JP2017007911A - Manufacturing method of zeolite mixed particle, honeycomb catalyst therewith and exhaust gas purifying equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of zeolite mixed particles which can give high NOx clarification performance when used for SCR system.SOLUTION: A manufacturing method of zeolite mixed particles includes: a synthesis step synthesizing zeolite particles A having CHA structure which mean particle size is 0.5-3 μm by using a raw material composition containing Si source, Al source, alkali source and structure provision agent; a miniaturization step getting zeolite particles B having CHA structure which mean particle size is lower than 0.5 μm by miniaturizing the zeolite particles A; and a blending step blending the zeolite particles A and the zeolite particles B.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing zeolite mixed particles, a honeycomb catalyst using the zeolite mixed particles, and an exhaust gas purification device.

  Conventionally, an SCR (Selective Catalytic Reduction) system that uses ammonia to reduce NOx to nitrogen and water has been known as one of systems for purifying exhaust gas from automobiles. Zeolite having a site (Chabazite: CHA) structure has attracted attention as a zeolite having an SCR catalytic action.

  Patent Document 1 discloses an SCR system using a zeolite having a CHA structure on which Cu is supported (hereinafter sometimes referred to as CHA-type zeolite), and has a plurality of longitudinally extending through holes through which exhaust gas passes. A side-by-side honeycomb unit is used as the SCR catalyst carrier.

Patent Document 2 discloses that the SiO ₂ / Al ₂ O ₃ composition ratio is less than 15 and the average particle size is 1.0 for the purpose of improving heat resistance and durability when used as an SCR catalyst carrier. ˜8.0 μm CHA-type zeolite is disclosed.

  On the other hand, in order to improve the packing rate of the zeolite structure, Patent Document 3 describes fine zeolite particles having a small average particle diameter and coarse zeolite particles having an average particle diameter three times or more than the fine zeolite particles. A technique to be used in combination is disclosed. ZSM-5 (MFI), beta (BEA), Y type faujasite (FAU), mordenite (MOR), ferrierite (FERRite): FERERITE: FER ) Is used.

JP 2007-296521 A JP 2012-211066 A JP 2011-201722 A

  In the SCR catalyst carrier, it is desired that the CHA-type zeolite is highly crystallized and the CHA-type zeolite is highly filled in order to improve the NOx purification performance. However, when trying to increase the crystallinity of the CHA-type zeolite, the average particle size must be increased, and the CHA-type zeolite cannot be packed in the honeycomb catalyst at a high density, which has a problem in NOx purification performance. Was. For this reason, it is conceivable to synthesize zeolite with a small average particle diameter. However, the CHA-type zeolite described in Patent Document 2 still has a large particle diameter and cannot solve the above problems. In addition, if the technique described in Patent Document 2 is employed to reduce the average particle size of the zeolite, it is necessary to shorten the synthesis time, and the obtained CHA-type zeolite has low crystallinity, resulting in an SCR system. There has been a problem that the catalyst performance in the case is reduced.

The present invention has been made to solve the above problems, and provides a method for producing CHA-type zeolite mixed particles having high crystallinity and capable of obtaining a sufficient catalyst density when used in an SCR system. The purpose is to provide.
Another object of the present invention is to provide a honeycomb catalyst and an exhaust gas purification device that are excellent in NOx purification performance using the zeolite mixed particles obtained by the production method.

  As a result of intensive studies, the present inventors have determined that zeolite particles A having a CHA structure having an average particle diameter in a specific range and zeolite particles B having a CHA structure having a smaller average particle diameter than the zeolite particles A in a specific range. The present inventors have found that zeolite mixed particles having a CHA structure obtained by mixing and can solve the above problems, and have completed the present invention.

  That is, the method for producing zeolite mixed particles of the present invention uses a raw material composition containing a Si source, an Al source, an alkali source, and a structure directing agent, and has a CHA structure with an average particle size of 0.5 to 3 μm. A synthesis step of synthesizing A, a refinement step of obtaining zeolite particles B having a CHA structure having an average particle size of less than 0.5 μm by refining the zeolite particles A, and the zeolite particles A and the zeolite particles B. Mixing step.

The zeolite mixed particles obtained by the production method of the present invention are composed of CHA-type zeolite particles A having an average particle size of 0.5 to 3 μm and CHA-type zeolite particles B having an average particle size of less than 0.5 μm and a small particle size. Since they are mixed, when used in the honeycomb catalyst, the gap between the zeolite particles A is filled with the zeolite particles B so that the honeycomb catalyst can be filled with high density. Therefore, the NOx purification performance of the catalyst can be enhanced. Furthermore, since it can be filled at a high density, it can contribute to the miniaturization of the entire SCR system by exhibiting a high NOx purification performance even in a small volume. Moreover, by manufacturing in this way, the manufacturing process can be simplified, the SiO ₂ / Al ₂ O ₃ composition ratio (SAR) of each zeolite particle can be adjusted to the same value, and the individual variation in NOx purification performance varies. Can be suppressed.

  In the method for producing zeolite mixed particles of the present invention, before performing the mixing step, the zeolite particles B having a CHA structure refined by the refinement step are mixed with a solution containing a Si source and an alkali source, and hydrated. It is preferable to further include the recrystallization process to process. By performing the recrystallization process, the crystal structure of the zeolite particles B damaged in the refinement process can be restored, and the NOx purification performance can be improved.

In the method for producing the mixed particles of zeolite of the present invention, the above-mentioned zeolite particles A have a sum of integrated intensities of the (211) plane, (104) plane and (220) plane of the X-ray diffraction spectrum by the powder X-ray analysis method being 50,000. Thus, the zeolite particles B preferably have a sum of the integrated strengths of 70% or more of the zeolite particles A. (211) plane of all the particles X-ray diffraction spectrum, the (104) plane and (220) plane of the sum of integrated intensity (hereinafter, also referred to as a sum X ₀ of integrated intensity) to have a high, i.e. higher crystallinity Therefore, the NOx purification performance can be further improved.

  In the method for producing mixed particles of zeolite of the present invention, the mixing ratio (mass ratio) of the zeolite particles A and the zeolite particles B is preferably 8: 2 to 4: 6. By mixing the zeolite particles A and the zeolite particles B in the above range, when used as an SCR honeycomb catalyst, the catalyst density can be sufficiently increased, and the contact efficiency between the exhaust gas and the catalyst can be sufficiently increased. As a result, the NOx purification performance can be improved.

In the method for producing zeolite mixed particles of the present invention, it is preferable that both the zeolite particles A and the zeolite particles B have a SiO ₂ / Al ₂ O ₃ composition ratio (SAR) of less than 15. If the SiO ₂ / Al ₂ O ₃ composition ratio (SAR) of zeolite particles A and zeolite particles B is both less than 15, the amount of alumina increases, and the supported amount of a metal such as Cu that functions as a catalyst in proportion thereto increases. Since it can be increased, the NOx purification performance can be further enhanced.

  In the method for producing zeolite mixed particles of the present invention, it is preferable that both the zeolite particles A and the zeolite particles B carry Cu, and the Cu / Al (molar ratio) is 0.2 to 0.5. When the supported amount of Cu is within the above range, high NOx purification performance can be obtained with a small amount of zeolite, that is, even if the volume of the catalyst is reduced.

  A honeycomb catalyst of the present invention includes a honeycomb unit in which a plurality of longitudinally extending through holes are arranged in parallel with a partition wall therebetween, and the honeycomb unit includes zeolite mixed particles and an inorganic binder, and the zeolite mixed particles are the above It is a zeolite mixed particle obtained by the method for producing a zeolite mixed particle of the present invention. Since the honeycomb catalyst of the present invention is configured using the zeolite mixed particles obtained by the method for producing mixed particles of zeolite of the present invention, a honeycomb catalyst composed of a honeycomb unit having high NOx purification performance can be obtained.

  In the exhaust gas purifying apparatus of the present invention, a holding sealing material is disposed on the outer periphery of the honeycomb catalyst and canned in a metal container. Since the exhaust gas purification apparatus of the present invention includes the honeycomb catalyst of the present invention, it is excellent in NOx purification performance.

ADVANTAGE OF THE INVENTION According to this invention, when it uses as a SCR catalyst with high crystallinity, the manufacturing method of the zeolite mixed particle which can be filled with a high density in a catalyst can be provided.
Further, according to the present invention, it is possible to provide a honeycomb catalyst and an exhaust gas purification device that are excellent in NOx purification performance using the zeolite mixed particles.

It is a perspective view which shows typically an example of the honeycomb catalyst of this invention. It is sectional drawing which shows typically an example of the exhaust gas purification apparatus of this invention. It is a perspective view which shows typically another example of the honeycomb catalyst of this invention. Fig. 4 is a perspective view schematically showing an example of a honeycomb unit constituting the honeycomb catalyst shown in Fig. 3. 3 is a chart showing an XRD pattern of zeolite particles A of Example 1. FIG. 2 is a chart showing an XRD pattern of zeolite particles obtained in the refinement process of Example 1. FIG. 3 is a chart showing an XRD pattern of zeolite particles B obtained in the recrystallization process of Example 1. FIG.

(Detailed description of the invention)
Hereinafter, the present invention will be specifically described. However, the present invention is not limited to the following description, and can be appropriately modified and applied without departing from the scope of the present invention.

  The method for producing zeolite mixed particles according to the present invention comprises using a raw material composition containing a Si source, an Al source, an alkali source, and a structure directing agent to produce zeolite particles A having a CHA structure having an average particle size of 0.5 to 3 μm. A synthesizing step for synthesizing, a micronizing step for refining the zeolite particles A to obtain a zeolite particle B having a CHA structure with an average particle diameter of less than 0.5 μm, and mixing the zeolite particles A and the zeolite particles B And a mixing step.

  Each zeolite particle in the present invention is named and classified by the structure code CHA in the International Zeolite Association (IZA), and has a crystal structure equivalent to that of naturally occurring chabazite. Zeolite.

<Zeolite particles A>
The zeolite particles A of the present invention have a CHA structure, and the average particle size is 0.5 to 3 μm. If the average particle size is 0.5 μm or more, highly crystalline CHA-structured zeolite particles can be obtained, and if it is 3 μm or less, the density of the catalyst layer can be easily increased. If the average particle diameter is larger than 3 μm, a large amount of zeolite fine particles are required to increase the density of the catalyst layer, and accordingly, a refinement step described later is required. From the viewpoint of increasing the density of the catalyst layer, the average particle size of the zeolite particles A is preferably 0.5 to 2.5 μm, more preferably 0.5 to 2.0 μm.

  The average particle size of the zeolite was measured using a scanning electron microscope (SEM, manufactured by Hitachi High-Tech, S-4800) at a magnification of 20000, and the total diagonal length of 10 particles in the SEM image was calculated. Measure and obtain from the average value. Measurement conditions are as follows: acceleration voltage: 1 kV, emission: 10 μA, WD: 2.2 mm or less. In general, the CHA-type zeolite particles are cubic, and become a square when two-dimensionally imaged by an SEM photograph. Therefore, there are two diagonal lines of particles.

  Analysis of the crystal structure of the zeolite particles A can be performed using an X-ray diffraction (XRD) apparatus. The CHA-type zeolite is an X-ray diffraction spectrum by a powder X-ray analysis method, and the (211) plane of the CHA-type zeolite crystals at 2θ = 20.7 °, 25.1 °, and 26.1 °, respectively ( The peaks corresponding to the (104) plane and the (220) plane appear.

XRD measurement is performed using an X-ray diffractometer (Uriga IV manufactured by Rigaku Corporation). The measurement conditions are as follows.
Radiation source: CuKα (λ = 0.154 nm), measurement method: FT method, diffraction angle: 2θ = 5-48 °, step width: 0.02 °, integration time: 1 second, divergence slit, scattering slit: 2 / 3 °, divergence length limiting slit: 10 mm, acceleration voltage: 40 kV, acceleration current: 40 mA.
The sample weight should not be changed by 0.1% or more before and after the XRD measurement. The obtained XRD data is subjected to peak search using the powder X-ray diffraction pattern comprehensive analysis software JADE 6.0, and the half width and integrated intensity of each peak are calculated. The peak search conditions are as follows.
Filter type: parabolic filter, Kα2 peak elimination: yes, peak position definition: peak top, threshold σ: 3, peak intensity% cutoff: 0.1, BG determination range: 1, BG averaging points: 7 .
From the obtained data, the (211) plane (near 2θ = 20.7 °), (104) plane (near 2θ = 25.1 °), (220) plane (near 2θ = 26.1 °) of the zeolite. it can be the sum X ₀ of the integrated intensity. The reason why the integrated intensity of the peaks of the (211) plane, (104) plane, and (220) plane of zeolite is used is that the influence of water absorption of the sample is small.

In the present invention, the sum _{X 0} of the integrated intensities of the zeolite particles A is preferably 50000 or more. When the sum _{X 0} of the integrated intensity is more than 50000, has high crystallinity, it is possible to improve the NOx purification performance. Sum _{X 0} of the integrated intensity, from the viewpoint of further improving the NOx purification performance, and more preferably from 52,000 to 70,000, more preferably 55,000 to 65,000.

The zeolite particles A of the present invention preferably have a SiO ₂ / Al ₂ O ₃ composition ratio (SAR) of less than 15. The composition ratio of SiO ₂ / Al ₂ O ₃ means the molar ratio (SAR) of SiO ₂ to Al ₂ O ₃ in the zeolite. When the composition ratio SiO ₂ / Al ₂ O ₃ is less than 15, the acid sites of the zeolite can be made a sufficient number, and the acid sites can be used for ion exchange with metal ions. Since the amount of the metal supported can be increased, the NOx purification performance is excellent.
A more preferable SiO ₂ / Al ₂ O ₃ composition ratio is 10 to 14.9.
In addition, the molar ratio (SiO ₂ / Al ₂ O ₃ ) of the zeolite particles A can be measured using fluorescent X-ray analysis (XRF).

<Synthesis process>
In the synthesis process of zeolite particles A of the present invention, first, a raw material composition comprising a Si source, an Al source, an alkali source, water and a structure directing agent is prepared.

The Si source refers to a compound, a salt, and a composition that are raw materials for the silicon component of zeolite.
As the Si source, for example, colloidal silica, amorphous silica, sodium silicate, tetraethylorthosilicate, aluminosilicate gel, and the like can be used, and two or more of these may be used in combination. Of these, colloidal silica is desirable.

  Examples of the Al source include aluminum sulfate, sodium aluminate, aluminum hydroxide, aluminum chloride, alumino-silicate gel, and dry aluminum hydroxide gel. Of these, dry aluminum hydroxide gel is preferred.

In the synthesis process of the present invention, the Si source and the Al source are desirably Si sources and Al sources having a molar ratio substantially the same as the molar ratio of the zeolite particles A to be produced (SiO ₂ / Al ₂ O ₃ ). The molar ratio (SiO ₂ / Al ₂ O ₃ ) in the raw material composition is preferably less than 15 and more preferably 10-15.

  In the synthesis step of the present invention, examples of the alkali source include sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide, lithium hydroxide, aluminate and alkali components in silicate, and aluminosilicate gel. An alkali component or the like can be used, and two or more of these may be used in combination. Of these, potassium hydroxide, sodium hydroxide, and lithium hydroxide are desirable. In order to obtain a single phase of zeolite, it is particularly preferable to use potassium hydroxide and sodium hydroxide in combination.

In the synthesis step of the present invention, the amount of water is not particularly limited, but the ratio of the number of moles of water to the total number of moles of Si of the Si source and Al of the Al source (H ₂ O moles / Si and The total number of moles of Al is preferably 12-30, and the ratio of the number of moles of water to the total number of moles of Si of the Si source and Al of the Al source (number of moles of H ₂ O / total number of moles of Si and Al) ) Is more preferably 15-25.

A structure directing agent (hereinafter also referred to as SDA) refers to an organic molecule that defines the pore diameter and crystal structure of zeolite. The structure of the obtained zeolite can be controlled by the type of the structure-directing agent.
In the synthesis process of the present invention, as the structure directing agent, hydroxides, halides, carbonates, methyl carbonate salts, sulfates and nitrates having N, N, N-trialkyladamantanammonium as a cation; and N, N , N-trimethylbenzylammonium ion, N-alkyl-3-quinuclidinol ion, or a hydroxide, halide, carbonate, methyl carbonate salt having N, N, N-trialkylexoaminonorbornane as a cation, At least one selected from the group consisting of sulfates and nitrates can be used. Among these, N, N, N-trimethyladamantanammonium hydroxide (hereinafter also referred to as TMAAOH), N, N, N-trimethyladamantanammonium halide, N, N, N-trimethyladamantanammonium carbonate, It is desirable to use at least one selected from the group consisting of N, N, N-trimethyladamantanammonium methyl carbonate salt and N, N, N-trimethyladamantanammonium sulfate, and it is more desirable to use TMAAOH.

  In the synthesis step of the present invention, zeolite seed crystals may be further added to the raw material composition. By using the seed crystal, the crystallization speed of the zeolite is increased, the time for producing the zeolite can be shortened, and the yield is improved.

  As a zeolite seed crystal, it is desirable to use CHA-type zeolite.

  The amount of zeolite seed crystals added is preferably small, but considering the reaction rate, the effect of suppressing impurities, etc., it should be 0.1 to 20% by mass with respect to the silica component contained in the raw material composition. Desirably, it is more desirable that it is 0.5-15 mass%. If it is less than 0.1% by mass, the contribution to improving the crystallization rate of the zeolite is small, and if it exceeds 20% by mass, impurities are likely to enter the zeolite obtained by synthesis.

  In the synthesis step of the present invention, zeolite is synthesized by reacting the prepared raw material composition. Specifically, it is desirable to synthesize zeolite by hydrothermal synthesis of the raw material composition.

  The reaction vessel used for hydrothermal synthesis is not particularly limited as long as it is used for known hydrothermal synthesis, and may be a heat and pressure resistant vessel such as an autoclave. The zeolite can be crystallized by putting the raw material composition into the reaction vessel, sealing and heating.

  When synthesizing the zeolite, the raw material mixture may be in a stationary state, but is preferably in a state of being stirred and mixed.

  The heating temperature in the synthesis step of the present invention is preferably 100 to 200 ° C, and more preferably 120 to 180 ° C. When the heating temperature is less than 100 ° C., the crystallization rate becomes slow, and the yield tends to decrease. On the other hand, when the heating temperature exceeds 200 ° C., impurities are likely to be generated.

  The heating time in the synthesis step is desirably 10 to 200 hours. If the heating time is less than 10 hours, unreacted raw materials remain and the yield tends to decrease. On the other hand, even when the heating time exceeds 200 hours, the yield and crystallinity are hardly improved.

  The pressure in the synthesis process is not particularly limited, and the pressure generated when the raw material composition placed in a closed container is heated to the above temperature range is sufficient, but if necessary, an inert gas such as nitrogen gas is added. May be boosted.

  It is desirable that the zeolite obtained by the synthesis step be sufficiently cooled, separated into solid and liquid, and washed with a sufficient amount of water.

  Since the zeolite obtained by the synthesis process contains SDA in the pores, it may be removed as necessary. For example, SDA can be removed by a liquid phase treatment using an acidic solution or a chemical solution containing an SDA decomposition component, an exchange treatment using a resin, a thermal decomposition treatment, or the like.

  The average particle diameter of the CHA-type zeolite particles A obtained by the above synthesis process is 0.5 to 3 μm.

Incidentally, the sum X ₀ of the integrated intensities of the zeolite particles A is described above, the raw material mixing ratio can be adjusted by such synthesis temperature and synthesis time.

<Cu ion exchange>
In the present invention, it is preferable to perform Cu ion exchange on the CHA-type zeolite particles A.
The Cu ion exchange method can be carried out by immersing CHA-type zeolite in a kind of aqueous solution selected from an aqueous copper acetate solution, an aqueous copper nitrate solution, an aqueous copper sulfate solution, and an aqueous copper chloride solution. Of these, it is preferable to use an aqueous copper acetate solution. This is because a large amount of Cu can be supported at one time. For example, an aqueous solution of copper (II) acetate having a copper concentration of 0.1 to 2.5% by mass is subjected to ion exchange at a solution temperature of room temperature to 50 ° C. and atmospheric pressure, thereby supporting Cu on the CHA-type zeolite particles A. it can.

When Cu ion exchange is performed, the Cu / Al (molar ratio) of the obtained zeolite carrying Cu is preferably 0.2 to 0.5, more preferably 0.25 to 0.48. preferable.
When the Cu / Al (molar ratio) is 0.2 or more, high NOx purification performance can be obtained with a small amount of zeolite. Further, when the molar ratio is 0.5 or less, it is possible to prevent NOx purification performance from being deteriorated due to ammonia oxidation at a high temperature. The amount of Cu supported can be measured by ICP emission spectroscopic analysis (ICP-AES). The amount of Al can be measured using the X-ray fluorescence analyzer described above, and the Cu / Al molar ratio can be calculated.

ICP-AES can be measured using an ICP emission spectroscopic analyzer (manufactured by Shimadzu Corporation: ICPE-9000). The measurement conditions are as follows.
As a pretreatment of the sample, 0.1 g of zeolite after Cu ion exchange dried at 400 ° C. for 4 hours is placed in a platinum dish, 5 ml of nitric acid, 20 ml of hydrofluoric acid, and 5 ml of sulfuric acid are added until sulfuric acid white smoke is generated. Heat. This is adjusted to be a 50 ml aqueous solution and used as a measurement sample.
A measurement sample is put into the apparatus, and Cu element is designated to perform measurement.

  By adopting the above conditions, the sum of the integrated intensities of the (211) plane, (104) plane and (220) plane of the X-ray diffraction spectrum by the powder X-ray analysis method is 50000 or more, and the average particle diameter is Zeolite particles A having a CHA structure of 0.5 to 3 μm can be obtained without extremely impairing the crystal structure.

<Zeolite particles B>
The zeolite particles B of the present invention have a CHA structure, and the average particle size is less than 0.5 μm. When the average particle diameter is less than 0.5 μm, the density can be increased when mixed particles with zeolite particles A are used. The average particle diameter of the zeolite particles B is preferably 0.05 to 0.49 μm, more preferably 0.1 to 0.49 μm from the viewpoint of increasing the density and improving the NOx purification performance.

Further, the sum X ₀ of the integrated intensity of the zeolite particles B of the present invention is preferably 70% or more of the sum X ₀ of the integrated intensity of the zeolite particles A. When the sum X ₀ of the integrated intensity is at least 70% of the zeolite particles A, since it has also high crystalline zeolite particles B, as a mixed particles, thereby improving the NOx purification performance. From the viewpoint of further improving the NOx purification performance, the sum X ₀ of the integrated intensity of the zeolite particles B is preferably 75 to 98%, more preferably 80 to 95% of the sum X ₀ of the integrated intensity of the zeolite particles A. The closer to 100%, the better. However, it is difficult to restore the crystal structure of zeolite particles B that have undergone the refining process and the recrystallization process described later to 100%.

The zeolite particles B of the present invention preferably have a SiO ₂ / Al ₂ O ₃ composition ratio (SAR) of less than 15. The composition ratio of SiO ₂ / Al ₂ O ₃ means the molar ratio (SAR) of SiO ₂ to Al ₂ O ₃ in the zeolite. When the composition ratio SiO ₂ / Al ₂ O ₃ is less than 15, the acid sites of the zeolite can be made a sufficient number, and the acid sites can be used for ion exchange with metal ions. Since the amount of the metal supported can be increased, the NOx purification performance is excellent.
A more preferable SiO ₂ / Al ₂ O ₃ composition ratio is 10 to 14.9.

  The zeolite particles B of the present invention can be obtained by a method of refining the zeolite particles A. That is, the CHA-type zeolite particles A obtained in the synthesis process described above can be manufactured through a refinement process and a recrystallization process.

<Refining process>
In the refinement process of the present invention, the average particle diameter of the CHA-type zeolite particles A obtained in the synthesis process is less than 0.5 μm, preferably 0.05 to 0.49 μm, more preferably 0.1. Grind to ˜0.49 μm.

  As a refining means employed in the refining step of the present invention, an apparatus capable of pulverizing CHA-type zeolite particles A to a desired average particle diameter may be appropriately used, and is not particularly limited. And may be a ball mill, a bead mill, a jet mill or the like. In the present invention, wet grinding using a wet bead mill is preferably employed. By using a wet bead mill, a CHA-type zeolite having a desired average particle diameter can be easily obtained while suppressing a decrease in crystallinity due to pulverization. In the wet bead mill, the coarse powder of the material to be crushed and the beads as a medium are placed in a pulverization chamber together with a liquid dispersion medium, and the beads are agitated by rotating a rotating blade rotating in the pulverization chamber at a high speed. Then, the object to be pulverized is pulverized by applying frictional force or shearing force generated by the beads to the object to be pulverized.

  When the micronization process of the present invention is performed using a wet bead mill, the beads used are preferably at least one selected from the group consisting of zirconia and alumina, and zirconia is particularly preferable.

  In the miniaturization step of the present invention, the particle size of the beads is preferably 30 to 1000 μm, more preferably 50 to 500 μm.

  It is preferable to use the beads 0.5 to 5 times, preferably 2 to 4 times the volume of the CHA-type zeolite. When the amount of beads used is within this range, it is possible to reduce the size to a target average particle size in a short time.

  In the micronization step of the present invention, as the operation condition of the wet bead mill, the rotational speed of the wet bead mill is preferably 1000 to 4200 rpm, and more preferably 1500 to 3500 rpm. The pulverization time is preferably 5 to 60 minutes, and more preferably 10 to 45 minutes. When the rotation speed and the pulverization time are within this range, the particle diameter can be sufficiently controlled. For example, the particle diameter can be controlled to a desired value by appropriately adjusting the grinding time.

  Examples of the dispersion medium include water, and the amount of the dispersion medium introduced into the wet bead mill is 2 to 10 times in terms of volume with respect to the amount of the CHA-type zeolite.

<Recrystallization process>
In the present invention, in order to repair the crystal structure of the zeolite particles damaged in the refinement process, it is preferable to perform a recrystallization process in which the zeolite particles are mixed with a solution containing an Si source and an alkali source and hydrated.

A solution containing an Si source and an alkali source (hereinafter referred to as a recrystallization solution) used in the recrystallization step of the present invention uses 0.03 to 0.5 mol / L of an Si source and 0 to an alkali source using water as a solvent. A solution containing 0.04 to 0.7 mol / L can be used. As the Si source and the alkali source, those listed in the above synthesis step can be used.
The recrystallization solution may contain an Al source. As the Al source, those listed in the above synthesis step can be used.
Furthermore, you may use the solution which has the same composition as the raw material composition containing the Si source in the said synthetic | combination process, Al source, an alkali source, and a structure-directing agent.
Separately from this, the recrystallization solution can be used as it is after the completion of the synthesis step, the CHA-type zeolite and the residual liquid of the reaction liquid taken out, and the residual liquid is concentrated 1 to 5 times, 1/3 It can also be used by diluting to 1-fold.

  The mixing ratio of the CHA-type zeolite particles obtained in the refining step of the present invention and the recrystallization solution is, for example, 1 to 12, when the mass of the CHA-type zeolite particles is 1, Preferably it is 1-8 (henceforth a solid-liquid ratio). By setting the solid-liquid ratio of the CHA-type zeolite particles and the recrystallization solution to 1 to 12, the crystal structure can be restored in a relatively short time.

  For the hydration treatment in the recrystallization step of the present invention, for example, the same conditions as in the hydrothermal synthesis of the raw material composition in the synthesis step can be adopted.

  By the recrystallization process as described above, the crystal structure of the CHA-type zeolite particles damaged in the refinement process is restored, and the crystallinity can be sufficiently enhanced.

  Note that the average particle size of the CHA-type zeolite particles B obtained after the recrystallization step is substantially the same as the average particle size of the CHA-type zeolite obtained after the refining step.

  By the above method, the sum of the integrated intensities of the (211) plane, (104) plane and (220) plane of the X-ray diffraction spectrum by the powder X-ray analysis method is 70% or more of the zeolite particles A, and the average particle diameter Zeolite particles B having a CHA structure having a diameter of less than 0.5 μm can be obtained.

In the present invention, the SiO ₂ / Al ₂ O ₃ composition ratio (SAR) of the zeolite particles A and B is preferably less than 15. If the SiO ₂ / Al ₂ O ₃ composition ratio (SAR) of zeolite particles A and zeolite particles B is both less than 15, the amount of alumina increases, and the supported amount of a metal such as Cu that functions as a catalyst in proportion thereto increases. Since it can be increased, the NOx purification performance can be further enhanced.

<Cu ion exchange process>
In the present invention, it is preferable to perform Cu ion exchange on the CHA-type zeolite particles B.
As a Cu ion exchange method, it can carry out similarly to the method of performing Cu ion exchange with respect to the CHA-type zeolite particle A mentioned above.
In addition, the Cu ion exchange process of the present invention may be performed for each of the CHA-type zeolite particles A and CHA-type zeolite particles B, and after performing the mixing process described later, Cu ion exchange may be performed simultaneously. Even when the Cu ion exchange step is performed after mixing, the same method can be used. By performing the Cu ion exchange at the same time after performing the mixing step, the dispersion of Cu ions supported on the mixed particles can be suppressed.

<Mixing process>
In the mixing step of the present invention, the zeolite particles A and the zeolite particles B obtained in the synthesis step, the refinement step, and the recrystallization step are mixed at a mass ratio of 8: 2 to 4: 6. When the mixing ratio of the zeolite particles A and the zeolite particles B is within the above range, the catalyst density can be sufficiently increased when used as an SCR honeycomb catalyst. Thereby, the contact efficiency between the exhaust gas and the catalyst can be sufficiently increased, and the NOx purification performance can be improved. The mixing ratio of the zeolite particles A and the zeolite particles B is more preferably 7: 3 to 5: 5.

  The mixing means employed in the mixing step of the present invention is not particularly limited as long as it is mixed so as not to impair the crystal structure of the zeolite, but a Henschel mixer, a super mixer, a V-type mixer, a universal mixer, etc. Can be mentioned. In the present invention, it is preferable to employ a Henschel mixer.

<Honeycomb catalyst>
Next, the honeycomb catalyst of the present invention will be described.
The honeycomb catalyst of the present invention is a honeycomb catalyst including a honeycomb unit in which a plurality of through holes extending in the longitudinal direction are arranged in parallel with a partition wall therebetween.

  FIG. 1 shows an example of the honeycomb catalyst of the present invention. A honeycomb catalyst 10 shown in FIG. 1 includes a single honeycomb unit 11 in which a plurality of longitudinally extending through-holes 11a are arranged in parallel with a partition wall 11b therebetween, and an outer peripheral coating layer is formed on the outer peripheral surface of the honeycomb unit 11. 12 is formed. The honeycomb unit 11 includes zeolite mixed particles obtained by the method for producing zeolite mixed particles of the present invention and an inorganic binder.

  In the honeycomb catalyst of the present invention, the maximum peak pore diameter of the partition walls of the honeycomb unit (hereinafter sometimes referred to as the maximum peak pore diameter of the honeycomb unit) is preferably 0.03 to 0.15 μm. It is more desirable that it is 05-0.10 micrometer. If the maximum peak pore size of the honeycomb unit is less than 0.03 μm, the exhaust gas cannot be sufficiently diffused into the partition walls, and the NOx purification performance may be deteriorated. If it exceeds 0.15 μm, the number of pores is reduced. Therefore, the zeolite may not be effectively used for NOx purification.

  The pore diameter of the honeycomb unit can be measured using a mercury intrusion method. The mercury contact angle is 130 °, the surface tension is 485 mN / m, and the pore diameter is in the range of 0.01 to 100 μm. The value of the pore diameter at the maximum peak in this range is called the maximum peak pore diameter.

  In the honeycomb catalyst of the present invention, the porosity of the honeycomb unit is desirably 50 to 55%. When the porosity of the honeycomb unit is less than 50%, the exhaust gas hardly enters the partition walls of the honeycomb unit, and the zeolite mixed particles are not effectively used for NOx purification. On the other hand, when the porosity of the honeycomb unit exceeds 55%, the density of the catalyst layer is too low, the NOx purification performance is lowered, and the strength of the honeycomb unit becomes insufficient. The density of the catalyst layer can be measured as the porosity of the honeycomb catalyst.

The porosity of the honeycomb unit can be measured by a gravimetric method.
The method for measuring the porosity by the gravimetric method is as follows.
The honeycomb unit is cut into a size of 7 cells × 7 cells × 10 mm to obtain a measurement sample. This sample is ultrasonically cleaned with ion-exchanged water and acetone, and then dried at 100 ° C. in an oven. Next, using a measurement microscope (Nikon, Measuring Microscope MM-40, magnification 100 times), the dimensions of the cross-sectional shape of the sample are measured, and the volume is obtained from geometric calculation. In addition, when a volume cannot be calculated | required from geometric calculation, a cross-sectional area is calculated | required by the image processing of a cross-sectional photograph, and a volume is calculated by cross-sectional area x height 10mm.
Thereafter, the weight when the sample is assumed to be a complete dense body is calculated from the calculated volume and the true density of the sample measured with a pycnometer.
The measurement procedure with a pycnometer is as follows. The honeycomb unit is pulverized to prepare 23.6 cc of powder, and the obtained powder is dried at 200 ° C. for 8 hours. Then, true density is measured based on JIS-R-1620 (1995) using Auto Pycnometer 1320 (made by Micromeritics). The exhaust time at this time is 40 minutes.
Next, the actual weight of the sample is measured with an electronic balance (HR202i manufactured by Shimadzu Corporation), and the porosity is calculated by the following calculation formula.
Porosity (%) = 100− (actual weight / weight as dense body) × 100

  In the honeycomb catalyst of the present invention, the zeolite contained in the honeycomb unit is the above-described zeolite mixed particles of the present invention.

  The content of the zeolite mixed particles in the honeycomb unit of the present invention is preferably 40 to 90% by volume, and more preferably 50 to 80% by volume. When the content of the zeolite mixed particles is less than 40% by volume, the NOx purification performance is lowered. On the other hand, if the content of the zeolite mixed particles exceeds 90% by volume, the amount of other materials contained is too small, and the strength tends to decrease.

  In the honeycomb catalyst of the present invention, the honeycomb unit may contain zeolite other than CHA-type zeolite and silicoaluminophosphate (SAPO) within a range not impairing the effects of the present invention.

  In the honeycomb catalyst of the present invention, the honeycomb unit preferably contains 100 to 320 g / L, more preferably 120 to 300 g / L of the zeolite mixed particles of the present invention per apparent volume of the honeycomb unit. If it is less than 100 g / L, the NOx purification performance is lowered, and if it exceeds 320 g / L, the strength of the honeycomb unit may be lowered.

  In the honeycomb catalyst of the present invention, the inorganic binder contained in the honeycomb unit is not particularly limited, but is contained in alumina sol, silica sol, titania sol, water glass, sepiolite, attapulgite, boehmite, etc. from the viewpoint of maintaining strength as a honeycomb catalyst. The solid content is suitable, and two or more kinds may be used in combination.

The content of the inorganic binder in the honeycomb unit is desirably 3 to 20% by volume, and more desirably 5 to 15% by volume. When the content of the inorganic binder is less than 3% by volume, the strength of the honeycomb unit is lowered.
On the other hand, when the content of the inorganic binder exceeds 20% by volume, the content of the zeolite mixed particles in the honeycomb unit is lowered, and the NOx purification performance is lowered.

  In the honeycomb catalyst of the present invention, the honeycomb unit may further contain inorganic particles in order to adjust the pore diameter of the honeycomb unit.

  The inorganic particles contained in the honeycomb unit are not particularly limited, and examples thereof include particles such as alumina, titania, zirconia, silica, ceria, and magnesia. Two or more of these may be used in combination. The inorganic particles are preferably one or more particles selected from the group consisting of alumina, titania and zirconia, and more preferably any one of alumina, titania and zirconia.

The average particle size of the inorganic particles is desirably 0.01 to 1.0 μm, and more desirably 0.03 to 0.5 μm. When the average particle size of the inorganic particles is 0.01 to 1.0 μm, the pore size of the honeycomb unit can be adjusted.
The average particle size of the inorganic particles is the particle size (Dv50) at an integrated value of 50% in the particle size distribution (volume basis) obtained by the laser diffraction / scattering method.

  The content of inorganic particles in the honeycomb unit is preferably 10 to 40% by volume, and more preferably 15 to 35% by volume. When the content of the inorganic particles is less than 10% by volume, the effect of lowering the absolute value of the linear expansion coefficient of the honeycomb unit due to the addition of the inorganic particles is small, and the honeycomb unit is easily damaged by thermal stress. On the other hand, when the content of the inorganic particles exceeds 40% by volume, the content of the zeolite mixed particles of the present invention is lowered, and the NOx purification performance is lowered.

  The volume ratio of the zeolite mixed particles and inorganic particles (zeolite mixed particles: inorganic particles) of the present invention is desirably 50:50 to 90:10, and more desirably 60:40 to 80:20. When the volume ratio of the zeolite mixed particles and the inorganic particles of the present invention is in the above range, the pore diameter of the honeycomb unit can be adjusted while maintaining the NOx purification performance.

  In the honeycomb catalyst of the present invention, the honeycomb unit may further include one or more selected from the group consisting of inorganic fibers and scale-like substances in order to improve strength.

  The inorganic fiber contained in the honeycomb unit is desirably composed of one or more selected from the group consisting of alumina, silica, silicon carbide, silica alumina, glass, potassium titanate, and aluminum borate. The scaly substance contained in the honeycomb unit is preferably made of one or more selected from the group consisting of glass, muscovite, alumina, and silica. This is because all of them have high heat resistance, and even when used as a catalyst carrier in an SCR system, there is no melting damage and the effect as a reinforcing material can be maintained.

  The content of inorganic fibers and / or scaly substances in the honeycomb unit is preferably 3 to 30% by volume, and more preferably 5 to 20% by volume. When the content is less than 3% by volume, the effect of improving the strength of the honeycomb unit is reduced. On the other hand, when the content exceeds 30% by volume, the content of the zeolite mixed particles in the honeycomb unit is lowered, and the NOx purification performance is lowered.

  In the honeycomb catalyst of the present invention, the opening ratio of the cross section perpendicular to the longitudinal direction of the honeycomb unit is preferably 50 to 75%. When the opening ratio of the cross section perpendicular to the longitudinal direction of the honeycomb unit is less than 50%, the zeolite mixed particles are not effectively used for NOx purification. On the other hand, when the opening ratio of the cross section perpendicular to the longitudinal direction of the honeycomb unit exceeds 75%, the strength of the honeycomb unit becomes insufficient.

In the honeycomb catalyst of the present invention, it is desirable that the density of through-holes in a cross section perpendicular to the longitudinal direction of the honeycomb unit is 31 to 155 holes / cm ² . If the density of the through-holes in the cross section perpendicular to the longitudinal direction of the honeycomb unit is less than 31 / cm ² , the zeolite mixed particles and the exhaust gas are less likely to come into contact with each other, and the NOx purification performance decreases. On the other hand, when the density of the through holes in the cross section perpendicular to the longitudinal direction of the honeycomb unit exceeds 155 holes / cm ² , the pressure loss of the honeycomb catalyst increases.

  In the honeycomb catalyst of the present invention, the thickness of the partition walls of the honeycomb unit is desirably 0.1 to 0.4 mm, and more desirably 0.1 to 0.3 mm. When the thickness of the partition walls of the honeycomb unit is less than 0.1 mm, the strength of the honeycomb unit decreases. On the other hand, when the thickness of the partition walls of the honeycomb unit exceeds 0.4 mm, the exhaust gas hardly enters the partition walls of the honeycomb unit, and the zeolite mixed particles are not effectively used for NOx purification.

  In the honeycomb catalyst of the present invention, when the outer peripheral coat layer is formed on the honeycomb unit, the thickness of the outer peripheral coat layer is preferably 0.1 to 2.0 mm. When the thickness of the outer peripheral coat layer is less than 0.1 mm, the effect of improving the strength of the honeycomb catalyst becomes insufficient. On the other hand, when the thickness of the outer peripheral coat layer exceeds 2.0 mm, the content of the zeolite mixed particles per unit volume of the honeycomb catalyst is lowered, and the NOx purification performance is lowered.

  The shape of the honeycomb catalyst of the present invention is not limited to a cylindrical shape, and examples thereof include a prismatic shape, an elliptical cylindrical shape, a long cylindrical shape, and a rounded chamfered prismatic shape (for example, a rounded chamfered triangular prism shape).

  In the honeycomb catalyst of the present invention, the shape of the through hole is not limited to a quadrangular prism shape, and examples thereof include a triangular prism shape and a hexagonal prism shape.

Next, an example of a method for manufacturing the honeycomb catalyst 10 shown in FIG. 1 will be described.
First, it includes zeolite mixed particles and an inorganic binder, and if necessary, is extruded using a raw material paste further containing one or more selected from the group consisting of inorganic fibers and scaly substances and inorganic particles, a plurality of longitudinal A cylindrical honeycomb formed body in which through-holes extending in the direction are arranged in parallel with a partition wall therebetween is produced.

  In addition, you may add an organic binder, a dispersion medium, a shaping | molding adjuvant, etc. to a raw material paste suitably as needed.

  Although it does not specifically limit as an organic binder, Methylcellulose, carboxymethylcellulose, hydroxyethylcellulose, polyethyleneglycol, a phenol resin, an epoxy resin etc. are mentioned, You may use 2 or more types together. In addition, as for the addition amount of an organic binder, it is desirable that it is 1-10% with respect to the total mass of a zeolite mixed particle, an inorganic particle, an inorganic binder, an inorganic fiber, and a scaly substance.

  Although it does not specifically limit as a dispersion medium, Alcohol, such as water, organic solvents, such as benzene, methanol, etc. are mentioned, You may use 2 or more types together.

  Although it does not specifically limit as a shaping | molding adjuvant, Ethylene glycol, dextrin, a fatty acid, fatty acid soap, a polyalcohol etc. are mentioned, You may use together 2 or more types.

Furthermore, a pore former may be added to the raw material paste as necessary.
Although it does not specifically limit as a pore making material, A polystyrene particle, an acrylic particle, starch, etc. are mentioned, You may use 2 or more types together. Of these, polystyrene particles are desirable.

  By controlling the particle diameter of the zeolite mixed particles and the pore former, the pore diameter distribution of the partition walls can be controlled within a predetermined range.

  Even when no pore former is added, the pore size distribution of the partition walls can be controlled within a predetermined range by controlling the particle sizes of the zeolite mixed particles and the inorganic particles.

  When preparing the raw material paste, it is desirable to mix and knead, and it may be mixed using a mixer, an attritor or the like, or may be kneaded using a kneader or the like.

  Next, the honeycomb formed body is dried by using a dryer such as a microwave dryer, a hot air dryer, a dielectric dryer, a vacuum dryer, a vacuum dryer, or a freeze dryer to produce a honeycomb dried body.

  Further, the honeycomb dried body is degreased to produce a honeycomb degreased body. The degreasing conditions can be appropriately selected depending on the type and amount of organic matter contained in the dried honeycomb body, but it is desirable that the degreasing conditions be 200 to 500 ° C. for 2 to 6 hours.

  Next, the honeycomb degreased body is fired to produce a columnar honeycomb unit 11. The firing temperature is desirably 600 to 1000 ° C, and more desirably 600 to 800 ° C. When the firing temperature is less than 600 ° C., the sintering does not proceed and the strength of the honeycomb unit 11 is lowered. On the other hand, if the firing temperature exceeds 1000 ° C., the sintering proceeds too much and the reaction sites of the zeolite mixed particles decrease.

  Next, the outer peripheral coat layer paste is applied to the outer peripheral surface excluding both end surfaces of the columnar honeycomb unit 11.

  Although it does not specifically limit as a paste for outer periphery coating layers, The mixture of an inorganic binder and an inorganic particle, the mixture of an inorganic binder and an inorganic fiber, the mixture of an inorganic binder, an inorganic particle, and an inorganic fiber etc. are mentioned.

  Although the inorganic binder contained in the outer periphery coating layer paste is not particularly limited, it is added as silica sol, alumina sol or the like, and two or more kinds may be used in combination. Among these, it is desirable to add as silica sol.

  The inorganic particles contained in the outer coat layer paste are not particularly limited, but oxide particles such as zeolite, eucryptite, alumina and silica, carbide particles such as silicon carbide, and nitride particles such as silicon nitride and boron nitride. Etc., and two or more of them may be used in combination. Among them, eucryptite particles having a thermal expansion coefficient close to that of the honeycomb unit are desirable.

  Although it does not specifically limit as an inorganic fiber contained in the paste for outer periphery coating layers, A silica alumina fiber, a mullite fiber, an alumina fiber, a silica fiber, etc. are mentioned, You may use 2 or more types together. Among these, alumina fibers are preferable.

The outer periphery coating layer paste may further contain an organic binder.
Although it does not specifically limit as an organic binder contained in the paste for outer periphery coating layers, Polyvinyl alcohol, methylcellulose, ethylcellulose, carboxymethylcellulose, etc. are mentioned, You may use 2 or more types together.

  The outer periphery coating layer paste may further include balloons, pore formers, and the like, which are fine hollow spheres of oxide ceramics.

  The balloon contained in the outer peripheral coat layer paste is not particularly limited, and examples thereof include alumina balloons, glass micro balloons, shirasu balloons, fly ash balloons, mullite balloons and the like, and two or more kinds may be used in combination. Among these, an alumina balloon is preferable.

  The pore former contained in the outer periphery coat layer paste is not particularly limited, and examples thereof include spherical acrylic particles and graphite, and two or more kinds may be used in combination.

  Next, the honeycomb unit 11 to which the outer peripheral coat layer paste is applied is dried and solidified to produce a columnar honeycomb catalyst 10. At this time, when the outer peripheral coat layer paste contains an organic binder, it is desirable to degrease. The degreasing conditions can be appropriately selected depending on the kind and amount of the organic substance, but it is desirable that the degreasing conditions be 500 ° C. for 1 hour.

As a specific application example of the honeycomb catalyst of the present invention, there is an exhaust gas purification device.
FIG. 2 shows an example of the exhaust gas purifying apparatus. The exhaust gas purification apparatus 100 shown in FIG. 2 can be manufactured by canning the metal container (shell) 30 in a state where the holding sealing material 20 is disposed on the outer peripheral portion of the honeycomb catalyst 10. Further, in the exhaust gas purifying apparatus 100, in the pipe (not shown) on the upstream side of the honeycomb catalyst 10 with respect to the flow direction of the exhaust gas (in FIG. 2, the exhaust gas is indicated by G and the flow of the exhaust gas is indicated by an arrow). Further, an injection means (not shown) such as an injection nozzle that injects ammonia or a compound that decomposes to generate ammonia is provided. As a result, ammonia is added to the exhaust gas flowing through the pipe, so that the NOx contained in the exhaust gas is reduced by the zeolite mixed particles contained in the honeycomb unit 11.

  The compound that decomposes to generate ammonia is not particularly limited as long as it can be hydrolyzed in the pipe to generate ammonia, but urea water is preferable because of excellent storage stability.

  FIG. 3 shows another example of the honeycomb catalyst of the present invention. In the honeycomb catalyst 10 ′ shown in FIG. 3, a plurality of honeycomb units 11 ′ (see FIG. 4) in which a plurality of longitudinally extending through holes 11 a are arranged with a partition wall 11 b therebetween are bonded via an adhesive layer 13. Except for this, the configuration is the same as that of the honeycomb catalyst 10.

The cross-sectional area of the cross section perpendicular to the longitudinal direction of the honeycomb unit 11 ′ is desirably 10 to ²⁰⁰ cm ² . When the cross-sectional area is less than 10 cm ² , the pressure loss of the honeycomb catalyst 10 ′ increases. On the other hand, when the cross-sectional area exceeds 200 cm ² , it is difficult to bond the honeycomb units 11 ′.

  The honeycomb unit 11 ′ has the same configuration as the honeycomb unit 11 except for the cross-sectional area of the cross section perpendicular to the longitudinal direction.

  The thickness of the adhesive layer 13 is desirably 0.1 to 3.0 mm. When the thickness of the adhesive layer 13 is less than 0.1 mm, the adhesive strength of the honeycomb unit 11 ′ becomes insufficient. On the other hand, when the thickness of the adhesive layer 13 exceeds 3.0 mm, the pressure loss of the honeycomb catalyst 10 ′ increases or cracks occur in the adhesive layer.

Next, an example of a method for manufacturing the honeycomb catalyst 10 ′ shown in FIG. 3 will be described.
First, in the same manner as the honeycomb unit 11 constituting the honeycomb catalyst 10, a fan-shaped honeycomb unit 11 ′ is manufactured. Next, an adhesive layer paste is applied to the outer peripheral surface excluding the arc side of the honeycomb unit 11 ′, the honeycomb unit 11 ′ is adhered, and dried and solidified to produce an aggregate of the honeycomb units 11 ′.

  Although it does not specifically limit as a paste for contact bonding layers, The mixture of an inorganic binder and an inorganic particle, the mixture of an inorganic binder and an inorganic fiber, the mixture of an inorganic binder, an inorganic particle, and an inorganic fiber etc. are mentioned.

  The inorganic binder contained in the adhesive layer paste is not particularly limited, but is added as silica sol, alumina sol or the like, and two or more kinds may be used in combination. Among these, it is desirable to add as silica sol.

  The inorganic particles contained in the adhesive layer paste are not particularly limited, but oxide particles such as zeolite, eucryptite, alumina and silica, carbide particles such as silicon carbide, nitride particles such as silicon nitride and boron nitride, etc. And two or more of them may be used in combination. Among them, eucryptite particles having a thermal expansion coefficient close to that of the honeycomb unit are desirable.

  Although it does not specifically limit as an inorganic fiber contained in the paste for contact bonding layers, A silica alumina fiber, a mullite fiber, an alumina fiber, a silica fiber etc. are mentioned, You may use 2 or more types together. Among these, alumina fibers are preferable.

The adhesive layer paste may contain an organic binder.
Although it does not specifically limit as an organic binder contained in the paste for contact bonding layers, Polyvinyl alcohol, methylcellulose, ethylcellulose, carboxymethylcellulose etc. are mentioned, You may use 2 or more types together.

  The adhesive layer paste may further include balloons, pore formers, and the like, which are fine hollow spheres of oxide ceramics.

  Although it does not specifically limit as a balloon contained in the paste for contact bonding layers, An alumina balloon, a glass micro balloon, a shirasu balloon, a fly ash balloon, a mullite balloon etc. are mentioned, You may use 2 or more types together. Among these, an alumina balloon is preferable.

  The pore former contained in the adhesive layer paste is not particularly limited, and examples thereof include spherical acrylic particles and graphite, and two or more kinds may be used in combination.

  Next, in order to increase the roundness, the aggregate of the honeycomb units 11 ′ is cut and polished as necessary to produce the aggregate of the cylindrical honeycomb units 11 ′.

  Next, the outer peripheral coat layer paste is applied to the outer peripheral surface excluding both end surfaces of the aggregate of the cylindrical honeycomb units 11 ′.

  The outer periphery coating layer paste may be the same as or different from the adhesive layer paste.

  Next, a columnar honeycomb catalyst 10 ′ is manufactured by drying and solidifying the aggregate of columnar honeycomb units 11 ′ to which the outer periphery coating layer paste has been applied. At this time, when the adhesive for the adhesive layer and / or the paste for the outer peripheral coat layer contains an organic binder, it is desirable to degrease. The degreasing conditions can be appropriately selected depending on the kind and amount of the organic substance, but it is desirable that the degreasing conditions be 500 ° C. for 1 hour.

  The honeycomb catalyst 10 ′ is configured by bonding four honeycomb units 11 ′ via the adhesive layer 13, but the number of honeycomb units constituting the honeycomb catalyst is not particularly limited. For example, a columnar honeycomb catalyst may be configured by adhering 16 square columnar honeycomb units via an adhesive layer.

  The honeycomb catalyst 10 or 10 ′ may not have the outer peripheral coat layer 12 formed thereon.

  As described above, in the honeycomb catalyst of the present invention, NOx purification performance can be improved by forming a honeycomb unit using the zeolite mixed particles of the present invention as zeolite.

  Examples in which the present invention is disclosed more specifically are shown below. In addition, this invention is not limited only to this Example.

<Analysis of crystal structure>
In each of the following examples, the crystal structure of zeolite was analyzed as follows.
Using an X-ray diffractometer (Rigaku Corp., Ultimate IV), XRD measurement was performed on zeolite particles A and zeolite particles B, and integration of (211), (104) and (220) planes of the X-ray diffraction spectrum was performed. The sum of the intensities (X ₀ ) was calculated.
Measurement conditions are: radiation source: CuKα (λ = 0.154 nm), measurement method: FT method, diffraction angle: 2θ = 5-48 °, step width: 0.02 °, integration time: 1 second, diverging slit, scattering Slit: 2/3 °, divergence length limiting slit: 10 mm, acceleration voltage: 40 kV, acceleration current: 40 mA.
Analysis of the obtained XRD data was performed using powder X-ray diffraction pattern comprehensive analysis software JADE 6.0. The analysis conditions are: filter type: parabolic filter, elimination of Kα2 peak: yes, peak position definition: peak top, threshold σ: 3, peak intensity% cutoff: 0.1, BG determination range: 1, BG average The number of conversion points was set to 7.

<Measurement of average particle diameter>
In each of the following examples, the average particle size of zeolite particles A and zeolite particles B was measured as follows.
Using a scanning electron microscope (SEM, Hitachi High-Tech, S-4800), SEM photographs of CHA-type zeolite were taken and their particle sizes were measured. The measurement conditions were acceleration voltage: 1 kV, emission: 10 μA, WD: 2.2 mm or less. The measurement magnification was 20000 times. The particle diameter was measured from two diagonal lines of 10 particles, and the average value was obtained.

<Measurement of molar ratio of zeolite (SiO ₂ / Al ₂ O ₃ )>
In each of the following examples, the measurement of the molar ratio of zeolite particles A and zeolite particles B (SAR: SiO ₂ / Al ₂ O ₃ ) was performed as follows.
The molar ratio (SAR: SiO ₂ / Al ₂ O ₃ ) of CHA-type zeolite was measured using an X-ray fluorescence analyzer (XRF, ZSX Primus 2 manufactured by Rigaku Corporation). The measurement conditions were: X-ray tube: Rh, rated maximum output: 4 kW, detection element range: F to U, quantitative method: SQX method, analysis region: 10 mmφ.

<Measurement of Cu loading>
In each of the following examples, the measurement of the amount of Cu supported on zeolite particles A and zeolite particles B was performed as follows.
The amount of Cu supported on the CHA-type zeolite was measured using an ICP emission spectroscopic analyzer (manufactured by Shimadzu Corporation: ICPE-9000).
As a pretreatment of the sample, 0.1 g of zeolite after Cu ion exchange dried at 400 ° C. for 4 hours is placed in a platinum dish, 5 ml of nitric acid, 20 ml of hydrofluoric acid, and 5 ml of sulfuric acid are added until sulfuric acid white smoke is generated. Heat. This is adjusted to be a 50 ml aqueous solution and used as a measurement sample.
The measurement sample was put in the apparatus, and Cu element was designated and measured. The Cu / Al molar ratio was calculated from the measured value of the Cu loading.

Example 1
<Preparation of zeolite particles A>
Colloidal silica (manufactured by Nissan Chemical Industries, Snowtex) as the Si source, dry aluminum hydroxide gel (manufactured by Tomita Pharmaceutical) as the Al source, sodium hydroxide (manufactured by Tokuyama) and potassium hydroxide (Toagosei Co., Ltd.) as the alkali source Manufactured), N, N, N-trimethyladamantanammonium hydroxide (TMAAOH) 25% aqueous solution (manufactured by Sachem) as a structure directing agent (SDA), SSZ-13 as a seed crystal, and deionized water A composition was prepared. The molar ratios of the raw material compositions were SiO ₂ : 15 mol, Al ₂ O ₃ : 1 mol, NaOH: 1.6 mol, KOH: 0.53 mol, TMAAOH: 1.62 mol, and H ₂ O: 300 mol. Further, 5.0% by mass of seed crystals was added to SiO ₂ and Al ₂ O ₃ in the raw material composition. The raw material composition was loaded into a 500 L autoclave, and hydrothermal synthesis was performed at a heating temperature of 160 ° C. and a heating time of 24 hours to synthesize zeolite particles A having a CHA structure.
The average particle diameter of the obtained zeolite particles A was 0.74 μm, the sum of integrated intensities (X ₀ ) was 54357, and the SAR was 12.2.

<Preparation of zeolite particles B>
Using 13 kg of zirconia (bead particle size: 300 μm) as pulverization beads, the zeolite particles A were pulverized for 60 minutes at a rotational speed of 9 m / s by a wet bead mill (Ashizawa Finetech Labstar Mini) and refined. Then, for evaluation, 550 ° C., 10 hours, and heated in an air atmosphere, was calculated sum of the average particle diameter of the integrated intensity of the (X _0).
As a result, the average particle size of the CHA-type zeolite was 0.47 μm, and the sum of integrated intensities (X ₀ ) was 44728.

Subsequently, after the zeolite particles A were produced, the solution excluding the zeolite particles A was used as a recrystallization solution without concentrating (concentration ratio: 1), and the solid-liquid ratio of twice the mass of the zeolite was obtained. Then, recrystallization was performed with stirring in an autoclave at 200 ° C. for 4 hours.
The average particle diameter, the sum of integrated intensities (X ₀ ) and SAR of the zeolite particles B obtained after the recrystallization step were determined. As a result, the average particle size was 0.47 μm, the sum of integrated intensities (X ₀ ) was 50171, and the SAR was 12.2.

<Preparation of zeolite mixed particles>
Zeolite particles A and zeolite particles B were uniformly mixed at a mass ratio of 6: 4 using a Henschel mixer to prepare zeolite mixed particles.

  For the obtained zeolite mixed particles, the first ion exchange uses a copper (II) acetate aqueous solution having a copper concentration of 2.34% by mass, and the second ion exchange has a copper concentration of 0.59% by mass of copper acetate. (II) Ion exchange was performed using an aqueous solution at a solution temperature of 50 ° C. and atmospheric pressure for 1 hour.

FIG. 5 shows the XRD pattern of the zeolite particles A of Example 1, FIG. 6 shows the XRD pattern of the zeolite particles refined from the zeolite particles A, and FIG. 7 shows the XRD pattern of the zeolite particles B of Example 1. .
From FIG. 5, the zeolite particles A are CHA-type zeolite, and from FIG. 6, the crystal structure of the zeolite particles A is impaired by the refinement process, and from FIG. 7, the zeolite particles B are the crystal structure that is impaired by the refinement process. Was recovered by the recrystallization process.

(Example 2)
<Preparation of zeolite particles A>
As the zeolite particles A, the same particles as in Example 1 were used.

<Preparation of zeolite particles B>
Using 13 kg of zirconia (bead particle size: 300 μm) as pulverizing beads, the zeolite particles A were pulverized for 60 minutes at a rotational speed of 12 m / s by a wet bead mill (Labstar Mini, manufactured by Ashizawa Finetech) and refined. Then, for evaluation, 550 ° C., 10 hours, and heated in an air atmosphere, was calculated sum of the average particle diameter of the integrated intensity of the (X _0).
As a result, the average particle size of the CHA-type zeolite was 0.12 μm, and the sum of integrated intensities (X ₀ ) was 33991.

Subsequently, a solution obtained by removing the zeolite particles A after the zeolite particles A were concentrated 3 times (concentration rate: 3) was used as a recrystallization solution, and the solid solution was 8 times the amount of the zeolite mass. It added so that it might become a liquid ratio, and it recrystallized, stirring with an autoclave at 200 degreeC for 24 hours.
The average particle diameter, the sum of integrated intensities (X ₀ ) and SAR of the zeolite particles B obtained after the recrystallization step were determined. As a result, the average particle size was 0.12 μm, the sum of integrated intensities (X ₀ ) was 53813, and the SAR was 12.2.

<Preparation of zeolite mixed particles>
Zeolite particles A and zeolite particles B were uniformly mixed at a mass ratio of 6: 4 using a Henschel mixer to prepare zeolite mixed particles.

  For the obtained zeolite mixed particles, the first ion exchange uses a copper (II) acetate aqueous solution having a copper concentration of 2.34% by mass, and the second ion exchange has a copper concentration of 0.59% by mass of copper acetate. (II) Ion exchange was performed using an aqueous solution at a solution temperature of 50 ° C. and atmospheric pressure for 1 hour.

(Example 3)
Zeolite mixed particles were prepared in the same manner as in Example 1, except that the mixing ratio of zeolite particles A and zeolite particles B was 7: 3 (mass ratio).

Example 4
Zeolite mixed particles were prepared in the same manner as in Example 2, except that the mixing ratio of zeolite particles A and zeolite particles B was 7: 3 (mass ratio).

(Comparative Example 1)
As the zeolite particles, only the zeolite particles A prepared in Example 1 were used.
For the zeolite particles A, the first ion exchange uses an aqueous solution of copper (II) acetate having a copper concentration of 2.34% by mass, and the second ion exchange comprises copper (II) acetate having a copper concentration of 0.59% by mass. Ion exchange was performed using an aqueous solution at a solution temperature of 50 ° C. and atmospheric pressure for 1 hour.

(Comparative Example 2)
Colloidal silica (manufactured by Nissan Chemical Industries, Snowtex) as the Si source, dry aluminum hydroxide gel (manufactured by Tomita Pharmaceutical) as the Al source, sodium hydroxide (manufactured by Tokuyama) and potassium hydroxide (Toagosei Co., Ltd.) as the alkali source Manufactured), N, N, N-trimethyladamantanammonium hydroxide (TMAAOH) 25% aqueous solution (manufactured by Sachem) as a structure directing agent (SDA), SSZ-13 as a seed crystal, and deionized water A composition was prepared. The molar ratios of the raw material compositions were SiO ₂ : 36 mol, Al ₂ O ₃ : 1 mol, KOH: 3.6 mol, TMAAOH: 2.9 mol, and H ₂ O: 468 mol. Further, _SiO 2, _Al 2 _{O 3} raw material composition was added 5.0 wt% of a seed crystal. The raw material composition was loaded into a 500 L autoclave, and hydrothermal synthesis was performed at a heating temperature of 160 ° C. and a heating time of 24 hours to synthesize zeolite particles having a CHA structure.
The average particle size of the obtained zeolite particles was 0.13 μm, the sum of integrated intensities (X ₀ ) was 49653, and the SAR was 32.

(Preparation of honeycomb catalyst)
40% by mass of the CHA-type zeolite particles obtained in Examples 1 to 4 and Comparative Examples 1 and 2 after supporting Cu, 8% by mass of pseudoboehmite as an inorganic binder, and 7% by mass of glass fibers having an average fiber length of 100 μm. Then, 6.5% by mass of methylcellulose, 3.5% by mass of surfactant and 35% by mass of ion-exchanged water were mixed and kneaded to prepare a raw material paste.

Next, the raw material paste was extruded using an extrusion molding machine to produce a honeycomb formed body. Then, using a vacuum microwave dryer, the honeycomb formed body was dried at an output of 4.5 kW and a reduced pressure of 6.7 kPa for 7 minutes, and then degreased and fired at an oxygen concentration of 1% and 700 ° C. for 5 hours. Unit). The honeycomb unit had a regular quadrangular prism shape with a side of 35 mm and a length of 150 mm, a through hole density of 124 holes / cm ² , and a partition wall thickness of 0.20 mm.

<Measurement of NOx purification rate>
A cylindrical test piece having a diameter of 25.4 mm and a length of 38.1 mm was cut out from the honeycomb unit using a diamond cutter. NOx flowing out from the test piece using a catalyst evaluation device (SIGU-2000 / MEXA-6000FT, manufactured by Horiba, Ltd.) while flowing a simulated gas at 200 ° C. at a space velocity (SV) of 100000 hr ^−1. The outflow amount was measured, and the NOx purification rate (%) represented by the following formula (1) was calculated. The constituent components of the simulated gas were 350 ppm nitrogen monoxide, 350 ppm ammonia, 10% oxygen, 5% carbon dioxide, 5% water, and nitrogen.
Purification rate (%) = (NOx inflow amount−NOx outflow amount) / (NOx inflow amount) × 100 (1)
Similarly, the NOx purification rate [%] was calculated while flowing a simulated gas at 525 ° C. at SV: 100000 hr ⁻¹ . The constituent components of the simulated gas at this time were 315 ppm nitric oxide, 35 ppm nitrogen dioxide, 385 ppm ammonia, 10% oxygen, 5% carbon dioxide, 5% water, and nitrogen. Table 2 shows the NOx purification rate of the honeycomb catalyst using the zeolite mixed particles obtained in each Example and Comparative Example.

<Measurement of porosity of honeycomb unit>
The honeycomb unit is cut into a size of 7 cells × 7 cells × 10 mm to obtain a measurement sample. This sample is ultrasonically cleaned with ion-exchanged water and acetone, and then dried at 100 ° C. in an oven. Subsequently, using a measurement microscope (manufactured by Nikon, Measuring Microscope MM-40, 100 times magnification), the dimensions of the cross-sectional shape of the sample were measured, and the volume was obtained from geometric calculation.
Thereafter, the weight when the sample was assumed to be a complete dense body was calculated from the volume obtained by calculation and the true density of the sample measured with a pycnometer.
The measurement procedure with a pycnometer is as follows. The honeycomb unit is pulverized to prepare 23.6 cc of powder, and the obtained powder is dried at 200 ° C. for 8 hours. Then, true density is measured based on JIS-R-1620 (1995) using Auto Pycnometer 1320 (made by Micromeritics). The exhaust time at this time is 40 minutes.
Next, the actual weight of the sample is measured with an electronic balance (HR202i manufactured by Shimadzu Corporation), and the porosity is calculated by the following calculation formula.
Porosity (%) = 100− (actual weight / weight as dense body) × 100
The results are shown in Table 2.

Since the honeycomb catalyst obtained in Examples 1 to 4 uses the zeolite mixed particles obtained by the method for producing zeolite mixed particles of the present invention, the catalyst density can be sufficiently increased, and the high flow rate, low It was found that the NOx purification performance can be increased from low temperature even under the condition of NO ₂ ratio. It was also found that the honeycomb catalysts obtained in Examples 1 to 4 were excellent in strength. On the other hand, in the honeycomb catalysts obtained in Comparative Examples 1 and 2, the results of NOx purification performance and strength were both inferior to those of Examples 1 to 4.

10, 10 'Honeycomb catalyst 11, 11' Honeycomb unit 11a Through-hole 11b Partition 12 Outer peripheral coat layer 13 Adhesive layer 20 Holding sealing material 30 Metal container 100 Exhaust gas purification device G Exhaust gas

Claims (8)

A synthesis step of synthesizing zeolite particles A having a CHA structure with an average particle size of 0.5 to 3 μm, using a raw material composition containing a Si source, an Al source, an alkali source and a structure-directing agent;
Refining the zeolite particles A to obtain zeolite particles B having a CHA structure with an average particle size of less than 0.5 μm;
A mixing step of mixing the zeolite particles A and the zeolite particles B;
A method for producing zeolite mixed particles. Before performing the mixing step, the zeolite particles B having a CHA structure refined by the refinement step are mixed with a solution containing a Si source and an alkali source, and a crystallization process is performed.
The method for producing zeolite mixed particles according to claim 1, further comprising: The zeolite particle A has a sum of integral intensities of (211) plane, (104) plane and (220) plane of X-ray diffraction spectrum by powder X-ray analysis method is 50000 or more,
The method for producing zeolite mixed particles according to claim 1 or 2, wherein the zeolite particles B have a sum of the integrated intensities of 70% or more of the zeolite particles A.   The method for producing zeolite mixed particles according to any one of claims 1 to 3, wherein a mixing ratio (mass ratio) of the zeolite particles A and the zeolite particles B is 8: 2 to 4: 6. The _SiO 2 / _Al 2 _{O 3} composition ratio of the zeolite particles A and the zeolite particles B (SAR) are both less than 15, the manufacturing method of the zeolite mixture particles according to any one of claims 1 to 4.   The zeolite mixed particles according to any one of claims 1 to 5, wherein both the zeolite particles A and the zeolite particles B carry Cu, and the Cu / Al (molar ratio) is 0.2 to 0.5. Manufacturing method. A honeycomb catalyst provided with a honeycomb unit in which a plurality of through holes extending in the longitudinal direction are arranged side by side across a partition wall,
The honeycomb unit includes zeolite mixed particles and an inorganic binder,
A honeycomb catalyst, wherein the zeolite mixed particles are zeolite mixed particles obtained by the method for producing zeolite mixed particles according to any one of claims 1 to 6.   An exhaust gas purifying apparatus, wherein a holding sealing material is disposed on the outer periphery of the honeycomb catalyst according to claim 7 and canned in a metal container.

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