JP4411098B2 - Cleaning method for metal supported catalyst - Google Patents
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- 239000003054 catalyst Substances 0.000 title claims description 83
- 229910052751 metal Inorganic materials 0.000 title claims description 62
- 239000002184 metal Substances 0.000 title claims description 62
- 238000000034 method Methods 0.000 title claims description 30
- 238000004140 cleaning Methods 0.000 title claims description 21
- 229910052717 sulfur Inorganic materials 0.000 claims description 60
- 239000011593 sulfur Substances 0.000 claims description 60
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 claims description 58
- 239000010931 gold Substances 0.000 claims description 55
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical group O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 claims description 35
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- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 claims description 25
- 229910052737 gold Inorganic materials 0.000 claims description 25
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 claims description 24
- OGIDPMRJRNCKJF-UHFFFAOYSA-N titanium oxide Inorganic materials [Ti]=O OGIDPMRJRNCKJF-UHFFFAOYSA-N 0.000 claims description 24
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 22
- XLOMVQKBTHCTTD-UHFFFAOYSA-N Zinc monoxide Chemical compound [Zn]=O XLOMVQKBTHCTTD-UHFFFAOYSA-N 0.000 claims description 20
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 claims description 19
- 239000007864 aqueous solution Substances 0.000 claims description 17
- 239000003638 chemical reducing agent Substances 0.000 claims description 12
- 239000011787 zinc oxide Substances 0.000 claims description 10
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 claims description 8
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- VEALVRVVWBQVSL-UHFFFAOYSA-N strontium titanate Chemical compound [Sr+2].[O-][Ti]([O-])=O VEALVRVVWBQVSL-UHFFFAOYSA-N 0.000 claims description 7
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- XOLBLPGZBRYERU-UHFFFAOYSA-N tin dioxide Chemical compound O=[Sn]=O XOLBLPGZBRYERU-UHFFFAOYSA-N 0.000 description 2
- 229910001887 tin oxide Inorganic materials 0.000 description 2
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- SCYULBFZEHDVBN-UHFFFAOYSA-N 1,1-Dichloroethane Chemical compound CC(Cl)Cl SCYULBFZEHDVBN-UHFFFAOYSA-N 0.000 description 1
- OSWFIVFLDKOXQC-UHFFFAOYSA-N 4-(3-methoxyphenyl)aniline Chemical compound COC1=CC=CC(C=2C=CC(N)=CC=2)=C1 OSWFIVFLDKOXQC-UHFFFAOYSA-N 0.000 description 1
- RWSOTUBLDIXVET-UHFFFAOYSA-N Dihydrogen sulfide Chemical compound S RWSOTUBLDIXVET-UHFFFAOYSA-N 0.000 description 1
- 229910001111 Fine metal Inorganic materials 0.000 description 1
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- YSVZGWAJIHWNQK-UHFFFAOYSA-N [3-(hydroxymethyl)-2-bicyclo[2.2.1]heptanyl]methanol Chemical group C1CC2C(CO)C(CO)C1C2 YSVZGWAJIHWNQK-UHFFFAOYSA-N 0.000 description 1
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- 150000002343 gold Chemical class 0.000 description 1
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- 229910000037 hydrogen sulfide Inorganic materials 0.000 description 1
- 238000005984 hydrogenation reaction Methods 0.000 description 1
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Description
本発明は、金属担持触媒のクリーニング方法に関する。 The present invention relates to a method for cleaning a metal-supported catalyst.
貴金属の微粒子からなる金属微粒子触媒は、多くの水素化反応および酸化反応に対して高い活性を示すことが知られており、自動車排ガス浄化をはじめ、様々な分野で実用化されている。貴金属触媒は、高価で貴重である。 Metal fine particle catalysts composed of noble metal fine particles are known to exhibit high activity for many hydrogenation reactions and oxidation reactions, and have been put into practical use in various fields including automobile exhaust gas purification. Precious metal catalysts are expensive and valuable.
この貴金属触媒の最大の課題は、その触媒寿命を延ばすことである。貴金属触媒の寿命を決める支配要因の一つは、原料中に含まれる硫黄化合物による被毒である。 The biggest challenge of this noble metal catalyst is to extend its catalyst life. One of the controlling factors that determine the life of a noble metal catalyst is poisoning by sulfur compounds contained in the raw material.
硫黄または硫黄化合物で被毒された金属微粒子触媒を清浄化するために、２００℃以上の高温熱処理によるいわゆるヒートクリーニングが行われている。しかし、この高温熱処理法では、高分散状態で担持された金属微粒子の凝集が起こり、有効反応表面積が減少する。したがって、高温熱処理により表面が清浄化されたとしても、触媒活性は低下する。さらに、高温熱処理法では、化学的に活性な金属表面が部分的に酸化され、これも活性低下の原因となる。 In order to clean the metal fine particle catalyst poisoned with sulfur or a sulfur compound, so-called heat cleaning is performed by high-temperature heat treatment at 200 ° C. or higher. However, in this high-temperature heat treatment method, aggregation of metal fine particles supported in a highly dispersed state occurs, and the effective reaction surface area decreases. Therefore, even if the surface is cleaned by high-temperature heat treatment, the catalytic activity decreases. Furthermore, in the high-temperature heat treatment method, the chemically active metal surface is partially oxidized, which also causes a decrease in activity.
この問題を解決する典型的な技術が、特許文献１に記載されている。特許文献１の触媒の活性維持／再生方法は、触媒であるＰｄ（パラジウム）を固定させた酸化チタン粉末が硫化水素で被毒され、その被毒されたＰｄを固定させた酸化チタン粉末について、混合空気などの気相中で、紫外線を照射することにより被毒性を失わせる。 A typical technique for solving this problem is described in Patent Document 1. In the catalyst activity maintaining / regeneration method of Patent Document 1, titanium oxide powder to which Pd (palladium) as a catalyst is fixed is poisoned with hydrogen sulfide, and the titanium oxide powder to which the poisoned Pd is fixed is Toxicity is lost by irradiating ultraviolet rays in a gas phase such as mixed air.
気相中で光照射をする方法では、硫黄によって被毒された金などの触媒の活性を再生することは、困難である。 In the method of irradiating light in the gas phase, it is difficult to regenerate the activity of a catalyst such as gold poisoned by sulfur.
本発明の目的は、硫黄または硫黄化合物で被毒を受けた金属微粒子触媒表面を、効率よくクリーニングできる方法を提供することである。 An object of the present invention is to provide a method capable of efficiently cleaning the surface of a metal fine particle catalyst that has been poisoned with sulfur or a sulfur compound.
本発明は、半導体からなる担体と前記担体に担持されている金属触媒とを有する金属担持触媒であって、硫黄単体および硫黄化合物のうち少なくとも１種が金属触媒に吸着された金属担持触媒に、還元剤を含む水溶液中で、光を照射して、金属触媒に吸着された硫黄単体および硫黄化合物のうち少なくとも１種を除去する金属担持触媒のクリーニング方法であって、前記還元剤は、メタノール、エタノール、およびプロパノールのうち少なくとも１つであることを特徴とする金属担持触媒のクリーニング方法である。 The present invention is a metal-supported catalyst comprising a semiconductor support and a metal catalyst supported on the support, wherein at least one of sulfur alone and a sulfur compound is adsorbed on the metal catalyst . in an aqueous solution containing instead Motozai is irradiated with light, a method of cleaning a metal supported catalyst removing at least one of elemental sulfur and sulfur compounds adsorbed on the metal catalyst, the reducing agent is methanol , Ethanol, and propanol . A method for cleaning a metal-supported catalyst, wherein:
本発明に従えば、還元剤を含む水溶液中で、光を照射することによって、硫黄および硫黄化合物のうち少なくとも１種で被毒を受けた金属触媒表面から硫黄および硫黄化合物が、気相で光を照射する場合よりも水または還元剤を含む水溶液では誘電率が高いため脱着しやすくなる。したがって、金属触媒表面を効率よくクリーニングできる方法を提供することができる。 According to the present invention, instead of in an aqueous solution containing Motozai, by irradiating light, sulfur and sulfur compounds from the metal catalyst surfaces poisoned at least one of sulfur and sulfur compounds in the gas phase The aqueous solution containing water or a reducing agent has a higher dielectric constant than the case of irradiating with light, and thus is easily desorbed. Therefore, it is possible to provide a method capable of efficiently cleaning the metal catalyst surface.
本件発明者らは、鋭意研究の結果、金属触媒を半導体からなる担体上に担持した金属担持触媒を、メタノール、エタノール、プロパノールなどの還元剤を含む水溶液中で、光を照射して半導体を光励起することにより、金属触媒表面の硫黄または硫黄化合物からなる被毒物を効率よく還元除去できることを見出し、本発明を完成させた。 The inventors intensively studied, the metal-supported catalyst supported on a carrier comprising a metal catalyst from the semiconductor, methanol, ethanol, in an aqueous solution containing a reducing agent, such as propanol, the semiconductor is irradiated with light The inventors have found that the poisoning substance composed of sulfur or a sulfur compound on the surface of the metal catalyst can be efficiently reduced and removed by photoexcitation, and the present invention has been completed.
また本発明は、前記還元剤を含む水溶液は、流動されていることを特徴とする。 The present invention is an aqueous solution containing a pre Kikae Motozai is characterized in that it is flowing.
本発明に従えば、一旦、脱着した硫黄イオンが金属触媒に再吸着しにくくなり、短時間でクリーニングすることができる。 According to the present invention, once desorbed sulfur ions are difficult to re-adsorb to the metal catalyst, and cleaning can be performed in a short time.
また本発明は、前記金属触媒は、金、銀、白金、ロジウム、イリジウム、ニッケルおよびそれらの合金のうち少なくとも１つであることを特徴とする。 In the invention, it is preferable that the metal catalyst is at least one of gold, silver, platinum, rhodium, iridium, nickel, and alloys thereof.
本発明に従えば、これらの金属触媒が硫黄または硫黄化合物で被毒された場合に、金属触媒の活性を低下させることなく効率的にこれらの金属触媒のクリーニングをすることができる。 According to the present invention, when these metal catalysts are poisoned with sulfur or a sulfur compound, these metal catalysts can be efficiently cleaned without reducing the activity of the metal catalysts.
また、還元剤がメタノール、エタノール、プロパノールのうち少なくとも１つであるので、これらの１分子当り２電子を半導体に与える効果によって、硫黄または硫黄化合物で被毒を受けた金属触媒表面を、さらに効率よくクリーニングすることができる。 Also, the reducing agent is methanol, ethanol, since at least one of propanol, the effect of these per molecule 2 electrons in the semiconductor, a metal catalyst surfaces poisoned with sulfur or a sulfur compound, further It can be cleaned efficiently.
また本発明は、前記半導体は、アナタース型酸化チタン、ルチル型酸化チタン、酸化亜鉛およびチタン酸ストロンチウムのうち少なくとも１つであることを特徴とする。 In the invention, it is preferable that the semiconductor is at least one of anatase type titanium oxide, rutile type titanium oxide, zinc oxide, and strontium titanate.
本発明に従えば、半導体が、アナタース型酸化チタン、ルチル型酸化チタン、酸化亜鉛およびチタン酸ストロンチウムのうち少なくとも１つであるので、硫黄または硫黄化合物で被毒を受けた金属触媒表面を、効率よくクリーニングできる。 According to the present invention, since the semiconductor is at least one of anatase-type titanium oxide, rutile-type titanium oxide, zinc oxide, and strontium titanate, the surface of the metal catalyst that has been poisoned with sulfur or a sulfur compound is efficiently used. Can be cleaned well.
請求項１記載の本発明によれば、硫黄または硫黄化合物で被毒を受けた金属触媒表面を、効率よくクリーニングできる方法を提供することができる。 According to the first aspect of the present invention, it is possible to provide a method capable of efficiently cleaning the surface of a metal catalyst that has been poisoned with sulfur or a sulfur compound.
請求項２記載の本発明によれば、一旦、脱着した硫黄イオンが触媒に再吸着しにくくなり、短時間でクリーニングすることができる。 According to the second aspect of the present invention, once desorbed sulfur ions are difficult to re-adsorb to the catalyst, and cleaning can be performed in a short time.
請求項３記載の本発明によれば、硫黄または硫黄化合物で被毒されたこれらの金属を用いた触媒のクリーニングをすることができる。 According to the third aspect of the present invention, it is possible to clean the catalyst using these metals poisoned with sulfur or a sulfur compound.
請求項４記載の本発明によれば、硫黄または硫黄化合物で被毒を受けた金属触媒表面を、効率よくクリーニングできる方法を提供することができる。 According to the present invention of claim 4 Symbol mounting, it is possible to provide a method of sulfur or sulfur compounds undergo metal catalyst surface poisoning can be efficiently cleaned.
図１は、水中での硫黄化合物脱着機構を概念的に示す断面図である。本発明の一実施形態は、金属微粒子からなる金属触媒表面のクリーニング方法であって、還元剤を含む水溶液中での還元的な硫黄脱着現象を利用するものである。このクリーニング方法は、硫黄単体および硫黄化合物の少なくとも１種が吸着された金属触媒（以下、金属クラスターともいう。）を担持した半導体を、水または還元剤を含む水溶液中で、光を照射することにより、金属触媒上に吸着された硫黄単体および硫黄化合物の少なくとも１種を除去するものである。 FIG. 1 is a sectional view conceptually showing a sulfur compound desorption mechanism in water. An embodiment of the present invention is a cleaning method of a metal catalyst surface made of fine metal particles utilizes a reductive sulfur desorption phenomena in an aqueous solution containing instead Motozai. In this cleaning method, a semiconductor carrying a metal catalyst (hereinafter also referred to as a metal cluster) on which at least one of sulfur alone and a sulfur compound is adsorbed is irradiated with light in an aqueous solution containing water or a reducing agent. Thus, at least one of sulfur alone and sulfur compounds adsorbed on the metal catalyst is removed.
半導体である酸化チタンに光が照射されると、価電子帯に正孔が生成され、伝導帯に電子が生成される。価電子帯の正孔は、酸化反応を起こし、水を水素イオンと水酸基ラジカルに分離させる。また、伝導帯の電子は、還元反応を起こし、吸着された硫黄又は硫黄化合物に電子を与え硫黄又は硫黄化合物を脱着させる。半導体表面に担持された金属クラスターは、還元サイトとして働き、硫黄はアニオン状態で脱着するので、大きな誘電率を有する水により効率的に除去できる。一旦、脱着したイオンは、酸化チタンには吸着されない。 When titanium oxide, which is a semiconductor, is irradiated with light, holes are generated in the valence band and electrons are generated in the conduction band. The holes in the valence band cause an oxidation reaction and separate water into hydrogen ions and hydroxyl radicals. In addition, electrons in the conduction band cause a reduction reaction to give electrons to the adsorbed sulfur or sulfur compound and desorb the sulfur or sulfur compound. The metal cluster supported on the semiconductor surface functions as a reduction site, and sulfur is desorbed in an anionic state, so that it can be efficiently removed with water having a large dielectric constant. The ions once desorbed are not adsorbed on the titanium oxide.
還元剤を含む水溶液を流しながら、脱着させれば、金属触媒への再吸着を抑制することができるので脱着率は、飛躍的に増大する。このクリーニング方法を用いる際、たとえば、アルミナあるいはシリカなどにアナタース型酸化チタン、ルチル型酸化チタン、酸化亜鉛あるいはチタン酸ストロンチウムなどの半導体を担持させ、その半導体上に金、銀、白金、ロジウム、イリジウム、ニッケルおよびそれらの合金のうち少なくとも１つの金属触媒を担持させることができる。この金属触媒が担持された半導体がさらに担持されたアルミナおよびシリカなどを用いてハニカム構造体にした触媒などの金属微粒子が担持された半導体が固定された触媒を製造することができる。また、金属触媒を担持した半導体を焼結してハニカム構造体などの構造体にすることができる。この金属触媒がハニカム構造体に固定されているから金属触媒が溶媒中に流れ出すことがないので、水または還元剤を含む水溶液を流しながら、硫黄または硫黄化合物を効率よく脱着させることができる。 Changed while flowing an aqueous solution containing Motozai, if desorption, the desorption rate can be suppressed re-adsorption to the metal catalyst is dramatically increased. When using this cleaning method, for example, a semiconductor such as anatase-type titanium oxide, rutile-type titanium oxide, zinc oxide or strontium titanate is supported on alumina or silica, and gold, silver, platinum, rhodium, iridium is supported on the semiconductor. At least one metal catalyst of nickel and alloys thereof can be supported. A catalyst on which a semiconductor on which metal fine particles such as a catalyst having a honeycomb structure are supported using alumina and silica on which the semiconductor on which the metal catalyst is supported is further supported is fixed can be manufactured. Further, a semiconductor carrying a metal catalyst can be sintered to form a structure such as a honeycomb structure. Since this metal catalyst is fixed to the honeycomb structure, the metal catalyst does not flow out into the solvent, so that sulfur or a sulfur compound can be efficiently desorbed while flowing an aqueous solution containing water or a reducing agent.
図２は、メタノール中での硫黄脱着機構を示す概念図である。アルコールの中でも、メタノール、エタノール、プロパノールについては、同様の硫黄脱着機構による。メタノール、エタノール、プロパノールが半導体の光励起で価電子帯に生じた正孔により１電子酸化を受けると、非常に強い還元力を有するラジカルになる。このラジカルは、半導体の伝導帯にさらにもう１電子を直接注入する、すなわち、１分子当り２電子を半導体に与える（カレントダブリング効果）。これらの過剰電子が、一般に大きな仕事関数をもつ金属クラスターに移動し、その表面に強く吸着した硫黄または硫黄化合物を効率的に還元除去することができる。 FIG. 2 is a conceptual diagram showing a sulfur desorption mechanism in methanol. Among alcohols, methanol, ethanol, and propanol have the same sulfur desorption mechanism. When methanol, ethanol, or propanol is subjected to one-electron oxidation by holes generated in the valence band by photoexcitation of a semiconductor, it becomes a radical having a very strong reducing power. This radical directly injects another electron into the semiconductor conduction band, that is, gives two electrons per molecule to the semiconductor (current doubling effect). These excess electrons generally move to a metal cluster having a large work function, and sulfur or sulfur compounds strongly adsorbed on the surface can be efficiently reduced and removed.
金属触媒が、たとえば、金、銀、白金、ロジウム、イリジウム、ニッケル若しくはそれらの合金であるとき、本方法を好適に使用することができる。 When the metal catalyst is, for example, gold, silver, platinum, rhodium, iridium, nickel or an alloy thereof, this method can be suitably used.
金属触媒に、硫黄単体のみ吸着されている場合または硫黄化合物のみ吸着されている場合に限られず、硫黄単体および硫黄化合物が複数種類吸着されている場合についても好適に本方法を使用できる。 The present method can be suitably used not only in the case where only the sulfur element is adsorbed on the metal catalyst but also in the case where only the sulfur compound is adsorbed, and also when a plurality of kinds of sulfur element and sulfur compound are adsorbed.
半導体には、たとえば、アナタース型酸化チタン、ルチル型酸化チタン、酸化亜鉛若しくはチタン酸ストロンチウムを用いることができる。 As the semiconductor, for example, anatase type titanium oxide, rutile type titanium oxide, zinc oxide, or strontium titanate can be used.
還元剤を含む水溶液は、アルゴンをバブリングすることによって、還元剤を含む水溶液中から溶存酸素を脱気することが望ましい。水には、たとえば、蒸留水を用いることができる。また、ｐＨを調節することができる。ｐＨが４以下のとき脱着した硫黄イオンはほとんど全てＨ２Ｓガスになる。ｐＨ６で脱着した硫黄イオンはＨＳ−とＨ２Ｓガスが約半分ずつとなり、ｐＨが６を超え１０未満のときは主にＨＳ−となり、ｐＨが１０以上のときは主にＨＳ２−になる。したがって、ｐＨが４以下のときは、脱着した硫黄イオンはＨ２Ｓガスとなるので、金属触媒に再吸着することがない。還元剤を含む水溶液を流しながら光を照射する方法を用いる場合、再吸着することはほとんどないので、ｐＨとは関係なく本発明の方法を用いることが可能である。 Aqueous solution containing changed Motozai is by bubbling argon, I am desirable to degas the dissolved oxygen from an aqueous solution containing a varied Motozai. For example, distilled water can be used as the water. Moreover, pH can be adjusted. When the pH is 4 or less, almost all desorbed sulfur ions become H 2 S gas. The sulfur ions desorbed at pH 6 are approximately half of HS − and H 2 S gas, mainly HS − when the pH exceeds 6 and less than 10, and mainly HS 2 − when the pH is 10 or more. . Therefore, when the pH is 4 or less, the desorbed sulfur ions become H 2 S gas, and therefore do not re-adsorb to the metal catalyst. When using a method of irradiating light while flowing an aqueous solution containing a changed Motozai, since it is hardly adsorbed again, it is possible to use the method of the present invention regardless of the pH.
還元剤には、たとえば、メタノール、エタノールおよびプロパノールを用いることができる。また、還元剤として、蟻酸、酢酸などを用いることもできる。たとえば、還元剤としてエタノールを加えたとき、１．１ｍｏｌ・Ｌ−３での２０分間光を照射したときの硫黄脱着率が５８％であったことから、１．１ｍｏｌ・Ｌ−３以上であることが好ましい。エタノールの場合、正孔によって酸化されたラジカルが、さらに金クラスターなどの金属触媒へと電子を供与することが考えられるので、基本的に還元剤濃度は高ければ高いほど脱着効率は向上するものと示唆される。ただし、ｐＨが大きくアルカリへ偏る還元剤および濃度では、脱着後の硫黄分が溶媒に残り金属触媒へと再吸着する量が増大するので適当でない。 As the reducing agent, for example, methanol, ethanol and propanol can be used. Further, formic acid, acetic acid and the like can also be used as the reducing agent. For example, when ethanol is added as a reducing agent, the sulfur desorption rate when irradiated with light at 1.1 mol·L -3 for 20 minutes was 58%, so that it is 1.1 mol·L -3 or more. It is preferable. In the case of ethanol, radicals oxidized by holes can be considered to donate electrons to metal catalysts such as gold clusters. Therefore, the higher the concentration of the reducing agent, the higher the desorption efficiency. It is suggested. However, reducing agents and concentrations that have a large pH and are biased toward alkali are not suitable because the sulfur content after desorption remains in the solvent and the amount of readsorption to the metal catalyst increases.
液温は、溶媒が凍結しないことが好ましい。さらに、担持されている金属触媒のシンタリング現象および熱的な作用による脱着反応がほとんど進行しなければ、溶媒の沸点より低温であることが好ましい。 Liquid temperature, have preferred that the solvent does not freeze. Furthermore, unless substantially proceed desorption reaction by sintering behavior and thermal action of the metal catalyst supported, it has preferably to be cooler than the boiling point of the solvent.
照射する光の波長については、使用する半導体に応じて選択する。脱着が進行するためには、担体である半導体のバンド間遷移が生じる波長が必要である。たとえば、もっともバンドギャップの大きいＳｎＯ２については、３３０ｎｍ以下の波長がこれに該当する。 About the wavelength of the light to irradiate, it selects according to the semiconductor to be used. In order for desorption to proceed, a wavelength at which an interband transition of a semiconductor as a carrier occurs is necessary. For example, for SnO 2 having the largest band gap, a wavelength of 330 nm or less corresponds to this.
（金微粒子担持アナタース型酸化チタンの調製）
４．８６×１０−３ｍｏｌ・Ｌ−１の塩化金酸水溶液を調製し、ＮａＯＨを用いてｐＨを６に調整した。この塩化金酸水溶液を、温浴を用いて７０℃に保ったまま、１０ｇのアナタース型酸化チタン微粒子（Ａ−ＴｉＯ２、Ａ−１００、石原産業株式会社製）を加え、１時間撹拌を行った。このようにして得られた微粒子を、蒸留水で洗浄し、遠心分離により上澄み液を取り除く操作を３回行った。室温で真空乾燥後、空気雰囲気下で４００℃、４時間焼成を行い、金微粒子担持アナタース型酸化チタン（Ａｕ/Ａ−ＴｉＯ２）を合成した。
(Preparation of anatase-type titanium oxide carrying fine gold particles)
A chloroauric acid aqueous solution of 4.86 × 10 −3 mol·L −1 was prepared, and the pH was adjusted to 6 using NaOH. While maintaining this chloroauric acid aqueous solution at 70 ° C. using a warm bath, 10 g of anatase type titanium oxide fine particles (A-TiO 2 , A-100, manufactured by Ishihara Sangyo Co., Ltd.) were added and stirred for 1 hour. . The fine particles thus obtained were washed with distilled water, and the supernatant was removed by centrifugation three times. After vacuum drying at room temperature, firing was performed in an air atmosphere at 400 ° C. for 4 hours to synthesize gold fine particle-supported anatase-type titanium oxide (Au / A-TiO 2 ).
金微粒子担持ルチル型酸化チタン（Ａｕ/Ｒ−ＴｉＯ２）、金微粒子担持酸化鉄（Ａｕ/Ｆｅ２Ｏ３）、金微粒子担持酸化スズ（Ａｕ/ＳｎＯ２）、金微粒子担持チタン酸ストロンチウム（Ａｕ/ＳｒＴｉＯ３）、金微粒子担持酸化亜鉛（Ａｕ/ＺｎＯ）についても、金微粒子担持アナタース型酸化チタン（Ａｕ/Ａ−ＴｉＯ２）と同様に析出沈殿法を用いて合成した。白金微粒子担持アナタース型酸化チタン（Ｐｔ/Ａ−ＴｉＯ２）については、塩化白金酸水溶液にＡ−ＴｉＯ２を分散させた後、紫外光を照射し、Ａ−ＴｉＯ２と担持Ｐｔクラスターとの接合を強固にする目的で、アルゴン雰囲気下で焼成を行い、これをサンプルとして用いた。 Gold fine particle supported rutile titanium oxide (Au / R-TiO 2 ), gold fine particle supported iron oxide (Au / Fe 2 O 3 ), gold fine particle supported tin oxide (Au / SnO 2 ), gold fine particle supported strontium titanate (Au / SrTiO 3 ) and gold fine particle-supported zinc oxide (Au / ZnO) were synthesized using the precipitation method similarly to the gold fine particle-supported anatase-type titanium oxide (Au / A-TiO 2 ). For platinum fine particle-supported anatase-type titanium oxide (Pt / A-TiO 2 ), A-TiO 2 is dispersed in a chloroplatinic acid aqueous solution and then irradiated with ultraviolet light to join A-TiO 2 and the supported Pt cluster. For the purpose of strengthening, firing was performed in an argon atmosphere, and this was used as a sample.
図３は、金属触媒が半導体に担持されていることを示す透過型電子顕微鏡によって得られた画像である。図３（１）は、金がアナタース型酸化チタンに担持されていることを示す透過型電子顕微鏡によって得られた画像である。図３（２）は、金がルチル型酸化チタンに担持されていることを示す透過型電子顕微鏡によって得られた画像である。図３（３）は、金が酸化鉄に担持されていることを示す透過型電子顕微鏡によって得られた画像である。図３（４）は、金が酸化スズに担持されていることを示す透過型電子顕微鏡によって得られた画像である。図３（５）は、金がチタン酸ストロンチウムに担持されていることを示す透過型電子顕微鏡によって得られた画像である。図３（６）は、金が酸化亜鉛に担持されていることを示す透過型電子顕微鏡によって得られた画像である。 FIG. 3 is an image obtained by a transmission electron microscope showing that the metal catalyst is supported on the semiconductor. FIG. 3 (1) is an image obtained by a transmission electron microscope showing that gold is supported on anatase-type titanium oxide. FIG. 3 (2) is an image obtained by a transmission electron microscope showing that gold is supported on rutile titanium oxide. FIG. 3 (3) is an image obtained by a transmission electron microscope showing that gold is supported on iron oxide. FIG. 3 (4) is an image obtained by a transmission electron microscope showing that gold is supported on tin oxide. FIG. 3 (5) is an image obtained by a transmission electron microscope showing that gold is supported on strontium titanate. FIG. 3 (6) is an image obtained by a transmission electron microscope showing that gold is supported on zinc oxide.
金属触媒が多量に半導体に担持されると、金属触媒が光を吸収してしまい半導体が励起電子を生成するための十分な光が届かないので、金属触媒は、金属担持触媒の１０重量パーセント以下であることが好ましい。 If the metal catalyst is supported in a large amount on the semiconductor, the metal catalyst absorbs light and the semiconductor does not receive enough light to generate excited electrons. Therefore, the metal catalyst is 10 weight percent or less of the metal supported catalyst. It is preferable that
（単体硫黄を飽和吸着させた金微粒子担持酸化アナタース型チタンの調製）
１．０×１０−３ｍｏｌ・Ｌ−１の硫黄単体（Ｓ８）のエタノール溶液５００ｍＬを調製し、これに５ｇのＡｕ/Ａ−ＴｉＯ２微粒子を加え、２４時間室温で撹拌を行った。蒸留水で洗浄し、遠心分離により上澄み液を取り除く操作を３回行った後、室温で真空乾燥を行い、単体硫黄を飽和吸着させたＡｕ/Ａ−ＴｉＯ２微粒子（Ｓ−Ａｕ/Ａ−ＴｉＯ２）を得た。
(Preparation of gold fine particle-supported anatase titanium with saturated adsorption of elemental sulfur)
A 500 mL ethanol solution of 1.0 × 10 −3 mol·L −1 sulfur alone (S 8 ) was prepared, 5 g of Au / A-TiO 2 fine particles were added thereto, and the mixture was stirred at room temperature for 24 hours. After washing with distilled water and removing the supernatant by centrifugation three times, Au / A-TiO 2 fine particles (S-Au / A-TiO 2) which were vacuum-dried at room temperature and saturated sulfur was adsorbed 2 ) was obtained.
同様の方法により、単体硫黄を飽和吸着させたＡｕ/Ｒ−ＴｉＯ２微粒子（Ｓ−Ａｕ/Ｒ−ＴｉＯ２）、単体硫黄を飽和吸着させたＡｕ/Ｆｅ２Ｏ３微粒子（Ｓ−Ａｕ/Ｆｅ２Ｏ３）、単体硫黄を飽和吸着させたＡｕ/ＳｎＯ２微粒子（Ｓ−Ａｕ/ＳｎＯ２）、単体硫黄を飽和吸着させたＡｕ/ＳｒＴｉＯ３微粒子（Ｓ−Ａｕ/ＳｒＴｉＯ３）、単体硫黄を飽和吸着させたＡｕ/ＺｎＯ（Ｓ−Ａｕ/ＺｎＯ）を合成した。同様の方法により、単体硫黄を飽和吸着させたＰｔ/Ａ−ＴｉＯ２（Ｓ−Ａｕ/Ａ−ＴｉＯ２）を合成した。 By the same method, Au / R—TiO 2 fine particles (S—Au / R—TiO 2 ) in which simple sulfur is adsorbed by saturation, and Au / Fe 2 O 3 fine particles (S—Au / Fe in which simple sulfur is adsorbed in saturation). 2 O 3 ), Au / SnO 2 fine particles (S—Au / SnO 2 ) with saturated adsorption of simple sulfur, Au / SrTiO 3 fine particles (S—Au / SrTiO 3 ) with saturated adsorption of simple sulfur, and single sulfur Saturated adsorbed Au / ZnO (S-Au / ZnO) was synthesized. By the same method, elemental sulfur Pt / A-TiO 2 obtained by saturation adsorption (S-Au / A-TiO 2) was synthesized.
（実施例１）
ダブルジャケットタイプのパイレックス（登録商標）ガラス製反応容器（直径７５ｍｍ、高さ１００ｍｍ）の内層に、エタノール１５０ｍＬと蒸留水１００ｍＬを入れ、ここに１ｇのＳ−Ａｕ/Ａ−ＴｉＯ２を分散させ、アルゴン脱気を行いながら高圧水銀灯の光（λｅｘ＞３００ｎｍ、光の強度＝５．４ｍＷ・ｃｍ−２）を８時間照射した。微粒子を蒸留水で洗浄し、遠心分離により上澄み液を取り除く操作を３回行った後、真空乾燥を行った。さらに、このサンプルを、上記と同様の条件で７時間光照射し、洗浄と真空乾燥を行い、光クリーニング微粒子（Photo-cleaned Ａｕ/Ａ−ＴｉＯ２）を得た。
Example 1
In an inner layer of a double jacket type Pyrex (registered trademark) glass reaction vessel (diameter 75 mm, height 100 mm), ethanol 150 mL and distilled water 100 mL were placed, and 1 g of S-Au / A-TiO 2 was dispersed therein, While performing argon deaeration, irradiation with light of a high-pressure mercury lamp (λ ex > 300 nm, light intensity = 5.4 mW · cm −2 ) was performed for 8 hours. The operation of washing the fine particles with distilled water and removing the supernatant by centrifugation was performed three times, followed by vacuum drying. Further, this sample was irradiated with light for 7 hours under the same conditions as above, washed and vacuum dried to obtain photo-cleaned fine particles (Photo-cleaned Au / A-TiO 2).
（試験例１）
上述の触媒サンプル（Ａｕ/Ａ−ＴｉＯ２、Ｓ−Ａｕ/Ａ−ＴｉＯ２、またはPhoto-cleaned Ａｕ/Ａ−ＴｉＯ２）について、ベンジルアルコールからベンズアルデヒドへの酸化反応に対する触媒活性を調べた。溶媒としてジクロロエタン５ｇを用いて、これに触媒を０．０５ｇ、反応基質であるベンジルアルコールを１．０６ｇ、共酸化剤として５ｇの１０％Ｈ２Ｏ２と、ハロゲン化塩である０．０５ｇのテトラブチルアンモニウムブロマイドを加え、室温で１６時間反応を行った。反応の転化率（Conversion）およびベンズアルデヒド生成の選択率（Selectivity）を表１に示す。
(Test Example 1)
For the above-mentioned catalyst sample (Au / A-TiO 2, S-Au / A-TiO 2 or Photo-cleaned Au / A-TiO 2,), was investigated catalytic activity for the oxidation of benzyl alcohol to benzaldehyde. Using 5 g of dichloroethane as a solvent, 0.05 g of a catalyst, 1.06 g of benzyl alcohol as a reaction substrate, 5 g of 10% H 2 O 2 as a co-oxidant, and 0.05 g of a halide salt Tetrabutylammonium bromide was added and reacted at room temperature for 16 hours. Table 1 shows the conversion of the reaction (Conversion) and the selectivity of benzaldehyde production (Selectivity).
表１の結果から、硫黄が被毒された金触媒が担持された酸化チタンのベンジルアルコールからベンズアルデヒドへの部分酸化反応に対する触媒活性は、選択率が若干低下し、転化率が大幅に低下しているので、低下していることがわかる。この硫黄が被毒された金触媒が担持された酸化チタンを光照射することにより、選択率は硫黄で被毒される前よりも高まり、転化率は硫黄で被毒される前の転化率近くまで回復していることが分かる。したがって、本発明の金属触媒のクリーニング法を用いることによって、Ａｕ/ＴｉＯ２のベンジルアルコールからベンズアルデヒドへの部分酸化反応に対する触媒活性は、硫黄によって被毒される前の水準に回復している。 From the results in Table 1, the catalytic activity for the partial oxidation reaction of titanium oxide supported by sulfur poisoned gold catalyst from benzyl alcohol to benzaldehyde is slightly reduced in selectivity and greatly reduced in conversion rate. As you can see, it is decreasing. By irradiating titanium oxide loaded with this sulfur-poisoned gold catalyst, the selectivity is higher than that before being poisoned with sulfur, and the conversion rate is close to that before sulfur poisoning. It turns out that it has recovered to. Therefore, by using the metal catalyst cleaning method of the present invention, the catalytic activity for the partial oxidation reaction of Au / TiO 2 from benzyl alcohol to benzaldehyde is restored to the level before being poisoned by sulfur.
（試験例２）
ダブルジャケット型のパイレックス（登録商標）ガラス製反応容器（内径＝３１ｍｍ、高さ＝１５０ｍｍ）の内槽に、蒸留水５０ｍＬとＳ−Ａｕ／Ａ−ＴｉＯ２ ０．３５ｇを入れ、マグネティックスターラーでかくはんしながら、アルゴンガスを３０分間バブリングさせて脱気したのち、高圧水銀灯の紫外光（東芝（株）製：Ｈ−４００Ｐ、λｅｘ＞３００ｎｍ）を照射した。光照射中は、温度上昇を防ぐために、ダブルジャケット型反応容器の外槽に冷却水を流し続け（反応温度＝２５．０±０．５℃）、アルゴンでのバブリングもしつづけた。光照射後の各微粒子を遠心分離して回収し、蒸留水で３回洗浄したのちに、真空乾燥した。この乾燥微粒子０．２５ｇに、過酸化水素水１５ｍＬと蒸留水１５ｍＬを加え、５時間かくはんし、微粒子に吸着した硫黄を硫酸イオン（ＳＯ４ ２−）に酸化させ、遠心分離して上澄み液を回収した。さらに、メンブランフィルター（孔径＝０．２０μｍ）でろ過したのち、イオンクロマトグラフィーで、溶液中の硫酸イオンを定量した。
(Test Example 2)
In a double-jacketed Pyrex (registered trademark) glass reaction vessel (inner diameter = 31 mm, height = 150 mm), 50 mL of distilled water and 0.35 g of S-Au / A-TiO 2 are placed and stirred with a magnetic stirrer. Then, after degassing by bubbling argon gas for 30 minutes, ultraviolet light from a high-pressure mercury lamp (manufactured by Toshiba Corporation: H-400P, λ ex > 300 nm) was irradiated. During light irradiation, in order to prevent the temperature from rising, cooling water was continuously supplied to the outer tank of the double-jacketed reaction vessel (reaction temperature = 25.0 ± 0.5 ° C.), and bubbling with argon was continued. Each fine particle after light irradiation was collected by centrifugation, washed with distilled water three times, and then vacuum-dried. To 0.25 g of the dried fine particles, 15 mL of hydrogen peroxide water and 15 mL of distilled water are added and stirred for 5 hours to oxidize sulfur adsorbed on the fine particles to sulfate ions (SO 4 2− ), and then centrifuged to obtain a supernatant. It was collected. Further, after filtration through a membrane filter (pore size = 0.20 μm), sulfate ions in the solution were quantified by ion chromatography.
ダブルジャケット型のパイレックス（登録商標）ガラス製反応容器（内径＝８０ｍｍ、高さ＝１２５ｍｍ）の内槽に、Ｓ−Ａｕ／Ａ−ＴｉＯ２ ０．３５ｇを敷き詰め、高圧水銀灯の紫外光（東芝（株）製：Ｈ−４００Ｐ、λｅｘ＞３００ｎｍ）を照射した。ただし、気相での反応は、液相での反応の約６倍強い光量の紫外光を照射した（液相：０．３μＷｃｍ−２、気相：１．８μＷｃｍ−２）。光照射中は、ダブルジャケット型反応容器の外槽に冷却水を流し続けた（反応温度＝２５．０±０．５℃）。光照射後の各微粒子を遠心分離して回収し、蒸留水で３回洗浄したのちに、真空乾燥した。この乾燥微粒子０．１５ｇに、過酸化水素水１５ｍＬと蒸留水１５ｍＬを加え、５時間かくはんし、微粒子に吸着した硫黄を硫酸イオン（ＳＯ４ ２−）に酸化させ、遠心分離して上澄み液を回収した。さらに、メンブランフィルター（孔径=０．２０μｍ）でろ過したのち、イオンクロマトグラフィーで、溶液中の硫酸イオンを定量した。 A double-jacketed Pyrex (registered trademark) glass reaction vessel (inner diameter = 80 mm, height = 125 mm) was laid with 0.35 g of S-Au / A-TiO2 and ultraviolet light from a high-pressure mercury lamp (Toshiba Corporation). ): H-400P, λ ex > 300 nm). However, the reaction in the gas phase was irradiated with ultraviolet light having a light intensity about 6 times stronger than that in the liquid phase (liquid phase: 0.3 μWcm −2 , gas phase: 1.8 μWcm −2 ). During the light irradiation, the cooling water was continuously supplied to the outer tank of the double jacket type reaction vessel (reaction temperature = 25.0 ± 0.5 ° C.). Each fine particle after light irradiation was collected by centrifugation, washed with distilled water three times, and then vacuum-dried. To 0.15 g of the dried fine particles, 15 mL of hydrogen peroxide water and 15 mL of distilled water are added and stirred for 5 hours. The sulfur adsorbed on the fine particles is oxidized to sulfate ions (SO 4 2− ), and centrifuged to obtain a supernatant. It was collected. Further, after filtration through a membrane filter (pore size = 0.20 μm), sulfate ions in the solution were quantified by ion chromatography.
液相での硫黄の脱着率は２２％となり、気相での硫黄の脱着率は、−０．５％となった。したがって、気相中では、硫黄はほとんど脱着しないことが実証された。 The desorption rate of sulfur in the liquid phase was 22%, and the desorption rate of sulfur in the gas phase was -0.5%. Therefore, it was demonstrated that sulfur hardly desorbs in the gas phase.
（試験例３）
ダブルジャケット型のパイレックス（登録商標）ガラス製反応容器（内径＝３１ｍｍ、高さ＝１５０ｍｍ）の内槽に、蒸留水５０ｍＬとＳ−Ａｕ/Ａ−ＴｉＯ２ ０．３５ｇを入れ、マグネティックスターラーでかくはんしながら、アルゴンガスを３０分間バブリングさせて脱気したのち、高圧水銀灯の紫外光（東芝（株）製：Ｈ−４００Ｐ、λｅｘ＞３００ｎｍ）を照射した。光照射中は、温度上昇を防ぐために、ダブルジャケット型反応容器の外槽に冷却水を流し続け（反応温度＝２５．０±０．５℃）、アルゴンでのバブリングもし続けた。光照射後の各微粒子を遠心分離して回収し、蒸留水で３回洗浄したのちに、真空乾燥した。この乾燥微粒子０．２５ｇに、過酸化水素水１５ｍＬと蒸留水１５ｍＬを加え、５時間かくはんし、微粒子に吸着した硫黄を硫酸イオン（ＳＯ４ ２−）に酸化させ、遠心分離して上澄み液を回収した。さらに、メンブランフィルター（孔径＝０．２０μｍ）でろ過したのち、イオンクロマトグラフィーで、溶液中の硫酸イオンを定量した。また、アルゴンガスのバブリングによって脱気を行わない条件で紫外光を照射した（他の条件はすべて同じ）。この試験例３での硫黄の脱着率は以下の値となった。アルゴンガスでのバブリングによって脱気を行ったものは、２２％であり、アルゴンガスでのバブリングによって脱気を行わない酸素溶存下においては、１８％であった。したがって、アルゴンガスでのバブリングによって脱気を行うことが好ましい。
(Test Example 3)
In a double-jacketed Pyrex (registered trademark) glass reaction vessel (inner diameter = 31 mm, height = 150 mm), 50 mL of distilled water and 0.35 g of S-Au / A-TiO 2 are placed and stirred with a magnetic stirrer. Then, after degassing by bubbling argon gas for 30 minutes, ultraviolet light from a high-pressure mercury lamp (manufactured by Toshiba Corporation: H-400P, λ ex > 300 nm) was irradiated. During light irradiation, in order to prevent temperature rise, cooling water was continuously supplied to the outer tub of the double-jacketed reaction vessel (reaction temperature = 25.0 ± 0.5 ° C.), and bubbling with argon was also continued. Each fine particle after light irradiation was collected by centrifugation, washed with distilled water three times, and then vacuum-dried. To 0.25 g of the dried fine particles, 15 mL of hydrogen peroxide water and 15 mL of distilled water are added and stirred for 5 hours to oxidize sulfur adsorbed on the fine particles to sulfate ions (SO 4 2− ), and then centrifuged to obtain a supernatant. It was collected. Further, after filtration through a membrane filter (pore size = 0.20 μm), sulfate ions in the solution were quantified by ion chromatography. Moreover, the ultraviolet light was irradiated on the conditions which do not deaerate by bubbling of argon gas (all other conditions are the same). The sulfur desorption rate in Test Example 3 was as follows. 22% were degassed by bubbling with argon gas, and 18% when oxygen was not dissolved by bubbling with argon gas. Therefore, it is preferable to perform deaeration by bubbling with argon gas.
図４は、ｐＨ３において、ＳＨＥ（標準水素電極電位）を基準とした伝導帯端値と硫黄の脱着率の関係を示すグラフである。このグラフから、半導体が、ｐＨ３において、標準水素電極電位を基準として伝導帯端（Conduction Band edge）の電位が負電位である場合に、硫黄の脱着率が好ましいことがわかる。 FIG. 4 is a graph showing the relationship between the conduction band edge value and the sulfur desorption rate based on SHE (standard hydrogen electrode potential) at pH3. From this graph, it can be seen that when the semiconductor has a pH of 3 and the potential at the conduction band edge is negative with respect to the standard hydrogen electrode potential, the sulfur desorption rate is preferable.
図５は、白金および金触媒における光照射時間と硫黄脱着率との関係を示すグラフである。試験例２の液相中での硫黄脱着率の特定と同様にイオンクロマトグラフィで定量した。金だけでなく、最も有用な金属触媒である白金についても、光誘導−硫黄脱着が起こることが実証された。このデータにおいて、硫黄の脱着率が低いのは、バッチ系で反応を行っているので、金属触媒からの脱着と金属触媒への再吸着との平衡が起きるためである。 FIG. 5 is a graph showing the relationship between light irradiation time and sulfur desorption rate in platinum and gold catalysts. The amount was determined by ion chromatography in the same manner as in the determination of the sulfur desorption rate in the liquid phase of Test Example 2. It has been demonstrated that photoinduced-sulfur desorption occurs not only for gold but also for platinum, the most useful metal catalyst. In this data, the sulfur desorption rate is low because the reaction is carried out in a batch system, so that equilibrium between desorption from the metal catalyst and resorption onto the metal catalyst occurs.
本発明のクリーニング方法および金属触媒は、硫黄または硫黄化合物が被毒される環境で使用される金属触媒に用いることができる。たとえば、自動車、発電所および化学工場の排気ガスを浄化するための金属触媒およびその金属触媒をクリーニングする方法に応用できる。 The cleaning method and metal catalyst of the present invention can be used for a metal catalyst used in an environment in which sulfur or a sulfur compound is poisoned. For example, the present invention can be applied to a metal catalyst for purifying exhaust gas from automobiles, power plants, and chemical factories, and a method for cleaning the metal catalyst.
１ 金属触媒
２ 半導体
1 Metal catalyst 2 Semiconductor
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