A low-temperature and high-efficiency ammonia decomposition catalyst and its preparation method

Abstract

The present invention provides a low-temperature and efficient ammonia decomposition catalyst and a preparation method thereof. The active group of the catalyst comprises a noble metal and an iron-based metal, the mass content of the active metal is 2-10%, the mass content ratio of the iron-based metal to the noble metal is 5-20:1, the particle size of the nanoparticles of the iron-based metal is 5-15nm, and the particle size of the nanoparticles of the noble metal is 2-10nm; the catalyst also comprises a molecular sieve carrier. The present invention has found that the low-temperature and efficient ammonia decomposition activity of the catalyst can be improved by optimizing the content of the noble metal and the iron-based metal, and controlling the particle size of the noble metal and the iron-based metal by a certain preparation method.

Description

Technical Field

[0001] The invention belongs to the technical field of catalysts, and in particular relates to a low-temperature and high-efficiency ammonia decomposition catalyst and a preparation method thereof. Background Art

[0002] With the continuous growth of energy demand and the continuous improvement of environmental protection requirements, the development and utilization of new clean energy sources have received more and more attention. Among them, hydrogen energy, as a secondary energy source, has the advantages of being clean and environmentally friendly, and its development has received much attention. Hydrogen can be directly burned to provide energy, or it can be used to generate electricity through hydrogen fuel cells to provide energy. There are no pollutants emitted during use, so it is very clean and environmentally friendly. However, hydrogen has a low volume energy density, high storage cost, and low transportation efficiency. High hopes are placed on the use of hydrogen storage carriers that are relatively easy to store and transport to achieve efficient transportation and storage.

[0003] Ammonia has high hydrogen storage density, easy liquefaction, mature transportation technology, low hydrogen production cost and no CO2 when decomposed. X It is considered to be one of the ideal hydrogen storage carriers due to its advantages such as high efficiency and high efficiency. Theoretically, the equilibrium conversion rate of ammonia decomposition to produce hydrogen can be as high as 99% at 400°C, but it actually needs to be above 1000°C to occur. The use of catalysts helps to reduce the decomposition conditions of ammonia, but the reaction temperature still needs to be above 650°C. High-temperature operation requires high engineering conditions and large energy input, which will reduce the energy efficiency of hydrogen energy. Therefore, the development of efficient catalysts to reduce the reaction temperature of ammonia decomposition will help improve the hydrogen energy efficiency of the ammonia-carrying hydrogen process, and plays a very critical role in the promotion of ammonia-carrying hydrogen industrial applications. Existing highly active catalysts usually contain a large amount of precious metals, or a large amount of precious metals and a small amount of non-precious metals, with high preparation costs, but the catalytic activity is low if the precious metal content is low. In addition, the activity of existing catalysts is not high enough.

[0004] At present, the catalysts with high ammonia decomposition activity mainly include ruthenium-based (Ru), nickel-based (Ni), iron-based (Fe) and cobalt-based (Co) catalysts. Among them, Ru-based catalysts show the highest catalytic activity, but their high cost and limited availability limit their industrial application. Relatively speaking, metal Ni is abundant in reserves, low in price and has high ammonia decomposition activity, so it has good application prospects. Literature results show that industrial ammonia decomposition to produce hydrogen mostly uses Ni-based catalysts, the reaction temperature is above 800°C, the energy consumption is high, and the catalyst is easily deactivated.

[0005] Therefore, the present invention provides a low-temperature and efficient ammonia decomposition catalyst and a preparation method thereof, wherein the active group of the catalyst comprises a noble metal and an iron-based metal, the mass content of the active metal is 2-10%, the mass content ratio of the iron-based metal to the noble metal is 5-20:1, the particle size of the nanoparticles of the iron-based metal is 5-15nm, and the particle size of the nanoparticles of the noble metal is 2-10nm; the catalyst also comprises a molecular sieve carrier. The present invention has found that the low-temperature and efficient ammonia decomposition activity of the catalyst can be improved by optimizing the content of the noble metal and the iron-based metal, and controlling the particle size of the noble metal and the iron-based metal by a certain preparation method. Summary of the invention

[0006] In view of this, the present invention provides a low-temperature and high-efficiency ammonia decomposition catalyst and a preparation method and application thereof, which overcomes the problems of high production cost of catalysts in the prior art, poor low-temperature catalytic activity of catalysts, and poor ammonia decomposition performance.

[0007] The present invention provides a low-temperature and high-efficiency ammonia decomposition catalyst and a preparation method thereof. The active components of the catalyst include precious metals and iron-based metals, the mass content of the active metals is 1-10%, the mass content ratio of the iron-based metals to the precious metals is 5-20:1, and the catalyst also includes a molecular sieve carrier.

[0008] In a preferred embodiment, the catalyst further comprises porous carbon, the metal nanoparticles are uniformly loaded on the porous carbon, and the porous carbon is coated on the molecular sieve. Further preferably, the content of the porous carbon is 0.05%-0.2% of the mass content of the catalyst.

[0009] The noble metal in the catalyst active component is one or more of gold (Au), silver (Ag), ruthenium (Ru), rhodium (Rh), palladium (Pd), and platinum (Pt); preferably one or more of ruthenium (Ru), rhodium (Rh), palladium (Pd) and platinum (Pt), preferably one or more of ruthenium (Ru) and rhodium (Rh).

[0010] The iron-based metal in the catalyst active component is one or more of iron (Fe), cobalt (Co) and nickel (Ni), preferably one or more of cobalt (Co) and nickel (Ni).

[0011] Preferably, the mass content of active metal is 2-8%, more preferably 2-5%; wherein the mass content ratio of iron-based metal to precious metal is preferably 10-20:1, more preferably 10-15:1.

[0012] Furthermore, the particle size of the iron-based metal nanoparticles is 5-15 nm, and the particle size of the noble metal nanoparticles is 2-10 nm; further, the particle size of the iron-based metal nanoparticles is 5-10 nm, and the particle size of the noble metal nanoparticles is 2-5 nm.

[0013] The molecular sieve carrier contained in the catalyst is one or more of ZSM-5 and Na-ZSM-5, preferably Na-ZSM-5. Studies have shown that using Na-ZSM-5 molecular sieve as a carrier has higher catalytic activity.

[0014] In one aspect, the present invention provides a method for preparing a low-temperature and high-efficiency ammonia decomposition catalyst, the preparation method comprising the following steps:

[0015] Purchase or prepare a molecular sieve carrier; mix and stir the molecular sieve carrier and the organic ligand to form a mixed solution A, stir and stir the metal salt solution and the solvent to form a mixed solution B, and then mix the mixed solution A and the mixed solution B to form a mixed solution C; transfer the mixed solution C to a high-pressure reactor to react for a period of time; after natural cooling, filter and dry to obtain a powdered product; post-treat the powdered product to obtain a low-temperature and high-efficiency ammonia decomposition catalyst. In a preferred embodiment, the molecular sieve carrier in step a is one or more of ZSM-5 and Na-ZSM-5, and in a preferred embodiment, the molecular sieve is homemade Na-ZSM-5 and ZSM-5. The specific preparation method is as follows:

[0016] Sodium aluminate is mixed with water, and then TPAOH is added. After stirring evenly, tetraethyl silicate is added, and sodium alginate (SA) is added dropwise after stirring evenly. After stirring evenly, the mixture is placed in a hydrothermal reactor for crystallization, and then cooled. The solid crystals are separated from the mother liquor, washed to neutrality, and dried. The mixture is calcined in air to remove the template agent to obtain a Na-ZSM-5 molecular sieve. The obtained Na-ZSM-5 molecular sieve is added to an ammonium sulfate solution for ion exchange reaction, and then dried and calcined to prepare a ZSM-5 molecular sieve.

[0017] The crystallization temperature is 120-150° C., and the crystallization time is 24-36 hours. The calcination is performed by heating the temperature at 2-5° C. / min to 500-550° C. and calcining for 1-3 hours.

[0018] The amount of reactants used in the molecular sieve preparation process is such that the substances in the reaction system have the following molar ratio relationship: SiO 2 :Al 2 O 3 :TPAOH:SA:H 2 O=1:(0.01~0.03):(0.15~0.35):(0.01~0.08):(30~40). More preferably, the amount of each reactant is such that each substance in the reaction system has the following molar ratio relationship: SiO 2 :Al 2 O 3 :TPAOH:SA:H 2O=1:0.02:0.15:0.04:40.

[0019] In the above step b, the organic ligand is selected from one or more of phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, trimellitic acid, trimesic acid, 1,4-naphthalene dicarboxylic acid, 2,6-naphthalene dicarboxylic acid, 2,7-naphthalene dicarboxylic acid, ethylenediaminetetraacetic acid, 2-methylimidazole, 2,4-dimethylimidazole, 2-ethylimidazole, and N-benzoylimidazole;

[0020] The metal salt solution in the above step b includes a noble metal salt solution and an iron-based metal salt solution, wherein the noble metal salt and the iron-based metal salt are selected from one or more of nitrates, acetates, chlorides, carbonates, and sulfates; the noble metal is one or more of gold (Au), silver (Ag), ruthenium (Ru), rhodium (Rh), palladium (Pd), and platinum (Pt); preferably one or more of ruthenium (Ru), rhodium (Rh), palladium (Pd) and platinum (Pt), preferably one or more of ruthenium (Ru) and rhodium (Rh); the iron-based metal is one or more of iron (Fe), cobalt (Co) and nickel (Ni), preferably one or more of cobalt (Co) and nickel (Ni).

[0021] The molar ratio of the metal salt and the organic ligand in the above step b is 1:(1-10); the mass content ratio of the iron-based metal to the precious metal-based metal in the metal salt is 5-20:1, preferably 10-15:1.

[0022] The solvent in the above step b is one or more selected from water, acetic acid, ethanol, DMF, cyclohexane, methanol, and ethylene glycol, preferably ethanol and water.

[0023] In the above step c, the high-pressure reactor is a hydrothermal reactor, the reaction temperature is 110-150° C., and the reaction time is 3-6 hours.

[0024] The post-treatment method for the powder product in step d of the above preparation method can be two different treatment methods, one of which is a carbonization reduction method and the other is a roasting reduction method. The carbonization reduction method specifically places the powder product in an inert gas atmosphere for direct carbonization reduction. The inert gas is nitrogen, argon or helium, etc. The carbonization temperature is 500-700°C. The actual principle of the carbonization reduction process is that under an inert atmosphere, the organic ligands in the metal skeleton material formed by the metal salt and the organic ligand are carbonized, and the metal salt is reduced. The metal salt is reduced to metal nanoparticles. The metal nanoparticles formed by the direct carbonization reduction method are uniformly dispersed on the porous carbon surface and the molecular sieve surface formed by carbonization, which is conducive to the uniform dispersion of the metal nanoparticles.

[0025] The above-mentioned roasting reduction method is to directly place the powder product in an air atmosphere for high-temperature roasting, and then place the roasted powder product in a hydrogen atmosphere for reduction. The high-temperature roasting temperature in the air atmosphere is 500-700°C, and the reduction temperature in the hydrogen atmosphere is 300-400°C. The roasting reduction method directly roasts the organic ligand in the metal organic framework material, and the active metal is fixed on the molecular sieve carrier in the form of oxide. After hydrogen reduction, the metal oxide forms metal nanoparticles fixed on the molecular sieve carrier. The metal nanoparticles are evenly dispersed and have a strong interaction force with the molecular sieve carrier. The metal nanoparticles are not easy to agglomerate and have good stability.

[0026] Another aspect of the present invention provides use of the above-mentioned low-temperature and high-efficiency ammonia decomposition catalyst or the low-temperature and high-efficiency ammonia decomposition catalyst prepared by the above-mentioned preparation method in ammonia decomposition hydrogen production reaction.

[0027] The application steps are: loading the catalyst into a quartz tube of an ammonia decomposition hydrogen production reaction device, activating it at 450°C for 2h in a high-purity ammonia atmosphere before the catalytic reaction, lowering the temperature to the reaction temperature at the beginning of the test after the activation, and finally performing an ammonia decomposition hydrogen production reaction in an ammonia atmosphere at 350-600°C. The ammonia activation flow rate is 30mL·min -1 The catalyst with an ammonia activation temperature of 450°C has better catalytic activity for ammonia decomposition.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The present invention utilizes precious metals and iron-based metals in combination, and it is found that precious metals and iron-based metals have a synergistic effect with each other. Compared with an equal amount of a single precious metal or iron-based metal as an active substance, the combination of the two can improve the catalyst's ammonia decomposition hydrogen production activity and reduce the preparation cost.

[0030] The present invention achieves low-temperature and high-efficiency activity for ammonia decomposition by controlling the content ratio of precious metals and iron-based metals and optimizing the particle size of the nanoparticles of the precious metals and iron-based metals, and adopts the molecular sieve ZSM-5 as a carrier to effectively improve the dispersibility of the active metals. In particular, studies have found that the use of Na-ZSM-5 can further improve the catalytic activity of the catalyst compared to ZSM-5, and reduce the preparation cost and environmental pollution.

[0031] The present invention realizes uniformly covering the metal organic framework material on the molecular sieve carrier by a one-step method of organic ligand solvent heat through a carrier and a metal salt solution, and then realizes that the active metal can be evenly dispersed on the surface of the molecular sieve carrier by a roasting or reduction method, thereby improving the dispersion performance of the active metal. In the post-treatment, the high dispersion of active metal nanoparticles is achieved by a carbonization reduction method, and graphitized porous carbon is intercalated between the molecular sieve and the nanometal particles, which effectively improves the dispersion of the active metal and can improve the low-temperature decomposition activity of ammonia of the catalyst. The roasting reduction method used in the post-treatment can improve the interaction between the active metal and the molecular sieve, and can improve the dispersion performance of the active metal and the stability performance of the catalyst.

[0032] The catalyst obtained by the preparation method of the present invention can achieve an ammonia conversion rate of 99% at a low temperature of 425° C., greatly improving the ammonia decomposition activity of the catalyst and having important industrial value. DETAILED DESCRIPTION

[0033] The following will be combined with Examples 1-18 of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] The present invention provides a low-temperature and high-efficiency ammonia decomposition catalyst and a preparation method thereof. The active components of the catalyst include precious metals and iron-based metals, the mass content of the active metals is 1-10%, the mass content ratio of the iron-based metals to the precious metals is 5-20:1, and the catalyst also includes a molecular sieve carrier.

[0035] In a preferred embodiment, the catalyst further comprises porous carbon, the metal nanoparticles are uniformly loaded on the porous carbon, and the porous carbon is coated on the molecular sieve. Further preferably, the content of the porous carbon is 0.05%-0.2% of the mass content of the catalyst.

[0036] The noble metal in the catalyst active component is one or more of gold (Au), silver (Ag), ruthenium (Ru), rhodium (Rh), palladium (Pd), and platinum (Pt); preferably one or more of ruthenium (Ru), rhodium (Rh), palladium (Pd) and platinum (Pt), preferably one or more of ruthenium (Ru) and rhodium (Rh).

[0037] The iron-based metal in the catalyst active component is one or more of iron (Fe), cobalt (Co) and nickel (Ni), preferably one or more of cobalt (Co) and nickel (Ni).

[0038] Preferably, the mass content of active metal is 2-8%, more preferably 2-5%; wherein the mass content ratio of iron-based metal to precious metal is preferably 10-20:1, more preferably 10-15:1.

[0039] Furthermore, the particle size of the iron-based metal nanoparticles is 5-15 nm, and the particle size of the noble metal nanoparticles is 2-10 nm; further, the particle size of the iron-based metal nanoparticles is 5-10 nm, and the particle size of the noble metal nanoparticles is 2-5 nm.

[0040] The molecular sieve carrier contained in the catalyst is one or more of ZSM-5 and Na-ZSM-5, preferably Na-ZSM-5. Studies have shown that using Na-ZSM-5 molecular sieve as a carrier has higher catalytic activity.

[0041] In one aspect, the present invention provides a method for preparing a low-temperature and high-efficiency ammonia decomposition catalyst, the preparation method comprising the following steps:

[0042] Purchase or prepare a molecular sieve carrier; mix and stir the molecular sieve carrier and the organic ligand to form a mixed solution A, stir and stir the metal salt solution and the solvent to form a mixed solution B, and then mix the mixed solution A and the mixed solution B to form a mixed solution C; transfer the mixed solution C to a high-pressure reactor to react for a period of time; after natural cooling, filter and dry to obtain a powdered product; post-treat the powdered product to obtain a low-temperature and high-efficiency ammonia decomposition catalyst. In a preferred embodiment, the molecular sieve carrier in step a is one or more of ZSM-5 and Na-ZSM-5, and in a preferred embodiment, the molecular sieve is homemade Na-ZSM-5 and ZSM-5. The specific preparation method is as follows:

[0043] Sodium aluminate is mixed with water, and then TPAOH is added. After stirring evenly, tetraethyl silicate is added, and sodium alginate (SA) is added dropwise after stirring evenly. After stirring evenly, the mixture is placed in a hydrothermal reactor for crystallization, and then cooled. The solid crystals are separated from the mother liquor, washed to neutrality, and dried. The mixture is calcined in air to remove the template agent to obtain a Na-ZSM-5 molecular sieve. The obtained Na-ZSM-5 molecular sieve is added to an ammonium sulfate solution for ion exchange reaction, and then dried and calcined to prepare a ZSM-5 molecular sieve.

[0044] The crystallization temperature is 120-150° C., and the crystallization time is 24-36 hours. The calcination is performed by heating the temperature at 2-5° C. / min to 500-550° C. and calcining for 1-3 hours.

[0045] The amount of reactants used in the molecular sieve preparation process is such that the substances in the reaction system have the following molar ratio relationship: SiO 2 :Al 2 O3 :TPAOH:SA:H 2 O=1:(0.01~0.03):(0.15~0.35):(0.01~0.08):(30~40). More preferably, the amount of each reactant is such that each substance in the reaction system has the following molar ratio relationship: SiO 2 :Al 2 O 3 :TPAOH:SA:H 2 O=1:0.02:0.15:0.04:40.

[0046] In the above step b, the organic ligand is selected from one or more of phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, trimellitic acid, trimesic acid, 1,4-naphthalene dicarboxylic acid, 2,6-naphthalene dicarboxylic acid, 2,7-naphthalene dicarboxylic acid, ethylenediaminetetraacetic acid, 2-methylimidazole, 2,4-dimethylimidazole, 2-ethylimidazole, and N-benzoylimidazole;

[0047] The metal salt solution in the above step b includes a noble metal salt solution and an iron-based metal salt solution, wherein the noble metal salt and the iron-based metal salt are selected from one or more of nitrates, acetates, chlorides, carbonates, and sulfates; the noble metal is one or more of gold (Au), silver (Ag), ruthenium (Ru), rhodium (Rh), palladium (Pd), and platinum (Pt); preferably one or more of ruthenium (Ru), rhodium (Rh), palladium (Pd) and platinum (Pt), preferably one or more of ruthenium (Ru) and rhodium (Rh); the iron-based metal is one or more of iron (Fe), cobalt (Co) and nickel (Ni), preferably one or more of cobalt (Co) and nickel (Ni).

[0048] The molar ratio of the metal salt to the organic ligand in the above step b is 1:(1-10); the mass content ratio of the iron-based metal to the precious metal in the metal salt is 5-20:1, preferably 10-15:1.

[0049] The solvent in the above step b is one or more selected from water, acetic acid, ethanol, DMF, cyclohexane, methanol, and ethylene glycol, preferably ethanol and water.

[0050] In the above step c, the high-pressure reactor is a hydrothermal reactor, the reaction temperature is 110-150° C., and the reaction time is 3-6 hours.

[0051] The post-treatment method for the powder product in step d of the above preparation method can be two different treatment methods, one of which is a carbonization reduction method and the other is a roasting reduction method. The carbonization reduction method specifically places the powder product in an inert gas atmosphere for direct carbonization reduction. The inert gas is nitrogen, argon or helium, etc. The carbonization temperature is 500-700°C. The actual principle of the carbonization reduction process is that under an inert atmosphere, the organic ligands in the metal skeleton material formed by the metal salt and the organic ligand are carbonized, and the metal salt is reduced. The metal salt is reduced to metal nanoparticles. The metal nanoparticles formed by the direct carbonization reduction method are uniformly dispersed on the porous carbon surface and the molecular sieve surface formed by carbonization, which is conducive to the uniform dispersion of the metal nanoparticles.

[0052] The above-mentioned roasting reduction method is to directly place the powder product in an air atmosphere for high-temperature roasting, and then place the roasted powder product in a hydrogen atmosphere for reduction. The high-temperature roasting temperature in the air atmosphere is 500-700°C, and the reduction temperature in the hydrogen atmosphere is 300-400°C. The roasting reduction method directly roasts the organic ligand in the metal organic framework material, and the active metal is fixed on the molecular sieve carrier in the form of oxide. After hydrogen reduction, the metal oxide forms metal nanoparticles fixed on the molecular sieve carrier. The metal nanoparticles are evenly dispersed and have a strong interaction force with the molecular sieve carrier. The metal nanoparticles are not easy to agglomerate and have good stability.

[0053] Another aspect of the present invention provides use of the above-mentioned low-temperature and high-efficiency ammonia decomposition catalyst or the low-temperature and high-efficiency ammonia decomposition catalyst prepared by the above-mentioned preparation method in ammonia decomposition hydrogen production reaction.

[0054] The application steps are: loading the catalyst into a quartz tube of an ammonia decomposition hydrogen production reaction device, activating it at 450°C for 2h in a high-purity ammonia atmosphere before the catalytic reaction, lowering the temperature to the reaction temperature at the beginning of the test after the activation, and finally performing an ammonia decomposition hydrogen production reaction in an ammonia atmosphere at 380-550°C. The ammonia activation flow rate is 30mL·min -1 The catalyst with an ammonia activation temperature of 450°C has better catalytic activity for ammonia decomposition.

[0055] The following are specific embodiments

[0056] Example 1

[0057] Sodium aluminate was mixed with water, and TPAOH was added. After stirring, tetraethyl silicate was added. After stirring, sodium alginate (SA) was added dropwise. After stirring, the mixture was placed in a hydrothermal reactor and crystallized at 120°C for 24 hours. The mixture was then cooled, and the solid crystals were separated from the mother liquor. The mixture was washed to neutrality and dried under vacuum at 100°C. The mixture was calcined at 500°C in an air atmosphere to remove the template agent, and a Na-ZSM-5 molecular sieve was obtained. The amount of each reactant was such that each substance in the reaction system had the following molar ratio relationship: SiO 2 :Al 2 O 3 :TPAOH:SA:H 2 O=1:0.02:0.15:0.04:40.

[0058] Take an appropriate amount of Na-ZSM-5 molecular sieve and trimesic acid and place them in a mixed solution of an appropriate amount of ethanol and water, and stir them ultrasonically at 35°C for 1 hour to obtain a mixed solution of Na-ZSM-5 and trimesic acid; prepare a mixed solution of ruthenium chloride and nickel chloride according to the mass content ratio of ruthenium metal to nickel metal of 1:12, add them to the mixed solution of ethanol and water at room temperature and stir them ultrasonically for 1 hour, then mix the mixed solution with the mixed solution containing Na-ZSM-5 and trimesic acid, stir them ultrasonically for 30 minutes, transfer them to a hydrothermal reactor and react at 120°C for 6 hours; after natural cooling, filter and dry to obtain a powdered product. The ratio of the total molar amount of metal salts (ruthenium chloride and nickel chloride) to the total molar amount of trimesic acid is 1:2.

[0059] The powder product was calcined at 500°C in an air atmosphere, and then reduced in a hydrogen atmosphere at 300°C to obtain a low-temperature and high-efficiency ammonia decomposition catalyst, which was labeled as catalyst 1. The composition, size, specific surface area and other parameters of the obtained catalyst were then characterized. The parameters obtained by the characterization are shown in Table 1. The characterization methods and instruments used are as follows:

[0060] The valence state and component content of each element on the catalyst surface were analyzed by X-ray photoelectron spectrometer. The X-ray photoelectron spectra of all experimental samples were completed on the instrument model ESCALAB250 Xi produced by ThermoFisher Technology Company of the United States. The test conditions of the samples are as follows: AlKa (1486.6eV) X-ray light source, C1s with a calibration bond energy of 284.8eV, a test voltage of 12KV, a test current of 6mA, and a CAE scanning mode.

[0061] The morphology and size of the catalyst were observed by Hitachi ultra-high resolution field emission scanning electron microscope (SU8100). Before observing the morphology and size of the sample, the sample was first placed in an anhydrous ethanol solution and placed in an ultrasonicator for 10 minutes to make it evenly dispersed in the anhydrous ethanol solution; then it was placed on a silicon wafer using a capillary tube, naturally air-dried at room temperature, and then waited for measurement.

[0062] The samples were analyzed by TEM and HRTEM on an electron microscope model JEOL JSEM-2010 produced by JEOL Ltd. Before the TEM and HRTEM tests, the samples were first placed in anhydrous ethanol solution and ultrasonicated in an ultrasonicator for 15 minutes to evenly disperse them in the anhydrous ethanol solution; then they were placed on a copper grid using a capillary tube and naturally air-dried at room temperature before being measured. TEM and HRTEM can analyze the distribution of metal nanoparticles and the average particle size.

[0063] BET analysis refers to the analysis of the specific surface area and pore size distribution of the catalyst by using the physical adsorption instrument ASPA 2020 of Micromeritics, USA. Before measuring the physical adsorption data of the sample, the sample is placed in a vacuum environment at 200°C for degassing to remove impurity gases in the sample, such as CO 2 , O 2 Then the sample was cooled by liquid nitrogen to 77K, thus recording N 2 Adsorption-desorption data and BET surface area and pore size distribution data of samples. The BET surface area of ​​the samples was calculated using the Brunauer-Emmett-Teller (BET) equation.

[0064] Example 2

[0065] Sodium aluminate was mixed with water, and TPAOH was added. After stirring, tetraethyl silicate was added. After stirring, sodium alginate (SA) was added dropwise. After stirring, the mixture was placed in a hydrothermal reactor and crystallized at 120°C for 24 hours. The mixture was then cooled, and the solid crystals were separated from the mother liquor. The mixture was washed to neutrality and dried under vacuum at 100°C. The mixture was calcined at 500°C in an air atmosphere to remove the template agent, and a Na-ZSM-5 molecular sieve was obtained. The amount of each reactant was such that each substance in the reaction system had the following molar ratio relationship: SiO 2 :Al 2 O 3 :TPAOH:SA:H 2 O = 1: 0.02: 0.15: 0.04: 40. The obtained Na-ZSM-5 molecular sieve was added into an ammonium sulfate solution to carry out an ion exchange reaction, and then dried at 100° C. and calcined at 550° C. to prepare a ZSM-5 molecular sieve.

[0066] Take an appropriate amount of ZSM-5 molecular sieve and trimesic acid and place them in a mixed solution of an appropriate amount of ethanol and water, and ultrasonically stir for 1 hour at 35°C to obtain a mixed solution of ZSM-5 and trimesic acid; prepare a mixed solution of ruthenium chloride and nickel chloride according to the mass content ratio of ruthenium metal to nickel metal of 1:12, add it to the mixed solution of ethanol and water at room temperature and ultrasonically stir for 1 hour, then mix the mixed solution with the mixed solution containing ZSM-5 and trimesic acid, ultrasonically stir for 30 minutes, transfer it to a hydrothermal kettle and react at 120°C for 6 hours; after natural cooling, filter and dry to obtain a powdered product. The ratio of the total molar amount of metal salts (ruthenium chloride and nickel chloride) to the total molar amount of trimesic acid is 1:2.

[0067] The powder product was calcined at 500°C in an air atmosphere, and then reduced in a hydrogen atmosphere at 300°C to obtain a low-temperature and high-efficiency ammonia decomposition catalyst, which was labeled as catalyst 2. The composition, size, specific surface area and other parameters of the obtained catalyst were then characterized using the same method as in Example 1. The parameters obtained by characterization are specifically shown in Table 1.

[0068] Example 3

[0069] Silver nitrate was used instead of ruthenium chloride, nickel nitrate was used instead of nickel chloride, the amounts of metallic silver and nickel were based on the amount ratio of ruthenium to nickel in Example 1, and other experimental conditions remained the same to obtain Catalyst 3. Various parameters of Catalyst 3 are shown in Table 1.

[0070] Example 4

[0071] Rhodium chloride was used instead of ruthenium chloride, the amounts of metal rhodium and nickel were based on the amount ratio of ruthenium to nickel in Example 1, and other experimental conditions remained the same to obtain catalyst 4. Various parameters of catalyst 4 are shown in Table 1.

[0072] Example 5

[0073] The ruthenium chloride was replaced by palladium chloride, the amounts of metal palladium and nickel were based on the amount ratio of ruthenium to nickel in Example 1, and other experimental conditions remained the same to obtain Catalyst 5. Various parameters of Catalyst 5 are shown in Table 1.

[0074] Example 6

[0075] Platinum chloride was used instead of ruthenium chloride, the amounts of metal palladium and nickel were based on the amount ratio of ruthenium to nickel in Example 1, and other experimental conditions remained consistent to obtain Catalyst 6. Various parameters of Catalyst 6 are shown in Table 1.

[0076] Example 7

[0077] Cobalt chloride was used instead of nickel chloride, the amounts of metal ruthenium and cobalt were based on the amount ratio of ruthenium to nickel in Example 1, and other experimental conditions remained the same to obtain catalyst 7. Various parameters of catalyst 7 are shown in Table 1.

[0078] Example 8

[0079] Ferric chloride was used instead of nickel chloride, the amounts of metal ruthenium and iron were based on the ratio of ruthenium to nickel in Example 1, and other experimental conditions remained the same to obtain catalyst 8. Various parameters of catalyst 8 are shown in Table 1.

[0080] Examples 9-13 (Studying the influence of content on catalyst)

[0081] The total amount of metallic ruthenium, metallic nickel and the carrier molecular sieve was adjusted, and the content of the total active metal amount in the catalyst weight mass was adjusted to 1%, 2%, 5%, 8% and 10%, the mass ratio of metallic ruthenium to metallic nickel remained unchanged from that in Example 1, and other experimental conditions were the same as in Example 1. The obtained catalysts were marked as Catalyst 9, Catalyst 10, Catalyst 11, Catalyst 12 and Catalyst 13 in sequence. Various parameters of the catalysts are shown in Table 1.

[0082] Examples 14-17 (Ratio of precious metal content to iron-based metal content)

[0083] The total amount of active metals remained unchanged from Example 1, and the ratio of metal ruthenium to nickel was changed to 1:5, 1:10, 1:15 and 1:20. The other experimental conditions remained consistent with Example 1. The corresponding catalysts were marked as catalyst 14, catalyst 15, catalyst 16, and catalyst 17. Various parameters of the catalysts are shown in Table 1.

[0084] Embodiment 18

[0085] Sodium aluminate was mixed with water, and TPAOH was added. After stirring, tetraethyl silicate was added. After stirring, sodium alginate (SA) was added dropwise. After stirring, the mixture was placed in a hydrothermal reactor and crystallized at 120°C for 24 hours. The mixture was then cooled, and the solid crystals were separated from the mother liquor. The mixture was washed to neutrality and dried under vacuum at 100°C. The mixture was calcined at 500°C in an air atmosphere to remove the template agent, and a Na-ZSM-5 molecular sieve was obtained. The amount of each reactant was such that each substance in the reaction system had the following molar ratio relationship: SiO 2 :Al 2 O 3 :TPAOH:SA:H 2 O=1:0.02:0.15:0.04:40.

[0086] Take an appropriate amount of Na-ZSM-5 molecular sieve and trimesic acid and place them in a mixed solution of an appropriate amount of ethanol and water, and ultrasonically stir for 1 hour at 35°C to obtain a mixed solution of Na-ZSM-5 and trimesic acid; prepare a mixed solution of ruthenium chloride and nickel chloride according to the mass content ratio of ruthenium metal to nickel metal of 12:1, add it to the mixed solution of ethanol and water at room temperature and ultrasonically stir for 1 hour, then mix the mixed solution with the mixed solution containing Na-ZSM-5 and trimesic acid, ultrasonically stir for 30 minutes, transfer it to a hydrothermal kettle and react at 120°C for 6 hours; after natural cooling, filter and dry to obtain a powdered product. The ratio of the total molar amount of metal salts (ruthenium chloride and nickel chloride) to the total molar amount of trimesic acid is 1:2.

[0087] The powder product was placed in an inert gas atmosphere for direct carbonization reduction, the inert gas was nitrogen, the carbonization temperature was 600°C, and the desired product catalyst was obtained, which was labeled as catalyst 18. Various parameters of the catalyst are shown in Table 1.

[0088] Comparative Example 1

[0089] The active metal salts in Example 1 were all replaced with ruthenium chloride, the total amount of active metal remained unchanged, and other conditions were kept consistent with Example 1. The obtained catalyst was marked as Comparative Example 1, and the parameters of the catalyst are shown in Table 1.

[0090] Comparative Example 2

[0091] The active metal salts in Example 1 were all replaced with nickel chloride, the total amount of active metal remained unchanged, and other conditions were kept consistent with Example 1. The obtained catalyst was marked as Comparative Example 2. The parameters of the catalyst are shown in Table 1.

[0092] Table 1 Performance parameters of catalysts

[0093]

[0094] The catalyst parameters in Table 1 show that the catalyst obtained by the preparation method of the present application has good dispersibility, a relatively small particle size of the active component, relatively uniform dispersion, and a large specific surface area.

[0095] Test Example 1

[0096] The activity test of the above catalyst was carried out on a gas chromatograph equipped with an ammonia decomposition hydrogen production reaction device. 100 mg of the catalyst (20-40 mesh) was loaded into a quartz tube. Before the catalytic reaction, it was activated at 450°C for 2 h in a high-purity ammonia atmosphere. After the activation, the temperature was lowered to the reaction temperature at the beginning of the test. The reaction conditions were: the raw gas was high-purity ammonia, and the flow rate was 10 mL min -1 , space velocity is 6000mL·gcat -1 ·h-1 , the reaction pressure is normal pressure, and the reaction temperature is selected as 380°C, 400°C, 425°C, 450°C, 500°C, and 550°C. According to the formula ammonia conversion rate = (initial ammonia flow rate - ammonia flow rate after reaction) / initial ammonia flow rate × 100%, the ammonia conversion rate is calculated, and the test results are shown in Table 2;

[0097] Table 2 Catalytic performance of catalysts

[0098]

[0099] The data in Table 2 show that the catalyst prepared by the present invention has good low-temperature decomposition activity of ammonia, can efficiently decompose ammonia starting at 380°C, and the decomposition of ammonia can reach 99% at 425°C, has good low-temperature activity, and has important industrial value.

[0100] Test Example 2

[0101] The long-term stability of catalyst 1 and catalyst 18 at 425°C for ammonia decomposition reaction was tested. The stability test of ammonia decomposition reaction was carried out in a fixed bed reactor at atmospheric pressure. The reaction conditions were: 100 mg catalyst, high-purity ammonia as feed gas, flow rate 10 mL min -1 , space velocity is 6000mL·gcat -1 ·h -1 , the time it takes for the test conversion rate to drop to 90%. The specific comparison is shown in Table 3:

[0102] Table 3 Catalyst stability data

[0103]

[0104] The data in Table 3 prove that the performance of catalysts obtained by different post-treatment methods is not the same. The catalyst 1 obtained by the air roasting reduction method has good stability of catalytic activity, but its catalytic activity is slightly lower than that of the catalyst 18 obtained by the carbonization reduction method. However, the catalytic stability of the catalyst obtained by the carbonization reduction method is slightly worse. However, both post-treatment methods are good methods and belong to the technical solutions protected by the present invention. The catalyst obtained by the preparation method of the present invention has high-efficiency low-temperature ammonia decomposition activity.

[0105] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. Application of a low-temperature and high-efficiency ammonia decomposition catalyst in ammonia decomposition hydrogen production reaction, It is characterized in that The catalyst comprises a molecular sieve carrier and an active component, wherein the active component comprises precious metal nanoparticles and iron-based metal nanoparticles, the mass content of the active component is 2-8%, the mass content ratio of the iron-based metal to the precious metal in the active component is 10-20:1, the molecular sieve carrier is Na-ZSM-5, the particle size of the iron-based metal nanoparticles is 5-15nm, and the particle size of the precious metal nanoparticles is 2-10nm; the precious metal in the active component of the catalyst is one or more of gold (Au), silver (Ag), ruthenium (Ru), rhodium (Rh), palladium (Pd), and platinum (Pt); the iron-based metal in the active component of the catalyst is one or more of iron (Fe), cobalt (Co) or nickel (Ni).

2. The use according to claim 1, It is characterized in that The catalyst also contains porous carbon, the metal nanoparticles are uniformly loaded on the porous carbon, the porous carbon is coated on the molecular sieve, and the mass content of the porous carbon is 0.05%-0.2% of the mass content of the catalyst.

3. The use according to any one of claims 1-2, It is characterized in that The mass content of the active component is 2-5%, wherein the mass content ratio of the iron-based metal to the precious metal is 10-15:

1.

4. The use according to any one of claims 1-2, It is characterized in that The particle size of the nanoparticles of the iron-based metal is 5-10 nm, and the particle size of the nanoparticles of the noble metal is 2-5 nm.

5. The use according to any one of claims 1 to 2, It is characterized in that The preparation method of the catalyst comprises the following steps: step a. purchasing or preparing a molecular sieve carrier; step b. mixing and stirring the molecular sieve carrier, the organic ligand and the solvent to form a mixed solution A, stirring and mixing the metal salt solution and the solvent to form a mixed solution B, and then mixing the mixed solution A and the mixed solution B to form a mixed solution C; step c. transferring the mixed solution C to a high-pressure reactor to react for a period of time; after natural cooling, filtering and drying to obtain a powdered product; step d. post-treating the powdered product to obtain a low-temperature and high-efficiency ammonia decomposition catalyst; the solvent in step b is selected from water, acetic acid, ethanol, D One or more of MF, cyclohexane, methanol, and ethylene glycol; the organic ligand in step b is selected from one or more of phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, trimesic acid, trimesic acid, 1,4-naphthalene dicarboxylic acid, 2,6-naphthalene dicarboxylic acid, 2,7-naphthalene dicarboxylic acid, ethylenediaminetetraacetic acid, 2-methylimidazole, 2,4-dimethylimidazole, 2-ethylimidazole, and N-benzoylimidazole; the metal salt solution in step b includes a noble metal salt solution and an iron-based metal salt solution, wherein the noble metal salt and the iron-based metal salt are selected from one or more of nitrates, acetates, chlorides, and sulfates.

6. The use according to claim 5, It is characterized in that The molar ratio of the metal salt to the organic ligand in step b is 1:(1-10); the mass content ratio of the noble metal in the metal salt to the mass content of the iron-based metal is 1:10-15; and the solvent in step b is a mixed solvent of water and ethanol.

7. The use according to claim 5, It is characterized in that In step c, the high-pressure reactor is a hydrothermal reactor, the reaction temperature is 110-150° C., and the reaction time is 3-6 hours.

8. The use according to claim 5, It is characterized in that The post-treatment method for the powder product in step d can be two different treatment methods, one of which is a carbonization reduction method and the other is a roasting reduction method. The carbonization reduction method specifically places the powder product in an inert gas atmosphere for direct carbonization reduction, the inert gas is nitrogen, argon or helium, and the carbonization temperature is 500-700°C; the roasting reduction method is to directly place the powder product in an air atmosphere for high-temperature roasting, and then place the roasted powder product in a hydrogen atmosphere for reduction, the high-temperature roasting temperature in the air atmosphere is 500-700°C, and the reduction temperature in the hydrogen atmosphere is 300-400°C.

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