Molecular sieve catalyst for selective reduction of nitrogen oxides by methane and its preparation method and application
By using a silicon-aluminum molecular sieve support and an indium-manganese-gallium active catalyst, the problems of high cost of precious metals and poor performance of catalysts in high-temperature water environments in existing technologies have been solved, achieving a low-cost and efficient selective reduction of nitrogen oxides by methane.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- GANJIANG INNOVATION ACAD CHINESE ACAD OF SCI
- Filing Date
- 2024-01-19
- Publication Date
- 2026-05-19
AI Technical Summary
In the existing technology, catalysts for the selective reduction of nitrogen oxides by methane have problems such as high cost of precious metals, difficulty in storing ammonia reducing agents and easy generation of secondary pollution, and poor performance of existing catalysts in high temperature and moisture environments.
A catalyst using a silica-alumina molecular sieve as a support and indium and manganese as active components is synthesized through a specific ratio and preparation method, with indium located inside the molecular sieve and manganese and gallium located outside the molecular sieve, thus avoiding the use of precious metals.
It exhibits excellent catalytic activity, high water resistance and high space velocity resistance in the selective reduction of nitrogen oxides by methane, and is low in cost and suitable for large-scale industrial production.
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Figure CN117884171B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of catalyst technology, and relates to a molecular sieve catalyst for the selective reduction of nitrogen oxides by methane, its preparation method and application. Background Technology
[0002] Nitrogen oxides (NO) x NO, as one of the major air pollutants, is not only a significant cause of environmental pollution such as haze, photochemical smog, and acid rain, but it also causes respiratory diseases and poses a serious threat to human health. Therefore, NO... x Emission reduction is particularly important. NOx emissions from industry, transportation, and energy are especially crucial. x It accounts for over 90% of total anthropogenic emissions and urgently needs to be controlled. Currently, NO... x Emission control technologies mainly include source control and end-of-pipe treatment (including adsorption, absorption, or chemical reduction).
[0003] For example, CN 113786828A discloses a method for NO x A catalyst for the synergistic removal of CVOCs, its preparation method, and its applications are disclosed. The catalyst comprises a matrix and an active component, wherein the active component is doped into the crystal lattice of the matrix. The active component includes vanadium and optionally a noble metal, and the matrix is cerium dioxide. The catalyst ensures highly efficient NO removal. x It can catalytically reduce and catalytically oxidize CVOCs (such as chlorobenzene, dichlorobenzene, dichloromethane, etc.) and has a wide reaction temperature window, but it uses precious metals in the active components, resulting in high cost.
[0004] For example, CN 116493040A discloses a method for preparing a high-performance Cu-based small-pore molecular sieve catalyst, the resulting product, and its applications. This method involves mixing NH4-type or H-type small-pore molecular sieves with Cu(CH3COO)2 or Cu(C2H5COO)2 solutions. By synergistically controlling multiple factors such as solution concentration, Cu / Al ratio, pH, temperature, time, and degree of washing during the reaction process, Cu-based small-pore molecular sieves with high Cu loading and consisting entirely of active Cu2+ species are obtained. This effectively avoids the problems of low Cu loading in traditional ion exchange methods and uncontrollable Cu species states in traditional impregnation methods. The prepared Cu-based small-pore molecular sieve catalyst exhibits excellent low-temperature activity and a wide active temperature window in the selective catalytic reduction of nitrogen oxides by ammonia. However, the ammonia-based reducing agent technology has disadvantages such as difficult storage, easy secondary pollution, and high cost.
[0005] Short-chain HC and oxygen-containing HC (with ≥2 directly bonded C atoms) exhibit excellent selective catalytic reduction of NO. xMethane, as an readily available reducing agent, has advantages such as large reserves, safety, reliability, ease of operation, and no environmental pollution after reaction. Furthermore, it is often accompanied by NO. x Methane is present in combustion exhaust gases and undergoes selective catalytic reduction of NO. x It can achieve synergistic control of two pollutants simultaneously, and has broad application prospects and economic value.
[0006] Based on the above research, there is a need to provide a molecular sieve catalyst for the selective reduction of nitrogen oxides from methane. This molecular sieve catalyst exhibits excellent catalytic activity, high water resistance, and high space velocity resistance in the CH4-SCR reaction. Summary of the Invention
[0007] The purpose of this invention is to provide a molecular sieve catalyst for the selective reduction of nitrogen oxides from methane, its preparation method and application. The molecular sieve catalyst uses a silica-alumina molecular sieve, indium and manganese as active components, and does not contain precious metals. It enables the molecular sieve catalyst to selectively reduce nitrogen oxides from methane, exhibiting excellent catalytic activity, high water resistance and high space velocity resistance.
[0008] To achieve this objective, the present invention employs the following technical solution:
[0009] In a first aspect, the present invention provides a molecular sieve catalyst for the selective reduction of nitrogen oxides by methane, the molecular sieve catalyst comprising an active component and a support, the active component comprising indium and manganese, and the support comprising a silica-alumina molecular sieve.
[0010] The molecular sieve catalyst described in this invention is specifically designed for the selective reduction of nitrogen oxides from methane. It does not contain precious metals and uses a silica-alumina molecular sieve as a support. With the synergistic effect of the active components indium and manganese, the silica-alumina molecular sieve composite catalyst exhibits excellent catalytic activity, high water resistance, and high space velocity resistance in the CH4-SCR reaction.
[0011] Preferably, the active component also includes gallium.
[0012] When the active components of this invention simultaneously include indium, manganese, and gallium, the performance of the molecular sieve catalyst can be further improved.
[0013] Preferably, the indium element is located inside the silicon-aluminum molecular sieve, and the manganese and gallium elements are located outside the silicon-aluminum molecular sieve.
[0014] In this invention, different active components are located at different positions on the molecular sieve. Indium is located inside the silicon-aluminum molecular sieve, while manganese and gallium are located outside the silicon-aluminum molecular sieve. This ensures that the active sites are physically separated, thus exhibiting excellent catalytic performance. If they are all located outside, there is essentially no activity; if they are all located inside, the strong oxidizing properties of manganese will lead to a decrease in performance.
[0015] Preferably, based on 100wt% of the molecular sieve catalyst, the mass fraction of indium is 4-8wt%, for example, it can be 5wt%, 6wt%, 7wt% or 8wt%, and the mass fraction of the silica-alumina molecular sieve is 60-88wt%, for example, it can be 65wt%, 70wt%, 75wt%, 80wt% or 85wt%, but is not limited to the listed values, and other unlisted values within the range are also applicable.
[0016] Preferably, based on 100 wt% of the molecular sieve catalyst, the mass fraction of manganese is 0-15 wt%, but not including 0 wt%. For example, it can be 2 wt%, 4 wt%, 6 wt%, 8 wt%, 10 wt%, 12 wt%, 14 wt%, or 15 wt%, but is not limited to the listed values. Other unlisted values within the range are also applicable, preferably 4.5-10 wt%.
[0017] Preferably, based on 100wt% of the molecular sieve catalyst, the mass fraction of gallium is 0-15wt%, but not including 0wt%. For example, it can be 2wt%, 4wt%, 6wt%, 8wt%, 10wt%, 12wt%, 14wt%, or 15wt%, but is not limited to the listed values. Other unlisted values within the range are also applicable, preferably 5-10wt%.
[0018] The indium, manganese, and gallium elements described in this invention can further enhance catalyst performance within specific ranges. If the manganese content is too high, the oxidizing power will be too strong; if the manganese content is too low, both the redox ability and acid content will be low, resulting in a decrease in catalytic performance. If the gallium content is too high, the redox ability and acid content will decrease significantly, leading to a decrease in catalytic performance. If the gallium content is too low, the redox ability and acid content will be mismatched, resulting in a decrease in performance.
[0019] Preferably, the aluminosilicate molecular sieve includes aluminosilicate molecular sieves with a BEA structure, aluminosilicate molecular sieves with an MFI structure, and aluminosilicate molecular sieves with a CHA structure.
[0020] Preferably, the silica-alumina molecular sieve with the BEA structure is a low silica-alumina atomic ratio Beta molecular sieve, wherein the silica-alumina atomic ratio of the low silica-alumina atomic ratio Beta molecular sieve is 1-100, for example, it can be 1, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 or 100, but is not limited to the listed values, and other unlisted values within the range are also applicable.
[0021] Preferably, the silica-alumina molecular sieve with the MFI structure is a low silica-alumina atomic ratio ZSM-5 molecular sieve, and the silica-alumina atomic ratio of the low silica-alumina atomic ratio ZSM-5 molecular sieve is 1-100, for example, it can be 1, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 or 100, but is not limited to the listed values, and other unlisted values within the range are also applicable.
[0022] Preferably, the silica-alumina molecular sieve with the CHA structure is a wide silica-alumina atomic ratio SSZ-13 molecular sieve, wherein the silica-alumina atomic ratio of the wide silica-alumina atomic ratio SSZ-13 molecular sieve is 1-100, for example, it can be 1, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 or 100, but is not limited to the listed values, and other unlisted values within the range are also applicable.
[0023] The present invention preferably uses a molecular sieve with a wide silicon-to-aluminum atomic ratio, which can be synthesized by various methods, has a wider versatility, and has more acidic sites.
[0024] In a second aspect, the present invention provides a method for preparing a molecular sieve catalyst for the selective reduction of nitrogen oxides by methane as described in the first aspect, the method comprising the following steps:
[0025] (1) The silica-alumina molecular sieve is mixed with an aqueous solution containing indium salt and ion exchanged. Then the active component containing indium loaded in the solvent is removed, and then dried and calcined to obtain the calcined product.
[0026] (2) The calcination product obtained in step (1) is mixed with a manganese source and calcined to obtain the molecular sieve catalyst for selective reduction of nitrogen oxides by methane.
[0027] The silica-aluminum molecular sieve in step (1) of this invention includes silica-aluminum molecular sieves with BEA structure, silica-aluminum molecular sieves with MFI structure and silica-aluminum molecular sieves with CHA structure.
[0028] Preferably, the silica-alumina molecular sieve with the BEA structure is a low silica-alumina atomic ratio Beta molecular sieve, and the synthesis method of the low silica-alumina atomic ratio Beta molecular sieve includes: synthesizing the low silica-alumina atomic ratio Beta molecular sieve by an organic template-free seed crystal method or an amino acid-assisted template agent method.
[0029] Preferably, the silica-alumina molecular sieve with the MFI structure is a low silica-alumina atomic ratio ZSM-5 molecular sieve, and the synthesis method of the low silica-alumina atomic ratio ZSM-5 molecular sieve includes: using urea, glucose or ammonium fluoride to assist in the synthesis of the low silica-alumina atomic ratio ZSM-5 molecular sieve.
[0030] Preferably, the silica-alumina molecular sieve with the CHA structure is a wide silica-alumina atomic ratio SSZ-13 molecular sieve, and the synthesis method of the wide silica-alumina atomic ratio SSZ-13 molecular sieve includes: synthesizing the wide silica-alumina atomic ratio SSZ-13 molecular sieve by template agent method or seed crystal incubation.
[0031] Preferably, a gallium source is added during the mixing process in step (2).
[0032] Preferably, when the gallium source is added, the calcination product in step (1) is mixed and calcined with the composite oxide of manganese and gallium.
[0033] Preferably, in the composite oxide of manganese and gallium, Mn exists in the form of one or at least two combinations of Mn2O3, MnO2 or Mn3O4, and Ga exists in the form of Ga2O3.
[0034] Preferably, the mixing method in step (2) includes grinding, and the grinding time is 10-60 min, for example, it can be 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min or 60 min, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0035] Preferably, the roasting temperature in step (2) is 500-700℃, for example, it can be 500℃, 520℃, 540℃, 560℃, 580℃, 600℃, 620℃, 640℃, 660℃, 680℃ or 700℃, and the time is 2-4h, for example, it can be 2h, 2.2h, 2.4h, 2.6h, 2.8h, 3.0h, 3.2h, 3.4h, 3.6h, 3.8h or 4h, but is not limited to the listed values, and other unlisted values within the range are also applicable.
[0036] Preferably, the silica-alumina molecular sieve in step (1) undergoes ammonium exchange before step (1).
[0037] Preferably, the ammonium exchange method includes: exchanging the silica-alumina molecular sieve with an ammonium salt solution, followed by filtration, washing, and drying.
[0038] Preferably, the ammonium salt solution comprises ammonium nitrate and / or ammonium chloride.
[0039] Preferably, the ammonium exchange is repeated 2-3 times.
[0040] Preferably, the ammonium exchange time is 2-8 hours, for example, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours or 8 hours, and the temperature is 60-100°C, for example, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C or 100°C, but not limited to the listed values. Other unlisted values within the range are also applicable.
[0041] Preferably, the concentration of the aqueous solution containing indium salt in step (1) is 0.1-1 mol / L, for example, it can be 0.3 mol / L, 0.5 mol / L, 0.7 mol / L, 0.9 mol / L or 1 mol / L, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0042] Preferably, the mixing method in step (1) includes ultrasonic mixing, wherein the ultrasonic mixing time is 10-60 min, for example, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min or 60 min, and the frequency is 10-100 Hz, for example, 20 Hz, 30 Hz, 40 Hz, 50 Hz, 60 Hz, 70 Hz, 80 Hz, 90 Hz or 100 Hz, but is not limited to the listed values, and other unlisted values within the range are also applicable.
[0043] Preferably, the stirring time for ion exchange in step (1) is 6-12 hours, for example, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours or 12 hours, and the stirring temperature is 60-100°C, for example, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C or 100°C, but not limited to the listed values. Other unlisted values within the range are also applicable.
[0044] Preferably, the solvent removal method in step (1) includes rotary evaporation at a temperature of 60-80°C, such as 60°C, 62°C, 64°C, 66°C, 68°C, 70°C, 72°C, 74°C, 76°C, 78°C, or 80°C, for a time of 20-120 min, such as 30 min, 50 min, 80 min, 100 min, or 120 min, but not limited to the listed values. Other unlisted values within the range are also applicable.
[0045] Preferably, the indium salt in step (1) includes any one or a combination of at least two of indium nitrate, chloride, sulfate or acetate, wherein typical but non-limiting combinations include a combination of indium nitrate and indium chloride, a combination of indium chloride and indium sulfate, or a combination of indium sulfate and indium acetate.
[0046] The present invention is a composite oxide of manganese and gallium, MnGaO. x In oxides, the molar ratio of Mn / Ga is from 0 to +∞, for example, it can be 1, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100 or +∞. When it is +∞, the system does not contain gallium.
[0047] Preferably, the drying temperature in step (1) is 80-150℃, for example, it can be 80℃, 85℃, 90℃, 95℃, 100℃, 105℃, 110℃, 115℃, 120℃, 125℃, 130℃, 135℃, 140℃, 145℃ or 150℃, and the time is 4-12h, for example, it can be 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h or 12h, but is not limited to the listed values, and other unlisted values within the range are also applicable.
[0048] Preferably, the roasting atmosphere in step (1) includes air and hydrogen, preferably air-hydrogen-air, wherein the gas flow rate is 50-500 mL / min, for example, it can be 100 mL / min, 200 mL / min, 300 mL / min, 400 mL / min or 500 mL / min, but is not limited to the listed values, and other unlisted values within the range are also applicable.
[0049] Preferably, the roasting temperature in step (1) is 400-600℃, for example, 400℃, 420℃, 440℃, 460℃, 480℃, 500℃, 520℃, 540℃, 560℃, 580℃ or 600℃, and the time is 0.5-4h, for example, 0.2h, 0.4h, 0.6h, 0.8h, 1h, 1.2h, 1.4h, 1.6h, 1.8h, 2h, 2.2h, 2.4h, 2.6h, 2.8h, 3.0h, 3.2h, 3.4h, 3.6h, 3.8h or 4h, but is not limited to the listed values, and other unlisted values within the range are also applicable.
[0050] As a preferred embodiment of the preparation method of the present invention, the preparation method includes the following steps:
[0051] (1) The silica-alumina molecular sieve is subjected to ammonium exchange with an ammonium salt solution, and then filtered, washed and dried to obtain the ammonium-exchanged silica-alumina molecular sieve.
[0052] The ammonium-exchanged silica-alumina molecular sieve was ultrasonically mixed with an aqueous solution containing indium salt at a frequency of 10-100 Hz for 10-60 min, then stirred at 60-100℃ for 6-12 h for ion exchange, then rotary evaporated at 60-80℃ for 20-120 min, then dried at 80-150℃ for 4-12 h and calcined at 400-600℃ for 0.5-4 h to obtain the calcined product.
[0053] (2) Grind and mix the calcination product of step (1) with the composite oxide of manganese and gallium for 10-60 min, and then calcine at 500-700℃ for 2-4 h to obtain the molecular sieve catalyst for selective reduction of nitrogen oxides by methane.
[0054] Thirdly, the present invention provides an application of the molecular sieve catalyst for the selective reduction of nitrogen oxides from methane as described in the first aspect, the application including its use in the field of environmental catalysis.
[0055] The oxide molecular sieve composite catalyst of this invention can be applied to the co-elimination of nitrogen oxides and methane in fields such as flue gas exhaust or natural gas vehicle exhaust.
[0056] Compared with the prior art, the present invention has the following beneficial effects:
[0057] The molecular sieve composite catalyst for the selective reduction of nitrogen oxides by methane provided by this invention has excellent catalytic activity, high water resistance and high space velocity resistance. The catalyst preparation method is simple and does not contain precious metals, and the cost is low, enabling large-scale industrial production. Attached Figure Description
[0058] Figure 1The nitrogen oxide conversion rate of the molecular sieve catalysts provided in Examples 1-4 and Comparative Example 1 of this invention is shown in the diagram under the first test conditions.
[0059] Figure 2 The graphs show the nitrogen oxide conversion rates of the molecular sieve catalysts provided in Examples 1-4 and Comparative Example 1 of this invention under water resistance test conditions. Detailed Implementation
[0060] 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.
[0061] Example 1
[0062] This embodiment provides a molecular sieve catalyst for the selective reduction of nitrogen oxides by methane. The molecular sieve catalyst, based on a mass of 100 wt%, includes 6 wt% indium, 7 wt% manganese, 7.5 wt% gallium, and the balance being a silica-alumina molecular sieve. The indium is located inside the silica-alumina molecular sieve, while the manganese and gallium are located outside the silica-alumina molecular sieve. The silica-alumina molecular sieve is an SSZ-13 molecular sieve with a silica-alumina atomic ratio of 6.
[0063] The preparation method of the molecular sieve catalyst includes the following steps:
[0064] (1) The silica-alumina molecular sieve is subjected to ammonium exchange with ammonium nitrate solution, and then filtered, washed and dried to obtain the ammonium-exchanged silica-alumina molecular sieve. The ammonium exchange is repeated twice, the ammonium exchange time is 6 hours, and the temperature is 80℃.
[0065] The ammonium-exchanged silica-alumina molecular sieve was ultrasonically mixed with a 0.6 mol / L indium nitrate aqueous solution at a frequency of 50 Hz for 30 min, then stirred at 70 °C for 8 h for ion exchange, then rotary evaporated at 80 °C for 70 min, then dried at 100 °C for 8 h, and then calcined at 600 °C for 2 h in an air-hydrogen-air atmosphere to obtain the calcined product.
[0066] (2) The calcination product described in step (1) is ground and mixed with the composite oxide of manganese and gallium for 15 min, and then calcined at 600°C for 2 h to obtain the molecular sieve catalyst for selective reduction of nitrogen oxides by methane.
[0067] Example 2
[0068] This embodiment provides a molecular sieve catalyst for the selective reduction of nitrogen oxides by methane. The molecular sieve catalyst, based on a mass of 100 wt%, includes 6 wt% indium, 4.6 wt% manganese, 10 wt% gallium, and the balance being a silica-alumina molecular sieve. The indium is located inside the silica-alumina molecular sieve, while the manganese and gallium are located outside the silica-alumina molecular sieve. The silica-alumina molecular sieve is an SSZ-13 molecular sieve with a silica-alumina atomic ratio of 6.
[0069] The preparation method of the molecular sieve catalyst includes the following steps:
[0070] (1) The silica-alumina molecular sieve is subjected to ammonium exchange with ammonium nitrate solution, and then filtered, washed and dried to obtain the ammonium-exchanged silica-alumina molecular sieve. The ammonium exchange is repeated 3 times, the ammonium exchange time is 8 hours, and the temperature is 60℃.
[0071] The ammonium-exchanged silica-alumina molecular sieve was ultrasonically mixed with a 0.6 mol / L indium nitrate aqueous solution at a frequency of 100 Hz for 10 min, then stirred at 100 °C for 6 h for ion exchange, then rotary evaporated at 80 °C for 120 min, then dried at 100 °C for 4 h, and then calcined at 500 °C for 1 h in an air-hydrogen-air atmosphere to obtain the calcined product.
[0072] (2) The calcination product described in step (1) is ground and mixed with the composite oxide of manganese and gallium for 60 min, and then calcined at 600 °C for 4 h to obtain the molecular sieve catalyst for selective reduction of nitrogen oxides by methane.
[0073] Example 3
[0074] This embodiment provides a molecular sieve catalyst for the selective reduction of nitrogen oxides by methane. The molecular sieve catalyst, based on a mass of 100 wt%, includes 6 wt% indium, 5 wt% manganese, 9.3 wt% gallium, and the balance being a silica-alumina molecular sieve. The indium is located inside the silica-alumina molecular sieve, while the manganese and gallium are located outside the silica-alumina molecular sieve. The silica-alumina molecular sieve is an SSZ-13 molecular sieve with a silica-alumina atomic ratio of 6.
[0075] The preparation method of the molecular sieve catalyst includes the following steps:
[0076] (1) The silicon-aluminum molecular sieve is subjected to ammonium exchange with ammonium nitrate solution, and then filtered, washed and dried to obtain the ammonium-exchanged silicon-aluminum molecular sieve. The ammonium exchange is repeated twice, the ammonium exchange time is 2 hours, and the temperature is 100℃.
[0077] The ammonium-exchanged silica-alumina molecular sieve was ultrasonically mixed with a 0.6 mol / L indium nitrate aqueous solution at a frequency of 10 Hz for 60 min, then stirred at 60 °C for 12 h for ion exchange, then rotary evaporated at 60 °C for 50 min, then dried at 100 °C for 6 h, and then calcined at 550 °C for 4 h in an air-hydrogen-air atmosphere to obtain the calcined product.
[0078] (2) The calcination product described in step (1) is ground and mixed with a composite oxide of manganese and gallium (the molar ratio of manganese and gallium is 2:1) for 15 min, and then calcined at 550°C for 2 h to obtain the molecular sieve catalyst for selective reduction of nitrogen oxides by methane.
[0079] Example 4
[0080] This embodiment provides a molecular sieve catalyst for the selective reduction of nitrogen oxides by methane. The molecular sieve catalyst, with a mass of 100 wt%, includes 6 wt% indium, 14 wt% manganese, and the balance being a silica-alumina molecular sieve. The indium is located inside the silica-alumina molecular sieve, and the manganese is located outside the silica-alumina molecular sieve. The silica-alumina molecular sieve is an SSZ-13 molecular sieve with a silica-alumina atomic ratio of 6.
[0081] The preparation method of the molecular sieve catalyst includes the following steps:
[0082] (1) The silica-alumina molecular sieve is subjected to ammonium exchange with ammonium nitrate solution, and then filtered, washed and dried to obtain the ammonium-exchanged silica-alumina molecular sieve. The ammonium exchange is repeated twice, the ammonium exchange time is 6 hours, and the temperature is 80℃.
[0083] The ammonium-exchanged silica-alumina molecular sieve was ultrasonically mixed with a 0.6 mol / L indium nitrate aqueous solution at a frequency of 50 Hz for 30 min, then stirred at 70 °C for 8 h for ion exchange, then rotary evaporated at 60 °C for 120 min, then dried at 100 °C for 6 h, and then calcined at 550 °C for 4 h in an air-hydrogen-air atmosphere to obtain the calcined product.
[0084] (2) Grind and mix the calcination product from step (1) with manganese oxide for 10 min, and then calcine at 600 °C for 2 h to obtain the molecular sieve catalyst for selective reduction of nitrogen oxides by methane.
[0085] Example 5
[0086] This embodiment provides a molecular sieve catalyst for the selective reduction of nitrogen oxides by methane. The molecular sieve catalyst is the same as that in Example 1, except that the gallium content is 15 wt% and the content of silicon-aluminum molecular sieve is reduced.
[0087] Example 6
[0088] This embodiment provides a molecular sieve catalyst for the selective reduction of nitrogen oxides by methane. The molecular sieve catalyst is the same as that in Example 1, except that the manganese content is 3.5 wt% and the content of silicon-aluminum molecular sieve is more adaptable.
[0089] Example 7
[0090] This embodiment provides a molecular sieve catalyst for the selective reduction of nitrogen oxides by methane. The molecular sieve catalyst is the same as that in Example 1, except that the manganese content is 18 wt% and the content of silicon-aluminum molecular sieve is reduced.
[0091] Example 8
[0092] This embodiment provides a molecular sieve catalyst for the selective reduction of nitrogen oxides by methane. Except that the indium, manganese and gallium elements are all located inside the silicon-aluminum molecular sieve, the molecular sieve catalyst is the same as that in Example 1.
[0093] The preparation method of the molecular sieve catalyst described in this embodiment is the same as that in Example 1, except that the aqueous solution of indium nitrate is replaced with a mixed solution of indium nitrate, manganese nitrate and gallium nitrate in the prescribed amount, and step (2) is not performed.
[0094] Example 9
[0095] This embodiment provides a molecular sieve catalyst for the selective reduction of nitrogen oxides by methane. Except that the indium, manganese and gallium elements are located outside the silicon-aluminum molecular sieve, the molecular sieve catalyst is the same as in Example 1.
[0096] The preparation method of the molecular sieve catalyst described in this embodiment is the same as that in Example 1, except that step (2) is performed on the ammonium-exchanged silicon-aluminum molecular sieve with the prescribed amount of manganese and gallium composite oxide and indium oxide, and step (1) is not performed.
[0097] Comparative Example 1
[0098] This comparative example provides a molecular sieve catalyst for the selective reduction of nitrogen oxides by methane. The molecular sieve catalyst is the same as that in Example 1, except that it does not contain manganese and gallium, and the reduced manganese and gallium are supplemented by silicon-aluminum molecular sieve.
[0099] The preparation method of the molecular sieve catalyst described in this comparative example is the same as that in Example 1, except that step (2) is not performed.
[0100] The molecular sieve catalysts obtained in the above examples and comparative examples were tested for catalytic activity and water resistance. The catalytic activity test method was divided into a first test condition and a water resistance test condition.
[0101] The first test conditions were as follows: 0.2 g of catalyst was placed in a fixed-bed reactor with an inner diameter of 5 mm, nitrogen was used as the balancer, and the space velocity was 18000 h⁻¹. -1 The reactant gases were continuously fed into the fixed-bed reactor. The concentration of methane in the reactant gases was 2000 ppm, the concentration of nitric oxide was 1200 ppm, and the oxygen content was 5%. Under the first test conditions, the nitrogen oxide conversion rates of the molecular sieve composite catalysts provided in Examples 1-4 and Comparative Example 1 are shown in the figure below. Figure 1 As shown;
[0102] The water resistance test method is as follows: 0.2g of catalyst is placed in a fixed-bed reactor with an inner diameter of 5mm, nitrogen is used as the balancer, and the space velocity is 18000h⁻¹. -1 The reactant gases were continuously fed into a fixed-bed reactor. The concentrations of the reactant gases were: methane 2000 ppm, nitric oxide 1200 ppm, oxygen 5%, and water 10%. Under these test conditions, the nitrogen oxide conversion rates of the molecular sieve catalysts provided in Examples 1-4 and Comparative Example 1 are shown in the figure below. Figure 2 As shown.
[0103] Under the first test conditions, NO x The temperature range corresponding to a conversion rate of 90%, and the NO content under water resistance test conditions. x The temperature range corresponding to a conversion rate of 90% is shown in Table 1.
[0104] Table 1
[0105]
[0106] As can be seen from Table 1:
[0107] The molecular sieve catalyst obtained by this invention exhibits excellent catalytic activity and high water resistance and high space velocity resistance for the selective reduction of nitrogen oxides from methane. As shown in Example 1 and Comparative Example 1, the catalytic performance of the molecular sieve catalyst decreases significantly when the active component is only indium. As shown in Examples 1 and 4-5, the catalytic performance of the molecular sieve catalyst is also affected if gallium is not added or if too much gallium is added. As shown in Examples 1 and 6-7, the catalytic performance of the molecular sieve catalyst is also affected if the amount of manganese added is too small or too large. As shown in Examples 1 and 8-9, when different active components are located at different positions within the molecular sieve, with indium located inside the silicon-aluminum molecular sieve and manganese and gallium located outside, the molecular sieve catalyst of this invention can maintain excellent catalytic performance, and the catalyst obtained in Example 9 is inactive.
[0108] In summary, this invention provides a molecular sieve catalyst for the selective reduction of nitrogen oxides from methane, its preparation method, and its application. The molecular sieve catalyst uses a silica-alumina molecular sieve, indium, and manganese as active components and does not contain precious metals. It enables the molecular sieve catalyst to selectively reduce nitrogen oxides from methane, exhibiting excellent catalytic activity, high water resistance, and high space velocity resistance.
[0109] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.
Claims
1. A molecular sieve catalyst for the selective reduction of nitrogen oxides from methane, characterized in that, The molecular sieve catalyst for selective reduction of nitrogen oxides by methane includes an active component and a support, wherein the active component includes indium and manganese, and the support includes a silica-alumina molecular sieve. The active component also includes gallium; The indium element is located inside the silicon-aluminum molecular sieve, and the manganese and gallium elements are located outside the silicon-aluminum molecular sieve; Based on a mass of 100 wt% for the molecular sieve catalyst, the mass fraction of indium is 4-8 wt%, the mass fraction of the silica-alumina molecular sieve is 60-88 wt%, the mass fraction of manganese is 4.5-15 wt%, and the mass fraction of gallium is 5-10 wt%. The molecular sieve catalyst for the selective reduction of nitrogen oxides from methane is prepared by the following method, which includes the following steps: (1) The silica-alumina molecular sieve is mixed with an aqueous solution containing indium salt and ion exchanged. Then the solvent is removed to obtain a molecular sieve support containing indium active components. Then it is dried and calcined to obtain the calcined product. (2) The calcination product of step (1) is mixed with a composite oxide of manganese and gallium and calcined to obtain the molecular sieve catalyst for selective reduction of nitrogen oxides by methane.
2. The molecular sieve catalyst according to claim 1, characterized in that, The silica-aluminum molecular sieve includes silica-aluminum molecular sieves with a BEA structure, silica-aluminum molecular sieves with an MFI structure, or silica-aluminum molecular sieves with a CHA structure.
3. The molecular sieve catalyst according to claim 2, characterized in that, The silica-aluminum molecular sieve with the BEA structure is a low silica-aluminum atomic ratio Beta molecular sieve, and the silica-aluminum atomic ratio of the low silica-aluminum atomic ratio Beta molecular sieve is 1-100.
4. The molecular sieve catalyst according to claim 2, characterized in that, The silicon-aluminum molecular sieve with MFI structure is a low silicon-aluminum atomic ratio ZSM-5 molecular sieve, and the silicon-aluminum atomic ratio of the low silicon-aluminum atomic ratio ZSM-5 molecular sieve is 1-100.
5. The molecular sieve catalyst according to claim 2, characterized in that, The silica-aluminum molecular sieve with the CHA structure is a wide silica-aluminum atomic ratio SSZ-13 molecular sieve, and the silica-aluminum atomic ratio of the wide silica-aluminum atomic ratio SSZ-13 molecular sieve is 1-100.
6. A method for preparing a molecular sieve catalyst for the selective reduction of nitrogen oxides from methane as described in any one of claims 1-5, characterized in that, The preparation method includes the following steps: (1) The silica-alumina molecular sieve is mixed with an aqueous solution containing indium salt and ion exchanged. Then the solvent is removed to obtain a molecular sieve support containing indium active components. Then it is dried and calcined to obtain the calcined product. (2) The calcination product of step (1) is mixed with a composite oxide of manganese and gallium and calcined to obtain the molecular sieve catalyst for selective reduction of nitrogen oxides by methane.
7. The preparation method according to claim 6, characterized in that, In the composite oxide of manganese and gallium, Mn exists in the form of one or at least two combinations of Mn2O3, MnO2 or Mn3O4, and Ga exists in the form of Ga2O3.
8. The preparation method according to claim 6, characterized in that, The mixing method in step (2) includes grinding, and the grinding time is 10-60 min.
9. The preparation method according to claim 6, characterized in that, The roasting temperature in step (2) is 500-700℃ and the time is 2-4h.
10. The preparation method according to claim 6, characterized in that, Before step (1), the silica-alumina molecular sieve described in step (1) undergoes ammonium exchange.
11. The preparation method according to claim 10, characterized in that, The ammonium exchange method includes: exchanging ammonium between a silica-alumina molecular sieve and an ammonium salt solution, followed by filtration, washing, and drying.
12. The preparation method according to claim 11, characterized in that, The ammonium salt solution includes ammonium nitrate and / or ammonium chloride.
13. The preparation method according to claim 11, characterized in that, The ammonium exchange is repeated 2-3 times.
14. The preparation method according to claim 11, characterized in that, The ammonium exchange time is 2-8 hours, and the temperature is 60-100℃.
15. The preparation method according to claim 6, characterized in that, The concentration of the aqueous solution containing indium salt in step (1) is 0.1-1 mol / L.
16. The preparation method according to claim 6, characterized in that, The mixing method in step (1) includes ultrasonic mixing, wherein the ultrasonic mixing time is 10-60 min and the frequency is 10-100 Hz.
17. The preparation method according to claim 6, characterized in that, The stirring time for the ion exchange in step (1) is 6-12 hours, and the stirring temperature is 60-100℃.
18. The preparation method according to claim 6, characterized in that, The solvent removal method described in step (1) includes rotary evaporation at a temperature of 60-80℃ for 20-120 min.
19. The preparation method according to claim 6, characterized in that, The indium salt in step (1) includes any one or a combination of at least two of the following: indium nitrate, chloride, sulfate or acetate.
20. The preparation method according to claim 6, characterized in that, The drying temperature in step (1) is 80-150℃ and the time is 4-12h.
21. The preparation method according to claim 6, characterized in that, The roasting atmosphere in step (1) includes air and hydrogen, wherein the gas flow rate is 50-500 mL / min.
22. The preparation method according to claim 6, characterized in that, The roasting temperature in step (1) is 400-600℃ and the time is 0.5-4h.
23. The preparation method according to claim 6, characterized in that, The preparation method includes the following steps: (1) The silica-alumina molecular sieve is subjected to ammonium exchange with an ammonium salt solution, and then filtered, washed and dried to obtain the ammonium-exchanged silica-alumina molecular sieve; The ammonium-exchanged silica-alumina molecular sieve was ultrasonically mixed with an aqueous solution containing indium salt at a frequency of 10-100 Hz for 10-60 min, then stirred at 60-100℃ for 6-12 h for ion exchange, then rotary evaporated at 60-80℃ for 20-120 min, then dried at 80-150℃ for 4-12 h and calcined at 400-600℃ for 0.5-4 h to obtain the calcined product. (2) Grind and mix the calcination product of step (1) with the composite oxide of manganese and gallium for 10-60 min, and then calcine at 500-700℃ for 2-4 h to obtain the molecular sieve catalyst for selective reduction of nitrogen oxides by methane.
24. The application of a molecular sieve catalyst for the selective reduction of nitrogen oxides from methane as described in any one of claims 1-5, characterized in that, The applications include the selective reduction of nitrogen oxides by methane.