JP4250971B2 - Inorganic material and shift catalyst using the same - Google Patents
Inorganic material and shift catalyst using the same Download PDFInfo
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- JP4250971B2 JP4250971B2 JP2003034117A JP2003034117A JP4250971B2 JP 4250971 B2 JP4250971 B2 JP 4250971B2 JP 2003034117 A JP2003034117 A JP 2003034117A JP 2003034117 A JP2003034117 A JP 2003034117A JP 4250971 B2 JP4250971 B2 JP 4250971B2
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- inorganic material
- shift catalyst
- cerium
- cerium oxide
- highest peak
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- 239000003054 catalyst Substances 0.000 title claims description 99
- 229910010272 inorganic material Inorganic materials 0.000 title claims description 80
- 239000011147 inorganic material Substances 0.000 title claims description 80
- 238000006243 chemical reaction Methods 0.000 claims description 39
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 claims description 36
- 229910000420 cerium oxide Inorganic materials 0.000 claims description 34
- BMMGVYCKOGBVEV-UHFFFAOYSA-N oxo(oxoceriooxy)cerium Chemical compound [Ce]=O.O=[Ce]=O BMMGVYCKOGBVEV-UHFFFAOYSA-N 0.000 claims description 34
- 239000000446 fuel Substances 0.000 claims description 27
- 239000010955 niobium Substances 0.000 claims description 27
- 238000002441 X-ray diffraction Methods 0.000 claims description 25
- 229910052684 Cerium Inorganic materials 0.000 claims description 22
- 229910052758 niobium Inorganic materials 0.000 claims description 19
- KDLHZDBZIXYQEI-UHFFFAOYSA-N Palladium Chemical compound [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 claims description 18
- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 claims description 18
- 229910052697 platinum Inorganic materials 0.000 claims description 16
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims description 15
- 238000000034 method Methods 0.000 claims description 15
- 239000001257 hydrogen Substances 0.000 claims description 14
- 229910052739 hydrogen Inorganic materials 0.000 claims description 14
- 229910000484 niobium oxide Inorganic materials 0.000 claims description 13
- URLJKFSTXLNXLG-UHFFFAOYSA-N niobium(5+);oxygen(2-) Chemical compound [O-2].[O-2].[O-2].[O-2].[O-2].[Nb+5].[Nb+5] URLJKFSTXLNXLG-UHFFFAOYSA-N 0.000 claims description 13
- 238000004519 manufacturing process Methods 0.000 claims description 10
- KJTLSVCANCCWHF-UHFFFAOYSA-N Ruthenium Chemical compound [Ru] KJTLSVCANCCWHF-UHFFFAOYSA-N 0.000 claims description 9
- 229910052741 iridium Inorganic materials 0.000 claims description 9
- GKOZUEZYRPOHIO-UHFFFAOYSA-N iridium atom Chemical compound [Ir] GKOZUEZYRPOHIO-UHFFFAOYSA-N 0.000 claims description 9
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- SYQBFIAQOQZEGI-UHFFFAOYSA-N osmium atom Chemical compound [Os] SYQBFIAQOQZEGI-UHFFFAOYSA-N 0.000 claims description 9
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- 239000010948 rhodium Substances 0.000 claims description 9
- 229910052703 rhodium Inorganic materials 0.000 claims description 9
- MHOVAHRLVXNVSD-UHFFFAOYSA-N rhodium atom Chemical compound [Rh] MHOVAHRLVXNVSD-UHFFFAOYSA-N 0.000 claims description 9
- 229910052707 ruthenium Inorganic materials 0.000 claims description 9
- 150000001785 cerium compounds Chemical class 0.000 claims description 8
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- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 claims description 3
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- 229910002091 carbon monoxide Inorganic materials 0.000 claims description 3
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- ZMIGMASIKSOYAM-UHFFFAOYSA-N cerium Chemical compound [Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce] ZMIGMASIKSOYAM-UHFFFAOYSA-N 0.000 claims 1
- 150000001875 compounds Chemical class 0.000 description 23
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- 239000000203 mixture Substances 0.000 description 12
- 229910052760 oxygen Inorganic materials 0.000 description 11
- 239000001301 oxygen Substances 0.000 description 11
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical group [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 10
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- 230000002829 reductive effect Effects 0.000 description 8
- MUBZPKHOEPUJKR-UHFFFAOYSA-N Oxalic acid Chemical compound OC(=O)C(O)=O MUBZPKHOEPUJKR-UHFFFAOYSA-N 0.000 description 6
- 238000010586 diagram Methods 0.000 description 6
- 238000009499 grossing Methods 0.000 description 6
- -1 halogen salts Chemical class 0.000 description 6
- 229910052751 metal Inorganic materials 0.000 description 6
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- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 6
- 230000009467 reduction Effects 0.000 description 6
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 5
- GHLITDDQOMIBFS-UHFFFAOYSA-H cerium(3+);tricarbonate Chemical compound [Ce+3].[Ce+3].[O-]C([O-])=O.[O-]C([O-])=O.[O-]C([O-])=O GHLITDDQOMIBFS-UHFFFAOYSA-H 0.000 description 5
- 150000002823 nitrates Chemical class 0.000 description 5
- 229910017604 nitric acid Inorganic materials 0.000 description 5
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- YLGXILFCIXHCMC-JHGZEJCSSA-N methyl cellulose Chemical compound COC1C(OC)C(OC)C(COC)O[C@H]1O[C@H]1C(OC)C(OC)C(OC)OC1COC YLGXILFCIXHCMC-JHGZEJCSSA-N 0.000 description 4
- 150000003839 salts Chemical class 0.000 description 4
- 239000000126 substance Substances 0.000 description 4
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 3
- 150000003863 ammonium salts Chemical class 0.000 description 3
- 230000015572 biosynthetic process Effects 0.000 description 3
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- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- BVKZGUZCCUSVTD-UHFFFAOYSA-M Bicarbonate Chemical class OC([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-M 0.000 description 2
- 229920002134 Carboxymethyl cellulose Polymers 0.000 description 2
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- 239000004354 Hydroxyethyl cellulose Substances 0.000 description 2
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 description 2
- XSQUKJJJFZCRTK-UHFFFAOYSA-N Urea Chemical compound NC(N)=O XSQUKJJJFZCRTK-UHFFFAOYSA-N 0.000 description 2
- 229910001361 White metal Inorganic materials 0.000 description 2
- 230000002411 adverse Effects 0.000 description 2
- 150000004703 alkoxides Chemical class 0.000 description 2
- 229910052782 aluminium Inorganic materials 0.000 description 2
- 150000001412 amines Chemical class 0.000 description 2
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- 239000001768 carboxy methyl cellulose Substances 0.000 description 2
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- 239000008112 carboxymethyl-cellulose Substances 0.000 description 2
- PUUPYXQOFNNGRK-UHFFFAOYSA-N cerium niobium Chemical compound [Nb].[Ce] PUUPYXQOFNNGRK-UHFFFAOYSA-N 0.000 description 2
- RCFVMJKOEJFGTM-UHFFFAOYSA-N cerium zirconium Chemical compound [Zr].[Ce] RCFVMJKOEJFGTM-UHFFFAOYSA-N 0.000 description 2
- 239000008120 corn starch Substances 0.000 description 2
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- 229910052736 halogen Inorganic materials 0.000 description 2
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- 150000002826 nitrites Chemical class 0.000 description 2
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- 235000006408 oxalic acid Nutrition 0.000 description 2
- 239000007800 oxidant agent Substances 0.000 description 2
- 230000003647 oxidation Effects 0.000 description 2
- 230000001590 oxidative effect Effects 0.000 description 2
- 230000036961 partial effect Effects 0.000 description 2
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- 229910052720 vanadium Inorganic materials 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- 239000010969 white metal Substances 0.000 description 2
- 244000144730 Amygdalus persica Species 0.000 description 1
- BVKZGUZCCUSVTD-UHFFFAOYSA-L Carbonate Chemical compound [O-]C([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-L 0.000 description 1
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 1
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- NIPNSKYNPDTRPC-UHFFFAOYSA-N N-[2-oxo-2-(2,4,6,7-tetrahydrotriazolo[4,5-c]pyridin-5-yl)ethyl]-2-[[3-(trifluoromethoxy)phenyl]methylamino]pyrimidine-5-carboxamide Chemical compound O=C(CNC(=O)C=1C=NC(=NC=1)NCC1=CC(=CC=C1)OC(F)(F)F)N1CC2=C(CC1)NN=N2 NIPNSKYNPDTRPC-UHFFFAOYSA-N 0.000 description 1
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Images
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
Description
【０００１】
【発明の属する技術分野】
本発明は、セリウムとニオブとの複合酸化物からなる無機材料および、ＣＯにＨ2Ｏを作用させて水素ガスを発生させ、同時にＣＯをＣＯ2に変換するいわゆるシフト反応に使用するシフト触媒、および該触媒の製造方法、該触媒を搭載した自動車などに関し、より詳細には、耐熱性に優れ、メタン生成率が低く、ＣＯ転化率が高いシフト触媒等に関する。
【０００２】
【従来の技術】
水素−酸素燃料電池は、電解質の種類や電極の種類等により種々のタイプに分類され、代表的なものとしてはアルカリ型、リン酸型、溶融炭酸塩型、固体電解質型、固体高分子型がある。この中でも低温（通常１００℃以下）で作動可能な固体高分子型燃料電池が注目を集め、近年自動車用低公害動力源としての開発・実用化が進んでいる。
【０００３】
固体高分子型燃料電池は、純粋な水素を燃料源として用いることがエネルギー効率からは最も好ましい。しかし、現段階においては、安全性・インフラ等を考慮して、メタノール、天然ガス、ガソリン等を燃料源として用い、これらを改質装置において水素リッチな改質ガスとする方法が模索されている。しかしながら、例えばメタノールを原料とする場合には、下記に示すメタノール改質反応
【０００４】
【化２】
によって一酸化炭素が発生し、このＣＯは燃料電池の電極の白金系触媒の触媒毒として作用する。このため、このＣＯを白金電極触媒に無害なＣＯ2に転化する必要があり、シフト反応（ＣＯ＋Ｈ2Ｏ→ＣＯ2＋Ｈ2）を利用して、改質ガス中に含まれるＣＯ濃度を１体積％程度にまで低減させている。
【０００６】
従来から、上記シフト反応にはＣｕ／Ｚｎ系触媒、Ｃｕ／Ｚｎ／Ａｌ系触媒、Ｃｕ／Ｃｒ系触媒等のＣｕ触媒が使用されている。しかしながらＣｕ触媒は、操業停止時に還元雰囲気下に置かないと、触媒自身が酸化され活性が低下するという問題があった。また、空間速度ＳＶ（Space Velocity）の増大とともにＣＯ低減率が急激に低下する場合がある。また、従来の触媒は、耐熱温度が低く、シンタリング、すなわち触媒を構成する金属の溶融および結合現象が生じ、触媒としての性能を著しく低下させる場合があった。シンタリングは不可逆的な現象であるため、過渡的な温度上昇が生じるとその後はシフト触媒の性能の著しい低下を招く。このためシフト反応部でＣＯを十分に処理できず、燃料ガス中の水素分圧の低下、燃料電池の電極の被毒などの弊害を招くことになる。そこで、ＣＯ低減率の向上、ＳＶ増による性能低下の抑制、耐熱性の向上を目的として、所定の酸化物が添加されたＴｉＯ2の多孔体にＰｔが担持されたシフト触媒が開示されている（特許文献１参照）。該文献１では、触媒性能が向上する原因は、酸化物を添加することによってＰｔを担持する担体の比表面積が向上することが一因と推察している。なお、酸化物としては、Ａｌ、Ｓｉ、Ｐ、Ｓ、Ｖの少なくとも一種の酸化物を用いている。
【０００７】
【特許文献１】
特開２００２−６６３２０号公報
【０００８】
【発明が解決しようとする課題】
しかしながら、上記公報記載の触媒を使用しても還元雰囲気下での活性の低下を防止するには不十分であり、ＳＶ増加の際のシフト反応（ＣＯ＋Ｈ2Ｏ→ＣＯ2＋Ｈ2）も十分でない。特に、搭載スペースが制限される燃料改質式燃料電池自動車等に使用するには、よりＣＯ低減率の高いシフト触媒の開発が望まれる。
【０００９】
【課題を解決するための手段】
本発明は、シフト触媒を構成する元素の種類、組成割合等について詳細に検討した結果、少なくともセリウムとニオブとを含有する複合酸化物からなる無機材料は、極めて耐熱性に優れる無機材料であること、および該無機材料を担体として調製したＣＯシフト触媒は、還元雰囲気下でもその活性を失わないことを見出し本発明を完成させた。
【００１０】
【発明の効果】
本発明の無機材料の製造方法によれば、耐熱性に優れる無機材料を調製することができる。該無機材料は、ハニカムモノリスとすることができ、該ハニカムに触媒活性成分を担持させるとＣＯシフト活性に優れる触媒を得る事ができる。特に、該無機材料を担体とするシフト触媒は、還元雰囲気下でも触媒活性を低下させることが少ない。
【００１１】
本発明のシフト触媒は、５０，０００ｈｒ-1以上の空間速度でも十分にシフト触媒活性が確保でき、シフト反応装置の小型化が可能で、自動車などの収納体積が制限されるものにおいて特に有効である。更に、耐熱性に優れ、起動停止時の触媒安定性にも優れる。
【００１２】
本発明のシフト触媒は、上記無機材料からなるハニカムモノリスに白金、ロジウム、パラジウム、ルテニウム、イリジウム、並びにオスミウムからなる群から選ばれる少なくとも１種類の元素を担持させ、これを乾燥および焼成することで得られ、調製が簡便である。しかも該方法によるシフト触媒はメタン生成率が低く、水素の無駄な消費がない。
【００１３】
【発明の実施の形態】
本発明の第一は、少なくともセリウムとニオブとを含有する複合酸化物からなり、ＣｕＫα線を用いたＸ線回折分析による酸化ニオブ由来の最高ピーク高さが、酸化セリウム由来の最高ピーク高さの１０分の１以下であることを特徴とする無機材料である。
【００１４】
セリウムは、希土類元素で展性・延性があり、発火合金としても用いられている鋼鉄状の金属である。一方、ニオブは周期律表第５族(バナジウム族)の元素で、展性、延性に富む金属である。従来からセリウムやニオブは触媒成分として使用されてきたが、本発明においてセリウムとニオブとの複合酸化物を調製したところ、該複合酸化物がセリウムやニオブ単独では得られない優れた耐熱性を有することを見出した。原料化合物のセリウム化合物とニオブ化合物から複合酸化物が形成されたことは、X線回折分析において該無機材料の酸化セリウム由来の最高ピークが、酸化セリウム単独の最高ピークよりも面間隔にして高間隔側にシフトしていることで確認することができる。なお、上記Ｘ線回折の数値は、以下の条件でＸ線回折分析を行った場合の値である。
【００１５】
分析機器は、装置：マックサイエンス製広角Ｘ線回折装置（ＭＸＰ１８ＶＡＨＦ型）によった。Ｘ線源：ＣｕＫα、印加電圧：４０ＫＶ、印加電流：３００ｍＡ、測定変化角度：２θ、走査速度：４．０００ｄｅｇ／ｍｉｎ、分析刻み幅：０．０２０ｄｅｇ、カウント時間：０．５０ｓｅｃ、カウント単位：ＣＰＳ、発散スリット：１．００ｄｅｇ、散乱スリット：１．００ｄｅｇ、受光スリット：０．３０ｍｍ。
【００１６】
該分析は、データを平滑化し、規格化し、および差分を回折して得た数値である。
【００１７】
平滑化として、測定して得られた分析生データを、下記式に示す加重平均法を用いて該当分析角度におけるピーク強度の加重平均値を算出した。
【００１８】
【数１】
Ｙ[ｘ]:分析角度ｘ°での加重平均カウント数
Ｙ（ｘ）：分析角度ｘ°での検出カウント数
加重平均処理を施す際の１点の平均値を求めるにあたり使用する数値の範囲は、より広角の分析値の加重平均を求めると確からしさが増大するが、きわめて微細な検出ピークを扱うには重要な情報を見失う場合がある。また、より狭角の分析値の加重平均を求めるとノイズが増加する。そこで本発明においては、上記式に従い、０．０８°の範囲内に入った値を元に加重平均値を算出した。
【００２０】
得られた平滑化処理結果は、例えば原料化合物として酸化セリウムと酸化ニオブを使用した場合に、得られた無機材料に含まれる酸化セリウムの最高ピークを例にすると、以下に示す方法で規格化した。図２に後記する実施例１〜５で得た無機材料および比較例１の担体の平滑化規格化したデータを示す。
【００２１】
【数２】
Ａ：定数
Ｙ0(main)：無機材料中の酸化セリウムの最高ピークの加重平均値
Ｙ(main)：酸化セリウムの最高ピークの加重平均カウント数
得られた平滑化処理結果は、該原料化合物に由来する回折ピークを含んでいる。担持量や相対強度、粒度などにもよるが、一般に原料化合物由来の回折ピークの方が強く観察され、場合によっては、求める無機材料の酸化セリウム由来の回折ピークはその強大なる原料化合物由来のピークに干渉し消滅したかのように観察される場合もある。そこで規格化した後、原料化合物由来の回折ピークとの差スペクトルを求め、無機材料に含まれる酸化セリウム由来の回折ピークと分離する。セリウム化合物とニオブ化合物とからセリウム−ニオブの複合酸化物が形成されると原料化合物由来のピークの固有ピークの存在比が低下する。そこで、原料化合物の最高ピークの回折強度が同一になるように上記式で定義する定数Ａを乗じて、規格化した。
【００２３】
差分とは、規格化して得られた分析結果から、同様に処理された原料化合物の分析結果を差し引き、差分回折ピークを作成して無機材料に含まれる酸化セリウム由来の回折ピークのみを抽出することである。図３〜５に後記する実施例１〜５で得た無機材料および比較例１の担体の差分回折パターンを示す。
【００２４】
本発明の無機材料は、酸化セリウム由来のＸ線回折ピークが、酸化セリウム自体のＸ線回折ピークより面間隔側にシフトする。このようなシフトは、原料化合物に含まれるセリウムとニオブとが複合酸化物を形成していることを示すものである。すなわち、原料化合物（セリウム化合物、ニオブ化合物）自体は、セリウム−ニオブ複合酸化物領域（界面）を持たないことから、ピークシフトする可能性は考えられない。しかし、後記する図３からも明らかなように複合酸化物を形成することで、明らかに高面間隔側にピークシフトしており、ニオブとセリウムとの間に結晶内酸素原子を通じての結合関係が形成されたと判断できる。複合酸化物の形成によって酸化ニオブと酸化セリウムとの結合が密になるため、格子欠陥酸素位置への母材からの酸素原子の供給がより行われ易くなり、効果的に結合構造を維持することができる。なお、第２番の高さのピークや第３番の高さのピーク、酸化ニオブの各ピークについても上記と同様にデータを平滑化、規格化および差分を回折して得た数値を使用する。
【００２５】
本発明の無機材料に使用できる原料化合物としては、これらの硝酸塩、硫酸塩、アンモニウム塩、アミン、炭酸塩、重炭酸塩、ハロゲン塩、亜硝酸塩、蓚酸などの無機塩類、ギ酸塩などのカルボン酸塩および水酸化物、アルコキサイドなどが例示でき、これらを溶解する溶媒の種類やｐＨなどによって適宜選択することができる。これらの中でも、工業的に使用するにあっては硝酸塩、炭酸塩、酸化物、水酸化物などが好ましい。本発明では原料化合物としてこれらのゾルを用いることもできる。
【００２６】
本発明では、上記原料化合物からなる複合酸化物であり、上記Ｘ線回折分析による酸化ニオブ由来の最高ピーク高さが、酸化セリウム由来の最高ピーク高さの１０分の１以下であることを特徴とする。無機材料に含まれる酸化ニオブ由来のピークと酸化セリウム由来のピークとは必ずしも無機材料中の酸化セリウムと酸化ニオブの配合量に比例するものではないが、この範囲で特に耐熱性に優れるからである。
【００２７】
また、本発明の無機材料は、上記Ｘ線回折分析によって、該無機材料の酸化セリウム由来の最高ピークが、原料として使用した酸化セリウム単独の最高ピークよりも面間隔にして高間隔側にシフトしている。原料化合物の酸化セリウムの該ピークよりも面間隔にして高間隔側にシフトということは、ニオブとの複合酸化物が形成されたことを意味するものである。
【００２８】
該Ｘ線回折分析による該無機材料の酸化セリウム由来の最高ピークは、２θにして２８．４４〜２８．６６°の範囲にはいることが好ましい。
【００２９】
また、該Ｘ線回折分析による該無機材料の酸化セリウム由来の第２番に高いピークが、面間隔にして１．６３Åであることが好ましい。
【００３０】
更に、該Ｘ線回折分析による該無機材料の酸化セリウム由来の第３番に高いピークが、面間隔にして１．９Åに存在することがこのましい。
【００３１】
また、本発明の無機材料は、Ｃｅ／Ｎｂ比が１以上、より好ましくは１．０〜５．０、特には３．０〜５．０であることが好ましい。Ｃｅ／Ｎｂ比が１を下回るとセリウムによる酸素移動能の効果が低下する場合がある。本発明の無機材料に使用できる他の元素としては、Ｓｉ、Ａｌ、Ｚｒ、Ｔｉ等がある。
【００３２】
また、本発明の無機材料は、ＢＥＴ比表面積が、４０ｍ2/ｇ以上であることが好ましく、より好ましくは６０ｍ2/ｇ以上、さらに好ましくは８０ｍ2/ｇ以上である。特に４０ｍ2/ｇ以上の比表面積があれば、十分な触媒活性が確保できる。
【００３３】
本発明の無機材料の製造方法には制限はないが、水溶性セリウム化合物またはそのゾルと、水溶性ニオブ化合物またはそのゾルとを含む水溶液に、有機増粘剤または澱粉質を分散した後、蒸発乾固後焼成することで製造できる。水溶性セリウム化合物や水溶性ニオブ化合物としては、上記したセリウム化合物、ニオブ化合物の中から水溶性の化合物を選択して使用することができる。このように水溶性の化合物を使用すれば有機溶媒を使用せずに調製でき取り扱いが容易となり、廃液処理などの問題を回避することができる。また、有機増粘剤を添加することで、乾燥時のＣｅとＮｂの分離を抑制し、かつ微細な細孔を有するより安定した複合酸化物を得ることができる。なお、使用できる有機増粘剤としては、メチルセルロースエーテル、メチルセルロース、ヒドロキシエチルセルロース、カルボキシメチルセルロースがあり、澱粉質としてはコーンスターチ等がある。
【００３４】
本発明の無機材料を製造するには、場合により水に分散させたセリウムとニオブ原料を十分攪拌し、これに有機増粘剤を添加して該増粘剤の粘度によって攪拌が困難となるまで混合する。乾燥方法は、例えば自然乾燥、蒸発乾固法、ロータリーエバポレーター、噴霧乾燥機、ドラムドライヤー、または沿送風乾燥機による乾燥などを用いることができる。乾燥時間は、使用する方法に応じて適宜選択すればよい。場合によっては、乾燥工程を行わずに、焼成工程において乾燥させることとしてもよい。また、該複合体の焼成は、温度２００〜１０００℃で３０〜４８０分で十分である。
【００３５】
本発明の無機材料を用いれば、下記式（１）で示されるシフト反応に使用されるシフト触媒であって、
【００３６】
【化３】
上記無機材料を担体として使用することを特徴とする、一酸化炭素シフト触媒を得ることができる。上記無機材料は耐熱性に優れるため触媒活性の低下を防止することができる。
【００３８】
本発明では、該無機材料を担体して使用するが、該触媒には、白金、ロジウム、パラジウム、ルテニウム、イリジウム、並びにオスミウムからなる群から選ばれる少なくとも１種類の貴金属元素を触媒成分として含むことが好ましい。これらの元素の供給源としては特に制限されず広くこれらの元素を含有する化合物を使用することができる。このような化合物としては、これらの硝酸塩、硫酸塩、アンモニウム塩、アミン、炭酸塩、重炭酸塩、ハロゲン塩、亜硝酸塩、蓚酸などの無機塩類、ギ酸塩などのカルボン酸塩および水酸化物、アルコキサイド、酸化物などが例示でき、これらを溶解する溶媒の種類やｐＨなどによって適宜選択することができる。これらの中でも、工業的に使用するにあっては硝酸塩、炭酸塩、酸化物、水酸化物などが好ましい。
【００３９】
上記無機材料を使用したシフト触媒が優れる理由については明確ではないが、耐熱性に優れる無機材料を担体に使用することのほかに、該無機材料に含まれるセリウムの酸素運搬能が関与していると考えられる。まず、上記式（１）で示されるシフト反応は、下記式に分解して理解することができる。
【００４０】
【化４】
該（ｉ）に基づく活性酸素（Ｏ）がＣＯ酸化触媒の酸化活性点に存在すれば、上記式（ｉｉ）が効率的に進行する。この活性酸素（Ｏ）の運搬能に優れたセリウム元素を使用すると、（ｉ）と（ｉｉ）との循環が円滑に回転し、水素生成反応が効率的に進行する。すなわち、Ｈ2ＯからＨ2を取り出すことのできる活性種（Ａ）としてニオブを使用し、ＣＯの酸化能を有する活性種（Ｂ）として白金、ロジウム、パラジウム、ルテニウム、イリジウムおよび／またはオスミウム元素、およびセリウム元素という酸素運搬能に優れる活性種（Ｃ）とが触媒中に存在することで、低温でもシフト反応性に優れる触媒となる。なお、上記活性種（Ａ）、（Ｂ）および（Ｃ）とは触媒中に存在すれば、気体状態のＨ2ＯからＨ2を生成することができ、触媒中でのこれらの成分の分散性などは問わない。活性種（Ａ）と（Ｂ）とが隣接しない場合でも、セリウム元素を介して活性酸素（Ｏ）が運搬され、円滑な反応の進行が確保できるからである。また、酸化セリウムやセリウム−ジルコニウム複合体は、結晶内の酸素原子が移動できる酸化還元能のある金属であり、これらの使用によってシフト反応で生成したＨ2を消費するいわゆるメタネーション反応を抑制し得る。すなわち、上記式（１）によってＣＯ2と共にＨ2が生成するが、改質反応ガスは高温であるため、逆シフト反応（ＣＯ2＋Ｈ2→ＣＯ＋Ｈ2Ｏ）やメタネーション反応（ＣＯ＋３Ｈ2→ＣＨ4＋Ｈ2Ｏ）が発生し、水素燃料が消費される場合がある。上記メタネーション反応はシフト反応とは独立した反応であるため、単にシフト触媒のＣＯ転化率を評価しただけでは最終的な水素製造率への寄与率を知ることはできない。
【００４２】
本発明では、上記元素に加え、白金、ロジウム、パラジウム、ルテニウム、イリジウムおよびオスミウムから選ばれる貴金属元素を含有する。使用する原料化合物のうち、白金原料としてはジニトロジアミン白金、塩化白金などを用いることができるが、特にジニトロジアミン白金が好ましい。分散性に優れるからである。また、塩化物を使用するには大規模工業的に触媒を製造するに際して、その焼成排ガスによる大気汚染等を考えなければならないほか、排気配管の塩素腐食は多大な悪影響を与える。同様に、ロジウム、パラジウム、ルテニウム、イリジウムおよびオスミウム等は、硝酸塩、アンモニウム塩等を使用することが好ましい。これらの元素の配合量は質量換算で、該シフト触媒中に０.０１〜２０.０質量％であることが好ましく、より好ましくは１.０〜２０.０質量％、特に好ましくは１０．０〜１５．０質量％である。０.０１質量％を下回ると、ＣＯ転化率が十分でない場合がある。これらの元素は該触媒の活性成分と考えられ、ＣＯ転化率を向上させるにはこれらいわゆる貴金属元素を触媒表面に分布させることが好ましい。低温でもＣＯとの接触率が向上し、ＣＯ転化率が向上するからである。本発明では、特にＣＯ転化率に優れる点で白金元素を含むことが好ましい。しかしながら、多大なる担持量では、経済性を考えるに不利となる場合がある。本発明では、特にＣＯ転化率に優れる点で白金元素を含むことが好ましい。
【００４３】
上記以外に、粘土鉱物や有機バインダー等を添加してもよい。有機バインダーとしては、メチルセルロースエーテル、メチルセルロース、ヒドロキシエチルセルロース、カルボキシメチルセルロース、コーンスターチなどがある。有機バインダーと共に、クルミ粒子、桃種粒子などを均一粒径に揃えたもの、あるいは粒子径が均一な高分子粒子など、焼成により消失する物質を気孔形成剤として用いてもよい。
【００４４】
本発明の触媒を調製する方法としては特に制限はなく、一般的な触媒調製方法で製造できる。例えば、予め上記無機材料に貴金属元素以外の化合物を含む複合体を形成、乾燥、焼成し、ついで該焼成物に上記貴金属元素を担持させる方法が採用できる。
【００４５】
該方法は、貴金属元素がより触媒外表面に多く存在し、少量でＣＯ転化率を向上できる点で経済的に有利である。予め上記無機材料を担体として、これに貴金属元素を担持させるが、このような調製方法としては、上記貴金属を溶解または分散した溶液を調製し、該無機材料にこれら元素を含浸させ、次いで該溶液を乾燥してこれら元素を担持させ、これを乾燥、焼成して目的触媒を得る。
【００４６】
該方法において、乾燥方法は、例えば自然乾燥、蒸発乾固法、ロータリーエバポレーター、噴霧乾燥機、ドラムドライヤーによる乾燥などを用いることができる。乾燥時間は、使用する方法に応じて適宜選択すればよい。場合によっては、乾燥工程を行わずに、焼成工程において乾燥させることとしてもよい。また、焼成は、温度２００〜１０００℃で３０〜４８０分で十分である。なお、上記貴金属元素を担持させるには、必要により、減圧、加熱、スプレー吹付けなどを併せ行なってもよい。また、貴金属元素の担持後の熱処理は、貴金属元素が触媒上に析出するに必要な温度と時間を選定して実施するが、貴金属元素ができるだけ均一に、微少な粒子で存在するような条件を選ぶことが最も好ましい。一般的に高温あるいは長時間の熱処理は、析出した白金族粒子の凝集を促進するので好ましくない。従って３００〜６００℃に加熱した空気（または窒素などの不活性ガス）または過熱スチームを使用して１０〜２４０分の短時間で処理するのが好ましい方法である。上記の短時間の熱処理は、触媒調製工程の時間短縮という観点からも好ましい。
【００４７】
また、本発明のシフト触媒は、上記無機材料を粒状物とした場合には、粒状物とすることができ、更に種々の外形を採用することができ、ペレット状、リング状、馬蹄状、リボン状などの任意の形状に成型してもよい。更に、第一の発明の無機材料から予めハニカムモノリスを形成し、該ハニカムモノリスに、白金、ロジウム、パラジウム、ルテニウム、イリジウムおよびオスミウムから選ばれる少なくとも１種類の貴金属元素をを担持させて、シフト触媒を製造してもよい。本発明の触媒は、粒状物、ペレット状、リング状、馬蹄状、リボン状などの不定形の場合には、該シフト触媒を反応容器に収納し、該容器に改質ガスを流入させれば、改質ガスに含まれるＣＯを効率的にＣＯ2に変換することができる。また、このような反応容器を使用せずに、上記のようにハニカムモノリスに上記貴金属元素をコーティングした場合には、そのまま反応器型のシフト触媒とすることができる。
【００４８】
本発明のシフト触媒は空間速度５０，０００ｈｒ-1以上で使用することができＣＯ転化率に優れるため、シフト触媒反応器を小型化でき特に有利である。なお、ハニカムモノリスへの該貴金属元素のコーティングは、例えば、上記無機材料からなるハニカムモノリスに、白金、ロジウム、パラジウム、ルテニウム、イリジウムおよびオスミウムから選ばれる少なくとも１種の元素を担持させ、該ハニカムモノリスを乾燥および焼成して製造することができる。更に、予め調製した貴金属元素を、バインダーを配合して上記無機材料からなるハニカムモノリスにコーティングしてもよい。
【００４９】
本発明のシフト触媒は、ＢＥＴ比表面積が、４０ｍ2/ｇ以上であることが好ましく、より好ましくは６０ｍ2/ｇ以上、さらに好ましくは８０ｍ2/ｇ以上である。特に４０ｍ2/ｇ以上の比表面積があれば、十分な触媒活性が確保できる。なお、触媒寿命の面では十分な白金属元素含有量および微細な白金属元素を焼成物に担持させることが重要であるが、４０ｍ2／ｇ未満の低い比表面積の担体はこの両方の因子を満足させることは難しい。また、このようなＢＥＴ比表面積を有することで、本発明のシフト触媒は、空間速度５０，０００ｈｒ-1以上、より好ましくは１００，０００ｈｒ-1以上で使用することができる。なお、本発明のシフト触媒は、その平均粒径がレーザー回折法で分析した場合において、１．０〜５０μｍであることが好ましい。この範囲で、ＣＯ転化率に優れるからである。
【００５０】
本願発明のシフト触媒やシフト触媒反応器を搭載して、燃料改質式水素発生システム、燃料電池システム、または燃料改質式燃料電池自動車とすることできる。図１に、燃料改質式水素発生システムのシステムフロー図を示す。図面を参照しながら説明すると、まず、燃料タンクにメタノール、ガソリン、炭化水素などの燃料を供給する。この燃料は気化器によって気化し、脱硫器によって含まれる硫黄分を除去する。改質部では、通常は水蒸気を用いた水蒸気改質によって、該燃料を水素リッチな改質ガスへと改質する。また、水蒸気に加え、酸素を含むガスを同時に供給し、部分酸化反応を併発したオートサーマル改質によっても、水素リッチな改質ガスを得ることができる。次に、改質ガスをシフト反応器に送り、改質ガス中に含まれるＣＯをＣＯ2に変換してＣＯ濃度を１体積％程度にまで低減する。ＣＯ濃度が１体積％程度にまで低減された改質ガスを、続いてＣＯ除去器に移送し、ＣＯ濃度をｐｐｍオーダーに低減する。このＣＯ濃度をｐｐｍオーダーにまで低減した改質ガスおよび酸化剤（通常は空気）を燃料電池発電機に供給し、発電反応を進行させる。なお、燃料電池発電機からは使用済み燃料および酸化剤が排出される。
【００５１】
本発明に係るシフト触媒は、上述の通り低温であっても優れたＣＯ転化率を発現しうる。このような特性を有するシフト触媒を燃料改質ガス中のＣＯ転化に用いることによって、燃料電池に供給される燃料ガス中のＣＯ濃度を効率よく低下させることが可能である。特に、空間速度が高くてもＣＯ濃度を極めて低濃度にまで低減させることができるため、搭載範囲の制限される自動車などでも有効に使用することができる。
【００５２】
【実施例】
以下、本発明を実施例を用いて説明する。
【００５３】
実施例１（Ｃｅ80Ｎｂ20）
炭酸セリウム２６．１ｇに対し、１０質量％酸化ニオブゾル１８．０ｇ、濃硝酸３０ｍｌを加え十分攪拌した。これにメチルセルロースエーテル（信越化学工業製、商品名「Ｈｉ−メトローズ」）０．５ｇを添加し、メチルセルロースエーテルの粘性により攪拌子が回らなくなるまで攪拌混合した。これを１５０℃にて一昼夜乾燥および粉砕した。その後５００℃にて１時間焼成し、ＢＥＴ比表面積約１００ｍ2／ｇの無機材料１を得た。該無機材料の組成は、それぞれの元素換算で、セリウム８０モル％、ニオブ２０モル％であった。
【００５４】
得られた無機材料のＸ線回折結果を図２〜５に示す。
【００５５】
また、該無機材料についてＴＧ−ＤＴＡ分析を行なった。まず、室温から１５０℃まで昇温後３０分保持し、１０℃／分で６００℃まで昇温した。重量減少率は２００℃に到達したときから、６００℃に到達したときの質量減少分を観測した。質量減少は０．７質量％であった。結果を図６にも示す。
【００５６】
実施例２（Ｃｅ80Ｎｂ20）
炭酸セリウム２６．１ｇに対し、１０質量％酸化ニオブゾル１８．０ｇ、濃硝酸３０ｍｌを加え十分攪拌した。これに等量の尿素を添加し、攪拌しながら３時間で９８℃まで昇温し次いで２時間温度を保持した。これを室温まで冷却した後にろ過し、１５０℃にて一昼夜乾燥および粉砕した。その後５００℃にて１時間焼成し、ＢＥＴ比表面積約１００ｍ2／ｇの無機材料２を得た。該無機材料の組成は、それぞれの元素換算で、セリウム８０モル％、ニオブ２０モル％であった。
【００５７】
得られた無機材料のＸ線回折結果を図２〜５に示す。
【００５８】
実施例３（Ｃｅ50Ｎｂ50）
実施例１において、炭酸セリウムを２６．１ｇ、濃硝酸を３０ｍｌ、１０質量％酸化ニオブゾルを８０ｇ使用する以外は実施例１と同じ方法で無機材料３を得た。該無機材料の組成は、それぞれの元素換算で、セリウム５０モル％、ニオブ５０モル％であった。
【００５９】
得られた無機材料のＸ線回折結果を図２〜５に示す。
【００６０】
参考例４（Ｃｅ２０Ｎｂ８０）
実施例１において、炭酸セリウムを２５．０ｇ、濃硝酸を３０ｍｌ、１０質量％、酸化ニオブゾルを３００ｇ使用する以外は実施例１と同じ方法で無機材料４を得た。該無機材料の組成は、それぞれの元素換算で、セリウム２０モル％、ニオブ８０モル％であった。
【００６１】
得られた無機材料のＸ線回折結果を図２〜５に示す。
【００６２】
実施例５（Ｃｅ50Ｎｂ50）
炭酸セリウムを２６．１ｇ、濃硝酸を３０ｍｌ、１０質量％、酸化ニオブゾルを８０ｇ使用し、１０ｇの尿素を添加後、還流しながら１００℃まで昇温し、沈殿物を得た。それを乾燥して無機材料５を得た。該無機材料の組成は、それぞれの元素換算で、セリウム５０モル％、ニオブ５０モル％であった。
【００６３】
得られた無機材料のＸ線回折結果を図２〜５に示す。
【００６４】
実施例６
実施例１〜３、５および参考例４で得た無機材料を使用し、以下の手法で触媒化した。Ｐｔ金属含有量が８．４５１質量％のジニトロジアミン白金錯塩１３．１５ｇと、該無機材料１０ｇとを加え十分に攪拌した。これを１５０℃で一昼夜乾燥したのち粉砕し、４００℃にて１時間焼成し、実施触媒例１〜３、５および参考触媒例４を得た。該触媒の組成は元素換算で、白金１０質量％であった。
【００６５】
比較例１
比較担体例１として酸化セリウム（ＢＥＴ比表面積：約１３０ｍ2／ｇ）のＸ線回折結果を図２〜５に示す。
【００６６】
また、無機材料に代えて上記酸化セリウムを使用したこと以外は、実施例６と同じ方法で比較触媒例１を得た。
【００６７】
また、該化合物について実施例１と同様にしてＴＧ−ＤＴＡ分析を行なった。質量減少は２．４であった。結果を図６に示す。
【００６８】
比較例２
比較担体例２としてＣｅ／Ｚｒ＝６８／３２（モル比）のセリウムジルコニウム複合酸化物粉末（ＢＥＴ比表面積７０ｍ2／ｇ）を調製した。
【００６９】
また、該化合物について実施例１と同様にしてＴＧ−ＤＴＡ分析を行なった。質量減少は４．１であった。結果を図６に示す。
【００７０】
活性試験１
実施触媒例１〜３、５、参考触媒例４および比較触媒例１で調製した触媒をディスク上で圧縮した後破砕し、７０〜３６μｍの粒径に整粒した。該触媒０．１ｇとケイ砂０．１３ｇとを混合した後にガラス管に充填し、空間速度６０，０００ｈｒ−１の流速で２％水素含有窒素雰囲気を流し、４００℃にて３０分活性化処理を行った。次いで、窒素雰囲気下で該触媒を１５０℃に冷却し、２００℃より昇温しながらガスクロマトグラフィーにて出口にて出口ガスを分析した。なお、投入ガス組成はいずれの触媒を使用した場合にも、ＣＯ／ＣＯ２／Ｈ２／Ｈ２Ｏ／Ｎ２が、１０／１３．３／４０／１６．８／１９．９体積％とした。出口ＣＯ濃度を測定し、下記式に基づいてＣＯ転化率を求めた。
【００７１】
【数３】
また、ＣＨ4生成率は規定のＣＨ4ボンベガスから検定された検量線を元に計算した。表１に実施例および比較例で調製した触媒の組成、温度３００℃での該触媒のＣＯ転化率を示す。結果を図７にも示す。
【００７３】
【表１】
【図面の簡単な説明】
【図１】 本発明のシフト触媒を使用した燃料改質式水素発生システムのシステムフロー図である。
【図２】 図２は、比較例１、実施例１〜５で調製した無機材料のＸ線回折データの平滑化および規格化した後のデータである。
【図３】 図３は、比較例１、実施例１〜５で調製した無機材料の、２７〜３０°の差分回折パターンを示す図である。
【図４】 図４は、比較例１、実施例１〜５で調製した無機材料の、５５〜５８°の差分回折パターンを示す図である。
【図５】 図５は、比較例１、実施例１〜５で調製した無機材料の、４６〜４９°の差分回折パターンを示す図である。
【図６】 図６は、実施例１の無機材料、比較例１，２で使用する比較担体１，２のＴＧ−ＤＴＡ分析の結果を示す図である。
【図７】 図７は、実施例６、比較例１で調製した触媒のCO転化率を示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an inorganic material comprising a complex oxide of cerium and niobium, and CO to H 2 O is allowed to act to generate hydrogen gas, and at the same time, CO is converted to CO. 2 More specifically, a shift catalyst used in a so-called shift reaction for conversion into a catalyst, a method for producing the catalyst, an automobile equipped with the catalyst, and the like, more specifically, a shift having excellent heat resistance, low methane production rate, and high CO conversion rate It relates to catalysts.
[0002]
[Prior art]
Hydrogen-oxygen fuel cells are classified into various types depending on the type of electrolyte, the type of electrode, etc., and representative types include alkaline type, phosphoric acid type, molten carbonate type, solid electrolyte type, and solid polymer type. is there. Among them, a polymer electrolyte fuel cell that can operate at a low temperature (usually 100 ° C. or less) attracts attention, and in recent years, development and practical application as a low-pollution power source for automobiles is progressing.
[0003]
In the polymer electrolyte fuel cell, it is most preferable from the viewpoint of energy efficiency to use pure hydrogen as a fuel source. However, at the present stage, in consideration of safety and infrastructure, etc., a method of using methanol, natural gas, gasoline, etc. as a fuel source and using these as hydrogen-rich reformed gas in the reformer is being sought. . However, for example, when methanol is used as a raw material, the methanol reforming reaction shown below
[0004]
[Chemical formula 2]
Carbon monoxide is generated by this, and this CO acts as a catalyst poison of the platinum-based catalyst of the electrode of the fuel cell. For this reason, this CO is harmless to the platinum electrode catalyst. 2 Conversion to a shift reaction (CO + H 2 O → CO 2 + H 2 ), The concentration of CO contained in the reformed gas is reduced to about 1% by volume.
[0006]
Conventionally, Cu catalysts such as Cu / Zn-based catalysts, Cu / Zn / Al-based catalysts, and Cu / Cr-based catalysts have been used for the shift reaction. However, if the Cu catalyst is not placed in a reducing atmosphere when the operation is stopped, the catalyst itself is oxidized and its activity is lowered. In addition, the CO reduction rate may rapidly decrease as the space velocity SV (Space Velocity) increases. Further, the conventional catalyst has a low heat-resistant temperature, and sintering, that is, a melting and bonding phenomenon of the metal constituting the catalyst occurs, and the performance as a catalyst may be significantly reduced. Since sintering is an irreversible phenomenon, if the temperature rises transiently, the performance of the shift catalyst is significantly reduced thereafter. For this reason, CO cannot be sufficiently processed in the shift reaction section, which causes adverse effects such as a decrease in hydrogen partial pressure in the fuel gas and poisoning of fuel cell electrodes. Therefore, for the purpose of improving CO reduction rate, suppressing performance degradation due to SV increase, and improving heat resistance, TiO to which a predetermined oxide is added 2 A shift catalyst in which Pt is supported on a porous body is disclosed (see Patent Document 1). According to the document 1, it is assumed that the reason why the catalyst performance is improved is that the specific surface area of the carrier supporting Pt is improved by adding an oxide. As the oxide, at least one oxide of Al, Si, P, S, and V is used.
[0007]
[Patent Document 1]
JP 2002-66320 A
[0008]
[Problems to be solved by the invention]
However, even if the catalyst described in the above publication is used, it is not sufficient to prevent a decrease in activity under a reducing atmosphere, and the shift reaction (CO + H 2 O → CO 2 + H 2 ) Is not enough. In particular, development of a shift catalyst with a higher CO reduction rate is desired for use in a fuel reforming fuel cell vehicle or the like in which a mounting space is limited.
[0009]
[Means for Solving the Problems]
In the present invention, as a result of detailed examination of the types and composition ratios of elements constituting the shift catalyst, the inorganic material composed of a composite oxide containing at least cerium and niobium is an inorganic material that is extremely excellent in heat resistance. The present invention was completed by finding that the CO shift catalyst prepared using the inorganic material as a carrier does not lose its activity even under a reducing atmosphere.
[0010]
【The invention's effect】
According to the method for producing an inorganic material of the present invention, an inorganic material having excellent heat resistance can be prepared. The inorganic material can be a honeycomb monolith. When a catalytically active component is supported on the honeycomb, a catalyst having excellent CO shift activity can be obtained. In particular, a shift catalyst using the inorganic material as a carrier is less likely to reduce the catalytic activity even in a reducing atmosphere.
[0011]
The shift catalyst of the present invention has 50,000 hr. -1 Even at the above space velocity, the shift catalyst activity can be sufficiently ensured, the shift reaction apparatus can be miniaturized, and it is particularly effective when the storage volume of an automobile or the like is limited. Furthermore, it is excellent in heat resistance and excellent in catalyst stability when starting and stopping.
[0012]
In the shift catalyst of the present invention, at least one element selected from the group consisting of platinum, rhodium, palladium, ruthenium, iridium, and osmium is supported on the honeycomb monolith made of the inorganic material, and dried and fired. It is obtained and easy to prepare. Moreover, the shift catalyst produced by this method has a low methane production rate and no wasteful consumption of hydrogen.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
The first of the present invention is a composite oxide containing at least cerium and niobium, and the highest peak height derived from niobium oxide by X-ray diffraction analysis using CuKα rays is the highest peak height derived from cerium oxide. It is an inorganic material characterized by being 1/10 or less.
[0014]
Cerium is a rare earth element that is malleable and ductile, and is a steel-like metal that is also used as an ignition alloy. On the other hand, niobium is an element belonging to Group 5 (Vanadium group) of the Periodic Table, and is a metal rich in malleability and ductility. Conventionally, cerium and niobium have been used as catalyst components, but when a composite oxide of cerium and niobium is prepared in the present invention, the composite oxide has excellent heat resistance that cannot be obtained with cerium or niobium alone. I found out. The formation of a complex oxide from the cerium compound and the niobium compound of the raw material compound indicates that the highest peak derived from the cerium oxide of the inorganic material is higher than the highest peak of cerium oxide alone in the X-ray diffraction analysis. This can be confirmed by shifting to the side. In addition, the numerical value of the said X-ray diffraction is a value at the time of performing an X-ray diffraction analysis on the following conditions.
[0015]
The analytical instrument was an apparatus: a wide-angle X-ray diffractometer (MXP18VAHF type) manufactured by Mac Science. X-ray source: CuKα, applied voltage: 40 KV, applied current: 300 mA, measurement change angle: 2θ, scanning speed: 4.000 deg / min, analysis step size: 0.020 deg, count time: 0.50 sec, count unit: CPS Divergence slit: 1.00 deg, scattering slit: 1.00 deg, light receiving slit: 0.30 mm.
[0016]
The analysis is a numerical value obtained by smoothing, normalizing and diffracting the data.
[0017]
As smoothing, the weighted average value of the peak intensity at the corresponding analysis angle was calculated using the weighted average method shown in the following formula for the analytical raw data obtained by measurement.
[0018]
[Expression 1]
Y [x]: Weighted average count at analysis angle x °
Y (x): Number of detection counts at analysis angle x °
The range of numerical values used to calculate the average value of one point when performing weighted average processing increases the accuracy when calculating the weighted average of a wider-angle analysis value, but is important for handling extremely fine detection peaks You may lose sight of important information. Further, noise is increased when a weighted average of narrower-angle analysis values is obtained. Therefore, in the present invention, the weighted average value is calculated based on the value within the range of 0.08 ° according to the above formula.
[0020]
The obtained smoothing result was normalized by the method shown below, for example, when the highest peak of cerium oxide contained in the obtained inorganic material was used as an example when cerium oxide and niobium oxide were used as raw material compounds. . FIG. 2 shows the smoothed and normalized data of the inorganic materials obtained in Examples 1 to 5 described later and the carrier of Comparative Example 1.
[0021]
[Expression 2]
A: Constant
Y 0 (main) : Weighted average value of the highest peak of cerium oxide in inorganic materials
Y (main) : Weighted average count of highest peak of cerium oxide
The obtained smoothing treatment result includes a diffraction peak derived from the raw material compound. Although depending on the supported amount, relative strength, particle size, etc., generally the diffraction peak derived from the raw material compound is observed more strongly, and in some cases, the diffraction peak derived from the cerium oxide of the desired inorganic material is the peak derived from the stronger raw material compound. It may be observed as if it disappeared by interfering with. Therefore, after normalization, a difference spectrum from the diffraction peak derived from the raw material compound is obtained and separated from the diffraction peak derived from cerium oxide contained in the inorganic material. When a cerium-niobium composite oxide is formed from a cerium compound and a niobium compound, the abundance ratio of the intrinsic peak of the peak derived from the raw material compound is lowered. Therefore, normalization was performed by multiplying by the constant A defined by the above formula so that the diffraction intensity of the highest peak of the raw material compound would be the same.
[0023]
The difference is to subtract the analysis result of the raw material compound processed in the same way from the analysis result obtained by normalization, create a differential diffraction peak and extract only the diffraction peak derived from cerium oxide contained in the inorganic material It is. 3 to 5 show the differential diffraction patterns of the inorganic material obtained in Examples 1 to 5 described later and the support of Comparative Example 1. FIG.
[0024]
In the inorganic material of the present invention, the X-ray diffraction peak derived from cerium oxide is shifted to the face spacing side from the X-ray diffraction peak of cerium oxide itself. Such a shift indicates that cerium and niobium contained in the raw material compound form a composite oxide. That is, since the raw material compound (cerium compound, niobium compound) itself does not have a cerium-niobium composite oxide region (interface), there is no possibility of a peak shift. However, as is clear from FIG. 3 to be described later, the formation of a complex oxide clearly shifts the peak to the high surface interval side, and the bonding relationship between niobium and cerium through the oxygen atoms in the crystal is present. It can be judged that it was formed. Since the formation of the complex oxide makes the bond between niobium oxide and cerium oxide dense, oxygen atoms from the base material are more easily supplied to the lattice defect oxygen position, and the bonded structure is effectively maintained. Can do. For the second height peak, the third height peak, and each niobium oxide peak, the values obtained by smoothing, normalizing, and diffracting the difference are used in the same manner as described above. .
[0025]
Examples of the raw material compounds that can be used in the inorganic material of the present invention include these nitrates, sulfates, ammonium salts, amines, carbonates, bicarbonates, halogen salts, nitrites, inorganic salts such as oxalic acid, and carboxylic acids such as formate. Examples thereof include salts, hydroxides, alkoxides, and the like, which can be appropriately selected depending on the type of solvent in which these are dissolved, pH, and the like. Among these, nitrates, carbonates, oxides, hydroxides and the like are preferable for industrial use. In the present invention, these sols can also be used as raw material compounds.
[0026]
In the present invention, it is a complex oxide composed of the above raw material compound, and the maximum peak height derived from niobium oxide by the X-ray diffraction analysis is 1/10 or less of the maximum peak height derived from cerium oxide. And This is because the peak derived from niobium oxide and the peak derived from cerium oxide contained in the inorganic material is not necessarily proportional to the blending amount of cerium oxide and niobium oxide in the inorganic material, but is particularly excellent in heat resistance within this range. .
[0027]
In the inorganic material of the present invention, according to the X-ray diffraction analysis, the highest peak derived from cerium oxide of the inorganic material is shifted to a higher interval side with a plane interval than the highest peak of cerium oxide alone used as a raw material. ing. Shifting from the peak of the cerium oxide of the raw material compound to the higher spacing side with respect to the plane means that a complex oxide with niobium was formed.
[0028]
The highest peak derived from cerium oxide of the inorganic material by the X-ray diffraction analysis is preferably in the range of 28.44 to 28.66 ° as 2θ.
[0029]
Moreover, it is preferable that the 2nd highest peak derived from the cerium oxide of the inorganic material by the X-ray diffraction analysis is 1.63 に し て in terms of the interplanar spacing.
[0030]
Further, it is preferable that the third highest peak derived from cerium oxide of the inorganic material by the X-ray diffraction analysis is present at 1.9 cm in terms of the plane spacing.
[0031]
The inorganic material of the present invention preferably has a Ce / Nb ratio of 1 or more, more preferably 1.0 to 5.0, and particularly preferably 3.0 to 5.0. If the Ce / Nb ratio is less than 1, the effect of oxygen mobility by cerium may be reduced. Other elements that can be used in the inorganic material of the present invention include Si, Al, Zr, Ti, and the like.
[0032]
The inorganic material of the present invention has a BET specific surface area of 40 m. 2 / g or more, more preferably 60 m 2 / g or more, more preferably 80 m 2 / g or more. Especially 40m 2 If the specific surface area is at least / g, sufficient catalytic activity can be ensured.
[0033]
The method for producing the inorganic material of the present invention is not limited, but the organic thickener or starch is dispersed in an aqueous solution containing the water-soluble cerium compound or its sol and the water-soluble niobium compound or its sol, and then evaporated. It can be manufactured by baking after drying. As the water-soluble cerium compound or water-soluble niobium compound, a water-soluble compound can be selected from the above-described cerium compounds and niobium compounds. Thus, if a water-soluble compound is used, it can be prepared without using an organic solvent and handling becomes easy, and problems such as waste liquid treatment can be avoided. Further, by adding an organic thickener, it is possible to suppress the separation of Ce and Nb during drying and to obtain a more stable composite oxide having fine pores. Examples of organic thickeners that can be used include methyl cellulose ether, methyl cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose. Examples of starch substances include corn starch.
[0034]
In order to produce the inorganic material of the present invention, the cerium and niobium raw materials dispersed in water as occasion demands are sufficiently stirred, and an organic thickener is added thereto until stirring becomes difficult due to the viscosity of the thickener. Mix. As the drying method, for example, natural drying, evaporation to dryness, rotary evaporator, spray dryer, drum dryer, or dry blower can be used. What is necessary is just to select drying time suitably according to the method to be used. Depending on the case, it is good also as drying in a baking process, without performing a drying process. Further, the firing of the composite is sufficient at a temperature of 200 to 1000 ° C. for 30 to 480 minutes.
[0035]
If the inorganic material of the present invention is used, it is a shift catalyst used in the shift reaction represented by the following formula (1),
[0036]
[Chemical 3]
A carbon monoxide shift catalyst characterized by using the inorganic material as a carrier can be obtained. Since the inorganic material is excellent in heat resistance, a decrease in catalytic activity can be prevented.
[0038]
In the present invention, the inorganic material is used as a carrier, and the catalyst contains at least one noble metal element selected from the group consisting of platinum, rhodium, palladium, ruthenium, iridium, and osmium as a catalyst component. Is preferred. The supply source of these elements is not particularly limited, and compounds containing these elements can be widely used. Such compounds include nitrates, sulfates, ammonium salts, amines, carbonates, bicarbonates, halogen salts, nitrites, inorganic salts such as oxalic acid, carboxylates and hydroxides such as formate, Examples include alkoxides and oxides, which can be appropriately selected depending on the type and pH of the solvent in which these are dissolved. Among these, nitrates, carbonates, oxides, hydroxides and the like are preferable for industrial use.
[0039]
Although it is not clear why the shift catalyst using the inorganic material is excellent, in addition to using an inorganic material having excellent heat resistance as a support, the oxygen carrying ability of cerium contained in the inorganic material is involved. it is conceivable that. First, the shift reaction represented by the above formula (1) can be understood by being decomposed into the following formula.
[0040]
[Formula 4]
If the active oxygen (O) based on (i) is present at the oxidation active point of the CO oxidation catalyst, the above formula (ii) proceeds efficiently. When a cerium element having an excellent ability to transport active oxygen (O) is used, the circulation between (i) and (ii) rotates smoothly, and the hydrogen generation reaction proceeds efficiently. That is, H 2 O to H 2 Niobium is used as the active species (A) from which oxygen can be taken out, and oxygen, oxygen, platinum, rhodium, palladium, ruthenium, iridium and / or osmium elements, and cerium elements as the active species (B) having the ability to oxidize CO When the active species (C) excellent in the presence of the catalyst is present in the catalyst, it becomes a catalyst excellent in shift reactivity even at a low temperature. The active species (A), (B), and (C) are H in the gaseous state if they are present in the catalyst. 2 O to H 2 There is no limitation on the dispersibility of these components in the catalyst. This is because even when the active species (A) and (B) are not adjacent to each other, the active oxygen (O) is transported through the cerium element, and a smooth reaction can be ensured. Further, cerium oxide and cerium-zirconium composite are redox-capable metals that can move oxygen atoms in the crystal, and H generated by the shift reaction by using these metals. 2 So-called methanation reaction can be suppressed. That is, the above equation (1) is used for CO 2 2 Together with H 2 Although the reforming reaction gas is hot, the reverse shift reaction (CO 2 + H 2 → CO + H 2 O) and methanation reaction (CO + 3H) 2 → CH Four + H 2 O) may occur and hydrogen fuel may be consumed. Since the methanation reaction is an independent reaction from the shift reaction, it is impossible to know the contribution rate to the final hydrogen production rate simply by evaluating the CO conversion rate of the shift catalyst.
[0042]
In the present invention, in addition to the above elements, a noble metal element selected from platinum, rhodium, palladium, ruthenium, iridium and osmium is contained. Among the raw material compounds to be used, dinitrodiamine platinum, platinum chloride and the like can be used as the platinum raw material, and dinitrodiamine platinum is particularly preferable. It is because it is excellent in dispersibility. In addition, in order to use chloride, when manufacturing a catalyst industrially on a large scale, air pollution caused by the calcined exhaust gas must be considered, and chlorine corrosion of the exhaust pipe has a great adverse effect. Similarly, rhodium, palladium, ruthenium, iridium and osmium are preferably nitrates, ammonium salts and the like. The compounding amount of these elements is preferably 0.01 to 20.0% by mass in the shift catalyst, more preferably 1.0 to 20.0% by mass, and particularly preferably 10.0 in terms of mass. ˜15.0 mass%. If it is less than 0.01% by mass, the CO conversion may not be sufficient. These elements are considered to be active components of the catalyst, and it is preferable to distribute these so-called noble metal elements on the catalyst surface in order to improve the CO conversion. This is because the contact rate with CO is improved even at low temperatures, and the CO conversion rate is improved. In the present invention, it is preferable that platinum element is contained particularly in terms of excellent CO conversion. However, a large loading amount may be disadvantageous in consideration of economy. In the present invention, it is preferable that platinum element is contained particularly in terms of excellent CO conversion.
[0043]
In addition to the above, clay minerals and organic binders may be added. Examples of the organic binder include methyl cellulose ether, methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, and corn starch. In addition to the organic binder, a substance that disappears upon firing, such as walnut particles, peach seed particles, etc., having a uniform particle diameter, or polymer particles having a uniform particle diameter, may be used as the pore-forming agent.
[0044]
There is no restriction | limiting in particular as a method of preparing the catalyst of this invention, It can manufacture with a general catalyst preparation method. For example, a method in which a composite containing a compound other than a noble metal element is previously formed on the inorganic material, dried and fired, and then the noble metal element is supported on the fired product can be employed.
[0045]
This method is economically advantageous in that a larger amount of noble metal element is present on the outer surface of the catalyst and the CO conversion can be improved with a small amount. The above-mentioned inorganic material is used as a carrier in advance and a noble metal element is supported on the carrier. As such a preparation method, a solution in which the above-mentioned noble metal is dissolved or dispersed is prepared, and the inorganic material is impregnated with these elements. Is dried to carry these elements, which are dried and calcined to obtain the target catalyst.
[0046]
In this method, for example, natural drying, evaporation to dryness, rotary evaporator, spray dryer, drying with a drum dryer or the like can be used. What is necessary is just to select drying time suitably according to the method to be used. Depending on the case, it is good also as drying in a baking process, without performing a drying process. Moreover, baking is sufficient at the temperature of 200-1000 degreeC for 30-480 minutes. In addition, in order to carry | support the said noble metal element, you may perform together pressure reduction, a heating, spray spraying, etc. as needed. The heat treatment after supporting the noble metal element is performed by selecting the temperature and time required for the noble metal element to deposit on the catalyst, but under such conditions that the noble metal element is present as uniformly as possible with fine particles. It is most preferable to choose. Generally, heat treatment at a high temperature or for a long time is not preferable because it promotes aggregation of precipitated platinum group particles. Accordingly, it is preferable to perform the treatment in a short time of 10 to 240 minutes using air (or an inert gas such as nitrogen) heated to 300 to 600 ° C. or superheated steam. The short heat treatment is preferable from the viewpoint of shortening the time of the catalyst preparation step.
[0047]
In addition, the shift catalyst of the present invention can be formed into a granular material when the inorganic material is formed into a granular material, and can adopt various shapes, such as a pellet shape, a ring shape, a horseshoe shape, and a ribbon. You may shape | mold into arbitrary shapes, such as a shape. Further, a honeycomb monolith is previously formed from the inorganic material of the first invention, and at least one noble metal element selected from platinum, rhodium, palladium, ruthenium, iridium and osmium is supported on the honeycomb monolith, and a shift catalyst May be manufactured. When the catalyst of the present invention is in an irregular shape such as a granular material, a pellet shape, a ring shape, a horseshoe shape, or a ribbon shape, the shift catalyst is accommodated in a reaction vessel, and the reformed gas is allowed to flow into the vessel. , CO efficiently contained in reformed gas 2 Can be converted to Further, when the above-mentioned noble metal element is coated on the honeycomb monolith without using such a reaction vessel, a reactor-type shift catalyst can be used as it is.
[0048]
The shift catalyst of the present invention has a space velocity of 50,000 hr. -1 Since it can be used as described above and is excellent in CO conversion, the shift catalyst reactor can be downsized, which is particularly advantageous. The noble metal element is coated on the honeycomb monolith, for example, by supporting at least one element selected from platinum, rhodium, palladium, ruthenium, iridium and osmium on the honeycomb monolith made of the inorganic material. Can be produced by drying and baking. Further, a precious metal element prepared in advance may be coated on a honeycomb monolith made of the above inorganic material by blending a binder.
[0049]
The shift catalyst of the present invention has a BET specific surface area of 40 m. 2 / g or more, more preferably 60 m 2 / g or more, more preferably 80 m 2 / g or more. Especially 40m 2 If the specific surface area is at least / g, sufficient catalytic activity can be ensured. In terms of catalyst life, it is important to support a sufficient amount of white metal element and a fine white metal element on the fired product. 2 A low specific surface area support of less than / g is difficult to satisfy both factors. Further, by having such a BET specific surface area, the shift catalyst of the present invention has a space velocity of 50,000 hr. -1 Or more, more preferably 100,000 hr -1 The above can be used. In addition, the shift catalyst of the present invention preferably has an average particle size of 1.0 to 50 μm when analyzed by a laser diffraction method. This is because the CO conversion rate is excellent within this range.
[0050]
The shift catalyst and shift catalyst reactor of the present invention can be mounted to provide a fuel reforming hydrogen generation system, a fuel cell system, or a fuel reforming fuel cell vehicle. FIG. 1 shows a system flow diagram of a fuel reforming hydrogen generation system. Referring to the drawings, first, fuel such as methanol, gasoline, hydrocarbons, etc. is supplied to the fuel tank. This fuel is vaporized by a vaporizer, and sulfur contained in the desulfurizer is removed. In the reforming section, the fuel is reformed into a hydrogen-rich reformed gas, usually by steam reforming using steam. Also, a hydrogen-rich reformed gas can be obtained by autothermal reforming in which a gas containing oxygen is simultaneously supplied in addition to water vapor and a partial oxidation reaction is also performed. Next, the reformed gas is sent to the shift reactor, and CO contained in the reformed gas is converted to CO. 2 And the CO concentration is reduced to about 1% by volume. The reformed gas whose CO concentration has been reduced to about 1% by volume is subsequently transferred to a CO remover to reduce the CO concentration to the order of ppm. The reformed gas and oxidant (usually air) whose CO concentration has been reduced to the order of ppm are supplied to the fuel cell generator, and the power generation reaction proceeds. Note that spent fuel and oxidant are discharged from the fuel cell generator.
[0051]
As described above, the shift catalyst according to the present invention can exhibit an excellent CO conversion rate even at a low temperature. By using the shift catalyst having such characteristics for CO conversion in the fuel reformed gas, it is possible to efficiently reduce the CO concentration in the fuel gas supplied to the fuel cell. In particular, even if the space velocity is high, the CO concentration can be reduced to a very low concentration, so that it can be used effectively even in an automobile or the like where the mounting range is limited.
[0052]
【Example】
Hereinafter, the present invention will be described using examples.
[0053]
Example 1 (Ce 80 Nb 20 )
To 26.1 g of cerium carbonate, 18.0 g of 10% by mass niobium oxide sol and 30 ml of concentrated nitric acid were added and sufficiently stirred. To this was added 0.5 g of methyl cellulose ether (trade name “Hi-Metroze”, manufactured by Shin-Etsu Chemical Co., Ltd.), and the mixture was stirred and mixed until the stirrer did not rotate due to the viscosity of methyl cellulose ether. This was dried and ground overnight at 150 ° C. Then, it is baked at 500 ° C. for 1 hour, and the BET specific surface area is about 100 m 2 / G of inorganic material 1 was obtained. The composition of the inorganic material was 80 mol% cerium and 20 mol% niobium in terms of each element.
[0054]
The X-ray diffraction results of the obtained inorganic material are shown in FIGS.
[0055]
Moreover, TG-DTA analysis was performed about this inorganic material. First, the temperature was raised from room temperature to 150 ° C. and held for 30 minutes, and the temperature was raised to 600 ° C. at 10 ° C./min. The weight reduction rate was observed from the time when it reached 200 ° C to the amount of mass reduction when it reached 600 ° C. The mass reduction was 0.7% by mass. The results are also shown in FIG.
[0056]
Example 2 (Ce 80 Nb 20 )
To 26.1 g of cerium carbonate, 18.0 g of 10% by mass niobium oxide sol and 30 ml of concentrated nitric acid were added and sufficiently stirred. An equal amount of urea was added thereto, the temperature was raised to 98 ° C. over 3 hours with stirring, and the temperature was maintained for 2 hours. This was cooled to room temperature, filtered, dried at 150 ° C. overnight and pulverized. Then, it is baked at 500 ° C. for 1 hour, and the BET specific surface area is about 100 m 2 / G of inorganic material 2 was obtained. The composition of the inorganic material was 80 mol% cerium and 20 mol% niobium in terms of each element.
[0057]
The X-ray diffraction results of the obtained inorganic material are shown in FIGS.
[0058]
Example 3 (Ce 50 Nb 50 )
Inorganic Example 3 was obtained in the same manner as in Example 1 except that 26.1 g of cerium carbonate, 30 ml of concentrated nitric acid, and 80 g of 10 mass% niobium oxide sol were used. The composition of the inorganic material was
[0059]
The X-ray diffraction results of the obtained inorganic material are shown in FIGS.
[0060]
reference Example 4 (Ce 20 Nb 80 )
Inorganic Example 4 was obtained in the same manner as in Example 1, except that 25.0 g of cerium carbonate, 30 ml of concentrated nitric acid, 10% by mass, and 300 g of niobium oxide sol were used. The composition of the inorganic material was 20 mol% cerium and 80 mol% niobium in terms of each element.
[0061]
The X-ray diffraction results of the obtained inorganic material are shown in FIGS.
[0062]
Example 5 (Ce 50 Nb 50 )
26.1 g of cerium carbonate, 30 ml of concentrated nitric acid and 10 g of niobium oxide sol were used. After adding 10 g of urea, the temperature was raised to 100 ° C. while refluxing to obtain a precipitate. It was dried to obtain
[0063]
The X-ray diffraction results of the obtained inorganic material are shown in FIGS.
[0064]
Example 6
Example 1 3, 5 and Reference Example 4 Using the inorganic material obtained in the above, it was catalyzed by the following method. 13.15 g of dinitrodiamine platinum complex salt having a Pt metal content of 8.451 mass% and 10 g of the inorganic material were added and sufficiently stirred. This was dried overnight at 150 ° C., pulverized, and calcined at 400 ° C. for 1 hour. 3, 5 and Reference Catalyst Example 4 Got. The composition of the catalyst was 10% by mass in terms of element.
[0065]
Comparative Example 1
Comparative carrier example 1 cerium oxide (BET specific surface area: about 130 m 2 / G) X-ray diffraction results are shown in FIGS.
[0066]
Further, Comparative Catalyst Example 1 was obtained in the same manner as in Example 6 except that the cerium oxide was used instead of the inorganic material.
[0067]
The compound was subjected to TG-DTA analysis in the same manner as in Example 1. The mass loss was 2.4. The results are shown in FIG.
[0068]
Comparative Example 2
As Comparative Carrier Example 2, Ce / Zr = 68/32 (molar ratio) cerium-zirconium composite oxide powder (BET specific surface area 70 m 2 / G) was prepared.
[0069]
The compound was subjected to TG-DTA analysis in the same manner as in Example 1. The mass loss was 4.1. The results are shown in FIG.
[0070]
Activity test 1
Example of catalyst 1 to 3, 5, Reference catalyst example 4 The catalyst prepared in Comparative Catalyst Example 1 was compressed on a disk and then crushed and sized to a particle size of 70 to 36 μm. After mixing 0.1 g of the catalyst and 0.13 g of silica sand, the mixture was filled in a glass tube, and the space velocity was 60,000 hr. -1 A 2% hydrogen-containing nitrogen atmosphere was allowed to flow at a flow rate of 30 ° C., and an activation treatment was performed at 400 ° C. for 30 minutes. Next, the catalyst was cooled to 150 ° C. in a nitrogen atmosphere, and the outlet gas was analyzed at the outlet by gas chromatography while raising the temperature from 200 ° C. The input gas composition is CO / CO regardless of which catalyst is used. 2 / H 2 / H 2 O / N 2 Was 10 / 13.3 / 40 / 16.8 / 19.9 volume%. The outlet CO concentration was measured, and the CO conversion rate was determined based on the following formula.
[0071]
[Equation 3]
CH Four The production rate is the specified CH Four The calculation was made based on a calibration curve verified from cylinder gas. Table 1 shows the compositions of the catalysts prepared in Examples and Comparative Examples, and the CO conversion rate of the catalysts at a temperature of 300 ° C. The results are also shown in FIG.
[0073]
[Table 1]
[Brief description of the drawings]
FIG. 1 is a system flow diagram of a fuel reforming hydrogen generation system using a shift catalyst of the present invention.
FIG. 2 is the data after smoothing and normalizing the X-ray diffraction data of the inorganic materials prepared in Comparative Example 1 and Examples 1 to 5.
FIG. 3 is a diagram showing a 27-30 ° differential diffraction pattern of the inorganic materials prepared in Comparative Example 1 and Examples 1-5.
4 is a diagram showing a differential diffraction pattern of 55 to 58 ° of the inorganic materials prepared in Comparative Example 1 and Examples 1 to 5. FIG.
FIG. 5 is a diagram showing a 46-49 ° differential diffraction pattern of inorganic materials prepared in Comparative Example 1 and Examples 1-5.
6 is a diagram showing the results of TG-DTA analysis of the inorganic material of Example 1 and Comparative Carriers 1 and 2 used in Comparative Examples 1 and 2. FIG.
7 is a graph showing the CO conversion rate of the catalysts prepared in Example 6 and Comparative Example 1. FIG.
Claims (15)
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| CN105377422B (en) | 2013-03-28 | 2018-09-21 | 新加坡科技研究局 | Methanation catalyst |
| SG2013050877A (en) | 2013-06-28 | 2015-01-29 | Agency Science Tech & Res | Methanation catalyst |
| JP6180032B2 (en) * | 2014-08-04 | 2017-08-16 | 株式会社豊田中央研究所 | Composite metal oxide and method for producing the same, nitrogen oxide decomposition catalyst using the composite metal oxide, and method for decomposing nitrogen oxide using the nitrogen oxide decomposition catalyst |
| JP7139567B2 (en) * | 2018-08-31 | 2022-09-21 | 国立研究開発法人量子科学技術研究開発機構 | Oxidation catalyst for fuel cell, method for producing the same, and fuel cell |
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