JP2017070901A - Exhaust gas purification catalyst and production method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust gas purification catalyst having excellent NOx adsorption performance under a cold condition, and also having excellent heat resistance in a low oxygen concentration atmosphere.SOLUTION: There is provided a NOx catalyst 12 provided in an exhaust pipe 3 of an engine 2, for purifying NOx in exhaust gas. The NOx catalyst 12 comprises a carrier comprising zeolite, Pd carried on the carrier, and at least one kind of additive element carried on the carrier and selected from a group comprising Ce, Pr, Sr, Ba and La.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an exhaust purification catalyst and a manufacturing method thereof.

  Conventionally, nitrogen oxides (hereinafter referred to as “NOx”), hydrocarbons (hereinafter referred to as “HC”), and carbon monoxide (hereinafter referred to as “CO”) contained in exhaust gas discharged from an internal combustion engine. In order to purify the exhaust gas, an exhaust gas purification catalyst is provided in the exhaust system of the internal combustion engine. In recent years, in particular, emission regulations for harmful substances have become more stringent, and exhaust gas can be efficiently purified under low temperature conditions such as cold start (hereinafter referred to as “cold start”) of internal combustion engines, which has been a problem in the past. There is a need to develop an exhaust purification catalyst that can be used.

  Therefore, for example, a cold start catalyst including a base metal such as iron, copper, manganese, chromium, cobalt, nickel, tin, a noble metal such as platinum, palladium, rhodium, and zeolite has been proposed (for example, Patent Document 1). reference). According to this catalyst, NOx and HC in the exhaust can be efficiently adsorbed and purified at the cold start.

Special table 2014-519975 gazette

  However, although the catalyst of Patent Document 1 has excellent NOx adsorption performance under low temperature conditions, there is a problem in that NOx adsorption performance is significantly reduced when exposed to high-temperature exhaust gas in a stoichiometric or rich low oxygen concentration atmosphere. there were.

  Furthermore, even if the NOx adsorption performance can be secured, if the NOx desorption temperature is too low, the temperature required for the NOx purification reaction will not be reached, so the NOx purification reaction does not occur and NOx is not purified and discharged. There is a problem that will be done. Further, when the NOx desorption temperature is too high, there is a problem that fuel consumption loss such as temperature increase control occurs.

  The present invention has been made in view of the above, and an object thereof is to have excellent NOx adsorption performance under low temperature conditions, excellent heat resistance in a low oxygen concentration atmosphere, and NOx desorption temperature. An object of the present invention is to provide an exhaust purification catalyst that can be adjusted and can appropriately set the NOx desorption temperature.

  (1) To achieve the above object, the present invention provides an exhaust purification catalyst (for example, an exhaust pipe 3 to be described later) of an internal combustion engine (for example, an engine 2 to be described later) that purifies NOx in the exhaust. For example, a NOx catalyst 12) described later, which is a support made of zeolite, Pd supported on the support, and supported on the support and made of Ce, Pr, Sr, Ba, La, Ga, In, and Mn. An exhaust purification catalyst comprising at least one additive element selected from the group is provided.

Here, usually, zeolite has a characteristic of adsorbing NOx supplied as NO ₂ in its pores. Therefore, in order to mainly convert NO constituting NOx in the exhaust gas into NO ₂ , an active species such as Pt is required in a high oxygen concentration and high temperature atmosphere with the exhaust gas being lean. However, under low-temperature conditions such as a warm-up state of the internal combustion engine, the air-fuel ratio of the air-fuel mixture is controlled stoichiometrically or richly for the purpose of stabilizing combustion and raising the temperature of the exhaust purification catalyst. Therefore, the oxygen concentration and reaction temperature for oxidizing NO to NO ₂ are insufficient, and water molecules that inhibit NOx adsorption on zeolite are contained in the exhaust gas, so NOx cannot be adsorbed efficiently.

In contrast, according to the exhaust purification catalyst of the present invention, excellent NOx adsorption performance can be obtained under low temperature conditions by supporting Pd on a support made of zeolite. That is, in the exhaust purification catalyst according to the present invention, Pd is disposed in the vicinity of Al, which is an acid point, among Al, Si and O constituting the zeolite. Thereby, the electronic state of Pd changes due to the interaction with Al, and exists as divalent Pd ²⁺ . This divalent Pd ²⁺ has a characteristic of adsorbing NO as it is. Therefore, according to the exhaust purification catalyst of the present invention, it is difficult to be affected by moisture adsorption, and it is not necessary to oxidize NO to NO ₂ , so that the exhaust gas is excellent even under low temperature conditions where the exhaust is stoichiometric or rich. NOx adsorption performance can be obtained.

In addition, divalent Pd ²⁺ on zeolite, which is a site that adsorbs NOx, is reduced to zero-valent Pd ⁰ when exposed to high temperature in a low oxygen concentration atmosphere. Then, the interaction between zeolite and Pd is weakened, and Pd moves and aggregates, so that the dispersibility of Pd deteriorates. Therefore, since the Pd particles cannot be maintained in a fine particle state, the surface area does not increase even if the loading amount is increased, and the NOx adsorption performance corresponding to the loading amount cannot be obtained. Further, when the loading amount is not increased, the NOx adsorption sites are reduced, and the NOx adsorption performance is lowered.

In contrast, according to the exhaust purification catalyst of the present invention, in addition to Pd, at least one additive element selected from the group consisting of Ce, Pr, Sr, Ba, La, Ga, In, and Mn is added to the zeolite. By co-supporting with, heat resistance in a low oxygen concentration atmosphere can be improved. That is, at least one additive element selected from the group consisting of Ce, Pr, Sr, Ba, La, Ga, In, and Mn is interposed between Pd, so that divalent Pd ²⁺ is zero-valent. While being able to suppress reduction to Pd ⁰ , it is possible to suppress the movement and aggregation of Pd, and thus it is possible to suppress the deterioration of the dispersibility of Pd. As a result, excellent NOx adsorption performance can be maintained, and heat resistance in a low oxygen concentration atmosphere can be improved. In addition, since the movement and aggregation of Pd can be suppressed, the state in which Pd is finely divided can be maintained even if the amount of Pd supported is increased, so that the NOx adsorption performance can be enhanced by increasing the amount of Pd supported. Become.

  Furthermore, according to the exhaust purification catalyst of the present invention, in addition to Pd, at least one additive element selected from the group consisting of Ce, Pr, Sr, Ba, La, Ga, In, and Mn is shared with the zeolite. By carrying it, the NOx desorption temperature can be adjusted. That is, if the NOx desorption temperature is too low, the NOx purification reaction does not occur and the adsorbed NOx is released to the outside. If the NOx desorption temperature is too high, the NOx at the next start after NOx desorption is present. Although there is a problem that fuel consumption loss such as temperature rise control to secure the adsorption amount occurs, the NOx desorption temperature can be adjusted appropriately by adjusting the NOx desorption temperature, and the above problems are prevented. it can.

  (2) It is preferable that the additional element is Ce, and the content of Ce with respect to the entire exhaust purification catalyst is 0.1 to 13% by mass.

  In the present invention, Ce is supported on zeolite in addition to Pd, and the Ce content with respect to the entire exhaust purification catalyst is set to 0.1 to 13% by mass. If the content of Ce is within this range, the effect of the invention of (1) can be obtained more reliably, and the content of Ce is too much, and the dispersibility of Pd is not inhibited.

  (3) The additive element is Pr, and the content of Pr with respect to the entire exhaust purification catalyst is preferably 0.05 to 0.4 mass%.

  In the present invention, Pr is supported on zeolite in addition to Pd, and the content of Pr with respect to the entire exhaust purification catalyst is set to 0.05 to 0.4 mass%. If the content of Pr is within this range, the effect of the invention of (1) can be obtained more reliably, and the content of Pr is too large and does not inhibit the dispersibility of Pd.

  (4) The additive element is Sr, and the content of Sr with respect to the entire exhaust purification catalyst is preferably 0.05 to 0.03% by mass.

  In this invention, in addition to Pd, Sr is supported on zeolite, and the Sr content with respect to the entire exhaust purification catalyst is set to 0.05 to 0.03% by mass. If the content of Sr is within this range, the effect of the invention of (1) can be obtained more reliably, and the content of Sr is too much to inhibit the dispersibility of Pd.

  (5) The additive element is Ba, and the content of Ba with respect to the entire exhaust purification catalyst is preferably 0.01 to 0.5 mass%.

  In the present invention, Ba is supported on zeolite in addition to Pd, and the content of Ba with respect to the entire exhaust purification catalyst is set to 0.01 to 0.5 mass%. If the content of Ba is within this range, the effect of the invention of (1) can be obtained more reliably, and the content of Ba will not be too high to inhibit the dispersibility of Pd.

  (6) It is preferable that the said additional element is La and content of La with respect to the said exhaust purification catalyst whole is 0.01-4.1 mass%.

  In the present invention, La is supported on zeolite in addition to Pd, and the content of La in the entire exhaust purification catalyst is set to 0.01 to 4.1 mass%. If the content of La is within this range, the effect of the invention of (1) can be obtained more reliably, and the content of La will not be too high to inhibit the dispersibility of Pd.

  (7) It is preferable that the said additional element is Ga and content of Ga with respect to the said whole exhaust gas purification catalyst is 0.01-2 mass%.

  In this invention, in addition to Pd, Ga is supported on the zeolite, and the Ga content with respect to the entire exhaust purification catalyst is set to 0.01 to 2% by mass. If the Ga content is within this range, the effect of the invention of (1) can be obtained more reliably, and the Ga content is too large to inhibit the dispersibility of Pd.

  (8) The additive element is In, and the content of In with respect to the entire exhaust purification catalyst is preferably 0.04 to 1% by mass.

  In this invention, in addition to Pd, In is supported on zeolite, and the content of In with respect to the entire exhaust purification catalyst is set to 0.04 to 1% by mass. If the content of In is within this range, the effect of the invention of (1) can be obtained more reliably, and the content of In is too large to inhibit the dispersibility of Pd.

  (9) It is preferable that the said additional element is Mn and content of Mn with respect to the said whole exhaust gas purification catalyst is 0.01-0.26 mass%.

  In the present invention, Mn is supported on zeolite in addition to Pd, and the Mn content with respect to the entire exhaust purification catalyst is set to 0.01 to 0.26 mass%. If the content of Mn is within this range, the effect of the invention of (1) can be obtained more reliably, and the content of Mn is too much to inhibit the dispersibility of Pd.

  (10) A method for producing an exhaust purification catalyst according to (1) to (9), wherein a catalyst powder prepared using zeolite, a Pd compound containing Pd, and an additive element compound containing the additive element is used. Baked at 750 to 950 ° C., a catalyst powder firing step for firing at 500 to 700 ° C., and a support coated with a slurry prepared using the catalyst powder fired in the catalyst powder firing step And a process for producing an exhaust purification catalyst comprising the steps.

According to the method for producing an exhaust purification catalyst according to the present invention, the heat resistance in a low oxygen concentration atmosphere can be further improved by providing a catalyst powder firing step of firing the catalyst powder at 500 to 700 ° C.
Moreover, according to the method for producing an exhaust purification catalyst according to the present invention, the support coated with the slurry prepared using the catalyst powder calcined in the catalyst powder calcining step is more than the calcining temperature in the catalyst powder calcining step. By providing the support baking process which bakes at high 750-950 degreeC, the dispersibility of Pd can be improved more and the NOx adsorption | suction performance in low temperature conditions can be improved more.

  According to the present invention, it has excellent NOx adsorption performance under low temperature conditions, has excellent heat resistance in a low oxygen concentration atmosphere, and the NOx desorption temperature can be adjusted, so that the NOx desorption temperature is appropriate. An exhaust purification catalyst that can be set to 1 can be provided.

It is a figure which shows the exhaust gas purification apparatus of an internal combustion engine provided with the NOx catalyst which concerns on one Embodiment of this invention. It is a figure which shows the adsorption | suction and desorption behavior of NOx in the NOx catalyst which concerns on the said embodiment. It is a figure which shows the relationship between Ba addition amount and Pd particle diameter in the NOx catalyst which concerns on the said embodiment, and the relationship between Pd particle diameter and NO adsorption amount. It is a figure which shows the relationship between the catalyst powder baking temperature of the NOx catalyst which concerns on the said embodiment, and the NOx adsorption amount after aging. It is a figure which shows the relationship between the support body baking temperature of the NOx catalyst which concerns on the said embodiment, and the NOx adsorption amount in an initial state. It is a figure which shows the NOx adsorption amount of the NOx catalyst which concerns on Examples 1-8 and the comparative example 1. FIG. FIG. 3 is a graph showing NOx desorption temperatures of NOx catalysts according to Example 1 and Comparative Example 2. 6 is a graph showing NOx desorption temperatures of NOx catalysts according to Example 2 and Comparative Example 2. FIG. 6 is a graph showing NOx desorption temperatures of NOx catalysts according to Example 3 and Comparative Example 2. FIG. 6 is a graph showing NOx desorption temperatures of NOx catalysts according to Example 4 and Comparative Example 2. FIG. 6 is a graph showing NOx desorption temperatures of NOx catalysts according to Example 5 and Comparative Example 2. FIG. 6 is a graph showing NOx desorption temperatures of NOx catalysts according to Example 6 and Comparative Example 2. FIG. 6 is a graph showing NOx desorption temperatures of NOx catalysts according to Example 7 and Comparative Example 2. FIG. 6 is a graph showing NOx desorption temperatures of NOx catalysts according to Example 8 and Comparative Example 2. FIG. It is a figure which shows the relationship between the added element amount of NOx catalyst and NOx adsorption amount concerning Examples 1-1 to 1-5 and Comparative Examples 1-1 to 1-5. It is a figure which shows the relationship between the addition element amount and NOx adsorption amount of the NOx catalyst which concern on Examples 2-1 to 2-2 and Comparative Examples 1-1 to 1-5. It is a figure which shows the relationship between the addition element amount and NOx adsorption amount of the NOx catalyst which concern on Examples 3-1 to 3-2 and Comparative Examples 1-1 to 1-5. It is a figure which shows the relationship between the addition element amount and NOx adsorption amount of the NOx catalyst which concern on Examples 4-1 to 4-4 and Comparative Examples 1-1 to 1-5. It is a figure which shows the relationship between the addition element amount and NOx adsorption amount of the NOx catalyst which concern on Examples 5-1 to 5-3 and Comparative Examples 1-1 to 1-5. It is a figure which shows the relationship between the additive element amount and NOx adsorption amount of the NOx catalyst which concern on Examples 6-1 to 6-4 and Comparative Examples 1-1 to 1-5. It is a figure which shows the relationship between the additive element amount and NOx adsorption amount of the NOx catalyst which concern on Examples 7-1 to 7-4 and Comparative Examples 1-1 to 1-5. It is a figure which shows the relationship between the addition element amount and NOx adsorption amount of the NOx catalyst which concern on Examples 8-1 to 8-4 and Comparative Examples 1-1 to 1-5.

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

  FIG. 1 is a diagram showing an exhaust purification device 1 for an internal combustion engine 2 including a NOx catalyst according to an embodiment of the present invention. The internal combustion engine (hereinafter referred to as “engine”) 2 is, for example, a four-cylinder gasoline engine mounted on a vehicle (not shown). Exhaust gas generated by the combustion of the air-fuel mixture by the engine 2 is discharged to an exhaust pipe 3 described later.

  The exhaust pipe 3 is provided with an exhaust purification device 1 for purifying exhaust. The exhaust purification device 1 includes a three-way catalyst (hereinafter referred to as “TWC”) 11 provided in the exhaust pipe 3 and a NOx catalyst 12 provided in the exhaust pipe 3 on the downstream side thereof. The TWC 11 is a conventionally known TWC supported on a honeycomb support, and purifies exhaust in a stoichiometric atmosphere by oxidation of HC and CO and reduction of NOx when the temperature is higher than the activation temperature.

  The NOx catalyst 12 mainly adsorbs and purifies NOx that has not been purified by the TWC 11 under low temperature conditions such as during cold start. The NOx catalyst 12 is supported on a conventionally known honeycomb support made of, for example, cordierite. The NOx catalyst 12 is at least one selected from the group consisting of a support made of zeolite, Pd supported on the zeolite, and supported on the zeolite and made of Ce, Pr, Sr, Ba, La, Ga, In and Mn. And an additive element.

  The zeolite of the present embodiment has a characteristic that HC contained in the exhaust gas in a stoichiometric or rich atmosphere is taken in and adsorbed in the pores under low temperature conditions, and the adsorbed HC is desorbed under high temperature conditions. Have. The HC desorption temperature at which HC desorption starts is substantially equal to the NOx desorption temperature at which NOx begins to desorb from Pd described later.

  Zeolite includes ZSM-5, ferrierite, mordenite, Y-type zeolite, beta-type zeolite, CHA-type zeolite, and SAPO-34. In the present embodiment, any of these may be used alone, or a plurality of them may be used in combination. By supporting Pd and additive elements described later on these zeolites, excellent NOx adsorption performance is exhibited.

Here, usually, zeolite has a characteristic of adsorbing NOx supplied as NO ₂ in its pores. Therefore, in order to mainly convert NO constituting NOx in the exhaust gas into NO ₂ , an active species such as Pt is required in a high oxygen concentration and high temperature atmosphere with the exhaust gas being lean. However, under low-temperature conditions such as a warm-up state of the engine, the air-fuel ratio of the air-fuel mixture is controlled stoichiometrically or richly for the purpose of stabilizing combustion and raising the temperature of the exhaust purification catalyst. Therefore, the oxygen concentration and reaction temperature for oxidizing NO to NO ₂ are insufficient, and water molecules that inhibit NOx adsorption on zeolite are contained in the exhaust gas, so NOx cannot be adsorbed efficiently.

On the other hand, in the NOx catalyst 12 of this embodiment, Pd is supported on the support zeolite in a well dispersed state by the action of the additive element described later. Pd is arranged in the vicinity of Al, which is an acid point, among Al, Si and O constituting the zeolite. Thereby, the electronic state of Pd changes due to the interaction with Al, and exists as divalent Pd ²⁺ . Unlike the conventional NOx adsorption of zeolite, this divalent Pd ²⁺ has a characteristic of adsorbing NO as it is without oxidizing NO to NO ₂ . As a result, the NOx catalyst 12 of the present embodiment is not easily affected by moisture in the exhaust gas, and exhibits excellent NOx adsorption performance even under low temperature conditions where the exhaust gas is stoichiometric or rich.

  The content of Pd with respect to the entire NOx catalyst 12 is preferably 0.01 to 10% by mass. If the content of Pd is within this range, excellent NOx adsorption performance can be obtained. A more preferable content is 0.1 to 3% by mass.

As the additive element, any of the above-listed elements may be used alone or in combination. These additive elements are co-supported with zeolite together with Pd, and are interposed between Pd. Here, divalent Pd ²⁺ has a characteristic of being reduced to zero-valent Pd ⁰ when exposed to high temperature in a low oxygen concentration atmosphere. In this embodiment, these additional elements are interposed between Pd. , Reduction to Pd ⁰ is suppressed. As a result, strong interaction between divalent Pd ²⁺ and zeolite is maintained, and Pd migration and aggregation are suppressed. As a result, good dispersibility of Pd is ensured, and Pd is in a finely divided state. Can be maintained. In addition, since Pd can maintain a finely divided state even when the loading amount is increased, it is possible to increase the loading amount and enhance NOx adsorption performance.

Here, FIG. 2 is a diagram showing NOx adsorption / desorption behavior in the NOx catalyst 12 according to the present embodiment. FIG. 2 shows that the NOx catalyst 12 according to the present embodiment introduces exhaust under the following adsorption conditions to adsorb NOx, and then introduces exhaust under the following desorption conditions to desorb NOx. In this case, the temperature of the exhaust gas flowing into the NOx catalyst 12 and the NOx concentration in the exhaust gas flowing out from the NOx catalyst are shown.
In FIG. 2, the horizontal axis represents time (seconds), and the right vertical axis represents the pre-catalyst temperature, that is, the temperature of the exhaust gas flowing into the NOx catalyst 12. Further, the left vertical axis indicates the NOx concentration (ppm) in the exhaust gas flowing out from the NOx catalyst 12.

[Adsorption conditions]
Exhaust composition: NO = 100 ppm, O ₂ = 10%, N ₂ balance gas exhaust flow rate: 20 L / min Exhaust temperature: 50 ° C.
[Desorption conditions]
Exhaust composition: O ₂ = 10%, N ₂ balance gas exhaust flow rate: 20 L / min Exhaust temperature: Temperature rise from 50 ° C. to 500 ° C. at 20 ° C./min

  As shown in FIG. 2, according to the adsorption conditions, first, immediately after starting to introduce exhaust gas having a low exhaust temperature of 50 ° C. and containing 100 ppm of NO into the NOx catalyst 12, the NOx in the exhaust gas flowing out from the NOx catalyst 12. The concentration is approximately 0 ppm. This means that almost all NOx (NO) contained in the exhaust gas flowing into the NOx catalyst 12 is adsorbed by the NOx catalyst 12. From this result, it can be seen that the NOx catalyst 12 according to the present embodiment can efficiently adsorb NOx (NO) under a low temperature condition of 50 ° C.

  Thereafter, the NOx concentration in the exhaust gas flowing out from the NOx catalyst 12 gradually increases and approaches 100 ppm (see around 400 seconds in FIG. 2). This means that as the NOx catalyst 12 approaches the NOx amount that can be adsorbed, the amount of NOx adsorbed decreases, and eventually it becomes impossible to adsorb NOx beyond the limit amount that can be adsorbed. A hatching region T1 in FIG. 2 represents the total amount of NOx adsorbed by the NOx catalyst 12.

  Next, when switching to the above desorption conditions and starting to introduce exhaust gas containing no NOx into the NOx catalyst 12 while raising the temperature at a constant speed, immediately after that, the NOx concentration in the exhaust gas flowing out from the NOx catalyst 12 once increases. (Refer to the vicinity of 500 to 600 seconds in FIG. 2). This means that NOx adsorbed to the NOx catalyst 12 with a weak adsorption force is desorbed.

  Thereafter, when the temperature of the exhaust gas to be introduced reaches around 200 ° C., the NOx concentration in the exhaust gas flowing out from the NOx catalyst 12 rises again (see 1000 seconds or more in FIG. 2). This means that NOx that has been adsorbed by the NOx catalyst 12 with a strong adsorbing force has begun to desorb. As shown in FIG. 2, the desorption of NOx ends when the exhaust temperature reaches 500 ° C., and all of the adsorbed NOx is desorbed. 2 represents the total amount of NOx desorbed from the NOx catalyst 12, which corresponds to the total amount of NOx adsorbed by the NOx catalyst 12.

  Further, the NOx catalyst 12 according to the present embodiment can control the NOx desorption temperature depending on the kind of additive element co-supported on Pd. For example, when the additive element is La, the peak of NOx desorption temperature shifts to the high temperature side, but when the additive element is Ce, Pr, Sr, Ba, Ga, In, and Mn, the NOx desorption concentration Shifts to the low temperature side. Furthermore, the degree of shift varies depending on the additive element. Therefore, the NOx desorption temperature can be controlled by adjusting the addition amount of these elements.

  As described above, the NOx catalyst 12 according to this embodiment desorbs NOx adsorbed in the low temperature region in the high temperature region. At this time, since the HC adsorbed on the zeolite is also desorbed as described above, the desorbed NOx is reduced and purified by the desorbed HC. At this time, by controlling the air-fuel ratio of the exhaust gas to stoichiometric, the desorbed NOx is reduced and purified by a reducing agent such as HC contained in the exhaust gas. The reduction and purification reaction with a reducing agent such as HC requires a certain temperature or more, but the NOx desorption temperature is adjusted to a temperature at which the reduction and purification reaction can be performed by the above-described method of controlling the NOx desorption temperature. Thus, the NOx catalyst 12 of this embodiment adsorbs and purifies NOx.

  If the NOx desorption temperature is too high, more energy is required for temperature control for NOx desorption and temperature control for performing NOx adsorption after NOx desorption. is there. However, the NOx catalyst 12 according to the present embodiment does not cause the above problem because the catalyst temperature at the time of NOx desorption is adjusted to a range that does not involve fuel consumption loss by the method of controlling the NOx desorption temperature.

Next, the kind and content of the above-described additive elements will be described.
The preferred content of the NOx catalyst 12 of this embodiment differs depending on the type of additive element. For example, when the additive element is Ce, the Ce content with respect to the entire NOx catalyst 12 is preferably 0.1 to 13% by mass. When the content of Ce with respect to the entire NOx catalyst 12 is less than 0.1% by mass, the effect of improving the heat resistance in a low oxygen concentration atmosphere cannot be obtained sufficiently. Moreover, when the content of Ce exceeds 13% by mass, too much Ce inhibits the dispersibility of Pd and lowers the NOx adsorption performance. A more preferable Ce content is 0.1 to 2.5% by mass.

Hereinafter, for the same reason, when the additive element is Pr, the content of Pr with respect to the entire NOx catalyst 12 is preferably 0.05 to 0.4% by mass, and more preferably 0.05 to 0.4% by mass. 0.15% by mass.
When the additive element is Sr, the content of Sr with respect to the entire NOx catalyst 12 is preferably 0.05 to 0.3% by mass, and more preferably 0.05 to 0.2% by mass. .
When the additive element is Ba, the content of Ba with respect to the entire NOx catalyst 12 is preferably 0.01 to 0.5% by mass, and more preferably 0.1 to 0.5% by mass. .
When the additive element is La, the content of La with respect to the entire NOx catalyst 12 is preferably 0.01 to 4.1% by mass, and more preferably 0.05 to 3% by mass.
When the additive element is Ga, the Ga content with respect to the entire NOx catalyst 12 is preferably 0.01 to 2% by mass, and more preferably 0.1 to 1.3% by mass.
When the additive element is In, the content of In with respect to the entire NOx catalyst 12 is preferably 0.04 to 1% by mass, and more preferably 0.1 to 0.5% by mass.
When the additive element is Mn, the Mn content relative to the entire NOx catalyst 12 is preferably 0.01 to 0.26% by mass, more preferably 0.05 to 0.26% by mass. .

Here, FIG. 3 is a diagram showing the NOx adsorption amount when Ba is added as an additional element to the NOx catalyst 12 according to the present embodiment. FIG. 3 shows the particle diameter of Pd when the amount of Ba added to the NOx catalyst 12 according to the present embodiment is changed when the amount of Pd supported is constant (1.0 mass%). It shows how the NO adsorption amount changes.
In FIG. 3, the horizontal axis represents the amount of Ba added (% by mass), and the right vertical axis represents the Pd particle diameter (nm). The left vertical axis represents the NOx adsorption amount (g / L) adsorbed to the NOx catalyst 12 as NO. The solid line shows the change in the NOx adsorption amount with respect to the Ba addition amount, and the broken line shows the change in the Pd particle diameter with respect to the Ba addition amount.

  As shown in FIG. 3, when the addition amount of Ba is in the range of 0.01 to 0.5, the NOx adsorption amount is improved. Also, it is clear that Pd is finely divided in the same range. Therefore, it is presumed that by adding an appropriate amount of Ba to the NOx catalyst, the surface area of Pd is increased and the NOx adsorption amount is improved because Pd is atomized even with the same loading amount. Further, it can be seen that the amount of Ba added needs to be within an appropriate range in order to make fine particles of Pd. That is, it is clear from FIG. 3 that if the addition amount is too small, the effect is insufficient, and if the addition amount is too large, the dispersibility of Pd is hindered and Pd fine particles cannot be maintained.

Next, a method for manufacturing the NOx catalyst 12 according to this embodiment will be described.
The NOx catalyst 12 according to the present embodiment includes a catalyst powder preparation step, a catalyst powder firing step, a slurry preparation step, a coating step, and a support firing step. Hereinafter, each step will be described.

In the catalyst powder preparation step, catalyst powder is prepared using zeolite, a Pd compound containing Pd, and an additive element compound containing the above-described additive element. Specifically, a Pd compound and an additive element compound are added and mixed with zeolite dispersed in ion-exchanged water. After mixing, the dried catalyst powder is obtained by drying under reduced pressure.
As the Pd compound, for example, Pd nitrate is used. Further, as the additive element compound, for example, Ce nitrate, Pr nitrate, Sr nitrate, Ba nitrate, La nitrate, Ga nitrate, Indium nitrate, and Mn nitrate are used.

  In the catalyst powder firing step, the catalyst powder prepared in the catalyst powder preparation step is fired at 500 to 700 ° C. In this step, for example, the firing time is preferably 2 hours. Moreover, this process is performed, for example using an electric furnace.

  Here, FIG. 4 is a diagram showing the relationship between the catalyst powder firing temperature of the NOx catalyst 12 according to this embodiment and the NOx adsorption amount after aging. In FIG. 4, after aging for 800 ° C. × 5 hours (introducing stoichiometric gas for 95 seconds and lean gas for 5 seconds alternately) for each NOx catalyst 12 in which the firing temperature of the catalyst powder was changed stepwise NOx adsorption amount is shown. In FIG. 4, the horizontal axis represents the firing temperature (° C.) of the catalyst powder, and the vertical axis represents the NOx adsorption amount (g / L).

As shown in FIG. 4, it can be seen that when the firing temperature of the catalyst powder is less than 500 ° C., the NOx adsorption amount is greatly reduced. This is because decomposition of each nitrate used in the catalyst powder preparation step is insufficient, and the effect of improving heat resistance in a low oxygen concentration atmosphere cannot be obtained sufficiently.
It can also be seen that the amount of NOx adsorbed greatly decreases even when the firing temperature of the catalyst powder exceeds 700 ° C. This is because the effect of improving heat resistance in a low oxygen concentration atmosphere cannot be obtained sufficiently.
Therefore, by firing the catalyst powder at 500 to 700 ° C., the effect of improving the heat resistance in a low oxygen concentration atmosphere can be obtained.

  In the slurry preparation step, a slurry is prepared using the catalyst powder fired in the catalyst powder firing step. Specifically, the calcined catalyst powder, ceramic balls, and a binder such as alumina sol are combined and wet pulverized overnight with a ball mill to prepare a slurry.

  In the coating step, the slurry prepared in the slurry preparation step is wash-coated on the cordierite honeycomb support so as to have a desired amount. Specifically, after the honeycomb support is immersed in the slurry, the NOx catalyst is applied onto the support by lifting and drying.

  In the support firing step, the support coated with the NOx catalyst is fired at 750 to 950 ° C. In this step, for example, the firing time is preferably 2 hours. Moreover, this process is performed, for example using an electric furnace.

  Here, FIG. 5 is a diagram showing the relationship between the support firing temperature of the NOx catalyst 12 according to this embodiment and the NOx adsorption amount in the initial state. FIG. 5 shows the NOx adsorption amount in the initial state (fresh state) for each NOx catalyst 12 in which the firing temperature of the support is changed stepwise. In FIG. 5, the horizontal axis represents the firing temperature (° C.) of the support, and the vertical axis represents the NOx adsorption amount (g / L).

As shown in FIG. 5, it can be seen that when the firing temperature of the support is lower than 750 ° C., the NOx adsorption amount is greatly reduced. This is because the dispersibility of Pd becomes insufficient and the NOx adsorption performance decreases.
It can also be seen that the NOx adsorption amount decreases even when the calcination temperature of the support exceeds 950 ° C. This is because Pd aggregates and the NOx adsorption performance decreases.
Therefore, by firing the support coated with the NOx catalyst at 750 to 950 ° C., good dispersibility of Pd can be obtained and high NOx adsorption performance can be obtained.

  Through the steps described above, the NOx catalyst 12 according to this embodiment is manufactured.

  Note that the present invention is not limited to the above-described embodiment, and modifications and improvements within the scope that can achieve the object of the present invention are included in the present invention.

  In the said embodiment, although this invention was applied to the gasoline engine mounted in the vehicle, it is not limited to this. For example, the present invention may be applied to a diesel engine mounted on a vehicle or an engine other than the vehicle.

  Moreover, in the said embodiment, although TWC11 was provided in the upstream of the NOx catalyst 12, it is not limited to this. For example, instead of the TWC 11, another exhaust purification catalyst may be provided upstream or downstream of the NOx catalyst 12.

  Next, examples of the present invention will be described, but the present invention is not limited to these examples.

<Examples 1 to 8 and Comparative Examples 1 and 2>
In Examples 1 to 8 and Comparative Examples 1 and 2, NOx catalysts having a Pd content of 1% by mass with respect to the entire NOx catalyst and different contents of each additive element with respect to the entire NOx catalyst were prepared.

The preparation procedure of the NOx catalyst will be described by taking the NOx catalyst of Example 1-1 described later as an example.
First, 50.5 g of Zeolist ZSM-5 zeolite and 125 g of ion-exchanged water were placed in a flask and mixed to disperse the zeolite in ion-exchanged water. Thereafter, 10.18 g of a 5% Pd nitric acid solution manufactured by Kojima Chemical Co., Ltd. and 0.21 g of Ce nitrate were mixed in the flask, and excess water was removed with a rotary evaporator.
In other examples and comparative examples, nitrates of each additive element (Ce nitrate in Example 1, Pr nitrate in Example 2, Sr nitrate in Example 3, Ba nitrate in Example 4 instead of Ce nitrate) In Example 5, La nitrate, Ga nitrate in Example 6, Indium nitrate in Example 7, Mn nitrate in Example 8, Fe nitrate in Comparative Example 1) were mixed in amounts to achieve the desired amount of additive elements. In Comparative Example 2, a NOx catalyst was prepared using only Pd nitrate without adding any additional elements.

  Next, after drying at 200 ° C. for 2 hours using a vacuum drying furnace, firing was performed at 600 ° C. for 2 hours using an electric furnace. Thereby, catalyst powders of Examples 1 to 8 and Comparative Examples 1 and 2 were obtained.

  Next, 35.3 g of the obtained catalyst powder, 19.8 g of an alumina sol binder (alumina concentration 20 mass%) manufactured by Nissan Chemical Industries, Ltd., 150 g of ceramic balls, and 70 g of ion-exchanged water were combined into a polyethylene container. The slurry of Examples 1-8 and Comparative Examples 1 and 2 was prepared by putting and ball-milling overnight.

Next, a cordierite honeycomb support (diameter: φ25.4 mm × length L60 mm (capacity 30 cc), cell density: 400 cells / in ² , wall thickness: 3.5 mil) is immersed in each prepared slurry. I let you. The amount of washcoat was set to 200 g / L, respectively. The honeycomb support was taken out of the slurry, and excess slurry was removed by air injection, followed by drying at 200 ° C. for 2 hours. This operation was repeated until a washcoat amount of 200 g / L was obtained.

  The honeycomb support having a washcoat amount of 200 g / L was fired at 850 ° C. for 2 hours using an electric furnace. Thereby, the NOx catalysts of Examples 1 to 8 and Comparative Examples 1 and 2 were obtained.

[Examples 1-1 to 1-5]
In Example 1, a NOx catalyst in which the content of the additive element Ce was varied in five stages was prepared according to the above-described preparation procedure. Specifically, the content of the additive element Ce is 0.1% by mass in Example 1-1, 0.7% by mass in Example 1-2, and 2.5% by mass in Example 1-3. In Example 1-4, it was prepared to be 6.7% by mass, and in Example 1-5, it was 13% by mass.

[Examples 2-1 to 2-5]
In Example 2, a NOx catalyst in which the content of the additive element Pr was varied in five stages was prepared according to the above-described preparation procedure. Specifically, the content of the additive element Pr is 0.05% by mass in Example 2-1, 0.14% by mass in Example 2-2, 0.5% by mass in Example 2-3, In Example 2-4, 1.0% by mass was prepared, and in Example 2-5, 2.6% by mass was prepared.

[Examples 3-1 to 3-5]
In Example 3, a NOx catalyst in which the content of the additive element Sr was varied in five stages was prepared according to the above-described preparation procedure. Specifically, the content of the additive element Sr was 0.05% by mass in Example 3-1, 0.1% by mass in Example 3-2, and 0.5% by mass in Example 3-3. In Example 3-4, 1.0% by mass was prepared, and in Example 3-5, 1.7% by mass was prepared.

[Examples 4-1 to 4-4]
In Example 4, a NOx catalyst in which the content of the additive element Ba was varied in five stages was prepared according to the above-described preparation procedure. Specifically, the content of the additive element Ba was 0.07% by mass in Example 4-1, 0.13% by mass in Example 4-2, 0.65% by mass in Example 4-3, In Example 4-4, 2.6% by mass was prepared, and in Example 4-5, 6.5% by mass was prepared.

[Examples 5-1 to 5-5]
In Example 1, a NOx catalyst in which the content of the additive element La was varied in five stages was prepared according to the above-described preparation procedure. Specifically, the content of the additive element La is 0.14% by mass in Example 5-1, 1.3% by mass in Example 5-2, 3.0% by mass in Example 5-3, In Example 5-4, 4.1% by mass was prepared, and in Example 5-5, 6.6% by mass was prepared.

[Examples 6-1 to 6-4]
In Example 6, a NOx catalyst in which the content of the additive element Ga was varied in four stages was prepared according to the above-described preparation procedure. Specifically, the content of the additive element Ga is 0.07% by mass in Example 6-1; 0.33% by mass in Example 6-2; 1.3% by mass in Example 6-3; In Example 6-4, it prepared so that it might become 3.3 mass%.

[Examples 7-1 to 7-6]
In Example 7, a NOx catalyst in which the content of the additive element In was varied in six steps was prepared according to the above-described preparation procedure. Specifically, the content of the additive element In was 0.04% by mass in Example 7-1, 0.08% by mass in Example 7-2, 0.1% by mass in Example 7-3, In Example 7-4, 0.5% by mass was prepared, in Example 7-5, 1% by mass, and in Example 7-6, 5.4% by mass was prepared.

[Examples 8-1 to 8-5]
In Example 8, a NOx catalyst in which the content of the additive element Mn was varied in five stages was prepared according to the above-described preparation procedure. Specifically, the content of the additive element Mn was 0.05% by mass in Example 8-1; 0.26% by mass in Example 8-2; 0.4% by mass in Example 8-3; In Example 8-4, 0.5% by mass was prepared, and in Example 8-5, 1% by mass was prepared.

[Comparative Examples 1-1 to 1-5]
In Comparative Example 1, a NOx catalyst in which the content of the additive element Fe was varied in five stages was prepared according to the above-described preparation procedure. Specifically, the content of the additive element Fe is 0.06% by mass in Comparative Example 1-1, 0.26% by mass in Comparative Example 1-2, and 1.0% by mass in Comparative Example 1-3. In Example 1-4, 2.6% by mass was prepared, and in Comparative Example 1-5, 5.2% by mass was prepared.

[NOx adsorption performance evaluation]
First, aging was performed on each NOx catalyst obtained in each of the examples and comparative examples at 800 ° C. for 5 hours (introducing the stoichiometric gas for 95 seconds and the lean gas for 5 seconds alternately). Next, exhaust was introduced under the following adsorption conditions to adsorb NOx to each NOx catalyst after aging, and then exhaust was introduced under the following desorption conditions to desorb NOx. The total amount of desorbed NOx was defined as the NOx adsorption amount. The results are shown in FIGS.

[Adsorption conditions]
Exhaust composition: NO = 100 ppm, O ₂ = 10%, N ₂ balance gas exhaust flow rate: 20 L / min Exhaust temperature: 50 ° C.
[Desorption conditions]
Exhaust composition: O ₂ = 10%, N ₂ balance gas exhaust flow rate: 20 L / min Exhaust temperature: Temperature rise from 50 ° C. to 500 ° C. at 20 ° C./min

FIG. 6 is a diagram showing the NOx catalyst having the maximum NOx adsorption amount and the NOx adsorption amount among the NOx catalysts according to the respective examples and comparative examples. In FIG. 6, the vertical axis represents the NOx adsorption amount (g / L).
As shown in FIG. 6, it was found that the amount of additive element that maximizes the NOx adsorption amount differs depending on the type of additive element. In addition, in the NOx catalysts of Examples 1 to 8 where the additive element species is Ce, Pr, Sr, Ba, La, Ga, In or Mn as defined in the present invention, any of the additive element species is outside the scope of the present invention. As compared with the NOx catalyst of Comparative Example 1 which is Fe, it was confirmed that it has a larger maximum NOx adsorption amount. From this result, the NOx catalyst of the present invention in which Pd and at least one additive element selected from the group consisting of Ce, Pr, Sr, Ba, La, Ga, In, or Mn are supported on zeolite is obtained. It was confirmed that it has excellent NOx adsorption performance under low temperature conditions and excellent heat resistance in a low oxygen concentration atmosphere.

7 to 14 are diagrams comparing NOx desorption temperatures of the NOx catalysts according to Examples 1 to 8 and Comparative Example 2. FIG. 7 to 14, the horizontal axis represents the catalyst temperature, and the vertical axis represents the relative NOx desorption concentration when the relative value of the NOx desorption concentration, that is, the maximum value of the NOx concentration desorbed from the NOx catalyst is 1. Indicates the value.
In addition, in the NOx catalysts of Examples 1 to 8, the content of each additive element was Ce (0.7% by mass), Pr (0.1% by mass), Sr (0.1% by mass), respectively, according to the above preparation procedure. %), Ba (0.1 mass%), La (1.3 mass%), Ga (0.3 mass%), In (0.1 mass%), Mn (0.3 mass%) A NOx catalyst was prepared.

The NOx catalyst of Example 5 in which the additive element is La shown in FIG. 11 has a peak NOx desorption concentration shifted to a higher temperature side than the NOx catalyst of Comparative Example 2.
On the other hand, the NOx catalysts of Examples 1 to 4 and 6 to 8 shown in FIGS. 7 to 10 and 12 to 14 in which the additive elements are Ce, Pr, Sr, Ba, Ga, In, and Mn are the NOx of Comparative Example 2. Compared with the catalyst, the peak of NOx desorption concentration shifted to the low temperature side. Therefore, it has been found that the peak of NOx desorption concentration shifts to the low temperature side or the high temperature side depending on the type of element added. Further, even if the shift is to the same low temperature side, the degree varies depending on the additive element. If there is a shift as small as In in Example 7 in FIG. 13, there is a shift like Mn in Example 8 in FIG. Some are big.
From this result, the NOx catalyst of the present invention in which Pd and at least one additive element selected from the group consisting of Ce, Pr, Sr, Ba, La, Ga, In, or Mn are supported on zeolite is obtained. It was confirmed that the NOx desorption temperature can be adjusted by adjusting the addition amount of each additive element, and the NOx desorption temperature can be set appropriately.

FIG. 15 is a diagram illustrating the relationship between the amount of added elements and the NOx adsorption amount of the NOx catalyst according to Examples 1-1 to 1-5 and Comparative Examples 1-1 to 1-5. In FIG. 6, the vertical axis represents the NOx adsorption amount (g / L) (the same applies to FIGS. 16 to 22).
As shown in FIG. 15, all of Examples 1-1 to 1-5 in which the additive element type is Ce defined in the present invention and the content of Ce is in the range of 0.1 to 13% by mass. As compared with the NOx catalysts of Comparative Examples 1-1 to 1-5 in which the additive element species is Fe outside the range of the present invention, it was confirmed that the additive element species has a large NOx adsorption amount. From this result, by making the content of Ce of the additive element within the range of 0.1 to 13% by mass, the NOx adsorption performance under the low temperature condition can be further improved, and the heat resistance in the low oxygen concentration atmosphere is further improved. It was confirmed that it was possible. Moreover, from this result, more preferable Ce content was considered to be 0.1 to 2.5% by mass.

FIG. 16 is a diagram illustrating the relationship between the amount of added elements and the NOx adsorption amount of the NOx catalyst according to Examples 2-1 to 2-5 and Comparative Examples 1-1 to 1-4.
As shown in FIG. 16, Examples 2-1 and 2-2, in which the additive element type is Pr defined in the present invention and the Pr content is in the range of 0.05 to 0.4 mass%, Compared with the NOx catalysts of Comparative Examples 1-1 to 1-4 in which the additive element species is Fe outside the scope of the present invention, it was confirmed that the additive element species has a large NOx adsorption amount. From this result, by making the content of Pr as an additive element in the range of 0.05 to 0.4 mass%, the NOx adsorption performance under low temperature conditions can be further improved, and the heat resistance in a low oxygen concentration atmosphere can be improved. It was confirmed that it could be improved further. Moreover, from FIG. 16, it was thought that more preferable Pr content is 0.05-0.15 mass%.

FIG. 17 is a diagram illustrating the relationship between the amount of added elements and the NOx adsorption amount of the NOx catalyst according to Examples 3-1 to 3-5 and Comparative Examples 1-1 to 1-3.
As shown in FIG. 17, Examples 3-1 and 3-2 in which the additive element type is Sr defined in the present invention and the Sr content is in the range of 0.05 to 0.3 mass%. Compared with the NOx catalysts of Comparative Examples 1-1 to 1-3 in which the additive element species is Fe outside the range of the present invention, it was confirmed that the additive element species has a large NOx adsorption amount. From this result, by setting the content of Sr as an additive element in the range of 0.05 to 0.3% by mass, the NOx adsorption performance under low temperature conditions can be further improved, and the heat resistance in a low oxygen concentration atmosphere can be improved. It was confirmed that it could be improved further. Moreover, from FIG. 17, it was thought that more preferable Sr content is 0.05-0.2 mass%.

FIG. 18 is a diagram illustrating a relationship between the amount of added elements and the NOx adsorption amount of the NOx catalyst according to Examples 4-1 to 4-4 and Comparative Examples 1-1 to 1-4.
As shown in FIG. 18, Example 4-1 and Example 4-2 in which the additive element type is Ba defined in the present invention and the Ba content is in the range of 0.01 to 0.5 mass%. Was confirmed to have a larger NOx adsorption amount than the NOx catalysts of Comparative Examples 1-1 to 1-4 in which the additive element species is Fe outside the scope of the present invention. From this result, by making the content of Ba of the additive element within the range of 0.01 to 0.5% by mass, the NOx adsorption performance under low temperature conditions can be further improved, and the heat resistance in a low oxygen concentration atmosphere can be improved. It was confirmed that it could be improved further. Moreover, from FIG. 18, it was thought that more preferable Ba content is 0.1-0.5 mass%.

FIG. 19 is a diagram illustrating the relationship between the amount of added elements and the NOx adsorption amount of the NOx catalyst according to Examples 5-1 to 5-5 and Comparative Examples 1-1 to 1-5.
As shown in FIG. 19, Examples 5-1 to 5-4 in which the additive element type is La defined in the present invention and the La content is in the range of 0.01 to 4.1% by mass, Compared with the NOx catalysts of Comparative Examples 1-1 to 1-5 in which the additive element species is Fe outside the range of the present invention, it was confirmed that the additive element species has a large NOx adsorption amount. From this result, by setting the content of La of the additive element within the range of 0.01 to 4.1% by mass, the NOx adsorption performance under low temperature conditions can be further improved, and the heat resistance in a low oxygen concentration atmosphere can be improved. It was confirmed that it could be improved further. Moreover, from FIG. 19, it was thought that more preferable La content is 0.05-3 mass%.

FIG. 20 is a diagram illustrating the relationship between the amount of added elements and the NOx adsorption amount of the NOx catalyst according to Examples 6-1 to 6-4 and Comparative Examples 1-1 to 1-4.
As shown in FIG. 20, Examples 6-1 to 6-3 in which the additive element type is Ga as defined in the present invention and the Ga content is in the range of 0.01 to 2 mass% include the additive element. Compared with the NOx catalysts of Comparative Examples 1-1 to 1-4 in which the seed is Fe outside the scope of the present invention, it was confirmed that it has a large NOx adsorption amount. From this result, by setting the Ga content of the additive element within the range of 0.01 to 2% by mass, the NOx adsorption performance under low temperature conditions can be further improved and the heat resistance in a low oxygen concentration atmosphere is further improved. It was confirmed that it was possible. Moreover, from FIG. 20, it was thought that more preferable Ga content is 0.1-1.3 mass%.

FIG. 21 is a diagram illustrating the relationship between the amount of added elements and the NOx adsorption amount of the NOx catalyst according to Examples 7-1 to 7-6 and Comparative Examples 1-1 to 1-5.
As shown in FIG. 21, Examples 7-1 to 7-5 in which the additive element type is In as defined in the present invention and the In content is in the range of 0.04 to 1% by mass are the additive elements. Compared with the NOx catalysts of Comparative Examples 1-1 to 1-5 whose seeds are Fe outside the scope of the present invention, it was confirmed that they have a large NOx adsorption amount. From this result, by setting the content of In as an additive element in the range of 0.04 to 1% by mass, the NOx adsorption performance under low temperature conditions can be further improved and the heat resistance in a low oxygen concentration atmosphere is further improved. It was confirmed that it was possible. Moreover, from FIG. 21, it was thought that more preferable In content is 0.1-0.5 mass%.

FIG. 22 is a diagram illustrating a relationship between the amount of added elements and the NOx adsorption amount of the NOx catalyst according to Examples 8-1 to 8-5 and Comparative Examples 1-1 to 1-3.
As shown in FIG. 22, Examples 8-1 to 8-2 in which the additive element type is Mn specified in the present invention and the Mn content is in the range of 0.01 to 0.26 mass%. Compared with the NOx catalysts of Comparative Examples 1-1 to 1-3 in which the additive element species is Fe outside the range of the present invention, it was confirmed that the additive element species has a large NOx adsorption amount. From this result, by making the content of Mn as an additive element in the range of 0.01 to 0.26% by mass, the NOx adsorption performance under low temperature conditions can be further improved and the heat resistance in a low oxygen concentration atmosphere can be improved. It was confirmed that it could be improved further. Moreover, from FIG. 22, it was thought that more preferable Mn content is 0.05-0.26 mass%.

DESCRIPTION OF SYMBOLS 1 ... Exhaust gas purification device 2 ... Engine (internal combustion engine)
3. Exhaust pipe (exhaust system)
11 ... Three-way catalyst 12 ... NOx catalyst (exhaust gas purification catalyst)

Claims (10)

An exhaust purification catalyst that is provided in an exhaust system of an internal combustion engine and purifies NOx in exhaust,
A support made of zeolite,
Pd supported on the carrier;
An exhaust purification catalyst comprising at least one additional element selected from the group consisting of Ce, Pr, Sr, Ba, La, Ga, In and Mn supported on the carrier. The additive element is Ce;
The exhaust purification catalyst according to claim 1, wherein the content of Ce with respect to the entire exhaust purification catalyst is 0.1 to 13 mass%. The additive element is Pr;
The exhaust purification catalyst according to claim 1, wherein the content of Pr in the entire exhaust purification catalyst is 0.05 to 0.4 mass%. The additive element is Sr;
The exhaust purification catalyst according to claim 1, wherein the content of Sr with respect to the whole exhaust purification catalyst is 0.05 to 0.3 mass%. The additive element is Ba,
The exhaust purification catalyst according to claim 1, wherein the content of Ba with respect to the entire exhaust purification catalyst is 0.01 to 0.5 mass%. The additive element is La,
The exhaust purification catalyst according to claim 1, wherein the content of La in the exhaust purification catalyst as a whole is 0.01 to 4.1 mass%. The additive element is Ga;
2. The exhaust purification catalyst according to claim 1, wherein a content of Ga with respect to the entire exhaust purification catalyst is 0.01 to 2 mass%. The additive element is In,
The exhaust purification catalyst according to claim 1, wherein the content of In with respect to the whole exhaust purification catalyst is 0.04 to 1 mass%. The additive element is Mn,
The exhaust purification catalyst according to claim 1, wherein the Mn content in the exhaust purification catalyst is 0.01 to 0.26 mass%. A method for producing an exhaust purification catalyst according to any one of claims 1 to 9,
A catalyst powder firing step of firing a catalyst powder prepared using zeolite, a Pd compound containing Pd, and an additive element compound containing the additive element at 500 to 700 ° C .;
A method for producing an exhaust purification catalyst, comprising: a support firing step of firing a support coated with a slurry prepared using the catalyst powder fired in the catalyst powder firing step at 750 to 950 ° C.

Images