JP2023064657A - Cha-type zeolite and production method thereof - Google Patents

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 The present disclosure relates to a CHA-type zeolite and a method for producing the same. In particular, the present invention relates to a CHA-type zeolite suitable for industrial use as a catalyst for reducing nitrogen oxides, and a method for producing the same.

CHA-type zeolite is an artificially synthesized small-pore zeolite. CHA-type zeolite, which has a relatively high SiO ₂ /Al ₂ O ₃ ratio, has high heat resistance and does not easily collapse its structure even when exposed to a hot water atmosphere. Therefore, CHA-type zeolite with a SiO ₂ /Al ₂ O ₃ ratio exceeding 20 has been put to practical use as a nitrogen oxide reduction catalyst. In contrast to such CHA-type zeolites, zeolites with a SiO ₂ /Al ₂ O ₃ ratio of 20 or less are known to have low heat resistance and tend to collapse the crystal structure when exposed to a hot water atmosphere. Its application has been limited to applications that do not require heat resistance.

In recent years, studies have focused on the distribution of aluminum in the framework structure of CHA-type zeolite, particularly the "paired aluminum structure". For example, Non-Patent Document 1 describes a CHA-type zeolite in which the ratio of a pair aluminum structure in aluminum is 5% or more and 17% or less, and Non-Patent Document 2 describes a CHA-type zeolite in which a ratio of a pair aluminum structure in aluminum is 60% or less. Zeolites have been reported.

Chem. Mater. , 28 (2016) 2236-2247 Chem. Mater. , 32 (2020) 273-285

In the present disclosure, a CHA-type zeolite that exhibits higher heat resistance despite having a silica-to-alumina molar ratio equivalent to that of conventional CHA-type zeolite having a silica-to-alumina molar ratio of 20 or less, and the same. and at least one of these production methods.

The present inventors investigated the application of CHA-type zeolite having a SiO ₂ /Al ₂ O ₃ ratio of 20 or less to a nitrogen oxide reduction catalyst. As a result, it was found that the distribution state of aluminum in the zeolite structure affects the heat resistance of CHA-type zeolite, and that the influence of the distribution state of aluminum differs depending on the SiO ₂ /Al ₂ O ₃ ratio. Furthermore, the present inventors have found that in a CHA-type zeolite having a SiO ₂ /Al ₂ O ₃ ratio of 20 or less, by controlling the aluminum distribution state, despite the low SiO ₂ /Al ₂ O ₃ ratio, It has been found that the heat resistance, particularly at high temperatures of 400° C. or higher, is high, and the deterioration of nitrogen oxide reduction properties in this temperature range is suppressed.

That is, the present invention is as defined in the scope of claims, and the gist of the present disclosure is as follows.
[1] A CHA-type zeolite characterized by having a molar ratio of silica to alumina of 20 or less and a pair aluminum ratio of 13% or less.
[2] The CHA-type zeolite according to [1] above, which has 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] comprising crystallizing a composition comprising 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 and a pair aluminum ratio of 13% or less.
[6] The production method according to [5] above, wherein the amorphous alumina source is at least one of dry aluminum hydroxide gel and sodium aluminate.
[7] The production method according to the above [5] or [6], wherein the amorphous silica-alumina source is amorphous aluminosilicate.
[8] The production method according to any one of [5] to [7] above, wherein the composition contains a silica source.
[9] The production 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 production 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 comprising 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.

According to the present disclosure, CHA-type zeolite that exhibits higher heat resistance despite having a silica-to-alumina molar ratio equivalent to conventional CHA-type zeolite having a silica-to-alumina molar ratio of 20 or less, and the same and at least one of these production methods can be provided.

Hereinafter, the present disclosure will be described by showing an example of its embodiment. The terms used in this embodiment are as follows.

“Aluminosilicate” is a composite oxide having a structure consisting of repeating networks of aluminum (Al) and silicon (Si) via oxygen (O). Among aluminosilicates, those having a crystalline XRD peak in the powder X-ray diffraction (hereinafter also referred to as “XRD”) pattern are “crystalline aluminosilicates”, and those that do not have a crystalline XRD peak The thing is "amorphous aluminosilicate".

The XRD pattern in this embodiment is measured using a CuKα ray as a radiation source, and measurement conditions include the following conditions.
Accelerating current/voltage: 40mA/40kV
Radiation source: CuKα ray (λ = 1.5405 Å)
Measurement mode: Continuous scan
Scan condition: 40°/min
Measurement range: 2θ = 3° to 43°
Divergence longitudinal limiting slit: 10mm
Divergence/Entrance Slit: 1°
Light receiving slit: open
Detector: D/teX Ultra
Use Ni filter

The XRD pattern can be measured using a general powder X-ray diffractometer (for example, Ultima IV, manufactured by Rigaku). In addition, the crystalline XRD peak is a peak whose peak top 2θ is specified and detected in XRD pattern analysis using general analysis software (e.g., SmartLab Studio II, manufactured by Rigaku), and the half width is 2θ. = 0.50° or less can be exemplified.

A “zeolite” is a compound having a regular structure in which skeleton atoms (hereinafter also referred to as “T atoms”) are interposed with oxygen (O), and the T atoms are at least one of a metal atom and/or a metalloid atom. It is a compound consisting of 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).

A “zeolite-like substance” is a compound having a regular structure in which T atoms intervene with oxygen and containing at least atoms other than metals and metalloids in the T atoms. Examples of zeolite-like substances include complex phosphorus compounds containing phosphorus (P) as a T atom, such as aluminophosphate (AlPO) and silicoaluminophosphate (SAPO).

The “regular structure (hereinafter also referred to as “zeolite structure”)” in zeolite and zeolite-like substances is a structure code defined by the Structure Commission of the International Zeolite Association (hereinafter simply “structure code”). It is also called.) It is a skeleton structure specified by. For example, the CHA structure is the backbone structure specified as structure code "CHA". Collection of simulated XRD powder patterns for zeolites, Fifth revised edition, p. 483 (2007) of each structure (hereinafter also referred to as "reference pattern"), the zeolite structure can be identified. With respect to zeolite structure, framework structure, crystalline structure or crystalline phase are used interchangeably.

In the present embodiment, "-type zeolite" such as "CHA-type zeolite" means a zeolite having the zeolite structure of the structure code, preferably a crystalline aluminosilicate having the zeolite structure of the structure code.

Next, an example of an embodiment of the CHA-type zeolite of the present disclosure will be described.

The CHA-type zeolite of the present embodiment is a CHA-type zeolite characterized by having a molar ratio of silica to alumina of 20 or less and a pair aluminum ratio of 13% or less. As a result, although the CHA-type zeolite has a low molar ratio of silica to alumina (hereinafter also referred to as “SiO ₂ /Al ₂ O ₃ ratio”), it has a similar SiO ₂ /Al ₂ O ₃ ratio. CHA-type zeolite having a higher nitrogen oxide reduction property.

The CHA-type zeolite of the present embodiment has a SiO ₂ /Al ₂ O ₃ ratio of 20 or less, preferably less than 20, 15 or less, or 13 or less. The SiO ₂ /Al ₂ O ₃ ratio is 5 or more or 10 or more.

The paired aluminum ratio (hereinafter also referred to as “paired Al ratio”) of the CHA-type zeolite of the present embodiment is 13% or less, preferably 10% or less. The pair Al ratio may be 0% or more, but the CHA-type zeolite of the present embodiment may have a pair Al ratio of more than 0%, 1% or less, or 5% or less.

The pair Al ratio is a value that can be obtained by quantifying the amount of cobalt ion-exchanged to the ion exchange sites of divalent ions having a pair 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 was immersed in an aqueous solution of cobalt nitrate. After measuring the cobalt (Co) content, the value obtained from the following formula is the pair Al ratio.

Pair Al ratio [%] = (M _Co [mol]/M _Al [mol]) × 2 × 100
In the above formula, M _Co [mol] is the cobalt content measured by ICP measurement, and M _Al [mol] is the aluminum content measured by ICP measurement.

Moreover, the following conditions are mentioned as immersion conditions to cobalt nitrate aqueous solution.
Immersion temperature: 10° C. to 40° C. Immersion time: 1 hour to 40 hours Cobalt nitrate concentration: 0.001 mol/L to 2.0 mol/L Solid-liquid ratio: (CHA type zeolite/cobalt nitrate aqueous solution)≦0. 5

Examples of CHA-type zeolite having an M/Al ratio of 0.01 or less include CHA-type zeolite with a proton-type or ammonium-type cation.

Note that even if a CHA-type zeolite with a M/Al ratio exceeding 0.01, such as a sodium-type, potassium-type, or calcium-type cation type, is subjected to the same treatment, the pair Al ratio (hereinafter referred to as The paired Al ratio determined by this is also referred to as "formal paired Al ratio."However, the formal Al ratio is determined by the cobalt ( Co ²⁺ ) is a value including cobalt derived from a structure other than Co 2+ ).Therefore, the value of the formal paired Al ratio is not a value reflecting the content of the paired aluminum structure of CHA-type zeolite, but the paired Al of the present embodiment. ratio (that is, the ratio of the actual paired aluminum structure).Since the formal paired Al ratio shows a value different from the paired Al ratio of the present embodiment, the paired Al ratio of the present embodiment and the formal pair Al ratio cannot be compared.

The BET specific surface area of the CHA-type zeolite of the present embodiment is 200 m ² /g or more or 500 m ² /g or more, and preferably 1000 m ² /g or less or 800 m ² /g or less.

The BET specific surface area can be obtained by the BET one-point method by the nitrogen adsorption method according to JIS Z8830:2013. Nitrogen adsorption can be measured on samples after pretreatment. Pretreatment conditions and nitrogen adsorption conditions are shown below.
Measurement method: Constant volume method Measurement temperature: 77K (-196°C)
Pretreatment: vacuum drying at 150°C for 1 hour and vacuum drying at 350°C for 2 hours

Nitrogen adsorption can be measured using a common nitrogen adsorption device (eg, BELSORP-mini II, manufactured by Microtrac Bell).

The CHA-type zeolite of the present 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.

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

The CHA-type zeolite of the present embodiment preferably contains a transition metal element. The transition metal element is one or more elements selected from the group of groups 8, 9, 10 and 11 of the periodic table, platinum (Pt), palladium (Pd), rhodium (Rh), iron (Fe) , copper (Cu), cobalt (Co), manganese (Mn) and indium (In), or at least one of iron and copper, or copper. The CHA-type zeolite of the present embodiment preferably contains a transition metal element other than the zeolite skeleton, for example, at least one of pores and ion-exchange sites.

The CHA-type zeolite of the present embodiment has a transition metal element content of 1.0% by mass or more, 1.5% by mass or more, or 2.0% by mass or more, and 5.0% by mass or less and 4.5% by mass. % or less or 4.0% by mass or less.

An example of an embodiment of the method for producing a CHA-type zeolite of the present disclosure will be described below.

The CHA-type zeolite of the present embodiment is obtained by a production method comprising crystallizing a composition containing an amorphous alumina source, an amorphous silica-alumina source, an organic structure-directing agent source, an alkalinity source and water. A step of crystallizing a composition (hereinafter also referred to as "raw material composition") containing an amorphous alumina source, an amorphous silica alumina source, an organic structure directing agent source, an alkali source and water (hereinafter referred to as "crystallization CHA-type zeolite of the present embodiment crystallizes.

The amorphous alumina source is an amorphous compound containing aluminum (Al) that is a precursor of alumina (Al ₂ O ₃ ), and contains aluminum and does not contain silicon (Si). A compound is preferred. By crystallizing a raw material composition containing an amorphous alumina source, CHA with a low pair Al ratio despite a low SiO ₂ /Al ₂ O ₃ ratio, that is, a large amount of aluminum contained in the zeolite skeleton type zeolite is more likely to be obtained. Specific amorphous alumina sources include one or more selected from the group consisting of aluminum hydroxide, aluminum chloride, aluminum sulfate, aluminum nitrate and sodium aluminate. A particularly preferred amorphous alumina source in this embodiment includes at least one of dry aluminum hydroxide gel and sodium aluminate, and further dry aluminum hydroxide gel.

Amorphous silica-alumina sources are amorphous compounds containing silicon and aluminum. Specific amorphous silica-alumina sources include at least one of amorphous aluminosilicate and aluminum silicate, and amorphous aluminosilicate. The amorphous aluminosilicate has a SiO ₂ /Al ₂ O ₃ ratio of 2 or more or 5 or more, and is 100 or less, 50 or less, or 20 or less. The cation type of amorphous aluminosilicate includes one or more selected from the group of sodium type (Na type), proton type (H ⁺ type) and ammonium type (NH ₄ type), or ammonium type.

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.

The mass ratio is the mass excluding physically adsorbed water (so-called dry mass), for example, the mass after drying treatment under the following conditions.
Treatment atmosphere: Air atmosphere Drying temperature: 500°C to 700°C Drying time: 0.5 hours to 4 hours

The raw material composition may not contain a silica source, but the raw material composition may contain a silica source in order to fine-tune the _SiO2 / _{Al2O3 ratio} of the raw material composition. The silica source is silica (SiO ₂ ) or a silicon compound that is a precursor thereof, or a silicon compound that does not contain aluminum. Specific silica sources include at least one selected from the group consisting of colloidal silica, amorphous silica, sodium silicate, tetraethoxysilane, precipitated silica and fumed silica, colloidal silica, amorphous silica, sodium silicate, and precipitated silica. and fumed silica, at least one of precipitated silica and fumed silica, or fumed silica.

The organic structure directing agent (hereinafter also referred to as "SDA") source is selected from the group of at least one of salts and compounds containing cations directing the CHA structure, SDA sulfates, nitrates, halides and hydroxides. and at least one of a halide or hydroxide of SDA, or a hydroxide of SDA.

SDA may be any cation that directs CHA-type zeolite. As cations for CHA-type zeolite, N,N,N-trialkyladamantane ammonium cations, N,N,N-trimethylbenzylammonium cations, N-alkyl-3-quinuclidinol cations, N,N,N- One or more selected from the group of trialkylexoaminonorbornane cations and N,N,N-trialkylcyclohexylammonium cations can be exemplified, preferably N,N,N-trialkyladamantane ammonium cations (hereinafter, “TAAd ⁺ ”) ), N,N,N-trimethylbenzylammonium cation (hereinafter also referred to as “TMBA ⁺ ”), and N,N,N-trialkylcyclohexylammonium cation (hereinafter also referred to as “TACH ⁺ ”) One or more selected from the group of, more preferably at least one of TAAd ⁺ and TACH ⁺ , particularly preferably TAAd ⁺ and TACH ⁺ .

Preferred TAAd ⁺ include N,N,N-trimethyladamantane ammonium cation (hereinafter TMAd+). Preferred TACH ⁺ are N,N,N-dimethylethylcyclohexylammonium cation (hereinafter also referred to as “CDMEA ⁺ ”) and N,N,N-methyldiethylcyclohexylammonium cation (hereinafter also referred to as “MDECH ⁺ ”). ), and also CDMEA ⁺ .

The alkali source is a compound containing an alkali metal element, a compound containing one or more selected from the group of sodium, potassium, rubidium and cesium, a compound containing one or more selected from the group of sodium, potassium and cesium, sodium and potassium. or a compound containing sodium. The alkali source can be exemplified by at least one of hydroxides and halides containing the alkali metal elements described above. The alkali source preferably contains a halide containing an alkali metal element, and more preferably contains a hydroxide and a halide, since rapid dissolution of aluminum is likely to be suppressed during preparation of the raw material composition. Specifically, one or more selected from the group of hydroxides, fluorides, chlorides, bromides, iodides, sulfates, nitrates and carbonates containing the above-mentioned alkali metal elements, further hydroxides, chlorides one or more selected from the group of compounds, bromides and iodides, and one or more selected from the group of hydroxides, chlorides and bromides, and further chlorides (hereinafter, sodium An alkaline source containing potassium is also called a "sodium source", and an alkaline source containing potassium is called a "potassium source", etc.). If starting materials such as amorphous alumina sources contain alkali metal elements, these starting materials may also be considered alkalinity sources. It is particularly preferred that the raw material composition contains a sodium source and a potassium source.

In addition to pure water and ion-exchanged water, water contained in other starting materials such as structural water, hydration water, and solvent may also be regarded as water in the raw material composition.

The following molar composition can be exemplified as a preferred composition of the raw material composition. SDA in the following compositions is an organic structure directing agent, M is an alkali metal element and OH is a hydroxide ion. The SDA/SiO ₂ ratio may be "TMAda ⁺ /SiO ₂ ratio" when SDA is TMAda ⁺ , and "CDMEA ⁺ /SiO ₂ ratio" when SDA is CDMEA ⁺ . The M/SiO ₂ ratio may be regarded as “Na/SiO ₂ ratio” when M is sodium, “(Na+K)/SiO ₂ ratio” when M is sodium and potassium, and the like.

SiO ₂ /Al ₂ O ₃ 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/SiO ₂ 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/SiO ₂ 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 H ₂ O/SiO ₂ ratio: 3 or more, 5 or more, or 8 or more, and
50 or less or 30 or less Further, the raw material composition preferably has a K/(Na+K) of 0.5 or less or less than 0.5, preferably greater than 0 or 0.1 or more.

In order to promote crystallization, the raw material composition may contain seed crystals, if necessary. The seed crystal is a crystalline aluminosilicate having a function of promoting crystallization of the raw material composition, and includes CHA-type zeolite. The seed crystals are obtained by dividing the silicon and aluminum of the seed crystals as SiO ₂ and Al ₂ O ₃ with respect to the total mass of silicon and aluminum in the raw material composition (not including seed crystals) converted as SiO ₂ and Al ₂ O ₃ , respectively. It may be mixed with the raw material composition so that the converted total mass (hereinafter also referred to as "seed crystal content") is 0.1% by mass or more and 30.0% by mass or less.

The raw material composition preferably does not substantially contain fluorine (F) and phosphorus (P). Considering the measurement limit of the measurement value obtained by the usual composition analysis method, the fluorine content of the raw material composition may be 0 ppm or more and 100 ppm or less, more preferably 0 ppm or more and 50 ppm or less.

In the crystallization step, the raw material composition may be crystallized by subjecting it to hydrothermal treatment. Conditions for the hydrothermal treatment include the following conditions.
Hydrothermal treatment temperature: 80°C or higher, 100°C or higher, or 120°C or higher, and
200°C or less, 190°C or less, or 180°C or less Hydrothermal treatment time: 1 hour or longer, 10 hours or longer, or 1 day or longer, and
10 days or less or 6 days or less Hydrothermal treatment pressure: Autogenous pressure Hydrothermal treatment state: At least one of stirring state and stationary state,
preferably under agitation

In the production method of the present embodiment, after the crystallization step, one or more selected from the group 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.

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

In the drying step, water is removed from the CHA-type zeolite. Drying conditions are arbitrary, but treatment of the small pore zeolite in the air at 50° C. or higher and 150° C. or lower for 2 hours or longer can be mentioned.

In the ion exchange step, the CHA-type zeolite is of any cation type. When the cation type is an ammonium type, CHA type zeolite and an aqueous ammonium chloride solution may be mixed. Further, when the cation type is proton type, calcination of an ammonium type CHA type zeolite can be mentioned.

In the metal-containing step, the CHA-type zeolite is made to contain an arbitrary active metal element, and preferably the CHA-type zeolite is loaded with an arbitrary transition metal element. Thereby, a metal-containing CHA-type zeolite (or a metal-supported CHA-type zeolite) is obtained. The inclusion of the metal may be any method as long as the CHA-type zeolite and the transition metal source are brought into contact, for example, one or more selected from the group of ion exchange method, impregnation support method, evaporation to dryness method, precipitation support method and physical mixing method. The transition metal source is at least one of a salt and a compound containing a transition metal element, and specific transition metal sources include nitrates, One or more selected from the group of sulfates, acetates, chlorides, complex salts, oxides and composite oxides, and one or more selected from the group of nitrates, sulfates and chlorides.

The transition metal element contained in the transition metal source is one or more selected from the group of groups 8, 9, 10 and 11 of the periodic table, preferably platinum (Pt), palladium (Pd), rhodium (Rh), One or more selected from the group consisting of iron (Fe), copper (Cu), cobalt (Co), manganese (Mn) and indium (In), at least one of iron and copper, or copper.

The production method of the present embodiment may optionally include a step of calcining the metal-containing CHA-type zeolite. Impurities are removed by firing. Although the firing method is arbitrary, treatment at 100° C. or higher and 650° C. or lower in at least one of an oxidizing atmosphere and a reducing atmosphere can be mentioned, and treatment at 400° C. or higher and 600° C. or lower in the atmosphere is preferable. .

EXAMPLES The present embodiment will be described below with reference to examples. However, this embodiment is not limited to these examples.
(Crystal structure)
A sample was subjected to XRD measurement using a general powder X-ray diffractometer (device name: Ultima IV Protectus, manufactured by Bruker). The measurement conditions are as follows.
Accelerating current/voltage: 40mA/40kV
Radiation source: CuKα ray (λ = 1.5405 Å)
Measurement mode: Continuous scan
Scan condition: 40°/min
Measurement range: 2θ = 3° to 43°
Divergence longitudinal limiting slit: 10mm
Divergence/Entrance Slit: 1°
Light receiving slit: open
Detector: D/TeX Ultra
Using Ni filter The XRD pattern obtained was compared with a reference pattern to identify the crystal structure of the sample.

(composition analysis)
A sample solution was prepared by dissolving the sample in a mixed aqueous solution of hydrofluoric acid and nitric acid. Using a general ICP device (device name: OPTIMA5300DV, manufactured by PerkinElmer), the sample solution was measured by inductively coupled plasma atomic emission spectrometry (ICP-AES) to determine each composition in the sample.
(BET specific surface area and micropore volume)
Using a general nitrogen adsorption device (device name: BELSORP-mini II, manufactured by Microtrac Bell Co., Ltd.), the amount of nitrogen gas adsorbed on the sample was measured. The BET specific surface area of the sample was determined by applying the BET method to the nitrogen gas adsorption results. Also, the micropore volume was obtained by applying the t-plot method to the nitrogen gas adsorption results. For the t-plot method, analysis software attached to the nitrogen adsorption apparatus (product name: BELMaster, manufactured by Microtrack Bell) was used. Nitrogen gas adsorption was carried out using a normal constant volume method. Measurement conditions are as shown below.
Measurement temperature: -196°C
Pretreatment: vacuum drying at 150°C for 1 hour and vacuum drying at 350°C for 2 hours

(Pair Al ratio)
As a pretreatment, after ion exchange with a 20% aqueous ammonium chloride solution, the sample was dried overnight at 110° C. in the atmosphere and immersed in an aqueous cobalt nitrate solution. The immersion conditions are shown below.

Immersion temperature: Room temperature Immersion time: 16 hours Cobalt nitrate concentration: 0.25 mol/L
Solid-liquid ratio: (sample/cobalt nitrate aqueous solution) ≤ 0.5
After the immersed sample was collected and washed with pure water, it was dried in air at 110° C. for 1 hour. The dried sample was subjected to ICP measurement, and the paired Al ratio was measured from the above formula.

Example 1
A TMAdaOH aqueous solution, a CDMEAOH aqueous solution, pure water, sodium hydroxide, sodium chloride, potassium chloride, amorphous aluminosilicate (SiO ₂ /Al ₂ O ₃ ratio = 22.0), and dry aluminum hydroxide gel were mixed to obtain the following: A raw material composition having the following composition was obtained.
_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

Also, the mass ratio of the amorphous silica alumina source to the dry aluminum hydroxide gel (amorphous alumina source) was 20.1.

The obtained raw material composition was filled in an 80 mL closed container, and the raw material composition was stirred while rotating the closed container at 55 rpm, and hydrothermally treated at 160° C. for 48 hours. After the hydrothermal treatment, the crystallized product was subjected to solid-liquid separation, washed with pure water, calcined in the atmosphere at 600° C., treated with an ammonium chloride aqueous solution, and dried to obtain the CHA-type zeolite of this example.

The obtained sample was a single-phase CHA-type zeolite, and had a pair Al ratio of 8.4%, a SiO ₂ /Al ₂ O ₃ ratio of 13.5, a BET specific surface area of 642 m ² /g, and micropores. The volume was 0.25 mL/g.

Comparative example 1
This comparative example was prepared in the same manner as in Example 1 except that dry aluminum hydroxide gel was not used and amorphous aluminosilicate having a SiO ₂ /Al ₂ O ₃ ratio of 13.0 was used. A type zeolite was obtained.

The zeolite for this comparison was a single-phase CHA-type zeolite, and had a pair Al ratio of 21.8% and a SiO ₂ /Al ₂ O ₃ ratio of 13.7.

Comparative example 2
No dry aluminum hydroxide gel was used, and an amorphous aluminosilicate with a SiO ₂ /Al ₂ O ₃ ratio of 13.0 was used, and a raw material composition having the following composition was used: A zeolite of this comparative example was obtained in the same manner as in Example 1 except for the above.
_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

The zeolite of this comparative example was a single-phase CHA-type zeolite, and had a pair Al ratio of 13.2% and a SiO ₂ /Al ₂ O ₃ ratio of 14.2.

Comparative example 3
Using hydrophilic fumed silica (product name: Cab-O-Sil M5, manufactured by Cabot Corporation) as a silica source, using dry aluminum hydroxide gel as an alumina source, and using a raw material composition having the following composition: A zeolite of this comparative example was obtained in the same manner as in Example 1, except that the hydrothermal treatment was performed for 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

The zeolite of this comparative example was a single-phase CHA-type zeolite, and had a pair Al ratio of 27.4% and a SiO ₂ /Al ₂ O ₃ ratio of 13.5.

Comparative example 4
Non-Patent Document 1 Table. CHA-type zeolite was obtained by a method according to SSZ-13 (15, 1.00) of No. 2. Namely. 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

The amorphous Al ratio of the raw material composition was zero. The obtained raw material composition was filled in a closed container, and the raw material composition was stirred while rotating the closed container at 40 rpm, and hydrothermally treated at 160° C. for 6 days. After the hydrothermal treatment, the crystallized product was subjected to solid-liquid separation, washed with pure water, and then calcined in air at 550° C. to obtain the CHA-type zeolite of this comparative example.

The CHA-type zeolite of this comparative example was a single-phase CHA-type zeolite, and had a pair Al ratio of 1.0% and a SiO ₂ /Al ₂ O ₃ ratio of 22.8.

Non-Patent Document 1 states that the ratio of paired Al obtained from the exchange amount of cobalt when the cation type is sodium is 16%. On the other hand, the pair Al ratio obtained from the amount of cobalt exchanged when the cation type is proton type is 1.0%. It can be confirmed that the pair Al ratio in Document 1 was a formal pair Al ratio.

The results are shown in the table below.

Measurement Example An aqueous copper nitrate solution was added dropwise to each of the CHA-type zeolites obtained in Example 1 and Comparative Example 3, and then mixed in a mortar for 10 minutes. After mixing, the mixture was dried overnight at 110°C in air, and then calcined at 550°C for 1 hour in air to obtain a metal-containing CHA-type zeolite supporting 3% by mass of copper (copper-supporting CHA-type zeolite). .

(Hydrothermal durability treatment)
A copper-supporting CHA-type zeolite was molded and crushed to form aggregated particles having an aggregate size of 12 to 20 mesh. After filling 3 mL of the aggregated particles into a normal-pressure fixed-bed flow-type reaction tube (hereinafter also simply referred to as "reaction tube"), hydrothermal durability treatment was performed under the following conditions.
Treatment atmosphere: Air circulation atmosphere with a moisture content of 10% by volume Space velocity: 9,000 h ^-1
Processing temperature: 900°C
Processing time: 1 hour

(Method for measuring nitrogen oxide reduction rate)
The nitrogen oxide reduction rate of the sample was measured by the ammonia SCR method described below.
After press molding, 1.5 mL of a sample sized to 12 mesh to 20 mesh was filled in the reaction tube. After that, the processing gas was passed through the reaction tube under the following conditions.
Process gas composition: NO 200 ppm
_NH3 200 ppm
_O2 10% by volume
_H2O 3% by volume
remainder N ₂
Process gas flow rate: 1.5 L/min
Space velocity (SV): 60,000hr ^-1

The nitrogen oxide concentration (ppm) in the treated gas after catalyst flow was determined with respect to the nitrogen oxide concentration (200 ppm) in the treated gas passed through the reaction tube, and the nitrogen oxide reduction rate was determined according to the following formula. .

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

Both Example 1 and Comparative Example 3 obtained from a raw material composition containing no silica-alumina source are CHA-type zeolites having the same SiO ₂ /Al ₂ O ₃ ratio. Nevertheless, it can be confirmed that Example 1 has a higher nitrogen oxide reduction rate than the CHA-type zeolite of Comparative Example 3 in any temperature range. In particular, in the CHA-type zeolite of Comparative Example 3, as the temperature rises to 400° C. or higher, the decrease in the nitrogen oxide reduction rate becomes remarkable, whereas in the CHA-type zeolite of Example 1, the decrease is remarkably suppressed. It can be confirmed that there is Furthermore, it can be confirmed that the CHA-type zeolite of Example 1 has a remarkably high nitrogen oxide reduction rate at low temperatures of 200°C and 150°C.

The method for producing CHA-type zeolite of the present disclosure can be used as a method for producing CHA-type zeolite that can be used as a zeolite catalyst incorporated in an exhaust gas treatment system and its base material. The CHA-type zeolite obtained by the production method of the present disclosure is particularly useful as an SCR catalyst for reducing and removing nitrogen oxides in the exhaust gas of automobiles such as diesel vehicles in the presence of a reducing agent. Can be used as a catalyst.

Claims (12)

A CHA-type zeolite characterized by having a molar ratio of silica to alumina of 20 or less and a pair aluminum ratio of 13% or less. CHA-type zeolite according to claim 1, having a micropore volume of 0.2 mL/g or more. CHA-type zeolite according to claim 1 or 2, containing a transition metal element. 4. The CHA-type zeolite according to claim 3, wherein said transition metal element is at least one of iron and copper. A silica to alumina molar ratio of 20 or less and paired aluminum comprising crystallizing a composition comprising an amorphous alumina source, an amorphous silica alumina source, an alkalinity source, an organic structure directing agent and water. A method for producing CHA-type zeolite, wherein the ratio is 13% or less. 6. The production method according to claim 5, wherein the amorphous alumina source is at least one of dry aluminum hydroxide gel and sodium aluminate. The production method according to claim 5 or 6, wherein the amorphous silica-alumina source is amorphous aluminosilicate. 8. The manufacturing method according to any one of claims 5 to 7, wherein said composition comprises a silica source. 9. The method according to any one of claims 5 to 8, wherein the composition has a molar ratio of silica to alumina of 22 or less. 10. The production 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. A nitrogen oxide reduction catalyst comprising the CHA-type zeolite according to any one of claims 1 to 4. A method for reducing nitrogen oxides using the CHA-type zeolite according to any one of claims 1 to 4.