JP5252250B2 - Noble metal catalyst and method for producing the same - Google Patents
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本発明は、貴金属触媒及びその製造方法に関する。 The present invention relates to a noble metal catalyst and a method for producing the same.
近年、内燃機関、ボイラー等の排気ガス中の微粒子や有害物質は、環境への影響を考慮して排気ガス中から除去する必要性が高まりつつあり、各種排ガス浄化技術が提案されている。例えば、自動車の排気系には、酸化触媒、三元触媒、ＮＯＸ吸蔵還元型触媒等が配置され、主として貴金属の触媒作用によって排ガス中のＮＯＸ、ＨＣ、ＣＯ等の有害成分を浄化している。特に、酸化触媒としては、例えば、アルミナやシリカ等の担体に酸化活性の高いＰｔを担持したものが知られている。 In recent years, there has been an increasing need to remove particulates and harmful substances in exhaust gas from internal combustion engines, boilers, and the like from the exhaust gas in consideration of environmental effects, and various exhaust gas purification technologies have been proposed. For example, the exhaust system of an automobile, an oxidation catalyst, three-way catalyst, NO X storage reduction catalyst and the like are arranged, to purify NO X in the exhaust gas, HC, harmful components such as CO mainly by the catalytic action of the noble metal Yes. In particular, as an oxidation catalyst, for example, a catalyst in which Pt having a high oxidation activity is supported on a carrier such as alumina or silica is known.
従来、多孔質セラミックス材料などの触媒担体に触媒金属を担持させるには、金属水溶液を用いた通常の含浸法による方法の他に、金属分散性を高めるために金属アルコキシドを用いたゾルゲル法が報告されている。従来のゾルゲル法によるアルミナ担持白金触媒の作製には、まずアルミニウムのアルコキシドをエステル系やジオル系のキレート剤で保護してからアルコール等の有機溶媒に溶解し、白金錯体塩と少量の水、触媒等と一緒に密閉容器に加え、場合によっては１週間ほど加温して徐々にアルミニウムの加水分解・ゲル化・ゲル熟成を進行させていた。 Conventionally, to support a catalytic metal on a catalyst carrier such as a porous ceramic material, a sol-gel method using a metal alkoxide to improve metal dispersibility has been reported in addition to a conventional impregnation method using a metal aqueous solution. Has been. In the preparation of an alumina-supported platinum catalyst by the conventional sol-gel method, an aluminum alkoxide is first protected with an ester-based or diol-based chelating agent and then dissolved in an organic solvent such as alcohol, and then a platinum complex salt, a small amount of water, a catalyst In some cases, it was heated for about a week, and the hydrolysis, gelation, and gel aging of aluminum were gradually advanced.
しかしながら、アルミニウムのアルコキシドは、加水分解速度が非常に高く、シリコンのそれに比べてその制御が難しいため、水分量や温度等を厳密に管理しながら、キレート剤で保護された有機溶媒中のアルミニウムアルコキシドを徐々に加水分解・重合させる、というデリケートな方法を採らざるを得なかった。 However, aluminum alkoxide has a very high hydrolysis rate and is difficult to control compared to that of silicon. Therefore, aluminum alkoxide in an organic solvent protected with a chelating agent while strictly controlling the amount of water and temperature is used. Therefore, the delicate method of gradually hydrolyzing and polymerizing the water must be taken.
しかも、上記アルコキシドを用いた従来のアルミナ系触媒の調製では、高価で危険な有機溶媒を使用し、且つ長時間掛けてゲル化を進行させる等、実用化に向けて多くの困難が立ちはだかっていた。更に、この方法で作製したゲルを凍結乾燥するためには、ゲル中の有機溶媒を水に置換する必要があり、その際、ゲルの破壊や白金金属イオンがゲルから流出してしまうという問題があった。 Moreover, in the preparation of the conventional alumina-based catalyst using the alkoxide, there are many difficulties for practical use, such as using an expensive and dangerous organic solvent and allowing the gelation to proceed for a long time. . Furthermore, in order to freeze-dry the gel produced by this method, it is necessary to replace the organic solvent in the gel with water, and in that case, there is a problem that the gel is broken or platinum metal ions flow out from the gel. there were.
本発明は、上述した従来技術の問題点に鑑みてなされたものであり、その目的とするところは、高表面積、高気孔率及び高耐熱性を有するとともに、５００〜７００℃の雰囲気下で白金微粒子のシンタリングが抑制される貴金属触媒、及びその貴金属触媒を安全且つ低コストで製造することができる貴金属触媒の製造方法を提供することにある。 The present invention has been made in view of the above-described problems of the prior art. The object of the present invention is to have a high surface area, a high porosity, and a high heat resistance, and to form platinum under an atmosphere of 500 to 700 ° C. An object of the present invention is to provide a noble metal catalyst in which sintering of fine particles is suppressed, and a method for producing a noble metal catalyst capable of producing the noble metal catalyst safely and at low cost.
上述の目的を達成するため、本発明は、以下の貴金属触媒及びその製造方法を提供するものである。 In order to achieve the above object, the present invention provides the following noble metal catalyst and a method for producing the same.
［１］ 白金微粒子が凍結乾燥ゲル中に埋没しており、前記白金微粒子が前記凍結乾燥ゲル中に埋没する度合いを示す埋没度（下記式（Ｉ））が４５〜６０％であり、且つ５００〜７００℃の雰囲気下で前記白金微粒子のシンタリングが抑制されるとともに、前記白金の添加量が、０．５〜５質量％である高温耐熱性を有するアルミナクリオゲルからなる、酸化反応において触媒として作用しうる貴金属触媒。
式（Ｉ）：埋没度（％）＝１００×［１−０．０１３８×ｄ ＶＡ ×Ｄ Ｍ ］
［但し、式（Ｉ）中、ｄ ＶＡ ：透過型電子顕微鏡（ＴＥＭ）を使用した観察により算出した白金粒子の直径（ｎｍ）、Ｄ Ｍ ：ＣＯ吸着法により算出した白金表面露出率（％）］
[1] The platinum fine particles are embedded in the freeze-dried gel, the degree of burying (the following formula (I)) indicating the degree of the platinum fine particles embedded in the freeze-dried gel is 45 to 60%, and 500 A catalyst in an oxidation reaction comprising an alumina cryogel having high-temperature heat resistance in which sintering of the platinum fine particles is suppressed in an atmosphere of ˜700 ° C. and the addition amount of the platinum is 0.5 to 5 mass% Noble metal catalyst that can act as
Formula (I): Degree of burial (%) = 100 × [1-0.0138 × d VA × D M ]
[However, in formula (I), d VA : diameter of platinum particles calculated by observation using a transmission electron microscope (TEM) (nm), D M : platinum surface exposure rate calculated by CO adsorption method (%) ]
［２］ 前記［１］に記載の貴金属触媒を得る貴金属触媒の製造方法であって、シュウ酸、マロン酸のいずれか１種であるジカルボン酸系キレート剤で錯体化し、保護された塩化白金酸を、ベーマイトゾルの水溶液に投入することによりゲル化物を作製し、次いで前記ゲル化物を凍結乾燥することにより、白金の添加量が０．５〜５質量％の高温耐熱性を有するアルミナクリオゲルからなる、酸化反応において触媒として作用しうる貴金属触媒を得る貴金属触媒の製造方法。 [2] A method for producing a noble metal catalyst to obtain the noble metal catalyst according to [1], wherein the chloroplatinic acid is complexed with a dicarboxylic acid chelating agent which is one of oxalic acid and malonic acid and protected. Is added to an aqueous solution of boehmite sol, and then the gelled product is freeze-dried to obtain a high temperature heat resistant alumina cryogel having an addition amount of platinum of 0.5 to 5% by mass. A process for producing a noble metal catalyst that obtains a noble metal catalyst that can act as a catalyst in an oxidation reaction .
［３］ ゲル化物が、アルミナを生成する金属アルコキシドから作製される前記［２］に記載の貴金属触媒の製造方法。 [ 3 ] The method for producing a noble metal catalyst according to [2 ] , wherein the gelled product is produced from a metal alkoxide that generates alumina.
［４］ 前記［１］に記載の貴金属触媒を得る貴金属触媒の製造方法であって、白金アセチルアセトナート、ジニトロジアミン白金、テトラアンミン白金硝酸、ヘキサアンミン白金クロライド、ヘキサヒドロキソ白金エタノールアミンから選択された少なくとも１種以上である白金錯体をベーマイトゾルの水溶液に投入することによりゲル化物を作製し、次いで前記ゲル化物を凍結乾燥することにより、白金の添加量が０．５〜５質量％の高温耐熱性を有するアルミナクリオゲルからなる、酸化反応において触媒として作用しうる貴金属触媒を得る貴金属触媒の製造方法。 [ 4 ] A method for producing a noble metal catalyst for obtaining the noble metal catalyst according to [1], wherein the noble metal catalyst is selected from platinum acetylacetonate, dinitrodiamine platinum, tetraammineplatinum nitrate, hexaammineplatinum chloride, and hexahydroxoplatinumethanolamine. A gelled product is prepared by putting at least one platinum complex into an aqueous boehmite sol solution, and then the gelled product is freeze-dried, whereby the amount of platinum added is 0.5 to 5% by mass at high temperature and heat resistance. A noble metal catalyst production method for obtaining a noble metal catalyst that can act as a catalyst in an oxidation reaction, comprising an alumina cryogel having a property .
［５］ ゲル化物が、アルミナを生成する金属アルコキシドから作製される前記［４］に記載の貴金属触媒の製造方法。 [ 5 ] The method for producing a noble metal catalyst according to [ 4] , wherein the gelled product is prepared from a metal alkoxide that generates alumina.
本発明の貴金属触媒及びその製造方法は、高表面積、高気孔率及び高耐熱性を有するとともに、５００〜７００℃の雰囲気下で白金微粒子のシンタリングが抑制される貴金属触媒、及びその貴金属触媒を安全且つ低コストで製造することができる。 The noble metal catalyst and the method for producing the same according to the present invention include a noble metal catalyst that has high surface area, high porosity, and high heat resistance, and that suppresses sintering of platinum fine particles in an atmosphere of 500 to 700 ° C., and the noble metal catalyst. It can be manufactured safely and at low cost.
以下、本発明の貴金属触媒及びその製造方法について詳細に説明するが、本発明は、これに限定されて解釈されるものではなく、本発明の範囲を逸脱しない限りにおいて、当業者の知識に基づいて、種々の変更、修正、改良を加え得るものである。 Hereinafter, the noble metal catalyst of the present invention and the method for producing the same will be described in detail. However, the present invention is not construed as being limited thereto, and is based on the knowledge of those skilled in the art without departing from the scope of the present invention. Various changes, modifications, and improvements can be added.
本発明に係る貴金属触媒は、白金微粒子のゲル中への埋没度が４５〜６０％（より好ましくは、５０〜５５％であり、且つ５００〜７００℃（より好ましくは、６００〜７００℃）の雰囲気下で白金微粒子のシンタリングが抑制されるとともに、高温耐熱性を有するものである。尚、本発明の貴金属触媒は、特に限定されないが、キセロゲル又はクリオゲルであることが好ましい。 The precious metal catalyst according to the present invention has an embedded degree of platinum fine particles in the gel of 45 to 60% (more preferably 50 to 55% and 500 to 700 ° C (more preferably 600 to 700 ° C)). The sintering of the platinum fine particles is suppressed under the atmosphere and the heat resistance is high, and the noble metal catalyst of the present invention is not particularly limited, but is preferably xerogel or cryogel.
ここで、本発明の貴金属触媒の製造方法（１）は、ジカルボン酸系キレート剤で錯体化し、保護された塩化白金酸の水溶液を、べーマイトゾルの水溶液に投入することによりゲル化物を作製して貴金属触媒を得るものである。 Here, the manufacturing method (1) of the noble metal catalyst of the present invention is a method of preparing a gelled product by introducing an aqueous solution of chloroplatinic acid, which is complexed with a dicarboxylic acid chelating agent, into a boehmite sol aqueous solution. A noble metal catalyst is obtained.
これにより、本発明の貴金属触媒の製造方法（１）は、ジカルボン酸系のキレート剤で合成した白金錯体を用いて、水溶液中でゲル化物を作製することができるため、従来の方法と比較して、安価で安全且つ短時間でゲル化物を作製することができるとともに、水溶液中にて製造しているため、通常乾燥の他に、作製されたゲルをそのまま凍結乾燥することもでき、溶媒置換等によるゲルの構造破壊やゲルからの白金金属イオンの流出を防止す
ることができる。
Thereby, since the manufacturing method (1) of the noble metal catalyst of this invention can produce a gelled material in aqueous solution using the platinum complex synthesize | combined with the dicarboxylic acid type chelating agent, compared with the conventional method. In addition to being able to produce a gelled product at a low cost, safely and in a short time, since it is produced in an aqueous solution, the gel produced can be freeze-dried as it is in addition to normal drying, and solvent replacement It is possible to prevent the gel structure from being broken and the platinum metal ions from flowing out of the gel.
また、本発明の貴金属触媒の製造方法（１）は、例えば、排ガス浄化触媒に用途が想定される０．５質量％前後の低濃度白金触媒から、液相有機合成用触媒に用途が想定される５質量％前後の高濃度白金触媒までの幅広い濃度領域において、白金ナノ粒子が担体上に高分散されたアルミナ担持白金触媒を得ることができるとともに、高温下（例えば、５００〜７００℃）においても白金の粒子成長が起きないため、長寿命であり、且つ白金表面露出度も比較的大きいため、触媒活性に優れたアルミナ担持白金触媒を得ることができる。 In addition, the production method (1) of the noble metal catalyst of the present invention is expected to be used for a liquid phase organic synthesis catalyst from, for example, a low concentration platinum catalyst of about 0.5% by mass which is supposed to be used for an exhaust gas purification catalyst. In a wide concentration range up to a high concentration platinum catalyst of about 5% by mass, an alumina-supported platinum catalyst in which platinum nanoparticles are highly dispersed on a support can be obtained, and at a high temperature (for example, 500 to 700 ° C.). In addition, since platinum particle growth does not occur, it has a long life and the platinum surface exposure is relatively large, so that an alumina-supported platinum catalyst having excellent catalytic activity can be obtained.
尚、本発明の貴金属触媒の製造方法（１）で用いるジカルボン酸系キレート剤は、特に限定されないが、例えば、シュウ酸、マロン酸のいずれか１種であることが好ましい。これは、２つのカルボキシル基が白金イオンと強く相互作用して安定したキレートを生成するからである。 The dicarboxylic acid chelating agent used in the production method (1) of the noble metal catalyst of the present invention is not particularly limited, but is preferably any one of oxalic acid and malonic acid. This is because two carboxyl groups interact strongly with platinum ions to produce a stable chelate.
次に、本発明の貴金属触媒の製造方法（２）は、白金錯体をべーマイトゾルの水溶液に投入することによりゲル化物を作製して貴金属触媒を得るものである。 Next, in the method (2) for producing a noble metal catalyst of the present invention, a platinum complex is introduced into an aqueous solution of a boehmite sol to produce a gelled product to obtain a noble metal catalyst.
このとき、本発明の貴金属触媒の製造方法（２）で用いる白金錯体は、白金アセチルアセトナート、ジニトロジアミン白金、テトラアンミン白金硝酸、へキサアンミン白金クロライド、ヘキサヒドロキソ白金エタノールアミンから選択された少なくとも１種以上を好適に用いることができる。これは、白金が有機物配位子等により保護されているため、アルコールを少量含むベーマイトゾル水溶液に投入しても白金黒を析出しないからである。 At this time, the platinum complex used in the method (2) for producing the noble metal catalyst of the present invention is at least one selected from platinum acetylacetonate, dinitrodiamine platinum, tetraammineplatinum nitrate, hexammineplatinum chloride, and hexahydroxoplatinumethanolamine. The above can be used suitably. This is because platinum is protected by an organic ligand or the like, so that platinum black does not precipitate even when it is added to a boehmite sol aqueous solution containing a small amount of alcohol.
本発明で貴金属触媒の製造方法（１）及び（２）では、ゲル化物がアルミナを生成する金属アルコキシドから作製されることが好ましい。尚、前記金属アルコキシドは、特に限定されないが、ＡＳＢ（Ａｌ（ｓｅｃ−ＢｕＯ）３）であることが、液体であるため、水への投入の際の取扱いやすさの観点から好ましい。 In the production methods (1) and (2) of the noble metal catalyst in the present invention, the gelled product is preferably produced from a metal alkoxide that forms alumina. In addition, although the said metal alkoxide is not specifically limited, Since it is a liquid, it is preferable from a viewpoint of the handleability at the time of throwing into water, because it is ASB (Al (sec-BuO) 3 ).
また、本発明の貴金属触媒の製造方法（１）及び（２）では、白金の添加量が０．５〜５質量％（より好ましくは、０．５〜３質量％）である。これは、白金量が多いと耐熱性がより低下しやすいからである。 Moreover, in the manufacturing methods (1) and (2) of the noble metal catalyst of the present invention, the amount of platinum added is 0.5 to 5% by mass (more preferably 0.5 to 3% by mass). This is because the heat resistance is more likely to decrease when the amount of platinum is large.
尚、本発明の貴金属触媒の製造方法（１）及び（２）では、ゲル化物を乾燥して乾燥ゲルを得るが、通常乾燥の他に、ゲル化物を凍結乾燥することがより好ましい。凍結乾燥では、トラップ部冷却温度が−８０℃以下、且つ真空度が１０Ｐａ以下であることが望ましい。これは、トラップ部冷却温度が−８０℃を超過する場合、湿潤ゲルの凍結乾燥が不完全となり、乾燥収縮による微構造の破壊が発生するためである。また、真空度は、真空に近ければ近いほど良いが、乾燥完了時の真空度が１０Ｐａを超過すると、凍結乾燥が完了しておらず、乾燥収縮による微構造の破壊が発生してしまう。 In the production methods (1) and (2) of the noble metal catalyst of the present invention, the gelled product is dried to obtain a dry gel. In addition to normal drying, it is more preferable to freeze-dry the gelled product. In freeze-drying, it is desirable that the trap portion cooling temperature is −80 ° C. or lower and the degree of vacuum is 10 Pa or lower. This is because when the trap portion cooling temperature exceeds −80 ° C., freeze-drying of the wet gel becomes incomplete, and the microstructure is destroyed due to drying shrinkage. Further, the vacuum degree is better as it is closer to the vacuum. However, when the degree of vacuum at the time of completion of drying exceeds 10 Pa, freeze-drying is not completed, and the microstructure is destroyed due to drying shrinkage.
更に詳細には、上記凍結乾燥は、初めに、ゲル化物（ウエットゲル）を、−８０℃以下で冷却し、ゲル化物（ウエットゲル）の凍結を確認した後、真空に引き、トラップ部冷却温度を−８０℃以下にて、１〜３日程度保持することが好ましい。このとき、上記保持時間は、対象となるゲル化物（ウエットゲル）の大きさ、密度や形状によって様々であるが、少なくとも真空度が１０Ｐａ以下になる保持時間が望ましい。また、ゲル化物（ウエットゲル）の初期冷却には、フリーザーを用いてもよいが、ドライアイス−エタノールや液体窒素等の冷媒で、できるだけ瞬間冷却する方が、凍結時間の短縮及びゲル化物（ウエットゲル）の凍結時における構造破壊を抑制することができるため好ましい。 More specifically, in the lyophilization, first, the gelled product (wet gel) is cooled at −80 ° C. or lower, and after the gelled product (wet gel) is confirmed to be frozen, it is evacuated to cool the trap portion cooling temperature. Is preferably maintained at -80 ° C or lower for about 1 to 3 days. At this time, the holding time varies depending on the size, density, and shape of the target gelled product (wet gel), but at least the holding time at which the degree of vacuum is 10 Pa or less is desirable. In addition, a freezer may be used for the initial cooling of the gelled product (wet gel). However, cooling as quickly as possible with a refrigerant such as dry ice-ethanol or liquid nitrogen shortens the freezing time and reduces the gelled product (wet gel). Gel) is preferable because structural destruction during freezing can be suppressed.
以上のことから、本発明の貴金属触媒の製造方法（１）及び（２）は、超臨界乾燥に代わり凍結乾燥を採用することにより、エアロゲルの優れた特性である高表面積、高気孔率及び高耐熱性を有するだけでなく、耐液体性であり、且つ液体との接触でエアロゲルのように構造破壊を起こさない多孔質構造体（クリオゲル）を得ることができる。 From the above, the production method (1) and (2) of the noble metal catalyst of the present invention employs freeze-drying instead of supercritical drying, thereby providing high surface area, high porosity and high airgel excellent characteristics. It is possible to obtain a porous structure (cryogel) that not only has heat resistance but also liquid resistance and does not cause structural breakdown like aerogel when in contact with liquid.
また、上記凍結乾燥は、臨界点以上の高温・高圧を必要としないため、即ち、低温・低圧下での乾燥方法であるため、安全性に優れているとともに、超臨界乾燥よりも省エネであり、且つウエットゲルの液相中の水をアルコールで置換することなくそのまま乾燥（凍結乾燥）することができるため、工程や設備の簡略化が可能であるため、コストを大幅に削減することができる。 In addition, the above freeze-drying does not require high temperature and high pressure above the critical point, that is, it is a drying method under low temperature and low pressure, so it is excellent in safety and energy saving than supercritical drying. In addition, since water in the liquid phase of the wet gel can be directly dried (freeze-dried) without substituting with alcohol, the process and equipment can be simplified, and the cost can be greatly reduced. .
次に、本発明の貴金属触媒の製造方法（１）の一例として、主組成がアルミナ（Ａｌ２Ｏ３）で構成され、且つ白金（Ｐｔ）が分散された貴金属触媒（Ｐｔ／Ａｌ２Ｏ３クリオゲル）について説明する。上記Ｐｔ／Ａｌ２Ｏ３クリオゲルの製造方法は、大まかな工程として、（１）ゾル化工程、（２）白金錯体化工程、（３）ゲル化工程、（４）乾燥工程から構成される。 Next, as an example of the method (1) for producing a noble metal catalyst of the present invention, a noble metal catalyst (Pt / Al 2 O 3 ) in which the main composition is composed of alumina (Al 2 O 3 ) and platinum (Pt) is dispersed. (Cryogel) will be explained. The manufacturing method of the Pt / Al 2 O 3 cryogel is composed of (1) a sol process, (2) a platinum complex process, (3) a gel process, and (4) a drying process as rough processes.
（１）ゾル化工程
ゾル化工程は、アルミナ源であるＡＳＢ（Ａｌ（ｓｅｃ−ＢｕＯ）３）又はＡＩＰ（Ａｌ（ｉｓｏ−ＰｒＯ）３）を溶媒である水に投入し、アルコキシド加水分解後、ＨＮＯ３溶液（硝酸）を加えて、所定時間保持することにより、ゾルを邂逅、透明なベーマイトゾル（ＡｌＯＯＨ）を作製する。
(1) Solation step In the solation step, ASB (Al (sec-BuO) 3 ) or AIP (Al (iso-PrO) 3 ), which is an alumina source, is added to water as a solvent, and after alkoxide hydrolysis, An HNO 3 solution (nitric acid) is added and held for a predetermined time, so that the sol is poured to produce a transparent boehmite sol (AlOOH).
（２）白金錯体化工程
白金錯体化工程は、ジカルボン酸系キレート剤を含む水溶液に、アンモニア水溶液を加えた溶液を調整後、白金酸（ＨＣＰＡ：ヘキサクロロ白金酸六水和物［Ｈ２（ＰｔＣｌ６）・６Ｈ２Ｏ］）から構成された白金ソースを投入し、沈殿物を生成させ、これを所定の温度で加熱・攪拌することにより、沈殿物が溶けて、均一な白金錯体溶液（白金ソース）を作製する。
(2) Platinum complexation step The platinum complexation step is a platinum acid (HCPA: hexachloroplatinic acid hexahydrate [H 2 (PtCl) after adjusting a solution obtained by adding an aqueous ammonia solution to an aqueous solution containing a dicarboxylic acid chelating agent. 6 ) · 6H 2 O]) is added to form a precipitate, which is heated and stirred at a predetermined temperature to dissolve the precipitate and form a uniform platinum complex solution (platinum). Source).
（３）ゲル化工程
ゲル化工程は、（２）で得られた白金ソースを投入後、尿素を加えて、所定時間保持した後、更に所定温度で所定時間保持することにより、ＨＣＰＡ／ベーマイトゲル（ＡｌＯＯＨ）を作製する。
(3) Gelation step In the gelation step, after adding the platinum source obtained in (2), after adding urea and holding it for a predetermined time, it is further held at a predetermined temperature for a predetermined time, whereby an HCPA / boehmite gel (AlOOH) is prepared.
（４）乾燥工程
乾燥工程は、通常乾燥によるキセロゲルを得る方法と、凍結乾燥によりクリオゲルを得る方法、とがある。後者は、ゲル化工程で得られたＨＣＰＡ／ベーマイトゲル（ＡｌＯＯＨ）を、−８０℃以下で凍結し、凍結確認後、更にトラップ部冷却温度−８０℃以下の真空下で所定時間保持し、凍結乾燥する。ゲル化過程で形成した微細なネットワークを維持するために、従来法では、超臨界流体を用いた乾燥が行われてきたが、本発明では、凍結乾燥法を用いることにより、表面張力をキャンセルさせ、微細なネットワークを維持したままで乾燥ゲル（クリオゲル）を得ることができる。
(4) Drying process The drying process includes a method of obtaining xerogel by normal drying and a method of obtaining cryogel by freeze drying. In the latter case, the HCPA / boehmite gel (AlOOH) obtained in the gelation step is frozen at −80 ° C. or lower, and after freezing is confirmed, the trap portion is cooled at a cooling temperature of −80 ° C. or lower for a predetermined time. dry. In order to maintain the fine network formed in the gelation process, drying using a supercritical fluid has been performed in the conventional method, but in the present invention, surface tension is canceled by using the freeze drying method. A dry gel (cryogel) can be obtained while maintaining a fine network.
本発明を実施例に基づいて、更に詳細に説明するが、本発明はこれらの実施例に限られるものではない。 The present invention will be described in more detail based on examples, but the present invention is not limited to these examples.
（評価方法） (Evaluation method)
（１）ＣＨ４酸化能評価（酸化触媒能評価）
Ａｒ及びＯ２を７９：２０（疑似大気組成）で混合し、それにＣＨ４を１％（ｖ／ｖ）含むガスを作成した。これを触媒に通じ、各温度でメタン酸化触媒活性を測定した。測定温度は、４００〜６００℃の範囲で、５０℃刻みとした。各温度で２５分流通させた後、サンプリングした。尚、触媒は、大気雰囲気下７００℃で焼成後、Ｈ２雰囲気下５００℃で還元処理したサンプル０．１ｇを、石英砂（和光純薬）と混合・希釈して合計約１ｇとし、それを石英反応管（φ４ｍｍ）に充填して用いた。評価は、ＦＩＤ（水素炎イオン検出器）及びＴＣＤ（熱伝導度検出器）ガスクロマトグラフで行った。ＦＩＤの結果から、ＣＨ４→ＣＯ２の変換効率を算出した。ＴＣＤは、検出感度が低いため、発生したガス組成の確認（ＣＨ４、ＣＯ２）と、変換効率算出のバックアップを目的として使用した。
(1) CH 4 oxidation ability evaluation (oxidation catalytic ability evaluation)
Ar and O 2 were mixed at 79:20 (pseudo atmospheric composition), and a gas containing 1% (v / v) CH 4 was produced. This was passed through the catalyst, and the methane oxidation catalytic activity was measured at each temperature. The measurement temperature was in the range of 400 to 600 ° C. and in increments of 50 ° C. The sample was sampled after 25 minutes at each temperature. In addition, the catalyst was mixed and diluted with quartz sand (Wako Pure Chemical Industries, Ltd.) 0.1 g of a sample calcined at 700 ° C. in an air atmosphere and then reduced at 500 ° C. in an H 2 atmosphere to make a total of about 1 g. A quartz reaction tube (φ4 mm) was filled and used. The evaluation was performed using a FID (hydrogen flame ion detector) and a TCD (thermal conductivity detector) gas chromatograph. From the FID result, the conversion efficiency of CH 4 → CO 2 was calculated. Since TCD has low detection sensitivity, it was used for the purpose of confirming the generated gas composition (CH 4 , CO 2 ) and for backup of conversion efficiency calculation.
（２）ＣＯ吸着法による金属露出度評価
ＴＣＤガスクロマトグラフを用いて評価を行った。サンプル０．１ｇを石英反応管（φ４ｍｍ）に充填し、ＨｅをキャリアとしてＣＯ（０．５ｍｌ）を５分毎に６回パルス導入し、ＣＯの総吸着量を算出した。尚、サンプルは、一度、ペレット化（φ２０ｍｍ、２０ＭＰａ／２ｍｉｎ保持）した後、粉砕・分級し、３００〜６００μｍに調整したものである。ＣＯ１分子は、金属白金１原子に吸着する特性があるため、ＣＯの総吸着量からサンプル表面に存在する金属白金の量を算出することができる。また、サンプルに含まれる白金量も組成から算出することができる。これらから、サンプル（触媒）に含まれる金属白金原子の内、表面に露出している金属白金の割合（露出度［％］）を算出した。
(2) Metal exposure evaluation by CO adsorption method It evaluated using the TCD gas chromatograph. A 0.1 g sample was filled into a quartz reaction tube (φ4 mm), CO (0.5 ml) was pulsed 6 times every 5 minutes using He as a carrier, and the total amount of CO adsorbed was calculated. The sample is once pelletized (held at 20 mm, 20 MPa / 2 min), pulverized and classified, and adjusted to 300 to 600 μm. Since the CO1 molecule has the property of adsorbing to one metal platinum atom, the amount of metal platinum present on the sample surface can be calculated from the total CO adsorption amount. The amount of platinum contained in the sample can also be calculated from the composition. From these, the ratio (exposure [%]) of metal platinum exposed on the surface among the metal platinum atoms contained in the sample (catalyst) was calculated.
（３）白金微粒子の担体中への埋没度の評価
下式を用いて、それぞれのサンプルにおける白金微粒子の担体中への埋没度を算出することにより、評価を行った。尚、下式は、「担体上に全金属粒子が球状で存在する」という仮定のもとに、担持金属触媒の金属粒子径を金属の表面露出率から求める際に使用される。
(3) Evaluation of degree of burying of platinum fine particles in carrier Using the following formula, evaluation was performed by calculating the degree of burying of platinum fine particles in the carrier in each sample. The following equation is used when the metal particle diameter of the supported metal catalyst is obtained from the metal surface exposure rate under the assumption that “all metal particles are present in a spherical shape on the support”.
ｄＶＡ＝αΣＶｉ／ΣＡｉ＝６（Ｍｗ／ρＮ０）（１／ａＭ）（１／ＤＭ）
（ここで、Ｖｉ：ｉ番目の金属粒子の体積、Ａｉ：ｉ番目の金属粒子の表面積、α：幾何学定数（球面粒子を仮定する場合は、６）、ｄＶＡ：平均直径、Ｍｗ：原子量、ρ：密度、Ｎ０：アボガトロ定数、ａＭ：表面１原子が占める有効面積、ＤＭ：表面露出率である。）
d VA = αΣV i / ΣA i = 6 (M w / ρN 0) (1 / a M) (1 / D M)
(Where V i is the volume of the i-th metal particle, A i is the surface area of the i-th metal particle, α is a geometric constant (6 if spherical particles are assumed), d VA is the average diameter, M w : atomic weight, ρ: density, N 0 : avocato constant, a M : effective area occupied by one surface atom, D M : surface exposure rate.)
（実施例）
アルミニウムトリブトキシド（Ａｌ（ｓｅｃ−ＢｕＯ）３）０．０２８６ｍｏｌを８６℃の水２０ｍＬに投入して加水分解した後、１Ｎ硝酸３〜４ｍｌを加えてゾルを邂逅、透明なベーマイトゾルを得る。一方で、０．０６８９Ｍのシュウ酸水溶液０．６ｍｌに２０質量％のアンモニア水溶液０．１ｍｌを加えた溶液を調製し、これに１．９９４質量％の塩化白金酸水溶液０．３６〜１．８ｇ投入すると沈殿物が生成、これを８６℃にて加熱攪拌すると沈殿物が解けて薄いレモンイエロー色の均一な溶液となる。これをベーマイトゾル溶液に加え、その後尿素を０．２ｇ添加、同温度にて一晩放置すると均一の黄色いベーマイトゲルが得られる。この湿潤ゲルを液体窒素で急速冷凍し、トラップ温度−８０℃、真空度１０Ｐａ以下の条件下で凍結乾燥を行い、白金−ベーマイト系クリオゲルをそれぞれ得た。尚、白金含有量は、それぞれ０．５、１．０、２．５、５．０質量％であった。それぞれ得られた白金−ベーマイト系クリオゲルを、５００℃又は７００℃の空気中で仮焼してＰｔ／Ａｌ２Ｏ３クリオゲル触媒を得た。それぞれのＰｔ／Ａｌ２Ｏ３クリオゲル触媒の仮焼温度５００℃における白金表面露出度（％）を図１に、それぞれのＰｔ／Ａｌ２Ｏ３クリオゲル触媒の仮焼温度７００℃における白金表面露出度（％）を図２に示す。
(Example)
0.0286 mol of aluminum tributoxide (Al (sec-BuO) 3 ) is added to 20 mL of water at 86 ° C. to hydrolyze, and then 3 to 4 mL of 1N nitric acid is added to dissolve the sol to obtain a transparent boehmite sol. On the other hand, a solution was prepared by adding 0.1 ml of a 20% by mass aqueous ammonia solution to 0.6 ml of a 0.0689M oxalic acid aqueous solution, and 0.36 to 1.8 g of a 1.994% by mass aqueous chloroplatinic acid solution was added thereto. When added, a precipitate is formed, and when this is heated and stirred at 86 ° C., the precipitate dissolves and becomes a thin lemon yellow uniform solution. When this is added to the boehmite sol solution and then 0.2 g of urea is added and left overnight at the same temperature, a uniform yellow boehmite gel is obtained. This wet gel was rapidly frozen with liquid nitrogen and freeze-dried under conditions of a trap temperature of −80 ° C. and a vacuum of 10 Pa or less to obtain platinum-boehmite cryogels, respectively. In addition, platinum content was 0.5, 1.0, 2.5, and 5.0 mass%, respectively. Each obtained platinum-boehmite cryogel was calcined in air at 500 ° C. or 700 ° C. to obtain a Pt / Al 2 O 3 cryogel catalyst. The platinum surface exposure (%) of each Pt / Al 2 O 3 cryogel catalyst at a calcining temperature of 500 ° C. is shown in FIG. 1, and the platinum surface exposure of each Pt / Al 2 O 3 cryogel catalyst at a calcining temperature of 700 ° C. is shown in FIG. (%) Is shown in FIG.
（比較例）
市販アルミナ（大明化学工業製：ＴＭ−３００Ｄ）を担体として、通常の含浸法により白金が０．５、１、２．５、５質量％担持された白金−アルミナ触媒をそれぞれ作製し、５００℃又は７００℃の空気中で仮焼した。それぞれの白金−アルミナ触媒の仮焼温度５００℃における白金表面露出度（％）を図１に、それぞれの白金−アルミナ触媒の仮焼温度７００℃における白金表面露出度（％）を図２に示す。
(Comparative example)
Platinum-alumina catalysts on which platinum is supported by 0.5, 1, 2.5, and 5% by mass are prepared by a conventional impregnation method using commercially available alumina (manufactured by Daimei Chemical Co., Ltd .: TM-300D) at 500 ° C. Or it calcined in the air of 700 degreeC. The platinum surface exposure (%) of each platinum-alumina catalyst at a calcining temperature of 500 ° C. is shown in FIG. 1, and the platinum surface exposure (%) of each platinum-alumina catalyst at a calcining temperature of 700 ° C. is shown in FIG. .
図１及び図２に示すように、実施例（Ｐｔ／Ａｌ２Ｏ３クリオゲル触媒）では、白金表面露出度（％）が３０〜４０％とほぼ一定であった。一方、比較例（白金−アルミナ触媒）では、白金濃度の増加とともに、白金表面露出度（％）が低下することが認められ、また７００℃で仮焼すると、５００℃での仮焼時と比較して、白金表面露出度（％）がかなり低下することを確認した。 As shown in FIGS. 1 and 2, in Example (Pt / Al 2 O 3 cryogel catalyst), platinum surface exposure value (%) was almost constant 30 to 40%. On the other hand, in the comparative example (platinum-alumina catalyst), it is recognized that the platinum surface exposure (%) decreases as the platinum concentration increases, and when calcined at 700 ° C, it is compared with that at 500 ° C. Then, it was confirmed that the platinum surface exposure (%) was considerably lowered.
また、ＴＥＭ観察によると、実施例（Ｐｔ／Ａｌ２Ｏ３クリオゲル触媒）では、白金濃度、仮焼温度によらず、約１ｎｍの白金微粒子が高分散で観察された。一方、比較例（白金−アルミナ触媒）では、白金濃度０．５質量％の白金−アルミナ触媒を５００℃で仮焼した時のみ、約１ｎｍの白金微粒子が観察されたが、その他の条件下では、２０〜１００ｎｍのシンタリングした大きな白金粒子が観測された。以上の結果から、実施例（Ｐｔ／Ａｌ２Ｏ３クリオゲル触媒）における白金の耐熱性が確認された。 According to TEM observation, in the example (Pt / Al 2 O 3 cryogel catalyst), platinum fine particles of about 1 nm were observed with high dispersion regardless of the platinum concentration and the calcining temperature. On the other hand, in the comparative example (platinum-alumina catalyst), platinum fine particles of about 1 nm were observed only when a platinum-alumina catalyst having a platinum concentration of 0.5% by mass was calcined at 500 ° C. Large platinum particles with 20-100 nm sintering were observed. From the above results, the heat resistance of platinum in the examples (Pt / Al 2 O 3 cryogel catalyst) was confirmed.
次に、Ｐｔ／Ａｌ２Ｏ３クリオゲル触媒の白金粒子径を約１ｎｍ、白金表面露出度（％）を約３０〜４０％として、アルミナゲル中に埋没された白金粒子の割合、即ち埋没度（「白金微粒子の担体中への埋没度の評価」参照）を算出した。このとき、Ｐｔ／Ａｌ２Ｏ３クリオゲル触媒の白金粒子径を約１ｎｍとした時、計算上の白金表面露出率は、７２．５％であった。一方、実施例で測定された白金表面露出率は、３０〜４０％であった。よって、アルミナクリオゲル担体表面に白金粒子が存在する割合は、１００×（３０〜４０）／７２．５＝４１．４〜５５．２％と算出され、従って、ゲル中に埋没された白金粒子の割合（埋没度）は、１００−（４１．４〜５５．２）＝４４．８〜５８．６％となった。以上のことから、Ｐｔ／Ａｌ２Ｏ３クリオゲル触媒は、白金ナノ粒子の約５０％前後がアルミナゲル中に埋没されているという結果となり、このように、白金粒子が適度にゲル中に埋め込まれていることが、Ｐｔ／Ａｌ２Ｏ３クリオゲル触媒の高温耐熱性を高めた要因であると考えられた。 Next, assuming that the platinum particle diameter of the Pt / Al 2 O 3 cryogel catalyst is about 1 nm and the platinum surface exposure (%) is about 30 to 40%, the ratio of platinum particles embedded in the alumina gel, that is, the degree of burying ( “Refer to“ Evaluation of degree of embedment of platinum fine particles in carrier ”) At this time, when the platinum particle diameter of the Pt / Al 2 O 3 cryogel catalyst was about 1 nm, the calculated platinum surface exposure rate was 72.5%. On the other hand, the platinum surface exposure rate measured in the Examples was 30 to 40%. Therefore, the ratio of the platinum particles existing on the surface of the alumina cryogel carrier is calculated as 100 × (30-40) /72.5=41.4-55.2%, and thus the platinum particles embedded in the gel. The ratio (the degree of burial) was 100− (41.4 to 55.2) = 44.8 to 58.6%. From the above, the Pt / Al 2 O 3 cryogel catalyst has a result that about 50% of the platinum nanoparticles are embedded in the alumina gel, and thus the platinum particles are appropriately embedded in the gel. This was considered to be a factor that increased the high temperature heat resistance of the Pt / Al 2 O 3 cryogel catalyst.
一方、比較のために、白金が０．５質量％担持された白金−アルミナ触媒を５００℃で仮焼したときの埋没度を上記と同様に算出した。その結果、白金表面露出率が５３．１％、観察された白金粒子が１ｎｍであることから、埋没度は２６．８％と計算された。これは、Ｐｔ／Ａｌ２Ｏ３クリオゲル触媒の埋没度と比較してかなり小さく、白金が含浸法で担持された白金−アルミナ触媒（比較例）の場合、白金粒子のほとんどがアルミナ担体表面に存在しているため、Ｐｔ／Ａｌ２Ｏ３クリオゲル触媒（実施例）と比較して、高温耐熱性が劣る原因であると考えられた。 On the other hand, for comparison, the degree of burial when a platinum-alumina catalyst carrying 0.5% by mass of platinum was calcined at 500 ° C. was calculated in the same manner as described above. As a result, since the platinum surface exposure rate was 53.1% and the observed platinum particles were 1 nm, the degree of burial was calculated to be 26.8%. This is considerably smaller than the degree of burying of the Pt / Al 2 O 3 cryogel catalyst, and in the case of a platinum-alumina catalyst (comparative example) in which platinum is supported by the impregnation method, most of the platinum particles are present on the surface of the alumina support. Therefore, it was considered that the high temperature heat resistance was inferior to that of the Pt / Al 2 O 3 cryogel catalyst (Example).
(実施例１及び実施例２)
アルミニウムトリブトキシド（Ａｌ（ｓｅｃ−ＢｕＯ）３）０．０２８６ｍｏｌを８６℃の水２０ｍＬに投入して加水分解した後、１Ｎ硝酸３〜４ｍｌを加えてゾルを邂逅、透明なベーマイトゾルを得た。一方で、０．０６８９Ｍのシュウ酸水溶液０．６ｍｌに２０質量％のアンモニア水溶液０．１ｍｌを加えた溶液を調製し、これに１．９９４質量％の塩化白金酸水溶液０．３６ｇ投入すると沈殿物が生成、これを８６℃にて加熱攪拌すると沈殿物が解けて薄いレモンイエロー色の均一な溶液となる。これをベーマイトゾル溶液に加え、その後尿素を０．２ｇ添加、同温度にて一晩放置すると均一の黄色いベーマイトゲルが得られる。この湿潤ゲルを液体窒素で急速冷凍し、トラップ温度−８０℃、真空度１０Ｐａ以下の条件下で凍結乾燥を行い、乾燥ゲル（クリオゲル触媒）を得た（実施例１）
。尚、白金含有量は、０．５質量％であった。実施例１の作製過程において、凍結乾燥を施さない乾燥方法（ロータリーエバポレーターを用いた減圧下での乾燥。到達真空度：約１３〜１５ｍｍＨｇ、乾燥時間：約１時間）による乾燥ゲル（キセロゲル触媒）も作製した（実施例２）。白金含有量は、０．５質量％であった。
(Example 1 and Example 2)
After 0.0286 mol of aluminum tributoxide (Al (sec-BuO) 3 ) was added to 20 mL of water at 86 ° C. for hydrolysis, 3-4 mL of 1N nitric acid was added to dissolve the sol to obtain a transparent boehmite sol. On the other hand, a solution is prepared by adding 0.1 ml of a 20% by mass aqueous ammonia solution to 0.6 ml of a 0.0689M oxalic acid aqueous solution, and 0.36 g of a 1.994% by mass aqueous chloroplatinic acid solution is added thereto. When this is heated and stirred at 86 ° C., the precipitate dissolves and becomes a thin lemon-yellow uniform solution. When this is added to the boehmite sol solution and then 0.2 g of urea is added and left overnight at the same temperature, a uniform yellow boehmite gel is obtained. This wet gel was rapidly frozen with liquid nitrogen and freeze-dried under conditions of a trap temperature of −80 ° C. and a vacuum of 10 Pa or less to obtain a dry gel (cryogel catalyst) (Example 1).
. In addition, platinum content was 0.5 mass%. In the production process of Example 1, a dry gel (xerogel catalyst) obtained by a drying method (drying under reduced pressure using a rotary evaporator. Ultimate vacuum: about 13 to 15 mmHg, drying time: about 1 hour) without applying freeze-drying (Example 2). The platinum content was 0.5% by mass.
（比較例１及び比較例２）
アルミナクリオゲルを担体として通常の含浸法により、同様の白金−アルミナ触媒を調製した（比較例１）。更に、市販アルミナ（大明化学工業製：ＴＭ−３００Ｄ）を担体として通常の含浸法により、同様の白金−アルミナ触媒を調製した（比較例２）。尚、白金含有量は、それぞれ０．５質量％であった。
(Comparative Example 1 and Comparative Example 2)
A similar platinum-alumina catalyst was prepared by a conventional impregnation method using alumina cryogel as a carrier (Comparative Example 1). Further, a similar platinum-alumina catalyst was prepared by a conventional impregnation method using commercially available alumina (manufactured by Daimei Chemical Co., Ltd .: TM-300D) as a carrier (Comparative Example 2). In addition, platinum content was 0.5 mass%, respectively.
実施例１及び実施例２のサンプルを、５００〜７００℃で仮焼して白金粒子の高温耐熱性をＸＲＤとＴＥＭで調査した。 The samples of Example 1 and Example 2 were calcined at 500 to 700 ° C., and the high temperature heat resistance of the platinum particles was investigated by XRD and TEM.
ＸＲＤ測定の結果、実施例１及び実施例２のサンプルでは、５００〜７００℃の仮焼温度範囲で白金粒子のシンタリングが認められなかった（図３［実施例１］及び図４［実施例２］参照）。また、ＴＥＭによっても白金のシンタリングは観察されなかった。 As a result of XRD measurement, no sintering of platinum particles was observed in the calcining temperature range of 500 to 700 ° C. in the samples of Example 1 and Example 2 (FIG. 3 [Example 1] and FIG. 4 [Example] 2]). Also, platinum sintering was not observed by TEM.
また、それぞれ得られた触媒（実施例１及び実施例２、比較例１及び比較例２）を、７００℃仮焼に引き続き、５００℃で還元処理してから、メタンの酸化反応を行った。その結果を図５に示す。 In addition, the obtained catalysts (Example 1 and Example 2, Comparative Example 1 and Comparative Example 2) were subjected to reduction treatment at 500 ° C. following calcination at 700 ° C., and then an oxidation reaction of methane was performed. The result is shown in FIG.
更に詳細には、触媒約０．１ｇを石英砂と混合して、合計約１ｇとし、常圧固定床流通反応装置の石英リアクター内にセットした。メタン酸化反応は、１％のメタンを含む擬似大気を触媒に導入し、４００〜６００℃の温度範囲で触媒反応を行い、生成物をガスクロマトグラフで分析した。尚、ガス組成は、メタン：酸素：アルゴン＝１：２０：７９で、ガス流速は１００ｍｌ／分であった。 More specifically, about 0.1 g of the catalyst was mixed with quartz sand to make a total of about 1 g, and set in a quartz reactor of an atmospheric pressure fixed bed flow reactor. In the methane oxidation reaction, simulated atmosphere containing 1% methane was introduced into the catalyst, the catalyst reaction was performed in the temperature range of 400 to 600 ° C., and the product was analyzed by gas chromatography. The gas composition was methane: oxygen: argon = 1: 20: 79, and the gas flow rate was 100 ml / min.
その結果、図５に示すように、５５０℃以下の低温領域においては、実施例１（クリオゲル触媒）と実施例２（キセロゲル触媒）、比較例１（含浸法触媒［アルミナクリオゲル担体］）が、比較例２に比べて高い活性を示した。更に詳細には、実施例１が最も高い活性を示し、ついで実施例２と比較例１の活性序列であった。 As a result, as shown in FIG. 5, Example 1 (cryogel catalyst), Example 2 (xerogel catalyst), and Comparative Example 1 (impregnation method catalyst [alumina cryogel support]) were produced in a low temperature region of 550 ° C. or lower. Compared with Comparative Example 2, the activity was high. More specifically, Example 1 showed the highest activity, followed by the activity sequence of Example 2 and Comparative Example 1.
このとき、ＴＥＭ観察によると、比較例２では７００℃仮焼により、白金がシンタリングして２０ｎｍ前後の大きな白金粒子が生成したが、それ以外（実施例１及び実施例２、比較例１）では、７００℃で仮焼しても１ｎｍ前後の白金微粒子が担体上に分散していた。以上のことから、ナノ微粒子白金が、メタン転化反応の低温触媒活性をもたらしたものと考えられた。 At this time, according to the TEM observation, in Comparative Example 2, platinum was sintered by 700 ° C. calcination, and large platinum particles of about 20 nm were formed, but other than that (Example 1 and Example 2, Comparative Example 1). Then, even if calcined at 700 ° C., platinum fine particles of about 1 nm were dispersed on the carrier. From the above, it was considered that nanoparticulate platinum brought about the low-temperature catalytic activity of the methane conversion reaction.
更に、それぞれ得られた触媒（実施例１及び実施例２、比較例１及び比較例２）について、ＣＯ吸着法による金属露出度評価を行った。その結果を図６に示す。 Furthermore, metal exposure evaluation by CO adsorption method was performed about the obtained catalyst (Example 1 and Example 2, Comparative Example 1 and Comparative Example 2), respectively. The result is shown in FIG.
図６に示すように、実施例１及び実施例２のサンプルでは、仮焼温度の上昇に伴っての白金表面露出率の低下がほとんど認められなかった。一方で、比較例１及び比較例２のサンプルでは、仮焼温度の上昇に伴って、表面露出度が急激に低下した。 As shown in FIG. 6, in the samples of Example 1 and Example 2, there was hardly any decrease in the platinum surface exposure rate as the calcining temperature increased. On the other hand, in the samples of Comparative Example 1 and Comparative Example 2, the degree of surface exposure sharply decreased as the calcining temperature increased.
(実施例３及び実施例４)
アルミニウムトリブトキシド（Ａｌ（ｓｅｃ−ＢｕＯ）３）０．０２８６ｍｏｌを８６℃の水２０ｍＬに投入して加水分解した後、１Ｎ硝酸６〜８ｍｌを加えてゾルを邂逅、透明なベーマイトゾルを得た。一方で、０．０６８９Ｍのシュウ酸水溶液０．６ｍｌに２０
質量％のアンモニア水溶液０．２ｍｌを加えた溶液を調製し、これに１．９９４質量％の塩化白金酸水溶液１．８ｇ投入すると沈殿物が生成、これを８６℃の水浴で溶解して薄黄色の溶液を得た。これを上記ベーマイトゾル溶液に加え、更に尿素を０．２ｇ加えると、白金黒析出のない均一分散された黄色いベーマイトゲルが得られた。この湿潤ゲルを液体窒素で急速冷凍し、トラップ温度−８０℃、真空度１０Ｐａ以下の条件下で凍結乾燥を行い、乾燥ゲル（クリオゲル触媒）を得た（実施例３）。尚、白金含有量は、５質量％であった。実施例３の作製過程において、凍結乾燥を施さない乾燥方法（ロータリーエバポレーターを用いた減圧下での乾燥。到達真空度：約１３〜１５ｍｍＨｇ、乾燥時間：約１時間）による乾燥ゲル（キセロゲル触媒）も作製した（実施例４）。白金含有量は、５質量％であった。
(Example 3 and Example 4)
After 0.0286 mol of aluminum tributoxide (Al (sec-BuO) 3 ) was added to 20 mL of water at 86 ° C. for hydrolysis, 6-8 mL of 1N nitric acid was added to dissolve the sol, thereby obtaining a transparent boehmite sol. On the other hand, 20 ml was added to 0.6 ml of 0.0689M oxalic acid aqueous solution.
A solution was prepared by adding 0.2 ml of a mass% ammonia aqueous solution, and when 1.8 g of a 1.994 mass% chloroplatinic acid aqueous solution was added thereto, a precipitate was formed, which was dissolved in a water bath at 86 ° C. Solution was obtained. When this was added to the boehmite sol solution and 0.2 g of urea was further added, a uniformly dispersed yellow boehmite gel without platinum black precipitation was obtained. This wet gel was rapidly frozen with liquid nitrogen and freeze-dried under conditions of a trap temperature of −80 ° C. and a vacuum of 10 Pa or less to obtain a dry gel (cryogel catalyst) (Example 3). In addition, platinum content was 5 mass%. Dry gel (xerogel catalyst) by a drying method (drying under reduced pressure using a rotary evaporator. Ultimate vacuum: about 13 to 15 mmHg, drying time: about 1 hour) without applying freeze-drying in the production process of Example 3 (Example 4). The platinum content was 5% by mass.
（比較例３及び比較例４）
アルミナクリオゲルを担体として通常の含浸法により、同様の白金−アルミナ触媒を調製した（比較例３）。更に、市販アルミナ（大明化学工業製：ＴＭ−３００Ｄ）を担体として通常の含浸法により、同様の白金−アルミナ触媒を調製した（比較例４）。尚、白金含有量は、それぞれ５質量％であった。
(Comparative Example 3 and Comparative Example 4)
A similar platinum-alumina catalyst was prepared by an ordinary impregnation method using alumina cryogel as a carrier (Comparative Example 3). Further, a similar platinum-alumina catalyst was prepared by a conventional impregnation method using commercially available alumina (manufactured by Daimei Chemical Industries: TM-300D) as a carrier (Comparative Example 4). In addition, platinum content was 5 mass%, respectively.
次に、それぞれ得られた触媒（実施例３及び実施例４、比較例３及び比較例４）について、７００℃仮焼に引き続き、５００℃で還元処理してから、メタンの酸化反応を行った。その結果を図７に示す。 Next, each of the obtained catalysts (Example 3 and Example 4, Comparative Example 3 and Comparative Example 4) was subjected to reduction treatment at 500 ° C. following calcination at 700 ° C., and then an oxidation reaction of methane was performed. . The result is shown in FIG.
図７に示すように、触媒成績（ＣＨ４酸化能力）は、実施例３（クリオゲル触媒）と実施例４（キセロゲル触媒）が圧倒的に高く、続いて比較例４（含浸法触媒［市販アルミナ担体］）、比較例３（含浸法触媒［アルミナクリオゲル担体］）の序列となった。 As shown in FIG. 7, the catalyst performance (CH 4 oxidation capability) was overwhelmingly higher in Example 3 (cryogel catalyst) and Example 4 (xerogel catalyst), followed by Comparative Example 4 (impregnation method catalyst [commercially available alumina). Support]) and Comparative Example 3 (impregnation method catalyst [alumina cryogel support]).
更に、それぞれ得られた触媒（実施例３及び実施例４、比較例３及び比較例４）について、ＣＯ吸着法による金属露出度評価を行った。その結果を図８に示す。 Furthermore, the metal exposure evaluation by CO adsorption method was performed about the obtained catalyst (Example 3 and Example 4, Comparative Example 3 and Comparative Example 4), respectively. The result is shown in FIG.
上記条件下で処理した触媒の白金表面露出度を計算したところ、実施例３（３６．２％）と実施例４（３０．８％）が高い表面露出度を示し、これらのサンプルでは、７００℃で仮焼しても露出度の低下は認められなかった。一方で、比較例４（８．５％）と比較例３（１．９％）では、７００℃仮焼により露出度の急激な低下が認められ、白金の耐熱性が劣ることが判明した。７００℃仮焼時における表面露出度の序列は触媒活性序列と同じであり、触媒成績が表面露出度に相関することを確認した。 When the platinum surface exposure of the catalyst treated under the above conditions was calculated, Example 3 (36.2%) and Example 4 (30.8%) showed high surface exposure. No reduction in exposure was observed even when calcined at ℃. On the other hand, in Comparative Example 4 (8.5%) and Comparative Example 3 (1.9%), a rapid decrease in exposure was observed due to 700 ° C. calcination, and it was found that the heat resistance of platinum was inferior. The order of the degree of surface exposure during calcination at 700 ° C. was the same as the order of catalyst activity, and it was confirmed that the catalyst performance correlated with the degree of surface exposure.
本発明の貴金属触媒及びその製造方法は、例えば、排ガス処理用の触媒の製造に好適に用いることができる。 The noble metal catalyst and the method for producing the same of the present invention can be suitably used for producing a catalyst for treating exhaust gas, for example.
Claims (5)
式（Ｉ）：埋没度（％）＝１００×［１−０．０１３８×ｄ ＶＡ ×Ｄ Ｍ ］
［但し、式（Ｉ）中、ｄ ＶＡ ：透過型電子顕微鏡（ＴＥＭ）を使用した観察により算出した白金粒子の直径（ｎｍ）、Ｄ Ｍ ：ＣＯ吸着法により算出した白金表面露出率（％）］ The platinum fine particles are buried in the freeze-dried gel, the degree of burying (the following formula (I)) indicating the degree of the platinum fine particles buried in the freeze-dried gel is 45 to 60%, and 500 to 700 ° C. Sintering of the platinum fine particles is suppressed under the atmosphere of the above, and the addition amount of the platinum is made of alumina cryogel having a high temperature heat resistance of 0.5 to 5% by mass , and acts as a catalyst in the oxidation reaction. A noble metal catalyst.
Formula (I): Degree of burial (%) = 100 × [1-0.0138 × d VA × D M ]
[However, in formula (I), d VA : diameter of platinum particles calculated by observation using a transmission electron microscope (TEM) (nm), D M : platinum surface exposure rate calculated by CO adsorption method (%) ]
シュウ酸、マロン酸のいずれか１種であるジカルボン酸系キレート剤で錯体化し、保護された塩化白金酸を、ベーマイトゾルの水溶液に投入することによりゲル化物を作製し、次いで前記ゲル化物を凍結乾燥することにより、白金の添加量が０．５〜５質量％の高温耐熱性を有するアルミナクリオゲルからなる、酸化反応において触媒として作用しうる貴金属触媒を得る貴金属触媒の製造方法。 A method for producing a noble metal catalyst for obtaining the noble metal catalyst according to claim 1,
A gelled product is prepared by adding a protected chloroplatinic acid into an aqueous boehmite sol complexed with a dicarboxylic acid chelating agent that is one of oxalic acid and malonic acid , and then freezing the gelated product. A method for producing a noble metal catalyst, which is obtained by drying to obtain a noble metal catalyst capable of acting as a catalyst in an oxidation reaction, comprising an alumina cryogel having a high-temperature heat resistance with an addition amount of platinum of 0.5 to 5% by mass .
白金アセチルアセトナート、ジニトロジアミン白金、テトラアンミン白金硝酸、ヘキサアンミン白金クロライド、ヘキサヒドロキソ白金エタノールアミンから選択された少なくとも１種以上である白金錯体をベーマイトゾルの水溶液に投入することによりゲル化物を作製し、次いで前記ゲル化物を凍結乾燥することにより、白金の添加量が０．５〜５質量％の高温耐熱性を有するアルミナクリオゲルからなる、酸化反応において触媒として作用しうる貴金属触媒を得る貴金属触媒の製造方法。 A method for producing a noble metal catalyst for obtaining the noble metal catalyst according to claim 1,
A gelled product is prepared by putting at least one platinum complex selected from platinum acetylacetonate, dinitrodiamine platinum, tetraammineplatinum nitrate, hexaammineplatinum chloride, and hexahydroxoplatinumethanolamine into an aqueous solution of boehmite sol. Then, the gelled product is freeze-dried to obtain a noble metal catalyst capable of acting as a catalyst in an oxidation reaction, which is made of an alumina cryogel having a high temperature heat resistance with an addition amount of platinum of 0.5 to 5% by mass. Manufacturing method.
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| CN105562701A (en) * | 2014-10-11 | 2016-05-11 | 南京理工大学 | Preparing method for copper-nickel alloy nano particles |
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