JP5589320B2 - Exhaust gas purification catalyst and method for producing the same - Google Patents
Exhaust gas purification catalyst and method for producing the same Download PDFInfo
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- 239000003054 catalyst Substances 0.000 title claims description 114
- 238000000746 purification Methods 0.000 title description 28
- 238000004519 manufacturing process Methods 0.000 title description 4
- 239000002131 composite material Substances 0.000 claims description 117
- 239000000843 powder Substances 0.000 claims description 93
- 239000002245 particle Substances 0.000 claims description 83
- 229910052783 alkali metal Inorganic materials 0.000 claims description 64
- 150000001340 alkali metals Chemical class 0.000 claims description 64
- 239000002184 metal Substances 0.000 claims description 49
- 229910052751 metal Inorganic materials 0.000 claims description 48
- 229910052684 Cerium Inorganic materials 0.000 claims description 15
- 229910052726 zirconium Inorganic materials 0.000 claims description 15
- 238000011068 loading method Methods 0.000 claims description 13
- 230000003197 catalytic effect Effects 0.000 claims description 12
- 239000000203 mixture Substances 0.000 claims description 11
- 239000011230 binding agent Substances 0.000 claims description 9
- 238000000975 co-precipitation Methods 0.000 claims description 5
- 239000011248 coating agent Substances 0.000 claims description 5
- 238000000576 coating method Methods 0.000 claims description 5
- 150000002500 ions Chemical class 0.000 claims description 5
- 229910052809 inorganic oxide Inorganic materials 0.000 claims description 3
- KDLHZDBZIXYQEI-UHFFFAOYSA-N palladium Substances [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 description 60
- 239000007789 gas Substances 0.000 description 48
- 239000011734 sodium Substances 0.000 description 46
- 230000000052 comparative effect Effects 0.000 description 24
- 239000000243 solution Substances 0.000 description 14
- 239000006104 solid solution Substances 0.000 description 9
- 238000002441 X-ray diffraction 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
- VWDWKYIASSYTQR-UHFFFAOYSA-N sodium nitrate Chemical compound [Na+].[O-][N+]([O-])=O VWDWKYIASSYTQR-UHFFFAOYSA-N 0.000 description 8
- 229910002651 NO3 Inorganic materials 0.000 description 7
- 239000007864 aqueous solution Substances 0.000 description 7
- MWUXSHHQAYIFBG-UHFFFAOYSA-N nitrogen oxide Inorganic materials O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 description 7
- GPNDARIEYHPYAY-UHFFFAOYSA-N palladium(ii) nitrate Chemical compound [Pd+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O GPNDARIEYHPYAY-UHFFFAOYSA-N 0.000 description 7
- 238000002360 preparation method Methods 0.000 description 7
- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 description 6
- 230000002776 aggregation Effects 0.000 description 6
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 6
- 238000000034 method Methods 0.000 description 6
- 150000002739 metals Chemical class 0.000 description 5
- 239000011259 mixed solution Substances 0.000 description 5
- 238000003860 storage Methods 0.000 description 5
- 238000004220 aggregation Methods 0.000 description 4
- 238000000635 electron micrograph Methods 0.000 description 4
- 238000010304 firing Methods 0.000 description 4
- 239000000446 fuel Substances 0.000 description 4
- 239000011163 secondary particle Substances 0.000 description 4
- 235000010344 sodium nitrate Nutrition 0.000 description 4
- 239000004317 sodium nitrate Substances 0.000 description 4
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 4
- MUBZPKHOEPUJKR-UHFFFAOYSA-N Oxalic acid Chemical compound OC(=O)C(O)=O MUBZPKHOEPUJKR-UHFFFAOYSA-N 0.000 description 3
- 239000003513 alkali Substances 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 description 2
- 229910017493 Nd 2 O 3 Inorganic materials 0.000 description 2
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 2
- 238000005054 agglomeration Methods 0.000 description 2
- 230000032683 aging Effects 0.000 description 2
- 235000011114 ammonium hydroxide Nutrition 0.000 description 2
- 229910002091 carbon monoxide Inorganic materials 0.000 description 2
- 229910052878 cordierite Inorganic materials 0.000 description 2
- JSKIRARMQDRGJZ-UHFFFAOYSA-N dimagnesium dioxido-bis[(1-oxido-3-oxo-2,4,6,8,9-pentaoxa-1,3-disila-5,7-dialuminabicyclo[3.3.1]nonan-7-yl)oxy]silane Chemical compound [Mg++].[Mg++].[O-][Si]([O-])(O[Al]1O[Al]2O[Si](=O)O[Si]([O-])(O1)O2)O[Al]1O[Al]2O[Si](=O)O[Si]([O-])(O1)O2 JSKIRARMQDRGJZ-UHFFFAOYSA-N 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 238000002156 mixing Methods 0.000 description 2
- 229910052763 palladium Inorganic materials 0.000 description 2
- 239000002243 precursor Substances 0.000 description 2
- 239000011164 primary particle Substances 0.000 description 2
- 239000000047 product Substances 0.000 description 2
- 229910052708 sodium Inorganic materials 0.000 description 2
- 229910052717 sulfur Inorganic materials 0.000 description 2
- 239000011593 sulfur Substances 0.000 description 2
- 239000002699 waste material Substances 0.000 description 2
- 239000004215 Carbon black (E152) Substances 0.000 description 1
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- 229910052779 Neodymium Inorganic materials 0.000 description 1
- GAJINTUZMJRZFR-UHFFFAOYSA-N O.O.O.O.[N+](=O)([O-])[O-].[Nd+3].[N+](=O)([O-])[O-].[N+](=O)([O-])[O-] Chemical compound O.O.O.O.[N+](=O)([O-])[O-].[Nd+3].[N+](=O)([O-])[O-].[N+](=O)([O-])[O-] GAJINTUZMJRZFR-UHFFFAOYSA-N 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 150000001339 alkali metal compounds Chemical class 0.000 description 1
- 229910001413 alkali metal ion Inorganic materials 0.000 description 1
- QGZKDVFQNNGYKY-UHFFFAOYSA-N ammonia Natural products N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 1
- 239000012298 atmosphere Substances 0.000 description 1
- 229910052788 barium Inorganic materials 0.000 description 1
- 229910052791 calcium Inorganic materials 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 210000004027 cell Anatomy 0.000 description 1
- 210000002421 cell wall Anatomy 0.000 description 1
- 238000005119 centrifugation Methods 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 238000011156 evaluation Methods 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
- 239000001257 hydrogen Substances 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 230000003993 interaction Effects 0.000 description 1
- 229910052744 lithium Inorganic materials 0.000 description 1
- 229910052749 magnesium Inorganic materials 0.000 description 1
- 229910021645 metal ion Inorganic materials 0.000 description 1
- 229910044991 metal oxide Inorganic materials 0.000 description 1
- 150000004706 metal oxides Chemical class 0.000 description 1
- 150000002823 nitrates Chemical class 0.000 description 1
- UJVRJBAUJYZFIX-UHFFFAOYSA-N nitric acid;oxozirconium Chemical compound [Zr]=O.O[N+]([O-])=O.O[N+]([O-])=O UJVRJBAUJYZFIX-UHFFFAOYSA-N 0.000 description 1
- 239000012299 nitrogen atmosphere Substances 0.000 description 1
- 229910000510 noble metal Inorganic materials 0.000 description 1
- 235000006408 oxalic acid Nutrition 0.000 description 1
- 229910052697 platinum Inorganic materials 0.000 description 1
- 231100000572 poisoning Toxicity 0.000 description 1
- 230000000607 poisoning effect Effects 0.000 description 1
- 238000006116 polymerization reaction Methods 0.000 description 1
- 229910052700 potassium Inorganic materials 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 229910052703 rhodium Inorganic materials 0.000 description 1
- 239000002002 slurry Substances 0.000 description 1
- 238000001179 sorption measurement Methods 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 229910052712 strontium Inorganic materials 0.000 description 1
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- Exhaust Gas After Treatment (AREA)
- Exhaust Gas Treatment By Means Of Catalyst (AREA)
- Catalysts (AREA)
Description
本発明は、排気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 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 accordance with fluctuations in the air-fuel ratio of 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、ＣｅＺｒ系複合酸化物にアルカリ金属を固溶させると、その塩基性が高まるなど、性質が変化することが知られている。 Further, it is known that when an alkali metal is dissolved in the CeZr-based composite oxide, its properties change, for example, its basicity increases.
例えば、特許文献３には、ＣｅＺｒ系複合酸化物に触媒金属と共にアルカリ金属を固溶させることにより、ＣｅＺｒ系複合酸化物に塩基性が高いサイトを形成し、該サイトに排気ガス中の硫黄を吸着させることにより、触媒金属の硫黄被毒を抑制することが記載されている。その調製法は、Ｃｅ、Ｚｒ、触媒金属及びアルカリ金属の各イオンを含む硝酸塩溶液にアンモニア水を添加して共沈を生じさせ、共沈物を乾燥・焼成する、というものであり、これにより、触媒金属及びアルカリ金属が固溶したＣｅＺｒ系複合酸化物を得ている。 For example, Patent Document 3 discloses that a highly basic site is formed in a CeZr composite oxide by dissolving an alkali metal together with a catalyst metal in a CeZr composite oxide, and sulfur in exhaust gas is formed in the site. It is described that sulfur poisoning of catalytic metals is suppressed by adsorption. The preparation method is that ammonia water is added to a nitrate solution containing Ce, Zr, catalyst metal and alkali metal ions to cause coprecipitation, and the coprecipitate is dried and calcined. Thus, a CeZr-based composite oxide in which a catalytic metal and an alkali metal are dissolved is obtained.
また、特許文献４には、ＣｅＺｒ系複合酸化物にアルカリ金属を固溶させることにより、該複合酸化物の酸素吸蔵放出量を増大させること、かかるアルカリ金属を固溶したＣｅＺｒ系複合酸化物と、Ｐｄを担持した活性アルミナとを排気ガス浄化用触媒に用いることが記載されている。さらに、アルカリ金属を固溶したＣｅＺｒ系複合酸化物は、共沈法や錯体重合法で調製することが記載されている。 Patent Document 4 discloses that an alkali metal is solid-dissolved in a CeZr-based composite oxide to increase the oxygen storage / release amount of the composite oxide, and a CeZr-based composite oxide in which the alkali metal is solid-solubilized. The use of activated alumina carrying Pd as an exhaust gas purifying catalyst is described. Furthermore, it is described that a CeZr-based composite oxide in which an alkali metal is dissolved is prepared by a coprecipitation method or a complex polymerization method.
しかし、上記アルカリ金属を固溶したＣｅＺｒ系複合酸化物の場合、アルカリ金属はＣｅＺｒ系複合酸化物の粒子内に固溶しているから、粒子表面に露出するアルカリ金属量は少なくなる。従って、アルカリ金属の固溶によるＣｅＺｒ系複合酸化物粉末の粒子表面特性の向上、触媒金属との相互作用の向上には限界がある。これに対して、アルカリ金属溶液を触媒層に含浸させてＣｅＺｒ系複合酸化物粉末の粒子表面にアルカリ金属を担持させることも考えられる。しかし、その場合は、アルカリ金属がＣｅＺｒ系複合酸化物粉末だけでなく、バインダなど触媒層の他の成分にもアルカリ金属が担持され、無駄が多くなるとともに、アルカリアタックによる担体の強度低下を招き易くなる。 However, in the case of the CeZr-based composite oxide in which the alkali metal is dissolved, since the alkali metal is dissolved in the CeZr-based composite oxide particles, the amount of alkali metal exposed on the particle surface is reduced. Therefore, there is a limit in improving the particle surface characteristics of CeZr-based composite oxide powder by solid solution of alkali metal and improving the interaction with the catalyst metal. On the other hand, it is also conceivable that the alkali metal solution is impregnated in the catalyst layer and the alkali metal is supported on the particle surfaces of the CeZr-based composite oxide powder. However, in this case, the alkali metal is supported not only on the CeZr-based composite oxide powder, but also on other components of the catalyst layer such as a binder, resulting in increased waste and a decrease in the strength of the carrier due to alkali attack. It becomes easy.
すなわち、本発明は、触媒金属及びＣｅＺｒ系複合酸化物粉末を含有する排気ガス浄化用触媒の向上にアルカリ金属を効果的に利用することを課題とする。 That is, this invention makes it a subject to use an alkali metal effectively for the improvement of the catalyst for exhaust gas purification containing a catalyst metal and CeZr type complex oxide powder.
本発明は、上記課題を解決するために、アルカリ金属をＣｅＺｒ系複合酸化物（Ｃｅ及びＺｒの各イオンを含む酸化物）粉末の粒子表面に担持されるように該粒子に組み込み、且つ触媒金属とアルカリ金属とが該ＣｅＺｒ系複合酸化物粒子表面において互いに近接した状態になるようにした。以下、具体的に説明する。 In order to solve the above-mentioned problems, the present invention incorporates an alkali metal into the particle so as to be supported on the particle surface of a CeZr-based composite oxide (oxide containing each ion of Ce and Zr), and a catalytic metal. And an alkali metal were brought close to each other on the CeZr-based composite oxide particle surface. This will be specifically described below.
本発明は、担体上に、触媒金属と、Ｃｅ及びＺｒを含有するＣｅＺｒ系複合酸化物粉末と、無機酸化物からなるバインダとを含む触媒層が設けられている排気ガス浄化用触媒であって、
上記触媒金属がＰｄであり、該Ｐｄは上記ＣｅＺｒ系複合酸化物粉末の粒子に固溶し、その一部が該粒子表面に露出し、
上記触媒層において、上記ＣｅＺｒ系複合酸化物粉末の粒子表面に担持されるように該粒子に組み込まれて、上記ＣｅＺｒ系複合酸化物粉末上に偏在させたアルカリ金属を備え、
上記ＣｅＺｒ系複合酸化物粉末の粒子に固溶したアルカリ金属の一部が当該粒子の表面に露出し、
上記ＣｅＺｒ系複合酸化物粉末の粒子表面において、上記触媒金属としてのＰｄと上記アルカリ金属とが互いに近接した状態で存在してい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 catalyst metal, a CeZr-based composite oxide powder containing Ce and Zr, and a binder made of an inorganic oxide is provided on a support. ,
The catalyst metal is Pd, the Pd is solid-solved in the particles of the CeZr-based composite oxide powder, a part of which is exposed on the particle surface,
The catalyst layer includes an alkali metal incorporated in the particle so as to be supported on the particle surface of the CeZr-based composite oxide powder and unevenly distributed on the CeZr-based composite oxide powder,
A part of the alkali metal dissolved in the particles of the CeZr-based composite oxide powder is exposed on the surface of the particles,
Pd as the catalyst metal and the alkali metal are present in close proximity to each other on the particle surface of the CeZr-based composite oxide powder.
このような排気ガス浄化用触媒によれば、アルカリ金属がＣｅＺｒ系複合酸化物粉末の粒子表面に担持され、該粒子表面において触媒金属Ｐｄとアルカリ金属とが互いに近接した状態で存在するから、アルカリ金属が立体障害となって、ＣｅＺｒ系複合酸化物粉末の粒子表面における触媒金属Ｐｄの凝集が抑制される。そして、アルカリ金属が有する電子供与性により、触媒金属ＰｄとＣｅＺｒ系複合酸化物とが酸素を介した結合状態をとり易くなり、触媒金属Ｐｄは酸化物としての性質が強くなって、ＨＣ（炭化水素）やＣＯを酸化浄化する活性が高くなり、同時にＮＯｘの還元浄化が図れる。また、上記電子供与性により、ＣｅＺｒ系複合酸化物に吸着される排気ガス成分の活性が高くなり、触媒金属Ｐｄによって浄化され易くなる。しかも、アルカリ金属は、ＣｅＺｒ系複合酸化物粉末の粒子表面に担持されるように該粒子に組み込まれているから、つまり、アルカリ金属を触媒層においてＣｅＺｒ系複合酸化物粉末上に偏在させているから、アルカリ金属がバインダ等に担持される無駄が防止されるとともに、担体に対するアルカリアタックが避けられ、触媒の耐久性向上に有利になる。 According to such an exhaust gas purifying catalyst, the alkali metal is supported on the particle surface of the CeZr-based composite oxide powder, and the catalyst metal Pd and the alkali metal are present in the state of being close to each other on the particle surface. The metal becomes a steric hindrance, and aggregation of the catalytic metal Pd on the particle surface of the CeZr-based composite oxide powder is suppressed. The electron donating property of the alkali metal makes it easy for the catalyst metal Pd and the CeZr-based composite oxide to take a bonded state via oxygen, and the catalyst metal Pd has a strong oxide property, and HC (carbonized). Hydrogen) and CO are oxidized and purified, and NOx can be reduced and purified at the same time. In addition, due to the electron donating property, the activity of the exhaust gas component adsorbed on the CeZr-based composite oxide is increased, and is easily purified by the catalyst metal Pd . Moreover, the alkali metal is incorporated in the particles so as to be supported on the particle surface of the CeZr-based composite oxide powder, that is, the alkali metal is unevenly distributed on the CeZr-based composite oxide powder in the catalyst layer. Thus, waste of alkali metal supported on the binder or the like is prevented, and an alkali attack on the carrier is avoided, which is advantageous for improving the durability of the catalyst.
また、上記触媒金属Ｐｄが上記ＣｅＺｒ系複合酸化物粉末の粒子に固溶し、その一部が該粒子表面に露出していることにより、ＣｅＺｒ系複合酸化物の酸素吸蔵放出能が高くなるとともに、触媒金属Ｐｄの凝集抑制に有利になる。 Moreover, the catalyst metal Pd are dissolved in the particles of the CeZr-based mixed oxide powder, a portion of more and this exposed on the surface of the particles, high oxygen storage capacity of the CeZr-based mixed oxide At the same time, it is advantageous for suppressing aggregation of the catalyst metal Pd .
上記ＣｅＺｒ系複合酸化物に対する上記アルカリ金属の好ましい担持比率は、酸化物に換算して１１モル％以下であり、さらに好ましいのは０．２モル％以上５モル％以下である。 A preferable supporting ratio of the alkali metal with respect to the CeZr-based composite oxide is 11 mol% or less in terms of oxide, and more preferably 0.2 mol% or more and 5 mol% or less.
上記ＣｅＺｒ系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がリッチである複合酸化物粉末である。ＣｅＺｒ系複合酸化物には、Ｃｅ及びＺｒの他にＮｄを配合することが好ましい。その場合の好ましい組成（質量比）は、ＣｅＯ２：ＺｒＯ２：Ｎｄ２Ｏ３＝（５〜４５）：（４５〜８５）：（５〜２０）である。さらに第四金属成分として、例えばＰｒ、Ｙ、Ｌａ、Ｈｆ、Ｂａ、Ｓｒ、Ｃａ、Ｍｇを０．１質量％以上１０質量％以下の範囲で配合することもできる。 The CeZr-based composite oxide powder is preferably a composite oxide powder having the same mass ratio of CeO 2 and ZrO 2 or rich in ZrO 2 . In addition to Ce and Zr, Nd is preferably added to the CeZr-based composite oxide. A preferable composition (mass ratio) in that case is CeO 2 : ZrO 2 : Nd 2 O 3 = (5-45) :( 45-85) :( 5-20). Furthermore, as a 4th metal component, Pr, Y, La, Hf, Ba, Sr, Ca, Mg can also be mix | blended in 0.1 mass% or more and 10 mass% or less, for example.
上記アルカリ金属としては、Ｌｉ、Ｎａ、Ｋが好ましい。 As the alkali metal, Li, Na, and K are preferable.
上記ＣｅＺｒ系複合酸化物粉末に対する触媒金属Ｐｄの担持比率は０．０１質量％以上１５質量％以下とすることが好ましい。 The supporting ratio of the catalyst metal Pd to the CeZr-based composite oxide powder is preferably 0.01% by mass or more and 15% by mass or less.
本発明の別の観点は、上述の如き排気ガス浄化用触媒を製造することに適した方法であり、Ｃｅ及びＺｒの各イオンを含む溶液から得たＣｅ及びＺｒを含むゲル形態の共沈物にアルカリ金属溶液を混合し、該混合物を焼成することによって、一部のアルカリ金属がＣｅＺｒ系複合酸化物粒子に固溶し且つこの固溶したアルカリ金属の一部が粒子表面に露出したＣｅＺｒ系複合酸化物粉末を得る工程と、
上記ＣｅＺｒ系複合酸化物粉末をバインダと共に担体にウォッシュコートして、該担体上に触媒層を形成する工程とを備え、
上記ＣｅＺｒ系複合酸化物粉末を得る工程において、上記溶液に触媒金属としてのＰｄのイオンを添加して上記Ｃｅ及びＺｒと共にＰｄを共沈させることにより、該Ｐｄを上記ＣｅＺｒ系複合酸化物の粒子に固溶させるとともに、その一部のＰｄを該粒子表面に露出させることを特徴とする。
Another aspect of the present invention is a method suitable for producing an exhaust gas purification catalyst as described above, and a coprecipitate in the form of a gel containing Ce and Zr obtained from a solution containing Ce and Zr ions. A CeZr system in which a part of the alkali metal is solid-dissolved in the CeZr-based composite oxide particles and a part of the solid-solution alkali metal is exposed on the particle surface by mixing the alkali metal solution and firing the mixture. Obtaining a composite oxide powder;
And a step of wash-coating the CeZr-based composite oxide powder together with a binder on a carrier to form a catalyst layer on the carrier,
In the step of obtaining the CeZr-based mixed oxide powder, by co-precipitation of Pd with the Ce and Zr were added ions Pd as the catalytic metal in the solution, the Pd in the CeZr-based mixed oxide particles And a part of Pd is exposed on the particle surface.
この製造方法の場合、Ｃｅ及びＺｒを含むゲル形態の共沈物にアルカリ金属溶液を混合し、該混合物を焼成するから、アルカリ金属溶液はゲルを構成する粒子表面に付着し、その後の焼成により、アルカリ金属が酸化物としてＣｅＺｒ系複合酸化物の粒子表面に担持された状態になる。ＣｅＺｒ系複合酸化物粉末の粒子に固溶したアルカリ金属の一部は当該粒子の表面に露出する。これにより、アルカリ金属を触媒層においてＣｅＺｒ系複合酸化物粉末上に偏在させることができる。そして、ＣｅＺｒ系複合酸化物粉末を得る工程において、触媒金属ＰｄをＣｅ及びＺｒと共に共沈させるから、該Ｐｄは当該ＣｅＺｒ系複合酸化物粒子に固溶するとともに、その一部のＰｄが該粒子表面に露出した状態になり、その結果、該粒子表面ではアルカリ金属とＰｄとが互いに近接した状態になる。 In the case of this production method, an alkali metal solution is mixed with a co-precipitate in the form of a gel containing Ce and Zr, and the mixture is fired. Therefore, the alkali metal solution adheres to the particle surface constituting the gel, and then fired. Then, the alkali metal is supported on the particle surface of the CeZr-based composite oxide as an oxide. Part of the alkali metal dissolved in the particles of the CeZr-based composite oxide powder is exposed on the surface of the particles. Thereby, an alkali metal can be unevenly distributed on the CeZr-based composite oxide powder in the catalyst layer. Then, in the step of obtaining a CeZr-based composite oxide powder, a catalytic metal Pd from coprecipitating with Ce and Zr, with the Pd is dissolved in the CeZr-based mixed oxide particles, of a part of Pd is particles As a result, the alkali metal and Pd are close to each other on the particle surface.
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、アルカリ金属はＣｅＺｒ系複合酸化物粉末の粒子表面に担持されるように該粒子に組み込まれて該ＣｅＺｒ系複合酸化物粉末上に偏在し、ＣｅＺｒ系複合酸化物粉末の粒子に固溶したアルカリ金属の一部が当該粒子の表面に露出し、ＣｅＺｒ系複合酸化物粉末の粒子に固溶したＰｄの一部が該粒子表面に露出し、該アルカリ金属と触媒金属ＰｄとがＣｅＺｒ系複合酸化物粉末の粒子表面において互いに近接した状態で存在しているから、アルカリ金属が立体障害となって、ＣｅＺｒ系複合酸化物粉末の粒子表面におけるＰｄの凝集が抑制され、また、アルカリ金属が有する電子供与性により、ＰｄはＨＣやＣＯを酸化浄化する活性が高くなり、或いは、ＣｅＺｒ系複合酸化物に吸着される排気ガス成分の活性が高くなり、優れた排気ガス浄化性能が得られるとともに、担体に対するアルカリアタックが避けられ、触媒の耐久性向上に有利になる。 As described above, according to the exhaust gas purifying catalyst of the present invention, the alkali metal is incorporated into the CeZr-based composite oxide powder so as to be supported on the particle surface of the CeZr-based composite oxide powder. A portion of the alkali metal that is unevenly distributed and dissolved in the particles of the CeZr-based composite oxide powder is exposed on the surface of the particles, and a part of Pd that is dissolved in the particles of the CeZr-based composite oxide powder is on the surface of the particles. Since the exposed alkali metal and catalyst metal Pd are present in the state of being close to each other on the particle surface of the CeZr-based composite oxide powder, the alkali metal becomes a steric hindrance, and the particles of the CeZr-based composite oxide powder aggregation of Pd is suppressed in the surface, and by electron-donating with an alkali metal, Pd is high activity to oxidize purify HC and CO, or adsorbed on CeZr-based mixed oxide Activity of the exhaust gas component becomes high that, together with the excellent exhaust gas purifying performance can be obtained, the alkali attack is avoided to the carrier, which is advantageous in improving durability of the catalyst.
本発明に係る排気ガス浄化用触媒の製造方法によれば、Ｃｅ及びＺｒを含むゲル形態の共沈物にアルカリ金属溶液を混合し、該混合物を焼成することによって、一部のアルカリ金属がＣｅＺｒ系複合酸化物粒子に固溶し且つこの固溶したアルカリ金属の一部が粒子表面に露出したＣｅＺｒ系複合酸化物粉末を得る工程と、該ＣｅＺｒ系複合酸化物粉末をバインダと共に担体にウォッシュコートして触媒層を形成する工程とを備え、上記ＣｅＺｒ系複合酸化物粉末を得る工程において、上記Ｃｅ及びＺｒと共にＰｄを共沈させることにより、該Ｐｄを上記ＣｅＺｒ系複合酸化物粒子に固溶させるとともに、その一部のＰｄを該粒子表面に露出させるようにしたから、アルカリ金属がＣｅＺｒ系複合酸化物の粒子表面に担持されてＣｅＺｒ系複合酸化物粉末上に偏在し、且つアルカリ金属と触媒金属ＰｄとはＣｅＺｒ系複合酸化物粉末の粒子表面において互いに近接した状態になる。 According to the method for producing an exhaust gas purifying catalyst of the present invention, an alkali metal solution is mixed with a gel-form coprecipitate containing Ce and Zr, and the alkali metal solution is calcined, whereby a portion of the alkali metal is converted into CeZr. A step of obtaining a CeZr-based composite oxide powder that is solid-dissolved in the composite oxide particles and a part of the dissolved alkali metal is exposed on the surface of the particles , and wash-coating the CeZr-based composite oxide powder together with a binder on a carrier and a step of forming a catalyst layer, in the step of obtaining the CeZr-based mixed oxide powder, by co-precipitation of Pd with the Ce and Zr, solid solution of the Pd to the CeZr-based mixed oxide particles together is, since a part of the Pd was expose to the particle surface, CeZr-based mixed alkali metal is supported on the particle surfaces of CeZr-based mixed oxide Unevenly distributed on the product powder, and a state close to each other in the particle surfaces of the CeZr-based mixed oxide powder and the alkali metal and the catalyst metal Pd.
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上に触媒層２が形成されている。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 purifying catalyst shown in FIG. 1, 1 is a carrier, and a catalyst layer 2 is formed 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。触媒層２は、触媒金属と、アルカリ金属と、酸素吸蔵放出材としてのＣｅＺｒ系複合酸化物粉末と、無機酸化物からなるバインダとを含有する。触媒層２は、さらに、活性アルミナ粉末など他の触媒成分を含有することができる。ＣｅＺｒ系複合酸化物粉末上には、アルカリ金属と触媒金属とが共存している。すなわち、アルカリ金属は、触媒層２おいて上記ＣｅＺｒ系複合酸化物粉末上に偏在しており、さらに、ＣｅＺｒ系複合酸化物粉末の粒子表面において、アルカリ金属と触媒金属とが互いに近接して設けられている。 The carrier 1 is, for example, a cordierite honeycomb carrier. The catalyst layer 2 contains a catalyst metal, an alkali metal, a CeZr-based composite oxide powder as an oxygen storage / release material, and a binder made of an inorganic oxide. The catalyst layer 2 can further contain other catalyst components such as activated alumina powder. An alkali metal and a catalyst metal coexist on the CeZr-based composite oxide powder. That is, the alkali metal is unevenly distributed on the CeZr-based composite oxide powder in the catalyst layer 2, and the alkali metal and the catalyst metal are provided close to each other on the particle surface of the CeZr-based composite oxide powder. It has been.
＜アルカリ金属・触媒金属共存型ＣｅＺｒ系複合酸化物粉末について＞
上記アルカリ金属と触媒金属とが共存したＣｅＺｒ系複合酸化物粉末について、アルカリ金属としてＮａを採用し、触媒金属としてＰｄを採用したケースで説明する。
<Alkali metal / catalyst coexisting CeZr-based composite oxide powder>
The CeZr-based composite oxide powder in which the alkali metal and the catalyst metal coexist will be described by using Na as the alkali metal and Pd as the catalyst metal.
−実施例に係るＮａドープ型ＣｅＺｒ系複合酸化物粉末の調製−
硝酸セリウム６水和物（１７．１５ｇ）とＺｒＯ２に換算して２５．１３質量％のＺｒを含有したオキシ硝酸ジルコニル溶液（７８．７８ｇ）と硝酸ネオジム４水和物（７．０７ｇ）と硝酸パラジウム（３．４４ｇ）をイオン交換水（３００ｍＬ）に溶かして硝酸塩混合溶液を得る。この硝酸塩混合溶液に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てゲルを得る。このゲル形態の共沈物に、アルカリ金属化合物としての硝酸ナトリウム（０．８２ｇ）を溶解させた水溶液を添加し、一昼夜攪拌混合する。得られた混合物を空気中において１５０℃の温度で乾燥させ、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。
-Preparation of Na-doped CeZr-based composite oxide powder according to Examples-
Cerium nitrate hexahydrate (17.15 g), a zirconyl oxynitrate solution (78.78 g) containing ZrO 2 in terms of ZrO 2 , neodymium nitrate tetrahydrate (7.07 g), Palladium nitrate (3.44 g) is dissolved in ion-exchanged water (300 mL) to obtain a nitrate mixed solution. A coprecipitate is obtained by mixing this nitrate mixed solution with an 8-fold diluted solution (900 mL) of 28% by mass aqueous ammonia to neutralize it. This coprecipitate is washed with water by centrifugation to obtain a gel. An aqueous solution in which sodium nitrate (0.82 g) as an alkali metal compound is dissolved is added to the coprecipitate in the gel form, and the mixture is stirred and mixed overnight. The obtained mixture is dried in air at a temperature of 150 ° C., pulverized, and then calcined in air at a temperature of 500 ° C. for 2 hours.
以上により、Ｐｄが固溶し且つ粒子表面にＮａが担持されたＣｅＺｒ系複合酸化物粉末３０ｇを得ることができる。一部のＰｄはＣｅＺｒ系複合酸化物粉末の粒子表面に露出した状態になる。また、硝酸ナトリウム水溶液をＣｅＺｒ系複合酸化物の前駆体であるゲル形態の共沈物に添加・混合（ドープ）するようにしているから、Ｎａは、得られるＣｅＺｒＮｄ複合酸化物粉末の粒子に組み込まれた状態になる。 Thus, 30 g of CeZr-based composite oxide powder in which Pd is dissolved and Na is supported on the particle surface can be obtained. Part of Pd is exposed on the particle surface of the CeZr-based composite oxide powder. In addition, since sodium nitrate aqueous solution is added and mixed (dope) with the gel-form coprecipitate which is a precursor of CeZr-based composite oxide, Na is incorporated into the obtained CeZrNd composite oxide powder particles. It will be in the state.
すなわち、上記ドープ後の焼成により、ＮａはＣｅＺｒ系複合酸化物粉末の二次粒子表面に担持されるだけでなく、該二次粒子内部に埋もれている一次粒子の表面にも担持された状態になる。この場合、一部のＮａがＣｅＺｒ系複合酸化物粒子に固溶し、残部のＮａが当該粒子表面に担持された状態になり、そして、粒子内に固溶したＮａの一部はその粒子表面に露出し、この露出したＮａに上記残部のＮａが結合するから、ＮａのＣｅＺｒ系複合酸化物粒子に対する結合強度が高くなっていると考えられる。その結果、このＣｅＺｒ系複合酸化物粒子表面にはＰｄと強く結合したＮａとが互いに近接した状態で存在し、そのＮａがＰｄの凝集を抑制する立体障害の機能を果たすと考えられる。また、ＮａがＣｅＺｒ系複合酸化物粒子（二次粒子）を構成する一次粒子間にあって、排気ガスを当該二次粒子内部に拡散させ易くしていると考えられる。 That is, by the baking after the doping, Na is not only supported on the secondary particle surface of the CeZr-based composite oxide powder, but also supported on the surface of the primary particle buried inside the secondary particle. Become. In this case, a part of Na is dissolved in CeZr-based composite oxide particles, the remaining Na is supported on the particle surface, and a part of the Na dissolved in the particles is the surface of the particles. Since the remaining Na binds to the exposed Na, it is considered that the bonding strength of Na to the CeZr-based composite oxide particles is high. As a result, it is considered that Na strongly bound to Pd is present in the CeZr-based composite oxide particle surface in a state of being close to each other, and that Na functions as a steric hindrance to suppress Pd aggregation. Further, it is considered that Na is present between the primary particles constituting the CeZr-based composite oxide particles (secondary particles), and makes it easy to diffuse the exhaust gas into the secondary particles.
得られたＮａドープ(Ｐｄ固溶)型ＣｅＺｒ系複合酸化物粉末のＰｄ及びＮａを除く組成は、ＣｅＯ２：ＺｒＯ２：Ｎｄ２Ｏ３＝２３：６７：１０（質量比）である。Ｎａの担持比率はＮａ２Ｏに換算してＣｅＺｒＮｄ複合酸化物粉末の１質量％であり、これは金属酸化物のモル数で換算すれば、２．３モル％に相当する。 The composition excluding Pd and Na of the obtained Na-doped (Pd solid solution) type CeZr-based composite oxide powder is CeO 2 : ZrO 2 : Nd 2 O 3 = 23: 67: 10 (mass ratio). The Na loading ratio is 1% by mass of the CeZrNd composite oxide powder in terms of Na 2 O, which corresponds to 2.3% by mol in terms of the number of moles of metal oxide.
−比較例に係るＮａ後担持型ＣｅＺｒ系複合酸化物粉末の調製−
上記Ｎａドープ型ＣｅＺｒ系複合酸化物粉末の調製法とは違って、上記硝酸塩混合溶液の調製工程では硝酸パラジウムを添加せず、上記ゲル形態の共沈物に対して硝酸パラジウム水溶液を添加して攪拌混合するようにした。また、硝酸ナトリウム水溶液は、上記ゲル形態の共沈物には添加せずに、該ゲル形態の共沈物を乾燥焼成して得られたＰｄ後担持ＣｅＺｒＮｄ複合酸化物粉末に含浸させるようにし、その後に焼成をした。その他は上記Ｎａドープ型ＣｅＺｒ系複合酸化物粉末の調製法と同様にして、Ｎａ後担持(Ｐｄ後担持)型ＣｅＺｒ系複合酸化物粉末を得た。
-Preparation of Na-supported CeZr-based composite oxide powder according to comparative example-
Unlike the method for preparing the Na-doped CeZr-based composite oxide powder, palladium nitrate is not added in the preparation step of the nitrate mixed solution, but an aqueous solution of palladium nitrate is added to the coprecipitate in the gel form. Stir and mix. Further, the aqueous sodium nitrate solution is not added to the coprecipitate in the gel form, but is impregnated in the post-Pd-supported CeZrNd composite oxide powder obtained by drying and firing the coprecipitate in the gel form. Thereafter, firing was performed. Other than that, the Na-supported CeZr-based composite oxide powder was obtained in the same manner as the Na-doped CeZr-based composite oxide powder.
−電子顕微鏡写真観察−
上記Ｎａドープ型ＣｅＺｒ系複合酸化物粉末及びＮａ後担持型ＣｅＺｒ系複合酸化物粉末各々に対して、大気雰囲気で１０００℃の温度に２４時間保持するエージングを行なった後に、それら粒子を電子顕微鏡で観察した。図２はＮａドープ型ＣｅＺｒ系複合酸化物粒子の電子顕微鏡写真であり、図３はＮａ後担持型ＣｅＺｒ系複合酸化物粒子の電子顕微鏡写真である。実施例のＮａドープ型ＣｅＺｒ系複合酸化物粒子では、該粒子に担持されているＰｄ粒子の粒径が約７９ｎｍであるが、比較例のＮａ後担持型ＣｅＺｒ系複合酸化物粒子では、該粒子に担持されているＰｄ粒子の粒径が約１５４ｎｍであり、実施例の法がＰｄ粒径は小さい。
-Observation of electron micrograph-
Each of the Na-doped CeZr-based composite oxide powder and the Na post-supported CeZr-based composite oxide powder was aged at a temperature of 1000 ° C. for 24 hours in an air atmosphere, and then the particles were observed with an electron microscope. Observed. FIG. 2 is an electron micrograph of Na-doped CeZr-based composite oxide particles, and FIG. 3 is an electron micrograph of Na-supported CeZr-based composite oxide particles. In the Na-doped CeZr-based composite oxide particles of the example, the particle size of the Pd particles supported on the particles is about 79 nm. However, in the Na post-supported CeZr-based composite oxide particles of the comparative example, the particles The particle size of the Pd particles carried on the slab is about 154 nm, and the Pd particle size is small in the method of the example.
−Ｘ線回折パターン−
図４は上記エージング後のＮａドープ型ＣｅＺｒ系複合酸化物粉末及びＮａ後担持型ＣｅＺｒ系複合酸化物粉末各々のＸＲＤ（Ｘ線回折分析）によるＸ線回折パターンを示す。このＸ線回折パターンに基いて、次のシェラーの式からＰｄの結晶子径を求めたところ、実施例のＮａドープ型ＣｅＺｒ系複合酸化物粉末では７０．２ｎｍとなり、比較例のＮａ後担持型ＣｅＺｒ系複合酸化物粉末では８６．３ｎｍになった。
結晶子径Ｄ(hkl)＝０．９λ／(β1/2・cosθ)
但し、hklはミラー指数、λは特性Ｘ線の波長（Å)、β1/2は(hkl)面の半価幅（ラジアン）、θはＸ線反射角度である（Ｘ線条件；Ｘ線源：ＣｕＫα，管電圧：５０ＫＶ，管電流：２４０ｍＡ）。
-X-ray diffraction pattern-
FIG. 4 shows X-ray diffraction patterns by XRD (X-ray diffraction analysis) of each of the Na-doped CeZr-based composite oxide powder and the Na-supported CeZr-based composite oxide powder after aging. Based on this X-ray diffraction pattern, the crystallite diameter of Pd was determined from the following Scherrer equation. In the Na-doped CeZr-based composite oxide powder of the example, it was 70.2 nm. With the CeZr-based composite oxide powder, it was 86.3 nm.
Crystallite diameter D (hkl) = 0.9λ / (β1 / 2 · cosθ)
Where hkl is the Miller index, λ is the characteristic X-ray wavelength (Å), β1 / 2 is the half width (radian) of the (hkl) plane, and θ is the X-ray reflection angle (X-ray condition; X-ray source) : CuKα, tube voltage: 50 KV, tube current: 240 mA).
また、実施例のＮａドープ型ＣｅＺｒ系複合酸化物粉末の場合、Ｘ線回折パターンに単斜晶（monoclinic）ＺｒＯ２に由来するピークが認められたが、比較例のＮａ後担持型ＣｅＺｒ系複合酸化物粉末のＸ線回折パターンにはそのようなピークは見られない。実施例のＮａドープ型ＣｅＺｒ系複合酸化物粉末に見られる単斜晶ＺｒＯ２由来のピークは、一部のＮａが当該ＣｅＺｒ系複合酸化物に固溶していることを推察させる。 In the case of the Na-doped CeZr composite oxide powder of the example, a peak derived from monoclinic ZrO 2 was observed in the X-ray diffraction pattern, but the Na post-supported CeZr composite of the comparative example was observed. Such a peak is not seen in the X-ray diffraction pattern of the oxide powder. The peak derived from monoclinic ZrO 2 found in the Na-doped CeZr-based composite oxide powder of the example infers that a part of Na is dissolved in the CeZr-based composite oxide.
＜実施例及び比較例に係る触媒の排気ガス浄化性能＞
−実施例１〜６に係る触媒−
上記Ｎａドープ型ＣｅＺｒ系複合酸化物粉末の調製法により、表１に示す仕込量にてＮａのＮａ２Ｏに換算した担持比率が異なる実施例１〜５の各Ｎａドープ(Ｐｄ固溶)型ＣｅＺｒ系複合酸化物粉末を調製した。Ｐｄ担持比率はいずれも０．５質量％である。実施例５では、硝酸Ｎａの仕込み量が実施例４と同じく０．０８ｇになっているが、Ｎａドープ(Ｐｄ固溶)型ＣｅＺｒ系複合酸化物粉末の調製後に、該粉末をシュウ酸で処理してＮａ成分を溶出させ、Ｎａ２Ｏ担持比率を０．０１質量％以下にしている。
<Exhaust Gas Purification Performance of Catalysts According to Examples and Comparative Examples>
-Catalysts according to Examples 1 to 6-
Each Na-doped (Pd solid solution) type of Examples 1 to 5 in which the loading ratio shown in Table 1 is converted into Na 2 O according to the preparation method of the Na-doped CeZr-based composite oxide powder. CeZr-based composite oxide powder was prepared. The Pd loading ratio is 0.5% by mass in all cases. In Example 5, the amount of Na nitrate charged was 0.08 g as in Example 4. After the preparation of the Na-doped (Pd solid solution) type CeZr-based composite oxide powder, the powder was treated with oxalic acid. Thus, the Na component is eluted to make the Na 2 O loading ratio 0.01% by mass or less.
また、実施例１〜５とは違って、上記硝酸塩混合溶液の調製工程では硝酸パラジウムを添加せずに、上記ゲル形態の共沈物に対して硝酸パラジウム水溶液を添加して攪拌混合するようにし、他は同様にして、Ｎａ２Ｏ担持比率が１質量％（２．３モル％）である実施例６のＮａドープ(Ｐｄ後担持)型ＣｅＺｒ系複合酸化物粉末を調製した。 In addition, unlike Examples 1 to 5, in the preparation step of the nitrate mixed solution, palladium nitrate is not added, but an aqueous solution of palladium nitrate is added to the gel-form coprecipitate and stirred and mixed. In the same manner, a Na-doped (supported after Pd) type CeZr-based composite oxide powder of Example 6 having a Na 2 O loading ratio of 1 mass% (2.3 mol%) was prepared.
なお、表１のオキシ硝酸Ｚｒ溶液は、２５．１３質量％オキシ硝酸ジルコニル溶液のことである。 In addition, the oxynitric acid Zr solution of Table 1 is a 25.13 mass% zirconyl oxynitrate solution.
そうして、実施例１〜６については、各々のＣｅＺｒ系複合酸化物粉末を硝酸ジルコニルバインダ及びイオン交換水と共に混合してスラリーとし、これをハニカム担体にコーティングして触媒層を形成した。担体１Ｌ当たりのＣｅＺｒ系複合酸化物粉末担持量は１００ｇ／Ｌである。ハニカム担体としては、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のもの（容量１Ｌ）を用いた。 Thus, in Examples 1 to 6, each CeZr-based composite oxide powder was mixed with a zirconyl nitrate binder and ion-exchanged water to form a slurry, which was coated on a honeycomb carrier to form a catalyst layer. The amount of CeZr-based composite oxide powder supported per liter of support is 100 g / L. As the honeycomb carrier, a cordierite product (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. .
−比較例１に係る触媒−
実施例６と同様に、上記硝酸塩混合溶液の調製工程では硝酸パラジウムを添加せずに、上記ゲル形態の共沈物に対して硝酸パラジウム水溶液を添加して攪拌混合するようにし、且つこのゲル形態の共沈物には硝酸ナトリウム水溶液は添加せずに、他は同様にして、Ｎａを担持させていない比較例１に係るＮａ無担持(Ｐｄ後担持)型ＣｅＺｒ系複合酸化物粉末を調製した。そして、このＣｅＺｒ系複合酸化物粉末を実施例と同様の方法で同様のハニカム担体にウォッシュコートし、比較例１に係る触媒を得た。
-Catalyst according to Comparative Example 1-
As in Example 6, in the step of preparing the nitrate mixed solution, palladium nitrate is not added, but the aqueous solution of palladium nitrate is added to the coprecipitate in the gel form, and the mixture is stirred and mixed. No sodium nitrate aqueous solution was added to the coprecipitate of No. 1 and the other was similarly prepared in the same manner as in Example 1 without Na supported (supported after Pd) type CeZr-based composite oxide powder not supporting Na. . Then, this CeZr-based composite oxide powder was wash-coated on the same honeycomb carrier in the same manner as in Example, and the catalyst according to Comparative Example 1 was obtained.
−比較例２に係る触媒−
先に説明した比較例に係るＮａ後担持型ＣｅＺｒ系複合酸化物粉末の調製法にて、Ｎａ２Ｏ担持比率が１質量％（２．３モル％）である比較例２に係るＮａ後担持(Ｐｄ後担持)型ＣｅＺｒ系複合酸化物粉末を調製した。そして、このＣｅＺｒ系複合酸化物粉末を実施例と同様の方法で同様のハニカム担体にウォッシュコートし、比較例２に係る触媒を得た。
-Catalyst according to Comparative Example 2-
In the method for preparing the Na post-supported CeZr-based composite oxide powder according to the comparative example described above, the Na post-support according to Comparative Example 2 in which the Na 2 O support ratio is 1% by mass (2.3 mol%). (Supported after Pd) type CeZr composite oxide powder was prepared. Then, this CeZr-based composite oxide powder was wash-coated on the same honeycomb carrier in the same manner as in Example, and a catalyst according to Comparative Example 2 was obtained.
−排気ガス浄化性能の評価テスト−
実施例及び比較例の各触媒には、２％の酸素と１０％の水を含んだ窒素雰囲気において、１０００℃の温度に２４時間保持するエージング処理を施した。
−Exhaust gas purification performance evaluation test−
Each catalyst of the examples and comparative examples was subjected to an aging treatment in which the catalyst was kept at a temperature of 1000 ° C. for 24 hours in a nitrogen atmosphere containing 2% oxygen and 10% water.
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ＮＯ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２に示す。 Thereafter, a core sample with 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 NO 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 2 shows the gas composition when A / F = 14.7, A / F = 13.8 and A / F = 15.6.
実施例１〜６及び比較例１のライトオフ温度Ｔ５０の測定結果を図５に示し、排気ガス浄化率Ｃ４００の測定結果を図６に示す。 The measurement result of the light-off temperature T50 of Examples 1 to 6 and Comparative Example 1 is shown in FIG. 5, and the measurement result of the exhaust gas purification rate C400 is shown in FIG.
図５の実施例１〜５のＮａドープ(Ｐｄ固溶)型触媒（黒塗り）をみると、Ｎａ２Ｏ担持比率が５質量％（１０．７モル％）、１質量％（２．３モル％）及び０．１質量％（０．２モル％）である実施例２〜４は、Ｎａ２Ｏ担持比率が０．０１質量％以下である（同図の「＊」を付けた）実施例５よりも、ＨＣ、ＣＯ及びＮＯの浄化に関するライトオフ温度Ｔ５０が低い。 When the Na-doped (Pd solid solution) type catalyst (black coating) of Examples 1 to 5 in FIG. 5 is seen, the Na 2 O loading ratio is 5 mass% (10.7 mol%), 1 mass% (2.3 In Examples 2 to 4, which are 0.1 mol%) and 0.1 mass% (0.2 mol%), the Na 2 O loading ratio is 0.01 mass% or less (marked with “*” in the figure). The light-off temperature T50 relating to the purification of HC, CO, and NO is lower than that in the fifth embodiment.
図６の実施例１〜５のＮａドープ(Ｐｄ固溶)型触媒（黒塗り）をみると、ライトオフ温度Ｔ５０と同じく、実施例２〜４は実施例５よりも排気ガス浄化率Ｃ４００が高い。また、Ｎａ２Ｏ担持比率が１質量％（２．３モル％）であるときに（実施例３）、ライトオフ温度Ｔ５０が最も低くなり、排気ガス浄化率Ｃ４００が最も高くなっている。 Looking at the Na-doped (Pd solid solution) type catalyst (black coating) of Examples 1 to 5 in FIG. 6, similarly to the light-off temperature T50, Examples 2 to 4 have an exhaust gas purification rate C400 higher than that of Example 5. high. When the Na 2 O loading ratio is 1% by mass (2.3 mol%) (Example 3), the light-off temperature T50 is the lowest and the exhaust gas purification rate C400 is the highest.
図５，６の両グラフから、Ｎａ２Ｏ担持比率を１１モル％以下にすると、Ｎａを担持させない場合よりも、触媒の排気ガス浄化性能の向上を見込めること、また、Ｎａ２Ｏ担持比率を０．２モル％以上５モル％以下にすると、高い排気ガス浄化性能を見込めることがわかる。 5 and 6, it can be expected that when the Na 2 O loading ratio is 11 mol% or less, the exhaust gas purification performance of the catalyst can be improved as compared with the case where Na is not loaded, and the Na 2 O loading ratio is It can be seen that high exhaust gas purification performance can be expected when the content is 0.2 mol% or more and 5 mol% or less.
実施例６のＮａドープ(Ｐｄ後担持)型触媒及び比較例１のＮａ無担持(Ｐｄ後担持)型触媒（図５，６の「白抜き」）では、対応する実施例４，５のＮａドープ(Ｐｄ固溶)型触媒よりも、ライトオフ温度Ｔ５０が高くなり、排気ガス浄化率Ｃ４００が低くなっている。従って、ＰｄはＣｅＺｒ系複合酸化物粉末の粒子に固溶させ、その一部のＰｄを該粒子表面に露出させることが好ましいということができる。 In the Na-doped (supported after Pd) type catalyst of Example 6 and the Na-unsupported (supported after Pd) -type catalyst of Comparative Example 1 (“open” in FIGS. 5 and 6), the corresponding Na of Examples 4 and 5 were used. The light-off temperature T50 is higher and the exhaust gas purification rate C400 is lower than that of the dope (Pd solid solution) type catalyst. Therefore, it can be said that Pd is preferably dissolved in the particles of the CeZr-based composite oxide powder, and a part of Pd is exposed on the particle surface.
図７は実施例６のＮａドープ(Ｐｄ後担持)型触媒、比較例２のＮａ後担持(Ｐｄ後担持)型触媒、並びに比較例１のＮａ無担持(Ｐｄ後担持)型触媒各々のライトオフ温度Ｔ５０を比較したグラフであり、図８はそれら３種の触媒各々の排気ガス浄化率Ｃ５００（触媒入口でのモデル排気ガス温度が５００℃であるときのガスの各成分の浄化率）を比較したグラフである。実施例６及び比較例２のＮａ２Ｏ担持比率はいずれも１質量％（２．３モル％）である。また、Ｐｄ担持比率はいずれの触媒も０．５質量％である。 FIG. 7 shows the light of each of the Na-doped (Pd post-supported) type catalyst of Example 6, the Na post-supported (Pd post-supported) type catalyst of Comparative Example 2, and the Na non-supported (Pd post-supported) type catalyst of Comparative Example 1. FIG. 8 is a graph comparing the off temperature T50, and FIG. 8 shows the exhaust gas purification rates C500 of each of the three types of catalysts (purification rates of respective components of the gas when the model exhaust gas temperature at the catalyst inlet is 500 ° C.). It is the graph compared. The Na 2 O loading ratio in Example 6 and Comparative Example 2 is 1% by mass (2.3 mol%). The Pd loading ratio is 0.5% by mass for all catalysts.
図７，８をみると、実施例６のＮａドープ(Ｐｄ後担持)型触媒は、比較例２のＮａ後担持(Ｐｄ後担持)型触媒よりも、ライトオフ温度が低く、排気ガス浄化率Ｃ５００が高い。特にＮＯの浄化に関するライトオフ温度では、実施例６と比較例２とに顕著な差が出ている。これから、ＣｅＺｒ系複合酸化物粉末において、Ｎａの担持形態をＮａドープ型（焼成前のゲル形態の共沈物（ＣｅＺｒ系複合酸化物前駆体）にＮａ化合物水溶液を添加）にすると、触媒の排気ガス浄化性能が高くなることがわかる。 7 and 8, the Na-doped (supported after Pd) type catalyst of Example 6 has a lower light-off temperature and the exhaust gas purification rate than the Na-supported (supported after Pd) type catalyst of Comparative Example 2. C500 is high. In particular, there is a significant difference between Example 6 and Comparative Example 2 at the light-off temperature related to NO purification. From this, in the CeZr-based composite oxide powder, when the Na-supported form is Na-doped type (added Na compound aqueous solution to the gel-form coprecipitate (CeZr-based composite oxide precursor) before firing), exhaust of the catalyst It turns out that gas purification performance becomes high.
なお、上記実施形態の触媒では、担体上に単一の触媒層が形成されているが、担体上に複数の触媒層を積層し、各触媒層に相異なる触媒金属を配置するようにしてもよい。例えば、上触媒層のＣｅＺｒ系複合酸化物粉末及び活性アルミナ粉末に触媒金属としてＲｈを担持し、下触媒層のＣｅＺｒ系複合酸化物粉末及び活性アルミナ粉末に触媒金属としてＰｄを担持するという触媒層構成である。そして、上下の触媒層のいずれかにおいて、或いは各触媒層において、アルカリ金属の担持形態を上述のドープ型として該アルカリ金属をＣｅＺｒ系複合酸化物粉末上に偏在させるようにすればよい。 In the catalyst of the above embodiment, a single catalyst layer is formed on the carrier. However, a plurality of catalyst layers may be stacked on the carrier, and different catalyst metals may be arranged in each catalyst layer. Good. For example, a catalyst layer in which Rh is supported as a catalyst metal on the CeZr-based composite oxide powder and active alumina powder of the upper catalyst layer, and Pd is supported as a catalyst metal on the CeZr-based composite oxide powder and active alumina powder of the lower catalyst layer. It is a configuration. Then, in any one of the upper and lower catalyst layers, or in each catalyst layer, the alkali metal may be unevenly distributed on the CeZr-based composite oxide powder with the alkali metal supported form described above.
１ 担体
２ 触媒層
1 Support 2 Catalyst layer
Claims (4)
上記触媒金属がＰｄであり、該Ｐｄは上記ＣｅＺｒ系複合酸化物粉末の粒子に固溶し、その一部が該粒子表面に露出し、
上記触媒層において、上記ＣｅＺｒ系複合酸化物粉末の粒子表面に担持されるように該粒子に組み込まれて、上記ＣｅＺｒ系複合酸化物粉末上に偏在させたアルカリ金属を備え、
上記ＣｅＺｒ系複合酸化物粉末の粒子に固溶したアルカリ金属の一部が当該粒子の表面に露出し、
上記ＣｅＺｒ系複合酸化物粉末の粒子表面において、上記触媒金属としてのＰｄと上記アルカリ金属とが互いに近接した状態で存在してい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 including a catalytic metal, a CeZr-based composite oxide powder containing Ce and Zr, and a binder made of an inorganic oxide is provided on a carrier,
The catalyst metal is Pd, the Pd is solid-solved in the particles of the CeZr-based composite oxide powder, a part of which is exposed on the particle surface,
The catalyst layer includes an alkali metal incorporated in the particle so as to be supported on the particle surface of the CeZr-based composite oxide powder and unevenly distributed on the CeZr-based composite oxide powder,
A part of the alkali metal dissolved in the particles of the CeZr-based composite oxide powder is exposed on the surface of the particles,
An exhaust gas purifying catalyst characterized in that Pd as the catalyst metal and the alkali metal are present close to each other on the particle surface of the CeZr-based composite oxide powder.
上記ＣｅＺｒ系複合酸化物に対する上記アルカリ金属の担持比率は、酸化物に換算して１１モル％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 ,
The CeZr-based loading ratio of the alkali metal against the composite oxide, the exhaust gas purifying catalyst, characterized in that in terms of oxide is not more than 11 mol%.
上記ＣｅＺｒ系複合酸化物に対する上記アルカリ金属の担持比率は、酸化物に換算して０．２モル％以上５モル％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 ,
The exhaust gas purifying catalyst, wherein a supporting ratio of the alkali metal to the CeZr-based composite oxide is 0.2 mol% or more and 5 mol% or less in terms of oxide.
上記ＣｅＺｒ系複合酸化物粉末をバインダと共に担体にウォッシュコートして、該担体上に触媒層を形成する工程とを備え、
上記ＣｅＺｒ系複合酸化物粉末を得る工程において、上記溶液に触媒金属としてのＰｄのイオンを添加して上記Ｃｅ及びＺｒと共にＰｄを共沈させることにより、該Ｐｄを上記ＣｅＺｒ系複合酸化物の粒子に固溶させるとともに、その一部のＰｄを該粒子表面に露出させることを特徴とする排気ガス浄化用触媒の製造方法。 An alkali metal solution is mixed with a gel-form coprecipitate containing Ce and Zr obtained from a solution containing Ce and Zr ions, and the mixture is baked, whereby a part of the alkali metal is CeZr-based composite oxide. Obtaining a CeZr-based composite oxide powder that is solid-dissolved in the particles and a part of the dissolved alkali metal is exposed on the particle surface ;
And a step of wash-coating the CeZr-based composite oxide powder together with a binder on a carrier to form a catalyst layer on the carrier,
In the step of obtaining the CeZr-based mixed oxide powder, by co-precipitation of Pd with the Ce and Zr were added ions Pd as the catalytic metal in the solution, the Pd in the CeZr-based mixed oxide particles And a part of the Pd is exposed on the particle surface.
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