JP4206813B2 - Carbon monoxide conversion catalyst and carbon monoxide conversion method using the catalyst - Google Patents
Carbon monoxide conversion catalyst and carbon monoxide conversion method using the catalyst Download PDFInfo
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- JP4206813B2 JP4206813B2 JP2003130379A JP2003130379A JP4206813B2 JP 4206813 B2 JP4206813 B2 JP 4206813B2 JP 2003130379 A JP2003130379 A JP 2003130379A JP 2003130379 A JP2003130379 A JP 2003130379A JP 4206813 B2 JP4206813 B2 JP 4206813B2
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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
- 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
- Y02E60/50—Fuel cells
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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
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Description
【0001】
【発明の属する技術分野】
本発明は、300℃程度の低い温度領域でも一酸化炭素を効率的に変成でき、経時的な活性低下も少ない一酸化炭素変成用触媒、並びに、該触媒の存在下少なくとも水蒸気と一酸化炭素からなるガス中の一酸化炭素濃度を低減させる一酸化炭素の変成方法、及び該触媒の存在下少なくとも水蒸気と一酸化炭素からなるガスに酸素を導入し反応させることにより一酸化炭素濃度を低減させる一酸化炭素の変成方法に関する。このような低温活性に優れ寿命の長い触媒は、一酸化炭素と水蒸気から残存一酸化炭素の少ない高純度水素を製造する場合や水素ガス中に含まれる一酸化炭素を低減させる場合の有利な工業的技術手段となる。
【0002】
【従来の技術】
一酸化炭素と水蒸気から水素を生成させる一酸化炭素変成反応は化学工業の重要な工程で古くから知られている。近年、需要の増大が予想される水素の供給法として炭化水素或いはアルコールなどを改質して水素を得る方法が広く研究されている。しかし、この方法で水素を発生させる場合、使用する原料や改質の方法により濃度に違いはあるものの、改質に伴なう一酸化炭素の副生が避けられず、この副生した一酸化炭素の濃度を低減するために、一酸化炭素変成反応が用いられている。
【0003】
従来、この一酸化炭素変成反応に用いられる触媒としては、反応温度が比較的低い低温シフト反応領域においては銅系触媒が、比較的高い高温シフト反応領域においては鉄−クロム系触媒が一般的に用いられてきた。
しかし、銅系触媒は、鉄−クロム系触媒に比較して低温領域での一酸化炭素変成活性が高いとはいえ、300℃近くにもなると触媒活性の低下が著しく、また経時的な触媒活性の低下も大きく、満足できるとは言い難い状況にあった。しかも、銅系触媒では使用前に還元処理を施して触媒を賦活する必要があり、その際起こる発熱により触媒層温度が上がるため温度管理に細心の注意を払わならなければならないという問題があった。さらに、一度活性化しても、装置停止時などに酸素が混入した場合、改めて賦活し直さなければない欠点があった。
【0004】
炭化水素或いはアルコール等を改質して得られる水素含有ガスを、定置型或いは車載型燃料電池等に用いる場合、燃料電池の種類によって、例えば固体高分子型燃料電池の場合、一般的に電極触媒がある濃度以上の一酸化炭素に曝され続けると劣化してしまうため、水素含有ガスを燃料電池に導入する以前に、何らかの方法を講じて共存している一酸化炭素を電極触媒に影響を与えない程度まで低減する必要がある。多くの場合、一酸化炭素は燃料電池のガス導入部の前に設置された水素精製装置で行われる選択的酸化反応によってppmオーダーまで低減されるが、この水素精製装置での一酸化炭素除去性能を長期間に亘って高い状態で保持するためには、改質器から出てくる水素含有ガス中の一酸化炭素そのものをできる限り低減させるとともに、選択的な一酸化炭素の変成活性に優れた寿命の長い触媒が不可欠である。
【0005】
然るに、これら問題の解決に適う水素精製装置が提案されているが(例えば、特許文献1、2、3参照。)、これらの技術において、一酸化炭素濃度が効果的に低減されると記載されてはいるものの、触媒の使用量に関して不明であり、その性能は明確ではない。
【0006】
【特許文献1】
特開2000−302410号公報
【特許文献2】
特開2001−342005号公報
【特許文献3】
特開2002−60206号公報
【0007】
【発明が解決しようとする課題】
本発明の目的は、反応温度が比較的低い低温シフト反応領域における一酸化炭素変成用触媒として、従来用いられている銅系触媒に比べて、さらに高い低温活性を示しかつ寿命の長い新たな触媒を提供することにある。また、併せて銅系触媒が持つ酸素に対する被毒性の問題を伴わない工業的に優れた触媒を提供することにある。
【0008】
【課題を解決するための手段】
本発明者らは、上記のごとき課題を有する一酸化炭素の変成方法について鋭意検討した結果、一般的に、低温領域における一酸化炭素の変成活性が銅系触媒に比較して劣る貴金属触媒を含有させた、白金と亜鉛−クロム複合酸化物からなる触媒が、300℃程度の低い温度領域でも、銅系触媒に比べて高い活性を示し、より少ない触媒量においても、すなわち高負荷条件でも効率よく一酸化炭素濃度を低減でき、しかも銅系触媒に比較して経時的な活性低下を小さくできることを見いだした。また、この白金と亜鉛−クロム複合酸化物からなる触媒では、使用を開始するに際して触媒の賦活処理を必要としないばかりか、酸素を導入して反応させることにより、さらに効率良く一酸化炭素濃度を低減できることを見出し本発明を完成するに至った。
【0009】
すなわち、本発明は、以下の(1)から(5)に示す、白金と亜鉛−クロム複合酸化物からなる一酸化炭素変成用触媒、並びに該触媒の存在下少なくとも水蒸気と一酸化炭素からなるガス中の一酸化炭素濃度を低減させる一酸化炭素の変成方法、及び該触媒の存在下少なくとも水蒸気と一酸化炭素からなるガスに酸素を導入し反応させることにより一酸化炭素濃度を低減させる一酸化炭素の変成方法に関するものである。
(1)白金と亜鉛−クロム複合酸化物からなる一酸化炭素変成用触媒。
(2)触媒中に含まれる白金量が、金属白金として、金属白金と亜鉛−クロム複合酸化物の合計量に対して、1〜50重量%の範囲である(1)記載の一酸化炭素変成用触媒。
(3)触媒中に含まれる亜鉛/クロムの原子比が、0.05〜20の範囲である(1)記載の一酸化炭素変成用触媒。
(4)(1)から(3)に記載の触媒の存在下、少なくとも水蒸気と一酸化炭素からなるガス中の一酸化炭素濃度を低減させる一酸化炭素の変成方法。
(5)(1)から(3)に記載の触媒の存在下、少なくとも水蒸気と一酸化炭素からなるガスに酸素を導入して反応させることにより一酸化炭素濃度を低減させる一酸化炭素の変成方法。
【0010】
【発明の実施の形態】
本発明における白金の原料について特に制限はないが、例えば、酸化白金、塩化白金酸及びそのアルカリ金属塩、白金アセチルアセトナート、並びにジニトロジアンミン白金等が使用できる。また、水に溶解させて触媒を調製する場合には塩化白金酸カリウムを用いるのが好ましい。一方、亜鉛及びクロム複合酸化物の原料となる亜鉛及びクロムについても特に制限はない。
【0011】
本発明の触媒中に含まれる白金含量は、金属白金として、金属白金と亜鉛−クロム複合酸化物の合計量に対して、1〜50重量%の範囲であることが好ましく、5〜30重量%であることがより好ましい。1重量%より少ない場合には活性の低下が認められ、50重量%より多い場合には貴金属である白金当たりの活性が低下することとなり経済的に不利である。
また、亜鉛/クロムの原子比は0.05〜20の範囲であることが好ましく、0.1〜10であることがより好ましい。亜鉛/クロムの原子比が0.05より小さかったり、20より大きかった場合には一酸化炭素の変成活性が相対的に小さくなる。
【0012】
本発明における、白金と亜鉛−クロム複合酸化物からなる触媒の調製法に特に制限はない。亜鉛及びクロム成分を溶解させた水溶液と沈澱剤から、共沈澱法により亜鉛−クロム複合酸化物の前駆体を得、これを濾過洗浄後、乾燥或いは焼成し必要に応じ粉砕を行なった後、白金塩の水溶液中に分散させ、ここへ沈澱剤あるいは還元剤を用いて白金を析出させる方法、亜鉛−クロム複合酸化物に白金を含浸させる方法、白金、亜鉛、及びクロムの3成分を溶解させた水溶液と沈澱剤から共沈澱法により沈澱を生成させる方法等がある。
【0013】
水溶液中で沈澱法により白金を析出させる場合、沈殿剤としては水酸化ナトリウム、水酸化カリウム、炭酸ナトリウム、炭酸カリウム、及び炭酸水素ナトリウムなどのアルカリ化合物が用いられる。沈殿物調製時の沈澱剤の量は、溶液中に含まれる白金塩の化学等量の1〜2倍、好ましくは1.1〜1.6倍が適当である。1倍を下回る場合は沈殿物の生成量が不充分となり、2倍を上回る場合には余剰となり経済的に不利となる。
沈澱調製時の温度は20〜90℃、好ましくは35〜85℃である。20℃より低い場合には沈殿物の熟成が不足となり、90℃より高い場合には沈澱剤添加時の発熱やそれに伴なうスラリー突沸の危険性が増す。
なお、沈澱法により得られた沈澱は沈澱剤や原料由来の塩化物やアルカリ金属等を除去するためイオン交換水、蒸留水などで洗浄するのが好ましい。
【0014】
上記のようにして得られた沈澱は、乾燥・焼成し、必要に応じ破砕して大きさを揃えて、或いは成型して使用される。また、スラリーの乾燥品、或いは乾燥・焼成したものを粉砕し、水に懸濁させ、必要に応じてアルミナゾルのようなバインダーを添加して、担体及び担体構造物に担持して使用することができる。この場合、担持後乾燥して、或いは再度焼成した上で使用することができる。
【0015】
本発明の触媒を用いることによって、少なくとも水蒸気と一酸化炭素からなるガス中の一酸化炭素濃度を効率的に低減することができる。変成対象となるガスには水蒸気、一酸化炭素の他に、水素、二酸化炭素、窒素等のガスが含まれていてもなんらかまわない。
また、本発明において酸素を導入して反応させる場合、酸素含有ガスとして空気を用いることもできる。酸素濃度としては0.1〜5%が好ましく、0.2〜2%がより好ましい。酸素濃度が0.1%を下回る場合は酸素導入効果が小さく、逆に5%を上回る場合には発熱が大きくなりすぎ危険を伴う可能性がある。
【0016】
【実施例】
本発明を以下の実施例により説明する。なお本発明はこれらの実施例により限定されるものではない。
(触媒調製)
触媒A
炭酸ナトリウム(無水)138gを1000mLのイオン交換水とともに5Lの丸底フラスコに入れ溶解し60℃とした。これに、硝酸亜鉛六水和物238gと硝酸クロム九水和物80gをイオン交換水800mLに溶解し60℃とした溶液を注加し30分間攪拌した。得られたスラリー状の沈殿物を含む混合液を濾過し、沈澱をイオン交換水12Lで洗浄した。続いて80℃で乾燥し、その後、380℃にて2時間焼成することにより、亜鉛/クロムの原子比が4となる亜鉛−クロム複合酸化物79.8gを得た。
この亜鉛−クロム複合酸化物の粉末15gを分散させた65℃の水溶液500mLに、塩化白金酸カリウム13.8gを溶解させた65℃の水溶液500mLを加えた。30分後に1NKOH水溶液66mLを加え、65℃にて60分間攪拌した。その後濾過して、濾液中の塩素が1ppm以下になるまで水洗浄を繰り返した。そして80℃で乾燥させた後に、380℃で2時間焼成し、白金と亜鉛−クロム複合酸化物からなる触媒20.8gを得た。
この触媒をスラリー濃度25重量%の条件で湿式粉砕し、これにアルミナゾルを混合してスラリーとした後、コージェライト製のハニカム(400セル/平方センチ)に、浸漬、過剰分の吹き飛ばし、及び乾燥という工程を繰り返し、乾燥後の触媒担持量が200g/Lになるように触媒を担持した。これを触媒Aとする。
【0017】
触媒B
炭酸ナトリウム(無水)138gを1000mLのイオン交換水とともに5Lの丸底フラスコに入れ溶解し60℃とした。これに硝酸亜鉛六水和物298gをイオン交換水800mLに溶解し60℃とした溶液を注加し、30分間攪拌した。得られたスラリー状の沈殿物を含む混合液を濾過し、沈澱をイオン交換水12Lで洗浄した。続いて80℃で乾燥し、その後、380℃にて2時間焼成することにより、酸化亜鉛80.9gを得た。
この酸化亜鉛の粉末15gを分散させた65℃の水溶液500mLに、塩化白金酸カリウム13.8gを溶解させた65℃の水溶液500mLを加えた。30分後に1NKOH水溶液66mLを加え、65℃にて60分間攪拌した。その後濾過して、濾液中の塩素が1ppm以下になるまで水洗浄を繰り返した。そして80℃で乾燥させた後に、380℃で2時間焼成し、白金と酸化亜鉛からなる触媒20.7gを得た。
この触媒をスラリー濃度25重量%の条件で湿式粉砕し、アルミナゾルを混合してスラリーとした後、コージェライト製のハニカム(400セル/平方センチ)に、浸漬、過剰分の吹き飛ばし、及び乾燥という工程を繰り返し、乾燥後の触媒担持量が200g/Lになるように触媒を担持した。これを触媒Bとする。
【0018】
触媒C
炭酸ナトリウム(無水)177gを1000mLのイオン交換水とともに5Lの丸底フラスコに入れ溶解し40℃とした。ここに硫酸銅(5水塩)315gとホウ酸19.7gをイオン交換水800mLに溶解して40℃に調節した溶液を注加し、続いて酸化亜鉛77.0gをイオン交換水300mLに分散したスラリーを加え、直ちに炭酸ガスを6L/hの割合で吹き込んだ。1時間後80℃に昇温し30分保持した。炭酸ガスの吹き込みは2時間で停止し、次いで60℃まで冷却した。ここに硫酸アルミニウム49gをイオン交換水45mLに溶解した溶液と水酸化ナトリウム10.2gを70mLのイオン交換水に溶解した溶液とから調製したスラリーを加え20分間攪拌した。このように調製した混合スラリーを濾過し、0.05% の水酸化ナトリウム水溶液12Lとイオン交換水3Lで洗浄した。続いて80℃で乾燥後、焼成し、Cu−Zn−Al触媒を190g得た。この触媒をスラリー濃度25重量%の条件で湿式粉砕した後、アルミナゾルを混合したスラリーにコージェライト製のハニカム(400セル/平方インチ)を浸漬、過剰分の吹き飛ばし、及び乾燥という工程を繰り返し、乾燥後の触媒担持量が200g/Lになるように触媒を担持した。これを触媒Cとする。
【0019】
(一酸化炭素変成反応)
実施例1
管型反応器に触媒A 7.2gを充填し、窒素ガスを100mL/min.流通させながら反応器温度を200℃に昇温した。続いて窒素ガスの代わりに組成が一酸化炭素20%、二酸化炭素6%、水素74%のガスを100mL/min.の流速で導入し、続いて反応器手前の蒸発器を通じて水を供給し、入口ガスの組成が一酸化炭素15%、二酸化炭素4.5%、水素56.2%、水24.3%、GHSV(ガス空間速度)15513(h-1)となるように調節した。次いで、各々15分を掛けて所定の温度に昇温した後、反応を開始した。反応ガスの組成はガスクロマトグラフィにより分析した。結果を表1に示す。
【0020】
実施例2
管型反応器に触媒A 7.2gを充填し、窒素ガスを100mL/min.流通させながら反応器温度を200℃に昇温した。続いて窒素ガスの代わりに組成が一酸化炭素20%、二酸化炭素6%、水素74%のガスを100mL/min.の流速で導入し、続いて反応器手前の蒸発器を通じて水を供給し、入口ガスの組成が一酸化炭素15%、二酸化炭素4.5%、水素56.2%、水24.3%、GHSV 15513(h-1)となるよう調節した。続いて空気を導入して入口ガスの組成が一酸化炭素14.3%、二酸化炭素4.3%、水素53.4%、酸素1%、窒素3.9%、水23.1%、GHSV 16317(h-1)となるよう調節した。次いで、各々15分を掛けて所定の温度に昇温した後、反応を開始した。反応ガスの組成はガスクロマトグラフィにより分析した。結果を表1に示す。
【0021】
実施例3
管型反応器に触媒A 7.2gを充填し、反応器設定温度を300℃にした以外は実施例1と同様に反応を行い、反応成績の経時変化を調べた。結果を表2に示す。
【0022】
比較例1
触媒B 7.1gを用いた以外は実施例1と同様とした。結果を表1に示す。
【0023】
比較例2
触媒B 7.1gを用いた以外は実施例2と同様とした。結果を表1に示す。
【0024】
比較例3
管型反応器に触媒C 7.3gを充填し、窒素ガスを100mL/min.流通させながら反応器温度を200℃に昇温した。続いて窒素ガスの代わりに組成が一酸化炭素20%、二酸化炭素6%、水素74%のガスを100mL/min.の流速で導入し触媒の賦活処理を行った。触媒層の発熱がおさまった後、前記導入ガスの流量を高めてから、反応器手前の蒸発器を通じて水を供給し、入口ガスの組成が一酸化炭素15%、二酸化炭素4.5%、水素56.2%、水24.3%、GHSV 15513(h-1)となるよう調節した。次いで、各々15分を掛けて所定の温度に昇温した後、反応を開始した。反応ガスの組成はガスクロマトグラフィにより分析した。結果を表1に示す。
【0025】
比較例4
管型反応器に触媒C 7.3gを充填し、窒素ガスを100mL/min.流通させながら反応器温度を200℃に昇温した。続いて窒素ガスの代わりに組成が一酸化炭素20%、二酸化炭素6%、水素74%のガスを100mL/min.の流速で導入し触媒の賦活処理を行った。触媒層の発熱がおさまった後、前記導入ガスの流量を高めてから、続いて反応器手前の蒸発器を通じて水を供給し、入口ガスの組成が一酸化炭素15%、二酸化炭素4.5%、水素56.2%、水24.3%、GHSV 15513(h-1)となるよう調節した。続いて空気を導入して入口ガスの組成が一酸化炭素14.3%、二酸化炭素4.3%、水素53.4%、酸素1%、窒素3.9%、水23.1%、GHSV 16317(h-1)となるよう調節した。次いで、各々15分を掛けて所定の温度に昇温した後、反応を開始した。反応ガスの組成はガスクロマトグラフィにより分析した。結果を表1に示す。
【0026】
比較例5
管型反応器に触媒C 7.3gを充填し、反応器設定温度を300℃にした以外は比較例3と同様に反応を行い、一酸化炭素変成率(mol%)の経時変化を調べた。結果を表2に示す。
【0027】
【0029】
【発明の効果】
白金と亜鉛−クロム複合酸化物からなる本発明の触媒は、反応温度が比較的低い低温シフト反応領域に適した一酸化炭素変成用触媒として用いられている従来の銅系触媒に比べ、より高くかつ経時的低下も少ない優れた活性を有する。また、本触媒は、酸素に対する被毒性を有さないばかりか、酸素存在下で更に効率よく一酸化炭素を低減できる特性を有する。
このように、本触媒は、一酸化炭素変成用触媒として、低温かつ酸素の存在する雰囲気下で、連続的に繰り返し使用することができるため、その工業上に果たす役割は極めて大きい。[0001]
BACKGROUND OF THE INVENTION
The present invention provides a carbon monoxide conversion catalyst capable of efficiently converting carbon monoxide even in a low temperature range of about 300 ° C. and having little decrease in activity over time, and at least water vapor and carbon monoxide in the presence of the catalyst. A method for converting carbon monoxide to reduce the concentration of carbon monoxide in the gas, and a method for reducing the carbon monoxide concentration by introducing oxygen and reacting it with a gas comprising at least water vapor and carbon monoxide in the presence of the catalyst. The present invention relates to a method for modifying carbon oxide. Such catalysts with excellent low-temperature activity and long life are advantageous industries for producing high-purity hydrogen with little residual carbon monoxide from carbon monoxide and water vapor, and for reducing carbon monoxide contained in hydrogen gas. Technical means.
[0002]
[Prior art]
Carbon monoxide shift reaction, which generates hydrogen from carbon monoxide and water vapor, has long been known as an important process in the chemical industry. In recent years, methods for obtaining hydrogen by reforming hydrocarbons or alcohols have been widely studied as hydrogen supply methods for which demand is expected to increase. However, when hydrogen is generated by this method, although there is a difference in concentration depending on the raw materials used and the reforming method, carbon monoxide by-product due to reforming cannot be avoided, and this by-product monoxide is generated. In order to reduce the concentration of carbon, a carbon monoxide shift reaction is used.
[0003]
Conventionally, as a catalyst used for this carbon monoxide shift reaction, a copper catalyst is generally used in a low temperature shift reaction region where the reaction temperature is relatively low, and an iron-chromium catalyst is generally used in a relatively high temperature shift reaction region. Has been used.
However, although the copper-based catalyst has a higher carbon monoxide conversion activity in the low temperature range than the iron-chromium-based catalyst, the catalytic activity decreases remarkably at temperatures close to 300 ° C., and the catalytic activity with time There was a big drop in the situation, and it was difficult to say that it was satisfactory. In addition, it is necessary to activate the catalyst by performing a reduction treatment before use with a copper catalyst, and there is a problem that careful attention must be paid to temperature control because the temperature of the catalyst layer rises due to the heat generated at that time. . In addition, even if activated once, when oxygen is mixed when the apparatus is stopped, there is a disadvantage that it must be reactivated.
[0004]
When a hydrogen-containing gas obtained by reforming hydrocarbons or alcohols is used in a stationary or in-vehicle fuel cell or the like, it is generally an electrode catalyst depending on the type of fuel cell, for example, in the case of a polymer electrolyte fuel cell. Since it deteriorates if it is continuously exposed to carbon monoxide at a certain concentration or higher, before introducing the hydrogen-containing gas into the fuel cell, some method is used to affect the coexisting carbon monoxide on the electrode catalyst. It is necessary to reduce it to a certain extent. In many cases, carbon monoxide is reduced to the order of ppm by a selective oxidation reaction performed in a hydrogen purifier installed in front of the gas introduction part of the fuel cell. In order to maintain a high state over a long period of time, the carbon monoxide itself in the hydrogen-containing gas coming out of the reformer is reduced as much as possible, and it has excellent selective carbon monoxide modification activity. A long-life catalyst is essential.
[0005]
However, hydrogen purifiers suitable for solving these problems have been proposed (see, for example, Patent Documents 1, 2, and 3), but these techniques describe that the carbon monoxide concentration is effectively reduced. However, the amount of catalyst used is unknown and its performance is not clear.
[0006]
[Patent Document 1]
JP 2000-302410 A [Patent Document 2]
JP 2001-342005 A [Patent Document 3]
Japanese Patent Laid-Open No. 2002-60206
[Problems to be solved by the invention]
The object of the present invention is to provide a new catalyst which exhibits a higher low-temperature activity and has a longer life as a carbon monoxide conversion catalyst in a low-temperature shift reaction region where the reaction temperature is relatively low as compared with a conventionally used copper-based catalyst. Is to provide. Another object of the present invention is to provide an industrially excellent catalyst that does not involve the problem of oxygen toxicity of copper-based catalysts.
[0008]
[Means for Solving the Problems]
As a result of intensive studies on the carbon monoxide conversion method having the above-mentioned problems, the present inventors generally contain a noble metal catalyst whose carbon monoxide conversion activity in a low temperature region is inferior to that of a copper-based catalyst. The catalyst composed of platinum and zinc-chromium composite oxide exhibits high activity compared to the copper catalyst even in a low temperature range of about 300 ° C., and even in a smaller amount of catalyst, that is, efficiently even under high load conditions. It has been found that the concentration of carbon monoxide can be reduced and the decrease in activity over time can be reduced as compared with a copper catalyst. In addition, in the catalyst comprising this platinum and zinc-chromium composite oxide, not only activation of the catalyst is not required at the start of use, but also by introducing oxygen and reacting it, the carbon monoxide concentration can be more efficiently increased. The inventors have found that this can be reduced, and have completed the present invention.
[0009]
That is, the present invention relates to a carbon monoxide conversion catalyst comprising platinum and a zinc-chromium composite oxide as shown in the following (1) to (5), and a gas comprising at least water vapor and carbon monoxide in the presence of the catalyst. Carbon monoxide conversion method for reducing the concentration of carbon monoxide, and carbon monoxide for reducing the concentration of carbon monoxide by introducing and reacting with at least a gas composed of water vapor and carbon monoxide in the presence of the catalyst Is related to the transformation method.
(1) A carbon monoxide conversion catalyst comprising platinum and a zinc-chromium composite oxide.
(2) The amount of platinum contained in the catalyst is in the range of 1 to 50% by weight with respect to the total amount of platinum metal and zinc-chromium composite oxide as metallic platinum. Catalyst.
(3) The carbon monoxide conversion catalyst according to (1), wherein the atomic ratio of zinc / chromium contained in the catalyst is in the range of 0.05 to 20.
(4) A carbon monoxide conversion method that reduces the concentration of carbon monoxide in a gas comprising at least water vapor and carbon monoxide in the presence of the catalyst according to (1) to (3).
(5) A carbon monoxide conversion method for reducing the concentration of carbon monoxide by introducing oxygen into at least a gas composed of water vapor and carbon monoxide and reacting them in the presence of the catalyst according to (1) to (3). .
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Although there is no restriction | limiting in particular about the raw material of platinum in this invention, For example, a platinum oxide, chloroplatinic acid and its alkali metal salt, platinum acetylacetonate, dinitrodiammine platinum, etc. can be used. Moreover, when preparing a catalyst by dissolving in water, it is preferable to use potassium chloroplatinate. On the other hand, there are no particular restrictions on zinc and chromium that are used as raw materials for the zinc and chromium composite oxide.
[0011]
The platinum content contained in the catalyst of the present invention is preferably in the range of 1 to 50% by weight, based on the total amount of metal platinum and zinc-chromium composite oxide as metal platinum, and 5 to 30% by weight. It is more preferable that When the amount is less than 1% by weight, a decrease in activity is observed. When the amount is more than 50% by weight, the activity per platinum which is a noble metal decreases, which is economically disadvantageous.
The atomic ratio of zinc / chromium is preferably in the range of 0.05 to 20, and more preferably 0.1 to 10. If the zinc / chromium atomic ratio is less than 0.05 or greater than 20, the carbon monoxide modification activity is relatively small.
[0012]
There is no restriction | limiting in particular in the preparation method of the catalyst which consists of platinum and zinc-chromium complex oxide in this invention. A zinc-chromium composite oxide precursor is obtained from an aqueous solution in which zinc and chromium components are dissolved and a precipitant by a coprecipitation method, filtered, washed, dried or fired, and pulverized as necessary. Dispersing in an aqueous solution of salt and depositing platinum using a precipitating agent or a reducing agent, a method of impregnating platinum in a zinc-chromium composite oxide, and dissolving three components of platinum, zinc and chromium There is a method of forming a precipitate from an aqueous solution and a precipitant by a coprecipitation method.
[0013]
When platinum is precipitated in an aqueous solution by a precipitation method, alkali compounds such as sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, and sodium bicarbonate are used as the precipitant. The amount of the precipitating agent at the time of preparing the precipitate is 1 to 2 times, preferably 1.1 to 1.6 times the chemical equivalent of the platinum salt contained in the solution. If it is less than 1 time, the amount of precipitate produced is insufficient, and if it is more than 2 times, it is surplus, which is economically disadvantageous.
The temperature during the preparation of the precipitate is 20 to 90 ° C, preferably 35 to 85 ° C. When the temperature is lower than 20 ° C., ripening of the precipitate becomes insufficient, and when the temperature is higher than 90 ° C., the heat generated when the precipitant is added and the risk of slurry bumping associated therewith increase.
The precipitate obtained by the precipitation method is preferably washed with ion exchanged water, distilled water or the like in order to remove the precipitant, chloride derived from the raw material, alkali metal and the like.
[0014]
The precipitate obtained as described above is dried and calcined, and is crushed as necessary to have a uniform size or molded. In addition, the dried product of the slurry or the dried and calcined product is pulverized and suspended in water, and if necessary, a binder such as alumina sol can be added and supported on the carrier and the carrier structure. it can. In this case, it can be used after drying after carrying or after firing again.
[0015]
By using the catalyst of the present invention, the concentration of carbon monoxide in the gas composed of at least water vapor and carbon monoxide can be efficiently reduced. The gas to be transformed may contain gas such as hydrogen, carbon dioxide and nitrogen in addition to water vapor and carbon monoxide.
In the present invention, when oxygen is introduced and reacted, air can be used as the oxygen-containing gas. The oxygen concentration is preferably 0.1 to 5%, more preferably 0.2 to 2%. When the oxygen concentration is less than 0.1%, the effect of introducing oxygen is small. Conversely, when the oxygen concentration is more than 5%, there is a possibility that the heat generation becomes too great and there is a danger.
[0016]
【Example】
The invention is illustrated by the following examples. The present invention is not limited to these examples.
(Catalyst preparation)
Catalyst A
138 g of sodium carbonate (anhydrous) was dissolved in a 5 L round bottom flask together with 1000 mL of ion exchange water, and the temperature was adjusted to 60 ° C. A solution in which 238 g of zinc nitrate hexahydrate and 80 g of chromium nitrate nonahydrate were dissolved in 800 mL of ion-exchanged water and poured to 60 ° C. was added thereto and stirred for 30 minutes. The obtained mixed liquid containing the slurry-like precipitate was filtered, and the precipitate was washed with 12 L of ion-exchanged water. Subsequently, it was dried at 80 ° C. and then calcined at 380 ° C. for 2 hours to obtain 79.8 g of a zinc-chromium composite oxide having an atomic ratio of zinc / chromium of 4.
To 500 mL of a 65 ° C. aqueous solution in which 15 g of this zinc-chromium composite oxide powder was dispersed, 500 mL of a 65 ° C. aqueous solution in which 13.8 g of potassium chloroplatinate was dissolved was added. After 30 minutes, 66 mL of 1NKOH aqueous solution was added and stirred at 65 ° C. for 60 minutes. Thereafter, filtration was performed, and washing with water was repeated until chlorine in the filtrate was 1 ppm or less. And after making it dry at 80 degreeC, it baked at 380 degreeC for 2 hours, and obtained 20.8g of catalysts which consist of platinum and zinc-chromium complex oxide.
This catalyst was wet pulverized under a slurry concentration of 25% by weight, mixed with alumina sol to make a slurry, immersed in a cordierite honeycomb (400 cells / cm 2), blown off excessively, and dried. The catalyst was supported so that the amount of the catalyst supported after drying was 200 g / L. This is referred to as catalyst A.
[0017]
Catalyst B
138 g of sodium carbonate (anhydrous) was dissolved in a 5 L round bottom flask together with 1000 mL of ion exchange water, and the temperature was adjusted to 60 ° C. To this was added a solution prepared by dissolving 298 g of zinc nitrate hexahydrate in 800 mL of ion exchange water to 60 ° C., and stirred for 30 minutes. The obtained mixed liquid containing the slurry-like precipitate was filtered, and the precipitate was washed with 12 L of ion-exchanged water. Subsequently, it was dried at 80 ° C. and then calcined at 380 ° C. for 2 hours to obtain 80.9 g of zinc oxide.
To 500 mL of a 65 ° C. aqueous solution in which 15 g of this zinc oxide powder was dispersed, 500 mL of a 65 ° C. aqueous solution in which 13.8 g of potassium chloroplatinate was dissolved was added. After 30 minutes, 66 mL of 1NKOH aqueous solution was added and stirred at 65 ° C. for 60 minutes. Thereafter, filtration was performed, and washing with water was repeated until chlorine in the filtrate was 1 ppm or less. And after making it dry at 80 degreeC, it baked at 380 degreeC for 2 hours, and obtained 20.7g of the catalyst which consists of platinum and a zinc oxide.
The catalyst is wet pulverized under a slurry concentration of 25% by weight, mixed with alumina sol to form a slurry, and then immersed in a cordierite honeycomb (400 cells / cm 2), blown off excessively, and dried. The catalyst was supported so that the amount of catalyst supported after drying was 200 g / L. This is referred to as catalyst B.
[0018]
Catalyst C
177 g of sodium carbonate (anhydrous) was dissolved in a 5 L round bottom flask together with 1000 mL of ion-exchanged water to obtain 40 ° C. A solution prepared by dissolving 315 g of copper sulfate (pentahydrate) and 19.7 g of boric acid in 800 mL of ion-exchanged water and adjusting the temperature to 40 ° C. was added, and then 77.0 g of zinc oxide was dispersed in 300 mL of ion-exchanged water. The slurry was added, and carbon dioxide gas was immediately blown at a rate of 6 L / h. After 1 hour, the temperature was raised to 80 ° C. and held for 30 minutes. The blowing of carbon dioxide gas was stopped in 2 hours and then cooled to 60 ° C. A slurry prepared from a solution in which 49 g of aluminum sulfate was dissolved in 45 mL of ion-exchanged water and a solution in which 10.2 g of sodium hydroxide was dissolved in 70 mL of ion-exchanged water was added and stirred for 20 minutes. The mixed slurry thus prepared was filtered and washed with 12 L of 0.05% aqueous sodium hydroxide and 3 L of ion-exchanged water. Then, after drying at 80 degreeC, it baked and obtained 190g of Cu-Zn-Al catalysts. This catalyst is wet pulverized under a slurry concentration of 25% by weight, and then a cordierite honeycomb (400 cells / in 2) is immersed in a slurry mixed with alumina sol, excessively blown, and dried repeatedly. The catalyst was supported so that the subsequent catalyst loading amount was 200 g / L. This is referred to as catalyst C.
[0019]
(Carbon monoxide transformation reaction)
Example 1
A tubular reactor was charged with 7.2 g of catalyst A, and nitrogen gas was supplied at 100 mL / min. The reactor temperature was raised to 200 ° C. while circulating. Subsequently, instead of nitrogen gas, a gas having a composition of 20% carbon monoxide, 6% carbon dioxide, and 74% hydrogen was added at 100 mL / min. The water is supplied through an evaporator before the reactor, and the composition of the inlet gas is 15% carbon monoxide, 4.5% carbon dioxide, 56.2% hydrogen, 24.3% water, It adjusted so that it might become GHSV (gas space velocity) 15513 (h < -1 >). Next, the reaction was started after the temperature was raised to a predetermined temperature over 15 minutes. The composition of the reaction gas was analyzed by gas chromatography. The results are shown in Table 1.
[0020]
Example 2
A tubular reactor was charged with 7.2 g of catalyst A, and nitrogen gas was supplied at 100 mL / min. The reactor temperature was raised to 200 ° C. while circulating. Subsequently, instead of nitrogen gas, a gas having a composition of 20% carbon monoxide, 6% carbon dioxide, and 74% hydrogen was added at 100 mL / min. The water is supplied through an evaporator before the reactor, and the composition of the inlet gas is 15% carbon monoxide, 4.5% carbon dioxide, 56.2% hydrogen, 24.3% water, It adjusted so that it might become GHSV 15513 (h < -1 >). Subsequently, air was introduced and the composition of the inlet gas was carbon monoxide 14.3%, carbon dioxide 4.3%, hydrogen 53.4%, oxygen 1%, nitrogen 3.9%, water 23.1%, GHSV It adjusted so that it might be 16317 (h < -1 >). Next, the reaction was started after the temperature was raised to a predetermined temperature over 15 minutes. The composition of the reaction gas was analyzed by gas chromatography. The results are shown in Table 1.
[0021]
Example 3
A reaction was carried out in the same manner as in Example 1 except that 7.2 g of catalyst A was charged in a tubular reactor and the reactor set temperature was set to 300 ° C., and changes with time in reaction results were examined. The results are shown in Table 2.
[0022]
Comparative Example 1
Example 1 was repeated except that 7.1 g of catalyst B was used. The results are shown in Table 1.
[0023]
Comparative Example 2
Example 2 was repeated except that 7.1 g of catalyst B was used. The results are shown in Table 1.
[0024]
Comparative Example 3
A tubular reactor was charged with 7.3 g of catalyst C, and nitrogen gas was supplied at 100 mL / min. The reactor temperature was raised to 200 ° C. while circulating. Subsequently, instead of nitrogen gas, a gas having a composition of 20% carbon monoxide, 6% carbon dioxide, and 74% hydrogen was added at 100 mL / min. The catalyst was activated at a flow rate of 2 to 5 to activate the catalyst. After the heat generation in the catalyst layer has subsided, the flow rate of the introduced gas is increased, and then water is supplied through the evaporator before the reactor. The composition of the inlet gas is 15% carbon monoxide, 4.5% carbon dioxide, hydrogen It adjusted so that it might become 56.2%, water 24.3%, and GHSV 15513 (h < -1 >). Next, the reaction was started after the temperature was raised to a predetermined temperature over 15 minutes. The composition of the reaction gas was analyzed by gas chromatography. The results are shown in Table 1.
[0025]
Comparative Example 4
A tubular reactor was charged with 7.3 g of catalyst C, and nitrogen gas was supplied at 100 mL / min. The reactor temperature was raised to 200 ° C. while circulating. Subsequently, instead of nitrogen gas, a gas having a composition of 20% carbon monoxide, 6% carbon dioxide, and 74% hydrogen was added at 100 mL / min. The catalyst was activated at a flow rate of 2 to 5 to activate the catalyst. After the heat generation in the catalyst layer has subsided, the flow rate of the introduced gas is increased, and then water is supplied through the evaporator in front of the reactor. The composition of the inlet gas is 15% carbon monoxide and 4.5% carbon dioxide. , Hydrogen 56.2%, water 24.3%, GHSV 15513 (h -1 ). Subsequently, air was introduced, and the composition of the inlet gas was carbon monoxide 14.3%, carbon dioxide 4.3%, hydrogen 53.4%, oxygen 1%, nitrogen 3.9%, water 23.1%, GHSV It adjusted so that it might be 16317 (h < -1 >). Next, the reaction was started after the temperature was raised to a predetermined temperature over 15 minutes. The composition of the reaction gas was analyzed by gas chromatography. The results are shown in Table 1.
[0026]
Comparative Example 5
The reaction was carried out in the same manner as in Comparative Example 3 except that 7.3 g of catalyst C was charged into a tubular reactor and the reactor set temperature was 300 ° C., and the change over time in the carbon monoxide conversion rate (mol%) was examined. . The results are shown in Table 2.
[0027]
[0028]
[0029]
【The invention's effect】
The catalyst of the present invention comprising platinum and zinc-chromium composite oxide is higher than the conventional copper catalyst used as a carbon monoxide conversion catalyst suitable for a low temperature shift reaction region where the reaction temperature is relatively low. In addition, it has excellent activity with little deterioration over time. In addition, the present catalyst is not only toxic to oxygen, but also has the property of more efficiently reducing carbon monoxide in the presence of oxygen.
Thus, since this catalyst can be continuously used repeatedly as a carbon monoxide conversion catalyst in a low temperature and oxygen atmosphere, it plays an extremely important role in the industry.
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