JP2016147255A - Method for producing catalyst and catalyst - Google Patents
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- 239000003054 catalyst Substances 0.000 title claims abstract description 115
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 31
- 239000002245 particle Substances 0.000 claims abstract description 200
- 229910000510 noble metal Inorganic materials 0.000 claims abstract description 186
- 239000002923 metal particle Substances 0.000 claims abstract description 115
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 claims abstract description 83
- 239000012298 atmosphere Substances 0.000 claims abstract description 54
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims abstract description 53
- 239000001301 oxygen Substances 0.000 claims abstract description 53
- 229910052760 oxygen Inorganic materials 0.000 claims abstract description 53
- 229910052697 platinum Inorganic materials 0.000 claims abstract description 42
- KDLHZDBZIXYQEI-UHFFFAOYSA-N Palladium Chemical compound [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 claims abstract description 33
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 claims abstract description 26
- OGIDPMRJRNCKJF-UHFFFAOYSA-N titanium oxide Inorganic materials [Ti]=O OGIDPMRJRNCKJF-UHFFFAOYSA-N 0.000 claims abstract description 22
- 229910000420 cerium oxide Inorganic materials 0.000 claims abstract description 20
- BMMGVYCKOGBVEV-UHFFFAOYSA-N oxo(oxoceriooxy)cerium Chemical compound [Ce]=O.O=[Ce]=O BMMGVYCKOGBVEV-UHFFFAOYSA-N 0.000 claims abstract description 20
- RVTZCBVAJQQJTK-UHFFFAOYSA-N oxygen(2-);zirconium(4+) Chemical compound [O-2].[O-2].[Zr+4] RVTZCBVAJQQJTK-UHFFFAOYSA-N 0.000 claims abstract description 18
- 229910001928 zirconium oxide Inorganic materials 0.000 claims abstract description 18
- 229910052763 palladium Inorganic materials 0.000 claims abstract description 16
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- 229910052703 rhodium Inorganic materials 0.000 claims abstract description 12
- MHOVAHRLVXNVSD-UHFFFAOYSA-N rhodium atom Chemical compound [Rh] MHOVAHRLVXNVSD-UHFFFAOYSA-N 0.000 claims abstract description 12
- 239000000969 carrier Substances 0.000 claims abstract description 11
- 238000000034 method Methods 0.000 claims description 79
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- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 10
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 10
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- 239000001257 hydrogen Substances 0.000 description 7
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- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 7
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- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 5
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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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- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 2
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 2
- MCMNRKCIXSYSNV-UHFFFAOYSA-N Zirconium dioxide Chemical compound O=[Zr]=O MCMNRKCIXSYSNV-UHFFFAOYSA-N 0.000 description 2
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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
- 230000002411 adverse Effects 0.000 description 1
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- 150000003841 chloride salts Chemical class 0.000 description 1
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- 238000010406 interfacial reaction Methods 0.000 description 1
- 238000005342 ion exchange Methods 0.000 description 1
- 229910052741 iridium Inorganic materials 0.000 description 1
- GKOZUEZYRPOHIO-UHFFFAOYSA-N iridium atom Chemical compound [Ir] GKOZUEZYRPOHIO-UHFFFAOYSA-N 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 229910044991 metal oxide Inorganic materials 0.000 description 1
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- 229910052759 nickel Inorganic materials 0.000 description 1
- 229910017604 nitric acid Inorganic materials 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
- 238000006213 oxygenation reaction Methods 0.000 description 1
- 229910003446 platinum oxide Inorganic materials 0.000 description 1
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- 229910000033 sodium borohydride Inorganic materials 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 238000001308 synthesis method Methods 0.000 description 1
- TYLYVJBCMQFRCB-UHFFFAOYSA-K trichlororhodium;trihydrate Chemical compound O.O.O.[Cl-].[Cl-].[Cl-].[Rh+3] TYLYVJBCMQFRCB-UHFFFAOYSA-K 0.000 description 1
- 239000002699 waste material Substances 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に関し、特には、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できる触媒の製造方法、およ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 for producing a catalyst for exhaust gas purification / fuel cell electrode, and more particularly, to a method for producing a catalyst capable of easily controlling the particle diameter of noble metal particles supported on an oxide carrier, and the production method. Relates to the catalyst produced by the above 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、以下の特許文献１には、白金の平均粒子径を１０ｎｍ程度とすることで耐熱性に優れた触媒とする方法が開示されており、メタン燃焼用触媒に関する以下の非特許文献１には、少なくともパラジウムの粒子径が２５ｎｍ以下の範囲においては、パラジウムの粒子径が大きいほど表面の原子一つあたりの触媒活性が向上することが示されている。 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, the noble metal particles It is known that the elution of the particles tends to proceed, and it is preferable to control the particle size to be suitable for the intended use. For example, the following Patent Document 1 discloses a method of making a catalyst excellent in heat resistance by setting the average particle diameter of platinum to about 10 nm, and the following Non-Patent Document 1 relating to a methane combustion catalyst includes It is shown that, at least in the range where the particle diameter of palladium is 25 nm or less, the catalytic activity per one atom on the surface is improved as the particle diameter of palladium is larger.
酸化チタン、酸化ジルコニウム及び酸化セリウムは、触媒担体として広く利用されている酸化物である。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おり、その後、高温で加熱処理を加えた場合にも貴金属粒子のサイズが大きくなりにくいことが知られている。例えば、酸化セリウムを担体として用いた場合には、大気雰囲気下での焼成温度を８００℃まで上昇させた場合においてさえ、貴金属の粒子が原子状で酸化セリウム表面に固着し、凝集が生じないことが以下の非特許文献２及び非特許文献３に示されている。 Titanium oxide, zirconium oxide and cerium oxide are oxides widely used as catalyst carriers. However, these oxides have a strong interaction with noble metal particles, and when 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 the size of the noble metal particles does not easily increase even when heat treatment is performed at a high temperature. For example, when cerium oxide is used as a carrier, noble metal particles adhere to the surface of cerium oxide in an atomic form and do not aggregate even when the firing temperature in the atmosphere is increased to 800 ° C. Is shown in Non-Patent Document 2 and Non-Patent Document 3 below.
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制御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。 In order to cope with this problem, when obtaining noble metal particles whose particle diameter is controlled on these oxide supports, a production method that is hardly affected by the interaction between the support and the noble metal is often used.
例えば、以下の特許文献２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。また、以下の特許文献３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。更に、以下の非特許文献４には、貴金属の前駆体溶液に紫外線を照射し、貴金属粒子を析出させる手法が開示されている。これらの手法によって粒子径３ｎｍ程度の貴金属粒子が担持された触媒を得ることができる。 For example, as shown in Patent Document 2 below, a reducing agent such as sodium borohydride or ethanol is added to a noble metal salt solution to reduce noble metal ions, thereby supporting noble metal particles on the oxide carrier. 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. Patent Document 3 below 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. Further, Non-Patent Document 4 below discloses a technique in which noble metal precursor solution is irradiated with ultraviolet rays to deposit noble metal particles. By these methods, a catalyst supporting noble metal particles having a particle diameter of about 3 nm can be obtained.
また、以下の特許文献１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。かかる手法によって、平均粒子径１０ｎｍ程度の貴金属粒子を担持した触媒を得ることができる。また、以下の特許文献４及び非特許文献５には、含浸法による試料作製時に、前駆体溶液のｐＨ制御と、焼成条件と、を検討することによって、平均粒子径２０ｎｍ超とすることもできることが報告されている。 Moreover, in the following Patent Document 1, a catalyst produced using an aluminum oxide as a carrier by an impregnation method is fired alternately at a high temperature of 1000 ° C. or higher using an oxidizing atmosphere and a reducing atmosphere, thereby slightly reducing the particle size. It also introduces a method of growing big by little. By this method, a catalyst supporting noble metal particles having an average particle diameter of about 10 nm can be obtained. Further, in the following Patent Document 4 and Non-Patent Document 5, it is possible to make the average particle diameter larger than 20 nm by examining the pH control of the precursor solution and the firing conditions at the time of sample preparation by the impregnation method. Has been reported.
しかしながら、上記特許文献２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不均一となりやすいため、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るために凝集が進行しやすく、また、平均粒子径４ｎｍ超の貴金属粒子を作成することが困難であるという課題がある。このような問題は、上記特許文献３に示される保護材や、上記非特許文献４に示される紫外線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 2, the particle diameter tends to be non-uniform if the reduction rate of the noble metal salt is increased. In order to obtain a particle size, 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. Further, the noble metal particles prepared in this way are not easily interacted with the carrier, so that aggregation is likely to proceed, and it is difficult to produce noble metal particles having an average particle diameter exceeding 4 nm. There are challenges. Such a problem similarly occurs in the protective material disclosed in Patent Document 3 and the technique using ultraviolet light disclosed in Non-Patent Document 4.
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.
上記特許文献１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が、上記特許文献１に開示の手法は、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であり、また、粒子径の制御も不十分であるために、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。 In the above-mentioned Patent Document 1, firing is performed at a high temperature of 1000 ° C. or higher, and control of the particle size is achieved by alternately using a reducing atmosphere and an oxidizing atmosphere. The technique is applicable only to an aluminum oxide carrier having excellent heat resistance, and has 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, since the control of the particle size is insufficient, there is a problem that there are many particles having a particle size that is twice or more the average particle size.
また、上記特許文献４及び非特許文献５に示されるような含浸法による作成条件の検討を行う手法では、平均粒子径を２０ｎｍ程度としたものについても、粒子径５ｎｍ未満の粒子が多量に残留しており、粒子径が不均一であるという課題がある。 Further, in the method of examining the preparation conditions by the impregnation method as shown in Patent Document 4 and Non-Patent Document 5, a large amount of particles having a particle diameter of less than 5 nm remain even when the average particle diameter is about 20 nm. However, there is a problem that the particle diameter is not uniform.
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、触媒反応に適した大きさに制御することを目的とする。 The present invention has been made in view of such circumstances, and the particle size of the catalytic metal particles supported on the oxide carrier is controlled to a size suitable for catalytic reaction with a narrow particle size distribution. The purpose is to do.
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 intensively studied paying attention to the interaction between the noble metal and the oxide support.
そして、本発明者らは、貴金属と強く相互作用する酸化物担体の特異な振る舞いに着目した検討を行った。すなわち、酸化雰囲気下で加熱処理を加えた場合には貴金属粒子が酸化され、酸化物表面に強固に固定されること、及び、還元雰囲気下で加熱処理を行った場合には、カプセル化等によって貴金属粒子の表面が酸化物担体の一部で被覆されることにそれぞれ着目して、検討を進めた。本発明者らによる鋭意研究の結果、含浸法にて貴金属を担持した触媒を少量の酸素を含む雰囲気下で焼成することによって、粒子径を制御する手法を見出し、本発明を為すに至った。 Then, the present inventors conducted an investigation focusing on the unique behavior of an oxide support that interacts strongly with a noble metal. That is, when heat treatment is applied in an oxidizing atmosphere, the noble metal particles are oxidized and firmly fixed to the oxide surface, and when heat treatment is performed in a reducing atmosphere, by encapsulation or the like Considering that the surface of the noble metal particles was covered with a part of the oxide carrier, the investigation was advanced. As a result of intensive studies by the present inventors, a method for controlling the particle diameter was found by calcining a catalyst supporting a noble metal by an impregnation method in an atmosphere containing a small amount of oxygen, and the present invention was achieved.
具体的には、本発明は、以下のようなものを提供する。
（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対して、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して、貴金属担持触媒とする工程と、酸素を０体積％以上５体積％以下含む非還元雰囲気中で、５５０℃超過７００℃以下の温度にて、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、を有する、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、前記粒子径の平均値を４ｎｍ以上２０ｎｍ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、前記粒子径の平均値を４ｎｍ以上２０ｎｍ以下に制御し、かつ、全貴金属粒子に対する平均粒子径±１．５ｎｍ以内の貴金属粒子の占める割合を個数比で５０％以上に制御する、（１）又は（２）に記載の触媒の製造方法。
（５）前記非還元雰囲気中における処理温度が、６００℃以上６５０℃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）前記非還元雰囲気中における酸素の占める割合が、体積％で０％以上３％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）前記酸化物担体が、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は、質量比で１．０％以上４０％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対して、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４．０ｎｍ以上２０．０ｎｍ以下の範囲内で、かつ、全体の貴金属粒子に占める平均粒子径±１．５ｎｍ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。
Specifically, the present invention provides the following.
(1) One or more kinds of noble metal particles selected from the group consisting of platinum, palladium and rhodium with respect to one or more kinds of oxide carriers selected from the group consisting of titanium oxide, zirconium oxide and cerium oxide. A step of supporting the noble metal-supported catalyst, and heat-treating the noble metal-supported catalyst at a temperature of 550 ° C. to 700 ° C. in a non-reducing atmosphere containing 0% by volume to 5% by volume of oxygen, And a step of controlling the particle diameter of the noble metal supported on the noble metal-supported catalyst within a predetermined range.
(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 value of the particle diameter is controlled to 4 nm or more and 20 nm or less.
(4) In the step of controlling the particle diameter of the noble metal within a predetermined range, the average value of the particle diameter is controlled to 4 nm or more and 20 nm or less, and the noble metal particles having an average particle diameter within ± 1.5 nm with respect to all the noble metal particles The method for producing a catalyst according to (1) or (2), wherein the ratio of the amount of the catalyst is controlled to 50% or more by the number ratio.
(5) The method for producing a catalyst according to any one of (1) to (4), wherein a treatment temperature in the non-reducing atmosphere is 600 ° C. or higher and 650 ° C. or lower.
(6) The method for producing a catalyst according to any one of (1) to (5), wherein a ratio of oxygen in the non-reducing atmosphere is 0% or more and 3% or less by volume%.
(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 of the precious metal supported on the oxide carrier in the produced catalyst is 1.0% to 40% by mass ratio, according to any one of (1) to (8) The manufacturing method of the catalyst of description.
(10) For one or more oxide carriers selected from the group consisting of titanium oxide, zirconium oxide and cerium oxide, one or more noble metal particles selected from the group consisting of platinum, palladium and rhodium The noble metal particles are supported by noble metal particles having an average particle diameter in the range of 4.0 nm to 20.0 nm and an average particle diameter in the range of ± 1.5 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、含浸法と当該含浸法に続く少量の酸素を含む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る。また、本発明によれば、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, a catalyst supporting noble metal particles having a particle diameter within a predetermined range is manufactured only by an impregnation method and a firing treatment in an atmosphere containing a small amount of oxygen following the impregnation method. Can provide a way to do. Further, according to the present invention, it is possible to provide a catalyst carrying noble metal particles having a particle diameter within a predetermined range.
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.
本発明の実施形態に係る触媒は、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１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、上記非特許文献１には、パラジウムを担持したメタン燃焼触媒では、少なくとも粒子径２５ｎｍ未満の範囲においては、粒子径が大きい程表面に露出したパラジウム原子一つ当りの触媒活性が高くなることが指摘されている。従って、粒子径２５ｎｍ未満の範囲にて均一な粒子径を持つ貴金属粒子を作成することによって、高い耐熱性と高活性とを両立することが出来ると考えられる。 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, in Patent Document 1, it is pointed out 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 has been pointed out that when coarse particles are present in part, such particles behave as nuclei for aggregating other noble metal particles, so that a narrow particle size distribution is preferable. Further, in Non-Patent Document 1, in the case of a methane combustion catalyst supporting palladium, the catalyst activity per palladium atom exposed on the surface increases as the particle diameter increases, at least in the range of particle diameter less than 25 nm. Has been pointed out. Therefore, it is considered that high heat resistance and high activity can be achieved at the same time by preparing noble metal particles having a uniform particle size in a range of particle size of less than 25 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、体積比で５％未満の酸素を含む弱い酸化雰囲気のガス中にて、５５０℃超７００℃以下の範囲で焼成処理を行うことで、平均粒子径４〜２０ｎｍの範囲に含まれる任意の均一な粒子径を持つ貴金属粒子が、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 changes in the particle diameter of the noble metal particles were observed. As a result, by performing the baking treatment in a range of more than 550 ° C. and 700 ° C. or less in a gas in a weak oxidizing atmosphere containing oxygen of less than 5% by volume ratio, an arbitrary particle size in the range of 4 to 20 nm is included. It was confirmed that it was possible to obtain a catalyst in which noble metal particles having a uniform particle diameter were distributed on an 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.
体積比で５％未満の酸素を含む弱い酸化雰囲気のガス中にて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、非特許文献３を参照。）。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、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、担体との結合面積が増大することで、系全体としてより安定となる。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 diameter can be obtained by firing in a gas in a weak oxidizing atmosphere containing oxygen of less than 5% by volume 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 (see, for example, Non-Patent Document 3). When the noble metal particles are strongly bonded to the oxide support through oxygen atoms, the movement of the noble metal particles is hindered, and coarsening is suppressed. In addition, since the bond between the noble metal particle and the carrier via oxygen is strong, the noble metal particle becomes finer and the bonding area with the carrier increases, 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（例えば、上記非特許文献６を参照。）。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、以下の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 thermodynamically when it exists as a metal at a temperature of 600 ° C. or higher even in an air atmosphere (see, for example, Non-Patent Document 6 above). 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 following examples.
一方、上記酸化物に貴金属粒子を担持した触媒を還元雰囲気にて焼成した場合には、貴金属粒子の表面の一部が酸化物担体によって被覆される現象が生じることが知られている。この現象は、カプセル化現象やデコレーション現象などと称されており、酸化物担体が部分的に還元されることが原因で生じると考えられている。部分的に還元された酸化物担体の一部は、貴金属の表面と合金的な相を形成し、強固な結合を形成すると考えられている。部分的に還元され、酸素欠損が多く導入されることで不安定化された酸化物担体の一部が、貴金属表面と結合を作るために移動する結果、貴金属表面が酸化物によって被覆されることになると予想されている。このカプセル化現象が、少なくとも焼成中に生じる結果、還元雰囲気で焼成を行った場合には、貴金属粒子の凝集がスムーズに進行しなくなってしまうことは、後に示す実施例の通りである。 On the other hand, it is known that when a catalyst in which noble metal particles are supported on the oxide is fired in a reducing atmosphere, a phenomenon that a part of the surface of the noble metal particles is covered with an oxide carrier occurs. This phenomenon is called an encapsulation phenomenon or a decoration phenomenon, and is considered to be caused by partial reduction of the oxide carrier. A part of the partially reduced oxide support is believed to form an alloy phase with the surface of the noble metal and form a strong bond. Part of the oxide support that has been partially reduced and destabilized by the introduction of many oxygen vacancies moves to form bonds with the noble metal surface, resulting in the noble metal surface being covered by the oxide. It is expected to become. As a result of this encapsulation phenomenon occurring at least during firing, when firing is performed in a reducing atmosphere, the aggregation of noble metal particles does not proceed smoothly as in the examples shown later.
本発明者らは、上記の内容を踏まえ、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、酸化ジルコニウム上にて、貴金属粒子の粒子径を、均一にかつ適切な大きさに凝集させるためには、貴金属粒子の酸化を抑制しつつ、酸化物担体の還元も抑制することが必要であると推察した。また、本発明者らは、貴金属粒子と酸化物担体との間に、過度に強固な結合が生じにくい環境を整えることによって、貴金属粒子の移動が促進されると考えた。更に、本発明者らは、粒子径の小さい貴金属粒子ほど、最表面に存在する原子の比率が高いため移動しやすく、粒子径の大きい貴金属粒子ほど移動しにくいため、各焼成温度で、移動が可能となる最大程度の粒子径を持つ貴金属粒子が選択的に作成することができると予想した。 Based on the above contents, the present inventors have made the particle size of the noble metal particles uniform and appropriate on the oxide oxide, titanium oxide, cerium oxide, and zirconium oxide, which have strong interaction with the noble metal. In order to agglomerate, it has been inferred that it is necessary to suppress the reduction of the oxide carrier while suppressing the oxidation of the noble metal particles. Further, the present inventors considered that the movement of the noble metal particles is promoted by preparing an environment in which an excessively strong bond is not easily generated between the noble metal particles and the oxide carrier. Furthermore, the present inventors are more likely to move at each firing temperature because the noble metal particles having a smaller particle diameter have a higher ratio of atoms existing on the outermost surface and are more likely to move, and the noble metal particles having a larger particle diameter are less likely to move. We anticipated that noble metal particles with the largest possible particle size could be made selectively.
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る工程ののちに、酸素を５体積％以下含む雰囲気中にて５５０℃超７００℃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、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 an impregnation method or a selective supporting method, the temperature exceeds 700 ° C. in an atmosphere containing 5% by volume or less of oxygen. It has been found that a catalyst carrying noble metal particles having a particle diameter within a predetermined range can be produced by applying a calcination treatment at a temperature of ℃ or lower, and the present invention has been completed.
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、酸化セリウムなど、担持された貴金属粒子を酸化させる傾向があり、かつ、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が利用できる。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、貴金属との相互作用は担体を構成する元素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、貴金属粒子の接触する部分が上記酸化物であれば、本発明の効果は得られると予想される。よって、酸化アルミニウム担体や、酸化ケイ素担体上に上記酸化物を添加し、その上で更に貴金属を担持した触媒についても、全く同様の効果が得られると考えられる。 The oxide carrier according to the embodiment of the present invention has a tendency to oxidize supported noble metal particles such as titanium oxide, zirconium oxide, and cerium oxide, and encapsulates the noble metal particles by a firing treatment in a reducing atmosphere. What causes the phenomenon can be used. All oxides of titanium oxide, zirconium oxide, and cerium oxide are known to have a plurality of stable phases, but the interaction with the noble metal largely depends on the elements constituting the support, Application is possible regardless of the crystal phase. Moreover, if the part which a noble metal particle contacts is the said oxide, it is anticipated that the effect of this invention will be acquired. Therefore, it is considered that the same effect can be obtained with a catalyst in which the above oxide is added onto an aluminum oxide carrier or a silicon oxide carrier and a noble metal is further supported thereon.
酸化物担体上に担持させる貴金属としては、酸化物担体上で酸化状態になることができ、かつ、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（例えば、非特許文献７を参照。）。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を選ぶことができる。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、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。 As the noble metal to be supported on the oxide carrier, any noble metal that can be in an oxidized state on the oxide carrier, has a large surface energy, and is likely to cause an encapsulation phenomenon can be used. (For example, see Non-Patent Document 7). Specifically, one or more types can be selected from platinum, palladium, rhodium, nickel, iridium, and the like. However, since the physical properties such as melting point, surface energy and oxidation enthalpy are different for each noble metal and the interaction with the carrier is also different, the optimal temperature and gas component can be set according to the combination of the noble metal and the carrier. preferable.
ここで、貴金属の担持量は、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 can be arbitrarily set, but if the loading amount is too small, it is not preferable because the catalytic activity is lowered, and if the loading amount is too large, fine noble metal particles are originally formed. It becomes difficult to carry.
例えば、比表面積６０ｍ２／ｇの酸化物担体上に、一辺２ｎｍの立方体状の白金粒子を、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、より一層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、貴金属粒子径は、触媒全体に対する質量比で、１．０％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 cubic platinum particles having a side of 2 nm are arranged every 2 nm on an oxide carrier 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 carrier is reduced. Therefore, when the amount supported is further increased, 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 1% by mass, the ratio of the oxide carrier in the cost of the entire 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 noble metal particle diameter is preferably 1.0% 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. It is even more preferable if there is.
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８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 8 mentioned 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いことから、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 precious metal particles on the surface tends to be non-uniform, it is expected that the preparation conditions will need to be considered when applying this method in mind.
貴金属粒子の粒子径を制御する工程である酸素を少量含む雰囲気下での焼成工程において利用されるガスは、残部を窒素や希ガスなどの不活性ガスとすることが最も簡便である。しかしながら、上記不活性ガス以外にも、製造装置から不可避的に混入するガスを含んでいても構わない。ただし、不純物ガスとして可燃性ガスを含む場合、かかる可燃性ガスの濃度は、ガス中の酸素で可燃成分の完全燃焼が可能な程度の濃度にとどめる必要がある。また、可燃性ガスの濃度が高すぎる場合には、焼成処理中に触媒表面で燃焼反応が発生し、加熱装置内部の温度が不均一となる原因となることから、可能な範囲で不純物ガスの濃度を低くすることが好ましい。 The most convenient gas used in the firing step in an atmosphere containing a small amount of oxygen, which is a step of controlling the particle size of the noble metal particles, is an inert gas such as nitrogen or a rare gas. However, in addition to the inert gas, a gas inevitably mixed from the manufacturing apparatus may be included. However, when a flammable gas is included as the impurity gas, the concentration of the flammable gas needs to be limited to such a level that the flammable component can be completely burned with oxygen in the gas. In addition, if the concentration of the combustible gas is too high, a combustion reaction occurs on the surface of the catalyst during the calcination process, causing the temperature inside the heating device to become non-uniform. It is preferable to reduce the concentration.
貴金属粒子の粒子径を制御する工程で利用する雰囲気は、酸素を少量含むことが好ましいが、以下の実施例に示す通り、不活性ガスを用いた場合にも、均一な粒子径を持つ貴金属粒子が得られることが確認されている。そのため、酸素を意図的に加えない条件にて焼成を行っても構わない。実際には、製造装置からの少量のガス漏れによって大気中の酸素が少量流入することも想定されるほか、エリンガム図を用いて、系内に含まれる酸化物と平衡となる、ゼロでない酸素分圧が計算可能であることから、厳密に酸素を含まないガスを準備することは困難であるが、本発明においては、市販の酸素濃度計を用いて酸素が検出されない場合には、酸素濃度０％であると看做すこととする。市販の酸素濃度計としては、ガスクロマトグラフィー、ジルコニア式酸素濃度測定装置や、発光式微量酸素分析計などが挙げられる。本明細書の実施例に示されるガスは、いずれもガスボンベ提供元にて、酸素濃度が０．１ｐｐｍ未満であることが確認されており、実質的に酸素濃度０％として扱うことが可能である。貴金属粒子の粒子径を制御する工程において、酸素を少量含む、又は無酸素雰囲気中に含める酸素の濃度は、０体積％以上５体積％以下であることが好ましく、０体積％以上３体積％以下であることがより好ましく、０体積％以上１体積％以下であることがより一層好ましい。 The atmosphere used in the step of controlling the particle diameter of the noble metal particles preferably contains a small amount of oxygen, but as shown in the following examples, noble metal particles having a uniform particle diameter even when an inert gas is used. Has been confirmed to be obtained. Therefore, firing may be performed under conditions in which oxygen is not intentionally added. Actually, it is assumed that a small amount of oxygen in the atmosphere flows in due to a small amount of gas leakage from the production equipment, and the non-zero oxygen content that is in equilibrium with the oxides contained in the system using the Ellingham diagram. Since the pressure can be calculated, it is difficult to prepare a gas that does not contain oxygen strictly. However, in the present invention, when oxygen is not detected using a commercially available oxygen concentration meter, the oxygen concentration is 0. %. Examples of the commercially available oxygen concentration meter include gas chromatography, a zirconia oxygen concentration measuring device, and a light-emitting trace oxygen analyzer. All of the gases shown in the examples of the present specification have been confirmed by the gas cylinder supplier to have an oxygen concentration of less than 0.1 ppm, and can be handled as an oxygen concentration of substantially 0%. . In the step of controlling the particle diameter of the noble metal particles, the concentration of oxygen containing a small amount of oxygen or included in the oxygen-free atmosphere is preferably 0% by volume or more and 5% by volume or less, and 0% by volume or more and 3% by volume or less. It is more preferable that it is 0 volume% or more and 1 volume% or less.
また、反応装置内を減圧又は加圧し、大気圧と異なる圧力とした場合にも、本発明では気体中の酸素が触媒に対して与える影響が重要であることから、酸素の分圧を前記の条件と同程度となるようにすることで、同様の効果が得られる。具体的には、製造装置内の酸素の分圧を０ｋＰａ以上５ｋＰａ未満とすることが好ましく、０ｋＰａ以上３ｋＰａ未満とすることがより好ましく、０ｋＰａ以上１ｋＰａ未満とすることがより一層好ましい。 Even when the inside of the reactor is depressurized or pressurized to a pressure different from the atmospheric pressure, the influence of oxygen in the gas on the catalyst is important in the present invention. The same effect can be obtained by setting the same level as the conditions. Specifically, the partial pressure of oxygen in the production apparatus is preferably 0 kPa or more and less than 5 kPa, more preferably 0 kPa or more and less than 3 kPa, and even more preferably 0 kPa or more and less than 1 kPa.
貴金属粒子の粒子径を制御する工程である酸素を少量含む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５５０度以下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他、そもそも粒子の凝集が進行しない。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９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することが示されており、特に８００℃以上の温度において、その変化が顕著であることが示されている。更に、上記のような高温では酸化物担体の構成原子の移動が促進される他、エントロピーの効果が優位となり、酸化物の結晶格子中に含まれる酸素が脱離しやすくなる。その結果、焼成雰囲気が総じて還元的な雰囲気となることから、還元性ガスを含まない真空下で加熱を行った場合であっても、カプセル化現象が生じてしまうことが知られている。そうした効果によって、７００℃以上の高温にて加熱を行った場合においては、貴金属の平均粒子径は寧ろ小さくなり、更に、昇温過程で貴金属粒子の凝集が一部で進行する他、担体の比表面積低下の影響により、粒子径の不均一性が増大する。これらのことは、後に実施例にて示す通りである。 The firing temperature in the firing step in an atmosphere containing a small amount of oxygen, 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 as low as 550 ° C. or less, it takes time to aggregate the noble metal particles, leading to an increase in process cost, and the aggregation of the particles does not proceed in the first place. 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 9 shows that the specific surface area of the titanium oxide support decreases as the firing temperature is raised, and it is shown that the change is remarkable particularly at a temperature of 800 ° C. or higher. . Furthermore, at a high temperature as described above, the movement of the constituent atoms of the oxide carrier is promoted, and the entropy effect is dominant, and oxygen contained in the oxide crystal lattice is easily desorbed. As a result, since the firing atmosphere is generally a reducing atmosphere, it is known that an encapsulation phenomenon occurs even when heating is performed in a vacuum that does not contain a reducing gas. Due to such effects, when heating is performed at a high temperature of 700 ° C. or higher, the average particle diameter of the noble metal is rather small. Due to the effect of surface area reduction, the non-uniformity of the particle size increases. These are as will be shown later in Examples.
よって、具体的な焼成温度としては、５５０℃超過７００℃以下とする。また、具体的な焼成温度は、６００℃以上７００℃以下とすることが好ましく、６００℃以上６５０℃以下とすることがより好ましい。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。 Therefore, the specific firing temperature is 550 ° C. and 700 ° C. or less. The specific firing temperature is preferably 600 ° C. or higher and 700 ° C. or lower, and more preferably 600 ° C. or higher and 650 ° C. or lower. 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酸素を少量含む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、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、酸素を少量含む雰囲気下での昇温過程を、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 an atmosphere containing a small amount of oxygen, which is a step for controlling the particle size, may be carried out after the step of supporting the noble metal particles inside the same heat treatment apparatus, or once the sample is removed from the system. You may carry out after taking out. Further, in the temperature raising process, if it is confirmed that the noble metal particles are finely and uniformly supported on the surface, the temperature raising process in an atmosphere containing a small amount of oxygen is carried on the noble metal particles. You can consider it.
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 to avoid arbitrary measurement during observation, it is important to determine the particle diameter of all the noble metal particles detected on the TEM observation image, and furthermore, one TEM observation. It is preferable that 10 or more noble metal particles are detected on the 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弱い酸化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 weak oxidizing 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 with samples prepared by other methods. It has become. 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およそ１５％ずれてしまうことになる。これは、粒子径１０ｎｍの貴金属粒子の場合では粒子径が１．５ｎｍ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±１．５ｎｍ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 about 15% depending on the viewing direction. This corresponds to the case where the particle diameter is shifted by 1.5 nm in the case of noble metal particles having a particle diameter of 10 nm. For these reasons, it can be determined that the average particle size is substantially equal to or smaller than the particles having the average particle size as long as ± 1.5 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±１．５ｎｍ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。粒子の個数比で５０％以上の貴金属粒子が、平均粒子径から±１．５ｎｍ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 ± 1.5 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 a particle number ratio of 50% or more are distributed within a range of ± 1.5 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、貴金属粒子は、平均粒子径の０．５倍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。平均粒子径の０．５倍未満の粒子径を持つ粒子を含む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、平均粒子径の０．５倍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。本発明の触媒製造方法で製造された触媒は、触媒の粒子径の平均値を４ｎｍ以上２０ｎｍ以下に調整することに特に適しているが、このような本発明の触媒は、メタンに代表されるガス中未燃成分の低温燃焼での使用に好的であると考えられる。 The noble metal particles are preferably composed only of particles having a particle size of 0.5 times or more the average particle size. However, as a matter of course, it is assumed that a part of the 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 containing particles having a particle size of less than 0.5 times the average particle size is exhibited, but even in that case, the effect is less than 0.5 times the average particle size. The noble metal particles are preferably less than 20% of the total number. The catalyst produced by the catalyst production method of the present invention is particularly suitable for adjusting the average value of the particle diameter of the catalyst to 4 nm or more and 20 nm or less. Such a catalyst of the present invention is represented by methane. It is considered to be favorable for use in low-temperature combustion of unburned components in gas.
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 designated as carriers 1, 2, and 3. 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１１：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]
(Precious metal loading step 11: 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)
0.15929 g of hexachloroplatinic acid hexahydrate was dissolved in 0.30 ml of 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. for 10 hours in the air, then heated to 400 ° C. and calcined 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：酸素１％／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、石鹸水を用いてリークチェックを行った。酸素１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とした（以下の表３、４を参照。）。
[Catalyst firing]
(Example 1: Firing treatment in an oxygen 1% / 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 soapy water. A standard gas of oxygen 1% by volume argon balance was heated for 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 600 ° C., 650 ° C., and 700 ° C., respectively. Samples obtained after firing were designated as Samples G, H, and I (see Tables 3 and 4 below).
（実施例２：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Ｊ、Ｋ、Ｌとした（以下の表３、４を参照。）。
(Example 2: Firing treatment in an inert gas atmosphere)
The same operation as in Example 1 was carried out except that the gas used was argon gas (purity 99.9999% or more). Sample 2 was subjected to firing temperatures of 600 ° C., 650 ° C., and 700 ° C., and samples obtained after firing were designated as samples J, K, and L, respectively (see Tables 3 and 4 below).
（実施例３：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Ｍ、Ｎ、Ｏとした（以下の表３、４を参照。）。
(Example 3: Firing treatment in 5% oxygen / nitrogen atmosphere)
The same procedure as in Example 1 was performed except that the gas used was a 5% nitrogen balance standard gas. Sample 2 was fired at 600 ° C., 650 ° C., and 700 ° C., and the samples obtained after firing were designated as samples M, N, and O, respectively (see Tables 3 and 4 below).
（実施例４：酸素３％／窒素雰囲気での焼成処理）
用いたガスを酸素３％窒素バランス標準ガスとした以外は、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Ｐ、Ｑ、Ｒとした（以下の表３、４を参照。）。
(Example 4: Oxygen 3% / calcination treatment in nitrogen atmosphere)
The same procedure as in Example 1 was performed except that the gas used was a 3% oxygen balance nitrogen standard gas. Sample 2 was fired at 600 ° C., 650 ° C., and 700 ° C., and the samples obtained after firing were designated as samples P, Q, and R, respectively (see Tables 3 and 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、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. 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., and the samples obtained after firing were designated as samples g, h, i, and j (see Table 3 below). .
（比較例２：水素５％／Ａｒ雰囲気での焼成処理）
水素検知機を用いてリークチェックを行い、水素５体積％アルゴンバランスの標準ガスを用いた以外は、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℃、８００℃として、それぞれ実施した。焼成後に得られた試料を試料ｌ、ｍ、ｎ、ｏ、ｐとした（以下の表３を参照。）。
(Comparative Example 2: Firing at 5% hydrogen / Ar atmosphere)
A leak check was performed using a hydrogen detector, and the same procedure as in Example 1 was performed, except that a standard gas with a hydrogen balance of 5 vol% was used. For Sample 2, the firing temperatures were 550 ° C., 600 ° C., 650 ° C., 700 ° C., and 800 ° C., respectively. Samples obtained after firing were designated as samples l, m, n, o, and p (see Table 3 below).
（比較例３：水素雰囲気での焼成処理）
水素検知器を用いてリークチェックを行い、水素ガス（純度９９．９９９９％以上）を用いた以外は、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℃、８００℃としてそれぞれ実施し、焼成後に得られた試料を試料ｑ、ｒ、ｓ、ｔ、ｕとした（以下の表３を参照。）。
(Comparative Example 3: Firing treatment in a hydrogen atmosphere)
A leak check was performed using a hydrogen detector, and a baking process was performed in the same manner as in Example 1 except that hydrogen gas (purity 99.9999% or more) was used. Sample 2 was fired at 550 ° C., 600 ° C., 650 ° C., 700 ° C., and 800 ° C., and the samples obtained after firing were designated as samples q, r, s, t, and u (Table 3 below). See).
（比較例４：酸素５％／Ｎ２雰囲気での焼成処理、５５０℃）
試料２について、焼成温度を５５０℃とした以外は、実施例１と同様に実施した。焼成後に得られた試料を試料ｖとした（以下の表３を参照。）。
(Comparative Example 4: Firing treatment in an oxygen 5% / N 2 atmosphere, 550 ° C.)
For Sample 2, the same procedure as in Example 1 was performed except that the firing temperature was 550 ° C. The sample obtained after firing was designated as sample v (see Table 3 below).
（比較例５：酸素３％／Ｎ２雰囲気での焼成処理、５５０℃）
試料２について、焼成温度を５５０℃とした以外は、実施例１と同様に実施した。焼成後に得られた試料を試料ｗとした（以下の表３を参照。）。
(Comparative example 5: Oxygen 3% / Baking treatment in N 2 atmosphere, 550 ° C.)
For Sample 2, the same procedure as in Example 1 was performed except that the firing temperature was 550 ° C. The sample obtained after firing was designated as sample w (see Table 3 below).
（比較例６：酸素１％／Ａｒ雰囲気での焼成処理、５５０℃）
試料２について、焼成温度を５５０℃とした以外は、実施例１と同様に実施した。焼成後に得られた試料を試料ｘとした（以下の表３を参照。）。
(Comparative Example 6: 1% oxygen / calcination treatment in Ar atmosphere, 550 ° C.)
For Sample 2, the same procedure as in Example 1 was performed except that the firing temperature was 550 ° C. The sample obtained after firing was designated as sample x (see Table 3 below).
（比較例７：不活性ガス雰囲気での焼成処理、５５０℃）
試料２について、焼成温度を５５０℃とした以外は、実施例２と同様に実施した。焼成後に得られた試料を試料ｙとした（以下の表３を参照。）。
(Comparative Example 7: calcination treatment in an inert gas atmosphere, 550 ° C.)
For Sample 2, the same procedure as in Example 2 was performed except that the firing temperature was 550 ° C. The sample obtained after firing was designated as sample y (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〜Ｒ、ａ〜ｙ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 R, and a to y 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.
各試料について、得られた平均粒子径を表２、３に示し、特に試料ｘ、試料Ｇ、試料Ｈ、試料Ｉ、試料ｙ、試料Ｊ、試料Ｋ、試料ｉ、試料ｊ、試料Ｍ、試料Ｐ、試料ｎについては、その粒度分布と表面の観察像を図１〜１２にそれぞれ示した。図１〜図１２に示した粒度分布については、横軸に粒子径、縦軸に度数を示した。また、表面の観察像は、図９については高角散乱環状暗視野像（ＨＡＡＤＦ−ＳＴＥＭ）を示し、それ以外の試料については明視野像を示した。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。更に、各試料について、平均粒子径を表２、３に示した。また、試料Ｇ〜Ｒについては、観測された貴金属粒子全体に対する平均粒子径±１．５ｎｍ以内に含まれる貴金属粒子の個数比、観測された貴金属粒子の中で最も粒子径の小さい粒子の粒子径を、それぞれ表４に示した。 The average particle diameters obtained for each sample are shown in Tables 2 and 3, and in particular, Sample x, Sample G, Sample H, Sample I, Sample y, Sample J, Sample K, Sample i, Sample j, Sample M, Sample About P and the sample n, the particle size distribution and the observed image of the surface were shown in FIGS. About the particle size distribution shown in FIGS. 1-12, the horizontal axis | shaft showed the particle diameter and the vertical axis | shaft showed frequency. Moreover, the surface observation image showed the high angle scattering cyclic | annular dark field image (HAADF-STEM) about FIG. 9, and showed the bright field image about the sample other than that. 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. Further, for each sample, the average particle diameter is shown in Tables 2 and 3. For samples G to R, the ratio of the number of noble metal particles contained within an average particle diameter of ± 1.5 nm with respect to the entire observed noble metal particles, and the particle diameter of the smallest particle diameter among the observed noble metal particles Are shown in Table 4, respectively.
表２の結果より、追加焼成を行っていない調製後の試料では、いずれも貴金属の粒子径は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。続いて、表３の結果を見ると、水素を含む還元雰囲気で焼成された試料に着目すると、試料ｌ〜ｏ、ｑ〜ｔのいずれの試料についても、粒子径は３ｎｍ程度、又は３ｎｍ未満となっており、平均粒子径４ｎｍ以上には制御できていないことが分かる。図１２に示すように、粒子径の分布は非常に狭く、均一な粒子が作成できていることは分かるものの、その平均粒子径は小さい。同様の傾向は、いずれの試料にも見られた。ただし、焼成温度を７００℃とした試料ｏ、ｔについては、担体の一部に変形が見られ、還元雰囲気にて高温で焼成されたことによる悪影響が確認された。また、更に焼成温度を高めた試料ｐ、ｕについては、担体の変形が著しく、担体の変形に伴って白金の凝集が進行してしまっていた。 From the results shown in Table 2, in the prepared samples that were not subjected to additional firing, the particle size of the noble metal was about 2 nm or less and was very small. Subsequently, when looking at the results of Table 3, when focusing on the sample fired in a reducing atmosphere containing hydrogen, the particle diameter is about 3 nm or less than 3 nm for any of the samples l to o and q to t. It can be seen that the average particle diameter cannot be controlled to 4 nm or more. As shown in FIG. 12, the particle size distribution is very narrow, and it can be seen that uniform particles can be produced, but the average particle size is small. Similar trends were seen in all samples. However, for samples o and t with a firing temperature of 700 ° C., some of the carrier was deformed, and an adverse effect due to firing at a high temperature in a reducing atmosphere was confirmed. Further, for the samples p and u whose firing temperature was further increased, the support was significantly deformed, and the aggregation of platinum proceeded with the deformation of the support.
空気雰囲気中にて焼成した試料では、表３に示すように、焼成温度を上昇させても粒子径の変化は見られなかった。図８に示すように、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、図９に示すように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る。図９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。一方、図１０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、表３に示すように平均粒子径は大きくなるものの、表４及び図１０に示すように粒子径のばらつきが大きくなってしまう。 In the sample fired in the air atmosphere, as shown in Table 3, no change in the particle diameter was observed even when the firing temperature was increased. As shown in FIG. 8, the sample fired at 650 ° C. has a uniform particle diameter, but its size is small, and the sample fired at 700 ° C. has a variation in particle diameter as shown in FIG. In addition to becoming larger, it can be seen that some particles become coarse. In accordance with the measurement of FIG. 9, elemental analysis by energy dispersive X-ray spectroscopy (EDX) is also performed. The particles indicated by points O 1 and O 4 are titanium oxide carrier particles, and the points O 2 and O 4 It has been confirmed that the light-colored particles indicated by 3 are platinum particles. On the other hand, as shown in FIG. 10, in the sample fired in a gas containing 5% by volume of oxygen, although the average particle size becomes large as shown in Table 3, the variation in particle size as shown in Table 4 and FIG. Will become bigger.
一方で、酸素１体積％アルゴンバランスガスフロー中、並びにアルゴンガス中にて焼成を行った試料Ａ〜Ｆ、試料Ｇ〜Ｉ、試料Ｊ〜Ｌでは、平均粒子径が４ｎｍ以上に制御できており、更にその粒子径も均一となっていた。表４に、酸素５％雰囲気、及び酸素３％雰囲気にて焼成を行った試料の評価結果とあわせて示す。試料Ｇ〜Ｌ、ではいずれも平均粒子径±１．５ｎｍの粒子径を持つ粒子の個数比が５０％以上となっており、更に、観測された最小の粒子の粒子径も、平均粒子径の０．５倍以上となっていた。これに対し、試料Ｍ〜Ｒでは粒子径の分布が広くなってしまっており、観測された最小の粒子の粒子径も、平均粒子径の０．５倍未満となっていた。酸素５％雰囲気と、酸素３％雰囲気で焼成された試料を比較すると、酸素３％雰囲気にて焼成された試料において粒子径の均一性が高まっている様子が分かり、酸素濃度５％以下１％以上の範囲においては、酸素濃度が低いほど、粒子径の均一性が高まるものと予想される。 On the other hand, in Samples A to F, Samples G to I, and Samples J to L fired in an argon 1% by volume argon balance gas flow and argon gas, the average particle diameter can be controlled to 4 nm or more. Furthermore, the particle diameter was uniform. Table 4 shows the evaluation results of the samples fired in an oxygen 5% atmosphere and an oxygen 3% atmosphere. In Samples G to L, the number ratio of particles having an average particle size of ± 1.5 nm is 50% or more, and the observed minimum particle size is also equal to the average particle size. It was 0.5 times or more. On the other hand, in the samples M to R, the particle size distribution is widened, and the observed minimum particle size is also less than 0.5 times the average particle size. Comparing a sample fired in an oxygen 5% atmosphere and a sample fired in an oxygen 3% atmosphere, it can be seen that the uniformity of the particle diameter is increased in the sample fired in an oxygen 3% atmosphere. In the above range, it is expected that the lower the oxygen concentration, the higher the particle size uniformity.
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)
酸素を０体積％以上５体積％以下含む非還元雰囲気中で、５５０℃超過７００℃以下の温度にて、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、
を有する、触媒の製造方法。 For one or more oxide carriers selected from the group consisting of titanium oxide, zirconium oxide and cerium oxide, carrying one or more noble metal particles selected from the group consisting of platinum, palladium and rhodium. , A process for making a noble metal supported catalyst,
Noble metal particles supported on the noble metal-supported catalyst by heat-treating the noble metal-supported catalyst in a non-reducing atmosphere containing 0% by volume to 5% by volume of oxygen at a temperature exceeding 550 ° C. and not more than 700 ° C. Controlling the diameter within a predetermined range;
A process for producing a catalyst comprising:
前記貴金属粒子は、平均粒子径が４．０ｎｍ以上２０．０ｎｍ以下の範囲内で、かつ、全体の貴金属粒子に占める平均粒子径±１．５ｎｍ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 kinds of noble metal particles selected from the group consisting of platinum, palladium and rhodium are supported on one or more kinds of 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 4.0 nm or more and 20.0 nm or less, and the ratio of the noble metal particles in the average particle diameter in the range of ± 1.5 nm in the total noble metal particles is the number ratio. The catalyst is 50% or more.
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