Iron-containing small-pore zeolite

Abstract

Provided are: an iron-containing small-pore zeolite that has improved nitrogen oxide reducing properties at lower temperatures even after being exposed to a high-temperature / high-humidity atmosphere having a water content of more than 10 vol% compared with the conventional iron-containing small-pore zeolites; a method for producing the iron-containing small-pore zeolite; and at least one of nitrogen oxide reduction catalysts each containing the iron-containing small-pore zeolite.

Description

Iron-containing small pore zeolite

[0001] The present disclosure relates to iron-containing small pore zeolites.

[0002] *Compared to large-pore zeolites such as BEA-type zeolites, small-pore zeolites such as CHA-type zeolites are less likely to lose crystallinity after exposure to high-temperature, high-humidity atmospheres. Therefore, small-pore zeolites can be used in applications where large-pore zeolites are difficult to use, such as applications involving exposure to high-temperature, high-humidity atmospheres with high water content. Small-pore zeolites containing iron or copper as the active metal (metal-containing small-pore zeolites) are widely used as nitrogen oxide reduction catalysts.

[0003] Compared with iron-containing small-pore zeolites, copper-containing small-pore zeolites are less likely to lose crystallinity even after exposure to high-temperature, high-humidity atmospheres. In addition, they have high nitrogen oxide reduction properties at low temperatures. On the other hand, in the reduction reaction of nitrogen oxides by copper-containing small-pore zeolites, nitrogen dioxide (N ２ O) is produced as a by-product. ２ As a nitrogen oxide reduction catalyst that suppresses the by-production of O, small pore zeolites containing iron and improvements in their nitrogen oxide reduction properties have been investigated.

[0004] For example, Patent Document 1 discloses that an iron-containing small pore zeolite is produced by mixing a small pore zeolite, SSZ-13 (CHA zeolite), with iron nitrate. Patent Document 2 discloses that an iron-containing small pore zeolite (AEI zeolite and CHA zeolite) can be directly produced by crystallization.

[0005] International Publication No. WO 2014 / 062949 International Publication No. WO 2017 / 134001

[0006] The iron-containing small-pore zeolite disclosed in Patent Document 1 is said to have no decrease in nitrogen oxide reduction properties even after exposure to a high-temperature, high-humidity atmosphere with a low water content, but its nitrogen oxide reduction properties were significantly decreased when exposed to a high-temperature, high-humidity atmosphere with a high water content. Furthermore, the iron-containing small-pore zeolite disclosed in Patent Document 2 showed a significant decrease in nitrogen oxide reduction properties after exposure to a high-temperature, high-humidity atmosphere with a water content of 10% by volume.

[0007] The present disclosure aims to provide at least one of an iron-containing small pore zeolite that has high nitrogen oxide reduction properties at low temperatures even after exposure to a high-temperature, high-humidity atmosphere with a water content exceeding 10% by volume, compared to conventional iron-containing small pore zeolites; a method for producing the same; and a nitrogen oxide reduction catalyst containing the same.

[0008] In this disclosure, the nitrogen oxide reduction properties of iron-containing small pore zeolites were investigated, focusing on the state of iron contained in the small pore zeolites. As a result, the molar ratio of silica to alumina (SiO ２ / Al ２ O ３ They found that the state of iron in small pore zeolites has a greater effect on nitrogen oxide reduction properties than conventional iron-supported small pore zeolites. As a result of further investigation, they found that iron-loaded small pore zeolites that contain a certain amount of iron or more and have specific IR and UV-VIS spectra have enhanced nitrogen oxide reduction properties, particularly at low temperatures after exposure to a severe high-temperature, high-quality atmosphere with a water content of more than 10% by volume.

[0009] That is, the present invention is as described in the claims, and the gist of the present disclosure is as follows: [1] A sintered body having an iron content of 1.0 mass % or more and an IR spectrum of 1860±10 cm －１ 3735±10 cm for the peak height intensity having a peak top at －１[1] An iron-containing small pore zeolite having a BET specific surface area of ​​530 m, a peak height intensity ratio of which has a peak top at 190 to 300 nm is 0.50 or less, and a peak area in the wavelength range of 190 to 600 nm in its UV-VIS spectrum is 60% or more. ２ [3] The iron-containing small-pore zeolite according to the above [1] or [2], having an isolated iron ion content of 0.8 mass% or more. [4] The iron-containing small-pore zeolite according to any one of the above [1] to [3], having a ratio of the volume of mesopores to the total volume of mesopores and micropores of 0.40 or less. [5] The iron-containing small-pore zeolite according to any one of the above [1] to [3], having an isolated iron ion content of 0.8 mass% or more. [6] The iron-containing small-pore zeolite according to the above [1] to [3], having an isolated iron ion content of 0.8 mass% or more. [7] The iron-containing small-pore zeolite according to the above [1] to [3], having a ratio of the volume of mesopores to the total volume of mesopores and micropores of 0.15 cm or less. [8] The iron-containing small-pore zeolite according to the above [1] to [3], having an isolated iron ion content of 0.8 mass% or more. [9] The iron-containing small-pore zeolite according to the above [1] to [3], having an isolated iron ion content of 0.8 mass% or more.

[10] The iron-containing small-pore zeolite according to the above [1] to [3], having an isolated iron ion content of 0.8 mass% or more.

[11] The iron-containing small-pore zeolite according to the above [1] to [3], having an isolated iron ion content of 0.8 mass% or more.

[12] The iron-containing small-pore zeolite according to the above [1] to [3], having an isolated iron ion content of 0.8 mass% or more.

[13] The iron-containing small-pore zeolite according to the above [1] to [3], having an isolated iron ion content of 0.8 ３ / g or more. [6] The iron-containing small pore zeolite according to any one of [1] to [4] above, having a molar ratio of silica to alumina of 10 or more. [7] The iron-containing small pore zeolite according to any one of [1] to [6] above, having a molar ratio of silica to alumina of 10 or more. [8] The iron-containing small pore zeolite according to any one of [1] to [7] above, having one or more structures selected from the group consisting of AEI, CHA, LEV, MWW, ERI, and AFX. [9] The iron-containing small pore zeolite according to any one of [1] to [8] above, having a nitrogen oxide reduction rate of 20% or more under the following nitrogen oxide reduction conditions after exposure to a high-temperature, high-humidity atmosphere under the following exposure conditions. <Exposure conditions> Atmosphere: Air with a moisture content of 20% by volume Flow rate: 300 mL / min Treatment temperature: 700°C Treatment time: 20 hours <Nitrogen oxide reduction conditions> Composition of nitrogen oxide-containing gas: NO 200 ppm NH ３ 200ppm O ２ 10% by volume H ２ O 3 volume% N２ Remainder: Flow rate of nitrogen oxide-containing gas: 1.5 L / min Space velocity: 60,000 hr －１ Measurement temperature: 200°C

[10] A method for producing a silica-alumina crystal, comprising: a step of crystallizing a composition containing a silica-alumina source, an iron source, an organic structure directing agent, an alkali source, and water, wherein the composition contains SiO ２

[10] A method for producing an iron-containing small pore zeolite according to any one of [1] to [9] above, wherein the ratio of iron to silicon converted is greater than 0.01 and the composition contains two or more alkali sources.

[11] The method for producing an iron-containing small pore zeolite according to

[10] above, wherein the composition does not contain a zeolite as a silica-alumina source.

[12] The method for producing an iron-containing small pore zeolite according to

[10] or

[11] above, wherein the alkali source contains at least a potassium source.

[13] A catalyst comprising the iron-containing small pore zeolite according to any one of [1] to [9] above.

[0010] The present disclosure can provide at least one of an iron-containing small pore zeolite that has high nitrogen oxide reduction properties at low temperatures even after exposure to a high-temperature, high-humidity atmosphere with a water content exceeding 10% by volume, compared to conventional iron-containing small pore zeolites; a method for producing the same; and a nitrogen oxide reduction catalyst containing the same.

[0011] UV-VIS spectrum of the iron-containing small pore zeolite of Example 1 UV-VIS spectrum of the iron-containing small pore zeolite of Example 2 UV-VIS spectrum of the iron-containing small pore zeolite of Example 3 UV-VIS spectrum of the iron-containing small pore zeolite of Example 4 UV-VIS spectrum of the iron-containing small pore zeolite of Comparative Example 1 UV-VIS spectrum of the iron-containing small pore zeolite of Comparative Example 2 UV-VIS spectrum of the iron-containing small pore zeolite of Comparative Example 4 UV-VIS spectrum of the iron-containing small pore zeolite of Example 5 UV-VIS spectrum of the iron-containing small pore zeolite of Comparative Example 5 SEM observation diagram of the iron-containing small pore zeolite of Example 5

[0012] Hereinafter, the present disclosure will be described with reference to an example embodiment.

[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. The metal atoms include one or more selected from the group consisting of aluminum (Al), titanium (Ti), iron (Fe), zinc (Zn), gallium (Ga), and tin (Sn), with at least one of aluminum and iron being preferred, and aluminum being more preferred. The 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), with silicon being preferred.

[0014] The "small pore zeolite" is a zeolite in which the largest pore formed in the zeolite structure is a pore formed by a ring structure consisting of eight oxygen atoms and a T atom (an eight-membered oxygen ring pore).

[0015] The "medium pore zeolite" is a zeolite in which the largest pore formed in the zeolite structure is a pore formed by a ring structure consisting of 10 oxygen atoms and a T atom (10-membered oxygen ring pore).

[0016] The "large pore zeolite" is a zeolite in which the largest pore formed in the zeolite structure is a pore formed by a ring structure consisting of 12 oxygen atoms and a T atom (12-membered oxygen ring pore).

[0017] 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 an atom other than a metal or a metalloid (hereinafter also referred to as a "non-metal atom"). An example of a non-metal atom is phosphorus (P). Examples of zeolite-like substances include complex phosphorus compounds containing phosphorus (P) as the T atom, such as aluminophosphate (AlPO) and silicoaluminophosphate (SAPO). For clarity, the zeolite in this embodiment does not include zeolite-like substances.

[0018] The "ordered structure (hereinafter also referred to as "zeolite structure")" of zeolite and zeolite-like substances is a skeletal structure specified by a structure code (hereinafter also referred to simply as "structure code") established by the Structure Commission of the International Zeolite Association. For example, a CHA structure is a skeletal structure specified by the structure code "CHA." Zeolite structures can be identified by comparing the XRD pattern with the XRD pattern (hereinafter also referred to as the "reference pattern") described in CHA of Zeolite Framework Types on the IZA Structure Commission's website, http: / / www.iza-structure.org / databases / . In this embodiment, the terms zeolite structure, framework structure, crystalline structure, and crystalline phase are used interchangeably.

[0019] In the present embodiment, "-type zeolite" such as "CHA-type zeolite" means a zeolite having a zeolite structure of the corresponding structure code.

[0020] 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."

[0021] The XRD pattern in this embodiment is an XRD pattern obtained by XRD measurement under the following conditions.

[0022] Acceleration current / voltage: 40 mA / 40 kV Radiation source: CuKα radiation (λ=1.5405 Å) Measurement mode: Step scan Scan conditions: 40° / min Measurement time: 3 seconds Measurement range: 2θ=3° to 43° Divergence vertical limiting slit: 10 mm Divergence / entrance slit: 1° Receiving slit: open Receiving solar slit: 5° Detector: Semiconductor detector (D / tex Ultra) Filter: Ni filter

[0023] The XRD pattern can be measured using a general powder X-ray diffractometer (e.g., UltimaIV Protectus, manufactured by Rigaku Corporation). The crystalline XRD peak is a peak whose peak top 2θ is identified and detected in an XRD pattern analysis using general analysis software (e.g., SmartLab StudioII, manufactured by Rigaku Corporation), and in particular, an XRD peak whose half-width is 2θ = 0.50° or less.

[0024] The XRD pattern analysis conditions are as follows:

[0025] Fitting conditions: Automatic, background refinement, dispersion-type pseudo-Voigt function (peak shape) Background removal method: Fitting method Kα2 removal method: Kα1 / Kα2 ratio = 0.497

[0026] [Iron-Containing Small Pore Zeolite] This embodiment provides an iron-containing small pore zeolite having an iron content of 1.0 mass% or more, and in its UV-VIS spectrum, the ratio of the peak area at wavelengths of 190 to 300 nm to the peak area at wavelengths of 190 to 600 nm is 60% or more (hereinafter also referred to as "area ratio"). By combining such an iron content and area ratio, it is believed that the iron-containing small pore zeolite of this embodiment becomes more active, particularly in a state of high catalytic activity. As a result, the iron-containing small pore zeolite has better nitrogen oxide reduction properties at low temperatures than conventional iron-containing small pore zeolites, even after exposure to a high-temperature, high-humidity atmosphere with a water content exceeding 10% by volume.

[0027] The iron-containing small pore zeolite of this embodiment is a small pore zeolite containing iron (Fe), and is preferably a crystalline aluminosilicate containing iron.As the iron-containing small pore zeolite, it can be zeolite containing iron and having one or more structures selected from the group consisting of AEI, CHA, LEV, MWW, ERI, KFI and AFX, and further zeolite containing iron and having one or more structures selected from the group consisting of AEI, CHA, LEV, ERI and AFX, and further zeolite containing iron and having one or more structures selected from the group consisting of AEI, CHA and AFX.The iron-containing small pore zeolite of this embodiment is preferably zeolite containing iron and having at least one of the structures of CHA and AFX, and more preferably zeolite containing iron and having a CHA structure or AFX structure. Specific examples of small pore zeolites include one or more selected from the group consisting of AEI zeolite, CHA zeolite, LEV zeolite, MWW zeolite, ERI zeolite, and AFX zeolite, and further one or more selected from the group consisting of AEI zeolite, CHA zeolite, LEV zeolite, ERI zeolite, and AFX zeolite, and further one or more selected from the group consisting of AEI zeolite, CHA zeolite, and AFX zeolite, with at least one of CHA zeolite and AFX zeolite being preferred, and CHA zeolite or AFX zeolite being more preferred. From the viewpoint of hydrothermal stability, AFX zeolite is preferred, and from the viewpoint of industrial production, CHA zeolite is preferred. In addition, when the small pore zeolite in the iron-containing small pore zeolite of this embodiment is a CHA-type zeolite or the like, it is also referred to as an iron-containing CHA-type zeolite or the like.

[0028] The iron contained in the iron-containing small pore zeolite of this embodiment functions as an active metal. The iron contained in the zeolite exhibits nitrogen oxide reduction ability. Iron is present in the form of iron ions (Fe ３＋ ), iron clusters (Fe ｘ O ｙ ) and iron oxide particles (Fe ２ O ３Since iron ions are thought to function as active species for nitrogen oxide reduction at low temperatures, the iron-containing small pore zeolite of the present embodiment contains at least iron ions, preferably contains a large amount of iron ions, and more preferably contains iron mainly as iron ions.

[0029] The iron contained in the iron-containing small pore zeolite of this embodiment may be contained by substituting into the zeolite structure, and preferably at least a portion of the iron is substituted into the zeolite structure (skeletal structure) of the iron-containing small pore zeolite. That is, the iron-containing small pore zeolite of this embodiment is preferably an iron-containing small pore zeolite in which at least a portion of the iron is substituted into the zeolite skeleton (iron-substituted small pore zeolite), or may be an iron-containing small pore zeolite in which iron is substituted into the zeolite skeleton and is also supported. Compared to an iron-containing small pore zeolite in which iron is contained only by supporting iron (iron-supported small pore zeolite), the degree of decrease in the nitrogen oxide reduction rate when the reaction temperature of nitrogen oxide reduction is lowered is more likely to be suppressed.

[0030] Furthermore, it is believed that it is virtually impossible to selectively remove iron species contained in iron-containing small pore zeolites. Therefore, for example, in iron-containing small pore zeolites containing iron ions, iron clusters, and iron oxide particles, it is not possible to remove only the iron clusters and iron oxide particles, leaving only iron ions. Furthermore, no specific technology capable of selectively removing iron species is known.

[0031] The iron content of the iron-containing small pore zeolite of this embodiment is 1.0 mass% or more, and preferably 1.1 mass% or more, 1.15 mass% or more, or 1.3 mass% or more. If the iron content is less than 1.0 mass%, even when the iron content and the area ratio described below are both present, the nitrogen oxide reduction properties at low temperatures will remain at the same level as conventional iron-containing small pore zeolites. The iron content may be any amount that allows nitrogen oxide reduction to proceed efficiently, and examples include 3.0 mass% or less, 2.5 mass% or less, 2.3 mass% or less, or 2.0 mass% or less. Preferably, the zeolite has the area ratio described below and the iron content is 1.0 mass% to 3.0 mass%, 1.1 mass% to 2.5 mass%, 1.15 mass% to 2.3 mass%, or 1.3 mass% to 2.0 mass%.

[0032] In this embodiment, the "iron content" refers to the mass ratio [mass %] of iron (Fe) to the mass of the iron-containing small pore zeolite. ２ O ３ Converted aluminum, SiO ２ This is the converted total mass of silicon and iron (Fe).

[0033] The iron content of the iron-containing small pore zeolite of this embodiment may be any value as long as it satisfies the above-mentioned value. The ratio of iron to silica (hereinafter also referred to as the "Fe / Si ratio") [mol / mol] of the iron-containing small pore zeolite of this embodiment is preferably 0.003 or more, 0.005 or more, or 0.010 or more, and 0.050 or less, 0.040 or less, or 0.030 or less, for example, 0.003 or more and 0.050 or less, 0.005 or more and 0.040 or less, or 0.010 or more and 0.030 or less.

[0034] In the iron-containing small pore zeolite of this embodiment, the ratio (area ratio) of the peak area at wavelengths of 190 to 300 nm to the peak area at wavelengths of 190 to 600 nm in its UV-VIS spectrum is 40% or more, preferably 60% or more, 70% or more, or 80% or more. After peak separation, if necessary, the state of iron (iron species) can be determined from the position (wavelength) of the peak in the UV-VIS spectrum, and the relative amount of iron species can be determined from the peak area. Meanwhile, the peak height of the peak in the UV-VIS spectrum is not considered to have any technical significance as an indicator of the state or content of iron. If the area ratio is less than 40%, even if the iron content is high, the nitrogen oxide reduction property at low temperatures, particularly at temperatures below 200°C, is low, and the nitrogen oxide reduction property is only comparable to that of conventional iron-containing small pore zeolites. The area ratio is preferably high, but may be 100% or less, less than 100%, 90% or less, or less than 90%, and is preferably 40% to 100%, 60% to less than 100%, 70% to 90%, or 80% to less than 90%. In order to easily exhibit practical nitrogen oxide reduction properties, the iron-containing small pore zeolite of this embodiment preferably contains iron at the above-mentioned iron content and has an area ratio of 40% to 100%, 60% to less than 100%, 70% to 90%, or 80% to less than 90%.

[0035] In this embodiment, the area ratio may be determined by analyzing a UV-VIS spectrum measured under the following conditions using a general UV-visible spectrophotometer (for example, UV-visible spectrophotometer V-770, manufactured by JASCO Corporation).

[0036] Integrating sphere unit: ISN-923 (JASCO Corporation) Measurement mode: Diffuse reflectance method Wavelength: 190-700 nm Temperature: Room temperature Slit width: 5 nm Background: Barium sulfate

[0037] The UV-VIS spectrum can be analyzed using analysis software (e.g., Fityk ver. 0.9.8) provided with the ultraviolet-visible-near-infrared spectrophotometer. After peak separation under the following conditions, the peak area at wavelengths of 190 nm to 600 nm and the peak area at wavelengths of 190 to 300 nm are determined, and the area ratio can be calculated from the ratio of these peak areas. That is, the obtained UV-VIS spectrum is corrected so that the reflectance (hereinafter also referred to as "γ∞" or "relative reflectance") of the iron-containing small pore zeolite of this embodiment relative to the reflectance of barium sulfate at a wavelength of 700 nm is 1. The corrected UV-VIS spectrum can then be subjected to KM (Kubelka-Munk) conversion using the KM function (f(γ∞)) shown below.

[0038] f(γ∞) = (1−γ∞) ２ / 2γ∞ (1)

[0039] The UV-VIS spectrum after KM conversion is fitted and waveform separated using general analysis software (e.g., Fityk 0.9.8) and a Gaussian fitting function, and then the areas of the peaks included in the wavelength range of 190 nm to 300 nm, the areas of the peaks included in the wavelength range of more than 300 nm to 400 nm, and the areas of the peaks included in the wavelength range of more than 400 nm to 600 nm are calculated to determine the peak areas for each wavelength range. The sum of the peak areas across all wavelength ranges is taken as the peak area (total area) for wavelengths of 190 nm to 600 nm. The area ratio for each wavelength range can be determined from the ratio of the peak area for each wavelength range to the obtained peak area (total area) for wavelengths of 190 nm to 600 nm. The peak area for each wavelength range can be determined by calculating the area of ​​the peak included in each wavelength range, regardless of the position of the peak top after waveform separation. For example, in the case of a peak having a wavelength range of 280 to 310 nm and a peak top of 290 nm, the area of ​​the peak having a wavelength of 280 nm or more and 300 nm or less may be regarded as the area of ​​the peak contained in the wavelength range of 190 nm or more and 300 nm or less, and the area of ​​the peak having a wavelength of more than 300 nm and 310 nm or less may be regarded as the area of ​​the peak contained in the wavelength range of more than 300 nm and 400 nm or less.

[0040] By combining these iron contents and area proportions, the nitrogen oxide reduction properties, particularly at low temperatures, are higher than those of conventional iron-containing small pore zeolites. One reason for this is thought to be that, compared to conventional iron-containing small pore zeolites, there are more highly dispersible iron species and the stability of the iron in this state is higher. That is, the peak at wavelengths of 190 to 300 nm in the UV-VIS spectrum is thought to correspond to iron ions in a state known as isolated iron ions. By combining the above-mentioned iron contents and area proportions, the iron-containing small pore zeolite of this embodiment does not simply have a high iron content, but rather the proportion of iron in a state capable of contributing to the reduction of nitrogen oxides at low temperatures is thought to be higher than that of conventional iron-containing small pore zeolites. The iron-containing small pore zeolite of this embodiment may have a high proportion of isolated iron ions in the iron-containing CHA-type zeolite, but preferably has an isolated iron ion content of 0.8% by mass or more, 1.0% by mass or more, or 1.3% by mass or more. The higher the isolated iron ion content, the better, and it is preferable that all iron is isolated ions. Examples of the isolated iron ion content include 3.0 mass% or less, 2.0 mass% or less, or 1.5 mass% or less, and further examples include 0.8 mass% to 3.0 mass%, 1.0 mass% to 2.0 mass%, or 1.3 mass% to 2.0 mass%.

[0041] The isolated iron ion content in this embodiment is a value calculated from the following formula.

[0042] Isolated iron ion content [mass%] = iron content [mass%] × area ratio [%] (2)

[0043] The iron-containing small pore zeolite of this embodiment preferably contains isolated iron ions in different states, and more preferably contains four different types of isolated iron ions in different states. By containing isolated iron ions in such states, the nitrogen oxide reduction properties at low temperatures tend to be improved after exposure to a high-temperature, high-humidity atmosphere compared to before the exposure.

[0044] The state of isolated iron ions can be confirmed by peak separation of peaks in the 190 to 300 nm wavelength range in the UV-VIS spectrum using the method described above, and the state of isolated iron ions can be confirmed by the number of peaks having peak tops in the 190 to 300 nm wavelength range. For example, when there are two peaks having peak tops in the 190 to 300 nm wavelength range, it can be considered that two types of isolated iron ions in different states are contained. When there are four peaks having peak tops in the 190 to 300 nm wavelength range, it can be considered that four types of isolated iron ions in different states are contained. The iron-containing small pore zeolite of this embodiment preferably has three or more peaks having peak tops in the 190 to 300 nm wavelength range in the UV-VIS spectrum, more preferably has four or more peaks having peak tops in the 190 to 300 nm wavelength range in the UV-VIS spectrum, and even more preferably has four peaks having peak tops in the 190 to 300 nm wavelength range in the UV-VIS spectrum. Specifically, in the UV-VIS spectrum, it is preferable that the compound has a peak having a peak top at a wavelength of 197.5±7.5 nm, a peak having a peak top at a wavelength of 213.0±8.0 nm, a peak having a peak top at a wavelength of 242.5±7.5 nm, and a peak having a peak top at a wavelength of 265±10.0 nm.

[0045] The iron-containing small pore zeolite of this embodiment may contain an alkali metal (i.e., the alkali metal content may be greater than 0% by mass). However, the lower the alkali metal content, the more likely it is that the deterioration of nitrogen oxide properties at low temperatures due to exposure to a high-temperature, high-humidity atmosphere is suppressed. Therefore, the alkali metal content is preferably 1.0% by mass or less, 0.5% by mass or less, or 0.1% by mass or less, and more preferably is substantially free of alkali metal (i.e., below the detection limit (0% by mass)). Examples of the alkali metal content of the iron-containing small pore zeolite of this embodiment include 0% by mass or more and 0.2% by mass or less, 0% by mass or more and 0.1% by mass or less, more than 0% by mass and 0.2% by mass or less, or more than 0% by mass and 0.1% by mass or less.

[0046] When an alkali metal is contained, the alkali metal contained in the iron-containing small pore zeolite of this embodiment may be one or more selected from the group consisting of sodium, potassium, lithium, and cesium, further one or more selected from the group consisting of sodium, potassium, and cesium, further at least one of sodium and potassium, or further sodium or potassium.

[0047] When the iron-containing small pore zeolite of this embodiment contains an alkali metal, the alkali metal may be contained as a cation or may be contained in an ion exchange site.

[0048] The iron-containing small pore zeolite of this embodiment may contain a metal element other than iron as long as the effect is exhibited. The metal element contained in the iron-containing small pore zeolite of this embodiment may include one or more selected from the group consisting of copper (Cu), manganese (Mn), and yttrium (Y), and further may include copper.

[0049] Since the collapse of the zeolite structure after exposure to a high-temperature, high-humidity atmosphere is easily suppressed, the iron-containing small pore zeolite of this embodiment has a silica to alumina molar ratio (Al ２ O ３ SiO relative to converted aluminum ２ The molar ratio of silicon converted into ２ / Al ２ O ３ It is preferable that the SiO ratio is 10.0 or more, 15.5 or more, or 16.5 or more. ２ / Al ２ O ３ The ratio may be 50.0 or less, 30.0 or less, 24.5 or less, or 20.0 or less. ２ / Al ２ O ３ The ratio can be, for example, 10.0 or more and 50.0 or less, 15.0 or more and 30.0 or less, 15.5 or more and 25.0 or less, or 16.5 or more and 20.0 or less. For example, when the small pore zeolite is a zeolite containing a CHA structure (a CHA type zeolite), a preferred SiO ２ / Al ２O ３ The ratio may be 15.5 or more and 24.5 or less, or 16.5 or more and 19.5 or less. When the small pore zeolite is a zeolite containing an AFX structure (when it is an AFX type zeolite), the preferred SiO ２ / Al ２ O ３ The ratio may be 15.5 or more and 30.0 or less, or 20.0 or more and 24.5 or less.

[0050] In this embodiment, SiO ２ / Al ２ O ３ The ratio is determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES) using a general high-frequency inductively coupled plasma device (e.g., OPTIMA 5300DV, manufactured by PerkinElmer) from the contents of aluminum (Al) and silicon (Si) in the iron-containing small pore zeolite of this embodiment. ２ O ３ SiO relative to converted aluminum ２ This can be calculated as the molar ratio of silicon.

[0051] Since the aggregation of iron when exposed to a high-temperature, high-humidity atmosphere is more easily suppressed, the BET specific surface area of ​​the iron-containing small pore zeolite of this embodiment is 530 m ２ / g or more, 550m ２ / g or more, 600m ２ / g or more or 620m ２ The BET specific surface area does not need to be higher than necessary, and is preferably 850 m ２ / g or less, 800m ２ / g or less, or 750m ２ or less or 700m ２ / g or less. A preferred BET specific surface area is 530 m ２ / g or more 850m ２ / g or less, 550m ２ / g or more 850m ２ / g or less, 600m ２ / g or more 800m ２ / g or less, or 620m ２ / g or more 700m ２ / g or less.

[0052] The BET specific surface area in this embodiment is a value measured by a method conforming to ISO 9277:2010(E), and can be determined by analyzing the range of relative pressures of 0.05 to 0.15 in a nitrogen adsorption isotherm obtained under the following measurement conditions using a general BET specific surface area measuring device (for example, a BELSOR P-mini II manufactured by Microtrac-Bell). <Nitrogen adsorption measurement conditions> Measurement sample: 30 mg Pretreatment: Vacuum atmosphere (≦10 Pa), 350°C, 2 hours Measurement temperature: −196°C Measurement pressure: Equilibrium relative pressure of 0.05 to 0.99

[0053] Since the iron-containing small-pore zeolite of this embodiment is less likely to experience a decrease in crystallinity after exposure to a high-temperature, high-humidity atmosphere, the volume of mesopores relative to the total volume of mesopores and micropores (hereinafter also referred to as the "mesopore volume ratio") is preferably 0.40 or less, 0.25 or less, or 0.20 or less. The mesopore volume ratio may be 0 or more or more than 0.10, and may be 0 or more and 0.40 or less, or more than 0.10 and 0.20 or less.

[0054] In order to increase the frequency of contact with nitrogen oxides in the nitrogen oxide reduction reaction, the iron-containing small pore zeolite of this embodiment has a total volume of mesopores and micropores (hereinafter also referred to as "total pore volume") of 0.15 cm ３ / g or more, 0.20cm ３ / g or more or 0.25 cm ３ On the other hand, the upper limit of the total pore volume is preferably 0.50 cm ３ / g or less, 0.40cm ３ / g or less, 0.30cm ３ / g or less or 0.29 cm ３ / g or less, and 0.15 cm ３ / g or more 0.50cm ３ / g or less, 0.20cm ３ / g or more 0.40cm ３ / g or less, 0.20cm ３ / g or more 0.30cm ３ / g or less, 0.25cm ３ / g or more 0.30cm ３ / g or less, or 0.25 cm３ / g or more 0.29cm ３ / g or less is preferable.

[0055] In this embodiment, the total pore volume is determined by the following formula from a nitrogen adsorption isotherm obtained in the same manner as in the measurement of the BET specific surface area.

[0056] Total pore volume (cm ３ / g) = V × 1.547 × 10 －３ (3) In the above formula, V is the equilibrium relative pressure in the nitrogen adsorption isotherm (hereinafter referred to as "p / p ０ ") is 0.99. ３ / g].

[0057] As long as the above-mentioned mesopore volume ratio and total pore volume are satisfied, the volume of the mesopores and the volume of the micropores may be any. ３ / g or less or 0.10 cm ３ / g or less, and ３ / g or more or 0.03 cm ３ / g or more. In addition, the volume of the micropores is 0.10 cm ３ / g or more or 0.15 cm ３ / g or more, and ３ / g or less or 0.25 cm ３ / g or less, and ３ / g or more 0.30cm ３ / g or less, or 0.15 cm ３ / g or more 0.25cm ３ / g or less is preferable.

[0058] The micropore volume in this embodiment is a value calculated by the t-plot method of nitrogen adsorption isotherm, and is expressed as a function of the average relative pressure (p / p ０ The measurement points between 0.6 and 0.8 are approximated to a straight line, and the intercept is taken as the micropore volume. In the t-plot method, the adsorption isotherm of silica can be used as the standard isotherm.

[0059] The mesopore volume can be calculated from the total pore volume and micropore volume obtained by the above-mentioned method using the following formula:

[0060] Mesopore volume (cm ３ / g) = total pore volume (cm ３ / g) - Micropore volume (cm ３ / g) (4)

[0061] In order to prevent the collapse of the zeolite structure due to exposure to a high-temperature, high-humidity atmosphere, the primary particle diameter of the iron-containing small pore zeolite of this embodiment is preferably 0.3 μm or more or 0.5 μm or more. On the other hand, from the viewpoint of handling (operability) such as catalysis, the primary particle diameter is preferably 10.0 μm or less or 5.0 μm or less, and examples thereof include 0.3 μm to 10.0 μm, or 0.5 μm to 5.0 μm. In this embodiment, the primary particle diameter refers to the size of the crystalline particles (crystal particle size) of the iron-containing small pore zeolite, and is the size (longest diameter) of the smallest unit crystalline particle observed as an independent particle in scanning electron microscope observation under the following conditions. Note that in this embodiment, the primary particles do not include aggregates (particles formed by physical aggregation of crystalline particles).

[0062] Acceleration voltage: 10 kV Measurement magnification: 5000x.

[0063] The iron-containing small pore zeolite of this embodiment may contain agglomerated particles formed by agglomeration of crystalline particles. Furthermore, the iron-containing small pore zeolite of this embodiment may be composed primarily of primary particles of 0.3 μm to 10.0 μm, and may essentially be composed of agglomerated particles formed by agglomeration of primary particles of 0.3 μm to 10.0 μm. Furthermore, the iron-containing small pore zeolite may be composed essentially of primary particles of 0.3 μm or larger, and may contain primary particles of less than 0.3 μm, as long as the amount does not impair handleability (operability).

[0064] The iron-containing small pore zeolite of this embodiment may be in any shape depending on the intended purpose, such as a powder or a molded body. The powder is suitable for coating a substrate such as a honeycomb.

[0065] The iron-containing small pore zeolite of this embodiment has an IR spectrum of 1860±10 cm －１ The height intensity of the peak having a peak top at ｐ１ ") for 3735±10cm －１ The height intensity of the peak having a peak top at ｐ２ ") ratio (hereinafter referred to as "IR ｐ２ / IR ｐ１ (also called "ratio") is 0.50 or less.

[0066] IR Ｐ１ and I.R. Ｐ２ are considered to be the peak heights of the IR peaks attributable to the skeletal vibration and silanol defects of the iron-containing zeolite, respectively, and IR ｐ２ / IR ｐ１ The ratio can be used as an indicator of the amount of silanol defects in the iron-containing zeolite. ｐ２ / IR ｐ１ A small ratio is considered to correspond to a small amount of silanol defects. ｐ２ / IR ｐ１ If the ratio exceeds 0.50, the amount of silanol defects increases, and the skeletal structure is likely to collapse when exposed to high temperature and high humidity. ｐ２ / IR ｐ１ The ratio is preferably 0.50 or less, 0.49 or less, or 0.48 or less, and is preferably 0.00 or more, more than 0.00, 0.01 or more, or 0.02 or more. ｐ２ / IR ｐ１ Specific combinations of the upper and lower limits of the ratio include 0.00 or more and 0.50 or less, more than 0.00 and 0.50 or less, 0.01 or more and 0.49 or less, or 0.02 or more and 0.48 or less.

[0067] IR ｐ１ and I.R. ｐ２ can be measured using a general FT-IR measurement device (for example, device name: Jasco FT / IR-6100, manufactured by JASCO Corporation) under the following conditions, and calculated from an IR spectrum obtained by Fourier transform infrared spectrophotometry (FT-IR).

[0068] Measurement sample: 0.01 g Pretreatment: Under vacuum, 450 ° C (product temperature), 1 hour Measurement mode: Continuous scan Measurement temperature: Under vacuum, 150 ° C (product temperature) Measurement range: 350 to 4000 cm －１ Resolution: 2.0cm －１ Number of accumulations: 128 times Zero filling: ON Detector: TGS (Triglycine sulfate) The obtained IR spectrum may be waveform processed using general analysis software (for example, Spectra Manager Version 2 Version 2.15.11, manufactured by JASCO Corporation). －１ and base end 1950cm －１ , and base start 2500cm －１ and base end 3800 cm －１ After baseline correction of these ranges, 1860 ± 10 cm －１ The height intensity of the peak having a peak top in the range of ｐ１ , 3735±10cm －１ The height intensity of the peak having a peak top in the range of ｐ２ The obtained IR ｐ２ and I.R. ｐ１ From the above, IR is calculated by the following formula: ｐ２ / IR ｐ１ Just find the ratio.

[0069] IR ｐ２ / IR ｐ１ Ratio = (IR ｐ２ ) / (IR ｐ１ ) (5)

[0070] The iron-containing small pore zeolite of this embodiment preferably has high nitrogen oxide reduction properties after exposure to a high-temperature, high-humidity atmosphere, and the nitrogen oxide reduction rate under the following nitrogen oxide reduction conditions after exposure to a high-temperature, high-humidity atmosphere under the following exposure conditions (hereinafter also referred to as "hydrothermal durability treatment") is preferably 20% or more, 25% or more, or 30% or more, and may be 70% or less or 50% or less. <Exposure conditions> Atmosphere: Air with a moisture content of 20% by volume Flow rate: 300 mL / min Treatment temperature: 700°C Treatment time: 20 hours <Nitrogen oxide reduction conditions> Composition of nitrogen oxide-containing gas: NO 200 ppm NH ３ 200ppm O ２ 10% by volume H ２ O 3 volume% N ２ Remainder: Flow rate of nitrogen oxide-containing gas: 1.5 L / min Space velocity: 60,000 hr －１ Measurement temperature: 200℃

[0071] The iron-containing small pore zeolite of this embodiment can be used in known applications of small pore zeolites, such as adsorbents, catalysts, and supports thereof, and is preferably used as a catalyst containing the same, particularly a nitrogen oxide reduction catalyst.

[0072] When used as a nitrogen oxide reduction catalyst, the iron-containing small pore zeolite of this embodiment may be applied to a substrate to form a nitrogen oxide reduction catalyst. Furthermore, the iron-containing small pore zeolite of this embodiment can be used as a nitrogen oxide reduction device or a nitrogen oxide reduction system.

[0073] Furthermore, the iron-containing small pore zeolite of the present embodiment may be used as a zeolite composition containing the same and other zeolites. For example, it may be used as two or more iron-containing small pore zeolites of the present embodiment that differ in one or more selected from the group consisting of framework structure, composition, and iron content, or it may be used as a zeolite composition containing the iron-containing small pore zeolite of the present embodiment and other metal-containing zeolites, or it may be used as a zeolite composition containing the iron-containing small pore zeolite of the present embodiment and a metal-free small pore zeolite.

[0074] [Method for producing iron-containing small pore zeolite] A preferred method for producing the iron-containing small pore zeolite of this embodiment includes a step of crystallizing a composition containing a silica-alumina source, an iron source, an organic structure-directing agent, an alkali source, and water, and the composition contains SiO ２ a method for producing an iron-containing small pore zeolite, wherein the ratio of iron to silicon calculated is greater than 0.01 and the zeolite contains two or more alkali sources.

[0075] Conventional methods for producing iron-containing small pore zeolites include treating small pore zeolites with iron compounds (hereinafter also referred to as "post-treatment methods") and crystallizing small pore zeolites in the presence of iron compounds (hereinafter also referred to as "crystallization methods"). In the post-treatment methods, iron is supported in the small pore zeolites, resulting in so-called iron-supported small pore zeolites. While the post-treatment methods produce iron-containing small pore zeolites with high iron content, the small pore zeolites contain a large amount of less active iron. Therefore, even when highly active iron is contained in the post-treatment methods, the small pore zeolites contain more less active iron. As a result, highly active iron-containing small pore zeolites, and even iron-containing small pore zeolites with high nitrogen oxide reduction properties at low temperatures below 200°C, cannot be obtained. Compared to the post-treatment methods, the crystallization methods can produce iron-containing small pore zeolites containing iron in a relatively highly active state. However, in conventional crystallization methods, when the iron content is increased, the crystallization of small pore zeolite does not substantially proceed. For example, in Patent Document 2, the molar ratio of iron to silica (Fe / SiO ２However, the manufacturing method specifically disclosed in Patent Document 2 is not suitable for crystallization at a Fe / SiO ２ is only 0.01, and Fe / SiO ２ Patent Document 2 does not disclose a specific method for producing an iron-containing small pore zeolite having a SiO2 content of more than 0.01. ２ Furthermore, as will be described later, the manufacturing method of Patent Document 2 does not suggest any conditions necessary for crystallizing an iron-containing small pore zeolite having a SiO ２ When a composition having a ρ of more than 0.01 is crystallized, an iron-containing small pore zeolite cannot be obtained. In contrast, in the production method of this embodiment, by using the above-mentioned composition, it is believed that the iron source is less likely to aggregate during crystallization, and crystallization proceeds while maintaining high dispersibility. This makes it possible to produce an iron-containing small pore zeolite that contains a large amount of iron in a highly active state compared to iron-containing small pore zeolites obtained by post-treatment methods and that has a higher iron content compared to iron-containing small pore zeolites obtained by conventional crystallization methods.

[0076] The production method of this embodiment includes a step of crystallizing a composition containing a silica-alumina source, an iron source, an organic structure-directing agent source, an alkali source, and water (hereinafter also referred to as a "raw material composition").

[0077] The silica-alumina source is a compound containing aluminum (Al) and silicon (Si), and is preferably an amorphous compound containing aluminum and silicon. Specific examples of the silica-alumina source include amorphous aluminosilicates, and it is preferable to include at least amorphous aluminosilicates.

[0078] Known methods for crystallizing small pore zeolites include crystallizing zeolites from amorphous compounds and decomposing zeolites into building units and then reconstructing them to crystallize the desired zeolite (the so-called conversion method). In the conversion method, zeolites are typically used as starting materials; for example, FAU zeolite is used to produce CHA zeolites, and FER zeolite is used to produce AEI zeolites. However, since zeolites are more expensive than amorphous compounds, the conversion method tends to increase production costs. Furthermore, compared with zeolites obtained by the conversion method, small pore zeolites obtained from amorphous compounds have stronger frameworks, and as a result, it is believed that the framework structure is less likely to collapse after exposure to a high-humidity atmosphere. Therefore, the crystallization in the crystallization step is preferably a method of crystallizing an iron-containing small pore zeolite from an amorphous compound, and the raw material composition preferably does not contain zeolite as a silica-alumina source, more preferably does not contain FAU zeolite, and even more preferably does not contain FAU zeolite or FER zeolite.

[0079] The iron source is a compound containing iron, and may be any iron compound that is uniformly dispersed in the raw material composition. A water-soluble iron compound is preferred as the iron source, as it provides higher dispersibility in the raw material composition. Specific examples of the iron compound include one or more selected from the group consisting of iron nitrate, iron sulfate, iron oxide, iron chloride, iron oxyhydroxide, and iron hydroxide, one or more selected from the group consisting of iron hydroxide, iron sulfate, and iron nitrate, at least one of iron sulfate and iron nitrate, and even iron sulfate.

[0080] Sources of organic structure directing agents include organic structure directing agent (hereinafter also referred to as "SDA") compounds capable of directing small pore zeolites, as well as quaternary ammonium salts capable of directing small pore zeolites.

[0081] Examples of SDAs directed to iron-containing AEI zeolites include one or more selected from the group consisting of N,N-alkyl-2,6-alkylpiperidinium cations (N,N-dialkyl-2,6-dialkylpiperidinium cations) and N,N-alkyl-3,5-alkylpiperidinium cations (N,N-dialkyl-3,5-dialkylpiperidinium cations), and further include 1,1-dimethyl-3,5-dimethylpiperidinium cations.

[0082] As an SDA directed to an iron-containing CHA-type zeolite, an N,N,N-trialkylcyclohexylammonium cation is preferred. Examples of the N,N,N-trialkylcyclohexylammonium cation include one or more selected from the group consisting of an N,N,N-methyldiethylcyclohexylammonium cation, an N,N,N-dimethylethylcyclohexylammonium cation, and an N,N,N-trimethylcyclohexylammonium cation.

[0083] An example of an SDA directed towards iron-containing AFX-type zeolite is 1,4-diazabicyclo[2.2.2]-octane-C4-diquat dibromide cation.

[0084] The SDA source may be two or more SDAs directed to small pore zeolites, two to five SDAs directed to small pore zeolites, or even two SDAs. When the SDA source is two or more SDAs directed to small pore zeolites, examples of the SDA source include a salt of an SDA directed to CHA zeolite and a salt of an SDA directed to AFX zeolite, two or more different salts of an SDA directed to CHA zeolite, or two or more different salts of an SDA directed to CHA zeolite.

[0085] When producing an iron-containing CHA-type zeolite, the raw material composition contains an N,N,N-trialkylcyclohexylammonium cation as the SDA. Among them, one or more selected from the group consisting of N,N,N-methyldiethylcyclohexylammonium (hereinafter also referred to as "CMDEA") cation, N,N,N-dimethylethylcyclohexylammonium (hereinafter also referred to as "CDMEA") cation, and N,N,N-trimethylcyclohexylammonium (hereinafter also referred to as "CTMA") cation are preferred, with at least one of the CMDEA cation and the CDMEA cation being more preferred, and the CDMEA cation being even more preferred. It is believed that the raw material composition containing these SDAs in addition to two types of alkali sources can promote crystallization while suppressing aggregation of the iron source and the generation of silanol defects in the zeolite structure. This allows for IR ｐ２ / IR ｐ１ It is believed that an iron-containing CHA-type zeolite with a lower ratio and a higher area ratio can be obtained. When producing an iron-containing CHA-type zeolite, the raw material composition only needs to contain an N,N,N-trialkylcyclohexylammonium cation as the SDA, and it is preferable that the SDA is only an N,N,N-trialkylcyclohexylammonium cation. On the other hand, as long as CHA-type zeolite is crystallized mainly due to the structure-directing action of the N,N,N-trialkylcyclohexylammonium cation, the raw material composition may contain other SDAs.

[0086] The SDA source may be at least one of a salt and a compound containing SDA, and may include one or more selected from the group consisting of hydroxides, halides other than fluorides, carbonate monoester salts, and sulfate monoester salts containing SDA, further including one or more selected from the group consisting of hydroxides, chlorides, bromides, and iodides, one or more selected from the group consisting of hydroxides, bromides, and iodides, or even at least bromides. It is particularly preferred that the SDA source contains hydroxide and bromide, which tends to increase the yield of the iron-containing small pore zeolite. The raw material composition may contain, as the SDA source, two or more selected from the group consisting of hydroxides, chlorides, bromides, and iodides, two or more selected from the group consisting of hydroxides, bromides, and iodides, or even at least bromides, or even hydroxide and bromide, all containing the same SDA.

[0087] The alkali source is a compound containing an alkali metal element, and examples thereof include compounds containing one or more selected from the group consisting of sodium, potassium, rubidium, and cesium, compounds containing one or more selected from the group consisting of sodium, potassium, and cesium, compounds containing at least one of sodium and potassium, compounds containing sodium or potassium, and compounds containing potassium.

[0088] Examples of the alkali source include one or more selected from the group consisting of hydroxides, fluorides, bromides, iodides, sulfates, nitrates, and carbonates containing the above-mentioned alkali metal elements, one or more selected from the group consisting of hydroxides, bromides, and iodides, or hydroxides (hereinafter, an alkali source containing sodium may be referred to as a "sodium source," an alkali source containing potassium may be referred to as a "potassium source," etc.).

[0089] The raw material composition contains two or more alkali sources and two or more alkali metal elements. The raw material composition preferably contains two to four alkali sources, and more preferably contains two alkali sources. The iron-containing small pore zeolite of this embodiment is not a naturally occurring zeolite but an artificially synthesized zeolite (synthetic zeolite). Crystallization of the synthetic small pore zeolite proceeds by SDA while directing the crystallization of the zeolite structure.

[0090] The alkali source contained in the raw material composition preferably contains at least a potassium source, and more preferably contains a sodium source and one or more selected from the group consisting of a potassium source, a lithium source, and a cesium source. Since the resulting iron-containing small pore zeolite is less likely to experience a decrease in crystallinity after exposure to a high-temperature, high-humidity atmosphere, the alkali source preferably contains a sodium source and a potassium source, and more preferably contains a sodium source and a potassium source. When the alkali source contains potassium, the crystallinity is less likely to decrease after exposure to a high-temperature, high-humidity atmosphere. Meanwhile, when the alkali source contains sodium, crystallization is further promoted.

[0091] Preferably, the molar ratio of potassium to sodium in the raw material composition (hereinafter also referred to as "K / Na") is greater than 1.0 and is 1.6 or 2.0 or greater, and is preferably 5.0 or less or 4.0 or less, and examples thereof include greater than 1.0 and 5.0 or less, or 1.6 or greater and 4.0 or less.

[0092] 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.

[0093] When a starting material such as an iron source contains an alkali metal element, the starting material may also be considered an alkali source. Similarly, when an iron source contains aluminum, the iron source may also be considered an alumina source.

[0094] The following molar compositions are preferred for the raw material composition: In the following compositions, Alk is an alkali metal, and Alk / SiO2 contains sodium and potassium as alkali metals. ２ is (Na + K) / SiO ２ It can be considered as such.

[0095] SiO ２ / Al ２ O ３ = 10 or more, 15 or more, or 18 or more, 100 or less, 50 or less, or 30 or less, SDA / SiO ２= 0.04 or more, 0.06 or more, or 0.08 or more; 1.0 or less, 0.6 or less, or 0.2 or less; 0.5 or less, 0.3 or less, or 0.1 or less; Alk / SiO ２ = 0.05 or more, 0.1 or more, or 0.15 or more, 1 or less, 0.5 or less, or 0.3 or less, Fe / SiO ２ = 0.005 or more, 0.01 or more, or 0.015 or more, 0.1 or less, 0.07 or less, or 0.05 or less, H ２ O / SiO ２ = 5 or more, 10 or more, or 12 or more, 50 or less, 30 or less, or 18 or less, OH / SiO ２ = 0.1 or more, 0.15 or more, or 0.2 or more, 1.0 or less, 0.5 or less, or 0.3 or less

[0096] Particularly preferred compositions of the raw material composition include the following molar compositions.

[0097] SiO ２ / Al ２ O ３ = 10 or more and 50 or less, preferably 15 or more and 25 or less SDA / SiO ２ = 0.04 or more and 1.0 or less, preferably 0.04 or more and 0.15 or less Alk / SiO ２ = 0.05 or more and 1 or less, preferably 0.1 or more and 0.35 or less Fe / SiO ２ = 0.005 or more and 0.1 or less, preferably 0.01 or more and 0.05 or less H ２ O / SiO ２ = 5 or more and 50 or less, preferably 8 or more and 25 or less OH / SiO ２ = 0.1 or more and 1.0 or less, preferably 0.1 or more and 0.5 or less, where Alk is sodium and potassium.

[0098] In the production of iron-containing CHA-type zeolite, the following molar compositions can be exemplified as preferred compositions of the raw material composition.

[0099] SiO ２ / Al ２ O ３ = 10 or more and 50 or less, preferably 15 or more and 25 or less, more preferably 15 or more and 20 or less SDA / SiO ２ = 0.04 or more and 1.0 or less, preferably 0.04 or more and 0.15 or less, more preferably 0.05 or more and 0.10 or less Alk / SiO ２ = 0.05 or more and 1 or less, preferably 0.1 or more and 0.40 or less, more preferably 0.2 or more and 0.35 or less K / Na = more than 1.0 and 5.0 or less, preferably 1.6 or more and 4.0 or less, more preferably 2.0 or more and 3.8 or less Fe / SiO ２ H = 0.005 or more and 0.1 or less, preferably 0.01 or more and 0.05 or less, more preferably 0.01 or more and 0.03 or less ２ O / SiO ２ OH / SiO = 5 or more and 50 or less, preferably 8 or more and 25 or less, more preferably 12 or more and 20 or less ２ = 0.1 or more and 1.0 or less, preferably 0.1 or more and 0.5 or less, more preferably 0.2 or more and 0.4 or less, wherein Alk is sodium and potassium, and SDA is an N,N,N-trialkylcyclohexylammonium cation.

[0100] In the production of iron-containing AFX zeolite, the following molar compositions can be exemplified as preferred compositions of the raw material composition.

[0101] SiO ２ / Al ２ O ３ = 10 or more and 50 or less, preferably 15 or more and 25 or less, more preferably 20 or more and 25 or less SDA / SiO ２ = 0.04 or more and 1.0 or less, preferably 0.04 or more and 0.15 or less, more preferably 0.04 or more and 0.10 or less Alk / SiO ２ = 0.05 or more and 1 or less, preferably 0.1 or more and 0.3 or less, more preferably 0.15 or more and 0.20 or less K / Na = 0.1 or more and less than 1.0, preferably 0.1 or more and 0.5 or less Fe / SiO ２ H = 0.005 or more and 0.1 or less, preferably 0.01 or more and 0.05 or less, more preferably 0.01 or more and 0.02 or less ２ O / SiO ２ OH / SiO = 5 or more and 50 or less, preferably 8 or more and 25 or less, more preferably 12 or more and 20 or less ２ = 0.1 or more and 1.0 or less, preferably 0.1 or more and 0.5 or less, more preferably 0.1 or more and 0.3 or less, wherein Alk is sodium and potassium, and SDA is a 1,3-di(1-adamantyl)imidazolium cation.

[0102] The raw material composition preferably does not contain fluorine (F) or phosphorus (P) because this facilitates the application of manufacturing equipment made of general-purpose materials. The fluorine content may be 0 ppm by mass or more and 100 ppm by mass or less, and is preferably below the detection limit (10 ppm by mass or less). Similarly, the phosphorus content is preferably 0 ppm by mass or more and 100 ppm by mass or less, and is preferably below the detection limit (0.01 ppm by mass or less).

[0103] The raw material composition may contain seed crystals to promote crystallization. The seed crystals are zeolites for promoting the crystallization of small pore zeolites, and are preferably one or more selected from the group consisting of AEI zeolite, CHA zeolite, OFF zeolite, ERI zeolite, HEU zeolite, MOR zeolite, KFI zeolite, AFX zeolite, AFT zeolite, EAB zeolite, GME zeolite, and LEV zeolite, more preferably one or more selected from the group consisting of CHA zeolite, AEI zeolite, MOR zeolite, and AFX zeolite, and even more preferably at least one of CHA zeolite and AFX zeolite, and even more preferably CHA zeolite.

[0104] The content of the seed crystals may be sufficiently small compared to the content of the silica-alumina source, and the SiO ２ Reduced silicon and Al ２ O ３ SiO of the seed crystal relative to the total converted aluminum ２ Reduced silicon and Al ２ O ３ The converted total mass proportion [mass %] of aluminum is 5 mass % or less, 3 mass % or less, and preferably 0 mass % or more, more than 0 mass %, or 0.1 mass % or more, and examples thereof include 0 mass % or more and 5 mass % or less, more than 0 mass % and 5 mass % or less, or more than 0 mass % and 3 mass % or less.

[0105] In the crystallization step, the raw material composition is crystallized. As a result, the crystallization proceeds while at least a portion of the iron is incorporated into the zeolite structure, and an iron-containing small pore zeolite can be obtained as a crystallized product. The crystallization may be carried out by hydrothermal treatment under conditions that allow the iron-containing small pore zeolite to crystallize. Preferred crystallization conditions include the following:

[0106] Pressure: Autogenous pressure Crystallization temperature: 100°C or higher, 130°C or higher, or 165°C or higher, and 200°C or lower, or 185°C or lower

[0107] The crystallization time may be any time sufficient to sufficiently crystallize the iron-containing small pore zeolite, and may be appropriately set depending on the amount of the raw material composition used for crystallization and the crystallization method. Examples of the crystallization time include 4 hours or more, 24 hours or more, or 48 hours or more, and 150 hours or less, 100 hours or less, or 80 hours or less. To produce the iron-containing small pore zeolite with practical productivity, the crystallization time is preferably 4 hours or more and 150 hours or less, 8 hours or more and 100 hours or less, or 24 hours or more and 48 hours or less.

[0108] In order to allow the crystallization to proceed more uniformly, it is preferable to carry out the crystallization while stirring the raw material composition. The stirring may be performed by directly stirring the raw material composition, or by stirring a container containing the raw material composition.

[0109] The crystallized product (iron-containing small pore zeolite) may be recovered by any method, for example, by solid-liquid separation, washing, drying, and then recovering the product.

[0110] The solid-liquid separation may be any method capable of separating the raw material composition after crystallization into a solid component (crystallized material) and a liquid phase, and examples thereof include one or more methods selected from the group consisting of filtration, decantation, and centrifugation.

[0111] The washing may be carried out by any method that can remove impurities contained in the recovered crystallized product, for example, washing with pure water.

[0112] The drying may be carried out by any method capable of removing moisture physically adsorbed on the crystallized product, for example, by at least one of static drying and spray drying, in an air atmosphere at 100°C or higher and 120°C or lower.

[0113] In order to remove the SDA contained in the iron-containing small pore zeolite (crystallized product after crystallization), the production method of this embodiment preferably includes a step of removing the organic structure-directing agent from the crystallized product (hereinafter also referred to as the "SDA removal step"). In the SDA removal step, any SDA removal method may be used, and examples thereof include one or more methods selected from the group consisting of liquid-phase treatment with an acidic aqueous solution, exchange treatment with a resin, pyrolysis treatment, and calcination treatment. From the viewpoint of production efficiency, the SDA removal step is preferably at least one of pyrolysis treatment and calcination treatment, and calcination treatment is more preferred. Examples of preferred calcination conditions include the following conditions.

[0114] Firing atmosphere: Air atmosphere Firing temperature: 400°C or higher or 560°C or higher, and 700°C or lower or 650°C or lower

[0115] The calcination time may be appropriately set depending on the crystallized material to be calcined and the calcination method, and may be, for example, from 1 hour to 24 hours, from 4 hours to 12 hours, or from 6 hours to 8 hours.

[0116] The production method of this embodiment may include a step of ion-exchanging the iron-containing small pore zeolite (hereinafter also referred to as an "ion-exchanging step") in order to reduce the alkali metal content of the iron-containing small pore zeolite. The ion-exchanging step may be any method that reduces the alkali metal content, and examples of the ion-exchanging step include mixing the iron-containing small pore zeolite with an ammonium chloride aqueous solution.

[0117] If necessary, the iron-containing small pore zeolite after ion exchange may be calcined.

[0118] The production method of this embodiment may include, in addition to or instead of the ion exchange step, a step of mixing the iron-containing small pore zeolite with a metal compound (hereinafter also referred to as a "metal loading step"). This allows any metal element depending on the purpose to be loaded on the iron-containing small pore zeolite.

[0119] The mixing method may be any method that can support the metal compound on the iron-containing small pore zeolite, and may include one or more methods selected from the group consisting of ion exchange, impregnation, evaporation to dryness, precipitation, and physical mixing.

[0120] The present disclosure will be described below with reference to examples. However, the present disclosure is not limited to these examples. The evaluation method and evaluation conditions are shown below. (Crystal Identification) XRD measurement of the sample was performed using a powder X-ray diffractometer (device name: Ultima IV, manufactured by Rigaku Corporation). The measurement conditions are as follows.

[0121] Acceleration current / voltage: 40 mA / 40 kV Radiation source: CuKα radiation (λ=1.5405 Å) Measurement mode: Step scan Scan conditions: 40° / min Measurement time: 3 seconds Measurement range: 2θ=3° to 43° Divergence vertical limiting slit: 10 mm Divergence / entrance slit: 1° Receiving slit: open Receiving solar slit: 5° Detector: Semiconductor detector (D / tex Ultra) Filter: Ni filter

[0122] The obtained XRD pattern was analyzed using analysis software attached to the device (SmartLab Studio II, manufactured by Rigaku Corporation) under the following conditions.

[0123] Fitting conditions: Automatic, background refinement, dispersion-type pseudo-Voigt function (peak shape) Background removal method: Fitting method Kα2 removal method: Kα1 / Kα2 ratio = 0.497

[0124] (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 an ICP apparatus (apparatus name: OPTIMA 5300DV, manufactured by PerkinElmer).

[0125] (Area Ratio) The area ratio was determined by analyzing a UV-VIS spectrum measured under the following conditions using an ultraviolet-visible spectrophotometer (device name: V-770, manufactured by JASCO Corporation).

[0126] Integrating sphere unit: ISN-923 (manufactured by JASCO Corporation) Measurement mode: Diffuse reflectance method Wavelength: 190 to 700 nm Temperature: Room temperature Slit width: 5 nm Background: Barium sulfate Using the analysis software (software name: Fityk ver. 0.9.8) attached to the ultraviolet-visible-near-infrared spectrophotometer, the obtained UV-VIS spectrum was corrected so that the relative reflectance was 1, and then the corrected UV-VIS spectrum was KM converted using the KM function (f(γ∞)) shown below.

[0127] f(γ∞) = (1−γ∞) ２ / 2γ∞ (1) The UV-VIS spectrum after KM conversion was fitted and separated using analysis software (e.g., Fityk 0.9.8) and a Gaussian fitting function, and then the peak areas were determined for the wavelength range of 190 nm to 300 nm, the wavelength range of more than 300 nm to 400 nm, and the wavelength range of more than 400 nm to 600 nm. The sum of these was taken as the peak area for wavelengths of 190 nm to 600 nm, and the area ratio was calculated as the ratio of the peak area for the wavelength range of 190 nm to 300 nm to the peak area for wavelengths of 190 nm to 600 nm.

[0128] (BET specific surface area) The BET specific surface area was determined by analyzing a nitrogen adsorption isotherm obtained under the following measurement conditions using a general BET specific surface area measurement device (for example, BELSORP-mini II, manufactured by Microtrac-Bell) over a relative pressure range of 0.05 to 0.15. <Nitrogen adsorption measurement conditions> Measurement sample: 30 mg Pretreatment: Vacuum atmosphere (≦10 Pa), 350°C, 2 hours Measurement temperature: −196°C Measurement pressure: Equilibrium relative pressure 0.05 to 0.99 (Total pore volume, micropore volume, mesopore volume) The total pore volume was determined from the nitrogen adsorption isotherm obtained in the same manner as in the measurement of the BET specific surface area, using the following formula:

[0129] Total pore volume (cm ３ / g) = V × 1.547 × 10 －３ (3) In the above formula, V is the equilibrium relative pressure in the nitrogen adsorption isotherm (hereinafter referred to as "p / p ０ ") is 0.99. ３ / g].

[0130] The micropore volume was calculated by the t-plot method of the nitrogen adsorption isotherm. ０ The measurement points from 0.6 to 0.8 were approximated to a straight line, and the intercept was taken as the micropore volume. In the t-plot method, the adsorption isotherm of silica was used as the standard isotherm.

[0131] The mesopore volume was calculated from the total pore volume and micropore volume obtained by the above-mentioned method using the following formula.

[0132] Mesopore volume (cm ３ / g) = total pore volume (cm ３ / g) - Micropore volume (cm ３ / g) (4) (IR ｐ２ / IR ｐ１ R) IR ｐ１ and I.R. ｐ２The measurement was carried out using a general FT-IR measurement device (device name: Jasco FT / IR-6100, manufactured by JASCO Corporation) under the following conditions, and calculation was carried out from the IR spectrum obtained by Fourier transform infrared spectrophotometric measurement (FT-IR).

[0133] Measurement sample: 0.01 g Pretreatment: Under vacuum, 450 ° C (product temperature), 1 hour Measurement mode: Continuous scan Measurement temperature: Under vacuum, 150 ° C (product temperature) Measurement range: 350 to 4000 cm －１ Resolution: 2.0cm －１ Number of accumulations: 128 times Zero filling: ON Detector: TGS (Triglycine sulfate) The obtained IR spectrum was subjected to waveform processing using a general analysis software (Spectra Manager Version 2 Version 2.15.11, manufactured by JASCO Corporation). －１ and base end 1950cm －１ , and base start 2500cm －１ and base end 3800 cm －１ After baseline correction of these ranges, 1860 (± 10) cm －１ The height intensity of the peak having a peak top in the range of ｐ１ , 3735 (±10) cm －１ The height intensity of the peak having a peak top in the range of ｐ２ The obtained IR ｐ２ and I.R. ｐ１ From the above, IR is calculated by the following formula: ｐ２ / IR ｐ１ The ratio was calculated.

[0134] IR ｐ２ / IR ｐ１ Ratio = (IR ｐ２ ) / (IR ｐ１ ) (5)

[0135] Example 1 Starting materials were a 35 mass% aqueous solution of cyclohexyldimethylethylammonium hydroxide, a 50 mass% aqueous solution of cyclohexyldimethylethyl bromide, a 48 mass% aqueous solution of sodium hydroxide, a 48 mass% aqueous solution of potassium hydroxide, iron (III) nitrate nonahydrate, pure water, and an amorphous aluminosilicate precursor (SiO ２ / Al ２ O ３ = 17.9) were mixed to obtain a raw material composition having the following molar composition:

[0136] SiO ２ / Al ２ O ３ =17.9 CDMEAOH / SiO ２ =0.02 CDMEABr / SiO ２ =0.06 Alk / SiO ２ =0.300 (Na / SiO ２ =0.075) (K / SiO ２ =0.225) K / Na =3.0 Fe / SiO ２ = 0.025 H ２ O / SiO ２ =18OH / SiO ２ = 0.32 CHA type zeolite (SiO ２ / Al ２ O ３ (=23.8%) was mixed with 55 g of the raw material composition, and then the mixture was filled into an 80 mL sealed container. After filling, the container was rotated at 55 rpm and subjected to hydrothermal treatment at 170°C for 40 hours under autogenous pressure to obtain a crystallized product. The obtained crystallized product was subjected to solid-liquid separation, washed with pure water, and dried at 110°C in an air atmosphere, and then collected. The crystallized product consisted of a single phase of CHA-type zeolite, and SiO ２ / Al ２ O ３ The zeolite was a CHA-type zeolite with a % SiO2 ratio of 18.6.

[0137] Next, the crystallized product was calcined in an air atmosphere at 600°C for 2 hours, and then the calcined crystallized product and NH ４ The crystallized product was mixed with an aqueous ammonium chloride solution having a Cl concentration of 20% by mass at 60°C so that the mass ratio of the crystallized product to the ammonium chloride was 1:1. ４ Replaced. NH ４ The iron content did not change due to the exchange. ４ After the exchange, the mixture was washed with pure water and dried in an air atmosphere at 110°C to obtain the iron-containing CHA-type zeolite of this example.

[0138] The iron-containing CHA-type zeolite of this example is a zeolite consisting of a single phase of CHA-type zeolite, and SiO ２ / Al ２ O ３ The iron-containing CHA-type zeolite of this example had a BET specific surface area of ​​637 m. ２ / g, total pore volume 0.29 cm ３ / g, mesopore volume ratio is 0.17, mesopore volume is 0.05 cm ３ / g, micropore volume is 0.24 cm ３ / g and IR ｐ２ / IR ｐ１ The ratio was 0.37.

[0139] Example 2 An iron-containing CHA-type zeolite of this example was obtained in the same manner as in Example 1, except that a raw material composition having the following molar composition was used.

[0140] SiO ２ / Al ２ O ３ =17.9 CDMEAOH / SiO ２ =0.02 CDMEABr / SiO ２ =0.06 Alk / SiO ２ =0.260 (Na / SiO ２=0.065) (K / SiO ２ =0.195) K / Na =3.0 Fe / SiO ２ = 0.016 H ２ O / SiO ２ =18OH / SiO ２ = 0.28

[0141] The crystallized product consists of a single phase of CHA-type zeolite, and SiO ２ / Al ２ O ３ The iron-containing CHA-type zeolite of this example is a zeolite consisting of a single phase of CHA-type zeolite, and the SiO ２ / Al ２ O ３ The iron-containing CHA-type zeolite of this example had a BET specific surface area of ​​661 m, an Fe / Si ratio of 0.017, an alkali metal content of less than 0.1 mass%, an iron content of 1.4 mass%, an area ratio of 86%, and an isolated iron ion content of 1.2 mass%. ２ / g, total pore volume 0.29 cm ３ / g, mesopore volume ratio is 0.17, mesopore volume is 0.05 cm ３ / g, micropore volume is 0.24 cm ３ / g and IR ｐ２ / IR ｐ１ The ratio was 0.44.

[0142] Furthermore, the UV-VIS spectrum showed a peak having a peak top at a wavelength of 192.5 nm, a peak having a peak top at a wavelength of 213.0 nm, a peak having a peak top at a wavelength of 243.0 nm, and a peak having a peak top at a wavelength of 267.5 nm, confirming that the product contained four types of isolated iron ions in different states.

[0143] Example 3 An iron-containing CHA-type zeolite of this example was obtained in the same manner as in Example 1, except that a raw material composition having the following molar composition was used.

[0144] SiO ２ / Al ２ O ３ =28.7 CDMEAOH / SiO ２ =0.02 CDMEABr / SiO ２ =0.06 Alk / SiO ２ =0.180 (Na / SiO ２ =0.045) (K / SiO ２ =0.135) K / Na =3.0 Fe / SiO ２ = 0.020 H ２ O / SiO ２ =18OH / SiO ２ = 0.20 The crystallized product consists of a single phase of CHA-type zeolite, and SiO ２ / Al ２ O ３ The iron-containing CHA-type zeolite of this example is a zeolite consisting of a single phase of CHA-type zeolite, and the SiO ２ / Al ２ O ３ The iron-containing CHA-type zeolite of this example had a BET specific surface area of ​​654 m. ２ / g, total pore volume 0.31 cm ３ / g, mesopore volume ratio is 0.15, mesopore volume is 0.04 cm ３ / g, micropore volume 0.25 cm ３ / g and IR ｐ２ / IR ｐ１ The ratio was 0.28.

[0145] Furthermore, the UV-VIS spectrum showed a peak having a peak top at a wavelength of 211.5 nm, a peak having a peak top at a wavelength of 247.0 nm, a peak having a peak top at a wavelength of 267.5 nm, and a peak having a peak top at a wavelength of 278.5 nm, confirming that the product contained four types of isolated iron ions in different states.

[0146] Example 4 An iron-containing CHA-type zeolite of this example was obtained in the same manner as in Example 1, except that a raw material composition having the following molar composition was used.

[0147] SiO ２ / Al ２ O ３ =28.7 CDMEAOH / SiO ２ =0.02 CDMEABr / SiO ２ =0.06 Alk / SiO ２ =0.280 (Na / SiO ２ =0.070) (K / SiO ２ =0.210) K / Na =3.0 Fe / SiO ２ = 0.040 H ２ O / SiO ２ =18OH / SiO ２ = 0.30 The crystallized product consists of a single phase of CHA-type zeolite, and SiO ２ / Al ２ O ３ The iron-containing CHA-type zeolite of this example is a zeolite consisting of a single phase of CHA-type zeolite, and the SiO ２ / Al ２ O ３ The iron-containing CHA-type zeolite of this example had a BET specific surface area of ​​663 m2, an alkali metal content of less than 0.1 mass%, an iron content of 2.9 mass%, an area ratio of 84%, and an isolated iron ion content of 2.4 mass%. ２ / g, total pore volume is 0.30 cm３ / g, mesopore volume ratio is 0.12, mesopore volume is 0.03 cm ３ / g, micropore volume is 0.26 cm ３ / g and IR ｐ２ / IR ｐ１ The ratio was 0.26.

[0148] Furthermore, the UV-VIS spectrum showed a peak having a peak top at a wavelength of 212.5 nm, a peak having a peak top at a wavelength of 247.5 nm, a peak having a peak top at a wavelength of 266.5 nm, and a peak having a peak top at a wavelength of 282.5 nm, confirming that the product contained four types of isolated iron ions in different states.

[0149] Comparative Example 1 A crystallized product was obtained in the same manner as in Example 1, except that iron (III) nitrate nonahydrate was not used and that a raw material composition having the following molar composition was used.

[0150] SiO ２ / Al ２ O ３ =19.0 CDMEAOH / SiO ２ =0.02 CDMEABr / SiO ２ =0.06 Alk / SiO ２ =0.16 (Na / SiO ２ =0.04) (K / SiO ２ =0.12) K / Na =3.0H ２ O / SiO ２ =18OH / SiO ２ = 0.18

[0151] The crystallized product was calcined in an air atmosphere at 600°C for 2 hours. After calcination, NH ４ After the exchange, the mixture was washed with pure water and dried in an air atmosphere at 110°C. This resulted in a single phase of CHA-type zeolite and SiO ２ / Al ２ O ３A zeolite (CHA-type zeolite) having a saturation of 19.8 and an alkali metal content of less than 0.1 mass % was obtained.

[0152] 7.0 g of the obtained zeolite, 1.0 g of iron (III) nitrate nonahydrate, and 2.4 g of pure water were mixed in a mortar, and then dried in an air atmosphere at 110°C for 5 hours and calcined in an air atmosphere at 500°C for 2 hours to obtain the iron-containing CHA-type zeolite of this comparative example.

[0153] The iron-containing CHA-type zeolite of this comparative example is a zeolite consisting of a single phase of CHA-type zeolite, and SiO ２ / Al ２ O ３ The iron-containing CHA-type zeolite of this comparative example had a BET specific surface area of ​​742 m2, an alkali metal content of less than 0.1 mass%, an iron content of 2.0 mass%, an area ratio of 36%, and an isolated iron ion content of 0.7 mass%. ２ / g, total pore volume is 0.30 cm ３ / g, mesopore volume ratio is 0.10, mesopore volume is 0.03 cm ３ / g, and a micropore volume of 0.27 cm ３ / g.

[0154] Furthermore, the UV-VIS spectrum showed a peak having a peak top at a wavelength of 192.5 nm, a peak having a peak top at a wavelength of 212.5 nm, and a peak having a peak top at a wavelength of 267.5 nm, confirming that the product contained three types of isolated iron ions in different states.

[0155] Comparative Example 2 An iron-containing CHA-type zeolite of this comparative example was obtained in the same manner as in Example 1, except that a raw material composition having the following molar composition was used.

[0156] SiO ２ / Al ２ O ３ =17.9 CDMEAOH / SiO ２ =0.02 CDMEABr / SiO ２ =0.06 Alk / SiO ２=0.15 (Na / SiO ２ =0.058) (K / SiO ２ =0.173) K / Na =2.98 Fe / SiO ２ = 0.009 H ２ O / SiO ２ =18OH / SiO ２ = 0.25

[0157] The crystallized product consists of a single phase of CHA-type zeolite, and SiO ２ / Al ２ O ３ The iron-containing CHA-type zeolite of this comparative example is a zeolite consisting of a single phase of CHA-type zeolite, and the SiO ２ / Al ２ O ３ The ratio was 19.0, the alkali metal content was less than 0.1% by mass, the iron content was 0.8% by mass, the area percentage was 90%, and the isolated iron ion content was 0.7% by mass.

[0158] Furthermore, the UV-VIS spectrum showed peaks with a peak top at wavelengths of 192.5 nm, 213.0 nm, 245.0 nm, and 267.5 nm, confirming the presence of four different types of isolated iron ions. On the other hand, the area ratio was low, confirming the presence of not only isolated iron ions but also iron clusters and iron oxide particles in large quantities.

[0159] Comparative Example 3: Iron content: Fe / SiO ２The raw material composition was crystallized by a method in accordance with Example 5 of Patent Document 2, except that the δ was set to 0.020. That is, a 25 mass % aqueous solution of trimethyl-1-adamantammonium hydroxide hydroxide, a 48 mass % aqueous solution of sodium hydroxide, colloidal silica (LUDOX AS-40), aluminum hydroxide (manufactured by Sigma-Aldrich), and iron (III) nitrate nonahydrate were added sequentially to pure water, and the resulting mixture was stirred for 15 minutes to obtain a raw material composition having the following molar composition.

[0160] SiO ２ / Al ２ O ３ =20.0 ADAH / SiO ２ =0.20 Alk / SiO ２ =0.20 (Na / SiO ２ =0.20) (K / SiO ２ =0.00) K / Na =0.0 Fe / SiO ２ = 0.020 H ２ O / SiO ２ = 20 The above raw material composition was filled into an 80 mL sealed container. After filling, the container was subjected to a hydrothermal reaction under static conditions at 160°C for 10 days under autogenous pressure to obtain a crystallized product. The obtained crystallized product was recovered after solid-liquid separation, washing with pure water, and drying in an air atmosphere at 100°C. The crystallized product was in an amorphous phase, and CHA-type zeolite was not obtained. This comparative example confirmed that iron-containing CHA zeolite having an iron content of 1.0 mass% or more cannot be easily synthesized by the method for producing iron-containing CHA-type zeolite described in Patent Document 2.

[0161] Comparative Example 4 An iron-containing CHA-type zeolite of this comparative example was obtained in the same manner as in Example 1, except that the 35 mass% cyclohexyldimethylethylammonium hydroxide aqueous solution and the 50 mass% cyclohexyldimethylethyl bromide aqueous solution were changed to a 25 mass% trimethyl-1-adamantammonium hydroxide hydroxide aqueous solution, and that a raw material composition having the following molar composition was used.

[0162] SiO ２ / Al ２ O ３ =17.9 ADAH / SiO ２ =0.08 Alk / SiO ２ =0.24 (Na / SiO ２ =0.24) (K / SiO ２ =0.00) K / Na =0.0 Fe / SiO ２ = 0.025 H ２ O / SiO ２ =18OH / SiO ２ = 0.32 The crystallized product consists of a single phase of CHA-type zeolite, and SiO ２ / Al ２ O ３ The iron-containing CHA-type zeolite of this comparative example is a zeolite consisting of a single phase of CHA-type zeolite, and the SiO ２ / Al ２ O ３ The ratio is 18.4, the alkali metal content is less than 0.1% by mass, the iron content is 2.0% by mass, the area fraction is 84%, the isolated iron ion content is 1.7% by mass, and the IR ｐ２ / IR ｐ１ The ratio was 0.94.

[0163] Furthermore, the UV-VIS spectrum showed peaks with a peak top at wavelengths of 192.5 nm, 213.0 nm, 245.0 nm, and 267.5 nm, confirming the presence of four different types of isolated iron ions. On the other hand, the area ratio was low, confirming the presence of not only isolated iron ions but also iron clusters and iron oxide particles in large quantities.

[0164] The results are shown in the table below, where "-" indicates not measured.

[0165]

[0166] Compared to the iron-containing CHA-type zeolite of Comparative Example 1, the iron-containing CHA-type zeolite of Example 1 exhibited a higher area ratio despite having the same iron content. Furthermore, when comparing Comparative Example 1 and Example 2, which have the same area ratio, it was shown that the iron content of Example 2 was higher. From this, it was confirmed that when the same amount of iron is contained in small pore zeolites, the iron-containing small pore zeolites of the Examples contain iron with high dispersibility. Furthermore, the iron-containing CHA-type zeolites of Examples 1 to 4 have higher IR values ​​than Comparative Example 4. ｐ２ / IR ｐ１ It was confirmed that the ratio was low and the number of silanol defects was small.

[0167] 1 to 4 show the UV-VIS spectra of Examples 1 and 2 and Comparative Examples 1 and 2. In Figures 1 to 4, the solid lines show the measured values, and the dashed lines show the spectra after separation.

[0168] Measurement Example 1 (Evaluation of Nitrogen Oxide Reduction Properties) The nitrogen oxide reduction properties of the zeolites obtained in the Examples and Comparative Examples after hydrothermal durability treatment were evaluated. That is, the iron-containing small pore zeolites of the Examples and Comparative Examples were each molded and pulverized to form agglomerated particles with an agglomerate diameter of 12 to 20 mesh. 3 mL of the obtained agglomerated particles were packed into an atmospheric pressure fixed-bed flow reactor, and then subjected to hydrothermal durability treatment by flowing air containing 20% ​​by volume of moisture through the reactor under the following conditions:

[0169] Air flow rate: 300 mL / min Treatment temperature: 700°C Treatment time: 20 hours

[0170] 1.5 mL of the sample in the form of agglomerated particles was packed into an atmospheric pressure fixed-bed flow reactor, and a nitrogen oxide-containing gas was passed through the reactor while maintaining the temperature at the following measurement temperature, and the nitrogen oxide concentrations at the inlet and outlet of the atmospheric pressure fixed-bed flow reactor were measured.

[0171] Composition of nitrogen oxide-containing gas: NO 200 ppm NH ３ 200ppm O ２ 10% by volume H ２ O 3 volume% N ２ Remainder: Flow rate of nitrogen oxide-containing gas: 1.5 L / min Space velocity: 60,000 hr －１ Measurement temperature: 150℃~500℃

[0172] The nitrogen oxide reduction rate was calculated from the obtained nitrogen oxide concentration using the following formula.

[0173] 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 atmospheric pressure fixed-bed flow-type reactor tube, and [NOx] out is the nitrogen oxide concentration of the nitrogen oxide-containing gas at the outlet of the atmospheric pressure fixed-bed flow-type reactor tube.

[0174] The results are shown in the table below.

[0175]

[0176] From the above table, it was confirmed that, compared to the iron-containing CHA-type zeolite of the comparative examples, the iron-containing CHA-type zeolites of the examples not only had high nitrogen oxide reduction properties at low temperatures below 200°C, but also at high temperatures above 300°C. Furthermore, in the iron-containing CHA-type zeolite of Comparative Example 1 obtained by the post-loading method, the nitrogen oxide reduction rate at 200°C relative to the nitrogen oxide reduction rate at 300°C was reduced to less than 40%, whereas the iron-containing CHA-type zeolites of Examples 1 and 2 were both 45% or higher. This confirmed that the iron-containing CHA-type zeolites of the examples are less likely to experience a decrease in nitrogen oxide reduction rate due to a decrease in the temperature for nitrogen oxide reduction. Comparative Examples 1 and 2 had similar contents of isolated iron ions. However, the iron-containing CHA-type zeolite of Comparative Example 1, which contained a large amount of iron clusters and iron oxide particles, had a lower nitrogen oxide reduction rate across the entire temperature range, from low to high, compared to the iron-containing CHA-type zeolite of Comparative Example 2. Furthermore, the iron-containing CHA-type zeolites of Example 1 and Comparative Example 4 had similar iron contents and isolated iron ion contents. ｐ２ / IR ｐ１ The iron-containing CHA-type zeolite of Comparative Example 1, which had a high ratio, had a lower nitrogen oxide reduction rate than the iron-containing CHA-type zeolite of Example 1 in the entire temperature range from low to high.

[0177] Example 5 1,3-di(1-adamantyl)imidazolium bromide (DAdIBr), 48% by mass aqueous sodium hydroxide solution, 48% by mass aqueous potassium hydroxide solution, iron (III) nitrate nonahydrate, pure water, and an amorphous aluminosilicate precursor (SiO ２ / Al ２ O ３ = 22.0) were mixed to obtain a raw material composition having the following molar composition:

[0178] SiO ２ / Al ２ O ３ =22.0 DAdIBr / SiO ２ =0.05 Alk / SiO ２ =0.16 (Na / SiO ２=0.14) (K / SiO ２ =0.02) K / Na =0.14 Fe / SiO ２ = 0.013 H ２ O / SiO ２ =18OH / SiO ２ = 0.16 CHA type zeolite (SiO ２ / Al ２ O ３ The iron-containing AFX-type zeolite of this example was obtained in the same manner as in Example 1, except that the raw material composition was mixed with 1,000 sachets of ...

[0179] The crystallized product consists of a single phase of AFX-type zeolite, and SiO ２ / Al ２ O ３ The iron-containing AFX zeolite of this example is a zeolite consisting of a single phase of AFX zeolite, and the SiO ２ / Al ２ O ３ The Fe / Si ratio was 23.3, the Fe / Si ratio was 0.014, the alkali metal content was less than 0.1% by mass, the iron content was 1.2% by mass, the area fraction was 83%, the isolated iron ion content was 1.0% by mass, and the IR ｐ２ / IR ｐ１ The ratio was 0.04.

[0180] Furthermore, the UV-VIS spectrum showed a peak having a peak top at a wavelength of 196.5 nm, a peak having a peak top at a wavelength of 219.5 nm, a peak having a peak top at a wavelength of 245.0 nm, and a peak having a peak top at a wavelength of 267.5 nm, confirming that the product contained four types of isolated iron ions in different states.

[0181] Comparative Example 5 A crystallized product was obtained in the same manner as in Example 5, except that iron (III) nitrate nonahydrate was not used and the starting materials were mixed to obtain a raw material composition with the following molar composition.

[0182] SiO ２ / Al２ O ３ =22.0 DAdIBr / SiO ２ =0.05 Alk / SiO ２ =0.15 (Na / SiO ２ =0.13) (K / SiO ２ =0.02) K / Na =0.15H ２ O / SiO ２ =18OH / SiO ２ = 0.15

[0183] The crystallized product was calcined in an air atmosphere at 600°C for 2 hours. After calcination, NH ４ After the exchange, the mixture was washed with pure water and dried in an air atmosphere at 110°C. This resulted in a single phase of AFX-type zeolite, with SiO ２ / Al ２ O ３ A zeolite (AFX type zeolite) having a molecular weight of 23.3 and an alkali metal content of less than 0.1 mass % was obtained.

[0184] 7.0 g of the obtained zeolite, 1.0 g of iron (III) nitrate nonahydrate, and 2.4 g of pure water were mixed in a mortar, and then the mixture was dried in an air atmosphere at 110°C for 5 hours and calcined in an air atmosphere at 500°C for 2 hours, thereby obtaining an iron-containing AFX-type zeolite of this comparative example.

[0185] The iron-containing AFX zeolite of this comparative example is a zeolite consisting of a single phase of AFX zeolite, and SiO ２ / Al ２ O ３ The Fe / Si ratio was 23.3, the Fe / Si ratio was 0.009, the alkali metal content was less than 0.1 mass %, the iron content was 1.4 mass %, the area fraction was 37%, and the isolated iron ion content was 0.5 mass %.

[0186] Furthermore, the UV-VIS spectrum showed a peak having a peak top at a wavelength of 194.0 nm, a peak having a peak top at a wavelength of 224.0 nm, and a peak having a peak top at a wavelength of 267.5 nm, confirming that the product contained three types of isolated iron ions in different states.

[0187] Comparative Example 6: Iron content: Fe / SiO ２ The raw material composition was crystallized by a method similar to Example 5 of Patent Document 2, except that the δ was set to 0.02. That is, 28.4 g of a 25% by mass aqueous solution of trimethyl-1-adamantammonium hydroxide (Tokyo Chemical Industry Co., Ltd.) was mixed with 2.0 g of a 48% by mass aqueous solution of sodium hydroxide. Next, 18.0 g of a silica colloidal suspension in water (40% by mass, LUDOX-AS, Sigma-Aldrich) and 0.6 g of aluminum oxide (Sigma-Aldrich) were added, and the resulting mixture was maintained under stirring for 15 minutes. Finally, 0.969 g of iron(III) nitrate nonahydrate (Fe(NO ３ ) ３ ・9H ２ SiO (Sigma-Aldrich, 98%) was added, and the synthesis mixture was kept under stirring for 15 minutes with the addition of water until the desired gel concentration was reached. The final gel composition was SiO ２ : 0.05Al ２ O ３ :0.02Fe:0.2TMAdaOH:0.2NaOH:20H ２ The gel was then filled into a stainless steel autoclave with a Teflon liner. Crystallization was then carried out at 160°C for 10 days under static conditions. The solid product was filtered, washed with a large amount of water, and dried at 100°C.

[0188] The obtained solid product was amorphous, and no XRD peaks attributable to the CHA structure were observed in its XRD pattern.

[0189] From this comparative example, it was confirmed that when the amount of iron was increased under the production conditions of Patent Document 2, the iron-containing CHA-type zeolite could not be crystallized.

[0190] The results are shown in the table below.

[0191]

[0192] Although Example 5 had a lower content of isolated iron ions than Comparative Example 5, the area ratio was more than twice as high. This confirmed that the iron-containing AFX zeolite of this example also contained iron in a more highly dispersed state, similar to the iron-containing CHA zeolite. ｐ２ / IR ｐ１ The ratio was found to be low.

[0193] 5 and 6 show the UV-VIS spectra of Example 5 and Comparative Example 5, respectively. In Figures 5 and 6, the solid lines show the measured values, and the dashed lines show the spectra after separation.

[0194] Furthermore, it was confirmed from FIG. 7 that the iron-containing AFX-type zeolite of Example 5 was essentially composed of agglomerated particles formed by agglomeration of crystalline particles having a primary particle size of 0.3 μm or more and 5.0 μm or less.

[0195] Measurement Example 2 (Evaluation of Nitrogen Oxide Reduction Properties) The nitrogen oxide reduction properties after the hydrothermal durability treatment of Example 5 and Comparative Example 5 were evaluated in the same manner as in Measurement Example 1. The results are shown in the table below.

[0196]

[0197] As with the iron-containing CHA-type zeolite, it was confirmed that the iron-containing AFX-type zeolite of Example 5 had higher nitrogen oxide reduction properties at low temperatures than the iron-containing AFX-type zeolite obtained by the post-loading method (iron-loaded AFX-type zeolite), and in particular, the nitrogen oxide reduction rates at both 150°C and 200°C were more than twice as high as those of Comparative Example 5. Furthermore, the nitrogen oxide reduction rate at 200°C relative to the nitrogen oxide reduction rate at 300°C decreased to 40% in Example 5, while it was less than 30% in both Comparative Example 5, confirming that the iron-containing FAX-type zeolite of the Examples is less susceptible to a decrease in the nitrogen oxide reduction rate due to a decrease in the reaction temperature for nitrogen oxide reduction.

[0198] Measurement Example 3 (Changes in nitrogen oxide reduction properties before and after hydrothermal durability treatment) The nitrogen oxide reduction properties of the examples were evaluated in the same manner as in Measurement Example 1, except that no hydrothermal durability treatment was performed and the measurement temperature was 150°C or 200°C.

[0199] The results are shown in the table below together with the nitrogen oxide reduction rate after hydrothermal durability treatment.

[0200]

[0201] It was confirmed that in all Examples, the hydrothermal durability treatment improved the nitrogen oxide reduction rate at both 150° C. and 200° C. From this, it can be expected that the iron-containing small pore zeolites of the Examples not only have the effect of having excellent nitrogen oxide reduction properties, but also have a long life when used as nitrogen oxide reduction catalysts.

[0202] The entire contents of the specification, claims and abstract of Japanese Patent Application No. 2024-004515, filed on January 16, 2024, are hereby incorporated by reference as the disclosure of the specification of the present disclosure.

Claims

1. An iron-containing microporous zeolite having an iron content of 1.0% by mass or more, wherein the ratio of the height intensity of the peak having a peak top at 3735 ± 10 cm －１ to the height intensity of the peak having a peak top at 1860 ± 10 cm in the IR spectrum is 0.50 or less, and in its UV-VIS spectrum, the ratio of the peak area at wavelengths of 190 to 300 nm to the peak area at wavelengths of 190 to 600 nm is 60% or more. －１ ​ 2. The iron-containing microporous zeolite according to claim 1, having a BET specific surface area of 530 m ２ / g or more.

3. The iron-containing microporous zeolite according to claim 1 or 2, wherein the content of isolated iron ions is 0.8% by mass or more.

4. The iron-containing microporous zeolite according to any one of claims 1 to 3, wherein the volume of mesopores relative to the total volume of mesopores and micropores is 0.40 or less.

5. The total volume of mesopores and micropores is 0.15 cm ３ / g or more, and the iron-containing microporous zeolite according to any one of claims 1 to 4.

6. The iron-containing microporous zeolite according to any one of claims 1 to 5, wherein the molar ratio of silica to alumina is 10 or more.

7. The iron-containing microporous zeolite according to any one of claims 1 to 6, wherein the microporous zeolite is a zeolite having one or more structures selected from the group consisting of AEI, CHA, LEV, MWW, ERI, and AFX.

8. The iron-containing microporous zeolite according to any one of claims 1 to 7, wherein the microporous zeolite is a CHA-type zeolite or an AFX-type zeolite.

9. The iron-containing microporous zeolite according to any one of claims 1 to 8, wherein the nitrogen oxide reduction rate under the following nitrogen oxide reduction conditions after exposure treatment to a high-temperature and high-humidity atmosphere under the following exposure conditions is 20% or more. <Exposure conditions> Atmosphere: Air with a moisture content of 20% by volume Flow rate: 300 mL / min Treatment temperature: 700 °C Treatment time: 20 hours <Nitrogen oxide reduction conditions> Composition of nitrogen oxide-containing gas: NO 200 ppm ３ NH 200 ppm ２ O 10% by volume ２ H 2 O 3% by volume ２ Balance Flow rate of nitrogen oxide-containing gas: 1.5 L / min Space velocity: 60,000 hr －１ Measurement temperature: 200 °C 10. A step of crystallizing a composition containing a silica-alumina source, an iron source, an organic structure-directing agent, an alkali source and water, wherein the composition has a ratio of iron to silicon in terms of SiO ２ converted silicon exceeding 0.01 and contains two or more kinds of alkali sources. The method for producing an iron-containing small-pore zeolite according to any one of claims 1 to 9.

11. The production method according to claim 10, wherein the composition does not contain zeolite as a silica-alumina source.

12. The production method according to claim 10 or 11, wherein the alkali source contains at least a potassium source.

13. A catalyst comprising the iron-containing microporous zeolite according to any one of claims 1 to 9.

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