CHA-type zeolite and its manufacturing method

Abstract

To provide a CHA type zeolite which is crystallized from a raw material composition including an N,N,N-trialkylcyclohexylammonium cation as a structure-directing agent, the CHA type zeolite having a low SiO2 / Al2O3 ratio and being able to give a catalyst showing a practical nitrogen oxide reduction rate, and a production method thereof and at least any of nitrogen oxide reduction catalysts including the same.SOLUTION: A CHA type zeolite is provided which has a molar ratio of silica to alumina of less than 13 and a sodium content of 100 ppm or more and 2000 ppm or less. Preferably, this CHA type zeolite is obtained by a production method comprising the steps of: crystallizing a composition including a structure-directing agent source containing at least an N,N,N-trialkylcyclohexylammonium cation, an alumina source, a silica source, a sodium source, and water and having a molar ratio of silica to alumina of 20 or less and a molar ratio of potassium to sodium of less than 0.05 to obtain a crystallized product; removing the N,N,N-trialkylcyclohexylammonium cation from the crystallized product; and bringing an ammonium salt-containing solution having an ammonium concentration of 1 mass% or more and the crystallized product into contact with each other.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to CHA-type zeolites, and in particular to CHA-type zeolites crystallized from raw material compositions containing N,N,N-trialkylcyclohexylammonium cations as structure directing agents. [Background technology]

[0002] CHA-type zeolite is an artificially synthesized zeolite reported in Patent Document 1, and is widely used as a nitrogen oxide reduction catalyst and a petrochemical catalyst.

[0003] In Patent Document 1, CHA zeolite is crystallized using an expensive structure-directing agent such as N,N,N-trimethyl-1-adamantanammonium cation. On the other hand, methods for producing CHA zeolite have been proposed using inexpensive N,N,N-trialkylcyclohexylammonium cations as the structure-directing agent (for example, Patent Documents 2 and 3). Patent Documents 2 and 3 disclose that CHA zeolite having a molar ratio of silica to alumina (hereinafter also referred to as "SiO2 / Al2O3 ratio") of more than 100 (Patent Document 2) and CHA zeolite having a SiO2 / Al2O3 ratio of 13 or more can be obtained (Patent Document 3). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent No. 4,544,538 [Patent Document 2] US Patent No. 2008 / 0045767 [Patent Document 3] US Patent No. 2019 / 0105639 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the method for producing CHA-type zeolite using N,N,N-trialkylcyclohexylammonium cation as a structure-directing agent, no specific report has been made on CHA-type zeolite with a low SiO2 / Al2O3 ratio.

[0006] The present disclosure aims to provide at least one of a CHA-type zeolite crystallized from a raw material composition containing N,N,N-trialkylcyclohexylammonium cations as a structure-directing agent, which has a low SiO2 / Al2O3 ratio and can provide a catalyst that exhibits a practical nitrogen oxide reduction rate, a method for producing the same, and a nitrogen oxide reduction catalyst containing the same. [Means for solving the problem]

[0007] The inventors have discovered that in a method for producing CHA-type zeolite by crystallizing a composition (hereinafter also referred to as the "raw material composition") containing N,N,N-trialkylcyclohexylammonium cations as a structure-directing agent, there is a problem that simply reducing the SiO2 / Al2O3 ratio of the raw material composition and crystallizing it does not result in a CHA-type zeolite that can provide a catalyst that exhibits a practical nitrogen oxide reduction rate, and that the above problem can be solved by focusing on the crystallization conditions and post-crystallization treatment, and further on the relationship between the crystallization conditions and post-crystallization treatment.

[0008] That is, the present invention is as defined in the claims, and the gist of the present disclosure is as follows. [1] A CHA-type zeolite having a silica to alumina molar ratio of less than 13 and a sodium content of 100 ppm or more and 2000 ppm or less. [2] The CHA-type zeolite according to [1] above, wherein the molar ratio of potassium to sodium is less than 0.05. [3] The content of silanol groups per mass of CHA-type zeolite is 0.50 × 10 20 The CHA-type zeolite according to [1] or [2] above, having a molecular weight of 100 or less per gram. [4] A CHA-type zeolite described in any one of [1] to [3] above, wherein the CHA-type zeolite is a CHA-type zeolite crystallized from a composition containing N,N,N-trialkylcyclohexylammonium cations. [5] A CHA-type zeolite according to any one of [1] to [3] above, wherein the cation type is either an ammonium type or a proton type. [6] A CHA-type zeolite according to any one of [1] to [4], containing one or more metal elements selected from the group consisting of platinum, palladium, rhodium, iron, copper, cobalt, manganese, and indium. [7] The CHA-type zeolite according to [5] above, wherein the metal element is contained in a state supported outside the zeolite framework. [8] A method for producing a CHA-type zeolite described in any one of [1] to [5] above, comprising the steps of: crystallizing a composition containing a structure-directing agent source containing at least N,N,N-trialkylcyclohexylammonium cations, an alumina source, a silica source, a sodium source, and water, wherein the molar ratio of silica to alumina is 20 or less and the molar ratio of potassium to sodium is less than 0.05, to obtain a crystallized product; removing N,N,N-trialkylcyclohexylammonium cations from the crystallized product; and contacting the crystallized product with an ammonium salt-containing solution having an ammonium concentration of 1 mass% or more. [9] The method according to the above [8], wherein the N,N,N-trialkylcyclohexylammonium cation is at least one of an N,N,N-dimethylethylcyclohexylammonium cation and an N,N,N-methyldiethylcyclohexylammonium cation.

[10] The method according to [8] or [9] above, wherein the composition contains at least an amorphous compound containing silicon and aluminum as a silica source and an alumina source, and further contains at least one of sodium hydroxide and sodium halide as a sodium source.

[11] The method according to any one of [8] to

[10] above, wherein the crystallization temperature is above 150°C.

[12] The method according to any one of [8] to

[11] above, wherein the composition contains at least an amorphous aluminosilicate.

[13] A nitrogen oxide reduction catalyst containing the CHA-type zeolite according to any one of [1] to [7] above.

[14] A method for reducing nitrogen oxides, which uses the nitrogen oxide reduction catalyst according to

[13] above. [Effects of the Invention]

[0009] The present disclosure makes it possible to provide at least one of a CHA-type zeolite crystallized from a raw material composition containing N,N,N-trialkylcyclohexylammonium cations as a structure-directing agent, which has a low SiO2 / Al2O3 ratio and can provide a catalyst that exhibits a practical nitrogen oxide reduction rate, a method for producing the CHA-type zeolite, and a nitrogen oxide reduction catalyst containing the CHA-type zeolite. [Brief explanation of the drawings]

[0010] [Figure 1] SEM observation image of CHA-type zeolite of Example 1 (scale in the image is 30 μm) [Figure 2] SEM observation image of CHA-type zeolite of Example 3 (scale in the figure is 1 μm) [Figure 3] SEM observation image of CHA-type zeolite of Example 4 (scale in the figure is 5 μm) DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, the CHA-type zeolite of the present disclosure will be described with reference to an example of an embodiment.

[0012] The terms used in this embodiment are as follows:

[0013] "Zeolite" is a compound having a regular structure in which skeleton atoms (hereinafter also referred to as "T atoms") are connected via oxygen (O), and the T atoms are at least one of metal atoms and / or metalloid atoms. Examples of metal atoms include one or more atoms selected from the group consisting of aluminum (Al), iron (Fe), and gallium (Ga). Examples of metalloid atoms include one or more atoms selected from the group consisting of boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), and tellurium (Te).

[0014] "Zeolite-like substances" are compounds with a regular structure in which T atoms are oxygen-mediated, and the T atoms contain at least one atom other than a metal or semimetal (hereinafter also referred to as a "non-metal atom"). Examples of non-metal atoms include phosphorus (P), and examples of zeolite-like substances include complex phosphorus compounds such as aluminophosphate (AlPO) and silicoaluminophosphate (SAPO).

[0015] The "regular structure in which T atoms are oxygen-mediated (hereinafter also referred to as "zeolite structure")" of zeolites and zeolite-like substances is a skeletal structure identified by the structure code (hereinafter also referred to simply as "structure code") established by the Structure Commission of the International Zeolite Association. For example, the CHA structure is a skeletal structure identified by the structure code "CHA." Zeolite structures can be identified by comparing the XRD patterns of each structure (hereinafter also referred to as "reference patterns") described in "Collection of simulated XRD powder patterns for zeolites, Fifth revised edition (2007)." In this embodiment, the terms "skeletal structure," "crystalline structure," and "crystalline phase" are used interchangeably.

[0016] An "aluminosilicate" is a composite oxide having a structure consisting of a repeating network of aluminum (Al) and silicon (Si) via oxygen (O; skeletal oxygen). In this embodiment, the aluminosilicate may also include a composite oxide having a structure consisting of a repeating network of aluminum (Al) and silicon (Si) via oxygen (O), in which a portion of the aluminum (e.g., 30% or less of the aluminum as T atoms) is substituted with another metal atom. Among aluminosilicates, those that have a crystalline XRD peak in their powder X-ray diffraction (hereinafter also referred to as "XRD") pattern are called "crystalline aluminosilicates," and those that do not have a crystalline XRD peak are called "amorphous aluminosilicates."

[0017] In this embodiment, the XRD pattern is measured using CuKα radiation as a radiation source, and the measurement conditions include the following. Acceleration current / voltage: 40mA / 40kV Radiation source: CuKα radiation (λ=1.5405Å) Measurement mode: Continuous scan Scan condition: 40° / min Measurement range: 2θ=3° to 43° Divergence vertical limit slit: 10mm Divergence / entrance slit: 1° Receiving slit: open Receiving solar slit: 5° Detector: Semiconductor detector (D / teX Ultra) Filter: Ni filter The XRD pattern can be measured using a general powder X-ray diffractometer (e.g., Ultima IV, manufactured by Rigaku Corporation). The crystalline XRD peak is a peak detected by identifying the 2θ of the peak top in the analysis of the XRD pattern using general analysis software (e.g., SmartLab Studio II, manufactured by Rigaku Corporation). The following conditions can be used for analyzing the XRD pattern. Fitting conditions: Automatic, refine background Dispersed pseudo-Voigt function (peak shape) Background removal method: Fitting method Kα2 removal method: Kα1 / Kα2 ratio = 0.497 Smoothing method: B-Spline curve Smoothing condition: Second derivative method, σ cut-off value = 3, χ threshold value = 1.5

[0018] The composition in this embodiment, such as the molar ratio of silica to alumina, may be measured by ICP analysis using a general inductively coupled plasma optical emission spectrometer (for example, OPTIMA 7300DV, manufactured by PERKIN ELMER).

[0019] <CHA-type zeolite> The CHA-type zeolite of this embodiment is a synthetic zeolite, which is a synthetic zeolite obtained by crystallizing a raw material composition containing a structure directing agent (hereinafter also referred to as "SDA"), and further an N,N,N-trialkylcyclohexylammonium cation (hereinafter + also referred to as "TACH"). It is a synthetic CHA-type zeolite crystallized from a raw material composition containing a structure directing agent. In this embodiment, "synthetic zeolite" is a term in contrast to zeolites produced naturally (natural zeolites).

[0020] The CHA-type zeolite of this embodiment has a molar ratio of silica to alumina (SiO2 / Al2O3 ratio) of less than 13, and may be 12 or less, 11 or less, or 10 or less. Despite such a low SiO2 / Al2O3 ratio, the CHA-type zeolite of this embodiment can be a catalyst and its carrier showing nitrogen oxide reduction characteristics equivalent to those of a CHA-type zeolite having a conventionally high SiO2 / Al2O3 ratio of about 22 - 24. The SiO2 / Al2O3 ratio of the CHA-type zeolite of this embodiment is preferably 6 or more, 8 or more, 9 or more, or 9.5 or more.

[0021] The CHA type zeolite of this embodiment has a sodium content of 100 ppm or more and 2000 ppm or less, preferably more than 100 ppm, 120 ppm or more, or 200 ppm or more, and more preferably 1500 ppm or less, 1300 ppm or less, 1000 ppm or less, 800 ppm or less, or 500 ppm or less. It has been known that sodium present in synthetic CHA type zeolite reduces properties such as heat resistance and catalytic activity. In contrast, TACH as SDA + In the crystallization of a raw material composition containing SDA and having a low SiO2 / Al2O3 ratio, it is believed that a portion of sodium is easily incorporated into the zeolite structure in a state that contributes to improving the properties of CHA-type zeolite. + In the CHA-type zeolite obtained by crystallizing a raw material composition containing and having a low SiO2 / Al2O3 ratio, by setting the sodium content within the range of this embodiment, it is believed that sodium in a state that deteriorates the properties is mainly removed, and sodium in a state that contributes to improving the properties remains. That is, the CHA-type zeolite of this embodiment preferably contains sodium (hereinafter also referred to as "residual Na") that was incorporated during the crystallization process. The sodium content in the CHA-type zeolite of this embodiment is preferably the content of residual Na. It is believed that the CHA-type zeolite of this embodiment mainly contains, among the residual Na, sodium in a state that particularly contributes to improving the properties. Furthermore, the CHA-type zeolite of this embodiment does not need to contain sodium (hereinafter also referred to as "post-supported Na") that is supported after the crystallization process, such as ion-exchanged sodium, but may contain post-supported Na as long as the effect is not impaired.

[0022] In this embodiment, the sodium content is the mass ratio [ppm by mass] of sodium (Na) calculated as NaO relative to the dry mass of CHA zeolite. The dry mass of CHA zeolite is the mass of CHA zeolite after treatment in air at 600°C for 1 hour.

[0023] In this embodiment, the sodium content may be determined by ICP analysis using a general inductively coupled plasma optical emission spectrometer (device name: OPTIMA7300DV, manufactured by PERKIN ELMER). Prior to composition analysis, the sample may be dissolved in a mixed solution of hydrofluoric acid and nitric acid to prepare a measurement solution.

[0024] The sodium content in this embodiment is, in particular, when the cation type is ammonium type (NH4 type) and proton type (H + It is preferable that the value is either of the proton type (proton type) or the ammonium type. In this embodiment, the ammonium type CHA zeolite is CHA zeolite in a state after ion exchange with a solution containing an ammonium salt (e.g., ammonium chloride: particularly, ammonium chloride having an ammonium concentration of 1 mass% or more, 5 mass% or more, or 10 mass% or more, and 40 mass% or less, or 30 mass% or less), and the proton type CHA zeolite is CHA zeolite in a state after heat treatment of ammonium type CHA zeolite in the air at 400°C or more and 800°C or less.

[0025] The CHA type zeolite of this embodiment may contain potassium as long as the molar ratio of potassium to sodium (hereinafter also referred to as the "K / Na ratio") is less than 0.05. The K / Na ratio of the CHA type zeolite of this embodiment is preferably less than 0.05, 0.03 or less, or 0.01 or less. It is preferable that the CHA type zeolite of this embodiment is substantially free of potassium (i.e., the K / Na ratio is 0 (zero)). However, taking into account measurement errors and the like, the K / Na ratio may be 0 or more, greater than 0, or 0.005 or more. Similarly, the CHA type zeolite of this embodiment preferably has a molar ratio of other alkali metals (i.e., one or more selected from the group consisting of lithium, rubidium, and cesium) to sodium (hereinafter also referred to as the "M / Na ratio") that is 0 or more, greater than 0, or 0.005 or more, and less than 0.05 or 0.01 or less.

[0026] The CHA-type zeolite of this embodiment preferably does not contain fluorine (F) or phosphorus (P), and the fluorine and phosphorus contents of the CHA-type zeolite are each below the measurement limit (for example, the fluorine content is 1 ppm or less, the phosphorus content is 1 ppm or less, or the fluorine content and the phosphorus content are 1 ppm or less).

[0027] The CHA-type zeolite of the present embodiment is a CHA-type zeolite crystallized from a raw material composition containing a structure-directing agent, and is a TACH + It is sufficient if the CHA-type zeolite is crystallized from a raw material composition containing TACH as a structure directing agent. + As long as the CHA-type zeolite is in a state where it is crystallized from a raw material composition containing as a structure-directing agent, it may contain a structure-directing agent. On the other hand, from the viewpoint of use as a catalyst, adsorbent, or the like, the CHA-type zeolite of this example does not need to contain a structure-directing agent.

[0028] The CHA zeolite of the present embodiment preferably has the characteristics of being crystallized from such a raw material composition. One of such characteristics is, for example, that the content of silanol groups per mass of the CHA zeolite (hereinafter also referred to as "SiOH amount") is 0.50 × 10 20 Pieces / g or less or 0.30 x 10 20 The silanol group is formed on silicon (Si) present at the end of the zeolite structure. In existing zeolites, the zeolite structure has an end. Therefore, the SiOH amount of the CHA zeolite of this embodiment is more than 0 / g, and is 0.10 × 10 20 For example, it can be more than 1 / g.

[0029] The amount of SiOH is calculated by multiplying the mass of CHA-type zeolite by the mass of CHA-type zeolite. 1 It can be determined by a calibration curve method from the area intensity of the peak (having a peak top at 2.0±0.4 ppm) assigned to a silanol group in the 1 H MAS NMR spectrum.

[0030] The mass of CHA-type zeolite in calculating the amount of SiOH is the mass after physically adsorbed water has been removed, for example, the mass of CHA-type zeolite after the pretreatment described below.

[0031] 1 The measurement conditions for the 1 H MAS NMR spectrum include the following conditions.

[0032] Resonance frequency: 400MHz Pulse width: π / 2 Measurement waiting time: 10 seconds Accumulation count: 32 times Rotation frequency: 15kHz Shift standard: TMS (tetramethylsilane) 1 The 1 H MAS NMR spectrum can be measured using a general NMR apparatus (for example, VNMRS-400, manufactured by Varian).

[0033] NMR spectra can be analyzed by performing waveform separation using a Gaussian function and determining the integrated intensity of the peak with a peak top at 2.0±0.4 ppm using general NMR spectrum analysis software (e.g., GRAMS / AI Ver. 8.0, Thermo Fisher Scientific).

[0034] Before NMR measurement, the sample is pretreated by any pretreatment that can remove physically adsorbed water, such as by holding the sample in a vacuum atmosphere at 400°C for 5±2 hours.

[0035] Prior to measurement, a calibration curve can be prepared using benzene as a standard substance. The calibration curve is prepared from three or more (e.g., 3 to 5) standard samples with different amounts of benzene (e.g., 0 mmol, 0.01 mmol, and 0.02 mol) in the range of 0 mmol to 0.02 mmol. NMR measurements are performed for each standard sample under the above conditions, and the correlation between the proton amount in each standard sample and the spectral area intensity is plotted to prepare a calibration curve that converts the area intensity to the proton amount.

[0036] The amount of SiOH may be calculated as the amount of protons [protons / g] relative to the mass of CHA-type zeolite.

[0037] The CHA-type zeolite of this embodiment is a single phase of the CHA structure, and further preferably has an XRD pattern similar to that of SSZ-13.

[0038] The CHA-type zeolite of this embodiment may include at least one of crystalline particles formed from individual primary particles and crystalline particles (aggregates) formed by chemically agglomerating primary particles together. The shape of the crystalline particles of this embodiment is arbitrary. Examples of the crystalline particles of the CHA-type zeolite of this embodiment include at least one selected from the group consisting of crystalline particles having a rhombohedral or cubic shape (a hexahedron with all sides of equal length), polyhedral crystalline particles including some faces of primary particles having at least one of a rhombohedral or cubic shape, and irregular crystalline particles. The crystalline particles of the CHA-type zeolite of this embodiment may be crystalline particles having at least one of a rhombohedral or cubic shape but lacking some faces, and may include, for example, irregularly shaped crystalline particles close to spherical, or even approximately spherical crystalline particles. The particle diameter of the crystalline particles (hereinafter also referred to as "crystalline particle diameter") can be, for example, 0.1 μm or more or 0.3 μm or more, and 2 μm or less or 1 μm or less. The CHA type zeolite of this embodiment preferably contains crystalline particles that are at least 0.1 μm or more or 0.5 μm or more, and 1 μm or less or 0.8 μm or less. Furthermore, the CHA type zeolite of this embodiment preferably has a matrix (parent phase) of crystalline particles that have a crystalline particle diameter of 0.1 μm or more or 0.5 μm or more, and 1 μm or less, 0.8 μm or less.

[0039] Furthermore, the CHA-type zeolite of this embodiment may be in a state in which crystalline particles are dispersed, or may form agglomerated particles (agglomerates) in which two or more crystalline particles are physically aggregated, or may further contain agglomerated particles, or may further be composed of agglomerated particles. The shape of the agglomerated particles may be irregular, and the agglomerated particle diameter may be, for example, 5 μm or more or 10 μm or more, and 100 μm or less or 70 μm or less.

[0040] Crystal particles are the smallest particle unit observed under SEM observation at a magnification of 30 to 20,000 times, and the crystal particle diameter can be measured by measuring the longest length observed under SEM observation. Furthermore, the agglomerated particle diameter can be measured by measuring the longest length of particles formed by agglomeration of crystal particles.

[0041] The CHA zeolite of this embodiment may contain an active metal element. The active metal element is preferably a transition metal element, and is one or more elements selected from the group consisting of Groups 8, 9, 10, and 11 of the periodic table, further one or more elements selected from the group consisting of platinum (Pt), palladium (Pd), rhodium (Rh), iron (Fe), copper (Cu), cobalt (Co), manganese (Mn), and indium (In), further one or more metal elements selected from the group consisting of cobalt (Co), nickel (Ni), iron (Fe), and copper (Cu), further at least one of iron and copper, or further copper.

[0042] The active metal element is preferably contained in a state other than as a T atom, for example, supported outside the zeolite framework, such as supported on at least one of pores and ion exchange sites.

[0043] The CHA-type zeolite of this embodiment may have an active metal element content of 2.5 mass% or more, 3.0 mass% or more, or 3.5 mass% or more, and 6.5 mass% or less, 6.0 mass% or less, or 5.5 mass% or less.

[0044] The CHA-type zeolite of the present embodiment can be applied to known uses of zeolites, such as catalysts, adsorbents, and carriers thereof, and further can be used as a nitrogen oxide reduction catalyst and its carrier, and still further can be used as a nitrogen oxide reduction catalyst. Also, the nitrogen oxide reduction catalyst can be subjected to a nitrogen oxide reduction method using the same. Furthermore, the CHA-type zeolite of the present embodiment can be used as an exhaust gas purification catalyst, still further as an exhaust gas treatment catalyst for an internal combustion engine, and still further as an automobile exhaust gas treatment catalyst, and can also be used as these carriers. <Method for Producing CHA-Type Zeolite> The method for producing a CHA-type zeolite of the present embodiment includes a step of crystallizing a composition containing at least a structure-directing agent source containing N,N,N-trialkylcyclohexylammonium cations, an alumina source, a silica source, a sodium source, and water, having a molar ratio of silica to alumina of 20 or less and a molar ratio of potassium to sodium of less than 0.05 to obtain a crystallized product, a step of removing N,N,N-trialkylcyclohexylammonium cations from the crystallized product, and a step of contacting the crystallized product with an ammonium salt-containing solution having an ammonium concentration of 1% by mass or more. (Crystallization Step) It is considered that the CHA-type zeolite crystallizes while a part of sodium (Na) is incorporated in a state of improving the characteristics of the CHA-type zeolite by crystallizing a composition (hereinafter also referred to as "raw material composition") containing at least a structure-directing agent source containing N,N,N-trialkylcyclohexylammonium cations, an alumina source, a silica source, a sodium source, and water, having a molar ratio of silica to alumina of 20 or less and a molar ratio of potassium to sodium of less than 0.05 (hereinafter also referred to as "crystallization step").

[0045] The crystallized product obtained in the crystallization step tends to have a lower SiO2 / Al2O3 ratio than the raw material composition. To crystallize the CHA-type zeolite of this embodiment, the molar ratio of silica to alumina (SiO2 / Al2O3 ratio) of the raw material composition is 20 or less, and preferably 15 or less, less than 13, 11 or less, or 10 or less. The SiO2 / Al2O3 ratio may be 3 or more, 5 or more, or 8 or more.

[0046] The molar ratio of potassium to sodium (K / Na ratio) of the raw material composition is less than 0.05, preferably 0.03 or less or 0.01 or less, and preferably 0 (i.e., potassium-free). In a raw material composition using N,N,N-trialkylcyclohexylammonium cation as a structure directing agent and having a SiO2 / Al2O3 ratio of around 20, increasing the K / Na ratio facilitates crystallization of CHA zeolite. In contrast, in a raw material composition using N,N,N-trialkylcyclohexylammonium cation as a structure directing agent and having a particularly low SiO2 / Al2O3 ratio of 15 or less, a by-product phase having a zeolite structure other than the CHA structure is likely to be produced if the K / Na ratio is high, making it difficult to obtain a single-phase CHA zeolite. However, by keeping the K / Na ratio within this range, the production of by-product phases, particularly ERI zeolite, is suppressed, and single-phase CHA zeolite is obtained.

[0047] The alumina source is at least one of alumina (Al2O3) and a precursor thereof, and examples thereof include one or more selected from the group consisting of alumina, aluminum sulfate, aluminum nitrate, sodium aluminate, aluminum hydroxide, aluminum chloride, amorphous aluminosilicate, metallic aluminum, crystalline aluminosilicate, and aluminum alkoxide. Further, an amorphous aluminum compound, further at least one of aluminum hydroxide and amorphous aluminosilicate, or further amorphous aluminosilicate is preferred.

[0048] The silica source is at least one of silica (SiO2) and its precursor, and examples thereof include one or more selected from the group consisting of colloidal silica, amorphous silica, sodium silicate, tetraethoxysilane, tetraethyl orthosilicate, precipitated silica, fumed silica, amorphous aluminosilicate, and crystalline aluminosilicate, with amorphous aluminosilicate being preferred.

[0049] The raw material composition preferably contains at least an amorphous alumina source and a silica source, and further contains at least an amorphous aluminosilicate. The raw material composition does not contain a crystalline aluminosilicate as an alumina source and a silica source, which tends to reduce production costs and is industrially advantageous.

[0050] The sodium source may be a salt or compound containing sodium. Examples of the sodium source include one or more selected from the group consisting of chloride, iodide, bromide, hydroxide, and oxide of sodium, and further, one or more selected from the group consisting of chloride, bromide, and hydroxide of sodium, and further, sodium hydroxide. Sodium contained in other starting materials can also be considered as a sodium source. The raw material composition preferably contains at least sodium hydroxide.

[0051] The raw material composition may contain an alkali metal other than sodium, that is, one or more selected from the group consisting of potassium, rubidium, and cesium, and may further contain potassium, as long as the amount is sufficiently small relative to the amount of sodium.

[0052] The source of structure directing agent comprises at least N,N,N-trialkylcyclohexylammonium cation (TACH + ) contains TACH +functions as a so-called structure-directing agent (hereinafter also referred to as "SDA") that directs the CHA structure. The SDA source is a salt containing SDA, and examples thereof include one or more selected from the group consisting of hydroxide, halide, carbonate monoester salt, and sulfate monoester salt of SDA; one or more selected from the group consisting of hydroxide, chloride, bromide, and iodide; one or more selected from the group consisting of hydroxide, bromide, and iodide; at least one of hydroxide and bromide; or hydroxide.

[0053] TACH included in SDA sources + is N,N,N-trimethylcyclohexylammonium cation (hereinafter referred to as "TMCH + "), N,N,N-dimethylethylcyclohexylammonium cation (hereinafter referred to as "DMECH + "), N,N,N-methyldiethylcyclohexylammonium cation (hereinafter referred to as "MDECH + ") and N,N,N-triethylcyclohexylammonium cation (hereinafter referred to as "TECH + ") group, DMECH + and MDECH + At least one of the above, or DMECH + In order to crystallize the CHA-type zeolite having the SiO2 / Al2O3 ratio of this embodiment, the TACH contained in the SDA source + TMCH + Other than TACH + Preferably, DMECH + and MDECH + At least one of these, and also DMECH + It is preferable that:

[0054] The SDA contained in the raw material composition is TACH + (TACH + only), and DMECH + , MDECH + and TECH + or more selected from the group consisting of DMECH + and MDECH +and / or DMECH + (DMECH + On the other hand, the raw material composition is an SDA directed to the CHA structure, and + The Add-SDA may contain other compounds (hereinafter also referred to as "Add-SDA"). + "), trimethylbenzylammonium cation, and tetraethylammonium cation. Specific examples of Add-SDA include TAad + , and further include N,N,N-trimethyladamantanammonium cation. When Add-SDA is included, the raw material composition is TACH + It is preferable that these are contained in a proportion smaller than 100%.

[0055] Mainly TMCH + In order to crystallize CHA-type zeolite by the structure-directing effect of + The molar ratio of Add-SDA to SDA (hereinafter also referred to as "Add-SDA / SDA ratio") may be 1 or less, less than 1, 0.5 or less, or 0.4 or less. The raw material composition may not contain Add-SDA, and the Add-SDA / SDA ratio may be 0 (zero), but it may also contain Add-SDA, and the Add-SDA / SDA ratio may be more than 0 or 0.05 or more.

[0056] The water contained in the raw material composition may be deionized water or pure water, or may be structured water, water as a solvent, or water (H2O) contained in other starting materials.

[0057] The raw material composition preferably does not contain fluorine (F) or phosphorus (P), and the fluorine and phosphorus contents of the raw material composition are each below the detection limit (for example, the fluorine content is 1 ppm or less, the phosphorus content is 1 ppm or less, or the fluorine content and the phosphorus content are both 1 ppm or less).

[0058] The raw material composition preferably contains at least an amorphous compound containing silicon and aluminum as a silica source and an alumina source, and also contains at least one of a hydroxide and a halide of sodium as a sodium source. + In a raw material composition containing the above as an SDA, the coexistence of the SDA, an amorphous compound containing silicon and aluminum, such as an amorphous aluminosilicate, and at least one of a hydroxide and a halide of sodium, which are sodium salts, is thought to allow CHA-type zeolite to be crystallized without uneven distribution of sodium. As a result, compared to crystallization of a raw material composition containing separate substances as the alumina source and the silica source, it is thought that sodium that inhibits gas diffusion and other sodium that may deteriorate the properties of zeolite can be easily removed during crystallization.

[0059] The preferred composition of the raw material composition is the following molar composition: + , TACH + DMECH + The SDA / SiO2 ratio is DMECH + In addition, when M is an alkali metal other than sodium and the raw material composition contains two or more alkali metals other than sodium (for example, potassium and cesium), the M / SiO2 ratio may be considered as a (K+Cs) / SiO2 ratio, etc. Furthermore, each composition ratio in the molar composition may be any combination of the upper and lower limits described below. SiO2 / Al2O3 ratio = 3 or more, 5 or more, or 8 or more, and 20 or less, 15 or less, less than 13, 11 or less, or 10 or less SDA / SiO2 ratio = 0.01 or more, 0.02 or more, 0.05 or more, or 0.075 or more, and 0.5 or less, 0.3 or less, 0.2 or less, or 0.1 or less Add-SDA / SDA ratio = 0 or more, more than 0 or 0.05 or more, and 1 or less, 0.5 or less, or 0.4 or less Na / SiO2 ratio = more than 0, 0.1 or more, or 0.2 or more, and 0.60 or less, 0.5 or less, 0.4 or less, or 0.3 or less K / Na ratio = 0 or more, 0.001 or more, or 0.005 or more, and Less than 0.05, 0.03 or less, or 0.01 or less M / Na ratio = 0 or more, 0.001 or more, or 0.005 or more, and Less than 0.05, 0.03 or less, or 0.01 or less H2O / SiO2 ratio = 3 or more, 5 or more, 10 or more, or 15 or more, and 50 or less, 30 or less, 20 or less, or 19 or less

[0060] Seed crystals may be mixed into the raw material composition to promote the crystallization of CHA zeolite. Examples of seed crystals include one or more selected from the group consisting of AEI zeolite, AFX zeolite, ERI zeolite, CHA zeolite, LEV zeolite, and OFF zeolite, and further include CHA zeolite. The seed crystals mixed into the raw material composition may have a ratio (hereinafter also referred to as "seed crystal content") of the total mass of silicon (Si) and aluminum (Al) of the seed crystals converted into SiO2 and Al2O3, respectively, to the total mass of silicon (Si) and aluminum (Al) of the raw material composition converted into SiO2 and Al2O3, respectively, of more than 0 mass%, 0.5 mass% or more, or 1 mass% or more, and 10 mass% or less, 5 mass% or less, or 3 mass% or less. It is also possible to not mix seed crystals into the raw material composition, i.e., the seed crystal content may be 0 mass%.

[0061] In the crystallization step, the raw material composition is crystallized. The crystallization method may be any method that crystallizes the raw material composition, and may be hydrothermal synthesis. The following conditions may be exemplified as conditions for hydrothermal synthesis. Crystallization temperature: 130°C or higher, 140°C or higher, more than 150°C or more than 155°C, and 200℃ or less, 180℃ or less, or 170℃ or less Crystallization time: 1 hour or more, 10 hours or more, or 24 hours or more, and 7 days or less, 5 days or less, 3 days or less, or 2 days or less Crystallization state: at least one of a stirring state and a static state, or a stirring state Crystallization pressure: Autogenous pressure For example, when crystallizing CHA-type zeolite having an SiO2 / Al2O3 ratio of less than 10, if the crystallization temperature is above 150°C or above 155°C and below 180°C or below 170°C, single-phase CHA-type zeolite can be crystallized in a crystallization time of 2 days or less.

[0062] (SDA removal process) Crystallization from TACH + In the step of removing TACH (hereinafter also referred to as "SDA removal step"), + can be removed from the crystallized product (CHA-type zeolite).

[0063] SDA removal from crystallized material + Any method capable of removing SDA may be used. Examples of SDA removal methods include calcination and acid treatment, with calcination being preferred. Examples of calcination include treating CHA zeolite in one or more atmospheres selected from the group consisting of an oxidizing atmosphere, an inert atmosphere, and a reducing atmosphere at 300°C or higher or 400°C or higher and 600°C or lower or 500°C or lower. Particularly preferred calcination methods include calcination in air at 300°C or higher and 600°C or lower. Examples of the time for the calcination (and acid treatment) include 1 hour to 5 hours, but this may be adjusted appropriately depending on the amount of crystallized material to be subjected to the calcination.

[0064] The crystallized product to be subjected to the SDA removal step may be the one recovered by solid-liquid separation or the like after the crystallization step, but may also be the one washed and dried.

[0065] The crystallized product can be washed by any method after crystallization, such as washing the recovered crystallized product (CHA zeolite) with pure water in an amount such that the mass of the pure water is 10 times or more the mass of the crystallized product. Drying can be performed by any method that can remove moisture physically adsorbed on the CHA-type zeolite, and examples include treating the CHA-type zeolite in at least one of an oxidizing atmosphere and an inert atmosphere at 100°C or higher and 200°C or lower for 2 hours or more.

[0066] (Alkali removal process) TACH + The crystallized material from which the TACH + CHA-type zeolite (not containing ammonium salt) is treated by a process of contacting the crystallized product with an ammonium salt-containing solution having an ammonium concentration of 1 mass % or more (hereinafter also referred to as the "alkali removal process"). By washing the crystallized product with such an ammonium salt-containing solution, sodium in a form that reduces the properties of CHA-type zeolite is efficiently removed, and furthermore, removal of sodium that contributes to improving the properties of CHA-type zeolite is suppressed.

[0067] The ammonium-containing solution contains ammonium (NH4 + ) and a solvent.

[0068] The solvent may be any medium in which the ammonium salt dissolves, and may be at least one of alcohol and water, and may be water, that is, the ammonium-containing solution may be an aqueous ammonium-containing solution.

[0069] Ammonium salts are ammonium (NH4 + ) may be used, and examples thereof include inorganic salts of ammonium, and further, one or more selected from the group consisting of ammonium carbonate, ammonium chloride and ammonium nitrate, and further, ammonium chloride.

[0070] The ammonium-containing solution is +The ammonium concentration is preferably 1% by mass or more, 2% by mass or more, 5% by mass or more, or 7% by mass or more. Treating the crystallized material (SDA-free CHA zeolite) with such a high-concentration ammonium-containing solution is thought to preferentially remove trace amounts of alkali metals in the form of compounds such as oxides, alkali metal ions that are easily liberated, and other alkali metals that may degrade the properties of CHA zeolite. As a result, it becomes easier to obtain a CHA zeolite that can serve as a nitrogen oxide reduction catalyst or its support, having nitrogen oxide reduction properties equivalent to those of a CHA zeolite having an SiO2 / Al2O3 ratio of about 22 to 24. The ammonium concentration of the ammonium-containing solution may be equal to or less than the saturation concentration, and examples of such an ammonium concentration include 30% by mass or less, 25% by mass or less, 20% by mass or less, 15% by mass or less, and 10% by mass or less.

[0071] In order to leave an appropriate amount of sodium (residual Na) in the CHA-type zeolite after the alkali removal step, and further to remove sodium that tends to deteriorate the properties of CHA-type zeolite, the ratio of the mass of the ammonium-containing solution to the mass of the crystallized product (CHA-type zeolite not containing SDA) (hereinafter also referred to as "NH4 / CHA") is preferably 10 or less, 8 or less, or 6 or less. NH4 / CHA may be greater than 1, 1.5 or more, or 2 or more.

[0072] The crystallinity of CHA-type zeolite tends to decrease due to post-treatment after crystallization, such as removal of SDA. Therefore, the crystallinity of CHA-type zeolite after alkali removal relative to CHA-type zeolite (as-synthesized) after the crystallization step (hereinafter also referred to as "crystallization retention rate") is 100% or less, 95% or less, 90% or less, or 86% or less. On the other hand, the crystallization retention rate is preferably 76.5% or more, 78% or more, or 80% or more. The crystallization retention rate can be determined from the ratio of the peak heights of the XRD peaks corresponding to the CHA-type zeolite (20-1) plane after the crystallization step and after the alkali removal step (CHA-type zeolite after alkali removal / CHA-type zeolite after the crystallization step; %). The peak having its top at 2θ=20.7±0.2° can be considered to be the XRD peak corresponding to the CHA-type zeolite (20-1) plane.

[0073] (Metal-containing process) When the CHA type zeolite of this embodiment is a metal-containing CHA type zeolite, the production method of this embodiment may include a step of contacting the CHA type zeolite with an active metal source (hereinafter also referred to as a "metal-containing step"). This results in a metal-containing CHA type zeolite (or a metal-supported CHA type zeolite).

[0074] In the metal-containing step, any active metal element is contained in the CHA-type zeolite after alkali removal, and preferably any transition metal element is supported on the CHA-type zeolite. The metal can be contained by any method that brings the CHA-type zeolite into contact with an active metal source so that the active metal element is contained as an atom other than the T atom of the CHA-type zeolite, and examples thereof include one or more methods selected from the group consisting of ion exchange, impregnation, evaporation to dryness, precipitation, and physical mixing, with the impregnation method being preferred. The active metal source is at least one of a salt and a compound containing an active metal element, and may be one or more selected from the group consisting of nitrates, sulfates, acetates, chlorides, complex salts, oxides, and composite oxides, or one or more selected from the group consisting of nitrates, sulfates, and chlorides, all of which contain an active metal element.

[0075] Preferably, the active metal element is a transition metal element, further one or more selected from the group consisting of Groups 8, 9, 10 and 11 of the periodic table, further one or more selected from the group consisting of platinum (Pt), palladium (Pd), rhodium (Rh), iron (Fe), copper (Cu), cobalt (Co), manganese (Mn) and indium (In), further at least one of iron and copper, or copper.

[0076] The production method of this embodiment may include a step of calcining the metal-containing CHA-type zeolite, if necessary. Impurities are removed by calcination. Any calcination method may be used, including treatment at 100°C to 600°C in one or more atmospheres selected from the group consisting of an oxidizing atmosphere, an inert atmosphere, and a reducing atmosphere. Treatment in air at 400°C to 600°C is preferred. [Example]

[0077] The present embodiment will be described below with reference to examples, but the present embodiment is not limited to these examples.

[0078] (zeolite structure) The sample was subjected to XRD measurement using a powder X-ray diffractometer (device name: Ultima IV, manufactured by Rigaku Corporation) under the following measurement conditions. Acceleration current / voltage: 40mA / 40kV Radiation source: CuKα radiation (λ=1.5405Å) Measurement mode: Continuous scan Scan condition: 40° / min Measurement range: 2θ=3° to 43° Divergence vertical limit slit: 10mm Divergence / entrance slit: 1° Receiving slit: open Receiving solar slit: 5° Detector: Semiconductor detector (D / teX Ultra) Filter: Ni filter

[0079] The obtained XRD pattern was analyzed using the analysis software attached to the device (software name: Smart Lab Studio II, manufactured by Rigaku Corporation) under the following conditions. Fitting conditions: Automatic, refine background Dispersive pseudo-Voigt function (peak shape) Background removal method: Fitting method Kα2 removal method: Kα1 / Kα2 ratio=0.497 Smoothing method: B-Spline curve Smoothing conditions: second-order differential method, σ cut value = 3, χ threshold = 1.5 The zeolite structure was identified by comparing the analyzed XRD pattern with a reference pattern.

[0080] (Crystallization maintenance rate) The crystallization retention rate is the ratio [%] of the peak height of the XRD peak corresponding to the (20-1) plane of the CHA structure of the CHA-type zeolite after ion exchange, washing, and drying to the crystallized product (CHA-type zeolite) after recovery, washing, and drying from the crystallization process. The XRD peak corresponding to the (20-1) plane was obtained by the same XRD measurement as in (zeolite structure), and was taken as a peak having a peak top at 2θ=20.7±0.2°.

[0081] (composition analysis) The composition of the sample was analyzed using a general inductively coupled plasma optical emission spectrometer (instrument name: OPTIMA7300DV, manufactured by PERKIN ELMER). The sample was dissolved in a mixed solution of hydrofluoric acid and nitric acid to prepare a measurement solution. The composition of the sample was analyzed using the obtained measurement solution.

[0082] (SiOH amount) 1 The silanol group content of the CHA-type zeolite was measured by 1 H MAS NMR. Prior to the measurement, the sample was pretreated by dehydrating it by holding it at 400°C for 5 hours in a vacuum atmosphere. After pretreatment, the sample was cooled to room temperature and then collected and weighed in a nitrogen atmosphere. A general NMR measurement device (device name: VNMRS-400, manufactured by Varian) was used as the measurement device. The measurement conditions were as follows: Resonance frequency: 399.8MHz Pulse width: π / 2 Measurement waiting time: 10 seconds Accumulation count: 32 times Rotation frequency: 15kHz Shift standard: TMS (tetramethylsilane) obtained 1 The peak with a peak top at 2.0±0.4 ppm in the H MAS NMR spectrum was determined as the peak attributable to silanol groups. This peak was subjected to waveform separation using spectrum analysis software (GRAMS / AI Ver. 8.0, Thermo Fisher Scientific) and then the area intensity was determined. A calibration curve was created using benzene as a standard substance. From the area intensity of the NMR spectrum attributable to the obtained silanol groups, the amount of protons derived from the silanol groups in the sample was determined by the calibration curve method, and the amount of SiOH was calculated from the amount of protons and the mass of the weighed sample.

[0083] Example 1 A 35 mass % DMECHAOH aqueous solution, a 48 mass % sodium hydroxide aqueous solution, water, and amorphous aluminosilicate (SiO2 / Al2O3=8.9) were mixed to obtain a raw material composition having the following molar composition. SiO2 / Al2O3=8.9 DMECH + / SiO2=0.08 Na / SiO2=0.27 H2O / SiO2=18 OH / SiO2=0.35

[0084] CHA-type zeolite was added as seed crystals to the obtained raw material composition so that the content was 2.0 mass% and mixed, and then the mixture was filled into a sealed container and subjected to hydrothermal treatment at 160°C for 48 hours to obtain a crystallized product consisting of a single phase of CHA-type zeolite. The obtained crystallized product was recovered by solid-liquid separation, washed with a sufficient amount of pure water, dried in the air, and then calcined at 600°C to obtain CHA-type zeolite.

[0085] The calcined CHA-type zeolite consisted of a single phase of CHA-type zeolite and contained sodium as an alkali metal, with an Na / Al ratio of 0.87.

[0086] The CHA-type zeolite and ammonium (NH4 +The ion exchange was carried out by mixing the zeolite with an aqueous ammonium chloride solution having a 20 mass% ammonium chloride concentration. The ammonium chloride solution used for the ion exchange was 4.5 times the mass of the CHA-type zeolite (NH4 / CHA = 4.5). After the ion exchange, the zeolite was washed with pure water and dried to obtain the CHA-type zeolite of this example. The CHA-type zeolite of this example (a CHA-type zeolite with an ammonium cation type) had a SiO2 / Al2O3 of 8.7 and a sodium content of 400 ppm. In addition, potassium was below the detection limit.

[0087] An SEM image of the CHA-type zeolite of this example is shown in Figure 1. The CHA-type zeolite of this embodiment was composed of aggregated particles formed by agglomerating crystalline particles that lacked some faces of primary particles having at least one of a rhombohedral or cubic shape. Furthermore, the crystalline particles had a crystal particle diameter of 0.5 μm or more and 1 μm or less, and the aggregated particle diameter of the main aggregated particles was 50 μm or more and 70 μm or less.

[0088] Example 2 Crystallization, washing, drying, and calcination were carried out in the same manner as in Example 1, except that a raw material composition having the following molar composition, which was a mixture of a 35 mass% DMECHAOH aqueous solution, a 48 mass% sodium hydroxide aqueous solution, water, and amorphous aluminosilicate (SiO / AlO = 10.6), was used. SiO2 / Al2O3=10.6 DMECH + / SiO2=0.08 Na / SiO2=0.29 H2O / SiO2=18 OH / SiO2=0.37

[0089] The calcined CHA-type zeolite consisted of a single phase of CHA-type zeolite and contained sodium as an alkali metal, with an Na / Al ratio of 0.79.

[0090] The CHA zeolite was subjected to ion exchange, washing, and drying in the same manner as in Example 1 to obtain the CHA zeolite of this example. The CHA zeolite of this example had an SiO / AlO ratio of 9.6, a sodium content of 700 ppm, and an SiOH content of 0.30×10 20 It was 1 / g.

[0091] Example 3 Crystallization, washing, drying, and calcination were carried out in the same manner as in Example 1, except that a raw material composition having the following molar composition, obtained by mixing a 35 mass% DMECHAOH aqueous solution, a 25 mass% TMAdOH aqueous solution, a 48 mass% sodium hydroxide aqueous solution, water, and amorphous aluminosilicate (SiO / AlO=10.6), was used. SiO2 / Al2O3=10.6 DMECH + / SiO2=0.06 TMAd + / SiO2=0.02 Na / SiO2=0.29 H2O / SiO2=18 OH / SiO2=0.37

[0092] The calcined CHA-type zeolite consisted of a single phase of CHA-type zeolite and contained sodium as an alkali metal, with an Na / Al ratio of 0.82.

[0093] The CHA zeolite of this example was obtained by ion-exchanging, washing, and drying the CHA zeolite in the same manner as in Example 1. The CHA zeolite of this example had a SiO2 / Al2O3 ratio of 9.9 and a sodium content of 140 ppm.

[0094] An SEM image of the CHA-type zeolite of this example is shown in Figure 2. The CHA-type zeolite of this embodiment was composed of aggregated particles formed by agglomerating crystalline particles that lacked some faces of primary particles having at least one of a rhombohedral or cubic shape. Furthermore, the crystalline particles had a crystalline particle diameter of 0.5 μm or more and 1 μm or less.

[0095] Example 4 Crystallization, washing, drying, and calcination were carried out in the same manner as in Example 1, except that a raw material composition having the following molar composition, obtained by mixing a 35 mass% DMECHAOH aqueous solution, a 48 mass% sodium hydroxide aqueous solution, water, and amorphous aluminosilicate (SiO / AlO=12.8), was used, and the crystallization time was set to 72 hours. SiO2 / Al2O3=12.8 DMECH + / SiO2=0.17 Na / SiO2=0.35 H2O / SiO2=18 OH / SiO2=0.52

[0096] The calcined CHA-type zeolite consisted of a single phase of CHA-type zeolite and contained sodium as an alkali metal, with an Na / Al ratio of 0.77.

[0097] The CHA zeolite was subjected to ion exchange, washing, and drying in the same manner as in Example 1 to obtain the CHA zeolite of this example. The CHA zeolite of this example had a sodium content of 300 ppm, an SiO2 / Al2O3 ratio of 9.7, and an SiOH amount of 0.27×10 20 It was 1 / g.

[0098] An SEM image of the CHA-type zeolite of this example is shown in Figure 3. The CHA-type zeolite of this embodiment was mainly composed of crystalline particles with some missing faces of primary particles having at least one of a rhombohedral or cubic shape, and the crystalline particles were in a dispersed state. The crystalline particles had a crystalline particle diameter of 0.5 μm or more and 1 μm or less.

[0099] Example 5 The crystallization, washing, drying and calcination were carried out in the same manner as in Example 2 to obtain CHA-type zeolite.

[0100] The CHA-type zeolite and ammonium (NH4 +The ion exchange was carried out by mixing the ammonium chloride aqueous solution with a 10 mass% ammonium chloride concentration. The ammonium chloride aqueous solution used for the ion exchange was 1.3 times the mass of the CHA-type zeolite (NH4 / CHA = 1.3). After the ion exchange, the zeolite was washed with pure water and dried to obtain the CHA-type zeolite of this example. The CHA-type zeolite of this example had a SiO2 / Al2O3 ratio of 9.6 and a sodium content of 1270 ppm.

[0101] Comparative Example 1 The crystallization, washing, drying and calcination were carried out in the same manner as in Example 2 to obtain CHA-type zeolite.

[0102] The CHA-type zeolite was mixed with an aqueous ammonium chloride solution with an ammonium concentration of 0.6% by mass to perform ion exchange. The amount of ammonium chloride solution used for ion exchange was 6.6 times the mass of the CHA-type zeolite (NH4 / CHA=6.6). After ion exchange, the zeolite was washed with pure water and dried to obtain the CHA-type zeolite of this comparative example. The CHA-type zeolite of this comparative example had a SiO2 / Al2O3 ratio of 9.8 and a Na content of 11,600 ppm.

[0103] Comparative Example 2 The crystallization, washing, drying and calcination were carried out in the same manner as in Example 4 to obtain CHA-type zeolite.

[0104] The CHA-type zeolite was mixed with a 7.1% aqueous hydrochloric acid solution to perform ion exchange. The 7.1% aqueous hydrochloric acid solution used for the ion exchange was 2.5 times the mass of the CHA-type zeolite (NH4 / CHA=0). After the ion exchange, the zeolite was washed with pure water and dried to obtain the CHA-type zeolite of this comparative example. The CHA-type zeolite of this comparative example had a SiO2 / Al2O3 ratio of 9.9 and a Na content of 100 ppm.

[0105] Comparative Example 3 A raw material composition having the following molar composition was obtained by mixing a 35 mass % DMECHAOH aqueous solution, a 48 mass % sodium hydroxide aqueous solution, a 48 mass % potassium hydroxide aqueous solution, and amorphous aluminosilicate (SiO2 / Al2O3=10.6). SiO2 / Al2O3=10.6 DMECH + / SiO2=0.08 Na / SiO2=0.275 K / Na =0.055 H2O / SiO2=18 OH / SiO2=0.37

[0106] Except for using the obtained raw material composition, seed crystals were mixed and crystallized in the same manner as in Example 1. The obtained crystallized product was a mixture of CHA zeolite and ERI zeolite, and a single phase of CHA zeolite was not obtained.

[0107] The results of the examples and comparative examples are shown in the table below.

[0108] [Table 1]

[0109] The CHA-type zeolites of the examples all have a Na / Al ratio of 0.05 or less, or even 0.01 or less, and it can be confirmed that the Na content is reduced compared to the CHA-type zeolite after calcination. Furthermore, from Comparative Example 1, it can be confirmed that the CHA-type zeolite ion-exchanged with a low-concentration NH4Cl aqueous solution has a reduced Na content and a low crystallization retention rate, and that the crystallinity is significantly reduced by the ion exchange. Furthermore, from Comparative Example 2, it can be seen that while the crystallinity is not reduced by ion exchange with hydrochloric acid, which is a strong acid, the reduction in Na is excessive, that is, even the remaining Na that can contribute to improving properties is removed.

[0110] Measurement example An aqueous copper nitrate solution was added dropwise to each of the CHA-type zeolites obtained in Examples 2, 3, and 5, and Comparative Examples 1 and 2, and then the mixture was mixed in a mortar for 10 minutes. After mixing, the mixture was dried overnight at 110°C in the air, and then calcined for 1 hour at 550°C in the air, thereby obtaining metal-containing CHA-type zeolites each supporting 4.6% by mass of copper (copper-supported CHA-type zeolites).

[0111] (Hydrothermal durability treatment) The copper-supported CHA-type zeolite was molded and crushed to form agglomerated particles with an agglomerate diameter of 12 to 20 mesh. 3 mL of the agglomerated particles was packed into an atmospheric fixed-bed flow-type reactor (hereinafter simply referred to as the "reactor") and then subjected to hydrothermal durability treatment under the following conditions. Treatment atmosphere: Air-flow atmosphere with a moisture content of 10% by volume Air flow rate: 300 mL / min Processing temperature: 800℃ Processing time: 16 hours

[0112] (nitrogen oxide reduction rate) 1.5 mL of the agglomerated particles after the hydrothermal durability treatment was filled into a reaction tube, and a nitrogen oxide-containing gas was passed through the reaction tube while maintaining the temperature at the following measurement temperature, and the nitrogen oxide concentrations at the inlet and outlet of the reaction tube were measured.

[0113] Composition of nitrogen oxide-containing gas: NO 200 ppm NH3 200 ppm O2 10% by volume H2O 3% by volume N2 remainder Flow rate of nitrogen oxide-containing gas: 1.5L / min Space velocity: 60,000hr -1 Measurement temperature: 150℃ or 600℃

[0114] The nitrogen oxide reduction rate (NOx reduction rate) was calculated from the obtained nitrogen oxide concentration using the following formula. Nitrogen oxide reduction rate (%) ={([NOx]in-[NOx]out) / [NOx]in}×100 [NOx]in is the nitrogen oxide concentration of the nitrogen oxide-containing gas at the inlet of the reaction tube, and [NOx]out is the nitrogen oxide concentration of the nitrogen oxide-containing gas at the outlet of the reaction tube.

[0115] [Table 2]

[0116] Example 3 is a copper-supported CHA-type zeolite in which copper is supported on CHA-type zeolite with a sodium content of 140 ppm, while Comparative Example 2 is a copper-supported CHA-type zeolite in which copper is supported on CHA-type zeolite with a sodium content of 100 ppm. Despite the difference in sodium content being only 40 ppm, the copper-supported CHA-type zeolite of Comparative Example 2 had lower nitrogen oxide reduction rates at both low temperature (150°C) and high temperature (600°C) than the copper-supported CHA-type zeolite of Example 3, and it was confirmed that the low-temperature nitrogen oxide reduction rate was about 0.5 times higher.

[0117] Furthermore, in CHA-type zeolites with a SiO2 / Al2O3 ratio of 10 or less, the nitrogen oxide reduction rate decreases significantly as the SiO2 / Al2O3 ratio decreases. However, it was confirmed that the copper-supported CHA-type zeolite of Example 2 (SiO2 / Al2O3 = 9.6) had a higher nitrogen oxide reduction rate at both low temperatures (150°C) and high temperatures (600°C) than the copper-supported CHA-type zeolite of Comparative Example 2 (SiO2 / Al2O3 = 9.9).

[0118] Furthermore, it was confirmed that the copper-loaded CHA-type zeolite, in which copper is loaded onto a CHA-type zeolite with a sodium content exceeding 1% by mass, has a higher SiO2 / Al2O3 than the copper-loaded CHA-type zeolite of Example 2, but the nitrogen oxide reduction rate is lower at both low and high temperatures.

Claims

1. A CHA-type zeolite having a molar ratio of silica to alumina of less than 13, a sodium content of 100 ppm or more and 2000 ppm or less, and a silanol group content per mass of 0.50×10 20 groups / g or less.

2. 2. The CHA-type zeolite according to claim 1, wherein the molar ratio of potassium to sodium is less than 0.

05.

3. A CHA-type zeolite as described in claim 1 or 2, having a sodium content of 100 ppm or more and 2000 ppm or less.

4. 4. A method for producing a CHA-type zeolite according to any one of claims 1 to 3, comprising the steps of: crystallizing a composition comprising a structure-directing agent source containing at least N,N,N-trialkylcyclohexylammonium cations, an alumina source, a silica source, a sodium source, and water, wherein the molar ratio of silica to alumina is 20 or less and the molar ratio of potassium to sodium is less than 0.05 to obtain a crystallized product; removing N,N,N-trialkylcyclohexylammonium cations from the crystallized product; and contacting the crystallized product with an ammonium salt-containing solution having an ammonium concentration of 1 mass% or more.

5. The method of claim 4, wherein the crystallization temperature is greater than 150°C.

6. The method according to claim 4 or 5, wherein the composition contains at least an amorphous aluminosilicate.

7. 7. The method according to claim 4, wherein the N,N,N-trialkylcyclohexylammonium cation is at least one of an N,N,N-dimethylethylcyclohexylammonium cation and an N,N,N-methyldiethylcyclohexylammonium cation.

8. 6. The method according to claim 4, wherein the composition contains at least an amorphous compound containing silicon and aluminum as a silica source and an alumina source, and further contains at least one of a hydroxide and a halide of sodium as a sodium source.

9. A nitrogen oxide reduction catalyst comprising the CHA-type zeolite according to any one of claims 1 to 3.

10. A method for reducing nitrogen oxides using the nitrogen oxide reduction catalyst according to claim 9.

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