Nickel-based ammonia decomposition catalyst and preparation method and application thereof

Abstract

The invention discloses a nickel-based ammonia decomposition catalyst as well as a preparation method and application thereof. The nickel-based ammonia decomposition catalyst comprises a carrier, an active component and an auxiliary agent, the active component is loaded on the carrier, and the auxiliary agent is loaded on the carrier containing the active component; the active component comprises an active component I and an active component II; the active component I is Ni, and the active component II is selected from Fe and / or Co; the auxiliary agent is alkali metal oxide; alkali metal in the alkali metal oxide is selected from at least one of Li, Na, K, Rb and Cs. Compared with the nickel-based catalyst used in the industry at present, the catalyst prepared by the method provided by the invention shows higher catalytic activity and stability in ammonia decomposition reaction, and the ammonia decomposition temperature can be reduced by 150-200 DEG C. When the gas production rate is the same, the loading amount of the catalyst and the equipment volume are greatly reduced, and the ammonia decomposition energy consumption is obviously reduced.

Description

Technical Field

[0001] The present application relates to a nickel-based ammonia decomposition catalyst, a preparation method and an application thereof, belonging to the technical field of catalyst preparation. Background Art

[0002] As a green and clean energy source, hydrogen energy has the characteristics of high energy density (142 MJ kg-1) and zero emissions, and is the most ideal alternative energy source for fossil fuels. Promoting the large-scale application of hydrogen energy is of great significance for building a clean, low-carbon, safe and efficient energy system. However, due to the characteristics of hydrogen itself, the large-scale storage and transportation of hydrogen still face huge challenges under current conditions. If the storage and transportation process of hydrogen can be avoided, the use cost of hydrogen will be greatly reduced, and the large-scale application of hydrogen energy will be promoted. Ammonia has the following advantages as a hydrogen storage carrier: 1. Ammonia is easy to be liquefied and stored (the liquefaction pressure is 0.8 MPa at 20 °C); 2. The high energy density (3000 Wh·kg -1 ) and high hydrogen-carrying capacity (17.6 wt%) of ammonia are much higher than those of methanol and other carbon-based compound fuels and compressed hydrogen; 3. The decomposition products of ammonia are N2 and H2, avoiding the poisoning of Pt electrodes by CO x substances. And the technology of synthesizing ammonia is very mature, and the price of ammonia is low. Therefore, ammonia as a hydrogen carrier can transform the storage and transportation of hydrogen into the storage and transportation of ammonia, and ammonia decomposition to produce hydrogen has great application prospects.

[0003] The ammonia decomposition to produce hydrogen reaction is shown in Equation (1). This reaction is an endothermic reaction with an increase in volume. Therefore, increasing the temperature and decreasing the pressure are beneficial to the progress of the reaction. According to the calculation of thermodynamics, at normal pressure and a temperature of 400 °C, the equilibrium conversion rate of ammonia decomposition can reach 99%. However, from a kinetic perspective, due to the very high activation energy of this reaction, the conversion rate of the ammonia decomposition reaction is extremely low under the condition of no catalyst catalysis at normal pressure. At normal pressure and without using any catalyst, the actual conversion rate of the ammonia decomposition reaction is lower than 10% at 700 °C. Therefore, a highly active catalyst is required to achieve the efficient decomposition of ammonia.

[0004] 2NH3 = N2 + 3H2, ΔH = 92.5 kJ mol -1 (1)

[0005] Currently, the ammonia decomposition catalysts mainly include noble metal catalysts (such as Ru, Ir, etc.), non-noble metal catalysts (such as Fe, Co, Ni, Mo, etc.), transition metal carbides and nitrides (such as WC x 、MoN xetc.), and mixed catalysts of transition metals or their nitrides - alkali (earth) metal imide compounds (such as Co - Ba(NH2)2, MnN - Li2NH, etc.). Ni - based catalysts are commonly used catalysts in industry at present, but they face problems such as high reaction temperature and low space velocity. This is mainly because for Ni - based catalysts prepared by the conventional precipitation method, the dispersion of Ni particles is poor, resulting in low reaction activity. Hydrotalcite - like compounds (LDHs) are a class of novel inorganic functional materials with a layered structure, and their layered structure is naturally conducive to the dispersion of ions. By utilizing the natural dispersion of two metal ions in the structure, uniform mixing of Ni and the second component M can be achieved, and it is expected to directly obtain a highly dispersed Ni - based catalyst.

[0006] Currently, several patent applications have been filed for the preparation of ammonia decomposition catalysts. The following lists several reported patents for detailed description:

[0007] Chinese Patent CN101352685A has a publication name of: A preparation method of a supported nickel catalyst for ammonia decomposition to hydrogen. This patent reports the preparation of a Ni - based catalyst by the precipitation method using alumina, silica, or titania as the support and nickel as the active component. The Ni particles of the catalyst involved in this patent are prone to agglomeration at high temperatures, resulting in low reaction activity.

[0008] Chinese Patent CN112337494A has a publication name of: An ammonia decomposition to hydrogen catalyst, its preparation method and application. This patent reports the preparation of a Ni - based catalyst using the sol - gel method with a BN rare earth metal oxide composite support. However, during the preparation process of the sol - gel method, some active components will be embedded in the support, resulting in the inability of all active components to play their roles.

[0009] Chinese Patent CN115920942A has a publication name of: A perovskite - type catalyst for ammonia decomposition, its preparation method and application. This patent reports that the catalyst support is a perovskite - type oxide and the active component is Ni, which is used for the ammonia decomposition reaction. However, perovskite - type oxides are difficult to be prepared on a large scale, and it is still very far from actual application.

[0010] Currently, there is an urgent need to develop an efficient ammonia decomposition catalyst that can meet the requirements of actual application and enable large - scale production while improving the catalyst efficiency. Summary of the Invention

[0011] Aiming at the problems of complex preparation process and difficulty in large - scale production in the above - mentioned ammonia decomposition catalysts, a nickel - based ammonia decomposition catalyst, its preparation method and application are provided. By adopting an optimized preparation method and a conventional support, a highly dispersed nickel - based catalyst is prepared, which can be prepared on a large scale and has high performance in the ammonia decomposition reaction.

[0012] According to one aspect of the present application, a nickel-based ammonia decomposition catalyst is provided. The nickel-based ammonia decomposition catalyst comprises a carrier, an active component, and a promoter;

[0013] The active component is loaded on the carrier, and the promoter is loaded on the carrier containing the active component;

[0014] The active component includes active component I and active component II;

[0015] The active component I is Ni, and the active component II is selected from Fe and / or Co;

[0016] The promoter is an alkali metal oxide;

[0017] The alkali metal in the alkali metal oxide is selected from at least one of Li, Na, K, Rb, and Cs;

[0018] The carrier is selected from at least one of Al2O3, MgO, CeO2, SiO2, and TiO2.

[0019] Optionally, the alkali metal in the alkali metal oxide is selected from at least one of Na, K, and Cs.

[0020] Optionally, the carrier is selected from at least one of Al2O3, MgO, and CeO2.

[0021] Optionally, the active component accounts for 5-20 wt.% of the mass of the nickel-based ammonia decomposition catalyst.

[0022] Optionally, the mass percentage of the active component in the nickel-based ammonia decomposition catalyst is independently selected from any value of 5 wt.%, 8 wt.%, 10 wt.%, 12 wt.%, 15 wt.%, 18 wt.%, 20 wt.% or the range value between any two of the above.

[0023] Optionally, the promoter accounts for 1-10 wt.% of the mass of the nickel-based ammonia decomposition catalyst.

[0024] Optionally, the mass percentage of the promoter in the nickel-based ammonia decomposition catalyst is independently selected from any value of 1 wt.%, 2 wt.%, 5 wt.%, 6 wt.%, 7 wt.%, 8 wt.%, 10 wt.% or the range value between any two of the above.

[0025] Optionally, the carrier accounts for 70-94 wt.% of the mass of the nickel-based ammonia decomposition catalyst.

[0026] Optionally, the mass percentage of the carrier in the nickel-based ammonia decomposition catalyst independently selects any value from 70 wt.%, 72 wt.%, 75 wt.%, 80 wt.%, 85 wt.%, 90 wt.%, 94 wt.% or a range value between any two of the above.

[0027] According to another aspect of the present application, a preparation method of the above-mentioned nickel-based ammonia decomposition catalyst is provided. The preparation method includes the following steps:

[0028] (1) A mixture I containing a Ni precursor, an active component II precursor, a carrier, a carbonate, and a strong base is subjected to a water bath, pH adjustment, aging, and drying I to obtain the Ni-based hydrotalcite matrix.

[0029] (2) The Ni-based hydrotalcite matrix is impregnated in a salt solution of an alkali metal, followed by drying II, calcination, and reduction to obtain the nickel-based ammonia decomposition catalyst.

[0030] Optionally, in the step (1), the Ni precursor is selected from at least one of nickel chloride, nickel nitrate, and nickel acetate.

[0031] Optionally, the active component II precursor is selected from at least one of iron chloride, iron nitrate, cobalt chloride, and cobalt nitrate.

[0032] Optionally, the carbonate is selected from sodium carbonate and / or potassium carbonate.

[0033] Optionally, the strong base is selected from sodium hydroxide and / or potassium hydroxide.

[0034] Optionally, in the step (1), the molar ratio of the Ni precursor to the active component II precursor is 5:1 to 1:5. The molar amount of the Ni precursor is based on the molar amount of the Ni element, and the molar amount of the active component II precursor is based on the molar amount of the active component II.

[0035] Optionally, in the step (1), the molar ratio of the Ni precursor to the active component II precursor independently selects any value from 5:1, 4:1, 3:1, 2:1, 1:1, 1:2, 1:3, 1:4, 1:5 or a range value between any two of the above.

[0036] Optionally, the concentration of the carbonate solution is 0.5 mol / L to 1 mol / L.

[0037] Optionally, the concentration of the strong base is 1.2 mol / L to 2.0 mol / L.

[0038] Optionally, the concentration of the carrier in the mixture I is 10 g / L to 50 g / L, based on the mass concentration of the carrier.

[0039] Optionally, in the step (2), the salt solution of the alkali metal is selected from at least one of nitrates and chlorides containing alkali metal elements.

[0040] Optionally, the alkali metal element is selected from at least one of Li, Na, K, Rb, and Cs.

[0041] Optionally, the concentration of the salt solution of the alkali metal is 0.1 wt.% to 10 wt.%, calculated based on the mass content of the alkali metal.

[0042] Optionally, in the step (1), the temperature of the water bath is 30 to 80 °C, and the time of the water bath is 1 to 12 h.

[0043] Optionally, the temperature of the aging is 50 to 90 °C, and the time of the aging is 6 to 24 h.

[0044] Optionally, the temperature of the first drying is 60 to 120 °C, and the time of the first drying is 4 to 12 h.

[0045] Optionally, the pH value is 10 to 11.

[0046] Optionally, in the step (2), the impregnation time is 0.5 to 48 h.

[0047] Optionally, in the step (2), the temperature of the second drying is 60 to 120 °C, and the time of the second drying is 4 to 12 h.

[0048] Optionally, the temperature of the calcination is 200 to 400 °C, and the time of the calcination is 4 to 12 h.

[0049] Optionally, in the step (2), the reduction is a high-temperature gas-phase reduction method.

[0050] Optionally, the reducing gas is selected from at least one of ammonia gas and hydrogen gas.

[0051] Optionally, the volume space velocity of the reducing gas is 100 to 3600 h -1 。

[0052] Optionally, the heating rate during the reduction is 1 to 10 °C / min.

[0053] Optionally, the temperature of the reduction is 400 to 800 °C, and the time of the reduction is 1 to 48 h.

[0054] Optionally, the pressure of the reduction is 0.1 to 1.0 MPa.

[0055] According to another aspect of the present application, a method for producing hydrogen by ammonia decomposition is provided, and the method includes:

[0056] The catalyst and ammonia are subjected to an ammonia decomposition reaction to obtain hydrogen and nitrogen;

[0057] The catalyst is selected from the nickel-based ammonia decomposition catalysts described above.

[0058] Optionally, the temperature of the ammonia decomposition reaction is 400-900 °C.

[0059] Optionally, the temperature of the ammonia decomposition reaction is independently selected from any value of 400 °C, 500 °C, 600 °C, 700 °C, 800 °C, 900 °C or the range value between any two of the above.

[0060] Optionally, the temperature of the ammonia decomposition reaction is 500-700 °C.

[0061] Optionally, the space velocity of the ammonia decomposition reaction is 200-60000 ml / g·h.

[0062] Optionally, the space velocity of the ammonia decomposition reaction is independently selected from any value of 200 ml / g·h, 500 ml / g·h, 1000 ml / g·h, 5000 ml / g·h, 10000 ml / g·h, 20000 ml / g·h, 30000 ml / g·h, 40000 ml / g·h, 50000 ml / g·h, 60000 ml / g·h or the range value between any two of the above.

[0063] As an optional implementation manner, the present application is realized through the following technical solutions:

[0064] The preparation method of the nickel-based ammonia decomposition catalyst includes the following steps:

[0065] a: Prepare a Ni-based hydrotalcite matrix: Dissolve a Ni precursor and an X precursor in water to form solution A; dissolve a carbonate and an alkali in water to form solution B; add an oxide support to solution B to form suspension C; add A to C in a water bath, and then adjust the pH value to H with an alkali; age for a period of time at a certain temperature, and then obtain a Ni-X / S sample through filtration, washing, and drying;

[0066] b: Preparation of the Ni-X-Y / S catalyst: Immerse the Ni-X / S sample prepared in step a in a salt solution of an alkali metal, impregnate, dry, calcine, and reduce to obtain the Ni-X-Y / S catalyst.

[0067] Optionally, after the Ni-X-Y / S ruthenium catalyst is heated to the reaction temperature of ammonia decomposition, ammonia is introduced to obtain the products hydrogen and nitrogen.

[0068] This application discloses an efficient ammonia decomposition catalyst, which includes a carrier, an assistant, and an active component. The carrier is aluminum oxide, magnesium oxide, or cerium dioxide; the assistant is an alkali metal; the active component is mainly Ni-Fe or Ni-Co. Preparation method: Synthesize a matrix of Ni-based hydrotalcite layer on the carrier, then load the assistant onto the above matrix, and finally treat it in a reducing atmosphere to obtain a Ni-X-Y / S catalytic material. The catalyst prepared according to the method provided by the present invention shows higher catalytic activity and stability in the ammonia decomposition reaction compared with the nickel-based catalysts currently used in industry, and the ammonia decomposition temperature can be reduced by 150-200 °C. When the gas production is the same, the loading amount of the catalyst and the equipment volume are greatly reduced, and the energy consumption of ammonia decomposition is significantly reduced.

[0069] The beneficial effects that this application can produce include:

[0070] 1) The ammonia decomposition catalyst provided by this application can achieve efficient decomposition of ammonia at a lower temperature.

[0071] 2) For the ammonia decomposition catalyst provided by this application, the carriers used are all commonly used carriers in industry, which are cheap and easily available, and large-scale production can be achieved.

[0072] 3) A nickel-based ammonia decomposition catalyst provided by this application, its preparation method and application have the advantages of low ammonia decomposition reaction temperature, high ammonia space velocity, high ammonia conversion rate, and low cost. Specific Embodiments

[0073] The following details this application in combination with embodiments, but this application is not limited to these embodiments.

[0074] Unless otherwise specified, the raw materials in the embodiments of this application are all purchased through commercial channels.

[0075] The products of ammonia decomposition are detected by an Agilent 7890B gas chromatograph, using a Propark Q chromatographic column and a TCD detector.

[0076]

[0077] The peak area of N2 in the reaction tail gas detected by the TCD detector;

[0078] The peak area of NH3 in the reaction tail gas detected by the TCD detector;

[0079] The molar correction factor of NH3 relative to N2, TCD detector.

[0080] Example 1

[0081] 1) Prepare a Ni-based hydrotalcite matrix.

[0082] Weigh 3.1218 g of Ni(NO3)2·6H2O and 0.8674 g of Fe(NO3)3·9H2O, dissolve them in 20 ml of deionized water to prepare solution A; weigh 1.252 g of Na2CO3 and 0.709 g of NaOH, dissolve them in 20 ml of deionized water to prepare solution B; weigh 5 g of Al2O3 support, add it to solution B to obtain suspension C. Place solution C in a 35 °C water bath and stir vigorously for 4 h, and use a constant flow pump to dropwise add solution A to solution C at a rate of 3 mL / min. After the addition is completed, add 3 mol / L NaOH solution to the mixed solution until the pH value of the mixed solution is 10. Then, place it in a 65 °C water bath and stir and age for 18 h, then filter, wash until neutral, and place it in an 80 °C oven to dry for 12 h to obtain the Ni-based hydrotalcite matrix, denoted as the Ni5-Fe1-15% / Al2O3 sample.

[0083] 2) Prepare the Ni-X-Y / S catalyst.

[0084] Weigh 5.0 g of the prepared Ni5-Fe1-15% / Al2O3 support, weigh 0.3888 g of KNO3, dissolve it in 2 g of deionized water to form a mixed solution with a K mass concentration of 7.5 wt%, drop it onto the Ni5-Fe1-15% / Al2O3 sample and mix them evenly. Impregnate at room temperature for 12 h, dry at 80 °C for 12 h, and calcine in an air atmosphere at 300 °C for 4 h, with a K mass content of 3%. Then, carry out hydrogen reduction at a temperature of 400 °C, with a heating rate from room temperature to the reduction temperature of 5 °C / min, a hydrogen volumetric space velocity of 1000 h -1 , at atmospheric pressure, and a reduction time of 4 h. Obtain the catalyst, denoted as Ni5-Fe1-15%-3%K / Al2O3.

[0085] Reaction conditions for the catalyst in ammonia decomposition: ammonia concentration is 99.9%, fixed-bed reactor, reaction temperature is 500 °C to 700 °C, and space velocity is 30000 ml / g·h. The reaction results are shown in Table 1.

[0086] Example 2

[0087] 1) Prepare the Ni-based hydrotalcite matrix.

[0088] Weigh 2.8211 g of Ni(NO3)2·6H2O and 1.3065 g of Fe(NO3)3·9H2O, dissolve them in 20 ml of deionized water to prepare solution A; weigh 1.131 g of Na2CO3 and 0.640 g of NaOH, dissolve them in 20 ml of deionized water to prepare solution B; weigh 5 g of Al2O3 support, add it to solution B to obtain suspension C. Place solution C in a 35°C water bath and stir vigorously for 4 h, and use a constant flow pump to dropwise add solution A to solution C at a rate of 3 mL / min. After the dropping is completed, add 3 mol / L NaOH solution to the mixed solution until the pH value of the mixed solution is 10. Then, place it in a 65°C water bath and stir and age for 18 h, then filter, wash until neutral, and place it in an 80°C oven to dry for 12 h to obtain the Ni-based hydrotalcite matrix, denoted as the Ni3-Fe1-15% / Al2O3 sample.

[0089] 2) Prepare the Ni-X-Y / S catalyst.

[0090] Weigh 5.0 g of the prepared Ni3-Fe1-15% / Al2O3 support, weigh 0.3888 g of KNO3, dissolve it in 2 g of deionized water to form a mixed solution with a K mass concentration of 7.5 wt%, drop it into the Ni3-Fe1-15% / Al2O3 sample and mix them evenly. Impregnate at room temperature for 12 h, dry at 80°C for 12 h, and calcine in an air atmosphere at 300°C for 4 h, with a K mass content of 3%. Then, carry out hydrogen reduction at a temperature of 500°C, with a heating rate from room temperature to the reduction temperature of 5°C / min, a hydrogen volume space velocity of 1000 h -1 , at atmospheric pressure, and a reduction time of 4 h. Obtain the catalyst, denoted as Ni3-Fe1-15%-3%K / Al2O3.

[0091] Reaction conditions for ammonia decomposition of the catalyst: ammonia concentration is 99.9%, fixed-bed reactor, reaction temperature is 500°C to 700°C, and space velocities are 200, 1000, 30000, and 60000 ml / g·h respectively. The reaction results are shown in Table 1.

[0092] Example 3

[0093] 1) Prepare the Ni-based hydrotalcite matrix.

[0094] Weigh 1.5564 g of NiCl2·6H2O and 1.7712 g of FeCl3·6H2O, dissolve them in 20 ml of deionized water to prepare solution A; weigh 1.448 g of K2CO3 and 0.882 g of KOH, dissolve them in 20 ml of deionized water to prepare solution B; weigh 5 g of Al2O3 support, add it to solution B to obtain suspension C. Place suspension C in a 30 °C water bath and stir vigorously for 12 h. Use a constant flow pump to dropwise add solution A to solution C at a rate of 3 mL / min. After the addition is complete, add 3 mol / L NaOH solution to the mixed solution until the pH value of the mixed solution is 11. Then, place it in a 50 °C water bath and stir and age for 24 h. Subsequently, filter and wash it until neutral, and place it in a 60 °C oven to dry for 12 h to obtain the Ni-based hydrotalcite matrix, denoted as the Ni1-Fe1-15% / Al2O3 sample.

[0095] 2) Prepare the Ni-X-Y / S catalyst.

[0096] Weigh 5.0 g of the prepared Ni1-Fe1-15% / Al2O3 support, weigh 0.2860 g of KCl, dissolve it in 2 g of deionized water to form a mixed solution with a K mass concentration of 7.5 wt%, drop it onto the Ni1-Fe1-15% / Al2O3 sample and mix them evenly. Impregnate at room temperature for 48 h, dry at 60 °C for 12 h, and calcine in an air atmosphere at 200 °C for 12 h, with a K mass content of 3%. Then, carry out ammonia reduction on it, with a temperature of 800 °C, a heating rate from room temperature to the reduction temperature of 1 °C / min, a hydrogen volume space velocity of 3600 h -1 , at atmospheric pressure, and a reduction time of 48 h. Obtain the catalyst, denoted as Ni1-Fe1-15%-3%K / Al2O3.

[0097] The reaction conditions for ammonia decomposition by the catalyst are: ammonia concentration of 99.9%, fixed-bed reactor, reaction temperature of 500 °C to 700 °C, and space velocity of 30000 ml / g·h. The reaction results are shown in Table 1.

[0098] Example 4

[0099] 1) Prepare the Ni-based hydrotalcite matrix.

[0100] Weigh 0.8249 g of Ni(CH3COO)2·4H2O and 4.0178 g of Fe(NO3)3·9H2O, dissolve them in 20 ml of deionized water to prepare solution A; weigh 1.406 g of Na2CO3 and 0.743 g of NaOH, dissolve them in 20 ml of deionized water to prepare solution B; weigh 5 g of Al2O3 support, add it to solution B to obtain suspension C. Place solution C in an 80°C water bath and stir vigorously for 1 h. Use a constant flow pump to dropwise add solution A to solution C at a rate of 3 mL / min. After the addition is complete, add 3 mol / L NaOH solution to the mixed solution until the pH value of the mixed solution is 11. Then, place it in a 90°C water bath and stir and age for 6 h. Subsequently, filter and wash it until it is neutral, and place it in an oven at 120°C to dry for 4 h to obtain the Ni-based hydrotalcite matrix, denoted as the Ni1-Fe3-15% / Al2O3 sample.

[0101] 2) Prepare the Ni-X-Y / S catalyst.

[0102] Weigh 5.0 g of the prepared Ni1-Fe3-15% / Al2O3 support, weigh 0.3888 g of KNO3, dissolve it in 2 g of deionized water to form a mixed solution with a K mass concentration of 7.5 wt%, drop it onto the Ni1-Fe3-15% / Al2O3 sample and mix them evenly. Immerse at room temperature for 0.5 h, dry at 120°C for 4 h, and calcine in an air atmosphere at 400°C for 4 h, with a K mass content of 3%. Then, reduce it with a mixed ammonia-hydrogen gas, where the hydrogen volume concentration is 10%, the temperature is 400°C, the heating rate from room temperature to the reduction temperature is 10°C / min, the hydrogen volume space velocity is 100 h -1 , the pressure is atmospheric pressure, and the reduction time is 1 h. Obtain the catalyst, denoted as Ni1-Fe3-15%-3%K / Al2O3.

[0103] The reaction conditions for the ammonia decomposition of the catalyst: the ammonia concentration is 99.9%, a fixed-bed reactor, the reaction temperature is 500°C to 700°C, and the space velocity is 30000 ml / g·h. The reaction results are shown in Table 1.

[0104] Example 5

[0105] 1) Prepare the Ni-based hydrotalcite matrix.

[0106] Weigh 0.6453 g of Ni(NO3)2·6H2O and 4.4830 g of Fe(NO3)3·9H2O, dissolve them in 20 ml of deionized water to prepare solution A; weigh 1.411 g of Na2CO3 and 0.799 g of NaOH, dissolve them in 20 ml of deionized water to prepare solution B; weigh 5 g of Al2O3 support, add it to solution B to obtain suspension C. Place solution C in a 60 °C water bath and stir vigorously for 6 h, and use a constant flow pump to dropwise add solution A to solution C at a rate of 3 mL / min. After the addition is complete, add 3 mol / L NaOH solution to the mixed solution until the pH value of the mixed solution is 10. Then, place it in an 80 °C water bath and stir and age for 18 h, then filter, wash until neutral, put it in an 80 °C oven and dry for 6 h to obtain the Ni-based hydrotalcite matrix, denoted as the Ni-Fe5-15% / Al2O3 sample.

[0107] 2) Prepare the Ni-X-Y / S catalyst.

[0108] Weigh 5.0 g of the prepared Ni-Fe5-15% / Al2O3 support, weigh 0.3888 g of KNO3, dissolve it in 2 g of deionized water to form a mixed solution with a K mass concentration of 7.5 wt%, drop it into the Ni1-Fe5-15% / Al2O3 sample and mix them evenly. Impregnate at room temperature for 12 h, dry at 80 °C for 10 h, and calcine in air atmosphere at 300 °C for 6 h, with the K mass content being 3%. Then, carry out hydrogen reduction at a temperature of 600 °C, with a heating rate from room temperature to the reduction temperature of 5 °C / min, a hydrogen volumetric space velocity of 1000 h -1 , at atmospheric pressure, and a reduction time of 8 h. Obtain the catalyst, denoted as Ni1-Fe5-15%-3%K / Al2O3.

[0109] Reaction conditions for the catalyst to decompose ammonia: ammonia concentration is 99.9%, fixed-bed reactor, reaction temperature is 500 °C to 700 °C, and space velocity is 30000 ml / g·h. The reaction results are shown in Table 1.

[0110] Example 6

[0111] 1) Prepare the Ni-based hydrotalcite matrix.

[0112] Weigh 2.8211 g of Ni(NO3)2·6H2O and 0.8919 g of Co(NO3)2·6H2O, dissolve them in 20 ml of deionized water to prepare solution A; weigh 1.131 g of Na2CO3 and 0.640 g of NaOH, dissolve them in 20 ml of deionized water to prepare solution B; weigh 5 g of Al2O3 support, add it to solution B to obtain suspension C. Place solution C in a 60 °C water bath and stir vigorously for 6 h. Use a constant flow pump to dropwise add solution A into solution C at a rate of 3 mL / min. After the addition is complete, add 3 mol / L NaOH solution to the mixed solution until the pH value of the mixed solution is 10. Then, place it in a 70 °C water bath and stir and age for 18 h, followed by filtration, washing until neutral, and drying in an 80 °C oven for 6 h to obtain the Ni-based hydrotalcite matrix, denoted as the Ni3-Co1-15% / Al2O3 sample.

[0113] 2) Prepare the Ni-X-Y / S catalyst.

[0114] Weigh 5.0 g of the prepared Ni3-Co1-15% / Al2O3 support, weigh 0.3888 g of KNO3, dissolve it in 2 g of deionized water to form a mixed solution with a K mass concentration of 7.5 wt%, drop it onto the Ni3-Co1-15% / Al2O3 sample and mix them evenly. Impregnate at room temperature for 12 h, dry at 80 °C for 10 h, and calcine in an air atmosphere at 300 °C for 6 h, with a K mass content of 3%. Then, perform hydrogen reduction on it at a temperature of 600 °C, with a heating rate from room temperature to the reduction temperature of 5 °C / min, a hydrogen volumetric space velocity of 1000 h -1 , at atmospheric pressure, and a reduction time of 8 h. Obtain the catalyst, denoted as Ni3-Co1-15%-3%K / Al2O3.

[0115] The reaction conditions for ammonia decomposition by the catalyst: ammonia concentration is 99.9%, fixed-bed reactor, reaction temperature is 500 °C to 700 °C, and space velocity is 30000 ml / g·h. The reaction results are shown in Table 1.

[0116] Example 7

[0117] 1) Prepare the Ni-based hydrotalcite matrix.

[0118] Weigh 0.9404 g of Ni(NO3)2·6H2O and 0.4355 g of Fe(NO3)2·9H2O, dissolve them in 20 ml of deionized water to prepare solution A; weigh 0.377 g of Na2CO3 and 0.213 g of NaOH, dissolve them in 20 ml of deionized water to prepare solution B; weigh 5 g of Al2O3 support, add it to solution B to obtain suspension C. Place solution C in a 60 °C water bath and stir vigorously for 6 h. Use a constant flow pump to dropwise add solution A to solution C at a rate of 3 mL / min. After the addition is complete, add 3 mol / L NaOH solution to the mixed solution until the pH value of the mixed solution is 10. Then, place it in a 65 °C water bath and stir and age for 18 h, followed by filtration, washing until neutral, and drying in an 80 °C oven for 6 h to obtain the Ni-based hydrotalcite matrix, denoted as the Ni3-Fe1-5% / Al2O3 sample.

[0119] 2) Prepare the Ni-X-Y / S catalyst.

[0120] Weigh 5.0 g of the prepared Ni3-Fe1-5% / Al2O3 support, weigh 0.3888 g of KNO3, dissolve it in 2 g of deionized water to form a mixed solution with a K mass concentration of 7.5 wt%, drop it onto the Ni3-Fe1-5% / Al2O3 sample and mix them evenly. Impregnate at room temperature for 12 h, dry at 80 °C for 10 h, and calcine in air atmosphere at 300 °C for 6 h, with a K mass content of 3%. Then, carry out hydrogen reduction at a temperature of 600 °C, with a heating rate from room temperature to the reduction temperature of 5 °C / min, a hydrogen volumetric space velocity of 1000 h -1 , at atmospheric pressure, and a reduction time of 8 h. Obtain the catalyst, denoted as Ni3-Fe1-5%-3%K / Al2O3.

[0121] Reaction conditions for the ammonia decomposition of the catalyst: ammonia concentration is 99.9%, fixed-bed reactor, reaction temperature is 500 °C to 700 °C, and space velocity is 30000 ml / g·h. The reaction results are shown in Table 1.

[0122] Example 8

[0123] 1) Prepare the Ni-based hydrotalcite matrix.

[0124] Weigh 3.7614 g of Ni(NO3)2·6H2O and 1.7420 g of Fe(NO3)2·9H2O, dissolve them in 20 ml of deionized water to prepare solution A; weigh 1.508 g of Na2CO3 and 0.854 g of NaOH, dissolve them in 20 ml of deionized water to prepare solution B; weigh 5 g of Al2O3 support, add it to solution B to obtain suspension C. Place solution C in a 60 °C water bath and stir vigorously for 6 h. Use a constant flow pump to dropwise add solution A to solution C at a rate of 3 mL / min. After the addition is complete, add 3 mol / L NaOH solution to the mixed solution until the pH value of the mixed solution is 10. Then, place it in a 65 °C water bath and stir and age for 18 h, followed by filtration, washing until neutral, and drying in an 80 °C oven for 6 h to obtain the Ni-based hydrotalcite matrix, denoted as the Ni3-Fe1-20% / Al2O3 sample.

[0125] 2) Prepare the Ni-X-Y / S catalyst.

[0126] Weigh 5.0 g of the prepared Ni3-Fe1-20% / Al2O3 support, weigh 0.3888 g of KNO3, dissolve it in 2 g of deionized water to form a mixed solution with a K mass concentration of 7.5 wt%, drop it onto the Ni3-Fe1-20% / Al2O3 sample and mix them evenly. Impregnate at room temperature for 12 h, dry at 80 °C for 10 h, and calcine in an air atmosphere at 300 °C for 6 h, with a K mass content of 3%. Then, carry out hydrogen reduction at a temperature of 600 °C, with a heating rate from room temperature to the reduction temperature of 5 °C / min and a hydrogen volumetric space velocity of 1000 h -1 , at atmospheric pressure, and the reduction time is 8 h. Obtain the catalyst, denoted as Ni3-Fe1-20%-3%K / Al2O3.

[0127] The reaction conditions for ammonia decomposition by the catalyst are as follows: ammonia concentration is 99.9%, fixed-bed reactor, reaction temperature is 500 °C to 700 °C, and space velocity is 30000 ml / g·h. The reaction results are shown in Table 1.

[0128] Example 9

[0129] Weigh 5.0 g of the Ni3-Fe1-15% / Al2O3 support prepared in Example 2, weigh 0.1296 g of KNO3, dissolve it in 2 g of deionized water to form a mixed solution with a K mass concentration of 2.5 wt%, drop it onto the Ni3-Fe1-15% / Al2O3 sample and mix them evenly. Impregnate at room temperature for 12 h, dry at 80 °C for 10 h, and calcine in an air atmosphere at 300 °C for 6 h, with a K mass content of 1%. Then, carry out hydrogen reduction at a temperature of 600 °C, with a heating rate from room temperature to the reduction temperature of 5 °C / min and a hydrogen volumetric space velocity of 1000 h-1 , the pressure is atmospheric pressure, and the reduction time is 8 h. The catalyst obtained is denoted as Ni3-Fe1-15%-1%K / Al2O3.

[0130] Reaction conditions for ammonia decomposition using the catalyst: ammonia concentration is 99.9%, fixed-bed reactor, reaction temperature is 500 °C to 700 °C, and space velocity is 30000 ml / g·h. The reaction results are shown in Table 1.

[0131] Example 10

[0132] Weigh 5.0 g of the Ni3-Fe1-15% / Al2O3 support prepared in Example 2. Weigh 0.6481 g of KNO3, dissolve it in 5 g of deionized water to form a mixed solution with a K mass concentration of 5 wt%, and add it dropwise to the Ni3-Fe1-15% / Al2O3 sample and mix them evenly. Impregnate at room temperature for 12 h, dry at 80 °C for 10 h, and calcine in air atmosphere at 300 °C for 6 h, with a K mass content of 5%. Then, carry out hydrogen reduction on it at a temperature of 600 °C, with a heating rate from room temperature to the reduction temperature of 5 °C / min and a hydrogen volume space velocity of 1000 h -1 , the pressure is atmospheric pressure, and the reduction time is 8 h. The catalyst obtained is denoted as Ni3-Fe1-15%-5%K / Al2O3.

[0133] Reaction conditions for ammonia decomposition using the catalyst: ammonia concentration is 99.9%, fixed-bed reactor, reaction temperature is 500 °C to 700 °C, and space velocity is 30000 ml / g·h. The reaction results are shown in Table 1.

[0134] Example 11

[0135] Weigh 5.0 g of the Ni3-Fe1-15% / Al2O3 support prepared in Example 2. Weigh 1.2962 g of KNO3, dissolve it in 5 g of deionized water to form a mixed solution with a K mass concentration of 10 wt%, and add it dropwise to the Ni3-Fe1-15% / Al2O3 sample and mix them evenly. Impregnate at room temperature for 12 h, dry at 80 °C for 10 h, and calcine in air atmosphere at 300 °C for 6 h, with a K mass content of 10%. Then, carry out hydrogen reduction on it at a temperature of 600 °C, with a heating rate from room temperature to the reduction temperature of 5 °C / min and a hydrogen volume space velocity of 1000 h -1 , the pressure is atmospheric pressure, and the reduction time is 8 h. The catalyst obtained is denoted as Ni3-Fe1-15%-10%K / Al2O3.

[0136] Reaction conditions for ammonia decomposition using the catalyst: ammonia concentration is 99.9%, fixed-bed reactor, reaction temperature is 500 °C to 700 °C, and space velocity is 30000 ml / g·h. The reaction results are shown in Table 1.

[0137] Example 12

[0138] Weigh 5.0 g of the Ni3-Fe1-15% / Al2O3 support prepared in Example 2. Weigh 2.4836 g of LiNO3, dissolve it in 5 g of deionized water to form a mixed solution with a mass concentration of Li of 5 wt%. Drop it onto the Ni3-Fe1-15% / Al2O3 sample and mix them evenly. Impregnate at room temperature for 12 h, dry at 80 °C for 10 h, and calcine in air atmosphere at 300 °C for 6 h, with the mass content of Li being 5%. Then, carry out hydrogen reduction on it at a temperature of 600 °C, with a heating rate from room temperature to the reduction temperature of 5 °C / min and a hydrogen volume space velocity of 1000 h -1 , at atmospheric pressure and a reduction time of 8 h. A catalyst is obtained, denoted as Ni3-Fe1-15%-5%Li / Al2O3.

[0139] Reaction conditions for ammonia decomposition by the catalyst: ammonia concentration is 99.9%, fixed-bed reactor, reaction temperature is 500 °C to 700 °C, and space velocity is 30000 ml / g·h. The reaction results are shown in Table 1.

[0140] Example 13

[0141] Weigh 5.0 g of the Ni3-Fe1-15% / Al2O3 support prepared in Example 2. Weigh 0.6352 g of NaCl, dissolve it in 5 g of deionized water to form a mixed solution with a mass concentration of Na of 5 wt%. Drop it onto the Ni3-Fe1-15% / Al2O3 sample and mix them evenly. Impregnate at room temperature for 12 h, dry at 80 °C for 10 h, and calcine in air atmosphere at 300 °C for 6 h, with the mass content of Na being 5%. Then, carry out hydrogen reduction on it at a temperature of 600 °C, with a heating rate from room temperature to the reduction temperature of 5 °C / min and a hydrogen volume space velocity of 1000 h -1 , at atmospheric pressure and a reduction time of 8 h. A catalyst is obtained, denoted as Ni3-Fe1-15%-5%Na / Al2O3.

[0142] Reaction conditions for ammonia decomposition by the catalyst: ammonia concentration is 99.9%, fixed-bed reactor, reaction temperature is 500 °C to 700 °C, and space velocity is 30000 ml / g·h. The reaction results are shown in Table 1.

[0143] Example 14

[0144] Weigh 5.0 g of the Ni3-Fe1-15% / Al2O3 support prepared in Example 2. Weigh 0.4314 g of RbNO3, dissolve it in 5 g of deionized water to form a mixed solution with a mass concentration of Rb of 5 wt%, add it dropwise to the Ni3-Fe1-15% / Al2O3 sample and mix them evenly. Impregnate at room temperature for 12 h, dry at 80 °C for 10 h, and calcine in an air atmosphere at 300 °C for 6 h, with the mass content of Rb being 5%. Then, perform hydrogen reduction on it at a temperature of 600 °C, with a heating rate from room temperature to the reduction temperature of 5 °C / min and a hydrogen volumetric space velocity of 1000 h -1 , at atmospheric pressure, and the reduction time is 8 h. A catalyst is obtained, denoted as Ni3-Fe1-15%-5%Rb / Al2O3.

[0145] Reaction conditions for ammonia decomposition over the catalyst: ammonia concentration is 99.9%, fixed-bed reactor, reaction temperature is 500 °C to 700 °C, and space velocity is 30000 ml / g·h. The reaction results are shown in Table 1.

[0146] Example 15

[0147] Weigh 5.0 g of the Ni3-Fe1-15% / Al2O3 support prepared in Example 2. Weigh 0.3666 g of CsNO3, dissolve it in 5 g of deionized water to form a mixed solution with a mass concentration of Cs of 5 wt%, add it dropwise to the Ni3-Fe1-15% / Al2O3 sample and mix them evenly. Impregnate at room temperature for 12 h, dry at 80 °C for 10 h, and calcine in an air atmosphere at 300 °C for 6 h, with the mass content of Cs being 5%. Then, perform hydrogen reduction on it at a temperature of 600 °C, with a heating rate from room temperature to the reduction temperature of 5 °C / min and a hydrogen volumetric space velocity of 1000 h -1 , at atmospheric pressure, and the reduction time is 8 h. A catalyst is obtained, denoted as Ni3-Fe1-15%-5%Cs / Al2O3.

[0148] Reaction conditions for ammonia decomposition over the catalyst: ammonia concentration is 99.9%, fixed-bed reactor, reaction temperature is 500 °C to 700 °C, and space velocity is 30000 ml / g·h. The reaction results are shown in Table 1.

[0149] Example 16

[0150] 1) Prepare a Ni-based hydrotalcite matrix.

[0151] Weigh 2.8211 g of Ni(NO3)2·6H2O and 1.3065 g of Fe(NO3)3·9H2O, dissolve them in 20 ml of deionized water to prepare solution A; weigh 1.131 g of Na2CO3 and 0.640 g of NaOH, dissolve them in 20 ml of deionized water to prepare solution B; weigh 5 g of MgO support, add it to solution B to obtain suspension C. Place solution C in a 35 °C water bath and stir vigorously for 4 h, and use a constant flow pump to dropwise add solution A into solution C at a rate of 3 mL / min. After the addition is completed, add 3 mol / L NaOH solution to the mixed solution until the pH value of the mixed solution is 10. Then, place it in a 65 °C water bath and stir and age for 18 h, then filter, wash until neutral, and place it in an 80 °C oven to dry for 12 h to obtain the Ni-based hydrotalcite matrix, denoted as the Ni3-Fe1-15% / MgO sample.

[0152] 2) Prepare the Ni-X-Y / S catalyst.

[0153] Weigh 5.0 g of the prepared Ni3-Fe1-15% / MgO support, weigh 0.3888 g of KNO3, dissolve it in 2 g of deionized water to form a mixed solution with a K mass concentration of 7.5 wt%, drop it into the Ni3-Fe1-15% / MgO sample and mix them evenly. Impregnate at room temperature for 12 h, dry at 80 °C for 12 h, and calcine in an air atmosphere at 300 °C for 4 h, with a K mass content of 3%. Then, carry out hydrogen reduction at a temperature of 500 °C, with a heating rate from room temperature to the reduction temperature of 5 °C / min, a hydrogen volumetric space velocity of 1000 h -1 , at atmospheric pressure, and a reduction time of 4 h. The catalyst is obtained, denoted as Ni3-Fe1-15%-3%K / MgO.

[0154] The reaction conditions for ammonia decomposition of the catalyst: ammonia concentration is 99.9%, fixed-bed reactor, reaction temperature is 500 °C to 700 °C, and space velocity is 30000 ml / g·h. The reaction results are shown in Table 1.

[0155] Example 17

[0156] 1) Prepare the Ni-based hydrotalcite matrix.

[0157] Weigh 2.8211 g of Ni(NO3)2·6H2O and 1.3065 g of Fe(NO3)3·9H2O, dissolve them in 20 ml of deionized water to prepare solution A; weigh 1.131 g of Na2CO3 and 0.640 g of NaOH, dissolve them in 20 ml of deionized water to prepare solution B; weigh 5 g of CeO2 support, add it to solution B to obtain suspension C. Place suspension C in a 35 °C water bath and stir vigorously for 4 h, and use a constant flow pump to dropwise add solution A to solution C at a rate of 3 mL / min. After the addition is completed, add 3 mol / L NaOH solution to the mixed solution until the pH value of the mixed solution is 10. Then, place it in a 65 °C water bath and stir and age for 18 h, then filter and wash until neutral, and place it in an 80 °C oven to dry for 12 h to obtain the Ni-based hydrotalcite matrix, denoted as the Ni3-Fe1-15% / CeO2 sample.

[0158] 2) Prepare the Ni-X-Y / S catalyst.

[0159] Weigh 5.0 g of the prepared Ni3-Fe1-15% / CeO2 support, weigh 0.3888 g of KNO3, dissolve it in 2 g of deionized water to form a mixed solution with a K mass concentration of 7.5 wt%, drop it into the Ni3-Fe1-15% / CeO2 sample and mix them evenly. Impregnate at room temperature for 12 h, dry at 80 °C for 12 h, and calcine in an air atmosphere at 300 °C for 4 h, with a K mass content of 3%. Then, carry out hydrogen reduction at a temperature of 500 °C, with a heating rate from room temperature to the reduction temperature of 5 °C / min, a hydrogen volumetric space velocity of 1000 h -1 , at atmospheric pressure, and a reduction time of 4 h. The catalyst is obtained, denoted as Ni3-Fe1-15%-3%K / CeO2.

[0160] The reaction conditions for the ammonia decomposition of the catalyst: the ammonia concentration is 99.9%, a fixed-bed reactor, the reaction temperature is 500 °C to 700 °C, and the space velocity is 30000 ml / g·h. The reaction results are shown in Table 1.

[0161] Example 18

[0162] 1) Prepare the Ni-based hydrotalcite matrix.

[0163] Weigh 2.8211 g of Ni(NO3)2·6H2O and 1.3065 g of Fe(NO3)3·9H2O, dissolve them in 20 ml of deionized water to prepare solution A; weigh 1.131 g of Na2CO3 and 0.640 g of NaOH, dissolve them in 20 ml of deionized water to prepare solution B; weigh 5 g of SiO2 support, add it to solution B to obtain suspension C. Place suspension C in a 35 °C water bath and stir vigorously for 4 h. Use a constant flow pump to dropwise add solution A to solution C at a rate of 3 mL / min. After the addition is complete, add 3 mol / L NaOH solution to the mixed solution until the pH value of the mixed solution is 10. Then, place it in a 65 °C water bath and stir and age for 18 h, followed by filtration, washing until neutral, and drying in an 80 °C oven for 12 h to obtain the Ni-based hydrotalcite matrix, denoted as the Ni3-Fe1-15% / SiO2 sample.

[0164] 2) Prepare the Ni-X-Y / S catalyst.

[0165] Weigh 5.0 g of the prepared Ni3-Fe1-15% / SiO2 support, weigh 0.3888 g of KNO3, dissolve it in 2 g of deionized water to form a mixed solution with a K mass concentration of 7.5 wt%, drop it into the Ni3-Fe1-15% / SiO2 sample and mix them evenly. Immerse at room temperature for 12 h, dry at 80 °C for 12 h, and calcine in an air atmosphere at 300 °C for 4 h, with a K mass content of 3%. Then, carry out hydrogen reduction at a temperature of 500 °C, with a heating rate from room temperature to the reduction temperature of 5 °C / min, a hydrogen volumetric space velocity of 1000 h -1 , at atmospheric pressure, and a reduction time of 4 h. Obtain the catalyst, denoted as Ni3-Fe1-15%-3%K / SiO2.

[0166] The reaction conditions for the catalyst in ammonia decomposition: ammonia concentration is 99.9%, fixed-bed reactor, reaction temperature is 500 °C to 700 °C, and space velocity is 30000 ml / g·h. The reaction results are shown in Table 1.

[0167] Example 19

[0168] 1) Prepare the Ni-based hydrotalcite matrix.

[0169] Weigh 2.8211 g of Ni(NO3)2·6H2O and 1.3065 g of Fe(NO3)3·9H2O, dissolve them in 20 ml of deionized water to prepare solution A; weigh 1.131 g of Na2CO3 and 0.640 g of NaOH, dissolve them in 20 ml of deionized water to prepare solution B; weigh 5 g of TiO2 support, add it to solution B to obtain suspension C. Place suspension C in a 35 °C water bath and stir vigorously for 4 h, and use a constant flow pump to dropwise add solution A to solution C at a rate of 3 mL / min. After the addition is complete, add 3 mol / L NaOH solution to the mixed solution until the pH value of the mixed solution is 10. Then, place it in a 65 °C water bath and stir and age for 18 h, then filter and wash until neutral, and place it in an 80 °C oven to dry for 12 h to obtain the Ni-based hydrotalcite matrix, denoted as the Ni3-Fe1-15% / TiO2 sample.

[0170] 2) Prepare the Ni-X-Y / S catalyst.

[0171] Weigh 5.0 g of the prepared Ni3-Fe1-15% / TiO2 support, weigh 0.3888 g of KNO3, dissolve it in 2 g of deionized water to form a mixed solution with a K mass concentration of 7.5 wt%, drop it into the Ni3-Fe1-15% / TiO2 sample and mix them evenly. Immerse at room temperature for 12 h, dry at 80 °C for 12 h, calcine in air atmosphere at 300 °C for 4 h, with a K mass content of 3%. Then, carry out hydrogen reduction at a temperature of 500 °C, with a heating rate from room temperature to the reduction temperature of 5 °C / min, a hydrogen volumetric space velocity of 1000 h -1 , at atmospheric pressure, and a reduction time of 4 h. Obtain the catalyst, denoted as Ni3-Fe1-15%-3%K / TiO2.

[0172] The reaction conditions for ammonia decomposition by the catalyst are: ammonia concentration of 99.9%, fixed-bed reactor, reaction temperature of 500 °C to 700 °C, and space velocity of 30000 ml / g·h. The reaction results are shown in Table 1.

[0173] Comparative Example 1

[0174] Weigh 3.7159 g of Ni(NO3)2·6H2O and dissolve it in 20 ml of deionized water to prepare solution A; weigh 1.131 g of Na2CO3 and 0.640 g of NaOH, dissolve them in 20 ml of deionized water to prepare solution B; weigh 5 g of Al2O3 support and add it to solution B to obtain suspension C. Place solution C in a 35°C water bath and stir vigorously for 4 h. Use a constant flow pump to slowly add solution A dropwise to solution C at a rate of 3 mL / min. After the addition is complete, add 3 mol / L NaOH solution to the mixed solution until the pH value of the mixed solution reaches 10. Then, place it in a 65°C water bath and stir and age for 18 h. Subsequently, filter and wash it until it is neutral, and place it in an 80°C oven to dry for 12 h to obtain a Ni-based sample, denoted as Ni-15% / Al2O3 sample.

[0175] Weigh 5.0 g of the prepared Ni-15% / Al2O3 support. Weigh 0.3888 g of KNO3 and dissolve it in 2 g of deionized water to form a mixed solution with a K mass concentration of 7.5 wt%. Drop it onto the Ni-15% / Al2O3 sample and mix them evenly. Immerse them at room temperature for 12 h, dry them at 80°C for 12 h, and calcine them in an air atmosphere at 300°C for 4 h, with a K mass content of 3%. Then, carry out hydrogen reduction on it at a temperature of 500°C, with a heating rate from room temperature to the reduction temperature of 5°C / min and a hydrogen volumetric space velocity of 1000 h -1 , at atmospheric pressure, and the reduction time is 4 h. Obtain a catalyst, denoted as Ni-15%-3%K / Al2O3.

[0176] The reaction conditions for the ammonia decomposition of the catalyst are as follows: the ammonia concentration is 99.9%, a fixed-bed reactor, the reaction temperature is 500°C to 700°C, and the space velocity is 30000 ml / g·h. The reaction results are shown in Table 1.

[0177] Comparative Example 2

[0178] Weigh 5.4252 g of Fe(NO3)3·9H2O and dissolve it in 20 ml of deionized water to prepare solution A; weigh 1.131 g of Na2CO3 and 0.640 g of NaOH, dissolve them in 20 ml of deionized water to prepare solution B; weigh 5 g of Al2O3 support and add it to solution B to obtain suspension C. Place solution C in a 35°C water bath and stir vigorously for 4 h. Use a constant flow pump to slowly add solution A dropwise to solution C at a rate of 3 mL / min. After the addition is complete, add 3 mol / L NaOH solution to the mixed solution until the pH value of the mixed solution reaches 10. Then, place it in a 65°C water bath and stir and age for 18 h. Subsequently, filter and wash it until it is neutral, and place it in an 80°C oven to dry for 12 h to obtain an Fe-based sample, denoted as Fe-15% / Al2O3 sample.

[0179] Weigh 5.0 g of the prepared Fe-15% / Al2O3 support. Weigh 0.3888 g of KNO3, dissolve it in 2 g of deionized water to form a mixed solution with a K mass concentration of 7.5 wt%, and drop it into the Ni-15% / Al2O3 sample and mix them evenly. Impregnate at room temperature for 12 h, dry at 80 °C for 12 h, and calcine in air atmosphere at 300 °C for 4 h, with the K mass content being 3%. Then, perform hydrogen reduction on it at a temperature of 500 °C, with a heating rate from room temperature to the reduction temperature of 5 °C / min and a hydrogen volumetric space velocity of 1000 h -1 , at atmospheric pressure, and the reduction time is 4 h. The catalyst obtained is denoted as Fe-15%-3%K / Al2O3.

[0180] Reaction conditions for the catalyst in ammonia decomposition: ammonia concentration is 99.9%, fixed-bed reactor, reaction temperature is 500 °C to 700 °C, and space velocity is 30000 ml / g·h. The reaction results are shown in Table 1.

[0181] Analysis of the results of the examples:

[0182] From the data analysis in Table 1, it can be seen that the Ni-X-Y / S catalyst prepared using the Ni-based hydrotalcite precursor has good activity in the ammonia decomposition reaction. For the Ni3-Fe1-15%-3%K / Al2O3 catalyst, ammonia conversion > 99% can be achieved at 700 °C. High-efficiency conversion of ammonia at high space velocity can be achieved at 700 °C and 30000 ml / g·h. While industrial catalysts need to reach 850 °C to achieve ammonia conversion under the same conditions. And the cost of the catalyst is low, large-scale preparation of the catalyst can be realized, and it has the potential for industrial application.

[0183] Table 1 Reaction performance of ammonia decomposition on different catalysts

[0184]

[0185]

[0186] As described above, these are only several embodiments of the present application and do not impose any form of limitation on the present application. Although the present application is disclosed with preferred embodiments as above, it is not intended to limit the present application. Any person skilled in the art, without departing from the scope of the technical solution of the present application, making some changes or modifications using the disclosed technical content is equivalent to equivalent implementation cases and all belong to the scope of the technical solution.

Claims

1. A nickel-based ammonia decomposition catalyst, characterized in that, The nickel-based ammonia decomposition catalyst includes a carrier, an active component, and an auxiliary agent; The active component is loaded on the carrier, and the auxiliary agent is loaded on the carrier containing the active component; The active component includes active component I and active component II; The active component I is Ni, and the active component II is selected from Fe and / or Co; The auxiliary agent is an alkali metal oxide; The alkali metal in the alkali metal oxide is selected from at least one of Li, Na, K, Rb, and Cs; The carrier is selected from at least one of Al2O3, MgO, CeO2, SiO2, and TiO2.

2. The nickel-based ammonia decomposition catalyst according to claim 1, characterized in that, The active component accounts for 5-20 wt.% of the mass percentage of the nickel-based ammonia decomposition catalyst; Preferably, the auxiliary agent accounts for 1-10 wt.% of the mass percentage of the nickel-based ammonia decomposition catalyst; Preferably, the carrier accounts for 70-94 wt.% of the mass percentage of the nickel-based ammonia decomposition catalyst.

3. The preparation method of the nickel-based ammonia decomposition catalyst according to any one of claims 1 to 2, characterized in that, The preparation method includes the following steps: (1) A mixture I containing a Ni precursor, an active component II precursor, a carrier, a carbonate, and a strong base is subjected to a water bath, pH adjustment, aging, and drying I to obtain the Ni-based hydrotalcite matrix; (2) The Ni-based hydrotalcite matrix is impregnated in a salt solution of an alkali metal, followed by drying II, calcination, and reduction to obtain the nickel-based ammonia decomposition catalyst.

4. The preparation method according to claim 3, characterized in that, In the step (1), the Ni precursor is selected from at least one of nickel chloride, nickel nitrate, and nickel acetate; Preferably, the active component II precursor is selected from at least one of iron chloride, iron nitrate, cobalt chloride, and cobalt nitrate; Preferably, the carbonate is selected from sodium carbonate and / or potassium carbonate; Preferably, the strong base is selected from sodium hydroxide and / or potassium hydroxide.

5. The preparation method according to claim 3, characterized in that, In the step (1), the molar ratio of the Ni precursor to the active component II precursor is 5:1 to 1:5, The molar amount of the Ni precursor is based on the molar amount of Ni element, and the molar amount of the active component II precursor is based on the molar amount of active component II; Preferably, the concentration of the carbonate solution is 0.5 mol / L to 1 mol / L; Preferably, the concentration of the strong base is 1.2 mol / L to 2.0 mol / L; Preferably, the concentration of the carrier in the mixture I is 10 g / L to 50 g / L, based on the mass concentration of the carrier.

6. The preparation method according to claim 3, wherein In the step (2), the salt solution of the alkali metal is selected from at least one of nitrates and chlorides containing alkali metal elements; Preferably, the alkali metal element is selected from at least one of Li, Na, K, Rb, and Cs; Preferably, the concentration of the salt solution of the alkali metal is 0.1 wt.% to 10 wt.%, based on the mass content of the alkali metal.

7. The preparation method according to claim 3, characterized in that, In the step (1), the temperature of the water bath is 30-80 °C, and the time of the water bath is 1-12 h; Preferably, the temperature of the aging is 50-90 °C, and the time of the aging is 6-24 h; Preferably, the temperature of the drying I is 60-120 °C, and the time of the drying I is 4-12 h; Preferably, the pH value is 10-11; Preferably, in the step (2), the time of the impregnation is 0.5-48 h; Preferably, in the step (2), the temperature of the second drying is 60 - 120 °C, and the time of the second drying is 4 - 12 h; Preferably, the temperature of the roasting is 200 - 400 °C, and the time of the roasting is 4 - 12 h.

8. The preparation method according to claim 3, characterized in that, In the step (2), the reduction is a high-temperature gas-phase reduction method; Preferably, the reducing gas is selected from at least one of ammonia gas and hydrogen gas; Preferably, the volumetric space velocity of the reducing gas is 100 to 3600 h -1 ; Preferably, the heating rate during reduction is 1 - 10 °C / min; Preferably, the temperature of the reduction is 400 - 800 °C, and the time of the reduction is 1 - 48 h; Preferably, the pressure of the reduction is 0.1 - 1.0 MPa.

9. A method for hydrogen production by ammonia decomposition, characterized in that, The method includes: reacting the catalyst with ammonia to perform an ammonia decomposition reaction to obtain hydrogen and nitrogen; The catalyst is selected from the nickel-based ammonia decomposition catalysts described in any one of claims 1 to 2.

10. The method according to claim 9, characterized in that, The temperature of the ammonia decomposition reaction is 400 - 900 °C; Preferably, the temperature of the ammonia decomposition reaction is 500 - 700 °C; Preferably, the space velocity of the ammonia decomposition reaction is 200 - 60000 ml / g·h.

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