Ammonia combustion catalyst, method for producing the same, and method for burning ammonia using the catalyst

Abstract

The present invention aims to provide a catalyst that exhibits excellent mechanical strength, can be used for a long period of time without damage, and shows a high raw material conversion rate even at low reaction temperatures, when a portion of ammonia is burned and the heat of combustion is used in the ammonia decomposition reaction to produce hydrogen from ammonia, and also aims to efficiently obtain the heat of ammonia combustion by using this catalyst. [Solution] An ammonia oxidation catalyst having an average crush strength Av of 5N or higher, calculated from 10 or more of the said molded catalysts.

Description

Technical Field

[0001] The present invention relates to a catalyst used for oxidatively combusting ammonia for use as a heat source and a method for producing hydrogen using the same.

Background Art

[0002] Regarding hydrogen production technology, there are existing industrial processes, for example, by-product hydrogen from the steel manufacturing process, hydrogen produced by reforming coal and petroleum, and the like. Hydrogen generated from such processes has a strong facility dependence and has little convenience in terms of appropriately and easily using hydrogen. Further, the existing hydrogen production technology generates a large amount of carbon dioxide during production, and it can be said that this technology has a high environmental load in that this carbon dioxide can lead to global warming and recent abnormal weather.

[0003] On the other hand, as a simple and environmentally friendly hydrogen production technology, there is a method that utilizes the decomposition reaction of ammonia. The reaction formula is NH3 → 0.5N2 + 1.5H2. Since this reaction is a large exothermic reaction of 10.9 kcal / mol, heat supply from outside the system is required. As a method for supplying this reaction heat, there is an autothermal reformer (ATR) that burns a part of ammonia as a raw material or hydrogen generated by the ammonia decomposition reaction and uses the combustion heat as the reaction heat for ammonia decomposition (Patent Document 1, Non-Patent Document 1). The combustion reactions are NH3 + 0.75O2 → 0.5N2 + 1.5H2O; H2 + 0.5O2 → H2O. As catalysts used for ATR, there are a catalyst in which Ru is supported on alumina (Patent Document 1), a catalyst using Ag (Patent Document 2), and a catalyst in which Pt and Rh are supported on alumina (Non-Patent Document 1). That is, this hydrogen production technology can be said to be a technology consisting of two-stage reactions: an oxidative combustion reaction (ammonia combustion reaction) of a mixed gas containing ammonia, oxygen, and optionally hydrogen, and a reaction (ammonia decomposition reaction) of decomposing high-temperature ammonia gas to obtain hydrogen.

[0004] In the ammonia combustion reaction, one of these two-stage reactions, when a catalyst is used, depending on the catalyst composition, reaction control can be difficult, leading to instability in the amount of reaction heat and ammonia supplied to the subsequent ammonia decomposition stage. As a result, it can be difficult to consistently obtain a constant concentration of hydrogen. Furthermore, if the combustion reaction proceeds erratically, changes in the catalyst layer temperature can damage the ammonia reformer and lead to catalyst degradation.

[0005] These factors make the ammonia decomposition reaction unstable, and if the decomposition rate is insufficient, a large amount of ammonia remains in the gas after the reaction, resulting in a fuel of poor quality for use as hydrogen fuel. Furthermore, the catalysts proposed so far all use precious metal elements such as Ru, Rh, and Pt, which are rare metals and resource-constrained, as catalytic active components, making the catalysts expensive and posing a significant practical problem in terms of cost. In addition, the prior art described in the above-mentioned patent document only provides technical information on the catalyst shape as a powder, and from the standpoint of practicality as an industrial catalyst, it is insufficient because the differential pressure in the reactor becomes high when the amount of catalyst packed is large, and this differential pressure can change over time. However, in this technology of burning ammonia and performing a catalytic reaction at high temperatures, even those skilled in the art did not know what level of strength was required for the molded catalyst. In other words, when using a powder made of inexpensive metal mixed oxides as a molded catalyst in the ammonia combustion reaction, there was a need for a catalyst and method that could achieve a high ammonia conversion rate, and that could stably and long-term obtain ammonia combustion heat without the catalyst being damaged or pulverized under high-temperature conditions. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] International Publication No. 01 / 87770 Pamphlet [Patent Document 2] Patent No. 5483705 [Non-patent literature]

[0007] [Non-Patent Document 1] Takagi Muroi, “Industrial Precious Metal Catalyst”, Saiwai Shobo, May 26, 2003, p297 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] The present invention aims to provide an ammonia oxidation catalyst that exhibits excellent mechanical strength, can be used for a long period of time without damage, and shows a high raw material conversion rate even at low reaction temperatures, when a portion of ammonia is burned and the heat of combustion is used in the ammonia decomposition reaction to produce hydrogen from ammonia, and also aims to efficiently obtain the heat of ammonia combustion by using this catalyst. [Means for solving the problem]

[0009] As a result of diligent research, the inventors of the present invention have found that by molding a powder of a metal composite oxide, which is the active ingredient, and using an ammonia oxidation molded catalyst having a mechanical strength such that the average crushing strength Av is 5 N (Newtons) or more, the catalyst does not break during the reaction, and the conversion rate of the raw material ammonia is improved even at low reaction temperatures, leading to the present invention. Furthermore, the crushing strength of the catalyst varies from particle to particle, and catalyst breakage is a phenomenon observed in catalysts that lack a specific strength. From this viewpoint, the catalyst of the present invention more preferably refers to one in which Av-Sg is above a certain value when the standard deviation of the crushing strength is Sg.

[0010] In other words, the present invention relates to the following 1) to 5). 1) An ammonia oxidation catalyst for burning ammonia by reacting ammonia with an oxygen-containing gas, wherein the average crush strength Av calculated from 10 or more such molded catalysts is 5N or higher. 2) The ammonia oxidation catalyst according to claim 1), characterized in that Av-Sg is 1N or greater when the standard deviation of the crushing strength is Sg. 3) An ammonia oxidation catalyst according to 1) or 2), comprising manganese and cerium as active ingredients. 4) The ammonia oxidation catalyst according to any one of 1) to 3), wherein the active ingredient contains manganese in an amount of 1 to 90% by mass on the basis of manganese dioxide. 5) A method for burning a gas containing ammonia and oxygen using an ammonia oxidation catalyst described in any one of items 1) to 4). [Effects of the Invention]

[0011] By using the catalyst according to the present invention, it is possible to carry out a stable, long-term reaction without the catalyst being damaged by the ammonia oxidation reaction. Furthermore, a high raw material conversion rate can be achieved even at lower reaction temperatures, and the heat of ammonia combustion can be efficiently obtained. Here, there is variation in the crushing strength of the catalyst from particle to particle, and catalyst damage is a phenomenon observed in catalysts that lack a specific strength. From this viewpoint, the catalyst of the present invention, more specifically, exhibits an Av-Sg value of or above when the standard deviation of the crushing strength is Sg. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 shows the XRD chart of the active components of catalyst 1 produced in Example 1. [Modes for carrying out the invention]

[0013] The present invention relates to a catalyst for burning ammonia by reacting a gas containing ammonia and oxygen, wherein the average crush strength Av calculated from 10 or more of these molded catalysts is 5N or higher.

[0014] [Crushing strength] The catalyst of the present invention is a catalyst having an average value Av of crushing strength of 5 N (Newton) or more. Here, the crushing strength is a physical property generally known as the pressure resistance strength of a granulated product. Usually, one molded body having a shape such as a pellet shape or a tablet shape is pressurized in the body direction (long axis direction) and the force at the time of crushing is measured. JIS Z8841 (1993) "Granulated Products - Strength Test Method" stipulates the test method. Examples of practical devices for carrying out the test method include a tablet hardness tester (manufactured by ERWEKA). As a method for measuring the crushing strength, for example, using a tablet hardness tester TBH425 manufactured by Erweka, measurement can be carried out under the conditions of a sensitivity of 1 N, a measurement speed of 0.1 mm / sec, a compression speed of 10 N / sec, and a measurement method "Force", but it is not limited to this as long as it does not deviate from the measurement principle stipulated in the above JIS. In this specification, the average value of the crushing strength means the value obtained by arithmetically averaging the values of 10 or more catalysts measured using the above measurement method. Here, the number of catalysts used for measurement is preferably 10 or more, and the larger the number of measurements, the better because the accurate crushing strength of the catalysts within the same lot can be calculated. Therefore, the number of catalysts to be measured is more preferably 15 or more, and particularly preferably 100 or more. The average value of the crushing strength in the present invention is preferably 5 N or more, but the lower limit values of the more preferable ranges are preferably 10 N, 15 N, 20 N, 25 N, 30 N in order, and particularly preferably 33 N. Also, the upper limit values of the preferable ranges are preferably 100 N, 90 N, 80 N, 70 N, 60 N, 50 N, 45 N, and particularly preferably 40 N. Therefore, the preferable range of the average value of the crushing strength is 5 N or more and 100 N or less, more preferably 10 N or more and 90 N or less, more preferably 10 N or more and 80 N or less, more preferably 15 N or more and 70 N or less, more preferably 20 N or more and 60 N or less, more preferably 25 N or more and 50 N or less, more preferably 30 N or more and 45 N or less, and particularly preferably 33 N or more and 40 N or less.

[0015] Also, here, there is variation in the crushing strength of each catalyst particle, and it can be said that catalyst breakage is a phenomenon observed in catalysts with insufficient specific strength. From this perspective, the catalyst of the present invention more preferably has a certain value or more for Av - Sg when the standard deviation of the values of 10 or more catalysts measured using the above measurement method for crushing strength is defined as Sg. The range of the Av - Sg value in the present invention is preferably 1 N or more. More preferably, the lower limit values of the range are 3 N, 5 N, 8 N, 10 N, 12 N, 15 N, 17 N, 18 N, 19 N, 20 N in order, and particularly preferably 21 N. Also, the upper limit values of the preferred range are preferably 100 N, 80 N, 60 N, 50 N, 40 N, 30 N, and particularly preferably 25 N. Therefore, the preferred range of the Av - Sg value is preferably 1 N or more and 100 N or less, more preferably 5 N or more and 80 N or less, more preferably 10 N or more and 60 N or less, more preferably 15 N or more and 50 N or less, more preferably 18 N or more and 40 N or less, more preferably 20 N or more and 30 N or less, and particularly preferably 21 N or more and 25 N or less.

[0016] The ammonia oxidation shaped catalyst of the present invention preferably contains cerium oxide as an active component, and particularly preferably contains a mixture (ceria - containing composite metal oxide) of a ceria - containing composite metal oxide and an oxide of at least one element selected from Groups 2 to 15 of the periodic table. Cerium oxide is a metal oxide represented by CeO2 and is also referred to as ceria. Also, at least one element selected from Groups 2 to 15 of the periodic table is not particularly limited as long as it is a metal other than Ce (cerium) and is at least one metal element selected from Groups 2 to 15 of the periodic table. For example, transition metals such as Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mn, Te, Pb, Mo, Bi, W, Sb, Sn, Mg, Si, Al, Ti, P can be used. Among these, manganese (Mn), cobalt (Co), iron (Fe), and nickel (Ni) are preferred, more preferably Mn and Co, and even more preferably Mn.

[0017] The catalytically active component according to the present invention is manganese oxide, which is particularly preferred as an oxide of at least one element selected from Group 2 to Group 15 of the periodic table. Therefore, the ceria-containing composite metal oxide is a mixture of manganese oxide and ceria (hereinafter referred to as the Mn-Ce system component). Furthermore, the manganese content in this Mn-Ce system component is preferably 1 to 99% by mass, when calculated as manganese dioxide, assuming that all manganese contained in the Mn-Ce system component is manganese dioxide. In addition, unless otherwise noted in this application, manganese oxide also refers to manganese dioxide. Similarly, cerium contained in the Mn-Ce system component is assumed to be cerium dioxide. In this specification, "~" includes the numbers before and after it.

[0018] The Mn-Ce component preferably has only a fluorite-type structure of cerium dioxide as measured by powder X-ray diffraction. In the ammonia combustion reaction, ammonia acts as a strong reducing agent, and to efficiently burn it, the catalyst itself needs to have a strong re-oxidation capacity; therefore, cerium dioxide is suitable as the base material of the component. On the other hand, manganese oxide has a mechanism of action that efficiently dissociates molecular oxygen contained in the reaction gas and converts it into lattice-type oxygen that burns ammonia. For this reason, a structure in which manganese oxide is solid-dissolved in cerium dioxide and highly dispersed is most preferable. In other words, the ceria-containing composite metal oxide, which is the preferred form of the Mn-Ce component of the present invention, is one in which, when measured by powder X-ray diffraction, no diffraction peak originating from manganese oxide is observed, and the crystal peak of fluorite-type cerium dioxide is the main peak. The crystal structure of the powder sample can be confirmed by measuring the lattice plane spacing (d value). X-ray diffraction can be performed under the following conditions: CuKα source, voltage 45KV, current 40mA, scanning range 10~90°, and scanning speed 0.198° / min. In the X-ray diffraction measurement results of the manganese-cerium homogeneous mixed oxide obtained by the present invention, the d value of the main peak is in the range of 3.07~3.15, which is in close agreement with the d value of 3.12 for the fluorite-type structure of cerium dioxide listed on the JCPDS (Joint Committee for Powder Diffraction Standards) card. Furthermore, the d values ​​of cerium dioxide listed on the card, in order of increasing relative intensity, are 3.12, 2.71, 1.91, 1.63, etc. Crystalline peaks were detected at positions (d value ±0.05) that were in close agreement with the main peak, suggesting that the crystal structure of the manganese-cerium homogeneous mixed oxide is in close agreement with the fluorite-type structure of cerium dioxide.

[0019] In the Mn-Ce component, it is preferable to contain manganese in an amount of 1 to 90% by mass in terms of manganese dioxide, but the lower limits of the more preferable range are, in order, 2% by mass, 3% by mass, 5% by mass, 10% by mass, 20% by mass, 30% by mass, 40% by mass, 50% by mass, and 60% by mass, with 65% by mass being particularly preferred. The upper limits are 95% by mass, 90% by mass, 85% by mass, 80% by mass, and 75% by mass, with 70% by mass being particularly preferred. Therefore, the preferred range for manganese content is preferably 1 to 99% by mass in terms of manganese dioxide, more preferably 2 to 95% by mass, more preferably 5 to 90% by mass, more preferably 30 to 80% by mass, and particularly preferably 60 to 75% by mass. If the manganese content in the Mn-Ce component, calculated as manganese dioxide, is less than 1% by mass, the ammonia combustion activity will be insufficient, and an efficient ammonia combustion reaction will not be possible. If it exceeds 99% by mass, the manganese oxide tends to coarseen, and the crystal structure of cerium dioxide cannot be maintained, leading to a decrease in ammonia combustion activity, which is undesirable.

[0020] Next, we will explain the method for producing an ammonia oxidation molding catalyst. The method for producing a spherical molded catalyst for a mobile bed according to the present invention comprises the following steps (A) to (E). It is not necessary to perform steps (A) to (E) in this order; as long as steps (A) and (B) are performed in this order, the method is included in the catalyst production method of the present invention even if the order is not specified and some steps are duplicated. For example, the pre-calcined granules obtained in (C) can also be used as the catalyst of the present invention. (A) Process of preparing an aqueous solution by mixing raw materials. (B) A step of drying the aqueous solution to obtain a dried powder. (C) A step of firing the dried powder at a temperature of less than 1300°C to obtain pre-fired granules. (D) A step of molding the pre-calcined granules to obtain a molded and dried product. (E) A step of firing the dried molded product to obtain a molding catalyst.

[0021] [(A) Process of preparing an aqueous solution by blending raw materials] Step (A) included in the manufacturing method of the present invention is a step of preparing an aqueous formulation (sometimes referred to as a mixed solution or aqueous solution) by blending raw materials (hereinafter simply referred to as the blending step). Generally, there are no particular restrictions on the starting materials for each element constituting ceria-containing composite metal oxides. As cerium component raw materials, cerium oxides such as cerium oxide, ceric acid, cerium acetate, cerium carbonate, cerium hydroxide, and salts such as cerium ammonium nitrate can be used, but cerium nitrate is preferred as it offers good solubility and exhaust gas treatment, as well as good handling characteristics and a good particle size distribution. As an example of dissimilar metals, manganese component raw materials can include nitrates, carbonates, organic acid salts, hydroxides, etc., such as manganese nitrate, manganese sulfate, and manganese acetate, or mixtures thereof. In addition, manganese oxide and metallic manganese can be used. It is preferable to use organic acid salts as raw materials for these dissimilar metals, and most preferably as acetate salts. For example, when manganese is used, organic acid salts such as manganese acetate are more preferable, as they offer good handling characteristics, increase the recovery rate of the dried powder, and allow for a uniform particle size distribution even after calcination. Regarding the formulation, the order of raw material addition is not particularly important; it is crucial that all raw materials are completely dissolved in distilled water.

[0022] Specific examples of process (A) include the following, but are not limited to this description. Distilled water is heated and stirred at 10-100°C to dissolve cerium nitrate hexahydrate and 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 the starting aqueous solution. In this specification, "~" includes the preceding and following numbers. The preferred lower limits for the stirring power used in the above heating and stirring process are 0.01 kW / m³, 0.10 kW / m³, 0.15 kW / m³, and 0.20 kW / m³, and the preferred upper limits are 1.50 kW / m³, 1.00 kW / m³, and 0.75 kW / m³, in that order. In other words, the most preferred range is 0.20 kW / m³ or more and 0.75 kW / m³ or less. Furthermore, the preferred lower viscosity of the aqueous solution is 0.01 cP, 0.1 cP, 0.5 cP, and 1 cP, in descending order, and the preferred upper viscosity is 1000 cP, 500 cP, 100 cP, 50 cP, 10 cP, and 5 cP, in descending order. That is, the most preferred range is 1 cP or more and 5 cP or less. Furthermore, the preferred maturation time for the aqueous mixture after the completion of step (A) and before moving on to the next step is, in order of preference, 1 minute, 5 minutes, 10 minutes, and 30 minutes as the lower limit, and in order of preference, 1 month, 15 days, 7 days, 3 days, 1 day, and 10 hours as the upper limit. That is, the most preferred range is 30 minutes or more and 10 hours or less. During this maturation time, the above heating and stirring may be maintained. Furthermore, when expressing the water content of the above aqueous solution in terms of solid content, the preferred lower limits are 10% by weight, 20% by weight, and 30% by weight, in descending order, and the preferred upper limits are 80% by weight, 70% by weight, and 60% by weight, in descending order. That is, the most preferred range is 30% by weight to 60% by weight. The weight of solid content here refers to the solid components of the raw materials added, but adhering water and crystal water contained in the raw materials are calculated as water by weight. One method for obtaining the ceria-containing composite metal oxide of the present invention is to control the temperature of the aqueous solution prepared in step (A). Specifically, the lower limit is preferably 30°C, and more preferably 40°C, 50°C, 60°C, and 70°C, while the upper limit is preferably 95°C, and more preferably 90°C, 85°C, and 80°C. In other words, the most preferred range is 70°C to 80°C.

[0023] [(B) A step of drying the aqueous solution to obtain a dried powder] Step (B) included in the manufacturing method of the present invention is a step of drying the aqueous mixture obtained in step (A) to obtain a dried powder (hereinafter simply referred to as the drying step). The drying method is not particularly limited as long as it can dry the aqueous mixture to the extent that it can be obtained as a solid, but examples include drum drying, freeze-drying, spray drying, and evaporation to dryness. Of these, spray drying, which can dry the slurry into powder or granules in a short time, is particularly preferred in the present invention. The drying temperature for spray drying varies depending on the slurry concentration, liquid delivery rate, etc., but is generally 150 to 350°C at the inlet of the dryer and 70 to 250°C at the outlet. Furthermore, it is preferable to dry the dried powder so that the average particle size is 10 to 500 μm. In this specification, methods similar to spray drying, such as jet turbo dryers, flash jet dryers, and spray pyrolizers, are also included in spray drying.

[0024] (B) The upper limit of the average particle size of the dried powder obtained in step (B) 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 μm to 460 μm is particularly preferred. The average particle size is determined by measuring the particle size distribution using the laser diffraction scattering particle size distribution analyzer described above, and calculating the volume average (median diameter D50).

[0025] Furthermore, in order to achieve the above average particle size, in the case of rotary-type spray drying, it is preferable to optimize the rotation speed of the atomizer. The rotation speed of the atomizer varies depending on the composition of the catalyst precursor, but is preferably between 8,000 rpm and 17,000 rpm. A more preferable upper limit for the atomizer rotation speed is 15,000 rpm, particularly preferably 14,000 rpm, and most preferably 13,000 rpm. A further preferable lower limit is 8,500 rpm, particularly preferably 9,000 rpm, and most preferably 9,500 rpm. In other words, the most preferable range for the atomizer rotation speed is between 9,500 rpm and 13,000 rpm. This rotation speed can also be expressed by the relative centrifugal acceleration, which is preferably between 2,000 G and 30,000 G. In the case of nozzle-type spray drying, known techniques can also be applied to achieve the above average particle size, and the use of any gas type, gas-liquid flow rate ratio, and nozzle shape is included in the present invention. Furthermore, the preferred lower limits for the time between the completion of process (B) and the start of the next process are 1 minute, 5 minutes, 10 minutes, and 30 minutes, and the preferred upper limits are 1 month, 15 days, 7 days, 3 days, 1 day, and 10 hours, in that order. In other words, the most preferred range is 5 minutes or more and 10 hours or less. To obtain the ceria-containing composite metal oxide of the present invention, the difference between the inlet and outlet temperatures of the spray dryer should be controlled. Specifically, the difference between the inlet temperature and outlet temperature of the spray dryer should be 120°C or less, with the upper limit being 110°C and 100°C in more preferable order, and the lower limit being around 60°C. In other words, the most preferable range is 60°C to 100°C.

[0026] In the manufacturing method of the present invention, a moisture adjustment step may be included after step (B) above.

[0027] [(C) A step of obtaining pre-calcined granules by calcining the dried powder at a temperature of less than 1300°C] The manufacturing method of the present invention further comprises (C) a step of firing the dried powder at a temperature of less than 1300°C to obtain pre-fired granules (hereinafter simply referred to as the pre-fired step). The main purpose of process (C) is to remove raw materials and by-products such as nitric acid and ammonia from the dried powder obtained in process (B). In other words, there are no particular limitations on the conditions as long as this objective is achieved, but the following methods are preferably used. The dried powder is placed in a tray inside the firing furnace and fired using a batch method. The firing conditions are as follows: The firing temperature is preferably 200°C under air circulation, and is less than 1300°C as the upper limit. The lower firing temperatures are preferably 250°C, 300°C, 350°C, 400°C, 450°C, and 500°C, and the upper firing temperatures are preferably 1200°C, 1100°C, 1000°C, 900°C, 800°C, 700°C, and 600°C, in that order. The firing time is preferably from 1 minute to 12 hours, and more preferably from 5 minutes to 2 hours. The firing time here excludes the time required for the heating and cooling processes, and means the time within the firing temperature ±5°C range. The heating rate is preferably 0.1 to 10°C / min, and more preferably 0.5 to 5°C / min. In this specification, the ceria-containing composite metal oxide obtained by process (C) is referred to as fired granules. For firing, tunnel furnaces, muffle furnaces, box-type firing furnaces, and even firing equipment such as rotary kilns can be used. Regarding the atmosphere during firing, air is preferred as the gas to be circulated for simplicity, but other inert gases such as nitrogen, carbon dioxide, nitrogen oxide-containing gases, ammonia-containing gases, hydrogen gas, and mixtures thereof can also be used to create a reducing atmosphere. Furthermore, the absolute humidity of the gas circulating during firing is preferably 0.0001 kg / kgDA to 0.02 kg / kgDA, more preferably 0.0001 kg / kgDA to 0.015 kg / kgDA, and even more preferably 0.0001 kg / kgDA to 0.01 kg / kgDA. Furthermore, process (C) may also be carried out in multiple stages by changing the above conditions. For example, the first stage may involve baking at 300°C for 10 minutes, followed by the second stage of baking at 1200°C for 1 hour.

[0028] Furthermore, in step (C) of the present invention, it is preferable to set the preparation thickness to 8 mm or more and 50 mm or less, which improves the recovery rate of the calcined granules. The reason for this is not clear, but the inventors have confirmed that when the preparation thickness is less than 8 mm, a thin film-like substance forms on the surface of the calcined granules. It is presumed that this thin film is causing the reduction in the recovery rate. The "filling thickness" refers to the depth of the dry powder in the tray. The measurement method involves using a ruler or similar tool to measure the distance from the bottom surface of the dry powder (the receiving part of the tray) to the top surface of the dry powder. More preferable upper limits for the fill thickness are 48 mm, 45 mm, 42 mm, and 40 mm, respectively, with a particularly preferred value of 38 mm. Similarly, more preferable lower limits are 9 mm, 10 mm, 11 mm, and 13 mm, respectively, with a particularly preferred value of 15 mm. Therefore, the most preferable range for the fill thickness is 15 mm to 38 mm. The recovery rate is calculated from the weight change before and after process (C). Specifically, the weight of the dry powder placed in the tray is measured using an electronic balance (this result is denoted as W1), and after going through process (C), the calcined granules and lumps recovered from the tray are sieved through a 1 mm mesh sieve, and the weight of the calcined granules obtained from the bottom of the sieve is measured using an electronic balance (this result is denoted as W2), and the recovery rate is calculated according to formula (2) below. [Formula 2] Recovery rate (%) = (W2 ÷ ​​W1) × 100 ... (2)

[0029] [(D) A step of molding the pre-fired granules to obtain a molded and dried product] The manufacturing method of the present invention further comprises (D) a step of molding the pre-calcined granules to obtain a molded and dried product (hereinafter simply referred to as the molding step). The molding process can employ either unsupported molding, which does not use a carrier, or supported molding, which uses a carrier such as silica. Specific molding methods include, for example, tableting, press molding, extrusion molding, and granulation molding. The shape of the molded product can be appropriately selected from cylindrical, ring-shaped, spherical, etc., depending on the operating conditions. However, it is preferable to use an unsupported catalyst with an average particle size of 1.0 mm to 10.0 mm, preferably 2.0 mm to 6.0 mm, which is formed into a cylindrical shape by extrusion molding and then into a spherical shape by a rolling granulator. Furthermore, it is preferable to use a binder during extrusion molding. Specific examples of binders that can be used include water, ethanol, methanol, propanol, polyhydric alcohols, polymeric binders such as polyvinyl alcohol, polyvinyl butyral, methylcellulose, carboxymethylcellulose, polyethylene glycol, ethylcellulose, hydroxypropylcellulose, and inorganic binders such as aqueous silica sol solutions. One or more types of binders may be used. The amount of binder per type of binder is 0.1 to 10% of the weight of the pre-calcined granules, preferably 0.2 to 8.0%, more preferably 0.3 to 6.0%, and even more preferably 0.4 to 5.0%. While it is common practice to follow the molding process with a drying step at around 70°C to 100°C, this is not mandatory.

[0030] [(D-1) A step of adding a fibrous inorganic additive having a fiber length three times or more than the average particle size (D50), which is the particle size at which the cumulative volume fraction of the pre-calcined granules is 50%.] In the manufacturing method of the present invention, it is preferable that step (D) includes a step of adding a fibrous inorganic additive as step (D-1).

[0031] <Average particle size (D50) where the cumulative volume fraction of pre-calcined granules is 50%> The average particle size (D50) can be determined by known methods, and can be measured using, for example, the following instruments. For example, the particle size distribution is measured using a laser diffraction scattering particle size distribution analyzer (manufactured by Seishin Corporation, product name "LMS-2000e"), and the average volume (median diameter) is determined. That is, it is the median value in volume fraction. As for the measurement conditions, any general conditions known to those skilled in the art are acceptable, but for example, the scattering range is set to 10-20%, the measurement time to 3 seconds, the number of snaps to 3000, the sample material to be Fraunhofer, the dispersion medium to water, the stirrer pump to 2500 rpm, and the measurement is performed without applying ultrasound. That is, the average particle size means the particle size at which the cumulative volume fraction is 50%, and in this specification it may be expressed as D50. The measurement method can be either wet or dry, but in this embodiment, the wet method is used.

[0032] <Fibrous inorganic additive> The fiber length of the fibrous inorganic additive used in process (D-1) is preferably at least twice, and more preferably at least three times, the D50 of the pre-fired granules. The upper limit is about five times, but preferably four times. With this length, the contact points between the granules and the fibrous inorganic additive increase, improving friction and making it more difficult for the granules to peel off the molded body, thus improving its strength. If the fiber length is too short, the above effect will not be sufficiently obtained, and if it is too long, the granules and fibrous inorganic additive will not mix well. Note that this fiber length is the average fiber length. Inorganic additives include, for example, glass fiber, ceramic fiber, and alumina fiber, with alumina fiber being preferred. For example, Ibiul-E alumina fiber #1500 bulk (manufactured by Ibiden) is available from the market.

[0033] [(E) A step of firing the dried molded product to obtain a molding catalyst] The manufacturing method of the present invention further comprises (E) a step of firing the dried molded product to obtain a molding catalyst (hereinafter referred to as the main firing step). The main purpose of step (E) is to remove the binder and other materials used in step (D) of the molding process and to sinter the catalyst to give it mechanical strength. In other words, as long as this objective is achieved, there are no particular limitations on the conditions, but the following methods are preferably used, for example. The molded and dried products are placed in a tray in the firing furnace and fired in a batch manner. Regarding the atmosphere during firing, air is preferred as the gas to be circulated, but other inert gases such as nitrogen, carbon dioxide, nitrogen oxide-containing gas, ammonia-containing gas, hydrogen gas, and mixtures thereof can also be used to create a reducing atmosphere. Furthermore, the absolute humidity of the gas circulating during firing is preferably 0.0001 kg / kgDA to 0.02 kg / kgDA, more preferably 0.0001 kg / kgDA to 0.015 kg / kgDA, and even more preferably 0.0001 kg / kgDA to 0.01 kg / kgDA.

[0034] [Hydrogen production methods] The hydrogen production method according to the present invention uses ATR to obtain hydrogen by decomposing ammonia, and produces hydrogen by supplying the amount of heat required for ammonia decomposition with the heat of combustion generated by the ammonia combustion reaction. Specifically, a predetermined amount of oxygen is added to ammonia to form a reaction gas, this reaction gas is brought into contact with an ammonia combustion catalyst component, the oxygen is substantially completely consumed by the combustion reaction to obtain heat of combustion (ammonia combustion reaction), and this heat of combustion is used to decompose the remaining ammonia with an ammonia decomposition catalyst component to produce hydrogen (ammonia decomposition reaction).

[0035] The ammonia decomposition reaction is an endothermic reaction, and to ensure efficient progress, external heat supply is necessary. However, simply heating from outside the reactor can easily lead to overheating in certain areas, particularly around the outer periphery. This can result in an uneven ammonia decomposition reaction, making it difficult to consistently obtain a constant concentration of hydrogen. Furthermore, partial overheating can lead to thermal degradation of the catalyst, reducing the ammonia decomposition rate. These problems can be solved by adding a predetermined amount of oxygen to the ammonia before the ammonia decomposition reaction to create a reaction gas. This reaction gas is then brought into contact with an ammonia combustion catalyst component, and the combustion reaction substantially consumes all of the oxygen to obtain combustion heat. By bringing the oxygen-free reaction gas, whose temperature has risen due to this combustion heat, into contact with the ammonia decomposition catalyst component, it becomes possible to decompose the ammonia in the gas and produce hydrogen without supplying external heat. Moreover, by oxidizing a portion of the ammonia in this way and efficiently supplying the heat necessary for the decomposition reaction within the reactor, problems caused by partial overheating that are likely to occur when heat is supplied from outside the reactor are suppressed, and the decomposition of ammonia into hydrogen and nitrogen can be effectively carried out. Furthermore, the catalyst of the present invention relates to efficiently and safely carrying out the ammonia combustion reaction over a long period of time.

[0036] The reaction gas used in this invention (including ammonia, hydrogen, oxygen, and all other inert gases) may contain ammonia and oxygen. The volume ratio of oxygen to ammonia is preferably 0.050 or more and less than 1.0, more preferably 0.10 or more and 0.90 or less, and most preferably 0.12 or more and 0.80 or less. When oxygen is added to ammonia, the combustion heat increases with increasing oxygen addition, thus improving the rate of the decomposition reaction. However, if excessive oxygen addition causes the catalyst layer to reach a temperature excessively high above the temperature required for the decomposition reaction, thermal degradation of the catalyst occurs, which is undesirable as it impairs the performance and lifespan of the catalyst. In addition, excessive oxygen addition reduces the hydrogen yield from ammonia, which is undesirable from the viewpoint of efficient hydrogen production.

[0037] The space velocity (SV) of the reaction gas is 100 to 700,000 h⁻¹. -1 Preferably, and more preferably, 1,000 to 100,000 h -1 And more preferably 5,000 to 50,000 hours -1 And especially 10,000-35,000h -1 This is preferable. 100h -1 If it is less than 700,000h, the reactor may be too large and inefficient. -1 If the value exceeds this, the reaction rate may decrease, potentially leading to a reduction in hydrogen yield.

[0038] This invention improves the mechanical strength of the catalyst itself by molding the active component, making it possible to increase the amount of catalyst used in the reaction compared to conventional methods. The catalyst packing amount (mL) for the ammonia combustion reaction is preferably 0.50 mL or more. There is no particular upper limit, but for example, it is 100 L. If the packing amount is less than 0.50 mL, productivity will be low, and if the catalyst packing amount is less than 0.50 mL, the amount of heat stored in the catalyst will be small, the catalyst temperature will drop and the reaction activity will decrease, which may prevent the ammonia combustion reaction from proceeding sufficiently. Regarding the upper limit of the packing amount, since the ammonia decomposition technology using the catalyst of this invention is positioned as a relatively large-scale hydrogen production technology, there is no clear upper limit, but if the packing amount exceeds 100 L, the exothermic temperature will be high, which may lead to catalyst degradation due to overheating and a reduction in catalyst life. Furthermore, the lower limit of the range of more preferable catalyst packing amounts is 1.0 mL, 1.5 mL, 1.6 mL, 1.7 mL, and 1.8 mL, with 1.9 mL being particularly preferred. Furthermore, the upper limits are 75L, 50L, 40L, 30L, 20L, 10L, 5L, 2L, 1L, 500mL, 250mL, 100mL, 10mL, and 5mL, with 3.0mL being particularly preferred. Therefore, the preferred range for catalyst packing is preferably 1.0mL to 50L, more preferably 1.5mL to 30L, more preferably 1.6mL to 20L, more preferably 1.7mL to 10L, more preferably 1.8mL to 5L, and particularly preferably 1.9mL to 1L.

[0039] The reaction temperature for the ammonia combustion reaction is preferably between 20°C and 700°C. If the reaction temperature is lower than 20°C, the ammonia may not react, and if it is higher than 700°C, the exothermic temperature becomes too high, which may lead to catalyst degradation due to overheating and a reduction in catalyst life, and the nitrogen produced by ammonia combustion may be oxidized to produce nitrogen dioxide and nitric oxide. Furthermore, the lower limits of the more preferable reaction temperature range are 50°C, 100°C, 150°C, 180°C, and 200°C, with 220°C being particularly preferred. The upper limits are 700°C, 600°C, 500°C, 400°C, 300°C, and 250°C, with 230°C being particularly preferred. Therefore, the preferred reaction temperature range is 20°C to 700°C, more preferably 50°C to 600°C, more preferably 150°C to 500°C, more preferably 180°C to 400°C, more preferably 180°C to 300°C, more preferably 200°C to 250°C, and particularly preferably 220°C to 230°C. The temperature (exothermic temperature) of the ammonia oxidation catalyst itself obtained by the above reaction temperature is preferably 500°C or higher. If the exothermic temperature exceeds 700°C, there is a risk of by-product formation as described above. [Examples]

[0040] The present invention will be described in detail below. However, the present invention is not limited to the examples provided, unless it deviates from the spirit of the invention.

[0041] [Example 1] Distilled water was heated to 80°C and stirred while dissolving cerium nitrate hexahydrate to obtain aqueous solution (A1). After confirming the complete dissolution of (A1), manganese acetate tetrahydrate was added and dissolved to prepare aqueous solution (B1). After confirming the complete dissolution of B1, ammonium nitrate was dissolved to prepare aqueous solution (C1). The above aqueous solutions were mixed sequentially with vigorous stirring to confirm complete dissolution, and spray drying was performed using a spray dryer with an inlet temperature of 240°C, an outlet temperature of 140°C, and an atomizer rotation speed of 10500 rpm to obtain dried powder (D1) with an atomic ratio of Ce=100 and Mn=16 (mass % ratio of cerium dioxide:manganese dioxide=93:7) excluding oxygen. Subsequently, the dried powder was heated from 50°C to 300°C at a rate of 0.5°C / min under air circulation, and then calcined for 5 minutes to obtain calcined granules (E1). 3% by weight of alumina fiber (fiber length: 150 μm) was added to calcined granules (E1), and 7.5% by weight of an organic molding aid was added. After thoroughly mixing in a mixer, the mixture was extruded into a Φ3 mm rod shape using an extruder. This molded product was placed in a rolling granulator (Dalton QJ-230T) and then dried at room temperature for several days to obtain a spherical molding catalyst intermediate (F1). Next, the molding catalyst intermediate (F1) was calcined at 600°C in a box-type calcination furnace to obtain the spherical ammonia oxidation molding catalyst (catalyst 1) of the present invention. X-ray diffraction measurements were performed on the obtained catalyst 1 using a CuKα source, voltage 40 KV, current 30 mA, scanning range 10-60°, scanning speed 10° / min, divergence slit 1 / 2°, and divergence longitudinal limiting slit 10 mm. The results showed that a main peak was detected at the position indicating the fluorite-type crystal structure of cerium dioxide, and no crystal peaks derived from manganese were observed. The XRD chart is shown in Figure 1. The average particle size of catalyst 1 was 3.2 mm. The crushing strength of catalyst 1 was measured using the method described below. Fifteen molded catalysts were used to calculate Av and Av-Sg. The results are shown in Table 1. [Comparative Example 1] The calcined granules (E1) obtained in Example 1 were packed into an alumina ring with an inner diameter of 35 mm and a thickness of 5 mm, and pressed into shape at a pressure of 70 MPa using a hand press machine. The ring was then crushed on a sieve with a mesh size of 4.75 mm and classified on a sieve with a mesh size of 2.00 mm to obtain an amorphous molded catalyst intermediate (F2) with an average particle size of approximately 3 mm. Next, the molded catalyst intermediate (F1) was calcined at 600°C in a box-type calcination furnace to obtain the amorphous ammonia oxidation molded catalyst (catalyst 2) of the present invention. The average particle size of catalyst 2 was 3.0 mm. The crushing strength of catalyst 2 was measured using the same method as in Example 1. The number of molded catalysts used to calculate Av and Av-Sg was 15. The results are shown in Table 1.

[0042] [Crush strength test] Crushing strength was measured using an Elveca TBH425 automatic tablet hardness tester. More than 10 molded catalysts were packed into the tablets, and measurements were taken sequentially under the following conditions: sensitivity: 1N, measurement speed: 0.1 mm / sec, compression speed: 10N / sec, and measurement method: Force. The arithmetic mean of the crushing strength values ​​of the obtained molded catalyst particles was defined as Av, and the standard deviation as Sg. The difference between Av and Sg (Av-Sg) was also calculated.

[0043] [Table 1]

[0044] [Example of reaction 1] 2 mL of catalyst 1 was packed into a reaction tube with an inner diameter of 13.6 mm. A reaction gas consisting of 10% ammonia, 7.5% oxygen, and 82.5% nitrogen was flowed through the tube using a mass flow meter so that the space velocity (GHSV) of all reaction gases was 30,000 hr-1. The reaction temperature was controlled to 150°C, 180°C, 200°C, and 225°C using a heater and thermocouples around the reaction tube. The reaction performance of the catalyst (exothermic temperature and ammonia reaction rate) was measured for each reaction temperature using the following method. For the exothermic temperature, a thermocouple was placed in the center of the catalyst in the axial direction of the tube (near the reaction gas inlet), and the catalyst temperature (exothermic temperature) was measured. For the ammonia reaction rate, a boric acid aqueous solution was used to collect ammonia gas from the outlet gas. After collection for 4 minutes, a blank measurement was performed using the boric acid aqueous solution with a coulometry-type ammonia meter (Central Scientific AT-2000), followed by the main measurement. The obtained ammonia concentration was divided by the collection time to calculate the flow rate as ammonia gas, and then the ammonia reaction rate was calculated according to equation (3) below. There were no fluctuations in the differential pressure in the reaction tube when catalyst 1 was filled, when the gas flow started, or during the reaction, and the ammonia oxidation reaction was carried out stably. No particular problems occurred during extraction, and no cracks or chips were observed in the extracted catalyst. The results of the series of reactions are shown in Table 2. Ammonia reaction rate / % = {(Ammonia flow rate when reaction gas is flowed without catalyst) - (Ammonia flow rate when reaction gas is flowed with catalyst)} ÷ (Ammonia flow rate when reaction gas is flowed without catalyst) × 100 ... (3) [Example of reaction 2] Except for packing 4 mL of catalyst 1 and setting the reaction temperature to 200°C, the reaction was carried out exactly as in Reaction Example 1, and the exothermic temperature and ammonia reaction rate were determined. The results are shown in Table 2. [Example of reaction 3] Except for packing 6 mL of catalyst 1 and setting the reaction temperature to 200°C, the reaction was carried out in exactly the same manner as in Reaction Example 1, and the exothermic temperature and ammonia reaction rate were determined. The results are shown in Table 2. [Reaction Example 4] Except for packing 8 mL of catalyst 1 and setting the reaction temperature to 200°C, the reaction was carried out in exactly the same manner as in Reaction Example 1, and the exothermic temperature and ammonia reaction rate were determined. The results are shown in Table 2. [Response Example 5] Except for filling the container with 10 mL of catalyst 1 and setting the reaction temperature to 50°C, 100°C, 150°C, 200°C, 250°C, and 300°C, the reaction was carried out in exactly the same manner as in Reaction Example 1, and the exothermic temperature and ammonia reaction rate at each reaction temperature were determined. The results are shown in Table 2. The catalysts extracted after evaluation had turned light brown, but no cracks or chips were observed. A crush strength test was performed on the extracted catalysts. The number of molded catalysts used to calculate Av and Av-Sg was 10. The results are shown in Table 3. [Response Example 6] Catalyst 1 was packed into a 10 mL container, and the reaction gas composition was set to 10% ammonia, 9% oxygen, 78% nitrogen, and 3% hydrogen. The reaction temperature was set to 20°C, 50°C, 100°C, 200°C, 235°C, and 250°C. The reaction was carried out in exactly the same manner as in Reaction Example 1, and the exothermic temperature and ammonia reaction rate at each reaction temperature were determined. The results are shown in Table 2. The catalyst extracted after evaluation was light brown, with some white discoloration, but no cracks or chips were observed. A crush strength test was performed on the extracted catalyst. Ten molded catalysts were used to calculate Av and Av-Sg. The results are shown in Table 3. [Response Example 7] The reaction was carried out in exactly the same manner as in Reaction Example 1, except that Catalyst 2 was packed as the catalyst and the reaction temperature was set to 200°C. However, due to catalyst damage that is thought to have occurred during catalyst packing and gas flow initiation, the differential pressure in the reaction tube increased by 65% ​​gauge pressure, making the gas flow unstable and creating a risk of runaway reaction, so the reaction was stopped. Most of the extracted catalyst had turned into powder, making it difficult to continue the test any further.

[0045] [Table 2]

[0046] [Table 3]

[0047] As is clear from the above results, the catalyst of the present invention allows for catalyst loading on a larger scale than conventional powdered catalysts, and there are no fluctuations in differential pressure in the reaction tube during loading, gas flow initiation, or reaction, enabling stable ammonia oxidation reactions. Furthermore, the catalyst of the present invention shows no cracks or chips even when extracted, suggesting that the reaction can continue for an even longer period. In other words, the catalyst of the present invention can be said to be practical even when considering long-term use in ammonia combustion reactions on a real-scale basis. [Industrial applicability]

[0048] According to the present invention, when a portion of ammonia is burned and the heat of combustion is used in the ammonia decomposition reaction to produce hydrogen from ammonia, stable plant operation over a long period of time becomes possible. Furthermore, since the heat of ammonia combustion can be obtained efficiently, it is also very useful for the subsequent hydrogen decomposition reaction.

Claims

1. An ammonia oxidation catalyst for burning ammonia by reacting ammonia with an oxygen-containing gas, wherein the average crush strength Av calculated from 10 or more such molded catalysts is 5N or higher.

2. The ammonia oxidation catalyst according to claim 1, characterized in that Av-Sg is 1N or more when the standard deviation of the crushing strength is Sg.

3. The ammonia oxidation catalyst according to claim 2, comprising manganese and cerium as active ingredients.

4. The ammonia oxidation catalyst according to claim 3, wherein the active ingredient contains manganese in an amount of 1 to 90% by mass on the basis of manganese dioxide.

5. A method for burning a gas containing ammonia and oxygen using an ammonia oxidation catalyst according to any one of claims 1 to 4.

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