JP2006035130A - Catalyst for exhaust gas purification and production method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To produce a catalyst for exhaust gas purification which can more efficiently purify cold HC (hydrocarbons) discharged at or immediately after engine starting while maintaining or improving adhesiveness between a metallic integral carrier and a catalyst coating layer formed on it, and a production method therefor. <P>SOLUTION: The catalyst for exhaust gas purification is produced by overlaying an HC adsorbent layer and a purification catalyst component layer onto the metallic integral carrier in this order. In the HC adsorbent layer, at least a layer that is brought into contact with the carrier contains metal-containing alumina and zeolite. The production method for the catalyst for exhaust gas purification comprises (1) a process for preparing HC adsorbent layer slurry containing the metal-containing alumina and the zeolite, (2) a process for preparing purification catalyst component layer slurry, and (3) a process for making the catalyst coating layer by overlaying the HC adsorbent layer slurry and purification catalyst component layer slurry obtained by the processes (1) and (2) onto the metallic integral carrier. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an exhaust gas purification catalyst and a method for producing the same, and more particularly, exhaust gas purification capable of efficiently purifying hydrocarbons (HC) discharged at the start of an engine or immediately after the start, so-called cold HC. The present invention relates to a catalyst for use and a production method thereof.

Conventionally, a laminated type HC adsorption catalyst is known in which a zeolite, which is a material having an HC adsorption function, is disposed on a monolithic support and a purification catalyst layer is disposed on an upper layer.
Also, when the monolithic structure type carrier is made of metal, it is known that an alumina layer having no catalytic function is provided as a precoat layer, and this is the adhesion between the lower layer zeolite and the monolithic structure type carrier. It is intended to efficiently develop the HC adsorption retention ability by preventing peeling due to shortage and making the adsorbent coat layer thickness uniform (see, for example, Patent Document 1).
JP 2001-129403 A

However, since the metal monolithic structure type carrier has a unique cell structure, the thickness of the adsorbent coat layer is not sufficiently uniform.
In addition, if the precoat amount of alumina that does not have a catalytic function is increased in order to obtain the uniformity of the adsorbent coat layer, the light off performance may decrease due to an increase in heat mass, and the catalyst performance may decrease. There is still room for improvement in terms of improving the adhesion between the manufactured monolithic support and the zeolite and improving the durability by preventing the catalyst coat layer from peeling off.
Furthermore, when a precoat layer is provided, as a result of considering exhaust pressure loss, the amount of zeolite that can be used is narrow because the amount of zeolite used as an adsorbent is limited, and the number of HC species that can be adsorbed and retained can be increased. In this respect, there was room for improvement.
Furthermore, in the stacked type HC adsorption catalyst, the activation of the purification catalyst component is incomplete at the point of time when the desorbed HC is purified (there is a difference between the desorption start temperature and the purification start temperature), and is discharged without purification. Since HC exists, there was room for improvement in this respect.

  The present invention has been made in view of such problems of the prior art, and the object of the present invention is to provide adhesion between a metal monolithic support and a catalyst coat layer formed thereon. An object of the present invention is to provide an exhaust gas purification catalyst capable of more efficiently purifying cold HC discharged at the start of the engine or immediately after the start, and a method for manufacturing the same, while maintaining or improving the engine.

  As a result of intensive studies to achieve the above object, the present inventors have made the metal element-containing alumina and zeolite contained in at least a layer of the HC adsorbent layer that is in contact with the metal monolithic structure type carrier. Thus, the inventors have found that the above object can be achieved and have completed the present invention.

  That is, the exhaust gas purifying catalyst of the present invention is obtained by laminating an HC adsorbent layer and a purifying catalyst component layer in this order on a metal monolithic support. Of these HC adsorbent layers, at least the layer in contact with the metal monolithic structure type carrier contains the metal element-containing alumina and zeolite.

Moreover, the manufacturing method of the exhaust gas purification catalyst of the present invention is a method of manufacturing the exhaust gas purification catalyst, and includes the following steps (1) to (3).
(1) A step of creating an HC adsorbent layer slurry for forming an HC adsorbent layer containing metal element-containing alumina and zeolite in contact with at least the monolithic structure type carrier of the HC adsorbent layer;
(2) a step of creating a purified catalyst component layer slurry for forming a purified catalyst component layer;
(3) A metal monolithic structure type carrier is coated with the HC adsorbent layer slurry and the purification catalyst component layer slurry obtained in steps (1) and (2) in this order, dried, and calcined. A step of laminating and forming an HC adsorbent layer and a purification catalyst component layer.

  According to the present invention, since the metal element-containing alumina and zeolite are included in at least the layer of the HC adsorbent layer in contact with the metal monolithic structure type carrier, the metal monolithic structure type carrier and the layer formed thereon are formed. It is possible to provide an exhaust gas purifying catalyst capable of more efficiently purifying cold HC discharged at the start of the engine or immediately after the start and a method for manufacturing the same while maintaining or improving the adhesion with the catalyst coat layer. it can.

Hereinafter, the exhaust gas purifying catalyst of the present invention will be described in detail. In the present specification, “%” represents mass percentage unless otherwise specified.
As described above, the exhaust gas purifying catalyst of the present invention is formed by laminating an HC adsorbent layer and a purifying catalyst component layer in this order on a metal monolithic support, and among these HC adsorbent layers, At least the layer in contact with the monolithic structure type carrier contains the metal element-containing alumina and zeolite.
Here, as a metal monolithic structure type carrier (hereinafter referred to as “metal carrier”), a conventionally known typical cell shape is a corrugated shape, in other words, a cell mouth shape is a so-called sign shape. However, the shape of the cell mouth is not limited to this, and various polygonal and circular shapes such as conventionally known triangles, squares, and hexagons can be used. Also, these materials are not particularly limited, and conventionally known materials such as ferritic stainless steel can be used.

The exhaust gas purifying catalyst of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a partially enlarged view showing one embodiment of the structure of the exhaust gas purifying catalyst of the present invention. FIG. 4A is a partially enlarged view showing an example of a cell cross-sectional shape, and FIG. 2B is a partially enlarged view showing an example (three-layer structure) of a laminated structure of catalyst coat layers. As shown in FIG. 6A, the metal carrier 1 is coated with a catalyst coating layer 10, and the catalyst coating layer 10 laminated on the metal carrier 1 as shown in FIG. 12 and a purification catalyst component layer 14. The HC adsorbent layer 12 includes a first layer 12a and a second layer 12b.

In the exhaust gas purifying catalyst of the present invention, at least the layer (first layer 12a) in contact with the metal carrier 1 of the HC adsorbent layer 12 contains the metal element-containing alumina and zeolite, so that the adhesion with the metal carrier 1 is maintained. In addition, the HC adsorption performance can be improved while improving, and as a result of maintaining or improving the adhesion, peeling of the catalyst coat layer 10 can be suppressed, and the durability of the catalyst can be improved.
Further, HC desorbed from the HC adsorbent layer 12 is delayed by the metal element supported on the alumina, and the desorbed HC is removed when the purification catalyst component layer 14 is warmed up and activated. As a result, the HC reaction proceeds efficiently, and the desorption HC conversion rate in the purification catalyst component layer 14 can be improved.
On the other hand, since it is not necessary to provide a precoat layer only for ensuring adhesion with the metal carrier, there is an advantage that the amount of coating can be reduced and as a result, an increase in exhaust pressure loss can be suppressed.
In the present invention, each of the HC adsorbent layer 12 and the purification catalyst component layer 14 may be a single layer or a multilayer structure of two or more layers.

In the present invention, the average particle size of the metal element-containing alumina is preferably larger than the average particle size of the zeolite.
If the average particle size of the metal element-containing alumina is larger than the average particle size of the zeolite, the content of fine particles of the metal-containing alumina that can inhibit HC diffusibility and block the zeolite pores is relatively small. HC adsorption performance can be exhibited well, which is preferable.
The average particle size of the metal-containing alumina is typically 3.5 to 4.5 μm, and the average particle size of the zeolite is typically 1.5 to less than 3.5 μm.

In the present invention, in the layer in contact with the metal carrier, the weight ratio of the metal element-containing alumina and the zeolite contained (metal element-containing alumina / zeolite) is preferably 20/80 to 80/20, and 40/60 More preferably, it is -60/40.
By setting it as such a range, HC adsorption | suction performance can be improved more and adhesiveness with a metal carrier can be kept favorable.

  Furthermore, in the present invention, the zeolite used preferably contains BEA type zeolite. The pore diameter (0.55 to 0.76 nm) and the three-dimensional pore structure of the BEA type zeolite are the sizes of the main HC components (for example, 2,2,4-trimethylpentane and toluene) in the exhaust gas. It can be adsorbed efficiently. Further, if the amount of BEA type zeolite is increased, the amount of HC that can be adsorbed can be increased, so that the HC conversion rate can be improved, and particularly the purification performance of cold HC can be improved.

Further, in the present invention, the HC adsorbent layer has a layer containing metal element-containing alumina, MFI type, FER type or ERI type and a mixture of these optionally, and the zeolite type is BEA type zeolite above the layer. It is desirable to have a layer that is
Adsorption performance of HC having a low C number can be improved by using zeolites such as the above MFI type, FER type, and ERI type having the same or smaller pore diameter (0.55 nm or less) as the BEA type.
In particular, HC having a low C number generally has good diffusibility, and therefore providing a layer containing zeolite such as MFI type on the metal carrier side of the catalyst coating layer further improves the HC adsorption performance and further the HC conversion rate. On the other hand, by providing a layer whose zeolite type is BEA type zeolite on the exhaust gas flow path side of the cell from the layer containing zeolite such as MFI type as described above, the main HC component in the exhaust gas is It is preferable from the viewpoint of further improving the adsorption performance and further the HC conversion rate.
The layer containing zeolite such as MFI may contain BEA type zeolite, and the layer whose zeolite type is BEA type zeolite may contain other components (for example, alumina, noble metal, etc.) other than zeolite. .

Furthermore, in the present invention, the metal element contained in the alumina is preferably a metal element related to a VB group, a VIB group, a VIIB group, a VIII group element, or any combination thereof. More specifically, group VB elements are vanadium, niobium and tantalum, group VIB elements are chromium, molybdenum and tungsten, group VIIB elements are manganese, technetium and rhenium, group VIII elements are iron, cobalt, nickel, ruthenium, rhodium, Palladium, osmium, iridium and platinum.
When such a metal element is contained in alumina, it may be in a metal or oxidized state, but since it easily interacts with HC desorbed from zeolite, it is more likely to desorb from the HC adsorbent layer. It can be delayed, and the HC conversion rate can be improved.

  Further, the metal element is preferably contained in the alumina in a proportion of 1 to 50%, and more preferably in the proportion of 10 to 30%. By setting it as such content, the desorption delay effect can be exhibited more efficiently and HC conversion rate can be improved more.

  Moreover, in this invention, it is preferable that the whole Si / 2Al ratio of the zeolite contained is 10-1000, and it is more preferable that it is 20-100. It goes without saying that the Si / 2Al ratio of some zeolites is not within the range of 10 to 1000, but is included in the scope of the present invention. It is preferable, and this makes it possible to ensure an appropriate HC adsorption amount and retention performance as well as durability.

Further, in the present invention, the purification catalyst component layer comprises 1 to 10 metal equivalents of platinum, rhodium or palladium and a noble metal related to any combination thereof and cerium, zirconium or lanthanum and any combination thereof. It is preferable to contain alumina containing atomic%, and cerium oxide containing 1 to 50 atomic% of metal elements related to zirconium, neodymium, praseodymium, yttrium, lanthanum, and any combination thereof in terms of metal.
The composition of the purification catalyst component layer is not particularly limited as long as at least desorbed HC from the HC adsorbent layer can be purified in an activated state, but the alumina and the promoter component to which the promoter component is added as described above, The inclusion of cerium oxide that acts as an added oxygen supply source can further enhance the HC oxidation activity of the noble metal.
In particular, since the effect of improving the activity on palladium is great, it is desirable to use a purification component layer in which palladium is supported as a noble metal species.

Furthermore, it is preferable that the purification catalyst component layer further contains a zirconium oxide containing 1 to 40 atomic% of metal elements related to cerium, neodymium or lanthanum and any combination thereof in terms of metal.
By adding such zirconium oxide, the noble metal can be activated. Since this effect is particularly effective for platinum and rhodium, it is desirable to use this zirconium oxide in a layer containing platinum and rhodium, thereby further improving the HC conversion rate.

Next, the manufacturing method of the exhaust gas purifying catalyst of the present invention will be described.
As described above, the method for producing an exhaust gas purification catalyst of the present invention is a method for producing the exhaust gas purification catalyst of the present invention, and includes the following steps (1) to (3).
(1) A step of creating an HC adsorbent layer slurry for forming an HC adsorbent layer that forms at least a layer in contact with the metal carrier, that is, an HC adsorbent layer containing metal element-containing alumina and zeolite (2) Purification catalyst component Step of creating a purified catalyst component layer slurry for forming a layer (3) HC adsorbent layer slurry and purified catalyst component layer slurry obtained in steps (1) and (2) on a metal monolithic support In this order, coating, drying, firing, and stacking the HC adsorbent layer and the purification catalyst component layer

By performing such a process, the desired exhaust gas purification catalyst can be produced.
In the step (1), as the HC adsorbent layer slurry for forming the HC adsorbent layer containing the metal element-containing alumina and zeolite, the average particle diameter β of the zeolite with respect to the average particle diameter α of the metal element-containing alumina It is preferable to use a slurry that satisfies the relationship that the ratio (α / β) is greater than 1. This makes it easier and more preferable to control the particle size ratio between the metal element-containing alumina and the zeolite contained in the exhaust gas purification catalyst. The average particle size α of the metal element-containing alumina used is typically 3.5 to 4.5 μm, and the average particle size β of the zeolite used is typically 1.5 to less than 3.5 μm.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited to these Examples.

[Creation of HC adsorbent layer slurry]
Manganese (Mn) was supported on alumina to obtain Mn-containing alumina. The supported concentration of Mn was 30%. A slurry was prepared by mixing BEA-type zeolite (Si / 2Al = 28) and the obtained Mn-containing alumina in such a ratio that the coating amounts were 120 g / L and 60 g / L, respectively. This was designated as HC adsorbent layer slurry 1.
Further, a BEA-type zeolite (Si / 2Al = 28) and the obtained Mn-containing alumina were mixed at a ratio such that the coating amounts were 80 g / L and 100 g / L, respectively, to prepare a slurry. This was designated as HC adsorbent layer slurry 2.

Nickel (Ni) was supported on alumina to obtain Ni-containing alumina. The supported Ni concentration was 20%. FER type zeolite (Si / 2Al = 25) and the obtained Ni-containing alumina were mixed at such a ratio that the coating amounts were 60 g / L and 60 g / L, respectively, to prepare a slurry. This was designated as HC adsorbent layer slurry 3.
Further, MFI-type zeolite (Si / 2Al = 23) and the above-obtained Ni-containing alumina were mixed at a ratio such that the coating amounts were 60 g / L and 60 g / L, respectively, to prepare a slurry. This was designated as HC adsorbent layer slurry 4.

  A slurry was prepared using BEA type zeolite (Si / 2Al = 28). This was used as a zeolite slurry, and a slurry was prepared using the same alumina as described above, in which no metal was supported. This was used as an alumina slurry.

[Preparation of purification catalyst component layer slurry]
Next, an alumina powder containing 3 mol% of Ce and 3 mol% of Ba (Al: 94 mol%) is impregnated with an aqueous palladium nitrate solution or sprayed with high-speed stirring, dried at 150 ° C. for 24 hours, then calcined at 400 ° C. for 1 hour, And calcining at 600 ° C. for 1 hour to obtain Pd-supported alumina powder (powder a). The Pd concentration of this powder a was 3.0%.
A cerium oxide powder containing 30 mol% of Zr (Ce 70 mol%) is impregnated with an aqueous solution of palladium nitrate or sprayed with high-speed stirring, dried at 150 ° C. for 24 hours, calcined at 400 ° C. for 1 hour, and then at 600 ° C. for 1 hour. Firing was performed to obtain Pd-supported cerium oxide powder (powder b). The Pd concentration of this powder b was 2.0%.
250 g of the above Pd-supported alumina powder (powder a), 1250 g of Pd-supported cerium oxide powder (powder b), and 2500 g of nitric acid acidic alumina sol (a sol obtained by adding 10% nitric acid to 10% boehmite alumina) 250 g in terms of ₂ O ₃ ) and 1750 g of pure water were put into a magnetic ball mill, mixed and ground to obtain a slurry liquid. This was used as a purification catalyst component layer slurry.

Example 1
HC adsorbent layer slurry 1 is applied to a metal carrier (cell mouth shape: corrugated, carrier capacity: 0.7 L, foil thickness: 50 μm, number of cells: 200 cells / in 2, material: stainless steel), and dried. After firing, the purification catalyst component layer slurry was applied, dried and fired to obtain the exhaust gas purification catalyst of this example. The HC adsorbent layer of the obtained catalyst contained 120 g / L of BEA type zeolite and 60 g / L of Mn-containing alumina. As for the amount of noble metal supported on the catalyst, Pd was 2 g / L.

(Example 2)
The HC adsorbent layer slurry 2 is applied to the same metal carrier as in Example 1, dried and fired, and then the purified catalyst component layer slurry is applied, dried and fired for exhaust gas purification of this example. A catalyst was obtained. The HC adsorbent layer of the obtained catalyst contained 80 g / L of BEA type zeolite and 100 g / L of Mn-containing alumina. As for the amount of noble metal supported on the catalyst, Pd was 2 g / L.

Example 3
HC adsorbent layer slurry 3 is applied to the same metal carrier as in Example 1, dried and calcined, then zeolite slurry is applied, dried and calcined, and further purified catalyst component layer slurry is applied and dried. And calcining to obtain the exhaust gas purifying catalyst of this example. The first layer of the HC adsorbent layer of the obtained catalyst contained 60 g / L of FER type zeolite and 60 g / L of Ni-containing alumina. The second layer contained 100 g / L of BEA type zeolite. As for the amount of noble metal supported on the catalyst, Pd was 2 g / L.

Example 4
The HC adsorbent layer slurry 4 is applied to the same metal carrier as in Example 1, dried and fired, then the zeolite slurry is applied, dried and fired, and further the purification catalyst component layer slurry is applied. Then, it was dried and calcined to obtain the exhaust gas purifying catalyst of this example. The first layer of the HC adsorbent layer of the obtained catalyst contained 60 g / L of MFI type zeolite and 60 g / L of Ni-containing alumina. The second layer contained 100 g / L of BEA type zeolite. As for the amount of noble metal supported on the catalyst, Pd was 2 g / L.

(Comparative Example 1)
Alumina slurry is applied to the same metal carrier as in Example 1, dried and calcined, then the zeolite slurry is applied, dried and calcined, and further, the purification catalyst component layer slurry is applied and dried. Firing was performed to obtain the exhaust gas purifying catalyst of this example. The obtained catalyst has a precoat layer containing 50 g / L of alumina and an HC adsorbent layer containing 100 g / L of BEA type zeolite. As for the amount of noble metal supported on the catalyst, Pd was 2 g / L. Table 1 shows the specifications of the HC adsorbent layer of the exhaust gas purifying catalyst in each of the above examples. The average particle size ratio between the metal element-containing alumina and zeolite in Table 1 was measured at the time of slurry preparation.

[Performance evaluation]
Under the following conditions, the catalyst of each example was rapidly deteriorated, the vehicle was evaluated, and the cold HC purification performance was compared. The obtained results are shown in Table 2.
(Endurance conditions)
Engine displacement 3000cc
Fuel Gasoline (Nisseki Dash)
Catalyst inlet gas temperature 750 ° C
Endurance time 100 hours (evaluation conditions)
Evaluation vehicle Nissan Motor inline 4 cylinder 1800cc
Evaluation mode LA4-Abag
The cold HC conversion rate represents the reduction rate of HC emission in LA4-Abag, 0 to 250 seconds, and is expressed by the following formula (1)
[(Eng. Out HC emission amount) − (System-Out HC emission amount)] / (Eng. Out HC emission amount) × 100 (1).

From Table 2, it can be seen that the catalysts of Examples 1 to 4 belonging to the scope of the present invention are superior in HC reduction rate, that is, HC conversion rate, compared to Comparative Example 1 outside the present invention.
At the present time, Example 3 seems to give the best results from the viewpoint of the combined effect of expanding the pore diameter range and the heterogeneous zeolite framework structure.

It is the elements on larger scale which show the one aspect | mode of the structure of the exhaust gas purification catalyst of this invention.

Explanation of symbols

1 Metal carrier 10 Catalyst coating layer 12a HC adsorbent layer (first layer)
12b HC adsorbent layer (second layer)
14 Purification catalyst component layer

Claims (12)

An exhaust gas purification catalyst in which an HC adsorbent layer and a purification catalyst component layer are laminated in this order on a metal monolithic structure type carrier,
An exhaust gas purifying catalyst characterized in that at least a layer in contact with the carrier in the HC adsorbent layer contains metal element-containing alumina and zeolite.   2. The exhaust gas purifying catalyst according to claim 1, wherein the average particle diameter of the metal element-containing alumina is larger than the average particle diameter of the zeolite.   The weight ratio of the metal element-containing alumina and the zeolite contained (metal element-containing alumina / zeolite) in the layer in contact with the carrier is 20/80 to 80/20. Exhaust gas purification catalyst.   The exhaust gas purifying catalyst according to any one of claims 1 to 3, wherein the zeolite contains BEA type zeolite.   The HC adsorbent layer has a layer containing a metal element-containing alumina and at least one kind of zeolite selected from the group consisting of MFI type, FER type and ERI type zeolite, and the zeolite type is BEA type zeolite above the layer. The exhaust gas purifying catalyst according to any one of claims 1 to 3, wherein the exhaust gas purifying catalyst according to any one of claims 1 to 3 is provided.   6. The metal element according to any one of claims 1 to 5, wherein the metal element is at least one metal element selected from the group consisting of Group VB, Group VIB, Group VIIB and Group VIII elements. Exhaust gas purification catalyst.   The exhaust gas purifying catalyst according to any one of claims 1 to 6, wherein the metal element is contained in alumina at a ratio of 1 to 50%.   The exhaust gas purification apparatus according to any one of claims 1 to 7, wherein the HC adsorbent layer has a Si / 2Al ratio of all or part of the zeolite contained therein of 10 to 1000. catalyst.   The purification catalyst component layer includes at least one noble metal selected from the group consisting of platinum, rhodium and palladium, and at least one metal element selected from the group consisting of cerium, zirconium and lanthanum in terms of metal. Alumina containing 10 atomic%, and a cerium oxide containing 1 to 50 atomic% in terms of metal of at least one metal element selected from the group consisting of zirconium, neodymium, praseodymium, yttrium and lanthanum The exhaust gas purifying catalyst according to any one of claims 1 to 8.   2. The purification catalyst component layer further contains a zirconium oxide containing 1 to 40 atomic% in terms of metal of at least one metal element selected from the group consisting of cerium, neodymium and lanthanum. The catalyst for exhaust gas purification as described in any one of -9. A method for producing the exhaust gas purifying catalyst according to any one of claims 1 to 10, comprising the following steps (1) to (3):
(1) A step of creating an HC adsorbent layer slurry for forming an HC adsorbent layer containing metal element-containing alumina and zeolite in contact with at least the carrier of the HC adsorbent layer,
(2) a step of creating a purified catalyst component layer slurry for forming a purified catalyst component layer;
(3) A metal monolithic structure type carrier is coated with the HC adsorbent layer slurry and the purification catalyst component layer slurry obtained in steps (1) and (2) in this order, dried, and calcined. A method for producing an exhaust gas purifying catalyst, comprising: a step of stacking an HC adsorbent layer and a purifying catalyst component layer.   In the step (1), as an HC adsorbent layer slurry for forming an HC adsorbent layer containing metal element-containing alumina and zeolite, the ratio of the average particle diameter β of zeolite to the average particle diameter α of metal element-containing alumina 12. The method for producing an exhaust gas purifying catalyst according to claim 11, wherein a slurry satisfying a relationship that (α / β) is larger than 1 is used.

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