JP5703924B2 - Columnar ceria catalyst - Google Patents
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- 239000003054 catalyst Substances 0.000 title claims description 66
- CETPSERCERDGAM-UHFFFAOYSA-N ceric oxide Chemical compound O=[Ce]=O CETPSERCERDGAM-UHFFFAOYSA-N 0.000 title description 27
- 229910000422 cerium(IV) oxide Inorganic materials 0.000 title description 27
- 239000002073 nanorod Substances 0.000 claims description 67
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- 239000002245 particle Substances 0.000 claims description 22
- 239000010419 fine particle Substances 0.000 claims description 21
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- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 9
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- 238000000746 purification Methods 0.000 claims description 4
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- 150000000703 Cerium Chemical class 0.000 claims description 3
- 239000011259 mixed solution Substances 0.000 claims description 3
- 238000002156 mixing Methods 0.000 claims description 3
- AXCZMVOFGPJBDE-UHFFFAOYSA-L calcium dihydroxide Chemical compound [OH-].[OH-].[Ca+2] AXCZMVOFGPJBDE-UHFFFAOYSA-L 0.000 claims description 2
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- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical group [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 26
- 229910052751 metal Inorganic materials 0.000 description 15
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- 150000004706 metal oxides Chemical class 0.000 description 5
- HSJPMRKMPBAUAU-UHFFFAOYSA-N cerium(3+);trinitrate Chemical compound [Ce+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O HSJPMRKMPBAUAU-UHFFFAOYSA-N 0.000 description 4
- 230000000052 comparative effect Effects 0.000 description 4
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- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 3
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- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 description 2
- MCMNRKCIXSYSNV-UHFFFAOYSA-N Zirconium dioxide Chemical compound O=[Zr]=O MCMNRKCIXSYSNV-UHFFFAOYSA-N 0.000 description 2
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- 239000006228 supernatant Substances 0.000 description 2
- 229910004631 Ce(NO3)3.6H2O Inorganic materials 0.000 description 1
- MYMOFIZGZYHOMD-UHFFFAOYSA-N Dioxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 description 1
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- VYLVYHXQOHJDJL-UHFFFAOYSA-K cerium trichloride Chemical compound Cl[Ce](Cl)Cl VYLVYHXQOHJDJL-UHFFFAOYSA-K 0.000 description 1
- VGBWDOLBWVJTRZ-UHFFFAOYSA-K cerium(3+);triacetate Chemical compound [Ce+3].CC([O-])=O.CC([O-])=O.CC([O-])=O VGBWDOLBWVJTRZ-UHFFFAOYSA-K 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
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- 230000033116 oxidation-reduction process Effects 0.000 description 1
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Description
本発明は、セリアを含む担体及びその上に担持された活性種を備える触媒及びその製造方法に関する。 The present invention relates to a catalyst comprising a support containing ceria, an active species supported thereon, and a method for producing the same.
例えば、自動車や二輪車などのエンジンから排出される排ガスには、ＨＣ、ＣＯ、ＮＯｘ等の有害成分が含まれている。これらの有害な排ガスを分解除去するために、活性種となるＰｔ、Ｐｄ、Ｒｈ等の白金族元素を主成分とする触媒粒子を、セリア、アルミナ等の金属酸化物の担体に担持させた排ガス浄化用触媒が使用されており、例えば、理論空燃比（ストイキ）において排ガス中のＣＯ、ＨＣ、ＮＯｘを同時に酸化・還元して浄化することができる三元触媒がよく用いられている。 For example, exhaust gas discharged from engines such as automobiles and motorcycles contains harmful components such as HC, CO, and NOx. In order to decompose and remove these harmful exhaust gases, exhaust gas in which catalyst particles mainly composed of platinum group elements such as Pt, Pd, and Rh as active species are supported on a metal oxide carrier such as ceria and alumina. A purification catalyst is used. For example, a three-way catalyst that can simultaneously purify by oxidizing and reducing CO, HC, and NOx in exhaust gas at a stoichiometric air-fuel ratio (stoichiometric) is often used.
近年、世界的に自動車の排ガス規制が強化されてきており、ＬＥＶＩＩＩやＥＵＲＯ６等の規制強化に対応するためのさらなる触媒性能の向上が求められている。また、上記のような三元触媒に限らず、工業用触媒等の触媒性能を向上し得る材料開発が求められている。 In recent years, exhaust gas regulations for automobiles have been strengthened globally, and further improvement in catalyst performance is required in order to respond to strengthened regulations such as LEVIII and EURO6. In addition to the above three-way catalyst, there is a demand for development of materials that can improve the catalyst performance of industrial catalysts and the like.
触媒性能を向上させる方法の１つとして、触媒粒子を微粒子化して、有害成分との接触面積を大きくすることが検討されており、例えば１ｎｍ〜１００ｎｍの粒子径を持つナノ金属微粒子を担体上に保持した触媒が開発されている（特許文献１）。 As one of the methods for improving the catalyst performance, it has been studied to make catalyst particles finer to increase the contact area with harmful components. For example, nanometal fine particles having a particle diameter of 1 nm to 100 nm are formed on a carrier. A retained catalyst has been developed (Patent Document 1).
また、金属酸化物担体としてセリアは、３価と４価の間の酸化還元電位が低いために、雰囲気の酸素分圧が高いときは雰囲気中の酸素を吸収して４価となり、該分圧が低いと３価となって酸素を雰囲気に放出する作用があることが知られている。この作用を利用すると酸素貯蔵が可能であり、触媒表面の酸素濃度を調整できることから、セリアを利用した触媒が開発されている。 Ceria as a metal oxide support has a low oxidation-reduction potential between trivalent and tetravalent, so when the oxygen partial pressure in the atmosphere is high, it absorbs oxygen in the atmosphere and becomes tetravalent. Is low, it is known to be trivalent and to release oxygen into the atmosphere. Utilizing this action makes it possible to store oxygen, and the oxygen concentration on the catalyst surface can be adjusted. Therefore, catalysts using ceria have been developed.
この酸素貯蔵能力は、酸素の吸着、酸素の拡散、及び酸素の脱離からなる３つの過程を経て発揮される。セリアが触媒あるいは助触媒として使用される温度では、気相中の酸素ガスがセリア固体内に浸透する深さは表面層に限られているので、酸素の吸着量や脱離量は比表面積に比例する。このため、比表面積が大きいナノサイズの針状セリア粉末が開発されている（特許文献２）。 This oxygen storage capacity is exhibited through three processes consisting of oxygen adsorption, oxygen diffusion, and oxygen desorption. At the temperature at which ceria is used as a catalyst or cocatalyst, the depth at which oxygen gas in the gas phase penetrates into the ceria solid is limited to the surface layer, so the amount of oxygen adsorbed and desorbed is limited to the specific surface area. Proportional. For this reason, nano-sized acicular ceria powder having a large specific surface area has been developed (Patent Document 2).
高温下で動作する触媒においては、担体に担持される触媒粒子がシンタリングによる凝集を起こしやすく、触媒粒子が凝集すると比表面積が低下するため、触媒活性が低下することがしばしば問題となる。特に、触媒粒子が微細で比表面積が大きいほどシンタリングが起きやすく、例えば、特許文献１のナノ金属微粒子を触媒粒子として用いた触媒では、触媒使用中に高温になるたびに、活性状態になった隣接する金属微粒子同士で凝集による粒成長が起こりやすく触媒活性が低下するおそれがある。 In a catalyst that operates at a high temperature, the catalyst particles supported on the carrier are likely to agglomerate due to sintering, and when the catalyst particles agglomerate, the specific surface area decreases, so that the catalyst activity often decreases. In particular, as the catalyst particles are finer and the specific surface area is larger, the sintering is more likely to occur. For example, in the catalyst using the nanometal fine particles of Patent Document 1 as the catalyst particles, the catalyst becomes active every time the catalyst is used at a high temperature. In addition, particle growth due to aggregation tends to occur between adjacent metal fine particles, and the catalytic activity may be reduced.
また、触媒粒子を担持する金属酸化物担体の形状によっても、触媒粒子の粒成長のし易さが変わることが判明した。例えば、特許文献２に記載されるようなナノサイズの針状セリア粒子についても、針状セリア粒子の表面に担持させた貴金属の粒成長が起きやすいことが分かった。 It has also been found that the ease of particle growth of the catalyst particles varies depending on the shape of the metal oxide carrier supporting the catalyst particles. For example, for nano-sized acicular ceria particles as described in Patent Document 2, it has been found that noble metal particles supported on the surface of acicular ceria particles are likely to grow.
本発明はかかる事情及び新たな知見に基づいてなされたものであり、セリアを含む担体と、担体上に担持された活性種からなる触媒において、活性種の粒成長を抑制することができる触媒及びその製造方法を提供することを目的とする。 The present invention has been made on the basis of such circumstances and new knowledge, and in a catalyst comprising a carrier containing ceria and an active species supported on the carrier, a catalyst capable of suppressing grain growth of the active species and It aims at providing the manufacturing method.
本発明者らは、高温下においても、活性種のシンタリングによる粒成長を抑制することができるセリアを担体とする触媒について鋭意研究を行った。その結果、活性種の粒成長の度合いが、活性種を担持させるセリアの結晶面に影響されることが判明し、セリアの｛１００｝面に活性種を担持させると、活性種の粒成長が発生しにくくなることを突き止めた。そこで、一次粒子レベルでセリアの面方位を制御したＣｅＯ2ナノロッドを触媒担体として用いてその上に活性種を担持させた触媒構成とすることによって、高温下でも活性種の粒成長を抑制できる触媒を見出した。 The present inventors have intensively studied a catalyst using ceria that can suppress grain growth due to sintering of active species even at high temperatures. As a result, it has been found that the degree of grain growth of the active species is affected by the ceria crystal plane supporting the active species. When the active species is supported on the {100} plane of ceria, the grain growth of the active species is reduced. I found out that it was hard to occur. Therefore, by using a CeO 2 nanorod in which the ceria plane orientation is controlled at the primary particle level as a catalyst carrier and supporting the active species thereon, a catalyst capable of suppressing the growth of active species grains even at high temperatures. I found.
本発明は、担体及び担体に担持された金属微粒子を備える触媒であって、担体が、｛１００｝面及び｛１１０｝面からなるＣｅＯ2ナノロッドを含む、触媒である。 The present invention is a catalyst comprising a support and metal fine particles supported on the support, wherein the support includes CeO 2 nanorods composed of {100} faces and {110} faces.
本発明の触媒によれば、｛１００｝面及び｛１１０｝面からなるたＣｅＯ2ナノロッドに活性種となる金属微粒子を担持させた触媒構成とすることによって、高温下でも、活性種の粒成長を抑制することが可能となる。 According to the catalyst of the present invention, the grain growth of active species can be achieved even at high temperatures by adopting a catalyst structure in which fine particles of active species are supported on CeO 2 nanorods composed of {100} faces and {110} faces. Can be suppressed.
本発明の触媒は、担体と、担体に担持された金属微粒子とを備え、担体が｛１００｝面及び｛１１０｝面からなるＣｅＯ2ナノロッドを含む。 The catalyst of the present invention includes a support and metal fine particles supported on the support, and the support includes CeO 2 nanorods having {100} faces and {110} faces.
｛１００｝面及び｛１１０｝面からなるＣｅＯ2ナノロッドを触媒担体として使用し、その上に活性種を担持させた触媒構成とすることによって、高温下でも、活性種の粒成長を抑制することが可能な触媒を得ることができる。 By using a CeO 2 nanorod consisting of {100} and {110} faces as a catalyst carrier and having the active species supported thereon, the grain growth of the active species can be suppressed even at high temperatures. Can be obtained.
｛１００｝面及び｛１１０｝面からなるＣｅＯ2ナノロッドは、ＣｅＯ2ナノロッドの表面全体において｛１１１｝面を実質的に含まない。これにより、活性種の粒成長を抑制することができる。好ましくは、ＣｅＯ2ナノロッドは角柱形状を有する。 CeO 2 nanorods composed of {100} faces and {110} faces are substantially free of {111} faces over the entire surface of the CeO 2 nanorods. Thereby, grain growth of active species can be suppressed. Preferably, the CeO 2 nanorod has a prismatic shape.
なお、｛１００｝面のみで構成されるキュービックＣｅＯ2ナノ粒子を触媒担体として用いた場合、触媒耐熱性の向上効果があまり得られないことが分かった。これは、｛１００｝面のみで構成されるキュービックＣｅＯ2ナノ粒子自体が４００℃程度で変性するためと考えられる。｛１００｝面に加えて｛１１０｝面からなるナノロッド構造にすることによって、ＣｅＯ2ナノ粒子自体の耐熱性も向上することが分かった。 Incidentally, cubic CeO 2 nanoparticles composed of only {100} plane when used as a catalyst carrier, the effect of improving the catalyst heat resistance was found not obtained very much. This is presumably because the cubic CeO 2 nanoparticles themselves composed only of {100} faces denature at about 400 ° C. It was found that the heat resistance of the CeO 2 nanoparticles themselves was improved by adopting a nanorod structure consisting of {110} faces in addition to the {100} faces.
本発明において、ＣｅＯ2ナノロッドに担持される活性種としては、一般に触媒として使用することができる金属微粒子を使用することができ、金属微粒子としては、例えば、Ｐｔ、Ｐｄ、Ｒｈ、Ａｕ等の貴金属、Ｃｕ、Ｆｅ、Ｎｉ等の遷移金属、それらの酸化物、またはそれらの任意の組み合わせが挙げられ、好ましくはＰｔを使用することができる。 In the present invention, metal fine particles that can be generally used as a catalyst can be used as the active species supported on the CeO 2 nanorods. Examples of the metal fine particles include noble metals such as Pt, Pd, Rh, and Au. , Transition metals such as Cu, Fe and Ni, oxides thereof, or any combination thereof, and Pt can be preferably used.
理論に束縛されるものではないが、従来のセリアのナノ粒子、例えば針状ナノ粒子は、概して｛１１１｝面を多く含む。そして、ＣｅＯ2粒子の｛１１１｝面は、その上に担持した貴金属等の活性種との相互作用が弱いために、高温下において活性種同士が凝集しやすく、シンタリングによる粒成長が発生しやすいと考えられる。 Without being bound by theory, conventional ceria nanoparticles, such as acicular nanoparticles, generally contain many {111} faces. The {111} plane of the CeO 2 particles has a weak interaction with active species such as noble metals supported thereon, so that the active species tend to aggregate at high temperatures, and grain growth occurs due to sintering. It is considered easy.
一方、本発明において、｛１００｝面及び｛１１０｝面からなるＣｅＯ2ナノロッド担体が、その上に担持した活性種の粒成長を抑制できるのは、ＣｅＯ2ナノロッドの｛１００｝面と活性種との相互作用が特に大きいために、高温下においても活性種の移動が抑制され、活性種のシンタリングを抑制することができるためと考えられる。 On the other hand, in the present invention, the CeO 2 nanorod carrier consisting of {100} face and {110} face can suppress the grain growth of the active species supported on the {100} face of the CeO 2 nanorod and the active species. This is considered to be because the movement of the active species is suppressed even at high temperatures and the sintering of the active species can be suppressed.
特に、活性種としてＰｔを使用する場合は、良好な粒成長抑制効果が得られることが分かった。理論に束縛されるものではないが、これは、ＣｅＯ2及びＰｔがそれぞれ面心立方構造をとり、ＣｅＯ2の｛２００｝面における原子間距離０．３８３ｎｍと、Ｐｔの｛１００｝面における原子間距離０．３９２ｎｍとがほぼ同じであることから、ＣｅＯ2ナノロッドの｛１００｝面とＰｔとの間の相互作用が大きくなり、Ｐｔのシンタリングが特に抑制され得るためと考えられる。 In particular, it has been found that when Pt is used as the active species, a good grain growth suppressing effect can be obtained. Without being bound by theory, this is because CeO 2 and Pt each have a face-centered cubic structure, an interatomic distance of 0.383 nm in the {200} plane of CeO 2 , and atoms in the {100} plane of Pt. This is probably because the interaction between the {100} face of the CeO 2 nanorods and Pt becomes large and the sintering of Pt can be particularly suppressed because the distance between them is almost the same as 0.392 nm.
ＣｅＯ2ナノロッドの幅及び長さは、透過型電子顕微鏡（ＴＥＭ）または高分解能透過型電子顕微鏡（ＨＲ−ＴＥＭ）により測定され得る。この場合、少なくとも１００個のＣｅＯ2ナノロッドの幅及び長さを測定することが好ましい。 The width and length of the CeO 2 nanorods can be measured by transmission electron microscope (TEM) or high resolution transmission electron microscope (HR-TEM). In this case, it is preferable to measure the width and length of at least 100 CeO 2 nanorods.
本発明において、ＣｅＯ2ナノロッドは、幅が平均で約２〜１５ｎｍ及び長さが平均で約２０〜４００ｎｍであることができ、さらに好ましくは幅が平均で約５〜８ｎｍ及び長さが平均で約３０〜１００ｎｍであることができる。 In the present invention, the CeO 2 nanorods may have an average width of about 2 to 15 nm and an average length of about 20 to 400 nm, and more preferably an average width of about 5 to 8 nm and an average length. It can be about 30-100 nm.
得られたＣｅＯ2ナノロッドの面方位については、ＨＲ−ＴＥＭによる原子配列の観察及び格子面間隔の測定から特定され得る。 The plane orientation of the obtained CeO 2 nanorods can be specified from observation of atomic arrangement by HR-TEM and measurement of lattice plane spacing.
本発明の触媒に用いる担体は｛１００｝面及び｛１１０｝面からなるナノロッドセリアを含むが、例えば三元触媒のような触媒の全体構成において、触媒担体として通常用いられる他の金属酸化物を組み合わせてもよく、他の金属酸化物としては、例えば、シリカ、アルミナ、ジルコニア、チタニア等が挙げられる。またシリカ−アルミナなどの複合酸化物を併用することも可能である。 The support used in the catalyst of the present invention includes nanorod ceria composed of {100} faces and {110} faces. For example, in the overall configuration of the catalyst such as a three-way catalyst, other metal oxides usually used as catalyst supports are used. They may be combined, and examples of other metal oxides include silica, alumina, zirconia, and titania. It is also possible to use a composite oxide such as silica-alumina in combination.
また、本発明においては、｛１００｝面及び｛１１０｝面からなるナノロッドを含むセリア担体中に、｛１１１｝面を多く含む多面体セリアやキュービックセリア等の、｛１００｝面及び｛１１０｝面からなるＣｅＯ2ナノロッド以外の不純物セリアが微量に含まれてもよいが、好ましくは不純物セリアの含有量はセリア全体に対して１５体積％以下であり、より好ましくは５体積％以下であり、さらに好ましくは１体積％以下であり、さらに好ましくは実質的に不純物セリアを含まない。体積％は、ＴＥＭ観察像に基づいて計測した面積％から算出することができる。 Further, in the present invention, the {100} plane and the {110} plane such as polyhedral ceria and cubic ceria containing many {111} planes in a ceria support including nanorods composed of {100} planes and {110} planes. Impurity ceria other than CeO 2 nanorods may be contained in a trace amount, but the content of impurity ceria is preferably 15% by volume or less, more preferably 5% by volume or less, and more preferably 5% by volume or less. Preferably it is 1 volume% or less, More preferably, it does not contain impurity ceria substantially. The volume% can be calculated from the area% measured based on the TEM observation image.
本発明はまた、担体及び担体に担持された金属微粒子を備える触媒の製造方法であって、
セリウム塩と強アルカリ水溶液とを混合して混合溶液を調製する工程、
混合溶液を水熱合成して、｛１００｝面及び｛１１０｝面からなるＣｅＯ2ナノロッドを含む担体を形成する工程、
水中にＣｅＯ2ナノロッドを含む担体を分散させて担体分散液を調製する工程、
水中に金属微粒子を分散させて金属微粒子分散液を調製する工程、並びに
担体分散液と金属微粒子分散液とを混合して加熱攪拌することにより、ＣｅＯ2ナノロッドを含む担体に金属微粒子を担持させる工程、
を含む、触媒の製造方法を対象とする。
The present invention is also a method for producing a catalyst comprising a carrier and metal fine particles supported on the carrier,
A step of preparing a mixed solution by mixing a cerium salt and a strong alkaline aqueous solution;
Hydrothermal synthesis of the mixed solution to form a support containing CeO 2 nanorods composed of {100} faces and {110} faces;
Preparing a carrier dispersion by dispersing a carrier containing CeO 2 nanorods in water;
A step of preparing a metal fine particle dispersion by dispersing metal fine particles in water, and a step of supporting the metal fine particles on a carrier containing CeO 2 nanorods by mixing and heating and stirring the carrier dispersion and the metal fine particle dispersion. ,
And a method for producing a catalyst.
本発明において、セリウム塩としては、例えば硝酸セリウム、酢酸セリウム、塩化セリウム等を使用することができ、好ましくは硝酸セリウムを使用することができる。 In the present invention, as the cerium salt, for example, cerium nitrate, cerium acetate, cerium chloride and the like can be used, and preferably cerium nitrate can be used.
本発明において、強アルカリ水溶液としては、水酸化ナトリウム、水酸化カリウム、水酸化カルシウム等の強アルカリ水溶液を用いることできる。強アルカリ水溶液として、４ｍｏｌ／Ｌ以上のＮａＯＨが好ましく、６ｍｏｌ／Ｌ以上の水酸化ナトリウムがさらに好ましい。水酸化ナトリウムの濃度が低すぎると｛１１１｝面が形成されやすくなる傾向がある。なお、水酸化ナトリウムの濃度が高い分には特に問題はないが、ＣｅＯ2ナノロッドが大きくなる傾向があり、微細なＣｅＯ2ナノロッドを得るためには、６〜９ｍｏｌ／Ｌの水酸化ナトリウムを用いることが好ましい。 In the present invention, a strong alkaline aqueous solution such as sodium hydroxide, potassium hydroxide, calcium hydroxide or the like can be used as the strong alkaline aqueous solution. As the strong alkaline aqueous solution, 4 mol / L or more of NaOH is preferable, and 6 mol / L or more of sodium hydroxide is more preferable. If the concentration of sodium hydroxide is too low, the {111} plane tends to be formed. In addition, although there is no particular problem for the high concentration of sodium hydroxide, CeO 2 nanorods tend to be large, and in order to obtain fine CeO 2 nanorods, 6-9 mol / L sodium hydroxide is used. It is preferable.
また、本発明において、｛１００｝面及び｛１１０｝面からなるＣｅＯ2ナノロッドを形成するためには、８０〜１３０℃、好ましくは９０〜１２０℃で、さらに好ましくは１００〜１１０℃で、１２〜３６時間、好ましくは２０〜２８時間、水熱合成を行う。水熱合成温度が高すぎると、｛１００｝面のみから形成されたキュービックＣｅＯ2が形成されやすい傾向があり、水熱合成温度が低すぎるとＣｅＯ2の結晶性が低下する恐れがある。水熱合成時間が短すぎるとＣｅＯ2の結晶性が低下する恐れがあり、水熱合成時間が長すぎるとキュービックＣｅＯ2が形成されやすくなる傾向がある。 Further, in the present invention, in order to form a CeO 2 nanorods formed of {100} plane and {110} plane, 80 to 130 ° C., preferably at 90 to 120 ° C., more preferably 100 to 110 ° C., 12 Hydrothermal synthesis is performed for ˜36 hours, preferably 20 to 28 hours. If the hydrothermal synthesis temperature is too high, cubic CeO 2 formed only from {100} faces tends to be formed, and if the hydrothermal synthesis temperature is too low, the crystallinity of CeO 2 may be lowered. If the hydrothermal synthesis time is too short, the crystallinity of CeO 2 may be lowered. If the hydrothermal synthesis time is too long, cubic CeO 2 tends to be formed.
活性種をＣｅＯ2ナノロッド担体に担持させる方法は、活性種を担体に担持させるために従来から用いられている含浸法等の方法を使用することができる。 As a method for supporting the active species on the CeO 2 nanorod carrier, a method such as an impregnation method conventionally used for supporting the active species on the carrier can be used.
活性種をＣｅＯ2ナノロッド担体に担持させる方法として、例えば、脱イオン水にＣｅＯ2ナノロッドを分散させた担体分散液と、脱イオン水に金属微粒子を分散させた分散液とを、加熱攪拌し、分散媒を除去し、約１００℃〜１４０℃で乾燥した後、乳鉢で粉砕することによって、金属微粒子をＣｅＯ2ナノロッドに担持させた触媒粉末を得ることができる。 As a method for supporting the active species on the CeO 2 nanorod carrier, for example, a carrier dispersion in which CeO 2 nanorods are dispersed in deionized water and a dispersion in which metal fine particles are dispersed in deionized water are heated and stirred. After removing the dispersion medium, drying at about 100 ° C. to 140 ° C., and then pulverizing with a mortar, a catalyst powder in which metal fine particles are supported on CeO 2 nanorods can be obtained.
金属微粒子はＣｅＯ2ナノロッド上に任意の量で担持され得るが、例えば、ＣｅＯ2ナノロッド担体質量基準で０．０１％〜１０ｗｔ％の金属微粒子を担持させることができる。 The metal fine particles can be supported in any amount on the CeO 2 nanorods. For example, 0.01% to 10% by weight of metal fine particles can be supported on the basis of the CeO 2 nanorod support mass.
本発明について、実施例及び比較例を用いて具体的に説明する。 The present invention will be specifically described using examples and comparative examples.
（実施例１）
ＣｅＯ2ナノロッドの合成
本発明の触媒に用いるＣｅＯ2ナノロッドを、水熱合成法によって合成した。
(Example 1)
The CeO 2 nanorods used in the catalyst synthesis the present invention CeO 2 nanorods were synthesized by hydrothermal synthesis.
テフロン（登録商標）容器に、Ｃｅ（ＮＯ3）3・６Ｈ2Ｏ（４．５ｍｍｏｌ）を溶解させた水溶液６ｇを入れ、６ｍｏｌ／ＬのＮａＯＨ水溶液（９０ｍＬ）を加えて、１０分間、室温にて攪拌した。そして、加圧容器に入れて密封し、１００℃で２４時間、水熱合成を行った。 In a Teflon (registered trademark) container, 6 g of an aqueous solution in which Ce (NO 3 ) 3 .6H 2 O (4.5 mmol) was dissolved was added, 6 mol / L NaOH aqueous solution (90 mL) was added, and the mixture was allowed to warm to room temperature for 10 minutes. And stirred. And it put in the pressurized container and sealed, and hydrothermal synthesis was performed at 100 degreeC for 24 hours.
得られたスラリーを遠心分離機で粉末と上澄み液とに分離し、分離した上澄み液を廃棄し、分離した粉末を脱イオン水及びエタノールで洗浄し、８０℃で２４時間減圧乾燥して、ＣｅＯ2ナノロッド粉末を得た。 The obtained slurry is separated into powder and supernatant with a centrifuge, the separated supernatant is discarded, the separated powder is washed with deionized water and ethanol, dried under reduced pressure at 80 ° C. for 24 hours, and then CeO. Two nanorod powders were obtained.
ＣｅＯ2ナノロッドの形状観察、寸法測定、及び面方位の特定
合成したＣｅＯ2ナノロッド粉末を、透過型電子顕微鏡（ＴＥＭ及びＨＲ−ＴＥＭ、日立製、Ｈ−９５００、加速電圧３００ｋＶ）で観察した。
CeO 2 nanorods shape observation, dimension measurement, and the specific synthetic CeO 2 nanorods powder surface orientation, transmission electron microscopy (TEM and HR-TEM, Hitachi, H-9500, accelerating voltage 300 kV) was observed in.
本実施例で合成したＣｅＯ2ナノロッドのＴＥＭ像及びＨＲ−ＴＥＭ像を図１及び２に示す。得られたＣｅＯ2ナノロッドは図１及び２から分かるように四角柱構造を有しており、幅が５〜８ｎｍ、長さが３０〜１００ｎｍであった。 The TEM image and HR-TEM image of the CeO 2 nanorod synthesized in this example are shown in FIGS. The obtained CeO 2 nanorods had a quadrangular prism structure as can be seen from FIGS. 1 and 2, and had a width of 5 to 8 nm and a length of 30 to 100 nm.
合成したＣｅＯ2ナノロッドの原子配列の観察及び格子面間隔の測定から、ＣｅＯ2ナノロッド表面の面方位を特定した。図３に、結晶の方向が＜１００＞及び＜１１０＞である方向指数を表したＣｅＯ2ナノロッドのＨＲ−ＴＥＭ像を示す。合成したＣｅＯ2ナノロッドは面心立方構造を有し、格子面間隔が０．２７ｎｍの｛２００｝面及び格子面間隔が０．１９ｎｍの｛２２０｝面がみられ、ＣｅＯ2ナノロッドが四角柱構造を有しており｛１００｝面及び｛１１０｝面からなることが分かった。また、｛１００｝面及び｛１１０｝面からなるＣｅＯ2ナノロッド以外の、｛１１１｝面を多く含む多面体セリア及びキュービックセリア等の不純物セリアが、セリア全体に占める体積含有量は１５％であった。 From the observation of the atomic arrangement of the synthesized CeO 2 nanorods and the measurement of the lattice spacing, the plane orientation of the CeO 2 nanorods surface was specified. FIG. 3 shows HR-TEM images of CeO 2 nanorods representing the direction index where the crystal directions are <100> and <110>. The synthesized CeO 2 nanorod has a face-centered cubic structure, a {200} plane having a lattice spacing of 0.27 nm and a {220} plane having a lattice spacing of 0.19 nm, and the CeO 2 nanorod has a quadrangular prism structure. It was found that it consists of {100} faces and {110} faces. In addition, the volume content of impurity ceria such as polyhedral ceria and cubic ceria containing many {111} faces other than CeO 2 nanorods consisting of {100} faces and {110} faces accounted for 15% of the whole ceria. .
合成したＣｅＯ2ナノロッドへの活性種の担持
次のように、ＣｅＯ2ナノロッドの質量を基準として１．０質量％のＰｔ濃度になるように、含浸法によってＣｅＯ2ナノロッドへＰｔを担持させた。
Synthesized as bearing the following active species to CeO 2 nanorods, so that the Pt concentration of 1.0 wt% based on the weight of the CeO 2 nanorods as a reference, was supported Pt to CeO 2 nanorods by impregnation.
脱イオン水２５０ｍＬに合成したＣｅＯ2ナノロッド５ｇを分散させた担体分散液と、Ｐｔ硝酸溶液とを分散させた分散液とを、ホットスターラーで１５０℃で加熱攪拌して分散媒を除去し、１１０℃で２４時間、乾燥した後、乳鉢で粉砕することによって、ＣｅＯ2ナノロッド担体質量基準で１ｗｔ％のＰｔを担持した触媒粉末を得た。 A carrier dispersion in which 5 g of CeO 2 nanorods synthesized in 250 mL of deionized water and a dispersion in which a Pt nitric acid solution is dispersed are heated and stirred at 150 ° C. with a hot stirrer to remove the dispersion medium. After drying at 24 ° C. for 24 hours, the mixture was pulverized in a mortar to obtain a catalyst powder supporting 1 wt% of Pt on the basis of the CeO 2 nanorod support mass.
（比較例１）
球状ＣｅＯ2への活性種の担持
直径７ｎｍの球状ＣｅＯ2（ナノテック製）に、実施例１と同様に、球状ＣｅＯ2の質量を基準として１．０質量％のＰｔ濃度になるように、含浸法によって球状ＣｅＯ2へＰｔを担持させた。
(Comparative Example 1)
The spherical active species supported diameter 7nm to CeO 2 spherical CeO 2 (manufactured by Nanotech), in the same manner as in Example 1, so that the Pt concentration of 1.0 wt% based on the weight of the spherical CeO 2 as a reference, impregnation Pt was supported on spherical CeO 2 by the method.
脱イオン水２５０ｍＬに球状ＣｅＯ2５ｇを分散させた担体分散液と、Ｐｔ硝酸溶液とを分散させた分散液とを、ホットスターラーで１５０℃で加熱攪拌して分散媒を除去し、１１０℃で２４時間、乾燥した後、乳鉢で粉砕することによって、球状ＣｅＯ2担体質量基準で１ｗｔ％のＰｔを担持した触媒粉末を得た。 A carrier dispersion in which 5 g of spherical CeO 2 is dispersed in 250 mL of deionized water and a dispersion in which a Pt nitric acid solution is dispersed are heated and stirred at 150 ° C. with a hot stirrer to remove the dispersion medium. After drying for 24 hours, the mixture was pulverized in a mortar to obtain catalyst powder supporting 1 wt% of Pt based on the spherical CeO 2 carrier mass.
ＣｅＯ2担体に担持させたＰｔの耐熱性評価
実施例１及び比較例１で得られたＰｔ担持ＣｅＯ2ナノロッド触媒粉末及びＰｔ担持球状ＣｅＯ2触媒粉末を熱処理して、熱処理前後のＰｔの粒径を測定することによって、Ｐｔの粒成長の度合いを比較した。それぞれの触媒を、４００℃、７００℃、及び９００℃で５時間、焼成炉で熱処理した。
Evaluation of heat resistance of Pt supported on CeO 2 carrier The Pt-supported CeO 2 nanorod catalyst powder and the Pt-supported spherical CeO 2 catalyst powder obtained in Example 1 and Comparative Example 1 were heat-treated, and the Pt particle size before and after the heat treatment was obtained. Were measured to compare the degree of Pt grain growth. Each catalyst was heat-treated in a firing furnace at 400 ° C., 700 ° C., and 900 ° C. for 5 hours.
熱処理前及び各温度における熱処理後の各触媒粉末について、ＣＯパルス吸着分析装置（日本ベル製）を用いて、ＣＯの飽和吸着量を測定し、半球モデルによりＰｔの粒径を算出し、比較した。 For each catalyst powder before heat treatment and after heat treatment at each temperature, the saturated adsorption amount of CO was measured using a CO pulse adsorption analyzer (manufactured by Nippon Bell), and the particle size of Pt was calculated and compared using a hemispheric model. .
図４に、熱処理温度と、Ｐｔ担持ＣｅＯ2ナノロッド触媒及びＰｔ担持球状ＣｅＯ2触媒のそれぞれのＰｔ粒径との関係を示す。実施例１で得られたＰｔ担持ＣｅＯ2ナノロッド触媒は、いずれの熱処理温度においても、比較例１のＰｔ担持球状ＣｅＯ2触媒よりも、初期のＰｔ粒径に対して熱処理後のＰｔ粒径が比較的小さく維持されていた。このことから、本発明のＰｔ担持ＣｅＯ2ナノロッド触媒は、高温下において、Ｐｔの粒成長抑制効果が優れていることが分かる。 FIG. 4 shows the relationship between the heat treatment temperature and the Pt particle sizes of the Pt-supported CeO 2 nanorod catalyst and the Pt-supported spherical CeO 2 catalyst. The Pt-supported CeO 2 nanorod catalyst obtained in Example 1 has a Pt particle size after the heat treatment with respect to the initial Pt particle size as compared with the Pt-supported spherical CeO 2 catalyst of Comparative Example 1 at any heat treatment temperature. It was kept relatively small. From this, it can be seen that the Pt-supported CeO 2 nanorod catalyst of the present invention has an excellent effect of suppressing the growth of Pt grains at high temperatures.
これらの結果から、｛１００｝面及び｛１１０｝面からなるＣｅＯ2ナノロッドに活性種となる金属微粒子を担持させた触媒構成とすることによって、活性種の粒成長を抑制することが可能となるため、耐熱性に優れた触媒を得ることができることが分かる。 From these results, it is possible to suppress grain growth of active species by adopting a catalyst configuration in which metal fine particles as active species are supported on CeO 2 nanorods composed of {100} faces and {110} faces. Therefore, it can be seen that a catalyst having excellent heat resistance can be obtained.
Claims (4)
前記担体が、｛１００｝面及び｛１１０｝面からなり｛１１１｝面を含まないＣｅＯ2ナノロッドを含み、前記｛１００｝面及び｛１１０｝面からなり｛１１１｝面を含まないＣｅＯ 2 ナノロッド以外の不純物ＣｅＯ 2 の含有量が、前記担体に含まれるＣｅＯ 2 全体に対して１５体積％以下である、
排ガス浄化用触媒。 An exhaust gas purifying catalyst comprising a carrier and Pt fine particles supported on the carrier,
CeO said carrier free of CeO 2 nanorods only contains made from said {100} plane and {110} plane {111} plane not containing Do Ri {111} plane of {100} plane and {110} plane The content of impurities CeO 2 other than 2 nanorods is 15% by volume or less with respect to the entire CeO 2 contained in the support ,
Exhaust gas purification catalyst.
セリウム塩と水酸化ナトリウム水溶液、水酸化カリウム水溶液、または水酸化カルシウム水溶液とを混合して混合溶液を調製する工程、
前記混合溶液を水熱合成して、｛１００｝面及び｛１１０｝面からなり｛１１１｝面を含まないＣｅＯ2ナノロッドを含み、前記｛１００｝面及び｛１１０｝面からなり｛１１１｝面を含まないＣｅＯ 2 ナノロッド以外の不純物ＣｅＯ 2 の含有量が、ＣｅＯ 2 全体に対して１５体積％以下である前記担体を形成する工程、
水中に前記ＣｅＯ2ナノロッドを含む担体を分散させて担体分散液を調製する工程、
水中に前記Ｐｔ微粒子を分散させてＰｔ微粒子分散液を調製する工程、並びに
前記担体分散液と前記Ｐｔ微粒子分散液とを混合して加熱攪拌することにより、前記ＣｅＯ2ナノロッドを含む担体にＰｔ微粒子を担持させる工程、
を含む、排ガス浄化用触媒の製造方法。 A method for producing an exhaust gas purifying catalyst comprising a carrier and Pt fine particles supported on the carrier,
Mixing a cerium salt with an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution, or an aqueous calcium hydroxide solution to prepare a mixed solution;
The mixture solution was hydrothermal synthesis, {100} viewed including the CeO 2 nanorods containing no Do Ri {111} plane from the plane and {110} plane, made from the {100} plane and {110} plane {111 } The step of forming the support, wherein the content of impurities CeO 2 other than CeO 2 nanorods not containing a surface is 15% by volume or less based on the whole CeO 2 ;
A step of preparing a carrier dispersion by dispersing a carrier containing the CeO 2 nanorods in water;
Preparing a Pt particulate dispersion wherein disperse the Pt particles in water, and by heating and stirring a mixture of said carrier dispersion and the Pt particle dispersion, Pt fine particles in a carrier containing the CeO 2 nanorods A process of supporting
The manufacturing method of the catalyst for exhaust gas purification containing this.
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| JP5798547B2 (en) * | 2012-11-29 | 2015-10-21 | 国立大学法人 名古屋工業大学 | Exhaust gas purification catalyst carrier and catalyst using the same |
| JP5990317B2 (en) * | 2013-02-20 | 2016-09-14 | 恒隆 川口 | Cerium oxide composite particles |
| US9209595B2 (en) * | 2014-01-31 | 2015-12-08 | Asml Netherlands B.V. | Catalytic conversion of an optical amplifier gas medium |
| JP6515419B2 (en) * | 2014-05-27 | 2019-05-22 | 国立大学法人信州大学 | Method of manufacturing metal oxide nanowire and nanowire |
| KR101472255B1 (en) | 2014-06-20 | 2014-12-16 | 한양대학교 산학협력단 | Exhaust gas treatment apparatus |
| CN114713217A (en) * | 2021-04-29 | 2022-07-08 | 上海科技大学 | Modified cerium oxide carrier and modification method thereof, palladium-cerium catalyst and preparation method and application thereof |
| CN115090293A (en) * | 2022-06-29 | 2022-09-23 | 贵州大学 | Core-shell cerium dioxide nanorod supported nickel catalyst and preparation method thereof |
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