JP7319293B2 - Exhaust gas purification catalyst and its manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to an exhaust gas purifying catalyst and a method for producing the same.

Exhaust gases emitted from internal combustion engines contain particulate matter (PM) mainly composed of carbon, ash composed of incombustible components, and the like, and are known to cause air pollution. In the past, diesel engines, which emit more particulate matter than gasoline engines, were subject to strict regulations on emissions of particulate matter. being strengthened.

As means for reducing the emission of particulate matter, there is known a method of providing a particulate filter for the purpose of accumulating and collecting particulate matter in an exhaust gas passage of an internal combustion engine. In particular, in recent years, from the viewpoint of space saving, etc., efforts have been made to reduce emissions of particulate matter and remove harmful components such as carbon monoxide (CO), hydrocarbons (HC) and nitrogen oxides (NOx). In order to do so at the same time, it has been considered to provide a catalyst layer by applying a catalyst slurry to a particulate filter and then calcining it.

A wall-flow type substrate in which 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 by porous partition walls. As a method of forming such a catalyst layer on the particulate filter provided, the properties of the slurry such as viscosity and solid content are adjusted, and one of the inlet-side cells or the outlet-side cells is pressurized to form the inlet-side A known method is to adjust the permeation of the catalyst slurry into the partition walls by creating a pressure difference between the cells and the discharge-side cells (see, for example, Patent Document 1).

WO2016/060048

A particulate filter as described in Patent Document 1 has a wall-flow structure from the viewpoint of removing particulate matter, and is configured so that exhaust gas passes through the pores of the partition wall. However, there is still room for improvement in terms of soot collection performance, pressure loss, and exhaust gas purification performance.

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 with improved NOx purification performance and a method for producing the same. It is to be noted that the present invention is not limited to the purpose described here, and that it is a function and effect derived from each configuration shown in the mode for carrying out the invention described later, and a function and effect that cannot be obtained by the conventional technology can be achieved. It can be positioned as another purpose.

The present inventors have extensively studied methods for improving purification performance. As a result, the inventors have found that the above problems can be solved by adjusting the pore size in the extending direction of the partition walls on which the catalyst layer is formed, and have completed the present invention. That is, the present invention provides various specific aspects shown below.

[1]
An exhaust gas purification catalyst for purifying exhaust gas emitted from an internal combustion engine,
a wall-flow type substrate in which 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 by porous partition walls; ,
a catalyst layer formed in the partition wall;
The catalyst layer has a first region formed along the extending direction of the partition wall from the exhaust gas introduction side end, and a second region formed along the extending direction of the partition wall from the exhaust gas discharge side end. and a third region where the first region and the second region overlap,
The ratio (D _in / _{D mid ) of the pore diameter D in calculated from the pore distribution of the first region to the pore diameter D mid calculated from} the pore distribution of the third region is 1.2 or more. ,
The ratio of the pore diameter D _out calculated from the pore distribution of the second region to the pore diameter D _mid (D _out /D _mid ) is 1.2 or more.
Exhaust gas purification catalyst.
[2]
The ratio of the pore volume V in with a pore diameter of 1 μm or more calculated from the pore distribution of the first region to the pore volume V _mid with a pore diameter of 1 μm or more calculated from the pore distribution of _the third region (V _in /V _mid ) is 1.3 or more,
The ratio of the pore volume V _out with a pore diameter of 1 μm or more calculated from the pore distribution of the second region to the pore volume V _mid (V _out /V _mid ) is 1.3 or more.
The exhaust gas purifying catalyst according to [1].
[3]
The difference between the pore diameter D _in or the pore diameter D _out and the pore diameter D _mid is 2.5 to 10 μm, respectively.
The exhaust gas purifying catalyst according to [1] or [2].
[4]
wherein the first region contains Pd;
The exhaust gas purifying catalyst according to any one of [1] to [3].
[5]
wherein the second region contains Rh;
The exhaust gas purifying catalyst according to [4].
[6]
wherein the first region contains Rh;
The exhaust gas purifying catalyst according to any one of [1] to [3].
[7]
wherein the second region contains Pd;
The exhaust gas purifying catalyst according to [6].
[8]
The catalyst layer is formed from the cell wall surface on the inlet 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 [7].
[9]
The formation range of the third region is 2 to 20% with respect to 100% of the total length in the extending direction of the partition wall.
The exhaust gas purifying catalyst according to any one of [1] to [8].
[10]
wherein the internal combustion engine is a gasoline engine;
The exhaust gas purifying catalyst according to any one of [1] to [9].
[11]
A method for producing an exhaust gas purifying catalyst for purifying exhaust gas emitted from an internal combustion engine, comprising:
A wall-flow type substrate in which 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 by porous partition walls. the process of preparing,
a catalyst layer forming step of forming a catalyst layer by applying a catalyst slurry to at least a portion of the pore surfaces in the partition walls of the wall-flow type substrate;
In the catalyst layer forming step,
A first region formed along the extending direction of the partition wall from the end on the exhaust gas introduction side, a second region formed along the extending direction of the partition wall from the end on the exhaust gas discharge side, and the second region A third region in which the first region and the second region overlap, and the pore diameter calculated from the pore distribution of the first region with respect to the pore diameter D _mid calculated from the pore distribution of the third region The ratio of D _in (D _in /D _mid ) is 1.2 or more, and the ratio of the pore diameter D _out calculated from the pore size distribution of the second region to the pore diameter D _mid (D _out /D _mid ) is 1.2 or more to produce the exhaust gas purification catalyst having the catalyst layer,
A method for producing an exhaust gas purification catalyst.

According to the present invention, it is possible to provide an exhaust gas purification catalyst with improved NOx purification performance and a method for producing the same. This exhaust gas purifying catalyst can be effectively used as a catalyst-carrying gasoline particulate filter (GPF), and the performance of an exhaust gas treatment system equipped with such a particulate filter can be further improved.

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which shows typically one aspect|mode of the exhaust gas purification catalyst of this embodiment. 4 is a graph showing NOx purification performance in Examples and Comparative Examples. FIG. 4 is a diagram showing the balance between NOx purification performance and soot collection rate in Examples and Comparative Examples.

BEST MODE FOR CARRYING OUT THE INVENTION 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 to these. In addition, the present invention can be arbitrarily changed and implemented without departing from the gist thereof. In this specification, the positional relationships such as up, down, left, and right are based on the positional relationships shown in the drawings unless otherwise specified. Also, the dimensional ratios in the drawings are not limited to the illustrated ratios. As used herein, the term "pore diameter" refers to the diameter (mode diameter: maximal value of distribution) with the highest appearance ratio in the frequency distribution of pore diameters (hereinafter also referred to as pore distribution). In addition, in this specification, when a numerical value or physical property value is sandwiched before and after the "~", it is used to include the values before and after it. For example, the notation of a numerical range of "1 to 100" includes both the lower limit of "1" and the upper limit of "100". The same applies to the notation of other numerical ranges.

[Exhaust gas purification catalyst]
The exhaust gas purifying catalyst of the present embodiment is an exhaust gas purifying catalyst 100 for purifying exhaust gas discharged from an internal combustion engine, and includes an introduction side cell 11 having an open end portion 11a on the exhaust gas introduction side, and an introduction side cell 11 adjacent to the introduction side cell. The discharge-side cell 12 having an open end 12a on the exhaust gas discharge side has a wall flow type substrate 10 defined by a porous partition wall 13, and a catalyst layer 21 formed in the partition wall 13, The catalyst layer has a first region formed along the extending direction of the partition wall from the exhaust gas introduction side end, and a second region formed along the extending direction of the partition wall from the exhaust gas discharge side end. and a third region where the first region and the second region overlap, and from the pore distribution of the first region with respect to the pore diameter D _mid calculated from the pore distribution of the third region The ratio (D _in /D _mid ) of the calculated pore diameter D _in is 1.2 or more, and the ratio of the pore diameter D _out calculated from the pore distribution of the second region to the pore diameter D _mid ( D _out /D _mid ) is 1.2 or more.

Hereinafter, each configuration will be described with reference to the cross-sectional view schematically showing the exhaust gas purifying catalyst of the present embodiment shown in FIG. The exhaust gas purifying catalyst of this embodiment has a wall-flow structure. In the exhaust gas purifying catalyst 100 having such a structure, the exhaust gas discharged from the internal combustion engine flows into the inlet-side cell 11 from the end portion 11a (opening) on the exhaust gas inlet side and passes through the pores of the partition wall 13. , and flows into the adjacent discharge-side cell 12, and flows out from the end 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 walls 13 is generally deposited on the partition walls 13 in the inlet-side cell 11 and/or in the pores of the partition walls 13, and the deposited particulate matter is 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 hydrocarbons (HC) contained in the exhaust gas are converted into water (H ₂ O) and carbon dioxide ( CO ₂ ) and the like, nitrogen oxides (NOx) are reduced to nitrogen (N ₂ ), and harmful components are purified (detoxified). In this specification, removal of particulate matter and purification of harmful components such as carbon monoxide (CO) are collectively referred to as "exhaust gas purification performance". Each configuration will be described in more detail below.

(pore size)
By creating a difference in pore size in the extending direction of the partition walls, there are areas where the exhaust gas flows easily and areas where it is difficult for the exhaust gas to flow, and the flow of the exhaust gas can be controlled. As a result, the exhaust gas passing through the exhaust gas purification catalyst can be brought into contact with the catalyst more effectively, and improvement in exhaust gas purification performance and improvement in soot collection performance can be expected. In the exhaust gas purifying catalyst of the present embodiment, from the viewpoint of improving the exhaust gas purifying performance and the soot collection performance by controlling the flow of exhaust gas, the catalyst layer 21 is arranged in the extending direction of the partition wall from the end on the exhaust gas introduction side. A first region 21a formed along the first region 21a, a second region 21b formed along the extending direction of the partition wall from the end on the exhaust gas discharge side, and a third region 21c where the first region 21a and the second region 21b overlap. formed to have Then, the pore diameter D _mid calculated from the pore distribution of the third region 21c is combined with the pore diameter D in calculated from the pore distribution of the first region 21a and the pore diameter D _in calculated from the pore distribution of the second region 21b. Each of them is made smaller than the hole diameter D _out by a predetermined value or more. In order for the exhaust gas to escape from the end portion 11a (opening) to the end portion 12a (opening) in the shortest distance, the exhaust gas must pass through the center of the partition wall. At this time, by making the pore diameter of the third region 21c smaller than the pore diameters of the first region 21a and the second region 21b to make it difficult for the exhaust gas to pass through, the exhaust gas can pass through the first region 21a and the second region 21b. It spreads evenly, and the exhaust gas purification performance and soot collection performance are further improved.

Specifically, the ratio (D _in /D _mid ) is 1.2 or more, preferably 1.3 or more, and more preferably 1.35 or more. The upper limit of the ratio (D _in /D _mid ) is not particularly limited, but is preferably 3 or less, more preferably 2.8 or less, and still more preferably 2.5 or less. Also, the ratio (D _out /D _mid ) is 1.2 or more, preferably 1.3 or more, more preferably 1.35 or more. The upper limit of the ratio (D _out /D _mid ) is not particularly limited, but is preferably 3 or less, more preferably 2.8 or less, and still more preferably 2.5 or less. When the ratio (D _in /D _mid ) and ratio (D _out /D _mid ) are respectively 1.2 or more, the flow of exhaust gas becomes uniform in the stretching direction, and the exhaust gas purification performance and soot collection performance are improved. improve more. In addition, when the ratio (D _in /D _mid ) and the ratio (D _out /D _mid ) are each 3 or less, the inflow of exhaust gas into and around the third region 21c, which is the central region of the partition wall, is inhibited. Excessive addition can rather suppress deterioration of the exhaust gas purification performance and the soot collection performance.

The pore diameter of the first region 21a is preferably 12-16 μm, more preferably 12.5-15 μm, and even more preferably 13-14.5 μm. Also, the pore diameter of the third region 21c is preferably 4 to 13 μm, more preferably 5 to 11.5 μm, still more preferably 7 to 10.5 μm. Furthermore, the pore diameter of the second region 21b is preferably 12-16 μm, more preferably 12.5-15 μm, and still more preferably 13-14.5 μm. When each pore diameter is within the above range, the exhaust gas purification performance and the soot collection performance tend to be further improved.

From the above viewpoint, the difference between the pore diameter D _in of the first region 21a or the pore diameter D _{out of} the second region 21b and the pore diameter D _mid of the third region 21c is preferably 2.5 to 10 μm. , more preferably 3 to 8 μm, still more preferably 3 to 6 μm.

Samples for measuring the pore diameter D _in of the first region 21a, the pore diameter D _out of the second region 21b, and the pore diameter D _mid of the third region 21c are the first region 21a, the second region 21b, and the Samples are taken from the middle portions of the three regions 21 c in the extending direction of the partition wall 13 . For example, when the total length L _W in the extending direction of the wall-flow type substrate 10 (the total length in the extending direction of the partition wall 13) is 100%, the first region 21a and the second region 21b are ends on the exhaust gas introduction side and the exhaust side. The third region 21c is formed between the first region 21a and the second region 21b, that is, the central 20% region in the extending direction of the wall flow type substrate 10. Assume an exhaust gas purifying catalyst such as that formed in In the case of such an exhaust gas purifying catalyst, a sample for measuring the pore diameter D _in of the first region 21a and the pore diameter D _out of the second region 21b is The sample for measuring the pore diameter _Dmid of the third region 21c, which is taken from each portion positioned at 20% (=40%/2), is 50% (=40%+20%) from the end portion 11a on the exhaust gas introduction side. %/2).

The ranges in which the first region 21a, the second region 21b, and the third region 21c are formed are not particularly limited. For example, the first region 21a and the second region 21b are formed with approximately the same coating length from the ends 11a and 12a on the exhaust gas introduction side and the discharge side, respectively, and the third region 21c is formed in the center in the extending direction of the partition wall 13. The coating length of the first region 21a is shorter than the coating length of the second region 21b, and the third region 21c is located closer to the end 11a on the exhaust gas introduction side than the center of the partition wall 13. In such a mode, the coating length of the second region 21b is shorter than the coating length of the first region 21a, and the third region 21c is located closer to the end 12a on the exhaust gas discharge side than the center of the partition wall 13. It may be in any form.

Specifically, in the extending direction (longitudinal direction) of the partition wall 13, the range L ₁ (coating length) in which the first region 21a is formed is the total length Lw ( It is preferably 20 to 80%, more preferably 25 to 75%, and still more preferably 30 to 70% when the total length in the extending direction of the partition walls 13) is taken as 100%. again. The range L ₂ (coating length) in which the second region 21b is formed is preferably 20% of the total length L _W in the extending direction of the wall-flow type substrate 10 (the total length in the extending direction of the partition walls 13). ~80%, more preferably 25-75%, still more preferably 30-70%. Furthermore, the range L ₃ (coating length) in which the third region 21c is formed is preferably It is 1 to 35%, more preferably 3 to 25%, still more preferably 5 to 15%.

The catalyst layer 21 is formed from the cell wall surface on the inlet side cell 11 side to the cell wall surface on the discharge side cell 12 side in the thickness direction of the partition wall 13 . , the inlet-side cell 11 side or the outlet-side cell 12 side. As a result, the soot collection performance and the exhaust gas purification performance can be further improved without increasing the pressure loss. In addition, "unevenly distributed" means that, when the wall thickness of the partition wall 13 is Tw, the catalyst layer 21 is formed in the depth region T1 from the cell wall surface on the inlet side cell 11 side or the discharge side cell 12 side to Tw*5/10. The presence of 60% or more of the total mass.

(pore volume)
From the same point of view as the pore diameter, the pore volume V _mid with a pore diameter of 1 μm or more calculated from the pore distribution of the third region 21c is replaced by the pore volume V mid of a pore diameter of 1 μm or more calculated from the pore distribution of the first region 21a. The pore volume V _in and the pore volume V _out with a pore diameter of 1 μm or more calculated from the pore distribution of the second region 21b are each made larger by a predetermined value or more.

Specifically, the ratio (V _in /V _mid ) is preferably 1.3 or more, more preferably 1.35 or more, and still more preferably 1.37 or more. The upper limit of the ratio (V _in /V _mid ) is not particularly limited, but is preferably 2 or less, more preferably 1.8 or less, and still more preferably 1.6 or less. Also, the ratio (V _out /V _mid ) is preferably 1.3 or more, more preferably 1.35 or more, and still more preferably 1.37 or more. The upper limit of the ratio (V _out /V _mid ) is not particularly limited, but is preferably 2 or less, more preferably 1.8 or less, and even more preferably 1.6 or less. When the ratio (V _in /V _mid ) and ratio (V _out /V _mid ) are respectively 1.3 or more, the flow of exhaust gas becomes uniform in the stretching direction, and the exhaust gas purification performance and soot collection performance are improved. improve more. In addition, when the ratio (V _in /V _mid ) and the ratio (V _out /V _mid ) are each 2 or less, the inflow of exhaust gas into the third region 21c is excessively inhibited, so that the exhaust gas purification performance is rather reduced. And it is possible to suppress the deterioration of the soot collection performance.

The pore volume of 1 μm or more in the first region 21a is preferably 0.30 to 0.60 cc/g, more preferably 0.35 to 0.55 cc/g, still more preferably 0.40 to 0.40 cc/g. .50 cc/g. Also, the pore diameter of the third region 21c is preferably 0.20 to 0.45 cc/g, more preferably 0.25 to 0.40 cc/g, still more preferably 0.30 to 0.35 cc. /g. Furthermore, the pore diameter of the second region 21b is preferably 0.30 to 0.60 cc/g, more preferably 0.35 to 0.55 cc/g, still more preferably 0.40 to 0.50 cc. /g. When the pore volume of 1 μm or more is within the above range, the soot trapping performance and the exhaust gas purification performance tend to be further improved.

The pore diameters and pore volumes of the first region 21a, the third region 21c, and the second region 21b mean values calculated by a mercury intrusion method under the conditions described in the examples below.

The method for adjusting the pore diameter and pore volume of the first region 21a, the third region 21c, and the second region 21b to a predetermined range is not particularly limited, but for example, a catalyst layer formed in the third region 21c It is conceivable to increase the thickness of the

(Base material)
The wall-flow type substrate 10 includes 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. It has a wall-flow structure separated by a thin partition 13 .

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

The inlet-side cells 11 and the outlet-side cells 12 are regularly arranged along the axial direction of the cylindrical shape, and adjacent cells alternately have one open end and the other open end in the extending direction. Sealed. The inlet-side cell 11 and the outlet-side cell 12 can be set to an appropriate shape and size in consideration of the flow rate and components of the exhaust gas to be supplied. For example, the mouth shape of the inlet cell 11 and the outlet cell 12 can be triangular; rectangles such as squares, parallelograms, rectangles, and trapezoids; other polygons such as hexagons and octagons; and circles. . Further, it may have a High Ash Capacity (HAC) structure in which the cross-sectional area of the inlet-side cell 11 and the cross-sectional area of the discharge-side cell 12 are different.

The numbers of the inlet-side cells 11 and the outlet-side cells 12 can be appropriately set so as to promote generation of turbulence in the exhaust gas and to suppress clogging due to fine particles contained in the exhaust gas. not required, but preferably between 200 cpsi and 400 cpsi. The thickness of the partition walls 13 (the length in the thickness direction orthogonal to the stretching direction) is preferably 6 to 12 mil, more preferably 6 to 10 mil.

The partition wall 13 that partitions adjacent cells is not particularly limited as long as it has a porous structure through which exhaust gas can pass. can be appropriately adjusted from the viewpoint of improvement of For example, when the catalyst layer 21 is formed on the surface of the pores in the partition walls 13 using a catalyst slurry to be described later, the pore diameter (for example, the mode diameter (the pore diameter with the largest appearance ratio in the frequency distribution of the pore diameters (maximum of the distribution value))) and the pore volume are large, the pores are less likely to be clogged by the catalyst layer 21, and the resulting exhaust gas purification catalyst tends to be one in which the pressure loss is less likely to increase. The collection ability tends to decrease, and the mechanical strength of the substrate also tends 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 collect particulate matter improves, and the mechanical strength of the substrate tends to improve as well.

From this point of view, the pore diameter (mode diameter) of the partition walls 13 of the wall flow type substrate 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. Moreover, the porosity of the partition walls 13 is preferably 20 to 80%, more preferably 40 to 70%, and even more preferably 60 to 70%. When the porosity is equal to or higher than the lower limit, an increase in pressure loss tends to be further suppressed. Further, when the porosity is equal to or lower than the upper limit, the strength of the substrate tends to be further improved. The pore diameter (mode diameter) and porosity mean values calculated by a mercury intrusion method under the conditions described in Examples below.

(catalyst layer)
Next, the catalyst layer 21 formed in the pores of the partition walls 13 will be described. The catalyst layer 21 can be of various forms that are conventionally used for this type of application. For example, as a mode of the catalyst layer 21, there is one formed by calcining a catalyst slurry containing catalyst metal particles and carrier particles. The catalyst layer 21 formed by firing the catalyst slurry containing various particles in this manner has a microporous structure in which the particles are bound together by firing.

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

The combination of such catalyst metals is not particularly limited, and includes a combination of two or more catalyst metals with excellent oxidation activity, a combination of two or more catalyst metals with excellent reduction activity, and a combination of two or more catalyst metals with excellent oxidation activity and reduction. A combination of catalytic metals with excellent activity can be mentioned. Among these, as one aspect of the synergistic effect, a combination of a catalytic metal excellent in oxidation activity and a catalytic metal excellent in reduction activity is preferred, and a combination containing at least Rh, Pd and Rh, or Pt and Rh is more preferred. Such a combination tends to further improve exhaust gas purification performance.

The fact that the catalyst layer 21 contains a catalyst metal can be confirmed by using a scanning electron microscope or the like on 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 conventionally used in this type of exhaust gas purifying catalyst can be considered. For example, oxygen storage materials (OSC materials) such as cerium oxide (ceria: CeO ₂ ), 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 ), titanium oxide (titania: TiO ₂ ), and composite oxides containing these oxides as main components. 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 are added. These carrier particles may be used singly or in combination of two or more. Here, the oxygen storage material (OSC material) stores 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 excess fuel side releases the oxygen that has been occluded.

The formation range of the third region is preferably 2 to 20%, more preferably 3 to 15%, and still more preferably 5 to 10%, with respect to 100% of the total length of the partition walls in the extending direction. As a result, the exhaust gas spreads evenly over the first region 21a and the second region 21b, and the exhaust gas purification performance and the soot collection performance tend to be further improved.

Moreover, when the catalyst layer has a plurality of regions formed of different catalyst metals along the stretching direction, the first regions 21a preferably contain Pd and/or Rh, more preferably Pd. On the other hand, the second region 21b preferably contains Pd and/or Rh, more preferably Rh. Since the first region 21a and the second region 21b contain the catalyst metal, the exhaust gas purification performance tends to be further improved.

In addition, the coating amount of the catalyst layer of the exhaust gas purification catalyst 100 is from the viewpoint that it is an exhaust gas purification catalyst that purifies exhaust gas emitted from an internal combustion engine, particularly a gasoline engine, and is particularly used for collecting particulate matter. (Coating amount of catalyst layer excluding catalyst metal mass per liter of wall-flow type substrate) is preferably 20 to 110 g/L, more preferably 40 to 90 g/L, and still more preferably 50 to 70 g. /L. In addition, the porosity of the partition walls 13 of the exhaust gas purifying catalyst 100 with the catalyst layer 21 formed thereon by the mercury injection method is preferably 20 to 80%, more preferably 30 to 70%, and preferably 35 to 35%. 60%.

[Method for producing exhaust gas purifying catalyst]
The manufacturing method of the present embodiment is a manufacturing method of an exhaust gas purifying catalyst 100 for purifying exhaust gas emitted from an internal combustion engine. a step S0 of preparing a wall-flow type substrate 10 in which a discharge-side cell 12 adjacent to the exhaust gas discharge side and having an open end 12a on the exhaust gas discharge side is defined by a porous partition wall 13; a catalyst layer forming step S1 for forming a catalyst layer 21 by applying a catalyst slurry to at least a part of the pore surfaces in 13, and in the catalyst layer forming step S1, the end on the exhaust gas introduction side A first region 21a formed along the extending direction of the partition wall 13 from the portion 11a, a second region 21b formed along the extending direction of the partition wall 13 from the end portion 12a on the exhaust gas discharge side, and the first region 21a. A third region 21c overlapping with _the second region 21b, and a pore diameter D in calculated from the pore distribution of the first region 21a relative to the pore diameter D _mid calculated from the pore distribution of the third region 21c The ratio (D _in /D _mid ) is 1.2 or more, and the ratio (D _out /D _mid ) of the pore diameter D _out calculated from the pore distribution of the second region 21b to the pore diameter D _mid is It is characterized by manufacturing an exhaust gas purification catalyst 100 having a catalyst layer 21 of 1.2 or more.

Each step will be described below. In this specification, the wall-flow type substrate before forming the catalyst layer 21 is referred to as "substrate 10", and the wall-flow type substrate after forming the catalyst layer 21 is referred to as "exhaust gas purification catalyst 100. ”.

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

<Catalyst layer forming step>
In this catalyst layer forming step S1, the catalyst layer 21 is formed by applying a catalyst slurry to the pore surfaces of the partition walls 13, drying it, and firing it. The method of applying the catalyst slurry is not particularly limited. A method of impregnating 11a and the end portion 12a on the exhaust gas discharge side with the catalyst slurry separately may be mentioned. More specifically, an impregnation step S1a in which the end portion 11a on the exhaust gas introduction side is impregnated with the catalyst slurry, and a gas is introduced into the substrate 10 from the end portion opposite to the end portion impregnated with the catalyst slurry. , a method having a discharging step S1b for discharging excess catalyst slurry impregnated in the base material 10 can be mentioned.

A method of impregnating the catalyst slurry in the impregnation step S1a is not particularly limited, but an example thereof includes a method of immersing the end portion of the substrate 10 in the catalyst slurry. In this method, if necessary, the catalyst slurry may be pulled up by discharging (sucking) the gas from the opposite end. The end portion to be impregnated with the catalyst slurry may be either the end portion 11a on the exhaust gas introduction side or the end portion 12a on the exhaust gas discharge side.

Further, in the discharge step S1b, the catalyst slurry is sucked up to a predetermined position from the introduction side of the base material 10, and then gas is introduced into the base material 10 from the end opposite to the end impregnated with the catalyst slurry. The surplus is discharged from the introduction side of the base material 10 by allowing the base material 10 to pass therethrough. In this process, the catalyst slurry passes through the pores of the partition walls 13, so that the catalyst slurry can be coated inside the pores, and the partition walls are coated with the catalyst slurry up to the position where the catalyst slurry is sucked up. Using such a method, for example, by coating the catalyst slurry overlapping the third region 21c, the pore diameter of the third region 21c is made smaller than the pore diameters of the first region 21a and the second region 21b. be able to.

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

In the baking step S1d, the catalyst slurry is baked to form the catalyst layer 21 . The firing conditions in the firing step S1d are not particularly limited as long as the catalyst layer 21 can be formed from the catalyst slurry. For example, the firing temperature is not particularly limited, but is preferably 400 to 650°C, more preferably 450 to 600°C, still 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)
A catalyst slurry for forming the catalyst layer 21 will be described. The catalyst slurry contains 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 calcination process described later. The catalyst particles are not particularly limited, and can be appropriately selected and used from known catalyst particles. From the viewpoint of coating properties into the pores of the partition walls 13, the solid content of the catalyst slurry is preferably 1 to 50% by mass, more preferably 15 to 40% by mass, and still more preferably 20 to 50% by mass. 35% by mass. Such a solid content ratio tends to make it easier to coat the catalyst slurry on the introduction side cell 11 side in the partition wall 13 .

The catalyst metal contained in the catalyst slurry is not particularly limited, and metal species capable of functioning as various oxidation catalysts and reduction catalysts can be used. Examples include platinum group metals such as platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), iridium (Ir) and osmium (Os). Among these, palladium (Pd) and platinum (Pt) are preferred from the viewpoint of oxidation activity, and rhodium (Rh) is preferred from the viewpoint of reduction activity.

Inorganic compounds conventionally used in this type of exhaust gas purifying catalyst can be considered as the carrier particles that support the catalytic metal particles. For example, oxygen storage materials (OSC materials) such as cerium oxide (ceria: CeO ₂ ), 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 ), titanium oxide (titania: TiO ₂ ), and composite oxides containing these oxides as main components. 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 are added. These carrier particles may be used singly or in combination of two or more. Here, the oxygen storage material (OSC material) stores 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 excess fuel side releases the oxygen that has been occluded. From the viewpoint of exhaust gas purification performance, the specific surface area of the carrier particles contained in the catalyst slurry is preferably 10 to 500 m ² /g, more preferably 30 to 200 m ² /g.

[Use]
An internal combustion engine (engine) is supplied with a mixture containing oxygen and fuel gas, and this mixture is combusted 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 purifying device equipped with an exhaust gas purifying catalyst, and the exhaust gas purifying catalyst removes harmful components contained in the exhaust gas (e.g., carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx )) are purified, and particulate matter (PM) contained in the exhaust gas is collected and removed. In particular, the exhaust gas purifying catalyst 100 of the present embodiment is preferably used for a gasoline particulate filter (GPF) capable of collecting and removing particulate matter contained in exhaust gas from a gasoline engine.

The features of the present invention will be described in more detail below with reference to test examples, examples and comparative examples, but the present invention is not limited to these. That is, materials, usage amounts, ratios, processing details, processing procedures, etc. shown in the following examples can be changed as appropriate without departing from the gist of the present invention. In addition, various production conditions and values of evaluation results in the following examples have the meaning of preferable upper limit values or preferable lower limit values in the embodiments of the present invention, and the preferable range is the above-described upper limit value or lower limit value and values in the following examples or values between examples.

(Example 1)
Alumina powder was impregnated with an aqueous solution of rhodium nitrate and then calcined at 500° C. for 1 hour to obtain a Rh-supported powder. 0.5 kg of the obtained Rh-supported powder, 2 kg of ceria-zirconia composite oxide powder, 195 g of a 46% lanthanum nitrate aqueous solution, and ion-exchanged water were mixed, and the obtained mixture was put into a ball mill to obtain catalyst powder. Milling was carried out until a predetermined particle size distribution was obtained to obtain a catalyst slurry. The resulting catalyst slurry was mixed with 183 g of barium hydroxide octahydrate and 60% nitric acid to obtain a catalyst slurry.

Also, the alumina powder was impregnated with an aqueous palladium nitrate solution and then calcined at 500° C. for 1 hour to obtain a Pd-supported powder. 0.5 kg of the obtained Pd-supported powder, 2 kg of ceria-zirconia composite oxide powder, 195 g of a 46% lanthanum nitrate aqueous solution, and ion-exchanged water were mixed, and the resulting mixture was put into a ball mill to obtain catalyst powder. Milling was carried out until a predetermined particle size distribution was obtained to obtain a catalyst slurry. The resulting catalyst slurry was mixed with 183 g of barium hydroxide octahydrate and 60% nitric acid to obtain a catalyst slurry.

Next, a cordierite wall-flow honeycomb substrate (number of cells/mil thickness: 300 cpsi/10 mil, diameter: 118.4 mm, total length: 127 mm, pore diameter (mode diameter): 16.4 μm, porosity: 65%) prepared. The end of the substrate on the exhaust gas introduction side is immersed in the catalyst slurry containing Rh, and vacuum suction is applied from the opposite end to impregnate and hold the catalyst slurry to the center of the substrate, and the pore surfaces in the partition walls. was coated with the catalyst slurry. After that, gas was allowed to flow into the substrate from the end on the exhaust gas discharge side, and the excess catalyst slurry was blown off from the end on the exhaust gas introduction side of the substrate.

In addition, the end of the substrate on the exhaust gas discharge side is immersed in the catalyst slurry containing Pd, and vacuum suction is applied from the opposite end to impregnate and hold the catalyst slurry to the center of the substrate, thereby removing the pores in the partition walls. A catalyst slurry was applied to the surface. Thereafter, gas was allowed to flow into the substrate from the end on the exhaust gas introduction side to blow off excess catalyst slurry from the end on the exhaust gas discharge side of the substrate. The coating region of the catalyst slurry containing Pd and the coating region of the catalyst slurry containing Rh overlapped each other by 2% with respect to the total length in the stretching direction.

After that, the base material coated with the catalyst slurry was dried at 150° C. and calcined at 550° C. in an air atmosphere to produce an exhaust gas purifying catalyst. The coating amount of the catalyst layer after firing was 57.8 g (excluding the weight of the platinum group metal) per 1 L of the substrate. In addition, the catalyst layer of the catalyst slurry containing Rh and the catalyst slurry containing Pd was formed from the cell wall surface on the inlet side cell to the cell wall surface on the discharge side in the thickness direction of the partition walls.

(Example 2)
Exhaust gas purifying catalyst produced in Example 1, except that the coating region of the catalyst slurry containing Pd and the coating region of the catalyst slurry containing Rh were coated so as to overlap by 7% with respect to the total length in the stretching direction. A similar catalyst was prepared.

(Example 3)
The exhaust gas purifying catalyst produced in Example 1, except that the coating region of the catalyst slurry containing Pd and the coating region of the catalyst slurry containing Rh overlapped by 22% with respect to the total length in the stretching direction. A similar catalyst was prepared.

(Comparative example 1)
0.5 kg of the Rh-supported powder, 0.5 kg of the Pd-supported powder, 2 kg of the ceria-zirconia composite oxide powder, 195 g of a 46% lanthanum nitrate aqueous solution, and ion-exchanged water were mixed, and the resulting mixture was placed in a ball mill. It was charged and milled until the catalyst powder had a predetermined particle size distribution to obtain a catalyst slurry. The resulting catalyst slurry was mixed with 183 g of barium hydroxide octahydrate and 60% nitric acid to obtain a catalyst slurry.

In the method of applying the catalyst slurry to the substrate, the end of the substrate on the exhaust gas introduction side is immersed in the catalyst slurry prepared as described above, and vacuum suction is performed from the opposite end to remove the substrate end. The part was impregnated with the catalyst slurry. Gas is allowed to flow into the substrate from the end on the exhaust gas introduction side to coat the catalyst slurry on the pore surfaces in the partition walls, and excess catalyst slurry is blown off from the end on the exhaust gas discharge side of the substrate. An exhaust gas purifying catalyst was produced in the same manner as in Example 1 , except that the inflow of gas was stopped. The coating amount of the catalyst layer after firing was 58.8 g (excluding the weight of the platinum group metal) per 1 L of substrate.

(Comparative example 2)
Instead of the catalyst slurry containing Rh and the catalyst slurry containing Pd, the catalyst slurry prepared in Comparative Example 1 was used, and the coating region of the catalyst slurry was immersed from the end on the exhaust gas introduction side and from the end on the exhaust gas discharge side. An exhaust gas purifying catalyst was produced in the same manner as in Example 1, except that the coated region of the immersed catalyst slurry was not overlapped. The coating amount of the catalyst layer after firing was 58.8 g (excluding the weight of the platinum group metal) per 1 L of substrate.

[Calculation of pore diameter and pore volume]
The pore diameter (mode A sample (1 cm ³ ) was taken for measurement of pore diameter) and pore volume. In addition, for the base material before the catalyst slurry was applied, the pore diameter (mode diameter) and pore volume were measured from the same position sampled in the exhaust gas purifying catalysts produced in Examples and Comparative Examples. A sample (1 cm ³ ) was taken from each. At this time, 10 or more samples for measurement were collected from each region, with a total of 1 cm ³ . After drying the measurement sample, the pore distribution was measured by the mercury intrusion method using a mercury porosimeter (manufactured by Thermo Fisher Scientific, trade names: PASCAL140 and PASCAL440). At this time, PASCAL140 was used to measure the low pressure range (0 to 400 Kpa), and PASCAL440 was used to measure the high pressure range (0.1 Mpa to 400 Mpa). From the obtained pore distribution, the pore diameter (mode diameter) was obtained, and the pore volume of pores having a pore diameter of 1 μm or more was calculated.

Then, porosity was calculated by the following formula. Some of these results are shown in Table 3 below.
Porosity (%) of exhaust gas purifying catalyst = pore volume (cc/g) of partition walls on which catalyst layer is formed ÷ pore volume (cc/g) of substrate × porosity (%) of substrate
Base material porosity (%) = 65%

[Vehicle NOx purification performance evaluation]
After storing a commercially available flow-through type three-way catalyst in the converter, the exhaust gas purifying catalysts prepared in Examples and Comparative Examples were stored in the converter after the stored three-way catalyst, and the converter was placed downstream of the exhaust port of the gasoline engine. I put it on. After that, the cycle of steady state, deceleration and acceleration was repeated for 10 hours. The temperature was set to 950° C. in a steady state, and heat durability treatment was performed.

After that, the commercially available flow-through type three-way catalyst after endurance treatment and the exhaust gas purifying catalyst produced in the examples and comparative examples are stored in the converter, and a gasoline engine equipped with a European specification 1.5L direct injection turbo engine is installed. Exhaust gas purification performance of the catalyst was investigated in WLTC mode using a car.

[Measurement of soot collection performance]
The exhaust gas purifying catalysts prepared in Examples and Comparative Examples are attached to a vehicle equipped with a 1.5L direct-injection turbo engine, and WLTC mode driving is performed using a solid particle number measuring device (trade name: MEXA-2100 SPCS, manufactured by Horiba, Ltd.). The amount of soot discharged (PN _test ) was measured. The soot collection rate was calculated by the following formula as a rate of decrease from the amount of soot (PN _blank ) measured when the above test was conducted without mounting an exhaust gas purification catalyst. The results are shown in FIG.
Soot collection rate (%) = (PN _blank - PN _test )/PN _blank x 100 (%)

As described above, in the examples, by adjusting the pore diameter, an improvement in exhaust gas purification performance was achieved while maintaining a high soot collection rate. is relatively uniform, the soot trapping efficiency is low, and the exhaust gas purification performance is also low.

This application is based on a Japanese patent application (Japanese Patent Application No. 2018-222097) filed with the Japan Patent Office on November 28, 2018, the contents of which are incorporated herein by reference.

INDUSTRIAL APPLICABILITY The exhaust gas purifying catalyst of the present invention can be widely and effectively used as an exhaust gas purifying catalyst for removing particulate matter contained in the exhaust gas of a gasoline engine. In addition, the exhaust gas purification catalyst of the present invention can be effectively used as an exhaust gas purification catalyst for removing particulate matter contained in exhaust gas not only from gasoline engines but also from jet engines, boilers, gas turbines, and the like.

REFERENCE SIGNS LIST 10 wall-flow type substrate 11 introduction-side cell 11a end on exhaust gas introduction side 12 discharge-side cell 12a end on exhaust gas discharge side 13 partition wall 21 Catalyst layer 21a First region 21b Second region 21c Third region 100 Exhaust gas purification catalyst

Claims (11)

An exhaust gas purification catalyst for purifying exhaust gas emitted from an internal combustion engine,
a wall-flow type substrate in which 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 by porous partition walls; ,
a catalyst layer formed in the partition wall;
The catalyst layer has a first region formed along the extending direction of the partition wall from the exhaust gas introduction side end, and a second region formed along the extending direction of the partition wall from the exhaust gas discharge side end. and a third region where the first region and the second region overlap,
the first region contains Pd and/or Rh,
the second region contains Pd and/or Rh,
The _ratio of the pore diameter D in calculated from the pore distribution of the first region formed within the partition wall to the pore diameter D _mid calculated from the pore distribution of the third region formed within the partition wall ( D _in /D _mid ) is 1.2 or more,
A ratio (D _out /D _mid ) of the pore diameter D _out calculated from the pore distribution of the second region formed in the partition wall to the pore diameter D _mid is 1.2 or more.
Exhaust gas purification catalyst. The fineness calculated from the pore distribution of the first region formed in the partition wall with respect to the pore volume V _mid having a pore diameter of 1 μm or more calculated from the pore distribution of the third region formed in the partition wall The ratio of the pore volume V _in with a pore diameter of 1 μm or more (V _in /V _mid ) is 1.3 or more,
The ratio (V _out /V _mid ) of the pore volume V _out having a pore diameter of 1 μm or more calculated from the pore distribution of the second region formed in the partition wall to the pore volume V _mid is 1.3. is more than
The exhaust gas purifying catalyst according to claim 1. The difference between the pore diameter D _in or the pore diameter D _out and the pore diameter D _mid is 2.5 to 10 μm, respectively.
The exhaust gas purifying catalyst according to claim 1 or 2. wherein the first region contains Pd;
The exhaust gas purifying catalyst according to any one of claims 1 to 3. wherein the second region contains Rh;
The exhaust gas purifying catalyst according to claim 4. wherein the first region contains Rh;
The exhaust gas purifying catalyst according to any one of claims 1 to 3. wherein the second region contains Pd;
The exhaust gas purifying catalyst according to claim 6. The catalyst layer is formed from the cell wall surface on the inlet 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 purifying catalyst according to any one of claims 1 to 5. The formation range of the third region is 2 to 20% with respect to 100% of the total length in the extending direction of the partition wall.
The exhaust gas purifying catalyst according to any one of claims 1 to 8. wherein the internal combustion engine is a gasoline engine;
The exhaust gas purification catalyst according to any one of claims 1 to 9. A method for producing an exhaust gas purifying catalyst for purifying exhaust gas emitted from an internal combustion engine, comprising:
A wall-flow type substrate in which 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 by porous partition walls. the process of preparing,
a catalyst layer forming step of forming a catalyst layer by applying a catalyst slurry to at least a portion of the pore surfaces in the partition walls of the wall-flow type substrate;
In the catalyst layer forming step,
A first region formed along the extending direction of the partition wall from the end on the exhaust gas introduction side, a second region formed along the extending direction of the partition wall from the end on the exhaust gas discharge side, and the second region a third region where the first region and the second region overlap, the first region containing Pd and/or Rh, the second region containing Pd and/or Rh, and formed within the partition wall The ratio of the pore diameter D in calculated from the pore distribution of the first region formed in the partition wall to the pore diameter D _mid calculated from the pore distribution of the third region (D _in / _{D mid} ) is 1.2 or more, and the ratio (D _out /D _mid ) of the pore diameter D _out calculated from the pore distribution of the second region formed in the partition wall to the pore diameter D _mid is 1. Producing the exhaust gas purification catalyst having the catalyst layer of 2 or more,
A method for producing an exhaust gas purification catalyst.

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