JP2011161349A - Noble metal particle size-controlled catalyst for cleaning exhaust gas - Google Patents
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- Inorganic Compounds Of Heavy Metals (AREA)
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Abstract
Description
本発明は、貴金属粒子径を制御した排ガス浄化用触媒とその製造方法に関する。 The present invention relates to an exhaust gas purifying catalyst having a controlled noble metal particle size and a method for producing the same.
自動車用触媒は、排気ガス中の有害な成分である炭化水素（ＨＣ）、窒素酸化物（ＮＯｘ）、一酸化炭素（ＣＯ）を分解除去する働きをもつ。これらの有害成分の分解除去は、コージェライト等の無機材料や金属を利用してハニカム状に成型した触媒の内部に排気ガスを通過させることで行われる。排気ガスとの接触効率を高めることを目的として、基材の表面には多孔質な無機材料のコーティングを行い、さらにその表層部には微量の貴金属を担持する。貴金属としては白金、パラジウム、ロジウム、イリジウム等に代表される白金族類を用いる。 Automobile catalysts have a function of decomposing and removing hydrocarbons (HC), nitrogen oxides (NOx), and carbon monoxide (CO), which are harmful components in exhaust gas. These harmful components are decomposed and removed by passing exhaust gas through a catalyst formed into a honeycomb shape using an inorganic material such as cordierite or a metal. For the purpose of increasing the contact efficiency with the exhaust gas, the surface of the substrate is coated with a porous inorganic material, and a trace amount of noble metal is supported on the surface layer portion. As the noble metal, a platinum group represented by platinum, palladium, rhodium, iridium or the like is used.
近年は自動車のエンジン始動時の排気ガスを速やかに処理するため触媒を低温から活性化することが求められており、貴金属使用量の増加により、浄化性能（低温活性）の向上を行っている。しかし、高価な貴金属の使用量の増加は、自動車のコストアップにつながり、消費者の不利益となるため、貴金属使用量を増加させずに有効利用しつつ浄化性能を向上することが求められている。 In recent years, it has been required to activate a catalyst from a low temperature in order to quickly process exhaust gas at the time of starting an automobile engine, and the purification performance (low temperature activity) has been improved by increasing the amount of noble metal used. However, an increase in the amount of expensive precious metal used leads to an increase in the cost of automobiles, which is disadvantageous for consumers.Therefore, it is required to improve the purification performance while effectively using the precious metal without increasing the amount of precious metal used. Yes.
触媒の浄化性能は、貴金属粒子の大きさと密接な関係にあることが知られている。従来、触媒への貴金属の担持工程について考えてみると、担持法の多くはイオンや錯体の状態の溶液を多孔質な無機材料表面に吸着し、熱処理により溶媒を除去、貴金属を析出させる工程を用いる。このため、溶媒除去中に溶液濃度やｐＨの変化が起こり貴金属イオンや錯体の状態が変化することが考えられる。このような貴金属の担持工程を経る場合、人為的な操作が難しく、貴金属粒子径を制御することは困難であり、最終的には粒子サイズにバラツキが生じる。 It is known that the purification performance of the catalyst is closely related to the size of the noble metal particles. Conventionally, considering the process of supporting a noble metal on a catalyst, many of the supporting methods involve adsorbing a solution in an ion or complex state on the surface of a porous inorganic material, removing the solvent by heat treatment, and precipitating the noble metal. Use. For this reason, it is considered that the solution concentration and pH change during the solvent removal and the state of the noble metal ions and the complex changes. When such a noble metal supporting step is performed, it is difficult to perform an artificial operation, and it is difficult to control the particle diameter of the noble metal, and eventually the particle size varies.
所望のクラスターサイズの貴金属を担持させるため、例えば、特許文献１では白金の二量体化による特性向上について開示されている。しかしながら、特許文献１では白金を二量体化するために、一度粉体に担持した後、硫酸溶液に分散しＣＯガスを吹き込むなど煩雑なプロセスを要しており、浄化性能が高く安価な触媒を提供することはできていない。
In order to support a noble metal having a desired cluster size, for example,
また、浄化性能を向上するために触媒製造時に使用する白金溶液を調製する方法として、金属コロイド溶液を調製する方法が特許文献２、特許文献３等に示されているが、粒子径のサイズをコントロールすることはできていない。
In addition, as a method for preparing a platinum solution used at the time of catalyst production in order to improve purification performance, a method of preparing a metal colloid solution is shown in
貴金属粒子サイズが小さいと、粒子上での安定なガス吸着が起こりにくいため、酸化や還元反応が進まず、結果として貴金属担持量に対して反応率の低下が引き起こされる。また、基材として用いるセラミックス材料は、ガス接触効率を上げるため高比表面積な材料が用いられることから、その表面には分布を有した細孔が形成されるか、もしくは凹凸形状となっている。このため、貴金属粒子が細孔の奥底に存在する状態が増加し、反応率が低下することも考えられる。 If the noble metal particle size is small, stable gas adsorption on the particle is difficult to occur, so that the oxidation or reduction reaction does not proceed, resulting in a decrease in the reaction rate with respect to the noble metal loading. Moreover, since the ceramic material used as the base material is a material having a high specific surface area in order to increase the gas contact efficiency, fine pores having a distribution are formed on the surface or the surface is uneven. . For this reason, it is also conceivable that the state in which the noble metal particles are present at the bottom of the pores increases and the reaction rate decreases.
一方貴金属サイズが大きい場合にも担持量に対する浄化率の低下が起こる。排気ガスの反応は、貴金属粒子の表面部分で起こることから、粒子内部は反応にほとんど関与せず、必要な浄化率を得るには貴金属量を増やすことが必要になる。また、粒子サイズが大きい場合は、熱負荷による貴金属の凝集も起こりやすくなり、これによっても反応率の低下が起こる。 On the other hand, when the noble metal size is large, the purification rate is lowered with respect to the loading amount. Since the reaction of the exhaust gas occurs at the surface portion of the noble metal particles, the inside of the particles hardly participates in the reaction, and it is necessary to increase the amount of noble metal in order to obtain a necessary purification rate. In addition, when the particle size is large, agglomeration of noble metals due to heat load is likely to occur, which also causes a reduction in the reaction rate.
本発明は、上記現状に鑑み、熱負荷による貴金属の凝集を抑制し、かつ貴金属の使用量を低減するために、触媒に担持される貴金属粒子サイズを簡便に制御する方法を提供することを目的とする。 In view of the above-mentioned present situation, the present invention aims to provide a method for simply controlling the size of noble metal particles supported on a catalyst in order to suppress aggregation of noble metal due to heat load and reduce the amount of noble metal used. And
本発明は、上記課題を解決するためになされたものである。すなわち、本発明に係る貴金属溶液の製造方法は、水酸基を配位した貴金属錯体溶液の濃度、酸濃度ならびに溶液の保持温度および／もしくは時間を制御することによって溶液中での貴金属粒子のメジアン径を制御する工程を含むことを特徴とする。 The present invention has been made to solve the above problems. That is, in the method for producing a noble metal solution according to the present invention, the median diameter of the noble metal particles in the solution is controlled by controlling the concentration of the noble metal complex solution coordinated with the hydroxyl group, the acid concentration, and the holding temperature and / or time of the solution. And a step of controlling.
本発明の貴金属溶液の製造方法により、貴金属の粒子径を溶液中の段階で予め制御することができ、貴金属最小単位が大きくなるので、溶媒除去時や熱処理時に懸念される貴金属の制御不能で不規則な凝集を抑制できる。これにより、最終的に形成される貴金属のサイズのバラツキを抑えることができるだけでなく、反応に寄与しにくい細孔内部の貴金属粒子の割合を減らすことができる。
さらに同じ貴金属担持量でライトオフ温度（浄化率５０％を達成する温度）を低減することができる。
According to the method for producing a noble metal solution of the present invention, the particle size of the noble metal can be controlled in advance in the solution, and the minimum unit of noble metal becomes large. Regular aggregation can be suppressed. Thereby, not only the variation in the size of the noble metal finally formed can be suppressed, but also the ratio of the noble metal particles inside the pores that hardly contribute to the reaction can be reduced.
Furthermore, the light-off temperature (temperature at which a purification rate of 50% is achieved) can be reduced with the same noble metal loading.
本発明にかかる貴金属溶液の製造方法においては、水酸基を配位した貴金属錯体を含む溶液を用いる。
この錯体は、塩化物錯体、ジニトロジアンミン錯体等の他の貴金属錯体と異なり、酸性溶液中で脱水縮合し、直列の錯体分子を形成する。本発明者らの研究により温度、濃度などを変えることにより縮合する個数が制御できることが判明した。他の貴金属錯体は浮遊している錯体が個別に触媒上に担持されるのに対して、水酸基を配位した貴金属錯体では溶液中で縮重合し、強固な錯体分子となった後に触媒上に担持されるため、錯体分子の大きさが触媒上に担持された貴金属粒子の大きさに反映される。したがって、溶液中の粒子径（錯体分子の大きさ）を制御することで触媒上の白金粒子径を制御することができる。
In the method for producing a noble metal solution according to the present invention, a solution containing a noble metal complex coordinated with a hydroxyl group is used.
Unlike other noble metal complexes such as chloride complexes and dinitrodiammine complexes, this complex undergoes dehydration condensation in an acidic solution to form a series of complex molecules. The inventors' research has revealed that the number of condensation can be controlled by changing the temperature, concentration and the like. In other noble metal complexes, floating complexes are individually supported on the catalyst, whereas in the noble metal complexes coordinated with hydroxyl groups, they are polycondensed in solution to form a strong complex molecule and then on the catalyst. Since it is supported, the size of the complex molecule is reflected in the size of the noble metal particles supported on the catalyst. Therefore, the platinum particle diameter on the catalyst can be controlled by controlling the particle diameter in the solution (the size of the complex molecule).
水酸基を配位した貴金属錯体は、貴金属を含む原料を溶媒に溶解させることにより得られる。
貴金属を含む原料としては特に限定されないが、例えば、白金、パラジウム、ロジウム、ルテニウム等の水酸化物；白金、パラジウム、ルテニウム等を含み溶液中で水酸基を配位する原料；白金、パラジウム、ロジウム、ルテニウム等の貴金属を含み溶媒中で配位子交換反応によって該貴金属に水酸基を配位する原料等を採用することができる。
白金を含む原料としては特に限定されないが、例えば、ヘキサヒドロキソ白金（ＩＶ）酸ナトリウム、ヘキサヒドロキソ白金（ＩＶ）酸カリウム、ヘキサヒドロキソ白金酸等が挙げられる。原料として水酸化物を用いることは、塩化物を用いた場合と異なり触媒に担持した後に塩化物イオンが残留し、反応活性を阻害することがない点も有利である。
A noble metal complex coordinated with a hydroxyl group can be obtained by dissolving a raw material containing a noble metal in a solvent.
Although it does not specifically limit as a raw material containing a noble metal, For example, hydroxides, such as platinum, palladium, rhodium, ruthenium; The raw material which coordinates platinum in a solution containing platinum, palladium, ruthenium etc .; Platinum, palladium, rhodium, A raw material that contains a noble metal such as ruthenium and coordinates a hydroxyl group to the noble metal by a ligand exchange reaction in a solvent can be employed.
Although it does not specifically limit as a raw material containing platinum, For example, hexahydroxo platinum (IV) acid sodium, hexahydroxo platinum (IV) potassium, hexahydroxo platinum acid, etc. are mentioned. The use of hydroxide as a raw material is advantageous in that chloride ions remain after being supported on the catalyst, unlike the case of using chloride, and the reaction activity is not hindered.
貴金属錯体溶液は、錯体同士の脱水縮合反応を進行させるため、通常、酸を添加することにより酸性溶液とする。溶液中の酸濃度は、好ましくは５規定以上、より好ましくは５〜６規定にする。５規定未満であると、沈殿の発生により溶液中の白金濃度が低下しやすくなる。
酸を添加する段階としては、溶液を加温する前に全て添加してもよいし、加温する過程で間欠的または連続的に追加してもよい。
In order to advance the dehydration condensation reaction between complexes, the noble metal complex solution is usually made acidic by adding an acid. The acid concentration in the solution is preferably 5 N or more, more preferably 5 to 6 N. If it is less than 5N, the platinum concentration in the solution tends to decrease due to the occurrence of precipitation.
The acid may be added before the solution is warmed, or may be added intermittently or continuously during the warming process.
貴金属錯体溶液中の白金濃度は触媒の担持量が０．３〜１．０ｇ／Ｌとなるように調整する。０．３ｇ／Ｌ未満であると浄化性能が不足する場合があり、１．０ｇ／Ｌを超えても浄化率が大きく向上することは無い。 The platinum concentration in the noble metal complex solution is adjusted so that the supported amount of the catalyst is 0.3 to 1.0 g / L. If it is less than 0.3 g / L, the purification performance may be insufficient, and even if it exceeds 1.0 g / L, the purification rate will not be greatly improved.
本発明の製造方法においては、貴金属錯体溶液の保持温度を制御することが好ましい。溶液の温度は、好ましくは５０℃以上、より好ましくは、５０℃〜８０℃とする。５０℃未満であると溶液中の粒子はほとんど成長しない。また粒子径には飽和する大きさがあり５０℃以上であれば溶液の温度の高い方が粒子径が大きくなるが、８０℃を超えると沈殿の発生により溶液中の白金濃度が低下しやすくなる。
保持時間としては、上記５０℃〜８０℃の温度範囲に通算で６００分から１５００分保持することが好ましい。保持時間が６００分未満であると、粒径が飽和する前の成長過程にあり、狙った粒径を安定して得られない場合があり、１５００分を超えてもそれ以上の粒径変化は無いため、保持する必要が無い。
ここで保持時間を通算時間としたのは、途中で５０℃未満の温度に下げても溶液中の粒子はほとんど成長せず支障がないからである。したがって本発明の製造方法において「保持温度を制御する」とは、所定の制御温度に到達したのち、一時的に５０℃未満に降温することも許容される。
In the production method of the present invention, it is preferable to control the holding temperature of the noble metal complex solution. The temperature of the solution is preferably 50 ° C or higher, more preferably 50 ° C to 80 ° C. When the temperature is lower than 50 ° C., the particles in the solution hardly grow. In addition, the particle size has a size that saturates, and if it is 50 ° C. or higher, the higher the solution temperature, the larger the particle size. .
The holding time is preferably 600 to 1500 minutes in the temperature range of 50 to 80 ° C. If the holding time is less than 600 minutes, it is in the growth process before the particle size is saturated, and the target particle size may not be stably obtained. There is no need to hold it.
The reason why the retention time is the total time here is that even if the temperature is lowered to a temperature lower than 50 ° C. during the course, the particles in the solution hardly grow and there is no problem. Therefore, “controlling the holding temperature” in the manufacturing method of the present invention also allows the temperature to be temporarily lowered to less than 50 ° C. after reaching a predetermined control temperature.
本発明にかかる製法においては特に、前記酸濃度を５規定以上とし、かつ前記溶液温度を５０℃〜８０℃に保持することが好ましい。保持温度および酸濃度を上記範囲内にすることにより、溶液中の貴金属粒子径を３ｎｍ〜７ｎｍの範囲にコントロールすることができる。
溶液中での貴金属錯体のメジアン径を３ｎｍ以上７ｎｍ以下に制御することで同じ貴金属担持量でも従来法より良いＴＨＣ，ＮＯｘ浄化性能を得ることができる。
本明細書において、溶液中の粒子径値は、すべて動的光散乱法［ＤＬＳ］により測定されたメジアン径である。
In the production method according to the present invention, it is particularly preferable that the acid concentration is 5 N or more and the solution temperature is maintained at 50 ° C to 80 ° C. By setting the holding temperature and the acid concentration within the above ranges, the noble metal particle diameter in the solution can be controlled in the range of 3 nm to 7 nm.
By controlling the median diameter of the noble metal complex in the solution between 3 nm and 7 nm, it is possible to obtain better THC and NOx purification performance than the conventional method even with the same amount of noble metal supported.
In the present specification, the particle diameter values in the solution are all median diameters measured by the dynamic light scattering method [DLS].
さらに、担持前の溶液中の白金粒子径を調製すれば従来を上回る浄化性能を持つ触媒を作製することができるため、担持前に触媒の浄化性能の良否を判別することができ、溶液に起因する不良を大幅に削減することが可能になる。 Furthermore, if the platinum particle size in the solution before loading is prepared, a catalyst with a purification performance exceeding that of the conventional one can be produced. Therefore, it is possible to determine whether the catalyst purification performance is good before loading. It is possible to greatly reduce the defects to be performed.
本発明にかかる貴金属溶液を触媒担体に担持させてなる排ガス触媒もまた本発明の１つである。触媒担体とは、ウォッシュコートを保持するものであって、強度が高く、耐熱性に優れるものをいい、こうした触媒担体としては、コージェライトハニカム担体を用いることができる。しかし、これには限定されることなく、その他にも、アルミナ製、ＳｉＣ製、ステンレス製のハニカム担体を用いることができる。
貴金属溶液の担持方法としては、通常の吸水法や含浸法と同様の担持方法を採用することができる。特殊な設備を必要としないため、従来の工程をそのまま利用できる。また、溶液の調製も薬液を調合した後に一定条件を保持するのみと単純であり、粒子径の安定度も高いので、粒子径のコントロールが容易であり、製造コストを上げることなく触媒の性能向上を図ることができる。
An exhaust gas catalyst obtained by supporting a noble metal solution according to the present invention on a catalyst carrier is also one aspect of the present invention. The catalyst carrier is one that holds a washcoat and has high strength and excellent heat resistance. As such a catalyst carrier, a cordierite honeycomb carrier can be used. However, the present invention is not limited to this, and other honeycomb carriers made of alumina, SiC, or stainless steel can be used.
As a method for supporting the noble metal solution, a supporting method similar to a normal water absorption method or impregnation method can be employed. Since no special equipment is required, the conventional process can be used as it is. In addition, the preparation of the solution is as simple as maintaining a certain condition after the chemical solution is prepared, and the stability of the particle size is high, so the particle size can be easily controlled and the catalyst performance can be improved without increasing production costs. Can be achieved.
＜触媒作製＞
水硬性アルミナ（ＢＫ−１０５、住友化学工業社製）６０ｇ、アルミナゾル（無機成分１０％）１８０ｇ、硝酸アルミニウム６水和物１２０ｇ、イオン交換水４０ｇを加え、２４時間以上ボールミル混合を行うことによりスラリーを調製した。これをコージェライト担体（φ３０×３０，４００ｃｅｌｌ／ｉｎｃｈ２，６．５ｍｉｌ）に流し入れ、エアブローにより余分なスラリーを除去することで、担体内部をコーティングした。コーティング後は、８０℃の熱風にて１０分程度乾燥を行い、その後、５００℃、１時間の熱処理を行った。
＜評価方法＞
試作触媒を模擬排気ガス装置を用いて評価した。模擬排気ガス装置での試験は、表１に示す試験条件で行い、触媒入口と出口の炭化水素（ＨＣ）、窒素酸化物（ＮＯｘ）、一酸化炭素（ＣＯ）の濃度変化率を浄化率として下記式１に基づいてそれぞれ算出した。
<Catalyst preparation>
60g of hydraulic alumina (BK-105, manufactured by Sumitomo Chemical Co., Ltd.), 180g of alumina sol (10% inorganic component), 120g of aluminum nitrate hexahydrate, 40g of ion-exchanged water and slurry by ball mill mixing for 24 hours or more Was prepared. This was poured into a cordierite carrier (φ30 × 30, 400 cell / inch 2 , 6.5 mil), and excess slurry was removed by air blowing to coat the inside of the carrier. After coating, it was dried with hot air at 80 ° C. for about 10 minutes, and then heat-treated at 500 ° C. for 1 hour.
<Evaluation method>
The prototype catalyst was evaluated using a simulated exhaust gas device. The test with the simulated exhaust gas device is performed under the test conditions shown in Table 1, and the concentration change rate of hydrocarbon (HC), nitrogen oxide (NOx), and carbon monoxide (CO) at the catalyst inlet and outlet is used as the purification rate. Calculations were made based on the following
浄化率（％）＝［１−（後排ガス中の濃度）／（前排ガス中の濃度）］×１００ （式１） Purification rate (%) = [1- (concentration in the exhaust gas after the exhaust) / (concentration in the exhaust gas before the exhaust)] × 100 (Formula 1)
測定は２００〜４５０℃の範囲で行い、測定前には４５０℃で１０分間模擬排気ガスに曝露させて活性化処理を行い、１００℃以下まで降温させた後、所定の温度（１６５℃、２１０℃、２６０℃、３００℃、３５０℃、４００℃、４５０℃）に順次昇温して評価した。 The measurement is performed in the range of 200 to 450 ° C., and before the measurement, the sample is exposed to simulated exhaust gas at 450 ° C. for 10 minutes for activation treatment. After the temperature is lowered to 100 ° C. or lower, a predetermined temperature (165 ° C., 210 ° C. , 260 ° C., 300 ° C., 350 ° C., 400 ° C., 450 ° C.).
（実施例１〜１４）
白金原料としてヘキサヒドロキソ白金酸（田中貴金属、白金重量６５質量％）を用い、硝酸濃度、白金濃度、溶液保持温度を表２のように設定することで粒子径を１〜６ｎｍに制御した溶液を調製した。表２中、溶液中の粒子径はＤＬＳ（シスメックス社製、ゼータサイザー）により求めた。
調製した溶液を、＜触媒作製＞の欄で述べた手順により作製した触媒に吸水担持させ、触媒の筐体体積あたりの白金担持量がそれぞれ０．３ｇ／Ｌ、０．５ｇ／Ｌ、１．０ｇ／Ｌとなるようにした。吸水担持に用いた白金溶液の濃度は、作製した触媒の吸水量から見積もり、それぞれ２．３８ｇ／Ｌ、３．９９ｇ／Ｌ、７．９７ｇ／Ｌとした。担持後は、８０℃の熱風にて１０分間程度乾燥を行い、その後、５００℃、１時間の熱処理を行うことで試作触媒とした。得られた試作触媒を用いてモデルガス装置により浄化率を測定した。
（比較例１〜３）
白金原料としてジニトロジアンミン白金溶液（田中貴金属、白金重量：65質量％）を用い、溶液温度をすべて室温とした以外は実施例と同じ手順により、触媒の筐体体積あたりの白金担持量がそれぞれ０．３ｇ／Ｌ、０．５ｇ／Ｌ、１．０ｇ／Ｌである比較用触媒を調製し浄化率を測定した。
以上の結果を表２および図２〜図１０に示す。
(Examples 1-14)
Using hexahydroxoplatinic acid (Tanaka noble metal, platinum weight 65% by mass) as a platinum raw material, and setting the nitric acid concentration, platinum concentration, and solution holding temperature as shown in Table 2, the particle diameter was controlled to 1 to 6 nm. Prepared. In Table 2, the particle size in the solution was determined by DLS (manufactured by Sysmex Corporation, Zetasizer).
The prepared solution was water-absorbed and supported on the catalyst prepared by the procedure described in the section <Catalyst preparation>, and platinum loadings per housing volume of the catalyst were 0.3 g / L, 0.5 g / L, and 1. It was set to 0 g / L. The concentration of the platinum solution used for water absorption was estimated from the water absorption of the produced catalyst, and was 2.38 g / L, 3.99 g / L, and 7.97 g / L, respectively. After loading, drying was performed for about 10 minutes with hot air at 80 ° C., and then heat treatment was performed at 500 ° C. for 1 hour to obtain a prototype catalyst. The purification rate was measured by a model gas apparatus using the obtained prototype catalyst.
(Comparative Examples 1-3)
Using the same procedure as in Example, except that dinitrodiammine platinum solution (Tanaka Precious Metal, platinum weight: 65 mass%) was used as the platinum raw material, and the solution temperature was all set to room temperature, the amount of platinum supported per case volume of the catalyst was 0, respectively. Comparative catalysts of 3 g / L, 0.5 g / L and 1.0 g / L were prepared and the purification rate was measured.
The above results are shown in Table 2 and FIGS.
図２〜図４に示すように、模擬排気ガステストの結果、ＴＨＣ，ＮＯｘ、ＣＯすべてにおいて白金粒子径３ｎｍ以上で急激に浄化率が向上し、メジアン径の大きい方が浄化率が高くなることがわかった。またＴＨＣ、ＮＯｘについては白金粒子径３ｎｍ以上で比較例よりもよい特性を示すことがわかった。
図５〜図７に示すようにＴＨＣ，ＮＯｘ、ＣＯすべてにおいて粒子径が大きい方でライトオフ温度が低下していることがわかった。またＨＣ、ＮＯｘについては白金粒子径３ｎｍ以上で比較例よりもよい特性を示すことがわかった。
As shown in FIGS. 2 to 4, as a result of the simulated exhaust gas test, the purification rate is drastically improved when the platinum particle diameter is 3 nm or more in all of THC, NOx, and CO, and the purification rate is higher when the median diameter is larger. I understood. Further, it was found that THC and NOx showed better characteristics than the comparative example at a platinum particle diameter of 3 nm or more.
As shown in FIG. 5 to FIG. 7, it was found that the light-off temperature was lowered with the larger particle diameter in all of THC, NOx, and CO. It was also found that HC and NOx showed better characteristics than the comparative example at a platinum particle diameter of 3 nm or more.
表３から表５、ならびに、図８〜図１０に示すように、特にＨＣ、ＮＯｘの除去に関して本願製法により得られた触媒が従来品より良好な特性を示すことがわかった。 As shown in Tables 3 to 5 and FIGS. 8 to 10, it was found that the catalyst obtained by the production method of the present invention particularly exhibits better characteristics than the conventional product with respect to the removal of HC and NOx.
図１１および図１２に示すように、溶液中の白金粒子径分布では、水酸化白金では粒子径をコントロールし増大させることができるが、ジニトロジアンミン白金では粒子径を増大させることができないことがわかった。
図１３に示すように、酸濃度を５Ｎ以上に調製し、溶液の温度を５０℃〜７０℃に保持することで、沈殿が発生することなく、溶液中の白金粒子径を３ｎｍ以上に成長させることができることがわかった。
また比較例においては、ジニトロジアンミン溶液にて粒子径のコントロールをするため、７０℃にて２２時間保持したが粒子径は１〜２ｎｍ程度であり、粒子径の増大は観察されなかった。
As shown in FIGS. 11 and 12, in the platinum particle size distribution in the solution, it is found that platinum hydroxide can control and increase the particle size, but dinitrodiammine platinum cannot increase the particle size. It was.
As shown in FIG. 13, by adjusting the acid concentration to 5N or more and maintaining the temperature of the solution at 50 ° C. to 70 ° C., the platinum particle diameter in the solution is grown to 3 nm or more without causing precipitation. I found out that I could do it.
In the comparative example, the particle size was controlled with a dinitrodiammine solution, and kept at 70 ° C. for 22 hours. However, the particle size was about 1 to 2 nm, and no increase in the particle size was observed.
（実施例１６）＜同じ貴金属錯体、同担持量での粒径依存性の検討＞
硝酸濃度５ｍｏｌ／ｌに調製した溶液３０ｍｌにヘキサヒドロキソ白金酸（田中貴金属社製、白金重量６５重量％）０．１８４ｇを加え、充分に攪拌した後、密閉容器に入れ、７０℃の恒温槽にて２２時間保持することにより、貴金属サイズを制御した溶液を調製した。溶液は薄い黄色から茶色に変化していたが、沈殿等は観察されなかった。このときの溶液中での白金粒子径のサイズは、動的光散乱法による測定の結果、３〜４ｎｍと見積もられた。
また、ESI−MS および EXAFSを用いた構造解析の結果、白金が１０個程度酸素を介して直鎖状に並んだ構造であることがわかった。
(Example 16) <Examination of particle size dependency at the same noble metal complex and the same loading amount>
Add 0.184 g of hexahydroxoplatinic acid (Tanaka Kikinzoku Co., Ltd., platinum weight 65 wt%) 0.184 g to 30 ml of the solution prepared to a nitric acid concentration of 5 mol / l. For 22 hours to prepare a solution with controlled noble metal size. The solution changed from pale yellow to brown, but no precipitation or the like was observed. The size of the platinum particle diameter in the solution at this time was estimated to be 3 to 4 nm as a result of measurement by the dynamic light scattering method.
Moreover, as a result of structural analysis using ESI-MS and EXAFS, it was found that the structure was a structure in which about 10 platinum were arranged in a straight chain via oxygen.
（比較例４）
硝酸濃度５ｍｏｌ／ｌに調製した溶液３０ｍｌにヘキサヒドロキソ白金酸０．１８４ｇを加え、充分に攪拌した後、密閉容器に入れ、室温中で２２時間保持した。溶液は薄い黄色から茶色に変化していたが、沈殿等は観察されなかった。このときの溶液中での白金粒子径のサイズは、動的光散乱法による測定の結果、１〜２ｎｍと見積もられた。
以上の結果を表６に示す。
(Comparative Example 4)
After adding 0.184 g of hexahydroxoplatinic acid to 30 ml of the solution prepared to have a nitric acid concentration of 5 mol / l and stirring sufficiently, it was put in a sealed container and kept at room temperature for 22 hours. The solution changed from pale yellow to brown, but no precipitation or the like was observed. The size of the platinum particle diameter in the solution at this time was estimated to be 1 to 2 nm as a result of measurement by a dynamic light scattering method.
The results are shown in Table 6.
表６および図１４から、模擬排気ガステストの結果、あらかじめ溶液中での白金サイズが３〜４ｎｍの範囲となるように調製した実施例１６の触媒は、粒子径を制御せず１〜２ｎｍにとどまった比較例４の触媒と比べて浄化の立ち上がり温度が約５０℃程度低く、触媒活性が高いことが明らかとなった。
図１５に浄化性能の指標である浄化率５０％における比較結果を示す。図１５から、同程度の触媒活性を得るための温度がＨＣ、ＮＯｘ、ＣＯの全てにおいて大幅に低下していることがわかった。
From Table 6 and FIG. 14, as a result of the simulated exhaust gas test, the catalyst of Example 16 prepared so that the platinum size in the solution was in the range of 3 to 4 nm was adjusted to 1 to 2 nm without controlling the particle diameter. It was revealed that the rising temperature of purification was about 50 ° C. lower than the catalyst of Comparative Example 4 which remained, and the catalytic activity was high.
FIG. 15 shows a comparison result at a purification rate of 50%, which is an index of purification performance. From FIG. 15, it was found that the temperature for obtaining the same level of catalytic activity was greatly reduced in all of HC, NOx, and CO.
Claims (6)
An exhaust gas catalyst obtained by supporting the noble metal solution according to claim 5 on a catalyst carrier.
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| JPH1192150A (en) * | 1997-09-19 | 1999-04-06 | Tanaka Kikinzoku Kogyo Kk | Preparation of platinum nitrate solution |
| JP2005332662A (en) * | 2004-05-19 | 2005-12-02 | Nissan Motor Co Ltd | Catalyst for fuel cell and its manufacturing method |
| JP2007532288A (en) * | 2004-04-09 | 2007-11-15 | ペミアス ゲーエムベーハー | Platinum catalyst obtained by reducing platinum dioxide formed in situ |
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| JPH1192150A (en) * | 1997-09-19 | 1999-04-06 | Tanaka Kikinzoku Kogyo Kk | Preparation of platinum nitrate solution |
| JP2007532288A (en) * | 2004-04-09 | 2007-11-15 | ペミアス ゲーエムベーハー | Platinum catalyst obtained by reducing platinum dioxide formed in situ |
| JP2005332662A (en) * | 2004-05-19 | 2005-12-02 | Nissan Motor Co Ltd | Catalyst for fuel cell and its manufacturing method |
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