JP2003265958A - Exhaust gas cleaning catalyst - Google Patents
Exhaust gas cleaning catalystInfo
- Publication number
- JP2003265958A JP2003265958A JP2002074719A JP2002074719A JP2003265958A JP 2003265958 A JP2003265958 A JP 2003265958A JP 2002074719 A JP2002074719 A JP 2002074719A JP 2002074719 A JP2002074719 A JP 2002074719A JP 2003265958 A JP2003265958 A JP 2003265958A
- Authority
- JP
- Japan
- Prior art keywords
- ceo
- exhaust gas
- zro
- purifying catalyst
- osc
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
- 239000003054 catalyst Substances 0.000 title claims abstract description 55
- 238000004140 cleaning Methods 0.000 title abstract 3
- 239000007789 gas Substances 0.000 claims abstract description 41
- 150000001768 cations Chemical class 0.000 claims abstract description 29
- 229910000510 noble metal Inorganic materials 0.000 claims abstract description 27
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims abstract description 12
- 239000001301 oxygen Substances 0.000 claims abstract description 12
- 229910052760 oxygen Inorganic materials 0.000 claims abstract description 12
- 239000002131 composite material Substances 0.000 claims description 39
- 229910018072 Al 2 O 3 Inorganic materials 0.000 claims description 12
- 229910044991 metal oxide Inorganic materials 0.000 claims description 11
- 150000004706 metal oxides Chemical class 0.000 claims description 11
- 239000002245 particle Substances 0.000 claims description 11
- 239000006104 solid solution Substances 0.000 claims description 11
- 230000001590 oxidative effect Effects 0.000 claims description 9
- 125000004430 oxygen atom Chemical group O* 0.000 abstract description 16
- 238000010521 absorption reaction Methods 0.000 abstract description 5
- 238000003860 storage Methods 0.000 abstract description 2
- 238000010438 heat treatment Methods 0.000 description 35
- 238000000034 method Methods 0.000 description 25
- 230000009467 reduction Effects 0.000 description 20
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 19
- 230000007423 decrease Effects 0.000 description 15
- 230000000694 effects Effects 0.000 description 13
- 239000002244 precipitate Substances 0.000 description 11
- 230000000052 comparative effect Effects 0.000 description 9
- 229910052751 metal Inorganic materials 0.000 description 9
- 239000002184 metal Substances 0.000 description 8
- 239000002243 precursor Substances 0.000 description 8
- 238000000746 purification Methods 0.000 description 8
- 239000008188 pellet Substances 0.000 description 7
- 239000000243 solution Substances 0.000 description 7
- 239000011206 ternary composite Substances 0.000 description 7
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 7
- 238000000975 co-precipitation Methods 0.000 description 6
- 229910052761 rare earth metal Inorganic materials 0.000 description 6
- 239000010970 precious metal Substances 0.000 description 5
- 238000005245 sintering Methods 0.000 description 5
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical group N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 4
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 description 4
- 230000032683 aging Effects 0.000 description 4
- 150000004703 alkoxides Chemical class 0.000 description 4
- 235000011114 ammonium hydroxide Nutrition 0.000 description 4
- 150000001785 cerium compounds Chemical class 0.000 description 4
- 238000004519 manufacturing process Methods 0.000 description 4
- 239000010948 rhodium Substances 0.000 description 4
- 150000003755 zirconium compounds Chemical class 0.000 description 4
- 229910004298 SiO 2 Inorganic materials 0.000 description 3
- 125000004429 atom Chemical group 0.000 description 3
- 238000006243 chemical reaction Methods 0.000 description 3
- 150000003839 salts Chemical class 0.000 description 3
- 238000001179 sorption measurement Methods 0.000 description 3
- 238000003756 stirring Methods 0.000 description 3
- 238000012360 testing method Methods 0.000 description 3
- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 description 2
- 229910010413 TiO 2 Inorganic materials 0.000 description 2
- 239000002253 acid Substances 0.000 description 2
- 239000007864 aqueous solution Substances 0.000 description 2
- IXSUHTFXKKBBJP-UHFFFAOYSA-L azanide;platinum(2+);dinitrite Chemical compound [NH2-].[NH2-].[Pt+2].[O-]N=O.[O-]N=O IXSUHTFXKKBBJP-UHFFFAOYSA-L 0.000 description 2
- 150000001875 compounds Chemical class 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
- 150000002736 metal compounds Chemical class 0.000 description 2
- 239000002923 metal particle Substances 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 238000006386 neutralization reaction Methods 0.000 description 2
- 229910052697 platinum Inorganic materials 0.000 description 2
- 239000011148 porous material Substances 0.000 description 2
- 238000001556 precipitation Methods 0.000 description 2
- 229910052703 rhodium Inorganic materials 0.000 description 2
- XNDZQQSKSQTQQD-UHFFFAOYSA-N 3-methylcyclohex-2-en-1-ol Chemical compound CC1=CC(O)CCC1 XNDZQQSKSQTQQD-UHFFFAOYSA-N 0.000 description 1
- NLXLAEXVIDQMFP-UHFFFAOYSA-N Ammonium chloride Substances [NH4+].[Cl-] NLXLAEXVIDQMFP-UHFFFAOYSA-N 0.000 description 1
- 238000004438 BET method Methods 0.000 description 1
- 229910052684 Cerium Inorganic materials 0.000 description 1
- 101100321669 Fagopyrum esculentum FA02 gene Proteins 0.000 description 1
- 229910021193 La 2 O 3 Inorganic materials 0.000 description 1
- 229910052779 Neodymium Inorganic materials 0.000 description 1
- 229910052777 Praseodymium Inorganic materials 0.000 description 1
- 229910052772 Samarium Inorganic materials 0.000 description 1
- 238000002441 X-ray diffraction Methods 0.000 description 1
- GEIAQOFPUVMAGM-UHFFFAOYSA-N ZrO Inorganic materials [Zr]=O GEIAQOFPUVMAGM-UHFFFAOYSA-N 0.000 description 1
- 230000002776 aggregation Effects 0.000 description 1
- 238000004220 aggregation Methods 0.000 description 1
- 229910000288 alkali metal carbonate Inorganic materials 0.000 description 1
- 150000008041 alkali metal carbonates Chemical class 0.000 description 1
- 150000008044 alkali metal hydroxides Chemical class 0.000 description 1
- 229910021529 ammonia Inorganic materials 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- 230000004888 barrier function Effects 0.000 description 1
- 239000002585 base Substances 0.000 description 1
- 230000033228 biological regulation Effects 0.000 description 1
- 229910002091 carbon monoxide Inorganic materials 0.000 description 1
- 230000003197 catalytic effect Effects 0.000 description 1
- XQTIWNLDFPPCIU-UHFFFAOYSA-N cerium(3+) Chemical class [Ce+3] XQTIWNLDFPPCIU-UHFFFAOYSA-N 0.000 description 1
- QQZMWMKOWKGPQY-UHFFFAOYSA-N cerium(3+);trinitrate;hexahydrate Chemical compound O.O.O.O.O.O.[Ce+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O QQZMWMKOWKGPQY-UHFFFAOYSA-N 0.000 description 1
- 150000003841 chloride salts Chemical class 0.000 description 1
- 239000003426 co-catalyst Substances 0.000 description 1
- 229910052878 cordierite Inorganic materials 0.000 description 1
- 238000000151 deposition Methods 0.000 description 1
- 238000003795 desorption Methods 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 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 1
- 239000002612 dispersion medium Substances 0.000 description 1
- 238000004090 dissolution Methods 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 238000001704 evaporation Methods 0.000 description 1
- 239000010419 fine particle Substances 0.000 description 1
- 238000010304 firing Methods 0.000 description 1
- 238000010335 hydrothermal treatment Methods 0.000 description 1
- 239000011261 inert gas Substances 0.000 description 1
- 230000003993 interaction Effects 0.000 description 1
- 229910052740 iodine Inorganic materials 0.000 description 1
- 229910052746 lanthanum Inorganic materials 0.000 description 1
- 238000011068 loading method Methods 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 239000011259 mixed solution Substances 0.000 description 1
- 238000012544 monitoring process Methods 0.000 description 1
- 230000003472 neutralizing effect Effects 0.000 description 1
- 150000002823 nitrates Chemical class 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 229910052763 palladium Inorganic materials 0.000 description 1
- KDLHZDBZIXYQEI-UHFFFAOYSA-N palladium Substances [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 description 1
- 231100000572 poisoning Toxicity 0.000 description 1
- 230000000607 poisoning effect Effects 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 229910001404 rare earth metal oxide Inorganic materials 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 238000001226 reprecipitation Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- MHOVAHRLVXNVSD-UHFFFAOYSA-N rhodium atom Chemical compound [Rh] MHOVAHRLVXNVSD-UHFFFAOYSA-N 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- 238000003980 solgel method Methods 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- 230000006641 stabilisation Effects 0.000 description 1
- 238000011105 stabilization Methods 0.000 description 1
- 239000000758 substrate Substances 0.000 description 1
- 150000003467 sulfuric acid derivatives Chemical class 0.000 description 1
- 230000002194 synthesizing effect Effects 0.000 description 1
- 238000002411 thermogravimetry Methods 0.000 description 1
- 229910052726 zirconium Inorganic materials 0.000 description 1
- GBNDTYKAOXLLID-UHFFFAOYSA-N zirconium(4+) ion Chemical class [Zr+4] GBNDTYKAOXLLID-UHFFFAOYSA-N 0.000 description 1
Abstract
Description
【０００１】[0001]
【発明の属する技術分野】本発明は、高い酸素吸蔵放出
能（以下 OSCという）を有し、しかも耐久性にも優れた
排ガス浄化用触媒に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying catalyst having a high oxygen storage / release capacity (hereinafter referred to as OSC) and excellent durability.
【０００２】[0002]
【従来の技術】従来より自動車の排ガス浄化用触媒とし
て、排ガス中のCO及びHCの酸化とNOxの還元とを同時に
行って浄化する三元触媒が用いられている。このような
三元触媒としては、例えばコーディエライトなどからな
る耐熱性ハニカム基材にγ-Al2O3からなる担体層を形成
し、その担体層に白金（Pt）やロジウム（Rh)などの触
媒金属を担持させたものが広く知られている。2. Description of the Related Art Conventionally, as a catalyst for purifying exhaust gas of automobiles, a three-way catalyst has been used which purifies the exhaust gas by simultaneously oxidizing CO and HC and reducing NO x . As such a three-way catalyst, for example, a carrier layer made of γ-Al 2 O 3 is formed on a heat-resistant honeycomb substrate made of cordierite or the like, and platinum (Pt) or rhodium (Rh) is formed on the carrier layer. It is widely known that the above catalyst metal is supported.
【０００３】ところで排ガス浄化用触媒に用いられる担
体の条件としては、比表面積が大きく耐熱性が高いこと
が挙げられ、一般には Al2O3、SiO2、ZrO2、TiO2などが
用いられることが多い。また OSCをもつCeO2を助触媒と
して併用することで、排ガスの雰囲気変動を緩和するこ
とも行われている。The condition of the carrier used for the exhaust gas purifying catalyst is that it has a large specific surface area and high heat resistance. Generally, Al 2 O 3 , SiO 2 , ZrO 2 , TiO 2 and the like are used. There are many. Also, by using CeO 2 with OSC as a co-catalyst together, it is possible to mitigate the atmospheric fluctuation of exhaust gas.
【０００４】ところが従来の排ガス浄化用触媒では、 8
00℃を超えるような高温にさらされると、シンタリング
による担体の比表面積の低下、触媒金属の粒成長が生
じ、さらにはCeO2のもつ OSCも低下するために、浄化性
能が著しく低下するという不具合があった。However, in the conventional exhaust gas purifying catalyst,
When exposed to a high temperature of more than 00 ° C, the specific surface area of the carrier decreases due to sintering, the grain growth of the catalytic metal occurs, and the OSC of CeO 2 also decreases, resulting in a marked decrease in purification performance. There was a problem.
【０００５】また近年の排ガス規制の強化により、エン
ジン始動からごく短い時間にも排ガスを浄化する必要性
がきわめて高くなっている。そのためには、より低温で
触媒を活性化し、排出規制成分を浄化しなければならな
い。中でもPtをCeO2に担持した触媒は、低温からCOを浄
化する性能に長けている。このような触媒を用いれば、
COが低温で着火されることによってPtのCO吸着被毒が緩
和され、HCの着火性が向上する。また、これによって触
媒表面の暖機が促進されるため、低温域からHCを浄化す
ることができる。さらに、この触媒では、水性ガスシフ
ト反応によって低温域でH2が生成されるため、そのH2と
NOx との反応により低温域からNOx を還元浄化すること
ができる。Further, due to the recent tightening of exhaust gas regulations, it becomes extremely necessary to purify exhaust gas within a very short time after the engine is started. For that purpose, the catalyst must be activated at a lower temperature to purify the emission control component. Above all, the catalyst in which Pt is supported on CeO 2 is excellent in the ability to purify CO from a low temperature. With such a catalyst,
By igniting CO at a low temperature, CO adsorption poisoning of Pt is mitigated, and the ignitability of HC is improved. Further, this promotes warm-up of the catalyst surface, so that HC can be purified from a low temperature range. Furthermore, in this catalyst, since the H 2 is generated in a low temperature region by water gas shift reaction, and its H 2
It is possible to reduce and purify NO x from the low temperature zone by reaction with NO x.
【０００６】しかし従来のCeO2にPtなどを担持した触媒
においては、実際の排ガス中における耐久性に乏しく、
熱によってCeO2がシンタリングしてしまい実用的ではな
い。実際の排ガス中で使用するためには、CeO2の性質を
失うことなく耐熱性を向上させる必要性がある。またCe
O2のシンタリングに伴ってPtに粒成長が生じ活性が低下
するため、担体上のPtの安定化が求められている。However, in the conventional catalyst in which Pt is supported on CeO 2 , the durability in actual exhaust gas is poor,
The heat causes CeO 2 to sinter, which is not practical. For use in actual exhaust gas, it is necessary to improve the heat resistance without losing the properties of CeO 2 . Also Ce
Stabilization of Pt on the carrier is required because grain growth of Pt occurs due to O 2 sintering and activity decreases.
【０００７】また担体にCeO2を含む三元触媒でも、高温
にさらされるとCeO2によって発現される OSCが低下す
る。これはCeO2のシンタリング及び担持されている貴金
属の粒成長と、貴金属の酸化、RhのCeO2への固溶などが
原因である。そして OSCが低い触媒においては、変動す
る雰囲気に貴金属がさらされやすく、貴金属の劣化（凝
集や固溶）がさらに促進されてしまう。Even with a three-way catalyst containing CeO 2 as a carrier, the OSC expressed by CeO 2 decreases when exposed to high temperatures. This is due to sintering of CeO 2 and grain growth of the precious metal supported, oxidation of the precious metal, and solid solution of Rh in CeO 2 . In a catalyst with a low OSC, the noble metal is easily exposed to the changing atmosphere, and the deterioration (aggregation or solid solution) of the noble metal is further promoted.
【０００８】そこで特開平8-215569号公報には、金属ア
ルコキシドから調製されたCeO2−ZrO2複合酸化物を用い
る技術が開示されている。金属アルコキシドからゾルゲ
ル法により調製されたCeO2−ZrO2複合酸化物は、CeとZr
とが原子又は分子レベルで複合化されて固溶体となって
いるため、耐熱性が向上し初期から耐久後まで高い OSC
が確保される。Japanese Unexamined Patent Publication (Kokai) No. 8-215569 discloses a technique using a CeO 2 --ZrO 2 composite oxide prepared from a metal alkoxide. CeO 2 -ZrO 2 composite oxide prepared by sol-gel method from metal alkoxide is Ce and Zr
Since and are compounded at the atomic or molecular level to form a solid solution, the heat resistance improves and the OSC is high from the beginning to the end of durability.
Is secured.
【０００９】このような複合酸化物は、アルコキシド
法、共沈法などにより複数の金属元素を含む酸化物前駆
体を調製し、それを焼成することで製造することができ
る。中でも共沈法は、アルコキシド法などに比べて原料
コストが安価であるため、得られる複合酸化物も安価と
なる利点があり、複合酸化物の製造に広く用いられてい
る。Such a complex oxide can be produced by preparing an oxide precursor containing a plurality of metal elements by an alkoxide method, a coprecipitation method or the like, and firing it. Among them, the coprecipitation method has a merit that the raw material cost is lower than that of the alkoxide method and the like, and thus the obtained composite oxide is also inexpensive, and is widely used in the production of the composite oxide.
【００１０】ところが上記した特開平8-215569号公報に
記載の複合酸化物では、 OSCがまだ不充分であり、さら
なる OSCの向上が求められている。そこで特開平11−16
5067号公報には、セリウム（ III）塩とジルコニウム
（IV）塩を含む溶液から共沈法によって沈殿を形成し、
その沈殿を不活性雰囲気又は非酸化性雰囲気下で 800〜
1000℃に加熱保持する方法が記載されている。この方法
によれば、得られる複合酸化物はパイロクロア相に帰属
するＸ線回折ピークを有し、高い OSCを示す。However, the composite oxide described in Japanese Patent Application Laid-Open No. 8-215569 mentioned above is still insufficient in OSC, and further improvement in OSC is required. Therefore, JP 11-16
No. 5067 discloses that a precipitate is formed by a coprecipitation method from a solution containing a cerium (III) salt and a zirconium (IV) salt,
800 ~ under an inert or non-oxidizing atmosphere
A method of heating and holding at 1000 ° C is described. According to this method, the obtained composite oxide has an X-ray diffraction peak attributed to the pyrochlore phase and exhibits a high OSC.
【００１１】また特開2001−104782号公報には、Al2O3-
CeO2-ZrO2複合酸化物に貴金属を担持し、非酸化性雰囲
気下にて1050〜1150℃で熱処理を行うことが記載されて
いる。これにより貴金属が担体の細孔内に物理的に固定
され、貴金属の粒成長を抑制することができる。Further, Japanese Patent Laid-Open No. 2001-104782 discloses Al 2 O 3-
It is described that a noble metal is supported on a CeO 2 —ZrO 2 composite oxide and heat treatment is performed at 1050-1150 ° C. in a non-oxidizing atmosphere. As a result, the precious metal is physically fixed in the pores of the carrier, and the grain growth of the precious metal can be suppressed.
【００１２】[0012]
【発明が解決しようとする課題】特開平11−165067号公
報に記載の方法によれば、確かに高い OSCを有するCeO2
−ZrO2複合酸化物が得られる。しかしながらこの方法で
は、 800〜1000℃に加熱保持しているためにCeO2−ZrO2
複合酸化物の比表面積の低下が避けられず、排ガス浄化
用助触媒として用いた場合には実用的な高い浄化活性を
得ることは困難である。According to the method described in Japanese Patent Laid-Open No. 11-165067, it is possible to obtain CeO 2 having a high OSC.
A -ZrO 2 composite oxide is obtained. However, in this method, since it is heated and held at 800 to 1000 ° C, CeO 2 -ZrO 2
It is unavoidable that the specific surface area of the composite oxide decreases, and it is difficult to obtain a practical high purification activity when used as an exhaust gas purification promoter.
【００１３】また特開2001−104782号公報に記載の方法
では、1050℃以上の熱処理によってAl2O3-CeO2-ZrO2複
合酸化物からなる担体にシンタリングが生じ、 OSCが低
下するため、排ガス浄化用触媒として実用的な性能を得
ることが困難となる。Further, in the method described in Japanese Patent Laid-Open No. 2001-104782, heat treatment at 1050 ° C. or higher causes sintering on the carrier composed of Al 2 O 3 —CeO 2 —ZrO 2 composite oxide, resulting in a decrease in OSC. However, it becomes difficult to obtain practical performance as an exhaust gas purifying catalyst.
【００１４】本発明はこのような事情に鑑みてなされた
ものであり、高い OSCを発現し、かつ微細な貴金属を担
持した排ガス浄化用触媒を提供することを目的とする。The present invention has been made in view of the above circumstances, and an object thereof is to provide an exhaust gas purifying catalyst which exhibits a high OSC and which carries a fine noble metal.
【００１５】[0015]
【課題を解決するための手段】上記課題を解決できる本
発明の排ガス浄化用触媒の特徴は、CeO2とZrO2を主成分
とする複合酸化物を含む担体に貴金属を担持した後、還
元性雰囲気中にて 600〜1000℃で熱処理されてなること
にある。The characteristics of the exhaust gas-purifying catalyst of the present invention that can solve the above-mentioned problems are that after reducing a noble metal on a carrier containing a complex oxide containing CeO 2 and ZrO 2 as main components, It is to be heat-treated at 600-1000 ℃ in the atmosphere.
【００１６】本発明の排ガス浄化用触媒は、酸化性雰囲
気下において 500℃程度で十分に酸化処理を行った後に
100〜 500℃の還元性雰囲気下において放出される酸素
量が、理論限界値の80％以上である特性をもつことが好
ましい。また比表面積が20m2／ｇ以上であること、貴金
属の粒子径が２〜10nmの範囲にあることが特に好まし
い。The exhaust gas-purifying catalyst of the present invention is used after being sufficiently oxidized at about 500 ° C. in an oxidizing atmosphere.
It is preferable that the amount of oxygen released in a reducing atmosphere at 100 to 500 ° C. is 80% or more of the theoretical limit value. It is particularly preferable that the specific surface area is 20 m 2 / g or more and the particle size of the noble metal is in the range of 2 to 10 nm.
【００１７】さらに本発明の排ガス浄化用触媒における
担体中では、CeO2とZrO2は少なくとも一部が互いに固溶
した固溶体を形成していることが望ましく、Ceカチオン
及びZrカチオンの少なくとも一部が規則配列しているこ
とがさらに望ましい。Further, in the carrier of the exhaust gas purifying catalyst of the present invention, it is desirable that at least a part of CeO 2 and ZrO 2 form a solid solution with each other, and at least a part of Ce cation and Zr cation are formed. It is more desirable to have a regular arrangement.
【００１８】またこの担体は、CeO2と、ZrO2と、CeO2及
びZrO2と反応しない金属酸化物との複合酸化物を含み、
CeO2及びZrO2と反応しない金属酸化物は Al2O3であるこ
とが望ましい。This carrier also contains a composite oxide of CeO 2 , ZrO 2, and a metal oxide that does not react with CeO 2 and ZrO 2 .
The metal oxide that does not react with CeO 2 and ZrO 2 is preferably Al 2 O 3 .
【００１９】[0019]
【発明の実施の形態】本発明の排ガス浄化用触媒では、
CeO2とZrO2を主成分とする複合酸化物を含む担体に貴金
属を担持した後、還元性雰囲気中にて 600〜1000℃で熱
処理されている。貴金属を担持した状態での還元熱処理
によって、酸化性雰囲気下において 500℃程度で十分に
酸化処理を行った後に 100〜 500℃の還元性雰囲気下に
おいて放出される酸素量が、理論限界値の80％以上であ
るという高い OSCが発現され、しかもきわめて高い活性
を示す。この理由は明らかではないが、以下のように推
定される。BEST MODE FOR CARRYING OUT THE INVENTION In the exhaust gas purifying catalyst of the present invention,
After supporting a noble metal on a carrier containing a complex oxide containing CeO 2 and ZrO 2 as main components, it is heat-treated at 600 to 1000 ° C in a reducing atmosphere. The amount of oxygen released in a reducing atmosphere at 100 to 500 ° C after the oxidizing treatment is sufficiently performed at about 500 ° C in an oxidizing atmosphere by the reduction heat treatment with the noble metal supported is 80% of the theoretical limit value. A high OSC of more than 100% is expressed, and extremely high activity is exhibited. The reason for this is not clear, but it is estimated as follows.
【００２０】通常のCeO2−ZrO2複合酸化物は固溶体を形
成しているが、単位格子内におけるCeカチオンとZrカチ
オンの配列に規則性はない。 OSCが発現される機構は、
単位格子内のCeカチオンが３価と４価の価数変化を起こ
す際に電気的中性の原理によって酸素原子が放出される
ものである。この際に放出される酸素原子は、バルクの
場合にはZrカチオンに対して４配位した酸素原子である
と考えられている。The usual CeO 2 -ZrO 2 composite oxide forms a solid solution, but the arrangement of Ce cations and Zr cations in the unit cell is not regular. The mechanism by which OSC is expressed is
When Ce cations in the unit cell undergo trivalent and tetravalent valence changes, oxygen atoms are released by the principle of electrical neutrality. The oxygen atom released at this time is considered to be an oxygen atom which is tetra-coordinated with the Zr cation in the case of bulk.
【００２１】したがってCeカチオンとZrカチオンの配列
に規則性がない通常のCeO2−ZrO2複合酸化物では、Zrカ
チオンに対して４配位した酸素原子の数が少ないこと、
並びにCeカチオンが４価から３価へ価数変化する際にイ
オン半径が0.86Åから1.15Åに拡大することによって格
子に歪みが生じるため酸素原子が放出されにくいこと、
などの理由により、通常のCeO2−ZrO2複合酸化物に貴金
属を担持した触媒では理論限界値よりはるかに少ない O
SCしか得られない。Therefore, in a normal CeO 2 -ZrO 2 composite oxide having no regularity in the arrangement of Ce cations and Zr cations, the number of oxygen atoms tetracoordinated with Zr cations is small,
Also, when the cation of the Ce cation changes from tetravalent to trivalent, the ionic radius expands from 0.86Å to 1.15Å, which causes strain in the lattice and makes it difficult for oxygen atoms to be released.
For the reasons described above, in the case of a catalyst in which a noble metal is supported on an ordinary CeO 2 -ZrO 2 composite oxide, the amount of O is much less than the theoretical limit value.
Only SC can be obtained.
【００２２】また通常のCeO2−ZrO2複合酸化物でも、10
00℃を超える温度の還元性雰囲気下で処理することによ
り、理論限界値の80％以上の酸素を吸放出できるように
なる。しかしこの場合には、比表面積の低下が著しく、
現実的な触媒担体とはなり難い。Further, even with a normal CeO 2 --ZrO 2 composite oxide, 10
By treating in a reducing atmosphere at a temperature above 00 ° C, 80% or more of the theoretical limit value of oxygen can be absorbed and released. However, in this case, the reduction of the specific surface area is remarkable,
It is difficult to become a realistic catalyst carrier.
【００２３】しかしながら、CeO2とZrO2を主成分とする
複合酸化物を含む担体に貴金属を担持しておくことで、
貴金属がCeO2の格子酸素の吸放出の出入り口となるた
め、従来より低温の還元性雰囲気下で酸素原子の放出が
可能となる。このように酸素原子の放出が容易となるこ
とで、CeカチオンとZrカチオンがより規則的な配列に近
づき、高い OSCが発現されると考えられる。そして還元
熱処理温度が 600〜1000℃であるので、熱処理時におけ
る比表面積の低下も抑制され、高い活性が発現される。However, by supporting a noble metal on a carrier containing a complex oxide containing CeO 2 and ZrO 2 as main components,
Since the noble metal serves as an inlet / outlet port for CeO 2 lattice oxygen absorption / release, it is possible to release oxygen atoms in a reducing atmosphere at a lower temperature than before. By facilitating the release of oxygen atoms in this way, it is considered that Ce cations and Zr cations approach a more regular arrangement and high OSC is expressed. Further, since the reduction heat treatment temperature is 600 to 1000 ° C., a decrease in specific surface area during heat treatment is also suppressed, and high activity is exhibited.
【００２４】さらにCeO2はPtを始めとする貴金属との親
和性が高いので、還元性雰囲気下での熱処理時には貴金
属とCeO2−ZrO2複合酸化物との相互作用が強くなり、熱
履歴による貴金属のシンタリングが抑制される。しかし
この熱処理時に貴金属にはある程度の粒成長が生じ、こ
のため貴金属の粒子径を２〜10nmの範囲とすることがで
きる。このように貴金属の粒子径が揃った状態では、貴
金属粒子どうしの表面分圧が揃うため粒成長が抑制さ
れ、耐久性が向上する。Further, since CeO 2 has a high affinity with noble metals such as Pt, the interaction between the noble metal and the CeO 2 —ZrO 2 composite oxide becomes strong during the heat treatment in a reducing atmosphere, which causes thermal history. Sintering of precious metals is suppressed. However, during this heat treatment, a certain amount of grain growth occurs in the noble metal, so that the grain size of the noble metal can be set in the range of 2 to 10 nm. In such a state where the particle diameters of the noble metals are uniform, the surface partial pressures of the noble metal particles are uniform, so that grain growth is suppressed and durability is improved.
【００２５】本発明の排ガス浄化用触媒における担体
は、CeO2とZrO2を主成分とするCeO2−ZrO2系複合酸化物
を含むものである。この複合酸化物以外に、 Al2O3，Ti
O2，SiO2，Y2O3などの他の酸化物又は複合酸化物を含ん
でもよいが、他の酸化物又は複合酸化物は担体全体の30
原子％以下とすることが望ましい。またCeO2−ZrO2系複
合酸化物におけるCe／Zr原子比は１／９〜９／１とする
ことが好ましく、３／７〜７／３とするのが特に好まし
い。Ceがこの範囲より少ないと OSCが不足し、Zrがこの
範囲より少ないとCeO2−ZrO2系複合酸化物の安定性が低
下するため比表面積が低くなってしまう。The carrier in the exhaust gas-purifying catalyst of the present invention contains CeO 2 -ZrO 2 -based composite oxide containing CeO 2 and ZrO 2 as main components. In addition to this composite oxide, Al 2 O 3 , Ti
Other oxides or complex oxides such as O 2 , SiO 2 and Y 2 O 3 may be included, but the other oxides or complex oxides may be included in the carrier.
It is desirable that the content be at most atomic%. Further, the Ce / Zr atomic ratio in the CeO 2 —ZrO 2 composite oxide is preferably 1/9 to 9/1, and particularly preferably 3/7 to 7/3. If Ce is less than this range, the OSC will be insufficient, and if Zr is less than this range, the stability of the CeO 2 —ZrO 2 -based composite oxide will decrease and the specific surface area will decrease.
【００２６】CeO2−ZrO2系複合酸化物は、CeO2と、ZrO2
と、CeO2及びZrO2と反応しない金属酸化物との三元系複
合酸化物であり、三元系複合酸化物では、CeO2とZrO2と
は少なくとも一部が互いに固溶していることが望まし
い。これにより耐熱性がさらに向上し、比表面積の低下
をさらに抑制できるとともにさらに高い OSCが発現され
る。さらにこの三元系複合酸化物はCeカチオン及びZrカ
チオンの少なくとも一部が規則配列していることが特に
望ましい。このような三元系複合酸化物を担体として用
いれば、CeO2及びZrO2と反応しない金属酸化物がCeO2−
ZrO2複合酸化物の間に介在しているため、還元性雰囲気
中にて 600〜1000℃で熱処理する際には、CeO2−ZrO2複
合酸化物とその反応しない金属酸化物が互いに障壁とな
るために粒成長が抑制される。The CeO 2 --ZrO 2 type composite oxide is composed of CeO 2 and ZrO 2
And a ternary complex oxide of a metal oxide that does not react with CeO 2 and ZrO 2 , and in the ternary complex oxide, at least a portion of CeO 2 and ZrO 2 are in solid solution with each other. Is desirable. As a result, the heat resistance is further improved, the decrease in specific surface area can be further suppressed, and a higher OSC can be expressed. Furthermore, it is particularly desirable that at least a part of Ce cations and Zr cations be regularly arranged in this ternary complex oxide. When such a ternary complex oxide is used as a carrier, a metal oxide that does not react with CeO 2 and ZrO 2 is CeO 2 −.
Since they are present between the ZrO 2 composite oxides, the CeO 2 —ZrO 2 composite oxides and the metal oxides that do not react with each other act as barriers to each other when performing heat treatment at 600 to 1000 ° C. in a reducing atmosphere. Therefore, grain growth is suppressed.
【００２７】上記三元系複合酸化物では、還元熱処理に
よってパイロクロア相などの規則相が形成され、Ceカチ
オン及びZrカチオンの少なくとも一部が規則配列する。
したがってZrカチオンに対して４配位した酸素原子の数
が多いこと、並びにCeカチオンが４価から３価へ価数変
化する際にイオン半径が0.86Åから1.15Åに拡大するこ
とによって生じる格子の歪みが小さくなり酸素原子が放
出され易いこと、などの理由により酸素原子の放出がさ
らに容易となるため OSCがさらに向上する。また高い比
表面積を維持できるとともに、前述した理由により貴金
属の粒成長も抑制されるので、耐久性に優れている。In the above ternary composite oxide, an ordered phase such as a pyrochlore phase is formed by the reduction heat treatment, and at least a part of Ce cations and Zr cations are regularly arranged.
Therefore, the number of oxygen atoms tetracoordinated to the Zr cation is large, and the lattice ionic radius is increased from 0.86Å to 1.15Å when the valence of Ce cation changes from tetravalent to trivalent. The OSC is further improved because the strain is reduced and the oxygen atoms are easily released, which makes it easier to release the oxygen atoms. In addition, a high specific surface area can be maintained, and grain growth of the noble metal can be suppressed for the above-mentioned reason, so that the durability is excellent.
【００２８】CeO2及びZrO2と反応しない金属酸化物とし
ては、 Al2O3、SiO2、TiO2などが例示される。中でも耐
熱性に優れた Al2O3が特に望ましい。またCe／Zr原子比
が１／９〜９／１とすることが好ましく、３／７〜７／
３とするのが特に好ましい。Ceがこの範囲より少ないと
OSCが不足し、Zrがこの範囲より少ないとCeO2−ZrO2複
合酸化物の安定性が低下するため比表面積が低くなって
しまう。またCeO2及びZrO2と反応しない金属酸化物の金
属をＭとすれば、原子比でＭ／（Ce＋Zr）＝１／５〜５
／１の範囲が好ましく、１／３〜３／１の範囲が特に好
ましい。金属Ｍがこの範囲より少ないと比表面積が低く
なり、金属Ｍがこの範囲より多くなるとCeO2量が相対的
に減少する結果 OSCが低くなってしまう。Examples of metal oxides that do not react with CeO 2 and ZrO 2 include Al 2 O 3 , SiO 2 and TiO 2 . Of these, Al 2 O 3 having excellent heat resistance is particularly desirable. Further, the Ce / Zr atomic ratio is preferably 1/9 to 9/1, and 3/7 to 7 /
It is particularly preferable that the number is 3. If Ce is less than this range
When the OSC is insufficient and the Zr is less than this range, the stability of the CeO 2 —ZrO 2 composite oxide decreases, and the specific surface area becomes low. If the metal of the metal oxide that does not react with CeO 2 and ZrO 2 is M, the atomic ratio is M / (Ce + Zr) = 1/5 to 5
The range of / 1 is preferable, and the range of 1/3 to 3/1 is particularly preferable. When the amount of the metal M is less than this range, the specific surface area is low, and when the amount of the metal M is more than this range, the amount of CeO 2 is relatively reduced, resulting in a lower OSC.
【００２９】CeO2及びZrO2と反応しない金属酸化物が A
l2O3である場合には、さらに希土類元素酸化物を含み、
希土類元素酸化物の70mol%以上が Al2O3中に固溶してい
ることが望ましい。これにより Al2O3の耐熱性が向上す
るとともに、希土類元素酸化物の固溶によるCeO2の OSC
の低下を抑制することができる。希土類元素酸化物の90
mol%以上が Al2O3中に固溶していることがさらに望まし
い。この希土類元素酸化物としては、La，Nd，Sm，Prな
どの酸化物が例示されるが、 La2O3が最も好ましい。A metal oxide that does not react with CeO 2 and ZrO 2 is A
In the case of l 2 O 3 , further contains a rare earth element oxide,
It is desirable that 70 mol% or more of the rare earth element oxide be in solid solution in Al 2 O 3 . As a result, the heat resistance of Al 2 O 3 is improved and the OSC of CeO 2 due to the solid solution of the rare earth element oxide is increased.
Can be suppressed. 90 of rare earth oxides
It is more desirable that at least mol% be solid-solved in Al 2 O 3 . Examples of the rare earth element oxide include oxides of La, Nd, Sm, Pr and the like, but La 2 O 3 is most preferable.
【００３０】なお希土類元素酸化物を含む場合には、希
土類元素原子数とAl原子数の合計を前記金属Ｍの原子数
とし、CeO2−ZrO2複合酸化物との組成比を上述の原子比
範囲とすればよい。When the rare earth element oxide is included, the total number of rare earth element atoms and Al atoms is the number of atoms of the metal M, and the composition ratio with the CeO 2 --ZrO 2 composite oxide is the above atomic ratio. It should be a range.
【００３１】そして上記した三元系複合酸化物は、上記
の特有の構成を有しているために還元熱処理後あるいは
高温耐久後にも、20〜60m2／ｇと従来のCeO2−ZrO2複合
酸化物に比べ大きな比表面積を有している。Since the above-mentioned ternary complex oxide has the above-mentioned specific constitution, it is 20 to 60 m 2 / g even after the reduction heat treatment or the high temperature endurance and the conventional CeO 2 --ZrO 2 complex oxide. It has a larger specific surface area than oxides.
【００３２】本発明の排ガス浄化用触媒の担体であるCe
O2−ZrO2系複合酸化物又は三元系複合酸化物は、共沈法
などで製造することができる。例えばセリウム化合物
と、ジルコニウム化合物の溶液に沈殿剤を添加して共沈
法により沈殿物を生成し、得られた沈殿物を焼成するこ
とでCeO2−ZrO2系複合酸化物を製造することができる。
なお三元系複合酸化物を製造する場合には、セリウム化
合物と、ジルコニウム化合物と、酸化物がCeO2及びZrO2
と反応しない金属の化合物の溶液の混合溶液を用いれば
よい。Ce, which is the carrier of the exhaust gas purifying catalyst of the present invention
O 2 -ZrO 2 composite oxide, or ternary composite oxide can be produced by such co-precipitation. For example, a CeO 2 -ZrO 2 -based composite oxide can be produced by adding a precipitant to a solution of a cerium compound and a zirconium compound to generate a precipitate by a coprecipitation method and baking the obtained precipitate. it can.
In the case of producing a ternary compound oxide, a cerium compound, a zirconium compound, and oxides of CeO 2 and ZrO 2
A mixed solution of a metal compound solution that does not react with may be used.
【００３３】セリウム化合物及びジルコニウム化合物、
あるいは酸化物がCeO2及びZrO2と反応しない金属の化合
物としては、硝酸塩、硫酸塩、塩化物などの水溶性化合
物を用いることができる。また沈殿剤は、アンモニア、
アルカリ金属の水酸化物、アルカリ金属の炭酸塩などを
用いることができる。セリウム化合物及びジルコニウム
化合物が共存する混合水溶液から共沈させた後に焼成し
てCeO2及びZrO2を生成してもよいし、CeO2前駆体の沈殿
とZrO2前駆体の沈殿をそれぞれ形成しこの２種類の沈殿
を混合してから焼成することもできる。三元系の場合も
同様である。Cerium compounds and zirconium compounds,
Alternatively, as the metal compound whose oxide does not react with CeO 2 and ZrO 2 , water-soluble compounds such as nitrates, sulfates and chlorides can be used. The precipitant is ammonia,
Alkali metal hydroxides, alkali metal carbonates and the like can be used. CeO 2 and ZrO 2 may be produced by coprecipitation from a mixed aqueous solution in which a cerium compound and a zirconium compound are coexistent, or a CeO 2 precursor precipitate and a ZrO 2 precursor precipitate may be formed, respectively. It is also possible to mix the two types of precipitates and then to bake. The same is true for the ternary system.
【００３４】沈殿の析出方法には様々な調節方法があ
り、アンモニア水などを瞬時に添加し強撹拌する方法
や、過酸化水素などを加えることで酸化物前駆体の沈殿
し始めるpHを調節した後、アンモニア水などで沈殿を析
出させる方法などがある。またアンモニア水などで中和
させる際にかかる時間を充分に長くし、好ましくは10分
以上で中和させる方法や、pHをモニターしながら段階的
に中和する又は所定のpHに保つような緩衝溶液を添加す
る方法などがある。There are various methods for adjusting the precipitation. There are various methods for adjusting the precipitation, such as a method of instantaneously adding aqueous ammonia or the like and vigorous stirring, or a method of adjusting the pH at which the oxide precursor starts to precipitate by adding hydrogen peroxide or the like. After that, there is a method of depositing a precipitate with aqueous ammonia. Also, the time required for neutralization with ammonia water, etc. should be sufficiently long, preferably 10 minutes or more, or a buffer that neutralizes stepwise while monitoring the pH or maintains a predetermined pH. There is a method of adding a solution.
【００３５】沈殿を生成する過程において、常に1000／
秒以上のせん断速度で撹拌することが望ましい。これに
より生成する酸化物前駆体の粒径を微細化することがで
き、複合酸化物の粒径をより小さくすることができる。
なお酸化物前駆体の粒径は３μｍ以下とすることが望ま
しい。粒径がこれより大きくなると、生成する複合酸化
物の粒径が大きくなりすぎて比表面積の低下により活性
が低下してしまう。In the process of producing a precipitate, 1000 /
It is desirable to stir at a shear rate of at least seconds. As a result, the particle size of the produced oxide precursor can be made finer, and the particle size of the composite oxide can be made smaller.
The particle size of the oxide precursor is preferably 3 μm or less. If the particle size is larger than this, the particle size of the produced composite oxide becomes too large and the specific surface area decreases, resulting in a decrease in activity.
【００３６】この製造方法で得られたCeO2−ZrO2系複合
酸化物又は三元系複合酸化物は、一般に平均直径50nm以
下の微粒子状をなすCeO2及びZrO2が凝集した平均粒径が
20μｍ以下の凝集粒子からなり、CeO2とZrO2は少なくと
も一部が固溶体を形成している。The CeO 2 —ZrO 2 -based composite oxide or the ternary composite oxide obtained by this production method generally has an average particle size in which fine particles of CeO 2 and ZrO 2 having an average diameter of 50 nm or less are aggregated.
It consists of agglomerated particles of 20 μm or less, and at least part of CeO 2 and ZrO 2 forms a solid solution.
【００３７】この製造方法において、沈殿物の焼成前
に、水又は水を含む溶液を分散媒とした懸濁状態または
系内に水が充分に存在する状態で、沈殿物の熟成処理を
行うことが望ましい。この熟成処理を行うことによっ
て、得られる複合酸化物の粒径が揃えられるため、粒成
長の駆動力の一つである表面分圧が揃い、還元処理時の
粒成長をさらに抑制することができる。In this production method, the precipitate is aged before being calcined in a suspended state using water or a solution containing water as a dispersion medium or in a state where water is sufficiently present in the system. Is desirable. By performing this aging treatment, the grain sizes of the obtained composite oxide are made uniform, so that the surface partial pressure, which is one of the driving forces for grain growth, is made uniform and the grain growth during the reduction treatment can be further suppressed. .
【００３８】熟成処理は、系内に水分が充分に存在して
いる状態で、沈殿を含む溶液ごとオートクレーブなどの
耐圧、耐熱容器中で加熱して行い、その後溶媒を蒸発さ
せ、焼成することで行うことができる。あるいは濾別さ
れた沈殿物を水蒸気の存在下で焼成してもよい。この場
合は、飽和水蒸気雰囲気で焼成することが好ましく、10
0〜 200℃で、さらに好ましくは 100〜 150℃で行う水
熱処理が特に望ましい。 100℃未満の加温では熟成の促
進効果が小さく、熟成に要する時間が長大となる。また
200℃より高い温度では、10気圧以上に耐えうる合成装
置が必要となり、設備コストが高くなる。The aging treatment is carried out by heating the solution containing the precipitate in a pressure-resistant, heat-resistant container such as an autoclave in a state where water is sufficiently present in the system, and then evaporating the solvent and baking it. It can be carried out. Alternatively, the filtered precipitate may be calcined in the presence of steam. In this case, it is preferable to fire in a saturated steam atmosphere,
A hydrothermal treatment carried out at 0 to 200 ° C, more preferably 100 to 150 ° C is particularly desirable. If the heating temperature is lower than 100 ° C, the aging-promoting effect is small and the aging time becomes long. Also
At temperatures higher than 200 ° C, a synthesizing device capable of withstanding 10 atm or more is required, resulting in high facility cost.
【００３９】上記した熟成処理を行った場合には、加温
の熱によって溶解・再析出が促進されるとともに粒子の
成長が生じる。この場合は、酸塩の全てを中和できる当
量以上の塩基で中和することが望ましい。これにより酸
化物前駆体がより均一に熟成され、細孔が効果的に形成
されるとともに、CeO2−ZrO2固溶体の生成がさらに促進
される。When the above-mentioned aging treatment is carried out, the heat of heating accelerates the dissolution / reprecipitation and causes the growth of particles. In this case, it is desirable to neutralize all of the acid salt with an equivalent amount or more of a base capable of neutralizing the acid salt. As a result, the oxide precursor is aged more uniformly, the pores are effectively formed, and the production of the CeO 2 —ZrO 2 solid solution is further promoted.
【００４０】本発明の排ガス浄化用触媒において、上記
した担体に担持される貴金属としては、Pt，Rh，Pd，I
r，Ruなどから一種又は複数種選択して用いることがで
き、その担持量は従来の排ガス浄化用触媒と同様でよ
い。また担持方法も、吸着担持法、吸水担持法など従来
の担持法を利用することができる。In the exhaust gas purifying catalyst of the present invention, the noble metal supported on the above-mentioned carrier is Pt, Rh, Pd, I.
One or a plurality of r, Ru, etc. may be selected and used, and the supported amount thereof may be the same as that of the conventional exhaust gas purifying catalyst. As the supporting method, a conventional supporting method such as an adsorption supporting method or a water absorption supporting method can be used.
【００４１】本発明の特色をなす還元熱処理は、上記担
体に貴金属を担持した後、還元性雰囲気中にて 600〜10
00℃で加熱保持することで行う。加熱保持温度が 600℃
より低いと複合酸化物中に規則相を生成するのが困難と
なり OSCが低下する。また1000℃より高くなると比表面
積の低下が著しいため好ましくない。加熱保持温度を60
0〜1000℃とすることで、CeカチオンとZrカチオンが規
則配列し、高い比表面積をもつとともに貴金属の粒径が
揃った本発明の排ガス浄化用触媒が得られる。The reduction heat treatment, which is a feature of the present invention, is carried out by supporting the noble metal on the above-mentioned carrier, and then performing the treatment in a reducing atmosphere at 600 to 10
It is performed by heating and holding at 00 ℃. Heating and holding temperature is 600 ℃
If it is lower, it is difficult to form an ordered phase in the composite oxide, and the OSC is lowered. On the other hand, when the temperature is higher than 1000 ° C, the specific surface area is significantly reduced, which is not preferable. Heating holding temperature 60
By setting the temperature to 0 to 1000 ° C., the exhaust gas-purifying catalyst of the present invention in which Ce cations and Zr cations are regularly arranged, has a high specific surface area, and has a noble metal particle size uniform.
【００４２】還元性雰囲気は、不活性ガス雰囲気又は非
酸化性雰囲気とするよりも、H2，COなどの還元性ガスを
積極的に含む雰囲気とすることが望ましい。還元性ガス
を含まないと、結晶格子からの酸素原子の脱離が充分に
速く進行しないため規則相が充分に生成できず、高い O
SCが得られない場合がある。The reducing atmosphere is preferably an atmosphere that positively contains a reducing gas such as H 2 or CO, rather than an inert gas atmosphere or a non-oxidizing atmosphere. If the reducing gas is not contained, the desorption of oxygen atoms from the crystal lattice does not proceed sufficiently fast, so that the ordered phase cannot be sufficiently generated and the high O 2
SC may not be obtained.
【００４３】したがって本発明の排ガス浄化用触媒で
は、貴金属が酸素吸放出の出入り口となるため、従来よ
り低温の 600〜1000℃程度の温度においても還元熱処理
時に酸素の放出が可能となる。このように酸素原子の放
出が容易となることで、還元熱処理によってCeカチオン
とZrカチオンがより規則的な配列となり、使用時の変動
雰囲気下における酸素の吸放出が容易となり高い OSCが
発現される。これにより触媒としての活性が大きく向上
する。Therefore, in the exhaust gas purifying catalyst of the present invention, since the noble metal serves as an inlet / outlet port for oxygen absorption / release, oxygen can be released during the reduction heat treatment even at a temperature of about 600 to 1000 ° C. which is lower than before. By facilitating the release of oxygen atoms in this way, Ce cations and Zr cations become more regular arrangement by the reduction heat treatment, and oxygen absorption and release in a fluctuating atmosphere during use becomes easy and a high OSC is expressed. . This greatly improves the activity as a catalyst.
【００４４】そして担体に前記三元系複合酸化物を含む
ことにより、CeO2及びZrO2と反応しない金属酸化物が介
在するために、還元熱処理時におけるCeO2−ZrO2複合酸
化物どうしの反応が抑制され、さらに粒成長が抑制され
ることで高い比表面積が維持されるため、酸素原子の放
出が一層容易となる。The inclusion of the ternary complex oxide in the carrier causes a metal oxide which does not react with CeO 2 and ZrO 2 to intervene, so that the reaction between the CeO 2 —ZrO 2 complex oxides during the reduction heat treatment is performed. Is suppressed, and the grain growth is suppressed, so that a high specific surface area is maintained, so that the release of oxygen atoms becomes easier.
【００４５】[0045]
【実施例】以下、実施例及び比較例により本発明を具体
的に説明する。EXAMPLES The present invention will be specifically described below with reference to Examples and Comparative Examples.
【００４６】（実施例１）硝酸アルミニウム９水和物、
硝酸セリウム６水和物及びオキシ硝酸ジルコニルの所定
量を純水中に溶解し、これを激しく撹拌しながら、各塩
の中和当量の 1.2倍モルの NH3を含むアンモニア水を加
えた。これにより析出した前駆体を 150℃で蒸発乾固し
た後、 300℃で３時間乾燥し、 500℃で１時間焼成し、
さらに 700℃で５時間熱処理して三元系複合酸化物を調
製した。この複合酸化物の組成比は、モル比で Al2O3／
CeO2／ZrO2＝１／ 0.9／ 1.1である。Example 1 Aluminum nitrate nonahydrate,
Predetermined amounts of cerium nitrate hexahydrate and zirconyl oxynitrate were dissolved in pure water, and ammonia solution containing 1.2 times mole NH 3 of neutralization equivalent of each salt was added to the solution while vigorously stirring. The precursor thus deposited is evaporated to dryness at 150 ° C, dried at 300 ° C for 3 hours, and calcined at 500 ° C for 1 hour.
Further, it was heat-treated at 700 ° C. for 5 hours to prepare a ternary complex oxide. The composition ratio of this composite oxide is Al 2 O 3 / molar ratio.
CeO 2 / ZrO 2 = 1 / 0.9 / 1.1.
【００４７】この複合酸化物に所定濃度のジニトロジア
ンミン白金（II）水溶液の所定量を含浸し、大気中にお
いて 300℃で３時間焼成してPtを担持した。Ptの担持量
は、複合酸化物 100重量部に対してPtが１重量部であ
る。This composite oxide was impregnated with a predetermined amount of a dinitrodiammineplatinum (II) aqueous solution having a predetermined concentration, and was baked in air at 300 ° C. for 3 hours to support Pt. The amount of Pt supported is 1 part by weight of Pt based on 100 parts by weight of the composite oxide.
【００４８】Ptが担持された複合酸化物を、H2を５％含
むN2ガス雰囲気下にて1000℃で５時間の還元熱処理を行
った。その後、成形圧1000 kgf／cm2 で圧粉成形し、粉
砕して 0.5〜１mmのペレット触媒とした。The Pt-supported composite oxide was subjected to reduction heat treatment at 1000 ° C. for 5 hours in an N 2 gas atmosphere containing 5% of H 2 . Then, the powder was compacted at a compacting pressure of 1000 kgf / cm 2 and pulverized to give a pellet catalyst of 0.5 to 1 mm.
【００４９】（実施例２）実施例１と同様のPtが担持さ
れた三元系複合酸化物に対して、H2を５％含むN2ガス雰
囲気下にて 900℃で５時間の還元熱処理を行ったこと以
外は実施例１と同様にして、ペレット触媒を調製した。Example 2 The same Pt-supported ternary composite oxide as in Example 1 was subjected to reduction heat treatment at 900 ° C. for 5 hours in an N 2 gas atmosphere containing 5% of H 2. A pellet catalyst was prepared in the same manner as in Example 1 except that the above was performed.
【００５０】（実施例３）実施例１と同様のPtが担持さ
れた三元系複合酸化物に対して、H2を５％含むN2ガス雰
囲気下にて 800℃で５時間の還元熱処理を行ったこと以
外は実施例１と同様にして、ペレット触媒を調製した。Example 3 The same Pt-supported ternary composite oxide as in Example 1 was subjected to reduction heat treatment at 800 ° C. for 5 hours in an N 2 gas atmosphere containing 5% of H 2. A pellet catalyst was prepared in the same manner as in Example 1 except that the above was performed.
【００５１】（比較例１）実施例１で製造された三元系
複合酸化物に対してH2を５％含むN2ガス雰囲気下にて10
00℃で５時間の還元熱処理を行い、その後実施例１と同
様にしてPtを担持し、ペレット触媒とした。(Comparative Example 1) 10% under an N 2 gas atmosphere containing 5% of H 2 with respect to the ternary composite oxide produced in Example 1.
A reduction heat treatment was carried out at 00 ° C. for 5 hours, and then Pt was carried in the same manner as in Example 1 to obtain a pellet catalyst.
【００５２】（比較例２）実施例１と同様のPtが担持さ
れた三元系複合酸化物に対して、N2ガス雰囲気下にて10
00℃で５時間の熱処理を行ったこと以外は実施例１と同
様にして、ペレット触媒を調製した。(Comparative Example 2) The same Pt-supported ternary composite oxide as in Example 1 was used under N 2 gas atmosphere.
A pellet catalyst was prepared in the same manner as in Example 1 except that the heat treatment was performed at 00 ° C for 5 hours.
【００５３】（比較例３）実施例１と同様のPtが担持さ
れた複合酸化物に対して、大気中にて1000℃で５時間の
熱処理を行ったこと以外は実施例１と同様にして、ペレ
ット触媒を調製した。Comparative Example 3 The same procedure as in Example 1 was carried out except that the same Pt-supported composite oxide as in Example 1 was heat-treated at 1000 ° C. for 5 hours in the atmosphere. , A pellet catalyst was prepared.
【００５４】＜試験・評価＞実施例１〜３及び比較例１
〜３のペレット触媒をそれぞれ評価装置に配置し、表１
に示すリッチモデルガスとリーンモデルガスを５分間ず
つSV＝10,000／hrで交互に流す雰囲気下、昇温速度12℃
／分の条件で昇温し 100〜 500℃におけるNO，CO及びC3
H6の浄化率を連続的に測定した。そして各50％浄化温度
を求め、結果を初期Ｔ50として表２に示す。<Test / Evaluation> Examples 1 to 3 and Comparative Example 1
Each of the pellet catalysts No. 3 to No.
In an atmosphere in which the rich model gas and the lean model gas shown in Figure 5 are alternately flowed for 5 minutes each at SV = 10,000 / hr, the heating rate is 12 ° C.
NO, CO and C 3 at 100-500 ℃
The H 6 purification rate was measured continuously. Then, each 50% purification temperature was determined, and the results are shown in Table 2 as the initial T50.
【００５５】[0055]
【表１】 [Table 1]
【００５６】また各触媒 0.1ｇを用い、熱重量分析法に
よって酸素吸放出量の測定を行った。測定は、H2を10体
積％含むN2ガスとO2を５体積％含むN2ガスを交互に流す
雰囲気中にて、 500℃における重量の減少量及び増加量
を測定し、その値から相当する OSCを算出した。なおN2
吸着を用いた BET法（１点法）によって、各触媒の比表
面積も測定した。これらの結果を表２に併せて示す。The amount of oxygen absorbed and released was measured by thermogravimetric analysis using 0.1 g of each catalyst. Measurements in an atmosphere of flowing N 2 gas containing N 2 gas and O 2 containing H 2 10 vol% 5 vol% alternating measures the decrease and increase in weight at 500 ° C., from that value The corresponding OSC was calculated. Note that N 2
The specific surface area of each catalyst was also measured by the BET method (one-point method) using adsorption. The results are also shown in Table 2.
【００５７】さらに各触媒について、表１に示すリッチ
モデルガスとリーンモデルガスを５分間ずつSV＝10,000
／hrで交互に流す雰囲気下にて1000℃で５時間の耐久試
験を行い、その後上記と同様にして50％浄化温度を測定
した。結果を初期Ｔ50として表２に示す。Further, for each catalyst, the rich model gas and the lean model gas shown in Table 1 were used for 5 minutes at SV = 10,000.
A durability test was performed at 1000 ° C. for 5 hours in an atmosphere of alternating flow of 1 hour / hour, and then the 50% purification temperature was measured in the same manner as above. The results are shown in Table 2 as the initial T50.
【００５８】[0058]
【表２】 [Table 2]
【００５９】表２より、各実施例の触媒は比較例２〜３
の触媒に比べて初期及び耐久後の浄化活性に優れ、 OSC
も高いことがわかる。すなわちPtを担持した後の還元性
雰囲気での熱処理により OSCが大きく向上し、それによ
って浄化活性が向上したことがわかる。また OSCに着目
すれば、実施例１〜３の比較より、還元性雰囲気での熱
処理温度は高いほど好ましいことがわかる。From Table 2, the catalysts of the respective Examples are Comparative Examples 2-3.
Compared with other catalysts, it has superior purification activity at the initial stage and after endurance.
You can see that it is also expensive. That is, it can be seen that the OSC is greatly improved by the heat treatment in the reducing atmosphere after supporting Pt, and thereby the purifying activity is improved. Further, focusing on OSC, it is understood from the comparison of Examples 1 to 3 that the higher the heat treatment temperature in the reducing atmosphere is, the more preferable.
【００６０】さらに実施例１〜３と比較例１を比較する
と、実施例１〜３のように予め複合酸化物にPtを担持し
た状態で還元熱処理することで、比較例１のようにPtを
担持しないで還元熱処理した場合に比べて、より低温の
処理でほぼ同等の OSCが発現されていることがわかる。
これはPtの担持によって結晶格子内からの酸素原子の放
出が容易になったためと推察される。Further, comparing Examples 1 to 3 with Comparative Example 1, as shown in Examples 1 to 3, Pt was reduced as in Comparative Example 1 by carrying out reduction heat treatment with Pt preliminarily supported on the composite oxide. It can be seen that, as compared with the case where the reduction heat treatment is not carried, the OSC is almost the same in the lower temperature treatment.
This is presumably because the loading of Pt facilitated the release of oxygen atoms from the crystal lattice.
【００６１】なお浄化活性面では、必ずしも還元熱処理
温度が高いほど活性が高いわけではない。これは、比表
面積の増大と OSCの向上とが還元熱処理温度に対して背
反事象の関係にあるためと考えられる。つまり還元熱処
理温度が高いほど OSCは高くなるものの比表面積が低下
するので、両者がバランスする最適値があることが示唆
される。また、これも理由は不明であるが、初期及び耐
久後の浄化活性は実施例１〜３の方が比較例１より高
く、これからもPtを担持後に還元熱処理するのが好まし
いことがわかる。In terms of purification activity, the higher the reduction heat treatment temperature, the higher the activity. It is considered that this is because the increase of the specific surface area and the improvement of the OSC have a trade-off relationship with the reduction heat treatment temperature. In other words, the higher the reduction heat treatment temperature, the higher the OSC, but the smaller the specific surface area, suggesting that there is an optimum value that balances both. Further, although the reason is not clear, it is understood that the purifying activities in Examples 1 to 3 are higher than those in Comparative Example 1 even after the initial stage and after the durability test, and it is preferable to carry out the reduction heat treatment after supporting Pt.
【００６２】[0062]
【発明の効果】すなわち本発明の排ガス浄化用触媒によ
れば、担体のCeカチオンとZrカチオンの規則性が向上し
OSCが向上するとともに、貴金属の粒径が揃うため粒成
長が抑制され耐久性がさらに向上する。EFFECTS OF THE INVENTION That is, according to the exhaust gas purifying catalyst of the present invention, the regularity of Ce cations and Zr cations in the carrier is improved.
As the OSC is improved, the grain size of the noble metal is made uniform, so grain growth is suppressed and durability is further improved.
───────────────────────────────────────────────────── フロントページの続き (51)Int.Cl.7 識別記号 ＦＩ テーマコート゛(参考） Ｂ０１Ｊ 37/14 Ｂ０１Ｊ 23/56 ３０１Ａ 37/18 Ｂ０１Ｄ 53/36 １０４Ａ Ｆ０１Ｎ 3/28 ３０１ ＺＡＢ (72)発明者 曽布川 英夫 愛知県愛知郡長久手町大字長湫字横道41番 地の１株式会社豊田中央研究所内 (72)発明者 鈴木 正 愛知県愛知郡長久手町大字長湫字横道41番 地の１株式会社豊田中央研究所内 Ｆターム(参考） 3G091 AA02 AB03 BA01 BA39 GB05W GB10W 4D048 AA06 AA13 AA18 AB05 AB07 BA03X BA08X BA19X BA30X BA31Y BA32Y BA33Y BA34Y BA41X BA42X BB17 EA04 4G069 AA03 AA08 BA01A BA01B BB06A BB06B BC32A BC33A BC43A BC43B BC51A BC51B BC69A BC75B CA03 CA09 EB18X EB19 EC02X EC03X EC04X EC05X EC27 FA01 FA02 FB30 FB40 FB44 FB64 FC07 ─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. 7 Identification code FI theme code (reference) B01J 37/14 B01J 23/56 301A 37/18 B01D 53/36 104A F01N 3/28 301 ZAB (72) Invention Person Hideo Sofukawa 41, Nagachote, Nagakute-cho, Aichi-gun, Aichi Prefecture 1st in Yokota Central Research Co., Ltd. (72) Inventor Masa Tadashi 41, Yokochi, Nagakute-cho, Aichi-gun, Aichi Prefecture 1st, 41st Yokomichi, Toyota central Research Institute of the F-term (reference) 3G091 AA02 AB03 BA01 BA39 GB05W GB10W 4D048 AA06 AA13 AA18 AB05 AB07 BA03X BA08X BA19X BA30X BA31Y BA32Y BA33Y BA34Y BA41X BA42X BB17 EA04 4G069 AA03 AA08 BA01A BA01B BB06A BB06B BC32A BC33A BC43A BC43B BC51A BC51B BC69A BC75B CA03 CA09 EB18X EB19 EC02X EC03X EC04X EC05X EC27 FA01 FA02 FB30 FB40 FB44 FB64 FC07
Claims (8)
含む担体に貴金属を担持した後、還元性雰囲気中にて 6
00〜1000℃で熱処理されてなることを特徴とする排ガス
浄化用触媒。1. A noble metal is supported on a carrier containing a composite oxide containing CeO 2 and ZrO 2 as main components, and then the carrier is placed in a reducing atmosphere.
An exhaust gas-purifying catalyst, which is characterized by being heat-treated at 100 to 1000 ° C.
分に酸化処理を行った後に 100〜 500℃の還元性雰囲気
下において放出される酸素量が、理論限界値の80％以上
である特性をもつ請求項１に記載の排ガス浄化用触媒。2. A characteristic that the amount of oxygen released in a reducing atmosphere at 100 to 500 ° C. after fully oxidizing at about 500 ° C. in an oxidizing atmosphere is 80% or more of the theoretical limit value. The exhaust gas purifying catalyst according to claim 1.
に記載の排ガス浄化用触媒。3. The specific surface area is 20 m 2 / g or more.
The exhaust gas purifying catalyst according to 1.
請求項１に記載の排ガス浄化用触媒。4. The exhaust gas purifying catalyst according to claim 1, wherein the particle size of the noble metal is in the range of 2 to 10 nm.
溶した固溶体を形成している請求項１に記載の排ガス浄
化用触媒。5. The exhaust gas purifying catalyst according to claim 1, wherein at least a part of CeO 2 and ZrO 2 form a solid solution in which they are solid-solved with each other.
部が規則配列している請求項５に記載の排ガス浄化用触
媒。6. The exhaust gas-purifying catalyst according to claim 5, wherein at least a part of Ce cations and Zr cations are regularly arranged.
温度で反応しない金属酸化物を含む請求項１に記載の排
ガス浄化用触媒。7. The exhaust gas-purifying catalyst according to claim 1, which contains CeO 2 and ZrO 2 , and a metal oxide that does not react with these at a temperature of 900 ° C. or less.
に記載の排ガス浄化用触媒。8. The metal oxide is Al 2 O 3
The exhaust gas purifying catalyst according to 1.
Priority Applications (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2002074719A JP3855262B2 (en) | 2002-03-18 | 2002-03-18 | Exhaust gas purification catalyst |
| EP02018807A EP1287876B1 (en) | 2001-08-30 | 2002-08-22 | Composite oxide, process for producing the same, and exhaust gas reducing co-catalyst |
| US10/225,186 US7247597B2 (en) | 2001-08-30 | 2002-08-22 | Composite oxide, process for producing the same, and exhaust gas reducing co-catalyst |
| DE60211260T DE60211260T2 (en) | 2001-08-30 | 2002-08-22 | Mixed oxide, process for its preparation and exhaust gas reduction CO catalyst |
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| JP2002074719A JP3855262B2 (en) | 2002-03-18 | 2002-03-18 | Exhaust gas purification catalyst |
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Cited By (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2005170774A (en) * | 2003-12-15 | 2005-06-30 | Tosoh Corp | Compound oxide, method for producing the same, and exhaust gas cleaning catalyst |
| JP2009119430A (en) * | 2007-11-19 | 2009-06-04 | Toyota Central R&D Labs Inc | Low-temperature oxidation catalyst, its production method and exhaust-gas cleaning method using the catalyst |
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| DE102014001205A1 (en) | 2013-02-21 | 2014-08-21 | Mazda Motor Corporation | Exhaust gas purifying catalyst and method for producing the same |
| JP2014168750A (en) * | 2013-03-04 | 2014-09-18 | Mazda Motor Corp | Catalyst for exhaust gas purification and method for producing the same |
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2002
- 2002-03-18 JP JP2002074719A patent/JP3855262B2/en not_active Expired - Fee Related
Cited By (13)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2005170774A (en) * | 2003-12-15 | 2005-06-30 | Tosoh Corp | Compound oxide, method for producing the same, and exhaust gas cleaning catalyst |
| JP2009119430A (en) * | 2007-11-19 | 2009-06-04 | Toyota Central R&D Labs Inc | Low-temperature oxidation catalyst, its production method and exhaust-gas cleaning method using the catalyst |
| JP2012516227A (en) * | 2009-01-28 | 2012-07-19 | ズード−ケミー アーゲー | Vanadium-free diesel oxidation catalyst and method for producing the same |
| US9539562B2 (en) | 2009-01-28 | 2017-01-10 | Clariant Produkte (Deutschland) Gmbh | Vanadium-free diesel oxidation catalyst and method for its production |
| JP2012187523A (en) * | 2011-03-10 | 2012-10-04 | Toyota Central R&D Labs Inc | Exhaust gas-purifying catalyst support, exhaust gas-purifying catalyst made using the support, and method for producing exhaust gas-purifying catalyst support |
| US9144788B2 (en) | 2013-02-21 | 2015-09-29 | Mazda Motor Corporation | Exhaust gas purification catalyst and method for producing the same |
| DE102014001205A1 (en) | 2013-02-21 | 2014-08-21 | Mazda Motor Corporation | Exhaust gas purifying catalyst and method for producing the same |
| US9266093B2 (en) | 2013-02-21 | 2016-02-23 | Mazda Motor Corporation | Exhaust gas purification catalyst and method for producing the same |
| DE102014001859A1 (en) | 2013-02-21 | 2014-08-21 | Mazda Motor Corporation | Exhaust gas purifying catalyst and method for producing the same |
| DE102014001205B4 (en) | 2013-02-21 | 2019-07-11 | Mazda Motor Corporation | purifying catalyst |
| JP2014168750A (en) * | 2013-03-04 | 2014-09-18 | Mazda Motor Corp | Catalyst for exhaust gas purification and method for producing the same |
| JP2014168751A (en) * | 2013-03-04 | 2014-09-18 | Mazda Motor Corp | Catalyst for exhaust gas purification and method for producing the same |
| WO2015076403A1 (en) | 2013-11-22 | 2015-05-28 | 株式会社キャタラー | Catalyst for exhaust gas purification |
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