JP3746401B2 - Selective oxidation catalyst for carbon monoxide in reformed gas - Google Patents
Selective oxidation catalyst for carbon monoxide in reformed gas Download PDFInfo
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- JP3746401B2 JP3746401B2 JP18990799A JP18990799A JP3746401B2 JP 3746401 B2 JP3746401 B2 JP 3746401B2 JP 18990799 A JP18990799 A JP 18990799A JP 18990799 A JP18990799 A JP 18990799A JP 3746401 B2 JP3746401 B2 JP 3746401B2
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- Prior art keywords
- carbon monoxide
- catalyst
- reformed gas
- selective oxidation
- ruthenium
- Prior art date
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Links
- 239000003054 catalyst Substances 0.000 title claims description 61
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 title claims description 58
- 229910002091 carbon monoxide Inorganic materials 0.000 title claims description 58
- 238000007254 oxidation reaction Methods 0.000 title claims description 33
- 230000003647 oxidation Effects 0.000 title claims description 32
- 239000007789 gas Substances 0.000 claims description 38
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 claims description 33
- PNEYBMLMFCGWSK-UHFFFAOYSA-N Alumina Chemical compound [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 claims description 32
- 229910052707 ruthenium Inorganic materials 0.000 claims description 29
- KJTLSVCANCCWHF-UHFFFAOYSA-N Ruthenium Chemical compound [Ru] KJTLSVCANCCWHF-UHFFFAOYSA-N 0.000 claims description 19
- 239000002245 particle Substances 0.000 claims description 18
- 229910052697 platinum Inorganic materials 0.000 claims description 18
- 239000000446 fuel Substances 0.000 claims description 16
- 239000005518 polymer electrolyte Substances 0.000 claims description 6
- MYMOFIZGZYHOMD-UHFFFAOYSA-N Dioxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 claims description 5
- 229910001882 dioxygen Inorganic materials 0.000 claims description 5
- 239000000203 mixture Substances 0.000 claims description 5
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 9
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 9
- 229910052751 metal Inorganic materials 0.000 description 9
- 239000002184 metal Substances 0.000 description 9
- 239000001301 oxygen Substances 0.000 description 9
- 229910052760 oxygen Inorganic materials 0.000 description 9
- 238000006243 chemical reaction Methods 0.000 description 7
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Natural products C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 7
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 6
- -1 natural gas hydrocarbon Chemical class 0.000 description 6
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 5
- 230000003197 catalytic effect Effects 0.000 description 5
- 230000000694 effects Effects 0.000 description 5
- 239000001257 hydrogen Substances 0.000 description 5
- 229910052739 hydrogen Inorganic materials 0.000 description 5
- 238000010248 power generation Methods 0.000 description 5
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 description 4
- ATUOYWHBWRKTHZ-UHFFFAOYSA-N Propane Chemical compound CCC ATUOYWHBWRKTHZ-UHFFFAOYSA-N 0.000 description 4
- 230000000052 comparative effect Effects 0.000 description 4
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 4
- 230000010718 Oxidation Activity Effects 0.000 description 3
- 230000004807 localization Effects 0.000 description 3
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 2
- 239000004215 Carbon black (E152) Substances 0.000 description 2
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 2
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- 229910000147 aluminium phosphate Inorganic materials 0.000 description 2
- 229910002092 carbon dioxide Inorganic materials 0.000 description 2
- 239000001569 carbon dioxide Substances 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 239000002737 fuel gas Substances 0.000 description 2
- 229930195733 hydrocarbon Natural products 0.000 description 2
- 238000000034 method Methods 0.000 description 2
- 231100000572 poisoning Toxicity 0.000 description 2
- 230000000607 poisoning effect Effects 0.000 description 2
- 239000001294 propane Substances 0.000 description 2
- 238000001179 sorption measurement Methods 0.000 description 2
- 238000000629 steam reforming Methods 0.000 description 2
- BVKZGUZCCUSVTD-UHFFFAOYSA-L Carbonate Chemical compound [O-]C([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-L 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 229910021529 ammonia Inorganic materials 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 239000006227 byproduct Substances 0.000 description 1
- 229910002090 carbon oxide Inorganic materials 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000004453 electron probe microanalysis Methods 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 150000002430 hydrocarbons Chemical class 0.000 description 1
- 150000002431 hydrogen Chemical class 0.000 description 1
- 238000011835 investigation Methods 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 239000003345 natural gas Substances 0.000 description 1
- 230000033116 oxidation-reduction process Effects 0.000 description 1
- 239000008188 pellet Substances 0.000 description 1
- 229920000642 polymer Polymers 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 239000012495 reaction gas Substances 0.000 description 1
- IKGXIBQEEMLURG-NVPNHPEKSA-N rutin Chemical compound O[C@@H]1[C@H](O)[C@@H](O)[C@H](C)O[C@H]1OC[C@@H]1[C@@H](O)[C@H](O)[C@@H](O)[C@H](OC=2C(C3=C(O)C=C(O)C=C3OC=2C=2C=C(O)C(O)=CC=2)=O)O1 IKGXIBQEEMLURG-NVPNHPEKSA-N 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
- 238000005245 sintering Methods 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 238000003786 synthesis reaction Methods 0.000 description 1
- 230000009466 transformation Effects 0.000 description 1
- 230000007704 transition Effects 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
- Y02E60/50—Fuel cells
-
- 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
Landscapes
- Fuel Cell (AREA)
- Hydrogen, Water And Hydrids (AREA)
- Catalysts (AREA)
Description
【０００１】
【発明の属する技術分野】
本発明は、改質ガス中の一酸化炭素を選択的に酸化する触媒に係り、更に詳細には、低温で作動する燃料電池、特に固体高分子型燃料電池に用いられる改質ガス中の一酸化炭素を選択酸化する触媒に関する。
本発明の触媒によれば、改質ガス中の一酸化炭素が選択的に酸化されるので、かかる燃料電池を低温においても効果的に作動させることができる。
【０００２】
【従来の技術】
従来、燃料電池用の燃料ガスとしては、コスト面を考慮して、メタンやプロパンなどの天然ガスの炭化水素、メタノール等のアルコール又はナフサ等を水蒸気改質して得られる改質ガスが広く用いられている。かかる改質ガスには、水素や二酸化炭素など以外にも一酸化炭素が含まれており、シフト反応で処理した後であっても、約１容量％の一酸化炭素が含まれていることが知られている。
【０００３】
かかる副生一酸化炭素は、溶融炭酸塩型などの高温作動型燃料電池では、燃料としても利用されるが、燐酸型や固体高分子型の低温作動型燃料電池では、電極触媒である白金系触媒に対して触媒毒作用を呈し、特に燐酸型燃料電池よりも低温で運転される固体高分子型燃料電池においては、改質ガス中に共存する一酸化炭素による触媒被毒が著しく、発電効率の低下という問題が生じた。
そして、このような問題に対し、従来は、種々の白金族金属を用いたアルミナ触媒が提案されていた。
【０００４】
【発明が解決しようとする課題】
しかしながら、かかる白金族金属を用いたアルミナ触媒にあっては、酸素による酸化反応の選択性や活性が低いため、改質ガスの主成分であり燃料ガスとなる水素が同時に酸化浪費されてしまい、燃料利用効率の低下を引き起こすという課題があった。
また、固体高分子型燃料電池においては、改質ガスを用いながら要求される発電効率を得るには、共存する一酸化炭素を当初の約１容量％からその１／１００程度以下に低減した後に供給する必要があるが、上記従来の白金−アルミナ系触媒では、一酸化炭素の酸化低減が十分でなく、残留する一酸化炭素により発電効率の劣化を招いていた。
【０００５】
本発明は、このような従来技術の有する課題に鑑みてなされたものであり、その目的とするところは、改質ガス中の一酸化炭素を選択的に酸化して低減し、良好な燃料利用効率や発電効率を実現し得る一酸化炭素選択酸化触媒を提供することにある。
【０００６】
【課題を解決するための手段】
本発明者らは、上記目的を達成すべく鋭意検討を重ねた結果、ルテニウム等をαアルミナ担体に適切に担持した触媒が、酸素ガスが一酸化炭素に対して過剰に存在する条件下で、優れた一酸化炭素の選択的酸化を行うことを見出し、本発明を完成するに至った。
【０００７】
即ち、本発明の一酸化炭素選択酸化触媒は、改質ガス中の一酸化炭素を酸素ガスによって選択的に酸化する触媒であって、ルテニウム又はルテニウムと白金をαアルミナ粒状又はペレット状担体に担持して成り、そのルテニウム又はルテニウムと白金が上記αアルミナ粒状又はペレット状担体の外表面から１００μｍ以内の深さに局在しており、このルテニウム又はルテニウムと白金の粒子径が２００Å以下であることを特徴とする。
【００１０】
また、本発明の一酸化炭素選択酸化触媒の他の好適形態は、上記ルテニウム又はルテニウムと白金の混合物を０．０１〜１０重量％の割合で含有することを特徴とする。
【００１１】
更にまた、本発明の一酸化炭素選択酸化触媒の更に他の好適形態は、上記改質ガスが固体高分子型燃料電池に用いられる改質ガスであることを特徴とする。
【００１２】
【作用】
本発明の選択酸化触媒が、一酸化炭素（ＣＯ）の優れた選択酸化性を発揮する理由の詳細は必ずしも明らかではないが、現時点では以下のように推察される。
【００１３】
即ち、本発明では、αアルミナ担体を用いることにより、触媒金属であるルテニウム（Ｒｕ）又はＲｕと白金（Ｐｔ）が該担体の最表面近傍に存在するようにした。
このように、触媒金属を担体表面に局在化させることによって、ＣＯの酸化が起こる温度を低温側にシフトさせることができ、他の反応に対する選択性を向上でき、これにより、反応後の改質ガス中のＣＯ濃度を低減させ、且つ水素の消費を防ぐことができるものと思われる。
【００１４】
また、本発明では、αアルミナを担体として好適に使用し、このαアルミナは上述した触媒金属の表面局在化を実現し得るが、これ以外にも、γアルミナやシリカの代わりにαアルミナを使用することにより、反応ガス中に含まれる水蒸気の影響を減らすことができる。
一般に、ガス中に水蒸気が混入することにより水蒸気吸着が起こり、ＣＯの酸化が起こる温度が高温側にシフトされるが、αアルミナを用いることにより、その吸着による反応温度の高温側へのシフトを回避できる。この結果、ＣＯ酸化の選択性を向上させることができ、反応後の改質ガス中のＣＯ濃度を低減させ、水素の消費を防ぐことができるものと考えられる。
【００１５】
【発明の実施の形態】
以下、本発明の一酸化炭素選択酸化触媒について詳細に説明する。
上述如く、本発明の一酸化炭素選択酸化触媒は、改質ガス中のＣＯを酸素ガスによって選択的に酸化する触媒である。
ここで、改質ガスは、一般にメタンやプロパン等の炭化水素、メタノール等のアルコール又はナフサ等を水蒸気改質して得られるガスをいい、代表的に、メタノール改質ガスは水素ガスを主成分とし、二酸化炭素（ＣＯ２）、メタン（ＣＨ４）、水（Ｈ２Ｏ）及びＣＯを含む。
なお、本発明の適用対象として効果的なものは、これらのうちでもシフト反応後の改質ガスであって、ＣＯ濃度が１容量％程度のものである。
【００１６】
次に、酸素ガスは、ＣＯとの反応当量よりも過剰に存在すれば特に限定されるものではないが、代表的には、ＣＯとの反応当量の１．１〜５倍の酸素を存在させることが好ましい。
１．１倍未満では、酸化されないＣＯが残留し、５倍を超えると、水素の消費量が増大することがあり、好ましくない。
【００１７】
また、本発明の一酸化炭素選択酸化触媒は、Ｒｕ又はＲｕとＰｔを、αアルミナ担体に担持して成る。
ここで、Ｒｕは優れた酸化触媒性能を有し、酸素によるＣＯの選択酸化を担うが、同様に酸化触媒性能を有するＰｔを混入することも可能である。
なお、Ｒｕの担持量は、得られる触媒全体の０．０１〜１０重量％、望ましくは０．０２〜０．５重量％とすることが好ましい。一方、ＲｕとＰｔとの混合物の担持量も、触媒全体の０．０１〜１０重量％、望ましくは０．０２〜５重量％とすることが好ましい。
Ｒｕの担持量が０．０２重量％未満では、ＣＯの酸化活性が十分でないことがあり、０．５重量％を超えると、Ｒｕが有効に利用されないことがある。
一方、ＲｕとＰｔの混合物の担持量が０．０２重量％未満では、ＣＯの酸化活性が十分でないことがあり、０．５重量％を超えると、Ｒｕ、Ｐｔが有効に利用されないことがある。
【００１８】
更に、本発明の選択酸化触媒では、担持されているＲｕ又はＰｔの粒子径が２００Å以下、望ましくは５〜２００Åであることが好ましい。
粒子径が２００Åを超えると、ＣＯの酸化活性が十分でなくなることがあり、好ましくない。
【００１９】
また、上記αアルミナ担体としては、Ｒｕ又はＲｕ−Ｐｔ混合物を当該担体外表面から１００μｍ以内、好ましくは２０μｍ以内に存在させることができる担体であれば、特に限定されるものではない。
なお、Ｒｕ等を担体外表面から１００μｍ以内に担持できない場合は、触媒表面のＲｕ濃度が薄くなり、所期の効果が得られないことがある。
【００２０】
更に、本発明の選択酸化触媒においては、αアルミナを担体として好適に使用できるが、この理由は、αアルミナは上述の局在化を容易に実現するからであり、また、上述のように水蒸気の影響を低減できるからである。
なお、γアルミナは、１０００℃以上の温度で保持すればαアルミナに転移するが、その温度に保つと触媒金属であるＲｕやＰｔがシンタリングを起こし、十分な活性が得られなくなるので、本発明の触媒に単独で用いるのには適していない。
但し、上述の特性を満足する多孔質担体とαアルミナを併用することは可能である。
【００２１】
本発明の選択酸化触媒は、上述のような構成を有し、優れたＣＯ選択酸化性を有するが、代表的には、改質ガス中に共存する１容量％程度のＣＯを１００ｐｐｍ程度に酸化除去する。
なお、使用条件も特に限定されるものではないが、空間速度（ＳＶ）を３０，０００／ｈｒ以下、触媒温度を８０〜１８０℃とすれば、顕著な効果が得られる。
【００２２】
また、触媒形態は、粒状やペレット状とする。
【００２３】
【実施例】
以下、本発明を実施例及び比較例により更に詳細に説明するが、本発明はこれら実施例に限定されるものではない。
なお、以下、特記しない限り「％」は「重量％」を示す。
【００２４】
［性能評価］
以下の実施例及び比較例において、得られた触媒の性能は下記の手法で評価した。
（触媒金属の担持粒子径）
触媒を粉砕して、透過型電子顕微鏡により担持金属を直接観察して、その粒径を確認した。
（触媒金属の担体表面局在化）
触媒をほぼ半分に割り、その断面をＥＰＭＡにより観察して担持幅を確認した。
【００２５】
（実施例１）
平均粒径が２ｍｍ程度のαアルミナにＲｕを約０．２％担持させて本例の選択酸化触媒を得た。この触媒において、Ｒｕはαアルミナ外表面から５０μｍまでの深さに存在していた。また、Ｒｕの担持粒子径は、平均で１００Åであった。
この選択酸化触媒に、１容量％の一酸化炭素を含む改質ガスに酸素を２．５容量％分投入した試験ガスをＳＶ３００００／ｈｒで通過させたところ、触媒層の温度が１００℃〜１６０℃の範囲において、ＣＯ濃度が１００ｐｐｍ以下になった。
【００２６】
（比較例１）
平均粒径が２ｍｍ程度のγアルミナにＲｕを約０．２％担持させて本例の触媒を得た。Ｒｕはγアルミナ外表面から５００μｍまでの深さに存在しており、Ｒｕの担持粒子径は平均で８０Åであった。
この触媒に、１容量％の一酸化炭素を含む改質ガスに酸素を２．５容量％分投入した試験ガスをＳＶ３００００／ｈｒで通過させたところ、触媒層の温度が１００℃〜１６０℃の範囲において、ＣＯ濃度は５０００ｐｐｍであった。
【００２７】
（実施例２）
平均粒径が２ｍｍ程度のαアルミナにＲｕを約０．２％担持させたて本例の選択酸化触媒を得た。Ｒｕはαアルミナ外表面から５０μｍまでの深さに存在しており、Ｒｕの担持粒子径は平均で１００Åであった。
この選択酸化触媒に、０．１容量％の一酸化炭素を含む改質ガスに酸素を０．１容量％分投入した試験ガスをＳＶ２００００／ｈｒで通過させたところ、触媒層の温度が１００℃〜１５０℃の範囲において、ＣＯ濃度が５０ｐｐｍ以下になった。
【００２８】
（比較例２）
平均粒径が２ｍｍ程度のγアルミナにＲｕを約０．２％担持させて本例の触媒を得た。Ｒｕはγアルミナ外表面から５００μｍまでの深さに存在しており、Ｒｕの担持粒子径は平均で８０Åであった。
この触媒に、０．１容量％の一酸化炭素を含む改質ガスに酸素を０．１容量％分投入した試験ガスをＳＶ２００００／ｈｒで通過させたところ、触媒層の温度が１００℃〜１６０℃の範囲において、ＣＯ濃度は１００ｐｐｍ以上であった。
【００２９】
（実施例３）
平均粒径が２ｍｍ程度のαアルミナにＲｕ：Ｐｔ（重量比４：１）を約０．２％担持させて本例の選択酸化触媒を得た。Ｒｕ及びＰｔはαアルミナ外表面から１００μｍまでの深さに存在しており、Ｒｕ及びＰｔの担持粒子径は平均で８０Åであった。
この選択酸化触媒に、１容量％の一酸化炭素を含む改質ガスに酸素を２．５容量％分投入した試験ガスをＳＶ３００００／ｈｒで通過させたところ、触媒層の温度が１００℃〜１５０℃の範囲において、ＣＯ濃度は５０ｐｐｍ以下になり、特に１１０℃付近においては、２０ｐｐｍ以下になっていた。
【００３０】
以上、本発明を好適実施例により詳細に説明したが、本発明はこれら実施例に限定されるものではなく、本発明の開示の範囲内において種々の変形実施が可能である。
例えば、本発明の選択酸化触媒の用途は、固体高分子型燃料電池に供給される改質ガスに限定されるものではなく、他の改質ガス中のＣＯの低減にも利用可能であり、高純度水素ガスを必要とするアンモニアの合成などの各種プロセスにも適用可能である。
【００３１】
【発明の効果】
以上説明してきたように、本発明によれば、ルテニウム等をαアルミナ担体に適切に担持して酸素過剰条件下で処理することとしたため、改質ガス中の一酸化炭素を選択的に酸化して低減し、良好な燃料利用効率や発電効率を実現し得る一酸化炭素選択酸化触媒を提供することができる。
例えば、本発明の触媒を用いることにより、改質ガス中に１容量％程度存在する一酸化炭素を過剰量の酸素の存在下１５０℃程度で反応させれば、一酸化炭素濃度を０．１容量％以下に低減することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a catalyst that selectively oxidizes carbon monoxide in a reformed gas. More specifically, the present invention relates to a catalyst in a reformed gas used in a fuel cell operating at a low temperature, particularly a polymer electrolyte fuel cell. The present invention relates to a catalyst that selectively oxidizes carbon oxide.
According to the catalyst of the present invention, carbon monoxide in the reformed gas is selectively oxidized, so that the fuel cell can be effectively operated even at a low temperature.
[0002]
[Prior art]
Conventionally, as a fuel gas for a fuel cell, in view of cost, a reformed gas obtained by steam reforming a natural gas hydrocarbon such as methane or propane, an alcohol such as methanol or naphtha is widely used. It has been. Such reformed gas contains carbon monoxide in addition to hydrogen, carbon dioxide, and the like, and it may contain about 1% by volume of carbon monoxide even after being processed by the shift reaction. Are known.
[0003]
Such by-product carbon monoxide is also used as a fuel in a high temperature operation type fuel cell such as a molten carbonate type, but in a phosphoric acid type or solid polymer type low temperature operation type fuel cell, a platinum-based electrode catalyst is used. Catalytic poisoning to the catalyst, especially in polymer electrolyte fuel cells that are operated at lower temperatures than phosphoric acid fuel cells, the catalyst poisoning due to carbon monoxide coexisting in the reformed gas is significant, and power generation efficiency There was a problem of decline.
For such problems, conventionally, alumina catalysts using various platinum group metals have been proposed.
[0004]
[Problems to be solved by the invention]
However, in the alumina catalyst using such a platinum group metal, since the selectivity and activity of the oxidation reaction with oxygen is low, hydrogen that is the main component of the reformed gas and the fuel gas is wasted and oxidized at the same time. There was a problem of causing a decrease in fuel utilization efficiency.
In the polymer electrolyte fuel cell, in order to obtain the required power generation efficiency using the reformed gas, the coexisting carbon monoxide is reduced from about 1% by volume to about 1/100 or less of the initial volume. Although it is necessary to supply the above-mentioned conventional platinum-alumina-based catalyst, the oxidation reduction of carbon monoxide is not sufficient, and the remaining carbon monoxide causes deterioration in power generation efficiency.
[0005]
The present invention has been made in view of such problems of the prior art, and an object of the present invention is to selectively oxidize and reduce carbon monoxide in the reformed gas, and to make good use of fuel. The object is to provide a carbon monoxide selective oxidation catalyst capable of realizing efficiency and power generation efficiency.
[0006]
[Means for Solving the Problems]
As a result of intensive investigations to achieve the above object, the present inventors have found that a catalyst in which ruthenium or the like is appropriately supported on an α-alumina support is in a condition where oxygen gas is excessively present relative to carbon monoxide. The inventors have found that excellent selective oxidation of carbon monoxide is performed, and have completed the present invention.
[0007]
That is, the carbon monoxide selective oxidation catalyst of the present invention is a catalyst that selectively oxidizes carbon monoxide in the reformed gas with oxygen gas, and ruthenium or ruthenium and platinum are supported on an α-alumina granular or pellet-like support. Ri formed by, the ruthenium or ruthenium and platinum are localized in depth within 100μm from the outer surface of the α-alumina granular or pellet-like carrier, the particle diameter of the ruthenium or ruthenium and platinum is 200Å or less It is characterized by that.
[0010]
In addition, another preferred embodiment of the carbon monoxide selective oxidation catalyst of the present invention is characterized by containing the ruthenium or a mixture of ruthenium and platinum in a proportion of 0.01 to 10% by weight.
[0011]
Yet another preferred embodiment of the carbon monoxide selective oxidation catalyst of the present invention is characterized in that the reformed gas is a reformed gas used in a polymer electrolyte fuel cell.
[0012]
[Action]
Although the details of the reason why the selective oxidation catalyst of the present invention exhibits the excellent selective oxidation property of carbon monoxide (CO) are not necessarily clear, at present, it is presumed as follows.
[0013]
That is, in the present invention, by using an α-alumina support , the catalytic metal ruthenium (Ru) or Ru and platinum (Pt) are made to exist in the vicinity of the outermost surface of the support.
Thus, by localizing the catalytic metal on the surface of the support, the temperature at which CO oxidation occurs can be shifted to the low temperature side, and the selectivity for other reactions can be improved. It seems that the concentration of CO in the gas can be reduced and the consumption of hydrogen can be prevented.
[0014]
Further, in the present invention, α-alumina is preferably used as a carrier , and this α-alumina can realize the above-mentioned surface localization of the catalytic metal. In addition to this, α-alumina is used instead of γ-alumina and silica. By using it, the influence of water vapor contained in the reaction gas can be reduced.
In general, when water vapor is mixed into the gas, water vapor adsorption occurs, and the temperature at which CO oxidation occurs is shifted to the high temperature side. By using α-alumina, the reaction temperature due to the adsorption is shifted to the high temperature side. Can be avoided. As a result, it is considered that the selectivity of CO oxidation can be improved, the CO concentration in the reformed gas after the reaction can be reduced, and the consumption of hydrogen can be prevented.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the carbon monoxide selective oxidation catalyst of the present invention will be described in detail.
As described above, the carbon monoxide selective oxidation catalyst of the present invention is a catalyst that selectively oxidizes CO in the reformed gas with oxygen gas.
Here, the reformed gas generally refers to a gas obtained by steam reforming a hydrocarbon such as methane or propane, an alcohol such as methanol or naphtha, and typically, the methanol reformed gas is mainly composed of hydrogen gas. And carbon dioxide (CO 2 ), methane (CH 4 ), water (H 2 O) and CO.
Of these, what is effective as an application target of the present invention is a reformed gas after the shift reaction, and has a CO concentration of about 1% by volume.
[0016]
Next, the oxygen gas is not particularly limited as long as it exists in excess of the reaction equivalent with CO, but typically, oxygen of 1.1 to 5 times the reaction equivalent with CO is present. It is preferable.
If it is less than 1.1 times, unoxidized CO remains, and if it exceeds 5 times, the consumption of hydrogen may increase, which is not preferable.
[0017]
Further, the carbon monoxide selective oxidation catalyst of the present invention comprises Ru or Ru and Pt supported on an α alumina support.
Here, Ru has excellent oxidation catalyst performance and is responsible for selective oxidation of CO by oxygen, but Pt having oxidation catalyst performance can also be mixed.
The supported amount of Ru is 0.01 to 10% by weight, preferably 0.02 to 0.5% by weight, based on the total catalyst obtained. On the other hand, the supported amount of the mixture of Ru and Pt is also 0.01 to 10% by weight, preferably 0.02 to 5% by weight, based on the whole catalyst.
If the supported amount of Ru is less than 0.02% by weight, the oxidation activity of CO may not be sufficient, and if it exceeds 0.5% by weight, Ru may not be used effectively.
On the other hand, if the supported amount of the mixture of Ru and Pt is less than 0.02% by weight, the oxidation activity of CO may not be sufficient, and if it exceeds 0.5% by weight, Ru and Pt may not be used effectively. .
[0018]
Furthermore, in the selective oxidation catalyst of the present invention, it is preferable that the particle diameter of the supported Ru or Pt is 200 mm or less, desirably 5 to 200 mm.
When the particle diameter exceeds 200 mm, the oxidation activity of CO may not be sufficient, which is not preferable.
[0019]
Also, as the α-alumina carrier, within 100μm Ru or Ru-Pt mixture The carrier outer surface, as long as the support preferably may be present within 20 [mu] m, especially limited not name.
When Ru or the like cannot be supported within 100 μm from the outer surface of the support, the Ru concentration on the catalyst surface becomes thin and the desired effect may not be obtained.
[0020]
Furthermore, in the selective oxidation catalyst of the present invention, α-alumina can be suitably used as a support, because α-alumina easily realizes the above localization, and as described above, This is because the influence of the can be reduced.
Note that γ-alumina transitions to α-alumina if kept at a temperature of 1000 ° C. or higher. However, if the temperature is kept at that temperature, the catalytic metals Ru and Pt cause sintering, and sufficient activity cannot be obtained. It is not suitable for use alone in the catalyst of the invention.
However, it is possible to use α-alumina in combination with a porous carrier that satisfies the above characteristics.
[0021]
The selective oxidation catalyst of the present invention has the above-described configuration and excellent CO selective oxidation properties. Typically, however, about 1 vol% CO coexisting in the reformed gas is typically oxidized to about 100 ppm. Remove.
The use conditions are not particularly limited, but a remarkable effect can be obtained if the space velocity (SV) is 30,000 / hr or less and the catalyst temperature is 80 to 180 ° C.
[0022]
The catalyst form is granular or pellet.
[0023]
【Example】
EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited to these Examples.
In the following, “%” means “% by weight” unless otherwise specified.
[0024]
[Performance evaluation]
In the following examples and comparative examples, the performance of the obtained catalyst was evaluated by the following method.
(Catalyst metal support particle size)
The catalyst was pulverized and the supported metal was directly observed with a transmission electron microscope to confirm the particle size.
(Localization of catalyst metal support surface)
The catalyst was divided almost in half, and the cross section was observed with EPMA to confirm the loading width.
[0025]
(Example 1)
About 0.2% of Ru was supported on α-alumina having an average particle size of about 2 mm to obtain the selective oxidation catalyst of this example. In this catalyst, Ru was present at a depth of 50 μm from the outer surface of α-alumina. In addition, the average particle size of the supported Ru particles was 100 mm.
When a test gas in which oxygen was added in an amount of 2.5% by volume to a reformed gas containing 1% by volume of carbon monoxide was passed through this selective oxidation catalyst at SV30000 / hr, the temperature of the catalyst layer was 100 ° C. to 160 ° C. In the range of ° C., the CO concentration became 100 ppm or less.
[0026]
(Comparative Example 1)
About 0.2% of Ru was supported on γ-alumina having an average particle size of about 2 mm to obtain the catalyst of this example. Ru was present at a depth of 500 μm from the outer surface of γ-alumina, and the average particle size of Ru was 80 mm.
When a test gas in which oxygen was added by 2.5 volume% to a reformed gas containing 1 volume% carbon monoxide was passed through this catalyst at SV30000 / hr, the temperature of the catalyst layer was 100 ° C. to 160 ° C. In the range, the CO concentration was 5000 ppm.
[0027]
(Example 2)
A selective oxidation catalyst of this example was obtained by supporting about 0.2% of Ru on α-alumina having an average particle diameter of about 2 mm. Ru was present at a depth of 50 μm from the outer surface of α-alumina, and the average particle size of Ru was 100 mm.
When a test gas in which 0.1 volume% of oxygen was introduced into a reformed gas containing 0.1 volume% carbon monoxide was passed through this selective oxidation catalyst at SV20000 / hr, the temperature of the catalyst layer was 100 ° C. In the range of ˜150 ° C., the CO concentration became 50 ppm or less.
[0028]
(Comparative Example 2)
About 0.2% of Ru was supported on γ-alumina having an average particle size of about 2 mm to obtain the catalyst of this example. Ru was present at a depth of 500 μm from the outer surface of γ-alumina, and the average particle size of Ru was 80 mm.
When a test gas in which 0.1 volume% of oxygen was introduced into a reformed gas containing 0.1 volume% carbon monoxide was passed through this catalyst at SV20000 / hr, the temperature of the catalyst layer was 100 ° C. to 160 ° C. In the range of ° C., the CO concentration was 100 ppm or more.
[0029]
(Example 3)
About 0.2% of Ru: Pt (weight ratio 4: 1) was supported on α-alumina having an average particle diameter of about 2 mm to obtain the selective oxidation catalyst of this example. Ru and Pt were present at a depth of 100 μm from the outer surface of the α alumina, and the average particle size of the supported particles of Ru and Pt was 80 mm.
When a test gas in which oxygen was added in an amount of 2.5% by volume to a reformed gas containing 1% by volume of carbon monoxide was passed through this selective oxidation catalyst at SV30000 / hr, the temperature of the catalyst layer was 100 ° C. to 150 ° C. In the range of ° C., the CO concentration was 50 ppm or less, and particularly around 110 ° C., it was 20 ppm or less.
[0030]
As mentioned above, although this invention was demonstrated in detail by the preferred embodiment, this invention is not limited to these Examples, A various deformation | transformation implementation is possible within the range of this indication.
For example, the use of the selective oxidation catalyst of the present invention is not limited to the reformed gas supplied to the polymer electrolyte fuel cell, and can be used to reduce CO in other reformed gases, It can also be applied to various processes such as ammonia synthesis that require high-purity hydrogen gas.
[0031]
【The invention's effect】
As described above, according to the present invention, ruthenium or the like is appropriately supported on an α-alumina carrier and treated under oxygen-excess conditions, so that carbon monoxide in the reformed gas is selectively oxidized. Therefore, it is possible to provide a carbon monoxide selective oxidation catalyst that can be reduced and realize good fuel utilization efficiency and power generation efficiency.
For example, by using the catalyst of the present invention, if carbon monoxide present in about 1% by volume in the reformed gas is reacted at about 150 ° C. in the presence of an excess amount of oxygen, the carbon monoxide concentration is reduced to 0.1. It can be reduced to a volume% or less.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JP2011005461A (en) * | 2009-06-29 | 2011-01-13 | National Institute Of Advanced Industrial Science & Technology | Catalyst for selectively oxidizing carbon monoxide |
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| AU2001236090A1 (en) * | 2000-03-03 | 2001-09-12 | Idemitsu Kosan Co. Ltd. | Method of preparation of catalyst for use in removing co in hydrogen containing gas |
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| KR100453466B1 (en) * | 2002-01-28 | 2004-10-20 | 한국과학기술연구원 | Catalyst for selective oxidation of carbon monoxide |
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| JP4772659B2 (en) * | 2006-12-26 | 2011-09-14 | 日揮触媒化成株式会社 | Catalyst for removing carbon monoxide and method for producing the same |
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1999
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JP2011005461A (en) * | 2009-06-29 | 2011-01-13 | National Institute Of Advanced Industrial Science & Technology | Catalyst for selectively oxidizing carbon monoxide |
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