JP5137083B2 - Catalyst for reductive decomposition of nitrate ion - Google Patents
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Description
本発明は、廃液中の硝酸イオンを還元分解する触媒に係り、特に耐久性を大幅に向上させることが可能となる硝酸イオンの還元分解用触媒に関するものである。 The present invention relates to a catalyst for reducing and decomposing nitrate ions in a waste liquid, and more particularly to a catalyst for reducing and decomposing nitrate ions that can greatly improve durability.
放射性廃液を処理するに際しては、当該廃液中に含まれる硝酸塩が処分時における性能に悪影響を与えることから、近年、上記廃液中の硝酸イオンを高い効率で除去する技術が開発されつつある。 In treating radioactive waste liquid, nitrates contained in the waste liquid adversely affect the performance at the time of disposal, and in recent years, techniques for removing nitrate ions in the waste liquid with high efficiency have been developed.
ちなみに、本発明者等は、先に高濃度の硝酸塩を含む放射性廃液に、パラジウム（Ｐｄ）と銅（Ｃｕ）を担持させた触媒（以下、Ｐｄ−Ｃｕ担持触媒と略す。）を加えて、ヒドラジン還元剤を滴下することにより、硝酸イオンを還元分解して、最終的に窒素（Ｎ2）に無害化し得る硝酸イオンの除去技術を開発した。 Incidentally, the present inventors previously added a catalyst (hereinafter abbreviated as a Pd—Cu supported catalyst) in which palladium (Pd) and copper (Cu) are supported on a radioactive waste liquid containing a high concentration of nitrate. We have developed a technology for removing nitrate ions that can be reduced and decomposed by dropping hydrazine reducing agent and finally detoxifying to nitrogen (N 2 ).
ところで、このようなＰｄ−Ｃｕ担持触媒を用いた硝酸イオンの除去技術によれば、９９％以上といった高い脱硝率により上記放射性廃液を処理することができるという利点があるものの、上記Ｐｄ−Ｃｕ担持触媒が、繰り返し使用を行った場合に早期に活性が低下してしまうという欠点があり、当該触媒の耐久性の向上が強く要請されていた。 By the way, according to the nitrate ion removal technology using such a Pd—Cu supported catalyst, although there is an advantage that the radioactive liquid waste can be treated with a high denitration rate of 99% or more, the Pd—Cu supported When the catalyst is used repeatedly, there is a drawback that the activity is quickly reduced, and there has been a strong demand for improving the durability of the catalyst.
なお、下記特許文献１においては、酸化還元反応用の触媒について、比表面積の高い結晶性炭素粒子に平均粒子径の小さい金属微粒子を担持させて、酸化還元活性を高めることにより、触媒寿命を向上させる技術が開示されている。 In the following Patent Document 1, the catalyst life is improved by increasing the redox activity of the catalyst for redox reaction by supporting fine metal particles having a small average particle diameter on crystalline carbon particles having a high specific surface area. Techniques for making them disclosed are disclosed.
本発明は、上記要請に応えるべくなされたものであり、Ｐｄ−Ｃｕ担持触媒の耐久性を高めて、触媒寿命の長期化を図ることが可能になる硝酸イオンの還元分解用触媒を提供することを課題とするものである。 The present invention has been made in response to the above-described demand, and provides a catalyst for reductive decomposition of nitrate ions that can enhance the durability of a Pd—Cu supported catalyst and extend the life of the catalyst. Is an issue.
上記課題を解決するため、本発明者等は、ＰｄーＣｕ担持触媒における早期の活性低下の原因を究明すべく、図５に示す反応装置を用いて、ＰｄーＣｕ担持触媒による脱硝反応を検証した。この際、ＰｄーＣｕ担持触媒としては、担体としての活性炭に、当該活性炭１ｇあたり０．７mmolのＰｄと０．３mmolのＣｕを担持させたものを用いた。 In order to solve the above problems, the present inventors verified the denitration reaction by the Pd-Cu supported catalyst using the reaction apparatus shown in FIG. 5 in order to investigate the cause of the early decrease in activity in the Pd-Cu supported catalyst. did. At this time, as the Pd—Cu supported catalyst, a catalyst obtained by supporting 0.7 mmol of Pd and 0.3 mmol of Cu per 1 g of the activated carbon was used on activated carbon as a carrier .
そして、恒温水槽内のフラスコに入れた６Ｍ ＮａＮＯ3５００mLの反応溶液に、Ｐｄ−Ｃｕが１g／Lの量となるように加えて、還元剤としてヒドラジン（Ｎ2Ｈ4）の水溶液１９７mLを、ポンプによって４９．２mL／hの滴下速度で供給することにより、反応溶液中の硝酸イオンＮＯ3 -を還元して、ＮＯ3 -→ＮＯ2 -→Ｎ2 で示す硝酸態窒素の還元除去を行った。なお、上記反応は、８０℃の温度において、５時間行った。
次いで、反応溶液を入れ替えて、上記脱硝反応を繰り返す試験を合計７回行った。そして、各試験において、反応溶液中のＮＯ3 -、ＮＯ2 -を定量した。
Then, 197 mL of an aqueous solution of hydrazine (N 2 H 4 ) as a reducing agent was added to a reaction solution of 500 M of 6M NaNO 3 placed in a flask in a thermostatic water bath so that the amount of Pd—Cu was 1 g / L The nitrate ion NO 3 − in the reaction solution is reduced by supplying it at a dropping rate of 49.2 mL / h by a pump, and nitrate nitrogen represented by NO 3 − → NO 2 − → N 2 is reduced and removed. It was. The above reaction was carried out at a temperature of 80 ° C. for 5 hours.
Subsequently, the reaction solution was replaced, and the test for repeating the above denitration reaction was performed seven times in total. In each test, NO 3 − and NO 2 − in the reaction solution were quantified.
この結果、図６に示すように、２回目の試験以降、ＮＯ3 - の転換率が、好ましいとされる０．９９から早期に低下することが判明した。なお、硝酸態窒素（ＮＯ3 - ）の転換率は、｛初期ＮＯ3 - 量−残存（ＮＯ3 -＋ＮＯ2 -）量｝／初期ＮＯ3 -量、によって算出した。
これにより、ＰｄーＣｕ担持触媒における早期の活性低下の主要因は、当該Ｐｄ−Ｃｕ担持触媒のＮＯ3 -還元活性の低下にあると推察された。
As a result, as shown in FIG. 6, after the second test, it was found that the conversion rate of NO 3 − was lowered early from the preferred 0.99. Incidentally, nitrate nitrogen (NO 3 -) conversion of the {initial NO 3 - amount - residual (NO 3 - + NO 2 -) weight} / initial NO 3 - amount was calculated by.
Accordingly, the main cause of premature decrease in activity in the Pd over Cu supported catalyst, NO 3 of the Pd-Cu-supported catalyst - was presumed to be the reduction of the reducing activity.
このようなＰｄ−Ｃｕ担持触媒のＮＯ3 -還元活性の低下の原因としては、以下の３点が考えられる。
１．活性成分Ｐｄ、Ｃｕの機械的または熱的破壊・剥離
２．活性成分Ｐｄ、Ｃｕの不活性・低活性な物質への変質
３．活性成分Ｐｄ、Ｃｕの凝集による活性点の比表面積の減少
Such Pd-Cu supported catalyst NO 3 - as the cause of the decrease in the reducing activity, the 3-point is considered below.
1. 1. Mechanical or thermal destruction / peeling of active components Pd and Cu 2. Transformation of active ingredients Pd and Cu into inactive and low activity substances Reduction of specific surface area of active site due to aggregation of active components Pd and Cu
そこで、先ず上記１．の金属剥離について、ICP−AESを用いて、反応前後における触媒金属（Ｐｄ、Ｃｕ）の回収率を算出したところ、ほとんど変化が無かった。このため、活性成分Ｐｄ、Ｃｕの機械的または熱的破壊・剥離が主原因とは考え難いとの結論に至った。 Therefore, first, the above 1. As for the metal peeling, the recovery rate of the catalytic metal (Pd, Cu) before and after the reaction was calculated using ICP-AES, and there was almost no change. For this reason, it came to the conclusion that it is hard to think that the main cause is mechanical or thermal destruction and peeling of the active components Pd and Cu.
次いで、上記２．の活性成分の変質について、Ｘ解回折法を用いて調べた。
この結果、反応後のＰｄ−Ｃｕ担持触媒においても、Ｐｄ−Ｃｕに同定されるピークが、反応前のＰｄ−Ｃｕ担持触媒とほぼ同様な一に出現した。また、反応前後において、上記Ｐｄ−Ｃｕ担持触媒には、Ｐｄ−Ｃｕ合金以外の金属化合物に帰属される明らかなピークは見られなかった。このため、活性成分Ｐｄ、Ｃｕの変質による、異なる金属化合物の生成は無いものと考えられた。
Next, 2. The alteration of the active ingredient was examined using the X solution diffraction method.
As a result, in the Pd—Cu supported catalyst after the reaction, the peak identified as Pd—Cu appeared in almost the same manner as the Pd—Cu supported catalyst before the reaction. Further, before and after the reaction, no clear peak attributed to the metal compound other than the Pd—Cu alloy was observed in the Pd—Cu supported catalyst. For this reason, it was thought that there was no production | generation of a different metal compound by the alteration of active component Pd and Cu.
次に、上記３．の活性成分の凝集について、EPMAマッピング分析により検証した。
この結果、図７（金属の分布は、黒が多いところを、白が少ないところを示す。）およびこれを模式的に図示した図８に見られるように、反応前の触媒金属Ｐｄ、Ｃｕは、ややムラがあるものの活性炭表面のほぼ全域に分離していたのに対して、反応後においては、Ｐｄ、Ｃｕの金属濃度の分布に偏りが見られた。このため、Ｐｄ−Ｃｕ担持触媒の場合、金属粒子の凝集により、触媒性能が劣化するものとの結論を得るに至った。
Next, the above 3. The aggregation of the active ingredients was verified by EPMA mapping analysis.
As a result, as shown in FIG. 7 (where the metal distribution shows a lot of black and a little white) and FIG. 8 schematically showing this, the catalyst metals Pd and Cu before the reaction are Although there was some unevenness, the activated carbon surface was separated almost entirely, whereas after the reaction, the distribution of metal concentrations of Pd and Cu was biased. For this reason, in the case of a Pd—Cu supported catalyst, it came to the conclusion that catalyst performance deteriorates by aggregation of a metal particle.
そこで次に、触媒金属であるＰｄ−Ｃｕの活性を阻害せずに、当該Ｐｄ−Ｃｕ合金粒子の保護効果が期待できる金属成分として、鉄（Ｆｅ）、コバルト（Ｃｏ）およびニッケル（Ｎｉ）を選択し、活性炭１ｇあたり０．７mmolのＰｄと０．３mmolのＣｕを担持させた上記Ｐｄ−Ｃｕ担持触媒に、Ｆｅ、Ｃｏ、Ｎｉを、各々０．５mmol添加した触媒を作製して、図５に示した反応装置を用いて、上述したＰｄ−Ｃｕ担持触媒の場合と同じ条件で、同様の繰り返しの脱硝反応試験を行った。 Then, as a metal component that can be expected to protect the Pd—Cu alloy particles without inhibiting the activity of the catalyst metal Pd—Cu, iron (Fe), cobalt (Co), and nickel (Ni) are used. A catalyst was prepared by adding 0.5 mmol each of Fe, Co, and Ni to the Pd—Cu supported catalyst in which 0.7 mmol of Pd and 0.3 mmol of Cu were supported per 1 g of activated carbon. The same denitration reaction test was repeated under the same conditions as in the case of the Pd—Cu supported catalyst described above using the reaction apparatus shown in FIG.
なお、これらの金属を添加したＰｄ−Ｃｕ担持触媒は、ＰｄＣｌ2、ＣｕＣｌ2および各金属（Ｆｅ、Ｃｏ、Ｎｉ）の塩化物を含むＮａＯＨ水溶液（ｐＨ１０）に、担持触媒の担体となる活性炭を加えて３３３Ｋの温度において１時間含浸させた後に、これにＮａＢＨ4を添加して金属イオンを上記活性炭上に還元析出させ、ついでろ過・洗浄して採りだした触媒を、３３３Ｋの温度で乾燥させることに作製した。 The Pd—Cu supported catalyst to which these metals are added is an aqueous NaOH solution (pH 10) containing chloride of PdCl 2 , CuCl 2 and each metal (Fe, Co, Ni), and activated carbon serving as a support for the supported catalyst. In addition, after impregnation for 1 hour at a temperature of 333 K, NaBH 4 is added thereto to reduce and deposit metal ions on the activated carbon, and then the catalyst extracted by filtration and washing is dried at a temperature of 333 K. Especially made.
図１は、上記脱硝反応試験における試験回数と、各回数時の硝酸態窒素の転換率の変化を各触媒について示したものである。
この結果、転換率０．９５以上を達成した試験回数は、従来のＰｄ−Ｃｕ担持触媒においては４回であり、Ｃｏ添加のＰｄ−Ｃｕ担持触媒では、逆に２回と低下したが、Ｆｅ添加のＰｄ−Ｃｕ担持触媒においては６回、Ｎｉ添加のＰｄ−Ｃｕ担持触媒においては７回と、大幅に耐久性が向上することが確認された。
FIG. 1 shows the number of tests in the denitration reaction test and the change in the conversion rate of nitrate nitrogen at each time for each catalyst.
As a result, the number of tests that achieved a conversion rate of 0.95 or more was 4 times for the conventional Pd—Cu supported catalyst, and was decreased to 2 times for the Co-added Pd—Cu supported catalyst. It was confirmed that the durability was significantly improved by 6 times for the added Pd—Cu supported catalyst and 7 times for the Ni added Pd—Cu supported catalyst.
本発明は、上記知見に基づいて成されたもので、請求項１に記載の本発明に係る硝酸イオンの還元分解用触媒は、Ｐｄ−Ｃｕ担持触媒に、ＦｅまたはＮｉを添加してなることを特徴とするものである。 The present invention has been made based on the above knowledge, and the catalyst for reductive decomposition of nitrate ions according to the present invention according to claim 1 is obtained by adding Fe or Ni to a Pd-Cu supported catalyst. It is characterized by.
ここで、請求項２に記載の発明は、請求項１に記載の発明において、上記担持触媒の担体が、活性炭であり、かつ上記Ｎｉを、上記活性炭１ｇに対して、０．１〜０．７mmol添加したことを特徴とするものである。 Here, the invention according to claim 2 is the invention according to claim 1, wherein the carrier of the supported catalyst is activated carbon, and the Ni is 0.1 to 0.00 with respect to 1 g of the activated carbon. 7 mmol is added.
さらに、請求項３に記載の発明は、請求項１に記載の発明において、上記担持触媒の担体が、活性炭であり、かつ上記Ｎｉを、上記活性炭１ｇに対して、０．２〜０．５mmol添加したことを特徴とするものである。 Furthermore, the invention according to claim 3 is the invention according to claim 1, wherein the carrier of the supported catalyst is activated carbon, and the Ni is 0.2 to 0.5 mmol with respect to 1 g of the activated carbon. It is characterized by being added.
また、請求項４に記載の発明は、請求項１に記載の発明において、上記担持触媒の担体が、活性炭であり、かつ上記Ｆｅを、上記活性炭１ｇに対して、０．５mmol添加したことを特徴とするものである。 The invention according to claim 4 is the invention according to claim 1, wherein the carrier of the supported catalyst is activated carbon, and 0.5 mmol of Fe is added to 1 g of the activated carbon. It is a feature.
図１に示したように、請求項１〜４のいずれかに記載の発明によれば、Ｐｄ−Ｃｕ担持触媒に、ＦｅまたはＮｉを添加することにより、従来のＰｄ−Ｃｕ担持触媒と比較して、その耐久性を高めることができ、よって触媒寿命を一段と延ばすことが可能になる。 As shown in FIG. 1, according to the invention described in any one of claims 1 to 4, by adding Fe or Ni to the Pd—Cu supported catalyst, compared with the conventional Pd—Cu supported catalyst. Thus, the durability of the catalyst can be increased, so that the catalyst life can be further extended.
ここで、後述するように、請求項２に記載の発明によれば、添加するＮｉの量を、上記活性炭１ｇに対して、０．１〜０．７mmolの範囲とすることにより、この種の廃液処理において最も好ましいとされる９９％以上の脱硝率を得るための耐久性を約１．５倍以上に延ばすことが可能になる。 Here, as described later, according to the invention described in claim 2, by adding the amount of Ni to be added in the range of 0.1 to 0.7 mmol with respect to 1 g of the activated carbon, It is possible to extend the durability for obtaining a denitration rate of 99% or more, which is most preferable in waste liquid treatment, to about 1.5 times or more.
さらに、請求項３に記載の発明のように、添加するＮｉの量を、上記活性炭１ｇに対して、０．２〜０．５mmolの範囲とすることにより、上記９９％以上の脱硝率を得るための耐久性を、約２．５倍以上に延ばすことが可能になる。 Furthermore, as in the invention described in claim 3, the amount of Ni to be added is in the range of 0.2 to 0.5 mmol with respect to 1 g of the activated carbon, thereby obtaining a denitration rate of 99% or more. Therefore, it is possible to extend the durability for about 2.5 times or more.
また、Ｆｅについては、請求項４に記載の発明のように、上記活性炭１ｇに対して、０．５mmol添加することにより、耐久性を約２倍以上に延ばすことが可能である。 As for the Fe, as in the invention described in claim 4, by adding 0.5 mmol to 1 g of the activated carbon, it is possible to extend the durability about twice or more.
以下、図面に基づいて、本発明に係る硝酸イオンの還元分解用触媒の実施形態について説明する。
先ず、図１に示したように、Ｐｄ−Ｃｕ担持触媒に、ＦｅまたはＮｉを添加することにより、従来のＰｄ−Ｃｕ担持触媒と比較して、耐久性を向上させ得ることが判明した。
Hereinafter, embodiments of a catalyst for reductive decomposition of nitrate ions according to the present invention will be described based on the drawings.
First, as shown in FIG. 1, it has been found that the durability can be improved by adding Fe or Ni to the Pd—Cu supported catalyst as compared with the conventional Pd—Cu supported catalyst.
そこで、次に、活性炭に、当該活性炭１ｇあたり０．７mmolのＰｄ、０．３mmolのＣｕおよびＮｉを担持させたＰｄ−Ｃｕ−Ｎｉ担持触媒に対して、Ｎｉの添加量を変化させた場合における耐久性の変化を検証した。この際に、Ｎｉの添加量としては、活性炭１ｇあたり、０．２mmol、０．５mmol、０．７mmolおよび１．０mmolの４種類を選択した。なお、各量のＮｉを添加したＰｄ−Ｃｕ担持触媒の作製は、図１の各種金属を添加した場合におけるＰｄ−Ｃｕ担持触媒等の作製方法と同様である。 Therefore, next, when the addition amount of Ni is changed with respect to the Pd—Cu—Ni supported catalyst in which 0.7 mmol of Pd, 0.3 mmol of Cu and Ni are supported per 1 g of the activated carbon on the activated carbon. The change in durability was verified. At this time, as the addition amount of Ni, four types of 0.2 mmol, 0.5 mmol, 0.7 mmol, and 1.0 mmol were selected per 1 g of the activated carbon. The production of the Pd—Cu supported catalyst to which each amount of Ni is added is the same as the production method of the Pd—Cu supported catalyst and the like in the case where various metals in FIG. 1 are added.
次いで、このようにして得られた添加量を変化させた４種類のＰｄ−Ｃｕ−Ｎｉ担持触媒について、各々図５に示した反応装置を用いて、恒温水槽内のフラスコに入れた６Ｍ ＮａＮＯ3５００mLの反応溶液に、Ｐｄ−Ｃｕが１g／Lの量（約５．６〜６．０g）となるように加えて、還元剤としてヒドラジン（Ｎ2Ｈ4）の水溶液１９７mLを、ポンプによって４９．２mL／hの滴下速度で４時間供給することにより、反応溶液中の硝酸イオンＮＯ3 -を還元して、ＮＯ3 -→ＮＯ2 -→Ｎ2で示す硝酸態窒素の還元除去を行った。なお、上記反応は、８０℃の温度において、５時間行った。 Next, for each of the four types of Pd—Cu—Ni supported catalysts obtained by changing the amount of addition thus obtained, 6M NaNO 3 placed in a flask in a constant temperature bath using the reaction apparatus shown in FIG. To 500 mL of the reaction solution, Pd—Cu was added in an amount of 1 g / L (about 5.6 to 6.0 g), and 197 mL of an aqueous solution of hydrazine (N 2 H 4 ) as a reducing agent was added by a pump. The nitrate ion NO 3 − in the reaction solution was reduced by supplying it at a dropping rate of 2 mL / h for 4 hours, and nitrate nitrogen represented by NO 3 − → NO 2 − → N 2 was reduced and removed. . The above reaction was carried out at a temperature of 80 ° C. for 5 hours.
そして、上記反応溶液を入れ替えて、上記脱硝反応を繰り返す試験を複数回行うとともに、各試験において、反応溶液中のＮＯ3 -、ＮＯ2 -を定量して、各試験のおける脱硝率を算出した。 Then, the reaction solution was replaced, and the test for repeating the denitration reaction was performed a plurality of times, and in each test, NO 3 − and NO 2 − in the reaction solution were quantified to calculate the denitration rate in each test. .
図２は、上記試験の結果を、Ｎｉを添加しない従来のＰｄ−Ｃｕ担持触媒の結果と対比して示すものであって、Ｎｉの添加量（横軸）に対して、当該添加量における９５％以上の脱硝率が得られた試験回数および９９％以上の脱硝率が得られた試験回数を示すものである。 FIG. 2 shows the result of the above test in comparison with the result of a conventional Pd—Cu supported catalyst to which Ni is not added. The number of tests in which a denitration rate of at least% was obtained and the number of tests in which a denitration rate of 99% or more was obtained are shown.
図２から、特に高濃度の硝酸塩を含む放射性廃液において好適とされる９９％以上の脱硝率が得られる回数が、従来のＰｄ−Ｃｕ担持触媒において２回であったのに対して、Ｎｉを０．２mmol添加した場合には５回、０．５mmol添加した場合には７回、０．７mmol添加した場合には３回と増加した。また、同図によれば、０．１mmol添加した場合においても、ほぼ２回（Ｎｉ添加無し）と５回（０．２mmolのＮｉ添加）の中間程度の試験回数が得られるものと推測できる。 From FIG. 2, the number of times that a NOx removal rate of 99% or more, which is suitable for a radioactive liquid waste containing a particularly high concentration of nitrate, was obtained was twice in the conventional Pd—Cu supported catalyst, whereas Ni was reduced. It increased 5 times when 0.2 mmol was added, 7 times when 0.5 mmol was added, and 3 times when 0.7 mmol was added. Moreover, according to the figure, even when 0.1 mmol is added, it can be estimated that the number of tests is about halfway between approximately 2 times (no addition of Ni) and 5 times (addition of 0.2 mmol of Ni).
このため、Ｐｄ−Ｃｕ担持触媒に添加するＮｉの量を、活性炭１ｇに対して、０．１〜０．７mmolの範囲とすることにより、９９％以上の脱硝率を得るための耐久性を約１．５倍以上に延ばすことが可能になり、さらに上記Ｎｉの量を、活性炭１ｇに対して、０．２〜０．５mmolの範囲とすることにより、上記９９％以上の脱硝率を得るための耐久性を、約２．５倍以上に延ばすことが可能になる。 For this reason, by setting the amount of Ni added to the Pd—Cu supported catalyst in the range of 0.1 to 0.7 mmol with respect to 1 g of activated carbon, the durability for obtaining a denitration rate of 99% or more is reduced to about 99%. In order to obtain a denitration rate of 99% or more by making the amount of Ni in the range of 0.2 to 0.5 mmol with respect to 1 g of activated carbon. It is possible to extend the durability of the steel to about 2.5 times or more.
次いで、上記試験に用いたＰｄ−Ｃｕ−Ｎｉ担持触媒について、活性成分（Ｐｄ、Ｃｕ）の凝集について、図７に示した場合と同様のEPMAマッピング分析により検証した。
この結果、図３（金属の分布は、黒が多いところを、白が少ないところを示す。）およびこれを模式的に図示した図４に示すように、反応前において、Ｐｄ、Ｃｕ、Ｎｉの各々の金属は、析出ムラはあるものの析出濃度は同程度であった。
Next, for the Pd—Cu—Ni supported catalyst used in the above test, the aggregation of the active components (Pd, Cu) was verified by the same EPMA mapping analysis as shown in FIG.
As a result, as shown in FIG. 3 (where the distribution of metal shows a place where there is much black and a place where there is little white) and FIG. 4 schematically showing this, before the reaction, Pd, Cu, Ni Although each metal had precipitation unevenness, the precipitation concentration was almost the same.
そして、反応後においても、Ｎｉについては凝集が見られたが、Ｐｄ、Ｃｕについては明らかな局在が見られなかった。このため、Ｎｉを添加することによって、活性成分であるＰｄ、Ｃｕの凝集が抑制され、この結果触媒性能の劣化が遅くなることにより、耐久性が向上したことが判る。 Even after the reaction, aggregation was observed for Ni, but no clear localization was observed for Pd and Cu. For this reason, it can be seen that by adding Ni, aggregation of active components Pd and Cu is suppressed, and as a result, deterioration of the catalyst performance is delayed, thereby improving durability.
また、図１において示したように、本発明の開発過程において、Ｐｄ−Ｃｕ担持触媒にＦｅを添加したＰｄ−Ｃｕ−Ｆｅ担持触媒についても、例えばＦｅを、活性炭１ｇに対して、０．５mmol添加することにより、耐久性を約２倍以上に延ばすことが可能であることが判っている。これは、Ｆｅを添加した場合においても、Ｎｉを添加した場合と同様に、活性成分であるＰｄ、Ｃｕの凝集が抑制された結果であると推察される。 Further, as shown in FIG. 1, in the development process of the present invention, for the Pd—Cu—Fe supported catalyst obtained by adding Fe to the Pd—Cu supported catalyst, for example, Fe is 0.5 mmol per 1 g of activated carbon. It has been found that the durability can be increased by about twice or more by adding. This is presumed to be a result of suppressing aggregation of Pd and Cu as active components even when Fe is added, as in the case of adding Ni.
このように、Ｐｄ−Ｃｕ担持触媒にＮｉまたはＦｅを添加したＰｄ−Ｃｕ−Ｎｉ担持触媒あるいはＰｄ−Ｃｕ−Ｆｅ担持触媒によれば、従来のＰｄ−Ｃｕ担持触媒の耐久性を向上させることができ、よって触媒寿命を大幅に延ばすことが可能になる。 Thus, according to the Pd—Cu—Ni supported catalyst or the Pd—Cu—Fe supported catalyst in which Ni or Fe is added to the Pd—Cu supported catalyst, the durability of the conventional Pd—Cu supported catalyst can be improved. Thus, the catalyst life can be greatly extended.
廃液中の硝酸イオンを還元分解するに際して、特に耐久性を大幅に向上させることが可能となる硝酸イオンの還元分解用触媒を製造するために利用可能である。 It can be used for producing a catalyst for reductive decomposition of nitrate ions that can greatly improve the durability particularly when the nitrate ions in the waste liquid are reductively decomposed.
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