WO2018116884A1

WO2018116884A1 - Honeycomb structure and exhaust gas-purifying apparatus

Info

Publication number: WO2018116884A1
Application number: PCT/JP2017/044364
Authority: WO
Inventors: 悠貴 ▲高▼石; 昌稔上谷; 俊博圓尾
Original assignee: 大塚化学株式会社
Priority date: 2016-12-20
Filing date: 2017-12-11
Publication date: 2018-06-28

Abstract

The present invention provides a honeycomb structure with high NO_x reduction efficiency and high mechanical strength without immersing the honeycomb structure after manufacture in a zeolite-containing solution or applying thereon a zeolite-containing solution. The honeycomb structure 11 has a shape wherein multiple cells 12 extending along the longitudinal direction X from one end face 11a to the other end face 11b are subdivided by cell walls 13, and the honeycomb structure 11 is characterized by being a sintered compact of a mixture containing zeolite, clay mineral and inorganic fiber.

Description

Honeycomb structure and exhaust gas purification device

The present invention relates to a honeycomb structure and an exhaust gas purification apparatus including the honeycomb structure.

Exhaust gas discharged from internal combustion engines such as diesel engines contains harmful substances such as particulate matter (PM), nitrogen oxides (NO _x ), hydrocarbons, and carbon monoxide. Various methods are being studied to remove harmful substances. In particular trucks, PM and NO _X discharged from diesel vehicles such as a bus from that one of the causes of air pollution in urban areas, it is increasingly strengthened regulations on these harmful substances.

Regarding PM, PM is collected in a honeycomb structure having a filtration function arranged in a flow path of exhaust gas, and when a predetermined amount of PM is deposited, the honeycomb structure is heated to remove PM by combustion decomposition. be able to. However, since the combustion temperature of PM is as high as 550 ° C. to 650 ° C., there is a problem that the apparatus becomes large and the energy cost for heating increases. In order to burn PM at a lower temperature, a honeycomb structure carrying a catalyst is used.

NO _X can be removed by disposing the honeycomb structure carrying the NO _X reduction catalyst in the exhaust gas flow path. For example, selective catalytic reduction (SCR: selective catalytic reduction) in which NO _x is reduced to nitrogen by supporting a zeolite catalyst on a honeycomb structure and injecting a reducing agent obtained from an ammonia precursor such as urea or ammonia itself into the honeycomb structure. reduction).

To purify the NO _X efficiently, since it is possible to increase the amount of zeolite contributing to the NO _X purification is important, honeycomb structure cell walls formed of zeolite has been studied. However, the cell wall of the honeycomb structure needs to use a large amount of an inorganic binder in addition to zeolite in order to ensure moldability and mechanical strength that can withstand practical use. For this reason, the honeycomb structure in which the cell wall is made of zeolite cannot increase the amount of zeolite contained in the cell wall so much, and the NO _x purification of the honeycomb structure is performed by the upper limit of the amount of zeolite contained in the cell wall. rate is substantially defined, there is a problem that it is difficult to obtain more of the NO _X purification rate. Therefore, in Patent Document 1, the honeycomb structure in which the cell wall is composed of zeolite is impregnated with a solution containing zeolite, and the ratio of zeolite on the surface of the cell wall is higher than the center of the cell wall. A featured honeycomb structure is proposed.

In order to remove both PM and NO _X , if PM adheres to the NO _X reduction catalyst, the NO _X reduction efficiency decreases. Therefore, it is necessary to arrange a device for removing NO _X downstream of the device for removing PM. There is. Moreover, the demand for market downsizing device with integrated device for removing apparatus and NO _X removing the PM has been desired. Therefore, in Patent Document 2, the wall surface of the honeycomb structure of wall flow, coated with NO _X reduction catalyst layer consisting of NO _X reduction catalyst, it has been proposed to coat by addition of an oxide catalyst oxidation catalyst layer .

JP 2010-229012 A JP 2000-282852 A

However, the honeycomb structure of Patent Document 1 has a problem that moldability and mechanical strength are not sufficient. If the sintering temperature of the honeycomb structure is increased or a large amount of a sintered material is added to increase the mechanical strength, there is a problem that the function of the zeolite is impaired. Further, when the pores on the wall surface of the honeycomb structure are blocked by the formed catalyst layer, the connected pores independently reduce the exhaust gas flow path, and as a result, the NO _X removal efficiency may be reduced. Concerned.

As in the method of Patent Document 2, when integrating the device for removing the device and NO _X removing the PM, the catalyst ratio may be coated on the honeycomb structure is reduced, that the purification performance of the PM and NO _X decreases Is concerned. In addition, when the pores on the wall surface of the honeycomb structure are closed by the formed catalyst layer, the connected pores independently reduce the exhaust gas flow path, resulting in an increase in pressure loss due to PM deposition, NO _X removal efficiency is a concern that or decreased. The same applies when the technique of Patent Document 2 is applied to the honeycomb structure of Patent Document 1.

The present invention is, or is impregnated with a solution containing zeolite after manufacturing of the honeycomb structure without solution was or coating containing zeolite high NO _X reduction efficiency, and high mechanical strength honeycomb structure, and the honeycomb It is a main object to provide an exhaust gas purification apparatus provided with a structure.

The present invention provides the following honeycomb structure and an exhaust gas purification apparatus including the honeycomb structure.

Item 1: A honeycomb structure having a shape in which a plurality of cells extending from one end face to the other end face are partitioned by a cell wall along a longitudinal direction, and the honeycomb structure includes zeolite, clay mineral, and inorganic It is a sintered body of a mixture containing fibers.

Item 2: The zeolite is at least one selected from mordenite type zeolite, faujasite type zeolite, A type zeolite, L type zeolite, β zeolite, ZSM-5 type zeolite, and CHA type zeolite. Item 2. The honeycomb structure according to Item 1.

Item 3. The honeycomb structure according to Item 1 or Item 2, wherein an average particle diameter of primary particles of the zeolite is 0.1 μm to 20 μm.

Item 4. The honeycomb structure according to any one of Items 1 to 3, wherein the clay mineral is a layered clay mineral.

Item 5. The honeycomb structure according to any one of Items 1 to 4, wherein an average fiber length of the inorganic fibers is 1 μm to 300 μm and an average aspect ratio is 3 to 200.

Item 6. The honeycomb structure according to any one of Items 1 to 5, wherein the inorganic fiber has a Mohs hardness of 5 or less.

Item 7 The honeycomb according to any one of Items 1 to 6, wherein a content of the clay mineral in the mixture is 1 to 50 parts by mass with respect to 100 parts by mass of the zeolite. Structure.

Item 8 The honeycomb according to any one of Items 1 to 7, wherein a content of the inorganic fiber in the mixture is 1 to 50 parts by mass with respect to 100 parts by mass of the zeolite. Structure.

Item 9 The honeycomb structure according to any one of Items 1 to 8, wherein the mixture further contains a ceramic raw material.

Item 10. The honeycomb structure according to Item 9, wherein the ceramic raw material is at least one selected from silicon carbide, cordierite, mullite, alumina, and aluminum titanate.

Item 11: The ratio of the concentration of the zeolite in the surface portion of the cell wall to the concentration of the zeolite contained in the central portion of the cell wall (surface portion / center portion) is in the range of 0.8 to 1.2. Item 11. The honeycomb structure according to any one of Items 1 to 10, wherein:

Item 12. The honeycomb structure according to any one of Items 1 to 11, wherein the zeolite is a catalyst for reducing nitrogen oxides to nitrogen.

Item 13 is a honeycomb structure used in an exhaust gas purification apparatus, wherein a transition metal oxide is supported on the surface of the cell wall on the exhaust gas inlet side of the honeycomb structure. The honeycomb structure according to any one of the above.

Item 14. The honeycomb structure according to Item 13, wherein an amount of the transition metal oxide supported per apparent volume in the honeycomb structure is 1 g / L to 70 g / L.

Item 15. An exhaust gas purification apparatus comprising the honeycomb structure according to any one of Items 1 to 14.

According to the present invention, provided or impregnated with a solution containing zeolite after manufacturing of the honeycomb structure without solution was or coating containing zeolite high NO _X reduction efficiency and the mechanical strength is high honeycomb structure can do.

FIG. 1 is a schematic perspective view showing a honeycomb structure according to an embodiment of the present invention. FIG. 2 is a schematic view showing an end face of a modification of the honeycomb structure of FIG. FIG. 3 is a schematic front view for explaining a method for measuring the bending strength.

Hereinafter, an example of a preferable embodiment in which the present invention is implemented will be described. However, the following embodiment is merely an example. The present invention is not limited to the following embodiments.

A honeycomb structure of the present invention is a honeycomb structure having a shape in which a plurality of cells extending from one end face to the other end face are partitioned by cell walls along a longitudinal direction, the honeycomb structure being It is a sintered body of a mixture containing zeolite, clay mineral and inorganic fiber. Further, from the viewpoint of further improving the mechanical strength of the honeycomb structure, the mixture may further contain a ceramic raw material, if necessary.

Hereinafter, a specific honeycomb structure of the present invention and each component thereof will be described.

(Zeolite)
Zeolite is a crystalline aluminosilicate, which is a porous body having a crystal structure in which four oxygen elements are regularly and three-dimensionally bonded around silicon and aluminum elements. Examples of the crystal structure of the zeolite used in the present invention include mordenite type zeolite, faujasite type zeolite, A type zeolite, L type zeolite, β zeolite, ZSM-5 type zeolite, CHA type zeolite and the like.

The silica / alumina ratio of the zeolite used in the present invention is preferably 15 or more, more preferably 20 or more, and still more preferably 30 or more. The upper limit of the silica / alumina ratio is preferably 100, more preferably 70, and still more preferably 50. Without further subject that the effect of alkali metal ions dissolved from the other additives With this structure, is believed to be more effectively reduce and remove NO _X.

Zeolite used in the present invention includes naturally-occurring and synthetic zeolites, and any zeolite having the above configuration can be used without any particular limitation. Preferably, synthetic zeolite is preferred because it has a more uniform silica / alumina ratio, crystal size, crystal morphology, and fewer impurities.

The zeolite is preferably one in which primary particles are aggregated to form secondary particles. The average particle size of the primary particles of the zeolite is preferably 0.1 μm to 20 μm, more preferably 1 μm to 20 μm, and even more preferably 5 μm to 15 μm. The average particle diameter of primary particles in the above range, it is possible to more effectively reduce and remove NO _X. What is necessary is just to measure the average particle diameter of a primary particle using the particulate matter before mixing raw material particles. In the present invention, the average particle diameter of the primary particles of zeolite is obtained by selecting 50 arbitrary primary particles from an electron micrograph and averaging the diameters.

The average particle size of the secondary particles of the zeolite is preferably 0.5 μm to 40 μm, more preferably 5 μm to 30 μm, and even more preferably 10 μm to 20 μm. By making the average particle diameter of the secondary particles in the above range, the reactivity between the zeolite and the sintered material can be further reduced in the firing in the manufacturing process of the honeycomb structure, and the zeolite skeleton structure is more reliably secured. Can be maintained. What is necessary is just to measure the average particle diameter of a secondary particle using the particulate matter before mixing raw material particles. Further, in the present invention, the average particle size of the secondary particles of zeolite is a volume-based cumulative 50% (volume-based cumulative 50% particle size) in a particle size distribution determined by a laser diffraction / scattering method, that is, D ₅₀ (median diameter). The particle size of This volume-based cumulative 50% particle diameter (D ₅₀ ) is obtained by calculating the particle size distribution on a volume basis, and counting the number of particles from the smallest particle size in the cumulative curve with the total volume being 100%. It is the particle size at a point where it becomes 50%.

The crushing strength of zeolite is preferably 50 MPa or more, and more preferably 60 MPa or more. The crushing strength of zeolite is preferably 500 MPa or less, and more preferably 300 MPa or less. By setting the crushing strength within the above range, it is possible to further suppress the primary particle diameter and / or the secondary particle diameter of the zeolite from being reduced by the forming pressure at the time of forming the honeycomb structure. What is necessary is just to measure the crushing strength of a zeolite using the particulate matter before mixing raw material particles.

The zeolite used in the present invention preferably contains ion exchanged zeolite obtained by ion exchange of the above zeolite. As the ion-exchanged zeolite, a honeycomb structure may be formed by using a previously ion-exchanged zeolite, or the zeolite may be ion-exchanged after the honeycomb structure is formed.

As the ion exchange zeolite, a zeolite ion exchanged with a transition metal is preferably used. Examples of the transition metal include Cu, Fe, Pt, Ag, Ti, Mn, Ni, Co, Pd, Rh, V, and Cr, and Cu and Fe are preferable. The total amount of transition metals is preferably 1% by mass to 15% by mass, and more preferably 1% by mass to 8% by mass with respect to the total mass of the zeolite.

(Clay mineral)
The clay mineral used in the present invention is a main component mineral constituting clay. Layered silicate mineral (phyllosilicate mineral), talc, calcite, dolomite, feldspar, quartz, zeolite (zeolite), and others with chain structure (attapulgite, Sepiolite, etc.) and those that do not have a clear crystal structure (allophane) are called clay minerals. In general, layered silicate minerals are sometimes called layered clay minerals. The clay mineral used in the present invention is preferably a layered clay mineral.

The layered clay mineral has a two-dimensional layer of positive and negative ions stacked and bonded in parallel to form a crystal structure. This layer structure has two structural units, one of which surrounds Si ^4+. A tetrahedral layer composed of O ^2−, and the other is composed of an octahedral layer composed of Si ³⁺ (or Mg ²⁺ , Fe ^2+, etc.) and (OH) ⁻ surrounding it.

In the tetrahedron layer, O at the four vertices of the tetrahedron and Si located at the center form an Si—O tetrahedron, which is connected to each other at the three vertices to spread two-dimensionally, and Si ₄ O A layer lattice having a composition of ₁₀ is formed. Si ⁴⁺ is often replaced by Al ³⁺ .

In the octahedron layer, the octahedron formed by (OH) or O at the six apexes of the octahedron and Al, Mg, Fe, etc. located at the center thereof is connected at each apex and is two-dimensionally. A layer lattice having a composition of Al ₂ (OH) ₆ or Mg ₃ (OH) ₆ is formed.

In the octahedral layer, a divalent cation (Mg ^2+, etc.) enters the lattice point of the cation surrounded by 6 anions, and occupies all of the lattice points. There is a 2-octahedron type in which trivalent cations (such as Al ³⁺ ) enter the lattice points and occupy 2/3, and the remaining 1/3 is empty.

There are two types of tetrahedron and octahedron combinations, one is a 1: 1 type structure with a unit of one tetrahedron layer and one octahedron layer, and the other is a tetrahedron. There is a 1: 1 type structure in which a unit is a unit of an octahedral layer sandwiched between layers.

In the tetrahedral layer, one Si ⁴⁺ is usually surrounded by four O atoms and has a stable coordination, but sometimes Al ³⁺ having a slightly larger ion radius than this Si ⁴⁺ replaces Si ⁴⁺ . Exists in the tetrahedral layer. Since there is no change in the number of coordinated O atoms, every time one Al ³⁺ replaces Si ⁴⁺ , a unit of negative charge is generated in the tetrahedral layer. Similarly, in the octahedron layer, negative charges are generated with the replacement of Al ³⁺ and Fe ³⁺ by Mg ²⁺ and Fe ²⁺ .

This negatively charged layer is a positive layer such as Li ⁺ , K ⁺ , Na ⁺ , NH ₄ ⁺ , H ₃ O ⁺ , Ca ²⁺ , Mg ²⁺ , Sr ²⁺ , Ba ²⁺ , Co ²⁺ , Fe ²⁺ , Al ^3+. The ions are electrically neutral due to the presence of ions, resulting in a laminated structure in which these exchangeable cations exist between layers.

Examples of the layered clay mineral include at least one selected from smectite, stevensite, vermiculite, mica group, brittle mica group natural product or synthetic product. These can be used in combination.

Examples of the smectite include montmorillonite, beidellite, nontronite, saponite, iron saponite, hectorite, and soconite. Montmorillonite is preferable from the viewpoint of further increasing NO _X reduction efficiency and mechanical strength. For example, bentonite mainly composed of montmorillonite can be used, and the content of montmorillonite in the bentonite is preferably 40% or more, and more preferably 70% or more.

The average particle size of the clay mineral is preferably 0.5 μm to 100 μm, and more preferably 1 μm to 20 μm. What is necessary is just to measure an average particle diameter using the particulate matter before mixing raw material particles. Further, in the present invention, the average particle diameter of the viscosity mineral is the volume-based cumulative 50% particle diameter (volume-based cumulative 50% particle diameter) in the particle size distribution determined by the laser diffraction / scattering method, that is, D ₅₀ (median diameter). It is. This volume-based cumulative 50% particle diameter (D ₅₀ ) is obtained by calculating the particle size distribution on a volume basis, and counting the number of particles from the smallest particle size in the cumulative curve with the total volume being 100%. It is the particle size at a point where it becomes 50%.

(Inorganic fiber)
The inorganic fiber used in the present invention is a powder composed of fibrous particles, and the average fiber length is preferably 1 μm to 300 μm, more preferably 1 μm to 200 μm. The average aspect ratio is preferably 3 to 200, more preferably 5 to 50.

The inorganic fiber preferably has a Mohs hardness of 5 or less from the viewpoint of wear of the extruder. Examples of the inorganic fiber include at least one selected from alkali metal titanate, wollastonite, magnesium borate, zonotlite, and basic magnesium sulfate. From the viewpoint of further enhancing the NO _X reduction efficiency and mechanical strength, it is preferred inorganic fibers are alkaline metal titanate. The Mohs hardness is an index representing the hardness of a substance, and a substance having a lower hardness is obtained when the minerals are rubbed against each other and damaged.

Examples of the alkali metal titanate include sodium titanate such as Na ₂ TiO ₃ , Na ₂ Ti ₂ O ₅ , Na ₂ Ti ₄ O ₉ , Na ₂ Ti ₆ O ₁₃ , Na ₂ Ti ₈ O ₁₇ ; K ₂ TiO ₃ , K ₂ Ti ₂ O ₅ , K ₂ Ti ₄ O ₉ , K ₂ Ti ₆ O ₁₃ , K ₂ Ti ₈ O _{17 and} other potassium titanates; Cs ₂ TiO ₃ , Cs ₂ Ti ₂ O ₅ , Cs ₂ Ti ₄ Examples thereof include cesium titanate such as O ₉ , Cs ₂ Ti ₆ O ₁₃ , and Cs ₂ Ti ₈ O ₁₇ .

The size of the alkali metal titanate is not particularly limited as long as it is within the above-mentioned range of the inorganic fiber, but usually the average fiber diameter is preferably 0.01 μm to 1 μm, more preferably 0.1 μm to 0.6 μm. The average fiber length is preferably 1 μm to 50 μm, more preferably 3 μm to 30 μm, and the average aspect ratio is preferably 10 or more, more preferably 15 to 40. In the present invention, commercially available products can also be used. For example, “TISMO D” (average fiber length 15 μm, average fiber diameter 0.5 μm) or “TISMO N” (average fiber length 15 μm) manufactured by Otsuka Chemical Co., Ltd. And an average fiber diameter of 0.5 μm) can be used.

The average fiber length and average fiber diameter of the inorganic fibers can be measured by observation with a scanning electron microscope, and the average aspect ratio (average fiber length / average fiber diameter) is calculated from the average fiber length and average fiber diameter. I can. For example, a plurality of inorganic fibers are photographed with an electron microscope, 300 inorganic fibers are arbitrarily selected from the observed images, their fiber lengths and fiber diameters are measured, and all the fiber diameters are integrated and divided by the number. The average fiber length can be obtained by integrating all of the average fiber length and fiber diameter and dividing the result by the number. What is necessary is just to measure an average fiber length and an average fiber diameter using the particulate matter before mixing raw material particles.

In the present invention, the term “fibrous particles” refers to the longest side of the rectangular parallelepiped having the smallest volume (the circumscribed rectangular parallelepiped) having the longest diameter L, the next longest side having the shortest diameter B, and the shortest side having the thickness T. When L is defined as (B> T), L / B and L / T are both particles of 3 or more, the major axis L corresponds to the fiber length, and the minor axis B corresponds to the fiber diameter.

(Ceramic raw material)
Examples of the ceramic raw material include at least one selected from silicon carbide, cordierite, mullite, alumina, and aluminum titanate, and these may be used in combination of two or more. The ceramic raw material is preferably aluminum titanate from the viewpoint of further improving heat resistance and stability.

The average particle size of the ceramic raw material is preferably 0.5 μm to 100 μm, and more preferably 1 μm to 20 μm. What is necessary is just to measure an average particle diameter using the particulate matter before mixing raw material particles. Further, in the present invention, the average particle size of the ceramic raw material is the particle size distribution of 50% by volume based on the particle size distribution obtained by the laser diffraction / scattering method (50% particle size by volume reference), that is, D ₅₀ (median diameter). It is. This volume-based cumulative 50% particle diameter (D ₅₀ ) is obtained by calculating the particle size distribution on a volume basis, and counting the number of particles from the smallest particle size in the cumulative curve with the total volume being 100%. It is the particle size at a point where it becomes 50%.

(Honeycomb structure)
FIG. 1 is a schematic perspective view showing a honeycomb structure according to an embodiment of the present invention.

As shown in FIG. 1, the honeycomb structure 11 of the present embodiment includes a first end surface 11a and a second end surface 11b facing each other, and a side surface 11c that connects the first end surface 11a and the second end surface 11b. And have. In the honeycomb structure 11, a plurality of cells 12 extending from the first end surface 11 a toward the second end surface 11 b along the longitudinal direction X shown in FIG. The side surface 11c (surface parallel to the longitudinal direction X) of the honeycomb structure 11 is provided with a coating layer in order to reinforce the side surface 11c and maintain strength, and to prevent the exhaust gas passing through the cells from leaking from the side surface 11c. It may be covered with. It does not specifically limit as a material which comprises the said coating layer, For example, what consists of an inorganic binder, an organic binder, an inorganic fiber, and / or an inorganic particle etc. can be mentioned.

The honeycomb structure 11 may be used as it is, or a plurality of honeycomb structures 11 may be joined with an adhesive or the like. When using as a joined body in which a plurality of honeycomb structures 11 are joined, it is desirable that the longitudinal directions X be arranged in parallel. In addition, the single honeycomb structure 11 or the joined body of the plurality of honeycomb structures 11 may be processed by cutting the side surface 11c side along a predetermined shape.

The shape of the cross section perpendicular to the longitudinal direction X of the honeycomb structure 11 is not particularly limited, and may be, for example, round, square (square, rectangular), hexagonal, or sector. Further, in the case of a cross-sectional shape such as a square having sharp corners, the sharp corners are chamfered from the viewpoint of relieving stress during regeneration of the honeycomb structure 11 and further suppressing the generation of cracks. It is preferable that In the present invention, the chamfered shape means a shape in which an inclined surface made of a flat surface or a curved surface is attached to the angle of intersection between the surfaces, and a shape having an inclined surface made of a curved surface from the viewpoint of stress relaxation. More preferably, for example, an R chamfered shape made of an arc is particularly preferable as shown in a modified example in FIG.

The cross-sectional shape perpendicular to the longitudinal direction X in the cells 12 of the honeycomb structure 11 is not particularly limited, and may be square (square, rectangular) as in the present embodiment. It may be a polygon. When the cross-sectional shape is square, from the viewpoint of improving the strength of the honeycomb structure 11 and heat and stress distribution, for example, as shown in a modified example in FIG. 2, the corner portions 15 of the outermost peripheral cells 12a of the honeycomb structure 11 are used. Is preferably provided with a filler having a right-angled triangular cross-sectional shape. The corner 15 provided with the filler is a corner 15 in contact with the outer edge wall 14 of the honeycomb structure 11 among the corners of the cell 12a whose outermost cross section of the honeycomb structure 11 is square. The length of one side of the right triangle filler is preferably 5% to 40% of the length of one side of the rectangular cell 12a.

The thickness of the cell wall 13 of the honeycomb structure 11 is not particularly limited, but the preferable lower limit is 100 μm from the viewpoint of further increasing the strength, and the preferable upper limit is 400 μm from the viewpoint of further improving the purification performance. The thickness of the cell wall 13a constituting the outer edge wall 14 of the honeycomb structure 11 may be the same as or thicker than the other cell walls 13b, but is 1.3 times that of the cell wall 13b not constituting the outer edge wall 14. By setting the ratio to ˜3.0 times, it is possible to ensure strength while maintaining a high aperture ratio.

The aperture ratio of the cells 12 of the honeycomb structure 11 is preferably 60% or more from the viewpoint of pressure loss. In the present invention, the aperture ratio of the cells 12 refers to the ratio of the cells 12 in a cross section perpendicular to the longitudinal direction X of the honeycomb structure 11. The vertical cross section is a cross section that is not plugged with a plugging material. The upper limit of the aperture ratio of the cells 12 of the honeycomb structure 11 is not particularly limited, but can be, for example, 70%.

The number of cells 12 in the honeycomb structure 11 is not particularly limited, but is preferably 200 cells / square inch to 400 cells / square inch. The wall surface of the cell 12 is not particularly limited as long as it is porous, but preferably has pores having a major axis of about 2 μm to 18 μm and a porosity of 45% to 65%.

Further, in the present invention, from the viewpoint of further increasing the NO _X reduction efficiency, or from the viewpoint of further enhancing both by integrating the NO _X removal function and the PM removal function, one end face is opened and the other end face is the eye. A wall flow type honeycomb filter formed of a honeycomb structure in which the sealed cells 12 and the remaining cells whose one end face is plugged and whose other end face is opened are alternately arranged. It is preferable.

(Production method)
An example of the above-described method for manufacturing the honeycomb structure of the present invention will be described. First, a raw material mixture containing, as necessary, a ceramic raw material as a main component in the above-described zeolite, clay mineral, and inorganic fiber is prepared. This raw material mixture is formed by extrusion molding or the like. In addition to these, a pore former, an organic binder, a dispersant, water and the like may be added to the raw material mixture. Examples of the pore former include graphite, graphite, wood powder, and polyethylene. Examples of the organic binder include methyl cellulose, ethyl cellulose, and polyvinyl alcohol. Examples of the dispersant include fatty acid soap and ethylene glycol. The amount of the pore former, the organic binder, the dispersant, and water can be appropriately adjusted in consideration of the porosity of the cell wall surface, moldability, and the like.

The raw material mixture is not particularly limited, but is preferably mixed and kneaded. For example, the raw material mixture may be mixed using a mixer or the like, or may be sufficiently kneaded using a kneader or the like. A method for forming the raw material mixture is not particularly limited, but it is preferable to form the raw material mixture into a shape having a predetermined cell density by, for example, extrusion molding.

Next, the obtained molded body is preferably dried after plugging on one side so that the opening of the cell has a checkered pattern, if necessary. Although the dryer used for drying is not specifically limited, A microwave dryer, a hot air dryer, a vacuum dryer, etc. are mentioned. Moreover, it is preferable to degrease the obtained molded object. The degreasing conditions are not particularly limited and are appropriately selected depending on the type of organic matter contained in the molded body, but are preferably approximately 400 ° C. and 2 hours.

Next, the obtained molded body is fired. The firing temperature is not particularly limited, but can be, for example, 600 ° C. to 1200 ° C., and the firing time can be, for example, 2 hours to 15 hours. If the firing temperature exceeds 1200 ° C, the zeolite crystals may collapse or the sintering may proceed too much to have an appropriate porosity. If the firing temperature is less than 600 ° C, the sintering does not proceed. The strength as a structure may not increase. The firing conditions when the ceramic raw material is used in combination are appropriately selected depending on the ceramic raw material. When aluminum titanate is used as the ceramic raw material, the firing temperature can be set to 900 ° C. to 1100 ° C., for example, as the firing time. For example, it can be 2 to 15 hours.

The content of zeolite in the raw material mixture (mixture) is preferably 10% by mass to 80% by mass, and more preferably 40% by mass to 70% by mass with respect to 100% by mass of the raw material mixture.

The content of the clay mineral in the mixture is preferably 1 part by mass to 50 parts by mass, more preferably 5 parts by mass to 30 parts by mass, with respect to 100 parts by mass of zeolite. More preferably. The content of the inorganic fiber in the mixture is preferably 1 part by mass to 50 parts by mass, more preferably 5 parts by mass to 30 parts by mass with respect to 100 parts by mass of zeolite, and 10 parts by mass to 20 parts by mass. More preferably. The content of the ceramic raw material in the mixture is preferably 1 part by mass to 50 parts by mass, more preferably 5 parts by mass to 30 parts by mass with respect to 100 parts by mass of zeolite, and 10 parts by mass to 20 parts by mass. More preferably.

By producing by the above method, zeolite can be uniformly distributed in the cell wall, and NO _X can be efficiently reduced. In the present invention, uniform means that the ratio of the concentration of zeolite in the surface portion of the cell wall to the concentration of zeolite in the central portion of the cell wall of the honeycomb structure (surface portion / center portion) is 0.8 to 1. It is in the range of 2. In the above manufacturing method, since the honeycomb structure is not impregnated with the solution containing zeolite or the solution containing zeolite is not applied, the ratio (surface portion / center portion) is within the above range.

In the present invention, examples of the exhaust gas to be treated include exhaust gas discharged from an internal combustion engine such as a diesel engine and a gasoline engine, and exhaust gas from various combustion facilities.

The honeycomb structure of the present invention is used in contact with exhaust gas by being disposed in the exhaust gas flow path. The removal of NO _{x in} these exhaust gases is performed in the presence of a reducing agent, for example, an ammonia precursor such as urea, ammonium carbonate, hydrazine, ammonium hydrogen carbonate, or ammonia itself. The reducing agent may be disposed upstream of the honeycomb structure of the present invention in the exhaust gas flow path, and a necessary amount may be appropriately supplied.

In the honeycomb structure of the present invention, a combination of a clay mineral that is exfoliated and highly dispersed during molding and an inorganic fiber that has a small area in contact with the other material and that is sintered with only a part of the other material is combined. Thus, it is considered that mechanical strength can be obtained and decomposition of zeolite can be suppressed to a minimum. As a result, it is considered that a highly efficient NO _x reduction removal performance and a honeycomb structure having high mechanical strength can be obtained.

In the manufacture of the honeycomb structure, a catalyst for burning PM can be included in the mixture, whereby the honeycomb structure of the present invention can burn PM, which is a harmful substance in exhaust gas, at a low temperature with one filter, NO _X can also be reduced and removed. Because of its excellent function, it can be suitably used for diesel engine filters (DPF), gasoline engine filters, etc., and can meet the demands of downsizing in the market.

(Exhaust gas purification device)
An exhaust gas purification apparatus of the present invention includes the honeycomb structure of the present invention. In addition to the honeycomb structure of the present invention, for example, a means for supplying a reducing agent or the like to the honeycomb structure is further provided. Alternatively, when the honeycomb structure of the present invention includes a catalyst for burning PM, the honeycomb structure further includes means for heating the honeycomb structure to decompose the deposited PM.

As a means for supplying the reducing agent or the like to the honeycomb structure, a known means can be adopted as long as the reducing agent or the like can be supplied to the honeycomb structure of the present invention. A means for disposing a reducing agent or the like on the honeycomb structure may be used, which is arranged on the more upstream side (internal combustion engine side). Moreover, you may arrange | position the mixer which supplies a reducing agent etc. uniformly suitably.

As a means for heating the honeycomb structure for decomposing the deposited PM, it is sufficient if the honeycomb structure of the present invention can be heated. For example, the fuel of the internal combustion engine is sprayed from the internal combustion engine onto the honeycomb structure, and the combustion heat thereof. And a means using electric heating.

Exhaust gas purifying apparatus of the present invention, further, in order from the upstream side of the exhaust gas flow channel (internal combustion engine side), the oxidation catalyst, NO _X storage catalyst, the first catalyst, such as PM combustion catalyst, the honeycomb structure of the present invention, SCR A second catalyst such as a catalyst or a slip oxidation catalyst may be disposed. The first catalyst and the honeycomb structure of the present invention may be disposed in order from the upstream side (internal combustion engine side) on the exhaust gas flow path. Further, the honeycomb structure of the present invention and the second catalyst may be arranged in order from the upstream side (internal combustion engine side) on the exhaust gas flow path. You may select 1 type, or 2 or more types for a 1st catalyst and a 2nd catalyst, respectively.

In the present invention, the oxidation catalyst means a catalyst that oxidizes HC, CO, NO _X to H ₂ O, CO ₂ , NO ₂ . The NO _X storage catalyst, to trap NO _X under lean conditions, when it becomes stoichiometric or rich conditions, released as NO _2, or catalytic means to _{N 2.} The PM combustion catalyst means a catalyst that burns PM at a temperature lower than the self-combustion temperature under rich conditions. The SCR catalyst means a catalyst capable of turning NO _X into N ₂ even under lean conditions. Further, the slip oxidation catalyst means a catalyst that captures excess NH ₃ used as a reducing agent and NO _X that cannot be reduced and purifies it to N ₂ . Examples of the oxidation catalyst include metals such as Pt, Pd, Rh, Ag, and Cu, oxides containing the metals, high heat resistant high specific surface area inorganic substances (alumina, zirconia, etc.), and acidic oxides (silica, etc.). Catalyst comprising at least one of basic oxide (titania, zirconia, alumina containing rare earth, etc.), oxygen storage / release material (ceria, ceria-zirconia composite oxide, sulfate containing rare earth, etc.), zeolite, etc. Is mentioned. These are used by being carried on a filter.

Examples of the NO _X storage catalyst include substances described in the above oxidation catalyst, compounds containing a basic alkali metal element (sodium carbonate, potassium carbonate, potassium titanate, etc.), and alkaline earth metal elements. Examples thereof include at least one type of catalyst such as a compound (strontium carbonate, barium carbonate, MgAl ₂ O _{4 and the} like) and a compound containing a rare earth element (ceria, ceria-zirconia composite oxide and the like). These are used by being carried on a filter.

Examples of PM combustion catalysts include PGM (Platinum Group Metal) catalysts (Pt, Pd, Rh, etc.), Ce-based oxides (ceria, ceria-zirconia composite oxide, etc.) having oxygen absorption / release capability, and alkali composite oxidation. objects _{_{_{(Na 2 ZrSi 3 O 9,}}} KAlSiO 4, LiAlSiO 4, K 2 TiSiO 5, K 2 Ti 4 O 9 , etc.), transition metal oxide _{_{_{_{(V 2 O 5, Fe 2}}}} O 3, MnO 2, CuO, CuFe And at least one type of catalyst such as a complex oxide. These are used by being carried on a filter.

Examples of the SCR catalyst include a catalyst composed of at least one kind such as zeolite and base metal composite TiO ₂ (base metals include V ₂ O ₅ , WO ₃ , MoO _{3 and the} like). These are used by being carried on a filter.

Examples of the slip oxidation catalyst include a catalyst composed of at least one of the substances described in the above oxidation catalyst, the substances described in the NO _X storage catalyst, and the substances described in the SCR catalyst. These are used by being carried on a filter.

In the exhaust gas purification apparatus of the present invention, the SCR catalyst size of the second catalyst can be reduced by using the honeycomb structure of the present invention that can efficiently reduce NO _x , or the second catalyst Since the SCR catalyst can be eliminated, the apparatus can be made compact. In addition, if a slip oxidation catalyst is supported on a part of the exhaust gas outlet side of the honeycomb structure of the present invention, the size of the slip oxidation catalyst of the second catalyst can be reduced, or the slip oxidation of the second catalyst. Since the catalyst can be eliminated, the apparatus can be made compact.

If the first catalyst is supported on the exhaust gas inlet side or part or all of the cell wall surface on the exhaust gas inlet side of the honeycomb structure of the present invention, the size of the first catalyst is reduced or the first catalyst is reduced. Can be eliminated, so that the apparatus can be made more compact.

The first catalyst supported on the honeycomb structure of the present invention is preferably a transition metal oxide such as V ₂ O ₅ , Fe ₂ O ₃ , MnO ₂ , CuO, or CuFe composite oxide. By carrying a transition metal oxide, as well as NO _X removal function, it is possible to further improve the PM removal function. Further, since the transition metal oxide is a non-alkali catalyst, there is no risk of the zeolite's function being lowered due to alkali.

The supported amount of transition metal oxide per apparent volume in the honeycomb structure of the present invention is preferably 1 g / L as the lower limit, more preferably 5 g / L, and even more preferably 8 g / L. preferable. In addition, the upper limit of the loading amount of the transition metal oxide per apparent volume in the honeycomb structure of the present invention is preferably 70 g / L, more preferably 60 g / L, and 50 g / L. Is more preferable. The supported amount of the transition metal oxide within the above range, it is difficult impair NO _X removal function, moreover it is possible to further improve the PM removal function.

The average particle diameter of the transition metal oxide is preferably larger than the pore diameter of the honeycomb structure of the present invention. In the present invention, the average particle diameter of the transition metal oxide is the volume-based cumulative 50% (volume-based cumulative 50% particle diameter) in the particle size distribution determined by the laser diffraction / scattering method, that is, the particle diameter of D ₅₀ (median diameter). It is. This volume-based cumulative 50% particle diameter (D ₅₀ ) is obtained by calculating the particle size distribution on a volume basis, and counting the number of particles from the smallest particle size in the cumulative curve with the total volume being 100%. It is the particle size at a point where it becomes 50%.

If the exhaust gas purifying apparatus of the present invention can be made compact by the above method, the exhaust gas purifying apparatus can be arranged at a more appropriate position than before. For example, the purification efficiency can be further improved by bringing the exhaust gas purification catalyst close to the internal combustion engine and promoting the activation of the exhaust gas purification catalyst by temperature. In addition, it is possible to expect effects such as improvement in fuel consumption due to weight reduction and securing of a space for installing a new device.

The honeycomb structure of the present invention is made of a material containing zeolite, and since the specific gravity of zeolite is small, the honeycomb structure can be further lightened. Also. Even if the pore diameter is as small as about 2 μm, it is considered that the above effect becomes more remarkable by the function that the pressure loss can be lowered and the amount of zeolite to be loaded can be increased. The pressure loss can be reduced even when the pore diameter of the honeycomb structure of the present invention is smaller than the pore diameter (10 μm to 20 μm) of a general DPF or SCRF (DFF with SCR catalyst). This is considered to be due to the low gas flow resistance. The reason why the amount of zeolite loaded can be increased is that the strength of the honeycomb structure can be maintained even if the zeolite forms a skeleton.

A light honeycomb structure is considered to contribute to weight reduction. Low pressure loss is thought to contribute to a reduction in exhaust gas resistance. Moreover, it can be considered that the fact that the pore diameter can be reduced in a state where the pressure loss is reduced contributes to efficiently capturing a substance smaller than PM2.5. Rich zeolites amount improves NO _X purification catalyst efficiency is believed to contribute to increasing the reducing agent storage amount. Further, the abundant amount of zeolite is considered to contribute also as a catalyst carrier and a catalyst when the first catalyst and the second catalyst are integrated.

Hereinafter, the present invention will be described in more detail based on examples. The present invention is not limited to the following examples, and can be implemented with appropriate modifications without departing from the scope of the invention. The meanings of the abbreviations are as follows. The average particle diameters of bentonite and ceramic raw material were measured with a laser diffraction particle size distribution measuring device (manufactured by Shimadzu Corporation, product number “SALD-2100”). The length and average fiber diameter were measured with a scanning electron microscope (manufactured by Hitachi High-Technology Corporation, product number “S-4800”).

Bentonite A: Bentonite (average particle size 10 μm, trade name: Bengel VA, manufactured by Kunimine Industries)
Bentonite B: Bentonite (average particle size 2 μm, trade name: Kunipia F, manufactured by Kunimine Industries)
Inorganic fiber A: K ₂ Ti ₄ O ₉ (average fiber length 20 μm, average fiber diameter 0.5 μm)
Inorganic fiber B: K ₂ Ti ₆ O ₁₃ (average fiber length 15 μm, average fiber diameter 0.5 μm, trade name: TISMON, manufactured by Otsuka Chemical Co., Ltd.)
Inorganic fiber C: K ₂ Ti ₈ O ₁₇ (average fiber length 15 μm, average fiber diameter 0.5 μm, trade name: TISMOD, manufactured by Otsuka Chemical Co., Ltd.)
Inorganic fiber D: Na ₂ Ti ₆ O ₁₃ (average fiber length 20 μm, average fiber diameter 0.6 μm)
Ceramic raw material: Aluminum titanate (average particle size 13 μm, manufactured by Marusu Glaze

<Manufacture of zeolite>
Zeolite A used in Examples and Comparative Examples was a commercially available ZSM-5 type zeolite (trade name: HSZ-840NHA, manufactured by Tosoh Corporation). In addition, zeolites B to G used in the examples were produced as follows. Table 1 shows the crystal structures of zeolites A to G, the silica / alumina ratio, the average particle diameter of primary particles, the average particle diameter of secondary particles, and the crushing strength. The crystal structure is confirmed by an X-ray diffractometer (Rigaku, product number “RINT2000-Utima +”), and the silica / alumina ratio is measured by a fluorescent X-ray analyzer (Rigaku, product number “ZSX Prmus II”). Calculated from the results, the average particle size of primary particles was measured with a scanning electron microscope (manufactured by Hitachi High-Technology Corporation, product number “S-4800”), and the average particle size of secondary particles was measured with a laser diffraction particle size distribution analyzer ( The product number was “SALD-2100” manufactured by Shimadzu Corporation. The crushing strength was measured using a micro compression tester MCTW-500MC (manufactured by Shimadzu Corporation, used indenter: Φ = 50 μm) and compressed at a load speed of 0.892 mN / s at room temperature (20 ° C.) and in the atmosphere. The strength was measured.

(Production Example 1: Zeolite B)
Silica as the silica source (Cabot, trade name “Cab-O-Sil M5”), aluminum hydroxide as the alumina source (Wako Pure Chemical Industries), and tetrabutylammonium hydroxide (TBAOH, Kanto Chemical) as the structure directing agent Co., Ltd.), potassium hydroxide (manufactured by Wako Pure Chemical Industries) is used as a mineralizer, and the composition is SiO ₂ / Al ₂ O ₃ = 40, TBAOH / SiO ₂ = 0.1, KOH / SiO ₂ = 0.05 , H ₂ O / SiO ₂ = 100 was prepared, and the aqueous gel was hydrothermally synthesized in an autoclave at 160 ° C. for 5 days. Thereafter, the solid was collected by filtration, washed with distilled water, and dried at 80 ° C. for 12 hours to obtain zeolite B.

(Production Example 2: Zeolite C)
Silica as the silica source (Cabot, trade name “Cab-O-Sil M5”), aluminum hydroxide as the alumina source (Wako Pure Chemical Industries), and tetrabutylammonium hydroxide (TBAOH, Kanto Chemical) as the structure directing agent ), Sodium fluoride (manufactured by Wako Pure Chemical Industries, Ltd.) is used as a mineralizer, and the composition is SiO ₂ / Al ₂ O ₃ = 40, TBAOH / SiO ₂ = 0.1, NaF / SiO ₂ = 1. 6. An aqueous gel having H ₂ O / SiO ₂ = 100 was prepared, and this aqueous gel was hydrothermally synthesized in an autoclave at 160 ° C. for 5 days. Thereafter, the solid was collected by filtration, washed with distilled water, and dried at 80 ° C. for 12 hours to obtain zeolite C.

(Production Example 3: Zeolite D)
Silica as the silica source (Cabot, trade name “Cab-O-Sil M5”), aluminum hydroxide as the alumina source (Wako Pure Chemical Industries), and tetrabutylammonium hydroxide (TBAOH, Kanto Chemical) as the structure directing agent ), Sodium fluoride (manufactured by Wako Pure Chemical Industries, Ltd.) is used as a mineralizer, and the composition is SiO ₂ / Al ₂ O ₃ = 40, TBAOH / SiO ₂ = 0.1, NaF / SiO ₂ = 0. 8. An aqueous gel was prepared so that H ₂ O / SiO ₂ = 100, and this aqueous gel was hydrothermally synthesized in an autoclave at 160 ° C. for 5 days. Thereafter, the solid was collected by filtration, washed with distilled water, and dried at 80 ° C. for 12 hours to obtain zeolite D.

(Production Example 4: Zeolite E)
Silica (Cabot, trade name “Cab-O-Sil M5”) as the silica source, aluminum hydroxide (Wako Pure Chemicals) as the alumina source, and tetrabutylammonium hydroxide (TBAOH, manufactured by Kanto Chemical) as the structure directing agent ), Potassium hydroxide (manufactured by Wako Pure Chemical Industries, Ltd.) is used as the mineralizer, and the composition is SiO ₂ / Al ₂ O ₃ = 40, TBAOH / SiO ₂ = 0.1, KOH / SiO ₂ = 1.0, H An aqueous gel was prepared so that ₂ O / SiO ₂ = 100, and this aqueous gel was hydrothermally synthesized in an autoclave at 160 ° C. for 5 days. Thereafter, the solid was collected by filtration, washed with distilled water, and dried at 80 ° C. for 12 hours to obtain zeolite E.

(Production Example 5: Zeolite F)
Silica as the silica source (Cabot, trade name “Cab-O-Sil M5”), aluminum hydroxide as the alumina source (Wako Pure Chemical Industries), and tetrabutylammonium hydroxide (TBAOH, Kanto Chemical) as the structure directing agent ), Sodium fluoride (manufactured by Wako Pure Chemical Industries, Ltd.) is used as a mineralizer, and the composition is SiO ₂ / Al ₂ O ₃ = 40, TBAOH / SiO ₂ = 0.1, NaF / SiO ₂ = 0. 4. An aqueous gel was prepared such that H ₂ O / SiO ₂ = 100, and this aqueous gel was hydrothermally synthesized in an autoclave at 160 ° C. for 5 days. Thereafter, the solid was collected by filtration, washed with distilled water, and dried at 80 ° C. for 12 hours to obtain zeolite F.

(Production Example 6: Zeolite G)
Silica as a silica source (Cabot, trade name “Cab-O-Sil M5”), Alumina as an aluminum source (Wako Pure Chemicals), Tetrapropylammonium hydroxide (TPAOH, Kanto Chemical) as a structure directing agent Company), sodium hydroxide (manufactured by Wako Pure Chemical Industries) is used as a mineralizer, and the composition is SiO ₂ / Al ₂ O ₃ = 40, TPAOH / SiO ₂ = 0.1, NaOH / SiO ₂ = 0.1 , H ₂ O / SiO ₂ = 100 was prepared, and the aqueous gel was hydrothermally synthesized in an autoclave at 160 ° C. for 5 days. Thereafter, the solid was collected by filtration, washed with distilled water, and dried at 80 ° C. for 12 hours to obtain zeolite G.

<Manufacture of honeycomb structure>
Example 1
To 70 parts by mass of zeolite A, 10 parts by mass of ceramic raw material, 8 parts by mass of inorganic fiber B, 8 parts by mass of bentonite A, 3 parts by mass of graphite, 10 parts by mass of methyl cellulose, and 0.5 parts by mass of fatty acid soap are blended. An appropriate amount of water was added and kneaded to obtain an extrudable clay (mixture).

The obtained kneaded material (mixture) was extruded and molded to form a honeycomb structure with an extruder, and a molded body was obtained. The cell density of the mold was 300 cells / square inch (46.5 cells / cm ² ), and the partition wall thickness was 300 μm. The aperture ratio was 63%.

A slurry was prepared in which the solid content was almost composed of ceramic raw material, zeolite A, inorganic fiber B, bentonite A, and additives such as viscosity modifiers were added. In addition, the ratio of the solid content in a slurry is the same as the above. In the formed body which is a honeycomb structure, the slurry was injected into the cells of the honeycomb structure and sealed so that the opened cells and the sealed cells were alternately in a checkered pattern.

The obtained molded body was held at 600 ° C. for 10 hours, then heated to 975 ° C. at 25 ° C./hour, and further held at 975 ° C. for 5 hours and fired to obtain a pore diameter of 2.0 μm and porosity. A 58% honeycomb structure was obtained.

The obtained honeycomb structure was impregnated with a 5% by mass aqueous copper acetate solution at 60 ° C. for 3 hours. Thereafter, the honeycomb structure of the present invention was manufactured by thoroughly washing with ion-exchanged water and heating at 700 ° C. for 10 hours.

(Example 2 to Example 53, Comparative Example 1 to Comparative Example 8)
A honeycomb structure was manufactured in the same manner as in Example 1 except that the mixture was blended so that the blend composition was as shown in Tables 2 to 5.

(Example 54)
The honeycomb structure obtained in Example 2 was impregnated with a slurry of cupric oxide powder (average particle size 4 μm) so that the supported amount of CuO per volume in the honeycomb structure was 10 g / L, and 700 ° C. The honeycomb structure was manufactured by supporting CuO by heating for 10 hours.

(Example 55 to Example 57)
A honeycomb structure was manufactured in the same manner as in Example 54 except that the supported amount of CuO was changed to the amount shown in Table 6.

The pore diameters and the porosity of the honeycomb structures obtained in Examples 1 to 53 and Comparative Examples 1 to 8 are shown in Tables 2 to 5 below.

<Evaluation of honeycomb structure>
(Evaluation of NO _X gas performance (250 ° C))
For the honeycomb structures obtained in Examples 1 to 57 and Comparative Examples 1 to 8, the honeycomb structures were dried in advance at 100 ° C., and the honeycomb structures were placed in a simulated exhaust gas exhaust line. Thereafter, the simulated exhaust gas (O ₂ : 10%, N ₂ : 85%, NO: 500 ppm, NH ₃ : 500 ppm, H ₂ O: 5%, SV = 50000 / h) is raised to 250 ° C., and the NO _X concentration is increased. It was measured. From the obtained results were calculated NO _X purification rate. The results are shown in Tables 2-6.

(Evaluation of NO _X gas performance (500 ° C))
Regarding the honeycomb structures obtained in Example 2 and Examples 54 to 57, the honeycomb structures were previously dried at 100 ° C., and the honeycomb structures were installed in the simulated exhaust gas exhaust line. Thereafter, the simulated exhaust gas (O ₂ : 10%, N ₂ : 85%, NO: 500 ppm, NH ₃ : 500 ppm, H ₂ O: 5%, SV = 50000 / h) is raised to 500 ° C., and the NO _X concentration is increased. It was measured. From the obtained results were calculated NO _X purification rate. The results are shown in Table 6.

(Bending strength)
With respect to the honeycomb structures obtained in Examples 1 to 53 and Comparative Examples 1 to 8, the honeycomb structure 2 of 3 × 3 cells was formed by supporting

points

21 and 22 as shown in FIG. In the supported state, the central portion of the honeycomb structure 2 was pressed with the pressing rod 20, and the bending strength was measured according to JIS R1601, and the results are shown in Tables 2 to 5.

(Zeolite concentration)
For the honeycomb structures obtained in Examples 1 to 53 and Comparative Examples 1 to 8, the ratio of the concentration of zeolite in the surface portion of the cell wall to the concentration of zeolite contained in the central portion of the cell wall (surface (Part / center part) was confirmed to be in the range of 0.8 to 1.2.

The confirmation method was as follows. Using tweezers or the like, the surface of the cell wall is scraped, and the surface portion components are recovered in a powder state. Similarly, a powdery sample is collected from the central portion of the cell wall thickness. From the X-ray diffraction analysis of these powdery samples, the concentration of zeolite containing zeolite was measured on the surface and center of the cell wall. For the X-ray diffraction analysis, a RINT 2500PC apparatus (manufactured by Rigaku Corporation) was used.

(Playback rate)
For the honeycomb structures obtained in Example 2 and Examples 54 to 57, the initial weight of the honeycomb structures was measured in advance. Next, an exhaust gas purification filter including an oxidation catalyst (DOC) and a honeycomb structure was sequentially installed in the exhaust line of the diesel engine. After installation, the diesel engine is started, PM is deposited in a predetermined amount (about 8 g / L) under the operating conditions where the exhaust temperature is low, the honeycomb structure is once removed, and the weight of the deposited PM (PM deposition weight) Was measured.

Next, after the honeycomb structure on which PM was deposited was installed in the exhaust line of the simulated exhaust gas, the simulated exhaust gas was raised to 480 ° C. and a regeneration test was started. The temperature of 480 ° C. ± 10 ° C. was maintained for 30 minutes from the time when the temperature reached 480 ° C., and after 30 minutes, the entire amount of the simulated exhaust gas was switched to nitrogen gas.

After the temperature dropped to room temperature, the honeycomb structure was taken out again, the weight loss (= PM combustion weight) was measured, and the regeneration rate was calculated by the following formula. The results are shown in Table 6.

Regeneration rate (%) = 100 − [(PM deposition weight (g) −PM combustion weight (g)) / PM deposition weight (g)] × 100

As is apparent from the results shown in Tables 1 to 5, when the honeycomb structures of Examples 1 to 18 and Examples 48 to 53 according to the present invention were used, NO _X reduction efficiency (NOx purification rate) And a honeycomb structure having high mechanical strength (bending strength). Further, from comparison between Example 1 to Example 18 and Example 19 to Example 36, the mechanical strength (bending strength) can be further improved by selecting bentonite and bentonite B in which the proportion of montmorillonite is higher than bentonite A. Can be high. In Example 2, from the comparison between Example 52 and Example 53 to Example 48 to Example 51, the average particle diameter of the zeolite primary particles by a specific range, NO _X reduction efficiency (NOx purification It can be seen that the ratio is further improved.

On the other hand, Comparative Examples 1 to 5 excluding either inorganic fibers or bentonite have low mechanical strength (bending strength). From Comparative Examples 6 to 8, when bentonite is replaced with aluminum hydroxide or silicon dioxide, the mechanical strength (bending strength) decreases in the same manner. When replaced with magnesium hydroxide, NO _X reduction efficiency (NOx (Purification rate) decreases.

NO _X reduction efficiency by using a combination of zeolite and inorganic fibers and bentonite (NOx purification rate) is high and the mechanical strength (flexural strength) becomes high honeycomb structure.

Even bentonite elemental composition is replaced with the same talc, although the same trend, in view of enhancing NO _X reduction efficiency (NOx purification rate) and mechanical strength (flexural strength) and the further, bentonite is preferred over talc .

As apparent from the results shown in Table 6, if according to the invention using the honeycomb structures of Examples 54 to Example 57, without reducing the NO _X reduction efficiency (NOx purification rate), PM removal efficiency (regeneration It can be seen that the rate is improved. It is confirmed that the honeycomb structures of Examples 54 to 57 have the same bending strength as that of Example 2 even when CuO is supported.

DESCRIPTION OF

SYMBOLS

2,11 ...

Honeycomb structure

11a, 11b ... 1st, 2nd end surface 11c ... Side surface 12 ... Cell 12a ... Outermost cell 13 ... Cell wall 13a ... Cell wall 13b which comprises an outer edge wall ... No outer edge wall is comprised Cell wall 14 ... outer edge wall 15 ... corner portion 20 ... pressing

bars

21, 22 ... support points

Claims

A honeycomb structure having a shape in which a plurality of cells extending from one end face to the other end face along a longitudinal direction is partitioned by a cell wall, wherein the honeycomb structure includes zeolite, clay mineral, and inorganic fiber. A honeycomb structure comprising a sintered body of a mixture containing
The zeolite is at least one selected from mordenite-type zeolite, faujasite-type zeolite, A-type zeolite, L-type zeolite, β-zeolite, ZSM-5-type zeolite, and CHA-type zeolite. Item 2. The honeycomb structure according to Item 1.
The honeycomb structure according to claim 1 or 2, wherein an average particle size of primary particles of the zeolite is 0.1 µm to 20 µm.
The honeycomb structure according to any one of claims 1 to 3, wherein the clay mineral is a layered clay mineral.
The honeycomb structure according to any one of claims 1 to 4, wherein the inorganic fibers have an average fiber length of 1 µm to 300 µm and an average aspect ratio of 3 to 200.
The honeycomb structure according to any one of claims 1 to 5, wherein the inorganic fiber has a Mohs hardness of 5 or less.
The honeycomb according to any one of claims 1 to 6, wherein a content of the clay mineral in the mixture is 1 to 50 parts by mass with respect to 100 parts by mass of the zeolite. Structure.
The honeycomb according to any one of claims 1 to 7, wherein a content of the inorganic fiber in the mixture is 1 to 50 parts by mass with respect to 100 parts by mass of the zeolite. Structure.
The honeycomb structure according to any one of claims 1 to 8, wherein the mixture further contains a ceramic raw material.
The honeycomb structure according to claim 9, wherein the ceramic raw material is at least one selected from silicon carbide, cordierite, mullite, alumina, and aluminum titanate.
The ratio of the concentration of the zeolite in the surface portion of the cell wall to the concentration of the zeolite contained in the central portion of the cell wall (surface portion / center portion) is in the range of 0.8 to 1.2. The honeycomb structure according to any one of claims 1 to 10, wherein the honeycomb structure is characterized.
The honeycomb structure according to any one of claims 1 to 11, wherein the zeolite is a catalyst for reducing nitrogen oxides to nitrogen.
An exhaust gas purification apparatus comprising the honeycomb structure according to any one of claims 1 to 12.