JP2005238173A - Hydrogen generation catalyst - Google Patents
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- JP2005238173A JP2005238173A JP2004054574A JP2004054574A JP2005238173A JP 2005238173 A JP2005238173 A JP 2005238173A JP 2004054574 A JP2004054574 A JP 2004054574A JP 2004054574 A JP2004054574 A JP 2004054574A JP 2005238173 A JP2005238173 A JP 2005238173A
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- 239000003054 catalyst Substances 0.000 title claims abstract description 80
- 229910052739 hydrogen Inorganic materials 0.000 title claims abstract description 64
- 239000001257 hydrogen Substances 0.000 title claims abstract description 62
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 title claims abstract description 60
- PNEYBMLMFCGWSK-UHFFFAOYSA-N Alumina Chemical compound [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 claims abstract description 73
- 229910000510 noble metal Inorganic materials 0.000 claims abstract description 19
- 239000000203 mixture Substances 0.000 claims abstract description 11
- 239000007789 gas Substances 0.000 claims description 29
- 238000004519 manufacturing process Methods 0.000 claims description 15
- 238000000634 powder X-ray diffraction Methods 0.000 claims description 6
- 238000012360 testing method Methods 0.000 abstract description 37
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 abstract description 30
- 229910052717 sulfur Inorganic materials 0.000 abstract description 30
- 239000011593 sulfur Substances 0.000 abstract description 30
- 231100000572 poisoning Toxicity 0.000 abstract description 23
- 230000000607 poisoning effect Effects 0.000 abstract description 23
- 230000000694 effects Effects 0.000 abstract description 19
- 238000000629 steam reforming Methods 0.000 abstract description 13
- 229930195733 hydrocarbon Natural products 0.000 abstract description 11
- 150000002430 hydrocarbons Chemical class 0.000 abstract description 11
- 239000004215 Carbon black (E152) Substances 0.000 abstract description 7
- 238000007254 oxidation reaction Methods 0.000 abstract description 7
- 229910052751 metal Inorganic materials 0.000 abstract description 3
- 239000002184 metal Substances 0.000 abstract description 3
- 238000003746 solid phase reaction Methods 0.000 abstract description 3
- 230000003647 oxidation Effects 0.000 abstract 1
- 239000010970 precious metal Substances 0.000 abstract 1
- 239000012071 phase Substances 0.000 description 36
- 239000000843 powder Substances 0.000 description 35
- 230000000052 comparative effect Effects 0.000 description 33
- 239000010948 rhodium Substances 0.000 description 27
- 238000006243 chemical reaction Methods 0.000 description 15
- MCMNRKCIXSYSNV-UHFFFAOYSA-N Zirconium dioxide Chemical compound O=[Zr]=O MCMNRKCIXSYSNV-UHFFFAOYSA-N 0.000 description 10
- 238000010304 firing Methods 0.000 description 9
- XTQHKBHJIVJGKJ-UHFFFAOYSA-N sulfur monoxide Chemical compound S=O XTQHKBHJIVJGKJ-UHFFFAOYSA-N 0.000 description 9
- 239000002585 base Substances 0.000 description 8
- 239000000446 fuel Substances 0.000 description 8
- 229910052760 oxygen Inorganic materials 0.000 description 8
- 230000007423 decrease Effects 0.000 description 7
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 6
- 238000002485 combustion reaction Methods 0.000 description 6
- 239000001301 oxygen Substances 0.000 description 6
- 238000002407 reforming Methods 0.000 description 6
- TXKMVPPZCYKFAC-UHFFFAOYSA-N disulfur monoxide Inorganic materials O=S=S TXKMVPPZCYKFAC-UHFFFAOYSA-N 0.000 description 5
- CETPSERCERDGAM-UHFFFAOYSA-N ceric oxide Chemical compound O=[Ce]=O CETPSERCERDGAM-UHFFFAOYSA-N 0.000 description 4
- 229910000422 cerium(IV) oxide Inorganic materials 0.000 description 4
- 239000006185 dispersion Substances 0.000 description 4
- 239000012495 reaction gas Substances 0.000 description 4
- 229910052815 sulfur oxide Inorganic materials 0.000 description 4
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 3
- 230000015572 biosynthetic process Effects 0.000 description 3
- 229910002091 carbon monoxide Inorganic materials 0.000 description 3
- 238000002156 mixing Methods 0.000 description 3
- 239000008188 pellet Substances 0.000 description 3
- 238000001228 spectrum Methods 0.000 description 3
- 238000003786 synthesis reaction Methods 0.000 description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- RUDFQVOCFDJEEF-UHFFFAOYSA-N yttrium(III) oxide Inorganic materials [O-2].[O-2].[O-2].[Y+3].[Y+3] RUDFQVOCFDJEEF-UHFFFAOYSA-N 0.000 description 3
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 2
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 description 2
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 description 2
- 229910052784 alkaline earth metal Inorganic materials 0.000 description 2
- 150000001342 alkaline earth metals Chemical class 0.000 description 2
- 229910052791 calcium Inorganic materials 0.000 description 2
- 239000011575 calcium Substances 0.000 description 2
- 150000002431 hydrogen Chemical class 0.000 description 2
- 230000001590 oxidative effect Effects 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 1
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 1
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 description 1
- 238000002441 X-ray diffraction Methods 0.000 description 1
- 230000002378 acidificating effect Effects 0.000 description 1
- 229910052783 alkali metal Inorganic materials 0.000 description 1
- 150000001340 alkali metals Chemical class 0.000 description 1
- 229910021529 ammonia Inorganic materials 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 125000004432 carbon atom Chemical group C* 0.000 description 1
- 239000013064 chemical raw material Substances 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 230000008021 deposition Effects 0.000 description 1
- 238000003795 desorption Methods 0.000 description 1
- 230000008030 elimination Effects 0.000 description 1
- 238000003379 elimination reaction Methods 0.000 description 1
- 238000004993 emission spectroscopy Methods 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 125000004435 hydrogen atom Chemical group [H]* 0.000 description 1
- 229910052741 iridium Inorganic materials 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 229910017604 nitric acid Inorganic materials 0.000 description 1
- 239000003921 oil Substances 0.000 description 1
- 125000004430 oxygen atom Chemical group O* 0.000 description 1
- 229910052763 palladium Inorganic materials 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 238000005504 petroleum refining Methods 0.000 description 1
- 229910052697 platinum Inorganic materials 0.000 description 1
- 238000000746 purification Methods 0.000 description 1
- 229910052761 rare earth metal Inorganic materials 0.000 description 1
- 229910052703 rhodium Inorganic materials 0.000 description 1
- VXNYVYJABGOSBX-UHFFFAOYSA-N rhodium(3+);trinitrate Chemical compound [Rh+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O VXNYVYJABGOSBX-UHFFFAOYSA-N 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- 238000010671 solid-state reaction Methods 0.000 description 1
- 238000001179 sorption measurement Methods 0.000 description 1
- 229910002076 stabilized zirconia Inorganic materials 0.000 description 1
- 239000011232 storage material Substances 0.000 description 1
- LSNNMFCWUKXFEE-UHFFFAOYSA-L sulfite Chemical compound [O-]S([O-])=O LSNNMFCWUKXFEE-UHFFFAOYSA-L 0.000 description 1
- 150000003464 sulfur compounds Chemical class 0.000 description 1
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P20/00—Technologies relating to chemical industry
- Y02P20/50—Improvements relating to the production of bulk chemicals
- Y02P20/52—Improvements relating to the production of bulk chemicals using catalysts, e.g. selective catalysts
Abstract
Description
本発明は水素生成触媒に関し、詳しくは水蒸気改質反応を利用して炭化水素、酸素及び水蒸気を含むガスから効率よく水素を生成する触媒に関する。 The present invention relates to a hydrogen generation catalyst, and more particularly to a catalyst that efficiently generates hydrogen from a gas containing hydrocarbons, oxygen, and steam using a steam reforming reaction.
アンモニア合成、メタノール合成、オキソ合成など多くの化学工業プロセスあるいは石油精製において、水素あるいは水素と一酸化炭素との混合ガスは重要な化学原料である。また最近では、燃料電池を始めとするクリーンエネルギー源としての水素の重要性が増大している。さらに内燃機関の排ガス浄化においても、NOx を還元する能力に優れ、かつ硫黄被毒したNOx 吸蔵材から硫黄酸化物を脱離させてNOx 吸蔵還元型触媒を回復させる能力にも優れた水素が注目されつつある。 In many chemical industrial processes such as ammonia synthesis, methanol synthesis, and oxo synthesis or petroleum refining, hydrogen or a mixed gas of hydrogen and carbon monoxide is an important chemical raw material. Recently, the importance of hydrogen as a clean energy source including fuel cells is increasing. Furthermore, in the exhaust gas purification of internal combustion engines, it has excellent ability to reduce NO x and also has the ability to recover NO x storage reduction catalyst by desorbing sulfur oxide from sulfur poisoned NO x storage material. Hydrogen is drawing attention.
そして水素を製造する方法として、次式に示す炭化水素の水蒸気改質反応が多用されている。 As a method for producing hydrogen, a hydrocarbon steam reforming reaction represented by the following formula is frequently used.
CnHm＋nH2O→ nCO＋ (n+m/2)H2 （−ΔＨ＜０）
この水蒸気改質反応は大きな吸熱を伴うので、外部から必要な熱を供給する必要がある。そこで多くの場合には反応ガス中に酸素を添加し、次式に示す部分酸化反応や酸化反応の反応熱を利用して、水蒸気改質反応の進行を促進させることが行われている。
C n H m + nH 2 O → nCO + (n + m / 2) H 2 (−ΔH <0)
Since this steam reforming reaction involves a large endotherm, it is necessary to supply necessary heat from the outside. Therefore, in many cases, oxygen is added to the reaction gas, and the progress of the steam reforming reaction is promoted by utilizing the reaction heat of the partial oxidation reaction or oxidation reaction shown by the following formula.
CnHm＋n/2O2 → nCO＋m/2 H2 （−ΔＨ＞０）
CnHm＋(n+m/4)O2 →nCO2＋m/2 H2 （−ΔＨ＞０）
また水蒸気改質反応においては、次式に示すCOシフト反応が同時に進行する。
C n H m + n / 2O 2 → nCO + m / 2 H 2 (−ΔH> 0)
C n H m + (n + m / 4) O 2 → nCO 2 + m / 2 H 2 (−ΔH> 0)
In the steam reforming reaction, the CO shift reaction represented by the following formula proceeds simultaneously.
CO＋ H2O→ CO2＋m/2 H2 （−ΔＨ＞０）
上記した反応を促進するために、各種の触媒が利用されている。例えば特開昭56−091844号公報には、ジルコニアにRhを担持した水素生成触媒が開示されている。しかしジルコニアは耐熱性が低く、使用時の熱により比表面積が減少し、これにより担持されているRhの分散性が低下して水素生成能が低下するという不具合があった。
CO + H 2 O → CO 2 + m / 2 H 2 (−ΔH> 0)
In order to promote the above-described reaction, various catalysts are used. For example, Japanese Patent Laid-Open No. 56-091844 discloses a hydrogen production catalyst in which Rh is supported on zirconia. However, zirconia has low heat resistance, and its specific surface area decreases due to heat during use. This causes a problem that the dispersibility of the supported Rh is lowered and the hydrogen generating ability is lowered.
そこで特公平06−004135号公報や特開平03−080937号公報には、イットリアあるいはセリアなどを添加して部分安定化されたジルコニア担体にRhを担持した水素生成触媒が開示されている。また特開平04−265156号公報にはアルカリ金属、アルカリ土類金属を含有するセリアに貴金属を担持した水素生成触媒が、特開平11−226404号公報にはアルカリ土類金属、希土類元素で安定化されたジルコニアにRhを担持した水素生成触媒が開示されている。 Japanese Patent Publication No. 06-004135 and Japanese Patent Application Laid-Open No. 03-080937 disclose a hydrogen generation catalyst in which Rh is supported on a zirconia support partially stabilized by adding yttria or ceria. Japanese Patent Laid-Open No. 04-265156 discloses a hydrogen generation catalyst in which a noble metal is supported on ceria containing an alkali metal or an alkaline earth metal, and Japanese Patent Laid-Open No. 11-226404 is stabilized by an alkaline earth metal or a rare earth element. A hydrogen generation catalyst in which Rh is supported on the obtained zirconia is disclosed.
ところで水素生成触媒を内燃機関の排ガス中で用いる場合、あるいは自動車などに搭載する内部改質型燃料電池の燃料改質システムに用いる場合などには、様々な反応条件で使用されるため、始動時での低温活性が要求される一方で、ときには高温雰囲気に曝される。さらにディーゼルエンジンなどの希薄燃焼方式の内燃機関からの排ガス中での反応に用いられる場合は、炭化水素、酸素及び水蒸気との反応が進行する還元雰囲気の他に、高温での酸化雰囲気にも曝される。 By the way, when the hydrogen generation catalyst is used in the exhaust gas of an internal combustion engine, or when used in a fuel reforming system of an internal reforming fuel cell mounted on an automobile or the like, it is used under various reaction conditions. While low temperature activity is required, it is sometimes exposed to a high temperature atmosphere. Furthermore, when used for reactions in exhaust gas from lean combustion internal combustion engines such as diesel engines, in addition to reducing atmospheres where reactions with hydrocarbons, oxygen and water vapor proceed, they are also exposed to oxidizing atmospheres at high temperatures. Is done.
一方、内燃機関からの排ガスや内部改質型燃料電池の燃料改質システムにおける反応ガス中には、燃料中の硫黄化合物が燃焼して生成する硫黄酸化物などが含まれるため、水素生成触媒はそれらにも曝されることになる。 On the other hand, the exhaust gas from the internal combustion engine and the reaction gas in the fuel reforming system of the internal reforming fuel cell contain sulfur oxides produced by combustion of sulfur compounds in the fuel. They will also be exposed.
しかし上記した従来の水素生成触媒は、このような用途に用いた場合には十分な効果が得られないという問題がある。この原因としては、以下のことが考えられる。
（１）担体上の貴金属が高温下で粒成長し、反応に有効な活性サイトが減少する。
（２）担体上の貴金属が酸化物状態で安定化し、低温域では反応に有効なメタル状態に還元されにくい。
（３）担体上に多く存在する塩基点が硫黄酸化物の触媒への付着を促進し、かつ触媒からの硫黄酸化物の脱離が阻害されるため、硫黄酸化物による担体や貴金属の反応阻害、いわゆる硫黄被毒が起こりやすい。
(1) The noble metal on the support grows at high temperature and the active sites effective for the reaction decrease.
(2) The noble metal on the support is stabilized in the oxide state and is not easily reduced to a metal state effective for the reaction in a low temperature range.
(3) Since the base points present on the support promote the adhesion of sulfur oxide to the catalyst and the elimination of the sulfur oxide from the catalyst is inhibited, the reaction of the support and noble metal by the sulfur oxide is inhibited. So-called sulfur poisoning is likely to occur.
本発明は上記した事情に鑑みてなされたものであり、高温耐久試験後も高い水素生成活性を示し、かつ耐硫黄被毒性にも優れた水素生成触媒とすることを目的とする。 The present invention has been made in view of the above-described circumstances, and an object thereof is to provide a hydrogen generation catalyst that exhibits high hydrogen generation activity even after a high-temperature endurance test and is excellent in sulfur poisoning resistance.
上記課題を解決する本発明の水素生成触媒の特徴は、α型アルミナとθ型アルミナとの混合物を含み比表面積が30m2／ｇ以上の担体と、該担体に担持された貴金属と、からなることにある。 A feature of the hydrogen generation catalyst of the present invention that solves the above problems is composed of a support containing a mixture of α-type alumina and θ-type alumina and having a specific surface area of 30 m 2 / g or more, and a noble metal supported on the support. There is.
担体は、粉末Ｘ線回折パターンにおいて最強回折ピークがα型アルミナ相に帰属し、θ型アルミナ相に帰属する少なくとも一つの回折ピークの強度がα型アルミナ相の最強回折ピークの強度の20％以上であることが望ましい。 The carrier has the strongest diffraction peak attributed to the α-type alumina phase in the powder X-ray diffraction pattern, and the intensity of at least one diffraction peak attributed to the θ-type alumina phase is 20% or more of the intensity of the strongest diffraction peak of the α-type alumina phase. It is desirable that
あるいは担体は、粉末Ｘ線回折パターンにおいて最強回折ピークがθ型アルミナ相に帰属し、α型アルミナ相に帰属する少なくとも一つの回折ピークの強度がθ型アルミナ相の最強回折ピークの強度の10％以上であることが望ましい。 Alternatively, in the powder X-ray diffraction pattern, the carrier has the strongest diffraction peak attributed to the θ-type alumina phase, and the intensity of at least one diffraction peak attributed to the α-type alumina phase is 10% of the intensity of the strongest diffraction peak of the θ-type alumina phase. The above is desirable.
また本発明の水素生成触媒は、貴金属は少なくともRhを含むことが好ましく、ディーゼルエンジンからの排ガス中で用いられることができる。 In the hydrogen generation catalyst of the present invention, the noble metal preferably contains at least Rh, and can be used in exhaust gas from a diesel engine.
本発明の水素生成触媒によれば、軽油に代表される炭化水素、酸素及び水蒸気を含む反応ガス中において、優れた水素生成活性を示す。また高温雰囲気に曝された場合でも、水素生成活性に優れ、硫黄酸化物を含む反応ガス中で使用しても硫黄被毒が生じにくく、優れた水素生成活性を維持する。 The hydrogen production catalyst of the present invention exhibits excellent hydrogen production activity in a reaction gas containing hydrocarbons represented by light oil, oxygen and water vapor. Further, even when exposed to a high temperature atmosphere, the hydrogen generation activity is excellent, and even when used in a reaction gas containing sulfur oxides, sulfur poisoning hardly occurs and the excellent hydrogen generation activity is maintained.
本発明の水素生成触媒では、α型アルミナとθ型アルミナとの混合物を含み比表面積が30m2／ｇ以上の担体を用いている。比表面積が30m2／ｇ以上と大きいため、担持されている貴金属は高分散担持され、有効な活性サイトが多く存在する。したがって炭化水素の水蒸気改質反応が効率よく進行する。 In the hydrogen generation catalyst of the present invention, a support containing a mixture of α-type alumina and θ-type alumina and having a specific surface area of 30 m 2 / g or more is used. Since the specific surface area is as large as 30 m 2 / g or more, the supported noble metal is supported in a highly dispersed manner and there are many effective active sites. Therefore, the hydrocarbon steam reforming reaction proceeds efficiently.
またγ型アルミナ担体に担持された貴金属は、高温下で担体と固相反応することによって酸化状態で安定化し不活性化する。しかしα型アルミナとθ型アルミナとの混合物を担体とすることで、貴金属と担体との固相反応が抑制され、高温雰囲気に曝された場合でも貴金属が酸化状態で安定化されるような不具合がなく、貴金属は容易にメタル状態へと還元され、炭化水素の水蒸気改質反応が効率よく進行する。 The noble metal supported on the γ-type alumina carrier is stabilized and inactivated in an oxidized state by a solid phase reaction with the carrier at a high temperature. However, by using a mixture of α-type alumina and θ-type alumina as a support, the solid-state reaction between the noble metal and the support is suppressed, and the noble metal is stabilized in an oxidized state even when exposed to a high temperature atmosphere. Noble metal is easily reduced to the metal state, and the hydrocarbon steam reforming reaction proceeds efficiently.
さらにθ型アルミナは塩基点を多く有するものの、α型アルミナと混合されているため塩基点が低減され、硫黄酸化物の近接が抑制されるとともに担体に付着した硫黄酸化物は容易に脱離する。したがって硫黄被毒が抑制され、炭化水素の水蒸気改質反応が円滑に進行する。 In addition, θ-type alumina has many basic points, but since it is mixed with α-type alumina, the base points are reduced, the proximity of sulfur oxides is suppressed, and sulfur oxides attached to the carrier are easily detached. . Therefore, sulfur poisoning is suppressed and the steam reforming reaction of hydrocarbon proceeds smoothly.
担体は、α型アルミナとθ型アルミナとの混合物を含み比表面積が30m2／ｇ以上のものである。α型アルミナとθ型アルミナとのみから構成することが望ましいが、特性に影響を与えない範囲でγ型アルミナ、チタニア、ジルコニア、セリアなどを混合して担体とすることもできる。 The carrier contains a mixture of α-type alumina and θ-type alumina and has a specific surface area of 30 m 2 / g or more. Although it is desirable to comprise only α-type alumina and θ-type alumina, γ-type alumina, titania, zirconia, ceria, etc. may be mixed to form a carrier within a range that does not affect the characteristics.
α型アルミナとθ型アルミナとの混合割合は、粉末Ｘ線回折パターンにおいて最強回折ピークがα型アルミナ相に帰属し、θ型アルミナ相に帰属する少なくとも一つの回折ピークの強度がα型アルミナ相の最強回折ピークの強度の20％以上であることが好ましい。θ型アルミナ相に帰属する少なくとも一つの回折ピークの強度がα型アルミナ相の最強回折ピークの強度の20％未満では、高温耐久試験後及び硫黄被毒耐久試験後の水素生成活性の低下が著しくなる。 The mixing ratio of α-type alumina and θ-type alumina is such that the strongest diffraction peak belongs to the α-type alumina phase in the powder X-ray diffraction pattern, and the intensity of at least one diffraction peak attributed to the θ-type alumina phase is α-type alumina phase. The intensity of the strongest diffraction peak is preferably 20% or more. If the intensity of at least one diffraction peak attributed to the θ-type alumina phase is less than 20% of the intensity of the strongest diffraction peak of the α-type alumina phase, the hydrogen generation activity is significantly reduced after the high-temperature endurance test and the sulfur poisoning endurance test. Become.
またα型アルミナとθ型アルミナとの混合割合は、粉末Ｘ線回折パターンにおいて最強回折ピークがθ型アルミナ相に帰属し、α型アルミナ相に帰属する少なくとも一つの回折ピークの強度がθ型アルミナ相の最強回折ピークの強度の10％以上であることも好ましい。α型アルミナ相に帰属する少なくとも一つの回折ピークの強度がθ型アルミナ相の最強回折ピークの強度の10％未満では、耐硫黄被毒性が低下してしまう。 The mixing ratio of α-type alumina and θ-type alumina is such that the strongest diffraction peak belongs to the θ-type alumina phase in the powder X-ray diffraction pattern, and the intensity of at least one diffraction peak attributed to the α-type alumina phase is θ-type alumina. It is also preferably 10% or more of the intensity of the strongest diffraction peak of the phase. When the intensity of at least one diffraction peak attributed to the α-type alumina phase is less than 10% of the intensity of the strongest diffraction peak of the θ-type alumina phase, sulfur poisoning resistance decreases.
α型アルミナとθ型アルミナとの混合物は、両粉末を混合して調製してもよいし、γ型アルミナ粉末を焼成することで調製することもできる。焼成する場合には、焼成温度が1100〜1175℃であれば最強回折ピークがθ型アルミナ相に帰属し、α型アルミナ相に帰属する少なくとも一つの回折ピークの強度がθ型アルミナ相の最強回折ピークの強度の10％以上であり、かつ比表面積が30m2／ｇ以上である混合物を調製することができる。また焼成温度を1175〜1250℃とすることで、最強回折ピークがα型アルミナ相に帰属し、θ型アルミナ相に帰属する少なくとも一つの回折ピークの強度がα型アルミナ相の最強回折ピークの強度の20％以上であり、かつ比表面積が30m2／ｇ以上である混合物を調製することができる。焼成温度が1250℃以上では、θ型アルミナ相が少なくなるとともに、比表面積も小さくなりすぎてしまう。 The mixture of α-type alumina and θ-type alumina may be prepared by mixing both powders, or may be prepared by firing γ-type alumina powder. When firing, if the firing temperature is 1100 to 1175 ° C., the strongest diffraction peak belongs to the θ-type alumina phase, and the intensity of at least one diffraction peak attributed to the α-type alumina phase is the strongest diffraction of the θ-type alumina phase. A mixture having a peak intensity of 10% or more and a specific surface area of 30 m 2 / g or more can be prepared. In addition, by setting the firing temperature to 1175-1250 ° C., the strongest diffraction peak belongs to the α-type alumina phase, and the intensity of at least one diffraction peak attributed to the θ-type alumina phase is the intensity of the strongest diffraction peak of the α-type alumina phase. And a mixture having a specific surface area of 30 m 2 / g or more can be prepared. When the firing temperature is 1250 ° C. or higher, the θ-type alumina phase decreases and the specific surface area becomes too small.
担体に担持される貴金属としては、Pt，Rh，Pd，Irなどから選択することができるが、少なくともRhを含むことが望ましい。少なくともRhを担持することにより、水素生成活性が特に向上する。この貴金属の担持量は、担体 100ｇあたり 0.1〜10ｇとするのが好ましい。担持量がこれより少ないと水素生成活性が低く、これより多く担持しても水素生成活性が飽和するとともに貴金属どうしの粒成長が生じる場合がある。 The noble metal supported on the carrier can be selected from Pt, Rh, Pd, Ir, etc., but it is preferable that at least Rh is included. By supporting at least Rh, the hydrogen generation activity is particularly improved. The amount of the noble metal supported is preferably 0.1 to 10 g per 100 g of the carrier. If the supported amount is less than this, the hydrogen generating activity is low, and even if the supported amount is more than this, the hydrogen generating activity is saturated and grain growth of noble metals may occur.
本発明の水素生成触媒は、少なくとも炭化水素と水蒸気を含むガスと接触されることで、水蒸気改質反応により低温域から高温域まで高い活性で水素を生成する。部分酸化反応や酸化反応による反応熱を利用するためには、さらに酸素を含むガスと接触させることが好ましい。そしてこのようなガスとして、ディーゼルエンジンからの排ガスを用いることが特に好ましい。ディーゼルエンジンからの排ガス中には、炭化水素、水蒸気及び酸素が豊富に存在するので、水素を生成するとともにディーゼルエンジンからの排ガスを浄化することができる。 The hydrogen generation catalyst of the present invention generates hydrogen with high activity from a low temperature range to a high temperature range by a steam reforming reaction by contacting with a gas containing at least hydrocarbon and steam. In order to use the partial oxidation reaction or reaction heat due to the oxidation reaction, it is preferable to contact with a gas containing oxygen. And as such gas, it is especially preferable to use the exhaust gas from a diesel engine. Since exhaust gas from a diesel engine is rich in hydrocarbons, water vapor and oxygen, hydrogen can be generated and exhaust gas from the diesel engine can be purified.
またディーゼルエンジンからの排ガス中には比較的多量の硫黄酸化物が含まれているが、本発明の水素生成触媒は耐硫黄被毒性に優れているので、このような排ガス中でも水素生成活性の耐久性に優れている。 Moreover, although a relatively large amount of sulfur oxide is contained in the exhaust gas from the diesel engine, the hydrogen generation catalyst of the present invention is excellent in sulfur poisoning resistance. Excellent in properties.
以下、実施例及び比較例により本発明を具体的に説明する。表１に、実施例及び比較例で用いたアルミナ粉末を示す。表１におけるR1、R2及びR3の各アルミナ粉末は、それぞれ市販品を用いた。またS1粉末はR1粉末を大気中1150℃で焼成することで調製し、S2粉末はR1粉末を大気中1200℃で焼成することで調製し、R4粉末はR1粉末を1300℃で焼成することで調製した。それぞれのアルミナ粉末のＸ線回折パターンを解析し、各結晶相で最も強度の高い回折ピークの相対強度を表１に示している。 Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. Table 1 shows the alumina powder used in the examples and comparative examples. Commercially available products were used for the alumina powders R1, R2 and R3 in Table 1. S1 powder is prepared by firing R1 powder in air at 1150 ° C, S2 powder is prepared by firing R1 powder in air at 1200 ° C, and R4 powder is fired at 1300 ° C in R1 powder. Prepared. The X-ray diffraction pattern of each alumina powder was analyzed, and the relative intensity of the diffraction peak having the highest intensity in each crystal phase is shown in Table 1.
（実施例１）
R1粉末を大気中1150℃で焼成することで調製されたS1粉末を所定量秤量し、所定濃度の硝酸ロジウム水溶液の所定量を吸水させ、大気中 300℃で３時間焼成してRhを担持した。Rhの担持量は２重量％である。これを定法によって粒径 0.5〜 1.0mmのペレットに成形し、ペレット触媒を調製した。用いたS1粉末では、最強回折ピークがθ型アルミナ相に帰属し、α型アルミナ相に帰属する最強回折ピークの強度がθ型アルミナ相の最強回折ピークの強度の36％である。
(Example 1)
Weighed a predetermined amount of S1 powder prepared by firing R1 powder at 1150 ° C in the air, absorbed a predetermined amount of rhodium nitrate aqueous solution with a predetermined concentration, and baked at 300 ° C for 3 hours to carry Rh. . The amount of Rh supported is 2% by weight. This was formed into pellets having a particle diameter of 0.5 to 1.0 mm by a conventional method to prepare a pellet catalyst. In the used S1 powder, the strongest diffraction peak belongs to the θ-type alumina phase, and the intensity of the strongest diffraction peak attributed to the α-type alumina phase is 36% of the intensity of the strongest diffraction peak of the θ-type alumina phase.
（実施例２）
S1粉末に代えてR1粉末を大気中1150℃で焼成することで調製されたS2粉末を用いたこと以外は、実施例１と同様である。用いたS2粉末では、最強回折ピークがα型アルミナ相に帰属し、θ型アルミナ相に帰属する最強回折ピークの強度がα型アルミナ相の最強回折ピークの強度の74％である。
(Example 2)
It is the same as that of Example 1 except having used S2 powder prepared by baking R1 powder at 1150 degreeC in air | atmosphere instead of S1 powder. In the S2 powder used, the strongest diffraction peak belongs to the α-type alumina phase, and the intensity of the strongest diffraction peak attributed to the θ-type alumina phase is 74% of the intensity of the strongest diffraction peak of the α-type alumina phase.
（比較例１）
S1粉末に代えてR1粉末を用いたこと以外は、実施例１と同様である。用いたR1粉末では、回折ピークの全てがγ型アルミナ相に帰属している。
(Comparative Example 1)
Example 1 is the same as Example 1 except that R1 powder was used instead of S1 powder. In the R1 powder used, all of the diffraction peaks belong to the γ-type alumina phase.
（比較例２）
S1粉末に代えてR2粉末を用いたこと以外は、実施例１と同様である。用いたR2粉末では、回折ピークの全てがθ型アルミナ相に帰属している。
(Comparative Example 2)
The same as Example 1 except that R2 powder was used instead of S1 powder. In the R2 powder used, all of the diffraction peaks belong to the θ-type alumina phase.
（比較例３）
S1粉末に代えてR3粉末を用いたこと以外は、実施例１と同様である。用いたR3粉末では、回折ピークの全てがα型アルミナ相に帰属している。
(Comparative Example 3)
The same as Example 1 except that R3 powder was used instead of S1 powder. In the R3 powder used, all of the diffraction peaks belong to the α-type alumina phase.
（比較例４）
S1粉末に代えてR1粉末を大気中1300℃で焼成することで調製されたR4粉末を用いたこと以外は、実施例１と同様である。用いたR4粉末では、最強回折ピークがα型アルミナ相に帰属し、θ型アルミナ相に帰属する最強回折ピークの強度がα型アルミナ相の最強回折ピークの強度の10％である。
(Comparative Example 4)
Example 1 is the same as Example 1 except that R4 powder prepared by firing R1 powder at 1300 ° C. in air is used instead of S1 powder. In the R4 powder used, the strongest diffraction peak belongs to the α-type alumina phase, and the intensity of the strongest diffraction peak attributed to the θ-type alumina phase is 10% of the intensity of the strongest diffraction peak of the α-type alumina phase.
（比較例５）
S1粉末に代えて、市販のイットリア含有安定化ジルコニア粉末（イットリア含有率５モル％、比表面積50m2／ｇ）を用いたこと以外は、実施例１と同様である。
(Comparative Example 5)
It is the same as that of Example 1 except having used the commercially available yttria containing stabilized zirconia powder (yttria content rate 5 mol%, specific surface area 50m < 2 > / g) instead of S1 powder.
（比較例６）
S1粉末に代えて、市販のカルシウム含有セリア粉末（カルシウム含有率１モル％、比表面積67m2／ｇ）を用いたこと以外は、実施例１と同様である。
(Comparative Example 6)
It is the same as Example 1 except having replaced with S1 powder and using commercially available calcium containing ceria powder (
＜試験・評価＞
上記した各ペレット触媒について、先ず、高温耐久試験と硫黄被毒耐久試験の２種類の耐久試験を行った。
<Test and evaluation>
For each of the pellet catalysts described above, first, two types of durability tests were conducted, a high temperature durability test and a sulfur poisoning durability test.
高温耐久試験は、表２に示すリーン雰囲気のモデルガスとリッチ雰囲気のモデルガスを４分／１分で交互に切り換えながら、ともに入ガス温度 700℃で５時間加熱した。 In the high temperature endurance test, the model gas in the lean atmosphere and the model gas in the rich atmosphere shown in Table 2 were alternately switched at 4 minutes / 1 minute, and both were heated at an inlet gas temperature of 700 ° C. for 5 hours.
硫黄被毒耐久試験は、各触媒２ｇに対して、表３に示す含硫黄ガスを1000ml／分で供給しながら入りガス温度 400℃で３時間加熱して、各触媒にそれぞれ硫黄成分を付着させた。次いで表３に示す無硫黄ガスを 10000ml／分で供給しながら、10℃／分の昇温速度で 600℃まで昇温し、さらに 600℃で15分保持することによって、弱く付着している硫黄成分を脱離させた。 In the sulfur poisoning endurance test, 2 g of each catalyst was heated at an inlet gas temperature of 400 ° C. for 3 hours while supplying the sulfur-containing gas shown in Table 3 at 1000 ml / min, and the sulfur component was adhered to each catalyst. It was. Next, while supplying the sulfur-free gas shown in Table 3 at 10000 ml / min, the temperature is raised to 600 ° C. at a rate of 10 ° C./min, and further maintained at 600 ° C. for 15 minutes, so that weakly adhering sulfur Components were desorbed.
そして高温耐久試験後の各触媒、及び硫黄被毒耐久試験後の各触媒２ｇを常圧固定床流通型反応装置にそれぞれ装填し、表４に示すモデル排ガスを 15000ml／分で供給しながら、10℃／分の昇温速度で 600℃まで昇温した。このモデル排ガスでは、触媒上で前述の水蒸気改質反応、部分酸化反応、酸化反応及びCOシフト反応が進行する。 Each catalyst after the high temperature endurance test and 2 g of each catalyst after the sulfur poisoning endurance test were loaded into a normal pressure fixed bed flow type reactor, and the model exhaust gas shown in Table 4 was supplied at 15000 ml / min. The temperature was raised to 600 ° C at a rate of temperature rise of ° C / min. In this model exhaust gas, the aforementioned steam reforming reaction, partial oxidation reaction, oxidation reaction and CO shift reaction proceed on the catalyst.
そこで反応前後のＣ、Ｈ及びＯ原子の物質収支が一致すると仮定して、以下の（１）〜（３）式より（４）式を導き、昇温中に測定した触媒出ガス中の CO2、CO及びO2の各濃度を（４）式に代入して生成した水素濃度[H2]を算出した。 Therefore, assuming that the mass balance of C, H, and O atoms before and after the reaction is the same, Equation (4) is derived from Equations (1) to (3) below, and CO in the catalyst output gas measured during the temperature rise is calculated. 2. The hydrogen concentration [H 2 ] produced by substituting the respective concentrations of CO, O 2 and (4) was calculated.
Ｃ：16 [n-C16H34]0＝16[n-C16H34]＋ [CO2]＋[CO] ・・（１）
Ｈ：34 [n-C16H34]0＋ 2[H2O]0＝34[n-C16H34]＋ 2 [H2O]＋ 2[H2] ・・（２）
Ｏ： 2[O2]0＋[H2O]0＝ 2[O2]＋ [H2O]＋ 2 [CO2]＋[CO] ・・（３）
（ここで [ｘ]0は反応前のｘの濃度、[ｘ]は反応後のｘの濃度を示す）
[H2](%)＝(49／16）[CO2] ＋(33／16）[CO]− 2（[O2]0−[O2]） ・・（４）
この反応条件では、水素生成濃度の最大値は0.93％である。（４）式より算出した水素生成濃度のこの最大値に対する割合を水素生成率と表記し、この水素生成率を活性の指標とする。
C: 16 [nC 16 H 34 ] 0 = 16 [nC 16 H 34 ] + [CO 2 ] + [CO] (1)
H: 34 [nC 16 H 34 ] 0 + 2 [H 2 O] 0 = 34 [nC 16 H 34] + 2 [H 2 O] + 2 [H 2] ·· (2)
O: 2 [O 2 ] 0 + [H 2 O] 0 = 2 [O 2 ] + [H 2 O] +2 [CO 2 ] + [CO] (3)
(Where [x] 0 represents the concentration of x before the reaction, and [x] represents the concentration of x after the reaction)
[H 2 ] (%) = (49/16) [CO 2 ] + (33/16) [CO] −2 ([O 2 ] 0 − [O 2 ]) (4)
Under this reaction condition, the maximum value of the hydrogen production concentration is 0.93%. The ratio of the hydrogen generation concentration calculated from the equation (4) to the maximum value is expressed as a hydrogen generation rate, and this hydrogen generation rate is used as an activity index.
高温耐久試験後の各触媒の水素生成率を図１、２に示す。図１、２より、各実施例の触媒は各比較例の触媒に比べて各温度で高い水素生成率を示していることがわかる。 The hydrogen production rate of each catalyst after the high temperature durability test is shown in FIGS. 1 and 2, it can be seen that the catalyst of each example shows a higher hydrogen production rate at each temperature than the catalyst of each comparative example.
また硫黄被毒耐久試験後の各触媒の水素生成率を図３、４に示す。図３、４より、各実施例の触媒は比較例１〜５の触媒に比べて低温域から高温域まで高い水素生成率を示し、比較例６の触媒に対しても高温域において高い水素生成率を示している。 Moreover, the hydrogen production rate of each catalyst after a sulfur poisoning endurance test is shown in FIGS. 3 and 4, the catalyst of each example shows a higher hydrogen generation rate from the low temperature range to the high temperature range than the catalysts of Comparative Examples 1 to 5, and higher hydrogen generation in the high temperature range than the catalyst of Comparative Example 6 as well. Shows the rate.
すなわち、α型アルミナとθ型アルミナとの混合物を含み比表面積が30m2／ｇ以上の担体にRhを担持した各実施例の触媒を用いることで、各比較例の触媒と比べて、高温耐久試験後と硫黄被毒耐久試験後のいずれの場合においても、高い水素生成活性が得られることが明らかである。 That is, the use of the catalyst of each example including a mixture of α-type alumina and θ-type alumina and having a specific surface area of 30 m 2 / g or more and supporting Rh, compared with the catalysts of each comparative example, high temperature durability It is clear that high hydrogen generation activity can be obtained in both cases after the test and after the sulfur poisoning endurance test.
次に、実施例１、２の触媒が高い水素生成活性を示す原因を明らかにすべく、以下の実験を行った。先ず高温耐久試験後の各実施例及び各比較例の触媒について、Rh分散度をCOパルス吸着法で測定した。この値が高いほどRhが微細に、すなわち高分散状態で担持されていることを示す。結果を図５に示す。 Next, the following experiment was conducted to clarify the cause of the high hydrogen generation activity of the catalysts of Examples 1 and 2. First, Rh dispersion degree was measured by the CO pulse adsorption method about the catalyst of each Example after a high temperature endurance test, and each comparative example. Higher values indicate that Rh is finely supported, that is, supported in a highly dispersed state. The results are shown in FIG.
各実施例の触媒のRh分散度は比較例１、２の触媒とは同等であるが、比較例３〜６の触媒に比べて著しく高い。したがって比較例３〜６の触媒では、高温耐久試験時にRhに粒成長が生じたと考えられる。 Although the Rh dispersion degree of the catalyst of each Example is equivalent to the catalyst of the comparative examples 1 and 2, it is remarkably high compared with the catalyst of the comparative examples 3-6. Therefore, in the catalysts of Comparative Examples 3 to 6, it is considered that grain growth occurred in Rh during the high temperature durability test.
次に、高温耐久試験後の各実施例及び各比較例の触媒に、O2を10％含むArガスを供給しながら 500℃で10分間加熱し、次いでH2を１％含むArガスを供給しながら室温から 800℃まで20℃／分の速度で昇温した時のH2-TPRスペクトルを測定した。結果を図６に示す。このH2-TPRスペクトルは、触媒出ガス中のH2濃度の温度変化を示す。H2濃度の低下はRhが次式のように還元されたことを示し、H2濃度の低下が起きる温度が低いほどRhが還元され易いことを示す。 Next, the catalyst of each Example and Comparative Example after the high temperature endurance test was heated at 500 ° C. for 10 minutes while supplying Ar gas containing 10% O 2 , and then Ar gas containing 1% H 2 was supplied. The H 2 -TPR spectrum was measured when the temperature was increased from room temperature to 800 ° C. at a rate of 20 ° C./min. The results are shown in FIG. This H 2 -TPR spectrum shows the temperature change of the H 2 concentration in the catalyst outgas. A decrease in H 2 concentration indicates that Rh has been reduced as in the following equation, and that the lower the temperature at which the decrease in H 2 concentration occurs, the easier Rh can be reduced.
Rh2O3＋ 3/2H2 → ２Rh＋3/2H2O
図６では、約 370℃を境界として低温側と高温側にそれぞれH2濃度低下のピークが示されていることから、これらの触媒では、低温側ピークに相当する還元され易いRhと、高温側ピークに相当する還元されにくいRhの２種類が存在すると考えられる。そこで低温側ピークの面積がピークの全面積に占める割合を算出し、それをRh易還元性として図７に示す。
Rh 2 O 3 + 3 / 2H 2 → 2Rh + 3 / 2H 2 O
In FIG. 6, since the peak of H 2 concentration decrease is shown on the low temperature side and the high temperature side at about 370 ° C. as a boundary, in these catalysts, Rh corresponding to the low temperature side peak and the high temperature side are easily reduced. It is thought that there are two types of Rh that are difficult to reduce corresponding to the peak. Therefore, the ratio of the area of the low-temperature side peak to the total area of the peak is calculated and shown in FIG.
図７から各実施例の触媒のRh易還元性は、比較例３〜６の触媒と比べると僅かに劣るものの、比較例１、２の触媒と比べると著しく高いことがわかる。 From FIG. 7, it can be seen that the Rh easy-reducibility of the catalyst of each Example is significantly higher than that of Comparative Examples 1 and 2, although it is slightly inferior to that of Comparative Examples 3 to 6.
以上の結果より、各実施例の触媒では、高温耐久試験後でもRh分散度及びRh易還元性の両方が高いため、水蒸気改質反応の活性サイトと考えられるメタル状のRhが多く存在し、炭化水素の水蒸気改質反応が効率良く進行した結果、図１、２に示すように高い水素生成活性を示したと考えられる。 From the above results, in the catalyst of each example, both the Rh dispersion degree and the Rh easy-reducibility are high even after the high temperature endurance test, so there are many metal-like Rhs that are considered active sites of the steam reforming reaction, As a result of the efficient progress of the hydrocarbon steam reforming reaction, it is considered that a high hydrogen generation activity was exhibited as shown in FIGS.
次に、硫黄被毒耐久試験後の各実施例及び各比較例の触媒について、Ｓ付着量を測定し、結果を図８に示す。なおＳ付着量は、濃硝酸により触媒を溶解した後、ＩＣＰ（誘電結合高周波プラズマ）発光分光分析法を用いて測定した。 Next, with respect to the catalysts of the respective examples and comparative examples after the sulfur poisoning durability test, the S adhesion amount was measured, and the results are shown in FIG. The S adhesion amount was measured using ICP (Dielectric Coupled High Frequency Plasma) emission spectroscopy after dissolving the catalyst with concentrated nitric acid.
各実施例の触媒のＳ付着量は、比較例１、２、５及び６の触媒に比べて少なく、これは、各実施例の触媒は硫黄成分が付着しにくい、あるいは付着しても脱離しやすいことを示している。酸化雰囲気で付着した硫黄成分は、通常、硫酸イオンあるいは亜硫酸イオンなどの酸性物質として存在することが知られている。そこでＳ付着量が少なかった原因を調査するため、硫黄被毒耐久試験後の各実施例及び各比較例の触媒について塩基点量を測定した。 The amount of S deposited on the catalyst of each example is small compared to the catalysts of Comparative Examples 1, 2, 5 and 6. This is because the catalyst of each example hardly adheres to the sulfur component or is desorbed even if it adheres. It shows that it is easy. It is known that sulfur components adhering in an oxidizing atmosphere usually exist as acidic substances such as sulfate ions or sulfite ions. Therefore, in order to investigate the cause of the small amount of S adhesion, the base point amount was measured for the catalyst of each Example and each Comparative Example after the sulfur poisoning endurance test.
先ず各触媒にそれぞれ CO2を２％含むHeガスを 100℃で20分間供給して CO2を吸着させ、次いでHeガスを 100℃で20分間供給することによって物理的に吸着していた CO2を除去した後、Heガスを供給しながら室温から 600℃まで20℃／分の速度で昇温したときの CＯ2脱離量を測定し、その値から塩基点量を算出した。結果を図９に示す。
First, a He gas containing 2% CO 2 was supplied to each catalyst at 100 ° C for 20 minutes to adsorb
各実施例の触媒は、比較例１、２、５及び６の触媒と比べて塩基点量が少なく、この結果は図６の結果と一致している。したがって各実施例の触媒では、触媒表面の塩基点量が少ないため、硫黄被毒耐久試験後においてもＳ付着量が少なくなり、硫黄成分によってRh及び担体の機能が阻害されることが少なく、図３、４に示すように高い水素生成活性を示したと考えられる。なお比較例３、４の触媒は、塩基点が少ないにもかかわらず硫黄被毒耐久試験後の水素生成活性が低いが、これらの触媒は担体の比表面積が30m2／ｇ未満ときわめて低いため、図５に示す高温耐久試験の結果と同様に、硫黄被毒耐久試験後においてもRh分散度が低いことが影響していると推察される。 The catalyst of each Example has a small amount of base sites compared with the catalysts of Comparative Examples 1, 2, 5 and 6, and this result is consistent with the result of FIG. Therefore, in the catalyst of each Example, since the amount of base points on the catalyst surface is small, the amount of S deposition is small even after the sulfur poisoning endurance test, and the functions of Rh and the carrier are hardly inhibited by the sulfur component. It is considered that high hydrogen generation activity was exhibited as shown in 3 and 4. Although the catalysts of Comparative Examples 3 and 4 have low hydrogen generation activity after the sulfur poisoning endurance test despite their low base point, these catalysts have a very low specific surface area of the support of less than 30 m 2 / g. Like the result of the high temperature endurance test shown in FIG. 5, it is presumed that the low Rh dispersity is also influenced after the sulfur poisoning endurance test.
以上のことから、本実施例の触媒は、高温耐久試験後及び硫黄被毒耐久試験後のいずれの場合においても、優れた水素生成活性を示すことが明らかであり、内燃機関の排ガスの浄化あるいは自動車などに搭載する内部改質型燃料電池の燃料改質システムなどに、きわめて有用であることがわかる。 From the above, it is clear that the catalyst of this example exhibits excellent hydrogen generation activity both in the high temperature endurance test and after the sulfur poisoning endurance test. It can be seen that it is extremely useful for a fuel reforming system of an internal reforming fuel cell mounted on an automobile or the like.
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