Fe-containing CHA zeolite and production method therefor

Abstract

Provided is an Fe-containing CHA zeolite having a high proportion of iron ions present at cation sites.　This method for producing Fe-containing CHA zeolite comprises: a first step, in which FAU zeolite is mixed with alkali metal ions and / or alkaline-earth metal ions, hydroxide ions (OH-) and water to prepare a mixture slurry; a second step, in which the mixture slurry is subjected to a hydrothermal treatment to prepare CHA zeolite; a third step, in which the CHA zeolite, an iron salt, and water are mixed together to prepare a mixture liquid; and a fourth step, in which the pH value of the mixture liquid is adjusted to a value less than 2.7.

Description

Fe-containing CHA zeolite and its manufacturing method

[0001] The present invention relates to an Fe-containing CHA zeolite and a method for producing the same.

[0002] Nitrogen oxides (especially N) emitted from diesel engines used on ships, etc. ２ Nitrogen oxides (NO) are greenhouse gases, and emission regulations are being implemented. Fe-containing CHA zeolite is known as an active species of a catalyst for removing these nitrogen oxides (see, for example, Patent Document 1). In Patent Document 1, Fe is incorporated into CHA zeolite by ion exchange. After molding, CHA zeolite becomes a catalyst through unit operations involving heat, such as drying and calcination.

[0003] Japanese Patent Application Laid-Open No. 2019-30875

[0004] In Patent Document 1, Fe is incorporated into CHA zeolite by ion exchange. However, Fe ions are unlikely to exist in the cation sites of CHA zeolite prepared using a structure-directing agent. The more Fe ions present in the cation sites, the higher the catalytic activity of the Fe-containing CHA zeolite. When producing the catalyst, Fe ions not present in the cation sites are converted into iron oxide by heat.

[0005] Therefore, an object of the present invention is to provide an Fe-containing CHA zeolite having a high proportion of Fe ions present on cationic sites.

[0006] The present inventors have found that by adjusting the pH of a mixture of a CHA zeolite produced using FAU zeolite (by the conversion method) and an aqueous solution containing Fe ions to a specific value, counter ions present at the cation sites are easily ion-exchanged with Fe ions. That is, the method for producing an Fe-containing CHA zeolite of the present invention involves mixing FAU zeolite with at least one of alkali metal ions and alkaline earth metal ions, and hydroxide ions (OH －The method includes a first step of mixing the above-mentioned zeolite with water to prepare a mixed slurry, a second step of hydrothermally treating the mixed slurry to prepare CHA zeolite, a third step of mixing the CHA zeolite with iron salt and water to prepare a mixed liquid, and a fourth step of adjusting the pH of the mixed liquid to less than 2.7.

[0007] In the present invention, the Fe-containing CHA zeolite is produced as follows: FAU zeolite, at least one of alkali metal ions and alkaline earth metal ions, and hydroxide ions (OH － (Step 1) is a process in which the CHA zeolite is mixed with water to prepare a blended slurry. (Step 2) is a process in which the blended slurry is hydrothermally treated to prepare CHA zeolite. Hereinafter, this CHA zeolite preparation method will be referred to as the conversion method. (Step 3) is a process in which the CHA zeolite is mixed with an iron salt and water to prepare a mixed solution. (Step 4) is a process in which the pH of this mixed solution is adjusted to less than 2.7. This process replaces the counter ions present near the cation sites with Fe ions. In other words, the counter ions in the CHA zeolite are ion-exchanged with Fe ions, resulting in an Fe-containing CHA zeolite. Here, aluminum in the CHA zeolite forms the cation sites.

[0008] In CHA zeolite prepared by the conversion method, the counter ions are easily exchanged with Fe ions. In CHA zeolite prepared using a structure-directing agent (SDA method), the counter ions are less likely to be exchanged with Fe ions. Furthermore, when the pH of the mixed solution is 2.7 or higher, the counter ions are less likely to be exchanged with Fe ions.

[0009] SiO of CHA zeolite ２ / Al ２ O ３ The lower the molar ratio (SAR), the greater the amount of aluminum in the CHA zeolite, resulting in a greater number of cationic sites in the CHA zeolite. This makes it easier for counter ions in the CHA zeolite to be ion-exchanged with Fe ions. Therefore, an SAR of 9 or less is preferred. In the conversion method, it is easy to lower the SAR of CHA zeolite. On the other hand, an SAR of 3 or more is preferred. This increases the hydrothermal resistance of the CHA zeolite.

[0010] Each step will be described below.

[0011] <First Step> In this step, FAU zeolite, at least one of alkali metal ions and alkaline earth metal ions, hydroxide ions, and water are mixed to prepare a compounded slurry. The lower the SAR of FAU zeolite, the lower the SAR of CHA zeolite, and the more cationic sites there are in the CHA zeolite. Therefore, the SAR of FAU zeolite is preferably 10 or less. On the other hand, the SAR of FAU zeolite is preferably 3 or more. This makes it easier for the SAR of CHA zeolite to be 3 or more. The higher the SAR of CHA zeolite, the higher the hydrothermal resistance of the CHA zeolite.

[0012] X-type and Y-type zeolites are known as FAU zeolites. Of these, the SAR of Y-type zeolite can be easily adjusted to 3 to 10. Y-type zeolite can be prepared by the method described in Japanese Patent No. 6320658. Examples of Y-type zeolites include NaY-type zeolite, ultrastable Y-type zeolite (USY zeolite), and rare earth ion-exchanged Y-type zeolite (REY). Of these, it is preferable to use USY zeolite.

[0013] As the ions of alkali metals or alkaline earth metals, salts containing these elements can be used. As the hydroxide ions, OH － As a salt that satisfies the above conditions, hydroxides of alkali metals and alkaline earth metals can be used. In particular, hydroxides of alkali metals are preferred, and potassium hydroxide is more preferred. OH － The salt containing may be added in small portions or all at once.

[0014] It is preferable to prepare a compounded slurry so that the molar ratio (M / Si) of the total molar amount (M) of alkali metals and alkaline earth metals to the molar amount (Si) of silicon in the compounded slurry is 0.3 or more. This makes it easier to produce CHA zeolite. On the other hand, the lower this molar ratio, the easier it is to produce CHA zeolite. Therefore, this molar ratio is preferably 1.0 or less, more preferably 0.9 or less, and even more preferably 0.7 or less.

[0015] The higher the solids concentration of the prepared slurry, the higher the production efficiency. Therefore, the solids concentration is preferably 5% by weight or more, and more preferably 10% by weight or more. On the other hand, the lower the solids concentration, the lower the viscosity, making the slurry easier to transport. Therefore, the solids concentration is preferably 50% by weight or less, more preferably 30% by weight or less, and even more preferably 20% by weight or less.

[0016] Furthermore, it is preferable to prepare a compounded slurry after pulverizing the FAU zeolite. This facilitates conversion of the crystalline structure of FAU zeolite to that of CHA zeolite. In other words, this facilitates the production of CHA zeolite. For example, FAU zeolite can be pulverized as follows: FAU zeolite is mixed with water to form a raw material slurry. The raw material slurry is wet-pulverized to obtain a pulverized slurry. A ball mill, a bead mill, or the like can be used for wet-pulverization. The use of zirconia beads can improve pulverization efficiency. It is preferable to wet-pulverize the FAU zeolite so that the total intensity (Hb) of the three peaks [peaks attributable to Miller indices (111), (331), and (533)] appearing in the X-ray diffraction pattern of the FAU zeolite contained in the slurry before wet-pulverization is half or less (0.5Ha≧Hb). By pulverizing FAU zeolite in this manner, CHA zeolite is easily produced even when the amount of hydroxide ions added is reduced. The lower the temperature of the raw slurry during wet pulverization, the higher the yield of CHA zeolite. Therefore, the temperature of the raw slurry during wet pulverization is preferably 65°C or lower, more preferably 50°C or lower. The lower limit of the temperature of the raw slurry should be higher than the melting point of the solvent. For example, in the case of water, it is 0°C or higher. When wet pulverizing, CHA zeolite is easily produced even when the molar ratio (M / Si) of the blended slurry is low. For example, CHA zeolite is easily produced even when the molar ratio (M / Si) is 0.55 or lower or 0.47 or lower. It is also preferable to mix the pulverized slurry with hydroxide ions to prepare the blended slurry. Because the surface area of ​​the pulverized slurry is large, FAU zeolite is likely to satisfy the condition of 0.5Ha≧Hb. When wet pulverization is not performed, the molar ratio (M / Si) in the prepared slurry is preferably greater than 0.55. When the molar ratio (M / Si) is in this range, CHA zeolite is easily produced.

[0017] Furthermore, it is preferable to prepare a blended slurry containing seed crystals in the first step. The seed crystals have the crystalline structure of CHA zeolite. Use of such a blended slurry facilitates the production of CHA zeolite. It is more preferable that the raw material slurry contains seed crystals. This allows CHA zeolite to be wet-pulverized together with FAU zeolite, making it less likely that a crystalline phase (heterogeneous phase) different from CHA zeolite will be produced. The greater the content of seed crystals in the blended slurry, the more easily CHA zeolite will be produced. Therefore, the content of seed crystals in the blended slurry is preferably 0.1 wt % or more, more preferably 0.5 wt % or more, relative to the total amount of seed crystals and FAU zeolite. On the other hand, in order to increase the yield of CHA zeolite, this content is preferably 30 wt % or less, more preferably 15 wt % or less.

[0018] <Second Step> In this step, the prepared slurry is hydrothermally treated to prepare CHA zeolite. In the hydrothermal treatment, the prepared slurry is filled into a sealed container such as an autoclave, so the pressure applied to the prepared slurry can be higher than atmospheric pressure. Therefore, the temperature of the prepared slurry can be higher than the boiling point of water. The temperature of the hydrothermal treatment is preferably 130°C or higher. On the other hand, if this temperature is 190°C or lower, crystals other than CHA are less likely to be produced. Furthermore, the longer the hydrothermal treatment time, the more likely CHA zeolite is produced. Therefore, this time is preferably 12 hours or more. On the other hand, the shorter this time, the lower the cost. Therefore, this time is preferably 96 hours or less. In the hydrothermal treatment, the prepared slurry may be stirred or left to stand.

[0019] Hydroxide ions may dissolve some of the Si and Al in the FAU zeolite. The dissolved Si and Al remain in the CHA zeolite. Therefore, it is preferable to wash the CHA zeolite. Examples of washing methods include ion exchange and filtering the hydrothermally treated slurry and then washing the CHA zeolite with water or the like. To improve washing efficiency, the water temperature is preferably 30°C or higher, and more preferably 40°C or higher.

[0020] In CHA zeolite prepared by the conversion method, counter ions such as alkali metals and alkaline earth metals exist near the cation sites. These counter ions may reduce catalytic activity. These counter ions are replaced by ammonium ions (NH ４ ＋ ) can reduce the number of counter ions. In addition, ammonium ions present in the cation sites are easily ion-exchanged with Fe ions. For example, the counter ions can be exchanged with ammonium ions as follows: Ammonium sulfate, water, and CHA zeolite are mixed to form a suspension slurry. In the suspension slurry, the counter ions of CHA zeolite are exchanged with ammonium ions. The CHA zeolite after ion exchange will be referred to as NH ４ - It is called CHA zeolite.

[0021] <Third Step> In this step, CHA zeolite, iron salt, and water are mixed to prepare a mixed solution. By lowering the molar ratio (Al / Fe) of the molar amount of Al to the molar amount of Fe in the mixed solution, the Fe content increases. Therefore, the molar ratio (Al / Fe) in the mixed solution is preferably 20 or less, and more preferably 10 or less. On the other hand, the higher this molar ratio, the less likely iron oxide is generated by heat. Therefore, this molar ratio (Al / Fe) is preferably 2.5 or more, and more preferably 3.0 or more.

[0022] Examples of iron salts include iron chloride, iron nitrate, iron acetate, and iron sulfate. Of these, it is preferable to use nitrate. By combining CHA zeolite prepared by the conversion method with iron nitrate, Fe ions are more likely to be present at the cation sites of the CHA zeolite, although the reason is unclear.

[0023] The higher the solids concentration of the mixed solution, the less solvent is used, resulting in lower costs. Therefore, the solids concentration is preferably 20% by weight or more. On the other hand, the lower the solids concentration, the more easily Fe ions are present at the cation sites. Therefore, the solids concentration of the mixed solution is preferably 35% by weight or less.

[0024] <Fourth Step> In this step, the pH of the mixed solution is adjusted to less than 2.7. This promotes ion exchange and produces Fe-containing CHA zeolite. The pH can be adjusted by adding an acid to the mixed solution. Examples of acids include hydrochloric acid, nitric acid, and sulfuric acid. When the pH of the mixed solution is adjusted to less than 2.7, the higher the temperature of the mixed solution, the more promoted the ion exchange. Therefore, this temperature is preferably 10°C or higher, more preferably 20°C or higher, and even more preferably 60°C or higher. On the other hand, since ion exchange is performed in water, this temperature is below the boiling point of water (100°C or lower at atmospheric pressure). The longer the pH of the mixed solution is maintained below 2.7, the more likely Fe ions are to reside on the cation sites. Therefore, this time is preferably 10 minutes or longer, more preferably 30 minutes or longer. On the other hand, from a cost perspective, this time is preferably 10 hours or shorter. The pH of the mixed solution is preferably 2.6 or lower, more preferably 2.5 or lower.

[0025] The Fe-containing CHA zeolite can be separated from water by filtration or drying. When drying, the water is evaporated, so the drying temperature is preferably 100°C or higher. On the other hand, from the viewpoint of cost, the drying temperature is preferably 300°C or lower. The longer the drying time, the less water remains in the Fe-containing CHA zeolite. Therefore, a drying time of 1 hour or more is preferred, and 3 hours or more is more preferred. On the other hand, from the viewpoint of cost, a drying time of 100 hours or less is preferred. Drying methods include drying under reduced pressure using a rotary evaporator or the like, and evaporating using a dryer (spray drying, etc.). After drying under reduced pressure, evaporation using a dryer may also be performed.

[0026] The Fe-containing CHA zeolite is preferably calcined at 300°C or higher. By calcining, the counter ions of the iron salt can be decomposed and removed from the Fe-containing CHA zeolite. The calcination time is preferably 0.5 hours or more, more preferably 1 hour or more. From the viewpoint of cost, the calcination time is preferably 100 hours or less.

[0027] Hereinafter, Fe-containing CHA zeolite will be described. When Fe-containing CHA zeolite is measured by X-ray diffraction (XRD), the Miller index (100) plane intensity I １００ and the intensity of the (20-1) plane I ２０－１ Intensity ratio [I１００ / I ２０－１ The Fe-containing CHA zeolite of the present invention has an intensity ratio [I １００ / I ２０－１ ] is 0.8 or less. This value indicates that the CHA zeolite in the Fe-containing CHA zeolite has a structure in which the iron in the Fe-containing CHA zeolite is likely to exist as Fe ions on the ion exchange sites (cation sites), and as a result, it is presumed that the proportion of iron in the form of Fe ions in the Fe-containing CHA zeolite is high. １００ / I ２０－１ When the value of ] is greater than 0.8, the iron in the Fe-containing CHA zeolite is Fe ｘ O ｙ Clusters and Fe ２ O ３ Therefore, the proportion of iron present as Fe ions at the ion exchange sites (cation sites) decreases.

[0028] Furthermore, ultraviolet-visible spectroscopy (UV-vis) can identify that the proportion of iron in the form of Fe ions in Fe-containing CHA zeolite is high. Iron exists as Fe ions in the cation sites, and iron ions (Fe ３＋ ) absorption band is 200-300 nm. ｘ O ｙ Clusters and Fe ２ O ３ Iron exists as Fe, and its absorption band is 300-700 nm. ｘ O ｙ The absorption band of the cluster is 300-400 nm, Fe ２ O ３ The absorption band of Fe-containing CHA zeolite is 400-700 nm. Therefore, when measuring Fe-containing CHA zeolite by UV-vis, the integral value S of the intensity from 300 nm to 700 nm and the integral value S of the intensity from 200 nm to 700 nm are Ａ Ratio to (S / S Ａ ) in which S Ａ When S / S is sufficiently larger than S, it indicates that the amount of iron ions is large. ＡThe ratio (S / S) is 0.55 or less. In other words, the proportion of iron in the form of Fe ions in the Fe-containing CHA zeolite is high. Ａ ) is preferably 0.52 or less, more preferably 0.50 or less. The lower this ratio, the higher the proportion of Fe in the form of Fe ions. The Fe-containing CHA zeolite of the present invention has an (S / S Ａ As shown by the ratio of the intensity of the XRD [I １００ / I ２０－１ ], the Fe ions are mainly present at the ion exchange sites (cation sites), and therefore the activity due to the Fe ions is high.

[0029] The lower the SAR of the Fe-containing CHA zeolite, the greater the amount of aluminum in the Fe-containing CHA zeolite and the greater the number of cationic sites in the Fe-containing CHA zeolite. Therefore, the SAR is preferably 9 or less. On the other hand, the higher the SAR, the higher the hydrothermal resistance of the CHA zeolite. Therefore, the SAR is preferably 3 or more.

[0030] The lower the molar ratio of Fe to Al (Al / Fe) in Fe-containing CHA zeolite, the higher the catalytic activity. Therefore, this molar ratio (Al / Fe) is preferably 20 or less, and more preferably 10 or less. On the other hand, the higher this molar ratio, the less likely iron oxide is generated in the Fe-containing CHA zeolite by heat. Therefore, this molar ratio (Al / Fe) is preferably 2.5 or more, and more preferably 3.0 or more.

[0031] The higher the Fe content in the Fe-containing CHA zeolite, the higher the catalytic activity tends to be. ２ O ３ The iron content is preferably 1 wt% or more, more preferably 1.5 wt% or more, and even more preferably 2 wt% or more, calculated as the iron content. On the other hand, the lower the iron content, the less likely iron oxide is generated in the Fe-containing CHA zeolite by heat. Therefore, the iron content is preferably 20 wt% or less, more preferably 10 wt% or less, and even more preferably 5 wt% or less.

[0032] In Fe-containing CHA zeolite, the lower the content of alkali metals and alkaline earth metals, the higher the catalytic activity. Therefore, the total content of these metals is preferably 5 wt% or less, more preferably 3 wt% or less, and even more preferably 1 wt% or less. Here, these contents are the same as for alkali metal (A), except that A ２ In the case of alkaline earth metals (B), the weight is calculated as BO.

[0033] A catalyst can be produced using the above-mentioned Fe-containing CHA zeolite. In addition to the Fe-containing CHA zeolite, binders, sintering aids, bulking agents, etc. may be added to the catalyst. Examples of binders include celluloses such as methyl cellulose, starch, polyvinyl alcohol, etc. Examples of sintering aids include inorganic oxides such as silica and alumina. The catalyst can be used mainly for reduction reactions, especially N ２ High O decomposition performance.

[0034] The catalyst may be produced by molding the Fe-containing CHA zeolite. Examples of molding methods include extrusion molding and tablet molding. The catalyst may be in the form of a pellet or honeycomb structure. The surface of the catalyst may be coated with CHA zeolite. Before molding, it is preferable to add a binder or sintering aid to the Fe-containing CHA zeolite. After molding, it is preferable to dry and calcinate the molded product. The drying temperature is preferably 20 to 150°C, and the calcination temperature is preferably 500 to 700°C.

[0035] The preparation method and properties of the Fe-containing CHA zeolite are specifically described below. The preparation conditions are shown in Table 1.

[0036] Example 1 First Step 870 g of pure water and 117 g of FAU zeolite (SAR 8.7) were mixed. Next, 13 g of CHA zeolite (SAR 4.5) was added as seed crystals to obtain a raw material slurry. The SAR of this raw material slurry was 8.2. The raw material slurry was wet-pulverized using a circulating bead mill (LMZ015 manufactured by Ashizawa Finetech Co., Ltd.) while the bead mill container and the raw material slurry container were cooled with a chiller. Wet-pulverization was carried out using 1.0 mm zirconia beads at a peripheral speed of 10 m / s. The bead filling amount was 85% of the container volume in volume terms. The total intensity (H) of three peaks [peaks attributable to Miller indices (111), (331), and (533)] appearing in the X-ray diffraction pattern of the FAU zeolite contained in the raw material slurry was measured. ａ ) and the total strength of the FAU zeolite (H ｂ ) is less than half (0.5H ａ ≧H ｂ The raw material slurry was wet-pulverized until the mixture reached a powder state, thereby obtaining a pulverized slurry.

[0037] The raw material slurry and the crushed slurry were dried at 180°C for 3 hours to obtain powders, which were then subjected to X-ray diffraction measurement under the following conditions. ａ and H ｂ asked for.

[0038] (Conditions) Apparatus: MiniFlex (manufactured by Rigaku Corporation), operating axis: 2θ / θ, radiation source: CuKα, measurement method: continuous, voltage: 40 kV, current: 15 mA, start angle: 2θ=5°, end angle: 2θ=50°, sampling width: 0.020°, scan speed: 10,000° / min.

[0039] The ground slurry and 28.7 g of potassium hydroxide (KOH concentration: 95.5% by mass) were mixed to prepare a compounded slurry having a molar ratio (M / Si) of 0.335.

[0040] <Second Step> The prepared slurry was hydrothermally treated at 150°C for 48 hours using an autoclave to obtain a slurry containing CHA zeolite. This slurry was filtered, washed, and dried to obtain CHA zeolite. The CHA zeolite was subjected to ion exchange as follows. 100 g of CHA-type zeolite was suspended in 1000 g of an aqueous solution in which 100 g of ammonium sulfate was dissolved to obtain a suspension slurry. The temperature of the suspension slurry was raised to 60°C while stirring and maintained for 1 hour. The suspension slurry was filtered, washed, and dried. These operations were repeated two more times to obtain NH ４ -CHA zeolite was prepared.

[0041] <Third and fourth steps> 113.8 g of an aqueous solution containing iron nitrate was added with NH ４ 50 g of CHA zeolite was dispersed in the mixture, and a mixed solution was prepared so that the molar ratio (Al / Fe) in the mixed solution was 10.96 (third step). The solid content concentration of the mixed solution was 32% by weight. The pH of the mixed solution was adjusted to 1.8. The mixed solution was heated to 80°C while stirring and maintained at that temperature for 1 hour (fourth step). This mixed solution was dried using a rotary evaporator (rotary evaporator) and further dried at 110°C for 12 hours. This was calcined at 600°C for 3 hours to prepare Fe-containing CHA-type zeolite.

[0042] The Fe-containing CHA-type zeolite was measured as follows (1) to (3). The measurement results of the following Examples and Comparative Examples are also shown in Table 1.

[0043] (1) Elemental analysis (SAR, K content, Fe content, molar ratio (Al / Fe)) Approximately 0.5 g of Fe-containing CHA zeolite was placed on a platinum dish, and 10 ml of hydrofluoric acid and 10 ml of (1+1) sulfuric acid were added. The mixture was heated on a sand bath until white smoke from sulfuric acid was released, and water was added to dissolve it. The mixture was then diluted to a constant volume in a 200 ml measuring flask. 10 ml of this was then diluted to a constant volume in a 100 ml measuring flask to prepare a test solution. K was measured using an atomic absorption spectrometer (Hitachi High-Tech Z-2310), and Al was measured using an ICP spectrometer (Shimadzu ICPS-8100). The contents of K, Al, and Fe were respectively ２ O, Al ２ O ３、 Fe ２ O ３was converted to SiO ２ The value of Al is calculated from 100% by weight. ２ O ３ , K. ２ O, Fe ２ O ３ The content (wt%) of this SiO ２ and Al ２ O ３ The content of Al was converted into a molar ratio to calculate the SAR. ２ O ３ and Fe ２ O ３ The molar ratio (Al / Fe) was calculated from the content (wt%) of Fe. The SAR of FAU zeolite and CHA zeolite was also measured and calculated in the same manner as for Fe-containing CHA-type zeolite. These measurement results are also shown in Table 1.

[0044] (2) UV-vis spectrum measurement (ratio (S / S A The Fe-containing CHA zeolite was crushed in a mortar, placed on a slide glass, and pressed with a cover glass. This was set in an ultraviolet-visible-near-infrared spectrophotometer (JASCO Corporation, V-670) and measured at a resolution of 1 cm. ―１ 200 to 700 cm －１ The UV-vis spectrum was measured in the range of . The ratio (S / S A ) was calculated.

[0045] (3) X-ray diffraction measurement (crystal system, intensity ratio [I １００ / I ２０－１]) The Fe-containing CHA-type zeolite was pulverized in a mortar and set on a sample plate. This was subjected to X-ray diffraction measurement under the same measurement conditions as described above. When the peak of the obtained X-ray diffraction pattern was within the range of ±0.2° of the 2θ value described on page 112 of "COLLECTION OF SIMULATED XRD POWDER PATTERNS FOR ZEOLITES M.M.J. Treacy and J.B. Higgins, Fifth Revised Edition 2007," it was determined that the Fe-containing CHA-type zeolite had a peak attributable to the Miller index of this 2θ. When an Fe-containing CHA-type zeolite has all of the peaks assigned to Miller indices (100), (111), (20-1), (21-1), (211), (3-1-1), (310), and (3-1-2), the Fe-containing CHA-type zeolite has a crystal system of chabazite structure. The intensity ratio of the peaks assigned to Miller indices (100) and (20-1) of the Fe-containing CHA-type zeolite [I １００ / I ２０－１ ] was calculated.

[0046] [Example 2] This example is the same as Example 1, except for the following differences. That is, in the fourth step, the pH of the mixed solution was adjusted to 2.2. The mixed solution was heated to 80°C while stirring and maintained at that temperature for 1 hour. The mixed solution was filtered. This step was repeated three times. Furthermore, the mixture was dried at 110°C for 12 hours and calcined at 600°C for 3 hours to prepare an Fe-containing CHA-type zeolite.

[0047] Example 3 This example is the same as Example 1, except for the following differences: In the first step, FAU zeolite (SAR 5) was used instead of FAU zeolite (SAR 8.7), and in the fourth step, the pH of the mixture was adjusted to 2.3.

[0048] [Example 4] This example is the same as Example 1, except for the following difference: In the third step, NH ４ 50 g of CHA zeolite was dispersed in the mixture to prepare a mixed solution with a molar ratio (Al / Fe) of 6.87. The solid content of the mixed solution was 32 wt %. In the fourth step, the pH of the mixed solution was adjusted to 1.9.

[0049] [Example 5] This example is the same as Example 1, except for the following differences. That is, in the third step, 50 g of the CHA zeolite obtained in the second step of Example 1 was dispersed in an aqueous solution containing iron nitrate to prepare a mixed solution with a molar ratio (Al / Fe) of 37.50. The solid content concentration of the mixed solution was 32 wt%. In the fourth step, the pH of the mixed solution was adjusted to 2.4. The mixed solution was heated to 80°C while stirring and held for 1 hour. The mixed solution was filtered. This fourth step was repeated three times. Furthermore, the mixture was dried at 110°C for 12 hours and calcined at 600°C for 3 hours to prepare an Fe-containing CHA-type zeolite.

[0050] Example 6 This example is similar to Example 1, except for the following difference: the Fe-containing CHA zeolite was not calcined.

[0051] Comparative Example 1 This comparative example is the same as Example 1 except for the following difference: In the fourth step, the pH of the mixed solution was adjusted to 3.5.

[0052] Comparative Example 2 This comparative example is the same as Example 1, except for the following difference: In the third step, NH ４ 50 g of CHA zeolite was dispersed in the mixture to prepare a mixed solution with a molar ratio (Al / Fe) of 11.05. The solid content of the mixed solution was 32 wt %. The pH of the mixed solution was 2.7.

[0053] Comparative Example 3 A mixture of 163 g of a 25% N,N,N-trimethyladamantanammonium aqueous solution (manufactured by Seichem Japan), 9 g of potassium hydroxide (KOH concentration: 95.5% by mass), and an aqueous sodium aluminate solution (Al ２ O ３ Concentration is 22% by mass, Na ２A slurry was obtained by adding and mixing 60 g of zeolite (equivalent to 17% by mass of zeolite) and 124 g of fumed silica (Reolosil QS40, manufactured by Tokuyama) to 1,397 g of pure water. This slurry was hydrothermally treated at 150°C for 96 hours. The hydrothermally treated slurry was filtered, washed, dried, and calcined (at 600°C for 3 hours) to obtain CHA zeolite. Subsequently, 50 g of CHA zeolite was dispersed in an aqueous solution containing 0.10 moles of iron nitrate per mole of aluminum in the CHA zeolite to obtain a mixed solution. The solids concentration of the mixed solution was 32 wt%. The pH of the mixed solution was 2.3.

[0054] Comparative Example 4 A mixture of 164 g of a 25% N,N,N-trimethyladamantanammonium aqueous solution (manufactured by Seichem Japan), 14 g of potassium hydroxide (KOH concentration: 95.5% by mass), and a sodium aluminate aqueous solution (Al ２ O ３ Concentration 22% by mass, Na ２ 33 g of ammonium hydroxide (O concentration 17% by mass) and 113 g of fumed silica (Reolosil QS40, manufactured by Tokuyama) were added to and mixed with 1,418 g of pure water to obtain a slurry. This slurry was hydrothermally treated at 150°C for 96 hours. The hydrothermally treated slurry was filtered, washed, dried, and calcined (at 600°C for 3 hours) to obtain CHA zeolite. 50 g of CHA zeolite was then dispersed in an aqueous solution containing 0.07 moles of iron nitrate per mole of aluminum in the CHA zeolite to obtain a mixed solution. The solids concentration of the mixed solution was 32% by weight. The pH of the mixed solution was 2.7.

[0055]

Claims

1. FAU zeolite, at least one of alkali metal ions and alkaline earth metal ions, and hydroxide ions (OH － a second step of hydrothermally treating the prepared slurry to prepare CHA zeolite; a third step of mixing the CHA zeolite, an iron salt, and water to prepare a mixed solution; and a fourth step of adjusting the pH of the mixed solution to less than 2.

7.

2. The method according to claim 1, wherein the CHA zeolite has an SAR of 9 or less.

3. Contains Fe, and when measured by ultraviolet-visible spectroscopy, the integral value S of the intensity from 300 nm to 700 nm and the integral value S of the intensity from 200 nm to 700 nm are Ａ Ratio to (S / S Ａ ) is 0.55 or less, and when measured by X-ray diffraction, the Miller index (100) plane intensity I １００ and the intensity of the (20-1) plane I ２０－１ The ratio [I １００ / I ２０－１ The Fe-containing CHA zeolite has a β-glutamic acid (β) value of 0.8 or less.

4. The Fe-containing CHA zeolite according to claim 3, characterized in that the SAR is 3 to 9.

5. N characterized by using the Fe-containing CHA zeolite according to claim 3. ２ A method for producing an O decomposition catalyst.

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