Magnesium titanate catalysts, their preparation methods and applications, and methods for hydrogen production from ammonia decomposition.

Abstract

This invention relates to the field of ammonia decomposition catalyst preparation, and discloses a magnesium titanate catalyst, its preparation method and application, as well as a method for ammonia decomposition to produce hydrogen. A magnesium titanate catalyst contains a magnesium titanate support and an active component, wherein the active component includes noble metals and non-noble metals, and the non-noble metals are selected from Group VIII metals; based on the total weight of the catalyst, the content of the active component, calculated by metal element, is 0.5-20% by weight; wherein, calculated by metal element, the mass ratio of noble metals to non-noble metals is 1:5-25. This catalyst exhibits high activity and, when applied to ammonia decomposition to produce hydrogen, demonstrates a high ammonia decomposition conversion rate.

Description

Technical Field

[0001] This invention relates to the field of ammonia decomposition catalyst preparation, specifically to a magnesium titanate catalyst, its preparation method and application, and a method for ammonia decomposition to produce hydrogen. 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, 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, a hydrogen-rich carrier, as a feedstock for carbon-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] Currently, ruthenium is the most active catalyst for ammonia decomposition, but its high price and the resulting catalyst preparation cost are significant. Therefore, improving the utilization rate of ruthenium atoms is crucial. Studies have found that the stability of ruthenium is highly correlated with the acidity / basicity and conductivity of the support. Extensive research has been conducted on noble metal ammonia decomposition catalysts. For example, CN115920942A discloses a Ru-based catalyst comprising a MOF-74-coated ZIF-8 or ZIF-67 support, with ruthenium as the active component and barium, lanthanum, and cesium as the promoter components, or a combination thereof. Although a stable reaction temperature of 500℃ was adopted, the poor dispersion of the promoter on the support surface easily leads to the formation of large particles, resulting in poor ammonia decomposition activity at low temperatures. Summary of the Invention

[0004] The purpose of this invention is to overcome the problem that the activity of existing ammonia decomposition catalysts needs further improvement, and to provide a magnesium titanate catalyst, its preparation method and application, as well as a method for ammonia decomposition to produce hydrogen. This catalyst exhibits high activity and achieves a high ammonia decomposition conversion rate when applied to ammonia decomposition to produce hydrogen.

[0005] To achieve the above objectives, the present invention provides a magnesium titanate catalyst, wherein the catalyst contains a magnesium titanate support and an active component, wherein the active component includes noble metals and non-noble metals, and the non-noble metals are selected from Group VIII metal elements; based on the total weight of the catalyst, the content of the active component, calculated by metal element, is 0.5-20% by weight.

[0006] The mass ratio of the precious metal to the non-precious metal, calculated by metallic elements, is 1:5-25.

[0007] A second aspect of the present invention provides a method for preparing a magnesium titanate 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 it to obtain a sol, the pH of which 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 the active component onto a magnesium titanate support, wherein the active component includes noble metals and non-noble metals, and the non-noble metals are selected from Group VIII metal elements.

[0013] The third aspect of this invention provides the application of the magnesium titanate catalyst described in the first aspect or the magnesium titanate 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 the magnesium titanate catalyst prepared by the preparation method described in the second aspect.

[0016] Compared with the prior art, the beneficial effects of the present invention include:

[0017] The magnesium titanate catalyst provided by this invention uses magnesium titanate as a support, which can adjust the electron transfer capacity between the active component and the support, regulate the adsorption and desorption intensity of NH3 on the catalyst surface, promote the transfer of NH3 between the active site and the support, and improve catalytic activity. The use of active components containing both noble and non-noble metals in combination with the magnesium titanate support results in high ammonia decomposition activity of the catalyst at low temperatures. Furthermore, controlling the content of the active component within the range of 1-15% by weight is beneficial for enhancing the interaction between the active component and the support, effectively weakening the interaction between the active component and ammonia decomposition products, thereby promoting the desorption of nitrogen and hydrogen, ultimately resulting in excellent catalytic performance.

[0018] The catalyst provided by this invention has a low precious metal content, controls raw material costs, 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 present invention provides a magnesium titanate catalyst, wherein the catalyst contains a magnesium titanate support and an active component, wherein the active component includes noble metals and non-noble metals, wherein the non-noble metals are selected from group VIII metal elements; based on the total weight of the catalyst, the content of the active component is 0.5-20% by weight in terms of metal elements;

[0021] The mass ratio of the precious metal to the non-precious metal, calculated by metallic elements, is 1:5-25.

[0022] In this invention, based on the total weight of the catalyst and calculated by metal element, the content of the active component is 0.5-20% by weight, preferably 1-15% by weight, for example, it can be 0.5% by weight, 1% by weight, 1.5% by weight, 2% by weight, 2.5% by weight, 3% by weight, 3.5% by weight, 4% by weight, 5% by weight, 5.5% by weight, 6% by weight, 6.5% by weight, 7% by weight, 7.5% by weight, 8% by weight, 8.5% by weight, 9% by weight, 9.5% by weight, etc. The concentrations are 10 wt%, 10.5 wt%, 11 wt%, 11.5 wt%, 12 wt%, 12.5 wt%, 13 wt%, 13.5 wt%, 14 wt%, 14.5 wt%, 15 wt%, 15.5 wt%, 16 wt%, 16.5 wt%, 17 wt%, 17.5 wt%, 18 wt%, 18.5 wt%, 19 wt%, 19.5 wt%, 20 wt%, and any value within the range formed by any two of these values. Controlling the content of the active component within the above range is beneficial for enhancing the interaction between the active component and the support, effectively weakening the interaction between the active component and ammonia decomposition products, thereby promoting the desorption of nitrogen and hydrogen.

[0023] The total content of all components in the catalyst described in this invention is 100%.

[0024] In this invention, the mass ratio of the precious metal to the non-precious metal, based on metallic elements, is 1:5-25, preferably 1:10-20. For example, it can be 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, 1:20, or any value within the range formed by any two of these values. This preferred embodiment facilitates the dispersion of the precious metal and enhances the interaction between the precious and non-precious metals; simultaneously, it uses a smaller amount of precious metal, saving costs.

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

[0026] Preferably, the content of the precious metal is 0.03-1% by weight, more preferably 0.03-0.8% by weight. Using this preferred embodiment, the catalyst of the present invention still exhibits high ammonia decomposition activity at low temperatures even with a low precious metal content. Furthermore, the amount of precious metal used is small, saving costs.

[0027] The present invention does not particularly limit the type of precious metal, and can use conventional choices in the art. Preferably, the precious metal is ruthenium and / or palladium.

[0028] The present invention allows for a wide range of selections of the non-precious metals. Preferably, the non-precious metal is selected from at least one of iron, cobalt, and nickel, with nickel being the most preferred. This preferred embodiment facilitates the interaction between the precious and non-precious metals, improving the catalyst activity and reducing the activation energy for nitrogen desorption.

[0029] A second aspect of the present invention provides a method for preparing a magnesium titanate catalyst, the method comprising the following steps:

[0030] S1. Dissolve the titanium source in a mixed solution of alcohol and glacial acetic acid to obtain solution A;

[0031] S2. Dissolve the magnesium source in a mixed solution of alcohol and glacial acetic acid to obtain solution B;

[0032] S3. Add solution B to solution A and then process it to obtain a sol, the pH of which is 1.5-5;

[0033] S4. The sol obtained in step S3 is dried and subjected to a first calcination to obtain a magnesium titanate support.

[0034] S5. Load the active component onto a magnesium titanate support, wherein the active component includes noble metals and non-noble metals, and the non-noble metals are selected from Group VIII metal elements.

[0035] The preparation method provided by this invention first uses a sol-gel method to prepare a magnesium titanate support, and then loads the active component onto the magnesium titanate support, resulting in a magnesium titanate-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 act as solvents, inhibiting the hydrolysis of the titanium source and improving 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 promotes the synergistic effect between the magnesium titanate support and the active component, thereby improving the catalyst activity.

[0036] 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.

[0037] According to the present invention, preferably, in S1, the mass ratio of the titanium source to the alcohol-glacial acetic acid mixed solution is 1:2-15, more preferably 1:4-10. This preferred embodiment facilitates the rapid formation of a uniform sol.

[0038] 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.

[0039] 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, more preferably 1:4-15. This preferred embodiment facilitates the rapid formation of a uniform sol.

[0040] 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.

[0041] 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.

[0042] The present invention does not particularly limit the amount of glacial acetic acid and alcohol used, as long as the sol with the above-mentioned pH is obtained. Preferably, in the alcohol-glacial acetic acid mixed solution in S1 and S2, the mass ratio of glacial acetic acid to alcohol is independently 1:0.1-2, preferably 1:1-2.

[0043] 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 described in S1 and S2 are C1-C5 alcohols, and are more preferably selected from at least one of methanol, ethanol, and propanol.

[0044] 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.

[0045] According to one specific embodiment of the present invention, solution B is added dropwise to solution A while stirring.

[0046] 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.

[0047] According to the present invention, preferably, the processing conditions include: a temperature of 30-50°C, more preferably 30-40°C; and a time of 0.5-10 hours, more preferably 0.5-8 hours. This preferred embodiment facilitates faster and better sol formation.

[0048] Preferably, the treatment is performed under static conditions.

[0049] The present invention does not particularly limit the specific drying conditions, and can refer to conventional methods in the art. Preferably, in step S4, the drying conditions include: a temperature of 70-100°C and a time of 8-48 hours.

[0050] According to the present invention, preferably, in step S4, the conditions for the first calcination include: a temperature of 600-1000°C and a time of 2-6 hours.

[0051] According to the present invention, preferably, in S5, the active component is loaded onto the magnesium titanate support by a co-precipitation method.

[0052] According to the present invention, preferably, the coprecipitation method described in S5 includes: mixing and reacting an aqueous solution containing an active component salt, 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.

[0053] This invention does not impose any particular limitation on the order in which the aqueous solution containing the active component salt, 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 containing the active component salt 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] Preferably, the concentration of the alkaline solution is 0.5-10 mol / L.

[0058] 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.

[0059] 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.

[0060] Preferably, the method further includes filtering and washing the reaction product to obtain a solid product.

[0061] The present invention does not particularly limit the specific methods of filtration and washing, and can refer to conventional methods in the art.

[0062] 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.

[0063] 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.

[0064] According to the present invention, preferably, the active component salt includes non-precious metal salts and precious metal salts.

[0065] The present invention allows for a wide range of selections of the non-precious metal salts and precious metal salts, which can be conventional choices in the art. Preferably, the non-precious metal salt and precious metal salt are each independently a nitrate and / or a hydrochloride.

[0066] According to the present invention, preferably, the amount of the active component salt is such that, based on the total weight of the catalyst and calculated by metal elements, the content of the active component in the prepared catalyst is 0.5-20% by weight, preferably 1-15% by weight.

[0067] According to the present invention, preferably, the amount of non-precious metal salt and precious metal salt is such that, in the prepared catalyst, the mass ratio of the precious metal to the non-precious metal, based on the metal element, is 1:5-25, preferably 1:10-20.

[0068] The present invention does not particularly limit the type of precious metal, and can use conventional choices in the art. Preferably, the precious metal is ruthenium and / or palladium.

[0069] The present invention has a wide range of choices for the types of non-precious metals. Preferably, the non-precious metals are selected from at least one of iron, cobalt and nickel, with nickel being the most preferred.

[0070] 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.

[0071] 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.

[0072] Preferably, the method further includes: reducing the product from the second calcination to obtain a catalyst.

[0073] Preferably, the reduction conditions include: a temperature of 600-800℃ and a time of 1-3 hours.

[0074] Preferably, the reduction is carried out in a reducing gas, which includes hydrogen and optionally an inert gas; in the reducing gas, the volume content of hydrogen is 10-100%.

[0075] 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.

[0076] Preferably, the inert gas is selected from at least one of nitrogen, helium, argon and neon, and is preferably nitrogen.

[0077] 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.

[0078] The third aspect of this invention provides the application of the magnesium titanate catalyst described in the first aspect or the magnesium titanate catalyst prepared by the preparation method described in the second aspect in the ammonia decomposition for hydrogen production.

[0079] 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;

[0080] The catalyst is either the catalyst described in the first aspect or the magnesium titanate catalyst prepared by the preparation method described in the second aspect.

[0081] While existing noble metal-containing catalysts can decompose ammonia at low temperatures, their ammonia decomposition activity is poor, and the reaction temperature is generally not lower than 550°C. In contrast, the catalyst described in this invention exhibits high ammonia decomposition activity even at low temperatures, with ammonia decomposition temperatures as low as 500°C.

[0082] Preferably, the conditions for ammonia decomposition include: a temperature of 500-650℃ and a volume hourly space velocity of 5000-20000 mL / (g·h).

[0083] The present invention will be described in detail below through embodiments.

[0084] In the following examples, the ammonia decomposition conversion rate formula is as follows:

[0085] Ammonia decomposition conversion rate = (raw material ammonia content - product ammonia content) / raw material ammonia content × 100%.

[0086] Example 1

[0087] 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.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 6) 8.5 g of the magnesium titanate support obtained in step 5) was ultrasonically dispersed in deionized water and heated to 40 °C to obtain solution C. 3.15 g of nickel chloride and 146.6 mg of ruthenium chloride were dissolved in water to obtain a metal salt solution with a total metal ion concentration of 0.5 mol / L. The metal salt solution and a 2 mol / L sodium hydroxide solution were added to solution C, the pH was controlled at 8, and the mixture was stirred for 3 h to obtain a precipitate. The precipitate was washed, dried, and calcined at 550 °C for 2 h to obtain the calcined product. The calcined product was reduced with a mixed gas of hydrogen and nitrogen (15% hydrogen integral) at 700 °C for 3 h to obtain 10 g of catalyst. The catalyst composition and characteristic parameters are shown in Table 1.

[0093] Example 2

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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 2.10g of nickel chloride and 97.7mg of ruthenium chloride 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 catalyst composition and characteristic parameters are shown in Table 1.

[0100] Example 3

[0101] 1) Prepare a propanol-glacial acetic acid mixed solution by mixing glacial acetic acid and propanol in a mass ratio of 2:3.

[0102] 2) Weigh 26.9g of tetrabutyl titanate and disperse it in 107.6g of a mixture of propanol and glacial acetic acid to obtain solution A.

[0103] 3) Weigh 7.7g of magnesium nitrate and disperse it in 30.8g of a propanol-glacial acetic acid mixed solution to obtain solution B.

[0104] 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 1 hour to obtain a sol with a pH of 4.

[0105] 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.

[0106] 6) 9.5 g of the magnesium titanate support obtained in step 5) was ultrasonically dispersed in deionized water and heated to 40 °C to obtain solution C. 1.05 g of nickel chloride and 48.9 mg of ruthenium chloride were dissolved in water to obtain a metal salt solution with a total metal ion concentration of 0.5 mol / L. The metal salt solution and a 2.0 mol / L sodium hydroxide solution were added to solution C, the pH was controlled at 8, and the mixture was stirred for 3 h to obtain a precipitate. The precipitate was washed, dried, and calcined at 550 °C for 2 h to obtain the calcined product. The calcined product was reduced with a mixed gas of hydrogen and nitrogen (hydrogen integral of 15%) at 700 °C for 3 h to obtain 10 g of catalyst. The catalyst composition and characteristic parameters are shown in Table 1.

[0107] Example 4

[0108] 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.

[0109] 2) Weigh 28.0g of tetrabutyl titanate and disperse it in 112g of anhydrous ethanol-glacial acetic acid mixed solution to obtain solution A.

[0110] 3) Weigh 8.0g of magnesium nitrate and disperse it in 32g of anhydrous ethanol-glacial acetic acid mixed solution to obtain solution B.

[0111] 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.

[0112] 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.

[0113] 6) 9.9 g of the magnesium titanate support obtained in step 5) was ultrasonically dispersed in deionized water and heated to 50 °C to obtain solution C. 210.3 mg of nickel chloride and 9.7 mg of ruthenium chloride were dissolved in water to obtain a metal salt solution with a total metal ion concentration of 0.5 mol / L. The metal salt solution and a 2 mol / L sodium hydroxide solution were added to solution C, the pH was controlled at 8, and the mixture was stirred for 3 h to obtain a precipitate. The precipitate was washed, dried, and calcined at 550 °C for 2 h to obtain the calcined product. The calcined product was reduced with a mixed gas of hydrogen and nitrogen (15% hydrogen integral) at 700 °C for 3 h to obtain 10 g of catalyst. The catalyst composition and characteristic parameters are shown in Table 1.

[0114] Example 5

[0115] 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.

[0116] 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.

[0117] 3) Weigh 4.9g of magnesium chloride and disperse it in 19.8g of anhydrous ethanol-glacial acetic acid mixed solution to obtain solution B.

[0118] 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.

[0119] 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.

[0120] 6) Disperse 8.5g of magnesium titanate obtained in step 5) ultrasonically in deionized water and heat to 40℃ to obtain solution C; dissolve 1.04g of nickel chloride and 64.1mg of ruthenium chloride in water to obtain a metal salt solution with a total 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 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 15% at 700℃ for 3h to obtain 10g of catalyst. The catalyst composition and characteristic parameters are shown in Table 1.

[0121] Example 6

[0122] 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.

[0123] 2) Weigh 18g of ethyl titanate and disperse it in 107.6g of anhydrous ethanol-glacial acetic acid mixed solution to obtain solution A.

[0124] 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.

[0125] 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 5 hours to obtain a sol with a pH of 3.

[0126] 5) The sol obtained in step 4) is dried at 70°C for 24 hours and then calcined at 800°C for 2 hours to obtain magnesium titanate support.

[0127] 6) 9.5 g of the magnesium titanate support obtained in step 5) was ultrasonically dispersed in deionized water and heated to 40 °C to obtain solution C. 1 g of nickel chloride and 93.3 mg of ruthenium chloride were dissolved in water to obtain a metal salt solution with a total metal ion concentration of 0.5 mol / L. The metal salt solution and a 2 mol / L sodium hydroxide solution were added to solution C, and the pH was controlled at 8. The mixture was stirred for 3 h to obtain a precipitate. The precipitate was washed, dried, and calcined at 550 °C for 2 h to obtain the calcined product. The calcined product was reduced with a mixed gas of hydrogen and nitrogen (15% hydrogen integral) at 700 °C for 3 h to obtain 10 g of catalyst. The catalyst composition and characteristic parameters are shown in Table 1.

[0128] Example 7

[0129] 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.

[0130] 2) Weigh 26.9g of tetrabutyl titanate and disperse it in 188.3g of anhydrous ethanol-glacial acetic acid mixed solution to obtain solution A.

[0131] 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.

[0132] 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 4 hours to obtain a sol with a pH of 3.

[0133] 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.

[0134] 6) 8.5 g of the magnesium titanate support obtained in step 5) was ultrasonically dispersed in deionized water and heated to 40 °C to obtain solution C. 1.04 g of nickel chloride and 64.1 mg of ruthenium chloride were dissolved in water to obtain a metal salt solution with a total metal ion concentration of 0.5 mol / L. The metal salt solution and a 2 mol / L sodium hydroxide solution were added to solution C, the pH was controlled at 8, and the mixture was stirred for 3 h to obtain a precipitate. The precipitate was washed, dried, and calcined at 550 °C for 2 h to obtain the calcined product. The calcined product was reduced with a mixed gas of hydrogen and nitrogen (hydrogen integral of 15%) at 700 °C for 3 h to obtain 10 g of catalyst. The catalyst composition and characteristic parameters are shown in Table 1.

[0135] Example 8

[0136] 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.

[0137] 2) Weigh 26.9g of tetrabutyl titanate and disperse it in 269g of anhydrous ethanol-glacial acetic acid mixed solution to obtain solution A.

[0138] 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.

[0139] 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 3.

[0140] 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.

[0141] 6) 8.5 g of the magnesium titanate support obtained in step 5) was ultrasonically dispersed in deionized water and heated to 40 °C to obtain solution C. 1.04 g of nickel chloride and 64.1 mg of ruthenium chloride were dissolved in water to obtain a metal salt solution with a total metal ion concentration of 0.5 mol / L. The metal salt solution and a 2 mol / L sodium hydroxide solution were added to solution C, the pH was controlled at 9, and the mixture was stirred for 3 h to obtain a precipitate. The precipitate was washed, dried, and calcined at 550 °C for 2 h to obtain the calcined product. The calcined product was reduced with a mixed gas of hydrogen and nitrogen (20% hydrogen integral) at 800 °C for 3 h to obtain 10 g of catalyst. The catalyst composition and characteristic parameters are shown in Table 1.

[0142] Example 9

[0143] 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.

[0144] 2) Weigh 26.9g of tetrabutyl titanate and disperse it in 188.3g of anhydrous ethanol-glacial acetic acid mixed solution to obtain solution A.

[0145] 3) Weigh 7.7g of magnesium nitrate and disperse it in 92.4g of anhydrous ethanol-glacial acetic acid mixed solution to obtain solution B.

[0146] 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.

[0147] 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.

[0148] 6) 8.5 g of the magnesium titanate support obtained in step 5) was ultrasonically dispersed in deionized water and heated to 40 °C to obtain solution C. 1.04 g of nickel chloride and 64.1 mg of ruthenium chloride were dissolved in water to obtain a metal salt solution with a total metal ion concentration of 0.5 mol / L. The metal salt solution and a 2 mol / L sodium hydroxide solution were added to solution C, the pH was controlled at 8, and the mixture was stirred for 3 h to obtain a precipitate. The precipitate was washed, dried, and calcined at 550 °C for 2 h to obtain the calcined product. The calcined product was reduced with a mixed gas of hydrogen and nitrogen (hydrogen integral of 15%) at 700 °C for 3 h to obtain 10 g of catalyst. The catalyst composition and characteristic parameters are shown in Table 1.

[0149] Example 10

[0150] 1) Prepare an anhydrous ethanol-glacial acetic acid mixed solution by mixing glacial acetic acid and anhydrous ethanol at a mass ratio of 2.3:1.

[0151] 2) Weigh 26.9g of tetrabutyl titanate and disperse it in 188.3g of anhydrous ethanol-glacial acetic acid mixed solution to obtain solution A.

[0152] 3) Weigh 7.7g of magnesium nitrate and disperse it in 153.9g of anhydrous ethanol-glacial acetic acid mixed solution to obtain solution B.

[0153] 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 1 hour to obtain a sol with a pH of 2.3.

[0154] 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.

[0155] 6) 8.5 g of the magnesium titanate support obtained in step 5) was ultrasonically dispersed in deionized water and heated to 40 °C to obtain solution C. 1.04 g of nickel chloride and 64.1 mg of ruthenium chloride were dissolved in water to obtain a metal salt solution with a total metal ion concentration of 0.5 mol / L. The metal salt solution and a 2 mol / L sodium hydroxide solution were added to solution C, the pH was controlled at 8, and the mixture was stirred for 3 h to obtain a precipitate. The precipitate obtained in step 8) was washed, dried, and calcined at 550 °C for 2 h to obtain the calcined product. The calcined product was reduced with a mixed gas of hydrogen and nitrogen (hydrogen integral of 15%) at 700 °C for 3 h to obtain 10 g of catalyst. The catalyst composition and characteristic parameters are shown in Table 1.

[0156] Example 11

[0157] The procedure was carried out according to Example 1, except that in step 1), glacial acetic acid and anhydrous ethanol were mixed at a mass ratio of 2:1 to obtain an anhydrous ethanol-glacial acetic acid mixed solution, resulting in a sol pH of 2.5. The catalyst was then obtained. The catalyst composition and characteristic parameters are shown in Table 1.

[0158] Example 12

[0159] The procedure was carried out according to Example 1, except that the water bath temperature in step 4) was 50°C. The catalyst was obtained. The catalyst composition and characteristic parameters are shown in Table 1.

[0160] Example 13

[0161] The procedure was carried out according to Example 1, except that the magnesium titanate support was prepared using existing techniques, specifically including:

[0162] 1) Weigh 25.5g of tetrabutyl titanate and disperse it in 61.9g of glacial acetic acid to obtain solution A.

[0163] 2) Weigh 7.3g of magnesium nitrate and disperse it in 61.9g of anhydrous ethanol to obtain solution B.

[0164] 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.

[0165] 4) The sol obtained in step 3) is dried at 70°C for 24 hours and then calcined at 600°C for 2 hours to obtain magnesium titanate support.

[0166] The catalyst composition and characteristic parameters are shown in Table 1.

[0167] Comparative Example 1

[0168] The method was carried out according to Example 1, except that instead of using magnesium titanate as a support, titanium dioxide was used as the support, i.e.:

[0169] 8.5 g of titanium dioxide was ultrasonically dispersed in deionized water and heated to 40 °C to obtain a base solution. 3.15 g of nickel chloride and 146.6 mg of ruthenium chloride were dissolved in water to obtain a metal salt solution with a total metal ion concentration of 0.5 mol / L. The metal salt solution obtained in step 2) and a 2 mol / L sodium hydroxide solution were added to the base solution obtained in step 1), and the pH was controlled at 8. 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 mixed gas of hydrogen and nitrogen (15% hydrogen integral) at 700 °C for 3 h to obtain 10 g of catalyst. The catalyst composition and characteristic parameters are shown in Table 1.

[0170] Comparative Example 2

[0171] 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.:

[0172] 8.5 g of titanium dioxide was ultrasonically dispersed in deionized water and heated to 40 °C to obtain a base solution. 2.1 g of nickel chloride and 97.7 mg of ruthenium chloride were dissolved in water to obtain a metal salt solution with a total metal ion concentration of 0.5 mol / L. The metal salt solution and a 2 mol / L sodium hydroxide solution were added to the obtained base solution, the pH was controlled at 8, and the mixture was stirred for 3 h to obtain a precipitate. The precipitate was washed, dried, and calcined at 550 °C for 2 h to obtain a calcined product. The calcined product was reduced with a mixed gas of hydrogen and nitrogen (15% hydrogen integral) at 700 °C for 3 h to obtain 10 g of catalyst. The catalyst composition and characteristic parameters are shown in Table 1.

[0173] Comparative Example 3

[0174] The procedure was carried out according to Example 1, 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 catalyst composition and characteristic parameters are shown in Table 1.

[0175] Table 1

[0176]

[0177]

[0178] Note: The remainder in the catalyst is magnesium titanate support.

[0179] Test Example 1

[0180] The activity of the catalyst was evaluated using ammonia nitrogen gas with an ammonia concentration of 15% by volume at different temperatures. 1g of 40-60 mesh catalyst and 4g of 40-60 mesh quartz sand were mixed and packed together, with a volume hourly space velocity of 15000mL / (g·h) and a reaction time of 6h. The results are shown in Table 2.

[0181] Table 2

[0182]

[0183] 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.

[0184] Meanwhile, compared with the comparative example, the example showed a significantly higher ammonia decomposition conversion rate at 500°C, indicating that the catalyst described in this invention has high ammonia decomposition activity at low temperatures.

[0185] 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 contacted with a magnesium titanate catalyst; The temperature for ammonia decomposition is 500-650℃; The catalyst contains a magnesium titanate support and an active component, the active component comprising noble metals and non-noble metals, wherein the non-noble metals are selected from Group VIII metals; based on the total weight of the catalyst, the content of the active component, calculated by metal element, is 0.5-20% by weight. The mass ratio of the precious metal to the non-precious metal, calculated by metallic elements, is 1:10-20.

2. The method according to claim 1, wherein, Based on the total weight of the catalyst, the content of the active component, expressed as metal element, is 1-15% by weight.

3. The method according to claim 1 or 2, wherein, The precious metal is ruthenium and / or palladium; The non-precious metal is nickel.

4. The method according to claim 1 or 2, wherein, The preparation method of the magnesium titanate 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 the active component onto a magnesium titanate support, wherein the active component includes noble metals and non-noble metals, and the non-noble metals are selected from Group VIII metal elements.

5. The method according to claim 4, wherein, In S1, the mass ratio of the titanium source to the alcohol-glacial acetic acid mixed solution is 1:2-15.

6. The method according to claim 5, wherein, In S1, the mass ratio of the titanium source to the alcohol-glacial acetic acid mixed solution is 1:4-10.

7. The method according to claim 4, wherein, The titanium source is a water-soluble titanium-containing compound.

8. The method according to claim 7, wherein, The titanium source is selected from at least one of tetrabutyl titanate, ethyl titanate, and isopropyl titanate.

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

10. The method according to claim 9, wherein, In S2, the mass ratio of the magnesium source to the alcohol-glacial acetic acid mixed solution is 1:4-15.

11. The method according to claim 4, wherein, The magnesium source is a soluble magnesium salt.

12. The method according to claim 4, 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 1:0.1-2.

13. The method according to claim 12, 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 1:1-2.

14. The method according to claim 4, wherein, The alcohols described in S1 and S2 are each independently C1-C5 alcohols.

15. The method according to claim 14, wherein, The alcohols mentioned in S1 and S2 are each independently selected from at least one of methanol, ethanol, and propanol.

16. The method according to claim 4, wherein, In S3, the pH of the sol is 3-5.

17. The method according to claim 4, wherein, The processing conditions include: a temperature of 30-50℃ and a time of 0.5-10h.

18. The method according to claim 17, wherein, The processing conditions include: a temperature of 30-40℃ and a time of 0.5-8h.

19. The method according to claim 4, wherein, In S4, the drying conditions include: a temperature of 70-100°C and a time of 8-48 hours; In S4, the conditions for the first calcination include: a temperature of 600-1000℃ and a time of 2-6 hours.

20. The method according to any one of claims 5-19, wherein, In S5, the active component is loaded onto a magnesium titanate support using a co-precipitation method.

21. The method according to claim 20, wherein, The coprecipitation method described in S5 includes: mixing and reacting an aqueous solution containing the active component salt, a suspension containing 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.

22. The method according to claim 21, 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%.

23. The method according to claim 22, wherein, The inert atmosphere is selected from at least one of nitrogen, helium, argon and neon.

24. The method according to claim 1 or 2, wherein, The conditions for ammonia decomposition include: a temperature of 500-650℃ and a space velocity of 5000-20000 mL / (g·h).

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