JP7527052B2 - Ammonia synthesis catalyst - Google Patents
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- JP7527052B2 JP7527052B2 JP2023116308A JP2023116308A JP7527052B2 JP 7527052 B2 JP7527052 B2 JP 7527052B2 JP 2023116308 A JP2023116308 A JP 2023116308A JP 2023116308 A JP2023116308 A JP 2023116308A JP 7527052 B2 JP7527052 B2 JP 7527052B2
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- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 title claims description 125
- 239000003054 catalyst Substances 0.000 title claims description 97
- 229910021529 ammonia Inorganic materials 0.000 title claims description 50
- 238000003786 synthesis reaction Methods 0.000 title description 48
- 230000015572 biosynthetic process Effects 0.000 title description 43
- 229910052739 hydrogen Inorganic materials 0.000 claims description 12
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 10
- 238000006243 chemical reaction Methods 0.000 claims description 10
- 239000001257 hydrogen Substances 0.000 claims description 10
- 238000004519 manufacturing process Methods 0.000 claims description 6
- 230000002194 synthesizing effect Effects 0.000 claims description 6
- 229910052757 nitrogen Inorganic materials 0.000 claims description 5
- 125000004435 hydrogen atom Chemical class [H]* 0.000 claims 1
- 229910000422 cerium(IV) oxide Inorganic materials 0.000 description 100
- CETPSERCERDGAM-UHFFFAOYSA-N ceric oxide Chemical compound O=[Ce]=O CETPSERCERDGAM-UHFFFAOYSA-N 0.000 description 70
- 230000000694 effects Effects 0.000 description 54
- 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 34
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 description 27
- 239000007864 aqueous solution Substances 0.000 description 27
- 239000000243 solution Substances 0.000 description 15
- 238000001354 calcination Methods 0.000 description 14
- 238000000034 method Methods 0.000 description 14
- 229910002651 NO3 Inorganic materials 0.000 description 12
- 229910000069 nitrogen hydride Inorganic materials 0.000 description 12
- KRKNYBCHXYNGOX-UHFFFAOYSA-N citric acid Chemical compound OC(=O)CC(O)(C(O)=O)CC(O)=O KRKNYBCHXYNGOX-UHFFFAOYSA-N 0.000 description 10
- 239000011777 magnesium Substances 0.000 description 10
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 9
- 238000002156 mixing Methods 0.000 description 8
- 239000012299 nitrogen atmosphere Substances 0.000 description 8
- 239000011148 porous material Substances 0.000 description 8
- 239000000203 mixture Substances 0.000 description 7
- 239000002244 precipitate Substances 0.000 description 7
- 230000001376 precipitating effect Effects 0.000 description 7
- 238000001556 precipitation Methods 0.000 description 7
- 238000002360 preparation method Methods 0.000 description 7
- 229910002788 Ru-CeO2 Inorganic materials 0.000 description 6
- 230000002378 acidificating effect Effects 0.000 description 6
- 125000002915 carbonyl group Chemical group [*:2]C([*:1])=O 0.000 description 5
- 150000002431 hydrogen Chemical class 0.000 description 5
- 239000000463 material Substances 0.000 description 5
- YLPJWCDYYXQCIP-UHFFFAOYSA-N nitroso nitrate;ruthenium Chemical compound [Ru].[O-][N+](=O)ON=O YLPJWCDYYXQCIP-UHFFFAOYSA-N 0.000 description 5
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 4
- WYURNTSHIVDZCO-UHFFFAOYSA-N Tetrahydrofuran Chemical compound C1CCOC1 WYURNTSHIVDZCO-UHFFFAOYSA-N 0.000 description 4
- 239000003929 acidic solution Substances 0.000 description 4
- 230000003197 catalytic effect Effects 0.000 description 4
- 238000000975 co-precipitation Methods 0.000 description 4
- 238000011068 loading method Methods 0.000 description 4
- YIXJRHPUWRPCBB-UHFFFAOYSA-N magnesium nitrate Chemical compound [Mg+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O YIXJRHPUWRPCBB-UHFFFAOYSA-N 0.000 description 4
- 239000011800 void material Substances 0.000 description 4
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 4
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 description 3
- 150000001875 compounds Chemical class 0.000 description 3
- 239000012153 distilled water Substances 0.000 description 3
- 239000000126 substance Substances 0.000 description 3
- NSNVGCNCRLAWOJ-UHFFFAOYSA-N [N+](=O)([O-])[O-].N(=O)[Ru+2].[N+](=O)([O-])[O-] Chemical compound [N+](=O)([O-])[O-].N(=O)[Ru+2].[N+](=O)([O-])[O-] NSNVGCNCRLAWOJ-UHFFFAOYSA-N 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 238000005470 impregnation Methods 0.000 description 2
- 239000004570 mortar (masonry) Substances 0.000 description 2
- 239000000843 powder Substances 0.000 description 2
- 239000002994 raw material Substances 0.000 description 2
- 229910052707 ruthenium Inorganic materials 0.000 description 2
- YLQBMQCUIZJEEH-UHFFFAOYSA-N tetrahydrofuran Natural products C=1C=COC=1 YLQBMQCUIZJEEH-UHFFFAOYSA-N 0.000 description 2
- PXRKCOCTEMYUEG-UHFFFAOYSA-N 5-aminoisoindole-1,3-dione Chemical compound NC1=CC=C2C(=O)NC(=O)C2=C1 PXRKCOCTEMYUEG-UHFFFAOYSA-N 0.000 description 1
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 1
- NLXLAEXVIDQMFP-UHFFFAOYSA-N Ammonium chloride Substances [NH4+].[Cl-] NLXLAEXVIDQMFP-UHFFFAOYSA-N 0.000 description 1
- 238000004438 BET method Methods 0.000 description 1
- 229910052684 Cerium Inorganic materials 0.000 description 1
- 238000009620 Haber process Methods 0.000 description 1
- KJTLSVCANCCWHF-UHFFFAOYSA-N Ruthenium Chemical compound [Ru] KJTLSVCANCCWHF-UHFFFAOYSA-N 0.000 description 1
- 235000011114 ammonium hydroxide Nutrition 0.000 description 1
- NQZFAUXPNWSLBI-UHFFFAOYSA-N carbon monoxide;ruthenium Chemical compound [Ru].[Ru].[Ru].[O+]#[C-].[O+]#[C-].[O+]#[C-].[O+]#[C-].[O+]#[C-].[O+]#[C-].[O+]#[C-].[O+]#[C-].[O+]#[C-].[O+]#[C-].[O+]#[C-].[O+]#[C-] NQZFAUXPNWSLBI-UHFFFAOYSA-N 0.000 description 1
- ZMIGMASIKSOYAM-UHFFFAOYSA-N cerium Chemical compound [Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce] ZMIGMASIKSOYAM-UHFFFAOYSA-N 0.000 description 1
- 229910000420 cerium oxide Inorganic materials 0.000 description 1
- 238000001739 density measurement Methods 0.000 description 1
- 238000004146 energy storage Methods 0.000 description 1
- 238000001704 evaporation Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- BMMGVYCKOGBVEV-UHFFFAOYSA-N oxo(oxoceriooxy)cerium Chemical compound [Ce]=O.O=[Ce]=O BMMGVYCKOGBVEV-UHFFFAOYSA-N 0.000 description 1
- 239000006069 physical mixture Substances 0.000 description 1
- 238000004088 simulation Methods 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P20/00—Technologies relating to chemical industry
- Y02P20/10—Process efficiency
- Y02P20/133—Renewable energy sources, e.g. sunlight
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P20/00—Technologies relating to chemical industry
- Y02P20/50—Improvements relating to the production of bulk chemicals
- Y02P20/52—Improvements relating to the production of bulk chemicals using catalysts, e.g. selective catalysts
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Description
本発明はＮ２とＨ２からＮＨ３を合成するアンモニア合成触媒に関する。 The present invention relates to an ammonia synthesis catalyst for synthesizing NH3 from N2 and H2 .
Ｎ２とＨ２からＮＨ３を合成する方法として、Ｆｅ３Ｏ４－Ａｌ２Ｏ３－Ｋ２ＯなどのＦｅ系触媒を用い、２３－３５ＭＰａ、約５００℃程度の高温高圧で反応を行うハーバー・ボッシュ法が知られている。
その後、Ｒｕ－ＣｅＯ２触媒を用いて、より低温低圧の温和な条件で反応を行う方法が開発された（特許文献１、２）。この方法で用いる触媒は、硝酸セリウムを、アンモニア水溶液を用いてアルカリ性条件下で沈殿させ、６００℃程度で焼成して得たＣｅＯ２に、Ｒｕカルボニルの溶液を含浸し、水素還元することで作製され、これにより、２００～６００℃程度の温度、１～２０気圧程度の低圧でのＮＨ３合成を実現している。
The Haber-Bosch process is known as a method for synthesizing NH 3 from N 2 and H 2 , in which an Fe-based catalyst such as Fe 3 O 4 --Al 2 O 3 --K 2 O is used to carry out the reaction at high temperatures and pressures of 23-35 MPa and approximately 500°C.
Later, a method was developed to carry out the reaction under milder conditions of lower temperature and pressure using a Ru- CeO2 catalyst (
Ｒｕ－ＣｅＯ２は、特許文献１、２に示されるように、アンモニア合成触媒として特許が出願されているが、ＣｅＯ２の物理的・化学的状態が異なることによってＲｕ－ＣｅＯ２の触媒性能は全く異なり、高いアンモニア合成活性を再現性よく引き出す調製法を示した特許等の文献はない。
また、Ｒｕ－ＣｅＯ２はＲｕおよびＣｅＯ２ともに高コストな素材であり、どちらの元素の使用量も低減することが望まれる。
本発明は、高いアンモニア合成活性を得ることができるＲｕ－ＣｅＯ２触媒の調製法を提供すること、およびＲｕ－ＣｅＯ２触媒におけるＣｅＯ２使用量削減に対して効果的な触媒調製法を提供することを課題とする。
As shown in
In addition, in Ru-- CeO2 , both Ru and CeO2 are high-cost materials, and it is desirable to reduce the amount of both elements used.
The present invention aims to provide a method for preparing a Ru- CeO2 catalyst that can obtain high ammonia synthesis activity, and to provide a catalyst preparation method that is effective for reducing the amount of CeO2 used in the Ru- CeO2 catalyst.
本発明者らは、硝酸セリウムを水酸化カリウムもしくはアンモニアの水溶液を用いて沈殿・焼成して作製したＣｅＯ２に強酸性のニトロシル硝酸ルテニウム（Ｒｕ（ＮＯ）（ＮＯ３）３）の溶液を含浸することにより作製したＲｕ－ＣｅＯ２触媒が、従来のＲｕカルボニルを用いて作製した触媒と比べて、高いアンモニア合成活性を有することを見出した。これに対し、硝酸セリウムを水酸化ナトリウムやクエン酸により沈殿・焼成して作製したＣｅＯ２を用いた場合は、アンモニア合成活性は、従来のＲｕカルボニルを用いて作製した触媒よりも低かった。
また、アンモニア合成活性は、ＣｅＯ２の焼成温度によっても変化し、水酸化カリウムにより沈殿させたＣｅＯ２を用いた触媒では、６００℃で焼成したものが最も活性が高かった。
The present inventors discovered that a Ru-CeO2 catalyst, which was prepared by impregnating CeO2, which was prepared by precipitating and calcining cerium nitrate with an aqueous solution of potassium hydroxide or ammonia, with a solution of strongly acidic ruthenium nitrosyl nitrate (Ru(NO)( NO3 ) 3 ), had higher ammonia synthesis activity than a catalyst prepared using a conventional Ru carbonyl. In contrast, when CeO2 prepared by precipitating and calcining cerium nitrate with sodium hydroxide or citric acid was used, the ammonia synthesis activity was lower than that of a catalyst prepared using a conventional Ru carbonyl.
In addition, the ammonia synthesis activity also changes depending on the calcination temperature of CeO2 . Among catalysts using CeO2 precipitated with potassium hydroxide, the one calcined at 600°C had the highest activity.
ＣｅＯ２は塩基性の担体であり、強酸性の溶液で処理するとその表面が一部溶解する。このことが、強酸性のニトロシル硝酸ルテニウムの溶液をＣｅＯ２に含浸することにより作製した本発明の触媒が高いアンモニア合成活性を有することと関連しているのではないかとの想定の下に、本発明者らは、ＣｅＯ２を強酸性の溶液で処理したときに生じるＣｅＯ２担体の表面の状態を模するものとして、結晶性のＣｅＯ２に硝酸セリウム水溶液を含浸させ、焼成することで、結晶性ＣｅＯ２の表面に非晶質のＣｅＯ２を、種々のＡｍｏ（非晶質）／Ｃｒｙ（結晶質）の比率で担持した担体を作製し、これにＲｕを担持した触媒を用いてアンモニア合成反応を行った。
その結果、Ａｍｏの比率を高めるにつれて担体の表面積及び細孔容積は大きくなるが、触媒のアンモニア合成活性も同様に一律に高まるわけではなく、Ａｍｏ／Ｃｒｙ比が１である場合をピークに、それ以上Ａｍｏの比率を高めるとアンモニア合成活性がかえって低くなることを見出した。
硝酸セリウムを水酸化カリウムもしくはアンモニアの水溶液を用いて沈殿・焼成して作製したＣｅＯ２に強酸性のニトロシル硝酸ルテニウムの溶液を含浸することにより作製したＲｕ－ＣｅＯ２触媒においては、ＣｅＯ２担体の表面が、上述のＡｍｏ／Ｃｒｙ比が１である場合と類似する構造を有しているものと推察される。
CeO 2 is a basic carrier, and when it is treated with a strong acidic solution, its surface is partially dissolved. Under the assumption that this is related to the fact that the catalyst of the present invention, which is produced by impregnating CeO 2 with a solution of strongly acidic nitrosyl ruthenium nitrate, has high ammonia synthesis activity, the present inventors have produced a carrier in which amorphous CeO 2 is supported on the surface of crystalline CeO 2 at various Amo (amorphous)/Cry (crystalline) ratios by impregnating crystalline CeO 2 with a cerium nitrate aqueous solution and calcining it, as a simulation of the surface state of the CeO 2 carrier that occurs when CeO 2 is treated with a strongly acidic solution, and performed an ammonia synthesis reaction using a catalyst that supports Ru on the carrier.
As a result, it was found that, although the surface area and pore volume of the carrier increase as the Amo ratio is increased, the ammonia synthesis activity of the catalyst does not increase uniformly. Rather, the ammonia synthesis activity peaks when the Amo/Cry ratio is 1, and if the Amo ratio is increased further, the ammonia synthesis activity actually decreases.
In the Ru- CeO2 catalyst prepared by impregnating CeO2, which is prepared by precipitating and calcining cerium nitrate using an aqueous solution of potassium hydroxide or ammonia, with a solution of strongly acidic ruthenium nitrosyl nitrate, the surface of the CeO2 support is presumed to have a structure similar to that in the case where the Amo/Cry ratio is 1 described above.
Ｒｕ－ＣｅＯ２触媒に用いられるＲｕもＣｅＯ２も高価な材料である。本発明者らは、Ｒｕ－ＣｅＯ２触媒にＭｇＯを混合することで、ＭｇＯの混合量に応じてＲｕ－ＣｅＯ２触媒に含まれるＣｅＯ２の量を減らすことができ、ＣｅＯ２の量を減らさない場合と匹敵し、あるいはそれを上回るアンモニア合成活性が得られることを見出した。これにより、高価な材料であるＣｅＯ２の、同一のＲｕの量に対する使用量を抑えることができる。
同様の量のＲｕ、ＣｅＯ２およびＭｇＯを用いても、共沈や物理的混合により得られたＣｅＯ２およびＭｇＯの混合物にＲｕを担持した場合や、ＭｇＯ外表面にＣｅＯ２を担持した後、これにＲｕを担持した場合には、このような効果は見られないことから、このような効果を得るためには、ＲｕはＣｅＯ２に集約されて担持されている必要があるものと考えられる。
Both Ru and CeO2 used in the Ru- CeO2 catalyst are expensive materials. The inventors have found that by mixing MgO into the Ru- CeO2 catalyst, the amount of CeO2 contained in the Ru-CeO2 catalyst can be reduced according to the amount of MgO mixed, and ammonia synthesis activity comparable to or exceeding that obtained when the amount of CeO2 is not reduced can be obtained. This makes it possible to reduce the amount of CeO2 , an expensive material, used relative to the same amount of Ru.
Even if similar amounts of Ru, CeO2 , and MgO are used, such effects are not observed when Ru is supported on a mixture of CeO2 and MgO obtained by coprecipitation or physical mixing, or when CeO2 is supported on the outer surface of MgO and then Ru is supported on this. Therefore, in order to obtain such effects, it is considered that Ru needs to be aggregated and supported on CeO2 .
本発明者らは、さらに、Ｒｕ－ＣｅＯ２触媒において、モル比Ｒｕ／Ｆｅ＝５～２００の範囲でＦｅを添加することにより、Ｆｅを添加しない場合を上回るアンモニア合成活性が得られることを見出した。
具体的には、Ｆｅ（ＮＯ３）３水溶液を用いてＣｅＯ２にＦｅを含浸担持させ、焼成した後、得られたＦｅ／ＣｅＯ２にニトロシル硝酸ルテニウムの溶液を用いてＲｕを含浸担持し、水素還元する。
第二成分の添加により触媒活性が向上することは、他の触媒系においても観察されることがあるが、モル比Ｒｕ／Ｆｅ＝１００～２００などの少ない量のＦｅの共存によっても上記効果が得られることは、本発明の際立った効果であるといえる。
The present inventors further discovered that by adding Fe to the Ru- CeO2 catalyst in a molar ratio of Ru/Fe in the range of 5 to 200, ammonia synthesis activity superior to that obtained when no Fe was added was obtained.
Specifically, Fe is impregnated and supported on CeO2 using an aqueous solution of Fe( NO3 ) 3 , and then calcined. After that, Ru is impregnated and supported on the obtained Fe/ CeO2 using a solution of ruthenium nitrosyl nitrate, and reduced with hydrogen.
Although the improvement of catalytic activity by the addition of a second component has been observed in other catalyst systems, the fact that the above effect can be obtained even in the presence of a small amount of Fe, such as a molar ratio of Ru/Fe=100 to 200, is a distinctive effect of the present invention.
本発明は、本発明者らが得た、これらの知見に基づいてなされたものであり、本出願は、具体的には、以下の発明を提供するものである。
〈１〉担体として酸化セリウム（ＣｅＯ２）を有し、触媒成分としてルテニウム（Ｒｕ）を有する、窒素と水素からアンモニアを合成する反応用の触媒の製造方法であって、硝酸セリウム水溶液へＫＯＨ水溶液またはアンモニア水溶液を沈殿剤として添加して得た沈殿を焼成することでＣｅＯ２を調製し、これをＲｕ（ＮＯ）（ＮＯ３）３水溶液に含浸させてＲｕを担持した後、水素処理して、ＣｅＯ２担持Ｒｕ触媒を調製することを特徴とする、触媒の製造方法。
〈２〉上記沈殿の焼成温度が５００－７００℃であることを特徴とする、〈１〉に記載の触媒の製造方法。
〈３〉上記水素処理を３００℃で行うことを特徴とする、〈１〉または〈２〉に記載の触媒の製造方法。
〈４〉窒素と水素からアンモニアを合成する反応用のＣｅＯ２担持Ｒｕ触媒であって、ＣｅＯ２担体のＢＥＴ比表面積が１７～１００ｍ２／ｇの範囲であり、細孔容積が０．０９～０．２５ｍＬ／ｇの範囲であることを特徴とする、触媒。
〈５〉ＣｅＯ２担持Ｒｕ触媒とＭｇＯが混合されてなる、窒素と水素からアンモニアを合成する反応用のＲｕ－ＣｅＯ２とＭｇＯの混合体触媒。
〈６〉混合体におけるＣｅとＭｇのモル比がＭｇ／Ｃｅ＝１～９である、〈５〉に記載の触媒。
〈７〉窒素と水素からアンモニアを合成する反応用のＣｅＯ２担持Ｒｕ触媒であって、ＣｅＯ２担体の表面にモル比Ｒｕ／Ｆｅ＝５～２００の範囲でＦｅが更に担持されていることを特徴とする、触媒。
The present invention has been made based on these findings obtained by the present inventors, and specifically, the present application provides the following inventions.
<1> A method for producing a catalyst for a reaction to synthesize ammonia from nitrogen and hydrogen, the catalyst having cerium oxide ( CeO2 ) as a support and ruthenium (Ru) as a catalytic component, the method comprising the steps of: adding a KOH aqueous solution or an ammonia aqueous solution as a precipitant to an aqueous solution of cerium nitrate to obtain a precipitate; calcining the precipitate to prepare CeO2 ; impregnating the precipitate with an aqueous solution of Ru(NO)( NO3 ) 3 to support Ru; and then treating with hydrogen to prepare a CeO2- supported Ru catalyst.
<2> The method for producing the catalyst according to <1>, wherein the calcination temperature of the precipitate is 500 to 700°C.
<3> The method for producing the catalyst according to <1> or <2>, wherein the hydrogen treatment is carried out at 300°C.
<4> A CeO2 -supported Ru catalyst for a reaction for synthesizing ammonia from nitrogen and hydrogen, characterized in that the BET specific surface area of the CeO2 support is in the range of 17 to 100 m2 /g and the pore volume is in the range of 0.09 to 0.25 mL/g.
<5> A mixed catalyst of Ru-CeO2 and MgO for use in a reaction for synthesizing ammonia from nitrogen and hydrogen, comprising a mixture of a CeO2- supported Ru catalyst and MgO.
<6> The catalyst according to <5>, wherein the mixture has a molar ratio of Ce to Mg of Mg/Ce=1 to 9.
<7> A CeO2 -supported Ru catalyst for a reaction for synthesizing ammonia from nitrogen and hydrogen, characterized in that Fe is further supported on the surface of the CeO2 support in a molar ratio of Ru/Fe in the range of 5 to 200.
アンモニア合成においてＲｕ－ＣｅＯ２触媒は、比較的低温・低圧で作用する触媒であるとともに、条件変化に対して応答性がよいため、変動性である再生可能エネルギーにより製造されたＣＯ２フリー水素を原料にするＣＯ２フリーアンモニア合成プロセスに適した触媒であり、よって、再生可能エネルギーの大量導入にむけた再生可能エネルギー貯蔵の面で社会実装されることが期待される触媒である。
本発明により、より高いアンモニア合成活性を有するＲｕ－ＣｅＯ２触媒を提供することができ、また、ＣｅＯ２の使用量を減らすことで、より安価でＲｕ－ＣｅＯ２触媒を提供することができる。これにより、上記再生可能エネルギーの利用の分野にも資することが期待される。
In ammonia synthesis, the Ru- CeO2 catalyst is a catalyst that functions at relatively low temperatures and pressures, and is responsive to changes in conditions. Therefore, it is a catalyst suitable for the CO2 -free ammonia synthesis process that uses CO2- free hydrogen produced by variable renewable energy as the raw material. Therefore, it is a catalyst that is expected to be implemented in society in terms of renewable energy storage toward the large-scale introduction of renewable energy.
According to the present invention, it is possible to provide a Ru- CeO2 catalyst having a higher ammonia synthesis activity, and by reducing the amount of CeO2 used, it is possible to provide a Ru- CeO2 catalyst at a lower cost. This is expected to contribute to the field of renewable energy utilization.
以下、本発明を実施例に基づいて更に詳細に説明する。但し、実施例は本発明の例示であって、本発明は実施例に限定されるものではない。 The present invention will be described in more detail below with reference to examples. However, the examples are merely illustrative of the present invention, and the present invention is not limited to the examples.
［実施例１］各種のＣｅＯ２担体を用いたＲｕ－ＣｅＯ２触媒の調製とそのＮＨ３合成活性
（１）以下の要領で、Ｒｕ－ＣｅＯ２触媒の担体として用いる各種のＣｅＯ２を準備した。
（アルカリ水溶液による沈殿法によるもの）
硝酸セリウム重量の約１０倍数の体積のイオン交換蒸留水で硝酸セリウム水溶液を調製し、２７％ＮＨ３水もしくは０．０５－０．１ｍｏｌ／ＬのＫＯＨ、ＮａＯＨを徐々に加えて、ｐＨを１０以上にして得られる沈殿を６００℃で空気中焼成して、ＣｅＯ２を調製した。
（クエン酸水溶液による沈殿法によるもの）
上述の硝酸セリウム水溶液にセリウムの２倍ｍｏｌ量を含むクエン酸水溶液を加え、蒸発乾固させて得た沈殿を６００℃で空気中焼成して、ＣｅＯ２を調製した。
（市販品）
市販されている、比表面積の異なるＣｅＯ２を２種（高表面積および中程度の表面積）、準備した。これらはそれぞれ第一稀元素化学工業製ＣｅＯ２ Ｔｙｐｅ－ＡおよびＴｙｐｅ－Ｂであり、比表面積はそれぞれ１５０ｍ２／ｇおよび１００ｍ２／ｇであった。
（低表面積ＣｅＯ２）
市販のＣｅＯ２ Ｔｙｐｅ－Ａを９００℃、６時間、空気中で焼成して、比表面積９ｍ２／ｇのＣｅＯ２を調製した。
（２）これらのＣｅＯ２に、Ｒｕ（ＮＯ）（ＮＯ３）３水溶液を含浸させて、各種のＲｕ－ＣｅＯ２触媒を調製した。ＣｅＯ２は、メスシリンダーによる見かけの密度および真密度計による真密度を測定し、それらの差分によって得られる見かけの空隙容積を算出した。ＣｅＯ２の重量に応じて、見かけの空隙容積の１．５倍の水に必要量のＲｕ（ＮＯ）（ＮＯ３）３を溶解し、そのＲｕ（ＮＯ）（ＮＯ３）３水溶液中にＣｅＯ２を室温で１時間浸漬した後、１００℃で１２時間乾燥させてＲｕ担持ＣｅＯ２を得た。Ｒｕ担持ＣｅＯ２は、管状炉中で１０％Ｈ２／Ｎ２気流中３００℃、１時間焼成して目的の触媒を調製した。
また、これに加えて、市販の高表面積ＣｅＯ２にＲｕ３（ＣＯ）１２溶液を含浸させて、Ｒｕ－ＣｅＯ２触媒を調製した。上記と同様に測定したＣｅＯ２の見かけの空隙容積の５０倍のテトラヒドロフラン（ＴＨＦ）にＲｕ３（ＣＯ）１２を溶解し、上記と同様の手順で目的の触媒を得た。
得られた各Ｒｕ－ＣｅＯ２触媒のＲｕ担持量は、それぞれ１Ｗｔ％である。
[Example 1] Preparation of Ru- CeO2 catalyst using various CeO2 supports and its NH3 synthesis activity (1) Various CeO2 to be used as supports for Ru- CeO2 catalyst were prepared as follows.
(By precipitation using an alkaline aqueous solution)
A cerium nitrate aqueous solution was prepared using ion-exchanged distilled water with a volume approximately 10 times the weight of cerium nitrate, and 27% NH3 water or 0.05-0.1 mol/L KOH or NaOH was gradually added to adjust the pH to 10 or higher. The resulting precipitate was calcined in air at 600 °C to prepare CeO2 .
(Precipitation method using citric acid solution)
A citric acid solution containing twice the molar amount of cerium was added to the above-mentioned cerium nitrate aqueous solution, and the precipitate obtained by evaporating to dryness was calcined in air at 600 °C to prepare CeO2 .
(Commercial goods)
Two types of commercially available CeO 2 with different specific surface areas (high surface area and medium surface area) were prepared. These were CeO 2 Type-A and Type-B manufactured by Daiichi Kigenso Kagaku Kogyo Co., Ltd., and had specific surface areas of 150 m 2 /g and 100 m 2 /g, respectively.
(Low surface area CeO 2 )
Commercially available CeO 2 Type-A was calcined in air at 900° C. for 6 hours to prepare CeO 2 with a specific surface area of 9 m 2 /g.
(2) These CeO 2 were impregnated with Ru(NO)(NO 3 ) 3 aqueous solution to prepare various Ru-CeO 2 catalysts. CeO 2 was measured for apparent density using a measuring cylinder and true density using a true density meter, and the apparent void volume obtained by the difference between them was calculated. Depending on the weight of CeO 2 , the required amount of Ru(NO)(NO 3 ) 3 was dissolved in water 1.5 times the apparent void volume, and CeO 2 was immersed in the Ru(NO)(NO 3 ) 3 aqueous solution at room temperature for 1 hour, and then dried at 100 ° C for 12 hours to obtain Ru-supported CeO 2. Ru-supported CeO 2 was calcined in a tubular furnace in a 10% H 2 /N 2 stream at 300 ° C for 1 hour to prepare the target catalyst.
In addition, a Ru- CeO2 catalyst was prepared by impregnating a commercially available high surface area CeO2 with a Ru3 (CO) 12 solution. Ru3(CO)12 was dissolved in tetrahydrofuran (THF) in an
The amount of Ru supported in each of the obtained Ru- CeO2 catalysts was 1 wt %.
これらのＲｕ－ＣｅＯ２触媒を用いて、アンモニアの合成試験を行った。試験は常圧固定床流通反応装置を用いて行った。反応温度４００℃で得られたその結果を、図１に示す。
図１に示されるように、硝酸セリウムを水酸化カリウムもしくはアンモニアの水溶液を用いて沈殿・焼成して作製したＣｅＯ２に強酸性のＲｕ（ＮＯ）（ＮＯ３）３（ニトロシル硝酸ルテニウム）の溶液を含浸することにより作製したＲｕ－ＣｅＯ２触媒は、従来のＲｕ３（ＣＯ）１２（Ｒｕカルボニル）を用いて作製した触媒と比べて、高いアンモニア合成活性を有する。これに対し、硝酸セリウムを水酸化ナトリウムやクエン酸により沈殿・焼成して作製したＣｅＯ２を用いた場合のアンモニア合成活性は、従来のＲｕカルボニルを用いて作製した触媒よりも低い。
Ammonia synthesis tests were carried out using these Ru- CeO2 catalysts. The tests were carried out using an atmospheric pressure fixed bed flow reactor. The results obtained at a reaction temperature of 400°C are shown in Figure 1.
As shown in Fig. 1, the Ru - CeO2 catalyst, which is produced by impregnating CeO2, which is produced by precipitating and calcining cerium nitrate with an aqueous solution of potassium hydroxide or ammonia, with a solution of strongly acidic Ru(NO)( NO3 ) 3 (ruthenium nitrosyl nitrate), has a higher ammonia synthesis activity than a catalyst produced using conventional Ru3 (CO) 12 (Ru carbonyl). In contrast, the ammonia synthesis activity of the catalyst produced by precipitating and calcining cerium nitrate with sodium hydroxide or citric acid is lower than that of the catalyst produced using conventional Ru carbonyl.
また、アンモニア合成活性は、ＣｅＯ２の焼成温度によっても変化し、水酸化カリウムにより沈殿させたＣｅＯ２を用いた上記触媒では、６００℃で焼成したものが最も活性が高かった（図２）。 In addition, the ammonia synthesis activity also changes depending on the calcination temperature of CeO2 . Among the above catalysts using CeO2 precipitated with potassium hydroxide, the one calcined at 600°C had the highest activity (Figure 2).
［実施例２］ＣｅＯ２担体の表面構造と触媒活性の関連性
ＣｅＯ２は塩基性の担体であり、強酸性の溶液で処理するとその表面が一部溶解する。このことが、強酸性のニトロシル硝酸ルテニウムの溶液をＣｅＯ２に含浸することにより作製した本発明の触媒が高いアンモニア合成活性を有することと関連しているのではないかとの想定の下に、ＣｅＯ２を強酸性の溶液で処理したときに生じるＣｅＯ２担体の表面の状態を模するものとして、結晶性のＣｅＯ２に硝酸セリウム水溶液を含浸させ、焼成することで、結晶性ＣｅＯ２の表面に非晶質のＣｅＯ２を、種々のＡｍｏ（非晶質）／Ｃｒｙ（結晶質）の比率で担持した担体を作製し、これにＲｕを担持した触媒を用いてアンモニア合成反応を行った。
[Example 2] Relationship between the surface structure of the CeO2 carrier and catalytic activity CeO2 is a basic carrier, and when treated with a strong acidic solution, its surface is partially dissolved. Under the assumption that this is related to the fact that the catalyst of the present invention, which is produced by impregnating CeO2 with a solution of strongly acidic nitrosyl ruthenium nitrate, has high ammonia synthesis activity, crystalline CeO2 was impregnated with a cerium nitrate aqueous solution and fired to simulate the surface state of the CeO2 carrier that occurs when CeO2 is treated with a strongly acidic solution, and a support was produced in which amorphous CeO2 was supported on the surface of crystalline CeO2 at various Amo (amorphous)/Cry (crystalline) ratios, and ammonia synthesis reaction was performed using a catalyst supported with Ru.
上記担体および触媒の調製、および、これを用いたアンモニア合成試験は、具体的には、以下のとおりに行った：
実施例１でも用いた市販の高表面積ＣｅＯ２を空気中９００℃で６時間焼成することで、結晶性のＣｅＯ２（以下、ＣｅＯ２（Ｃｒｙ）という）を調製した。
所定量のＣｅＯ２（Ｃｒｙ）を各種濃度のＣｅ（ＮＯ３）３水溶液に含浸し、１００℃で１２時間乾燥させた後、１０％Ｈ２／Ｎ２雰囲気中３００℃で１時間焼成することで、ＣｅＯ２（Ａｍｏ）／ＣｅＯ２（ｃｒｙ）のモル比が、それぞれ０．０１、０．０２、０．１、０．２、０．５、１、２、１０であるＣｅＯ２（Ａｍｏ）／ＣｅＯ２（ｃｒｙ）を調製した。また、硝酸セリウムを３００℃で４時間焼成することで、ＣｅＯ２（Ａｍｏ）のみからなるＣｅＯ２を調製した。これらのＣｅＯ２について測定されたＢＥＴ法による比表面積および細孔容積を図３に示す。黒バーが比表面積を、また白抜き丸が細孔容積を示す。
このようにして調製した各種のＣｅＯ２を、Ｒｕ担持量が１Ｗｔ％となるように濃度調節したＲｕ（ＮＯ）（ＮＯ３）３水溶液中に含浸し、１００℃で８時間乾燥させた後、１０％Ｈ２／Ｎ２雰囲気中３００℃で１時間焼成することで、各種のＲｕ－ＣｅＯ２触媒を調製した。
これらのＲｕ－ＣｅＯ２触媒を用いて、アンモニアの合成試験を行った。アンモニア合成反応の反応条件は、実施例１と同様である。その結果を、図４に示す。
The preparation of the above-mentioned carrier and catalyst, and the ammonia synthesis test using the same were specifically carried out as follows:
The commercially available high surface area CeO 2 used in Example 1 was calcined in air at 900° C. for 6 hours to prepare crystalline CeO 2 (hereinafter referred to as CeO 2 (Cry)).
A predetermined amount of CeO 2 (Cry) was impregnated into various concentrations of Ce(NO 3 ) 3 aqueous solutions, dried at 100° C. for 12 hours, and then baked at 300° C. for 1 hour in a 10% H 2 /N 2 atmosphere to prepare CeO 2 (Amo) / CeO 2 (cry) with a molar ratio of CeO 2 (Amo) / CeO 2 (cry) of 0.01, 0.02, 0.1, 0.2, 0.5, 1, 2, and 10, respectively. CeO 2 consisting only of CeO 2 (Amo) was also prepared by baking cerium nitrate at 300° C. for 4 hours. The specific surface area and pore volume measured for these CeO 2 by the BET method are shown in FIG. 3. The black bars indicate the specific surface area, and the open circles indicate the pore volume.
The various CeO2 thus prepared were impregnated into an aqueous solution of Ru(NO)( NO3 ) 3 whose concentration was adjusted so that the Ru loading amount was 1 wt%, and then dried at 100°C for 8 hours, and then calcined at 300°C for 1 hour in a 10% H2 / N2 atmosphere to prepare various Ru- CeO2 catalysts.
Using these Ru- CeO2 catalysts, an ammonia synthesis test was carried out. The reaction conditions for the ammonia synthesis reaction were the same as those in Example 1. The results are shown in FIG.
これらの実験の結果、Ａｍｏの比率を高めるにつれて担体の比表面積及び細孔容積は大きくなる（図３）が、触媒のアンモニア合成活性も同様に一律に高まるわけではなく、Ａｍｏ／Ｃｒｙ比が１である場合をピークに、それ以上Ａｍｏの比率を高めるとアンモニア合成活性がかえって低くなる（図４）ことを見出した。図３と４とから、担体の比表面積１７～１００ｍ２／ｇ、細孔容積０．０９～０．２５ｍＬ／ｇの範囲、より好ましくは、２０～６０ｍ２／ｇ、０．０９～０．２ｍＬ／ｇの範囲で高いアンモニア合成活性が得られたことが分かる。
硝酸セリウムを水酸化カリウムもしくはアンモニアの水溶液を用いて沈殿・焼成して作製したＣｅＯ２に強酸性のニトロシル硝酸ルテニウムの溶液を含浸することにより作製したＲｕ－ＣｅＯ２触媒においては、ＣｅＯ２担体の表面が、上述のＡｍｏ／Ｃｒｙ比が１である場合と類似する構造を有しているものと推察される。
As a result of these experiments, it was found that, as the ratio of Amo is increased, the specific surface area and pore volume of the support increase (Figure 3), but the ammonia synthesis activity of the catalyst does not increase uniformly either, and the ammonia synthesis activity peaks when the Amo/Cry ratio is 1, and decreases when the ratio of Amo is further increased (Figure 4). Figures 3 and 4 show that high ammonia synthesis activity was obtained when the specific surface area of the support was in the range of 17 to 100 m 2 /g and the pore volume was in the range of 0.09 to 0.25 mL/g, more preferably in the range of 20 to 60 m 2 /g and 0.09 to 0.2 mL/g.
In the Ru- CeO2 catalyst prepared by impregnating CeO2, which is prepared by precipitating and calcining cerium nitrate using an aqueous solution of potassium hydroxide or ammonia, with a solution of strongly acidic ruthenium nitrosyl nitrate, the surface of the CeO2 support is presumed to have a structure similar to that in the case where the Amo/Cry ratio is 1 described above.
［実施例３］Ｒｕ－ＣｅＯ２触媒へのＭｇＯの混合効果
Ｒｕ－ＣｅＯ２触媒に用いられるＲｕもＣｅＯ２も高価な材料である。本発明者らは、Ｒｕ－ＣｅＯ２触媒におけるＣｅＯ２の一部をＭｇＯで置き換えることで、Ｒｕ－ＣｅＯ２触媒に含まれるＣｅＯ２の量を減らすことを試みた。
[Example 3] Effect of mixing MgO into Ru-CeO2 catalyst Both Ru and CeO2 used in Ru-CeO2 catalyst are expensive materials. The present inventors attempted to reduce the amount of CeO2 contained in the Ru- CeO2 catalyst by replacing a part of CeO2 in the Ru- CeO2 catalyst with MgO.
具体的には、以下に示す４種類の触媒を調製し、そのアンモニア合成活性を調べた：
（共沈）
硝酸マグネシウム＋硝酸セリウム重量の約１０倍数の体積のイオン交換蒸留水で硝酸マグネシウムと硝酸セリウムの共水溶液（モル比Ｍｇ／Ｃｅ＝５）を調製し、これに２７％ＮＨ３水溶液を徐々に添加することによりｐＨを１０以上にして得られる沈殿を６００℃、４時間、空気中で焼成し、これにＲｕ（ＮＯ３）３水溶液をＲｕ含有量が１Ｗｔ％となるように含浸担持した後、Ｈ２／Ｎ２雰囲気中３００℃で焼成する。
（物理混合）
ＭｇＯとＣｅＯ２を上述の共沈法と同様の方法でそれぞれ沈殿から調製し、モル比Ｍｇ／Ｃｅ＝５で乳鉢によって混合し、得られたものに、Ｒｕ（ＮＯ３）３水溶液をＲｕ含有量が１Ｗｔ％となるように含浸担持した後、Ｈ２／Ｎ２雰囲気中３００℃で焼成する。
（表面担持）
所定量を秤量した硝酸セリウム水溶液中に上述の沈殿法によって調製したＭｇＯ粉体を浸漬し、蒸発乾固させることで、ＭｇＯ外表面にＣｅを析出させ、続いて、空気中６００℃で４時間焼成し、ＣｅＯ２が表面に担持したＭｇＯ（モル比Ｍｇ／Ｃｅ＝５）を得、これにＲｕ（ＮＯ３）３水溶液をＲｕ含有量が１Ｗｔ％となるように含浸担持した後、Ｈ２／Ｎ２雰囲気中３００℃で焼成する。
（Ｒｕ－ＣｅＯ２＋ＭｇＯ混合）
実施例１においてＮＨ３を用いた沈殿法により得られたＣｅＯ２にＲｕ（ＮＯ３）３水溶液をＲｕ含有量が２．２Ｗｔ％となるように含浸担持し、Ｈ２／Ｎ２雰囲気中３００℃で焼成した後、モル比Ｍｇ／Ｃｅ＝５となるようにＭｇＯをＲｕ－ＣｅＯ２に加えて、乳鉢で混合し、Ｒｕ含有量が混合物全体で１Ｗｔ％となるＲｕ－ＣｅＯ２＋ＭｇＯ混合触媒を得た。
これらの触媒、及び比較対象として、実施例１においてＮＨ３を用いた沈殿法により得られたＣｅＯ２にＲｕ（ＮＯ）（ＮＯ３）３水溶液をＲｕ含有量が１Ｗｔ％となるように含浸担持した後、Ｈ２／Ｎ２雰囲気中３００℃で焼成した触媒について、アンモニアの合成試験を行った。アンモニア合成反応の反応条件は、実施例１と同様である。その結果を、図５に示す。
Specifically, the following four types of catalysts were prepared and their ammonia synthesis activity was examined:
(Coprecipitation)
A co-aqueous solution of magnesium nitrate and cerium nitrate (molar ratio Mg/Ce=5) was prepared using ion-exchanged distilled water with a volume approximately 10 times the weight of magnesium nitrate and cerium nitrate, and a 27% NH3 aqueous solution was gradually added to the solution to adjust the pH to 10 or higher. The resulting precipitate was calcined in air at 600°C for 4 hours, impregnated with an aqueous Ru( NO3 ) 3 solution so that the Ru content was 1 wt%, and then calcined in a H2 / N2 atmosphere at 300°C.
(Physical Mixture)
MgO and CeO2 are prepared from precipitation in a manner similar to the above-mentioned coprecipitation method, mixed in a mortar at a molar ratio of Mg/Ce = 5, impregnated with an aqueous solution of Ru( NO3 ) 3 so that the Ru content is 1 wt%, and then fired at 300°C in a H2 / N2 atmosphere.
(Surface Loading)
The MgO powder prepared by the above-mentioned precipitation method is immersed in a weighed amount of cerium nitrate aqueous solution, and evaporated to dryness to precipitate Ce on the outer surface of the MgO. The powder is then fired in air at 600°C for 4 hours to obtain MgO with CeO2 supported on the surface (molar ratio Mg/Ce=5). This is impregnated with an aqueous Ru( NO3 ) 3 solution so that the Ru content becomes 1 wt%, and then fired in a H2 / N2 atmosphere at 300°C.
(Ru-CeO2+MgO mixture)
In Example 1, CeO2 obtained by the precipitation method using NH3 was impregnated with an aqueous solution of Ru( NO3 ) 3 so that the Ru content was 2.2 wt%. The mixture was then fired at 300°C in a H2 / N2 atmosphere. MgO was then added to the Ru- CeO2 so that the molar ratio was Mg/Ce = 5, and mixed in a mortar to obtain a Ru- CeO2 +MgO mixed catalyst with a Ru content of 1 wt% in the entire mixture.
These catalysts and, as a comparison, a catalyst obtained by impregnating CeO2 obtained by the precipitation method using NH3 in Example 1 with an aqueous solution of Ru(NO)( NO3 ) 3 so that the Ru content was 1 wt%, and then calcining the catalyst at 300°C in a H2 / N2 atmosphere were subjected to an ammonia synthesis test. The reaction conditions for the ammonia synthesis reaction were the same as those in Example 1. The results are shown in Figure 5.
図５に示されるように、Ｒｕ－ＣｅＯ２触媒にＭｇＯを混合することで、ＭｇＯの混合量に応じてＲｕ－ＣｅＯ２触媒に含まれるＣｅＯ２の量を減らすことができ、ＣｅＯ２の量を減らさない場合と匹敵するアンモニア合成活性が得られることを見出した。これにより、高価な材料であるＣｅＯ２の、同一のＲｕの量に対する使用量を抑えることができる。
一方、同様の量のＲｕ、ＣｅＯ２およびＭｇＯを用いても、共沈や物理的混合により得られたＣｅＯ２およびＭｇＯの混合物にＲｕを担持した場合や、ＭｇＯ外表面にＣｅＯ２を担持した後、これにＲｕを担持した場合には、このような効果は見られないことから、このような効果を得るためには、ＲｕはＣｅＯ２に集約されて担持されている必要があるものと考えられる。
As shown in Figure 5, by mixing MgO into the Ru- CeO2 catalyst, the amount of CeO2 contained in the Ru- CeO2 catalyst can be reduced according to the amount of MgO mixed, and it was found that ammonia synthesis activity comparable to that obtained when the amount of CeO2 is not reduced can be obtained. This makes it possible to reduce the amount of CeO2 , which is an expensive material, used for the same amount of Ru.
On the other hand, even if similar amounts of Ru, CeO2 and MgO are used, such effects are not observed when Ru is supported on a mixture of CeO2 and MgO obtained by coprecipitation or physical mixing, or when CeO2 is supported on the outer surface of MgO and then Ru is supported on this. Therefore, in order to obtain such effects, it is considered that Ru needs to be aggregated and supported on CeO2 .
図６に、上述のＲｕ－ＣｅＯ２＋ＭｇＯ混合触媒において、モル比Ｍｇ／Ｃｅが１、３または９の混合触媒を更に調製し、これらと、モル比Ｍｇ／Ｃｅが５の触媒、及び、上述の（物理混合）に記載した調製法で調製したＭｇＯを含まない触媒、並びに、ＣｅＯ２を含まない触媒のアンモニア合成活性を調べた結果を示す。
図６から、上述のＲｕ－ＣｅＯ２触媒にＭｇＯを混合することの効果は、少なくともＭｇ／Ｃｅ比が１～９の範囲で得られ、この範囲で、同じＲｕ担持法による、ＭｇＯを含まない触媒のアンモニア合成活性を上回ることが分かる。
FIG. 6 shows the results of investigating the ammonia synthesis activity of the above-mentioned Ru-CeO 2 +MgO mixed catalyst, which was further prepared with a molar ratio of Mg/Ce of 1, 3, or 9, as well as a catalyst with a molar ratio of Mg/Ce of 5, a catalyst not containing MgO prepared by the preparation method described above (physical mixing), and a catalyst not containing CeO 2 .
From FIG. 6, it can be seen that the effect of mixing MgO with the above-mentioned Ru-CeO 2 catalyst is obtained at least in the range of Mg/Ce ratio of 1 to 9, and in this range, the ammonia synthesis activity exceeds that of a catalyst not containing MgO by the same Ru supporting method.
［実施例４］Ｒｕ－ＣｅＯ２触媒へのＦｅ配合の効果
多くの触媒において、第二成分を添加することにより活性が向上する現象が観察されることがある。そこで、本発明者らは、Ｒｕ－ＣｅＯ２触媒において、さらにＦｅを添加することが触媒のアンモニア合成活性に与える影響について検討した。
[Example 4] Effect of Fe addition to Ru- CeO2 catalyst In many catalysts, the phenomenon of activity improvement by adding a second component is observed. Therefore, the present inventors investigated the effect of further adding Fe to the Ru- CeO2 catalyst on the ammonia synthesis activity of the catalyst.
具体的には、実施例１で用いた市販の高表面積ＣｅＯ２の見かけの密度および真密度測定から見かけの空隙容積を算出し、その１．５倍体積のイオン交換蒸留水にＦｅ（ＮＯ３）３を溶解した水溶液中にＣｅＯ２を浸漬させ、６００℃、４時間、空気中で焼成し、Ｆｅ／ＣｅＯ２を調製した。これにＲｕ（ＮＯ）（ＮＯ３）３水溶液を用いてＲｕを１Ｗｔ％含浸担持した後、Ｈ２／Ｎ２雰囲気中３００℃で焼成することで、Ｒｕ／Ｆｅ／ＣｅＯ２触媒を得た。Ｒｕ／Ｆｅモル比が０．２～２００の範囲の１０種類の触媒を、Ｆｅ仕込み量を調整しながら調製し、これらの触媒、およびＦｅを担持させない触媒（Ｒｕ／Ｆｅが無限大）ならびにＲｕを担持させない５Ｗｔ％Ｆｅ担持触媒について、アンモニア合成活性を調べた。得られた結果を図７に示す。
Specifically, the apparent void volume was calculated from the apparent density and true density measurements of the commercially available high surface area CeO 2 used in Example 1, and
図７から、上述の触媒において、モル比Ｒｕ／Ｆｅ＝５～２００の範囲でＦｅを添加することにより、Ｆｅを添加しない場合を上回るアンモニア合成活性が得られることが分かる。特に、モル比Ｒｕ／Ｆｅ＝１００～２００などの極めて少ない量のＦｅの共存によっても上記効果が得られることは、本発明の際立った効果であるといえる。 From Figure 7, it can be seen that by adding Fe to the above catalyst in a molar ratio of Ru/Fe in the range of 5 to 200, ammonia synthesis activity that exceeds that obtained when no Fe is added can be obtained. In particular, the fact that the above effect can be obtained even with the coexistence of an extremely small amount of Fe, such as a molar ratio of Ru/Fe in the range of 100 to 200, is a notable effect of the present invention.
アンモニアは、各種化合物の合成反応において原料化合物の１つとして用いられる等、化学工業において広く使用されている化合物であり、本発明は、これらの化学工業の分野で広く利用し得るものである。
また、アンモニアは、再生可能エネルギーの貯蔵の形態の一つとして期待されており、本発明は、この分野での利用も期待される。
Ammonia is a compound that is widely used in the chemical industry, for example as one of raw material compounds in the synthesis reactions of various compounds, and the present invention can be widely used in these chemical industrial fields.
Furthermore, ammonia is expected to be one form of storage for renewable energy, and the present invention is also expected to be used in this field.
Claims (2)
ＣｅＯ２にＦｅを担持させてＦｅ／ＣｅＯ２を得て、モル比Ｒｕ／Ｆｅ＝５～２００となるように、このＦｅ／ＣｅＯ２にＲｕを担持させる触媒の製造方法。 A method for producing a catalyst for a reaction of synthesizing ammonia from nitrogen and hydrogen, comprising the steps of:
A method for producing a catalyst in which Fe is supported on CeO 2 to obtain Fe/CeO 2 , and Ru is supported on this Fe/CeO 2 so that the molar ratio of Ru/Fe is 5 to 200.
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