A methylated manganese-based reference metal organic framework low-temperature denitration catalyst with high water resistance and a preparation method thereof

Abstract

The present application relates to a kind of methylated manganese-based reference metal organic framework low-temperature denitration catalyst (IPA-Mn-BTC) with high water resistance and its preparation method.The catalyst is prepared by solvothermal method, inorganic methylation occurs in the self-assembly process of organic ligand and metal coordination ion, and nanorod structure with methyl functional group is generated.Methylation not only regulates the pore structure of catalyst, makes the pore less than 4.3nm disappear, so as to inhibit the adsorption and diffusion of H2O, to achieve the purpose of improving water resistance, also regulates the electronic structure, reduces the adsorption energy of active site to H2O to improve water resistance.The design of methylation not only improves the water resistance of low-temperature denitration catalyst, but also solves the problem that sulfate species is difficult to decompose at low temperature, so as to cause catalyst deactivation.The catalyst effectively improves the water resistance on the basis of excellent low-temperature denitration activity and sulfur resistance, and has wide application prospect in the field of low-temperature denitration catalyst, especially in the flue gas with high water content.

Description

TECHNICAL FIELD

[0001] The present application belongs to a new material and a preparation method of the material, in particular to a methylated manganese-based benchmark metal organic framework material (IPA-Mn-BTC) and a preparation method thereof. The material can be used as a catalyst for selective catalytic reduction denitration of flue gas with high water content at low temperature (90-270℃), and has excellent denitration activity and outstanding water resistance and sulfur resistance. BACKGROUND

[0002] Currently, in the global power generation structure, coal combustion still accounts for the largest proportion, and coal energy is still the top priority for people's livelihood needs in China. However, coal combustion will produce a large amount of smoke, sulfur dioxide (SO2) and nitrogen oxides (NO x ), among which NO x will cause serious harm to the natural environment, human health and plant growth. Therefore, it is crucial to treat the flue gas of coal combustion to make the NO x in the flue gas meet the emission standard or even lower.

[0003] The selective catalytic reduction (SCR) technology uses ammonia (NH3) or urea as a reducing agent to selectively reduce NO x into N2 and H2O under the action of a catalyst, and is the mainstream technology for NO x treatment. However, this technology has limitations in use. At present, the denitration process is often set before dust removal and desulfurization, and dust and SO2 will cause wear and poisoning of the catalyst, resulting in rapid deactivation of the catalyst. Therefore, researchers have developed a low-dust process to set the denitration process after dust removal and desulfurization. However, the temperature of the flue gas will decrease after dust removal and desulfurization, and the flue gas needs to be reheated to meet the activity temperature window (300-400℃) of the traditional vanadium-based catalyst (V2O5-WO3 / TiO2). Reheating of the flue gas will cause excessive energy loss, and high temperature will cause NH3 to be oxidized, consuming reducing gas NH3 while NO xThe generation amount is increased, and the N2 selectivity is reduced. To solve the above contradictions, it is necessary to develop a low-temperature denitration catalyst. At present, there are still some problems in the low-temperature denitration catalyst which need to be broken through, such as: the water and sulfur resistance needs to be improved. In the flue gas with high water content, H2O will compete with NH3 and NO for adsorption, thereby causing the denitration activity to decrease, and H2O and SO2 will generate sulfates which are difficult to decompose under low-temperature conditions and cover the active sites, thereby causing the catalyst to be deactivated. Therefore, in the low-dust process, how to enhance the water resistance of the denitration catalyst on the basis of ensuring the sulfur resistance, so that it can be more effectively applied to the flue gas with high water content, while realizing high low-temperature denitration activity and excellent water and sulfur resistance is the key research direction. At present, many studies focus on improving the low-temperature denitration activity and sulfur resistance, but there are few studies on improving the water resistance. Therefore, it is of great significance to develop a new type of environmentally friendly catalyst which has excellent low-temperature denitration activity and high water and sulfur resistance.

[0004] Metal-organic frameworks (MOFs) formed by self-assembly of metal cations and organic ligands have attracted much attention in the field of catalytic denitration due to their tunable pore size, large number of adjustable active sites, and high specific surface area. Highly dispersed and fully exposed active sites can effectively improve catalytic activity, and the tunable pore size also provides a way to improve water and sulfur resistance. Our team prepared quasi-MOFs using special calcination conditions, which improved the thermal stability of MOFs and constructed quasi-Mn-BTC, a low-temperature denitration catalyst with high sulfur tolerance, breaking the bottleneck of poor sulfur resistance of manganese-based denitration catalysts (ACS Catal. 2023, 13, 5020-5032). However, the defect of this catalyst is poor water resistance, and the denitration activity decreases by 25% under the condition of introducing 6% H2O. If hydrophobic functional groups (such as methyl) can be connected to the catalyst structure and the pore structure is regulated, it may be possible to improve the water resistance of the catalyst while ensuring excellent low-temperature denitration activity and sulfur resistance. However, the introduction of functional groups may affect the formation of MOF structures, and the introduced functional groups may be inert functional groups, so functionalized MOFs are also a challenge. The present invention prepared IPA-Mn-BTC, a methylated MOF low-temperature denitration catalyst, by solvothermal method and two-stage calcination, which has excellent low-temperature denitration activity and outstanding water and sulfur resistance. SUMMARY

[0005] One of the purposes of the present invention is to provide a methylated manganese-based metal-organic framework low-temperature denitration catalyst with high water resistance, which is IPA-Mn-BTC and mainly applied to the removal of NO x Selective catalytic reduction removal in a lower temperature range.

[0006] The second object of the present application is to provide a preparation method of a methylated manganese-based metal organic framework low-temperature denitration catalyst with high water resistance, which forms a methyl-functionalized MOF under a solvothermal reaction with benzene-1,3,5-tricarboxylic acid (BTC) as a ligand and isopropyl alcohol (IPA) and ethanol, water as a mixed solvent.

[0007] (1) 2-3 g of benzene-1,3,5-tricarboxylic acid (BTC) is placed in 50-150 ml of an ethanol solution, and magnetic stirring is performed at room temperature until complete dissolution to form solution A.

[0008] (2) 1-3 g of manganese acetate tetrahydrate is dissolved in 30-50 ml of ultrapure water to form solution B.

[0009] (3) After mixing solution A and solution B, 30-60 ml of isopropyl alcohol is added to the mixed solution, magnetic stirring is performed at room temperature for 2 hours, and a solvothermal reaction occurs at 110-150°C for 15-20 hours.

[0010] (4) After the solvothermal reaction is completed, the solid product is collected by centrifugation, washed with ethanol 4-6 times, and then dried under vacuum at 60-100°C for 8-12 hours, and after grinding, a white solid powder is obtained.

[0011] (5) The white solid powder is pretreated at 300-350°C under a nitrogen atmosphere for 2-4 hours, and then calcined at 300-350°C under an air atmosphere for 4-6 hours to obtain an IPA-Mn-BTC catalyst.

[0012] The methylated manganese-based metal organic framework low-temperature denitration catalyst of the present application is characterized in that: the catalyst is a methyl-functionalized metallo-organic framework material (IPA-Mn-BTC) in the form of nanorods; it exhibits obvious methyl stretching vibration and methyl deformation vibration peaks at 3000 cm -1 and 1300 cm -1 in the infrared spectrum; methyl functionalization causes the disappearance of pore structures less than 4.3 nm in the IPA-Mn-BTC, and the increase in pore structure hinders the adsorption and further diffusion of water molecules; methyl functionalization reduces the adsorption energy of the active sites of the catalyst to H2O, inhibiting the adsorption of H2O; the IPA-Mn-BTC contains uniformly distributed Mn, C, H, and O, wherein Mn is composed of Mn 2+ , Mn 3+ , and Mn 4+ in three valence states, with Mn 3+ predominant; the IPA-Mn-BTC exhibits an obvious hierarchical porous structure and has a large specific surface area, with a specific surface area of 80-120 m 2 / g.

[0013] The catalyst preparation method of the present application is characterized in that the methyl functional groups are generated in-situ on the manganese-based metal organic framework structure by a solvothermal reaction under the condition of adding isopropyl alcohol.

[0014] Compared with the prior art, the present application has the following advantages:

[0015] The catalyst prepared by the present application grows methyl functional groups in-situ in the self-assembly process, and the structure of the catalyst is stabilized by two-stage calcination, and the active methyl functional groups are retained. The uniqueness of the structural design and the special activation treatment result in a large number of oxygen vacancies of the catalyst which are beneficial to improve the denitration activity, thereby ensuring excellent low-temperature denitration activity. At a space velocity of 36,000 h -1 At a space velocity of 36,000 h

[0016] The design of the methyl functional groups reduces the electronic transmission between the active sites of the catalyst and H2O and the adsorption energy of H2O by regulating the electronic structure. On the other hand, the pore structure smaller than 4.3 nm disappears, thereby inhibiting the adsorption and diffusion of H2O. By regulating the electronic structure and the pore structure, the IPA-Mn-BTC catalyst effectively improves the water resistance of the catalyst while ensuring excellent low-temperature denitration activity and sulfur resistance, and solves the problem that the sulfate species covering the surface of the active sites is difficult to decompose at low temperature.

[0017] The IPA-Mn-BTC catalyst is prepared only by solvothermal synthesis and two-stage calcination, which is low in cost and safe and environmentally friendly. BRIEF DESCRIPTION OF DRAWINGS

[0018] [1] Figure 1 and Figure 2 are scanning electron microscope photos of the IPA-Mn-BTC low-temperature denitration catalyst.

[0019] [2] Figure 3 is the denitration performance of the IPA-Mn-BTC catalyst obtained according to Example 1, Figure 4 is the water resistance test result. DETAILED DESCRIPTION EMBODIMENT

[0020] The IPA-Mn-BTC low-temperature denitration catalyst is prepared according to the preparation method proposed by the present application:

[0021] (1) 2.1 grams of trimesic acid (BTC) are placed in 100 milliliters of an ethanol solution, and magnetically stirred at room temperature until completely dissolved to form a solution A.

[0022] (2) 1.05 g of manganese acetate tetrahydrate was dissolved in 30 ml of ultrapure water to form solution B.

[0023] (3) After mixing solution A and solution B, 30 ml of isopropanol was added to the mixed solution, which was magnetically stirred at room temperature for 2 hours and underwent a solvothermal reaction at 120°C for 15 hours.

[0024] (4) After the solvothermal reaction, the solid product was collected by centrifugation, washed with ethanol 4 times, and then dried at 80°C under vacuum for 8 hours. After grinding, a white solid powder was obtained.

[0025] (5) The white solid powder was pretreated at 300°C under a nitrogen atmosphere for 2 hours, and then calcined at 320°C under an air atmosphere for 4 hours to obtain the IPA-Mn-BTC catalyst.

[0026] The catalyst is a methyl-functionalized manganese-based metal-organic framework low-temperature denitration catalyst constructed with benzene-1, 3, 5-tricarboxylic acid (BTC) as an organic ligand. The coordination center manganese element is highly dispersed and uniformly distributed on the nanorod structure. The integrity of the methyl functional group is retained during the calcination process, and obvious vibration peaks belonging to the methyl group are presented at 3000 cm -1 and 1300 cm -1 in the infrared spectrum. The methyl functionalization regulates the pore size distribution, resulting in the disappearance of pore structures less than 4.3 nm, thereby hindering the adsorption and further diffusion of water molecules. At the same time, the methyl functionalization also reduces the adsorption energy of the active site to H2O, thereby enhancing the water resistance of the catalyst. The denitration activity still remains above 90% at 150°C with the introduction of 6% H2O. The IPA-Mn-BTC contains uniformly distributed Mn, C, H, and O, wherein Mn 2+ , Mn 3+ , and Mn 4+ are composed of three valence states, mainly Mn 3+ . The IPA-Mn-BTC presents an obvious hierarchical porous structure and has a large specific surface area, with a specific surface area of 80 m 2 / g.

[0027] Example 2:

[0028] According to the preparation method proposed in the present application, the IPA-Mn-BTC dual-ligand low-temperature denitration catalyst is prepared:

[0029] (1) 3.1 g of benzene-1, 3, 5-tricarboxylic acid (BTC) was placed in 120 ml of an ethanol solution and magnetically stirred at room temperature until completely dissolved to form solution A.

[0030] (2) 2.2 g of manganese acetate tetrahydrate was dissolved in 40 ml of ultrapure water to form solution B.

[0031] (3) After mixing solution A and solution B, 40 ml of isopropanol was added to the mixed solution, which was magnetically stirred at room temperature for 2 hours and underwent a solvothermal reaction at 130°C for 18 hours.

[0032] (4) After the solvothermal reaction, the solid product was collected by centrifugation, washed with ethanol 6 times, and then dried at 100°C under vacuum for 10 hours. After grinding, a white solid powder was obtained.

[0033] (5) The white solid powder was pretreated at 310°C under a nitrogen atmosphere for 4 hours, and then calcined at 350°C under an air atmosphere for 6 hours to obtain the IPA-Mn-BTC catalyst.

[0034] The catalyst is a methyl-functionalized manganese-based metal-organic framework low-temperature denitration catalyst. The manganese element is highly dispersed and uniformly distributed in the nanorod structure formed by self-assembly of benzene-1, 3, 5-tricarboxylic acid (BTC) and manganese ions. Through testing of infrared spectra, it was found that there were obvious vibration peaks belonging to methyl groups at 3000 cm -1 and 1300 cm -1 , indicating that the methyl groups still exist stably after calcination and activation. The design of methyl functionalization regulates the pore size distribution, and the disappearance of small pore sizes hinders the adsorption and further diffusion of water molecules. At the same time, methyl functionalization also reduces the adsorption energy of active sites to H2O, thereby enhancing the water resistance of the catalyst. During the performance test, 6% H2O was introduced, and the performance of IPA-Mn-BTC only decreased by 7%. IPA-Mn-BTC contains uniformly distributed Mn, C, H, and O, in which Mn is composed of Mn 2+ , Mn 3+ , and Mn 4+ , mainly Mn 3+ . IPA-Mn-BTC presents an obvious hierarchical porous structure and has a large specific surface area, with a specific surface area of 91 m 2 / g.

Claims

1. A methylated manganese-based reference metal-organic framework low-temperature de-NOx catalyst having high water tolerance, characterized in that: The catalyst is a methyl-functionalized metallo-organic framework IPA-Mn-BTC in nanorod structure; obvious methyl stretching vibration and methyl deformation vibration peaks are presented at 3000 cm -1 and 1300 cm -1 in infrared spectrum; the methyl functionalization causes the disappearance of pore structures less than 4.3 nm in IPA-Mn-BTC, and the increase of pore structures hinders the adsorption and further diffusion of water molecules; the methyl functionalization reduces the adsorption energy of active sites of the catalyst to H2O, and inhibits the adsorption of H2O; IPA-Mn-BTC contains uniformly distributed Mn, C, H and O, wherein Mn 2+ , Mn 3+ and Mn 4+ are composed of three valence states, and Mn 3+ is the main component; IPA-Mn-BTC presents obvious hierarchical porous structure and has a large specific surface area, and the specific surface area is 80-120 m 2 / g; and the preparation method of the methylated manganese-based metallo-organic framework low-temperature denitration catalyst with high water resistance comprises the following steps: (1) 2-3 grams of benzene-1,3,5-tricarboxylic acid (BTC) is placed in 50-150 milliliters of ethanol solution, and stirred magnetically at room temperature until completely dissolved to form solution A; (2) 1-3 grams of manganese acetate tetrahydrate is dissolved in 30-50 milliliters of ultrapure water to form solution B; (3) After mixing solution A and solution B, 30-60 milliliters of isopropyl alcohol is added to the mixed solution, and stirred magnetically at room temperature for 2 hours, and then subjected to a solvothermal reaction at 110-150°C for 15-20 hours; (4) After the solvothermal reaction is completed, the solid product is collected by centrifugation, washed with ethanol 4-6 times, and then dried under vacuum at 60-100°C for 8-12 hours, and after grinding, a white solid powder is obtained; under the condition of adding isopropyl alcohol, methyl functional groups are generated in situ on the manganese-based metal-organic framework structure through a solvothermal reaction; (5) The white solid powder is pretreated at 300-350°C for 2-4 hours under a nitrogen atmosphere, and then calcined at 300-350°C for 4-6 hours under an air atmosphere, to obtain an IPA-Mn-BTC catalyst.

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