JP2006346522A - Catalyst for exhaust gas purification - Google Patents
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- JP2006346522A JP2006346522A JP2005172285A JP2005172285A JP2006346522A JP 2006346522 A JP2006346522 A JP 2006346522A JP 2005172285 A JP2005172285 A JP 2005172285A JP 2005172285 A JP2005172285 A JP 2005172285A JP 2006346522 A JP2006346522 A JP 2006346522A
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- 238000000746 purification Methods 0.000 title abstract description 27
- 239000011800 void material Substances 0.000 claims abstract description 40
- 239000011247 coating layer Substances 0.000 claims abstract description 17
- 239000000758 substrate Substances 0.000 claims abstract description 15
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- 239000011248 coating agent Substances 0.000 claims description 20
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- 238000000034 method Methods 0.000 claims description 17
- 238000004519 manufacturing process Methods 0.000 claims description 16
- 239000011232 storage material Substances 0.000 claims description 11
- 239000011148 porous material Substances 0.000 claims description 10
- 239000004372 Polyvinyl alcohol Substances 0.000 claims description 7
- 229920002451 polyvinyl alcohol Polymers 0.000 claims description 7
- 238000005245 sintering Methods 0.000 claims description 5
- 229920000642 polymer Polymers 0.000 claims description 3
- 229920000915 polyvinyl chloride Polymers 0.000 claims description 3
- 239000004800 polyvinyl chloride Substances 0.000 claims description 3
- OEPOKWHJYJXUGD-UHFFFAOYSA-N 2-(3-phenylmethoxyphenyl)-1,3-thiazole-4-carbaldehyde Chemical compound O=CC1=CSC(C=2C=C(OCC=3C=CC=CC=3)C=CC=2)=N1 OEPOKWHJYJXUGD-UHFFFAOYSA-N 0.000 claims description 2
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- 239000004417 polycarbonate Substances 0.000 claims description 2
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- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Substances [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 5
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- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 4
- QSHDDOUJBYECFT-UHFFFAOYSA-N mercury Chemical compound [Hg] QSHDDOUJBYECFT-UHFFFAOYSA-N 0.000 description 4
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- 229910052783 alkali metal Inorganic materials 0.000 description 2
- 150000001340 alkali metals Chemical class 0.000 description 2
- 229910052784 alkaline earth metal Inorganic materials 0.000 description 2
- 150000001342 alkaline earth metals Chemical class 0.000 description 2
- ITHZDDVSAWDQPZ-UHFFFAOYSA-L barium acetate Chemical compound [Ba+2].CC([O-])=O.CC([O-])=O ITHZDDVSAWDQPZ-UHFFFAOYSA-L 0.000 description 2
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- 229920000620 organic polymer Polymers 0.000 description 2
- BMMGVYCKOGBVEV-UHFFFAOYSA-N oxo(oxoceriooxy)cerium Chemical compound [Ce]=O.O=[Ce]=O BMMGVYCKOGBVEV-UHFFFAOYSA-N 0.000 description 2
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- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 1
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 1
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- BVKZGUZCCUSVTD-UHFFFAOYSA-N carbonic acid Chemical compound OC(O)=O BVKZGUZCCUSVTD-UHFFFAOYSA-N 0.000 description 1
- 230000003197 catalytic effect Effects 0.000 description 1
- 229910052878 cordierite Inorganic materials 0.000 description 1
- 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 1
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- 229910052763 palladium Inorganic materials 0.000 description 1
- 229910001404 rare earth metal oxide Inorganic materials 0.000 description 1
- 229910052703 rhodium Inorganic materials 0.000 description 1
- 150000003839 salts Chemical class 0.000 description 1
- 239000000523 sample Substances 0.000 description 1
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- Exhaust Gas After Treatment (AREA)
- Exhaust Gas Treatment By Means Of Catalyst (AREA)
- Catalysts (AREA)
Abstract
Description
本発明は、高分子材料を含むコーティング溶液で基材をコーティングすることにより、コート層内に一定の気孔率の空隙が形成し、排ガス浄化性能が向上した排ガス浄化用触媒に関する。 The present invention relates to an exhaust gas purification catalyst in which voids having a certain porosity are formed in a coating layer by coating a substrate with a coating solution containing a polymer material, and the exhaust gas purification performance is improved.
近年、世界的に排ガス規制が強化されており、ＨＣ、ＣＯ、ＮＯｘの中でも特にＮＯｘについての規制を強化する動きが存在している。排ガス用浄化触媒において、ＮＯｘ吸蔵能を向上させるために、アルカリ金属、アルカリ土類金属及び希土類元素から成るＮＯｘ吸蔵材を貴金属等の担体に担持させたＮＯｘ吸蔵還元型触媒が利用されている。このＮＯｘ吸蔵還元型触媒は、ＮＯｘ浄化性能が特に要求されるリーンバーンエンジンにおいて、酸素過剰のリーン雰囲気の排ガス中のＮＯｘを吸蔵し、そして排ガスがストイキ〜リッチ雰囲気になると吸蔵されていたＮＯｘを放出し、その結果雰囲気中に豊富に存在するＨＣなどの還元性成分と反応させて浄化するという特徴を有するものである。 In recent years, exhaust gas regulations have been strengthened worldwide, and there is a movement to strengthen regulations on NOx among HC, CO, and NOx. In the exhaust gas purification catalyst, in order to improve the NOx occlusion ability, a NOx occlusion reduction type catalyst in which a NOx occlusion material composed of an alkali metal, an alkaline earth metal and a rare earth element is supported on a carrier such as a noble metal is used. This NOx occlusion reduction type catalyst occludes NOx in the exhaust gas in a lean atmosphere with excess oxygen in a lean burn engine that requires NOx purification performance, and the NOx that has been occluded when the exhaust gas becomes a stoichiometric to rich atmosphere. It is characterized by being released and, as a result, reacted with a reducing component such as HC that is abundant in the atmosphere to be purified.
ＮＯｘ吸蔵材の利用に加え、それと一緒に利用される触媒としての貴金属の組み合わせ、更にはそれらの担持方法等を工夫した排ガス浄化用触媒も発明されているが（特開２００５−８３４、特許３３９１８７８）、ＮＯｘはもちろん、それ以外の排ガス成分に対しての更なる性能向上の要請が現実に存在している。また、ＮＯｘ吸蔵能の向上は、ＮＯｘ吸蔵材量を増加することにより対処されているが十分ではない。 In addition to the use of NOx storage material, a combination of noble metals as a catalyst used together with the NOx occlusion material, and further an exhaust gas purifying catalyst that has been devised such as a supporting method thereof have been invented (Japanese Patent Laid-Open No. 2005-834, Patent 3391878) ) In addition to NOx, there is actually a demand for further performance improvement for other exhaust gas components. Moreover, although the improvement of NOx occlusion ability is coped with by increasing the amount of NOx occlusion material, it is not sufficient.
しかしながら、ＮＯｘ吸蔵材の増加によるＮＯｘ浄化性能の向上には限界があり、このような問題に関しての改良が望まれていた。 However, there is a limit to the improvement in NOx purification performance due to the increase in NOx occlusion material, and improvements regarding such problems have been desired.
従って、本発明の目的は、排ガス浄化性能、特にＮＯｘ浄化性能が向上した排ガス浄化用触媒を提供することにある。 Accordingly, an object of the present invention is to provide an exhaust gas purification catalyst having improved exhaust gas purification performance, particularly NOx purification performance.
本発明者は、ＮＯｘ浄化性能の向上について鋭意検討した結果、ＮＯｘ吸蔵材の十分な増量効果が得られない理由として、本来排ガスとの接触面に増量したＮＯｘ吸蔵材が効率よく分散担持されていないことが原因であると結論付けた。 As a result of earnestly examining the improvement of the NOx purification performance, the present inventor, as a reason why a sufficient increase effect of the NOx occlusion material cannot be obtained, the NOx occlusion material originally increased on the contact surface with the exhaust gas is efficiently dispersed and supported. It was concluded that there was no cause.
この考えの下、ＮＯｘ吸蔵材が担持されるコート層における排気ガスとの接触面、更にはコート層に含まれる触媒成分と排気ガスとの接触面を増大させるため、コーティング溶液に有機性高分子材料を含ませ、且つ基材上にコーティング層を形成する際に当該有機性高分子材料が消失して空隙を形成するような処理を行った結果、所望の気孔率、更には孔径を有する空隙が確実に形成することが可能となり、その結果として得られた一定の気孔率を有する排ガス用触媒が優れた排ガス浄化作用を有することを見出した。 Under this concept, the organic polymer is added to the coating solution in order to increase the contact surface with the exhaust gas in the coat layer on which the NOx storage material is supported, and further the contact surface between the catalyst component contained in the coat layer and the exhaust gas. A void having a desired porosity and further a pore diameter is obtained as a result of the treatment including the material and forming the coating layer on the substrate so that the organic polymer material disappears to form a void. It has been found that the exhaust gas catalyst having a certain porosity obtained as a result has an excellent exhaust gas purification action.
即ち、本発明は、基材上のコート層に一定の気孔率を有する空隙が形成されている排ガス浄化用触媒、を提供する。 That is, the present invention provides an exhaust gas purifying catalyst in which voids having a certain porosity are formed in a coat layer on a substrate.
本発明は更に、空隙形成材料を含むコーティング溶液で基材をコーティングする工程、及び空隙形成材料を消失させて空隙を形成させる工程を含んで成ることを特徴とする、排ガス浄化用触媒の製造方法、を提供する。 The present invention further comprises a step of coating a substrate with a coating solution containing a void-forming material, and a step of forming voids by eliminating the void-forming material. ,I will provide a.
続いて、本発明者がＮＯｘ吸蔵材の担持方法について検討した結果、ＮＯｘ吸蔵材を担持させる際に通風して乾燥させる従来の方法によると、吸蔵材の増量に伴って乾燥むらが生じるという問題が発生することを突き止めた。そこで、本発明者は、この乾燥むらが上記増量効果を阻害しているとの仮定の下、コート層形成後にＮＯｘ吸蔵材を担持させる工程を回避するため、空隙形成材料である上記有機性高分子材料にあらかじめＮＯｘ吸蔵材を封入させたものを用いてコート層を形成させた。その結果、乾燥むらの問題が生じないだけでなく、更には形成した空隙の表面上に多量にＮＯｘ吸蔵材が担持された触媒が得られることを見出した。このようにして得られた触媒は、従来の製法により得られるものと比較して遥かに低下したＮＯｘエミッション効果を有していた。 Subsequently, as a result of the study of the method for supporting the NOx storage material by the present inventor, the conventional method in which the NOx storage material is ventilated and dried when the NOx storage material is supported has a problem that uneven drying occurs as the amount of the storage material increases. Was found to occur. Therefore, the present inventor assumes that the drying unevenness hinders the effect of increasing the weight, and avoids the step of supporting the NOx occlusion material after the formation of the coat layer. A coat layer was formed using a molecular material in which a NOx occlusion material was previously encapsulated. As a result, it has been found that not only the problem of uneven drying but also a catalyst having a large amount of NOx occlusion material supported on the surface of the formed voids can be obtained. The catalyst thus obtained had a NOx emission effect that was much lower than that obtained by the conventional process.
即ち、本発明は、ＮＯｘ吸蔵材が空隙の表面により多量に存在することを特徴とする排ガス浄化用触媒、を提供する。 That is, the present invention provides an exhaust gas purification catalyst characterized in that a large amount of NOx occlusion material is present on the surface of the void.
本発明は更に、ＮＯｘ吸蔵材が封入されている空隙形成材料を用いることを特徴とする、排ガス浄化用触媒の製造方法、を提供する。 The present invention further provides a method for producing an exhaust gas purifying catalyst, characterized by using a void forming material in which a NOx occlusion material is enclosed.
空隙形成材料を含むコーティング溶液を用いて基材をコーティングすることにより、形成されたコート層に存在する当該材料が消失した後、その部位に一定の気孔率を有する空隙が形成される。更に、上記空隙形成材料にＮＯｘ吸蔵材を封入した場合、空隙表面に対しＮＯｘ吸蔵材が分散して均一且つ重点的に担持される。その結果、このようにして製造される触媒は、形成された空隙により排ガスとの接触面が増大し、且つＮＯｘ吸蔵材がその接触面に対し均一且つ重点的に担持されることにより、従来の排ガス浄化用触媒、特にＮＯｘ吸蔵材がコート層上に担持されている触媒と比較して、排ガス浄化性能、特にＮＯｘ浄化性能の向上を達成することができる。これにより、ＮＯｘ吸蔵材の増量効果の限界についても、空隙表面の形成によりコート層全体の表面積が増大したことで対応可能となり、その結果吸蔵材の増量効果が最大限発揮される。また、上記空隙は、排ガスとＮＯｘ吸蔵材との接触効率を増大させるだけでなく、触媒成分等との接触率を高め、それにより排ガス成分全体に対する浄化性能の向上にも寄与しうる。 By coating the base material with a coating solution containing a void-forming material, the material present in the formed coating layer disappears, and then a void having a certain porosity is formed at that site. Further, when the NOx occlusion material is sealed in the gap forming material, the NOx occlusion material is dispersed and uniformly and preferentially supported on the surface of the gap. As a result, the catalyst produced in this way has an increased contact surface with the exhaust gas due to the formed voids, and the NOx occlusion material is uniformly and intensively supported on the contact surface. Compared with a catalyst for purifying exhaust gas, particularly a catalyst in which a NOx occlusion material is supported on the coat layer, an improvement in exhaust gas purification performance, particularly NOx purification performance can be achieved. Thereby, the limit of the increase effect of the NOx occlusion material can be dealt with by increasing the surface area of the entire coat layer due to the formation of the void surface, and as a result, the increase effect of the occlusion material is maximized. The voids not only increase the contact efficiency between the exhaust gas and the NOx storage material, but also increase the contact ratio with the catalyst component and the like, thereby contributing to the improvement of the purification performance for the entire exhaust gas component.
尚、空隙の形成方法として、ガス発生物質又は可燃性物質を含む混合物でコーティング層を形成させ、焼結時に上記物質を消失させることにより連通孔を形成させる排ガス浄化用フィルタの製造方法が存在しているが（特開平８−３３２３２９、特許文献３）、当該製造方法は、対象がディーゼルパティキュレートフィルターである以上その圧力損失の低減化を目的とする点で本願発明と異なる。更に、コーティング層の気孔率又は孔径が特定されているものの、それらの具体的な制御方法に関しての記載はなく、一方、本発明は、後述するように使用する空隙形成材料の種類、大きさ等を変更することにより所望の気孔率又は孔径を有する空隙を形成することが可能な点で上記製造方法と比較して有利なものである。また、基材上に形成されるコート層の気孔率も異なる。 As a method for forming the void, there is a method for manufacturing a filter for purifying exhaust gas in which a coating layer is formed with a mixture containing a gas generating substance or a combustible substance, and a communicating hole is formed by eliminating the substance during sintering. However, this manufacturing method is different from the present invention in that the object is a diesel particulate filter and the purpose is to reduce the pressure loss thereof (JP-A-8-332329, Patent Document 3). Furthermore, although the porosity or the pore diameter of the coating layer is specified, there is no description about the specific control method thereof, while the present invention is the kind and size of the void forming material used as described later. This is advantageous in comparison with the above production method in that it is possible to form voids having a desired porosity or pore diameter by changing. Moreover, the porosity of the coating layer formed on the substrate is also different.
排ガス浄化用触媒
本発明の排ガス浄化用触媒は、基材上のコート層に一定の気孔率の空隙が形成されていることを特徴とする。本明細書で使用する「気孔率」とは、コート層内に形成された空隙、即ち気孔の容積の、コート層全体の容積に対する比率（ｖ／ｖ％）を意味し、一般的な水銀ポロシメーターにおいて水銀圧入法により測定される。例えば、気孔率が０％とは、コート層中に空隙が全くない状態を指す。この気孔率は、排ガスとの接触面積を増大させる観点、更にはＮＯｘ吸蔵材を担時させる表面積を増大させる観点から高いほど好ましいが、排ガスエミッション、特にＮＯｘエミッションを低下させるための気孔率は、５％以上あればよく、好ましくは５％〜６０％である。更に好ましくは、当該気孔率は５％〜４０％であり、これは、４０％超の気孔率においては、高すぎる気孔率のためにコート層が剥離するという強度上の問題が生じることがあるためである。また、気孔率を３０％超に調節した触媒を製造する場合、大量の空隙形成材料を必要とするため製造コストの面で望ましくないこともある。従って、上記の点を全て考慮した場合、本発明における最も好ましい気孔率は１０％〜３０％の範囲である。
Exhaust gas purification catalyst The exhaust gas purification catalyst of the present invention is characterized in that voids having a certain porosity are formed in a coat layer on a substrate. As used herein, “porosity” means a ratio (v / v%) of voids formed in a coating layer, ie, the volume of pores, to the volume of the entire coating layer (v / v%). In the mercury intrusion method. For example, a porosity of 0% refers to a state where there are no voids in the coat layer. The porosity is preferably as high as possible from the viewpoint of increasing the contact area with the exhaust gas, and further from the viewpoint of increasing the surface area for supporting the NOx occlusion material, but the porosity for reducing exhaust gas emission, particularly NOx emission, is It may be 5% or more, preferably 5% to 60%. More preferably, the porosity is 5% to 40%, which may cause a strength problem that the coating layer peels off due to the porosity being too high at a porosity of more than 40%. Because. Further, when producing a catalyst having a porosity adjusted to more than 30%, a large amount of void forming material is required, which may be undesirable in terms of production cost. Therefore, when all the above points are considered, the most preferable porosity in the present invention is in the range of 10% to 30%.
本発明で使用する「基材」は、空隙形成材料を含有するコーティング溶液が担持されるものであり、排ガス浄化用触媒の製造に一般的に使用されるものを意味する。当該基材としては、コーディライト等の材料により形成されるハニカム、フィルターなどの多孔質形態のものが挙げられる。 The “base material” used in the present invention is a material on which a coating solution containing a void forming material is supported, and means a material generally used in the manufacture of exhaust gas purification catalysts. Examples of the substrate include porous forms such as honeycombs and filters formed of a material such as cordierite.
上記基材上には、触媒又はＮＯｘ吸蔵材との接触面積を拡大して触媒等の性能を最大限に発揮させるための「コート層」が形成される。ここで、当該コート層は「コーティング溶液」を用いて形成されるが、本明細書においては、当該コーティング溶液の構成成分にはＡｌ2Ｏ3、ＳｉＯ2、ＴｉＯ2、ＺｒＯ2、ＣｅＯ2、その他遷移金属酸化物、希土類酸化物、アルカリ金属酸化物、アルカリ土類金属酸化物のうちの少なくとも１種以上が含有され、更に触媒活性成分として、Ｐｔ、Ｐｄ、Ｒｈ、Ｉｒ、Ａｕ、その他の貴金属元素のうち少なくとも１種以上及び１又は複数の空隙形成材料が含有される。しかしながら、当該コーティング溶液は、上記成分に限定されず、触媒を構成する上で基材上に担持されることが考えられるあらゆるものを包含する。 On the base material, a “coat layer” is formed for enlarging the contact area with the catalyst or the NOx storage material so as to maximize the performance of the catalyst or the like. Here, the coating layer is formed using the "coating solution" as used herein, the components of the coating solution Al 2 O 3, SiO 2, TiO 2, ZrO 2, CeO 2, In addition, at least one of transition metal oxides, rare earth oxides, alkali metal oxides, and alkaline earth metal oxides is contained. Further, Pt, Pd, Rh, Ir, Au, and the like as catalytic active components Among the noble metal elements, at least one kind and one or a plurality of void forming materials are contained. However, the coating solution is not limited to the above components, and includes all of those that are considered to be supported on the substrate in constituting the catalyst.
当該基材へのコーティング溶液のコーティングは、触媒の製造において採用されている一般的な方法、例えば浸漬担持方法によって行うことが可能であり、具体的には基材をコーティング溶液中に浸し、コーティング成分を基材表面に吸着させ、乾燥、焼結、還元することによって行うことができる。 The coating of the coating solution onto the substrate can be performed by a general method adopted in the production of a catalyst, for example, a dip-supporting method. Specifically, the substrate is immersed in the coating solution and coated. The components can be adsorbed onto the substrate surface, dried, sintered, and reduced.
本発明において使用する「空隙形成材料」とは、基材上にコーティング成分と共にコーティングされた後に、なんらかの作用を受けて消失する性質のものを意味する。例えば、焼結工程において当該材料を高温に曝すことにより消失させる場合、当該空隙形成材料は、最低でも１００度で当該材料が消失するものが望ましい。しかしながら、空隙の形成は、焼結工程に限定されず、コート層の形成後であればどの工程であっても行うことができ、その形成方法についても、空隙形成材料を消失させることができるものであれば、加温以外のあらゆる物理的又は化学的な作用によるものが考えられる。また、別の態様として、空隙形成材料にＮＯｘ吸蔵材が封入される場合、当該空隙形成材料の形態は中空のものであり、且つ、中に封入されているＮＯｘ吸蔵材成分がその周囲に放出されて担持される性質のものであることが望ましい。尚、本明細書において使用する「ＮＯｘ吸蔵材」とは、当業界で一般的に使用されているものを指し、アルカリ金属、アルカリ土類金属及び希土類元素から選択される金属の酸化物、炭酸塩等を意味する。 The “void forming material” used in the present invention means a material having a property of disappearing under some action after being coated on a substrate together with a coating component. For example, when the material is eliminated by exposing it to a high temperature in the sintering process, it is desirable that the material for forming the void disappears at a minimum of 100 degrees. However, the formation of voids is not limited to the sintering step, and can be performed at any step after the formation of the coat layer, and the void forming material can be eliminated with respect to the formation method. If so, it may be due to any physical or chemical action other than heating. As another aspect, when the NOx occlusion material is enclosed in the void forming material, the form of the void forming material is hollow, and the NOx occlusion material component enclosed therein is released to the surroundings. It is desirable that it is of a nature to be supported. The “NOx occlusion material” used in the present specification refers to a material generally used in the industry, and is an oxide or carbonic acid of a metal selected from alkali metals, alkaline earth metals and rare earth elements. Means salt and the like.
具体的には、空隙形成材料は、その構成成分が高分子、例えば、ポリビニルアルコール、ポリアクリロニトリル、ポリカーボネート、塩化ビニリデン、ポリ塩化ビニル等で形成されたものが挙げられる。これらの中でもポリビニルアルコールは、所望する空隙形成に必要な温度が低いことから好ましい。尚、空隙形成材料は、１又は複数種類の構成成分を含んでもよい。形態は、上述のようにＮＯｘ吸蔵材等を含めるためには中空のものであることが必要であるが、空隙形成のみを目的としてコーティング溶液に配合する場合には中空である必要はない。具体的な空隙形成材料の態様としては、カプセル型のものが考えられる。更にその形状は、所望とする空隙の形状に応じて適宜変更される。 Specific examples of the void-forming material include those whose constituents are formed of a polymer such as polyvinyl alcohol, polyacrylonitrile, polycarbonate, vinylidene chloride, polyvinyl chloride and the like. Among these, polyvinyl alcohol is preferable because it has a low temperature necessary for forming a desired void. Note that the void forming material may include one or more kinds of constituent components. As described above, the form needs to be hollow in order to include the NOx occlusion material and the like, but it need not be hollow when blended into the coating solution only for the purpose of forming voids. As a specific embodiment of the void forming material, a capsule type can be considered. Furthermore, the shape is appropriately changed according to the desired shape of the gap.
また、空隙形成材料には、ＮＯｘ吸蔵材以外に、触媒活性成分としての貴金属、その他触媒のコーティング層において添加される物質を含めてもよい。空隙形成材料に含めるものは、形成した空隙への均一な分散担持の観点から、スラリー状態であることが好ましい。 In addition to the NOx storage material, the void forming material may include a noble metal as a catalyst active component and other substances added in the coating layer of the catalyst. What is included in the void forming material is preferably in a slurry state from the viewpoint of uniform dispersion support in the formed void.
空隙形成材料にＮＯｘ吸蔵材が封入された場合に形成される空隙は、その表面にＮＯｘ吸蔵材が重点的に担持されうる。即ち、ＮＯｘ吸蔵材が空隙形成材料に封入された結果、コート層の形成後にその上にＮＯｘ吸蔵材が担持される従来の方法と比較して、本発明は、ＮＯｘ吸蔵材が空隙部分に特に多く担持されることを特徴とする。この特徴については、一般的なＥＰＭＡ（電子プローブマイクロアナライザー）等により確認することができる。排ガスとの接触を考慮すると、空隙部又はその周辺のＮＯｘ吸蔵材担持量は、コート層の他の部位と比較して多いほど望ましい。 The void formed when the NOx occlusion material is sealed in the void forming material can be preferentially loaded with the NOx occlusion material on the surface thereof. That is, as a result of the NOx occlusion material being encapsulated in the void forming material, the present invention is particularly effective in the NOx occlusion material in the void portion as compared with the conventional method in which the NOx occlusion material is supported thereon after the formation of the coat layer. It is characterized by being supported in large numbers. This feature can be confirmed by a general EPMA (Electron Probe Microanalyzer) or the like. Considering contact with the exhaust gas, it is preferable that the amount of the NOx occlusion material supported in the gap portion or the vicinity thereof is larger as compared with other portions of the coat layer.
従って、別の側面として、本発明は空隙表面にＮＯｘ吸蔵材が大量に担持されていることを特徴とする排ガス浄化用触媒を提供する。 Therefore, as another aspect, the present invention provides an exhaust gas purifying catalyst characterized in that a large amount of NOx occlusion material is supported on the surface of the gap.
排ガス浄化用触媒の製造方法
本発明の排ガス浄化用触媒の製造方法は、空隙形成材料を含むコーティング溶液で基材をコーティングする工程、及び空隙形成材料を消失させて空隙を形成させる工程を含んで成ることを特徴とする。この方法によれば、形成した空隙により、排ガスとの接触面積が増大し、その結果排ガス浄化性能が向上した排ガス浄化用触媒を製造することができる。
Manufacturing method of exhaust gas purifying catalyst The manufacturing method of the exhaust gas purifying catalyst of the present invention includes a step of coating a base material with a coating solution containing a void forming material, and a step of forming voids by eliminating the void forming material. It is characterized by comprising. According to this method, the contact area with the exhaust gas is increased by the formed gap, and as a result, an exhaust gas purification catalyst with improved exhaust gas purification performance can be manufactured.
当該製造方法で使用する材料等は、上記排ガス浄化用触媒で述べたものと基本的に同様である。例えば、空隙形成材料は、排ガス浄化性能を向上させるためにその内部にＮＯｘ吸蔵材、貴金属等を封入していてもよい。また、空隙形成材料の消失に関しても上述の通りであるが、製造効率の観点から焼結時に高温に曝すことにより行われるのが好ましい。 The materials used in the manufacturing method are basically the same as those described for the exhaust gas purification catalyst. For example, in order to improve the exhaust gas purification performance, the void forming material may contain NOx occlusion material, noble metal, or the like. The disappearance of the void-forming material is also as described above, but it is preferably performed by exposing it to a high temperature during sintering from the viewpoint of production efficiency.
上記空隙は、空隙形成材料の種類、サイズ等を変更することによってその気孔率び／又は孔径を制御することが可能である。具体的には、気孔率については、主に空隙形成材料の量を調整することによりその比率を所望の値に変更することができる。更に、空隙の孔径についても、主に空隙形成材料のサイズ、種類を調整することにより制御することができる。 It is possible to control the porosity and / or the pore diameter of the voids by changing the type and size of the void-forming material. Specifically, the porosity can be changed to a desired value mainly by adjusting the amount of the void forming material. Furthermore, the pore diameter of the voids can be controlled mainly by adjusting the size and type of the void forming material.
従って、別の態様として、本発明は、形成される空隙の気孔率孔径及び／又は孔径が空隙形成材料の量、サイズ、種類を変更することにより制御されることを特徴とする排ガス浄化用触媒の製造方法を提供する。 Therefore, as another aspect, the present invention provides an exhaust gas purifying catalyst characterized in that the porosity pore diameter and / or the pore diameter of the void formed is controlled by changing the amount, size, and type of the void-forming material. A manufacturing method is provided.
以下の実施例を用いて、本発明の発明を更に具体的に説明する。尚、本発明はこれらの実施例に限定されるものではない。 The invention of the present invention will be described more specifically with reference to the following examples. The present invention is not limited to these examples.
（実施例１〜５）
気孔率５〜６０％の排気ガス浄化用触媒の製造
アルミナ１００ｇ、セリウム酸化物５０ｇ、アルミナゾル５０ｇ、水２００ｇ、酢酸バリウムを、それぞれ１．３ｇ、２．５ｇ、５．０ｇ、１０ｇ、１５ｇのポリビニルアルコール（ＰＶＡ）カプセル内に封入し、当該カプセルと白金硝酸溶液（白金３ｇ）を混合してスラリー１を調製した。このスラリーにモノリスハニカムにコーティングし、２５０℃で乾燥させた。更に、コーティングされたモノリスハニカムを５００℃で１時間焼成して、本発明の排気ガス浄化用触媒を調製した。この触媒のコート層内に形成された空隙は、水銀ポロシメーター（島津製作所オートポア９５２０形）により測定した結果、１．３ｇのＰＶＡから調製したもの（実施例１）が５％、２．５ｇのもの（実施例２）が１０％、５．０ｇのもの（実施例３）が２０％、１０ｇのもの（実施例４）が４０％、そして１５ｇのもの（実施例５）が６０％の気孔率をそれぞれ有していた。
(Examples 1-5)
Production of catalyst for purifying exhaust gas having a porosity of 5 to 60% Alumina 100 g, cerium oxide 50 g, alumina sol 50 g, water 200 g, and barium acetate 1.3 g, 2.5 g, 5.0 g, 10 g, and 15 g of polyvinyl chloride, respectively The mixture was sealed in an alcohol (PVA) capsule, and the capsule and a platinum nitric acid solution (platinum 3 g) were mixed to prepare
（比較例１）
気孔率１．５％の排気ガス浄化用触媒の製造
白金硝酸溶液（白金３ｇ）とアルミナ１００ｇ、セリウム酸化物５０ｇ、アルミナゾル５０ｇ、水２００ｇを混合し、スラリー２を調製した。このスラリー２をモノリスハニカムにコーティングし、２５０℃で乾燥させた。更に、コーティングされたモノリスハニカムを５００℃で１時間焼成して、酢酸バリウムをモノリスハニカム全体に０．２mol/L担持した。これにより調製された触媒Ｂのコート層内に形成された空隙は、水銀ポロシメーター（島津製作所オートポア９５２０形）により測定した結果、１．５％の気孔率を有していた。
(Comparative Example 1)
Production of Exhaust Gas Purifying Catalyst with a Porosity of 1.5% A platinum nitric acid solution (platinum 3 g), 100 g of alumina, 50 g of cerium oxide, 50 g of alumina sol, and 200 g of water were mixed to prepare slurry 2. The slurry 2 was coated on a monolith honeycomb and dried at 250 ° C. Further, the coated monolith honeycomb was fired at 500 ° C. for 1 hour, and 0.2 mol / L of barium acetate was supported on the entire monolith honeycomb. The voids formed in the coating layer of the catalyst B thus prepared had a porosity of 1.5% as a result of measurement with a mercury porosimeter (Shimadzu Autopore 9520 type).
（比較例２）
気孔率３％の排気ガス浄化用触媒の製造
ＰＶＡカプセルの重量を０．８ｇとしたことを除き、実施例１〜５の排気ガス浄化用触媒と同様に触媒を調製した。水銀ポロシメーター（島津製作所オートポア９５２０形）により測定した結果、３％の気孔率を有する触媒（比較例２）が得られた。
(Comparative Example 2)
Production of Exhaust Gas Purification Catalyst with 3% Porosity A catalyst was prepared in the same manner as the exhaust gas purification catalyst of Examples 1 to 5, except that the weight of the PVA capsule was 0.8 g. As a result of measurement with a mercury porosimeter (Shimadzu Corporation Autopore 9520 type), a catalyst having a porosity of 3% (Comparative Example 2) was obtained.
排ガスエミッション測定
排気量２０００ｃｃの車両に触媒を取り付け、１０・１５モードで走行させ、テールパイプから排出されるＮＯｘ、ＣＯ及びＮＨＭＣのエミッション（ｇ／ｋｍ）を測定した。その結果、ＰＶＡカプセルにより気孔率が５〜６０％に調整された実施例１〜５の触媒は、比較例１のような従来のＮＯｘ吸蔵材担持方法で調製された１．５％の気孔率を有する触媒、及び比較例２のような３％の気孔率を有する触媒と比較して排ガスエミッションが明らかに低下した（図１〜３を参照のこと）。中でもＮＯｘエミッション低下作用は顕著である（図１）。具体的な排ガスエミッションの値を次の表１に示す。
Exhaust gas emission measurement A catalyst was attached to a vehicle with a displacement of 2000 cc, and the vehicle was run in the 10.15 mode, and NOx, CO, and NHMC emissions (g / km) discharged from the tail pipe were measured. As a result, the catalysts of Examples 1 to 5 with the porosity adjusted to 5 to 60% by the PVA capsule were 1.5% porosity prepared by the conventional NOx storage material supporting method as in Comparative Example 1. The exhaust gas emission was clearly reduced as compared with the catalyst having NO and the catalyst having a porosity of 3% as in Comparative Example 2 (see FIGS. 1 to 3). Among them, the NOx emission reducing effect is remarkable (FIG. 1). Specific exhaust gas emission values are shown in Table 1 below.
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