JP2010142741A - Catalyst for purifying exhaust gas, and method for producing the same - Google Patents
Catalyst for purifying exhaust gas, and method for producing the same Download PDFInfo
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- 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
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- NWAHZABTSDUXMJ-UHFFFAOYSA-N platinum(2+);dinitrate Chemical compound [Pt+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O NWAHZABTSDUXMJ-UHFFFAOYSA-N 0.000 description 1
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Abstract
Description
本発明は、排ガス浄化技術に関する。 The present invention relates to an exhaust gas purification technology.
近年、自動車等に対する排ガス規制が強化されてきている。そのため、これに対応すべく、排ガス中の炭化水素（ＨＣ）、一酸化炭素（ＣＯ）及び窒素酸化物（ＮＯx）等を浄化するための種々の排ガス浄化用触媒が開発されている。 In recent years, exhaust gas regulations for automobiles and the like have been strengthened. For this reason, various exhaust gas purifying catalysts for purifying hydrocarbons (HC), carbon monoxide (CO), nitrogen oxides (NO x ) and the like in the exhaust gas have been developed.
排ガス浄化用触媒には、その排ガス浄化性能を最適化すべく、吸蔵材が使用される場合がある。例えば、ＮＯx吸蔵還元型触媒には、アルカリ土類金属元素などを含んだＮＯx吸蔵材が使用される。このＮＯx吸蔵材は、ＮＯxの還元反応に不利な条件である酸化雰囲気においてＮＯxを吸蔵し、上記反応に有利な条件である還元雰囲気及び当量点においてＮＯxを放出することにより、触媒の排ガス浄化性能を最適化している（例えば、非特許文献１参照）。
しかしながら、このような吸蔵材には、排ガス中の硫黄成分等による被毒を受け易いという問題がある。また、この被毒の解消等のために反応温度を高くした場合には、吸蔵材のシンタリングによる熱劣化が生じ易いという問題がある。そのため、吸蔵材を含んだ排ガス浄化用触媒は、排ガス浄化性能の経時劣化が生じ易い。 However, such a storage material has a problem that it is easily poisoned by sulfur components in exhaust gas. In addition, when the reaction temperature is increased to eliminate this poisoning, there is a problem that thermal degradation is likely to occur due to sintering of the occlusion material. Therefore, the exhaust gas purifying catalyst containing the occlusion material is likely to deteriorate with time in the exhaust gas purifying performance.
そこで、本発明は、耐久後においても優れた排ガス浄化性能を示す排ガス浄化用触媒を提供することを目的とする。 Therefore, an object of the present invention is to provide an exhaust gas purification catalyst that exhibits excellent exhaust gas purification performance even after durability.
本発明の第１側面によると、基材と、前記基材上に形成され且つ触媒金属及び吸蔵材を含んだ触媒層とを具備し、次式によって表される標準偏差σが０．０８以下であることを特徴とする排ガス浄化用触媒が提供される。
ここで、ａ1は、第１部分における前記触媒層の表面の単位面積に対する前記触媒層の前記表面に露出した前記吸蔵材の面積の割合を表し、ａ2は、第２部分における前記触媒層の表面の単位面積に対する前記触媒層の前記表面に露出した前記吸蔵材の面積の割合を表し、ａ3は、第３部分における前記触媒層の表面の単位面積に対する前記触媒層の前記表面に露出した前記吸蔵材の面積の割合を表し、ａavは、ａ1，ａ2及びａ3の相加平均値を表し、前記第１乃至第３部分は、前記排ガス浄化用触媒のうち前記触媒層が形成された部分を前記排ガスの流れ方向について３等分して得られる。 Here, a 1 represents the ratio of the area of the occlusion material exposed on the surface of the catalyst layer to the unit area of the surface of the catalyst layer in the first portion, and a 2 represents the catalyst layer in the second portion. represents the percentage of the area of the storage material is exposed to the surface of the catalyst layer per unit area of the surface of, a 3 is exposed on the surface of the catalyst layer per unit area of the surface of the catalyst layer in the third portion A av represents an arithmetic mean value of a 1 , a 2 and a 3 , and the first to third parts are the catalyst layers of the exhaust gas purifying catalyst. Is formed by dividing the portion where the gas is formed into three equal parts in the flow direction of the exhaust gas.
本発明の第２側面によると、触媒金属を支持した担体を含有し且つ基材上に形成された層に吸蔵材の原料と極性液体との混合物を含浸させた後、マイクロ波乾燥を行うことにより製造されることを特徴とする排ガス浄化用触媒が提供される。 According to the second aspect of the present invention, microwave drying is performed after impregnating a layer containing a carrier supporting a catalyst metal and impregnating a layer formed on the base material with the raw material of the occlusion material and the polar liquid. An exhaust gas purifying catalyst characterized by being manufactured by the method is provided.
本発明の第３側面によると、触媒金属を支持した担体を含有し且つ基材上に形成された層に吸蔵材の原料と極性液体との混合物を含浸させた後、マイクロ波乾燥を行うことを具備したことを特徴とする排ガス浄化用触媒の製造方法が提供される。 According to the third aspect of the present invention, microwave drying is performed after impregnating the layer formed on the substrate containing the carrier supporting the catalyst metal with the mixture of the raw material of the occlusion material and the polar liquid. A method for producing an exhaust gas purifying catalyst is provided.
本発明によると、耐久後においても優れた排ガス浄化性能を示す排ガス浄化用触媒を提供することが可能となる。 According to the present invention, it is possible to provide an exhaust gas purification catalyst that exhibits excellent exhaust gas purification performance even after durability.
以下、本発明の態様について説明する。なお、ここで「複合酸化物」とは、複数の酸化物が単に物理的に混合されたものではなく、複数の酸化物が固溶体を形成しているものを意味することとする。 Hereinafter, embodiments of the present invention will be described. Here, the “composite oxide” means that a plurality of oxides are not merely physically mixed but a plurality of oxides form a solid solution.
本態様に係る排ガス浄化用触媒は、基材と、基材上に形成された触媒層とを備えている。触媒層は、触媒金属と吸蔵材とを含んでいる。触媒金属及び吸蔵材は、典型的には、担体に支持されている。 The exhaust gas purifying catalyst according to this aspect includes a base material and a catalyst layer formed on the base material. The catalyst layer includes a catalyst metal and an occlusion material. The catalyst metal and the occlusion material are typically supported on a support.
基材としては、例えば、モノリスハニカム型の基材を使用する。典型的には、基材は、コージェライトなどのセラミックス製である。 As the substrate, for example, a monolith honeycomb substrate is used. Typically, the substrate is made of a ceramic such as cordierite.
担体は、後述する触媒金属及び吸蔵材の比表面積を増大させると共に、反応による発熱を消散させて触媒金属及び吸蔵材のシンタリングを抑制する役割を担っている。担体は、例えば、アルミニウム又はチタンを含んでいる。典型的には、担体として、アルミナ又はチタニアを使用する。なお、担体として、複数の化合物の混合物又は複合酸化物を使用してもよい。 The carrier plays a role of increasing the specific surface areas of the catalyst metal and the occlusion material, which will be described later, and suppressing the sintering of the catalyst metal and the occlusion material by dissipating heat generated by the reaction. The support contains, for example, aluminum or titanium. Typically, alumina or titania is used as the support. In addition, you may use the mixture or composite oxide of a some compound as a support | carrier.
触媒金属は、排ガス浄化反応を触媒する役割を担っている。この触媒金属としては、例えば、貴金属を使用する。貴金属としては、例えば、白金、パラジウム及びロジウムなどの白金族元素を使用する。なお、触媒金属として、複数種の元素を使用してもよい。 The catalytic metal plays a role of catalyzing the exhaust gas purification reaction. As this catalyst metal, for example, a noble metal is used. As the noble metal, for example, platinum group elements such as platinum, palladium and rhodium are used. In addition, you may use multiple types of elements as a catalyst metal.
吸蔵材は、排ガス中の気体分子を一時的に吸蔵することにより、排ガス浄化用触媒の排ガス浄化性能を最適化する役割を担っている。吸蔵材としては、例えば、後述するＮＯx吸蔵材、ゼオライトなどのＨＣ吸蔵材、又は、セリアなどの酸素貯蔵材を使用することができる。以下では、一例として、ＮＯx吸蔵材を使用した場合について説明する。 The storage material plays a role of optimizing the exhaust gas purification performance of the exhaust gas purification catalyst by temporarily storing gas molecules in the exhaust gas. As the occlusion material, for example, an NO x occlusion material described later, an HC occlusion material such as zeolite, or an oxygen storage material such as ceria can be used. In the following, as an example, it will be described using the NO x storage material.
このＮＯx吸蔵材としては、例えば、アルカリ金属元素を含んだ化合物、アルカリ土類金属元素を含んだ化合物、又はこれらの混合物を使用する。アルカリ金属元素としては、例えば、カリウム、ナトリウム又はリチウムを使用する。アルカリ土類金属元素としては、例えば、バリウム又はカルシウムを使用する。典型的には、ＮＯx吸蔵材として、カリウム化合物、バリウム化合物、又はこれらの混合物を使用する。 As the NO x storage material, for example, a compound containing an alkali metal element, a compound containing an alkaline earth metal element, or a mixture thereof is used. As the alkali metal element, for example, potassium, sodium or lithium is used. For example, barium or calcium is used as the alkaline earth metal element. Typically, potassium compounds, barium compounds, or mixtures thereof are used as the NO x storage material.
ＮＯx吸蔵材は、酸化雰囲気では、排ガス中のＮＯx分子を、例えば硝酸塩として吸蔵する。一方、還元雰囲気及び当量点では、この硝酸塩等が分解して、周囲に存在する触媒金属の作用により、Ｎ2へと還元される。このように、ＮＯx吸蔵材を含んだ排ガス浄化用触媒では、ＮＯxの吸蔵及び還元を繰り返すことにより、排ガス中のＮＯxを浄化している。 In the oxidizing atmosphere, the NO x storage material stores NO x molecules in the exhaust gas, for example, as nitrate. On the other hand, in a reducing atmosphere and an equivalent point, this nitrate or the like is decomposed and reduced to N 2 by the action of the catalytic metal present in the surroundings. As described above, the exhaust gas purifying catalyst including the NO x storage material purifies NO x in the exhaust gas by repeatedly storing and reducing NO x .
本態様では、触媒層の表面において、吸蔵材を均一に分布させる。吸蔵材の分布の均一性は、例えば、以下のようにして評価する。 In this embodiment, the occlusion material is uniformly distributed on the surface of the catalyst layer. The uniformity of the distribution of the occlusion material is evaluated as follows, for example.
まず、排ガス浄化用触媒のうち触媒層が形成された部分を排ガスの流れ方向について３等分した各部分について、触媒層の表面をＳＥＭ（走査電子顕微鏡）により観察し、触媒層の表面に占める吸蔵材の割合ａi（ｉ＝１，２，３；以下同様）を測定する。即ち、上記の３等分した各部分について、触媒層の表面を上記表面に垂直な方向から観察し、各部分における前記触媒層の表面の単位面積に対する触媒層の表面に露出した吸蔵材の面積の割合ａiを測定する。なお、以下では、上述した各部分を、第ｉ部分と呼ぶ。 First, the surface of the catalyst layer is observed with an SEM (scanning electron microscope) for each portion obtained by dividing the portion of the exhaust gas purification catalyst in which the catalyst layer is formed into three equal parts in the flow direction of the exhaust gas, and occupies the surface of the catalyst layer. The ratio a i (i = 1, 2, 3; hereinafter the same) of the occlusion material is measured. That is, the area of the occlusion material exposed on the surface of the catalyst layer with respect to the unit area of the surface of the catalyst layer in each part is observed from the direction perpendicular to the surface for each of the three parts. The ratio a i is measured. In the following, each part described above is referred to as an i-th part.
上記割合ａｉは、具体的には、以下のようにして求める。即ち、第ｉ部分に含まれる６つの位置において、触媒層の表面の０．５ｍｍ×０．５ｍｍの領域をＳＥＭにより拡大観察し、この領域内における触媒層の表面に露出した吸蔵材の面積を測定し、その測定値を上記領域の面積で除した値を割合ａi,j（ｊ＝１，２，…，６；以下同様）とする。そして、第ｉ部分の各々において、上記６箇所における割合ａi,jの相加平均値を計算し、これを割合ａｉとする。即ち、割合ａｉは、割合ａi,jに基づいて、次式により計算する。
次に、これら割合ａiに基づいて、次式により標準偏差σを求める。ここで、ａavは、割合ａ1、ａ2及びａ3の相加平均値である。
本態様に係る排ガス浄化用触媒では、この標準偏差σは、０．０８以下である。典型的には、この標準偏差σは、０．０５以下である。即ち、この排ガス浄化用触媒では、吸蔵材は、触媒層の表面において、極めて均一に分散している。それゆえ、吸蔵材と周囲の気体とが接触する部分の表面積が比較的大きく、吸蔵材からの硫黄成分等の脱離が生じ易い。即ち、本態様に係る排ガス浄化用触媒では、硫黄被毒等による吸蔵材の性能の低下が生じ難い。 In the exhaust gas purifying catalyst according to this embodiment, the standard deviation σ is 0.08 or less. Typically, this standard deviation σ is 0.05 or less. That is, in this exhaust gas purifying catalyst, the occlusion material is very uniformly dispersed on the surface of the catalyst layer. Therefore, the surface area of the portion where the occlusion material and the surrounding gas are in contact with each other is relatively large, and the desorption of sulfur components and the like from the occlusion material is likely to occur. That is, in the exhaust gas purifying catalyst according to this aspect, the performance of the occlusion material is not easily lowered due to sulfur poisoning or the like.
また、この場合、吸蔵材は、加熱等によるシンタリングを生じ難い。それゆえ、例えば吸蔵材の硫黄被毒を低減又は解消するために反応温度を向上させても、吸蔵材の熱劣化による性能の低下を生じ難い。したがって、この排ガス浄化用触媒は、高温で長期間に亘り使用した後であっても、優れた排ガス浄化性能を達成できる。
なお、この標準偏差σに下限値はないが、通常は、０．０１以上である。
Further, in this case, the occlusion material hardly causes sintering due to heating or the like. Therefore, for example, even if the reaction temperature is increased in order to reduce or eliminate sulfur poisoning of the storage material, it is difficult for the performance to decrease due to thermal deterioration of the storage material. Therefore, the exhaust gas purification catalyst can achieve excellent exhaust gas purification performance even after being used at a high temperature for a long period of time.
The standard deviation σ has no lower limit, but is usually 0.01 or more.
触媒層は、バインダを更に含んでいてもよい。バインダは、担体粒子同士の結合及び担体粒子と触媒金属及び／又は吸蔵材との結合をより強固にして触媒の耐久性を向上させる役割を担っている。バインダとしては、例えば、アルミナゾル、チタニアゾル又はシリカゾルを使用する。 The catalyst layer may further contain a binder. The binder plays a role of improving the durability of the catalyst by strengthening the bond between the carrier particles and the bond between the carrier particles and the catalyst metal and / or the occlusion material. As the binder, for example, alumina sol, titania sol, or silica sol is used.
触媒層は、単層構造であってもよく、多層構造であってもよい。触媒層が多層構造からなる場合、これら層では、担体、触媒金属、吸蔵材及びバインダ等のうち少なくとも１つの成分の種類及び／又は単位容積当りの含有量等を互いに異ならしめる。これにより、触媒の排ガス浄化性能を最適化することができる。 The catalyst layer may have a single layer structure or a multilayer structure. When the catalyst layer has a multilayer structure, in these layers, the kind of at least one component and / or the content per unit volume among the support, the catalyst metal, the occlusion material, and the binder are different from each other. Thereby, the exhaust gas purification performance of the catalyst can be optimized.
この排ガス浄化用触媒は、例えば、以下のようにして製造する。 This exhaust gas-purifying catalyst is produced, for example, as follows.
まず、担体を構成する化合物に溶剤を添加して混合し、スラリーを形成する。そして、このスラリーを基材にコートし、乾燥させた後、焼成を行う。 First, a solvent is added to and mixed with the compound constituting the carrier to form a slurry. Then, the slurry is coated on a substrate, dried, and then fired.
次に、基材上に形成した担体に、触媒金属を担持させる。その後、任意に、乾燥処理を行う。なお、触媒金属の少なくとも一部は、コート前に上記担体に担持しておいてもよい。その場合、本工程は、省略することができる。 Next, the catalyst metal is supported on the carrier formed on the substrate. Thereafter, a drying process is optionally performed. Note that at least a part of the catalyst metal may be supported on the carrier before coating. In that case, this step can be omitted.
次いで、触媒金属を支持した担体を含んだ層に、吸蔵材の原料と極性液体との混合物を含浸させる。吸蔵材の原料としては、例えば、吸蔵材の塩を使用する。極性液体としては、例えば、水又はアルコールを使用する。吸蔵材の原料は、極性液体に溶解させてもよく、極性液体に分散させてもよい。 Next, the layer containing the carrier supporting the catalyst metal is impregnated with the mixture of the raw material of the storage material and the polar liquid. As a material for the occlusion material, for example, a salt of the occlusion material is used. For example, water or alcohol is used as the polar liquid. The raw material for the occlusion material may be dissolved in a polar liquid or dispersed in a polar liquid.
その後、マイクロ波を用いた乾燥を行う。このマイクロ波乾燥は、例えば、乾燥前に含まれていた極性液体の７０％以上且つ９５％以下が除去されるまで行う。より好ましくは、このマイクロ波乾燥は、乾燥前に含まれていた極性液体の８０％以上且つ９０％以下が除去されるまで行う。マイクロ波乾燥により除去する極性液体の量が少ないと、後述する吸蔵材の排ガスの流れ方向に沿った組成のばらつきの抑制が困難となる場合がある。マイクロ波乾燥により除去する極性液体の量が多いと、過度の温度上昇が生じ、場合によっては発火を生ずるおそれがある。 Thereafter, drying using microwaves is performed. This microwave drying is performed, for example, until 70% or more and 95% or less of the polar liquid contained before drying is removed. More preferably, the microwave drying is performed until 80% or more and 90% or less of the polar liquid contained before drying is removed. If the amount of polar liquid to be removed by microwave drying is small, it may be difficult to suppress variation in composition along the flow direction of the exhaust gas of the storage material described later. If the amount of polar liquid removed by microwave drying is large, an excessive temperature rise may occur and, in some cases, ignition may occur.
マイクロ波乾燥は、乾燥させるべき対象にマイクロ波を照射して、上記対象中に含まれる水等の極性分子の振動及び回転等の運動を誘起することにより行う。この乾燥法によると、マイクロ波が上記極性分子の振動及び回転等の運動を生じさせるため、排ガスの流れ方向と厚さ方向との双方について比較的均一に加熱される。それゆえ、上記対象を比較的均一且つ迅速に乾燥させることができる。従って、乾燥工程に起因した成分の排ガスの流れ方向に沿った組成のばらつきが生じ難い。即ち、上述したマイクロ波乾燥を行うと、触媒層の表面における吸蔵材の排ガスの流れ方向に沿った組成のばらつきが生じ難い。 Microwave drying is performed by irradiating a target to be dried with microwaves and inducing motion such as vibration and rotation of polar molecules such as water contained in the target. According to this drying method, since the microwaves cause movements such as vibration and rotation of the polar molecules, they are heated relatively uniformly in both the flow direction and the thickness direction of the exhaust gas. Therefore, the object can be dried relatively uniformly and quickly. Therefore, it is difficult for variations in the composition along the flow direction of the exhaust gas of the components due to the drying process to occur. That is, when the above-described microwave drying is performed, composition variation along the flow direction of the exhaust gas of the storage material on the surface of the catalyst layer hardly occurs.
これに対し、例えば触媒の下流側から熱風を吹き付けて乾燥を行った場合、触媒の上流側と下流側とで温度差を生じる。加えて、触媒層の加熱は熱風中の気体分子が触媒層表面の分子と衝突することによって生じるため、触媒層の乾燥は、その表面から進行する。それゆえ、熱風のみを利用した場合、触媒層の乾燥には比較的長い時間を要する。触媒層の乾燥が均一に進行せず且つ短時間で完了しない場合、液体成分が、乾燥の進行が遅い部分から乾燥の進行が速い部分へと移動する可能性がある。また、触媒層の乾燥が短時間で完了しない場合、液体成分が、熱風の流れ方向に沿って移動する可能性がある。そのため、熱風のみを利用した場合、排ガスの流れ方向について又は排ガスの流れ方向と触媒層の厚さ方向との双方について、触媒層の組成のばらつきを生じ易い。 On the other hand, for example, when drying is performed by blowing hot air from the downstream side of the catalyst, a temperature difference is generated between the upstream side and the downstream side of the catalyst. In addition, since heating of the catalyst layer is caused by gas molecules in the hot air colliding with molecules on the surface of the catalyst layer, drying of the catalyst layer proceeds from the surface. Therefore, when only hot air is used, it takes a relatively long time to dry the catalyst layer. If the drying of the catalyst layer does not proceed uniformly and does not complete in a short time, the liquid component may move from a portion where the drying progress is slow to a portion where the drying progress is fast. Moreover, when drying of a catalyst layer is not completed in a short time, a liquid component may move along the flow direction of hot air. Therefore, when only hot air is used, the composition of the catalyst layer tends to vary in the flow direction of the exhaust gas or in both the flow direction of the exhaust gas and the thickness direction of the catalyst layer.
なお、マイクロ波乾燥を行った後、触媒中の極性液体を更に除去すべく、熱風を用いた乾燥を行ってもよい。この場合、事前のマイクロ波乾燥によって極性液体がある程度除去されているため、熱風乾燥を行っても、吸蔵材の移動による排ガスの流れ方向に沿った組成のばらつきは生じ難い。但し、この熱風乾燥は、例えば６００℃以下の温度で行う。この温度が高いと、触媒層の表面における吸蔵材の排ガスの流れ方向に沿った組成のばらつきが生じる場合がある。 In addition, after performing microwave drying, in order to remove the polar liquid in a catalyst further, you may dry using a hot air. In this case, since the polar liquid is removed to some extent by microwave drying in advance, even if hot air drying is performed, composition variation along the flow direction of the exhaust gas due to the movement of the occlusion material hardly occurs. However, this hot air drying is performed at a temperature of 600 ° C. or less, for example. When this temperature is high, there may be a variation in composition along the flow direction of the exhaust gas of the storage material on the surface of the catalyst layer.
以上のようにして、排ガス浄化用触媒を得る。このようにして製造される排ガス浄化用触媒では、触媒層の表面において、吸蔵材を極めて均一に分散させることができる。それゆえ、上述した通り、排ガス浄化用触媒を高温で長期間に亘って使用した場合でも、吸蔵材の熱劣化等を生じ難い。 As described above, an exhaust gas purifying catalyst is obtained. In the exhaust gas purifying catalyst manufactured in this way, the occlusion material can be dispersed extremely uniformly on the surface of the catalyst layer. Therefore, as described above, even when the exhaust gas purifying catalyst is used at a high temperature for a long period of time, it is difficult to cause thermal deterioration of the occlusion material.
＜例１：触媒Ｃ１の製造＞
まず、ジルコニアと、ジルコニアの質量を基準として１質量％のロジウムを含んだ塩化ロジウム水溶液とを混合した後、これを乾燥させて、ロジウム担持粉末を得た。そして、
１００質量部のチタニアとジルコニアとの複合酸化物と、１００質量部のアルミナと、５０質量部のロジウム担持粉末と、２０質量部のセリアとジルコニアとの複合酸化物と、適量の水とを混合し、これを湿式粉砕して、スラリーを調製した。
<Example 1: Production of catalyst C1>
First, after mixing zirconia and a rhodium chloride aqueous solution containing 1% by mass of rhodium based on the mass of zirconia, this was dried to obtain a rhodium-supported powder. And
100 parts by mass of a composite oxide of titania and zirconia, 100 parts by mass of alumina, 50 parts by mass of rhodium-supported powder, 20 parts by mass of a complex oxide of ceria and zirconia, and an appropriate amount of water are mixed. This was wet pulverized to prepare a slurry.
次に、このスラリーを、コージェライトからなり且つ容積が１Ｌであるモノリスハニカム基材にコートし、余分なスラリーを吹き払った。なお、このスラリーは、上記基材の全体に亘ってコートした。次いで、これを乾燥及び焼成に供した。続いて、これに硝酸白金水溶液を含浸させた後、乾燥させた。 Next, this slurry was coated on a monolith honeycomb substrate made of cordierite and having a volume of 1 L, and excess slurry was blown off. This slurry was coated over the entire substrate. This was then subjected to drying and calcination. Subsequently, this was impregnated with an aqueous platinum nitrate solution and then dried.
次いで、触媒金属を支持した担体からなる層に、０．１ｍｏｌ／Ｌ−ｓｏｌの酢酸リチウムと０．１５ｍｏｌ／Ｌ−ｓｏｌの酢酸カリウムと０．２ｍｏｌ／Ｌ−ｓｏｌの酢酸バリウムとを含んだ水溶液を含浸させた。続いて、これをマイクロ波乾燥に供した。このマイクロ波乾燥は、乾燥前に含まれていた水の８０％が除去されるまで行った。その後、３００℃乃至６００℃の温度範囲の熱風を用いて、熱風乾燥を行った。 Next, an aqueous solution containing 0.1 mol / L-sol lithium acetate, 0.15 mol / L-sol potassium acetate, and 0.2 mol / L-sol barium acetate in a layer made of a carrier supporting a catalyst metal. Was impregnated. Subsequently, this was subjected to microwave drying. This microwave drying was performed until 80% of the water contained before drying was removed. Thereafter, hot air drying was performed using hot air in a temperature range of 300 ° C. to 600 ° C.
このようにして、排ガス浄化用触媒を得た。以下、この触媒を「触媒Ｃ１」と呼ぶ。 In this way, an exhaust gas purification catalyst was obtained. Hereinafter, this catalyst is referred to as “catalyst C1”.
続いて、この触媒Ｃ１における標準偏差σを、以下のようにして測定した。
まず、触媒Ｃ１の第１部分、第２部分及び第３部分の各々について、上記割合ａ1、ａ2及びａ3を求めた。具体的には、まず、第１部分に含まれる任意の６つの位置において、上記各位置を中心とする０．５ｍｍ×０．５ｍｍの領域について、その表面をＦＥ−ＳＥＭ（電界放出型走査電子顕微鏡）により観察し、上記領域において吸蔵材が占めていた面積を上記領域の面積で除すことにより、割合ａ1,jを得た。次いで、これら割合ａ1,jの相加平均値として、割合ａ1を求めた。その後、同様にして、割合ａ2及びａ3を求めた。
Subsequently, the standard deviation σ of the catalyst C1 was measured as follows.
First, the ratios a 1 , a 2 and a 3 were determined for each of the first part, the second part and the third part of the catalyst C1. Specifically, first, at any six positions included in the first portion, the surface of an area of 0.5 mm × 0.5 mm centered on each position is subjected to FE-SEM (field emission scanning electron). The ratio a 1, j was obtained by dividing the area occupied by the occlusion material in the region by the area of the region. Next, a ratio a 1 was obtained as an arithmetic average value of these ratios a 1, j . Thereafter, the ratios a 2 and a 3 were determined in the same manner.
次に、これら割合ａ1、ａ2及びａ3に基づいて、標準偏差σを計算した。その結果、触媒Ｃ１における標準偏差σは、０．０４２であった。 Next, the standard deviation σ was calculated based on these ratios a 1 , a 2 and a 3 . As a result, the standard deviation σ of the catalyst C1 was 0.042.
＜例２：触媒Ｃ２＞
マイクロ波乾燥を乾燥前に含まれていた水の８０％が除去されるまで行う代わりに、乾燥前に含まれていた水の７０％が除去されるまで行ったこと以外は、触媒Ｃ１について説明したのと同様にして、排ガス浄化用触媒を製造した。以下、このようにして得られた触媒を「触媒Ｃ２」と呼ぶ。
<Example 2: Catalyst C2>
Instead of performing microwave drying until 80% of the water contained before drying was removed, the catalyst C1 was described except that it was performed until 70% of the water contained before drying was removed. In the same manner as described above, an exhaust gas purification catalyst was produced. Hereinafter, the catalyst thus obtained is referred to as “catalyst C2”.
続いて、この触媒Ｃ２における標準偏差σを、触媒Ｃ１について述べたのと同様の方法により測定した。その結果、触媒Ｃ２における標準偏差σは、０．０６８であった。 Subsequently, the standard deviation σ of the catalyst C2 was measured by the same method as described for the catalyst C1. As a result, the standard deviation σ of the catalyst C2 was 0.068.
＜例３：触媒Ｃ３（比較例）＞
マイクロ波乾燥を乾燥前に含まれていた水の８０％が除去されるまで行う代わりに、乾燥前に含まれていた水の５０％が除去されるまで行ったこと以外は、触媒Ｃ１について説明したのと同様にして、排ガス浄化用触媒を製造した。以下、このようにして得られた触媒を「触媒Ｃ３」と呼ぶ。
<Example 3: Catalyst C3 (Comparative Example)>
Instead of performing microwave drying until 80% of the water contained before drying was removed, catalyst C1 was described except that it was performed until 50% of the water contained before drying was removed. In the same manner as described above, an exhaust gas purification catalyst was produced. Hereinafter, the catalyst thus obtained is referred to as “catalyst C3”.
続いて、この触媒Ｃ３における標準偏差σを、触媒Ｃ１について述べたのと同様の方法により測定した。その結果、触媒Ｃ３における標準偏差σは、０．１１７であった。 Subsequently, the standard deviation σ of the catalyst C3 was measured by the same method as described for the catalyst C1. As a result, the standard deviation σ of the catalyst C3 was 0.117.
＜例４：触媒Ｃ４（比較例）＞
マイクロ波乾燥を省略し、熱風乾燥の前に、８０℃乃至１００℃の温度範囲で予備乾燥を行ったこと以外は、触媒Ｃ１について説明したのと同様にして、排ガス浄化用触媒を製造した。以下、このようにして得られた触媒を「触媒Ｃ４」と呼ぶ。
<Example 4: Catalyst C4 (Comparative Example)>
A catalyst for exhaust gas purification was produced in the same manner as described for the catalyst C1, except that microwave drying was omitted and preliminary drying was performed in a temperature range of 80 ° C. to 100 ° C. before hot air drying. Hereinafter, the catalyst thus obtained is referred to as “catalyst C4”.
続いて、この触媒Ｃ４における標準偏差σを、触媒Ｃ１について述べたのと同様の方法により測定した。その結果、触媒Ｃ４における標準偏差σは、０．１２９であった。 Subsequently, the standard deviation σ of the catalyst C4 was measured by the same method as described for the catalyst C1. As a result, the standard deviation σ of the catalyst C4 was 0.129.
＜例５：触媒Ｃ５（比較例）＞
マイクロ波乾燥を省略し、熱風乾燥のみにより乾燥を行ったこと以外は、触媒Ｃ１について説明したのと同様にして、排ガス浄化用触媒を製造した。以下、このようにして得られた触媒を「触媒Ｃ５」と呼ぶ。
<Example 5: Catalyst C5 (Comparative Example)>
A catalyst for exhaust gas purification was produced in the same manner as described for the catalyst C1, except that microwave drying was omitted and drying was performed only by hot air drying. Hereinafter, the catalyst thus obtained is referred to as “catalyst C5”.
続いて、この触媒Ｃ５における標準偏差σを、触媒Ｃ１について述べたのと同様の方法により測定した。その結果、触媒Ｃ５における標準偏差σは、０．１４６であった。 Subsequently, the standard deviation σ of the catalyst C5 was measured by the same method as described for the catalyst C1. As a result, the standard deviation σ of the catalyst C5 was 0.146.
＜触媒層の表面における吸蔵材の分布＞
上述したように、標準偏差σを求めるために、各触媒における触媒層の表面をＦＥ−ＳＥＭにより観察した。そのうち、触媒Ｃ１及びＣ５の中流部についての観察結果を図１及び図２に示す。
<Distribution of occlusion material on the surface of the catalyst layer>
As described above, in order to obtain the standard deviation σ, the surface of the catalyst layer in each catalyst was observed by FE-SEM. Among these, the observation result about the middle stream part of the catalysts C1 and C5 is shown in FIG.1 and FIG.2.
図１は、実施例に係る排ガス浄化用触媒（触媒Ｃ１）の触媒層の表面における吸蔵材の分布を示すＳＥＭ写真である。図２は、比較例に係る排ガス浄化用触媒（触媒Ｃ５）の触媒層の表面における吸蔵材の分布を示すＳＥＭ写真である。 FIG. 1 is an SEM photograph showing the distribution of the occlusion material on the surface of the catalyst layer of the exhaust gas purifying catalyst (catalyst C1) according to the example. FIG. 2 is an SEM photograph showing the distribution of the occlusion material on the surface of the catalyst layer of the exhaust gas purifying catalyst (catalyst C5) according to the comparative example.
図１及び図２から分かるように、触媒Ｃ１では、吸蔵材が微細粒子として均一に分散していたのに対し、触媒Ｃ５では、吸蔵材粒子の排ガスの流れ方向に沿った組成のばらつきにより、その分布に比較的大きなムラが生じていた。 As can be seen from FIGS. 1 and 2, in the catalyst C1, the occlusion material was uniformly dispersed as fine particles, whereas in the catalyst C5, due to the variation in the composition of the occlusion material particles along the flow direction of the exhaust gas, A relatively large unevenness occurred in the distribution.
また、図示は省略するが、触媒Ｃ１では、触媒の上流部、中流部及び下流部の何れにおいても、吸蔵材が均一に分散していた。それゆえ、上述したように、触媒Ｃ１では、標準偏差σが極めて小さかった。一方、触媒Ｃ５では、触媒の上流部、中流部及び下流部における吸蔵材の分布は、互いに大きく異なっていた。それゆえ、上述したように、触媒Ｃ５では、標準偏差σが比較的大きかった。 Moreover, although illustration is abbreviate | omitted, in the catalyst C1, the occlusion material was disperse | distributing uniformly in any of the upstream part of a catalyst, a midstream part, and a downstream part. Therefore, as described above, the standard deviation σ was extremely small in the catalyst C1. On the other hand, in the catalyst C5, the distribution of the occlusion material in the upstream, middle and downstream portions of the catalyst was greatly different from each other. Therefore, as described above, the standard deviation σ is relatively large in the catalyst C5.
＜耐熱試験後の排ガス浄化性能の評価＞
触媒Ｃ１乃至Ｃ５を排気量４Ｌのエンジンの排気系に取り付け、排ガスの空燃比がストイキ条件となるようにフィードバック制御しながら、７００℃で５０時間に亘り耐熱試験を行った。この際、燃料としては、硫黄分が２０ｐｐｍであるレギュラーガソリンを使用した。
<Evaluation of exhaust gas purification performance after heat resistance test>
Catalysts C1 to C5 were attached to an exhaust system of an engine with a displacement of 4 L, and a heat resistance test was performed at 700 ° C. for 50 hours while performing feedback control so that the air-fuel ratio of the exhaust gas became a stoichiometric condition. At this time, regular gasoline having a sulfur content of 20 ppm was used as the fuel.
その後、耐熱試験後の触媒Ｃ１乃至Ｃ５を排気量１．８Ｌのリーンバーンエンジンの排気系に取り付け、リッチスパイク条件下、２５０℃、３００℃、３５０℃、４００℃、４５０℃及び５００℃の各温度において、ＮＯx還元量の測定を行った。その結果を表１及び図３に示す。 After that, the catalysts C1 to C5 after the heat resistance test are attached to the exhaust system of a lean burn engine having a displacement of 1.8 L, and each of 250 ° C., 300 ° C., 350 ° C., 400 ° C., 450 ° C. and 500 ° C. under rich spike conditions. in the temperature was measured of the NO x reduction amount. The results are shown in Table 1 and FIG.
表１は、耐熱試験後の触媒Ｃ１乃至Ｃ５によるＮＯx還元量を示している。図３は、耐熱試験後の触媒Ｃ１乃至Ｃ５によるＮＯx還元量を示すグラフである。
表１及び図３に示す結果から分かるように、触媒Ｃ１及びＣ２は、触媒Ｃ３乃至Ｃ５と比較して耐熱試験後のＮＯx浄化性能がより優れていた。特に、触媒Ｃ１は、耐熱試験後のＮＯx浄化性能が極めて優れていた。 Table 1 and as can be seen from the results shown in FIG. 3, the catalyst C1 and C2, NO x purifying performance after compared to the heat resistance test with the catalyst C3 to C5 were superior. In particular, the catalyst C1 is, NO x purifying performance after the heat resistance test was extremely excellent.
＜硫黄被毒試験後の排ガス浄化性能の評価＞
触媒Ｃ１乃至Ｃ５を排気量１．８Ｌのリーンバーンエンジンの排気系に取り付け、５５０℃で２０時間に亘り耐久試験を行った。この際、燃料としては、硫黄分が２９０ｐｐｍである硫黄リッチガソリンを使用した。
<Evaluation of exhaust gas purification performance after sulfur poisoning test>
The catalysts C1 to C5 were attached to an exhaust system of a lean burn engine with a displacement of 1.8 L, and an endurance test was conducted at 550 ° C. for 20 hours. At this time, sulfur-rich gasoline having a sulfur content of 290 ppm was used as the fuel.
その後、上記の耐久試験後の触媒Ｃ１乃至Ｃ５について、上述したのと同様にして、ＮＯx還元量の測定を行った。その結果を表２及び図４に示す。 Then, for the catalysts C1 to C5 after the durability test described above, in the same manner as described above, was measured of the NO x reduction amount. The results are shown in Table 2 and FIG.
表２は、硫黄被毒試験後の触媒Ｃ１乃至Ｃ５によるＮＯx還元量を示している。図４は、硫黄被毒試験後の触媒Ｃ１乃至Ｃ５によるＮＯx還元量を示すグラフである。
表２及び図４に示す結果から分かるように、触媒Ｃ１及びＣ２は、触媒Ｃ３乃至Ｃ５と比較して耐硫黄被毒試験後のＮＯx浄化性能がより優れていた。 Table 2 and as can be seen from the results shown in FIG. 4, the catalyst C1 and C2, NO x purifying performance after as compared to the catalyst C3 to C5 sulfur-poisoning test it was superior.
Claims (4)
ａ1は、第１部分における前記触媒層の表面の単位面積に対する前記触媒層の前記表面に露出した前記吸蔵材の面積の割合を表し、
ａ2は、第２部分における前記触媒層の表面の単位面積に対する前記触媒層の前記表面に露出した前記吸蔵材の面積の割合を表し、
ａ3は、第３部分における前記触媒層の表面の単位面積に対する前記触媒層の前記表面に露出した前記吸蔵材の面積の割合を表し、
ａavは、ａ1，ａ2及びａ3の相加平均値を表し、
前記第１乃至第３部分は、前記排ガス浄化用触媒のうち前記触媒層が形成された部分を前記排ガスの流れ方向について３等分して得られる。 An exhaust gas purification comprising a base material and a catalyst layer formed on the base material and containing a catalyst metal and an occlusion material, and a standard deviation σ represented by the following formula is 0.08 or less Catalyst.
a 1 represents the ratio of the area of the occlusion material exposed on the surface of the catalyst layer to the unit area of the surface of the catalyst layer in the first portion;
a 2 represents the ratio of the area of the occlusion material exposed on the surface of the catalyst layer to the unit area of the surface of the catalyst layer in the second portion;
a 3 represents the ratio of the area of the occlusion material exposed on the surface of the catalyst layer to the unit area of the surface of the catalyst layer in the third portion;
a av represents the arithmetic mean value of a 1 , a 2 and a 3 ,
The first to third portions are obtained by dividing the portion of the exhaust gas purifying catalyst where the catalyst layer is formed into three equal parts in the flow direction of the exhaust gas.
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