JP2016147256A - Method for producing catalyst and catalyst - Google Patents
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- 239000003054 catalyst Substances 0.000 title claims abstract description 117
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 29
- 229910000510 noble metal Inorganic materials 0.000 claims abstract description 187
- 239000002245 particle Substances 0.000 claims abstract description 172
- 239000002923 metal particle Substances 0.000 claims abstract description 105
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 claims abstract description 70
- 239000012298 atmosphere Substances 0.000 claims abstract description 44
- 229910052697 platinum Inorganic materials 0.000 claims abstract description 34
- 239000007789 gas Substances 0.000 claims abstract description 32
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 claims abstract description 30
- OGIDPMRJRNCKJF-UHFFFAOYSA-N titanium oxide Inorganic materials [Ti]=O OGIDPMRJRNCKJF-UHFFFAOYSA-N 0.000 claims abstract description 26
- KDLHZDBZIXYQEI-UHFFFAOYSA-N Palladium Chemical compound [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 claims abstract description 25
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims abstract description 21
- 229910000420 cerium oxide Inorganic materials 0.000 claims abstract description 19
- BMMGVYCKOGBVEV-UHFFFAOYSA-N oxo(oxoceriooxy)cerium Chemical compound [Ce]=O.O=[Ce]=O BMMGVYCKOGBVEV-UHFFFAOYSA-N 0.000 claims abstract description 19
- RVTZCBVAJQQJTK-UHFFFAOYSA-N oxygen(2-);zirconium(4+) Chemical compound [O-2].[O-2].[Zr+4] RVTZCBVAJQQJTK-UHFFFAOYSA-N 0.000 claims abstract description 19
- 229910001928 zirconium oxide Inorganic materials 0.000 claims abstract description 19
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- 229910052703 rhodium Inorganic materials 0.000 claims abstract description 12
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- 239000000969 carrier Substances 0.000 claims abstract description 11
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 claims abstract description 8
- 229910002091 carbon monoxide Inorganic materials 0.000 claims abstract description 8
- 238000000034 method Methods 0.000 claims description 66
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- 239000010970 precious metal Substances 0.000 claims description 9
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- TWNQGVIAIRXVLR-UHFFFAOYSA-N oxo(oxoalumanyloxy)alumane Chemical compound O=[Al]O[Al]=O TWNQGVIAIRXVLR-UHFFFAOYSA-N 0.000 description 5
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- 229910001887 tin oxide Inorganic materials 0.000 description 4
- QHGNHLZPVBIIPX-UHFFFAOYSA-N tin(II) oxide Inorganic materials [Sn]=O QHGNHLZPVBIIPX-UHFFFAOYSA-N 0.000 description 4
- 239000002253 acid Substances 0.000 description 3
- 239000007864 aqueous solution Substances 0.000 description 3
- 230000015572 biosynthetic process Effects 0.000 description 3
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- 238000004438 BET method Methods 0.000 description 1
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- 229910002651 NO3 Inorganic materials 0.000 description 1
- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 description 1
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 1
- 238000002441 X-ray diffraction Methods 0.000 description 1
- MCMNRKCIXSYSNV-UHFFFAOYSA-N ZrO2 Inorganic materials O=[Zr]=O MCMNRKCIXSYSNV-UHFFFAOYSA-N 0.000 description 1
- 238000005054 agglomeration Methods 0.000 description 1
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- 229910052787 antimony Inorganic materials 0.000 description 1
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- 150000003841 chloride salts Chemical class 0.000 description 1
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- 239000003574 free electron Substances 0.000 description 1
- 229910052734 helium Inorganic materials 0.000 description 1
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- SWQJXJOGLNCZEY-UHFFFAOYSA-N helium atom Chemical compound [He] SWQJXJOGLNCZEY-UHFFFAOYSA-N 0.000 description 1
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- 229910052741 iridium Inorganic materials 0.000 description 1
- GKOZUEZYRPOHIO-UHFFFAOYSA-N iridium atom Chemical compound [Ir] GKOZUEZYRPOHIO-UHFFFAOYSA-N 0.000 description 1
- 229910044991 metal oxide Inorganic materials 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
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- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 description 1
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- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- MUMZUERVLWJKNR-UHFFFAOYSA-N oxoplatinum Chemical compound [Pt]=O MUMZUERVLWJKNR-UHFFFAOYSA-N 0.000 description 1
- 125000004430 oxygen atom Chemical group O* 0.000 description 1
- 230000000737 periodic effect Effects 0.000 description 1
- 229910003446 platinum oxide Inorganic materials 0.000 description 1
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- 239000012279 sodium borohydride Substances 0.000 description 1
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- TYLYVJBCMQFRCB-UHFFFAOYSA-K trichlororhodium;trihydrate Chemical compound O.O.O.[Cl-].[Cl-].[Cl-].[Rh+3] TYLYVJBCMQFRCB-UHFFFAOYSA-K 0.000 description 1
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Abstract
Description
本発明は、排ガス浄化用・燃料電池電極用触媒の製造方法及び触媒に関し、特に、酸化物担体の上に担持された貴金属粒子の粒子径を容易に制御可能な、触媒の製造方法、及び当該製造方法にて製造された触媒に関する。 The present invention relates to a method and a catalyst for producing a catalyst for exhaust gas purification / fuel cell electrode, and in particular, a method for producing a catalyst capable of easily controlling the particle diameter of noble metal particles supported on an oxide carrier, and the catalyst The present invention relates to a catalyst produced by the production method.
白金、パラジウム、ロジウムなどの貴金属は、高い触媒活性をもつことが知られており、排ガス浄化用触媒や燃料電池電極用触媒として利用されている。しかしながら、これらの貴金属はいずれも高価であることから、より少ない使用量で高い活性が得られることが好ましく、広い比表面積をもつ担体上に微細な粒子として担持されて利用されることが一般的である。 Precious metals such as platinum, palladium and rhodium are known to have high catalytic activity, and are used as exhaust gas purifying catalysts and fuel cell electrode catalysts. However, since these noble metals are all expensive, it is preferable that high activity is obtained with a smaller amount of use, and it is generally used as fine particles supported on a carrier having a large specific surface area. It is.
貴金属を微細な粒子として触媒担体上に担持させる方法は様々であるが、簡便な手法として含浸法が利用される。この方法では、貴金属塩の水溶液中に担体を含浸させ、その後、乾燥や焼成工程を経て、貴金属塩を分解して貴金属微粒子とする。貴金属の粒子径は、担体と貴金属塩との組み合わせや作成条件によって大きく変化するが、担体として酸化アルミニウム、酸化チタン、酸化ジルコニウム、酸化セリウムなどを用いた場合には、微細な粒子が生成しやすく、粒子径１ｎｍ程度の粒子が得られることも多い。しかしながら、貴金属の粒子径があまりに小さすぎる場合には、使用温度や使用雰囲気によって粒子径が変化し易くなり、却って凝集が進行することや、燃料電池電極用触媒として利用した場合には貴金属粒子の溶出が進行しやすくなることが知られており、使用目的に適した粒子径に制御することが好ましい。例えば、高温での反応用の触媒や、燃料電池電極用触媒としては、粒子径３〜４ｎｍ程度の粒子とすることが好ましいとされている。 There are various methods for supporting the noble metal as fine particles on the catalyst carrier, but an impregnation method is used as a simple method. In this method, a carrier is impregnated in an aqueous solution of a noble metal salt, and then the noble metal salt is decomposed into noble metal fine particles through a drying and firing step. The particle size of the noble metal varies greatly depending on the combination of the carrier and the noble metal salt and the preparation conditions. However, when aluminum oxide, titanium oxide, zirconium oxide, cerium oxide, etc. are used as the carrier, fine particles are likely to be generated. In many cases, particles having a particle diameter of about 1 nm are obtained. However, when the particle size of the noble metal is too small, the particle size is likely to change depending on the use temperature and the use atmosphere, and on the contrary, the agglomeration proceeds, or when used as a catalyst for a fuel cell electrode, It is known that elution is likely to proceed, and it is preferable to control the particle size suitable for the intended purpose. For example, as a catalyst for reaction at a high temperature or a catalyst for a fuel cell electrode, it is preferable to use particles having a particle diameter of about 3 to 4 nm.
近年、酸化物を担体として利用した燃料電池電極用触媒の開発が進められており、酸化チタン、酸化スズなどが、担体酸化物の候補として利用されている。しかしながら、これら酸化物は、貴金属粒子との相互作用が強く、簡便な含浸法にて貴金属を担持した場合には、酸化物表面に貴金属粒子が強く固着され、粒子径が１ｎｍ程度に小さくなり過ぎてしまうことが知られている。 In recent years, development of a catalyst for a fuel cell electrode using an oxide as a support has been developed, and titanium oxide, tin oxide, and the like are used as candidates for a support oxide. However, these oxides have a strong interaction with the noble metal particles, and when the noble metal is supported by a simple impregnation method, the noble metal particles are strongly fixed on the oxide surface and the particle diameter becomes too small to about 1 nm. It is known that
この問題に対応するために、これら酸化物担体上で、粒子径を３〜４ｎｍ程度とした貴金属粒子を得る際には、担体と貴金属の相互作用の影響を受け難い作製方法が用いられることが多い。例えば、以下の特許文献１に示されるように、貴金属塩溶液中に水素化ホウ素ナトリウムやエタノールなどの還元剤を添加し、貴金属イオンを還元することで、酸化物担体上に貴金属の粒子を担持させる方法が用いられている。こうした方法によれば、貴金属塩や還元剤の種類、還元の速度等をコントロールすることで、粒子径を制御することが可能となる。 In order to cope with this problem, when obtaining noble metal particles having a particle diameter of about 3 to 4 nm on these oxide carriers, a production method that is hardly affected by the interaction between the carrier and the noble metal is used. Many. For example, as shown in the following Patent Document 1, a noble metal particle is supported on an oxide carrier by adding a reducing agent such as sodium borohydride or ethanol to a noble metal salt solution and reducing noble metal ions. Is used. According to such a method, the particle diameter can be controlled by controlling the kind of the noble metal salt and the reducing agent, the speed of reduction, and the like.
また、以下の特許文献２には、保護材を用いた方法も開示されている。この手法によれば、粒子同士が寄り集まってしまうことを抑制しつつ、粒子径の制御された貴金属粒子を担体上に分散させることが可能となる。 Moreover, the following patent document 2 also discloses a method using a protective material. According to this method, it is possible to disperse the noble metal particles whose particle diameter is controlled on the carrier while suppressing the particles from gathering together.
また、以下特許文献３では、含浸法にて酸化アルミニウムを担体として作製された触媒を、１０００℃以上の高温で、酸化雰囲気と還元雰囲気を用いて交互に焼成することによって、粒子径を少しずつ大きく成長させる手法も紹介されている。 Further, in Patent Document 3 below, a catalyst produced using an aluminum oxide carrier as a support by an impregnation method is alternately baked at a high temperature of 1000 ° C. or higher using an oxidizing atmosphere and a reducing atmosphere, thereby gradually reducing the particle size. It also introduces a method of growing greatly.
しかしながら、上記特許文献１に示されるような、液相での貴金属塩の還元を経由する手法では、貴金属塩の還元速度を高めてしまうと粒子径が大きくなりやすいため、貴金属粒子を目的の粒子径とするには還元速度を低減する必要が生じ、製造に時間がかかるという課題がある。また、多量の廃液が生じることから、大量製造を行う場合に問題となる。更に、このようにして作成された貴金属粒子は、担体との相互作用が不十分であり、凝集が進行しやすいことが知られている。これらの課題は、上記特許文献２に示されるような、保護材を用いる手法においても、同様に生じる。 However, in the method via the reduction of the noble metal salt in the liquid phase as shown in Patent Document 1, the particle diameter tends to increase if the reduction rate of the noble metal salt is increased. In order to obtain a diameter, it is necessary to reduce the reduction rate, and there is a problem that it takes time to manufacture. Further, since a large amount of waste liquid is generated, it becomes a problem when mass production is performed. Furthermore, it is known that the noble metal particles prepared in this way have insufficient interaction with the carrier, and aggregation is likely to proceed. These problems also occur in the method using a protective material as shown in Patent Document 2 above.
一方、含浸法によって貴金属を酸化物担体上に担持させた場合には、粒子径の制御は困難である。特に、貴金属との相互作用の強い酸化チタン、酸化セリウム、酸化ジルコニウムなどの担体を利用した場合には、粒子径が１ｎｍ程度の微粒子となりやすい。こうした酸化物担体を利用した場合には、固着された貴金属粒子は動くことが出来ず、加熱昇温しても粒子径を大きくすることが困難である。また、貴金属粒子の凝集を進めるために更に温度を上昇させた場合には、著しく粗大な粒子が部分的に生成する。更に、耐熱性が不十分な酸化チタン、酸化セリウム、酸化ジルコニウムを用いた場合には、担体が著しく変性する原因となる。 On the other hand, when a noble metal is supported on an oxide support by an impregnation method, it is difficult to control the particle size. In particular, when a carrier such as titanium oxide, cerium oxide, or zirconium oxide having a strong interaction with a noble metal is used, it tends to be a fine particle having a particle diameter of about 1 nm. When such an oxide support is used, the fixed noble metal particles cannot move, and it is difficult to increase the particle diameter even if the temperature is raised by heating. Further, when the temperature is further increased in order to advance the aggregation of the noble metal particles, extremely coarse particles are partially generated. Furthermore, when titanium oxide, cerium oxide, or zirconium oxide having insufficient heat resistance is used, the carrier may be significantly modified.
また、上記特許文献３では、１０００℃以上という高温で焼成を行い、更に、還元雰囲気と酸化雰囲気とを交互に利用することで、粒子径の制御を達成している。しかしながら、かかる手法は、耐熱性に優れる酸化アルミニウム担体であってこそ適用可能な手法であり、酸化チタン、酸化セリウム、酸化ジルコニウムのいずれに対しても適用は困難であるという課題がある。また、水素を含む還元性ガスと、酸素を含む酸化性ガスとを交互に吹き込むことから、燃焼・爆発などの危険性があり、大型の加熱炉を用いた製造法への適用は困難という課題があるほか、粒子径の制御も不十分であり、平均粒子径の２倍以上の粒子径を持つ粒子も多数存在するという課題がある。 Moreover, in the said patent document 3, the particle diameter is controlled by performing baking at a high temperature of 1000 ° C. or higher and further using a reducing atmosphere and an oxidizing atmosphere alternately. However, such a technique is applicable only to an aluminum oxide carrier having excellent heat resistance, and there is a problem that it is difficult to apply to any of titanium oxide, cerium oxide, and zirconium oxide. In addition, since reducing gas containing hydrogen and oxidizing gas containing oxygen are alternately blown, there is a risk of combustion and explosion, and it is difficult to apply to a manufacturing method using a large heating furnace. In addition, there is a problem that the particle size is not sufficiently controlled, and there are many particles having a particle size twice or more the average particle size.
そこで、本発明は、このような事情に鑑みてなされたものであり、酸化物担体に担持されている触媒金属粒子の粒子径を、粒径分布を狭く、かつ、微細でありながらも触媒反応に適した大きさに制御することが可能な、触媒の製造方法及び触媒を提供することを目的とする。 Therefore, the present invention has been made in view of such circumstances, and the catalytic metal particles supported on the oxide support have a particle size, a narrow particle size distribution, and a fine catalytic reaction. It is an object of the present invention to provide a catalyst production method and a catalyst that can be controlled to a size suitable for the above .
本発明者らは、上記課題を解決するために、貴金属と酸化物担体との相互作用に着目して、鋭意研究を行った。 In order to solve the above-mentioned problems, the present inventors have conducted extensive research focusing on the interaction between a noble metal and an oxide support.
そして、本発明者らは、酸化チタン、酸化ジルコニウム、酸化セリウム等の貴金属と強く相互作用する酸化物担体は、還元雰囲気下で焼成処理を行った場合に、カプセル化等の特異な振る舞いをすることを知見した。そこで、かかる知見に着目して検討を進めた結果、貴金属を担持した触媒を還元雰囲気下で、触媒担体への熱的な悪影響の比較的小さい８００℃未満の温度で焼成することによって、貴金属粒子を、ｎｍオーダーの微細な粒子径の範囲内で、粒度分布狭く制御することができることを見出して、本発明を完成した。 The inventors of the present invention have a unique behavior such as encapsulation when an oxide carrier that strongly interacts with a noble metal such as titanium oxide, zirconium oxide, or cerium oxide is subjected to a firing treatment in a reducing atmosphere. I found out. Accordingly, as a result of investigations focusing on such knowledge, noble metal particles are calcined by firing a catalyst supporting a noble metal in a reducing atmosphere at a temperature of less than 800 ° C., which has a relatively small thermal adverse effect on the catalyst carrier. The present invention has been completed by finding that the particle size distribution can be controlled narrowly within the range of a fine particle diameter of the order of nm.
かかる知見に基づき完成された本発明の要旨は、以下の通りである。
（１）酸化チタン、酸化ジルコニウム、及び酸化セリウムからなる群から選ばれる一種又は二種以上の酸化物担体に、白金、パラジウム、及びロジウムからなる群から選ばれる一種又は二種以上の貴金属粒子を担持させて貴金属担持触媒とする工程と、水素ガス又は一酸化炭素ガスの少なくとも何れか一方の還元性ガスを含む還元雰囲気中で、５００℃以上８００℃未満の温度にて、前記貴金属担持触媒を加熱処理して、当該貴金属担持触媒に担持されている貴金属の粒子径を所定の範囲に制御する工程と、を含む、触媒の製造方法。
（２）前記貴金属粒子を担持して貴金属触媒とする工程は、含浸法を用いて実施される、（１）に記載の触媒の製造方法。
（３）前記貴金属の粒子径を所定の範囲に制御する工程では、前記貴金属の平均粒子径を、２．５ｎｍ以上４ｎｍ以下に制御する、（１）又は（２）に記載の触媒の製造方法。
（４）前記貴金属の粒子径を所定の範囲に制御する工程では、前記貴金属を、平均粒子径が２．５ｎｍ以上４．０ｎｍ以下、かつ、全貴金属粒子に対する平均粒子径±０．４ｎｍ以内の貴金属粒子の占める割合が個数比で５０％以上に制御する、（１）又は（２）に記載の触媒の製造方法。
（５）前記還元雰囲気中における処理温度は、５５０℃以上７００℃以下である、（１）〜（４）の何れか１項に記載の触媒の製造方法。
（６）前記還元性ガスは、少なくとも水素ガスを含み、当該水素ガスの前記還元雰囲気中に占める割合が、１体積％以上１００体積％以下である、（１）〜（５）の何れか１項に記載の触媒の製造方法。
（７）前記酸化物担体は、酸化チタンである、（１）〜（６）の何れか１項に記載の触媒の製造方法。
（８）前記貴金属が、白金である、（１）〜（７）の何れか１項に記載の触媒の製造方法。
（９）前記酸化物担体に担持される貴金属が、製造される触媒中に占める割合が、１質量％以上４０質量％以下である、（１）〜（８）の何れか１項に記載の触媒の製造方法。
（１０）酸化チタン、酸化ジルコニウム、及び酸化セリウムからなる群から選ばれる一種又は二種以上の酸化物担体に、白金、パラジウム、及びロジウムからなる群から選ばれる一種又は二種以上の貴金属粒子が担持されており、前記貴金属粒子は、平均粒子径が２．５ｎｍ以上４．０ｎｍ以下の範囲内であり、かつ、全貴金属粒子に占める平均粒子径±０．４ｎｍの範囲内にある貴金属粒子の割合が、個数比で５０％以上である、触媒。
The gist of the present invention completed based on such findings is as follows.
(1) One or more kinds of noble metal particles selected from the group consisting of platinum, palladium, and rhodium are added to one or more kinds of oxide carriers selected from the group consisting of titanium oxide, zirconium oxide, and cerium oxide. The noble metal-supported catalyst is supported at a temperature of 500 ° C. or more and less than 800 ° C. in a reducing atmosphere containing a reducing gas containing at least one of hydrogen gas and carbon monoxide gas. And a step of controlling the particle diameter of the noble metal supported on the noble metal-supported catalyst within a predetermined range by heat treatment.
(2) The method for producing a catalyst according to (1), wherein the step of supporting the noble metal particles to form a noble metal catalyst is performed using an impregnation method.
(3) The method for producing a catalyst according to (1) or (2), wherein in the step of controlling the particle diameter of the noble metal within a predetermined range, the average particle diameter of the noble metal is controlled to 2.5 nm or more and 4 nm or less. .
(4) In the step of controlling the particle diameter of the noble metal within a predetermined range, the noble metal has an average particle diameter of 2.5 nm or more and 4.0 nm or less and an average particle diameter of ± 0.4 nm or less with respect to all noble metal particles. The method for producing a catalyst according to (1) or (2), wherein the ratio of the precious metal particles is controlled to 50% or more in terms of the number ratio.
(5) The process for producing a catalyst according to any one of (1) to (4), wherein a treatment temperature in the reducing atmosphere is 550 ° C. or higher and 700 ° C. or lower.
(6) Any one of (1) to (5), wherein the reducing gas contains at least hydrogen gas, and a proportion of the hydrogen gas in the reducing atmosphere is 1% by volume to 100% by volume. A method for producing the catalyst according to item.
(7) The method for producing a catalyst according to any one of (1) to (6), wherein the oxide carrier is titanium oxide.
(8) The method for producing a catalyst according to any one of (1) to (7), wherein the noble metal is platinum.
(9) The ratio according to any one of (1) to (8), wherein a ratio of the noble metal supported on the oxide support in the produced catalyst is 1% by mass or more and 40% by mass or less. A method for producing a catalyst.
(10) One or more noble metal particles selected from the group consisting of platinum, palladium, and rhodium are added to one or more oxide carriers selected from the group consisting of titanium oxide, zirconium oxide, and cerium oxide. The noble metal particles that are supported are noble metal particles having an average particle diameter in the range of 2.5 nm to 4.0 nm and an average particle diameter in the range of ± 0.4 nm in the total noble metal particles. The catalyst whose ratio is 50% or more by number ratio.
以上説明したように本発明によれば、還元雰囲気下における焼成処理のみで、粒子径が所定の範囲内とされた貴金属粒子を担持した触媒を製造する方法を提供でき、粒子径が所定の範囲内となった貴金属粒子を担持した触媒を提供できる。 As described above, according to the present invention, it is possible to provide a method for producing a catalyst carrying noble metal particles having a particle diameter within a predetermined range only by a calcination treatment in a reducing atmosphere, and the particle diameter is within a predetermined range. A catalyst carrying the precious metal particles inside can be provided.
以下に添付図面を参照しながら、本発明の好適な実施の形態について詳細に説明する。 Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
先だって説明したように、本発明は、酸化物担体に担持されている触媒金属粒子の粒子径を、粒径分布を狭く、かつ、微細でありながらも触媒反応に適した大きさに制御することが可能な、触媒の製造方法及び触媒を提供する。特に、本発明は、問題が多かった液相での貴金属塩の還元を行う工程を経由することなく、更に、触媒担体への熱的な悪影響を抑制すべく、触媒の１０００℃以上の高温焼成を行わなくても上記のような粒子径の制御が可能な、触媒の製造方法および触媒を提供する。 As described earlier, the present invention controls the particle size of the catalytic metal particles supported on the oxide support to a size suitable for catalytic reaction while having a narrow particle size distribution and fineness. A method for producing a catalyst and a catalyst are provided. In particular, the present invention does not go through the step of reducing the noble metal salt in the liquid phase, which has been problematic, and further calcinates the catalyst at a high temperature of 1000 ° C. or higher in order to suppress thermal adverse effects on the catalyst support. A method for producing a catalyst and a catalyst capable of controlling the particle diameter as described above without performing the above are provided.
本発明の実施形態に係る触媒では、白金、パラジウム、ロジウムなどに代表される貴金属が、貴金属との相互作用が強い酸化物担体である酸化チタン、酸化セリウム、酸化ジルコニウムに担持されている。 In the catalyst according to the embodiment of the present invention, a noble metal typified by platinum, palladium, rhodium or the like is supported on titanium oxide, cerium oxide, or zirconium oxide, which is an oxide carrier having a strong interaction with the noble metal.
貴金属粒子の粒子径には、対象とする反応に応じた最適な値が存在することが近年の研究によって明らかとなってきている。例えば、上記特許文献３では、貴金属粒子の粒子径があまりに小さすぎると、反応中に粒子の凝集が生じやすくなり、かえって触媒の寿命を短くすることが指摘されている。更に、粗大な粒子が一部に存在する場合には、かかる粗大な粒子が他の貴金属粒子を凝集させる核として振る舞うことから、粒子径の分布が狭い方が好ましいことも指摘されている。また、近年開発が進められている燃料電池電極用触媒にあっては、粒子径を３〜４ｎｍ程度とすることによって、触媒活性と触媒寿命との両立が可能となることが知られている。 Recent research has revealed that there is an optimum value for the particle size of the noble metal particles according to the target reaction. For example, it is pointed out in Patent Document 3 that if the particle diameter of the noble metal particles is too small, the particles are likely to aggregate during the reaction, which shortens the life of the catalyst. Furthermore, it is pointed out that when coarse particles are present in part, the coarse particles behave as nuclei for agglomerating other noble metal particles, so that a narrow particle size distribution is preferable. In addition, it is known that a catalyst for a fuel cell electrode, which has been developed in recent years, can achieve both catalyst activity and catalyst life by setting the particle diameter to about 3 to 4 nm.
上記のように、貴金属の粒子径制御は重要であるが、簡便な触媒合成法である含浸法を用いた場合や、貴金属塩の水溶液に酸化物担体を浸漬させることで貴金属イオンを担体に吸着させ、その後、乾燥と焼成する選択担持法などを用いた場合には、粒子が微細になり過ぎることが知られている。特に、酸化チタン、酸化セリウム、酸化ジルコニウムを担体として利用した場合には、上記の傾向が顕著であり、焼成温度を上昇させた場合にも粒子径の増大は少なく、また、これらの酸化物担体は耐熱性が高くないことから、担体の比表面積低下が生じてしまう。 As mentioned above, control of the particle size of the noble metal is important, but when the impregnation method, which is a simple catalyst synthesis method, is used, or by immersing the oxide carrier in an aqueous solution of a noble metal salt, the noble metal ions are adsorbed on the carrier. Then, it is known that the particles become too fine when using a selective support method such as drying and firing. In particular, when titanium oxide, cerium oxide, or zirconium oxide is used as a support, the above-mentioned tendency is remarkable, and even when the firing temperature is increased, the increase in particle diameter is small. Since the heat resistance is not high, the specific surface area of the carrier is reduced.
一方で、これらの酸化物担体上では、貴金属の粒子がほぼ均一な粒子径を有し、かつ、ほぼ均一な個数密度である状態で、貴金属を酸化物担体上に担持させることが可能である。そこで、本発明者らは、適切な熱処理工程を用いて貴金属の粒子を成長させることができれば、均一な粒子径の貴金属粒子を、均一な個数密度で担体上に担持させることが可能となると推察し、含浸法や選択担持法で作成された触媒に対して、様々な雰囲気と温度にて焼成処理を施し、貴金属粒子の粒子径の変化を観察した。その結果、特に、水素及び一酸化炭素を含む還元性ガス中にて５００℃以上８００℃未満の範囲で焼成処理を行うことで、平均粒子径２．５〜４ｎｍの均一な粒子径をもつ貴金属粒子が、均一な個数密度で酸化物担体上に分布した触媒を得ることが可能であることが確認された。本発明の触媒製造方法で製造された触媒、及び、本発明の触媒は、排ガス処理用触媒として利用が可能である他、燃料電池の酸素極用触媒としての利用が期待される。 On the other hand, on these oxide supports, it is possible to support the noble metal on the oxide support in a state where the particles of the noble metal have a substantially uniform particle diameter and a substantially uniform number density. . Accordingly, the present inventors presume that if noble metal particles can be grown using an appropriate heat treatment step, noble metal particles having a uniform particle diameter can be supported on the carrier with a uniform number density. Then, the catalyst prepared by the impregnation method or the selective support method was subjected to a calcination treatment in various atmospheres and temperatures, and the change in the particle diameter of the noble metal particles was observed. As a result, a noble metal having a uniform particle size of 2.5 to 4 nm in average particle size is obtained by performing a baking treatment in a range of 500 ° C. or higher and lower than 800 ° C. in a reducing gas containing hydrogen and carbon monoxide. It was confirmed that it was possible to obtain a catalyst in which the particles were distributed on the oxide support with a uniform number density. The catalyst produced by the catalyst production method of the present invention and the catalyst of the present invention can be used as an exhaust gas treatment catalyst and are expected to be used as an oxygen electrode catalyst for fuel cells.
還元性ガス中で焼成処理を行うことで均一な粒子径が得られる理由については、以下のように推察している。酸化チタン、酸化セリウム、酸化ジルコニウム上で貴金属粒子が微細な粒子となりやすい理由として、酸化物状態の貴金属が安定化されやすいことが指摘されている（例えば、上記非特許文献１を参照。）。これにより、貴金属の粒子が、酸素原子を介して酸化物担体と強く結合することによって、貴金属粒子の移動が妨げられ、粗大化が抑制される。また、この酸素を介した貴金属粒子と担体との結合が強いことから、貴金属粒子が微細化し、担体との結合面積を増大させることで、系全体としてより安定な状態となる。これが、上記酸化物担体上で貴金属粒子が微細に分散し、かつ、凝集が抑制される理由である。 The reason why a uniform particle size can be obtained by performing the baking treatment in the reducing gas is presumed as follows. It has been pointed out that the precious metal particles in the oxide state are likely to be stabilized as the reason why the precious metal particles tend to be fine particles on titanium oxide, cerium oxide, and zirconium oxide (for example, see Non-Patent Document 1 above). As a result, the noble metal particles are strongly bonded to the oxide carrier via the oxygen atoms, thereby preventing the movement of the noble metal particles and suppressing the coarsening. In addition, since the bond between the noble metal particle and the carrier via oxygen is strong, the noble metal particle is refined and the bonding area with the carrier is increased, so that the entire system becomes more stable. This is the reason why noble metal particles are finely dispersed on the oxide carrier and aggregation is suppressed.
しかしながら、焼成温度を上昇させ、貴金属粒子の一部が酸化物状態から金属状態へと変化した場合には、状況が変化する。例えば、白金の酸化物は、熱力学的には、大気雰囲気下でも６００℃以上の温度では、金属として存在する方が安定である。上に示したような貴金属と担体との相互作用によって、より高い温度まで貴金属酸化物が安定に存在することは可能であるが、更に高温にした場合には、少なくとも一部の貴金属は金属状態に変化する。すると、貴金属と担体との酸素を介した強固な結合が解けてしまい、速やかに貴金属粒子の凝集が進行し、粗大な粒子が生成する。かかる現象は、後に示す実施例にて示す通りである。 However, the situation changes when the firing temperature is raised and some of the noble metal particles change from the oxide state to the metal state. For example, platinum oxide is more stable in terms of thermodynamics when it exists as a metal at a temperature of 600 ° C. or higher even in an air atmosphere. It is possible for the noble metal oxide to exist stably up to a higher temperature due to the interaction between the noble metal and the support as shown above, but at higher temperatures, at least some of the noble metal is in the metallic state. To change. Then, the strong bond between the noble metal and the carrier via oxygen is broken, the aggregation of the noble metal particles proceeds rapidly, and coarse particles are generated. Such a phenomenon is as shown in the examples described later.
一方、上記酸化物に貴金属粒子を担持した触媒では、高温、還元雰囲気下にて、酸化物担体の一部が貴金属粒子上にせり上がる現象が起こることが知られており、カプセル化、又は、デコレーションなどと呼ばれている。この現象は、以下に示すような大きく二つのメカニズムによって進行すると予想されている。 On the other hand, in a catalyst in which noble metal particles are supported on the oxide, it is known that a phenomenon occurs in which a part of the oxide support rises on the noble metal particles at a high temperature and in a reducing atmosphere. It is called decoration. This phenomenon is expected to proceed by two major mechanisms as shown below.
第一のメカニズムは、貴金属粒子の表面エネルギーの低減である。貴金属粒子は、高い表面エネルギーを持つことが知られている（例えば、上記非特許文献２を参照。）。そこで、表面がより低い表面エネルギーを持つ物質で覆われることで、系全体が安定化されることになる。第二のメカニズムは、貴金属粒子と還元された酸化物との強固な結合である。カプセル化された貴金属粒子の表面に存在する酸化物は、部分的に酸素が欠損した酸化物となっていることが知られている。部分的に還元された酸化物と、貴金属とが合金的な相を生成することによって、強固な結合が生まれると推定されており、強固な結合が広い面積で生じることで、系全体のエネルギーが安定化されるものと考えられる。本発明者らは、これらの二つのメカニズム、特に表面エネルギーの影響について、貴金属粒子の粒子径に依存する可能性があると推察した。 The first mechanism is a reduction in the surface energy of the noble metal particles. It is known that noble metal particles have a high surface energy (see, for example, Non-Patent Document 2 above). Therefore, the entire system is stabilized by covering the surface with a material having a lower surface energy. The second mechanism is a strong bond between the noble metal particles and the reduced oxide. It is known that the oxide present on the surface of the encapsulated noble metal particles is an oxide partially deficient in oxygen. It is presumed that a strong bond is created by the formation of an alloy-like phase between the partially reduced oxide and the noble metal, and the strong bond is generated over a wide area, so that the energy of the entire system is reduced. It is thought to be stabilized. The present inventors speculated that these two mechanisms, particularly the influence of surface energy, may depend on the particle size of the noble metal particles.
物質の表面エネルギーは、大きく二つの機構によって生じると考えられる。第一の機構は、固体表面からの電子雲の染み出しである。自由電子を多く持つ金属では、表面からの電子雲の染み出しによって、エネルギーの大きい電子の存在量が増え、系全体としてもエネルギーが増大する。第二の機構は、結晶構造の乱れである。固体の表面では結合先の無いダングリングボンドが生成することから、表面構造の再構成などが生じ、周期的な構造とは異なった構造が生じることが知られている。こうした構造の乱れも、バルクと比較した場合に、固体表面が相対的に高いエネルギーを持つ原因となる。これら二つの因子は、いずれも酸化物担体上に担持された微細な粒子では、その影響の程度が変化する。 It is thought that the surface energy of a substance is generated mainly by two mechanisms. The first mechanism is oozing out of the electron cloud from the solid surface. For metals with many free electrons, the amount of high energy electrons increases due to the seepage of electron clouds from the surface, and the energy of the entire system increases. The second mechanism is disorder of the crystal structure. It is known that a dangling bond having no bonding destination is generated on the surface of the solid, so that the surface structure is reconstructed, and a structure different from the periodic structure is generated. Such structural disturbances also cause the solid surface to have a relatively high energy when compared to the bulk. Both of these two factors change the degree of influence of fine particles supported on an oxide carrier.
第一の機構である電子状態に関して、酸化チタン、酸化ジルコニウム、酸化セリウムなどの担体上において、貴金属粒子は酸化された状態になりやすいことが知られている。これはすなわち、貴金属粒子中の電子量が、バルクの電子量と比べて低減することを意味しており、結果として、表面エネルギーの低下につながる。第二の機構である構造の乱れに関して、微細な構造は、表面の再構成の影響に伴うバルク構造の変化に影響を受ける。例えば白金原子は、直径が０．３ｎｍ程度であり、粒子径２ｎｍ以下の貴金属結晶粒では、直径方向に高々５個程度の白金原子しか並ばない計算になる。一般に、表面構造の再構成は、最表面と、かかる最表面の一つ下の層において、強く生じることが知られている。これはすなわち、直径２ｎｍ以下の微細な粒子では、表面の再構成の影響を強く受けないのは粒子の中央に位置する原子のみ、ということを意味している。この場合、表面に特異的な構造変化による表面エネルギーの増大を考慮することに、大きな意味がなくなる。更に、微細な粒子は、酸化物の粒子表面に固定されている。粒子は、担体である酸化物との化学結合によって結びつけられており、化学結合は、原子と原子の結びつきであることから、酸化物表面の原子の並びに依存して貴金属粒子の原子の並びが歪められることになる。こうした要因によって、微粒子表面の特異構造によるエネルギーの増大による寄与は、相対的に小さいものとなる。 Regarding the electronic state as the first mechanism, it is known that noble metal particles tend to be oxidized on a carrier such as titanium oxide, zirconium oxide, cerium oxide or the like. This means that the amount of electrons in the noble metal particles is reduced as compared with the amount of bulk electrons, resulting in a decrease in surface energy. With respect to structural disorder, the second mechanism, the fine structure is affected by changes in the bulk structure that accompany the effects of surface reconstruction. For example, a platinum atom has a diameter of about 0.3 nm, and a noble metal crystal grain having a particle diameter of 2 nm or less has a calculation in which only about 5 platinum atoms are arranged in the diameter direction. In general, it is known that the reconstruction of the surface structure strongly occurs at the outermost surface and a layer immediately below the outermost surface. This means that in a fine particle having a diameter of 2 nm or less, only the atom located at the center of the particle is not strongly affected by the surface reconstruction. In this case, it does not make much sense to consider the increase in surface energy due to structural changes specific to the surface. Furthermore, the fine particles are fixed on the surface of the oxide particles. The particles are linked by a chemical bond with the oxide that is the carrier. Since the chemical bond is a bond between atoms, the arrangement of atoms in the noble metal particles is distorted depending on the arrangement of atoms on the oxide surface. Will be. Due to these factors, the contribution due to the increase in energy due to the specific structure of the fine particle surface is relatively small.
上記の考察より、貴金属粒子の表面エネルギーによる影響は、貴金属粒子の粒子径が一定以上の大きさとなった場合に、初めて顕在化すると予想した。更に、表面エネルギーの影響によって引き起こされる現象である貴金属粒子のカプセル化現象についても、貴金属の粒子径がある一定以上となった場合に、初めて生じるものと予想した。カプセル化現象によって、表面を酸化チタンの膜で被覆された貴金属粒子は、付近の貴金属粒子と結合することが困難となると予想される。これより、焼成条件の検討によって、ある一定程度の粒子径を持つ貴金属粒子を、選択的に酸化物担体上に作成可能であると推察した。 From the above consideration, it was predicted that the influence of the surface energy of the noble metal particles will be manifested only when the particle diameter of the noble metal particles becomes a certain size or more. Furthermore, it was predicted that the encapsulation phenomenon of noble metal particles, which is a phenomenon caused by the influence of surface energy, will occur for the first time when the particle diameter of the noble metal exceeds a certain level. Due to the encapsulation phenomenon, it is expected that the noble metal particles whose surfaces are coated with a titanium oxide film will be difficult to bond with the nearby noble metal particles. From this, it was speculated that noble metal particles having a certain particle size can be selectively formed on the oxide support by examining the firing conditions.
本発明者らによる鋭意研究の結果、含浸法又は選択担持法によって、微細な貴金属粒子を酸化物担体上に担持させて、貴金属担持触媒とする工程ののちに、還元雰囲気中にて５００℃以上８００℃以下にて焼成処理を加えることによって、所定の範囲内の粒子径を持つ、貴金属粒子を担持した触媒を作成することが出来ることを見出した。その上で、かかる知見をもとに更なる検討を行った結果、本発明を完成した。 As a result of intensive studies by the present inventors, after the step of supporting fine noble metal particles on an oxide support by the impregnation method or selective support method to form a noble metal-supported catalyst, 500 ° C. or higher in a reducing atmosphere. It has been found that a catalyst carrying noble metal particles having a particle diameter within a predetermined range can be prepared by applying a calcination treatment at 800 ° C. or lower. Based on this finding, the present invention was completed as a result of further studies.
本発明の実施形態に係る酸化物担体には、酸化チタン、酸化ジルコニウム、酸化セリウム、酸化スズ、酸化鉄など、還元雰囲気中での焼成処理によって貴金属粒子のカプセル化現象が生じるものであれば、適宜利用可能である。しかしながら、常温で安定の二酸化スズは、容易に還元されて一酸化スズへと変化することが知られており、還元雰囲気で焼成を行った場合には、一酸化スズの融点が低いことに起因して比表面積が低下し易いことが知られている。また、酸化鉄を担体として利用した場合には、含浸法などの手法で微細な貴金属粒子を担持することが困難である。よって、酸化スズ、酸化鉄を担体として利用した場合には、プロセス条件の更なる検討が必要となる。 In the oxide carrier according to the embodiment of the present invention, titanium oxide, zirconium oxide, cerium oxide, tin oxide, iron oxide, and the like, as long as the encapsulating phenomenon of noble metal particles is caused by firing treatment in a reducing atmosphere, It can be used as appropriate. However, it is known that tin dioxide that is stable at room temperature is easily reduced to change to tin monoxide, and when firing in a reducing atmosphere, the melting point of tin monoxide is low. Thus, it is known that the specific surface area tends to decrease. In addition, when iron oxide is used as a carrier, it is difficult to carry fine noble metal particles by a technique such as an impregnation method. Therefore, when tin oxide or iron oxide is used as a carrier, further examination of process conditions is required.
こうした理由により、酸化チタン、酸化ジルコニウム、及び酸化セリウムが、特に本発明における課題解決効果が高いことから、これら３種のうちから選ばれる一種又は二種以上を、本発明では好適に用いることができる。酸化チタン、酸化ジルコニウム、酸化セリウムのいずれの酸化物も、複数の安定な相を持つことを知られているが、カプセル化現象は担体を構成する元素の還元し易さに依存する部分が大きいことから、結晶相に関係なく適用が可能である。また、セリア−ジルコニアの複合酸化物など、これら酸化物を複数組み合わせた系でもカプセル化現象が観察されることが知られている。これらの酸化物の混合物、複合酸化物においても、同様の効果が発揮されることから、本発明に使用することができる。 For these reasons, since titanium oxide, zirconium oxide, and cerium oxide have a particularly high problem-solving effect in the present invention, one or two or more selected from these three types can be preferably used in the present invention. it can. All oxides of titanium oxide, zirconium oxide, and cerium oxide are known to have a plurality of stable phases, but the encapsulation phenomenon largely depends on the ease of reduction of the elements constituting the carrier. Therefore, it can be applied regardless of the crystal phase. It is also known that the encapsulation phenomenon is observed even in a system in which a plurality of these oxides are combined, such as ceria-zirconia composite oxide. Since the same effect is exhibited also in the mixture and complex oxide of these oxides, it can be used for this invention.
また、貴金属粒子が接触する部分がこれらの酸化物であることが重要であるため、上記酸化物を酸化アルミニウム、酸化ケイ素に担持し、更に貴金属を担持したものについても、同様の手法が適用可能である。更に、燃料電池電極用触媒として利用する場合には、酸化チタンではニオブやタンタルなどをドープし、酸化スズではアンチモンなどをドープすることが知られている。こうした電子ドープ効果のある元素をドープした場合にもカプセル化現象が生じることが、上記非特許文献２等で報告されている。そのため、これら元素がドープされた場合においても、本発明が適用可能であると考えられる。 In addition, since it is important that the part in which the noble metal particles are in contact with these oxides, the same method can be applied to those in which the oxide is supported on aluminum oxide or silicon oxide and further supported on the noble metal. It is. Furthermore, when used as a catalyst for a fuel cell electrode, it is known that titanium oxide is doped with niobium, tantalum or the like, and tin oxide is doped with antimony or the like. It has been reported in Non-Patent Document 2 and the like that an encapsulation phenomenon occurs even when such an element having an electron doping effect is doped. Therefore, it is considered that the present invention can be applied even when these elements are doped.
酸化物担体上に担持させる貴金属としては、表面エネルギーが大きく、カプセル化現象が起きやすいことが報告されている任意の貴金属が利用可能である。具体的には、白金、パラジウム、ロジウム、ニッケル、イリジウムなどから一種あるいは複数種類の貴金属を選ぶことができる。 As the noble metal supported on the oxide carrier, any noble metal having a large surface energy and reported to easily cause an encapsulation phenomenon can be used. Specifically, one or more kinds of noble metals can be selected from platinum, palladium, rhodium, nickel, iridium and the like.
複数の貴金属を同時に担体上に担持した場合、各金属単相と合金相とが生じる。単相であれば、一種のみを担持したものと同様の現象が生じると判断できる。更に、合金相は一般に各金属の中間的な性質を示すことから、カプセル化現象が生じやすいことが知られている貴金属の組合せであれば、任意の組合せが利用可能である。ただし、貴金属毎に融点、表面エネルギー、酸化エンタルピーなどの物性値が異なり、担体との相互作用も異なることから、複数の貴金属を同時に担体上に担持する場合には、貴金属と担体との組み合わせに応じて、最適な温度とガス成分を設定することが好ましい。 When a plurality of noble metals are simultaneously supported on the support, each metal single phase and alloy phase are generated. If it is a single phase, it can be judged that the same phenomenon as that in which only one kind is supported occurs. Furthermore, since the alloy phase generally exhibits an intermediate property of each metal, any combination can be used as long as it is a combination of noble metals known to be susceptible to encapsulation. However, physical properties such as melting point, surface energy, oxidation enthalpy, etc. are different for each noble metal, and the interaction with the carrier is also different, so when supporting multiple noble metals on the carrier at the same time, the combination of the noble metal and the carrier Accordingly, it is preferable to set an optimum temperature and gas component.
ここで、貴金属の酸化物担体への担持量は、任意に設定可能であるが、担持量が少なすぎる場合には触媒活性が低下することから好ましくなく、担持量が多すぎる場合には、そもそも微細な貴金属粒子を担持させることが困難となる。 Here, the loading amount of the noble metal on the oxide carrier can be arbitrarily set, but if the loading amount is too small, it is not preferable because the catalytic activity is lowered. It becomes difficult to carry fine noble metal particles.
例えば、比表面積６０ｍ２／ｇの酸化物担体上に、一辺２ｎｍの立方体上の白金粒子を、２ｎｍおきに配置した場合には、およそ４０質量％の白金を含む触媒となる。貴金属担持量が増大するに従って、酸化物担体の質量比率が低減されることから、更に担持量を増加しようとした場合には、更に高密度に貴金属粒子を担持する必要が生じてしまう。また、貴金属担持量が少なく、例えば０．１質量％未満である場合には、触媒全体に占めるコストのうち酸化物担体による割合が増大する。更に、貴金属担持量が少なくなることによって触媒活性が低下する結果、必要となる触媒の量が増大するため、触媒コスト増大に繋がる。よって、貴金属の担持量は、触媒全体に対する質量比で、０．１％以上４０％以下であることが好ましく、１．０％以上３０％以下であることが更に好ましく、５％以上１５％以下であるとより一層好ましい。 For example, when platinum particles on a cube with a side of 2 nm are arranged every 2 nm on an oxide support having a specific surface area of 60 m 2 / g, a catalyst containing approximately 40% by mass of platinum is obtained. As the amount of the noble metal supported increases, the mass ratio of the oxide support is reduced. Therefore, when further increasing the amount supported, it becomes necessary to support the noble metal particles at a higher density. In addition, when the amount of noble metal supported is small, for example, less than 0.1% by mass, the ratio of the oxide carrier to the total cost of the catalyst increases. Furthermore, as a result of a decrease in catalyst activity due to a decrease in the amount of noble metal supported, the amount of catalyst required increases, leading to an increase in catalyst cost. Therefore, the supported amount of the noble metal is preferably 0.1% or more and 40% or less, more preferably 1.0% or more and 30% or less, and more preferably 5% or more and 15% or less in terms of mass ratio with respect to the whole catalyst. Is even more preferable.
貴金属粒子の担持量が上記の範囲外であった場合にも、焼成条件の検討によって、ある程度の対応が可能と予想される。具体的には、貴金属担持量が多すぎる場合には、貴金属を担持させる工程における焼成条件の検討を通じて、より微細な粒子として担持させたり、粒子径を所定の範囲内とする工程における焼成温度を低く設定したりするなどの対策が可能と考えられる。ただし、焼成温度を低く設定する場合には、焼成時間を長く設定することも併せて検討するべきと予想される。 Even when the loading amount of the noble metal particles is out of the above range, it is expected that a certain degree of response is possible by examining the firing conditions. Specifically, when the amount of the precious metal supported is too large, through the examination of the firing conditions in the step of supporting the precious metal, the finer particles are supported, or the firing temperature in the step of setting the particle diameter within a predetermined range is set. It is considered possible to take measures such as setting it low. However, when the firing temperature is set low, it is expected that the firing time should be set longer.
貴金属を酸化物担体上に担持させる工程は、任意の手法が適用可能であるが、貴金属粒子が微細な粒子として高分散に担持される方法であることが好ましい。具体的には、含浸法や選択担持法の他に、イオン交換法、平衡吸着法などを用いることが簡便である。これらいずれの方法も、上記非特許文献３などの触媒調製に関する参考図書にて、詳細に説明されている。これらの複数の手法のうち、触媒合成操作の簡便さという観点から、含浸法や選択担持法を用いることが好ましい。 Although any method can be applied to the step of supporting the noble metal on the oxide carrier, a method in which the noble metal particles are supported in a highly dispersed manner as fine particles is preferable. Specifically, it is convenient to use an ion exchange method, an equilibrium adsorption method, etc. in addition to the impregnation method and the selective support method. Both of these methods are described in detail in reference books on catalyst preparation such as Non-Patent Document 3 described above. Among these methods, it is preferable to use an impregnation method or a selective support method from the viewpoint of easy catalyst synthesis operation.
貴金属を酸化物担体上に担持させる際に利用する貴金属塩は、硝酸塩、塩化物塩、有機錯体など任意のものが適用可能である。なぜなら、いずれの貴金属塩を前駆体とした場合においても、貴金属粒子の粒子径を制御する工程の初期、もしくは前段階において、金属塩は分解され、貴金属粒子となるからである。貴金属塩の水溶液に、酸化物担体を浸漬させ、還元剤を用いて貴金属粒子を析出させる手法なども適用可能であるが、これらの方法は、上記含浸法などに比べて高コストであり、担体表面での貴金属粒子の空間分布が不均一になり易く、更に、酸化物担体との相互作用が不十分となることから、貴金属と担体との相互作用を積極的に利用する本手法への適用を念頭に置く場合には、作成条件の検討が必要となると予想される。 Arbitrary things, such as a nitrate, a chloride salt, and an organic complex, are applicable as a noble metal salt utilized when carrying a noble metal on an oxide support. This is because in any case where any noble metal salt is used as a precursor, the metal salt is decomposed into noble metal particles in the initial stage or the previous stage of the step of controlling the particle diameter of the noble metal particles. A method of immersing an oxide carrier in an aqueous solution of a noble metal salt and precipitating noble metal particles using a reducing agent can also be applied. However, these methods are more expensive than the above impregnation method and the like. Since the spatial distribution of noble metal particles on the surface tends to be non-uniform and the interaction with the oxide support becomes insufficient, it is applied to this method that actively uses the interaction between the noble metal and the support. It is expected that the preparation conditions will need to be considered if the above is in mind.
貴金属粒子の粒子径を制御する工程である還元雰囲気下での焼成工程で利用される還元性ガスとしては、任意のガスが適用可能である。しかしながら、窒素やヘリウム、アルゴンなどといった不活性なガスを利用するだけでは不十分であることは、以下の実施例に示す通りである。還元性ガスとしては、水素、一酸化炭素、メタンなど任意のガスが利用可能であるが、一酸化炭素は人体への有毒性が高いことが問題となり、メタンを用いた場合には貴金属表面上への炭素分析出の恐れがあることから、水素を用いることが簡便である。任意の分圧の水素が利用可能であるが、水素の分圧は、１体積％以上かつ１００体積％以下であることが好ましく、５体積％以上かつ１００体積％以下であると更に好ましい。 Any gas can be used as the reducing gas used in the firing step in a reducing atmosphere, which is a step of controlling the particle diameter of the noble metal particles. However, as shown in the following examples, it is insufficient to use an inert gas such as nitrogen, helium, or argon. Any gas such as hydrogen, carbon monoxide, and methane can be used as the reducing gas. However, carbon monoxide has a problem that it is highly toxic to the human body. It is easy to use hydrogen because there is a risk of carbon analysis. Although hydrogen having an arbitrary partial pressure can be used, the partial pressure of hydrogen is preferably 1% by volume or more and 100% by volume or less, and more preferably 5% by volume or more and 100% by volume or less.
貴金属粒子の粒子径を制御する工程である還元雰囲気下での焼成工程における焼成温度は、貴金属粒子の凝集に要する時間と、触媒担体へのダメージの観点とから制限を受ける。焼成温度が例えば５００℃未満のように低い場合には、貴金属粒子の凝集に時間がかかり、プロセスコスト増大につながる。一方、焼成温度を高くする場合、カプセル化現象を引き起こすことで知られる酸化チタン、酸化ジルコニウム、酸化セリウムなどの酸化物は、酸化アルミニウムや酸化ケイ素などと比べて耐熱性が低く、高温での焼成処理によって著しくその比表面積が変化することが知られている。上記非特許文献４には、焼成温度を上昇させるに従って酸化チタン担体の比表面積が低下し、特に８００℃付近にて比表面積が著しく低減することが示されている。従って、還元雰囲気下での焼成工程における具体的な焼成温度としては、５００℃以上８００℃未満とすることが好ましく、５５０℃以上７００℃以下とするとより好ましく、５５０℃以上６５０℃以下とするとより一層好ましい。以下に示す実施例では、焼成時間を１時間と設定しているが、用いる焼成炉の昇温速度や、焼成を行う温度に応じて、適切な時間に設定することが好ましい。 The firing temperature in the firing step in a reducing atmosphere, which is a step for controlling the particle diameter of the noble metal particles, is limited from the viewpoint of the time required for aggregation of the noble metal particles and the damage to the catalyst support. When the firing temperature is low, for example, less than 500 ° C., it takes time to aggregate the noble metal particles, leading to an increase in process cost. On the other hand, when the firing temperature is increased, oxides such as titanium oxide, zirconium oxide, and cerium oxide, which are known to cause an encapsulation phenomenon, have lower heat resistance than aluminum oxide and silicon oxide, and are fired at a high temperature. It is known that the specific surface area is remarkably changed by the treatment. Non-Patent Document 4 shows that the specific surface area of the titanium oxide support decreases as the firing temperature is raised, and the specific surface area is particularly reduced in the vicinity of 800 ° C. Therefore, the specific firing temperature in the firing step in a reducing atmosphere is preferably 500 ° C. or higher and lower than 800 ° C., more preferably 550 ° C. or higher and 700 ° C. or lower, and more preferably 550 ° C. or higher and 650 ° C. or lower. Even more preferred. In the examples shown below, the firing time is set to 1 hour, but it is preferable to set the firing time to an appropriate time according to the heating rate of the firing furnace to be used and the temperature at which the firing is performed.
粒子径を制御する工程である還元雰囲気下での焼成工程は、同一の加熱処理装置内部で、貴金属粒子を担持させる工程後に続けて実施してもよいし、一度、試料を系外に取り出してから実施してもよい。また、還元雰囲気下での昇温過程において、貴金属粒子が微細に、かつ、表面に均一に担持されることが確認されているならば、還元雰囲気での昇温過程を、貴金属粒子を担持させる工程と見なしても構わない。 The firing step in a reducing atmosphere, which is a step for controlling the particle diameter, may be carried out after the step of supporting the noble metal particles inside the same heat treatment apparatus, or once the sample is taken out of the system. You may carry out from. Further, if it is confirmed that the noble metal particles are supported finely and uniformly on the surface in the temperature raising process in a reducing atmosphere, the temperature raising process in the reducing atmosphere is carried on the noble metal particles. It may be regarded as a process.
本発明は、貴金属粒子の粒子径を制御する手法に関するものであり、その効果を確認するためには、透過型電子顕微鏡（Ｔｒａｎｓｍｉｓｓｉｏｎ Ｅｌｅｃｔｒｏｎ Ｍｉｃｒｏｓｃｏｐｅ：ＴＥＭ）を用いて触媒上の貴金属粒子径を観察することが好ましい。他の貴金属粒子径を決定する手法として知られるＸ線回折測定結果を利用したシェラーの式による計算法や、化学吸着法による貴金属粒子径の評価では、平均粒子径の見積もりは可能であるものの、その分布を知ることは困難であり、本発明の効果を正確に把握することはできない。一方、各粒子の形状は球状でないものも多いことから、ＴＥＭ観察像上での長さを計測することで、粒子径を一意に決定することは困難である。そこで、本発明では、ＴＥＭ観察像上での各粒子の面積を計算し、かかる粒子の面積と同じ面積を持つ円の直径を計算して、得られた値を粒子径とする。これにより、本発明では、観察者に依存せずに粒子径の評価を行うことが可能である。各触媒について、ＴＥＭ測定にて観測された貴金属粒子について、その粒子径の算術平均をとることで、平均粒子径の計算を実施する。 The present invention relates to a method for controlling the particle diameter of noble metal particles, and in order to confirm the effect, the diameter of the noble metal particles on the catalyst is observed using a transmission electron microscope (TEM). It is preferable. In the calculation method by Scherrer's formula using the X-ray diffraction measurement result known as a method for determining other noble metal particle size, and evaluation of noble metal particle size by chemical adsorption method, although the average particle size can be estimated, It is difficult to know the distribution, and the effect of the present invention cannot be accurately grasped. On the other hand, since the shape of each particle is often not spherical, it is difficult to uniquely determine the particle diameter by measuring the length on the TEM observation image. Therefore, in the present invention, the area of each particle on the TEM observation image is calculated, the diameter of a circle having the same area as that of the particle is calculated, and the obtained value is used as the particle diameter. Thereby, in this invention, it is possible to evaluate a particle diameter, without depending on an observer. For each catalyst, the average particle diameter is calculated by taking the arithmetic average of the particle diameters of the noble metal particles observed by TEM measurement.
観測した少なくとも５０個以上、好ましくは１００個以上の粒子について、粒子径の分布を表す度数分布表を作成することによって、粒子径の均一性に関する情報を得ることができる。観察の際に、恣意的な測定を行わないようにするためには、ＴＥＭ観察像上に検出された全ての貴金属粒子について、粒子径の決定を行うことが重要であり、更に、一つのＴＥＭ観察像上で１０個以上の貴金属粒子が検出されている状態とすることが好ましい。これによって、特定の粒子径の粒子のみが偶然観測されることを、防ぐことができる。 By creating a frequency distribution table representing the particle size distribution for at least 50 or more, preferably 100 or more particles observed, information on the particle size uniformity can be obtained. In order not to perform arbitrary measurement during observation, it is important to determine the particle diameter of all the noble metal particles detected on the TEM observation image. It is preferable that 10 or more noble metal particles are detected on the observed image. This can prevent accidental observation of only particles having a specific particle size.
粒子径を制御する工程である還元雰囲気での焼成工程を経た後の試料は、他の手法で作成された試料と比較しても、均一な粒子径を持つ貴金属粒子が担持された試料となっている。しかしながら、上記手法にて評価された貴金属粒子の粒子径は、以下の二つの事情から完全に一致することはない。 The sample after the firing step in a reducing atmosphere, which is a step for controlling the particle size, is a sample on which noble metal particles having a uniform particle size are supported even when compared to samples prepared by other methods. ing. However, the particle diameter of the noble metal particles evaluated by the above method does not completely coincide with the following two circumstances.
第一の原因は、貴金属粒子が球形でないことである。ＴＥＭ観察像は３次元空間に存在する試料の平面への射影である。触媒の試料観察に利用されるＴＥＭでは、各貴金属粒子を全方位から観察することは困難であり、ある方向から観察した二次元像をもとに粒子径を決定することとなる。しかしながら、上記の通り貴金属粒子は必ずしも球状ではなく、長軸と短軸の比が１．３程度となるような粒子も観察されていた。こうした試料では、仮に貴金属粒子がアスペクト比１．３：１．３：１となる楕円であった場合には、見る方向によって粒子径が最大１４％ずれてしまうことになる。これは、粒子径３ｎｍの貴金属粒子の場合では、粒子径が０．４ｎｍずれてしまうことに対応する。こうした事情により、平均粒子径から±０．４ｎｍ以下であれば、平均粒子径を持つ粒子と実質的に同程度の粒子径を持つと判断できる。 The first cause is that the noble metal particles are not spherical. A TEM observation image is a projection onto a plane of a sample existing in a three-dimensional space. In a TEM used for observing a sample of a catalyst, it is difficult to observe each noble metal particle from all directions, and the particle diameter is determined based on a two-dimensional image observed from a certain direction. However, as described above, noble metal particles are not necessarily spherical, and particles having a major axis / minor axis ratio of about 1.3 have been observed. In such a sample, if the noble metal particle is an ellipse having an aspect ratio of 1.3: 1.3: 1, the particle diameter is shifted by up to 14% depending on the viewing direction. This corresponds to the case where the particle diameter is shifted by 0.4 nm in the case of noble metal particles having a particle diameter of 3 nm. For these reasons, it can be determined that the average particle diameter is substantially equal to or smaller than the average particle diameter as long as it is ± 0.4 nm or less.
第二の原因は、貴金属粒子を担持する工程で不可避的に生じてしまう、表面の不均一性である。担体に利用される酸化物は、それ自体が液相・気相を介する方法で製造された微粒子である。そのため、必然的に担体微粒子間でわずかに形状の違いが生じ、また、担体微粒子の凝集の仕方にも場所ごとに若干の違いが生じる。含浸法は、均一な粒子径の貴金属粒子を均一に分散させることができる簡便な手法であるが、酸化物担体自体の持つ不均一性に由来し、作製された試料についても貴金属粒子の分布の仕方に僅かに不均一性が生じる。こうした事情から、粒子径を制御する工程の前段階にて、不可避的に不均一性が生じてしまう。平均粒子径から±０．４ｎｍの範囲内に分布する粒子の比率が高い程、厳密に貴金属粒子の粒子径が制御できたと言え、好ましいが、上記の事情より１００％とすることは著しく困難である。粒子数で半分以上の貴金属粒子が、平均粒子径から±０．４ｎｍの範囲内に分布すれば、高い精度で貴金属粒子の粒子径が制御できたと判断でき、好ましい。 The second cause is surface non-uniformity that inevitably occurs in the process of supporting the noble metal particles. The oxide used for the carrier is a fine particle produced by a method via a liquid phase / gas phase itself. For this reason, there is inevitably a slight difference in shape between the carrier fine particles, and there is also a slight difference in the manner of aggregation of the carrier fine particles from place to place. The impregnation method is a simple technique that can uniformly disperse noble metal particles having a uniform particle diameter, but is derived from the non-uniformity of the oxide support itself, and the distribution of noble metal particles in the prepared sample is also There is a slight non-uniformity in the way. For these reasons, non-uniformity is inevitably generated in the stage prior to the step of controlling the particle size. It can be said that the higher the ratio of particles distributed within the range of ± 0.4 nm from the average particle size, the more precisely the particle size of the noble metal particles could be controlled. However, it is extremely difficult to achieve 100% due to the above circumstances. is there. If noble metal particles having more than half the number of particles are distributed within a range of ± 0.4 nm from the average particle diameter, it can be determined that the particle diameter of the noble metal particles can be controlled with high accuracy, which is preferable.
また、粒子径を制御する工程の前段階で観察された粒子径２ｎｍ未満の貴金属微粒子が実質的に含まれず、粒子径２ｎｍ以上の粒子径を持つ粒子のみで構成されていると好ましい。ただし、触媒の焼成処理工程で、一部未焼成の試料が混入してしまうことや、加熱装置内の一部の温度が制御できないことも、当然のことながら想定される。粒子径２ｎｍ未満の粒子を持つ部分が少量含まれていても本発明の効果は発揮されるが、その場合においても、貴金属粒子径２ｎｍ未満の貴金属粒子は、個数比で全体の２０％未満であることが好ましい。 Further, it is preferable that noble metal fine particles having a particle diameter of less than 2 nm observed in the previous stage of the step of controlling the particle diameter are substantially not contained and only particles having a particle diameter of 2 nm or more are used. However, as a matter of course, it is assumed that a partially unfired sample is mixed in the catalyst firing treatment step, and that a part of the temperature in the heating apparatus cannot be controlled. The effect of the present invention is exhibited even if a small amount of a part having particles having a particle diameter of less than 2 nm is contained, but even in that case, the number of noble metal particles having a particle diameter of less than 2 nm is less than 20% of the whole. Preferably there is.
次に、実施例及び比較例並びに試験例に基づいて本発明を具体的に説明するが、本発明は、当該実施例及び比較例並びに試験例により何ら限定されるものではない。 Next, the present invention will be specifically described based on examples, comparative examples, and test examples, but the present invention is not limited to the examples, comparative examples, and test examples.
［触媒担体の事前焼成］
（担体１〜３）
酸化チタン担体ＴＩＯ−６（触媒学会参照触媒）、酸化ジルコニウム担体ＺＲＯ−４（触媒学会参照触媒）、酸化セリウム担体ＣＥＯ−３（触媒学会参照触媒）を用意し、電気炉を用いて、大気雰囲気下５００℃にてそれぞれ１時間焼成した。得られた担体を、それぞれ担体１、２、３とした。担体の形状は、いずれも粉状である。担体１〜３の各担体の物性を、以下の表１にまとめて示す。
[Pre-firing of catalyst support]
(Carriers 1 to 3)
Titanium oxide support TIO-6 (catalyst society reference catalyst), zirconium oxide support ZRO-4 (catalysis society reference catalyst), cerium oxide support CEO-3 (catalysis society reference catalyst) are prepared, and an atmospheric atmosphere using an electric furnace Each was calcined at 500 ° C. for 1 hour. The obtained carriers were named carriers 1, 2, and 3, respectively. The shape of the carrier is powdery. The physical properties of the carriers 1 to 3 are summarized in Table 1 below.
なお、以下の表１において、各担体の比表面積は、液体窒素温度での窒素吸着等温線を用いて、ＢＥＴ法によって評価を行った。また、吸着等温線の相対分圧０．９９の値を用いて、細孔容積を計算した。 In Table 1 below, the specific surface area of each carrier was evaluated by the BET method using a nitrogen adsorption isotherm at liquid nitrogen temperature. The pore volume was calculated using the value of the relative partial pressure 0.99 of the adsorption isotherm.
［触媒の作製］
（貴金属担持工程１：試料１、白金担持量５ｍａｓｓ％触媒）
ヘキサクロロ白金酸六水和物０．０６６３５ｇを、０．３０ｍｌの純水に溶解させた。得られた白金前駆体溶液を、０．４７５ｇの担体１に対して十分な混合を行いながら滴下し、含浸させた。ホットスターラー上にて攪拌を継続しながら、６０℃に昇温して乾燥させた。得られた粉末を、空気雰囲気の電気炉中で、１００℃にて１０時間、５００℃にて１時間焼成し、得られた触媒を試料１とした。このような含浸法により得られた触媒における白金の担持量は、金属状態の白金換算で、触媒全体の質量に対する質量比で５％である。
[Catalyst preparation]
(Noble metal loading step 1: sample 1, platinum loading amount 5 mass% catalyst)
0.06635 g of hexachloroplatinic acid hexahydrate was dissolved in 0.30 ml of pure water. The obtained platinum precursor solution was dropped and impregnated while sufficiently mixing with 0.475 g of the carrier 1. While stirring on a hot stirrer, the temperature was raised to 60 ° C. to dry. The obtained powder was calcined in an electric furnace in an air atmosphere at 100 ° C. for 10 hours and at 500 ° C. for 1 hour, and the obtained catalyst was used as Sample 1. The supported amount of platinum in the catalyst obtained by such an impregnation method is 5% in terms of mass ratio to the mass of the entire catalyst in terms of platinum in a metal state.
（貴金属担持工程２：試料２〜４、白金担持量１０ｍａｓｓ％触媒）
ヘキサクロロ白金酸六水和物０．１０６１９ｇを、０．３０ｍｌの純水に溶解させた。得られた白金前駆体溶液を、０．３６００ｇの担体１、２、３それぞれに対し、十分な混合を行いながら滴下し、含浸させた。ホットスターラー上にて攪拌を継続しながら、６０℃に昇温して乾燥させた。得られた粉末を、空気雰囲気の電気炉中で、１００℃にて１０時間、５００℃にて１時間焼成し、得られた触媒をそれぞれ試料２、３、４とした。このような含浸法により得られた触媒における白金の担持量は、金属状態の白金換算で、触媒全体の質量に対する質量比で１０％である。
(Noble metal loading process 2: Samples 2 to 4, platinum loading 10 mass% catalyst)
Hexachloroplatinic acid hexahydrate 0.10619 g was dissolved in 0.30 ml of pure water. The obtained platinum precursor solution was dropped and impregnated into 0.3600 g of each of the carriers 1, 2, and 3 while being sufficiently mixed. While stirring on a hot stirrer, the temperature was raised to 60 ° C. to dry. The obtained powder was calcined in an electric furnace in an air atmosphere at 100 ° C. for 10 hours and at 500 ° C. for 1 hour, and the obtained catalysts were used as Samples 2, 3, and 4, respectively. The supported amount of platinum in the catalyst obtained by such an impregnation method is 10% in terms of a mass ratio with respect to the total mass of the catalyst in terms of platinum in a metal state.
（貴金属担持工程３：試料５、白金担持量１５ｍａｓｓ％触媒）
ヘキサクロロ白金酸六水和物０．１５９２９ｇを０．３０ｍｌの純水に溶解させた。得られた白金前駆体溶液を、０．３４００ｇの担体１に対し、十分な混合を行いながら滴下し、含浸させた。ホットスターラー上にて攪拌を継続しながら、６０℃に昇温して乾燥させた。得られた粉末を、空気雰囲気の電気炉中で、１００℃にて１０時間、５００℃にて１時間焼成し、得られた触媒をそれぞれ試料５とした。このような含浸法により得られた触媒における白金の担持量は、金属状態の白金換算で触媒全体の質量に対する質量比で１５％である。
(Noble metal loading step 3: sample 5, platinum loading 15 mass% catalyst)
Hexachloroplatinic acid hexahydrate 0.15929g was dissolved in 0.30ml pure water. The obtained platinum precursor solution was dropped into 0.3400 g of the carrier 1 while being sufficiently mixed, and impregnated. While stirring on a hot stirrer, the temperature was raised to 60 ° C. to dry. The obtained powder was calcined in an electric furnace in an air atmosphere at 100 ° C. for 10 hours and at 500 ° C. for 1 hour, and the obtained catalyst was used as Sample 5. The supported amount of platinum in the catalyst obtained by such an impregnation method is 15% in terms of a mass ratio with respect to the total mass of the catalyst in terms of platinum in a metal state.
（貴金属担持工程４：試料６、パラジウム担持量１０ｍａｓｓ％触媒）
ジニトロジアンミンパラジウム（小島化学薬品）０．０８７３６ｇを、硝酸３０ｍｌに溶解し、担体１の酸化物担体０．３６００ｇを加えた。１時間攪拌を行った後に、ホットスターラー上８０℃にて攪拌を行い、蒸発乾固した。得られた固体を、大気下１２０℃にて１０時間乾燥させた後に４００℃まで昇温し、３０分焼成した。冷却後得られた触媒を、試料６とした。このような含浸法により得られた触媒におけるパラジウムの担持量は、金属状態のパラジウム換算で、触媒全体の質量に対する質量比で１０％である。
(Noble metal loading process 4: sample 6, palladium loading 10 mass% catalyst)
0.08736 g of dinitrodiammine palladium (Kojima Chemical) was dissolved in 30 ml of nitric acid, and 0.3600 g of the oxide carrier of carrier 1 was added. After stirring for 1 hour, the mixture was stirred on a hot stirrer at 80 ° C. and evaporated to dryness. The obtained solid was dried at 120 ° C. in the atmosphere for 10 hours, heated to 400 ° C., and baked for 30 minutes. The catalyst obtained after cooling was designated as Sample 6. The supported amount of palladium in the catalyst obtained by such an impregnation method is 10% in terms of mass ratio to the mass of the entire catalyst in terms of palladium in the metal state.
（貴金属担持工程５：試料７、ロジウム担持量１０ｍａｓｓ％触媒）
塩化ロジウム（ＩＩＩ）三水和物０．１０２９ｇを、０．３０ｍｌの純水に溶解させた。得られたロジウム前駆体水溶液を、担体１の酸化物担体０．３６００ｇに対して、十分な混合を行いながら滴下し、含浸させた。得られた粉末を、１００℃にて１０時間、５００℃にて１時間焼成し、得られた触媒を試料７とした。このような含浸法により得られた触媒におけるロジウムの担持量は、金属状態のロジウム換算で、触媒全体の質量に対する質量比で１０％である。
(Noble metal loading step 5: sample 7, rhodium loading 10 mass% catalyst)
Rhodium (III) chloride trihydrate (0.1029 g) was dissolved in 0.30 ml of pure water. The obtained aqueous rhodium precursor solution was added dropwise and impregnated to 0.3600 g of the oxide carrier of carrier 1 while thoroughly mixing. The obtained powder was calcined at 100 ° C. for 10 hours and at 500 ° C. for 1 hour, and the obtained catalyst was used as Sample 7. The supported amount of rhodium in the catalyst obtained by such an impregnation method is 10% in terms of a mass ratio to the mass of the entire catalyst in terms of rhodium in a metal state.
［触媒の焼成処理］
（実施例１：水素５％／Ａｒ雰囲気での焼成処理）
各試料を２０ｍｇ秤量し、石英ガラス製の反応管内にシリカウールを用いて固定した。反応管を管状電気炉に設置し、水素検知機を用いてリークチェックを行った。水素５体積％アルゴンバランスの標準ガスを、マスフローコントローラーを用いて５０ｃｍ３／分の流量で反応管内部にガスをフローさせながら３時間かけて昇温し、各温度で１時間焼成処理を行った。試料１、３、４，５、６、７については、焼成温度を６５０℃として実施し、焼成後に得られた試料を試料Ａ、Ｂ、Ｃ、Ｄ、Ｅ、Ｆとした（以下の表２を参照。）。試料２については、焼成温度を５５０℃、６００℃、６５０℃、７００℃としてそれぞれ実施した。焼成後に得られた試料を試料Ｇ、Ｈ、Ｉ、Ｊとした（以下の表３を参照。）。
[Catalyst firing]
(Example 1: Baking treatment in 5% hydrogen / Ar atmosphere)
20 mg of each sample was weighed and fixed using silica wool in a reaction tube made of quartz glass. The reaction tube was installed in a tubular electric furnace, and a leak check was performed using a hydrogen detector. A standard gas of hydrogen 5 vol% argon balance was heated over 3 hours while flowing the gas into the reaction tube at a flow rate of 50 cm 3 / min using a mass flow controller, and calcination was performed at each temperature for 1 hour. . For samples 1, 3, 4, 5, 6, and 7, the firing temperature was 650 ° C., and the samples obtained after firing were designated as samples A, B, C, D, E, and F (Table 2 below). See). For sample 2, the firing temperatures were 550 ° C., 600 ° C., 650 ° C., and 700 ° C., respectively. Samples obtained after firing were designated as Samples G, H, I, and J (see Table 3 below).
（実施例２：水素雰囲気での焼成処理）
用いたガスを水素ガス（純度９９．９９９９％以上）とした以外は実施例１と同様に、焼成処理を行った。試料２について、焼成温度を５５０℃、６００℃、６５０℃、７００℃としてそれぞれ実施し、焼成後に得られた試料を試料Ｋ、Ｌ、Ｍ、Ｎとした（以下の表３を参照。）。
(Example 2: Firing treatment in a hydrogen atmosphere)
A baking treatment was performed in the same manner as in Example 1 except that the gas used was hydrogen gas (purity 99.9999% or more). Sample 2 was subjected to firing temperatures of 550 ° C., 600 ° C., 650 ° C., and 700 ° C., and samples obtained after firing were designated as samples K, L, M, and N (see Table 3 below).
（実施例３：一酸化炭素雰囲気での焼成処理）
用いたガスを一酸化炭素５体積％アルゴンバランスの標準ガスとし、石鹸水を用いてリークチェックを行った以外は実施例１と同様に、焼成処理を行った。試料２、３、４、６、７について、焼成温度を６５０℃としてそれぞれ実施し、焼成後に得られた試料を試料Ｏ、Ｐ、Ｑ、Ｒ、Ｓとした（以下の表４を参照。）。
(Example 3: Firing treatment in a carbon monoxide atmosphere)
A firing process was performed in the same manner as in Example 1 except that the gas used was a standard gas of carbon monoxide 5% by volume argon balance and a leak check was performed using soapy water. Samples 2, 3, 4, 6, and 7 were each fired at a firing temperature of 650 ° C., and samples obtained after firing were designated as samples O, P, Q, R, and S (see Table 4 below). .
（比較例１：空気雰囲気での焼成処理）
各試料を２０ｍｇ秤量し、大気雰囲気下にて電気炉を用いて焼成処理を行った。３時間かけて昇温し、各温度で１時間焼成処理を行った。試料１、３、４，５、６、７については、焼成温度を６００℃として実施し、焼成後に得られた試料を試料ａ、ｂ、ｃ、ｄ、ｅ、ｆとした（以下の表２を参照。）。試料２については、焼成温度を５５０℃、６００℃、６５０℃、７００℃としてそれぞれ実施し、焼成後に得られた試料を試料ｇ、ｈ、ｉ、ｊとした（以下の表３を参照。）。
(Comparative Example 1: Firing treatment in an air atmosphere)
20 mg of each sample was weighed and fired using an electric furnace in an air atmosphere. The temperature was increased over 3 hours, and a firing treatment was performed at each temperature for 1 hour. Samples 1, 3, 4, 5, 6, and 7 were carried out at a firing temperature of 600 ° C., and samples obtained after firing were designated as samples a, b, c, d, e, and f (Table 2 below). See). For sample 2, the firing temperatures were 550 ° C., 600 ° C., 650 ° C., and 700 ° C., and the samples obtained after firing were designated as samples g, h, i, and j (see Table 3 below). .
（比較例２：酸素５％／窒素雰囲気での焼成処理）
用いたガスを酸素５％窒素バランス標準ガスとし、リークチェックに石鹸水を用いた以外は、実施例１と同様にして実施した。試料２について、焼成温度を５５０℃、６００℃、６５０℃、７００℃としてそれぞれ実施し、焼成後に得られた試料をそれぞれ試料ｋ、ｌ、ｍ、ｎとした（以下の表３を参照。）。
(Comparative Example 2: Firing treatment in 5% oxygen / nitrogen atmosphere)
The same procedure as in Example 1 was performed except that the gas used was a nitrogen balance standard gas with 5% oxygen and soap water was used for leak check. Sample 2 was fired at 550 ° C., 600 ° C., 650 ° C., and 700 ° C., and the samples obtained after firing were designated as samples k, l, m, and n (see Table 3 below). .
（比較例３：不活性ガス雰囲気での焼成処理）
用いたガスをアルゴンガス（純度９９．９９９９％以上）とし、リークチェックに石鹸水を用いた以外は、実施例１と同様にして実施した。試料２について、焼成温度を５５０℃、６００℃、６５０℃、７００℃としてそれぞれ実施し、焼成後に得られた試料をそれぞれ試料ｏ、ｐ、ｑ、ｒとした（以下の表３を参照。）。
(Comparative Example 3: Firing treatment in an inert gas atmosphere)
The same procedure as in Example 1 was carried out except that the gas used was argon gas (purity 99.9999% or higher) and soap water was used for the leak check. Sample 2 was fired at 550 ° C., 600 ° C., 650 ° C., and 700 ° C., and the samples obtained after firing were designated as samples o, p, q, and r (see Table 3 below). .
（比較例４：水素５％／Ａｒ雰囲気での８００℃焼成処理）
試料２について、焼成温度を８００℃とした以外は実施例１と同様にして、焼成処理を行った。焼成後に得られた試料を試料ｓとした（以下の表３を参照。）。
(Comparative example 4: 800% calcination treatment in 5% hydrogen / Ar atmosphere)
Sample 2 was fired in the same manner as in Example 1 except that the firing temperature was 800 ° C. The sample obtained after firing was designated as sample s (see Table 3 below).
（比較例５：水素雰囲気での８００℃焼成処理）
試料２について、焼成温度を８００℃とした以外は実施例２と同様にして、焼成処理を行った。焼成後に得られた試料を試料ｔとした（以下の表３を参照。）。
(Comparative example 5: 800 degreeC baking process in hydrogen atmosphere)
Sample 2 was fired in the same manner as in Example 2 except that the firing temperature was 800 ° C. The sample obtained after firing was designated as sample t (see Table 3 below).
（貴金属粒子径評価：ＴＥＭ測定による粒子径評価）
試料１〜７、Ａ〜Ｓ、ａ〜ｔそれぞれをＦＥＩ社製透過型電子顕微鏡装置ＴＥＣＮＡＩ Ｇ−２を用いて観察した。各試料について１００個以上の白金粒子貴金属粒子について、その粒子径の算術平均をとることで実施した。各粒子の形状は、球状でないものも多いことから、ＴＥＭ観察像上での各粒子の面積と同じ面積を持つ円の直径を計算し、粒子径とした。画像上における各粒子の面積計算には、任意の画像処理ソフトが利用可能だが、本発明者らはＧＩＭＰ（ＧＮＵ Ｉｍａｇｅ Ｍａｎｉｐｕｌａｔｉｏｎ Ｐｒｏｇｒａｍ）を利用した。粒子径の度数分布から粒子径の均一性について評価を行った。
(Noble metal particle size evaluation: particle size evaluation by TEM measurement)
Samples 1 to 7, A to S, and a to t were observed using a transmission electron microscope apparatus TECNAI G-2 manufactured by FEI. It implemented by taking the arithmetic average of the particle diameter about 100 or more platinum particle noble metal particles about each sample. Since the shape of each particle is often not spherical, the diameter of a circle having the same area as the area of each particle on the TEM observation image was calculated and used as the particle diameter. Arbitrary image processing software can be used to calculate the area of each particle on the image, but the present inventors have used GIMP (GNU Image Manipulation Program). The uniformity of the particle size was evaluated from the frequency distribution of the particle size.
得られた平均粒子径を表２、３、４に示し、特に試料Ｉ、試料ｉ、試料ｊ、試料ｌ、試料ｑについては、その粒度分布を図１〜５にそれぞれ示した。図１〜図５において、横軸に粒子径、縦軸に度数を示した。また、同じ試料について、その表面の観察像の一部を図６〜１０に併せて示す。なお、図６、７、９、１０は明視野像であり、図８は高角散乱環状暗視野像（ＨＡＡＤＦ−ＳＴＥＭ）である。明視野像では、白金粒子は暗い色で示され、ＨＡＡＤＦ−ＳＴＥＭ像では明るい色で示される。 The obtained average particle diameters are shown in Tables 2, 3, and 4, and the particle size distributions of Sample I, Sample i, Sample j, Sample 1, and Sample q are shown in FIGS. 1 to 5, the horizontal axis indicates the particle diameter and the vertical axis indicates the frequency. Moreover, about the same sample, a part of observation image of the surface is combined with FIGS. 6, 7, 9, and 10 are bright-field images, and FIG. 8 is a high-angle scattering annular dark-field image (HAADF-STEM). In the bright field image, the platinum particles are shown in a dark color, and in the HAADF-STEM image, they are shown in a bright color.
表２の結果より、調製後の試料では、いずれも貴金属の平均粒子径は２ｎｍ程度又はそれ以下となっており、非常に小さくなっていた。一方、表２、３、４に示す通り、それらの試料を還元雰囲気で焼成処理した試料Ａ〜Ｓでは、貴金属の平均粒子径が２．５〜４ｎｍの範囲内とすることができていた。また、試料Ｇ〜Ｎの結果より、還元雰囲気にて焼成処理を行った試料では、１００℃以上の広い温度範囲において、貴金属粒子の平均粒子径を３ｎｍ程度に制御することが可能であることが分かった。 From the results of Table 2, in the prepared samples, the average particle diameter of the noble metal was about 2 nm or less and was very small. On the other hand, as shown in Tables 2, 3, and 4, in Samples A to S obtained by firing these samples in a reducing atmosphere, the average particle diameter of the noble metal could be in the range of 2.5 to 4 nm. Further, from the results of Samples G to N, it is possible to control the average particle diameter of the noble metal particles to about 3 nm in a wide temperature range of 100 ° C. or higher in the sample that is fired in a reducing atmosphere. I understood.
試料Ｉについては、図１、図６より明らかなように、水素を含む還元雰囲気で焼成した試料では、平均粒子径３ｎｍ程度の均一な白金粒子を持つ試料が得られており、過半数の粒子が平均粒子径±０．２ｎｍの範囲内であった。試料Ｇ〜Ｎまで、粒子径が平均粒子径±０．４ｎｍ以内となる粒子の個数比、及び、観測された最小の粒子径を表５に示す。試料Ｎについては、粒子径が平均粒子径±０．４ｎｍ以内となる粒子の割合が５０％を下回ってしまったことが確認され、また、試料Ｊについては最小の貴金属粒子の粒子径が２．０ｎｍを下回ってしまった。これは即ち、７００℃にて焼成処理を行った試料Ｊ、Ｎについては、もともと存在していた微細な粒子を凝集させ、均一な粒子径にすることが不完全にしか出来ていないことを示唆している。事実、試料Ｊ、Ｎについては、還元条件での焼成処理後に担体に変形が生じていることが確認されている。 As is clear from FIG. 1 and FIG. 6, for sample I, a sample having uniform platinum particles with an average particle diameter of about 3 nm was obtained in a sample fired in a reducing atmosphere containing hydrogen. The average particle size was within a range of ± 0.2 nm. Table 5 shows the ratio of the number of particles having a particle size within an average particle size of ± 0.4 nm and the minimum observed particle size from Samples G to N. For sample N, it was confirmed that the proportion of particles with an average particle size within ± 0.4 nm was less than 50%, and for sample J, the minimum noble metal particle size was 2. It was below 0 nm. This suggests that the samples J and N fired at 700 ° C. can only incompletely agglomerate the fine particles that were originally present to form a uniform particle size. doing. In fact, it has been confirmed that Samples J and N are deformed in the support after the firing treatment under reducing conditions.
水素５体積％のガス中で焼成温度を７００℃とした試料Ｊでは、担体の一部がアモルファス化していることが確認された他、一部の担体に明らかな変形がみられた。水素１００体積％中で焼成温度６５０℃、７００℃とした試料Ｍ、Ｎについても同様であり、特に水素濃度の高いガスを利用する場合には、焼成温度を高くしないようにする必要があると考えられる。また、焼成温度を８００℃とした試料では、担体の変形が著しくなり、担体の変形に起因して白金の粒子の粗大化も確認されていたことから、少なくとも８００℃未満の温度にて焼成を行うことが好ましい。 In Sample J in which the calcination temperature was 700 ° C. in a gas of 5% by volume of hydrogen, it was confirmed that a part of the support was amorphous, and some of the support was clearly deformed. The same applies to samples M and N having a firing temperature of 650 ° C. and 700 ° C. in 100% by volume of hydrogen. In particular, when a gas with a high hydrogen concentration is used, it is necessary not to raise the firing temperature. Conceivable. In addition, in the sample with a firing temperature of 800 ° C., the deformation of the support was significant, and it was confirmed that the platinum particles were coarsened due to the deformation of the support. Preferably it is done.
図２、３、７、８に示すように、大気雰囲気中にて焼成した試料では、６５０℃にて焼成した試料については、粒子径は均一であるものの、そのサイズは小さく、７００℃で焼成したものについては、粒子径のばらつきが大きくなるのに加え、一部の粒子が粗大化することが分かった。図８の測定に合わせて、エネルギー分散型Ｘ線分光法（ＥＤＸ）による元素分析も実施しており、点Ｏ１、Ｏ４で示される粒子は酸化チタン担体粒子であり、点Ｏ２、Ｏ３で示される明るい色の粒子が白金粒子であることが確認されている。 As shown in FIGS. 2, 3, 7, and 8, in the sample fired in the air atmosphere, the sample fired at 650 ° C. has a uniform particle diameter, but the size is small and fired at 700 ° C. It was found that some of the particles were coarsened in addition to the large variation in particle size. In accordance with the measurement of FIG. 8, elemental analysis by energy dispersive X-ray spectroscopy (EDX) is also performed, and the particles indicated by points O 1 and O 4 are titanium oxide support particles, and the points O 2 and O 4 It has been confirmed that the light-colored particles indicated by 3 are platinum particles.
また、図４、９に示すように、酸素を５体積％含むガス中で焼成した試料では、粒子径のばらつきが大きくなってしまう。一方、図５、１０に示すように、酸素を含まない不活性ガス中では、粒子の凝集が促進され、均一な粒子径を持つ試料が得られるものの、そのサイズは大きくなり過ぎてしまっている。また、焼成温度が５０℃変化するだけでも、貴金属粒子径が著しく変化していることから、貴金属粒子径を所定の範囲内とすることは必ずしも容易でないと言える。 Moreover, as shown in FIGS. 4 and 9, in a sample fired in a gas containing 5% by volume of oxygen, the variation in particle diameter becomes large. On the other hand, as shown in FIGS. 5 and 10, in an inert gas not containing oxygen, the aggregation of particles is promoted, and a sample having a uniform particle diameter is obtained, but the size is too large. . Further, it can be said that it is not always easy to make the noble metal particle diameter within a predetermined range because the noble metal particle diameter is remarkably changed only by changing the firing temperature by 50 ° C.
以上、添付図面を参照しながら本発明の好適な実施形態について詳細に説明したが、本発明はかかる例に限定されない。本発明の属する技術の分野における通常の知識を有する者であれば、特許請求の範囲に記載された技術的思想の範疇内において、各種の変更例または修正例に想到し得ることは明らかであり、これらについても、当然に本発明の技術的範囲に属するものと了解される。
The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.
Claims (10)
水素ガス又は一酸化炭素ガスの少なくとも何れか一方の還元性ガスを含む還元雰囲気中で、５００℃以上８００℃未満の温度にて、前記貴金属担持触媒を加熱処理して、当該貴金属担持触媒に担持されている貴金属の粒子径を所定の範囲に制御する工程と、
を含む、触媒の製造方法。 One or more kinds of oxide carriers selected from the group consisting of titanium oxide, zirconium oxide, and cerium oxide are supported on one or more kinds of noble metal particles selected from the group consisting of platinum, palladium, and rhodium. A step of making a noble metal supported catalyst;
The noble metal-supported catalyst is heat-treated at a temperature of 500 ° C. or more and less than 800 ° C. in a reducing atmosphere containing at least one of hydrogen gas and carbon monoxide gas and supported on the noble metal-supported catalyst. A step of controlling the particle size of the precious metal being in a predetermined range;
A method for producing a catalyst, comprising:
前記貴金属粒子は、平均粒子径が２．５ｎｍ以上４．０ｎｍ以下の範囲内であり、かつ、全貴金属粒子に占める平均粒子径±０．４ｎｍの範囲内にある貴金属粒子の割合が、個数比で５０％以上である、触媒。
One or more noble metal particles selected from the group consisting of platinum, palladium, and rhodium are supported on one or more oxide carriers selected from the group consisting of titanium oxide, zirconium oxide, and cerium oxide. And
The noble metal particles have an average particle diameter in the range of 2.5 nm to 4.0 nm, and the ratio of the noble metal particles in the average particle diameter in the range of ± 0.4 nm to the total noble metal particles is the number ratio. The catalyst is 50% or more.
Priority Applications (1)
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Cited By (13)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2020175142A1 (en) | 2019-02-28 | 2020-09-03 | 株式会社キャタラー | Supported catalyst particles |
| KR20200116243A (en) * | 2019-04-01 | 2020-10-12 | 한국과학기술연구원 | Platinum-titanium dioxide catalyst, its production method, and its production apparatus |
| CN113042046A (en) * | 2019-12-26 | 2021-06-29 | 丰田自动车株式会社 | Catalyst for exhaust gas purification |
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Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH01148334A (en) * | 1987-09-08 | 1989-06-09 | Phillips Petroleum Co | Oxidation of carbon monoxide and production of catalyst composition used therein |
| JP2002102701A (en) * | 2000-09-28 | 2002-04-09 | Toyota Central Res & Dev Lab Inc | Ordinary temperature catalyst |
| JP2005095763A (en) * | 2003-09-24 | 2005-04-14 | Toyota Motor Corp | Manufacturing method of catalyst for cleaning exhaust gas and catalyst for cleaning exhaust gas |
| JP2007021439A (en) * | 2005-07-20 | 2007-02-01 | Kansai Coke & Chem Co Ltd | Gas cleaning catalyst and production method of the same |
| JP2007239054A (en) * | 2006-03-09 | 2007-09-20 | Osaka Univ | Tetrahedral palladium particulate and method for producing metal particulate |
| 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 |
-
2015
- 2015-02-13 JP JP2015026977A patent/JP6464791B2/en active Active
Patent Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH01148334A (en) * | 1987-09-08 | 1989-06-09 | Phillips Petroleum Co | Oxidation of carbon monoxide and production of catalyst composition used therein |
| JP2002102701A (en) * | 2000-09-28 | 2002-04-09 | Toyota Central Res & Dev Lab Inc | Ordinary temperature catalyst |
| JP2005095763A (en) * | 2003-09-24 | 2005-04-14 | Toyota Motor Corp | Manufacturing method of catalyst for cleaning exhaust gas and catalyst for cleaning exhaust gas |
| JP2007021439A (en) * | 2005-07-20 | 2007-02-01 | Kansai Coke & Chem Co Ltd | Gas cleaning catalyst and production method of the same |
| JP2007239054A (en) * | 2006-03-09 | 2007-09-20 | Osaka Univ | Tetrahedral palladium particulate and method for producing metal particulate |
| 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 |
Cited By (19)
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| KR20200116243A (en) * | 2019-04-01 | 2020-10-12 | 한국과학기술연구원 | Platinum-titanium dioxide catalyst, its production method, and its production apparatus |
| KR102212649B1 (en) | 2019-04-01 | 2021-02-08 | 한국과학기술연구원 | Platinum-titanium dioxide catalyst, its production method, and its production apparatus |
| US11400436B2 (en) | 2019-12-26 | 2022-08-02 | Toyota Jidosha Kabushiki Kaisha | Exhaust gas purification catalyst |
| US11719144B2 (en) | 2019-12-26 | 2023-08-08 | Toyota Jidosha Kabushiki Kaisha | Exhaust gas purification catalyst |
| CN113042045B (en) * | 2019-12-26 | 2023-11-24 | 丰田自动车株式会社 | Exhaust gas purifying catalyst |
| CN113042045A (en) * | 2019-12-26 | 2021-06-29 | 丰田自动车株式会社 | Catalyst for exhaust gas purification |
| CN113042046A (en) * | 2019-12-26 | 2021-06-29 | 丰田自动车株式会社 | Catalyst for exhaust gas purification |
| US11426710B2 (en) | 2019-12-26 | 2022-08-30 | Toyota Jidosha Kabushiki Kaisha | Exhaust gas control catalyst |
| US11577226B2 (en) | 2019-12-26 | 2023-02-14 | Toyota Jidosha Kabushiki Kaisha | Exhaust gas purification catalyst |
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| US11643958B2 (en) | 2021-03-24 | 2023-05-09 | Toyota Jidosha Kabushiki Kaisha | Exhaust gas purification material and exhaust gas purification device |
| CN113996295A (en) * | 2021-11-12 | 2022-02-01 | 华东理工大学 | Composite catalyst and preparation method and application thereof |
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