Method for producing phosphorus element-containing zeolite

Abstract

The present invention provides a small pore size zeolite which is modified with phosphorus, has high hydrothermal endurance and has an 8-membered oxygen ring structure selected from the group consisting of CHA, AEI and AFX types. This zeolite is a small pore size zeolite which contains at least elemental aluminum, elemental silica and elemental phosphorus wherein the elemental phosphorus is specified by expression (1), and which has an 8-membered oxygen ring structure selected from the group consisting of CHA, AEI and AFX types. The elemental phosphorus modifying the zeolite is present in such a manner that the concentration thereof is higher on the surface layer side of the zeolite.　(1): P1<P2 [In formula (1): P1 represents the ratio (atom%) of elemental phosphorus to elemental aluminum determined by X-ray fluorescence analysis (XRF); and P2 represents the ratio (atom%) of elemental phosphorus to elemental aluminum determined by X-ray photoelectron spectroscopy (XPS).]

Description

Technical Field

[0001] The present invention relates to a novel phosphorus element-containing zeolite and a method for producing the same.

Background Art

[0002] Zeolites have a framework structure with regular and constant-sized pores and are used in various industrial applications such as exhaust gas purification catalysts. Such zeolites are individually assigned a three-letter alphabet code by the International Zeolite Association (IZA) according to their framework structure.

[0003] Among such zeolites, CHA, AEI, and AFX-type small-pore zeolites having an oxygen 8-membered ring structure are known as catalyst materials for purifying nitrogen oxides in exhaust gas discharged from internal combustion engines using gasoline or light oil as fuel. In the purification of nitrogen oxides, an ammonia component is used as a reducing agent. Such a catalyst for purifying nitrogen oxides is called a selective catalytic reduction (SCR) catalyst, and the zeolite used as a main material is modified with copper, iron elements, etc. to promote its activity.

[0004] Catalysts used for purifying exhaust gas discharged from internal combustion engines need to exhibit purification performance over a long period of time and are required to have high durability. However, the exhaust gas discharged from internal combustion engines contains various components that reduce the activity of the catalyst components. Among such activity-reducing components in the exhaust gas, water supplied at a high temperature to the zeolite can be mentioned. The water in the exhaust gas is generated in large quantities by the combustion of hydrocarbons and oxygen in fossil fuels. Therefore, it can be said that the zeolite in the exhaust gas is constantly exposed to high-temperature water.

[0005] In the case of zeolites for exhaust gas purification catalysts, durability against moisture supplied at such high temperatures is required, which is sometimes referred to as hydrothermal durability. Various methods have been proposed for improving the hydrothermal durability of zeolites for exhaust gas purification catalysts. As one of such means for improving hydrothermal durability, modification of zeolites with phosphorus element is known (Non-Patent Document 1).

[0006] In Non-Patent Document 1, in order to increase the durability of zeolites, zeolites are impregnated with a phosphoric acid compound. This protects aluminum elements, which are considered to have relatively low durability in the zeolite structure, with phosphorus elements, thereby improving the durability of zeolites.

[0007] Aluminum elements are also contained in the framework structure of zeolites. In Non-Patent Document 1, by impregnating with an aqueous solution of a phosphorus compound and heating to allow phosphorus elements to penetrate from the pores in the framework structure of zeolites, aluminum elements are modified with phosphorus elements.

[0008] Non-Patent Document 1 describes zeolites with an MFI structure as zeolites modified with phosphorus elements. In zeolites with an MFI structure, pores derived from an oxygen 10-membered ring structure are formed, and since the pore size exceeds 5 angstroms and is large, it can be said that modification of aluminum elements in the zeolite structure with phosphorus elements is relatively easy.

[0009] On the other hand, the pores in the framework structure of small-pore zeolites of the CHA, AEI, and AFX types are derived from an oxygen 8-membered ring structure, and since the maximum pore size is less than 4 angstroms, it is more difficult for phosphorus elements to approach aluminum elements in the zeolite framework structure than in zeolites with large-diameter pores such as MFI-type zeolites.

[0010] For example, when using diammonium hydrogen phosphate, which is readily available as a compound containing phosphorus element, as a phosphorus element raw material, it is known that diammonium hydrogen phosphate dissociates ammonia at 155°C to become ammonium dihydrogen phosphate. And it is known that ammonium dihydrogen phosphate becomes ammonium metaphosphate, which is a polymeric non-combustible polymer, at 216°C or higher. Therefore, in the impregnation heat modification using a phosphorus compound that polymerizes in the phosphorus modification step, it has been difficult to modify the aluminum element with the phosphorus element in the small-pore zeolite structures such as CHA, AEI, and AFX type zeolites, and it has been difficult to improve the hydrothermal durability thereby (Non-Patent Document 2 and Non-Patent Document 3).

[0011] Therefore, when modifying the phosphorus element to CHA, AEI, and AFX type zeolites, it has been necessary to blend orthophosphoric acid when synthesizing the zeolite and introduce the phosphorus element into the structural framework (framework) at the synthesis step (Patent Document 1), or introduce the phosphorus element into the pores outside the framework structure using a structure-directing agent containing the phosphorus element at the synthesis stage (Patent Document 2). When the phosphorus element is contained in the framework structure as in Patent Document 1, the phosphorus element is incorporated as a T atom (the atom constituting the zeolite framework structure, where T is an abbreviation for Tetrahedral) in the zeolite framework structure like silicon. The phosphorus atoms incorporated into the framework structure in this way may lack stability compared to the aluminum atoms incorporated as T atoms as well.

[0012] When there are phosphorus atoms and aluminum atoms in the zeolite structure, they form TO4 units with a tetrahedral structure similar to that of silicon as pentavalent phosphorus atoms and trivalent aluminum atoms, and it is said that they maintain electrical neutrality by connecting alternately. Due to this connection, zeolites containing phosphorus atoms and aluminum atoms in the framework structure have framework flexibility, and it becomes easy to introduce various transition metals, which are said to promote the activity as a catalyst, into the cation sites (Non-Patent Document 4). However, it is considered that this flexibility may lead to low durability. In addition, the aluminum phosphate framework is weak against liquid water, and when there are phosphorus atoms and aluminum atoms in the zeolite structure, a decrease in durability is also a concern in an environment where water in the state of water vapor aggregates into liquid water. An example of such an environment is the exhaust gas of an automobile equipped with a large diesel engine. The exhaust gas of a large diesel engine is relatively low in temperature among internal combustion engines, and when it is in a low-speed operation state for a long time in a cold environment, moisture in the exhaust gas may condense in the catalyst, and when zeolite is used as an SCR catalyst, a decrease in performance is a concern.

[0013] Zeolites used as catalysts for purifying exhaust gas discharged from internal combustion engines are required to have high reactivity (activity) in addition to such hydrothermal durability. The abundance of cation sites in the zeolite structure is known as an index of such highly reactive zeolites.

[0014] In zeolites, when atoms such as aluminum are included in addition to silicon as the T atoms constituting the framework structure, atoms with different valences such as trivalent aluminum are included in the lattice composed of tetravalent silicon, resulting in local negative charges in the framework structure. Such negative charges are called cation sites, and the cation sites can promote the adsorption of reactants into the pores inside the zeolite structure and improve the reactivity in the catalyst. It is also known that by modifying this cation site with transition metals having positive charges such as copper and iron, the reactivity of the zeolite can be further promoted.

[0015] Regarding such zeolites composed of silicon and aluminum, the silicon and aluminum in the zeolite may be represented by the SAR (Silica Alumina Ratio), which is the ratio of [silica / alumina]. When this SAR is small, it can be said that the zeolite contains a large amount of aluminum element and is rich in cation sites.

[0016] However, zeolites with abundant cation sites have a concern of dealumination in a hydrothermal environment. This is considered to be because the proton H + acts on the oxygen of Si-O-Al in the zeolite and breaks the bond. When such dealumination progresses, the skeletal structure of the zeolite is destroyed. Therefore, although zeolites containing a large amount of aluminum element in the skeletal structure can be expected to have high activity, they are inferior in hydrothermal durability, and it is difficult to expect high durability when used as a catalyst component for purifying exhaust gas of internal combustion engines.

Prior Art Documents

Patent Documents

[0017]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0018]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Non-Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0019] Regarding zeolites containing aluminum elements in such a framework structure, it is also conceivable to improve the hydrothermal durability by the modification with phosphorus elements as described above. However, phosphorus elements bind to cation sites, and although the durability can be improved, there is a concern that the reactivity of the cation sites will decrease this time.

[0020] Further, when attempting to improve the durability by modifying small-pore zeolites such as CHA, AEI, and AFX-type zeolites with phosphorus elements, a method of synthesizing zeolites using a phosphonium compound as a structure-directing agent has also been reported as described above (Patent Document 2). However, phosphonium compounds are generally expensive compounds, and some of them have concerns about toxicity, and they are not preferable as industrial materials.

[0021] In addition, in the method of adding a phosphonium compound from the synthesis stage of zeolites, there is also a concern that the cation sites of the resulting zeolites will be uniformly modified with phosphorus elements. Phosphorus elements themselves are hardly expected to contribute to the catalytic reaction, and in this case, there is also a risk of reducing the reactivity using the cation sites in zeolites, and it may no longer be said to be a highly active zeolite as a catalyst material.

[0022] The present invention has been made in view of the above problems, and provides CHA, AEI, and AFX-type small-pore zeolites having an oxygen 8-membered ring structure with high activity and high hydrothermal durability (hereinafter, may be referred to only as CHA, AEI, and AFX in this specification), and also provides an inexpensive production method for such CHA, AEI, and AFX with high activity and high hydrothermal durability.

Means for Solving the Problems

[0023] The inventors have conducted intensive studies to solve the above problems and have found that by modifying the CHA, AEI, and AFX with a completed skeletal structure with phosphorus elements, CHA, AEI, and AFX with excellent hydrothermal durability can be obtained. At the same time, an inexpensive manufacturing method for this CHA, AEI, and AFX has been found, leading to the completion of the present invention.

[0024] That is, the first aspect of the present invention is a CHA, AEI, or AFX type small pore zeolite containing at least an aluminum element, a silica element, and a phosphorus element, and having an oxygen 8-membered ring structure in which the content of the phosphorus element is specified by the following formula. ·P1 < P2 ··P1: [Ratio (atomic%) of phosphorus element to aluminum element by X-ray fluorescence analysis (XRF)] ··P2: [Ratio (atomic%) of phosphorus element to aluminum element by X-ray photoelectron spectroscopy (XPS)]

[0025] And the second aspect of the present invention is a CHA, AEI, or AFX type small pore zeolite containing at least an aluminum element, a silica element, and a phosphorus element, and having an oxygen 8-membered ring structure in which the content ratio of the phosphorus element is specified by the following formula. ·P2 / P1 = 2 to 20 ··P1: [Ratio (atomic%) of phosphorus element to aluminum element by X-ray fluorescence analysis (XRF)] ··P2: [Ratio (atomic%) of phosphorus element to aluminum element by X-ray photoelectron spectroscopy (XPS)]

[0026] Further, the third aspect of the present invention is a method for producing a phosphorus element-containing zeolite, which comprises impregnating a CHA, AEI, or AFX having an oxygen 8-membered ring structure containing at least an aluminum element and a silica element with an aqueous solution containing a phosphoric acid or a phosphate and an organic base that neutralizes the phosphoric acid or the phosphate.

Advantages of the Invention

[0027] According to the present invention, by increasing the content of phosphorus element on the surface layer of zeolite and decreasing the content of phosphorus element inside it, the number of cation sites not modified by phosphorus element inside the zeolite is increased, and in the zeolite surface layer that is most easily exposed to the hydrothermal atmosphere under the use environment as a catalyst, the number of cation sites modified by phosphorus element is increased, so that CHA, AEI, and AFX with high hydrothermal durability and high activity can be obtained. Further, by impregnating an aqueous solution containing inexpensive phosphoric acid or phosphate as a phosphorus element raw material and an organic base for neutralizing the phosphoric acid or phosphate, CHA, AEI, and AFX with abundant phosphorus element on the zeolite surface layer and low phosphorus element content inside can be obtained with a very simple operation.

Embodiments for Carrying Out the Invention

[0028] Hereinafter, embodiments of the present invention will be described in detail. The following embodiments are examples of the embodiments of the present invention, and the present invention is not limited thereto. Further, the present invention can be arbitrarily modified and implemented without departing from the gist thereof. In this specification, when expressing numerical values or physical property values before and after using "~", the values before and after are included. For example, the numerical range notation of "1~100" includes both the lower limit value "1" and the upper limit value "100". The same applies to other numerical range notations.

[0029] <Phosphorus-Element-Containing Zeolite> The phosphorus-element-containing zeolite of this embodiment contains at least an aluminum element, a silica element, and a phosphorus element. The content of the phosphorus element satisfies the following formula (1) and has an oxygen 8-membered ring structure selected from the group consisting of CHA, AEI, and AFX types. Here, in formula (1), P1 represents the ratio (atomic %) of the phosphorus element to the aluminum element by fluorescent X-ray analysis (XRF), and P2 represents the ratio (atomic %) of the phosphorus element to the aluminum element by X-ray photoelectron spectroscopy (XPS). P1 < P2 ··· (1)

[0030] [CHA, AEI, AFX] In this specification, CHA, AEI, and AFX are codes representing framework structures registered with the IZA and having an oxygen 8-membered ring structure. The pore sizes formed by this oxygen 8-membered ring structure are CHA [3.8×3.8], AEI [3.8×3.8], and AFX [3.4×3.6] in angstrom units. Therefore, compared with the widely known MFI-type zeolite having a pore size exceeding 5 angstroms, CHA, AEI, and AFX have small pores.

[0031] In addition, CHA, AEI, and AFX contain at least aluminum, silicon, and phosphorus elements. As described above, the aluminum element forms cation sites in the CHA, AEI, and AFX framework structures. The amount of the aluminum element in CHA, AEI, and AFX of this embodiment is not particularly limited, and the effects of the present invention can be expected as long as the framework structure contains the aluminum element. The amount of the aluminum element in terms of alumina represented by SAR (molar ratio represented by SiO2 / Al2O3) is preferably 5 to 100, more preferably 10 to 50, and even more preferably 12 to 17. By having a certain size of SAR, the stability and durability of the framework structure are high. Also, by not having too large a SAR, it has a sufficient amount of cation sites that can contribute to the catalytic reaction. In this embodiment, it is possible to improve the durability even for CHA, AEI, and AFX with a small SAR that are generally considered to have poor hydrothermal durability.

[0032] When CHA, AEI, and AFX are in particulate form, their particle sizes are not particularly limited. On the other hand, as will be described later, when making the amount of phosphorus element contained in the surface layer and the interior of the particles different, if the particle size is too small, there is a concern that the phosphorus element will be uniformly impregnated throughout the particles. Due to such a concern, the size of CHA, AEI, and AFX particles is preferably 0.5 to 20 μm, more preferably 1 to 5 μm, in terms of the size of crystal particles (average particle diameter D50). If the particle size is too large, in the catalytic reaction, the access of reactants to the central part of the particles deteriorates, and even when using CHA, AEI, and AFX as catalyst components for purifying exhaust gases of internal combustion engines, it may be difficult to obtain an activity commensurate with the amount used. In this specification, the average particle diameter D50 means the median diameter measured by a laser diffraction particle size distribution measuring device (for example, a laser diffraction particle size distribution measuring device SALD-7100 manufactured by Shimadzu Corporation, etc.). Also, the particle shapes of CHA, AEI, and AFX are not particularly limited, and may be any of, for example, cuboid shape, spherical shape, ellipsoidal shape, crushed shape, flat shape, irregular shape, etc.

[0033] Also, when CHA, AEI, and AFX are in particulate form, the particles may be any of single crystal particles, polycrystalline particles, and aggregated crystal particles, may be secondary particles in which a plurality of crystal particles are aggregated and bonded, or may be CHA, AEI, and AFX coated and supported on a structured carrier such as a honeycomb. Thus, CHA, AEI, and AFX can be applied in various forms and states. However, when in particulate form, since the particle surface layer can be uniformly phosphorus-modified to improve hydrothermal durability, it is preferably single crystal particles.

[0034] [State of Phosphorus Modification] One of the characteristics of the phosphorus element-containing zeolite of this embodiment relates to the relative amount of phosphorus elements, so to speak, the distribution in the surface layer and the interior of CHA, AEI, and AFX. Here, the relative amount (distribution state) of phosphorus elements is defined by analyzing using X-ray Photoelectron Spectroscopy (XPS) and X-ray Fluorescence (XRF) analysis methods. Therefore, regarding the distribution of phosphorus elements, for example, in terms of particles, it is not limited to geometrically defined particles. The particles in the distribution of phosphorus elements refer to aggregates of particles, that is, particles in the sense that they correlate with the analysis results from the bulk. Based on such a definition, in this specification, unless otherwise specified, when referring to the amount of phosphorus elements in particles, it represents the amount of phosphorus elements analyzed as the entire bulk.

[0035] [X-ray Photoelectron Spectroscopy (XPS)] In XPS, by irradiating the sample surface with X-rays and analyzing the constituent elements of the sample and their electronic states from the energy of the generated photoelectrons, the type and quantification of the elements can be determined at a depth of several nm to a dozen or so nm in the sample surface layer. In the following examples, as XPS, the device name: PHI Quantera SXM manufactured by ULVAC-PHI, Inc. was used, and the surface phosphorus element concentration was specified by the phosphorus element concentration when measured with a monochromatic Al-Kα excitation line of about 1.5 keV. Unless otherwise specified, the same applies to the descriptions other than the examples in this specification.

[0036] [X-ray Fluorescence (XRF) Analysis Method] In XRF analysis, by irradiating specific X-rays to elements with an energy above a certain level and analyzing the energy difference between the inner shell and the outer shell unique to each element emitted, the type and quantification of the elements constituting the sample can be determined up to a depth of several tens of μm of the sample for general XRF specifications.

[0037] [Phosphorus Element Ratio] In the phosphorus element-containing zeolite of the present embodiment, phosphorus elements are contained in CHA, AEI, and AFX, and their distribution has characteristics. That is, in the phosphorus element-containing zeolite of the present embodiment, the amount of phosphorus element quantified as the composition ratio of constituent elements using XPS is larger than the amount of phosphorus element quantified as the composition ratio of constituent elements in the whole particle using XRF analysis method.

[0038] In the analysis by XRF, since it is the composition ratio of constituent elements in the whole particle, it does not uniquely quantify the amount of phosphorus element inside the particle. However, by comparing with the result by XPS and clarifying the phosphorus element content of the whole particle (the whole bulk) with respect to the surface layer, it can be detected that CHA, AEI, and AFX contain less phosphorus element inside and more phosphorus element in the surface layer.

[0039] In the phosphorus element-containing zeolite of the present embodiment, the ratio of the phosphorus element content quantified by XPS and XRF, that is, the ratio of the phosphorus element between the sample surface layer and the sample interior, when represented by the formula (2): P2 / P1, where P1 is the phosphorus element content (atomic %) of the whole particle quantified by XRF and P2 is the phosphorus element content (atomic %) of the particle surface layer quantified by XPS, it is preferable that P2 / P1 is 2 to 20, and more preferably 2 to 15. If P2 / P1 is too large, an excessive amount of phosphorus element covers the surfaces of CHA, AEI, and AFX, which may hinder the reaction using the pores derived from the original skeletal structure of the zeolite. If the ratio is too small, the surfaces of CHA, AEI, and AFX are not sufficiently modified with phosphorus element, and the hydrothermal durability may not be sufficiently improved in some cases.

[0040] [Production method] The phosphorus element-containing zeolite of the present embodiment can be obtained by impregnating small-pore zeolite particles having an oxygen 8-membered ring structure, such as CHA, AEI, and AFX, with an aqueous solution containing phosphoric acid or a phosphate and an organic base that neutralizes the phosphoric acid or phosphate. By performing neutralization, it is possible to prevent the aluminum atoms from desorbing from CHA, AEI, and AFX due to phosphoric acid or a phosphate, and by preventing the polymerization of phosphoric acid or a phosphate, it becomes easier for phosphoric acid species to diffuse into the pores of CHA, AEI, and AFX, and it is possible to suppress the condensation of phosphoric acid species outside the pores of CHA, AEI, and AFX even when heated by drying or the like. In this way, by using a neutralized solution, phosphorus modification for obtaining the phosphorus element-containing zeolite of the present embodiment can be performed in one step, the equipment required for phosphorus modification can be simplified, and the amount of energy used can be reduced, so it can be said that this is an industrially advantageous method.

[0041] CHA, AEI, and AFX that undergo such phosphorus modification are not particularly limited, and may contain, for example, an alkali metal ion such as a sodium ion or a hydrogen ion as a counter cation. Also, regarding the phosphorus modification step, as long as it does not deviate from the gist of the present invention, appropriate changes or additions to the steps may be made. Examples of such a process configuration include performing phosphorus modification on CHA, AEI, and AFX containing sodium ions as counter cations, and then exchanging the sodium ions for hydrogen ions.

[0042] [Phosphoric acid] The phosphoric acid or phosphate to be impregnated into CHA, AEI, and AFX is not particularly limited as long as it is water-soluble, but from the viewpoints of price, availability, and safety, phosphoric acid, sodium phosphate, ammonium phosphate, vinylphosphonic acid, etc. are preferable, and phosphoric acid is more preferable.

[0043] The organic base that neutralizes phosphoric acid or phosphate is not particularly limited. As long as it has high solubility in water and can suppress the polymerization of phosphoric acid or phosphate when heated in a mixed state with phosphoric acid or phosphate, it is not particularly limited. Examples of such organic bases include tetraalkylammonium, pyridine, trialkylamine, dialkylamine, alkylamine, ethanolamine, ethylenediamine, piperazine, piperidine, morpholine, N-alkylmorpholine, etc., but are not particularly limited thereto. Among these, ethanolamine, morpholine, and N-alkylmorpholine are preferred in terms of relatively weak odor and difficulty in deteriorating the working environment, and those that are not strong bases such as morpholine and N-ethylmorpholine are more preferred in terms of safety.

[0044] <Method for producing phosphorus element-containing zeolite> [Production method: Amount of organic base used relative to phosphoric acid] When using an organic base that neutralizes phosphoric acid or phosphate with phosphoric acid or phosphate during phosphorus modification, the amount of the organic base used is not particularly limited. Any amount that can neutralize phosphoric acid or phosphate may be used, but as described later, it is not limited thereto. The amount of the organic base is not particularly limited, but is preferably 50 to 300 mol%, more preferably 80 to 250 mol%, and even more preferably 120 to 220 mol% based on the total amount of phosphoric acid and / or phosphate. Even if phosphoric acid or phosphate is not completely neutralized, it is sufficient if a predetermined amount of phosphoric acid or phosphate can be impregnated into CHA, AEI, or AFX, and it is also sufficient if there is no such situation that the surface of CHA, AEI, or AFX is coated with phosphoric acid or phosphate polymerized in a large excess.

[0045] [Production method: Amount of mixed aqueous solution (phosphoric acid - organic base) used] When performing phosphorus modification on CHA, AEI, or AFX, as described above, it is preferable to use an aqueous mixed solution of phosphoric acid or phosphate and an organic base. The usage amount thereof is preferably 70 to 120% by mass, more preferably 90 to 110% by mass, of the saturated water content of CHA, AEI, or AFX impregnated with the aqueous mixed solution. If the impregnation amount of the aqueous mixed solution is too small, CHA, AEI, or AFX may not be sufficiently phosphorus-modified, and if it is too large, phosphoric acid or phosphate and the organic base will be wasted. Note that the saturated water content in this specification is obtained by allowing CHA, AEI, or AFX dried in an air atmosphere at 120°C for 6 hours or more to stand in water for 1 hour, then filtering, and setting the increased mass from the dry state as a water content of 100% by mass.

[0046] [Production Method: Drying, Firing] When using phosphoric acid or phosphate and an organic base that neutralizes phosphoric acid, the treatment after impregnation with the aqueous mixed solution is optional, but drying and firing are preferable. When drying and firing, the temperature and atmosphere are not particularly limited. However, when drying, if it is in the air, the temperature is preferably 100 to 200°C, more preferably 130 to 190°C, and most preferably 140 to 180°C. Also, the drying time is not particularly limited, and it is preferably generally 1 hour or more.

[0047] As described above, in the method for producing the phosphorus element-containing zeolite of this embodiment, the firing treatment is optional. However, when firing is performed for the purpose of decomposing the phosphorus species, if it is in the air, it is preferably 300 to 800°C. If the temperature is too low, phosphoric acid may not be sufficiently decomposed, and if it is too high, there may be problems with the framework structure, pore shape, and particle shape of CHA, AEI, or AFX.

[0048] [Physical Properties and Applications] [Hydrothermal Durability Conditions] The phosphorus element-containing zeolite of this embodiment has excellent hydrothermal durability, but the evaluation method is not particularly limited and may be appropriately determined, for example, assuming the use environment. As an example of such an evaluation method, the crystallinity of CHA, AEI, and AFX before phosphorus modification analyzed using powder X-ray fluorescence analysis (XRD: X-ray diffraction) is used as the denominator, and the crystallinity of the phosphorus element-containing zeolite after a hydrothermal durability test after phosphorus modification is used as the numerator, and the result is evaluated as the relative crystallinity expressed as a percentage.

[0049] [Catalytic use] The use of the phosphorus element-containing zeolite of this embodiment is not particularly limited, but since it has excellent hydrothermal durability in a high-temperature environment, it is preferably used as a catalyst for purifying exhaust gas discharged from internal combustion engines, particularly a catalyst for purifying exhaust gas discharged from automobiles using gasoline or light oil as fuel.

[0050] Also, for the purpose of purifying exhaust gas discharged from large diesel vehicles such as trucks and buses for automotive use, it is preferably used as a filter catalyst for capturing particulate components such as soot discharged from these large vehicles, or as a selective reduction catalyst for purifying NOx using an ammonia component disposed downstream of this filter catalyst as a reducing agent. The filter catalyst may get hot when burning and removing the captured particulate components such as soot to regenerate the filter, and the selective reduction catalyst disposed downstream of the filter is exposed to the heat during filter regeneration. Therefore, the excellent effect of hydrothermal durability of the phosphorus element-containing zeolite of this embodiment is fully exerted.

Examples

[0051] Hereinafter, the features of the present invention will be described more specifically with reference to examples and comparative examples of the present invention. However, the present invention is not limited to the following examples. That is, it goes without saying that materials, usage amounts, ratios, processing contents, processing procedures, etc. shown in the following examples can be appropriately changed within the scope of the gist of the present invention without departing from the gist of the present invention. In addition, the values of various manufacturing conditions and evaluation results in the following examples have the meaning as the preferable upper limit value or preferable lower limit value in the embodiments of the present invention, and the preferable range may be a range defined by a combination of the above-mentioned upper or lower limit values and the values of the following examples or the values between the examples.

[0052] [Preparation of Seed Crystal: FAU-Type Zeolite (SAR = 14.0)] In synthesizing the phosphorus-modified AFX-type zeolite according to one aspect of the present invention, FAU-type zeolite used as a silica-alumina source was prepared. Regarding the FAU-type zeolite to be used, in order to further improve the durability of the synthesized AFX zeolite, dealumination treatment was performed as follows.

[0053] While stirring, 84.0 g of 60% by mass nitric acid was mixed with 4,000 g of water, and 400.0 g of FAU-type zeolite HSZ-350HUA (manufactured by Tosoh Corporation, silica-alumina ratio SAR 11.1) was added. After stirring at room temperature for 24 hours, solid-liquid separation was performed, and it was dried at 105°C. When the FAU-type zeolite as the silica-alumina source subjected to dealumination treatment was analyzed by XRF, the SAR was 14.0, and it was confirmed that dealumination had occurred.

[0054] [Synthesis of AFX-Type Zeolite] Subsequently, 17.9 g of a 4.8 mass% sodium hydroxide aqueous solution, 18.8 g of a 19.43 mass% N,N,N’,N’-tetraethylbicyclo[2.2.2]octane-2,3:5,6-dipyrrolidinium dihydroxide (manufactured in-house by N.E. Chemcat, molecular weight 340.55) aqueous solution as a structure-directing agent for AFX-type zeolite, 10.0 g of dealuminated FAU-type zeolite (SAR = 14.0) as the silica-alumina source described above, and 70.0 g of water were stirred in a stainless steel beaker for 16 hours. The composition of the mixture was as follows. The numerical values in the following composition represent the molar ratio when the amount of substance of SiO2 is taken as 1.

[0055] SiO2 0.071 Al2O3 0.082 OSDA 2+ 0.166 Na + 0.330 OH - 44.25 H2O

[0056] Next, this raw material composition (mixture) was placed in a 200 cc stainless steel autoclave and stirred at 20°C for 16 hours at 400 rpm using a stir bar, and then further stirred and held at 160°C for 240 hours at 400 rpm. The product after this hydrothermal treatment was subjected to solid-liquid separation, the obtained solid phase was washed with a sufficient amount of water, and dried at 105°C to obtain a product. The total amount of the obtained product was calcined at 600°C for 5 hours while flowing air. When powder X-ray fluorescence analysis (XRD: X-ray diffraction) was performed on the product (solid phase) thus obtained, it was confirmed that it was a single-phase AFX-type zeolite. Also, when analyzed by XRF, the SAR was 13.4. Further, this calcined AFX-type zeolite was used as Reference Example 1 when determining the relative crystallinity.

[0057] [Example 1: Preparation of Phosphorus-Modified AFX-Type Zeolite] To 4.0 g of the fired AFX-type zeolite of Reference Example 1 above, a mixed solution of 0.2 g (2.3 mmol) of morpholine (molecular weight 87.12) as an organic base, 0.15 g (1.3 mmol) of 85% by mass phosphoric acid, and 1.55 g of water was impregnated in a container and aged overnight at room temperature while sealed. Subsequently, it was dried at 105 °C for 16 hours to obtain a phosphorus-modified AFX-type zeolite (SAR = 13.4).

[0058] [Hydrothermal Durability Test] 1.0 g of the phosphorus-modified AFX-type zeolite powder of Example 1 was placed in a crucible, and this was placed in an electric furnace (trade name OXK-600X, manufactured by Koei Electric Furnace Co., Ltd.) connected to a gas humidifying device (trade name RMG-1000, manufactured by J Science Lab Co., Ltd.). While supplying an atmosphere containing 10% water vapor at a flow rate of 70 L / min, the temperature was raised to 950 °C and held for 1 hour. The relative intensity was calculated from the peak intensity of the powder X-ray diffraction of the obtained powder. The results are shown in Table 1 together with those of other Examples and Comparative Examples.

[0059] [Comparative Example 1: Phosphorus-Unmodified AFX-Type Zeolite (SAR = 13.4)] For the fired AFX-type zeolite powder of Reference Example 1 without phosphorus modification used in Example 1, the same hydrothermal durability test and analysis by XRD as in Example 1 were performed. The results are shown in Table 1.

[0060] [Preparation of Seed Crystal: FAU-Type Zeolite (SAR = 17.0)] In synthesizing the phosphorus-modified AFX-type zeolite of one aspect of the present invention, a FAU-type zeolite used as a silica-alumina source was prepared. Dealumination of the FAU-type zeolite was performed to further improve the durability of the AFX zeolite in the same manner as [Preparation of Seed Crystal: FAU-Type Zeolite (SAR = 14.0)] except that 126.0 g of 60% by mass nitric acid was used instead of 84.0 g of 60% by mass nitric acid. When analyzed by XRF, the SAR was 17.0.

[0061] [Synthesis of AFX-Type Zeolite] Subsequently, 19.0 g of a 4.8 mass% aqueous sodium hydroxide solution, 20.0 g of an aqueous solution of 19.43 mass% N,N,N’,N’-tetraethylbicyclo[2.2.2]octane-2,3:5,6-dipyrrolidinium dihydroxide (manufactured in-house by N.E. Chemcat Corporation, molecular weight 340.55) as a structure-directing agent for AFX-type zeolite, 11.0 g of dealuminated FAU-type zeolite (SAR = 17.0) as the silica-alumina source described above, and 70.0 g of water were stirred in a stainless steel beaker for 16 hours. The composition of the mixture was as follows. The numerical values in the following composition represent the molar ratios when the amount of substance of SiO2 is taken as 1.

[0062] SiO2 0.059 Al2O3 0.075 OSDA 2+ 0.151 Na + 0.301 OH - 38.67 H2O

[0063] Next, this raw material composition (mixture) was placed in a 200 cc stainless steel autoclave and stirred at 20°C for 16 hours at 400 rpm using a magnetic stirrer, and then further stirred and maintained at 165°C for 216 hours at 400 rpm. The product after this hydrothermal treatment was subjected to solid-liquid separation, the obtained solid phase was washed with a sufficient amount of water, and dried at 105°C to obtain a product. The total amount of the obtained product was calcined at 600°C for 5 hours while flowing air. When powder X-ray diffraction analysis (XRD) was performed on the product (solid phase) thus obtained, it was confirmed that it was a single-phase AFX-type zeolite. Also, when analyzed by XRF, the SAR was 16.0. In addition, this calcined AFX-type zeolite was used as Reference Example 2 when determining the relative crystallinity.

[0064] [Example 2: Preparation of Phosphorus-Modified AFX-Type Zeolite] An AFX-type zeolite modified with phosphorus (SAR = 16.0) was obtained in the same manner as in Example 1, except that 4.0 g of the calcined AFX-type zeolite of Reference Example 2 was used instead of the calcined AFX-type zeolite of Reference Example 1. This was subjected to the same hydrothermal durability test and XRD analysis as in Example 1. The results are shown in Table 1.

[0065] [Comparative Example 2: Unmodified AFX-type zeolite (SAR = 16.0)] The calcined AFX-type zeolite powder of Reference Example 2 without phosphorus modification used in Example 2 was subjected to the same hydrothermal durability test and XRD analysis as in Example 1. The results are shown in Table 1.

[0066]

Table 1

[0067] The relative crystallinity in Table 1 is a comparison with the crystallinity of the calcined AFX-type zeolite before hydrothermal durability in Comparative Example 2. There are Reference Example 1 (Comparative Example 1) and Reference Example 2 (Comparative Example 2) of the calcined AFX-type zeolite. For Reference Example 2 (Comparative Example 2) with a large SAR and expected high crystallinity, the crystallinity determined by XRD diffraction was taken as 100%, and based on this, the crystallinity after hydrothermal durability was expressed as a relative value.

[0068] From the results in Table 1, it was found that the AFX-type zeolites of Example 1 and Example 2 modified with phosphorus both have higher hydrothermal durability than the AFX-type zeolites of Comparative Example 1 and Comparative Example 2 unmodified with phosphorus element. In particular, from the results of Example 1 and Comparative Example 1, it can be seen that the hydrothermal durability is significantly improved in zeolites with a low SAR and generally considered to have low hydrothermal durability.

[0069] [Distribution analysis of phosphorus element] For the phosphorus-modified AFX-type zeolites of Example 1 and Example 2, the amount of phosphorus element contained in the whole particle was determined by XRF as the elemental content rate of the whole bulk, and the results are shown in Table 2. Also, the content rate of the phosphorus element in the particle surface layer was determined by XPS, and the results are shown in Table 3. Note that the numerical values in Tables 2 and 3 both represent atomic %.

[0070]

Table 2

[0071]

Table 3

[0072] Also, it is considered that the phosphorus element selectively adsorbs to the cation sites in the zeolite. Regarding the results in Tables 2 and 3, the ratio of the phosphorus element to the aluminum element in the particle surface layer and the ratio of the concentration of the phosphorus element to the aluminum element in the whole bulk of the whole particle are summarized in Table 4.

[0073]

Table 4

[0074] From the results in Table 4, it can be seen that in both Example 1 and Example 2, the phosphorus element is unevenly distributed in the zeolite particle surface layer.

[0075] Subsequently, the AEI-type zeolite was also processed in the same manner as the AFX-type zeolite, and the effect of phosphorus modification on the AEI-type zeolite particle surface layer was verified. [Synthesis of AEI-Type Zeolite] 410.0 g of an aqueous solution of 20.40 mass% 1,1,3,5 - tetramethylpiperidinium hydroxide (manufactured by Seikem, molecular weight 159.27), 350.0 g of water, 48.0 g of FAU - type zeolite CBV - 712 (SAR = 10.9, manufactured by Zeolyst), and 600.0 g of sodium metasilicate solution No. 3 (29.0% SiO₂, manufactured by Nippon Chemical Industry Co., Ltd.) were stirred in a stainless - steel beaker for 1 hour. The composition of the mixture was as follows. The numerical values in the following composition represent the molar ratio when the amount of substance of SiO₂ is taken as 1.

[0076] SiO₂ 0.015 Al₂O₃ 0.152 OSDA + 0.540 Na + 0.692 OH - 17.03 H₂O

[0077] Next, this raw material composition (mixture) was put into a 1,200 cc stainless - steel autoclave and stirred at 150 °C for 96 hours at 70 rpm using a stirrer, and then further stirred and maintained at 160 °C for 24 hours. After the hydrothermal treatment, the product was subjected to solid - liquid separation, and the obtained solid phase was washed with a sufficient amount of water and dried at 105 °C to obtain a product. The total amount of the obtained product was calcined at 600 °C for 5 hours while flowing air. When the obtained product (solid phase) was analyzed by XRD, it was confirmed to be an AEI - type zeolite with a crystallinity of 90% or more. Also, when analyzed by XRF, the SAR was 14.3. This calcined AEI - type zeolite was used as Reference Example 3 when determining the relative crystallinity.

[0078] [Example 3: Preparation of Phosphorus - Modified AEI - Type Zeolite] To 3.0 g of the calcined AEI-type zeolite synthesized as described above, a mixed solution of 0.15 g (1.7 mmol) of morpholine (molecular weight 87.12) as an organic base, 0.1 g (0.9 mmol) of 85% by mass phosphoric acid, and 1.05 g of water was impregnated in a container and left to age for 2 nights while sealed. Then, it was dried at 105 °C for 16 hours to obtain a phosphorus-modified AEI-type zeolite (SAR = 14.3). The ratio of phosphorus element to aluminum element (P / Al ratio) by XRF was 0.16, and the content of P (solid content basis) was 1.0% by mass. This was subjected to the same hydrothermal durability test and XRD analysis as in Example 1. Together with Example 4 and Comparative Example 3, the results are shown in Table 5. Also, the comparison of the P / Al ratio between the whole bulk and the surface was carried out in the same manner as in Example 1. The results are shown in Table 6.

[0079] [Example 4: Preparation of Phosphorus-Modified AEI-Type Zeolite] In Example 3, the amount of morpholine used was changed to 0.3 g (3.4 mmol), and a phosphorus-modified AEI-type zeolite (SAR = 14.3) was obtained in the same manner as in Example 3 except that 0.2 g (1.7 mmol) of vinylphosphonic acid (molecular weight 108.03) and 0.8 g of water were used instead of 85% by mass phosphoric acid. The ratio of phosphorus element to aluminum element (P / Al ratio) by XRF was 0.31, and the content of P (solid content basis) was 1.9% by mass. This was subjected to the same hydrothermal durability test and XRD analysis as in Example 1. The results are shown in Table 5. Also, the comparison of the P / Al ratio between the whole bulk and the surface was carried out in the same manner as in Example 1. The results are shown in Table 6.

[0080] [Comparative Example 3: Phosphorus-Unmodified AEI-Type Zeolite] The phosphorus-unmodified calcined AEI-type zeolite powder used in Example 3 was analyzed by the same hydrothermal durability test and XRD as in Example 1 without any phosphorus modification. The results are shown in Table 5. Also, the comparison of the P / Al ratio between the whole bulk and the surface was carried out in the same manner as in Example 1. The results are shown in Table 6.

[0081]

Table 5

Table 6

[0082] The relative crystallinity in Table 5 is a relative value obtained by setting the crystallinity determined by performing XRD analysis on the calcined AEI-type zeolite (Reference Example 3) before hydrothermal durability to 100% and comparing it with this. From the results in this Table 5, it can be seen that for the AEI-type zeolite as well, by unevenly distributing and concentrating phosphorus element on the surface layer of the zeolite particles by the same operation as for the AFX-type zeolite, the hydrothermal durability is improved.

[0083] Subsequently, the CHA-type zeolite was also treated in the same manner as the AFX-type zeolite, and the effect of phosphorus modification on the surface layer of the CHA-type zeolite particles was verified.

[0084] [Synthesis of CHA-Type Zeolite] 1,220.0 g of an aqueous solution of 25 mass% N,N,N-trimethyladamantylammonium hydroxide (molecular weight 211.35, manufactured by Seikem), 1,710.0 g of water, 74 g of sodium hydroxide (special grade, manufactured by Fujifilm Wako Pure Chemical Corporation), 590.0 g of Kyoward KW700SEN-S (synthetic aluminum silicate, manufactured by Kyowa Chemical Industry Co., Ltd.), 880.0 g of Snowtex 40 (manufactured by Nissan Chemical Industries, Ltd., 39.7% SiO2), and 31.0 g of chabazite seed crystal (SAR16) were stirred in a stainless steel beaker for 1 hour. The composition of the mixture was as follows. The numerical values in the following composition represent the molar ratio when the amount of substance of SiO2 is taken as 1.

[0085] SiO2 0.053 Al2O3 0.120 OSDA + 0.190 Na + 0.310 OH - 15.06 H2O

[0086] Next, this raw material composition (mixture) was placed in a 5,000 cc stainless steel autoclave, and stirring was maintained at 170 °C for 55 hours at 300 rpm. After cooling, the product after this hydrothermal treatment was subjected to solid-liquid separation, the obtained solid phase was washed with a sufficient amount of water, and dried at 105 °C to obtain a product. After holding the total amount of the obtained product at 380 °C for 6 hours, while allowing air to flow, it was further calcined at 380 °C for 3 hours, 440 °C for 3 hours, 500 °C for 3 hours, and then 600 °C for 1 hour. When the product (solid phase) thus obtained was analyzed by XRD, it was confirmed to be CHA-type zeolite.

[0087] [Preparation of CHA-Type Zeolite] 519.0 g of the calcined CHA-type zeolite synthesized as described above was put into a solution prepared by dissolving 519.0 g of ammonium nitrate (special grade, manufactured by Fujifilm Wako Pure Chemical Corporation) in 4152 g of water, and heated and stirred and held at 80 °C for 2 hours or more. After cooling, solid-liquid separation was performed, and the same operation was repeated. After solid-liquid separation, it was washed with a sufficient amount of water and dried at 105 °C to obtain NH4 + type CHA-type zeolite. After holding the total amount of the obtained product at 120 °C for 2 hours, it was calcined at 500 °C for 5 hours to obtain H + type CHA-type zeolite. When analyzed by XRF, the SAR was 15.2. This calcined H + type CHA-type zeolite was used as Reference Example 4 when determining the relative crystallinity.

[0088] [Example 5: Preparation of Phosphorus-Modified CHA-Type Zeolite] H synthesized as described above +3.0 g of type CHA zeolite was impregnated in a container with a mixed solution of 0.15 g (1.7 mmol) of morpholine (molecular weight 87.12) as an organic base, 0.1 g (0.9 mmol) of 85% by mass phosphoric acid, and 1.05 g of water, and left to age for 2 nights while sealed. Then, it was dried at 105 °C for 16 hours to obtain phosphorus-modified CHA zeolite (SAR = 15.2). The ratio of phosphorus element to aluminum element (P / Al ratio) by XRF was 0.20, and the phosphorus content (on a solids basis) was 1.19% by mass. This was subjected to the same hydrothermal durability test and XRD analysis as in Example 1. The results are shown in Table 7 together with Example 5 and Comparative Example 4. Also, the P / Al ratio was compared between the whole bulk and the surface in the same manner as in Example 1. The results are shown in Table 8.

[0089] [Comparative Example 4: Unmodified Phosphorus CHA-Type Zeolite] For the unmodified H + type CHA zeolite powder used in Example 5, without phosphorus modification, the same hydrothermal durability test and XRD analysis as in Example 1 were carried out. The results are shown in Table 7. Also, the P / Al ratio was compared between the whole bulk and the surface in the same manner as in Example 1. The results are shown in Table 8.

[0090]

Table 7

Table 8

[0091] The relative crystallinity in Table 7 is a relative value compared with the crystallinity determined by performing XRD diffraction on the H + type CHA zeolite (Reference Example 4) before hydrothermal durability as 100%. From the results in this Table 7, it can be seen that for CHA zeolite as well, by unevenly distributing and concentrating phosphorus element on the surface layer of zeolite particles by the same operation as for AFX type zeolite, the hydrothermal durability is improved.

Claims

Claim 1 A method for producing a phosphorus element-containing zeolite, comprising impregnating small pore zeolite particles containing at least an aluminum element and a silica element and having an oxygen 8-membered ring structure selected from the group consisting of CHA, AEI, and AFX types with an aqueous solution containing phosphoric acid or a phosphate and an organic base that neutralizes the phosphoric acid or the phosphate. A method for producing a phosphorus element-containing zeolite. Claim 2 The small pore zeolite particles have a silica alumina ratio [silica / alumina] of 5 to 100 The method for producing a phosphorus element-containing zeolite according to claim 1. Claim 3 The phosphoric acid or phosphate contains one or more selected from the group consisting of phosphoric acid, sodium phosphate, ammonium phosphate, and vinylphosphonic acid The method for producing a phosphorus element-containing zeolite according to claim 1 or 2. Claim 4 The organic base contains one or more selected from the group consisting of tetraalkylammonium, pyridine, trialkylamine, dialkylamine, alkylamine, ethanolamine, ethylenediamine, piperazine, piperidine, morpholine, and N-alkylmorpholine The method for producing a phosphorus element-containing zeolite according to any one of claims 1 to 3.

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