Ammonia purification composite molecular sieve catalyst, its preparation method and application

Abstract

The application provides an ammonia purification composite molecular sieve catalyst and a preparation method and application thereof, and the preparation method comprises the following steps: first mixing an ammonia type molecular sieve and a copper salt solution, and then sequentially performing first solid-liquid separation, first drying and first calcination to obtain a copper-loaded molecular sieve; second mixing the ammonia type molecular sieve and a platinum salt solution, and then sequentially performing second solid-liquid separation, second drying and second calcination to obtain a platinum-loaded molecular sieve; mixing the copper-loaded molecular sieve and the platinum-loaded molecular sieve, and then sequentially performing first ball milling and second ball milling to obtain the ammonia purification composite molecular sieve catalyst; and the platinum-loaded molecular sieve and the copper-loaded molecular sieve are mixed through multi-stage ball milling, active components platinum and copper are introduced, respectively, the two active components are ensured to not interfere with each other and to have a synergistic effect, and on the basis of ensuring that a platinum mode distribution is basically unchanged and the catalyst has high ammonia oxidation low-temperature activity and nitrogen selectivity, the use amount of the noble metal platinum is reduced.

Description

Technical Field

[0001] This invention belongs to the field of ammonia internal combustion engine exhaust gas purification technology, and relates to an ammonia purification composite molecular sieve catalyst, its preparation method and application. Background Technology

[0002] Currently, due to the scarcity of fossil fuels, ammonia is an ideal energy storage substance. Its molecules contain no carbon, and its complete combustion products consist only of water and nitrogen. Furthermore, compared to most gaseous fuels, it is easily compressed into a liquid state, making it convenient for storage and transportation. As the world's second-largest chemical product, ammonia has relatively well-developed storage and transportation facilities. Therefore, ammonia has the potential to become an alternative fuel for internal combustion engines.

[0003] CN114575996A discloses an ammonia internal combustion engine and its control method, providing a carbon-emission-free internal combustion engine device. Considering the difficulties in hydrogen storage and transportation, it employs ammonia as the primary fuel. By introducing the exhaust gas from the internal combustion engine into an ammonia cracking device, partial cracking of the ammonia is achieved. The hydrogen produced by ammonia cracking enhances the reactivity of the in-cylinder gases, enabling stable operation of the entire internal combustion engine. The hydrogen used is only for starting the internal combustion engine, requiring a small amount and avoiding the problem of hydrogen transport difficulties. This scheme selects the fuel supply strategy based on operating conditions, thereby achieving efficient operation of the ammonia internal combustion engine. The designed ammonia internal combustion engine starts with pure hydrogen, and after starting, pure ammonia is used as the sole fuel supply to the internal combustion engine.

[0004] However, during the combustion process of ammonia in an internal combustion engine, some ammonia fuel remains unburned and enters the atmosphere with the exhaust, causing pollution. Therefore, ammonia purification catalysts are needed to catalytically purify the ammonia in the exhaust. Currently, ammonia purification catalysts mainly use precious metal catalysts, but existing catalysts require large amounts of precious metals to fully catalytically oxidize ammonia. This leads to high catalyst costs and also causes deep oxidation of ammonia, producing nitrogen oxides and causing secondary pollution. However, directly reducing the amount of precious metal platinum would significantly reduce catalyst performance. These problems result in high costs and secondary pollution issues with existing catalysts, making it impossible to effectively purify the ammonia emitted from the exhaust of ammonia internal combustion engines.

[0005] In summary, providing a low-cost, highly active, and highly selective ammonia purification catalyst and its preparation method is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] The purpose of this invention is to provide an ammonia purification composite molecular sieve catalyst, its preparation method, and its application. This ammonia purification composite molecular sieve catalyst couples dual functional sites for ammonia oxidation and nitrogen oxide reduction, exhibiting high low-temperature activity and nitrogen selectivity for ammonia purification even with extremely low platinum content. This solves the problems of high cost and secondary pollution caused by excessive use of precious metals in existing ammonia purification catalysts, as well as the problem of catalyst performance degradation due to directly reducing the amount of platinum.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a method for preparing an ammonia purification composite molecular sieve catalyst, the preparation method comprising the following steps:

[0009] (1) A first mixed ammonia molecular sieve and a copper salt solution are then subjected to a first solid-liquid separation, a first drying and a first calcination to obtain a copper-loaded molecular sieve.

[0010] (2) The second mixture of ammonia-type molecular sieve and platinum salt solution is then subjected to a second solid-liquid separation, a second drying and a second calcination to obtain a loaded platinum molecular sieve;

[0011] (3) Mix the copper molecular sieve loaded in step (1) and the platinum molecular sieve loaded in step (2), and then perform a first ball milling and a second ball milling in sequence to obtain the ammonia purification composite molecular sieve catalyst.

[0012] Steps (1) and (2) are not in any particular order.

[0013] The preparation method provided by this invention involves exchanging copper ions into the pores of a molecular sieve support. After high-temperature calcination, copper is uniformly distributed in the cation sites of the molecular sieve, mainly in the form of copper ions. Platinum is uniformly loaded onto the molecular sieve support using an impregnation method. After high-temperature calcination, platinum exists mainly in a metallic state. The metallic platinum has high activity and can effectively catalyze the oxidation of ammonia in the exhaust gas of an ammonia internal combustion engine. Finally, the loaded platinum molecular sieve and the loaded copper molecular sieve are mixed by multi-stage ball milling. This ensures that the two sets of molecular sieves are mixed uniformly while ensuring that the two active components do not interfere with each other and have a synergistic effect. In addition, multi-stage ball milling can also reduce the amount of precious metal platinum used in the composite molecular sieve catalyst.

[0014] It is worth noting that the multi-stage ball milling and mixing of supported platinum molecular sieves and supported copper molecular sieves is the reason for reducing the amount of precious metal platinum used. This ensures that the morphological distribution of platinum remains basically unchanged, while the atomic utilization rate is higher and the activity is stronger. This allows the composite molecular sieve catalyst to couple the dual functional sites of ammonia oxidation and nitrogen oxide reduction. Even with a low content of precious metal platinum, it still has high low-temperature ammonia oxidation activity and nitrogen selectivity.

[0015] As a preferred technical solution of the present invention, the ammonia-type molecular sieve includes any one or a combination of at least two of ZSM-5 molecular sieve, SSZ-13 molecular sieve, SSZ-39 molecular sieve, SAPO-34 molecular sieve or Y molecular sieve.

[0016] Preferably, the copper salt in the copper salt solution in step (1) includes any one or a combination of at least two of copper chloride, copper sulfate, copper nitrate, or copper acetate.

[0017] In this invention, the solvent in the copper salt solution includes water, such as deionized water or qualified industrial recycled water.

[0018] Preferably, the molar concentration of copper in the copper salt solution in step (1) is 0.01-0.1 mol / L, for example, it can be 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, 0.05 mol / L, 0.06 mol / L, 0.07 mol / L, 0.08 mol / L, 0.09 mol / L or 0.1 mol / L, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0019] Preferably, the solid-liquid ratio of the ammonia molecular sieve and the copper salt solution in step (1) is 1:(20-70) g / mL, for example, it can be 1:20 g / mL, 1:25 g / mL, 1:30 g / mL, 1:35 g / mL, 1:40 g / mL, 1:45 g / mL, 1:50 g / mL, 1:55 g / mL, 1:60 g / mL, 1:65 g / mL or 1:70 g / mL, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0020] As a preferred technical solution of the present invention, the first mixing in step (1) is carried out under stirring.

[0021] Preferably, the temperature of the first mixing in step (1) is 40-60°C, for example, it can be 40°C, 41°C, 42°C, 43°C, 44°C, 45°C, 46°C, 47°C, 48°C, 49°C, 50°C, 51°C, 52°C, 53°C, 54°C, 55°C, 56°C, 57°C, 58°C, 59°C or 60°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0022] Preferably, the mixing time in step (1) is 4-8 hours, for example, it can be 4 hours, 4.1 hours, 4.2 hours, 4.3 hours, 4.4 hours, 4.5 hours, 4.6 hours, 4.7 hours, 4.8 hours, 4.9 hours, 5 hours, 5.1 hours, 5.2 hours, 5.3 hours, 5.4 hours, 5.5 hours, 5.6 hours, 5.7 hours, 5.8 hours, 5.9 hours, 6 hours, 6.1 hours, 6.2 hours, 6.3 hours, 6.4 hours, 6.5 hours, 6.6 hours, 6.7 hours, 6.8 hours, 6.9 hours, 7 hours, 7.1 hours, 7.2 hours, 7.3 hours, 7.4 hours, 7.5 hours, 7.6 hours, 7.7 hours, 7.8 hours, 7.9 hours, or 8 hours, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0023] Preferably, step (1) the first solid-liquid separation includes any one or a combination of at least two of vacuum filtration, pressure filtration or centrifugation.

[0024] Preferably, the temperature of the first drying step (1) is 30-90℃, for example, it can be 30℃, 32℃, 34℃, 36℃, 38℃, 40℃, 42℃, 44℃, 46℃, 48℃, 50℃, 52℃, 53℃, 54℃, 56℃, 58℃, 60℃, 62℃, 64℃, 66℃, 68℃, 69℃, 70℃, 72℃, 74℃, 76℃, 78℃, 80℃, 82℃, 84℃, 86℃, 88℃ or 90℃, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0025] As a preferred technical solution of the present invention, after the first drying in step (1) and before the first calcination, the method further includes: replacing the ammonia molecular sieve in step (1) with the first dried copper molecular sieve precursor, and then repeating step (1) until the first drying.

[0026] In this invention, in order to ensure the loading of the active component copper, the copper element can be loaded multiple times.

[0027] Preferably, the repetition is at least once, for example, once, twice or three times, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0028] Preferably, when repeating step (1), the molar concentration of copper in the copper salt solution is different each time.

[0029] Preferably, the first roasting temperature in step (1) is 450-550℃, for example, it can be 450℃, 460℃, 470℃, 480℃, 490℃, 500℃, 510℃, 520℃, 530℃, 540℃ or 550℃, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0030] Preferably, the first roasting time in step (1) is 4-8 hours, for example, it can be 4 hours, 4.1 hours, 4.2 hours, 4.3 hours, 4.4 hours, 4.5 hours, 4.6 hours, 4.7 hours, 4.8 hours, 4.9 hours, 5 hours, 5.1 hours, 5.2 hours, 5.3 hours, 5.4 hours, 5.5 hours, 5.6 hours, 5.7 hours, 5.8 hours, 5.9 hours, 6 hours, 6.1 hours, 6.2 hours, 6.3 hours, 6.4 hours, 6.5 hours, 6.6 hours, 6.7 hours, 6.8 hours, 6.9 hours, 7 hours, 7 hours, 7.1 hours, 7.2 hours, 7.3 hours, 7.4 hours, 7.5 hours, 7.6 hours, 7.7 hours, 7.8 hours, 7.9 hours, or 8 hours, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0031] As a preferred technical solution of the present invention, the platinum salt in the platinum salt solution in step (2) includes any one or a combination of at least two of tetraammineplatinum nitrate, chloroplatinic acid, platinum chloride or ammonium chloroplatinate.

[0032] In this invention, the solvent in the platinum salt solution includes water, such as deionized water or qualified industrial recycled water.

[0033] Preferably, the mass ratio of platinum in the ammonia molecular sieve and platinum salt solution in step (2) is 1:(0.002-0.02), for example, it can be 1:0.002, 1:0.003, 1:0.004, 1:0.005, 1:0.006, 1:0.007, 1:0.008, 1:0.009, 1:0.01, 1:0.011, 1:0.012, 1:0.013, 1:0.014, 1:0.015, 1:0.016, 1:0.017, 1:0.018, 1:0.019 or 1:0.02, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 1:(0.002-0.01).

[0034] As a preferred technical solution of the present invention, the second mixing in step (2) is carried out under stirring.

[0035] Preferably, the temperature of the second mixing in step (2) is 20-40°C, for example, it can be 20°C, 21°C, 22°C, 23°C, 24°C, 25°C, 26°C, 27°C, 28°C, 29°C, 30°C, 31°C, 32°C, 33°C, 34°C, 35°C, 36°C, 37°C, 38°C, 39°C or 40°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0036] Preferably, the mixing time in step (2) is 0.5-3h, for example, it can be 0.5h, 0.6h, 0.7h, 0.8h, 0.9h, 1h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h, 2h, 2.1h, 2.2h, 2.3h, 2.4h, 2.5h, 2.6h, 2.7h, 2.8h, 2.9h or 3h, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0037] Preferably, step (2) the second solid-liquid separation includes any one or a combination of at least two of vacuum filtration, pressure filtration or centrifugation.

[0038] Preferably, the temperature of the second drying step (2) is 30-90℃, for example, it can be 30℃, 32℃, 34℃, 36℃, 38℃, 40℃, 42℃, 44℃, 46℃, 48℃, 50℃, 52℃, 53℃, 54℃, 56℃, 58℃, 60℃, 62℃, 64℃, 66℃, 68℃, 69℃, 70℃, 72℃, 74℃, 76℃, 78℃, 80℃, 82℃, 84℃, 86℃, 88℃ or 90℃, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0039] Preferably, the second roasting temperature in step (2) is 500-600℃, for example, it can be 500℃, 510℃, 520℃, 530℃, 540℃, 550℃, 560℃, 570℃, 580℃, 590℃ or 600℃, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0040] Preferably, the second roasting time in step (2) is 3-7 hours, for example, it can be 3 hours, 3.1 hours, 3.2 hours, 3.3 hours, 3.4 hours, 3.5 hours, 3.6 hours, 3.7 hours, 3.8 hours, 3.9 hours, 4 hours, 4.1 hours, 4.2 hours, 4.3 hours, 4.4 hours, 4.5 hours, 4.6 hours, 4.7 hours, 4.8 hours, 4.9 hours, 5 hours, 5.1 hours, 5.2 hours, 5.3 hours, 5.4 hours, 5.5 hours, 5.6 hours, 5.7 hours, 5.8 hours, 5.9 hours, 6 hours, 6.1 hours, 6.2 hours, 6.3 hours, 6.4 hours, 6.5 hours, 6.6 hours, 6.7 hours, 6.8 hours, 6.9 hours, or 7 hours, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0041] As a preferred technical solution of the present invention, the mass ratio of the copper-loaded molecular sieve and the platinum-loaded molecular sieve in step (3) is (1-10):1, for example, it can be 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1 or 10:1, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0042] Preferably, the rotation speed of the first ball mill in step (3) is 50-100 rpm, for example, it can be 50 rpm, 55 rpm, 60 rpm, 65 rpm, 70 rpm, 75 rpm, 80 rpm, 85 rpm, 90 rpm, 95 rpm or 100 rpm, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0043] Preferably, in step (3), the ball-to-material ratio of the first ball mill is (5-50):1, for example, it can be 5:1, 10:1, 15:1, 20:1, 25:1, 30:1, 35:1, 40:1, 45:1 or 50:1, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0044] Preferably, the first ball milling time in step (3) is 5-30 min, for example, it can be 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, 11 min, 12 min, 13 min, 14 min, 15 min, 16 min, 17 min, 18 min, 19 min, 20 min, 21 min, 22 min, 23 min, 24 min, 25 min, 26 min, 27 min, 28 min, 29 min or 30 min, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0045] Preferably, the rotational speed of the second ball mill in step (3) is 200-400 rpm, for example, it can be 200 rpm, 210 rpm, 220 rpm, 230 rpm, 240 rpm, 250 rpm, 260 rpm, 270 rpm, 280 rpm, 290 rpm, 300 rpm, 310 rpm, 320 rpm, 330 rpm, 340 rpm, 350 rpm, 360 rpm, 370 rpm, 380 rpm, 390 rpm or 400 rpm, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0046] Preferably, in step (3), the ball-to-material ratio of the second ball mill is (5-50):1, for example, it can be 5:1, 10:1, 15:1, 20:1, 25:1, 30:1, 35:1, 40:1, 45:1 or 50:1, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0047] Preferably, the second ball milling time in step (3) is 5-20 min, for example, it can be 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, 11 min, 12 min, 13 min, 14 min, 15 min, 16 min, 17 min, 18 min, 19 min or 20 min, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0048] It is worth noting that by controlling the process parameters of the first and second ball mills, this invention ensures that the two sets of molecular sieves are fully and uniformly mixed, and can also significantly improve the utilization rate of molecular sieve powder.

[0049] As a preferred technical solution of the present invention, the preparation method includes the following steps:

[0050] (1) The ammonia molecular sieve and copper salt solution were mixed and stirred at 40-60℃ for 4-8 hours according to a solid-liquid ratio of 1:(20-70)g / mL. After the first solid-liquid separation, the solution was dried at 30-90℃ and then calcined at 450-550℃ for 4-8 hours to obtain the loaded copper molecular sieve.

[0051] The copper salt in the copper salt solution includes any one or a combination of at least two of copper chloride, copper sulfate, copper nitrate, or copper acetate; the molar concentration of copper in the copper salt solution is 0.01-0.1 mol / L.

[0052] After the first drying and before the first calcination, the process further includes: replacing the ammonia-type molecular sieve in step (1) with the first-dried loaded copper molecular sieve precursor, and then repeating step (1) until the first drying; the number of repetitions is at least 1; and the molar concentration of copper in the copper salt solution is different each time the step (1) is repeated.

[0053] (2) The ammonia molecular sieve and platinum salt solution are mixed and stirred for 0.5-3h at a temperature of 20-40℃. After the second solid-liquid separation, the solution is dried at a temperature of 30-90℃ and then calcined at a temperature of 500-600℃ for 3-7h to obtain the supported platinum molecular sieve.

[0054] The platinum salt in the platinum salt solution includes any one or a combination of at least two of tetraammineplatinum nitrate, chloroplatinic acid, platinum chloride, or ammonium chloroplatinate; the mass ratio of platinum in the ammonia-type molecular sieve and the platinum salt solution is 1:(0.002-0.02).

[0055] (3) Mix the copper molecular sieve loaded in step (1) and the platinum molecular sieve loaded in step (2) at a mass ratio of (1-10):1, and then perform a first ball milling for 5-30 min at a speed of 50-100 rpm and a ball-to-material ratio of (5-50):1, followed by a second ball milling for 5-20 min at a speed of 200-400 rpm and a ball-to-material ratio of (5-50):1 to obtain the ammonia purification composite molecular sieve catalyst;

[0056] Steps (1) and (2) are not in any particular order.

[0057] In a second aspect, the present invention provides an ammonia purification composite molecular sieve catalyst, wherein the ammonia purification composite molecular sieve catalyst is prepared by the preparation method described in the first aspect;

[0058] Based on a mass percentage of 100%, the ammonia purification composite molecular sieve catalyst comprises: 0.01-0.095% platinum, 1-4% copper, and the balance being ammonia-type molecular sieve.

[0059] In this invention, the platinum content in the ammonia purification composite molecular sieve catalyst is 0.01-0.095% by mass, for example, it can be 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, or 0.095%, etc., and the copper content in the ammonia purification composite molecular sieve catalyst is 1-4% by mass, for example, it can be 1%, 1.1%, 1.2%, 1.3%, etc. 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, or 4%, etc., but not limited to the listed values; other unlisted values ​​within this range also apply.

[0060] In this invention, the ammonia purification composite molecular sieve catalyst has dual functional sites coupling ammonia oxidation and nitrogen oxide reduction. Even with low platinum content, it still exhibits high low-temperature ammonia purification activity and nitrogen selectivity, ensuring efficient ammonia purification reaction under high humidity and low oxygen conditions, thus meeting the purification requirements of ammonia internal combustion engines for unburned ammonia. Furthermore, the high activity across the entire temperature range is due to the platinum content in the ammonia purification composite molecular sieve catalyst. Platinum possesses excellent oxidizing power and is distributed as small nanoparticles on the molecular sieve support, effectively catalyzing the oxidation of ammonia in the exhaust gas of ammonia internal combustion engines, ensuring complete oxidation. Additionally, the active copper in the ammonia purification composite molecular sieve catalyst exists in a highly dispersed ionic form within the molecular sieve support, selectively reducing byproduct nitrogen oxides to nitrogen, thereby improving nitrogen selectivity.

[0061] Thirdly, the present invention provides an application of an ammonia purification composite molecular sieve catalyst, the application of which includes using the ammonia purification composite molecular sieve catalyst described in the second aspect to catalytically purify the exhaust gas formed during the operation of an ammonia internal combustion engine.

[0062] The temperature for catalytic purification is 150-350℃;

[0063] Based on a volume percentage of 100%, the water content in the exhaust gas of the ammonia internal combustion engine is 5-15%, and the oxygen content in the exhaust gas of the ammonia internal combustion engine is 2-10%.

[0064] The volume concentration of ammonia in the exhaust gas generated during the operation of the ammonia internal combustion engine is 300-1500 ppm.

[0065] In this invention, the total flow rate of the gas in the catalytic purification process can be 300-1000 mL / min, and the space velocity can be 100,000-300,000 h⁻¹. -1 .

[0066] Compared with the prior art, the present invention has the following beneficial effects:

[0067] (1) The preparation method provided by the present invention uses multi-stage ball milling to mix supported platinum molecular sieve and supported copper molecular sieve, ensuring that the two groups of molecular sieves are mixed evenly, while ensuring that the two active components do not interfere with each other and have a synergistic effect. In addition, multi-stage ball milling ensures that the ammonia purification composite molecular sieve catalyst has dual functional sites coupled with ammonia oxidation and nitrogen oxide reduction, and can also reduce the amount of precious metal platinum. While ensuring that the morphological distribution of platinum remains basically unchanged, the atomic utilization rate is higher and the activity is stronger, so that the composite molecular sieve catalyst has high ammonia oxidation low temperature activity and nitrogen selectivity.

[0068] (2) The ammonia purification composite molecular sieve catalyst provided by the present invention has high activity in the range of 200-350℃ and in the presence of 10% water vapor and 5% oxygen, which can meet the requirements of the catalyst for purifying ammonia under high temperature and high humidity conditions in ammonia internal combustion engines; at the same time, it also has high nitrogen selectivity in the range of 200-350℃, which meets the requirements for purifying gas in ammonia internal combustion engines. Attached Figure Description

[0069] Figure 1 The graph shows the ammonia conversion rate and nitrogen selectivity of the ammonia purification composite molecular sieve catalyst obtained in Example 1 for the catalytic purification reaction of ammonia in the exhaust gas of an ammonia internal combustion engine. Detailed Implementation

[0070] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0071] Example 1

[0072] This embodiment provides an ammonia purification composite molecular sieve catalyst and its preparation method. The ammonia purification composite molecular sieve catalyst comprises, by weight percentage, 0.05% platinum, 2.5% copper, and the balance being SSZ-39 molecular sieve.

[0073] The preparation method includes the following steps:

[0074] (1) SSZ-39 molecular sieve and copper nitrate aqueous solution were mixed and stirred at 60°C for 6 hours according to a solid-liquid ratio of 1:50 g / mL. After filtration, the mixture was dried at 60°C and then calcined at 500°C for 6 hours to obtain copper-loaded molecular sieve.

[0075] After the first drying and before the first calcination, the process further includes: replacing the SSZ-39 molecular sieve in step (1) with the first dried copper molecular sieve precursor, and then repeating step (1) until the first drying; the number of repetitions is 1; when the step (1) is repeated, the molar concentration of copper in the copper nitrate aqueous solution is different each time, and is 0.1 mol / L and 0.05 mol / L respectively;

[0076] (2) SSZ-39 molecular sieve and tetraammine nitrate platinum aqueous solution were mixed and stirred for 0.5 h at 25 °C. After centrifugation, they were dried for the second time at 60 °C and then calcined for the second time at 550 °C for 6 h to obtain the supported platinum molecular sieve.

[0077] The mass ratio of platinum in the ammonia-type molecular sieve and platinum salt solution is 1:0.004;

[0078] (3) The copper molecular sieve loaded in step (1) and the platinum molecular sieve loaded in step (2) are mixed at a mass ratio of 4:1. Then, the mixture is ball-milled for 10 minutes at a speed of 80 rpm and a ball-to-material ratio of 8:1. Then, the mixture is ball-milled for 10 minutes at a speed of 300 rpm and a ball-to-material ratio of 10:1 to obtain the ammonia purification composite molecular sieve catalyst.

[0079] Steps (1) and (2) are not in any particular order.

[0080] Example 2

[0081] This embodiment provides an ammonia purification composite molecular sieve catalyst and its preparation method. The ammonia purification composite molecular sieve catalyst comprises, by weight percentage, 0.09% platinum, 2% copper, and the balance being SSZ-39 molecular sieve.

[0082] The preparation method includes the following steps:

[0083] (1) SSZ-39 molecular sieve and copper nitrate aqueous solution were mixed and stirred at 60°C for 6 hours according to a solid-liquid ratio of 1:60 g / mL. After filtration, the mixture was dried at 60°C and then calcined at 550°C for 6 hours to obtain copper-loaded molecular sieve.

[0084] After the first drying and before the first calcination, the process further includes: replacing the SSZ-39 molecular sieve in step (1) with the first dried copper molecular sieve precursor, and then repeating step (1) until the first drying; the number of repetitions is 1; when repeating step (1), the molar concentration of copper in the copper nitrate aqueous solution is different each time, and is 0.08 mol / L and 0.09 mol / L respectively;

[0085] (2) The SSZ-39 molecular sieve and the aqueous solution of tetraammine nitrate were mixed and stirred for 0.5 h at 25 °C. After centrifugation, the mixture was dried for the second time at 60 °C and then calcined for the second time at 600 °C for 5 h to obtain the supported platinum molecular sieve.

[0086] The mass ratio of platinum in the ammonia-type molecular sieve and platinum salt solution is 1:0.008;

[0087] (3) Mix the copper molecular sieve loaded in step (1) and the platinum molecular sieve loaded in step (2) at a mass ratio of 3:1, and then perform a first ball milling for 6 minutes at a speed of 100 rpm and a ball-to-material ratio of 10:1, followed by a second ball milling for 9 minutes at a speed of 280 rpm and a ball-to-material ratio of 15:1 to obtain the ammonia purification composite molecular sieve catalyst.

[0088] Steps (1) and (2) are not in any particular order.

[0089] Example 3

[0090] This embodiment provides an ammonia purification composite molecular sieve catalyst and its preparation method. Except that the second calcination temperature in step (2) is 520°C, the first ball milling speed is 50 rpm and the time is 5 min, and the second ball milling speed is 200 rpm and the time is 10 min, all other conditions are the same as in Example 1.

[0091] Example 4

[0092] This embodiment provides an ammonia purification composite molecular sieve catalyst and its preparation method. Except for the mass ratio of supported copper molecular sieve and supported platinum molecular sieve in step (3) being 15:1, all other conditions are the same as in Example 1.

[0093] Example 5

[0094] This embodiment provides an ammonia purification composite molecular sieve catalyst and its preparation method. Except that the rotation speed of the second ball mill in step (3) is the same as that of the first ball mill (80 rpm), all other conditions are the same as in Example 1.

[0095] Example 6

[0096] This embodiment provides an ammonia purification composite molecular sieve catalyst and its preparation method. Except for the second ball milling speed of 500 rpm in step (3), the other conditions are the same as in Example 1.

[0097] Example 7

[0098] This embodiment provides an ammonia purification composite molecular sieve catalyst and its preparation method. Except for the first ball milling and the second ball milling in step (3), the other conditions are the same as in Example 1.

[0099] Comparative Example 1

[0100] This comparative example provides an ammonia purification composite molecular sieve catalyst and its preparation method. Except for the first ball milling in step (3), the other conditions are the same as in Example 1.

[0101] Application Examples 1-7 and Comparative Application Example 1

[0102] The ammonia purification composite molecular sieve catalysts prepared in Examples 1-7 and Comparative Example 1 were used to catalytically purify ammonia gas in a simulated ammonia internal combustion engine. The catalytic purification temperature was 225°C. The water content in the exhaust gas of the ammonia internal combustion engine was 10% by volume, and the oxygen content in the exhaust gas was 5%. The total gas flow rate in the exhaust gas of the ammonia internal combustion engine was 500 mL / min, and the space velocity was 200,000 h⁻¹. -1 The volume concentration of ammonia in the exhaust gas generated during the operation of the ammonia internal combustion engine is 1000 ppm.

[0103] The purified gas was measured using an infrared spectrometer. The parameters of the purified gas are detailed in Table 1.

[0104] Table 1

[0105] Ammonia conversion rate / % Nitrogen selectivity / % Application Example 1 99.9 80.7 Application Example 2 98.2 85.2 Application Example 3 93.3 88.5 Application Example 4 80.2 98.0 Application Example 5 95.7 78.8 Application Example 6 83.4 80.2 Application Example 7 100.0 73.9 Comparative Application Example 1 98.6 76.4

[0106] As shown in Table 1:

[0107] (1) The ammonia purification composite molecular sieve catalyst and its preparation method provided in Examples 1-3 of the present invention introduce active components platinum and copper respectively by multi-stage ball milling to mix supported platinum molecular sieve and supported copper molecular sieve. This ensures that the two active components do not interfere with each other and have a synergistic effect. While reducing the amount of precious metal platinum, it ensures that the composite molecular sieve catalyst still has high ammonia oxidation low temperature activity and nitrogen selectivity, and can also avoid the generation of nitrogen oxides by deep oxidation of ammonia.

[0108] (2) By comparing Application Example 1 and Application Example 4, it can be seen that when the proportion of copper molecular sieve in the composite molecular sieve catalyst is too high, the low-temperature activity of ammonia oxidation will be greatly reduced due to the low amount of noble metal platinum introduced.

[0109] (3) By comparing Application Example 1 and Application Examples 5-7, it can be seen that when the speed of the second ball mill is too low or the milling time is too short, it is not conducive to the uniform mixing of the supported copper molecular sieve and the supported platinum molecular sieve. The spatial distribution of the two active components is poor and they cannot work together effectively, resulting in a significant decrease in nitrogen selectivity. When the speed of the second ball mill is too high, the structure of the obtained composite molecular sieve catalyst is destroyed, resulting in a significant decrease in the low-temperature activity of ammonia oxidation and a slight decrease in nitrogen selectivity.

[0110] (4) Comparing the comprehensive application example 1 and the comparative application example 1, it can be seen that when only the first ball milling is performed, it is not conducive to the uniform mixing of the supported copper molecular sieve and the supported platinum molecular sieve. The spatial distribution of the two active components is poor and they cannot work together effectively, resulting in a significant decrease in nitrogen selectivity.

[0111] The ammonia purification composite molecular sieve catalyst prepared in Example 1 was used to catalytically purify ammonia in a simulated ammonia internal combustion engine. Gradient temperature tests were conducted on the catalytic purification temperature at 150℃, 175℃, 200℃, 225℃, 250℃, 275℃, 300℃, 325℃, and 350℃.

[0112] Based on a volume percentage of 100%, the water content in the exhaust gas of the ammonia internal combustion engine is 10%, and the oxygen content in the exhaust gas is 5%; the total gas flow rate in the exhaust gas of the ammonia internal combustion engine is 500 mL / min, and the space velocity is 200,000 h⁻¹. -1 The volume concentration of ammonia in the exhaust gas of the ammonia internal combustion engine is 1000 ppm.

[0113] For details of the purified gas results, please refer to [link / reference]. Figure 1 And Table 2.

[0114] Table 2

[0115]

[0116]

[0117] Depend on Figure 1 As shown in Table 2, the ammonia purification composite molecular sieve catalyst and its preparation method provided by the present invention introduce active components platinum and copper respectively by multi-stage ball milling and mixing of supported platinum molecular sieves and supported copper molecular sieves. This ensures that the two active components do not interfere with each other and have a synergistic effect. While ensuring that the platinum morphology distribution remains basically unchanged and that the catalyst has high low-temperature activity for ammonia oxidation and nitrogen selectivity, the amount of precious metal platinum used is reduced, and the generation of nitrogen oxides from deep oxidation of ammonia is avoided. This solves the problem of high cost caused by excessive platinum use in current ammonia purification catalysts, as well as the problem of catalyst performance degradation caused by directly reducing the amount of precious metal platinum.

[0118] The applicant declares that the detailed structural features of the present invention are illustrated through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the components selected in the present invention, additions of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing an ammonia purification composite molecular sieve catalyst, characterized in that, The preparation method includes the following steps: (1) The first mixed ammonia molecular sieve and copper salt solution are then subjected to the first solid-liquid separation, the first drying and the first calcination in sequence to obtain the loaded copper molecular sieve; (2) The second mixture of ammonia-type molecular sieve and platinum salt solution is then subjected to a second solid-liquid separation, a second drying, and a second calcination to obtain a loaded platinum molecular sieve; (3) Mix the copper molecular sieve loaded in step (1) and the platinum molecular sieve loaded in step (2), and then perform a first ball milling and a second ball milling in sequence to obtain the ammonia purification composite molecular sieve catalyst; The mass ratio of the copper-loaded molecular sieve to the platinum-loaded molecular sieve is (1-10):1; the first ball mill has a rotation speed of 50-100 rpm, a ball-to-material ratio of (5-50):1, and a time of 5-30 min; the second ball mill has a rotation speed of 200-400 rpm, a ball-to-material ratio of (5-50):1, and a time of 5-20 min. Steps (1) and (2) are not in any particular order.

2. The preparation method according to claim 1, characterized in that, The ammonia-type molecular sieve includes any one or a combination of at least two of ZSM-5 molecular sieve, SSZ-13 molecular sieve, SSZ-39 molecular sieve, SAPO-34 molecular sieve or Y molecular sieve; The copper salt in the copper salt solution in step (1) includes any one or a combination of at least two of copper chloride, copper sulfate, copper nitrate or copper acetate; The molar concentration of copper in the copper salt solution in step (1) is 0.01-0.1 mol / L; The solid-liquid ratio of the ammonia molecular sieve and copper salt solution in step (1) is 1:(20-70)g / mL.

3. The preparation method according to claim 1, characterized in that, Step (1) The first mixing is carried out under stirring; Step (1) The temperature of the first mixture is 40-60℃; Step (1) The first mixing time is 4-8 hours; Step (1) The first solid-liquid separation includes any one or a combination of at least two of vacuum filtration, pressure filtration or centrifugation; Step (1) The temperature of the first drying is 30-90℃.

4. The preparation method according to claim 1, characterized in that, After the first drying in step (1), before the first calcination, the process further includes: replacing the ammonia-type molecular sieve in step (1) with the first dried copper molecular sieve precursor, and then repeating step (1) until the first drying. The repetition is at least once; When repeating step (1), the molar concentration of copper in the copper salt solution is different each time. Step (1) The temperature of the first roasting is 450-550℃; Step (1) The first roasting time is 4-8 hours.

5. The preparation method according to claim 1, characterized in that, The platinum salt in the platinum salt solution in step (2) includes any one or a combination of at least two of the following: platinum tetraammine nitrate, chloroplatinic acid, platinum chloride, or ammonium chloroplatinate; The mass ratio of platinum in the ammonia molecular sieve and platinum salt solution in step (2) is 1:(0.002-0.02).

6. The preparation method according to claim 1, characterized in that, The mass ratio of platinum in the ammonia molecular sieve and platinum salt solution in step (2) is 1:(0.002-0.01).

7. The preparation method according to claim 1, characterized in that, Step (2) The second mixing is carried out under stirring; In step (2), the temperature of the second mixing is 20-40℃; Step (2) The second mixing time is 0.5-3 hours; Step (2) The second solid-liquid separation includes any one or a combination of at least two of vacuum filtration, pressure filtration or centrifugation; Step (2) The temperature for the second drying step is 30-90℃; Step (2) The second roasting temperature is 500-600℃; Step (2) The second roasting time is 3-7 hours.

8. The preparation method according to claim 1, characterized in that, The preparation method includes the following steps: (1) The ammonia molecular sieve and copper salt solution are mixed and stirred at 40-60℃ for 4-8 hours according to a solid-liquid ratio of 1:(20-70)g / mL. After the first solid-liquid separation, the first drying is carried out at 30-90℃, and then the first calcination is carried out at 450-550℃ for 4-8 hours to obtain the loaded copper molecular sieve. The copper salt in the copper salt solution includes any one or a combination of at least two of copper chloride, copper sulfate, copper nitrate, or copper acetate; the molar concentration of copper in the copper salt solution is 0.01-0.1 mol / L. After the first drying and before the first calcination, the process further includes: replacing the ammonia-type molecular sieve in step (1) with the first-dried loaded copper molecular sieve precursor, and then repeating step (1) until the first drying; the number of repetitions is at least 1; and the molar concentration of copper in the copper salt solution is different each time the step (1) is repeated. (2) The ammonia molecular sieve and platinum salt solution are mixed and stirred for 0.5-3h at a temperature of 20-40℃. After the second solid-liquid separation, the solution is dried for the second time at a temperature of 30-90℃. Then, the solution is calcined for the second time at a temperature of 500-600℃ for 3-7h to obtain the supported platinum molecular sieve. The platinum salt in the platinum salt solution includes any one or a combination of at least two of tetraammineplatinum nitrate, chloroplatinic acid, platinum chloride, or ammonium chloroplatinate; the mass ratio of platinum in the ammonia-type molecular sieve and the platinum salt solution is 1:(0.002-0.02). (3) Mix the copper molecular sieve loaded in step (1) and the platinum molecular sieve loaded in step (2) at a mass ratio of (1-10):1, and then perform a first ball milling for 5-30 min at a speed of 50-100 rpm and a ball-to-material ratio of (5-50):1, followed by a second ball milling for 5-20 min at a speed of 200-400 rpm and a ball-to-material ratio of (5-50):1 to obtain the ammonia purification composite molecular sieve catalyst; Steps (1) and (2) are not in any particular order.

9. A composite molecular sieve catalyst for ammonia purification, characterized in that, The ammonia purification composite molecular sieve catalyst is prepared by the preparation method described in any one of claims 1-8; Based on a mass percentage of 100%, the ammonia purification composite molecular sieve catalyst comprises: 0.01-0.095% platinum, 1-4% copper, and the balance being ammonia-type molecular sieve.

10. An application of a composite molecular sieve catalyst for ammonia purification, characterized in that, The application includes using the ammonia purification composite molecular sieve catalyst as described in claim 9 to catalytically purify the exhaust gas generated during the operation of an ammonia internal combustion engine. The temperature for catalytic purification is 150-350℃; Based on a volume percentage of 100%, the water content in the exhaust gas of the ammonia internal combustion engine is 5-15%, and the oxygen content in the exhaust gas of the ammonia internal combustion engine is 2-10%. The volume concentration of ammonia in the exhaust gas generated during the operation of the ammonia internal combustion engine is 300-1500 ppm.

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