JP7167614B2 - Exhaust gas purifier - Google Patents

Description

TECHNICAL FIELD The present invention relates to an exhaust gas purifier that collects and burns particulate matter (PM) contained in exhaust gas from an internal combustion engine.

2. Description of the Related Art Conventionally, as an exhaust gas purifying device for purifying exhaust gas (exhaust gas) of an internal combustion engine, one that removes harmful components using a carrier on which a catalyst is supported is known. That is, a catalyst component is fixed inside a carrier (carrier) through which a large number of fine holes are formed, and exhaust gas is circulated to remove carbon monoxide, unburned combustion components, nitrogen oxides, and particulate matter contained in the exhaust gas. (Particulate Matter; hereinafter referred to as PM). Types of carriers include ceramic molded products and metal products (metal carriers). Further, the type of catalyst supported on the carrier is variously selected according to the substance to be purified (see Patent Documents 1 to 3).

WO2016/133086 WO2017/119101 Japanese Patent Application Laid-Open No. 2010-269205

By the way, the distribution of PM trapped on the carrier is not necessarily uniform, and deviations occur according to the shape of the carrier, the flow of the exhaust gas, and the like. For example, in a wall-flow type carrier, PM tends to accumulate on the carrier surface facing the inlet cell and near the inlet of the exhaust gas channel inside the carrier. Therefore, there is a problem that it is difficult to uniformly burn PM on the upstream side and the downstream side of the carrier. It should be noted that the incineration time tends to be longer on the upstream side, where the amount of accumulated PM tends to increase, and there is a risk of performance deterioration due to excessive temperature rise.

One of the purposes of the present invention is to provide an exhaust gas purifying apparatus that can uniformly burn PM. In addition to this purpose, it is also possible to achieve actions and effects derived from each configuration shown in the "Mode for Carrying out the Invention" described later and which cannot be obtained with the conventional technology. can be positioned as a goal.

(1) The disclosed exhaust gas purifying device is an exhaust gas purifying device that collects and burns particulate matter contained in exhaust gas from an internal combustion engine, and includes partition walls of carriers. The partition has a layer formed on the surface of the partition and a layer formed inside the partition. A noble metal is carried on a layer formed inside the partition wall. Further, the layer formed on the surface of the partition wall carries a combustion promoting catalyst that promotes combustion of the particulate matter and allows the particulate matter to be burned at a lower temperature than the noble metal. Furthermore, the combustion-promoting catalyst is supported at a higher density on the upstream side than on the downstream side in the layer formed on the surface of the partition wall . Specific examples of the combustion promoting catalyst include silver (Ag), cerium oxide (CeO ₂ ), silver ceria (Ag/CeO ₂ ), tin ceria (Sn/CeO ₂ ), ceria zirconia (CeO ₂ /ZrO ₂ ), etc. is mentioned.

Specific examples of noble metals supported inside the partition walls include gold (Au), silver (Ag), platinum group elements [ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium ( Ir), platinum (Pt)] and the like. At least one of these is carried inside the partition wall. Preferably, rhodium (Rh) or palladium (Pd), which has higher catalytic performance than platinum (Pt), is supported inside the partition walls.

(2) It is preferable that the combustion promoting catalyst is also supported on a layer formed inside the partition wall. In other words, it is preferable that the combustion-promoting catalyst is supported on the upstream side inside the partition wall at a high density.
(3) The carrier is a wall-flow carrier having inlet cells and outlet cells, and the combustion-promoting catalyst is in a range in which the distance to the inlet cells in the layer formed inside the partition wall is equal to or less than a predetermined value. It is preferably carried within. For example, when the interior of the partition wall is partitioned at the center in the thickness direction, the combustion promoting catalyst may be supported on the side closer to the inlet cell.

(4) It is preferable that the layer formed on the surface of the partition wall includes an inlet upstream portion provided on the upstream side of the surface of the partition wall facing the inlet cell and supporting the combustion promoting catalyst.
(5) It is preferable that the layer formed on the surface of the partition wall has an outlet downstream portion provided on the downstream side of the surface of the partition wall facing the outlet cell and supporting the noble metal.
(6) It is preferable that the upstream portion of the inlet and the downstream portion of the outlet are arranged so as to overlap each other in the vertical direction in a side view.

(7) It is preferable that the layer formed inside the partition wall contains a nitrogen oxide trapping catalyst for trapping nitrogen oxides. Specific examples of the nitrogen oxide trap catalyst include alkali metals and alkaline earth metals. Examples include barium (Ba), potassium (K), rubidium (Rb), strontium (Sr), cesium (Cs), francium (Fr), and radium (Ra).

(8) It is preferable that the nitrogen oxide trap catalyst is supported at a higher density on the downstream side than on the upstream side.
(9) It is preferable that the nitrogen oxide trapping catalyst contains barium and potassium, and that the content ratio of potassium relative to the entire nitrogen oxide trapping catalyst is set higher on the downstream side than on the upstream side.

By supporting the combustion-promoting catalyst at a high density on the upstream side, PM (particulate matter) can be efficiently burned, and the exhaust gas purification performance can be efficiently improved.

It is a figure which shows the inside of the vehicle to which the exhaust gas purification apparatus was applied. Fig. 3 is a cross-sectional view showing the structure of a carrier of the exhaust gas purifying device; FIG. 3 is an enlarged cross-sectional view showing the internal structure of the carrier (part A in FIG. 2); 4 is a graph showing the relationship between the loading density of noble metals and the purification efficiency of hydrocarbon components. 4 is a graph for explaining the NOx conversion efficiency of barium and potassium. 4 is a graph for explaining the distribution of the supported density of the PM combustion promoting catalyst. 4 is a graph for explaining the distribution of loading density of the NOx trap catalyst. It is a graph for demonstrating the content rate of barium and potassium. (A) to (C) are graphs for explaining changes in pressure loss, purification performance, and PM collection efficiency when the catalyst coverage ratio on the outlet cell side is changed. (A) to (C) are graphs for explaining changes in pressure loss, purification performance, and PM collection efficiency when the catalyst coverage ratio on the inlet cell side is changed.

[1. Constitution]
Hereinafter, an exhaust gas purifier as an embodiment will be described with reference to the drawings. As shown in FIG. 1, the exhaust gas purifier 3 of the present invention is applied to a vehicle 10 equipped with an engine 1 (internal combustion engine). The type of engine 1 may be a diesel engine or a gasoline engine. It should be noted that the exhaust gas purifier 3 of this case is suitable for a gasoline engine capable of lean burn operation.

The exhaust gas purification device 3 is interposed in the exhaust passage 2 of the engine 1 . The exhaust gas purification device 3 is a catalyst device for efficiently purifying various harmful components contained in the exhaust gas, and has a function as a three-way catalyst, a function as a nitrogen oxide (NOx) storage reduction catalyst, and a PM removal filter. It also has the function as For example, as shown in FIG. 1, the exhaust gas purification device 3 may be arranged at a position close to the engine 1 (directly downstream of the exhaust manifold, directly downstream of the supercharger, etc.), It may be set at a position away from the engine 1 . Further, a three-way catalytic converter may be provided separately upstream or downstream of the exhaust gas purifying device 3 to improve the exhaust gas purifying performance.

Inside the exhaust gas purification device 3, there is provided a porous body in which a large number of flow paths through which the exhaust gas can pass are formed. The porous body is a catalyst 9 supported on a porous carrier 7, and is formed in the shape of a cylinder, an elliptical cylinder, or a rectangular parallelepiped. The material of the carrier 7 may be ceramics such as silicon carbide or cordierite (cordierite), or metal. The higher the porosity of the carrier 7, the better. The carrier 7 of the present embodiment has a porosity of more than 50 [%] and a pore volume of more than 0.2 [mL/g] for pores having a diameter of 1 [μm] or more.

Examples of the base material for supporting the catalyst 9 on the carrier 7 include aluminum oxide (alumina, Al ₂ O ₃ ), cerium oxide (ceria, CeO ₂ ), and zirconium oxide (zirconia, ZrO ₂ ). The base material may contain an oxygen storage material that stores oxygen in a reducing environment. Examples of oxygen storage materials include ceria-zirconia composite solid solutions (CeO ₂ —ZrO ₂ -based materials) and rare earth oxysulfates (Ln ₂ O ₂ SO ₄ ).

The structure of the porous body to be installed in the exhaust gas purifier 3 may be of a wall-flow type or a straight type. In this embodiment, a wall-flow type as shown in FIG. 2 will be described in detail. The inside of the carrier 7 is divided into a plurality of cells (small chamber-like passages) along the flow direction of the exhaust gas, and each cell is partitioned by porous partition walls 6 (ribs). Each cell is closed with a plug 8 at either the inlet side or the outlet side. A cell with a closed end on the outlet side is called an inlet cell 4 , and a cell with a closed end on the inlet side is called an outlet cell 5 .

Each inlet cell 4 is arranged adjacent to at least one or more outlet cells 5 and preferably adjacent to multiple outlet cells 5 . As a result, the exhaust gas that has flowed in from the inlet end face 11 of the carrier 7 first enters the inlet cell 4, passes through the partition wall 6, enters the outlet cell 5, and flows out from the outlet end face 12 of the carrier 7. do. In other words, all the exhaust gas passes through the inside of the partition wall 6, improving the PM collection efficiency.

The carrier 7 carries a catalyst 9 of a type corresponding to its site. First, different catalysts 9 are supported inside and on the surface of the partition walls 6 . Here, the inside of the partition wall 6 is called the "partition wall interior 13". As shown in FIG. 3, the partition wall interior 13 is divided into two regions, one near the entrance cell 4 and one near the exit cell 5 . The former is a portion where the distance to the partition wall surface (or the entrance cell 4) on the side of the entrance cell 4 is equal to or less than a predetermined value T, and the latter is a portion where the distance to the entrance cell 4 exceeds the predetermined value T. The value of the predetermined value T is arbitrary, and is set so as to satisfy the relationship "T≦0.5T _WALL ", where T _WALL is the thickness of the partition wall 6 . Hereinafter, the side of the partition wall interior 13 closer to the inlet cell 4 will be referred to as the "inner inlet side 14", and the side closer to the outlet cell 5 will be referred to as the "inner outlet side 15".

Different catalyst layers are formed on the surfaces of the partition walls 6 on the inlet cell 4 side and the outlet cell 5 side. As shown in FIGS. 2 and 3 , an inlet upstream portion 16 is provided on the upstream side of the partition surface of the carrier 7 facing the inlet cell 4 . The inlet upstream portion 16 is provided so as to cover a range from the inlet end surface 11 to the front of the innermost portion of the inlet cell 4 . That is, the catalyst 9 is not carried on the outlet end face 12 side of the inlet upstream portion 16 of the partition wall surfaces facing the inlet cells 4 . The length L ₁ of the inlet upstream portion 16 in a side view satisfies at least the relationship of “0<L ₁ <L _UP ” with respect to the total length L _UP of the inlet cell, preferably “0.5 L _UP ≦L ₁ <0.75 L _UP " is set to satisfy the relationship.

As shown in FIG. 3, the inlet upstream portion 16 may have a multilayer structure including a base layer 17 and a surface layer 18 . In this case, the surface layer 18 is the surface of the inlet upstream portion 16 in contact with the inlet cell 4, or a portion close to the surface (the portion whose distance to the surface is equal to or less than the second predetermined value). The base layer 17 is a portion positioned closer to the carrier 7 than the surface layer 18 and is preferably provided so as to contact the carrier 7 . In the example shown in FIG. 3, the portion other than the surface layer 18 is the base layer 17 . In such a multi-layer structure, it is preferable to support different catalysts 9 on the base layer 17 and the surface layer 18 .

Further, an outlet downstream portion 19 is provided on the downstream side of the partition wall surface of the carrier 7 facing the outlet cell 5 . The outlet downstream portion 19 is provided so as to cover the range from the outlet end surface 12 to the front of the outlet cell 5 from the innermost portion. That is, the catalyst 9 is not carried on the inlet end face 11 side of the outlet downstream portion 19 of the partition wall surfaces facing the outlet cells 5 . The length L2 of the outlet downstream portion 19 in a side view satisfies the relationship of at least " ₀ <L2<_{LDOWN" with respect to the total length LDOWN of the} outlet cell, preferably " _{0.5LDOWN≤L2} <0.75" _. is set so as to satisfy the relationship of "L _DOWN ".

More preferably, as shown in FIGS. 2 and 3, the inlet upstream portion 16 and the outlet downstream portion 19 are arranged so as to vertically overlap each other in a side view. For example, the length L ₁ of the inlet upstream portion 16 is 60% of the total length L _UP of the inlet cell 4 in side view. Also, the length L ₂ of the outlet downstream portion 19 is 60% of the total length L _DOWN of the outlet cell 5 . In this case, the downstream end of the inlet upstream portion 16 and the upstream end of the outlet downstream portion 19 overlap vertically in FIGS. As a result, the amount of exhaust gas flowing out without passing near the inlet upstream portion 16 or the outlet downstream portion 19 is reduced, and the PM collection efficiency and the exhaust gas purification efficiency are improved.

Here, the types of the catalyst 9 supported on the carrier 7 will be described in detail.
A noble metal catalyst is carried in the inside 13 of the partition wall. Specific examples of noble metals include platinum group elements [platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh), osmium (Os), iridium (Ir)], gold (Au), silver (Ag ) and the like. Rhodium and palladium, which have higher catalytic performance than platinum, are preferably used. As shown in FIG. 4, rhodium and palladium have a higher catalytic activity (conversion efficiency for all hydrocarbons) per supported amount than platinum. Therefore, by using rhodium or palladium, exhaust gas purification performance can be efficiently improved. When rhodium is used, its supporting density is set to about 1.0 [g/L].

The inlet upstream portion 16 preferably carries silver (Ag), cerium oxide (CeO ₂ ), silver ceria (Ag/CeO ₂ ), rare-earth elements (REE), and the like. Silver and cerium oxide function as a PM combustion promoting material (combustion promoting catalyst), and can burn PM at a lower temperature than the noble metal carried in the partition wall interior 13 . Specific examples of other combustion accelerators include tin ceria (Sn/CeO ₂ ) and ceria zirconia (CeO ₂ /ZrO ₂ ). On the other hand, rare earth elements function as P/Zn traps (phosphorus and zinc traps) to suppress poisoning by phosphorus and zinc contained in the exhaust gas. When silver is used, its supporting density is set to about 2.0 [g/L].

When both the former (silver, cerium oxide, silver ceria) and the latter (rare earth elements) are supported on the inlet upstream portion 16, it is preferable to expose the portion containing the former to the inlet cell 4 side. For example, in the drawing shown in FIG. 3, it is preferable that the portion containing the rare earth element is the base layer 17 and the portion containing silver, cerium oxide, and silver ceria is the surface layer 18 . In this case, the surface layer 18 containing silver, cerium oxide, and silver ceria may be formed again by wash coating after the base layer 17 containing rare earth elements is formed by wash coating. By exposing silver and cerium oxide to the inlet cell 4 side, PM combustibility is improved. When either the former (silver, cerium oxide, silver ceria) or the latter (rare earth element) is carried on the inlet upstream portion 16, the inlet upstream portion 16 may have a single-layer structure instead of a multi-layer structure. good.

Specific examples of the rare earth elements here include scandium (Sc), yttrium (Y), lanthanides [lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium ( Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu)]. be done. By carrying at least one of these on the inlet upstream portion 16, the P/Zn trap performance is improved.

A noble metal is preferably supported on the outlet downstream portion 19 . Specific examples of the noble metal carried on the outlet downstream portion 19 include platinum group elements [platinum, palladium, ruthenium, rhodium, osmium, iridium], gold, and silver. The type of noble metal carried here may be the same as that carried in the partition wall interior 13, or may be different. Rhodium or palladium is preferably used. When rhodium is used, its supporting density is set to about 0.4 [g/L].

A NOx trap catalyst (nitrogen oxide trap catalyst) that temporarily stores and adsorbs NOx may be included in the inside 13 of the partition wall. Specific examples of NOx trap catalysts include alkali metals and alkaline earth metals. For example, barium (Ba), potassium (K), rubidium (Rb), strontium (Sr), cesium (Cs), francium (Fr), radium (Ra), etc., preferably barium and potassium are used together.

As shown in FIG. 5, potassium is more suitable than barium for purifying NOx at high temperatures, and is suitable for purifying exhaust gas in gasoline engines with high combustion temperatures. In addition, potassium has a higher NO2 trapping performance _than barium, and has a higher NOx purification efficiency. On the other hand, potassium is thermally unstable and may fall and scatter from the supporting position. In this case, the scattered potassium can inhibit the catalytic action of other catalysts and precious metals (three-way activity, especially THC purification performance). Therefore, it is preferable to use barium and potassium together.

Combinations of types of catalysts 9 and supporting positions are exemplified in Tables 1 to 8 below. Here, 64 examples (No. 1 to No. 64) are shown. "Pd/Rh" in the table means containing palladium and rhodium. In all embodiments, the diaphragm interior 13 contains a precious metal. Also, "Ag/CeO ₂ " in the table means that silver ceria, which is a PM combustion promoting catalyst, is included. Silver ceria is carried in the partition wall interior 13 and the inlet upstream section 16 (Nos. 2 to 16, 18 to 32, 34 to 48, 50 to 64).

"Ba/K" in the table means containing barium and potassium. Barium and potassium are carried on the partition wall interior 13, preferably at least on the interior outlet side 15 (Nos. 33-64). "REE" in the table means containing rare earth elements. Rare earth elements are carried in the inlet upstream portion 16 (No. , 39-40, 43-44, 47-48, 51-52, 55-56, 59-60, 63-64). If the inlet upstream portion 16 does not contain both silver ceria and rare earth elements, it is not necessary to form a two-layer structure (forming the base layer 17 and the surface layer 18).

Blanks in Tables 1 to 8 may be unsupported catalysts, or may be supported with some catalysts (eg, platinum, transition metal sulfates, alkali metal sulfates, etc.). However, at least for No. 1, No. 17, No. 33, and No. 49 inlet upstream portions 16, some kind of PM combustion promoting catalyst [for example, silver (Ag), cerium oxide (CeO ₂ ), tin ceria (Sn) /CeO ₂ ), ceria zirconia (CeO ₂ /ZrO ₂ ), etc.]. Therefore, all examples include some PM combustion promoting catalyst on carrier 7 .

Examples without barium and potassium are listed in Tables 1-4, and examples with barium and potassium are listed in Tables 5-8. Further, examples in which the outlet downstream portion 19 does not contain a noble metal are described in Tables 1 and 2, and examples in which the outlet downstream portion 19 contains a precious metal are described in Tables 3 to 8. Examples containing no silver ceria on the internal outlet side 15 are shown in Tables 1, 3, 5 and 7, while examples containing silver ceria on the internal outlet side 15 are shown in Tables 2, 4 and 7. It is described in Tables 6 and 8.

In all the above examples (Nos. 1 to 64), the PM combustion promoting catalyst is supported at a higher density on the upstream side than on the downstream side. The terms "upstream side" and "downstream side" as used herein refer to upstream (distribution source) and downstream (distribution destination) with respect to the flow direction of the exhaust gas. The following (A) to (G) are conceivable as specific techniques for setting the loading density of the PM combustion promoting catalyst, for example.

(A) In the inlet upstream portion 16, the surface layer 18 (upstream side) is supported at a higher density than the base layer 17 (downstream side).
(B) In the inside 13 of the partition wall, the particles are supported at a higher density on the inner inlet side 14 (upstream side) than on the inner outlet side 15 (downstream side).
(C) In the inlet upstream portion 16 and the partition wall inner portion 13, the carrier is carried so that the carrying density becomes lower in the order of the surface layer 18, the base layer 17, the inner inlet side 14, and the inner outlet side 15.

(D) In the surface layer 18 , the surface (upstream side) is supported at a higher density than the portion (downstream side) near the base layer 17 .
(E) In the base layer 17, the portion (upstream side) closer to the surface layer 18 is supported at a higher density than the portion (downstream side) farther from the surface layer 18.
(F) On the internal inlet side 14, the portion closer to the inlet cell 4 (upstream side) is supported at a higher density than the portion farther from the inlet cell 4 (downstream side).
(G) On the internal outlet side 15, the portion farther from the outlet cell 5 (upstream side) than the portion closer to the outlet cell 5 (downstream side) is supported at a higher density.

FIG. 6 is a graph showing a setting example of the loading density of the PM combustion promoting catalyst. The dashed lines in FIG. 6 correspond to the settings according to (A) and (D) above. 6 correspond to the settings according to (B) and (F) above, and the thick solid lines correspond to the settings according to (C) to (G) above. In this way, by making the carrying density of the PM combustion promoting catalyst carried on the upstream side where PM tends to accumulate higher than that on the downstream side, the PM is uniformly burned on the upstream side and the downstream side of the carrier 7. easier. This makes it easier to incinerate the PM deposited in various places on the carrier 7 in the same incineration time, thereby preventing local overheating.

Further, in the above examples (Nos. 33 to 64) containing barium and potassium as the NOx trap catalyst, the NOx trap catalyst may be supported at a higher density downstream than at the upstream side. Specific techniques for setting the loading density of the NOx trap catalyst include, for example, the following (H) to (J).

(H) In the inside 13 of the partition wall, the particles are supported at a higher density on the inner outlet side 15 (downstream side) than on the inner inlet side 14 (upstream side).
(I) On the internal outlet side 15, the portion closer to the outlet cell 5 (downstream side) than the portion farther from the outlet cell 5 (upstream side) is supported at a higher density.
(J) On the internal inlet side 14, the portion farther from the inlet cell 4 (downstream side) than the portion closer to the inlet cell 4 (upstream side) is supported at a higher density.

FIG. 7 is a graph showing setting examples of loading density of the NOx trap catalyst. The dashed line in FIG. 7 corresponds to the setting according to (H) above, the dashed-dotted line corresponds to the setting according to (H) to (I) above, and the solid line corresponds to (H) to (J) above. corresponds to the setting according to In this way, NOx slip is effectively suppressed by setting the carrying density of the NOx trap catalyst carried inside the partition wall 13 higher on the downstream side than on the upstream side.

The content ratio of barium and potassium may be changed for each part of the carrier 7 as shown in FIG. That is, the content of barium may be set high on the upstream side and low on the downstream side. In other words, the potassium content may be set low on the upstream side and high on the downstream side. Such a setting suppresses deterioration of other catalytic actions due to scattering of potassium.

[2. Action/effect]
9A to 9C, the length L ₁ of the inlet upstream portion 16 is fixed to half (50%) of the total length L _UP of the inlet cell 4, and the length L ₂ of the outlet downstream portion 19 is changed from zero to 5 is a graph showing how pressure loss, exhaust gas purification performance, and PM collection efficiency change when the total length L _DOWN of the outlet cell 5 is changed (from 0% to 100%).

The pressure loss can be suppressed to a relatively small value by setting the length L2 of the outlet downstream portion 19 to 70 to 80% or less of the _total length _LDOWN . Further, the purification performance and PM collection efficiency are rapidly increased by making the length L2 of the outlet downstream portion 19 half or more of the _total length _LDOWN . Therefore, the preferable range of the length L2 of the outlet downstream portion 19 is considered to be _{approximately 0.5LDOWN≤L2} < _{0.75LDOWN .} The dashed lines in FIGS. 9A to 9C show the pressure loss, the exhaust gas purification performance, and the PM collection efficiency when the amount of noble metal carried inside the partition wall 13 is increased. Thus, even when the outlet downstream portion 19 is not formed over a wide range extending over the entire length L _DOWN of the outlet cell 5, good exhaust gas purification performance can be maintained by increasing the amount of noble metal carried in the partition wall interior 13. .

10(A) to (C), the length L ₂ of the outlet downstream portion 19 is fixed to half (50%) of the total length L _DOWN of the outlet cell 5, and the length L ₁ of the inlet upstream portion 16 is changed from zero to 4 is a graph showing how the pressure loss, exhaust gas purification performance, and PM collection efficiency change when the total length L _UP of the inlet cell 4 is changed (from 0% to 100%). By setting the length L ₁ of the inlet upstream portion 16 to 70 to 80% or less of the total length L _DOWN , it is possible to keep the pressure loss small. Further, the purification performance and the PM collection efficiency sharply increase by setting the length L1 of the inlet upstream portion 16 to _half or more of the total length _LUP . Therefore, the preferable range of the length L1 of the inlet upstream portion 16 is considered to be _{about 0.5LUP≤L1 < 0.75LUP} .

(1) As shown in FIG. 6, by supporting the PM combustion promoting catalyst at a high density on the upstream side, PM can be efficiently burned, and the exhaust gas purification performance can be efficiently improved. In particular, rapid ignition can be promoted on the upstream side where PM tends to accumulate, and combustion can be easily triggered. As a result, the PM can be uniformly burned on the upstream side and the downstream side of the carrier 7, and the incineration time on the upstream side and the downstream side can be substantially the same. As a result, local overheating can be prevented, and the exhaust gas purification performance can be efficiently improved.

(2) As shown in Nos. 5 to 16, 21 to 32, 37 to 48, and 53 to 64 in Tables 1 to 8, PM combustion promoting catalyst is deposited in the partition wall interior 13 by supporting it in the partition wall interior 13. PM can be burned at a lower temperature. Therefore, the PM combustion efficiency can be enhanced, and clogging due to PM and an increase in pressure loss can be prevented.
(3) PM combustion efficiency can be further increased by carrying a PM combustion promotion catalyst on the inner inlet side 14 where PM tends to accumulate inside the partition wall 13 .

(4) By supporting the PM combustion promoting catalyst in the inlet upstream portion 16 where the probability of contact with PM in the exhaust gas is the highest, the PM combustion efficiency can be further increased and, for example, the carrier 7 can be quickly removed immediately after cold start. can be heated to In addition, it becomes possible to burn PM before it enters the partition wall interior 13, and the pressure loss in the exhaust passage 2 can be reduced. Therefore, comprehensive exhaust gas purification performance can be enhanced.

(5) As shown in Nos. 17 to 64 in Tables 3 to 8, by including a noble metal catalyst in the outlet downstream portion 19, the NOx reduction efficiency on the outlet cell 5 side can be increased. As a result, the slip amount of NOx from the exhaust gas purifying device 3 can be reduced, and the exhaust gas purifying performance can be efficiently improved.

(6) As shown in FIGS. 2 and 3, by vertically overlapping the inlet upstream portion 16 and the outlet downstream portion 19 in a side view, PM collection efficiency and exhaust gas purification efficiency can be enhanced. _The length L1 of the inlet upstream portion 16 is set within the range of 0.5L _UP ≤ L1 < _{0.75L UP} , and the length L2 of the outlet downstream portion 19 is set to _{0.5L DOWN} ≤ L2 < _{0.75L DOWN.} If it is set within the range of , as shown in FIGS. 9 and 10, the purification performance and the PM collection efficiency can be maintained at a high level without excessively increasing the pressure loss.

(7) As shown in Nos. 33 to 64 in Tables 5 to 8, the NOx storage amount of the partition wall interior 13 can be increased by including the NOx trap catalyst (barium and potassium) in the partition wall interior 13. . In addition, since the inside 13 of the partition wall also contains a noble metal, NOx occluded by barium or potassium can be easily reduced in situ, and the NOx purification efficiency can be enhanced.

(8) As shown in FIG. 7, by supporting the NOx trap catalyst at a high density on the downstream side, it is possible to more reliably capture NOx that is about to slip from the exhaust gas purification device 3, and effectively prevent NOx slip. can be suppressed to Therefore, the slip amount of NOx from the exhaust gas purifying device 3 can be reduced, and the exhaust gas purifying performance can be efficiently improved.

(9) As shown in FIG. 8, by setting the potassium loading ratio on the downstream side to be high, scattering of potassium can be suppressed and deterioration of other catalytic actions due to scattering can be prevented. Therefore, exhaust gas purification performance can be efficiently improved. In addition, since barium is supported on the upstream side of potassium, it is possible to improve the NOx trapping performance at low temperatures.

[3. Modification]
The above embodiment is merely an example, and there is no intention to exclude various modifications and application of techniques not explicitly described in this embodiment. Each configuration of this embodiment can be modified in various ways without departing from the gist thereof. Also, they can be selected or combined as needed.

Although the vehicle 10 equipped with the engine 1 is illustrated in the above-described embodiment, the application target of this case is not limited to the vehicle 10 . The exhaust gas purifying device 3 can be installed in the exhaust passage 2 of the engine 1 mounted on a ship, an aircraft, or the like, for example. Alternatively, it can be used as an exhaust gas purification device 3 for an engine 1 built in a generator or industrial machine.

1 engine (internal combustion engine)
2 Exhaust passage 3 Exhaust gas purifying device 4 Inlet cell 5 Outlet cell 6 Partition wall 7 Carrier 8 Plugging 9 Catalyst 10 Vehicle 11 Inlet end face 12 Outlet end face 13 Inner partition wall 14 Inner inlet side 15 Inner outlet side 16 Inlet upstream portion 17 Base layer 18 Surface layer 19 Exit downstream

Claims (9)

In an exhaust gas purification device that collects and burns particulate matter contained in exhaust gas from an internal combustion engine,
comprising a septum of the carrier;
The partition has a layer formed on the surface of the partition and a layer formed inside the partition,
A noble metal is supported on a layer formed inside the partition wall,
The layer formed on the surface of the partition wall carries a combustion promotion catalyst capable of promoting combustion of the particulate matter and burning the particulate matter at a lower temperature than the noble metal,
The combustion promoting catalyst is supported at a higher density on the upstream side than on the downstream side in the layer formed on the surface of the partition wall.
An exhaust gas purifying device characterized by: 2. An exhaust gas purifier according to claim 1, wherein said combustion promoting catalyst is also supported on a layer formed inside said partition wall. The carrier is a wall-flow carrier having inlet cells and outlet cells,
3. An exhaust gas purifying apparatus according to claim 2, wherein said combustion promoting catalyst is supported in a layer formed inside said partition wall within a range in which the distance to said inlet cell is equal to or less than a predetermined value. 3. The layer formed on the surface of the partition wall includes an inlet upstream portion provided on the upstream side of the surface of the partition wall facing the inlet cell and supporting the combustion promoting catalyst. 3. The exhaust gas purifier according to 3. 3. The layer formed on the surface of the partition wall has an outlet downstream portion provided on the surface of the partition wall facing the outlet cell and on the downstream side and supporting the noble metal. 5. The exhaust gas purifier according to 4. 6. An exhaust gas purifying apparatus according to claim 5, depending on claim 4, wherein said inlet upstream portion and said outlet downstream portion are arranged so as to vertically overlap with each other in a side view. 7. The exhaust gas purifier according to claim 1, wherein the layer formed inside the partition wall contains a nitrogen oxide trapping catalyst for trapping nitrogen oxides. 8. An exhaust gas purifier according to claim 7, wherein said nitrogen oxide trap catalyst is supported at a higher density on the downstream side than on the upstream side. 9. The nitrogen oxide trapping catalyst according to claim 7, wherein said nitrogen oxide trapping catalyst contains barium and potassium, and the content ratio of said potassium with respect to the entire nitrogen oxide trapping catalyst is set higher on the downstream side than on the upstream side. exhaust gas purification equipment.

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