A non-supported ammonia decomposition catalyst, a preparation method and application thereof

Abstract

The application discloses a non-supported ammonia decomposition catalyst and a preparation method and application thereof, and belongs to the technical field of catalysis. The catalyst is composed of at least one group VIII metal oxide, +2 valence metal oxide, +3 valence metal oxide and +4 valence metal oxide, wherein the catalyst contains 30-70 wt.% of group VIII metal, 1-30 wt.% of +2 valence metal, 5-25 wt.% of +3 valence metal and 1-20 wt.% of +4 valence metal in terms of metal oxides. The non-supported catalyst disclosed by the application effectively improves the dispersion degree of active metals and optimizes the interaction between metal components by introducing a dispersant, and the catalyst can realize an ammonia decomposition rate of not less than 99.9%.

Description

Technical Field

[0001] This invention belongs to the field of catalysis technology, specifically relating to an unsupported ammonia decomposition catalyst, its preparation method, and its application. Background Technology

[0002] To address the shortage and pollution problems of traditional fossil fuels, hydrogen energy, as a viable and sustainable clean energy source, has garnered increasing attention from researchers. Hydrogen is a widely available, clean, carbon-free, flexible, efficient, and versatile secondary energy source with excellent energy density and environmental friendliness, making it one of the most feasible pathways to achieve carbon peaking and carbon neutrality. However, the storage and transportation of hydrogen are two major challenges currently facing the hydrogen energy industry due to its incompressibility, difficulty in liquefaction, flammability, and explosiveness, coupled with the "hydrogen embrittlement" phenomenon. In contrast, ammonia has mild liquefaction conditions, is easy to store and transport, has high safety, and a high energy density (hydrogen storage density). Furthermore, ammonia decomposition only produces nitrogen and hydrogen, without generating greenhouse gases such as CO2, making it an ideal hydrogen storage medium. Hydrogen production through ammonia decomposition has also received widespread attention and research.

[0003] Ammonia decomposition is an endothermic reaction. Although thermodynamic data show that the equilibrium conversion rate of ammonia exceeds 99% at 450℃, kinetic barriers limit its reaction rate. Therefore, this reaction requires high temperature and the presence of a catalyst to proceed smoothly. Currently, catalysts for ammonia decomposition to hydrogen production can be mainly classified into noble metal (Ru, Ir, and Pt, etc.) based catalysts and transition metal (Fe, Co, and Ni, etc.) based catalysts according to their active components. Among them, Ru-based catalysts exhibit the best ammonia decomposition activity, but their high price leads to high catalyst preparation costs, limiting their industrial application. In contrast, non-noble metal based catalysts are less expensive and more suitable for large-scale industrial applications. LDH materials have good component dispersion properties, and catalyst preparation based on LDH materials has been reported. However, LDH materials have limited thermal stability and are prone to thermal dehydration and decomposition at high temperatures. At this time, the crystal particles of the material undergo significant aggregation and growth, resulting in limited exposure of internal active components and decreased dispersion. Therefore, existing reported catalysts only use calcined LDH materials as a support and then re-impregnate them to introduce active components to obtain the final catalyst, which does not fully utilize the excellent component dispersion properties of LDH materials. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a non-supported ammonia decomposition catalyst, its preparation method, and its application. LDH precursor materials are prepared using non-precious metals as active components, and the catalytic performance of the non-precious metal-based catalyst is improved by optimizing the dispersion of active components in the calcined LDH material.

[0005] To achieve the above objectives, the technical solution of the present invention includes:

[0006] In a first aspect, the present invention provides an unsupported ammonia decomposition catalyst, wherein the unsupported ammonia decomposition catalyst is composed of at least one group VIII metal oxide, a +2 valence metal oxide, a +3 valence metal oxide and a +4 valence metal oxide;

[0007] The unsupported ammonia decomposition catalyst contains 30-70 wt.% of Group VIII metal oxides, 1-30 wt.% of +2 valence metal oxides, 5-25 wt.% of +3 valence metal oxides and 1-20 wt.% of +4 valence metal oxides.

[0008] Furthermore, in the above technical solution, the at least one Group VIII metal is the main active component, which is one or a combination of two of Fe, Co, and Ni;

[0009] The +2 valent metal is an additive, namely Mg;

[0010] The +3 valence metal is Al;

[0011] The +4 valent metal is a dispersant, and is one of Ti and Zr.

[0012] Furthermore, in the above technical solution, the specific surface area of ​​the unsupported ammonia decomposition catalyst is 50-200 m². 2 / g, pore volume 0.1-0.5cm 3 / g.

[0013] Secondly, the present invention provides a method for preparing an unsupported ammonia decomposition catalyst, comprising the following steps:

[0014] S1. Dissolve at least one soluble salt of a Group VIII metal, a soluble salt of a +2 valence metal, and a soluble salt of a +3 valence metal in water to prepare solution A; dissolve a soluble precipitant in water to prepare solution B; and dissolve a soluble salt of a +4 valence metal in water to prepare solution C.

[0015] S2. When solution B is added dropwise to solution A, precipitate X is formed.

[0016] S3. Immediately after the addition of solution B is completed, solution C is added dropwise to the turbid liquid containing precipitate X and subjected to constant temperature treatment. After the reaction is completed, the obtained solid is an LDH material with a layered structure.

[0017] S4. Calcining the LDH material yields the unsupported ammonia decomposition catalyst.

[0018] In this invention, a mixed solution A of soluble salts of +2 valence metal Mg and +3 valence metal Al can generate MgAl-LDH with a layered structure through a co-precipitation reaction under the action of a precipitant. In step S1, a group VIII metal component as an active metal is added to solution A, which can replace part of the +2 valence metal Mg to participate in the formation of LDH material with highly dispersed active components, which can be denoted as Fe / Co / Ni-Mg-Al composite LDH.

[0019] In step S3 of this invention, solution C is added immediately after the addition of solution B to introduce a +4 valent metal component, which is deposited on the surface of the LDH particles. This aims to improve the high-temperature stability of the Fe / Co / Ni-Mg-Al composite LDH material, inhibit particle aggregation and growth during calcination, and enhance the dispersion and exposure of the active components on the particle surface in the resulting composite oxide, thereby fully utilizing the excellent component dispersion performance of the LDH material. Simultaneously, the +4 valent metal component also optimizes the interaction between LDH metal components to some extent, which is beneficial for the reduction and activation of the active components. Both of these factors contribute to the formation of active sites on the catalyst, thereby improving the overall activity of the catalyst.

[0020] Furthermore, in the above technical solution, in step S3, after the reaction is completed, the solid obtained by filtering, washing and drying the precipitate is an LDH material with a layered structure.

[0021] Furthermore, in the above technical solution, the soluble salt of at least one Group VIII metal is one or a combination of two of cobalt nitrate, nickel nitrate, ferrous chloride, cobalt chloride, nickel chloride, ferrous sulfate, cobalt sulfate, and nickel sulfate.

[0022] Preferably, the soluble salt of the at least one Group VIII metal is one or a combination of two of ferrous chloride, cobalt nitrate, nickel nitrate, cobalt chloride, and nickel chloride.

[0023] Furthermore, in the above technical solution, the soluble salt of the +2 valence metal is one of magnesium nitrate, magnesium chloride, and magnesium sulfate.

[0024] Preferably, the soluble salt of the +2 valence metal is one of magnesium nitrate and magnesium chloride.

[0025] Furthermore, in the above technical solution, the soluble salt of the +3 valent metal is one of aluminum nitrate, aluminum chloride, and aluminum sulfate.

[0026] Preferably, the soluble salt of the +3 valent metal is selected from aluminum nitrate and aluminum chloride.

[0027] Furthermore, in the above technical solution, the soluble salt of the +4 valence metal is one of titanium oxynitrate, titanium chloride, titanium oxysulfate, zirconium nitrate, zirconium chloride, and zirconium sulfate.

[0028] Preferably, the soluble salt of the +4 valence metal is selected from one of titanium oxynitrate, titanium chloride, zirconium nitrate, and zirconium chloride.

[0029] In selecting the soluble salts of at least one Group VIII metal, the soluble salts of the +2 valence metal, the soluble salts of the +3 valence metal, and the soluble salts of the +4 valence metal, the present invention preferably uses salts whose anions are easily decomposed and volatilized during calcination (such as nitrates or chlorides), so as to minimize the residue of their anionic components.

[0030] Furthermore, in the above technical solution, the soluble precipitant is one of sodium carbonate, sodium bicarbonate, sodium hydroxide, potassium carbonate, potassium bicarbonate, potassium hydroxide, and ammonium carbonate.

[0031] Preferably, the soluble precipitant is selected from sodium carbonate, potassium carbonate, and ammonium carbonate.

[0032] Regarding the selection of the soluble precipitant, since the obtained LDH is a layered material with anions between its layers, selecting carbonates or bicarbonates can yield LDH materials with carbonate or bicarbonate ions between the layers. During subsequent calcination, CO2 gas can be released, which is beneficial for reducing particle size. However, because bicarbonates are less basic, their precipitation effect is not as good as that of carbonates; therefore, carbonates are preferred.

[0033] Furthermore, in the above technical solution, the concentration of the soluble salt of at least one Group VIII metal in solution A is 0.04-1.2 mol / L.

[0034] Preferably, the concentration of the soluble salt of at least one Group VIII metal in solution A is 0.04-0.6 mol / L.

[0035] Furthermore, in the above technical solution, the concentration of the soluble salt of the +2 valence metal in solution A is 0.002-1 mol / L.

[0036] Preferably, the concentration of the soluble salt of the +2 valence metal in solution A is 0.002-0.5 mol / L.

[0037] Furthermore, in the above technical solution, the concentration of the soluble salt of the +3 valence metal in solution A is 0.01-0.3 mol / L.

[0038] Preferably, the concentration of the soluble salt of the +3 valence metal in solution A is 0.01-0.15 mol / L.

[0039] Al in solution 3+ The concentration of the ion may be one or two times the concentration of the corresponding salt, depending on the specific type of anion, while the concentrations of other metal ions are equal to the concentrations of their corresponding salts. Therefore, if expressed in terms of metal ion concentration, we have:

[0040] The concentration of at least one Group VIII metal ion in solution A is 0.04-1.2 mol / L;

[0041] Preferably, the concentration of the soluble salt of at least one Group VIII metal ion in solution A is 0.04-0.6 mol / L;

[0042] The concentration of the +2 valence metal ions in solution A is 0.002-1 mol / L;

[0043] Preferably, the concentration of the +2 valence metal ions in solution A is 0.002-0.5 mol / L;

[0044] The concentration of the +3 valent metal ions in solution A is 0.02-0.6 mol / L;

[0045] Preferably, the concentration of the +3 valence metal ions in solution A is 0.02-0.3 mol / L;

[0046] The concentration of the soluble precipitant in solution B is 0.01-1 mol / L;

[0047] Preferably, the concentration of the soluble precipitant in solution B is 0.05-0.5 mol / L;

[0048] The concentration of the soluble salt of the +4 valence metal in solution C is 0.001-0.1 mol / L;

[0049] Preferably, the concentration of the soluble salt of the +4 valence metal in solution C is 0.01-0.1 mol / L.

[0050] Furthermore, in the above technical solution, in step S2, the reaction temperature is 50-100℃.

[0051] The precipitation temperature of LDH material has a significant impact on its particle nucleation rate. Preferably, in step S2, the reaction temperature is 80-100℃.

[0052] In step S3, the pH of the reaction system is 7-10 when the solution B is added.

[0053] The pH value of the solution determines the degree of precipitation of the metal components. Preferably, in step S3, the pH of the reaction system is 8-10 when the solution B is added dropwise.

[0054] In step S3, the temperature of the constant temperature treatment is 80-120℃, and the treatment time is 1-12h.

[0055] The conditions of the isothermal treatment step affect the crystallization effect of LDH material and also have an important impact on the deposition effect of +4 valence metal. Preferably, in step S3, the isothermal treatment temperature is 100-120℃ and the treatment time is 1-4h.

[0056] In step S4, the roasting temperature is 300-500℃ and the roasting time is 1-24h.

[0057] The purpose of the calcination step is to dehydrate the LDH material to generate a high-temperature stable composite oxide phase. In this step, carbonate ions will also decompose to produce gas, which is beneficial to reduce the particle size. The effect is affected by the calcination conditions. Preferably, in step S4, the calcination temperature is 300-500℃ and the calcination time is 1-24h.

[0058] Thirdly, the present invention provides an application of the unsupported ammonia decomposition catalyst described above or the unsupported ammonia decomposition catalyst prepared by the preparation method in ammonia decomposition for hydrogen production.

[0059] Furthermore, in the above technical solution, the catalyst needs to undergo the following pretreatment before carrying out the ammonia decomposition catalytic reaction:

[0060] S1. Grinding, shaping, and sieving;

[0061] S2. Activation treatment is carried out in a fixed-bed reactor under the following conditions by introducing a reducing atmosphere:

[0062] The activation temperature is 300-800℃;

[0063] Preferably, the activation temperature is 500-800℃;

[0064] The activation atmosphere is an H2 / Ar mixture, in which the volume percentage of H2 is 0.01-0.1 and the pressure is 0.05-1 MPa;

[0065] Preferably, the pressure of the activating atmosphere is 0.05-0.1 MPa;

[0066] Activation time is 2-12 hours;

[0067] Preferably, the activation time is 2-6 hours.

[0068] Furthermore, in the above technical solution, the conditions for ammonia decomposition to produce hydrogen are as follows:

[0069] The temperature is 400-800℃;

[0070] The pressure is 0.05-1 MPa;

[0071] The reaction feed gas can be pure ammonia or a mixture of ammonia and other gases, wherein the volume percentage of ammonia is 1-100%.

[0072] The reactant gas, excluding ammonia, consists of one or more of nitrogen, hydrogen, argon, and helium. This component cannot react with the catalyst component and therefore cannot contain oxygen, carbon dioxide, carbon monoxide, etc.

[0073] Beneficial effects (1) The catalyst provided by this invention is a non-supported catalyst. By adding a group VIII metal component to the LDH material, it serves as an active metal on the one hand, and on the other hand, it can replace part of the +2 valence metal Mg to participate in the formation of a highly dispersed active component LDH material. This avoids the loss of catalytic performance caused by the interaction between the support and the active component in the supported catalyst. All components do not contain precious metal components, and the preparation cost is low.

[0074] (2) The catalyst of this invention is prepared from an LDH precursor, utilizing the excellent dispersion performance of the active components of the LDH material. Furthermore, the thermal stability of the material is improved by introducing a +4 valent metal dispersant, further enhancing the effective dispersion of the active components and optimizing the interaction between the metal components, resulting in high ammonia decomposition catalytic activity. The catalyst is prepared by a co-precipitation method, which is simple, easy to operate, and can be industrialized. Attached Figure Description

[0075] Figure 1 These are the XRD patterns of the unsupported CoNiMgAlZr catalyst Cat-4 prepared in Example 4 and the unsupported CoNiMgAl catalyst Cat-a-3 prepared in Comparative Example 3. Detailed Implementation

[0076] To further illustrate the present invention, the following embodiments are listed based on experimental results, but these do not limit the scope of the invention as defined by the claims.

[0077] Example 1

[0078] This embodiment illustrates the preparation of the unsupported FeMgAlZr catalyst.

[0079] Weigh out 5 mmol ferrous chloride tetrahydrate, 2 mmol magnesium chloride hexahydrate, and 2.5 mmol aluminum chloride hexahydrate, and dissolve them in water to prepare a 100 mL solution, denoted as solution a (where Fe... 2+ The concentration is 0.05 mol / L, Mg 2+The concentration is 0.02 mol / L, Al 3+ The concentration is 0.025 mol / L. Prepare a 0.2 mol / L sodium carbonate solution, denoted as solution b. Weigh 0.5 mmol of zirconium nitrate trihydrate and dissolve it in water to prepare a 10 mL solution, denoted as solution c (where Zr is present). 4+ (Concentration is 0.05 mol / L).

[0080] Solution a was heated to 90°C and kept at a constant temperature. Solution b was added dropwise to solution a until the pH reached 10. Then solution c was immediately added. The solution was then kept at 110°C for 2 hours. Finally, the solution was filtered, washed, and dried to obtain the LDH precursor.

[0081] The obtained LDH precursor was calcined at 400℃ for 6 h to obtain an unsupported FeMgAlZr catalyst, denoted as Cat-1.

[0082] Example 2

[0083] This embodiment illustrates the preparation of the unsupported CoMgAlZr catalyst.

[0084] Weigh out 5 mmol of cobalt nitrate hexahydrate, 2 mmol of magnesium nitrate hexahydrate, and 2.5 mmol of aluminum nitrate nonahydrate, and dissolve in water to prepare a 100 mL solution, denoted as solution a (where Co... 2+ The concentration is 0.05 mol / L, Mg 2+ The concentration is 0.02 mol / L, Al 3+ The concentration is 0.025 mol / L. Prepare a 0.2 mol / L sodium carbonate solution, denoted as solution b. Weigh 0.5 mmol of zirconium nitrate trihydrate and dissolve it in water to prepare a 10 mL solution, denoted as solution c (where Zr is present). 4+ (Concentration is 0.05 mol / L).

[0085] Solution a was heated to 90°C and kept at a constant temperature. Solution b was added dropwise to solution a until the pH reached 10. Then solution c was immediately added. The solution was then kept at 110°C for 2 hours. Finally, the solution was filtered, washed, and dried to obtain the LDH precursor.

[0086] The obtained LDH precursor was calcined at 400℃ for 6 h to obtain an unsupported CoMgAlZr catalyst, denoted as Cat-2.

[0087] Example 3

[0088] This embodiment illustrates the preparation of the unsupported NiMgAlZr catalyst.

[0089] Weigh out 5 mmol nickel nitrate hexahydrate, 2 mmol magnesium nitrate hexahydrate, and 2.5 mmol aluminum nitrate nonahydrate, and dissolve them in water to prepare a 100 mL solution, denoted as solution a (where Ni... 2+The concentration is 0.05 mol / L, Mg 2+ The concentration is 0.02 mol / L, Al 3+ The concentration is 0.025 mol / L. Prepare a 0.2 mol / L sodium carbonate solution, denoted as solution b. Weigh 0.5 mmol of zirconium nitrate trihydrate and dissolve it in water to prepare a 10 mL solution, denoted as solution c (where Zr is present). 4+ (Concentration is 0.05 mol / L).

[0090] Solution a was heated to 90°C and kept at a constant temperature. Solution b was added dropwise to solution a until the pH reached 10. Then solution c was immediately added. The solution was then kept at 110°C for 2 hours. Finally, the solution was filtered, washed, and dried to obtain the LDH precursor.

[0091] The obtained LDH precursor was calcined at 400℃ for 6 h to obtain an unsupported NiMgAlZr catalyst, denoted as Cat-3.

[0092] Example 4

[0093] This embodiment illustrates the preparation of the unsupported CoNiMgAlZr catalyst.

[0094] Weigh out 2.5 mmol of cobalt nitrate hexahydrate, 2.5 mmol of nickel nitrate hexahydrate, 2 mmol of magnesium nitrate hexahydrate, and 2.5 mmol of aluminum nitrate nonahydrate, and dissolve in water to prepare a 100 mL solution, denoted as solution a (where Co... 2+ The concentration is 0.025 mol / L, Ni 2+ The concentration is 0.025 mol / L, Mg 2+ The concentration is 0.02 mol / L, Al 3+ The concentration is 0.025 mol / L. Prepare a 0.2 mol / L sodium carbonate solution, denoted as solution b. Weigh 0.5 mmol of zirconium nitrate trihydrate and dissolve it in water to prepare a 10 mL solution, denoted as solution c (where Zr is present). 4+ (Concentration is 0.05 mol / L).

[0095] Solution a was heated to 90°C and kept at a constant temperature. Solution b was added dropwise to solution a until the pH reached 10. Then solution c was immediately added. The solution was then kept at 110°C for 2 hours. Finally, the solution was filtered, washed, and dried to obtain the LDH precursor.

[0096] The obtained LDH precursor was calcined at 400℃ for 6 h to obtain an unsupported CoNiMgAlZr catalyst, denoted as Cat-4.

[0097] XRD tests were performed on Cat-4, and the results are as follows: Figure 1 As shown.

[0098] Comparative Example 1

[0099] This comparative example illustrates the preparation of the unsupported CoMgAl catalyst.

[0100] Weigh out 5 mmol of cobalt nitrate hexahydrate, 2 mmol of magnesium nitrate hexahydrate, and 2.5 mmol of aluminum nitrate nonahydrate, and dissolve in water to prepare a 100 mL solution, denoted as solution a (where Co... 2+ The concentration is 0.05 mol / L, Mg 2+ The concentration is 0.02 mol / L, Al 3+ (The concentration is 0.025 mol / L). Prepare a sodium carbonate solution with a concentration of 0.2 mol / L, denoted as solution b.

[0101] Solution a was heated to 90°C and kept at that temperature. Solution b was added dropwise to solution a until the pH reached 10. The solution was then kept at 110°C for 2 hours. After that, the solution was filtered, washed, and dried to obtain the LDH precursor.

[0102] The obtained LDH precursor was calcined at 400℃ for 6 h to obtain an unsupported CoMgAl catalyst, denoted as Cat-a-1.

[0103] Comparative Example 2

[0104] This comparative example illustrates the preparation of the unsupported NiMgAl catalyst.

[0105] Weigh out 5 mmol nickel nitrate hexahydrate, 2 mmol magnesium nitrate hexahydrate, and 2.5 mmol aluminum nitrate nonahydrate, and dissolve them in water to prepare a 100 mL solution, denoted as solution a (where Ni... 2+ The concentration is 0.05 mol / L, Mg 2+ The concentration is 0.02 mol / L, Al 3+ (The concentration is 0.025 mol / L). Prepare a sodium carbonate solution with a concentration of 0.2 mol / L, denoted as solution b.

[0106] Solution a was heated to 90°C and kept at that temperature. Solution b was added dropwise to solution a until the pH reached 10. The solution was then kept at 110°C for 2 hours. After that, the solution was filtered, washed, and dried to obtain the LDH precursor.

[0107] The obtained LDH precursor was calcined at 400℃ for 6 h to obtain an unsupported NiMgAl catalyst, denoted as Cat-a-2.

[0108] Comparative Example 3

[0109] This comparative example illustrates the preparation of the unsupported CoNiMgAl catalyst.

[0110] Weigh out 2.5 mmol of cobalt nitrate hexahydrate, 2.5 mmol of nickel nitrate hexahydrate, 2 mmol of magnesium nitrate hexahydrate, and 2.5 mmol of aluminum nitrate nonahydrate, and dissolve in water to prepare a 100 mL solution, denoted as solution a (where Co... 2+ The concentration is 0.025 mol / L, Ni 2+ The concentration is 0.025 mol / L, Mg 2+ The concentration is 0.02 mol / L, Al 3+ (The concentration is 0.025 mol / L). Prepare a sodium carbonate solution with a concentration of 0.2 mol / L, denoted as solution b.

[0111] Solution a was heated to 90°C and kept at that temperature. Solution b was added dropwise to solution a until the pH reached 10. The solution was then kept at 110°C for 2 hours. After that, the solution was filtered, washed, and dried to obtain the LDH precursor.

[0112] The obtained LDH precursor was calcined at 400℃ for 6 h to obtain an unsupported CoNiMgAl catalyst, denoted as Cat-a-3.

[0113] XRD tests were performed on Cat-a-3, and the results are as follows: Figure 1 As shown.

[0114] The XRD results show that, compared with the unsupported CoNiMgAl catalyst Cat-a-3 prepared in Comparative Example 3, the unsupported CoNiMgAlZr catalyst Cat-4 prepared in Example 4 has a wider and weaker diffraction peak, indicating that the introduction of +4 valence metal Zr can effectively reduce the crystallite size of the catalyst.

[0115] Example 5

[0116] This embodiment illustrates the catalytic performance evaluation of the unsupported catalyst for ammonia decomposition to hydrogen production.

[0117] The catalysts obtained in Examples 1-4 and Comparative Examples 1-3 were ground, pressed into tablets, and sieved to 40-60 mesh particles, and then 1g was weighed and placed in a fixed-bed reactor.

[0118] The catalyst was activated by reduction at 600℃ and 0.05MPa for 4 hours using 5 vol.% H2 / Ar as the reducing atmosphere.

[0119] Pure ammonia gas was introduced into the fixed-bed reactor as the feed gas, and the space velocity was set to 30,000 mL·h. -1 ·gcat -1 The reactions were carried out at 500℃, 550℃, and 600℃ respectively. After 6 hours of reaction, the ammonia concentration in the tail gas product was measured by gas chromatography, and the ammonia decomposition rate was calculated. The results are shown in the table below:

[0120]

[0121]

[0122] It can be seen that introducing a +4 valent metal component as a dispersant into the unsupported catalyst can effectively improve its ammonia decomposition catalytic performance.

[0123] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. The application of a non-supported ammonia decomposition catalyst in ammonia decomposition for hydrogen production, characterized in that, The unsupported ammonia decomposition catalyst is composed of at least one group VIII metal oxide, a +2 valence metal oxide, a +3 valence metal oxide, and a +4 valence metal oxide; The unsupported ammonia decomposition catalyst contains 30-70 wt.% of Group VIII metal oxides, 1-30 wt.% of +2 valence metal oxides, 5-25 wt.% of +3 valence metal oxides and 1-20 wt.% of +4 valence metal oxides; The preparation method of the unsupported ammonia decomposition catalyst includes the following steps: S1. Dissolve at least one soluble salt of a Group VIII metal, a soluble salt of a +2 valence metal, and a soluble salt of a +3 valence metal in water to prepare solution A; dissolve a soluble precipitant in water to prepare solution B; and dissolve a soluble salt of a +4 valence metal in water to prepare solution C. S2. Solution B is added dropwise to solution A, and the reaction yields a turbid liquid containing precipitate X; S3. Immediately after the addition of solution B is completed, solution C is added dropwise to the turbid liquid containing precipitate X and subjected to constant temperature treatment. After the reaction is completed, the obtained solid is an LDH material with a layered structure. S4. Calcining the LDH material yields the unsupported ammonia decomposition catalyst. The at least one Group VIII metal is one or a combination of two of Fe, Co, and Ni; The +2 valence metal is Mg; The +3 valence metal is Al; The +4 valence metal is one of Ti or Zr.

2. The application according to claim 1, characterized in that, The specific surface area of ​​the unsupported ammonia decomposition catalyst is 50-200 m². 2 / g, pore volume 0.1-0.5 cm³ 3 / g.

3. The application according to claim 1, characterized in that, The soluble salt of at least one Group VIII metal is one or a combination of two of the following: cobalt nitrate, nickel nitrate, ferrous chloride, cobalt chloride, nickel chloride, ferrous sulfate, cobalt sulfate, and nickel sulfate. The soluble salt of the +2 valence metal is one of magnesium nitrate, magnesium chloride, and magnesium sulfate; The soluble salt of the +3 valent metal is one of aluminum nitrate, aluminum chloride, and aluminum sulfate. The soluble salt of the +4 valence metal is one of titanium oxynitrate, titanium chloride, titanium oxysulfate, zirconium nitrate, zirconium chloride, and zirconium sulfate. The soluble precipitant is one of sodium carbonate, sodium bicarbonate, sodium hydroxide, potassium carbonate, potassium bicarbonate, potassium hydroxide, and ammonium carbonate.

4. The application according to claim 1, characterized in that, The concentration of the soluble salt of at least one Group VIII metal in solution A is 0.04-1.2 mol / L; The concentration of the soluble salt of the +2 valence metal in solution A is 0.002-1 mol / L; The concentration of the soluble salt of the +3 valence metal in solution A is 0.01-0.3 mol / L; The concentration of the soluble precipitant in solution B is 0.01-1 mol / L; The concentration of the soluble salt of the +4 valence metal in solution C is 0.001-0.1 mol / L.

5. The application according to claim 1, characterized in that, In step S2, the reaction temperature is 50-100°C. o C; In step S3, the pH of the reaction system is 7-10 when the solution B is added dropwise. In step S3, the temperature of the isothermal treatment is 80-120°C. o C, the processing time is 1-12 hours; In step S4, the calcination temperature is 300-500°C. o C, the roasting time is 1-24 h.

6. The application according to claim 1, characterized in that, The catalyst needs to undergo the following pretreatment before it can carry out the ammonia decomposition catalytic reaction: S1. Grinding, shaping, and sieving; S2. Activation treatment is carried out in a fixed-bed reactor under the following conditions by introducing a reducing atmosphere: Activation temperature is 300-800℃ o C; The activation atmosphere is an H2 / Ar mixture, in which the volume percentage of H2 is 0.01-0.1 and the pressure is 0.05-1 MPa; The activation time is 2-12 h.

7. The application according to claim 1, characterized in that, The conditions for hydrogen production from ammonia decomposition are as follows: Temperature is 400-800 o C; The pressure is 0.05-1 MPa; The volume percentage of ammonia in the reaction feed gas is 1-100%.

8. The application according to claim 7, characterized in that, The reactant gas, excluding ammonia, consists of one or more of nitrogen, hydrogen, argon, and helium.

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