阅读说明：本技术 废气净化催化剂 (Exhaust gas purifying catalyst ) 是由 高山豪人 望月大司 于 2019-05-16 设计创作，主要内容包括：目的在于提供具有废气净化性能、且能够抑制灰烬堆积后的压力损失上升的废气净化催化剂。废气净化催化剂,其是对从内燃机所排出的废气进行净化的废气净化催化剂,所述废气净化催化剂具有：壁流型基材,其利用多孔质的隔壁来划定废气导入侧的端部开口的导入侧腔室和与该导入侧腔室相邻且废气排出侧的端部开口的排出侧腔室；和催化剂层,其形成于所述隔壁的气孔内的多个部位、且包含至少一种以上的催化剂金属,该催化剂层在所述隔壁的厚度方向上偏在于所述排出侧腔室侧。(An exhaust gas purifying catalyst which has exhaust gas purifying performance and can suppress an increase in pressure loss after ash deposition. An exhaust gas purification catalyst that purifies exhaust gas discharged from an internal combustion engine, the exhaust gas purification catalyst comprising: a wall-flow type base material which defines, by a porous partition wall, an introduction-side chamber having an end opening on an exhaust gas introduction side and an exhaust-side chamber adjacent to the introduction-side chamber and having an end opening on an exhaust gas discharge side; and a catalyst layer which is formed at a plurality of positions in the pores of the partition wall and contains at least one or more catalyst metals, and which is offset in the thickness direction of the partition wall on the discharge-side chamber side.)

1. An exhaust gas purifying catalyst for purifying exhaust gas discharged from an internal combustion engine,

the exhaust gas purifying catalyst has:

a wall-flow type base material which defines, by a porous partition wall, an introduction-side chamber having an end opening on an exhaust gas introduction side and an exhaust-side chamber adjacent to the introduction-side chamber and having an end opening on an exhaust gas discharge side; and

a catalyst layer formed at a plurality of positions in the pores of the partition walls and containing at least one or more catalyst metals,

the catalyst layer is offset in the thickness direction of the partition wall on the discharge-side chamber side.

2. The exhaust gas purification catalyst according to claim 1, wherein the catalyst layer has a tendency of: the loading rate increases as the chamber wall surface on the discharge-side chamber side is closer to the partition in the thickness direction.

3. The exhaust gas purification catalyst according to claim 1 or 2, wherein when the wall thickness of the partition wall is Tw, 60% or more of the total mass of the catalyst layer is present in a depth region from the chamber wall surface on the discharge-side chamber side to Tw 5/10.

4. The exhaust gas purification catalyst according to any one of claims 1 to 3, wherein when the wall thickness of the partition wall is Tw, 15% or less of the total mass of the catalyst layer is present in a depth region from the chamber wall surface on the introduction-side chamber side to Tw 3/10.

5. The exhaust gas purification catalyst according to any one of claims 1 to 4, wherein the catalyst layer is formed over the entire extending direction of the partition walls.

6. The exhaust gas purification catalyst according to any one of claims 1 to 5, wherein the catalyst layer is formed on a wall surface of the chamber from the introduction-side chamber side to the discharge-side chamber side in a thickness direction of the partition wall.

7. The exhaust gas purification catalyst according to any one of claims 1 to 6, wherein the catalyst metal comprises: rh, Pd and Rh; or Pt and Rh.

8. The exhaust gas purifying catalyst according to any one of claims 1 to 7, wherein the internal combustion engine is a gasoline engine.

Technical Field

The present invention relates to an exhaust gas purifying catalyst.

Background

It is known that: exhaust gas discharged from an internal combustion engine includes Particulate Matter (PM) containing carbon as a main component, ash (ash) formed of incombustible components, and the like, and causes air pollution. Although the amount of particulate matter discharged has been strictly limited in diesel engines that are more likely to discharge particulate matter than in gasoline engines, in recent years, the amount of particulate matter discharged has been increasingly limited in gasoline engines.

As a means for reducing the amount of particulate matter discharged, a method is known in which a particulate filter is provided for the purpose of depositing and trapping particulate matter in an exhaust passage of an internal combustion engine. In recent years, from the viewpoint of space saving of a mounting space, the following studies have been made: in order to simultaneously suppress the discharge of particulate matter and remove harmful components such as carbon monoxide (CO), Hydrocarbons (HC), and nitrogen oxides (NOx), a catalyst layer is provided by coating a particulate filter with a catalyst slurry and firing the catalyst slurry.

However, if a catalyst layer is provided in a particulate filter, which is originally liable to cause an increase in pressure loss due to the deposition of particulate matter, there is a problem as follows: the flow path of the exhaust gas becomes narrower, and the pressure loss tends to rise even further, resulting in a decrease in the engine output. In order to solve such a problem, for example, patent documents 1 to 3 propose the following: for the purpose of suppressing the increase in pressure loss and improving the exhaust gas purification performance, the kind of the catalyst layer and the position where the catalyst layer is provided are examined.

Disclosure of Invention

Problems to be solved by the invention

Specifically, patent document 1 discloses the following: the purification performance is improved in comparison with the case where the catalyst layer is formed over the entire partition wall by forming the 1 st catalyst layer in the partition wall on the inlet chamber side, forming the 2 nd catalyst layer in the partition wall on the outlet chamber side, and making the lengths of the 1 st catalyst layer and the 2 nd catalyst layer shorter than the entire length of the partition wall. Patent document 2 discloses the following: the purification performance can be maintained and improved by forming the 1 st catalyst layer inside the partition wall on the inlet chamber side and the 2 nd catalyst layer shorter than the entire length of the partition wall on the surface of the partition wall on the outlet chamber side. Patent document 3 discloses the following: by providing an upstream coating region inside the partition wall on the inlet side chamber side, a downstream coating region shorter than the entire length of the partition wall is formed inside the partition wall on the outlet side chamber side, and the catalyst metal is biased to the surface layer portion of the partition wall in the downstream coating region, whereby the purification performance can be maintained and improved.

Thus, various studies have been made on the suppression of the increase in pressure loss and the improvement of the exhaust gas purification performance by forming catalyst layers separately on both the exhaust gas introduction side and the exhaust gas discharge side of the inside or the surface of the partition wall (outside the partition wall) (hereinafter, also referred to as "inside-wall separation type catalyst layers"), but no sufficient studies have been made on whether the suppression of the increase in pressure loss and the further improvement of the exhaust gas purification performance can be achieved by forming a catalyst layer containing two or more different catalyst metals on only one of the exhaust gas introduction side and the exhaust gas discharge side of the inside of the partition wall.

The present invention has been made in view of the above problems, and an object thereof is to provide an exhaust gas purification catalyst which has exhaust gas purification performance and can suppress an increase in pressure loss after ash deposition. It should be noted that the present invention is not limited to the above-mentioned objects, and other objects can be achieved by the respective configurations described in the embodiments below, which are not obtained by the conventional techniques.

Means for solving the problems

The inventors of the present application have made intensive studies to solve the above problems. As a result, they found that: by forming a catalyst layer containing two or more different catalytic metals on the exhaust gas discharge side (the downstream side region in the exhaust gas flow direction) inside the partition wall, there is room for suppressing the increase in pressure loss after ash deposition while having exhaust gas purification performance. The present invention has been made based on this finding. That is, the present invention provides various specific embodiments shown below.

[ 1] an exhaust gas purifying catalyst for purifying exhaust gas discharged from an internal combustion engine,

the exhaust gas purifying catalyst has:

a wall-flow type base material which defines, by a porous partition wall, an introduction-side chamber having an end opening on an exhaust gas introduction side and an exhaust-side chamber adjacent to the introduction-side chamber and having an end opening on an exhaust gas discharge side; and

a catalyst layer formed at a plurality of positions in the pores of the partition walls and containing at least one or more catalyst metals,

the catalyst layer is offset in the thickness direction of the partition wall on the discharge-side chamber side.

[ 2 ] the exhaust gas purifying catalyst according to [ 1], wherein the catalyst layer has a tendency of: the amount of the load increases as the chamber wall surface on the discharge-side chamber side is closer to the partition wall in the thickness direction.

[ 3 ] the exhaust gas purification catalyst according to any one of [ 1] and [ 2 ], wherein when the wall thickness of the partition wall is Tw, 60% or more of the total mass of the catalyst layer is present in a depth region from the chamber wall surface on the discharge-side chamber side to Tw 5/10.

[ 4 ] the exhaust gas purification catalyst according to any one of [ 1] to [ 3 ], wherein when the wall thickness of the partition wall is Tw, 15% or less of the total mass of the catalyst layer is present in a depth region from the chamber wall surface on the introduction-side chamber side to Tw 3/10.

The exhaust gas purification catalyst according to any one of [ 1] to [ 4 ], wherein the catalyst layer is formed over an entire extending direction of the partition walls.

The exhaust gas purification catalyst according to any one of [ 1] to [ 5 ], wherein the catalyst layer is formed on a wall surface of a chamber from the chamber wall surface on the introduction-side chamber side to the chamber wall surface on the discharge-side chamber side in a thickness direction of the partition wall.

The exhaust gas purifying catalyst according to any one of [ 1] to [ 6 ], wherein the catalyst metal contains: rh, Pd and Rh; or Pt and Rh.

[ 8 ] the exhaust gas purifying catalyst according to any one of [ 1] to [ 7 ], wherein the internal combustion engine is a gasoline engine.

Effects of the invention

According to the present invention, an exhaust gas purifying catalyst having exhaust gas purifying performance and capable of suppressing an increase in pressure loss after ash deposition can be provided. The exhaust gas purifying catalyst can be used not only for a Gasoline Particulate Filter (GPF) but also for other particulate filters such as a Diesel Particulate Filter (DPF) as a particulate filter carrying a catalyst, and further improvement in performance of an exhaust gas treatment system equipped with such a particulate filter can be achieved.

Drawings

Fig. 1 is a sectional view schematically showing one embodiment of an exhaust gas purifying catalyst according to the present embodiment.

Fig. 2 is a cross-sectional view schematically showing a mode in which the catalyst layer 21 is deviated to the discharge-side chamber 12 side.

Fig. 3 is a cross-sectional view schematically showing a mode in which the catalyst layer 21 is deviated to the introduction-side chamber 11 side.

Fig. 4 is a graph showing the measurement results of the pressure loss of the exhaust gas purifying catalysts produced in example 1 and comparative examples 1 to 2.

Fig. 5 is a graph showing the results of measuring the pressure loss after ash deposition of the exhaust gas purifying catalysts produced in example 1 and comparative examples 1 to 2.

Fig. 6 is a cross-sectional view (traced drawing) of the exhaust gas purifying catalyst produced in example 1 and comparative examples 1 to 2.

Detailed Description

Hereinafter, embodiments of the present invention will be described in detail. The following embodiments are examples (representative examples) of the embodiments of the present invention, and the present invention is not limited to these examples. The present invention can be implemented by arbitrarily changing the configuration without departing from the scope of the present invention. In the present specification, unless otherwise specified, positional relationships such as up, down, left, and right are based on positional relationships shown in the drawings. The dimensional ratios in the drawings are not limited to the illustrated ratios. In the present specification, the "D50 particle size" refers to a particle size at which the cumulative value from the small particle size in the cumulative distribution of the volume-based particle sizes reaches 50% of the total, and the "D90 particle size" refers to a particle size at which the cumulative value from the small particle size in the cumulative distribution of the volume-based particle sizes reaches 90% of the total. In the present specification, when a numerical value or a physical property value is expressed by inserting a numerical value or a physical property value before and after the "to" is used, the numerical value or the physical property value before and after the "to" is used to include the numerical value. For example, the expression of a numerical range of "1 to 100" includes both the lower limit value "1" and the upper limit value "100". The same applies to other numerical ranges.

[ exhaust gas purifying catalyst ]

An exhaust gas purification catalyst 100 according to the present embodiment is an exhaust gas purification catalyst 100 for purifying an exhaust gas discharged from an internal combustion engine, the exhaust gas purification catalyst including: a wall-flow substrate 10 having porous partition walls 13 defining an introduction-side cell 11 in which an end 11a on an exhaust gas introduction side is open and a discharge-side cell 12 adjacent to the introduction-side cell 11 and in which an end 12a on an exhaust gas discharge side is open; and a catalyst layer 21 formed at a plurality of locations in the gas holes of the partition walls 13 and containing at least one or more catalyst metals, the catalyst layer 21 being offset in the thickness direction of the partition walls 13 on the discharge-side chamber 12 side.

Hereinafter, each configuration will be described with reference to a cross-sectional view schematically showing the exhaust gas purifying catalyst of the present embodiment shown in fig. 1. The exhaust gas purifying catalyst of the present embodiment has a wall-flow structure. In the exhaust gas purifying catalyst 100 having such a configuration, the exhaust gas discharged from the internal combustion engine flows into the intake-side chamber 11 from the end 11a (opening) on the exhaust gas introduction side, flows into the adjacent discharge-side chamber 12 through the pores of the partition wall 13, and flows out from the end 12a (opening) on the exhaust gas discharge side. In this process, the Particulate Matter (PM) that is difficult to pass through the pores of the partition walls 13 is generally deposited on the partition walls 13 and/or in the pores of the partition walls 13 in the introduction-side chamber 11, and the deposited particulate matter is removed by the catalyst function of the catalyst layer 21 or by burning at a predetermined temperature (for example, about 500 to 700 ℃). Further, when the exhaust gas contacts the catalyst layer 21 formed in the pores of the partition walls 13, carbon monoxide (CO) and Hydrocarbons (HC) contained in the exhaust gas are oxidized into water (H)₂O), carbon dioxide (CO)₂) Etc. nitrogen oxides (NOx) are reduced to nitrogen (N)₂) The harmful components are purified (detoxified). In the present specification, the removal of particulate matter and the purification of harmful components such as carbon monoxide (CO) are also collectively referred to as "exhaust gas purification performance". Hereinafter, each configuration will be described in more detail.

(substrate)

The wall-flow-type substrate 10 has a wall-flow structure in which an introduction-side cell 11 having an open end 11a on the exhaust gas introduction side and a discharge-side cell 12 adjacent to the introduction-side cell 11 and having an open end 12a on the exhaust gas discharge side are partitioned by a porous partition wall 13.

As the substrate 10, substrates of various materials and forms conventionally used for such applications can be used. For example, a substrate made of a heat-resistant material is preferable in order to be able to cope with exposure to high-temperature (for example, 400 ℃ or higher) exhaust gas generated when an internal combustion engine is operated under high load conditions, removal of particulate matter by high-temperature combustion, and the like. Examples of the heat-resistant material include: ceramics such as cordierite, mullite, aluminum titanate, and silicon carbide (SiC); stainless steel and the like. The form of the substrate may be appropriately adjusted from the viewpoints of exhaust gas purification performance, suppression of pressure loss increase, and the like. For example, the outer shape of the substrate may be a cylindrical shape, an elliptic cylindrical shape, a polygonal cylindrical shape, or the like. In addition, also depending on the space of the loading place, the volume of the substrate (total volume of the chamber) is preferably 0.1-5L, more preferably 0.5-3L. The total length of the base material in the extending direction (the total length of the partition walls 13 in the extending direction) is preferably 10 to 500mm, and more preferably 50 to 300 mm.

The introduction-side chamber 11 and the discharge-side chamber 12 are regularly arranged along the axial direction of the cylindrical shape, and one open end and the other open end in the extending direction of adjacent chambers are alternately sealed. The introduction-side chamber 11 and the discharge-side chamber 12 may be set to have appropriate shapes and sizes in consideration of the flow rate and composition of the exhaust gas to be supplied. For example, the shapes of the mouths of the introduction-side chamber 11 and the discharge-side chamber 12 may be: a triangle shape; rectangles such as square, parallelogram, rectangle and trapezoid; other polygons such as a hexagon and an octagon; and (4) a circular shape. Further, the port shape may have a High Ash Capacity (HAC) structure in which the cross-sectional area of the introduction-side chamber 11 and the cross-sectional area of the discharge-side chamber 12 are different. The number of the introduction-side chamber 11 and the discharge-side chamber 12 is not particularly limited, and may be appropriately set so as to promote the generation of the turbulent flow of the exhaust gas and suppress clogging due to particles and the like contained in the exhaust gas, but is preferably 200cpsi to 400 cpsi.

The partition wall 13 partitioning the adjacent chambers is not particularly limited as long as it has a porous structure through which exhaust gas can pass, and the configuration thereof can be appropriately adjusted from the viewpoints of exhaust gas purification performance, suppression of an increase in pressure loss, improvement in mechanical strength of the base material, and the like. For example, in the case where the catalyst layer 21 is formed on the pore surfaces in the partition walls 13 using the catalyst slurry 21a described later, when the pore diameter (for example, the mode diameter (the pore diameter at which the frequency distribution of the pore diameter appears at the maximum ratio (maximum value of distribution)) and the pore volume are large, the pores are less likely to be clogged by the catalyst layer 21, and the pressure loss of the obtained exhaust gas purification catalyst is less likely to increase, but the ability to trap particulate matter is also reduced, and the mechanical strength of the substrate is also likely to decrease. On the other hand, when the pore diameter and pore volume are small, the pressure loss tends to increase, but the ability to trap particulate matter tends to increase, and the mechanical strength of the substrate also tends to increase.

From such a viewpoint, the pore diameter (mode diameter) of the partition walls 13 of the wall-flow-type substrate 10 before the catalyst layer 21 is formed is preferably 8 to 25 μm, more preferably 10 to 22 μm, and still more preferably 13 to 20 μm. The thickness (length in the thickness direction orthogonal to the extending direction) of the partition wall 13 is preferably 6 to 12 mils, and more preferably 6 to 10 mils. Further, the pore volume of the partition wall 13 by the mercury intrusion method is preferably 0.2 to 1.5cm³A concentration of 0.25 to 0.9cm³A concentration of 0.3 to 0.8cm³(ii) in terms of/g. The porosity of the partition wall 13 by the mercury intrusion method is preferably 20 to 80%, more preferably 40 to 70%, and still more preferably 60 to 70%. By setting the pore volume or porosity to be not less than the lower limit, the increase in pressure loss tends to be further suppressed. Further, the strength of the base material tends to be further improved by setting the pore volume or porosity to be not more than the upper limit. The pore diameter (mode diameter), pore volume, and porosity are values calculated by mercury intrusion method under the conditions described in the following examples.

(catalyst layer)

Next, the catalyst layer 21 will be described. The catalyst layers 21 are formed at a plurality of locations in the pores of the partition walls 13, contain at least one or more catalyst metals, and are offset in the thickness direction of the partition walls 13 toward the discharge-side chamber 12 (fig. 2). With such a configuration, the exhaust gas purifying performance is provided, and the pressure loss, particularly the increase in pressure loss after ash deposition, tends to be suppressed.

The reason for this is considered as follows. When the catalyst layer 21 is biased toward the introduction-side chamber 11, ash tends to accumulate on the surface of the partition wall 13 of the introduction-side chamber 11 without penetrating into the pores in the partition wall 13 (see fig. 3). Since ash formed of incombustible components cannot be removed by combustion, the pressure loss of the exhaust gas purification catalyst slowly rises while the ash is accumulated. On the other hand, when the catalyst layer 21 is located on the side of the discharge-side chamber 12, it is considered that ash formed of incombustible components is likely to intrude not only into the surface of the partition wall 13 of the introduction-side chamber 11 but also into the pores on the side of the introduction-side chamber 11, and therefore, the ash is likely to be deposited in the pores (see fig. 2), and the pressure loss increase after the ash deposition is suppressed. The life of the exhaust gas purifying catalyst is also improved by suppressing the increase in pressure loss after ash accumulation. However, the reason why the increase in pressure loss after the ash deposition is suppressed is not limited to the above reason.

The mode of the catalyst layer 21 is not particularly limited as long as it can exhibit the desired exhaust gas purification performance and the effect of suppressing the increase in pressure loss after ash deposition, and the catalyst layer 21 preferably has the following tendency: the amount of the load increases as the chamber wall surface on the discharge-side chamber 12 side is closer to the partition wall 13 in the thickness direction. From the same viewpoint as described above, the pressure loss increase after ash deposition tends to be suppressed.

As one mode of displaying such a bias, it is preferable that: when the wall thickness of the partition wall 13 is Tw, 60% or more of the total mass of the catalyst layer 21 is present in the depth region T1 from the chamber wall surface on the discharge-side chamber 12 side to Tw × 5/10. The amount of the catalyst layer 21 supported in the depth region T1 is preferably 65% or more, more preferably 70% or more, and still more preferably 75% or more, based on the total mass of the catalyst layer 21 in the cross section of the partition wall 13. By offsetting the loading amount of the catalyst layer 21 so as to be 60% or more in the depth region T1 from the chamber wall surface on the discharge-side chamber 12 side to Tw × 5/10, the loading amount of the catalyst layer 21 disposed in the pores on the introduction-side chamber 11 side is relatively reduced, and a space in which ash can be deposited can be secured.

In addition, as another aspect, it is preferable that: when the wall thickness of the partition wall 13 is Tw, 15% or less of the total mass of the catalyst layer 21 is present in the depth region T2 from the chamber wall surface on the introduction-side chamber 11 side to Tw × 3/10. The amount of the catalyst layer 21 supported in the depth region T2 is preferably 12% or less, more preferably 10% or less, and still more preferably 8% or less, based on the total mass of the catalyst layer 21 in the cross section of the partition wall 13. By offsetting the loading amount of the catalyst layer 21 so as to be 15% or less in the depth region T2 from the chamber wall surface on the introduction-side chamber 11 side to Tw × 3/10, the loading amount of the catalyst layer 21 disposed in the pores on the introduction-side chamber 11 side is reduced, and a space in which ash can be deposited can be secured.

In the present embodiment, as long as the catalyst layer 21 is present on the discharge-side chamber 12 side in the thickness direction of the partition wall 13, a part of the catalyst layer 21 may be present on the introduction-side chamber 11 side. In other words, the catalyst layer 21 may be formed on the chamber wall surface from the introduction-side chamber 11 side to the discharge-side chamber 12 side in the thickness direction of the partition wall 13 as long as the catalyst layer 21 is offset in the thickness direction of the partition wall 13 on the discharge-side chamber 12 side.

The deviation of the catalyst layer 21 can be confirmed by a scanning electron microscope of the cross section of the partition wall 13 of the exhaust gas purifying catalyst 100. Specifically, the area of the catalyst layer 21 is determined in a scanning electron micrograph of a cross section of the partition wall 13, and the area is determined by dividing the area into 10 parts in the thickness direction of the partition wall 13 and accumulating the area of the catalyst layer 21 for each region. At this time, it is desirable to measure at least 3 points of a portion close to the end 11a on the exhaust gas introduction side of the partition wall 13, a portion close to the end 12a on the exhaust gas discharge side, and a central portion therebetween, and to obtain an average value thereof.

In addition, in the extending direction (longitudinal direction) of the partition walls 13, the total length L1 in the extending direction of the wall flow type substrate 10 (coating length of the catalyst layer 21) in the range L1 where the catalyst layer 21 is formed (coating length of the catalyst layer 21)_WThe total length of the partition walls 13 in the extending direction is preferably 100%, and is preferably formed over the entire structure, specifically, 80 to 100%, more preferably 90 to 100%, and still more preferably 95 to 100%.

The catalyst metal contained in the catalyst layer 21 is not particularly limited, and various kinds of metals that can function as various oxidation catalysts and reduction catalysts can be used. Examples of the platinum group metal include platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), iridium (Ir), and osmium (Os). Among them, palladium (Pd) and platinum (Pt) are preferable from the viewpoint of oxidation activity, and rhodium (Rh) is preferable from the viewpoint of reduction activity. In the present embodiment, the catalyst layer 21 is provided in a state where one or more kinds of catalyst metals are mixed as described above. In particular, by using two or more catalyst metals in combination, a synergistic effect due to different catalyst activities can be expected.

The combination mode of such a catalyst metal is not particularly limited, and examples thereof include a combination of two or more catalyst metals having excellent oxidation activity, a combination of two or more catalyst metals having excellent reduction activity, and a combination of a catalyst metal having excellent oxidation activity and a catalyst metal having excellent reduction activity. Among them, as one mode of the synergistic effect, a combination of a catalyst metal excellent in oxidation activity and a catalyst metal excellent in reduction activity is preferable, and a combination including at least Rh, Pd, and Rh, or a combination including at least Pt and Rh is more preferable. By combining these, exhaust gas purification performance tends to be further improved.

The presence of the catalyst metal in the catalyst layer 21 can be confirmed by a scanning electron microscope or the like of the cross section of the partition wall 13 of the exhaust gas purifying catalyst. Specifically, it can be confirmed by performing energy dispersive X-ray analysis in the field of view of a scanning electron microscope.

As the carrier particles contained in the catalyst layer 21 and supporting the catalytic metal, inorganic compounds used in conventional exhaust gas purifying catalysts of this type can be considered. Examples thereof include: cerium oxide (cerium oxide: CeO)₂) Oxygen occlusion material (OSC material) such as ceria-zirconia composite oxide (CZ composite oxide), alumina (alumina: al (Al)₂O₃) Zirconium oxide (zirconium dioxide: ZrO (ZrO)₂) Silicon oxide (silicon dioxide: SiO 2₂) Titanium oxide (titanium dioxide: TiO 2₂) And composite oxides containing these oxides as a main component. They may be a composite oxide or a solid solution to which a rare earth element such as lanthanum or yttrium, a transition metal element, or an alkaline earth metal element is added. These carrier particles may be used alone or in combination of two or more. Here, the oxygen storage material (OSC material) is a material that stores oxygen in the exhaust gas when the air-fuel ratio of the exhaust gas is lean (i.e., an atmosphere on the oxygen-excess side) and releases the stored oxygen when the air-fuel ratio of the exhaust gas is rich (i.e., an atmosphere on the fuel-excess side).

The catalyst layer 21 preferably has a catalyst metal supporting ratio (mass of catalyst metal per 1L of substrate) of 0.5 to 10g/L, more preferably 1 to 8g/L, and still more preferably 1 to 6g/L, from the viewpoints of improving exhaust gas purification performance, suppressing progress of crystal grain growth (sintering) of catalyst metal, and the like.

The pore diameter (mode diameter) of the partition wall 13 obtained by mercury intrusion method of the exhaust gas purifying catalyst in the state where the catalyst layer 21 is formed is preferably 10 to 23 μm, more preferably 12 to 20 μm, and further preferably 14 to 18 μm. The pore volume of the partition wall 13 of the exhaust gas purifying catalyst having the catalyst layer 21 formed thereon, which is obtained by mercury intrusion method, is preferably 0.2 to 1.0cm³A concentration of 0.25 to 0.9cm³A concentration of 0.3 to 0.8cm³(ii) in terms of/g. Further, the porosity of the partition wall 13 of the exhaust gas purifying catalyst in the state where the catalyst layer 21 is formed by the mercury intrusion method is preferably 20 to 80%, more preferably 30 to 70%, and preferably 35 to 60%. The pore diameter (mode diameter)The pore volume and the porosity are values calculated by mercury intrusion method under the conditions described in the following examples.

[ method for producing exhaust gas purifying catalyst ]

A method for manufacturing an exhaust gas purification catalyst according to the present embodiment is a method for manufacturing an exhaust gas purification catalyst 100 for purifying exhaust gas discharged from an internal combustion engine, the method including the steps of: a step S0 of preparing a wall-flow-type substrate 10 in which an introduction-side cell 11 having an end 11a on the exhaust gas introduction side open and a discharge-side cell 12 adjacent to the introduction-side cell 11 and having an end 12a on the exhaust gas discharge side open are defined by porous partition walls 13; and a catalyst layer forming step S1 of forming the catalyst layer 21 such that the catalyst layer 21 is biased to the surface of the pores present on the discharge side chamber 12 side of the partition wall 13.

Hereinafter, each step will be explained. In the present specification, the wall-flow type substrate before the catalyst layer 21 is formed is referred to as "substrate 10", and the wall-flow type substrate after the catalyst layer 21 is formed is referred to as "exhaust gas purification catalyst 100".

< preparation Process >

In the preparation step S0, the wall-flow substrate 10 described above for the exhaust gas purification catalyst 100 is prepared as a substrate.

< Process for Forming catalyst layer >

In the catalyst layer forming step S1, the catalyst slurry 21a is applied to the surfaces of the pores present on the discharge side chamber 12 side of the partition walls 13, dried, and fired, thereby forming the uneven catalyst layers 21. The method of applying catalyst paste 21a is not particularly limited, and examples thereof include the following methods: a part of the substrate 10 is impregnated with the catalyst slurry 21a and extends over the entire partition walls 13 of the substrate 10. More specifically, a method comprising the following steps: a step S1a of impregnating the end 12a of the substrate 10 on the exhaust gas discharge side with the catalyst slurry 21 a; and a step S1b of introducing gas into the base material 10 from the end 12a side on the exhaust gas discharge side, thereby coating the catalyst paste 21a impregnated in the base material 10 on the surfaces of the pores.

As a method of making the catalyst layer 21 offset to the discharge-side chamber 12 side of the partition wall 13, there is a method including a drying step S1c of introducing a gas F from the end 12a on the exhaust gas discharge side to the coated wall-flow substrate 10 and drying the coated catalyst slurry 21a in the drying step S1 c. The introduced gas F promotes drying of the catalyst slurry 21a from the surface side of the partition wall 13 on the exhaust gas discharge side, whereby the catalyst slurry 21a is gathered from the part of the non-dried partition wall 13 toward the dried part according to the capillary phenomenon, with the result that the dried catalyst slurry 21 a' is biased toward the dried part. This makes it possible to bias the dried catalyst slurry 21 a' in the thickness direction of the partition wall 13 toward the discharge-side chamber 12 into which the gas F is introduced.

In addition to the above method, any method may be used without any particular limitation as long as the method is a method of applying the catalyst paste 21a on the discharge-side chamber 12 side of the partition wall 13, and drying and firing the applied catalyst paste 21 a. Examples thereof include the following methods: on the discharge-side chamber 12 side of the partition wall 13, the viscosity and solid content of the catalyst slurry 21a are adjusted, or if necessary, the coating condition and the drying condition after coating are adjusted, in order to adjust the penetration distance into the pores in the partition wall 13.

The impregnation method of catalyst paste 21a in step S1a is not particularly limited, and for example, a method of impregnating the end portion of substrate 10 with catalyst paste 21a may be mentioned. In this method, the catalyst slurry 21a can be pulled by discharging (sucking) gas from the end on the opposite side as necessary. The catalyst slurry 21a is supplied into the wall-flow substrate 10 from the end 12a on the exhaust gas discharge side.

In step S1b, gas is introduced into the substrate 10 from the end portion side impregnated with the catalyst slurry 21a, and the catalyst slurry 21a is applied to the pores present on the discharge-side chamber 12 side. As a method of applying the catalyst paste 21a, a method of generating a gas pressure difference at both ends of the substrate 10 can be cited. Specifically, the catalyst slurry 21a can be applied by applying the impregnated catalyst slurry 21a from the end 12a on the exhaust gas discharge side toward the end 11a on the exhaust gas introduction side by setting the end 12a on the exhaust gas discharge side to a relatively high air pressure and applying a pressure.

In step S1c, the applied catalyst slurry 21a is dried to produce a dried catalyst slurry 21 a'. The drying conditions in the step S1c are not particularly limited as long as the solvent is volatilized from the catalyst slurry 21 a. For example, the drying temperature is preferably 100 to 225 ℃, more preferably 100 to 200 ℃, and still more preferably 125 to 175 ℃. The drying time is preferably 0.5 to 2 hours, and more preferably 0.5 to 1.5 hours.

As a method which can be considered as a drying method, in addition to a method in which the substrate 10 after the step S1b is left to stand at a predetermined drying temperature, a method in which the gas F is introduced into the substrate 10 from the end portion 12a on the exhaust gas discharge side to promote drying can be cited.

Next, in step S1d, the catalyst layer 21 is formed by baking the catalyst slurry 21 a' dried as described above. The firing conditions in step S1d are not particularly limited as long as the catalyst layer 21 can be formed from the dried catalyst slurry 21 a'. For example, the firing temperature is not particularly limited, but is preferably 400 to 650 ℃, more preferably 450 to 600 ℃, and still more preferably 500 to 600 ℃. The firing time is preferably 0.5 to 2 hours, more preferably 0.5 to 1.5 hours.

(catalyst slurry)

The catalyst paste 21a for forming the catalyst layer 21 will be explained. The catalyst slurry 21a contains a catalyst powder and a solvent such as water. The catalyst powder is a group of a plurality of catalyst particles including catalyst metal particles and carrier particles supporting the catalyst metal particles, and forms the catalyst layer 21 through a firing step described later. The catalyst particles are not particularly limited, and can be appropriately selected from known catalyst particles. From the viewpoint of coatability in the pores of the partition walls 13, the solid content fraction of the catalyst slurry 21a is preferably 1 to 50% by mass, more preferably 10 to 40% by mass, and still more preferably 15 to 30% by mass. By setting the solid content to such a fraction, the catalyst slurry 21a tends to be easily applied to the discharge-side chamber 12 side in the partition wall 13.

The D90 particle size of the catalyst powder contained in the catalyst slurry 21a is preferably 1 to 7 μm, more preferably 1 to 6 μm, and still more preferably 1 to 5 μm. By setting the particle size of D90 to 1 μm or more, the time required for crushing the catalyst powder by the grinding device can be shortened, and the work efficiency tends to be further improved. Further, when the particle diameter of D90 is 7 μm or less, clogging of the pores in partition wall 13 by coarse particles is suppressed, and the increase in pressure loss tends to be suppressed. In the present specification, the D90 particle size may be measured by a laser diffraction particle size distribution measuring apparatus (for example, a laser diffraction particle size distribution measuring apparatus SALD-3100 manufactured by shimadzu corporation).

As the catalyst metal contained in the catalyst paste 21a, two or more kinds of metals that can function as various oxidation catalysts and reduction catalysts can be used in combination. Specifically, the same metals as those exemplified as the catalytic metals contained in the catalyst layer 21 can be cited. As one embodiment, the combination of the catalyst metals contained in the catalyst paste 21a can be exemplified in the same manner as described in the description of the catalyst layer 21 formed of these catalyst pastes 21 a. Specifically, a combination of two or more kinds of catalytic metals having excellent oxidation activity, a combination of two or more kinds of catalytic metals having excellent reduction activity, and a combination of a catalytic metal having excellent oxidation activity and a catalytic metal having excellent reduction activity can be cited. Among them, as one mode of the synergistic effect, a combination of a catalyst metal excellent in oxidation activity and a catalyst metal excellent in reduction activity is preferable, and a combination including at least Pd and Rh is more preferable.

From the viewpoint of increasing the contact area with the exhaust gas, it is preferable to make the average particle diameter of the catalyst metal particles in the catalyst slurry 21a small. Specifically, the average particle diameter of the catalyst metal particles is preferably 1 to 15nm, more preferably 1 to 10nm, and still more preferably 1 to 7 nm. The average particle diameter of the catalyst metal particles can be confirmed, for example, by using a Scanning transmission electron Microscope (STEM: Scanning Transmission Electron Microscope) such as HD-2000 manufactured by Hitachi high and New technology, and in the present specification, the equivalent circle diameter of the catalyst metal particles of 10 dots randomly extracted is calculated, and the average value thereof is defined as the average particle diameter of the catalyst metal particles.

As the carrier particles contained in the catalyst slurry 21a, inorganic compounds used in conventional exhaust gas purifying catalysts of this type can be considered. Specifically, the same inorganic compounds as those exemplified for the support particles contained in the catalyst layer 21 can be exemplified. These carrier particles may be used alone or in combination of two or more.

The specific surface area of the support particles contained in the catalyst slurry 21a is preferably 10 to 500m from the viewpoint of exhaust gas purification performance²A more preferable range is 30 to 200m²/g。

From the viewpoints of improving exhaust gas purification performance, suppressing the progress of crystal grain growth (sintering) of the catalyst metal, and the like, the catalyst metal supporting ratio (mass of catalyst metal per 1L of substrate) from the catalyst slurry 21a in the state of being supported on the wall flow type substrate 10 is preferably 0.5 to 10g/L, more preferably 1 to 8g/L, and further preferably 1 to 6 g/L.

[ use ]

A mixed gas containing oxygen and fuel gas is supplied to an internal combustion engine (engine), the mixed gas is combusted, and combustion energy is converted into mechanical energy. The mixed gas burned at this time becomes an exhaust gas and is discharged to an exhaust system. An exhaust system is provided with an exhaust gas purification device provided with an exhaust gas purification catalyst, and the exhaust gas purification device purifies harmful components (for example, carbon monoxide (CO), Hydrocarbons (HC), and nitrogen oxides (NOx)) contained in exhaust gas by the exhaust gas purification catalyst and traps and removes Particulate Matter (PM) contained in the exhaust gas. The exhaust gas purification catalyst 100 of the present embodiment is particularly preferably used for a Gasoline Particulate Filter (GPF) capable of trapping and removing particulate matter contained in exhaust gas of a gasoline engine.