JP2009208029A - Crystalline ceria thin film catalyst - Google Patents
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- JP2009208029A JP2009208029A JP2008055797A JP2008055797A JP2009208029A JP 2009208029 A JP2009208029 A JP 2009208029A JP 2008055797 A JP2008055797 A JP 2008055797A JP 2008055797 A JP2008055797 A JP 2008055797A JP 2009208029 A JP2009208029 A JP 2009208029A
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- 239000010409 thin film Substances 0.000 title claims abstract description 133
- CETPSERCERDGAM-UHFFFAOYSA-N ceric oxide Chemical compound O=[Ce]=O CETPSERCERDGAM-UHFFFAOYSA-N 0.000 title claims abstract description 101
- 229910000422 cerium(IV) oxide Inorganic materials 0.000 title claims abstract description 101
- 239000003054 catalyst Substances 0.000 title claims abstract description 54
- 239000013078 crystal Substances 0.000 claims abstract description 84
- 239000000463 material Substances 0.000 claims abstract description 18
- 239000000758 substrate Substances 0.000 claims description 52
- UQSXHKLRYXJYBZ-UHFFFAOYSA-N Iron oxide Chemical compound [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 claims description 14
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 abstract description 26
- 229910002091 carbon monoxide Inorganic materials 0.000 abstract description 26
- 230000010718 Oxidation Activity Effects 0.000 abstract description 14
- 230000003197 catalytic effect Effects 0.000 abstract description 14
- 239000007789 gas Substances 0.000 description 38
- 238000006243 chemical reaction Methods 0.000 description 19
- 230000000052 comparative effect Effects 0.000 description 13
- 238000004519 manufacturing process Methods 0.000 description 12
- 238000010438 heat treatment Methods 0.000 description 11
- 238000000034 method Methods 0.000 description 10
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 8
- 238000005229 chemical vapour deposition Methods 0.000 description 8
- MYMOFIZGZYHOMD-UHFFFAOYSA-N Dioxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 description 7
- 229910001882 dioxygen Inorganic materials 0.000 description 7
- 238000001878 scanning electron micrograph Methods 0.000 description 6
- 239000002245 particle Substances 0.000 description 5
- 239000010453 quartz Substances 0.000 description 5
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 4
- 238000002441 X-ray diffraction Methods 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 4
- 229910052684 Cerium Inorganic materials 0.000 description 3
- GWXLDORMOJMVQZ-UHFFFAOYSA-N cerium Chemical compound [Ce] GWXLDORMOJMVQZ-UHFFFAOYSA-N 0.000 description 3
- 239000010408 film Substances 0.000 description 3
- 230000001678 irradiating effect Effects 0.000 description 3
- 239000002994 raw material Substances 0.000 description 3
- 238000005245 sintering Methods 0.000 description 3
- 238000007740 vapor deposition Methods 0.000 description 3
- 239000004215 Carbon black (E152) Substances 0.000 description 2
- 229910052786 argon Inorganic materials 0.000 description 2
- 239000011324 bead Substances 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 238000011156 evaluation Methods 0.000 description 2
- 229930195733 hydrocarbon Natural products 0.000 description 2
- 150000002430 hydrocarbons Chemical class 0.000 description 2
- 229910044991 metal oxide Inorganic materials 0.000 description 2
- 150000004706 metal oxides Chemical class 0.000 description 2
- 229910052697 platinum Inorganic materials 0.000 description 2
- 239000004065 semiconductor Substances 0.000 description 2
- 238000003980 solgel method Methods 0.000 description 2
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 1
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 1
- 239000000919 ceramic Substances 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
- 229910052804 chromium Inorganic materials 0.000 description 1
- 239000011651 chromium Substances 0.000 description 1
- 229910052878 cordierite Inorganic materials 0.000 description 1
- JSKIRARMQDRGJZ-UHFFFAOYSA-N dimagnesium dioxido-bis[(1-oxido-3-oxo-2,4,6,8,9-pentaoxa-1,3-disila-5,7-dialuminabicyclo[3.3.1]nonan-7-yl)oxy]silane Chemical compound [Mg++].[Mg++].[O-][Si]([O-])(O[Al]1O[Al]2O[Si](=O)O[Si]([O-])(O1)O2)O[Al]1O[Al]2O[Si](=O)O[Si]([O-])(O1)O2 JSKIRARMQDRGJZ-UHFFFAOYSA-N 0.000 description 1
- KZHJGOXRZJKJNY-UHFFFAOYSA-N dioxosilane;oxo(oxoalumanyloxy)alumane Chemical compound O=[Si]=O.O=[Si]=O.O=[Al]O[Al]=O.O=[Al]O[Al]=O.O=[Al]O[Al]=O KZHJGOXRZJKJNY-UHFFFAOYSA-N 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
- 239000010419 fine particle Substances 0.000 description 1
- 239000006260 foam Substances 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 229910052863 mullite Inorganic materials 0.000 description 1
- WWZKQHOCKIZLMA-UHFFFAOYSA-N octanoic acid Chemical compound CCCCCCCC(O)=O WWZKQHOCKIZLMA-UHFFFAOYSA-N 0.000 description 1
- 125000002524 organometallic group Chemical group 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- 239000008188 pellet Substances 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 description 1
- 229910010271 silicon carbide Inorganic materials 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
- 229910001220 stainless steel Inorganic materials 0.000 description 1
- 239000010935 stainless steel Substances 0.000 description 1
- 239000010936 titanium Substances 0.000 description 1
- 229910052719 titanium Inorganic materials 0.000 description 1
- 239000011800 void material Substances 0.000 description 1
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- Exhaust Gas After Treatment (AREA)
- Exhaust Gas Treatment By Means Of Catalyst (AREA)
- Catalysts (AREA)
Abstract
Description
本発明は、結晶性セリア薄膜触媒に関する。 The present invention relates to a crystalline ceria thin film catalyst.
基材にセリア等の金属酸化物の薄膜を形成する方法として、一般的にはゾルゲル法や化学的気相成長法（ＣＶＤ法）が採用されている。例えば、特開２００４−２１７９７３号公報（特許文献１）には、粒径１〜１００ｎｍの微小粒子を気相中に導入しながら化学的気相成長法によって薄膜を形成する薄膜形成方法が開示されている。 In general, a sol-gel method or a chemical vapor deposition method (CVD method) is employed as a method for forming a thin film of a metal oxide such as ceria on a substrate. For example, Japanese Patent Application Laid-Open No. 2004-217773 (Patent Document 1) discloses a thin film forming method for forming a thin film by chemical vapor deposition while introducing fine particles having a particle diameter of 1 to 100 nm into the gas phase. ing.
しかしながら、特許文献１に記載のような化学的気相成長法やゾルゲル法といった従来一般的に採用されている薄膜形成方法により薄膜を形成する場合には、薄膜中の金属酸化物の結晶構造といった微細構造を制御することが困難であるという問題があった。また、これらの薄膜形成方法によりセリア薄膜を形成した場合には、薄膜中のセリアの結晶構造を十分に制御することができず、例えば一酸化炭素（ＣＯ）酸化活性を有するようなセリア薄膜を得ることはできなかった。
本発明は、上記従来技術の有する課題に鑑みてなされたものであり、一酸化炭素酸化活性といった触媒活性を有し、しかも十分な熱安定性を有しているため高温（例えば、６００℃以上）の排ガス中でも使用することが可能な結晶性セリア薄膜触媒を提供することを目的とする。 The present invention has been made in view of the above-described problems of the prior art, has catalytic activity such as carbon monoxide oxidation activity, and has sufficient thermal stability, and thus has a high temperature (for example, 600 ° C. or higher). It is an object of the present invention to provide a crystalline ceria thin film catalyst that can be used even in exhaust gas.
本発明者らは、上記目的を達成すべく鋭意研究を重ねた結果、化学的気相成長法によりセリア薄膜を形成する方法において、基材を予め特定の温度に保持し且つ基材に特定の強度のレーザー光を照射しつつ、特定の圧力下において基材上にセリアの蒸着膜を形成することにより、基材の表面に形成されたセリアを主成分とする結晶からなる薄膜であって、前記薄膜が前記基材表面から成長してなる柱状結晶からなり、且つ前記薄膜の結晶面の方位が前記基材表面の法線に対して（１００）方向となっている結晶性セリア薄膜触媒が得られ、驚くべきことに、かかる結晶性セリア薄膜触媒が一酸化炭素（ＣＯ）酸化活性といった触媒活性を有し、しかも十分な熱安定性を有していることを見出し、本発明を完成するに至った。 As a result of intensive studies to achieve the above object, the inventors of the present invention have been described in the method of forming a ceria thin film by a chemical vapor deposition method. A thin film composed of crystals mainly composed of ceria formed on the surface of the substrate by irradiating intense laser light and forming a deposited film of ceria on the substrate under a specific pressure, A crystalline ceria thin film catalyst, in which the thin film is formed of columnar crystals grown from the surface of the base material, and the orientation of the crystal plane of the thin film is a (100) direction with respect to the normal line of the base material surface. Surprisingly, the present inventors have found that such a crystalline ceria thin film catalyst has catalytic activity such as carbon monoxide (CO) oxidation activity and sufficient thermal stability, and completes the present invention. It came to.
すなわち、本発明の結晶性セリア薄膜触媒は、基材の表面に形成されたセリアを主成分とする結晶からなる薄膜であって、前記薄膜が前記基材表面から成長してなる柱状結晶からなり、且つ前記薄膜の結晶面の方位が前記基材表面の法線に対して（１００）方向となっていることを特徴とするものである。 That is, the crystalline ceria thin film catalyst of the present invention is a thin film composed of crystals mainly composed of ceria formed on the surface of a substrate, and the thin film is composed of columnar crystals formed from the surface of the substrate. In addition, the orientation of the crystal plane of the thin film is a (100) direction with respect to the normal of the substrate surface.
また、本発明の結晶性セリア薄膜触媒においては、下記の条件（i）〜（iii）のうち少なくとも一つの条件を満たしていることが好ましい。
（i）前記柱状結晶の平均直径が０．１〜１０μｍの範囲内であること。
（ii）前記柱状結晶同士の間に平均間隔が５〜１００ｎｍの空隙が形成されていること。
（iii）前記柱状結晶が（１００）面又は該（１００）面と結晶学的に等価な結晶面を有するものであること。
In the crystalline ceria thin film catalyst of the present invention, it is preferable that at least one of the following conditions (i) to (iii) is satisfied.
(I) The average diameter of the columnar crystals is in the range of 0.1 to 10 μm.
(Ii) Voids having an average interval of 5 to 100 nm are formed between the columnar crystals.
(Iii) The columnar crystal has a (100) plane or a crystallographically equivalent crystal plane to the (100) plane.
さらに、本発明の結晶性セリア薄膜触媒は酸化鉄が担持されているものであってもよい。 Furthermore, the crystalline ceria thin film catalyst of the present invention may be one in which iron oxide is supported.
なお、本発明の結晶性セリア薄膜触媒が一酸化炭素酸化活性といった触媒活性を有し、しかも十分な熱安定性を有しており高温の排ガス中でも使用することが可能なものとなる理由は必ずしも定かではないが、本発明者らは以下のように推察する。すなわち、本発明の結晶性セリア薄膜触媒においては、基材の表面から成長してなる柱状結晶が配列することによりセリア薄膜が構成されている。そして、このような柱状結晶とは基材の表面から一定の方向に結晶が成長することにより形成される柱状の結晶のことをいうが、前記柱状結晶は通常触媒担体に用いるセリア系粒子と比較して大きいものであり、前記柱状結晶における柱の直径（太さ）も前記セリア系粒子の粒子径の１０倍以上の大きさがある。そのため、柱状結晶の熱安定性は通常のセリア系粒子の結晶と比較して高くなる。さらに、本発明の結晶性セリア薄膜触媒は前記柱状結晶が配列することにより構成されているため、前記柱状結晶同士の間には空隙が形成されることになる。そのため、本発明の結晶性セリア薄膜触媒においては、セリア結晶同士の間で焼結が進みにくく、熱安定性が優れるものと本発明者らは推察する。 The reason why the crystalline ceria thin film catalyst of the present invention has catalytic activity such as carbon monoxide oxidation activity and has sufficient thermal stability and can be used even in high-temperature exhaust gas is not necessarily the reason. Although not certain, the present inventors speculate as follows. That is, in the crystalline ceria thin film catalyst of the present invention, the ceria thin film is configured by arranging columnar crystals grown from the surface of the substrate. Such a columnar crystal refers to a columnar crystal formed by growing a crystal in a certain direction from the surface of the substrate. The columnar crystal is compared with ceria-based particles usually used for a catalyst carrier. The diameter (thickness) of the column in the columnar crystal is 10 times or more the particle diameter of the ceria-based particle. Therefore, the thermal stability of the columnar crystal is higher than that of a normal ceria-based particle crystal. Furthermore, since the crystalline ceria thin film catalyst of the present invention is formed by arranging the columnar crystals, voids are formed between the columnar crystals. For this reason, in the crystalline ceria thin film catalyst of the present invention, the inventors speculate that sintering does not easily proceed between ceria crystals and that the thermal stability is excellent.
また、本発明の結晶性セリア薄膜触媒においては、セリア薄膜の結晶面の方位が前記基材表面の法線に対して（１００）方向となっている。そして、このようにセリア薄膜の結晶面の方位が前記基材表面の法線に対して（１００）方向となっている場合には、前記柱状結晶が（１００）面のようにエネルギー的に不安定な結晶面を有しているものとなるため、本発明の結晶性セリア薄膜触媒は一酸化炭素酸化活性といった触媒活性を有するものと本発明者らは推察する。さらに、本発明の結晶性セリア薄膜触媒は、直接レーザー光の照射が届かないハニカム基材の孔内においても基材表面から略垂直方向に前記柱状結晶が成長してなるものであり、好適なモノリス型触媒を形成することが可能なものである。 In the crystalline ceria thin film catalyst of the present invention, the orientation of the crystal face of the ceria thin film is the (100) direction with respect to the normal of the substrate surface. When the orientation of the crystal plane of the ceria thin film is in the (100) direction with respect to the normal of the substrate surface, the columnar crystal is not energetic as in the (100) plane. The inventors speculate that the crystalline ceria thin film catalyst of the present invention has catalytic activity such as carbon monoxide oxidation activity because it has a stable crystal face. Furthermore, the crystalline ceria thin film catalyst of the present invention is such that the columnar crystals grow in a substantially vertical direction from the surface of the substrate even in the holes of the honeycomb substrate that cannot be directly irradiated with laser light. A monolithic catalyst can be formed.
本発明によれば、一酸化炭素酸化活性といった触媒活性を有し、しかも十分な熱安定性を有しているため高温の排ガス中でも使用することが可能な結晶性セリア薄膜触媒を提供することが可能となる。 According to the present invention, it is possible to provide a crystalline ceria thin film catalyst that has catalytic activity such as carbon monoxide oxidation activity and has sufficient thermal stability, and can be used even in high-temperature exhaust gas. It becomes possible.
以下、本発明をその好適な実施形態に即して詳細に説明する。 Hereinafter, the present invention will be described in detail with reference to preferred embodiments thereof.
先ず、本発明の結晶性セリア薄膜触媒について説明する。すなわち、本発明の結晶性セリア薄膜触媒は、基材の表面に形成されたセリアを主成分とする結晶からなる薄膜であって、前記薄膜が前記基材表面から成長してなる柱状結晶からなり、且つ前記薄膜の結晶面の方位が前記基材表面の法線に対して（１００）方向となっていることを特徴とするものである。 First, the crystalline ceria thin film catalyst of the present invention will be described. That is, the crystalline ceria thin film catalyst of the present invention is a thin film composed of crystals mainly composed of ceria formed on the surface of a substrate, and the thin film is composed of columnar crystals formed from the surface of the substrate. In addition, the orientation of the crystal plane of the thin film is a (100) direction with respect to the normal of the substrate surface.
本発明において用いる基材としては、耐熱性を有する基材であればよく、特に限定されない。このような基材は、触媒の用途等に応じて適宜選択されるが、排ガス浄化用触媒等として用いる場合は、モノリス担体基材（ハニカムフィルタ、高密度ハニカム等）、フォームフィルタ基材、ペレット状基材、プレート状基材等が好適に採用される。また、このような基材の材質も特に制限されないが、排ガス浄化用触媒等として用いる場合は、コージエライト、炭化ケイ素、ムライト、アルミナ、チタン、シリカ、石英ガラス等のセラミックスからなる基材や、クロム及びアルミニウムを含むステンレススチール等の金属からなる基材が好適に採用される。 The substrate used in the present invention is not particularly limited as long as it is a substrate having heat resistance. Such a substrate is appropriately selected depending on the use of the catalyst, etc., but when used as an exhaust gas purifying catalyst or the like, a monolith support substrate (honeycomb filter, high density honeycomb, etc.), foam filter substrate, pellet A plate-like substrate, a plate-like substrate and the like are preferably employed. The material of such a substrate is not particularly limited, but when used as an exhaust gas purifying catalyst, a substrate made of ceramics such as cordierite, silicon carbide, mullite, alumina, titanium, silica, quartz glass, chromium, etc. In addition, a substrate made of a metal such as stainless steel including aluminum is preferably used.
本発明にかかる柱状結晶とは、前記基材の表面から一定の方向に結晶が成長することにより形成される柱状の結晶のことをいう。また、このような柱状結晶はセリアを主成分とするものであり、セリアを５０質量％以上（好ましくは８０質量％以上）含有するものであることが好ましい。さらに、このような柱状結晶は、（１００）面又は該（１００）面と結晶学的に等価な結晶面を有するものであることが好ましい。このように柱状結晶が（１００）面のようにエネルギー的に不安定な結晶面を有しているものである場合には、結晶の表面における触媒活性が高まる傾向にある。 The columnar crystal according to the present invention refers to a columnar crystal formed by growing a crystal in a certain direction from the surface of the substrate. Such columnar crystals are mainly composed of ceria, and preferably contain ceria at 50% by mass or more (preferably 80% by mass or more). Further, such a columnar crystal preferably has a (100) plane or a crystal plane crystallographically equivalent to the (100) plane. Thus, when the columnar crystal has an energetically unstable crystal plane such as the (100) plane, the catalytic activity on the surface of the crystal tends to increase.
このような柱状結晶における柱の直径（太さ）は０．１〜１０μｍの範囲内（好ましくは０．２〜５μｍ）であることが好ましい。柱状結晶の太さが前記下限未満では、得られるセリア薄膜触媒の熱安定性が低下する傾向にあり、他方、前記上限を超えると、ガスと接触する結晶の表面積が小さくなるため、得られるセリア薄膜触媒の触媒活性が低下する傾向にある。 The diameter (thickness) of the column in such a columnar crystal is preferably in the range of 0.1 to 10 μm (preferably 0.2 to 5 μm). If the thickness of the columnar crystal is less than the lower limit, the thermal stability of the resulting ceria thin film catalyst tends to be reduced. On the other hand, if the thickness exceeds the upper limit, the surface area of the crystal in contact with the gas is reduced, so that the obtained ceria is obtained. The catalytic activity of the thin film catalyst tends to decrease.
本発明の結晶性セリア薄膜触媒は、前記基材表面から成長してなる柱状結晶が配列することにより構成される。このように結晶性セリア薄膜触媒は前記柱状結晶が配列することにより構成されているため、前記柱状結晶同士の間には空隙が形成されることになる。このような結晶性セリア薄膜触媒においては、前記柱状結晶同士の間に平均間隔が５〜１００ｎｍの空隙が形成されていることが好ましい。このような空隙の存在によってセリア結晶同士の間で焼結が進みにくくなるため、得られる結晶性セリア薄膜触媒における熱安定性が向上する傾向にある。 The crystalline ceria thin film catalyst of the present invention is configured by arranging columnar crystals grown from the substrate surface. Thus, since the crystalline ceria thin film catalyst is formed by arranging the columnar crystals, voids are formed between the columnar crystals. In such a crystalline ceria thin film catalyst, it is preferable that voids having an average interval of 5 to 100 nm are formed between the columnar crystals. Since the presence of such voids makes it difficult for sintering to proceed between the ceria crystals, the thermal stability of the obtained crystalline ceria thin film catalyst tends to be improved.
また、本発明の結晶性セリア薄膜触媒においては、薄膜の結晶面の方位が前記基材表面の法線に対して（１００）方向となっていることが必要である。薄膜の結晶面の方位が前記方向以外である場合には、一酸化炭素酸化活性といった触媒活性が不十分なものとなる。薄膜の結晶面とは、薄膜を構成する原子が規則的に配列している面のことをいい、薄膜の結晶面の方位とは、このような結晶面の法線方向を面指数（ミラー指数）で表した方位のことをいう。そして、基材表面の法線に対する薄膜の結晶面の方位とは、基材表面の法線を（１００）方向とした場合における薄膜の結晶面の方位のことをいう。このような薄膜の結晶面の方位は、Ｘ線回折装置を用いて薄膜のＸ線回折パターンを測定し、そのＸ線回折パターンから解析することができる。 In the crystalline ceria thin film catalyst of the present invention, it is necessary that the orientation of the crystal plane of the thin film is the (100) direction with respect to the normal of the substrate surface. When the orientation of the crystal plane of the thin film is other than the above direction, the catalytic activity such as carbon monoxide oxidation activity becomes insufficient. The crystal plane of a thin film refers to a plane in which atoms constituting the thin film are regularly arranged. The orientation of the crystal plane of the thin film refers to the normal direction of such a crystal plane as a plane index (Miller index). ) Refers to the orientation represented. The orientation of the crystal plane of the thin film with respect to the normal of the substrate surface refers to the orientation of the crystal plane of the thin film when the normal of the substrate surface is the (100) direction. The orientation of the crystal plane of such a thin film can be analyzed from the X-ray diffraction pattern obtained by measuring the X-ray diffraction pattern of the thin film using an X-ray diffractometer.
本発明の結晶性セリア薄膜触媒の厚みは特に限定されないが、１〜５０μｍ（好ましくは５〜２０μｍ）であることが好ましい。薄膜の厚みが前記下限未満では、有効な結晶面の配向制御が十分に行えないため、得られるセリア薄膜触媒の一酸化炭素酸化活性といった触媒活性が低下する傾向にあり、他方、前記上限を超える場合には、触媒活性への寄与の程度が低い基材側に存在する結晶の割合が増えることから触媒活性の更なる向上は見込めないものの、例えばハニカム基材上に薄膜を形成したときにガスの通過する断面積が増えるため圧力損失が大きくなる傾向にある。 Although the thickness of the crystalline ceria thin film catalyst of this invention is not specifically limited, It is preferable that it is 1-50 micrometers (preferably 5-20 micrometers). If the thickness of the thin film is less than the lower limit, the orientation of the effective crystal plane cannot be sufficiently controlled, so that the catalytic activity such as the carbon monoxide oxidation activity of the resulting ceria thin film catalyst tends to decrease, and on the other hand, exceeds the upper limit. In this case, since the ratio of crystals existing on the substrate side having a low degree of contribution to the catalyst activity increases, further improvement in the catalyst activity cannot be expected, but for example, a gas is formed when a thin film is formed on the honeycomb substrate. Since the cross-sectional area through which the gas passes increases, the pressure loss tends to increase.
さらに、本発明の結晶性セリア薄膜触媒は酸化鉄が担持されているものであってもよい。このように、薄膜の表面や柱状結晶同士の間に形成されている空隙部に触媒活性点としての酸化鉄が担持されることにより、薄膜触媒の触媒活性をさらに向上させることができ、低温域（例えば１５０〜３００℃）においても高い一酸化炭素（ＣＯ）酸化活性や炭化水素（ＨＣ）酸化活性を達成することができる。このような酸化鉄の担持量は、前記基材の単位面積１ｍ３に対して１〜１０ｇの範囲であることが好ましい。酸化鉄の担持量が前記下限未満では触媒活性を向上させるという効果が不十分となる傾向にあり、他方、前記上限を超えて酸化鉄を担持しても活性が飽和する傾向にある。 Furthermore, the crystalline ceria thin film catalyst of the present invention may be one in which iron oxide is supported. Thus, the iron oxide as a catalytic active point is supported in the void formed between the surface of the thin film or between the columnar crystals, so that the catalytic activity of the thin film catalyst can be further improved, and the low temperature region High carbon monoxide (CO) oxidation activity and hydrocarbon (HC) oxidation activity can be achieved even at (for example, 150 to 300 ° C.). The amount of iron oxide supported is preferably in the range of 1 to 10 g per unit area of 1 m 3 of the base material. If the amount of iron oxide supported is less than the lower limit, the effect of improving the catalytic activity tends to be insufficient, while the activity tends to be saturated even if iron oxide is supported exceeding the upper limit.
次に、本発明の結晶性セリア薄膜触媒を製造する方法について説明する。本発明の結晶性セリア薄膜触媒は、例えば、化学的気相成長法（ＣＶＤ法）によりセリア薄膜を形成する方法において、基材を予め特定の温度に保持し且つ基材に特定の強度のレーザー光を照射しつつ、特定の圧力下において基材上にセリアの蒸着膜を形成することにより製造することができる。 Next, a method for producing the crystalline ceria thin film catalyst of the present invention will be described. The crystalline ceria thin film catalyst of the present invention is a method for forming a ceria thin film by, for example, chemical vapor deposition (CVD). It can be manufactured by forming a deposited film of ceria on a substrate under a specific pressure while irradiating light.
このような方法におけるセリア薄膜の材料としては、ＣＶＤ法において用いることが可能なものであればよく、例えば、セリウムのジピバロイルメタナト錯体〔Ｃｅ（ｄｐｍ）４錯体〕、酢酸セリウム〔Ｃｅ（Ｃ２Ｈ５Ｏ２）３・ｎＨ２Ｏ〕、オクチル酸セリウム〔Ｃｅ（Ｃ８Ｈ１５Ｏ２）３〕等のセリウムを含有する有機金属錯体が挙げられる。 The material for the ceria thin film in such a method may be any material that can be used in the CVD method. For example, a cerium dipivaloylmethanato complex [Ce (dpm) 4 complex], cerium acetate [Ce ( Examples thereof include organometallic complexes containing cerium such as C 2 H 5 O 2 ) 3 · nH 2 O] and cerium octylate [Ce (C 8 H 15 O 2 ) 3 ].
このように蒸着膜を形成する蒸着装置としては、大気を遮断して特定のガスを基材近傍に流通させることができ、また反応後のガスを一定の圧力を維持したまま排出することができる装置を適宜使用でき、具体的には特に限定されず、公知の蒸着装置を使用することができる。 As a vapor deposition apparatus for forming a vapor deposition film in this way, the atmosphere can be shut off and a specific gas can be circulated in the vicinity of the substrate, and the gas after the reaction can be discharged while maintaining a constant pressure. An apparatus can be used as appropriate, and is not particularly limited, and a known vapor deposition apparatus can be used.
本発明の結晶性セリア薄膜触媒は、例えば、図１に示す製造装置を用いることにより製造することができる。以下、本発明の結晶性セリア薄膜触媒を製造する方法をより詳細に説明するために、図面を参照しながら、本発明の結晶性セリア薄膜触媒を製造するために好適に用いることが可能な製造装置の一実施形態について説明する。なお、以下の説明及び図面中、同一又は相当する要素には同一の符号を付し、重複する説明は省略する。 The crystalline ceria thin film catalyst of the present invention can be produced, for example, by using the production apparatus shown in FIG. Hereinafter, in order to explain the method for producing the crystalline ceria thin film catalyst of the present invention in more detail, the production that can be suitably used for producing the crystalline ceria thin film catalyst of the present invention with reference to the drawings. An embodiment of the apparatus will be described. In the following description and drawings, the same or corresponding elements are denoted by the same reference numerals, and duplicate descriptions are omitted.
図１は、本発明の結晶性セリア薄膜触媒を製造するのに好適な製造装置の一例を示す模式図である。図１に示す製造装置は、原料ガス供給管１と、酸素ガス供給管２と、反応炉３と、基材加熱ステージ４と、レーザー５と、ガス排出管６とを備えている。また、このような製造装置においては、圧力調整機（例えばバックプレッシャーレギュレーター）によって反応炉３内の圧力の調整が可能となっている。 FIG. 1 is a schematic view showing an example of a production apparatus suitable for producing the crystalline ceria thin film catalyst of the present invention. The manufacturing apparatus shown in FIG. 1 includes a source gas supply pipe 1, an oxygen gas supply pipe 2, a reaction furnace 3, a substrate heating stage 4, a laser 5, and a gas discharge pipe 6. Moreover, in such a manufacturing apparatus, the pressure in the reaction furnace 3 can be adjusted by a pressure regulator (for example, a back pressure regulator).
このような原料ガス供給管１、酸素ガス供給管２及びガス排出管としては特に制限されず、原料ガス等を所定の速度で供給又は排出することが可能なものを適宜利用できる。また、基材加熱ステージ４は、基材を１００〜８００℃の温度に保持することが可能なものであればよく、特に制限されない。このような基材加熱ステージ４としては、公知の加熱装置を適宜利用することができる。さらに、レーザー５としては、公知のレーザーを適宜利用でき、例えば、半導体レーザー、Ｎｄ−ＹＡＧレーザー、ＣＯ２レーザーを用いることができる。また、レーザー５としては、発光波長が６００〜１００００ｎｍのものを用いることが好ましい。 Such raw material gas supply pipe 1, oxygen gas supply pipe 2 and gas discharge pipe are not particularly limited, and those capable of supplying or discharging the raw material gas at a predetermined speed can be used as appropriate. Moreover, the base material heating stage 4 should just be a thing which can hold | maintain a base material at the temperature of 100-800 degreeC, and is not restrict | limited in particular. As such a substrate heating stage 4, a known heating apparatus can be used as appropriate. Further, as the laser 5 can be appropriately using known laser, for example, a semiconductor laser, Nd-YAG laser, CO 2 laser. Moreover, as the laser 5, it is preferable to use a laser whose emission wavelength is 600 to 10,000 nm.
このような図１に示す製造装置を用いて、例えば以下に示すようにして本発明の結晶性セリア薄膜触媒を製造することができる。すなわち、先ず、基材加熱ステージ４に基材を配置し、基材の温度が２００〜１０００℃となるように基材加熱ステージ４の温度を調整する。基材の温度が前記下限未満では、薄膜を成膜することが困難となる傾向にあり、他方、前記上限を超えると、結晶が無配向で且つ空隙が形成されず緻密な薄膜となりやすい傾向にある。 Using the production apparatus shown in FIG. 1, for example, the crystalline ceria thin film catalyst of the present invention can be produced as follows. That is, first, a base material is arranged on the base material heating stage 4, and the temperature of the base material heating stage 4 is adjusted so that the temperature of the base material becomes 200 to 1000 ° C. If the temperature of the substrate is less than the lower limit, it tends to be difficult to form a thin film. On the other hand, if the temperature exceeds the upper limit, crystals tend to be non-oriented and voids are not formed, resulting in a dense thin film. is there.
次に、原料ガス供給管１から温度１５０〜３００℃に加熱して気化させたＣｅ（ｄｐｍ）４錯体とアルゴンガスとを反応炉３内に供給すると共に、酸素ガス供給管２から酸素ガスを反応炉３内に供給し、反応炉３内においてこれらのガスを混合せしめる。 Next, the Ce (dpm) 4 complex vaporized by heating to a temperature of 150 to 300 ° C. from the source gas supply pipe 1 and the argon gas are supplied into the reaction furnace 3, and oxygen gas is supplied from the oxygen gas supply pipe 2. The gas is supplied into the reaction furnace 3 and these gases are mixed in the reaction furnace 3.
そして、圧力調整機により反応炉３内の圧力を０．１〜３ｋＰａに保持し、また、これらの混合ガスにレーザー５を用いて基材に対して３０〜７５°の方向からレーザー光を照射しながら、セリア薄膜を形成せしめることによって本発明の結晶性セリア薄膜触媒を得ることができる。なお、反応炉３内の圧力が前記下限未満では、薄膜を成膜することが困難となる傾向にあり、他方、前記上限を超えると、結晶が無配向な薄膜となりやすい傾向にある。また、レーザー光の出力は２０〜２００Ｗとすることが好ましい。レーザー光の出力が前記下限未満では、結晶が無配向な薄膜となりやすい傾向にあり、他方、前記上限を超えると、結晶が無配向な薄膜となりやすい傾向にある。 And the pressure in the reaction furnace 3 is kept at 0.1 to 3 kPa by a pressure regulator, and laser light is irradiated from 30 to 75 ° with respect to the substrate using a laser 5 for these mixed gases. However, the crystalline ceria thin film catalyst of the present invention can be obtained by forming a ceria thin film. When the pressure in the reaction furnace 3 is less than the lower limit, it tends to be difficult to form a thin film. On the other hand, when the pressure exceeds the upper limit, the crystal tends to be a non-oriented thin film. Moreover, it is preferable that the output of a laser beam shall be 20-200W. If the output of the laser beam is less than the lower limit, the crystal tends to be a non-oriented thin film, whereas if it exceeds the upper limit, the crystal tends to be a non-oriented thin film.
以下、実施例及び比較例に基づいて本発明をより具体的に説明するが、本発明は以下の実施例に限定されるものではない。 EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.
（実施例１）
前述の図１に示す製造装置を用いて結晶性セリア薄膜を製造した。すなわち、先ず、基材（材質：石英、大きさ：１５ｍｍ×１０ｍｍ×１ｍｍ）を図１に示す製造装置の基材加熱ステージ４上に配置し、基材の温度が４００℃となるように基材加熱ステージ４の温度を調整した。そして、原料ガス供給管１から温度２４０℃に加熱して気化させたＣｅ（ｄｐｍ）４錯体とアルゴンガスとを反応炉３内に供給すると共に、酸素ガス供給管２から酸素ガスを反応炉３内に供給し、反応炉３内においてこれらのガスを混合せしめた。そして、圧力調整機により反応炉３内の圧力を０．８ｋＰａに保持し、また、これらの混合ガスにレーザー５（半導体レーザー、発光波長：８０８ｎｍ、レーザー出力：１５０Ｗ）を用いて基材に対して４５°の方向からレーザー光を照射しながら、セリア薄膜を形成せしめて結晶性セリア薄膜を得た。
Example 1
A crystalline ceria thin film was manufactured using the manufacturing apparatus shown in FIG. That is, first, a substrate (material: quartz, size: 15 mm × 10 mm × 1 mm) is placed on the substrate heating stage 4 of the manufacturing apparatus shown in FIG. 1, and the substrate temperature is set to 400 ° C. The temperature of the material heating stage 4 was adjusted. Then, the Ce (dpm) 4 complex vaporized by heating to a temperature of 240 ° C. from the source gas supply pipe 1 and the argon gas are supplied into the reaction furnace 3, and oxygen gas is supplied from the oxygen gas supply pipe 2 to the reaction furnace 3. And these gases were mixed in the reactor 3. And the pressure in the reaction furnace 3 is kept at 0.8 kPa by a pressure regulator, and laser 5 (semiconductor laser, emission wavelength: 808 nm, laser output: 150 W) is used for these mixed gases with respect to the substrate. A ceria thin film was formed while irradiating laser light from a direction of 45 ° to obtain a crystalline ceria thin film.
ＳＥＭ（走査型電子顕微鏡）を用い、得られた結晶性セリア薄膜の表面及び断面の形態を観察した。結晶性セリア薄膜の表面及び断面のＳＥＭ写真を図２及び図３にそれぞれ示す。図２及び図３に示すように、得られた結晶性セリア薄膜触媒は柱状結晶の間に微小な空隙が形成されているものであるため、結晶間での焼結が生じにくいものであることが確認された。また、得られた結晶性セリア薄膜の厚みは２０μｍであった。さらに、得られた結晶性セリア薄膜における任意の２０個の柱状結晶を観察し、柱状結晶の平均直径及び柱状結晶同士の間の平均間隔について確認した。その結果、柱状結晶の平均直径は０．８μｍであり、０．１〜１０μｍの範囲内であることが確認された。また、柱状結晶同士の間の平均間隔は５０ｎｍであり、５〜１００ｎｍの範囲内であることが確認された。 Using SEM (scanning electron microscope), the surface and cross-sectional morphology of the obtained crystalline ceria thin film were observed. SEM photographs of the surface and cross section of the crystalline ceria thin film are shown in FIGS. 2 and 3, respectively. As shown in FIGS. 2 and 3, since the obtained crystalline ceria thin film catalyst has minute voids formed between columnar crystals, it is difficult to cause sintering between crystals. Was confirmed. Further, the thickness of the obtained crystalline ceria thin film was 20 μm. Furthermore, arbitrary 20 columnar crystals in the obtained crystalline ceria thin film were observed, and the average diameter of the columnar crystals and the average interval between the columnar crystals were confirmed. As a result, it was confirmed that the average diameter of the columnar crystals was 0.8 μm and was within the range of 0.1 to 10 μm. Moreover, it was confirmed that the average space | interval between columnar crystals is 50 nm, and exists in the range of 5-100 nm.
（比較例１）
反応炉３内の圧力を０．６ｋＰａに保持した以外は実施例１と同様にして結晶性セリア薄膜を得た。ＳＥＭ（走査型電子顕微鏡）を用い、得られた結晶性セリア薄膜の表面及び断面の形態を観察した。結晶性セリア薄膜の表面及び断面のＳＥＭ写真を図４及び図５にそれぞれ示す。得られた結晶性セリア薄膜の厚みは１５μｍであった。
(Comparative Example 1)
A crystalline ceria thin film was obtained in the same manner as in Example 1 except that the pressure in the reaction furnace 3 was maintained at 0.6 kPa. Using SEM (scanning electron microscope), the surface and cross-sectional morphology of the obtained crystalline ceria thin film were observed. SEM photographs of the surface and cross section of the crystalline ceria thin film are shown in FIGS. 4 and 5, respectively. The thickness of the obtained crystalline ceria thin film was 15 μm.
（比較例２）
反応炉３内の圧力を０．４ｋＰａに保持した以外は実施例１と同様にして結晶性セリア薄膜を得た。ＳＥＭ（走査型電子顕微鏡）を用い、得られた結晶性セリア薄膜の表面及び断面の形態を観察した。結晶性セリア薄膜の表面及び断面のＳＥＭ写真を図６及び図７にそれぞれ示す。得られた結晶性セリア薄膜の厚みは１０μｍであった。
(Comparative Example 2)
A crystalline ceria thin film was obtained in the same manner as in Example 1 except that the pressure in the reaction furnace 3 was maintained at 0.4 kPa. Using SEM (scanning electron microscope), the surface and cross-sectional morphology of the obtained crystalline ceria thin film were observed. SEM photographs of the surface and cross section of the crystalline ceria thin film are shown in FIGS. 6 and 7, respectively. The thickness of the obtained crystalline ceria thin film was 10 μm.
＜薄膜の配向状態の評価＞
Ｘ線回折装置を用い、実施例１及び比較例１〜２で得られた結晶性セリア薄膜のＸ線回折パターンを測定した。得られた結果を図８に示す。図８に示したように、実施例１で得られた結晶性セリア薄膜〔反応炉内の圧力（Ｐｔｏｔ）＝０．８ｋＰａ〕の結晶面の方位は基材表面の法線に対して（１００）方向となっていることが確認された。また、比較例１で得られた結晶性セリア薄膜〔反応炉内の圧力（Ｐｔｏｔ）＝０．６ｋＰａ〕の結晶面の方位は基材表面の法線に対して（３１１）方向となっていることが確認された。さらに、比較例２で得られた結晶性セリア薄膜〔反応炉内の圧力（Ｐｔｏｔ）＝０．４ｋＰａ〕の結晶面の方位は基材表面の法線に対して（１１０）方向となっていることが確認された。
<Evaluation of orientation state of thin film>
Using an X-ray diffractometer, the X-ray diffraction patterns of the crystalline ceria thin films obtained in Example 1 and Comparative Examples 1 and 2 were measured. The obtained result is shown in FIG. As shown in FIG. 8, the orientation of the crystal plane of the crystalline ceria thin film [pressure in reactor (P tot ) = 0.8 kPa] obtained in Example 1 is normal to the surface of the substrate ( 100) direction. Further, the orientation of the crystal plane of the crystalline ceria thin film [pressure in reactor (P tot ) = 0.6 kPa] obtained in Comparative Example 1 is the (311) direction with respect to the normal of the substrate surface. It was confirmed that Furthermore, the orientation of the crystal plane of the crystalline ceria thin film [pressure in reactor (P tot ) = 0.4 kPa] obtained in Comparative Example 2 is the (110) direction with respect to the normal of the substrate surface. It was confirmed that
＜薄膜のＣＯ酸化活性の評価＞
実施例１及び比較例１〜２で得られた結晶性セリア薄膜、並びに石英基材（大きさ：１５ｍｍ×１０ｍｍ×１ｍｍ、参考例１）及び石英基材上に形成された白金薄膜（基材の大きさ：１５ｍｍ×１０ｍｍ×１ｍｍ、白金薄膜の厚み：１０ｎｍ、参考例２）について、以下のようにＣＯ転化率の測定を行い、ＣＯ酸化活性を評価した。すなわち、図９に示すように、ガス供給装置１１と、試料容器１２と、ヒーター１３と、質量分析器１４（ＵＬＶＡＣ社製、製品名「ＭＭＣ−２００」）とを備えているＣＯ転化率測定装置（大倉理研社製、製品名「ＴＰ５１０２ＳＰ」）に試料２０を配置した。なお、このようなＣＯ転化率測定装置おいては、試料容器１２はガス供給装置１１及び質量分析器１４とそれぞれガス管１５により接続されており、試料容器１２内には石英管ビーズ１６が投入されている。また、試料容器１２は熱電対１７を備えている。そして、ＣＯ（２０００ｐｐｍ）、Ｏ２（１０００ｐｐｍ）及びＨｅ（残部）からなるモデルガスを１００ｍｌ／分のガス流量で試料の配置された試料容器１２に供給し、モデルガスの温度を４０分間で１００℃から５００℃に変化させつつ、試料容器１２から排出されるガス中のＣＯ２濃度を質量分析器１４により測定し、それらの測定値からＣＯ転化率を算出した。得られた結果を図１０に示す。図１０に示した結果から明らかなように、薄膜の結晶面の方位が基材表面の法線に対して（１００）方向となっている本発明の結晶性セリア薄膜（実施例１）はＣＯ酸化活性を有していることが確認された。
<Evaluation of CO oxidation activity of thin film>
The crystalline ceria thin film obtained in Example 1 and Comparative Examples 1 and 2, and a quartz substrate (size: 15 mm × 10 mm × 1 mm, Reference Example 1) and a platinum thin film (substrate) formed on the quartz substrate Size: 15 mm × 10 mm × 1 mm, platinum thin film thickness: 10 nm, Reference Example 2), CO conversion was measured as follows, and CO oxidation activity was evaluated. That is, as shown in FIG. 9, CO conversion measurement including a gas supply device 11, a sample container 12, a heater 13, and a mass analyzer 14 (product name “MMC-200” manufactured by ULVAC). The sample 20 was placed in an apparatus (manufactured by Okura Riken Co., Ltd., product name “TP5102SP”). In such a CO conversion rate measuring apparatus, the sample container 12 is connected to the gas supply device 11 and the mass analyzer 14 by the gas pipe 15, and quartz tube beads 16 are placed in the sample container 12. Has been. The sample container 12 is provided with a thermocouple 17. Then, a model gas composed of CO (2000 ppm), O 2 (1000 ppm) and He (remainder) is supplied to the sample container 12 where the sample is arranged at a gas flow rate of 100 ml / min, and the temperature of the model gas is set to 100 for 40 minutes. The CO 2 concentration in the gas discharged from the sample container 12 was measured by the mass analyzer 14 while changing from 0 ° C. to 500 ° C., and the CO conversion rate was calculated from these measured values. The obtained result is shown in FIG. As is clear from the results shown in FIG. 10, the crystalline ceria thin film of the present invention (Example 1) in which the orientation of the crystal plane of the thin film is the (100) direction with respect to the normal of the substrate surface is CO 2. It was confirmed to have oxidative activity.
以上説明したように、本発明によれば、一酸化炭素酸化活性といった触媒活性を有し、しかも十分な熱安定性を有しているため高温の排ガス中でも使用することが可能な結晶性セリア薄膜触媒を提供することが可能となる。 As described above, according to the present invention, a crystalline ceria thin film that has catalytic activity such as carbon monoxide oxidation activity and has sufficient thermal stability and can be used even in high-temperature exhaust gas. A catalyst can be provided.
１…原料ガス供給管、２…酸素ガス供給管、３…反応炉、４…基材加熱ステージ、５…レーザー、６…ガス排出管、１１…ガス供給装置、１２…試料容器、１３…ヒーター、１４…質量分析器、１５…ガス管、１６…石英管ビーズ、１７…熱電対、２０…試料。 DESCRIPTION OF SYMBOLS 1 ... Raw material gas supply pipe, 2 ... Oxygen gas supply pipe, 3 ... Reactor, 4 ... Substrate heating stage, 5 ... Laser, 6 ... Gas discharge pipe, 11 ... Gas supply apparatus, 12 ... Sample container, 13 ... Heater , 14 ... mass analyzer, 15 ... gas tube, 16 ... quartz tube bead, 17 ... thermocouple, 20 ... sample.
Claims (5)
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| CN115770570A (en) * | 2023-01-31 | 2023-03-10 | 中国科学院金属研究所 | Cerium oxide loaded atomic-scale dispersed Pt catalyst and redispersion preparation method thereof |
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