JP2004351236A - Catalyst for oxidizing/removing methane in exhaust gas and method for purifying exhaust gas - Google Patents
Catalyst for oxidizing/removing methane in exhaust gas and method for purifying exhaust gas Download PDFInfo
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- JP2004351236A JP2004351236A JP2003148279A JP2003148279A JP2004351236A JP 2004351236 A JP2004351236 A JP 2004351236A JP 2003148279 A JP2003148279 A JP 2003148279A JP 2003148279 A JP2003148279 A JP 2003148279A JP 2004351236 A JP2004351236 A JP 2004351236A
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- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 title claims abstract description 194
- 239000003054 catalyst Substances 0.000 title claims abstract description 127
- 238000000034 method Methods 0.000 title claims abstract description 31
- 230000001590 oxidative effect Effects 0.000 title claims abstract description 26
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 claims abstract description 111
- 238000007254 oxidation reaction Methods 0.000 claims abstract description 63
- 230000003647 oxidation Effects 0.000 claims abstract description 62
- 238000002485 combustion reaction Methods 0.000 claims abstract description 49
- XTQHKBHJIVJGKJ-UHFFFAOYSA-N sulfur monoxide Chemical compound S=O XTQHKBHJIVJGKJ-UHFFFAOYSA-N 0.000 claims abstract description 42
- XOLBLPGZBRYERU-UHFFFAOYSA-N tin dioxide Chemical compound O=[Sn]=O XOLBLPGZBRYERU-UHFFFAOYSA-N 0.000 claims abstract description 40
- 229910001887 tin oxide Inorganic materials 0.000 claims abstract description 40
- 229910052697 platinum Inorganic materials 0.000 claims abstract description 35
- TXKMVPPZCYKFAC-UHFFFAOYSA-N disulfur monoxide Inorganic materials O=S=S TXKMVPPZCYKFAC-UHFFFAOYSA-N 0.000 claims abstract description 17
- 238000004519 manufacturing process Methods 0.000 claims abstract description 16
- 239000007789 gas Substances 0.000 claims description 84
- 239000011148 porous material Substances 0.000 claims description 26
- 229910052815 sulfur oxide Inorganic materials 0.000 claims description 26
- 239000008188 pellet Substances 0.000 claims description 18
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 claims description 12
- 150000003058 platinum compounds Chemical class 0.000 claims description 12
- 239000007864 aqueous solution Substances 0.000 claims description 11
- 239000003546 flue gas Substances 0.000 claims description 9
- 239000000758 substrate Substances 0.000 claims description 7
- 238000005470 impregnation Methods 0.000 claims description 5
- 239000000919 ceramic Substances 0.000 claims description 4
- 229910052751 metal Inorganic materials 0.000 claims description 4
- 239000002184 metal Substances 0.000 claims description 4
- 238000001179 sorption measurement Methods 0.000 claims description 3
- 239000000567 combustion gas Substances 0.000 claims 2
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 claims 1
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 claims 1
- 229910052717 sulfur Inorganic materials 0.000 claims 1
- 239000011593 sulfur Substances 0.000 claims 1
- KDLHZDBZIXYQEI-UHFFFAOYSA-N Palladium Chemical compound [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 abstract description 30
- 229910052763 palladium Inorganic materials 0.000 abstract description 14
- 229910000510 noble metal Inorganic materials 0.000 abstract description 9
- 229910006404 SnO 2 Inorganic materials 0.000 description 40
- 229910005965 SO 2 Inorganic materials 0.000 description 16
- 238000006243 chemical reaction Methods 0.000 description 12
- 239000000843 powder Substances 0.000 description 12
- MWUXSHHQAYIFBG-UHFFFAOYSA-N nitrogen oxide Inorganic materials O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 description 9
- 238000011056 performance test Methods 0.000 description 9
- 238000012360 testing method Methods 0.000 description 9
- 229930195733 hydrocarbon Natural products 0.000 description 8
- 150000002430 hydrocarbons Chemical class 0.000 description 8
- 238000010586 diagram Methods 0.000 description 7
- 230000000694 effects Effects 0.000 description 7
- 229910018879 Pt—Pd Inorganic materials 0.000 description 6
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 6
- 238000011068 loading method Methods 0.000 description 6
- 238000002360 preparation method Methods 0.000 description 6
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 5
- 230000007423 decrease Effects 0.000 description 5
- 238000009826 distribution Methods 0.000 description 5
- 229910052760 oxygen Inorganic materials 0.000 description 5
- 239000000126 substance Substances 0.000 description 5
- 239000004215 Carbon black (E152) Substances 0.000 description 4
- MCMNRKCIXSYSNV-UHFFFAOYSA-N Zirconium dioxide Chemical compound O=[Zr]=O MCMNRKCIXSYSNV-UHFFFAOYSA-N 0.000 description 4
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 4
- 239000000969 carrier Substances 0.000 description 4
- 230000003197 catalytic effect Effects 0.000 description 4
- 239000001301 oxygen Substances 0.000 description 4
- 229910002091 carbon monoxide Inorganic materials 0.000 description 3
- 239000000446 fuel Substances 0.000 description 3
- -1 natural gas Chemical class 0.000 description 3
- IXSUHTFXKKBBJP-UHFFFAOYSA-L azanide;platinum(2+);dinitrite Chemical compound [NH2-].[NH2-].[Pt+2].[O-]N=O.[O-]N=O IXSUHTFXKKBBJP-UHFFFAOYSA-L 0.000 description 2
- 150000001875 compounds Chemical class 0.000 description 2
- 238000007796 conventional method Methods 0.000 description 2
- 230000001747 exhibiting effect Effects 0.000 description 2
- 238000001125 extrusion Methods 0.000 description 2
- 239000008187 granular material Substances 0.000 description 2
- 238000000465 moulding Methods 0.000 description 2
- 239000002994 raw material Substances 0.000 description 2
- 150000003839 salts Chemical class 0.000 description 2
- 239000000243 solution Substances 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- 229910000599 Cr alloy Inorganic materials 0.000 description 1
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 1
- KJTLSVCANCCWHF-UHFFFAOYSA-N Ruthenium Chemical compound [Ru] KJTLSVCANCCWHF-UHFFFAOYSA-N 0.000 description 1
- 238000009825 accumulation Methods 0.000 description 1
- 150000001242 acetic acid derivatives Chemical class 0.000 description 1
- 230000002378 acidificating effect Effects 0.000 description 1
- 150000003841 chloride salts Chemical class 0.000 description 1
- 239000000788 chromium alloy Substances 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 229910052878 cordierite Inorganic materials 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 230000002542 deteriorative effect Effects 0.000 description 1
- JSKIRARMQDRGJZ-UHFFFAOYSA-N dimagnesium dioxido-bis[(1-oxido-3-oxo-2,4,6,8,9-pentaoxa-1,3-disila-5,7-dialuminabicyclo[3.3.1]nonan-7-yl)oxy]silane Chemical compound [Mg++].[Mg++].[O-][Si]([O-])(O[Al]1O[Al]2O[Si](=O)O[Si]([O-])(O1)O2)O[Al]1O[Al]2O[Si](=O)O[Si]([O-])(O1)O2 JSKIRARMQDRGJZ-UHFFFAOYSA-N 0.000 description 1
- 238000003912 environmental pollution Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 238000010304 firing Methods 0.000 description 1
- 239000003205 fragrance Substances 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 230000005764 inhibitory process Effects 0.000 description 1
- 239000003350 kerosene Substances 0.000 description 1
- 239000003345 natural gas Substances 0.000 description 1
- 150000002823 nitrates Chemical class 0.000 description 1
- 229910017604 nitric acid Inorganic materials 0.000 description 1
- GPNDARIEYHPYAY-UHFFFAOYSA-N palladium(ii) nitrate Chemical compound [Pd+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O GPNDARIEYHPYAY-UHFFFAOYSA-N 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 229910052703 rhodium Inorganic materials 0.000 description 1
- 239000010948 rhodium Substances 0.000 description 1
- MHOVAHRLVXNVSD-UHFFFAOYSA-N rhodium atom Chemical compound [Rh] MHOVAHRLVXNVSD-UHFFFAOYSA-N 0.000 description 1
- 229910052707 ruthenium Inorganic materials 0.000 description 1
- 239000002002 slurry Substances 0.000 description 1
- 239000004071 soot Substances 0.000 description 1
- 239000010935 stainless steel Substances 0.000 description 1
- 229910001220 stainless steel Inorganic materials 0.000 description 1
- 150000003464 sulfur compounds Chemical class 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
Images
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
- B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
- B01J23/54—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
- B01J23/56—Platinum group metals
- B01J23/62—Platinum group metals with gallium, indium, thallium, germanium, tin or lead
- B01J23/622—Platinum group metals with gallium, indium, thallium, germanium, tin or lead with germanium, tin or lead
- B01J23/626—Platinum group metals with gallium, indium, thallium, germanium, tin or lead with germanium, tin or lead with tin
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
- B01D53/86—Catalytic processes
- B01D53/8668—Removing organic compounds not provided for in B01D53/8603 - B01D53/8665
-
- B01J35/647—
Abstract
Description
【０００１】
【発明の属する技術分野】
本発明は、硫黄酸化物を含む燃焼排ガス中のメタンを低温域において酸化除去するための触媒、該触媒を用いて硫黄酸化物を含む燃焼排ガス中のメタンを酸化除去する方法及び該触媒の製造方法に関する。
【０００２】
【従来の技術】
ボイラー、加熱炉、あるいはガスエンジンやガスタービンなどの燃料としては天然ガス、都市ガス、軽油、灯油などの炭化水素が使用される。それら燃料を燃焼させた排ガスには窒素酸化物（ＮＯＸ）、硫黄酸化物（ＳＯＸ）、一酸化炭素、あるいは臭気物質、ばいじん等のほか、未燃焼の炭化水素が含有されている。これらの成分は環境汚染の原因となるので無害にして排出する必要がある。
【０００３】
この点は、コージェネレーションシステムやＧＨＰ（Ｇａｓ Ｈｅａｔ Ｐｕｍｐ）における希薄燃焼ガスエンジンからの排ガスについても同様である。希薄燃焼ガスエンジンのような希薄燃焼方式の場合には、その排ガス中に少量の炭化水素、特にメタン、窒素酸化物、一酸化炭素等とともに、多量の酸素及び水蒸気が共存することになる。従来、排ガス中の３成分すなわち炭化水素、窒素酸化物、一酸化炭素を同時に浄化する三元触媒による処理法が開発されている。
【０００４】
ところが、三元触媒による処理法は酸素が殆んど存在しない燃焼排ガスに対してしか有効に適用することはできず、三元触媒は酸素過剰で且つ燃焼排ガス中の炭化水素がとりわけメタンである場合には有効に作用しない。炭化水素の酸化触媒としてはパラジウム、白金、ロジウムなどの貴金属が用いられるが、それら貴金属触媒は担体に担持した形で使用される。その担体としてはアルミナ（Ａｌ２Ｏ３）やジルコニア（ＺｒＯ２）などが知られている。
【０００５】
ところで、炭化水素が特にメタンの場合には、従来、その酸化にはパラジウムが有効とされ、白金についてはそれ単独では有効でなく、補助的に使用されているだけである。例えば、特開２０００−３３２６６や特開２０００−２５４５０５には、酸化スズ担体にパラジウムを担持してなる触媒が、硫黄酸化物による触媒活性の阻害に対して高い抵抗性を示すことが示されている。このうち特開２０００−３３２６６では、酸化スズ担体にパラジウムと白金を担持してなる触媒についても開示されているが、白金はパラジウムと一緒に補足的に使用されるに過ぎない。この点、特開２００１−１９０９３１においても同様である。
【０００６】
【特許文献１】特開２０００−３３２６６号公報
【特許文献２】特開２０００−２５４５０５号公報
【特許文献３】特開２００１−１９０９３１号公報
【０００７】
また、例えば希薄燃焼ガスエンジンからの排ガスの温度は５００℃以下、通常５００−４００℃程度と低いため、酸化触媒によるメタンの酸化は困難である。特に４５０℃以下という低温域においては、酸化触媒は、排ガス中に含まれる微量の硫黄酸化物の蓄積による被毒劣化が著しく、これによりメタンの酸化除去性能は経時的に劣化してしまい、実用に供し得る十分な耐久性能が得られないのが現状である。
【０００８】
【発明が解決しようとする課題】
本発明者らは、白金、ルテニウム、パラジウムなどの貴金属とアルミナやジルコニアなどの担体、また酸化スズ担体を各種組み合せて実験、検討を繰り返して追求したところ、全く偶然にも、従来メタンの酸化活性貴金属と考えられていたパラジウムを一切含まず、また従来単独では有効でないと考えられていた白金をそれ単独で、すなわち白金のみを多孔質の酸化スズに担持した触媒が低温域、特に４５０℃以下という低温域におけるメタンの酸化除去触媒として有効で、高い耐ＳＯＸ性を有することを見い出し、本発明に到達するに至ったものである。
【０００９】
すなわち、本発明は、白金を多孔質の酸化スズに担持してなる硫黄酸化物を含む燃焼排ガス中のメタン酸化除去用触媒を提供することを目的とし、また、硫黄酸化物を含む燃焼排ガスを該酸化除去触媒に５００℃以下の低温域、特に４５０−３５０℃という低温域で通すことにより燃焼排ガス中のメタンを長期にわたり有効に酸化除去する方法を提供することを目的とし、さらに、その酸化触媒の製造方法を提供することを目的とする。
【００１０】
【課題を解決するための手段】
本発明は、硫黄酸化物を含む燃焼排ガス中のメタンを低温域において酸化除去するための触媒であって、該酸化除去触媒が多孔質の酸化スズに白金を担持させてなる触媒であることを特徴とする硫黄酸化物を含む燃焼排ガス中のメタンの低温酸化除去用触媒を提供する。
【００１１】
また、本発明は、硫黄酸化物を含む燃焼排ガス中のメタンを低温域で酸化除去する方法であって、該燃焼排ガスを多孔質の酸化スズに白金を担持させてなる酸化除去触媒に低温域で通すことによりメタンを酸化除去することを特徴とする硫黄酸化物を含む燃焼排ガス中のメタンの低温酸化除去方法を提供する。
【００１２】
さらに、本発明は、多孔質の酸化スズに白金を担持してなる硫黄酸化物を含む燃焼排ガス中のメタンの低温酸化除去用触媒の製造方法であって、白金化合物を多孔質の酸化スズに対して白金化合物の水溶液による含浸法または平衡吸着法により担持させた後、焼成することを特徴とする硫黄酸化物を含む燃焼排ガス中のメタンの低温酸化除去用触媒の製造方法を提供する。
【００１３】
【発明の実施の形態】
本発明に係る燃焼排ガス中のメタンの酸化除去用触媒は、多孔質の酸化スズ（ＳｎＯ２）に白金を担持させてなる触媒であり、硫黄酸化物を含む燃焼排ガス中のメタンを低温域で酸化除去する触媒である。本発明によれば、従来メタンの酸化活性貴金属とされていたパラジウムを一切含まず、また従来単独では有効でないと考えられていた白金をそれ単独で、すなわち白金のみを多孔質の酸化スズに担持することにより、５００℃以下の低温域、特に４５０−３５０℃という低温域においてメタンを長期にわたり極めて有効に酸化除去することができる。
【００１４】
本酸化除去用触媒の製造法としては、多孔質の酸化スズに対して白金を均一に担持させ得る手法であれば特に限定はないが、好ましくは含浸法や平衡吸着法が適用される。担体である酸化スズ（ＳｎＯ２）は、多孔質であればよいが、特に２０〜５０ｎｍの範囲内にピーク細孔径があり、その範囲内に全細孔容積の６０％以上の細孔容積を有するものであるのが好ましい。白金の原料としては白金化合物を用いる。その例としては白金の硝酸塩、塩化物、酢酸塩、錯塩（テトラアンミン白金塩、ジニトロジアンミン白金等）などが挙げられる。
【００１５】
一例として含浸法の場合の態様例を述べると、白金化合物を水に溶解して水溶液とし、その水溶液に粉末状等の多孔質の酸化スズを投入して撹拌し、該酸化スズに白金化合物を含浸させて担持する。ここで、白金化合物水溶液のｐＨは、酸性域からアルカリ性域まで広い範囲で設定できるが、ｐＨ値をより大きくするのが好ましく、これによりメタンの酸化性能を向上させることができる。そのｐＨ値は特に１２以上であるのが好ましい。
【００１６】
また、多孔質の酸化スズに対して白金を分割担持することによりメタンの酸化性能を格段に向上させることができる。当該白金の分割担持は、多孔質の酸化スズに対して白金化合物水溶液を２回以上に繰り返して担持する。例えば１回で白金を２ｗｔ％（白金換算）担持し、この担持を２回、３回というように複数回繰り返して、４ｗｔ％、６ｗｔ％というように担持する。当該Ｐｔの分割担持は２回以上５回以下であるのが好ましい。その後、常法により乾燥し、焼成する。
【００１７】
本酸化触媒における酸化スズ担体に対する白金の担持量は、酸化スズに対して０．０２５〜１５．０ｗｔ％の範囲であり、より好ましくは０．８〜９．０ｗｔ％の範囲である。白金の担持量が０．０２５ｗｔ％を下回る場合にもなお有効であるが、その分触媒効果は減少する。その担持量が１５．０ｗｔ％程度を上回る場合にも同様に有効な触媒効果が得られるが、白金を１５ｗｔ％程度まで担持させていれば所期の触媒効果が得られるのでコスト等の面からしても上限１５．０ｗｔ％程度で十分である。もちろん、上記範囲０．０２５〜１５．０ｗｔ％の前後としても差し支えない。本発明の酸化触媒をハニカム状の形態で使用する場合には、これらに準じた量を担持させる。
【００１８】
触媒の形態としては粉末状、粒状、顆粒状（含：球状）、ペレット（円筒型、環状型）状、タブレット（錠剤）状、或いはハニカム（モノリス体）状等適宜の形状として使用することができる。なお、本発明ではこれら形状の触媒に排ガスを通す必要があるため、粉末状の場合には、これを充填した触媒層から逸散しないように所定粒度範囲に整粒するかまたは造粒し、あるいは加圧成形や押出し成形して用いるのが望ましい。このうち押出し成形の場合には適宜所定長さに切断してペレット化して使用される。
【００１９】
本触媒の形態としてハニカム（モノリス体）状の形態は好ましい形状である。特に希薄燃焼ガスエンジンからの排ガスを処理する場合には、好ましくはハニカム状として用いられる。ハニカム状触媒の製造態様としては、例えば（１）ハニカム状構造の基材に酸化スズをウォッシュコートして担持させた後、該酸化スズ担持のハニカム基材に白金化合物の水溶液を担持させる、（２）白金化合物の水溶液に酸化スズを分散させてスラリーとし、これをハニカム状構造の基材にウォッシュコートして担持させる。次いで、常法により乾燥させ、焼成する。
【００２０】
ハニカム状の形態での基材としてはセラミックス製またはメタル製の基材を使用することができる。セラミックスの好ましい例としてはコージェライトが挙げられ、メタルの好ましい例としてはステンレス鋼や鉄ーアルミニウムークロム系合金などが挙げられる。
【００２１】
従来、貴金属触媒は、排ガス中のＳＯ２により被毒し性能劣化を来すことが知られている。これに対して、本発明に係る酸化スズ（ＳｎＯ２）担体に白金を担持した酸化触媒は、長期間にわたり高い耐ＳＯＸ性を有し、従来における認識とは全く逆に、排ガス中のＳＯ２の存在により、反ってメタンの酸化除去活性が向上する。この原因は不明であるが、酸化スズと白金との間、あるいは酸化スズと白金とＳＯ２との間で何らかの有意な作用が生起しているものと思われる。
【００２２】
本発明の酸化触媒を使用する装置としては固定床流通型反応装置などを用いることができる。図１は本発明の酸化触媒を使用する装置態様例を示す図である。図１中、Ａは被処理燃焼排ガス導入管、Ｂは酸化触媒層（反応管）、Ｃは処理済み排ガスの導出管であり、矢印（→）は燃焼排ガスの流れ方向を示している。本酸化触媒は、図１のような装置態様とは限らず、燃焼排ガス流に対して配置し得る態様であれば各種装置態様で使用される。ハニカム状の本酸化触媒を図１のような触媒層にセットするには、その断面開口が燃焼排ガスの流れ方向に向くように配置される。
【００２３】
【実施例】
以下、実施例に基づき本発明をさらに詳しく説明するが、本発明が実施例に限定されないことはもちろんである。
【００２４】
《実施例１》
〈実施例ペレット触媒の調製〉
ペレット触媒を含浸法により調製した。担体粉末は、原料酸化スズ〔関東化学社製（特級）〕を１℃／ｍｉｎ、６００℃、３時間焼成して得た。該担体粉末とジニトロジアンミン白金〔Ｐｔ（ＮＯ２）２（ＮＨ３）２〕の硝酸酸性水溶液（ｐＨ≒３）の所定量をフラスコに入れ、ロータリーエバポレータにより、５０℃で減圧乾燥させた後、残った粉末を１７５℃で６時間、次いで２７５℃で１２時間乾燥し、その後昇温速度１０℃／ｍｉｎ、２００℃で３時間、昇温速度１℃／ｍｉｎ、２７０℃で６時間、昇温速度１℃／ｍｉｎ、５５０℃で３時間焼成して触媒粉末を得た。得られた触媒粉末を打錠成形器により５００ｋｇ／ｃｍ２で成形した後、３５５−７１０μｍ（＝３５−３１メッシュ）に分級した。こうしてペレット触媒を得た。
【００２５】
〈比較例ペレット触媒の調製〉
また、上記と同様にして、酸化スズ担体にＰｔとＰｄを担持したペレット触媒（Ｐｔ−Ｐｄ／ＳｎＯ２ペレット触媒）、酸化スズにＰｄを担持したペレット触媒（Ｐｄ／ＳｎＯ２ペレット触媒）、アルミナにＰｔとＰｄを担持したペレット触媒（Ｐｔ−Ｐｄ／Ａｌ２Ｏ３ペレット触媒）を調製した。Ｐｄ源としては硝酸パラジウム〔Ｐｄ（ＮＯ３）２〕を用い、原料酸化スズとしては前記と同じ酸化スズを使用し、Ａｌ２Ｏ３（アルミナ）としては触媒担体として用いられる通常のアルミナ粉末を使用した。
【００２６】
〈性能試験〉
上記ペレット触媒の調製で得た各種ペレット触媒を用いて、図１に示すような通常の固定床流通型反応装置を用いて触媒耐久試験を実施した。使用ペレット触媒は、Ｐｔ／ＳｎＯ２（Ｐｔ＝１．３３ｗｔ％：ＳｎＯ２に対する担持量、以下同じ）、Ｐｔ−Ｐｄ／ＳｎＯ２（Ｐｔ＝０．６７ｗｔ％、Ｐｄ＝０．６７ｗｔ％）、Ｐｄ／ＳｎＯ２（Ｐｄ＝１．３３ｗｔ％）、Ｐｔ−Ｐｄ／Ａｌ２Ｏ３（Ｐｔ＝２．０ｗｔ％、Ｐｄ＝２．０ｗｔ％）である。
【００２７】
試験条件は下記のとおりである。排ガス温度（＝反応温度）：５００〜３５０℃、空間速度（ＳＶ）：１６０，０００ｈ−１（全流量３．３５Ｌ／ｍｉｎ、触媒体積：１．２６ｃｍ３）、排ガスすなわち試験ガス：ＣＨ４＝２０００ｐｐｍ、ＣＯ＝８２０ｐｐｍ、ＮＯ＝８０ｐｐｍ、ＣＯ２＝４．９％、Ｏ２＝１０．５％、Ｈ２Ｏ＝１０％、ＳＯ２＝１ｐｐｍ、Ｎ２＝バランス。これら試験条件は、特に記載しない限り、以下の実施例についても同じである。
【００２８】
試験ガスの分析は、ＦＩＤ式全炭化水素計、赤外線式ＣＯ／ＣＯ２計、化学発光式ＮＯＸ計及び磁気式酸素計からなる排ガス分析計（堀場製作所製）を用いて行った。ＣＨ４酸化除去活性は、反応管前後のＣＨ４の濃度差から評価した。酸化除去活性〔＝メタン除去率（％）〕は以下の式により求めた。これらの点は以下の性能試験についても同じである。図２は本性能試験の結果のうち反応温度４００℃での結果を示す図である。
【００２９】
【数１】
図２のとおり、まず、Ｐｔ−Ｐｄ／ＳｎＯ２触媒の場合、メタン除去率は初期段階で４１％であり、以降徐々に低下し、５０時間経過時で２６％、１００時間経過時で２３％と低下し、１４５時間経過時においては２２％にまで低下している。次に、Ｐｄ／ＳｎＯ２触媒の場合、メタン除去率は初期段階で４１％であり、以降急激に低下し、４０時間経過時で２％、１４５時間経過時においても２％に低下したままである。さらに、Ｐｔ−Ｐｄ／Ａｌ２Ｏ３の場合、メタン除去率は初期段階で３４％であり、以降徐々に低下し、５０時間経過時で１０％、１００時間経過時で２％と低下し、１４０時間経過時においては１％に低下している。
【００３１】
これに対して、Ｐｔ／ＳｎＯ２触媒の場合、メタン除去率は初期段階で４０％程度であり、以降４１〜４４％の除去率を保持し、１４５時間経過時においても４２％で初期の性能を維持している。このように、４種のメタン酸化触媒のうち、Ｐｔ／ＳｎＯ２触媒だけが、ＳＯ２を１ｐｐｍ含む試験ガスについて長期間にわたり性能劣化がなく、高いメタン除去率を維持している。図２は温度４００℃の場合であるが、それより高い反応温度、例えば５００℃の場合や４５０℃の場合のメタン除去率は相対的に高く、またそれより低い反応温度、例えば３７５℃の場合や３５０℃の場合にも、４００℃の場合と同じく良好なメタン除去率、耐久性を示した。
【００３２】
《実施例２》
市販の各種ＳｎＯ２を担体として実施例１の〈実施例ペレット触媒の調製〉と同様にして各種Ｐｔ（２ｗｔ％）／ＳｎＯ２触媒を調製した。得られた各Ｐｔ／ＳｎＯ２触媒を用い、反応温度４００℃での耐久試験を実施した。図３は本性能試験の結果を示す図である。図３のとおり、メタン除去率は、ＳｎＯ２担体の種類によって左右されるが、いずれも初期段階の性能をほぼ維持し長期間にわたり経時的に変化はないことが分かる。例えば、ＳｎＯ２担体が関東化学社製（特級）の場合、初期段階から１４０時間経過時まで５０〜５３％のメタン除去率を示している。またＳｎＯ２担体が日本化学産業社製（ＳＬグレード）の場合、それに準じた性能を示している。
【００３３】
図４は以上の各Ｐｔ／ＳｎＯ２触媒で用いた各種ＳｎＯ２の細孔径の分布を示した図である。最も高性能である関東化学社製（特級）のＳｎＯ２担体の場合、比較的大きな細孔を有し、そのピークは４０ｎｍで０．３２ｃｃ／ｇ強の細孔容積を示している。これに準じる性能を示す日本化学産業社製（ＳＬグレード）のＳｎＯ２担体の場合、そのピークは３０ｎｍで０．３１ｃｃ／ｇの細孔容積を示している。また、図４の細孔分布を図３の結果と併せて対比すると、高いメタン除去性能を長期間にわたり発揮する上では、特に２０〜５０ｎｍの範囲内にピーク細孔径があり、その範囲内に全細孔容積の６０％以上の細孔容積を有することが好ましいことを示している。
【００３４】
図５は各Ｐｔ／ＳｎＯ２触媒で用いた各種ＳｎＯ２の比表面積を示した図である。最も高性能を示す関東化学社製（特級）のＳｎＯ２担体の場合、比表面積も大きく、１３ｍ２／ｇの値を示している。また、これに準じる性能を示す日本化学産業社製（ＳＬグレード）のＳｎＯ２担体の場合、１２．５ｍ２／ｇの値を示している。
【００３５】
《実施例３》
Ｐｔを分割して担持した点以外は、実施例１の〈実施例ペレット触媒の調製〉と同様にして各種Ｐｔ／ＳｎＯ２触媒を調製した。得られた各Ｐｔ／ＳｎＯ２触媒を用いて反応温度４００℃、ＳＶ＝１６０，０００ｈ−１で性能試験を実施した。図６は本性能試験の結果を示す図である。図６には、１回でのＰｔの担持量を２ｗｔ％とし、これを１回で担持した場合〔Ｐｔ＝２ｗｔ％（２ｗｔ％×１回担持）〕、２回で担持した場合〔Ｐｔ＝４ｗｔ％（２ｗｔ％×２回担持）〕、３回で担持した場合〔Ｐｔ＝６ｗｔ％（２ｗｔ％×３回担持）〕の３種のＰｔ／ＳｎＯ２触媒と、１回でＰｔを４ｗｔ％担持した場合〔Ｐｔ＝４ｗｔ％（４ｗｔ％×１回担持）〕の結果を示している。
【００３６】
図６のとおり、メタン除去率は、ＳｎＯ２担体に対してＰｔを分割担持することにより向上することを示している。まず、１回で４ｗｔ％担持した場合〔Ｐｔ＝４ｗｔ％（４ｗｔ％×１回担持）〕には、初期段階で３８％程度と低く、１４０時間経過時にも４１％の性能を示すに過ぎない。これに対して、Ｐｔ＝２ｗｔ％（２ｗｔ％×１回担持）の場合、初期段階から５０％前後のメタン除去率を示し、１４０時間経過時でも変化はなく同様の性能を示し、また、Ｐｔ＝４ｗｔ％（２ｗｔ％×２回担持）の場合、メタン除去率は、１回の担時の場合に比べて格段に向上し、初期段階で６６％前後、１４０時間経過時には７０％の性能を示している。
【００３７】
これらの事実からして、酸化スズ担体に対してＰｔを同量担持する場合にも、Ｐｔを分割して担持し、担持回数を増やすことによりメタン酸化除去性能の向上に有効であることを示している。また、Ｐｔ＝６ｗｔ％（２ｗｔ％×３回担持）の場合、メタン除去率は、２回の分割担時の場合に比べてさらに向上し、初期段階で８０％前後、１４０時間経過時には８２％の性能を示している。
【００３８】
《実施例４》
Ｐｔの担持時におけるＰｔ化合物水溶液のｐＨ値を変えた点以外は、実施例１の〈実施例ペレット触媒の調製〉と同様にして各種Ｐｔ／ＳｎＯ２触媒を調製した。Ｐｔの担持量はいずれもＳｎＯ２担体に対して２ｗｔ％とした。得られた各Ｐｔ／ＳｎＯ２触媒について、反応温度４００℃、ＳＶ＝１６０，０００ｈ−１で性能試験を実施した。図７は本性能試験の結果である。図７には、水溶液について、ｐＨ＝３、ｐＨ＝７、ｐＨ＝１２の３種変えた場合を示している。
【００３９】
図７のとおり、メタン除去率は、ｐＨ値を上げるに従い向上させ得ることを示している。ｐＨ＝３で担持した場合、初期段階から５０％前後のメタン除去率を示し、１４０時間経過時でも変化はなく同様の性能を示している。ｐＨ＝７の場合、初期段階で５２％前後のメタン除去率を示し、１４０時間経過時では５５％前後のメタン除去率を示している。ｐＨ＝１２の場合、初期段階では５０％程度であるが、１４０時間経過時では５８％のメタン除去率を示している。このように、Ｐｔ担持時の白金水溶液のｐＨを上げることが、メタン酸化除去性能の向上に有効であることを示している。
【００４０】
図８は、各種ｐＨで担持したＰｔ（２ｗｔ％）／ＳｎＯ２触媒の細孔径の分布を示した図である。図８中、ＳｎＯ２として示しているのは、Ｐｔを担持しないＳｎＯ２担体そのものの場合であり、これは図４中、関東化学（特級）として示すものと同じである。図８のとおり、高いｐＨ値でＰｔを担持した場合は、ＳｎＯ２担体そのものの細孔径分布に近い細孔径分布を示している。これはＰｔの担持に際してＰｔ化合物のｐＨ値を高くすると細孔の閉塞が起きないことを示している。すなわち、ＳｎＯ２担体に対する高いｐＨ値でのＰｔの担持がメタン酸化除去性能の向上に有効であることを示している。
【００４１】
《実施例５》
本実施例ではＰｔ／ＳｎＯ２（Ｐｔ＝２ｗｔ％）触媒の耐久性に及ぼすＳＯ２の影響について試験した。すなわち、排ガス中のＳＯ２の有無如何によるメタンの酸化除去性能を試験した。触媒は、実施例４のｐＨ＝１２の条件と同様にして調製した。排ガス温度（反応温度）は４００℃とした。図９は本性能試験の結果を示す図である。図９には、ＳＯ２＝１ｐｐｍすなわち排ガス中のＳＯ２濃度が１ｐｐｍの場合と、ＳＯ２＝０ｐｐｍすなわちＳＯ２を含まない排ガス場合（試験ガス中ＳＯ２を含まない点以外は前記実施例１の試験ガスと同じである）を示している。
【００４２】
図９のとおり、ＳＯ２＝１ｐｐｍの場合、メタン除去率は、初期段階で５０％前後のメタン除去率を示し、３０時間経過時に６０％に達し、以降殆ど変化はなく、１４０時間経過時で５９％という高性能を示している。これに対して、ＳＯ２＝０ｐｐｍの場合、メタン除去率は、初期段階でも４６％前後であり、以降徐々に低下し、１４０時間経過時には４１％に低下している。
【００４３】
このように、ＳＯ２の存在によりメタンの酸化除去活性が向上している。この事実は、本発明の酸化触媒が従来の認識とは全く異なる挙動を示すことを裏付けるものである。従来、貴金属担持のアルミナ系触媒は、排ガス中のＳＯ２により被毒し性能劣化を来すことが知られている。これに対して、本発明の酸化触媒は、排ガス中にＳＯ２が含まれていると、性能劣化どころか、反ってメタンの酸化除去活性が向上する。
【００４４】
【発明の効果】
本発明によれば、従来メタンの酸化活性貴金属と考えられていたパラジウムを一切含まず、また、従来単独では有効でないと考えられていた白金を、それ単独で多孔質の酸化スズに担持することにより、５００℃以下の低温域、特に４５０−３５０℃という低温域においてメタンを長期にわたり極めて有効に酸化除去することができる。このため、特に硫黄化合物を付臭剤として含む都市ガス等を燃料とする希薄燃焼ガスエンジンからの排ガスに対しても有効に適用できる。また本発明の酸化除去触媒は、有効な耐久性を有することから、交換頻度を少なくでき、排ガス処理システムの低コスト化を図ることができる。
【図面の簡単な説明】
【図１】本発明の酸化触媒を使用する装置態様例を示す図
【図２】実施例１の結果を示す図
【図３】実施例２の結果を示す図
【図４】実施例２の結果を示す図
【図５】実施例２の結果を示す図
【図６】実施例３の結果を示す図
【図７】実施例４の結果を示す図
【図８】実施例４の結果を示す図
【図９】実施例５の結果を示す図
【符号の説明】
Ａ 被処理排ガス導入管
Ｂ 酸化触媒層（反応管）
Ｃ 処理済み排ガスの導出管[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a catalyst for oxidizing and removing methane in a combustion exhaust gas containing sulfur oxides in a low temperature range, a method for oxidizing and removing methane in a combustion exhaust gas containing sulfur oxide using the catalyst, and production of the catalyst. About the method.
[0002]
[Prior art]
Hydrocarbons such as natural gas, city gas, light oil, and kerosene are used as fuel for boilers, heating furnaces, gas engines, gas turbines, and the like. Nitrogen oxides in exhaust gas by burning them fuel (NO X), sulfur oxides (SO X), carbon monoxide or odor substances, as well, such as soot, unburned hydrocarbons are contained. Since these components cause environmental pollution, they must be discharged harmlessly.
[0003]
The same applies to the exhaust gas from the lean burn gas engine in the cogeneration system or GHP (Gas Heat Pump). In the case of a lean burn system such as a lean burn gas engine, a large amount of oxygen and water vapor coexist in the exhaust gas together with a small amount of hydrocarbons, particularly methane, nitrogen oxides, carbon monoxide and the like. Conventionally, a treatment method using a three-way catalyst for simultaneously purifying three components, that is, hydrocarbons, nitrogen oxides, and carbon monoxide in exhaust gas has been developed.
[0004]
However, the treatment method using a three-way catalyst can be effectively applied only to flue gas having almost no oxygen, and the three-way catalyst has an excess of oxygen and the hydrocarbon in the flue gas is particularly methane. Does not work effectively in some cases. As a hydrocarbon oxidation catalyst, noble metals such as palladium, platinum and rhodium are used, and these noble metal catalysts are used in a form supported on a carrier. Known carriers include alumina (Al 2 O 3 ) and zirconia (ZrO 2 ).
[0005]
By the way, when the hydrocarbon is methane in particular, palladium has conventionally been regarded as effective for the oxidation thereof, and platinum is not effective alone but is merely used as an auxiliary. For example, JP-A-2000-33266 and JP-A-2000-254505 show that a catalyst comprising palladium supported on a tin oxide carrier exhibits high resistance to inhibition of catalytic activity by sulfur oxides. I have. Of these, Japanese Patent Application Laid-Open No. 2000-33266 discloses a catalyst comprising palladium and platinum supported on a tin oxide carrier, but platinum is only used supplementarily together with palladium. This point is the same in JP-A-2001-190931.
[0006]
[Patent Document 1] JP-A-2000-33266 [Patent Document 2] JP-A-2000-254505 [Patent Document 3] JP-A-2001-190931 [0007]
Further, for example, since the temperature of exhaust gas from a lean burn gas engine is as low as 500 ° C. or lower, usually about 500 to 400 ° C., it is difficult to oxidize methane using an oxidation catalyst. Particularly, in a low temperature range of 450 ° C. or less, the oxidation catalyst is remarkably poisoned due to the accumulation of a small amount of sulfur oxides contained in the exhaust gas. At present, it is not possible to obtain a sufficient durability performance that can be provided for the above.
[0008]
[Problems to be solved by the invention]
The present inventors have repeatedly conducted experiments and studies on various combinations of noble metals such as platinum, ruthenium, and palladium with carriers such as alumina and zirconia, and tin oxide carriers. It does not contain any palladium, which was considered a noble metal, and the catalyst that supported platinum alone, which was conventionally considered to be ineffective alone, that is, only platinum supported on porous tin oxide was in a low temperature range, especially 450 ° C or lower. It has been found that the catalyst is effective as a catalyst for oxidizing and removing methane in a low temperature range and has high SO X resistance, and has reached the present invention.
[0009]
That is, an object of the present invention is to provide a catalyst for removing methane oxidation in a combustion exhaust gas containing a sulfur oxide obtained by supporting platinum on porous tin oxide. An object of the present invention is to provide a method for effectively oxidizing and removing methane in combustion exhaust gas over a long period of time by passing the catalyst at a low temperature of 500 ° C. or lower, particularly at a low temperature of 450 to 350 ° C. An object of the present invention is to provide a method for producing a catalyst.
[0010]
[Means for Solving the Problems]
The present invention relates to a catalyst for oxidizing and removing methane in a combustion exhaust gas containing sulfur oxides in a low temperature range, wherein the oxidation removing catalyst is a catalyst in which platinum is supported on porous tin oxide. Disclosed is a catalyst for low-temperature oxidation removal of methane in a combustion exhaust gas containing a sulfur oxide.
[0011]
Further, the present invention is a method for oxidizing and removing methane in combustion exhaust gas containing sulfur oxides in a low temperature range, wherein the combustion exhaust gas is subjected to an oxidation removal catalyst comprising platinum supported on porous tin oxide in a low temperature range. A low-temperature oxidative removal method for methane in combustion exhaust gas containing sulfur oxides, characterized in that methane is oxidized and removed by passing through.
[0012]
Further, the present invention relates to a method for producing a catalyst for low-temperature oxidation removal of methane in combustion exhaust gas containing a sulfur oxide obtained by supporting platinum on porous tin oxide, wherein the platinum compound is converted into porous tin oxide. On the other hand, there is provided a method for producing a catalyst for low-temperature oxidation removal of methane in combustion exhaust gas containing sulfur oxides, which is carried out by impregnation or equilibrium adsorption with an aqueous solution of a platinum compound and then calcined.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
The catalyst for oxidizing and removing methane in combustion exhaust gas according to the present invention is a catalyst in which platinum is supported on porous tin oxide (SnO 2 ), and converts methane in combustion exhaust gas containing sulfur oxides into a low-temperature region. It is a catalyst that is oxidized and removed. According to the present invention, it does not contain any palladium, which was conventionally regarded as an oxidation-active noble metal of methane, and carries platinum alone, which was conventionally considered to be ineffective alone, that is, only platinum on porous tin oxide. By doing so, methane can be very effectively oxidized and removed over a long period of time in a low temperature range of 500 ° C. or lower, particularly in a low temperature range of 450 to 350 ° C.
[0014]
The method for producing the present oxidation removal catalyst is not particularly limited as long as platinum can be uniformly supported on porous tin oxide, but an impregnation method or an equilibrium adsorption method is preferably used. Tin oxide (SnO 2 ), which is a carrier, may be porous as long as it has a peak pore diameter in the range of 20 to 50 nm, and a pore volume of 60% or more of the total pore volume in that range. It is preferable to have one. A platinum compound is used as a raw material for platinum. Examples thereof include nitrates, chlorides, acetates and complex salts of platinum (tetraammineplatinum salt, dinitrodiammineplatinum, etc.).
[0015]
As an example, an embodiment in the case of the impregnation method will be described.A platinum compound is dissolved in water to form an aqueous solution, and a porous tin oxide such as powder is poured into the aqueous solution and stirred, and the platinum compound is added to the tin oxide. Impregnated and carried. Here, the pH of the aqueous platinum compound solution can be set in a wide range from an acidic range to an alkaline range, but it is preferable to increase the pH value, thereby improving the methane oxidation performance. The pH value is particularly preferably 12 or more.
[0016]
Further, by separately supporting platinum on porous tin oxide, oxidizing performance of methane can be remarkably improved. The divided loading of platinum is carried out by repeatedly carrying a platinum compound aqueous solution twice or more on porous tin oxide. For example, 2 wt% (in terms of platinum) of platinum is carried at one time, and this carrying is repeated a plurality of times, such as twice or three times, to carry 4 wt% or 6 wt%. It is preferable that the Pt is divided and carried twice or more and 5 times or less. Then, it is dried and fired by a conventional method.
[0017]
The amount of platinum carried on the tin oxide carrier in the present oxidation catalyst is in the range of 0.025 to 15.0 wt%, more preferably 0.8 to 9.0 wt%, based on tin oxide. It is still effective when the supported amount of platinum is less than 0.025 wt%, but the catalytic effect is reduced accordingly. Similarly, an effective catalytic effect can be obtained when the supported amount exceeds about 15.0 wt%. However, if platinum is supported up to about 15 wt%, the desired catalytic effect can be obtained, so that from the viewpoint of cost and the like. Even so, the upper limit of about 15.0 wt% is sufficient. Of course, the above range may be around 0.025 to 15.0% by weight. When the oxidation catalyst of the present invention is used in the form of a honeycomb, an amount equivalent to these is carried.
[0018]
The catalyst may be used in any suitable form such as powder, granule, granule (including spherical), pellet (cylindrical or annular), tablet (tablet), or honeycomb (monolith). it can. In the present invention, since it is necessary to pass exhaust gas through the catalyst of these shapes, in the case of powder, the powder is sized or granulated in a predetermined particle size range so as not to escape from the catalyst layer filled with the powder, Alternatively, it is desirable to use them by pressure molding or extrusion molding. Among them, in the case of extrusion molding, it is cut into a predetermined length and pelletized before use.
[0019]
As a form of the present catalyst, a honeycomb (monolith) form is a preferable form. In particular, when treating exhaust gas from a lean burn gas engine, it is preferably used as a honeycomb. Examples of the production mode of the honeycomb catalyst include, for example, (1) washing and supporting tin oxide on a substrate having a honeycomb structure, and then supporting an aqueous solution of a platinum compound on the honeycomb substrate supporting tin oxide. 2) Tin oxide is dispersed in an aqueous solution of a platinum compound to form a slurry, which is wash-coated and supported on a substrate having a honeycomb structure. Next, it is dried and fired by a conventional method.
[0020]
As the substrate in the form of a honeycomb, a ceramic or metal substrate can be used. Preferable examples of the ceramic include cordierite, and preferable examples of the metal include stainless steel and iron-aluminum-chromium alloy.
[0021]
Conventionally, it has been known that noble metal catalysts are poisoned by SO 2 in exhaust gas and deteriorate performance. On the other hand, the oxidation catalyst according to the present invention in which platinum is supported on a tin oxide (SnO 2 ) carrier has high resistance to SO X over a long period of time, and contrary to the conventional recognition, the SOx in the exhaust gas is completely opposite to the conventional recognition. By the presence of 2, the activity of oxidizing and removing methane is improved. Although the cause is unknown, it is considered that some significant action occurs between tin oxide and platinum or between tin oxide and platinum and SO 2 .
[0022]
As a device using the oxidation catalyst of the present invention, a fixed bed flow type reaction device or the like can be used. FIG. 1 is a view showing an example of an apparatus using the oxidation catalyst of the present invention. In FIG. 1, A is a pipe for introducing a treated flue gas, B is an oxidation catalyst layer (reaction tube), C is a lead pipe for a treated flue gas, and an arrow (→) indicates a flow direction of the flue gas. The present oxidation catalyst is not limited to the device mode as shown in FIG. 1, and may be used in various device modes as long as it can be disposed with respect to the flue gas flow. In order to set the honeycomb-shaped main oxidation catalyst in the catalyst layer as shown in FIG. 1, it is arranged such that its cross-section opening faces the flow direction of the combustion exhaust gas.
[0023]
【Example】
Hereinafter, the present invention will be described in more detail with reference to Examples, but it is needless to say that the present invention is not limited to Examples.
[0024]
<< Example 1 >>
<Preparation of Example pellet catalyst>
The pellet catalyst was prepared by the impregnation method. The carrier powder was obtained by firing raw material tin oxide [Kanto Chemical Co., Ltd. (special grade)] at 1 ° C./min at 600 ° C. for 3 hours. A predetermined amount of the carrier powder and a nitric acid aqueous solution (pH 白金 3) of dinitrodiammineplatinum [Pt (NO 2 ) 2 (NH 3 ) 2 ] are put in a flask, and dried under reduced pressure at 50 ° C. by a rotary evaporator. The remaining powder was dried at 175 ° C. for 6 hours, then at 275 ° C. for 12 hours, and then heated at a rate of 10 ° C./min, at 200 ° C. for 3 hours, at a rate of 1 ° C./min, and heated at 270 ° C. for 6 hours. The powder was calcined at a rate of 1 ° C./min at 550 ° C. for 3 hours to obtain a catalyst powder. The obtained catalyst powder was molded at 500 kg / cm 2 using a tablet molding machine, and then classified to 355-710 μm (= 35-31 mesh). Thus, a pellet catalyst was obtained.
[0025]
<Preparation of comparative example pellet catalyst>
In the same manner as above, a pellet catalyst supporting Pt and Pd on a tin oxide carrier (Pt-Pd / SnO 2 pellet catalyst), a pellet catalyst supporting Pd on tin oxide (Pd / SnO 2 pellet catalyst), alumina A Pt-Pd / Al 2 O 3 pellet catalyst was prepared in which Pt and Pd were supported. Palladium nitrate [Pd (NO 3 ) 2 ] is used as a Pd source, the same tin oxide as the above is used as a raw tin oxide, and ordinary alumina powder used as a catalyst carrier is used as Al 2 O 3 (alumina). used.
[0026]
<performance test>
Using the various pellet catalysts obtained in the above-mentioned preparation of the pellet catalyst, a catalyst durability test was carried out using a usual fixed bed flow type reactor as shown in FIG. The pellet catalyst used was Pt / SnO 2 (Pt = 1.33 wt%: supported amount on SnO 2 , the same applies hereinafter), Pt-Pd / SnO 2 (Pt = 0.67 wt%, Pd = 0.67 wt%), Pd / SnO 2 (Pd = 1.33 wt%) and Pt-Pd / Al 2 O 3 (Pt = 2.0 wt%, Pd = 2.0 wt%).
[0027]
The test conditions are as follows. Exhaust gas temperature (= reaction temperature): 500-350 ° C., space velocity (SV): 160,000 h −1 (total flow rate 3.35 L / min, catalyst volume: 1.26 cm 3 ), exhaust gas, ie, test gas: CH 4 = 2000 ppm, CO = 820 ppm, NO = 80 ppm, CO 2 = 4.9%, O 2 = 10.5%, H 2 O = 10%, SO 2 = 1 ppm, N 2 = balance. These test conditions are the same for the following examples unless otherwise specified.
[0028]
Analysis of the test gas, FID type total hydrocarbon analyzer, infrared CO / CO 2 meter, exhaust gas analyzer comprising a chemiluminescent NO X meter and magnetic oxygen analyzer (manufactured by Horiba) was used. The CH 4 oxidation removal activity was evaluated from the difference in CH 4 concentration before and after the reaction tube. The oxidation removal activity [= methane removal rate (%)] was determined by the following equation. These points are the same for the following performance tests. FIG. 2 is a diagram showing the results at a reaction temperature of 400 ° C. among the results of this performance test.
[0029]
(Equation 1)
As shown in FIG. 2, first, in the case of the Pt-Pd / SnO 2 catalyst, the methane removal rate is 41% in the initial stage, and gradually decreases thereafter, and 26% after 50 hours and 23% after 100 hours. And after 22 hours, it has dropped to 22%. Next, in the case of the Pd / SnO 2 catalyst, the methane removal rate is 41% at the initial stage, and thereafter drops sharply, and remains at 2% after 40 hours and 2% after 145 hours. is there. Further, in the case of Pt-Pd / Al 2 O 3 , the methane removal rate is 34% in the initial stage, gradually decreases thereafter, decreases to 10% after 50 hours, 2% after 100 hours, After 140 hours, it has decreased to 1%.
[0031]
On the other hand, in the case of the Pt / SnO 2 catalyst, the methane removal rate is about 40% in the initial stage, and thereafter maintains the removal rate of 41 to 44%, and the initial performance is 42% even after 145 hours. Has been maintained. As described above, among the four types of methane oxidation catalysts, only the Pt / SnO 2 catalyst maintains the high methane removal rate without deterioration in performance over a long period of time for the test gas containing 1 ppm of SO 2 . FIG. 2 shows the case where the temperature is 400 ° C., but when the reaction temperature is higher, for example, 500 ° C. or 450 ° C., the methane removal rate is relatively high, and when the reaction temperature is lower, for example, 375 ° C. Also, when the temperature was 350 ° C., the methane removal rate and the durability were as good as those at the temperature of 400 ° C.
[0032]
<< Example 2 >>
Various Pt (2 wt%) / SnO 2 catalysts were prepared in the same manner as in <Preparation of Example Pellet Catalyst> in Example 1 using various commercially available SnO 2 carriers. Using each of the obtained Pt / SnO 2 catalysts, a durability test at a reaction temperature of 400 ° C. was performed. FIG. 3 is a diagram showing the results of the performance test. As shown in FIG. 3, although the methane removal rate depends on the type of the SnO 2 carrier, it can be seen that the performance in the initial stage is almost maintained and does not change over time for a long period of time. For example, when the SnO 2 support is manufactured by Kanto Chemical Co., Ltd. (special grade), the methane removal rate of 50 to 53% is shown from the initial stage to the elapse of 140 hours. Also, when the SnO 2 support is made by Nippon Chemical Industry Co., Ltd. (SL grade), the performance according to it is shown.
[0033]
FIG. 4 is a diagram showing the distribution of pore sizes of various SnO 2 used in each of the above Pt / SnO 2 catalysts. In the case of the highest performance SnO 2 carrier manufactured by Kanto Chemical Co., Ltd. (special grade), it has relatively large pores, and its peak shows a pore volume of slightly more than 0.32 cc / g at 40 nm. In the case of a SnO 2 carrier manufactured by Nippon Chemical Industry Co., Ltd. (SL grade) exhibiting performance equivalent to this, the peak shows a pore volume of 0.31 cc / g at 30 nm. Further, comparing the pore distribution of FIG. 4 with the results of FIG. 3, in order to exhibit high methane removal performance over a long period of time, there is a peak pore diameter particularly in the range of 20 to 50 nm, and within that range. This indicates that it is preferable to have a pore volume of 60% or more of the total pore volume.
[0034]
FIG. 5 is a diagram showing the specific surface area of various SnO 2 used in each Pt / SnO 2 catalyst. In the case of the SnO 2 carrier (special grade) manufactured by Kanto Chemical Co., which has the highest performance, the specific surface area is large, showing a value of 13 m 2 / g. In addition, in the case of a SnO 2 carrier manufactured by Nippon Chemical Industry Co., Ltd. (SL grade) exhibiting performance equivalent to this, the value is 12.5 m 2 / g.
[0035]
<< Example 3 >>
Various Pt / SnO 2 catalysts were prepared in the same manner as in <Preparation of Example Pellet Catalyst> of Example 1 except that Pt was separately supported. A performance test was performed at a reaction temperature of 400 ° C. and an SV of 160,000 h −1 using each of the obtained Pt / SnO 2 catalysts. FIG. 6 is a diagram showing the results of the performance test. FIG. 6 shows that the amount of Pt carried at one time is 2 wt%, and this is carried once (Pt = 2 wt% (2 wt% × one carried)), and two times carried [Pt = 4 wt% (2 wt% × supported 2 times)], three types of Pt / SnO 2 catalyst when loaded 3 times [Pt = 6 wt% (2 wt% × supported 3 times)], and 4 wt% of Pt at one time The graph shows the result when [Pt = 4 wt% (4 wt% × support once)].
[0036]
As shown in FIG. 6, it is shown that the methane removal rate is improved by dividing and supporting Pt on the SnO 2 support. First, in the case where 4 wt% is carried at one time [Pt = 4 wt% (4 wt% × one time carrying)], the performance is as low as about 38% at the initial stage, and shows only 41% performance after 140 hours. . On the other hand, when Pt = 2 wt% (2 wt% × supported once), the methane removal rate is about 50% from the initial stage, and the same performance is exhibited without any change even after 140 hours. = 4 wt% (2 wt% x 2 loadings), the methane removal rate is much higher than in the case of one loading, with a performance of around 66% in the initial stage and 70% after 140 hours. Is shown.
[0037]
From these facts, it is shown that, even when Pt is supported on the tin oxide carrier in the same amount, Pt is divided and supported, and increasing the number of times Pt is effective in improving the methane oxidation removal performance. ing. In the case of Pt = 6 wt% (2 wt% × supported three times), the methane removal rate is further improved as compared with the case of performing the division twice, about 80% in the initial stage, and 82% after 140 hours. Shows the performance of
[0038]
<< Example 4 >>
Various Pt / SnO 2 catalysts were prepared in the same manner as in <Preparation of Example Pellet Catalyst> in Example 1 except that the pH value of the aqueous solution of the Pt compound when Pt was supported was changed. The loading amount of Pt was 2 wt% based on the SnO 2 carrier. For each of the obtained Pt / SnO 2 catalysts, a performance test was performed at a reaction temperature of 400 ° C. and an SV of 160,000 h −1 . FIG. 7 shows the results of this performance test. FIG. 7 shows a case in which three kinds of aqueous solutions of pH = 3, pH = 7, and pH = 12 are changed.
[0039]
FIG. 7 shows that the methane removal rate can be improved as the pH value is increased. When loaded at pH = 3, the methane removal rate was around 50% from the initial stage, and there was no change even after 140 hours, showing the same performance. In the case of pH = 7, a methane removal rate of about 52% is shown in the initial stage, and a methane removal rate of about 55% is shown after 140 hours. In the case of pH = 12, it is about 50% in the initial stage, but shows a methane removal rate of 58% after 140 hours. Thus, it is shown that increasing the pH of the aqueous platinum solution at the time of supporting Pt is effective in improving the performance of removing methane by oxidation.
[0040]
FIG. 8 is a diagram showing the distribution of the pore diameter of the Pt (2 wt%) / SnO 2 catalyst supported at various pHs. In FIG. 8, what is shown as SnO 2 is the case of the SnO 2 carrier itself that does not carry Pt, which is the same as that shown in FIG. 4 as Kanto Chemical (special grade). As shown in FIG. 8, when Pt is supported at a high pH value, a pore size distribution close to the pore size distribution of the SnO 2 carrier itself is shown. This indicates that pores are not blocked when the pH value of the Pt compound is increased during Pt loading. That is, it is shown that the loading of Pt on the SnO 2 support at a high pH value is effective for improving the methane oxidation removal performance.
[0041]
<< Example 5 >>
In this example, the effect of SO 2 on the durability of a Pt / SnO 2 (Pt = 2 wt%) catalyst was tested. That is, the oxidative removal performance of methane depending on the presence or absence of SO 2 in the exhaust gas was tested. The catalyst was prepared in the same manner as in Example 4 at pH = 12. The exhaust gas temperature (reaction temperature) was 400 ° C. FIG. 9 is a diagram showing the results of this performance test. FIG. 9 shows the case where SO 2 = 1 ppm, that is, the SO 2 concentration in the exhaust gas is 1 ppm, and the case where SO 2 = 0 ppm, that is, the exhaust gas that does not contain SO 2 (except for the point that SO 2 is not contained in the test gas. Is the same as that of the test gas).
[0042]
As shown in FIG. 9, when SO 2 = 1 ppm, the methane removal rate shows a methane removal rate of about 50% in the initial stage, reaches 60% after 30 hours, hardly changes thereafter, and after 140 hours. It shows a high performance of 59%. On the other hand, in the case of SO 2 = 0 ppm, the methane removal rate is around 46% even in the initial stage, gradually decreases thereafter, and decreases to 41% after 140 hours.
[0043]
Thus, the activity of oxidizing and removing methane is improved by the presence of SO 2 . This fact confirms that the oxidation catalyst of the present invention behaves completely different from the conventional recognition. Conventionally, it has been known that an alumina-based catalyst supporting a noble metal is poisoned by SO 2 in exhaust gas and deteriorates performance. On the other hand, in the oxidation catalyst of the present invention, when SO 2 is contained in the exhaust gas, the activity of oxidizing and removing methane is improved rather than deteriorating the performance.
[0044]
【The invention's effect】
According to the present invention, it does not contain any palladium, which was conventionally considered to be an oxidation-active noble metal of methane, and also supports platinum, which was conventionally considered to be ineffective alone, on porous tin oxide alone. Thus, methane can be very effectively oxidized and removed over a long period of time in a low temperature range of 500 ° C. or lower, particularly in a low temperature range of 450 to 350 ° C. Therefore, the present invention can be effectively applied particularly to exhaust gas from a lean burn gas engine using city gas or the like containing a sulfur compound as an odorant as a fuel. Further, since the oxidation removal catalyst of the present invention has effective durability, the frequency of replacement can be reduced, and the cost of the exhaust gas treatment system can be reduced.
[Brief description of the drawings]
FIG. 1 is a view showing an example of an apparatus using the oxidation catalyst of the present invention. FIG. 2 is a view showing the results of Example 1. FIG. 3 is a view showing the results of Example 2. FIG. FIG. 5 shows the result of Example 2. FIG. 6 shows the result of Example 3. FIG. 7 shows the result of Example 4. FIG. 8 shows the result of Example 4. FIG. 9 shows the result of Example 5. [Description of References]
A Exhaust gas introduction pipe B Oxidation catalyst layer (reaction pipe)
C Outgoing pipe for treated exhaust gas
Claims (18)
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| JP2003148279A JP4283037B2 (en) | 2003-05-26 | 2003-05-26 | Catalyst for oxidation removal of methane in exhaust gas and exhaust gas purification method |
| PCT/JP2004/007578 WO2004103554A1 (en) | 2003-05-26 | 2004-05-26 | Catalyst for oxidizing and removing methane in exhaust gas method for clarifying exhaust gas |
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| JP2003148279A JP4283037B2 (en) | 2003-05-26 | 2003-05-26 | Catalyst for oxidation removal of methane in exhaust gas and exhaust gas purification method |
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| JP2009262131A (en) * | 2008-03-27 | 2009-11-12 | Osaka Gas Co Ltd | Catalyst for purification of exhaust gas and method of purifying exhaust gas |
| WO2018034050A1 (en) * | 2016-08-17 | 2018-02-22 | 三井金属鉱業株式会社 | Methane oxidation catalyst |
| WO2019039513A1 (en) | 2017-08-22 | 2019-02-28 | 三井金属鉱業株式会社 | Methane oxidizing catalyst |
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| JP6883135B1 (en) | 2020-05-15 | 2021-06-09 | 田中貴金属工業株式会社 | Methane combustion catalyst, its manufacturing method, and combustion exhaust gas purification method |
| WO2022149319A1 (en) | 2021-01-07 | 2022-07-14 | 田中貴金属工業株式会社 | Methane combustion catalyst, production method therefor, and combustion exhaust gas cleaning method |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP3263105B2 (en) * | 1991-12-02 | 2002-03-04 | 大阪瓦斯株式会社 | Nitrogen oxide treatment method and treatment apparatus |
| JP4171849B2 (en) * | 1998-07-16 | 2008-10-29 | 大阪瓦斯株式会社 | Hydrocarbon-containing exhaust gas purification catalyst and hydrocarbon-containing exhaust gas purification method |
| JP2001190931A (en) * | 2000-01-11 | 2001-07-17 | Osaka Gas Co Ltd | Method for purifying waste gas containing methane |
| JP4822374B2 (en) * | 2000-04-05 | 2011-11-24 | 三井金属鉱業株式会社 | Method for producing exhaust gas purification catalyst |
| JP2002253969A (en) * | 2001-03-02 | 2002-09-10 | Osaka Gas Co Ltd | Catalyst for purifying waste gas and method of purifying waste gas |
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- 2003-05-26 JP JP2003148279A patent/JP4283037B2/en not_active Expired - Lifetime
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2009262131A (en) * | 2008-03-27 | 2009-11-12 | Osaka Gas Co Ltd | Catalyst for purification of exhaust gas and method of purifying exhaust gas |
| WO2018034050A1 (en) * | 2016-08-17 | 2018-02-22 | 三井金属鉱業株式会社 | Methane oxidation catalyst |
| WO2019039513A1 (en) | 2017-08-22 | 2019-02-28 | 三井金属鉱業株式会社 | Methane oxidizing catalyst |
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| Publication number | Publication date |
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| WO2004103554A1 (en) | 2004-12-02 |
| JP4283037B2 (en) | 2009-06-24 |
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