Synthetic ammonia catalyst with good stability and preparation method thereof

Abstract

The application discloses a synthetic ammonia catalyst with good stability and a preparation method thereof, and belongs to the technical field of catalyst preparation. The synthetic ammonia catalyst with good stability is prepared from the following raw materials: iron nitrate, ammonium molybdate, manganese nitrate, deionized water, sodium polyacrylate, neodymium nitrate, yttrium nitrate, lanthanum phosphate and a MgAl2O4-TiO2-BN composite carrier. The MgAl2O4-TiO2-BN composite carrier is prepared from the following raw materials in parts by weight: 14-16.5 parts of magnesium nitrate, 85-90 parts of aluminum nitrate, 25-29 parts of modified TiO2-BN nanosheets, 46-51 parts of citric acid and 400-450 parts of water. The modified TiO2-BN nanosheet is prepared from the following raw materials: h-BN powder, tetrabutyl titanate, anhydrous ethanol, a dilute nitric acid solution and a hydrogen peroxide solution. The synthetic ammonia catalyst has high sintering resistance and high resistance to poisoning.

Description

Technical Field

[0001] This invention discloses a stable ammonia synthesis catalyst and its preparation method, belonging to the field of catalyst preparation technology. Background Technology

[0002] Ammonia is one of the world's largest-produced chemical products, widely used in agriculture, chemical industry, electronics industry, food industry, military and many other fields. The synthetic ammonia industry is a pillar industry of the national economy, and the performance of synthetic ammonia catalysts, as a core technology, directly determines production efficiency and energy consumption.

[0003] In current technologies, molten iron catalysts, represented by the K2O-Al2O3-CaO-Fe3O4 system, require operation at high temperatures of 400-500℃. The Fe active particles are prone to Ostwald ripening, leading to a decrease in activity. Ruthenium-based (Ru) catalysts have more than twice the activity of iron-based catalysts, but Ru metal is expensive, and the carbon support it is compatible with is prone to methanation in an ammonia atmosphere. Furthermore, Ru particles will still agglomerate during long-term operation.

[0004] Trace amounts of H2S in the ammonia synthesis feed gas can form strongly adsorbed metal sulfides with Fe / Ru, leading to catalyst poisoning or even permanent deactivation. Current technologies mostly enhance desulfurization capacity by adding K2O, but K... + The high mobility of iron can lead to blockage of active sites, resulting in accelerated deactivation. Furthermore, traditional iron-based catalysts lack effective structural stabilization mechanisms and are prone to support collapse under temperature and pressure fluctuations, leading to a reduction in specific surface area. Current research projects utilize carbon nanotubes and SiO2 molecular sieves to confine Fe / Ru particles; however, due to the high-temperature oxidation of carbon materials and the weak interaction between SiO2 and the metal, the confinement effect is not sustainable, indirectly increasing the cost of use.

[0005] In summary, existing ammonia synthesis catalysts still suffer from technical problems such as high-temperature sintering, weak resistance to sulfur poisoning, and unstable support. Summary of the Invention

[0006] In order to solve the above-mentioned problems in the prior art, the present invention provides a synthetic ammonia catalyst with good stability and its preparation method, and achieves the following objectives: to improve the anti-sintering and anti-poisoning ability of the synthetic ammonia catalyst.

[0007] To achieve the above objectives, the following technical solution is adopted:

[0008] A stable ammonia synthesis catalyst is prepared from the following raw materials by weight: 61-66 parts ferric nitrate, 12.4-15.7 parts ammonium molybdate, 11-14 parts manganese nitrate, 350-400 parts deionized water, 2.5-3.5 parts sodium polyacrylate, 15.4-17.5 parts neodymium nitrate, 9.2-12.3 parts yttrium nitrate, 3-5.5 parts lanthanum phosphate, and 100-120 parts MgAl2O4-TiO2-BN composite support.

[0009] The ferric nitrate is one of Fe(NO3)3·9H2O and Fe(NO3)3, preferably Fe(NO3)3·9H2O.

[0010] The ammonium molybdate is (NH4)6Mo7O 24 ·4H2O、(NH4)6Mo7O 24 One of them, preferably (NH4)6Mo7O 24 ·4H2O.

[0011] The manganese nitrate is one of Mn(NO3)2·4H2O, Mn(NO3)2·6H2O, and Mn(NO3)2, preferably Mn(NO3)2·4H2O.

[0012] The sodium polyacrylate has a molecular weight of 2000~4000.

[0013] The neodymium nitrate is one of Nd(NO3)3·6H2O and Nd(NO3)3, preferably Nd(NO3)3·6H2O.

[0014] The yttrium nitrate is one of Y(NO3)3·6H2O and Y(NO3)3, preferably Y(NO3)3·6H2O.

[0015] The MgAl2O4-TiO2-BN composite carrier is prepared by means of the following raw materials in parts by weight: 14-16.5 parts magnesium nitrate, 85-90 parts aluminum nitrate, 25-29 parts modified TiO2-BN nanosheets, 46-51 parts citric acid, and 400-450 parts water.

[0016] The magnesium nitrate is one of Mg(NO3)2·6H2O and Mg(NO3)2, preferably Mg(NO3)2·6H2O.

[0017] The aluminum nitrate is one of Al(NO3)3·9H2O and Al(NO3)3, preferably Al(NO3)3·9H2O;

[0018] The modified TiO2-BN nanosheets are prepared by means of 2.4-3.5 parts by weight of h-BN powder, 4.8-7 parts by weight of tetrabutyl titanate, 40-50 parts by weight of anhydrous ethanol, 10-16 parts by weight of dilute nitric acid solution, and 80-88 parts by weight of hydrogen peroxide solution.

[0019] The concentration of the dilute nitric acid solution is 0.01~0.05 mol / L.

[0020] The hydrogen peroxide solution has a mass concentration of 10-15%.

[0021] The h-BN powder d 50 It is 10μm.

[0022] A method for preparing a stable ammonia synthesis catalyst includes the following steps:

[0023] Step 1: Preparation of modified TiO2-BN nanosheets

[0024] Tetrabutyl titanate was dissolved in anhydrous ethanol to form a solution. h-BN powder was added to the solution and ultrasonically dispersed at 1.5 kW for 30–45 min. A dilute nitric acid solution with a concentration of 0.01–0.05 mol / L was added dropwise to the solution while stirring. After the addition was complete, the mixture was stirred for 2–3 h to obtain Ti-BN sol. The Ti-BN sol was placed in a water bath at 70–80 °C and evaporated to a gel state. It was then transferred to a vacuum drying oven and dried at 80 °C for 12 h to obtain Ti-BN gel. The obtained Ti-BN gel was placed in a tube furnace. The air inside the tube furnace was replaced with N2 for 30 min, and then N2 was introduced. The temperature was increased to 430–460 °C at a rate of 2–5 °C / min and heat-treated for 3–4 h. After cooling to room temperature, TiO2-BN nanosheets were obtained.

[0025] TiO2-BN nanosheets were mixed with a 10-15% (w / w) hydrogen peroxide solution and added to a hydrothermal reactor. The reactor was sealed and reacted for 6-8 hours at 120-130°C. After the reaction solution cooled naturally to room temperature, the precipitate was separated by centrifugation. The precipitate was washed with deionized water until the washing solution was neutral and then transferred to a vacuum drying oven and dried at 80°C for 10 hours to obtain modified TiO2-BN nanosheets. The TiO2-BN nanosheets introduce hydroxyl groups through a hydrothermal reaction with H2O2, enhancing the bonding with MgAl2O4 and improving the interfacial bonding strength.

[0026] Step 2: Preparation of MgAl2O4-TiO2-BN composite support

[0027] The raw materials used are in the following weight proportions: magnesium nitrate 14~16.5 parts, aluminum nitrate 85~90 parts, modified TiO2-BN nanosheets 25~29 parts, citric acid 46~51 parts, and water 400~450 parts.

[0028] Magnesium nitrate (Mg(NO3)2·6H2O) and aluminum nitrate (Al(NO3)3·9H2O) were added to water and stirred until completely dissolved. Citric acid was added and stirred for 1-1.5 h to form a sol. Modified TiO2-BN nanosheets were added to the sol and ultrasonically treated for 10 min at a power of 500 W. The sol was then vacuum dried at 80 °C for 10-12 h to obtain a loose solid dry gel. The dry gel was ground and passed through a 200-mesh sieve. The sieved dry gel powder was placed in a tube furnace and heated to 800-850 °C at a rate of 3-5 °C / min under a N2 atmosphere. The temperature was kept constant for 3.5-4 h. After natural cooling, the powder was ground to obtain a MgAl2O4-TiO2-BN composite carrier.

[0029] MgAl2O4 has a spinel structure and can provide a stable support framework; TiO2-BN nanosheets can form open nanochannels between layers, resulting in low mass transfer resistance.

[0030] Step 3: Loading active ingredients and additives

[0031] The raw materials used are in the following weight proportions: 61-66 parts ferric nitrate, 12.4-15.7 parts ammonium molybdate, 11-14 parts manganese nitrate, 350-400 parts deionized water, 2.5-3.5 parts sodium polyacrylate, 15.4-17.5 parts neodymium nitrate, 9.2-12.3 parts yttrium nitrate, 3-5.5 parts lanthanum phosphate, and 100-120 parts MgAl2O4-TiO2-BN composite carrier.

[0032] Weigh out ferric nitrate, ammonium molybdate, manganese nitrate, and deionized water, add them to the reactor, and stir until completely dissolved. Then add lanthanum phosphate, sodium polyacrylate, neodymium nitrate, and yttrium nitrate, and continue stirring for 1-2 hours to obtain the active component sol. Add a MgAl2O4-TiO2-BN composite carrier to the active component sol, and impregnate at 45℃ for 14-18 hours, stirring for 20 minutes every 2 hours during impregnation. After impregnation, adjust the pH of the reaction system to 9.5-10.5 with 10-15% ammonia water, continue stirring for 1.5 hours, and age at room temperature for 40-50 hours to form a catalyst precursor gel. Break the catalyst precursor gel into 5-10 mm particles, wash with water until the washing solution is neutral, and then wash three times with anhydrous ethanol for later use.

[0033] Ferric nitrate, ammonium molybdate, and manganese nitrate are precursors for the active components.

[0034] Neodymium nitrate, yttrium nitrate, and lanthanum phosphate are precursors for stabilizing agents. Among them, LaPO4 can form mechanical support and also stabilize La. 3+ The nearby active sites form a protective layer, preventing gaseous sulfides from contacting and reacting with the active metal components.

[0035] Sodium polyacrylate acts as a dispersant and gelling agent, preventing premature aggregation or precipitation of metal ions, resulting in a more uniform component distribution and promoting the formation of catalyst precursor gel.

[0036] Step 4: Reduction and Crystallization

[0037] The cleaned catalyst precursor gel was dried by blowing air at 100-110℃ under a N2 atmosphere for 8-10 hours. The dried gel was then ground into powder and transferred to a microwave reactor for heating. A H2-Ar mixed gas was introduced simultaneously, with a volume ratio of H2 to Ar of 1:(2-3). The reduction temperature was controlled at 350-380℃, and the reduction time was 2-2.5 hours. Subsequently, the introduction of the H2-Ar mixed gas was stopped, and N2 was introduced. The temperature was raised to 570-600℃ and crystallized at this temperature for 3-4 hours. Heating was then stopped, and N2 was continuously introduced while the mixture was allowed to cool naturally to room temperature to obtain a highly stable ammonia synthesis catalyst.

[0038] The beneficial effects of this invention are as follows:

[0039] The ammonia synthesis catalyst prepared according to this invention can be used to catalyze the production of ammonia gas with an ammonia yield of 21.5~23 mmol·g. -1 ·h -1 The ammonia synthesis catalyst prepared according to this invention, after continuous use for 1000 hours, catalyzed the production of ammonia gas with an ammonia yield of 21-22.3 mmol·g. -1 ·h -1 The ammonia synthesis catalyst prepared using this invention, after high-temperature treatment, can then be used to catalyze the production of ammonia gas, with an ammonia yield of 20.2–21.5 mmol·g. -1 ·h -1 The ammonia synthesis catalyst prepared using this invention, after sulfur treatment, catalyzes the production of ammonia gas with an ammonia yield of 19.6–20.7 mmol·g. -1 ·h -1 It has the advantages of high stability, high temperature resistance, and good sulfur resistance. Attached Figure Description

[0040] Appendix Figure 1 The physical sample of the ammonia synthesis catalyst prepared in Example 1.

[0041] Appendix Figure 2 This is a SEM image of the ammonia synthesis catalyst prepared in Example 1. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0043] Example 1: A stable ammonia synthesis catalyst

[0044] A stable ammonia synthesis catalyst, the raw materials for preparation include, by weight, 66 parts of ferric nitrate (Fe(NO3)3·9H2O) and ammonium molybdate ((NH4)6Mo7O). 24 15.7 parts of manganese nitrate (Mn(NO3)2·4H2O), 13 parts of manganese nitrate (Mn(NO3)2·4H2O), 400 parts of deionized water, 3.5 parts of sodium polyacrylate, 15.4 parts of neodymium nitrate (Nd(NO3)3·6H2O), 9.2 parts of yttrium nitrate (Y(NO3)3·6H2O), 3 parts of lanthanum phosphate (LaPO4), and 100 parts of MgAl2O4-TiO2-BN composite carrier.

[0045] The MgAl2O4-TiO2-BN composite carrier is prepared by means of the following raw materials in parts by weight: 15 parts magnesium nitrate (Mg(NO3)2·6H2O), 85 parts aluminum nitrate (Al(NO3)3·9H2O), 29 parts modified TiO2-BN nanosheets, 51 parts citric acid, and 400 parts water.

[0046] The modified TiO2-BN nanosheets are prepared from raw materials including 3 parts h-BN powder, 6 parts tetrabutyl titanate, 50 parts anhydrous ethanol, 14 parts dilute nitric acid solution, and 80 parts hydrogen peroxide solution.

[0047] A method for preparing a stable ammonia synthesis catalyst includes the following steps:

[0048] Step 1: Preparation of modified TiO2-BN nanosheets

[0049] The raw materials used are in the following weight proportions: 3 parts h-BN powder, 6 parts tetrabutyl titanate, 50 parts anhydrous ethanol, 14 parts dilute nitric acid solution, and 80 parts hydrogen peroxide solution.

[0050] Tetrabutyl titanate was dissolved in anhydrous ethanol to form a solution. h-BN powder was added to the solution and ultrasonically dispersed at 1.5 kW for 30 min. A 0.05 mol / L dilute nitric acid solution was added dropwise to the solution while stirring. After the addition was complete, the mixture was stirred for 2 h to obtain Ti-BN sol. The sol was placed in a 70℃ water bath and evaporated to a gel state. It was then transferred to a vacuum drying oven and dried at 80℃ for 12 h to obtain Ti-BN gel. The obtained Ti-BN gel was placed in a tube furnace, and the air inside the furnace was replaced with N2 for 30 min. The temperature was then increased to 450℃ at a rate of 5℃ / min and heat-treated for 4 h. After cooling to room temperature, TiO2-BN nanosheets were obtained.

[0051] TiO2-BN nanosheets were mixed with a 15% (w / w) hydrogen peroxide solution and added to a hydrothermal reactor. The reactor was sealed and reacted at 130°C for 7 hours. After the reaction solution cooled naturally to room temperature, the precipitate was separated by centrifugation. The precipitate was washed with deionized water until the washing solution was neutral and then transferred to a vacuum drying oven and dried at 80°C for 10 hours to obtain modified TiO2-BN nanosheets.

[0052] Step 2: Preparation of MgAl2O4-TiO2-BN composite support

[0053] The raw materials used are in the following weight proportions: 15 parts magnesium nitrate (Mg(NO3)2·6H2O), 85 parts aluminum nitrate (Al(NO3)3·9H2O), 29 parts modified TiO2-BN nanosheets, 51 parts citric acid, and 400 parts water.

[0054] Magnesium nitrate (Mg(NO3)2·6H2O) and aluminum nitrate (Al(NO3)3·9H2O) were added to water and stirred until completely dissolved. Citric acid was added and stirred for 1.5 h to form a sol. Modified TiO2-BN nanosheets were added to the sol and ultrasonically treated for 10 min at a power of 500 W. The mixture was then vacuum dried at 80 °C for 12 h to obtain a loose solid dry gel. The dry gel was ground and passed through a 200-mesh sieve. The sieved dry gel powder was placed in a tube furnace and heated to 850 °C at a rate of 3 °C / min under a N2 atmosphere. The temperature was kept constant for 3.5 h and then ground after natural cooling to obtain the MgAl2O4-TiO2-BN composite carrier.

[0055] Step 3: Loading active ingredients and additives

[0056] The raw materials used are in the following weight proportions: ferric nitrate (Fe(NO3)3·9H2O) 66 parts, ammonium molybdate ((NH4)6Mo7O) 24 15.7 parts of manganese nitrate (Mn(NO3)2·4H2O), 13 parts of manganese nitrate (Mn(NO3)2·4H2O), 400 parts of deionized water, 3.5 parts of sodium polyacrylate, 15.4 parts of neodymium nitrate (Nd(NO3)3·6H2O), 9.2 parts of yttrium nitrate (Y(NO3)3·6H2O), 3 parts of lanthanum phosphate (LaPO4), and 100 parts of MgAl2O4-TiO2-BN composite carrier.

[0057] Ferric nitrate, ammonium molybdate, manganese nitrate, and deionized water were weighed and added to a reactor, stirred until completely dissolved. Lanthanum phosphate, sodium polyacrylate, neodymium nitrate, and yttrium nitrate were then added, and stirring continued for 2 hours to obtain the active component sol. A MgAl₂O₄-TiO₂-BN composite carrier was added to the sol, and the mixture was impregnated at 45°C for 18 hours, stirring for 20 minutes every 2 hours during impregnation. After impregnation, the pH of the active component sol was adjusted to 10 using 10% ammonia solution, and stirring continued for 1.5 hours. The mixture was then aged at room temperature for 45 hours to form a catalyst precursor gel. The catalyst precursor gel was broken into 10mm particles, washed with water until the washing solution was neutral, and then washed three times with anhydrous ethanol for later use.

[0058] Step 4: Reduction and Crystallization

[0059] The cleaned catalyst precursor gel was dried by blowing air at 100°C under a N2 atmosphere for 10 hours. The dried gel was then ground into powder and transferred to a microwave reactor for heating. Simultaneously, a H2-Ar mixed gas was introduced, with a volume ratio of H2 to Ar of 1:2. The reduction temperature was controlled at 380°C for 2.5 hours. Then, the H2-Ar mixed gas was stopped and N2 was introduced. The temperature was raised to 600°C and crystallized for 3 hours. Heating was then stopped, and N2 was continuously introduced while the mixture was allowed to cool naturally to room temperature, yielding a highly stable ammonia synthesis catalyst.

[0060] Example 2: A stable ammonia synthesis catalyst

[0061] A stable ammonia synthesis catalyst, the raw materials for preparation include, by weight, 65 parts of ferric nitrate (Fe(NO3)3·9H2O) and ammonium molybdate ((NH4)6Mo7O). 24 15.5 parts of manganese nitrate (Mn(NO3)2·4H2O), 11 parts of manganese nitrate (Mn(NO3)2·4H2O), 350 parts of deionized water, 2.5 parts of sodium polyacrylate, 17.5 parts of neodymium nitrate (Nd(NO3)3·6H2O), 10 parts of yttrium nitrate (Y(NO3)3·6H2O), 3.5 parts of lanthanum phosphate (LaPO4), and 120 parts of MgAl2O4-TiO2-BN composite carrier.

[0062] The MgAl2O4-TiO2-BN composite carrier is prepared by means of the following raw materials in parts by weight: 16.5 parts magnesium nitrate (Mg(NO3)2·6H2O), 90 parts aluminum nitrate (Al(NO3)3·9H2O), 25 parts modified TiO2-BN nanosheets, 50 parts citric acid, and 400 parts water.

[0063] The modified TiO2-BN nanosheets are prepared from raw materials including 2.4 parts h-BN powder, 4.8 parts tetrabutyl titanate, 40 parts anhydrous ethanol, 10 parts dilute nitric acid solution, and 85 parts hydrogen peroxide solution.

[0064] A method for preparing a stable ammonia synthesis catalyst includes the following steps:

[0065] Step 1: Preparation of modified TiO2-BN nanosheets

[0066] The raw materials used are in the following weight proportions: 2.4 parts h-BN powder, 4.8 parts tetrabutyl titanate, 40 parts anhydrous ethanol, 10 parts dilute nitric acid solution, and 85 parts hydrogen peroxide solution.

[0067] Tetrabutyl titanate was dissolved in anhydrous ethanol to form a solution. h-BN powder was added to the solution and ultrasonically dispersed at 1.5 kW for 30 min. A 0.02 mol / L dilute nitric acid solution was added dropwise to the solution while stirring. After the addition was complete, the mixture was stirred for 3 h to obtain Ti-BN sol. The Ti-BN sol was placed in an 80℃ water bath and evaporated to a gel state. It was then transferred to a vacuum drying oven and dried at 80℃ for 12 h to obtain Ti-BN gel. The obtained Ti-BN gel was placed in a tube furnace, and the air inside the furnace was replaced with N2 for 30 min. The temperature was then increased to 460℃ at a rate of 2℃ / min and heat-treated for 3 h. After cooling to room temperature, TiO2-BN nanosheets were obtained.

[0068] TiO2-BN nanosheets were mixed with a 10% (w / w) hydrogen peroxide solution and added to a hydrothermal reactor. The reactor was sealed and reacted at 120°C for 8 hours. After the reaction solution cooled naturally to room temperature, the precipitate was separated by centrifugation. The precipitate was washed with deionized water until the washing solution was neutral and then transferred to a vacuum drying oven and dried at 80°C for 10 hours to obtain modified TiO2-BN nanosheets.

[0069] Step 2: Preparation of MgAl2O4-TiO2-BN composite support

[0070] The raw materials used are in the following weight proportions: 16.5 parts magnesium nitrate (Mg(NO3)2·6H2O), 90 parts aluminum nitrate (Al(NO3)3·9H2O), 25 parts modified TiO2-BN nanosheets, 50 parts citric acid, and 400 parts water.

[0071] Magnesium nitrate (Mg(NO3)2·6H2O) and aluminum nitrate (Al(NO3)3·9H2O) were added to water and stirred until completely dissolved. Citric acid was added and stirred for 1 hour to form a sol. Modified TiO2-BN nanosheets were added to the sol and ultrasonically treated for 10 minutes at a power of 500W. The mixture was then vacuum dried at 80℃ for 10 hours to obtain a loose solid dry gel. The dry gel was ground and passed through a 200-mesh sieve. The sieved dry gel powder was placed in a tube furnace and heated to 800℃ at a rate of 5℃ / min under a N2 atmosphere. The temperature was kept constant for 4 hours. After natural cooling, the mixture was ground and pulverized to obtain the MgAl2O4-TiO2-BN composite carrier.

[0072] Step 3: Loading active ingredients and additives

[0073] The raw materials used are in the following weight proportions: ferric nitrate (Fe(NO3)3·9H2O) 65 parts, ammonium molybdate ((NH4)6Mo7O) 24 15.5 parts of manganese nitrate (Mn(NO3)2·4H2O), 11 parts of manganese nitrate (Mn(NO3)2·4H2O), 350 parts of deionized water, 2.5 parts of sodium polyacrylate, 17.5 parts of neodymium nitrate (Nd(NO3)3·6H2O), 10 parts of yttrium nitrate (Y(NO3)3·6H2O), 3.5 parts of lanthanum phosphate (LaPO4), and 120 parts of MgAl2O4-TiO2-BN composite carrier.

[0074] Ferric nitrate, ammonium molybdate, manganese nitrate, and deionized water were weighed and added to a reactor, stirred until completely dissolved. Lanthanum phosphate, sodium polyacrylate, neodymium nitrate, and yttrium nitrate were then added, and stirring continued for 1 hour to obtain the active component sol. A MgAl₂O₄-TiO₂-BN composite support was added to the active component sol, and the mixture was impregnated at 45°C for 16 hours, stirring for 20 minutes every 2 hours during impregnation. After impregnation, the pH of the sol was adjusted to 9.5 using 10% ammonia solution, and stirring continued for 1.5 hours. The mixture was then aged at room temperature for 50 hours to form a catalyst precursor gel. The catalyst precursor gel was broken into 5mm particles, washed with water until the washing solution was neutral, and then washed three times with anhydrous ethanol for later use.

[0075] Step 4: Reduction and Crystallization

[0076] The cleaned catalyst precursor gel was dried by blowing air at 110°C under a N2 atmosphere for 8 hours. The dried gel was then ground into powder and transferred to a microwave reactor for heating. Simultaneously, a H2-Ar mixed gas was introduced, with a volume ratio of H2 to Ar of 1:3. The reduction temperature was controlled at 350°C for 2.5 hours. Then, the H2-Ar mixed gas was stopped and N2 was introduced. The temperature was raised to 570°C and maintained for crystallization for 4 hours. Heating was then stopped, and N2 was continuously introduced while the mixture was allowed to cool naturally to room temperature, yielding a highly stable ammonia synthesis catalyst.

[0077] Example 3: A stable ammonia synthesis catalyst

[0078] A stable ammonia synthesis catalyst, the raw materials for preparation include, by weight, 61 parts of ferric nitrate (Fe(NO3)3·9H2O) and ammonium molybdate ((NH4)6Mo7O). 2412.4 parts of manganese nitrate (Mn(NO3)2·4H2O), 14 parts of manganese nitrate (Mn(NO3)2·4H2O), 350 parts of deionized water, 2.5 parts of sodium polyacrylate, 16 parts of neodymium nitrate (Nd(NO3)3·6H2O), 12.3 parts of yttrium nitrate (Y(NO3)3·6H2O), 3 parts of lanthanum phosphate (LaPO4), and 120 parts of MgAl2O4-TiO2-BN composite carrier.

[0079] The MgAl2O4-TiO2-BN composite carrier is prepared by means of the following raw materials in parts by weight: 14 parts magnesium nitrate (Mg(NO3)2·6H2O), 85 parts aluminum nitrate (Al(NO3)3·9H2O), 25 parts modified TiO2-BN nanosheets, 46 parts citric acid, and 450 parts water.

[0080] The modified TiO2-BN nanosheets are prepared from raw materials including 3.5 parts h-BN powder, 7 parts tetrabutyl titanate, 40 parts anhydrous ethanol, 16 parts dilute nitric acid solution, and 88 parts hydrogen peroxide solution.

[0081] A method for preparing a stable ammonia synthesis catalyst includes the following steps:

[0082] Step 1: Preparation of modified TiO2-BN nanosheets

[0083] The raw materials used are in the following weight proportions: 3.5 parts h-BN powder, 7 parts tetrabutyl titanate, 40 parts anhydrous ethanol, 16 parts dilute nitric acid solution, and 88 parts hydrogen peroxide solution.

[0084] Tetrabutyl titanate was dissolved in anhydrous ethanol to form a solution. h-BN powder was added to the solution and ultrasonically dispersed at 1.5 kW for 45 min. A 0.01 mol / L dilute nitric acid solution was added dropwise to the solution while stirring. After the addition was complete, the mixture was stirred for 3 h to obtain Ti-BN sol. The Ti-BN sol was placed in a 70℃ water bath and evaporated to a gel state. It was then transferred to a vacuum drying oven and dried at 80℃ for 12 h to obtain Ti-BN gel. The obtained Ti-BN gel was placed in a tube furnace, and the air inside the furnace was replaced with N2 for 30 min. The temperature was then increased to 430℃ at a rate of 2℃ / min and heat-treated for 4 h. After cooling to room temperature, TiO2-BN nanosheets were obtained.

[0085] TiO2-BN nanosheets were mixed with a 10% (w / w) hydrogen peroxide solution and added to a hydrothermal reactor. The reactor was sealed and reacted at 120°C for 6 hours. After the reaction solution cooled naturally to room temperature, the precipitate was separated by centrifugation. The precipitate was washed with deionized water until the washing solution was neutral and then transferred to a vacuum drying oven and dried at 80°C for 10 hours to obtain modified TiO2-BN nanosheets.

[0086] Step 2: Preparation of MgAl2O4-TiO2-BN composite support

[0087] The raw materials used are in the following weight proportions: 14 parts magnesium nitrate (Mg(NO3)2·6H2O), 85 parts aluminum nitrate (Al(NO3)3·9H2O), 25 parts modified TiO2-BN nanosheets, 46 parts citric acid, and 450 parts water.

[0088] Magnesium nitrate (Mg(NO3)2·6H2O) and aluminum nitrate (Al(NO3)3·9H2O) were added to water and stirred until completely dissolved. Citric acid was added and stirred for 1 hour to form a sol. Modified TiO2-BN nanosheets were added to the sol and ultrasonically treated for 10 minutes at a power of 500W. The mixture was then vacuum dried at 80℃ for 10 hours to obtain a loose solid dry gel. The dry gel was ground and passed through a 200-mesh sieve. The sieved dry gel powder was placed in a tube furnace and heated to 800℃ at a rate of 3℃ / min under a N2 atmosphere. The temperature was maintained for 4 hours and then ground after natural cooling to obtain the MgAl2O4-TiO2-BN composite carrier.

[0089] Step 3: Loading active ingredients and additives

[0090] The raw materials used are in the following weight proportions: ferric nitrate (Fe(NO3)3·9H2O) 61 parts, ammonium molybdate ((NH4)6Mo7O) 24 12.4 parts of manganese nitrate (Mn(NO3)2·4H2O), 14 parts of manganese nitrate (Mn(NO3)2·4H2O), 350 parts of deionized water, 2.5 parts of sodium polyacrylate, 16 parts of neodymium nitrate (Nd(NO3)3·6H2O), 12.3 parts of yttrium nitrate (Y(NO3)3·6H2O), 3 parts of lanthanum phosphate (LaPO4), and 120 parts of MgAl2O4-TiO2-BN composite carrier.

[0091] Ferric nitrate, ammonium molybdate, manganese nitrate, and deionized water were weighed and added to a reactor, stirred until completely dissolved. Lanthanum phosphate, sodium polyacrylate, neodymium nitrate, and yttrium nitrate were then added, and stirring continued for 1 hour to obtain the active component sol. A MgAl₂O₄-TiO₂-BN composite carrier was added to the active component sol, and the mixture was impregnated at 50°C for 14 hours, stirring for 20 minutes every 2 hours during impregnation. After impregnation, the pH of the sol was adjusted to 10.5 using 10% ammonia solution, and stirring continued for 1.5 hours. The mixture was then aged at room temperature for 40 hours to form a catalyst precursor gel. The catalyst precursor gel was broken into 5mm particles, washed with water until the washing solution was neutral, and then washed three times with anhydrous ethanol for later use.

[0092] Step 4: Reduction and Crystallization

[0093] The cleaned catalyst precursor gel was dried by blowing air at 100°C under a N2 atmosphere for 8 hours. The dried gel was then ground into powder and transferred to a microwave reactor for heating. Simultaneously, a H2-Ar mixed gas was introduced, with a volume ratio of H2 to Ar of 1:3. The reduction temperature was controlled at 380°C for 2 hours. Then, the H2-Ar mixed gas was stopped and N2 was introduced. The temperature was raised to 570°C and maintained for crystallization for 4 hours. Heating was then stopped, and N2 was continuously introduced while the mixture was allowed to cool naturally to room temperature, yielding a highly stable ammonia synthesis catalyst.

[0094] Comparative Example 1: A catalyst for ammonia synthesis

[0095] A catalyst for ammonia synthesis, the raw materials for which, by weight, include 65 parts of ferric nitrate (Fe(NO3)3·9H2O) and ammonium molybdate ((NH4)6Mo7O) 24 15.5 parts of manganese nitrate (Mn(NO3)2·4H2O), 11 parts of manganese nitrate (Mn(NO3)2·4H2O), 350 parts of deionized water, 2.5 parts of sodium polyacrylate, 17.5 parts of neodymium nitrate (Nd(NO3)3·6H2O), 10 parts of yttrium nitrate (Y(NO3)3·6H2O), 3.5 parts of lanthanum phosphate (LaPO4), and 120 parts of MgAl2O4-TiO2-BN composite carrier.

[0096] The MgAl2O4-TiO2-BN composite carrier is prepared by means of the following raw materials in parts by weight: 16.5 parts magnesium nitrate (Mg(NO3)2·6H2O), 90 parts aluminum nitrate (Al(NO3)3·9H2O), 25 parts TiO2-BN nanosheets, 50 parts citric acid, and 400 parts water.

[0097] The TiO2-BN nanosheet raw material includes 2.4 parts of h-BN powder, 4.8 parts of tetrabutyl titanate, 40 parts of anhydrous ethanol, and 10 parts of dilute nitric acid solution.

[0098] A method for preparing an ammonia synthesis catalyst includes the following steps:

[0099] Step 1: Preparation of TiO2-BN nanosheets

[0100] The raw materials used are in the following weight proportions: 2.4 parts h-BN powder, 4.8 parts tetrabutyl titanate, 40 parts anhydrous ethanol, and 10 parts dilute nitric acid solution.

[0101] Tetrabutyl titanate was dissolved in anhydrous ethanol to form a solution. h-BN powder was added to the solution and ultrasonically dispersed at 1 kW for 30 min. Dilute nitric acid solution was added dropwise to the solution while stirring. After the addition was complete, the mixture was stirred for 3 h to obtain Ti-BN sol. The Ti-BN sol was placed in an 80℃ water bath and evaporated to a gel state. It was then transferred to a vacuum drying oven and dried at 80℃ for 12 h to obtain Ti-BN gel. The obtained Ti-BN gel was placed in a tube furnace, and the air inside the tube furnace was replaced with N2 for 30 min. The temperature was then increased to 460℃ at 2℃ / min and heat-treated for 3 h. After cooling to room temperature, TiO2-BN nanosheets were obtained.

[0102] Step 2: Preparation of MgAl2O4-TiO2-BN support

[0103] The raw materials used are in the following weight proportions: 16.5 parts magnesium nitrate (Mg(NO3)2·6H2O), 90 parts aluminum nitrate (Al(NO3)3·9H2O), 25 parts TiO2-BN nanosheets, 50 parts citric acid, and 400 parts water.

[0104] Based on step two of Example 2, the modified TiO2-BN nanosheets were replaced with unmodified TiO2-BN nanosheets, and the remaining operations and conditions were the same as in step two of Example 2.

[0105] Step 3: Loading active ingredients and additives

[0106] The raw materials used are in the following weight proportions: ferric nitrate (Fe(NO3)3·9H2O) 65 parts, ammonium molybdate ((NH4)6Mo7O) 24 The following ingredients were used: 15.5 parts of manganese nitrate (Mn(NO3)2·4H2O), 11 parts of manganese nitrate (Mn(NO3)2·4H2O), 350 parts of deionized water, 2.5 parts of sodium polyacrylate, 17.5 parts of neodymium nitrate (Nd(NO3)3·6H2O), 10 parts of yttrium nitrate (Y(NO3)3·6H2O), 3.5 parts of lanthanum phosphate (LaPO4), and 120 parts of MgAl2O4-TiO2-BN composite carrier. The specific operation and conditions were the same as step three in Example 2.

[0107] Step 4: Reduction and Crystallization

[0108] The specific operation and conditions are the same as step four in Example 2.

[0109] Comparative Example 2: A catalyst for ammonia synthesis

[0110] A catalyst for ammonia synthesis, the raw materials for which, by weight, include 65 parts of ferric nitrate (Fe(NO3)3·9H2O) and ammonium molybdate ((NH4)6Mo7O) 2415.5 parts of manganese nitrate (Mn(NO3)2·4H2O), 11 parts of manganese nitrate (Mn(NO3)2·4H2O), 350 parts of deionized water, 2.5 parts of sodium polyacrylate, 17.5 parts of cerium nitrate (Ce(NO3)3·6H2O), 10 parts of zirconium nitrate (Zr(NO3)4·5H2O), and 120 parts of MgAl2O4-TiO2-BN composite carrier.

[0111] A method for preparing an ammonia synthesis catalyst includes the following steps:

[0112] Step 1: Preparation of modified TiO2-BN nanosheets

[0113] The specific operation and conditions are the same as step one in Example 2.

[0114] Step 2: Preparation of MgAl2O4-TiO2-BN composite support

[0115] The specific operation and conditions are the same as step two in Example 2.

[0116] Step 3: Loading active ingredients and additives

[0117] The raw materials used are in the following weight proportions: ferric nitrate (Fe(NO3)3·9H2O) 65 parts, ammonium molybdate ((NH4)6Mo7O) 24 15.5 parts of manganese nitrate (Mn(NO3)2·4H2O), 11 parts of manganese nitrate (Mn(NO3)2·4H2O), 350 parts of deionized water, 2.5 parts of sodium polyacrylate, 17.5 parts of cerium nitrate (Ce(NO3)3·6H2O), 10 parts of zirconium nitrate (Zr(NO3)4·5H2O), and 120 parts of MgAl2O4-TiO2-BN composite carrier.

[0118] Ferric nitrate, ammonium molybdate, manganese nitrate, deionized water, cerium nitrate, and zirconium nitrate were added to a reactor and stirred until completely dissolved. Sodium polyacrylate was then added, and stirring was continued for 1 hour to obtain the active component sol. The remaining operations and conditions were the same as step three in Example 2.

[0119] Step four, the operation and conditions are the same as step four in Example 2.

[0120] Comparative Example 3

[0121] A method for preparing an ammonia synthesis catalyst includes the following steps:

[0122] Step 1: Preparation of composite carrier

[0123] Weigh 12.8 parts of Mg(NO3)2·6H2O and 87.3 parts of Al(NO3)3·9H2O, dissolve them in 300 parts of deionized water, add 36.0 parts of citric acid, stir in a water bath at 75℃ for 1.5h to form a sol, dry the sol at 120℃ for 10h to form a dry gel, and calcine the dry gel at 700℃ for 4h to obtain the composite carrier.

[0124] Step 2: Loading active components and additives

[0125] Weigh out 61 parts of Fe(NO3)3·9H2O and (NH4)6Mo7O 24 15.5 parts of 4H2O and 12 parts of Mn(NO3)2·4H2O were dissolved in 350 parts of deionized water; 14.4 parts of Ce(NO3)3·6H2O, 8.6 parts of LaPO4, and 5 parts of 30% silica sol were added, and the mixture was sonicated for 30 min at a power of 500 W; then 65 parts of composite carrier were added, and the mixture was impregnated at 50℃ for 14 h, with stirring for 20 min every 2 h during impregnation. After impregnation, the pH of the sol was adjusted to 10.5 with 10% ammonia water, and stirring was continued for 1.5 h. The mixture was then aged at room temperature for 40 h to form a catalyst precursor gel; the catalyst precursor gel was broken into 5 mm particles, washed with water until the washing solution was neutral, and then washed three times with anhydrous ethanol for later use.

[0126] Step 3: Reduction and Crystallization

[0127] The specific operations and conditions are the same as those in step four of Example 2.

[0128] Performance testing

[0129] The catalysts of Examples 1-3 and Comparative Examples 1-3 were subjected to performance tests, and the test methods are as follows:

[0130] 1. Ammonia Yield Determination Test

[0131] Experimental method: Catalyst loading was 20g; feed gas was a mixture of H2 and N2 at a volume ratio of 3:1; reactor pressure was 12MPa; and mass hourly space velocity (MSV) based on catalyst mass was 15000h. -1 The temperature is 380℃; the amount of ammonia generated at the reactor outlet is measured, which is the ammonia yield and recorded as the initial ammonia yield.

[0132] The ammonia yield is calculated based on the conversion rate of N2 in the feed gas. Ammonia yield = (amount of N in ammonia production / amount of N2 in feed gas × 2) × 100%.

[0133] 2. Experiment to determine ammonia yield after 1000 hours of catalyst use: The ammonia synthesis reaction was carried out for 1000 hours according to the conditions of the ammonia yield determination experiment; the catalyst after 1000 hours of reaction was reused to catalyze ammonia synthesis, and the amount of ammonia generated was determined according to the method of the ammonia yield determination experiment. The ammonia yield after 1000 hours of catalyst use was calculated.

[0134] 3. Experiment to determine the ammonia yield using a catalyst treated at high temperature:

[0135] High-temperature treatment method: The catalyst was placed in a tube furnace and treated at 550℃, 15MPa, and N2 atmosphere for 200h. The catalyst after high-temperature treatment was then subjected to ammonia yield determination tests under the initial ammonia yield test conditions, and the ammonia yield of the catalyst after high-temperature treatment was calculated.

[0136] 4. Ammonia yield after 200h sulfur poisoning test of catalyst: Add 50ppm H2S to the feed gas. Except for the feed gas, other reaction conditions are the same as the initial ammonia yield test conditions. After 200h of reaction, the amount of ammonia generated is measured according to the ammonia yield determination test method. The ammonia yield is calculated, which is the ammonia yield after 200h of catalyst sulfur poisoning test.

[0137] The test results are shown in Table 1.

[0138] Table 1 Catalyst performance test results

[0139]

[0140] Analysis of the data in Table 1 shows that the initial ammonia yields for the experimental groups corresponding to the catalysts in Examples 1-3 were 21.5-23 mmol·g. -1 ·h -1 After continuous operation of the catalyst for 1000 hours, the ammonia yield was 21–22.3 mmol·g. -1 ·h -1 The ammonia yield after high-temperature treatment of the catalyst was 20.2–21.5 mmol·g. -1 ·h -1 The ammonia yield of the catalyst after a 200-hour sulfur poisoning test was 19.6–20.7 mmol·g. -1 ·h -1 Calculations showed that, relative to the initial ammonia yield, the ammonia yield decreased by 2.3-3.0% after 1000 hours of catalyst operation, by 5.5-6.8% after high-temperature treatment, and by 8.9-9.8% after sulfur poisoning test. This indicates that the ammonia synthesis catalyst prepared in this invention has good high-temperature resistance, sulfur resistance, and high stability.

[0141] In Comparative Example 1, without modification of the TiO2-BN nanosheets, the ammonia yield of the prepared catalyst decreased by 8.5% after 1000 hours of operation, decreased by 24.8% after heat treatment, and decreased by 14.8% after sulfur treatment compared to the initial ammonia yield. In Comparative Example 3, without TiO2-BN nanosheets, the ammonia yield of the prepared catalyst decreased by 10.7% after 1000 hours of operation, decreased by 29.2% after heat treatment, and decreased by 19.7% after a 200-hour sulfur poisoning test compared to the initial ammonia yield. This indicates that the MgAl2O4-TiO2-BN composite support prepared in this invention has a certain high-temperature resistance effect and can improve the stability of the catalyst. In Comparative Example 2, without the use of neodymium nitrate, yttrium nitrate, and lanthanum phosphate, the ammonia yield of the prepared catalyst decreased by 5.9% after 1000 hours of operation, decreased by 9.0% after heat treatment, and decreased by 27.7% after a 200-hour sulfur poisoning test compared to the initial ammonia yield.

[0142] Obviously, there are many other possible implementation methods under the concept of this invention. It should be stated here that any changes made under the inventive concept of this invention will fall within the protection scope of this invention.

Claims

1. A synthetic ammonia catalyst having stability, characterized by: The synthetic ammonia catalyst comprises, in parts by weight, 61-66 parts of iron nitrate, 12.4-15.7 parts of ammonium molybdate, 11-14 parts of manganese nitrate, 350-400 parts of deionized water, 2.5-3.5 parts of sodium polyacrylate, 15.4-17.5 parts of neodymium nitrate, 9.2-12.3 parts of yttrium nitrate, 3-5.5 parts of lanthanum phosphate, and 100-120 parts of MgAl2O4-TiO2-BN composite carrier; The MgAl2O4-TiO2-BN composite carrier comprises, in parts by weight, 14-16.5 parts of magnesium nitrate, 85-90 parts of aluminum nitrate, 25-29 parts of modified TiO2-BN nanosheet, 46-51 parts of citric acid, and 400-450 parts of water; The modified TiO2-BN nanosheet comprises, in parts by weight, 2.4-3.5 parts of h-BN powder, 4.8-7 parts of tetrabutyl titanate, 40-50 parts of anhydrous ethanol, 10-16 parts of dilute nitric acid solution, and 80-88 parts of hydrogen peroxide solution; The concentration of the dilute nitric acid solution is 0.01-0.05 mol / L, and the mass concentration of the hydrogen peroxide solution is 10-15%; The preparation method of the synthetic ammonia catalyst comprises the steps of preparing a modified TiO2-BN nanosheet, preparing a MgAl2O4-TiO2-BN composite carrier, loading active components and additives, and reducing and crystallizing; The modified TiO2-BN nanosheet is prepared as follows: tetrabutyl titanate is dissolved in anhydrous ethanol to form a solution, h-BN powder is added to the solution and ultrasonically dispersed for 30-45 min, the dilute nitric acid solution is added dropwise, and after the dropwise addition is completed, the solution is stirred to react for 2-3 h to obtain a Ti-BN sol; the sol is placed in a 70-80℃ water bath to evaporate into a Ti-BN gel, the Ti-BN gel is dried and heat-treated for 3-4 h to obtain TiO2-BN nanosheet; the TiO2-BN nanosheet is mixed with the hydrogen peroxide solution and added to a hydrothermal reaction kettle, and the mixture is sealed to react for 6-8 h; the precipitate is separated by centrifugation, and the modified TiO2-BN nanosheet is obtained after the precipitate is washed with water and dried; The MgAl2O4-TiO2-BN composite carrier is prepared as follows: magnesium nitrate, aluminum nitrate, and citric acid are dissolved in water and stirred for 1-1.5 h to form a sol, the modified TiO2-BN nanosheet is added to the sol and ultrasonically treated for 10 min, and the dry gel is obtained by drying the sol at 80℃ under vacuum for 10-12 h; the dry gel is placed in a tube furnace and heat-treated at a constant temperature for 3.5-4 h in a N2 atmosphere, and the MgAl2O4-TiO2-BN composite carrier is obtained after the dry gel is ground and pulverized after being naturally cooled; The active components and additives are loaded as follows: iron nitrate, ammonium molybdate, and manganese nitrate are dissolved in deionized water, and lanthanum phosphate, sodium polyacrylate, neodymium nitrate, and yttrium nitrate are added, and the mixture is stirred to form an active component sol; the MgAl2O4-TiO2-BN composite carrier is added to the active component sol, and the pH value is adjusted to 9.5-10.5; the catalyst precursor gel is formed after the mixture is aged at room temperature for 40-50 h, and the catalyst precursor gel is broken into gel particles; The reduction and crystallization: the catalyst precursor gel particles are blast dried, the dried gel is ground into powder and transferred to a microwave reactor for heating while H2-Ar mixed gas is introduced, and the reduction is carried out at 350-380 ℃ for 2-2.5 h; the introduction of H2-Ar mixed gas is stopped, N2 is introduced and the temperature is raised to 570-600 ℃, and the crystallization is carried out for 3-4 h, then the heating is stopped, N2 is continuously introduced and the temperature is naturally cooled to room temperature, to obtain the ammonia synthesis catalyst.

2. The ammonia synthesis catalyst according to claim 1, characterized in that: The ultrasonic dispersion: the power is 1-1.5 kW; the heat treatment: the heat treatment temperature is 430-460 ℃; the closed reaction: the reaction temperature is 120-130 ℃.

3. The ammonia synthesis catalyst with good stability according to claim 1, characterized in that: The constant-temperature calcination: the temperature is 800-850 ℃.

4. The ammonia synthesis catalyst with good stability according to claim 1, characterized in that: The constant-temperature impregnation: the constant-temperature impregnation time is 14-18 h.

5. The ammonia synthesis catalyst of claim 1, wherein the catalyst has a stability of 0.1% or less. 5 The blast drying temperature is 100-110 ℃.

6. The ammonia synthesis catalyst of claim 1, wherein the catalyst has a stability of 0.1% or less. 5 The H2-Ar mixed gas: the volume ratio of H2 to Ar is 1: (2-3). The blast drying temperature is 100-110 ℃. The H2-Ar mixed gas: the volume ratio of H2 to Ar is 1: (2-3).

Images