Method for producing ammonia decomposition catalyst and ammonia decomposition catalyst

Abstract

To provide a production method for easily producing an ammonia decomposition catalyst.SOLUTION: A production method of ammonia of the present invention comprises: a supporting step of impregnating a support with any one or both of ruthenium and lithium as catalyst; a drying step of drying the support with the catalyst supported; and a nitriding step of nitriding the dried support. The support has an A-type or X-type crystal structure, being an aluminosilicate with a pore size of 0.3 nm or more and 0.9 nm or less. The present invention also provides an ammonia decomposition catalyst.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an ammonia decomposition catalyst and a method for producing the same. [Background technology]

[0002] Systems that use hydrogen as an energy source are being developed as a means of reducing carbon dioxide emissions. Hydrogen is lighter than air and has a wide flammable range, so transporting and storing it in gaseous form is costly. For this reason, technology that uses ammonia as a hydrogen carrier is being considered. By transporting ammonia to hydrogen consumption areas, decomposing it into hydrogen and nitrogen according to the required amount, and then separating and using the hydrogen, it is possible to supply hydrogen more efficiently than before.

[0003] Techniques using catalysts to decompose ammonia to generate hydrogen have been known for some time. For example, Patent Document 1 discloses an ammonia decomposition catalyst in which ruthenium and an alkali metal are supported on a carrier such as alumina, silica, silica-alumina, activated carbon, titania, magnesia, etc., and subjected to a reducing hot gas treatment with hydrogen or ammonia. The ammonia decomposition catalyst of Patent Document 1 is a catalyst intended to obtain a 3:1 mixed gas of hydrogen and nitrogen used as an atmospheric gas in bright annealing and brazing processes for stainless steel and the like. Using the catalyst of Patent Document 1, a 3:1 mixed gas of hydrogen and nitrogen was obtained at a reaction temperature of 500°C and a space velocity of 5000 h -1 When ammonia is decomposed under these conditions, the yield of hydrogen is 99.76% (Example 1).

[0004] Patent Document 2 also discloses an ammonia decomposition catalyst in which ruthenium is supported on a magnesium oxide carrier, and a method for producing the same. The ammonia decomposition catalyst of Patent Document 2 is intended to use the generated hydrogen as fuel for a fuel cell. For this reason, the purpose is to provide an ammonia decomposition catalyst with higher catalytic activity that can improve the ammonia decomposition rate. The method for producing the ammonia decomposition catalyst disclosed in Patent Document 2 is a method in which a magnesium compound and a ruthenium compound are precipitated in an aqueous solution with an alkali metal carbonate, and then dried, fired, and reduced. In Patent Document 2, in order to disperse ruthenium as uniformly as possible on the carrier and to increase the specific surface area, a precipitation process is performed to make the particle size of the catalyst micrometer-sized. Using the catalyst of Patent Document 2, a reaction temperature of 400 to 600°C and a space velocity of 15,000 h -1 When ammonia is decomposed using this method, the yield of hydrogen is 62 to 99.9% (Examples 1 to 4).

[0005] Conventionally, complex manufacturing processes have been required to obtain highly active catalysts, and improvements in this area have been required.

[0006] The inventors invented an apparatus for generating hydrogen from ammonia using plasma discharge, and disclosed it in Patent Document 3. The hydrogen generation apparatus of Patent Document 3 can generate pure hydrogen with a hydrogen content of 100% under conditions of room temperature and normal pressure. However, in the hydrogen generation apparatus of Patent Document 3, it is preferable to uniformly convert the raw material gas into plasma in the plasma reactor, so when a large reactor is used, energy efficiency can be poor.

[0007] In order to mass-produce pure hydrogen using plasma discharge, it is more efficient to use a mixed gas of hydrogen, nitrogen, and ammonia as a raw material gas than to use ammonia. Therefore, the inventors developed a novel hydrogen generation device, which is disclosed in Patent Document 4, in which ammonia, which is a raw material gas, is partially decomposed with a catalyst to produce a mixed gas of hydrogen, nitrogen, and ammonia, the mixed gas is turned into plasma to completely decompose ammonia, and only the obtained hydrogen is separated by a hydrogen separation membrane. The device in Patent Document 4 discloses an ammonia decomposition catalyst in which a catalytic metal such as nickel or ruthenium is supported on magnesium oxide or alumina as a catalyst, but the optimized characteristics have not been obtained so far. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 10-85601 [Patent Document 2] JP 2016-159209 A [Patent Document 3] JP 2014-070012 A [Patent Document 4] Patent No. 6241804 Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention has been made in view of the above-mentioned circumstances, and has as its object to provide a method for producing an ammonia decomposition catalyst that can be produced easily and safely at low cost.Furthermore, the present invention has as its object to provide an ammonia decomposition catalyst that can be produced by this production method and that has a small pressure loss when a raw material gas is passed through the catalyst while contained in a reactor.

[0010] The ammonia decomposition catalyst obtained by the present invention is a catalyst optimized in particular for obtaining a raw material gas for producing pure hydrogen by a plasma reaction. [Means for solving the problem]

[0011] The method for producing an ammonia decomposition catalyst of the present invention comprises the steps of: a supporting step of impregnating a support with either or both of ruthenium and lithium as a catalyst; a drying step of drying the support carrying the catalyst; a nitriding step of nitriding the dried carrier; It is equipped with The carrier is characterized in that it has an A-type or X-type crystal structure and is an aluminosilicate with a pore size of 0.3 nm or more and 0.9 nm or less.

[0012] In the method for producing an ammonia decomposition catalyst of the present invention, the supporting step is preferably a step of impregnating a support with both ruthenium and lithium. Also, it is preferable that the support has an X-type crystal structure and the molar ratio (SiO2 / Al2O3) of silicon dioxide (SiO2) to aluminum oxide (Al2O3) is 2.0 or more and 2.5 or less.

[0013] The supporting step of the present invention is preferably a step of impregnating the support with an aqueous solution of ruthenium trichloride and lithium hydroxide to support 2.5 to 12.5 g of ruthenium and 2.5 to 7.5 g of lithium per 100 g of support.

[0014] The supporting step of the present invention comprises a first impregnation step of impregnating the support with an aqueous solution of lithium hydroxide; The process may further include a second impregnation step of impregnating the support carrying lithium hydroxide with an aqueous solution containing ruthenium trichloride.

[0015] The supporting step of the present invention can be a step of impregnating the support with an aqueous solution containing both lithium hydroxide and ruthenium trichloride.

[0016] The present invention also provides an ammonia decomposition catalyst. The ammonia decomposition catalyst of the present invention comprises a ruthenium- and lithium-supported catalyst. HoldThe ammonia decomposition catalyst is made of an aluminosilicate, and is characterized in that the aluminosilicate has an X-type crystal structure and the chemical formula of the aluminosilicate is CaO·Al2O3·xSiO2·yH2O, where x is a value between 2.0 and 2.5 and y is a value equal to or greater than 0. Effect of the Invention

[0017] The method for producing an ammonia decomposition catalyst of the present invention specifies the crystal structure and pore size, which are optimal carrier characteristics for an ammonia decomposition catalyst, and thereby makes it possible to produce an ammonia decomposition catalyst that exhibits small pressure loss when ammonia is supplied.

[0018] The method for producing an ammonia decomposition catalyst of the present invention allows an optimal catalyst to be supported on a carrier by impregnation, thereby making it possible to produce the catalyst easily and safely at low cost. The method for producing an ammonia decomposition catalyst of the present invention does not use hydrogen in the activation step, making it possible to produce the catalyst more safely than conventional methods.

[0019] The ammonia decomposition catalyst obtained by the production method of the present invention is a catalyst that is highly active at low temperatures.

[0020] By combining the ammonia decomposition catalyst of the present invention with a hydrogen generation device that generates hydrogen by decomposing ammonia through a plasma reaction, it becomes possible to mass-produce pure hydrogen from ammonia. [Brief description of the drawings]

[0021] [Figure 1] FIG. 1 is a flow chart of the method for producing the ammonia decomposition catalyst of Example 1. [Diagram 2] FIG. 2 is a flow chart of the method for producing the ammonia decomposition catalyst of Example 2. [Diagram 3] FIG. 3(a) is a photograph of the ammonia decomposition catalyst produced by the method of Example 1, and FIG. 3(b) is a photograph of the ammonia decomposition catalyst produced by the method of Example 2. [Figure 4] FIG. 4 is a graph showing the ammonia decomposition rate of ammonia decomposition catalysts with different supporting processes. [Diagram 5] FIG. 5 is a graph showing the relationship between the amount of catalyst supported and the ammonia decomposition rate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] The carrier usable in the ammonia decomposition catalyst of the present invention is an aluminosilicate having an A-type or X-type crystal structure and a pore size of 0.3 nm to 0.9 nm. The size of an ammonia molecule is 0.28 nm (2.8 angstroms), and this pore size range is preferred for a carrier that adsorbs ammonia. The most preferred crystal structure of the carrier is X-type. The composition of the carrier is preferably such that the molar ratio (SiO2 / Al2O3) of silicon dioxide (SiO2) to aluminum oxide (Al2O3) is 2.0 to 2.5.

[0023] The hydrogen-containing gas produced by the ammonia decomposition catalyst of the present invention can be optimized as a raw material gas for mass production of pure hydrogen by introducing it into a plasma reactor. The requirements for the hydrogen-containing gas to be introduced into the plasma reactor are an ammonia decomposition rate of 99.5%, an introduction temperature of 500°C or less, and a space velocity of 3000 to 5000 h -1 It is.

[0024] Space velocity (hereinafter abbreviated as SV) is the ratio of the packed volume (m 3 Ventilation volume per m 3 / h), and generally, the larger the amount of gas passing through, the higher the spatial velocity. The smaller the spatial velocity, the higher the ammonia decomposition rate, but in the case of a catalyst with a large pressure loss, it is difficult to control the spatial velocity to a small value. The pressure loss of a packed bed of solid particles can be calculated according to the Kozeny-Carman formula. For example, when particles with a particle size of 30 μm are packed to form a 10 cm layer as in the conventional technology, the pressure loss is 4000 Pa. When the pressure loss is large, it is difficult to reduce the spatial velocity. However, the ammonia decomposition catalyst of the present invention can easily reduce the spatial velocity by using a carrier with an appropriate particle size, so that the amount of raw material gas introduced into the plasma reactor can be appropriately controlled. When 1.5 mm particles are packed in a 10 cm packed bed as in the present application, the pressure loss is 0.2 Pa, which is 1 / 20,000 of the value when a packed bed of particles with a particle size of 30 μm is used.

[0025] The ammonia decomposition catalyst of the present invention has a wide range of controllable space velocity by making the average particle diameter of the carrier 1.5 to 3.0 mm. By making the particle diameter of the carrier millimeter-sized, the pressure loss during gas passage can be reduced regardless of the shape, and as a result, the space velocity can be easily controlled.

[0026] Catalysts that can be used in the ammonia decomposition catalyst of the present invention are ruthenium and lithium, and it is preferable to use both ruthenium and lithium. EXAMPLES

[0027] Hereinafter, a method for producing an ammonia decomposition catalyst and an ammonia decomposition catalyst embodying the present invention will be described.

[0028] [Example 1] 1 shows a flow chart of a method for producing an ammonia decomposition catalyst in Example 1. The production method of this example includes a supporting step of supporting a catalyst on a support, a drying step, and a nitriding step.

[0029] The carrier used in this embodiment is an aluminosilicate having a chemical formula of CaO·Al2O3·xSiO2·yH2O, where x=2.0 to 2.5 and y is a value of 0 or more. This aluminosilicate has an X-type crystal structure, and the molar ratio (SiO2 / Al2O3) of silicon dioxide (SiO2) to aluminum oxide (Al2O3) is substantially 2.0 or more and 2.5 or less. The average particle size of the carrier is 1.5 mm, and the pore size is 0.9 nm (9 Å). An aluminosilicate with such characteristics is available as a synthetic zeolite (Zeolum (registered trademark), SA-600A, manufactured by Tosoh Corporation).

[0030] The catalyst used in this example is ruthenium and lithium.

[0031] The person in charge of this embodiment Hold The process includes a first impregnation step (S1) of impregnating the support with an aqueous solution of lithium hydroxide, and a second impregnation step (S3) of impregnating the support with an aqueous solution containing ruthenium trichloride after the first impregnation step.

[0032] The first impregnation step (S1) is a step of impregnating the support with an aqueous solution of lithium hydroxide to support 2.5 to 7.5 g of lithium per 100 g of support. After the first impregnation step (S1), an intermediate drying step (S2) is performed in which the support is dried at 100°C or higher to remove moisture. The second impregnation step (S3) is a step of impregnating the support supporting lithium with an aqueous solution containing ruthenium trichloride to support an additional 2.5 to 12.5 g of ruthenium per 100 g of support.

[0033] After the second impregnation step (S3), a drying step (S4) is performed in which the support is dried at 100°C or higher for 10 to 12 hours to remove moisture. The dried support is activated by a nitriding step (S5) in which the support is exposed to a nitrogen atmosphere or an ammonia atmosphere at 500°C for 5 to 7 hours. The manufacturing method of this embodiment can manufacture an ammonia decomposition catalyst without performing a hydrogen reduction treatment.

[0034] Figure 3(a) shows an image of the surface of the ammonia decomposition catalyst obtained by the manufacturing method of this example, taken at 10,000 times by energy dispersive X-ray spectroscopy (SEM-EDX method). As shown in Figure 3(a), it was confirmed that the catalyst was uniformly dispersed and supported on the support surface.

[0035] [Example 2] 2 shows a flow chart of a method for producing an ammonia decomposition catalyst in Example 2. The production method in this example includes a supporting step (S11), a drying step (S12), and a nitriding step (S13).

[0036] In this embodiment, as in Example 1, an aluminosilicate (synthetic zeolite) having the chemical formula CaO·Al2O3·xSiO2·yH2O, where x = 2.0 to 2.5 and y is a value of 0 or more, can be used as the carrier.

[0037] The catalyst used in this example is the same ruthenium and lithium as in Example 1, but the supporting step is different from that in Example 1. In the supporting step (S11) of this example, the support is impregnated with an aqueous solution containing both lithium hydroxide and ruthenium trichloride, thereby supporting 2.5 to 12.5 g of ruthenium and 2.5 to 7.5 g of lithium on the support at the same time.

[0038] After the supporting step (S11), a drying step (S12) is performed in which the support is dried at 100° C. or higher for 10 to 12 hours, and a nitriding step (S13) is performed in which the dried support is exposed to a nitrogen atmosphere or an ammonia atmosphere at 500° C. for 5 to 7 hours, as in Example 1. The manufacturing method of this example also makes it possible to manufacture an ammonia decomposition catalyst without carrying out a hydrogen reduction treatment.

[0039] Figure 3(b) shows an image of the surface of the ammonia decomposition catalyst obtained by the manufacturing method of this example, taken at 10,000 times by energy dispersive X-ray spectroscopy (SEM-EDX method). As shown in Figure 3(b), it was confirmed that the catalyst was uniformly dispersed and supported on the support surface. Furthermore, no difference in surface state was observed between the ammonia decomposition catalyst obtained by the manufacturing method of Example 1 and the ammonia decomposition catalyst obtained by the manufacturing method of this example.

[0040] [Example 3] The method for producing an ammonia decomposition catalyst of this embodiment includes a supporting step, a drying step, and a nitriding step. In this embodiment, an aluminosilicate (synthetic zeolite) having a chemical formula of CaO·Al2O3·xSiO2·yH2O, where x=2.0-2.5 and y=0 or more, can be used as the carrier. In addition, in this embodiment, an aluminosilicate having an A-type crystal structure, an average particle size of 3.0 mm, a pore size of 0.3 nm (3 Å), and a chemical formula of K2O·Al2O3·xSiO2·yH2O, where x=2.0-2.5 and y=0 or more can also be used as the carrier. This aluminosilicate is available as a synthetic zeolite (Zeolum (registered trademark), CGS, manufactured by Tosoh Corporation).

[0041] In this embodiment, only one of ruthenium and lithium is supported as a catalyst. That is, in the supporting step of this embodiment, the support is impregnated with either an aqueous solution of lithium hydroxide or an aqueous solution of ruthenium trichloride, thereby supporting ruthenium or lithium on the support. The steps after the supporting step are the same as those in Example 1, and therefore a duplicated explanation will be omitted.

[0042] [ Example 4 ] Example 4 As an ammonia decomposition catalyst, the same carrier as in Example 1 was first impregnated with an aqueous solution containing ruthenium trichloride, and after an intermediate drying step, was impregnated with an aqueous solution of lithium hydroxide to produce an ammonia decomposition catalyst.

[0043] [Catalyst characteristic evaluation results depending on the support process] Example 1 and Example 2, Example 4 According to each of the manufacturing methods, an ammonia decomposition catalyst was manufactured in which 4.3 g of lithium and 12.5 g of ruthenium were supported per 100 g of carrier. Then, the ammonia decomposition rate of each ammonia decomposition catalyst was evaluated. The evaluation method is as follows.

[0044] Ammonia decomposition catalyst 20cm 3 The mixture was charged into a reactor with an inner diameter of 16 mm, and ammonia gas was pumped at a space velocity of 3000 h -1 The reaction vessel was heated while the ammonia was being fed through the reaction vessel, and the temperature inside the vessel was gradually increased. The hydrogen concentration contained in the outlet gas discharged from the outlet of the reaction vessel was measured with a hydrogen sensor. The ammonia decomposition rate was calculated using the obtained hydrogen concentration according to the following formula (1). Ammonia decomposition rate [%] = H2out / H2max (1) Where: H2out: Hydrogen concentration at the outlet of the reactor [L / min] H2max: The amount of hydrogen when all the ammonia is decomposed = 3 / 2 × Ammonia gas flow rate [L / min]

[0045] The relationship between reaction temperature and ammonia decomposition rate for each ammonia decomposition catalyst is shown in Figure 4. The ammonia decomposition catalyst produced by the production method of Example 1 achieved an ammonia decomposition rate of 99.7% at a reaction temperature of 510°C. The ammonia decomposition catalyst produced by the production method of Example 2 also achieved an ammonia decomposition rate of 99.6% at a reaction temperature of 510°C. Example 4 It was confirmed that the ammonia decomposition catalyst produced by this manufacturing method had an ammonia decomposition rate of 98.8% at a reaction temperature of 510°C, which was a significantly lower decomposition rate.

[0046] [Relationship between catalyst content and ammonia decomposition rate] Furthermore, nine types of ammonia decomposition catalysts were produced according to the production method of Example 2 by changing the amount of catalyst impregnated into the carrier in three levels each.

[0047] Table 1 shows the results of measuring the ammonia decomposition rate (%) at each reaction temperature for ammonia decomposition catalysts manufactured with three different amounts of lithium supported, 2.5 g, 4.3 g, and 12.5 g, and three different amounts of ruthenium supported, 2.5 g, 7.5 g, and 12.5 g, per 100 g of carrier.

[0048] [Table 1]

[0049] Figure 5(a) shows the relationship between reaction temperature and ammonia decomposition rate (%) for an ammonia decomposition catalyst in which 2.5g of lithium is supported on 100g of support and ruthenium is supported in any of the amounts of 2.5g, 7.5g, and 12.5g. Figure 5(b) shows the relationship between reaction temperature and ammonia decomposition rate (%) for an ammonia decomposition catalyst in which 4.3g of lithium is supported on 100g of support and ruthenium is supported in any of the amounts of 2.5g, 7.5g, and 12.5g. Figure 5(c) shows the relationship between reaction temperature and ammonia decomposition rate (%) for an ammonia decomposition catalyst in which 7.5g of lithium is supported on 100g of support and ruthenium is supported in any of the amounts of 2.5g, 7.5g, and 12.5g.

[0050] Among the ammonia decomposition catalysts that were measured, the ammonia decomposition catalyst of the embodiment, which supports 7.5 g of lithium and 12.5 g of ruthenium per 100 g of support, had the highest activity at a space velocity of 3000 h -1 At a reaction temperature of 490°C, an ammonia decomposition rate of 99.9% was achieved.

[0051] [Relationship between carrier properties and ammonia decomposition rate] Table 2 below shows the ammonia decomposition rate when 3.0% by weight of ruthenium is supported on aluminosilicates having different physical properties.

[0052] [Table 2]

[0053] As shown in Table 2, ammonia decomposition catalysts in which ruthenium is supported on aluminosilicates with A-type or X-type crystal structure and pore sizes of 0.3 nm to 0.9 nm show a high ammonia decomposition rate. It has also been confirmed that high ammonia decomposition rates are also shown when nickel or lithium is supported on these aluminosilicates.

[0054] The method for producing an ammonia decomposition catalyst described in the examples can be modified as appropriate. For example, the amounts of ruthenium and lithium supported on the carrier can be selected from the ranges of 2.5 to 12.5 g of ruthenium and 2.5 to 7.5 g of lithium per 100 g of carrier. The temperature and time of the drying step and the nitriding step can also be set as appropriate. The aluminosilicate as the raw material can also be freely selected.

Claims

1. a supporting step of impregnating a support with both ruthenium and lithium as catalysts; a drying step of drying the carrier on which the catalyst is supported; an activation step of exposing the dried carrier to a nitrogen atmosphere or an ammonia atmosphere for heat treatment; It is equipped with 13. A method for producing an ammonia decomposition catalyst, comprising the steps of: (a) preparing an aluminosilicate support having an A-type or X-type crystal structure and a pore size of 0.3 nm or more and 0.9 nm or less;

2. The method for producing an ammonia decomposition catalyst described in claim 1, wherein the activation step is carried out in a nitrogen atmosphere.

3. the supporting step is a step of impregnating the support with ruthenium and lithium, The support has an X-type crystal structure and is made of silicon dioxide (SiO ２ ) and aluminum oxide (Al ２ O ３ ) molar ratio (SiO ２ / Al ２ O ３ 2. The method for producing an ammonia decomposition catalyst according to claim 1, wherein the ratio of the cation amount to the total cation amount is 2.0 or more and 2.5 or less.

4. 2. The method for producing an ammonia decomposition catalyst according to claim 1, wherein the supporting step is a step of supporting 2.5 to 12.5 g of ruthenium and 2.5 to 7.5 g of lithium per 100 g of the carrier by impregnating the carrier with an aqueous solution of ruthenium trichloride and lithium hydroxide.

5. The supporting step includes a first impregnation step of impregnating the support with an aqueous solution of lithium hydroxide; a second impregnation step of impregnating the support carrying lithium hydroxide with an aqueous solution containing ruthenium trichloride; The method for producing an ammonia decomposition catalyst according to claim 4, further comprising:

6. 5. The method for producing an ammonia decomposition catalyst according to claim 4, wherein the supporting step is a step of impregnating the support with an aqueous solution containing both lithium hydroxide and ruthenium trichloride.

7. a supporting step of impregnating a support with ruthenium as a catalyst; a drying step of drying the carrier on which the catalyst is supported; an activation step of exposing the dried carrier to a nitrogen atmosphere and heat treating the carrier; It is equipped with 13. A method for producing an ammonia decomposition catalyst, comprising the steps of: (a) preparing an aluminosilicate support having an A-type or X-type crystal structure and a pore size of 0.3 nm or more and 0.9 nm or less;

8. An ammonia decomposition catalyst comprising an aluminosilicate carrying ruthenium and lithium, the aluminosilicate having an X-type crystal structure and a chemical formula of the aluminosilicate being: CaO.Al ２ O ３ xSiO ２ ・yH ２ O, where x is a value of 2.0 to 2.5 and y is a value of 0 or more.

9. The ammonia decomposition catalyst according to claim 8, wherein 2.5 to 12.5 g of ruthenium and 2.5 to 7.5 g of lithium are supported per 100 g of the aluminosilicate support.

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