WO2019059032A1

WO2019059032A1 - Exhaust gas purification filter

Info

Publication number: WO2019059032A1
Application number: PCT/JP2018/033529
Authority: WO
Inventors: 知弘足立; 一樹白田
Original assignee: パナソニックＩｐマネジメント株式会社
Priority date: 2017-09-21
Filing date: 2018-09-11
Publication date: 2019-03-28

Abstract

An exhaust gas purification filter comprises a porous filter base material having a plurality of cells demarcated by cell walls, a PM combustion catalyst layer including a PM combustion catalyst that combusts and purifies PM, and a NOx reduction catalyst layer including a NOx reduction/removal catalyst that reduces and purifies NOx. The PM combustion catalyst layer comprises part or all of the surface of the cell walls on the side at which exhaust gas flows in. The NOx reduction catalyst layer comprises part or all of the surface of the cell walls on the side at which the exhaust gas flows out. The PM combustion catalyst is configured as a molten salt catalyst which includes a composite oxide of cesium and vanadium and in which the molar ratio (Cs/V) of cesium to vanadium is 0.5 ≤ Cs/V ≤ 1.5, whereby there is obtained an exhaust gas purification filter has both high PM combustion performance and high NOx reduction performance.

Description

Exhaust gas purification filter

The present invention relates to an exhaust gas purification filter used to purify the exhaust gas of an internal combustion engine such as a diesel engine.

Exhaust gas from diesel engines contains particulate matter (PM: Particulate Matter) such as solid carbon particulates, liquid or solid high molecular weight hydrocarbon particulates, and nitrogen oxides (NOx) as harmful components. . Various methods for removing these have been studied.

One method of removing PM is to use a heat-resistant exhaust gas purification filter (DPF: Diesel Particulate Filter) such as ceramic honeycomb, ceramic foam, metal foam or the like. In this method, the DPF collects PM. In the DPF, pressure loss increases as PM is collected. Therefore, when the pressure loss of the DPF rises, it is necessary to regenerate the DPF. In the regeneration of the DPF, the DPF is heated by a burner or a heater to burn the deposited PM, convert it to carbon dioxide gas, and release it to the outside.

There are other ways to regenerate the DPF. The catalyst is supported on the DPF, and the PM is burned by the catalytic action. In this method, the combustion operation by a burner or a heater can be reduced. For example, when the PM combustion catalyst is supported in advance on the DPF made of heat resistant ceramic, it is possible to carry out the combustion reaction as well as the PM collection. From the viewpoint of PM combustion performance (performance of burning PM at a low temperature) and durability, platinum group metals such as platinum and palladium are widely used as PM combustion catalysts.

Further, the method of removing NOx is to perform selective catalytic reduction (SCR) using a reducing agent. In this method, mainly, an SCR filter in which a NOx reduction and removal catalyst is supported on a filter base made of a ceramic honeycomb, and ammonia as a reducing agent are used. Then, when the exhaust gas passes through the SCR filter, on the SCR filter, ammonia reduces NOx contained in the exhaust gas and converts it to nitrogen. That is, NOx is removed from the exhaust gas that has passed through the SCR filter. Urea water is generally used as a source of ammonia. Urea water can be supplied upstream of the SCR filter to hydrolyze urea in the exhaust gas to produce ammonia.

In order to meet strict exhaust gas standards, diesel engine exhaust gas purification systems often include a DPF having a function of collecting PM and an SCR filter having a function of purifying NOx separately as described above ( For example, refer to Patent Document 1).

Such an exhaust gas purification system is expensive and has a problem that the volume occupied by the system is large. Therefore, there is an increasing demand for cost reduction and downsizing of the exhaust gas purification system. In order to meet these needs, there is disclosed an SCRF (SCR on Filter) in which a DPF carries an PM combustion catalyst and an SCR catalyst for reducing and removing NOx (see, for example, Patent Document 2).

In such SCRF, although the NOx reduction and removal catalyst is supported on the filter substrate, it is necessary to consider the combination of the NOx reduction and removal catalyst and the PM combustion catalyst when supporting up to the PM combustion catalyst.

The reason is that the combined use of the NOx reduction and removal catalyst and the PM combustion catalyst impairs the function of reducing and removing NOx. More specifically, a platinum group metal used as a PM combustion catalyst has a strong oxidizing action, and thus oxidizes ammonia. In SCRF, even if ammonia is supplied from the upstream side, the function of reducing and removing NOx is impaired by the platinum group metal used for the PM combustion catalyst.

That is, no consideration was given to burning the PM deposited on the filter at a lower temperature using the PM combustion catalyst that does not impair the function of reducing and removing NOx.

Therefore, an object of the present invention is to provide an exhaust gas purification filter having high PM combustion performance that can be burned at a lower temperature and NOx reduction performance in one filter substrate.

JP 2014-224536 A JP, 2015-186802, A

In the conventional SCRF, it is necessary to burn the PM deposited on the filter at a very high temperature.

The present invention comprises a porous filter base having a plurality of cells partitioned by cell walls, a PM combustion catalyst which burns and purifies PM, and an NOx reduction and removal catalyst which reduces and purifies NOx. There is. In addition, the PM combustion catalyst forms a PM combustion catalyst layer included in part or all of the surface of the cell wall on the side where the exhaust gas flows. Further, the NOx reduction and removal catalyst forms a NOx reduction catalyst layer contained in part or all of the surface of the cell wall on the side where the exhaust gas flows out. In addition, the PM combustion catalyst is a molten salt type catalyst including a composite oxide of cesium and vanadium in which the molar ratio of cesium to vanadium (Cs / V) is 0.5 ≦ Cs / V ≦ 1.5.

The molten salt type catalyst containing a composite oxide of cesium and vanadium is a direct oxidation type catalyst that burns PM using oxygen in the gas phase. In addition, the molten salt catalyst melts in the vicinity of the reaction temperature with PM and becomes a liquid phase. Therefore, in the combustion of PM involving catalyst (solid) -PM (solid) -oxygen (gas), when the catalyst becomes a liquid phase, the contact with PM increases dramatically, and high PM combustion performance is expressed. It is considered. Further, the composite oxide of cesium and vanadium is characterized in that the interaction with ammonia acting as a reducing agent in the NOx reduction reaction is weak. Therefore, in a temperature range where the exhaust gas temperature is relatively low, ammonia can be supplied to the NOx reduction catalyst layer located downstream of the exhaust gas flow without being oxidized, and NOx reduction performance can be exhibited.

As a result, it is possible to provide an exhaust gas purification filter having both high PM combustion performance and NOx reduction performance.

FIG. 1 is a cross-sectional view showing a part of an exhaust gas purification filter according to a first embodiment of the present invention. FIG. 2 is a cross-sectional view showing a part of an exhaust gas purification filter according to a second embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

First Embodiment
One embodiment of the present invention will be described with reference to the attached drawings.

As shown in FIG. 1, the exhaust gas purification filter 1 is provided, for example, in an exhaust passage (not shown) of an internal combustion engine such as a diesel engine, and collects particulate matter (hereinafter referred to as PM) in exhaust gas. It is a thing. On the upstream side of the exhaust gas purification filter 1, a reducing agent supply device (not shown) can be disposed.

The exhaust gas purification filter 1 has a porous filter base 4 having a plurality of cells 3 partitioned by cell walls 2, a PM combustion catalyst layer 5 including a PM combustion catalyst for burning and purifying PM, and NOx. And the NOx reduction catalyst layer 6 including the NOx reduction removal catalyst to be purified.

The filter substrate 4 is a wall flow type structure. That is, a plurality of cells 3 partitioned by the cell walls 2 are provided, and the end portions of adjacent cells 3 are alternately sealed. Thus, two types of cells 3 are adjacent to each other via the cell wall 2. The first is the exhaust gas inflow side cell 3 which is open at the upstream side of the exhaust gas and the downstream side is closed. The second is the exhaust gas outlet side cell 3 in which the upstream side of the exhaust gas is blocked and the downstream side is open.

The PM combustion catalyst layer 5 is provided on the entire surface of the cell wall 2 on the side where the exhaust gas flows. Further, the NOx reduction catalyst layer 6 is provided on the entire surface of the cell wall 2 on the exhaust gas outflow side.

That is, the exhaust gas purification filter 1 has the PM combustion catalyst layer 5 disposed on the upstream side and the NOx reduction catalyst layer 6 disposed on the downstream side across the cell wall 2.

The exhaust gas purification filter 1 can circulate the exhaust gas through the pores provided in the cell wall 2 of the filter substrate 4. The exhaust gas contains harmful substances such as PM and NOx. Among these, PM is collected by the inside and the surface of the cell wall 2 on the side where the exhaust gas flows in, and further by the PM combustion catalyst layer 5. The NOx in the exhaust gas moves to the downstream side of the filter substrate 4 through the pores of the cell wall 2. When the exhaust gas passes through the exhaust gas purification filter 1, when a reducing agent such as ammonia is supplied from the upstream side of the exhaust gas purification filter 1, NOx is reduced and removed by the NOx reduction catalyst contained in the NOx reduction catalyst layer 6. At the time of filter regeneration treatment, PM in the collected exhaust gas is burned and removed promptly by the PM combustion catalyst contained in the PM combustion catalyst layer 5.

The exhaust gas purification filter 1 of the present embodiment particularly has the following configuration.

The material of the filter substrate 4 may be a porous material made of heat-resistant ceramic, metal material or the like. As heat resistant ceramics, silicon carbide (SiC), cordierite, silicon nitride, aluminum titanate etc. can be used, for example. As the metal material, for example, a stainless alloy, an Fe-Cr-Al alloy or the like can be used. Among these, silicon carbide or cordierite is preferable from the viewpoint of heat resistance and catalyst coatability.

The average pore diameter of the pores provided in the cell wall 2 is not particularly limited. For example, by setting the average pore diameter to 5 μm to 50 μm, it is possible to efficiently collect PM while suppressing an excessive increase in pressure loss at the time of PM deposition.

The cross-sectional shape of the cell 3 is not particularly limited. From the viewpoint of increasing the contact area between the catalyst and PM, it is preferable to use any one of four to octagonal shapes.

Further, the formation density of the cells 3 is not particularly limited. Similarly to the above, the number of cells 3 is preferably 200 to 400 cells per square inch from the viewpoint that the contact area between the catalyst and PM can be increased. By setting the number of cells to 200 cells or more, the contact area between the catalyst and PM can be sufficiently secured. Further, by setting the number of cells to 400 cells or less, clogging due to PM deposition on the cells 3 can be less likely to occur.

Further, the PM combustion catalyst of the present embodiment is a molten salt type catalyst including a composite oxide of cesium and vanadium (hereinafter, described as a Cs-V composite oxide). The molar ratio of cesium to vanadium (Cs / V) is 0.5 ≦ Cs / V ≦ 1.5. The molten salt type catalyst containing the Cs-V complex oxide is a direct oxidation type catalyst that burns PM using oxygen in the gas phase. In addition, the molten salt catalyst melts in the vicinity of the reaction temperature with PM and becomes a liquid phase. Therefore, in the combustion of PM involving catalyst (solid)-PM (solid)-oxygen (gas), the catalyst is in a liquid phase, the contact with PM is dramatically increased, and PM combustion in a low temperature range It can be performed. From the above, it is considered that the molten salt type catalyst containing the Cs-V complex oxide exhibits high PM combustion performance.

As the above-mentioned Cs-V complex oxide, for example, Cs ₂ V ₄ O ₁₁ (Cs: V = 0.5: 1.0), CsVO ₃ (Cs: V = 1.0: 1.0), Cs ₅ V ₃ O ₁₀ (Cs: V = 1.7: 1.0), Cs ₃₂ V ₁₈ O ₆₁ (Cs: V = 1.8: 1.0), Cs ₄ V ₂ O ₇ (Cs: V = 2.0: 1.0), Cs ₃ VO ₄ (Cs: V = 3.0: 1.0), and the like. Among these, from the viewpoint of PM combustion activity and chemical stability, Cs ₂ V ₄ O ₁₁ where the molar ratio of cesium to vanadium (Cs / V) is Cs / V = 0.5, or Cs / V = 1. preferably comprises a CSVO ₃ is 0.

Further, the PM combustion catalyst preferably includes a carrier for holding the Cs-V complex oxide. Although the Cs-V complex oxide alone has high PM flammability, there is a concern that the contact ratio between PM and the catalyst is lowered due to the low specific surface area of the catalyst, and the combustion reaction is unlikely to occur. In addition, when the carrier is not used, there is a concern that aggregation easily occurs under the influence of temperature and composition fluctuation of the exhaust gas, and PM combustion activity decreases. Therefore, by holding the Cs-V complex oxide in contact with the surface of the carrier, the specific surface area of the Cs-V complex oxide can be increased to suppress aggregation in a high temperature atmosphere. As the carrier, for example, Al ₂ O ₃ , SiO ₂ , TiO ₂ , CeO ₂ , ZrO ₂ , CeO ₂ -ZrO ₂ , MgO or the like can be used.

The thickness of the PM combustion catalyst layer 5 is preferably 10 μm or more and 50 μm or less. By setting the thickness of the PM combustion catalyst layer 5 to 10 μm or more, the amount of inflowing PM can be reduced to the inside of the cell wall 2. That is, by reducing the rate of depth filtration (filtration inside the cell wall 2) in the PM deposition process, it is possible to suppress an increase in pressure loss during PM deposition. Further, by setting the thickness of the PM combustion catalyst layer 5 to 50 μm or less, the adhesion between the surface of the cell wall 2 and the PM combustion catalyst layer 5 can be secured while keeping the initial pressure loss after the catalyst coating low.

In the present embodiment, the PM combustion catalyst layer 5 is provided on the entire surface of the cell wall 2 on the side where the exhaust gas flows, but may be provided on a part of the surface. In the case of providing them all, although the entire area of the surface of the cell wall 2 can be catalyzed, it may cause an increase in pressure loss. Therefore, the PM combustion performance of the exhaust gas purification filter 1 and the pressure can be reduced by making the length of the PM combustion catalyst layer 5 shorter than the length (depth) of the cell 3 and providing it on a part of the surface of the cell wall 2 It is preferable to adjust the balance of losses.

In addition, a part of the PM combustion catalyst may enter into the cell wall 2. Thereby, the combustion of PM collected deep in the cell wall 2 can be promoted. However, if a large amount of PM combustion catalyst enters the inside of the cell wall 2, pressure loss increases, so it is necessary to adjust the amount of PM combustion catalyst that enters inside.

In addition, the Cs-V complex oxide can promote the PM combustion reaction utilizing oxygen in the gas phase in a temperature range lower than that in the case of using a platinum group metal. That is, it can be said that high PM combustion performance is exhibited.

It also has a feature that the interaction with ammonia acting as a reducing agent in the NOx reduction reaction is weak. That is, ammonia is less oxidized by the Cs-V complex oxide in a relatively low temperature range. When combined with the high PM twisting performance of the Cs-V complex oxide, even if a reducing agent such as ammonia is supplied on the upstream side of the exhaust gas purification filter 1, it is supplied to the NOx reduction catalyst layer 6 located downstream of the exhaust gas flow. The NOx reduction performance can be demonstrated.

As the NOx reduction catalyst contained in the NOx reduction catalyst layer 6, those already known can be used. For example, a zeolite containing a base metal component selected from one or more of V ₂ O ₅ -TiO ₂ -WO ₃ , TiO ₂ -WO ₃ , copper and iron components can be used. Among them, zeolite containing a copper component is preferable from the viewpoint of NOx reduction performance and heat resistance.

In the present embodiment, the NOx reduction catalyst layer 6 is provided on the entire surface of the cell wall 2 on the side where the exhaust gas flows out, but may be provided on part of the surface. In the case of providing them all, although the entire area of the surface of the cell wall 2 can be catalyzed, it may cause an increase in pressure loss. By setting the length of the NOx reduction catalyst layer 6 shorter than the length (depth) of the cell 3 and providing it on a part of the surface of the cell wall 2, the NOx reduction performance of the exhaust gas purification filter 1 and the pressure loss You can also adjust the balance.

In addition, a part of the NOx reduction catalyst may enter into the cell wall 2. Thereby, when the exhaust gas passes through the inside of the cell wall 2, the reduction of NOx can be promoted. However, if a large amount of the NOx reduction catalyst enters the inside of the cell wall 2, this causes an increase in pressure loss, so it is necessary to adjust the amount of the NOx reduction catalyst introduced inside.

In the above configuration, PM in the exhaust gas flowing into the exhaust gas purification filter 1 is collected by the inside and the surface of the cell wall 2 on the side where the exhaust gas flows in, and further by the PM combustion catalyst layer 5.

The NOx in the exhaust gas flowing into the exhaust gas purification filter 1 moves to the downstream side of the filter substrate 4 through the pores of the cell wall 2 together with the reducing agent (ammonia) supplied from the upstream side of the exhaust gas purification filter 1. The NOx in the exhaust gas having moved to the downstream side of the filter substrate 4 is reduced and removed by the NOx reduction catalyst contained in the NOx reduction catalyst layer 6 provided on the surface of the cell wall 2 on the exhaust gas outflow side.

The collected PM is oxygen in the gas phase at a temperature range lower than that in the case of using a platinum group metal by the catalytic action of the Cs-V complex oxide contained in the PM combustion catalyst layer 5 at the time of filter regeneration treatment. React with it and burn off quickly.

As a result, in the exhaust gas purification filter 1, high PM combustion performance is exhibited in the cell 3 on the exhaust gas inflow side, and NOx reduction performance is exhibited in the cell 3 on the exhaust gas outflow side. That is, it is possible to provide the exhaust gas purification filter 1 having both high PM combustion performance and NOx reduction performance with one filter base 4.

Second Embodiment
In the configuration in which the NOx reduction catalyst is coated uniformly on the outlet side of the DPF, it was found that there is a case where a part of the gas has a short creepage distance in contact with the NOx reduction catalyst and can not effectively operate the NOx reduction catalyst. . Therefore, the configuration of an exhaust gas purification filter capable of further efficiently removing NOx will be described.

The exhaust gas purification filter 1 is, as shown in FIG. 2, a porous filter base 4 having a plurality of cells 3 partitioned by cell walls 2 and a particulate matter combustion catalyst for burning and purifying particulate matter. A PM combustion catalyst layer 5 that is a first catalyst layer that includes the catalyst and a NOx reduction catalyst layer 6 that is a second catalyst layer that includes a NOx reduction catalyst that reduces and purifies NOx are provided.

The PM combustion catalyst layer 5 is provided on part or all of the surface of the cell wall 2 on the side where the exhaust gas flows. Further, the NOx reduction catalyst layer 6 is provided on part or all of the surface of the cell wall 2 on the side where the exhaust gas flows out.

The exhaust gas purification filter 1 can circulate the exhaust gas through the pores provided in the cell wall 2 of the filter substrate 4.

The exhaust gas contains harmful substances such as particulate matter and NOx. Among them, particulate matter is collected by the inside and the surface of the cell wall 2 and further by the PM combustion catalyst layer 5. Further, NOx in the exhaust gas moves to the downstream side of the filter base 4 through the pores of the cell wall 2.

When allowing the exhaust gas to pass through the exhaust gas purification filter 1, the reducing agent such as ammonia is supplied from the upstream side of the exhaust gas purification filter 1 to make the NOx reduction catalyst contained in the NOx reduction catalyst layer 6 work to reduce and remove it. Can.

At the time of the filter regeneration process, the particulate matter in the exhaust gas collected in the PM combustion catalyst layer 5 is promptly burned and removed by the particulate matter combustion catalyst contained in the PM combustion catalyst layer 5.

The filter substrate 4 has a wall flow type structure, and includes a plurality of cells 3 partitioned by the cell walls 2, and the end portions of adjacent cells are alternately sealed. Thus, two types of cells 3 are adjacent to each other via the cell wall 2. The first is an exhaust gas inflow cell in which the upstream side of the exhaust gas is opened as the inlet 7 and the downstream side is closed to form the back 8. The second is an exhaust gas outflow cell in which the upstream side of the exhaust gas is closed to form a back 9 and the downstream side is opened as the outlet 10.

The material of the filter substrate 4 may be a porous material made of heat-resistant ceramic, metal material or the like. As heat resistant ceramics, silicon carbide (SiC), cordierite, silicon nitride, aluminum titanate etc. can be used, for example. As the metal material, for example, a stainless alloy, an Fe-Cr-Al alloy or the like can be used. Among these, silicon carbide is preferable from the viewpoint of heat resistance and catalyst coatability. The average pore diameter of the pores provided in the cell wall 2 is not particularly limited, but can be, for example, 5 μm to 50 μm. When the average pore size is 5 μm or more, an excessive increase in pressure loss can be suppressed even if particulate matter is deposited. In addition, when the average pore size is 50 μm or less, excessive loss of particulate matter can be suppressed. The cross-sectional shape of the cell 3 is not particularly limited, but is preferably any one of four to octagonal from the viewpoint that the contact area between the catalyst and the particulate matter can be increased.

The formation density of the cells 3 is not particularly limited, but the number of the cells 3 is preferably 200 to 400 cells per square inch from the viewpoint that the contact area between the catalyst and the particulate matter can be increased as described above. . By setting the number of cells to 200 cells or more, the contact area between the catalyst and the particulate matter can be sufficiently secured. In addition, by setting the number of cells to 400 cells or less, clogging due to particulate matter deposition on the cells 3 can be less likely to occur.

In addition, the particulate matter combustion catalyst of the present embodiment is a molten salt type catalyst including a composite oxide of cesium and vanadium (hereinafter, described as a Cs-V composite oxide). The molar ratio of cesium to vanadium (Cs / V) is 0.5 ≦ Cs / V ≦ 1.5. The molten salt type catalyst containing the Cs-V complex oxide is a direct oxidation type catalyst that burns particulate matter using oxygen in the gas phase. In addition, the molten salt catalyst melts in the vicinity of the reaction temperature with the particulate matter to form a liquid phase. Therefore, in the combustion of particulate matter involving catalyst (solid)-particulate matter (solid)-oxygen (gas), the catalyst becomes a liquid phase and contact with particulate matter is dramatically increased, which is high. It is believed to exhibit particulate matter combustion performance.

As the above-mentioned Cs-V complex oxide, for example, Cs ₂ V ₄ O ₁₁ (Cs: V = 0.5: 1.0), CsVO ₃ (Cs: V = 1.0: 1.0), Cs ₅ V ₃ O ₁₀ (Cs: V = 1.7: 1.0), Cs ₃₂ V ₁₈ O ₆₁ (Cs: V = 1.8: 1.0), Cs ₄ V ₂ O ₇ (Cs: V = 2.0: 1.0), Cs ₃ VO ₄ (Cs: V = 3.0: 1.0), and the like. Among them, from the viewpoint of particulate matter combustion activity and chemical stability, Cs ₂ V ₄ O ₁₁ where the molar ratio of cesium to vanadium (Cs / V) is Cs / V = 0.5, or Cs / V = It is preferred to include CsVO ₃ which is 1.0.

In addition, the particulate matter combustion catalyst preferably includes a carrier for retaining the Cs-V complex oxide. Although Cs-V complex oxide alone has high particulate matter combustibility, the contact ratio between particulate matter and catalyst decreases due to the low specific surface area of the catalyst, which may make it difficult to cause a combustion reaction. is there. In addition, in the case where the carrier is not used, there is a risk that aggregation may be easily performed and particulate matter combustion activity may be reduced under the influence of temperature and composition fluctuations of the exhaust gas. Therefore, by bringing the Cs-V complex oxide into contact with the surface of the carrier and holding it, aggregation in a high temperature atmosphere can be suppressed while increasing the specific surface area of the Cs-V complex oxide. As the carrier, for example, Al ₂ O ₃ , SiO ₂ , TiO ₂ , CeO ₂ , ZrO ₂ , CeO ₂ -ZrO ₂ , MgO or the like can be used.

Further, the particulate matter combustion catalyst forms a PM combustion catalyst layer 5 on the inlet 7 side of the filter base 4 across the cell wall 2, and the NOx reduction catalyst on the outlet 10 side across the cell wall 2. The NOx reduction catalyst layer 6 is formed. Either or both of the particulate matter combustion catalyst and the reduction catalyst may be present in the cell wall 2, but the abundance ratio in the cell wall 2 is 50% or less in order to reduce pressure loss desirable.

The PM combustion catalyst layer 5 is thicker as going from the inlet 7 of the filter substrate 4 to the depth, and the NOx reduction catalyst layer 6 is formed thicker as it goes from the depth of the filter substrate 4 to the outlet 10 It is characterized by The thicknesses of the PM combustion catalyst layer 5 and the NOx reduction catalyst layer 6 may be changed linearly, but may be changed stepwise, such as stepwise. Further, since the pressure difference can be provided only by changing either one of the thickness of the PM combustion catalyst layer 5 and the thickness of the NOx reduction catalyst layer 6, it is sufficient to change at least one of the thicknesses.

The thickness of the PM combustion catalyst layer 5 is preferably 10 μm or more and 100 μm or less. By setting the thickness of the PM combustion catalyst layer 5 to 10 μm or more, the amount of the inflowing particulate matter entering the inside of the cell wall 2 can be reduced, and the depth filtration rate can be reduced. By reducing the depth filtration rate, it is possible to suppress an increase in pressure loss during particulate matter deposition. Further, by setting the thickness of the PM combustion catalyst layer 5 to 100 μm or less, the adhesiveness between the surface of the cell wall 2 and the PM combustion catalyst layer 5 can be secured while keeping the initial pressure loss after the catalyst coating low.

In addition, the Cs-V complex oxide is characterized in that the interaction with ammonia acting as a reducing agent in the NOx reduction reaction is weak. Therefore, in the temperature range where the exhaust gas temperature is relatively low, the ammonia can be supplied to the NOx reduction catalyst layer 6 located downstream of the exhaust gas flow without being oxidized, and the NOx reduction performance can be exhibited.

With the above configuration, PM in the exhaust gas flowing into the exhaust gas purification filter 1 is collected on the inside and the surface of the cell wall 2 on the side where the exhaust gas flows in, and further on the PM combustion catalyst layer 5. With the reducing agent (ammonia) supplied from the upstream side of the exhaust gas purification filter 1, NOx in the exhaust gas flowing into the exhaust gas purification filter 1 moves to the downstream side of the filter substrate 4 through the pores of the cell wall 2, The catalyst is reduced and removed by the NOx reduction catalyst contained in the NOx reduction catalyst layer 6 provided on the surface of the cell wall 2 on the side where it flows out.

Here, since the Cs-V complex oxide has a weak interaction with ammonia acting as a reducing agent in the NOx reduction reaction, the reducing agent such as ammonia is added from the upstream side of the exhaust gas purification filter 1 in a relatively low temperature range. Even when supplied, the Cs-V complex oxide can be circulated to the downstream side of the filter substrate 4 without oxidizing the reducing agent. During the filter regeneration process, the catalyst of the Cs-V complex oxide contained in the PM combustion catalyst layer 5 has oxygen of the collected PM in the gas phase in a temperature range lower than that of a catalyst using a platinum group metal. It can be made to react quickly and burn off. As a result, in the exhaust gas purification filter 1, high PM combustion performance can be exhibited in the cell 3 on the exhaust gas inflow side, and NOx reduction performance can be exhibited also on the cell 3 on the exhaust gas outflow side.

In particular, in the present embodiment, in the exhaust gas purification filter 1, the PM combustion catalyst layer 5 is made thicker as going from the inlet 7 of the filter base 4 to the inner side, or from the back of the filter base 4 to the outlet 10. By making the NOx reduction catalyst layer 6 thicker as it goes, it is possible to make a difference in pressure loss. Since the air passes preferentially through the low pressure drop, the exhaust gas will flow preferentially in the vicinity of the inlet 7 of the filter substrate 4. As a result, the distance in which the exhaust gas flows on the surface of the NOx reduction catalyst layer 6 (NOx reduction catalyst), that is, the creepage distance in which the exhaust gas flows through the NOx reduction catalyst layer 6 can be lengthened, and the PM combustion catalyst layer 5 and the NOx reduction catalyst layer As compared with the case where the thickness of 6 is made uniform, NOx can be purified with high efficiency.

That is, in the exhaust gas purification filter 1, the exhaust gas purification filter 1 can exhibit high particulate matter combustion performance in the cell 3 on the exhaust gas inflow side, and can exhibit NOx reduction performance in the cell 3 on the exhaust gas outflow side. Can be provided.

As described above, the exhaust gas purification filter 1 reduces the NOx by the porous filter base 4 having the plurality of cells 3 partitioned by the cell walls 2, the PM combustion catalyst that burns and cleans the PM, and And a NOx reduction and removal catalyst for purification. The PM combustion catalyst is included in part or all of the surface of the cell wall 2 on the side where the exhaust gas flows, and forms a PM combustion catalyst layer 5. Further, the NOx reduction and removal catalyst is included in part or all of the surface of the cell wall 2 on the side where the exhaust gas flows out, and forms the NOx reduction catalyst layer 6. And, the PM combustion catalyst is a molten salt type catalyst containing a composite oxide of cesium and vanadium, wherein the molar ratio of cesium to vanadium (Cs / V) is 0.5 ≦ Cs / V ≦ 1.5. There is.

The molten salt type catalyst containing a composite oxide of cesium and vanadium is a direct oxidation type catalyst that burns PM using oxygen in the gas phase. In addition, the molten salt catalyst melts in the vicinity of the reaction temperature with PM and becomes a liquid phase. Therefore, in the combustion of PM involving catalyst (solid) -PM (solid) -oxygen (gas), when the catalyst becomes a liquid phase, the contact with PM increases dramatically, and high PM combustion performance is expressed. Conceivable.

Further, the composite oxide of cesium and vanadium is characterized in that the interaction with ammonia acting as a reducing agent in the NOx reduction reaction is weak. Therefore, in the temperature range where exhaust gas temperature is relatively low, ammonia can be supplied to the NOx reduction catalyst layer 6 located downstream of the exhaust gas flow without oxidizing ammonia, so the exhaust gas purification filter 1 has NOx reduction performance. Can be demonstrated.

Therefore, an exhaust gas purification filter having high PM combustion performance and NOx reduction performance can be provided.

Further, the exhaust gas purification filter 1 is a wall flow type filter base 4 having a plurality of cells partitioned by porous cell walls 2 and particles supported on the filter base 4 to burn and purify particulate matter. And a NOx reduction catalyst for purifying NOx. Further, the particulate matter combustion catalyst forms a first catalyst layer on the inlet 7 side of the filter substrate 4 with the cell wall 2 interposed therebetween, and the NOx reduction catalyst forms a second catalyst layer on the outlet 10 side with the cell wall 2 interposed therebetween. I am Furthermore, at least the first catalyst layer is formed thicker as it goes from the inlet 7 of the filter substrate 4 to the back, or the second catalyst layer is formed thicker as it goes from the back of the filter substrate 4 to the outlet 10 It is good to be doing.

Thereby, a difference can be provided to the pressure loss by providing a change to the thickness of the catalyst layer. Since air passes preferentially through the low pressure drop, it preferentially flows near the inlet 7 of the filter substrate 4. As a result, the distance in which the exhaust gas flows on the surface of the NOx reduction catalyst, that is, the creepage distance in which the exhaust gas flows in the NOx reduction catalyst can be increased, and NOx can be purified with high efficiency.

In the exhaust gas purification filter 1, the particulate matter combustion catalyst is a cesium-vanadium composite oxide in which the molar ratio of cesium to vanadium (Cs / V) is 0.5 ≦ Cs / V ≦ 1.5, It may be a molten salt type catalyst containing a cerium-containing oxide.

In a general platinum group-containing particulate matter combustion catalyst, it is necessary to use the NO ₂ contained in the exhaust gas in order to burn the soot effectively. That is, the exhaust gas must permeate through the entire cell wall 2 supporting the particulate matter combustion catalyst to bring the NO ₂ into contact with the particulate matter combustion catalyst. However, as in this embodiment, the particulate matter combustion catalyst comprising a catalyst comprising a composite oxide of vanadium and cesium, does not require the NO ₂ in the combustion of the soot, the exhaust gas particulate containing NO ₂ Even if some of the cell wall 2 carrying the material combustion catalyst may permeate, the particulate matter combustion catalyst staying in the cell 3 on the inflow side has a large particle size compared to NO ₂ It can be burned.

Furthermore, the fact that the exhaust gas containing NO ₂ permeates through a part of the cell wall 2 supporting the particulate matter combustion catalyst means that the exhaust gas flows on the surface of the NOx reduction catalyst at the outlet 10 side of the filter substrate 4 The distance can be increased, and efficient NOx purification can be performed.

In the exhaust gas purification filter, the thickness of the first catalyst layer may be 10 μm or more and 100 μm or less.

As a result, the amount of catalyst necessary for particulate matter combustion is satisfied, and the pressure loss does not become too high.

In the exhaust gas purification filter, the particulate matter combustion catalyst may be supported on an oxide carrier.

Thus, it is considered that fine unevenness of the carrier suppresses unintended movement of the molten salt catalyst in the liquid phase. In addition, by covering the surface of the carrier with the molten salt catalyst, the specific surface area of the molten salt catalyst can be increased, and the contact with combustion and combustion can be promoted.

Since the exhaust gas purification filter according to the present invention has both high PM combustion performance and NOx reduction performance, the exhaust gas purification filter for purifying the exhaust gas generated from various internal combustion engines and the catalyst DPF for purifying the exhaust gas of a diesel engine It is useful as etc.

1 exhaust gas purification filter 2 cell wall 3 cell 4 filter base material 5 PM combustion catalyst layer 6 NOx reduction catalyst layer 7 inlet 8 back 9 back 10 outlet

Claims

A porous filter substrate having a plurality of cells partitioned by cell walls;
PM combustion catalyst that burns and cleans PM,
A PM combustion catalyst layer in which the PM combustion catalyst is contained in part or all of the surface of the cell wall on the side where exhaust gas flows;
A NOx reduction and removal catalyst that reduces and purifies NOx;
A NOx reduction catalyst layer including the NOx reduction and removal catalyst on part or all of the surface of the cell wall on the side where the exhaust gas flows out;
The PM combustion catalyst is a molten salt catalyst containing cesium and vanadium complex oxide, wherein the molar ratio of cesium to vanadium (Cs / V) is 0.5 ≦ Cs / V ≦ 1.5. filter.
A wall flow type filter substrate having a plurality of cells partitioned by porous cell walls, a particulate matter combustion catalyst supported on the filter substrate and burning and purifying particulate matter, and NOx purification The particulate matter combustion catalyst comprises a first catalyst layer on the inlet side of the filter base with the cell wall interposed therebetween, and the NOx reduction catalyst comprises the second catalyst layer in the cell wall Form a second catalyst layer on the outlet side, and at least the first catalyst layer becomes thicker as it goes deeper from the inlet of the filter substrate, or the second catalyst layer is viewed from the back of the filter substrate An exhaust gas purification filter characterized by being formed thicker as it goes to the outlet.
The particulate matter combustion catalyst includes a composite oxide of cesium and vanadium and a cerium-containing oxide, wherein a molar ratio of cesium to vanadium (Cs / V) is 0.5 ≦ Cs / V ≦ 1.5. The exhaust gas purification filter according to claim 2, which is a molten salt type catalyst.
The exhaust gas purification filter according to claim 2, wherein the thickness of the first catalyst layer is 10 μm to 100 μm.
The exhaust gas purification filter according to claim 3, wherein the particulate matter combustion catalyst is supported by an oxide carrier.