CN115739160A - Nickel-based efficient ammonia decomposition catalyst and preparation method thereof - Google Patents
Nickel-based efficient ammonia decomposition catalyst and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a nickel-based high-efficiency ammonia decomposition catalyst and a preparation method thereof, relating to the technical field of catalysts for hydrogen production by ammonia decomposition, wherein the preparation method of the catalyst comprises the following steps: 1) 2-methylimidazole and metal nitrate are synthesized into ZIF-8 or ZIF-67 through a room temperature crystallization method; 2) Dissolving nickel salt in methanol to prepare a steeping fluid, and performing steeping treatment on ZIF-8 or ZIF-67; 3) Preparing an MOF-74-coated ZIF-8 or ZIF-67 core-shell structure catalyst precursor by using the impregnated ZIF-8 or ZIF-67 as a seed crystal and using a solvothermal method; 4) Tabletting and forming a precursor of the core-shell structure catalyst, and then roasting; 5) Reducing the roasted catalyst precursor in a reducing atmosphere to obtain the catalyst; the catalyst prepared by the method has very high active metal Ni dispersion degree, exposes more alkaline sites, remarkably enhances the electron donating capability, shows excellent activity and stability of hydrogen production by low-temperature ammonolysis, and has very good application prospect.
Description
Technical Field
The invention relates to the technical field of catalysts for hydrogen production by ammonia decomposition, in particular to a nickel-based high-efficiency ammonia decomposition catalyst and a preparation method thereof.
Background
China has huge scale of primary energy production and consumption and is the first place in the world. However, domestic oil and gas production is difficult to meet the rapidly-growing production requirements and has greater dependence on import. According to the reports of the Lu Tuo society, the global energy market has a serious periodic energy shortage, which is mainly characterized in that the stock of fossil energy such as petroleum, coal and natural gas in the main energy consumption area of the world is far lower than the average level, and the price of the fossil energy is sharply increased and is far higher than the ordinary level. From the viewpoint of energy safety, once fossil energy such as petroleum, coal, and natural gas is exhausted, human energy supply becomes a significant problem. Human beings must look for new energy sources to ensure energy safety in addition to fossil energy sources.
The hydrogen energy is a secondary energy source which is wide in source, clean, free of carbon, flexible, efficient and rich in application scene, and is an ideal interconnection medium for promoting clean and efficient utilization of traditional fossil energy and supporting large-scale development of renewable energy. The utilization of hydrogen energy is one of the most feasible ways to achieve carbon peak reaching and carbon neutralization, so the development of the hydrogen energy industry is imperative. However, the first challenge to achieve large-scale application of hydrogen energy is the problem of hydrogen storage and transportation. The hydrogen is extremely easy to combust, has wide explosion limit range, is easy to generate hydrogen brittleness, has low volume energy density and leads the storage and transportation of the hydrogen to become a problem to be solved urgently.
Ammonia has high energy density and weight hydrogen storage capacity, wherein the mass fraction of hydrogen is 17.7%, and the decomposition of the ammonia only generates nitrogen and hydrogen and does not generate COx greenhouse gas. The ammonia gas is easy to be compressed, is safe to store and transport, has smaller density than air, can not be accumulated after leakage, is quick to spread and has higher safety. And the technology for synthesizing ammonia is mature, and the ammonia is low in price. Therefore, the ammonia is used as a carrier of the hydrogen, the storage and transportation of the hydrogen are converted into the storage and transportation of the ammonia, and the hydrogen is prepared by decomposing the ammonia, so that the method has a wide application prospect.
Chinese patent document CN114570361A discloses a ruthenium-based ammonia decomposition hydrogen production catalyst using carbon layer coated silicon dioxide as a carrier and a preparation method thereof, and the catalyst shows higher ammonia decomposition activity at 500-600 ℃. However, the catalyst is easy to have methanation reaction in application, so that the loss of the catalyst carrier is caused, the structure of the catalyst is damaged, and the ammonia decomposition activity of the catalyst is further influenced.
Chinese patent document CN114192144A discloses a method for preparing an ammonia decomposition catalyst by pyrolyzing MOFs containing transition metals at high temperature. The active components in the prepared catalyst are easy to control and are not easy to agglomerate, and the ammonia decomposition activity of the catalyst is improved. However, the synthesis process of the catalyst is complex, the synthesis period is long, the cost is high, and the catalyst is difficult to apply to large-scale production.
Chinese patent document CN112387274 discloses a magnesium oxide supported ruthenium based catalyst prepared by a precipitation method. The preparation process of the catalyst is simple, the catalytic activity and the stability are good, and the large-scale production is easy to realize. However, the ruthenium content of the catalyst is so high that the cost thereof is high.
In summary, no catalyst is available at present, which can achieve both high activity and strong stability. Therefore, it is of great significance to search for and develop a new ammonia decomposition catalyst.
Disclosure of Invention
The invention aims to provide a nickel-based high-efficiency ammonia decomposition catalyst and a preparation method thereof aiming at the defects in the prior art.
The technical scheme of the invention is as follows: a preparation method of a nickel-based high-efficiency ammonia decomposition catalyst comprises the following steps:
1) 2-methylimidazole and metal nitrate are synthesized into ZIF-8 or ZIF-67 by a solvothermal method;
2) Dissolving nickel salt in methanol to prepare a steeping fluid, and performing steeping treatment on ZIF-8 or ZIF-67;
3) Preparing an MOF-74-coated ZIF-8 or ZIF-67 core-shell structure catalyst precursor by using the impregnated ZIF-8 or ZIF-67 as a seed crystal and using a solvothermal method;
4) Tabletting and forming the core-shell structure catalyst precursor, and then roasting;
5) And reducing the roasted catalyst precursor in a reducing atmosphere to obtain the catalyst.
Preferably, the metal nitrate in step 1) is at least one of zinc nitrate hexahydrate and cobalt nitrate hexahydrate.
Preferably, the synthesis method of ZIF-8 or ZIF-67 in step 1) comprises: mixing the components in a molar ratio of (3-4): dissolving 2-methylimidazole 1 and metal nitrate in methanol, fully stirring, centrifugally washing by using the methanol as a solvent after stirring is finished, and drying the obtained product to obtain ZIF-8 or ZIF-67.
Preferably, the nickel salt in step 2) is at least one of nickel nitrate, nickel chloride, nickel sulfate and nickel acetylacetonate.
Preferably, the MOF-74-coated ZIF-8 or ZIF-67 core-shell structure catalyst precursor in the step 3) is synthesized by a method comprising the following steps: and (2) fully stirring the ZIF-8 or ZIF-67 in a mixed solvent of DMF (dimethyl formamide), ethanol and water to uniformly disperse the ZIF-8 or ZIF-67 in the mixed solvent, wherein the mass ratio of the ZIF-8 or ZIF-67 to the mixed solvent is (3-9): 100; 2, 5-dihydroxy terephthalic acid and magnesium acetate tetrahydrate are placed in a mixed solvent containing ZIF-8 or ZIF-67, and stirred at room temperature until the components are completely dissolved; then the medicine is put into an oven for crystallization at 155-165 ℃; after crystallization is finished, washing a crystallized product by using DMF and methanol; finally, the obtained product is dried in vacuum at 165-175 ℃ to obtain the catalyst precursor.
Preferably, in the step 4), the core-shell structure catalyst precursor is tabletted and molded, and is crushed into particles of 20-40 meshes.
Preferably, the roasting atmosphere in the step 4) is one of air, nitrogen and argon, the roasting temperature is 400-920 ℃, and the roasting time is 1-5h.
Preferably, the reducing atmosphere in the step 5) is one of ammonia gas, hydrogen gas and ammonia-hydrogen mixed gas, the reducing temperature is 300-900 ℃, and the reducing time is 1-10h.
The nickel-based high-efficiency ammonia decomposition catalyst prepared by the preparation method has the advantages that the mass of nickel accounts for 1-20% of the total mass of the catalyst, and the mass of magnesium oxide accounts for 20-40% of the total mass of the catalyst.
Compared with the prior art, the invention has the following advantages:
the invention prepares a novel MgO-coated CN anchored high-dispersion Ni-based catalyst with a core-shell structure by a solvothermal method; the catalyst prepared by the method has very high active metal Ni dispersion degree, exposes more alkaline sites, obviously enhances the electron donating capability, shows excellent activity and stability for preparing hydrogen by low-temperature ammonolysis, and has very good application prospect.
The nickel-based catalyst provided by the invention has good reproducibility and high catalytic activity, and has huge industrial application potential.
Detailed Description
The following is a further description of the invention with reference to the examples.
Example one
2.62g of 2-methylimidazole and 3.17g of zinc nitrate hexahydrate are dissolved in 80mL of methanol and stirred magnetically at room temperature for 24h. And transferring the turbid solution to a centrifuge cup after stirring, and performing centrifugal washing by taking methanol as a solvent, wherein the rotation speed of a centrifugal machine is 5000r/min. And after the centrifugation is finished, drying the obtained product in an oven at 60 ℃ for 12 hours to obtain ZIF-8. 0.39g of nickel nitrate hexahydrate was dissolved in methanol to prepare a dipping solution, and dipped on ZIF-8 by an equal volume dipping method. 9g of impregnated ZIF-8 was placed in 200mL of DMF: ethanol: water =15:1:1 and ultrasonically homogenizing. A mixture of 3.17g of 2, 5-dihydroxyterephthalic acid and 6.86g of magnesium acetate tetrahydrate was placed in the mixed solvent, and stirred to be completely dissolved. Then transferring the medicine into a crystallization kettle, and placing the crystallization kettle in a rotary oven for crystallization for 16 hours at 160 ℃. After crystallization is finished and the temperature is reduced to normal temperature, the medicine in the kettle is transferred to a beaker, and is washed three times by DMF and four times by methanol. Finally, pouring out the methanol supernatant, and performing suction filtration on the residual medicine, and then performing vacuum drying for 5 hours in a vacuum drying oven at 170 ℃. And tabletting the dried particles to prepare 20-40-mesh catalyst precursor particles. And then roasting in a tubular furnace, wherein the roasting atmosphere is nitrogen, the roasting temperature is 920 ℃, and the roasting time is 4 hours. Finally, reducing the mixture by using hydrogen at the reduction temperature of 550 ℃ for 2h.
The prepared catalyst is used for ammonia decomposition reaction in a laboratory quartz tube micro fixed bed reactor, the feed gas is 99.999 percent high-purity ammonia, and the airspeed is 6000cm 3 /(g cat 8729h), and the ammonia decomposition rate is 71.70% when the reaction temperature is 500 ℃.
Example two
3.50g of 2-methylimidazole and 3.17g of zinc nitrate hexahydrate are dissolved in 80mL of methanol and stirred magnetically at room temperature for 24h. And transferring the turbid solution into a centrifuge cup after stirring, and performing centrifugal washing by using methanol as a solvent, wherein the rotating speed of a centrifugal machine is 5000r/min. And after the centrifugation is finished, drying the product in an oven at 60 ℃ for 12h to obtain ZIF-8. 0.39g of nickel nitrate hexahydrate was dissolved in methanol to prepare a dipping solution, and dipped on ZIF-8 by an equal volume dipping method. And then roasting the carbon material by using a tubular furnace, wherein the roasting atmosphere is nitrogen, the roasting temperature is 700 ℃, and the roasting time is 2 hours, so that the black powdery CN material can be obtained. 3g of CN material was placed in 200mL of DMF: ethanol: water =15:1:1 and ultrasonically homogenizing. A mixture of 3.17g of 2, 5-dihydroxyterephthalic acid and 6.86g of magnesium acetate tetrahydrate was placed in the mixed solvent, and it was stirred to be completely dissolved. Then transferring the medicine into a crystallization kettle, and placing the crystallization kettle in a rotary oven for crystallization for 16 hours at 160 ℃. After crystallization is finished and the temperature is reduced to normal temperature, the medicine in the kettle is transferred to a beaker, and is washed three times by DMF and four times by methanol. Finally, pouring off the methanol supernatant, filtering the residual medicine, and then drying the medicine in vacuum for 5 hours in a vacuum drying oven at 170 ℃. And tabletting the dried particles to prepare 20-40-mesh catalyst precursor particles. And then roasting in a tubular furnace, wherein the roasting atmosphere is nitrogen, the roasting temperature is 700 ℃, and the roasting time is 4 hours. Finally, reducing the mixture by using hydrogen at 550 ℃ for 2h.
The prepared catalyst is used for ammonia decomposition reaction in a laboratory quartz tube micro fixed bed reactor, the raw material gas is 99.999 percent of high-purity ammonia, and the airspeed is 6000cm 3 /(g cat 8729h), and the ammonia decomposition rate is 62.72 percent when the reaction temperature is 500 ℃.
EXAMPLE III
3.28g of 2-methylimidazole and 3.08g of cobalt nitrate hexahydrate are dissolved in 80mL of methanol and stirred magnetically at room temperature for 24 hours. And transferring the turbid solution into a centrifuge cup after stirring, and performing centrifugal washing by using methanol as a solvent, wherein the rotating speed of a centrifugal machine is 5000r/min. And after the centrifugation is finished, drying the product in an oven at 60 ℃ for 12 hours to obtain ZIF-67. 0.39g of nickel nitrate hexahydrate was dissolved in methanol to prepare a dipping solution, and dipped on ZIF-67 by an equal volume dipping method. 8g of impregnated ZIF-67 was placed in 200mL of DMF: ethanol: water =15:1:1 and ultrasonically homogenizing. A mixture of 3.17g of 2, 5-dihydroxyterephthalic acid and 6.86g of magnesium acetate tetrahydrate was placed in the mixed solvent, and it was stirred to be completely dissolved. Then transferring the medicine into a crystallization kettle, and placing the crystallization kettle in a rotary oven for crystallization for 12 hours at 140 ℃. After crystallization is finished and the temperature is reduced to normal temperature, the medicine in the kettle is transferred to a beaker, and is washed three times by DMF and four times by methanol. Finally, pouring off the methanol supernatant, filtering the residual medicine, and then drying the medicine in vacuum for 5 hours in a vacuum drying oven at 170 ℃. And tabletting the dried particles to prepare 20-40-mesh catalyst precursor particles. And then roasting in a tubular furnace, wherein the roasting atmosphere is nitrogen, the roasting temperature is 700 ℃, and the roasting time is 4 hours. Finally, reducing the mixture by using hydrogen at 550 ℃ for 2h.
The prepared catalyst is used for ammonia decomposition reaction in a laboratory quartz tube micro fixed bed reactor, the feed gas is 99.999 percent high-purity ammonia, and the airspeed is 6000cm 3 /(g cat 8729h), and the ammonia decomposition rate is 89.16% when the reaction temperature is 500 ℃.
Example four
3.28g of 2-methylimidazole and 3.08g of cobalt nitrate hexahydrate are dissolved in 80mL of methanol and stirred magnetically at room temperature for 24 hours. And transferring the turbid solution into a centrifuge cup after stirring, and performing centrifugal washing by using methanol as a solvent, wherein the rotating speed of a centrifugal machine is 5000r/min. And (3) after the centrifugation is finished, drying the product in an oven at 60 ℃ for 12h to obtain the ZIF-67. 0.39g of nickel acetylacetonate hexahydrate was dissolved in methanol to prepare a solution, which was then impregnated onto ZIF-67 by an isovolumetric impregnation method. And then roasting the carbon material by using a tubular furnace, wherein the roasting atmosphere is nitrogen, the roasting temperature is 600 ℃, and the roasting time is 2 hours, so that the black powdery CN material can be obtained. 4g of CN material was placed in 200mL of DMF: ethanol: water =15:1:1 and ultrasonically homogenizing. A mixture of 3.17g of 2, 5-dihydroxyterephthalic acid and 6.86g of magnesium acetate tetrahydrate was placed in the mixed solvent, and stirred to be completely dissolved. Then transferring the medicine into a crystallization kettle, and placing the crystallization kettle in a rotary oven for crystallization for 10 hours at 180 ℃. After crystallization is finished and the temperature is reduced to normal temperature, the medicine in the kettle is transferred to a beaker, and is washed three times by DMF and four times by methanol. Finally, pouring off the methanol supernatant, filtering the residual medicine, and then drying the medicine in vacuum for 5 hours in a vacuum drying oven at 170 ℃. And tabletting the dried particles to prepare 20-40-mesh catalyst precursor particles. And then roasting in a tubular furnace, wherein the roasting atmosphere is nitrogen, the roasting temperature is 800 ℃, and the roasting time is 4 hours. Finally, reducing the mixture by using hydrogen at the reduction temperature of 500 ℃ for 3h.
The prepared catalyst is used for ammonia decomposition reaction in a laboratory quartz tube micro fixed bed reactor, the raw material gas is 99.999 percent of high-purity ammonia, and the airspeed is 6000cm 3 /(g cat 8729h), and the ammonia decomposition rate is 76.38% when the reaction temperature is 500 ℃.
EXAMPLE five
3.28g of 2-methylimidazole and 3.17g of zinc nitrate hexahydrate are dissolved in 80mL of methanol and stirred magnetically at room temperature for 24 hours. And transferring the turbid solution to a centrifuge cup after stirring, and performing centrifugal washing by taking methanol as a solvent, wherein the rotation speed of a centrifugal machine is 5000r/min. And (3) after the centrifugation is finished, drying the obtained product in an oven at 60 ℃ for 12h to obtain the ZIF-8. 0.39g of nickel nitrate hexahydrate was dissolved in methanol to prepare a maceration extract, which was impregnated onto ZIF-8 by an equal-volume impregnation method. 9g of impregnated ZIF-8 was placed in 200mL of DMF: ethanol: water =15:1:1 and ultrasonically homogenizing. A mixture of 3.17g of 2, 5-dihydroxyterephthalic acid and 6.86g of magnesium acetate tetrahydrate was placed in the mixed solvent, and stirred to be completely dissolved. Then transferring the medicine into a crystallization kettle, and placing the crystallization kettle in a rotary oven for crystallization for 16 hours at 160 ℃. After crystallization is finished and the temperature is reduced to normal temperature, the medicine in the kettle is transferred to a beaker, and is washed three times by DMF and four times by methanol. Finally, pouring off the methanol supernatant, filtering the residual medicine, and then drying the medicine in vacuum for 5 hours in a vacuum drying oven at 170 ℃. And tabletting the dried particles to prepare 20-40 mesh catalyst precursor particles. And then roasting in a tubular furnace, wherein the roasting atmosphere is nitrogen, the roasting temperature is 400 ℃, and the roasting time is 1h. Finally, reducing the mixture by using hydrogen at the temperature of 300 ℃ for 10h.
The prepared catalyst is used for ammonia decomposition reaction in a laboratory quartz tube micro fixed bed reactor, the raw material gas is 99.999 percent of high-purity ammonia, and the airspeed is 6000cm 3 /(g cat 8729h), the ammonia decomposition rate is 59.44% when the reaction temperature is 500 ℃.
EXAMPLE six
3.28g of 2-methylimidazole and 3.17g of zinc nitrate hexahydrate are dissolved in 80mL of methanol and stirred magnetically at room temperature for 24 hours. And transferring the turbid solution to a centrifuge cup after stirring, and performing centrifugal washing by taking methanol as a solvent, wherein the rotation speed of a centrifugal machine is 5000r/min. And (3) after the centrifugation is finished, drying the obtained product in an oven at 60 ℃ for 12h to obtain the ZIF-8. 0.39g of nickel nitrate hexahydrate was dissolved in methanol to prepare a dipping solution, and dipped on ZIF-8 by an equal volume dipping method. 9g of impregnated ZIF-8 was placed in 200mL of DMF: ethanol: water =15:1:1 and ultrasonically homogenizing. A mixture of 3.17g of 2, 5-dihydroxyterephthalic acid and 6.86g of magnesium acetate tetrahydrate was placed in the mixed solvent, and stirred to be completely dissolved. Then the medicine is transferred into a crystallization kettle, and the crystallization kettle is placed in a rotary oven to be crystallized for 16 hours at 160 ℃. After crystallization is finished and the temperature is reduced to normal temperature, the medicine in the kettle is transferred to a beaker, and is washed three times by DMF and four times by methanol. Finally, pouring off the methanol supernatant, filtering the residual medicine, and then drying the medicine in vacuum for 5 hours in a vacuum drying oven at 170 ℃. And tabletting the dried particles to prepare 20-40-mesh catalyst precursor particles. And then roasting in a tubular furnace, wherein the roasting atmosphere is nitrogen, the roasting temperature is 800 ℃, and the roasting time is 5 hours. Finally, reducing the mixture by using hydrogen at 900 ℃ for 1h.
The prepared catalyst is used for ammonia decomposition reaction in a laboratory quartz tube micro fixed bed reactor, the raw material gas is 99.999 percent of high-purity ammonia, and the airspeed is 6000cm 3 /(g cat 8729h), and the ammonia decomposition rate is 64.87% when the reaction temperature is 500 ℃.
Comparative example 1
A mixture of 3.17g of 2, 5-dihydroxyterephthalic acid, 0.35g of nickel acetate tetrahydrate and 6.56g of magnesium acetate tetrahydrate was placed in 200mL of DMF: ethanol: water =15:1:1, stirring the mixture to completely dissolve the solvent. Then the medicine is transferred into a crystallization kettle, and the crystallization kettle is placed in a rotary oven to be crystallized for 16 hours at 160 ℃. And (4) after crystallization is finished and the temperature is reduced to normal temperature, transferring the medicine in the kettle to a beaker, adding DMF (dimethyl formamide) for washing for 12h, pouring off supernate and washing with DMF for 12h again. This operation was repeated and finally the sample was washed three times with DMF and four times with methanol. Finally, pouring off the methanol supernatant, filtering the residual medicine, and then drying the medicine in vacuum for 5 hours in a vacuum drying oven at 170 ℃. And tabletting the dried product to prepare the catalyst precursor with 20-40 meshes. Then roasting in a tubular furnace in a roasting atmosphere of N 2 The roasting temperature is 700 ℃, and the roasting time is 4 hours. Finally, reducing the mixture by using hydrogen at 550 ℃ for 2h.
The prepared catalyst is used for ammonia decomposition reaction in a laboratory quartz tube micro fixed bed reactor, the raw material gas is 99.999 percent of high-purity ammonia, and the airspeed is 6000cm 3 /(g cat 8729h), and the ammonia decomposition rate is 44.70% when the reaction temperature is 500 ℃.
Comparative example No. two
5.04g of basic nickel carbonate, 6.12g of aluminum hydroxide powder and 8.00g of sesbania powder are mechanically and uniformly mixed, diluted 3wt% concentrated nitric acid is added into the powder for pulping, and the powder is placed into a die for extruding after being kneaded for 2-3 times in an extruding machine to obtain a formed catalyst precursor. And standing the obtained precursor for 12h at room temperature, drying the precursor for 2h at 120 ℃, and roasting the precursor for 4h at 550 ℃ in a muffle furnace. Finally, reducing the mixture by using hydrogen at the reduction temperature of 550 ℃ for 2h.
The prepared catalyst is used for ammonia decomposition reaction in a laboratory quartz tube micro fixed bed reactor, the raw material gas is 99.999 percent of high-purity ammonia, and the airspeed is 6000cm 3 /(g cat 8729h), and the ammonia decomposition rate is 29.30% when the reaction temperature is 500 ℃.
Comparative example No. three
Mixing 3.06g aluminum hydroxide powder, 4.34g magnesium hydroxide and 8.00g sesbania powder, adding diluted 3wt% concentrated nitric acid into the powder, pulping, kneading for 2-3 times in a bar extruder, loading into a mold, and extruding to obtain the shaped MgO-Al 2 O 3 Carrier precursor, standing the obtained precursor at room temperature for 12h, air-drying, drying in a drying oven at 120 ℃ for 2h, and roasting in a muffle furnace at 550 ℃ for 4h to obtain the formed MgO-Al 2 O 3 And (3) a carrier. The impregnation solution was prepared by nickel nitrate hexahydrate, and 20wt% of nickel was impregnated on the carrier by an equal volume impregnation method. Then placing the mixture into a muffle furnace to be roasted for 4 hours at 550 ℃. Finally, reducing the mixture by using hydrogen at the reduction temperature of 550 ℃ for 2h.
The prepared catalyst is used for ammonia decomposition reaction in a laboratory quartz tube micro fixed bed reactor, the feed gas is 99.999 percent high-purity ammonia, and the airspeed is 6000cm 3 /(g cat 8729h), and the ammonia decomposition rate is 29.30% when the reaction temperature is 500 ℃.
Comparative example No. four
The foamed nickel is directly used as a finished catalyst, and the ammonia decomposition reaction is carried out in a quartz tube micro fixed bed reactor for a laboratory, wherein the raw material gas is 99.999 percent of high-purity ammonia, and the airspeed is 6000cm 3 /(g cat 8729h), the ammonia decomposition rate is 2.05% when the reaction temperature is 500 ℃.
The catalysts of the above examples and comparative examples were operated under the same conditions (raw material gas 99.999% high purity ammonia, space velocity 6000 cm) 3 /(g cat 8729h), reaction temperature 500 deg.CThe test results are shown in table 1:
table 1 results of activity evaluation of examples and comparative examples
As can be seen from the data in table 1, the active metal Ni content of the example catalyst was 10%, which is significantly lower than that of the comparative example catalyst, but showed more excellent ammonia decomposition activity. Comparing example 1 with example 2, it can be seen that the catalyst prepared by directly coating ZIF-8 with MOF-74 has better catalytic activity. The catalyst prepared in example 3 has a small amount of cobalt oxide, which in combination with nickel oxide, shows a higher ammonia decomposition activity.
The present invention is not limited to the above-described embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the gist of the present invention, and the contents of the changes still fall within the scope of the present invention.
Claims (9)
1. The preparation method of the nickel-based high-efficiency ammonia decomposition catalyst is characterized by comprising the following steps of:
1) 2-methylimidazole and metal nitrate are synthesized into ZIF-8 or ZIF-67 by a solvothermal method;
2) Dissolving nickel salt in methanol to prepare a steeping liquor, and carrying out steeping treatment on ZIF-8 or ZIF-67;
3) Preparing an MOF-74-coated ZIF-8 or ZIF-67 core-shell structure catalyst precursor by using the impregnated ZIF-8 or ZIF-67 as a seed crystal and using a solvothermal method;
4) Tabletting and forming the core-shell structure catalyst precursor, and then roasting;
5) And reducing the roasted catalyst precursor in a reducing atmosphere to obtain the catalyst.
2. The method for preparing a nickel-based high-efficiency ammonia decomposition catalyst according to claim 1, wherein the method comprises the following steps: the metal nitrate in the step 1) is at least one of zinc nitrate hexahydrate and cobalt nitrate hexahydrate.
3. The preparation method of the nickel-based high-efficiency ammonia decomposition catalyst according to claim 1, characterized by comprising the following steps: the synthesis method of the ZIF-8 or ZIF-67 in the step 1) comprises the following steps: mixing the components in a molar ratio of (3-4): dissolving 2-methylimidazole of 1 and metal nitrate in methanol, fully stirring, centrifugally washing by taking the methanol as a solvent after stirring is finished, and drying the obtained product to obtain ZIF-8 or ZIF-67.
4. The preparation method of the nickel-based high-efficiency ammonia decomposition catalyst according to claim 1, characterized by comprising the following steps: the nickel salt in the step 2) is at least one of nickel nitrate, nickel chloride, nickel sulfate and nickel acetylacetonate.
5. The preparation method of the nickel-based high-efficiency ammonia decomposition catalyst according to claim 1, characterized by comprising the following steps: the MOF-74 coated ZIF-8 or ZIF-67 core-shell structure catalyst precursor in the step 3) is synthesized by a method comprising the following steps: and (2) putting the ZIF-8 or ZIF-67 into a mixed solvent of DMF, ethanol and water, and fully stirring to uniformly disperse the ZIF-8 or ZIF-67 in the mixed solvent, wherein the mass ratio of the ZIF-8 or ZIF-67 to the mixed solvent is (3-9): 100, respectively; 2, 5-dihydroxy terephthalic acid and magnesium acetate tetrahydrate are placed in a mixed solvent containing ZIF-8 or ZIF-67, and stirred at room temperature until the components are completely dissolved; then crystallizing at 155-165 ℃; after crystallization is finished, washing a crystallization product by using DMF and methanol; and finally drying the obtained product to obtain the catalyst precursor.
6. The preparation method of the nickel-based high-efficiency ammonia decomposition catalyst according to claim 1, characterized by comprising the following steps: and 4) tabletting and forming the precursor of the core-shell structure catalyst, and crushing the precursor into particles of 20-40 meshes.
7. The method for preparing a nickel-based high-efficiency ammonia decomposition catalyst according to claim 1, wherein the method comprises the following steps: in the step 4), the roasting atmosphere is one of air, nitrogen and argon, the roasting temperature is 400-920 ℃, and the roasting time is 1-5h.
8. The preparation method of the nickel-based high-efficiency ammonia decomposition catalyst according to claim 1, characterized by comprising the following steps: in the step 5), the reducing atmosphere is one of ammonia gas, hydrogen gas and ammonia-hydrogen mixed gas, the reducing temperature is 300-900 ℃, and the reducing time is 1-10h.
9. A nickel-based high-efficiency ammonia decomposition catalyst prepared by the preparation method of any one of claims 1 to 8, characterized in that: the mass of the nickel accounts for 1-20% of the total mass of the catalyst, and the mass of the magnesium oxide accounts for 20-40% of the total mass of the catalyst.
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