Method for producing heterometal-doped cerium oxide

Abstract

To obtain dissimilar metal-doped cerium oxide catalyst at a high recovery rate with respect to a loading amount of dry powder in firing by causing a loading thickness of the dry powder in the firing to fall within a certain range in a firing step in production of the dissimilar metal-doped cerium oxide catalyst so as to improve the productivity.SOLUTION: A production method of dissimilar metal-doped cerium oxide includes (A) a step of blending raw materials to prepare an aqueous solution, (B) a step of spray-drying the aqueous solution, and (C) a firing step. In (C) the firing step, a loading thickness of dry powder is 8 mm or more and 50 mm or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing cerium oxide doped with a heterogeneous metal. More specifically, the present invention relates to a production method for improving the recovery rate after a firing process and enhancing productivity.

Background Art

[0002] Inorganic materials mainly composed of cerium oxide have high heat resistance and remarkable oxygen storage and release ability, and thus are widely used industrially in various applications such as catalysts for reforming reactions and hydrogen production, catalyst carriers, photocatalyst paints, gas sensors, and solid electrolytes for fuel cells. Among them, spherical particles mainly composed of cerium oxide have been proposed for numerous applications due to the convenience of the material. Inorganic materials mainly composed of cerium oxide are required to have uniform particle sizes due to their applications. Therefore, if particles with the desired particle size can be uniformly prepared, an improvement in productivity can be expected.

[0003] As a general method for producing spherical cerium oxide, a method of mixing a cerium salt and other metal salts required for adding functions in an aqueous system, adding oxalate thereto to obtain a precipitate is disclosed in Cited Document 1, a method of adding ammonia or ammonium carbonate as a precipitating agent is disclosed in Cited Document 2, and a method of forming a precipitate using an alkoxide is disclosed in Cited Document 3. In addition, Cited Document 4 discloses a method of obtaining a precipitate by adding an alkali.

[0004] However, when using oxalate, in the firing process, it has a drawback of easily forming large lumps of aggregates. Also, when using ammonia or ammonium carbonate, it has been reported that due to the remaining ammonia component, it easily becomes columnar substances from spherical in the firing process. In addition, alkoxides are expensive and thus have low practicality. The coprecipitation method using an alkali also has many practical problems in the production method as an industrial catalyst, such as low recovery rate, residue treatment, and low productivity because it is a batch process such as a precipitation method or a coprecipitation method.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the synthesis of spherical cerium oxide mainly by the coprecipitation method, there is still much room for improvement from the viewpoints of industrial cost and productivity, such as maintaining the spherical shape, cost, and treatment of solvents and residues after precipitation formation, and from the viewpoint of the uniformity of the particle size distribution of the catalyst. There is a demand for a method for producing oxide particles mainly composed of cerium oxide that can be manufactured at low cost and has a uniform particle size distribution with high efficiency. Among them, as will be described later, in the synthesis of cerium oxide, preventing the breakage of the shape during firing and obtaining particles with a uniform particle size distribution are very important for improving the fluidity and productivity of spherical cerium oxide. The breakage ratio affects the amount of raw materials used in production and has a great impact on the production cost, so particular improvement is required. In addition, by continuing production at a low recovery rate, it is said that it is difficult to reuse the by-products that have become oxides after passing through the firing process. Furthermore, sorting and removing broken pieces, etc. also impose a large load on the subsequent processes such as sieving, resulting in problems such as an extended process time and an increase in the cost of operating equipment.

[0007] As the manufacturing techniques up to now, numerous methods mainly using the coprecipitation method have been proposed. This involves causing precipitation by adding an acid, ammonia, ammonium carbonate, alkoxide, aqueous alkali solution, etc. to a solution mainly composed of an aqueous cerium salt, recovering it by a filter press or the like, and purifying it by a washing operation. However, considering the use and treatment of a large amount of solvents and additives, it is more efficient and preferable to continuously dry the cerium mixed solution with a continuous spray dryer such as a spray dryer (spray drying).

[0008] On the other hand, it has been confirmed that after firing the dry powder obtained by spray drying the aqueous solution containing the above cerium salt, agglomeration of the dry powder causes the formation of a lump. Due to the formation of this lump, the recovery rate deteriorates without a pulverization process. In addition, there are drawbacks such as the need for a pulverization process for the lump to improve the recovery rate, which increases the manufacturing cost and reduces productivity. As the cause, it is considered to be due to the handling method of the dry powder before firing, but the details are unknown.

[0009] As a result of intensive studies on these above-mentioned current situations and problems, the inventors of the present application have found that the formation of lumps can be suppressed by the charging thickness of the dry powder in the firing process, the recovery rate changes, and as a result, it affects productivity.

Means for Solving the Problems

[0010] That is, the present invention relates to the following 1) to 3). 1) (A) A step of preparing an aqueous solution by formulating raw materials, (B) a step of spray drying the aqueous solution, and (C) a firing step, which is a method for producing a hetero-metal doped cerium oxide, wherein (C) the charging thickness of the dry powder in the firing step is 8 mm or more and 50 mm or less, a method for producing a hetero-metal doped cerium oxide. 2) The method for producing a hetero-metal doped cerium oxide according to the above 1), wherein the charging thickness is 10 mm or more and 40 mm or less. 3) The method for producing a hetero-metal doped cerium oxide according to 1) or 2) above, wherein the hetero-metal is one or more metals selected from the group consisting of manganese (Mn), cobalt (Co), iron (Fe), and nickel (Ni). [Advantages of the Invention]

[0011] According to the present invention, it is possible to produce a hetero-metal doped cerium oxide with a high yield. [Embodiments for Carrying Out the Invention]

[0012] [Regarding Hetero-Metal Doped Cerium Oxide] The present invention relates to a method for producing a hetero-metal doped cerium oxide. Cerium oxide is a metal oxide represented by CeO2 and is also referred to as ceria. The hetero-metal is not particularly limited as long as it is a metal other than Ce (cerium). For example, transition metals such as Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mn, W, Sb, Sn, Mg, Si, Al, Ti, and P can be used. Among these, manganese (Mn), cobalt (Co), iron (Fe), and nickel (Ni) are preferred, and Mn and Co are more preferred. The hetero-metal doped cerium oxide can be expressed by the following formula (1) as a composition. [Chemical Formula 1] Ce 1-x M x O 2-y ···(1) In formula (1), x is 0.03 or more and 0.40 or less, and y is a numerical value depending on the oxidation state of the oxide. More preferably, the value of x is 0.05 or more and 0.35 or less, and even more preferably, 0.07 or more and 0.30 or less. In formula (1), M is the above-mentioned hetero-metal. In this specification, the hetero-metal doped cerium oxide may sometimes be simply referred to as cerium oxide.

[0013] [(C) The charged thickness of the dry powder in the firing step is 8 mm or more and 50 mm or less] The method for producing a hetero-metal-doped cerium oxide of the present invention includes (A) a step of preparing an aqueous solution by formulating raw materials, (B) a step of spray-drying the aqueous solution, and (C) a firing step. First, the step (C) will be described. The main purpose of the step (C) is to remove raw materials and by-products such as nitric acid and ammonia from the dried powder of the hetero-metal-doped cerium oxide obtained in the step (B) (hereinafter sometimes simply referred to as the dried powder). That is, as long as the object is achieved, there is no particular limitation on the conditions, but for example, the methods shown below are preferably used. The dried powder obtained in the steps (A) and (B) is charged into a bat in a firing furnace and fired in a batch manner. As the firing conditions, for example, in the presence of air flow, firing at about 200°C to 1500°C, preferably 250°C to 700°C, and more preferably 250°C to 600°C can remove unnecessary salts such as nitrate radicals. The firing time is preferably about 1 minute to 12 hours, more preferably 5 minutes to 2 hours. The firing time here means the time excluding the time required for the temperature increase and decrease steps, and means the time within the range of the set temperature ±5°C. The heating rate is preferably 0.1 to 10°C / min, more preferably 0.5 to 5°C / min. In this specification, the hetero-metal-doped cerium oxide obtained by the step (C) is referred to as fired granules. Regarding firing, it is possible to use a tunnel furnace, a muffle furnace, a box-type firing furnace, etc., and further, it is also possible to use a firing device such as a rotary kiln. Regarding the atmosphere during firing, air is simple and preferable as the gas to be circulated, but it is also possible to use other inert gases such as nitrogen, carbon dioxide, nitrogen oxide-containing gas for a reducing atmosphere, ammonia-containing gas, hydrogen gas, and mixtures thereof. Regarding the absolute humidity of the gas flowing during firing, 0.0001 kg / kgDA to 0.02 kg / kgDA is preferable, more preferably 0.0001 kg / kgDA to 0.015 kg / kgDA, and even more preferably 0.0001 kg / kgDA to 0.01 kg / kgDA. Note that step (C) also includes performing it in multiple steps by changing the above conditions. For example, it is the case where after firing at 300 °C for 10 minutes in the first step, firing is performed at 1300 °C for 1 hour in the second step. The fired granules obtained via this firing step (C) can be passed through a molding step etc. described below, but can also be used as a catalyst as they are.

[0014] In the present invention, in step (C), the charged thickness is characterized in that it is 8 mm or more and 50 mm or less, whereby the recovery rate of the fired granules can be improved. The reason for this is not clear, but the inventors have confirmed that when the charged thickness is less than 8 mm, a film-like substance is formed on the surface of the fired granules. Presumably, this film is causing a reduction in the recovery rate. The charged thickness means the depth of the dry powder in the vat, and as a measurement method, the distance from the lowermost surface of the dry powder (the receiving part of the vat) to the upper surface of the dry powder is measured using a ruler etc. More preferable values for the upper limit of this charged thickness are 48 mm, 45 mm, 42 mm, 40 mm in order, and particularly preferably 38 mm. Also, more preferable values for the lower limit are 9 mm, 10 mm, 11 mm, 13 mm in order, and particularly preferably 15 mm. Therefore, the most preferable range of the charged thickness is 15 mm or more and 38 mm or less. Note that the recovery rate is calculated from the weight change before and after step (C). Specifically, the weight of the dry powder charged into the vat is measured with an electronic balance (this result is designated as W1), and after passing through step (C), the fired granules and lumps recovered from the vat are passed through a sieve with a mesh size of 1 mm, and the weight of the fired granules obtained from below the sieve is measured with an electronic balance (this result is designated as W2), and calculated according to the following formula (2). [Formula 1] Recovery rate (%) = (W2 ÷ W1) × 100 ··· (2)

[0015] [Regarding manufacturing steps (A) and (B)] The method for producing a heterometal-doped cerium oxide of the present invention comprises: (A) a step of preparing an aqueous solution by formulating raw materials; and (B) a step of drying the aqueous solution. <Regarding step (A)> Step (A) is a step of formulating raw materials to prepare an aqueous formulation or an aqueous solution. Generally, the starting materials for each element constituting the metal-added cerium oxide are not particularly limited. As the cerium component raw material, cerium oxides such as cerium oxide, cerium acid, cerium acetate, cerium carbonate, cerium hydroxide, salts such as cerium ammonium nitrate, etc. can be used, but it is preferable to use cerium nitrate, which has good operability from the viewpoints of solubility and exhaust gas treatment and can obtain a good particle size distribution. In the example of the added metal, as the manganese component raw material, nitrates such as manganese nitrate, manganese sulfate, manganese acetate, carbonates, organic acid salts, hydroxides, etc. or mixtures thereof can be used. Salts, manganese oxide, metallic manganese, etc. can be used. Note that as the metal raw material, it is preferably used as an organic acid salt, and most preferably used as an acetate. For example, when using manganese, it is more preferably an organic acid salt such as manganese acetate. When this is used, the operability is good, the recovery rate of the dried product increases, and a uniform particle size distribution can be obtained even after firing. Regarding the formulation, the order of adding the raw materials is not particularly relevant, and it is important to completely dissolve all the raw materials in distilled water. Regarding the temperature during the formulation, 10°C to 100°C is preferable, 20 to 90°C is more preferable, and more preferably 30 to 80°C. In this specification, "~" includes the numerical values before and after. Specific examples of step (A) include the following. However, it is not limited to this description. While heating and stirring distilled water maintained at 10 to 100°C, cerium nitrate hexahydrate is dissolved to obtain an aqueous solution. After confirming the complete dissolution of this aqueous solution, manganese acetate tetrahydrate is added and dissolved, and complete dissolution is confirmed. Then, ammonium nitrate is dissolved to obtain an aqueous solution of the raw materials. As the stirring power for the above heating and stirring, in descending order of preference as the lower limit, 0.01 kW / m 3 , 0.10 kW / m 3, 0.15 kW / m 3 , 0.20 kW / m 3 and, in descending order of preference as the upper limit, 1.50 kW / m 3 , 1.00 kW / m 3 , 0.75 kW / m 3 . That is, the most preferred range is 0.20 kW / m 3 or more and 0.75 kW / m 3 or less. Also, as the solution viscosity of the above aqueous solution, in descending order of preference as the lower limit, they are 0.01 cP, 0.1 cP, 0.5 cP, 1 cP, and in descending order of preference as the upper limit, they are 1000 cP, 500 cP, 100 cP, 50 cP, 10 cP, 5 cP. That is, the most preferred range is 1 cP or more and 5 cP or less. Furthermore, as the time from the completion of step A until moving to the next step, in descending order of preference as the lower limit, they are 1 minute, 5 minutes, 10 minutes, 30 minutes, and in descending order of preference as the upper limit, they are 1 month, 15 days, 7 days, 3 days, 1 day, 10 hours. That is, the most preferred range is 30 minutes or more and 10 hours or less. Furthermore, as the water content in the above aqueous solution, expressed in terms of the content of solid components, in descending order of preference as the lower limit, they are 10% by weight, 20% by weight, 30% by weight, and in descending order of preference as the upper limit, they are 80% by weight, 70% by weight, 60% by weight. That is, the most preferred range is from 30% by weight to 60% by weight. Here, the weight of the solid components refers to the solid components of the reagent to be added, but the attached water and crystal water contained in the reagent are calculated as water in terms of weight.

[0016] <Regarding step (B)> Step (B) is a step of spray-drying the aqueous solution adjusted in step (A). Through this process, the above-mentioned formulation liquid or slurry is made into a dry powder. The drying method is not particularly limited as long as it can completely dry the formulation liquid. Examples include drum drying, freeze drying, spray drying, evaporation to dryness, etc. Among these, in the present invention, spray drying, which can dry the slurry into powder or granules in a short time, is particularly preferred. The drying temperature in spray drying varies depending on the concentration of the slurry, the liquid feeding rate, etc., but generally, the temperature at the inlet of the dryer is 150 - 350°C, and the temperature at the outlet is 70 - 250°C. Also, it is preferable to dry such that the average particle size of the obtained dry powder is 10 - 500 μm. In this specification, methods similar to spray drying, such as jet turbo dryer, flash jet dryer, spray pyrolizer, etc., are also included in spray drying. The upper limit of the temperature at the above-mentioned inlet in spray drying is more preferably 330°C, and even more preferably 310°C. The lower limit is more preferably 170°C, and even more preferably 190°C. Therefore, the range of 190°C - 310°C is a particularly preferred range. The upper limit of the temperature at the above-mentioned outlet in spray drying is preferably 200°C, more preferably 180°C, even more preferably 160°C, and still more preferably 150°C. The lower limit is more preferably 80°C, and even more preferably 90°C. Therefore, the range of 90°C - 150°C is a particularly preferred range. Also, the residence time of the dry powder in the drying device in spray drying is preferably 1 second to 3 minutes, more preferably 5 seconds to 1 minute, even more preferably 7 seconds to 45 seconds, and most preferably 10 seconds to 30 seconds. The upper limit regarding the average particle size of the dry powder is more preferably 480 μm, and even more preferably 460 μm. The lower limit is more preferably 20 μm, and even more preferably 40 μm. Therefore, the range of 40 - 460 μm is a particularly preferred range. The average particle size is determined as the volume average (median diameter D50) by measuring the particle size distribution with the above-mentioned laser diffraction scattering particle size distribution measuring device. In addition, in order to achieve the above average particle diameter, in the case of rotary type spray drying, it is preferable to optimize the rotation speed of the sprayer (atomizer). The rotation of the atomizer varies depending on the composition of the catalyst precursor, but is preferably 8,000 rpm or more and 17,000 rpm or less. The upper limit of the more preferable atomizer rotation speed is 16,500 rpm, particularly preferably 16,000 rpm, and most preferably 15,500 rpm. Further, the more preferable lower limit is 8,500 rpm, the particularly preferable lower limit is 9,000 rpm, and the most preferable lower limit is 9,500 rpm. That is, the most preferable range of the atomizer rotation speed is 9,500 rpm or more and 16,000 rpm or less. Also, this rotation speed can also be represented by the relative centrifugal acceleration, and is preferably 2,000 G or more and 30,000 G or less. Also, in the case of nozzle type spray drying, in order to achieve the above average particle diameter, known techniques can be applied, and the use of any gas type, gas-liquid flow rate ratio, and nozzle shape is included in the present invention. Furthermore, after the completion of step B, as the time until moving to the next step, the lower limits are preferably 1 minute, 5 minutes, 10 minutes, 30 minutes in order, and the upper limits are preferably 1 month, 15 days, 7 days, 3 days, 1 day, 10 hours in order. That is, the most preferable range is 5 minutes or more and 10 hours or less. When storing the granules after the completion of step (B), in order to prevent moisture absorption, put them in a plastic bag and then store them in an aluminum zip-lock bag.

[0017] In the production method of the present invention, in addition to the above steps (A) to (C), for example, it may also have a high-temperature firing step or a molding step performed after step (C), or a moisture adjustment step performed between step (B) and step (C).

[0018] <High-temperature firing step performed after step (C)> In the high-temperature firing process, the aim is to improve the stability of the particles and increase the purity as an oxide by treating at a temperature higher than that of the firing in step (C). In this specification, the hetero-metal doped cerium oxide obtained by the high-temperature firing process is referred to as high-temperature fired particles. The high-temperature fired particles can be used directly as a catalyst. The temperature range in this firing can be from 600 °C to 2000 °C, preferably from 700 °C to 1500 °C, under air circulation. The firing time is preferably from 1 hour to 40 hours, and the heating rate is preferably from 0.1 to 10 °C / min, more preferably from 0.5 to 5 °C / min. Regarding the atmosphere during this firing, air is a convenient and preferred gas to be circulated. However, it is also possible to use other inert gases such as nitrogen, carbon dioxide, nitrogen oxide-containing gases for a reducing atmosphere, ammonia-containing gases, hydrogen gas, and mixtures thereof. Regarding the absolute humidity of the gas circulated during firing, it is preferably from 0.0001 kg / kgDA to 0.02 kg / kgDA, more preferably from 0.0001 kg / kgDA to 0.015 kg / kgDA, and even more preferably from 0.0001 kg / kgDA to 0.01 kg / kgDA.

[0019] <Moisture adjustment process carried out between step (B) and step (C)> As an operation of the moisture adjustment process, for example, an intermediate for producing hetero-metal doped cerium oxide is placed in a metal or magnetic container to a thickness of 1 to 30 mm and left in the atmosphere to adjust the water content. At this time, it is not essential to cover the container with a lid, but it is preferred, and it is even more preferred to use a lid without holes. As the environment for performing moisture adjustment, the absolute humidity is 5 g / m 3 to 25 g / m 3 is preferably the following. As the lower limit, more preferably, in order, 7 g / m 3 , 8 g / m 3 , 9 g / m 3 , 10 g / m 3 respectively. As the upper limit, more preferably, in order, 22 g / m 3 , 20 g / m 3 , 15 g / m 3, 12 g / m 3 That is, the absolute humidity is 10 g / m 3 or more and 12 g / m 3 or less, and the time for moisture adjustment is 10 minutes or more, preferably 1 hour or more, more preferably 3 hours or more, and most preferably 5 hours or more. Also, when considering relative humidity, for example, it is preferable to perform moisture adjustment under a temperature environment of 15°C to 30°C and a humidity condition of 10%RH or more and 45%RH or less. The preferable lower limits of the temperature are 17°C, 19°C, and 20°C in order, and the upper limits are 27°C, 25°C, and 22°C in order. For the humidity, the preferable lower limits are 12%RH, 15%RH, and 17%RH in order, and the upper limits are preferably 40%RH, 35%RH, 30%RH, 25%RH, and 20%RH in order.

[0020] <Molding process> As the forming process, either a supported forming method in which a catalyst is supported on a carrier such as silica or an unsupported forming method without using a carrier can be adopted. Specific forming methods include, for example, tableting, pressing, extrusion, granulation, etc. As the shape of the formed product, for example, cylindrical, ring-shaped, spherical, etc. can be appropriately selected in consideration of the operating conditions. However, it is preferably a supported catalyst in which a catalyst active component is supported on a spherical carrier, particularly an inert carrier such as silica or alumina, with an average particle size of 3.0 mm or more and 10.0 mm or less, preferably an average particle size of 3.0 mm or more and 8.0 mm or less. Widely known supported methods include a rolling granulation method, a method using a centrifugal fluid coating device, a washcoat method, etc. There is no particular limitation as long as it is a method capable of uniformly supporting the calcined powder on the carrier. However, considering the production efficiency of the catalyst, etc., the rolling granulation method is preferred. Specifically, it is a method in which a device having a flat or uneven disk is placed at the bottom of a fixed cylindrical container, and the disk is rotated at a high speed to vigorously stir the carrier charged in the container by repeating the rotation and revolution movements of the carrier itself, and the calcined granule component is supported on the carrier by adding the calcined granules here. In addition, it is preferable to use a binder during the supporting. Specific examples of the binder that can be used include water, ethanol, methanol, propanol, polyhydric alcohols, polyvinyl alcohol as a polymer binder, silica sol aqueous solution as an inorganic binder, etc. Ethanol, methanol, propanol, and polyhydric alcohols are preferred, diols such as ethylene glycol and triols such as glycerin are more preferred, and an aqueous solution with a glycerin concentration of 5 mass% or more is even more preferred. By using an appropriate amount of the glycerin aqueous solution, good formability is achieved, and a high-performance catalyst with high mechanical strength can be obtained. The usage amount of these binders is usually 2 to 60 parts by mass with respect to 100 parts by mass of the calcined granules, but in the case of the glycerin aqueous solution, 15 to 50 parts by mass is preferred. During the supporting, the binder and the calcined powder may be supplied alternately or simultaneously to the forming machine. Also, during the forming, a small amount of a known additive, for example, graphite, talc, etc. may be added.In addition, regardless of whether the molding aids, pore formers, and carriers added during molding have any activity in the sense of converting the raw materials into some other product, they shall not be considered as constituent elements of the active ingredient in the present invention. The molded body obtained through the molding process can be used as a catalyst after drying if necessary and then performing the aforementioned high-temperature firing process.

[0021] <Others> In the method for producing the heterogeneous metal-doped cerium oxide of the present invention, it is preferable that the raw materials used in step (A) satisfy the following formula (3). By this, the particle size distribution of the particles after drying can be controlled. Furthermore, the recovery efficiency can be improved by reducing adhesion and the like in the drying process. Moreover, it is expected that there will be no quality change even when firing is carried out under loading conditions of several centimeters in the firing process. If this value is too small, adhesion may occur in the dryer, and it may not be possible to obtain a sufficient recovery rate of the dried body. Conversely, if it is too large, the shape of the dried particles cannot be maintained as spherical. [Formula 2] 0.7 ≦ (a + b) / c ≦ 8.0 ··· (3) Here, a to c have the following meanings. a: The amount of substance (mol) of cerium (Ce) in the raw material The amount of substance of cerium in the raw material means the content of cerium in the compound containing cerium used as the raw material. For example, when 1667.7 g of cerium nitrate hexahydrate is used as the raw material, a is 3.838 mol. b: The amount of substance (mol) of metals other than cerium in the raw material The amount of substance of metals other than cerium in the raw material means the content of the metals other than cerium in the compound containing metals other than cerium used as the raw material. For example, when 141.1 g of manganese acetate tetrahydrate is used as the raw material, it means the content of manganese, and b is 0.576 mol. c: The amount of substance (mol) of the moisture-proof agent It is the amount of the moisture-proof agent used as a raw material. Ammonium nitrate is common as the moisture-proof agent, but other salts can also be used. For example, ammonium carbonate, ammonium chloride, ammonium acetate, ammonium hydroxide (aqueous ammonia), etc. may be mentioned. Preferably, it is ammonium nitrate, which has good effects and convenience.

[0022] The range of (a + b) / c in the above formula (3) is 0.7 to 8.0, but the upper limit may be 20, more preferably 10, still more preferably 8.0, and particularly preferably 5.0. Also, as the lower limit, it is 0.7, but more preferably 1.2, still more preferably 1.3, particularly preferably 1.4, and most preferably 1.5. Therefore, the range of (a + b) / c is most preferably 1.5 to 5.0.

[0023] In the method for producing the hetero-metal-doped cerium oxide of the present invention, there is also a preferable range for the raw material used in the above step (A) in terms of b / c. As the upper limit of b / c, more preferably 0.80, still more preferably 0.60, particularly preferably 0.50, and most preferably 0.40. Also, as the lower limit, more preferably 0.10, still more preferably 0.15, particularly preferably 0.20, and most preferably 0.25. Therefore, the range of b / c is most preferably 0.25 to 0.40.

[0024] In addition, the preferable ranges for each of a to c above are as follows. However, the following values of a, b, and c in this section are the case where the distilled water charged during the raw material input in the preparation step (A) is 1500 parts by mass, and it is necessary to adjust according to the ratio with distilled water appropriately according to the scale. Preferably, a is 1.0 mol or more and 10 mol or less. As its lower limit, in order of preference, they are 2.0 mol and 3.0 mol, and as the upper limit, in order of preference, they are 5.0 mol and 4.0 mol. That is, it is most preferably 3.0 mol or more and 4.0 mol or less. b is preferably in the range of 0.01 mol or more and 1.0 mol or less. More preferably, the lower limit is 0.1 mol, 0.3 mol, or 0.5 mol in order of preference, and the upper limit is 0.9 mol, 0.8 mol, or 0.7 mol in order of preference. That is, it is most preferably in the range of 0.5 mol or more and 0.7 mol or less. c is preferably in the range of 0.5 mol or more and 10.0 mol or less. More preferably, the lower limit is 0.6 mol or 0.7 mol in order of preference, and the upper limit is 5.0 mol or 4.0 mol in order of preference. That is, it is most preferably in the range of 0.7 mol or more and 4.0 mol or less.

[0025] The heterogeneous metal-doped cerium oxide obtained by the production method of the present invention preferably has a bulk density of 0.51 g / cc or more and 1.50 g / cc. The bulk density is important, for example, when it is used in a fluidized state. If it is too small, the amount that can be charged per unit volume will be reduced, and when used as a catalyst, the reaction efficiency may decrease, resulting in increased running costs. On the other hand, if it is too large, the velocity and pressure of the fluid required for fluidization will increase, which will also cause an increase in running costs. More preferably, the lower limit of the bulk density is 0.53 g / cc, 0.55 g / cc, 0.58 g / cc, or 0.60 g / cc in order of preference. The upper limit is more preferably 1.40 g / cc, 1.30 g / cc, 1.20 g / cc, or 1.10 g / cc in order of preference. That is, the most preferred bulk density is 0.60 g / cc or more and 1.10 g / cc or less.

[0026] The heterogeneous metal-doped cerium oxide obtained by the production method of the present invention has a high uniformity of particle size distribution. Furthermore, the heterogeneous metal-doped cerium oxide produced by the production method of the present invention is characterized by a low content of fine particles having a particle diameter of 10 μm or less. Therefore, it has excellent properties in the following applications, for example. When used as industrial powders in general, such as catalysts, battery materials, sensor materials, pigments, dispersoids, cosmetics, abrasives themselves or their raw materials, the fluidity is improved, and they are excellent in handling and operability as powders. Specifically, there is an advantage that the residue of the powder in the freight containers, feeders or hoppers is reduced, and the manufacturing loss is reduced. Such operability as powders can be easily evaluated by known methods. For example, in addition to the true density, bulk density and compressibility, known methods can be applied to the angle of repose, angle of collapse, and difference angle. Particularly when used as a catalyst, it can be used for exhaust gas treatment catalysts, hydrogen production catalysts, etc. by forming. The performance is improved due to the uniform particle size distribution, and further, the discharge from the reactor to the outside of the system is suppressed due to the small amount of fine particles, and stable reaction results can be expected. When used as a battery material or a sensor material, high density can be expected due to the uniform particle size distribution, the conductivity is improved, and an improvement in performance can be expected. When used as an abrasive, for example, when used as a CMP abrasive for semiconductors, due to the uniform particle size distribution, polishing with improved flatness of the surface roughness after polishing becomes possible.

Examples

[0027] Hereinafter, examples are shown with specific examples, but the present invention is not limited to the examples as long as the gist thereof is not deviated.

[0028] [Example 1] An aqueous solution (A1) obtained by mixing 38,800 parts by mass of distilled water, 44,440 parts by mass of cerium nitrate hexahydrate, 3,760 parts by mass of manganese acetate tetrahydrate, and 4,000 parts by mass of ammonium nitrate was spray-dried using a spray dryer at an inlet temperature of 260 ° C and an outlet temperature of 130 ° C, and the rotation speed of the atomizer was 13,000 rpm to obtain a dried powder (B1). The obtained dried powder (B1) was charged into a firing pan so as to have a thickness of 15 mm, and heated from room temperature to 300 ° C at 0.6 ° C / min. in a tunnel furnace, and then fired for 10 minutes to obtain fired granules (C1). The recovery rate of the fired granules (C1) at this time was 49.3%.

[0029] [Example 2] An aqueous solution (A1) prepared by mixing 38,800 parts by mass of distilled water, 44,440 parts by mass of cerium nitrate hexahydrate, 3,760 parts by mass of manganese acetate tetrahydrate, and 4,000 parts by mass of ammonium nitrate was spray-dried using a spray dryer at an inlet temperature of 260°C and an outlet temperature of 130°C with the atomizer rotation speed at 17,000 rpm to obtain a dried powder (B2). The obtained dried powder (B2) was charged into a firing pan to a thickness of 10 mm, heated in a tunnel furnace from room temperature to 300°C at 0.6°C / min, and then fired for 10 minutes to obtain fired granules (C2). The recovery rate of the fired granules (C2) at this time was 48.6%.

[0030] [Example 3] An aqueous solution (A1) prepared by mixing 38,800 parts by mass of distilled water, 44,440 parts by mass of cerium nitrate hexahydrate, 3,760 parts by mass of manganese acetate tetrahydrate, and 4,000 parts by mass of ammonium nitrate was spray-dried using a spray dryer at an inlet temperature of 260°C and an outlet temperature of 130°C with the atomizer rotation speed at 15,000 rpm to obtain a dried powder (B3). The obtained dried powder (B3) was charged into a firing pan to a thickness of 27 mm, heated in a tunnel furnace from room temperature to 300°C at 0.6°C / min, and then fired for 10 minutes to obtain fired granules (C3). The recovery rate of the fired granules (C3) at this time was 48.2%.

[0031] [Example 4] Fired granules (C4) were obtained in the same manner as in Example 1 except that the dried powder (B1) was charged into a firing pan to a thickness of 40 mm. The recovery rate of the fired granules (C4) at this time was 48.0%.

[0032] [Comparative Example 1] Fired granules (C5) were obtained in the same manner as in Example 2 except that the dried powder (B2) was charged into a firing pan to a thickness of 5.8 mm. The recovery rate of the fired granules (C5) at this time was 45.5%.

[0033] [Comparative Example 2] A fired granule (C6) was obtained in the same manner as in Example 3, except that the dry powder (B3) was charged into the baked bread so that the thickness became 7.0 mm. The recovery rate of the fired granule (C6) at this time was 46.4%.

Table 1

[0034] As shown in Table 1, it can be seen that by the manufacturing method of the heterogeneous metal-doped cerium oxide catalyst of the present invention, it is possible to increase the recovery rate of the fired granules. Considering the price of cerium as a raw material, even a difference in the recovery rate of a few percent can greatly contribute to reducing the raw material cost of the catalyst, and it can be said that it is a highly productive manufacturing method.

Industrial Applicability

[0035] When manufacturing a heterogeneous metal-doped cerium oxide catalyst, in the firing step, by setting the thickness of the charged dry powder during firing within a certain range, a heterogeneous metal-doped cerium oxide catalyst can be obtained with a high recovery rate with respect to the charged amount of the dry powder during firing, and it becomes possible to enhance productivity.

Claims

**Claim 1** A method for producing a hetero-metal doped cerium oxide, comprising: (A) a step of preparing an aqueous solution by formulating raw materials; (B) a step of spray-drying the aqueous solution; and (C) a firing step, wherein in the (C) firing step, the charged thickness of the dry powder is 8 mm or more and 50 mm or less. **Claim 2** The method for producing a hetero-metal doped cerium oxide according to claim 1, wherein the charged thickness is 10 mm or more and 40 mm or less. **Claim 3** The method for producing a hetero-metal doped cerium oxide according to claim 1 or 2, wherein the hetero-metal is one or more metals selected from the group consisting of manganese (Mn), cobalt (Co), iron (Fe), and nickel (Ni).

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