JP4038311B2 - Ammonia synthesis catalyst, production method thereof, and ammonia synthesis method - Google Patents
Ammonia synthesis catalyst, production method thereof, and ammonia synthesis method Download PDFInfo
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- JP4038311B2 JP4038311B2 JP27977299A JP27977299A JP4038311B2 JP 4038311 B2 JP4038311 B2 JP 4038311B2 JP 27977299 A JP27977299 A JP 27977299A JP 27977299 A JP27977299 A JP 27977299A JP 4038311 B2 JP4038311 B2 JP 4038311B2
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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
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Description
【０００１】
【発明の属する技術分野】
本発明はアンモニア合成触媒及びアンモニア合成方法に関する。
【０００２】
【従来の技術】
従来、アンモニアを合成するには、鉄を主成分とし、アルミナ、酸化カリウムなどを助触媒として添加した鉄系触媒が広く用いられている。
【０００３】
【発明が解決しようとする課題】
しかし、アンモニア合成装置の建設経費、運転経費を低減するためには、アンモニア合成活性が従来の鉄系触媒に比べてさらに高い触媒が望まれている。
【０００４】
本発明は、高活性なアンモニア合成触媒及びアンモニア合成方法を提供することを目的とする。
【０００５】
【課題を解決するための手段】
上記の課題は次の発明により解決される。
【０００６】
第１の発明に係るアンモニア合成触媒は、アンモニア合成活性を示す成分としてコバルト添加窒化モリブデンを含むことを特徴としている。
【０００７】
第２の発明に係るアンモニア合成触媒は、アンモニア合成活性を示す成分として窒化モリブデンと窒化コバルトの混合物を含むことを特徴としている。
【００１１】
第３の発明に係るアンモニア合成触媒の製造方法は、アンモニア合成活性を示す成分としてコバルト・モリブデン複合窒化物を含むものの製造方法であって、硝酸コバルトを含浸させた酸化モリブデンを窒化する工程を有することを特徴としている。
【００１２】
第４の発明に係るアンモニア合成触媒の製造方法は、アンモニア合成活性を示す成分としてコバルト・モリブデン複合窒化物を含むものの製造方法であって、酸化モリブデンと酸化コバルトの混合物を窒化する工程を有することを特徴としている。
また、第５の発明に係るアンモニア合成触媒の製造方法は、アンモニア合成活性を示す成分としてコバルト・モリブデン複合窒化物を含むものの製造方法であって、モリブデン酸コバルトの水和物を窒化する工程を有することを特徴としている。
また、第６の発明に係るアンモニア合成触媒の製造方法は、第５の発明において、モリブデン酸コバルトの水和物は、硝酸コバルトと、モリブデン酸カリウム又はモリブデン酸セシウムの水溶液とが混合されて得られたものであることを特徴としている。
また、第７の発明に係るアンモニア合成触媒の製造方法は、第５の発明において、モリブデン酸コバルトの水和物は、硝酸カリウム又は硝酸セシウムが含浸されているものであることを特徴としている。
【００１３】
第８の発明に係るアンモニア合成方法は、第１または第２の発明に係るアンモニア合成触媒を使用することを特徴としている。
【００１４】
アンモニア合成においては、鉄系触媒、ルテニウム系触媒、モリブデン系触媒が高いアンモニア合成活性を有することが知られているが、これらの中で、モリブデン系触媒については、鉄系触媒やルテニウム系触媒に比べて、触媒機能に関する研究例が少なく、高活性触媒の開発はあまりなされていない。このような状況にあって、モリブデン系触媒の一つとして、窒化モリブデン（Ｍｏ2 Ｎ）が知られている。酸化モリブデンをアンモニア気流下、適切な温度と時間で処理して得た窒化モリブデンは比表面積が大きいと言う特性を有しているが、触媒活性はそれほど大きくはない。
【００１５】
しかし、本発明者らは、上記のような方法でモリブデンが窒化されると、比表面積が非常に大きくなることと、モリブデンとコバルト、ニッケル、鉄などの遷移金属がバイメタル化することにより高活性を有することに着目し、モリブデン系複合窒化物触媒が高活性触媒であるとの結果を得た。このため、本発明においては、モリブデンと組み合わせる遷移金属としてコバルトを選定し、触媒を高活性化することを図っている。
【００１６】
本発明におけるモリブデンとコバルトよりなる窒化物としては、▲１▼コバルト添加窒化モリブデン（Ｃｏ／Ｍｏ2 Ｎ）、▲２▼窒化モリブデンと窒化コバルトの混合物、▲３▼コバルト・モリブデン複合窒化物（Ｃｏ3 Ｍｏ3 Ｎ）の何れであってもよいが、上記の中、特に、コバルト・モリブデン複合窒化物を主成分とするものが高活性を有する。これは、モリブデンとコバルトがバイメタル化することにより、一段と活性化されためである。▲２▼及び▲３▼におけるモリブデンとコバルトの含有比（Ｃｏ／Ｍｏモル比）が１／１程度であると、長期間触媒活性が保たれ、安定しているので、Ｃｏ／Ｍｏモル比は１／１程度が好ましい。
【００１７】
コバルト・モリブデン複合窒化物（Ｃｏ3 Ｍｏ3 Ｎ）はモリブデン酸コバルト又はモリブデン酸コバルト水和物を窒化処理したものであって、前駆体であるモリブデン酸コバルト又はモリブデン酸コバルト水和物の調製の方法によって、触媒活性が異なる。
【００１８】
さらに、上記のコバルト・モリブデン複合窒化物（Ｃｏ3 Ｍｏ3 Ｎ）に、セシウムやカリウムなどのアルカリが添加されると、一層高活性を有するものになる。
【００１９】
本発明に係るアンモニア合成方法によれば、アンモニア合成活性が高い、上記何れかのアンモニア合成触媒を使用するので、アンモニア合成反応が効率よく行われる。
【００２０】
【発明の実施の形態】
各触媒は次に記載する方法により製造される。
（第１の発明に係る触媒（Ａ）の製法）
硝酸コバルトの水溶液中に酸化モリブデンを浸漬して、酸化モリブデンに硝酸コバルトを含浸させ、これを乾燥した後、窒化処理する。窒化処理においては、硝酸コバルトを含浸させた酸化モリブデンをアンモニア雰囲気の中に置き、所定の昇温速度で所定温度まで加熱した後、その温度で所定時間以上保持する。具体的な窒化条件の一例を示せば、例えば、６２３Ｋまでの昇温速度を１０Ｋ／min 、６２３Ｋ〜７２３Ｋまでの昇温速度を０．６Ｋ／min 、７２３Ｋ〜９７３Ｋまでの昇温速度を３Ｋ／min で行い、９７３Ｋで１時間保持する。
【００２１】
この処理により、コバルト添加窒化モリブデン（Ｃｏ／Ｍｏ2 Ｎ）を主成分とする触媒物質が得られる。この触媒におけるコバルトとモリブデンの含有比（Ｃｏ／Ｍｏモル比）は１／２０程度であることが好ましい。
【００２２】
（第２の発明に係る触媒（Ｂ）の製法）
酸化モリブデンの粉末と酸化コバルトの粉末を混合し、この混合物を窒化処理する。窒化処理は触媒（Ａ）を製造する場合と同じ条件で行う。この製法によれば、窒化モリブデンと窒化コバルトの混合物を主成分とするものが得られる。この触媒におけるコバルトとモリブデンの含有比（Ｃｏ／Ｍｏモル比）は１／１程度であることが好ましい。
【００２３】
（第４の発明に係る触媒（Ｃ）の製法）
硝酸コバルト（Ｃｏ（ＮＯ3）2・６Ｈ2Ｏ）とモリブデン酸アンモニウム（（ＮＨ4）6 Ｍｏ7Ｏ24・４Ｈ2Ｏ）を混合し、この混合物を空気中で焼成する。この焼成によりモリブデン酸コバルト（ＣｏＭｏＯ4）を主成分とする焼成物が得られる。焼成条件の一例を挙げれば、１０７３Ｋで３時間焼成する。
【００２４】
次いで、上記モリブデン酸コバルト（ＣｏＭｏＯ4）を主成分とする焼成物をアンモニア雰囲気の中に置き、所定の昇温速度で所定温度まで加熱した後、その温度で所定時間以上保持する。具体的な窒化条件の一例を示せば、例えば、加熱は昇温速度を５Ｋ／min にして行い、９７３Ｋで６時間保持する。
【００２５】
上記の処理により、コバルト・モリブデン複合窒化物（Ｃｏ3 Ｍｏ3 Ｎ）を主成分とする物質が得られる。この触媒におけるコバルトとモリブデンの含有比（Ｃｏ／Ｍｏモル比）は１／１程度であることが好ましい。
【００２６】
（第５の発明に係る触媒（Ｄ）の製法）
硝酸コバルト（Ｃｏ（ＮＯ3）2・６Ｈ2Ｏ）とモリブデン酸アンモニウム（（ＮＨ4）6 Ｍｏ7Ｏ24・４Ｈ2Ｏ）の水溶液を混合し、 沸騰させる。生成した沈殿物（モリブデン酸コバルトの水和物（ＣｏＭｏＯ4・０．９Ｈ2Ｏ））を濾別し、洗浄する。次いで、濾別・洗浄して得たモリブデン酸コバルトの水和物を窒化処理する。窒化処理は、例えば、触媒（Ｃ）を製造する場合と同じ条件で行う。上記の処理により、コバルト・モリブデン複合窒化物（Ｃｏ3 Ｍｏ3 Ｎ）を主成分とする物質が得られる。この触媒におけるコバルトとモリブデンの含有比（Ｃｏ／Ｍｏモル比）は１／１程度であることが好ましい。
【００２７】
（第６の発明に係る触媒（Ｅ）の製法）
硝酸コバルト（Ｃｏ（ＮＯ3）2・６Ｈ2Ｏ）と、モリブデン酸カリウム（Ｋ2 ＭｏＯ4）又はモリブデン酸セシウム（Ｃｓ2 ＭｏＯ4）の水溶液を混合し、 加熱して沸騰させる。生成した沈殿物（モリブデン酸コバルトの水和物（ＣｏＭｏＯ4・０．９Ｈ2Ｏ））を濾別し、洗浄する。次いで、濾別・洗浄して得たモリブデン酸コバルトの水和物を窒化処理する。窒化処理は、例えば、触媒（Ｃ）を製造する場合と同じ条件で行う。この処理により、コバルト・モリブデン複合窒化物（Ｃｏ3 Ｍｏ3 Ｎ）を主成分とする物質が得られる。
【００２８】
上記の製法によって得られる触媒（Ｅ）は触媒（Ｄ）よりも高いアンモニア合成活性を示す。これは、残存するカリウム又はセシウムが電子供与効果を発揮し、触媒表面での窒素活性化を促進する作用をしているためと考えられる。この触媒におけるコバルトとモリブデンの含有比（Ｃｏ／Ｍｏモル比）は１／１程度であることが好ましい。
【００２９】
（第７の発明に係る触媒（Ｆ）の製法）
硝酸カリウム（ＫＮＯ3）又、は硝酸セシウム（ＣｓＮＯ3）の水溶液中にモリブデン酸コバルトの水和物（ＣｏＭｏＯ4・０．９Ｈ2Ｏ）を浸漬して、モリブデン酸コバルトの水和物に硝酸カリウム又、は硝酸セシウムを含浸させ、これを乾燥した後、窒化処理する。窒化処理は、例えば、触媒（Ｃ）を製造する場合と同じ条件で行う。この処理により、カリウム又はセシウムが添加されたコバルト・モリブデン複合窒化物（Ｃｏ3 Ｍｏ3 Ｎ）を主成分とする物質が得られる。前述のように、カリウム又はセシウムを添加することにより触媒表面での窒素活性化が促進されるので、触媒（Ｆ）は極めて高いアンモニア合成活性を示す。
【００３０】
カリウム又はセシウムの添加量は、カリウム添加の場合、Ｋ／Ｍｏ（モル比）＝３０／１００程度、セシウム添加の場合、Ｃｓ／Ｍｏ（モル比）＝１０／１００程度であるのが好ましい。
【００３１】
本発明に係るアンモニア合成方法は、第１の発明〜第７の発明に係るアンモニア合成触媒の何れかの触媒上で窒素と水素の混合ガスを反応させることにより行う。反応は、反応温度２００〜５５０℃、好ましくは３００〜５５０℃、反応圧力０．１〜３０ＭＰａ、好ましくは０．５〜２０ＭＰａ、空間速度３６０〜３６０００、窒素と水素のモル比１／１０〜１／１の条件で行うことが好ましい。
【００３２】
【実施例】
上記の方法によって製造した各触媒について、アンモニア合成実験を行い、アンモニア合成活性を測定した。実験は次のように行った。実験装置に上記各触媒０．４ｇを充填し、Ｎ2／Ｈ2 比が１／３の原料ガスを６０ｃｍ3／ｍｉｎの流量で流通させ、反応温度を６７３Ｋ、反応圧力を０．１〜３ＭＰａに調整してアンモニア合成反応を行った。そして、反応後ガスを採取してアンモニア濃度の分析を行い、この分析値からアンモニア合成活性を求めた。
【００３３】
なお、比較のために、触媒として窒化モリブデン（Ｍｏ2 Ｎ）を用いた実験も行った。
【００３４】
実験結果は、表１及び図１〜図３に示す。表１は圧力を０．１ＭＰａで反応させた際の結果である。表１により明らかなように、本発明の各触媒を用いた場合のアンモニア合成活性は、窒化モリブデンを用いた比較例の値に対し、格段に高い値であった。特に、コバルト・モリブデン複合窒化物にアルカリを添加した触媒Ｆ-1（Ｋ添加）、触媒Ｆ-2（Ｃｓ添加）を用いた場合には、極めて高いアンモニア合成活性が得られた。
【００３５】
図１は各触媒のアンモニア合成活性に係る経時変化を示す図である。この実験においては、反応圧力０．１ＭＰａで行った。この図に示すように、窒化モリブデンを用いた比較例（○印）においては、触媒活性が低い上に、短時間使用しただけで失活してしまった。これに対し、実施例においては、何れの触媒を使用した場合にも、高い活性が持続した。特に、◆で示した触媒（Ｄ）を使用した場合には、他の触媒と比べて一段と高い活性が得られている。
【００３６】
図２はコバルト・モリブデン複合窒化物にアルカリを添加した触媒において、アルカリの添加量とアンモニア合成活性の関係を示す図である。この実験においては、反応圧力を０．１ＭＰａにして行った。図２によれば、カリウムを添加した触媒（Ｆ-1）においては、Ｋ／Ｍｏ（モル比）＝３０／１００の付近で触媒活性が最も大きくなる。又、セシウムを添加した触媒（Ｆ-2）においては、Ｃｓ／Ｍｏ（モル比）＝１０／１００の場合に最も大きい触媒活性が得られた。
【００３７】
図３は反応圧力とアンモニア合成活性の関係を示す図である。この図によれば、コバルト・モリブデン複合窒化物を主成分とする触媒（Ｄ）、これにセシウムを添加した触媒（Ｆ-2）の何れにおいても、反応圧力の増加に伴い触媒活性も増加している。この傾向は、本発明の触媒がルテニウム系触媒などの他の触媒とは違い、水素被毒の度合いが非常に小さいものであることを示している。
【００３８】
【表１】
【発明の効果】
本発明に係る触媒は、コバルト添加窒化モリブデン、窒化モリブデンと窒化コバルトの混合物、及びコバルト・モリブデン複合窒化物などの窒化物を主成分とするものであって、アンモニア合成活性が極めて高い触媒である。このため、この触媒を使用すれば、アンモニアの転化率が向上し、効率のよいアンモニア合成を行うことができる。
【００４０】
又、本発明に係るアンモニア合成方法によれば、使用する触媒がコバルト添加窒化モリブデン、窒化モリブデンと窒化コバルトの混合物、及びコバルト・モリブデン複合窒化物などの窒化物を主成分とするものであり、アンモニア合成活性が極めて高いものであるので、アンモニアの転化率が高くなり、原料ガスのリサイクル比を小さくすることができる。このため、アンモニア合成装置が小型化され、装置の建設費及び運転費が低減される。
【図面の簡単な説明】
【図１】各触媒のアンモニア合成活性に係る経時変化を示す図である。
【図２】アルカリの添加量とアンモニア合成活性の関係を示す図である。
【図３】反応圧力とアンモニア合成活性の関係を示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ammonia synthesis catalyst and an ammonia synthesis method.
[0002]
[Prior art]
Conventionally, in order to synthesize ammonia, an iron-based catalyst containing iron as a main component and alumina or potassium oxide as a co-catalyst has been widely used.
[0003]
[Problems to be solved by the invention]
However, in order to reduce the construction cost and operation cost of the ammonia synthesis apparatus, a catalyst having higher ammonia synthesis activity than the conventional iron-based catalyst is desired.
[0004]
An object of the present invention is to provide a highly active ammonia synthesis catalyst and an ammonia synthesis method.
[0005]
[Means for Solving the Problems]
The above problems are solved by the following invention.
[0006]
The ammonia synthesis catalyst according to the first invention is characterized by containing cobalt-added molybdenum nitride as a component exhibiting ammonia synthesis activity .
[0007]
The ammonia synthesis catalyst according to the second invention is characterized by containing a mixture of molybdenum nitride and cobalt nitride as a component exhibiting ammonia synthesis activity .
[0011]
A method for producing an ammonia synthesis catalyst according to a third aspect of the invention is a method for producing a compound containing cobalt-molybdenum composite nitride as a component exhibiting ammonia synthesis activity, and includes a step of nitriding molybdenum oxide impregnated with cobalt nitrate. It is characterized by that.
[0012]
A method for producing an ammonia synthesis catalyst according to a fourth invention is a method for producing a compound containing cobalt-molybdenum composite nitride as a component exhibiting ammonia synthesis activity, and includes a step of nitriding a mixture of molybdenum oxide and cobalt oxide. It is characterized by.
A method for producing an ammonia synthesis catalyst according to a fifth aspect of the invention is a method for producing cobalt-molybdenum composite nitride as a component exhibiting ammonia synthesis activity, comprising the step of nitriding cobalt molybdate hydrate. It is characterized by having.
The method for producing an ammonia synthesis catalyst according to the sixth invention is the method for producing an ammonia synthesis catalyst according to the fifth invention, wherein the hydrated cobalt molybdate is obtained by mixing cobalt nitrate and an aqueous solution of potassium molybdate or cesium molybdate. It is characterized by being.
A method for producing an ammonia synthesis catalyst according to a seventh invention is characterized in that, in the fifth invention, the hydrate of cobalt molybdate is impregnated with potassium nitrate or cesium nitrate.
[0013]
An ammonia synthesis method according to an eighth invention is characterized in that the ammonia synthesis catalyst according to the first or second invention is used.
[0014]
In ammonia synthesis, iron-based catalysts, ruthenium-based catalysts, and molybdenum-based catalysts are known to have high ammonia synthesis activity. Among these, molybdenum-based catalysts are classified into iron-based catalysts and ruthenium-based catalysts. In comparison, there are few examples of research on catalyst functions, and development of highly active catalysts has not been made much. Under such circumstances, molybdenum nitride (Mo 2 N) is known as one of molybdenum-based catalysts. Molybdenum nitride obtained by treating molybdenum oxide in an ammonia stream at an appropriate temperature and time has a characteristic that the specific surface area is large, but the catalytic activity is not so great.
[0015]
However, the present inventors have found that when molybdenum is nitrided by the above-described method, the specific surface area becomes very large, and the transition metal such as molybdenum, cobalt, nickel, and iron becomes bimetallic, resulting in high activity. In particular, the molybdenum composite nitride catalyst was obtained as a highly active catalyst. For this reason, in this invention, cobalt is selected as a transition metal combined with molybdenum, and it aims at making a catalyst highly active.
[0016]
The nitrides composed of molybdenum and cobalt in the present invention include (1) cobalt-added molybdenum nitride (Co / Mo 2 N), ( 2 ) a mixture of molybdenum nitride and cobalt nitride, and (3) cobalt-molybdenum composite nitride (Co 3 Mo 3 N) may be used, but among the above, particularly, those mainly composed of cobalt-molybdenum composite nitride have high activity. This is because molybdenum and cobalt are further activated by bimetalization. When the molybdenum / cobalt content ratio (Co / Mo molar ratio) in (2) and (3) is about 1/1, the catalytic activity is maintained for a long period of time, and the Co / Mo molar ratio is About 1/1 is preferable.
[0017]
Cobalt-molybdenum composite nitride (Co 3 Mo 3 N) is obtained by nitriding cobalt molybdate or cobalt molybdate hydrate, and is used for the preparation of the precursor cobalt molybdate or cobalt molybdate hydrate. Depending on the method, the catalytic activity varies.
[0018]
Further, when an alkali such as cesium or potassium is added to the cobalt-molybdenum composite nitride (Co 3 Mo 3 N), the activity becomes higher.
[0019]
According to the ammonia synthesizing method of the present invention, any of the above ammonia synthesis catalysts having high ammonia synthesis activity is used, so that the ammonia synthesis reaction is efficiently performed.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Each catalyst is produced by the method described below.
(Method for producing catalyst (A) according to the first invention)
Molybdenum oxide is immersed in an aqueous solution of cobalt nitrate so that molybdenum oxide is impregnated with cobalt nitrate, dried, and then nitrided. In the nitriding treatment, molybdenum oxide impregnated with cobalt nitrate is placed in an ammonia atmosphere, heated to a predetermined temperature at a predetermined temperature increase rate, and then held at that temperature for a predetermined time or more. An example of specific nitriding conditions is, for example, a temperature increase rate of up to 623 K is 10 K / min, a temperature increase rate of 623 K to 723 K is 0.6 K / min, and a temperature increase rate of 723 K to 973 K is 3 K / min. Perform at min and hold at 973K for 1 hour.
[0021]
By this treatment, a catalyst material mainly composed of cobalt-added molybdenum nitride (Co / Mo 2 N) is obtained. The content ratio of cobalt and molybdenum (Co / Mo molar ratio) in this catalyst is preferably about 1/20.
[0022]
(Method for producing catalyst (B) according to the second invention)
Molybdenum oxide powder and cobalt oxide powder are mixed, and the mixture is nitrided. The nitriding treatment is performed under the same conditions as in the production of the catalyst (A). According to this manufacturing method, a product mainly composed of a mixture of molybdenum nitride and cobalt nitride can be obtained. The content ratio of cobalt to molybdenum (Co / Mo molar ratio) in this catalyst is preferably about 1/1.
[0023]
(Method for producing catalyst (C) according to the fourth invention)
Cobalt nitrate (Co (NO 3 ) 2 .6H 2 O) and ammonium molybdate ((NH 4 ) 6 Mo 7 O 24 · 4H 2 O) are mixed and the mixture is calcined in air. By this firing, a fired product containing cobalt molybdate (CoMoO 4 ) as a main component is obtained. If an example of baking conditions is given, it will bake at 1073K for 3 hours.
[0024]
Next, the fired product mainly composed of cobalt molybdate (CoMoO 4 ) is placed in an ammonia atmosphere, heated to a predetermined temperature at a predetermined temperature increase rate, and then held at that temperature for a predetermined time or more. As an example of specific nitriding conditions, for example, heating is performed at a heating rate of 5 K / min, and held at 973 K for 6 hours.
[0025]
By the above treatment, a substance mainly composed of cobalt-molybdenum composite nitride (Co 3 Mo 3 N) is obtained. The content ratio of cobalt to molybdenum (Co / Mo molar ratio) in this catalyst is preferably about 1/1.
[0026]
(Method for producing catalyst (D) according to the fifth invention)
An aqueous solution of cobalt nitrate (Co (NO 3 ) 2 .6H 2 O) and ammonium molybdate ((NH 4 ) 6 Mo 7 O 24 · 4H 2 O) is mixed and boiled. The formed precipitate (cobalt molybdate hydrate (CoMoO 4 .0.9H 2 O)) is filtered off and washed. Next, the hydrated cobalt molybdate obtained by filtration and washing is subjected to nitriding treatment. For example, the nitriding treatment is performed under the same conditions as in the production of the catalyst (C). By the above treatment, a substance mainly composed of cobalt-molybdenum composite nitride (Co 3 Mo 3 N) is obtained. The content ratio of cobalt to molybdenum (Co / Mo molar ratio) in this catalyst is preferably about 1/1.
[0027]
(Production method of catalyst (E) according to sixth invention)
Cobalt nitrate (Co (NO 3 ) 2 .6H 2 O) and an aqueous solution of potassium molybdate (K 2 MoO 4 ) or cesium molybdate (Cs 2 MoO 4 ) are mixed and heated to boil. The formed precipitate (cobalt molybdate hydrate (CoMoO 4 .0.9H 2 O)) is filtered off and washed. Next, the hydrated cobalt molybdate obtained by filtration and washing is subjected to nitriding treatment. For example, the nitriding treatment is performed under the same conditions as in the production of the catalyst (C). By this treatment, a substance mainly composed of cobalt-molybdenum composite nitride (Co 3 Mo 3 N) is obtained.
[0028]
The catalyst (E) obtained by the above production method exhibits higher ammonia synthesis activity than the catalyst (D). This is presumably because the remaining potassium or cesium exerts an electron donating effect and promotes the activation of nitrogen on the catalyst surface. The content ratio of cobalt to molybdenum (Co / Mo molar ratio) in this catalyst is preferably about 1/1.
[0029]
(Production method of catalyst (F) according to seventh invention)
Cobalt molybdate hydrate (CoMoO 4 .0.9H 2 O) is immersed in an aqueous solution of potassium nitrate (KNO 3 ) or cesium nitrate (CsNO 3 ), and potassium nitrate or hydrate is added to the hydrate of cobalt molybdate. Is impregnated with cesium nitrate, dried, and then nitrided. For example, the nitriding treatment is performed under the same conditions as in the production of the catalyst (C). By this treatment, a substance mainly composed of cobalt-molybdenum composite nitride (Co 3 Mo 3 N) to which potassium or cesium is added is obtained. As described above, the addition of potassium or cesium promotes nitrogen activation on the catalyst surface, so that the catalyst (F) exhibits extremely high ammonia synthesis activity.
[0030]
The addition amount of potassium or cesium is preferably about K / Mo (molar ratio) = 30/100 when potassium is added, and about Cs / Mo (molar ratio) = 10/100 when cesium is added.
[0031]
The ammonia synthesis method according to the present invention is performed by reacting a mixed gas of nitrogen and hydrogen on any one of the ammonia synthesis catalysts according to the first to seventh inventions. The reaction is performed at a reaction temperature of 200 to 550 ° C., preferably 300 to 550 ° C., a reaction pressure of 0.1 to 30 MPa, preferably 0.5 to 20 MPa, a space velocity of 360 to 36000, a molar ratio of nitrogen and hydrogen of 1/10 to 1 / 1 is preferable.
[0032]
【Example】
About each catalyst manufactured by said method, ammonia synthesis experiment was conducted and ammonia synthesis activity was measured. The experiment was performed as follows. The experimental apparatus is filled with 0.4 g of each of the above catalysts, a raw material gas having a N 2 / H 2 ratio of 1/3 is circulated at a flow rate of 60 cm 3 / min, the reaction temperature is 673 K, and the reaction pressure is 0.1 to 3 MPa. The ammonia synthesis reaction was carried out by adjusting to And after reaction, gas was extract | collected, the ammonia concentration was analyzed, and ammonia synthesis activity was calculated | required from this analytical value.
[0033]
For comparison, an experiment using molybdenum nitride (Mo 2 N) as a catalyst was also conducted.
[0034]
The experimental results are shown in Table 1 and FIGS. Table 1 shows the results when the pressure is reacted at 0.1 MPa. As is clear from Table 1, the ammonia synthesis activity when using each catalyst of the present invention was much higher than the value of the comparative example using molybdenum nitride. In particular, when the catalyst F-1 (K addition) and the catalyst F-2 (Cs addition) in which an alkali was added to cobalt-molybdenum composite nitride were used, extremely high ammonia synthesis activity was obtained.
[0035]
FIG. 1 is a graph showing the change with time of the ammonia synthesis activity of each catalyst. In this experiment, the reaction pressure was 0.1 MPa. As shown in this figure, in the comparative example (◯ mark) using molybdenum nitride, the catalytic activity was low, and it was deactivated only by using for a short time. On the other hand, in the examples, high activity was maintained regardless of which catalyst was used. In particular, when the catalyst (D) indicated by ◆ is used, a much higher activity is obtained as compared with other catalysts.
[0036]
FIG. 2 is a graph showing the relationship between the amount of alkali added and the ammonia synthesis activity in a catalyst in which alkali is added to cobalt-molybdenum composite nitride. In this experiment, the reaction pressure was 0.1 MPa. According to FIG. 2, in the catalyst (F-1) to which potassium is added, the catalytic activity becomes the largest in the vicinity of K / Mo (molar ratio) = 30/100. Further, in the catalyst (F-2) to which cesium was added, the largest catalytic activity was obtained when Cs / Mo (molar ratio) = 10/100.
[0037]
FIG. 3 is a graph showing the relationship between reaction pressure and ammonia synthesis activity. According to this figure, in both the catalyst (D) mainly composed of cobalt-molybdenum composite nitride and the catalyst (F-2) added with cesium, the catalytic activity increases as the reaction pressure increases. ing. This tendency indicates that the catalyst of the present invention has a very low degree of hydrogen poisoning unlike other catalysts such as a ruthenium-based catalyst.
[0038]
[Table 1]
【The invention's effect】
The catalyst according to the present invention is mainly composed of a nitride such as cobalt-added molybdenum nitride, a mixture of molybdenum nitride and cobalt nitride, and a cobalt-molybdenum composite nitride, and has a very high ammonia synthesis activity. . For this reason, if this catalyst is used, the conversion rate of ammonia is improved, and efficient ammonia synthesis can be performed.
[0040]
Further, according to the ammonia synthesis method of the present invention, the catalyst used is mainly composed of nitride such as cobalt-added molybdenum nitride, a mixture of molybdenum nitride and cobalt nitride, and cobalt-molybdenum composite nitride, Since the ammonia synthesis activity is extremely high, the conversion rate of ammonia is increased, and the recycle ratio of the raw material gas can be reduced. For this reason, the ammonia synthesis apparatus is reduced in size, and the construction cost and operation cost of the apparatus are reduced.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a graph showing a change with time of ammonia synthesis activity of each catalyst.
FIG. 2 is a graph showing the relationship between the amount of alkali added and the ammonia synthesis activity.
FIG. 3 is a graph showing the relationship between reaction pressure and ammonia synthesis activity.
Claims (8)
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| JP4554752B2 (en) * | 2000-02-29 | 2010-09-29 | Ｊｆｅエンジニアリング株式会社 | Ammonia synthesis catalyst |
| IS2972B (en) | 2014-06-13 | 2017-07-15 | Háskóli Íslands | Process and system for electrolytic production of ammonia |
| SG11201901826XA (en) * | 2016-10-05 | 2019-04-29 | Exxonmobil Chemical Patents Inc | Method for producing metal nitrides and metal carbides |
| JP7099722B2 (en) * | 2017-03-07 | 2022-07-12 | 国立研究開発法人理化学研究所 | Ammonia synthesis catalyst and its use |
| CN111790428B (en) * | 2020-07-13 | 2021-09-28 | 福州大学 | Co-based interstitial compound catalyst, preparation method and application thereof in ammonia synthesis |
| CN111744525B (en) * | 2020-07-13 | 2023-04-07 | 上饶师范学院 | Molybdenum nitride catalyst for hydrogen production from formic acid |
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