JP4296259B2 - Method for producing hydrogen - Google Patents
Method for producing hydrogen Download PDFInfo
- Publication number
- JP4296259B2 JP4296259B2 JP2003129083A JP2003129083A JP4296259B2 JP 4296259 B2 JP4296259 B2 JP 4296259B2 JP 2003129083 A JP2003129083 A JP 2003129083A JP 2003129083 A JP2003129083 A JP 2003129083A JP 4296259 B2 JP4296259 B2 JP 4296259B2
- Authority
- JP
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- Prior art keywords
- photocatalyst
- hydrogen
- titanium oxide
- graphite silica
- alcohol
- Prior art date
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Links
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 title claims description 40
- 229910052739 hydrogen Inorganic materials 0.000 title claims description 40
- 239000001257 hydrogen Substances 0.000 title claims description 39
- 238000004519 manufacturing process Methods 0.000 title claims description 7
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 71
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 39
- 239000011941 photocatalyst Substances 0.000 claims description 35
- 239000000377 silicon dioxide Substances 0.000 claims description 35
- 229910002804 graphite Inorganic materials 0.000 claims description 32
- 239000010439 graphite Substances 0.000 claims description 32
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 claims description 30
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 29
- OGIDPMRJRNCKJF-UHFFFAOYSA-N titanium oxide Inorganic materials [Ti]=O OGIDPMRJRNCKJF-UHFFFAOYSA-N 0.000 claims description 25
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 17
- 238000006243 chemical reaction Methods 0.000 claims description 14
- 230000001678 irradiating effect Effects 0.000 claims description 4
- 150000002431 hydrogen Chemical class 0.000 claims description 2
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 24
- 239000000243 solution Substances 0.000 description 16
- BDERNNFJNOPAEC-UHFFFAOYSA-N propan-1-ol Chemical compound CCCO BDERNNFJNOPAEC-UHFFFAOYSA-N 0.000 description 12
- 239000000126 substance Substances 0.000 description 12
- 239000000843 powder Substances 0.000 description 11
- 239000007864 aqueous solution Substances 0.000 description 8
- 238000000354 decomposition reaction Methods 0.000 description 7
- 230000000694 effects Effects 0.000 description 7
- 229910052760 oxygen Inorganic materials 0.000 description 7
- 239000003054 catalyst Substances 0.000 description 6
- 238000000034 method Methods 0.000 description 6
- 229910021536 Zeolite Inorganic materials 0.000 description 5
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 5
- 150000001875 compounds Chemical class 0.000 description 5
- HNPSIPDUKPIQMN-UHFFFAOYSA-N dioxosilane;oxo(oxoalumanyloxy)alumane Chemical compound O=[Si]=O.O=[Al]O[Al]=O HNPSIPDUKPIQMN-UHFFFAOYSA-N 0.000 description 5
- 239000001301 oxygen Substances 0.000 description 5
- 239000002245 particle Substances 0.000 description 5
- 239000010457 zeolite Substances 0.000 description 5
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 4
- 150000001298 alcohols Chemical class 0.000 description 4
- 239000007789 gas Substances 0.000 description 4
- 230000001699 photocatalysis Effects 0.000 description 4
- 230000000052 comparative effect Effects 0.000 description 3
- 238000003756 stirring Methods 0.000 description 3
- 229910010413 TiO 2 Inorganic materials 0.000 description 2
- 239000000654 additive Substances 0.000 description 2
- 229910052786 argon Inorganic materials 0.000 description 2
- 230000005587 bubbling Effects 0.000 description 2
- 230000003197 catalytic effect Effects 0.000 description 2
- 238000000227 grinding Methods 0.000 description 2
- 238000011835 investigation Methods 0.000 description 2
- 238000002156 mixing Methods 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical group [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 2
- 239000004065 semiconductor Substances 0.000 description 2
- 239000000725 suspension Substances 0.000 description 2
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 1
- 241000206761 Bacillariophyta Species 0.000 description 1
- WKBOTKDWSSQWDR-UHFFFAOYSA-N Bromine atom Chemical class [Br] WKBOTKDWSSQWDR-UHFFFAOYSA-N 0.000 description 1
- 229910004298 SiO 2 Inorganic materials 0.000 description 1
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- 230000000996 additive effect Effects 0.000 description 1
- 239000003463 adsorbent Substances 0.000 description 1
- 239000003905 agrochemical Substances 0.000 description 1
- 239000012300 argon atmosphere Substances 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- ODINCKMPIJJUCX-UHFFFAOYSA-N calcium oxide Inorganic materials [Ca]=O ODINCKMPIJJUCX-UHFFFAOYSA-N 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- BVKZGUZCCUSVTD-UHFFFAOYSA-N carbonic acid Chemical class OC(O)=O BVKZGUZCCUSVTD-UHFFFAOYSA-N 0.000 description 1
- 150000004649 carbonic acid derivatives Chemical class 0.000 description 1
- 238000004140 cleaning Methods 0.000 description 1
- 239000003426 co-catalyst Substances 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000005265 energy consumption Methods 0.000 description 1
- 238000004146 energy storage Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 239000010419 fine particle Substances 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- 238000010574 gas phase reaction Methods 0.000 description 1
- 230000036571 hydration Effects 0.000 description 1
- 238000006703 hydration reaction Methods 0.000 description 1
- 238000005470 impregnation Methods 0.000 description 1
- 150000002496 iodine Chemical class 0.000 description 1
- 238000004898 kneading Methods 0.000 description 1
- CPLXHLVBOLITMK-UHFFFAOYSA-N magnesium oxide Inorganic materials [Mg]=O CPLXHLVBOLITMK-UHFFFAOYSA-N 0.000 description 1
- QSHDDOUJBYECFT-UHFFFAOYSA-N mercury Chemical compound [Hg] QSHDDOUJBYECFT-UHFFFAOYSA-N 0.000 description 1
- 229910052753 mercury Inorganic materials 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 239000000575 pesticide Substances 0.000 description 1
- 239000012071 phase Substances 0.000 description 1
- 238000007146 photocatalysis Methods 0.000 description 1
- 238000013032 photocatalytic reaction Methods 0.000 description 1
- 238000002256 photodeposition Methods 0.000 description 1
- 238000006303 photolysis reaction Methods 0.000 description 1
- 230000029553 photosynthesis Effects 0.000 description 1
- 238000010672 photosynthesis Methods 0.000 description 1
- 230000015843 photosynthesis, light reaction Effects 0.000 description 1
- 238000010248 power generation Methods 0.000 description 1
- 230000005855 radiation Effects 0.000 description 1
- 238000006722 reduction reaction Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 150000003839 salts Chemical class 0.000 description 1
- 238000007789 sealing Methods 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 235000012239 silicon dioxide Nutrition 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 238000003746 solid phase reaction Methods 0.000 description 1
- 238000001179 sorption measurement Methods 0.000 description 1
- 239000004575 stone Substances 0.000 description 1
- 239000000758 substrate Substances 0.000 description 1
- 239000010409 thin film Substances 0.000 description 1
- 229910052723 transition metal Inorganic materials 0.000 description 1
- 150000003624 transition metals Chemical class 0.000 description 1
- 238000010792 warming Methods 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
Classifications
-
- 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
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/36—Hydrogen production from non-carbon containing sources, e.g. by water electrolysis
Landscapes
- Hydrogen, Water And Hydrids (AREA)
- Catalysts (AREA)
Description
【０００１】
【発明が属する技術分野】
本発明は、太陽光などに含まれる紫外線および可視光線を効率よく吸収する酸化チタンおよびグラファイトシリカからなる高活性な紫外線および可視光応答型光触媒、及び助触媒からなる水素製造用光触媒、水分解用光触媒及び有害物質分解除去用光触媒を用いた水素の製造方法に関するものである。
【０００２】
【従来の技術】
新しいエネルギー源として原子力発電が実用化されているが、安全性や廃棄物処理等の問題を抱えているのでクリーンで安全な新エネルギーの開発が注目されている。現在、化石資源の制約やそれらの大量消費によって引き起こされた深刻な地球温暖化など環境問題が注目されている。
【０００３】
これに対して、一年間で地上に届く太陽エネルギーは人類の年間エネルギー消費量の１万倍に相当するほど莫大なものであり、その効率的な利用研究が最近活発となっている。その代表的な研究に光触媒がある。この光触媒、たとえば紫外線および可視光応答型光触媒は、無尽蔵な太陽光と水から、クリーンな燃料となる水素と酸素を直接製造することができる極めて有用な触媒として注目されている。
酸化チタン（ＴｉＯ２）単体の系、グラファイトと酸化チタンの混合系、活性炭と酸化チタンの混合系、シリカと酸化チタンの混合系の触媒系を用いても、ほとんど水素の発生は見られなかった。
【０００４】
この反応は下記の反応式（ａ）に示すようにエネルギー蓄積型の反応であり、光合成において、光を必要とする明反応下で起こる酸素発生も、この分解反応にほかならない。
Ｈ２Ｏ→Ｈ２＋（１／２）Ｏ２ （ａ）
一般に、この種の光触媒は、そのバンドギャップ以上のエネルギーを吸収すると、正孔と電子を生成しこれらがそれぞれ酸化反応、還元反応を行い、酸素、水素を発生させる。この光触媒の実用化を考えた場合、光源として太陽光の利用は不可欠である。地表に降り注ぐ太陽光は、可視光である波長５００ｎｍ付近に放射の最大強度をもっており、波長が約４００〜７５０ｎｍの可視光領域のエネルギー量は全太陽光の約４３％である。
一方、波長が約４００ｎｍ以下の紫外線領域では全太陽光の５％にも満たない。
【０００５】
【発明が解決しようとする課題】
しかしながら、従来の多くの半導体光触媒はエネルギーの高い紫外光を照射したときには水素と酸素の双方を生成できることが知られているものの光触媒活性はそれほど高いものではなく効率の低いものであった。従って、太陽光を効率よく利用するための高効率の光触媒が望まれている。
【０００６】
また、近年、このような光触媒の応用は有害化学物質の分解の分野で広く研究検討されている。たとえば、水中や大気中の農薬や悪臭物質などの有機物の分解除去あるいは光触媒を塗布した固体表面のセルフクリーニングなどの数多くの応用例がある。
【０００７】
本発明は、太陽光などに含まれる紫外線および可視光線を効率よく吸収する光触媒を使用することによって、水素含有化合物（アルコール類）を含む水や有害化学物質に光を照射し、水素含有化合物（アルコール類）を含む水あるいは有害物質を分解して、高効率の水素の製造方法あるいは有害物質の無害化処理方法を提供しようというものである。
【０００８】
【課題を解決するための手段】
本発明者は上記課題をゼオライトと酸化チタンとの混合系、グラファイトシリカと酸化チタンとの混合系について検討し、水和クラスターに影響を及ぼす可能性のある中間赤外線の効用を持ったグラファイトシリカが酸化チタンの光触媒の活性を高める重要因子であることを見いだした。従来公知の光触媒である酸化チタンＴｉＯ２で代表される酸化物にグラファイトシリカを適切な比率で混合することにより高効率の水素発生の光触媒として有効であることを見いだし、本発明に至った。
【０００９】
本発明で用いるグラファイトシリカは、Ｃ、ＳｉＯ2、Ｆｅ2Ｏ3、Ａｌ2Ｏ3、ＣａＯ、ＭｇＯ、ＴｉＯ2、Ｎａ2Ｏ、Ｋ2Ｏ及びＨ2Ｏからなり、炭素含有量が約５％の黒色物で約８０％のシリカ（ＳｉＯ2）を主成分としていて、吸着作用がある。常温で高放射率の中間赤外線（波長４μｍ〜１４μｍの育成光線）を放射する性質がある。グラファイトシリカは通称ブラックシリカ、シリカブラック、神明石などと呼ばれ数億年前の海底の珪藻類が地表に隆起して層状堆積して形成された天然鉱石であると考えられている。このグラファイトシリカは、光触媒の活性作用を高めるものとは考えられていなかった。
【００１０】
本発明で用いるアルコール水溶液は、アルコール分子と水分子が水素結合でつながった会合体を形成し、さらに上下のアルコール会合体を水分子が水素結合のネットワークでつなぎ水和クラスターを形成していると考えられている。
【００１１】
また、反応溶液として水に水素含有化合物（アルコール類）、たとえばメタノール、エタノール、１−プロパノールなどを添加し検討した結果、水にアルコール類を適正な比率で混合し反応溶液（アルコール水溶液）にすることで水素発生効率において高効率を達成できることを見いだし、本発明に至った。すなわち、
【００１２】
本発明の水素の製造方法は、酸化チタンと、グラファイトシリカとを主成分とした光触媒を用い、反応溶液として水にアルコール類を１０〜９０ｖｏｌ％添加し、アルコール水溶液とし、これに紫外線および可視光線を照射することを特徴とする。このとき、光触媒として、グラファイトシリカの含有量が３０〜７０ｗｔ％のものを用いることが好ましい。
【００１３】
【発明の実施の形態】
以下、本発明を具体的に説明するが、本発明は、この具体例のみに限られるものではない。本発明において、光触媒として使用する酸化チタンとグラファイトシリカの混合物は、４０ｖｏｌ％のメタノール水溶液では酸化チタンに混合したグラファイトシリカの光触媒全体に対する割合が３０〜７０ｗｔ％のとき、水素発生効率が良く、この範囲外ではグラファイトシリカが多くても少なくても水素発生効率は低下する。
【００１４】
本発明で用いた光触媒である酸化チタンは、アナターゼを主成分とし、ルチルを少量含む粉末である。これにグラファイトシリカ粉末を混合する。
【００１５】
本発明で用いる光触媒の形態は、粉末のまま、成形加工、あるいは焼結されて使用されるが、いずれにしても光を有効に利用するために、比表面積の大きいものが望ましいことは言うまでもない。一般に固相反応法で調製した酸化物は粒子が大きく、その比表面積は小さいが、ボールミルなどで粉砕を行うことなどにより粒子径を小さくできる。一般には粒子の大きさは小さいほどよいが、好ましくは１０ｎｍ〜２００μｍである。また微粒子を成型して板状および／または薄膜として使用することもできる。
【００１６】
更に、本発明で用いる光触媒は、Ｐｔなどの白金族元素、Ｎｉなどの遷移金属、ＮｉＯ、ＩｒＯ2、ＲｕＯ2等からなる群から選択される１種又は２種以上の成分からなる助触媒によって修飾、担持することができる。担持方法は混練法や含浸法，光電着法などで行うことができる。
【００１７】
反応溶液は、水に限らず、通常水の分解反応によく用いられるように、炭酸塩や炭酸水素塩、ヨウ素塩、臭素塩等の塩類を混合、溶解した水を用いてもよい。この溶液に水素含有化合物（アルコール類）を適正比率にて混合し、アルコール水溶液として、反応溶液を調製する。
【００１８】
上記，反応溶液に本発明で用いる光触媒を添加する。触媒の添加量は、基本的に入射した光が効率よく吸収できる量を選ぶ。このように光分解用触媒を添加したアルコール水溶液に光を照射することによって水素が発生する。照射する光の波長は半導体光触媒の吸収がある領域の波長の光を含むことが必要である。本発明では太陽光を照射してもよい。
【００１９】
本発明で用いる光触媒は、水素含有化合物（アルコール類）を含む水の分解だけでなく多くの光触媒反応に応用できる。たとえば有機物の分解の場合、アルコールや農薬、悪臭物質などは一般に電子供与体として働き、正孔によって酸化分解されるとともに、電子によって水素が発生するか、酸素が還元される。反応形態は、有機物を含む水溶液に触媒を懸濁して光照射しても良いし、触媒を基板に固定しても良い。悪臭物質の分解のように気相反応でも良い。
【００２０】
【実施例】
〔実施例１〕
代表的光触媒である酸化チタンの光触媒活性を向上させるために、添加剤としてグラファイトシリカを加えた。アナターゼ８０％、ルチル２０％の酸化チタン粉末（粒径約０．０２１μｍ）とグラファイトシリカを粉砕した粉末（平均粒径５〜６μｍ）を溶液中で混合し光触媒を得る。この光触媒を含む反応溶液（アルコール水溶液）に紫外線（３００ｎｍ〜４１０ｎｍ）を照射して生成する水素ガスを定量的に調べることによって、酸化チタンの光触媒活性を評価した。１００ｍｌ（以下、１ｍｌ＝１ｃｍ３である）シュレンク管の中に、酸化チタン粉末とグラファイトシリカ粉末の混合物を３０ｍｇ、アルコール水溶液を２０ｍｌ、そして攪拌用の攪拌子（反応に影響のないようにできるだけ小さいものを用いた）を１個入れた。アルコールとして、メタノール、エタノール、１−プロパノールを用いた。
【００２１】
シュレンク管に密閉用のシリコンキャップを取り付け、１分間超音波で分散した。次に、アルゴンガスでバブリングすることによって、シュレンク管内の溶存空気を脱気した。バブリングは丁寧に１時間行い、その後常圧のまま気相にもアルゴンガスを加え、シュレンク管内をアルゴン雰囲気にした。
続いて、脱気した水―アルコール―光触媒―添加剤の懸濁溶液を攪拌しながら、超高圧水銀ランプからの光を紫外線透過フィルターと水フィルターに通した後、紫外線で光照射した。一定の光照射時間ごとに発生した水素ガスをロック型シリンジで採取し、ガスクロマトグラフを用いて発生量を測定した。光照射３時間後の懸濁溶液をシリンジフィルターでろ過して、水素ガス以外の生成物（溶液）を回収した。
【００２２】
そこで、水素発生量のグラファイトシリカ含量（単位はｗｔ％（重量百分率）である）依存性をメタノールの濃度が４０ｖｏｌ％（体積百分率））の場合について調べた結果、酸化チタンとグラファイトシリカの両方を加えた系では、３時間照射後で約９１００ｐｐｍの水素が発生した。酸化チタン単独の系よりも２００倍以上の発生であった。グラファイトシリカの添加効果は非常に大きいと言える。
また、グラファイトシリカの添加量には最適値があり、メタノール、エタノール、１−プロパノールの各水溶液では光触媒に対して５０ｗｔ％前後が最適含量であることがわかった。
【００２３】
各アルコール水溶液（アルコール含量を４０ｖｏｌ％に固定）について得られた水素発生量のグラファイトシリカ含量依存性を調べ、比較を行った。その結果、３時間照射後の最大水素発生量（グラファイトシリカ含量が光触媒に対して５０ｗｔ％のときの水素発生量で比較した）は、メタノール（約６６００ｐｐｍ）＞エタノール（約４１００ｐｐｍ）＞１−プロパノール（約５２０ｐｐｍ）の順で大きいことがわかった。
【００２４】
〔比較例１〕
混合系の代わりに酸化チタンおよびグラファイトシリカ単独系で、実施例１と同様に実施した。酸化チタンおよびグラファイトシリカ単独では、３時間照射後それぞれ４０ｐｐｍ程度と１５ｐｐｍ程度しか水素ガスが発生しなかった。
混合系の２００分の１の水素ガスしか発生しなかったことがわかる。
【００２５】
〔比較例２〕
グラファイトシリカ粉末の代わりに、グラファイト、活性炭、シリカの各粉末を用いて調べた。グラファイトの場合は、酸化チタン単独の系での水素発生量と比較すると、３倍程度の水素しか発生しなかった。活性炭の場合は水素発生への効果は小さかった。シリカ（二酸化ケイ素）の場合は、その含量の増加と共に水素発生量は減少していき、むしろ酸化チタンの触媒活性を阻害していた。このようにグラファイトシリカの場合の方が比較にならないほど水素発生量が多いことがわかる。
【００２６】
〔比較例３〕
吸着剤・触媒としてよく知られているゼオライト粉末をグラファイトシリカ粉末の代わりに用いて実験を行った。用いたゼオライトはＡ−４（Ａ型）、Ｆ−９（Ｘ型）、ＨＳＺ−３６０ＨＵＡ（Ｙ型）である。最大の水素発生量を示したのは、１０ｗｔ％のゼオライトＡ−４を含むメタノール水溶液（メタノール含量は３０ｖｏｌ％）を用いた場合であった。この場合は、水素発生量は酸化チタン単独系の場合の約８倍であった。
このようにゼオライトと酸化チタンとの混合系においても、水素の発生に効果があった。
【００２７】
【発明の効果】
本発明で用いる光触媒は、太陽光に対しても優れた触媒活性能を有する。従って、本発明によれば、太陽光エネルギーを直接利用してたとえば水と水素含有化合物（アルコール類）から高効率に水素を発生できる。将来的には無尽蔵の太陽光で効率よく水素を大量に製造できるなどといった利点を有するものであり、近年のエネルギー問題の克服に大きく貢献するものである。 [0001]
[Technical field to which the invention belongs]
The present invention relates to a highly active ultraviolet and visible light responsive photocatalyst comprising titanium oxide and graphite silica, which efficiently absorbs ultraviolet rays and visible light contained in sunlight, etc., and a hydrogen production photocatalyst comprising a cocatalyst, for water splitting The present invention relates to a method for producing hydrogen using a photocatalyst and a photocatalyst for decomposing and removing harmful substances.
[0002]
[Prior art]
Nuclear power generation has been put to practical use as a new energy source, but because of problems such as safety and waste disposal, the development of clean and safe new energy has attracted attention. Currently, environmental problems such as severe global warming caused by fossil resource constraints and mass consumption are attracting attention.
[0003]
On the other hand, the solar energy that reaches the ground in one year is enormous, equivalent to 10,000 times the annual energy consumption of mankind, and its efficient utilization research has recently become active. A typical study is photocatalysis. Such photocatalysts, such as ultraviolet and visible light responsive photocatalysts, are attracting attention as extremely useful catalysts capable of directly producing hydrogen and oxygen as clean fuels from inexhaustible sunlight and water.
Even when using a titanium oxide (TiO 2 ) simple substance system, a mixed system of graphite and titanium oxide, a mixed system of activated carbon and titanium oxide, or a mixed system of silica and titanium oxide, almost no generation of hydrogen was observed. .
[0004]
This reaction is an energy storage type reaction as shown in the following reaction formula (a), and in the photosynthesis, oxygen generation that occurs under a light reaction that requires light is none other than this decomposition reaction.
H 2 O → H 2 + (1/2) O 2 (a)
In general, when this type of photocatalyst absorbs energy that exceeds the band gap, holes and electrons are generated, and these undergo oxidation and reduction reactions to generate oxygen and hydrogen, respectively. Considering the practical application of this photocatalyst, it is essential to use sunlight as a light source. Sunlight falling on the surface of the earth has a maximum intensity of radiation in the vicinity of a wavelength of 500 nm that is visible light, and the amount of energy in the visible light region having a wavelength of about 400 to 750 nm is about 43% of the total sunlight.
On the other hand, in the ultraviolet region where the wavelength is about 400 nm or less, it is less than 5% of the total sunlight.
[0005]
[Problems to be solved by the invention]
However, although many conventional semiconductor photocatalysts are known to be able to generate both hydrogen and oxygen when irradiated with high energy ultraviolet light, the photocatalytic activity is not so high and the efficiency is low. Therefore, a highly efficient photocatalyst for efficiently using sunlight is desired.
[0006]
In recent years, the application of such a photocatalyst has been extensively studied in the field of decomposition of harmful chemical substances. For example, there are many applications such as decomposition and removal of organic substances such as pesticides and malodorous substances in water and air, or self-cleaning of a solid surface coated with a photocatalyst.
[0007]
The present invention uses a photocatalyst that efficiently absorbs ultraviolet rays and visible light contained in sunlight and the like to irradiate water and harmful chemical substances containing hydrogen-containing compounds (alcohols) with light. It is intended to provide a highly efficient method for producing hydrogen or a method for detoxifying harmful substances by decomposing water or harmful substances containing alcohols).
[0008]
[Means for Solving the Problems]
The present inventor has studied the above problems with a mixed system of zeolite and titanium oxide, and a mixed system of graphite silica and titanium oxide, and graphite silica having the effect of mid-infrared rays that may affect hydration clusters. It was found to be an important factor to increase the activity of titanium oxide photocatalyst. The present inventors have found that it is effective as a photocatalyst for high-efficiency hydrogen generation by mixing graphite silica in an appropriate ratio with an oxide typified by titanium oxide TiO 2 , which is a conventionally known photocatalyst.
[0009]
The graphite silica used in the present invention is composed of C, SiO 2 , Fe 2 O 3 , Al 2 O 3 , CaO, MgO, TiO 2 , Na 2 O, K 2 O and H 2 O, and has a carbon content of about 5 % Black matter and about 80% silica (SiO 2 ) as a main component, and has an adsorption action. It has the property of emitting mid-infrared rays having a high emissivity at room temperature (growth rays having a wavelength of 4 to 14 μm). Graphite silica is commonly known as black silica, silica black, and shinmei stone, and is considered to be a natural ore formed by layering diatoms on the sea floor several hundred million years ago. This graphite silica was not considered to enhance the activity of the photocatalyst.
[0010]
The aqueous alcohol solution used in the present invention forms an association in which alcohol molecules and water molecules are connected by hydrogen bonds, and the water molecules are connected to each other by a network of hydrogen bonds to form a hydrated cluster. It is considered.
[0011]
In addition, as a reaction solution, hydrogen-containing compounds (alcohols) such as methanol, ethanol, 1-propanol and the like were added to water as a result of the investigation. As a result, alcohol was mixed with water at an appropriate ratio to obtain a reaction solution (alcohol aqueous solution). As a result, it was found that high efficiency in hydrogen generation efficiency can be achieved, and the present invention has been achieved. That is,
[0012]
In the method for producing hydrogen of the present invention, a photocatalyst mainly composed of titanium oxide and graphite silica is used, and an alcohol is added to water as a reaction solution in an amount of 10 to 90% by volume to obtain an alcohol aqueous solution. It is characterized by irradiating. At this time, it is preferable to use a photocatalyst having a graphite silica content of 30 to 70 wt%.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail, but the present invention is not limited to this specific example. In the present invention, a mixture of titanium oxide and graphite silica used as a photocatalyst has a high hydrogen generation efficiency when the proportion of graphite silica mixed with titanium oxide in the 40 vol% methanol aqueous solution is 30 to 70 wt% with respect to the total photocatalyst. Outside the range, the efficiency of hydrogen generation decreases even if the amount of graphite silica is large or small.
[0014]
Titanium oxide as a photocatalyst used in the present invention is a powder containing anatase as a main component and a small amount of rutile. This is mixed with graphite silica powder.
[0015]
The form of the photocatalyst used in the present invention is used in the form of powder, molded or sintered, but in any case, it is needless to have a large specific surface area in order to effectively use light. . In general, an oxide prepared by a solid phase reaction method has large particles and a small specific surface area, but the particle size can be reduced by grinding with a ball mill or the like. In general, the smaller the particle size, the better, but it is preferably 10 nm to 200 μm. Fine particles can be molded and used as a plate and / or a thin film.
[0016]
Furthermore, the photocatalyst used in the present invention is a co-catalyst composed of one or more components selected from the group consisting of platinum group elements such as Pt, transition metals such as Ni, NiO, IrO 2 , RuO 2 and the like. It can be modified and supported. The supporting method can be performed by a kneading method, an impregnation method, a photo-deposition method, or the like.
[0017]
The reaction solution is not limited to water, and water in which salts such as carbonates, hydrogen carbonates, iodine salts, bromine salts, etc. are mixed and dissolved may be used so as to be commonly used for water decomposition reactions. A hydrogen-containing compound (alcohol) is mixed with this solution at an appropriate ratio to prepare a reaction solution as an aqueous alcohol solution.
[0018]
The photocatalyst used in the present invention is added to the reaction solution. The amount of catalyst added is basically selected so that incident light can be efficiently absorbed. In this way, hydrogen is generated by irradiating the aqueous alcohol solution to which the photolysis catalyst is added with light. The wavelength of light to be irradiated needs to include light having a wavelength in a region where the semiconductor photocatalyst is absorbed. In the present invention, sunlight may be irradiated.
[0019]
The photocatalyst used in the present invention can be applied not only to the decomposition of water containing hydrogen-containing compounds (alcohols) but also to many photocatalytic reactions. For example, in the case of decomposition of organic substances, alcohol, agricultural chemicals, malodorous substances and the like generally act as electron donors, and are oxidatively decomposed by holes, and hydrogen is generated by electrons or oxygen is reduced. As a reaction form, the catalyst may be suspended in an aqueous solution containing an organic substance and irradiated with light, or the catalyst may be fixed to a substrate. A gas phase reaction may be used, such as decomposition of malodorous substances.
[0020]
【Example】
[Example 1]
In order to improve the photocatalytic activity of titanium oxide, which is a typical photocatalyst, graphite silica was added as an additive. A photocatalyst is obtained by mixing titanium oxide powder of 80% anatase and 20% rutile (particle size: about 0.021 μm) and powder obtained by grinding graphite silica (average particle size: 5-6 μm) in a solution. The photocatalytic activity of titanium oxide was evaluated by quantitatively examining the hydrogen gas produced by irradiating the reaction solution (alcohol aqueous solution) containing this photocatalyst with ultraviolet rays (300 nm to 410 nm). In a 100 ml Schlenk tube (hereinafter 1 ml = 1 cm 3 ), 30 mg of a mixture of titanium oxide powder and graphite silica powder, 20 ml of an aqueous alcohol solution, and a stir bar for stirring (as small as possible so as not to affect the reaction) 1) was used. As alcohol, methanol, ethanol, and 1-propanol were used.
[0021]
A silicon cap for sealing was attached to the Schlenk tube and dispersed with ultrasonic waves for 1 minute. Next, the dissolved air in the Schlenk tube was degassed by bubbling with argon gas. Bubbling was performed carefully for 1 hour, and then argon gas was also added to the gas phase at normal pressure to create an argon atmosphere in the Schlenk tube.
Subsequently, while stirring the degassed suspension solution of water-alcohol-photocatalyst-additive, the light from the ultra-high pressure mercury lamp was passed through an ultraviolet transmission filter and a water filter, and then irradiated with ultraviolet light. Hydrogen gas generated at every constant light irradiation time was collected with a lock type syringe, and the generated amount was measured using a gas chromatograph. The suspension solution after 3 hours of light irradiation was filtered with a syringe filter, and a product (solution) other than hydrogen gas was recovered.
[0022]
Therefore, as a result of investigating the dependency of hydrogen generation amount on the graphite silica content (unit is wt% (weight percentage)) in the case of methanol concentration of 40 vol% (volume percentage)), both titanium oxide and graphite silica were analyzed. In the added system, about 9100 ppm of hydrogen was generated after 3 hours of irradiation. Occurrence was 200 times or more than the system of titanium oxide alone. It can be said that the addition effect of graphite silica is very large.
Further, it was found that there is an optimum value for the amount of graphite silica added, and in each aqueous solution of methanol, ethanol, and 1-propanol, an optimum content is around 50 wt% with respect to the photocatalyst .
[0023]
The dependence of the hydrogen generation amount obtained on each alcohol aqueous solution (alcohol content fixed at 40 vol%) on the graphite silica content was examined and compared. As a result, the maximum hydrogen generation amount after irradiation for 3 hours (compared with the hydrogen generation amount when the graphite silica content is 50 wt% with respect to the photocatalyst ) is methanol (about 6600 ppm)> ethanol (about 4100 ppm)> 1-propanol It turned out that it is large in order of (about 520 ppm).
[0024]
[Comparative Example 1]
The same procedure as in Example 1 was carried out using titanium oxide and graphite silica alone instead of the mixed system. With titanium oxide and graphite silica alone, hydrogen gas was generated only at about 40 ppm and about 15 ppm after irradiation for 3 hours, respectively.
It can be seen that only 1 / 200th of hydrogen gas in the mixed system was generated.
[0025]
[Comparative Example 2]
Instead of graphite silica powder, graphite, activated carbon, and silica powder were used for investigation. In the case of graphite, only about three times as much hydrogen was generated as compared with the amount of hydrogen generated in the system of titanium oxide alone. In the case of activated carbon, the effect on hydrogen generation was small. In the case of silica (silicon dioxide), the amount of hydrogen generation decreased as the content thereof increased, but rather the catalytic activity of titanium oxide was inhibited. Thus, it can be seen that the amount of hydrogen generation is larger in the case of graphite silica than in comparison.
[0026]
[ Comparative Example 3 ]
Experiments were conducted using zeolite powder, which is well known as an adsorbent / catalyst, instead of graphite silica powder. The zeolite used is A-4 (A type), F-9 (X type), HSZ-360HUA (Y type). The maximum hydrogen generation amount was shown when a methanol aqueous solution containing 10 wt% of zeolite A-4 (methanol content was 30 vol%) was used. In this case, the amount of hydrogen generated was about 8 times that in the case of titanium oxide alone.
Thus, even in a mixed system of zeolite and titanium oxide, there was an effect in generating hydrogen.
[0027]
【The invention's effect】
The photocatalyst used in the present invention has excellent catalytic activity against sunlight. Therefore, according to the present invention, it is possible to efficiently generate hydrogen from, for example, water and a hydrogen-containing compound (alcohol) by directly using solar energy. In the future, it has the advantage of being able to efficiently produce a large amount of hydrogen with inexhaustible sunlight, and greatly contributes to overcoming recent energy problems .
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| JP5493449B2 (en) * | 2009-04-22 | 2014-05-14 | パナソニック株式会社 | Photocatalytic hydrogen generation device |
| JP2010269295A (en) * | 2009-05-19 | 2010-12-02 | Kyoji Takada | Water ph control only by heat source and natural ore water |
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