JP2011036834A - Catalyst for cleaning exhaust, and method of producing the same - Google Patents
Catalyst for cleaning exhaust, and method of producing the same Download PDFInfo
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- 239000003054 catalyst Substances 0.000 title claims abstract description 181
- 238000000034 method Methods 0.000 title claims description 6
- 238000004140 cleaning Methods 0.000 title abstract 2
- 239000000843 powder Substances 0.000 claims abstract description 292
- 239000002245 particle Substances 0.000 claims abstract description 157
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 claims abstract description 101
- 229910052751 metal Inorganic materials 0.000 claims abstract description 77
- 239000002184 metal Substances 0.000 claims abstract description 77
- 238000009826 distribution Methods 0.000 claims abstract description 65
- 239000011164 primary particle Substances 0.000 claims abstract description 61
- 230000001186 cumulative effect Effects 0.000 claims abstract description 57
- 239000011163 secondary particle Substances 0.000 claims abstract description 32
- 230000003197 catalytic effect Effects 0.000 claims abstract description 14
- 239000002131 composite material Substances 0.000 claims description 151
- 238000000746 purification Methods 0.000 claims description 35
- 238000010298 pulverizing process Methods 0.000 claims description 25
- 239000002002 slurry Substances 0.000 claims description 17
- 239000011230 binding agent Substances 0.000 claims description 15
- 238000002360 preparation method Methods 0.000 claims description 14
- 230000002776 aggregation Effects 0.000 claims description 11
- 238000004220 aggregation Methods 0.000 claims description 7
- 239000011248 coating agent Substances 0.000 claims description 6
- 238000000576 coating method Methods 0.000 claims description 6
- 238000004519 manufacturing process Methods 0.000 claims description 5
- 229910052726 zirconium Inorganic materials 0.000 claims description 4
- 230000004931 aggregating effect Effects 0.000 claims description 2
- 229910052746 lanthanum Inorganic materials 0.000 claims description 2
- 230000008569 process Effects 0.000 claims description 2
- KDLHZDBZIXYQEI-UHFFFAOYSA-N palladium Substances [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 description 87
- 239000007789 gas Substances 0.000 description 60
- 239000010948 rhodium Substances 0.000 description 46
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 25
- 229910052760 oxygen Inorganic materials 0.000 description 25
- 239000001301 oxygen Substances 0.000 description 25
- 238000003860 storage Methods 0.000 description 20
- MWUXSHHQAYIFBG-UHFFFAOYSA-N nitrogen oxide Inorganic materials O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 description 17
- 230000000052 comparative effect Effects 0.000 description 16
- 238000011068 loading method Methods 0.000 description 12
- 239000000243 solution Substances 0.000 description 10
- MCMNRKCIXSYSNV-UHFFFAOYSA-N Zirconium dioxide Chemical compound O=[Zr]=O MCMNRKCIXSYSNV-UHFFFAOYSA-N 0.000 description 8
- 239000000203 mixture Substances 0.000 description 8
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 8
- UJVRJBAUJYZFIX-UHFFFAOYSA-N nitric acid;oxozirconium Chemical compound [Zr]=O.O[N+]([O-])=O.O[N+]([O-])=O UJVRJBAUJYZFIX-UHFFFAOYSA-N 0.000 description 7
- 238000000635 electron micrograph Methods 0.000 description 6
- 239000000446 fuel Substances 0.000 description 6
- 238000002156 mixing Methods 0.000 description 6
- 239000011148 porous material Substances 0.000 description 6
- 229910052703 rhodium Inorganic materials 0.000 description 6
- 239000006185 dispersion Substances 0.000 description 5
- 239000000463 material Substances 0.000 description 5
- 229910017493 Nd 2 O 3 Inorganic materials 0.000 description 4
- 238000005054 agglomeration Methods 0.000 description 4
- CETPSERCERDGAM-UHFFFAOYSA-N ceric oxide Chemical compound O=[Ce]=O CETPSERCERDGAM-UHFFFAOYSA-N 0.000 description 4
- 229910000422 cerium(IV) oxide Inorganic materials 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- 238000000227 grinding Methods 0.000 description 4
- GPNDARIEYHPYAY-UHFFFAOYSA-N palladium(ii) nitrate Chemical compound [Pd+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O GPNDARIEYHPYAY-UHFFFAOYSA-N 0.000 description 4
- 229910052697 platinum Inorganic materials 0.000 description 4
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Substances [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 4
- 229910021193 La 2 O 3 Inorganic materials 0.000 description 3
- 229910052878 cordierite Inorganic materials 0.000 description 3
- 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 3
- 150000002500 ions Chemical class 0.000 description 3
- 150000002739 metals Chemical class 0.000 description 3
- 229910000510 noble metal Inorganic materials 0.000 description 3
- 231100000572 poisoning Toxicity 0.000 description 3
- 230000000607 poisoning effect Effects 0.000 description 3
- 239000000047 product Substances 0.000 description 3
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 description 2
- 229910052684 Cerium Inorganic materials 0.000 description 2
- 235000011114 ammonium hydroxide Nutrition 0.000 description 2
- 239000011324 bead Substances 0.000 description 2
- 230000015556 catabolic process Effects 0.000 description 2
- 210000004027 cell Anatomy 0.000 description 2
- 210000002421 cell wall Anatomy 0.000 description 2
- 229910000420 cerium oxide Inorganic materials 0.000 description 2
- 238000006731 degradation reaction Methods 0.000 description 2
- 238000001704 evaporation Methods 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- BMMGVYCKOGBVEV-UHFFFAOYSA-N oxo(oxoceriooxy)cerium Chemical compound [Ce]=O.O=[Ce]=O BMMGVYCKOGBVEV-UHFFFAOYSA-N 0.000 description 2
- 229910052763 palladium Inorganic materials 0.000 description 2
- 239000002244 precipitate Substances 0.000 description 2
- 230000002265 prevention Effects 0.000 description 2
- 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 2
- 239000007787 solid Substances 0.000 description 2
- 239000006104 solid solution Substances 0.000 description 2
- OERNJTNJEZOPIA-UHFFFAOYSA-N zirconium nitrate Chemical compound [Zr+4].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O OERNJTNJEZOPIA-UHFFFAOYSA-N 0.000 description 2
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 1
- 239000004215 Carbon black (E152) Substances 0.000 description 1
- 229910002651 NO3 Inorganic materials 0.000 description 1
- 229910052779 Neodymium Inorganic materials 0.000 description 1
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 1
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 1
- QCWXUUIWCKQGHC-UHFFFAOYSA-N Zirconium Chemical compound [Zr] QCWXUUIWCKQGHC-UHFFFAOYSA-N 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 230000032683 aging Effects 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
- 229910052788 barium Inorganic materials 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 229910052797 bismuth Inorganic materials 0.000 description 1
- JCXGWMGPZLAOME-UHFFFAOYSA-N bismuth atom Chemical compound [Bi] JCXGWMGPZLAOME-UHFFFAOYSA-N 0.000 description 1
- 229910052791 calcium Inorganic materials 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
- 230000008859 change Effects 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 238000000975 co-precipitation Methods 0.000 description 1
- 238000013329 compounding Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000010304 firing Methods 0.000 description 1
- 229910052737 gold Inorganic materials 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 229930195733 hydrocarbon Natural products 0.000 description 1
- 150000002430 hydrocarbons Chemical class 0.000 description 1
- 238000005470 impregnation Methods 0.000 description 1
- 229910052738 indium Inorganic materials 0.000 description 1
- 238000005342 ion exchange Methods 0.000 description 1
- 238000010030 laminating Methods 0.000 description 1
- FYDKNKUEBJQCCN-UHFFFAOYSA-N lanthanum(3+);trinitrate Chemical compound [La+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O FYDKNKUEBJQCCN-UHFFFAOYSA-N 0.000 description 1
- 229910052749 magnesium Inorganic materials 0.000 description 1
- 229910021645 metal ion Inorganic materials 0.000 description 1
- 239000011259 mixed solution Substances 0.000 description 1
- VQVDTKCSDUNYBO-UHFFFAOYSA-N neodymium(3+);trinitrate;hexahydrate Chemical compound O.O.O.O.O.O.[Nd+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O VQVDTKCSDUNYBO-UHFFFAOYSA-N 0.000 description 1
- 230000003472 neutralizing effect Effects 0.000 description 1
- 150000002823 nitrates Chemical class 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 125000004430 oxygen atom Chemical group O* 0.000 description 1
- RVTZCBVAJQQJTK-UHFFFAOYSA-N oxygen(2-);zirconium(4+) Chemical compound [O-2].[O-2].[Zr+4] RVTZCBVAJQQJTK-UHFFFAOYSA-N 0.000 description 1
- 229910052698 phosphorus Inorganic materials 0.000 description 1
- 239000011574 phosphorus Substances 0.000 description 1
- 229910052700 potassium Inorganic materials 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 229910052761 rare earth metal Inorganic materials 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 230000004044 response Effects 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 229910052709 silver Inorganic materials 0.000 description 1
- -1 slurrying it Substances 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 239000011232 storage material Substances 0.000 description 1
- 229910052712 strontium Inorganic materials 0.000 description 1
- 229910052717 sulfur Inorganic materials 0.000 description 1
- 239000011593 sulfur Substances 0.000 description 1
- 150000003755 zirconium compounds Chemical class 0.000 description 1
- 229910001928 zirconium oxide Inorganic materials 0.000 description 1
Abstract
Description
本発明は、排気ガス浄化用触媒およびその製造方法に関する。 The present invention relates to an exhaust gas purification catalyst and a method for producing the same.
排気ガス浄化用触媒では、触媒金属の凝集による性能の低下が従来より問題になっている。この触媒金属の凝集は、触媒が高温の排気ガスに晒されることによって生ずる。例えば、自動車エンジンの排気マニホールドに直結される排気ガス浄化用触媒では、触媒温度が１１００℃程度の高温になることがある。触媒金属を活性アルミナのような大きな比表面積を有するサポート材に分散担持させても、その触媒金属が次第に凝集していくことは避けられない。従来の触媒では、触媒金属が凝集してもある程度の触媒性能が得られるように、触媒金属量が多めになっている。しかし、触媒金属として一般に採用されるＰｔ、Ｐｄ、Ｒｈ等の貴金属は高価であり、しかも、近年はそのようなレアメタル資源の確保が求められている。 In exhaust gas purifying catalysts, performance degradation due to agglomeration of catalytic metals has been a problem. This agglomeration of the catalytic metal occurs when the catalyst is exposed to hot exhaust gas. For example, an exhaust gas purification catalyst directly connected to an exhaust manifold of an automobile engine may have a catalyst temperature as high as about 1100 ° C. Even when the catalyst metal is dispersed and supported on a support material having a large specific surface area such as activated alumina, it is inevitable that the catalyst metal gradually aggregates. In conventional catalysts, the amount of catalyst metal is large so that a certain degree of catalyst performance can be obtained even if the catalyst metal aggregates. However, noble metals such as Pt, Pd, and Rh that are generally employed as catalyst metals are expensive, and in recent years, it is required to secure such rare metal resources.
これに対して、触媒金属を活性アルミナ等の表面に担持するだけでなく、排気ガスの空燃比の変動に応じて酸素を吸蔵・放出する酸素吸蔵放出材として機能するＣｅＺｒ系複合酸化物に触媒金属を固溶させることが行なわれている（特許文献１，２）。このＣｅＺｒ系複合酸化物に触媒金属を固溶させると、その酸素吸蔵放出能が大幅に改善される。そのため、この触媒金属を固溶したＣｅＺｒ系複合酸化物を三元触媒に使用し、理論空燃比を中心として排気ガスの空燃比をリーンとリッチとに繰り返し変化させると、少ない触媒金属量でも優れた排気ガス浄化性能が得られる。 On the other hand, the catalyst metal is not only supported on the surface of activated alumina or the like, but also catalyzed by a CeZr-based composite oxide that functions as an oxygen storage / release material that stores and releases oxygen in response to fluctuations in the air-fuel ratio of the exhaust gas. Metals are dissolved (Patent Documents 1 and 2). When a catalytic metal is dissolved in this CeZr-based composite oxide, its oxygen storage / release capability is greatly improved. For this reason, using a CeZr-based composite oxide in which this catalytic metal is dissolved in a three-way catalyst and repeatedly changing the air-fuel ratio of the exhaust gas to lean and rich centering on the theoretical air-fuel ratio is excellent even with a small amount of catalyst metal Exhaust gas purification performance can be obtained.
また、アルミナに微細な酸素吸蔵材粒子（Ｃｅ含有複合酸化物粒子）と触媒貴金属とを担持させることによって触媒性能を向上させるという提案も知られている。例えば特許文献３には、アルミナ粉末とセリウム酸化物ゾルを含むスラリーをコートし焼成し、そのコート層にジルコニウム化合物溶液を含浸させて焼成することにより、セリウム酸化物とジルコニウム酸化物とが互いに固溶した平均粒径５〜１００ｎｍの固溶体をアルミナ粒子上に形成し、さらに、当該コート層に触媒貴金属を担持すること、固溶体の平均粒径５〜１００ｎｍとすることにより、酸素吸蔵効果が充分に発揮され、しかもアルミナの細孔の閉塞が防止されることが記載されている。 There is also known a proposal that catalyst performance is improved by supporting fine oxygen storage material particles (Ce-containing composite oxide particles) and catalytic noble metal on alumina. For example, in Patent Document 3, a slurry containing alumina powder and a cerium oxide sol is coated and fired, and the coat layer is impregnated with a zirconium compound solution and fired, whereby the cerium oxide and the zirconium oxide are fixed to each other. A dissolved solid solution having an average particle diameter of 5 to 100 nm is formed on the alumina particles, and further, the catalyst layer is loaded with the catalyst noble metal, and the average particle diameter of the solid solution is set to 5 to 100 nm. It is demonstrated that blockage of the pores of alumina is prevented.
また、特許文献４には、一次粒子径６ｎｍ、二次粒子径１０μｍのセリア粉末をジルコニア粉末又は硝酸ジルコニル水溶液と共に攪拌ミルに投入して粉砕することにより、セリアとジルコニアとが互いに固溶し且つ５０質量％以上の粒子の粒径が１００ｎｍ以下である触媒粉末を得ること、得られた触媒粉末を２．５重量倍のγアルミナと混合し、さらにＰｔ及びＲｈを添加して排気ガス浄化用触媒とすること、粒径を上記のように設定することにより、粉末の比表面積が高くなり、酸素吸蔵効果が高くなることが記載されている。 Patent Document 4 discloses that ceria powder having a primary particle diameter of 6 nm and a secondary particle diameter of 10 μm is put into a stirring mill together with zirconia powder or an aqueous solution of zirconyl nitrate and pulverized, so that ceria and zirconia are dissolved in each other and Obtaining a catalyst powder having a particle size of 50% by mass or more and a particle size of 100 nm or less, mixing the obtained catalyst powder with 2.5 times by weight of γ-alumina, and further adding Pt and Rh for exhaust gas purification It is described that by using a catalyst and setting the particle size as described above, the specific surface area of the powder is increased and the oxygen storage effect is increased.
しかし、特許文献３，４は、Ｃｅ含有複合酸化物粉末の粒径を、酸素吸蔵効果の向上という観点から、アルミナの細孔を閉塞することにならない限度において、できるだけ小さくすることを開示するが、そこには、Ｃｅ含有複合酸化物粉末の凝集防止の観点が欠けている。すなわち、過度に微細なＣｅ含有複合酸化物粉末を触媒に使用すると、触媒が高温になったときに、Ｃｅ含有複合酸化物粉末が、微細であるがために、アルミナ粒子上で凝集し、早期の性能低下を招き易くなる。 However, Patent Documents 3 and 4 disclose that the particle diameter of the Ce-containing composite oxide powder is made as small as possible without limiting the pores of alumina from the viewpoint of improving the oxygen storage effect. There is a lack of aggregation prevention of the Ce-containing composite oxide powder. That is, when an excessively fine Ce-containing composite oxide powder is used as a catalyst, when the catalyst becomes high temperature, the Ce-containing composite oxide powder is agglomerated on the alumina particles because it is fine, It becomes easy to invite the performance fall.
また、特許文献４には、一次粒子径６ｎｍ、二次粒子径１０μｍのセリア粉末を粉砕して５０質量％以上の粒子の粒径が１００ｎｍ以下になるように微細化することが記載されているが、その場合、一次粒子も破壊されるため、一次粒子間の細孔も極めて微細なものになり、二次粒子の表面に存する一次粒子は優れた酸素吸蔵効果を発揮するとしても、内部に埋もれている一次粒子には排気ガスが接触し難くなるため、仮に個々の一次粒子に触媒金属が担持されていても、高い酸素吸蔵放出能ないしは触媒活性は望めない。さらに、本特許文献４は、粉砕エネルギーによってセリアと、ジルコニウム又はセリウムを除く希土類元素とを固溶させるものであるため、１０時間乃至５０時間という長い処理時間が必要で、効率的とは言えない。 Patent Document 4 describes that a ceria powder having a primary particle diameter of 6 nm and a secondary particle diameter of 10 μm is pulverized and refined so that the particle diameter of 50% by mass or more becomes 100 nm or less. However, in this case, since the primary particles are also destroyed, the pores between the primary particles become very fine, and even though the primary particles existing on the surface of the secondary particles exhibit an excellent oxygen storage effect, Since the exhaust gas is difficult to come into contact with the buried primary particles, a high oxygen storage / release capacity or catalytic activity cannot be expected even if a catalyst metal is supported on each primary particle. Furthermore, since this patent document 4 dissolves ceria and rare earth elements excluding zirconium or cerium by pulverization energy, a long treatment time of 10 to 50 hours is required, which is not efficient. .
かかる点に鑑み、本発明では、酸素吸蔵放出能を有するＣｅ含有複合酸化物（Ｃｅイオンと他の金属イオンとを含む酸化物）粉末の一次粒子径及び二次粒子径を、触媒の分野においては月並みな単なる微細化という観点ではなく、内部に埋もれている一次粒子の有効利用の観点、Ｃｅ含有複合酸化物粉末の凝集防止の観点から見直している。すなわち、本発明者が、Ｃｅ含有複合酸化物粉末の一次粒子径及び二次粒子径を上記観点から検討したところ、それら粒径の制御及び活性アルミナ粉末の粒径の制御により、排気ガス浄化性能の向上に驚く効果が得られたものである。以下、具体的に説明する。 In view of this point, in the present invention, in the present invention, the primary particle size and the secondary particle size of Ce-containing complex oxide (oxide containing Ce ions and other metal ions) powder having oxygen storage / release ability are determined. Is reviewed from the viewpoint of effective utilization of primary particles buried inside, and the prevention of agglomeration of Ce-containing composite oxide powders, not from the viewpoint of mere miniaturization as usual. That is, the present inventor examined the primary particle size and the secondary particle size of the Ce-containing composite oxide powder from the above viewpoint. By controlling the particle size and the particle size of the activated alumina powder, the exhaust gas purification performance A surprising effect was obtained in the improvement. This will be specifically described below.
本発明は、触媒金属を担持したＣｅ含有複合酸化物粉末と活性アルミナ粉末とを混合状態で含有する触媒層が担体上に設けられている排気ガス浄化用触媒であって、
上記触媒金属を担持したＣｅ含有複合酸化物粉末は、上記触媒金属が分散担持された平均粒径５ｎｍ以上１０ｎｍ以下の多数の一次粒子が凝集してなる二次粒子によって構成され、該二次粒子の累積分布１０質量％粒径が９０ｎｍ以上、累積分布５０質量％粒径が１５０ｎｍ以上２１０ｎｍ以下、累積分布９０質量％粒径が３００ｎｍ以下である特定Ｃｅ含有複合酸化物粉末であり、
上記活性アルミナ粉末の平均粒径は、上記特定Ｃｅ含有複合酸化物粉末の上記累積分布９０質量％粒径よりも大きく、
上記活性アルミナ粉末に対する上記特定Ｃｅ含有複合酸化物粉末の質量比が１／１００以上５０／１００以下であることを特徴とする。
The present invention is an exhaust gas purification catalyst in which a catalyst layer containing a Ce-containing composite oxide powder supporting a catalytic metal and an activated alumina powder in a mixed state is provided on a carrier,
The Ce-containing composite oxide powder supporting the catalyst metal is composed of secondary particles formed by aggregation of a large number of primary particles having an average particle diameter of 5 nm to 10 nm on which the catalyst metal is dispersed and supported. A specific Ce-containing composite oxide powder having a cumulative distribution of 10% by mass particle size of 90 nm or more, a cumulative distribution of 50% by mass particle size of from 150 nm to 210 nm, and a cumulative distribution of 90% by mass of particle size of 300 nm or less.
The average particle size of the activated alumina powder is larger than the cumulative distribution 90 mass% particle size of the specific Ce-containing composite oxide powder,
The mass ratio of the specific Ce-containing composite oxide powder to the activated alumina powder is 1/100 or more and 50/100 or less.
ここに、触媒層において特定Ｃｅ含有複合酸化物粉末と活性アルミナ粉末とが混合状態にあれば、特定Ｃｅ含有複合酸化物粉末の少なくとも一部の粒子は活性アルミナ粉末の粒子に接触した状態になる。その場合、上述の如く、活性アルミナ粉末の粒径が特定Ｃｅ含有複合酸化物粉末の上記累積分布９０質量％粒径よりも大きいから、特定Ｃｅ含有複合酸化物粒子が活性アルミナ粒子に分散して担持された状態になる。 Here, if the specific Ce-containing composite oxide powder and the active alumina powder are in a mixed state in the catalyst layer, at least some of the particles of the specific Ce-containing composite oxide powder are in contact with the particles of the active alumina powder. . In that case, as described above, since the particle size of the activated alumina powder is larger than the 90 mass% particle size of the specific Ce-containing composite oxide powder, the specific Ce-containing composite oxide particles are dispersed in the activated alumina particles. It becomes a supported state.
そうして、特定Ｃｅ含有複合酸化物粉末は、二次粒子の累積分布１０質量％粒径が９０ｎｍ以上、累積分布５０質量％粒径が１５０ｎｍ以上２１０ｎｍ以下、累積分布９０質量％粒径が３００ｎｍ以下であるから、触媒が高温になったときの粒子の凝集が抑制される一方で、比較的高い酸素吸蔵放出能が得られる。すなわち、累積分布１０質量％粒径が９０ｎｍ以上であることにより、触媒が高温になったときの粒子の凝集防止に有利になり、累積分布９０質量％粒径が３００ｎｍ以下であることにより、比較的高い酸素吸蔵放出能が得られる。特に活性アルミナ粒子上に担持されている特定Ｃｅ含有複合酸化物粒子の分散安定化が図れ、触媒性能の維持に有利になる。 Thus, the specific Ce-containing composite oxide powder has a secondary particle cumulative distribution of 10% by mass particle size of 90 nm or more, a cumulative distribution of 50% by mass particle size of 150 nm or more and 210 nm or less, and a cumulative distribution of 90% by mass particle size of 300 nm. Since it is the following, the aggregation of particles when the temperature of the catalyst becomes high is suppressed, while a relatively high oxygen storage / release capability can be obtained. That is, when the cumulative distribution 10 mass% particle size is 90 nm or more, it is advantageous for preventing aggregation of the particles when the catalyst becomes high temperature, and the cumulative distribution 90 mass% particle size is 300 nm or less, High oxygen storage / release capability can be obtained. In particular, it is possible to stabilize the dispersion of the specific Ce-containing composite oxide particles supported on the activated alumina particles, which is advantageous for maintaining the catalyst performance.
しかも、特定Ｃｅ含有複合酸化物粉末の一次粒子の平均粒径が５ｎｍ以上１０ｎｍ以下であるということは、該Ｃｅ含有複合酸化物粉末の各粒子（二次粒子）においては、一次粒子間に、排気ガスが比較的円滑に流入する細孔が形成されているということである。従って、一次粒子に分散担持されている触媒金属が、排気ガスとの接触により、当該Ｃｅ含有複合酸化物の酸素吸蔵放出能の助長及び排気ガスの浄化に有効に働く。 In addition, the average particle size of the primary particles of the specific Ce-containing composite oxide powder is 5 nm or more and 10 nm or less, and in each particle (secondary particle) of the Ce-containing composite oxide powder, That is, the pores into which the exhaust gas flows relatively smoothly are formed. Therefore, the catalyst metal dispersedly supported on the primary particles effectively works to promote the oxygen storage / release capability of the Ce-containing composite oxide and to purify the exhaust gas through contact with the exhaust gas.
さらに、上記活性アルミナ粉末に対する特定Ｃｅ含有複合酸化物粉末の質量比が１／１００以上５０／１００以下であるから、Ｃｅ含有複合酸化物粉末の酸素吸蔵放出能による排気ガス浄化性能の向上に有利になる。すなわち、その質量比が１／１００未満であれば、Ｃｅ含有複合酸化物粉末が有する酸素吸蔵放出能の排気ガス浄化への利用が充分に図れず、５０／１００を超える質量比になると、特定Ｃｅ含有複合酸化物粉末の凝集が進み易くなるだけで、排気ガス浄化性能の向上にはかえって不利になる。 Furthermore, since the mass ratio of the specific Ce-containing composite oxide powder to the activated alumina powder is 1/100 or more and 50/100 or less, it is advantageous for improving the exhaust gas purification performance due to the oxygen storage / release ability of the Ce-containing composite oxide powder. become. That is, if the mass ratio is less than 1/100, the oxygen storage / release ability of the Ce-containing composite oxide powder cannot be sufficiently utilized for exhaust gas purification, and if the mass ratio exceeds 50/100, Only the aggregation of the Ce-containing composite oxide powder is facilitated, which is disadvantageous for improving the exhaust gas purification performance.
上記活性アルミナ粉末に対する上記特定Ｃｅ含有複合酸化物粉末の質量比が１／１００以上３０／１００以下であることが好ましい。 The mass ratio of the specific Ce-containing composite oxide powder to the activated alumina powder is preferably 1/100 or more and 30/100 or less.
好ましい実施形態では、活性アルミナ粉末の平均粒径は５μｍ以上３０μｍ以下である。 In a preferred embodiment, the average particle size of the activated alumina powder is 5 μm or more and 30 μm or less.
特定Ｃｅ含有複合酸化物粉末として好ましいのは、ＣｅＯ２とＺｒＯ２との質量比が同じか、ＺｒＯ２がリッチ（ＺｒＯ２含有量がＣｅＯ２含有量よりも多い）である複合酸化物（Ｃｅ及びＺｒの各イオンを含む酸化物）粉末であり、また、他の金属成分として好ましいのはＮｄである。Ｎｄを添加した特定Ｃｅ含有複合酸化物（Ｃｅ、Ｚｒ及びＮｄの各イオンを含む酸化物）の場合、好ましい組成（質量比）は、ＣｅＯ２：ＺｒＯ２：Ｎｄ２Ｏ３＝（５〜４５）：（４５〜８５）：（５〜２０）である。触媒金属の担持量は０．０１質量％以上２０質量％以下であることが好ましい。Ｎｄ以外の他の金属成分としては、例えばＰｒ、Ｙ、Ｌａ、Ｈｆ、Ｂａ、Ｓｒ、Ｃａ、Ｋ、Ｍｇがあげられる。触媒金属としては、Ｐｄ、Ｐｔ、Ｒｈ、Ｉｎ、Ａｕ、Ａｇがあげられる。 Preferred as certain Ce-containing composite oxide powder, or the mass ratio of CeO 2 and ZrO 2 are the same, the composite oxide ZrO 2 is rich (ZrO 2 content is more than CeO 2 content) (Ce And oxides containing each ion of Zr) and Nd is preferred as the other metal component. In the case of a specific Ce-containing composite oxide to which Nd is added (an oxide containing Ce, Zr and Nd ions), the preferred composition (mass ratio) is CeO 2 : ZrO 2 : Nd 2 O 3 = (5-45 ): (45-85): (5-20). The amount of catalyst metal supported is preferably 0.01% by mass or more and 20% by mass or less. Examples of other metal components other than Nd include Pr, Y, La, Hf, Ba, Sr, Ca, K, and Mg. Examples of the catalyst metal include Pd, Pt, Rh, In, Au, and Ag.
好ましい実施形態では、上記担体上に複数の触媒層が積層され、該複数の触媒層のうちの一つが、上記触媒金属を担持した特定Ｃｅ含有複合酸化物粉末と活性アルミナ粉末とを混合状態で含有する。 In a preferred embodiment, a plurality of catalyst layers are laminated on the support, and one of the plurality of catalyst layers is a mixture of the specific Ce-containing composite oxide powder supporting the catalyst metal and the activated alumina powder. contains.
また、好ましい実施形態では、上記複数の触媒層のうち表面が排気ガスに晒される上側触媒層よりも下側の触媒層が、上記触媒金属を担持した特定Ｃｅ含有複合酸化物粉末と活性アルミナ粉末とを混合状態で含有し、該特定Ｃｅ含有複合酸化物粉末が上記触媒金属としてＰｄを担持している。すなわち、Ｐｄは、ＰｔやＲｈと比較して劣化し易く、イオウ被毒やリン被毒を生じ易い。そこで、特定Ｃｅ含有複合酸化物粉末が触媒金属としてＰｄを担持する場合は、これを下側触媒層に配置すると、上側触媒層によってＰｄが保護され、上記熱劣化及び被毒の問題が軽減される。 Further, in a preferred embodiment, a specific Ce-containing composite oxide powder and an activated alumina powder in which the catalyst layer below the upper catalyst layer whose surface is exposed to exhaust gas among the plurality of catalyst layers carries the catalyst metal. In a mixed state, and the specific Ce-containing composite oxide powder carries Pd as the catalyst metal. That is, Pd is more likely to be deteriorated than Pt and Rh, and sulfur poisoning and phosphorus poisoning are likely to occur. Therefore, when the specific Ce-containing composite oxide powder carries Pd as a catalyst metal, if this is placed in the lower catalyst layer, the upper catalyst layer protects Pd, and the above problems of thermal degradation and poisoning are reduced. The
下側触媒層が特定Ｃｅ含有複合酸化物粉末と活性アルミナ粉末とを混合状態で含有する場合は、上記活性アルミナ粉末に触媒金属としてＰｄを担持することが好ましい。 When the lower catalyst layer contains the specific Ce-containing composite oxide powder and the activated alumina powder in a mixed state, it is preferable to support Pd as a catalyst metal on the activated alumina powder.
下側触媒層が特定Ｃｅ含有複合酸化物粉末と活性アルミナ粉末とを混合状態で含有する場合は、さらに一次粒子及び二次粒子の平均粒径が上記特定Ｃｅ含有複合酸化物粉末よりも大きな別のＣｅ含有複合酸化物粉末を含め、該下側触媒層において、特定Ｃｅ含有複合酸化物粉末と活性アルミナ粉末と上記別のＣｅ含有複合酸化物とが混合された状態にすることが好ましい。これにより、上記触媒金属を担持した特定Ｃｅ含有複合酸化物粉末の粒子を活性アルミナ粉末の粒子及び上記粒径が大きな別のＣｅ含有複合酸化物粉末の粒子に担持させることができ、該触媒金属を担持した特定Ｃｅ含有複合酸化物粉末の分散安定性が図れ、排気ガス浄化性能の向上に有利になる。 When the lower catalyst layer contains the specific Ce-containing composite oxide powder and the activated alumina powder in a mixed state, the average particle diameter of the primary particles and the secondary particles is larger than that of the specific Ce-containing composite oxide powder. In the lower catalyst layer, including the Ce-containing composite oxide powder, it is preferable that the specific Ce-containing composite oxide powder, the activated alumina powder, and the other Ce-containing composite oxide are mixed. As a result, the particles of the specific Ce-containing composite oxide powder supporting the catalyst metal can be supported on the particles of the activated alumina powder and the particles of another Ce-containing composite oxide powder having a large particle size. Dispersion stability of the specific Ce-containing composite oxide powder supporting bismuth can be achieved, which is advantageous in improving exhaust gas purification performance.
担体上に複数の触媒層を積層するケースにおいて、上記特定Ｃｅ含有複合酸化物粉末に触媒金属としてＲｈを担持する場合は、複数の触媒層のうち表面が排気ガスに晒される上側触媒層に、当該Ｒｈを担持した特定Ｃｅ含有複合酸化物粉末と活性アルミナ粉末とを混合状態で設けることが好ましい。これにより、特定Ｃｅ含有複合酸化物粉末の酸素吸蔵放出能によって排気ガスの空燃比変動を吸収し、ＲｈによってＨＣ、ＣＯ及びＮＯｘを効率良く浄化する上で有利になる。 In the case of laminating a plurality of catalyst layers on a support, when the specific Ce-containing composite oxide powder supports Rh as a catalyst metal, the upper catalyst layer whose surface is exposed to exhaust gas among the plurality of catalyst layers, It is preferable to provide the specific Ce-containing composite oxide powder supporting Rh and the activated alumina powder in a mixed state. Thereby, the oxygen storage capacity of the specific Ce-containing composite oxide powder absorbs the air-fuel ratio fluctuation of the exhaust gas, which is advantageous for efficiently purifying HC, CO and NOx by Rh.
上側触媒層にＲｈを担持した特定Ｃｅ含有複合酸化物粉末と活性アルミナ粉末とを混合状態で設けるケースにおいて、該活性アルミナ粉末の一部には、ＺｒとＬａとを含むＺｒＬａ複合酸化物と、上記特定Ｃｅ含有複合酸化物粉末の粒子とが共存担持されていることが好ましい。すなわち、Ｒｈは酸化状態にあるときにＨＣやＣＯを効率良く酸化浄化し、同時にＮＯｘの還元浄化が進むところ、上記共存担持形態にすると、雰囲気（排気ガスの空燃比）がリーンからリッチに変わってもＺｒＬａ複合酸化物がＲｈを酸化状態に保つように働く。これは、上記共存担持により、ＺｒＬａ複合酸化物とＲｈとの間にＬａ−Ｏ−Ｒｈの結合が形成され易くなり、Ｌａの働きによってＲｈが酸化状態をとり易くなっていると考えられる。 In the case where the specific Ce-containing composite oxide powder supporting Rh on the upper catalyst layer and the active alumina powder are provided in a mixed state, a part of the active alumina powder includes a ZrLa composite oxide containing Zr and La, It is preferable that particles of the specific Ce-containing composite oxide powder are coexistingly supported. In other words, Rh efficiently oxidizes and purifies HC and CO when in an oxidized state, and at the same time the reduction and purification of NOx proceeds, the atmosphere (exhaust gas air-fuel ratio) changes from lean to rich when the above-mentioned coexistence support mode is adopted. Even so, the ZrLa composite oxide works to keep Rh in an oxidized state. It is considered that this coexistence loading facilitates formation of a La—O—Rh bond between the ZrLa composite oxide and Rh, and Rh easily takes an oxidized state by the action of La.
また、上述の如くＲｈは、酸化状態になり易いから、ＨＣやＣＯとの反応によって酸素がとれると、周囲から新たな酸素原子を取り込むように働く。その結果、特定Ｃｅ含有複合酸化物から酸素が盛んに放出されるようになる。つまり、該特定Ｃｅ含有複合酸化物粉末の酸素吸蔵放出能も高まる。 Further, as described above, Rh tends to be in an oxidized state, so that when oxygen is removed by reaction with HC or CO, it functions to take in new oxygen atoms from the surroundings. As a result, oxygen is actively released from the specific Ce-containing composite oxide. That is, the oxygen storage / release capability of the specific Ce-containing composite oxide powder is also increased.
好ましいのは、上記活性アルミナ粉末は、上記触媒金属を担持した特定Ｃｅ含有酸化物粉末をバインダとして上記担体に保持されていることである。 Preferably, the activated alumina powder is supported on the carrier using the specific Ce-containing oxide powder supporting the catalyst metal as a binder.
すなわち、上記特定Ｃｅ含有酸化物粉末は、酸素吸蔵放出材として働くだけでなく、それが、累積分布１０質量％粒径が９０ｎｍ以上、累積分布５０質量％粒径が１５０ｎｍ以上２１０ｎｍ以下、累積分布９０質量％粒径が３００ｎｍ以下の微細二次粒子によって構成されているから、活性アルミナ粉末、さらには必要に応じて添加される他の触媒粉末の粒子間に介在して、それらの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バインダとしても機能することができる。そして、この特定Ｃｅ含有酸化物粉末をバインダとして利用することにより、専用のバインダ量を減らし、或いは零にすることが可能になり、触媒の軽量化、コスト低減に有利になる。 That is, the specific Ce-containing oxide powder not only functions as an oxygen storage / release material, but also has a cumulative distribution of 10% by mass particle size of 90 nm or more, a cumulative distribution of 50% by mass particle size of 150 nm to 210 nm, and a cumulative distribution. Since the 90 mass% particle size is composed of fine secondary particles of 300 nm or less, it is interposed between particles of activated alumina powder, and other catalyst powder added as necessary, and these particles are interlinked. In addition to being bonded, it can also function as a binder that enters a large number of minute recesses or pores on the surface of the carrier and prevents the catalyst layer from peeling off from the carrier. By using this specific Ce-containing oxide powder as a binder, the amount of the dedicated binder can be reduced or made zero, which is advantageous for reducing the weight and cost of the catalyst.
本発明の別の観点は、上述の如き排気ガス浄化用触媒の製造方法であって、
Ｃｅ含有複合酸化物粉末に触媒金属を担持させる工程と、
上記触媒金属を担持したＣｅ含有複合酸化物粉末を粉砕することにより、該触媒金属が分散担持された平均粒径５ｎｍ以上１０ｎｍ以下の多数の一次粒子が凝集してなる二次粒子によって構成され、該二次粒子の累積分布１０質量％粒径が９０ｎｍ以上、累積分布５０質量％粒径が１５０ｎｍ以上２１０ｎｍ以下、累積分布９０質量％粒径が３００ｎｍ以下である特定Ｃｅ含有複合酸化物粉末にする工程と、
上記触媒金属を担持した特定Ｃｅ含有複合酸化物粉末と、該特定Ｃｅ含有複合酸化物粉末の上記累積分布９０質量％粒径よりも平均粒径が大きい活性アルミナ粉末とを含むスラリーを調製する工程と、
上記スラリーを担体にコーティングして触媒層を形成する工程とを備え、
上記スラリー調製工程においては、上記活性アルミナ粉末に対する上記特定Ｃｅ含有複合酸化物粉末の質量比が１／１００以上５０／１００以下となるようにすることを特徴とする。
Another aspect of the present invention is a method for producing an exhaust gas purification catalyst as described above,
A step of supporting a catalytic metal on Ce-containing composite oxide powder;
By pulverizing the Ce-containing composite oxide powder supporting the catalyst metal, secondary particles formed by aggregating a large number of primary particles having an average particle diameter of 5 nm to 10 nm on which the catalyst metal is dispersed and supported, A specific Ce-containing composite oxide powder having a cumulative distribution of 10% by mass of the secondary particles of 90 nm or more, a cumulative distribution of 50% by mass of 150 to 210 nm, and a cumulative distribution of 90% by mass of 300% or less is used. Process,
A step of preparing a slurry comprising the specific Ce-containing composite oxide powder supporting the catalyst metal, and an activated alumina powder having an average particle size larger than the cumulative distribution of 90% by mass of the specific Ce-containing composite oxide powder. When,
Coating the slurry on a carrier to form a catalyst layer,
In the slurry preparation step, a mass ratio of the specific Ce-containing composite oxide powder to the activated alumina powder is 1/100 or more and 50/100 or less.
この製法の重要な特徴は、予め触媒金属を担持させておいたＣｅ含有複合酸化物粉末を粉砕することによって特定Ｃｅ含有複合酸化物粉末を調製している点にある。すなわち、Ｃｅ含有複合酸化物粉末を例えば共沈法によって調製した場合、その一次粒子径は１０ｎｍ以上２０ｎｍ以下程度、二次粒子径は４００ｎｍ以上２０００ｎｍ以下程度になる。かかるＣｅ含有複合酸化物を粒径（二次粒子径）が小さくなるように粉砕すると、その二次粒子を構成する一次粒子も同時に破壊されて複数の微細一次粒子に分割される。これに伴い、粉砕前の一次粒子に担持されていた触媒金属も、その一次粒子から生ずる複数の微細一次粒子に分かれ、さらに、各微細一次粒子の表面全体に分散した担持状態になるように該粒子上を移動する。 An important feature of this production method is that a specific Ce-containing composite oxide powder is prepared by pulverizing a Ce-containing composite oxide powder on which a catalyst metal is previously supported. That is, when the Ce-containing composite oxide powder is prepared by, for example, a coprecipitation method, the primary particle size is about 10 nm to 20 nm and the secondary particle size is about 400 nm to 2000 nm. When the Ce-containing composite oxide is pulverized so as to have a small particle size (secondary particle size), the primary particles constituting the secondary particles are simultaneously broken and divided into a plurality of fine primary particles. Along with this, the catalyst metal supported on the primary particles before pulverization is also divided into a plurality of fine primary particles generated from the primary particles, and further, the catalyst metal is dispersed in the entire surface of each fine primary particle. Move on the particles.
この場合、一次粒子が破壊されて複数の微細一次粒子に分割されるということは、一次粒子数が増え、全体として表面積が増大するということである。この表面積増大により、触媒金属は分散度合が大きくなるとともに、粉砕前の一次粒子に担持されているときよりも一次粒子に対する担持状態が安定になり、触媒金属がＣｅ含有複合酸化物の酸素吸蔵放出能の助長及び排気ガスの浄化に有効に働くことになる。 In this case, the fact that the primary particles are broken and divided into a plurality of fine primary particles means that the number of primary particles increases and the surface area as a whole increases. By increasing the surface area, the degree of dispersion of the catalyst metal is increased and the supported state of the primary particles is more stable than when the catalyst metal is supported on the primary particles before pulverization, and the catalyst metal absorbs and releases oxygen from the Ce-containing composite oxide. It works effectively for the promotion of performance and purification of exhaust gas.
以上のように本発明に係る排気ガス浄化用触媒によれば、Ｃｅ含有複合酸化物粉末として、触媒金属が分散担持された平均粒径５ｎｍ以上１０ｎｍ以下の多数の一次粒子が凝集してなる二次粒子によって構成され、該二次粒子の累積分布１０質量％粒径が９０ｎｍ以上、累積分布５０質量％粒径が１５０ｎｍ以上２１０ｎｍ以下、累積分布９０質量％粒径が３００ｎｍ以下である特定Ｃｅ含有複合酸化物粉末を採用して、上記累積分布９０質量％粒径よりも大きい粒径の活性アルミナ粉末と混合し、且つ活性アルミナ粉末に対する特定Ｃｅ含有複合酸化物粉末の質量比を１／１００以上５０／１００以下としたから、特定Ｃｅ含有複合酸化物粉末の少なくとも一部の粒子が活性アルミナ粉末の粒子に接触して担持された状態になり、特定Ｃｅ含有複合酸化物粉末の凝集が抑制される一方で、比較的高い酸素吸蔵放出能が得られ、しかも、一次粒子に分散担持されている触媒金属が、排気ガスとの接触により、当該Ｃｅ含有複合酸化物の酸素吸蔵放出能の助長及び排気ガスの浄化に有効に働くことになり、優れた排気ガス浄化性能が得られる。 As described above, according to the exhaust gas purifying catalyst of the present invention, as the Ce-containing composite oxide powder, a large number of primary particles having an average particle diameter of 5 nm to 10 nm on which a catalytic metal is dispersed and supported are aggregated. Containing specific Ce containing secondary particles, wherein the secondary particles have a cumulative distribution of 10% by mass particle size of 90 nm or more, a cumulative distribution of 50% by mass particle size of from 150 nm to 210 nm, and a cumulative distribution of 90% by mass of particle size of 300 nm or less Adopting the composite oxide powder, mixing with the activated alumina powder having a particle size larger than the cumulative distribution of 90% by mass particle size, and the mass ratio of the specific Ce-containing composite oxide powder to the activated alumina powder is 1/100 or more Since it is 50/100 or less, at least a part of the particles of the specific Ce-containing composite oxide powder is in contact with and supported by the particles of the activated alumina powder. While the aggregation of the composite oxide powder is suppressed, a relatively high oxygen storage / release capability is obtained, and the catalyst metal dispersedly supported on the primary particles is brought into contact with the exhaust gas, whereby the Ce-containing composite It effectively works to promote the oxygen storage and release ability of oxides and to purify exhaust gas, so that excellent exhaust gas purification performance can be obtained.
また、本発明に係る排気ガス浄化用触媒の製造方法によれば、触媒金属を担持したＣｅ含有複合酸化物粉末を粉砕することにより、該触媒金属が分散担持された平均粒径５ｎｍ以上１０ｎｍ以下の多数の一次粒子が凝集してなる二次粒子によって構成され、該二次粒子の累積分布１０質量％粒径が９０ｎｍ以上、累積分布５０質量％粒径が１５０ｎｍ以上２１０ｎｍ以下、累積分布９０質量％粒径が３００ｎｍ以下である特定Ｃｅ含有複合酸化物粉末とし、該特定Ｃｅ含有複合酸化物粉末と、粒径が大きい活性アルミナとを質量比が１／１００以上５０／１００以下で含むスラリーを調製し、該スラリーを担体にコーティングして触媒層を形成するようにしたから、触媒金属が微細一次粒子に対して安定に分散担持され、Ｃｅ含有複合酸化物の酸素吸蔵放出能の助長及び排気ガスの浄化に有効に働く排気ガス浄化用触媒が得られる。 Further, according to the method for producing an exhaust gas purifying catalyst according to the present invention, an average particle diameter of 5 nm to 10 nm in which the catalyst metal is dispersed and supported by pulverizing the Ce-containing composite oxide powder supporting the catalyst metal. Secondary particles formed by agglomeration of a large number of primary particles, and the secondary particles have a cumulative distribution of 10% by mass particle size of 90 nm or more, a cumulative distribution of 50% by mass particle size of 150 nm to 210 nm, and a cumulative distribution of 90% by mass. A slurry containing a specific Ce-containing composite oxide powder having a% particle size of 300 nm or less and a specific Ce-containing composite oxide powder and activated alumina having a large particle size in a mass ratio of 1/100 or more and 50/100 or less. Since the catalyst layer was formed by coating the slurry on the support, the catalyst metal was stably dispersed and supported on the fine primary particles, and the Ce-containing composite oxide Oxygen storage capacity of promoting and exhaust gas purification catalyst works effectively to purify the exhaust gas is obtained.
以下、本発明を実施するための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 for carrying out 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に示す排気ガス浄化用触媒において、１は担体であり、この担体１上に上触媒層２と下触媒層３とが積層されている。この排気ガス浄化用触媒１は自動車のガソリンエンジンが理論空燃比付近で運転されるときの排気ガスに含まれるＨＣ（炭化水素）、ＣＯ及びＮＯｘ（窒素酸化物）を同時に浄化する三元触媒に適する。 In the exhaust gas purification catalyst shown in FIG. 1, reference numeral 1 denotes a carrier, and an upper catalyst layer 2 and a lower catalyst layer 3 are laminated on the carrier 1. The exhaust gas purification catalyst 1 is a three-way catalyst that simultaneously purifies HC (hydrocarbon), CO, and NOx (nitrogen oxides) contained in exhaust gas when an automobile gasoline engine is operated near the stoichiometric air-fuel ratio. Suitable.
担体１は例えばコージェライト製のハニカム担体とされる。上触媒層２及び下触媒層３各々は、触媒金属と酸素吸蔵放出材とを含有する。上触媒層２は、触媒金属が担持された粒径が小さな特定Ｃｅ含有複合酸化物粉末と活性アルミナ粉末とを混合状態で含有する。その特定Ｃｅ含有複合酸化物粉末は酸素吸蔵放出能を有する。この触媒金属が担持された粒径が小さな特定Ｃｅ含有複合酸化物粉末と活性アルミナ粉末とは、下触媒層３に設けることもでき、或いは上触媒層２及び下触媒層３の両層に設けることができる。 The carrier 1 is, for example, a cordierite honeycomb carrier. Each of the upper catalyst layer 2 and the lower catalyst layer 3 contains a catalyst metal and an oxygen storage / release material. The upper catalyst layer 2 contains a specific Ce-containing composite oxide powder having a small particle size on which a catalyst metal is supported and an activated alumina powder in a mixed state. The specific Ce-containing composite oxide powder has an oxygen storage / release capability. The specific Ce-containing composite oxide powder having a small particle size on which the catalyst metal is supported and the activated alumina powder can be provided in the lower catalyst layer 3 or in both the upper catalyst layer 2 and the lower catalyst layer 3. be able to.
図２は触媒金属６が担持された粒径が小さな特定Ｃｅ含有複合酸化物粒子４と該特定Ｃｅ含有複合酸化物粒子４よりも粒径が大きい活性アルミナ粒子５との関係を模式的に示す。すなわち、触媒層においては、特定Ｃｅ含有複合酸化物粉末と活性アルミナ粉末とが混合された状態にある。従って、少なくとも一部の特定Ｃｅ含有複合酸化物粒子４は活性アルミナ粒子５に接触した状態になる。その場合、上述の如く、活性アルミナ粒子５の粒径が特定Ｃｅ含有複合酸化物粒子４の粒径よりも大きいから、多数の特定Ｃｅ含有複合酸化物粒子４が活性アルミナ粒子５に分散して担持された状態になる。 FIG. 2 schematically shows the relationship between the specific Ce-containing composite oxide particles 4 on which the catalyst metal 6 is supported and the activated alumina particles 5 having a larger particle size than the specific Ce-containing composite oxide particles 4. . That is, in the catalyst layer, the specific Ce-containing composite oxide powder and the activated alumina powder are in a mixed state. Accordingly, at least some of the specific Ce-containing composite oxide particles 4 are in contact with the activated alumina particles 5. In that case, since the particle diameter of the activated alumina particles 5 is larger than the particle diameter of the specific Ce-containing composite oxide particles 4 as described above, a large number of the specific Ce-containing composite oxide particles 4 are dispersed in the activated alumina particles 5. It becomes a supported state.
また、触媒金属６を担持した小径の特定Ｃｅ含有複合酸化物粒子４は、触媒成分として機能する一方、活性アルミナ粒子５間に介在して該活性アルミナ粒子５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バインダとしても機能する。 The small-diameter specific Ce-containing composite oxide particles 4 carrying the catalyst metal 6 function as a catalyst component, and are interposed between the activated alumina particles 5 to bond the activated alumina particles 5 to each other. It also functions as a binder that enters a large number of minute recesses or pores and prevents the catalyst layer from peeling off from the carrier.
＜触媒金属を担持したＣｅ含有複合酸化物粉末について＞
以下、触媒金属を担持した特定Ｃｅ含有複合酸化物粉末、並びに触媒金属を担持した通常Ｃｅ含有複合酸化物粉末及び触媒金属を担持した特定Ｃｅ含有複合酸化物について説明する。先に後者の調製法から説明する。
<About Ce-containing composite oxide powder supporting catalyst metal>
Hereinafter, the specific Ce-containing composite oxide powder supporting the catalyst metal, the normal Ce-containing composite oxide powder supporting the catalyst metal, and the specific Ce-containing composite oxide supporting the catalyst metal will be described. The latter preparation method will be described first.
−触媒金属を担持した通常Ｃｅ含有複合酸化物粉末の調製−
後述比較例１等に使用する粉末例で当該調製法を説明する。すなわち、硝酸セリウム６水和物（１７．４１ｇ）とＺｒＯ２に換算して２５．１３質量％のＺｒを含有するオキシ硝酸ジルコニル溶液（７９．９８ｇ）と硝酸ネオジム６水和物（７．８２ｇ）とをイオン交換水（３００ｍＬ）に溶かす。この硝酸塩溶液に２８質量％アンモニア水の８倍希釈液（９００ｍＬ）を混合して中和させることにより、共沈物を得る。この共沈物を遠心分離法で水洗した後、空気中において１５０℃の温度で一昼夜乾燥させ、粉砕した後、空気中において５００℃の温度に２時間保持する焼成を行なうことにより、ＣｅＺｒＮｄ複合酸化物粉末（Ｃｅ含有複合酸化物粉末）を３０ｇ得ることができる。このＣｅＺｒＮｄ複合酸化物粉末の組成は、ＣｅＯ２：ＺｒＯ２：Ｎｄ２Ｏ３＝２３：６７：１０（質量比）である。
-Preparation of normal Ce-containing composite oxide powder supporting catalyst metal-
The preparation method will be described using powder examples used in Comparative Example 1 and the like described later. That is, cerium nitrate hexahydrate (17.41 g), zirconyl oxynitrate solution (79.98 g) containing ZrO 2 in terms of ZrO 2 , and neodymium nitrate hexahydrate (7.82 g) ) Is dissolved in ion-exchanged water (300 mL). A coprecipitate is obtained by mixing and neutralizing this nitrate solution with an 8-fold diluted solution (900 mL) of 28% by mass ammonia water. The coprecipitate is washed with water by a centrifugal separation method, dried in air at a temperature of 150 ° C. for a whole day and night, pulverized, and then fired in air at a temperature of 500 ° C. for 2 hours, whereby CeZrNd composite oxidation is performed. 30 g of product powder (Ce-containing composite oxide powder) can be obtained. The composition of this CeZrNd composite oxide powder is CeO 2 : ZrO 2 : Nd 2 O 3 = 23: 67: 10 (mass ratio).
上記ＣｅＺｒＮｄ複合酸化物粉末（２０ｇ）にイオン交換水を混合してスラリーとし、さらにＰｄ濃度４．３３質量％の硝酸パラジウム溶液（１３．２ｇ）を混合する。これを蒸発乾固した後、乾固物を粉砕し、空気中において５００℃の温度に２時間保持する焼成を行なうことにより、ＣｅＺｒＮｄ複合酸化物粉末にＰｄを担持させてなるＰｄ濃度が２．７８質量％の通常Ｐｄ／ＣｅＺｒＮｄ粉末を得ることができる。 Ion exchange water is mixed with the CeZrNd composite oxide powder (20 g) to make a slurry, and further a palladium nitrate solution (13.2 g) with a Pd concentration of 4.33 mass% is mixed. After evaporating this to dryness, the dried product is pulverized and calcined in air at a temperature of 500 ° C. for 2 hours, whereby the Pd concentration obtained by supporting Pd on the CeZrNd composite oxide powder is 2. 78% by mass of normal Pd / CeZrNd powder can be obtained.
−触媒金属を担持した特定Ｃｅ含有複合酸化物粉末の調製−
後述実施例１等に使用する粉末例で当該調製法を説明する。上記通常Ｐｄ／ＣｅＺｒＮｄ粉末にイオン交換水を添加してスラリー（固形分２５質量％）とし、このスラリーをボールミルに投入して、０．５ｍｍのジルコニアビーズによって粉砕する（約３時間）ことにより、粒径が小さくなった特定Ｐｄ／ＣｅＺｒＮｄ粉末（触媒金属を担持した特定Ｃｅ含有複合酸化物粉末）が分散したゾルを得ることができる。この特定Ｐｄ／ＣｅＺｒＮｄ粉末は、粒径が小さくなった特定ＣｅＺｒＮｄ複合酸化物粉末にＰｄが担持されたものであり、特定ＣｅＺｒＮｄ複合酸化物粉末の組成及びＰｄ濃度は通常Ｐｄ／ＣｅＺｒＮｄ粉末と同じである。
-Preparation of specific Ce-containing composite oxide powder supporting catalyst metal-
The preparation method will be described using powder examples used in Example 1 and the like described later. By adding ion-exchanged water to the normal Pd / CeZrNd powder to make a slurry (solid content 25% by mass), this slurry is put into a ball mill and pulverized with 0.5 mm zirconia beads (about 3 hours). It is possible to obtain a sol in which the specific Pd / CeZrNd powder (specific Ce-containing composite oxide powder supporting a catalyst metal) having a reduced particle size is dispersed. The specific Pd / CeZrNd powder is obtained by supporting Pd on a specific CeZrNd composite oxide powder having a reduced particle size, and the composition and Pd concentration of the specific CeZrNd composite oxide powder are usually the same as those of the Pd / CeZrNd powder. is there.
−粒度分布−
図３は通常Ｐｄ／ＣｅＺｒＮｄ粉末及び特定Ｐｄ／ＣｅＺｒＮｄ粉末の粒度分布（頻度分布）を示す。図４は通常Ｐｄ／ＣｅＺｒＮｄ粉末の累積粒度分布を示し、図５は特定Ｐｄ／ＣｅＺｒＮｄ粉末の累積粒度分布を示す。これら粒度分布の測定には、株式会社島津製作所製レーザー回折式粒度分布測定装置を用いた。粉砕前の通常Ｐｄ／ＣｅＺｒＮｄ粉末の場合、累積分布１０質量％粒径が５９１ｎｍ、累積分布５０質量％粒径が８５４ｎｍ、累積分布９０質量％粒径が１２７７ｎｍである。すなわち、累積分布１０質量％粒径は５５０ｎｍ以上、累積分布５０質量％粒径は８００ｎｍ以上９００ｎｍ以下、累積分布９０質量％粒径は１３００ｎｍ以下である。これに対して、粉砕によって得られた特定Ｐｄ／ＣｅＺｒＮｄ粉末の場合、累積分布１０質量％粒径が９６ｎｍ、累積分布５０質量％粒径が１７８ｎｍ、累積分布９０質量％粒径が２８５ｎｍである。すなわち、累積分布１０質量％粒径は９０ｎｍ以上、累積分布５０質量％粒径は１５０ｎｍ以上２１０ｎｍ以下、累積分布９０質量％粒径は３００ｎｍ以下である。
-Particle size distribution-
FIG. 3 shows the particle size distribution (frequency distribution) of normal Pd / CeZrNd powder and specific Pd / CeZrNd powder. FIG. 4 shows the cumulative particle size distribution of normal Pd / CeZrNd powder, and FIG. 5 shows the cumulative particle size distribution of specific Pd / CeZrNd powder. For the measurement of these particle size distributions, a laser diffraction particle size distribution measuring device manufactured by Shimadzu Corporation was used. In the case of normal Pd / CeZrNd powder before pulverization, the cumulative distribution 10 mass% particle size is 591 nm, the cumulative distribution 50 mass% particle size is 854 nm, and the cumulative distribution 90 mass% particle size is 1277 nm. That is, the cumulative distribution 10 mass% particle size is 550 nm or more, the cumulative distribution 50 mass% particle size is 800 nm to 900 nm, and the cumulative distribution 90 mass% particle size is 1300 nm or less. In contrast, in the case of the specific Pd / CeZrNd powder obtained by pulverization, the cumulative distribution 10% by mass particle size is 96 nm, the cumulative distribution 50% by mass particle size is 178 nm, and the cumulative distribution 90% by mass particle size is 285 nm. That is, the cumulative distribution 10 mass% particle size is 90 nm or more, the cumulative distribution 50 mass% particle size is 150 nm or more and 210 nm or less, and the cumulative distribution 90 mass% particle size is 300 nm or less.
−電子顕微鏡写真−
図６は通常Ｐｄ／ＣｅＺｒＮｄ粉末の粒子（二次粒子）の一部を示す電子顕微鏡写真であり、図７は特定Ｐｄ／ＣｅＺｒＮｄ粉末の粒子（二次粒子）の一部を示す電子顕微鏡写真である。電子顕微鏡写真での観察によれば、通常Ｐｄ／ＣｅＺｒＮｄ粉末では、一次粒子径の平均粒径は１０ｎｍ以上２０ｎｍ以下であると認められ、特定Ｐｄ／ＣｅＺｒＮｄ粉末では、一次粒子径の平均粒径は５ｎｍ以上１０ｎｍ以下であると認められる。
-Electron micrograph-
FIG. 6 is an electron micrograph showing a part of particles (secondary particles) of a normal Pd / CeZrNd powder, and FIG. 7 is an electron micrograph showing a part of particles (secondary particles) of a specific Pd / CeZrNd powder. is there. According to the observation with an electron micrograph, the average primary particle diameter is usually 10 nm or more and 20 nm or less in the Pd / CeZrNd powder, and the average primary particle diameter in the specific Pd / CeZrNd powder is It is recognized that it is 5 nm or more and 10 nm or less.
特定Ｐｄ／ＣｅＺｒＮｄ粉末は、上記ボールミルでの粉砕により、二次粒子が粉砕されて小径になるとともに、この二次粒子を構成する一次粒子が破壊されて微細一次粒子に分割され、一次粒子径が小さくなったものである。 The specific Pd / CeZrNd powder is pulverized by the above ball mill so that the secondary particles are pulverized to have a small diameter, and the primary particles constituting the secondary particles are broken and divided into fine primary particles. It has become smaller.
−一次粒子の微細化−
図８は通常Ｐｄ／ＣｅＺｒＮｄ粉末の一次粒子７が上記粉砕によって破壊分割されて特定Ｐｄ／ＣｅＺｒＮｄ粉末の微細一次粒子８になる様子を模式的に示す。すなわち、一次粒子７には触媒金属としてのＰｄ６が分散担持されている（図８の（Ａ））。この一次粒子７が粉砕によって破壊されて複数（図例では４つ）の微細一次粒子８に分割される（図８の（Ｂ）。元の一次粒子７に担持されていたＰｄ群は各微細一次粒子８に分かれて担持された状態になる。微細一次粒子８に粉砕時に加わる外部エネルギーにより、或いはその後の触媒層焼成時の熱エネルギーにより、微細一次粒子８に偏在して担持されていたＰｄ６は該粒子８上を移動して、粒子表面全体にわたって略均一に分散担持された状態になる（図８の（Ｃ））。
-Refinement of primary particles-
FIG. 8 schematically shows a state in which the primary particles 7 of the normal Pd / CeZrNd powder are broken and divided by the pulverization to become fine primary particles 8 of the specific Pd / CeZrNd powder. That is, Pd6 as a catalyst metal is dispersedly supported on the primary particles 7 ((A) in FIG. 8). The primary particles 7 are broken by pulverization and divided into a plurality of (four in the illustrated example) fine primary particles 8 (FIG. 8B). The Pd group supported on the original primary particles 7 It is in a state of being supported by being divided into primary particles 8. Pd6 that is unevenly distributed and supported on the fine primary particles 8 by external energy applied to the fine primary particles 8 at the time of pulverization or by thermal energy at the time of subsequent firing of the catalyst layer. Moves on the particles 8 and is dispersed and supported substantially uniformly over the entire particle surface ((C) of FIG. 8).
この場合、一次粒子７が破壊されて複数の微細一次粒子８に分割されるということは、一次粒子数が増え、全体として表面積が増大するということである。この表面積増大により、Ｐｄ６は分散度合が大きくなるとともに、粉砕前の一次粒子７に担持されているときよりも微細一次粒子８に対する担持状態が安定になる。 In this case, the fact that the primary particles 7 are broken and divided into a plurality of fine primary particles 8 means that the number of primary particles increases and the surface area as a whole increases. Due to this increase in the surface area, the degree of dispersion of Pd6 is increased, and the supported state of the fine primary particles 8 is more stable than when supported on the primary particles 7 before pulverization.
＜単一触媒層に係る実施例及び比較例＞
[実施例１]
上記粒径が小さい特定Ｐｄ／ＣｅＺｒＮｄ粉末（Ｐｄ濃度２．７８質量％）のゾルに活性アルミナ粉末（平均粒径１３．８μｍ）を混合してなるスラリーを担体にコーティングすることにより単一触媒層を形成した。この場合、特定Ｐｄ／ＣｅＺｒＮｄ粉末がバインダとして働くため、バインダ専用材は使用していない。
<Examples and comparative examples relating to a single catalyst layer>
[Example 1]
A single catalyst layer is formed by coating a support with a slurry obtained by mixing an active alumina powder (average particle diameter: 13.8 μm) with a sol having a specific Pd / CeZrNd powder having a small particle diameter (Pd concentration: 2.78% by mass). Formed. In this case, since the specific Pd / CeZrNd powder works as a binder, a binder-specific material is not used.
担体１Ｌ当たりの担持量は、特定Ｐｄ／ＣｅＺｒＮｄ粉末が７．２ｇ／Ｌ（Ｐｄが０．２ｇ／Ｌ、ＣｅＺｒＮｄ複合酸化物粉末が７ｇ／Ｌ）、活性アルミナ粉末が３５ｇ／Ｌであり、活性アルミナ粉末に対するＣｅＺｒＮｄ複合酸化物粉末の質量比は２０／１００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１Ｌ）を用いた。 The supported amount per liter of the carrier is 7.2 g / L for the specific Pd / CeZrNd powder (Pd is 0.2 g / L, CeZrNd composite oxide powder is 7 g / L), and the activated alumina powder is 35 g / L. The mass ratio of CeZrNd composite oxide powder to alumina powder is 20/100. As the carrier, a cordierite honeycomb carrier (capacity 1 L) 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 used.
[実施例２]
活性アルミナ粉末担持量を７０ｇ／Ｌとする他は実施例１と同じ構成にした。活性アルミナ粉末に対するＣｅＺｒＮｄ複合酸化物粉末の質量比は１０／１００である。
[Example 2]
The same configuration as in Example 1 was adopted except that the active alumina powder loading was 70 g / L. The mass ratio of the CeZrNd composite oxide powder to the activated alumina powder is 10/100.
[実施例３]
上記特定Ｐｄ／ＣｅＺｒＮｄ粉末の調製において、ＣｅＺｒＮｄ複合酸化物粉末２０ｇに対するＰｄ濃度４．３３質量％の硝酸パラジウム溶液の添加量を２６．４ｇとすることにより、特定Ｐｄ／ＣｅＺｒＮｄ粉末のＰｄ濃度を５．４１質量％とし、該特定Ｐｄ／ＣｅＺｒＮｄ粉末担持量を３．７ｇ／Ｌ（Ｐｄが０．２ｇ／Ｌ、ＣｅＺｒＮｄ複合酸化物粉末が３．５ｇ／Ｌ）とする他は実施例１と同じ構成にした。活性アルミナ粉末に対するＣｅＺｒＮｄ複合酸化物粉末の質量比は１０／１００である。
[Example 3]
In the preparation of the specific Pd / CeZrNd powder, the addition amount of the palladium nitrate solution having a Pd concentration of 4.33 mass% with respect to 20 g of the CeZrNd composite oxide powder is 26.4 g, whereby the Pd concentration of the specific Pd / CeZrNd powder is 5 The same Pd / CeZrNd powder loading as 3.7 g / L (Pd is 0.2 g / L, CeZrNd composite oxide powder is 3.5 g / L). Made the configuration. The mass ratio of the CeZrNd composite oxide powder to the activated alumina powder is 10/100.
[実施例４]
活性アルミナ粉末担持量を７０ｇ／Ｌとする他は実施例３と同じ構成にした。活性アルミナ粉末に対するＣｅＺｒＮｄ複合酸化物粉末の質量比は５／１００である。
[Example 4]
The configuration was the same as that of Example 3 except that the active alumina powder loading was 70 g / L. The mass ratio of the CeZrNd composite oxide powder to the activated alumina powder is 5/100.
[実施例５]
活性アルミナ粉末担持量を２３ｇ／Ｌとする他は実施例１と同じ構成にした。活性アルミナ粉末に対するＣｅＺｒＮｄ複合酸化物粉末の質量比は３０／１００である。
[Example 5]
The same configuration as in Example 1 was adopted except that the active alumina powder loading was 23 g / L. The mass ratio of the CeZrNd composite oxide powder to the activated alumina powder is 30/100.
[実施例６]
活性アルミナ粉末担持量を１４ｇ／Ｌとする他は実施例１と同じ構成にした。活性アルミナ粉末に対するＣｅＺｒＮｄ複合酸化物粉末の質量比は５０／１００である。
[Example 6]
The configuration was the same as that of Example 1 except that the active alumina powder loading was 14 g / L. The mass ratio of the CeZrNd composite oxide powder to the activated alumina powder is 50/100.
[比較例１]
上記特定Ｐｄ／ＣｅＺｒＮｄ粉末に代えて上記通常Ｐｄ／ＣｅＺｒＮｄ粉末（Ｐｄ濃度２．７８質量％）を採用する他は実施例１と同じ構成にした。従って、通常Ｐｄ／ＣｅＺｒＮｄ粉末担持量は７．２ｇ／Ｌ（Ｐｄが０．２ｇ／Ｌ、ＣｅＺｒＮｄ複合酸化物粉末が７ｇ／Ｌ）、活性アルミナ粉末担持量は３５ｇ／Ｌであり、活性アルミナ粉末に対するＣｅＺｒＮｄ複合酸化物粉末の質量比は２０／１００である。バインダとしては硝酸ジルコニルを用いた。
[Comparative Example 1]
The same configuration as in Example 1 was adopted except that the normal Pd / CeZrNd powder (Pd concentration: 2.78% by mass) was used instead of the specific Pd / CeZrNd powder. Therefore, the supported amount of Pd / CeZrNd powder is usually 7.2 g / L (Pd is 0.2 g / L, CeZrNd composite oxide powder is 7 g / L), and the active alumina powder is supported at 35 g / L. The mass ratio of CeZrNd composite oxide powder to is 20/100. Zirconyl nitrate was used as the binder.
[比較例２]
活性アルミナ粉末担持量を７０ｇ／Ｌとする他は比較例１と同じ構成にした。活性アルミナ粉末に対するＣｅＺｒＮｄ複合酸化物粉末の質量比は１０／１００である。
[Comparative Example 2]
The configuration was the same as that of Comparative Example 1 except that the active alumina powder loading was 70 g / L. The mass ratio of the CeZrNd composite oxide powder to the activated alumina powder is 10/100.
[比較例３]
上記通常Ｐｄ／ＣｅＺｒＮｄ粉末の調製において、ＣｅＺｒＮｄ複合酸化物粉末２０ｇに対するＰｄ濃度４．３３質量％の硝酸パラジウム溶液の添加量を２．６４ｇとすることにより、Ｐｄ濃度が０．５７質量％の通常Ｐｄ／ＣｅＺｒＮｄ粉末を調製し、これをスラリー化して担体にコーティングすることにより単一触媒層を形成した。バインダとしては硝酸ジルコニルを用いた。通常Ｐｄ／ＣｅＺｒＮｄ粉末担持量は３５．２ｇ／Ｌ（Ｐｄが０．２ｇ／Ｌ、ＣｅＺｒＮｄ複合酸化物粉末が３５ｇ／Ｌ）である。なお、活性アルミナ粉末担持量は零である。
[Comparative Example 3]
In the preparation of the normal Pd / CeZrNd powder, the amount of palladium nitrate solution having a Pd concentration of 4.33 mass% with respect to 20 g of the CeZrNd composite oxide powder is 2.64 g, so that the Pd concentration is 0.57 mass%. A single catalyst layer was formed by preparing Pd / CeZrNd powder, slurrying it, and coating the support. Zirconyl nitrate was used as the binder. Usually, the supported amount of Pd / CeZrNd powder is 35.2 g / L (Pd is 0.2 g / L, CeZrNd composite oxide powder is 35 g / L). Note that the amount of active alumina powder supported is zero.
−排気ガス浄化性能−
実施例１〜６及び比較例１〜３の各触媒にベンチエージング処理を施した。これは、各触媒をエンジン排気系に取り付け、(1)Ａ／Ｆ＝１４の排気ガスを１５秒間流す→(2)Ａ／Ｆ＝１７の排気ガスを５秒間流す→(3)Ａ／Ｆ＝１４．７の排気ガスを４０秒間流す、というサイクルが合計５０時間繰り返されるように、且つ触媒入口ガス温度が９００℃となるように、エンジンを運転するというものである。
−Exhaust gas purification performance−
Each catalyst of Examples 1 to 6 and Comparative Examples 1 to 3 was subjected to bench aging treatment. This is because each catalyst is attached to the engine exhaust system, (1) A / F = 14 exhaust gas flows for 15 seconds → (2) A / F = 17 exhaust gas flows for 5 seconds → (3) A / F = 14.7 The exhaust gas flowing for 40 seconds is repeated for a total of 50 hours, and the engine is operated so that the catalyst inlet gas temperature is 900 ° C.
しかる後、各触媒から担体容量２５ｍＬのコアサンプルを切り出し、これをモデルガス流通反応装置に取り付け、ＨＣ、ＣＯ及びＮＯｘの浄化に関するライトオフ温度Ｔ５０（℃）及び排気ガス浄化率Ｃ４００を測定した。Ｔ５０（℃）は、触媒に流入するモデルガス温度を常温から漸次上昇させていき、浄化率が５０％に達したときの触媒入口のガス温度である。排気ガス浄化率Ｃ４００は、触媒入口でのモデル排気ガス温度が４００℃であるときのガスの各成分の浄化率である。モデルガスは、Ａ／Ｆ＝１４．７±０．９とした。すなわち、Ａ／Ｆ＝１４．７のメインストリームガスを定常的に流しつつ、所定量の変動用ガスを１Ｈｚでパルス状に添加することにより、Ａ／Ｆを±０．９の振幅で強制的に振動させた。空間速度ＳＶは６００００ｈ−１、昇温速度は３０℃／分である。Ａ／Ｆ＝１４．７、Ａ／Ｆ＝１３．８及びＡ／Ｆ＝１５．６のときのガス組成を表１に示し、ライトオフ温度Ｔ５０及び排気ガス浄化率Ｃ４００の測定結果を表２に示す。 Thereafter, a core sample having a carrier volume of 25 mL was cut out from each catalyst, and this was attached to a model gas flow reactor, and the light-off temperature T50 (° C.) and the exhaust gas purification rate C400 related to the purification of HC, CO, and NOx were measured. T50 (° C.) is the gas temperature at the catalyst inlet when the model gas temperature flowing into the catalyst is gradually increased from room temperature and the purification rate reaches 50%. The exhaust gas purification rate C400 is the purification rate of each component of the gas when the model exhaust gas temperature at the catalyst inlet is 400 ° C. The model gas was A / F = 14.7 ± 0.9. That is, the A / F is forced at an amplitude of ± 0.9 by adding a predetermined amount of fluctuation gas in a pulse form at 1 Hz while constantly flowing the main stream gas of A / F = 14.7. Vibrated. The space velocity SV is 60000 h −1 , and the heating rate is 30 ° C./min. Table 1 shows the gas composition when A / F = 14.7, A / F = 13.8 and A / F = 15.6, and Table 2 shows the measurement results of the light-off temperature T50 and the exhaust gas purification rate C400. Shown in
表２において、「特定Pd/CeZrNd」は特定Ｐｄ／ＣｅＺｒＮｄ粉末を、「アルミナ」は活性アルミナ粉末を、「CeZrNd」はＣｅＺｒＮｄ複合酸化物粉末を、「CeZrNd/アルミナ質量比」は活性アルミナ粉末に対するＣｅＺｒＮｄ複合酸化物粉末の質量比を、それぞれ意味する。また、Ｐｄ濃度は、ＣｅＺｒＮｄ複合酸化物粉末と、これに担持したＰｄとの合計質量に対する当該担持したＰｄの質量の比率である。 In Table 2, “specific Pd / CeZrNd” indicates specific Pd / CeZrNd powder, “alumina” indicates active alumina powder, “CeZrNd” indicates CeZrNd composite oxide powder, and “CeZrNd / alumina mass ratio” indicates active alumina powder. The mass ratio of CeZrNd composite oxide powder is meant respectively. The Pd concentration is a ratio of the mass of the supported Pd to the total mass of the CeZrNd composite oxide powder and the Pd supported thereon.
表２によれば、特定ＣｅＺｒＮｄ複合酸化物粉末のゾルを用いてなる実施例１〜６は、通常Ｐｄ／ＣｅＺｒＮｄ粉末を用いてなる比較例１〜３に比べて、ライトオフ温度Ｔ５０が低くなり、排気ガス浄化率Ｃ４００が高くなっている。具体的に比較すると、実施例１，２と比較例１，２とは、前者が特定ＣｅＺｒＮｄ複合酸化物粉末ゾルを用い、後者が通常Ｐｄ／ＣｅＺｒＮｄ粉末を用いた点で相違し、各成分の担持量、並びに活性アルミナ粉末に対するＣｅＺｒＮｄ複合酸化物粉末の質量比は同じである。この実施例１，２は、比較例１，２よりも、ライトオフ温度Ｔ５０については、ＨＣが３０℃前後、ＣＯが５０℃以上、ＮＯｘも２０℃前後低くなっており、また、排気ガス浄化率Ｃ４００については、ＨＣ及びＣＯが２０％以上、ＮＯｘも１０％近く高くなっており、驚くような排気ガス浄化性能の向上が認められる。なお、比較例３はＰｄ濃度が低い０．５７質量％の通常Ｐｄ／ＣｅＺｒＮｄ粉末を用い、その担持量を多くする（３５．２ｇ／Ｌとする）ことにより、Ｐｄ担持量を実施例１〜６と同じ０．２ｇ／Ｌとしたものであるが、性能は比較例１，２よりも若干悪くなっている。 According to Table 2, Examples 1-6 using the sol of specific CeZrNd composite oxide powder have lower light-off temperature T50 than Comparative Examples 1-3, which normally use Pd / CeZrNd powder. The exhaust gas purification rate C400 is high. In specific comparison, Examples 1 and 2 differ from Comparative Examples 1 and 2 in that the former uses a specific CeZrNd composite oxide powder sol and the latter uses a normal Pd / CeZrNd powder. The supported amount and the mass ratio of the CeZrNd composite oxide powder to the activated alumina powder are the same. In Examples 1 and 2, the light-off temperature T50 is lower than that of Comparative Examples 1 and 2 by about 30 ° C for HC, 50 ° C for CO, and about 20 ° C for NOx. Regarding the rate C400, HC and CO are 20% or more and NOx is also nearly 10% higher, and a surprising improvement in exhaust gas purification performance is recognized. Comparative Example 3 uses a normal Pd / CeZrNd powder having a low Pd concentration of 0.57% by mass and increases the loading amount (set to 35.2 g / L). However, the performance is slightly worse than those of Comparative Examples 1 and 2.
実施例同士を比較するに、実施例１，２，５，６は、Ｐｄ担持量及びＣｅＺｒＮｄ複合酸化物粉末担持量を互いに同じとし、活性アルミナ粉末担持量を変化させて活性アルミナ粉末に対するＣｅＺｒＮｄ複合酸化物粉末の質量比を変えたものである。この実施例１，２，５，６の中では、上記質量比が２０／１００である実施例１の性能が最も良い。しかし、上記質量比が１０／１００である実施例２及び上記質量比が５０／１００である実施例６でも、比較的高い性能を示すことから、その質量比が１／１００以上５０／１００以下である場合には、排気ガス浄化性能の向上に効果があることがわかる。 Comparing Examples, Examples 1, 2, 5 and 6 are the same in Pd loading and CeZrNd composite oxide powder loading, and the active alumina powder loading is changed to change the CeZrNd composite with respect to the activated alumina powder. The mass ratio of the oxide powder is changed. Among Examples 1, 2, 5, and 6, the performance of Example 1 in which the mass ratio is 20/100 is the best. However, even in Example 2 where the mass ratio is 10/100 and Example 6 where the mass ratio is 50/100, relatively high performance is exhibited, so the mass ratio is 1/100 or more and 50/100 or less. In this case, it can be seen that the exhaust gas purification performance is effective.
また、実施例３，４は、Ｐｄ濃度が高い５．４１質量％の特定Ｐｄ／ＣｅＺｒＮｄ粉末を用いたものであるが、他の実施例と同様に高い排気ガス浄化性能を示しており、Ｐｄ濃度が高いケースでも良好な結果が得られることがわかる。 In Examples 3 and 4, the specific Pd / CeZrNd powder having a high Pd concentration of 5.41% by mass was used, and as in the other examples, high exhaust gas purification performance was exhibited. It can be seen that good results can be obtained even in high concentration cases.
＜積層触媒層に係る実施例及び比較例＞
[実施例７]
図１に示す二層構造の排気ガス浄化用触媒の上触媒層及び下触媒層を次の方法によって形成した。
<Examples and comparative examples relating to laminated catalyst layers>
[Example 7]
The upper catalyst layer and the lower catalyst layer of the exhaust gas purification catalyst having a two-layer structure shown in FIG. 1 were formed by the following method.
−通常Ｒｈ／ＣｅＺｒＮｄ粉末の調製−
先に説明した通常Ｐｄ／ＣｅＺｒＮｄ粉末の調製の場合と同じく、ＣｅＺｒＮｄ複合酸化物粉末（ＣｅＯ２：ＺｒＯ２：Ｎｄ２Ｏ３＝２３：６７：１０（質量比））２０ｇにイオン交換水を混合してスラリーとし、さらにＲｈ濃度８．１５質量％の硝酸ロジウム溶液０．２９ｇを混合する。これを蒸発乾固した後、乾固物を粉砕し、空気中において５００℃の温度に２時間保持する焼成を行なうことにより、ＣｅＺｒＮｄ複合酸化物粉末にＲｈを担持させてなるＲｈ濃度が０．１２質量％の通常Ｒｈ／ＣｅＺｒＮｄ粉末を得ることができる。
-Preparation of normal Rh / CeZrNd powder-
As in the preparation of the normal Pd / CeZrNd powder described above, ion-exchanged water was mixed with 20 g of CeZrNd composite oxide powder (CeO 2 : ZrO 2 : Nd 2 O 3 = 23: 67: 10 (mass ratio)). The slurry is further mixed with 0.29 g of a rhodium nitrate solution having an Rh concentration of 8.15% by mass. After evaporating this to dryness, the dried product is pulverized and calcined in air at a temperature of 500 ° C. for 2 hours, whereby the Rh concentration obtained by supporting Rh on the CeZrNd composite oxide powder is 0.00. 12% by mass of normal Rh / CeZrNd powder can be obtained.
−特定Ｒｈ／ＣｅＺｒＮｄ粉末の調製−
先に説明した特定Ｐｄ／ＣｅＺｒＮｄ粉末の調製の場合と同じく、上記通常Ｒｈ／ＣｅＺｒＮｄ粉末にイオン交換水を添加してスラリー（固形分２５質量％）とし、このスラリーをボールミルに投入して、０．５ｍｍのジルコニアビーズによって粉砕する（約３時間）ことにより、粒径が小さくなった特定Ｒｈ／ＣｅＺｒＮｄ粉末（触媒金属を担持した特定Ｃｅ含有複合酸化物粉末）が分散したゾルを得ることができる。この特定Ｒｈ／ＣｅＺｒＮｄ粉末の組成及びＰｄ濃度は通常Ｒｈ／ＣｅＺｒＮｄ粉末と同じである。
-Preparation of specific Rh / CeZrNd powder-
As in the case of the preparation of the specific Pd / CeZrNd powder described above, ion-exchanged water is added to the normal Rh / CeZrNd powder to form a slurry (solid content: 25% by mass). By pulverizing with .5 mm zirconia beads (about 3 hours), it is possible to obtain a sol in which the specific Rh / CeZrNd powder (specific Ce-containing composite oxide powder supporting a catalyst metal) with a reduced particle size is dispersed. . The composition and Pd concentration of this specific Rh / CeZrNd powder are usually the same as those of the Rh / CeZrNd powder.
また、上記通常Ｒｈ／ＣｅＺｒＮｄ粉末及び特定Ｒｈ／ＣｅＺｒＮｄ粉末各々の粒度分布は、先に説明した通常Ｐｄ／ＣｅＺｒＮｄ粉末及び特定Ｐｄ／ＣｅＺｒＮｄ粉末の粒度分布と略同じである。すなわち、粉砕前の通常Ｒｈ／ＣｅＺｒＮｄ粉末の場合、累積分布１０質量％粒径は５５０ｎｍ以上、累積分布５０質量％粒径は８００ｎｍ以上９００ｎｍ以下、累積分布９０質量％粒径は１２００ｎｍ以下である。粉砕によって得られた特定Ｒｈ／ＣｅＺｒＮｄ粉末の場合、累積分布１０質量％粒径は９０ｎｍ以上、累積分布５０質量％粒径は１５０ｎｍ以上２１０ｎｍ以下、累積分布９０質量％粒径は３００ｎｍ以下である。また、電子顕微鏡写真での観察によれば、通常Ｒｈ／ＣｅＺｒＮｄ粉末では、一次粒子径の平均粒径は１０ｎｍ以上２０ｎｍ以下であり、特定Ｒｈ／ＣｅＺｒＮｄ粉末では、一次粒子径の平均粒径は５ｎｍ以上１０ｎｍ以下であった。 The particle size distributions of the normal Rh / CeZrNd powder and the specific Rh / CeZrNd powder are substantially the same as the particle size distributions of the normal Pd / CeZrNd powder and the specific Pd / CeZrNd powder described above. That is, in the case of normal Rh / CeZrNd powder before pulverization, the cumulative distribution 10 mass% particle size is 550 nm or more, the cumulative distribution 50 mass% particle size is 800 nm to 900 nm, and the cumulative distribution 90 mass% particle size is 1200 nm or less. In the case of the specific Rh / CeZrNd powder obtained by pulverization, the cumulative distribution 10% by mass particle size is 90 nm or more, the cumulative distribution 50% by mass particle size is 150 nm to 210 nm, and the cumulative distribution 90% by mass particle size is 300 nm or less. In addition, according to observation with an electron micrograph, the average particle size of the primary particle size is usually 10 nm or more and 20 nm or less in the Rh / CeZrNd powder, and the average particle size of the primary particle size is 5 nm in the specific Rh / CeZrNd powder. It was 10 nm or less.
−下触媒層の形成−
ＣｅＺｒＮｄ複合酸化物（ＣｅＯ２：ＺｒＯ２：Ｎｄ２Ｏ３＝２３：６７：１０（質量比））粉末と、Ｌａ２Ｏ３を４質量％含有する活性アルミナ粉末（平均粒径１３．８μｍ）にＰｄを担持させたＰｄ／Ｌａ含有アルミナ粉末と、通常Ｐｄ／ＣｅＺｒＮｄ粉末と、硝酸ジルコニル（バインダ）とをイオン交換水と共に混合してスラリー化し、担体にウォッシュコートして下触媒層を形成した。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１Ｌ）を用いた。通常Ｐｄ／ＣｅＺｒＮｄ粉末については、先に説明した通常Ｐｄ／ＣｅＺｒＮｄ粉末の調製法において、ＣｅＺｒＮｄ複合酸化物粉末２０ｇに対するＰｄ濃度４．３３質量％の硝酸パラジウム溶液の添加量を２．５６ｇとすることにより、Ｐｄ濃度を０．５５質量％とした。触媒成分等の配合量（担体１Ｌ当たりの質量）については表３に記載した。
-Formation of lower catalyst layer-
CeZrNd composite oxide (CeO 2 : ZrO 2 : Nd 2 O 3 = 23: 67: 10 (mass ratio)) powder and activated alumina powder containing 4% by mass of La 2 O 3 (average particle size 13.8 μm) Pd / La-containing alumina powder with Pd supported thereon, usually Pd / CeZrNd powder, and zirconyl nitrate (binder) were mixed together with ion-exchanged water to form a slurry, and the lower catalyst layer was formed by wash-coating the support. . As the carrier, a cordierite honeycomb carrier (capacity 1 L) 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 used. For normal Pd / CeZrNd powder, in the preparation method of normal Pd / CeZrNd powder described above, the amount of palladium nitrate solution with a Pd concentration of 4.33 mass% to 20 g of CeZrNd composite oxide powder is 2.56 g. Thus, the Pd concentration was set to 0.55% by mass. The blending amounts of catalyst components and the like (mass per liter of carrier) are shown in Table 3.
−上触媒層の形成−
特定Ｒｈ／ＣｅＺｒＮｄ粉末ゾルと、通常Ｒｈ／ＣｅＺｒＮｄ粉末と、ＺｒＬａ複合酸化物を担持した活性アルミナ粉末（平均粒径３３μｍ）にＲｈを担持させてなるＲｈ／ＺｒＬａ含有アルミナ粉末と、Ｌａ２Ｏ３を４質量％含有するＬａ含有活性アルミナ粉末（平均粒径１９μｍ）とを、イオン交換水と共に混合してスラリー化し、下触媒層の上にウォッシュコートして上触媒層を形成した。この場合、上触媒層では、特定Ｒｈ／ＣｅＺｒＮｄ粉末の粒子は、通常Ｒｈ／ＣｅＺｒＮｄ粉末の粒子に担持された状態になるだけでなく、Ｒｈ／ＺｒＬａ含有アルミナ粉末の粒子にも担持された状態になる。従って、このＲｈ／ＺｒＬａ含有アルミナ粉末の活性アルミナ粒子には、ＺｒＬａ複合酸化物と特定Ｒｈ／ＣｅＺｒＮｄ粉末の粒子とが共存担持された状態になる。
-Formation of upper catalyst layer-
Rh / ZrLa-containing alumina powder obtained by supporting Rh on specific Rh / CeZrNd powder sol, normal Rh / CeZrNd powder, activated alumina powder (average particle size 33 μm) supporting ZrLa composite oxide, La 2 O 3 Was mixed with ion-exchanged water to form a slurry, and wash coated on the lower catalyst layer to form an upper catalyst layer. In this case, in the upper catalyst layer, the particles of the specific Rh / CeZrNd powder are not only normally supported on the particles of Rh / CeZrNd powder, but also supported on the particles of the Rh / ZrLa-containing alumina powder. Become. Therefore, the activated alumina particles of the Rh / ZrLa-containing alumina powder are in a state where the ZrLa composite oxide and the particles of the specific Rh / CeZrNd powder are co-supported.
Ｒｈ／ＺｒＬａ含有アルミナ粉末は次のようにして調製した。すなわち、硝酸ジルコニウム及び硝酸ランタンの混合溶液に活性アルミナ粉末を分散させ、これにアンモニア水を加えて沈殿を生成した。得られた沈殿物を濾過、洗浄し、２００℃で２時間保持する乾燥、並びに５００℃に２時間保持する焼成を行なうことにより、表面がＺｒＬａ複酸化物で被覆された活性アルミナ粒子を得た。これに硝酸ロジウム水溶液を混合し、蒸発乾固を行なうことにより、Ｒｈ／ＺｒＬａ含有アルミナ粉末を得た。ＺｒＬａ含有アルミナの組成はＺｒＯ２：Ｌａ２Ｏ３：Ａｌ２Ｏ３＝３８：２：６０（質量比）である。 The Rh / ZrLa-containing alumina powder was prepared as follows. That is, activated alumina powder was dispersed in a mixed solution of zirconium nitrate and lanthanum nitrate, and ammonia water was added thereto to form a precipitate. The obtained precipitate was filtered, washed, dried at 200 ° C. for 2 hours, and fired at 500 ° C. for 2 hours to obtain activated alumina particles whose surfaces were coated with ZrLa double oxide. . This was mixed with an aqueous rhodium nitrate solution and evaporated to dryness to obtain an Rh / ZrLa-containing alumina powder. The composition of the ZrLa-containing alumina is ZrO 2 : La 2 O 3 : Al 2 O 3 = 38: 2: 60 (mass ratio).
触媒成分等の配合量については表３に記載した。上触媒層では、特定Ｒｈ／ＣｅＺｒＮｄ粉末ゾルがバインダとして機能するため、専用のバインダ原料（硝酸ジルコニル）は配合していない。なお、表３の各成分の配合量は乾燥重量である。 The blending amounts of catalyst components and the like are shown in Table 3. In the upper catalyst layer, since the specific Rh / CeZrNd powder sol functions as a binder, a dedicated binder raw material (zirconyl nitrate) is not blended. In addition, the compounding quantity of each component of Table 3 is a dry weight.
[実施例８]
下触媒層については、実施例７の硝酸ジルコニル（バインダ）に代えて特定Ｐｄ／ＣｅＺｒＮｄ粉末（１０．０５５ｇ／Ｌ）を配合し、他は実施例７と同じ構成にした。特定Ｐｄ／ＣｅＺｒＮｄ粉末は、Ｐｄ濃度０．５５質量％の通常Ｐｄ／ＣｅＺｒＮｄ粉末を先に説明した湿式粉砕したものであり、図３及び図５の「特定Ｐｄ／ＣｅＺｒＮｄ粉末」と同様の粒度分布を有し、また、その一次粒子は、平均粒径が５ｎｍ以上１０ｎｍ以下の微細一次粒子になっている。
[Example 8]
About the lower catalyst layer, it replaced with the zirconyl nitrate (binder) of Example 7, the specific Pd / CeZrNd powder (10.55g / L) was mix | blended, and it was set as the same structure as Example 7. The specific Pd / CeZrNd powder is obtained by wet pulverization of the normal Pd / CeZrNd powder having a Pd concentration of 0.55% by mass, and the particle size distribution similar to that of the “specific Pd / CeZrNd powder” in FIGS. 3 and 5 In addition, the primary particles are fine primary particles having an average particle diameter of 5 nm to 10 nm.
この下触媒層においては、上記特定Ｐｄ／ＣｅＺｒＮｄ粉末の一部の粒子が、二次粒子径及び一次粒子径が大きな通常Ｐｄ／ＣｅＺｒＮｄ粉末の粒子（図３、図４及び図６参照）、並びに同じく二次粒子径が大きなＰｄ／Ｌａ含有アルミナ粉末の粒子に分散担持された状態になり、特定Ｐｄ／ＣｅＺｒＮｄ粉末の分散安定性が高い。 In this lower catalyst layer, some particles of the specific Pd / CeZrNd powder are particles of normal Pd / CeZrNd powder having a large secondary particle size and primary particle size (see FIGS. 3, 4 and 6), and Similarly, it is in a state of being dispersed and supported on particles of Pd / La-containing alumina powder having a large secondary particle size, and the dispersion stability of the specific Pd / CeZrNd powder is high.
上触媒層については、実施例７の特定Ｒｈ／ＣｅＺｒＮｄ粉末に代えて硝酸ジルコニル（バインダ）を１０．０００ｇ／Ｌ配合し、また、Ｒｈ／ＲｈドープＣｅＺｒＮｄ粉末のＲｈドープＣｅＺｒＮｄ粉末量を１０．０００ｇ／Ｌだけ増やし（Ｒｈ含浸担持量は実施例７と同じく０．０１２ｇ／Ｌ）、他は実施例７と同じ構成にした。 For the upper catalyst layer, in place of the specific Rh / CeZrNd powder of Example 7, 10.000 g / L of zirconyl nitrate (binder) was blended, and the amount of Rh-doped CeZrNd powder in the Rh / Rh-doped CeZrNd powder was 10.000 g. / L was increased (Rh impregnation loading was 0.012 g / L as in Example 7), and the other configuration was the same as in Example 7.
[比較例４]
下触媒層は実施例７と同じ構成とした。上触媒層は実施例８と同じ構成にした。
[Comparative Example 4]
The lower catalyst layer had the same configuration as in Example 7. The upper catalyst layer had the same configuration as in Example 8.
−排気ガス浄化性能−
実施例７，８及び比較例４の各触媒のライトオフ性能を先に説明した方法によって調べた。結果を表４に示す。
−Exhaust gas purification performance−
The light-off performance of each catalyst of Examples 7 and 8 and Comparative Example 4 was examined by the method described above. The results are shown in Table 4.
表４によれば、ＨＣ、ＣＯ及びＮＯｘのいずれに関しても、実施例７，８は比較例４よりもライトオフ温度Ｔ５０が低く、優れた排気ガス浄化性能を有することがわかる。すなわち、触媒層が二層構造であるケースにおいても、粉砕によって粒径を小さくした特定Ｒｈ／ＣｅＺｒＮｄ粉末を上触媒層に用いると、或いは粉砕によって粒径を小さくした特定Ｐｄ／ＣｅＺｒＮｄ粉末を下触媒層に用いると、排気ガスの浄化性能を効率良く高めることができる。 According to Table 4, for any of HC, CO, and NOx, Examples 7 and 8 have a light-off temperature T50 lower than that of Comparative Example 4 and have excellent exhaust gas purification performance. That is, even in the case where the catalyst layer has a two-layer structure, the specific Rh / CeZrNd powder having a particle size reduced by pulverization is used for the upper catalyst layer, or the specific Pd / CeZrNd powder having a particle size reduced by pulverization is used as the lower catalyst. When used in the layer, the exhaust gas purification performance can be improved efficiently.
１ 担体
２ 上触媒層
３ 下触媒層
４ 特定Ｃｅ含有複合酸化物粒子
５ 活性アルミナ粒子
６ 触媒金属
７ 元の一次粒子
８ 微細一次粒子
DESCRIPTION OF SYMBOLS 1 Support | carrier 2 Upper catalyst layer 3 Lower catalyst layer 4 Specific Ce containing complex oxide particle 5 Activated alumina particle 6 Catalyst metal 7 Original primary particle 8 Fine primary particle
Claims (10)
上記触媒金属を担持したＣｅ含有複合酸化物粉末は、上記触媒金属が分散担持された平均粒径５ｎｍ以上１０ｎｍ以下の多数の一次粒子が凝集してなる二次粒子によって構成され、該二次粒子の累積分布１０質量％粒径が９０ｎｍ以上、累積分布５０質量％粒径が１５０ｎｍ以上２１０ｎｍ以下、累積分布９０質量％粒径が３００ｎｍ以下である特定Ｃｅ含有複合酸化物粉末であり、
上記活性アルミナ粉末の平均粒径は、上記特定Ｃｅ含有複合酸化物粉末の上記累積分布９０質量％粒径よりも大きく、
上記活性アルミナ粉末に対する上記特定Ｃｅ含有複合酸化物粉末の質量比が１／１００以上５０／１００以下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 containing a mixed metal powder containing Ce containing a catalytic metal and activated alumina powder in a mixed state is provided on a carrier,
The Ce-containing composite oxide powder supporting the catalyst metal is composed of secondary particles formed by aggregation of a large number of primary particles having an average particle diameter of 5 nm to 10 nm on which the catalyst metal is dispersed and supported. A specific Ce-containing composite oxide powder having a cumulative distribution of 10% by mass particle size of 90 nm or more, a cumulative distribution of 50% by mass particle size of from 150 nm to 210 nm, and a cumulative distribution of 90% by mass of particle size of 300 nm or less.
The average particle size of the activated alumina powder is larger than the cumulative distribution 90 mass% particle size of the specific Ce-containing composite oxide powder,
A catalyst for exhaust gas purification, wherein a mass ratio of the specific Ce-containing composite oxide powder to the activated alumina powder is from 1/100 to 50/100.
上記活性アルミナ粉末に対する上記特定Ｃｅ含有複合酸化物粉末の質量比が１／１００以上３０／１００以下であることを特徴とする排気ガス浄化用触媒。 In claim 1,
An exhaust gas purifying catalyst, wherein a mass ratio of the specific Ce-containing composite oxide powder to the activated alumina powder is from 1/100 to 30/100.
上記担体上に複数の触媒層が積層され、該複数の触媒層のうちの一つが、上記触媒金属を担持した特定Ｃｅ含有複合酸化物粉末と活性アルミナ粉末とを混合状態で含有していることを特徴とする排気ガス浄化用触媒。 In claim 1 or claim 2,
A plurality of catalyst layers are laminated on the support, and one of the plurality of catalyst layers contains the specific Ce-containing composite oxide powder supporting the catalyst metal and the activated alumina powder in a mixed state. An exhaust gas purifying catalyst characterized by.
上記複数の触媒層のうち表面が排気ガスに晒される上側触媒層よりも下側の触媒層が、上記触媒金属を担持した特定Ｃｅ含有複合酸化物粉末と活性アルミナ粉末とを混合状態で含有し、該特定Ｃｅ含有複合酸化物粉末が上記触媒金属としてＰｄを担持していることを特徴とする排気ガス浄化用触媒。 In claim 3,
The catalyst layer below the upper catalyst layer whose surface is exposed to the exhaust gas among the plurality of catalyst layers contains the specific Ce-containing composite oxide powder supporting the catalyst metal and the activated alumina powder in a mixed state. An exhaust gas purifying catalyst, wherein the specific Ce-containing composite oxide powder carries Pd as the catalyst metal.
上記活性アルミナ粉末に触媒金属としてＰｄが担持されていることを特徴とする排気ガス浄化用触媒。 In claim 4,
An exhaust gas purifying catalyst, wherein Pd is supported as a catalytic metal on the activated alumina powder.
上記下側の触媒層は、上記触媒金属を担持した特定Ｃｅ含有複合酸化物粉末と、上記活性アルミナ粉末と、一次粒子及び二次粒子の平均粒径が上記特定Ｃｅ含有複合酸化物粉末よりも大きな別のＣｅ含有複合酸化物粉末とを混合状態で含有することを特徴とする排気ガス浄化用触媒。 In claim 4 or claim 5,
The lower catalyst layer has a specific Ce-containing composite oxide powder supporting the catalyst metal, the activated alumina powder, and the average particle size of primary particles and secondary particles is higher than that of the specific Ce-containing composite oxide powder. An exhaust gas purifying catalyst comprising a large amount of another Ce-containing composite oxide powder in a mixed state.
上記複数の触媒層のうち表面が排気ガスに晒される上側触媒層が上記触媒金属を担持した特定Ｃｅ含有複合酸化物粉末と活性アルミナ粉末とを混合状態で含有し、該特定Ｃｅ含有複合酸化物粉末が上記触媒金属としてＲｈを担持していることを特徴とする排気ガス浄化用触媒。 In any one of Claims 3 thru | or 6,
The upper catalyst layer whose surface is exposed to the exhaust gas among the plurality of catalyst layers contains the specific Ce-containing composite oxide powder supporting the catalyst metal and the activated alumina powder in a mixed state, and the specific Ce-containing composite oxide An exhaust gas purifying catalyst, wherein the powder carries Rh as the catalyst metal.
上記上側触媒層が含有する活性アルミナ粉末の一部には、ＺｒとＬａとを含む複合酸化物と、上記特定Ｃｅ含有複合酸化物粉末の粒子とが共存担持されていることを特徴とする排気ガス浄化用触媒。 In claim 7,
Exhaust gas characterized in that a part of the activated alumina powder contained in the upper catalyst layer co-supports a composite oxide containing Zr and La and particles of the specific Ce-containing composite oxide powder. Gas purification catalyst.
上記活性アルミナ粉末は、上記触媒金属を担持した特定Ｃｅ含有酸化物粉末をバインダとして上記担体に保持されてい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 8,
The catalyst for purifying exhaust gas, wherein the activated alumina powder is held on the carrier using a specific Ce-containing oxide powder carrying the catalyst metal as a binder.
上記触媒金属を担持したＣｅ含有複合酸化物粉末を粉砕することにより、該触媒金属が分散担持された平均粒径５ｎｍ以上１０ｎｍ以下の多数の一次粒子が凝集してなる二次粒子によって構成され、該二次粒子の累積分布１０質量％粒径が９０ｎｍ以上、累積分布５０質量％粒径が１５０ｎｍ以上２１０ｎｍ以下、累積分布９０質量％粒径が３００ｎｍ以下である特定Ｃｅ含有複合酸化物粉末にする工程と、
上記触媒金属を担持した特定Ｃｅ含有複合酸化物粉末と、該特定Ｃｅ含有複合酸化物粉末の上記累積分布９０質量％粒径よりも平均粒径が大きい活性アルミナ粉末とを含むスラリーを調製する工程と、
上記スラリーを担体にコーティングして触媒層を形成する工程とを備え、
上記スラリー調製工程においては、上記活性アルミナ粉末に対する上記特定Ｃｅ含有複合酸化物粉末の質量比が１／１００以上５０／１００以下となるようにすることを特徴とする排気ガス浄化用触媒の製造方法。 A step of supporting a catalytic metal on Ce-containing composite oxide powder;
By pulverizing the Ce-containing composite oxide powder supporting the catalyst metal, secondary particles formed by aggregating a large number of primary particles having an average particle diameter of 5 nm to 10 nm on which the catalyst metal is dispersed and supported, A specific Ce-containing composite oxide powder having a cumulative distribution of 10% by mass of the secondary particles of 90 nm or more, a cumulative distribution of 50% by mass of 150 to 210 nm, and a cumulative distribution of 90% by mass of 300% or less is used. Process,
A step of preparing a slurry comprising the specific Ce-containing composite oxide powder supporting the catalyst metal, and an activated alumina powder having an average particle size larger than the cumulative distribution of 90% by mass of the specific Ce-containing composite oxide powder. When,
Coating the slurry on a carrier to form a catalyst layer,
In the slurry preparation step, a mass ratio of the specific Ce-containing composite oxide powder to the activated alumina powder is 1/100 or more and 50/100 or less, and a method for producing an exhaust gas purification catalyst .
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