JP7051186B2 - Exhaust gas purification catalyst - Google Patents

Description

The present invention relates to an exhaust gas purification catalyst.

Exhaust gas emitted from an internal combustion engine contains particulate matter (PM) containing carbon as a main component, ash composed of a non-combustible component, and the like, and is known to cause air pollution. Conventionally, the emission of particulate matter has been strictly regulated in diesel engines, which are relatively easier to emit particulate matter than gasoline engines, but in recent years, the emission of particulate matter has also been regulated in gasoline engines. It is being strengthened.

As a means for reducing the emission of particulate matter, a method of providing a particulate filter for the purpose of depositing and collecting particulate matter in the exhaust gas passage of an internal combustion engine is known. In particular, in recent years, from the viewpoint of saving space for mounting, it has been possible to suppress the emission of particulate matter and remove harmful components such as carbon monoxide (CO), hydrocarbons (HC) and nitrogen oxides (NOx). In order to carry out at the same time, it is considered to apply a catalyst slurry to a particulate filter and to provide a catalyst layer by firing the catalyst slurry.

However, if a catalyst layer is provided in the particulate filter where the pressure loss tends to increase due to the accumulation of particulate matter, the flow path of the exhaust gas becomes narrower and the pressure loss tends to increase further, which causes a decrease in engine output. There is a problem. In order to solve such a problem, for example, in Patent Documents 1 to 3, it is necessary to devise the type of the catalyst layer and the position where they are provided for the purpose of suppressing the increase in pressure loss and improving the exhaust gas purification performance. Proposed.

WO2016 / 060048 WO2016 / 060049 WO2016 / 06050

Specifically, in Patent Document 1, the first catalyst layer is formed inside the partition wall on the entry side cell side, the second catalyst layer is formed inside the partition wall on the exit side cell side, and the first catalyst layer and the second catalyst layer are formed. It is disclosed that by making the length of the catalyst layer shorter than the total length of the partition wall, the purification performance is higher than that the catalyst layer is widely formed over the entire partition wall. Further, in Patent Document 2, a first catalyst layer is formed inside the partition wall on the entry side cell side, and a second catalyst layer shorter than the total length of the partition wall is formed on the partition wall surface on the exit side cell side, thereby performing purification performance. It is disclosed that it can be maintained and improved. Further, in Patent Document 3, an upstream coat region is provided inside the partition wall on the entry side cell side, a downstream coat region shorter than the total length of the partition wall is formed inside the partition wall on the exit side cell side, and the surface layer of the partition wall is formed in the downstream coat region. It is disclosed that the purification performance can be maintained and improved by unevenly distributing the catalyst metal in the portion.

In this way, the catalyst layer is formed separately on both the exhaust gas introduction side and the exhaust gas discharge side inside the partition wall or on the partition wall surface (outside the partition wall) (hereinafter, also referred to as "in-wall separation type catalyst layer"), and pressure loss. Although various studies have been made on suppressing the increase in the amount of exhaust gas and improving the exhaust gas purification performance, only one of the exhaust gas introduction side and the exhaust gas emission side inside the partition wall contains two or more different catalyst metals. It has not been sufficiently investigated whether or not it is possible to further improve the exhaust gas purification performance while suppressing the increase in pressure loss by forming the catalyst layer.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an exhaust gas purification catalyst capable of suppressing an increase in pressure loss after ash deposition while having exhaust gas purification performance. It should be noted that the present invention is not limited to the above-mentioned purpose, and it is an action and effect derived by each configuration shown in the embodiment for carrying out the invention described later, and it is also possible to exert an action and effect which cannot be obtained by the conventional technique. It can be positioned as another purpose.

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

[1]
An exhaust gas purification catalyst that purifies the exhaust gas emitted from an internal combustion engine.
An introduction-side cell having an open end on the exhaust gas introduction side and an exhaust-side cell adjacent to the introduction-side cell and having an open end on the exhaust gas discharge side are defined as a wall-flow type base material by a porous partition wall. ,
It has a catalyst layer containing at least one kind of catalyst metal, which is formed at a plurality of places in the pores of the partition wall.
The catalyst layer is unevenly distributed on the discharge side cell side in the thickness direction of the partition wall.
Exhaust gas purification catalyst.
[2]
The catalyst layer has a tendency to increase the supported amount as it is closer to the cell wall surface on the discharge side cell side in the thickness direction of the partition wall.
The exhaust gas purification catalyst according to [1].
[3]
When the wall thickness of the partition wall is Tw, 60% or more of the total mass of the catalyst layer is present in the depth region from the cell wall surface on the discharge side cell side to Tw * 5/10.
The exhaust gas purification catalyst according to [1] or [2].
[4]
When the wall thickness of the partition wall is Tw, 15% or less of the total mass of the catalyst layer exists in the depth region from the cell wall surface on the introduction side cell side to Tw * 3/10.
The exhaust gas purification catalyst according to any one of [1] to [3].
[5]
The catalyst layer is formed over the entire extension direction of the partition wall.
The exhaust gas purification catalyst according to any one of [1] to [4].
[6]
The catalyst layer is formed from the cell wall surface on the introduction side cell side to the cell wall surface on the discharge side cell side in the thickness direction of the partition wall.
The exhaust gas purification catalyst according to any one of [1] to [5].
[7]
The catalyst metal comprises Rh, Pd and Rh, or Pt and Rh.
The exhaust gas purification catalyst according to any one of [1] to [6].
[8]
The internal combustion engine is a gasoline engine.
The exhaust gas purification catalyst according to any one of [1] to [7].

According to the present invention, it is possible to provide an exhaust gas purification catalyst which has exhaust gas purification performance and can suppress an increase in pressure loss after ash deposition. The exhaust gas purification catalyst can be used not only in a gasoline particulate filter (GPF) but also in other particulate filters such as a diesel particulate filter (DPF) as a particulate filter carrying a catalyst. The performance of the exhaust gas treatment system equipped with such a particulate filter can be further improved.

It is sectional drawing which shows typically one aspect of the exhaust gas purification catalyst of this embodiment. It is sectional drawing which shows typically the mode that the catalyst layer 21 is unevenly distributed on the discharge side cell 12. It is sectional drawing which shows typically the mode that the catalyst layer 21 is unevenly distributed on the introduction side cell 11. It is a graph which shows the measurement result of the pressure loss in the exhaust gas purification catalyst produced in Example 1 and Comparative Examples 1 and 2. It is a graph which shows the measurement result of the pressure loss after ash deposition in the exhaust gas purification catalyst produced in Example 1 and Comparative Examples 1 and 2. It is a trace figure which shows the cross section of the exhaust gas purification catalyst produced in Example 1 and Comparative Examples 1 and 2.

Hereinafter, embodiments of the present invention will be described in detail. The following embodiments are examples (representative examples) of embodiments of the present invention, and the present invention is not limited thereto. Further, the present invention can be arbitrarily modified and implemented without departing from the gist thereof. In addition, in this specification, the positional relationship such as up, down, left and right shall be based on the positional relationship shown in the drawings unless otherwise specified. Further, the dimensional ratios in the drawings are not limited to the ratios shown in the drawings. In the present specification, the "D50 particle size" refers to the particle size when the integrated value from the small particle size reaches 50% of the total in the cumulative distribution of the particle size based on the volume, and is referred to as "D90 particle size". Refers to the particle size when the integrated value from the small particle size reaches 90% of the total in the cumulative distribution of the particle size based on the volume. Further, in the present specification, when a numerical value or a physical property value is inserted before and after using "-", it is used as including the values before and after that. For example, the notation of the numerical range of "1 to 100" includes both the lower limit value "1" and the upper limit value "100". The same applies to the notation of other numerical ranges.

[Exhaust gas purification catalyst]
The exhaust gas purification catalyst of the present embodiment is an exhaust gas purification catalyst 100 that purifies the exhaust gas discharged from the internal combustion engine, and is adjacent to the introduction side cell 11 in which the end portion 11a on the exhaust gas introduction side is opened and the introduction side cell 11. The exhaust gas discharge side cell 12 in which the end portion 12a on the exhaust gas discharge side is opened is formed at least at a plurality of places in the pores of the wall flow type base material 10 defined by the porous partition wall 13. It has a catalyst layer 21 containing one or more catalyst metals, and the catalyst layer 21 is unevenly distributed on the discharge side cell 12 side in the thickness direction of the partition wall 13.

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

(Base material)
In the wall flow type base material 10, the introduction side cell 11 in which the end portion 11a on the exhaust gas introduction side is opened and the discharge side cell 12 in which the end portion 12a on the exhaust gas discharge side is opened adjacent to the introduction side cell 11 are porous. It has a wall flow structure partitioned by a quality partition wall 13.

As the base material 10, various materials and shapes used in conventional applications of this type can be used. For example, the material of the base material may be exposed to high-temperature (for example, 400 ° C. or higher) exhaust gas generated when an internal combustion engine is operated under high load conditions, or when particulate matter is burned off at high temperature. It is preferably made of a heat-resistant material so that it can be used. Examples of the heat-resistant material include ceramics such as cordierite, mullite, aluminum silicate, and silicon carbide (SiC); alloys such as stainless steel. Further, the shape of the base material can be appropriately adjusted from the viewpoint of exhaust gas purification performance and suppression of pressure loss increase. For example, the outer shape of the base material may be a cylindrical shape, an elliptical cylinder shape, a polygonal cylinder shape, or the like. Further, although it depends on the space to be incorporated, the capacity of the base material (total volume of the cell) is preferably 0.1 to 5 L, more preferably 0.5 to 3 L. The total length of the base material in the stretching direction (total length of the partition wall 13 in the stretching direction) is preferably 10 to 500 mm, more preferably 50 to 300 mm.

The introduction-side cell 11 and the discharge-side cell 12 are regularly arranged along the axial direction of the tubular shape, and adjacent cells have one open end in the extension direction and another open end alternately. It is sealed. The introduction side cell 11 and the discharge side cell 12 can be set to an appropriate shape and size in consideration of the flow rate and components of the supplied exhaust gas. For example, the mouth shape of the introduction side cell 11 and the discharge side cell 12 can be a triangle; a rectangle such as a square, a parallelogram, a rectangle, and a trapezoid; another polygon such as a hexagon and an octagon; a circle. .. Further, it may have a High Ash Capacity (HAC) structure in which the cross-sectional area of the introduction-side cell 11 and the cross-sectional area of the discharge-side cell 12 are different from each other. The number of introduction-side cells 11 and discharge-side cells 12 can be appropriately set so as to promote the generation of turbulent flow of exhaust gas and suppress clogging due to fine particles or the like contained in the exhaust gas, and is particularly limited. However, it is preferably 200 cpsi to 400 cpsi.

The partition wall 13 that separates adjacent cells from each other is not particularly limited as long as it has a porous structure through which exhaust gas can pass. It can be adjusted as appropriate from the viewpoint of improvement of the above. For example, when the catalyst layer 21 is formed on the pore surface in the partition wall 13 by using the catalyst slurry 21a described later, the pore diameter (for example, the mode diameter (the pore diameter (of the distribution) having the largest appearance ratio in the frequency distribution of the pore diameter). When the maximum value))) or the pore volume is large, the pores are less likely to be blocked by the catalyst layer 21, and the obtained exhaust gas purification catalyst tends to be less likely to increase the pressure loss, but captures particulate matter. The collecting ability tends to decrease, and the mechanical strength of the base material also tends to decrease. On the other hand, when the pore diameter and the pore volume are small, the pressure loss tends to increase, but the ability to collect particulate matter is improved and the mechanical strength of the base material tends to be improved.

From this point of view, the pore diameter (mode diameter) of the partition wall 13 of the wall flow type base material 10 before forming the catalyst layer 21 is preferably 8 to 25 μm, more preferably 10 to 22 μm, and further. It is preferably 13 to 20 μm. The thickness of the partition wall 13 (the length in the thickness direction orthogonal to the stretching direction) is preferably 6 to 12 mil, more preferably 6 to 10 mil. Further, the pore volume of the partition wall 13 by the mercury intrusion method is preferably 0.2 to 1.5 cm ³ / g, more preferably 0.25 to 0.9 cm ³ / g, and further preferably 0.3. It is ~ 0.8 cm ³ / g. The porosity of the partition wall 13 by the mercury intrusion method is preferably 20 to 80%, more preferably 40 to 70%, and further preferably 60 to 70%. When the pore volume or porosity is equal to or higher than the lower limit, the increase in pressure loss tends to be further suppressed. Further, when the pore volume or the porosity is not more than the upper limit, the strength of the base material tends to be further improved. The pore diameter (mode diameter), pore volume, and porosity mean values calculated by the mercury intrusion method under the conditions described in the following examples.

(Catalyst layer)
Next, the catalyst layer 21 will be described. The catalyst layer 21 is formed at a plurality of places in the pores of the partition wall 13, contains at least one kind of catalyst metal, and is unevenly distributed on the discharge side cell 12 side in the thickness direction of the partition wall 13 (FIG. 2). By having such a configuration, there is a tendency that the pressure loss, particularly the increase in the pressure loss after ash deposition, is suppressed while having the exhaust gas purification performance.

The following points can be considered as the reason for this. When the catalyst layer 21 is unevenly distributed on the introduction side cell 11, the ash does not enter the pores in the partition wall 13 and tends to be easily deposited on the surface of the partition wall 13 of the introduction side cell 11 (see FIG. 3). Since ash composed of non-combustible components cannot be burned off, the pressure loss of the exhaust gas purification catalyst gradually increases with the accumulation of ash. On the other hand, when the catalyst layer 21 is unevenly distributed on the discharge side cell 12, the ash composed of the non-combustible component easily invades not only the surface of the partition wall 13 of the introduction side cell 11 but also the pores on the introduction side cell 11. Therefore, it is considered that deposition is possible even in the same pores (see FIG. 2), and the increase in pressure loss after ash deposition is suppressed. By suppressing the increase in pressure loss after ash deposition, the life of the exhaust gas purification catalyst is also improved. However, the reason why the increase in pressure loss after ash deposition is suppressed is not limited to the above.

The aspect in which the catalyst layer 21 is unevenly distributed is not particularly limited as long as it can exhibit desired exhaust gas purification performance and an effect of suppressing an increase in pressure loss after ash deposition, and the catalyst layer 21 is formed in the thickness direction of the partition wall 13. In the above, it is preferable that the closer to the cell wall surface on the discharge side cell 12 side, the more the loading amount tends to increase. As a result, from the same viewpoint as above, the increase in pressure loss after ash deposition tends to be suppressed.

As one aspect showing such uneven distribution, when the wall thickness Tw of the partition wall 13 is set, the total mass of the catalyst layer 21 is formed in the depth region T1 from the cell wall surface on the discharge side cell 12 side to Tw * 5/10. It is preferable that 60% or more is present. The amount of the catalyst layer 21 supported in the depth region T1 is preferably 65% or more, more preferably 70% or more, still more preferably 75, with respect to the total mass of the catalyst layer 21 in the cross section of the partition wall 13. % Or more. In the depth region T1 from the cell wall surface on the discharge side cell 12 side to Tw * 5/10, the catalyst layer 21 is unevenly distributed so that the supported amount is 60% or more, so that the introduction side cell is relatively relative. The amount of the catalyst layer 21 supported in the pores on the 11 side is reduced, and a space where ash can be deposited can be secured.

Further, as another embodiment, when the wall thickness Tw of the partition wall 13 is set, 15% or less of the total mass of the catalyst layer 21 is in the depth region T2 from the cell wall surface on the introduction side cell 11 side to Tw * 3/10. It is preferable to be present. The amount of the catalyst layer 21 supported in the depth region T2 is preferably 12% or less, more preferably 10% or less, still more preferably 8 with respect to the total mass of the catalyst layer 21 in the cross section of the partition wall 13. % Or less. In the depth region T2 from the cell wall surface on the introduction side cell 11 side to Tw * 3/10, the catalyst layer 21 is unevenly distributed so that the supported amount is 15% or less, so that the pores on the introduction side cell 11 side are distributed. The amount of the catalyst layer 21 supported inside is reduced, and a space where ash can be deposited can be secured.

In the present embodiment, a part of the catalyst layer 21 may be present on the introduction side cell 11 side as long as the catalyst layer 21 is biased toward the discharge side cell 12 in the thickness direction of the partition wall 13. .. In other words, as long as the catalyst layer 21 is biased toward the discharge side cell 12 in the thickness direction of the partition wall 13, the catalyst layer 21 is present from the cell wall surface on the introduction side cell 11 side in the thickness direction of the partition wall 13. It may be formed over the cell wall surface on the discharge side cell 12 side.

The uneven distribution of the catalyst layer 21 can be confirmed by a scanning electron microscope on the cross section of the partition wall 13 of the exhaust gas purification catalyst 100. Specifically, in the scanning electron micrograph of the cross section of the partition wall 13, the portion occupied by the catalyst layer 21 is specified, divided into 10 parts in the thickness direction of the partition wall 13, and the area of the catalyst layer 21 is integrated for each area. By doing so, you can ask for it. At this time, it is desirable to measure at least three points of the partition wall 13 near the end portion 11a on the exhaust gas introduction side, the portion near the end portion 12a on the exhaust gas discharge side, and the central portion between them, and obtain the average value thereof. ..

Further, in the stretching direction (length direction) of the partition wall 13, the range L1 (coating length of the catalyst layer 21) in which the catalyst layer 21 is formed is the total length L _W (the coating length of the catalyst layer 21) in the stretching direction of the wall flow type base material 10. The total length of the partition wall 13 in the extending direction) is preferably 100%, and the partition wall 13 is preferably formed over the entire surface, specifically, preferably 80 to 100%, more preferably 90 to 100%, and even more preferably. It is 95 to 100%.

The catalyst metal contained in the catalyst layer 21 is not particularly limited, and various metal species capable of functioning as an oxidation catalyst or a reduction catalyst can be used. Examples thereof include platinum group metals such as platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), iridium (Ir) and osmium (Os). Of these, palladium (Pd) and platinum (Pt) are preferable from the viewpoint of oxidizing activity, and rhodium (Rh) is preferable from the viewpoint of reducing activity. In the present embodiment, as described above, the catalyst layer 21 contains one or more catalyst metals in a mixed state. In particular, the combined use of two or more catalytic metals is expected to have a synergistic effect due to having different catalytic activities.

The mode of such a combination of catalyst metals is not particularly limited, and a combination of two or more kinds of catalyst metals having excellent oxidation activity, a combination of two or more kinds of catalyst metals having excellent reduction activity, and a catalyst metal having excellent oxidation activity and reduction Examples thereof include a combination of catalyst metals having excellent activity. Among these, as one aspect of the synergistic effect, a combination of a catalytic metal having excellent oxidative activity and a catalytic metal having excellent reducing activity is preferable, and a combination containing at least Rh, Pd and Rh, or Pt and Rh is more preferable. With such a combination, the exhaust gas purification performance tends to be further improved.

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

As the carrier particles contained in the catalyst layer 21 and supporting the catalyst metal, an inorganic compound conventionally used in this type of exhaust gas purification catalyst can be considered. For example, oxygen storage materials (OSC materials) such as cerium oxide (ceria: CeO ₂ ) and ceria-zirconia composite oxide (CZ composite oxide), aluminum oxide (alumina: Al ₂ O ₃ ), zirconium oxide (zirconia: ZrO). ₂ ), oxides such as silicon oxide (silica: SiO ₂ ) and titanium oxide (titania: TiO ₂ ) and composite oxides containing these oxides as main components can be mentioned. These may be composite oxides or solid solutions to which rare earth elements such as lanthanum and yttrium, transition metal elements, and alkaline earth metal elements have been added. These carrier particles may be used alone or in combination of two or more. Here, the oxygen occlusal material (OSC material) occludes oxygen in the exhaust gas when the air-fuel ratio of the exhaust gas is lean (that is, the atmosphere on the oxygen excess side), and when the air-fuel ratio of the exhaust gas is rich (that is, the atmosphere on the oxygen excess side). That is, the atmosphere on the excess fuel side) is the one that releases the stored oxygen.

From the viewpoint of improving the exhaust gas purification performance and suppressing the progress of grain growth (sintering) of the catalyst metal, the catalyst metal loading ratio (catalyst metal mass per 1 L of the base material) of the catalyst layer 21 is preferably 0.5 to. It is 10 g / L, more preferably 1 to 8 g / L, and even more preferably 1 to 6 g / L.

Further, the pore diameter (mode diameter) of the partition wall 13 of the exhaust gas purification catalyst in the state where the catalyst layer 21 is formed by the mercury injection method is preferably 10 to 23 μm, more preferably 12 to 20 μm, and further preferably 12 to 20 μm. It is 14 to 18 μm. Further, the pore volume of the partition wall 13 by the mercury intrusion method of the exhaust gas purification catalyst in the state where the catalyst layer 21 is formed is preferably 0.2 to 1.0 cm ³ / g, more preferably 0.25 to 0. It is 9 cm ³ / g, more preferably 0.3 to 0.8 cm ³ / g. Further, the porosity of the partition wall 13 by the mercury intrusion method of the exhaust gas purification catalyst in the state where the catalyst layer 21 is formed is preferably 20 to 80%, more preferably 30 to 70%, and preferably 35 to 60%. %. The pore diameter (mode diameter), pore volume, and porosity mean values calculated by the mercury intrusion method under the conditions described in the following examples.

[Manufacturing method of exhaust gas purification catalyst]
The method for manufacturing the exhaust gas purification catalyst of the present embodiment is a method for manufacturing the exhaust gas purification catalyst 100 that purifies the exhaust gas discharged from the internal combustion engine, the introduction side cell 11 having the end portion 11a on the exhaust gas introduction side open, and the introduction side cell 11. The discharge side cell 12 adjacent to the introduction side cell 11 and the end portion 12a on the exhaust gas discharge side is open prepares the wall flow type base material 10 defined by the porous partition wall 13, and the discharge of the partition wall 13. It is characterized by having a catalyst layer forming step S1 for forming a catalyst layer 21 unevenly distributed on the surface of pores existing on the side cell 12 side.

Hereinafter, each step will be described. In the present specification, the wall flow type base material before forming the catalyst layer 21 is referred to as "base material 10", and the wall flow type base material after forming the catalyst layer 21 is referred to as "exhaust gas purification catalyst 100". It is written as.

<Preparation process>
In this preparation step S0, the wall flow type base material 10 described in the exhaust gas purification catalyst 100 is prepared as the base material.

<Catalyst layer formation process>
In this catalyst layer forming step S1, the catalyst slurry 21a is applied to the pore surface existing on the discharge side cell 12 side of the partition wall 13, dried, and fired to form an unevenly distributed catalyst layer 21. The coating method of the catalyst slurry 21a is not particularly limited, and examples thereof include a method of impregnating a part of the base material 10 with the catalyst slurry 21a and spreading it over the entire partition wall 13 of the base material 10. More specifically, the step S1a of impregnating the end portion 12a on the exhaust gas discharge side of the base material 10 with the catalyst slurry 21a and the gas being introduced into the base material 10 from the end portion 12a side on the exhaust gas discharge side are introduced. Examples thereof include a method having a step S1b of applying the catalyst slurry 21a impregnated in the base material 10 to the pore surface existing on the discharge side cell 12 side.

As a method of unevenly distributing the catalyst layer 21 on the discharge side cell 12 side of the partition wall 13, the catalyst slurry 21a is coated on the discharge side cell 12 side of the partition wall 13, and the coated catalyst slurry 21a is dried and fired. However, there are no particular restrictions. For example, the viscosity and solid content of the catalyst slurry 21a can be adjusted with respect to the discharge side cell 12 side of the partition wall 13 in order to adjust the permeation distance into the pores in the partition wall 13, and the coating conditions and coating can be adjusted as necessary. A method of adjusting the drying conditions after construction can be mentioned.

The method of impregnating the catalyst slurry 21a in the step S1a is not particularly limited, and examples thereof include a method of immersing the end portion of the base material 10 in the catalyst slurry 21a. In this method, if necessary, the catalyst slurry 21a may be pulled up by discharging (sucking) gas from the opposite end. The catalyst slurry 21a is supplied into the wall flow type base material 10 from the end portion 12a on the exhaust gas discharge side.

Further, in step S1b, gas is introduced into the base material 10 from the end side impregnated with the catalyst slurry 21a, and the catalyst slurry 21a is applied to the pores existing on the discharge side cell 12 side. Examples of the method of applying the catalyst slurry 21a include a method of causing a pressure difference between both ends of the base material 10. Specifically, the end portion 12a on the exhaust gas discharge side is set to a relatively high pressure, and the catalyst slurry 21a impregnated from the end portion 12a on the exhaust gas discharge side is coated toward the end portion 11a on the exhaust gas introduction side. By applying pressure, the catalyst slurry 21a can be applied.

In step S1c, the coated catalyst slurry 21a is dried to obtain a dried catalyst slurry 21a'. The drying conditions in step S1c are not particularly limited as long as the solvent volatilizes from the catalyst slurry 21a. For example, the drying temperature is preferably 100 to 225 ° C, more preferably 100 to 200 ° C, and even more preferably 125 to 175 ° C. The drying time is preferably 0.5 to 2 hours, preferably 0.5 to 1.5 hours.

As a method considered as a drying method, in addition to a method in which the base material 10 after the step S1b is allowed to stand at a predetermined drying temperature, the inside of the base material 10 is formed from the ends 11a and 12a on the exhaust gas introduction side and / or the exhaust gas discharge side. A method of introducing a gas F into the air to promote drying can be mentioned.

Next, in step S1d, the catalyst slurry 21a'dried as described above is fired to form the catalyst layer 21. 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 21a'. For example, the firing temperature is not particularly limited, but is preferably 400 to 650 ° C, more preferably 450 to 600 ° C, and even more preferably 500 to 600 ° C. The firing time is preferably 0.5 to 2 hours, preferably 0.5 to 1.5 hours.

(Catalyst slurry)
The catalyst slurry 21a for forming the catalyst layer 21 will be described. 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 a catalyst layer 21 through a firing step described later. The catalyst particles are not particularly limited, and can be appropriately selected and used from known catalyst particles. From the viewpoint of coatability in the pores of the partition wall 13, the solid content of the catalyst slurry 21a is preferably 1 to 50% by mass, more preferably 10 to 40% by mass, and further preferably 15. ~ 30% by mass. With such a solid content ratio, the catalyst slurry 21a tends to be easily applied to the discharge side cell 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 further preferably 1 to 5 μm. When the D90 particle size is 1 μm or more, the crushing time when the catalyst powder is crushed by the milling device can be shortened, and the work efficiency tends to be further improved. Further, when the D90 particle diameter is 7 μm or less, it is suppressed that the coarse particles block the pores in the partition wall 13, and the increase in pressure loss tends to be suppressed. In the present specification, the D90 particle size can be measured by a laser diffraction type particle size distribution measuring device (for example, a laser diffraction type particle size distribution measuring device SALD-3100 manufactured by Shimadzu Corporation, etc.).

As the catalyst metal contained in the catalyst slurry 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 as those exemplified for the catalyst metal contained in the catalyst layer 21 can be mentioned. As one embodiment, as for the combination of the catalyst metals contained in the catalyst slurry 21a, the same embodiments as those described in the catalyst layer 21 formed by the catalyst slurry 21a are exemplified. Specific examples thereof include a combination of two or more kinds of catalyst metals having excellent oxidative activity, a combination of two or more kinds of catalytic metals having excellent reducing activity, and a combination of a catalytic metal having excellent oxidative activity and a catalytic metal having excellent reducing activity. Among these, as one aspect of the synergistic effect, a combination of a catalytic metal having excellent oxidative activity and a catalytic metal having excellent reducing activity is preferable, and a combination containing at least Pd and Rh is more preferable.

From the viewpoint of increasing the contact area with the exhaust gas, it is preferable that the average particle size of the catalyst metal particles in the catalyst slurry 21a is small. Specifically, the average particle size of the catalyst metal particles is preferably 1 to 15 nm, more preferably 1 to 10 nm, and even more preferably 1 to 7 nm. The average particle size of the catalyst metal particles can be confirmed by using, for example, a scanning transmission electron microscope (STEM) such as HD-2000 manufactured by Hitachi High-Technologies Co., Ltd., which is not described in the present specification. The circle-equivalent diameters of the 10 catalytic metal particles extracted at random are calculated, and the average value thereof is taken as the average particle diameter of the catalytic metal particles.

As the carrier particles contained in the catalyst slurry 21a, an inorganic compound conventionally used in this type of exhaust gas purification catalyst can be considered. Specifically, the same as those exemplified for the carrier particles contained in the catalyst layer 21 can be mentioned. These carrier particles may be used alone or in combination of two or more.

From the viewpoint of exhaust gas purification performance, the specific surface area of the carrier particles contained in the catalyst slurry 21a is preferably 10 to 500 m ² / g, more preferably 30 to 200 m ² / g.

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

[Use]
An air-fuel mixture containing oxygen and fuel gas is supplied to an internal combustion engine (engine), and the air-fuel mixture is burned to convert combustion energy into mechanical energy. The air-fuel mixture burned at this time becomes exhaust gas and is discharged to the exhaust system. The exhaust system is provided with an exhaust gas purification device equipped with an exhaust gas purification catalyst, and harmful components (for example, carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx) contained in the exhaust gas by the exhaust gas purification catalyst are provided. )) Is purified, and particulate matter (PM) contained in the exhaust gas is collected and removed. In particular, the exhaust gas purification catalyst 100 of the present embodiment is preferably used for a gasoline particulate filter (GPF) capable of collecting and removing particulate matter contained in the exhaust gas of a gasoline engine.

Hereinafter, the features of the present invention will be described in more detail with reference to Test Examples, Examples and Comparative Examples, but the present invention is not limited thereto. That is, the materials, amounts used, ratios, treatment contents, treatment procedures, etc. shown in the following examples can be appropriately changed as long as they do not deviate from the gist of the present invention. Further, the values of various production conditions and evaluation results in the following examples have meanings as a preferable upper limit value or a preferable lower limit value in the embodiment of the present invention, and the preferable range is the above-mentioned upper limit value or the lower limit value. And may be in the range specified by the combination of the values of the following examples or the values of the examples.

(Example 1)
Alumina powder having a D50 particle size of 28 μm and a BET specific surface area of 141 m ² / g is impregnated with an aqueous solution of palladium nitrate and then fired at 500 ° C. for 1 hour to obtain Pd-supported alumina powder (Pd content: 8.6 mass). %) Was obtained. Further, a zirconia-lanthanate-modified alumina powder having a D50 particle diameter of 29 μm and a BET specific surface area of 145 m ² / g was impregnated with a rhodium nitrate aqueous solution and then calcined at 500 ° C. for 1 hour to carry Rh-supported zirconia-lanthanate-modified alumina. A powder (Rh content: 1.4% by mass) was obtained.

0.5 kg of Pd-supported alumina powder and 0.5 kg of Rh-supported zirconia-lantern-modified alumina powder, and 2 kg of ceria zirconia composite oxide powder having a D50 particle size of 10 μm and a BET specific surface area of 71 m ² / g, 46%. 195 g of an aqueous solution of lanthanum nitrate and ion-exchanged water are mixed, and the obtained mixture is put into a ball mill and milled until the catalyst powder has a predetermined particle size distribution to obtain a catalyst slurry having a D90 particle size of 3.0 μm. Obtained.

Next, a wall-flow type honeycomb substrate made of Cordellite (number of cells / mill thickness: 300 cpsi / 8 mil, diameter: 118.4 mm, total length: 127 mm, porosity: 65%) was prepared. The end portion of the base material on the exhaust gas discharge side was immersed in the catalyst slurry and sucked under reduced pressure from the opposite end side to impregnate and hold the catalyst slurry on the end portion of the base material. Gas flows into the base material from the end face side impregnated and held with the catalyst slurry, and the catalyst slurry is applied to the pore surface in the partition wall so as to be unevenly distributed on the discharge side cell side in the thickness direction, and the base material is coated with the catalyst slurry. The excess catalyst slurry was blown off from the end on the exhaust gas introduction side. Then, the base material coated with the catalyst slurry was dried at 150 ° C. while allowing gas to flow into the base material, and then calcined at 550 ° C. under an atmospheric atmosphere. As a result, an exhaust gas purification catalyst having a catalyst layer unevenly distributed on the discharge side cell side in the thickness direction from the sealed end to the exhaust gas discharge side opening end was produced. In this exhaust gas purification catalyst, the catalyst layer is formed over the entire total length Lw of the wall flow type base material 10 in the extending direction (length direction) of the partition wall 13, and is formed in the thickness direction of the partition wall. , It is formed from the cell wall surface on the introduction side cell side to the cell wall surface on the discharge side cell side, and the catalyst layer has a tendency to increase the loading ratio as it is closer to the cell wall surface on the discharge side cell side, and the discharge side cell. More than 60% of the total mass of the catalyst layer exists in the depth region from the cell wall surface on the side cell side to Tw * 5/10, and the catalyst layer exists in the depth region from the cell wall surface on the introduction side cell side to Tw * 3/10. There was less than 15% of the total mass of the catalyst. The amount of the catalyst layer coated after firing was 60.9 g per 1 L of the base material (excluding the weight of the platinum group metal).

(Comparative Example 1)
The end of the cell on the introduction side is immersed in the catalyst slurry and sucked under reduced pressure from the opposite end side to impregnate and hold the catalyst slurry on the end of the base material, and the base material is impregnated and held from the end face side where the catalyst slurry is impregnated and held. The gas is allowed to flow in, and the catalyst slurry is coated on the pore surface in the partition wall so as to be unevenly distributed on the introduction side cell side in the thickness direction, and the excess catalyst slurry is applied from the end portion of the base material on the exhaust gas discharge side. Exhaust gas purification having a catalyst layer unevenly distributed on the introduction side cell side in the thickness direction from the sealed opening end to the exhaust gas introduction side opening end by the same operation as in Example 1 except that A catalyst was prepared.

(Comparative Example 2)
A wall flow type honeycomb base material made of Cordellite (number of cells / mill thickness: 300 cpsi / 8 mil, diameter: 118.4 mm, total length: 127 mm, porosity: 65%) was prepared. The end portion of the base material on the exhaust gas introduction side was immersed in the catalyst slurry and sucked under reduced pressure from the opposite end side to impregnate and hold the catalyst slurry on the end portion of the base material. Gas is allowed to flow into the base material from the end face side impregnated and held with the catalyst slurry, and the catalyst slurry is applied to the pore surface in the partition wall so as to be unevenly distributed on the introduction side cell side in the thickness direction, and the base material is coated with the catalyst slurry. The excess catalyst slurry was blown off from the end on the exhaust gas discharge side. The amount of catalyst at this time was set to half the final total mass. Then, the base material coated with the catalyst slurry was dried at 150 ° C. while allowing gas to flow into the base material, and then calcined at 550 ° C. under an atmospheric atmosphere. As a result, a catalyst layer in which the catalyst metal is unevenly distributed on the introduction side cell side in the thickness direction is formed from the sealed end to the opening end on the exhaust gas introduction side.

Further, in the same manner, the end portion of the base material on the exhaust gas discharge side was immersed in the catalyst slurry and sucked under reduced pressure from the end portion on the opposite side to impregnate and hold the catalyst slurry on the end portion of the base material. Gas flows into the base material from the end face side impregnated and held with the catalyst slurry, and the catalyst slurry is applied to the pore surface in the partition wall so as to be unevenly distributed on the discharge side cell side in the thickness direction, and the base material is coated with the catalyst slurry. The excess catalyst slurry was blown off from the end on the exhaust gas introduction side. The amount of catalyst at this time was set to be half of the final total mass in the same manner as above. Then, the base material coated with the catalyst slurry was dried at 150 ° C. while allowing gas to flow into the base material, and then calcined at 550 ° C. under an atmospheric atmosphere. As a result, a catalyst layer in which the catalyst metal is unevenly distributed on the discharge side cell side in the thickness direction is formed from the sealed open end to the open end on the exhaust gas discharge side, and as a result, the catalyst layer is substantially uniformly present over the entire partition wall. An exhaust gas purification catalyst having a catalyst layer was produced. The amount of the catalyst layer coated after firing was 60.9 g per 1 L of the base material (excluding the weight of the platinum group metal).

[Measurement of particle size distribution]
The D90 particle size of the catalyst slurry was measured by a laser scattering method using a laser diffraction type particle size distribution measuring device SALD-3100 manufactured by Shimadzu Corporation.

[Calculation of porosity]
Pore diameter (mode diameter) from each partition wall of the exhaust gas introduction side portion, the exhaust gas discharge side portion, and the intermediate portion of the exhaust gas purification catalyst produced in Examples and Comparative Examples and the base material before coating the catalyst slurry. And a sample (1 cm ³ ) for measuring the pore volume was collected. After the measurement sample was dried, the pore distribution was measured by a mercury intrusion method using a mercury porosimeter (manufactured by Thermo Fisher Scientific, trade names: PASCAL 140 and PASCAL 440). At this time, the low pressure region (0 to 400 Kpa) was measured by PASCAL 140, and the high pressure region (0.1 Mpa to 400 Mpa) was measured by PASCAL 440. From the obtained pore distribution, the pore diameter (mode diameter) was obtained, and the pore volume in the pores having a pore diameter of 1 μm or more was calculated. As the values of the pore diameter and the pore volume, the average value of the values obtained in each of the exhaust gas introduction side portion, the exhaust gas discharge side portion, and the intermediate portion was adopted.

Next, the porosity of the exhaust gas purification catalyst produced in Examples and Comparative Examples was calculated by the following formula. The results are shown in Table 1 below.
Porosity of exhaust gas purification catalyst (%) = Porosity of exhaust gas purification catalyst (cc / g) ÷ Porosity of base material (cc / g) x Porosity of base material (%)
Porosity of the substrate (%) = 65%

[Measurement of pressure loss before ash deposition]
The exhaust gas purification catalysts produced in Examples and Comparative Examples were installed in pressure loss measuring devices (manufactured by Tsukubarika Seiki Co., Ltd.), and air at room temperature was allowed to flow into the installed exhaust gas purification catalysts. The value obtained by measuring the differential pressure between the introduction side and the exhaust side of the air when the amount of air outflow from the exhaust gas purification catalyst was 2 m ³ / min was defined as the pressure loss of the exhaust gas purification catalyst. The results are shown in FIG. As shown in FIG. 4, the exhaust gas purification catalyst produced in the example has the same pressure loss as the exhaust gas purification catalyst produced in the comparative example, and the pressure loss before ash deposition differs depending on the position of the catalyst layer. It turns out that there is no such thing.

[Measurement of pressure loss after ash deposition]
The pressure loss after ash deposition was measured in the same manner as above, except that the exhaust gas purification catalyst after depositing 100 g of ash was used in the exhaust gas purification catalyst produced in Examples and Comparative Examples. The results are shown in FIG. As shown in FIG. 5, the exhaust gas purification catalyst produced in the example has a lower pressure loss than the exhaust gas purification catalyst produced in the comparative example, and there is a difference in the pressure loss after ash deposition depending on the position of the catalyst layer. You can see that.

[Observation of coat condition]
Measurement samples (1 cm ³ ) of a scanning electron microscope (SEM) were prepared from the partition walls of the exhaust gas purification catalysts prepared in Examples and Comparative Examples, respectively. The measurement sample was embedded in resin and pretreated for carbon vapor deposition. The measurement sample after the pretreatment was observed using a scanning electron microscope (manufactured by Carl Zeiss, trade name: ULTRA55), and the state of supporting the catalyst on the substrate was confirmed. The trace diagram is shown in FIG.

The exhaust gas purification catalyst of the present invention can be widely and effectively used as an exhaust gas purification catalyst for removing particulate matter contained in the exhaust gas of a gasoline engine. Further, the exhaust gas purification catalyst of the present invention can be effectively used as an exhaust gas purification catalyst because it removes particulate matter contained in exhaust gas of not only gasoline engines but also diesel engines, jet engines, boilers, gas turbines and the like. be.

10 ・ ・ ・ Wall flow type base material 11 ・ ・ ・ Introduction side cell 11a ・ ・ ・ Exhaust gas introduction side end 12 ・ ・ ・ Exhaust gas discharge side cell 12a ・ ・ ・ Exhaust gas discharge side end 13 ・ ・ ・ Bulkhead 21 ・・ ・ Catalyst layer 21a ・ ・ ・ Catalyst slurry 21a'・ ・ Dried catalyst slurry 100 ・ ・ ・ Exhaust gas purification catalyst

Claims (5)

An exhaust gas purification catalyst that purifies the exhaust gas emitted from an internal combustion engine.
An introduction-side cell having an open end on the exhaust gas introduction side and an exhaust-side cell adjacent to the introduction-side cell and having an open end on the exhaust gas discharge side are defined as a wall-flow type base material by a porous partition wall. ,
It has a catalyst layer containing at least one kind of catalyst metal, which is formed at a plurality of places in the pores of the partition wall.
The catalyst layer is unevenly distributed on the discharge side cell side in the thickness direction of the partition wall .
The catalyst layer has a tendency to increase the loading ratio as it is closer to the cell wall surface on the discharge side cell side in the thickness direction of the partition wall.
Exhaust gas purification catalyst. An exhaust gas purification catalyst that purifies the exhaust gas emitted from an internal combustion engine.
An introduction-side cell having an open end on the exhaust gas introduction side and an exhaust-side cell adjacent to the introduction-side cell and having an open end on the exhaust gas discharge side are defined as a wall-flow type base material by a porous partition wall. ,
It has a catalyst layer containing at least one kind of catalyst metal, which is formed at a plurality of places in the pores of the partition wall.
The catalyst layer is unevenly distributed on the discharge side cell side in the thickness direction of the partition wall .
When the wall thickness of the partition wall is Tw, 60% or more of the total mass of the catalyst layer is present in the depth region from the cell wall surface on the discharge side cell side to Tw * 5/10.
Exhaust gas purification catalyst. An exhaust gas purification catalyst that purifies the exhaust gas emitted from an internal combustion engine.
An introduction-side cell having an open end on the exhaust gas introduction side and an exhaust-side cell adjacent to the introduction-side cell and having an open end on the exhaust gas discharge side are defined as a wall-flow type base material by a porous partition wall. ,
It has a catalyst layer containing at least one kind of catalyst metal, which is formed at a plurality of places in the pores of the partition wall.
The catalyst layer is unevenly distributed on the discharge side cell side in the thickness direction of the partition wall .
When the wall thickness of the partition wall is Tw, 15% or less of the total mass of the catalyst layer exists in the depth region from the cell wall surface on the introduction side cell side to Tw * 3/10.
Exhaust gas purification catalyst. The catalyst metal comprises Rh, Pd and Rh, or Pt and Rh.
The exhaust gas purification catalyst according to any one of claims 1 to 3 . The internal combustion engine is a gasoline engine.
The exhaust gas purification catalyst according to any one of claims 1 to 4 .

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