JP4158850B2 - Carbon dioxide reduction method using photocatalyst - Google Patents
Carbon dioxide reduction method using photocatalyst Download PDFInfo
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- JP4158850B2 JP4158850B2 JP2002220494A JP2002220494A JP4158850B2 JP 4158850 B2 JP4158850 B2 JP 4158850B2 JP 2002220494 A JP2002220494 A JP 2002220494A JP 2002220494 A JP2002220494 A JP 2002220494A JP 4158850 B2 JP4158850 B2 JP 4158850B2
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- Prior art keywords
- carbon dioxide
- photocatalyst
- dioxide reduction
- copper
- cell
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- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 title claims description 114
- 239000001569 carbon dioxide Substances 0.000 title claims description 57
- 229910002092 carbon dioxide Inorganic materials 0.000 title claims description 57
- 239000011941 photocatalyst Substances 0.000 title claims description 38
- 238000000034 method Methods 0.000 title claims description 19
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 claims description 48
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 23
- 239000003054 catalyst Substances 0.000 claims description 22
- 239000002131 composite material Substances 0.000 claims description 22
- 239000004065 semiconductor Substances 0.000 claims description 21
- 239000010936 titanium Substances 0.000 claims description 18
- VODBHXZOIQDDST-UHFFFAOYSA-N copper zinc oxygen(2-) Chemical compound [O--].[O--].[Cu++].[Zn++] VODBHXZOIQDDST-UHFFFAOYSA-N 0.000 claims description 15
- BDAGIHXWWSANSR-UHFFFAOYSA-N methanoic acid Natural products OC=O BDAGIHXWWSANSR-UHFFFAOYSA-N 0.000 claims description 12
- OSWFIVFLDKOXQC-UHFFFAOYSA-N 4-(3-methoxyphenyl)aniline Chemical compound COC1=CC=CC(C=2C=CC(N)=CC=2)=C1 OSWFIVFLDKOXQC-UHFFFAOYSA-N 0.000 claims description 6
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical group [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 claims description 6
- 235000019253 formic acid Nutrition 0.000 claims description 6
- 229910052719 titanium Inorganic materials 0.000 claims description 6
- WSFSSNUMVMOOMR-NJFSPNSNSA-N methanone Chemical compound O=[14CH2] WSFSSNUMVMOOMR-NJFSPNSNSA-N 0.000 claims description 5
- 229910000510 noble metal Inorganic materials 0.000 claims description 5
- 150000001875 compounds Chemical class 0.000 claims description 3
- 239000000203 mixture Substances 0.000 claims description 2
- 238000006722 reduction reaction Methods 0.000 description 25
- 238000006243 chemical reaction Methods 0.000 description 20
- 239000012153 distilled water Substances 0.000 description 17
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Substances [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 16
- 239000012494 Quartz wool Substances 0.000 description 15
- 229910052739 hydrogen Inorganic materials 0.000 description 10
- 239000001257 hydrogen Substances 0.000 description 10
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 9
- 239000000047 product Substances 0.000 description 9
- 229910052697 platinum Inorganic materials 0.000 description 8
- 239000010453 quartz Substances 0.000 description 8
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 8
- CDBYLPFSWZWCQE-UHFFFAOYSA-L Sodium Carbonate Chemical compound [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 description 6
- 239000007864 aqueous solution Substances 0.000 description 5
- 239000010949 copper Substances 0.000 description 5
- XTVVROIMIGLXTD-UHFFFAOYSA-N copper(II) nitrate trihydrate Substances [Cu+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O XTVVROIMIGLXTD-UHFFFAOYSA-N 0.000 description 5
- 150000002894 organic compounds Chemical class 0.000 description 5
- 238000002441 X-ray diffraction Methods 0.000 description 4
- 230000001678 irradiating effect Effects 0.000 description 4
- 238000004519 manufacturing process Methods 0.000 description 4
- 239000000243 solution Substances 0.000 description 4
- ONDPHDOFVYQSGI-UHFFFAOYSA-N zinc nitrate Chemical compound [Zn+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O ONDPHDOFVYQSGI-UHFFFAOYSA-N 0.000 description 4
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 3
- WSFSSNUMVMOOMR-UHFFFAOYSA-N Formaldehyde Chemical compound O=C WSFSSNUMVMOOMR-UHFFFAOYSA-N 0.000 description 3
- 230000000052 comparative effect Effects 0.000 description 3
- 229910052802 copper Inorganic materials 0.000 description 3
- 239000002245 particle Substances 0.000 description 3
- 239000000843 powder Substances 0.000 description 3
- 150000003839 salts Chemical class 0.000 description 3
- 229910000029 sodium carbonate Inorganic materials 0.000 description 3
- 150000004684 trihydrates Chemical class 0.000 description 3
- 239000011701 zinc Substances 0.000 description 3
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 2
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 2
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 2
- 229910010413 TiO 2 Inorganic materials 0.000 description 2
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 description 2
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 2
- 235000019441 ethanol Nutrition 0.000 description 2
- -1 for example Substances 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- QSHDDOUJBYECFT-UHFFFAOYSA-N mercury Chemical compound [Hg] QSHDDOUJBYECFT-UHFFFAOYSA-N 0.000 description 2
- 229910052753 mercury Inorganic materials 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 2
- 239000011259 mixed solution Substances 0.000 description 2
- BWHMMNNQKKPAPP-UHFFFAOYSA-L potassium carbonate Chemical compound [K+].[K+].[O-]C([O-])=O BWHMMNNQKKPAPP-UHFFFAOYSA-L 0.000 description 2
- 239000002244 precipitate Substances 0.000 description 2
- 229910052725 zinc Inorganic materials 0.000 description 2
- 239000011787 zinc oxide Substances 0.000 description 2
- XLOMVQKBTHCTTD-UHFFFAOYSA-N zinc oxide Inorganic materials [Zn]=O XLOMVQKBTHCTTD-UHFFFAOYSA-N 0.000 description 2
- ZFYIQPIHXRFFCZ-QMMMGPOBSA-N (2s)-2-(cyclohexylamino)butanedioic acid Chemical compound OC(=O)C[C@@H](C(O)=O)NC1CCCCC1 ZFYIQPIHXRFFCZ-QMMMGPOBSA-N 0.000 description 1
- 229910005540 GaP Inorganic materials 0.000 description 1
- 229910002367 SrTiO Inorganic materials 0.000 description 1
- 239000011358 absorbing material Substances 0.000 description 1
- 150000001298 alcohols Chemical class 0.000 description 1
- 229910021529 ammonia Inorganic materials 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 229910052980 cadmium sulfide Inorganic materials 0.000 description 1
- 230000003197 catalytic effect Effects 0.000 description 1
- 238000009903 catalytic hydrogenation reaction Methods 0.000 description 1
- 239000007795 chemical reaction product Substances 0.000 description 1
- 239000003638 chemical reducing agent Substances 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 238000000151 deposition Methods 0.000 description 1
- 231100000676 disease causative agent Toxicity 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 150000002431 hydrogen Chemical class 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- VUZPPFZMUPKLLV-UHFFFAOYSA-N methane;hydrate Chemical compound C.O VUZPPFZMUPKLLV-UHFFFAOYSA-N 0.000 description 1
- 229910003465 moissanite Inorganic materials 0.000 description 1
- 239000004570 mortar (masonry) Substances 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 238000013032 photocatalytic reaction Methods 0.000 description 1
- CLSUSRZJUQMOHH-UHFFFAOYSA-L platinum dichloride Chemical compound Cl[Pt]Cl CLSUSRZJUQMOHH-UHFFFAOYSA-L 0.000 description 1
- 229910000027 potassium carbonate Inorganic materials 0.000 description 1
- 230000001376 precipitating effect Effects 0.000 description 1
- 238000010298 pulverizing process Methods 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 229910052707 ruthenium Inorganic materials 0.000 description 1
- 229910010271 silicon carbide Inorganic materials 0.000 description 1
- 239000011734 sodium Substances 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 239000004408 titanium dioxide Substances 0.000 description 1
- 238000010792 warming Methods 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
Images
Classifications
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P20/00—Technologies relating to chemical industry
- Y02P20/50—Improvements relating to the production of bulk chemicals
- Y02P20/52—Improvements relating to the production of bulk chemicals using catalysts, e.g. selective catalysts
Description
【0001】
【発明の属する技術分野】
本発明は、太陽光を利用して、水と二酸化炭素から有用な有機化合物、すなわちホルムアルデヒド、ギ酸、メチルアルコールを製造する方法に関するものである。
【0002】
【従来の技術】
地球温暖化の原因物質と目される二酸化炭素の固定化方法の1つとして、二酸化炭素を有用な有機化合物、例えばメチルアルコールやエチルアルコールに変換する試みが大きな注目を集めて久しい。
しかしながら、その変換には多量のエネルギーを必要とすることから、現状の技術では二酸化炭素を利用して有用な有機化合物を製造することはかなり難しい状況下にある。
【0003】
それに対して、最近工業的に利用され始めている光触媒は、無尽蔵の太陽エネルギーを化学エネルギーに変換できるという点において、上記の問題点を解決する1つの手段になりうる。
【0004】
二酸化炭素の還元固定化法の代表的なものとしては、鉄系又は銅系の二酸化炭素還元触媒の存在下で水素と二酸化炭素を暗反応させて、アルコール類を合成する接触水素化固定化法、金属電極上で二酸化炭素を直接還元する電気化学的固定化法が知られているが、前者は高温での触媒プロセスであり、後者は高い電力を必要とするため、いずれにしても二酸化炭素を固定化する場合には多量のエネルギーを消費するため、実用化の大きな障害となっている。
【0005】
一方、光触媒を用いて、二酸化炭素を固定化する試みは、1970年代の後半に既に提案されており、水銀光を水に懸濁させたTiO2 、ZnO、CdS、GaP、SiC、SrTiO3などの半導体粉末触媒に照射することで、ホルムアルデヒド、ギ酸、メタン、メチルアルコールを得ている〔「ネイチャア(Nature)」,第277巻,第637ページ(1979)〕。この反応は人工光ではなく、太陽光の照射によって行うのが理想的であるが、単に太陽光を照射するだけでは二酸化炭素の変換率が低く、実用に供することはできない。
【0006】
また、銅−酸化亜鉛系触媒の存在下で、二酸化炭素と水素とを反応させると、メチルアルコールが生成するが、これまで二酸化炭素と水を原料として太陽光の照射下で光反応によりメチルアルコールを効率よく製造する方法は知られていなかった。
【0007】
【発明が解決しようとする課題】
本発明は、このような事情のもとで、太陽光を光及び熱エネルギー源とし、効率よく二酸化炭素を還元してメチルアルコールその他の有用な化合物を製造することを目的としてなされたものである。
【0008】
【課題を解決するための手段】
本発明者らは、太陽光を用いて二酸化炭素を有用な有機化合物に変換するための方法について鋭意研究を重ねた結果、光触媒反応は、光照射により半導体表面に生成する電子と正孔の高い還元力及び酸化力を利用する反応であるが、この際ある種の半導体光触媒を用いると水を水素と酸素に分解して、この水素を二酸化炭素の還元剤として使用しうること、したがって、このようにして水素が生成すれば、これと二酸化炭素とを銅−酸化亜鉛系触媒の存在下で反応させることにより、メチルアルコールを製造しうることを見出し、この知見に基づいて本発明をなすに至った。
【0009】
すなわち、本発明は、半導体光触媒成分と銅−酸化亜鉛系二酸化炭素還元触媒成分とからなる複合光触媒の存在下で、水と二酸化炭素の混合物に太陽光を照射し、ホルムアルデヒド、ギ酸及びメチルアルコールから選ばれる少なくとも1種の化合物を生成させることを特徴とする二酸化炭素還元方法を提供するものである。
【0010】
【発明の実施の形態】
本発明方法においては、半導体光触媒成分と銅−酸化亜鉛系二酸化炭素還元触媒成分からなる複合光触媒を用いることが必要である。
上記の半導体光触媒成分としては、例えばチタン系層状複合酸化物に貴金属助触媒を担持させたものが用いられる。そして、このチタン系層状複合酸化物の例としては、TiO2、Na2Ti6O13、K2Ti6O13、KTiNbO5などを挙げることができ、貴金属助触媒の例としては、Pt、Ni、Ruなどを挙げることができる。この助触媒の担持量は、チタン系層状複合酸化物と助触媒との合計質量に基づき0.1〜1.0質量%、好ましくは0.2〜0.4質量%の範囲で選ばれる。
【0011】
チタン系層状複合酸化物に助触媒を担持させる方法には、特に制限はなく、一般に助触媒を主触媒に担持させる場合に慣用されている方法の中から任意に選ぶことができるが、チタン系層状複合酸化物に助触媒形成材料、例えば貴金属の可溶性塩を含む溶液を含浸させたのち、焼成する方法か、助触媒形成材料を含む溶液中にチタン系層状複合酸化物粒子を分散させ、光を照射して当該粒子表面に貴金属を沈積させる光デポジション法が有利である。特に後者は、白金族金属を担持させる場合に好適である。
【0012】
次に、銅−酸化亜鉛系二酸化炭素還元触媒成分は、例えば、銅と亜鉛の各水溶性塩を所定の割合で含む水溶液に、炭酸ナトリウムやアンモニアなどの沈殿剤を含む水溶液を加えて沈殿を形成させ、得られた沈殿を分別し、洗浄後350〜500℃で焼成し、かつ200〜450℃で水素還元することによって得られる。
【0013】
本発明方法で用いる二酸化炭素還元用複合光触媒は、前記の半導体光触媒成分と二酸化炭素還元触媒成分とを質量比1:5ないし5:1、好ましくは1:2ないし2:1の割合で混合し、粉砕後、100〜850μmの粒径に造粒することによって製造することができる。
【0014】
この場合、半導体光触媒成分に、銅と亜鉛の各水溶性塩を含む水溶液を含浸させ、その半導体光触媒成分を含む溶液を蒸発乾固したのち、乾燥し、焼成及び還元することによっても、所望の二酸化炭素還元用複合光触媒を製造することができる。この方法によれば、半導体光触媒と二酸化炭素還元触媒が、ち密に接触し合う形となるので、半導体光触媒上で生成した水素が二酸化炭素還元触媒に移動しやすくなり、効率よくメチルアルコールを生成させることができる。また、本発明方法によると、メチルアルコール以外にもホルムアルデヒドやギ酸を生成させることもできる。
【0015】
本発明方法においては、例えば石英製太陽光受光セル中に吸水材料、例えば蒸留水を吸収させた石英ウールを充填し、その上に二酸化炭素還元用複合光触媒を配置し、50〜300kPaの圧力で二酸化炭素を導入し、太陽光を照射することによって光反応させることができる。この際の二酸化炭素の供給速度としては、二酸化炭素還元用複合光触媒の質量に基づき、1〜100ml/分、好ましくは5〜20ml/分の範囲で選ばれる。
【0016】
【実施例】
次に、本発明を実施例によりさらに詳細に説明するが、本発明はこれらの例によってなんら限定されるものではない。
【0017】
実施例1
硝酸銅(II)三水和物と硝酸亜鉛(II)三水和物の混合溶液(それぞれ1.0モル/リットル)に炭酸ナトリウム水溶液(1.1モル/リットル)を滴下し、沈殿物をろ過、洗浄したのち、350℃で2時間焼成した。さらに300℃で3時間、水素気流中(20ml/分)で還元することによって、銅−酸化亜鉛系二酸化炭素還元触媒を調製した。
【0018】
次に、炭酸カリウム0.0208モルと、二酸化チタン0.125モルとを、蒸留水80mlに加え、かき混ぜながら蒸発乾固した。得られた固形物を乾燥したのち、空気中940℃で2時間焼成することによりK2Ti6O13を得た。このようにして得たK2Ti6O13粉末3.0gを2モル/リットル濃度の炭酸ナトリウム水溶液60mlと0.1%塩化白金水溶液9mlに加え、よく分散させたのち、水銀ランプを10時間照射して白金を担持させた。このようにして得た0.3質量%の白金を担持したK2Ti6O13を120℃で12時間乾燥した。
【0019】
石英製太陽光受光セルの底部に、石英ウールを入れ、蒸留水2.0mlを加え、さらに受光セルの石英ウール上部に、上記の銅−酸化亜鉛系二酸化炭素還元触媒0.15gと0.3質量%の白金を担持したK2Ti6O13半導体光触媒0.15gを2層に分けて入れ、蒸留水2.0mlを加えた。次いで受光セル内部を真空脱気したのち、二酸化炭素を2×105Pa導入し、太陽光を6時間照射した。この際のセル中の最高反応温度は300℃であった。このようにして得た生成物を表1に示す。
【0020】
実施例2
石英製太陽光受光セルの底部に石英ウールを入れ、蒸留水2.0mlを加えた。さらに、石英ウール上部に、実施例1で得た銅−酸化亜鉛系二酸化炭素還元触媒0.15gと同じく実施例1で得た0.3質量%の白金を担持したK2Ti6O13半導体光触媒0.30gを2層に分けて受光セルに入れ、蒸留水2.0mlを加えた。受光セル内部を真空脱気したのち、二酸化炭素を2×105Pa導入し、太陽光を反応セルに6時間照射した。この際のセル中の最高反応温度は280℃であった。このようにして得た生成物を表1に示す。
【0021】
実施例3
実施例1で得た銅−酸化亜鉛系二酸化炭素還元触媒0.15gと実施例1で得た0.3質量%の白金を担持したK2Ti6O13半導体光触媒0.15gを乳鉢で混合することによって、二酸化炭素還元用複合光触媒を調製した。
石英製太陽光受光セルの底部に石英ウールを入れ、蒸留水2.0mlを加えた。さらに、石英ウール上部に、このようにして得た複合化光触媒0.30gを受光セルに入れ、蒸留水2.0mlを加えた。受光セル内部を真空脱気したのち、二酸化炭素を2×105Pa導入し、太陽光を反応セルに6時間照射した。この際のセル中の最高反応温度は303℃であった。このようにして得た生成物を表1に示す。
【0022】
実施例4
硝酸銅(II)三水和物と硝酸亜鉛(II)三水和物の混合溶液に実施例1で得たK2Ti6O13粉末を加え、蒸発乾固を行った。蒸発乾固物を乳棒で粉砕したのち、空気中、600℃で2時間焼成し、水素気流(流量=20ml/分)中、300℃で6時間還元した。各成分の質量比は、Cu:Zn:K2Ti6O13=0.05:0.05:0.9とした。その後、この複合化光触媒に助触媒である白金を0.3質量%光担持させた。得られた複合体のXRDパターンを図1に示す。XRDパターンにおいては、Cu/ZnOとK2Ti6O13のピーク以外は認められず、銅−酸化亜鉛系触媒成分を担持した半導体光触媒が得られたことが分る。
【0023】
石英製太陽光受光セルの底部に石英ウールを入れ、蒸留水2.0mlを加えた。さらに、石英ウール上部に、このようにして得た複合化光触媒0.30gを受光セルに入れ、蒸留水2.0mlを加えた。受光セル内部を真空脱気したのち、二酸化炭素を2×105Pa導入し、太陽光を反応セルに6時間照射した。この際、セル中の最高反応温度は312℃であった。このようにして得られた生成物を表1に示す。
【0024】
実施例5
石英製太陽光受光セルの底部に石英ウールを入れ、蒸留水2.0mlを加えた。さらに、石英ウール上部に、実施例3で得た複合化光触媒0.30gを受光セルに入れ、蒸留水2.0mlを加えた。受光セル内部を真空脱気したのち、二酸化炭素を1×105Pa導入し、太陽光を反応セルに6時間照射した。この際、セル中の最高反応温度は275℃であった。このようにして得た生成物を表1に示す。
【0025】
比較例1
石英製太陽光受光セルの底部に、石英ウールを入れ、蒸留水2.0mlを加えた。さらに、石英ウール上部に、実施例1で得た銅−酸化亜鉛系二酸化炭素還元触媒0.30gを受光セルに入れ、蒸留水2.0mlを加えた。受光セル内部を真空脱気したのち、二酸化炭素を2×105Pa導入し、太陽光を反応セルに6時間照射した。この際、セル中の最高反応温度は310℃であった。得られた生成物を表1に示す。この場合、反応生成物が得られなかったことから、銅−酸化亜鉛系二酸化炭素還元触媒のみでは、二酸化炭素は還元されないことが分る。
【0026】
比較例2
石英製太陽光受光セルの底部に石英ウールを入れ、蒸留水2.0mlを加えた。さらに、石英ウール上部に、実施例1で得た0.3質量%の白金を担持したK2Ti6O13半導体光触媒0.30gを受光セルに入れ、蒸留水2.0mlを加えた。受光セル内部を真空脱気したのち、二酸化炭素を2×105Pa導入し、太陽光を反応セルに6時間照射した。この際、セル中の最高反応温度は290℃であった。このようにして得た生成物を表1に示す。この場合には、メチルアルコールの生成を確認できないことから、メチルアルコールの生成には、銅−酸化亜鉛系二酸化炭素還元触媒が必要であり、また実施例1〜3の結果と合わせて考えると、半導体光触媒上で生成した水素が銅−酸化亜鉛系二酸化炭素還元触媒に移動することで二酸化炭素が還元され、メチルアルコールが生成することが分る。
【0027】
比較例3
薄型円筒状受光セルに、濾紙上に静置した実施例3で得た複合化光触媒0.30gを入れ、蒸留水4.0mlを加えた。受光セル内部を真空脱気したのち、二酸化炭素を1×105Pa導入し、太陽光を6時間照射した。この場合、反応温度は20℃であった。このようにして得た生成物を表1に示す。この結果より、メチルアルコールの生成には、高い反応温度が必要であることが分る。
【0028】
【表1】
【0029】
【発明の効果】
本発明によれば、太陽のエネルギーを利用して、二酸化炭素の還元反応を高い効率で行わせることにより、ホルムアルデヒド、ギ酸、メチルアルコールなどの有用な有機化合物を製造することができる。
【図面の簡単な説明】
【図1】 二酸化炭素還元用複合光触媒の1例のXRDパターン。
【図2】 半導体光触媒の1例のXRDパターン。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing useful organic compounds, that is, formaldehyde, formic acid, and methyl alcohol from water and carbon dioxide using sunlight.
[0002]
[Prior art]
As one of the methods for fixing carbon dioxide, which is considered to be a causative agent of global warming, attempts to convert carbon dioxide into useful organic compounds such as methyl alcohol and ethyl alcohol have been attracting much attention for a long time.
However, since a large amount of energy is required for the conversion, it is quite difficult to produce useful organic compounds using carbon dioxide with the current technology.
[0003]
On the other hand, a photocatalyst that has recently begun to be used industrially can be a means for solving the above problems in that inexhaustible solar energy can be converted into chemical energy.
[0004]
A typical carbon dioxide reduction and immobilization method is a catalytic hydrogenation immobilization method that synthesizes alcohols by dark reaction of hydrogen and carbon dioxide in the presence of an iron-based or copper-based carbon dioxide reduction catalyst. There is known an electrochemical immobilization method that directly reduces carbon dioxide on a metal electrode. However, the former is a catalytic process at a high temperature, and the latter requires high power. In the case of fixing a large amount of energy, a large amount of energy is consumed, which is a major obstacle to practical use.
[0005]
On the other hand, attempts to fix carbon dioxide using a photocatalyst have already been proposed in the latter half of the 1970s, such as TiO 2 , ZnO, CdS, GaP, SiC, SrTiO 3 and the like in which mercury light is suspended in water. The formaldehyde, formic acid, methane, and methyl alcohol are obtained by irradiating the semiconductor powder catalyst [Nature, Vol. 277, page 637 (1979)]. This reaction is ideally performed by irradiating sunlight instead of artificial light, but simply converting it to sunlight does not provide a practical conversion rate for carbon dioxide and cannot be put to practical use.
[0006]
In addition, when carbon dioxide and hydrogen are reacted in the presence of a copper-zinc oxide catalyst, methyl alcohol is produced. Until now, carbon dioxide and water are used as raw materials, and methyl alcohol is produced by photoreaction under sunlight irradiation. There has been no known method for efficiently producing the.
[0007]
[Problems to be solved by the invention]
Under such circumstances, the present invention has been made for the purpose of producing methyl alcohol and other useful compounds by efficiently reducing carbon dioxide using sunlight as a light and heat energy source. .
[0008]
[Means for Solving the Problems]
As a result of intensive studies on a method for converting carbon dioxide into useful organic compounds using sunlight, the present inventors have found that the photocatalytic reaction has a high number of electrons and holes generated on the semiconductor surface by light irradiation. This is a reaction that uses reducing power and oxidizing power. In this case, when a certain type of semiconductor photocatalyst is used, water can be decomposed into hydrogen and oxygen, and this hydrogen can be used as a reducing agent for carbon dioxide. Thus, when hydrogen is produced, it is found that methyl alcohol can be produced by reacting this with carbon dioxide in the presence of a copper-zinc oxide catalyst, and the present invention is made based on this finding. It came.
[0009]
That is, the present invention irradiates a mixture of water and carbon dioxide with sunlight in the presence of a composite photocatalyst composed of a semiconductor photocatalyst component and a copper-zinc oxide-based carbon dioxide reduction catalyst component, from formaldehyde, formic acid and methyl alcohol. The present invention provides a carbon dioxide reduction method characterized by producing at least one selected compound.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
In the method of the present invention, it is necessary to use a composite photocatalyst comprising a semiconductor photocatalyst component and a copper-zinc oxide-based carbon dioxide reduction catalyst component.
As said semiconductor photocatalyst component, what carried the noble metal promoter on the titanium system layered complex oxide is used, for example. Examples of the titanium-based layered composite oxide include TiO 2 , Na 2 Ti 6 O 13 , K 2 Ti 6 O 13 , KTiNbO 5 , and examples of the noble metal promoter include Pt, Ni, Ru, etc. can be mentioned. The amount of the cocatalyst supported is selected in the range of 0.1 to 1.0 mass%, preferably 0.2 to 0.4 mass%, based on the total mass of the titanium-based layered composite oxide and the cocatalyst.
[0011]
The method for supporting the cocatalyst on the titanium-based layered composite oxide is not particularly limited, and can be arbitrarily selected from methods generally used when the cocatalyst is supported on the main catalyst. The layered composite oxide is impregnated with a solution containing a cocatalyst-forming material, such as a soluble salt of a noble metal, and then calcined, or the titanium-based layered composite oxide particles are dispersed in a solution containing the cocatalyst-forming material to produce light. An optical deposition method in which a noble metal is deposited on the surface of the particles by irradiating is advantageous. The latter is particularly suitable when a platinum group metal is supported.
[0012]
Next, the copper-zinc oxide-based carbon dioxide reduction catalyst component is precipitated, for example, by adding an aqueous solution containing a precipitating agent such as sodium carbonate or ammonia to an aqueous solution containing each water-soluble salt of copper and zinc at a predetermined ratio. The precipitate obtained is formed, fractionated, washed, calcined at 350 to 500 ° C., and hydrogen reduced at 200 to 450 ° C.
[0013]
In the composite photocatalyst for carbon dioxide reduction used in the method of the present invention, the semiconductor photocatalyst component and the carbon dioxide reduction catalyst component are mixed in a mass ratio of 1: 5 to 5: 1, preferably 1: 2 to 2: 1. After pulverization, it can be produced by granulating to a particle size of 100 to 850 μm.
[0014]
In this case, the semiconductor photocatalyst component is impregnated with an aqueous solution containing each of the water-soluble salts of copper and zinc, and the solution containing the semiconductor photocatalyst component is evaporated to dryness, then dried, calcined and reduced. A composite photocatalyst for carbon dioxide reduction can be produced. According to this method, since the semiconductor photocatalyst and the carbon dioxide reduction catalyst are in close contact with each other, hydrogen generated on the semiconductor photocatalyst is easily transferred to the carbon dioxide reduction catalyst, and methyl alcohol is efficiently generated. be able to. Moreover, according to the method of the present invention, formaldehyde and formic acid can be generated in addition to methyl alcohol.
[0015]
In the method of the present invention, for example, a quartz solar light receiving cell is filled with a water-absorbing material, for example, quartz wool having absorbed distilled water, and a composite photocatalyst for carbon dioxide reduction is disposed thereon, and the pressure is 50 to 300 kPa. Photoreaction can be performed by introducing carbon dioxide and irradiating sunlight. The supply rate of carbon dioxide at this time is selected in the range of 1 to 100 ml / min, preferably 5 to 20 ml / min, based on the mass of the composite photocatalyst for carbon dioxide reduction.
[0016]
【Example】
EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples.
[0017]
Example 1
An aqueous sodium carbonate solution (1.1 mol / liter) was dropped into a mixed solution of copper (II) nitrate trihydrate and zinc nitrate (II) trihydrate (each 1.0 mol / liter), and the precipitate was After filtration and washing, it was calcined at 350 ° C. for 2 hours. Further, a copper-zinc oxide-based carbon dioxide reduction catalyst was prepared by reduction in a hydrogen stream (20 ml / min) at 300 ° C. for 3 hours.
[0018]
Next, 0.0208 mol of potassium carbonate and 0.125 mol of titanium dioxide were added to 80 ml of distilled water and evaporated to dryness while stirring. The obtained solid was dried and then calcined in air at 940 ° C. for 2 hours to obtain K 2 Ti 6 O 13 . After adding 3.0 g of the K 2 Ti 6 O 13 powder thus obtained to 60 ml of 2 mol / liter sodium carbonate aqueous solution and 9 ml of 0.1% platinum chloride aqueous solution and dispersing well, the mercury lamp was turned on for 10 hours. Irradiation supported platinum. The K 2 Ti 6 O 13 carrying 0.3% by mass of platinum thus obtained was dried at 120 ° C. for 12 hours.
[0019]
Quartz solar light receiving cell is filled with quartz wool, and 2.0 ml of distilled water is added thereto. Further, the above copper-zinc oxide based carbon dioxide reduction catalysts 0.15 g and 0.3 are placed on the quartz wool upper portion of the light receiving cell. 0.15 g of a K 2 Ti 6 O 13 semiconductor photocatalyst carrying platinum in mass% was added in two layers, and 2.0 ml of distilled water was added. Next, after the inside of the light receiving cell was vacuum degassed, carbon dioxide was introduced at 2 × 10 5 Pa and sunlight was irradiated for 6 hours. The maximum reaction temperature in the cell at this time was 300 ° C. The products thus obtained are shown in Table 1.
[0020]
Example 2
Quartz wool was put into the bottom of the quartz solar cell and 2.0 ml of distilled water was added. Furthermore, a K 2 Ti 6 O 13 semiconductor carrying 0.3% by mass of platinum obtained in Example 1 as well as 0.15 g of the copper-zinc oxide-based carbon dioxide reduction catalyst obtained in Example 1 on the quartz wool. 0.30 g of photocatalyst was divided into two layers and placed in a light-receiving cell, and 2.0 ml of distilled water was added. After the inside of the light receiving cell was vacuum degassed, carbon dioxide was introduced at 2 × 10 5 Pa, and the reaction cell was irradiated with sunlight for 6 hours. The maximum reaction temperature in the cell at this time was 280 ° C. The products thus obtained are shown in Table 1.
[0021]
Example 3
0.15 g of the copper-zinc oxide carbon dioxide reduction catalyst obtained in Example 1 and 0.15 g of the K 2 Ti 6 O 13 semiconductor photocatalyst carrying 0.3% by mass of platinum obtained in Example 1 were mixed in a mortar. Thus, a composite photocatalyst for carbon dioxide reduction was prepared.
Quartz wool was put into the bottom of the quartz solar cell and 2.0 ml of distilled water was added. Further, 0.30 g of the composite photocatalyst thus obtained was placed in the light receiving cell on top of the quartz wool, and 2.0 ml of distilled water was added. After the inside of the light receiving cell was vacuum degassed, carbon dioxide was introduced at 2 × 10 5 Pa, and the reaction cell was irradiated with sunlight for 6 hours. The maximum reaction temperature in the cell at this time was 303 ° C. The products thus obtained are shown in Table 1.
[0022]
Example 4
The K 2 Ti 6 O 13 powder obtained in Example 1 was added to a mixed solution of copper nitrate (II) trihydrate and zinc nitrate (II) trihydrate, and evaporated to dryness. The evaporated and dried product was pulverized with a pestle, calcined in air at 600 ° C. for 2 hours, and reduced in a hydrogen stream (flow rate = 20 ml / min) at 300 ° C. for 6 hours. The mass ratio of each component was Cu: Zn: K 2 Ti 6 O 13 = 0.05: 0.05: 0.9. Thereafter, this composite photocatalyst was supported with 0.3% by mass of platinum as a promoter. The XRD pattern of the obtained complex is shown in FIG. In the XRD pattern, except for Cu / ZnO and K 2 Ti 6 O 13 peaks, no semiconductor photocatalyst carrying a copper-zinc oxide catalyst component was obtained.
[0023]
Quartz wool was put into the bottom of the quartz solar cell and 2.0 ml of distilled water was added. Further, 0.30 g of the composite photocatalyst thus obtained was placed in the light receiving cell on top of the quartz wool, and 2.0 ml of distilled water was added. After the inside of the light receiving cell was vacuum degassed, carbon dioxide was introduced at 2 × 10 5 Pa, and the reaction cell was irradiated with sunlight for 6 hours. At this time, the maximum reaction temperature in the cell was 312 ° C. The products thus obtained are shown in Table 1.
[0024]
Example 5
Quartz wool was put into the bottom of the quartz solar cell and 2.0 ml of distilled water was added. Furthermore, 0.30 g of the composite photocatalyst obtained in Example 3 was placed in the light receiving cell on top of the quartz wool, and 2.0 ml of distilled water was added. After the inside of the light receiving cell was vacuum degassed, carbon dioxide was introduced at 1 × 10 5 Pa, and the reaction cell was irradiated with sunlight for 6 hours. At this time, the maximum reaction temperature in the cell was 275 ° C. The products thus obtained are shown in Table 1.
[0025]
Comparative Example 1
Quartz wool was put into the bottom of the quartz solar cell, and 2.0 ml of distilled water was added. Further, 0.30 g of the copper-zinc oxide-based carbon dioxide reduction catalyst obtained in Example 1 was placed in the light receiving cell on top of the quartz wool, and 2.0 ml of distilled water was added. After the inside of the light receiving cell was vacuum degassed, carbon dioxide was introduced at 2 × 10 5 Pa, and the reaction cell was irradiated with sunlight for 6 hours. At this time, the maximum reaction temperature in the cell was 310 ° C. The resulting products are shown in Table 1. In this case, since the reaction product was not obtained, it is understood that carbon dioxide is not reduced only by the copper-zinc oxide-based carbon dioxide reduction catalyst.
[0026]
Comparative Example 2
Quartz wool was put into the bottom of the quartz solar cell and 2.0 ml of distilled water was added. Further, 0.30 g of a K 2 Ti 6 O 13 semiconductor photocatalyst carrying 0.3% by mass of platinum obtained in Example 1 was placed in a light receiving cell on top of quartz wool, and 2.0 ml of distilled water was added. After the inside of the light receiving cell was vacuum degassed, carbon dioxide was introduced at 2 × 10 5 Pa, and the reaction cell was irradiated with sunlight for 6 hours. At this time, the maximum reaction temperature in the cell was 290 ° C. The products thus obtained are shown in Table 1. In this case, since the production of methyl alcohol cannot be confirmed, the production of methyl alcohol requires a copper-zinc oxide-based carbon dioxide reduction catalyst, and when considered together with the results of Examples 1 to 3, It can be seen that the hydrogen produced on the semiconductor photocatalyst moves to the copper-zinc oxide-based carbon dioxide reduction catalyst to reduce the carbon dioxide and produce methyl alcohol.
[0027]
Comparative Example 3
Into a thin cylindrical light-receiving cell, 0.30 g of the composite photocatalyst obtained in Example 3 placed on a filter paper was placed, and 4.0 ml of distilled water was added. After the inside of the light receiving cell was vacuum degassed, carbon dioxide was introduced at 1 × 10 5 Pa and sunlight was irradiated for 6 hours. In this case, the reaction temperature was 20 ° C. The products thus obtained are shown in Table 1. From this result, it can be seen that a high reaction temperature is required for the production of methyl alcohol.
[0028]
[Table 1]
[0029]
【The invention's effect】
According to the present invention, a useful organic compound such as formaldehyde, formic acid, methyl alcohol, and the like can be produced by performing the reduction reaction of carbon dioxide with high efficiency using solar energy.
[Brief description of the drawings]
FIG. 1 is an XRD pattern of one example of a composite photocatalyst for carbon dioxide reduction.
FIG. 2 is an XRD pattern of one example of a semiconductor photocatalyst.
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