A denitration catalyst, a preparation method and application thereof

Abstract

The application provides a denitration catalyst, a preparation method and application thereof, and the denitration catalyst comprises a layered MCM molecular sieve carrier and a composite oxide active component loaded on the surface of the layered MCM molecular sieve carrier, and the chemical formula of the composite oxide active component is CeCuO x The denitration catalyst has high surface acidity and redox capacity, the CeCuO x The alkali metal poisoning resistance of the catalyst is improved, so that the catalyst has high catalytic activity and nitrogen selectivity in the use temperature range of 250-400 DEG C after being poisoned by alkali metal.

Description

Technical Field

[0001] This invention belongs to the field of environmental catalyst technology, and relates to a denitrification catalyst, its preparation method and application. Background Technology

[0002] Nitrogen oxides (NO) x Nitrogen oxides (NOx) are a major air pollutant, primarily originating from the combustion of fossil fuels. Excessive NOx emissions cause a series of environmental and climate problems, including acid rain, photochemical smog, and global warming. Traditional stationary source flue gas denitrification mainly uses ammonia selective catalytic reduction (NH3-SCR) technology, employing V2O5-WO3 / TiO2 or its modified forms as catalysts, with operating temperatures typically between 300 and 400°C. This catalyst exhibits low catalytic activity at 250°C, and V2O5 is a toxic substance; its recovery and post-treatment have become bottlenecks restricting its development. Meanwhile, catalysts using cerium dioxide (CeO2) and modified cerium dioxide as active components have attracted widespread attention from researchers due to their excellent oxygen storage and release performance, high nitrogen selectivity, and environmentally friendly characteristics.

[0003] Currently, SCR denitrification catalysts for boiler flue gas face the problem of alkali metal poisoning leading to catalyst deactivation in practical applications. This is because the coal ash produced during boiler combustion contains a certain amount of alkali metal and alkaline earth metal oxides, which can coat the catalyst surface or react with active components, thereby reducing surface area. The number of acidic sites can also lead to the formation of nitrate intermediates that are difficult to decompose.

[0004] CN102416320A discloses a denitrification catalyst, relating to the field of catalyst technology. The catalyst comprises the following components in parts by weight: 75-85 parts titanium dioxide; 10-12 parts tungsten trioxide; 3-6 parts silicon dioxide; 2-3 parts vanadium pentoxide; 3-6 parts kapok pulp; 2-7 parts glass fiber; and 2-3 parts stearic acid. The components are mixed according to the specified parts by weight, stirred evenly, and then sequentially subjected to aging, pre-extrusion, secondary aging, extrusion molding, primary drying, secondary drying, high-temperature calcination, and finished product trimming before packaging to obtain the finished catalyst.

[0005] CN107737588A discloses a denitrification catalyst, the raw materials of which are, by weight, 35-45 parts titanium dioxide, 2-5 parts antimony oxide, 10-20 parts glass fiber, 1-3 parts vanadium pentoxide, 3-6 parts molybdenum oxide, and 3-6 parts tungsten oxide.

[0006] The denitrification catalyst described in the above scheme is difficult to balance high-temperature and low-temperature catalytic activity, and its activity drops sharply after alkali poisoning. Therefore, improving the denitrification performance of the denitrification catalyst in the presence of alkali metals is very important for saving flue gas purification costs in the coal-fired industry and improving waste gas treatment efficiency. Summary of the Invention

[0007] The purpose of this invention is to provide a denitrification catalyst, its preparation method, and its application. The denitrification catalyst of this invention has high surface acidity and redox ability, and contains CeCuO. x The catalyst's resistance to alkali metal poisoning has been improved, thus ensuring that it maintains high catalytic activity and nitrogen selectivity within the operating temperature range of 250–400℃ after alkali metal poisoning.

[0008] To achieve this objective, the present invention employs the following technical solution:

[0009] In a first aspect, the present invention provides a denitrification catalyst, the denitrification catalyst comprising a layered MCM molecular sieve support and a composite oxide active component supported on the surface of the layered MCM molecular sieve support, wherein the chemical formula of the composite oxide active component is CeCuO. x Where x is 1 to 2, for example: 1, 1.2, 1.5, 1.8 or 2, etc.

[0010] The denitration catalyst of this invention functions in the low-temperature range (below 300℃) for Cu and in the high-temperature range for Ce; the combination of the two can cover an ultra-wide temperature range of 200–500℃. Simultaneously, CeCuO… x The presence of Ce-O-Cu asymmetric oxygen vacancies can enhance NO production. x The adsorption capacity of copper and cerium is enhanced. Simultaneously, the combination of copper and cerium improves the overall surface acidity and redox capacity of the catalyst, thereby increasing its resistance to alkali metal poisoning and ensuring high catalytic activity and nitrogen selectivity even after alkali metal poisoning. The layered morphology of the MCM molecular sieve support provides strong interlayer mass transfer capabilities, enabling it to adsorb NO. x Gases such as NH3 diffuse rapidly to the active sites. The denitrification catalyst of this invention has strong Bronsted and Lewis acidic sites, which can increase the catalyst's NH3 adsorption capacity and resistance to alkali metal poisoning.

[0011] Preferably, the layered MCM molecular sieve carrier includes any one or a combination of at least two of MCM-22 molecular sieve, MCM-56 molecular sieve, MCM-49 molecular sieve or MCM-36 molecular sieve, preferably MCM-49 molecular sieve.

[0012] Preferably, the silicon-to-aluminum ratio of the layered MCM molecular sieve support is (5-30):1.

[0013] Preferably, in the active component of the composite oxide, the molar ratio of copper to cerium is (0.05-0.2):1, for example: 0.05:1, 0.08:1, 0.1:1, 0.15:1 or 0.2:1, etc.

[0014] Preferably, the active component of the composite oxide further comprises a dopant element.

[0015] Preferably, the doped rare earth element includes any one or a combination of at least two of neodymium, samarium, cobalt, europium, yttrium, dysprosium, ytterbium, lanthanum, or praseodymium.

[0016] Preferably, based on the mass of the denitrification catalyst as 100%, the mass fraction of the composite oxide active component is 5-45%, for example: 5%, 10%, 20%, 30% or 45%, etc., preferably 10-25%.

[0017] In a second aspect, the present invention provides a method for preparing the denitrification catalyst as described in the first aspect, the method comprising the following steps:

[0018] (1) The layered MCM molecular sieve support was ground and dispersed in a solvent to obtain a dispersion;

[0019] (2) The cerium source and copper source are mixed with the dispersion, evaporated to dryness and then calcined to obtain the denitrification catalyst.

[0020] The preparation method of the denitrification catalyst described in this invention is relatively simple. Compared with other methods, it eliminates the steps of adding additives such as ammonia and urea, and does not require pH adjustment, thus saving preparation time and cost.

[0021] Preferably, the mesh size of the layered MCM molecular sieve carrier after grinding in step (1) is 20 to 100 mesh, preferably 20 to 100 mesh, for example: 20 mesh, 50 mesh, 60 mesh, 80 mesh or 100 mesh, etc., preferably 40 to 60 mesh.

[0022] Preferably, the dispersion process is performed using ultrasound.

[0023] Preferably, the dispersion time is 10 to 60 minutes, for example: 10 minutes, 20 minutes, 30 minutes, 50 minutes or 60 minutes.

[0024] Preferably, the concentration of the dispersion is 2 to 8 g / L, for example: 2 g / L, 3 g / L, 5 g / L, 6 g / L or 8 g / L, etc.

[0025] Preferably, the cerium source in step (2) includes cerium nitrate.

[0026] Preferably, the copper source includes copper nitrate.

[0027] Preferably, a doped metal source is also added during the mixing process.

[0028] Preferably, the dopant metal source includes any one or a combination of at least two of neodymium nitrate, samarium nitrate, europium nitrate, yttrium nitrate, dysprosium nitrate, ytterbium nitrate, lanthanum nitrate, or praseodymium nitrate.

[0029] Preferably, the temperature for evaporation in step (2) is 80 to 100°C, for example: 80°C, 85°C, 90°C, 95°C or 100°C.

[0030] Preferably, the heating rate of the calcination is 1 to 10 °C / min, for example: 1 °C / min, 2 °C / min, 5 °C / min, 8 °C / min or 10 °C / min, etc.

[0031] Preferably, the roasting temperature is 400-600℃, for example: 400℃, 450℃, 500℃, 550℃ or 600℃.

[0032] Preferably, the roasting time is 3 to 10 hours, for example: 30°C, 50°C, 60°C, 80°C or 100°C.

[0033] Thirdly, the present invention provides an application of the denitrification catalyst as described in the first aspect, wherein the denitrification catalyst is used for the selective catalytic reduction of nitrogen oxides by ammonia.

[0034] Preferably, the catalyst operates at a temperature of 150–550°C, for example, 150°C, 200°C, 300°C, 400°C, or 550°C, with 200–400°C being the most preferred.

[0035] Fourthly, the present invention provides a denitrification reactor comprising a denitrification catalyst as described in the first aspect, the denitrification reactor being used in a mobile source gas denitrification device and / or a stationary source gas denitrification device.

[0036] Preferably, the mobile source gas denitrification device includes any one or a combination of at least two of a diesel engine, a gas turbine, or an aircraft engine.

[0037] Preferably, the stationary source gas denitrification device includes an industrial kiln and / or a calcining kiln.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] (1) The denitrification catalyst of the present invention has high surface acidity and redox ability, CeCuO xThe catalyst's resistance to alkali metal poisoning has been improved, thus ensuring that it maintains high catalytic activity and nitrogen selectivity within the operating temperature range of 250–400℃ after alkali metal poisoning.

[0040] (2) The synthesis conditions of the method described in this invention are simple and mild, with no by-products or pollution, and can significantly save synthesis costs and raw material costs.

[0041] (3) The denitrification catalyst of the present invention at 250-400℃ NO x The removal rate can reach over 81%, and the nitrogen selectivity can reach over 90% at 250–450℃. After K poisoning, NO at 250–400℃ x The removal rate can reach over 75%, and the nitrogen selectivity for K poisoning at 250–450℃ can reach over 90%. Among them, the catalyst doped with rare earth elements other than cerium has a stronger denitrification ability than other catalysts, and the comparison of catalyst supports shows that MCM-49 is more effective than MCM-56. Attached Figure Description

[0042] Figure 1 This is a TEM image of the denitrification catalyst described in Example 1 of the present invention. Detailed Implementation

[0043] 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.

[0044] Example 1

[0045] This embodiment provides a denitration catalyst, and the preparation method of the denitration catalyst is as follows:

[0046] (1) Grind 0.18g of MCM-49 molecular sieve with a silicon-to-aluminum ratio of 25:1 into 50-mesh powder, add it to 50mL of deionized water, and sonicate it in an ultrasonic bath for 30min. Transfer the suspension to a crucible.

[0047] (2) 0.048 g of cerium nitrate hexahydrate and 0.0023 g of copper nitrate (Cu:Ce = 0.084:1) were added to the above suspension. After stirring for 30 min, the mixture was evaporated to dryness at 95 °C, and then calcined in a muffle furnace at 500 °C for 4 h to obtain a denitrification catalyst with an active component mass fraction of 10%. The denitrification catalyst comprises a layered MCM-49 molecular sieve support and a composite oxide active component supported on the surface of the layered MCM-49 molecular sieve support. The chemical formula of the composite oxide active component is CeCuO. 1.92 The TEM image of the denitrification catalyst is shown below. Figure 1 As shown.

[0048] Example 2

[0049] This embodiment provides a denitration catalyst, and the preparation method of the denitration catalyst is as follows:

[0050] (1) Grind 0.1486g of MCM-56 molecular sieve with a silicon-to-aluminum ratio of 15:1 into 50-mesh powder, add it to 30mL of deionized water, and sonicate it in an ultrasonic bath for 30min. Transfer the suspension to a crucible.

[0051] (2) 0.192 g of cerium nitrate hexahydrate, 0.0092 g of copper nitrate, and 0.001814 g of neodymium nitrate (Nd:Cu:Ce = 0.006:0.084:1) were added to the above suspension. After stirring for 30 min, the mixture was evaporated to dryness at 90 °C, and then calcined in a muffle furnace at 400 °C for 10 h to obtain a denitrification catalyst with an active component mass fraction of 35%. The denitrification catalyst comprises a layered MCM-56 molecular sieve support and a composite oxide active component supported on the surface of the layered MCM-56 molecular sieve support. The chemical formula of the composite oxide active component is CeCuO. 1.91 .

[0052] Example 3

[0053] This embodiment provides a denitration catalyst, and the preparation method of the denitration catalyst is as follows:

[0054] (1) Grind 0.2g of MCM-49 molecular sieve with a silicon-to-aluminum ratio of 25:1 into 50-mesh powder, add it to 50mL of deionized water, and sonicate it in an ultrasonic bath for 30min. Transfer the suspension to a crucible.

[0055] (2) 0.024 g of cerium nitrate hexahydrate and 0.0025 g of (Cu:Ce = 0.18:1) were added to the above suspension. After stirring for 30 min, the mixture was evaporated to dryness at 100 °C. Subsequently, it was calcined in a muffle furnace at 600 °C for 3 h to obtain a denitrification catalyst with an active component mass fraction of 20%. The denitrification catalyst includes a layered MCM-49 molecular sieve support and a composite oxide active component supported on the surface of the layered MCM-49 molecular sieve support. The chemical formula of the composite oxide active component is CeCuO. 1.85 .

[0056] Example 4

[0057] The only difference between this embodiment and Embodiment 1 is that Cu:Ce = 0.02:1; all other conditions and parameters are exactly the same as in Embodiment 1.

[0058] Example 5

[0059] The only difference between this embodiment and Embodiment 1 is that Cu:Ce = 0.3:1; all other conditions and parameters are exactly the same as in Embodiment 1.

[0060] Comparative Example 1

[0061] The only difference between this comparative example and Example 1 is that copper is not added; all other conditions and parameters are exactly the same as in Example 1.

[0062] Comparative Example 2

[0063] The only difference between this comparative example and Example 1 is that copper is replaced with iron; all other conditions and parameters are exactly the same as in Example 1.

[0064] Comparative Example 3

[0065] The only difference between this comparative example and Example 1 is that MCM-49 is replaced with titanium dioxide (TiO2), while the other conditions and parameters are exactly the same as in Example 1.

[0066] Performance testing:

[0067] The catalysts prepared using the above examples and comparative examples were subjected to denitrification activity experiments on simulated flue gas. The simulated flue gas contained 500 ppm NH3, 500 ppm NO, and 5% O2, with nitrogen as the balance gas. 0.495 g of the above denitrification catalyst was added to 50 mL of water, followed by 0.005 g of potassium chloride. After stirring for 30 minutes, the mixture was evaporated to dryness at 95 °C, and then calcined in a muffle furnace at 500 °C for 4 hours to obtain the denitrification catalyst after potassium poisoning. The catalytic activity was further tested under the above conditions, and the test results are shown in Table 1.

[0068] Table 1

[0069]

[0070] As can be seen from Table 1, and from Examples 1-3, the denitrification catalyst of the present invention has a NO content of 250-400℃. x The removal rate can reach over 81%, and the nitrogen selectivity can reach over 90% at 250–450℃. After K poisoning, NO at 250–400℃ x The removal rate can reach over 75%, and the nitrogen selectivity for K poisoning at 250–450℃ can reach over 90%. Among them, the catalyst doped with rare earth elements other than cerium has a stronger denitrification ability than other catalysts, and the comparison of catalyst supports shows that MCM-49 is more effective than MCM-56.

[0071] A comparison of Examples 1 and 4-5 shows that the molar ratio of cerium to copper in the denitration catalyst of this invention affects its performance. By controlling the molar ratio of copper to cerium at (0.05-0.2):1, the denitration catalyst can maintain high-temperature catalytic activity and also exhibit excellent low-temperature activity. If the copper content is too high, the high-temperature performance of the catalyst will decrease after 350°C. If the copper content is too low, the low-temperature performance of the catalyst will be poor before 300°C.

[0072] As can be seen from the comparison between Example 1 and Comparative Example 1, copper plays an important role in resisting poisoning and enhancing low-temperature performance. When copper is replaced with other elements such as iron, the redox ability of the catalyst decreases, the low-temperature activity decreases, and the resistance to alkali metal poisoning also decreases.

[0073] As can be seen from the comparison between Example 1 and Comparative Example 3, the layered MCM molecular sieve support of the present invention has a strong interlayer mass transfer capability, and can transfer NO... x Gases such as NH3 diffuse rapidly to the active sites.

[0074] The applicant declares that 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 denitrification catalyst, characterized in that, The denitrification catalyst comprises a layered MCM molecular sieve support and a composite oxide active component supported on the surface of the layered MCM molecular sieve support. The chemical formula of the composite oxide active component is CeCuOx, where x is 1 to 2. In the active component of the composite oxide, the molar ratio of copper to cerium is (0.05~0.2):1; The active component of the composite oxide further includes doping elements, which include any one or a combination of at least two of neodymium, samarium, cobalt, europium, yttrium, dysprosium, ytterbium, lanthanum, or praseodymium.

2. The denitrification catalyst according to claim 1, characterized in that, The layered MCM molecular sieve carrier includes any one or a combination of at least two of MCM-22 molecular sieve, MCM-56 molecular sieve, MCM-49 molecular sieve, or MCM-36 molecular sieve.

3. The denitrification catalyst as described in claim 1, characterized in that, The layered MCM molecular sieve carrier is MCM-49 molecular sieve.

4. The denitrification catalyst according to claim 1, characterized in that, The silicon-to-aluminum ratio of the layered MCM molecular sieve support is (5~30):

1.

5. The denitrification catalyst as described in claim 1, characterized in that, Based on the mass of the denitrification catalyst being 100%, the mass fraction of the composite oxide active component is 5-45%.

6. The denitrification catalyst according to claim 5, characterized in that, Based on the mass of the denitrification catalyst being 100%, the mass fraction of the composite oxide active component is 10-25%.

7. A method for preparing a denitrification catalyst as described in any one of claims 1-6, characterized in that, The preparation method includes the following steps: (1) The layered MCM molecular sieve support is ground and dispersed in a solvent to obtain a dispersion; (2) The cerium source and copper source are mixed with the dispersion, evaporated to dryness and then calcined to obtain the denitrification catalyst.

8. The preparation method according to claim 7, characterized in that, The mesh size of the layered MCM molecular sieve carrier after grinding in step (1) is 20~100 mesh.

9. The preparation method according to claim 8, characterized in that, The mesh size of the layered MCM molecular sieve carrier after grinding in step (1) is 40~60 mesh.

10. The preparation method according to claim 7, characterized in that, Ultrasonication is performed during the dispersion process.

11. The preparation method according to claim 7, characterized in that, The dispersion time is 10~60 minutes.

12. The preparation method according to claim 7, characterized in that, The concentration of the dispersion is 2~8 g / L.

13. The preparation method according to claim 7, characterized in that, The cerium source in step (2) includes cerium nitrate.

14. The preparation method according to claim 7, characterized in that, The copper source includes copper nitrate.

15. The preparation method according to claim 7, characterized in that, A doped metal source is also added during the mixing process.

16. The preparation method according to claim 15, characterized in that, The dopant metal source includes any one or a combination of at least two of neodymium nitrate, samarium nitrate, europium nitrate, yttrium nitrate, dysprosium nitrate, ytterbium nitrate, lanthanum nitrate, or praseodymium nitrate.

17. The preparation method according to claim 7, characterized in that, The temperature for evaporation in step (2) is 80~100℃.

18. The preparation method according to claim 7, characterized in that, The heating rate during roasting is 1~10℃ / min.

19. The preparation method according to claim 7, characterized in that, The roasting temperature is 400~600℃.

20. The preparation method according to claim 7, characterized in that, The roasting time is 3 to 10 hours.

21. The application of a denitrification catalyst as described in any one of claims 1-6, characterized in that, The denitrification catalyst is used for the selective catalytic reduction of nitrogen oxides by ammonia.

22. The application of the denitrification catalyst as described in claim 21, characterized in that, The catalyst operates at a temperature of 150~550℃.

23. The application of the denitrification catalyst as described in claim 22, characterized in that, The catalyst operates at a temperature of 200~400℃.

24. A denitrification reactor, characterized in that, The denitrification reactor comprises a denitrification catalyst as described in any one of claims 1-6, and the denitrification reactor is used in mobile source gas denitrification devices and / or stationary source gas denitrification devices.

25. The denitrification reactor according to claim 24, characterized in that, The mobile source gas denitrification device includes any one or a combination of at least two of diesel engines, gas turbines, or aircraft engines.

26. The denitrification reactor according to claim 24, characterized in that, The stationary source gas denitrification device includes industrial kilns and / or calcining kilns.

Images