CHA-type zeolite and its manufacturing method

Abstract

To provide CHA-type zeolite having fewer paired aluminum structures and exhibiting higher heat resistance compared with conventional CHA-type zeolite, catalysts containing the same, and at least one of their manufacturing methods.SOLUTION: CHA-type zeolite is characterized by a molar ratio of silica to alumina of 20 or less and a paired aluminum ratio of 13% or less. The CHA-type zeolite is preferably obtained by a production method that includes a step of crystallizing a composition containing an amorphous alumina source, an amorphous silica-alumina source, an alkaline source, an organic structure-directing agent and water.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a CHA-type zeolite and a method for producing the same, and more particularly to a CHA-type zeolite suitable for industrial use as a nitrogen oxide reduction catalyst and a method for producing the same. [Background technology]

[0002] CHA-type zeolite is an artificially synthesized small-pore zeolite. CHA-type zeolites with a relatively high SiO2 / Al2O3 ratio are highly heat-resistant, and their structure is resistant to collapse even when exposed to a hydrothermal atmosphere. For this reason, CHA-type zeolites with an SiO2 / Al2O3 ratio of more than 20 have been put to practical use as nitrogen oxide reduction catalysts. In contrast to these CHA-type zeolites, zeolites with an SiO2 / Al2O3 ratio of less than 20 are known to have low heat resistance and to be prone to collapse of their crystalline structure when exposed to a hydrothermal atmosphere, so their application has been limited to applications where heat resistance is not required.

[0003] In recent years, studies have been conducted focusing on the distribution of aluminum in the framework structure of CHA zeolite, particularly on the "paired aluminum structure." For example, Non-Patent Document 1 reports a CHA zeolite in which the proportion of paired aluminum structures in the aluminum is 5% or more and 17% or less, and Non-Patent Document 2 reports a CHA zeolite in which the proportion of paired aluminum structures in the aluminum is 60% or less. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Chem.Mater.,28(2016)2236-2247 [Non-patent document 2] Chem.Mater.,32(2020)273-285 Summary of the Invention [Problem to be solved by the invention]

[0005] The present disclosure aims to provide a CHA-type zeolite that exhibits higher heat resistance despite having a molar ratio of silica to alumina equivalent to that of conventional CHA-type zeolites, which have a molar ratio of silica to alumina of 20 or less, and a catalyst containing the same, as well as at least one of methods for producing these. [Means for solving the problem]

[0006] The present inventors investigated the application of CHA-type zeolites with an SiO2 / Al2O3 ratio of 20 or less to nitrogen oxide reduction catalysts. As a result, they found that the distribution of aluminum in the zeolite structure affects the heat resistance of CHA-type zeolites, and that the effect of the aluminum distribution varies depending on the SiO2 / Al2O3 ratio. Furthermore, the present inventors found that by controlling the distribution of aluminum in CHA-type zeolites with an SiO2 / Al2O3 ratio of 20 or less, heat resistance, particularly at high temperatures of 400°C or higher, is high despite the low SiO2 / Al2O3 ratio, and that deterioration of nitrogen oxide reduction properties in this temperature range is suppressed.

[0007] 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 characterized by a silica to alumina molar ratio of 20 or less and a pair aluminum ratio of 13% or less. [2] The CHA-type zeolite according to [1] above, having a micropore volume of 0.2 mL / g or more. [3] The CHA-type zeolite according to [1] or [2] above, which contains a transition metal element. [4] The CHA-type zeolite according to [3] above, wherein the transition metal element is at least one of iron and copper. [5] A method for producing CHA-type zeolite, comprising a step of crystallizing a composition containing an amorphous alumina source, an amorphous silica-alumina source, an alkali source, an organic structure-directing agent, and water, wherein the molar ratio of silica to alumina is 20 or less and the ratio of aluminum to silica is 13% or less. [6] The method according to the above [5], wherein the amorphous alumina source is at least one of dried aluminum hydroxide gel and sodium aluminate. [7] The method according to the above [5] or [6], wherein the amorphous silica-alumina source is an amorphous aluminosilicate. [8] The method according to any one of [5] to [7] above, wherein the composition contains a silica source. [9] The method according to any one of [5] to [8] above, wherein the molar ratio of silica to alumina in the composition is 22 or less.

[10] The method according to any one of [5] to [9] above, wherein the mass ratio of the amorphous silica-alumina source to the amorphous alumina source is 15 or more.

[11] A nitrogen oxide reduction catalyst containing the CHA-type zeolite according to any one of [1] to [4] above.

[12] A method for reducing nitrogen oxides using the CHA-type zeolite according to any one of [1] to [4] above. [Effects of the Invention]

[0008] The present disclosure makes it possible to provide a CHA-type zeolite and a catalyst containing the same that exhibit higher heat resistance despite having a molar ratio of silica to alumina equivalent to that of conventional CHA-type zeolites, which have a molar ratio of silica to alumina of 20 or less, as well as at least one of methods for producing these. DETAILED DESCRIPTION OF THE INVENTION

[0009] The present disclosure will be described below by showing an example of an embodiment. Note that the terms used in this embodiment are as follows.

[0010] An "aluminosilicate" is a composite oxide having a structure consisting of a repeating network of aluminum (Al) and silicon (Si) via oxygen (O). 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."

[0011] 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 Detector: D / teX Ultra Ni filter used

[0012] 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 an XRD pattern analysis using general analysis software (e.g., SmartLab Studio II, manufactured by Rigaku Corporation), and an example of such a peak is an XRD peak with a half-width of 2θ=0.50° or less.

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

[0014] A "zeolite-like substance" is a compound having a regular structure in which T atoms are oxygen-mediated, and the T atoms contain at least one atom other than a metal or metalloid. Examples of zeolite-like substances include complex phosphorus compounds containing phosphorus (P) as the T atom, such as aluminophosphate (AlPO) and silicoaluminophosphate (SAPO).

[0015] The "regular structure" (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 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 (hereinafter also referred to as "reference patterns") of each structure listed in "Collection of simulated XRD powder patterns for zeolites," Fifth revised edition, p. 483 (2007). With regard to the zeolite structure, the terms skeletal structure, crystalline structure, and crystalline phase are used interchangeably.

[0016] In the present embodiment, "CHA-type zeolite" and other "CHA-type zeolite" refer to a zeolite having a zeolite structure of the relevant structure code, and preferably refer to a crystalline aluminosilicate having a zeolite structure of the relevant structure code.

[0017] Next, the CHA-type zeolite of the present disclosure will be described with reference to an example of an embodiment.

[0018] The CHA-type zeolite of this embodiment is characterized by a silica to alumina molar ratio of 20 or less and a pair aluminum ratio of 13% or less. As a result, despite being a CHA-type zeolite with a low silica to alumina molar ratio (hereinafter also referred to as "SiO2 / Al2O3 ratio"), it exhibits higher nitrogen oxide reduction properties than CHA-type zeolites with similar SiO2 / Al2O3 ratios.

[0019] The SiO2 / Al2O3 ratio of the CHA-type zeolite of this embodiment is 20 or less, and is preferably less than 20, 15 or less, or 13 or less. The SiO2 / Al2O3 ratio is 5 or more, or 10 or more.

[0020] The pair aluminum ratio (hereinafter also referred to as "pair Al ratio") of the CHA type zeolite of this embodiment is 13% or less, and preferably 10% or less. The pair Al ratio may be 0% or more, but the CHA type zeolite of this embodiment can have a pair Al ratio of more than 0%, 1% or less, or 5% or less, for example.

[0021] The paired Al ratio is a value that can be determined by quantifying the amount of cobalt ion-exchanged into the ion exchange sites of divalent ions having a paired aluminum structure. Specifically, a CHA-type zeolite having a ratio of alkali metal elements and alkaline earth metal elements to aluminum (hereinafter also referred to as "M / Al ratio") of 0.01 or less is immersed in a cobalt nitrate aqueous solution, and the cobalt (Co) content is measured. The paired Al ratio is the value calculated from the following formula:

[0022] Pair Al ratio [%] = (M Co [mol] / M Al [mol]) x 2 x 100 In the above equation, M Co [mol] is the cobalt content measured by ICP measurement, and M Al [mol] is the aluminum content measured by ICP measurement.

[0023] The conditions for immersion in the cobalt nitrate aqueous solution include the following. Immersion temperature: 10℃ or higher and 40℃ or lower Immersion time: 1 hour to 40 hours Cobalt nitrate concentration: 0.001 mol / L or more and 2.0 mol / L or less Solid-liquid ratio: (CHA-type zeolite / cobalt nitrate aqueous solution)≦0.5

[0024] Examples of CHA-type zeolites having an M / Al ratio of 0.01 or less include CHA-type zeolites whose cation type is a proton type or an ammonium type.

[0025] Even when a similar treatment is performed on a CHA-type zeolite whose cation type is sodium, potassium, calcium, or the like and whose M / Al ratio exceeds 0.01, a formal pair Al ratio (hereinafter, the pair Al ratio thus determined is also referred to as the "formal pair Al ratio") is determined. However, the formal Al ratio is determined based on the ratio of cobalt (Co) supported on the ion exchange sites of divalent ions having a pair aluminum structure, such as cobalt complexes. 2+ ) is a value including cobalt derived from structures other than the above. Therefore, the value of the formal pair Al ratio does not reflect the content of pair aluminum structures in the CHA-type zeolite, but is greater than the pair Al ratio of this embodiment (i.e., the proportion of actual pair aluminum structures). Since the formal pair Al ratio shows a different value from the pair Al ratio of this embodiment, the pair Al ratio of this embodiment cannot be compared with the formal pair Al ratio.

[0026] The BET specific surface area of ​​the CHA-type zeolite of this embodiment is 200 m 2 / g or more or 500m 2 / g or more, and 1000m 2 / g or less or 800m 2 / g or less.

[0027] The BET specific surface area can be determined by the BET single-point method using nitrogen adsorption in accordance with JIS Z8830:2013. Nitrogen adsorption can be measured on a sample after pretreatment. The pretreatment conditions and nitrogen adsorption conditions are shown below. Measurement method: constant volume method Measurement temperature: 77K (-196℃) Pretreatment: Vacuum drying at 150°C for 1 hour, and vacuum drying at 350°C for 2 hours

[0028] Nitrogen adsorption can be measured using a common nitrogen adsorption apparatus (e.g., BELSORP-mini II, manufactured by Microtrack-Bell).

[0029] The CHA-type zeolite of this embodiment has a pore volume (hereinafter also referred to as "micropore volume") of 0.18 mL / g or more or 0.20 mL / g or more, and 0.40 mL / g or less or 0.35 mL / g or less.

[0030] The micropore volume can be determined by t-plot analysis of the nitrogen adsorption isotherm obtained in the same manner as the BET specific surface area measurement. The t-plot analysis can be performed under the following conditions using the analysis software provided with the nitrogen adsorption apparatus (e.g., BELMASTER, manufactured by Microtrack-Bell). Adsorbate cross section: 0.162nm 2 Saturated water vapor pressure: 103.72kPa First line: A line connecting the points t=0 nm and t=0.26±0.01 nm Second line: A line connecting the points t=0.35±0.01 nm and t=0.66±0.01 nm

[0031] The CHA-type zeolite of this embodiment preferably contains a transition metal element. The transition metal element 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 at least one of iron and copper, and further copper. The CHA-type zeolite of this embodiment preferably contains the transition metal element outside the zeolite framework, for example, in at least one of the pores and the ion exchange sites.

[0032] The CHA zeolite of this embodiment may have a transition metal element content of 1.0 mass% or more, 1.5 mass% or more, or 2.0 mass% or more, and 5.0 mass% or less, 4.5 mass% or less, or 4.0 mass% or less.

[0033] Hereinafter, the method for producing CHA-type zeolite according to the present disclosure will be described with reference to an example embodiment.

[0034] The CHA-type zeolite of this embodiment is obtained by a production method including a step of crystallizing a composition containing an amorphous alumina source, an amorphous silica-alumina source, an organic structure-directing agent source, an alkali source, and water. The CHA-type zeolite of this embodiment is crystallized by a step (hereinafter also referred to as a "crystallization step") of crystallizing a composition (hereinafter also referred to as a "raw material composition") containing an amorphous alumina source, an amorphous silica-alumina source, an organic structure-directing agent source, an alkali source, and water.

[0035] The amorphous alumina source is an amorphous compound containing aluminum (Al), which serves as a precursor of alumina (Al2O3), and is preferably an amorphous compound containing aluminum but not silicon (Si). Crystallization of a raw material composition containing an amorphous alumina source makes it easier to obtain a CHA-type zeolite having a low SiO2 / Al2O3 ratio, i.e., a low Al-to-SiO2 ratio despite the high aluminum content in the zeolite framework. Specific examples of the amorphous alumina source include one or more selected from the group consisting of aluminum hydroxide, aluminum chloride, aluminum sulfate, aluminum nitrate, and sodium aluminate. Particularly preferred amorphous alumina sources in this embodiment include at least one of dried aluminum hydroxide gel and sodium aluminate, and further include dried aluminum hydroxide gel.

[0036] The amorphous silica-alumina source is an amorphous compound containing silicon and aluminum. Specific examples of the amorphous silica-alumina source include at least one of amorphous aluminosilicate and aluminum silicate, and also amorphous aluminosilicate. The amorphous aluminosilicate has an SiO2 / Al2O3 ratio of 2 or more or 5 or more, and 100 or less, 50 or less, or 20 or less. The cation type of the amorphous aluminosilicate includes sodium type (Na type), proton type (H + The ammonium type may be one or more selected from the group consisting of ammonium type (NH4 type) and ammonium type (NH4 type).

[0037] The mass ratio of the amorphous silica-alumina source to the amorphous alumina source is preferably 15 or more, or 18 or more, and may be 40 or less, or 30 or less.

[0038] The mass ratio is the mass excluding physically adsorbed water (so-called dry mass), and examples thereof include the mass after drying treatment under the following conditions. Treatment atmosphere: Air Drying temperature: 500℃ or higher and 700℃ or lower Drying time: 0.5 to 4 hours

[0039] The raw material composition does not necessarily contain a silica source, but may contain a silica source to finely adjust the SiO / AlO ratio of the raw material composition. The silica source is silica (SiO) or a silicon compound that serves as a precursor thereof, or even an aluminum-free silicon compound. Specific examples of the silica source include at least one selected from the group consisting of colloidal silica, amorphous silica, sodium silicate, tetraethoxysilane, precipitated silica, and fumed silica; at least one selected from the group consisting of colloidal silica, amorphous silica, sodium silicate, precipitated silica, and fumed silica; at least one selected from the group consisting of precipitated silica and fumed silica; or fumed silica.

[0040] The source of the organic structure-directing agent (hereinafter also referred to as "SDA") is at least one of a salt and a compound containing a cation that directs the CHA structure, one or more selected from the group consisting of sulfate, nitrate, halide and hydroxide of SDA, at least one of a halide or hydroxide of SDA, or hydroxide of SDA.

[0041] The SDA may be any cation that is directed toward CHA-type zeolite. Examples of the cation that is directed toward CHA-type zeolite include one or more selected from the group consisting of N,N,N-trialkyladamantanammonium cation, N,N,N-trimethylbenzylammonium cation, N-alkyl-3-quinuclidinol cation, N,N,N-trialkylexoaminonorbornane cation, and N,N,N-trialkylcyclohexylammonium cation, and preferably N,N,N-trialkyladamantanammonium cation (hereinafter referred to as "TAAd"). + "), N,N,N-trimethylbenzylammonium cation (hereinafter referred to as "TMBA"). + "), and N,N,N-trialkylcyclohexylammonium cation (hereinafter referred to as "TACH + "), more preferably TAAd + and TACH+ At least one of the above, particularly preferably TAAd + and TACH + is.

[0042] Preferred TAAd + As an example of the cation, N,N,N-trimethyladamantanammonium cation (hereinafter referred to as TMAd+) is mentioned. + N,N,N-dimethylethylcyclohexylammonium cation (hereinafter referred to as "CDMEA") + ") and N,N,N-methyldiethylcyclohexylammonium cation (hereinafter referred to as "MDECH + ") and CDMEA + , are mentioned.

[0043] The alkali source is a compound containing an alkali metal element, and examples thereof include a compound containing one or more selected from the group consisting of sodium, potassium, rubidium, and cesium, a compound containing one or more selected from the group consisting of sodium, potassium, and cesium, a compound containing at least one of sodium and potassium, or a compound containing sodium. Examples of the alkali source include at least one of hydroxides and halides containing the alkali metal elements described above. Since this helps to suppress rapid dissolution of aluminum during preparation of the raw material composition, the alkali source preferably contains a halide containing an alkali metal element, and more preferably contains a hydroxide and a halide. Specifically, examples of alkali metal sources include at least one selected from the group consisting of hydroxides, fluorides, chlorides, bromides, iodides, sulfates, nitrates, and carbonates containing the alkali metal elements, at least one selected from the group consisting of hydroxides, chlorides, bromides, and iodides, at least one selected from the group consisting of hydroxides, chlorides, and bromides, and even chlorides (hereinafter, an alkali source containing sodium will be referred to as a "sodium source," and an alkali source containing potassium will be referred to as a "potassium source," etc.). When starting materials such as an amorphous alumina source contain an alkali metal element, these starting materials can also be considered alkali sources. It is particularly preferred that the raw material composition contain a sodium source and a potassium source.

[0044] The water in the raw material composition may include not only pure water and ion-exchanged water, but also structural water, hydration water, and water contained in other starting materials such as solvents.

[0045] The following molar compositions are examples of preferred compositions of the raw material composition. In the following compositions, SDA is an organic structure directing agent, M is an alkali metal element, and OH is a hydroxide ion. The SDA / SiO2 ratio is determined by the ratio of SDA to TMAda. + If it is "TMAda + / SiO2 ratio, SDA is CDMEA + If it is "CDMEA + The M / SiO2 ratio can be regarded as the "Na / SiO2 ratio" when M is sodium, or as the "(Na+K) / SiO2 ratio" when M is sodium and potassium.

[0046] SiO2 / Al2O3 ratio: 5 or more, 6 or more, or 8 or more, and 40 or less, 30 or less, 20 or less, or less than 16 SDA / SiO2 ratio: 0.01 or more or 0.05 or more, and 0.50 or less, 0.40 or less, or 0.30 or less M / SiO2 ratio: 0.05 or more, 0.1 or more, or 0.15 or more, and 1.5 or less, 1.0 or less, or 0.4 or less OH / SiO2 ratio: 0.1 or more or 0.15 or more, and 0.8 or less or 0.5 or less H2O / SiO2 ratio: 3 or more, 5 or more, or 8 or more, and 50 or less or 30 or less Furthermore, the raw material composition preferably has a K / (Na+K) ratio of 0.5 or less or less than 0.5, and more preferably exceeds 0 or is 0.1 or greater.

[0047] To promote crystallization, the raw material composition may contain seed crystals as needed. The seed crystals are crystalline aluminosilicates that have the function of promoting crystallization of the raw material composition, and examples thereof include CHA-type zeolite. The seed crystals may be mixed with the raw material composition so that the total mass of the silicon and aluminum of the seed crystals converted into SiO and AlO, respectively (hereinafter also referred to as the "seed crystal content") is 0.1 mass% or more and 30.0 mass% or less relative to the total mass of the silicon and aluminum of the raw material composition (excluding the seed crystals) converted into SiO and AlO, respectively.

[0048] The raw material composition preferably contains substantially no fluorine (F) or phosphorus (P). Considering the measurement limits of measurements obtained by ordinary composition analysis methods, the fluorine content of the raw material composition may be 0 ppm or more and 100 ppm or less, and more preferably 0 ppm or more and 50 ppm or less.

[0049] In the crystallization step, the raw material composition may be crystallized by hydrothermal treatment. The conditions for the hydrothermal treatment include the following. Hydrothermal treatment temperature: 80°C or higher, 100°C or higher, or 120°C or higher, and 200℃ or less, 190℃ or less, or 180℃ or less Hydrothermal treatment time: 1 hour or more, 10 hours or more, or 1 day or more, and 10 days or less or 6 days or less Hydrothermal treatment pressure: Autogenous pressure Hydrothermal treatment state: at least one of a stirring state and a static state; Preferably in a stirred state

[0050] In the manufacturing method of this embodiment, after the crystallization step, one or more steps selected from the group consisting of a washing step, a drying step, an ion exchange step, and a metal-containing step (hereinafter also referred to as a "post-treatment step") may be included, if necessary.

[0051] In the washing step, the CHA-type zeolite is washed. Recovery and washing can be performed by any method, and examples thereof include washing the small pore zeolite obtained as a solid phase by solid-liquid separation after the crystallization step with pure water.

[0052] In the drying process, water is removed from the CHA-type zeolite. Drying conditions are optional, but examples include treating the small pore zeolite in air at 50°C to 150°C for 2 hours or more.

[0053] In the ion exchange process, CHA-type zeolite is converted to any cation type. To convert the cation type to ammonium type, CHA-type zeolite is mixed with an ammonium chloride aqueous solution. To convert the cation type to proton type, ammonium-type CHA-type zeolite is calcined.

[0054] In the metal-containing step, any active metal element is contained in the CHA-type zeolite, and preferably any transition metal element is supported on the CHA-type zeolite. This results in a metal-containing CHA-type zeolite (or a metal-supported CHA-type zeolite). The metal can be contained by any method that brings the CHA-type zeolite into contact with a transition metal source, and examples of the method include one or more selected from the group consisting of ion exchange, impregnation, evaporation to dryness, precipitation, and physical mixing. The impregnation method is preferred. The transition metal source is at least one of a salt and a compound containing a transition metal element, and specific examples of the transition metal source include one or more selected from the group consisting of nitrates, sulfates, acetates, chlorides, complex salts, oxides, and composite oxides containing a transition metal element, and further one or more selected from the group consisting of nitrates, sulfates, and chlorides.

[0055] The transition metal element contained in the transition metal source is one or more selected from the group consisting of Groups 8, 9, 10 and 11 of the periodic table, preferably 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), at least one of iron and copper, or copper.

[0056] The manufacturing 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, but examples include treatment in at least one of an oxidizing atmosphere and a reducing atmosphere at a temperature of 100°C to 650°C, and treatment in air at a temperature of 400°C to 600°C is preferred. [Example]

[0057] The present embodiment will be described below with reference to examples, but the present embodiment is not limited to these examples. (crystal structure) The samples were subjected to XRD measurement using a general powder X-ray diffractometer (device name: Ultima IV Protectus, manufactured by Bruker) 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 Detector: D / teX Ultra Ni filter used The obtained XRD pattern was compared with a reference pattern to identify the crystal structure of the sample.

[0058] (composition analysis) A sample solution was prepared by dissolving the sample in a mixed aqueous solution of hydrofluoric acid and nitric acid. The sample solution was measured by inductively coupled plasma atomic emission spectrometry (ICP-AES) using a general ICP device (device name: OPTIMA5300DV, manufactured by PerkinElmer) to determine the composition of each component in the sample. (BET specific surface area and micropore volume) The amount of nitrogen gas adsorbed onto the sample was measured using a standard nitrogen adsorption apparatus (apparatus name: BELSORP-mini II, manufactured by Microtrac-Bell Co., Ltd.). The BET specific surface area of ​​the sample was determined by applying the BET method to the nitrogen gas adsorption results. The micropore volume was also determined by applying the t-plot method to the nitrogen gas adsorption results. The t-plot method was performed using the analysis software (product name: BELMaster, manufactured by Microtrac-Bell Co., Ltd.) that came with the nitrogen adsorption apparatus. The standard constant volume method was used for nitrogen gas adsorption. The measurement conditions are as follows: Measurement temperature: -196℃ Pretreatment: Vacuum drying at 150°C for 1 hour, and vacuum drying at 350°C for 2 hours

[0059] (pair Al ratio) As a pretreatment, the sample was subjected to ion exchange with a 20% aqueous solution of ammonium chloride, and then dried overnight at 110°C in the air. The immersion conditions were as follows:

[0060] Soaking temperature: room temperature Soaking time: 16 hours Cobalt nitrate concentration: 0.25 mol / L Solid-liquid ratio: (sample / cobalt nitrate aqueous solution)≦0.5 The sample was collected after immersion, washed with pure water, and then dried in air at 110°C for 1 hour. The dried sample was subjected to ICP measurement, and the Al pair ratio was calculated using the above formula.

[0061] Example 1 A raw material composition having the following composition was obtained by mixing a TMAdaOH aqueous solution, a CDMEAOH aqueous solution, pure water, sodium hydroxide, sodium chloride, potassium chloride, amorphous aluminosilicate (SiO2 / Al2O3 ratio = 22.0), and dried aluminum hydroxide gel. SiO2 / Al2O3 ratio =13.0 TMAda / SiO2 ratio =0.05 CDMEA / SiO2 ratio =0.03 OH / SiO2 ratio =0.21 Na / SiO2 ratio =0.16 K / SiO2 ratio =0.04 H2O / SiO2 ratio =15.0

[0062] The mass ratio of the amorphous silica-alumina source to the dry aluminum hydroxide gel (amorphous alumina source) was 20.1.

[0063] The obtained raw material composition was filled into an 80 mL sealed container, and the raw material composition was stirred while rotating the sealed container at 55 rpm, followed by hydrothermal treatment for 48 hours at 160°C. The crystallized product after the hydrothermal treatment was separated into solid and liquid, washed with pure water, calcined in air at 600°C, further treated with an ammonium chloride aqueous solution, and then dried to obtain the CHA-type zeolite of this example.

[0064] The obtained sample was a single phase of CHA-type zeolite, with a pair Al ratio of 8.4%, a SiO2 / Al2O3 ratio of 13.5, and a BET specific surface area of ​​642 m 2 / g and the micropore volume was 0.25 mL / g.

[0065] Comparative Example 1 The zeolite of this comparative example was obtained in the same manner as in Example 1, except that no dried aluminum hydroxide gel was used and that an amorphous aluminosilicate with a SiO2 / Al2O3 ratio of 13.0 was used.

[0066] The zeolite in this comparison was a single phase CHA-type zeolite, with a pair Al ratio of 21.8% and a SiO2 / Al2O3 ratio of 13.7.

[0067] Comparative Example 2 The zeolite of this comparative example was obtained in the same manner as in Example 1, except that no dried aluminum hydroxide gel was used, that an amorphous aluminosilicate with a SiO / AlO ratio of 13.0 was used, and that a raw material composition having the following composition was used. SiO2 / Al2O3 ratio =13.0 TMAda / SiO2 ratio =0.08 OH / SiO2 ratio =0.21 Na / SiO2 ratio =0.13 K / SiO2 ratio =0.07 H2O / SiO2 ratio =15.0

[0068] The zeolite of this comparative example was a single phase CHA-type zeolite, with an Al pair ratio of 13.2% and an SiO2 / Al2O3 ratio of 14.2.

[0069] Comparative Example 3 The zeolite of this comparative example was obtained in the same manner as in Example 1, except that hydrophilic fumed silica (product name: Cab-O-Sil M5, manufactured by Cabot Corporation) was used as the silica source, dried aluminum hydroxide gel was used as the alumina source, a raw material composition having the following composition was used, and the hydrothermal treatment time was 110 hours. SiO2 / Al2O3 ratio =13.0 CDMEA / SiO2 ratio =0.20 OH / SiO2 ratio =0.40 Na / SiO2 ratio =0.20 K / SiO2 ratio =0 H2O / SiO2 ratio =40.0

[0070] The zeolite of this comparative example was a single phase CHA-type zeolite, with an Al pair ratio of 27.4% and an SiO2 / Al2O3 ratio of 13.5.

[0071] Comparative Example 4 CHA-type zeolite was obtained by a method similar to SSZ-13 (15,1.00) in Table 2 of Non-Patent Document 1. That is, a TMAdaOH aqueous solution, pure water, sodium hydroxide, colloidal silica, and aluminum hydroxide (crystalline aluminum hydroxide) were mixed to obtain a raw material composition having the following composition. SiO2 / Al2O3 ratio =30.63 TMAda / SiO2 ratio =0.25 OH / SiO2 ratio =0.50 Na / SiO2 ratio =0.25 H2O / SiO2 ratio =44.0

[0072] The amorphous Al ratio of the raw material composition was 0. The obtained raw material composition was filled into a sealed container, and the raw material composition was stirred while rotating the sealed container at 40 rpm, and then hydrothermal treated at 160°C for 6 days. The crystallized product after the hydrothermal treatment was separated into solid and liquid, washed with pure water, and then calcined in air at 550°C to obtain the CHA-type zeolite of this comparative example.

[0073] The CHA-type zeolite of this comparative example was a single phase CHA-type zeolite, with an Al pair ratio of 1.0% and an SiO2 / Al2O3 ratio of 22.8.

[0074] In Non-Patent Document 1, the pair Al ratio calculated from the amount of cobalt exchanged when the cation type is sodium type is 16%. In contrast, the pair Al ratio calculated from the amount of cobalt exchanged when the cation type is proton type is 1.0%, confirming that the pair Al ratio varies greatly depending on the cation type of the CHA-type zeolite being measured, and that the pair Al ratio in Non-Patent Document 1 was a formal pair Al ratio.

[0075] The results are shown in the table below.

[0076] [Table 1]

[0077] Measurement example A copper nitrate aqueous solution was added dropwise to each of the CHA zeolites obtained in Example 1 and Comparative Example 3, 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 fired at 550°C in the air for 1 hour to obtain a metal-containing CHA zeolite carrying 3% by mass of copper (copper-loaded CHA zeolite).

[0078] (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 Space velocity: 9,000h -1 Processing temperature: 900℃ Processing time: 1 hour

[0079] (Method for measuring nitrogen oxide reduction rate) The nitrogen oxide reduction rate of the sample was measured by the ammonia SCR method shown below. After press molding, 1.5 mL of the sample was sized to 12 to 20 mesh and filled into a reaction tube. Thereafter, a treatment gas was passed through the reaction tube under the following conditions. Treated gas composition: NO 200ppm NH3 200 ppm O210 capacity% H2O 3% by volume Remainder N2 Processing gas flow rate: 1.5L / min Space velocity (SV): 60,000hr -1

[0080] The nitrogen oxide concentration (ppm) in the treated gas after passing through the catalyst relative to the nitrogen oxide concentration (200 ppm) in the treated gas passed through the reaction tube was determined, and the nitrogen oxide reduction rate was calculated according to the following formula.

[0081] Nitrogen oxide reduction rate (%) = {1 - (nitrogen oxide concentration in treated gas after contact)} / nitrogen oxide concentration in treated gas before contact) × 100

[0082] [Table 2]

[0083] Example 1 and Comparative Example 3, which was obtained from a raw material composition that did not contain a silica-alumina source, both have the same SiO2 / Al2O3 ratio. Nevertheless, it can be confirmed that Example 1 has a higher nitrogen oxide reduction rate in all temperature ranges compared to the CHA zeolite of Comparative Example 3. In particular, it can be confirmed that the CHA zeolite of Comparative Example 3 exhibits a significant decrease in nitrogen oxide reduction rate as the temperature increases to 400°C or higher, whereas the CHA zeolite of Example 1 significantly suppresses this decrease. Furthermore, it can be confirmed that the CHA zeolite of Example 1 also exhibits a significantly higher nitrogen oxide reduction rate at low temperatures of 200°C and 150°C. [Industrial Applicability]

[0084] The method for producing CHA-type zeolite according to the present disclosure can be used as a method for producing a CHA-type zeolite that can be used as a zeolite catalyst incorporated into an exhaust gas treatment system and as a substrate for the catalyst. The CHA-type zeolite obtained by the method for producing the present disclosure can be used, in particular, as an SCR catalyst that reduces and removes nitrogen oxides in the exhaust gas of automobiles such as diesel vehicles in the presence of a reducing agent, and further as an SCR catalyst integrated with a DPF.

Claims

1. A CHA-type zeolite characterized by a micropore volume of 0.2 mL / g or more, a molar ratio of silica to alumina of 20 or less, and a pair aluminum ratio of 13% or less.

2. A CHA-type zeolite as described in claim 1, wherein the ratio of alkali metal elements and alkaline earth metal elements to aluminum is 0.01 or less.

3. 3. The CHA-type zeolite according to claim 1 or 2, which contains a transition metal element.

4. 4. The CHA-type zeolite according to claim 3, wherein the transition metal element is at least one of iron and copper.

5. A method for producing CHA-type zeolite, comprising a step of crystallizing a composition containing an amorphous alumina source, an amorphous silica-alumina source, an alkali source, an organic structure-directing agent, and water, wherein the molar ratio of silica to alumina is 20 or less and the pair aluminum ratio is 13% or less.

6. 6. The method according to claim 5, wherein the amorphous alumina source is at least one of dry aluminum hydroxide gel and sodium aluminate.

7. 7. The method according to claim 5, wherein the amorphous silica-alumina source is an amorphous aluminosilicate.

8. The method according to any one of claims 5 to 7, wherein the composition comprises a silica source.

9. 9. The method of claim 5, wherein the composition has a silica to alumina molar ratio of 22 or less.

10. The method according to any one of claims 5 to 9, wherein the mass ratio of the amorphous silica-alumina source to the amorphous alumina source is 13 or more.

11. A nitrogen oxide reduction catalyst comprising the CHA-type zeolite according to any one of claims 1 to 4.

12. A method for reducing nitrogen oxides, which uses the CHA-type zeolite according to any one of claims 1 to 4.

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