JP2004122122A - Exhaust gas purifying catalyst and exhaust gas purifying apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust gas purifying catalyst of which the NO<SB>x</SB>purifying capacity is not largely damaged by the effect of oxygen discharged in a rich state from by a ceria material. <P>SOLUTION: The exhaust gas purifying catalyst is provide with a carrier and a single catalyst layer covering the carrier. The single catalyst layer has an NO<SB>x</SB>absorbing material for absorbing NO<SB>x</SB>in an exhaust gas in the presence of oxygen while discharging NO<SB>x</SB>when the concentration of oxygen in the exhaust gas lowers and the ceria material containing a Ce-Zr type compound oxide being a ceria material of which the amount of support per 1L of the carrier is 80-280 g or the ceria material containing a Ce-Pr type compound oxide being a ceria material of which the amount of support per 1L of the carrier is 30-50 g. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to an exhaust gas purifying catalyst and an exhaust gas purifying device.

As an exhaust gas purifying catalyst provided in an exhaust passage of an engine, a catalyst having a NOx absorbent is widely known. The NOx absorbent absorbs NOx (nitrogen oxide) in the exhaust gas when the air-fuel ratio of the air-fuel mixture is in a lean state (in the presence of oxygen), while the oxygen concentration of the exhaust gas is reduced to a rich state. When this occurs, NOx is released for reduction purification.

By the way, such a NOx absorbent also has a property of easily absorbing sulfur compounds such as SOx (sulfur oxide) and H ₂ S contained in the exhaust gas together with NOx. The NOx absorbent has a problem that once the sulfur compound is absorbed, the NOx absorption performance is significantly reduced.

To solve the problem of poisoning by such sulfur compounds, Patent Document 1 discloses an exhaust gas provided with an exhaust gas purifying material in which a NOx absorbent is supported on a carrier and a means for changing the oxygen concentration of the exhaust gas. In a gas purifying apparatus, an exhaust gas purifying material includes a layer containing a NOx absorbent and sulfur that absorbs a sulfur compound in the exhaust gas in the presence of oxygen and releases the sulfur compound when the oxygen concentration in the exhaust gas decreases. There is disclosed a layer in which a layer containing a compound absorbent is provided in a layered manner such that the former is on the inside and the latter is on the outside, and a ceria material is used as the sulfur compound absorbent. According to this, it is described that a NOx absorbent that absorbs NOx in exhaust gas can be prevented from being poisoned by a sulfur compound in the exhaust gas.
JP-A-11-156159

The ceria material of the exhaust gas purifying material disclosed in Patent Document 1 has not only a sulfur compound absorbing ability but also an oxygen absorbing ability. When the air-fuel ratio is lean and the oxygen concentration of the exhaust gas is high, the ceria material absorbs oxygen and oxidizes NO in the exhaust gas to NO ₂ , thereby absorbing NOx into the NOx absorbent. On the other hand, when the air-fuel ratio is rich and the oxygen concentration of the exhaust gas is low, oxygen is released to activate HC in the exhaust gas by partial oxidation, and from the activated HC and the NOx absorbent, It has a function of promoting an oxidation-reduction reaction with the released NOx.

However, as described above, since the ceria material releases oxygen into the exhaust gas when it is in a rich state, if the amount of the ceria material carried in the catalyst is too large, the oxygen concentration of the exhaust gas in the rich state will be reduced. It becomes too high and the exhaust gas becomes an oxidizing atmosphere. Then, since HC and CO cause an oxidation-reduction reaction with O ₂ released from the ceria material, there is a problem that the oxidation-reduction reaction between HC and CO and NOx is suppressed, and the purification performance of NOx is lowered. In particular, in a diesel engine, a high purification performance by a catalyst cannot be obtained due to a relatively low exhaust gas temperature, and in combination with this, this problem is particularly remarkable.

The present invention has been made in view of such a point, and an object of the present invention is to provide an exhaust gas purifying catalyst and a catalyst for purifying exhaust gas in which the NOx purification performance is not significantly impaired by the influence of oxygen released from the ceria material in a rich state. An object of the present invention is to provide an exhaust gas purification device.

(4) The present inventors have found that the above objects can be achieved depending on the type of ceria material and its use, and have reached the present invention.

The invention according to claim 1 is a catalyst for purifying exhaust gas of a diesel engine comprising a carrier and a single catalyst layer covering the carrier,
The single catalyst layer,
A NOx absorber that absorbs NOx in the exhaust gas in the presence of oxygen while releasing the NOx when the oxygen concentration of the exhaust gas decreases;
A ceria material containing a Ce-Zr-based double oxide, and having a carrying amount per liter of the carrier of 80 g or more and 280 g or less;
It is characterized by having.

In the above configuration, a ceria material containing a Ce-Zr-based composite oxide is selected, and the amount of the ceria material is 80 g or more and 280 g or less per 1 L of the carrier. Even in a relatively low diesel engine, in a rich state, a high NOx purification rate can be exhibited without significantly impairing the NOx purification performance due to the influence of oxygen released from the ceria material.

The invention according to claim 2 is the exhaust gas purifying catalyst for a diesel engine according to claim 1,
The ceria material is characterized in that the supported amount per 1 L of the carrier is 110 g or more and 240 g or less.

(4) In the above configuration, the carried amount of the ceria material is 110 g or more and 240 g or less, so that the operation and effect of the invention according to claim 1 is more remarkably performed.

The invention according to claim 3 is the exhaust gas purifying catalyst for a diesel engine according to claim 1,
The ceria material is characterized in that CeO ₂ accounts for 50% by mass or more.

In the above configuration, CeO ₂ accounts for 50% by mass or more of the ceria material, so that the operation and effect of the invention according to claim 1 can be properly performed.

The invention according to claim 4 is an exhaust gas purifying catalyst comprising a carrier and a single catalyst layer covering the carrier,
The single catalyst layer,
A NOx absorber that absorbs NOx in the exhaust gas in the presence of oxygen while releasing the NOx when the oxygen concentration of the exhaust gas decreases;
A ceria material containing a Ce-Pr-based double oxide and having a supported amount per liter of the carrier of 30 g or more and 50 g or less;
It is characterized by having.

In the above configuration, a ceria material containing a Ce-Pr-based composite oxide is selected, and the supported amount is 30 g or more and 50 g or less per 1 L of the carrier. A high NOx purification rate is exhibited without significantly impairing the NOx purification performance due to the influence of oxygen released from the ceria material.

The invention according to claim 5 is an exhaust gas purifying apparatus provided with an exhaust gas purifying catalyst comprising a carrier and a single catalyst layer covering the carrier,
The single catalyst layer,
A NOx absorbent that absorbs NOx in the exhaust gas in the presence of oxygen while releasing the NOx when the oxygen concentration of the exhaust gas decreases;
A ceria material containing a Ce-Pr-based composite oxide, wherein the carrier amount per liter of the carrier is larger on the upstream side than on the downstream side in the flow direction of the exhaust gas;
It is characterized by having.

(4) The relationship between the NOx purification rate and the amount of ceria material carried in the rich state changes depending on the exhaust gas temperature. Specifically, when the temperature of the exhaust gas is high, the ceria material releases oxygen as described above, so that the NOx purification rate decreases as the carried amount of the ceria material increases. On the other hand, when the temperature of the exhaust gas is relatively low, the influence of oxygen released from the ceria material is small, and in a certain range, the NOx purification rate increases with an increase in the carried amount of the ceria material. Further, in a diesel engine, since catalytic activity cannot be obtained due to low exhaust gas temperature, the exhaust gas temperature is increased by burning HC upstream of the catalyst in the flow direction of the exhaust gas. For this reason, the temperature of the exhaust gas is higher when passing through the downstream side of the catalyst than when passing through the upstream side in the flow direction of the exhaust gas. In the above configuration, the amount of the ceria material carried is relatively large on the upstream side in the flow direction where the exhaust gas temperature is low, and relatively high on the downstream side in the flow direction where the exhaust gas temperature is high. In the rich state, the NOx purification performance is not significantly impaired by the effect of the oxygen released by the ceria material in the rich state, and as a result, a high NOx purification rate is exhibited as a whole. .

The invention according to claim 6 is the exhaust gas purifying apparatus according to claim 5,
The ceria material is characterized in that the carrying amount per 1 L of the carrier is 0 g or more and 120 g or less on the downstream side in the flow direction of the exhaust gas.

In the above configuration, the carried amount of the ceria material per 1 L of the carrier is 0 g or more and 120 g or less, and as shown in Examples later, when the exhaust gas temperature is high, a high NOx purification rate is exhibited. The operation and effect of the invention are properly performed.

The invention according to claim 7 is the exhaust gas purifying device according to claim 5,
The ceria material is characterized in that the carrying amount per 1 L of the carrier is 160 g or more and 240 g or less on the upstream side in the flow direction of the exhaust gas.

In the above configuration, the carried amount of the ceria material per 1 L of the carrier is 160 g or more and 240 g or less, and as described later in the examples, when the exhaust gas temperature is low, a high NOx purification rate is exhibited. The operation and effect of the invention are properly performed.

As described above, according to the present invention, by including an appropriate amount of ceria material, in a rich state, a high NOx purification rate can be achieved without significantly impairing the NOx purification performance due to the influence of oxygen released from the ceria material. Obtainable.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

<Overall configuration>
FIG. 1 shows a part of one cylinder of a multi-cylinder diesel engine 5 mounted on a vehicle.

In the engine 5, the fuel injection valve 7 directly injects and supplies the fuel to the combustion chamber 6, and the intake is performed through the intake passage 8 and the exhaust is performed through the exhaust passage 9, respectively. The exhaust gas purification device 1 is disposed in the exhaust passage 9. The exhaust gas purifying apparatus 1 is provided with an exhaust gas purifying catalyst in which a carrier carries a single catalyst layer containing a catalytic noble metal, a NOx absorbent, and a ceria material. In addition, an EGR (exhaust gas recirculation; the same applies hereinafter) passage 10 extends from the exhaust passage 9 upstream of the exhaust gas purification device 1 toward the intake passage 8, and an EGR valve 11 is provided in the EGR passage 10. ing. The fuel injection valve 7 and the EGR valve 11 are controlled by an ECU (exhaust control means) 12 according to the operating state of the engine and the like.

In this control, when the engine is operated at an air-fuel ratio lean (A / F = 18 to 80), an oxygen-excess atmosphere where the oxygen concentration of the exhaust gas is usually 4 to 5% to 20% is formed. The oxygen concentration of the exhaust gas is intermittently reduced to 2.0% or less, or 0.5% or less. In the oxygen concentration reduction control, the EGR rate is increased, the main fuel injection is performed near the top dead center of the compression stroke by the fuel injection valve 7, and then the post fuel injection is performed in the expansion stroke or the exhaust stroke. This reduces the oxygen concentration of the exhaust gas, increases the amount of HC in the exhaust gas, and reduces the amount of NOx absorbed by the NOx absorbent of the exhaust gas purifying catalyst when the air-fuel ratio is operated at a rich air-fuel ratio. This will encourage release from the NOx absorber.

That is, if the lean operation continues for a long time, the NOx absorption amount of the NOx absorbent of the exhaust gas purifying catalyst becomes saturated and the NOx purification performance is reduced. The operation is performed to increase the oxygen concentration of the exhaust gas, and the oxygen concentration reduction control is performed in the second period shorter than the first period. The high oxygen concentration state and the low oxygen concentration state are alternately repeated by the ECU 12. In this way, the emission of NOx is appropriately promoted.

<Exhaust gas purifier equipped with exhaust gas purifying catalyst A>
FIG. 2 shows an exhaust gas purifying apparatus 1 provided with an exhaust gas purifying catalyst A.

The exhaust gas purifying apparatus 1 has a cylindrical casing 16 on the upstream side formed with an inlet 18 communicating with the exhaust passage 9 of the engine 5 and an outlet 19 communicating with the muffler on the downstream side. In the casing 16, an exhaust gas purifying catalyst A17 is loaded. The exhaust gas purifying catalyst A17 can be divided into an upstream catalyst 17a and a downstream catalyst 17b at a position slightly downstream from the center in the longitudinal direction.

The exhaust gas purifying catalyst A17 has a single catalyst layer carried on the surface of a cordierite honeycomb monolithic carrier (400 cells per inch, wall thickness 6 mil separating adjacent cells). . The single catalyst layer contains Pt and Rh as catalytic noble metals, Ba, Mg, Sr and K, ceria material as NOx absorbent, alumina as a support material (supporting base material) thereof, and hydrated alumina as a binder. are doing.

Here, the ceria material refers to an oxide containing cerium. In the exhaust gas purifying catalyst A17, a catalyst containing a Ce-Zr-based double oxide as a ceria material is used. The supporting amount of the ceria material per 1 L of the carrier is 80 to 280 g, preferably 110 to 240 g. In the ceria material, CeO ₂ accounts for 50% by mass or more.

In the exhaust gas purifying catalyst A17, a ceria material containing a Ce-Zr-based double oxide is used, and the carried amount is 80 to 280 g (preferably 110 to 240 g) per liter of the carrier. Even in a diesel engine having a relatively low NOx, in a rich state, a high NOx purification rate can be exhibited without significantly impairing the NOx purification performance due to the effect of oxygen released from the ceria material.

  The exhaust gas purifying catalyst A17 according to this embodiment described above can be prepared as follows.

First, alumina, ceria material, and hydrated alumina are mixed at a predetermined weight ratio, and water and nitric acid for pH adjustment are added thereto to form a slurry.

(4) Next, the carrier is immersed in the slurry and pulled up. Excess slurry is removed by air blow, and then dried (150 ° C. for 2 hours) and fired (500 ° C. for 2 hours). This forms a porous layer on the carrier.

Next, the porous layer formed on the surface of the carrier is impregnated with a solution containing a catalytic noble metal and a NOx absorbent component, and dried and calcined again to form a single catalyst layer.

Then, the exhaust gas purifying catalyst A17 thus obtained is mounted in the casing 16 to constitute the exhaust gas purifying apparatus 1.

<Exhaust gas purifier equipped with exhaust gas purifying catalyst B>
The configuration of the exhaust gas purifying apparatus provided with the exhaust gas purifying catalyst B is the same as that provided with the exhaust gas purifying catalyst A, and thus will be described with reference to FIG.

The exhaust gas purifying apparatus 1 has a cylindrical casing 16 on the upstream side formed with an inlet 18 communicating with the exhaust passage 9 of the engine 5 and an outlet 19 communicating with the muffler on the downstream side. In the casing 16, an exhaust gas purifying catalyst B17 is loaded. The exhaust gas purifying catalyst B17 is divided into an upstream catalyst 17a and a downstream catalyst 17b at a position slightly downstream from the center in the longitudinal direction.

Each of the upstream catalyst 17a and the downstream catalyst 17b constituting the exhaust gas purifying catalyst B17 is a cordierite honeycomb monolith carrier (400 cells per inch, wall thickness 6 mil separating adjacent cells). A single catalyst layer is supported on the surface of the substrate. The single catalyst layer contains Pt and Rh as catalytic noble metals, Ba, Mg, Sr and K, ceria material as NOx absorbent, alumina as a support material (supporting base material) thereof, and hydrated alumina as a binder. are doing.

Here, in the exhaust gas purifying catalyst B17, a catalyst containing a Ce-Pr-based double oxide is used as the ceria material.

The amount of ceria material carried per liter of carrier is preferably 30 to 50 g. In this case, a ceria material containing a Ce-Pr-based double oxide is used, and the amount of the ceria material supported is 30 to 50 g per liter of the carrier. Therefore, in a rich state, the NOx purification performance is affected by the oxygen released from the ceria material. Presents a high NOx purification rate without being greatly impaired.

In addition, the amount of ceria material carried per liter of the carrier is such that the amount of the upstream catalyst 17a is large and the amount of the downstream catalyst 17b is small, that is, the amount is larger on the upstream side than on the downstream side in the flow direction of the exhaust gas. Good. The relationship between the NOx purification rate in a rich state and the carried amount of ceria material is such that when the exhaust gas temperature is high, the NOx purification rate decreases with an increase in the carried amount of ceria material, while the exhaust gas temperature When the temperature is extremely low, the influence of oxygen released from the ceria material is small, and within a certain range, the NOx purification rate increases with an increase in the carried amount of the ceria material. Further, in a diesel engine, since catalytic activity cannot be obtained due to low exhaust gas temperature, the exhaust gas temperature is increased by burning HC on the upstream side of the catalyst in the flow direction of the exhaust gas. Is higher when passing through the catalyst on the downstream side than on the upstream side in the flow direction of the exhaust gas. Therefore, in this case, the amount of ceria material carried is relatively large on the upstream side in the flow direction where the exhaust gas temperature is low, and relatively high on the downstream side in the flow direction where the exhaust gas temperature is high. Since the amount of material carried is small, the NOx purification performance is not significantly impaired by the influence of oxygen released from the ceria material on each of the upstream side and the downstream side in the rich state, and as a result, a high NOx purification rate as a whole is obtained. Present. Here, the amount of ceria material carried per liter of carrier in the upstream catalyst 17a is preferably 160 to 240 g. The amount of the ceria material carried per liter of the carrier in the downstream catalyst 17b is preferably 0 to 120 g.

  The exhaust gas purifying catalyst B17 according to the present embodiment described above can be prepared as follows.

First, alumina, ceria material, and hydrated alumina are mixed at a predetermined weight ratio, and water and nitric acid for pH adjustment are added thereto to form a slurry. When changing the amount of ceria loaded on the upstream catalyst 17a and the downstream catalyst 17b, two types of slurries are prepared for each.

(4) Next, the carrier is immersed in the slurry and pulled up. Excess slurry is removed by air blow, and then dried (150 ° C. for 2 hours) and fired (500 ° C. for 2 hours). This forms a porous layer on the carrier. When changing the amount of ceria material carried by the upstream catalyst 17a and the downstream catalyst 17b, the carrier for the upstream catalyst is changed to a slurry having a high ceria material concentration, and the carrier for the downstream catalyst is changed to a slurry having a low ceria material concentration. Immerse and pull up.

Next, the porous layer formed on the surface of the carrier is impregnated with a solution containing a catalytic noble metal and a NOx absorbent component, and dried and calcined again to form a single catalyst layer.

Then, the exhaust gas purifying catalyst B17 thus obtained is mounted in the casing 16 to configure the exhaust gas purifying apparatus 1.

In the above embodiment, the upstream catalyst 17a and the downstream catalyst 17b are housed in one casing 16, but the present invention is not limited to this. The upstream catalyst 17a and the downstream catalyst 17b are respectively They may be housed in separate casings and arranged in series in the exhaust passage 9.

An exhaust gas purifying catalyst in which a carrier is coated with a single catalyst layer, which contains a Ce-Pr-based composite oxide or a Ce-Zr-based composite oxide as a ceria material, the NOx purification rate in a rich state and A test evaluation was conducted to examine the relationship between the amount of ceria material and the amount of ceria carried.

(Test evaluation 1)
<Catalyst for test evaluation>
An exhaust gas purifying catalyst having the same configuration as the exhaust gas purifying catalyst B of the above embodiment using a Ce-Pr-based double oxide as a ceria material was prepared. Table 1 shows the supported amounts of Al ₂ O ₃ as a binder and Ce-Pr-based double oxide as a ceria material in each exhaust gas purifying catalyst.

　また、触媒貴金属及びＮＯｘ吸収材の担持量は以下の通りとした。

The supported amounts of the catalytic noble metal and the NOx absorbent were as follows.

Noble metal catalyst: Pt = 3.5 g / L, Rh = 0.3 g / L
NOx absorbent: Ba = 30 g / L, Mg = 10 g / L, Sr = 10 g / L
K = 6g / L
Here, (g / L) indicates the amount of the catalyst carried per liter of the carrier.

<Test evaluation method>
The respective exhaust gas purifying catalysts were subjected to an aging treatment at 900 ° C. for 24 hours in an air atmosphere.

Then, the aging-treated exhaust gas purifying catalyst is attached to a fixed bed flow type reaction evaluation apparatus, and lean simulated exhaust gas (gas composition A) is flowed for 60 seconds. After repeating a cycle of switching to the composition B) and flowing the same for 60 seconds five times or more, the NOx purification rate (rich NOx purification rate) was measured for 60 seconds from the time when the gas composition was switched to rich. The gas compositions A and B were as shown in Table 2. The test evaluation was performed for each of the simulated exhaust gas temperatures at the catalyst inlet of 300 ° C., 350 ° C., 400 ° C., and 450 ° C.

　＜試験評価結果＞
　図３は、各排気ガス温度におけるＣｅ−Ｐｒ系複酸化物の担持量とＮＯｘ浄化率との関係を示す。

<Test evaluation results>
FIG. 3 shows the relationship between the amount of Ce-Pr-based composite oxide carried and the NOx purification rate at each exhaust gas temperature.

According to FIG. 3, when the exhaust gas temperature is T = 450 ° C., the NOx purification rate gradually decreases with an increase in the supported amount when the supported amount of the Ce—Pr-based double oxide is 0 to 120 g / L. , And over 120 g / L, it can be seen that it is 40-50% at 240-320 g / L. Therefore, at this temperature, the supported amount of the Ce-Pr-based double oxide is preferably set to 120 g / L or less.

When the exhaust gas temperature is T = 400 ° C., the NOx purification rate slightly increases with an increase in the supported amount of the Ce—Pr-based composite oxide when the supported amount is 0 to 40 g / L, and substantially increases when the supported amount is 40 to 120 g / L. It can be seen that it is constant, and when it exceeds 120 g / L, it decreases sharply with an increase in the supported amount, and it becomes 60 to 70% at 240 to 320 g / L. Therefore, at this temperature, the supported amount of the Ce-Pr-based composite oxide is preferably set to 40 to 120 g / L.

When the exhaust gas temperature is T = 350 ° C., the NOx purification rate gradually increases with an increase in the carried amount of the Ce—Pr-based double oxide when the carried amount is 0 to 160 g / L, and is about 20 g / L. It can be seen that although the L exceeds 90%, it gradually decreases to less than 90% at 240 to 320 g / L exceeding 120 g / L. At this temperature, a NOx purification rate of 90% or more can be obtained by setting the supported amount of the Ce-Pr-based double oxide to 20 to 240 g / L. In addition, when the carried amount is 20 g / L or more, there is no significant difference in the NOx purification rate. Therefore, when the carried amount is, for example, 20 to 50 g / L, a high NOx purification rate can be obtained with a small amount of ceria material.

When the exhaust gas temperature is T = 300 ° C., the NOx purification rate gradually increases with an increase in the carried amount of the Ce—Pr-based double oxide when the carried amount is 0 to 240 g / L, and is about 30 g / L. It can be seen that although the ratio exceeds 90% for L, it gradually decreases to slightly less than 90% for 240 to 320 g / L. At this temperature, a NOx purification rate of 90% or more can be obtained by setting the supported amount of the Ce-Pr-based double oxide to 30 to 240 g / L. Further, when the carried amount is 30 g / L or more, there is no significant difference in the NOx purification rate. Therefore, when the carried amount is, for example, 30 to 50 g / L, a high NOx purification rate can be obtained with a small amount of ceria material. On the other hand, if the carried amount is, for example, 160 to 240 g / L, the highest NOx purification rate can be obtained.

From the above results, for example, when the present invention is applied to a gasoline-powered vehicle or a general diesel engine-powered exhaust gas purifying catalyst which is expected to perform low-power driving such as running in an urban area, the temperature of the exhaust gas is determined at the inlet of the catalyst. Since the temperature is about 350 ° C. and the temperature on the downstream side of the catalyst is about 300 ° C., both of them are Ce-Pr-based composites so that the NOx purification rates are increased in both the upstream catalyst and the downstream catalyst. The loading amount of the oxide may be 30 to 240 g / L, and if the loading amount of the ceria material is reduced, it may be 30 to 50 g / L.

Further, in a diesel engine vehicle, when HC is burned on the upstream side in the exhaust gas flow direction to increase the exhaust gas temperature to increase the catalytic activity, the exhaust gas temperature is determined by the flow rate of the exhaust gas in the catalyst. It is higher when passing on the downstream side than when passing on the upstream side in the direction. For example, assuming that the exhaust gas temperature is about 300 ° C. at the catalyst inlet temperature and the downstream temperature of the catalyst is about 450 ° C., the NOx purification rate at 300 ° C. in the upstream catalyst is increased. The loading amount of the Ce-Pr-based composite oxide is set to 160 to 240 g / L, and the loading amount of the Ce-Pr-based composite oxide is set to 0 to 120 g so that the NOx purification rate at 450 ° C. in the downstream catalyst is increased. / L.

(Test evaluation 2)
<Catalyst for test evaluation>
An exhaust gas purifying catalyst having the same configuration as the exhaust gas purifying catalyst A of the above embodiment using a Ce—Zr-based double oxide as a ceria material was prepared. Table 3 shows the carrying amounts of Al ₂ O ₃ as a binder and Ce-Zr-based double oxide as a ceria material in each exhaust gas purifying catalyst. In the ceria material, the Ce-Zr-based composite oxide contains Sr,
CeO ₂ : ZrO ₂ : SrO ₂ = 73: 26: 1 (% by mass).

　また、触媒貴金属及びＮＯｘ吸収材の担持量は以下の通りとした。

The supported amounts of the catalytic noble metal and the NOx absorbent were as follows.

Noble metal catalyst: Pt = 3.5 g / L, Rh = 0.3 g / L
NOx absorbent: Ba = 30 g / L, Mg = 10 g / L, Sr = 10 g / L
K = 6g / L
<Test evaluation method>
The NOx purification rate of each exhaust gas purification catalyst was measured by the same method as in Test Evaluation 1. The test evaluation was performed for each of the simulated exhaust gas temperatures at the catalyst inlet at 300 ° C., 350 ° C., 400 ° C. and 450 ° C.

<Test evaluation results>
FIG. 4 shows the relationship between the amount of Ce-Zr-based mixed oxide carried and the NOx purification rate at each exhaust gas temperature.

According to FIG. 4, when the exhaust gas temperature is T = 450 ° C., the NOx purification rate decreases with an increase in the amount of the supported Ce—Zr-based double oxide.

も It can be seen that even when the exhaust gas temperature is T = 400 ° C., the NOx purification rate decreases with an increase in the amount of Ce—Zr-based double oxide carried.

When the exhaust gas temperature is T = 350 ° C., the NOx purification rate gradually increases with an increase in the carried amount of the Ce—Zr-based double oxide when the carried amount is 0 to 160 g / L, and is about 20 g / L. L exceeds 90%, and is certainly 90% or more at 80 g / L, and gradually decreases at 160 to 240 g / L, but is a high level in the range of 110 to 240 g / L as a whole, and is 240 g / L. It can be seen that when the amount exceeds 240 g / L, the amount greatly decreases, and when the amount exceeds 260 g / L, the amount falls below 90%.
You can see that

When the exhaust gas temperature is T = 300 ° C., the NOx purification rate gradually increases with an increase in the carried amount of the Ce—Zr-based double oxide when the carried amount is 0 to 160 g / L, and is about 40 g / L. L is more than 90%, is definitely 90% or more at 80 g / L, is almost constant at 160 to 240 g / L, and is a high level in the range of 110 to 240 g / L as a whole, and is 240 g / L. It can be seen that when the amount exceeds 240 g / L, the amount greatly decreases, and when the amount exceeds 280 g / L, the amount falls below 90%.

From the above results, when the present invention is applied to an exhaust gas purifying catalyst for a diesel engine vehicle in which the exhaust gas temperature is about 300 to 350 ° C., the NOx purification rate is high for both the upstream catalyst and the downstream catalyst. In any case, the supported amount of the Ce-Zr-based double oxide may be 80 to 280 g / L, and more preferably 110 to 240 g / L.

As described above, the present invention is useful for an exhaust gas purifying catalyst and an exhaust gas purifying apparatus.

1 is an overall configuration diagram of an exhaust gas purification device for an engine according to an embodiment of the present invention. It is a sectional view of an exhaust gas purification device concerning an embodiment. It is a graph which shows the relationship between the carrying amount of Ce-Pr-based double oxide and the NOx purification rate at each exhaust gas temperature. 5 is a graph showing the relationship between the amount of Ce-Zr-based mixed oxide carried and the NOx purification rate at each exhaust gas temperature.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 Exhaust gas purification apparatus 7 Fuel injection valve 13 Exhaust passage 14 Exhaust gas purification apparatus 17 Exhaust gas purification catalyst 17a Upstream catalyst 17b Downstream catalyst

Claims (7)

A catalyst for purifying exhaust gas of a diesel engine, comprising a carrier and a single catalyst layer covering the carrier,
The single catalyst layer,
A NOx absorbent that absorbs NOx in the exhaust gas in the presence of oxygen while releasing the NOx when the oxygen concentration of the exhaust gas decreases;
A ceria material containing a Ce-Zr-based composite oxide, wherein the supported amount per 1 L of the carrier is 80 to 280 g;
An exhaust gas purifying catalyst comprising: The exhaust gas purifying catalyst for a diesel engine according to claim 1,
The catalyst for purifying exhaust gas of a diesel engine, wherein the ceria material has a loading amount of 110 to 240 g per 1 L of the carrier. The exhaust gas purifying catalyst for a diesel engine according to claim 1,
The ceria material is a catalyst for purifying exhaust gas of a diesel engine, wherein CeO ₂ accounts for 50% by mass or more. A carrier, a catalyst for exhaust gas purification comprising a single catalyst layer covering the carrier,
The single catalyst layer,
A NOx absorbent that absorbs NOx in the exhaust gas in the presence of oxygen while releasing the NOx when the oxygen concentration of the exhaust gas decreases;
A ceria material containing a Ce-Pr-based double oxide and having a loading of 30 to 50 g per liter of the carrier,
An exhaust gas purifying catalyst comprising: A carrier, a single catalyst layer covering the carrier, an exhaust gas purifying device including an exhaust gas purifying catalyst comprising:
The single catalyst layer,
A NOx absorbent that absorbs NOx in the exhaust gas in the presence of oxygen while releasing the NOx when the oxygen concentration of the exhaust gas decreases;
A ceria material containing a Ce-Pr-based composite oxide, wherein the carrier amount per liter of the carrier is larger on the upstream side than on the downstream side in the flow direction of the exhaust gas;
An exhaust gas purification apparatus comprising: The exhaust gas purifying apparatus according to claim 5,
The exhaust gas purifying apparatus, wherein the ceria material has a carrying amount of 1 to 120 g per 1 L of the carrier on a downstream side in a flow direction of the exhaust gas. The exhaust gas purifying apparatus according to claim 5,
The exhaust gas purifying apparatus, wherein the ceria material has a carrying amount of 160 to 240 g per 1 L of the carrier on an upstream side in a flow direction of the exhaust gas.

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