JP6180348B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine that is disposed in an exhaust system of an internal combustion engine and purifies NOx in the exhaust gas.

  As a conventional exhaust gas purification catalyst for an internal combustion engine that purifies NOx in exhaust gas, for example, one disclosed in Patent Document 1 is known. The exhaust gas purification catalyst includes a low temperature NOx catalyst. This NOx catalyst is a zeolite catalyst composed of zeolite, and β zeolite, A-type zeolite, Y-type zeolite, X-type zeolite, ZSM-5, USY, mordenite, ferrierite, etc. are used as the zeolite.

  In this NOx catalyst, NOx is adsorbed by appropriately controlling the moisture concentration of the exhaust gas to the dry side and appropriately controlling the oxygen concentration of the exhaust gas to the lean side even under a low temperature condition of 100 ° C. or lower. It is possible to improve the NOx adsorption performance especially under low temperature conditions.

Japanese Patent No. 3632614

  As described above, in the conventional NOx catalyst, in order to adsorb NOx well at low temperatures, it is necessary to control the moisture concentration of the exhaust gas to the dry side and to control the oxygen concentration to the lean side. This is because the adsorption ability of the zeolite composing the NOx catalyst is exhibited by incorporating molecules into the skeleton, so that the adsorption of NOx is inhibited by the moisture adsorbed on the zeolite, and the NO in the exhaust gas is oxidized. This is because NOx cannot be adsorbed unless converted to NO2.

  For this reason, when a conventional NOx catalyst is used, in order to remove moisture from the exhaust gas, for example, it is necessary to provide a device containing a desiccant upstream of the NOx catalyst in the exhaust system. Further, under low temperature conditions such as a warm-up state of the internal combustion engine, the air-fuel ratio of the air-fuel mixture may be controlled to the stoichiometric or rich side in order to stabilize combustion and raise the temperature of the catalyst. In that case, since the oxygen concentration of the exhaust gas cannot be controlled to the lean side, the conventional NOx catalyst cannot adsorb NOx well.

  The present invention has been made to solve such a problem, and it is preferable to reduce NOx in exhaust gas at low temperature conditions without requiring moisture removal from exhaust gas and control of the exhaust gas to the lean side. An object of the present invention is to provide an exhaust gas purification device for an internal combustion engine that can be adsorbed.

To this end, the invention according to claim 1 is arranged in an exhaust system of an internal combustion engine, an exhaust gas purification system for an internal combustion engine to purify NOx in the exhaust gas, and a zeolite, an acid point of the zeolite A NOx catalyst that is disposed on a certain Al and supported on zeolite and that adsorbs NOx in the state of NO is provided, and is characterized in that the Al2O3 / SiO2 of the zeolite is larger than 0.003.

According to this configuration, the NOx catalyst has zeolite and palladium supported on the zeolite. Moreover, palladium is arrange | positioned on Al which is the acid point of a zeolite, and the electronic state is changing by interaction with an acid point. For this reason, since NO is adsorbed as it is to palladium whose electronic state has changed, it is not easily affected by moisture adsorption, and it is not necessary to oxidize NO to NO2.

  Therefore, NOx in the exhaust gas can be favorably adsorbed under low temperature conditions without requiring moisture removal from the exhaust gas and control of the exhaust gas to the lean side. As a result, unlike the conventional exhaust gas purification device, it is not necessary to provide a device for removing moisture from the exhaust gas, and the air-fuel ratio of the air-fuel mixture is controlled to the stoichiometric or rich side in the warm-up state of the internal combustion engine. Even in this case, NOx can be favorably adsorbed.

  In addition, if the amount of Al, which is the acid point of the zeolite, is small, the amount of palladium disposed thereon cannot be secured sufficiently, so that the ability to adsorb NOx by palladium is not fully exhibited. As will be described later, it has been confirmed that the NOx adsorption performance required for the NOx catalyst can be obtained when Al2O3 / SiO2 of the zeolite is larger than 0.003.

  According to the present invention, since Al2O3 / SiO2 of zeolite is larger than 0.003, it is possible to sufficiently exhibit the NOx adsorption ability by palladium and to realize the required NOx adsorption performance.

  The invention according to claim 2 is the exhaust gas purification apparatus for an internal combustion engine according to claim 1, characterized in that the zeolite is ZSM-5, ferrierite, mordenite, Y-type zeolite or beta-type zeolite.

  As will be described later, it has been confirmed that the NOx adsorption performance required for the NOx catalyst can be obtained when the zeolite is of the above type. Therefore, according to this configuration, the required NOx adsorption performance can be realized.

  The invention according to claim 3 is the exhaust gas purifying apparatus for an internal combustion engine according to claim 2, wherein the weight of palladium per unit volume of the NOx catalyst is larger than 0.1 g / L.

  If the actual amount of palladium supported on the zeolite is small, the adsorption ability of NOx by palladium cannot be fully exhibited. As will be described later, it has been confirmed that the NOx adsorption performance required for the NOx catalyst can be obtained when the weight of palladium per unit volume of the NOx catalyst is larger than 0.1 g / L. Therefore, according to this configuration, the required NOx adsorption performance can be realized.

  The invention according to claim 4 is the exhaust gas purification apparatus for an internal combustion engine according to claim 3, wherein the weight of palladium per unit volume of the NOx catalyst is less than 2.0 g / L.

  As will be described later, it has been confirmed that when the unit palladium weight is 2.0 g / L or more, the NOx adsorption performance does not change much even if palladium is increased. Therefore, according to this configuration, it is possible to achieve the required NOx adsorption performance while efficiently using relatively expensive palladium.

1 is a diagram schematically showing an exhaust gas purification apparatus according to an embodiment of the present invention together with an internal combustion engine. It is a figure which shows typically the adsorption | suction state in which NOx was estimated to palladium in a NOx catalyst. It is a figure for demonstrating the basis of the setting of target NO adsorption amount. It is a figure which shows Examples 1-14 of a NOx catalyst as a table | surface. It is a figure which shows the comparative examples 1-4 of a NOx catalyst as a table | surface. It is a figure which shows the comparative examples 5-7 of a NOx catalyst as a table | surface. It is a figure which shows the evaluation result of the NOx adsorption | suction form performed with respect to the Example. It is a figure which shows the relationship between the kind of zeolite of NOx catalyst, and NO adsorption amount. It is a figure which shows the relationship between the Keiban ratio reciprocal number of zeolite, and NO adsorption amount. It is a figure which shows the relationship between the amount of palladium carrying | support of a NOx catalyst, and NO adsorption amount. It is a figure which shows the relationship between the unit palladium weight of a NOx catalyst, and NO adsorption amount.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an exhaust gas purification apparatus 1 to which the present invention is applied, together with an internal combustion engine 3. The internal combustion engine (hereinafter referred to as “engine”) 3 is, for example, a four-cylinder gasoline engine mounted on a vehicle (not shown).

  An intake pipe 4 is connected to each cylinder 3a through an intake manifold 4a, and an exhaust pipe 5 is connected through an exhaust manifold 5a. A mixture of air sucked from the intake pipe 4 and fuel injected from a fuel injection valve (not shown) burns in a combustion chamber (not shown) of each cylinder 3a, and a gas generated by the combustion is generated. The exhaust gas is discharged to the exhaust pipe 5.

  The exhaust pipe 5 is provided with an exhaust gas purification device 1 for purifying the exhaust gas, and the exhaust gas purification device 1 includes a three-way catalyst 6 and a NOx catalyst 7 disposed downstream thereof. The three-way catalyst 6 has a well-known configuration, and purifies exhaust gas in a stoichiometric atmosphere by oxidizing HC and CO and reducing NOx when the temperature is equal to or higher than the activation temperature.

  On the other hand, the NOx catalyst 7 according to the present invention is mainly for purifying NOx that has not been purified by the three-way catalyst 6 at a low temperature, and has zeolite and palladium (Pd) supported on the zeolite.

  The zeolite is composed of ZSM-5, ferrierite, mordenite, Y-type zeolite or beta-type zeolite. In addition, the reciprocal number (hereinafter referred to as “reciprocal number of the Keiban ratio”) Al 2 O 3 / SiO 2 of the zeolite's silica-ban ratio SiO 2 / Al 2 O 3 is set to a value larger than 0.003.

  As shown in FIG. 2, palladium is arranged in the vicinity of Al which is an acid point among aluminum (Al), silicon (Si) and oxygen (O) constituting the zeolite, and due to the interaction with Al. The electronic state is changing. For this reason, it is estimated that NO and OH are adsorbed on palladium.

  The weight of palladium per unit volume of the NOx catalyst 7 (hereinafter referred to as “unit Pd weight”) PdU is set to a value larger than 0.1 g / L, and more preferably from 0.1 g / L. It is large and set to less than 2.0 g / L.

  The configuration and specifications of the NOx catalyst 7 described above are determined so that the target NO adsorption amount of the NOx catalyst 7 is set to 5 μmol / g or more and this target NO adsorption amount is achieved. The basis for setting the target NO adsorption amount is as follows.

  FIG. 3 shows the relationship between the NO adsorption amount of the NOx catalyst and the NOx emission amount finally discharged from the tail pipe of the vehicle. As shown in this figure, as the NO adsorption amount increases, the NOx emission amount decreases almost linearly. Further, for example, according to the laws and regulations of the state of California, the amount of NOx emission is regulated to SULEV30 (= 0.02 g / mile) or less. From the above relationship, the target NO adsorption amount is set to 5 μmol / g or more in order to surely clear the regulation level SULEV30 or less.

  Hereinafter, an embodiment of the NOx catalyst 7 will be described in detail with reference to FIG. In addition, these Examples are illustrations and this invention is not limited to an Example. Further, unless otherwise specified, “%” represents% by weight.

<Examples 1-8>
[Pd / zeolite catalyst]
As shown in FIG. 4, Examples 1 to 4 are examples in which ZSM-5 (manufactured by Zeolis) is used as the zeolite (support) and the Keiban ratio SiO 2 / Al 2 O 3 is different from each other. Examples 5 to 8 are examples in which ferrierite, mordenite, Y-type zeolite, and beta-type zeolite (manufactured by Zeolisto) were used as zeolites. Their production methods are as follows.

(1) Each amount shown in the table of zeolite and palladium nitrate (made by Kojima Chemical Co., Ltd .: Pd concentration 5%) shown in the table of FIG. 4 and ion-exchanged water having a weight 2.5 times that of zeolite, The flask was placed in a flask and excess water was removed with a rotary evaporator. Subsequently, catalyst powder was obtained by baking for 2 hours at 200 ° C. in a drying furnace and for 2 hours at 600 ° C. in a muffle furnace.

(2) Each amount shown in Table 1 of the obtained catalyst powder and alumina sol (manufactured by Nissan Chemical Industries, Ltd .: Al2O3 concentration 20%), ion-exchanged water and alumina balls having twice the weight of the catalyst powder were made of polyethylene. Into a container (250 ml) and wet pulverized for 14 hours to obtain a slurry.

(3) A honeycomb support (manufactured by Cordierite: honeycomb φ25.4 mm × L60 mm (30 cc), 400 cells / in 2, 3.5 mil) was immersed in the obtained slurry. The amount of washcoat in this case is 200 g / L. Next, after removing the honeycomb support from the slurry and removing the excess slurry by air injection, the honeycomb support was heated at 200 ° C. for 2 hours. This operation was repeated until a predetermined loading amount was obtained. After a predetermined loading amount was obtained, the honeycomb support was fired at 600 ° C. for 2 hours in a muffle furnace to obtain a Pd / zeolite catalyst.

<Examples 9 to 14>
[Pd ion exchange zeolite catalyst]
As shown in FIG. 4, Examples 9 to 14 are examples in which ZSM-5 (manufactured by Zeolisto) is used as the zeolite (support) and the amounts of palladium are different from each other. The manufacturing method is as follows.

(4) Ion exchange of each amount shown in the same table of the support (zeolite) and palladium nitrate (made by “Kojima Chemical Co., Ltd .: Pd concentration 5%) shown in the table of FIG. 4 and 10 times the weight of zeolite. Water was placed in a beaker and stirred, and further adjusted to pH = 8 using 28% aqueous ammonia, and then stirred for 4 hours to obtain a suspension. The resulting suspension was filtered with suction and washed with ion-exchanged water. After repeating such suction filtration and washing 2 to 3 times, catalyst powder was obtained by firing at 200 ° C. for 2 hours in a drying furnace and at 600 ° C. for 2 hours in a muffle furnace.

(5) Then, Pd ion exchange zeolite catalyst was obtained by performing the same operation as (2) and (3) of Examples 1-8.

  Next, a comparative example for comparison with the embodiment will be described in detail with reference to FIGS.

<Comparative Example 1>
[Pd / zeolite catalyst]
As shown in FIG. 5, Comparative Example 1 is an example in which zeolite (ZSM-5) is used as the support, while the reciprocal number of Caiban ratio Al2O3 / SiO2 = 0.003. The manufacturing method is the same as in Examples 1-8.

<Comparative Examples 2-4>
[Pd / oxide catalyst]
In Comparative Examples 2 to 4, silica (SiO 2), alumina (Al 2 O 3), and cerium oxide (CeO 2) were used as the support instead of zeolite. The manufacturing method is the same as in Examples 1-8.

<Comparative Examples 5-6>
[Precious metal / zeolite catalyst]
As shown in FIG. 6, Comparative Examples 5 to 6 are examples in which zeolite (ZSM-5) is used as a support, while platinum (Pt) and rhodium (Rh) are used in place of palladium. The manufacturing method is the same as in Examples 1-8.

<Comparative Example 7>
[Zeolite catalyst]
Moreover, the comparative example 7 is an example comprised as a zeolite catalyst, without using palladium at all. The manufacturing method is as follows.
(6) Catalyst powder was obtained by calcining zeolite (ZSM-5 (50)) in a muffle furnace at 600 ° C. for 2 hours.
(7) Then, the same operation as (2) and (3) in Examples 1 to 8 was performed to obtain a zeolite catalyst.

<Pd content evaluation>
For the catalyst powders prepared in Examples 1 to 14, the Pd content was evaluated by the following method.
About 50 mg of catalyst powder and 25 ml of 10% HF aqueous solution were put in a pressure vessel, and heated at 230 ° C. for 30 minutes using a microwave decomposition apparatus (manufactured by Analytikjena) to completely dissolve the catalyst powder. Subsequently, after cooling at room temperature and diluting, the Pd supported amount PdR (%), which is the content of palladium in the NOx catalyst 7, was evaluated using ICP-OES (manufactured by Agilent Technologies).

  Further, the unit Pd weight PdU (g / L), which is the content of palladium per unit volume of the NOx catalyst 7, was calculated from the Pd carrying amount PdR and the weight and volume of the NOx catalyst. The above results are shown in the right column of Table 1.

<NOx adsorption form evaluation>
The catalyst powder prepared in Example 3 was subjected to oxidation treatment, moisture adsorption treatment and NO adsorption treatment under the following conditions, and then subjected to diffuse reflection FT-IR spectroscopic analysis under the following analysis conditions to obtain a NOx catalyst. The adsorption form of NOx was evaluated.

[Analysis conditions]
・ Measurement device: FTS-60A (Bio-Rad Digilab)
・ Attachment device: Diffuse reflection measurement device (PIKE Technologies)
・ Light source: Glover (SiC)
・ Detector: DTGS
・ Measured wave number range: 4000-1100 cm-1
・ Wave number resolution: 4cm-1
・ Number of integration: 256 times ・ Reference: Au
・ Deposition film temperature rising condition: 20 ° C./min

[Oxidation conditions]
・ Temperature: 500 ℃
・ Time: 30 minutes ・ Gas composition: O2 = 10%, N2 = balance gas ・ Gas flow rate: 100 cc / min

[Moisture adsorption treatment conditions]
・ Temperature: 50 ℃
・ Time: 30 minutes ・ Gas composition: O2 = 10%, H2O = 2%, N2 = balance gas ・ Gas flow rate: 100 cc / min

[NO adsorption treatment conditions]
・ Temperature: 50 ℃
・ Time: 60 minutes ・ Gas composition: O2 = 10%, NO = 200 ppm, N2 = balance gas ・ Gas flow rate: 100 cc / min

  FIG. 7 shows the FT-IR difference spectra before and after the NO adsorption treatment, obtained by evaluating this NOx adsorption form. As shown in the figure, the vicinity of wave numbers 1900 to 1800 (1 / cm) corresponds to the Pd-NO structure, and a peak appears in this vicinity. Further, as described above, the NOx catalyst is preliminarily subjected to moisture adsorption treatment, and the temperature condition of the NO adsorption treatment is 50 ° C. From the above, it was confirmed that NOx was adsorbed in the form of nitric oxide (NO) on palladium under the low temperature condition of 50 ° C. where moisture was adsorbed.

<Evaluation of NO adsorption amount>
For the NOx catalysts of Examples 1 to 14 and Comparative Examples 1 to 7 obtained as described above, oxidation treatment, moisture adsorption treatment and NO adsorption treatment were performed under the following conditions.

[Oxidation conditions]
・ Temperature: 500 ℃
・ Time: 30 minutes ・ Gas composition: O2 = 10%, N2 = balance gas ・ Gas flow rate: 20 L / min

[Moisture adsorption treatment conditions]
・ Temperature: 50 ℃
・ Time: 5 minutes ・ Gas composition: O2 = 2%, H2O = 2%, N2 = balance gas ・ Gas flow rate: 20 L / min

[NO adsorption treatment conditions]
・ Temperature: 50 ℃
・ Time: 3 minutes ・ Gas composition: O2 = 2%, NO = 400 ppm, N2 = balance gas ・ Gas flow rate: 20 L / min

After performing the NO adsorption treatment, the total NO release amount when the temperature of the NOx treatment was raised under the following conditions was evaluated as the NO adsorption amount.
[Heating conditions]
-Temperature range: 50-500 ° C
・ Temperature increase rate: 20 ° C./min ・ Gas composition: N 2
・ Gas flow rate: 20L / min

  The above evaluation results of the NO adsorption amount are shown in the rightmost column of each table of FIGS. Hereinafter, based on this result, the NO adsorption characteristics of the NOx catalyst will be described. First, an overview of the results shows that in Comparative Examples 1 to 7, the NO adsorption amount remained at 0.6 to 4.7 μmol / g, and the above conditions (moisture adsorption treatment, temperature = 50 ° C., O 2 = 2%). ), The target NO adsorption amount (5 μmol / g or more) is not achieved.

  On the other hand, in each of Examples 1 to 14, a NO adsorption amount exceeding 5 μmol / g was obtained, and the target NO adsorption amount was achieved under the above conditions of moisture adsorption, temperature, and oxygen concentration.

  Hereinafter, the relationship between various factors of the NOx catalyst and the NO adsorption amount will be described in detail. FIG. 8 shows the relationship between the type of zeolite and the NO adsorption amount. Samples were Example 5 (ferrierite (FER)), Example 6 (mordenite (MOR)), Example 2 (ZSM-5), Example 7 (Y-type zeolite), and Example 8 (beta-type zeolite). (BET)).

  As shown in the figure, the NO adsorption amount is large in the above order. Further, in any of the examples, the NO adsorption amount exceeded 5 μmol / g, and it was confirmed that the target NO adsorption amount could be achieved by using the above-mentioned kind of zeolite.

  FIG. 9 shows the relationship between the reciprocal number of the Keiban ratio (= AL 2 O 3 / SiO 2) of zeolite and the NO adsorption amount. Samples are Comparative Example 1 (reciprocal number of Keiban ratio = 0.003) and Examples 1 to 4 (0.013, 0.020, 0.033, 0.043, respectively).

  As shown in the figure, in Comparative Example 1 in which the reciprocal number of the Keiban ratio is 0.003, the NO adsorption amount is slightly lower than the target NO adsorption amount. On the other hand, in Examples 1-4 in which the reciprocal number of the Keiban ratio is greater than 0.003, the NO adsorption amount greatly exceeds 5 μmol / g. From the above, it was confirmed that the target NO adsorption amount can be achieved when the reciprocal number of the Keiban ratio is larger than 0.003.

  FIG. 10 shows the relationship between the Pd carrying amount PdR and the NO adsorption amount. The samples are Comparative Example 7 (PdR = 0%) and Examples 9-14 (PdR = 0.06, 0.11, 0.23, 0.47, 0.89, 2.4%, respectively).

  As shown in the figure, in Comparative Example 7 in which palladium is not supported, the NO adsorption amount is 0.6 μmol / g, and almost no NO adsorption is observed, which is far below the target NO adsorption amount. On the other hand, in all of Examples 9 to 14 in which the Pd carrying amount PdR is 0.06 to 2.4%, the NO adsorption amount exceeds 5 μmol / g, and the target NO adsorption amount is achieved. Further, when the Pd carrying amount PdR was 0.5% or more, it was recognized that the NO adsorption amount did not increase so much even if the Pd carrying amount PdR was increased.

  FIG. 11 shows the relationship between the unit Pd weight PdU and the NO adsorption amount. As in FIG. 10, the samples were Comparative Example 7 (PdR = 0%) and Examples 9 to 14 (PdU = 0.12, 0.22, 0.46, 0.94, 1.78, 4.8 g, respectively). / L).

  As described above, in Comparative Example 7 in which palladium is not supported, the NO adsorption amount is significantly lower than the target NO adsorption amount. On the other hand, in Examples 9 to 14 in which the unit Pd weight PdU is 0.12 to 4.8 g / L, the NO adsorption amount exceeds 5 μmol / g. From the above, it was confirmed that the target NO adsorption amount can be achieved when the unit Pd weight PdU is larger than 0.1 g / L. Further, when the unit Pd weight PdU was 2.0 g / L or more, there was a tendency that the NO adsorption amount did not increase so much even if the unit Pd weight PdU was increased.

  As described above, the NOx catalyst 7 according to the present embodiment includes zeolite and palladium supported on the zeolite, and the palladium is disposed in the vicinity of the acid point of the zeolite. For this reason, since NO is adsorbed to palladium whose electronic state has changed due to the interaction with the acid sites, it is not easily affected by moisture adsorption, and it is not necessary to oxidize NO to NO2.

  Therefore, NOx in the exhaust gas can be favorably adsorbed under low temperature conditions without requiring moisture removal from the exhaust gas and control of the exhaust gas to the lean side. As a result, unlike the conventional exhaust gas purification device, it is not necessary to provide a device for removing moisture from the exhaust gas, and the air-fuel ratio of the air-fuel mixture is controlled to the stoichiometric or rich side when the engine 3 is warmed up. Even in this case, NOx can be favorably adsorbed.

  Further, when the NOx catalyst 7 has a reciprocal Al 2 O 3 / SiO 2 ratio of zeolite greater than 0.003, the NO adsorption amount exceeds 5 μmol / g, and the target NO adsorption amount can be achieved.

  Furthermore, when the zeolite of the NOx catalyst 7 is ZSM-5, ferrierite, mordenite, Y-type zeolite or beta-type zeolite, and the unit Pd weight PdU is larger than 0.1 g / L, the target NO adsorption amount Can be achieved more reliably.

  Further, by setting the unit Pd weight PdU to be greater than 0.1 g / L and less than 2.0 g / L, it is possible to achieve the target NO adsorption amount while efficiently using relatively expensive palladium. it can.

  In addition, this invention can be implemented in various aspects, without being limited to the described embodiment. For example, Examples 1 to 14 shown in the embodiment are merely examples, and the configuration and specifications thereof can be changed within the scope of the gist of the present invention.

  For example, the embodiment is configured under the condition that the target NO adsorption amount is 5 μmol / g or more in order to clear the regulation level SULEV30 in California, which is considered to be strict in the world. Therefore, when this rule is amended or when other rules are targeted, it is possible to change the embodiment so as to satisfy it.

  Further, the specific composition and manufacturing method of the NOx catalyst 7 shown in each example are also merely examples, and can be changed according to the application. Furthermore, in the embodiment, the three-way catalyst 6 is arranged on the upstream side of the NOx catalyst 7, but this may be omitted.

  Further, the embodiment is an example in which the present invention is applied to a gasoline engine mounted on a vehicle. However, the present invention is not limited to this, and a diesel engine for a vehicle or an engine other than a vehicle, for example, a crankshaft. The present invention can also be applied to a marine vessel propulsion engine such as an outboard motor arranged vertically. In addition, it is possible to appropriately change the detailed configuration within the scope of the gist of the present invention.

1 exhaust gas purification device 3 engine (internal combustion engine)
5 Exhaust pipe (exhaust system)
7 NOx catalyst Al2O3 / SiO2 Zeolite ratio reciprocal of zeolite
PdU unit Pd weight (palladium weight per unit volume of NOx catalyst)

Claims (4)

An exhaust gas purification device for an internal combustion engine that is disposed in an exhaust system of an internal combustion engine and purifies NOx in the exhaust gas,
A NOx catalyst having zeolite and palladium that is disposed on Al that is the acid point of the zeolite and supported on the zeolite and that adsorbs NOx in the state of NO;
An exhaust gas purifying apparatus for an internal combustion engine, wherein Al2O3 / SiO2 of the zeolite is larger than 0.003.   The exhaust gas purifying device for an internal combustion engine according to claim 1, wherein the zeolite is ZSM-5, ferrierite, mordenite, Y-type zeolite or beta-type zeolite.   The exhaust gas purification apparatus for an internal combustion engine according to claim 2, wherein the weight of the palladium per unit volume of the NOx catalyst is greater than 0.1 g / L.   The exhaust gas purifying apparatus for an internal combustion engine according to claim 3, wherein the weight of the palladium per unit volume of the NOx catalyst is less than 2.0 g / L.

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