JP2012213774A - Filter for cleaning exhaust gas and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust gas cleaning catalyst having high catalytic activity relative to a particulate in a diesel exhaust gas and heat-resistance, to provide an exhaust gas cleaning filter having high particulate capturing efficiency, and to provide a manufacturing method for the exhaust gas cleaning catalyst and the exhaust gas cleaning filter.SOLUTION: The exhaust gas cleaning catalyst contains a metal oxide, a sulfate of alkali metal and silica, and a molar ratio of silica relative to the metal oxide and the sulfate of alkali metal is in a range of 0.1-6. A partition wall of a ternary structure body comprising a porous material is uniformly carried with the exhaust gas cleaning catalyst, and it is manufactured such that an average fine aperture diameter of fine apertures of the partition wall is 5-15 μm, a fine aperture volume of the fine aperture of less than 5 μm is 50% or less of the whole fine aperture volume, and the fine aperture volume of the fine aperture exceeding 15 μm becomes 10% or less of the whole fine aperture volume. Thereby, the exhaust gas cleaning filter having high catalytic activity, heat-resistance and the capturing efficiency can be obtained.

Description

  The present invention relates to an exhaust gas purification catalyst, an exhaust gas purification filter, which purifies exhaust gas by burning particulates (solid carbon fine particles, liquid or solid high molecular weight hydrocarbon fine particles) contained in exhaust gas discharged from a diesel engine, And a manufacturing method thereof.

  Particulates contained in the exhaust gas discharged from the diesel engine have a particle diameter of approximately 1 μm or less and are likely to float in the atmosphere, and are easily taken into the human body during breathing.

  In addition, since this particulate matter also contains a carcinogenic substance, regulations on particulates discharged from diesel engines are being strengthened.

  As an exhaust gas purification filter for removing particulates from exhaust gas, there is a diesel particulate filter (hereinafter referred to as DPF) in the exhaust gas flow. A DPF is a three-dimensional structure having a plurality of cells serving as exhaust gas passages partitioned by partition walls made of a porous material such as ceramics, and a honeycomb in which one of both ends of the cells is alternately plugged with a plug It is a filter. When exhaust gas discharged from a diesel engine flows into many cells of the DPF and exhaust gas passes through the partition walls of the porous material, the particulates included in the exhaust gas on the partition wall surface and the wall surfaces in the pores existing in the partition walls Is a mechanism to collect.

  Collecting particulates increases the pressure loss of the DPF and adversely affects the engine. Generally, an exhaust gas purification catalyst containing a metal oxide or the like is supported on the DPF, and the particulates collected in the DPF by the catalyst. It is decomposed into gas by oxidizing and burning. This makes it possible to continuously collect and decompose the particulates discharged from the engine. In addition, a highly active exhaust gas purifying catalyst capable of oxidizing and burning particulates at a temperature about the exhaust gas is required, and various catalysts have been devised.

  Patent Document 1 discloses an exhaust gas purification catalyst in which a transition metal is supported on a noble metal supported on an oxide carrier. Patent Document 2 discloses a cerium-zirconium composite oxide exhaust gas purification catalyst containing one or more kinds of metals. Patent Document 3 discloses a composite noble metal colloidal exhaust gas purification catalyst having silver supported on its surface layer. Patent Document 4 discloses an exhaust gas purification filter in which a coat layer made of alumina or the like is formed on a partition wall of a DPF, and a catalyst metal such as platinum is supported on the coat layer.

JP 2003-251186 A JP 2003-334443 A Japanese Patent Laid-Open No. 2004-57949 JP-A-9-220423

  Such conventional exhaust gas purification catalysts have the following problems.

The exhaust gas purification catalysts described in Patent Document 1 and Patent Document 2 can start burning particulates even in a relatively low temperature exhaust gas. However, a higher temperature is required for complete combustion, and sufficient catalytic activity is not achieved. There wasn't. Such an exhaust gas purifying catalyst has a catalyst supported in the pores of the porous carrier and cannot contact with particulates of particles larger than the pores, so that sufficient catalytic activity cannot be obtained. Conceivable.

  Patent Document 3 does not support the catalyst in the pores of the porous support as in Patent Document 1 and Patent Document 2, but supports a composite noble metal colloid having a particle diameter larger than several nanometers on the support surface. Therefore, the catalytic activity is improved because the contact with particulates is improved, but the noble metal colloid with a large particle size has a small surface area, so the contact area with the carrier is small, and the noble metal colloid is baked at a low temperature of 450 ° C. Since it was supported on the carrier, the durability against heat was not sufficient.

  Further, the exhaust gas purification filter in which the noble metal-based exhaust gas purification catalyst described in Patent Document 4 is supported on the DPF requires a high exhaust gas temperature to completely burn the particulates, and the catalytic activity against the particulates is not sufficient, Further, the durability against high temperature is not sufficient, and the average pore diameter of the pores existing in the DPF partition is as large as about 20 μm, so the efficiency of collecting particulates is basically low. The particulates are collected in the particulate matter and the particulate deposit layer is formed, so that the collection efficiency is kept high. However, since the particulate deposit layer must always be formed on the DPF partition wall, When conditions change suddenly, the particulate deposit layer burns at a stretch, and the DPF itself melts down. Collection efficiency of the rate there has been a problem that the lowered.

  The present invention solves the above-mentioned conventional problems, and provides an exhaust gas purification catalyst having high catalytic activity capable of completely burning particulates at a lower exhaust gas temperature and having excellent heat resistance, In addition, high catalytic activity that allows complete combustion of particulates at lower exhaust gas temperatures and high durability against high temperatures, and high particulate collection efficiency even if the particulate deposit layer disappears due to catalytic combustion. An object of the present invention is to provide an exhaust gas purification filter and to provide a method for producing such an exhaust gas purification catalyst and an exhaust gas purification filter.

  In order to achieve the above object, an exhaust gas purification filter of the present invention has a three-dimensional structure having a plurality of cells serving as exhaust gas flow passages partitioned by a partition made of a porous material, and a surface of the partition and / or a partition. An exhaust gas purification filter comprising an exhaust gas purification catalyst comprising a metal oxide supported on a wall surface in the existing pores, an alkali metal sulfate and / or an alkaline earth metal sulfate, and silica. Among the pores of the purification filter, the pore volume of pores less than 5 μm is 50% or less of the total pore volume, and the pore volume of pores exceeding 15 μm is 10% of the total pore volume. It is characterized by the following.

  The pores of the exhaust gas purification filter are characterized in that the average pore diameter is in the range of 5 to 15 μm.

  Further, the thickness of the partition wall of the exhaust gas purification filter is 450 μm or less.

  Further, the number of cells of the exhaust gas purification filter is 100 cells or more per square inch.

  In addition, the porous material is one or more of cordierite, silicon carbide, and stainless steel.

  In addition, silica is attached to the surface of the partition wall of the three-dimensional structure and / or the wall surface in the pores existing in the partition wall using an aqueous solution in which silica having an average particle diameter of 1 μm or less is dispersed. is there.

  Further, when silica is attached to the three-dimensional structure, the atmosphere around the three-dimensional structure and the aqueous solution is reduced in pressure.

  In addition, after the silica is attached to the three-dimensional structure, the three-dimensional structure is brought into contact with the hygroscopic material to remove excess aqueous solution.

  In addition, after adding silica to the three-dimensional structure, an excess aqueous solution is removed by applying a centrifugal force to the three-dimensional structure.

  Further, after silica is attached to the three-dimensional structure, an excessive aqueous solution is removed and freeze-dried.

  Further, when freeze-drying, the three-dimensional structure is frozen in advance and dried under reduced pressure before being dried.

  Further, the partition wall of the three-dimensional structure is prepared by using a catalyst aqueous solution in which a metal salt and an alkali metal sulfate and / or an alkaline earth metal sulfate are dissolved after silica is attached to the three-dimensional structure. And / or a catalyst is attached to the wall surfaces in the pores existing in the partition walls.

  In addition, when the catalyst is attached to the three-dimensional structure, the atmosphere around the three-dimensional structure and the aqueous solution is reduced.

  In addition, after the catalyst is attached to the three-dimensional structure, the three-dimensional structure is brought into contact with a hygroscopic material to remove excess aqueous solution.

  In addition, after the catalyst is attached to the three-dimensional structure, excess aqueous solution is removed by applying centrifugal force to the three-dimensional structure.

  Further, after the catalyst is attached to the three-dimensional structure, the excess aqueous solution is removed and lyophilized.

  Further, when freeze-drying, the three-dimensional structure is frozen in advance and dried under reduced pressure before being dried.

  According to the exhaust gas purification catalyst of the present invention, there is provided an exhaust gas purification catalyst having high catalytic activity capable of completely burning particulates at a lower exhaust gas temperature and having excellent heat resistance, and lower exhaust gas. Providing an exhaust gas purification filter that can burn particulates completely at high temperatures, has high catalytic activity and high durability against high temperatures, and maintains high particulate collection efficiency even if the particulate deposit layer disappears due to catalytic combustion In addition, a method for producing such an exhaust gas purification catalyst or exhaust gas purification filter can be provided.

The graph which shows the carbon residual rate in the performance evaluation test of the Example of this invention The graph which shows the result of the performance evaluation test (T10) of Examples 1-5 of this invention, and the comparative example 1 The graph which shows the result of the performance evaluation test (T90) of Examples 1-5 of this invention and the comparative example 1 The graph which shows the result of the pore distribution of Examples 1-5 of the present invention and Comparative Example 1 The figure showing the exhaust gas test of Evaluation Example 3 The figure showing the exhaust gas test of Evaluation Example 4

  According to the first aspect of the present invention, there is provided a three-dimensional structure having a plurality of cells serving as exhaust gas passages partitioned by a partition made of a porous material, and pores present on the surface of the partition and / or the partition. An exhaust gas purification filter having an exhaust gas purification catalyst comprising a metal oxide supported on an inner wall surface, an alkali metal sulfate and / or an alkaline earth metal sulfate, and silica, the exhaust gas purification filter having Among the pores, the pore volume of pores less than 5 μm is 50% or less of the total pore volume, and the pore volume of pores exceeding 15 μm is 10% or less of the total pore volume. An exhaust gas purification filter characterized by the above.

  With this configuration, by including an alkali metal sulfate and / or an alkaline earth metal sulfate, the catalytic activity of the metal oxide can be increased, and the particulates collected in the DPF are burned at about the exhaust gas temperature. It can be decomposed.

  In addition, by selecting an alkali metal sulfate and / or alkaline earth metal sulfate, it has the highest thermal stability and high heat resistance compared to nitrate, acetate, carbonate, chloride, etc. In addition, by using a sulfate excellent in poisoning resistance by sulfur oxides, it becomes possible to maintain a high catalytic activity with respect to particulate combustion.

  Further, by including silica, it becomes possible to support metal oxide, alkali metal sulfate and / or alkaline earth metal sulfate on the surface of silica having a large surface area. As the surface area increases and the probability of contact with the particulates increases, the catalytic activity can be improved.

  In addition, the metal oxide, alkali metal sulfate and / or alkaline earth metal sulfate is appropriately solid-solved and combined in the boundary layer with the silica surface to stabilize the catalyst, and for a long period of time. Durability against high temperature exhaust gas to be exposed is improved.

  Further, when the exhaust gas purifying catalyst is supported on the surface of a filter such as DPF, silica becomes an intermediate layer between the catalyst and the filter material, and it is possible to suppress a decrease in catalytic activity caused by the reaction between the catalyst and the filter material.

  Moreover, it becomes possible to oxidize and burn the particulates efficiently by containing copper.

Copper takes divalent and number monovalent value, as the oxides of copper, CuO (divalent) and Cu 2 _{O (monovalent)} are present, between atoms when changing from divalent to monovalent Oxygen can be applied to the particulates for oxidation. Since the copper oxide reduced to monovalent is easily oxidized by oxygen in the exhaust gas and returns to the divalent state, the repetition of this makes it possible to oxidize and burn the particulate continuously.

  Further, when the metal oxide contains one or more of vanadium and molybdenum, it becomes possible to oxidize and burn the particulates efficiently.

Vanadium has many valences such as monovalent, divalent, trivalent, tetravalent, and pentavalent, and vanadium oxides include V ₂ O (monovalent), V ₂ O ₂ (divalent), and V _2. O ₃ (trivalent), V ₂ O ₄ (tetravalent), and V ₂ O ₅ (pentavalent) exist, and when changing to a low valence, oxygen between atoms is given to the particulates to be oxidized. it can. Since vanadium oxide reduced to a low valence is easily oxidized by oxygen in the exhaust gas, the repetition of this makes it possible to oxidize and burn the particulate continuously.

Molybdenum takes many valences such as divalent, trivalent, tetravalent, pentavalent, and hexavalent, and molybdenum oxides include MoO (divalent), Mo ₂ O ₃ (trivalent), and MoO ₂ (4 Valence), Mo ₂ O ₅ (pentavalent), and MoO ₃ (hexavalent), and when changing to a low valence, oxygen can be given to the particulates to oxidize. Since molybdenum oxide reduced to a low valence is easily oxidized by oxygen in the exhaust gas, the repetition of this makes it possible to oxidize and burn the particulate continuously.

  Further, by containing copper and vanadium, it becomes possible to efficiently oxidize and burn the particulates and to provide an exhaust gas purification catalyst having excellent durability.

Various composite oxides of copper and vanadium exist, but the crystal structure of CuV ₂ O ₆ in particular is very stable, so that oxygen between atoms can be stably supplied to the particulates and oxidized. .

Further, by adopting a crystal structure of CuV ₂ O ₆ , it becomes an exhaust gas purification catalyst that is thermally stable and excellent in durability.

  Further, the inclusion of copper and molybdenum makes it possible to efficiently oxidize and burn the particulates and to provide an exhaust gas purification catalyst having excellent durability.

  In addition, in metal oxides containing copper and vanadium, a part of copper is made of lithium, sodium, magnesium, potassium, calcium, chromium, manganese, iron, cobalt, nickel, zinc, strontium, cesium, barium, molybdenum, tungsten. By replacing any one or more, it becomes possible to oxidize and burn the particulates efficiently.

  By substituting a part of copper with another metal that is different from the size of copper, the crystal structure of a part of the complex oxide of copper and vanadium is broken, and oxygen in / out between atoms is promoted, and the particulates are efficiently particulated. It becomes possible to oxidize by providing oxygen.

  In addition, in metal oxides containing copper and vanadium, a part of vanadium is lithium, sodium, magnesium, potassium, calcium, chromium, manganese, iron, cobalt, nickel, zinc, strontium, cesium, barium, molybdenum, tungsten. By replacing any one or more, it becomes possible to oxidize and burn the particulates efficiently.

  By substituting a part of vanadium with another metal whose size is different from the size of vanadium, the crystal structure of a part of the complex oxide of copper and vanadium is broken, and the entry and exit of oxygen between atoms is promoted, and the particulates are efficiently It becomes possible to oxidize by providing oxygen.

In addition, in metal oxides containing copper and molybdenum, a portion of molybdenum can be lithium, sodium, magnesium, potassium, calcium, chromium, manganese, iron, cobalt, nickel, zinc, strontium, cesium, barium, or tungsten. By replacing it with one or more, it becomes possible to oxidize and burn the particulates efficiently.

  By substituting a part of molybdenum with another metal whose size is different from the size of molybdenum, the crystal structure of a part of the composite oxide of copper and molybdenum is broken, and the entry and exit of oxygen between atoms is promoted. It becomes possible to oxidize by providing oxygen.

  Further, when the alkali metal sulfate contains one or more of lithium, sodium, potassium, and cesium, the particulate can be efficiently oxidized and burned.

  Alkali metal sulfates themselves are chemically stable and therefore have low combustion activity against particulates, but the presence of metal oxides facilitates the release of sulfur oxides from alkali metal sulfates to form particulates. On the other hand, it changes into highly active alkali metal oxides, hydroxides and carbonates, and the particulates can be immediately oxidized. The alkali metal quickly reacts with the sulfur oxide in the exhaust gas to form a stable alkali metal sulfate. By repeating this, it becomes possible to oxidize and burn the particulate continuously.

  Further, since lithium, sodium, potassium, and cesium are selected as the alkali metal, the material is less expensive than expensive rubidium, and therefore, it becomes an inexpensive exhaust gas purification catalyst.

  Further, by using cesium as the alkali metal, it is possible to maximize the combustion efficiency of the particulates.

  Cesium exhibits the strongest reducibility among alkali metals and easily gives outermost electrons, so that active oxygen is generated and particulates can be oxidized and burned efficiently. Moreover, it is thought that by changing to a cesium compound having a low melting point, adhesion with the particulates is improved, and as a result, catalytic combustion activity is improved.

  Further, when the alkaline earth metal sulfate contains one or more of calcium, strontium, and barium, the particulate can be oxidized and burned efficiently.

  By adding at least one of calcium, strontium and barium sulfates to the metal oxide, the catalytic activity of the metal oxide alone can be improved.

  By coexistence of alkaline earth metal sulfate and metal oxide, by changing to an alkaline earth metal compound having a low melting point, adhesion with particulates is improved, and as a result, catalytic combustion activity is improved. Conceivable.

  Moreover, by including any one or more of rhodium, palladium, iridium, and platinum, it becomes possible to oxidize and burn the particulates efficiently and also to oxidize gas components in the exhaust gas. .

  The noble metal has an action of dissociating oxygen molecules adsorbed on its surface, and can generate active oxygen atoms that strongly oxidize not only particulates but also gas components in exhaust gas. However, since noble metals have a high affinity with the generated active oxygen atoms, there is a disadvantage that even if active oxygen atoms with high reactivity are generated, they are stored on the surface of the noble metal, but a metal with a low affinity with active oxygen atoms. When the oxide coexists in the vicinity of the noble metal, active oxygen atoms generated from the noble metal can be efficiently applied to the particulates and oxidized.

  In addition, rhodium, palladium, iridium, and platinum are inexpensive materials compared to expensive ruthenium and osmium, resulting in an inexpensive exhaust gas purification catalyst.

  In addition, by adding a silica in an appropriate range, the molar ratio of silica to metal oxide and alkali metal sulfate and / or alkaline earth metal sulfate is in the range of 0.1-6. The durability of the exhaust gas purification catalyst against heat can be improved.

  If the molar ratio of silica to metal oxide and alkali metal sulfate and / or alkaline earth metal sulfate is less than 0.1, the effect of improving durability is lowered, which is not preferable. A larger value is not preferable because it leads to a decrease in the activity of the catalyst against particulates. Therefore, by setting it in the range of 0.1 to 6, durability can be improved while maintaining the activity of the catalyst.

  Further, by using silica having an average particle diameter of 1 μm or less as a raw material, the surface area of silica can be increased, and metal oxide, alkali metal sulfate and / or alkaline earth metal sulfate can be formed on the silica surface. Since the catalyst can be supported, the surface area of the exhaust gas purifying catalyst is increased and the contact probability with the particulates is increased, whereby the catalytic activity can be improved.

  In addition, the metal oxide, alkali metal sulfate and / or alkaline earth metal sulfate is appropriately solid-solved and combined in the boundary layer with the silica surface to stabilize the catalyst, and for a long period of time. Durability against high temperature exhaust gas to be exposed is improved.

  Further, when the exhaust gas purification catalyst is supported on a filter made of a porous material such as DPF, if the average particle diameter is silica of 1 μm or less, the silica is also contained in the filter pores (average pore diameter is about 20 μm). Can be dispersed and uniformly supported, and since silica is an intermediate layer between the catalyst and the filter material, it is possible to suppress a decrease in catalytic activity caused by the reaction between the catalyst and the filter material. It becomes possible.

  In addition, silica is impregnated in a solution in which a metal salt that is a raw material of metal oxide and an alkali metal sulfate and / or alkaline earth metal sulfate is dissolved, freeze-dried, and then heat-treated in an oxidizing atmosphere. Thus, an exhaust gas purifying catalyst having high activity with respect to particulates can be obtained by the manufacturing method to be manufactured.

  By using a solution in which a metal salt used as a raw material of a metal oxide and an alkali metal sulfate and / or an alkaline earth metal sulfate is dissolved, the catalyst component is attached in a highly dispersed state on the silica surface. be able to.

  Metal oxide particles, alkali metal sulfate particles and / or alkaline earth metal sulfate particles may be impregnated with silica, but the catalyst particles must be finely pulverized to improve the catalytic activity, and In contrast to the various finely divided particles that must be uniformly mixed, if various metal salts can be dissolved as an aqueous solution, the resulting solution will be a very uniform aqueous solution, resulting in uniform adhesion to the silica surface. Is possible.

  Furthermore, after the catalyst component is uniformly attached to the silica surface, freeze-drying can maintain the state where the catalyst component is uniformly attached to the silica surface.

In lyophilization, the catalyst component-dispersed solution is once frozen and solidified, and dried while sublimating from the solid state to the gas state, preventing partial drying and transferring the catalyst component during drying on the silica surface. The catalyst component can be more uniformly supported on the silica surface, the contact between the obtained exhaust gas purification catalyst and the particulates is improved, and the particulates are reduced at a lower exhaust gas temperature. It can be burned off.

  By subjecting the dried product in a state where the catalyst is uniformly attached to the silica surface to a heat treatment in an oxidizing atmosphere, various catalyst components can be uniformly supported on the silica surface.

  The activity and heat resistance of the exhaust gas purifying catalyst of the present invention strongly depend on the heat treatment temperature during production, and it is preferable to treat at 700 to 900 ° C. in order to exhibit high catalyst activity and heat resistance.

  In addition, the diesel exhaust gas purification catalyst may rarely reach a temperature around 600 ° C. under actual use conditions, and the heat treatment at 700 ° C. or less causes the catalyst composition to change during use, resulting in a decrease in activity. Since there is a possibility, it is not preferable. On the contrary, when the treatment is performed at a high temperature of 900 ° C. or higher, the activity of the catalyst itself may be lowered, or the ceramic supporting the catalyst may be damaged, which is not preferable.

  The particulates accumulated at a lower exhaust gas temperature can be burned and removed by the oxidation catalyst supported on the surface of the partition wall and / or the wall surface in the pores existing in the partition wall, so that the pressure loss of the exhaust gas purification filter is increased. By controlling the pore size of the exhaust gas purification filter, the probability that the particulates will collide with the partition wall surface increases, and even if the accumulated particulates are removed by combustion, the particulate collection efficiency is improved. An exhaust gas purification filter that can be maintained high is obtained.

  In addition, when the oxidation catalyst carried on the exhaust gas purification filter is activated by the relatively high temperature exhaust gas generated when the diesel engine is operated at a high load, and the particulates accumulated on the exhaust gas purification filter are burned and removed. However, it is possible to maintain a high collection efficiency.

  Moreover, when the pore volume of the pores of less than 5 μm among the pores of the exhaust gas purification filter is in a range exceeding 50% of the total pore volume, the particulate collection efficiency can be maintained high. The pressure loss generated when the exhaust gas passes through the partition wall of the exhaust gas purification filter increases.

  Moreover, when the pore volume of pores exceeding 15 μm in the pores of the exhaust gas purification filter is in a range exceeding 10% of the total pore volume, the particulate collection efficiency cannot be maintained high.

  The fine pores of the exhaust gas purification filter are exhaust gas purification filters having an average pore diameter in the range of 5 to 15 μm.

  With this configuration, it is possible to keep the pressure loss of the exhaust gas purification filter low while maintaining the high collection efficiency of the exhaust gas purification filter.

  Further, when the average pore diameter is less than 5 μm, the pressure loss when the exhaust gas discharged from the diesel engine passes through the partition wall of the exhaust gas purification filter increases, which may lead to a decrease in engine output and fuel consumption. .

In addition, when the average pore diameter exceeds 15 μm, when the particulates contained in the exhaust gas discharged from the diesel engine pass through the partition walls of the exhaust gas purification filter, the collection efficiency for collecting the particulates in the partition walls is increased. May decrease. As in the prior art, when the collection efficiency is kept high by the particulate deposition layer formed on the partition wall of the exhaust gas purification filter, it is possible to keep the collection efficiency high even when it exceeds 15 μm. When the operating conditions of the engine change suddenly, the particulate deposit layer burns at a stroke, and the exhaust gas purification filter itself may be melted down or the particulate collection efficiency may be reduced. On the other hand, the exhaust gas purification filter of the present invention has a feature that the collection efficiency can be maintained high without depending on the deposited layer of the particulate, and the particulate collection is always performed while removing the particulate by catalytic combustion. The constraint condition for maintaining high efficiency is that the average pore diameter is 15 μm or less.

  The exhaust gas purification filter is characterized in that the partition wall of the exhaust gas purification filter has a thickness of 450 μm or less.

  With this configuration, the pressure loss of the exhaust gas purification filter can be kept low while maintaining the high collection efficiency of the exhaust gas purification filter.

  When the partition wall thickness exceeds 450 μm, the pressure loss when the exhaust gas passes through the partition wall may increase, leading to a decrease in engine output and fuel consumption.

  The exhaust gas purification filter is characterized in that the number of cells of the exhaust gas purification filter is 100 cells or more per square inch.

  With this configuration, it is possible to keep the pressure loss of the exhaust gas purification filter low while maintaining the high collection efficiency of the exhaust gas purification filter.

  The number of cells of the exhaust gas purification filter affects the pressure loss when the exhaust gas passes through the cells. In the case of passing a normal temperature atmosphere in which no particulates are present, the smaller the number of cells, the smaller the area in the cell that comes into contact with the atmosphere, so that the pressure loss can be reduced. However, when passing exhaust gas containing particulates, unlike the above state, the particulate filtration area increases as the number of cells increases and the area inside the cells increases, so that particulates accumulate. As a result, the probability of closing the exhaust gas flow path is lowered, and it becomes possible to prevent engine output reduction and fuel consumption deterioration. Therefore, as the number of cells of the exhaust gas purification filter increases, the pressure loss can be reduced, and at least the number of cells needs to be 100 cells per square inch. May decrease.

  The exhaust gas purifying filter is characterized in that the porous material is one or more of cordierite, silicon carbide, and stainless steel.

  With this configuration, the exhaust gas purification filter that will be exposed to the exhaust gas over a long period of time can be ensured the thermal durability against the exhaust gas temperature, and the vibration resistance against mechanical vibration can be ensured, and the corrosive gas contained in the exhaust gas It becomes possible to ensure corrosion resistance against. In addition, since the adhesion between the oxidation catalyst and the porous material is improved, the oxidation catalyst can be prevented from peeling off from the exhaust gas purification filter. Moreover, since it can be obtained at a relatively low cost, the product cost can be reduced, and the high mechanical strength improves the handling in the manufacturing process of the exhaust gas purification filter.

  In the case of a stainless material, a material having a foam metal structure or a metal fiber structure having pores that communicate with each other can be employed.

Further, exhaust gas purification, characterized in that silica is attached to the surface of the partition wall of the three-dimensional structure and / or the wall surface in the pores existing in the partition wall using an aqueous solution in which silica having an average particle diameter of 1 μm or less is dispersed. It is a manufacturing method of a filter.

  With this configuration, silica can be uniformly supported on the surfaces of the partition walls of the three-dimensional structure and the wall surfaces in the pores existing in the partition walls, and the deposited particulates and the oxidation catalyst supported on the silica The exhaust gas filter capable of burning and removing particulates at a lower exhaust gas temperature can be manufactured.

  In addition, as a method of attaching to the surface of the partition wall of the three-dimensional structure and / or the wall surface in the pores existing in the partition wall using an aqueous solution in which silica is dispersed, the attachment is performed by immersing the three-dimensional structure in the aqueous solution. The aqueous solution may be attached by ascending and / or descending or parallel transport while the three-dimensional structure is fixed, or the aqueous solution may be attached by spraying or dropping while the three-dimensional structure is fixed. You may let them.

  Further, the present invention provides a method for producing an exhaust gas purification filter, wherein when the silica is attached to the three-dimensional structure, the atmosphere around the three-dimensional structure and the aqueous solution is reduced.

  With this configuration, the surface of the partition walls of the three-dimensional structure and the gas in the pores existing in the partition walls and the gas contained in the aqueous solution are removed by reducing the pressure, and the aqueous solution in which silica is dispersed is efficiently removed from the three-dimensional structure. Silica can be supported uniformly by permeating into the surface of the partition walls and the pores existing in the partition walls, and the contact between the deposited particulates and the oxidation catalyst supported on the silica is improved. An exhaust gas filter capable of burning and removing particulates at a lower exhaust gas temperature can be produced.

  Since there are so many pores in the partition walls of the three-dimensional structure, the gas inside the pores remains unextruded even if it is brought into contact with the aqueous solution as it is, and the space where the gas has remained is filled with the aqueous solution. In other words, the surface of the unfilled partition walls does not get wet with the aqueous solution, and it is not possible to carry silica uniformly. For this reason, the decompression operation is a very important manufacturing process.

  In addition, the present invention provides a method for producing an exhaust gas purification filter, wherein silica is attached to a three-dimensional structure, and then the three-dimensional structure is brought into contact with a hygroscopic material to remove excess aqueous solution.

  By this configuration, the silica is uniformly supported by uniformly removing the aqueous solution in which the silica that has permeated into the surface of the partition walls of the three-dimensional structure and the pores in the partition walls is dispersed, and the oxidation supported on the silica. It is possible to uniformly support the catalyst, improve the contact between the deposited particulates and the oxidation catalyst, and manufacture an exhaust gas filter capable of burning and removing particulates at a lower exhaust gas temperature. become able to.

  Generally, the excess liquid can be removed by air blow or the like. However, when the excess aqueous solution is removed by air blow, a part of the aqueous solution held in the three-dimensional structure evaporates to air, and the three-dimensional structure Partial drying proceeds. As the partial drying proceeds, the aqueous solution moves to the dried portion, so that the silica in the aqueous solution also moves, resulting in uneven support of silica on the three-dimensional structure. Even if the exhaust gas flows evenly into the exhaust gas purification filter, if there is unevenness in the loading of silica in the exhaust gas purification filter, there is also an unevenness in the loading of the oxidation catalyst supported on the silica, whereby the oxidation catalyst The particulates are not uniformly combusted due to the poor contact between the particles and the particulates, and the particulates are clogged at the places where the combustion is insufficient, the pressure loss of the exhaust gas purification filter increases, and the worst is the melting. There is a risk that.

  In order to prevent such non-uniform combustion of the particulates, the three-dimensional structure must be uniformly loaded with silica. By bringing the three-dimensional structure infiltrated with the aqueous solution containing silica into contact with the hygroscopic material, it is possible to move the excess aqueous solution from the three-dimensional structure to the hygroscopic material while preventing partial drying. A nonwoven fabric etc. can be used as a hygroscopic material.

  In addition, the present invention provides a method for manufacturing an exhaust gas purification filter, wherein after adding silica to a three-dimensional structure, an excess aqueous solution is removed by applying centrifugal force to the three-dimensional structure.

  This configuration makes it possible to uniformly support silica by uniformly removing the aqueous solution in which silica that has permeated into the pores existing in the partition walls and the surface of the partition walls of the three-dimensional structure is removed. The contact between the particulates and the oxidation catalyst supported on silica is improved, and an exhaust gas filter capable of burning and removing particulates at a lower exhaust gas temperature can be manufactured.

  Since the aqueous solution is extruded out of the 3D structure as a bulk by directly applying centrifugal force to the aqueous solution that has penetrated into the surface of the 3D structure partition walls and pores existing in the partition walls, partial evaporation is prevented. Therefore, it is possible to remove the excess aqueous solution from the three-dimensional structure without drying. Note that the excess solution may be completely removed by removing the excess aqueous solution from the three-dimensional structure by centrifugal force, and further bringing the three-dimensional structure into contact with the hygroscopic material.

  In addition, the present invention provides a method for producing an exhaust gas purification filter, in which silica is attached to a three-dimensional structure, and then an excess aqueous solution is removed and lyophilized.

  With this configuration, after freezing the aqueous solution held in the three-dimensional structure, the aqueous solution frozen by depressurizing the surroundings of the three-dimensional structure is dried while sublimating from the solid state to the gaseous state. Prevents partial drying of the original structure, suppresses the movement of silica during drying, makes it possible to support silica more uniformly, and is supported on the deposited particulates and silica. The contact property with the oxidation catalyst is improved, and an exhaust gas filter capable of burning and removing particulates at a lower exhaust gas temperature can be produced.

  As a means for freezing the filter, the three-dimensional structure and the retained aqueous solution can be frozen by the heat of vaporization taken away by vaporizing the solvent by reducing the pressure using a vacuum freeze-drying apparatus or the like.

  Moreover, when freeze-drying, the exhaust gas purification filter manufacturing method is characterized in that the three-dimensional structure is frozen in advance and dried under reduced pressure before being dried.

  With this configuration, it is possible to instantaneously freeze the three-dimensional structure, prevent evaporation of the aqueous solution held in the three-dimensional structure, and thereby suppress the movement of silica during drying. Thus, the contact between the deposited particulates and the oxidation catalyst supported on silica is improved, and an exhaust gas filter capable of burning and removing particulates at a lower exhaust gas temperature can be manufactured.

  Since liquid nitrogen has a very low temperature of 77 K (−196 ° C.), it is a low temperature range sufficient to instantaneously freeze the silica dispersion held in the three-dimensional structure.

  Further, since liquid nitrogen can be obtained relatively easily and inexpensively, it is possible to provide an inexpensive exhaust gas purification filter with reduced manufacturing costs.

  In addition, the liquid dispersion of silica held in the three-dimensional structure can be instantaneously frozen by pouring liquid nitrogen into the three-dimensional structure or by introducing the three-dimensional structure into the liquid nitrogen. Can be made.

  Note that any low temperature liquid or gas can be applied, such as liquid nitrogen (temperature is 77K), liquid oxygen (temperature is 90K), liquid argon (temperature is 87K), liquid hydrogen (temperature is 20K), dry Cooling using low-temperature liquid obtained from ice and ethyl alcohol, dry ice and ethyl ether, air cooled by a cold solid such as dry ice, cooling air obtained by a refrigeration cycle, cooling air obtained by a Peltier device, or vortex effect cooling Air may be used. The term “low temperature” as used herein means about −20 ° C. (253K) or less, and if it is higher than this, it is difficult to instantly freeze, and even if it is frozen, it melts immediately, which is not preferable.

  Further, the partition wall of the three-dimensional structure is prepared by using a catalyst aqueous solution in which a metal salt and an alkali metal sulfate and / or an alkaline earth metal sulfate are dissolved after silica is attached to the three-dimensional structure. The exhaust gas purification filter manufacturing method is characterized in that a catalyst is attached to the surface of the metal and / or the wall surface in the pores present on the partition walls.

  With this configuration, the oxidation catalyst can be uniformly supported on the surface of the partition walls of the three-dimensional structure and the wall surfaces in the pores existing in the partition walls, and the contact between the deposited particulates and the oxidation catalyst is improved. Thus, an exhaust gas filter capable of burning and removing particulates at a lower exhaust gas temperature can be manufactured. When using various metals as an oxidation catalyst, it is possible to attach to a three-dimensional structure using a slurry in which particles containing various metals are dispersed in water. Even if finely pulverized, the particles containing various metals in the slurry cannot be uniformly supported unless they are dispersed as primary particles. On the other hand, if various metal salts can be dissolved as an aqueous solution, the aqueous solution will be very uniform compared to the particle-dispersed slurry, and the surface of the partition walls of the three-dimensional structure and the wall surfaces in the pores existing in the partition walls It becomes possible to attach uniformly to the surface.

  Further, the surface of the partition of the three-dimensional structure and / or the pores existing in the partition using the aqueous solution in which the metal salt and the alkali metal sulfate and / or the alkaline earth metal sulfate are dissolved. As a method of attaching to the wall surface, the three-dimensional structure may be attached by immersing it in an aqueous solution, or the three-dimensional structure may be attached by ascending and / or descending or moving in parallel while the aqueous solution is fixed. Alternatively, the aqueous solution may be applied by spraying or dropping while the three-dimensional structure is fixed.

  Further, the present invention provides a method for producing an exhaust gas purification filter, wherein when the catalyst is attached to the three-dimensional structure, the atmosphere around the three-dimensional structure and the aqueous solution is reduced.

  With this configuration, the surface of the partition walls of the three-dimensional structure, the gas in the pores existing in the partition walls, and the gas contained in the aqueous solution are removed by reducing the pressure, so that the metal salt and the alkali metal sulfate and / or alkaline earth are removed. It becomes possible to uniformly support the oxidation catalyst by efficiently infiltrating the dissolved aqueous solution with the sulfate of a similar metal into the surface of the partition wall of the three-dimensional structure or the pores existing in the partition wall, The contact property between the accumulated particulates and the oxidation catalyst is improved, and an exhaust gas filter capable of burning and removing particulates at a lower exhaust gas temperature can be manufactured.

Since there are so many pores in the partition walls of the three-dimensional structure, the gas inside the pores remains unextruded even if it is brought into contact with the aqueous solution as it is, and the space where the gas has remained is filled with the aqueous solution. In other words, the surface of the partition wall that is not filled does not get wet with the aqueous solution, and it is impossible to uniformly support the oxidation catalyst. For this reason, the decompression operation is a very important manufacturing process.

  In addition, the present invention provides a method for producing an exhaust gas purification filter, wherein after adding a catalyst to a three-dimensional structure, the three-dimensional structure is brought into contact with a hygroscopic material to remove excess aqueous solution.

  With this configuration, an aqueous solution in which the metal salt that has permeated into the surface of the partition walls of the three-dimensional structure and the pores in the partition walls and the alkali metal sulfate and / or alkaline earth metal sulfate is dissolved is uniform. An exhaust gas filter that can uniformly support an oxidation catalyst by removing it, improves the contact between the deposited particulate and the oxidation catalyst, and burns and removes the particulate at a lower exhaust gas temperature. Can be manufactured.

  Generally, the excess liquid can be removed by air blow or the like. However, when the excess aqueous solution is removed by air blow, a part of the aqueous solution held in the three-dimensional structure evaporates to air, and the three-dimensional structure Partial drying proceeds. As the partial drying proceeds, the aqueous solution moves to the dried portion, so that the metal salt in the aqueous solution also moves, resulting in uneven support of the metal on the three-dimensional structure. Even if the exhaust gas flows evenly into the exhaust gas purification filter, if there is unevenness in the catalyst support in the exhaust gas purification filter, the combustion of the particulates becomes non-uniform, and the particulates are noticeable in places where the combustion is insufficient. There is a risk of clogging, increasing the pressure loss of the exhaust gas purification filter, or in the worst case melting.

  In order to prevent such non-uniform combustion of the particulates, the three-dimensional structure needs to carry the catalyst component metal uniformly. By bringing the three-dimensional structure infiltrated with the aqueous solution containing the metal salt into contact with the hygroscopic material, it is possible to move the excess aqueous solution from the three-dimensional structure to the hygroscopic material while preventing partial drying. A nonwoven fabric etc. can be used as a hygroscopic material.

  In addition, the present invention provides a method for manufacturing an exhaust gas purification filter, in which excess aqueous solution is removed by applying a centrifugal force to a three-dimensional structure after the catalyst is attached to the three-dimensional structure.

  With this configuration, an aqueous solution in which the metal salt that has permeated into the surface of the partition walls of the three-dimensional structure and the pores in the partition walls and the alkali metal sulfate and / or alkaline earth metal sulfate is dissolved is uniform. An exhaust gas filter that can uniformly support an oxidation catalyst by removing it, improves the contact between the deposited particulate and the oxidation catalyst, and burns and removes the particulate at a lower exhaust gas temperature. Can be manufactured.

  Since the aqueous solution is extruded out of the 3D structure as a bulk by directly applying centrifugal force to the aqueous solution that has penetrated into the surface of the 3D structure partition walls and pores existing in the partition walls, partial evaporation is prevented. Therefore, it is possible to remove the excess aqueous solution from the three-dimensional structure without drying. Note that the excess solution may be completely removed by removing the excess aqueous solution from the three-dimensional structure by centrifugal force, and further bringing the three-dimensional structure into contact with the hygroscopic material.

  Further, the present invention provides a method for manufacturing an exhaust gas purification filter, wherein after adding a catalyst to a three-dimensional structure, an excess aqueous solution is removed and freeze-dried.

With this configuration, after freezing the aqueous solution held in the three-dimensional structure, the aqueous solution frozen by depressurizing the surroundings of the three-dimensional structure is dried while sublimating from the solid state to the gaseous state. Prevents partial drying of the original structure, suppresses the movement of catalyst components during drying, makes it possible to carry the catalyst more uniformly, and contacts the deposited particulates with the oxidation catalyst. Thus, it becomes possible to manufacture an exhaust gas filter capable of burning and removing particulates at a lower exhaust gas temperature.

  As a means for freezing the filter, the three-dimensional structure and the retained aqueous solution can be frozen by the heat of vaporization taken away by vaporizing the solvent by reducing the pressure using a vacuum freeze-drying apparatus or the like.

  Moreover, when freeze-drying, the exhaust gas purification filter manufacturing method is characterized in that the three-dimensional structure is frozen in advance and dried under reduced pressure before being dried.

  With this configuration, the three-dimensional structure can be instantaneously frozen, the evaporation of the aqueous solution held in the three-dimensional structure can be prevented, and thereby the movement of the catalyst component during drying can be suppressed. Thus, the contact between the deposited particulates and the oxidation catalyst is improved, and an exhaust gas filter capable of burning and removing particulates at a lower exhaust gas temperature can be manufactured.

  Since liquid nitrogen has a very low temperature of 77 K (-196 ° C.), a dispersion of a metal salt held in a three-dimensional structure and an alkali metal sulfate and / or alkaline earth metal sulfate This is a low-temperature region sufficient to freeze the water instantaneously.

  Further, since liquid nitrogen can be obtained relatively easily and inexpensively, it is possible to provide an inexpensive exhaust gas purification filter with reduced manufacturing costs.

  Also, by pouring liquid nitrogen into the three-dimensional structure or putting the three-dimensional structure into the liquid nitrogen, a metal salt held in the three-dimensional structure by a relatively easy method, and an alkali metal sulfate And / or the alkaline earth metal sulfate dispersion can be frozen instantly.

  Note that any low temperature liquid or gas can be applied, such as liquid nitrogen (temperature is 77K), liquid oxygen (temperature is 90K), liquid argon (temperature is 87K), liquid hydrogen (temperature is 20K), dry Cooling using low-temperature liquid obtained from ice and ethyl alcohol, dry ice and ethyl ether, air cooled by a cold solid such as dry ice, cooling air obtained by a refrigeration cycle, cooling air obtained by a Peltier device, or vortex effect cooling Air may be used. The term “low temperature” as used herein means about −20 ° C. (253K) or less, and if it is higher than this, it is difficult to instantly freeze, and even if it is frozen, it melts immediately, which is not preferable.

  In addition, an oxidization catalyst honeycomb is provided on the upstream side of the exhaust gas flow path, and the exhaust gas purification filter is provided on the downstream side, so that the volatile components contained in the particulates are burned and removed by the effect of the oxidation catalyst supported on the oxidation catalyst honeycomb. In combination with the exhaust gas purification filter, a very high particulate purification ability can be exhibited. Here, the particulate is composed of volatile components derived from unburned fuel and lubricating oil and soot that is a solid component, and the volatile components are present in an adsorbed or agglomerated form in the soot. It exists in the exhaust gas, and it becomes possible to burn and remove particulates in various states by using the oxidation catalyst honeycomb and the exhaust gas purification filter in combination.

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

(Embodiment)
The exhaust gas purification catalyst of the present invention is an exhaust gas purification catalyst composed of a metal oxide, an alkali metal and / or alkaline earth metal sulfate, and silica.

  Examples of the metal oxide include one containing copper, one containing vanadium or molybdenum, one containing both copper and vanadium, and one containing both copper and molybdenum.

  In the case of containing both copper and vanadium, a part of copper or a part of vanadium is lithium, sodium, magnesium, potassium, calcium, chromium, manganese, iron, cobalt, nickel, zinc, strontium, cesium, barium The same catalytic activity can be obtained by substituting any one or more of molybdenum, tungsten and tungsten. The substitution ratio is 0.001 to 0.3% with respect to copper, and if it becomes smaller than 0.001%, the effect of accelerating the entry / exit of oxygen between atoms by breaking some crystal structures. Therefore, it becomes impossible to efficiently oxidize the particulates with oxygen. On the other hand, if it exceeds 0.3%, the crystal structure of the catalyst is completely destroyed, so that the catalytic activity is lowered.

  In the case of containing both copper and molybdenum, a part of copper or a part of molybdenum is lithium, sodium, magnesium, potassium, calcium, chromium, manganese, iron, cobalt, nickel, zinc, strontium, cesium. The same catalytic activity can be obtained by substituting one or more of barium and tungsten. The substitution ratio is 0.001 to 0.3% with respect to copper, and if it becomes smaller than 0.001%, the effect of accelerating the entry / exit of oxygen between atoms by breaking some crystal structures. Therefore, it becomes impossible to efficiently oxidize the particulates with oxygen. On the other hand, if it exceeds 0.3%, the crystal structure of the catalyst is completely destroyed, so that the catalytic activity is lowered.

  Examples of the alkali metal include lithium, sodium, potassium, and cesium. Among these, when cesium is selected, the catalytic combustion activity of the particulates becomes the highest. Almost the same catalytic combustion activity can be obtained for lithium, sodium and potassium. In addition, by selecting an alkali metal sulfate, it has the highest thermal stability and heat resistance compared to nitrate, acetate, carbonate, chloride, etc., and excellent resistance to sulfur oxides. By using the sulfate, high catalytic activity can be maintained for particulate combustion.

  Examples of the alkaline earth metal include calcium, strontium, and barium. Even if any of these is used, substantially the same catalytic combustion activity can be obtained. In addition, by selecting alkaline earth metal sulfate, it is the most thermally stable and highly heat resistant compared to nitrate, acetate, carbonate, chloride, etc. By using a sulfate superior to the above, it becomes possible to maintain a high catalytic activity against particulate combustion.

  Examples of the silica include silica sol, sodium silicate, potassium silicate, lithium silicate, and a hydrolyzate of a silicate compound. Examples of the silicate compound include tetraethoxysilane and its polymer methoxypolysiloxane, ethoxypolysiloxane, butoxypolysiloxane, and lithium silicate.

  As for the silica particle diameter, if the average particle diameter is 1 μm or less, for example, the silica can be dispersed and uniformly supported in the pores of the DPF (average pore diameter is about 20 μm). Thus, since the silica is surely an intermediate layer between the catalyst and the filter material, it is possible to suppress a decrease in the catalyst activity caused by the reaction between the catalyst and the filter material.

Further, the silica content is preferably adjusted to be in the range of 0.1 to 6 mol% with respect to the exhaust gas purification catalyst, and if it is too small, the effect of improving the catalyst activity and heat resistance cannot be obtained. Also, it does not function as a catalyst carrier. On the other hand, when the amount is too large, the catalytic action by the metal oxide, the composite metal oxide, and the sulfate is inhibited, and when supported on the filter, the pressure loss of the filter is increased more than necessary.

  Furthermore, a noble metal may be added to an exhaust gas purification catalyst composed of a metal oxide, an alkali metal and / or alkaline earth metal sulfate, and silica.

  The noble metal has an action of dissociating oxygen molecules adsorbed on its surface, and can generate active oxygen atoms that strongly oxidize not only particulates but also gas components in exhaust gas. However, since noble metals have a high affinity with the generated active oxygen atoms, there is a disadvantage that even if active oxygen atoms with high reactivity are generated, they are stored on the surface of the noble metal, but a metal with a low affinity with active oxygen atoms. When the oxide coexists in the vicinity of the noble metal, active oxygen atoms generated from the noble metal can be efficiently applied to the particulates and oxidized.

  Examples of the noble metal include rhodium, palladium, iridium, and platinum. Even if any of these is used, the same catalytic activity improvement can be expected. In addition, although the same catalytic activity can be obtained even if ruthenium or osmium is used, it is practically difficult to use because it is expensive.

  Further, the addition amount of the noble metal is preferably 30: 1 to 10: 1 in terms of a metal oxide: noble metal molar ratio. When the ratio is less than 30: 1, the effect of improving the catalytic activity due to the addition of the noble metal is lost, and when the ratio is more than 10: 1, the catalytic activity of the metal oxide is hindered.

  As a method for producing an exhaust gas purification catalyst, silica is impregnated in a solution in which a metal salt that is a raw material of a metal oxide and an alkali metal sulfate and / or an alkaline earth metal sulfate is dissolved, and after freeze-drying When the heat treatment is performed in an oxidizing atmosphere, an exhaust gas purification catalyst having the highest activity with respect to particulates can be obtained.

  By using a solution in which a metal salt used as a raw material of a metal oxide and an alkali metal sulfate and / or an alkaline earth metal sulfate is dissolved, the catalyst component is attached in a highly dispersed state on the silica surface. be able to.

  Metal oxide particles, alkali metal sulfate particles and / or alkaline earth metal sulfate particles may be impregnated with silica, but the catalyst particles must be finely pulverized to improve the catalytic activity, and In contrast to the various finely divided particles that must be uniformly mixed, if various metal salts can be dissolved as an aqueous solution, the resulting solution will be a very uniform aqueous solution, resulting in uniform adhesion to the silica surface. Is possible.

  Furthermore, after the catalyst component is uniformly attached to the silica surface, freeze-drying can maintain the state where the catalyst component is uniformly attached to the silica surface.

  In lyophilization, the catalyst component-dispersed solution is once solidified and dried while sublimating from the solid state to the gaseous state, preventing partial drying and allowing the catalyst component to move on the silica surface during drying. The catalyst component can be more uniformly supported on the silica surface, the contact between the obtained exhaust gas purification catalyst and the particulate is improved, and the particulate is burned at a lower exhaust gas temperature. Can be removed.

  By subjecting the dried product in a state where the catalyst is uniformly attached to the silica surface to a heat treatment in an oxidizing atmosphere, various catalyst components can be uniformly supported on the silica surface.

Moreover, as heat processing temperature, 700-900 degreeC can exhibit the highest catalyst activity and heat resistance. Diesel exhaust gas purification catalysts may rarely reach temperatures of around 600 ° C under actual use conditions, and heat treatment at 700 ° C or less may change the catalyst composition during use and reduce activity. This is not preferable. On the contrary, when the treatment is performed at a high temperature of 900 ° C. or higher, the activity of the catalyst itself may be lowered, or the ceramic supporting the catalyst may be damaged, which is not preferable.

  As a material of the three-dimensional structure having a plurality of cells serving as exhaust gas passages partitioned by a partition made of a porous material used as an exhaust gas purification filter, any one or more of cordierite, silicon carbide, and stainless steel is used. If so, there is no difference in the effect of the present invention. Further, the pore structure of the three-dimensional structure having a plurality of cells serving as exhaust gas flow passages partitioned by partition walls made of a porous material may be cordierite DPF or silicon carbide DPF, It may be a foam metal DPF or a metal fiber DPF.

  As a method for controlling the pores of the partition walls of the exhaust gas purification filter, the pores may be controlled by adjusting the amount and density of the exhaust gas purification catalyst supported, or the aggregate that is the raw material for DPF production It is also possible to control the pores by adjusting the type, particle size, and mixing ratio of the pore former, and what is important is the purification of the exhaust gas on the partition walls of the three-dimensional structure and / or the walls in the pores existing in the partition walls. Whether or not the pores of the exhaust gas purification filter formed when the catalyst is supported is controlled.

  The pore diameter of the partition wall of the exhaust gas purification filter can be measured by a mercury intrusion pore distribution measuring device.

  Examples of the present invention will be described below.

Example 1
A cordierite piece is impregnated in silica sol (silica concentration 2 wt%, particle diameter 10-20 nm), and the inside of the decompression device is used to remove the bubbles held in the pores of the cordierite piece and the bubbles held in the impregnation liquid. The pressure was reduced to 10 kPa and held for 5 minutes. Next, the cordierite piece was pulled up from the impregnating solution, and excess silica sol was removed by pressing against the water absorbent sheet. This was immersed in liquid nitrogen, frozen, and dried for 24 hours while reducing the pressure with a vacuum dryer. Next, heat treatment was performed in an electric furnace at 700 ° C. for 5 hours in an air atmosphere to produce a silica-coated cordierite piece. The coated silica was 0.9 wt% with respect to the cordierite pieces.

  On the other hand, copper sulfate, vanadium oxide sulfate, and cesium sulfate were dissolved in ion exchange water to prepare an aqueous catalyst solution. At this time, the weight concentration of each component is 7.0 wt% for copper sulfate, 11.7 wt% for vanadium oxide sulfate, and 20.5 wt% for cesium sulfate.

  The silica-coated cordierite pieces prepared above are impregnated with an aqueous catalyst solution, and the pressure is reduced to 10 kPa in a decompression device in order to remove the bubbles held in the pores of the cordierite pieces and the bubbles held in the impregnation liquid. Hold for 5 minutes. Next, the cordierite piece was pulled up from the impregnating solution, and the excess aqueous solution was pressed against the water absorbent sheet and removed. This was immersed in liquid nitrogen, frozen, and dried for 24 hours while reducing the pressure with a vacuum dryer. Next, heat treatment was performed in an electric furnace at 700 ° C. for 5 hours in an air atmosphere to produce a catalyst-supported silica-coated cordierite piece. The supported catalyst was 19.8 wt% with respect to the cordierite piece.

(Example 2)
A catalyst-supported silica-coated cordierite piece was produced in the same manner as in Example 1 except that the silica sol (silica concentration: 4 wt%) was changed. The coated silica and supported catalyst were 1.8 wt% and 19.7 wt%, respectively, based on the weight of the cordierite pieces.

(Example 3)
A catalyst-supported silica-coated cordierite piece was produced in the same manner as in Example 1 except that the silica sol (silica concentration: 12 wt%) was changed. The coated silica and the supported catalyst were 5.8 wt% and 18.2 wt%, respectively, with respect to the cordierite pieces.

Example 4
A catalyst-supported silica-coated cordierite piece was produced in the same manner as in Example 1 except that the silica sol (silica concentration 28 wt%) was changed. The coated silica and supported catalyst were 13.6 wt% and 17.3%, respectively, on cordierite pieces.

(Example 5)
A catalyst-supported silica-coated cordierite piece was produced in the same manner as in Example 1 except that the silica sol (silica concentration: 40 wt%) was changed. The coated silica and supported catalyst were 23.9 wt% and 15.0 wt%, respectively, with respect to the cordierite pieces.

(Comparative Example 1)
A cordierite piece similar to that in Example 1 was cut out from a commercially available DPF made by carrying a platinum-based catalyst (1 g / L or more per cordierite unit volume) as Comparative Example 1.

(Evaluation example 1)
Regarding Examples 1 to 5 and Comparative Example 1, the following performance evaluation test was performed using a thermogravimetric analyzer.

  Examples 1 to 5 and Comparative Example 1 were each pulverized in an agate mortar. The obtained pulverized powder and a commercially available carbon powder as a simulated particulate were mixed at a weight ratio of 4: 1, and further pulverized and mixed in an agate mortar to obtain an evaluation sample. About 10 mg of this sample was placed in a platinum sample container, and the change in weight during heating was observed. As test conditions, air was circulated in the sample chamber at a flow rate of 100 ml / min, and the temperature was raised from room temperature to 700 ° C. at a heating rate of 5 ° C./min. The carbon residual ratio was defined by defining the weight at 200 ° C. as the initial weight and the weight at 600 ° C. as the weight when the carbon was completely burned. As an example, a model of the performance evaluation test result is shown in FIG. Plotting is performed with the horizontal axis representing temperature and the vertical axis representing carbon residual ratio. As shown in FIG. 1, when the temperature exceeds a certain temperature, the carbon suddenly starts to burn and reaches a complete combustion, which is a profile representing the relationship between weight and temperature. As shown in FIG. 1, the temperature at which 10% of the carbon burned (the temperature when the carbon residual ratio was 90%) was defined as T10, which was used as a reference for comparison. The lower the temperature of T10, the more the catalyst can be burned from the lower exhaust gas temperature, indicating that the catalyst performance is good.

  In addition, the temperature at which 90% of the carbon burned (temperature when the carbon residual ratio was 10%) was defined as T90 and used as a reference for comparison. The lower the T90 temperature, the more the carbon can be burned at a lower exhaust gas temperature, indicating that the catalyst performance is good.

  In FIG. 2, the initial T10 in Examples 1 to 5 and Comparative Example 1 (the initial state is a state immediately after manufacturing, which is not subjected to heat treatment), and heat treatment at 600 ° C. for 100 hours. A comparison of T10 results after a given thermal load is shown.

  Compared with the initial T10 of Comparative Example 1 in which a platinum-based catalyst is supported on a cordierite piece, the initial T10 of Examples 1 to 5 implemented according to the present invention is very low, and carbon can be burned from a low temperature. It was found to be a highly active catalyst.

  Moreover, also in T10 after a heat load, compared with the comparative example 1, the catalyst of Examples 1-5 became a low result, and it turned out that the catalyst performance after the deterioration by a heat load is also high.

  Furthermore, in Examples 1-5, it turned out that the catalyst deterioration by a heat load can be suppressed by adding a silica, since the difference of T10 of initial stage and T10 after a heat load became small, so that the load of silica increased. It was.

  The diesel exhaust gas purification catalyst provided in a diesel vehicle or the like is expected to maintain its performance over a long period of time, and the catalysts of Examples 3 to 5 having high performance both in the initial stage and after the heating load are It can be said that it is particularly excellent.

  In FIG. 3, the initial T90 in Examples 1 to 5 and Comparative Example 1 (the initial state is the state immediately after manufacturing and the heat treatment is not given) and the heat treatment at 600 ° C. for 100 hours. A comparison of T90 results after a given heat load is shown.

  Compared with the initial T90 of Comparative Example 1 in which a platinum-based catalyst is supported on a cordierite piece, the initial T90 of Examples 1 to 5 implemented according to the present invention is very low, and carbon is completely discharged at a lower exhaust gas temperature. It was found to be a highly active catalyst that can be combusted.

  Moreover, also in T90 after a heat load, compared with the comparative example 1, the catalyst of Examples 1-5 became a low result, and it turned out that the catalyst performance after the deterioration by a heat load is also high.

  Further, in Examples 1 to 5, the difference between the initial T90 and the T90 after the heat load became smaller as the silica loading increased, and it was found that the catalyst deterioration due to the heat load can be suppressed by adding silica. It was.

  Since an exhaust gas purification filter carrying an exhaust gas purification catalyst provided in a diesel vehicle or the like must continuously collect and oxidize and burn particulates continuously discharged from a diesel engine, T90 as in Comparative Example 1 Exhaust gas purification catalysts having a high value of may continue to increase the amount of particulates that remain unburned, resulting in increased pressure loss of the exhaust gas purification filter, which may adversely affect the engine. Further, even in an exhaust gas purification system that forcibly raises the exhaust gas temperature by adding fuel when the particulates cannot be combusted, the exhaust gas purification catalyst having a high T90 value as in Comparative Example 1 consumes a large amount of fuel. In contrast, the exhaust gas purification catalyst shown in the first to fifth embodiments of the present invention requires less fuel to be added, and as a result, deterioration of fuel consumption can be minimized. It can be said that the catalysts of Examples 1 to 5 are very excellent exhaust gas purification catalysts.

(Evaluation example 2)
Next, regarding Examples 1 to 5 and Comparative Example 1, the pore characteristics (average pore diameter, pore volume) of these cordierite pieces were evaluated by a mercury intrusion method.

  FIG. 4 is a graph showing the relative pore volume with respect to the pore diameter of the pores of the cordierite pieces of Examples 1 to 5 and Comparative Example 1. Here, the relative pore volume is a value obtained by dividing the pore volume of the pores of the cordierite pieces in each example by the total pore volume of Comparative Example 1. Compared with the pore distribution of Comparative Example 1, the pore distributions of Examples 1 to 5 have many small pore diameters, and the pore distribution of Comparative Example 1 is very wide. It can be seen that the pore distributions of Examples 1 to 5 can be controlled narrowly.

Next, as Example 6, a catalyst-supported silica-coated cordierite piece was prepared in the same procedure as in Example 1, and the coated silica and the supported catalyst were 12.9 wt% with respect to the cordierite piece, respectively. Example 1 was 16.0 wt%.

  Table 1 shows the average pore diameter of the cordierite pieces of Examples 1 to 6 and Comparative Example 1, and the ratio of the pore volume of the pores of the cordierite pieces of each example to the total pore volume.

  Moreover, the exhaust gas purification filter of the same content as Examples 1-6 and the comparative example 1 is prepared, and the particulate collection efficiency in the exhaust gas purification filter when the exhaust gas actually discharged from a diesel engine is flowed is also shown in Table 1. Organized together. In addition, in order to obtain the particulate collection efficiency of each exhaust gas purification filter, each exhaust gas purification filter is installed in the exhaust gas line of a 4.3L diesel engine, the engine speed is kept constant at 1,500 rpm, and the exhaust gas temperature is The particulate concentration at the upstream and downstream positions of the exhaust gas purification filter at a constant 450 ° C. was measured using a smoke meter. The DPF used in Examples 1 to 6 is a cordierite DPF having a diameter of 7.5 inches, a height of 8 inches, a cell number of 200 cells per square inch, and a wall thickness of 305 μm. The DPF used in Comparative Example 1 is a cordierite DPF having a diameter of 7.5 inches, a height of 10 inches, a cell number of 300 cells per square inch, and a wall thickness of 254 μm. Is one in which platinum as an oxidation catalyst is supported at a rate of about 2 g per liter of DPF volume.

  Focusing on the average pore diameter of the pores of the partition walls of the exhaust gas purification filter and the particulate collection efficiency when the exhaust gas temperature is constant at 450 ° C., in Examples 1 to 6, the particulate trapping becomes smaller as the average pore diameter becomes smaller. It can be seen that the collection efficiency has increased. In the pores on the partition wall surface and / or in the partition walls, the fine structure formed by the exhaust gas purification catalyst and silica improves the probability that the particulates in the exhaust gas are collected into the fine structure, and the particulate collection The efficiency is thought to have increased. When the exhaust gas temperature is as high as 450 ° C., the catalytic activity is higher than when the exhaust gas temperature is low, so that particulate combustion is promoted, and the particulate deposition layer is difficult to form on the exhaust gas purification filter. In Examples 1 to 6, even when the particulate deposition layer is not formed on the exhaust gas purification filter, the particulate collection efficiency can be maintained high if the average pore diameter of the pores of the partition walls of the exhaust gas purification filter is appropriately controlled. I understood. In addition, the particulate collection efficiency of Example 1 is 75%, whereas Example 2 is as high as 83%, and the collection efficiency is improved at an average pore diameter of about 15 μm. Since the collection efficiency is as high as 93%, it was found that the collection efficiency was most improved when the average pore diameter was about 10 μm. On the other hand, all of the collection efficiencies of Example 6 having an average pore diameter of 5 μm and Examples 4 and 5 having an average pore diameter of 4 μm are 100%, and it is not necessary to make the average pore diameter smaller than 5 μm. It was found that the collection efficiency was maximized if the pore diameter was reduced to the vicinity.

  Therefore, the average pore diameter of the pores of the partition walls of the exhaust gas purification filter is the most appropriate range of 5 to 15 μm. If the pore diameter is controlled within this range, a particulate deposition layer is formed on the exhaust gas purification filter. Even in a situation where it is not performed, the particulate collection efficiency can be maintained high.

  Further, in the exhaust gas purification filter, paying attention to the ratio of the pore volume of the pores to the total pore volume and the particulate collection efficiency, the particulate deposition layer is formed on the exhaust gas purification filter as in Examples 2, 3, and 4. In order to keep the particulate collection efficiency high even in a situation where the pores are not formed, the pore volume of pores less than 5 μm is 50% or less of the total pore volume and more than 15 μm. However, it was found that it was necessary to be 10% or less of the total pore volume. If the number of pores of less than 5 μm increases and the pore volume of the pores of less than 5 μm exceeds 50% of the total pore volume, the particulate collection efficiency does not improve any more, so that is not necessary. Further, if the number of pores exceeding 15 μm increases and the pore volume of pores exceeding 15 μm exceeds 10% of the total pore volume, the particulate collection efficiency decreases, which is not preferable.

  In Comparative Example 1, the particulate collection efficiency was as high as 96%, although the average pore diameter was 20 μm, compared with Examples 1-6. Unlike the exhaust gas purification catalyst of the present invention, the platinum-based catalyst used in Comparative Example 1 burns particulates using the oxidizing power of nitrogen oxides in the exhaust gas, but the exhaust gas temperature is 450 ° C. If it is too high, it will be difficult to use the oxidizing power of nitrogen oxides, so the particulates cannot be burned sufficiently, and a particulate deposit layer is formed, thereby increasing the collection efficiency. Conceivable. Here, the oxidizing power of nitrogen oxides is the ability of nitric oxide in exhaust gas to be converted to nitrogen dioxide by a platinum-based catalyst and oxidize the generated nitrogen dioxide particulates. Since the nitrogen dioxide generated from the equilibrium relationship returns to nitric oxide, the oxidizing power that oxidizes the particulates tends to decrease.

  Although not shown as data, the smaller the thickness of the partition wall of the exhaust gas purification filter, the lower the pressure loss of the exhaust gas purification filter itself. Although not shown in the data, the larger the number of cells per unit cross-sectional area of the exhaust gas purification filter, the greater the exhaust gas ventilation resistance, but the larger the filtration area of the particulate, the greater the probability of contact between the particulate and the oxidation catalyst. As the number of cells is larger than 100 cells per square inch, it is better.

(Evaluation example 3)
Next, the following exhaust gas tests were performed using the exhaust gas purification filters obtained in Example 3 and Comparative Example 1. The exhaust gas test conducted will be described with reference to FIG.

  A 4.3L diesel engine 1 is used, a switching valve 2 is provided in the exhaust line from the diesel engine 1, two lines, a bypass line 3 and a main line 4, are installed, and exhaust gas purification is performed on the main line 4 side. The filter 6 was installed in the subsequent stage. After exhausting to the bypass line 3 side, the diesel engine 1 was operated for 1 hour under conditions of 1,500 rpm and a torque of 21 kgm to stabilize the exhaust, and then the exhaust gas was discharged to the main line 4 side where the exhaust gas purification filter 6 was installed by the switching valve 2. Was introduced.

The engine speed is constant at 1,500 rpm, and the exhaust gas temperature is measured by measuring the exhaust gas temperature just before flowing into the exhaust gas purification filter 6 with a thermocouple, and in five steps from 280 ° C to 400 ° C, and from 400 ° C to 500 ° C. A total of 8 set temperatures in 3 stages are provided. By changing the load on the diesel engine 1 with a dynamo, each set temperature can be set in increments of 30 ° C. from 400 ° C. in the range of 280 ° C. to 400 ° C. In the range of 500 ° C., the exhaust gas test was conducted by raising the temperature in increments of 50 ° C. The holding time for each set temperature was 30 minutes. Here, the set temperature of 280 ° C. to 500 ° C. is an exhaust gas temperature level generated when the diesel engine 1 is normally operated. During the exhaust gas test, the pressure sensor 7 is used to measure the static pressure at the upstream and downstream positions of the exhaust gas purification filter 6 to calculate the differential pressure before and after the exhaust gas purification filter 6 and the upstream and downstream positions of the exhaust gas purification filter 6. The particulate concentration was measured using a smoke meter 8.

  As the particulate matter contained in the exhaust gas is collected by the exhaust gas purification filter 6, the differential pressure before and after the exhaust gas purification filter 6 increases. However, as the exhaust gas temperature rises, the catalytic activity increases, so the particulate pressure was collected. The differential pressure decreases as the particulates are burned off.

  By calculating the differential pressure change rate per unit time at each temperature from such a differential pressure profile, the temperature when the differential pressure change rate becomes zero is defined as BPT (Balance Point of Temperature), and this BPT is low. The exhaust gas purification filter 6 was evaluated as having high catalytic activity. In addition, the average particulate collection efficiency in the entire region from 280 ° C. to 500 ° C. was calculated from the particulate concentration measured at the upstream and downstream positions of the exhaust gas purification filter 6. Further, the weight of the exhaust gas purification filter 6 before and after the exhaust gas test was measured under a constant condition of 120 ° C., and the remaining amount of particulates remaining in the exhaust gas purification filter 6 was calculated. Furthermore, in order to confirm the durability of the exhaust gas purification filter to high temperatures, not only the initial state immediately after production but also the BPT and average particulate collection efficiency in a state after applying a heat load at 600 ° C. for 100 hours in an electric furnace Was also measured.

  Table 2 shows the initial and endurance BPT, average particulate collection efficiency of Example 6 and Comparative Example 2, and the remaining amount of particulate after the test.

  BPT, which is an index of catalytic activity for particulates, is 347 ° C. in Example 3 and 386 ° C. in Comparative Example 1 in the initial state immediately after production, and Example 3 has a value as low as 39 ° C. compared to Comparative Example 1. Thus, it was found that the exhaust gas purification filter can burn and remove particulates from a lower exhaust gas temperature. In addition, the results of the average collection efficiency of the particulates in the entire region from 280 ° C. to 500 ° C. are 94% for Example 3 and 92% for Comparative Example 1, and high trapping is achieved by controlling the pore diameter as in Example 3. It was found that collection efficiency can be obtained.

  Further, the BPT in the state after endurance after applying a heat load at 600 ° C. for 100 hours is 349 ° C. in Example 3 and 393 ° C. in Comparative Example 1, and changes in Example 3 as compared with the BPT in the initial state It was found that the filter was an exhaust gas purification filter having high durability against heat because it was not as low as 44 ° C. compared to Comparative Example 1.

Furthermore, the results of the average collection efficiency of the particulates after endurance were 95% in Example 3 and 95% in Comparative Example 1, and it was found that each example had high collection efficiency. However, the residual amount of particulates after the exhaust gas test is 0.0 g in Example 3, whereas 3.3 g in Comparative Example 1 is captured by the particulate deposition layer. It became clear that the collection efficiency was maintained high.

  In disclosing the present invention, the pores of the partition walls of the DPF were controlled by supporting the exhaust gas purification catalyst on the DPF, but the type of aggregate and pore former, the particle diameter, The pores may be controlled by adjusting the mixing ratio, and the important thing is the exhaust gas formed when the exhaust gas purification catalyst is supported on the partition walls of the three-dimensional structure and / or the wall surfaces in the pores existing in the partition walls. Whether or not the pores of the purification filter are controlled.

(Evaluation example 4)
Next, the oxidation catalyst honeycomb 5 was placed in front of the exhaust gas purification filter 6 for which the exhaust gas test was performed in Example 3 and Comparative Example 1, and the exhaust gas test similar to that in Evaluation Example 3 (see FIG. 6) was performed.

  The oxidation catalyst honeycomb 5 used in this exhaust gas test is a cordierite honeycomb having a diameter of 7.5 inches, a height of 3 inches, a cell number of 300 cells per square inch, and a wall thickness of 200 μm. On the surface, platinum as an oxidation catalyst is supported at a rate of about 5 g per liter of honeycomb volume.

  Table 3 shows the initial BPT of Example 3 and Comparative Example 1, the average particulate collection efficiency in the entire region from 280 ° C. to 500 ° C., and the residual amount of particulates after the test.

  BPT, which is an index of catalytic activity for particulates, is 347 ° C. in Example 3 and 386 ° C. in Comparative Example 1 in the initial state immediately after production, and Example 3 has a value as low as 39 ° C. compared to Comparative Example 1. Thus, it was found that the exhaust gas purification filter can burn and remove particulates from a lower exhaust gas temperature. In addition, the results of the average collection efficiency of the particulates in the entire region from 280 ° C. to 500 ° C. are 94% for Example 3 and 92% for Comparative Example 1, and high trapping is achieved by controlling the pore diameter as in Example 3. It was found that collection efficiency can be obtained.

  Further, the BPT in the state after endurance after applying a heat load at 600 ° C. for 100 hours is 349 ° C. in Example 3 and 393 ° C. in Comparative Example 1, and changes in Example 3 as compared with the BPT in the initial state. It was found that the filter was an exhaust gas purification filter having high durability against heat because it was not as low as 44 ° C. compared to Comparative Example 1.

  Furthermore, the results of the average collection efficiency of the particulates after endurance were 95% in Example 3 and 95% in Comparative Example 1, and it was found that each example had high collection efficiency. However, the residual amount of particulates after the exhaust gas test is 0.0 g in Example 3, whereas 3.3 g in Comparative Example 1 is captured by the particulate deposition layer. It became clear that the collection efficiency was maintained high.

The exhaust gas purification catalyst of the present invention has a high catalytic activity capable of completely burning particulates at a lower exhaust gas temperature, and has excellent heat resistance, and the exhaust gas purification filter has a lower exhaust gas temperature. It has high catalytic activity capable of burning particulates and excellent durability at high temperatures, and is very useful because it maintains the high particulate collection efficiency even if the particulate deposition layer disappears. It can be applied not only to automobiles but also to purification of exhaust gas from construction machines, generators, forklifts, cultivators, ships, etc.

DESCRIPTION OF SYMBOLS 1 Diesel engine 2 Switching valve 3 Bypass line 4 This line 5 Oxidation catalyst honeycomb 6 Exhaust gas purification filter 7 Pressure sensor 8 Smoke meter

Claims (17)

A three-dimensional structure having a plurality of cells serving as exhaust gas flow passages partitioned by partition walls made of a porous material, and a metal oxide supported on the surfaces of the partition walls and / or the wall surfaces in the pores present in the partition walls, In an exhaust gas purification filter provided with an exhaust gas purification catalyst containing an alkali metal sulfate and / or an alkaline earth metal sulfate and silica,
Among the pores of the exhaust gas purification filter, the pore volume of pores of less than 5 μm is 50% or less of the total pore volume, and the pore volume of pores exceeding 15 μm is 10% of the total pore volume. % Exhaust gas purification filter characterized by being less than or equal to%. The exhaust gas purification filter according to claim 1, wherein the pores of the exhaust gas purification filter have an average pore diameter in the range of 5 to 15 µm. The exhaust gas purification filter according to claim 1 or 2, wherein the partition wall of the exhaust gas purification filter has a thickness of 450 µm or less. The exhaust gas purification filter according to any one of claims 1 to 3, wherein the number of cells of the exhaust gas purification filter is 100 cells or more per square inch. The exhaust gas purification filter according to any one of claims 1 to 4, wherein the porous material is at least one of cordierite, silicon carbide, and stainless steel. The silica is attached to the surfaces of the partition walls of the three-dimensional structure and / or the wall surfaces in the pores existing in the partition walls using an aqueous solution in which silica having an average particle diameter of 1 µm or less is dispersed. 6. A method for producing an exhaust gas purification filter according to any one of 5 above. The method for producing an exhaust gas purification filter according to claim 6, wherein when the silica is attached to the three-dimensional structure, the atmosphere around the three-dimensional structure and the aqueous solution is decompressed. The exhaust gas purification filter according to claim 6 or 7, wherein after the silica is attached to the three-dimensional structure, the three-dimensional structure is brought into contact with a hygroscopic material to remove excess aqueous solution. Method. The method for producing an exhaust gas purification filter according to claim 6 or 7, wherein after adding silica to the three-dimensional structure, an excessive aqueous solution is removed by applying a centrifugal force to the three-dimensional structure. The method for producing an exhaust gas purification filter according to claim 6 or 7, wherein after adding silica to the three-dimensional structure, an excess aqueous solution is removed and freeze-dried. The method for producing an exhaust gas purification filter according to claim 10, wherein when freeze-drying, the three-dimensional structure is frozen in advance and dried under reduced pressure before drying. After impregnating silica to the three-dimensional structure, the surface of the partition walls of the three-dimensional structure using an aqueous catalyst solution in which a metal salt and an alkali metal sulfate and / or alkaline earth metal sulfate are dissolved. The method for producing an exhaust gas purification filter according to any one of claims 6 to 11, wherein a catalyst is attached to a wall surface in a pore existing in the partition wall. 13. The method for producing an exhaust gas purification filter according to claim 12, wherein when the catalyst is attached to the three-dimensional structure, the atmosphere around the three-dimensional structure and the aqueous solution is reduced. The method for producing an exhaust gas purification filter according to claim 12 or 13, wherein after the catalyst is attached to the three-dimensional structure, the three-dimensional structure is brought into contact with a hygroscopic material to remove excess aqueous solution. . The method for producing an exhaust gas purification filter according to claim 12 or 13, wherein after the catalyst is attached to the three-dimensional structure, an excess aqueous solution is removed by applying a centrifugal force to the three-dimensional structure. The method for producing an exhaust gas purification filter according to claim 12 or 13, wherein after the catalyst is attached to the three-dimensional structure, an excess aqueous solution is removed and freeze-dried. The method for producing an exhaust gas purification filter according to claim 16, wherein, when freeze-drying, the three-dimensional structure is immersed in liquid nitrogen before drying, and the three-dimensional structure is previously frozen and dried under reduced pressure.