Iron-containing catalysts, methods of making and using the same, and methods of hydrogen production by ammonia decomposition

Abstract

The application relates to the field of ammonia decomposition catalyst preparation, and discloses an iron-containing catalyst, a preparation method and application thereof, and an ammonia decomposition hydrogen production method. The iron-containing catalyst comprises a magnesium titanate carrier and iron elements supported on the magnesium titanate carrier; wherein the content of the iron elements is 5-20% by weight based on the total weight of the catalyst. The catalyst has high activity, and is applied to ammonia decomposition hydrogen production, and has higher ammonia decomposition conversion rate at low temperature and under a higher reaction space velocity.

Description

Technical Field

[0001] This invention relates to the field of ammonia decomposition catalyst preparation, specifically to an iron-containing catalyst, its preparation method and application, and a method for producing hydrogen from ammonia decomposition. Background Technology

[0002] Currently, hydrogen is almost entirely derived from catalytic steam reforming of fossil fuels, which is also the most commercially mature hydrogen production technology. However, the hydrogen produced by catalytic reforming contains impurities such as carbon monoxide and carbon dioxide, making it unsuitable for direct use as fuel in fuel cells. Therefore, using ammonia as a feedstock for carbon-emission-free hydrogen production is a highly efficient, clean, and safe hydrogen production technology. To achieve safe and green hydrogen production, developing catalysts capable of efficiently catalyzing ammonia decomposition is particularly important. Currently, ammonia decomposition catalysts are divided into noble metal catalysts with ruthenium and platinum as active components and non-noble metal catalysts with iron and nickel as active components.

[0003] The high cost and low reserves of precious metals limit their application in large-scale industrial applications. Therefore, the core of developing efficient and inexpensive ammonia decomposition hydrogen production technology lies in low-cost, highly active, and highly stable non-precious metal catalysts. However, non-precious metal catalysts require relatively harsh reaction conditions, and the operating temperature is generally higher than 800℃. Extensive research has been conducted on low-temperature non-precious metal ammonia decomposition catalysts. For example, CN1506299A discloses a nickel-based ammonia decomposition hydrogen-nitrogen mixed gas catalyst, whose main active component is Ni; the support is SiO2 or Al2O3; the promoter is one or more of IA, IIA, IIIB, VIII, or rare earth elements; the nickel weight percentage is 1-40%; and the promoter component weight percentage is 0.1-20%. Catalysts prepared using SiO2 or Al2O3 as supports, although improved by introducing promoters, can achieve ammonia decomposition at 650℃, a significant reduction compared to the 800℃ reaction temperature of industrial catalysts. However, the poor dispersion of the promoters on the support surface leads to the formation of large particles, resulting in poor ammonia decomposition activity at low temperatures. CN115646500A discloses an ammonia decomposition hydrogen production catalyst comprising an active metal component, an alkaline earth metal component, a lanthanide metal component, and promoters. This patent application uses doping with alkaline earth metals to improve the dispersion of the nickel-based catalyst and reduce particle size. Compared to the unmodified catalyst, the catalyst activity is improved to some extent. Although the reaction temperature is reduced to 550℃, the reaction space velocity is only 6000 mL / (g·h), indicating room for further improvement. Summary of the Invention

[0004] The purpose of this invention is to overcome the problem that the activity and stability of existing ammonia decomposition catalysts at low temperatures need further improvement, and to provide an iron-containing catalyst, its preparation method and application, as well as a method for ammonia decomposition to produce hydrogen. This catalyst exhibits high activity and, when applied to ammonia decomposition to produce hydrogen, demonstrates a higher ammonia decomposition conversion rate at low temperatures and high reaction space velocities.

[0005] To achieve the above objectives, the present invention provides an iron-containing catalyst, wherein the catalyst comprises a magnesium titanate support and an iron element supported on the magnesium titanate support;

[0006] Based on the total weight of the catalyst, the iron content is 5-20% by weight (calculated as iron element).

[0007] A second aspect of the present invention provides a method for preparing an iron-containing catalyst, the method comprising the following steps:

[0008] S1. Dissolve the titanium source in a mixed solution of alcohol and glacial acetic acid to obtain solution A;

[0009] S2. Dissolve the magnesium source in a mixed solution of alcohol and glacial acetic acid to obtain solution B;

[0010] S3. Add solution B to solution A, and then process to obtain a sol, wherein the pH of the sol is 1.5-5;

[0011] S4. The sol obtained in step S3 is dried and subjected to a first calcination to obtain a magnesium titanate support.

[0012] S5. Load iron onto a magnesium titanate support.

[0013] The third aspect of this invention provides the application of the iron-containing catalyst described in the first aspect or the iron-containing catalyst prepared by the preparation method described in the second aspect in the ammonia decomposition for hydrogen production.

[0014] A fourth aspect of the present invention provides a method for producing hydrogen by ammonia decomposition, the method comprising: contacting ammonia with a catalyst under ammonia decomposition conditions;

[0015] The catalyst is either the catalyst described in the first aspect or an iron-containing catalyst prepared by the preparation method described in the second aspect.

[0016] The beneficial effects of the present invention through the above technical solution include:

[0017] The iron-containing catalyst provided by this invention utilizes the synergistic effect of iron and magnesium titanate support, which is beneficial to improving the catalytic activity of the catalyst. At the same time, controlling the iron content within the range of 5-20% by weight is beneficial to enhancing the interaction between the iron active component and the support, effectively weakening the interaction between the iron active component and ammonia decomposition products, thereby promoting the desorption of nitrogen and hydrogen.

[0018] The catalyst of this invention uses non-precious metal raw materials, does not contain precious metals such as Ru, is inexpensive, has a simple preparation process, good reproducibility, and is easy to scale up for production. Detailed Implementation

[0019] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0020] The first aspect of the present invention provides an iron-containing catalyst, the catalyst comprising a magnesium titanate support and an iron element supported on the magnesium titanate support;

[0021] Based on the total weight of the catalyst, the iron content is 5-20% by weight (calculated as iron element).

[0022] The inventors of this invention have discovered that by using magnesium titanate as a support, the electron transfer capacity between the active component and the support in the catalyst can be adjusted, the adsorption and desorption intensity of NH3 on the catalyst surface can be adjusted, the transfer of NH3 between the active site and the support can be promoted, and the catalytic activity can be improved.

[0023] In this invention, based on the total weight of the catalyst, the iron content, calculated by elemental iron, is 5-20% by weight, preferably 10-20% by weight, for example, 5% by weight, 6% by weight, 7% by weight, 8% by weight, 9% by weight, 10% by weight, 11% by weight, 12% by weight, 13% by weight, 14% by weight, 15% by weight, 16% by weight, 17% by weight, 18% by weight, 19% by weight, 20% by weight, and any value within any two of these ranges. This preferred embodiment enhances the interaction between the iron active component and the support, effectively weakens the interaction between the iron active component and ammonia decomposition products, thereby promoting the desorption of nitrogen and hydrogen.

[0024] The total content of all components in the catalyst described in this invention is 100%.

[0025] The content of the active component in the catalyst of the present invention was determined by XRF characterization.

[0026] Preferably, the catalyst does not contain precious metals. This preferred embodiment can save costs.

[0027] A second aspect of the present invention provides a method for preparing an iron-containing catalyst, the method comprising the following steps:

[0028] S1. Dissolve the titanium source in a mixed solution of alcohol and glacial acetic acid to obtain solution A;

[0029] S2. Dissolve the magnesium source in a mixed solution of alcohol and glacial acetic acid to obtain solution B;

[0030] S3. Add solution B to solution A and then process it to obtain a sol, the pH of which is 1.5-5;

[0031] S4. The sol obtained in step S3 is dried and subjected to a first calcination to obtain a magnesium titanate support.

[0032] S5. Load iron onto a magnesium titanate support.

[0033] The preparation method provided by this invention first uses a sol-gel method to prepare a magnesium titanate support, and then loads the iron active component onto the magnesium titanate support, resulting in an iron-containing catalyst with higher activity. In the preparation of the magnesium titanate support, the titanium source and magnesium source are first dissolved separately in an alcohol-glacial acetic acid mixed solution. The alcohol and glacial acetic acid, acting as solvents, inhibit the hydrolysis of the titanium source and also help to improve the gel formation time. Then, solution B is added to solution A to mix the two, and the pH of the resulting sol is controlled within the range of 1.5-5, which helps to promote the synergistic effect between the magnesium titanate support and the iron element, thereby improving the catalyst activity.

[0034] According to the present invention, preferably, in S1, the mass ratio of the titanium source to the alcohol-glacial acetic acid mixed solution is 1:4-10. This preferred embodiment facilitates the rapid formation of a uniform sol.

[0035] The present invention does not impose any particular limitation on the type of titanium source, and any conventional choice in the art can be used. Preferably, the titanium source is a water-soluble titanium-containing compound, preferably selected from at least one of tetrabutyl titanate, ethyl titanate, and isopropyl titanate. All of the above titanium sources are commercially available and inexpensive.

[0036] According to the present invention, preferably, in S2, the mass ratio of the magnesium source to the alcohol-glacial acetic acid mixed solution is 1:4-20. This preferred embodiment facilitates the rapid formation of a uniform sol.

[0037] The present invention does not impose any particular limitation on the type of magnesium source, and any conventional choice in the art can be made. Preferably, the magnesium source is a soluble magnesium salt, and is preferably selected from at least one of magnesium nitrate, magnesium sulfate, and magnesium chloride.

[0038] In this invention, "soluble" means that it can be directly dissolved in a solvent, or dissolved in a solvent with the help of a co-solvent.

[0039] The present invention does not have a particular limitation on the amount of glacial acetic acid used, as long as the sol with the following pH is obtained.

[0040] According to the present invention, preferably, in the alcohol-glacial acetic acid mixed solutions S1 and S2, the mass ratio of glacial acetic acid to alcohol is independently 1:0.5-2.

[0041] The alcohol described in this invention is used as a solvent to dissolve magnesium and titanium sources. This invention offers a wide range of alcohols that can be conventionally chosen in the art. Preferably, the alcohols in S1 and S2 are each independently a C1-C5 alcohol, and are preferably selected from at least one of methanol, ethanol, and propanol.

[0042] In this invention, in step S3, the pH of the sol is 1.5-5, preferably 3-5, for example 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, and any value within any range of two of these values. This preferred embodiment further promotes the synergistic effect between the obtained magnesium titanate support and the active component, thereby improving the catalyst activity.

[0043] The chemical formula for magnesium titanate is MgO3Ti. To ensure complete reaction between solution A and solution B, the molar ratio of titanium to magnesium must satisfy the above chemical formula. Preferably, the molar ratio of solution A (based on titanium content) to solution B (based on magnesium content) is 1:1.

[0044] According to one specific embodiment of the present invention, solution B is added dropwise to solution A while stirring.

[0045] The present invention does not impose a particular limitation on the stirring rate, which can be appropriately selected according to the specific circumstances, with the goal of uniformly mixing solution B and solution A.

[0046] According to the present invention, preferably, the processing conditions include: a temperature of 30-50℃, preferably 30-40℃, for example, 30℃, 31℃, 32℃, 33℃, 34℃, 35℃, 36℃, 37℃, 38℃, 39℃, 40℃, 41℃, 42℃, 43℃, 44℃, 45℃, 46℃, 47℃, 48℃, 49℃, 50℃, and any value within any range formed by any two of these values; and a time of 0.5-10h, preferably 0.5-8h, for example, 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h, 8.5h, 9h, 9.5h, 10h, and any value within any range formed by any two of these values. This preferred embodiment facilitates faster and better sol formation.

[0047] Preferably, the treatment is performed under static conditions.

[0048] The present invention does not particularly limit the specific conditions for drying, and can refer to conventional methods in the art. Preferably, in S4, the drying conditions include: a temperature of 70-100°C and a time of 8-48 hours.

[0049] According to the present invention, preferably, in S4, the conditions for the first calcination include: a temperature of 600-1000°C and a time of 2-6 hours.

[0050] According to the present invention, preferably, in S5, iron is loaded onto a magnesium titanate support by a co-precipitation method.

[0051] More preferably, the coprecipitation method described in S5 includes: mixing and reacting an aqueous solution containing an iron compound, a suspension containing a magnesium titanate support, and an alkaline solution to obtain a solid product, and then drying and second calcining the solid product.

[0052] According to the present invention, preferably, the amount of the iron-containing compound is such that the iron content in the prepared catalyst, based on the total weight of the catalyst and calculated as iron element, is 5-20% by weight, preferably 10-20% by weight.

[0053] This invention does not impose any particular limitation on the order in which the aqueous solution of the iron-containing compound, the suspension containing the magnesium titanate support, and the alkaline solution are added during the mixing process described in S5. They can be added separately or together. In a preferred embodiment of this invention, the aqueous solution of the iron-containing compound and the alkaline solution are added together to the suspension containing the magnesium titanate support.

[0054] According to the present invention, preferably, the reaction conditions include: a temperature of 40-70°C, a time of 3-8 hours, and a pH of 8-10.

[0055] Preferably, the reaction is carried out under stirring conditions.

[0056] The present invention does not impose a particular limitation on the stirring rate, which can be appropriately selected according to specific circumstances to accelerate the reaction process.

[0057] The present invention allows for a wide range of choices of the iron-containing compound, which can be conventional choices in the art. Preferably, the iron-containing compound is selected from at least one of ferric nitrate, ferric sulfate, and ferric chloride.

[0058] Preferably, the concentration of the alkaline solution is 0.5-10 mol / L.

[0059] The present invention allows for a wide range of choices of the alkali, including various alkalis commonly used in the art. Preferably, the alkali is an organic alkali and / or an inorganic alkali, and is more preferably selected from at least one of sodium hydroxide, sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, and ammonia water.

[0060] The present invention does not have a particular limitation on the amount of alkaline solution used, as long as the pH of the above reaction is within the above range.

[0061] Preferably, the method further includes filtering and washing the reaction product to obtain a solid product.

[0062] The present invention does not particularly limit the specific methods of filtration and washing, and can refer to conventional methods in the art.

[0063] Preferably, the preparation of the suspension containing the magnesium titanate support includes: dispersing the magnesium titanate support in water and heating it to 40-70°C to obtain the suspension containing the magnesium titanate support.

[0064] In this invention, conventional techniques such as stirring or ultrasound can be used to disperse the magnesium titanate carrier in water to achieve uniform mixing, and this invention does not have any particular limitations on this.

[0065] The present invention does not have any particular limitation on the drying described in S5, and it can be carried out with reference to conventional methods in the art, which will not be described in detail here.

[0066] The present invention does not particularly limit the second calcination, and it can be carried out with reference to conventional methods in the art. Preferably, the conditions for the second calcination include: a temperature of 550-780°C and a time of 2-5 hours.

[0067] According to the present invention, preferably, the method further includes: reducing the product of the second calcination to obtain the catalyst.

[0068] According to the present invention, preferably, the reduction conditions include: a temperature of 600-800°C and a time of 1-3 hours.

[0069] According to the present invention, preferably, the reduction is carried out in a reducing gas, which includes hydrogen and optionally an inert gas; wherein the volume content of hydrogen in the reducing gas is 10-100%.

[0070] In this invention, unless otherwise specified, "optionally" means containing or not containing, adding or not adding, or using or not using. Specifically, in the reduction step of this invention, an inert gas may or may not be added.

[0071] According to the present invention, preferably, the inert gas is selected from at least one of nitrogen, helium, argon and neon.

[0072] In this invention, the terms "first" and "second" do not limit the substances and operations, but are only used to distinguish the substances introduced in different steps and the operations performed in different stages.

[0073] The third aspect of this invention provides the application of the iron-containing catalyst described in the first aspect or the iron-containing catalyst prepared by the preparation method described in the second aspect in the ammonia decomposition for hydrogen production.

[0074] A fourth aspect of the present invention provides a method for producing hydrogen by ammonia decomposition, the method comprising: contacting ammonia with a catalyst under ammonia decomposition conditions;

[0075] The catalyst is either the catalyst described in the first aspect or an iron-containing catalyst prepared by the preparation method described in the second aspect.

[0076] In existing technologies, the temperature for ammonia decomposition reactions using catalysts without precious metals is generally above 550°C. However, the catalyst described in this invention maintains high ammonia decomposition activity even at low temperatures, with ammonia decomposition temperatures as low as 550°C. Furthermore, the ammonia decomposition reaction described in this invention can proceed at high space velocities, and it maintains high ammonia decomposition activity even after long-term evaluation experiments, indicating that the catalyst described in this invention has good stability.

[0077] According to the present invention, preferably, the conditions for the ammonia decomposition include: a temperature of 550-650°C and a volume hourly space velocity of 5000-20000 mL / (g·h).

[0078] The present invention will be described in detail below through embodiments.

[0079] In the following examples, the ammonia decomposition conversion rate formula is as follows:

[0080] Ammonia decomposition conversion rate = (raw material ammonia content - product ammonia content) / raw material ammonia content × 100%.

[0081] Example 1

[0082] 1) Prepare an anhydrous ethanol-glacial acetic acid mixed solution by mixing glacial acetic acid and anhydrous ethanol at a mass ratio of 1:1.

[0083] 2) Weigh 26.9g of tetrabutyl titanate and disperse it in 107.6g of anhydrous ethanol-glacial acetic acid mixed solution to obtain solution A.

[0084] 3) Weigh 7.7g of magnesium nitrate and disperse it in 30.8g of anhydrous ethanol-glacial acetic acid mixed solution to obtain solution B.

[0085] 4) Add the above solution B dropwise to solution A while stirring, and then place it in a 30°C water bath for 0.5 hours to obtain a sol with a pH of 3.

[0086] 5) The sol obtained in step 4) is dried at 70°C for 24 hours and then calcined at 600°C for 2 hours to obtain magnesium titanate support.

[0087] 6) Disperse 9.5g of the magnesium titanate support obtained in step 5) ultrasonically in deionized water and heat to 40℃ to obtain solution C; dissolve 2.2g of ferric nitrate in water to obtain a metal salt solution with a metal ion concentration of 0.5mol / L; add the metal salt solution and a 2mol / L sodium hydroxide solution to solution C, control the pH to 8, and stir for 3h to obtain a precipitate. Wash and dry the precipitate, and calcine it at 550℃ for 2h to obtain the calcined product. Reduce the calcined product with a mixed gas of hydrogen and nitrogen with a hydrogen integral of 15% at 700℃ for 3h to obtain 10g of catalyst. The iron content in the catalyst, calculated as elemental iron, is 5% by weight.

[0088] Example 2

[0089] 1) Prepare an anhydrous ethanol-glacial acetic acid mixed solution by mixing glacial acetic acid and anhydrous ethanol at a mass ratio of 1:1.

[0090] 2) Weigh 25.5g of tetrabutyl titanate and disperse it in 101.9g of anhydrous ethanol-glacial acetic acid mixed solution to obtain solution A.

[0091] 3) Weigh 7.3g of magnesium nitrate and disperse it in 29.2g of anhydrous ethanol-glacial acetic acid mixed solution to obtain solution B.

[0092] 4) Add solution B dropwise to solution A while stirring, then place the solution in a 30°C water bath and let it stand for 0.5 hours to obtain a sol with a pH of 3.

[0093] 5) The sol obtained in step 4) is dried at 70°C for 24 hours and then calcined at 600°C for 2 hours to obtain magnesium titanate support.

[0094] 6) Disperse 9g of the magnesium titanate support obtained in step 5) ultrasonically in deionized water and heat to 40℃ to obtain solution C; dissolve 4.3g of ferric nitrate in water to obtain a metal salt solution with a metal ion concentration of 0.5mol / L; add the obtained metal salt solution and a 2mol / L sodium hydroxide solution to solution C, control the pH to 8, and stir for 3h to obtain a precipitate. Wash and dry the precipitate, and calcine it at 550℃ for 2h to obtain the calcined product. Reduce the calcined product with a mixed gas of hydrogen and nitrogen with a hydrogen integral of 15% at 700℃ for 3h to obtain 10g of catalyst. The iron content in the catalyst, calculated as elemental iron, is 10% by weight.

[0095] Example 3

[0096] 1) Prepare an anhydrous ethanol-glacial acetic acid mixed solution by mixing glacial acetic acid and anhydrous ethanol at a mass ratio of 2:3.

[0097] 2) Weigh 24.1g of tetrabutyl titanate and disperse it in 96.3g of anhydrous ethanol-glacial acetic acid mixed solution to obtain solution A.

[0098] 3) Weigh 4.4g of magnesium chloride and disperse it in 17.6g of anhydrous ethanol-glacial acetic acid mixed solution to obtain solution B.

[0099] 4) Add solution B dropwise to solution A while stirring, then place the solution in a 30°C water bath and let it stand for 0.5 hours to obtain a sol with a pH of 4.

[0100] 5) The sol obtained in step 4) is dried at 70°C for 24 hours and then calcined at 600°C for 4 hours to obtain magnesium titanate support.

[0101] 6) Disperse 8.5g of the magnesium titanate support obtained in step 5) ultrasonically in deionized water and heat to 40℃ to obtain solution C; dissolve 6.5g of ferric nitrate in water to obtain a metal salt solution with a metal ion concentration of 0.5mol / L; add the metal salt solution and a 2.0mol / L sodium hydroxide solution to solution C, control the pH to 8, and stir for 3h to obtain a precipitate. Wash and dry the precipitate, and calcine it at 600℃ for 2h to obtain the calcined product. Reduce the calcined product with a mixed gas of hydrogen and nitrogen with a hydrogen integral of 30% at 800℃ for 3h to obtain 10g of catalyst. The iron content in the catalyst, calculated as elemental iron, is 15% by weight.

[0102] Example 4

[0103] 1) Prepare an anhydrous ethanol-glacial acetic acid mixed solution by mixing glacial acetic acid and anhydrous ethanol at a mass ratio of 1:1.

[0104] 2) Weigh 22.7g of tetrabutyl titanate and disperse it in 90.6g of anhydrous ethanol-glacial acetic acid mixed solution to obtain solution A.

[0105] 3) Weigh 6.5g of magnesium nitrate and disperse it in 25.9g of anhydrous ethanol-glacial acetic acid mixed solution to obtain solution B.

[0106] 4) Add solution B dropwise to solution A while stirring, then place the solution in a 35°C water bath and let it stand for 0.5 hours to obtain a sol with a pH of 3.

[0107] 5) The sol obtained in step 4) is dried at 70°C for 24 hours and then calcined at 650°C for 2 hours to obtain magnesium titanate support.

[0108] 6) Disperse 8g of the magnesium titanate support obtained in step 5) ultrasonically in deionized water and heat to 40℃ to obtain solution C. Dissolve 8.7g of ferric nitrate in water to obtain a metal salt solution with a metal ion concentration of 0.5mol / L. Add the metal salt solution and a 2mol / L sodium hydroxide solution to solution C, control the pH to 9, and stir for 3h to obtain a precipitate. Wash and dry the precipitate, and calcine it at 550℃ for 4h to obtain the calcined product. Reduce the calcined product with a mixed gas of hydrogen and nitrogen (hydrogen integral of 15%) at 600℃ for 5h to obtain 10g of catalyst. The iron content in the catalyst, calculated as elemental iron, is 20% by weight.

[0109] Example 5

[0110] 1) Prepare a propanol-glacial acetic acid mixed solution by mixing glacial acetic acid and propanol in a mass ratio of 2:3.

[0111] 2) Weigh 24.1g of tetrabutyl titanate and disperse it in 168.5g of a mixture of propanol and glacial acetic acid to obtain solution A.

[0112] 3) Weigh 6.9g of magnesium nitrate and disperse it in 27.5g of propanol-glacial acetic acid mixed solution to obtain solution B.

[0113] 4) Add solution B dropwise to solution A while stirring, then place the solution in a 40°C water bath and let it stand for 5 hours to obtain a sol with a pH of 3.8.

[0114] 5) The sol obtained in step 4) is dried at 70°C for 24 hours and then calcined at 600°C for 2 hours to obtain magnesium titanate support.

[0115] 6) Disperse 8.5g of magnesium titanate obtained in step 5) ultrasonically in deionized water and heat to 40℃ to obtain solution C; dissolve 6.5g of ferric nitrate in water to obtain a metal salt solution with a metal ion concentration of 0.5mol / L; add the metal salt solution and a 2mol / L sodium hydroxide solution to solution C, control the pH to 8, and stir for 3h to obtain a precipitate. Wash and dry the precipitate, and calcine it at 550℃ for 2h to obtain a calcined product. Reduce the calcined product with a mixed gas of hydrogen and nitrogen with a hydrogen integral of 15% at 700℃ for 3h to obtain 10g of catalyst. The iron content in the catalyst, calculated as elemental iron, is 15% by weight.

[0116] Example 6

[0117] 1) Prepare an anhydrous ethanol-glacial acetic acid mixed solution by mixing glacial acetic acid and anhydrous ethanol at a mass ratio of 1:2.

[0118] 2) Weigh 24.1g of tetrabutyl titanate and disperse it in 240.7g of anhydrous ethanol-glacial acetic acid mixed solution to obtain solution A.

[0119] 3) Weigh 6.9g of magnesium nitrate and disperse it in 27.5g of anhydrous ethanol-glacial acetic acid mixed solution to obtain solution B.

[0120] 4) Add solution B dropwise to solution A while stirring, then place the solution in a 30°C water bath and let it stand for 7.5 hours to obtain a sol with a pH of 4.7.

[0121] 5) The sol obtained in step 4) is dried at 70°C for 24 hours and then calcined at 600°C for 2 hours to obtain magnesium titanate support.

[0122] 6) Disperse 8.5g of the magnesium titanate support obtained in step 5) ultrasonically in deionized water and heat to 40℃ to obtain solution C; dissolve 6.5g of ferric nitrate in water to obtain a metal salt solution with a metal ion concentration of 0.5mol / L; add the metal salt solution and a 2mol / L sodium hydroxide solution to solution C, control the pH to 8, and stir for 6h to obtain a precipitate. Wash and dry the precipitate, and calcine it at 550℃ for 2h to obtain the calcined product. Reduce the calcined product with a mixed gas of hydrogen and nitrogen with a hydrogen integral of 40% at 700℃ for 3h to obtain 10g of catalyst. The iron content in the catalyst, calculated as elemental iron, is 15% by weight.

[0123] Example 7

[0124] 1) Prepare an anhydrous ethanol-glacial acetic acid mixed solution by mixing glacial acetic acid and anhydrous ethanol at a mass ratio of 1:1.

[0125] 2) Weigh 18.03g of ethyl titanate and disperse it in 72.1g of anhydrous ethanol-glacial acetic acid mixed solution to obtain solution A.

[0126] 3) Weigh 6.9g of magnesium nitrate and disperse it in 82.6g of anhydrous ethanol-glacial acetic acid mixed solution to obtain solution B.

[0127] 4) Add solution B dropwise to solution A while stirring, then place the solution in a 30°C water bath and let it stand for 0.5 hours to obtain a sol with a pH of 3.

[0128] 5) The sol obtained in step 4) is dried at 70°C for 24 hours and then calcined at 600°C for 2 hours to obtain magnesium titanate support.

[0129] 6) Disperse 8.5g of the magnesium titanate support obtained in step 5) ultrasonically in deionized water and heat to 40℃ to obtain solution C; dissolve 6.5g of ferric nitrate in water to obtain a metal salt solution with a metal ion concentration of 0.5mol / L; add the metal salt solution and a 2mol / L sodium hydroxide solution to solution C, control the pH to 10, and stir for 5h to obtain a precipitate. Wash and dry the precipitate, and calcine it at 550℃ for 2h to obtain the calcined product. Reduce the calcined product with a mixed gas of hydrogen and nitrogen with a hydrogen integral of 15% at 700℃ for 3h to obtain 10g of catalyst. The iron content in the catalyst, calculated as elemental iron, is 15% by weight.

[0130] Example 8

[0131] 1) Prepare an anhydrous ethanol-glacial acetic acid mixed solution by mixing glacial acetic acid and anhydrous ethanol at a mass ratio of 1:1.

[0132] 2) Weigh 24.1g of tetrabutyl titanate and disperse it in 168.5g of anhydrous ethanol-glacial acetic acid mixed solution to obtain solution A.

[0133] 3) Weigh 6.9g of magnesium nitrate and disperse it in 137.7g of anhydrous ethanol-glacial acetic acid mixed solution to obtain solution B.

[0134] 4) Add solution B dropwise to solution A while stirring, then place the solution in a 30°C water bath and let it stand for 4 hours to obtain a sol with a pH of 3.

[0135] 5) The sol obtained in step 4) is dried at 70°C for 24 hours and then calcined at 600°C for 2 hours to obtain magnesium titanate support.

[0136] 6) Disperse 8.5g of the magnesium titanate support obtained in step 5) ultrasonically in deionized water and heat to 40℃ to obtain solution C; dissolve 6.5g of ferric nitrate in water to obtain a metal salt solution with a metal ion concentration of 0.5mol / L; add the metal salt solution and a 2mol / L sodium hydroxide solution to solution C, control the pH to 8, and stir for 3h to obtain a precipitate. Wash and dry the precipitate, and calcine it at 550℃ for 2h to obtain the calcined product. Reduce the calcined product with a mixed gas of hydrogen and nitrogen with a hydrogen integral of 15% at 700℃ for 3h to obtain 10g of catalyst. The iron content in the catalyst, calculated as elemental iron, is 15% by weight.

[0137] Example 9

[0138] The procedure was carried out according to Example 2, except that in step 1), glacial acetic acid and anhydrous ethanol were mixed in a mass ratio of 2:1 to obtain an anhydrous ethanol-glacial acetic acid mixed solution, resulting in a sol pH of 2. The catalyst was then obtained.

[0139] Example 10

[0140] The procedure was carried out according to Example 2, except that the water bath temperature in step 4) was 55°C. The catalyst was then obtained.

[0141] Example 11

[0142] The procedure was carried out according to Example 2, except that the magnesium titanate support was prepared using existing techniques, specifically including:

[0143] 1) Weigh 25.5g of tetrabutyl titanate and disperse it in 65.5g of glacial acetic acid to obtain solution A.

[0144] 2) Weigh 7.3g of magnesium nitrate and disperse it in 65.6g of anhydrous ethanol to obtain solution B.

[0145] 3) Add solution A dropwise to solution B while stirring, and then place the mixture in a 30°C water bath to stand and obtain a sol.

[0146] Comparative Example 1

[0147] The method was carried out according to Example 2, except that instead of using magnesium titanate as a support, titanium dioxide was used as the support, i.e.:

[0148] 8.5 g of titanium dioxide was ultrasonically dispersed in deionized water and heated to 40 °C to obtain a base solution. 6.5 g of ferric nitrate was dissolved in water to obtain a metal salt solution with a metal ion concentration of 0.5 mol / L. The metal salt solution obtained in step 2) and a sodium hydroxide solution with a concentration of 2 mol / L were added to the base solution obtained in step 1), the pH was controlled at 8, and the mixture was stirred for 3 h to obtain a precipitate. The precipitate obtained in step 3) was washed, dried, and calcined at 550 °C for 2 h to obtain a calcined product. The calcined product was reduced with a mixture of hydrogen and nitrogen gas with a hydrogen integral of 15% at 700 °C for 3 h to obtain 10 g of catalyst. The iron content in the catalyst, calculated as elemental iron, was 15% by weight.

[0149] Comparative Example 2

[0150] The procedure was carried out according to Example 2, except that in step 3), instead of adding magnesium nitrate, an equimolar amount of barium nitrate was added to obtain 10 g of catalyst. The iron content of the catalyst, calculated as iron element, was 10% by weight.

[0151] Test Example 1

[0152] The activity of the catalyst was evaluated using ammonia nitrogen gas with an ammonia concentration of 15% by volume at different temperatures. 1 g of 40-60 mesh catalyst and 4 g of 40-60 mesh quartz sand were mixed and packed together, and the volume hourly space velocity was 15000 mL / (g·h). The results after 6 h of reaction are shown in Table 1.

[0153] Table 1

[0154]

[0155]

[0156] As can be seen from the results in Table 2, under the same reaction conditions, the catalyst described in this invention has a significantly higher ammonia decomposition conversion rate when applied to the ammonia decomposition hydrogen production reaction.

[0157] Meanwhile, compared with the comparative example, the example showed a significantly higher ammonia decomposition conversion rate at 550°C, indicating that the catalyst described in this invention has high ammonia decomposition activity at low temperatures.

[0158] Meanwhile, at higher space velocities, the examples exhibit significantly higher ammonia decomposition conversion rates compared to the comparative examples, indicating that the catalyst described in this invention has better stability.

[0159] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for producing hydrogen by ammonia decomposition, the method comprising: Under conditions of ammonia decomposition, ammonia is brought into contact with a catalyst; The temperature for ammonia decomposition is 550-650℃, and the space velocity is 5000-20000mL / (g·h); The catalyst is an iron-containing catalyst; the iron-containing catalyst comprises a magnesium titanate support and iron elements supported on the magnesium titanate support; Based on the total weight of the catalyst, the iron content is 5-20% by weight.

2. The method according to claim 1, wherein, Based on the total weight of the catalyst, the iron content is 10-20% by weight.

3. The method according to claim 1, wherein, The preparation method of the iron-containing catalyst includes the following steps: S1. Dissolve the titanium source in a mixed solution of alcohol and glacial acetic acid to obtain solution A; S2. Dissolve the magnesium source in a mixed solution of alcohol and glacial acetic acid to obtain solution B; S3. Add solution B to solution A and then process it to obtain a sol, the pH of which is 1.5-5; S4. The sol obtained in step S3 is dried and subjected to a first calcination to obtain a magnesium titanate support. S5. Load iron onto a magnesium titanate support.

4. The method according to claim 3, wherein, In S1, the mass ratio of the titanium source to the alcohol-glacial acetic acid mixed solution is 1:4-10.

5. The method according to claim 3, wherein, The titanium source is a water-soluble titanium-containing compound.

6. The method according to claim 5, wherein, The titanium source is selected from at least one of tetrabutyl titanate, ethyl titanate, and isopropyl titanate.

7. The method according to claim 3, wherein, In S2, the mass ratio of the magnesium source to the alcohol-glacial acetic acid mixed solution is 1:4-20.

8. The method according to claim 3, wherein, The magnesium source is a soluble magnesium salt.

9. The method according to claim 3, wherein, In the alcohol-glacial acetic acid mixed solutions described in S1 and S2, the mass ratio of glacial acetic acid to alcohol is independently 1:0.5-2.

10. The method according to claim 3, wherein, The alcohols described in S1 and S2 are each independently C1-C5 alcohols.

11. The method according to claim 10, wherein, The alcohols mentioned in S1 and S2 are each independently selected from at least one of methanol, ethanol, and propanol.

12. The method according to claim 3, wherein, In S3, the pH of the sol is 3-5.

13. The method according to claim 3, wherein, The processing conditions described in S3 include: a temperature of 30-50℃ and a time of 0.5-10h.

14. The method according to any one of claims 3-13, wherein, In S4, the drying conditions include a temperature of 70-100°C and a time of 8-48 hours.

15. The method according to any one of claims 3-13, wherein, In S4, the conditions for the first calcination include: a temperature of 600-1000℃ and a time of 2-6 hours.

16. The method according to any one of claims 3-13, wherein, In S5, iron is loaded onto a magnesium titanate support using a co-precipitation method.

17. The method according to claim 16, wherein, The coprecipitation method described in S5 includes: mixing and reacting an aqueous solution containing an iron compound, a suspension containing a magnesium titanate support, and an alkaline solution to obtain a solid product, and then drying and second-calcining the solid product. The reaction conditions include: a temperature of 40-70℃, a time of 3-8h, and a pH of 8-10; The conditions for the second roasting include: a temperature of 550-780℃ and a time of 2-5 hours.

18. The method according to claim 17, wherein, The method further includes: reducing the product from the second calcination to obtain the catalyst; The reduction conditions include: a temperature of 600-800℃ and a time of 1-3 hours; The reduction is carried out in a reducing gas, which includes hydrogen and optionally an inert atmosphere; the hydrogen volume content in the reducing gas is 10-100%.

19. The method according to claim 18, wherein, The inert atmosphere is selected from at least one of nitrogen, helium, argon and neon.

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