JP6015238B2 - Catalyst for producing hydrogen, method for producing the same, and method for producing hydrogen - Google Patents
Catalyst for producing hydrogen, method for producing the same, and method for producing hydrogen Download PDFInfo
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- 239000003054 catalyst Substances 0.000 title claims description 236
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 title claims description 166
- 239000001257 hydrogen Substances 0.000 title claims description 159
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- 150000002431 hydrogen Chemical class 0.000 title claims description 9
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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
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/50—Fuel cells
-
- 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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- Hydrogen, Water And Hydrids (AREA)
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- Fuel Cell (AREA)
Description
本発明は、メタンガス等の炭化水素系ガスおよび水蒸気を用いて水素を取り出す水素製造用触媒、その製造方法および水素製造用触媒を用いた水素製造方法に関する。 The present invention relates to a hydrogen production catalyst that extracts hydrogen using a hydrocarbon gas such as methane gas and water vapor, a production method thereof, and a hydrogen production method using the hydrogen production catalyst.
近年、水素を燃料源とする燃料電池は天然ガスから水素を取り出して、水のみを排出するという点で注目を集めており、中でも水素製造プラント、小型水素製造装置および家庭用燃料電池に用いられる触媒の研究開発が年々盛んになっている。 In recent years, fuel cells using hydrogen as a fuel source have attracted attention in that they extract hydrogen from natural gas and discharge only water, and are used especially in hydrogen production plants, small hydrogen production devices, and household fuel cells. Research and development of catalysts has become active year after year.
従来、燃料電池用触媒としてはニッケル（Ｎｉ）を担持粒子とするニッケルアルミニウム合金触媒やニッケルクロム合金触媒が代表的な触媒であった。これらの触媒は貴金属の触媒に比べて、比較的安価であり、入手も容易であった。 Conventionally, as a catalyst for a fuel cell, a nickel aluminum alloy catalyst or a nickel chromium alloy catalyst using nickel (Ni) as support particles has been a typical catalyst. These catalysts are relatively inexpensive and easily available compared to precious metal catalysts.
例えば、特許文献１には、アルミナ（Ａｌ２Ｏ３）を含むニッケルとアルミニウムとの化合物（金属間化合物：Ｎｉ３Ａｌ）表面にニッケル（Ｎｉ）微粒子が分散している水素製造用のニッケルアルミニウム合金触媒が開示されている。触媒の製造方法については、金属間化合物Ｎｉ３Ａｌを酸化処理することで表面にニッケル酸化物（ＮｉＯ）とアルミニウム酸化物（アルミナ）を形成し、ニッケル酸化物を水素ガスで還元することでニッケル微粒子とアルミナからなる表面を形成したニッケルアルミニウム合金触媒を生成すると記載されている（同文献の段落〔００１５〕等参照）。 For example, Patent Document 1 discloses nickel aluminum for hydrogen production in which nickel (Ni) fine particles are dispersed on the surface of a compound (intermetallic compound: Ni 3 Al) of nickel and aluminum containing alumina (Al 2 O 3 ). An alloy catalyst is disclosed. Regarding the method for producing the catalyst, nickel oxide (NiO) and aluminum oxide (alumina) are formed on the surface by oxidizing the intermetallic compound Ni 3 Al, and nickel oxide is reduced by hydrogen gas to reduce nickel. It is described that a nickel-aluminum alloy catalyst having a surface composed of fine particles and alumina is produced (see paragraph [0015], etc.).
また、特許文献２にはニッケル酸化物（ＮｉＯ）とクロム酸化物（Ｃｒ２Ｏ３）との酸化物の層を形成したニッケルクロム合金上にニッケル（Ｎｉ）が微細に高分散しているカーボンナノチューブ生成用触媒が開示されている。触媒となる材料（ニッケルクロム合金）については、カーボンナノチューブ生成用触媒として作用する金属（Ｎｉ）と、カーボンナノチューブ生成用触媒として作用しない金属（Ｃｒ）とからなる材料を酸素雰囲気下で酸化処理することで、Ｎｉの触媒原子間に酸素を介在させるとともに、安定なＮｉＯとＣｒ２Ｏ３との酸化物の層を表面に形成させて、触媒としてＮｉの凝集を抑制することを特徴としている。また、ニッケルクロム合金の好ましい化学成分としては、Ｎｉが７７ｍａｓｓ％以上、Ｃｒが１９〜２１ｍａｓｓ％であると記載されている（同文献の段落〔００１８〕等参照）。 Patent Document 2 discloses carbon in which nickel (Ni) is finely and highly dispersed on a nickel chromium alloy in which an oxide layer of nickel oxide (NiO) and chromium oxide (Cr 2 O 3 ) is formed. A nanotube production catalyst is disclosed. As for the material (nickel-chromium alloy) that becomes a catalyst, a material consisting of a metal (Ni) that acts as a catalyst for producing carbon nanotubes and a metal (Cr) that does not act as a catalyst for producing carbon nanotubes is oxidized in an oxygen atmosphere. Thus, oxygen is interposed between the catalyst atoms of Ni, and a stable oxide layer of NiO and Cr 2 O 3 is formed on the surface to suppress aggregation of Ni as a catalyst. Moreover, as a preferable chemical component of a nickel chromium alloy, it is described that Ni is 77 mass% or more and Cr is 19-21 mass% (refer paragraph [0018] etc. of the same literature).
さらに、本発明者らは非特許文献１において、クロム含有量が質量％で２０ｍａｓｓ％であるニッケルクロム合金を酸化処理および還元処理することで、水素ガスの製造効率の指標となるメタン転化率が他のニッケル基合金に比べて優れていることを発表した。あわせて、そのニッケルクロム合金には厚さ１μｍ程度のクロム酸化物の層が形成されて、その上に直径０．３μｍ程度のニッケルを主成分とする微粒子が多く析出していることも発表した。 Furthermore, in the non-patent document 1, the present inventors perform oxidation treatment and reduction treatment on a nickel chromium alloy having a chromium content of 20% by mass, whereby a methane conversion rate that is an index of hydrogen gas production efficiency is obtained. Announced that it is superior to other nickel-based alloys. At the same time, it was announced that a chromium oxide layer with a thickness of about 1 μm was formed on the nickel-chromium alloy, and many fine particles mainly composed of nickel with a diameter of about 0.3 μm were deposited on the layer. .
しかし、ニッケルアルミニウム合金触媒やニッケルクロム合金触媒は、ニッケルがカーボン析出を起こしやすい元素であることから水素ガスを製造する際の原料ガス（混合ガス）に含まれる水蒸気の分子数と炭素の原子数との比、いわゆるスチームカーボン比（Ｓ／Ｃ比）を大きく設定しなければ、長時間の使用において触媒上にカーボンが析出して触媒としての機能を果たせなくなるという問題があった。同時に、供給すべき水蒸気の量が多くなり、水素を製造するコスト面においても非効率的であった。 However, nickel-aluminum alloy catalyst and nickel-chromium alloy catalyst, since nickel is an element that easily causes carbon deposition, the number of water vapor molecules and the number of carbon atoms contained in the raw gas (mixed gas) when producing hydrogen gas If the ratio of so-called steam carbon ratio (S / C ratio) is not set large, there is a problem that carbon does not deposit on the catalyst and can not function as a catalyst even when used for a long time. At the same time, the amount of water vapor to be supplied is increased, which is inefficient in terms of the cost of producing hydrogen.
そこで、特許文献３および４に開示されている、Ｓ／Ｃ比が小さくても長時間の使用においてカーボン析出が起こりにくいルテニウム（Ｒｕ）系の触媒が、水素製造用触媒として提案されている。これは、ルテニウムがカーボン析出の抑制効果を有する元素であるからである。
Therefore, ruthenium (Ru) -based catalysts that are disclosed in
例えば、特許文献３には、アルミナを主成分としてルテニウムを高分散した水素製造用の（水蒸気改質）触媒が開示されている。この触媒は、表面上のカーボン析出を抑制しつつ、Ｓ／Ｃ比が３〜１０の条件下にてナフサ等の炭素数が６以上の液状炭化水素を原料とした水蒸気改質による水素製造が可能であることを特徴としている（同文献の段落〔００２０〕等参照）。 For example, Patent Document 3 discloses a hydrogen production (steam reforming) catalyst in which ruthenium is highly dispersed with alumina as a main component. This catalyst is capable of producing hydrogen by steam reforming using liquid hydrocarbons having 6 or more carbon atoms such as naphtha as raw materials under the conditions of S / C ratio of 3 to 10 while suppressing carbon deposition on the surface. It is possible (see paragraph [0020] etc. of the same document).
また、特許文献４には、マグネシウム、アルミニウム、およびニッケルから構成される金属材料に、平均粒子径が０．５ｎｍ〜１０ｎｍであるルテニウム粒子が０．０５ｍａｓｓ％〜５．０ｍａｓｓ％含有されている触媒が開示されている。この触媒は、反応温度が２５０℃〜８５０℃、Ｓ／Ｃ比が１〜６の条件下にて都市ガス、天然ガス、灯油、ガソリン、軽油等の炭化水素と水蒸気とを反応させることで水素ガスを製造できることを特徴としている（同文献の段落〔００６６〕等参照）。
しかし、例えば、特許文献３および４に開示されているルテニウム系触媒を用いた水素製造用改質器内において、配管の故障など不測の事態により、供給される原料となる水蒸気の量が炭化水素系ガスの量を下回ると、結果としてＳ／Ｃ比が１．０未満になるので、改質器内には未反応の炭化水素系ガスが過剰に残留する。その結果、水素製造工程では触媒表面にカーボンが析出し始めて、ついには触媒機能が低下するという問題があった。
However, for example, in a hydrogen production reformer using a ruthenium-based catalyst disclosed in
また、ルテニウム系触媒は触媒機能を有する微粒子の粒径が１μｍ未満のナノオーダーであるため、長期間の使用によって微粒子同士が凝集しやすいという性質がある。そのため、微粒子同士の凝集が一旦開始すると触媒としての機能が徐々に劣化する。さらに、ルテニウム系触媒は再生処理等を施すことで初期の機能を回復させることができず、その度ごとに新たな触媒と交換する必要が生じて、水素ガスを製造する面から非常にコスト高になるという問題があった。 In addition, ruthenium-based catalysts have a property that fine particles having a catalytic function are nano-order having a particle size of less than 1 μm, so that the fine particles are likely to aggregate with long-term use. Therefore, once aggregation of the fine particles starts, the function as a catalyst gradually deteriorates. Furthermore, ruthenium-based catalysts cannot be restored to their initial functions by applying regeneration treatment, etc., and each time they need to be replaced with new catalysts, which is very expensive in terms of producing hydrogen gas. There was a problem of becoming.
そこで、本発明においては前述した問題点に鑑みて、水素製造用改質器内において不測の事態等により水素ガスを製造する原料ガスのＳ／Ｃ比が１．０未満の場合であっても触媒表面にカーボン（Ｃ）を析出し難く、安定した触媒機能を持続できる水素製造用触媒およびその製造方法を提供することを課題とする。また、長期にわたる水素製造において水素ガスの製造原価を低減できる水素製造用触媒、その製造方法および水素製造方法を提供することを課題とする。 Therefore, in the present invention, in view of the above-described problems, even when the S / C ratio of the raw material gas for producing hydrogen gas is less than 1.0 due to unforeseen circumstances in the reformer for hydrogen production, etc. It is an object of the present invention to provide a hydrogen production catalyst that hardly deposits carbon (C) on the catalyst surface and can maintain a stable catalytic function, and a method for producing the same. It is another object of the present invention to provide a hydrogen production catalyst, a production method thereof, and a hydrogen production method capable of reducing the production cost of hydrogen gas in long-term hydrogen production.
本発明者は、かかる課題を解決するために従来の触媒であったニッケルクロム合金について更に鋭意研究した結果、ニッケルクロム合金（固溶体）上にクロム化合物の層が形成されており、クロム化合物の層上にはニッケルを主成分とする微粒子が分散されていることが水素製造用触媒として有効であること、およびその微粒子にはニッケルを除く他の成分として酸素が含有されていることが触媒機能を発揮する微粒子として有効であることを知得した。 As a result of further diligent research on a nickel-chromium alloy that has been a conventional catalyst in order to solve such problems, the inventor has formed a chromium compound layer on the nickel-chromium alloy (solid solution). The catalyst function is that fine particles containing nickel as the main component are effective as a catalyst for hydrogen production, and that the fine particles contain oxygen as a component other than nickel. It was found that it was effective as a fine particle to be exhibited.
これらの知得により、本発明においてはニッケルクロム（Ｎｉ−Ｃｒ）合金上にクロム化合物の層が形成されており、クロム化合物の層上にはニッケルを主成分とする微粒子が分散されており、その微粒子には他の成分として酸素が含有されている水素製造用触媒とした。これにより本発明に係る水素製造用触媒は、水素ガスを製造する原料ガスのＳ／Ｃ比が１．０未満の場合であっても水素製造時において触媒表面に析出するカーボンを抑制する。同時に、触媒が長期にわたり使用された場合であっても、その触媒に対して所定の処理を施すことにより初期の機能を回復させる（再生させる）ことができる。 With these knowledge, in the present invention, a chromium compound layer is formed on a nickel chromium (Ni-Cr) alloy, and fine particles mainly composed of nickel are dispersed on the chromium compound layer. The fine particles used as a catalyst for hydrogen production in which oxygen was contained as another component. Thereby, the catalyst for hydrogen production according to the present invention suppresses carbon deposited on the catalyst surface during hydrogen production even when the S / C ratio of the raw material gas for producing hydrogen gas is less than 1.0. At the same time, even if the catalyst has been used for a long period of time, the initial function can be recovered (regenerated) by applying a predetermined treatment to the catalyst.
また、第２の発明は微粒子には質量％で０．７ｍａｓｓ％以上９．９ｍａｓｓ％以下の酸素が含有されている水素製造用触媒とした（請求項２）。さらに、第３の発明は微粒子の粒径が０．０５μｍ（５０ｎｍ）以上５μｍ以下である水素製造用触媒とした（請求項３）。また、第４の発明は微粒子の投影面積が占める割合が水素製造用触媒の表面の投影面積に対して１３．１％以上２７．５％以下である水素製造用触媒とした（請求項４）。 The second invention is a hydrogen production catalyst in which the fine particles contain oxygen in a mass% of 0.7 mass% or more and 9.9 mass% or less (claim 2). Further, the third invention provides a hydrogen production catalyst in which the particle size of the fine particles is 0.05 μm (50 nm) or more and 5 μm or less (invention 3). According to a fourth aspect of the present invention, there is provided a hydrogen production catalyst wherein the proportion of the projected area of the fine particles is 13.1% or more and 27.5% or less with respect to the projected area of the surface of the hydrogen production catalyst. .
クロム化合物については、第５の発明をクロム化合物はクロム酸化物である水素製造用触媒とした（請求項５）。また、第６の発明はクロム酸化物が酸化クロム（ＩＩＩ）（Ｃｒ２Ｏ３）である水素製造用触媒とした（請求項６）。さらに、第７の発明はクロム化合物の層の厚さが０．１０μｍ以上である水素製造用触媒とした（請求項７）。母材であるニッケルクロム合金については、第８の発明をニッケルクロム合金中のクロム含有量が質量％で５ｍａｓｓ％以上２０ｍａｓｓ％以下である水素製造用触媒とした（請求項８）。 As for the chromium compound, the fifth invention is a hydrogen production catalyst in which the chromium compound is a chromium oxide. The sixth invention is a hydrogen production catalyst in which the chromium oxide is chromium (III) oxide (Cr 2 O 3 ) (claim 6). Further, the seventh invention provides a hydrogen production catalyst having a chromium compound layer thickness of 0.10 μm or more (invention 7). Regarding the nickel-chromium alloy as the base material, the eighth invention is a catalyst for hydrogen production in which the chromium content in the nickel-chromium alloy is 5 mass% or more and 20 mass% or less by mass (invention 8).
水素製造用触媒の製造方法の発明については、第９の発明を酸化性ガスと還元性ガスとの混合ガスの雰囲気下において、ニッケルクロム合金が活性化処理温度で加熱処理される水素製造用触媒の製造方法とした（請求項９）。また、第１０の発明は加熱処理される前に酸化処理が行われる水素製造用触媒の製造方法とした（請求項１０）。 Regarding the invention of the method for producing a catalyst for hydrogen production, the ninth invention is a catalyst for producing hydrogen in which the nickel chromium alloy is heat-treated at the activation treatment temperature in an atmosphere of a mixed gas of oxidizing gas and reducing gas. (Claim 9). The tenth invention is a method for producing a catalyst for producing hydrogen in which an oxidation treatment is performed before the heat treatment (claim 10).
水素製造用触媒を用いた水素製造方法の発明については、第１１の発明を水素製造用触媒の存在下にて、水蒸気と炭素原子を含むガスを用いて、水蒸気の分子数と炭素原子を含むガス中の炭素原子数との比であるスチームカーボン比（Ｓ／Ｃ）が、Ｓ／Ｃ＝１〜３の関係式を満たす条件で水素が製造される水素製造方法とした（請求項１１）。 Regarding the invention of the hydrogen production method using the hydrogen production catalyst, the eleventh invention uses the gas containing water vapor and carbon atoms in the presence of the hydrogen production catalyst, and contains the number of water vapor molecules and carbon atoms. A hydrogen production method in which hydrogen is produced under conditions where the steam carbon ratio (S / C), which is the ratio to the number of carbon atoms in the gas, satisfies the relational expression of S / C = 1 to 3 (claim 11). .
以上述べたように、本発明においては、ニッケルクロム合金上にクロム化合物の層が形成されており、クロム化合物の層上にはニッケルを主成分とする微粒子が分散されている水素製造用触媒であって、微粒子には他の成分として酸素が含有されている水素製造用触媒とした。この水素製造用触媒を用いることにより、水素ガスを製造する原料ガスのＳ／Ｃ比が１．０未満の条件であっても水素製造時に触媒表面へのカーボンの析出が抑制される。その結果、長時間にわたり安定した触媒機能を持続できるという効果を奏する。また、本発明に係る水素製造用触媒は、長時間の使用により触媒機能が低下しても、所定の処理を施すことで当初の触媒機能を取り戻す（再生する）ことができるので、長期にわたり水素ガスの製造コストを低減できるという効果も奏する。 As described above, in the present invention, there is provided a hydrogen production catalyst in which a chromium compound layer is formed on a nickel chromium alloy, and fine particles mainly composed of nickel are dispersed on the chromium compound layer. Thus, the catalyst for hydrogen production, in which fine particles contain oxygen as another component, was used. By using this hydrogen production catalyst, carbon deposition on the catalyst surface is suppressed during hydrogen production even when the S / C ratio of the raw material gas for producing hydrogen gas is less than 1.0. As a result, there is an effect that a stable catalyst function can be maintained for a long time. Further, the catalyst for hydrogen production according to the present invention can recover (regenerate) the original catalytic function by performing a predetermined treatment even if the catalytic function is deteriorated by long-term use. There is also an effect that the gas production cost can be reduced.
さらに、本発明に係る水素製造用触媒は、金属間化合物を含有する他の合金触媒に比べて延性や展性に優れているので、箔状への圧延加工の他に、線材やシームレス管などの管材への加工も容易に行うことができる。したがって、加工した線材を編みこむことで織物状の触媒として生産できる他に、線材と線材間との目開きを自在に調節することで様々なメッシュサイズの網目状の触媒も生産できるという効果も奏する。 Furthermore, since the catalyst for hydrogen production according to the present invention is superior in ductility and malleability compared to other alloy catalysts containing intermetallic compounds, in addition to rolling into a foil shape, wire rods, seamless tubes, etc. The tube material can be easily processed. Therefore, in addition to being able to produce a woven catalyst by weaving the processed wire, it is also possible to produce mesh catalysts of various mesh sizes by freely adjusting the opening between the wire and the wire. Play.
本発明に係る水素製造用触媒の製造方法については、酸化性ガスと還元性ガスとの混合ガスの雰囲気下において、ニッケルクロム合金を活性化処理温度で加熱処理する水素製造用触媒の製造方法とする。これにより、クロム化合物の層上にニッケルを主成分とする微粒子が現れる割合が増加するので、触媒機能が向上するという効果を奏する。その上、ニッケルアルミニウム合金触媒のように前加工や特殊な熱処理も不要であるため、低コストにて触媒を製造できるという効果も奏する。 The method for producing a catalyst for hydrogen production according to the present invention includes a method for producing a catalyst for hydrogen production in which a nickel chromium alloy is heat-treated at an activation treatment temperature in an atmosphere of a mixed gas of an oxidizing gas and a reducing gas. To do. As a result, the ratio of the appearance of fine particles containing nickel as a main component on the chromium compound layer increases, and the catalytic function is improved. In addition, since no pre-processing or special heat treatment is required unlike the nickel-aluminum alloy catalyst, the catalyst can be produced at low cost.
本発明に係る水素製造方法については、水素製造用触媒の存在下にて、水蒸気と炭素原子を含むガスを原料として、水蒸気の分子数と炭素原子を含むガス中の炭素原子数との比であるスチームカーボン比（Ｓ／Ｃ）が、Ｓ／Ｃ＝１〜３の関係式を満たす条件にて水素を製造することにより、原料となる水蒸気と炭化水素系ガスを同量で製造しても触媒表面にカーボンの析出を抑制して、水素が製造できる。その結果、ルテニウムなどの貴金属材料の触媒を使用して水素ガスを製造する場合に比べて、水素ガスの製造原価を大幅に低減できるという効果を奏する。 About the hydrogen production method according to the present invention, in the presence of a hydrogen production catalyst, using a gas containing water vapor and carbon atoms as a raw material, the ratio of the number of water vapor molecules to the number of carbon atoms in the gas containing carbon atoms Even if the steam and hydrocarbon gas used as raw materials are produced in the same amount by producing hydrogen under the condition that a certain steam carbon ratio (S / C) satisfies the relational expression of S / C = 1 to 3 Hydrogen can be produced while suppressing carbon deposition on the catalyst surface. As a result, the production cost of hydrogen gas can be greatly reduced as compared with the case of producing hydrogen gas using a catalyst of a noble metal material such as ruthenium.
本発明の実施の形態について、以下に詳細に説明する。本発明に係る水素製造用触媒は、ニッケルクロム合金上にクロム化合物の層が形成されており、クロム化合物の層上にニッケルを主成分とする微粒子が分散されており、微粒子には他の成分として酸素が含有されている水素製造用触媒とした。本発明に係る水素製造用触媒が表面におけるカーボンの析出を抑制できる理由について、本発明者らは以下のように推測する。 Embodiments of the present invention will be described in detail below. The catalyst for hydrogen production according to the present invention has a chromium compound layer formed on a nickel chromium alloy, and fine particles mainly composed of nickel are dispersed on the chromium compound layer. As a hydrogen production catalyst containing oxygen. The present inventors presume the reason why the hydrogen production catalyst according to the present invention can suppress the precipitation of carbon on the surface as follows.
すなわち、本発明に係る触媒を用いた水素製造の過程は原料となるメタンガス等の炭化水素系ガスを水蒸気により酸化することで行い、この過程で水素ガスのほかに一酸化炭素（ＣＯ）が同時に生成（化学反応式１参照）されて、雰囲気の状況に応じて一酸化炭素と水蒸気とが反応することで、二酸化炭素も生成される（化学反応式２参照）。この場合、下記に示す化学反応式により、触媒表面にはカーボンが析出することがある（化学反応式３参照）。また、触媒表面に吸着した炭化水素系ガスが十分に酸化されず、カーボンとなって析出することがある（化学反応式４参照）。
Ｈ２Ｏ＋ＣＨ４→３Ｈ２＋ＣＯ ・・・・（化学反応式１：メタン水蒸気改質反応）
ＣＯ＋Ｈ２Ｏ→Ｈ２＋ＣＯ２・・・（化学反応式２：水性シフト反応）
２ＣＯ←→Ｃ+ＣＯ２・・・・（化学反応式３：一酸化炭素の不均化反応）
ＣＨ４←→Ｃ+２Ｈ２・・・・（化学反応式４：メタンの熱分解反応）
That is, the process of hydrogen production using the catalyst according to the present invention is performed by oxidizing a hydrocarbon-based gas such as methane gas, which is a raw material, with steam, and in this process, carbon monoxide (CO) is simultaneously added to the hydrogen gas. Generated (see chemical reaction formula 1), and carbon monoxide and water vapor react with each other according to the state of the atmosphere, so that carbon dioxide is also generated (see chemical reaction formula 2). In this case, carbon may be deposited on the catalyst surface by the chemical reaction formula shown below (see chemical reaction formula 3). Further, the hydrocarbon gas adsorbed on the catalyst surface may not be sufficiently oxidized and may be deposited as carbon (see chemical reaction formula 4).
H 2 O + CH 4 → 3H 2 + CO (chemical reaction formula 1: methane steam reforming reaction)
CO + H 2 O → H 2 + CO 2 (chemical reaction formula 2: aqueous shift reaction)
2CO ← → C + CO 2 ... (chemical reaction formula 3: disproportionation of carbon monoxide)
CH 4 ← → C + 2H 2 ... (chemical reaction formula 4: thermal decomposition reaction of methane)
上述した事実に加えて、本発明者らは本発明に係る水素製造用触媒を形成しているクロム化合物の層の厚さに関して、図１に示す触媒処理システムのガス入口側に設置された触媒のクロム化合物の層の厚さは、同図に示すガス出口側に設置された触媒のクロム化合物の層の厚さに比べて、水素製造過程の前後におけるクロム化合物の層の厚さの増加量が少ないことを発見した。これらの事実から判断して、炭化水素系ガスから発生する余分なカーボンがクロム化合物（特にクロム酸化物）によっても酸化されて、一酸化炭素が生成されたと推測した。すなわち、炭化水素系ガスが酸化される際に生成するカーボンは水蒸気だけではなく、水素製造用触媒を形成するクロム化合物によっても酸化されて、一酸化炭素の生成に貢献しているので、カーボン単独では存在し難い状況が作り出されているためと考えられる。以下、水素製造用触媒を構成する、ニッケルを主成分とする微粒子、クロム化合物の層および母材であるニッケルクロム合金について各々詳細に説明する。 In addition to the above-mentioned facts, the present inventors are concerned with the catalyst installed on the gas inlet side of the catalyst treatment system shown in FIG. 1 with respect to the thickness of the chromium compound layer forming the hydrogen production catalyst according to the present invention. The amount of increase in the thickness of the chromium compound layer before and after the hydrogen production process compared to the thickness of the chromium compound layer of the catalyst installed on the gas outlet side shown in the figure. I found that there are few. Judging from these facts, it was presumed that excess carbon generated from the hydrocarbon-based gas was oxidized by the chromium compound (particularly chromium oxide) to generate carbon monoxide. In other words, the carbon produced when the hydrocarbon gas is oxidized is oxidized not only by water vapor but also by the chromium compound forming the hydrogen production catalyst, contributing to the production of carbon monoxide. It is thought that this is because a situation that does not exist is created. Hereinafter, the fine particles mainly composed of nickel, the chromium compound layer, and the nickel-chromium alloy as the base material, which constitute the hydrogen production catalyst, will be described in detail.
ニッケル（Ｎｉ）を主成分とする微粒子は、本発明に係る水素製造用ニッケルクロム合金触媒において主に触媒機能を果す役割がある。当該微粒子は、ニッケル（Ｎｉ）を主成分として、酸素（Ｏ）、クロム（Ｃｒ）、炭素（Ｃ）などの元素が他の成分として含有されている。ここで、主成分とは微粒子を構成する元素として質量％で５１ｍａｓｓ％以上が含有されていることをいう。また、その微粒子が酸化皮膜や窒化皮膜等の皮膜に覆われている場合には、当該皮膜を構成する元素（酸素や窒素など）についてもその微粒子を構成する元素に含むものとする。微粒子を構成する他の成分割合（ｍａｓｓ％）としては、酸素が０．７ｍａｓｓ％以上９．９ｍａｓｓ％以下、クロムが１．２ｍａｓｓ％以上１１．０ｍａｓｓ％以下、炭素が１．６ｍａｓｓ％以下であることが好ましい。 The fine particles mainly composed of nickel (Ni) have a role of mainly performing a catalytic function in the nickel chromium alloy catalyst for hydrogen production according to the present invention. The fine particles contain nickel (Ni) as a main component and elements such as oxygen (O), chromium (Cr), and carbon (C) as other components. Here, the main component means that 51% by mass or more is contained in mass% as an element constituting the fine particles. Further, when the fine particles are covered with a film such as an oxide film or a nitride film, the elements constituting the film (oxygen, nitrogen, etc.) are also included in the elements constituting the fine particles. As other component ratios (mass%) constituting the fine particles, oxygen is 0.7 mass% or more and 9.9 mass% or less, chromium is 1.2 mass% or more and 11.0 mass% or less, and carbon is 1.6 mass% or less. It is preferable.
また、微粒子の粒径については０．０５μｍ（５０ｎｍ）以上５μｍ以下であることが好ましい。ここで、微粒子の粒径とはその微粒子を取り囲む外接円の直径をいう。微粒子の粒径を０．０５μｍ以上５μｍ以下に限定する理由は、微粒子の粒径が０．０５μｍ未満であると微粒子が（下地である）クロム化合物の層内に埋没されてしまい、触媒機能が低下する原因となるためである。また、微粒子の粒径が５μｍを超えると触媒表面に占める微粒子の表面積の割合が減少し、同様に触媒機能が低下する原因となる。水素製造用ニッケルクロム合金触媒の表面における微粒子の投影面積が占める割合については、水素製造用触媒の表面の投影面積に対して１３．１％以上２７．５％以下であることが好ましい。 The particle size of the fine particles is preferably 0.05 μm (50 nm) or more and 5 μm or less. Here, the particle diameter of the fine particles refers to the diameter of a circumscribed circle surrounding the fine particles. The reason why the particle size of the fine particles is limited to 0.05 μm or more and 5 μm or less is that if the particle size of the fine particles is less than 0.05 μm, the fine particles are buried in the layer of the chromium compound (underlying) and the catalytic function is reduced. This is because it causes a decrease. On the other hand, when the particle diameter of the fine particles exceeds 5 μm, the ratio of the surface area of the fine particles to the catalyst surface is reduced, and the catalyst function is similarly lowered. The proportion of the projected area of the fine particles on the surface of the nickel-chromium alloy catalyst for hydrogen production is preferably 13.1% or more and 27.5% or less with respect to the projected area of the surface of the catalyst for hydrogen production.
ここで、水素製造用触媒の表面における微粒子の投影面積とは、水素製造用触媒表面の鉛直上方から光を照射した場合に平面上に投影される微粒子部分の面積をいう。微粒子の投影面積の割合を１３．１％以上２７．５％以下とする理由は、投影面積の割合が１３．１％未満であると触媒機能を担う微粒子の割合が少ないので、触媒機能を十分に発揮できなくなるためである。また、投影面積の割合が２７．５％を超えると、微粒子の下地層であるクロム化合物が触媒表面に現れる割合が減少するので、触媒表面におけるカーボン析出を十分に抑制できなくなるためである。 Here, the projected area of the fine particles on the surface of the hydrogen production catalyst means the area of the fine particle portion projected on a plane when light is irradiated from vertically above the hydrogen production catalyst surface. The reason why the ratio of the projected area of the fine particles is 13.1% or more and 27.5% or less is that if the ratio of the projected area is less than 13.1%, the ratio of the fine particles having the catalytic function is small, so that the catalytic function is sufficient It is because it becomes impossible to demonstrate to. Further, when the proportion of the projected area exceeds 27.5%, the proportion of the chromium compound, which is a fine particle underlayer, appears on the catalyst surface, so that carbon deposition on the catalyst surface cannot be sufficiently suppressed.
クロム化合物の層は、ニッケルを主成分とする微粒子をニッケルクロム合金から脱落しないように固定させておく接着層の役割を果すと共に、炭化水素系ガス等の炭素原子を含むガスに由来するカーボン析出を抑制する役割を果す。クロム化合物には、クロムの酸化物、水酸化物、窒化物、炭化物などのクロムと非金属元素との化合物（例えば、Ｃｒ２Ｏ３、Ｃｒ（ＯＨ）２、Ｃｒ２Ｏ３・ｎＨ２Ｏ、ＣｒＮ、ＣｒＣ、Ｃｒ３Ｃ２）やクロムとニッケルと酸素、水素、窒素、炭素の中から選ばれる非金属元素との化合物（例えば、ＮａＣｒ２Ｏ４）が挙げられる。特に、クロム化合物がクロム酸化物である場合には、主にクロム酸化物はＣｒ２Ｏ３（酸化クロム（ＩＩＩ））の形態で存在する。他のクロム酸化物の形態としては、ＣｒＯ（酸化クロム（ＩＩ））、ＣｒＯ２（酸化クロム（ＩＶ））、ＣｒＯ３（酸化クロム（ＶＩ））がある。また、クロム化合物の層の厚さは０．１０μｍ以上であることが好ましい。クロム化合物の層の厚さを０．１０μｍ以上に限定する理由は、クロム化合物の層の厚さが０．１０μｍ未満であると微粒子を固定する接着層としての機能が低下するためである。 The chromium compound layer serves as an adhesive layer that fixes the nickel-based fine particles so that they do not fall off the nickel-chromium alloy, and carbon deposition derived from gases containing carbon atoms such as hydrocarbon gases. It plays a role to suppress. The chromium compound includes a compound of chromium and a nonmetallic element such as chromium oxide, hydroxide, nitride, carbide (for example, Cr 2 O 3 , Cr (OH) 2 , Cr 2 O 3 .nH 2 O , CrN, CrC, Cr 3 C 2 ) or a compound of chromium, nickel, and a nonmetallic element selected from oxygen, hydrogen, nitrogen, and carbon (for example, NaCr 2 O 4 ). In particular, when the chromium compound is a chromium oxide, the chromium oxide is mainly present in the form of Cr 2 O 3 (chromium oxide (III)). Other forms of chromium oxide include CrO (chromium oxide (II)), CrO 2 (chromium oxide (IV)), and CrO 3 (chromium oxide (VI)). The thickness of the chromium compound layer is preferably 0.10 μm or more. The reason for limiting the thickness of the chromium compound layer to 0.10 μm or more is that when the thickness of the chromium compound layer is less than 0.10 μm, the function as an adhesive layer for fixing fine particles is lowered.
ニッケルクロム（Ｎｉ−Ｃｒ）合金は、本発明に係る水素製造用触媒を構成する主原料（母材）であり、かつ基板材料を担う合金である。ここで、本発明におけるニッケルクロム合金とは、主成分がニッケルであり、他の成分としてクロムが含有されている合金（クロムが含有されているニッケル基合金）を言う。ニッケルクロム合金におけるクロムの含有量については、質量％で５ｍａｓｓ％以上２０ｍａｓｓ％以下であることが好ましい。クロムの含有量を限定する理由は、クロムの含有量が５ｍａｓｓ％未満となると上述したクロム化合物の層の厚さが０．１μｍ未満となり、微粒子を固定する接着層としての機能が低下し、触媒としての耐熱性も低下するためである。また、クロムの含有量が２０ｍａｓｓ％を超えると、上述したクロム化合物の層の厚さが過大になり、触媒全体に占めるクロムの割合が増加し、逆に微粒子の主成分であるニッケルの割合が減少することで触媒としての機能が低下し、触媒としての加工性も同時に低下するからである。 A nickel chromium (Ni—Cr) alloy is an alloy that is a main raw material (base material) constituting the catalyst for hydrogen production according to the present invention and bears a substrate material. Here, the nickel-chromium alloy in the present invention refers to an alloy having a main component of nickel and containing chromium as another component (nickel-based alloy containing chromium). The chromium content in the nickel-chromium alloy is preferably 5 mass% or more and 20 mass% or less in mass%. The reason for limiting the chromium content is that when the chromium content is less than 5 mass%, the thickness of the above-mentioned chromium compound layer is less than 0.1 μm, and the function as an adhesive layer for fixing fine particles is reduced, and the catalyst This is because the heat resistance is also reduced. Moreover, if the chromium content exceeds 20 mass%, the thickness of the above-mentioned chromium compound layer becomes excessive, the proportion of chromium in the entire catalyst increases, and conversely, the proportion of nickel as the main component of the fine particles is increased. It is because the function as a catalyst falls by reducing and the workability as a catalyst also falls simultaneously.
次に、本発明に係る水素製造用触媒の製造方法について詳細に説明する。本発明に係る水素製造用触媒の製造方法は、酸化性ガスと還元性ガスとの混合ガスの雰囲気下において、ニッケルクロム合金を活性化処理温度で加熱処理する製造方法である。ここで、酸化性ガスとは混合ガス内で酸化反応を促進させるガスをいい、例えば水（水蒸気：Ｈ２Ｏ）、酸素（Ｏ２）、オゾン（Ｏ３）、二酸化炭素（ＣＯ２）のガスが挙げられる。また、還元性ガスとは混合ガス内で還元反応を促進させるガスをいい、例えば水素（Ｈ２）、一酸化炭素（ＣＯ）、メタン（ＣＨ４）やエタン（Ｃ２Ｈ６）などの炭化水素系ガスなどのガスが挙げられる。加熱処理を酸化性ガスと還元性ガスとの混合ガスの雰囲気下にて行うことで、前処理にて酸化処理が行われていない場合であっても、この加熱処理中に酸化反応が同時に進行する。なお、水素ガスの発生効率を向上させる観点から加熱処理の前に水蒸気雰囲気にて酸化処理を行っておくことが好ましい。 Next, the method for producing a catalyst for producing hydrogen according to the present invention will be described in detail. The method for producing a hydrogen production catalyst according to the present invention is a production method in which a nickel chromium alloy is heated at an activation treatment temperature in an atmosphere of a mixed gas of an oxidizing gas and a reducing gas. Here, the oxidizing gas refers to a gas that promotes the oxidation reaction in the mixed gas. For example, water (water vapor: H 2 O), oxygen (O 2 ), ozone (O 3 ), carbon dioxide (CO 2 ) Gas. The reducing gas refers to a gas that promotes a reduction reaction in a mixed gas. For example, carbonization such as hydrogen (H 2 ), carbon monoxide (CO), methane (CH 4 ), and ethane (C 2 H 6 ). Examples of the gas include hydrogen-based gas. By performing the heat treatment in an atmosphere of a mixed gas of an oxidizing gas and a reducing gas, the oxidation reaction proceeds simultaneously during the heat treatment even when the oxidation treatment is not performed in the pretreatment. To do. Note that, from the viewpoint of improving the generation efficiency of hydrogen gas, it is preferable to perform an oxidation treatment in a steam atmosphere before the heat treatment.
ここで、活性化処理とはメタンやエタンなどの活性化ガスにより本発明に係る水素製造用触媒の母材であるニッケルクロム合金表面の化学的反応性を高める（活性化させる）処理をいい、活性化処理温度とは本発明に係る水素製造用触媒の母材であるニッケルクロム合金が活性化処理される際の雰囲気の温度を言う。加熱処理については、本発明に係る水素製造用触媒の母材であるニッケルクロム合金を封入した大気雰囲気下または減圧雰囲気下の容器または炉内を常温から加熱することで行う。前処理として酸化処理を行っている場合には、酸化処理が一旦終了してからその触媒の母材であるニッケルクロム合金を封入した容器や炉内を再加熱することで行うこともできる。また、酸化処理にてその触媒の母材であるニッケルクロム合金を封入した容器や炉内を加熱している状態であれば、昇温（加熱）または降温（冷却）することで酸化処理から連続して行うこともできる。 Here, the activation treatment refers to a treatment that increases (activates) the chemical reactivity of the surface of the nickel chromium alloy that is the base material of the catalyst for hydrogen production according to the present invention using an activation gas such as methane or ethane. The activation treatment temperature refers to the temperature of the atmosphere when the nickel chromium alloy which is the base material of the catalyst for hydrogen production according to the present invention is activated. About heat processing, it carries out by heating from the normal temperature in the container or furnace in the air atmosphere or pressure-reduced atmosphere which enclosed the nickel chromium alloy which is a base material of the catalyst for hydrogen production which concerns on this invention. In the case where the oxidation treatment is performed as the pretreatment, it can be performed by reheating the vessel or the furnace in which the nickel-chromium alloy which is the base material of the catalyst is sealed after the oxidation treatment is once completed. In addition, if the vessel or furnace in which the nickel chrome alloy that is the base material of the catalyst is enclosed is heated in the oxidation treatment, the temperature can be increased (heating) or lowered (cooling) to continue from the oxidation treatment. It can also be done.
この加熱処理は、本発明に係る水素製造用触媒の反応温度よりも高い温度で行うことが好ましい。ここで反応温度とは触媒反応が進行する温度をいう。特に、本願においては原料ガスとなる水蒸気等の酸素原子を含むガスと炭化水素系ガス等の炭素原子および水素原子を含むガスとの反応によって水素を発生させるために水素製造用触媒が触媒としての機能を発揮する特定の温度をいう。例えば、本発明に係る触媒の反応温度（触媒反応が進行する温度）が７００℃（９７３Ｋ）の場合には７２０℃（９９３Ｋ）や７６０℃（１０３３Ｋ）など７００℃を超える温度で予め加熱処理を行う。 This heat treatment is preferably performed at a temperature higher than the reaction temperature of the catalyst for hydrogen production according to the present invention. Here, the reaction temperature refers to the temperature at which the catalytic reaction proceeds. In particular, in the present application, a catalyst for producing hydrogen is used as a catalyst in order to generate hydrogen by a reaction between a gas containing oxygen atoms such as water vapor as a raw material gas and a gas containing carbon atoms and hydrogen atoms such as a hydrocarbon-based gas. A specific temperature at which a function is performed. For example, when the reaction temperature of the catalyst according to the present invention (temperature at which the catalytic reaction proceeds) is 700 ° C. (973K), the heat treatment is performed in advance at a temperature exceeding 700 ° C. such as 720 ° C. (993K) or 760 ° C. (1033K). Do.
また、反応温度が９００℃（１１７３Ｋ）の場合には９１０℃（１１８３Ｋ）や９５０℃（１２２３Ｋ）など９００℃（１１７３Ｋ）を超える温度で予め加熱処理を行う。すなわち、本発明において活性化処理温度とは本発明に係る水素製造用触媒による触媒反応を進行させる温度（反応温度）によって定まる温度である。加熱時間については触媒全体が加熱温度に充分に到達する時間であることが好ましい。なお、本発明に係る水素製造用触媒を改質器内に設置して使用する場合には、上述した反応温度を作動温度、運転温度、使用温度と呼ぶこともできる。 When the reaction temperature is 900 ° C. (1173 K), heat treatment is performed in advance at a temperature exceeding 900 ° C. (1173 K), such as 910 ° C. (1183 K) and 950 ° C. (1223 K). That is, in the present invention, the activation treatment temperature is a temperature determined by the temperature (reaction temperature) at which the catalytic reaction by the hydrogen production catalyst according to the present invention proceeds. The heating time is preferably a time for the entire catalyst to sufficiently reach the heating temperature. When the hydrogen production catalyst according to the present invention is installed in a reformer and used, the reaction temperatures described above can also be called operating temperature, operating temperature, and operating temperature.
次に、本発明に係る水素製造用触媒を用いた水素製造方法について詳細に説明する。本発明に係る水素製造方法は、上述した水素製造用触媒の存在下にて、水蒸気と炭素原子を含むガスを原料として、水蒸気の分子数と炭素原子を含むガス中の炭素原子数との比であるスチームカーボン比（Ｓ／Ｃ）を、Ｓ／Ｃ＝１〜３の関係式を満たす条件にて水素を製造する。ここで炭素原子を含むガスとは、メタン（ＣＨ４）、エタン（Ｃ２Ｈ６）、プロパン（Ｃ３Ｈ８）、ブタン（Ｃ４Ｈ１０）などの鎖式飽和炭化水素ガスやエチレン（Ｃ２Ｈ４）、プロピレン（Ｃ３Ｈ６）などの不飽和炭化水素やアセチレン（Ｃ２Ｈ２）などの鎖式炭化水素、灯油、軽油、ガソリン、ナフサなどの油類を指す。 Next, the hydrogen production method using the hydrogen production catalyst according to the present invention will be described in detail. In the hydrogen production method according to the present invention, in the presence of the above-described catalyst for hydrogen production, a gas containing water vapor and carbon atoms is used as a raw material, and the ratio between the number of water vapor molecules and the number of carbon atoms in the gas containing carbon atoms. Hydrogen is produced under the condition that the steam carbon ratio (S / C) satisfying the relational expression of S / C = 1-3. Here, the gas containing a carbon atom is a chain saturated hydrocarbon gas such as methane (CH 4 ), ethane (C 2 H 6 ), propane (C 3 H 8 ), butane (C 4 H 10 ), ethylene ( C 2 H 4 ), unsaturated hydrocarbons such as propylene (C 3 H 6 ), chain hydrocarbons such as acetylene (C 2 H 2 ), and oils such as kerosene, light oil, gasoline, and naphtha.
クロム含有量が異なるニッケルクロム合金製の水素製造用触媒（以下、本触媒という）を用いて触媒反応試験を行い、ニッケルクロム合金中のクロム含有量の変化によるメタン転化率への影響を確認した。その試験結果について表１および図１を用いて説明する。表１はクロム含有量が質量％で５ｍａｓｓ％（残部はニッケルであり、その含有量は９４．９ｍａｓｓ％以上）、１０ｍａｓｓ％（残部はニッケルであり、その含有量は８９．９ｍａｓｓ％以上）、１５ｍａｓｓ％（残部はニッケルであり、その含有量は８４．９ｍａｓｓ％以上）および２０ｍａｓｓ％（残部はニッケルであり、その含有量は７９．９ｍａｓｓ％以上）である本触媒を用いた触媒反応試験後（測定開始から２０時間後）の石英管のガス出口側から排出されるガス組成の割合およびメタン転化率（単位：％）を示す。また、図１は実施例の触媒反応試験で用いた触媒処理システム２０の模式図を示す。
A catalytic reaction test was conducted using a nickel-chromium alloy hydrogen production catalyst (hereinafter referred to as the present catalyst) with a different chromium content, and the effect of changes in chromium content in the nickel-chromium alloy on methane conversion was confirmed. . The test results will be described with reference to Table 1 and FIG. Table 1 shows that the chromium content is 5% by mass (the balance is nickel, the content is 94.9 mass% or more), 10 mass% (the balance is nickel, and the content is 89.9 mass% or more), After a catalytic reaction test using this catalyst of 15 mass% (the balance is nickel, the content is 84.9 mass% or more) and 20 mass% (the balance is nickel, the content is 79.9 mass% or more) The ratio of the gas composition discharged from the gas outlet side of the quartz tube (after 20 hours from the start of measurement) and the methane conversion rate (unit:%) are shown. FIG. 1 is a schematic diagram of the
なお、本実施例で用いた全ての水素製造用触媒は、図１に示す石英管２内にニッケルクロム合金を封入させた後、水素ガスと水蒸気との混合ガスの雰囲気下にて常温から９００℃（１１７３Ｋ、活性化処理温度）まで昇温させた後、その温度にて保持し、その後に常温まで冷却する処理（加熱処理）を施した触媒を用いた。また、本実施例ではクロム含有量が０ｍａｓｓ％である触媒（ニッケルの含有量が９９ｍａｓｓ％以上である、いわゆる純ニッケル）は触媒反応時の高温雰囲気に耐えられない（耐熱性に問題がある）こと、およびクロム含有量が２５ｍａｓｓ％以上である触媒は試験装置内の所定形状に加工し難い（加工性に問題がある）ことの理由から予め除外した。 All of the hydrogen production catalysts used in this example were sealed at room temperature to 900 ° C. in a mixed gas atmosphere of hydrogen gas and water vapor after encapsulating a nickel chromium alloy in the quartz tube 2 shown in FIG. After raising the temperature to 0 ° C. (1173 K, activation treatment temperature), a catalyst that was subjected to a treatment (heat treatment) that was held at that temperature and then cooled to room temperature was used. In this example, a catalyst having a chromium content of 0 mass% (a so-called pure nickel having a nickel content of 99 mass% or more) cannot withstand a high temperature atmosphere during the catalytic reaction (has a problem with heat resistance). The catalyst having a chromium content of 25 mass% or more was excluded in advance because it was difficult to process into a predetermined shape in the test apparatus (there was a problem in processability).
触媒処理システム２０は、図１に示すように所定の形状・寸法の試料（ニッケルクロム合金製の水素製造用触媒）１を複数個積層させた上で、最上層および最下層に設置された試料１の上下方向に厚さ約１０ｍｍの石英ウール１０を内径８ｍｍの石英管２内にそれぞれ装填した状態で触媒反応試験を行えるシステムになっている。また、本システム２０は図示しない窒素ボンベより蒸発器９を通して窒素ガスを石英管２内へ供給しながら、アルミニウムブロック炉３に内蔵した図示しない電熱ヒータにより石英管２の外周面を加熱できる構造となっている。そして、ガスクロマトグラフ４により石英管２内に水素が残留していないことを確認した後、純水収容部５よりポンプ６を経由して蒸発器９にて気化した水蒸気および図示しないメタンガスボンベよりメタンガスをそれぞれ石英管２内へ供給することで触媒反応試験を行った。
As shown in FIG. 1, the
ここで、メタン転化率とは触媒反応試験中に供給したメタン量に対する水素発生に寄与したメタン量の割合（比率）をいう。具体的には、図１に示すガスクロマトグラフ４およびフローメータ８により測定された、１分間当たりの一酸化炭素（ＣＯ）量（ｍＬ／ｍｉｎ）、二酸化炭素（ＣＯ２）量（ｍＬ／ｍｉｎ）およびメタン（ＣＨ４）量（ｍＬ／ｍｉｎ）を用いて、
メタン転化率（％）＝（ＣＯ量＋ＣＯ２量）／（ＣＯ量＋ＣＯ２量＋ＣＨ４量）×
１００ の式に基づいてメタン転化率が算出される。
Here, the methane conversion rate refers to the ratio (ratio) of the amount of methane that contributed to hydrogen generation relative to the amount of methane supplied during the catalytic reaction test. Specifically, the amount of carbon monoxide (CO) (mL / min) and the amount of carbon dioxide (CO 2 ) (mL / min) per minute measured by the
Methane conversion rate (%) = (CO amount + CO 2 amount) / (CO amount + CO 2 amount + CH 4 amount) ×
Based on the formula of 100, the methane conversion is calculated.
また、本試験に用いたクロム含有量が質量％で５ｍａｓｓ％、１０ｍａｓｓ％、１５ｍａｓｓ％および２０ｍａｓｓ％である計４水準の触媒の形状は、ニッケルクロム合金を幅５ｍｍ、長さ２００ｍｍ、厚さ０．０３ｍｍの箔状に圧延加工した後、前述した条件で加熱処理を行い、直径８ｍｍ、高さ２０ｍｍの形状に変形したものを触媒（試料）として使用した。 In addition, the shape of the catalyst in four levels in which the chromium content used in this test is 5 mass%, 10 mass%, 15 mass%, and 20 mass% in mass% is a nickel chromium alloy having a width of 5 mm, a length of 200 mm, and a thickness of 0 After rolling into a 0.03 mm foil, heat treatment was performed under the conditions described above, and the catalyst was deformed into a shape having a diameter of 8 mm and a height of 20 mm as a catalyst (sample).
また、本試験は触媒の母材であるニッケルクロム合金に対して事前の処理として上述した活性化処理を行った後、引き続いて図１に示す触媒処理システム２０にて一酸化炭素等のガス量の測定を行った。本試験における各処理の手順について以下に説明する。触媒反応により発生する種々のガスの測定方法は、石英管２の温度を８００℃（１０７３Ｋ）まで昇温しながらメタンガスを毎分１０ｍＬ（１０ｍＬ／ｍｉｎ）および水蒸気を毎分１０ｍＬ（１０ｍＬ／ｍｉｎ）の各割合で石英管２内へ供給し続けた。石英管２の温度が８００℃（１０７３Ｋ）に達して、３０分間保持した後に石英管２から排出されるＣＯ（一酸化炭素）、ＣＯ２（二酸化炭素）、ＣＨ４（メタン）およびＨ２Ｏ（水蒸気）の全てのガス量の測定をコールドトラップ７に通した後にフローメータ８を用いて測定を開始した。なお、一般的な水素製造用触媒を用いた水素製造ではＳ／Ｃが３以上となる条件で原料ガスを供給して行うが、本試験ではＳ／Ｃ＝１．０となるよう水素製造時において最も過酷な原料ガスの供給条件で行った。
Further, in this test, after the activation treatment described above was performed as a preliminary treatment on the nickel-chromium alloy which is the base material of the catalyst, the amount of gas such as carbon monoxide was subsequently continued in the
表１に示すように測定開始から２０時間後の石英管から排出されるガス組成の割合（単位：％）は、クロム含有量が質量％で５ｍａｓｓ％の触媒では水素が５３．３％、メタンが１４．７％、一酸化炭素が１４．０％、二酸化炭素が３．０％、水蒸気が１５．０％であった。クロム含有量が１０ｍａｓｓ％まで増加すると、石英管から排出されるガス組成の割合は水素が６５．４％、メタンが６．４％、一酸化炭素が１８．８％、二酸化炭素が２．１％、水蒸気が７．３％であった。さらに、クロム含有量が１５ｍａｓｓ％まで増加すると、石英管から排出されるガス組成の割合は水素が６３．２％、メタンが７．９％、一酸化炭素が１７．９％、二酸化炭素が２．４％、水蒸気が８．６％であった。そして、クロム含有量が２０ｍａｓｓ％の場合では、石英管から排出されるガス組成の割合は水素が６０．８％、メタンが９．９％、一酸化炭素が１７．１％、二酸化炭素が２．６％、水蒸気が９．６％であった。以上の結果より、石英管から排出されるガス組成の割合、特に水素ガスの占める割合は触媒のクロム含有量が１０ｍａｓｓ％、１５ｍａｓｓ％、２０ｍａｓｓ％および５ｍａｓｓ％の順に多いことがわかった。
As shown in Table 1, the ratio (unit:%) of the gas composition discharged from the
同様に、表１に示すように測定開始から２０時間後のメタン転化率はクロム含有量が質量％で５ｍａｓｓ％の触媒では５３．６％であり、クロム含有量が１０ｍａｓｓ％まで増加するとメタン転化率は７６．６％にまで上昇した。クロム含有量が１５ｍａｓｓ％まで増加すると、メタン転化率は一転して７２．０％にまで減少した。そして、クロム含有量が２０ｍａｓｓ％の場合ではメタン転化率は６６．６％まで再び減少した。一般的な触媒反応試験において、試験開始から２０時間後のメタン転化率が５０％以上であれば、長時間の触媒機能を発揮できる基準とされている。したがって、この基準から判断してクロム含有量が質量％で５ｍａｓｓ％、１０ｍａｓｓ％、１５ｍａｓｓ％および２０ｍａｓｓ％である計４水準全ての触媒は、メタン転化率が５０％以上であったので長時間の触媒機能を発揮できた（請求項８）。また、クロム含有量が５〜２０ｍａｓｓ％の水素製造用触媒は他のクロム含有量のニッケルクロム合金製水素製造用触媒に比べて、耐熱性と加工性の点に関して優れている。 Similarly, as shown in Table 1, the methane conversion rate after 20 hours from the start of measurement is 53.6% in the case of a catalyst having a chromium content of 5% by mass and 5 mass%, and when the chromium content is increased to 10 mass%, the methane conversion is achieved. The rate rose to 76.6%. As the chromium content increased to 15 mass%, the methane conversion was reversed and decreased to 72.0%. When the chromium content was 20 mass%, the methane conversion rate decreased again to 66.6%. In a general catalytic reaction test, if the methane conversion rate after 20 hours from the start of the test is 50% or more, it is regarded as a standard capable of exhibiting a long-term catalytic function. Therefore, judging from this standard, all the four levels of the catalysts having a chromium content of 5 mass%, 10 mass%, 15 mass%, and 20 mass% in mass% had a methane conversion rate of 50% or more. The catalyst function was demonstrated (Claim 8). Further, a hydrogen production catalyst having a chromium content of 5 to 20 mass% is superior in terms of heat resistance and workability as compared with other nickel production hydrogen production catalysts having a chromium content.
次に、実施例１で用いた水素製造用触媒（クロム含有量：５ｍａｓｓ％〜２０ｍａｓｓ％）におけるクロム化合物の層の厚さを、任意に選定した観察位置にて撮影された電子顕微鏡写真により測定した。その結果について図２および表２を用いて説明する。図２は実施例１で用いたクロム含有量が１０ｍａｓｓ％の水素製造用触媒の透過型電子顕微鏡（ＴＥＭ）の代表写真（倍率：２００００倍）、表２は実施例１で用いたクロム含有量が５ｍａｓｓ％〜２０ｍａｓｓ％である水素製造用触媒において任意に選定した複数個所におけるクロム化合物の層の厚さの測定結果を示す。なお、透過型電子顕微鏡には日本電子社製のＪＥＭ−２１００Ｆ（型式）を用いた。 Next, the thickness of the chromium compound layer in the hydrogen production catalyst used in Example 1 (chromium content: 5 mass% to 20 mass%) was measured by an electron micrograph taken at an arbitrarily selected observation position. did. The results will be described with reference to FIG. 2 and Table 2. FIG. 2 shows a representative photograph (magnification: 20000 times) of a transmission electron microscope (TEM) of a hydrogen production catalyst having a chromium content of 10 mass% used in Example 1, and Table 2 shows the chromium content used in Example 1. The measurement result of the thickness of the layer of the chromium compound in the several places arbitrarily selected in the catalyst for hydrogen production whose is 5 mass%-20 mass% is shown. Note that JEM-2100F (model) manufactured by JEOL Ltd. was used for the transmission electron microscope.
本発明に係る水素製造用触媒は、図２に示すように母材であるニッケルクロム合金上は約１μｍ厚さのクロム化合物の層によって覆われており、そのクロム化合物の層上にはニッケルを主成分とする微粒子が分散された状態である。詳しく観察すると、微粒子はその大部分がクロム化合物の層に埋没した状態（担持）で存在し、下地層であるクロム化合物の層によって微粒子の周囲が覆われている。本発明者は、ニッケルを主成分とする微粒子の大部分がクロム化合物の層に覆い被さっていることで堅固に固定されているため、本発明に係る水素製造用触媒が長期の水素製造時においても触媒表面から微粒子が遊離することを防止し、結果として触媒表面へのカーボンの発生を抑制していると考える。 As shown in FIG. 2, the catalyst for hydrogen production according to the present invention is covered with a chromium compound layer having a thickness of about 1 μm on a nickel chromium alloy as a base material, and nickel is coated on the chromium compound layer. In this state, fine particles as a main component are dispersed. When observing in detail, most of the fine particles exist in a state where they are buried (supported) in the chromium compound layer, and the periphery of the fine particles is covered with the chromium compound layer as the underlayer. Since the present inventor is firmly fixed by covering most of the fine particles mainly composed of nickel with a chromium compound layer, the catalyst for hydrogen production according to the present invention is used for long-term hydrogen production. It is also considered that the fine particles are prevented from being liberated from the catalyst surface, and as a result, the generation of carbon on the catalyst surface is suppressed.
クロム化合物の層の厚さについては表２に示すように、クロム含有量が５ｍａｓｓ％の場合には、その厚さは０．１０〜０．２９μｍの範囲であり、クロム含有量が１０ｍａｓｓ％の場合には、その厚さは０．２９〜０．５６μｍの範囲であった。また、クロム含有量が１５ｍａｓｓ％の場合には、その厚さは０．４５〜０．６６μｍの範囲であり、クロム含有量が２０ｍａｓｓ％の場合には、その厚さは０．５６〜０．７１μｍの範囲であった。以上の測定結果より、本発明に係る水素製造用触媒におけるクロム化合物の層の厚さが０．１０μｍ以上であれば、長時間における触媒機能を発揮できることがわかった（請求項７）。なお、実施例１で用いたクロム含有量が５ｍａｓｓ％〜２０ｍａｓｓ％の触媒表面には、目視による観察をした結果、カーボンの析出は確認されなかった。 Regarding the thickness of the chromium compound layer, as shown in Table 2, when the chromium content is 5 mass%, the thickness is in the range of 0.10 to 0.29 μm, and the chromium content is 10 mass%. In some cases, the thickness ranged from 0.29 to 0.56 μm. In addition, when the chromium content is 15 mass%, the thickness is in the range of 0.45 to 0.66 μm, and when the chromium content is 20 mass%, the thickness is 0.56 to 0.00. The range was 71 μm. From the above measurement results, it was found that if the thickness of the chromium compound layer in the catalyst for hydrogen production according to the present invention is 0.10 μm or more, the catalyst function can be exhibited for a long time (Claim 7). In addition, as a result of visual observation on the catalyst surface having a chromium content of 5 mass% to 20 mass% used in Example 1, no carbon deposition was confirmed.
次に、実施例１で用いたクロム含有量５ｍａｓｓ％〜２０ｍａｓｓ％の水素製造用触媒における微粒子の組成を、ＷＤＳ（波長分散形Ｘ線分光器）を用いて複数箇所について測定（分析）した。その測定結果について表３を用いて説明する。表３は、実施例１で用いたクロム含有量５ｍａｓｓ％〜２０ｍａｓｓ％の水素製造用触媒における微粒子の構成元素とその割合（単位：ｍａｓｓ％）の範囲を示す。なお、微粒子の組成分析においては、粒径が１μｍ未満の場合には下地層であるクロム化合物の層の組成も合わせて分析する恐れがあるため、分析対象は粒径が１μｍ以上の微粒子のみとした。 Next, the composition of fine particles in the hydrogen production catalyst having a chromium content of 5 mass% to 20 mass% used in Example 1 was measured (analyzed) at a plurality of locations using a WDS (wavelength dispersive X-ray spectrometer). The measurement results will be described with reference to Table 3. Table 3 shows the constituent elements of fine particles and the range (unit: mass%) of the fine particles in the hydrogen production catalyst having a chromium content of 5 mass% to 20 mass% used in Example 1. In the fine particle composition analysis, if the particle size is less than 1 μm, the composition of the chromium compound layer, which is the underlayer, may be analyzed together. Therefore, the analysis target is only fine particles having a particle size of 1 μm or more. did.
微粒子の組成は、表３に示すように主成分であるニッケルが８３．１〜９７．６ｍａｓｓ％であり、次いでクロムが１．２〜１１．０ｍａｓｓ％、酸素が０．７〜９．９ｍａｓｓ％、最後に炭素が０．０〜１．６ｍａｓｓ％であった。これらの結果より、ニッケルクロム合金製（クロム含有量：５ｍａｓｓ％〜２０ｍａｓｓ％）の水素製造用触媒において、触媒表面に現れる微粒子はニッケルを主成分とし、他の成分としてはクロム（Ｃｒ）以外に酸素（Ｏ）が必須の構成元素であること（請求項１）、および微粒子中の酸素の割合は０．７〜９．９ｍａｓｓ％であること（請求項２）がわかった。 As shown in Table 3, the composition of the fine particles is 83.1 to 97.6 mass% for nickel as the main component, followed by 1.2 to 11.0 mass% for chromium, and 0.7 to 9.9 mass% for oxygen. Finally, carbon was 0.0 to 1.6 mass%. From these results, in the catalyst for hydrogen production made of nickel-chromium alloy (chromium content: 5 mass% to 20 mass%), the fine particles appearing on the catalyst surface are mainly composed of nickel, and other components are other than chromium (Cr). It was found that oxygen (O) is an essential constituent element (Claim 1), and the ratio of oxygen in the fine particles is 0.7 to 9.9 mass% (Claim 2).
次に、実施例１および２で用いた水素製造用触媒の中で、クロム含有量が１０ｍａｓｓ％の水素製造用触媒に限定して実施例１と同様の条件で長期の触媒反応試験を行い、メタン転化率（％）の変化を測定した。その測定結果について表４を用いて説明する。表４は、水素製造用触媒（クロム含有量：１０ｍａｓｓ％）の（試験）経過時間とメタン転化率の変化を示す。本実施例で用いた水素製造用触媒は、図１に示す石英管２内にニッケルクロム合金を封入させた後、水蒸気の雰囲気下にて石英管２内の温度を常温から６００℃（８７３Ｋ）まで昇温させた後、６００℃（８７３Ｋ）にて保持させた（酸化処理）。その後、水素ガスと水蒸気との混合ガスの雰囲気下にて再び石英管２内の温度を６００℃（８７３Ｋ）から９００℃（１１７３Ｋ）まで昇温させた後、９００℃（活性化処理温度）で保持して、その後に常温まで冷却する処理（加熱処理）を施して製造した触媒を用いた。 Next, among the hydrogen production catalysts used in Examples 1 and 2, a long-term catalytic reaction test was performed under the same conditions as in Example 1 by limiting to a hydrogen production catalyst having a chromium content of 10 mass%. Changes in methane conversion (%) were measured. The measurement results will be described using Table 4. Table 4 shows changes in (test) elapsed time and methane conversion rate of a catalyst for hydrogen production (chromium content: 10 mass%). The catalyst for hydrogen production used in this example was obtained by encapsulating a nickel chromium alloy in the quartz tube 2 shown in FIG. 1, and then changing the temperature in the quartz tube 2 from normal temperature to 600 ° C. (873 K) in a water vapor atmosphere. Was raised to 600 ° C. (873 K) (oxidation treatment). Thereafter, the temperature in the quartz tube 2 is again raised from 600 ° C. (873 K) to 900 ° C. (1173 K) in an atmosphere of a mixed gas of hydrogen gas and water vapor, and then at 900 ° C. (activation processing temperature). The catalyst manufactured by performing the process (heat processing) which hold | maintained and cooled to normal temperature after that was used.
なお、触媒反応試験に用いた使用装置については実施例１の場合と同様であるが、試験条件については図１に示す石英管２の温度を８００℃（１０７３Ｋ）まで昇温しながらメタンガスを毎分２１ｍＬ（２１ｍＬ／ｍｉｎ）および水蒸気を毎分２１ｍＬ（２１ｍＬ／ｍｉｎ）の各割合で石英管２内へ供給して、通常の経過時間の約１０倍速となるような促進条件で行った。例えば、本試験において経過時間が１０時間であれば通常速度で約４日間の長期使用に相当し、経過時間が１００時間であれば通常速度で約４２日間の長期使用に相当する促進条件となる。 The apparatus used for the catalytic reaction test is the same as that in Example 1. However, the test conditions are as follows. The temperature of the quartz tube 2 shown in FIG. The reaction was carried out under such an acceleration condition that the water was supplied into the quartz tube 2 at a rate of 21 mL (21 mL / min) and water vapor at a rate of 21 mL (21 mL / min) per minute into the quartz tube 2. For example, in this test, if the elapsed time is 10 hours, it corresponds to a long-term use of about 4 days at a normal speed, and if the elapsed time is 100 hours, the acceleration condition corresponds to a long-term use of about 42 days at a normal speed. .
表４に示すように、試験開始後５０時間経過後でメタン転化率は７９．８％、１００時間経過後でメタン転化率は７６．３％、３００時間経過後でメタン転化率は７１．７％、５００時間経過後でメタン転化率は６７．１％、７８０時間経過後でメタン転化率は６０．６％であった。最終の７８０時間経過後であってもメタン転化率は６０．６％まで低下したが、長時間（長期）の触媒機能を発揮できる触媒の適否の基準（メタン転化率５０％以上）を満たしていた。 As shown in Table 4, the methane conversion was 79.8% after 50 hours from the start of the test, the methane conversion was 76.3% after 100 hours, and the methane conversion was 71.7 after 300 hours. %, After 500 hours, the methane conversion was 67.1%, and after 780 hours, the methane conversion was 60.6%. Even after the lapse of the last 780 hours, the methane conversion rate has decreased to 60.6%, but it meets the criteria for the suitability of a catalyst that can exhibit a long-term (long-term) catalytic function (methane conversion rate of 50% or more). It was.
試験終了後の触媒表面を実施例２の場合と同様に電子顕微鏡により、クロム化合物の層の厚さを複数箇所について測定した。その結果、試験開始から７８０時間経過（通常速度で約３２５日経過相当）後の触媒表面におけるクロム化合物の層の厚さは１．５０〜２．５０μｍの範囲であった。したがって、本発明に係る水素製造用触媒のクロム化合物の層は、使用開始から時間が経過するごとに徐々に厚くなっていき、水素製造用触媒の長期使用時におけるクロム化合物の層の厚さの上限は２．５０μｍであることがわかった。 The thickness of the chromium compound layer was measured at a plurality of locations on the catalyst surface after the test using an electron microscope in the same manner as in Example 2. As a result, the thickness of the chromium compound layer on the catalyst surface after 780 hours (equivalent to about 325 days at normal speed) from the start of the test was in the range of 1.50 to 2.50 μm. Therefore, the chromium compound layer of the catalyst for hydrogen production according to the present invention gradually increases with the passage of time from the start of use, and the thickness of the chromium compound layer during the long-term use of the hydrogen production catalyst. The upper limit was found to be 2.50 μm.
次に、クロム含有量が１０ｍａｓｓ％である水素製造用触媒を実施例１で用いた触媒の代表として、試験終了後に常温まで冷却した石英管のガス入口側およびガス出口側の両側から各１個ずつ触媒を取り出した。その後、各触媒の表面組織を電子顕微鏡により観察（倍率：５０００倍）して、微粒子の大きさおよび分布を確認した。その確認結果について図３ないし図５ならびに表５および表６を用いて説明する。図３は実施例１において図１に示す石英管２のガス入口側から最も近い位置に設置された触媒表面の電子顕微鏡の代表写真（倍率：５０００倍）、図４は実施例１において図１に示す石英管２のガス出口側から最も近い位置に設置された触媒表面の電子顕微鏡の代表写真（倍率：５０００倍）を示す。また、図５は、図４に示す触媒表面の一部の低加速電子顕微鏡（ＳＥＭ）の代表写真（倍率：２４万倍）を示す。なお、図３および図４の電子顕微鏡には日本電子社製のＪＸＡ−８５００Ｆ（型式）、図５の低加速電子顕微鏡にはエスアイアイ・ナノテクノロジー社製のＳＭＦ−１０００（型式）をそれぞれ用いた。 Next, as a representative of the catalyst used in Example 1, a hydrogen production catalyst having a chromium content of 10 mass%, one each from the gas inlet side and the gas outlet side of the quartz tube cooled to room temperature after the test was completed. The catalyst was taken out one by one. Thereafter, the surface structure of each catalyst was observed with an electron microscope (magnification: 5000 times), and the size and distribution of the fine particles were confirmed. The confirmation result will be described with reference to FIGS. 3 to 5 and Tables 5 and 6. FIG. 3 is a representative photograph of an electron microscope (magnification: 5000 times) of the catalyst surface installed at a position closest to the gas inlet side of the quartz tube 2 shown in FIG. 1 in Example 1, and FIG. The representative photograph (magnification: 5000 times) of the electron microscope of the catalyst surface installed in the position nearest from the gas outlet side of the quartz tube 2 shown in FIG. FIG. 5 shows a representative photograph (magnification: 240,000 times) of a part of the catalyst surface shown in FIG. 4 of a low acceleration electron microscope (SEM). In addition, JXA-8500F (model) manufactured by JEOL Ltd. is used for the electron microscope of FIGS. 3 and 4, and SMF-1000 (model) manufactured by SII NanoTechnology is used for the low acceleration electron microscope of FIG. It was.
表５は図３に示す電子顕微鏡写真に基づいて計測した触媒表面における微粒子の粒径とその微粒子が占める累積投影面積率（単位：％）との関係、表６は図４に示す電子顕微鏡写真に基づいて計測した触媒表面における微粒子の粒径とその微粒子が占める累積投影面積率（単位：％）との関係を示す。以下、微粒子の粒径とその累積投影面積率の測定結果について、石英管のガス入口側に設置された触媒とガス出口側に設置された触媒とにそれぞれ分けて説明する。 Table 5 shows the relationship between the particle diameter of the fine particles on the catalyst surface measured based on the electron micrograph shown in FIG. 3 and the cumulative projected area ratio (unit:%) occupied by the fine particles, and Table 6 shows the electron micrograph shown in FIG. 3 shows the relationship between the particle diameter of the fine particles on the catalyst surface measured based on the above and the cumulative projected area ratio (unit:%) occupied by the fine particles. Hereinafter, the measurement results of the particle size of the fine particles and the cumulative projected area ratio will be described separately for the catalyst installed on the gas inlet side of the quartz tube and the catalyst installed on the gas outlet side.
石英管のガス入口側から近い位置に設置された触媒表面は、図３に示すようにニッケルを主成分とする微粒子（白い粒状の物質）とクロム化合物の層（黒い組織）が確認できた。ニッケルを主成分とする微粒子の形状については、球形状、多角形状、芋虫形状など様々な形態が確認できた。また、微粒子の粒径については１μｍ以下の、いわゆるナノオーダーサイズから数μｍまでの広範囲に及んでいた。 As shown in FIG. 3, fine particles (white granular material) mainly composed of nickel and a chromium compound layer (black structure) were confirmed on the surface of the catalyst installed near the gas inlet side of the quartz tube. Various shapes such as a spherical shape, a polygonal shape, and a worm shape were confirmed with respect to the shape of the fine particles mainly composed of nickel. In addition, the particle diameter of the fine particles was in a wide range from a so-called nano-order size to several μm, which is 1 μm or less.
触媒表面の投影面積に対するニッケルを主成分とする微粒子の投影面積の割合は、表５に示すように微粒子の粒径が０．３μｍまでのもの（微粒子の最小粒径は０．１μｍ）は累計で２．０％、０．４μｍまでのものが累計で３．５％、０．５μｍまでのものが累計で４．６％、１μｍまでのものが累計で１４．０％であり、最大粒径５μｍまでのものが累計で２７．５％であった。この結果から、石英管のガス入口側に設置された触媒表面における微粒子の粒径の分布範囲は０．１μｍ〜５μｍであった。また、（触媒表面の投影面積に対する）微粒子の投影面積が占める割合は最大２７．５％であった。 The ratio of the projected area of the fine particles mainly composed of nickel to the projected area of the catalyst surface is cumulative when the particle diameter of the fine particles is up to 0.3 μm as shown in Table 5 (the minimum particle diameter of the fine particles is 0.1 μm). The maximum grain size is 2.0%, the total up to 0.4μm is 3.5%, the total up to 0.5μm is 4.6%, the total up to 1μm is 14.0%. Those with a diameter up to 5 μm were 27.5% in total. From this result, the particle size distribution range of the fine particles on the surface of the catalyst installed on the gas inlet side of the quartz tube was 0.1 μm to 5 μm. Further, the ratio of the projected area of the fine particles (relative to the projected area of the catalyst surface) was 27.5% at the maximum.
同様に、石英管のガス出口側から近い位置に設置された触媒表面は、図４に示す様に図３と同様でニッケルを主成分とする微粒子（白色の粒状の部分）とクロム化合物の層（黒色の部分）が確認できた。ニッケルを主成分とする微粒子の形状については、入口側と同様に球形状、多角形状、芋虫形状など様々な形態が確認できた。また、微粒子の粒径については、１μｍ以下のナノオーダーサイズの微粒子がほぼ全てを占めていた。 Similarly, as shown in FIG. 4, the catalyst surface installed at a position near the gas outlet side of the quartz tube is similar to FIG. 3, and is a layer of fine particles (white granular portions) mainly composed of nickel and a chromium compound. (Black part) was confirmed. Regarding the shape of the fine particles containing nickel as a main component, various shapes such as a spherical shape, a polygonal shape, and a worm shape were confirmed as in the case of the entrance side. As for the particle size of the fine particles, nano-order fine particles of 1 μm or less occupied almost all.
触媒の投影面積に対するニッケルを主成分とする微粒子の投影面積の割合は、表６に示すように微粒子の粒径が０．３μｍまでのもの（微粒子の最小粒径は０．０５μｍ）が累計で２．３％、０．４μｍまでのものが累計で３．４％、０．５μｍまでのものが累計で４．９％、０．６μｍのものが累計で６．８％であり、最大粒径１．２μｍのものが累計で１３．１％であった。この結果から、石英管のガス出口側に設置された触媒表面における微粒子の粒径の分布範囲は０．０５μｍ〜１．２μｍであった。また、触媒の表面における微粒子の投影面積が占める割合は最大１３．１％であった。ここで、図４に示す触媒表面の一部について更に倍率を２４万倍まで拡大すると、図５に示すように触媒表面に存在する微粒子には、粒径が５０ｎｍ（０．０５μｍ）程度の微粒子（一次微粒子）と、複数個の一次微粒子が集まることで形成された、粒径が０．３μｍ以上の微粒子（二次微粒子）との２種類の微粒子が存在していたことがわかった。 As shown in Table 6, the ratio of the projected area of fine particles mainly composed of nickel to the projected area of the catalyst is cumulative when the particle diameter of the fine particles is up to 0.3 μm (the minimum particle diameter of the fine particles is 0.05 μm). 2.3%, up to 0.4μm is cumulative 3.4%, up to 0.5μm is 4.9%, and 0.6μm is 6.8%. Those with a diameter of 1.2 μm were 13.1% in total. From this result, the particle size distribution range of the fine particles on the catalyst surface installed on the gas outlet side of the quartz tube was 0.05 μm to 1.2 μm. Further, the ratio of the projected area of the fine particles on the surface of the catalyst was 13.1% at maximum. Here, when the magnification is further increased up to 240,000 times for a part of the catalyst surface shown in FIG. 4, the fine particles present on the catalyst surface are fine particles having a particle size of about 50 nm (0.05 μm) as shown in FIG. It was found that there were two types of fine particles, ie, (primary fine particles) and fine particles (secondary fine particles) having a particle diameter of 0.3 μm or more formed by collecting a plurality of primary fine particles.
以上の測定（観察）結果から、本発明に係る水素製造用触媒を構成するニッケルを主成分とする微粒子の粒径は０．０５μｍ（５０ｎｍ）以上５μｍ以下であること（請求項３）、およびその微粒子の投影面積が占める割合は、触媒表面の投影面積に対して１３．１％以上２７．５％以下であること（請求項４）により、長時間における触媒機能を発揮することができた。 From the above measurement (observation) results, the particle size of the fine particles mainly composed of nickel constituting the hydrogen production catalyst according to the present invention is 0.05 μm (50 nm) to 5 μm (Claim 3), and The proportion of the projected area of the fine particles is 13.1% or more and 27.5% or less with respect to the projected area of the catalyst surface. .
次に、クロム含有量が１０ｍａｓｓ％である水素製造用触媒を実施例１で用いた触媒の代表として、試験終了後に石英管から取り出した後、触媒の表面に対してＸ線回折装置（ＸＲＤ）を用いて、触媒表面を構成する物質を定性分析した。その分析結果について図６を用いて説明する。図６は実施例１の触媒反応試験の終了後の本発明に係る水素製造用触媒（クロム含有量：１０ｍａｓｓ％）および圧延直後で触媒反応試験には供していないニッケルクロム合金（クロム含有量：１０ｍａｓｓ％）のＸ線回折結果を示す。なお、Ｘ線回折装置にはリガク社製のＲＩＮＴ２２００（型式）を用いた。 Next, as a representative of the catalyst used in Example 1, a hydrogen production catalyst having a chromium content of 10 mass% was taken out of the quartz tube after the test was completed, and then subjected to an X-ray diffractometer (XRD) with respect to the surface of the catalyst. Was used to qualitatively analyze substances constituting the catalyst surface. The analysis result will be described with reference to FIG. FIG. 6 shows a catalyst for hydrogen production (chromium content: 10 mass%) according to the present invention after completion of the catalytic reaction test of Example 1 and a nickel chromium alloy (chromium content: 10 mass%) X-ray diffraction results are shown. Note that RINT2200 (model) manufactured by Rigaku Corporation was used as the X-ray diffractometer.
圧延工程を経た直後のニッケルクロム合金（クロム含有量：１０ｍａｓｓ％）のＸ線回折結果は、図６に示すように基地組織であるニッケルクロム合金（Ｎｉ−Ｃｒ）およびニッケルが解析された。これに対して、触媒反応試験後の本発明に係る水素製造用触媒（クロム含有量：１０ｍａｓｓ％）のＸ線回折結果は、基地組織であるニッケルクロム合金およびニッケルの他に、触媒表面を構成しているクロム化合物、すなわちＣｒ２Ｏ３（酸化クロム（ＩＩＩ））が解析された。これらの解析結果より、本発明に係るクロム含有量が５〜２０ｍａｓｓ％である水素製造用触媒の表面が酸化クロム（ＩＩＩ）（Ｃｒ２Ｏ３）に覆われていることが触媒機能を十分に発揮する上で有効であることが確認された（請求項６）。 The X-ray diffraction results of the nickel chromium alloy (chromium content: 10 mass%) immediately after the rolling process were analyzed for nickel chromium alloy (Ni-Cr) and nickel as the base structure as shown in FIG. On the other hand, the X-ray diffraction result of the catalyst for hydrogen production (chromium content: 10 mass%) according to the present invention after the catalytic reaction test constitutes the catalyst surface in addition to the nickel-chromium alloy and nickel as the base structure. Chrome compound, ie Cr 2 O 3 (chromium oxide (III)) was analyzed. From these analysis results, it is confirmed that the surface of the hydrogen production catalyst having a chromium content of 5 to 20 mass% according to the present invention is covered with chromium (III) oxide (Cr 2 O 3 ). It was confirmed that it was effective in exhibiting (claim 6).
次に、水素製造用触媒（クロム含有量：１０ｍａｓｓ％）を用いて触媒反応試験を行い、水素製造原料である水蒸気の分子数と炭素原子を含むガス中の炭素原子数との比である、スチームカーボン比（Ｓ／Ｃ）を変化させた場合のメタン転化率を測定した。その測定結果について表７を用いて説明する。 Next, a catalytic reaction test is performed using a catalyst for hydrogen production (chromium content: 10 mass%), which is a ratio between the number of water vapor molecules as a hydrogen production raw material and the number of carbon atoms in the gas containing carbon atoms. The methane conversion was measured when the steam carbon ratio (S / C) was changed. The measurement results will be described using Table 7.
本実施例の触媒反応試験に用いた試料形状は、水素製造用触媒を直径１６ｍｍ、高さ１００ｍｍの形状に変形したものとした。触媒反応試験により発生した種々のガスの測定は、図１に示す石英管２の温度を８００℃（１０７３Ｋ）まで昇温しながらメタンガスを毎分８４ｍＬ供給した状態で、クロマトグラフ４およびフローメータ８を用いて行った。また、図１に示す石英管２内へ供給する水蒸気の量は、Ｓ／Ｃ＝０．８、０．９、１．０、１．１、１．２、１．５、２．０および３．０（計８水準）の関係式を満たすように、水蒸気を毎分６７．２〜２５２ｍＬ（６７．２〜２５２ｍＬ／ｍｉｎ）の範囲でメタンガスと同時に石英管２内へ供給した。メタン転化率は、試験開始後１０分経過時の一酸化炭素、二酸化炭素およびメタンの流量を測定して、それらの流量値から算出した。表７は、触媒反応試験中でスチームカーボン比（Ｓ／Ｃ）を変化させた場合のメタン転化率（単位：％）の変化を示す。
The sample shape used in the catalytic reaction test of this example was a hydrogen production catalyst deformed into a shape with a diameter of 16 mm and a height of 100 mm. The various gases generated by the catalytic reaction test were measured with the
水素製造用触媒（クロム含有量：１０ｍａｓｓ％）を用いた水素製造効率の指標の１つであるＳ／Ｃを０．８〜３．０までの範囲で変化させて触媒反応試験を行った際のメタン転化率は、表７に示すようにＳ／Ｃ＝３．０（水蒸気供給量：毎分２５２ｍＬ、メタンガス供給量：毎分８４ｍＬ）の場合、メタン転化率は９１．９％であり、Ｓ／Ｃ＝２．０（水蒸気供給量：毎分１６８ｍＬ、メタンガス供給量：毎分８４ｍＬ）の場合、メタン転化率は９５．８％であった。また、Ｓ／Ｃ＝１．５（水蒸気供給量：毎分１２６ｍＬ、メタンガス供給量：毎分８４ｍＬ）の場合、メタン転化率は９５．０％であり、Ｓ／Ｃ＝１．２（水蒸気供給量：毎分１００．８ｍＬ、メタンガス供給量：毎分８４ｍＬ）の場合、メタン転化率は９０．６％であった。さらに、Ｓ／Ｃ＝１．１（水蒸気供給量：毎分９２．４ｍＬ、メタンガス供給量：毎分８４ｍＬ）の場合、メタン転化率は８９．０％であり、Ｓ／Ｃ＝１．０（水蒸気供給量：毎分８４ｍＬ、メタンガス供給量：毎分８４ｍＬ）の場合、メタン転化率は７９．０％であった。 When a catalytic reaction test was conducted by changing S / C, which is one of the indices of hydrogen production efficiency using a hydrogen production catalyst (chromium content: 10 mass%), in the range of 0.8 to 3.0 As shown in Table 7, when S / C = 3.0 (steam supply rate: 252 mL / min, methane gas supply rate: 84 mL / min), the methane conversion rate is 91.9%. In the case of S / C = 2.0 (water vapor supply amount: 168 mL / min, methane gas supply amount: 84 mL / min), the methane conversion was 95.8%. When S / C = 1.5 (steam supply amount: 126 mL / min, methane gas supply rate: 84 mL / min), the methane conversion is 95.0% and S / C = 1.2 (steam supply) In the case of amount: 100.8 mL / min, methane gas supply amount: 84 mL / min), the methane conversion was 90.6%. Further, in the case of S / C = 1.1 (water vapor supply rate: 92.4 mL / min, methane gas supply rate: 84 mL / min), the methane conversion is 89.0%, and S / C = 1.0 ( In the case of water vapor supply rate: 84 mL / min, methane gas supply rate: 84 mL / min), the methane conversion was 79.0%.
Ｓ／Ｃが１．０未満では、Ｓ／Ｃ＝０．９（水蒸気供給量：毎分７５．６ｍＬ、メタンガス供給量：毎分８４ｍＬ）の場合、メタン転化率は７８．０％、Ｓ／Ｃ＝０．８（水蒸気供給量：毎分６７．２ｍＬ、メタンガス供給量：毎分８４ｍＬ）の場合、メタン転化率は７４．０％であった。以上の測定結果より、本発明に係る水素製造用触媒を用いて、Ｓ／Ｃが１．０未満の条件下で水素製造を行っても、Ｓ／Ｃが１．０以上の条件下の場合に比べてメタン転化率が極度に減少することはなく、ほぼ比例的に減少することがわかった。同時に、水素製造用改質器内にて不測の事態（例えば、水道配管の凍結等によって水蒸気の供給量が炭化水素系ガスの供給量を下回る様な状況）により水素ガスを製造する原料ガスのＳ／Ｃ比が１．０未満となる条件下であっても、メタン転化率は長期使用の基準となる５０％以上を上回っていたので、本発明に係る水素製造用触媒は長期使用においても触媒機能を十分に維持できる（請求項１１）。 When S / C is less than 1.0, when S / C = 0.9 (water vapor supply rate: 75.6 mL / min, methane gas supply rate: 84 mL / min), the methane conversion is 78.0%, S / C When C = 0.8 (water vapor supply rate: 67.2 mL / min, methane gas supply rate: 84 mL / min), the methane conversion was 74.0%. From the above measurement results, even when hydrogen production is carried out under the condition where the S / C is less than 1.0 using the hydrogen production catalyst according to the present invention, the case where the S / C is 1.0 or more. It was found that the methane conversion rate did not decrease drastically compared to, but decreased almost proportionally. At the same time, the raw material gas that produces hydrogen gas due to an unexpected situation in the reformer for hydrogen production (for example, a situation where the supply amount of water vapor is lower than the supply amount of hydrocarbon gas due to freezing of water pipes, etc.) Even under conditions where the S / C ratio is less than 1.0, the methane conversion rate exceeded 50% or more, which is the standard for long-term use. Therefore, the hydrogen production catalyst according to the present invention can be used even for long-term use. The catalyst function can be sufficiently maintained (claim 11).
次に、本発明に係る水素製造用触媒（クロム含有量：１０ｍａｓｓ％）および比較材としてニッケル基の粒状触媒（多孔質のアルミナにニッケルを含浸させた市販の触媒：粒径は約３ｍｍ）を用いて、Ｓ／Ｃ＝０．８の条件下にて触媒反応試験を行い、メタン転化率の経時変化を測定した。その測定結果について表８を用いて説明する。本発明に係る水素製造用触媒の試料形状は、水素製造用触媒を直径８ｍｍ、高さ２０ｍｍの形状のものとした。また、触媒反応試験中に発生する種々のガス量の測定は、図１に示す石英管２の温度を８００℃（１０７３Ｋ）まで昇温しながらメタンガスを毎分１０ｍＬ、水蒸気を毎分８．０ｍＬ供給した（Ｓ／Ｃ＝０．８）状態で、クロマトグラフ４およびフローメータ８を用いて行った。表８は、本発明に係る水素製造用触媒およびニッケル基の粒状触媒（比較材）のメタン転化率と石英管の内圧の経時変化を示す。
Next, a catalyst for hydrogen production according to the present invention (chromium content: 10 mass%) and a nickel-based granular catalyst (commercially available catalyst in which nickel is impregnated into porous alumina: particle size is about 3 mm) are used as comparative materials. Then, a catalytic reaction test was performed under the condition of S / C = 0.8, and the change with time in the methane conversion was measured. The measurement results will be described using Table 8. The sample shape of the hydrogen production catalyst according to the present invention was a hydrogen production catalyst having a diameter of 8 mm and a height of 20 mm. In addition, various gas amounts generated during the catalytic reaction test are measured by raising the temperature of the quartz tube 2 shown in FIG. 1 to 800 ° C. (1073 K), 10 mL of methane gas per minute, and 8.0 mL of water vapor per minute. It was carried out using the
本発明に係る水素製造用触媒（以下、本発明品という）は、表８に示すようにメタン転化率は試験開始から１時間経過後に７４％、３時間経過後に７５％であり、試験終了後の１４時間後に７５％であり、試験開始から大きな変化は見られなかった。また、本発明品が封入された石英管内の圧力は試験開始から１４時間経過後でも変化は無く、常に０ＭＰａ（０ｂａｒ）であった。さらに、試験終了後に常温に冷却した石英管から本発明品を取り出して、目視による表面観察を行ったが、カーボンの析出は確認されなかった。 As shown in Table 8, the hydrogen production catalyst according to the present invention (hereinafter referred to as the present product) has a methane conversion rate of 74% after 1 hour from the start of the test and 75% after the lapse of 3 hours. It was 75% after 14 hours, and no significant change was observed from the start of the test. Further, the pressure in the quartz tube in which the product of the present invention was sealed did not change even after 14 hours from the start of the test, and was always 0 MPa (0 bar). Further, after completion of the test, the product of the present invention was taken out from the quartz tube cooled to room temperature and visually observed on the surface, but no carbon deposition was confirmed.
これに対して、比較材のメタン転化率は試験開始から１時間経過後に８２％、３時間経過後に８３％、７時間経過後に８４％であり、大きな変化は見られなかった。ところが、試験開始から１０時間経過後にメタン転化率は７９％まで低下して、試験終了後の１４時間後には７４％まで更に低下した。また、比較材が封入された石英管内の圧力は試験開始から５時間経過後でも変化は無く、０ＭＰａ（０ｂａｒ）であったが、試験開始から７時間経過後には石英管内の圧力は０．０１ＭＰａ（０．１ｂａｒ）、１０時間経過後には０．０３ＭＰａ（０．３ｂａｒ）、１３時間経過後に０．１０ＭＰａ（１．０ｂａｒ）まで上昇した。最終的に比較材が封入された石英管内の圧力は、試験開始から１４時間経過後に０．１１ＭＰａ（１．１ｂａｒ）まで上昇して、石英管が管内圧力の上昇により破損する恐れがあったため、試験開始から１４時間を経過した時点で触媒反応試験を終了した。 In contrast, the methane conversion rate of the comparative material was 82% after 1 hour from the start of the test, 83% after 3 hours, and 84% after 7 hours, and no significant change was observed. However, the methane conversion decreased to 79% after 10 hours from the start of the test, and further decreased to 74% after 14 hours after the end of the test. In addition, the pressure in the quartz tube in which the comparative material was sealed did not change even after 5 hours from the start of the test and was 0 MPa (0 bar), but after 7 hours from the start of the test, the pressure in the quartz tube was 0.01 MPa. (0.1 bar) It rose to 0.03 MPa (0.3 bar) after 10 hours, and to 0.10 MPa (1.0 bar) after 13 hours. Finally, the pressure in the quartz tube in which the comparative material was sealed rose to 0.11 MPa (1.1 bar) after 14 hours from the start of the test, and the quartz tube might be damaged by the increase in the pressure in the tube. The catalytic reaction test was completed when 14 hours had elapsed from the start of the test.
試験終了後、石英管が常温まで冷却したことを確認してから石英管内から比較材を取り出して、目視により比較材の表面の観察を行ったところ、試験開始時は白色を呈していた比較材の表面が黒色の物質に覆われていた。この黒色の物質を実施例５で用いた日本電子社製の電子顕微鏡（ＳＥＭ）で分析した結果、カーボン（Ｃ）であることがわかった。触媒反応試験中に比較材が封入された石英管の管内圧力が上昇した原因は、試験時間の経過と共に比較材の表面にカーボンが徐々に発生したことで石英管の内面と封入された比較材との隙間が徐々に閉塞された結果、触媒反応によって発生した水素の流れが途中で遮断されて、石英管内に滞留したためと考えられる。以上の試験結果より、ニッケルが含有された従来の触媒を用いた水素製造工程では触媒表面にカーボンが発生する条件であるＳ／Ｃが１．０未満の場合において、本発明に係る水素製造用触媒を用いることで触媒機能を長時間維持した状態であっても触媒表面にカーボンは析出し難いことがわかった（請求項１１）。 After the test was completed, after confirming that the quartz tube had cooled to room temperature, the comparative material was taken out from the quartz tube and the surface of the comparative material was visually observed. The surface of was covered with a black substance. As a result of analyzing this black substance with an electron microscope (SEM) manufactured by JEOL Ltd. used in Example 5, it was found to be carbon (C). The reason for the increase in pressure inside the quartz tube containing the comparative material during the catalytic reaction test was that the comparative material was sealed with the inner surface of the quartz tube due to the gradual generation of carbon on the surface of the comparative material over time. This is probably because the hydrogen flow generated by the catalytic reaction was interrupted in the middle and stayed in the quartz tube. From the above test results, in the hydrogen production process using the conventional catalyst containing nickel, when S / C, which is a condition for generating carbon on the catalyst surface, is less than 1.0, the hydrogen production according to the present invention is used. It was found that carbon was hardly deposited on the catalyst surface even when the catalyst function was maintained for a long time by using the catalyst (claim 11).
１ 試料（ニッケルクロム合金製の水素製造用触媒） 1 Sample (nickel-chromium alloy hydrogen production catalyst)
Claims (10)
前記微粒子には他の成分として酸素が含有されており、
前記ニッケルクロム合金におけるクロムの含有量は、質量％で５ｍａｓｓ％以上１５ｍａｓｓ％以下であることを特徴とする水素製造用触媒。 A catalyst for hydrogen production, in which a chromium compound layer is formed on a nickel chromium alloy, and fine particles mainly containing nickel are dispersed on the chromium compound layer,
The fine particles contain oxygen as another component ,
The content of chromium in the nickel-chromium alloy, mass% with 5 mass% or more 15 mass% or less hydrogen production catalyst, wherein the this is.
In the presence of the hydrogen production catalyst according to any one of claims 1 to 7, a gas containing water vapor and carbon atoms is used in a gas containing the number of molecules of water vapor and the carbon atoms. A method for producing hydrogen, characterized in that hydrogen is produced under a condition that a steam carbon ratio (S / C), which is a ratio with respect to the number of carbon atoms, satisfies a relational expression of S / C = 1-3.
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