WO2016133213A1 - Ammonia synthesis catalyst and method for producing same - Google Patents

Ammonia synthesis catalyst and method for producing same Download PDF

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WO2016133213A1
WO2016133213A1 PCT/JP2016/054941 JP2016054941W WO2016133213A1 WO 2016133213 A1 WO2016133213 A1 WO 2016133213A1 JP 2016054941 W JP2016054941 W JP 2016054941W WO 2016133213 A1 WO2016133213 A1 WO 2016133213A1
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Prior art keywords
catalyst
praseodymium oxide
ruthenium
supported
ammonia synthesis
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PCT/JP2016/054941
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French (fr)
Japanese (ja)
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勝俊 永岡
和也 今村
勝俊 佐藤
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国立大学法人大分大学
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Priority claimed from JP2016021712A external-priority patent/JP2016155123A/en
Application filed by 国立大学法人大分大学 filed Critical 国立大学法人大分大学
Priority to US15/552,203 priority Critical patent/US20180071719A1/en
Priority to EP16752599.7A priority patent/EP3260198A4/en
Priority to CN201680011209.5A priority patent/CN107530686A/en
Publication of WO2016133213A1 publication Critical patent/WO2016133213A1/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
    • B01J23/54—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
    • B01J23/56—Platinum group metals
    • B01J23/63—Platinum group metals with rare earths or actinides
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/04—Mixing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/08—Heat treatment
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01C—AMMONIA; CYANOGEN; COMPOUNDS THEREOF
    • C01C1/00—Ammonia; Compounds thereof
    • C01C1/02—Preparation, purification or separation of ammonia
    • C01C1/04—Preparation of ammonia by synthesis in the gas phase
    • 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

Definitions

  • the present invention relates to an ammonia synthesis catalyst, and more particularly to a rare earth oxide-supported noble metal catalyst that exhibits a very high ammonia synthesis ability under mild conditions.
  • Ammonia is an important chemical raw material used for fertilizers and has recently attracted attention as an energy carrier. In particular, in recent years, attention has been focused on processes and catalysts for synthesizing ammonia using renewable energy.
  • the Harbor Bosch process using an iron catalyst that has already been industrialized is a high-temperature, high-pressure process, and it is difficult to operate this process using renewable energy. Therefore, there is a need for the development of ammonia synthesis catalysts and processes that are milder than the Harbor Bosch process, that is, exhibit high activity under low temperature and low pressure conditions.
  • Non-Patent Documents 1 and 2 a catalyst in which ruthenium is supported on various supports exhibits high ammonia generation activity even at low temperature and low pressure.
  • the present invention aims to provide a new rare earth oxide-supported noble metal catalyst that synthesizes ammonia under mild conditions in order to meet such demands.
  • the rare earth oxide-supported noble metal catalyst for synthesizing ammonia of the present invention under mild conditions is characterized in that ruthenium is supported in a layered manner on a praseodymium oxide support.
  • the ammonia synthesis catalyst of the present invention having this unique structure which has not been known so far is obtained by calcining a praseodymium oxide precursor (for example, praseodymium hydroxide) in the order of low temperature, intermediate temperature and high temperature to form praseodymium oxide, which is used as a solvent.
  • a praseodymium oxide precursor for example, praseodymium hydroxide
  • it can be obtained by stirring together with a ruthenium source, followed by solvent removal and baking.
  • a catalyst in which ruthenium is supported on a praseodymium oxide support may be represented by “Ru / PrO x ”.
  • ruthenium is supported on the surface of the praseodymium oxide support in a layered state in a uniform and highly dispersed state, so that high catalytic activity is exhibited and ammonia production per catalyst weight and supported metal amount.
  • the activity is greatly improved compared to the conventional catalyst using ruthenium.
  • HAADF image high angle annular dark field image
  • STEM image high angle annular dark field image
  • EDX energy dispersive X-ray analyzer
  • Pr 6 O 11 shows a high-resolution observation of confirmed locations of Ru in STEM-EDX mapping in a typical catalysts of the prior art was supported Ru on a carrier. Is a graph showing the effect of Ru supported amount for NH 3 synthesis activity of the catalyst according to the present invention.
  • the pressure during the reaction is a diagram showing the effect on ammonia synthesis activity of Ru / PrO x.
  • a feature of the rare earth oxide-supported noble metal catalyst for synthesizing ammonia of the present invention under mild conditions is that ruthenium Ru is supported in a layered manner on a praseodymium oxide support.
  • the supported amount of Ru is preferably 1 to 10 wt% of the total weight of the catalyst supporting Ru. If it is less than 1 wt%, sufficient NH 3 synthesis activity cannot be expected, and if it exceeds 10 wt%, the effect is saturated and uneconomical. More preferably, the supported amount of Ru is about 3 to 5 wt%.
  • FIG. 1 shows a HAADF image obtained by observing the catalyst of the present invention with a STEM.
  • FIG. 2 shows an element mapping diagram of the catalyst of FIG. In the figure, the position where the element exists is displayed brightly.
  • (A), (b), and (c) are mappings of Pr, O, and Ru elements, respectively, and (d) shows a superposition of them. From (c) and (d), it can be seen that Ru is distributed almost throughout the catalyst. Further, since the edge of the catalyst is particularly bright, it is confirmed that Ru is supported on the surface of the carrier uniformly in a layered manner.
  • FIG. 3 shows the result of high-resolution observation of the location where the presence of Ru was confirmed by EDX observation of FIG. It is not seen that Ru is supported as particles.
  • FIG. 4 shows a HAADF image of another Ru / PrO x catalyst of the present invention. It has been confirmed that Ru is deposited in a layered manner on the surface of the PrO x carrier and an egg shell structure is formed. If the deposited Ru layer has a thickness of 0.1 nm or more, a high ammonia yield can be obtained. However, in order to obtain a stable high ammonia yield, it is preferably 0.2 to 0.3 nm. Even if the thickness of the Ru layer is excessively increased, the amount of Ru coming into contact with the raw material gas on the outermost surface of the catalyst is saturated, and the ammonia yield effect is saturated. For this reason, the upper limit of the Ru layer thickness may be appropriately determined to a thickness at which the effect is saturated.
  • FIG. 5 shows the result of high-resolution observation of a location where Ru was confirmed in a conventional catalyst (commercially available from Kanto Chemical Co.) in which ruthenium Ru was supported on a praseodymium oxide Pr 6 O 11 carrier. . A state where Ru is uniformly distributed is not observed.
  • the difference in the loading state of Ru between the praseodymium oxide-supported ruthenium catalyst of the present invention and the above-described conventional praseodymium oxide-supported ruthenium catalyst is due to the characteristics of the praseodymium oxide support used in each, more specifically, rapid firing to high temperature or low temperature This is presumed to be due to the difference in surface structure such as specific surface area, defects, functional groups, etc. of the praseodymium carrier caused by the difference in the firing process of multi-stage firing from high temperature to high temperature.
  • the precursor of praseodymium oxide is calcined in the order of low temperature, intermediate temperature, and high temperature to convert it into praseodymium oxide having a high specific surface area, which is stirred with a ruthenium source in an organic solvent. It can be produced by a method of removing the solvent and further baking.
  • the precursor of praseodymium oxide used in the present invention can be prepared by various methods such as a precipitation method and a complex polymerization method.
  • a neutralizing precipitation method can be used in which a precipitation agent such as ammonia, sodium hydroxide, or cesium hydroxide is reacted with an aqueous praseodymium salt solution such as praseodymium nitrate, praseodymium chloride, or praseodymium carbonate to obtain a hydroxide.
  • first, praseodymium hydroxide which is a precursor of praseodymium oxide serving as a carrier
  • the mixing molar ratio of ammonia and praseodymium nitrate is preferably about 5: 1 to 2: 1 and more preferably about 3: 1.
  • the concentrations of ammonia and praseodymium nitrate in the aqueous ammonia and praseodymium nitrate solution are preferably about 4 to 32 mol / liter and 0.1 to 1 mol / liter, respectively, and 8 to 16 mol / liter and 0.25 to 0.5, respectively. More preferably, it is about mol / liter.
  • Mixing can be performed at room temperature.
  • the produced praseodymium oxide precursor is changed to praseodymium oxide having a high specific surface area by three-stage firing at different temperatures.
  • the composition of praseodymium oxide to be obtained by calcination is not particularly limited, and compositions having various O / Pr ratios can be used as the catalyst support of the present invention.
  • a preferable O / Pr ratio is 1.5 to 1.9.
  • the reason for performing the three-stage firing is to prevent the praseodymium oxide from being sintered by rapid heating and decomposition of the praseodymium oxide precursor in the process of changing the praseodymium oxide precursor to praseodymium oxide. Furthermore, the praseodymium oxide surface is fixed with an excellent metastable structure through such a multi-step firing process from low temperature to high temperature, and has surface structures such as defects and functional groups prepared by conventional processes. It is assumed that it is different from the carrier.
  • the first low-temperature firing is preferably performed at a low temperature of about 200 to 400 ° C. for about 1 to 10 hours.
  • the second-stage medium temperature firing is preferably performed at an intermediate temperature of about 400 to 600 ° C. for about 1 to 10 hours.
  • the final high temperature firing is preferably performed at a high temperature of about 600 to 900 ° C. for about 1 to 10 hours.
  • the firing can be performed in air or under any oxygen concentration such as a mixed gas of oxygen with an inert gas
  • the praseodymium oxide thus obtained is stirred together with a ruthenium source in an appropriate organic solvent, and then the solvent is removed and the subsequent firing is performed, whereby the ruthenium is deposited in a layered manner on the praseodymium oxide support.
  • the praseodymium oxide-supported ruthenium catalyst is obtained.
  • the ruthenium source various compounds containing Ru can be used.
  • an organometallic compound such as triruthenium dodecacarbonyl Ru 3 (CO) 12 or ruthenium acetylacetonate can be used. It is also possible to use other ruthenium sources capable of supporting ruthenium on praseodymium oxide, such as ruthenium chloride.
  • an organometallic compound such as ruthenium carbonyl
  • an organic solvent examples include tetrahydrofuran (THF), methanol, ethanol, hexane, toluene and the like. These solvents can be used without any pretreatment as long as they are general commercial products, but it is more preferable to use those subjected to purification and dehydration.
  • the solid content concentrations of praseodymium oxide and ruthenium source in the solvent are generally preferably about 1 to 30 g / liter and 0.1 to 3 g / liter, respectively, and 10 to 30 g / liter and 0.1 to 0.3 g / liter, respectively.
  • Stirring can be performed at room temperature, and the stirring time is preferably 1 to 24 hours, more preferably 6 to 12 hours.
  • the removal of the solvent can be carried out by heating by various methods. For example, it is preferably carried out in a reduced-pressure, low-temperature atmosphere using an evaporator or the like.
  • Firing is performed in an inert atmosphere, such as a helium, argon or nitrogen atmosphere.
  • Baking can be performed even in an atmosphere containing hydrogen. Firing is performed at a temperature of about 200 to 450 ° C. for about 1 to 12 hours. A more preferable baking temperature is about 300 to 400 ° C., and a more preferable baking time is about 3 to 6 hours.
  • a mixed solution obtained by adding 0.25 liter of an 8% aqueous solution of praseodymium nitrate to 0.25 liter of 28% ammonia water was stirred at room temperature for 11 hours.
  • the resulting praseodymium hydroxide precipitate was separated, washed with room temperature water, filtered, and dried overnight at 70 ° C.
  • the dried praseodymium hydroxide was converted to praseodymium oxide by performing a stepwise baking treatment at 300 ° C. for 3 hours, then at 550 ° C. for 3 hours, and then at 700 ° C. for 5 hours. Subsequently, 4 g of praseodymium oxide cooled to room temperature was added to a 0.2 liter tetrahydrofuran solution in which 0.46 g of ruthenium carbonyl was dissolved, and stirred overnight. Next, tetrahydrofuran was removed from the solution by evaporation, and calcined at 350 ° C. in an atmosphere in which argon gas was circulated to obtain a catalyst in which ruthenium was supported in layers on a praseodymium oxide support.
  • the ammonia synthesis activity of the obtained catalyst was examined as follows. A pipe filled with 0.2 g of catalyst pretreated in an H 2 reducing atmosphere for 1 hour was charged with hydrogen gas and nitrogen gas at a molar ratio of 3: 1 at 1390 mL / h ⁇ g ⁇ at 390 ° C. and 0.9 MPa. Ammonia is synthesized by flowing at the space velocity of the catalyst, the effluent gas (containing the generated ammonia and residual hydrogen and nitrogen) is transferred into the dilute sulfuric acid aqueous solution, and the ammonia is collected with the dilute sulfuric acid aqueous solution. Activity was evaluated by changes in electrical conductivity.
  • FIG. 6 shows the results of examining the effect of the loading amount on the NH 3 synthesis activity of the catalyst at 0.1 MPa and 0.9 MPa.
  • Table 1 shows the NH 3 synthesis activity of the praseodymium oxide-supported ruthenium catalyst according to the present invention for the catalyst in which Ru is supported on the MgO support or CeO 2 support and the above-described conventional Ru / Pr 6 O 11 catalyst (commercially available). The data compared with is shown.
  • TOF in the table represents the number of reactions of ammonia synthesis per one active point and one second calculated based on the amount of hydrogen adsorbed on the Ru catalyst.
  • the ruthenium layer thickness in the table means the thickness of the thinnest ruthenium layer.
  • Table 2 shows the NH 3 synthesis activity of the catalysts according to Non-Patent Documents 1 and 2, which are reported to show high ammonia production activity even at low temperature and low pressure, from the examples of the present invention shown in Table 1, and 5 wt% Ru / PrO x. It shows data comparing the NH 3 synthesis activity of the catalyst examples.
  • the praseodymium oxide-supported ruthenium catalyst of the present invention had a higher yield of ammonia produced than other catalysts, that is, high catalytic activity. Further, as apparent from the comparison of the synthesis rates, it was found that the ammonia generation activity per catalyst weight and the amount of supported metal was greatly improved as compared with other catalysts.
  • FIG. 7 shows the results of examining the influence of the pressure during the reaction on the ammonia synthesis activity of the Ru / PrO x catalyst of the present invention produced as described above.
  • ammonia yield increased with increasing pressure. Since the yield is improved even when the pressure is increased from 0.9 MPa to 1.0 MPa, a higher yield can be expected under practical conditions of higher pressure.
  • Table 3 shows the results of examining the influence of the molar ratio of nitrogen gas to hydrogen gas on the activity of the 5 wt% Ru / PrO x catalyst of the present invention produced as described above.
  • Table 4 shows the results of investigating the influence of the space velocity on the ammonia synthesis rate of the 5 wt% Ru / PrO x catalyst of the present invention produced as described above.
  • Table 5 shows the results of the ammonia synthesis activity of the 5 wt% Ru / PrO x catalyst of the present invention produced as described above when the pressure was increased from 1.0 MPa to 3.0 MPa.
  • the productivity of the Ru / PrO x catalyst of the present invention can be further improved by changing the reaction conditions.

Abstract

The present invention provides a rare earth oxide-supported noble metal catalyst which has a high catalytic activity, is greatly improved in the ammonia production activity per weight of the catalyst and per amount of the supported metal, and enables the synthesis of ammonia under mild conditions. The catalyst according to the present invention is characterized in that ruthenium is supported in a layered form on a praseodymium oxide carrier. The catalyst according to the present invention can be produced by burning a praseodymium oxide precursor at a lower temperature, then at a medium temperature and then at a higher temperature to produce praseodymium oxide, then agitating the resultant praseodymium oxide together with a ruthenium supply source in a solvent, then removing the solvent from the mixture, and then burning the resultant product.

Description

アンモニア合成触媒とその製造方法Ammonia synthesis catalyst and production method thereof
　本発明は、アンモニア合成触媒に関し、より詳しく言えば、温和な条件下で非常に高いアンモニア合成能を示す希土類酸化物担持貴金属触媒に関する。 The present invention relates to an ammonia synthesis catalyst, and more particularly to a rare earth oxide-supported noble metal catalyst that exhibits a very high ammonia synthesis ability under mild conditions.
　アンモニアは、肥料などに用いられる重要な化学原料であり、近年はエネルギーキャリアとしても注目されている。特に近年は、再生可能エネルギーを利用してアンモニアを合成するプロセスや触媒に注目が集まっている。 Ammonia is an important chemical raw material used for fertilizers and has recently attracted attention as an energy carrier. In particular, in recent years, attention has been focused on processes and catalysts for synthesizing ammonia using renewable energy.
　既に工業化されている鉄触媒を用いたハーバー・ボッシュプロセスは、高温・高圧のプロセスであり、再生可能エネルギーを用いてこのプロセスを運転することは困難である。このため、ハーバー・ボッシュプロセスよりも温和な、すなわち低温且つ低圧な条件下で高い活性を示すアンモニア合成触媒とプロセスの開発が必要とされている。 The Harbor Bosch process using an iron catalyst that has already been industrialized is a high-temperature, high-pressure process, and it is difficult to operate this process using renewable energy. Therefore, there is a need for the development of ammonia synthesis catalysts and processes that are milder than the Harbor Bosch process, that is, exhibit high activity under low temperature and low pressure conditions.
　これまでに、種々の担体にルテニウムを担持した触媒が低温・低圧でも高いアンモニア生成活性を示すことが報告されている（例えば、非特許文献１、２）。 So far, it has been reported that a catalyst in which ruthenium is supported on various supports exhibits high ammonia generation activity even at low temperature and low pressure (for example, Non-Patent Documents 1 and 2).
　しかし、未だに、触媒の実用プロセス化にとって重要な触媒重量当たり、あるいは担持金属量当たりのアンモニア生成活性は充分でなく、低温・低圧条件下での触媒の高活性化が求められている。 However, the ammonia production activity per catalyst weight or the amount of supported metal, which is important for the practical use of catalysts, is still insufficient, and there is a demand for high activation of catalysts under low temperature and low pressure conditions.
　本発明は、かかる要請に応えるため、温和な条件でアンモニアを合成する新しい希土類酸化物担持貴金属触媒を提供することを目的とするものである。 The present invention aims to provide a new rare earth oxide-supported noble metal catalyst that synthesizes ammonia under mild conditions in order to meet such demands.
　本発明のアンモニアを温和な条件で合成する希土類酸化物担持貴金属触媒は、酸化プラセオジム担体にルテニウムを層状に担持したことを特徴とするものである。 The rare earth oxide-supported noble metal catalyst for synthesizing ammonia of the present invention under mild conditions is characterized in that ruthenium is supported in a layered manner on a praseodymium oxide support.
　従来知られていないこの特異構造を備えた本発明のアンモニア合成触媒は、酸化プラセオジム前駆体（例えば水酸化プラセオジム）を、低温、中間温度及び高温の順で焼成して酸化プラセオジムにし、これを溶媒中でルテニウム供給源にとともに撹拌後、溶媒除去及び焼成することにより得ることができる。 The ammonia synthesis catalyst of the present invention having this unique structure which has not been known so far is obtained by calcining a praseodymium oxide precursor (for example, praseodymium hydroxide) in the order of low temperature, intermediate temperature and high temperature to form praseodymium oxide, which is used as a solvent. In particular, it can be obtained by stirring together with a ruthenium source, followed by solvent removal and baking.
　以下の説明においては、酸化プラセオジム担体にルテニウムを担持させた触媒を、「Ｒｕ／ＰｒＯx」で表すこともある。 In the following description, a catalyst in which ruthenium is supported on a praseodymium oxide support may be represented by “Ru / PrO x ”.
　本発明による触媒においては、ルテニウムが酸化プラセオジム担体表面に層状に一様且つ高分散の状態で担持されていることにより、高い触媒活性が発現するとともに、触媒重量当たり及び担持金属量当たりのアンモニア生成活性がルテニウムを用いた従来の触媒に比べて大幅に向上する。 In the catalyst according to the present invention, ruthenium is supported on the surface of the praseodymium oxide support in a layered state in a uniform and highly dispersed state, so that high catalytic activity is exhibited and ammonia production per catalyst weight and supported metal amount. The activity is greatly improved compared to the conventional catalyst using ruthenium.
本発明による触媒を走査透過型電子顕微鏡（ＳＴＥＭ）で観察した高角環状暗視野像（ＨＡＡＤＦ像）である。It is the high angle annular dark field image (HAADF image) which observed the catalyst by this invention with the scanning transmission electron microscope (STEM). 図１の触媒をエネルギー分散型Ｘ線分析装置（ＥＤＸ）を備えたＳＴＥＭにより観察した元素マッピング図である。It is the element mapping figure which observed the catalyst of FIG. 1 by STEM provided with the energy dispersive X-ray analyzer (EDX). 図２のＥＤＸ観察でＲｕの存在が確認された箇所の高分解能観察結果を示す図である。It is a figure which shows the high-resolution observation result of the location where presence of Ru was confirmed by EDX observation of FIG. 本発明による触媒におけるＲｕ堆積層を示すＨＡＡＤＦ像である。It is a HAADF image which shows the Ru deposit layer in the catalyst by this invention. Ｐｒ6Ｏ11担体にＲｕを担持させた従来技術の典型的な触媒においてＳＴＥＭ－ＥＤＸマッピングでＲｕの確認された箇所の高分解能観察結果を示す図である。Pr 6 O 11 shows a high-resolution observation of confirmed locations of Ru in STEM-EDX mapping in a typical catalysts of the prior art was supported Ru on a carrier. 本発明による触媒のＮＨ3合成活性に対するＲｕ担持量の影響を示すグラフである。Is a graph showing the effect of Ru supported amount for NH 3 synthesis activity of the catalyst according to the present invention. 反応時の圧力がＲｕ／ＰｒＯｘのアンモニア合成活性に与える影響を示す図である。The pressure during the reaction is a diagram showing the effect on ammonia synthesis activity of Ru / PrO x.
　本発明のアンモニアを温和な条件で合成する希土類酸化物担持貴金属触媒の特徴は、酸化プラセオジム担体にルテニウムＲｕを層状に担持していることである。Ｒｕの担持量は、Ｒｕを担持した触媒の全重量の１～１０ｗｔ％が好ましい。１ｗｔ％未満では充分なＮＨ3合成活性が期待できず、１０ｗｔ％を超えると効果が飽和し、不経済である。Ｒｕの担持量は３～５ｗｔ％程度であるのがより好ましい。 A feature of the rare earth oxide-supported noble metal catalyst for synthesizing ammonia of the present invention under mild conditions is that ruthenium Ru is supported in a layered manner on a praseodymium oxide support. The supported amount of Ru is preferably 1 to 10 wt% of the total weight of the catalyst supporting Ru. If it is less than 1 wt%, sufficient NH 3 synthesis activity cannot be expected, and if it exceeds 10 wt%, the effect is saturated and uneconomical. More preferably, the supported amount of Ru is about 3 to 5 wt%.
　本発明の触媒をＳＴＥＭで観察したＨＡＡＤＦ像を図１に示す。図２は、図１の触媒の元素マッピング図を示すものである。図上では元素が存在する位置が明るく表示されている。（ａ）、（ｂ）、（ｃ）はそれぞれＰｒ、Ｏ、Ｒｕ元素のマッピングであり、（ｄ）はそれらを重ねたものを示す。(ｃ)、（ｄ）より、Ｒｕは触媒のほぼ全体に分布していることが分かる。また、触媒のふちの部分が特に明るくなっていることから、Ｒｕは主に担体の表面に一様に層状に担持されていることが確認される。 FIG. 1 shows a HAADF image obtained by observing the catalyst of the present invention with a STEM. FIG. 2 shows an element mapping diagram of the catalyst of FIG. In the figure, the position where the element exists is displayed brightly. (A), (b), and (c) are mappings of Pr, O, and Ru elements, respectively, and (d) shows a superposition of them. From (c) and (d), it can be seen that Ru is distributed almost throughout the catalyst. Further, since the edge of the catalyst is particularly bright, it is confirmed that Ru is supported on the surface of the carrier uniformly in a layered manner.
　図３は、図２のＥＤＸ観察でＲｕの存在が確認された箇所の高分解能観察の結果を示している。Ｒｕが粒子として担持されている様子は見られない。 FIG. 3 shows the result of high-resolution observation of the location where the presence of Ru was confirmed by EDX observation of FIG. It is not seen that Ru is supported as particles.
　図４は、本発明の別のＲｕ／ＰｒＯx触媒のＨＡＡＤＦ像を示している。ＲｕはＰｒＯｘ担体表面に層状に堆積し、エッグシェル構造が形成されていることが確認されている。堆積したＲｕ層は、０．１ｎｍ以上あればアンモニア収率が高く得られるが、より安定して高いアンモニア収率を得るためには０．２～０．３ｎｍあることが好ましい。尚、Ｒｕ層の厚みを過度に厚くしても触媒最表面で原料気体と接触するＲｕの量が飽和しアンモニア収率効果が飽和する。このためＲｕ層厚の上限は、効果が飽和する厚みに適宜決定すればよい。 FIG. 4 shows a HAADF image of another Ru / PrO x catalyst of the present invention. It has been confirmed that Ru is deposited in a layered manner on the surface of the PrO x carrier and an egg shell structure is formed. If the deposited Ru layer has a thickness of 0.1 nm or more, a high ammonia yield can be obtained. However, in order to obtain a stable high ammonia yield, it is preferably 0.2 to 0.3 nm. Even if the thickness of the Ru layer is excessively increased, the amount of Ru coming into contact with the raw material gas on the outermost surface of the catalyst is saturated, and the ammonia yield effect is saturated. For this reason, the upper limit of the Ru layer thickness may be appropriately determined to a thickness at which the effect is saturated.
　図５は、酸化プラセオジムＰｒ6Ｏ11担体にルテニウムＲｕを担持させた従来技術による触媒（関東化学社より入手可能な市販品）においてＲｕの確認された箇所の高分解能観察の結果を示している。Ｒｕが一様に分布している様子は観察されない。 FIG. 5 shows the result of high-resolution observation of a location where Ru was confirmed in a conventional catalyst (commercially available from Kanto Chemical Co.) in which ruthenium Ru was supported on a praseodymium oxide Pr 6 O 11 carrier. . A state where Ru is uniformly distributed is not observed.
　本発明の酸化プラセオジム担持ルテニウム触媒と上述の従来技術による酸化プラセオジム担持ルテニウム触媒とにおけるＲｕの担持状態の違いは、それぞれで用いる酸化プラセオジム担体の特性、より詳しくは高温度への急速焼成か低温度から高温度への多段焼成かの焼成プロセスの違いによって生じるプラセオジム担体の比表面積、欠陥、官能基などの表面構造の差異によるものと推測される。 The difference in the loading state of Ru between the praseodymium oxide-supported ruthenium catalyst of the present invention and the above-described conventional praseodymium oxide-supported ruthenium catalyst is due to the characteristics of the praseodymium oxide support used in each, more specifically, rapid firing to high temperature or low temperature This is presumed to be due to the difference in surface structure such as specific surface area, defects, functional groups, etc. of the praseodymium carrier caused by the difference in the firing process of multi-stage firing from high temperature to high temperature.
　この従来技術の酸化プラセオジム担持ルテニウム触媒以外に、酸化マグネシウム（ＭｇＯ）又は酸化セリウム（ＣｅＯ2）担体にＲｕを担持させた触媒についても、同様の観察を行った結果、Ｒｕが結晶化した微粒子として担持されていること、あるいは担体上にＲｕが極端に凝集している箇所と微粒子として担持されている箇所のあることが示された。このように、ＭｇＯ又はＣｅＯ2担体にＲｕを担持させた触媒においても、Ｒｕが層状に担持されてはいないことが分かった。 In addition to this conventional praseodymium oxide-supported ruthenium catalyst, the same observation was made on a catalyst in which Ru was supported on a magnesium oxide (MgO) or cerium oxide (CeO 2 ) support. It was shown that there are portions where Ru is extremely agglomerated on the carrier and portions where it is supported as fine particles. Thus, it was found that Ru was not supported in a layered manner even in a catalyst in which Ru was supported on an MgO or CeO 2 support.
　本発明のＲｕ／ＰｒＯx触媒は、酸化プラセオジムの前駆体を、低温、中間温度及び高温の順で焼成して高比表面積の酸化プラセオジムに変え、これを有機溶媒中でルテニウム供給源とともに撹拌後、溶媒を除去し、更に焼成する方法によって製造することができる。 In the Ru / PrO x catalyst of the present invention, the precursor of praseodymium oxide is calcined in the order of low temperature, intermediate temperature, and high temperature to convert it into praseodymium oxide having a high specific surface area, which is stirred with a ruthenium source in an organic solvent. It can be produced by a method of removing the solvent and further baking.
　本発明に用いる酸化プラセオジムの前駆体は沈殿法、錯体重合法などの種々の方法によって調製することができる。例えば、アンモニア、水酸化ナトリウム、水酸化セシウムなどの沈殿剤と硝酸プラセオジム、塩化プラセオジム、炭酸プラセオジムなどのプラセオジム塩水溶液を反応させて水酸化物を得る中和沈殿法を用いることができる。 The precursor of praseodymium oxide used in the present invention can be prepared by various methods such as a precipitation method and a complex polymerization method. For example, a neutralizing precipitation method can be used in which a precipitation agent such as ammonia, sodium hydroxide, or cesium hydroxide is reacted with an aqueous praseodymium salt solution such as praseodymium nitrate, praseodymium chloride, or praseodymium carbonate to obtain a hydroxide.
　好ましくは、まず、担体となる酸化プラセオジムの前駆物質である水酸化プラセオジムを、アンモニア水と硝酸プラセオジム水溶液を混合して調製する。アンモニアと硝酸プラセオジムとの混合モル比は、５：１～２：１程度が好ましく、３：１程度がより好ましい。アンモニア水と硝酸プラセオジム水溶液におけるアンモニア及び硝酸プラセオジムの濃度は、それぞれ４～３２モル／リットル、０．１～１モル／リットル程度が好ましく、それぞれ８～１６モル／リットル、０．２５～０．５モル／リットル程度であるのがより好ましい。混合は、常温で行うことができる。 Preferably, first, praseodymium hydroxide, which is a precursor of praseodymium oxide serving as a carrier, is prepared by mixing ammonia water and praseodymium nitrate aqueous solution. The mixing molar ratio of ammonia and praseodymium nitrate is preferably about 5: 1 to 2: 1 and more preferably about 3: 1. The concentrations of ammonia and praseodymium nitrate in the aqueous ammonia and praseodymium nitrate solution are preferably about 4 to 32 mol / liter and 0.1 to 1 mol / liter, respectively, and 8 to 16 mol / liter and 0.25 to 0.5, respectively. More preferably, it is about mol / liter. Mixing can be performed at room temperature.
　次に、生成した酸化プラセオジム前駆体を、温度を異にする３段階の焼成により高比表面積の酸化プラセオジムに変える。焼成によって得ようとする酸化プラセオジムの組成は特に限定されるものではなく種々のＯ／Ｐｒ比の組成のものが本発明の触媒担体として利用できる．好ましいＯ／Ｐｒ比は１．５～１．９である。 Next, the produced praseodymium oxide precursor is changed to praseodymium oxide having a high specific surface area by three-stage firing at different temperatures. The composition of praseodymium oxide to be obtained by calcination is not particularly limited, and compositions having various O / Pr ratios can be used as the catalyst support of the present invention. A preferable O / Pr ratio is 1.5 to 1.9.
　３段階の焼成を行う理由は、酸化プラセオジム前駆体が酸化プラセオジムに変化する過程において、酸化プラセオジム前駆体の急速な加熱、分解によって酸化プラセオジムの焼結が起きるのを防ぐためである。さらには、この様な低温度から高温度への多段階焼成プロセスを経ることによって酸化プラセオジム表面が準安定な優れた構造で固定され、従来プロセスで調製した欠陥、官能基などの表面構造をもつ担体とは異なるものと推察している。最初の低温度焼成は、２００～４００℃程度の低温で、約１～１０時間行うのが好ましい。２段階目の中温度焼成は、４００～６００℃程度の中間温度で、約１～１０時間行うのが好ましい。最後の高温度焼成は、６００～９００℃程度の高温で、約１～１０時間行うのが好ましい。これの焼成は、空気中や、不活性ガスとの酸素の混合ガスなど、任意の酸素濃度下で行うことができる。 The reason for performing the three-stage firing is to prevent the praseodymium oxide from being sintered by rapid heating and decomposition of the praseodymium oxide precursor in the process of changing the praseodymium oxide precursor to praseodymium oxide. Furthermore, the praseodymium oxide surface is fixed with an excellent metastable structure through such a multi-step firing process from low temperature to high temperature, and has surface structures such as defects and functional groups prepared by conventional processes. It is assumed that it is different from the carrier. The first low-temperature firing is preferably performed at a low temperature of about 200 to 400 ° C. for about 1 to 10 hours. The second-stage medium temperature firing is preferably performed at an intermediate temperature of about 400 to 600 ° C. for about 1 to 10 hours. The final high temperature firing is preferably performed at a high temperature of about 600 to 900 ° C. for about 1 to 10 hours. The firing can be performed in air or under any oxygen concentration such as a mixed gas of oxygen with an inert gas.
　次に、こうして得られた酸化プラセオジムを、適当な有機溶媒中でルテニウム供給源とともに撹拌後、溶媒の除去とこれに続く焼成を行うことで、酸化プラセオジム担体上にルテニウムが層状に堆積した本発明の酸化プラセオジム担持ルテニウム触媒が得られる。ルテニウム供給源としては、Ｒｕを含有する種々の化合物を使用することができる。好ましくは、トリルテニウムドデカカルボニルＲｕ3（ＣＯ）12やルテニウムアセチルアセトナトなどの有機金属化合物を用いることができる。酸化プラセオジムにルテニウムを担持させることができるこれ以外のルテニウム供給源、例えば塩化ルテニウムなどを使用することも可能である。ルテニウムカルボニルのような有機金属化合物をルテニウム供給源として使用する場合は、溶媒としては有機溶媒を使用するのが有利である。有機溶媒の例として、テトラヒドロフラン（ＴＨＦ）、メタノール、エタノール、ヘキサン、トルエンなどを挙げることができる。これらの溶媒は一般的な市販品であれば特に前処理を行わなくとも使用できるが、精製脱水等を行ったものを使用することがより好ましい。溶媒中における酸化プラセオジムとルテニウム供給源の固形分濃度は、一般にそれぞれ１～３０ｇ／リットル、０．１～３ｇ／リットル程度が好ましく、それぞれ１０～３０ｇ／リットル、０．１～０．３ｇ／リットル程度であるのがより好ましい。撹拌は、常温で行うことができ、撹拌時間は１～２４時間が好ましく、６～１２時間がより好ましい。溶媒の除去は種々の方法による加熱によって行うことができるが、例えばエバポレーターなどを利用した減圧、低温の雰囲気で行うことが好ましい。焼成は、不活性雰囲気、例えばヘリウム、アルゴン又は窒素雰囲気中においておこなう。水素を含む雰囲気中でも焼成することが出来る。焼成は、２００～４５０℃程度の温度で約１～１２時間行う。より好ましい焼成温度は３００～４００℃程度、より好ましい焼成時間は約３～６時間である。 Next, the praseodymium oxide thus obtained is stirred together with a ruthenium source in an appropriate organic solvent, and then the solvent is removed and the subsequent firing is performed, whereby the ruthenium is deposited in a layered manner on the praseodymium oxide support. The praseodymium oxide-supported ruthenium catalyst is obtained. As the ruthenium source, various compounds containing Ru can be used. Preferably, an organometallic compound such as triruthenium dodecacarbonyl Ru 3 (CO) 12 or ruthenium acetylacetonate can be used. It is also possible to use other ruthenium sources capable of supporting ruthenium on praseodymium oxide, such as ruthenium chloride. When an organometallic compound such as ruthenium carbonyl is used as the ruthenium source, it is advantageous to use an organic solvent as the solvent. Examples of the organic solvent include tetrahydrofuran (THF), methanol, ethanol, hexane, toluene and the like. These solvents can be used without any pretreatment as long as they are general commercial products, but it is more preferable to use those subjected to purification and dehydration. The solid content concentrations of praseodymium oxide and ruthenium source in the solvent are generally preferably about 1 to 30 g / liter and 0.1 to 3 g / liter, respectively, and 10 to 30 g / liter and 0.1 to 0.3 g / liter, respectively. More preferred is the degree. Stirring can be performed at room temperature, and the stirring time is preferably 1 to 24 hours, more preferably 6 to 12 hours. The removal of the solvent can be carried out by heating by various methods. For example, it is preferably carried out in a reduced-pressure, low-temperature atmosphere using an evaporator or the like. Firing is performed in an inert atmosphere, such as a helium, argon or nitrogen atmosphere. Baking can be performed even in an atmosphere containing hydrogen. Firing is performed at a temperature of about 200 to 450 ° C. for about 1 to 12 hours. A more preferable baking temperature is about 300 to 400 ° C., and a more preferable baking time is about 3 to 6 hours.
　次に、実施例により本発明を更に説明するが、本発明はここに提示する実施例に限定されるものではない。 Next, the present invention will be further described with reference to examples, but the present invention is not limited to the examples presented here.
　０．２５リットルの２８％アンモニア水に硝酸プラセオジムの８％水溶液０．２５リットルを加えた混合液を、常温で１１時間撹拌した。その結果得られた水酸化プラセオジム沈殿物を分離後、常温の水で洗浄し、ろ過してから、７０℃で一晩乾燥させた。 A mixed solution obtained by adding 0.25 liter of an 8% aqueous solution of praseodymium nitrate to 0.25 liter of 28% ammonia water was stirred at room temperature for 11 hours. The resulting praseodymium hydroxide precipitate was separated, washed with room temperature water, filtered, and dried overnight at 70 ° C.
　乾燥した水酸化プラセオジムを、３００℃で３時間、次に５５０℃で３時間、次に７００℃で５時間の段階的焼成処理を施すことにより、酸化プラセオジムに変えた。続いて常温まで冷却した酸化プラセオジムの４ｇを、０．４６ｇのルテニウムカルボニルを溶解した０．２リットルのテトラヒドロフラン溶液に加えて、一晩撹拌した。次に、蒸発により溶液からテトラヒドロフランを除去し、アルゴンガスが流通する雰囲気中において３５０℃で焼成して、酸化プラセオジム担体にルテニウムを層状に担持した触媒を得た。 The dried praseodymium hydroxide was converted to praseodymium oxide by performing a stepwise baking treatment at 300 ° C. for 3 hours, then at 550 ° C. for 3 hours, and then at 700 ° C. for 5 hours. Subsequently, 4 g of praseodymium oxide cooled to room temperature was added to a 0.2 liter tetrahydrofuran solution in which 0.46 g of ruthenium carbonyl was dissolved, and stirred overnight. Next, tetrahydrofuran was removed from the solution by evaporation, and calcined at 350 ° C. in an atmosphere in which argon gas was circulated to obtain a catalyst in which ruthenium was supported in layers on a praseodymium oxide support.
　得られた触媒のアンモニア合成活性を、次のようにして調べた。Ｈ2還元雰囲気で１時間前処理した０．２ｇの触媒を詰めたパイプに、３：１のモル比の水素ガスと窒素ガスを、３９０℃及び０．９ＭＰａで１８，０００ｍＬ／ｈ・ｇ－触媒の空間速度で流してアンモニアを合成し、流出ガス（生成したアンモニアと残留水素及び窒素を含有している）を希硫酸水溶液中に移送してアンモニアを希硫酸水溶液で捕集し、水溶液の電気伝導率の変化によって活性を評価した。 The ammonia synthesis activity of the obtained catalyst was examined as follows. A pipe filled with 0.2 g of catalyst pretreated in an H 2 reducing atmosphere for 1 hour was charged with hydrogen gas and nitrogen gas at a molar ratio of 3: 1 at 1390 mL / h · g− at 390 ° C. and 0.9 MPa. Ammonia is synthesized by flowing at the space velocity of the catalyst, the effluent gas (containing the generated ammonia and residual hydrogen and nitrogen) is transferred into the dilute sulfuric acid aqueous solution, and the ammonia is collected with the dilute sulfuric acid aqueous solution. Activity was evaluated by changes in electrical conductivity.
　図６に、触媒のＮＨ3合成活性に対する担持量の影響を、０．１ＭＰａと０．９ＭＰａで調べた結果を示す。 FIG. 6 shows the results of examining the effect of the loading amount on the NH 3 synthesis activity of the catalyst at 0.1 MPa and 0.9 MPa.
　表１は、本発明による酸化プラセオジム担持ルテニウム触媒のＮＨ3合成活性を、ＭｇＯ担体又はＣｅＯ2担体にＲｕを担持した触媒及び前述の従来技術のＲｕ／Ｐｒ6Ｏ11触媒（市販品）のものと比較したデータを示している。表中のＴＯＦは、Ｒｕ触媒への水素吸着量を元に算出した、１活性点、１秒間あたりのアンモニア合成の反応回数を表している。また、表中のルテニウム層厚は、ルテニウム層の最も薄いところの厚さを意味している。 Table 1 shows the NH 3 synthesis activity of the praseodymium oxide-supported ruthenium catalyst according to the present invention for the catalyst in which Ru is supported on the MgO support or CeO 2 support and the above-described conventional Ru / Pr 6 O 11 catalyst (commercially available). The data compared with is shown. TOF in the table represents the number of reactions of ammonia synthesis per one active point and one second calculated based on the amount of hydrogen adsorbed on the Ru catalyst. The ruthenium layer thickness in the table means the thickness of the thinnest ruthenium layer.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　表２は、低温・低圧でも高いアンモニア生成活性を示すと報告されている非特許文献１、２による触媒のＮＨ3合成活性を、表１に示す本発明の実施例から５ｗｔ％Ｒｕ／ＰｒＯｘ触媒例のＮＨ3合成活性と比較したデータを示している。 Table 2 shows the NH 3 synthesis activity of the catalysts according to Non-Patent Documents 1 and 2, which are reported to show high ammonia production activity even at low temperature and low pressure, from the examples of the present invention shown in Table 1, and 5 wt% Ru / PrO x. It shows data comparing the NH 3 synthesis activity of the catalyst examples.
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
　これらのデータから明らかなように、本発明の酸化プラセオジム担持ルテニウム触媒はその他の触媒と比べて生成するアンモニアの収率が高く、すなわち触媒活性の高いことが分かった。また、合成速度の比較から明らかなように、触媒重量当たり及び担持金属量当たりのアンモニア生成活性も、その他の触媒に比べて大幅に向上していることが分かった。 As is clear from these data, it was found that the praseodymium oxide-supported ruthenium catalyst of the present invention had a higher yield of ammonia produced than other catalysts, that is, high catalytic activity. Further, as apparent from the comparison of the synthesis rates, it was found that the ammonia generation activity per catalyst weight and the amount of supported metal was greatly improved as compared with other catalysts.
　図７に、反応時の圧力が上述のように作製した本発明のＲｕ／ＰｒＯｘ触媒のアンモニア合成活性に与える影響を調べた結果を示す。 FIG. 7 shows the results of examining the influence of the pressure during the reaction on the ammonia synthesis activity of the Ru / PrO x catalyst of the present invention produced as described above.
　圧力を上げるとアンモニア収率が高くなった。０．９ＭＰａから１．０ＭＰａに昇圧したときも収率が向上していることから、より高圧の実用的な条件ではさらに高い収率が期待できる。 The ammonia yield increased with increasing pressure. Since the yield is improved even when the pressure is increased from 0.9 MPa to 1.0 MPa, a higher yield can be expected under practical conditions of higher pressure.
　表３は、流通させる窒素ガスと水素ガスのモル比が上述のように作製した本発明の５ｗｔ％Ｒｕ／ＰｒＯｘ触媒の活性に与える影響を調べた結果である。 Table 3 shows the results of examining the influence of the molar ratio of nitrogen gas to hydrogen gas on the activity of the 5 wt% Ru / PrO x catalyst of the present invention produced as described above.
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000003
　表４は、空間速度が上述のように作製した本発明の５ｗｔ％Ｒｕ／ＰｒＯｘ触媒のアンモニア合成速度に与える影響を調査した結果である。 Table 4 shows the results of investigating the influence of the space velocity on the ammonia synthesis rate of the 5 wt% Ru / PrO x catalyst of the present invention produced as described above.
Figure JPOXMLDOC01-appb-T000004
Figure JPOXMLDOC01-appb-T000004
　表５は、圧力を１．０ＭＰaから３．０ＭＰaに昇圧したときの上述のように作製した本発明の５ｗｔ％Ｒｕ／ＰｒＯｘ触媒のアンモニア合成活性の結果である。 Table 5 shows the results of the ammonia synthesis activity of the 5 wt% Ru / PrO x catalyst of the present invention produced as described above when the pressure was increased from 1.0 MPa to 3.0 MPa.
Figure JPOXMLDOC01-appb-T000005
Figure JPOXMLDOC01-appb-T000005
　これらのデータからわかるように、反応条件を変えることで本発明のＲｕ／ＰｒＯｘ触媒の生産性をさらに向上させることができる。 As can be seen from these data, the productivity of the Ru / PrO x catalyst of the present invention can be further improved by changing the reaction conditions.

Claims (8)

  1. 　酸化プラセオジム担体にルテニウムを層状に担持したことを特徴とする、アンモニア合成触媒。 An ammonia synthesis catalyst characterized in that ruthenium is supported in layers on a praseodymium oxide support.
  2. 　Ｒｕの担持量がＲｕを担持した触媒の全重量の１～１０ｗｔ％であることを特徴とする、請求項１に記載のアンモニア合成触媒。 The ammonia synthesis catalyst according to claim 1, wherein the supported amount of Ru is 1 to 10 wt% of the total weight of the catalyst supporting Ru.
  3. 　担体上のＲｕ層の厚さが０．１ｎｍ以上であることを特徴とする、請求項１又は２に記載のアンモニア合成触媒。 The ammonia synthesis catalyst according to claim 1 or 2, wherein the Ru layer on the support has a thickness of 0.1 nm or more.
  4. 　酸化プラセオジム前駆体を、低温、中間温度及び高温の順で焼成して酸化プラセオジムにし、これを溶媒中でルテニウム供給源とともに撹拌後、溶媒除去及び焼成することによって、酸化プラセオジム担体にルテニウムを層状に担持させることを特徴とする、アンモニア合成触媒の製造方法。 The praseodymium oxide precursor is calcined in the order of low temperature, intermediate temperature, and high temperature to form praseodymium oxide, and this is stirred with a ruthenium source in a solvent, and then the solvent is removed and calcined to form a layer of ruthenium on the praseodymium oxide support. A method for producing an ammonia synthesis catalyst, comprising supporting the catalyst.
  5. 　酸化プラセオジム前駆体の焼成を、２００～４００℃で１～１０時間、次に４００～６００℃で１～１０時間、そして次に６００～９００℃で１～１０時間行うことを特徴とする、請求項４に記載のアンモニア合成触媒の製造方法。 Calcining the praseodymium oxide precursor at 200-400 ° C. for 1-10 hours, then at 400-600 ° C. for 1-10 hours, and then at 600-900 ° C. for 1-10 hours, Item 5. A process for producing an ammonia synthesis catalyst according to Item 4.
  6. 　ルテニウム供給源として有機金属化合物を使用することを特徴とする、請求項４又は５に記載のアンモニア合成触媒の製造方法。 The method for producing an ammonia synthesis catalyst according to claim 4 or 5, wherein an organometallic compound is used as a ruthenium supply source.
  7. 　溶媒として有機溶媒を使用することを特徴とする、請求項６に記載のアンモニア合成触媒の製造方法。 The method for producing an ammonia synthesis catalyst according to claim 6, wherein an organic solvent is used as the solvent.
  8. 　ルテニウム供給源としてトリルテニウムドデカカルボニルを用い、溶媒としてテトラヒドロフランを用いることを特徴とする、請求項４又は５に記載のアンモニア合成触媒の製造方法。 The method for producing an ammonia synthesis catalyst according to claim 4 or 5, wherein triruthenium dodecacarbonyl is used as a ruthenium supply source and tetrahydrofuran is used as a solvent.
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