JP4719181B2 - Hydrocarbon reforming catalyst - Google Patents
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- JP4719181B2 JP4719181B2 JP2007124494A JP2007124494A JP4719181B2 JP 4719181 B2 JP4719181 B2 JP 4719181B2 JP 2007124494 A JP2007124494 A JP 2007124494A JP 2007124494 A JP2007124494 A JP 2007124494A JP 4719181 B2 JP4719181 B2 JP 4719181B2
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Description
本発明は、炭化水素を水蒸気や二酸化炭素で改質して水素製造や合成ガス製造を行うための炭化水素改質用触媒に関するものである。 The present invention relates to a hydrocarbon reforming catalyst for reforming a hydrocarbon with steam or carbon dioxide to produce hydrogen or synthesis gas.
炭化水素を改質して水素を製造する技術は、工業的に重要な技術であり、水素ステーション用水素製造、燃料電池用水素製造、工業用オンサイト水素製造等の手段として用いられることが期待されている。 Technology for reforming hydrocarbons to produce hydrogen is an industrially important technology, and is expected to be used as a means for hydrogen production for hydrogen stations, hydrogen production for fuel cells, industrial on-site hydrogen production, etc. Has been.
改質ガスとしては水蒸気または二酸化炭素を用いることができるが、水蒸気を用いると前処理である還元工程から次工程である改質工程への移行時間を短縮することができるので、工業上有利である。炭化水素として例えばＣnＨ2n+2を水蒸気で改質すると炭素数ｎが大きいものが改質され易く、ｎが最小であるメタンが副生成される。そのため、メタンを改質する反応が最も重要となる。メタンを水蒸気改質して合成ガスを生成させる主反応は、下記（１）式で示される。 Steam or carbon dioxide can be used as the reformed gas, but if steam is used, the transition time from the pretreatment reduction step to the next reforming step can be shortened, which is industrially advantageous. is there. When hydrocarbons such as C n H 2n + 2 are reformed with steam, those having a large carbon number n are easily reformed, and methane having the smallest n is by-produced. Therefore, the reaction for reforming methane is the most important. The main reaction for producing synthesize gas by steam reforming methane is represented by the following equation (1).
生成ガスとしてはＣＯの他にＣＯ2も一部発生する。この炭化水素改質反応は、反応効率を高くするために例えば１〜４ＭＰａの高圧力と８００〜１０００℃の高温で実施されるが、吸熱反応なので省エネルギーの観点から更なる反応効率向上が望まれている。ここで、反応効率はメタンから水素が生成される指数として下記（２）式のメタン転化率で定義する。 In addition to CO, part of CO 2 is also generated as product gas. This hydrocarbon reforming reaction is performed, for example, at a high pressure of 1 to 4 MPa and a high temperature of 800 to 1000 ° C. in order to increase the reaction efficiency. However, since it is an endothermic reaction, further improvement in reaction efficiency is desired from the viewpoint of energy saving. ing. Here, the reaction efficiency is defined by the methane conversion rate of the following formula (2) as an index for generating hydrogen from methane.
炭化水素改質反応に用いられる触媒として、Ｎｉ含有ＭｇＯ−ＣａＯ触媒が提案されている（非特許文献１、特許文献１及び２）。この触媒は、ＭｇＯ−ＣａＯ混合物の担体上にニッケル金属化合物を固溶化させることにより高度に微細分散させることに特徴があり、ニッケルの塊状化合物をＭｇＯ−ＣａＯ混合物に単に担持したものよりも触媒活性に優れている。塩基性酸化物であるＣａＯは、炭化水素改質反応中にニッケル金属上への炭素析出を抑制する効果を有するので、耐久性向上に有利である。しかしながら、固溶体を生成するため反応活性種であるニッケルが難還元性であり、反応活性が依然として低く実用触媒としての性能はそれほど高くないことが特許文献３にて指摘されている。 As a catalyst used for the hydrocarbon reforming reaction, a Ni-containing MgO-CaO catalyst has been proposed (Non-patent Document 1, Patent Documents 1 and 2). This catalyst is characterized by highly fine dispersion by dissolving a nickel metal compound on a MgO—CaO mixture support, and it is more catalytically active than a nickel bulk compound simply supported on an MgO—CaO mixture. Is excellent. CaO, which is a basic oxide, has an effect of suppressing carbon deposition on nickel metal during the hydrocarbon reforming reaction, which is advantageous for improving durability. However, it is pointed out in Patent Document 3 that nickel, which is a reactive species, is difficult to reduce because it generates a solid solution, and its reaction activity is still low and its performance as a practical catalyst is not so high.
そこで、特許文献３においては、Ｎｉ含有ＭｇＯ−ＣａＯ触媒に白金族金属を担持させることが提案されているが、高価な貴金属系の元素を使用するので工業生産規模として使用するにはランニングコストの点から問題があった。更に、特許文献３の実施例において、カルシウムを含まない０．１質量％Ｐｔ／Ｎｉ0.03Ｍｇ0.97Ｏのメタン転化率が６３％と高いのに対して、カルシウムを含む０．１質量％Ｐｔ／Ｎｉ0.03Ｃａ0.13Ｍｇ0.84Ｏのメタン転化率が５５％と低いことが示されており、また同様に特許文献２においてもマグネシウム金属と比較してカルシウム金属を含む触媒の活性が低いことが指摘されている。つまり、Ｎｉ含有ＭｇＯ−ＣａＯ触媒中のカルシウムは、何らかの原因でその効果を最大限には発揮できていないと考えられる。 Therefore, in Patent Document 3, it is proposed to support a platinum group metal on a Ni-containing MgO-CaO catalyst. However, since an expensive noble metal element is used, running cost is low for use as an industrial production scale. There was a problem in terms. Furthermore, in the example of Patent Document 3, the 0.1% by mass Pt / Ni 0.03 Mg 0.97 O containing 0.1% by mass of calcium containing 0.1% by mass Pt / Ni containing calcium, whereas the methane conversion rate is as high as 63%. Ni 0.03 Ca 0.13 Mg 0.84 O has a low methane conversion rate of 55%. Similarly, Patent Document 2 points out that the activity of a catalyst containing calcium metal is lower than that of magnesium metal. ing. That is, it is considered that the calcium in the Ni-containing MgO—CaO catalyst cannot exert its effect to the maximum for some reason.
また、特許文献４にマグネシウム及びカルシウムの化合物としてドロマイト（ＣａＭｇ（ＣＯ3）2）類を用いてニッケル塩との複合体を有する触媒が提案されているが、マグネシウムとカルシウムの組成比が１対１と固定されているため、両元素の存在比率の最適化による触媒活性向上を期待できなかった。また、ドロマイトは天然鉱物なので組成に若干ばらつきがあり、安定性に問題があった。 Further, Patent Document 4 proposes a catalyst having a composite with a nickel salt using dolomite (CaMg (CO 3 ) 2 ) as a compound of magnesium and calcium, but the composition ratio of magnesium and calcium is one pair. Since it was fixed at 1, the catalyst activity could not be improved by optimizing the ratio of both elements. Further, since dolomite is a natural mineral, its composition varies slightly and there is a problem in stability.
本発明は、上記従来技術の現状に鑑みて、高価な貴金属系の元素を使用しないで、炭化水素を長時間高い反応効率で改質する触媒の提供を目的とする。 An object of the present invention is to provide a catalyst for reforming hydrocarbons with high reaction efficiency for a long time without using expensive noble metal elements in view of the current state of the prior art.
本発明は上記課題を解決するものであって、その発明の要旨とするところは、以下の通りである。
（１）金属元素がニッケル及びマグネシウムからなる複合酸化物にカルシウム化合物が含まれる炭化水素改質用触媒であって、前記複合酸化物中のニッケルとマグネシウムのモル比が、Ｍｇ1-xＮｉxＯにおいて０．０１≦ｘ≦０．５で表され、前記ニッケルと前記マグネシウムの合計のモル数１に対する前記カルシウム化合物中のカルシウムのモル数ｙの比が、１：ｙにおいて０．０１≦ｙ≦０．４で表され、更に、前記カルシウム化合物が濃化している領域の平均直径が０．７μｍ未満であることを特徴とする炭化水素改質用触媒。
（２）前記カルシウム化合物が、水酸化カルシウム及び酸化カルシウムのうちのいずれか１種または２種混合であることを特徴とする前記（１）項に記載の炭化水素改質用触媒。
The present invention solves the above problems, and the gist of the invention is as follows.
(1) A hydrocarbon reforming catalyst in which a calcium oxide is contained in a composite oxide in which the metal element is nickel and magnesium, and the molar ratio of nickel to magnesium in the composite oxide is Mg 1-x Ni x In O, 0.01 ≦ x ≦ 0.5, and the ratio of the number of moles y of calcium in the calcium compound to the total number of moles 1 of nickel and magnesium is 0.01 ≦ y at 1: y. A hydrocarbon reforming catalyst represented by ≦ 0.4, and further having an average diameter of a region where the calcium compound is concentrated being less than 0.7 μm.
(2) The hydrocarbon reforming catalyst as described in (1) above, wherein the calcium compound is any one or a mixture of calcium hydroxide and calcium oxide.
ここで、ｘはマグネシウムへのニッケルの置換モル比、ｙはＭｇ1-xＮｉxＯに対するカルシウム化合物中のカルシウムのモル比。 Here, x is the molar substitution ratio of nickel to magnesium, and y is the molar ratio of calcium in the calcium compound to Mg 1-x Ni x O.
本発明の炭化水素改質用触媒は、高価な貴金属系の元素を使用せずとも反応効率と耐久性とに優れた特性を示し、バイオマス由来の炭化水素ガスや天然ガス等の各種の炭化水素を原料として、水素製造や合成ガス製造を高生産性かつ低コストで安定して行うことができる。 The hydrocarbon reforming catalyst of the present invention exhibits excellent characteristics in reaction efficiency and durability without using expensive noble metal elements, and various hydrocarbons such as biomass-derived hydrocarbon gas and natural gas. As a raw material, hydrogen production and synthesis gas production can be stably performed with high productivity and low cost.
本発明の最良な実施形態について、以下に説明する。 The best embodiment of the present invention will be described below.
本発明者らは、カルシウム化合物含有Ｍｇ1-xＮｉxＯ複合酸化物を研究した結果、カルシウム化合物の存在分布が不均一になりやすく、カルシウム化合物が濃化している領域（カルシウム濃化領域）の直径が２μｍに達するものもあり、カルシウム濃化領域の直径が触媒製造の都度ばらつくので、それにともなって触媒活性もばらつくという問題に直面した。 As a result of studying the calcium compound-containing Mg 1-x Ni x O composite oxide, the present inventors have found that the presence distribution of the calcium compound tends to be non-uniform, and the region where the calcium compound is concentrated (calcium concentrated region). In some cases, the diameter of the calcium reaches 2 μm, and the diameter of the calcium-concentrated region varies every time the catalyst is produced, so that the catalyst activity varies accordingly.
そこで濃化の原因を解明するために様々な触媒製造条件を試して鋭意実験した結果、触媒を製造する工程において原料となる水酸化カルシウムが溶媒水溶液のｐＨに依存して沈殿しにくいために微細分散できずに凝集しやすいこと、また、乾燥温度が低いと乾燥するまでの時間が長くなるのでその間に水酸化カルシウムが凝集しやすいことを見出した。この新知見を基に触媒製造条件を適切に制御することにより、カルシウム濃化領域の平均直径を０．７μｍ未満に制御することができれば、炭化水素改質反応を効率良くかつ安定的に行うことが可能であることが判明した。 Therefore, as a result of diligent experimentation by trying various catalyst production conditions in order to elucidate the cause of concentration, the calcium hydroxide used as a raw material in the catalyst production process is difficult to precipitate depending on the pH of the aqueous solvent solution. It has been found that it cannot be dispersed and is likely to aggregate, and if the drying temperature is low, the time until drying is prolonged, so that calcium hydroxide is likely to aggregate during that time. By appropriately controlling the catalyst production conditions based on this new knowledge, the hydrocarbon reforming reaction can be carried out efficiently and stably if the average diameter of the calcium enriched region can be controlled to less than 0.7 μm. Turned out to be possible.
本発明による炭化水素改質用触媒の詳細構成を以下に説明する。還元後の主構成を図１の模式図に示す。マトリックスとしてＭｇ1-xＮｉxＯが主体でカルシウムが濃化していない領域１２が一面に存在しており、その領域からニッケル金属が析出してニッケル金属クラスター１３が形成されている。カルシウム濃化領域１１とは、マグネシウム元素、ニッケル元素、及びカルシウム元素の三金属元素の中でのカルシウム元素のモル比率が１０％以上の領域のことである。上記三元素の存在モル比率の測定は、例えば、オージェ電子分光装置、分析機能付き透過型電子顕微鏡、電子プローブマイクロアナリシス装置、あるいはＸ線検出器を備えた走査型電子顕微鏡等の高分解能元素分析装置を用いて元素分析することにより実行できる。これらの高分解能元素分析装置の検出感度（下限）は装置にも依存するが元素比で概ね０．１〜２％程度である。Ｍｇ1-xＮｉxＯが主体でカルシウムが濃化していない領域１２をオージェ電子分光装置で測定すると、カルシウム元素は検出されない。つまり、大部分のカルシウムはカルシウム濃化領域１１に存在していると考えられる。 The detailed structure of the hydrocarbon reforming catalyst according to the present invention will be described below. The main structure after reduction is shown in the schematic diagram of FIG. A region 12 in which Mg 1-x Ni x O is mainly contained and calcium is not concentrated exists as a matrix, and nickel metal is precipitated from the region 12 to form a nickel metal cluster 13. The calcium concentration area | region 11 is an area | region whose molar ratio of the calcium element in the trimetallic element of a magnesium element, a nickel element, and a calcium element is 10% or more. The measurement of the molar ratio of the three elements is, for example, high-resolution elemental analysis such as an Auger electron spectrometer, a transmission electron microscope with an analysis function, an electron probe microanalysis device, or a scanning electron microscope equipped with an X-ray detector. It can be performed by elemental analysis using an apparatus. The detection sensitivity (lower limit) of these high-resolution elemental analyzers is approximately 0.1 to 2% in terms of element ratio, although it depends on the apparatus. When the region 12 containing mainly Mg 1-x Ni x O and not concentrated in calcium is measured by an Auger electron spectrometer, no calcium element is detected. In other words, most of the calcium is considered to be present in the calcium enriched region 11.
ニッケルの置換モル比について以下に説明する。Ｍｇ2+とＮｉ2+のイオン半径は同程度であって相互に置換されやく、ＭｇＯとＮｉＯは共に岩塩型構造で全率固溶し、Ｍｇ1-xＮｉxＯなる固溶体を形成する。還元工程においてはＭｇ1-xＮｉxＯ中の酸化状態のニッケルが還元され、Ｍｇ1-xＮｉxＯ結晶粒の表面にニッケル金属が微細に析出し、直径が０．０１μｍ以下のニッケル金属クラスターが多数形成される。 The substitution molar ratio of nickel will be described below. Mg 2+ and Ni 2+ have the same ionic radii and are easily replaced with each other, and both MgO and NiO are solid-solved in a rock salt type structure to form a solid solution of Mg 1-x Ni x O. In the reduction step, nickel in the oxidized state in Mg 1-x Ni x O is reduced, nickel metal is finely deposited on the surface of the Mg 1-x Ni x O crystal grains, and the nickel metal has a diameter of 0.01 μm or less. Many clusters are formed.
このニッケル金属クラスターが炭化水素改質用触媒の主機能を有するので、反応効率はニッケル金属クラスターの全表面積に依存する。ニッケルの置換モル比ｘが０．０１未満であると、ニッケル原子数が少なすぎ、還元雰囲気中において熱的に安定なニッケル金属クラスターを十分に生成することができない。またニッケルの置換モル比ｘが０．５超であると、ニッケル原子数が多すぎ、還元雰囲気中で析出したニッケル金属クラスターが互いに合体して大きなニッケル金属粒を形成し、ニッケル金属の単位質量当たりの表面積(比表面積)が低下して触媒活性が低下してしまう。そのため、ニッケルの置換モル比ｘは０．０１≦ｘ≦０．５の範囲に保つのが好ましい。 Since this nickel metal cluster has the main function of a hydrocarbon reforming catalyst, the reaction efficiency depends on the total surface area of the nickel metal cluster. If the substitution molar ratio x of nickel is less than 0.01, the number of nickel atoms is too small to sufficiently produce nickel metal clusters that are thermally stable in a reducing atmosphere. When the nickel substitution molar ratio x is more than 0.5, the number of nickel atoms is too large, and the nickel metal clusters deposited in the reducing atmosphere coalesce with each other to form large nickel metal grains. The contact surface area (specific surface area) decreases, and the catalytic activity decreases. Therefore, the nickel substitution molar ratio x is preferably kept in the range of 0.01 ≦ x ≦ 0.5.
ここで、ニッケル金属粒を観察するにはＸ線検出器を備えた走査型電子顕微鏡を用いるのが簡便であり、また、この観察により、ニッケル量の概略を定性的に評価することもできる。例えばニッケルの置換モル比ｘが０．５超の場合には０．０５μｍ以上の比較的大きなニッケル金属粒が観察される。更に微細なニッケル金属クラスターを観察するためには、分析機能付き透過型電子顕微鏡を用いることができる。 Here, in order to observe nickel metal grains, it is easy to use a scanning electron microscope equipped with an X-ray detector, and the outline of the nickel amount can also be qualitatively evaluated by this observation. For example, when the nickel substitution molar ratio x is more than 0.5, relatively large nickel metal grains of 0.05 μm or more are observed. In order to observe a finer nickel metal cluster, a transmission electron microscope with an analysis function can be used.
カルシウム化合物について以下に説明する。触媒活性を高くするためにはニッケル金属クラスターの比表面積を大きくすればよいが、そのためにはＭｇ1-xＮｉxＯ結晶粒を微細化することによりＭｇ1-xＮｉxＯ結晶粒の比表面積を大きくし、Ｍｇ1-xＮｉxＯ結晶粒の表面から析出するニッケル金属クラスターを多くかつその結果として微細にするのがよい。Ｍｇ1-xＮｉxＯ結晶粒を微細化するには、炭化水素改質用触媒の製造過程において、Ｍｇ1-xＮｉxＯとカルシウム化合物を適量形成させ、それぞれの結晶粒が互いに接触して結晶成長が相互に抑制されるようにし、両方の結晶を微細にするのがよい。特に、カルシウム化合物の結晶成長を抑制して結晶を微細化することができると、カルシウム濃化領域の微小化およびカルシウム濃化領域数の増加を図ることができ、触媒の活性向上および耐久性の向上に繋がることが判った。 The calcium compound will be described below. In order to increase the catalytic activity, the specific surface area of the nickel metal cluster may be increased. For that purpose, the ratio of the Mg 1-x Ni x O crystal grains is reduced by refining the Mg 1-x Ni x O crystal grains. It is desirable to increase the surface area and to increase the number of nickel metal clusters deposited from the surface of the Mg 1-x Ni x O crystal grains and, as a result, to become finer. In order to refine the Mg 1-x Ni x O crystal grains, in the process of producing the hydrocarbon reforming catalyst, Mg 1-x Ni x O and calcium compounds are formed in appropriate amounts, and the respective crystal grains contact each other. Thus, it is preferable that the crystal growth is suppressed mutually and both crystals are made fine. In particular, if the crystal growth of the calcium compound can be suppressed and the crystal can be refined, the calcium-concentrated region can be miniaturized and the number of calcium-concentrated regions can be increased. It turns out that it leads to improvement.
カルシウム化合物とＭｇ1-xＮｉxＯとを微細化するための適切な混合比としては、Ｍｇ1-xＮｉxＯに対するカルシウム化合物中のカルシウムのモル比ｙを０．０１≦ｙ≦０．４の範囲に保つのが好ましい。というのは、ｙが０．０１未満であるとカルシウム化合物の量が少なすぎてＭｇ1-xＮｉxＯの粒成長が顕著に生じてしまい、一方ｙが０．４超であるとカルシウム化合物の量が多すぎて凝集しやすいため、カルシウム濃化領域が大きくなりやすく、その直径を０．７μｍ未満に制御することが困難になってしまうからである。 As an appropriate mixing ratio for refining the calcium compound and Mg 1-x Ni x O, the molar ratio y of calcium in the calcium compound to Mg 1-x Ni x O is set to 0.01 ≦ y ≦ 0. It is preferable to keep it in the range of 4. This is because if y is less than 0.01, the amount of calcium compound is too small and Mg 1-x Ni x O grain growth remarkably occurs, whereas if y exceeds 0.4, the calcium compound This is because the calcium concentration region is likely to be large and the diameter thereof becomes difficult to be controlled to be less than 0.7 μm.
また、カルシウム化合物の物質種を同定するために本発明者らが焼成後の炭化水素改質用触媒をＸ線回折分析したところ、水酸化カルシウムが多く存在し更に酸化カルシウムも少量存在していることを確認した。これらのカルシウム化合物は後述する炭化水素改質用触媒の製造過程において生成されたものである。つまり、原料水溶液中に水酸化カルシウムが沈殿し、この水酸化カルシウムの一部が乾燥工程において脱水されて酸化カルシウムとなり、更に高温の焼成工程で完全に脱水されてほとんど全てが酸化カルシウムになったものである。この酸化カルシウムは大気中の水分を吸収すると容易に水酸化カルシウムに戻ってしまうので、Ｘ線回折分析しても少量しか検出されなかったと考えられる。ここで、水酸化カルシウムと酸化カルシウムはともに強い塩基性の化合物である。 Further, when the present inventors conducted X-ray diffraction analysis of the hydrocarbon reforming catalyst after calcination in order to identify the species of the calcium compound, a large amount of calcium hydroxide and a small amount of calcium oxide are also present. It was confirmed. These calcium compounds are produced in the manufacturing process of the hydrocarbon reforming catalyst described later. In other words, calcium hydroxide precipitated in the raw material aqueous solution, and a part of this calcium hydroxide was dehydrated in the drying process to become calcium oxide, and further completely dehydrated in the high-temperature firing process to become almost all calcium oxide. Is. Since this calcium oxide easily returns to calcium hydroxide when it absorbs moisture in the atmosphere, it is considered that only a small amount was detected even by X-ray diffraction analysis. Here, both calcium hydroxide and calcium oxide are strong basic compounds.
これらの水酸化カルシウム及び酸化カルシウムは、本発明の触媒において、Ｍｇ1-xＮｉxＯ固溶体の多結晶の粒界部分に分散して存在していると考えられる。 It is considered that these calcium hydroxide and calcium oxide are dispersed in the polycrystalline grain boundary portion of the Mg 1-x Ni x O solid solution in the catalyst of the present invention.
カルシウム濃化領域の長所を以下に三点挙げる。第一に、カルシウム化合物がＭｇ1-xＮｉxＯ結晶粒に接触することによってＭｇ1-xＮｉxＯ結晶粒に歪応力を与え、還元工程においてニッケル金属の析出を促進し、その結果として反応効率を向上させる。第二に、炭化水素改質反応中にニッケル金属クラスター上に炭素が析出して触媒活性が低下するという問題に対し、カルシウム化合物は析出した炭素を酸化して一酸化炭素として除去する効果があり、触媒としての耐久性を向上させる。第三に、原料ガスに不純物として含まれる硫化水素（Ｈ2Ｓ）ガスによりニッケル金属クラスターが硫化され触媒活性が低下するという問題に対し、カルシウム化合物は硫化水素を分解して硫化を抑制することにより耐久性を向上させる。上記第二と第三の長所は、強い塩基性を示す水酸化カルシウムと酸化カルシウムとによって顕著に現れ、耐久性向上に重要である。 The following are three advantages of the calcium concentration region. First, given the strain stress to Mg 1-x Ni x O grain by calcium compound is in contact with the Mg 1-x Ni x O grain, to facilitate the deposition of nickel metal in the reduction step, as a result Improve reaction efficiency. Secondly, the calcium compound has the effect of oxidizing the deposited carbon to remove it as carbon monoxide, in response to the problem that the catalytic activity decreases due to the deposition of carbon on the nickel metal cluster during the hydrocarbon reforming reaction. , Improve durability as a catalyst. Third, the calcium compound decomposes hydrogen sulfide and suppresses sulfidation against the problem that nickel metal clusters are sulfided by the hydrogen sulfide (H 2 S) gas contained as an impurity in the source gas and the catalytic activity is reduced. To improve durability. The second and third advantages are remarkably manifested by calcium hydroxide and calcium oxide exhibiting strong basicity, and are important for improving durability.
カルシウム濃化領域の大きさの影響を以下に説明する。前述の通り、ニッケル金属クラスターを微細に保つには、ニッケル金属クラスター結晶粒の個数を多くすることにより、個々のニッケル金属クラスター結晶粒を大きく成長させないようにするのがよく、そのためには核生成サイトであるＭｇ1-xＮｉxＯ結晶粒表面の合計表面積を大きくするのがよい。このためには個々のＭｇ1-xＮｉxＯ結晶粒を微細化することにより、Ｍｇ1-xＮｉxＯ結晶粒の比表面積を大きくするのがよい。Ｍｇ1-xＮｉxＯ結晶粒の微細化のためには、炭化水素改質用触媒の製造過程においてカルシウム化合物とＭｇ1-xＮｉxＯのそれぞれの結晶粒が互いに接触して結晶成長を相互に抑制するのが好都合であり、そのためには両方の結晶粒が微細なままで粗大化しないことが望ましい。このようにカルシウム化合物もできるだけ微細であることが望ましい。 The influence of the size of the calcium concentration region will be described below. As described above, in order to keep the nickel metal clusters fine, it is better to prevent the individual nickel metal cluster crystal grains from growing large by increasing the number of nickel metal cluster crystal grains. It is preferable to increase the total surface area of the Mg 1-x Ni x O crystal grain surface as a site. By refining the individual Mg 1-x Ni x O crystal grains for this, it is preferable to increase the specific surface area of Mg 1-x Ni x O grain. In order to refine the Mg 1-x Ni x O crystal grains, the crystal grains of the calcium compound and Mg 1-x Ni x O come into contact with each other during the production process of the hydrocarbon reforming catalyst. It is convenient to suppress each other, and for this purpose, it is desirable that both crystal grains remain fine and do not become coarse. Thus, it is desirable that the calcium compound is as fine as possible.
個々のカルシウム濃化領域の平均直径が小さければカルシウム濃化領域の比表面積が大きい。カルシウム濃化領域の表面付近のＭｇ1-xＮｉxＯ結晶粒表面から析出するニッケル金属クラスターは、カルシウムの炭素析出抑制効果と硫化抑制効果により耐久性が非常に高い。よって、カルシウム濃化領域の平均直径が小さいほど耐久性の高いニッケル金属クラスターが多く析出する。これを示す概念図を図１に示し、逆にカルシウム濃化領域の直径が大きくて比表面積が小さくその結果としてカルシウム濃化領域の表面付近に析出するニッケル金属クラスターの総個数が少ない概念図を図２に示す。図１のようにカルシウム濃化領域の平均直径が０．７μｍ未満と小さければ、炭化水素改質用触媒の耐久性が十分に高い。なお、カルシウム濃化領域からはニッケル金属クラスターはあまり析出しないが、その理由はＮｉ2+のイオン半径がＣａ2+のイオン半径よりもかなり小さいので、カルシウム化合物へのニッケルの固溶量が少ないためである。 If the average diameter of each calcium-concentrated region is small, the specific surface area of the calcium-concentrated region is large. Nickel metal clusters deposited from the surface of Mg 1-x Ni x O crystal grains in the vicinity of the surface of the calcium enriched region have extremely high durability due to the carbon precipitation inhibiting effect and the sulfuration inhibiting effect of calcium. Therefore, as the average diameter of the calcium-concentrated region is smaller, more highly durable nickel metal clusters are precipitated. A conceptual diagram showing this is shown in FIG. 1, and conversely a conceptual diagram in which the diameter of the calcium concentrated region is large and the specific surface area is small, and as a result, the total number of nickel metal clusters deposited near the surface of the calcium concentrated region is small. As shown in FIG. If the average diameter of the calcium-concentrated region is as small as less than 0.7 μm as shown in FIG. 1, the durability of the hydrocarbon reforming catalyst is sufficiently high. Nickel metal clusters do not precipitate so much from the calcium-concentrated region, because the ionic radius of Ni 2+ is considerably smaller than the ionic radius of Ca 2+ , so the amount of nickel dissolved in the calcium compound is small. Because.
カルシウム濃化領域の判別には、前記の高分解能元素分析装置を用いてカルシウム元素のモル比率が１０％以上であるかどうかを分析することにより確認できる。すなわち、マグネシウム元素、ニッケル元素、及びカルシウム元素を面分析し、これら三金属元素の中でのカルシウムの検出モル比率が１０％以上である領域のみを色分けすれば、カルシウム濃化領域のマップ画像が得られる。ここで、１０％なる値は、高分解能元素分析装置での分析において元素が確実に存在すると考えられる経験値である。 The discrimination of the calcium concentration region can be confirmed by analyzing whether or not the molar ratio of the calcium element is 10% or more using the high resolution elemental analyzer. That is, if a surface analysis of magnesium element, nickel element, and calcium element is performed, and only a region where the detected molar ratio of calcium in these three metal elements is 10% or more is color-coded, a map image of the calcium concentrated region can be obtained. can get. Here, the value of 10% is an empirical value that is considered to ensure the presence of an element in the analysis with a high-resolution elemental analyzer.
分析例として、オージェ電子分光装置を用いて測定したカルシウムの元素マップ像で、カルシウム濃化領域の直径が０．７μｍ未満の例を図３に、０．７μｍ以上の例を図４に示す。これらの図に示される淡色部がカルシウム濃化領域であり、カルシウム濃化領域の直径はこれらのマップ画像を粒子画像解析することにより算出できる。粒子画像解析では、カルシウム濃化領域が複雑な形状であっても、同面積の円とみなした場合の直径として算出するので、この値を用いることができる。 As an analysis example, FIG. 3 shows an example of a calcium elemental map image measured using an Auger electron spectrometer and the diameter of the calcium concentrated region is less than 0.7 μm, and FIG. 4 shows an example of 0.7 μm or more. The light-colored portion shown in these figures is a calcium-concentrated region, and the diameter of the calcium-concentrated region can be calculated by analyzing these map images. In the particle image analysis, even if the calcium-enriched region has a complicated shape, it is calculated as a diameter when it is regarded as a circle having the same area, so this value can be used.
平均直径は、計測された全てのカルシウム濃化領域の直径の平均をとればよい。粒子画像解析はコンピューターソフトウェアで実行することができ、そのコンピューターソフトウェアは用いた高分解能元素分析装置に付属のものでもよいし、あるいは市販のものでもよい。 What is necessary is just to take the average of the diameter of all the calcium concentration area | regions measured as an average diameter. The particle image analysis can be executed by computer software, and the computer software may be attached to the high-resolution elemental analyzer used or may be commercially available.
分析視野を例えば図１で説明すると、領域１２にはＭｇ1-xＮｉxＯが存在しその粒径は０．０１〜０．３μｍ程度、カルシウム濃化領域１１の直径は０．０１〜０．７μｍ程度であるので、カルシウム濃化領域の上限直径である０．７μｍを計測するための分析領域面積としては１０μｍ2は最低限必要であり、精度を考慮すると多数のカルシウム濃化領域の平均直径を算出するのが好ましく、比較的大きな分析領域を高分解能分析するかあるいは比較的小さな視野を複数箇所分析して分析総面積を１００μｍ2以上として１００個以上の評価個数で算出する。 The analysis visual field will be described with reference to FIG. 1, for example. Mg 1-x Ni x O is present in the region 12, its particle size is about 0.01 to 0.3 μm, and the diameter of the calcium concentrated region 11 is 0.01 to 0. Since it is about 7 μm, 10 μm 2 is the minimum required for the analysis region area for measuring 0.7 μm, which is the upper limit diameter of the calcium-concentrated region. The diameter is preferably calculated, and a comparatively large analysis region is analyzed with high resolution, or a plurality of comparatively small fields of view are analyzed, and the total analysis area is set to 100 μm 2 or more, and the evaluation number is 100 or more.
但し、分析総面積内のカルシウム濃化領域数が１００個に満たない場合は、評価個数が１００個以上になるまで分析総面積を拡大して評価することが好ましい。 However, when the number of calcium-concentrated regions in the total analysis area is less than 100, it is preferable that the total analysis area is expanded and evaluated until the evaluation number reaches 100 or more.
本発明の炭化水素改質用触媒の製造方法は、例えば、以下の製造方法を用いることが好ましい。但し、以下に説明する製造方法および条件は好ましい実施形態の一例として例示するものであり、本発明がこれらに限定されるものではない。 For example, the following production method is preferably used as the method for producing the hydrocarbon reforming catalyst of the present invention. However, the manufacturing method and conditions described below are given as examples of preferred embodiments, and the present invention is not limited to these.
ニッケル化合物、マグネシウム化合物、カルシウム化合物を所定の比に混合して、水に溶解し、スターラー等で溶液を攪拌して混合水溶液を作製する。これらの化合物としては、硝酸塩、塩化物等の水溶液への溶解度の大きいものが好ましい。そして、これらの化合物を含む水溶液のｐＨを調整し、水溶液中に溶解しているニッケル、マグネシウム、カルシウムの各元素を水酸化物、もしくはオキシ水酸化物等の形態で析出させる。ｐＨを高くするには炭酸カリウム水溶液等のアルカリ性水溶液を適量混合する。 A nickel compound, a magnesium compound, and a calcium compound are mixed in a predetermined ratio, dissolved in water, and the solution is stirred with a stirrer or the like to prepare a mixed aqueous solution. As these compounds, those having high solubility in aqueous solutions of nitrates, chlorides and the like are preferable. And the pH of the aqueous solution containing these compounds is adjusted, and each element of nickel, magnesium, and calcium dissolved in the aqueous solution is precipitated in the form of hydroxide or oxyhydroxide. To raise the pH, an appropriate amount of an alkaline aqueous solution such as an aqueous potassium carbonate solution is mixed.
上記のような共沈法でのｐＨは、従来８〜１１の範囲に調整するのが一般的であったが、水酸化カルシウムの溶解度がｐＨに大きく依存するので、ｐＨ許容条件が広い場合にはカルシウム濃化領域の平均直径がばらついていた。そこで、本発明ではカルシウム濃化領域の平均直径を０．７μｍ未満に保つために、水溶液のｐＨを１０〜１１の範囲に保つのが好ましい。ｐＨが高いほど水酸化物を形成しやすいので水酸化物析出を制御しやすいが、ｐＨを１１超に精密制御するのは工業的にはやや困難なので１０〜１１の範囲が好適である。その他の条件としては、例えば、攪拌時間を１〜５時間、酸素分圧を０．３〜０．５気圧、水溶液の温度を５０〜７５℃、とすればよい。 The pH in the coprecipitation method as described above has been conventionally adjusted in the range of 8 to 11, but the solubility of calcium hydroxide greatly depends on the pH, so when the pH tolerance is wide. There was a variation in the average diameter of the calcium-enriched region. Therefore, in the present invention, it is preferable to maintain the pH of the aqueous solution in the range of 10 to 11 in order to keep the average diameter of the calcium-concentrated region less than 0.7 μm. The higher the pH, the easier it is to form hydroxides and the easier it is to control the precipitation of hydroxides. However, since it is somewhat difficult industrially to precisely control the pH above 11, a range of 10 to 11 is suitable. As other conditions, for example, the stirring time may be 1 to 5 hours, the oxygen partial pressure may be 0.3 to 0.5 atm, and the temperature of the aqueous solution may be 50 to 75 ° C.
このようにして得られた沈殿物を７０〜９０℃の純水で十分に洗浄する。その後、例えば吸引ろ過により水を分離した後、１５０℃超の温度範囲で乾燥させることで触媒前駆体を得る。従来の乾燥温度は５０〜１５０℃であったが、低温では乾燥するまでの時間が長くなるのでその間に水酸化カルシウムが凝集しやすかった。そこで、水酸化カルシウムを高分散のまま乾燥させて凝集を抑制するために、乾燥温度を高めの１５０℃超にすることが好ましい。乾燥を安定的に継続するために更に望ましい温度は、１５０℃超〜１８０℃である。このように、ｐＨを１０〜１１とし、かつ乾燥温度を１５０℃超の条件とすることで、カルシウム濃化領域の平均直径を０．７μｍ未満に保って製造することが容易となる。 The precipitate thus obtained is thoroughly washed with pure water at 70 to 90 ° C. Then, after separating water by, for example, suction filtration, the catalyst precursor is obtained by drying in a temperature range exceeding 150 ° C. The conventional drying temperature was 50 to 150 ° C., but at low temperatures, the time until drying was long, so that calcium hydroxide easily aggregated during that time. Therefore, in order to dry the calcium hydroxide with high dispersion and suppress aggregation, it is preferable to increase the drying temperature to above 150 ° C. A more desirable temperature for stably continuing drying is above 150 ° C to 180 ° C. As described above, when the pH is set to 10 to 11 and the drying temperature is set to more than 150 ° C., it becomes easy to manufacture while maintaining the average diameter of the calcium concentrated region at less than 0.7 μm.
次いで、得られた触媒前駆体を空気中で焼成する。例えば、大気中で、７５０〜１１００℃の温度で、５〜３０時間加熱すればよい。これにより、本発明の炭化水素改質用触媒が得られ、そのまま用いてもよいが、通常の乾式成形機を用いて成形体の形にしてもよい。この際の成形機としては、例えば、打錠機あるいはブリケッティングマシン等の圧縮成形機が好適に用いられる。また、その場合の成形体の形状は、球状、シリンダー状、リング状、もしくは小粒状等いずれでもよい。 Next, the obtained catalyst precursor is calcined in air. For example, what is necessary is just to heat for 5 to 30 hours at the temperature of 750-1100 degreeC in air | atmosphere. Thereby, the hydrocarbon reforming catalyst of the present invention is obtained and may be used as it is, but it may be formed into a molded body using an ordinary dry molding machine. As the molding machine at this time, for example, a compression molding machine such as a tableting machine or a briquetting machine is preferably used. In addition, the shape of the molded body in that case may be any of a spherical shape, a cylindrical shape, a ring shape, or a small granular shape.
本発明の炭化水素改質用触媒を用いて炭化水素を改質する反応例としては以下のようなものがある。例えば、ＣnＨ2n+2と表現される炭化水素を水蒸気で改質する反応は次式で表すことができる。 Examples of reactions for reforming hydrocarbons using the hydrocarbon reforming catalyst of the present invention include the following. For example, the reaction of reforming a hydrocarbon expressed as C n H 2n + 2 with steam can be expressed by the following equation.
（３）式の反応において、炭素数ｎが小さい炭化水素は改質され難く、特にｎが最小であるメタンが副生成される。そのため、メタンを改質するための反応効率が工業的に最も重要であり、前記（２）式のメタン転化率が炭化水素改質用触媒の特性をよく現す指標となる。また、改質ガスとしては水蒸気の他に二酸化炭素を用いることができ、メタンの二酸化炭素改質反応は次式で表すことができる。 In the reaction of formula (3), hydrocarbons having a small carbon number n are difficult to be reformed, and in particular, methane having the smallest n is by-produced. Therefore, the reaction efficiency for reforming methane is the most important industrially, and the methane conversion rate of the above formula (2) serves as an index that clearly shows the characteristics of the hydrocarbon reforming catalyst. In addition to water vapor, carbon dioxide can be used as the reformed gas, and the carbon dioxide reforming reaction of methane can be expressed by the following equation.
（４）式の反応は前記（１）式と比較して水素の収率が低いという短所があるものの、温室効果ガスである二酸化炭素を消費することができるので環境保全の分野で重要である。このように、本発明の炭化水素改質用触媒は、各種の炭化水素の改質に適用できる。 Although the reaction of the formula (4) has a disadvantage that the yield of hydrogen is lower than that of the formula (1), it is important in the field of environmental conservation because it can consume carbon dioxide, which is a greenhouse gas. . Thus, the hydrocarbon reforming catalyst of the present invention can be applied to the reforming of various hydrocarbons.
［実施例１〜９］
Ｍｇ1-xＮｉxＯ（０．０１≦ｘ≦０．５）及びカルシウムのモル比率ｙで０．０１≦ｙ≦０．４のカルシウム化合物を含む炭化水素改質用触媒１〜９を以下の方法にて作製した。
[Examples 1 to 9]
Hydrocarbon reforming catalysts 1 to 9 containing Mg 1-x Ni x O (0.01 ≦ x ≦ 0.5) and a calcium compound having a calcium molar ratio y of 0.01 ≦ y ≦ 0.4 are described below. It produced by the method of.
酢酸ニッケル、硝酸マグネシウム、及び硝酸カルシウムを各金属元素のモル比が所定の値になるように精秤して、６５℃の加温下で混合水溶液を調製したものに、６５℃に加温した炭酸カリウム水溶液をｐＨが１０〜１１になるように加え、大気圧下で５時間の間ビーカー中でスターラーを用いて攪拌した。その後、吸引ろ過を行い、８０℃の純水で十分に洗浄した。洗浄後に得られた沈殿物を１６０〜１８０℃の乾燥温度で１０時間乾燥後、空気中で９５０℃にて１２時間焼成し、化合物粉末を得た。実施例１〜９の触媒の作製条件は、表１のＮｉのモル比ｘ、Ｃａのモル比ｙ、水溶液のｐＨ、及び乾燥温度の欄に示した。 Nickel acetate, magnesium nitrate, and calcium nitrate were precisely weighed so that the molar ratio of each metal element was a predetermined value, and a mixed aqueous solution was prepared at 65 ° C. and heated to 65 ° C. Potassium carbonate aqueous solution was added so that pH might be set to 10-11, and it stirred using the stirrer in the beaker for 5 hours under atmospheric pressure. Thereafter, suction filtration was performed, and the film was sufficiently washed with 80 ° C. pure water. The precipitate obtained after washing was dried at a drying temperature of 160 to 180 ° C. for 10 hours and then calcined in air at 950 ° C. for 12 hours to obtain a compound powder. The production conditions for the catalysts of Examples 1 to 9 are shown in the columns of Ni molar ratio x, Ca molar ratio y, aqueous solution pH, and drying temperature in Table 1.
得られた化合物粉末を、圧縮成形器で６００Ｋｇ／ｃｍ2の圧力でプレスした後、十分に粉砕して、１００〜３００メッシュ（６３〜１５０μｍ）の大きさに整粒することにより、炭化水素改質用触媒の粉末をそれぞれ約２０ｇ得た。 The obtained compound powder was pressed with a compression molding machine at a pressure of 600 kg / cm 2 , and then sufficiently pulverized and sized to a size of 100 to 300 mesh (63 to 150 μm). About 20 g of quality catalyst powder was obtained.
この炭化水素改質用触媒の粉末をＸ線回折分析したところ、カルシウム化合物としては水酸化カルシウムが多く検出され、酸化カルシウムも少量検出された。 As a result of X-ray diffraction analysis of this hydrocarbon reforming catalyst powder, a large amount of calcium hydroxide and a small amount of calcium oxide were detected as calcium compounds.
この炭化水素改質用触媒の粉末をオージェ電子分光装置を用いてカルシウム元素分析し、粒子画像解析することによりカルシウム濃化領域の平均直径を算出した。分析領域は、カルシウム濃化領域の直径に応じて２０〜５０００μｍ2とし、カルシウム濃化領域の合計計測個数が１００個以上になるようにした。図３に実施例３の炭化水素改質用触媒におけるカルシウムの元素マップ像を示す。カルシウム濃化領域の直径が０．７μｍ未満である。 The powder of this hydrocarbon reforming catalyst was subjected to elemental calcium analysis using an Auger electron spectrometer and the particle diameter was analyzed to calculate the average diameter of the calcium enriched region. The analysis region was set to 20 to 5000 μm 2 depending on the diameter of the calcium enriched region, and the total number of measured calcium enriched regions was 100 or more. FIG. 3 shows an element map image of calcium in the hydrocarbon reforming catalyst of Example 3. The diameter of the calcium enriched region is less than 0.7 μm.
炭化水素改質反応を実行するため、予め管内部の中央位置に多孔質石英板を取りつけた石英製反応管に、この炭化水素改質用触媒粉末１．０００ｇを充填し、反応管を電気炉内にセットした。炭化水素改質反応を始める前に、まず反応器をアルゴンガス雰囲気下で９００℃まで昇温した後、水素ガスを５０ｍｌ／ｍｉｎの流量で流しながら、９００℃で３０分間還元処理を行った（還元工程）。その後、５０ｐｐｍの硫化水素を含有するメタンと水蒸気を流し、水素ガスと一酸化炭素ガスを生成した（改質工程）。原料ガスのメタンと水蒸気のモル比率は、メタン：水蒸気＝１：２とした。反応温度を９００℃、反応圧力を絶対圧で０．１ＭＰａ、炭化水素改質反応のガス流量（ｍｏｌ／ｈ）当たりの触媒重量（ｇ）を２．００（ｇｈ／ｍｏｌ）で２４時間運転した。メタン転化率（％）は、検知器で測定した出口ガスの濃度(体積％)を前記（２）式に代入して算出した。運転の初期である３０分後と終期である２４時間後においてメタン転化率を測定し、それぞれの測定値を表１の初期メタン転化率と終期メタン転化率の欄に示した。表１の結果から、本発明による炭化水素改質用触媒では、カルシウム濃化領域の平均直径が０．７μｍ未満と小さく、メタン原料ガスに硫化水素が不純物として含まれていても初期メタン転化率は６０％以上の高い値を示し最終メタン転化率も５８％以上の高い値を示している。 In order to carry out the hydrocarbon reforming reaction, 1.000 g of this hydrocarbon reforming catalyst powder was charged into a quartz reaction tube in which a porous quartz plate was previously attached at the center position inside the tube, and the reaction tube was placed in an electric furnace. Set inside. Before starting the hydrocarbon reforming reaction, the reactor was first heated to 900 ° C. in an argon gas atmosphere, and then reduced at 900 ° C. for 30 minutes while flowing hydrogen gas at a flow rate of 50 ml / min ( Reduction step). Thereafter, methane containing 50 ppm of hydrogen sulfide and water vapor were flown to generate hydrogen gas and carbon monoxide gas (reforming step). The molar ratio of the raw material gas methane to water vapor was methane: water vapor = 1: 2. The reaction temperature was 900 ° C., the reaction pressure was 0.1 MPa in absolute pressure, and the catalyst weight (g) per gas flow rate (mol / h) of the hydrocarbon reforming reaction was operated at 2.00 (gh / mol) for 24 hours. . The methane conversion rate (%) was calculated by substituting the concentration (volume%) of the outlet gas measured by the detector into the equation (2). The methane conversion was measured 30 minutes after the initial operation and 24 hours after the final operation, and the measured values are shown in the columns of initial methane conversion and final methane conversion in Table 1. From the results of Table 1, in the hydrocarbon reforming catalyst according to the present invention, the average diameter of the calcium enriched region is as small as less than 0.7 μm, and even if hydrogen sulfide is contained as an impurity in the methane raw material gas, the initial methane conversion rate Shows a high value of 60% or more, and the final methane conversion also shows a high value of 58% or more.
以下の比較例１〜７の触媒の作製条件は、表１のＮｉのモル比ｘ、Ｃａのモル比ｙ、水溶液のｐＨ、及び乾燥温度の欄に示した。その他の条件は、実施例と同様に行った。
［比較例１〜４］
比較例１ではＮｉのモル比ｘを０．００５とし、比較例２ではＮｉのモル比ｘを０．６とし、比較例３ではＣａのモル比ｙを０．００５とし、比較例４ではＣａのモル比ｙを０．５とし、その他の条件は実施例３と同様にして作製し、また同様にして測定した。
The preparation conditions of the following Comparative Examples 1 to 7 are shown in the columns of Ni molar ratio x, Ca molar ratio y, aqueous solution pH, and drying temperature in Table 1. Other conditions were the same as in the example.
[Comparative Examples 1-4]
In Comparative Example 1, the Ni molar ratio x is 0.005, in Comparative Example 2, the Ni molar ratio x is 0.6, in Comparative Example 3, the Ca molar ratio y is 0.005, and in Comparative Example 4, the Ca molar ratio x is 0.005. The molar ratio y was 0.5, and other conditions were prepared in the same manner as in Example 3 and measured in the same manner.
表１の比較例１〜４の結果から、Ｎｉのモル比が０．０１≦ｘ≦０．５の範囲外である場合、あるいはＣａのモル比ｙが０．０１≦ｙ≦０．４の範囲外である場合、カルシウム濃化領域の平均直径は比較的小さいものの、初期メタン転化率が６０％を下回り最終メタン転化率も５０％以下であり、反応効率の点で本発明の炭化水素改質用触媒よりも劣位であることが認められる。
［比較例５〜７］
比較例５では水溶液のｐＨを９．５とし、その他の条件は実施例３と同様にして作製し、また同様にして測定した。
From the results of Comparative Examples 1 to 4 in Table 1, when the molar ratio of Ni is outside the range of 0.01 ≦ x ≦ 0.5, or the molar ratio y of Ca is 0.01 ≦ y ≦ 0.4. If it is out of the range, the average diameter of the calcium-concentrated region is relatively small, but the initial methane conversion is less than 60% and the final methane conversion is also 50% or less. It is recognized that it is inferior to the quality catalyst.
[Comparative Examples 5 to 7]
In Comparative Example 5, the pH of the aqueous solution was set to 9.5, and other conditions were prepared in the same manner as in Example 3 and measured in the same manner.
比較例６では水溶液のｐＨを１０．０、乾燥温度を１２０℃とし、その他の条件は実施例３と同様にして作製し、また同様にして測定した。図４に比較例６の炭化水素改質用触媒におけるカルシウムの元素マップ像を示す。カルシウム濃化領域の直径が０．７μｍ以上である。 In Comparative Example 6, the pH of the aqueous solution was 10.0, the drying temperature was 120 ° C., and other conditions were prepared in the same manner as in Example 3 and measured in the same manner. FIG. 4 shows an element map image of calcium in the hydrocarbon reforming catalyst of Comparative Example 6. The diameter of the calcium enriched region is 0.7 μm or more.
比較例７では水溶液のｐＨを８．０、乾燥温度を５０℃とし、その他の条件は実施例３と同様にして作製し、また同様にして測定した。 In Comparative Example 7, the pH of the aqueous solution was 8.0, the drying temperature was 50 ° C., and other conditions were prepared in the same manner as in Example 3 and measured in the same manner.
表１の比較例５〜７の結果から、水溶液のｐＨが１０〜１１の範囲外である場合、あるいは乾燥温度が１５０℃未満である場合、カルシウム濃化領域の平均直径が０．７μｍ以上と大きく、初期メタン転化率が６０％を下回り最終メタン転化率も５０％以下であり、反応効率の点で本発明の炭化水素改質用触媒よりも劣位であることが認められる。
［比較例８］
比較例８では、比較例６で作製した炭化水素改質用触媒のうちの１０ｇに、特許文献３に記載されている方法で白金を０．１質量％担持するようにＰｔ（Ｃ5Ｈ7Ｏ2）2をアセトンに溶解した溶液を含浸し、２０℃で１２時間乾燥させた。測定は実施例と同様にして行った。表１に示した比較例８と比較例６との結果を比較すると、白金を０．１質量％担持した比較例８の触媒の初期メタン転化率と最終メタン転化率がともに高いので、白金担持による反応効率向上が認められる。しかしながら、初期メタン転化率は６０％を下回り最終メタン転化率も５０％以下であり、反応効率の点で本発明の炭化水素改質用触媒よりもやや劣位であることが認められる。
From the results of Comparative Examples 5 to 7 in Table 1, when the pH of the aqueous solution is outside the range of 10 to 11, or when the drying temperature is less than 150 ° C., the average diameter of the calcium concentrated region is 0.7 μm or more. The initial methane conversion rate is less than 60% and the final methane conversion rate is also 50% or less, which is inferior to the hydrocarbon reforming catalyst of the present invention in terms of reaction efficiency.
[Comparative Example 8]
In Comparative Example 8, 10 g of the hydrocarbon reforming catalyst produced in Comparative Example 6 was supported by Pt (C 5 H 7 so that 0.1% by mass of platinum was supported by the method described in Patent Document 3. A solution of O 2 ) 2 dissolved in acetone was impregnated and dried at 20 ° C. for 12 hours. The measurement was performed in the same manner as in the example. When the results of Comparative Example 8 and Comparative Example 6 shown in Table 1 are compared, the initial methane conversion rate and final methane conversion rate of the catalyst of Comparative Example 8 supporting 0.1% by mass of platinum are both high. The reaction efficiency is improved by. However, the initial methane conversion rate is less than 60%, and the final methane conversion rate is also 50% or less, which is recognized to be slightly inferior to the hydrocarbon reforming catalyst of the present invention in terms of reaction efficiency.
以上の実施例と比較例の結果から、メタン原料ガスに硫化水素が不純物として含まれている場合、比較例では初期メタン転化率が６０％を下回り最終メタン転化率も５０％以下であるが、本本発明による炭化水素改質用触媒では初期メタン転化率が６０％以上と高く反応効率が非常に高いことを示しており、また最終メタン転化率も５８％以上と高く耐久性が優れていることを示しており、発明の効果が明瞭に認められる。 From the results of the above Examples and Comparative Examples, when hydrogen sulfide is contained as an impurity in the methane raw material gas, in the Comparative Example, the initial methane conversion is less than 60% and the final methane conversion is also 50% or less. The hydrocarbon reforming catalyst according to the present invention has an initial methane conversion rate as high as 60% or higher and a very high reaction efficiency, and a final methane conversion rate as high as 58% or higher and excellent durability. The effect of the invention is clearly recognized.
このように本発明の炭化水素改質用触媒はメタンを水蒸気改質する反応に有効に作用することが示されたが、メタンよりも炭素数が多くて改質容易なその他の炭化水素にも適用でき、また従来の改質用触媒と同様に水蒸気改質だけでなく二酸化炭素改質にも適用できる。 As described above, it has been shown that the hydrocarbon reforming catalyst of the present invention effectively acts on the reaction of steam reforming methane, but other hydrocarbons having a larger number of carbon than methane and easily reforming can be used. The present invention can be applied and can be applied not only to steam reforming but also to carbon dioxide reforming as in the case of conventional reforming catalysts.
本発明による炭化水素改質用触媒では、ニッケル金属クラスターが微細で、その表面への炭素析出を抑制でき、更にニッケル金属クラスターの硫化を抑制できる。そのため、触媒活性が高くかつ耐久性に優れるという特性を示すので、ＣnＨ2n+2、ＣnＨ2n、あるいはタールなどの炭化水素を改質して、水素あるいは合成ガスを長時間安定に製造する反応に応用することができる。 In the hydrocarbon reforming catalyst according to the present invention, the nickel metal cluster is fine, carbon deposition on the surface thereof can be suppressed, and sulfuration of the nickel metal cluster can be further suppressed. Therefore, since it has the characteristic of high catalytic activity and excellent durability, hydrocarbons such as C n H 2n + 2 , C n H 2n , or tar are reformed to stabilize hydrogen or synthesis gas for a long time. It can be applied to the reaction to be produced.
１１ カルシウム濃化領域（斜線部）
１２ Ｍｇ1-xＮｉxＯが主体でカルシウムが濃化していない領域
１３ ニッケル金属クラスター（黒点部）
11 Calcium concentration area (shaded area)
12 Mg 1-x Ni x O is the main region where calcium is not concentrated 13 Nickel metal cluster (black spot)
Claims (2)
前記複合酸化物中のニッケルとマグネシウムのモル比が、Ｍｇ1-xＮｉxＯにおいて０．０１≦ｘ≦０．５で表され、
前記ニッケルと前記マグネシウムの合計のモル数１に対する前記カルシウム化合物中のカルシウムのモル数ｙの比が、１：ｙにおいて０．０１≦ｙ≦０．４で表され、
更に、前記カルシウム化合物が濃化している領域の平均直径が０．７μｍ未満であることを特徴とする炭化水素改質用触媒。 A hydrocarbon reforming catalyst in which a calcium compound is contained in a composite oxide in which a metal element is nickel and magnesium,
The molar ratio of nickel and magnesium in the composite oxide is expressed as 0.01 ≦ x ≦ 0.5 in Mg 1-x Ni x O,
The ratio of the number of moles y of calcium in the calcium compound to the total number of moles of nickel and magnesium is represented by 0.01 ≦ y ≦ 0.4 at 1: y,
The hydrocarbon reforming catalyst is characterized in that an average diameter of a region where the calcium compound is concentrated is less than 0.7 μm.
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