JP2007319795A - Catalyst for purifying exhaust gas and its production method - Google Patents
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- 239000003054 catalyst Substances 0.000 title claims abstract description 86
- 238000004519 manufacturing process Methods 0.000 title claims description 11
- 239000002245 particle Substances 0.000 claims abstract description 120
- 239000000463 material Substances 0.000 claims abstract description 82
- 239000002243 precursor Substances 0.000 claims description 17
- 238000000746 purification Methods 0.000 claims description 17
- 238000002156 mixing Methods 0.000 claims description 7
- 229910018072 Al 2 O 3 Inorganic materials 0.000 claims description 6
- 229910004298 SiO 2 Inorganic materials 0.000 claims description 4
- 229910010413 TiO 2 Inorganic materials 0.000 claims description 4
- 239000007787 solid Substances 0.000 claims description 2
- 239000002131 composite material Substances 0.000 abstract description 29
- 239000010948 rhodium Substances 0.000 description 132
- 239000007789 gas Substances 0.000 description 72
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 23
- 150000001875 compounds Chemical class 0.000 description 20
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 18
- 239000002002 slurry Substances 0.000 description 17
- 230000003197 catalytic effect Effects 0.000 description 14
- 239000000843 powder Substances 0.000 description 14
- 230000000052 comparative effect Effects 0.000 description 13
- 229910000510 noble metal Inorganic materials 0.000 description 13
- 239000000084 colloidal system Substances 0.000 description 12
- 229910000422 cerium(IV) oxide Inorganic materials 0.000 description 11
- 239000002923 metal particle Substances 0.000 description 11
- 239000011324 bead Substances 0.000 description 10
- 239000000243 solution Substances 0.000 description 10
- 230000002776 aggregation Effects 0.000 description 9
- CETPSERCERDGAM-UHFFFAOYSA-N ceric oxide Chemical compound O=[Ce]=O CETPSERCERDGAM-UHFFFAOYSA-N 0.000 description 9
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 description 8
- 238000004220 aggregation Methods 0.000 description 8
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 8
- 239000001301 oxygen Substances 0.000 description 8
- 229910052760 oxygen Inorganic materials 0.000 description 8
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 7
- 230000007423 decrease Effects 0.000 description 7
- 239000010410 layer Substances 0.000 description 7
- 229910017604 nitric acid Inorganic materials 0.000 description 7
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 7
- 239000011148 porous material Substances 0.000 description 7
- 239000002344 surface layer Substances 0.000 description 7
- 238000009826 distribution Methods 0.000 description 6
- 238000010304 firing Methods 0.000 description 6
- 230000000694 effects Effects 0.000 description 5
- 239000011268 mixed slurry Substances 0.000 description 5
- 239000000203 mixture Substances 0.000 description 5
- 229910052703 rhodium Inorganic materials 0.000 description 5
- MHOVAHRLVXNVSD-UHFFFAOYSA-N rhodium atom Chemical compound [Rh] MHOVAHRLVXNVSD-UHFFFAOYSA-N 0.000 description 5
- XLUNHTOEZZRWFO-UHFFFAOYSA-N [La+3].[O-2].[O-2].[Zr+4] Chemical compound [La+3].[O-2].[O-2].[Zr+4] XLUNHTOEZZRWFO-UHFFFAOYSA-N 0.000 description 4
- 238000007254 oxidation reaction Methods 0.000 description 4
- 238000002360 preparation method Methods 0.000 description 4
- 238000010298 pulverizing process Methods 0.000 description 4
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 4
- 239000002904 solvent Substances 0.000 description 4
- KDLHZDBZIXYQEI-UHFFFAOYSA-N Palladium Chemical compound [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 description 3
- MCMNRKCIXSYSNV-UHFFFAOYSA-N ZrO2 Inorganic materials O=[Zr]=O MCMNRKCIXSYSNV-UHFFFAOYSA-N 0.000 description 3
- DDPNPTNFVDEJOH-UHFFFAOYSA-N [O-2].[Zr+4].[O-2].[Ce+3] Chemical compound [O-2].[Zr+4].[O-2].[Ce+3] DDPNPTNFVDEJOH-UHFFFAOYSA-N 0.000 description 3
- 229910001593 boehmite Inorganic materials 0.000 description 3
- 238000006243 chemical reaction Methods 0.000 description 3
- 239000011247 coating layer Substances 0.000 description 3
- 239000013078 crystal Substances 0.000 description 3
- 229930195733 hydrocarbon Natural products 0.000 description 3
- 150000002430 hydrocarbons Chemical class 0.000 description 3
- FAHBNUUHRFUEAI-UHFFFAOYSA-M hydroxidooxidoaluminium Chemical compound O[Al]=O FAHBNUUHRFUEAI-UHFFFAOYSA-M 0.000 description 3
- MWUXSHHQAYIFBG-UHFFFAOYSA-N nitrogen oxide Inorganic materials O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 description 3
- 230000003647 oxidation Effects 0.000 description 3
- 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 3
- RMAQACBXLXPBSY-UHFFFAOYSA-N silicic acid Chemical compound O[Si](O)(O)O RMAQACBXLXPBSY-UHFFFAOYSA-N 0.000 description 3
- 239000000377 silicon dioxide Substances 0.000 description 3
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 2
- 229910052684 Cerium Inorganic materials 0.000 description 2
- 239000003929 acidic solution Substances 0.000 description 2
- 229910002091 carbon monoxide Inorganic materials 0.000 description 2
- 239000011248 coating agent Substances 0.000 description 2
- 238000000576 coating method Methods 0.000 description 2
- 230000007613 environmental effect Effects 0.000 description 2
- 238000011156 evaluation Methods 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 238000000034 method Methods 0.000 description 2
- 238000003756 stirring Methods 0.000 description 2
- BNGXYYYYKUGPPF-UHFFFAOYSA-M (3-methylphenyl)methyl-triphenylphosphanium;chloride Chemical compound [Cl-].CC1=CC=CC(C[P+](C=2C=CC=CC=2)(C=2C=CC=CC=2)C=2C=CC=CC=2)=C1 BNGXYYYYKUGPPF-UHFFFAOYSA-M 0.000 description 1
- QTBSBXVTEAMEQO-UHFFFAOYSA-M Acetate Chemical compound CC([O-])=O QTBSBXVTEAMEQO-UHFFFAOYSA-M 0.000 description 1
- 229910002651 NO3 Inorganic materials 0.000 description 1
- 229910052779 Neodymium Inorganic materials 0.000 description 1
- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 description 1
- BOTDANWDWHJENH-UHFFFAOYSA-N Tetraethyl orthosilicate Chemical compound CCO[Si](OCC)(OCC)OCC BOTDANWDWHJENH-UHFFFAOYSA-N 0.000 description 1
- 229910007746 Zr—O Inorganic materials 0.000 description 1
- SLODBEHWNYQCRC-UHFFFAOYSA-N [La+3].[O-2].[Zr+4] Chemical compound [La+3].[O-2].[Zr+4] SLODBEHWNYQCRC-UHFFFAOYSA-N 0.000 description 1
- 230000002378 acidificating effect Effects 0.000 description 1
- 238000005054 agglomeration Methods 0.000 description 1
- SMZOGRDCAXLAAR-UHFFFAOYSA-N aluminium isopropoxide Chemical compound [Al+3].CC(C)[O-].CC(C)[O-].CC(C)[O-] SMZOGRDCAXLAAR-UHFFFAOYSA-N 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
- 230000033228 biological regulation Effects 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- GWXLDORMOJMVQZ-UHFFFAOYSA-N cerium Chemical compound [Ce] GWXLDORMOJMVQZ-UHFFFAOYSA-N 0.000 description 1
- QQZMWMKOWKGPQY-UHFFFAOYSA-N cerium(3+);trinitrate;hexahydrate Chemical compound O.O.O.O.O.O.[Ce+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O QQZMWMKOWKGPQY-UHFFFAOYSA-N 0.000 description 1
- 239000003426 co-catalyst Substances 0.000 description 1
- -1 composed of Zr oxide Chemical class 0.000 description 1
- RKTYLMNFRDHKIL-UHFFFAOYSA-N copper;5,10,15,20-tetraphenylporphyrin-22,24-diide Chemical compound [Cu+2].C1=CC(C(=C2C=CC([N-]2)=C(C=2C=CC=CC=2)C=2C=CC(N=2)=C(C=2C=CC=CC=2)C2=CC=C3[N-]2)C=2C=CC=CC=2)=NC1=C3C1=CC=CC=C1 RKTYLMNFRDHKIL-UHFFFAOYSA-N 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 239000010419 fine particle Substances 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-M hydroxide Chemical compound [OH-] XLYOFNOQVPJJNP-UHFFFAOYSA-M 0.000 description 1
- 230000002401 inhibitory effect Effects 0.000 description 1
- 229910052746 lanthanum Inorganic materials 0.000 description 1
- MRELNEQAGSRDBK-UHFFFAOYSA-N lanthanum oxide Inorganic materials [O-2].[O-2].[O-2].[La+3].[La+3] MRELNEQAGSRDBK-UHFFFAOYSA-N 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 229910044991 metal oxide Inorganic materials 0.000 description 1
- 150000004706 metal oxides Chemical class 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 239000011259 mixed solution Substances 0.000 description 1
- 229910052763 palladium Inorganic materials 0.000 description 1
- 229910052697 platinum Inorganic materials 0.000 description 1
- NWAHZABTSDUXMJ-UHFFFAOYSA-N platinum(2+);dinitrate Chemical compound [Pt+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O NWAHZABTSDUXMJ-UHFFFAOYSA-N 0.000 description 1
- 239000011164 primary particle Substances 0.000 description 1
- 230000009257 reactivity Effects 0.000 description 1
- 238000005245 sintering Methods 0.000 description 1
- 239000006104 solid solution Substances 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
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Abstract
Description
本発明は、自動車のエンジンから排出される排ガスを浄化する排ガス浄化用触媒及びその製造方法に関する。 The present invention relates to an exhaust gas purifying catalyst for purifying exhaust gas discharged from an automobile engine and a method for manufacturing the same.
環境保全意識の高まりに伴い、自動車等の排ガス量についての規制が強化されている。そのため、自動車のエンジンから排出される排ガスを浄化する排ガス浄化用触媒の性能向上を図る研究が各種行われている。 With increasing awareness of environmental conservation, regulations on the amount of exhaust gas from automobiles and the like have been strengthened. For this reason, various studies have been conducted to improve the performance of exhaust gas purifying catalysts that purify exhaust gas discharged from automobile engines.
排ガス浄化用触媒は、通常、アルミナ（Ａｌ２Ｏ３）等よりなる粒状の金属酸化物の担体表面に、白金（Ｐｔ）やパラジウム（Ｐｄ）やロジウム（Ｒｈ）等の貴金属の微粒子を担持した構成を有していて、これらの貴金属粒子の触媒作用により、排ガス中に含まれる未燃焼炭化水素（ＨＣ）や一酸化炭素（ＣＯ）や窒素酸化物（ＮＯＸ）等の有害なガスを、無害な水やガスに変換している。 The exhaust gas purifying catalyst usually carries fine particles of noble metal such as platinum (Pt), palladium (Pd) and rhodium (Rh) on the surface of a granular metal oxide carrier made of alumina (Al 2 O 3 ) or the like. Due to the catalytic action of these noble metal particles, harmful gases such as unburned hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NO x ) contained in the exhaust gas, It is converted into harmless water and gas.
排ガス浄化用触媒に用いられる貴金属のなかでも、Ｒｈは、低温浄化性能に優れていることから、排ガス浄化用触媒に含有される貴金属である。このＲｈを含む排ガス浄化用触媒に関し、Ｒｈを担持する化合物として低熱劣化性セリア（ＣｅＯ２）−ジルコニア（ＺｒＯ２）複合酸化物を用いたものがある（例えば、特許文献１）。この複合酸化物中のセリアは、酸素吸蔵放出能を有するため、貴金属粒子の近傍に位置させることで、助触媒としての機能、具体的には、排ガスの雰囲気の変動による浄化性能の変動を抑制する機能を有する。そのため、ロジウムを担持する化合物としてセリアを含む複合酸化物を用いた排ガス浄化用触媒は、Ｃｅ酸化物の酸素吸放出効果が発揮され、貴金属粒子周辺の雰囲気変動を緩和し、触媒の活性が高まり、ひいては排ガス浄化用触媒の性能を向上させることができる。
しかしながら、Ｒｈを担持する化合物にＣｅＯ２（セリア）を含む複合酸化物を用いた従来の排ガス浄化用触媒は、このＣｅ酸化物が排ガス浄化用触媒中でＲｈと接触していることにより、Ｒｈの酸化が促進され、触媒性能が低下する場合があった。 However, a conventional exhaust gas purification catalyst using a composite oxide containing CeO 2 (ceria) as a compound supporting Rh is in contact with Rh in the exhaust gas purification catalyst. Oxidation of the catalyst was promoted, and the catalyst performance sometimes deteriorated.
また、排ガス浄化用触媒の性能を高めるために、排ガス浄化用触媒中の貴金属粒子の粒径は調整直後はできるだけ小さく担持されているが、排ガス浄化用触媒の使用時、つまり高温の酸化雰囲気と還元雰囲気とが交互に繰り返す雰囲気中に晒されているうちに、近隣する貴金属粒子が互いに凝集、合体して数十ｎｍに粗大化してしまい、貴金属粒子の表面積が低下して有害物質の浄化率が経時的に低下することがあった。また、Ｒｈ等の貴金属粒子をセリアを含む複合酸化物に担持させた触媒においては、排ガス雰囲気では熱劣化に加え、高温水蒸気によりＺｒ−Ｏ結合やＣｅ−Ｏ結合の分解が生じることにより、通常の空気気流下などと比較して、セリアを含む複合酸化物の担体の凝集が進行し易いと考えられる。このような凝集によりＲｈ粒子周囲でガス拡散性が低下し、排ガスがＲｈ粒子に十分には接触できなくなって、経時的に触媒性能が低下することがあった。 In order to improve the performance of the exhaust gas purification catalyst, the particle size of the noble metal particles in the exhaust gas purification catalyst is supported as small as possible immediately after adjustment. While being exposed to an atmosphere that alternates with the reducing atmosphere, neighboring noble metal particles agglomerate and coalesce with each other and coarsen to several tens of nm, reducing the surface area of the noble metal particles and reducing the harmful substances Sometimes decreased over time. In addition, in a catalyst in which noble metal particles such as Rh are supported on a composite oxide containing ceria, in addition to thermal degradation in an exhaust gas atmosphere, decomposition of Zr-O bonds and Ce-O bonds is caused by high-temperature steam, It is considered that the aggregation of the carrier of the complex oxide containing ceria is more likely to proceed than in an air stream of Due to such agglomeration, the gas diffusibility is reduced around the Rh particles, and the exhaust gas cannot sufficiently contact the Rh particles, and the catalyst performance may deteriorate with time.
上述した問題を有利に解決する本発明の排ガス浄化用触媒は、Ｒｈ粒子と、このＲｈ粒子の周囲に形成され、当該Ｒｈ粒子を担持する多孔質の緩衝材と、このＲｈ粒子及び緩衝材の周囲に形成され、この緩衝材とは実質的に非固溶な酸化物とをそなえ、前記緩衝材は、Ｒｈ粒子と複合化可能な材料よりなることを要旨とする。 The exhaust gas purifying catalyst of the present invention that advantageously solves the above-described problems includes Rh particles, a porous buffer material formed around the Rh particles and carrying the Rh particles, and the Rh particles and the buffer material. The gist of the present invention is that the buffer material is formed of a material that can be combined with Rh particles.
また、本発明の排ガス浄化用触媒の製造方法は、Ｒｈ粒子と、このＲｈ粒子の周囲に形成され、当該Ｒｈ粒子を担持する多孔質の緩衝材と、この緩衝材及び前記Ｒｈ粒子の周囲に形成され、この緩衝材とは実質的に非固溶な酸化物とをそなえる排ガス浄化用触媒の製造方法であって、Ｒｈ前駆体と緩衝材前駆体とを混合しRｈ−緩衝材ユニットを形成する工程を含み、更には該ユニットを酸化物前駆体と混合して該ユニットを酸化物で包接する工程を含むことを要旨とする。 Further, the method for producing an exhaust gas purifying catalyst of the present invention includes Rh particles, a porous buffer material formed around the Rh particles, and supporting the Rh particles, and the buffer material and the Rh particles. A method for producing an exhaust gas purifying catalyst having a substantially non-solid oxide, which is formed by mixing a Rh precursor and a buffer material precursor to form a Rh-buffer material unit. And further including a step of mixing the unit with an oxide precursor to include the unit with an oxide.
本発明に係る排ガス浄化用触媒によれば、貴金属粒子の酸化を抑制して触媒活性の低下を防止するとともに、貴金属粒子の移動、凝集を抑制し、製造コストや環境負荷を大きくすることなく、貴金属粒子の活性向上効果を維持することができる。 According to the exhaust gas purifying catalyst according to the present invention, the oxidation of the noble metal particles is suppressed to prevent a decrease in the catalytic activity, the movement and aggregation of the noble metal particles are suppressed, and the production cost and the environmental load are not increased. The effect of improving the activity of the noble metal particles can be maintained.
本発明に係る排ガス浄化用触媒の製造方法によれば、本発明に係る排ガス浄化用触媒を確実に安定して製造することができる。 According to the method for producing an exhaust gas purification catalyst according to the present invention, the exhaust gas purification catalyst according to the present invention can be produced reliably and stably.
以下、本発明の排ガス浄化用触媒の実施形態を図面を用いつつ説明する。 Hereinafter, embodiments of the exhaust gas purifying catalyst of the present invention will be described with reference to the drawings.
図１は、本発明に係る排ガス浄化用触媒の微視的な最小構成の一例の模式図である。同図において、排ガス浄化用触媒１は、排ガスに接触して有害成分を浄化させる活性金属の粒子であるＲｈ粒子２と、このＲｈ粒子２の周囲に形成され、このＲｈ粒子２を担持する多孔質の緩衝材３と、Ｒｈ粒子２を担持した緩衝材３の周囲に形成された酸化物４とを有している。緩衝材３はＲｈと複合可能な材料よりなり、酸化物４は、緩衝材３とは実質的に非固溶な酸化物である。 FIG. 1 is a schematic view of an example of a microscopic minimum configuration of an exhaust gas purifying catalyst according to the present invention. In the figure, an exhaust gas purifying catalyst 1 is formed of Rh particles 2 that are active metal particles that come into contact with exhaust gas to purify harmful components, and a porous material that is formed around the Rh particles 2 and carries the Rh particles 2. It has a quality buffer material 3 and an oxide 4 formed around the buffer material 3 carrying the Rh particles 2. The buffer material 3 is made of a material that can be combined with Rh, and the oxide 4 is an oxide that is substantially insoluble in the buffer material 3.
触媒活性を有するＲｈ粒子２を担持する担体は、Ｒｈ粒子２の酸化を抑制すべく、Ｒｈ粒子２と活性酸素の授受や化合物の形成を行わない化合物であることが好ましい。この点で、例えばＺｒ酸化物の粒子は、好ましい化合物である。Ｚｒ酸化物を主成分とする粒子のような、活性酸素の授受や化合物の形成を行わない化合物担体上にＲｈ粒子２を担持すれば、その化合物担体の一次粒子が、クラスター状にＲｈ粒子２の周囲を取り囲むことになる。したがって、Ｒｈ粒子２同士の接触、移動を阻害する役割を果たすことができる。このことにより、Ｒｈ粒子２の凝集を抑制し、ひいてはＲｈ粒子２の活性表面積の低下を抑制することで高温、長時間使用後も優れた触媒活性を維持することが可能となる。 The carrier supporting the Rh particles 2 having catalytic activity is preferably a compound that does not exchange active oxygen with the Rh particles 2 or form a compound in order to suppress oxidation of the Rh particles 2. In this respect, for example, Zr oxide particles are a preferred compound. If Rh particles 2 are supported on a compound carrier that does not give or receive active oxygen or form a compound, such as particles mainly composed of Zr oxide, the primary particles of the compound carrier become Rh particles 2 in clusters. Will be surrounded. Therefore, it can play a role of inhibiting contact and movement between the Rh particles 2. As a result, it is possible to maintain excellent catalytic activity even after high temperature use for a long period of time by suppressing aggregation of the Rh particles 2 and thus suppressing a decrease in the active surface area of the Rh particles 2.
もっとも、このＲｈ粒子２を、活性酸素の授受や化合物の形成を行わない化合物担体上に直接的に担持しただけでは、この化合物担体が、排ガスを浄化する環境下では熱及び高温の水蒸気に晒されて凝集することにより、Ｒｈ粒子２の周囲のガス拡散性が悪化してしまうことがある。Ｒｈ粒子２周囲のガス拡散性が悪化すると、Ｒｈ粒子２に接触する排ガス量が低下するので、触媒活性が低下してしまう。 However, if the Rh particles 2 are directly supported on a compound carrier that does not exchange active oxygen or form a compound, the compound carrier is exposed to heat and high-temperature water vapor in an environment for purifying exhaust gas. As a result, the gas diffusibility around the Rh particles 2 may deteriorate. When the gas diffusibility around the Rh particles 2 is deteriorated, the amount of exhaust gas in contact with the Rh particles 2 is reduced, so that the catalytic activity is lowered.
そこで、本発明に係る排ガス浄化用触媒１は、Ｒｈ粒子２と、活性酸素の授受や化合物の形成を行わない化合物である酸化物４との間に、このＲｈ粒子２周囲のガス拡散性を維持するための緩衝材３が形成されている。この緩衝材３は、例えば多孔質粒子の集合物であって、その粒子自体に形成されている一次細孔及び粒子間に形成されている二次細孔（メソ細孔）により、全体として多孔質の材料となっている。この多孔質の材料は、後で詳述するが、このＲｈ粒子と複合化可能な材料が適合する。 Therefore, the exhaust gas purifying catalyst 1 according to the present invention has a gas diffusivity around the Rh particles 2 between the Rh particles 2 and the oxide 4 which is a compound that does not exchange active oxygen or form a compound. The buffer material 3 for maintaining is formed. The buffer material 3 is an aggregate of porous particles, for example, and is porous as a whole by primary pores formed in the particles themselves and secondary pores (mesopores) formed between the particles. It is a quality material. The porous material will be described in detail later, but a material that can be combined with the Rh particles is suitable.
本実施形態の排ガス浄化用触媒は、多孔質の緩衝材３を、Ｒｈ粒子２の周囲に形成させ、この緩衝材３の周囲に酸化物４を形成させた構造とすることにより、酸化物４が凝集したとしても、この緩衝材３の細孔を通して排ガスはＲｈ粒子２に容易に到達するので、Ｒｈ粒子２周囲のガス拡散性が維持される。したがって、本実施形態の排ガス浄化用触媒は、高温、長時間使用後においても排ガス浄化性能の低下の少ない、優れた触媒活性を有する排ガス浄化用触媒である。 The exhaust gas purifying catalyst of the present embodiment has a structure in which the porous buffer material 3 is formed around the Rh particles 2, and the oxide 4 is formed around the buffer material 3. Even if agglomerates, the exhaust gas easily reaches the Rh particles 2 through the pores of the buffer material 3, so that the gas diffusibility around the Rh particles 2 is maintained. Therefore, the exhaust gas purifying catalyst of the present embodiment is an exhaust gas purifying catalyst having excellent catalytic activity with little deterioration in exhaust gas purifying performance even after high temperature and long time use.
緩衝材３の作用効果のためには、本実施形態の排ガス浄化用触媒において、Ｒｈ粒子２の８０％以上が緩衝材３と接していることが好ましい。Ｒｈ粒子２の８０％以上が緩衝材３と接していることにより、触媒使用の経時後も酸化物４の凝集によるガス拡散性の低下が効果的に抑制され、高い触媒活性を維持することが可能である。８０％に満たないと、Ｒｈ粒子２が酸化物４の凝集に巻き込まれ易くなり、触媒の使用の経時後に、Ｒｈ粒子２の周囲が酸化物４で覆われ、排ガス中の有害ガス成分が、触媒活性を有するＲｈ粒子２に到達できず、触媒活性が低下する。このＲｈ粒子２の緩衝材３への接触率は、例えば、ＴＥＭ−ＥＤＸにより、所定領域内に存在するＲｈ粒子２と緩衝材３との量比を測定し、この量比を、排ガス浄化用触媒中のＲｈ粒子２及び緩衝材３の含有量比と対比することにより求めることができる。 In order to achieve the effect of the buffer material 3, it is preferable that 80% or more of the Rh particles 2 are in contact with the buffer material 3 in the exhaust gas purifying catalyst of the present embodiment. Since 80% or more of the Rh particles 2 are in contact with the buffer material 3, a decrease in gas diffusibility due to the aggregation of the oxide 4 can be effectively suppressed even after the catalyst is used, and high catalytic activity can be maintained. Is possible. If it is less than 80%, the Rh particles 2 are likely to be involved in the aggregation of the oxide 4, and after use of the catalyst, the periphery of the Rh particles 2 is covered with the oxide 4, and harmful gas components in the exhaust gas are The Rh particles 2 having catalytic activity cannot be reached, and the catalytic activity decreases. The contact ratio of the Rh particles 2 to the buffer material 3 is determined, for example, by measuring the quantity ratio between the Rh particles 2 and the buffer material 3 existing in a predetermined region by TEM-EDX, and using this quantity ratio for exhaust gas purification. It can be determined by comparing with the content ratio of the Rh particles 2 and the buffer material 3 in the catalyst.
緩衝材３は、Ｒｈ粒子２と複合化可能な材料であるＡｌ２Ｏ３、ＳｉＯ２及びＴｉＯ２から選ばれる少なくとも1種の酸化物を含むことが好ましい。これらの酸化物は、いずれも耐熱性に優れ、細孔を有することから、本発明に係る排ガス浄化用触媒における緩衝材３として好適である。これらの酸化物のなかでも、Ａｌ２Ｏ３は、特に排ガス雰囲気のような高温かつ多量の水蒸気を含む条件下での耐熱性に優れ、多くの細孔を有することで、Ｒｈ粒子２周囲のガス拡散性を維持する緩衝材として優れている。緩衝材３は、上掲したＡｌ２Ｏ３、ＳｉＯ２及びＴｉＯ２のうち１種類を含んでも良いし、２種類以上を複合して含んでもよい。また、緩衝材３は、これらの酸化物のほかに、副成分としてＺｒＯ２やＣｅＯ２を含むことができる。このＺｒＯ２やＣｅＯ２は、緩衝材３の耐熱性を向上させる材料であり、緩衝材３全体に対する割合で１０ｍｏｌ％以下程度の量で含有させることができる。１０ｍｏｌ％以下程度の量であれば、ＣｅＯ２を含む場合であっても、Ｒｈ粒子が高酸化状態にはならない。 The buffer material 3 preferably contains at least one oxide selected from Al 2 O 3 , SiO 2, and TiO 2 , which is a material that can be combined with the Rh particles 2. Since these oxides are all excellent in heat resistance and have pores, they are suitable as the buffer material 3 in the exhaust gas purifying catalyst according to the present invention. Among these oxides, Al 2 O 3 is particularly excellent in heat resistance under conditions including a high temperature and a large amount of water vapor such as an exhaust gas atmosphere, and has many pores. It is excellent as a buffer material that maintains gas diffusibility. The buffer material 3 may include one of Al 2 O 3 , SiO 2 and TiO 2 listed above, or may include two or more in combination. Also, the buffer member 3, in addition to these oxides, can be as an auxiliary component containing ZrO 2 and CeO 2. This ZrO 2 or CeO 2 is a material that improves the heat resistance of the buffer material 3, and can be contained in an amount of about 10 mol% or less with respect to the entire buffer material 3. If the amount is about 10 mol% or less, the Rh particles will not be in a highly oxidized state even when CeO 2 is contained.
緩衝材３に担持されるＲｈ粒子２は、緩衝材３がＡｌ２Ｏ３、ＳｉＯ２及びＴｉＯ２を含むものであるとき、これらの酸化物から活性酸素を受けて酸化されることが考えられるが、発明者らの研究により、緩衝材３とＲｈ粒子２とのモル比を適切に調整することにより、Ｒｈ粒子２の触媒活性の低下を極力抑制できることが確認されている。このモル比については、後述する。 The Rh particles 2 supported on the buffer material 3 may be oxidized by receiving active oxygen from these oxides when the buffer material 3 contains Al 2 O 3 , SiO 2 and TiO 2 . It has been confirmed by the inventors' research that a decrease in the catalytic activity of the Rh particles 2 can be suppressed as much as possible by appropriately adjusting the molar ratio between the buffer material 3 and the Rh particles 2. This molar ratio will be described later.
酸化物４は、少なくともＺｒを含む酸化物であることが好ましい。より好ましくは、酸化物４の主成分がＺｒを含む酸化物であることである。ここでいう主成分とは、Ｚｒが５０ｍｏｌ％以上含まれることを指す。Ｒｈ粒子２は、Ｚｒに対し反応性が低く、活性酸素の授受や複合化合物の生成が生じ難い。このため酸化物４の主成分がＺｒを含む酸化物であることにより、Ｒｈ粒子２の電子状態にほとんど影響を与えることがなく、Ｒｈ粒子２を活性なメタル状態か活性なＲｈ２Ｏ３の状態で維持することができる。また、酸化物４の主成分がＺｒを含む酸化物であることにより、この酸化物４は緩衝材３とは実質的に非固溶となり、よって高温、長時間での排ガス浄化処理後も、本発明の排ガス浄化用触媒の構造を維持することができる。酸化物４は、Ｚｒを含む酸化物以外の酸化物を含むことができ、例えば、Ｎｄ、Ｐｒ、Ｙ、Ｌａ及びＣｅから選ばれる１種又は２種以上の金属の酸化物を含むことができる。ＺｒＯ２単独では熱に対し結晶成長の早い単斜晶をとり易く、著しく比表面積が低下する傾向がある。このため、上掲した元素をｍｏｌ％で１〜１０％程度、好ましくは１〜７％程度の量でドープすることにより安定な正方晶又は立方晶へ転移させ、耐久性を高めることが可能である。 The oxide 4 is preferably an oxide containing at least Zr. More preferably, the main component of the oxide 4 is an oxide containing Zr. The main component here means that Zr is contained by 50 mol% or more. The Rh particles 2 have low reactivity with respect to Zr, and do not easily generate active oxygen or generate complex compounds. For this reason, since the main component of the oxide 4 is an oxide containing Zr, the Rh particles 2 are hardly affected by the Rh particles 2 in the active metal state or the active Rh 2 O 3 . Can be maintained in a state. In addition, since the main component of the oxide 4 is an oxide containing Zr, the oxide 4 becomes substantially non-solid solution with the buffer material 3, and thus after exhaust gas purification treatment at a high temperature for a long time, The structure of the exhaust gas purifying catalyst of the present invention can be maintained. The oxide 4 can include an oxide other than an oxide containing Zr. For example, the oxide 4 can include an oxide of one or more metals selected from Nd, Pr, Y, La, and Ce. . ZrO 2 alone tends to form a monoclinic crystal whose crystal growth is fast with respect to heat, and the specific surface area tends to decrease remarkably. For this reason, the elements listed above can be transformed into a stable tetragonal or cubic crystal by doping in an amount of about 1 to 10%, preferably about 1 to 7% in mol%, and durability can be improved. is there.
Ｒｈ粒子２の平均粒子径は２〜１０ｎｍであることが望ましい。これは、平均粒子径が２ｎｍに満たないと、Ｒｈ粒子の急激な融点降下が起こり、シンタリングが発生し易くなるためである。また、平均粒子径が１０ｎｍを超えると、単位重量あたりの活性表面積が著しく低下し、その結果、十分な触媒活性が得られず、所望の触媒性能を確保するためにはより多くの量のＲｈを触媒中に使用する必要があるためである。 The average particle size of the Rh particles 2 is desirably 2 to 10 nm. This is because if the average particle diameter is less than 2 nm, a sharp melting point drop of Rh particles occurs and sintering is likely to occur. On the other hand, when the average particle diameter exceeds 10 nm, the active surface area per unit weight is remarkably reduced. As a result, sufficient catalytic activity cannot be obtained, and a larger amount of Rh is required to ensure desired catalyst performance. This is because it is necessary to use in the catalyst.
Ｒｈ粒子２の周囲に存在する緩衝材３と、このＲｈ粒子２と緩衝材３とのモル比は、［緩衝材／Ｒｈ］としたとき、０．５〜３であることが望ましい。このモル比は、更には０．５〜２であることがより好ましい。このモル比が０．５未満ではＲｈ粒子２を担持する緩衝材３の量が足りず、酸化物４中にＲｈ粒子２が巻き込まれ、ガス拡散性が低下するおそれがある。また、モル比が３超では緩衝材３の量が多過ぎ、Ｒｈ粒子２と緩衝材３との酸化反応等が進行し易く、Ｒｈ粒子２が高酸化状態となって触媒活性が低下するおそれがある。モル比が０．５〜２の範囲であるときは特に、Ｒｈ粒子２の触媒活性の低下を招くことなく、優れたガス拡散性を維持することが可能である。 The molar ratio of the buffer material 3 present around the Rh particles 2 and the Rh particles 2 to the buffer material 3 is preferably 0.5 to 3 when [buffer material / Rh]. This molar ratio is more preferably 0.5-2. If the molar ratio is less than 0.5, the amount of the buffer material 3 supporting the Rh particles 2 is insufficient, and the Rh particles 2 are involved in the oxide 4 and the gas diffusibility may be lowered. On the other hand, if the molar ratio is more than 3, the amount of the buffer material 3 is too large, the oxidation reaction between the Rh particles 2 and the buffer material 3 easily proceeds, and the Rh particles 2 may be in a highly oxidized state and the catalytic activity may be reduced. There is. In particular, when the molar ratio is in the range of 0.5 to 2, it is possible to maintain excellent gas diffusibility without causing a decrease in the catalytic activity of the Rh particles 2.
本発明に係る排ガス浄化用触媒は、例えば、Ｒｈ前駆体と緩衝材前駆体とを混合しRｈ−緩衝材ユニットを形成する工程を含み、更には該ユニットを酸化物前駆体と混合して該ユニットを酸化物で包接する工程を経て、製造することができる。 The exhaust gas purifying catalyst according to the present invention includes, for example, a step of mixing an Rh precursor and a buffer material precursor to form an Rh-buffer material unit, and further mixing the unit with an oxide precursor to The unit can be manufactured through a process of inclusion with an oxide.
この製造工程においては、まず、Ｒｈ前駆体と緩衝材前駆体とを混合してＲｈ−緩衝材ユニットを形成する。このＲｈ前駆体としては、硝酸ロジウム溶液、ヘキサアンミンロジウム溶液、ＰＶＰ−Ｒｈコロイド、ＰＥＩ−Ｒｈコロイド等を任意に用いることができる。また、緩衝材の前駆体としては、アルミニウムイソプロポキシド、硝酸アルミニウム、アルミナゾル、ベーマイト、ＴＥＯＳ、シリカゾル、などを任意で用いることができる。 In this manufacturing process, first, an Rh-buffer material unit is formed by mixing an Rh precursor and a buffer material precursor. As this Rh precursor, a rhodium nitrate solution, a hexaammine rhodium solution, a PVP-Rh colloid, a PEI-Rh colloid, or the like can be arbitrarily used. Moreover, as a precursor of the buffer material, aluminum isopropoxide, aluminum nitrate, alumina sol, boehmite, TEOS, silica sol, and the like can be arbitrarily used.
次に、該ユニットを酸化物で包接する工程において用いる酸化物前駆体としては、硝酸塩、酢酸塩、水酸化物、ゾルなどを任意に用いることができる。 Next, as an oxide precursor used in the step of clathrating the unit with an oxide, nitrate, acetate, hydroxide, sol, or the like can be arbitrarily used.
本発明の排ガス浄化用触媒の製造方法においては、上記工程を含むことで、まず、Ｒｈ粒子前駆体周囲に緩衝材前駆体を形成し、しかる後に酸化物前駆体によりＲｈ−緩衝材のユニットを包接することで、本発明に係る排ガス浄化用触媒を設計どおりに製造することができる。 In the method for producing an exhaust gas purifying catalyst of the present invention, by including the above-described steps, first, a buffer material precursor is formed around the Rh particle precursor, and then the Rh-buffer material unit is formed by the oxide precursor. By inclusion, the exhaust gas purifying catalyst according to the present invention can be manufactured as designed.
その後に焼成することにより排ガス浄化用触媒粉末を得る。この粉末はスラリー化し、ハニカム担体に塗布したのち、乾燥及び焼成することにより、排ガス浄化用触媒として使用される。 Thereafter, the catalyst powder for exhaust gas purification is obtained by firing. This powder is slurried, applied to a honeycomb carrier, dried and fired, and used as an exhaust gas purifying catalyst.
１．表層触媒粉末調製
［実施例１］
ＰＶＰ−Ｒｈコロイド（Ｒｈ粒径：２ｎｍ、Ｒｈ：２ｗｔ％）と、アルミナゾル（１０ｗｔ％）とを純水中に分散させ、約１時間マグネットスターラにて攪拌した。更に、５％硝酸溶液を加えて適宜ｐＨを調整することにより、Ｒｈコロイド周囲にアルミナゾルが吸着したＲｈ−アルミナ複合ゾルを得た。その一方で、酸化ジルコニウム−酸化ランタン複合化合物（比表面積：７０ｍ２／ｇ）を純水中に分散させたスラリを、ビーズミル（ビーズ径：０．１ｍｍ）により、レーザ回折散乱型粒度分布計でメジアン径が１２０ｎｍになるよう粉砕した。このスラリ中に、先ほどのＲｈ−アルミナ複合ゾルをゆっくりと混合し１時間攪拌した。この混合スラリを１２０℃のオイルバス中でエバポレータを用いて減圧下で水分を留去させ、得られた粉末を８０℃で６時間、更に１５０℃で１２時間乾燥した後に、５５０℃で２時間空気気流下で焼成した。
1. Preparation of surface layer catalyst powder [Example 1]
PVP-Rh colloid (Rh particle size: 2 nm, Rh: 2 wt%) and alumina sol (10 wt%) were dispersed in pure water and stirred with a magnetic stirrer for about 1 hour. Furthermore, by adding a 5% nitric acid solution and adjusting the pH appropriately, an Rh-alumina composite sol in which the alumina sol was adsorbed around the Rh colloid was obtained. On the other hand, a slurry in which a zirconium oxide-lanthanum oxide composite compound (specific surface area: 70 m 2 / g) is dispersed in pure water is subjected to a laser diffraction scattering type particle size distribution analyzer by a bead mill (bead diameter: 0.1 mm). It grind | pulverized so that a median diameter might be set to 120 nm. In this slurry, the Rh-alumina composite sol was slowly mixed and stirred for 1 hour. Water was distilled off from this mixed slurry in an oil bath at 120 ° C. under reduced pressure using an evaporator, and the resulting powder was dried at 80 ° C. for 6 hours and further at 150 ° C. for 12 hours, and then at 550 ° C. for 2 hours. Firing was performed under an air stream.
これによりＲｈ粒子の周囲にアルミナが存在し、更にＺｒ−Ｌａ−Ｏｘ複合酸化物で覆われた触媒を得た。 As a result, an alumina was present around the Rh particles, and a catalyst covered with a Zr—La—O x composite oxide was obtained.
［実施例２］
ＰＶＰ−Ｒｈコロイド（Ｒｈ粒径：２ｎｍ、Ｒｈ：２ｗｔ％）とアルミナゾル（１０ｗｔ％）とを純水中に分散させ、約１時間マグネットスターラにて攪拌した。更に、５％硝酸溶液を加えて適宜ｐＨを調整することにより、Ｒｈコロイド周囲にアルミナゾルが吸着したＲｈ−アルミナ複合ゾルを得た。その一方で、酸化ジルコニウム−酸化セリウム複合化合物（比表面積７０ｍ２／ｇ）を純水中に分散させたスラリを、ボールミル（ボール径：１０ｍｍ）で湿式粉砕によりメジアン径を２μｍ以下に粉砕した後、更にビーズミル（ビーズ径：０．１ｍｍ）により、レーザ回折散乱型粒度分布計でメジアン径が１２０ｎｍになるよう粉砕した。このスラリ中に、先ほどのＲｈ−アルミナ複合ゾルをゆっくりと混合し１時間攪拌した。この混合スラリを１２０℃のオイルバス中でエバポレータを用いて減圧下で水分を留去させ、得られた粉末を８０℃で６時間、更に１５０℃で１２時間乾燥した後に、５５０℃で２時間空気気流下で焼成した。
[Example 2]
PVP-Rh colloid (Rh particle size: 2 nm, Rh: 2 wt%) and alumina sol (10 wt%) were dispersed in pure water and stirred with a magnetic stirrer for about 1 hour. Furthermore, by adding a 5% nitric acid solution and adjusting the pH appropriately, an Rh-alumina composite sol in which the alumina sol was adsorbed around the Rh colloid was obtained. Meanwhile, after a slurry in which a zirconium oxide-cerium oxide composite compound (specific surface area 70 m 2 / g) is dispersed in pure water is pulverized to a median diameter of 2 μm or less by wet pulverization with a ball mill (ball diameter: 10 mm). Further, it was pulverized with a bead mill (bead diameter: 0.1 mm) with a laser diffraction / scattering particle size distribution meter so that the median diameter became 120 nm. In this slurry, the Rh-alumina composite sol was slowly mixed and stirred for 1 hour. Water was distilled off from this mixed slurry in an oil bath at 120 ° C. under reduced pressure using an evaporator, and the resulting powder was dried at 80 ° C. for 6 hours and further at 150 ° C. for 12 hours, and then at 550 ° C. for 2 hours. Firing was performed under an air stream.
これによりＲｈ粒子の周囲にZr-Al-Ox複合酸化物が存在し、さらにＺｒ−Ce−Ｏｘ複合酸化物で覆われた触媒を得た。 As a result, a Zr—Al—Ox composite oxide was present around the Rh particles, and a catalyst covered with the Zr—Ce—O x composite oxide was obtained.
［実施例３］
ＰＶＰ−Ｒｈコロイド（Ｒｈ粒径：２ｎｍ、Ｒｈ：２ｗｔ％）と、シリカゾル（１０ｗｔ％）とを純水中に分散させ、約１時間マグネットスターラにて攪拌した。更に、５％硝酸溶液を加えて適宜ｐＨを調整することにより、Ｒｈコロイド周囲にシリカゾルが吸着したＲｈ−シリカ複合ゾルを得た。その一方で、酸化ジルコニウム−酸化ランタン複合化合物（比表面積：７０ｍ２／ｇ）を純水中に分散させたスラリを、ボールミル（ボール径：１０ｍｍ）で湿式粉砕によりメジアン径を２μｍ以下に粉砕した後、更にビーズミル（ビーズ径：０．１ｍｍ）により、レーザ回折散乱型粒度分布計でメジアン径が１２０ｎｍになるよう粉砕した。このスラリ中に、先ほどのＲｈ−シリカ複合ゾルをゆっくりと混合し１時間攪拌した。この混合スラリを１２０℃のオイルバス中でエバポレータを用いて減圧下で水分を留去させ、得られた粉末を８０℃で６時間、更に１５０℃で１２時間乾燥した後に、５５０℃で２時間空気気流下で焼成した。
[Example 3]
PVP-Rh colloid (Rh particle size: 2 nm, Rh: 2 wt%) and silica sol (10 wt%) were dispersed in pure water and stirred with a magnetic stirrer for about 1 hour. Furthermore, by adding a 5% nitric acid solution and adjusting the pH appropriately, an Rh-silica composite sol in which the silica sol was adsorbed around the Rh colloid was obtained. Meanwhile, a slurry in which a zirconium oxide-lanthanum oxide composite compound (specific surface area: 70 m 2 / g) was dispersed in pure water was pulverized to a median diameter of 2 μm or less by wet pulverization with a ball mill (ball diameter: 10 mm). Thereafter, the mixture was further pulverized with a bead mill (bead diameter: 0.1 mm) with a laser diffraction / scattering particle size distribution meter so that the median diameter became 120 nm. In this slurry, the Rh-silica composite sol was mixed slowly and stirred for 1 hour. Water was distilled off from this mixed slurry in an oil bath at 120 ° C. under reduced pressure using an evaporator, and the resulting powder was dried at 80 ° C. for 6 hours and further at 150 ° C. for 12 hours, and then at 550 ° C. for 2 hours. Firing was performed under an air stream.
これによりＲｈ粒子の周囲にシリカが存在し、さらにＺｒ−Ｌａ−Ｏｘ複合酸化物で覆われた触媒を得た。 As a result, a catalyst in which silica was present around the Rh particles and covered with the Zr—La—O x composite oxide was obtained.
［実施例４］
ＰＶＰ−Ｒｈコロイド（Ｒｈ粒径：２ｎｍ、Ｒｈ：２ｗｔ％）と、アルミナゾル（１０ｗｔ％）、セリアゾル（１５ｗｔ％）とを純水中に分散させ、約１時間マグネットスターラにて攪拌した。更に、５％硝酸溶液を加えて適宜ｐＨを調整することにより、Ｒｈコロイド周囲にアルミナゾルとセリアゾルとが吸着したＲｈ−アルミナ−セリア複合ゾルを得た。その一方で、酸化ジルコニウム−酸化ランタン複合化合物（比表面積：７０ｍ２／ｇ）を純水中に分散させ、このスラリをボールミル（ボール径：１０ｍｍ）で湿式粉砕によりメジアン径を２μｍ以下に粉砕した後、更にビーズミル（ビーズ径：０．１ｍｍ）により、レーザ回折散乱型粒度分布計でメジアン径が１２０ｎｍになるよう粉砕した。このスラリ中に、先ほどのＲｈ−アルミナ−セリア複合ゾルをゆっくりと混合し１時間攪拌した。この混合スラリを１２０℃のオイルバス中でエバポレータを用いて減圧下で水分を留去させ、得られた粉末を８０℃で６時間、更に１５０℃で１２時間乾燥した後に、５５０℃で２時間空気気流下で焼成した。
[Example 4]
PVP-Rh colloid (Rh particle size: 2 nm, Rh: 2 wt%), alumina sol (10 wt%), and ceria sol (15 wt%) were dispersed in pure water and stirred with a magnetic stirrer for about 1 hour. Further, a 5% nitric acid solution was added to adjust the pH appropriately to obtain an Rh-alumina-ceria composite sol in which the alumina sol and ceria sol were adsorbed around the Rh colloid. Meanwhile, a zirconium oxide-lanthanum oxide composite compound (specific surface area: 70 m 2 / g) was dispersed in pure water, and the slurry was pulverized to a median diameter of 2 μm or less by wet pulverization with a ball mill (ball diameter: 10 mm). Thereafter, the mixture was further pulverized with a bead mill (bead diameter: 0.1 mm) with a laser diffraction / scattering particle size distribution meter so that the median diameter became 120 nm. In this slurry, the Rh-alumina-ceria composite sol was slowly mixed and stirred for 1 hour. Water was distilled off from this mixed slurry in an oil bath at 120 ° C. under reduced pressure using an evaporator, and the resulting powder was dried at 80 ° C. for 6 hours and further at 150 ° C. for 12 hours, and then at 550 ° C. for 2 hours. Firing was performed under an air stream.
これによりＲｈ粒子の周囲にアルミナ及びセリアが存在し、さらにＺｒ−Ｌａ−Ｏｘ複合酸化物で覆われた触媒を得た。 As a result, alumina and ceria were present around the Rh particles, and a catalyst covered with a Zr—La—O x composite oxide was obtained.
［実施例５］
ＰＶＰ−Ｒｈコロイド（Ｒｈ粒径：２ｎｍ、Ｒｈ：２ｗｔ％）と、チタニアゾル（１０ｗｔ％）とを純水中に分散させ、約１時間マグネットスターラにて攪拌した。更に、５％硝酸溶液を加えて適宜ｐＨを調整することにより、Ｒｈコロイド周囲にチタニアゾルが吸着したＲｈ−チタニア複合ゾルを得た。その一方で、酸化ジルコニウム−酸化ランタン複合化合物（比表面積：７０ｍ２／ｇ）を純水中に分散させたスラリを、ボールミル（ボール径：１０ｍｍ）で湿式粉砕によりメジアン径を２μｍ以下に粉砕した後、更にビーズミル（ビーズ径：０．１ｍｍ）により、レーザ回折散乱型粒度分布計でメジアン径が１２０ｎｍになるよう粉砕した。このスラリ中に、先ほどのＲｈ−チタニア複合ゾルをゆっくりと混合し１時間攪拌した。この混合スラリを１２０℃のオイルバス中でエバポレータを用いて減圧下で水分を留去させ、得られた粉末を８０℃で６時間、更に１５０℃で１２時間乾燥した後に、５５０℃で２時間空気気流下で焼成した。
[Example 5]
PVP-Rh colloid (Rh particle size: 2 nm, Rh: 2 wt%) and titania sol (10 wt%) were dispersed in pure water and stirred with a magnetic stirrer for about 1 hour. Further, by adjusting the pH appropriately by adding a 5% nitric acid solution, an Rh-titania composite sol in which the titania sol was adsorbed around the Rh colloid was obtained. Meanwhile, a slurry in which a zirconium oxide-lanthanum oxide composite compound (specific surface area: 70 m 2 / g) was dispersed in pure water was pulverized to a median diameter of 2 μm or less by wet pulverization with a ball mill (ball diameter: 10 mm). Thereafter, the mixture was further pulverized with a bead mill (bead diameter: 0.1 mm) with a laser diffraction / scattering particle size distribution meter so that the median diameter became 120 nm. In this slurry, the Rh-titania composite sol was slowly mixed and stirred for 1 hour. Water was distilled off from this mixed slurry in an oil bath at 120 ° C. under reduced pressure using an evaporator, and the resulting powder was dried at 80 ° C. for 6 hours and further at 150 ° C. for 12 hours, and then at 550 ° C. for 2 hours. Firing was performed under an air stream.
これによりＲｈ粒子の周囲にチタニアが存在し、更にＺｒ−Ｌａ−Ｏｘ複合酸化物で覆われた触媒を得た。 As a result, a catalyst in which titania was present around the Rh particles and was further covered with a Zr—La—O x composite oxide was obtained.
［比較例１］
硝酸ロジウム硝酸酸性溶液（Ｒｈ：８．１ｗｔ％）と純水とを混合し、市販の酸化ジルコニア−酸化ランタン複合酸化物（比表面積：７０ｍ２／ｇ）をこの溶液中に分散させ、約２時間マグネットスターラで攪拌した。溶媒を留去した後、１５０℃で１２時間乾燥し、４００℃で１時間空気気流下で焼成した。
[Comparative Example 1]
A rhodium nitrate acidic solution (Rh: 8.1 wt%) and pure water are mixed, and a commercially available zirconia oxide-lanthanum oxide composite oxide (specific surface area: 70 m 2 / g) is dispersed in this solution. Stir with a magnetic stirrer for hours. After distilling off the solvent, it was dried at 150 ° C. for 12 hours and calcined at 400 ° C. for 1 hour in an air stream.
これにより酸化ランタン−ジルコニウム上にＲｈ粒子が担持された触媒を得た。 As a result, a catalyst having Rh particles supported on lanthanum oxide-zirconium was obtained.
［比較例２］
硝酸ロジウム硝酸酸性溶液（Ｒｈ：８．１ｗｔ％）と純水とを混合し、市販の酸化ジルコニウム−酸化セリウム複合酸化物（比表面積：７０ｍ２／ｇ）をこの溶液中に分散させ、約２時間マグネットスターラで攪拌した。溶媒を留去した後、１５０℃で１２時間乾燥し、４００℃で１時間空気気流下で焼成した。
[Comparative Example 2]
A rhodium nitrate acidic solution (Rh: 8.1 wt%) and pure water are mixed, and a commercially available zirconium oxide-cerium oxide composite oxide (specific surface area: 70 m 2 / g) is dispersed in this solution. Stir with a magnetic stirrer for hours. After distilling off the solvent, it was dried at 150 ° C. for 12 hours and calcined at 400 ° C. for 1 hour in an air stream.
これにより酸化ジルコニウム−酸化セリウム上にＲｈ粒子が担持された触媒を得た。 As a result, a catalyst having Rh particles supported on zirconium oxide-cerium oxide was obtained.
２．内層触媒粉末調製
硝酸セリウム６水和物を純水中に溶解させた溶液中に、活性アルミナ（比表面積１００ｍ２／ｇ）を分散させ、約２時間マグネットスターラにて攪拌した。溶媒を留去した後、１５０℃で１２時間乾燥し、空気気流下にて４００℃、１時間焼成を行った。この粉末をジニトロジアミン白金硝酸酸性水溶液（Ｐｔ：８．８３ｗｔ％）と純水とを混合した溶液中に分散させてマグネットスターラにて２時間攪拌した。溶媒を留去した後、１５０℃で１２時間乾燥し、空気気流下にて４００℃、１時間焼成を行い、Ｐｔを担持した酸化セリウム−アルミナを得た。
2. Preparation of inner layer catalyst powder Activated alumina (specific surface area 100 m 2 / g) was dispersed in a solution of cerium nitrate hexahydrate dissolved in pure water, and stirred for about 2 hours with a magnetic stirrer. After the solvent was distilled off, it was dried at 150 ° C. for 12 hours, and baked in an air stream at 400 ° C. for 1 hour. This powder was dispersed in a mixed solution of dinitrodiamine platinum nitrate acidic aqueous solution (Pt: 8.83 wt%) and pure water and stirred with a magnetic stirrer for 2 hours. After the solvent was distilled off, it was dried at 150 ° C. for 12 hours, and baked at 400 ° C. for 1 hour in an air stream to obtain cerium oxide-alumina carrying Pt.
３．ハニカム状基体へのコート層の作成
上述した内層触媒粉末調製の操作で得られた触媒粉末を３６３．６ｇ、ベーマイトを５０．９ｇ、１０％硝酸を４２．０ｇ、イオン交換水を５７５．３ｇ、磁性ポットに投入し、アルミナボールとともに振とう粉砕し、内層用触媒スラリーを得た。このときのスラリ粒径は２．８μｍであった。
3. Preparation of coat layer on honeycomb substrate 363.6 g of catalyst powder obtained by the above-described operation of preparing the inner layer catalyst powder, 50.9 g of boehmite, 42.0 g of 10% nitric acid, 575.3 g of ion-exchanged water, It was put into a magnetic pot and shaken and pulverized with alumina balls to obtain an inner layer catalyst slurry. The slurry particle size at this time was 2.8 μm.
また、前述した表層触媒粉末調製の操作で得られた各実施例及び各比較例の触媒粉末をそれぞれ３６３．６ｇ、ベーマイトを５０．９ｇ、１０％硝酸を４２．０ｇ、イオン交換水を５７５．３ｇ、磁性ポットに投入し、アルミナボールとともに振とう粉砕し、各表層用触媒スラリーを得た。このときのスラリ粒径は２．８μｍであった。 In addition, 363.6 g of each of the catalyst powders obtained in the above-described preparation of the surface catalyst powder and the comparative examples, 50.9 g of boehmite, 42.0 g of 10% nitric acid, and 575. 3 g was put into a magnetic pot and shaken and ground together with alumina balls to obtain catalyst slurry for each surface layer. The slurry particle size at this time was 2.8 μm.
上記内層用触媒スラリをセラミック製、ハニカム担体（４００セル／６ミル、１．２Ｌ）に投入し、空気流にて、余剰スラリを除去し、120℃にて乾燥、400℃、空気気流中で焼成した。コート量は１００ｇ／Lであった。次に、上記表層用触媒スラリをそれぞれ同様に塗布した。コート量は１００ｇ／Lであった。 The above inner layer catalyst slurry is put into a ceramic honeycomb support (400 cell / 6 mil, 1.2 L), excess slurry is removed by air flow, dried at 120 ° C., 400 ° C. in an air stream Baked. The coating amount was 100 g / L. Next, the catalyst slurry for the surface layer was applied in the same manner. The coating amount was 100 g / L.
以上の工程により、内層にＰｔが１．０ｇ／L、表層には表１中にそれぞれ示された量のＲｈを含む各実施例及び各比較例の触媒を得た。すなわち、各々の触媒は、内層は共通のＰｔを含むコート層を持ち、表層には各実施例及び各比較例の成分とＲｈを含むコート層を有する。 Through the above-described steps, the catalyst of each Example and each Comparative Example including Pt of 1.0 g / L for the inner layer and the amount of Rh indicated in Table 1 for the surface layer was obtained. That is, in each catalyst, the inner layer has a common coating layer containing Pt, and the surface layer has a coating layer containing the components of each Example and each Comparative Example and Rh.
また、以下に述べる耐久試験を行う前の初期状態において、表層のロジウム粒子の粒径は、いずれも２ｎｍ以下であった。また、表層のコート層についてＴＥＭ−ＥＤＸを用いて調べたところ、実施例１〜５の試料はいずれも、ロジウム粒子の８０％以上が、緩衝材上に存在していることが確認された。
４．触媒の耐久試験
実施例及び比較例の各触媒について、耐久試験を行った。耐久試験は、日産自動車製Ｖ型６気筒エンジンの両バンクに各々１個の触媒コンバータを設置し、使用燃料に無鉛ガソリンを用い、触媒入口温度が８５０℃、５０時間の条件で行った。この温度調整は、触媒入口温度が上記温度となるようコンバータの位置を調整することにより行った。
4). Endurance test of catalyst The endurance test was done about each catalyst of an Example and a comparative example. The endurance test was conducted under the conditions that one catalytic converter was installed in each bank of Nissan Motor's V-type 6-cylinder engine, unleaded gasoline was used as the fuel, and the catalyst inlet temperature was 850 ° C. for 50 hours. This temperature adjustment was performed by adjusting the position of the converter so that the catalyst inlet temperature was the above temperature.
５．触媒性能評価条件
上記耐久試験を施した触媒の一部をくり抜き、４０ｃｃとして、模擬排ガス流通装置に組み込んだ。次に、表２に示す組成のモデルガスを触媒に導入し、１０℃／ｍｉｎの昇温速度で入口ガス温度を上昇させた。出口ガス組成を連続分析計にて測定し、得られた入口及び出口ガス濃度から、各温度での排ガス転化率を算出した。入口ガス濃度に対して出口ガス濃度が半分、すなわち転化率５０％となる温度をＴ５０と表し、ＨＣの転化率５０％温度をＨＣ−Ｔ５０として表１中に記載した。また、この表１には、耐久試験後のＲｈ粒子の平均粒径及びＲｈ粒子の周囲の緩衝材の接触率についても併記した。Ｒｈ粒子の平均粒径は、ＴＥＭにより測定したものである。またＲｈ粒子周囲の緩衝材の接触率は、ＴＥＭ−ＥＤＸにより、ＥＤＸ同一スポット（５ｎｍ）内に存在するＲｈと緩衝材の比を測定することにより求めた。具体的には、スポットを１０点とり、各点で測定したＲｈと緩衝材の比を、縦軸がＲｈ（ａｔｍ％）、横軸が緩衝材主元素（Ａｌ等）（ａｔｍ％）とするグラフにして比の直線を求め、その直線のグラフ上の傾きの値を、触媒製造時に添加したＲｈ量と緩衝材量とから求められる理論的な比の値を１００とする百分率により接触率を計算した。例えば、触媒中の含有量についてＲｈが３ａｔｍ％、Ａｌが１０ａｔｍ％とした時、ＲｈがＡｌと１００％接触していれば比の直線の傾きは３／１０＝０．３である（これを１００％とする。）。そして、実際にＴＥＭ−ＥＤＸにより計測して、得られた直線の傾きが２／１０＝０．２であるとき、接触率は０．２／０．３＝０．６７、すなわち、６７％と計算できる。同様にして、各実施例及び各比較例の触媒についての接触率を求めた。
表１に示された触媒性能評価から分かるように、本発明に従う実施例１〜５は、緩衝材を有していない比較例１及び比較例２と比べて、耐久試験後のＲｈ粒子が小さく、Ｒｈ粒子の凝集が抑制されていることがわかる。これは、実施例１〜５は、緩衝材がＲｈ粒子の周囲に形成されていることから、Ｒｈ粒子同士の凝集が抑制されたためと考えられる。 As can be seen from the catalyst performance evaluation shown in Table 1, Examples 1 to 5 according to the present invention have smaller Rh particles after the endurance test compared to Comparative Example 1 and Comparative Example 2 that do not have a buffer material. It can be seen that aggregation of Rh particles is suppressed. This is probably because in Examples 1 to 5, the buffer material was formed around the Rh particles, and thus aggregation of the Rh particles was suppressed.
また、実施例１〜５は、緩衝材を有していない比較例１及び比較例２と比べて、ＨＣ−Ｔ５０の温度が低く、耐久試験後においても、優れた排ガス浄化性能を具備していることが分かる。これは、緩衝材がＲｈ粒子の周囲に形成されていることから、比較例１及び比較例２のように複合酸化物の凝集に伴ってガス拡散性が低下することがかったためと考えられる。 Moreover, Examples 1-5 are low in the temperature of HC-T50 compared with the comparative example 1 and the comparative example 2 which do not have a buffer material, and have comprised the exhaust gas purification performance outstanding after the endurance test. I understand that. This is probably because the buffer material is formed around the Rh particles, so that the gas diffusibility is likely to be lowered with the aggregation of the composite oxide as in Comparative Example 1 and Comparative Example 2.
１ 排ガス浄化用触媒
２ Ｒｈ粒子
３ 緩衝材
４ 酸化物
DESCRIPTION OF SYMBOLS 1 Exhaust gas purification catalyst 2 Rh particle 3 Buffer material 4 Oxide
Claims (7)
このＲｈ粒子の周囲に形成され、当該Ｒｈ粒子を担持する多孔質の緩衝材と、
このＲｈ粒子及び緩衝材の周囲に形成され、この緩衝材とは実質的に非固溶な酸化物とをそなえ、
前記緩衝材は、Ｒｈ粒子と複合化可能な材料よりなることを特徴とする排ガス浄化用触媒。 Rh particles,
A porous buffer formed around the Rh particles and carrying the Rh particles;
Formed around the Rh particles and the buffer material, the buffer material having a substantially non-solid oxide,
The said buffer material consists of material which can be combined with Rh particle | grains, The exhaust gas purification catalyst characterized by the above-mentioned.
Ｒｈ前駆体と緩衝材前駆体とを混合しRｈ−緩衝材ユニットを形成する工程を含み、更には該ユニットを酸化物前駆体と混合して該ユニットを酸化物で包接する工程を含むことを特徴とする排ガス浄化用触媒の製造方法。 Rh particles, a porous buffer material formed around the Rh particles and supporting the Rh particles, and formed around the buffer material and the Rh particles. The buffer material is substantially insoluble. A method for producing an exhaust gas purifying catalyst comprising an oxide and comprising:
Mixing the Rh precursor and the buffer material precursor to form a Rh-buffer material unit, and further including the step of mixing the unit with the oxide precursor and including the unit with the oxide. A method for producing an exhaust gas purifying catalyst.
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| JP2014176848A (en) * | 2008-08-27 | 2014-09-25 | Umicore Shokubai Japan Co Ltd | Exhaust gas purification catalyst and exhaust gas purification method using the same |
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