JP2023155230A - Reduction catalyst structure for automobile and method for producing the same and exhaust gas treatment device for automobile - Google Patents

Abstract

To provide a highly active reduction catalyst structure for an automobile having excellent catalytic functions and a method for producing the same and to provide an exhaust gas treatment device for an automobile.SOLUTION: There is provided a reduction catalyst structure for an automobile 1 which comprises a carrier 10 with a porous structure composed of a zeolite-type compound and at least one NOx reduction catalyst 20 which is inherent in the carrier and is composed of a metal. The carrier 10 has mutually communicating passages 11. In particular, the carrier 10 has passages 11 formed so that a plurality of holes with the porous structure 11a, 11a,... are mutually communicated inside the carrier 10. The NOx reduction catalyst 20 is at least present in the passages 11 of the carrier 10.SELECTED DRAWING: Figure 1

Description

The present invention relates to an automotive reduction catalyst structure comprising a porous carrier and a Knox reduction catalyst, a method for manufacturing the same, and an automotive exhaust gas treatment device.

As environmental awareness has increased in recent years, automobile exhaust gas regulations have become stricter. Exhaust gas emitted from automobiles contains _NOx (nitrogen oxides). Environmental standards require that the amount of NOX in exhaust gas be below a predetermined concentration. In particular, since the amount of NOX contained in the exhaust gas discharged from automobiles equipped with diesel engines is large, there is a strong demand for reducing the amount of NOX in the exhaust gas.

Therefore, conventionally, automobiles have built-in exhaust gas treatment devices to reduce the amount of NOx in exhaust gas so as to comply with environmental standards. For example, a method of reducing Knox using ammonia produced by a hydrolysis reaction of urea has been used. In order to efficiently reduce Knox as described above, selective catalytic reduction is generally performed, and a Knox reduction catalyst is used for this process. The Knox reduction catalyst is generally supported on a heat-resistant carrier.
Non-Patent Document 1 discloses a Knox reduction reaction by selective catalytic reduction using a nitrogen-based reducing agent such as ammonia or urea.

Hideki Abe, “Current Status and Future of Automobile Exhaust Gas Catalysts,” Science and Technology Trends, National Institute for Science and Technology Policy, December 2010 issue, p. 2, 8-16

In order to efficiently perform the selective catalytic reduction of Knox, it is necessary to raise the temperature of the exhaust gas to a high temperature so that the Knox reduction catalyst has high catalytic activity. However, immediately after starting the car engine, the Knox concentration was relatively high and the exhaust gas temperature was low. For this reason, there was a problem in that the Knox reduction catalyst could not exhibit sufficient catalytic activity, and the amount of Knox in the exhaust gas could not be sufficiently reduced immediately after the engine of the automobile was started. Therefore, there has been a need for a highly active Knox reduction catalyst that has sufficient catalytic function even at low exhaust gas temperatures.

An object of the present invention is to provide a highly active reduction catalyst structure for automobiles having excellent catalytic function, a method for manufacturing the same, and an automobile exhaust gas treatment device.

The gist of the present invention is as follows.
[1] A carrier with a porous structure composed of a zeolite type compound,
at least one Knox reduction catalyst made of a metal and present in the carrier;
Equipped with
the carrier has passages that communicate with each other,
A reduction catalyst structure for an automobile, characterized in that the Knox reduction catalyst is present in at least the passageway of the carrier.
[2] The passageway is one of one-dimensional pores, two-dimensional pores, and three-dimensional pores defined by the skeletal structure of the zeolite-type compound, and one of the one-dimensional pores, two-dimensional pores, and three-dimensional pores defined by the skeletal structure of the zeolite-type compound. The reduction catalyst structure for an automobile according to [1] above, which has an enlarged diameter portion that is different from any of the enlarged diameter portions, and wherein the Knox reduction catalyst is present at least in the enlarged diameter portion.
[3] [2] above, wherein the enlarged diameter portion communicates with each other a plurality of holes constituting any one of the one-dimensional hole, the two-dimensional hole, and the three-dimensional hole. The automotive reduction catalyst structure described above.
[4] The Knox reduction catalyst is metal fine particles,
The automotive reduction catalyst structure according to [2] or [3] above, wherein the average particle diameter of the metal fine particles is larger than the average inner diameter of the passageway and smaller than or equal to the inner diameter of the enlarged diameter portion. .
[5] The method according to [4] above, wherein the metal element (M) of the metal fine particles is contained in an amount of 0.5 to 2.5% by mass based on the automotive reduction catalyst structure. Automotive reduction catalyst structure.
[6] The automotive reduction catalyst structure according to [4] or [5] above, wherein the metal fine particles have an average particle size of 0.08 nm to 30 nm.
[7] The reduction catalyst structure for an automobile as described in [6] above, wherein the metal fine particles have an average particle size of 0.4 nm to 11.0 nm.
[8] The automobile according to any one of [4] to [7] above, wherein the ratio of the average particle diameter of the metal fine particles to the average inner diameter of the passage is 0.05 to 300. Reduction catalyst structure for use.
[9] The reduction catalyst structure for an automobile as described in [8] above, wherein the ratio of the average particle diameter of the metal fine particles to the average inner diameter of the passage is 0.1 to 30.
[10] The automotive reduction catalyst structure according to [9] above, wherein the ratio of the average particle diameter of the metal fine particles to the average inner diameter of the passage is 1.4 to 3.6.
[11] The average inner diameter of the passage is 0.1 nm to 1.5 nm,
The reduction catalyst structure for an automobile according to any one of [2] to [10] above, wherein the inner diameter of the enlarged diameter portion is 0.5 nm to 50 nm.
[12] The automotive reduction catalyst structure according to any one of [1] to [11] above, further comprising at least one other functional substance held on the outer surface of the carrier. body.
[13] The content of the at least one Knox reduction catalyst inherent in the carrier is larger than the content of the at least one other functional substance held on the outer surface of the carrier. The automotive reduction catalyst structure according to [12] above.
[14] The automotive reduction catalyst structure according to any one of [1] to [13] above, wherein the zeolite-type compound is a silicate compound.
[15] An automobile exhaust gas treatment device comprising the automobile reduction catalyst structure according to any one of [1] to [14] above.
[16] A firing step of firing a precursor material (B) in which the precursor material (A) is impregnated with a metal-containing solution to obtain a carrier with a porous structure composed of a zeolite type compound;
a hydrothermal treatment step of hydrothermally treating the precursor material (C) obtained by firing the precursor material (B);
a step of performing a reduction treatment on the hydrothermally treated precursor material (C);
1. A method for producing a reduction catalyst structure for an automobile, comprising:
[17] The automotive reduction according to [16] above, characterized in that 50 to 500% by mass of a nonionic surfactant is added to the precursor material (A) before the firing step. Method for manufacturing catalyst structure.
[18] Before the firing step, the metal-containing solution is added to the precursor material (A) in multiple portions to impregnate the precursor material (A) with the metal-containing solution. A method for producing a reduction catalyst structure for an automobile as described in [16] or [17] above.
[19] When impregnating the precursor material (A) with the metal-containing solution before the firing step, the amount of the metal-containing solution added to the precursor material (A) In terms of the ratio of silicon (Si) constituting the precursor material (A) to the metal element (M) contained in the metal-containing solution added to (A) (atomic ratio Si/M), The method for producing a reduction catalyst structure for an automobile according to any one of [16] to [18] above, characterized in that the reduction catalyst structure is adjusted to have a molecular weight of 10 to 1,000.
[20] The method for producing a reduced catalyst structure for an automobile according to [16] above, characterized in that in the hydrothermal treatment step, the precursor material (C) and a structure-directing agent are mixed.
[21] The method for producing a reduction catalyst structure for an automobile according to [16] above, wherein the hydrothermal treatment step is performed in a basic atmosphere.

According to the present invention, it is possible to provide a highly active reduction catalyst structure for automobiles having excellent catalytic function, a method for manufacturing the same, and an automobile exhaust gas treatment device.

FIG. 1 schematically shows the internal structure of an automotive reduction catalyst structure according to an embodiment of the present invention, and FIG. 1(a) is a perspective view (partially shown in cross section). ), FIG. 1(b) is a partially enlarged sectional view. FIG. 2 is a partially enlarged sectional view for explaining an example of the function of the automotive reduction catalyst structure in FIG. It is. FIG. 3 is a flowchart showing an example of a method for manufacturing the automotive reduction catalyst structure of FIG. 1. FIG. 4 is a schematic diagram showing a modification of the automotive reduction catalyst structure of FIG. 1.

Embodiments of the present invention will be described in detail below with reference to the drawings.

[Configuration of automotive reduction catalyst structure]
FIG. 1 is a diagram schematically showing the structure of an automotive reduction catalyst structure according to an embodiment of the present invention, in which (a) is a perspective view (partially shown in cross section), and (b) is a partial view. It is an enlarged sectional view. Note that the automotive reduction catalyst structure shown in FIG. 1 shows one example thereof, and the shapes, dimensions, etc. of each structure according to the present invention are not limited to those shown in FIG. 1.

As shown in FIG. 1(a), the automotive reduction catalyst structure 1 includes a porous carrier 10 made of a zeolite compound, and at least one Knox reduction catalyst 20 contained in the carrier 10. Equipped with

In the automobile reduction catalyst structure 1 , a plurality of Knox reduction catalysts 20 , 20 , . . . are present inside the porous structure of the carrier 10 . The Knox reduction catalyst 20 may be any substance as long as it has reduction catalytic ability (reduction catalytic activity), and is preferably metal fine particles. The metal fine particles will be described in detail later.

The carrier 10 has a porous structure, and preferably has a plurality of pores 11a, 11a, . . . , so as to have passages 11 that communicate with each other, as shown in FIG. 1(b). Here, the Knox reduction catalyst 20 is present in at least the passages 11 of the carrier 10 , and is preferably held in at least the passages 11 of the carrier 10 .

With this configuration, movement of the Knox reduction catalyst 20 within the carrier 10 is restricted, and aggregation of the Knox reduction catalysts 20, 20 is effectively prevented. As a result, reduction in the effective surface area of the Knox reduction catalyst 20 can be effectively suppressed, and the reduction catalytic activity of the Knox reduction catalyst 20 can be maintained for a long period of time. That is, according to the automotive reduction catalyst structure 1, it is possible to suppress the decrease in the reduction catalyst activity due to agglomeration of the Knox reduction catalyst 20, and it is possible to extend the life of the Knox reduction catalyst 1. Furthermore, by extending the life of the Knox reduction catalyst 1, the frequency of replacing the Knox reduction catalyst 1 can be reduced, and the amount of discarded used Knox reduction catalyst 1 can be significantly reduced, leading to resource conservation. .

Normally, when a Knox reduction catalyst is used in a fluid (such as automobile exhaust gas), there is a possibility that it will receive an external force from the fluid. In this case, if the Knox reduction catalyst is merely held in an attached state on the outer surface of the carrier 10, there is a problem that it is likely to separate from the outer surface of the carrier 10 due to the influence of external force from the fluid. On the other hand, in the automotive reduction catalyst structure 1, the Knox reduction catalyst 20 is present at least in the passage 11 of the carrier 10, so even if it is affected by an external force due to fluid, the Knox reduction catalyst 20 is removed from the carrier 10. Hard to leave. That is, when the automotive reduction catalyst structure 1 is in a fluid, the fluid flows into the passage 11 from the hole 11a of the carrier 10, so the speed of the fluid flowing inside the passage 11 is determined by the passage resistance (frictional force). ), it is considered that the speed of the fluid flowing on the outer surface of the carrier 10 is slower than that of the fluid flowing on the outer surface of the carrier 10. Due to the influence of such flow path resistance, the pressure that the Knox reduction catalyst 20 in the passage 11 receives from the fluid is lower than the pressure that the Knox reduction catalyst outside the carrier 10 receives from the fluid. Therefore, detachment of the Knox reduction catalyst 20 contained in the carrier 11 can be effectively suppressed, and the reduction catalytic activity of the Knox reduction catalyst 20 can be stably maintained over a long period of time. Note that the flow path resistance as described above is considered to increase as the passage 11 of the carrier 10 has a plurality of bends and branches and the interior of the carrier 10 has a more complex three-dimensional structure. .

Moreover, the passage 11 is formed of one of one-dimensional pores, two-dimensional pores, and three-dimensional pores defined by the skeleton structure of the zeolite-type compound, and one of the one-dimensional pores, two-dimensional pores, and three-dimensional pores defined by the skeletal structure of the zeolite-type compound. It is preferable that the metal particles 20 have an enlarged diameter part 12 that is different from either of them, and in this case, it is preferable that the metal fine particles 20 exist at least in the enlarged diameter part 12 and are included in at least the enlarged diameter part 12. It is more preferable. The one-dimensional pore referred to here refers to a tunnel-shaped or cage-shaped pore forming a one-dimensional channel, or a plurality of tunnel- or cage-shaped pores (multiple one-dimensional holes) forming a plurality of one-dimensional channels. channel). Furthermore, a two-dimensional hole refers to a two-dimensional channel in which multiple one-dimensional channels are two-dimensionally connected, and a three-dimensional hole refers to a three-dimensional channel in which a plurality of one-dimensional channels are three-dimensionally connected. Point.
Thereby, the movement of the Knox reduction catalyst 20 within the carrier 10 is further restricted, and separation of the Knox reduction catalyst 20 and aggregation of the Knox reduction catalysts 20, 20 can be further effectively prevented. Inclusion refers to a state in which the Knox reduction catalyst 20 is encapsulated in the carrier 10. At this time, the Knox reduction catalyst 20 and the carrier 10 do not necessarily have to be in direct contact with each other, and other substances (such as a surfactant) may be present between the Knox reduction catalyst 20 and the carrier 10. In this state, the Knox reduction catalyst 20 may be indirectly present on the carrier 10.

Although FIG. 1(b) shows a case where the Knox reduction catalyst 20 is present in the enlarged diameter portion 12, the structure is not limited to this, and the Knox reduction catalyst 20 is partially located in the enlarged diameter portion 12. It may exist in the passage 11 in a state of protruding outside. Further, the Knox reduction catalyst 20 may be partially embedded in a portion of the passage 11 other than the enlarged diameter portion 12 (for example, an inner wall portion of the passage 11), or may be fixedly present.
Further, it is preferable that the enlarged diameter portion 12 communicates with each other a plurality of holes 11a, 11a constituting any one of the one-dimensional hole, the two-dimensional hole, and the three-dimensional hole. As a result, separate passages different from the one-dimensional holes, two-dimensional holes, or three-dimensional holes are provided inside the carrier 10, so that the function of the Knox reduction catalyst 20 can be exhibited more effectively.

Furthermore, the passage 11 is three-dimensionally formed inside the carrier 10, including a branching part or a merging part, and the enlarged diameter part 12 is preferably provided at the branching part or the merging part of the passage 11. .

The average inner diameter _DF of the passages 11 formed in the carrier 10 is calculated from the average value of the short axis and long axis of the holes 11a constituting any one of the one-dimensional holes, two-dimensional holes, and three-dimensional holes, for example. It is 0.1 nm to 1.5 nm, preferably 0.5 nm to 0.8 nm. Further, the inner diameter D _E of the enlarged diameter portion 12 is, for example, 0.5 nm to 50 nm, preferably 1.1 nm to 40 nm, and more preferably 1.1 nm to 3.3 nm. The inner diameter D _E of the enlarged diameter portion 12 depends on, for example, the pore diameter of the precursor material (A) described below and the average particle diameter D _C of the Knox reduction catalyst 20 present. The inner diameter _DE of the enlarged diameter portion 12 is large enough to accommodate the Knox reduction catalyst 20.

The carrier 10 is composed of a zeolite type compound. Examples of zeolite-type compounds include zeolite (aluminosilicate), cation exchange zeolite, silicate compounds such as silicalite, zeolite analogs such as aluminoborate, aluminoarsenate, and germanate, molybdenum phosphate, etc. Examples include phosphate-based zeolite-like substances. Among these, the zeolite type compound is preferably a silicate compound.

The skeleton structures of zeolite compounds are FAU type (Y type or X type), MTW type, MFI type (ZSM-5), FER type (ferrierite), LTA type (A type), and MWW type (MCM-22). , MOR type (mordenite), LTL type (L type), BEA type (beta type), etc., preferably MFI type, more preferably ZSM-5. A zeolite type compound has a plurality of pores with a pore diameter depending on each skeleton structure. For example, the maximum pore diameter of the MFI type is 0.636 nm (6.36 Å), and the average pore diameter is 0.560 nm (5.60 Å). be.

Hereinafter, the case where the Knox reduction catalyst 20 is metal fine particles will be described in detail.

The metal fine particles 20 may be primary particles or secondary particles formed by agglomeration of primary particles, but the average particle diameter D _C of the metal fine particles 20 is preferably the average inner diameter D _F of the passage 11. and is smaller than or equal to the inner diameter D _E of the enlarged diameter portion 12 (D _F <D _C ≦D _E ). Such metal fine particles 20 are present in the enlarged diameter portion 12 in the passage 11 and are preferably included, so that movement of the metal fine particles 20 within the carrier 10 is regulated. Therefore, even if the metal fine particles 20 receive an external force from the fluid, movement of the metal fine particles 20 within the carrier 10 is suppressed, and the enlarged diameter portions 12, 12, . It is possible to effectively prevent the metal fine particles 20, 20, . . . present in each of the above from coming into contact with each other.

Further, the average particle diameter D _C of the metal fine particles 20 is preferably 0.08 nm to 30 nm, more preferably 0.08 nm or more and less than 25 nm, and even more preferably It is 0.4 nm to 11.0 nm, particularly preferably 0.8 nm to 2.7 nm. Further, the ratio of the average particle diameter D _C of the metal fine particles 20 to the average inner diameter D _F of the passage 11 (D _C /D _F ) is preferably 0.05 to 300, more preferably 0.1 to 30. , more preferably from 1.1 to 30, particularly preferably from 1.4 to 3.6.
Further, when the Knox reduction catalyst 20 is a metal fine particle, the metal element (M) of the metal fine particle is preferably contained in an amount of 0.5 to 2.5% by mass based on the automotive reduction catalyst structure 1. It is more preferable that the content is 0.5 to 1.5% by mass based on the automotive reduction catalyst structure 1. For example, when the metal element (M) is Co, the content (mass%) of the Co element is [(mass of Co element)/(mass of all elements in automotive reduction catalyst structure 1)]×100. expressed.

The metal fine particles may be composed of an unoxidized metal, and may be composed of a single metal or a mixture of two or more metals. In addition, in this specification, "metal" (as a material) constituting metal fine particles refers to a single metal containing one type of metal element (M) and a metal alloy containing two or more types of metal elements (M). It is a general term for metals containing one or more metal elements.

The metal fine particles 20 include gold, silver, rhodium (Rh), iridium (Ir), osmium (Os), platinum (Pt), palladium (Pd), ruthenium (Ru), nickel (Ni), cobalt (Co), The main component is molybdenum (Mo), tungsten (W), iron (Fe), chromium (Cr), cerium (Ce), copper (Cu), magnesium (Mg), or aluminum (Al). It is preferable that the metal is made of a composite metal. The metal fine particles 20 are more preferably metal fine particles made of at least one noble metal selected from the group consisting of gold, silver, platinum, palladium, rhodium, iridium, ruthenium, and osmium. In the present embodiment, the "metal" of the metal fine particles refers to a metal that is a simple metal element and is not oxidized.

Further, the ratio of silicon (Si) constituting the carrier 10 to the metal element (M) constituting the metal fine particles 20 (atomic ratio Si/M) is preferably 10 to 1000, and preferably 50 to 200. is more preferable. If the ratio is greater than 1000, the reduction catalyst activity will be low and there is a possibility that the function as a Knox reduction catalyst will not be obtained sufficiently. On the other hand, if the ratio is smaller than 10, the ratio of the metal fine particles 20 becomes too large, and the strength of the carrier 10 tends to decrease. Note that the metal fine particles 20 referred to herein refer to fine particles that exist inside the carrier 10 and are preferably held or supported, and do not include metal fine particles attached to the outer surface of the carrier 10.

[Function of automotive reduction catalyst structure]
The automotive reduction catalyst structure 1 has a molecular sieving ability that allows NOx (nitrogen oxides) to pass therethrough. Specifically, as shown in FIG. 2(a), since NOX has a size smaller than the inner diameter of the hole 11a formed on the outer surface 10a of the carrier 10, it can penetrate into the carrier 10 and fill the hole. Exhaust gas component 15 having a size exceeding the inner diameter of 11a is restricted from entering into carrier 10. This molecular sieving ability allows the Nox that can enter the pores 11a to react preferentially. Here, "Knox" means nitrogen oxides, including nitric oxide (NO), nitrogen dioxide (NO ₂ ), nitrous oxide (dinitrogen monoxide) (N ₂ O), and dinitrogen trioxide (N ₂ O ₃ ), dinitrogen tetroxide (N ₂ O ₄ ), dinitrogen pentoxide (N ₂ O ₅ ), and the like. Nox is also represented by the chemical formula NOx. NOX in automobile exhaust gas is mainly composed of nitrogen monoxide.

Of the molecules generated within the pores 11a by the above reaction, only molecules that can exit from the carrier 10 through the pores 11a can be obtained as products, and molecules that cannot exit from the carrier 10 through the pores 11a can be obtained as products. After being converted into molecules of a size that can exit from the pores 11a, they exit from the carrier 10 through the pores 11a. Thereby, the molecules that exit the carrier 10 can be restricted to predetermined molecules.

Further, in the automotive reduction catalyst structure 1, the Knox reduction catalyst 20 is present in the enlarged diameter portion 12 of the passage 11. Therefore, the Knox that has entered the hole 11a, that is, the passage 11, comes into contact with the Knox reduction catalyst 20. Further, in the case where the Knox reduction catalyst 20 is, for example, metal fine particles, the average particle diameter D _C of the metal fine particles is larger than the average inner diameter D _F of the passage 11 and smaller than the inner diameter D _E of the enlarged diameter portion 12 . (D _F <D _C <D _E ), a small passage 13 is formed between the metal fine particles and the expanded diameter portion 12 (arrow in the figure), and the Nox that has entered the small passage 13 comes into contact with the metal fine particles. At this time, the movement of the Knox reducing catalyst 20 is restricted by being present in the enlarged diameter portion 12, and a large contact area with the fluid containing Knox that has entered the passage 11 can be maintained.

When the Nox that has entered the passage 11 comes into contact with the metal fine particles serving as the Nox reduction catalyst 20, the Nox is reduced by, for example, the following reduction reaction.
NO _x →1/2N ₂ +x/2O ₂ (1)
NO _x +2x/3NH ₃ → (1/2+x/3) N ₂ +xH ₂ O (2)
The reduction reaction of the above formula (1) is a heterogeneous catalytic reaction in which the Knox reduction catalyst functions as a heterogeneous catalyst. Moreover, the reduction reaction of the above formula (2) is a reaction by SCR (selective catalytic reduction).

Here, when the exhaust gas is at a high temperature, there is a concern that the metal fine particles 20 will be diffused by the heat received from the exhaust gas, and the metal fine particles 20 will become ultra-fine metal particles due to the diffusion and be detached from the enlarged diameter portion 12. However, the phenomenon in which small metal particles with a particle size of about 5 nm, for example, diffuse as smaller metal particles, is unstable, and high activation energy is required for the diffusion to proceed, so the above diffusion does not proceed. hard. Further, even if the diffusion progresses, the metal fine particles 20 become ultrafine particles, so the effective surface area as a catalyst after diffusion increases compared to before diffusion. Furthermore, although the passage 11 is shown in a simplified manner in FIG. It is presumed that the movement of the metal fine particles along the line can be regulated to some extent, and aggregation (sintering) caused by the movement of the metal fine particles 20 can be suppressed. Furthermore, even if the metal fine particles 20 are detached from the enlarged diameter portion 12, it is presumed that the above-described structure of the passage 11 causes the metal ultrafine particles to remain in the carrier 10 for a long time. Therefore, the presence of the metal fine particles 20 in the enlarged diameter portion 12 allows it to function as a Knox reduction catalyst for a long period of time. Furthermore, by maintaining a large surface area of the Knox reduction catalyst, a highly active Knox reduction catalyst having excellent catalytic function can be obtained. Therefore, even when the temperature of the exhaust gas is low, such as immediately after starting the engine, it is possible to reduce Knox with high efficiency.

[Automobile exhaust gas treatment equipment]
In one embodiment, an automotive exhaust gas treatment device having an automotive reduction catalyst structure may be provided. An automobile exhaust gas treatment device may have an automobile reduction catalyst structure alone, or may be combined with another catalyst structure such as an automobile oxidation catalyst structure, a particulate matter collection filter, etc. It's okay. By using the automotive reduction catalyst structure in a device having such a configuration, the same effects as described above can be achieved.

[Method for manufacturing automotive reduction catalyst structure]
FIG. 3 is a flowchart showing a method for manufacturing the automotive reduction catalyst structure 1 of FIG. Hereinafter, an example of a method for producing a reduction catalyst structure for an automobile will be described, taking as an example the case where the Knox reduction catalyst contained in the carrier is metal fine particles.

(Step S1: Preparation process)
As shown in FIG. 3, first, a precursor material (A) for obtaining a carrier having a porous structure composed of a zeolite type compound is prepared. Precursor material (A) is preferably a regular mesoporous material, and can be appropriately selected depending on the type (composition) of the zeolite compound constituting the carrier of the automotive reduction catalyst structure.

Here, when the zeolite type compound constituting the carrier of the reduction catalyst structure for automobiles is a silicate compound, the regular mesoporous material has pores with a pore diameter of 1 to 50 nm in one dimension and two dimensions. Alternatively, it is preferably a compound consisting of an Si--O skeleton that is three-dimensionally uniform in size and regularly developed. Such regular mesoporous materials can be obtained as various synthetic products depending on the synthesis conditions, but specific examples of synthetic products include SBA-1, SBA-15, SBA-16, KIT-6, FSM- No. 16, MCM-41, etc., among which MCM-41 is preferred. The pore diameter of SBA-1 is 10 to 30 nm, the pore diameter of SBA-15 is 6 to 10 nm, the pore diameter of SBA-16 is 6 nm, the pore diameter of KIT-6 is 9 nm, and the pore diameter of FSM-16 is 3. ~5 nm, and the pore size of MCM-41 is 1-10 nm. Examples of such regular mesoporous materials include mesoporous silica, mesoporous aluminosilicate, mesoporous metallosilicate, and the like.

The precursor material (A) may be either a commercially available product or a synthetic product. When synthesizing the precursor material (A), it can be performed by a known method for synthesizing regular mesoporous substances. For example, a mixed solution containing a raw material containing the constituent elements of the precursor material (A) and a templating agent for defining the structure of the precursor material (A) is prepared, and the pH is adjusted as necessary. , perform hydrothermal treatment (hydrothermal synthesis). Thereafter, the precipitate (product) obtained by the hydrothermal treatment is collected (e.g., filtered), washed and dried as necessary, and further calcined to form a powdered regular mesoporous material. A precursor material (A) is obtained. Here, as the solvent for the mixed solution, for example, water, an organic solvent such as alcohol, or a mixed solvent thereof can be used. The raw material is selected depending on the type of carrier, and examples thereof include silica agents such as tetraethoxysilane (TEOS), fumed silica, and quartz sand. In addition, various surfactants, block copolymers, etc. can be used as the template agent, and it is preferable to select it depending on the type of composite of the regular mesoporous material. For example, when producing MCM-41, Preferably, a surfactant such as hexadecyltrimethylammonium bromide is used. The hydrothermal treatment can be carried out, for example, in a closed container under treatment conditions of 80 to 800° C., 5 hours to 240 hours, and 0 to 2000 kPa. The firing treatment can be performed, for example, in air at 350 to 850° C. for 2 to 30 hours.

(Step 2: Impregnation process)
Next, the prepared precursor material (A) is impregnated with a metal-containing solution to obtain a precursor material (B).

The metal-containing solution may be any solution containing a metal component (for example, a metal ion) corresponding to the metal element (M) constituting the metal fine particles of the automotive reduction catalyst structure. It can be prepared by dissolving a metal salt containing M). Examples of such metal salts include metal salts such as chlorides, hydroxides, oxides, sulfates, and nitrates, of which nitrates are preferred. As the solvent, for example, water, an organic solvent such as alcohol, or a mixed solvent thereof can be used.

The method for impregnating the precursor material (A) with the metal-containing solution is not particularly limited, but for example, before the firing step described below, a plurality of metal-containing solutions are impregnated while stirring the powdered precursor material (A). It is preferable to add small amounts in batches. In addition, from the viewpoint of making it easier for the metal-containing solution to penetrate into the pores of the precursor material (A), a surfactant may be added as an additive to the precursor material (A) before adding the metal-containing solution. It is preferable to add it in advance. Such additives have the function of coating the outer surface of the precursor material (A), suppressing the adhesion of the metal-containing solution added thereafter to the outer surface of the precursor material (A), and preventing metal-containing solutions from adhering to the outer surface of the precursor material (A). It is thought that the solution contained therein can more easily penetrate into the pores of the precursor material (A). As for the method of adding the nonionic surfactant, for example, it is preferable to add 50 to 500% by mass of the nonionic surfactant to the precursor material (A) before the firing step described below. If the amount of the nonionic surfactant added to the precursor material (A) is less than 50% by mass, the above-mentioned suppressing effect will be difficult to exhibit, and the amount of the nonionic surfactant added to the precursor material (A) will be less than 50% by mass. Adding more than % by mass is not preferable because the viscosity increases too much. Therefore, the amount of nonionic surfactant added to the precursor material (A) is set within the above range.

Examples of such additives include nonionic surfactants such as polyoxyethylene oleyl ether, polyoxyethylene alkyl ether, and polyoxyethylene alkylphenyl ether. These surfactants have a large molecular size and cannot penetrate into the pores of the precursor material (A), so they do not adhere to the inside of the pores and prevent the metal-containing solution from entering the pores. It is thought that it will not interfere.

The amount of the metal-containing solution added to the precursor material (A) is determined by the amount of the metal element (M) contained in the metal-containing solution impregnated into the precursor material (A) (i.e., the amount of the metal element (M) contained in the metal-containing solution to be impregnated into the precursor material (A)). It is preferable to adjust it appropriately by taking into account the amount of the metal element (M) contained in ). For example, the amount of the metal-containing solution added to the precursor material (A) before the firing step described below is based on the metal element (M) contained in the metal-containing solution added to the precursor material (A). The ratio of silicon (Si) constituting the precursor material (A) (atomic ratio Si/M) is preferably adjusted to 10 to 1000, and preferably adjusted to 50 to 200. It is more preferable. For example, if a surfactant is added as an additive to the precursor material (A) before adding the metal-containing solution to the precursor material (A), the addition of the metal-containing solution to the precursor material (A) By setting the amount to 50 to 200 in terms of the atomic ratio Si/M, the metal element (M) of the metal fine particles is 0.5 to 2.5% by mass with respect to the automotive reduction catalyst structure 1. It can be contained in The amount of the metal element (M) present inside the pores in the state of the precursor material (B) is determined under the same conditions as the metal concentration of the metal-containing solution, the presence or absence of the above additives, and other conditions such as temperature and pressure. If so, it is approximately proportional to the amount of the metal-containing solution added to the precursor material (A). Further, the amount of the metal element (M) inherent in the precursor material (B) is in a proportional relationship with the amount of the metal element constituting the metal fine particles inherent in the support of the automotive reduction catalyst structure. Therefore, by controlling the amount of the metal-containing solution added to the precursor material (A) within the above-mentioned range, the metal-containing solution can be sufficiently impregnated into the pores of the precursor material (A). , it is possible to adjust the amount of metal fine particles contained in the carrier of the reduction catalyst structure for automobiles.

After impregnating the precursor material (A) with the metal-containing solution, a cleaning treatment may be performed as necessary. As the cleaning solution, water, an organic solvent such as alcohol, or a mixed solution thereof can be used. Further, it is preferable to impregnate the precursor material (A) with a metal-containing solution, perform a cleaning treatment if necessary, and then further perform a drying treatment. Examples of the drying treatment include natural drying for about one night and drying at a high temperature of 150° C. or lower. Note that if the firing treatment described below is performed with a large amount of water contained in the metal-containing solution or water in the cleaning solution remaining in the precursor material (A), the regular mesopores of the precursor material (A) will be removed. Since there is a risk that the skeletal structure of the material may be broken, it is preferable to dry it thoroughly.

(Step S3: Firing process)
Next, the precursor material (B) obtained by impregnating the precursor material (A) with a metal-containing solution to obtain a carrier with a porous structure composed of a zeolite type compound is fired, and the precursor material (C) is obtained. get.

The firing treatment is preferably carried out in air at 350 to 850° C. for 2 to 30 hours, for example. Through such firing treatment, the metal component impregnated into the pores of the regular mesoporous material undergoes crystal growth, and metal fine particles are formed within the pores.

(Step S4: Hydrothermal treatment step)
Next, a mixed solution of the precursor material (C) and a structure-directing agent is prepared, and the precursor material (C) obtained by firing the precursor material (B) is hydrothermally treated to produce an automotive material. A reduced catalyst structure is obtained.

The structure-directing agent is a template agent for defining the skeletal structure of the carrier of the automotive reduction catalyst structure, and for example, a surfactant can be used. The structure directing agent is preferably selected depending on the skeleton structure of the support of the reduction catalyst structure for automobiles, and examples thereof include tetramethylammonium bromide (TMABr), tetraethylammonium bromide (TEABr), and tetrapropylammonium bromide (TPABr). Surfactants are preferred.

The precursor material (C) and the structure-directing agent may be mixed during the main hydrothermal treatment step, or may be mixed before the hydrothermal treatment step. The method for preparing the mixed solution is not particularly limited, and the precursor material (C), the structure-directing agent, and the solvent may be mixed simultaneously, or the precursor material (C) and the structure-directing agent are mixed in the solvent. After the agents are dispersed in individual solutions, the respective dispersion solutions may be mixed. As the solvent, for example, water, an organic solvent such as alcohol, or a mixed solvent thereof can be used. Moreover, it is preferable to adjust the pH of the mixed solution using an acid or a base before performing the hydrothermal treatment.

The hydrothermal treatment can be carried out by a known method, and is preferably carried out under treatment conditions of 80 to 800° C., 5 hours to 240 hours, and 0 to 2000 kPa in a closed container, for example. Moreover, it is preferable that the hydrothermal treatment is performed in a basic atmosphere. Although the reaction mechanism here is not necessarily clear, by performing hydrothermal treatment using the precursor material (C) as a raw material, the skeletal structure of the precursor material (C) as a regular mesoporous material gradually collapses; While the position of the metal fine particles inside the pores of the precursor material (C) is generally maintained, a new skeletal structure (porous structure) is created as a support for the reduction catalyst structure for automobiles by the action of the structure directing agent. It is formed. The thus obtained reduction catalyst structure for automobiles includes a carrier having a porous structure and fine metal particles contained in the carrier, and furthermore, the carrier has passages in which a plurality of pores communicate with each other due to its porous structure. , at least a portion of the metal fine particles are present in the passageway of the carrier.
Furthermore, in the present embodiment, in the hydrothermal treatment step, a mixed solution of the precursor material (C) and the structure-directing agent is prepared, and the precursor material (C) is hydrothermally treated. However, the precursor material (C) may be hydrothermally treated without mixing the precursor material (C) and the structure-directing agent.

The precipitate (reduced catalyst structure for automobiles) obtained after the hydrothermal treatment is preferably washed, dried, and calcined as necessary after recovery (for example, filtration). As the cleaning solution, water, an organic solvent such as alcohol, or a mixed solution thereof can be used. Examples of the drying treatment include natural drying for about one night and drying at a high temperature of 150° C. or lower. Note that if the calcination treatment is performed with a large amount of moisture remaining in the precipitate, there is a risk that the skeletal structure as a carrier of the automotive reduction catalyst structure may be broken, so it is preferable to thoroughly dry the precipitate. Further, the firing treatment can be performed, for example, in air at 350 to 850° C. for 2 to 30 hours. Through such firing treatment, the structure directing agent adhering to the automotive reduction catalyst structure is burned off. In addition, the automotive reduction catalyst structure can be used as it is, depending on the purpose of use, without subjecting the collected precipitate to calcination treatment. For example, if the environment in which the reduction catalyst structure for automobiles is used is a high-temperature environment with an oxidizing atmosphere, the structure-directing agent will be burnt out by exposing it to the use environment for a certain period of time, and the structure will remain in the same car as if it had been subjected to firing treatment. Since a reduced catalyst structure is obtained, it can be used as is.

The manufacturing method described above is an example in which the metal element (M) contained in the metal-containing solution impregnated into the precursor material (A) is a metal species that is difficult to oxidize (for example, a noble metal).

If the metal element (M) contained in the metal-containing solution impregnated into the precursor material (A) is a metal species that is easily oxidized (for example, Fe, Co, Cu, etc.), after the hydrothermal treatment step, It is preferable to perform a reduction treatment on the hydrothermally treated precursor material (C). If the metal element (M) contained in the metal-containing solution is a metal species that is easily oxidized, the metal component will be oxidized by the heat treatment in the steps (steps 3 to 4) after the impregnation treatment (step 2). . Therefore, the carrier formed in the hydrothermal treatment step (step 4) contains metal oxide fine particles. Therefore, in order to obtain a reduction catalyst structure for automobiles in which metal fine particles are contained in the carrier, it is necessary to perform a calcination treatment on the recovered precipitate after the above-mentioned hydrothermal treatment, and further perform a reduction treatment in an atmosphere of a reducing gas such as hydrogen gas. desirable. By performing the reduction treatment, the metal oxide fine particles contained in the carrier are reduced, and metal fine particles corresponding to the metal element (M) constituting the metal oxide fine particles are formed. As a result, a reduced catalyst structure for automobiles in which fine metal particles are contained in the carrier is obtained. Note that such a reduction treatment may be performed as necessary. For example, if the environment in which the automotive reduction catalyst structure is used is a reducing atmosphere, metal oxidation can be reduced by exposing it to the usage environment for a certain period of time. Since the oxide fine particles are reduced, a reduced catalyst structure for automobiles similar to that obtained by reduction treatment can be obtained, so that it can be used as is with the oxide fine particles contained in the carrier.

[Modified example of automotive reduction catalyst structure 1]
FIG. 4 is a schematic diagram showing a modification of the automobile reduction catalyst structure 1 of FIG. 1. In FIG. Although the automobile reduction catalyst structure 1 in FIG. 1 is shown to include a carrier 10 and a Knox reduction catalyst 20 contained in the carrier 10, the structure is not limited to this structure, and for example, as shown in FIG. As such, the automotive reduction catalyst structure 2 may further include another functional substance (for example, a catalytic substance) 30 held on the outer surface 10a of the carrier 10. An example in which the functional substance 30 is a catalyst substance will be described below.

This catalytic material 30 is a material that exhibits one or more catalytic abilities. The catalytic ability of the other catalyst substance 30 may be the same as or different from the reduction catalytic ability of the Knox reduction catalyst 20. Further, when both the Knox reduction catalyst 20 and the catalyst substance 30 are substances having the same reduction catalytic ability, the material of the other catalyst substance 30 may be the same as the material of the Knox reduction catalyst 20, May be different. According to this configuration, the content of the catalyst held in the automobile reduction catalyst structure 2 can be increased, and the catalyst activity can be further promoted.

In this case, it is preferable that the content of the automotive reduction catalyst structure 20 present in the carrier 10 is greater than the content of the other catalyst substance 30 held on the outer surface 10a of the carrier 10. As a result, the catalytic ability of the Knox reduction catalyst 20 held inside the carrier 10 becomes dominant, and the reduction catalytic ability is stably exhibited.

Although the automotive reduction catalyst structure according to the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications and changes can be made based on the technical idea of the present invention. be.

(Examples 1 to 480)
[Synthesis of precursor material (A)]
A mixed aqueous solution of a silica agent (tetraethoxysilane (TEOS), manufactured by Wako Pure Chemical Industries, Ltd.) and a surfactant as a template agent was prepared, the pH was adjusted as appropriate, and the solution was heated to 80 to Hydrothermal treatment was performed at 350°C for 100 hours. Thereafter, the generated precipitate was filtered, washed with water and ethanol, and further calcined in air at 600°C for 24 hours to obtain precursor materials (A) of the type and pore size shown in Tables 1 to 10. Obtained. The following surfactants were used depending on the type of precursor material (A) ("Type of precursor material (A): surfactant").
・MCM-41: Hexadecyltrimethylammonium bromide (CTAB) (manufactured by Wako Pure Chemical Industries, Ltd.)
・SBA-1: Pluronic P123 (manufactured by BASF)

[Preparation of precursor materials (B) and (C)]
Next, depending on the metal element (M) constituting the metal fine particles of the types shown in Tables 1 to 10, a metal salt containing the metal element (M) is dissolved in water to prepare a metal-containing aqueous solution. did. The following metal salts were used depending on the type of metal fine particles ("metal fine particles: metal salt").
・Co: Cobalt(II) nitrate hexahydrate (manufactured by Wako Pure Chemical Industries, Ltd.)
・Ni: Nickel (II) nitrate hexahydrate (manufactured by Wako Pure Chemical Industries, Ltd.)
・Fe: Iron (III) nitrate nonahydrate (manufactured by Wako Pure Chemical Industries, Ltd.)
・Cu: Copper (II) nitrate trihydrate (manufactured by Wako Pure Chemical Industries, Ltd.)
・Pt: Platinum chloride (IV) acid hexahydrate (manufactured by Wako Pure Chemical Industries, Ltd.)

Next, the metal-containing aqueous solution is added in small portions to the powdered precursor material (A) in multiple portions, dried at room temperature (20°C ± 10°C) for 12 hours or more, and then the precursor material (B) is prepared. I got it.

In addition, when the condition of the presence or absence of additives shown in Tables 1 to 10 is "presence", polyoxyethylene (15) as an additive is added to the precursor material (A) before adding the metal-containing aqueous solution. Pretreatment was performed by adding an aqueous solution of oleyl ether (NIKKOL BO-15V, manufactured by Nikko Chemicals Co., Ltd.), and then a metal-containing aqueous solution was added as described above. Note that in the case of "absent" in the condition of the presence or absence of additives, the pretreatment with the additives as described above was not performed.

The amount of the metal-containing aqueous solution added to the precursor material (A) is determined by the ratio of silicon (Si) constituting the precursor material (A) to the metal element (M) contained in the metal-containing aqueous solution ( The values were adjusted so that the values when converted to atomic ratio (Si/M) were as shown in Tables 1 to 10.

Next, the precursor material (B) impregnated with the metal-containing aqueous solution obtained as described above was fired in air at 600° C. for 24 hours to obtain a precursor material (C).

The precursor material (C) obtained as described above and the structure directing agent shown in Tables 1 to 10 were mixed to prepare a mixed aqueous solution, and the mixture was heated at 80 to 350°C in a closed container. Hydrothermal treatment was performed under the conditions of pH and time shown below. Thereafter, the generated precipitate was filtered, washed with water, dried at 100°C for 12 hours or more, and further calcined in air at 600°C for 24 hours. Thereafter, the calcined product was collected and subjected to reduction treatment at 400°C for 350 minutes under the inflow of hydrogen gas to obtain a reduction catalyst structure having the carrier shown in Tables 1 to 10 and metal fine particles as a Knox reduction catalyst. (Examples 1-480).

(Comparative example 1)
In Comparative Example 1, cobalt oxide powder (II, III) (manufactured by Sigma-Aldrich Japan LLC) with an average particle size of 50 nm or less was mixed with MFI type silicalite, and hydrogen reduction treatment was performed in the same manner as in the example to form a carrier. A reduction catalyst structure was obtained in which fine cobalt particles were attached as a Knox reduction catalyst to the outer surface of silicalite. MFI type silicalite was synthesized in the same manner as in Examples 52 to 57, except for the step of adding metal.

(Comparative example 2)
In Comparative Example 2, MFI type silicalite was synthesized in the same manner as Comparative Example 1, except that the step of attaching cobalt fine particles was omitted.

[evaluation]
Various characteristic evaluations were conducted under the conditions shown below for the reduction catalyst structure of the above example and the silicalite of the comparative example, which are provided with a carrier and a Knox reduction catalyst.

[A] Cross-sectional observation Observation samples were prepared by a pulverization method for the reduction catalyst structure of the above example and the silicalite of Comparative Example 1, which are equipped with a carrier and a Knox reduction catalyst, and were examined using a transmission electron microscope (TEM) (TITAN G2, FEI). A cross-sectional observation was performed using the following: As a result, it was confirmed that in the reduction catalyst structure of the above example, the Knox reduction catalyst was contained and retained inside the carrier made of silicalite or zeolite. On the other hand, in the silicalite of Comparative Example 1, the Knox reduction catalyst was only attached to the outer surface of the carrier and was not present inside the carrier.
In addition, among the above examples, a cross section of the Knox reduction catalyst in which the metal is iron fine particles (Fe) was cut out by FIB (focused ion beam) processing, and SEM (SU8020, manufactured by Hitachi High-Technologies), EDX (X-Max , manufactured by Horiba, Ltd.) for cross-sectional elemental analysis. As a result, Fe element was detected inside the carrier.
From the results of cross-sectional observation using TEM and SEM/EDX, it was confirmed that iron fine particles were present inside the carrier.

[B] Average inner diameter of carrier passages and average particle diameter of Knox reduction catalyst In the TEM image taken by cross-sectional observation performed in the above evaluation [A], 500 carrier passages were arbitrarily selected, and the major diameter of each and the short axis were measured, and the inner diameter of each was calculated from the average value (N=500), and the average value of the inner diameter was determined to be the average inner diameter D _F of the carrier passage. Similarly, for the Knox reduction catalyst, 500 Knox reduction catalysts were arbitrarily selected from the above TEM image, the particle size of each was measured (N=500), the average value was found, and the Knox reduction catalyst was The average particle diameter of the catalyst was defined as _DC . The results are shown in Tables 1 to 10.
Further, in order to confirm the average particle size and dispersion state of the Knox reduction catalyst, analysis was performed using SAXS (small angle X-ray scattering). Measurements by SAXS were performed using Spring-8 beamline BL19B2. The obtained SAXS data was fitted with a spherical model using the Guinier approximation method, and the particle size was calculated. The particle size was measured for a Knox reduction catalyst in which the metal was iron fine particles. In addition, as a comparison object, commercially available iron fine particles (manufactured by Wako) were observed and measured using a SEM.
As a result, in commercial products, iron fine particles of various sizes exist randomly in the particle size range of about 50 nm to 400 nm, whereas iron particles with an average particle size of 1.2 nm to 2.0 nm as determined from the TEM image. In the Knox reduction catalyst of the example, a scattering peak with a particle size of 10 nm or less was also detected in the SAXS measurement results. From the SAXS measurement results and the SEM/EDX cross-sectional measurement results, it was found that the Knox reduction catalyst with a particle size of 10 nm or less existed inside the carrier in a highly dispersed state with uniform particle size.

[C] Relationship between the amount of metal-containing solution added and the amount of metal clathrated inside the carrier Added amount of atomic ratio Si/M = 50, 100, 200, 1000 (M = Co, Ni, Fe, Cu) A reduction catalyst structure in which fine metal particles were included inside the carrier was prepared, and then the amount of metal (mass%) clathrated inside the support of the reduction catalyst structure prepared with the above addition amount was measured. . In this measurement, the reduction catalyst structures with atomic number ratios Si/M=100, 200, and 1000 are the reduction catalyst structures with atomic number ratios Si/M=100, 200, and 1000 in Examples 1 to 480, respectively. The reduction catalyst structures with an atomic ratio Si/M = 50 were prepared by adjusting the amount of the metal-containing solution added in the same manner as in the above, and the atomic ratio was It was produced in the same manner as the reduction catalyst structures with Si/M=100, 200, and 1000.
The amount of metal was determined by ICP (inductively coupled plasma) alone or by a combination of ICP and XRF (X-ray fluorescence analysis). XRF (energy dispersive X-ray fluorescence spectrometer "SEA1200VX", manufactured by SSI Nanotechnology) was carried out under the conditions of a vacuum atmosphere and an accelerating voltage of 15 kV (using a Cr filter) or 50 kV (using a Pb filter).
XRF is a method for calculating the amount of metal present based on fluorescence intensity, and a quantitative value (in terms of mass %) cannot be calculated using XRF alone. Therefore, the amount of metal in the reduced catalyst structure with metal added at Si/M=100 was determined by ICP analysis, and the amount of metal in the reduced catalyst structure added with metal at Si/M=50 and less than 100 was determined by XRF analysis. Calculated based on measurement results and ICP measurement results.
As a result, it was confirmed that the amount of metal included in the reduction catalyst structure increased as the amount of metal-containing solution added increased, at least within the range of atomic number ratio Si/M of 50 to 1000. It was done.

[D] Performance Evaluation The catalytic ability of the Knox reduction catalyst was evaluated for the reduction catalyst structure of the above-mentioned example and the silicalite of the comparative example, which are provided with a carrier and a Knox reduction catalyst.

(1) Catalytic activity of reduction catalyst structure The catalysts of Examples 1 to 480 and Comparative Example 1 obtained above were charged with the same metal content into a normal pressure flow reactor, and NO gas was introduced at a flow rate. The flow rate was 1.0 cc/h, and the Knox reduction reaction was carried out in a steam atmosphere. Furthermore, as Comparative Example 2, an experiment was conducted using only silicalite as a carrier. The produced gas was measured using a gas chromatograph (GC) (manufactured by Shimadzu Corporation, device name "GC-8A", "GS-20B"). In addition, the amount of coke formed on the catalyst after the reaction was analyzed using an organic trace element analyzer (manufactured by J Science Lab Co., Ltd., device name: "JM10").

Evaluation was performed according to the following criteria.
If the amount of _N2 gas produced during the catalytic reaction is 80% of the recovered product gas (total product gas), the catalytic activity is considered to be particularly good and is marked "◎".
When the amount of _N2 gas produced during the catalytic reaction is 50% or more and less than 80% of the recovered produced gas (total produced gas), the catalytic activity is considered to be good and marked as "○".
When the amount of _N2 gas produced during the catalytic reaction is 20% or more and less than 50% of the recovered product gas (total product gas), the catalytic activity is considered to be slightly poor and is marked "△".
If the amount of _N2 gas produced during the catalytic reaction is less than 20% of the recovered produced gas (total produced gas), the catalytic activity is considered to be poor and marked with a "x".
And so.

(2) Durability (life span) of reduction catalyst structure
The reduced catalyst structure was heated at 650° C. for 12 hours, then cooled to room temperature and left for 30 minutes, which was repeated 10 times, and then a catalytic reaction test was conducted in the same manner as in (1) above to evaluate durability. Evaluation was performed according to the following criteria.
If the amount of _N2 gas produced during the catalytic reaction is 80% of the recovered product gas (total product gas), the catalytic activity is considered to be particularly good and is marked "◎".
When the amount of _N2 gas produced during the catalytic reaction is 50% or more and less than 80% of the recovered produced gas (total produced gas), the catalytic activity is considered to be good and marked as "○".
When the amount of _N2 gas produced during the catalytic reaction is 20% or more and less than 50% of the recovered product gas (total product gas), the catalytic activity is considered to be slightly poor and is marked "△".
If the amount of _N2 gas produced during the catalytic reaction is less than 20% of the recovered produced gas (total produced gas), the catalytic activity is considered to be poor and marked with a "x".
And so.

These evaluation results are shown in Tables 1 to 10.

As is clear from Tables 1 to 10, in the reduction catalyst structures (Examples 1 to 480) in which it was confirmed through cross-sectional observation that metal fine particles were retained inside the carrier, the metal fine particles simply remained on the outer surface of the carrier. It also showed superior catalytic activity in the NO reduction reaction compared to the reduction catalyst structure simply attached to the NOx reduction catalyst (Comparative Example 1) or the carrier itself without any Knox reduction catalyst (Comparative Example 2). It was also found that it has excellent durability as a catalyst.

On the other hand, the carrier itself of Comparative Example 2, which does not support metal fine particles, shows almost no catalytic activity in the NO reduction reaction, and has poor catalytic activity and durability compared to the reduction catalyst structures of Examples 1 to 480. Both were inferior.

In addition, the reduction catalyst structure of Comparative Example 1, in which metal fine particles were attached only to the outer surface of the carrier, was more effective as a catalyst in the NO reduction reaction than the carrier itself of Comparative Example 2, which did not have any metal fine particles. Although the activity was improved, the durability as a catalyst was inferior to that of the reduced catalyst structures of Examples 1 to 480.

In addition, when the above-mentioned reduction catalyst structure was used as a reduction catalyst structure for automobiles, it also had excellent catalytic activity against the Knox reduction reaction and excellent durability. In particular, it had excellent catalytic activity for the Knox reduction reaction even in a low-temperature environment. Therefore, it was confirmed that the above-described catalyst structure exhibits excellent effects as a reduction catalyst structure for automobiles.

[Other embodiments]
(1) A method of using a catalyst structure to purify (reduce) automobile exhaust gas, the method comprising:
The catalyst structure is a carrier having a porous structure composed of a zeolite type compound;
at least one Knox reduction catalyst made of a metal and present in the carrier;
Equipped with
the carrier has passages that communicate with each other,
A method using a catalyst structure, wherein the Knox reduction catalyst is present in at least the channels of the support.

1 Automotive reduction catalyst structure 10 Carrier 10a Outer surface 11 Passage 11a Hole 12 Expanded diameter portion 15 Exhaust gas component 20 Metal fine particles 30 Metal fine particles D _C Average particle size _DF Average inner diameter _DE Inner diameter

Claims (21)

A carrier with a porous structure composed of a zeolite type compound,
at least one Knox reduction catalyst made of a metal and present in the carrier;
Equipped with
the carrier has passages that communicate with each other,
A reduction catalyst structure for an automobile, characterized in that the Knox reduction catalyst is present in at least the passageway of the carrier. The passageway is one of one-dimensional pores, two-dimensional pores, and three-dimensional pores defined by the skeletal structure of the zeolite-type compound, and one of the one-dimensional pores, the two-dimensional pores, and the three-dimensional pores. The reduction catalyst structure for an automobile according to claim 1, further comprising an enlarged diameter portion that is different from the enlarged diameter portion, and wherein the Knox reduction catalyst is present at least in the enlarged diameter portion. 3. The automotive vehicle according to claim 2, wherein the expanded diameter portion communicates with each other a plurality of holes constituting any one of the one-dimensional hole, the two-dimensional hole, and the three-dimensional hole. Reduction catalyst structure. The Knox reduction catalyst is metal fine particles,
The reduction catalyst structure for an automobile according to claim 2 or 3, wherein the average particle diameter of the metal fine particles is larger than the average inner diameter of the passageway and smaller than the inner diameter of the enlarged diameter portion. The automotive reduction catalyst according to claim 4, wherein the metal element (M) of the metal fine particles is contained in an amount of 0.5 to 2.5% by mass based on the automotive reduction catalyst structure. Structure. The automotive reduction catalyst structure according to claim 4 or 5, wherein the metal fine particles have an average particle size of 0.08 nm to 30 nm. 7. The automotive reduction catalyst structure according to claim 6, wherein the metal fine particles have an average particle size of 0.4 nm to 11.0 nm. The reduction catalyst structure for an automobile according to any one of claims 4 to 7, wherein the ratio of the average particle diameter of the metal fine particles to the average inner diameter of the passage is 0.05 to 300. 9. The reduction catalyst structure for an automobile according to claim 8, wherein the ratio of the average particle diameter of the metal fine particles to the average inner diameter of the passage is 0.1 to 30. 10. The reduction catalyst structure for an automobile according to claim 9, wherein the ratio of the average particle diameter of the metal fine particles to the average inner diameter of the passage is 1.4 to 3.6. The average inner diameter of the passage is 0.1 nm to 1.5 nm,
The reduction catalyst structure for an automobile according to any one of claims 2 to 10, wherein the inner diameter of the enlarged diameter portion is 0.5 nm to 50 nm. The automotive reduction catalyst structure according to any one of claims 1 to 11, further comprising at least one other functional substance held on the outer surface of the carrier. Claim 12, characterized in that the content of the at least one Knox reduction catalyst inherent in the carrier is greater than the content of the at least one other functional substance retained on the outer surface of the carrier. The automotive reduction catalyst structure described above. The automotive reduction catalyst structure according to any one of claims 1 to 13, wherein the zeolite type compound is a silicate compound. An automobile exhaust gas treatment device comprising the automobile reduction catalyst structure according to any one of claims 1 to 14. A firing step of firing a precursor material (B) in which the precursor material (A) is impregnated with a metal-containing solution to obtain a carrier with a porous structure composed of a zeolite type compound;
a hydrothermal treatment step of hydrothermally treating the precursor material (C) obtained by firing the precursor material (B);
a step of performing a reduction treatment on the hydrothermally treated precursor material (C);
1. A method for producing a reduction catalyst structure for an automobile, comprising: 17. The reduced catalyst structure for an automobile according to claim 16, wherein 50 to 500% by mass of a nonionic surfactant is added to the precursor material (A) before the calcination step. Production method. Before the firing step, the metal-containing solution is added to the precursor material (A) in multiple portions to impregnate the precursor material (A) with the metal-containing solution. 18. The method for producing a reduction catalyst structure for an automobile according to claim 16 or 17. When impregnating the precursor material (A) with the metal-containing solution before the firing step, the amount of the metal-containing solution added to the precursor material (A) is determined by adjusting the amount of the metal-containing solution added to the precursor material (A). The ratio of silicon (Si) constituting the precursor material (A) to the metal element (M) contained in the metal-containing solution added to the solution (atomic ratio Si/M) is 10 to 1000. The method for manufacturing a reduction catalyst structure for an automobile according to any one of claims 16 to 18, characterized in that the method is adjusted so that the following is achieved. 17. The method for manufacturing a reduced catalyst structure for an automobile according to claim 16, wherein the precursor material (C) and a structure-directing agent are mixed in the hydrothermal treatment step. 17. The method for manufacturing a reduction catalyst structure for an automobile according to claim 16, wherein the hydrothermal treatment step is performed in a basic atmosphere.

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