JP2009285620A - Exhaust gas purification catalyst - Google Patents
Exhaust gas purification catalyst Download PDFInfo
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- JP2009285620A JP2009285620A JP2008143511A JP2008143511A JP2009285620A JP 2009285620 A JP2009285620 A JP 2009285620A JP 2008143511 A JP2008143511 A JP 2008143511A JP 2008143511 A JP2008143511 A JP 2008143511A JP 2009285620 A JP2009285620 A JP 2009285620A
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- iron oxide
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- exhaust gas
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- 239000003054 catalyst Substances 0.000 title claims abstract description 182
- 238000000746 purification Methods 0.000 title claims abstract description 34
- UQSXHKLRYXJYBZ-UHFFFAOYSA-N Iron oxide Chemical compound [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 claims abstract description 298
- 239000002245 particle Substances 0.000 claims abstract description 210
- 239000000463 material Substances 0.000 claims abstract description 76
- 239000007789 gas Substances 0.000 claims abstract description 59
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims abstract description 44
- 239000001301 oxygen Substances 0.000 claims abstract description 44
- 229910052760 oxygen Inorganic materials 0.000 claims abstract description 44
- 238000003860 storage Methods 0.000 claims abstract description 24
- 229910052751 metal Inorganic materials 0.000 claims abstract description 22
- 239000002184 metal Substances 0.000 claims abstract description 22
- 239000011230 binding agent Substances 0.000 claims description 31
- 229910052595 hematite Inorganic materials 0.000 claims description 6
- 239000011019 hematite Substances 0.000 claims description 6
- LIKBJVNGSGBSGK-UHFFFAOYSA-N iron(3+);oxygen(2-) Chemical compound [O-2].[O-2].[O-2].[Fe+3].[Fe+3] LIKBJVNGSGBSGK-UHFFFAOYSA-N 0.000 claims description 6
- 229910052598 goethite Inorganic materials 0.000 claims description 4
- AEIXRCIKZIZYPM-UHFFFAOYSA-M hydroxy(oxo)iron Chemical compound [O][Fe]O AEIXRCIKZIZYPM-UHFFFAOYSA-M 0.000 claims description 4
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 claims description 4
- 239000002994 raw material Substances 0.000 claims 1
- 229910052717 sulfur Inorganic materials 0.000 abstract description 20
- 239000011593 sulfur Substances 0.000 abstract description 20
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 abstract description 19
- 231100000572 poisoning Toxicity 0.000 abstract description 17
- 230000000607 poisoning effect Effects 0.000 abstract description 17
- 230000003197 catalytic effect Effects 0.000 abstract description 4
- MWUXSHHQAYIFBG-UHFFFAOYSA-N Nitric oxide Chemical compound O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 description 240
- VCJMYUPGQJHHFU-UHFFFAOYSA-N iron(3+);trinitrate Chemical compound [Fe+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O VCJMYUPGQJHHFU-UHFFFAOYSA-N 0.000 description 60
- 239000010410 layer Substances 0.000 description 38
- 239000002131 composite material Substances 0.000 description 30
- 238000001179 sorption measurement Methods 0.000 description 27
- 230000032683 aging Effects 0.000 description 25
- 230000000052 comparative effect Effects 0.000 description 21
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 19
- 239000000843 powder Substances 0.000 description 19
- 208000005374 Poisoning Diseases 0.000 description 17
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 17
- 238000009826 distribution Methods 0.000 description 16
- 238000013507 mapping Methods 0.000 description 16
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Substances [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 15
- 239000002002 slurry Substances 0.000 description 15
- 238000010304 firing Methods 0.000 description 14
- 229910052742 iron Inorganic materials 0.000 description 10
- 238000001035 drying Methods 0.000 description 9
- 239000000243 solution Substances 0.000 description 9
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 9
- 239000013078 crystal Substances 0.000 description 8
- 230000009467 reduction Effects 0.000 description 8
- 229910052684 Cerium Inorganic materials 0.000 description 7
- 210000002421 cell wall Anatomy 0.000 description 7
- 238000005259 measurement Methods 0.000 description 7
- 229910044991 metal oxide Inorganic materials 0.000 description 7
- 150000004706 metal oxides Chemical class 0.000 description 7
- 229910000510 noble metal Inorganic materials 0.000 description 7
- 239000000047 product Substances 0.000 description 7
- 238000000851 scanning transmission electron micrograph Methods 0.000 description 7
- 239000000446 fuel Substances 0.000 description 6
- MVFCKEFYUDZOCX-UHFFFAOYSA-N iron(2+);dinitrate Chemical compound [Fe+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O MVFCKEFYUDZOCX-UHFFFAOYSA-N 0.000 description 6
- 239000007864 aqueous solution Substances 0.000 description 5
- 230000000694 effects Effects 0.000 description 5
- 239000011521 glass Substances 0.000 description 5
- 238000011068 loading method Methods 0.000 description 5
- 239000011148 porous material Substances 0.000 description 5
- 239000010948 rhodium Substances 0.000 description 5
- 229910052726 zirconium Inorganic materials 0.000 description 5
- 229910002651 NO3 Inorganic materials 0.000 description 4
- 229910021536 Zeolite Inorganic materials 0.000 description 4
- 230000008859 change Effects 0.000 description 4
- HNPSIPDUKPIQMN-UHFFFAOYSA-N dioxosilane;oxo(oxoalumanyloxy)alumane Chemical compound O=[Si]=O.O=[Al]O[Al]=O HNPSIPDUKPIQMN-UHFFFAOYSA-N 0.000 description 4
- 150000002739 metals Chemical class 0.000 description 4
- 238000002156 mixing Methods 0.000 description 4
- 229910052759 nickel Inorganic materials 0.000 description 4
- 238000002360 preparation method Methods 0.000 description 4
- 229910052723 transition metal Inorganic materials 0.000 description 4
- 150000003624 transition metals Chemical class 0.000 description 4
- 239000010457 zeolite Substances 0.000 description 4
- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 description 3
- 238000002441 X-ray diffraction Methods 0.000 description 3
- 229910052784 alkaline earth metal Inorganic materials 0.000 description 3
- 150000001342 alkaline earth metals Chemical class 0.000 description 3
- 239000002585 base Substances 0.000 description 3
- 238000001354 calcination Methods 0.000 description 3
- 229910000420 cerium oxide Inorganic materials 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 230000006872 improvement Effects 0.000 description 3
- 239000000203 mixture Substances 0.000 description 3
- BMMGVYCKOGBVEV-UHFFFAOYSA-N oxo(oxoceriooxy)cerium Chemical compound [Ce]=O.O=[Ce]=O BMMGVYCKOGBVEV-UHFFFAOYSA-N 0.000 description 3
- 229910052697 platinum Inorganic materials 0.000 description 3
- 238000011946 reduction process Methods 0.000 description 3
- 229910052703 rhodium Inorganic materials 0.000 description 3
- 239000011232 storage material Substances 0.000 description 3
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 2
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 2
- -1 Pt and Rh Chemical class 0.000 description 2
- MCMNRKCIXSYSNV-UHFFFAOYSA-N Zirconium dioxide Chemical compound O=[Zr]=O MCMNRKCIXSYSNV-UHFFFAOYSA-N 0.000 description 2
- 229910052783 alkali metal Inorganic materials 0.000 description 2
- 150000001340 alkali metals Chemical class 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 2
- 210000004027 cell Anatomy 0.000 description 2
- 239000011247 coating layer Substances 0.000 description 2
- 238000002485 combustion reaction Methods 0.000 description 2
- 229910052878 cordierite Inorganic materials 0.000 description 2
- 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 2
- 229910001873 dinitrogen Inorganic materials 0.000 description 2
- 230000003993 interaction Effects 0.000 description 2
- 238000011084 recovery Methods 0.000 description 2
- 230000036962 time dependent Effects 0.000 description 2
- 238000011144 upstream manufacturing Methods 0.000 description 2
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 description 1
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- 229910017493 Nd 2 O 3 Inorganic materials 0.000 description 1
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 1
- 239000003463 adsorbent Substances 0.000 description 1
- 238000005054 agglomeration Methods 0.000 description 1
- 230000002776 aggregation Effects 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- 235000011114 ammonium hydroxide Nutrition 0.000 description 1
- 229910001566 austenite Inorganic materials 0.000 description 1
- 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 1
- ITHZDDVSAWDQPZ-UHFFFAOYSA-L barium acetate Chemical compound [Ba+2].CC([O-])=O.CC([O-])=O ITHZDDVSAWDQPZ-UHFFFAOYSA-L 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- CETPSERCERDGAM-UHFFFAOYSA-N ceric oxide Chemical compound O=[Ce]=O CETPSERCERDGAM-UHFFFAOYSA-N 0.000 description 1
- GWXLDORMOJMVQZ-UHFFFAOYSA-N cerium Chemical group [Ce] GWXLDORMOJMVQZ-UHFFFAOYSA-N 0.000 description 1
- 229910000422 cerium(IV) oxide Inorganic materials 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 239000008119 colloidal silica Substances 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000008034 disappearance Effects 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 238000001704 evaporation Methods 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- JEGUKCSWCFPDGT-UHFFFAOYSA-M hydroxide;hydrate Chemical compound O.[OH-] JEGUKCSWCFPDGT-UHFFFAOYSA-M 0.000 description 1
- 229910052809 inorganic oxide Inorganic materials 0.000 description 1
- 238000005342 ion exchange Methods 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 230000007774 longterm Effects 0.000 description 1
- 238000004643 material aging Methods 0.000 description 1
- 150000002736 metal compounds Chemical class 0.000 description 1
- 239000011259 mixed solution Substances 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 230000001376 precipitating effect Effects 0.000 description 1
- 239000002243 precursor Substances 0.000 description 1
- 229910052761 rare earth metal Inorganic materials 0.000 description 1
- 150000002910 rare earth metals Chemical class 0.000 description 1
- 238000010992 reflux Methods 0.000 description 1
- 238000011160 research Methods 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
- 239000011163 secondary particle Substances 0.000 description 1
- 238000005245 sintering Methods 0.000 description 1
- 239000006104 solid solution Substances 0.000 description 1
- RXSHXLOMRZJCLB-UHFFFAOYSA-L strontium;diacetate Chemical compound [Sr+2].CC([O-])=O.CC([O-])=O RXSHXLOMRZJCLB-UHFFFAOYSA-L 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 238000003878 thermal aging Methods 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
- 229910000859 α-Fe Inorganic materials 0.000 description 1
Classifications
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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
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
- Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
Landscapes
- Exhaust Gas After Treatment (AREA)
- Exhaust Gas Treatment By Means Of Catalyst (AREA)
- Catalysts (AREA)
Abstract
Description
本発明は、排気ガス浄化用触媒に関する。 The present invention relates to an exhaust gas purification catalyst.
軽油を主成分とする燃料を用いるディーゼルエンジンや、ガソリンを主成分とする燃料を用いて希薄燃焼させるリーンバーンガソリンエンジンのような希薄燃焼式エンジンでは、その排気ガス中にＮＯｘ（窒素酸化物）が多く含まれる。そこで、排気ガスの酸素濃度が高いときに排気ガス中のＮＯｘを吸蔵し、その酸素濃度が低下したときに当該ＮＯｘを放出するＮＯｘトラップ材を設け、放出するＮＯｘを排気ガス中のＨＣ（炭化水素）と反応させることにより還元するようにした、所謂ＮＯｘ吸蔵還元型触媒が一般に知られている。 NOx (nitrogen oxide) is contained in the exhaust gas of a lean combustion engine such as a diesel engine using a fuel mainly composed of light oil or a lean burn gasoline engine that performs a lean combustion using a fuel mainly composed of gasoline. Many are included. Therefore, a NOx trap material that stores NOx in the exhaust gas when the oxygen concentration of the exhaust gas is high and releases the NOx when the oxygen concentration decreases is provided, and the released NOx is converted into HC (carbonized carbon) in the exhaust gas. So-called NOx occlusion reduction type catalysts which are reduced by reacting with (hydrogen) are generally known.
このＮＯｘ吸蔵還元型触媒は、一般には、アルミナ、酸素吸蔵放出能をもつＣｅ含有酸化物、触媒金属としてのＰｔやＲｈ、並びにＮＯｘトラップ材としてのアルカリ金属やアルカリ土類金属を含有する。そのＰｔを担持したアルミナは、排気ガス中のＮＯをＮＯ２に酸化することでＮＯｘトラップ材に吸蔵され易くする。例えば、ＮＯｘトラップ材としてＢａを採用した場合、Ｂａ(ＮＯ３)２となってＮＯｘが吸蔵される。Ｃｅ含有酸化物は、ＰｔやＲｈの酸化還元状態をコントロールしてＮＯｘ浄化を促進するとともに、ＮＯｘを捕捉する働きも有する。しかし、このＣｅ含有酸化物によるＮＯｘの捕捉は、Ｂａ等のＮＯｘトラップ材とは違って、ＮＯｘの表面吸着を主体にしていると考えられ、Ｃｅ含有酸化物の比表面積はそれほど大きくないことから、ＮＯｘを多量に吸着することはできないと考えられている。 This NOx storage-reduction catalyst generally contains alumina, a Ce-containing oxide having oxygen storage / release ability, Pt and Rh as catalyst metals, and alkali metals and alkaline earth metals as NOx trap materials. Its Pt alumina carrying is easily occluded in the NOx trap material by oxidizing NO in the exhaust gas to NO 2. For example, when Ba is adopted as the NOx trap material, it becomes Ba (NO 3 ) 2 and NOx is occluded. The Ce-containing oxide controls NOx reduction of Pt and Rh to promote NOx purification and also has a function of capturing NOx. However, unlike NOx trap materials such as Ba, NOx trapping by this Ce-containing oxide is considered to be mainly due to the surface adsorption of NOx, and the specific surface area of the Ce-containing oxide is not so large. It is believed that NOx cannot be adsorbed in large amounts.
ところで、近年はＰｔ、Ｒｈ等の希少金属の資源保護のため、触媒中へのこれら触媒金属の含有量を低減する研究が活発化している。 By the way, in recent years, in order to protect resources of rare metals such as Pt and Rh, research for reducing the content of these catalytic metals in the catalyst has been activated.
例えば特許文献１には、触媒金属量を増大させることなく、酸素吸蔵材の酸素吸蔵放出能を向上させるようにした触媒の例が記載されている。それは、セリウム酸化物を含む担体と、この担体に担持された遷移金属及び貴金属からなる触媒金属とよりなり、セリウム原子及び貴金属各々に対する遷移金属の原子比を所定の範囲にするというものである。遷移金属としては、Ｃｏ、Ｎｉ及びＦｅの少なくとも一種が好ましいとされている。但し、実施例として開示されているのはＣｏ及びＮｉだけであり、Ｆｅについての実施例はない。 For example, Patent Document 1 describes an example of a catalyst that improves the oxygen storage / release capability of an oxygen storage material without increasing the amount of catalyst metal. It consists of a support containing cerium oxide and a catalyst metal comprising a transition metal and a noble metal supported on the support, and the atomic ratio of the transition metal to each of the cerium atom and the noble metal is within a predetermined range. As the transition metal, at least one of Co, Ni and Fe is considered preferable. However, only Co and Ni are disclosed as examples, and there is no example about Fe.
また、特許文献１では、セリアジルコニア固溶体粉末に硝酸Ｎｉ（又は硝酸Ｃｏ）を含浸させ、蒸発乾固、乾燥及び焼成を行ない、得られた粉末にＰｔ溶液を含浸させ、蒸発乾固、乾燥及び焼成を行なうことにより触媒粉末を得るとされている。そして、この触媒粉末とＲｈ／ＺｒＯ２粉末とＡｌ２Ｏ３粉末とアルミナゾルとイオン交換水とを混合してスラリーを調製し、このスラリーをハニカム担体にウォッシュコートして触媒層を形成するとされている。 In Patent Document 1, ceria zirconia solid solution powder is impregnated with Ni nitrate (or Co nitrate), evaporated to dryness, dried and fired, and the obtained powder is impregnated with Pt solution, evaporated to dryness, dried and dried. It is said that catalyst powder is obtained by firing. The catalyst powder, Rh / ZrO 2 powder, Al 2 O 3 powder, alumina sol, and ion exchange water are mixed to prepare a slurry, and this slurry is washed on a honeycomb carrier to form a catalyst layer. Yes.
特許文献２には、ＣｅＯ２−ＺｒＯ２複合酸化物よりなる担体と、該担体に担持されたＡｌ、Ｎｉ及びＦｅから選ばれる少なくとも一種の金属酸化物粒子と、該担体に担持された貴金属とからなる排気ガス浄化用触媒が開示されている。担体上での貴金属の移動を金属酸化物粒子によって規制することにより、貴金属のシンタリングを抑制するというものである。但し、実施例として開示されている金属酸化物粒子はＡｌ２Ｏ３のみであり、ＣｅＯ２−ＺｒＯ２複合酸化物と硝酸Ａｌ水溶液とを混合し、これにアンモニア水を滴下・中和して沈殿を析出させ、濾過・洗浄・乾燥・焼成を行ない、得られた粉末にＰｔ溶液を含浸させ、蒸発乾固、乾燥及び焼成を行なうことにより触媒粉末を得るとされている。Ｎｉ及びＦｅについての実施例はない。 Patent Document 2 discloses a support made of a CeO 2 —ZrO 2 composite oxide, at least one metal oxide particle selected from Al, Ni, and Fe supported on the support, and a noble metal supported on the support. An exhaust gas purifying catalyst is disclosed. By restricting the movement of the noble metal on the support by the metal oxide particles, sintering of the noble metal is suppressed. However, the metal oxide particles disclosed as examples are only Al 2 O 3 , CeO 2 —ZrO 2 composite oxide and Al nitrate aqueous solution are mixed, and ammonia water is dropped and neutralized thereto. It is said that a catalyst powder is obtained by precipitating a precipitate, filtering, washing, drying and calcining, impregnating the obtained powder with a Pt solution, and evaporating to dryness, drying and calcining. There are no examples for Ni and Fe.
また、特許文献３には、Ｆｅ及び／又はＣｅを含有するβゼオライトを含む第一触媒層（上層）と、貴金属と酸化セリウム系材料とを含む第二触媒層（下層）とを有するＮＯｘ浄化触媒が記載されている。これは、上述のＮＯｘ吸蔵還元型触媒とは異なり、排気ガスの空燃比をリーンにして、排気ガス中のＮＯを第一触媒層の貴金属によりＮＯ２に酸化させて酸化セリウム系材料に吸着させ、次いで排気ガスの空燃比をリッチにすることにより、当該吸着ＮＯ２をＮＨ３に還元させて第一触媒層のゼオライトに吸着させ、再び排気ガスの空燃比をリーンにすることにより、上記ＮＨ３と排気ガス中のＮＯｘとを反応させてＮ２とＨ２Ｏとに転化するというものである。従来のゼオライトを含有するリーンＮＯｘ浄化触媒においては、Ｐｔがゼオライトに担持ないしはイオン交換されているケースが多いが、Ｐｔの一部をＦｅ又はＣｅで置き換えることができるならば、Ｐｔの使用量を低減することができる。
ところで、酸化鉄は、ＣｅＯ２と同じく、酸素吸蔵放出能を有することが知られている。従って、特許文献１，２に記載されているＣｅＯ２−ＺｒＯ２複合酸化物のようなＣｅ含有酸化物粒子に酸化鉄を担持させることが考えられる。そこで、本願発明者は、Ｃｅ含有酸化物粉末に硝酸鉄を含浸させて蒸発乾固、乾燥及び焼成を行ない、得られた粉末の酸素吸蔵放出能を調べた。その結果、酸素吸蔵放出能の向上が認められたものの、その向上はそれほど大きなものではなく、また、長期の使用を想定した所定の熱エージングを行なったところ、酸素吸蔵放出能がかなり低いレベルまで低下することがわかった。また、上記硝酸鉄により得られる酸化鉄粒子はその粒径が５００ｎｍ以上の大きな粒子であることがわかった。 By the way, it is known that iron oxide has an oxygen storage / release capability like CeO 2 . Therefore, it is conceivable that iron oxide is supported on Ce-containing oxide particles such as CeO 2 —ZrO 2 composite oxides described in Patent Documents 1 and 2 . Therefore, the inventors of the present application impregnated Ce-containing oxide powder with iron nitrate, evaporated to dryness, dried and fired, and examined the oxygen storage / release ability of the obtained powder. As a result, although an improvement in the oxygen storage / release capability was observed, the improvement was not so great, and when the prescribed thermal aging was performed assuming long-term use, the oxygen storage / release capability was reduced to a considerably low level. It turns out that it falls. Moreover, it turned out that the iron oxide particle obtained by the said iron nitrate is a big particle | grain whose particle size is 500 nm or more.
また、本願発明者は、酸素吸蔵放出能を有するＣｅ含有酸化物がＮＯｘ吸着能を有することから、同じく酸素吸蔵放出能を有する酸化鉄がＮＯｘの吸着に何らかの効果を発現するのではないかという点に着眼し、Ｃｅ含有酸化物に硝酸鉄を含浸させて、ＮＯｘ吸着能を評価した。その結果、硝酸鉄を含浸担持させると、ＮＯｘ吸着能が幾分向上するものの、大きな向上効果は望めなかった。 In addition, the present inventor said that the Ce-containing oxide having oxygen storage / release ability has NOx adsorption ability, so that iron oxide having the same oxygen storage / release ability may have some effect on NOx adsorption. Focusing on the point, the NOx adsorption ability was evaluated by impregnating Ce-containing oxide with iron nitrate. As a result, when iron nitrate was impregnated and supported, the NOx adsorption ability was somewhat improved, but a great improvement effect could not be expected.
以上の説明から明らかなように、本発明の課題は、酸化鉄を有効に利用して触媒のＮＯｘ浄化性能を高める、特に排気ガス温度が低い低温時から高温時まで広い温度範囲にわたってＮＯｘを効率良く浄化できるようにすることにある。 As is apparent from the above description, the object of the present invention is to effectively utilize iron oxide to improve the NOx purification performance of the catalyst. In particular, the efficiency of NOx is improved over a wide temperature range from a low exhaust gas temperature to a high temperature. There is to be able to clean well.
また、従来より、ＮＯｘ浄化触媒では、ＮＯｘトラップ材の硫黄被毒による性能低下が問題になっている点に鑑み、本発明は、ＮＯｘ浄化触媒の耐硫黄被毒性を改善することを課題とする。 Further, in view of the problem that the NOx purification catalyst has a problem in that the NOx trapping material is poisoned by sulfur poisoning, it is an object of the present invention to improve the sulfur poisoning resistance of the NOx purification catalyst. .
また、ＮＯｘ浄化触媒では、排気ガスの空燃比がリーンからリッチ側へ変化しＮＯｘトラップ材からＮＯｘが放出されたときに、該ＮＯｘがＮＨ３に還元されて排出されてしまう点に鑑み、本発明は、そのＮＨ３の排出を抑制することも課題とする。 Further, in the NOx purification catalyst, in view of the fact that when the air-fuel ratio of the exhaust gas changes from lean to rich and NOx is released from the NOx trap material, the NOx is reduced to NH 3 and discharged. Another object of the invention is to suppress the discharge of NH 3 .
また、別の本発明の課題は、酸化鉄を、上記ＮＯｘ浄化に利用するだけでなく、担体に触媒層を形成するためのバインダとしても利用することにある。 Another object of the present invention is to use iron oxide not only for the NOx purification, but also as a binder for forming a catalyst layer on the carrier.
本発明は、このような課題を解決するために、粒径の小さな微細酸化鉄粒子を触媒層に多数分散させるようにした。 In the present invention, in order to solve such problems, a large number of fine iron oxide particles having a small particle diameter are dispersed in the catalyst layer.
すなわち、本発明は、担体上に、酸素吸蔵放出能をもつＣｅ含有酸化物粒子と、該Ｃｅ含有酸化物粒子以外のＮＯｘトラップ材と、触媒金属とを有する触媒層が形成されている排気ガス浄化用触媒であって、
上記触媒層には、酸化鉄粒子が多数分散して含まれ、少なくとも一部の酸化鉄粒子は粒径が３００ｎｍ以下の微細酸化鉄粒子であり、上記Ｃｅ含有酸化物粒子及びＮＯｘトラップ材に当該微細酸化鉄粒子が接触しており、電子顕微鏡観察において、上記微細酸化鉄粒子の酸化鉄粒子総面積に占める面積比率が３０％以上であることを特徴とする。
That is, the present invention provides an exhaust gas in which a catalyst layer comprising Ce-containing oxide particles having oxygen storage / release capability, a NOx trap material other than the Ce-containing oxide particles, and a catalyst metal is formed on a carrier. A purification catalyst,
The catalyst layer includes a large number of dispersed iron oxide particles, at least some of the iron oxide particles are fine iron oxide particles having a particle size of 300 nm or less, and the Ce-containing oxide particles and the NOx trap material The fine iron oxide particles are in contact with each other, and the area ratio of the fine iron oxide particles to the total area of the iron oxide particles is 30% or more in observation with an electron microscope.
上記粒径３００ｎｍ以下の微細酸化鉄粒子の酸化鉄粒子総面積に占める面積比率が３０％以上であるということは、この微細酸化鉄粒子が触媒層に多数分散して含まれていることを意味する。また、上記Ｃｅ含有酸化物粒子はその二次粒子径が数μｍであることが通常であるから、少なくとも一部のＣｅ含有酸化物粒子には、複数の微細酸化鉄粒子が分散して接触しており、且つ該Ｃｅ含有酸化物粒子に対する微細酸化鉄粒子の付着量が比較的多いことを意味する。そうして、後述の実施例で明らかになるが、本発明によれば、触媒のＮＯｘ浄化性能が高くなるとともに、耐硫黄被毒性が高まり、さらに、ＮＨ３の排出が抑制される。 That the area ratio of the fine iron oxide particles having a particle size of 300 nm or less to the total area of the iron oxide particles is 30% or more means that a large number of fine iron oxide particles are dispersed in the catalyst layer. To do. Further, since the Ce-containing oxide particles usually have a secondary particle diameter of several μm, at least some of the Ce-containing oxide particles are dispersed and contacted with a plurality of fine iron oxide particles. And the amount of fine iron oxide particles attached to the Ce-containing oxide particles is relatively large. Thus, as will be apparent from the examples described later, according to the present invention, the NOx purification performance of the catalyst is enhanced, the sulfur poisoning resistance is increased, and the emission of NH 3 is further suppressed.
その理由は明確ではないが、上述の硝酸鉄から得られる酸化鉄粒子は、その粒径が５００ｎｍ以上の大きな粒子であることから、Ｃｅ含有酸化物粒子との相互作用を発現し難いと考えられる。また、Ｃｅ含有酸化物粒子の表面ないし細孔に付着した硝酸鉄が、触媒焼成に伴って酸化鉄に変化し、凝集・粒成長することにより、さらにはその後の高温の排気ガスに晒されて凝集・粒成長することにより、Ｃｅ含有酸化物粒子の表面積の低下を招く、と推察される。 The reason for this is not clear, but the iron oxide particles obtained from the iron nitrate described above are large particles having a particle size of 500 nm or more, and therefore, it is considered difficult to express the interaction with the Ce-containing oxide particles. . In addition, iron nitrate adhering to the surface or pores of Ce-containing oxide particles is changed to iron oxide as the catalyst is fired, and is aggregated and grain-grown, and further exposed to high-temperature exhaust gas thereafter. It is presumed that the surface area of the Ce-containing oxide particles is reduced by agglomeration and grain growth.
これに対して、本発明の場合は、上述の如く粒径３００ｎｍ以下の微細酸化鉄粒子がＣｅ含有酸化物粒子及びＮＯｘトラップ材各々に分散して接触しているから、Ｃｅ含有酸化物粒子やＮＯｘトラップ材と酸化鉄粒子との相互作用を発現し易くなっていると考えられる。そのため、触媒金属量が少ない場合でも、その微細酸化鉄粒子がＣｅ含有酸化物粒子と相俟って触媒層の酸素吸蔵放出能の向上に有効に働くと考えられる。また、Ｃｅ含有酸化物粒子に接触している微細酸化鉄粒子が該Ｃｅ含有酸化物粒子の塩基性を強くして、そのＮＯｘ吸着能を高め、ＮＯｘの還元浄化に有利になっていると考えられる。また、後にデータで説明するが、微細酸化鉄粒子は、硫黄成分の吸着及びＮＨ３吸着にも寄与しており、そのため、ＮＯｘトラップ材の硫黄被毒が抑制され、さらに、ＮＨ３の排出が抑制される。従って、本発明に係る触媒はリーンＮＯｘ触媒として有用である。 On the other hand, in the case of the present invention, as described above, fine iron oxide particles having a particle size of 300 nm or less are dispersed and in contact with the Ce-containing oxide particles and the NOx trap material. It is considered that the interaction between the NOx trap material and the iron oxide particles is easily developed. Therefore, even when the amount of catalytic metal is small, it is considered that the fine iron oxide particles work together with the Ce-containing oxide particles to effectively improve the oxygen storage / release capacity of the catalyst layer. Further, it is considered that fine iron oxide particles in contact with Ce-containing oxide particles strengthen the basicity of the Ce-containing oxide particles, increase their NOx adsorption ability, and are advantageous for NOx reduction and purification. It is done. As will be described later in the data, the fine iron oxide particles contribute to the adsorption of sulfur components and the adsorption of NH 3. Therefore, sulfur poisoning of the NOx trap material is suppressed, and further, the emission of NH 3 is reduced. It is suppressed. Therefore, the catalyst according to the present invention is useful as a lean NOx catalyst.
上記微細酸化鉄粒子の酸化鉄粒子総面積に占める面積比率は４０％以上であることが好ましい。粒径５０ｎｍ以上３００ｎｍ以下の酸化鉄粒子についてみれば、酸化鉄粒子総面積に占める面積比率が４０％以上９５％以下程度であることが好ましい。 The area ratio of the fine iron oxide particles to the total iron oxide particle area is preferably 40% or more. In view of iron oxide particles having a particle size of 50 nm or more and 300 nm or less, the area ratio in the total area of the iron oxide particles is preferably about 40% or more and 95% or less.
上記微細酸化鉄粒子は、上記触媒層において上記Ｃｅ含有酸化物粒子等を上記担体に保持するバインダの少なくとも一部を構成するものとすることができる。すなわち、触媒一般におけるバインダについては次のように定義することができる。
Ａ．バインダは、担体にウォッシュコートするスラリーに粘性を与えることにより、触媒金属を担持する酸素吸蔵材、その他の助触媒粒子をスラリー中に均一に分散させるとともに、乾燥・焼成前のウォッシュコート層を担体に安定した状態に保持する。
The fine iron oxide particles may constitute at least a part of a binder that holds the Ce-containing oxide particles and the like on the carrier in the catalyst layer. That is, the binder in general catalysts can be defined as follows.
A. The binder uniformly disperses the oxygen storage material and other promoter particles supporting the catalyst metal in the slurry by imparting viscosity to the slurry to be coated on the carrier, and the washcoat layer before drying and firing is supported on the carrier. To keep it stable.
そのため、粒径が１ｎｍ〜５０ｎｍ程度のコロイド粒子（水酸化物、含水物、酸化物等）が分散したコロイド溶液（市販のアルミナゾルやコロイダルシリカではコロイド粒子の粒径は１０ｎｍ〜３０ｎｍ程度）がバインダとして一般に使用される。
Ｂ．バインダは、上記乾燥・焼成後は微粒子となって触媒層に略均一に分散し、上記助触媒粒子間に介在して該助触媒粒子同士を結合するとともに、担体表面の多数の微小凹部ないし細孔に入り、触媒層が担体から剥離しないようにする（アンカー効果）。
Therefore, a colloidal solution in which colloidal particles (hydroxide, hydrate, oxide, etc.) having a particle size of about 1 nm to 50 nm are dispersed (in the case of commercially available alumina sol or colloidal silica, the particle size of the colloidal particles is about 10 nm to 30 nm) is a binder. As commonly used.
B. The binder is finely dispersed in the catalyst layer after drying and firing, and is substantially uniformly dispersed in the catalyst layer. The binder is interposed between the promoter particles and bonds the promoter particles to each other. Enter the hole so that the catalyst layer does not peel from the carrier (anchor effect).
そのため、乾燥・焼成後において、助触媒粒子よりも粒径が小さな酸化物粒子となって助触媒粒子や担体に固着するものがバインダとして一般に使用される。
Ｃ．触媒層に、触媒金属やＮＯｘ吸蔵材、ＨＣ吸着材等が後から含浸担持されるケースでは、バインダはそれら触媒成分を担持するサポート材となる。
Ｄ．バインダ粒子間、バインダ粒子と助触媒粒子との間には排気ガスが通る微細孔が形成される。
Ｅ．触媒層におけるバインダ量は、一般には触媒層全体の５質量％〜２０質量％とされる。
Therefore, what is fixed to the promoter particles or the carrier in the form of oxide particles having a particle diameter smaller than that of the promoter particles after drying and firing is generally used as the binder.
C. In the case where the catalyst layer is impregnated and supported with catalyst metal, NOx occlusion material, HC adsorbent, etc., the binder serves as a support material for supporting these catalyst components.
D. Micropores through which exhaust gas passes are formed between the binder particles and between the binder particles and the promoter particles.
E. The amount of binder in the catalyst layer is generally 5% by mass to 20% by mass of the entire catalyst layer.
本発明の場合、上記粒径３００ｎｍ以下の微細酸化鉄粒子は、上記Ｃｅ含有酸化物粒子等の助触媒粒子の平均粒径（数μｍ程度）よりも小さく、上記触媒層に略均一に分散し、上記助触媒粒子間に介在して該助触媒粒子同士を結合するとともに、担体表面の多数の微小凹部ないし細孔に入り、触媒層が担体から剥離しないようにする。このため、当該微細酸化鉄粒子は上記触媒層においてバインダとしての機能も発揮するものである。 In the case of the present invention, the fine iron oxide particles having a particle diameter of 300 nm or less are smaller than the average particle diameter (about several μm) of the promoter particles such as the Ce-containing oxide particles, and are dispersed substantially uniformly in the catalyst layer. The cocatalyst particles are bonded to each other by interposing between the cocatalyst particles, and the catalyst layer is prevented from peeling from the support by entering a large number of minute recesses or pores on the support surface. For this reason, the said fine iron oxide particle also exhibits the function as a binder in the said catalyst layer.
上記触媒層のバインダは、上記微細酸化鉄粒子のみで構成するようにしてよいが、安定な触媒層を得るために、この微細酸化鉄粒子の他に、遷移金属及び希土類金属から選ばれる少なくとも一種の金属の酸化物粒子（例えば、アルミナ粒子、ＺｒＯ２粒子、ＣｅＯ２粒子等）をバインダとして含ませるようにしてもよい。このようなバインダ粒子（上記微細酸化鉄粒子及び上記金属酸化物粒子）は、担体にウォッシュコートするスラリーに粘性を与えることにより、触媒成分をスラリー中に均一に分散させるとともに、乾燥・焼成前のウォッシュコート層を担体に安定した状態で保持することができるように、前駆体である金属化合物がそれぞれコロイド粒子として分散したゾルを原料とすることが好ましい。 The binder of the catalyst layer may be composed only of the fine iron oxide particles, but in order to obtain a stable catalyst layer, in addition to the fine iron oxide particles, at least one selected from transition metals and rare earth metals These metal oxide particles (for example, alumina particles, ZrO 2 particles, CeO 2 particles, etc.) may be included as a binder. Such binder particles (the fine iron oxide particles and the metal oxide particles) impart viscosity to the slurry to be coated on the carrier to uniformly disperse the catalyst component in the slurry, and before drying / calcination. It is preferable to use a sol in which the precursor metal compound is dispersed as colloidal particles, so that the washcoat layer can be stably held on the carrier.
上記微細酸化鉄粒子の少なくとも一部はヘマタイトであることが好ましく、また、上記酸化鉄粒子は、マグヘマイト、ゲータイト及びウスタイトがコロイド粒子として分散したゾルを原料とすることが好ましい。 At least a part of the fine iron oxide particles is preferably hematite, and the iron oxide particles are preferably made from a sol in which maghemite, goethite and wustite are dispersed as colloidal particles.
また、上記ＮＯｘトラップ材としては、Ｂａに代表されるアルカリ土類金属やアルカリ金属を採用することができる。 Moreover, as the NOx trap material, an alkaline earth metal typified by Ba or an alkali metal can be employed.
以上のように本発明によれば、担体上に、酸素吸蔵放出能をもつＣｅ含有酸化物粒子と、該Ｃｅ含有酸化物粒子以外のＮＯｘトラップ材と、触媒金属とを有する触媒層が形成されている排気ガス浄化用触媒において、上記触媒層には、上記Ｃｅ含有酸化物粒子及びＮＯｘトラップ材に接触する粒径３００ｎｍ以下の微細酸化鉄粒子が多数分散して含まれているから、触媒のＮＯｘ浄化性能が高くなるとともに、耐硫黄被毒性が高まり、さらに、ＮＨ３の排出が抑制される。 As described above, according to the present invention, a catalyst layer including Ce-containing oxide particles having oxygen storage / release ability, a NOx trap material other than the Ce-containing oxide particles, and a catalyst metal is formed on the support. In the exhaust gas purifying catalyst, the catalyst layer contains a large number of fine iron oxide particles having a particle size of 300 nm or less in contact with the Ce-containing oxide particles and the NOx trap material. While NOx purification performance is enhanced, sulfur poisoning resistance is increased, and further, NH 3 emissions are suppressed.
以下、本発明の実施形態を図面に基づいて説明する。尚、以下の好ましい実施形態の説明は、本質的に例示に過ぎず、本発明、その適用物或いはその用途を制限することを意図するものではない。 Hereinafter, embodiments of the present invention will be described with reference to the drawings. It should be noted that the following description of the preferred embodiment is merely illustrative in nature, and is not intended to limit the present invention, its application, or its use.
図１に、本発明に係る排気ガス浄化用触媒の一例として、自動車の排気ガス中のＮＯｘを浄化するリーンＮＯｘ触媒（ＮＯｘ吸蔵還元型触媒）を模式的に示す。同図において、１は無機酸化物によるハニカム担体のセル壁、２はセル壁１に形成された触媒層である。触媒層２は、酸素吸蔵放出能を持つＣｅ含有酸化物粒子３と、バインダ粒子４と、Ｆｅ以外の触媒金属５とを有し、図例では、Ｃｅ含有酸化物粒子３以外の助触媒粒子として、さらにアルミナ粒子６及びＮＯｘトラップ材８を有する。なお、触媒層２には、Ｃｅ含有酸化物粒子３及びアルミナ粒子６以外に、ＮＯｘ吸蔵材など他の助触媒粒子を含ませることができる。バインダ粒子４は、Ｃｅ含有酸化物粒子３及びアルミナ粒子６各々の平均粒径よりも小さな金属酸化物粒子よりなり、少なくとも一部のバインダ粒子４は粒径３００ｎｍ以下の微細酸化鉄粒子で構成されている。すなわち、当該微細酸化鉄粒子と他の金属酸化物粒子とを組み合わせてバインダとすることもできる。 FIG. 1 schematically shows a lean NOx catalyst (NOx occlusion reduction type catalyst) that purifies NOx in automobile exhaust gas as an example of an exhaust gas purification catalyst according to the present invention. In the figure, 1 is a cell wall of a honeycomb carrier made of an inorganic oxide, and 2 is a catalyst layer formed on the cell wall 1. The catalyst layer 2 includes Ce-containing oxide particles 3 having an oxygen storage / release capability, binder particles 4, and catalyst metals 5 other than Fe. In the illustrated example, promoter particles other than Ce-containing oxide particles 3. As a further example, alumina particles 6 and a NOx trap material 8 are included. In addition to the Ce-containing oxide particles 3 and the alumina particles 6, the catalyst layer 2 can contain other promoter particles such as a NOx storage material. The binder particles 4 are made of metal oxide particles smaller than the average particle size of each of the Ce-containing oxide particles 3 and the alumina particles 6, and at least some of the binder particles 4 are composed of fine iron oxide particles having a particle size of 300 nm or less. ing. That is, the fine iron oxide particles and other metal oxide particles can be combined to form a binder.
上記微細酸化鉄粒子を含むバインダ粒子４は、触媒層２の全体にわたって略均一に分散していて、助触媒粒子（Ｃｅ含有酸化物粒子３、アルミナ粒子６等）間に介在し該助触媒粒子同士を結合している。従って、少なくとも一部の微細酸化鉄粒子はＣｅ含有酸化物粒子３に接触している。また、上記バインダ粒子４は、担体セル壁１の表面ポア（微小凹部ないし細孔）７に充填され、アンカー効果によって触媒層２をセル壁１に保持している。触媒金属５は助触媒粒子（Ｃｅ含有酸化物粒子３、アルミナ粒子６等）に担持されている。 The binder particles 4 containing the fine iron oxide particles are substantially uniformly dispersed throughout the catalyst layer 2, and are interposed between the promoter particles (Ce-containing oxide particles 3, alumina particles 6, etc.). They are connected to each other. Accordingly, at least some of the fine iron oxide particles are in contact with the Ce-containing oxide particles 3. The binder particles 4 are filled in the surface pores (microscopic recesses or pores) 7 of the carrier cell wall 1 and hold the catalyst layer 2 on the cell wall 1 by an anchor effect. The catalyst metal 5 is supported on promoter particles (Ce-containing oxide particles 3, alumina particles 6 and the like).
＜触媒の調製＞
エタノール１００ｍＬ当たり硝酸第二鉄４０．４ｇを溶かし、９０℃から１００℃の温度で２時間から３時間の還流を行なうことによって、スラリー状の液体、すなわち、酸化鉄ゾル（バインダ）を得る。Ｃｅ含有酸化物粉末及び他の助触媒材料を混合し、これに酸化鉄ゾル及びイオン交換水を適量混合してスラリーとする。必要に応じて、他のバインダを添加する。上記スラリーを担体にコーティングし、乾燥及び焼成を施す。担体上にコーティング層に、触媒金属溶液、並びにＮＯｘトラップ材となるアルカリ土類金属等の溶液を含浸させ、乾燥及び焼成を行なう。以上により排気ガス浄化用触媒（リーンＮＯｘ触媒）が得られる。
<Preparation of catalyst>
By dissolving 40.4 g of ferric nitrate per 100 mL of ethanol and refluxing at a temperature of 90 ° C. to 100 ° C. for 2 to 3 hours, a slurry-like liquid, that is, an iron oxide sol (binder) is obtained. Ce-containing oxide powder and other promoter material are mixed, and an appropriate amount of iron oxide sol and ion-exchanged water is mixed with this to form a slurry. If necessary, other binder is added. The slurry is coated on a carrier, dried and fired. A coating layer is impregnated with a catalyst metal solution and a solution of an alkaline earth metal or the like serving as a NOx trap material on the support, followed by drying and firing. Thus, an exhaust gas purification catalyst (lean NOx catalyst) is obtained.
＜酸化鉄粒子の粒径等＞
上記酸化鉄ゾルとＣｅ含有酸化物粉末としてのＣｅＺｒＮｄ複合酸化物（ＣｅＯ２：ＺｒＯ２：Ｎｄ２Ｏ３＝２３：６７：１０（質量比））とイオン交換水とを混合することによりスラリーを調製し、このスラリーを基材にコーティングし、乾燥（１５０℃）及び焼成（大気中において５００℃の温度に２時間保持）を行なうことにより、触媒材を得た。酸化鉄ゾルとＣｅＺｒＮｄ複合酸化物粉末とは、上記焼成後における質量比で、酸化鉄とＣｅＺｒＮｄ複合酸化物とが２：８となるように混合した。
<Iron oxide particle size>
The slurry was prepared by mixing the iron oxide sol and CeZrNd composite oxide (CeO 2 : ZrO 2 : Nd 2 O 3 = 23: 67: 10 (mass ratio)) as Ce-containing oxide powder and ion-exchanged water. The catalyst material was obtained by preparing, coating this slurry on a base material, and performing drying (150 ° C.) and firing (maintaining at a temperature of 500 ° C. for 2 hours in the air). The iron oxide sol and the CeZrNd composite oxide powder were mixed so that the iron oxide and the CeZrNd composite oxide were in a mass ratio of 2: 8 after firing.
図２は得られた触媒材の透過電子顕微鏡を用いたＳＴＥＭ（走査透過）像、図３乃至図５はＦｅ、Ｚｒ及びＣｅ各原子の相対濃度分布をマッピングしたものである。図２乃至図５から、ＣｅＺｒＮｄ複合酸化物粒子の粒径は１μｍ程度であること、酸化鉄粒子は粒径が３００ｎｍ以下であり、５０ｎｍ以上３００ｎｍ以下の大きさの複数個の酸化鉄粒子がＣｅＺｒＮｄ複合酸化物粒子に接触（粒子上に分布）していることがわかる。この場合、当該顕微鏡観察において、粒径３００ｎｍ以下の微細酸化鉄粒子の酸化鉄粒子総面積に占める面積比率は１００％である（つまり、全ての酸化鉄粒子が粒径３００ｎｍ以下である）ということができる。 FIG. 2 is an STEM (scanning transmission) image of the obtained catalyst material using a transmission electron microscope, and FIGS. 3 to 5 are maps of relative concentration distributions of Fe, Zr and Ce atoms. From FIG. 2 to FIG. 5, the particle size of the CeZrNd composite oxide particles is about 1 μm, the iron oxide particles have a particle size of 300 nm or less, and a plurality of iron oxide particles having a size of 50 nm or more and 300 nm or less are CeZrNd. It can be seen that the composite oxide particles are in contact (distributed on the particles). In this case, in the microscopic observation, the area ratio of fine iron oxide particles having a particle diameter of 300 nm or less to the total area of iron oxide particles is 100% (that is, all iron oxide particles have a particle diameter of 300 nm or less). Can do.
図６乃至図９は上記触媒材のエージング（酸素を２％、水蒸気を１０％含む窒素ガス中で９００℃の温度に２４時間保持）後でのＳＴＥＭ像及び各原子の相対濃度分布のマッピングである。ＣｅＺｒＮｄ複合酸化物粒子の粒径は１μｍ程度であり、酸化鉄粒子の粒径は３００ｎｍ以下であり、５０ｎｍ以上３００ｎｍ以下の大きさの酸化鉄粒子がＣｅＺｒＮｄ複合酸化物粒子に複数個接触（粒子上に分布）している。エージング後においても、当該電子顕微鏡観察によれば、全ての酸化鉄粒子の粒径が３００ｎｍ以下になっている。 6 to 9 are mappings of the STEM image and the relative concentration distribution of each atom after aging of the above catalyst material (held at a temperature of 900 ° C. for 24 hours in nitrogen gas containing 2% oxygen and 10% water vapor). is there. The particle size of the CeZrNd composite oxide particles is about 1 μm, the particle size of the iron oxide particles is 300 nm or less, and a plurality of iron oxide particles having a size of 50 nm to 300 nm are in contact with the CeZrNd composite oxide particles (on the particle Distributed). Even after aging, according to the observation with the electron microscope, the particle diameter of all iron oxide particles is 300 nm or less.
図１０は酸化鉄ゾルを１５０℃で乾燥したもの（乾燥品）、上記エージング前の触媒材（焼成品）、並びに上記エージング後の触媒材（焼成・エージング品）各々のＸ線回折チャートである。なお、同図の「ＯＳＣ」は上記ＣｅＺｒＮｄ複合酸化物のことを意味する（この点は他の図面でも同様である。）。酸化鉄ゾルは、マグヘマイト（γ-Ｆｅ２Ｏ３）、ゲータイト（Ｆｅ３＋Ｏ(ＯＨ)）及びウスタイト（ＦｅＯ）がコロイド粒子として分散したものであることがわかる。そして、酸化鉄ゾルのコロイド粒子は焼成によってヘマタイト（α-Ｆｅ２Ｏ３）になっている。 FIG. 10 is an X-ray diffraction chart of the iron oxide sol dried at 150 ° C. (dried product), the catalyst material before aging (fired product), and the catalyst material after aging (fired / aged product). . In addition, “OSC” in the figure means the CeZrNd composite oxide (this is the same in other drawings). It can be seen that the iron oxide sol is one in which maghemite (γ-Fe 2 O 3 ), goethite (Fe 3+ O (OH)) and wustite (FeO) are dispersed as colloidal particles. The colloidal particles of the iron oxide sol are converted into hematite (α-Fe 2 O 3 ) by firing.
上記エージング前の焼成品におけるヘマタイトの、結晶面（１０４）のピーク強度を１００とする各結晶面の相対ピーク強度は表１に示す通りである。また、上記エージング後のヘマタイトの、結晶面（１０４）のピーク強度を１００とする各結晶面の相対ピーク強度は表２に示す通りである。なお、表中「−」はピーク重複や、ピーク小のために、正確な数値が得られなかったものである。 Table 1 shows the relative peak intensities of the crystal faces of hematite in the fired product before aging, with the peak intensity of the crystal face (104) being 100. Further, the relative peak intensity of each crystal plane with the peak intensity of the crystal plane (104) of the hematite after aging as 100 is shown in Table 2. Note that “−” in the table indicates that an exact numerical value could not be obtained due to peak overlap or small peak.
エージング後において、Ｘ線回折測定によって得られるヘマタイトの各結晶面のピーク強度は、結晶面（１０４）、結晶面（１１０）、結晶面（１１６）の順で小さくなっている。 After aging, the peak intensity of each crystal plane of hematite obtained by X-ray diffraction measurement decreases in the order of crystal plane (104), crystal plane (110), and crystal plane (116).
一方、比較のために、上記酸化鉄ゾルに代えて、硝酸第二鉄水溶液を上記ＣｅＺｒＮｄ複合酸化物粉末に含浸させ、同様の乾燥及び焼成を行なった。硝酸第二鉄とＣｅＺｒＮｄ複合酸化物粉末とは、上記焼成後における質量比で、酸化鉄とＣｅＺｒＮｄ複合酸化物とが２：８となるように混合した。 On the other hand, for comparison, the CeZrNd composite oxide powder was impregnated with the ferric nitrate aqueous solution instead of the iron oxide sol, and the same drying and firing were performed. The ferric nitrate and the CeZrNd composite oxide powder were mixed so that the iron oxide and the CeZrNd composite oxide were in a mass ratio of 2: 8 after firing.
図１１乃至図１４は得られた上記硝酸第二鉄による触媒材のＳＴＥＭ像及び各原子の相対濃度分布のマッピングである。ＣｅＺｒＮｄ複合酸化物粒子の粒径は１μｍ程度であるが、酸化鉄粒子の粒径は６００〜７００ｎｍ程度になっている。 FIG. 11 to FIG. 14 are mapping of the obtained STEM image of the catalyst material by ferric nitrate and the relative concentration distribution of each atom. The particle size of CeZrNd composite oxide particles is about 1 μm, while the particle size of iron oxide particles is about 600 to 700 nm.
図１５乃至図１８は上記硝酸第二鉄による触媒材のエージング（酸化鉄ゾルの場合と同じ条件）後でのＳＴＥＭ像及び各原子の相対濃度分布のマッピングである。ＣｅＺｒＮｄ複合酸化物粒子の粒径は１．５〜２μｍ程度であるが、酸化鉄粒子としては、粒径が６００〜７００ｎｍ程度の粒子が１個と、１００ｎｍ程度の粒子が３個見られる。当該電子顕微鏡観察において、粒径３００ｎｍ以下の酸化鉄粒子の酸化鉄粒子総面積に占める面積比率は１０％未満である。 15 to 18 are STEM images after mapping of the catalyst material with ferric nitrate (same conditions as in the case of iron oxide sol) and mapping of the relative concentration distribution of each atom. The particle size of the CeZrNd composite oxide particles is about 1.5 to 2 μm. As the iron oxide particles, one particle having a particle size of about 600 to 700 nm and three particles of about 100 nm are seen. In the electron microscope observation, the area ratio of the iron oxide particles having a particle size of 300 nm or less to the total iron oxide particle area is less than 10%.
上記酸化鉄ゾルの場合、焼成によって酸化鉄粒子となるコロイド粒子（マグヘマイト、ゲータイト及びウスタイト）が比較的安定なＦｅ化合物であり、そのために、酸化鉄粒子の粒成長を生じ難い。これに対して、上記硝酸第二鉄の場合は、反応性が高いＦｅイオンから酸化鉄粒子を生ずるから、粒成長し易い。このことが、上記酸化鉄ゾルから得られる酸化鉄粒子と上記硝酸第二鉄から得られる酸化鉄粒子の粒径の差違となっていると考えられる。 In the case of the iron oxide sol, colloidal particles (maghemite, goethite, and wustite) that become iron oxide particles upon firing are relatively stable Fe compounds, and therefore, iron oxide particle growth hardly occurs. On the other hand, in the case of ferric nitrate, iron oxide particles are generated from highly reactive Fe ions, so that the grains are easily grown. This is considered to be the difference in particle diameter between the iron oxide particles obtained from the iron oxide sol and the iron oxide particles obtained from the ferric nitrate.
＜酸素吸蔵放出能＞
上記酸化鉄ゾルを用いて調製した触媒サンプルＡと、上記硝酸第二鉄を用いて調製した触媒サンプルＢと、鉄成分を含まない触媒サンプルＣとについて、各々の酸素吸蔵放出能を調べた。但し、いずれのサンプルも触媒金属量は零とした。
<Oxygen storage and release ability>
Each of the catalyst samples A prepared using the iron oxide sol, the catalyst sample B prepared using the ferric nitrate, and the catalyst sample C containing no iron component were examined for oxygen storage / release capacity. However, the amount of catalyst metal in all samples was zero.
−触媒サンプルＡの調製−
上記ＣｅＺｒＮｄ複合酸化物と上記酸化鉄ゾルとＺｒＯ２バインダとイオン交換水とを混合することによりスラリーを調製し、このスラリーを担体にコーティングし、乾燥（１５０℃）及び焼成（大気中において５００℃の温度に２時間保持）を行なった。上記スラリーは、上記ＣｅＺｒＮｄ複合酸化物の担持量が８０ｇ／Ｌ、上記酸化鉄ゾルによる酸化鉄の担持量が２０ｇ／Ｌ、上記ＺｒＯ２バインダによるＺｒＯ２の担持量が１０ｇ／Ｌとなるように調製した。なお、各担持量は上記焼成後における上記担体１Ｌ当たりの各成分の量である。担体としては、セル壁厚さ３．５mil（８．８９×１０−２ｍｍ）、１平方インチ（６４５．１６ｍｍ２）当たりのセル数６００のコージェライト製ハニカム担体（容量２５ｍＬ）を採用した。
-Preparation of catalyst sample A-
A slurry is prepared by mixing the CeZrNd composite oxide, the iron oxide sol, the ZrO 2 binder, and ion-exchanged water. The slurry is coated on a support, dried (150 ° C.) and fired (500 ° C. in the air). For 2 hours). The slurry is such that the supported amount is 80 g / L of the CeZrNd mixed oxide, the supported amount of iron oxide by the iron oxide sol 20 g / L, the amount of supported ZrO 2 by the ZrO 2 binder is 10 g / L Prepared. Each supported amount is the amount of each component per 1 L of the carrier after the firing. As the carrier, a cordierite honeycomb carrier (capacity: 25 mL) having a cell wall thickness of 3.5 mil (8.89 × 10 −2 mm) and 600 cells per square inch (645.16 mm 2 ) was employed.
−触媒サンプルＢの調製−
上記酸化鉄ゾルに代えて硝酸第二鉄水溶液を採用し、他は触媒サンプルＡと同じ条件で第２触媒サンプル２を調製した。硝酸第二鉄水溶液による酸化鉄担持量は触媒サンプルＡの上記酸化鉄ゾルによる酸化鉄担持量と同じく、２０ｇ／Ｌである。
-Preparation of catalyst sample B-
Instead of the iron oxide sol, a ferric nitrate aqueous solution was employed, and a second catalyst sample 2 was prepared under the same conditions as in catalyst sample A. The amount of iron oxide supported by the ferric nitrate aqueous solution is 20 g / L, the same as the amount of iron oxide supported by the iron oxide sol of catalyst sample A.
−触媒サンプルＣの調製−
上記酸化鉄ゾルを用いず（酸化鉄担持量＝０ｇ／Ｌ）、上記ＣｅＺｒＮｄ複合酸化物担持量が１００ｇ／Ｌ、上記ＺｒＯ２バインダによるＺｒＯ２の担持量が１０ｇ／Ｌとなるようにする他は、触媒サンプルＡと同じ条件で触媒サンプルＣを調製した。
-Preparation of catalyst sample C-
Other to make without using the iron oxide sol (iron oxide supported amount = 0g / L), the CeZrNd mixed oxide support amount was 100 g / L, the amount of supported ZrO 2 by the ZrO 2 binder is 10 g / L Prepared catalyst sample C under the same conditions as catalyst sample A.
−酸素吸蔵放出能の評価−
図１９は、酸素吸蔵放出量を測定するための試験装置の構成を示す。同図において、符号１１は触媒サンプル１２を保持するガラス管であり、触媒サンプル１２はヒータ１３によって所定温度に加熱保持される。ガラス管１１の触媒サンプル１２よりも上流側には、ベースガスＮ２を供給しながらＯ２及びＣＯの各ガスをパルス状に供給可能なパルスガス発生装置１４が接続され、ガラス管１１の触媒サンプル１２よりも下流側には排気部１８が設けられている。ガラス管１１の触媒サンプル１２よりも上流側及び下流側にはＡ／Ｆセンサ（酸素センサ）１５，１６が設けられている。ガラス管１１のサンプル保持部には温度制御用の熱電対１９が取付けられている。
-Evaluation of oxygen storage capacity-
FIG. 19 shows the configuration of a test apparatus for measuring the oxygen storage / release amount. In the figure, reference numeral 11 denotes a glass tube that holds a catalyst sample 12, and the catalyst sample 12 is heated and held at a predetermined temperature by a heater 13. Connected to the upstream side of the catalyst sample 12 of the glass tube 11 is a pulse gas generator 14 capable of supplying O 2 and CO gases in pulses while supplying the base gas N 2. An exhaust unit 18 is provided on the downstream side of 12. A / F sensors (oxygen sensors) 15 and 16 are provided upstream and downstream of the catalyst sample 12 of the glass tube 11. A temperature control thermocouple 19 is attached to the sample holder of the glass tube 11.
測定にあたっては、ガラス管１１内の触媒サンプル温度を所定値に保ち、ベースガスＮ２を供給して排気部１８から排気しながら、図２０に示すようにＯ２パルス（２０秒）とＣＯパルス（２０秒）とを交互に且つ間隔（２０秒）をおいて発生させることにより、リーン→ストイキ→リッチ→ストイキのサイクルを繰り返すようにした。ストイキからリッチに切り換えた直後から、図２１に示すように、触媒サンプル前後のＡ／Ｆセンサ１５，１６によって得られるＡ／Ｆ値出力差（前側Ａ／Ｆ値−後側Ａ／Ｆ値）がなくなるまでの時間における、当該出力差をＯ２量に換算し、これを触媒サンプルのＯ２放出量（酸素吸蔵放出量）とした。このＯ２放出量を２００℃から６００℃までの５０℃刻みの各温度で測定した。 In the measurement, the catalyst sample temperature in the glass tube 11 is kept at a predetermined value, the base gas N 2 is supplied and exhausted from the exhaust unit 18, and as shown in FIG. 20, an O 2 pulse (20 seconds) and a CO pulse By alternately generating (20 seconds) and intervals (20 seconds), the cycle of lean → stoichi → rich → stoichi was repeated. Immediately after switching from stoichiometric to rich, as shown in FIG. 21, the A / F value output difference (front A / F value−rear A / F value) obtained by the A / F sensors 15 and 16 before and after the catalyst sample. The output difference in the time until disappearance is converted into an O 2 amount, and this is defined as an O 2 release amount (oxygen occlusion release amount) of the catalyst sample. The amount of released O 2 was measured at each temperature in increments of 50 ° C. from 200 ° C. to 600 ° C.
結果を図２２に示す。触媒サンプルＡ（酸化鉄ゾル＋ＯＳＣ）及び触媒サンプルＢ（硝酸第二鉄＋ＯＳＣ）のいずれも、酸化鉄を含まない触媒サンプルＣ（ＯＳＣのみ）よりも酸素放出量が多くなっている。（酸化鉄ゾル＋ＯＳＣ）と（硝酸第二鉄＋ＯＳＣ）とを比較すると、２５０℃〜６００℃において、酸化鉄ゾルの方が硝酸第二鉄よりも酸素放出量が多くなっている。 The results are shown in FIG. Both the catalyst sample A (iron oxide sol + OSC) and the catalyst sample B (ferric nitrate + OSC) have a larger oxygen release amount than the catalyst sample C not containing iron oxide (OSC only). When comparing (iron oxide sol + OSC) and (ferric nitrate + OSC), the amount of oxygen released from iron oxide sol is larger than that from ferric nitrate at 250 ° C. to 600 ° C.
図２３は（酸化鉄ゾル＋ＯＳＣ）及び（硝酸第二鉄＋ＯＳＣ）の各触媒サンプルのエージング（酸素を２％、水蒸気を１０％含む窒素ガス中で９００℃の温度に２４時間保持）後の酸素放出量を測定した結果を示す。いずれもエージング後は酸素放出量が少なくなっているが、それでも、酸化鉄ゾルの方が硝酸第二鉄よりも酸素放出量が多い。 FIG. 23 shows oxygen after aging of each of (iron oxide sol + OSC) and (ferric nitrate + OSC) catalyst samples (held at a temperature of 900 ° C. for 24 hours in nitrogen gas containing 2% oxygen and 10% water vapor). The result of measuring the release amount is shown. In both cases, the amount of oxygen released after aging is reduced, but the iron oxide sol still has a higher amount of released oxygen than ferric nitrate.
触媒サンプルＡの場合は、酸化鉄ゾルによる複数の粒径３００ｎｍ以下の酸化鉄粒子がＣｅＺｒＮｄ複合酸化物（ＯＳＣ）粒子に分散して接触しており（図２乃至図５参照）、そのため、それら酸化鉄粒子がＣｅＺｒＮｄ複合酸化物粒子と相俟って触媒の酸素吸蔵放出能の向上に有効に働いているものと認められる。これに対して、触媒サンプルＢの場合は、硝酸第二鉄による酸化鉄粒子の粒径が大きく（図１１乃至図１４参照）、そのため、酸化鉄粒子による酸素吸蔵放出能の向上が酸化鉄ゾルによるものに比べて低いものと認められる。 In the case of the catalyst sample A, a plurality of iron oxide particles having a particle size of 300 nm or less made of iron oxide sol are dispersed and in contact with CeZrNd composite oxide (OSC) particles (see FIGS. 2 to 5). It is recognized that the iron oxide particles work together with the CeZrNd composite oxide particles to effectively improve the oxygen storage / release capability of the catalyst. On the other hand, in the case of the catalyst sample B, the particle size of the iron oxide particles due to ferric nitrate is large (see FIGS. 11 to 14). It is recognized that it is lower than that by
図２４は上記エージング後の触媒サンプルＡ（酸化鉄ゾル＋ＯＳＣ）及び触媒サンプルＢ（硝酸第二鉄＋ＯＳＣ）の酸素放出量（測定温度５００℃）を、従来触媒及び実施例触媒各々の当該エージング後の酸素放出量（測定温度５００℃）と共に示すグラフである。従来触媒は、上記触媒サンプルＣ（ＯＳＣのみ）においてそのＣｅＺｒＮｄ複合酸化物粒子に触媒金属としてＰｔを１ｇ／Ｌ担持させたものである。実施例触媒は、上記触媒サンプルＡ（酸化鉄ゾル＋ＯＳＣ）においてそのＣｅＺｒＮｄ複合酸化物粒子に触媒金属としてＰｔを１ｇ／Ｌ担持させたものである。 FIG. 24 shows the oxygen release amounts (measurement temperature 500 ° C.) of the catalyst sample A (iron oxide sol + OSC) and the catalyst sample B (ferric nitrate + OSC) after the aging after the aging of the conventional catalyst and the example catalyst, respectively. It is a graph shown with the amount of oxygen release (measurement temperature 500 degreeC). The conventional catalyst is obtained by supporting 1 g / L of Pt as a catalyst metal on the CeZrNd composite oxide particles in the catalyst sample C (OSC only). In the catalyst sample A (iron oxide sol + OSC), the catalyst of the example was obtained by supporting 1 g / L of Pt as a catalyst metal on the CeZrNd composite oxide particles.
触媒サンプルＡ（酸化鉄ゾル＋ＯＳＣ）は、触媒金属ＰｔをＣｅＺｒＮｄ複合酸化物粒子に担持させていないにも拘わらず、ＣｅＺｒＮｄ複合酸化物粒子に触媒金属Ｐｔを担持させた従来触媒と同程度の酸素放出量になっている。また、触媒サンプルＡにおいてＣｅＺｒＮｄ複合酸化物粒子に触媒金属Ｐｔを担持させた実施例触媒は、従来触媒に比べて酸素放出量が格段に多くなっている。これらから、酸化鉄ゾルによる粒径の小さな酸化鉄粒子が酸素吸蔵放出能の向上に大きな効果を示すことがわかる。 The catalyst sample A (iron oxide sol + OSC) has oxygen equivalent to that of the conventional catalyst in which the catalyst metal Pt is supported on the CeZrNd composite oxide particles even though the catalyst metal Pt is not supported on the CeZrNd composite oxide particles. The amount is released. Further, in the catalyst sample A, the example catalyst in which the catalyst metal Pt is supported on the CeZrNd composite oxide particles has a much larger oxygen release amount than the conventional catalyst. From these, it can be seen that the iron oxide particles having a small particle diameter by the iron oxide sol have a great effect in improving the oxygen storage / release ability.
＜ＮＯ吸着能及びＮＨ３吸着能＞
Ｃｅ含有酸化物系触媒材料（実施例材料Ａ，比較例材料Ｂ，比較例材料Ｃ）を調製し、各々のＮＯｘ吸着能及びＮＨ３吸着能を評価した。
<NO adsorption capacity and NH 3 adsorption capacity>
Ce-containing oxide-based catalyst materials (Example material A, Comparative example material B, Comparative example material C) were prepared, and their NOx adsorption ability and NH 3 adsorption ability were evaluated.
−実施例材料Ａ−
ＣｅＺｒ複合酸化物粉末（ＣｅＯ２：ＺｒＯ２＝９０：１０（質量比））４０ｇに、上記酸化鉄ゾル及び水を混合し、１５０℃の温度に２時間保持する乾燥、並びに５００℃の温度に２時間保持する焼成を行なうことにより、実施例材料Ａを得た。酸化鉄ゾルの混合量は、焼成によって得られる酸化鉄量が８ｇとなるように調整した。
-Example material A-
The iron oxide sol and water are mixed with 40 g of CeZr composite oxide powder (CeO 2 : ZrO 2 = 90: 10 (mass ratio)), dried at a temperature of 150 ° C. for 2 hours, and heated to a temperature of 500 ° C. Example material A was obtained by baking for 2 hours. The amount of iron oxide sol mixed was adjusted so that the amount of iron oxide obtained by firing was 8 g.
−比較例材料Ｂ−
酸化鉄ゾルに代えて硝酸第二鉄水溶液を採用する他は実施例材料Ａと同じ条件で比較例材料Ｂを得た。硝酸第二鉄による酸化鉄量は、実施例材料Ａと同じく、８ｇとなるようにした。
-Comparative Example Material B-
Comparative Example Material B was obtained under the same conditions as Example Material A, except that an aqueous ferric nitrate solution was used instead of the iron oxide sol. The amount of iron oxide by ferric nitrate was set to 8 g as in Example material A.
−比較例材料Ｃ−
酸化鉄ゾルに代えてアルミナゾルを採用する他は実施例材料Ａと同じ条件で比較例材料Ｃを得た。但し、ＣｅＺｒ複合酸化物粉末量は４８ｇとし、アルミナゾルによるアルミナ量は９．６ｇとなるようにした。
-Comparative material C-
Comparative Example Material C was obtained under the same conditions as Example Material A, except that alumina sol was used instead of iron oxide sol. However, the CeZr composite oxide powder amount was 48 g, and the alumina amount by alumina sol was 9.6 g.
−ＮＯ吸着量の測定−
上記実施例及び比較例の各触媒材料Ａ，Ｂ，Ｃ各々０．０５ｇを準備し、ガス流通反応装置及びガス分析装置を用いて、プリコンディショニングを行なった後、ＮＯ吸着量を測定した。プリコンディショニングは、試料をＨｅ気流中で６００℃の温度に１０分間保持するというものである。次いで、モデルガス（ＮＯ；５０００ｐｐｍ，Ｏ２；５％，残Ｈｅ）を１００ｍＬ／分の流量で流しながら、ガス温度を室温から６００℃まで上昇させ、その間に吸着されたＮＯ成分量を算出して、ＮＯ吸着量とした。
-Measurement of NO adsorption amount-
0.05 g of each of the catalyst materials A, B, and C of the above Examples and Comparative Examples was prepared, preconditioned using a gas flow reactor and a gas analyzer, and then the NO adsorption amount was measured. Preconditioning is to hold the sample at a temperature of 600 ° C. for 10 minutes in a He stream. Next, while flowing the model gas (NO; 5000 ppm, O 2 ; 5%, remaining He) at a flow rate of 100 mL / min, the gas temperature is increased from room temperature to 600 ° C., and the amount of NO components adsorbed during that time is calculated. Thus, the NO adsorption amount was used.
−ＮＨ３吸着量の測定−
上記実施例及び比較例の各触媒材料Ａ，Ｂ，Ｃ各々０．０５ｇを準備し、それぞれガス流通反応装置及びガス分析装置を用いて、ＮＯ吸着量の測定の場合と同じプリコンディショニングを行なった後、ＮＨ３吸着量を測定した。
-Measurement of NH 3 adsorption amount-
0.05 g of each of the catalyst materials A, B, and C of the above Examples and Comparative Examples was prepared, and the same preconditioning as that in the case of measuring the NO adsorption amount was performed using a gas flow reactor and a gas analyzer, respectively. Then, the amount of NH 3 adsorption was measured.
ＮＨ３吸着量の測定にあたっては、モデルガス（ＮＨ３；２％，残Ｈｅ）を温度１００℃、１００ｍＬ／分の流量で流してＮＨ３を試料に吸着させ、次いで、ＮＨ３濃度０％のＨｅガスに切り換えて、１００℃から６００℃まで、１０℃／分の速度で昇温し、このときに、試料を通過したガス中に含まれるＮＨ３量を算出してＮＨ３吸着量とした。 In measuring the NH 3 adsorption amount, a model gas (NH 3 ; 2%, remaining He) was flowed at a temperature of 100 ° C. and a flow rate of 100 mL / min to adsorb NH 3 to the sample, and then the NH 3 concentration was 0%. Switching to He gas, the temperature was raised from 100 ° C. to 600 ° C. at a rate of 10 ° C./min. At this time, the amount of NH 3 contained in the gas that passed through the sample was calculated and used as the NH 3 adsorption amount .
−結果−
結果を図２５に示す。酸化鉄ゾルを採用した実施例材料ＡではＮＯ吸着量が１１０×１０−５mol／ｇ以上あるのに対して、比較例材料Ｂ，ＣではＮＯ吸着量が極めて少ない。ＮＨ３吸着量に関しても、実施例材料Ａは比較例材料Ｂ，Ｃよりも多くなっている。実施例材料ＡのＮＯ吸着量が顕著に多いのは、酸化鉄ゾルによる微細酸化鉄粒子がＣｅ含有酸化物の塩基性を強くしたためと考えられる。実施例材料ＡのＮＨ３吸着量が多いのは、酸化鉄ゾルによる微細酸化鉄粒子がＮＨ３の吸着に関与しているためである。
-Result-
The results are shown in FIG. In the example material A employing the iron oxide sol, the NO adsorption amount is 110 × 10 −5 mol / g or more, whereas in the comparative material B and C, the NO adsorption amount is extremely small. Regarding the NH 3 adsorption amount, the example material A is larger than the comparative example materials B and C. The reason why the NO adsorption amount of Example Material A is remarkably large is considered that the fine iron oxide particles by the iron oxide sol strengthened the basicity of the Ce-containing oxide. The reason why the amount of NH 3 adsorbed in Example Material A is large is that fine iron oxide particles by the iron oxide sol are involved in the adsorption of NH 3 .
以上の結果から、酸化鉄ゾルによる微細酸化鉄粒子を触媒層に分散させると、触媒のＮＯｘ浄化性能が高まること、並びに吸蔵したＮＯｘを脱離させて還元したときに、ＮＨ３が多く発生しても、該ＮＨ３の排出が少なくなることがわかる。 From the above results, when fine iron oxide particles made of iron oxide sol are dispersed in the catalyst layer, the NOx purification performance of the catalyst is increased, and a large amount of NH 3 is generated when the stored NOx is desorbed and reduced. However, it can be seen that the emission of NH 3 is reduced.
＜リーンＮＯｘ浄化性能＞
次の実施例及び比較例１，２のリーンＮＯｘ触媒を調製し、エージング後のリーンＮＯｘ浄化率、耐硫黄被毒性、硫黄被毒からの回復性を評価した。
<Lean NOx purification performance>
The lean NOx catalysts of the following examples and comparative examples 1 and 2 were prepared, and the lean NOx purification rate, sulfur poisoning resistance, and recoverability from sulfur poisoning after aging were evaluated.
−実施例−
γ−アルミナ粉末とＣｅＺｒ複合酸化物粉末（ＣｅＯ２：ＺｒＯ２＝７５：２５（質量比））とを混合し、これにバインダとしての上記酸化鉄ゾル及びイオン交換水を混合することによりスラリーを調製し、このスラリーを担体にコーティングし、乾燥（１５０℃の温度に２時間保持）及び焼成（大気中において５００℃の温度に２時間保持）を行なった。次いで、酢酸バリウム及び酢酸ストロンチウムをイオン交換水に溶かし、その溶液とジニトロジアンミン白金硝酸溶液と硝酸ロジウム溶液とを混合した。この混合溶液を上記担体のコーティング層に含浸させ、乾燥（１５０℃の温度に２時間保持）及び焼成（大気中において５００℃の温度に２時間保持を行なうことにより、実施例に係る触媒を得た。
-Example-
A slurry is prepared by mixing γ-alumina powder and CeZr composite oxide powder (CeO 2 : ZrO 2 = 75: 25 (mass ratio)), and mixing the iron oxide sol and ion-exchanged water as a binder. The slurry was prepared, coated on the support, dried (held at a temperature of 150 ° C. for 2 hours) and fired (held at a temperature of 500 ° C. for 2 hours in the air). Subsequently, barium acetate and strontium acetate were dissolved in ion-exchanged water, and the solution, a dinitrodiammine platinum nitrate solution, and a rhodium nitrate solution were mixed. This mixed solution is impregnated in the coating layer of the carrier, dried (kept at 150 ° C. for 2 hours), and calcined (kept at 500 ° C. in the atmosphere for 2 hours) to obtain the catalyst according to the example. It was.
当該触媒は、γ−アルミナ担持量が１２０ｇ／Ｌ、ＣｅＺｒ複合酸化物担持量が１２０ｇ／Ｌ、Ｂａ担持量が３０ｇ／Ｌ、Ｓｒ担持量が３ｇ／Ｌ、Ｐｔ担持量が２ｇ／Ｌ、Ｒｈ担持量が０．３ｇ／Ｌ、酸化鉄ゾルによる酸化鉄担持量が２４ｇ／Ｌである。なお、各担持量は上記焼成後における上記担体１Ｌ当たりの各成分の量である。また、担体としては、セル壁厚さ４mil（１０．１６×１０−２ｍｍ）、１平方インチ（６４５．１６ｍｍ２）当たりのセル数４００のコージェライト製ハニカム担体（容量５５ｍＬ）を採用した。 The catalyst has a γ-alumina loading of 120 g / L, a CeZr composite oxide loading of 120 g / L, a Ba loading of 30 g / L, a Sr loading of 3 g / L, a Pt loading of 2 g / L, and Rh. The supported amount is 0.3 g / L, and the supported amount of iron oxide by the iron oxide sol is 24 g / L. Each supported amount is the amount of each component per 1 L of the carrier after the firing. As the carrier, a cordierite honeycomb carrier (capacity 55 mL) having a cell wall thickness of 4 mil (10.16 × 10 −2 mm) and 400 cells per square inch (645.16 mm 2 ) was employed.
−比較例１−
酸化鉄ゾルに代えて硝酸第二鉄水溶液を採用する他は実施例と同じ条件で比較例１に係る触媒を調製した。硝酸第二鉄による酸化鉄担持量は２４ｇ／Ｌである。
-Comparative Example 1-
A catalyst according to Comparative Example 1 was prepared under the same conditions as in the Examples except that a ferric nitrate aqueous solution was used instead of the iron oxide sol. The amount of iron oxide supported by ferric nitrate is 24 g / L.
−比較例２−
酸化鉄ゾルに代えてアルミナゾルを採用する他は実施例と同じ条件で比較例２に係る触媒を調製した。アルミナゾルによるアルミナ担持量は２４ｇ／Ｌである。
-Comparative Example 2-
A catalyst according to Comparative Example 2 was prepared under the same conditions as in Examples except that alumina sol was used instead of iron oxide sol. The amount of alumina supported by the alumina sol is 24 g / L.
−リーンＮＯｘ浄化性能評価−
上記実施例及び比較例１，２の各触媒について、８００℃の大気雰囲気に２０時間保持するエージングを行なった後、モデルガス流通反応装置及び排気ガス分析装置を用いてリーンＮＯｘ浄化性能を調べた。すなわち、リーン（Ａ／Ｆ＝２２）のモデル排気ガスを６０秒間流し、次にガス組成をリッチ（Ａ／Ｆ＝１４．５）のモデル排気ガスに切り換えてこれを６０秒間流す、というサイクルを数回繰り返した後、ガス組成をリッチからリーンに切り換えた時点から６０秒間のＮＯｘ浄化率（リーンＮＯｘ浄化率）を測定した。リーンモデル排気ガス及びリッチのモデル排気ガスの組成は表３に示すとおりであり、空間速度は３５０００／ｈとした。
-Lean NOx purification performance evaluation-
For each of the catalysts in Examples and Comparative Examples 1 and 2, after performing aging for 20 hours in an air atmosphere at 800 ° C., the lean NOx purification performance was examined using a model gas flow reactor and an exhaust gas analyzer. . That is, a cycle in which lean (A / F = 22) model exhaust gas is flowed for 60 seconds, then the gas composition is switched to rich (A / F = 14.5) model exhaust gas, and this is flowed for 60 seconds. After repeating several times, the NOx purification rate (lean NOx purification rate) for 60 seconds was measured from the time when the gas composition was switched from rich to lean. The composition of the lean model exhaust gas and the rich model exhaust gas is as shown in Table 3, and the space velocity was 35000 / h.
触媒入口ガス温度１８０℃、３００℃及び４５０℃でのリーンＮＯｘ浄化率を図２６に示す。バインダとして酸化鉄ゾルを採用した実施例は、１８０℃、３００℃及び４５０℃のいずれにおいても、比較例１，２よりもＮＯｘ浄化率が高い。酸化鉄ゾルによる微細酸化鉄粒子を触媒層に分散させると、低温から高温にわたる広い温度範囲でＮＯｘ浄化能が高まることがわかる。比較例１は、実施例と同じく、酸化鉄粒子が触媒層に分散しているものの、酸化鉄を含有しない比較例２よりも性能が悪くなっている。比較例１の場合、その酸化鉄粒子は硝酸第二鉄によるものであって、その粒径が大きいことから、ＣｅＺｒ複合酸化物の酸素吸蔵放出能及びＮＯｘ吸着能を高めるに至らず、かえって、酸化鉄粒子がＣｅＺｒ複合酸化物粒子の比表面積を低下させて性能が悪くなったものと考えられる。 FIG. 26 shows lean NOx purification rates at catalyst inlet gas temperatures of 180 ° C., 300 ° C., and 450 ° C. The Example which employ | adopted iron oxide sol as a binder has a higher NOx purification rate than Comparative Examples 1 and 2 in any of 180 degreeC, 300 degreeC, and 450 degreeC. It can be seen that when fine iron oxide particles by the iron oxide sol are dispersed in the catalyst layer, the NOx purification ability is enhanced over a wide temperature range from low temperature to high temperature. Although the comparative example 1 has the iron oxide particle disperse | distributed to the catalyst layer like an Example, its performance is worse than the comparative example 2 which does not contain an iron oxide. In the case of Comparative Example 1, the iron oxide particles are derived from ferric nitrate and the particle size is large, so the oxygen storage capacity and NOx adsorption capacity of the CeZr composite oxide are not increased. It is considered that the iron oxide particles lowered the specific surface area of the CeZr composite oxide particles and deteriorated the performance.
−耐硫黄被毒性、硫黄被毒からの回復性−
上記実施例及び比較例１，２の各触媒について、上記エージング→硫黄被毒処理→還元処理（硫黄被毒からの回復処理）を順に行ない、該エージング後、硫黄被毒後及び還元処理後各々の触媒入口ガス温度３５０℃でのリーンＮＯｘ浄化率を測定した。
-Sulfur resistance and recovery from sulfur poisoning-
About each catalyst of the said Example and Comparative Examples 1 and 2, the said aging-> sulfur poisoning process-> reduction process (recovery process from sulfur poisoning) is performed in order, and after this aging, after sulfur poisoning, and after a reduction process, respectively The lean NOx purification rate at a catalyst inlet gas temperature of 350 ° C. was measured.
硫黄被毒処理は、触媒にＮ２１００％ガスを流通させながら、３５０℃まで昇温して同温度に保持し、次いで同温度でＳＯ２＝１００ｐｐｍ，Ｏ２＝１０％，残Ｎ２の硫黄被毒用ガスに切り替えてこれを１時間流通させ（ＳＶ＝３５０００／ｈ）、その後Ｎ２１００％ガスに切り替えて室温まで温度を下げる、というものである。還元処理は、触媒にＡ／Ｆ＝１４相当のリッチモデル排気ガスを流通させながら（ＳＶ＝８００００／ｈ）、３０℃／分で６００℃まで昇温させ、その温度に１０分間保持した後、Ｎ２１００％ガスに切り替えて室温まで温度を下げるというものである。 In the sulfur poisoning treatment, while flowing 100% N 2 gas through the catalyst, the temperature was raised to 350 ° C. and maintained at the same temperature, and then at the same temperature, SO 2 = 100 ppm, O 2 = 10%, and the remaining N 2 The gas is switched to sulfur poisoning gas and allowed to flow for 1 hour (SV = 35000 / h), and then switched to N 2 100% gas to lower the temperature to room temperature. In the reduction treatment, the rich model exhaust gas corresponding to A / F = 14 was circulated through the catalyst (SV = 80000 / h), the temperature was raised to 600 ° C. at 30 ° C./min, and maintained at that temperature for 10 minutes. The temperature is lowered to room temperature by switching to N 2 100% gas.
結果を図２７に示す。実施例は、硫黄被毒処理によるリーンＮＯｘ浄化率の低下度合いが比較例１，２に比べて小さい。これは、酸化鉄ゾルによる微細酸化鉄粒子が硫黄成分ＳＯ２を吸着し、ＮＯｘトラップ材の被毒を抑制したためと考えられる。そうして、実施例では、還元処理により、リーンＮＯｘ浄化率が硫黄被毒前の値まで略完全に回復しており、還元処理を適宜行なうことにより、触媒を長期間にわたって使用することができることがわかる。 The results are shown in FIG. In the embodiment, the degree of decrease in the lean NOx purification rate due to the sulfur poisoning treatment is smaller than those in Comparative Examples 1 and 2. This is considered because the fine iron oxide particles by the iron oxide sol adsorbed the sulfur component SO 2 and suppressed poisoning of the NOx trap material. Thus, in the examples, the reduction treatment has almost completely recovered the lean NOx purification rate to the value before sulfur poisoning, and the catalyst can be used for a long period of time by appropriately performing the reduction treatment. I understand.
１ ハニカム担体のセル壁
２ 触媒層
３ Ｃｅ含有酸化物粒子
４ バインダ粒子（酸化鉄粒子）
５ 触媒金属
６ アルミナ粒子
７ ポア
８ ＮＯｘトラップ材
1 Cell wall of honeycomb carrier 2 Catalyst layer 3 Ce-containing oxide particles 4 Binder particles (iron oxide particles)
5 Catalytic metal 6 Alumina particles 7 Pore 8 NOx trap material
Claims (5)
上記触媒層には、酸化鉄粒子が多数分散して含まれ、少なくとも一部の酸化鉄粒子は粒径が３００ｎｍ以下の微細酸化鉄粒子であり、上記Ｃｅ含有酸化物粒子及びＮＯｘトラップ材に当該微細酸化鉄粒子が接触しており、電子顕微鏡観察において、上記微細酸化鉄粒子の酸化鉄粒子総面積に占める面積比率が３０％以上であることを特徴とする排気ガス浄化用触媒。 An exhaust gas purifying catalyst in which a catalyst layer having Ce-containing oxide particles having oxygen storage / release capability, a NOx trap material other than the Ce-containing oxide particles, and a catalyst metal is formed on a carrier. ,
The catalyst layer includes a large number of dispersed iron oxide particles, at least some of the iron oxide particles are fine iron oxide particles having a particle size of 300 nm or less, and the Ce-containing oxide particles and the NOx trap material An exhaust gas purifying catalyst, wherein the fine iron oxide particles are in contact with each other, and the area ratio of the fine iron oxide particles to the total area of the iron oxide particles is 30% or more in an electron microscope observation.
上記微細酸化鉄粒子は、上記触媒層においてバインダの少なくとも一部を構成していることを特徴とする排気ガス浄化用触媒。 In claim 1,
The exhaust gas purifying catalyst, wherein the fine iron oxide particles constitute at least a part of a binder in the catalyst layer.
上記微細酸化鉄粒子の少なくとも一部はヘマタイトであることを特徴とする排気ガス浄化用触媒。 In claim 1 or claim 2,
An exhaust gas purifying catalyst, wherein at least a part of the fine iron oxide particles is hematite.
上記微細酸化鉄粒子は、マグヘマイト、ゲータイト及びウスタイトがコロイド粒子として分散したゾルを原料とすることを特徴とする排気ガス浄化用触媒。 In any one of Claim 1 thru | or 3,
The fine iron oxide particles are made from a sol in which maghemite, goethite, and wustite are dispersed as colloidal particles as a raw material.
自動車の排気ガスのＮＯｘを浄化するリーンＮＯｘ触媒として用いられることを特徴とする排気ガス浄化用触媒。 In any one of Claims 1 thru | or 4,
An exhaust gas purification catalyst characterized by being used as a lean NOx catalyst for purifying NOx in automobile exhaust gas.
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