Catalyst, catalyst composition, catalyst manufacturing method, and method for removing volatile organic compounds

Abstract

To provide a catalyst having an increased ability to decompose volatile organic compounds despite its simplified structure.SOLUTION: A catalyst comprises an oxide represented by the formula of La10Si5CoO27-δ, meeting 0.5≤δ≤1, and having an apatite crystal structure. The catalyst comprises a secondary particle, which is aggregation of a plurality of primary particles. On at least a surface of the secondary particle, clearances are formed between adjacent primary particles. The catalyst is used to decompose volatile organic compounds.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a catalyst, a catalyst composition, a method for producing a catalyst, and a method for removing volatile organic compounds. [Background technology]

[0002] Catalysts are used to decompose volatile organic compounds contained in exhaust gases emitted from factories and the like (for example, Patent Document 1). Patent Document 1 discloses a combustion catalyst containing one or more metal oxides selected from the group consisting of zirconium oxide, titanium oxide, and silicon oxide, and one or more precious metals selected from the group consisting of platinum, palladium, and iridium. Patent Document 2 also discloses a catalyst that is a mixture containing at least two types of particles as a catalyst for decomposing volatile organic compounds. Patent Document 2 discloses a catalyst that has a perovskite-type crystal structure as a main catalyst, and is composed of LaCoO3 or La 1-x Ba x CoO 3-x / 2 and a compound represented by the formula: 10 Si5CoO 27-δ A catalyst composition containing an oxide represented by the formula (0.5≦δ≦1) is disclosed. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2009 / 157434 [Patent Document 2] Japanese Patent Publication No. 2020-116570 Summary of the Invention [Problem to be solved by the invention]

[0004] A catalyst for decomposing volatile organic compounds preferably has a simpler structure and a high decomposition ability for volatile organic compounds. Therefore, one of the objects of the present invention is to provide a catalyst having a simpler structure and a high decomposition ability for volatile organic compounds. [Means for solving the problem]

[0005] The catalyst according to the present disclosure is 10 Si5CoO 27-δ wherein δ satisfies 0.5≦δ≦1 and is made of an oxide having an apatite-type crystal structure, the catalyst containing secondary particles formed by aggregation of a plurality of primary particles, and gaps being formed between adjacent primary particles at least on the surfaces of the secondary particles, for decomposing volatile organic compounds. [Effects of the Invention]

[0006] The catalyst can easily decompose volatile organic compounds without the need for a promoter. [Brief explanation of the drawings]

[0007] [Figure 1] 3 is a flowchart showing a method for removing volatile organic compounds using a catalyst according to the first embodiment. [Figure 2] FIG. 2 is a perspective view showing a first structure in which a catalyst is disposed inside a substrate. [Figure 3] FIG. 3 is a schematic cross-sectional view showing the structure of a first structure. [Figure 4] 1 is a schematic diagram showing the structure of an exhaust gas treatment device. [Figure 5] FIG. 1 is a view showing an SEM image of the catalyst obtained in Example 1. [Figure 6] FIG. 1 is a view showing an SEM image of the catalyst obtained in Example 4. [Figure 7] FIG. 1 is a view showing an SEM image of the catalyst obtained in Comparative Example 1. [Figure 8] FIG. 1 is a diagram showing the results of XRD measurement of the catalysts obtained in Example 1, Example 4 and Comparative Example 1. [Figure 9] FIG. 1 shows the results of XRD measurement of the catalysts obtained in Examples 2, 3, 4 and 5. [Figure 10] FIG. 1 is a diagram showing the results of measuring the catalytic activity of the catalysts obtained in Example 1, Example 4, and Comparative Example 1. [Figure 11] FIG. 1 is a diagram showing the results of measuring the catalytic activity of the catalysts obtained in Examples 2, 3, 4 and 5. DETAILED DESCRIPTION OF THE INVENTION

[0008] [Outline of the embodiment] The catalyst according to the present disclosure is 10 Si5CoO 27-δ The catalyst is represented by the composition formula: and is composed of an oxide having an apatite-type crystal structure, satisfying 0.5≦δ≦1. The catalyst contains secondary particles formed by aggregation of a plurality of primary particles, and gaps are formed between adjacent primary particles at least on the surfaces of the secondary particles. The catalyst is for decomposing volatile organic compounds.

[0009] When the catalyst according to the present disclosure is heated while being in contact with volatile organic compounds (hereinafter sometimes referred to as VOCs), the intra-lattice oxygen (O 2- ) is thought to cause an oxidation reaction of VOCs. Although oxygen in the lattice is lost through this reaction, oxygen molecules (O2) in the air are decomposed and oxide ions (O 2- ) is thought to be compensated for by being incorporated as a catalyst. The catalyst according to the present disclosure includes secondary particles formed by an aggregation of a plurality of primary particles, and gaps are formed between adjacent primary particles at least on the surface of the secondary particles. Without being bound by a particular theory, it is thought that the gaps formed between the primary particles in the catalyst according to the present disclosure act as diffusion paths for VOCs and oxygen, thereby exhibiting excellent catalytic activity for decomposing VOCs.

[0010] Conventionally, La 10 Si5CoO 27-δThe oxides represented by the formula (0.5≦δ≦1) are the main catalysts, lanthanum cobaltate (LaCoO3) and lanthanum barium cobaltate (La 1-x Ba x CoO 3-x / 2 ) has been known as a promoter used in combination with the main catalyst (for example, Patent Document 2). Although the oxide plays a role in supplying oxide ions to the main catalyst, it was thought that it did not have sufficient activity to be used alone as the main catalyst. 10 Si5CoO 27-δ It has been reported that when an oxide (0.5≦δ≦1) is used alone, the toluene complete conversion temperature is 360°C, which is lower than the toluene complete conversion temperature (310 to 340°C) when used in combination with lanthanum cobaltate or the like. In contrast, the catalyst according to the present disclosure has been found to have excellent VOC decomposition catalytic activity and can be used alone as a catalyst when the oxide is expressed by a similar composition formula and has a specific three-dimensional structure. The catalyst according to the present disclosure can easily decompose VOCs at a lower temperature (for example, 320°C or lower) without the use of a cocatalyst.

[0011] The present disclosure also relates to a catalyst composition containing the catalyst. 10 Si5CoO 27-δ The catalyst composition for decomposing VOCs is represented by the composition formula below, satisfies 0.5≦δ≦1, and the content of oxides containing La other than oxides having an apatite-type crystal structure is 1 mass % or less relative to the catalyst composition. As described above, the catalyst of the present disclosure exhibits sufficient activity alone or as a main catalyst. Therefore, excellent VOC decomposition performance can be obtained with a simple structure that does not contain other types of La oxides.

[0012] The present disclosure also provides: A step of obtaining a mixed solution by dropping an aqueous solution containing lanthanum nitrate and cobalt nitrate into an alkaline solution to which a silicate has been added; a step of stirring the mixture to obtain a precipitate; a recovery step of recovering and drying the precipitate; A calcination step of calcining the precipitate, La 10 Si5CoO 27-δ The present invention relates to a method for producing a catalyst for decomposing volatile organic compounds, which is composed of an oxide having an apatite-type crystal structure and is represented by the composition formula: According to this production method, La 10 Si5CoO 27-δ A catalyst made of an oxide having an apatite-type crystal structure represented by the composition formula (0.5≦δ≦1) is preferably obtained, which includes secondary particles formed by aggregation of a plurality of primary particles, with gaps formed between adjacent primary particles at least on the surface of the secondary particles. This production method is a catalyst production method using the so-called coprecipitation method, and a highly active catalyst can be obtained by a general-purpose process.

[0013] The present disclosure also provides: A step of obtaining a raw material powder by mixing powdered silicon dioxide, powdered lanthanum oxide, and powdered tricobalt tetroxide; a step of solidifying the raw material powder to obtain pellets; A firing step of firing the pellets. 10 Si5CoO 27-δ The present invention relates to a method for producing a catalyst for decomposing volatile organic compounds, which is composed of an oxide having an apatite-type crystal structure and is represented by the composition formula: According to this production method, La 10 Si5CoO 27-δ A catalyst made of an oxide having an apatite-type crystal structure represented by the composition formula (0.5≦δ≦1) is preferably obtained, which includes secondary particles formed by aggregation of a plurality of primary particles, with gaps formed between adjacent primary particles at least on the surface of the secondary particles. This production method is a so-called solid-phase catalyst production method, and a highly active catalyst can be obtained by an industrially applicable and general-purpose process.

[0014] The present disclosure also relates to a method for removing volatile organic compounds, comprising the steps of: preparing the catalyst or the catalyst composition; and decomposing the volatile organic compounds by bringing the catalyst or the catalyst composition into contact with a gas containing the volatile organic compounds and heating the catalyst or the catalyst composition to a temperature of 200° C. or higher and 340° C. or lower. By doing so, the lattice oxygen (O ) contained in the catalyst itself can be decomposed on the surface of the particles constituting the catalyst. 2- ) is thought to cause an oxidation reaction of VOCs. In addition, although oxygen in the lattice is lost through the reaction, oxygen molecules (O2) in the air are decomposed and oxide ions (O 2- Therefore, according to the method for removing volatile organic compounds of the present invention, volatile organic compounds can be easily decomposed.

[0015] [Specific example of embodiment] (catalyst) The catalyst according to the present disclosure is 10 Si5CoO 27-δ It is composed of an oxide with an apatite-type crystal structure, with a composition formula of 0.5≦δ≦1. This oxide is durable at high temperatures and is a stable material that does not become inactivated even when subjected to heat treatment at around 1000°C. Oxygen in the air decomposes on the surface of catalyst particles made of this oxide, causing an oxidation reaction of VOCs.

[0016] The catalyst according to the present disclosure includes secondary particles formed by aggregation of multiple primary particles. The size of the primary particles is, for example, approximately 50 nm to 10 μm. Here, the "primary particle size" refers to a value measured for the particle portion appearing in an SEM image of the catalyst particle surface. For example, the size of approximately 10 to 1,000 primary particles can be measured, and the average value can be used as the "primary particle size." In addition to primary particles of approximately 50 nm to 10 μm, small particles less than 50 nm and large particles exceeding 10 μm may be mixed. The shape of the primary particles may be, but is not limited to, spherical. For example, they may be ellipsoidal, coin-shaped, or irregularly shaped clumps. The shape of the primary particles contained in the catalyst particle may be uniform, or may be an aggregation of primary particles of various shapes. Note that the term "primary particle" refers to the three-dimensional structure observed as the smallest structural unit when observing the three-dimensional structure constituting the catalyst using an electron microscope (SEM) or the like.

[0017] The primary particles aggregate to form secondary particles. The size of the secondary particles is not particularly limited and is, for example, approximately 10 μm to 100 μm. Here, the "size of secondary particles" refers to the value measured for the particle portion appearing in an SEM image of the catalyst particle surface. For example, the size of approximately 10 to 1,000 secondary particles can be measured and the average value can be used as the "size of secondary particles." In addition to secondary particles of approximately 10 μm to 100 μm, small particles less than 10 μm and large particles exceeding 100 μm may be mixed. The shape of the secondary particles is not particularly limited and may be an amorphous mass, or may be spherical, spindle-shaped, or the like. The secondary particles contained in the catalyst may have a uniform size and shape, or secondary particles of various sizes and shapes may be mixed. Note that the term "secondary particles" refers to three-dimensional structures formed by aggregation of primary particles that are observed as the smallest structural units when the three-dimensional structure constituting the catalyst is observed using an electron microscope (SEM) or the like.

[0018] Gaps are formed between adjacent primary particles at least on the surface of the secondary particles. The gaps between the primary particles are observed as voids in, for example, SEM images. The shape of the voids is not particularly limited, but for example, they may be open on the surface of the secondary particles and have a certain amount of space formed in the depth direction from the surface of the secondary particles. For example, voids may be formed that are larger in the depth direction of the secondary particles than the openings on the surface of the secondary particles. The catalyst according to the present disclosure does not include catalysts composed of aggregated particles that have uneven surfaces but do not contain substantial voids.

[0019] (Catalyst composition) The catalyst composition according to the present disclosure contains La 10 Si5CoO 27-δ The catalyst composition according to the present disclosure exhibits excellent VOC decomposition activity even in the absence of a compound that functions as a promoter. Specifically, in the composition according to the present disclosure, La 10 Si5CoO 27-δ The content of oxides containing La other than oxides having an apatite-type crystal structure, which is represented by the composition formula and satisfies 0.5≦δ≦1, may be 1 mass % or less, preferably 0.1 mass % or less, and more preferably 0 mass % relative to the catalyst composition. 10 Si5CoO 27-δ The composition may be expressed by the following composition formula, satisfying 0.5≦δ≦1, and not including any oxide containing La (0 mass %) other than the oxide having an apatite-type crystal structure.

[0020] The catalyst composition according to the present disclosure may contain, in addition to the oxides described above that function as the main catalyst, other oxides that function as the main catalyst. For example, oxides containing La include oxides contained in perovskite-type crystals represented by the composition formula LaCoO3 and La 1-x Ba x CoO 3-x / 2Examples of suitable catalyst compositions include oxides having perovskite-type crystals represented by the following compositional formula, where x satisfies 0.05≦x≦0.15. The catalyst composition according to the present disclosure exhibits high catalytic activity even without the use of a co-catalyst, but may contain a compound that functions as a co-catalyst. Examples of suitable co-catalysts include cerium oxide (CeO2). When a co-catalyst is contained, the proportion of the co-catalyst relative to the entire catalyst composition is not particularly limited and can be selected appropriately depending on the type and properties of the co-catalyst used. The proportion of the co-catalyst relative to the entire catalyst composition can be, for example, 0 to 80 mass %, and preferably approximately 60 to 80 mass %.

[0021] In the catalyst composition, La 10 Si5CoO 27-δ In addition to the oxide having an apatite-type crystal structure, which satisfies the formula 0.5≦δ≦1, a dispersant may also be included. Examples of such dispersants include ceramic particles. Examples of ceramic particles include alumina (Al2O3), silica (SiO2), cordierite (2MgO·2Al2O3·5SiO2), and mullite (3Al2O3·2SiO2). For example, γ-alumina, which has a cubic crystal structure, is preferably used as the ceramic particles. The inclusion of a dispersant prevents the particles that function as catalysts from agglomerating, thereby preventing a decrease in the catalyst's surface area. Therefore, the oxidation reaction of VOCs is promoted.

[0022] When the catalyst composition contains a dispersion medium, the average particle size of the dispersion medium may be, for example, 5 nm or more, preferably 10 nm or more. The upper limit of the average particle size of the dispersion medium is not particularly limited, but is, for example, less than 1 μm. The content of the dispersion medium in the catalyst composition can be appropriately determined in relation to the content of the catalyst particles, and is not particularly limited, but can be, for example, 0 to 30 mass%.

[0023] (catalytic function) The catalyst or catalyst composition according to the present disclosure can be used as a catalyst for decomposing VOCs. VOCs is a general term for organic compounds that are volatile and become gaseous in the atmosphere. VOCs include, but are not limited to, toluene, xylene, ethyl acetate, etc. Typically, toluene is the target of decomposition. The activity of a catalyst is indicated by the temperature at which toluene can be completely decomposed when a certain amount of toluene is brought into contact with a certain amount of catalyst at a certain temperature. The temperature at which toluene is completely decomposed (toluene complete decomposition temperature) is also called the toluene complete conversion temperature. It is preferable to be able to decompose toluene at a lower temperature. The toluene complete decomposition temperature is preferably 200°C or higher and 340°C or lower, more preferably 330°C or lower, and even more preferably 320°C or lower.

[0024] (Catalyst manufacturing method) The catalyst according to the present disclosure can be suitably obtained by a so-called coprecipitation method. Specifically, the production method includes the steps of: obtaining a mixed solution by dropping an aqueous solution containing lanthanum nitrate and cobalt nitrate into an alkaline solution obtained by adding sodium silicate to an aqueous ammonia solution; stirring the mixed solution to obtain a precipitate; recovering and drying the precipitate; and calcining the obtained precipitate. By such a production method, La 10 Si5CoO 27-δ The resulting oxide particles are represented by the composition formula: and satisfy 0.5≦δ≦1, and have an apatite-type crystal structure, with gaps formed between the primary particles.

[0025] Each step of the coprecipitation production method can be carried out by appropriately selecting known conditions or methods. Specifically, for example, in the step of obtaining a mixed solution, sodium silicate nonahydrate (Na2SiO3·9H2O), lanthanum nitrate hexahydrate (La(NO3)2·6H2O), and cobalt nitrate hexahydrate (Co(NO3)2·6H2O) are mixed in a 14% to 30% aqueous ammonia solution at a molar ratio of 4.5 to 5.5:9.5 to 10.5:0.5 to 1.5 to prepare a mixed solution. Specifically, the amounts of the ingredients can be determined so that the La:Co:Si ratio is 10:1:5 (molar ratio). The stirring step can be carried out, for example, at 30 to 80°C for 1 to 24 hours. Recovery can be carried out, for example, by suction filtration, followed by drying at 80 to 100°C. In the calcination step, for example, calcination can be carried out in the atmosphere at 600° C. to 1600° C. for 1 to 24 hours. By using these calcination temperatures and times, a catalyst having excellent activity for decomposing VOCs can be obtained.

[0026] The catalyst according to the present disclosure can be suitably obtained by a so-called solid phase method. Specifically, the production method includes the steps of obtaining a raw material powder by mixing powdered silicon dioxide, powdered lanthanum oxide, and powdered tricobalt tetroxide, solidifying the raw material powder to obtain pellets, and calcining the pellets. By such a production method, La 10 Si5CoO 27-δ The resulting oxide particles are represented by the composition formula: and satisfy 0.5≦δ≦1, and have an apatite-type crystal structure, with gaps formed between the primary particles.

[0027] Each step of the solid-phase production method can be carried out by appropriately selecting known conditions or methods. Specifically, for example, in the step of obtaining the raw material powder, powdered silicon dioxide (SiO), powdered lanthanum oxide (LaO), and powdered tricobalt tetroxide (CoO) are mixed in a molar ratio of 4.5-5.5:9.5-10.5:0.5-1.5. Specifically, for example, the amounts charged can be determined so that the La:Co:Si ratio is 10:1:5 (molar ratio). To improve the homogeneity of the mixture or for other purposes, pulverization using a ball mill or the like may be performed after mixing. Pellets can be molded by pressure molding. In the calcination step, for example, calcination can be performed in the atmosphere at 600°C to 1600°C for 1 to 24 hours. These calcination temperatures and times result in a catalyst with excellent VOC decomposition activity.

[0028] The obtained catalyst may be used alone or may be mixed with other materials to form a catalyst composition. Prior to the calcination step, the catalyst material according to the present disclosure may be mixed with other materials and calcined together.

[0029] (VOC removal method) A method for removing VOCs using the above-mentioned catalyst or catalyst composition will be described. Figure 1 is a flowchart showing a method for removing VOCs using the catalyst according to the present disclosure. The case of removing toluene as an example of VOCs will be described.

[0030] Referring to FIG. 1, in the method for removing toluene using the catalyst or catalyst composition of this embodiment, first, in step (S10), a step of preparing the catalyst or catalyst composition is carried out. For example, a powdered catalyst is attached to the surface of a ceramic substrate such as cordierite. For example, the catalyst can be attached to the surface of the substrate by applying a slurry-like catalyst to the surface of the substrate. This makes it easier to handle the catalyst.

[0031] FIG. 2 is a perspective view showing a first structure in which a catalyst according to the present disclosure is disposed inside a ceramic substrate. FIG. 3 is a cross-sectional view showing a portion of a cross section taken along line AA in FIG. 2. In FIG. 2, the Y-axis direction is a direction along the central axis of the main body portion. The XZ plane is a plane perpendicular to the Y-axis direction. With reference to FIGS. 2 and 3, the first structure 1 includes a ceramic substrate 10 and a catalyst 20. The material constituting the substrate 10 is, for example, cordierite. The substrate 10 includes a main body portion 101, first inner wall portions 111-119, and second inner wall portions 120-128.

[0032] The main body 101 has a hollow cylindrical shape. The first inner wall portions 111-119 have flat plate shapes and are arranged parallel to each other at intervals in the X-axis direction. The second inner wall portions 120-128 have flat plate shapes and are arranged parallel to each other at intervals in the Z-axis direction. The first inner wall portions 111-119 and the second inner wall portions 120-128 are arranged perpendicular to each other. The first inner wall portions 111-119 and the second inner wall portions 120-128 intersect with each other to form a plurality of through holes S extending from one opening to the other opening of the main body 101. When viewed in a plan view from the Y-axis direction, the outer shape of the through holes S is square. Referring to FIG. 3, a catalyst 20 is attached to cover the surfaces of the second inner wall portions 123, 124, and 125. The catalyst 20 is attached so as to cover not only the second inner wall portions 123, 124, and 125, but also the inner wall surfaces of the main body portion 101, the surfaces of the first inner wall portions 111 to 119, and the second inner wall portions 120 to 128. In other words, the catalyst 20 is attached so as to cover the wall surfaces that define the through-holes S in the base 10.

[0033] Next, step (S20) is carried out to decompose toluene. In step (S20), toluene is brought into contact with the first structure 1 prepared in step (S10). Specifically, while bringing a gas containing toluene into contact with the catalyst 20 held on the substrate 10, the catalyst 20 is heated to a temperature of 200°C or higher and 340°C or lower. The gas containing toluene comes into contact with the catalyst 20 by passing through the through holes S. This allows the toluene to be decomposed.

[0034] Next, step (S30) is carried out to regenerate the catalyst 20. In step (S30), the catalyst 20 held on the substrate 10 of the first structure 1 is regenerated. Specifically, after the step of decomposing toluene, the catalyst 20 is heated to a temperature of 600°C or higher and 1000°C or lower, and maintained at that temperature for 30 minutes or longer. The heating temperature in the step of regenerating the catalyst 20 is preferably 700°C or higher and 1000°C or lower, and more preferably 800°C or higher and 1000°C or lower. The maintenance time in the step of regenerating the catalyst 20 is preferably 1 hour or longer. This allows the catalyst 20 to be regenerated.

[0035] Next, in step (S40), a step of decomposing toluene is carried out again. Specifically, while contacting the catalyst 20 with a gas containing toluene, the catalyst 20 is heated to a temperature of 200° C. or more and 340° C. or less. This allows the toluene to be decomposed.

[0036] Volatile organic compounds contained in factory exhaust gases and the like may contain silicon (Si). In such cases, if silicon adheres to the catalyst 20, the activity of the catalyst will decrease. 10 Si5CoO 27-δ contains silicon in its structure. Therefore, by performing heat treatment, the silicon can be incorporated into the structure. 10 Si5CoO 27-δ is stable even if the silicon content in the structure increases slightly. Therefore, the adhesion of silicon to the catalyst particles is suppressed. Therefore, the catalyst or catalyst composition according to the present disclosure suppresses the decrease in catalytic activity due to the adhesion of silicon.

[0037] The catalyst 20 of the above embodiment is used, for example, by being attached to an exhaust gas treatment device. FIG. 4 is a schematic diagram showing the structure of the exhaust gas treatment device. Referring to FIG. 4, the exhaust gas treatment device 2 includes a housing 30 and pipes 31 and 32. The housing 30 includes a side wall 301 and lids 302 and 303. The side wall 301 has a hollow cylindrical shape. The lid 302 is arranged to close one opening of the side wall 301. The lid 303 is arranged to close the other opening of the side wall 301. A first structure 1 including the catalyst 20 is arranged in an internal space T surrounded by the side wall 301 and the lids 302 and 303. One end of the pipe 31 is connected to the lid 303. The other end of the pipe 31 is connected to equipment that discharges exhaust gas to the outside, for example, equipment for manufacturing chemical products such as paints and adhesives. The pipe 31 is an inflow path for exhaust gas. One end of the pipe 32 is connected to the lid 302. The other end of the pipe 32 is arranged to be located in the external space to which the exhaust gas is discharged. The pipe 32 is an exhaust path for discharging the exhaust gas. The pipe 32 may be connected to an additional exhaust gas treatment device. The exhaust gas containing toluene flows into the storage unit 30 through the pipe 31. The decomposition of the toluene contained in the exhaust gas that has flowed into the storage unit 30 is promoted by the catalyst 20 contained in the first structure 1. The exhaust gas is then discharged to the external space through the pipe 32. [Example]

[0038] A sample of the catalyst according to the present disclosure was prepared, and an experiment was conducted to confirm the structure of the catalyst and its effect on decomposing toluene. The experimental procedure was as follows.

[0039] Example 1 0.426 g of sodium silicate nonahydrate was added to a mixture of 10 ml of 28% aqueous ammonia and 10 ml of water and dissolved. Then, an aqueous solution prepared by dissolving 1.299 g of lanthanum nitrate hexahydrate and 0.0873 g of cobalt nitrate hexahydrate in 10 ml of water was added dropwise to obtain a raw material mixture. This raw material mixture was stirred at 60°C for 1 hour to obtain a mixture containing a precipitate. The precipitate was recovered from the mixture by suction filtration. Next, the recovered precipitate was dried at 80°C and then calcined in air at 1000°C for 2 hours to produce an apatite-type oxide. The apatite-type oxide was prepared by adding La 10 Si5CoO 27-δ and satisfies 0.5≦δ≦1.

[0040] Example 2 0.652 g of lanthanum oxide, 0.032 g of tricobalt tetroxide, and 0.120 g of silicon dioxide were mixed and then molded into pellets. The resulting pellets were placed on a Pt plate and fired in air at 1400°C for 2 hours to produce an apatite-type oxide. The apatite-type oxide was 10 Si5CoO 27-δ and satisfies 0.5≦δ≦1.

[0041] Examples 3 to 5 As Example 3, a sample was prepared by repeating the same procedure as in Example 2. In Example 4, a sample was prepared in the same manner as in Example 2, except that the raw materials were mixed, then crushed using a ball mill (PULVERISETTE 7 premium line, manufactured by Fritsch) and then pelletized. In Example 5, the raw materials were mixed, and then the mixture was crushed using a ball mill (PULVERISETTE 7 premium line, manufactured by Fritsch) and then pelletized. A sample was prepared using the same procedure as in Example 2, except that the pellets were fired without being placed on a Pt plate.

[0042] (Comparative Example 1) 2.72 g of lanthanum nitrate hexahydrate and 0.182 g of cobalt nitrate hexahydrate were dissolved in a mixture of 3 ml of acetic acid and 75 ml of ethanol, and then 0.71 ml of tetraethoxysilane was added and stirred for 1 hour. 22.3 g of polyvinylpyrrolidone was then added as a dispersant and stirred at 80°C for 6 hours. The mixture was then heated to 180°C using a hot stirrer to remove the solvent, and heated at 80°C for 12 hours in a constant temperature dryer to produce a gel. The resulting gel was calcined at 350°C using a mantle heater, and then baked at 1000°C for 2 hours in a circulating stream of synthetic air to produce an apatite-type oxide. The apatite-type oxide was prepared using La 10 Si5CoO 27-δ and satisfies 0.5≦δ≦1.

[0043] (Evaluation 1: Confirmation of catalyst particle shape) The morphology of the catalyst particles obtained in Examples 1 to 5 and Comparative Example 1 was observed using an SEM (SSX-550, manufactured by Shimadzu Corporation). The observation results are shown in Table 1 and FIGS.

[0044] (Evaluation 2: Powder X-ray diffraction (XRD) measurement) The crystalline phases of the samples of Examples 1 to 5 and Comparative Example 1 were confirmed by powder X-ray diffraction. XRD measurements were performed using a powder X-ray diffractometer (SmartLab, manufactured by Rigaku) ​​with a Cu-Kα tube (40 kV, 30 mA) in the range of 10 to 70°, at a scan speed of 10° / min, and at intervals of 0.04°. The measurement results are shown in Table 1 and Figures 8 and 9.

[0045] (Evaluation 3: Measurement of catalytic activity) Catalytic activity measurements were carried out for the samples of Examples 1 to 5 and Comparative Example 1. Catalytic activity measurements were evaluated using a fixed-bed flow apparatus. As a pretreatment, argon gas was passed through 0.1 g of the sample, and the sample was heated at 200°C for 2 hours. Then, a mixed gas containing air and toluene (toluene concentration: 900 ppm) was passed through the sample at a flow rate of 20 ml / min, and the toluene conversion rate at each temperature was measured. Here, the toluene conversion rate refers to the proportion of toluene that reacted. The toluene conversion rate was calculated by analyzing the mixed gas after passing through the sample using a gas chromatograph. A "SunPak-A" manufactured by Shinwa Chemical Industry Co., Ltd. was used as the gas chromatograph column. The measurement results are shown in Figures 10 and 11.

[0046] (result) The evaluation results are summarized in Table 1. [Table 1]

[0047] As shown in Table 1, the oxides obtained in Examples 1 to 5 had toluene complete decomposition temperatures of 270°C to 330°C, even without the use of other compounds such as a promoter, and exhibited good VOC decomposition catalytic activity. Furthermore, all of the oxide particles obtained in Examples 1 to 5 formed secondary particles with numerous gaps formed between the primary particles (FIGS. 5 and 6). On the other hand, the oxide obtained in Comparative Example 1 had a toluene complete decomposition temperature of 390°C, and its VOC decomposition activity was insufficient compared to Examples 1 to 5. Furthermore, the particles in Comparative Example 1 formed dense particles with uneven surfaces, and did not have a form in which primary particles aggregate to form secondary particles (FIG. 7). Thus, it was confirmed that the catalyst according to the present disclosure has sufficient activity and can easily decompose toluene, even with a simple configuration without the use of a promoter.

[0048] It should be understood that the embodiments and examples disclosed herein are illustrative in all respects and are not limiting in any respect. The scope of the present invention is defined not by the above meaning but by the scope of the claims, and is intended to include all modifications within the meaning and scope of the claims. [Industrial Applicability]

[0049] The catalyst of the present invention is particularly advantageously applied as a catalyst for decomposing volatile organic compounds. [Explanation of symbols]

[0050] 1 First structure, 2 Exhaust gas treatment device, 10 Base, 20 Catalyst, 30 Storage section, 31, 32 Pipe, 101 Main body section, 111, 112, 113, 114, 115, 116, 117, 118, 119 First inner wall section, 120, 121, 122, 123, 124, 125, 126, 127, 128 Second inner wall section, 301 Side wall section, 302, 303 Lid section.

Claims

1. La １０ Si ５ CoO ２７－δ A catalyst comprising an oxide having an apatite-type crystal structure, which is represented by the composition formula: The catalyst contains secondary particles formed by aggregation of a plurality of primary particles, Gaps are formed between adjacent primary particles at least on the surfaces of the secondary particles. Catalyst for decomposing volatile organic compounds.

2. A catalyst composition comprising the catalyst of claim 1, La １０ Si ５ CoO ２７－δ wherein the content of La-containing oxides other than oxides having an apatite-type crystal structure is 1 mass % or less relative to the catalyst composition.

3. A step of obtaining a mixed solution by dropping an aqueous solution containing lanthanum nitrate and cobalt nitrate into an alkaline solution to which a silicate has been added; a step of stirring the mixture to obtain a precipitate; a recovery step of recovering and drying the precipitate; A calcination step of calcining the precipitate, La １０ Si ５ CoO ２７－δ The present invention relates to a method for producing a catalyst for decomposing volatile organic compounds, which is composed of an oxide having an apatite-type crystal structure and is represented by the following composition formula:

4. A step of obtaining a raw material powder by mixing powdered silicon dioxide, powdered lanthanum oxide, and powdered tricobalt tetroxide; a step of solidifying the raw material powder to obtain pellets; A firing step of firing the pellets. La １０ Si ５ CoO ２７－δ The present invention relates to a method for producing a catalyst for decomposing volatile organic compounds, which is composed of an oxide having an apatite-type crystal structure and is represented by the following composition formula:

5. Providing a catalyst according to claim 1 or a catalyst composition according to claim 2; and decomposing the volatile organic compounds by heating the catalyst or the catalyst composition to a temperature of 200°C or higher and 340°C or lower while bringing the gas containing the volatile organic compounds into contact with the catalyst or the catalyst composition.

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