JP2003200047A - Catalyst for exhaust gas purification - Google Patents
Catalyst for exhaust gas purificationInfo
- Publication number
- JP2003200047A JP2003200047A JP2002196299A JP2002196299A JP2003200047A JP 2003200047 A JP2003200047 A JP 2003200047A JP 2002196299 A JP2002196299 A JP 2002196299A JP 2002196299 A JP2002196299 A JP 2002196299A JP 2003200047 A JP2003200047 A JP 2003200047A
- Authority
- JP
- Japan
- Prior art keywords
- noble metal
- catalyst
- exhaust gas
- polycrystal
- supported
- 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 description 54
- 238000000746 purification Methods 0.000 title claims description 5
- 229910000510 noble metal Inorganic materials 0.000 claims abstract description 41
- 239000013078 crystal Substances 0.000 claims abstract description 23
- 229910000000 metal hydroxide Inorganic materials 0.000 claims abstract description 3
- 150000004692 metal hydroxides Chemical class 0.000 claims abstract description 3
- 229910044991 metal oxide Inorganic materials 0.000 claims abstract description 3
- 150000004706 metal oxides Chemical class 0.000 claims abstract description 3
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 claims description 29
- WNROFYMDJYEPJX-UHFFFAOYSA-K aluminium hydroxide Chemical compound [OH-].[OH-].[OH-].[Al+3] WNROFYMDJYEPJX-UHFFFAOYSA-K 0.000 claims description 14
- 230000007547 defect Effects 0.000 claims description 9
- 239000002245 particle Substances 0.000 abstract description 22
- 239000002923 metal particle Substances 0.000 abstract description 5
- 230000001112 coagulating effect Effects 0.000 abstract 1
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 28
- 239000007789 gas Substances 0.000 description 19
- 230000000694 effects Effects 0.000 description 12
- 239000000843 powder Substances 0.000 description 11
- 230000000052 comparative effect Effects 0.000 description 9
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 6
- 238000004519 manufacturing process Methods 0.000 description 6
- 229910052760 oxygen Inorganic materials 0.000 description 6
- 239000001301 oxygen Substances 0.000 description 6
- 239000008188 pellet Substances 0.000 description 6
- 239000010970 precious metal Substances 0.000 description 6
- 230000007423 decrease Effects 0.000 description 5
- 239000011164 primary particle Substances 0.000 description 4
- 239000011163 secondary particle Substances 0.000 description 4
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 3
- 238000004220 aggregation Methods 0.000 description 3
- 230000002776 aggregation Effects 0.000 description 3
- 230000003197 catalytic effect Effects 0.000 description 3
- 239000010948 rhodium Substances 0.000 description 3
- 239000000243 solution Substances 0.000 description 3
- 239000000126 substance Substances 0.000 description 3
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 description 2
- MCMNRKCIXSYSNV-UHFFFAOYSA-N Zirconium dioxide Chemical compound O=[Zr]=O MCMNRKCIXSYSNV-UHFFFAOYSA-N 0.000 description 2
- ANBBXQWFNXMHLD-UHFFFAOYSA-N aluminum;sodium;oxygen(2-) Chemical compound [O-2].[O-2].[Na+].[Al+3] ANBBXQWFNXMHLD-UHFFFAOYSA-N 0.000 description 2
- 229910002091 carbon monoxide Inorganic materials 0.000 description 2
- 230000006866 deterioration Effects 0.000 description 2
- 238000011156 evaluation Methods 0.000 description 2
- 239000012535 impurity Substances 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 230000001590 oxidative effect Effects 0.000 description 2
- 229910052697 platinum Inorganic materials 0.000 description 2
- 239000011148 porous material Substances 0.000 description 2
- 239000011347 resin Substances 0.000 description 2
- 229920005989 resin Polymers 0.000 description 2
- 229910052703 rhodium Inorganic materials 0.000 description 2
- 229910001388 sodium aluminate Inorganic materials 0.000 description 2
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
- 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 1
- 229910001570 bauxite Inorganic materials 0.000 description 1
- 229910002092 carbon dioxide Inorganic materials 0.000 description 1
- 239000001569 carbon dioxide Substances 0.000 description 1
- 239000000969 carrier Substances 0.000 description 1
- CETPSERCERDGAM-UHFFFAOYSA-N ceric oxide Chemical compound O=[Ce]=O CETPSERCERDGAM-UHFFFAOYSA-N 0.000 description 1
- 229910000422 cerium(IV) oxide Inorganic materials 0.000 description 1
- 229910052878 cordierite Inorganic materials 0.000 description 1
- 238000009792 diffusion process Methods 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
- 238000010304 firing Methods 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-M hydroxide Chemical compound [OH-] XLYOFNOQVPJJNP-UHFFFAOYSA-M 0.000 description 1
- 229910052741 iridium Inorganic materials 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 239000000203 mixture Substances 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
- 239000002244 precipitate Substances 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- MHOVAHRLVXNVSD-UHFFFAOYSA-N rhodium atom Chemical compound [Rh] MHOVAHRLVXNVSD-UHFFFAOYSA-N 0.000 description 1
- 229910052707 ruthenium Inorganic materials 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
- 239000011232 storage material Substances 0.000 description 1
- 239000000758 substrate Substances 0.000 description 1
Landscapes
- Exhaust Gas Treatment By Means Of Catalyst (AREA)
- Catalysts (AREA)
Abstract
Description
【０００１】[0001]
【発明の属する技術分野】本発明は、自動車のエンジン
などからの排ガスを浄化する排ガス浄化用触媒に関し、
詳しくは耐久性に優れた排ガス浄化用触媒に関する。TECHNICAL FIELD The present invention relates to an exhaust gas purifying catalyst for purifying exhaust gas from an automobile engine or the like,
Specifically, it relates to an exhaust gas purifying catalyst having 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、CO及びHCの酸化とNOx の還元とを同時に行って排
気ガスを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、コーディエライトなどからなる耐
熱性基材にγ−アルミナからなる多孔質担体層を形成
し、その多孔質担体層に白金（Pt）、ロジウム（Rh）な
どの貴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, a three-way catalyst for purifying exhaust gas by simultaneously oxidizing CO and HC and reducing NO x has been used as an exhaust gas purifying catalyst for automobiles. As such a three-way catalyst, a porous carrier layer made of γ-alumina is formed on a heat resistant substrate made of cordierite, and platinum (Pt), rhodium (Rh), etc. are formed on the porous carrier layer. Those carrying a noble metal are widely known.
【０００３】ところで近年、排ガス浄化用触媒の設置場
所がエンジンに近いマニホールド直下とされる傾向があ
り、また高速走行時には排ガス温度が高くなることか
ら、排ガス浄化用触媒は高温に晒される場合が多くなっ
ている。ところが従来の排ガス浄化用触媒では、高温の
排ガスによりγ−アルミナの熱劣化が進行し、これに伴
う貴金属の粒成長によって触媒活性点が減少するため触
媒性能が劣化するという不具合があった。By the way, in recent years, the exhaust gas purifying catalyst tends to be installed immediately below the manifold close to the engine, and the exhaust gas temperature becomes high during high-speed traveling. Therefore, the exhaust gas purifying catalyst is often exposed to high temperatures. Has become. However, the conventional exhaust gas-purifying catalyst has a problem that the catalytic performance is deteriorated because the thermal deterioration of γ-alumina proceeds due to the high-temperature exhaust gas, and the catalyst active points are reduced due to the particle growth of the precious metal.
【０００４】そこで、例えば特開平4-122441号公報に
は、予め熱処理されたアルミナを用いて貴金属を担持さ
せる排ガス浄化用触媒の製造方法が開示されている。こ
の製造方法によれば、アルミナは既に熱処理されている
ため、得られた排ガス浄化用触媒は高温の排ガスに晒さ
れても熱劣化がほとんど進行せず、貴金属の粒成長を防
止することができる。Therefore, for example, Japanese Patent Application Laid-Open No. 4-122441 discloses a method for producing an exhaust gas purifying catalyst in which a noble metal is supported by using alumina which has been heat treated in advance. According to this manufacturing method, since the alumina has already been heat-treated, the resulting exhaust gas-purifying catalyst undergoes almost no thermal deterioration even when exposed to high-temperature exhaust gas, and can prevent grain growth of noble metals. .
【０００５】また近年では、二酸化炭素の排出量を抑制
するために、酸素過剰の混合気を供給するリーンバーン
エンジンが主流になっている。しかしながら上記公報に
開示された製造方法で製造されたような排ガス浄化用触
媒では、酸素過剰のリーン雰囲気下で 800℃以上の高温
が作用した場合に貴金属の粒成長が著しく、触媒性能が
低下するという不具合があった。In recent years, lean-burn engines, which supply an air-fuel mixture in excess of oxygen, have become the mainstream in order to suppress carbon dioxide emissions. However, in the exhaust gas-purifying catalyst produced by the production method disclosed in the above publication, when a high temperature of 800 ° C. or higher acts in a lean atmosphere with excess oxygen, the grain growth of the noble metal is remarkable and the catalytic performance deteriorates. There was a problem.
【０００６】例えばアルミナ表面に担持されたPtは、高
温で酸素が共存する雰囲気においてはPtO2となり、気相
移動により拡散・凝集が促進される。そのため酸素過剰
のリーン雰囲気又はストイキ雰囲気では、高温に晒され
るとPtに粒成長が生じ表面積の低下により触媒性能が大
きく低下する。For example, Pt supported on the surface of alumina becomes PtO 2 in an atmosphere where oxygen coexists at high temperature, and diffusion and aggregation are promoted by gas phase transfer. Therefore, in a lean atmosphere or stoichiometric atmosphere with excess oxygen, when exposed to high temperatures, grain growth occurs in Pt and the surface area decreases, resulting in a large decrease in catalyst performance.
【０００７】そこで本願出願人は、特開平8-338897号公
報にみられるように、貴金属を担持した担体を非酸化性
雰囲気中にて 800℃以上で熱処理する製造方法を提案し
ている。この製造方法によれば、多孔質担体が焼結して
細孔が収縮するため、担持されている貴金属は多孔質担
体で緊密に取り囲まれる。したがってリーン雰囲気下で
高温が作用しても貴金属の移動が多孔質担体によって規
制されているため、貴金属の粒成長を抑制することがで
きる。Therefore, the applicant of the present application has proposed a manufacturing method in which a carrier carrying a noble metal is heat-treated at 800 ° C. or higher in a non-oxidizing atmosphere, as disclosed in JP-A-8-338897. According to this manufacturing method, since the porous carrier is sintered and the pores are shrunk, the supported precious metal is tightly surrounded by the porous carrier. Therefore, since the movement of the noble metal is regulated by the porous carrier even when a high temperature acts in the lean atmosphere, the grain growth of the noble metal can be suppressed.
【０００８】ところが特開平8-338897号公報に記載の製
造方法で製造された排ガス浄化用触媒であっても、大気
中など酸素過剰のリーン雰囲気下で 800℃を超える高温
が長時間作用すると、貴金属に粒成長が生じることが明
らかとなった。これは、細孔外に担持されている貴金属
粒子が物理的及び化学的に担体に固定されておらず、自
由に移動できることが原因であると考えられる。However, even with the exhaust gas-purifying catalyst produced by the production method described in Japanese Patent Application Laid-Open No. 8-338897, when a high temperature exceeding 800 ° C. acts for a long time in a lean atmosphere with excess oxygen, such as in the air, It became clear that grain growth occurs in the precious metal. It is considered that this is because the noble metal particles supported outside the pores are not physically and chemically fixed to the carrier and can move freely.
【０００９】[0009]
【発明が解決しようとする課題】本発明はこのような事
情に鑑みてなされたものであり、担持されている貴金属
粒子の移動を抑制することで粒成長を抑制できる排ガス
浄化用触媒とすることを目的とする。SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances and provides an exhaust gas purifying catalyst capable of suppressing grain growth by suppressing the movement of supported noble metal particles. With the goal.
【００１０】[0010]
【課題を解決するための手段】上記課題を解決する本発
明の排ガス浄化用触媒の特徴は、金属水酸化物多結晶体
及び金属酸化物多結晶体の少なくとも一方よりなる担体
と、担体のグレインどうしの結晶境界に担持された貴金
属と、よりなることにある。The features of the exhaust gas-purifying catalyst of the present invention for solving the above-mentioned problems are that a carrier comprising at least one of a metal hydroxide polycrystal and a metal oxide polycrystal, and a grain of the carrier. It consists of a noble metal supported on the crystal boundaries between them.
【００１１】貴金属は担体の内部欠陥にも担持されてい
ることができる。The noble metal can also be supported on internal defects of the carrier.
【００１２】担体は、水酸化アルミニウム多結晶体及び
γ−アルミナを除くアルミナ多結晶体の少なくとも一方
であることが望ましく、α−アルミナであることが特に
望ましい。The carrier is preferably at least one of aluminum hydroxide polycrystal and alumina polycrystal excluding γ-alumina, and particularly preferably α-alumina.
【００１３】[0013]
【発明の実施の形態】本発明の排ガス浄化用触媒では、
貴金属は多結晶体からなる担体のグレインどうしの結晶
境界に担持されている。つまり貴金属はグレイン間に挟
み込まれた状態となっているので、高温時においても貴
金属粒子が移動するのが抑制され、貴金属粒子どうしが
凝集して粒成長するのが抑制される。したがって酸素過
剰のリーン雰囲気下で 800℃を超える高温が長時間作用
しても、貴金属は高分散状態を維持し活性点が多く存在
するため、本発明の排ガス浄化用触媒は高い活性が発現
される。BEST MODE FOR CARRYING OUT THE INVENTION In the exhaust gas purifying catalyst of the present invention,
The noble metal is supported on the crystal boundaries between the grains of the support made of polycrystalline material. That is, since the noble metal is sandwiched between the grains, the noble metal particles are prevented from moving even at a high temperature, and the noble metal particles are prevented from agglomerating and growing. Therefore, even if a high temperature exceeding 800 ° C. is operated for a long time in a lean atmosphere with excess oxygen, the precious metal maintains a highly dispersed state and has many active sites, so the exhaust gas purifying catalyst of the present invention exhibits high activity. It
【００１４】また多結晶体からなる担体中には、間隔の
狭いクラック状の内部欠陥が存在している場合が多い。
したがってこの内部欠陥にも貴金属を担持すれば、結晶
境界に担持した場合と同様の作用によって、高温時にお
ける貴金属の粒成長を抑制することができる。さらに内
部欠陥にも貴金属を担持することで、貴金属の担持量を
多くすることができ活性が向上する。In many cases, crack-shaped internal defects having narrow intervals are present in the carrier made of a polycrystalline material.
Therefore, if the noble metal is also supported on this internal defect, grain growth of the noble metal at a high temperature can be suppressed by the same action as when the noble metal is supported on the crystal boundary. Further, by supporting the noble metal on the internal defects, the amount of the noble metal supported can be increased, and the activity is improved.
【００１５】担体には、水酸化物多結晶体及び酸化物多
結晶体の少なくとも一方が用いられる。これらの多結晶
体は、例えば六角板状のグレインがいろいろの方位をも
って集合してなり、グレインどうしの結晶境界が多数存
在している。この結晶境界に貴金属を担持することで、
高温時における貴金属の粒成長を抑制することができ
る。At least one of a hydroxide polycrystal and an oxide polycrystal is used for the carrier. In these polycrystals, for example, hexagonal plate-shaped grains are aggregated in various orientations, and there are many crystal boundaries between the grains. By supporting a noble metal on this crystal boundary,
It is possible to suppress grain growth of noble metal at high temperature.
【００１６】このような担体としては、水酸化アルミニ
ウム多結晶体、α−アルミナ多結晶体、χ−アルミナ多
結晶体、θ−アルミナ多結晶体、シリカ多結晶体などを
用いることができる。中でも耐熱性に優れ、かつ不純物
の影響が少ないアルミナ系多結晶体が好ましい。なお水
酸化アルミニウム多結晶体は、加熱によりα−アルミナ
多結晶体あるいはχ−アルミナ多結晶体などとなる。As such a carrier, aluminum hydroxide polycrystal, α-alumina polycrystal, χ-alumina polycrystal, θ-alumina polycrystal, silica polycrystal or the like can be used. Above all, an alumina-based polycrystal having excellent heat resistance and being less affected by impurities is preferable. The aluminum hydroxide polycrystal becomes α-alumina polycrystal or χ-alumina polycrystal when heated.
【００１７】γ−アルミナはきわめて比表面積が大きい
ために、グレインどうしの結晶境界に貴金属を担持しよ
うとしても、貴金属は結晶境界以外にも多く担持されて
しまう。そして高温雰囲気では結晶境界以外に担持され
た貴金属に粒成長が生じ、活性が低下してしまう。した
がって本発明では、担体として用いられる多結晶体から
γ−アルミナを除いている。Since γ-alumina has a very large specific surface area, even if an attempt is made to support a noble metal on the crystal boundaries between grains, a large amount of the noble metal is supported on other than the crystal boundaries. Then, in a high temperature atmosphere, grain growth occurs in the noble metal supported other than at the crystal boundaries, and the activity decreases. Therefore, in the present invention, γ-alumina is excluded from the polycrystal used as the carrier.
【００１８】担体の粒径は、一次粒子で 0.5〜10μｍ、
二次粒子で５〜30μｍの範囲が好ましい。粒径がこれら
の範囲より小さいと凝集しやすくなり、粒径がこれらの
範囲より大きくなると結晶界面が少なくなって結晶界面
に担持される貴金属の絶対量が不足するため、結果的に
耐久後の活性が低下するようになる。またグレインのア
スペクト比は、 0.5〜５の範囲が好ましい。グレインの
アスペクト比がこの範囲より小さいと凝集しやすくな
り、この範囲より大きくなると結晶界面が少なくなって
結晶界面に担持される貴金属の絶対量が不足するように
なる。The particle size of the carrier is 0.5 to 10 μm as primary particles,
The range of secondary particles is preferably 5 to 30 μm. If the particle size is smaller than these ranges, aggregation tends to occur, and if the particle size is larger than these ranges, the crystal interface decreases and the absolute amount of the noble metal supported on the crystal interface becomes insufficient. It becomes less active. The grain aspect ratio is preferably in the range of 0.5 to 5. If the grain aspect ratio is smaller than this range, aggregation tends to occur, and if it is larger than this range, the crystal interface becomes small and the absolute amount of the noble metal supported on the crystal interface becomes insufficient.
【００１９】貴金属としては、Pt，Rh，Pd，Ir，Ruなど
従来の排ガス浄化用触媒に用いられているものを用いる
ことができる。特に、高い触媒活性を有するものの粒成
長しやすいPtの場合に本発明は効果的である。また貴金
属の担持量は、担体に対して0.1重量％以上であり、好
ましくは 0.5〜20重量％である。担持量がこの範囲より
少ないと排ガス浄化用触媒としての活性が低すぎて実用
的でなく、この範囲より多く担持しても活性が飽和する
とともにコストが高騰してしまう。As the noble metal, those used in conventional exhaust gas purifying catalysts such as Pt, Rh, Pd, Ir and Ru can be used. In particular, the present invention is effective in the case of Pt which has a high catalytic activity but is prone to grain growth. The amount of the noble metal supported is 0.1% by weight or more, preferably 0.5 to 20% by weight, based on the carrier. If the supported amount is less than this range, the activity as an exhaust gas purifying catalyst is too low to be practical, and if the supported amount is more than this range, the activity is saturated and the cost rises.
【００２０】貴金属をグレインの結晶境界及び内部欠陥
に担持するには、貴金属薬液を用い毛細管現象を利用し
て担持することができる。この場合、担体に吸着しにく
い貴金属薬液を用いることが望ましい。吸着しやすい薬
液を用いると、グレインの結晶境界及び内部欠陥以外に
担持される貴金属が多くなり、それらが粒成長するとい
う不具合がある。In order to support the noble metal on the crystal boundaries and internal defects of the grains, the noble metal can be supported by utilizing a capillary phenomenon using a noble metal chemical solution. In this case, it is desirable to use a precious metal chemical liquid that is difficult to be adsorbed on the carrier. If a chemical solution that is easily adsorbed is used, there is a problem that the amount of noble metal supported other than the crystal boundaries and internal defects of grains increases, and these particles grow.
【００２１】なお本発明の排ガス浄化用触媒は、そのま
まで酸化触媒、三元触媒などとして利用することがで
き、さらにBaやＫなどのNOx 吸蔵材を担持すればNOx 吸
蔵還元型触媒として利用することができる。また貴金属
を担持する担体としては上記した多孔質体が必須である
ものの、場合によってはアルミナ、ジルコニア、セリ
ア、チタニアなど他の酸化物担体を併用してもよい。The exhaust gas-purifying catalyst of the present invention can be used as it is as an oxidation catalyst, a three-way catalyst, etc., and if it carries a NO x storage material such as Ba or K, it will serve as a NO x storage reduction catalyst. Can be used. Although the above-mentioned porous body is essential as the carrier for supporting the noble metal, other oxide carriers such as alumina, zirconia, ceria, and titania may be used in combination depending on the case.
【００２２】[0022]
【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.
【００２３】（実施例１）ボーキサイトを水酸化ナトリ
ウムで処理してアルミン酸ナトリウムとして溶かし、鉱
石中の不純物を沈殿させて分離した後、アルミン酸ナト
リウム溶液を加水分解した。得られた沈殿を乾燥させ、
水酸化アルミニウム多結晶体からなる粉末を得た。Example 1 Bauxite was treated with sodium hydroxide to dissolve it as sodium aluminate, and impurities in the ore were precipitated and separated, and then the sodium aluminate solution was hydrolyzed. The precipitate obtained is dried,
A powder of aluminum hydroxide polycrystal was obtained.
【００２４】この水酸化アルミニウム多結晶体は、平均
一次粒子径が８μｍ、平均二次粒子径が20μｍ、グレイ
ンは六角板状をなしそのアスペクト比は約２であった。
また400℃で焼成して AlO(OH)とした時の比表面積は 25
6m2／ｇであった。The aluminum hydroxide polycrystal had an average primary particle diameter of 8 μm, an average secondary particle diameter of 20 μm, grains were hexagonal plate-like, and the aspect ratio was about 2.
The specific surface area of AlO (OH) after firing at 400 ℃ is 25
It was 6 m 2 / g.
【００２５】この水酸化アルミニウム多結晶体からなる
粉末 120ｇに対し、所定濃度のジニトロジアンミン白金
水溶液の所定量を含浸させ、蒸発乾固後、大気中にて 1
20℃で２時間乾燥し 400℃で２時間焼成した。Ptの担持
量は２ｇである。得られた触媒粉末を圧粉成形して、
0.5mm〜 1.7mmのペレット触媒とした。120 g of this aluminum hydroxide polycrystal powder was impregnated with a predetermined amount of a dinitrodiammineplatinum aqueous solution having a predetermined concentration, evaporated to dryness, and then dried in air.
It was dried at 20 ° C for 2 hours and calcined at 400 ° C for 2 hours. The amount of Pt supported is 2 g. The obtained catalyst powder is compacted,
The pellet catalyst was 0.5 mm to 1.7 mm.
【００２６】上記で調製された触媒粉末の説明図を図１
に、後述の耐久試験と同様の試験後の触媒粉末のＴＥＭ
写真を図２に示す。図２は粉末を樹脂に埋めてＦＩＢに
て薄くスライスした試料の写真である。灰色の部分は水
酸化アルミニウム多結晶体から形成されたχ−アルミナ
多結晶体であり、黒い点がPt粒子であって、図２におけ
る５mmが 100nmである。An explanatory view of the catalyst powder prepared above is shown in FIG.
In addition, TEM of the catalyst powder after the same test as the durability test described below.
The photograph is shown in FIG. FIG. 2 is a photograph of a sample in which the powder is embedded in a resin and thinly sliced by FIB. The gray part is the χ-alumina polycrystal formed from the aluminum hydroxide polycrystal, the black dots are Pt particles, and 5 mm in FIG. 2 is 100 nm.
【００２７】水酸化アルミニウム多結晶体１は六角板状
のグレイン10がいろいろの方位をもって集合してなり、
グレイン10どうしの結晶境界11が多数存在している。そ
して図２から、Pt粒子２は直線状に担持されているのが
確認され、Pt粒子２は結晶境界11に担持されていると考
えられる。The aluminum hydroxide polycrystal 1 is composed of hexagonal plate-shaped grains 10 aggregated in various directions.
There are many crystal boundaries 11 between the grains 10. From FIG. 2, it was confirmed that the Pt particles 2 were supported linearly, and it is considered that the Pt particles 2 are supported on the crystal boundary 11.
【００２８】（実施例２）実施例１の水酸化アルミニウ
ム多結晶体からなる粉末を1200℃で焼成してα化し、そ
れに実施例１と同様にしてPtを担持し、ペレット触媒と
した。このα−アルミナ多結晶体は、平均一次粒子径が
８μｍ、平均二次粒子径が20μｍ、比表面積は８m2／
ｇ、グレインは六角板状をなしそのアスペクト比は約２
であった。またＴＥＭ観察の結果、Ptは結晶境界に担持
されていることが確認された。(Example 2) A powder of the aluminum hydroxide polycrystal of Example 1 was fired at 1200 ° C to be converted into α, and Pt was carried thereon in the same manner as in Example 1 to obtain a pellet catalyst. This α-alumina polycrystal has an average primary particle size of 8 μm, an average secondary particle size of 20 μm, and a specific surface area of 8 m 2 /
g, the grain has a hexagonal plate shape and its aspect ratio is about 2
Met. As a result of TEM observation, it was confirmed that Pt was supported on the crystal boundary.
【００２９】（比較例）市販のγ−アルミナ粉末（「 M
I386」グレース（株）製）を用意し、実施例１と同様に
してPtを担持し、ペレット触媒とした。このγ−アルミ
ナ粉末は、平均一次粒子径（針状の長さ方向）が10nm、
平均二次粒子径が４μｍ、比表面積が 150〜 200m2／ｇ
である。またＴＥＭ観察の結果、Ptは全体に均一に高分
散担持されていることが確認された。Comparative Example Commercially available γ-alumina powder (“M
“I386” Grace Co., Ltd. was prepared, and Pt was loaded in the same manner as in Example 1 to obtain a pellet catalyst. This γ-alumina powder has an average primary particle diameter (needle length direction) of 10 nm,
Average secondary particle size 4μm, specific surface area 150-200m 2 / g
Is. As a result of TEM observation, it was confirmed that Pt was uniformly and highly dispersed and supported on the entire surface.
【００３０】＜試験・評価＞実施例及び比較例のペレッ
ト触媒について、それぞれ大気中にて 800℃で５時間加
熱する耐久試験を行った。そして耐久試験後の各ペレッ
ト触媒を評価装置に配置し、表１に示すストイキ雰囲気
のモデルガス流通下にて、空間速度SV＝40万／ｈで、 5
00℃×20分の前処理後20℃／分で連続昇温して、その間
のHC，CO及びNOx 浄化率を連続的に測定した。この結果
からHC，CO及びNOx の50％浄化温度を算出し、結果を図
３に示す。<Test / Evaluation> Each of the pellet catalysts of Examples and Comparative Examples was subjected to a durability test of heating in air at 800 ° C. for 5 hours. Then, each pellet catalyst after the durability test was placed in the evaluation device, and under the model gas flow in the stoichiometric atmosphere shown in Table 1, at a space velocity SV of 400,000 / h, 5
After pretreatment at 00 ° C for 20 minutes, the temperature was continuously raised at 20 ° C / minute, and HC, CO and NO x purification rates during that period were continuously measured. From this result, 50% purification temperature of HC, CO and NO x was calculated, and the result is shown in FIG.
【００３１】なお実施例１の触媒では、耐久試験によっ
て水酸化アルミニウムがχ−アルミナとなったが、水酸
化アルミニウム多結晶体の多結晶構造はそのまま維持さ
れていた。そして耐久試験後の各担体の比表面積は、χ
−アルミナ多結晶体が 100m2／ｇ、α−アルミナ多結晶
体が１〜30m2／ｇ、γ−アルミナが 150〜 200m2／ｇで
あった。In the catalyst of Example 1, the aluminum hydroxide was changed to χ-alumina by the durability test, but the polycrystalline structure of the aluminum hydroxide polycrystal was maintained as it was. The specific surface area of each carrier after the durability test is χ
-Alumina polycrystal was 100 m 2 / g, α-alumina polycrystal was 1 to 30 m 2 / g, and γ-alumina was 150 to 200 m 2 / g.
【００３２】[0032]
【表１】 [Table 1]
【００３３】また耐久試験後の実施例１及び比較例のペ
レット触媒について、 Al2O3を溶かし、担持されている
Ptの粒径をＴＥＭにて測定した。結果を図４に示す。Further, the pellet catalysts of Example 1 and Comparative Example after the durability test were loaded with Al 2 O 3 dissolved therein.
The particle size of Pt was measured by TEM. The results are shown in Fig. 4.
【００３４】図３より、比較例の触媒は耐久試験後の活
性が低いのに対し、各実施例の触媒は比表面積が小さい
にも関わらず耐久試験後にも高い活性を示している。ま
た、実施例１の触媒より実施例２の触媒の方が高い活性
を示している。そして図４から、比較例の触媒は耐久試
験後にPtが大きく粒成長しているのに対し、実施例１の
触媒は耐久試験後にもPtは微細な粒径を維持している。From FIG. 3, the catalyst of the comparative example has a low activity after the durability test, while the catalysts of the respective examples show a high activity even after the durability test despite the small specific surface area. Further, the catalyst of Example 2 exhibits higher activity than the catalyst of Example 1. From FIG. 4, the catalyst of the comparative example shows large Pt particle growth after the durability test, whereas the catalyst of Example 1 maintains a fine Pt particle size even after the durability test.
【００３５】すなわち比較例の触媒では、Ptの粒成長に
よって活性が低下したと認められ、実施例の触媒ではPt
の粒成長が抑制されたため活性の低下が抑制されたと認
められる。これは、多結晶体のグレインの結晶境界に貴
金属を担持した効果であることが明らかである。That is, it was recognized that the activity of the catalyst of the comparative example was lowered by the grain growth of Pt, and that of the catalyst of the example was Pt.
It is considered that the decrease in the activity was suppressed because the grain growth of was suppressed. It is clear that this is an effect of supporting the noble metal on the crystal boundaries of the grains of the polycrystalline body.
【００３６】（実施例３）実施例１と同様にして調製さ
れ、上記と同様に耐久試験を行った後の触媒粉末のＴＥ
Ｍ写真を図５に示す。図５は粉末を樹脂に埋めてＦＩＢ
にて薄くスライスした試料の写真である。灰色の部分は
水酸化アルミニウム多結晶体から形成されたχ−アルミ
ナ多結晶体であり、黒い点がPt粒子であって、図５にお
ける５mmが100nmである。(Example 3) TE of a catalyst powder prepared in the same manner as in Example 1 and subjected to the durability test as described above
The M photograph is shown in FIG. Fig. 5 shows FIB by filling powder with resin.
It is a photograph of a sample thinly sliced at. The gray part is the χ-alumina polycrystal formed from the aluminum hydroxide polycrystal, the black dots are Pt particles, and 5 mm in FIG. 5 is 100 nm.
【００３７】図５から、直線状の隙間に担持されている
Pt粒子は結晶境界に担持されていると考えられ、その隙
間と交差するように担持されているPt粒子は内部欠陥に
担持されていると考えられる。From FIG. 5, it is carried in a linear gap.
It is considered that the Pt particles are supported on the crystal boundary, and the Pt particles supported so as to intersect the gap are considered to be supported on the internal defect.
【００３８】そして図５は図２と同一倍率の写真であ
り、図５のPt粒子の粒径は図２と同等であるので、内部
欠陥に担持されたPtも結晶境界に担持されたPtと同様に
粒成長が抑制されていることが明らかである。FIG. 5 is a photograph at the same magnification as FIG. 2. Since the particle size of the Pt particles in FIG. 5 is the same as that in FIG. 2, the Pt supported on the internal defect is also the Pt supported on the crystal boundary. Similarly, it is clear that grain growth is suppressed.
【００３９】[0039]
【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、貴金属の粒成長が防止され、耐熱耐久性に優れて
いる。[Effects of the Invention] That is, according to the catalyst for purifying exhaust gas of the present invention, the growth of precious metal particles is prevented and the heat resistance and durability are excellent.
【図１】実施例１の触媒の模式的断面図である。FIG. 1 is a schematic sectional view of a catalyst of Example 1.
【図２】実施例１の触媒の粒子構造を示すＴＥＭ写真で
ある。2 is a TEM photograph showing the particle structure of the catalyst of Example 1. FIG.
【図３】実施例及び比較例の触媒の耐久後の50％浄化温
度を示すグラフである。FIG. 3 is a graph showing the 50% purification temperature after durability of the catalysts of Examples and Comparative Examples.
【図４】実施例及び比較例の触媒の耐久後のPt粒径を示
すグラフである。FIG. 4 is a graph showing Pt particle size after durability of the catalysts of Examples and Comparative Examples.
【図５】実施例３の触媒の粒子構造を示すＴＥＭ写真で
ある。5 is a TEM photograph showing the particle structure of the catalyst of Example 3. FIG.
１：水酸化アルミニウム多結晶体 ２：Pt粒子
10：グレイン
11：結晶境界1: Aluminum hydroxide polycrystal 2: Pt particles
10: Grain 11: Crystal boundary
フロントページの続き Ｆターム(参考） 4D048 AA06 AA13 AA18 AB05 BA03X BA30X BA31Y BA32Y BA33Y BA41X BB01 4G069 AA01 AA03 BA01A BA01B BB04A BC69A BC70A BC71A BC72A BC74A BC75A BC75B CA03 CA09 EA02Y EB18Y EC22X EC22Y Continued front page F-term (reference) 4D048 AA06 AA13 AA18 AB05 BA03X BA30X BA31Y BA32Y BA33Y BA41X BB01 4G069 AA01 AA03 BA01A BA01B BB04A BC69A BC70A BC71A BC72A BC74A BC75A BC75B CA03 CA09 EA02Y EB18Y EC22X EC22Y
Claims (4)
結晶体の少なくとも一方よりなる担体と、該担体のグレ
インどうしの結晶境界に担持された貴金属と、よりなる
ことを特徴とする排ガス浄化用触媒。1. Exhaust gas comprising: a carrier comprising at least one of a metal hydroxide polycrystal and a metal oxide polycrystal, and a noble metal carried on a crystal boundary between grains of the carrier. Purification catalyst.
れている請求項１に記載の排ガス浄化用触媒。2. The exhaust gas-purifying catalyst according to claim 1, wherein the noble metal is also supported on internal defects of the carrier.
体及びγ−アルミナを除くアルミナ多結晶体の少なくと
も一方である請求項１又は請求項２に記載の排ガス浄化
用触媒。3. The exhaust gas purifying catalyst according to claim 1 or 2, wherein the carrier is at least one of an aluminum hydroxide polycrystal and an alumina polycrystal excluding γ-alumina.
請求項３に記載の排ガス浄化用触媒。4. The exhaust gas-purifying catalyst according to claim 3, wherein the carrier is an α-alumina polycrystal.
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2016193295A1 (en) * | 2015-06-03 | 2016-12-08 | IFP Energies Nouvelles | Catalyst comprising a porous support, the pores of which contain metal particles having a "sea urchin" morphology |
| WO2023151688A1 (en) * | 2022-02-14 | 2023-08-17 | 有研稀土高技术有限公司 | Catalyst for loading noble metal on grain boundary and surface, preparation method therefor, and use thereof |
| WO2023151687A1 (en) * | 2022-02-14 | 2023-08-17 | 有研稀土高技术有限公司 | Grain boundary and surface-supported noble metal catalyst, and preparation method therefor and application thereof |
-
2002
- 2002-07-04 JP JP2002196299A patent/JP3879992B2/en not_active Expired - Fee Related
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2016193295A1 (en) * | 2015-06-03 | 2016-12-08 | IFP Energies Nouvelles | Catalyst comprising a porous support, the pores of which contain metal particles having a "sea urchin" morphology |
| FR3036979A1 (en) * | 2015-06-03 | 2016-12-09 | Ifp Energies Now | CATALYST COMPRISING A POROUS CARRIER IN WHICH ARE METALLIC PARTICLES HAVING "OURSIN" TYPE MORPHOLOGY. |
| WO2023151688A1 (en) * | 2022-02-14 | 2023-08-17 | 有研稀土高技术有限公司 | Catalyst for loading noble metal on grain boundary and surface, preparation method therefor, and use thereof |
| WO2023151687A1 (en) * | 2022-02-14 | 2023-08-17 | 有研稀土高技术有限公司 | Grain boundary and surface-supported noble metal catalyst, and preparation method therefor and application thereof |
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