JP4529463B2 - Exhaust gas purification catalyst and exhaust gas purification method - Google Patents
Exhaust gas purification catalyst and exhaust gas purification method Download PDFInfo
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Description
本発明は、酸素過剰雰囲気で燃焼された排ガス中で用いられる排ガス浄化用触媒と、その触媒を用いた排ガス浄化方法に関する。 The present invention relates to an exhaust gas purification catalyst used in exhaust gas burned in an oxygen-excess atmosphere, and an exhaust gas purification method using the catalyst.
自動車用の排ガス浄化用触媒として、酸化触媒、三元触媒、NOx 選択還元触媒、NOx 吸蔵還元触媒などが用いられている。このうち酸化触媒は、各種雰囲気の排ガス中でHC及びCOを酸化して浄化する。三元触媒は、ストイキ近傍雰囲気の排ガス中でHC及びCOを酸化し、NOx を還元して浄化する。またNOx 選択還元触媒は、酸素過剰のリーン雰囲気でNOx を選択的に還元して浄化する。さらにNOx 吸蔵還元触媒は、リーン雰囲気でNOx を吸蔵し、ストイキ又はリッチ雰囲気でNOx を放出するとともに雰囲気中に豊富に存在する還元成分によって放出されたNOx を還元浄化する。 As an exhaust gas purification catalyst for automobiles, an oxidation catalyst, a three-way catalyst, a NO x selective reduction catalyst, a NO x storage reduction catalyst, and the like are used. Of these, the oxidation catalyst oxidizes and purifies HC and CO in exhaust gas in various atmospheres. The three-way catalyst oxidizes HC and CO in the exhaust gas of near stoichiometric atmosphere, to purify by reduction the NO x. The NO x selective reduction catalyst selectively reduces and purifies NO x in a lean atmosphere containing excess oxygen. Moreover the NO x storage reduction catalyst occludes NO x in a lean atmosphere to reduce and purify the released NO x by reducing component abundantly present in the atmosphere as well as releasing the NO x in the stoichiometric or rich atmosphere.
ところで、地球温暖化の原因物質であるCO2 の排出を抑制するとともに燃費を低減するために、酸素過剰雰囲気で燃焼するリーンバーンエンジンが開発され、実用に供されている。しかしリーンバーンエンジンからの排ガスはリーン雰囲気であるために、上記した触媒単独では有害成分の浄化が困難であり、複数種の触媒を併用することが行われている。 By the way, a lean burn engine that burns in an oxygen-excess atmosphere has been developed and put into practical use in order to suppress CO 2 emission, which is a cause of global warming, and to reduce fuel consumption. However, since the exhaust gas from the lean burn engine has a lean atmosphere, it is difficult to purify harmful components with the above-described catalyst alone, and a plurality of types of catalysts are used in combination.
例えばエンジン直下に酸化触媒あるいは三元触媒を配置し、その下流側にNOx 吸蔵還元触媒を配置することが行われている。この場合、エンジン直下の触媒によって排ガスは比較的低温域から浄化され、その反応熱によってさらに温度が高くなった排ガスが下流側の触媒に流入するため、下流側の触媒の活性が向上する。またエンジン直下の触媒によって排ガス中のNOが酸化されてNO2 となり、下流側のNOx 吸蔵還元触媒に吸蔵されやすくなる。したがってエンジン直下に配置された触媒は、スタートアップ触媒（以下、 S/Cという）と称されている。 For example, an oxidation catalyst or a three-way catalyst is disposed immediately below the engine, and a NO x storage reduction catalyst is disposed downstream thereof. In this case, the exhaust gas is purified from a relatively low temperature range by the catalyst directly under the engine, and the exhaust gas whose temperature is further increased by the reaction heat flows into the downstream catalyst, so that the activity of the downstream catalyst is improved. Further, NO in the exhaust gas is oxidized by the catalyst directly under the engine to become NO 2 and is easily stored in the NO x storage reduction catalyst on the downstream side. Therefore, the catalyst placed directly under the engine is called the startup catalyst (hereinafter referred to as S / C).
しかし下流側のNOx 吸蔵還元触媒のみでは、全てのNOx を還元浄化することは困難である。またNOx 吸蔵還元触媒を用いる場合には、通常はリーン雰囲気で運転し間欠的にリッチスパイクを打つ必要があるが、燃費の観点からリッチスパイクの頻度を低減させることが望まれている。そこで、 S/CにもNOx 還元活性をもたせることが望ましい。さらにNOx 吸蔵還元触媒はHC及びCOの酸化活性が比較的低いので、 S/CはHC及びCOの酸化能に優れていることが望ましい。 However, it is difficult to reduce and purify all NO x only with the downstream side NO x storage reduction catalyst. In the case of using the NO x storage reduction catalyst, it is usually necessary to operate in a lean atmosphere and intermittently apply rich spikes, but it is desired to reduce the frequency of rich spikes from the viewpoint of fuel consumption. Therefore, it is desirable that S / C also has NO x reduction activity. Furthermore, since the NO x storage reduction catalyst has a relatively low HC and CO oxidation activity, it is desirable that the S / C is excellent in HC and CO oxidation ability.
ところが S/Cとして三元触媒を用いた場合には、リーン雰囲気でNOx を還元浄化することは困難である。また S/CとしてNOx 選択還元触媒を用いた場合には、NOx を還元浄化できる温度ウィンドウが狭く、ある温度範囲ではNOx を還元浄化することが困難となる。さらにNOx 選択還元触媒は、ストイキ近傍雰囲気においてHC及びCOの酸化活性が低いという問題があった。 However, when a three-way catalyst is used as S / C, it is difficult to reduce and purify NO x in a lean atmosphere. When a NO x selective reduction catalyst is used as S / C, the temperature window for reducing and purifying NO x is narrow, and it becomes difficult to reduce and purify NO x within a certain temperature range. Furthermore, the NO x selective reduction catalyst has a problem that the oxidation activity of HC and CO is low in an atmosphere near the stoichiometric atmosphere.
特開平05−285388号公報には、貴金属とCo、Znなどを担持した触媒が提案されている。この触媒によれば、CoなどによってNOx 選択還元活性が発現され、貴金属によってHC及びCOの酸化活性が発現されるので、ストイキ及びリーン雰囲気においてHC、CO及びNOx を高い浄化率で浄化することができる。 Japanese Patent Laid-Open No. 05-285388 proposes a catalyst supporting a noble metal and Co, Zn or the like. According to this catalyst, NO x selective reduction activity is expressed by Co and the like, and HC and CO oxidation activity is expressed by noble metals, so HC, CO and NO x are purified at a high purification rate in a stoichiometric and lean atmosphere. be able to.
また特開平06−343829号公報には、CuとAlを担持し、さらにGa、Znなどを担持した触媒が提案されている。この触媒によれば、リーン雰囲気においてNOx を効率的に還元浄化でき、しかも幅広い温度ウィンドウを有するので、三元触媒の代替品として利用できる。 Japanese Laid-Open Patent Publication No. 06-343829 proposes a catalyst supporting Cu and Al and further supporting Ga, Zn and the like. According to this catalyst, NO x can be efficiently reduced and purified in a lean atmosphere, and furthermore, since it has a wide temperature window, it can be used as an alternative to a three-way catalyst.
ところがこれらの触媒を S/Cとして用いても、今後さらに厳しくなる厳しい排ガス規制に対応することは困難であり、さらなる活性の向上が求められている。
本発明は上記した事情に鑑みてなされたものであり、HC及びCOの酸化活性が高く、かつリーン雰囲気においても広い温度ウィンドウでNOx を効率よく還元浄化でき、 S/Cとして有用な触媒とすることを目的とする。 The present invention has been made in view of the above circumstances, and has a high oxidation activity of HC and CO, and can efficiently reduce and purify NO x over a wide temperature window even in a lean atmosphere, and is a catalyst useful as S / C. The purpose is to do.
上記課題を解決する本発明の排ガス浄化用触媒の特徴は、ハニカム基材と、ハニカム基材に形成されたコート層とからなる排ガス浄化用触媒であって、コート層にはGa、Zn、Cu、Co及び貴金属から選ばれる触媒金属が担持され、ハニカム基材の一端部に形成されCoのみを担持した第１金属領域と、第１金属領域に隣接しCoとCuを担持した第２金属領域と、第１金属領域と反対側で第２金属領域に隣接しCoとCuとZnを担持した第３金属領域と、第２金属領域と反対側で第３金属領域に隣接しCoとCuとZnとGaを担持した第４金属領域と、第３金属領域と反対側のハニカム基材の他端部で第４金属領域に隣接しCoとCuとZnとGaと貴金属とを担持した第５金属領域と、を有することにある。
A feature of the exhaust gas purifying catalyst of the present invention that solves the above problems is an exhaust gas purifying catalyst comprising a honeycomb substrate and a coat layer formed on the honeycomb substrate, and the coat layer includes Ga, Zn, Cu , A catalytic metal selected from Co and a noble metal is supported, and is formed at one end portion of the honeycomb base material, a first metal region supporting only Co, and a second metal region adjacent to the first metal region and supporting Co and Cu. And a third metal region supporting Co, Cu and Zn on the side opposite to the first metal region and supporting Co, Cu and Zn, and adjacent to the third metal region on the side opposite to the second metal region. A fourth metal region supporting Zn and Ga; and a fifth metal region supporting Co, Cu, Zn, Ga, and a noble metal adjacent to the fourth metal region at the other end of the honeycomb substrate opposite to the third metal region. A metal region .
また、貴金属はパラジウムであることが望ましい。The noble metal is preferably palladium.
また本発明の排ガス浄化方法の特徴は、本発明の排ガス浄化用触媒を用い、排ガスがハニカム基材の一端部から他端部へ向かって又は他端部から一端部へ向かって流れるように配置して排ガスを浄化することにある。 The exhaust gas purification method of the present invention is characterized in that the exhaust gas purification catalyst of the present invention is used so that the exhaust gas flows from one end to the other end of the honeycomb substrate or from the other end to the one end. It is to purify the exhaust gas.
本発明の排ガス浄化用触媒によれば、従来の S/Cに比べて、リーン雰囲気におけるHC及びCOの酸化活性とNOx の還元活性が共に向上する。したがってNOx 吸蔵還元触媒の S/Cとして用いることで、 S/Cからの出ガス中のHC、CO及びNOx 濃度が低減されるため、NOx 吸蔵還元触媒のNOx 吸蔵効率が向上する。これにより、リーンでの走行時間を延長して還元剤を供給するためのリッチスパイクの頻度を低下させることができるので、燃費が向上する。またNOx 吸蔵還元触媒に担持されている貴金属の担持量を少なくすることもでき、この場合はコストを低下させることができる。 According to the exhaust gas purifying catalyst of the present invention, both HC and CO oxidation activity and NO x reduction activity in a lean atmosphere are improved as compared with conventional S / C. Thus by using as the S / C of the NO x storage-reduction catalyst, since the HC outgoing gas from S / C, CO and NO x concentration is reduced, thereby improving the NO x storage efficiency of the NO x storage-reduction catalyst . As a result, it is possible to extend the lean travel time and reduce the frequency of the rich spike for supplying the reducing agent, thereby improving the fuel efficiency. In addition, the amount of noble metal supported on the NO x storage reduction catalyst can be reduced, and in this case, the cost can be reduced.
本発明の排ガス浄化用触媒及び排ガス浄化方法において、Ga、Zn、Cu、Co及び貴金属から選ばれる触媒金属は、それぞれNOx 選択還元活性を備えている。Ga、Zn、Cu、Co及び貴金属をそれぞれ同一担持量で担持した場合の、リーン雰囲気におけるNOx 選択還元浄化率を図４に、HC浄化率を図５に示す。図４に示されるように、NOx の選択還元浄化率が最高となる最高NOx 浄化温度は、貴金属＜Ga＜Zn＜Cu＜Coの順となり、図５に示されるように、HCを効率よく浄化できる温度で並べても同じ順序である。なお貴金属としてはPdを用いているが、他の貴金属も順位は同等である。 In the catalyst and the exhaust gas purifying method for purifying an exhaust gas of the present invention, the catalytic metal selected Ga, Zn, Cu, Co and noble metal is provided with the NO x selective reduction activity, respectively. FIG. 4 shows the NO x selective reduction purification rate in a lean atmosphere and FIG. 5 shows the HC purification rate when Ga, Zn, Cu, Co, and noble metal are supported in the same loading amount. As shown in FIG. 4, the highest the NO x purification temperature selective reduction purification ratio of the NO x becomes maximum becomes the order of the noble metal <Ga <Zn <Cu <Co , as shown in FIG. 5, the efficiency of HC Even if they are arranged at a temperature that can be purified well, the order is the same. Pd is used as the noble metal, but the ranking is the same for other noble metals.
そこで本発明では、単位担持量当たりのNOx の選択還元浄化率が最高となる最高NOx 浄化温度が低い触媒金属ほど、又は最高NOx 浄化温度が高い触媒金属ほど、排ガス上流側又は下流側で排ガスと接触可能に担持したところに特徴を有している。図１に示されるように、最高NOx 浄化温度が低い触媒金属ほど排ガス上流側で排ガスと接触可能に担持されている場合には、先ず低温活性が高い触媒金属によってHC及びCOが酸化浄化される。そしてその領域で酸化されなかったHC及びCOは、中温での活性が高い触媒金属によって酸化浄化され、次いで高温での活性が高い触媒金属によって酸化浄化される。排ガスは、それぞれの領域で酸化される際の反応熱によって下流側ほど温度が高くなり、触媒金属の活性も下流側ほど高温域での酸化活性が高くなるように配置されているので、HC及びCOの浄化活性がきわめて高い。 In this invention, as the best the NO x purification temperature is lower catalytic metal selective reduction purification ratio of the NO x per unit carrying amount is the highest, or maximum NO x as purification temperature higher catalytic metal, the exhaust gas upstream or downstream It is characterized in that it is supported so as to be in contact with exhaust gas. As shown in FIG. 1, when a catalyst metal having a lower maximum NO x purification temperature is supported on the upstream side of the exhaust gas so as to be able to come into contact with the exhaust gas, first, HC and CO are oxidized and purified by the catalyst metal having a higher low-temperature activity. The HC and CO that have not been oxidized in that region are oxidized and purified by a catalytic metal having a high activity at medium temperature, and then oxidized and purified by a catalytic metal having a high activity at high temperature. The exhaust gas is arranged so that the temperature on the downstream side becomes higher due to the reaction heat when it is oxidized in each region, and the activity of the catalytic metal is arranged so that the oxidation activity in the high temperature region becomes higher on the downstream side. CO purification activity is extremely high.
一方、NOx についても、最高NOx 浄化温度が低い触媒金属が担持された領域における反応熱によって加熱された排ガスが中温での活性が高い領域を通過して高温での活性が高い領域に流入し、上流側から下流側に向かって最高NOx 浄化温度が高くなっているため、排ガスの熱によって各領域の触媒金属が効果的に活性化され、広い温度ウィンドウでNOx が選択還元され浄化される。したがってリーン雰囲気においてHC、CO及びNOx を高い浄化率で浄化することができる。 On the other hand, for NO x , exhaust gas heated by reaction heat in the region where the catalyst metal with the lowest maximum NO x purification temperature is supported passes through the region with high activity at medium temperature and flows into the region with high activity at high temperature. However, since the maximum NO x purification temperature increases from the upstream side to the downstream side, the catalyst metal in each region is effectively activated by the heat of the exhaust gas, and NO x is selectively reduced and purified over a wide temperature window. Is done. Therefore it is possible to purify HC, and CO and NO x at a high purification rate in a lean atmosphere.
また図２に示されるように、最高NOx 浄化温度が高い触媒金属ほど排ガス上流側で排ガスと接触可能に担持されている場合には、排ガスは先ず高温での活性が高い領域に流入し、次いで中温での活性が高い領域を通過し、最後に低温での活性が高い領域を通過する。これにより、NOの選択還元によりNO浄化率が向上し、貴金属のみでは不可能なHC浄化温度が高い領域でのHC浄化も可能となる。そしてNOx 浄化率が飛躍的に向上し、最高NOx 浄化温度が低い触媒金属ほど排ガス上流側で排ガスと接触可能に担持されている場合に比べても高いNOx 浄化活性が発現される。また高温での活性が高い領域及び中温での活性が高い領域でHC及びCOがNOx の還元に消費され、残ったHC及びCOは最下流の低温での活性が高い領域において酸化浄化されるので、最高NOx 浄化温度が低い触媒金属ほど排ガス上流側で排ガスと接触可能に担持されている場合には及ばないものの、HC及びCOの浄化活性も高い。 In addition, as shown in FIG. 2, when the catalyst metal having the highest maximum NO x purification temperature is supported on the upstream side of the exhaust gas so as to be in contact with the exhaust gas, the exhaust gas first flows into a region where the activity at a high temperature is high, Next, it passes through a region having high activity at medium temperature, and finally passes through a region having high activity at low temperature. As a result, the NO purification rate is improved by selective reduction of NO, and HC purification in a region where the HC purification temperature is impossible, which is impossible with only a noble metal, becomes possible. The NO x purification rate is dramatically improved, and the catalyst metal having a lower maximum NO x purification temperature exhibits a higher NO x purification activity than when it is supported on the upstream side of the exhaust gas so as to be in contact with the exhaust gas. The HC and CO in the region of high activity in the active region of high and medium temperature at a high temperature are consumed in the reduction of NO x, the remaining HC and CO are oxidized and purified in the region is high activity in the most downstream cold Therefore, although the catalyst metal having the lowest maximum NO x purification temperature does not reach the case where it is supported so as to be in contact with the exhaust gas upstream of the exhaust gas, the HC and CO purification activity is also high.
触媒金属としては、図４に示される順位に従って、最高NOx 浄化温度が高いものを第１の金属として選択し、選択された第１の金属より最高NOx 浄化温度が低いものを第２の金属として選択し、選択された第２の金属より最高NOx 浄化温度が低いものを第３の金属として選択すればよい。なお選択される金属は少なくとも３種であるが、４種以上選択することもできる。この場合は、最高NOx 浄化温度が、第１の金属＞第２の金属＞第３の金属＞第４の金属・・となるように選択し、その順に相対的に高温での活性が高い領域、中温での活性が高い領域及び低温での活性が高い領域を形成すればよい。 According to the order shown in FIG. 4, a catalyst metal having a highest maximum NO x purification temperature is selected as the first metal, and a catalyst metal having a maximum NO x purification temperature lower than the selected first metal is selected as the second catalyst metal. selected as the metal, may be selected to best the NO x purification temperature is lower than a second metal selected as the third metal. In addition, although the metal selected is at least 3 types, 4 or more types can also be selected. In this case, the highest NO x purification temperature is selected as follows: first metal> second metal> third metal> fourth metal... A region, a region having a high activity at a medium temperature, and a region having a high activity at a low temperature may be formed.
低温での活性が高い領域には、少なくとも貴金属が担持されていることが望ましい。貴金属は低温域におけるHC及びCOの酸化活性が特に高いからである。この貴金属としてはPt、Rh、Pd、Irなどの白金族貴金属が好ましいが、中でもリーン雰囲気において低温域からHC及びCOの酸化活性に優れるPdを用いることが望ましい。 It is desirable that at least a noble metal is supported in a region having high activity at a low temperature. This is because noble metals have particularly high oxidation activity of HC and CO at low temperatures. The noble metal is preferably a platinum group noble metal such as Pt, Rh, Pd, or Ir, but it is desirable to use Pd that is excellent in HC and CO oxidation activity from a low temperature range in a lean atmosphere.
高温での活性が高い領域、中温での活性が高い領域、低温での活性が高い領域は、互いに分断されていてもよいし、オーバーラップする部分が存在していてもよい。実際の製造方法を考慮すると、オーバーラップする部分が存在するのが自然である。 The region having high activity at high temperature, the region having high activity at medium temperature, and the region having high activity at low temperature may be separated from each other, or overlapping portions may exist. Considering the actual manufacturing method, it is natural that there are overlapping portions.
本発明の排ガス浄化用触媒は、それぞれの金属が担持されたペレットを上記した順序となるように排気流路に充填してペレット触媒としてもよいし、フォーム基材あるいはハニカム基材のそれぞれの金属を順に担持したフォーム触媒あるいはハニカム触媒とすることもできる。例えばハニカム触媒とする場合には、コージェライトあるいは金属箔から形成されたハニカム基材に、アルミナ、ジルコニア、チタニア、セリア、セリア−ジルコニアなどから選ばれる酸化物からウォッシュコート法にてコート層を形成し、そのコート層に第１の金属、第２の金属及び第３の金属を含む薬液をそれぞれ所定位置に含浸して焼成することで、高温での活性が高い領域、中温での活性が高い領域及び低温での活性が高い領域を形成することができる。 The exhaust gas purifying catalyst of the present invention may be used as a pellet catalyst by filling the exhaust channels so that the pellets carrying the respective metals are in the above-described order, or each metal of the foam substrate or the honeycomb substrate. It is also possible to use a foam catalyst or a honeycomb catalyst that supports the catalyst in order. For example, when a honeycomb catalyst is used, a coat layer is formed by a wash coat method from an oxide selected from alumina, zirconia, titania, ceria, ceria-zirconia, etc. on a honeycomb substrate formed of cordierite or metal foil. Then, the coating layer is impregnated with a chemical solution containing the first metal, the second metal, and the third metal at predetermined positions and baked, so that the activity at a high temperature is high and the activity at a medium temperature is high. Regions and regions with high activity at low temperatures can be formed.
高温での活性が高い領域、中温での活性が高い領域及び低温での活性が高い領域における第１の金属、第２の金属及び第３の金属の担持量は、それぞれ基材１リットルあたり0.01〜 0.5モルが好ましく、低温での活性が高い領域における貴金属の担持量は基材１リットルあたり 0.1〜５ｇが好ましい。第１の金属、第２の金属及び第３の金属の担持量がこの範囲より少ないとNOx 浄化率が低すぎて実用的でなく、この範囲を超えるとNO浄化率が低下する場合がある。また貴金属の担持量がこの範囲より少ないとHC及びCOの浄化率が低すぎて実用的でなく、この範囲を超えて担持しても効果が飽和するとともに高価となる。 The loading amounts of the first metal, the second metal, and the third metal in the region having a high activity at high temperature, the region having a high activity at medium temperature, and the region having a high activity at low temperature were 0.01 per liter of the substrate, respectively. The amount of noble metal supported in a region having high activity at low temperatures is preferably 0.1 to 5 g per liter of the substrate. If the loading amount of the first metal, the second metal, and the third metal is less than this range, the NO x purification rate is too low to be practical, and if it exceeds this range, the NO purification rate may decrease. . If the amount of noble metal supported is less than this range, the purification rate of HC and CO is too low to be practical, and if it exceeds this range, the effect is saturated and expensive.
本発明の排ガス浄化用触媒は、リーンバーンエンジンからの排ガスを浄化するのに最適であり、特にその下流側にNOx 吸蔵還元触媒を配置して S/Cとして用いることが望ましい。これにより下流側のNOx 吸蔵還元触媒のNOx 浄化性能を最大に引き出すことができ、HC及びCOもほぼ 100％浄化することができる。 The exhaust gas purifying catalyst of the present invention is optimal for purifying exhaust gas from a lean burn engine, and in particular, it is desirable to use an NO x storage reduction catalyst downstream as the S / C. As a result, the NO x purification performance of the downstream NO x storage reduction catalyst can be maximized, and HC and CO can also be substantially 100% purified.
以下、実施例及び比較例により本発明を具体的に説明する。 Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples.
（実施例１）
図１に本実施例の触媒を模式的に示す。この触媒は、表面にアルミナを主とするコート層が形成されたハニカム基材１と、排ガス最下流のコート層にCoが担持された第１金属領域２と、第１金属領域２の上流側のコート層にCu及びCoが担持された第２金属領域３と、第２金属領域３の上流側のコート層にZn、Cu及びCoが担持された第３金属領域４と、第３金属領域４の上流側のコート層にGa、Zn、Cu及びCoが担持された第４金属領域５と、第４金属領域５の上流側のコート層にPd、Ga、Zn、Cu及びCoが担持された貴金属領域６と、から構成されている。以下、この触媒の製造方法を説明し、構成の詳細な説明に代える。
Example 1
FIG. 1 schematically shows the catalyst of this example. This catalyst includes a
コージェライト製で体積 0.7Ｌのハニカム基材（ 600セル／in2 、直径93mm、長さ 100mm）を用意し、アルミナ粉末と硫酸バリウム粉末、アルミナゾル及び水からなるスラリーをウォッシュコートし乾燥、焼成してコート層を形成した。コート層はハニカム基材１Ｌあたり 115ｇ形成された。コート層中の硫酸バリウムは、PdのHC被毒を抑制するために添加している。
Prepare a honeycomb substrate made of cordierite with a volume of 0.7 L (600 cells / in 2 , diameter 93 mm,
コート層をもつハニカム基材全体に、所定濃度の硝酸コバルト水溶液の所定量を吸水させ、乾燥後 500℃で焼成してコート層全体にCoを担持した。Coの担持量は、ハニカム基材１Ｌあたり 0.1モルである。 A predetermined amount of a cobalt nitrate aqueous solution having a predetermined concentration was absorbed into the entire honeycomb base material having the coat layer, dried, and fired at 500 ° C. to carry Co on the entire coat layer. The amount of Co supported is 0.1 mol per liter of honeycomb substrate.
次に、所定濃度の硝酸銅水溶液の所定量を、排ガス上流側端面から全長の80％の位置までのコート層に吸水させ、同様に乾燥、焼成してCuを担持した。Cuの担持量は、ハニカム基材１Ｌあたり 0.125モルである。 Next, a predetermined amount of a copper nitrate aqueous solution having a predetermined concentration was absorbed into the coating layer from the end face on the exhaust gas upstream side to a position of 80% of the total length, and dried and baked in the same manner to carry Cu. The amount of Cu supported is 0.125 mol per liter of honeycomb substrate.
続いて所定濃度の硝酸亜鉛水溶液の所定量を、排ガス上流側端面から全長の60％の位置までのコート層に吸水させ、同様に乾燥、焼成してZnを担持した。Znの担持量は、ハニカム基材１Ｌあたり 0.167モルである。 Subsequently, a predetermined amount of a zinc nitrate aqueous solution having a predetermined concentration was absorbed into the coating layer from the exhaust gas upstream side end surface to a position of 60% of the total length, and dried and fired in the same manner to carry Zn. The amount of Zn supported is 0.167 mol per liter of honeycomb substrate.
続いて所定濃度の硝酸ガリウム水溶液の所定量を、排ガス上流側端面から全長の40％の位置までのコート層に吸水させ、同様に乾燥、焼成してGaを担持した。Gaの担持量は、ハニカム基材１Ｌあたり0.25モルである。 Subsequently, a predetermined amount of a gallium nitrate aqueous solution having a predetermined concentration was absorbed in the coating layer from the exhaust gas upstream side end surface to a position of 40% of the total length, and similarly dried and fired to carry Ga. The amount of Ga supported is 0.25 mol per liter of honeycomb substrate.
続いて所定濃度の硝酸パラジウムの硝酸酸性水溶液の所定量を、排ガス上流側端面から全長の20％の位置までのコート層に吸水させ、同様に乾燥、焼成してPdを担持した。Pdの担持量は、ハニカム基材１Ｌあたり３ｇである。 Subsequently, a predetermined amount of a nitric acid aqueous solution of palladium nitrate having a predetermined concentration was absorbed into the coating layer from the end face on the upstream side of the exhaust gas to a position of 20% of the total length, and similarly dried and fired to carry Pd. The amount of Pd supported is 3 g per liter of honeycomb substrate.
こうして第１金属領域２、第２金属領域３、第３金属領域４、第４金属領域５、貴金属領域６を形成した。第１金属領域２と第２金属領域３を比較すると、Coは両方に同量担持されているが、Cuは第１金属領域には担持されていない。したがってCuが担持されている第２金属領域３の方が、Coのみを担持した第１金属領域２より最高NOx 浄化温度が低いことになる。以下同様にして、第１金属領域２、第２金属領域３、第３金属領域４及び第４金属領域５の範囲では、排ガス上流側ほど最高NOx 浄化温度が低くなっている。そして排ガス最上流側に貴金属領域６が形成されている。
Thus, the
得られた触媒を２Ｌのリーンバーンエンジンを搭載したエンジンベンチの排気系に、貴金属領域６が排ガス上流側、第１金属領域１が排ガス下流側となるように配置し、空燃比（ A/F）を23で希薄燃焼させた排ガスを流通させながら、触媒入りガス温度 250℃の時のHC浄化率及びNOx 浄化率を測定した。結果を図３に示す。
The obtained catalyst is arranged in the exhaust system of an engine bench equipped with a 2 L lean burn engine so that the noble metal region 6 is on the exhaust gas upstream side and the
（実施例２）
実施例１と同様の触媒を逆に用いることで実施例２の触媒とした。すなわち図２に示すように、実施例１と同様の触媒を、エンジンベンチの排気系に第１金属領域２が排ガス上流側に、貴金属領域６が排ガス下流側になるように配置した。そして実施例１と同様にしてHC浄化率及びNOx 浄化率を測定した。結果を図３に示す。
(Example 2)
The catalyst of Example 2 was obtained by using the same catalyst as in Example 1 in reverse. That is, as shown in FIG. 2, the same catalyst as in Example 1 was disposed in the exhaust system of the engine bench so that the
（比較例１）
実施例１と同様にコート層が形成されたハニカム基材を用い、所定濃度の硝酸パラジウムの硝酸酸性水溶液の所定量を、コート層全体に均一に吸水させ、実施例１と同様に乾燥、焼成してPdを担持した。Pdの担持量は、ハニカム基材１Ｌあたり３ｇである。
(Comparative Example 1)
Using a honeycomb substrate on which a coating layer was formed as in Example 1, a predetermined amount of a nitric acid aqueous solution of palladium nitrate having a predetermined concentration was uniformly absorbed throughout the coating layer, and dried and fired in the same manner as in Example 1. To support Pd. The amount of Pd supported is 3 g per liter of honeycomb substrate.
次に、予めRhが 0.4重量％含浸担持されたZrO2粉末（Rh／ZrO2粉末）をスラリー化し、Pdが担持されたコート層の表面にさらにウォッシュコートし乾燥、焼成して第２のコート層を形成した。第２のコート層は、ハニカム基材１Ｌあたり70ｇ形成された。 Next, ZrO 2 powder impregnated and supported by 0.4% by weight of Rh (Rh / ZrO 2 powder) was slurried in advance, and the surface of the coating layer on which Pd was supported was further washed, dried and fired to form a second coat. A layer was formed. 70 g of the second coat layer was formed per 1 L of the honeycomb substrate.
得られた触媒は、NOx 吸蔵還元触媒の上流側に配置されるリーンバーン用 S/Cとして一般に用いられているものである。この触媒を用い、実施例１と同様にしてHC浄化率及びNOx 浄化率を測定した。結果を図３に示す。 The obtained catalyst is generally used as a lean burn S / C disposed upstream of the NO x storage reduction catalyst. Using this catalyst, the HC purification rate and the NO x purification rate were measured in the same manner as in Example 1. The results are shown in FIG.
（比較例２）
実施例１と同様にコート層が形成されたハニカム基材を用い、所定濃度の硝酸コバルト水溶液の所定量を全体に均一に吸水させ、乾燥後 500℃で焼成してコート層全体にCoを担持した。Coの担持量は、ハニカム基材１Ｌあたり 0.1モルである。
(Comparative Example 2)
Using a honeycomb substrate with a coating layer formed in the same manner as in Example 1, a predetermined amount of a cobalt nitrate aqueous solution having a predetermined concentration is uniformly absorbed throughout, dried, and fired at 500 ° C. to carry Co on the entire coating layer. did. The amount of Co supported is 0.1 mol per liter of honeycomb substrate.
次に、所定濃度の硝酸銅水溶液の所定量を、コート層全体に均一に吸水させ、同様に乾燥、焼成してCuを担持した。Cuの担持量は、ハニカム基材１Ｌあたり 0.1モルである。 Next, a predetermined amount of a copper nitrate aqueous solution having a predetermined concentration was uniformly absorbed throughout the coating layer, and similarly dried and fired to carry Cu. The supported amount of Cu is 0.1 mol per liter of honeycomb substrate.
続いて所定濃度の硝酸亜鉛水溶液の所定量を、コート層全体に均一に吸水させ、同様に乾燥、焼成してZnを担持した。Znの担持量は、ハニカム基材１Ｌあたり 0.1モルである。 Subsequently, a predetermined amount of a zinc nitrate aqueous solution having a predetermined concentration was uniformly absorbed throughout the coating layer, and similarly dried and fired to carry Zn. The amount of Zn supported is 0.1 mol per liter of honeycomb substrate.
続いて所定濃度の硝酸ガリウム水溶液の所定量を、コート層全体に均一に吸水させ、同様に乾燥、焼成してGaを担持した。Gaの担持量は、ハニカム基材１Ｌあたり 0.1モルである。 Subsequently, a predetermined amount of a gallium nitrate aqueous solution having a predetermined concentration was uniformly absorbed throughout the coating layer, and similarly dried and fired to carry Ga. The amount of Ga supported is 0.1 mol per liter of honeycomb substrate.
続いて所定濃度の硝酸パラジウムの硝酸酸性水溶液の所定量を、コート層全体に均一に吸水させ、同様に乾燥、焼成してPdを担持した。Pdの担持量は、ハニカム基材１Ｌあたり３ｇである。 Subsequently, a predetermined amount of a nitric acid aqueous solution of palladium nitrate having a predetermined concentration was uniformly absorbed by the entire coating layer, and similarly dried and fired to carry Pd. The amount of Pd supported is 3 g per liter of honeycomb substrate.
この触媒を用い、実施例１と同様にしてHC浄化率及びNOx 浄化率を測定した。結果を図３に示す。 Using this catalyst, the HC purification rate and the NO x purification rate were measured in the same manner as in Example 1. The results are shown in FIG.
＜評価＞
図３より、Co、Cu、Zn及びGaを均一に担持した比較例２の触媒は、比較例１の触媒に比べてHC及びNOx の浄化率が向上している。これは、比較例２の触媒でNOx 選択還元活性が発現したことによるものであると考えられる。しかし実施例１及び実施例２の触媒は、触媒金属の担持量は比較例２の触媒と同等であるにも関わらず、比較例２の触媒よりHC及びNOx の浄化率が向上し、これは触媒金属を所定の順に担持した効果である。
<Evaluation>
As shown in FIG. 3, the catalyst of Comparative Example 2 in which Co, Cu, Zn, and Ga are uniformly supported has an improved HC and NO x purification rate as compared with the catalyst of Comparative Example 1. This is believed to be due to the NO x selective reduction activity in the catalyst of Comparative Example 2 was expressed. However, the catalyst of Example 1 and Example 2 has an improved purification rate of HC and NO x compared with the catalyst of Comparative Example 2, although the supported amount of catalyst metal is equivalent to that of Comparative Example 2. Is the effect of supporting the catalyst metals in a predetermined order.
そして実施例１と実施例２を比べると、実施例１の触媒はHC浄化率が特に高く、実施例２の触媒はNOx 浄化率が特に高い。すなわち、排ガス上流側から下流側に向かって貴金属領域６、第４金属領域５、第３金属領域４、第２金属領域３及び第１金属領域２がこの順で並んでいることで、HCの酸化活性が格段に向上し、排ガス上流側から下流側に向かって第１金属領域２、第２金属領域３、第３金属領域４、第４金属領域５及び貴金属領域６がこの順で並んでいることで、NOx 還元活性が格段に向上していることが明らかである。
When comparing Example 1 and Example 2, the catalyst of Example 1 has a particularly high HC purification rate, and the catalyst of Example 2 has a particularly high NO x purification rate. That is, the noble metal region 6, the
本発明の排ガス浄化用触媒は、NOx 吸蔵還元触媒の上流側に配置される S/Cとしてきわめて有用である。また単独で、リーンバーン用の排ガス浄化用触媒として用いることも可能である。 The exhaust gas purifying catalyst of the present invention is extremely useful as S / C disposed upstream of the NO x storage reduction catalyst. It can also be used alone as an exhaust gas purification catalyst for lean burn.
１：ハニカム基材 ２：第１金属領域 ３：第２金属領域
４：第３金属領域 ５：第４金属領域 ６：貴金属領域
1: Honeycomb substrate 2: First metal region 3: Second metal region 4: Third metal region 5: Fourth metal region 6: Noble metal region
Claims (3)
該ハニカム基材の一端部に形成されCoのみを担持した第１金属領域と、該第１金属領域に隣接しCoとCuを担持した第２金属領域と、該第１金属領域と反対側で該第２金属領域に隣接しCoとCuとZnを担持した第３金属領域と、該第２金属領域と反対側で該第３金属領域に隣接しCoとCuとZnとGaを担持した第４金属領域と、該第３金属領域と反対側の前記ハニカム基材の他端部で該第４金属領域に隣接しCoとCuとZnとGaと貴金属とを担持した第５金属領域と、を有することを特徴とする排ガス浄化用触媒。 A catalyst for exhaust gas purification comprising a honeycomb substrate and a coating layer formed on the honeycomb substrate, and the coating layer carries a catalyst metal selected from Ga, Zn, Cu, Co and a noble metal ,
A first metal region formed on one end of the honeycomb substrate and supporting only Co; a second metal region supporting Co and Cu adjacent to the first metal region; and a side opposite to the first metal region. A third metal region adjacent to the second metal region and supporting Co, Cu, and Zn; and a second metal region adjacent to the third metal region opposite to the second metal region and supporting Co, Cu, Zn, and Ga. A fifth metal region carrying Co, Cu, Zn, Ga, and a noble metal adjacent to the fourth metal region at the other end of the honeycomb substrate opposite to the third metal region; An exhaust gas purifying catalyst characterized by comprising:
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| JPH05146639A (en) * | 1991-11-27 | 1993-06-15 | Nippon Steel Corp | Catalytic reactor |
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| JPH06134258A (en) * | 1992-10-23 | 1994-05-17 | Hitachi Ltd | Denitration method and catalyst used therein |
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| JPH10156144A (en) * | 1996-10-04 | 1998-06-16 | Masakazu Iwamoto | Exhaust gas purifying catalyst |
| JPH10252455A (en) * | 1997-03-13 | 1998-09-22 | Nippon Soken Inc | Exhaust emission cleaning catalyst device and exhaust emission control method for internal combustion engine |
| JPH10272341A (en) * | 1997-03-28 | 1998-10-13 | Sekiyu Sangyo Kasseika Center | Removal of nitrogen oxides |
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- 2004-02-10 JP JP2004033961A patent/JP4529463B2/en not_active Expired - Fee Related
Patent Citations (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH0416239A (en) * | 1990-05-07 | 1992-01-21 | Mitsubishi Heavy Ind Ltd | Treatment of exhaust gas |
| JPH05237389A (en) * | 1990-09-25 | 1993-09-17 | Riken Corp | Purifier of exhaust gas and method for purification of exhaust gas |
| JPH05146639A (en) * | 1991-11-27 | 1993-06-15 | Nippon Steel Corp | Catalytic reactor |
| JPH06134258A (en) * | 1992-10-23 | 1994-05-17 | Hitachi Ltd | Denitration method and catalyst used therein |
| JPH07148438A (en) * | 1993-11-29 | 1995-06-13 | Riken Corp | Exhaust gas cleaning material and exhaust gas cleaning method |
| JPH09253453A (en) * | 1996-03-19 | 1997-09-30 | Nissan Motor Co Ltd | Cleaning of exhaust gas |
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| JPH10252455A (en) * | 1997-03-13 | 1998-09-22 | Nippon Soken Inc | Exhaust emission cleaning catalyst device and exhaust emission control method for internal combustion engine |
| JPH10272341A (en) * | 1997-03-28 | 1998-10-13 | Sekiyu Sangyo Kasseika Center | Removal of nitrogen oxides |
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