JP6792426B2 - Zeolite and honeycomb catalyst - Google Patents

Description

The present invention relates to zeolites and honeycomb catalysts containing zeolites.

Conventionally, as one of the systems for purifying automobile exhaust gas, an SCR (Selective Catalytic Reduction) system that reduces NOx to nitrogen and water using ammonia has been known, and is a zeolite having a CHA structure in which Cu is supported. Is attracting attention as a zeolite having an SCR catalytic action.

Further, Patent Document 1 discloses a catalyst composition containing Ce in addition to Cu.
Patent Document 1 describes that Ce is present in the catalyst composition in a state selected from exchanged cerium ions, monomeric ceria, oligomeric ceria and combinations thereof.

Special Table 2015-500138

Patent Document 1 describes that any known technique (ion exchange, impregnation, isomorphic substitution, etc.) can be used as a method for allowing Cu to be present in the catalyst composition. Further, an initial wetting method in which ce nitrate is added is described as a method for allowing Ce to be present in the catalyst composition.

In Patent Document 1, it is stated that the existence state of Cu and Ce may be any state, but as a result of repeated studies by the present inventors, it was found that the NOx purification performance greatly differs depending on the existence state of Cu and Ce. It was.
Further investigation of this cause revealed that NOx purification performance was inferior if Ce was not sufficiently ion-exchanged in the zeolite.
In particular, it has been found that when Ce is supported by an initial wetting method using nitric acid Ce as described in Patent Document 1, Ce is not sufficiently ion-exchanged and the NOx purification performance is inferior.

The present invention has been made to solve the above problems, a zeolite in which Ce exists in a zeolite in a sufficiently ion-exchanged state, and a zeolite that can be used as an SCR catalyst having high NOx purification performance. , An object of the present invention is to provide a honeycomb catalyst containing the above-mentioned zeolite.

The zeolite of the present invention for achieving the above object is a CHA-type zeolite ion-exchanged with Cu and Ce, and the Ce occupancy rate obtained by crystal structure analysis by the XRD-Rietveld method is 0.05 or more. It is characterized by being.

The zeolite of the present invention is a CHA-type zeolite that is ion-exchanged with Cu and Ce. Here, as an index of the amount of Ce elements actually ion-exchanged in Ce, the occupancy rate of Ce obtained by crystal structure analysis by the XRD-Rietveld method can be used. Zeolites having an occupancy rate of 0.05 or more are zeolites in which Ce exists in the zeolite in a sufficiently ion-exchanged state, and can be used as an SCR catalyst having high NOx purification performance. ..
The term "ion-exchanged" in the present specification is not a term used to describe a production method that has undergone an ion exchange step, but Cu ions and Ce ions are located at the cation sites of zeolite. It is a term that specifies the structure or characteristics by indicating the state of being
In the Rietveld analysis, the space group was No. It is set to 166 (R-3m) and is performed using software (PDXL2 manufactured by Rigaku).

In the zeolite of the present invention, the lattice constants of the zeolite obtained by crystal structure analysis by the XRD-Rietveld method are a = b = 13.55 to 13.65 Å and c = 14.8 to 14.9 Å, and the arrangement of Cu is Is preferably 0.2 to 0.35 in Z-axis coordinates.

The fact that the arrangement of Cu is 0.2 to 0.35 in the Z-axis coordinates means that the position of Cu shifts due to the inclusion of Ce in the crystal structure. It is considered that the NOx purification performance is also improved by shifting the position of Cu.

In the zeolite of the present invention, the amount of Cu element supported on the zeolite is preferably 2 to 6% by weight, and the amount of Ce element supported on the zeolite is preferably 3 to 5% by weight.
When the amount of Cu elements carried on the zeolite is within the above range, high NOx purification performance can be obtained with a small amount of zeolite, and deterioration of NOx purification performance due to ammonia oxidation at high temperature can be prevented.
Further, when the amount of Ce element supported on the zeolite is 3% by weight or more, the NOx purification performance can be further enhanced. Further, even if the amount of the Ce element supported on the zeolite is increased by more than 5% by weight, the occupancy rate of Ce does not increase so much, so that the effect of supporting Ce as a catalyst becomes difficult to be exhibited.

In the zeolite of the present invention, the SiO ₂ / Al ₂ O ₃ composition ratio (SAR) of the zeolite is preferably 5 to 15.
When the composition ratio SiO ₂ / Al ₂ O ₃ is 15 or less, the NOx purification performance can be further improved. The reason is that when SiO ₂ / Al ₂ O ₃ is 15 or less, the amount of alumina in the zeolite increases, and the amount of Cu and Ce that function as catalysts can be increased proportionally.

In the zeolite of the present invention, the ratio of Ce supported as CeO _{2 to the} amount of Ce element supported on the zeolite is preferably 0.5 or less.
Further, it is more preferable that the ratio of Ce supported as CeO _{2 to the} amount of Ce element supported on the zeolite is 0.3 or less.
The ratio of Ce carried as CeO ₂ is an index of the ratio of the amount of Ce elements that have not been ion-exchanged. Therefore, if this ratio is low, the ratio of Ce that is ion-exchanged is high and the NOx purification performance is excellent. It becomes.

In the zeolite of the present invention, the CHA-type zeolite is preferably SSZ-13. It has high durability and can improve NOx purification performance.

The honeycomb catalyst of the present invention is characterized by containing the zeolite of the present invention and an inorganic binder.
Since the honeycomb catalyst of the present invention contains the zeolite of the present invention, it is suitable as a honeycomb catalyst used in an SCR system.

FIG. 1 is a perspective view schematically showing an example of the honeycomb catalyst of the present invention. FIG. 2 is a perspective view schematically showing another example of the honeycomb catalyst of the present invention. FIG. 3 is a perspective view schematically showing an example of a fired honeycomb body constituting the honeycomb catalyst shown in FIG. 2. FIG. 4 is an SEM photograph of the ion-exchanged zeolite obtained in Example 1. FIG. 5 is an SEM photograph of the ion-exchanged zeolite obtained in Comparative Example 1.

(Detailed description of the invention)
Hereinafter, the zeolite of the present invention will be described.
The zeolite of the present invention is a CHA-type zeolite that is ion-exchanged with Cu and Ce.
CHA-type zeolite is a zeolite named and classified by the structural code CHA in the International Zeolite Association (IZA), and has a crystal structure equivalent to that of naturally occurring chabazite.

In the zeolite of the present invention, the occupancy rate of Ce determined by crystal structure analysis by the XRD-Rietveld method is 0.05 or more.
The XRD-Rietveld method is obtained by optimizing the XRD data obtained by measuring a certain crystal with an XRD (X-ray diffractometer) by the minimum square method assuming a possible crystal structure. It is a method of estimating the crystal structure corresponding to the obtained XRD data, and is a method known as a method of estimating the crystal structure.
According to this method, the occupancy rate of Ce when the optimum structure is obtained when the structure is optimized assuming a structure in which Cu and Ce are ion-exchanged with CHA-type zeolite is obtained, and in the zeolite of the present invention, Ce Occupancy rate is 0.05 or more.
Zeolites having a Ce occupancy rate of 0.05 or more are zeolites in which Ce is sufficiently ion-exchanged in the zeolite, and can be used as an SCR catalyst having high NOx purification performance. Become.

Further, it is preferable that the lattice constants of zeolite obtained by crystal structure analysis by the XRD-Rietveld method are a = b = 13.55 to 13.65 Å and c = 14.8 to 14.9 Å.
Further, the arrangement of Cu is preferably 0.2 to 0.35 in Z-axis coordinates.
The fact that the arrangement of Cu is 0.2 to 0.35 in the Z-axis coordinates means that the position of Cu shifts due to the inclusion of Ce in the crystal structure. It is considered that the NOx purification performance is also improved by shifting the position of Cu.

The amount of Cu element supported on the zeolite is preferably 2 to 6% by weight.
The amount of Ce element supported on the zeolite is preferably 3 to 5% by weight.
Cu element content supported on zeolites and Ce element amount, in addition containing Cu element and Ce element is ion exchanged, including Cu element deposited in the form of oxides such as CuO or CeO ₂ in the zeolite particles and the Ce element such The amount.
The amount of Cu element and the amount of Ce element carried on the zeolite can be obtained from the element ratio contained in the zeolite measured by ICP emission spectroscopic analysis.

Further, the ratio of Ce supported as CeO _{2 to the} amount of Ce element supported on the zeolite is preferably 0.5 or less, and more preferably 0.3 or less.
The ratio of Ce carried as CeO ₂ is an index of the ratio of the amount of Ce elements that have not been ion-exchanged. Therefore, if this ratio is low, the ratio of Ce that is ion-exchanged is high and the NOx purification performance is excellent. It becomes.
The amount of CeO ₂ supported can be determined by XRD analysis. Specifically, first, the zeolite powder and the CeO ₂ powder are mixed at an arbitrary ratio and XRD measurement is performed to prepare a calibration curve of CeO ₂ . Then, the supported amount of CeO ₂ can be obtained by similarly measuring the powder to be obtained by XRD and comparing it with the calibration curve.

The zeolite of the present invention preferably has a SiO ₂ / Al ₂ O ₃ composition ratio (SAR) of 5 to 15. The SiO ₂ / Al ₂ O ₃ composition ratio means the molar ratio (SAR) of SiO ₂ to Al ₂ O _{3 in} zeolite. Since the composition ratio SiO ₂ / Al ₂ O ₃ is 5 to 15, the acid points of the zeolite can be made sufficient, and the acid points can be used for ion exchange with metal ions. Since it can carry a large amount of Cu and Ce, it has excellent NOx purification performance.
The molar ratio of zeolite (SiO ₂ / Al ₂ O ₃ ) can be measured by using fluorescent X-ray analysis (XRF).

The zeolite of the present invention preferably has an average particle size of 0.5 μm or less. By setting the average particle size to 0.5 μm or less, the zeolite and Cu salt powder can be easily mixed, and a mixed powder with no bias in the Cu salt powder can be obtained. Therefore, the amount of Cu supported is partially different. You can prevent that.
Examples of the method for obtaining zeolite having a desired particle size include a method of selecting a silica sol having a specific surface area of 150 to 500 m ² / g as a Si source and a dry aluminum hydroxide gel as an Al source.

The average particle size of zeolite is determined by taking a SEM photograph using a scanning electron microscope (SEM, manufactured by Hitachi High-Tech, Ltd., S-4800) and measuring the total diagonal length of 10 particles. Ask from. The measurement conditions are an accelerating voltage: 1 kV, an emission: 10 μA, and a WD: 2.2 mm or less. Generally, the particles of CHA-type zeolite are cubes, and when they are imaged two-dimensionally by SEM photography, they become square. Therefore, there are two diagonal lines of the particles.

The specific surface area of the silica sol can be determined by imaging the solid content of the silica sol with a transmission electron microscope (TEM: Transmission Electron Microscope) at a magnification of 500,000, measuring the particle size, and converting the particle size into the specific surface area. it can. The major axis and minor axis of the particles in the TEM image are measured using a scale, and the average value is taken as the particle size of the particles. The 20 particles are measured in the same manner, and the average value of their particle diameters is taken as the total particle diameter. The specific surface area is calculated by the following formula. The density of silica used is 2.2 g / cm ³ . Specific surface area (m ² / g) = 6000 / (particle diameter (nm) x density (g / cm ³ ))

Next, an example of a method for producing a zeolite capable of producing the zeolite of the present invention will be described.
Zeolites having a CHA structure (hereinafter referred to as CHA-type zeolite) may be synthesized or commercially available products may be used, but when synthesizing, first, Si source, Al source, alkali source, water and structural specifications are used. A raw material composition consisting of an agent is prepared.

The Si source refers to a compound, salt and composition that are raw materials for the silicon component of zeolite.
As the Si source, for example, colloidal silica, amorphous silica, sodium silicate, tetraethyl orthosilicate, aluminosilicate gel and the like can be used, and two or more of these may be used in combination. Of these, colloidal silica is desirable.

Examples of the Al source include aluminum sulfate, sodium aluminate, aluminum hydroxide, aluminum chloride, alumino-silicate gel, and dry aluminum hydroxide gel. Of these, dry aluminum hydroxide gel is preferred.

The molar ratio of the zeolite is substantially produced _{(SiO 2 / Al 2 O 3} ) and Si source in the same molar ratio, it is desirable to use the Al source, the molar ratio of the raw material composition in _{(SiO 2 / Al 2 O 3} ) , 5 to 15 is desirable.

As the alkali source, for example, an alkali component in sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide, lithium hydroxide, aluminate and silicate, an alkali component in aluminosilicate gel and the like can be used. It is possible, and two or more of these may be used in combination.

The amount of water is not particularly limited, the ratio of moles of water to the total number of moles of Al in the Si and Al sources Si source (H 2 _O moles / Si and the total number of moles of Al) is is preferably a 12 to 30, Si and Al sources Al total moles ratio of moles of water to the of the Si source _{(H 2} O moles / Si and the total number of moles of Al) is 15 to 25 Is more desirable.

The structure-determining agent (hereinafter, also referred to as SDA) refers to an organic molecule that regulates the pore size and crystal structure of zeolite. The structure of the obtained zeolite can be controlled by the type of the structure defining agent and the like.
Structural defining agents include hydroxides, halides, carbonates, methyl carbonates, sulfates and nitrates with N, N, N-trialkyladamantanammonium as cations; and N, N, N-trimethylbenzylammonium ions. , N-alkyl-3-quinucridinol ion, or N, N, N-trialkyl exoaminonorbornane as a cation group consisting of hydroxides, halides, carbonates, methyl carbonates, sulfates and nitrates. At least one selected from can be used. Among these, N, N, N-trimethyladamantanammonium hydroxide (hereinafter, also referred to as TMAAOH), N, N, N-trimethyladamantanammonium halide, N, N, N-trimethyladamantanammonium carbonate, It is desirable to use at least one selected from the group consisting of N, N, N-trimethyladamantanammonium methyl carbonate and N, N, N-trimethyladamantanammonium sulfate, and more preferably TMAAOH.

In the synthesis of zeolite, seed crystals of zeolite may be further added to the raw material composition. By using the seed crystal, the crystallization rate of zeolite is increased, the time in zeolite production can be shortened, and the yield is improved.

As the seed crystal of zeolite, it is desirable to use zeolite having a CHA structure.

The amount of zeolite seed crystals added is preferably small, but in consideration of the reaction rate, the effect of suppressing impurities, etc., it is preferably 0.1 to 20% by weight with respect to the silica component contained in the raw material composition. It is desirable, and more preferably 0.5 to 15% by weight.

In the synthesis of zeolite, zeolite is synthesized by reacting the prepared raw material composition. Specifically, it is desirable to synthesize zeolite by hydrothermal synthesis of the raw material composition.

The reaction vessel used for hydrothermal synthesis is not particularly limited as long as it is used for known hydrothermal synthesis, and may be a heat-resistant pressure-resistant vessel such as an autoclave. Zeolites can be crystallized by putting the raw material composition into the reaction vessel, sealing it, and heating it.

When synthesizing zeolite, the raw material mixture may be in a stationary state, but is preferably in a stirred and mixed state.

The heating temperature for synthesizing zeolite is preferably 100 to 200 ° C, more preferably 120 to 180 ° C. If the heating temperature is less than 100 ° C., the crystallization rate becomes slow and the yield tends to decrease. On the other hand, if the heating temperature exceeds 200 ° C., impurities are likely to be generated.

The heating time for synthesizing zeolite is preferably 10 to 200 hours. If the heating time is less than 10 hours, the unreacted raw material remains and the yield tends to decrease. On the other hand, even if the heating time exceeds 200 hours, the yield and crystallinity are hardly improved.

The pressure in the synthesis of zeolite is not particularly limited, and the pressure generated when the raw material composition placed in the closed container is heated to the above temperature range is sufficient, but if necessary, an inert gas such as nitrogen gas is used. In addition, the pressure may be increased.

It is desirable that the CHA-type zeolite obtained as described above is sufficiently allowed to cool, solid-liquid separated, and washed with a sufficient amount of water.

Since the CHA-type zeolite obtained as described above contains SDA in the pores, it may be removed if necessary. For example, SDA can be removed by a liquid phase treatment using an acidic solution or a chemical solution containing an SDA decomposition component, an exchange treatment using a resin or the like, a thermal decomposition treatment, or the like.

The CHA-type zeolite obtained as described above is subjected to Cu ion exchange and Ce ion exchange. The order of Cu ion exchange and Ce ion exchange is not particularly limited, but a method of performing Cu ion exchange and then performing Ce ion exchange (ion exchange method 1), or simultaneously performing Cu ion exchange and Ce ion exchange. It is preferable to adopt the method (ion exchange method 2).
Each method will be described below.

First, a method of performing Cu ion exchange and then performing Ce ion exchange (ion exchange method 1) will be described.
The Cu ion exchange is preferably carried out by mixing the CHA-type zeolite powder and the Cu salt powder to form a mixed powder, and heating the mixed powder.
The Cu salt is preferably one or more salts selected from the group consisting of copper sulfate, copper nitrate, copper acetate and copper chloride from the viewpoint of production cost.

As the mixing conditions in the mixing method, for example, a known mixer such as a mortar, a food processor, or a Henschel mixer is used, and the mixing time is, for example, 1 minute to 30 minutes, preferably 1 minute to 10 minutes.

In this way, a mixed powder composed of CHA-type zeolite powder and Cu salt powder is obtained. The water content of the mixed powder is preferably 40% by weight or less.
As described above, the ion exchange performed by mixing the CHA-type zeolite powder and the Cu salt powder is the ion exchange in the solid phase, but does not extremely regulate the amount of water in the mixed powder.
The water content of the mixed powder may be 40% by weight or less, and even the water content does not impair the effect of increasing the ion exchange efficiency of Cu. The water content of the preferred mixed powder is 1 to 20% by weight. By setting the water content to 1% by weight or more, the powder is not charged with static electricity in the mixing step, and the powder can be mixed more evenly. The water content of the mixed powder can be measured with a heat-drying moisture meter (MX-50 manufactured by A & D Co., Ltd.) at a set temperature of 200 ° C.

Next, the mixed powder is heated to fix Cu ions on the zeolite to obtain CHA-type zeolite exchanged with Cu ions.
As the heating means, a heating furnace such as a muffle furnace (KDF-S100 manufactured by Denken Hydental), an atmosphere furnace (FQ-5270 manufactured by Chugai Ro Co., Ltd.), or the like can be used.

The heating temperature is preferably 300 to 800 ° C. When the heating temperature is 300 ° C. or higher, Cu can be efficiently supported on the zeolite. Further, when the heating temperature is 800 ° C. or lower, the crystal structure of zeolite is not destroyed. A more preferable heating temperature is 400 to 800 ° C.

The heating atmosphere may be in the air or in an atmosphere of an inert gas such as nitrogen or argon. The pressure for heating can be atmospheric pressure. The heating time is, for example, 0.5 hour to 24 hours, preferably 1 hour to 12 hours.
By the above step, CHA-type zeolite obtained by Cu ion exchange is obtained.

Subsequently, Ce ion exchange is performed.
The Ce ion exchange is preferably carried out by mixing the Cu ion-exchanged CHA-type zeolite powder and the Ce compound to form a mixed powder, and heating the mixed powder.
The mixing conditions for obtaining the mixed powder can be the same as the conditions for mixing the CHA-type zeolite powder and the Cu salt powder in Cu ion exchange.

The water content of the mixed powder is preferably 40% by weight or less.
As described above, the ion exchange performed by mixing the CHA-type zeolite powder and the Ce compound is the ion exchange in the solid phase, but does not extremely regulate the water content in the mixed powder.
The Ce compound is a concept including a powder of a salt of Ce and a solution containing Ce ions, and the Ce compound may be added to CHA-type zeolite in the form of powder or in the form of a solution.
Normally, the amount of Cu ion-exchanged CHA-type zeolite powder is larger than the amount of Ce compound, so even if the Ce compound is added in the form of a solution, the water is absorbed by the zeolite powder. The state of the powder is maintained. That is, ion exchange occurs in the solid phase.

The salt of Ce is preferably one or more salts selected from the group consisting of cerium sulfate, cerium nitrate, cerium acetate and cerium chloride. Further, it is more preferable that it is at least one selected from the group consisting of cerium sulfate and cerium acetate.

Next, the mixed powder is heated to fix Ce ions on the zeolite to obtain CHA-type zeolite ion-exchanged with Cu and Ce.
The heating means and heating conditions can be the same as the heating conditions for the mixed powder in Cu ion exchange.
By the above steps, CHA-type zeolite ion-exchanged with Cu and Ce can be obtained.

Next, a method of simultaneously performing Cu ion exchange and Ce ion exchange (ion exchange method 2) will be described.
In the ion exchange method 2, CHA-type zeolite powder, Cu salt powder, and Ce compound are mixed together to form a mixed powder, and Cu ion exchange and Ce ion exchange are simultaneously performed by heating the mixed powder. Is preferable.

As the Cu salt and the Ce compound, the same compounds as in the ion exchange method 1 can be used. In the ion exchange method 2, there are preferable combinations of the Cu salt and the Ce compound, and it is preferable to use the combination of copper acetate as the Cu salt and cerium acetate as the Ce compound.
This combination is preferable because both Cu and Ce are easily ion-exchanged.
The mixing conditions for obtaining the mixed powder and the preferable water content of the mixed powder can be the same as in the ion exchange method 1.

Next, the mixed powder is heated to fix Cu ions and Ce ions on the zeolite to obtain CHA-type zeolite ion-exchanged with Cu and Ce.
The heating means and heating conditions can be the same as in the ion exchange method 1.

Incidentally, in either ion-exchange method, CHA-type zeolite prior to the ion exchange is preferably NH ₄ ⁺ -type zeolite or H ⁺ form zeolite. By performing ion exchange on such zeolite, CHA-type zeolite ion-exchanged with Cu and Ce can be efficiently produced.

The process for the preparation of NH ₄ ⁺ -type zeolite, with respect to zeolite after synthesis, and a method of performing ion exchange using the ammonia solution. Examples of the ammonia solution include aqueous ammonia, an aqueous solution of ammonium sulfate, and an aqueous solution of ammonium nitrate. The ammonia concentration in the ammonia solution is, for example, 1 to 10% by weight.
The ion exchange method using the ammonia solution can be carried out by immersing the zeolite in the above-mentioned ammonia solution. The temperature of the ammonia solution is, for example, 4 to 50 ° C., atmospheric pressure, and the immersion time is, for example, 0.1 hour to 2 hours. In this way, _NH ^{4 +} -type zeolite is obtained.

A process of preparing the H ⁺ form zeolite, a method of heating the NH ₄ ⁺ type zeolite obtained as described above can be mentioned.
The heating temperature is, for example, 350 to 650 ° C.
The heating time is, for example, 0.5 hour to 48 hours.
As the heating means, a commercially available heating furnace can be used.

[Honeycomb catalyst]
Hereinafter, the honeycomb catalyst of the present invention will be described.
The honeycomb catalyst of the present invention is characterized by containing the zeolite of the present invention and an inorganic binder.
The honeycomb catalyst preferably includes a honeycomb fired body in which a plurality of through holes are arranged side by side in the longitudinal direction with a partition wall separated.

The honeycomb fired body comprises the zeolite of the present invention, that is, an extruded body containing CHA-type zeolite ion-exchanged with Cu and Ce and an inorganic binder. As will be described later, the honeycomb fired body is produced by extrusion-molding a raw material paste containing the zeolite of the present invention and an inorganic binder, and then firing the paste.

The honeycomb catalyst obtained by the production method of the present invention may include a single honeycomb fired body, or may include a plurality of honeycomb fired bodies bonded via an adhesive layer.

In the honeycomb catalyst of the present invention, it is desirable that an outer peripheral coat layer is formed on the outer peripheral surface of the honeycomb fired body.

FIG. 1 is a perspective view schematically showing an example of the honeycomb catalyst of the present invention.
The honeycomb catalyst 10 shown in FIG. 1 includes a single honeycomb fired body 11 in which a plurality of through holes 11a are arranged side by side in the longitudinal direction with a partition wall 11b interposed therebetween. The honeycomb fired body 11 is made of an extruded body containing CHA-type zeolite and an inorganic binder that are ion-exchanged with Cu and Ce. Further, an outer peripheral coat layer 12 is formed on the outer peripheral surface of the honeycomb fired body 11.

FIG. 2 is a perspective view schematically showing another example of the honeycomb catalyst of the present invention.
FIG. 3 is a perspective view schematically showing an example of a fired honeycomb body constituting the honeycomb catalyst shown in FIG. 2.

In the honeycomb catalyst 20 shown in FIG. 2, a plurality of honeycomb fired bodies 21 (see FIG. 3) in which a plurality of through holes 21a are arranged side by side in the longitudinal direction with a partition wall 21b interposed therebetween are bonded to each other via an adhesive layer 23. Has the same configuration as the honeycomb catalyst 10 shown in FIG. Further, an outer peripheral coat layer 22 is formed on the outer peripheral surface of the honeycomb fired body 21.

In the honeycomb catalysts 10 and 20, the outer peripheral coat layers 12 and 22 may not be formed, respectively.

The shape of the honeycomb catalyst is not limited to a columnar shape, and examples thereof include a prismatic shape, an elliptical columnar shape, an oblong columnar shape, and a round chamfered prismatic shape (for example, a round chamfered triangular pillar shape).

In the honeycomb catalyst, the shape of the through hole of the honeycomb fired body is not limited to the square columnar shape, and examples thereof include a triangular columnar column and a hexagonal columnar column.

In the honeycomb catalyst, it is desirable that the density of through holes in the cross section perpendicular to the longitudinal direction of the honeycomb fired body is 31 to 155 pieces / cm ² .

In the honeycomb catalyst, the thickness of the partition wall of the honeycomb fired body is preferably 0.10 to 0.50 mm, and more preferably 0.20 to 0.40 mm.

In the honeycomb catalyst, when the outer peripheral coat layer is formed on the outer peripheral surface of the fired honeycomb body, the thickness of the outer peripheral coat layer is preferably 0.1 to 2.0 mm.

[Honeycomb catalyst manufacturing method]
Next, an example of the method for producing the honeycomb catalyst of the present invention will be described.
The honeycomb catalyst of the present invention can be produced by extrusion-molding a raw material paste containing the zeolite of the present invention and an inorganic binder and then firing the paste.

(Molding process)
In the molding step, a raw material paste containing zeolite and an inorganic binder is extruded to produce a honeycomb molded body in which a plurality of through holes are arranged side by side in the longitudinal direction with a partition wall in between. Specifically, a honeycomb molded body is produced by extrusion molding using a raw material paste containing zeolite and an inorganic binder, and further containing inorganic fibers and the like, if necessary.

The amount of zeolite contained in the raw material paste is preferably 25 to 60% by weight, more preferably 30 to 50% by weight.

The inorganic binder is not particularly limited, and examples thereof include solids contained in alumina sol, silica sol, titania sol, water glass, sepiolite, attapulsite, boehmite, and the like, and two or more kinds may be used in combination.
The amount of the inorganic binder contained in the raw material paste is preferably 5 to 20% by weight, more preferably 7 to 15% by weight.

The raw material paste may further contain inorganic fibers.
The material constituting the inorganic fiber is not particularly limited, and examples thereof include alumina, silica, silicon carbide, silica alumina, glass, potassium titanate, aluminum borate, and the like, and two or more kinds thereof may be used in combination.
The amount of the inorganic fiber contained in the raw material paste is preferably 2 to 15% by weight, more preferably 5 to 10% by weight.

Further, the raw material paste may further contain an organic binder, a dispersion medium, a molding aid and the like, if necessary.

The organic binder is not particularly limited, and examples thereof include methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, polyethylene glycol, phenol resin, epoxy resin, and the like, and two or more kinds may be used in combination.

The dispersion medium is not particularly limited, and examples thereof include water, an organic solvent such as benzene, an alcohol such as methanol, and two or more thereof may be used in combination.

The molding aid is not particularly limited, and examples thereof include ethylene glycol, dextrin, fatty acid, fatty acid soap, and polyalcohol, and two or more of them may be used in combination.

When preparing the raw material paste, it is desirable to mix and knead, and the paste may be mixed using a mixer, an tryter or the like, or may be kneaded using a kneader or the like.

Next, the honeycomb molded body can be dried to produce a honeycomb dried body using a dryer such as a microwave dryer, a hot air dryer, a dielectric dryer, a vacuum dryer, a vacuum dryer, or a freeze dryer. desirable.

(Baking process)
In the firing step, the honeycomb molded body is fired to produce a honeycomb fired body. Since this step is degreasing and firing of the honeycomb molded body, it can be referred to as a "defatting / firing step", but for convenience, it is referred to as a "baking step".

The temperature of the firing step is preferably 600 to 1000 ° C, more preferably 600 to 800 ° C. The firing step time is preferably 1 to 10 hours, more preferably 1.5 to 5 hours. The atmosphere of the firing step is not particularly limited, but it is desirable that the oxygen concentration is 1 to 10%.

(Other processes)
When the outer peripheral coat layer is formed on the outer peripheral surface of the honeycomb fired body, the outer peripheral coat layer may be formed by applying the outer peripheral coat layer paste to the outer peripheral surface excluding both end faces of the honeycomb fired body and then drying and solidifying. it can.

In the case of producing a honeycomb catalyst in which a plurality of honeycomb fired bodies are bonded via an adhesive layer, an adhesive layer paste is applied to the outer peripheral surfaces of the plurality of honeycomb fired bodies excluding both end faces and bonded. After that, it can be produced by drying and solidifying.

Hereinafter, examples in which the present invention is disclosed more specifically will be shown. The present invention is not limited to this embodiment.

(Example 1)
(Preparation of H ⁺ type zeolite)
Colloidal silica (manufactured by Nissan Chemical Industry Co., Ltd., Snowtex) as Si source, dry aluminum hydroxide gel (manufactured by Tomita Pharmaceutical Co., Ltd.) as Al source, sodium hydroxide (manufactured by Tokuyama Co., Ltd.) and potassium hydroxide (Toa Synthetic Co., Ltd.) as alkali sources , N, N, N-trimethyladamantanamium hydroxide (TMAAOH) 25% aqueous solution (manufactured by Sachem) as a structure defining agent (SDA), SSZ-13 as a seed crystal, and deionized water are mixed to form a raw material composition. I prepared things. The molar ratio of the raw material composition was SiO ₂ : 15 mol, Al ₂ O ₃ : 1 mol, NaOH: 2.6 mol, KOH: 0.9 mol, TMAAOH: 1.1 mol, H ₂ O: 300 mol. Further, 5.0% by weight of seed crystals were added to SiO ₂ and Al ₂ O ₃ in the raw material composition. The raw material composition was loaded into a 500 L autoclave, and hydrothermal synthesis was carried out at a heating temperature of 160 ° C. and a heating time of 48 hours to synthesize zeolite. Subsequently, in order to remove TMAAOH remaining in the zeolite pores, heat treatment was performed in air at 550 ° C. for 4 hours.

Was dissolved ammonium sulfate 1mol of water 1L, the zeolite obtained above for the resulting solution 4g was added at a ratio of 1g, it was stirred for 1 hour at atmospheric pressure, to give the NH ₄ ⁺ -type zeolite ..

The NH ₄ ⁺ -type zeolite obtained above, in the air, 550 ° C., subjected to a heat treatment under conditions of 4 hours to obtain a H ⁺ type zeolite.

(Cu ion exchange)
Subsequently, a powder of copper (II) nitrate was mixed with the H ⁺ type zeolite obtained above so that the amount of Cu was 3.6% by weight to obtain a mixed powder. In this mixing step, a mortar was used, the mixing temperature was room temperature, and the mixing time was 0.5 hours. The water content of the mixed powder was 20% by weight.

The mixed powder obtained in the above mixing step was subjected to heat treatment. The heating device and heating conditions are as follows.
Heating device: Chugai Ro Co., Ltd., device model number FQ-5270
Heating temperature: 700 ° C
Heating atmosphere: N ₂ atmosphere Heating pressure: Atmospheric pressure Heating time: 5 hours or more to produce a CHA-type zeolite with Cu ion exchange.

(Ce ion exchange)
Subsequently, cerium (III) acetate was mixed with the Cu ion-exchanged CHA-type zeolite so that the amount of Ce was 5.0% by weight to obtain a mixed powder. In this mixing step, a mortar was used, the mixing temperature was room temperature, and the mixing time was 0.5 hours. The water content of the mixed powder was 20% by weight.

The mixed powder obtained in the above mixing step was subjected to heat treatment. The heating device and heating conditions are as follows.
Heating device: Chugai Ro Co., Ltd., device model number FQ-5270
Heating temperature: 700 ° C
Heating atmosphere: N ₂ atmosphere Pressure during heating: Atmospheric pressure Heating time: 5 hours or more to produce CHA-type zeolite ion-exchanged with Cu and Ce.

(Example 2)
In the Ce ion exchange step, CHA-type zeolite that is ion-exchanged with Cu and Ce in the same manner as in Example 1 except that the blending amount of cerium (III) acetate is changed so that the amount of Ce is 3.0% by weight. Manufactured.

(Comparative Example 1)
The Ce ion exchange step in Example 1 was changed as follows.
CHA-type zeolite that has undergone Cu ion exchange is immersed in an aqueous solution of cerium (III) nitrate prepared so that the amount of Ce is 5.0% by weight, and an ion exchange step is performed. CHA in which Cu and Ce are supported. Molded zeolite was produced.

(Comparative Example 2)
For reference in the Rietveld analysis described later, the CHA-type zeolite that had been Cu ion-exchanged and had not undergone Ce ion exchange in Example 1 was designated as Comparative Example 2.

<XRD measurement of zeolite>
Using an X-ray diffractometer (Smart Lab manufactured by Rigaku Co., Ltd.), XRD measurements were performed on the zeolites obtained in each Example and Comparative Example to obtain XRD data.
The measurement conditions are: source: CuKα (λ = 0.154 nm), measurement method: continuous method, diffraction angle: 2θ = 5 to 90 °, step width: 0.01 °, scan speed: main peak exceeds 10,000 counts. IS slit: 1/6 °, IS length: 10 mm, IS solar slit: 2.5 °, PAS: open, accelerating voltage: 40 kV, accelerating current: 30 mA.

<Rietveld analysis>
Based on the obtained XRD data, the space group was designated as No. Rietveld analysis was performed as 166 (R-3m). The software used was PDXL-2 manufactured by Rigaku. The results are shown in Table 1.

<Measurement of Cu-supported amount and Ce-supported amount>
The amount of Cu element and the amount of Ce element carried on the zeolite were measured by ICP emission spectroscopy. As a result, it was confirmed that the total amount of the charged elements was supported in each Example and Comparative Example.
For example, in Example 1, Cu is 3.6% by weight and Ce is 5.0% by weight.

<Analysis of the amount of Ce supported as CeO ₂ >
A high proportion of Ce supported as CeO ₂ means a high proportion of non-ion-exchanged Ce. Therefore, the higher the proportion of Ce supported as CeO ₂ , the higher the ion exchange. It means that the efficiency is low.
The amount of CeO ₂ supported is determined by XRD analysis by the following method. First, the zeolite powder and the CeO ₂ powder are mixed at an arbitrary ratio and XRD measurement is performed to prepare a calibration curve of CeO ₂ . Then, the zeolite powders obtained in Examples and Comparative Examples are similarly XRD-measured and compared with a calibration curve to determine the amount of CeO ₂ supported.
The XRD measurement is performed using an X-ray diffractometer (Ultima IV manufactured by Rigaku Corporation). The measurement conditions are as follows. Source: CuKα (λ = 0.154 nm), Measurement method: FT method, Diffraction angle: 2θ = 2-50 °, Step width: 0.02 °, Integration time: 5 seconds, Divergence slit, Scattering slit: 2 / 3 °, divergence vertical limiting slit: 10 mm, accelerating voltage: 40 kV, accelerating current: 40 mA. Make sure that the sample weight does not change by 0.1% or more before and after the XRD measurement. The obtained XRD data is subjected to a peak search using the powder X-ray diffraction pattern comprehensive analysis software JADE 6.0, and the half width and integrated intensity of each peak are calculated. The conditions for peak search are as follows. Filter type: Parabolic filter, Kα2 peak elimination: Yes, Peak position definition: Peak top, Threshold σ: 3, Peak intensity% cutoff: 0.1, BG determination range: 1, BG averaging points: 7 ..
The results are shown in Table 1.

<Measurement of zeolite molar ratio (SAR: SiO ₂ / Al ₂ O ₃ )>
Using a fluorescent X-ray analyzer (XRF, ZSX Primus2 manufactured by Rigaku Co., Ltd.), the molar ratio (SAR: SiO ₂ / Al ₂ O ₃ ) of the zeolite used in each Example and Comparative Example before Cu ion exchange was measured. did. The measurement conditions were X-ray tube: Rh, rated maximum output: 4 kW, detection element range: FU, quantitative method: SQX method, analysis area: 10 mmφ.
Since it is considered that the SAR does not change before and after the ion exchange, it is considered that the SAR of the zeolites obtained in each Example and Comparative Example also have the same value.

<SEM observation>
The ion-exchanged zeolites obtained in Example 1 and Comparative Example 1 were observed by a SEM (scanning electron microscope). The accelerating voltage was 10.0 kV and the measurement magnification was 50,000 times.
FIG. 4 is an SEM photograph of the ion-exchanged zeolite obtained in Example 1, and FIG. 5 is an SEM photograph of the ion-exchanged zeolite obtained in Comparative Example 1.
In SEM photographs, Ce tends to appear white because it is a heavy element. The fact that the entire zeolite particles are white in FIG. 4 suggests that Ce is ion-exchanged and contained in the zeolite particles. On the other hand, in FIG. 5, Ce is attached to the surface of the zeolite particles, suggesting that the proportion of Ce that has not been ion-exchanged is high.

[Manufacturing of honeycomb catalyst]
40% by weight of ion-exchanged zeolite, 8% by weight of pseudo-bemite as an inorganic binder, 7% by weight of glass fiber having an average fiber length of 100 μm, and 6.5% by weight of methylcellulose obtained in each Example and Comparative Example. %, 3.5% by weight of surfactant and 35% by weight of ion-exchanged water were mixed and kneaded to prepare a raw material paste.

Next, the raw material paste was extruded using an extrusion molding machine to prepare a honeycomb molded body. Then, using a vacuum microwave dryer, the honeycomb molded product was dried at an output of 4.5 kW and a reduced pressure of 6.7 kPa for 7 minutes, and then degreased and fired at an oxygen concentration of 1% and 700 ° C. for 5 hours to obtain a honeycomb catalyst (honeycomb). Unit) was produced. The honeycomb unit had a regular square columnar shape with a side of 35 mm and a length of 150 mm, a density of through holes of 124 pieces / cm ² , and a partition wall thickness of 0.20 mm.

[Measurement of NOx purification rate]
A columnar test piece having a diameter of 25.4 mm and a length of 38.1 mm was cut out from the honeycomb unit using a diamond cutter. NOx flowing out of the test piece using a catalyst evaluation device (SIGU-2000 / MEXA-6000FT manufactured by HORIBA, Ltd.) while flowing a simulated gas at 200 ° C. at a space velocity (SV) of 40,000 / hr. Measure the outflow amount and use the following formula (1)
(NOx inflow amount-NOx outflow amount) / (NOx inflow amount) x 100 ... (1)
The purification rate [%] of NOx represented by is calculated. The constituents of the simulated gas were nitric oxide 262.5 ppm, nitrogen dioxide 87.5 ppm, ammonia 350 ppm, oxygen 10%, carbon dioxide 5%, water 5%, and nitrogen (balance).
Similarly, the purification rate [%] of NOx was calculated while flowing a simulated gas at 525 ° C. at SV: 100,000 / hr. The components of the simulated gas at this time were 315 ppm of nitric oxide, 35 ppm of nitrogen dioxide, 385 ppm of ammonia, 10% oxygen, 5% carbon dioxide, 5% water, and balance.
The NOx purification rate by the above method was measured both immediately after the production of the honeycomb catalyst (initial stage) and after the honeycomb catalyst was dried at 400 ° C. for 2 hours (after the 400 ° C. durability test).
Table 2 shows the NOx purification rate of the honeycomb catalyst using the zeolites obtained in each Example and Comparative Example.

From the results shown in Tables 1 and 2, in each example in which Cu was ion-exchanged and the Ce occupancy rate was 0.05 or more, the comparison in which Ce was not ion-exchanged due to Ce ion exchange. The NOx purification rate was higher than that of Example 2.

Further, Comparative Example 1 is an example in which ion exchange is performed by ion exchange in the liquid phase, but from the result of Rietveld analysis, the structure is optimized in a state where Ce is not included in the crystal structure, so the Ce occupancy rate. Is 0. That is, it is presumed that in Comparative Example 1, the ion exchange of Ce was not performed at all or was hardly performed.
Since the proportion of Ce supported as CeO ₂ is high in Comparative Example 1, in the zeolite produced in Comparative Example 1, Ce is not contained in the crystal structure of zeolite by ion exchange, but is a zeolite particle. It is presumed that it is highly likely that it is attached to the surroundings of.
Then, in Comparative Example 1, the NOx purification rate was lower than that in each Example.

10,20 Honeycomb catalyst 11,21 Honeycomb fired body 11a, 21a Through holes 11b, 21b Partition wall 12,22 Outer coat layer 23 Adhesive layer

Claims (8)

A CHA-type zeolite that is ion-exchanged with Cu and Ce.
A zeolite characterized in that the occupancy rate of Ce determined by crystal structure analysis by the XRD-Rietveld method is 0.05 or more. The lattice constants of zeolite determined by crystal structure analysis by the XRD-Rietveld method are a = b = 13.55 to 13.65 Å and c = 14.8 to 14.9 Å, and the Cu arrangement is 0 in Z-axis coordinates. The zeolite according to claim 1, which is 2 to 0.35. The zeolite according to claim 1 or 2, wherein the amount of Cu element carried on the zeolite is 2 to 6% by weight, and the amount of Ce element supported on the zeolite is 3 to 5% by weight. The zeolite according to any one of claims 1 to 3, wherein the SiO ₂ / Al ₂ O ₃ composition ratio (SAR) of the zeolite is 5 to 15. The zeolite according to any one of claims 1 to 4, wherein the ratio of Ce supported as CeO _{2 to the} amount of Ce element supported on the zeolite is 0.5 or less. The zeolite according to claim 5, wherein the ratio of Ce supported as CeO _{2 to the} amount of Ce elements supported on the zeolite is 0.3 or less. The zeolite according to any one of claims 1 to 6, wherein the CHA-type zeolite is SSZ-13. A honeycomb catalyst comprising the zeolite according to any one of claims 1 to 7 and an inorganic binder.