JP2018122270A - Exhaust gas purifier and exhaust gas purifying catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust gas purifier capable of suitably reducing the emission of harmful components.SOLUTION: An exhaust gas purifier disclosed herein includes a plurality of exhaust gas purifying catalysts. In such an exhaust gas purifier, at least one of the exhaust gas purifying catalysts arranged at the second and subsequent positions from the upstream side among the plurality of exhaust gas purifying catalysts comprises a base material 1 having a wall-flow structure, an inlet-side catalyst layer 6a formed on the upstream side within a partition wall 4 of the base material 1, and an outlet-side catalyst layer 6b formed on the downstream side within the partition wall 4 of the base material 1, and is a catalyst for high load operation configured so that the amount of a noble metal catalyst present in the outlet-side catalyst layer 6b is more than the amount of a noble metal catalyst present in the inlet-side catalyst layer 6a.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an exhaust gas purification device for purifying exhaust gas discharged from an internal combustion engine and an exhaust gas purification catalyst used in the exhaust gas purification device.

Exhaust gas discharged from internal combustion engines such as automobile engines contains harmful components such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). Conventionally, in order to prevent these harmful components from being discharged to the outside (so-called harmful component emissions), an exhaust gas purification device is attached to the internal combustion engine described above.
Generally, the above-described exhaust gas purification device includes a plurality of exhaust gas purification catalysts, and purifies harmful components in the exhaust gas by passing the exhaust gas through the exhaust gas purification catalyst. Each of the plurality of exhaust gas purifying catalysts is disposed in an exhaust pipe of an internal combustion engine, and includes a honeycomb structure base material and a catalyst layer formed inside the base material. The catalyst layer of the exhaust gas purifying catalyst contains a noble metal catalyst made of platinum group elements (PGM) such as Pt, Pd, and Rh, and harmful components are brought into contact with the noble metal catalyst by contacting the exhaust gas. Purified.

As an example of the above-described exhaust gas purification catalyst, a wall flow type exhaust gas purification catalyst may be mentioned. This wall flow type exhaust gas purifying catalyst is composed of an inlet cell (an inlet channel) having only an end on the exhaust gas inflow side and an outlet cell (an outlet channel) having only an end on the exhaust gas outlet side. ) And a porous partition wall (rib wall) partitioning these cells, and a catalyst layer is formed inside the porous partition wall.
In such a wall flow type exhaust gas purifying catalyst, the exhaust gas that has flowed into the inlet cell passes through the porous partition wall, and then is discharged outside the catalyst through the outlet cell. At this time, harmful components are purified by the exhaust gas coming into contact with the catalyst layer formed inside the partition walls. An example of an exhaust gas purifying catalyst having such a structure is described in Patent Document 1.

JP-A-2006-150305

By the way, in recent years, exhaust gas regulations for vehicles and the like tend to be further strengthened, and in order to comply with such regulations, there is a demand for an exhaust gas purification apparatus that can more appropriately reduce emission of harmful components.
This invention is made | formed in view of this request, and it aims at providing the exhaust gas purification apparatus which can reduce the emission of a harmful component more suitably than before.

  In order to achieve the above object, the present invention provides an exhaust gas purification apparatus having the following configuration.

The exhaust gas purification device disclosed herein includes a plurality of exhaust gas purification catalysts disposed in an exhaust pipe of an internal combustion engine, and exhaust gas discharged from the internal combustion engine is passed through the plurality of exhaust gas purification catalysts. To purify.
In the exhaust gas purification apparatus disclosed herein, at least one of the plurality of exhaust gas purification catalysts described above disposed at the second and subsequent positions from the upstream side in the exhaust gas flow direction is an exhaust gas inflow side. An inlet cell having an open end only, an outlet cell adjacent to the inlet cell and having only an end on the exhaust gas outflow side, and a porous partition wall that separates the inlet cell and the outlet cell. A wall flow structure base material having a predetermined thickness from the surface of the partition wall in contact with the inlet side cell to the inside of the partition wall and having a predetermined length along the extending direction of the partition wall from the vicinity of the end on the exhaust gas inflow side. An inlet catalyst layer formed by the inlet catalyst layer containing a noble metal catalyst that purifies harmful components contained in the exhaust gas, and a predetermined thickness from the surface of the partition wall in contact with the outlet cell to the inside of the partition wall. Formed and exhaust gas An exit side catalyst layer that is formed with a predetermined length along the extending direction of the partition wall from the vicinity of the exit side end portion and includes an exit side catalyst layer containing a noble metal catalyst, and is present in the exit side catalyst layer The high-load operation catalyst is configured such that the precious metal catalyst is larger than the precious metal catalyst present in the inlet catalyst layer.

As a result of various studies and experiments in order to more suitably reduce harmful component emissions, the present inventor has come up with an exhaust gas purification apparatus having the above-described configuration.
In the exhaust gas purification apparatus disclosed herein, at least one of the exhaust gas purification catalysts arranged second and later from the upstream side in the exhaust gas flow direction is such that the noble metal catalyst in the exit side catalyst layer is more than the noble metal catalyst in the entrance side catalyst layer. It is comprised so that it may become the catalyst for high load operation | movement comprised so that it may increase.
Hereinafter, the background of the inventor's creation of the exhaust gas purifying apparatus having the above-described configuration will be described.

In general, it is considered that emission of harmful components is likely to occur in any one of a warm-up operation immediately after the start of operation of the internal combustion engine and a high-load operation when the internal combustion engine is operated at a high speed.
Of these operating conditions, emissions during warm-up operation account for about 80% of the total emissions, and various measures have been devised, while emissions during high-load operation take sufficient measures. The current situation is that it cannot be said.
The present inventor believes that if the emission in such a high load operation can be suitably reduced, the total amount of harmful components can be greatly reduced, and a technique for suitably reducing the emission in such a high load operation. Was examined.

In creating such a technique, the present inventor first paid attention to the relationship between the flow rate of exhaust gas in each operation state and the distribution state of the noble metal catalyst in the exhaust gas purification catalyst.
Specifically, in the warm-up operation, exhaust gas having a slower flow rate than that in other operation states is supplied. Therefore, as shown by an arrow A in FIG. There is a tendency to pass upstream. In order to appropriately purify the exhaust gas in the warm-up operation that easily flows in this way, conventionally, it is common to form a catalyst layer so that many noble metal catalysts exist in the partition 4 on the upstream side in the exhaust gas flow direction. It was the target.
On the other hand, in high load operation, the exhaust gas flow rate is significantly faster than in other operating conditions including warm-up operation, and as shown by arrow B in FIG. There is a tendency that the exhaust gas that passes through the partition wall 4 in the vicinity of the exhaust gas outflow side end after colliding with the side end portion (sealing member 3a in the figure) increases.
The present inventor believes that a general exhaust gas purifying catalyst in which many precious metal catalysts exist on the upstream side cannot appropriately purify exhaust gas in a high load operation that easily flows as indicated by an arrow B in the figure. In view of this, we considered the creation of a new exhaust gas purification catalyst (hereinafter also referred to as a “high load operation catalyst”) that purifies the exhaust gas from such a high load operation.

  In creating such a high-load operation catalyst, various experiments and studies were repeated, and the inventors came up with a configuration in which the noble metal catalyst in the outgoing catalyst layer was larger than the noble metal catalyst in the incoming catalyst layer. The high-load operation catalyst having such a configuration has a flow rate as indicated by an arrow B in FIG. 3 because many noble metal catalysts exist in the outlet catalyst layer formed inside the partition wall on the downstream side. Fast exhaust gas is suitably purified, and emissions during high-load operation can be suitably reduced.

However, as described above, about 80% of the total emission amount of harmful components occurs in the warm-up operation in which exhaust gas having a slow flow rate is generated, and therefore, the upstream side of all of the plurality of exhaust gas purification catalysts constituting the exhaust gas purification device. When a high-load operation catalyst with a small amount of noble metal catalyst is used, it is difficult to appropriately reduce the emission during the warm-up operation, and the total amount of harmful components may increase.
For this reason, the present inventor has provided an exhaust gas purification apparatus that includes both a high-load operation catalyst and an exhaust gas purification catalyst that can appropriately purify exhaust gas during warm-up operation (hereinafter also referred to as “warm-up operation catalyst”). Thought to build.

As a result of further investigation on the arrangement position of the catalyst for high load operation in such an exhaust gas purification device, if the catalyst for high load operation is arranged on the most upstream side in the gas flow direction, emission during warm-up operation is appropriately reduced. Based on this knowledge, the inventors have come up with the idea that the catalyst for high-load operation is arranged second or later from the upstream side in the gas flow direction.
Specifically, in the warm-up operation immediately after the start of operation, it is difficult to raise the temperature of all exhaust gas purification catalysts to a temperature at which appropriate exhaust gas purification ability can be exhibited. To purify the exhaust gas. At this time, if the above-described high-load operation catalyst is arranged on the most upstream side in the gas flow direction, it is difficult to appropriately reduce the emission during the warm-up operation.
On the other hand, when high-load operation is performed, since all exhaust gas purification catalysts have already been heated to a sufficient temperature, the exhaust gas purification catalysts arranged second and later from the upstream side are also suitable. A purification action can be exhibited.
Based on the above knowledge, when using the above-described catalyst for high-load operation, the present inventor only needs to arrange the second and subsequent ones from the upstream side in the gas flow direction. It came to mind that the emission of harmful components in both load operation can be reduced appropriately. And based on this knowledge, it came to complete this invention by creating the exhaust gas purification apparatus disclosed here and confirming the effect of this apparatus by various experiments.

  Further, in a preferred aspect of the exhaust gas purification apparatus disclosed herein, the exhaust gas purification catalyst disposed on the uppermost stream side in the exhaust gas flow direction is a downstream side of the noble metal catalyst present in the upstream catalyst layer in the exhaust gas flow direction. The catalyst for warm-up operation is configured so as to be more than the noble metal catalyst present in the catalyst layer.

As described above, the exhaust gas in the warm-up operation has a slow flow rate, and tends to pass through the upstream side of the partition wall in each catalyst. Therefore, the warm-up operation catalyst arranged on the most upstream side in the exhaust gas flow direction is configured such that the precious metal catalyst in the upstream catalyst layer in the exhaust gas flow direction is larger than the precious metal catalyst in the downstream catalyst layer. It is preferable that Thereby, the emission in warm-up operation can be suitably reduced.
Note that the structure of the warm-up operation catalyst arranged on the most upstream side in the exhaust gas flow direction is not limited to the above-described mode, and can be appropriately changed in consideration of the exhaust gas flow rate in the warm-up operation. For example, when using an internal combustion engine in which exhaust gas having a high flow rate is generated from the beginning of operation, an exhaust gas purification catalyst in which the amount of noble metal catalyst in the upstream catalyst layer and the downstream catalyst layer is approximately the same amount is warmed. It can be preferably used as a machine operation catalyst.

In another preferable aspect of the exhaust gas purification apparatus disclosed herein, in the catalyst for high load operation, the precious metal catalyst present in the outlet catalyst layer is 60 wt% when the total amount of the precious metal catalyst present in the partition is 100 wt%. % Or more and 70 wt% or less.
As described above, when the amount of the noble metal catalyst in the outlet catalyst layer is less than half of the total amount of the noble metal catalyst, there is a risk that the noble metal catalyst in the downstream partition wall is insufficient and the emission during high load operation cannot be sufficiently reduced. There is. Also, some exhaust gas passes through the upstream partition even during high-load operation, so even if it is a high-load operation catalyst, there is some precious metal catalyst in the inlet catalyst layer. Emission can be reduced appropriately. Considering these matters, the amount of the noble metal catalyst in the outlet catalyst layer of the catalyst for high load operation is preferably 60 wt% or more and 70 wt% or less of the total amount of the noble metal catalyst present in the partition walls.

Further, in another preferable aspect of the exhaust gas purifying apparatus disclosed herein, in the catalyst for high load operation, the length in the extending direction of the outlet catalyst layer is shorter than the length of the inlet catalyst layer, and in the outlet catalyst layer The density of the noble metal catalyst is higher than the density of the noble metal catalyst in the inlet catalyst layer.
As shown by the arrow B in FIG. 3 described above, the exhaust gas in the high load operation passes through the partition wall 4 on the downstream side after colliding with the end portion (sealing member 3a) on the exhaust gas outflow side of the base material 1. The exhaust gas at that time easily passes through the most downstream region near the end on the exhaust gas outflow side.
In order to appropriately purify the exhaust gas passing through the most downstream region, it is preferable to shorten the length of the outgoing catalyst layer and increase the density of the noble metal catalyst in the outgoing catalyst layer. As a result, the exhaust gas passing through the region on the most downstream side of the partition wall as shown by the arrow B in FIG. 3 can be brought into contact with the exit catalyst layer containing the high-density noble metal catalyst. Emission can be reduced more suitably.

In another preferable embodiment of the exhaust gas purifying apparatus disclosed herein, the length of the outlet catalyst layer is 25% to 45% when the total length of the partition walls in the extending direction is 100% in the catalyst for high load operation. It is characterized by being.
When the length of the outgoing catalyst layer is shortened and the noble metal catalyst in the outgoing catalyst layer is made high in density as in the above-described embodiment, the length of the outgoing catalyst layer with respect to the entire length of the partition wall is 25% to It is preferable to set it to 45%. As a result, the exhaust gas colliding with the end portion on the exhaust gas outflow side can be appropriately brought into contact with the exit catalyst layer having a high-density noble metal catalyst.

In another preferred embodiment of the exhaust gas purifying apparatus disclosed herein, the noble metal catalyst includes at least one platinum group element selected from the group of Pt, Pd, and Rh.
The noble metal catalyst that purifies harmful components in the exhaust gas preferably contains at least one platinum group element (PGM) selected from the group of Pt, Pd, and Rh. By using a noble metal catalyst containing these platinum group elements, harmful components in the exhaust gas can be suitably purified.

Moreover, as another aspect of the present invention, there is provided an exhaust gas purifying catalyst arranged second or later from the upstream side in the exhaust gas flow direction of the exhaust gas purifying apparatus.
The exhaust gas purifying catalyst disclosed herein includes an inlet cell in which only an end portion on the exhaust gas inflow side is opened, an outlet cell in which only an end portion on the exhaust gas outlet side is adjacent to the inlet cell, and A base material having a wall flow structure having a porous partition wall that separates the entry side cell and the exit side cell, and a predetermined thickness from the surface of the partition wall in contact with the entry side cell to the inside of the partition wall, and the exhaust gas inflow side An inlet catalyst layer including a noble metal catalyst for purifying harmful components contained in exhaust gas, and an outlet cell, which is an inlet catalyst layer formed with a predetermined length along the extending direction of the partition walls from the vicinity of the end of the partition wall The outlet side catalyst layer is formed in a predetermined thickness from the surface of the partition wall in contact with the inner wall of the partition wall and has a predetermined length from the vicinity of the end on the exhaust gas outflow side along the extending direction of the partition wall. And an exit side catalyst layer containing a noble metal catalyst. Noble metal catalyst present in is characterized in that it is configured to be larger than the noble metal catalyst present in the inlet side catalyst layer.

  By disposing the exhaust gas purification catalyst disclosed here in the second and subsequent positions from the upstream side in the exhaust gas flow direction of the exhaust gas purification device, and using it as a high load operation catalyst for purifying exhaust gas in high load operation, The harmful components in the exhaust gas during the load operation can be appropriately purified, and the emission of harmful components can be suitably reduced.

It is a figure showing typically an exhaust gas purification device concerning one embodiment of the present invention. 1 is a perspective view schematically showing an exhaust gas purifying catalyst used in an exhaust gas purifying apparatus according to an embodiment of the present invention. It is a figure which shows typically the cross-section of the base material of the catalyst for exhaust gas purification. It is sectional drawing which shows typically the structure inside the partition of the exhaust gas purification catalyst in one Embodiment of this invention. It is a graph which shows the 50% purification temperature of the exhaust gas purification catalyst of Test Example 1 to Test Example 4 when the intake air amount is set to 20 g / sec. It is a graph which shows the 50% purification temperature of the exhaust gas purification catalyst of Test Example 1 to Test Example 4 when the intake air amount is set to 35 g / sec. It is a graph which shows the measurement result of the NOx emission amount of the exhaust gas purification apparatus which used the exhaust gas purification catalyst of Test Example 1-Test Example 4 as a catalyst for high load operation. It is a graph which shows the measurement result of the NOx emission amount of the exhaust gas purification apparatus which used the exhaust gas purification catalyst of Test Example 5-Test Example 8 as a catalyst for high load operation.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In the following drawings, members / parts having the same action are denoted by the same reference numerals, and redundant description may be omitted or simplified. In addition, the dimensional relationship (length, width, thickness, etc.) in each drawing does not necessarily reflect the actual dimensional relationship. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be implemented based on the contents disclosed in the present specification and technical knowledge in the field.

1. FIG. 1 is a diagram schematically showing an exhaust gas purification apparatus according to this embodiment. 1 is attached to an internal combustion engine (not shown) so that the exhaust gas flows from the left side to the right side in the drawing.
As shown in FIG. 1, in the exhaust gas purification apparatus 100 according to the present embodiment, two exhaust gas purification catalysts 10 and 20 are arranged in an exhaust pipe 50 of an internal combustion engine. Each exhaust gas purifying catalyst 10, 20 includes a cylindrical base material 1 having a honeycomb structure as shown in FIG. 2 and a catalyst layer (not shown) formed inside the base material 1. Yes. In the exhaust gas purification catalysts 10 and 20 having such a configuration, harmful components (HC, CO, NOx) are purified by bringing the exhaust gas flowing into the substrate 1 into contact with the catalyst layer.

Then, in the exhaust gas flow direction F of the exhaust gas purification apparatus 100 according to the present embodiment shown in FIG. 1, the warm-up operation for purifying exhaust gas in the warm-up operation is provided on the most upstream side (in other words, directly below the internal combustion engine). A catalyst 10 for use is arranged. In addition, second from the upstream side in the exhaust gas flow direction F of the exhaust gas purification apparatus 100, a high load operation catalyst 20 for purifying exhaust gas in high load operation is disposed.
Hereinafter, each of the exhaust gas purifying catalysts 10 and 20 provided in the exhaust gas purifying apparatus 100 according to the present embodiment will be specifically described.

2. Exhaust gas purification catalyst In the present specification, first, a structure common to the respective exhaust gas purification catalysts (the warm-up operation catalyst 10 and the high-load operation catalyst 20) will be described.

FIG. 3 is a diagram schematically showing a cross-sectional structure of the base material of the exhaust gas purifying catalyst. FIG. 4 is a cross-sectional view schematically showing the structure inside the partition wall of the exhaust gas purifying catalyst in the present embodiment.
As described above, each of the exhaust gas purifying catalysts 10 and 20 in the present embodiment includes the base material 1 having a honeycomb structure and the catalyst layer formed on the partition walls 4 inside the base material 1. The harmful components (HC, CO, NOx) are purified by bringing the exhaust gas flowing into the substrate 1 into contact with the catalyst layer.

(1) Base Material As shown in FIG. 3, in this embodiment, a base material having a wall flow structure is used as the base material 1 of each of the exhaust gas purifying catalysts 10 and 20. The base material 1 having such a wall flow structure includes an inlet cell 2a in which only an end 1a on the exhaust gas inflow side is open, and an outlet cell 2b in which only an end 1b on the exhaust gas outflow side is open. Yes. The end 1b on the exhaust gas outflow side of the entry cell 2a is sealed by a sealing member 3a, and the end 1a on the exhaust gas inflow side of the exit cell 2b is sealed by a sealing member 3b. In the base material 1 having such a wall flow structure, the entrance cell 2a and the exit cell 2b are formed adjacent to each other in a checkered pattern (see FIG. 2), and the entrance cell 2a and the exit cell 2b are based on the base cell 1a. The material 1 is partitioned by a partition wall 4 extending along the cylinder axis direction X.

  The thickness T (that is, the average thickness from the surface in contact with the entry side cell 2a to the surface in contact with the exit side cell 2b) of the partition wall 4 of the base material 1 is 0. It is preferable to set within the range of 05 mm or more and 2 mm or less. Moreover, it is preferable to set normally the full length Lw of the partition 4 in an extending | stretching direction in the range of 10 mm-500 mm (for example, 50 mm-300 mm). Moreover, the volume of the whole base material 1 (total volume of the entry side cell 2a and the exit side cell 2b) is normally set to 0.1L-5L (preferably 0.5L-3L, for example, 1.25L).

  Moreover, the base material 1 in this embodiment can be comprised with the various material which can be used for the base material of the catalyst for general exhaust gas purification. Preferable examples of the material of the substrate 1 include cordierite, silicon carbide (SiC), ceramics such as aluminum titanate, and alloys such as stainless steel. Since these materials have high heat resistance, they can be prevented from being damaged when exposed to a high temperature environment (for example, 400 ° C. or higher) in a high load operation.

  Further, as shown in FIGS. 1 and 2, in the present embodiment, the exhaust gas purification catalysts 10 and 20 are arranged so that the cylinder axis direction X and the gas flow direction F of the substrate 1 are substantially the same direction. Is arranged. As described above, the partition wall 4 of the substrate 1 is formed so as to extend along the cylinder axis direction X. That is, the exhaust gas purification apparatus 100 according to the present embodiment is configured such that the gas flow direction F, the cylinder axis direction X of the base material 1, and the extending directions of the partition walls 4 are substantially the same. .

  In addition, in this embodiment, although the cylindrical base material 1 like FIG. 2 is used as a base material, the external shape of the base material 1 is not restricted to a cylindrical shape, An elliptical cylinder shape, a polygonal cylinder shape, etc. There may be.

(2) Catalyst Layer As described above, the catalyst layers of the exhaust gas purifying catalysts 10 and 20 are formed inside the partition walls 4 of the substrate 1. FIG. 4 is a cross-sectional view schematically showing the structure inside the partition wall of the exhaust gas purifying catalyst in the present embodiment.
As shown in FIG. 4, each of the exhaust gas purifying catalysts 10, 20 in this embodiment includes an inlet catalyst layer 6 a formed inside the upstream partition 4 and an outlet formed inside the downstream partition 4. Two types of catalyst layers of the side catalyst layer 6b are provided.
Specifically, the inlet side catalyst layer 6a is formed with a predetermined thickness from the surface of the partition wall 4 in contact with the inlet side cell 2a to the inside of the partition wall 4, and from the vicinity of the end 1a on the exhaust gas inflow side. It is formed with a predetermined length L1 along the extending direction X.
On the other hand, the exit side catalyst layer 6b is formed with a predetermined thickness from the surface of the partition wall 4 in contact with the exit side cell 2b to the inside of the partition wall 4, and the extending direction X of the partition wall 4 from the vicinity of the end portion 1b on the exhaust gas outflow side. Is formed with a predetermined length L2.
In addition, it is preferable that the sum of the length L1 of the entry side catalyst layer 6a and the length L2 of the exit side catalyst layer 6b in the extending direction X is longer than the total length Lw of the partition walls 4. Thereby, in the extending direction X, the inlet side catalyst layer 6a and the outlet side catalyst layer 6b are partially overlapped, and the catalyst layer is not formed between the inlet side catalyst layer 6a and the outlet side catalyst layer 6b. Can be prevented.

The inlet catalyst layer 6a and the outlet catalyst layer 6b contain a noble metal catalyst that purifies harmful components in the exhaust gas. The noble metal catalyst preferably contains at least one platinum group element (PGM) selected from the group consisting of Pt, Pd, and Rh, for example. Thus, when exhaust gas comes into contact with the noble metal catalyst, harmful components can be appropriately purified by the catalytic action of the platinum group element.
In order to suitably reduce the emission of harmful components, the noble metal present in the inlet catalyst layer 6a and the outlet catalyst layer 6b in consideration of the content of harmful components (CO, HC, NOx) in the exhaust gas. It is preferable to adjust the total amount of the catalyst as appropriate.

Further, the inlet catalyst layer 6a and the outlet catalyst layer 6b contain the above-mentioned carrier for supporting the noble metal catalyst, other additives, and the like. In the present embodiment, the material constituting the carrier is not particularly limited, and a carrier material used for a catalyst layer of a general exhaust gas purifying catalyst can be used. Specific examples of such carrier materials include alumina, titania, zirconia, silica, ceria, cerium-zirconium composite oxide, and the like.
Moreover, it is preferable that the inlet side catalyst layer 6a and the outlet side catalyst layer 6b contain an OSC material that functions as a co-catalyst by occluding and releasing oxygen. By adding such an OSC material to each catalyst layer, it is possible to efficiently purify harmful components by assisting the catalytic action of the noble metal catalyst. As the OSC material, a polycrystal (or single crystal) containing cerium-zirconium composite oxide as a main component and containing rare earth oxide, alkali metal oxide, transition metal, alumina, silica, or the like is used. it can.

(A) Catalyst for high load operation As described above, the exhaust gas purifying apparatus 100 according to the present embodiment is a catalyst for warm-up operation 10 that purifies exhaust gas in warm-up operation, and purifies exhaust gas in high-load operation. The high-load operation catalyst 20 is provided. Here, the high-load operation catalyst 20 in the present embodiment will be described.

As described above, in the exhaust gas purification apparatus 100 according to the present embodiment, the high-load operation catalyst 20 (see FIG. 1) is arranged second from the upstream side in the exhaust gas flow direction F, and the high-load operation catalyst is concerned. 20 is configured such that the precious metal catalyst present in the outlet catalyst layer 6b in FIG. 4 is larger than the precious metal catalyst present in the inlet catalyst layer 6a.
The exhaust gas purification apparatus 100 according to the present embodiment can efficiently purify harmful components in the exhaust gas during high load operation by using the high load operation catalyst 20, and suitably reduce the emission of harmful components during high load operation. it can.

Specifically, in the present embodiment, the high-load operation catalyst 20 is disposed second from the upstream side in the exhaust gas flow direction F, but when the high-load operation is performed, the high-load operation catalyst 20 Since 20 has been heated to a sufficient temperature, the noble metal catalyst contained in the high-load operation catalyst 20 can function properly.
When high load operation is performed in this state, exhaust gas having a high flow velocity is supplied to the high load operation catalyst 20, and after colliding with the exhaust gas outlet side sealing member 3a as shown by an arrow B in FIG. Then, it passes through the partition wall 4 in the vicinity of the sealing member 3a (that is, the most downstream side). In the high load operation catalyst 20 of the present embodiment, the outlet catalyst layer 6b is formed in the most downstream partition wall 4, and the noble metal catalyst in the outlet catalyst layer 6b is larger than the inlet catalyst layer 6a. Thus, the exhaust gas passing through the most downstream partition 4 can be brought into contact with a large amount of noble metal catalyst. For this reason, in the exhaust gas purification apparatus 100 according to the present embodiment, the high load operation catalyst 20 disposed second from the upstream side in the exhaust gas flow direction F sufficiently purifies harmful components in the exhaust gas and performs high load operation. Emissions in can be suitably reduced.

  In the high-load operation catalyst 20, the specific value of the noble metal catalyst present in each of the inlet side catalyst layer 6 a and the outlet side catalyst layer 6 b can be changed as appropriate according to the capacity of the substrate 1, etc. Although not limited, when the total amount of the noble metal catalyst present in the partition walls 4 is 100 wt%, the noble metal catalyst present in the outlet catalyst layer 6b is 60 wt% or more and 80 wt% or less (preferably 60 wt% or more and 70 wt% or less). ) Is preferable. As a result, it is possible to more suitably reduce emissions during high-load operation.

  Further, in the high load operation catalyst 20, the density of the noble metal catalyst in each catalyst layer is appropriately adjusted according to the length L1 of the inlet catalyst layer 6a in the extending direction X and the length L2 of the outlet catalyst layer 6b. It is preferable to do. For example, when the length L2 of the exit side catalyst layer 6b is shortened compared to the length L1 of the entrance side catalyst layer 6a in the stretching direction X, and the density of the noble metal catalyst in the exit side catalyst layer 6b is increased, sealing is performed. Since the exhaust gas passing in the vicinity of the member 3a can be brought into contact with the high-density noble metal catalyst, it is possible to more suitably reduce the emission in the high load operation. Note that the length L2 of the outlet catalyst layer 6b in the extending direction X at this time is more preferably set to 25% to 45% of the total length Lw of the partition walls 4.

(B) Catalyst for warm-up operation Next, the catalyst 10 for warm-up operation in the present embodiment will be described. As shown in FIG. 1, the warm-up operation catalyst 10 is disposed on the most upstream side in the exhaust gas flow direction F.
The warm-up operation catalyst 10 is different from the above-described high-load operation catalyst 20 in that the precious metal catalyst present in the inlet catalyst layer 6a is larger than the precious metal catalyst present in the outlet catalyst layer 6b. ing.
The exhaust gas purification apparatus 100 according to the present embodiment can efficiently purify harmful components in the exhaust gas during the warm-up operation by the warm-up operation catalyst 10 and suitably reduce the emission of harmful components during the warm-up operation. it can.

Specifically, in this embodiment, since the warm-up operation catalyst 10 is arranged on the most upstream side in the exhaust gas flow direction F, the warm-up operation is performed in spite of the warm-up operation at the initial stage of operation. The precious metal catalyst contained in the warm-up operation catalyst 10 can function appropriately by raising the temperature of the pre-use catalyst 10 to a sufficient temperature.
In such warm-up operation, exhaust gas having a low flow rate is supplied to the warm-up operation catalyst 10, and as shown by an arrow A in FIG. 3, upstream of the exhaust gas flow direction F (that is, the cylinder axis direction X). Pass through the partition wall 4. The warm-up operation catalyst 10 of the present embodiment is configured such that the noble metal catalyst in the inlet catalyst layer 6a formed in the upstream partition 4 is larger than the outlet catalyst layer 6b. Exhaust gas passing through the upstream partition 4 can be brought into contact with a large amount of noble metal catalyst. For this reason, in the exhaust gas purification apparatus 100 according to the present embodiment, the warm-up operation catalyst 10 disposed on the most upstream side in the exhaust gas flow direction F sufficiently purifies harmful components in the exhaust gas in the warm-up operation. Emission can be reduced suitably.

  As described above, according to the exhaust gas purification apparatus 100 according to the present embodiment, the warm-up operation catalyst 10 arranged on the most upstream side can suitably reduce emissions during the warm-up operation, and from the upstream side. Since the emission during high load operation can be suitably reduced by the high load operation catalyst 20 arranged after the second, the total amount of harmful components can be greatly reduced.

5. Other Embodiments While the exhaust gas purification apparatus 100 according to an embodiment of the present invention has been described above, the exhaust gas purification apparatus disclosed herein is not limited to the above-described embodiment, and various structures can be changed.

For example, in the above-described embodiment, a wall flow type exhaust gas purification catalyst is used as the warm-up operation catalyst arranged on the most upstream side in the exhaust gas flow direction F, and the noble metal catalyst in the inlet catalyst layer of the catalyst is output. More than the noble metal catalyst in the side catalyst layer.
However, the warm-up operation catalyst disposed on the most upstream side in the exhaust gas flow direction is not particularly limited as long as it can appropriately reduce the emission during the warm-up operation. For example, depending on the exhaust gas flow rate in the warm-up operation, an exhaust gas purification catalyst in which the precious metal catalyst in the inlet catalyst layer and the precious metal catalyst in the outlet catalyst layer have substantially the same amount can be preferably used as the warm-up catalyst. .
The warm-up operation catalyst may not be a wall flow type exhaust gas purification catalyst as described above. For example, a straight flow type exhaust gas purification catalyst may be used.

Further, the exhaust gas purification apparatus 100 according to the above-described embodiment includes two exhaust gas purification catalysts, but the number of exhaust gas purification catalysts constituting the exhaust gas purification apparatus is not particularly limited, and three or more exhaust gas purification catalysts. A purification catalyst may be provided.
Thus, in the case of the exhaust gas purification apparatus provided with three or more exhaust gas purification catalysts, the warm-up operation catalyst is arranged on the most upstream side in the gas flow direction, and the second highest load operation catalyst from the upstream side. In addition, an exhaust gas purifying catalyst for NOx occlusion can be arranged downstream of the high load operation catalyst. In the case of the exhaust gas purification apparatus having such a configuration, it is possible to obtain an effect of reducing NOx emission in operation under lean conditions after appropriately reducing emission of harmful components in both warm-up operation and high load operation. . Further, a plurality of high load operation catalysts may be arranged at the second and subsequent positions from the upstream side in the exhaust gas flow direction.

[Test example]
Test examples relating to the present invention will be described below, but the following description is not intended to limit the present invention.

<Experiment A>
In Experiment A, an entry-side catalyst layer and an exit-side catalyst layer are formed inside the partition walls. The noble metal catalyst in the entry-side catalyst layer and the noble metal catalyst in the exit-side catalyst layer are as shown in Table 1 below. Four exhaust gas purification catalysts were produced (Test Example 1 to Test Example 4), and the exhaust gas purification ability of each exhaust gas purification catalyst was evaluated.

1. Production of each test example (1) Test example 1
In Test Example 1, a cylindrical base material 1 (manufactured by cordierite: volume 1.25 L) having a wall flow structure with a total length Lw in the stretching direction X of 100 mm and a diameter of 160 mm was prepared. And the entrance side catalyst layer 6a and the exit side catalyst layer 6b containing the noble metal catalyst (Pd: total amount 1.1g, Rh: total amount 0.25g) were formed in the partition 4 of this base material 1. .
In each catalyst layer, alumina was used as a support, and ceria-zirconia composite oxide was added as an OSC material. At this time, the density of each catalyst layer excluding the noble metal catalyst was set to 100 g / L.

  In Test Example 1, the length L1 of the inlet catalyst layer 6a and the length L2 of the outlet catalyst layer 6b are both set to 55% of the total length Lw of the substrate 1, and then the partition walls of the substrate 1 4 Each catalyst layer was formed so that the amount of the noble metal catalyst in the outgoing catalyst layer 6b was 50 wt% when the total amount of the noble metal catalyst present in 4 was 100 wt%.

(2) Test Example 2 to Test Example 4
In Test Example 2 to Test Example 4, the amount of the noble metal catalyst in the outlet catalyst layer 6b when the total amount of the noble metal catalyst present in the partition walls 4 of the base material 1 was 100 wt% was changed as shown in Table 1 below. Except for this point, an exhaust gas purifying catalyst was produced under the same conditions as in Test Example 1. Specifically, in Test Example 2, the amount of the noble metal catalyst in the outlet catalyst layer 6b was 60 wt% of the total amount of the noble metal catalyst, Test Example 3 was 70 wt%, and Test Example 4 was 80 wt%.

2. Evaluation Test In this experiment, in order to evaluate the exhaust gas purification catalyst of each test example, the 50% purification temperature (T50) of harmful components of the exhaust gas purification catalyst of each test example and the NOx emission amount were measured. Hereinafter, specific measurement methods in each evaluation test will be described.

(1) 50% purification temperature of harmful components (T50)
In this evaluation, the exhaust gas purifying catalyst of each test example is disposed in the exhaust pipe of the internal combustion engine, the internal combustion engine is operated, and the exhaust gas discharged from the internal combustion engine is 150 ° C. to 50 ° C./min with a heat exchanger. The catalyst was supplied to the exhaust gas purifying catalyst of each test example while increasing the temperature at a temperature increase rate of. While the internal combustion engine is in operation, the purification rate of harmful components (CO, HC, NOx) in the exhaust gas is continuously measured based on the measurement results of sensors attached upstream and downstream of the exhaust gas purification catalyst. The exhaust gas temperature when the purification rate of each harmful component reached 50% was evaluated as the 50% purification temperature (T50) of the harmful component.

In this evaluation, the 50% purification temperature (T50) when the intake air amount of the internal combustion engine is set to 20 g / sec to reproduce the warm-up operation, and the intake air amount to reproduce the high load operation. And 50% purification temperature (T50) when 35 g / sec was set.
FIG. 6 shows the measurement result of the 50% purification temperature when reproducing the warm-up operation, and FIG. 7 shows the measurement result of the 50% purification temperature when reproducing the high load operation.

(2) Measurement of NOx emission amount In this evaluation, a warm-up operation catalyst and a high-load operation catalyst are attached to an exhaust pipe of a vehicle equipped with an internal combustion engine having an engine displacement of about 2200 cc. The amount of NOx emission (g / km) during running was measured. In this test, a warm-up operation catalyst in which the precious metal catalyst (Pd and Rh) in the upstream catalyst layer is set to 60 wt% of the total amount of the precious metal catalyst is disposed on the most upstream side, and second from the upstream side. The exhaust gas purifying catalysts of Test Examples 1 to 4 were used as the high load operation catalysts to be arranged. The measurement result of the NOx emission amount in each test example is shown in FIG.

3. Test Results As shown in FIG. 5, when the warm-up operation is reproduced by slowing the flow rate of the exhaust gas, the 50% purification temperature (T50) of harmful components increases as the precious metal catalyst in the outlet catalyst layer 6b is increased. It was rising. From this, it is difficult for the exhaust gas purifying catalyst having a large amount of the noble metal catalyst in the outlet catalyst layer 6b as in Test Example 2 to Test Example 4 to appropriately purify harmful components in the warm-up operation in which the exhaust gas flow rate is slow. It has been found that it is better not to use the catalyst for warm-up operation arranged on the most upstream side in the exhaust gas flow direction.

On the other hand, as shown in FIG. 6, when the exhaust gas flow rate was increased and the high load operation was reproduced, in Test Examples 2 to 4, the 50% purification temperature (T50) of harmful components was lowered. Further, as shown in FIG. 7, when the exhaust gas purifying catalyst of each test example is used as a catalyst for high load operation and actually mounted on a vehicle, the NOx emission amount in Test Example 2 to Test Example 4 is It was confirmed that it was reduced.
From these results, the exhaust gas purifying catalyst having a large amount of noble metal catalyst in the outlet catalyst layer 6b as in Test Example 2 to Test Example 4 can suitably purify harmful components in high-load operation where the exhaust gas flow rate is high. Therefore, it has been found that the catalyst can be preferably used for a catalyst for high load operation that is arranged second or later from the upstream side in the exhaust gas flow direction.

  Further, comparing Test Example 2 to Test Example 4, in Test Example 2 and Test Example 3, the 50% purification temperature (T50) when the exhaust gas flow rate shown in FIG. From this, it was found that in the case of the exhaust gas purifying catalyst used for the high load operation catalyst, it is preferable to adjust the amount of the noble metal catalyst in the outlet catalyst layer 6b within the range of 60 wt% to 70 wt%.

<Experiment B>
In Experiment B, the influence of the length L2 of the outlet catalyst layer 6b and the density of the noble metal catalyst in the outlet catalyst layer 6b on the NOx emission amount was investigated.

1. Production of test examples (1) Test examples 5 to 8
In Experiment B, four types of exhaust gas-purifying catalysts having more noble metal catalysts in the exit side catalyst layer than noble metal catalysts in the entrance side catalyst layer were produced (Test Example 5 to Test Example 8).
In this experiment, Rh (total amount: 0.28 g) was used as a noble metal catalyst in each test example, except that the length of each catalyst layer and the density of the noble metal catalyst were changed as shown in Table 2. An exhaust gas purifying catalyst was prepared under the same conditions as in Experiment A described above. Specifically, in this experiment B, the exhaust gas purification catalyst of each test example was prepared so that the noble metal catalyst density of the exit side catalyst layer 6b increased as the length L2 of the exit side catalyst layer 6b became shorter. . In addition, “the length of the catalyst layer” in the following Table 2 is a ratio when the total length Lw of the partition walls is 100%.

2. Evaluation Test In Experiment B, the NOx emission amounts of Test Example 5 to Test Example 8 were measured according to the same procedure as “Measurement of NOx Emission Amount” in Experiment A described above. The measurement results are shown in FIG.

3. Test Results As shown in FIG. 8, in any of Test Examples 5 to 8, a low NOx emission amount of 0.02 g / km or less was measured. And as a result of comparing each test example, in test example 6-test example 8, the further lower NOx emission amount of about 0.01 g / km was measured.
From these experimental results, when the length L2 of the outgoing catalyst layer 6b is shortened and the noble metal catalyst concentration in the outgoing catalyst layer 6b is increased as shown in Test Example 6 to Test Example 8, in the high load operation. It was found that the emission of harmful components can be reduced more suitably. This is because the exhaust gas with a high flow velocity supplied in high-load operation collides with the exhaust gas outflow side end of the base material and passes through the region on the most downstream side of the partition wall. It is understood that Test Example 6 to Test Example 8 were able to purify NOx in the exhaust gas more suitably.

  As mentioned above, although the specific example of this invention was demonstrated in detail, these are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

DESCRIPTION OF SYMBOLS 1 Substrate 1a End 1b on the exhaust gas inflow side End 2b on the exhaust gas outflow side 2a Inlet cell 2b Outlet cell 3a, 3b Sealing member 4 Partition wall 6a Inlet catalyst layer 6b Outlet catalyst layer 10 Exhaust gas purification catalyst (warm Catalyst for machine operation)
20 Exhaust gas purification catalyst (high load operation catalyst)
50 Exhaust pipe 100 Exhaust gas purification device A Exhaust gas flow path B during warm-up operation Exhaust gas flow path F during high load operation F Exhaust gas flow direction L1 Length of inlet side catalyst layer L2 Length of outlet side catalyst layer Lw Total length T of partition wall Partition thickness X Base axis direction of substrate (stretching direction of partition wall)

Claims (7)

An exhaust gas purifying apparatus comprising a plurality of exhaust gas purifying catalysts arranged in an exhaust pipe of an internal combustion engine, and purifying exhaust gas by passing the exhaust gas discharged from the internal combustion engine through the plurality of exhaust gas purifying catalysts. ,
Among the plurality of exhaust gas purification catalysts, at least one of the exhaust gas purification catalysts arranged after the second upstream from the exhaust gas flow direction,
An inlet cell in which only an end portion on the exhaust gas inflow side is opened; an outlet cell in which only an end portion on the exhaust gas outlet side is open adjacent to the inlet cell; and the inlet cell and the outlet cell. A base material having a wall flow structure having porous partition walls, and
It is formed with a predetermined thickness from the surface of the partition wall in contact with the inlet side cell to the inside of the partition wall, and with a predetermined length along the extending direction of the partition wall from the vicinity of the end on the exhaust gas inflow side. An inlet-side catalyst layer comprising a noble metal catalyst for purifying harmful components contained in the exhaust gas,
It is formed with a predetermined thickness from the surface of the partition wall in contact with the outlet cell to the inside of the partition wall, and with a predetermined length along the extending direction of the partition wall from the vicinity of the end portion on the exhaust gas outflow side. An exit side catalyst layer comprising the noble metal catalyst,
With
An exhaust gas purification apparatus, wherein the noble metal catalyst present in the outlet catalyst layer is a catalyst for high load operation configured to be larger than the noble metal catalyst present in the inlet catalyst layer.   The exhaust gas purifying catalyst disposed on the most upstream side in the exhaust gas flow direction has more noble metal catalyst present in the upstream catalyst layer in the exhaust gas flow direction than the noble metal catalyst present in the downstream catalyst layer. The exhaust gas purifying apparatus according to claim 1, wherein the exhaust gas purifying apparatus is a warm-up operation catalyst.   In the high-load operation catalyst, the noble metal catalyst present in the outlet catalyst layer is 60 wt% or more and 70 wt% or less when the total amount of the noble metal catalyst existing in the partition is 100 wt%. The exhaust gas purifying device according to claim 1 or 2.   In the catalyst for high load operation, the length of the outlet catalyst layer in the extending direction is shorter than the length of the inlet catalyst layer, and the density of the noble metal catalyst in the outlet catalyst layer is lower in the inlet catalyst layer. The exhaust gas purification device according to claim 1 or 2, wherein the exhaust gas purification device has a density higher than that of the noble metal catalyst.   5. The high-load operation catalyst according to claim 4, wherein a length of the outgoing catalyst layer is 25% to 45% when a total length of the partition walls in the extending direction is 100%. Exhaust gas purification equipment.   The exhaust gas purifying apparatus according to any one of claims 1 to 5, wherein the noble metal catalyst includes at least one platinum group element selected from the group consisting of Pt, Pd, and Rh. . The exhaust gas purifying device according to any one of claims 1 to 6, wherein the exhaust gas purifying catalyst is disposed second or later from the upstream side in the exhaust gas flow direction,
An inlet cell in which only an end portion on the exhaust gas inflow side is opened; an outlet cell in which only an end portion on the exhaust gas outlet side is open adjacent to the inlet cell; and the inlet cell and the outlet cell. A base material having a wall flow structure having porous partition walls, and
It is formed with a predetermined thickness from the surface of the partition wall in contact with the inlet side cell to the inside of the partition wall, and with a predetermined length along the extending direction of the partition wall from the vicinity of the end on the exhaust gas inflow side. An inlet-side catalyst layer comprising a noble metal catalyst for purifying harmful components contained in the exhaust gas,
It is formed with a predetermined thickness from the surface of the partition wall in contact with the outlet cell to the inside of the partition wall, and with a predetermined length along the extending direction of the partition wall from the vicinity of the end portion on the exhaust gas outflow side. An exit side catalyst layer comprising the noble metal catalyst,
With
An exhaust gas purifying catalyst, wherein the precious metal catalyst present in the outlet catalyst layer is configured to be larger than the precious metal catalyst present in the inlet catalyst layer.

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