JP2010201302A - Catalyst for steam reforming of methane - Google Patents
Catalyst for steam reforming of methane Download PDFInfo
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- JP2010201302A JP2010201302A JP2009047471A JP2009047471A JP2010201302A JP 2010201302 A JP2010201302 A JP 2010201302A JP 2009047471 A JP2009047471 A JP 2009047471A JP 2009047471 A JP2009047471 A JP 2009047471A JP 2010201302 A JP2010201302 A JP 2010201302A
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- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 title claims abstract description 64
- 239000003054 catalyst Substances 0.000 title claims abstract description 30
- 238000000629 steam reforming Methods 0.000 title claims abstract description 23
- 239000002105 nanoparticle Substances 0.000 claims abstract description 27
- 229910003310 Ni-Al Inorganic materials 0.000 claims abstract description 12
- 229910000765 intermetallic Inorganic materials 0.000 claims abstract description 9
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims abstract description 8
- 239000001257 hydrogen Substances 0.000 claims abstract description 8
- 229910052739 hydrogen Inorganic materials 0.000 claims abstract description 8
- 229910045601 alloy Inorganic materials 0.000 claims abstract description 6
- 239000000956 alloy Substances 0.000 claims abstract description 6
- 238000000151 deposition Methods 0.000 claims abstract description 4
- NPXOKRUENSOPAO-UHFFFAOYSA-N Raney nickel Chemical compound [Al].[Ni] NPXOKRUENSOPAO-UHFFFAOYSA-N 0.000 claims description 10
- 229910000943 NiAl Inorganic materials 0.000 claims description 7
- 230000003197 catalytic effect Effects 0.000 abstract description 15
- 238000006243 chemical reaction Methods 0.000 description 36
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 15
- 239000007789 gas Substances 0.000 description 14
- 239000000203 mixture Substances 0.000 description 8
- 239000002245 particle Substances 0.000 description 7
- 238000004519 manufacturing process Methods 0.000 description 6
- 229930195733 hydrocarbon Natural products 0.000 description 5
- 150000002430 hydrocarbons Chemical class 0.000 description 5
- 239000004215 Carbon black (E152) Substances 0.000 description 4
- 239000007788 liquid Substances 0.000 description 4
- 239000000047 product Substances 0.000 description 4
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 4
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 239000000446 fuel Substances 0.000 description 3
- 238000000034 method Methods 0.000 description 3
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 2
- 238000006555 catalytic reaction Methods 0.000 description 2
- 238000009826 distribution Methods 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 229910000510 noble metal Inorganic materials 0.000 description 2
- 238000000634 powder X-ray diffraction Methods 0.000 description 2
- 229910052703 rhodium Inorganic materials 0.000 description 2
- 229910052707 ruthenium Inorganic materials 0.000 description 2
- 238000004438 BET method Methods 0.000 description 1
- 239000012494 Quartz wool Substances 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 239000003513 alkali Substances 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 239000007795 chemical reaction product Substances 0.000 description 1
- 230000008021 deposition Effects 0.000 description 1
- 229910001873 dinitrogen Inorganic materials 0.000 description 1
- 230000001747 exhibiting effect Effects 0.000 description 1
- 238000004817 gas chromatography Methods 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- 238000007561 laser diffraction method Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 239000012299 nitrogen atmosphere Substances 0.000 description 1
- 229910052763 palladium Inorganic materials 0.000 description 1
- 238000010587 phase diagram Methods 0.000 description 1
- 229910052697 platinum Inorganic materials 0.000 description 1
- 239000010453 quartz Substances 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 229910052702 rhenium Inorganic materials 0.000 description 1
- 238000000790 scattering method Methods 0.000 description 1
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 1
- 238000001179 sorption measurement Methods 0.000 description 1
- 230000000087 stabilizing effect Effects 0.000 description 1
- 238000003786 synthesis reaction Methods 0.000 description 1
- 229910052723 transition metal Inorganic materials 0.000 description 1
- 150000003624 transition metals Chemical class 0.000 description 1
Classifications
-
- 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
Abstract
Description
本発明は、メタンと水蒸気と反応して水素を生成する触媒に関する。 The present invention relates to a catalyst that reacts with methane and water vapor to produce hydrogen.
近年、水素は燃焼すると水しか発生せず、地球環境の保全という観点からクリーンなエネルギー媒体として期待されており、最近では、特に燃料電池の燃料として注目されている。このような燃料としての水素の製造方法としてはこれまでに様々なものが知られている。そのうちの最も重要な方法として、メタンなどの炭化水素（ＣｎＨｍ）と水蒸気との反応により水素及び合成ガスを製造する方法があり、水蒸気改質反応とよばれる。その総括反応式は次の式で示され、大きな吸熱を伴う反応である。
ＣｎＨｍ ＋ ｎＨ２Ｏ → ｎＣＯ ＋（ｎ＋ｍ／２）Ｈ２
下記のメタン（ＣＨ４）の水蒸気改質はこれらの炭化水素の水蒸気改質の中の重要な反応である。
ＣＨ４ ＋ Ｈ２Ｏ → ＣＯ ＋ ３Ｈ２
これらの反応は、熱力学的には高温ほど有利であり、炭化水素の種類にもよるが、７００℃（５０℃単位、以下同じ。）以上の反応温度が必要である。従って、炭化水素の水蒸気改質用触媒には、高い活性と共に、優れた耐熱性、高温安定性及び一定の高温強度が求められている。従来、炭化水素の水蒸気改質用触媒としては、担体上に担持された遷移金属が一般的に用いられている。メタン（ＣＨ４）の水蒸気改質に対する金属の触媒活性について、次の順序を示す。
Ｒｈ，Ｒｕ＞Ｎｉ＞Ｉｒ＞Ｐｄ，Ｐｔ，Ｒｅ＞Ｆｅ，Ｃｏ
この中で、貴金属Ｒｈ， Ｒｕが最も活性が高いが、コストが高いという問題がある。Ｎｉは比較的に安く、工業的によく使用されているが、活性と耐熱性が十分ではないという問題がある。
以上のような従来技術の状況において、発明者らは、メタンの水蒸気改質用触媒として、降伏強度が正の温度依存性を示し（強度の逆温度依存性と呼ばれている）、優れた高温特性、耐摩耗性を持っている金属間化合物Ｎｉ３Ａｌに着目した。金属間化合物Ｎｉ３Ａｌは触媒用成形体として提案されている（特許文献１）。
メタンの水蒸気改質用触媒としての適用については、特許文献２に示されている。
しかし、その触媒能は十分とは言えないばかりか、低温（６００℃）以下では、良好な触媒能を発現できないという問題があった。
In recent years, hydrogen generates only water when combusted, and is expected as a clean energy medium from the viewpoint of conservation of the global environment. Recently, it has attracted attention as a fuel for fuel cells. Various methods for producing hydrogen as such a fuel have been known so far. Among them, the most important method is a method of producing hydrogen and synthesis gas by a reaction between a hydrocarbon such as methane (C n H m ) and steam, which is called a steam reforming reaction. The general reaction formula is shown by the following formula, and is a reaction with a large endotherm.
C n H m + nH 2 O → nCO + (n + m / 2) H 2
The steam reforming of methane (CH 4 ) described below is an important reaction in the steam reforming of these hydrocarbons.
CH 4 + H 2 O → CO + 3H 2
These reactions are thermodynamically more advantageous at higher temperatures, and require a reaction temperature of 700 ° C. (50 ° C. unit, the same shall apply hereinafter) or higher, depending on the type of hydrocarbon. Accordingly, hydrocarbon steam reforming catalysts are required to have high activity, excellent heat resistance, high temperature stability, and constant high temperature strength. Conventionally, transition metals supported on a carrier are generally used as hydrocarbon steam reforming catalysts. The following order is shown for the catalytic activity of the metal for the steam reforming of methane (CH 4 ).
Rh, Ru>Ni>Ir> Pd, Pt, Re> Fe, Co
Among these, the noble metals Rh and Ru have the highest activity, but there is a problem that the cost is high. Ni is relatively cheap and is often used industrially, but has a problem that its activity and heat resistance are not sufficient.
In the state of the prior art as described above, the inventors have shown that the yield strength shows a positive temperature dependency as a catalyst for steam reforming of methane (referred to as the reverse temperature dependency of strength) and is excellent. Attention was paid to the intermetallic compound Ni 3 Al having high temperature characteristics and wear resistance. Intermetallic compound Ni 3 Al has been proposed as a molded article for catalyst (Patent Document 1).
Application of methane as a steam reforming catalyst is disclosed in Patent Document 2.
However, the catalytic ability is not sufficient, and there is a problem that good catalytic ability cannot be expressed at a low temperature (600 ° C.) or lower.
本願発明は、このような実情に鑑み、６００℃以下においても、従来の触媒より高いメタン水蒸気改質触媒活性を発現させることができる触媒を提供することを特徴とする。 In view of such circumstances, the present invention is characterized by providing a catalyst capable of exhibiting higher methane steam reforming catalytic activity than conventional catalysts even at 600 ° C. or lower.
発明１の触媒は、メタンの水蒸気改質反応により水素を生成する触媒であって、少なくともその表面が主にＮｉ−Ａｌ相よりなるＮｉ−Ａｌ金属間化合物のナノ粒子からなることを特徴とする。 The catalyst of the invention 1 is a catalyst that generates hydrogen by a steam reforming reaction of methane, and is characterized in that at least the surface thereof is composed of nanoparticles of a Ni—Al intermetallic compound mainly composed of a Ni—Al phase. .
発明２は、発明１の触媒において、ナノ粒子のＢＥＴ比表面積が５０m２／ｇ以上であることを特徴とすることを特徴とする。 Invention 2 is characterized in that, in the catalyst of Invention 1, the BET specific surface area of the nanoparticles is 50 m 2 / g or more.
発明３は、 発明１または２の触媒において、ＮｉＡｌ合金インゴットを真空アークプラズマ蒸着法によりナノ粒子化されたものであることを特徴とする。 Invention 3 is characterized in that, in the catalyst of Invention 1 or 2, the NiAl alloy ingot is made into nanoparticles by a vacuum arc plasma deposition method.
本発明の触媒は、貴金属や希少元素を含有しないにもかかわらず、メタンの水蒸気改質反応を６００℃以下においても高効率で発揮し、かつそのメタンの転化率は、理論のメタン平衡転化率に近い値であった。 The catalyst of the present invention exhibits a high-efficiency steam reforming reaction of methane even at 600 ° C. or lower, despite the fact that it does not contain a noble metal or a rare element, and the methane conversion rate is the theoretical methane equilibrium conversion rate. It was close to the value.
金属間化合物ナノ粒子の粒径の好ましい範囲は１ｎｍから１００ｎｍである。その範囲のサイズの粒子は安定的に存在することができ、高い比表面積を有するためである。
Ｎｉ−Ａｌの重量比の範囲は、Ｎｉは７６−９５重量％、Ａｌは５−２４重量％である。Ｎｉ−Ａｌの２元状態図により、この範囲では、Ｎｉ３ＡｌとＮｉＡｌの金属間化合物相は存在する。
この金属間化合物ナノ粒子の相構造が、Ｎｉ３Ａｌ，ＮｉＡｌ，Ｎｉ，ＮｉＯ及びＡｌ２Ｏ３相のすべてを表面に有する必要がなく、触媒活性を有するＮｉ３Ａｌ，ＮｉＡｌ等のＡｌ成分を含有する相があれば良い。
A preferable range of the particle size of the intermetallic compound nanoparticles is 1 nm to 100 nm. This is because particles having a size within that range can exist stably and have a high specific surface area.
The range of the Ni-Al weight ratio is 76-95% by weight for Ni and 5-24% by weight for Al. In this range, there is an intermetallic compound phase of Ni 3 Al and NiAl according to the Ni—Al binary phase diagram.
The phase structure of the intermetallic compound nanoparticles does not need to have all of the Ni 3 Al, NiAl, Ni, NiO and Al 2 O 3 phases on the surface, and Al components such as Ni 3 Al and NiAl having catalytic activity can be used. It is sufficient if there is a phase to be contained.
Ｎｉ−Ａｌ金属間化合物ナノ粒子の作製
Ｎｉ（ニッケル）とＡｌ（アルミニウム）をアーク溶解炉で以下の組成の合金インゴットを作製した。
Production of Ni-Al Intermetallic Compound Nanoparticles An alloy ingot having the following composition was produced using Ni (nickel) and Al (aluminum) in an arc melting furnace.
上記のＮｉＡｌ合金インゴットを用いて、１−５０ Ｐａでの真空アークプラズマ蒸着法により、表２に示すように各組成のナノ粒子試料を作製した。粉末Ｘ線回折測定によりこれらのナノ粒子試料の相の構成を確認したところ、図１に示すように、これらのナノ粒子試料は、Ｎｉ３Ａｌ，ＮｉＡｌ，Ｎｉ，ＮｉＯ及びＡｌ２Ｏ３相を主相とするものであった。
なお、図中の略称は、原材料とした合金の略称を示すものである。
Using the above-mentioned NiAl alloy ingot, nanoparticle samples of each composition were prepared as shown in Table 2 by vacuum arc plasma deposition at 1-50 Pa. When the composition of the phases of these nanoparticle samples was confirmed by powder X-ray diffraction measurement, as shown in FIG. 1, these nanoparticle samples contained Ni 3 Al, NiAl, Ni, NiO and Al 2 O 3 phases. It was the main phase.
In addition, the abbreviation in a figure shows the abbreviation of the alloy used as a raw material.
マイクロトラック粒度分布測定装置を用いてレーザー回折・散乱法により粒子の全体的粒度分布を測定した。表２のＮｏ．２のナノ粒子は１ｎｍから６００ｎｍまでの範囲で、Ｎｏ．５のナノ粒子は１ｎｍから８００ｎｍまでの範囲であることが分かった。透過電子顕微鏡（ＴＥＭ）及び走査透過電子顕微鏡（ＳＴＥＭ）により作製したナノ粒子のサイズ、形状、組成を分析した。粒子サイズは主に１ｎｍから１００ｎｍまでの範囲に分布することが分かった（図２）。
窒素ガス吸着により比表面積を測定した。これらのナノ粒子試料の比表面積（ＢＥＴ法）は、５０から１１２m２／ｇであることが分かった（表２）。これは、従来のラネーＮｉ触媒に匹敵する（大きな比表面積（５０−１００m２／ｇ）である。
さらに、本ナノ粒子触媒はラネーＮｉより安定であるという大きなメリットがある。ラネーＮｉ触媒は空気中で強烈に酸化・燃焼するため、水などの液体中に保存する必要がある。そのため、主に液体反応にしか適用できない。これに対して、本ナノ粒子触媒は空気中でも安定で燃えることはないので、取扱いが簡単で、高温ガス反応にも応用できる。
The overall particle size distribution of the particles was measured by a laser diffraction / scattering method using a microtrack particle size distribution measuring device. No. in Table 2 No. 2 nanoparticles range from 1 nm to 600 nm. 5 nanoparticles were found to range from 1 nm to 800 nm. The size, shape and composition of the nanoparticles prepared by transmission electron microscope (TEM) and scanning transmission electron microscope (STEM) were analyzed. It was found that the particle size was distributed mainly in the range from 1 nm to 100 nm (FIG. 2).
The specific surface area was measured by nitrogen gas adsorption. The specific surface area (BET method) of these nanoparticle samples was found to be 50 to 112 m 2 / g (Table 2). This is comparable to a conventional Raney Ni catalyst (large specific surface area (50-100 m 2 / g).
Furthermore, this nanoparticle catalyst has a great merit that it is more stable than Raney Ni. Raney Ni catalyst oxidizes and burns strongly in the air, so it must be stored in a liquid such as water. Therefore, it can be mainly applied only to liquid reactions. On the other hand, the nanoparticle catalyst is stable even in air and does not burn, so it is easy to handle and can be applied to high temperature gas reactions.
触媒反応装置システム
触媒反応は固定床流通式触媒反応装置により行った。１０ｍｇ程度のナノ粒子試料を内径８ｍｍの石英反応管に導入し、試料層の上下に石英ウールを１０ｍｍ厚さ程度詰めて、試料層を固定する。反応管を電気炉により加熱し、所定の温度で触媒反応を行った。温度制御は試料層に接触する熱電対により行った。反応管上部に，ＣＨ４， Ｈ２，Ｎ２などのガスライン及びＨ２Ｏの液体ラインに接続した。反応に応じて必要なガスと液体を反応管に導入した。反応管下部にガスクロマトグラフィ及びガス流量計に接続し、反応物の組成と生成量を測定した。図３は触媒反応装置システムを示す。
Catalytic reactor system The catalytic reaction was carried out by a fixed bed flow type catalytic reactor. About 10 mg of a nanoparticle sample is introduced into a quartz reaction tube having an inner diameter of 8 mm, and quartz wool is packed on the top and bottom of the sample layer to a thickness of about 10 mm to fix the sample layer. The reaction tube was heated by an electric furnace to carry out a catalytic reaction at a predetermined temperature. Temperature control was performed by a thermocouple in contact with the sample layer. The upper part of the reaction tube was connected to a liquid line of the gas line and H 2 O, such as CH4, H 2, N 2. Necessary gases and liquids were introduced into the reaction tube according to the reaction. A gas chromatograph and a gas flow meter were connected to the lower part of the reaction tube, and the composition and amount of the reaction product were measured. FIG. 3 shows a catalytic reactor system.
メタンの水蒸気改質反応に対する触媒特性
組成Ｎｉ２５Ａｌのナノ粒子試料を用いて、メタンの水蒸気改質反応を行った。反応する前に５００℃で水素と窒素の混合ガス（Ｈ２ ３０ ｍｌ／ｍｉｎ ＋ Ｎ２ ５ ｍｌ／ｍｉｎ））により１時間の還元処理を行った。その後、Ｎ２雰囲気中（Ｎ２流量 ３０ ｍｌ／ｍｉｎ）、メタンガス（１８ ｍｌ／ｍｉｎ）と純水（５０μｌ／ｍｉｎ）と、Ｎ２キャリーガス（３０ｍｌ／ｍｉｎ）と一緒に反応管に導入した。６００℃から３５０℃までの温度範囲に、５０℃ごとに３０分を保持し、各温度を安定させてから、ガスクロマイトグラフィにより生成物の組成を測定した。ガス流量計によりガス流量を測定した。次の式により各温度でのメタンの転化率を計算した。表３は表２のＮｏ．２の触媒性能を示し、計算した各温度でのメタンの転化率及び書く生成ガスの生成速度である。図４はこれらのメタンの転化率を反応温度の関数として示した結果である。
メタンの転化率〔％〕＝（供給メタン−残留メタン）／供給メタン×１０２
Catalytic characteristics for methane steam reforming reaction A methane steam reforming reaction was carried out using a nanoparticle sample of composition Ni25Al. Prior to the reaction, reduction treatment was performed at 500 ° C. with a mixed gas of hydrogen and nitrogen (H 2 30 ml / min + N 2 5 ml / min) for 1 hour. Thereafter, in a N 2 atmosphere (N 2 flow rate 30 ml / min), methane gas (18 ml / min), pure water (50 μl / min), and N 2 carry gas (30 ml / min) were introduced into the reaction tube. . The temperature range from 600 ° C. to 350 ° C. was maintained for 30 minutes every 50 ° C., and after stabilizing each temperature, the composition of the product was measured by gas chromatography. The gas flow rate was measured with a gas flow meter. The conversion of methane at each temperature was calculated by the following formula. Table 3 shows No. 1 in Table 2. 2 shows the catalyst performance of 2, the calculated methane conversion rate at each temperature and the product gas production rate written. FIG. 4 shows the results of the conversion of these methanes as a function of reaction temperature.
Conversion rate of methane [%] = (Supply methane−Residual methane) / Supply methane × 10 2
４００℃から触媒活性を示し始めた。４５０℃で約１１％の転化率を示した。反応温度の増加に伴い、転化率が増加した。６００℃では、６２％以上の転化率が得られた。本実験条件の５００℃と６００℃でのメタンの理論平衡転化率を計算した結果、５００℃での平衡転化率は４０％、６００℃での平衡率は７５％程度である。これらの結果も図４に示す。本ナノ粒子触媒は６００℃及びそれ以下の温度では、高い触媒性能を示すことが分かる。
図５は各生成ガスの生成速度を反応温度の関数として示した結果である。５００℃以下の温度範囲では、温度の上昇に伴い、主にＨ２とＣＯ２が生成された。５００℃以上の温度範囲では、Ｈ２とＣＯ２のほか、ＣＯも生成された。温度の上昇に伴い、Ｈ２，ＣＯ２，ＣＯ生成速度が共に増加した。これらの結果から、５００℃以下の温度では、メタンの水蒸気改質反応以外、ＣＯ２の生成反応（ＣＯ＋Ｈ２Ｏ→ＣＯ２＋３Ｈ２）も起っていることを示した。５００℃以上の温度では、メタンの水蒸気改質反応の割合は大きくなり、ＣＯの生成量が増加することが分かった。
この傾向からすれば、７００℃、８００℃においても６００℃と同等若しくはそれ以上の触媒機能を発現することは、特許文献２からも容易に推測できる。
本発明は、特許文献２に比べ極めて高い触媒機能を発現し得るものであるが、その要因として考えられるのは、特許文献２の粒子は、酸及びアルカリ処理により、粒子表面のＡｌ成分が除去されており、Ｎｉ−Ａｌ系相が実質的に存在しないのに比べ、本発明では、酸及びアルカリ処理を施さないために、表面は、内部と同様に、主にＮｉ−Ａｌ系相よりなる点、又は／及び、比表面積の相違によりもたらされたものであると思われる。
特に、６００℃以下においても良好な触媒機能を発現できるのは、Ｎｉ系触媒が７００℃以上でないと良好な触媒機能を発揮しなかったことから推察すると、表面の相の違いによるものと考えられる。
It started to show catalytic activity from 400 ° C. The conversion was about 11% at 450 ° C. As the reaction temperature increased, the conversion increased. At 600 ° C., a conversion rate of 62% or more was obtained. As a result of calculating the theoretical equilibrium conversion rate of methane at 500 ° C. and 600 ° C. in this experimental condition, the equilibrium conversion rate at 500 ° C. is 40%, and the equilibrium rate at 600 ° C. is about 75%. These results are also shown in FIG. It can be seen that the present nanoparticle catalyst exhibits high catalyst performance at temperatures of 600 ° C. and lower.
FIG. 5 shows the results of the production rate of each product gas as a function of reaction temperature. In the temperature range of 500 ° C. or lower, mainly H 2 and CO 2 were generated as the temperature increased. In the temperature range of 500 ° C. or higher, CO was generated in addition to H 2 and CO 2 . As the temperature increased, the H 2 , CO 2 , and CO production rates all increased. From these results, it was shown that a CO 2 production reaction (CO + H 2 O → CO 2 + 3H 2 ) occurred at a temperature of 500 ° C. or lower in addition to the steam reforming reaction of methane. It was found that at a temperature of 500 ° C. or higher, the rate of steam reforming reaction of methane increases and the amount of CO produced increases.
From this tendency, it can be easily estimated from Patent Document 2 that a catalytic function equal to or higher than 600 ° C. is exhibited even at 700 ° C. and 800 ° C.
Although the present invention can exhibit an extremely high catalytic function compared to Patent Document 2, it is considered that the Al component on the surface of the particle of Patent Document 2 is removed by acid and alkali treatment. In the present invention, the surface is mainly composed of the Ni-Al phase, as in the case of the inside, in comparison with the fact that the Ni-Al phase is not substantially present in the present invention. This is probably due to a point or / and a difference in specific surface area.
In particular, the reason why a good catalytic function can be expressed even at 600 ° C. or lower is presumed to be due to the difference in surface phase, assuming that the Ni-based catalyst does not exhibit a good catalytic function unless it is 700 ° C. or higher. .
Claims (3)
3. The catalyst according to claim 1, wherein the NiAl alloy ingot is made into nanoparticles by a vacuum arc plasma deposition method.
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| JP2007179963A (en) * | 2005-12-28 | 2007-07-12 | Kasatani:Kk | Manufacturing method of catalyst for fuel cell, and method for carrying catalyst |
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