Iron-containing small pore zeolite

Abstract

To provide at least one of an iron-containing small pore zeolite having high nitrogen oxide reduction characteristics at low temperature even after being exposed to a high-temperature high-humidity atmosphere with a water content exceeding 10 volume% compared to conventional iron-containing small pore zeolites, a method for producing the same, and a nitrogen oxide reduction catalyst comprising the same.SOLUTION: An iron-containing small pore zeolite has an iron content of 1.0 mass% or more, wherein a ratio of height intensity of a peak having a peak top at 3735±10 cm-1 to height intensity of a peak having a peak top at 1860±10 cm-1 in an IR spectrum is 0.50 or less, and a proportion of a peak area at wavelength 190 to 300 nm to a peak area at wavelength 190 to 600 nm in a UV-VIS spectrum thereof is 60% or more.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] Compared with large-pore zeolites such as BEA-type zeolites, small-pore zeolites such as CHA-type zeolites are less likely to have reduced crystallinity after exposure to a high-temperature and high-humidity atmosphere. Therefore, small-pore zeolites can be applied to uses where it is difficult to apply large-pore zeolites, such as uses involving exposure to a high-temperature and high-humidity atmosphere with a high water content, and small-pore zeolites containing iron or copper as an active metal (metal-containing small-pore zeolites) are widely used as nitrogen oxide reduction catalysts.

[0003] Compared with small-pore zeolites containing iron, small-pore zeolites containing copper are less likely to have reduced crystallinity even after exposure to a high-temperature and high-humidity atmosphere. In addition to this, they have high nitrogen oxide reduction characteristics at low temperatures. On the other hand, in the reduction reaction of nitrogen oxides by small-pore zeolites containing copper, by-production of nitrous oxide (N2O) occurs. Therefore, small-pore zeolites containing iron and improvement of their nitrogen oxide reduction characteristics have been studied as nitrogen oxide reduction catalysts in which by-production of N2O is suppressed.

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

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] The iron-containing microporous zeolite disclosed in Patent Document 1 is said not to have its nitrogen oxide reduction characteristics deteriorated even after being exposed to a high-temperature and high-humidity atmosphere with a low water content. However, when it is exposed to a high-temperature and high-humidity atmosphere with a high water content, its nitrogen oxide reduction characteristics are significantly deteriorated. Further, the iron-containing microporous zeolite of Patent Document 2 showed a significant deterioration in nitrogen oxide reduction characteristics after being exposed to a high-temperature and high-humidity atmosphere with a water content of 10% by volume.

[0007] An object of the present disclosure is to provide at least one of an iron-containing microporous zeolite having high nitrogen oxide reduction characteristics at low temperatures even after being exposed to a high-temperature and high-humidity atmosphere with a water content exceeding 10% by volume, a method for producing the same, and a nitrogen oxide reduction catalyst containing the same, as compared with conventional iron-containing microporous zeolites.

Means for Solving the Problems

[0008] In the present disclosure, regarding the nitrogen oxide reduction characteristics of the iron-containing microporous zeolite, we focused on the state of iron contained in the microporous zeolite and conducted an investigation. As a result, it was found that the state of iron in the microporous zeolite has a greater influence on the nitrogen oxide reduction characteristics than the molar ratio of silica to alumina (SiO2 / Al2O3 ratio). As a result of further investigation, it was found that an iron-containing microporous zeolite containing a certain amount or more of iron and having specific IR spectra and UV-VIS spectra has higher nitrogen oxide reduction characteristics, particularly at low temperatures, after being exposed to a harsh high-temperature and high-quality atmosphere with a water content exceeding 10% by volume, as compared with conventional iron-supported microporous zeolites.

[0009] That is, the present invention is as described in the claims, and the gist of the present disclosure is as follows. [1] The iron content is 1.0% by mass or more, and 1860 ± 10 cm in the IR spectrum-1 The height intensity of the peak having a peak top to 3735 ± 10 cm -1 The ratio of the height intensity of the peak having a peak top to -1 is 0.50 or less, and in the UV-VIS spectrum thereof, the ratio of the peak area of wavelengths 190 to 300 nm to the peak area of wavelengths 190 to 600 nm is 60% or more. An iron-containing small pore zeolite. [2] The BET specific surface area is 530 m 2 / g or more, the iron-containing small pore zeolite according to [1] above. [3] The content of isolated iron ions is 0.8 mass% or more, the iron-containing small pore zeolite according to [1] or [2] above. [4] The volume of mesopores with respect to the total volume of mesopores and micropores is 0.40 or less, the iron-containing small pore zeolite according to any one of [1] to [3] above. [5] The total volume of mesopores and micropores is 0.15 cm 3 / g or more, the iron-containing small pore zeolite according to any one of [1] to [4] above. [6] The molar ratio of silica to alumina is 10 or more, the iron-containing small pore zeolite according to any one of [1] to [5] above. [7] The small pore zeolite is a zeolite having one or more structures selected from the group of AEI, CHA, LEV, MWW, ERI, and AFX, the iron-containing small pore zeolite according to any one of [1] to [6] above. [8] The small pore zeolite is a CHA type zeolite or an AFX type zeolite, the iron-containing small pore zeolite according to any one of [1] to [7] above. [9] 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, the iron-containing small pore zeolite according to any one of [1] to [8] above. <Exposure conditions> Atmosphere: Air with a moisture content of 20% by volume Flow rate: 300 mL / min Treatment temperature: 700 °C Processing time: 20 hours <Nitrogen oxide reduction conditions> Composition of nitrogen oxide-containing gas: NO 200 ppm NH3 200 ppm O2 10 vol% H2O 3 vol% N2 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 SiO2 exceeding 0.01 and contains two or more kinds of alkali sources, and the method for producing an iron-containing small-pore zeolite according to any one of [1] to [9] above.

[11] The production method according to

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

[12] The production method according to

[10] or

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

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

[0010] According to the present disclosure, there can be provided at least one of an iron-containing small-pore zeolite having high nitrogen oxide reduction characteristics at low temperatures even after being exposed to a high-temperature and high-humidity atmosphere with a water content exceeding 10 vol%, a method for producing the same, and a nitrogen oxide reduction catalyst containing the same, as compared with conventional iron-containing small-pore zeolites. [Brief Description of the Drawings]

[0011]

Figure 1

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Figure 9

Figure 10

Mode for Carrying Out the Invention

[0012] Hereinafter, an example of an embodiment of the present disclosure will be shown and described.

[0013] "Zeolite" is a compound in which framework atoms (hereinafter also referred to as "T atoms") have a regular structure via oxygen (O), and the T atoms are composed of at least one of a metal atom and a metalloid atom. The metal atom includes one or more selected from the group consisting of aluminum (Al), titanium (Ti), iron (Fe), zinc (Zn), gallium (Ga), and tin (Sn), and at least one of aluminum and iron is preferable, and aluminum is more preferable. The metalloid atom includes one or more selected from the group consisting of boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), and tellurium (Te), and silicon is preferable.

[0014] "Small-pore zeolite" is a zeolite in which the largest pore formed in the zeolite structure is a pore (oxygen 8-membered ring pore) formed by a cyclic structure composed of 8 oxygen atoms and a T atom.

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

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

[0017] The "zeolite-like substance" is a compound in which the T atom has a regular structure via oxygen, and is a compound containing at least an atom other than a metal and a semi-metal in the T atom (hereinafter also referred to as a "non-metal atom"). Phosphorus (P) can be exemplified as the non-metal atom. As zeolite-like substances, composite phosphorus compounds containing phosphorus (P) as the T atom, such as aluminophosphate (AlPO) and silicoaluminophosphate (SAPO), can be exemplified. For the sake of clarity, the zeolite in the present embodiment does not include zeolite-like substances.

[0018] The "regular structure (hereinafter also referred to as the "zeolite structure")" in zeolites and zeolite-like substances is a framework structure specified by the structure code (hereinafter also simply referred to as the "structure code") determined by the Structure Commission of the International Zeolite Association. For example, the CHA structure is a framework structure specified as the structure code "CHA". The identification of the zeolite structure can be performed by comparing with the XRD pattern (hereinafter also referred to as the "reference pattern") described in CHA of Zeolite Framework Types on the homepage of the IZA Structure Commission at http: / / www.iza-struture.org / databases / . In the present embodiment, the zeolite structure, framework structure, crystal structure, or crystal phase are used synonymously.

[0019] In this embodiment, "zeolite of the CHA type" and other "zeolites of the ~ type" mean zeolites having the zeolite structure of the corresponding structure code.

[0020] "Aluminosilicate" is a composite oxide having a structure composed of a network of aluminum (Al) and silicon (Si) via oxygen (O). Among aluminosilicates, those having crystalline XRD peaks in their powder X-ray diffraction (hereinafter also referred to as "XRD") patterns are "crystalline aluminosilicates", and those not having crystalline XRD peaks are "amorphous aluminosilicates".

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

[0022] Accelerating current and voltage: 40 mA · 40 kV X-ray source: CuKα ray (λ = 1.5405 Å) Measurement mode: step scan Scan condition: 40° / min Measurement time: 3 s Measurement range: 2θ = 3° to 43° Divergence vertical limit slit: 10 mm Divergence / incidence 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 (for example, UltimaIV Protectus, manufactured by Rigaku Corporation). Also, the crystalline XRD peak is a peak in which the 2θ at the peak top is specified and detected in the analysis of the XRD pattern using general analysis software (for example, SmartLab StudioII, manufactured by Rigaku Corporation), and in particular, it is an XRD peak having a half-value width of 2θ = 0.50° or less.

[0024] As the analysis conditions of the XRD pattern, the following conditions can be mentioned.

[0025] Fitting condition: Automatic, refine the background Dispersed 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 is an iron-containing small-pore zeolite in which the iron content is 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 having such an iron content and area ratio, it is considered that the iron-containing small-pore zeolite of this embodiment is in a more active state, particularly a state with high catalytic activity. As a result, even after being exposed to a high-temperature and high-humidity atmosphere with a water content exceeding 10% by volume, it becomes an iron-containing small-pore zeolite with high nitrogen oxide reduction characteristics at low temperatures compared to conventional iron-containing small-pore zeolites.

[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, zeolites having one or more structures selected from the group of AEI, CHA, LEV, MWW, ERI, KFI, and AFX containing iron, further zeolites having one or more structures selected from the group of AEI, CHA, LEV, ERI, and AFX containing iron, and still further zeolites having one or more structures selected from the group of AEI, CHA, and AFX containing iron can be mentioned. The iron-containing small-pore zeolite of this embodiment is preferably a zeolite having at least one of the CHA and AFX structures containing iron, and more preferably a zeolite having a CHA structure or an AFX structure containing iron. As specific small-pore zeolites, one or more selected from the group of AEI-type zeolite, CHA-type zeolite, LEV-type zeolite, MWW-type zeolite, ERI-type zeolite, and AFX-type zeolite, further one or more selected from the group of AEI-type zeolite, CHA-type zeolite, LEV-type zeolite, ERI-type zeolite, and AFX-type zeolite, and still further one or more selected from the group of AEI-type zeolite, CHA-type zeolite, and AFX-type zeolite can be mentioned. At least one of the CHA-type zeolite and the AFX-type zeolite is preferable, and it is more preferably a CHA-type zeolite or an AFX-type zeolite. From the viewpoint of hydrothermal stability, the AFX-type zeolite is preferable, and from the viewpoint of industrial production, the CHA-type zeolite is preferable. 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, respectively.

[0028] The iron contained in the iron-containing small-pore zeolite of this embodiment functions as an active metal. By containing iron, it exhibits the ability to reduce nitrogen oxides. The iron is iron ions (Fe 3+ ), iron clusters (Fe x O y) and is considered to be included as at least one of the iron species of iron oxide particles (Fe2O3). Since iron ions are considered 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 the present embodiment may be contained by substituting the zeolite structure, and preferably at least a part of it is substituted for the zeolite structure (skeletal structure) of the iron-containing small-pore zeolite. That is, the iron-containing small-pore zeolite of the present embodiment is preferably an iron-containing small-pore zeolite (iron-substituted small-pore zeolite) in which at least part of the iron is substituted for the zeolite skeleton, and may be an iron-containing small-pore zeolite in which iron is substituted for the zeolite skeleton and supported. Compared with an iron-containing small-pore zeolite (iron-supported small-pore zeolite) containing iron only by being supported, the degree of decrease in the nitrogen oxide reduction rate when the reaction temperature of nitrogen oxide reduction decreases is likely to be suppressed.

[0030] Also, the iron species contained in the iron-containing small-pore zeolite is considered to be substantially unable to be selectively removed. Therefore, for example, in an iron-containing small-pore zeolite containing iron ions, iron clusters, and iron oxide particles, it is not possible to remove only the iron clusters and iron oxide particles and leave only iron ions. Also, specific techniques for selectively obtaining iron species are not known.

[0031] The iron content of the iron-containing microporous zeolite of this embodiment is 1.0 mass% or more, preferably 1.1 mass% or more, 1.15 mass% or more, or 1.3 mass% or more. When the iron content is less than 1.0 mass%, even when the iron content and the area ratio described later are both satisfied, the nitrogen oxide reduction characteristics at low temperatures remain at the same level as those of conventional iron-containing microporous zeolites. The iron content may be an amount that allows efficient progress of nitrogen oxide reduction, and examples thereof include 3.0 mass% or less, 2.5 mass% or less, 2.3 mass% or less, or 2.0 mass% or less. Preferably, it has the area ratio described later, and the iron content is 1.0 mass% or more and 3.0 mass% or less, 1.1 mass% or more and 2.5 mass% or less, 1.15 mass% or more and 2.3 mass% or less, or 1.3 mass% or more and 2.0 mass% or less.

[0032] The "iron content" in this embodiment is the mass ratio [mass%] of iron (Fe) to the mass of the iron-containing microporous zeolite. Also, the mass of the iron-containing microporous zeolite is the total mass of aluminum in terms of Al2O3, silicon in terms of SiO2, and iron (Fe) contained in the iron-containing microporous zeolite.

[0033] The iron content of the iron-containing microporous zeolite of this embodiment only needs to satisfy the above values. Also, as the ratio of iron to silica (hereinafter, also referred to as "Fe / Si ratio") [mol / mol] of the iron-containing microporous zeolite of this embodiment, it is 0.003 or more, 0.005 or more, or 0.010 or more, and preferably 0.050 or less, 0.040 or less, or 0.030 or less. Examples thereof include 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] The iron-containing microporous zeolite of the present embodiment has, in its UV-VIS spectrum, a 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 of 40% or more, preferably 60% or more, 70% or more, or 80% or more. The peaks in the UV-VIS spectrum can, if necessary after peak separation, confirm the state (iron species) of iron at the position (wavelength) of the peak, and can also confirm the relative amount of iron species from the peak area. On the other hand, the peak height of the peaks in the UV-VIS spectrum is considered to have no technical meaning as an index of the state and content of iron. When the area ratio is less than 40%, even when the iron content is high, the nitrogen oxide reduction characteristics at low temperatures, particularly at low temperatures of 200°C or lower, are low, and it shows only the same level of nitrogen oxide reduction characteristics as conventional iron-containing microporous zeolites. The area ratio is preferably high but 100% or less, less than 100%, 90% or less, or less than 90%, and it is preferably 40% or more and 100% or less, 60% or more and less than 100%, 70% or more and 90% or less, or 80% or more and 90% or less. Since it is likely to exhibit practical nitrogen oxide reduction characteristics, the iron-containing microporous zeolite of the present embodiment contains iron at the above-mentioned iron content and, in addition, preferably has an area ratio of 40% or more and 100% or less, 60% or more and less than 100%, 70% or more and 90% or less, or 80% or more and 90% or less.

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

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

[0037] The analysis of the UV-VIS spectrum was carried out using the analysis software (e.g., Fityk ver.0.9.8) attached to the ultraviolet-visible-near-infrared spectrophotometer. After peak separation under the following conditions, the peak area in the wavelength range of 190 nm to 600 nm and the peak area in the wavelength range of 190 to 300 nm were determined, and the area ratio was obtained from the ratio thereof. That is, the obtained UV-VIS spectrum was corrected so that the reflectance of the iron-containing microporous zeolite of the present embodiment with respect to the reflectance of barium sulfate at a wavelength of 700 nm (hereinafter also referred to as "γ∞" or "relative reflectance") became 1. Thereafter, the corrected UV-VIS spectrum may be subjected to KM (Kubelka-Munk) conversion by the KM function (f(γ∞)) of the following formula.

[0038] f(γ∞) = (1 - γ∞) 2 / 2γ∞ (1)

[0039] After the UV-VIS spectrum after KM conversion is fitted and waveform-separated using general analysis software (e.g., Fityk 0.9.8) and the Gaussian function for the fitting function, the area of the peak included in the wavelength range of 190 nm or more and 300 nm or less, the area of the peak included in the wavelength range of more than 300 nm and 400 nm or less, and the area of the peak included in the wavelength range of more than 400 nm and 600 nm or less are determined, and the peak areas in the respective wavelength ranges may be obtained. Also, the total of the peak areas in the entire wavelength range may be set as the peak area (total area) in the wavelength range of 190 nm or more and 600 nm or less. The area ratio of each wavelength range may be obtained from the ratio of the peak area of each wavelength range to the peak area (total area) in the wavelength range of 190 nm or more and 600 nm or less obtained. Note that the area of the peak in each wavelength range may be obtained by determining 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 with a wavelength range of 280 to 310 nm and a peak top of 290 nm, the area from 280 nm to 300 nm may be set as the area of the peak included in the wavelength range of 190 nm or more and 300 nm or less, and the area exceeding 300 nm and 310 nm or less may be set as the area of the peak included in the wavelength range of more than 300 nm and 400 nm or less.

[0040] By having such iron content and area ratio, one of the reasons why the nitrogen oxide reduction characteristics, particularly the nitrogen oxide reduction characteristics at low temperatures, are higher than those of conventional iron-containing small-pore zeolites is that, compared with conventional iron-containing small-pore zeolites, there are more highly dispersed iron species, and moreover, the stability of the iron in that state is higher. That is, the peak at a wavelength of 190 to 300 nm in the UV-VIS spectrum is considered to correspond to iron ions in a state called so-called isolated iron ions. By having the above-mentioned iron content and area ratio, the iron-containing small-pore zeolite of the present embodiment not only has a simply high iron content, but also the ratio of iron in a state that can contribute to the reduction of nitrogen oxides at low temperatures in the contained iron is considered to be higher than that of conventional iron-containing small-pore zeolites. The iron-containing small-pore zeolite of the present embodiment preferably has a high ratio of isolated iron ions in the iron-containing CHA-type zeolite, but the isolated iron ion content is preferably 0.8 mass% or more, 1.0 mass% or more, or 1.3 mass% or more. The higher the isolated iron ion content, the more preferable it is, and it is preferable that all iron is isolated ions, but the isolated iron ion content may be 3.0 mass% or less, 2.0 mass% or less, or 1.5 mass% or less, and examples include 0.8 mass% or more and 3.0 mass% or less, 1.0 mass% or more and 2.0 mass% or less, or 1.3 mass% or more and 2.0 mass% or less.

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

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

[0043] The iron-containing small-pore zeolite of the present embodiment may contain isolated iron ions in different states, and particularly preferably contains four types of isolated iron ions in different states. By containing isolated iron ions in such a state, after exposure to a high-temperature and high-humidity atmosphere, the nitrogen oxide reduction characteristics at low temperatures are likely to be higher than before the exposure.

[0044] The state of isolated iron ions can be confirmed by separating the peaks at wavelengths of 190 to 300 nm in the UV-VIS spectrum by the above method, and the state of isolated iron ions can be confirmed by the number of peaks having peak tops between wavelengths of 190 to 300 nm. For example, when there are two peaks having peak tops between wavelengths of 190 to 300 nm, it can be considered that two types of isolated iron ions with different states are contained. Also, when there are four peaks having peak tops between wavelengths of 190 to 300 nm, it can be considered that four types of isolated iron ions with different states are contained. The iron-containing microporous zeolite of the present embodiment preferably has three or more peaks having peak tops in the range of wavelengths of 190 to 300 nm in the UV-VIS spectrum, more preferably has four or more peaks having peak tops in the range of wavelengths of 190 to 300 nm in the UV-VIS spectrum, and even more preferably has four peaks having peak tops in the range of wavelengths of 190 to 300 nm in the UV-VIS spectrum. Specifically, in the UV-VIS spectrum, it preferably 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 microporous zeolite of the present embodiment may contain an alkali metal (that is, the content of the alkali metal may be more than 0% by mass). However, the lower the content of the alkali metal, the more easily the decrease in the nitrogen oxide characteristics at low temperatures due to exposure to a high-temperature and high-humidity atmosphere is suppressed. Therefore, the content of the alkali metal is preferably 1.0% by mass or less, 0.5% by mass or less, or 0.1% by mass or less, and more preferably substantially does not contain an alkali metal (that is, is below the detection limit (0% by mass)). Examples of the alkali metal content of the iron-containing microporous zeolite of the present 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 containing an alkali metal, as the alkali metal contained in the iron-containing small-pore zeolite of the present embodiment, 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, still further at least any one of sodium and potassium, and still further sodium or potassium can be mentioned.

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

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

[0049] Since the collapse of the zeolite structure is likely to be suppressed after exposure to a high-temperature and high-humidity atmosphere, the iron-containing small-pore zeolite of the present embodiment preferably has a molar ratio of silica to alumina (molar ratio of silicon in terms of SiO2 to aluminum in terms of Al2O3; hereinafter, also referred to as "SiO2 / Al2O3 ratio") of 10.0 or more, 15.5 or more, or 16.5 or more. The SiO2 / Al2O3 ratio may be 50.0 or less, 30.0 or less, 24.5 or less, or 20.0 or less. Since it is likely to have heat resistance suitable as a nitrogen oxide reduction catalyst, examples of the SiO2 / Al2O3 ratio include 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 (when it is a CHA-type zeolite), preferable SiO2 / Al2O3 ratios include 15.5 or more and 24.5 or less, or 16.5 or more and 19.5 or less. Also, when the small-pore zeolite is a zeolite containing an AFX structure (when it is an AFX-type zeolite), preferable SiO2 / Al2O3 ratios include 15.5 or more and 30.0 or less, or 20.0 or more and 24.5 or less.

[0050] In the present embodiment, the SiO2 / Al2O3 ratio may be determined as the molar ratio of silicon in terms of SiO2 to aluminum in terms of Al2O3 from the contents of aluminum (Al) and silicon (Si) in the iron-containing small-pore zeolite of the present embodiment by inductively coupled plasma atomic emission spectrometry (ICP-AES) using a general high-frequency inductively coupled plasma apparatus (for example, OPTIMA5300DV, manufactured by PerkinElmer).

[0051] Since the aggregation of iron is more likely to be suppressed in exposure to a high-temperature and high-humidity atmosphere, the BET specific surface area of the iron-containing small-pore zeolite of the present embodiment is 530 m 2 / g or more, 550 m 2 / g or more, 600 m 2 / g or more, or 620 m 2 / g or more, which is preferable. The BET specific surface area does not need to be higher than necessary, and is 850 m 2 / g or less, 800 m 2750 m or less 2 700 m or less 2 It can be exemplified that it is 530 m 2 / g or more and 850 m 2 / g or less, 550 m 2 / g or more and 850 m 2 / g or less, 600 m 2 / g or more and 800 m 2 / g or less, or 620 m 2 / g or more and 700 m 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). It can be obtained by using a general BET specific surface area measuring device (for example, BELSOR P-miniII, manufactured by MicrotracBEL Corporation) and analyzing the range of relative pressure from 0.05 to 0.15 in the nitrogen adsorption isotherm. <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 from 0.05 to 0.99

[0053] Since the decrease in crystallinity after exposure to a high-temperature and high-humidity atmosphere is less likely to occur, for the iron-containing microporous zeolite of this embodiment, the volume of mesopores with respect to the total volume of mesopores and micropores (hereinafter, also referred to as "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 examples include 0 or more and 0.40 or less, or more than 0.10 and 0.20 or less.

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

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

[0056] Total pore volume (cm 3 / g) = V × 1.547 × 10 -3 (3) In the above formula, V is the adsorption amount [cm 3 / g] when the equilibrium relative pressure (hereinafter also referred to as "p / p0") in the nitrogen adsorption isotherm is 0.99.

[0057] If the above-mentioned mesopore volume ratio and total pore volume are satisfied, the volume of mesopores and the volume of micropores may be arbitrary. As the volume of mesopores, 0.15 cm 3 / g or less or 0.10 cm 3 / g or less, and also 0.01 cm 3 / g or more or 0.03 cm 3 / g or more can be exemplified. Also, as the volume of micropores, 0.10 cm 3 / g or more or 0.15 cm 3above / g and also 0.30 cm 3 / g or less or 0.25 cm 3 / g or less, and 0.10 cm 3 / g or more and 0.30 cm 3 / g or less, or 0.15 cm 3 / g or more and 0.25 cm 3 / g or less is preferable.

[0058] The micropore volume in this embodiment is a value calculated by the t-plot method of the nitrogen adsorption isotherm. The measurement points with an average relative pressure (p / p0) of 0.6 to 0.8 may be linearly approximated, and the intercept may be taken as the micropore volume. In the t-plot method, the adsorption isotherm of silica may be used as the standard isotherm.

[0059] Also, the mesopore volume may be obtained from the following formula using the total pore volume and the micropore volume obtained by the above method.

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

[0061] Since the collapse of the zeolite structure due to exposure to a high-temperature and high-humidity atmosphere is suppressed, 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 it can be exemplified as 0.3 μm or more and 10.0 μm or less, or 0.5 μm or more and 5.0 μm or less. The primary particle diameter in this embodiment is the size (crystal grain size) of the crystal particles of the iron-containing small-pore zeolite, and is the size (longest diameter) of the smallest unit of crystal particles observed as independent particles by scanning electron microscope observation under the following conditions. In this embodiment, the primary particles do not include aggregate particles (aggregates) in which crystal particles are physically aggregated.

[0062] Accelerating voltage: 10 kV Magnification for measurement: 5000 times.

[0063] The iron-containing small-pore zeolite of this embodiment may contain aggregated particles in which crystal particles are aggregated. Further, the iron-containing small-pore zeolite of this embodiment may be mainly composed of primary particles having a size of 0.3 μm or more and 10.0 μm or less, and may be essentially composed of aggregated particles in which primary particles having a size of 0.3 μm or more and 10.0 μm or less are aggregated. Furthermore, the iron-containing small-pore zeolite may be essentially composed of primary particles having a size of 0.3 μm or more, and may contain primary particles having a size of less than 0.3 μm as long as the handleability (operability) is not deteriorated.

[0064] The shape of the iron-containing small-pore zeolite of this embodiment may be any shape according to the intended purpose, and examples thereof include powder and molded body. Powder is suitable for coating on a substrate such as a honeycomb. The iron-containing small-pore zeolite of this embodiment has, in its IR spectrum, a peak height intensity (hereinafter also referred to as "IR -1 ") of a peak having a peak top at 1860 ± 10 cm p1 with respect to the peak height intensity (hereinafter also referred to as "IR -1 ") of a peak having a peak top at 3735 ± 10 cm p2 " ratio (hereinafter also referred to as "IR p2 / IR p1 ratio") of 0.50 or less. IR P1 and IR P2 are considered to be the peak heights of IR peaks attributed to the skeletal vibration and silanol defects of the iron-containing zeolite, respectively, and the IR p2 / IR p1 ratio can be used as an index of the amount of silanol defects in the iron-containing zeolite. A small IR p2 / IR p1 ratio is considered to correspond to a small amount of silanol defects. The IR p2 / IR p1When 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. IR p2 / IR p1 The ratio is preferably 0.50 or less, 0.49 or less, or 0.48 or less, and also preferably 0.00 or more, more than 0.00, 0.01 or more, or 0.02 or more. IR 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. IR p1 and IR p2 The measurement of and IR can be calculated from the IR spectrum obtained by Fourier transform infrared spectrophotometry (FT-IR) performed under the following conditions using a general FT-IR measuring device (for example, device name: Jasco FT / IR-6100, manufactured by JASCO Corporation). Measurement sample: 0.01 g Pretreatment: Under vacuum, 450 °C (sample temperature), 1 hour Measurement mode: Continuous scan Measurement temperature: Under vacuum, 150 °C (sample temperature) Measurement range: 350 - 4000 cm -1 Resolution: 2.0 cm -1 Number of accumulations: 128 times Zero filling: ON Detector: TGS (Triglycine sulfate) The obtained IR spectrum may be waveform-processed with general analysis software (for example, Spectra Mnager Version 2 Version 2.15.11, manufactured by JASCO Corporation). That is, with the base start at 1750 cm -1 and the base end at 1950 cm -1 , and also with the base start at 2500 cm -1 and the base end at 3800 cm -1 , after baseline correction of these ranges, the height intensity of the peak having a peak top in the range of 1860 ± 10 cm -1 is IR p1, 3735 ± 10 cm -1 The height intensity of the peak having a peak top within the range of p2 may be made IR p2 and IR p1 From the obtained IR p2 / IR p1 The ratio may be determined. IR p2 / IR p1 Ratio = (IR p2 ) / (IR p1 ) (5)

[0065] The iron-containing small-pore zeolite of the present embodiment preferably has high nitrogen oxide reduction characteristics after exposure treatment in a high-temperature and high-humidity atmosphere. After exposure treatment in a high-temperature and high-humidity atmosphere according to the following exposure conditions (hereinafter also referred to as "hydrothermal durability treatment"), the nitrogen oxide reduction rate under the following nitrogen oxide reduction conditions 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 NH3 200 ppm O2 10% by volume H2O 3% by volume N2 balance Flow rate of nitrogen oxide-containing gas: 1.5 L / min Space velocity: 60,000 hr -1 Measurement temperature: 200 °C

[0066] The iron-containing small-pore zeolite of the present embodiment can be used for known uses of small-pore zeolites such as adsorbents, catalysts, and carriers thereof, and preferably can be used as a catalyst containing the same, particularly as a nitrogen oxide reduction catalyst.

[0067] When used as a nitrogen oxide reduction catalyst, it can be exemplified as a nitrogen oxide reduction catalyst having a structure in which the iron-containing small-pore zeolite of the present embodiment is coated on a substrate. Further, the iron-containing small-pore zeolite of the present embodiment can be used as a nitrogen oxide reduction device provided with the same, and further as a nitrogen oxide reduction system provided with the same.

[0068] 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 in which one or more selected from the group of framework structure, composition, and iron content are different, or as a zeolite composition containing the iron-containing small-pore zeolite of the present embodiment and other metal-containing zeolites. Furthermore, it may be used as a zeolite composition containing the iron-containing small-pore zeolite of the present embodiment and a small-pore zeolite containing no metal.

[0069] [Method for producing iron-containing small-pore zeolite] A preferred method for producing the iron-containing small-pore zeolite of the present 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, wherein the composition has a ratio of iron to silicon in terms of SiO2 of more than 0.01 and contains two or more kinds of alkali sources. A method for producing an iron-containing small-pore zeolite can be mentioned.

[0070] As a method for producing an iron-containing small-pore zeolite, conventionally, a method of treating a small-pore zeolite with an iron compound (hereinafter also referred to as the "post-treatment method") and a method of crystallizing a small-pore zeolite in the presence of an iron compound (hereinafter also referred to as the "crystallization method") are known. In the post-treatment method, it is contained in the small-pore zeolite by loading, and so-called iron-supported small-pore zeolite is obtained. In the post-treatment method, while an iron-containing small-pore zeolite with a high iron content can be obtained, a large amount of iron in a low-active state is contained in the small-pore zeolite. Therefore, in the post-treatment method, even when iron in a highly active state is contained, iron in a low-active state is further contained. As a result, an iron-containing small-pore zeolite with high activity, and further an iron-containing small-pore zeolite with high nitrogen oxide reduction characteristics at a low temperature of 200°C or lower cannot be obtained. Compared with the post-treatment method, the crystallization method can obtain an iron-containing small-pore zeolite containing iron in a relatively highly active state. However, in the conventional crystallization method, when the iron content is increased, the crystallization of the small-pore zeolite does not substantially proceed. For example, in Patent Document 2, a production method for crystallization with a molar ratio of iron to silica (Fe / SiO2) of 0.001 to 0.2 is disclosed to some extent. However, in the production method specifically disclosed in Patent Document 2, Fe / SiO2 is only at one point of 0.01, and a specific production method for an iron-containing small-pore zeolite with Fe / SiO2 exceeding 0.01 is not disclosed. On the contrary, Patent Document 2 does not even suggest the conditions necessary for crystallizing an iron-containing small-pore zeolite with Fe / SiO2 exceeding 0.01. Furthermore, as will be described later, in the production method of Patent Document 2, when a composition with Fe / SiO2 exceeding 0.01 is crystallized, an iron-containing small-pore zeolite cannot be obtained. On the other hand, in the production method of the present embodiment, by using the above-described composition, it is considered that the iron source is less likely to aggregate during crystallization, and crystallization proceeds while maintaining high dispersibility. As a result, it is possible to produce an iron-containing small-pore zeolite that contains more iron in a highly active state compared to the iron-containing small-pore zeolite obtained by the post-treatment method and has a higher iron content compared to the iron-containing small-pore zeolite obtained by the conventional crystallization method.

[0071] The manufacturing method of this embodiment has 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 "raw material composition") (hereinafter, also referred to as "crystallization step").

[0072] 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 aluminosilicate, and it is preferably included at least amorphous aluminosilicate.

[0073] For the crystallization of small-pore zeolite, a method of crystallizing zeolite from an amorphous compound and a method of decomposing zeolite into building units and reconstituting them to crystallize the target zeolite (so-called conversion method) are known. In the conversion method, usually, zeolite is used as a starting material. For example, in the production of CHA-type zeolite, FAU-type zeolite is used, and in the production of AEI-type zeolite, FER-type zeolite is used. However, since zeolite is more expensive than amorphous compound, the conversion method tends to have a high production cost. Furthermore, compared with the zeolite obtained by the conversion method, the small-pore zeolite obtained from the amorphous compound is considered to have a stronger framework, and as a result, the collapse of the framework structure after exposure to a high-humidity atmosphere is less likely to occur. 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-type zeolite, and even more preferably does not contain FAU-type zeolite and FER-type zeolite.

[0074] The iron source is an iron-containing compound, and any iron compound that can be uniformly dispersed in the raw material composition is acceptable. Since the dispersibility in the raw material composition is higher, the iron source is preferably a water-soluble iron compound. Specific iron compounds include one or more selected from the group consisting of iron nitrate, iron sulfate, iron oxide, iron chloride, iron oxyhydroxide, and iron hydroxide, further one or more selected from the group consisting of iron hydroxide, iron sulfate, and iron nitrate, still further at least either iron sulfate or iron nitrate, and still further iron sulfate.

[0075] The organic structure-directing agent source includes compounds of organic structure-directing agents (hereinafter also referred to as "SDA") that can direct small-pore zeolites, and further quaternary ammonium salts that can direct small-pore zeolites.

[0076] As the SDA that directs iron-containing AEI-type zeolite, for example, 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 1,1-dimethyl-3,5-dimethylpiperidinium cation can be mentioned.

[0077] As the SDA that directs iron-containing CHA-type zeolite, N,N,N-trialkylcyclohexylammonium cation is preferred. Examples of N,N,N-trialkylcyclohexylammonium cation include one or more selected from the group consisting of N,N,N-methyldiethylcyclohexylammonium cation, N,N,N-dimethylethylcyclohexylammonium cation, and N,N,N-trimethylcyclohexylammonium cation.

[0078] As the SDA that directs iron-containing AFX-type zeolite, for example, 1,4-diazabicyclo[2.2.2]-octane-C4-diquat dibromide cation can be mentioned.

[0079] The SDA source may be two or more types of SDA that direct towards small-pore zeolite, and may be two or more and five or less types, further two or more and three or less types, or even two types of SDA that direct towards small-pore zeolite. When the SDA source is two or more types of SDA that direct towards small-pore zeolite, for example, the SDA source may be a salt of SDA that directs towards CHA-type zeolite and a salt of SDA that directs towards AFX-type zeolite, further two or more different salts of SDA that direct towards CHA-type zeolite, or even two or more different salts of SDA that direct towards CHA-type zeolite.

[0080] When producing an iron-containing CHA-type zeolite, the raw material composition contains an N,N,N-trialkylcyclohexylammonium cation as the SDA. Among them, it is preferably one or more selected from the group 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. More preferably, it is at least one of the CMDEA cation and the CDMEA cation, and even more preferably, it is the CDMEA cation. By the raw material composition containing these SDAs in addition to two types of alkali sources, it is considered that crystallization can be promoted while suppressing the aggregation of the iron source and the generation of silanol defects in the zeolite structure. As a result, it is considered that an iron-containing CHA-type zeolite with a low IR p2 / IR p1 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 the N,N,N-trialkylcyclohexylammonium cation. On the other hand, as long as the CHA-type zeolite crystallizes mainly due to the structure-directing action of the N,N,N-trialkylcyclohexylammonium cation, other SDAs may be included.

[0081] The SDA source may be at least any one of salts and compounds containing SDA, and one or more selected from the group consisting of hydroxides, halides other than fluorides, monoester carbonates and monosulfate esters containing SDA, further 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, and further may contain at least bromide. It is particularly preferable that the SDA source contains hydroxide and bromide, whereby the yield of the iron-containing microporous zeolite tends to be high. The raw material composition may contain, as the SDA source, two or more selected from the group consisting of hydroxides, chlorides, bromides and iodides containing the same SDA, two or more selected from the group consisting of hydroxides, bromides and iodides, further at least bromide, and further hydroxide and bromide.

[0082] The alkali source is a compound containing an alkali metal element, a compound containing one or more selected from the group consisting of sodium, potassium, rubidium and cesium, further a compound containing one or more selected from the group consisting of sodium, potassium and cesium, further a compound containing at least any one of sodium and potassium, further a compound containing sodium or potassium, and further a compound containing potassium.

[0083] The alkali source may be exemplified by one or more selected from the group consisting of hydroxides, fluorides, bromides, iodides, sulfates, nitrates and carbonates containing the above-mentioned alkali metal element, one or more selected from the group consisting of hydroxides, bromides and iodides, or hydroxide (hereinafter, the alkali source containing sodium is also referred to as "sodium source", the alkali source containing potassium is also referred to as "potassium source", etc.).

[0084] The raw material composition contains two or more alkali sources and contains 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 microporous zeolite of the present embodiment is not a naturally occurring zeolite but an artificially synthesized zeolite (synthetic zeolite). The synthetic microporous zeolite crystallizes while its zeolite structure is directed by the SDA.

[0085] 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 of a potassium source, a lithium source, and a cesium source. Since the resulting iron-containing microporous zeolite is less likely to have a decrease in crystallinity after exposure to a high-temperature and high-humidity atmosphere, the alkali source preferably contains a sodium source and a potassium source, and more preferably is a sodium source and a potassium source. When the alkali source contains potassium, a decrease in crystallinity after exposure to a high-temperature and high-humidity atmosphere is less likely to occur. On the other hand, when the alkali source contains sodium, crystallization is more promoted.

[0086] Preferably, the molar ratio of potassium to sodium in the raw material composition (hereinafter also referred to as "K / Na") exceeds 1.0, is 1.6 or 2.0 or more, and is preferably 5.0 or less or 4.0 or less, and examples include exceeding 1.0 and being 5.0 or less, or being 1.6 or more and 4.0 or less.

[0087] Water may be regarded as the water in the raw material composition, including not only pure water and ion-exchanged water but also water contained in other starting materials such as structural water, hydrated water, and solvents.

[0088] In addition, when starting materials such as an iron source contain an alkali metal element, these starting materials may also be regarded as an alkali source. Similarly, when an iron source or the like contains aluminum, the iron source is also regarded as an alumina source.

[0089] Preferred compositions of the starting composition include the following molar compositions. In the following compositions, Alk is an alkali metal, and when the alkali metal includes sodium and potassium, Alk / SiO2 may be regarded as (Na + K) / SiO2.

[0090] SiO2 / Al2O3 = 10 or more, 15 or more, or 18 or more, 100 or less, 50 or less, or 30 or less, SDA / SiO2 = 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 / SiO2 = 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 / SiO2 = 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, H2O / SiO2 = 5 or more, 10 or more, or 12 or more, 50 or less, 30 or less, or 18 or less, OH / SiO2 = 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

[0091] Particularly preferred compositions of the starting composition include the following molar compositions.

[0092] SiO2 / Al2O3 = 10 or more and 50 or less, preferably 15 or more and 25 or less SDA / SiO2 = 0.04 or more and 1.0 or less preferably 0.04 or more and 0.15 or less Alk / SiO2 = 0.05 or more and 1 or less preferably 0.1 or more and 0.35 or less Fe / SiO2 = 0.005 or more and 0.1 or less preferably 0.01 or more and 0.05 or less H2O / SiO2 = 5 or more and 50 or less Preferably 8 or more and 25 or less OH / SiO2 = 0.1 or more and 1.0 or less Preferably 0.1 or more and 0.5 or less However, Alk is sodium and potassium.

[0093] In the production of an iron-containing CHA-type zeolite, the following molar compositions can be exemplified as the composition of a preferred raw material composition.

[0094] SiO2 / Al2O3 = 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 / SiO2 = 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 / SiO2 = 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 > 1.0 and ≤ 5.0 Preferably 1.6 or more and 4.0 or less More preferably 2.0 or more and 3.8 or less Fe / SiO2 = 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 H2O / SiO2 = 5 or more and 50 or less Preferably 8 or more and 25 or less More preferably 12 or more and 20 or less OH / SiO2 = 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 However, Alk is sodium and potassium, and SDA is an N,N,N-trialkylcyclohexylammonium cation.

[0095] In the production of iron-containing AFX-type zeolite, the following molar compositions can be exemplified as the composition of a preferred raw material composition.

[0096] SiO2 / Al2O3 = 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 / SiO2 = 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 / SiO2 = 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 / SiO2 = 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 H2O / SiO2 = 5 or more and 50 or less preferably 8 or more and 25 or less more preferably 12 or more and 20 or less OH / SiO2 = 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 However, Alk is sodium and potassium, and SDA is 1,3-di(1-adamantyl)imidazolium cation.

[0097] Since manufacturing equipment composed of general-purpose materials is more likely to be applicable, the raw material composition preferably does not contain fluorine (F) and phosphorus (P). The fluorine content may be 0 mass ppm or more and 100 mass ppm or less, but more preferably it is below the detection limit (10 mass ppm or less). Similarly, the phosphorus content is preferably 0 mass ppm or more and 100 mass ppm or less, and more preferably it is below the detection limit (0.01 mass ppm or less).

[0098] For promoting crystallization, the raw material composition may contain seed crystals. The seed crystals are zeolites for promoting the crystallization of small-pore zeolites, and are one or more selected from the group consisting of AEI-type zeolite, CHA-type zeolite, OFF-type zeolite, ERI-type zeolite, HEU-type zeolite, MOR-type zeolite, KFI-type zeolite, AFX-type zeolite, AFT-type zeolite, EAB-type zeolite, GME-type zeolite and LEV-type zeolite, and further preferably one or more selected from the group consisting of CHA-type zeolite, AEI-type zeolite, MOR-type zeolite, and AFX-type zeolite, and still further preferably at least one of CHA-type zeolite and AFX-type zeolite, and still further preferably CHA-type zeolite.

[0099] The content of the seed crystals only needs to be sufficiently small compared to the content of the silica-alumina source. The mass ratio [mass%] of the total of silicon in terms of SiO2 and aluminum in terms of Al2O3 of the seed crystals to the total of silicon in terms of SiO2 and aluminum in terms of Al2O3 of the raw material composition (excluding seed crystals) is 5 mass% or less, 3 mass% or less, and preferably 0 mass% or more, more than 0 mass%, 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.

[0100] In the crystallization step, the raw material composition is crystallized. Thereby, crystallization proceeds while at least a part of 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, and may be carried out under conditions under which the iron-containing small-pore zeolite crystallizes. Preferred crystallization conditions include the following conditions. 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

[0101] The crystallization time may be any time as long as the iron-containing microporous zeolite is sufficiently crystallized, and may be appropriately set according to the amount of the raw material composition to be subjected to 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. In order to produce the iron-containing microporous 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.

[0102] In order for crystallization to proceed more uniformly, it is preferable that the crystallization is carried out with the raw material composition being stirred. The stirring may be directly performed on the raw material composition, or the container containing the raw material composition may be stirred.

[0103] The crystallized product (iron-containing microporous zeolite) of crystallization may be recovered by any method. For example, solid-liquid separation, washing, and drying, and then recovering it may be mentioned.

[0104] The solid-liquid separation may be any method that can separate the raw material composition after crystallization into a solid component (crystallized product) and a liquid phase. For example, one or more selected from the group consisting of filtration, decantation, and centrifugation may be mentioned.

[0105] The washing may be any method that can remove impurities contained in the recovered crystallized product. For example, pure water washing may be sufficient.

[0106] The drying may be any method that can remove the moisture physically adsorbed on the crystallized product. For example, at least one of static drying and spray drying may be mentioned, and it may be dried in an air atmosphere at 100°C or more and 120°C or less.

[0107] In order to remove the SDA contained in the iron-containing microporous 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, the SDA removal method is arbitrary, and examples thereof include one or more 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, at least either pyrolysis treatment or calcination treatment is preferable for the SDA removal step, and calcination treatment is more preferable. As preferable calcination conditions, the following conditions can be exemplified. Calcination atmosphere: air atmosphere Calcination temperature: 400 °C or higher or 560 °C or higher, and 700 °C or lower or 650 °C or lower

[0108] The calcination time may be appropriately set according to the crystallized product to be calcined and the calcination method. For example, it may be 1 hour or more and 24 hours or less, 4 hours or more and 12 hours or less, or 6 hours or more and 8 hours or less.

[0109] The production method of this embodiment may have a step of ion-exchanging the iron-containing microporous zeolite (hereinafter also referred to as the "ion exchange step") in order to reduce the alkali metal content of the iron-containing microporous zeolite. Ion exchange may be any method as long as the alkali metal content is reduced. For example, the iron-containing microporous zeolite may be mixed with an aqueous ammonium chloride solution for ion exchange.

[0110] If necessary, the iron-containing microporous zeolite after ion exchange may be calcined.

[0111] The production method of this embodiment may have a step of mixing the iron-containing microporous zeolite and a metal compound (hereinafter also referred to as the "metal loading step") in addition to or instead of the ion exchange step. Thereby, any metal element according to the purpose can be loaded on the iron-containing microporous zeolite.

[0112] The hybrid method may be any method in which a metal compound can be supported on an iron-containing microporous zeolite, and examples include one or more selected from the group consisting of an ion exchange method, an impregnation loading method, an evaporation to dryness method, a precipitation loading method, and a physical mixing method.

Examples

[0113] Hereinafter, the present disclosure will be described by way of examples. However, the present disclosure is not limited to these examples. The evaluation methods and evaluation conditions are shown below. (Identification of crystals) Using a powder X-ray diffractometer (device name: UltimaIV, manufactured by Rigaku Corporation), XRD measurement of the sample was performed. The measurement conditions are as follows. Accelerating current and voltage: 40 mA·40 kV X-ray source: CuKα ray (λ = 1.5405 Å) Measurement mode: Step scan Scan condition: 40° / min Measurement time: 3 seconds Measurement range: 2θ = 3° to 43° Divergent vertical limiting slit: 10 mm Divergent / incident slit: 1° Receiving slit: open Receiving solar slit: 5° Detector: Semiconductor detector (D / teX Ultra) Filter: Ni filter

[0114] Using the obtained XRD pattern and the attached analysis software (SmartLab StudioII, manufactured by Rigaku Corporation), analysis was performed under the following conditions. Fitting condition: Automatic, refine background Dispersed pseudo-Voigt function (peak shape) Background removal method: Fitting method Kα2 removal method: Kα1 / Kα2 ratio = 0.497

[0115] (Composition analysis) A sample solution was prepared by dissolving a sample in a mixed aqueous solution of hydrofluoric acid and nitric acid. Using an ICP device (device name: OPTIMA5300DV, manufactured by PerkinElmer), the sample solution was measured by inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0116] (Area ratio) The area ratio was determined by analyzing the UV-VIS spectrum measured under the following conditions using an ultraviolet-visible spectrophotometer (device name: V-770, manufactured by JASCO Corporation). Integrating sphere unit: ISN-923 (manufactured by JASCO Corporation) Measurement mode: Diffuse reflection method Wavelength: 190 - 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, after correcting the obtained UV-VIS spectrum so that the relative reflectance becomes 1, the corrected UV-VIS spectrum was subjected to KM conversion using the following KM function (f(γ∞)). f(γ∞) = (1 - γ∞) 2 / 2γ∞ (1) After fitting and waveform separation of the UV-VIS spectrum after KM conversion using analysis software (for example, Fityk 0.9.8) and using Gaussian as the fitting function, the peak areas in the wavelength ranges of 190 nm or more and 300 nm or less, 300 nm or more and 400 nm or less, and 400 nm or more and 600 nm or less were determined. The sum of these was taken as the peak area from 190 nm to 600 nm, and the area ratio was determined from the ratio of the peak area in the wavelength range of 190 nm or more and 300 nm or less to the peak area from 190 nm to 600 nm.

[0117] (BET specific surface area) The BET specific surface area was determined by analyzing the range of relative pressure from 0.05 to 0.15 in the nitrogen adsorption isotherm obtained under the following measurement conditions using a general BET specific surface area measuring device (for example, BELSORP-miniII, manufactured by MicrotracBEL). <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 from 0.05 to 0.99 (Total pore volume, micropore volume, mesopore volume) The total pore volume was determined from the nitrogen adsorption isotherm obtained by the same method as the measurement of the BET specific surface area, using the following formula.

[0118] Total pore volume (cm 3 / g) = V × 1.547 × 10 -3 (3) In the above formula, V is the adsorption amount [cm 3 / g] when the equilibrium relative pressure (hereinafter also referred to as "p / p0") in the nitrogen adsorption isotherm is 0.99.

[0119] The micropore volume was calculated by the t-plot method of the nitrogen adsorption isotherm. That is, the measurement points with an average relative pressure (p / p0) of 0.6 to 0.8 were linearly approximated, 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.

[0120] The mesopore volume was determined from the following formula using the total pore volume and micropore volume obtained by the above method. Mesopore volume (cm 3 / g) = Total pore volume (cm 3 / g) - Micropore volume (cm 3 / g) (4)(IR p2 / IR p1 ratio) IR p1 and IR p2The measurement was calculated from the IR spectrum obtained by Fourier transform infrared spectrophotometry (FT-IR) using a general FT-IR measuring device (device name: Jasco FT / IR-6100, manufactured by JASCO Corporation) under the following conditions. Measurement sample: 0.01 g Pretreatment: Under vacuum, 450 °C (sample temperature), 1 hour Measurement mode: Continuous scan Measurement temperature: Under vacuum, 150 °C (sample temperature) Measurement range: 350 - 4000 cm -1 Resolution: 2.0 cm -1 Number of accumulations: 128 times Zero filling: ON Detector: TGS (Triglycine sulfate) The obtained IR spectrum was waveform-processed with general analysis software (Spectra Mnager Version 2 Version 2.15.11, manufactured by JASCO Corporation). That is, the base start was set to 1750 cm -1 and the base end was set to 1950 cm -1 , and also the base start was set to 2500 cm -1 and the base end was set to 3800 cm -1 , and after baseline correction of these ranges, the height intensity of the peak having a peak top in the range of 1860 (±10) cm -1 was defined as IR p1 , and the height intensity of the peak having a peak top in the range of 3735 (±10) cm -1 was defined as IR p2 . From the obtained IR p2 and IR p1 , the IR p2 / IR p1 ratio was determined by the following formula. IR p2 / IR p1 Ratio = (IR p2 ) / (IR p1 ) (5)

[0121] Example 1 As starting materials, an aqueous solution of 35% by mass cyclohexyldimethylethylammonium hydroxide, an aqueous solution of 50% by mass cyclohexyldimethylethyl bromide, an aqueous solution of 48% by mass sodium hydroxide, an aqueous solution of 48% by mass potassium hydroxide, iron(III) nitrate nonahydrate, pure water, and an amorphous aluminosilicate precursor (SiO2 / Al2O3 = 17.9) were mixed to obtain a raw material composition having the following molar composition. SiO2 / Al2O3 = 17.9 CDMEAOH / SiO2 = 0.02 CDMEABr / SiO2 = 0.06 Alk / SiO2 = 0.300 (Na / SiO2 = 0.075) (K / SiO2 = 0.225) K / Na = 3.0 Fe / SiO2 = 0.025 H2O / SiO2 = 18 OH / SiO2 = 0.32 CHA-type zeolite (SiO2 / Al2O3 = 23.8)% was mixed with 55 g of the raw material composition so that the seed crystal content became 2% by mass, and then this was filled into a sealed container with a volume of 80 mL. After filling, the container was reacted by hydrothermal treatment at 170 °C for 40 hours and under autogenous pressure while rotating at 55 rpm 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 110 °C. The crystallized product consisted of a single phase of CHA-type zeolite and was a zeolite (CHA-type zeolite) having an SiO2 / Al2O3 ratio of 18.6.

[0122] Next, the crystallized product was calcined in an air atmosphere at 600 °C for 2 hours, and then the calcined crystallized product and an aqueous ammonium chloride solution having an NH4Cl concentration of 20% by mass were mixed at 60 °C so that the mass ratio of the crystallized product to ammonium chloride was crystallized product:ammonium chloride = 1:1, thereby performing NH4 exchange on the iron-containing CHA-type zeolite. There was no change in the iron content due to NH4 exchange. After NH4 exchange, washing with pure water and drying in an air atmosphere at 110 °C gave the iron-containing CHA-type zeolite of this example.

[0123] The iron-containing CHA zeolite of this example is a zeolite composed of a single phase of CHA zeolite, with an SiO2 / Al2O3 ratio of 18.6, an alkali metal content of less than 0.1% by mass, an iron content of 2.1% by mass, an area ratio of 79%, and an isolated iron ion content of 1.7% by mass. Also, the iron-containing CHA zeolite of this example has a BET specific surface area of 637 m 2 / g, a total pore volume of 0.29 cm 3 / g, a mesopore volume ratio of 0.17, a mesopore volume of 0.05 cm 3 / g, a micropore volume of 0.24 cm 3 / g, and an IR p2 / IR p1 ratio of 0.37.

[0124] Example 2 The iron-containing CHA 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. SiO2 / Al2O3 = 17.9 CDMEAOH / SiO2 = 0.02 CDMEABr / SiO2 = 0.06 Alk / SiO2 = 0.260 (Na / SiO2 = 0.065) (K / SiO2 = 0.195) K / Na = 3.0 Fe / SiO2 = 0.016 H2O / SiO2 = 18 OH / SiO2 = 0.28

[0125] The crystallized product is a zeolite (CHA zeolite) composed of a single phase of CHA zeolite with an SiO2 / Al2O3 ratio of 18.9. Also, the iron-containing CHA zeolite of this example is a zeolite composed of a single phase of CHA zeolite, with an SiO2 / Al2O3 ratio of 18.9, an Fe / Si ratio of 0.017, an alkali metal content of less than 0.1% by mass, an iron content of 1.4% by mass, an area ratio of 86%, and an isolated iron ion content of 1.2% by mass. Also, the iron-containing CHA zeolite of this example has a BET specific surface area of 661 m2 / g, the total pore volume is 0.29 cm 3 / g, the mesopore volume ratio is 0.17, the volume of mesopores is 0.05 cm 3 / g, the volume of micropores is 0.24 cm 3 / g, and the IR p2 / IR p1 ratio was 0.44.

[0126] Also, in the UV-VIS spectrum, there are peaks with peak tops at wavelengths of 192.5 nm, 213.0 nm, 243.0 nm, and 267.5 nm, and it was confirmed that it contains four types of isolated iron ions in different states. Example 3 The 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. SiO2 / Al2O3 = 28.7 CDMEAOH / SiO2 = 0.02 CDMEABr / SiO2 = 0.06 Alk / SiO2 = 0.180 (Na / SiO2 = 0.045) (K / SiO2 = 0.135) K / Na = 3.0 Fe / SiO2 = 0.020 H2O / SiO2 = 18 OH / SiO2 = 0.20 The crystallized product consists of a single phase of CHA-type zeolite, which is a zeolite with an SiO2 / Al2O3 ratio of 30.8 (CHA-type zeolite). Also, the iron-containing CHA-type zeolite of this example is a zeolite consisting of a single phase of CHA-type zeolite, with an SiO2 / Al2O3 ratio of 30.8, an alkali metal content of less than 0.1 mass%, an iron content of 1.5 mass%, an area ratio of 85%, and an isolated iron ion content of 1.3 mass%. Also, the iron-containing CHA-type zeolite of this example has a BET specific surface area of 654 m 2 / g, the total pore volume is 0.31 cm 3 / g, the mesopore volume fraction is 0.15, the volume of mesopores is 0.04 cm 3 / g, the volume of micropores is 0.25 cm 3 / g, and the IR p2 / IR p1 ratio was 0.28. Also, in the UV-VIS spectrum, it has peaks with peak tops at wavelengths of 211.5 nm, 247.0 nm, 267.5 nm, and 278.5 nm, and it was confirmed that it contains four types of isolated iron ions in different states. Example 4 The 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. SiO2 / Al2O3 = 28.7 CDMEAOH / SiO2 = 0.02 CDMEABr / SiO2 = 0.06 Alk / SiO2 = 0.280 (Na / SiO2 = 0.070) (K / SiO2 = 0.210) K / Na = 3.0 Fe / SiO2 = 0.040 H2O / SiO2 = 18 OH / SiO2 = 0.30 The crystallized product consists of a single phase of CHA-type zeolite, which is a zeolite with an SiO2 / Al2O3 ratio of 30.7 (CHA-type zeolite). Also, the iron-containing CHA-type zeolite of this example is a zeolite consisting of a single phase of CHA-type zeolite, with an SiO2 / Al2O3 ratio of 30.7, an alkali metal content of less than 0.1% by mass, an iron content of 2.9% by mass, an area ratio of 84%, and an isolated iron ion content of 2.4% by mass. Also, the iron-containing CHA-type zeolite of this example has a BET specific surface area of 663 m 2 / g, the total pore volume is 0.30 cm 3 / g, the mesopore volume fraction is 0.12, the volume of mesopores is 0.03 cm 3 / g, the volume of micropores is 0.26 cm 3 / g and IR p2 / IR p1 The ratio was 0.26. In addition, in the UV-VIS spectrum, there were peaks having peak tops at wavelengths of 212.5 nm, 247.5 nm, 266.5 nm, and 282.5 nm, and it was confirmed that four types of isolated iron ions in different states were contained.

[0127] 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 a raw material composition having the following molar composition was used. SiO2 / Al2O3 = 19.0 CDMEAOH / SiO2 = 0.02 CDMEABr / SiO2 = 0.06 Alk / SiO2 = 0.16 (Na / SiO2 = 0.04) (K / SiO2 = 0.12) K / Na = 3.0 H2O / SiO2 = 18 OH / SiO2 = 0.18

[0128] The crystallized product was calcined in an air atmosphere at 600 °C for 2 hours. After calcination, after NH4 exchange in the same manner as in Example 1, it was washed with pure water and dried in an air atmosphere at 110 °C to obtain a zeolite (CHA-type zeolite) consisting of a single phase of CHA-type zeolite, having SiO2 / Al2O3 of 19.8 and an alkali metal content of less than 0.1 mass%.

[0129] 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, then dried in an air atmosphere at 110 °C for 5 hours, and this was calcined in an air atmosphere at 500 °C for 2 hours to obtain the iron-containing CHA-type zeolite of this comparative example.

[0130] The iron-containing CHA zeolite of this comparative example is a zeolite composed of a single phase of CHA zeolite, with an SiO2 / Al2O3 ratio of 19.8, an alkali metal content of less than 0.1% by mass, an iron content of 2.0% by mass, an area ratio of 36%, and an isolated iron ion content of 0.7% by mass. Also, the iron-containing CHA zeolite of this comparative example had a BET specific surface area of 742 m 2 / g, a total pore volume of 0.30 cm 3 / g, a mesopore volume ratio of 0.10, a mesopore volume of 0.03 cm 3 / g, and a micropore volume of 0.27 cm 3 / g.

[0131] Also, in the UV-VIS spectrum, it had peaks with peak tops at wavelengths of 192.5 nm, 212.5 nm, and 267.5 nm, and it was confirmed that it contained three types of isolated iron ions in different states.

[0132] Comparative Example 2 The iron-containing CHA 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. SiO2 / Al2O3 = 17.9 CDMEAOH / SiO2 = 0.02 CDMEABr / SiO2 = 0.06 Alk / SiO2 = 0.15 (Na / SiO2 = 0.058) (K / SiO2 = 0.173) K / Na = 2.98 Fe / SiO2 = 0.009 H2O / SiO2 = 18 OH / SiO2 = 0.25

[0133] The crystallized product is a zeolite consisting of a single phase of CHA-type zeolite with an SiO2 / Al2O3 ratio of 19.0 (CHA-type zeolite). Also, the iron-containing CHA-type zeolite of this comparative example is a zeolite consisting of a single phase of CHA-type zeolite, with an SiO2 / Al2O3 ratio of 19.0, an alkali metal content of less than 0.1% by mass, an iron content of 0.8% by mass, an area ratio of 90%, and an isolated iron ion content of 0.7% by mass.

[0134] Also, in the UV-VIS spectrum, it has peaks with peak tops at wavelengths of 192.5 nm, 213.0 nm, 245.0 nm, and 267.5 nm, and it was confirmed that it contains four types of isolated iron ions in different states. On the other hand, it was confirmed that the area ratio is low and it contains not only isolated iron ions but also a large amount of iron clusters and iron oxide particles. Comparative Example 3 The raw material composition was crystallized by a method according to Example 5 of Patent Document 2, except that the iron content was set to Fe / SiO2 = 0.020. That is, a 25% by mass aqueous solution of trimethyl-1-adamantammonium hydroxide, a 48% by mass aqueous solution of sodium hydroxide, colloidal silica (LUDOX AS-40), aluminum hydroxide (manufactured by Sigma-Aldrich), and iron(III) nitrate nonahydrate were sequentially added to pure water, and the resulting mixture was stirred for 15 minutes to obtain a raw material composition having the following molar composition. SiO2 / Al2O3 = 20.0 ADAH / SiO2 = 0.20 Alk / SiO2 = 0.20 (Na / SiO2 = 0.20) (K / SiO2 = 0.00) K / Na = 0.0 Fe / SiO2 = 0.020 H2O / SiO2 = 20 The above raw material composition was filled into a sealed container with a volume of 80 mL. After filling, the container was reacted by hydrothermal treatment at 160 °C for 10 days under static conditions and autogenous pressure to obtain a crystallized product. The obtained crystallized product was recovered after solid-liquid separation, washing with pure water, and drying at 100 °C in an air atmosphere. The crystallized product was in an amorphous phase, and CHA-type zeolite was not obtained. From this comparative example, it was confirmed that in the method for producing iron-containing CHA-type zeolite described in Patent Document 2, iron-containing CHA zeolite with an iron content of 1.0 mass% or more cannot be easily synthesized. Comparative Example 4 The 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 aqueous solution, and a raw material composition having the following molar composition was used. SiO2 / Al2O3 = 17.9 ADAH / SiO2 = 0.08 Alk / SiO2 = 0.24 (Na / SiO2 = 0.24) (K / SiO2 = 0.00) K / Na = 0.0 Fe / SiO2 = 0.025 H2O / SiO2 = 18 OH / SiO2 = 0.32 The crystallized product consisted of a single phase of CHA-type zeolite, and was a zeolite (CHA-type zeolite) with an SiO2 / Al2O3 ratio of 18.4. Also, the iron-containing CHA-type zeolite of this comparative example was a zeolite consisting of a single phase of CHA-type zeolite, with an SiO2 / Al2O3 ratio of 18.4, an alkali metal content of less than 0.1 mass%, an iron content of 2.0 mass%, an area ratio of 84%, an isolated iron ion content of 1.7 mass%, and an IR p2 / IR p1 ratio of 0.94. In addition, in the UV-VIS spectrum, it was confirmed to have peaks with peak tops at wavelengths of 192.5 nm, 213.0 nm, 245.0 nm, and 267.5 nm, and to contain four types of isolated iron ions in different states. On the other hand, it was confirmed that the area ratio was low and it contained not only isolated iron ions but also a large amount of iron clusters and iron oxide particles.

[0135] The results are shown in the table below. Here, "-" indicates unmeasured.

[0136]

Table 1

[0137] For the iron-containing CHA-type zeolite of Comparative Example 1, the iron-containing CHA-type zeolite of Example 1 showed a high area ratio despite having a similar iron content. Furthermore, when comparing Comparative Example 1 and Example 2 having a similar area ratio, it was shown that the iron content of Example 2 was high. From this, when the same amount of iron was incorporated into small-pore zeolites, it was confirmed that the iron in the iron-containing small-pore zeolites in the examples was contained with high dispersibility. Also, the iron-containing CHA-type zeolites of Examples 1 to 4 had a lower IR p2 / IR p1 ratio and a smaller amount of silanol defects compared to Comparative Example 4.

[0138] In addition, the UV-VIS spectra of Examples 1 and 2, and Comparative Examples 1 and 2 are shown in FIGS. 1 to 4, respectively. In FIGS. 1 to 4, the solid line is the measured value and the broken line is the spectrum after separation.

[0139] Measurement Example 1 (Evaluation of Nitrogen Oxide Reduction Characteristics) The nitrogen oxide reduction characteristics of the zeolites obtained in the examples and comparative examples after hydrothermal durability treatment were evaluated. That is, the iron-containing microporous zeolites of the examples and comparative examples were formed and pulverized respectively to obtain agglomerated particles with an agglomeration diameter of 12 to 20 mesh. After filling 3 mL of the obtained agglomerated particles into an atmospheric pressure fixed bed flow type reaction tube, hydrothermal durability treatment was carried out by flowing air containing 20% by volume of water under the following conditions. Flow rate of air: 300 mL / min Treatment temperature: 700 °C Treatment time: 20 hours

[0140] 1.5 mL of the agglomerated particle-like sample was filled into an atmospheric pressure fixed bed flow type reaction tube, held at the following measurement temperatures, and a nitrogen oxide-containing gas was flowed through. The nitrogen oxide concentrations at the inlet and outlet of the atmospheric pressure fixed bed flow type reaction tube were measured. The flow conditions of the nitrogen oxide-containing gas are as follows. Composition of nitrogen oxide-containing gas: NO 200 ppm NH3 200 ppm O2 10 vol% H2O 3 vol% N2 the balance Flow rate of nitrogen oxide-containing gas: 1.5 L / min Space velocity: 60,000 hr -1 Measurement temperature: 150 °C to 500 °C

[0141] The nitrogen oxide reduction rate was determined from the obtained nitrogen oxide concentrations by the following formula.

[0142] 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 reaction 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 reaction tube.

[0143] The results are shown in the following table.

[0144]

Table 2

[0145] From the above table, it was confirmed that the iron-containing CHA-type zeolite of the example not only has high nitrogen oxide reduction characteristics at low temperatures of 200 °C or lower, but also has high nitrogen oxide reduction characteristics in the high temperature range of 300 °C or higher, compared with the iron-containing CHA-type zeolite of the comparative example. Further, in the iron-containing CHA-type zeolite of Comparative Example 1 obtained by the post-impregnation method, the nitrogen oxide reduction rate at 200 °C decreased to less than 40% with respect to the nitrogen oxide reduction rate at 300 °C, whereas the iron-containing CHA-type zeolites of Examples 1 and 2 were both 45% or more. From this, it was confirmed that the iron-containing CHA-type zeolite of the example is less likely to have a decrease in the nitrogen oxide reduction rate due to a decrease in the temperature of nitrogen oxide reduction. Comparative Examples 1 and 2 had the same content of isolated iron ions. However, the iron-containing CHA-type zeolite of Comparative Example 1 containing many iron clusters and iron oxide particles had a lower nitrogen oxide reduction rate in all temperature ranges from low temperature to high temperature than the iron-containing CHA-type zeolite of Comparative Example 2. Further, the iron-containing CHA-type zeolites of Example 1 and Comparative Example 4 had the same iron content and the same content of isolated iron ions. However, the iron-containing CHA-type zeolite of Comparative Example 1 with a high IR p2 / IR p1 ratio had a lower nitrogen oxide reduction rate in all temperature ranges from low temperature to high temperature than the iron-containing CHA-type zeolite of Example 1.

[0146] Example 5 1,3-di(1-adamantyl)imidazolium bromide (DAdIBr), 48 mass% aqueous sodium hydroxide solution, 48 mass% aqueous potassium hydroxide solution, iron(III) nitrate nonahydrate, pure water and amorphous aluminosilicate precursor (SiO2 / Al2O3 = 22.0) were mixed to obtain a raw material composition having the following molar composition. SiO2 / Al2O3 = 22.0 DAdIBr / SiO2 = 0.05 Alk / SiO2 = 0.16 (Na / SiO2 = 0.14) (K / SiO2 = 0.02) K / Na = 0.14 Fe / SiO2 = 0.013 H2O / SiO2 = 18 OH / SiO2 = 0.16 The iron-containing AFX-type zeolite of this example was obtained in the same manner as in Example 1, except that CHA-type zeolite (SiO2 / Al2O3 = 24.9) was mixed into the raw material composition so that the seed crystal content was 1% by mass.

[0147] The crystallized product consists of a single phase of AFX-type zeolite, which is a zeolite with an SiO2 / Al2O3 ratio of 23.3 (AFX-type zeolite). Also, the iron-containing AFX-type zeolite of this example is a zeolite consisting of a single phase of AFX-type zeolite, with an SiO2 / Al2O3 ratio of 23.3, an Fe / Si ratio of 0.014, an alkali metal content of less than 0.1% by mass, an iron content of 1.2% by mass, an area ratio of 83%, an isolated iron ion content of 1.0% by mass, and an IR p2 / IR p1 ratio of 0.04.

[0148] Also, in the UV-VIS spectrum, it has peaks with peak tops at wavelengths of 196.5 nm, 219.5 nm, 245.0 nm, and 267.5 nm, and it was confirmed that it contains four types of isolated iron ions in different states.

[0149] 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 so that the composition of the raw material composition had the following molar composition. SiO2 / Al2O3 = 22.0 DAdIBr / SiO2 = 0.05 Alk / SiO2 = 0.15 (Na / SiO2 = 0.13) (K / SiO2 = 0.02) K / Na = 0.15 H2O / SiO2 = 18 OH / SiO2 = 0.15

[0150] The crystallized product was calcined in an air atmosphere at 600 °C for 2 hours. After calcination, NH4 exchange was carried out in the same manner as in Example 1, followed by washing with pure water and drying in an air atmosphere at 110 °C to obtain a zeolite (AFX-type zeolite) consisting of a single phase of AFX-type zeolite, with SiO2 / Al2O3 being 23.3 and the alkali metal content being less than 0.1% by mass.

[0151] 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, then dried in an air atmosphere at 110 °C for 5 hours, and this was calcined in an air atmosphere at 500 °C for 2 hours to obtain the iron-containing AFX-type zeolite of this Comparative Example.

[0152] The iron-containing AFX-type zeolite of this Comparative Example is a zeolite consisting of a single phase of AFX-type zeolite, with an SiO2 / Al2O3 ratio of 23.3, an Fe / Si ratio of 0.009, an alkali metal content of less than 0.1% by mass, an iron content of 1.4% by mass, an area ratio of 37%, and an isolated iron ion content of 0.5% by mass.

[0153] Also, in the UV-VIS spectrum, it was confirmed to have a peak with a peak top at a wavelength of 194.0 nm, a peak with a peak top at a wavelength of 224.0 nm, and a peak with a peak top at a wavelength of 267.5 nm, containing three types of isolated iron ions in different states.

[0154] Comparative Example 6 The raw material composition was crystallized by a method according to Example 5 of Patent Document 2, except that the iron content was set to Fe / SiO2 = 0.02. That is, 28.4 g of an aqueous solution of 25% by mass trimethyl-1-adamantammonium hydroxide (Tokyo Chemical Industry) was mixed with 2.0 g of an aqueous solution of 48% by mass sodium hydroxide. Subsequently, 18.0 g of an aqueous silica colloid suspension (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(NO3)3·9H2O, Sigma Aldrich, 98%) was added, water was added until the synthetic mixture reached the desired gel concentration, and it was maintained under stirring for 15 minutes. The final gel composition was SiO2:0.05Al2O3:0.02Fe:0.2TMAdaOH:0.2NaOH:20H2O. The resulting gel was filled into a stainless steel autoclave with a Teflon (registered trademark) liner. Then, crystallization was 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.

[0155] The obtained solid product was amorphous, and no XRD peaks attributable to the CHA structure could be confirmed in its XRD pattern.

[0156] 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.

[0157] The results are shown in the table below.

[0158]

Table 3

[0159] Example 5 had an iron content ratio that was more than twice as high as that of Comparative Example 5, despite having a lower isolated iron ion content. In the iron-containing AFX-type zeolite of this example, as with the iron-containing CHA-type zeolite, it was confirmed that iron was contained in a more highly dispersed state. Also, the iron-containing AFX-type zeolite of Example 5 had a low IR p2 / IR p1 ratio, as confirmed.

[0160] Also, the UV-VIS spectra of Example 5 and Comparative Example 5 are shown in FIGS. 5 and 6, respectively. In FIGS. 5 and 6, the solid line represents the measured value and the dashed line represents the spectrum after separation.

[0161] Furthermore, from FIG. 7, it was confirmed that the iron-containing AFX-type zeolite of Example 5 was essentially composed of aggregated particles formed by aggregation of crystal particles having a primary particle diameter of 0.3 μm or more and 5.0 μm or less.

[0162] Measurement Example 2 (Evaluation of Nitrogen Oxide Reduction Characteristics) The nitrogen oxide reduction characteristics after 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.

[0163]

Table 4

[0164] Similar to the iron-containing CHA-type zeolite, in the iron-containing AFX-type zeolite as well, compared to the iron-containing AFX-type zeolite obtained by the post-impregnation method (iron-supported AFX-type zeolite), the iron-containing AFX-type zeolite of Example 5 had high nitrogen oxide reduction characteristics at low temperatures. In particular, it was confirmed that the nitrogen oxide reduction rate at both 150°C and 200°C was more than twice that of Comparative Example 5. Also, with respect to the nitrogen oxide reduction rate at 300°C, the nitrogen oxide reduction rate at 200°C decreased by up to 40% in Example 5, while in Comparative Example 5, it was less than 30% in all cases. It was confirmed that the iron-containing FAX-type zeolite of the example was less likely to have a decrease in the nitrogen oxide reduction rate due to a decrease in the reaction temperature for nitrogen oxide reduction.

[0165] Measurement Example 3 (Change in Nitrogen Oxide Reduction Characteristics Before and After Hydrothermal Durability Treatment) The nitrogen oxide reduction characteristics of the examples were evaluated in the same manner as in Measurement Example 1, except that the hydrothermal durability treatment was not performed and the measurement temperature was set to 150°C or 200°C.

[0166] The results are shown in the following table together with the nitrogen oxide reduction rate after the hydrothermal durability treatment.

[0167]

Table 5

[0168] It was confirmed that in all examples, the nitrogen oxide reduction rates at 150°C and 200°C were improved by the hydrothermal durability treatment. From this, in addition to the effect that the iron-containing microporous zeolite of the example has excellent nitrogen oxide reduction characteristics, it can be expected that it can be used as a catalyst with a long life when used as a nitrogen oxide reduction catalyst.

Claims

1. The iron content is 1.0 mass% or more, and the IR spectrum shows 1860±10 cm －１ 3735±10 cm for the peak height intensity having a peak top at －１ and a ratio of the peak height intensity having a peak top at 190 to 300 nm in the UV-VIS spectrum to the peak area at 190 to 600 nm in the wavelength range is 60% or more.

2. The BET specific surface area is 530 m ２ / g or more, the iron-containing microporous zeolite according to claim 1.

3. The iron-containing small-pore 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 small-pore zeolite according to claim 1 or 2, 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 3. The iron-containing small pore zeolite according to claim 1, wherein the SiO 2 content is 1 / g or more.

6. The iron-containing small-pore zeolite according to claim 1 or 2, wherein the molar ratio of silica to alumina is 10 or more.

7. The iron-containing small-pore zeolite according to claim 1 or 2, wherein the small-pore 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 small-pore zeolite according to claim 1 or 2, wherein the small-pore zeolite is a CHA-type zeolite or an AFX-type zeolite.

9. The iron-containing small-pore zeolite according to claim 1 or 2, 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 NH ３ 200 ppm O ２ 10% by volume H ２ O₃ volume percentage N ２ Remaining part Flow rate of nitrogen oxide-containing gas: 1.5 L / min Space speed: 60,000 hr －１ Measurement temperature: 200 °C

10. The method 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, wherein the composition contains SiO ２ 2. The method for producing an iron-containing small pore zeolite according to claim 1, wherein the ratio of iron to silicon converted is greater than 0.01 and two or more alkali sources are contained.

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 small-pore zeolite according to claim 1 or 2.

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