物粒子は、中空殻を構成する一次粒子の結晶格子又は原子間に触媒金属としてＲｈが配置されたものである。このような中空状複酸化物粒子は、中実の塊状粒子に比べて、その中空殻表面に露出する一次粒子が多くなるととともに、排気ガスが殻壁を拡散して通り抜け易くなることから、排気ガスとＲｈとが接触し易くなり、排気ガス浄化性能の向上に有利に働く。この特許文献１では、噴霧熱分解法によって中空状複酸化物粒子を製造すること、その際に原料溶液を噴霧する加熱炉の温度を１０００℃とすること、また、中空状複酸化物粒子のＣｅＯ２／ＺｒＯ２質量比を２２／６８とすることが開示されている。
上記中空状複酸化物粒子では中空状になっているから、それら粒子が多数集合した状態になっても、その一次粒子同士の接触が少なく、シンタリングを生じ難い、すなわち、耐熱性が高いということができる。しかし、それでも、例えば１０００℃を越えるような高温雰囲気に晒されると、結晶子（ないしは一次粒子）の粗大化を招き、中空構造の維持が困難になる。その際に、当該中空状粒子に担持されている触媒金属がシンタリングし、或いは中空殻表面に露出していた触媒金属が粗大化した粒子の内部に埋没し、触媒の排気ガス浄化性能が低下する。 Since the hollow complex oxide particles are hollow, even if they are in a state of aggregation, there is little contact between the primary particles, and sintering hardly occurs, that is, heat resistance is high. be able to. However, when exposed to a high-temperature atmosphere exceeding 1000 ° C., for example, crystallites (or primary particles) are coarsened, making it difficult to maintain a hollow structure. At that time, the catalyst metal supported on the hollow particles is sintered, or the catalyst metal exposed on the hollow shell surface is buried inside the coarsened particles, and the exhaust gas purification performance of the catalyst is lowered. To do.
本発明は、このような中空状複酸化物粒子の構造破壊を抑制することができるようにして、触媒の耐熱性の向上を図ることを課題とする。 It is an object of the present invention to improve the heat resistance of a catalyst so as to suppress the structural breakdown of such hollow multi-oxide particles.
本発明は、中空状複酸化物粒子を構成する立方晶を所定の割合にすることによって、上記課題を解決するようにした。 In the present invention, the above-described problems are solved by setting the cubic crystals constituting the hollow double oxide particles to a predetermined ratio.
すなわち、本発明は、ＣｅとＺｒとを含有する中空状複酸化物粒子が担体上の触媒層に含まれている排気ガス浄化用触媒において、
上記複酸化物は、ＣｅＯ２／ＺｒＯ２質量比が５０／５０以上、すなわち、ＣｅＯ２／（ＣｅＯ２＋ＺｒＯ２）比が５０質量％以上であって、立方晶を含む複数種の結晶相が混在し、該複数種の結晶相中の立方晶の質量分率が７４％以上８２％以下であることを特徴とする。
That is, the present invention provides an exhaust gas purification catalyst in which hollow double oxide particles containing Ce and Zr are included in a catalyst layer on a carrier.
The complex oxide has a CeO 2 / ZrO 2 mass ratio of 50/50 or more, that is, a CeO 2 / (CeO 2 + ZrO 2 ) ratio of 50 mass% or more, and a plurality of types of crystal phases including cubic crystals. It is mixed, and the mass fraction of cubic crystals in the plurality of types of crystal phases is 74% or more and 82% or less.
上記中空状複酸化物粒子の立方晶の質量分率が上述の如き範囲になると、触媒が長時間にわたって高温雰囲気下におかれても、排気ガス浄化性能の低下が少なくなる。つまり、触媒の耐熱性が高くなる。そのことは、中空状複酸化物粒子の構造破壊が抑制されていることを意味する。その理由は定かではないが、複酸化物粒子を構成する立方晶以外の結晶相が立体障害となって、多量に存在する立方晶結晶子の粗大化を抑制すると考えられるところ、当該質量分率によってその立体障害としての働きが顕著になっていると推測される。 When the cubic mass fraction of the hollow double oxide particles is in the above-described range, the exhaust gas purification performance is less deteriorated even if the catalyst is placed in a high temperature atmosphere for a long time. That is, the heat resistance of the catalyst is increased. This means that structural destruction of the hollow double oxide particles is suppressed. The reason for this is not clear, but it is considered that the crystal phase other than the cubic crystals constituting the double oxide particles becomes a steric hindrance and suppresses the coarsening of a large amount of cubic crystallites. It is speculated that the action as a steric hindrance is remarkable.
上記ＣｅとＺｒとを含有する複酸化物においては、立方晶以外の結晶相として正方晶を生じ易い。この場合は、この正方晶が上記立方晶の粗大化を妨げる立体障害として働くことになる。 In the double oxide containing Ce and Zr, tetragonal crystals are likely to be generated as crystal phases other than cubic crystals. In this case, this tetragonal crystal acts as a steric hindrance that prevents the cubic crystal from coarsening.
ところで、ＣｅＯ２が立方晶を作ることは知られているが、ＣｅとＺｒとを含有する複酸化物においては、必ずしもＣｅＯ２／ＺｒＯ２質量比が大きくなるほど立方晶の上記質量分率が大きくなるというものではない。後述の実施例で明らかになるが、ＣｅＯ２／ＺｒＯ２質量比が６５／３５であっても、その質量比が７５／２５のものよりも立方晶の上記質量分率が大きくなるケースがある。本発明者は、実験研究の結果、上記ＣｅＯ２／ＺｒＯ２質量比を７０／３０以上８０／２０以下（ＣｅＯ２／（ＣｅＯ２＋ＺｒＯ２）比を７０質量％以上８０質量％以下）としたときに、立方晶の上記質量分率を上述の如き範囲にすることにより耐熱性の高い触媒が得られることを見いだした。但し、ＣｅＯ２／ＺｒＯ２質量比が５０／５０未満になると、立方晶の生成に不利になる。 By the way, it is known that CeO 2 forms a cubic crystal. However, in a double oxide containing Ce and Zr, the mass fraction of the cubic crystal is necessarily increased as the CeO 2 / ZrO 2 mass ratio is increased. It's not to be. As will be apparent from the examples described later, even when the CeO 2 / ZrO 2 mass ratio is 65/35, there is a case where the mass fraction of the cubic crystal is larger than that of the mass ratio of 75/25. . As a result of experimental research, the present inventor set the CeO 2 / ZrO 2 mass ratio to 70/30 or more and 80/20 or less (CeO 2 / (CeO 2 + ZrO 2 ) ratio is 70 to 80 mass%). At times, it has been found that a catalyst having high heat resistance can be obtained by setting the mass fraction of cubic crystals in the above range. However, when the CeO 2 / ZrO 2 mass ratio is less than 50/50, it is disadvantageous for the formation of cubic crystals.
上記排気ガス浄化用触媒は、自動車エンジンの排気ガス中のＨＣ、ＣＯ及びＮＯｘを浄化する三元触媒として、或いは自動車エンジンのリーン燃焼運転時にその排気ガス（酸素過剰雰囲気）中のＮＯｘを吸収しエンジンの空燃比が理論空燃比又はリッチ側に変化したときにその吸収したＮＯｘを還元浄化するリーンＮＯｘ触媒として好適に用いることができる。 The exhaust gas purification catalyst absorbs NOx in the exhaust gas (oxygen-excess atmosphere) as a three-way catalyst for purifying HC, CO and NOx in the exhaust gas of the automobile engine or during the lean combustion operation of the automobile engine. When the air-fuel ratio of the engine changes to the stoichiometric air-fuel ratio or the rich side, it can be suitably used as a lean NOx catalyst that reduces and purifies the absorbed NOx.
以上のように、本発明によれば、ＣｅとＺｒとを含有する中空状複酸化物粒子が触媒層に含まれている排気ガス浄化用触媒に関し、上記複酸化物のＣｅＯ２／ＺｒＯ２質量比を５０／５０以上として、立方晶の質量分率を７４％以上８２％以下としたから、触媒が長時間にわたって高温雰囲気下におかれても、排気ガス浄化性能の低下が少なくなり、触媒の耐熱性向上に有利になる。 As described above, according to the present invention, the exhaust gas purification catalyst in which the hollow double oxide particles containing Ce and Zr are included in the catalyst layer, the CeO 2 / ZrO 2 mass of the double oxide is described. The ratio is 50/50 or more, and the mass fraction of the cubic crystal is 74% or more and 82% or less. Therefore, even if the catalyst is left in a high temperature atmosphere for a long time, the exhaust gas purification performance is less deteriorated. It is advantageous for improving the heat resistance.
以下、本発明の実施形態を図面に基づいて説明する。 Hereinafter, embodiments of the present invention will be described with reference to the drawings.
本発明の実施形態に係る排気ガス浄化用触媒は、自動車エンジンの排気ガス中のＨＣ、ＣＯ及びＮＯｘを浄化する三元触媒や、エンジンのリーン燃焼運転時にその排気ガス（酸素過剰雰囲気）中のＮＯｘを吸収しエンジンの空燃比が理論空燃比又はリッチ側に変化したときにその吸収したＮＯｘを還元浄化するリーンＮＯｘ触媒とすることに適したものであって、触媒層がコージェライト等の無機多孔質によって形成されたハニカム形状等の担体上に形成されている。触媒層は次に説明する酸素吸蔵材として働く中空状複酸化物粒子及び触媒金属を含有する。 The exhaust gas purifying catalyst according to the embodiment of the present invention includes a three-way catalyst that purifies HC, CO, and NOx in the exhaust gas of an automobile engine, and the exhaust gas (oxygen-excess atmosphere) in the lean combustion operation of the engine. It is suitable for a lean NOx catalyst that absorbs NOx and reduces and purifies the absorbed NOx when the air-fuel ratio of the engine changes to the stoichiometric air-fuel ratio or rich side, and the catalyst layer is inorganic such as cordierite It is formed on a carrier having a honeycomb shape or the like formed of a porous material. The catalyst layer contains hollow double oxide particles and a catalyst metal that function as an oxygen storage material described below.
上記複酸化物は、Ｃｅ及びＺｒを金属元素として含有するＣｅ−Ｚｒ系複酸化物である。そのＣｅＯ２／ＺｒＯ２質量比は５０／５０以上であって、立方晶と正方晶とが混在し、該複酸化物における立方晶の質量分率は７４％以上８２％以下である。この複酸化物は中空の略球状の殻及びその破片のいずれかの形態になって上記触媒層に含まれる。 The complex oxide is a Ce-Zr complex oxide containing Ce and Zr as metal elements. The CeO 2 / ZrO 2 mass ratio is 50/50 or more, cubic crystals and tetragonal crystals are mixed, and the mass fraction of cubic crystals in the double oxide is 74% or more and 82% or less. This double oxide is included in the catalyst layer in the form of a hollow, substantially spherical shell or a fragment thereof.
＜三元触媒に関する実施例及び比較例＞
−触媒調製法−
上記中空状複酸化物粒子は噴霧熱分解法によって調製することができる。すなわち、オキシ硝酸ジルコニウム、硝酸セリウム及び硫酸マグネシウムの各所定量を水に溶解させることにより、上記複酸化物の原料溶液を調製する。ここで、硫酸マグネシウムは、中空状複合酸化物粒子を製造する際の結晶子のシンタリングを抑制する、結晶子同士の接触点を減らしつつ中空構造に導く、という作用を有するものとして、各種添加化合物の中から選定されたものであり、その添加量、濃度等は適宜決定することができる。次いで、上記原料溶液を、空気をキャリアガスとして噴霧することにより、液滴化させて加熱炉に供給する。加熱炉の炉室温度は１０００℃を超え且つ１１５０℃以下が好ましく、より好ましいのは１０１０℃以上１１００℃以下である。加熱炉を出た粒子はバグフィルターによって捕集し、これを水洗後、乾燥させることにより、当該中空状複酸化物粒子を得ることができる。
<Examples and comparative examples regarding three-way catalysts>
-Catalyst preparation method-
The hollow double oxide particles can be prepared by spray pyrolysis. That is, a raw material solution of the complex oxide is prepared by dissolving predetermined amounts of zirconium oxynitrate, cerium nitrate, and magnesium sulfate in water. Here, magnesium sulfate is added in various ways as having an action of suppressing sintering of crystallites when producing hollow composite oxide particles and leading to a hollow structure while reducing contact points between crystallites. The compound is selected from the compounds, and the addition amount, concentration, and the like thereof can be appropriately determined. Next, the raw material solution is atomized by spraying air as a carrier gas, and supplied to the heating furnace. The furnace chamber temperature of the heating furnace exceeds 1000 ° C. and is preferably 1150 ° C. or less, more preferably 1010 ° C. or more and 1100 ° C. or less. The particles exiting the heating furnace are collected by a bag filter, washed with water, and then dried to obtain the hollow double oxide particles.
上記中空状複酸化物粒子に触媒貴金属としてＲｈを担持する。その担持には減圧脱気法を採用した。即ち、上記中空状複酸化物粒子、貴金属溶液（硝酸ロジウム溶液）及び水の所定量を容器に入れて攪拌することにより懸濁液とし、この懸濁液を攪拌しながら、容器内圧力を２０ｋＰａに減圧・脱気しつつ７０〜８０℃に加熱することにより、水分を蒸発させる。しかる後、Ｒｈを担持した中空状複酸化物粒子を５００℃×２時間の条件で焼成する。 Rh is supported as a catalyst noble metal on the hollow double oxide particles. A vacuum degassing method was adopted for the loading. That is, a predetermined amount of the hollow double oxide particles, the noble metal solution (rhodium nitrate solution) and water are put into a container and stirred to form a suspension, and the pressure in the container is set to 20 kPa while stirring the suspension. The water is evaporated by heating to 70-80 ° C. while reducing the pressure and degassing. Thereafter, the hollow double oxide particles carrying Rh are fired under conditions of 500 ° C. × 2 hours.
次に得られた中空状複酸化物粒子とγ−アルミナ粉末とを混合してこれにＺｒＯ２バインダ及び水を加えてスラリーを調製し、このスラリーを例えばコージェライト製のハニカム担体にコーティングし、乾燥工程、５００℃×２時間の焼成工程を経て三元触媒を得る。 Next, the obtained hollow double oxide particles and γ-alumina powder are mixed, and a ZrO 2 binder and water are added thereto to prepare a slurry, and this slurry is coated on, for example, a cordierite honeycomb carrier, A three-way catalyst is obtained through a drying step and a firing step at 500 ° C. for 2 hours.
ハニカム担体１Ｌ当たりの中空状複酸化物粒子担持量は９３ｇ以上１１６ｇ以下が好ましい。その担持量が少なすぎると、充分な量の貴金属を高分散に担持することが難しくなり、また、その担持量が多すぎると、ハニカム担体の目詰まりを生じ易くなるからである。また、ハニカム担体１Ｌ当たりのγ−アルミナ粉末の担持量は４３ｇ以上５１ｇ以下が好ましい。γ−アルミナ粉末は、触媒が高温に加熱されたときの中空状複酸化物粒子の粒成長を抑制する働きがあり、その担持量が少なすぎると、当該粒成長の抑制効果が充分に得られず、また、その担持量が多すぎると、ハニカム担体の目詰まりを生じ易くなるからである。 The amount of hollow double oxide particles supported per liter of honeycomb carrier is preferably 93 g or more and 116 g or less. This is because if the supported amount is too small, it becomes difficult to support a sufficient amount of noble metal in a highly dispersed state, and if the supported amount is too large, the honeycomb carrier is likely to be clogged. The supported amount of γ-alumina powder per liter of honeycomb carrier is preferably 43 g or more and 51 g or less. The γ-alumina powder has a function of suppressing the growth of hollow double oxide particles when the catalyst is heated to a high temperature. If the amount of the supported particles is too small, the effect of suppressing the growth of the particles can be sufficiently obtained. In addition, if the amount is too large, the honeycomb carrier is likely to be clogged.
−実施例１−５及び比較例１，２に係る触媒−
上記調製法によって実施例１−５及び比較例１，２に係る触媒を調製した。まず、実施例１−３及び比較例１，２の各触媒は、中空状複合酸化物粒子を調製するときの上記加熱炉の炉室温度を互いに異なる温度にしたものであり、他の調製条件は同じである。すなわち、炉室温度を、比較例１は９５０℃、比較例２は１０００℃（特許文献１と同じ炉室温度）、実施例１は１０２５℃、実施例２は１０５０℃、実施例３は１１００℃とした。また、実施例１−３及び比較例１，２の各触媒はいずれも、中空状複酸化物粒子のＣｅＯ２／ＺｒＯ２質量比は７５／２５であり、ハニカム担体１Ｌ当たりの中空状複酸化物粒子の担持量は１０３ｇ／Ｌ、同じくγ−アルミナ粉末の担持量は４７ｇ／Ｌ、同じくＲｈ担持量は約０．１３ｇ／Ｌであり、ハニカム担体は１平方インチ（約６．５４ｃｍ２）当たりのセル数４００、相隣るセルを隔てる壁厚４ミル（約０．１０ｍｍ）のものである。
-Catalysts according to Example 1-5 and Comparative Examples 1 and 2-
Catalysts according to Example 1-5 and Comparative Examples 1 and 2 were prepared by the above preparation method. First, each catalyst of Example 1-3 and Comparative Examples 1 and 2 was obtained by changing the furnace chamber temperature of the heating furnace when preparing the hollow composite oxide particles to different temperatures, and other preparation conditions. Are the same. That is, the furnace chamber temperature was 950 ° C. in Comparative Example 1, 1000 ° C. in Comparative Example 2 (the same furnace chamber temperature as in Patent Document 1), 1025 ° C. in Example 1, 1050 ° C. in Example 2, and 1100 in Example 3. C. Further, in each of the catalysts of Example 1-3 and Comparative Examples 1 and 2, the hollow double oxide particles had a CeO 2 / ZrO 2 mass ratio of 75/25, and the hollow double oxide per 1 L of the honeycomb carrier. The amount of the support particles is 103 g / L, the amount of the γ-alumina powder is 47 g / L, the amount of Rh is about 0.13 g / L, and the honeycomb carrier is 1 square inch (about 6.54 cm 2 ). The number of cells per cell is 400, and the wall thickness separating adjacent cells is 4 mils (about 0.10 mm).
実施例４，５に係る触媒は、上記炉室温度はいずれも１０５０℃とし、ＣｅＯ２／ＺｒＯ２質量比を、実施例４では６５／３５とし、実施例５では８５／１５としたものであり、他は上記実施例１−３及び比較例１，２と同じ条件で調製した。 In the catalysts according to Examples 4 and 5, the furnace chamber temperature was 1050 ° C., and the CeO 2 / ZrO 2 mass ratio was 65/35 in Example 4 and 85/15 in Example 5. The others were prepared under the same conditions as in Examples 1-3 and Comparative Examples 1 and 2 above.
−物性評価−
上記実施例１−５及び比較例１，２の各触媒の中空状複酸化物粒子について、１０００℃の大気雰囲気に２４時間保持するエージングを行なった後、Ｘ線回折装置によりＸＲＤパターンを求めた。そして、解析プログラムRIETAN-2000を用いて、それらＸＲＤパターンのリートベルト解析を行なうことにより、各々の立方晶（及び正方晶）の質量分率、それら立方晶及び正方晶各々におけるＣｅ及びＺｒ各元素の占有率を求めた。結果を表１及び表２に示す。表１は、ＣｅＯ２／ＺｒＯ２質量比が同じく７５／２５であって炉室温度が相異なる実施例１，３及び比較例１，２の中空状複酸化物粒子に関するものであり、表２は、炉室温度が同じく１０５０℃であってＣｅＯ２／ＺｒＯ２質量比が相異なる実施例２，４，５の中空状複酸化物粒子に関するものである。
-Physical property evaluation-
The hollow double oxide particles of the catalysts of Examples 1-5 and Comparative Examples 1 and 2 were subjected to aging that was maintained in an air atmosphere at 1000 ° C. for 24 hours, and then an XRD pattern was obtained using an X-ray diffractometer. . Then, by performing Rietveld analysis of these XRD patterns using the analysis program RIETAN-2000, the mass fraction of each cubic crystal (and tetragonal crystal), and each element of Ce and Zr in each of these cubic crystals and tetragonal crystals The occupancy rate was calculated. The results are shown in Tables 1 and 2. Table 1 relates to the hollow double oxide particles of Examples 1 and 3 and Comparative Examples 1 and 2 having different CeO 2 / ZrO 2 mass ratios of 75/25 and different furnace chamber temperatures. Relates to the hollow double oxide particles of Examples 2, 4 and 5 having the same furnace chamber temperature of 1050 ° C. and different CeO 2 / ZrO 2 mass ratios.
表１によれば、炉室温度が高くなるほど、立方晶の質量分率が小さくなり、また、立方晶及び正方晶各々におけるＣｅの占有率が大きくなっている。表２によれば、ＣｅＯ２／ＺｒＯ２質量比が７５／２５の実施例２では、その質量比が６５／３５の実施例４及び８５／１５の実施例５よりも、立方晶の質量分率が小さくなっている。また、ＣｅＯ２／ＺｒＯ２質量比が大きくなるほど、立方晶及び正方晶各々におけるＣｅの占有率が大きくなっている。 According to Table 1, the higher the furnace chamber temperature, the smaller the mass fraction of cubic crystals, and the larger the occupation ratio of Ce in each of cubic crystals and tetragonal crystals. According to Table 2, in Example 2 where the CeO 2 / ZrO 2 mass ratio is 75/25, the mass fraction of cubic crystals is higher than in Example 4 where the mass ratio is 65/35 and Example 5 where 85/15. The rate is getting smaller. Further, as the CeO 2 / ZrO 2 mass ratio increases, the occupation ratio of Ce in each of the cubic and tetragonal crystals increases.
−排気ガス浄化性能評価−
上記実施例１−５及び比較例１，２の各触媒について、１０００℃の大気雰囲気に２４時間保持するエージングを行なった後、モデルガス流通反応装置及び排気ガス分析装置を用いて排気ガス浄化性能を調べた。すなわち、空燃比リッチのモデルガス（温度６００℃）を空間速度ＳＶ＝１２００００ｈ−１で２０分間流す前処理を行なった後、浄化性能評価用モデルガスを用いて、ＨＣ、ＣＯ及びＮＯｘの浄化に関するライトオフ温度Ｔ５０及び高温浄化率Ｃ５００を測定した。Ｔ５０は、触媒に流入するモデルガス温度を常温から漸次上昇させていき、浄化率が５０％に達したときの触媒入口のガス温度である。Ｃ５００は触媒入口ガス温度が５００℃のときの浄化率である。浄化性能評価用モデルガスは、Ａ／Ｆ＝１４．７±０．９とした。すなわち、Ａ／Ｆ＝１４．７のメインストリームガスを定常的に流しつつ、所定量の変動用ガスを１Ｈｚでパルス状に添加することにより、Ａ／Ｆを±０．９の振幅で強制的に振動させた。浄化性能評価用モデルガスの組成は表３のとおりである。また、触媒入口ガス温度は１００℃から５００℃まで昇温速度で３０℃／分で上昇させた。空間速度ＳＶは６００００ｈ−１とした。
−Evaluation of exhaust gas purification performance−
About each catalyst of the said Example 1-5 and the comparative examples 1 and 2, after performing the aging which hold | maintains to 1000 degreeC air | atmosphere for 24 hours, exhaust gas purification performance using a model gas circulation reaction apparatus and an exhaust gas analyzer I investigated. That is, after performing pretreatment for flowing an air-fuel ratio rich model gas (temperature 600 ° C.) at a space velocity SV = 120,000 h −1 for 20 minutes, the purification performance evaluation model gas is used to purify HC, CO, and NOx. The light-off temperature T50 and the high temperature purification rate C500 were measured. T50 is the gas temperature at the catalyst inlet when the temperature of the model gas flowing into the catalyst is gradually increased from room temperature and the purification rate reaches 50%. C500 is the purification rate when the catalyst inlet gas temperature is 500 ° C. The model gas for purification performance evaluation was A / F = 14.7 ± 0.9. That is, the A / F is forced at an amplitude of ± 0.9 by adding a predetermined amount of fluctuation gas in a pulse form at 1 Hz while constantly flowing the main stream gas of A / F = 14.7. Vibrated. Table 3 shows the composition of the model gas for purification performance evaluation. Further, the catalyst inlet gas temperature was increased from 100 ° C. to 500 ° C. at a rate of temperature increase of 30 ° C./min. The space velocity SV was 60000h- 1 .
Ｔ５０の結果を図１乃至図３に示し、Ｃ５００の結果を図４乃至図６に示す。まず、図１乃至図３（Ｔ５０）をみると、中空状複酸化物粒子における立方晶の質量分率によってＴ５０が変化することがわかる。同図によれば、炉室温度１０５０℃の実施例２（立方晶の質量分率＝７７．１％）のときに、Ｔ５０が最も低くなり、それよりも当該質量分率が大きくなるとき及び小さくなるときのいずれもＴ５０が高くなっている。また、図４乃至図６（Ｃ５００）をみると、立方晶の質量分率によってＣ５００が変化しており、炉室温度１０５０℃の実施例２（立方晶の質量分率＝７７．１％）でＣ５００が最も高く、その質量分率が大きくなるほどＣ５００が低下している。 The results of T50 are shown in FIGS. 1 to 3, and the results of C500 are shown in FIGS. First, when FIG. 1 thru | or FIG. 3 (T50) is seen, it turns out that T50 changes with the mass fraction of the cubic crystal in a hollow double oxide particle. According to the figure, in Example 2 (cubic mass fraction = 77.1%) at a furnace chamber temperature of 1050 ° C., T50 is the lowest and the mass fraction is larger than that. T50 is high in every case of decreasing. Moreover, when FIG. 4 thru | or FIG. 6 (C500) is seen, C500 is changing with the mass fraction of the cubic crystal, Example 2 (mass fraction of a cubic crystal = 77.1%) of furnace chamber temperature 1050 degreeC. C500 is the highest, and C500 decreases as the mass fraction increases.
以上から、上記立方晶の質量分率を炉室温度１０００℃の比較例２よりも小さい８２％以下とすることにより、そして、当該質量分率を７４％以上とすることにより、触媒の耐熱性が向上し、エージング後でも優れた低温活性及び高温活性が得られることがわかる。
From the above, by making the mass fraction of the
図７は、上記実施例１−３及び比較例１，２のＨＣ浄化に関するＴ５０の結果を、中空状複酸化物粒子における立方晶中のＣｅ占有率との関係でグラフ化したものである。同図によれば、立方晶中のＣｅ占有率が７５mol％以上８３mol％以下であるときに、耐熱性が高くなる、つまりエージング後も良好な低温活性を示すということができる。これは、表１に示したように、立方晶中のＣｅ占有率が７５mol％未満（比較例１及び比較例２）の場合、立方晶に対する正方晶の割合、すなわち、立方晶と正方晶との合計に対する正方晶の分率が小さく、正方晶が立体障害となって立方晶結晶子の粗大化を抑制する効果が小さくなるが、立方晶中のＣｅ占有率が７５mol％以上８３mol％以下（実施例１〜３）では、正方晶の上記分率が増加するため、該正方晶が立体障害となって立方晶結晶子の粗大化を抑制する効果が大きくなったものと推察する。 FIG. 7 is a graph showing the results of T50 relating to HC purification in Examples 1-3 and Comparative Examples 1 and 2 in relation to the Ce occupancy in the cubic crystals in the hollow double oxide particles. According to the figure, it can be said that when the Ce occupancy in the cubic crystal is 75 mol% or more and 83 mol% or less, the heat resistance is increased, that is, good low temperature activity is exhibited even after aging. As shown in Table 1, when the Ce occupation ratio in the cubic crystal is less than 75 mol% (Comparative Example 1 and Comparative Example 2), the ratio of the tetragonal crystal to the cubic crystal, that is, the cubic and tetragonal crystals, The proportion of tetragonal crystals relative to the total of these is small, and the effect of suppressing the coarsening of cubic crystallites due to tetragonal crystals becomes steric hindrance, but the Ce occupancy in the cubic crystals is 75 mol% or more and 83 mol% or less ( In Examples 1 to 3), since the above-mentioned fraction of tetragonal crystals is increased, it is presumed that the tetragonal crystals became steric hindrance and the effect of suppressing the coarsening of the cubic crystallites was increased.
図８は炉室温度を１０５０℃としてＣｅＯ２／ＺｒＯ２質量比を変化させた、表２に示す実施例２，４，５のＴ５０の結果に基いて、ＣｅＯ２／（ＣｅＯ２＋ＺｒＯ２）比とＴ５０との関係をグラフ化したものである。同図から、ＣｅＯ２／（ＣｅＯ２＋ＺｒＯ２）比を７０質量％以上８０質量％以下にすると、すなわち、ＣｅＯ２／ＺｒＯ２質量比を７０／３０以上８０／２０以下にすると、耐熱性が高くなる、つまりエージング後も良好な低温活性を示すということができる。 FIG. 8 shows the results of T50 of Examples 2, 4, and 5 shown in Table 2 in which the CeO 2 / ZrO 2 mass ratio was changed at a furnace chamber temperature of 1050 ° C., and CeO 2 / (CeO 2 + ZrO 2 ). The relationship between the ratio and T50 is graphed. From the figure, when the CeO 2 / (CeO 2 + ZrO 2 ) ratio is 70% by mass or more and 80% by mass or less, that is, when the CeO 2 / ZrO 2 mass ratio is 70/30 or more and 80/20 or less, the heat resistance is improved. It can be said that it becomes high, that is, it exhibits good low-temperature activity even after aging.
＜リーンＮＯｘ触媒に関する実施例及び比較例＞
−触媒調製法−
Ｃｅ−Ｚｒ系の中空状複酸化物粒子（貴金属担持なし）、γ−アルミナ粉末、貴金属溶液（ジニトロジアミン白金硝酸溶液及び硝酸ロジウム溶液）、ＮＯｘ吸蔵材（酢酸バリウム、酢酸ストロンチウム）及び水の各所定量を容器に入れ攪拌しながら、１００℃まで加熱することにより、水分を蒸発させる。得られた乾固物を粉砕して粉末状にし、これを５００℃の温度に２時間加熱保持する焼成を行なうことにより、上記中空状複酸化物粒子及びγ−アルミナ粉末をサポート材として、これに貴金属及びＮＯｘ吸蔵材が担持された触媒粉末を得る。
<Examples and comparative examples regarding lean NOx catalysts>
-Catalyst preparation method-
Ce-Zr-based hollow double oxide particles (no noble metal supported), γ-alumina powder, noble metal solution (dinitrodiamine platinum nitrate solution and rhodium nitrate solution), NOx storage material (barium acetate, strontium acetate) and water Water is evaporated by heating to 100 ° C. while stirring the fixed amount in a container. The dried product thus obtained is pulverized into a powder form, and this is heated and held at a temperature of 500 ° C. for 2 hours, thereby using the hollow double oxide particles and γ-alumina powder as a support material. A catalyst powder carrying a precious metal and a NOx occlusion material is obtained.
次に上記触媒粉末を塩基性Ｚｒバインダ及び水と混合してスラリーとし、このスラリーにハニカム担体を浸漬して引き上げ、余分なスラリーをエアブローで吹き飛ばす。次いで、コート層を乾燥させた後、５００℃の温度に２時間加熱保持する焼成を行なうことにより、リーンＮＯｘ触媒を得る。 Next, the catalyst powder is mixed with a basic Zr binder and water to form a slurry, the honeycomb carrier is immersed in the slurry and pulled up, and excess slurry is blown off by air blow. Next, after the coating layer is dried, a lean NOx catalyst is obtained by performing firing by heating and holding at a temperature of 500 ° C. for 2 hours.
ハニカム担体１Ｌ当たりの中空状複酸化物粒子担持量は３０ｇ以上２００ｇ以下が好ましく、同じくγ−アルミナ粉末の担持量は３０ｇ以上２００ｇ以下が好ましい。これらは貴金属（Ｐｔ，Ｒｈ）及びＮＯｘ吸蔵材（Ｂａ，Ｓｒ）のサポート材となるものであり、各々の担持量が少なすぎると、充分な量の貴金属及びＮＯｘ吸蔵材を高分散に担持することが難しくなり、また、その担持量が多すぎると、ハニカム担体の目詰まりを生じ易くなるからである。 The amount of hollow double oxide particles supported per liter of honeycomb carrier is preferably 30 g to 200 g, and the amount of γ-alumina powder supported is preferably 30 g to 200 g. These serve as support materials for the noble metal (Pt, Rh) and the NOx storage material (Ba, Sr). When the supported amount is too small, a sufficient amount of the noble metal and the NOx storage material are supported in a highly dispersed manner. This is because it becomes difficult, and if the amount of the carrier supported is too large, the honeycomb carrier is likely to be clogged.
ハニカム担体１Ｌ当たりのＰｔ担持量は０．０５ｇ以上２０ｇ以下が好ましく、同じくＲｈ担持量は０．０５ｇ以上２０ｇ以下が好ましい。これらはＮＯの浄化（酸化還元）に働くところ、その担持量が少なすぎると、ＮＯの酸化還元反応が充分に行なわれず、また、その担持量が多すぎても、凝集を起こし易くなるだけで、浄化性能の向上にはあまり働かず、かえってコスト高になるからである。 The amount of Pt supported per liter of honeycomb carrier is preferably 0.05 to 20 g, and the amount of Rh supported is preferably 0.05 to 20 g. These work for NO purification (oxidation and reduction). If the loading amount is too small, the oxidation / reduction reaction of NO is not performed sufficiently, and if the loading amount is too large, aggregation is easily caused. This is because it does not work very much to improve the purification performance, but rather increases the cost.
ハニカム担体１Ｌ当たりのＢａ担持量は５ｇ以上６０ｇ以下が好ましく、同じくＳｒ担持量は５ｇ以上６０ｇ以下が好ましい。これらはＮＯｘを吸蔵するところ、その担持量が少なすぎると、ＮＯｘの吸蔵が不十分になり、また、その担持量が多すぎても、凝集を起こし易くなるだけで、ＮＯｘ吸蔵量はそれほど増大せず、かえってコスト高になるからである。 The amount of Ba supported per liter of honeycomb carrier is preferably 5 g or more and 60 g or less, and the amount of Sr supported is preferably 5 g or more and 60 g or less. These occlude NOx. If the amount of NOx is too small, the amount of NOx occludes becomes insufficient, and if the amount is too much, the NOx occlusion amount increases so much that it only causes aggregation. This is because the cost is rather high.
−実施例Ａ，Ｂ，Ｅ，Ｆ，Ｇ及び比較例Ｃ，Ｄに係る触媒−
上記調製法によって実施例Ａ，Ｂ，Ｅ，Ｆ，Ｇ及び比較例Ｃ，Ｄに係る触媒を調製した。これら触媒では、その中空状複酸化物粒子として、上記＜三元触媒に関する実施例及び比較例＞で説明した炉室温度又はＣｅＯ２／ＺｒＯ２質量比が相異なるものを採用した。
-Catalysts according to Examples A, B, E, F, G and Comparative Examples C, D-
Catalysts according to Examples A, B, E, F, G and Comparative Examples C and D were prepared by the above preparation method. In these catalysts, those having different furnace chamber temperatures or CeO 2 / ZrO 2 mass ratios described in the above <Examples and comparative examples relating to three-way catalysts> were used as the hollow double oxide particles.
すなわち、表４に示すように、実施例Ａ，Ｂ，Ｅ及び比較例Ｃ，Ｄの中空状複酸化物粒子はいずれも、ＣｅＯ２／ＺｒＯ２質量比が７５／２５であり、炉室温度が、実施例Ａは１０２５℃のもの、実施例Ｂは１０５０℃のもの、実施例Ｅは１１００℃のもの、比較例Ｃは９５０℃のもの、比較例Ｄは１０００℃のものである。実施例Ｆの中空状複酸化物粒子は、ＣｅＯ２／ＺｒＯ２質量比６５／３５で炉室温度１０５０℃のものであり、実施例Ｇの中空状複酸化物粒子は、ＣｅＯ２／ＺｒＯ２質量比８５／１５で炉室温度１０５０℃のものである。 That is, as shown in Table 4, all of the hollow double oxide particles of Examples A, B, and E and Comparative Examples C and D had a CeO 2 / ZrO 2 mass ratio of 75/25, and the furnace chamber temperature. However, Example A is at 1025 ° C, Example B is at 1050 ° C, Example E is at 1100 ° C, Comparative Example C is at 950 ° C, and Comparative Example D is at 1000 ° C. The hollow double oxide particles of Example F are those having a CeO 2 / ZrO 2 mass ratio of 65/35 and a furnace chamber temperature of 1050 ° C., and the hollow double oxide particles of Example G are CeO 2 / ZrO 2. The mass ratio is 85/15 and the furnace chamber temperature is 1050 ° C.
ハニカム担体１Ｌ当たりの中空状複酸化物粒子の担持量は８０ｇ／Ｌ、γ−アルミナ担持量は８０ｇ／Ｌ、Ｐｔ担持量は３．５ｇ／Ｌ、Ｒｈ担持量は０．３ｇ／Ｌ、Ｂａ担持量は３５ｇ／Ｌ、Ｓｒ担持量５ｇ／Ｌである。 The amount of hollow double oxide particles supported per liter of honeycomb carrier is 80 g / L, the amount of γ-alumina supported is 80 g / L, the amount of Pt supported is 3.5 g / L, the amount of Rh supported is 0.3 g / L, Ba The supported amount is 35 g / L, and the Sr supported amount is 5 g / L.
−排気ガス浄化性能評価−
上記実施例Ａ，Ｂ，Ｅ，Ｆ，Ｇ及び比較例Ｃ，Ｄの各触媒について、７５０℃の大気雰囲気に２４時間保持するエージングを行なった後、モデルガス流通反応装置及び排気ガス分析装置を用いてリーンＮＯｘ浄化性能を調べた。すなわち、Ａ／Ｆリーンのモデル排気ガスを６０秒間流し、次にガス組成をＡ／Ｆリッチのモデル排気ガスに切り換えてこれを６０秒間流す、というサイクルを数回繰り返した後、ガス組成をＡ／ＦリッチからＡ／Ｆリーンに切り換えた時点から６０秒間のＮＯｘ浄化率（リーンＮＯｘ浄化率）を測定した。触媒入口ガス温度は２５０℃とした。Ａ／Ｆリーンのモデル排気ガス及びＡ／Ｆリッチのモデル排気ガスの組成は表５に示すとおりである。
−Evaluation of exhaust gas purification performance−
The catalysts of Examples A, B, E, F, G and Comparative Examples C and D were aged for 24 hours in an air atmosphere at 750 ° C., and then the model gas flow reactor and the exhaust gas analyzer were used. Used to examine the lean NOx purification performance. That is, after repeating the cycle of flowing the A / F lean model exhaust gas for 60 seconds, then switching the gas composition to the A / F rich model exhaust gas and flowing it for 60 seconds, the gas composition was changed to A The NOx purification rate (lean NOx purification rate) was measured for 60 seconds from the time of switching from / F rich to A / F lean. The catalyst inlet gas temperature was 250 ° C. The compositions of the A / F lean model exhaust gas and the A / F rich model exhaust gas are shown in Table 5.
図９は上記実施例Ａ，Ｂ，Ｅ及び比較例Ｃ，Ｄの各触媒のリーンＮＯｘ浄化率を示す。実施例Ａ，Ｂ，Ｅは比較例Ｃ，ＤよりもリーンＮＯｘ浄化率が高くなっている。従って、リーンＮＯｘ触媒の場合も、上記中空状複酸化物粒子の立方晶の質量分率を７４％以上８２％以下にすることが好ましい。特に７５％以上８２％以下に、さらには７６％以上８２％以下にすることが好ましい。 FIG. 9 shows the lean NOx purification rates of the catalysts of Examples A, B, E and Comparative Examples C, D. In Examples A, B, and E, the lean NOx purification rate is higher than in Comparative Examples C and D. Therefore, also in the case of a lean NOx catalyst, it is preferable that the cubic mass fraction of the hollow double oxide particles be 74% or more and 82% or less. In particular, it is preferably 75% or more and 82% or less, and more preferably 76% or more and 82% or less.
図１０は炉室温度を１０５０℃としてＣｅＯ２／ＺｒＯ２質量比を変化させた実施例Ｂ，Ｆ，Ｇの評価結果に基いて、ＣｅＯ２／（ＣｅＯ２＋ＺｒＯ２）比とリーンＮＯｘ浄化率との関係をグラフ化したものである。同図から、ＣｅＯ２／（ＣｅＯ２＋ＺｒＯ２）比を７０質量％以上８０質量％以下にすると、すなわち、ＣｅＯ２／ＺｒＯ２質量比を７０／３０以上８０／２０以下にすると、耐熱性が高くなる、つまりエージング後も良好なリーンＮＯｘ浄化性能を示すということができる。 FIG. 10 shows the CeO 2 / (CeO 2 + ZrO 2 ) ratio and the lean NOx purification rate based on the evaluation results of Examples B, F, and G in which the furnace chamber temperature was 1050 ° C. and the CeO 2 / ZrO 2 mass ratio was changed. Is a graph of the relationship. From the figure, when the CeO 2 / (CeO 2 + ZrO 2 ) ratio is 70% by mass or more and 80% by mass or less, that is, when the CeO 2 / ZrO 2 mass ratio is 70/30 or more and 80/20 or less, the heat resistance is improved. It can be said that a high lean NOx purification performance is exhibited even after aging.
なし None
Claims (4)
上記複酸化物は、ＣｅＯ２／ＺｒＯ２質量比が５０／５０以上であって、立方晶を含む複数種の結晶相が混在し、該複数種の結晶相中の立方晶の質量分率が７４％以上８２％以下であることを特徴とする排気ガス浄化用触媒。 In the exhaust gas purifying catalyst in which the hollow double oxide particles containing Ce and Zr are included in the catalyst layer on the carrier,
The double oxide has a CeO 2 / ZrO 2 mass ratio of 50/50 or more, and a plurality of types of crystal phases including cubic crystals are mixed, and the mass fraction of the cubic crystals in the plurality of types of crystal phases is An exhaust gas purifying catalyst characterized by being 74% or more and 82% or less.
上記複酸化物は、上記立方晶の他に正方晶を含むことを特徴とする排気ガス浄化用触媒。 In claim 1,
The double oxide contains a tetragonal crystal in addition to the cubic crystal.
上記ＣｅＯ２／ＺｒＯ２質量比が７０／３０以上８０／２０以下であることを特徴とする排気ガス浄化用触媒。 In claim 1 or claim 2,
The exhaust gas purification catalyst, wherein the CeO 2 / ZrO 2 mass ratio is 70/30 or more and 80/20 or less.
自動車の排気ガスを浄化する三元触媒又はリーンＮＯｘ触媒として用いられることを特徴とする排気ガス浄化用触媒。 In any one of Claim 1 thru | or 3,
An exhaust gas purification catalyst characterized by being used as a three-way catalyst or a lean NOx catalyst for purifying automobile exhaust gas.
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| JPH09202607A (en) * | 1996-01-25 | 1997-08-05 | Toyota Central Res & Dev Lab Inc | Production of oxide powder |
| JPH11165067A (en) * | 1997-12-03 | 1999-06-22 | Kinya Adachi | Production of ceria-zirconia compound oxide for exhaust gas purifying auxiliary catalyst |
| JP2001348223A (en) * | 2000-06-01 | 2001-12-18 | Kcm Corp | Ceria-zirconia solid-solution particulate and method for manufacturing the same |
| JP2005224707A (en) * | 2004-02-13 | 2005-08-25 | Toyota Central Res & Dev Lab Inc | Ceria oxide assistant catalyst |
| JP2005334791A (en) * | 2004-05-28 | 2005-12-08 | Toda Kogyo Corp | Catalyst for cleaning exhaust gas and oxygen storage material for the catalyst |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JPH0873221A (en) * | 1994-07-01 | 1996-03-19 | Toyota Central Res & Dev Lab Inc | Production of multiple oxide powder |
| JPH09202607A (en) * | 1996-01-25 | 1997-08-05 | Toyota Central Res & Dev Lab Inc | Production of oxide powder |
| JPH11165067A (en) * | 1997-12-03 | 1999-06-22 | Kinya Adachi | Production of ceria-zirconia compound oxide for exhaust gas purifying auxiliary catalyst |
| JP2001348223A (en) * | 2000-06-01 | 2001-12-18 | Kcm Corp | Ceria-zirconia solid-solution particulate and method for manufacturing the same |
| JP2005224707A (en) * | 2004-02-13 | 2005-08-25 | Toyota Central Res & Dev Lab Inc | Ceria oxide assistant catalyst |
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| CN111396179A (en) * | 2020-03-31 | 2020-07-10 | 潍柴动力股份有限公司 | Method and device for determining urea crystal amount in engine |
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