Preparation method and application of Mn-based integral catalyst

Abstract

The invention relates to a Mn-based integral catalyst preparation method, which specifically comprises: (1) cutting a melamine sponge into a regular shape, placing into a beaker, sequentially carrying out ultrasonic cleaning with an organic solvent, an inorganic acid, H2O and an organic acid, carrying out drying treatment on the cleaned MS, drying in an inert atmosphere, and cooling to a room temperature to obtain the treated melamine sponge; (2) adding KMnO4 and metal salt into deionized water, and mixing and stirring to obtain a dipping precursor solution; (3) immersing the treated melamine sponge into the impregnation precursor solution obtained in the step (2) for 8-12 hours to obtain the impregnated melamine sponge, and then drying the impregnated melamine sponge to obtain a monolithic catalyst precursor; and (4) roasting the monolithic catalyst precursor in an H2 atmosphere to obtain the Mn-based monolithic catalyst. The catalyst prepared by the method has the characteristics of high activity, high selectivity and high stability.

Description

Technical Field

[0001] The present invention relates to the field of air pollutant control, and in particular to a Mn-based integral catalyst for NH3-SCR and CO oxidation synergy, and a preparation method and application thereof. Background Art

[0002] The sintering process is an important part of steel production and also a major source of nitrogen oxides (NO x ) and carbon monoxide (CO) are important sources of pollutants. The steel industry accounts for about 45% to 65% of NO x Emissions originate from steel sintering. Currently, ammonia selective catalytic reduction (NH3-SCR) technology is a commonly used denitrification method in the steel industry. This technology uses ammonia (NH3) as a reducing agent to reduce NO in flue gas under the action of a catalyst. x Converted into harmless nitrogen (N2) and water (H2O). However, the temperature of sintering flue gas is usually low (100-180°C), which is far lower than the optimal temperature range of SCR reaction (280-300°C). Therefore, in order to meet the reaction requirements of SCR technology, it is usually necessary to increase the flue gas temperature by supplementing the heating of blast furnace gas, but this supplementary combustion method will increase additional gas consumption and CO2 emissions, resulting in additional energy consumption and carbon emissions. It is estimated that the national sintering machine will emit about 32 million tons of CO2 per year due to denitrification heating. In order to solve this problem, low-temperature catalytic denitrification technology (below 150°C) has become an important research direction because it can reduce dependence on blast furnace gas and reduce energy consumption and emissions.

[0003] At present, low-temperature catalytic denitrification catalysts still face problems such as insufficient activity and poor stability, which makes the application effect of SCR technology at low temperatures unsatisfactory. In order to further improve the denitrification efficiency and reduce energy consumption, researchers have proposed a method of combining CO oxidation with SCR denitrification technology. The CO content in sintering flue gas is usually high (0.5% to 1%), and this feature is effectively utilized. In this technical route, CO is first oxidized by a catalyst and converted into carbon dioxide (CO2), releasing a large amount of heat. This heat can be used to heat the flue gas, thereby increasing the flue gas temperature and helping to meet the temperature conditions required for the SCR reaction. Specifically, 1% of CO complete oxidation can increase the flue gas temperature by about 90°C, which significantly reduces the need for traditional coal gas supplementary heating. Therefore, the combined technology of CO oxidation and SCR denitrification can effectively increase the temperature of the flue gas, reduce dependence on external heat sources (such as blast furnace gas), thereby reducing CO2 emissions, and increasing NO x This combined solution is expected to achieve efficient denitrification under low temperature conditions while reducing energy consumption and carbon emissions, which is of great significance for energy conservation and consumption reduction in the steel industry.

[0004] At present, the combined use of CO oxidation and SCR denitrification technologies generally involves independently developing CO oxidation catalysts and SCR catalysts, and arranging the two in series for application, but this increases the complexity of the equipment and the difficulty of modification.

[0005] CN 118988408A and CN 116037115 B use CO-SCR technology to remove CO and NO simultaneously x However, the main disadvantage of this technology is that under oxygen-rich conditions, CO tends to be oxidized to CO2 rather than to NO. x reaction, thereby reducing NO x The catalytic efficiency is low, so it is difficult to meet the application requirements under actual flue gas conditions. Summary of the invention

[0006] The purpose of this invention is to develop a bifunctional catalyst that cooperates with NH3-SCR and CO oxidation, and utilize the heat released by CO oxidation to directly heat the flue gas, thereby increasing the flue gas temperature and supplementing the SCR technology to achieve CO and NO x It can achieve efficient synergistic emission reduction and has the characteristics of high activity, high selectivity and high stability.

[0007] Mn-based catalysts for CO and NO x It exhibits good catalytic activity in purification. Its various oxidation states and unstable oxygen improve the adsorption and activation of reactants on the catalyst surface, and can effectively catalyze the conversion of CO and NO x The Mn-based catalyst has high stability and can maintain its catalytic performance for a long time without being easily deactivated.

[0008] In order to give full play to the catalytic performance of transition metals, the construction of bimetallic catalysts has a good development prospect in practical applications. The two metals in the bimetallic catalyst can play a synergistic effect, promote each other, and improve the catalytic activity and selectivity. The stability of metal catalysts is usually higher than that of single metal catalysts because the two metals can stabilize each other and extend the service life of the catalyst.

[0009] When powder catalysts are filled in fixed bed reactors, they usually tend to form dense packing structures, which will greatly increase the flow resistance of the fixed bed system and hinder active sites. Monolithic catalysts are not only conducive to separation and regeneration after the reaction, but are also more suitable for fixed bed reactors than traditional powder catalysts.

[0010] Melamine sponge (MS) has the advantages of low cost, rich pore structure, large specific surface area, extremely light specific gravity, and good mechanical strength. It is an ideal three-dimensional porous flexible skeleton for loading active nanomaterials. Therefore, using it as a carrier can effectively improve the efficiency of the catalytic reaction. Melamine sponge will shrink significantly as the calcination temperature increases, and the elasticity of the sample gradually decreases with the increase in temperature. When the temperature is below 350°C, the sponge is not carbonized enough, resulting in a brown appearance. However, the sponge still maintains its elasticity and appears black at 400°C. As the temperature further increases, the shrinkage of the sample becomes more obvious. The sample has already undergone severe deformation at 500°C. Therefore, the calcination temperature should be selected reasonably.

[0011] Oxygen vacancies play an important role in catalytic reactions, especially on the surface of solid catalysts, which significantly affect the electronic structure, surface properties and reaction activity of the catalyst. During the H2 calcination process, hydrogen can reduce the metal oxide in the catalyst to a metallic state, and can also remove oxygen on the surface or in the lattice. When oxygen ions are removed from the lattice of the catalyst, oxygen vacancies are formed. The catalyst disclosed in the present invention further enhances the activation ability of the reaction gas by calcining the catalyst under H2 to increase oxygen vacancies.

[0012] The experimental results confirm that the Mn-based monolithic catalyst can efficiently and quickly remove CO and NO from exhaust gas simultaneously. x The present invention can make CO and NO x The conversion efficiency is improved, the reaction window is reduced, and NO x It can be removed well under high O2 concentration and has a wider application range. The bimetallic catalyst of the present invention can provide a theoretical reference for the development of efficient and promising selective catalytic reduction technology and has a good practical application prospect.

[0013] The purpose of the present invention is achieved through the following technical solutions:

[0014] A preparation method and application of a Mn-based integral catalyst for NH3-SCR and CO oxidation synergy, the preparation method specifically comprising the following steps:

[0015] (1) cutting the melamine sponge into regular shapes, placing it in a beaker, and ultrasonically cleaning it with an organic solvent, an inorganic acid, H2O, and an organic acid in sequence, drying the MS obtained by cleaning, and then cooling it to room temperature after drying under an inert atmosphere to obtain a treated melamine sponge;

[0016] (2) adding KMnO4 and metal salt into deionized water, mixing and stirring to obtain an impregnation precursor solution;

[0017] (3) immersing the treated melamine sponge into the impregnation precursor solution obtained in step (2) for 8-12 hours to obtain an impregnated melamine sponge, and then drying the impregnated melamine sponge to obtain a monolithic catalyst precursor;

[0018] (4) The integral catalyst precursor is calcined in a H2 atmosphere to obtain a Mn-based integral catalyst.

[0019] In step (1), the regular shape is one or more of a cube, a cuboid, a cylinder, a ring, a sphere, and an octahedron; the organic solvent is one of acetone, methyl ethyl ketone, ethanol, ether, and petroleum ether; the organic acid is a carboxylic acid having 1 to 8 carbon atoms, preferably acetic acid; the inorganic acid is one of hydrochloric acid, nitric acid, and sulfuric acid; when using the organic solvent, inorganic acid, H2O, and organic acid for ultrasonic cleaning, the volume ratio of the organic solvent, inorganic acid, H2O, and organic acid to the volume of the melamine sponge is 2-5:1, wherein the concentration of the inorganic acid and the organic acid is 2-5 mol / L, preferably, the concentration of the organic acid and the inorganic acid is 3-5 mol / L; the inert gas is one of nitrogen, carbon dioxide, and argon.

[0020] In step (1), the vacuum drying temperature is 60-80°C, and the drying time is 3-5h, preferably, the vacuum drying time is 3-4h; in step (1), the heating temperature under N2 atmosphere is 200-350°C, and the heating time is 1-4h, preferably, the heating temperature under N2 atmosphere is 300-350°C, and the heating time is 2-3h.

[0021] In step (2), the metal salt is one or more of halides, nitrates, sulfates or soluble carboxylates of copper, iron, cobalt or cerium, preferably, the metal salt is one or more of copper nitrate, iron nitrate, cobalt nitrate or cerium nitrate; the molar ratio of KMnO4 and the metal salt is 0.5-2:1; the molar concentration of the metal salt in the impregnation precursor solution is 0.5-2 mol / L.

[0022] In step (3), the volume ratio of the treated melamine sponge to the impregnated precursor solution is 1:1.5-5, more preferably 1:2-3; the drying temperature is 60-80°C, and the drying time is 10-14h, preferably, the drying time is 60°C and the drying time is 12h.

[0023] In step (4), the calcination temperature is 300-450°C, and the calcination time is 3-6h. Preferably, the calcination temperature is 350-400°C, and the calcination time is 3-4h.

[0024] Another aspect of the present invention discloses a Mn-based integral catalyst prepared by the preparation method of the present invention.

[0025] Another aspect of the present invention discloses a method for denitrifying low-temperature flue gas using the catalyst of the present invention, wherein the denitrification reaction temperature is 100-350°C, and the volume concentration of CO in the flue gas is above 0.5%, more preferably 0.5-2%. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The performance diagram of catalytic removal of CO by Mn-Cu prepared in Comparative Example 1 and Mn-Cu / MS catalyst prepared in Example 1;

[0027] Figure 2 The Mn-Cu prepared in Comparative Example 1 and the Mn-Cu / MS catalyst prepared in Example 1 catalyze the removal of NO x Performance graphs;

[0028] Figure 3 Mn-Cu prepared in Comparative Example 1 and Mn-Cu / MS catalyst prepared in Example 1 for simultaneous removal of CO and NO x NO x Performance graphs;

[0029] Figure 4 Mn-Cu prepared in Comparative Example 1 and Mn-Cu / MS catalyst prepared in Example 1 for simultaneous removal of CO and NO x CO performance diagram;

[0030] Figure 5 Simultaneous removal of CO and NO by Mn-Cu / MS catalyst prepared in Example 1 and Comparative Examples 2-4 x NO x Performance graphs;

[0031] Figure 6 Simultaneous removal of CO and NO by Mn-Cu / MS catalyst prepared in Example 1 and Comparative Examples 2-4 x CO performance diagram;

[0032] Figure 7 Simultaneous removal of CO and NO by Mn-Cu / MS catalyst prepared in Example 1 and Comparative Example 5 x NO x Performance graphs;

[0033] Figure 8 Simultaneous removal of CO and NO by Mn-Cu / MS catalyst prepared in Example 1 and Comparative Example 5 x CO performance diagram;

[0034] Fig. 9 The stability of the Mn-Cu / MS catalyst prepared in Example 1 at 275°C. DETAILED DESCRIPTION

[0035] The technical solution of the present invention is further described in detail below in conjunction with embodiments.

[0036] Example 1

[0037] The present embodiment provides a method for preparing a Mn-Cu / MS catalyst for synergistic NH3-SCR and CO oxidation, the preparation method comprising the following steps: (1) cutting a melamine sponge (MS) into a rectangular shape, placing the MS in a 200 mL beaker, and sequentially soaking and ultrasonically cleaning the MS with 2 mol / L acetone, HCl, H2O, and CH3CH2OH for 2 h; placing the cleaned MS in a vacuum drying oven and drying it at 60°C for 10 h to obtain a cleaned MS; heating the obtained MS at 300°C for 2 h under a N2 atmosphere, and then cooling the MS to room temperature to obtain a treated MS; (2) adding 2.11 g of MS to a mol / L acetone solution; and KMnO4 is added into deionized water, and then 0.63g of copper nitrate is added and stirred for 2h to obtain a mixed solution Mn-Cu precursor; (3) a piece of MS is immersed in the mixed solution and repeatedly squeezed and immersed for 12h to obtain a Mn-Cu / MS precursor, and then the Mn-X / MS precursor is dried at 80°C for 10h; (4) the dried Mn-X / MS precursor is placed in a H2 atmosphere and calcined at 350°C for 3h to obtain a Mn-X / MS integral catalyst.

[0038] Example 2

[0039] This embodiment provides a method for preparing a Mn-Co / MS catalyst for synergistic NH3-SCR and CO oxidation. The preparation method is different from that of Example 1 only in that 0.63 g of copper nitrate in step (2) is replaced with 0.97 g of cobalt nitrate, and other conditions are the same as those of Example 1.

[0040] Example 3

[0041] This embodiment provides a method for preparing a Mn-Fe / MS catalyst for synergistic NH3-SCR and CO oxidation. The preparation method is different from that in Example 1 only in that 0.63 g of copper nitrate in step (2) is replaced by 1.34 g of iron nitrate, and other conditions are the same as those in Example 1.

[0042] Example 4

[0043] This embodiment provides a method for preparing a Mn-Ce / MS catalyst for synergistic NH3-SCR and CO oxidation. The preparation method is different from that in Example 1 only in that 0.63 g of copper nitrate in step (2) is replaced by 1.09 g of cerium nitrate, and other conditions are the same as those in Example 1.

[0044] Comparative Example 1

[0045] This comparative example provides a method for preparing a Mn-Cu catalyst for NH3-SCR and CO oxidation synergy, the preparation method comprising the following steps:

[0046] (1) 2.11 g of KMnO4 was added to deionized water, and then 0.63 g of copper nitrate was added and stirred for 2 h to obtain a mixed solution of Mn-Cu precursor; (2) The Mn-Cu precursor obtained in (1) was dried at 80 °C for 10 h, and then calcined at 350 °C for 3 h in a H2 atmosphere to obtain a Mn-Cu catalyst.

[0047] Comparative Example 2

[0048] This comparative example provides a method for preparing a Mn-Cu / MS catalyst for synergistic NH3-SCR and CO oxidation. The preparation method is different from that of Example 1 only in that the dried Mn-X / MS precursor in step (4) is calcined at 300°C for 3h in a H2 atmosphere.

[0049] Comparative Example 3

[0050] This comparative example provides a method for preparing a Mn-Cu / MS catalyst for synergistic NH3-SCR and CO oxidation. The preparation method is different from that in Example 1 only in that the dried Mn-X / MS precursor in step (4) is calcined at 350°C for 3h under a H2 atmosphere.

[0051] Comparative Example 4

[0052] This comparative example provides a method for preparing a Mn-Cu / MS catalyst for synergistic NH3-SCR and CO oxidation. The preparation method is different from that of Example 1 only in that the dried Mn-X / MS precursor in step (4) is calcined at 700°C for 3h in a H2 atmosphere.

[0053] Comparative Example 5

[0054] This comparative example provides a method for preparing a Mn-Cu / MS catalyst for synergistic NH3-SCR and CO oxidation. The preparation method is different from that of Example 1 only in that the dried Mn-X / MS precursor in step (4) is calcined at 350°C for 3h under a N2 atmosphere.

[0055] The catalysts prepared by the methods of Examples 1 to 4 and Comparative Examples 1 to 5 were used to test the catalytic performance of the catalysts prepared by Examples 1 to 4 and Comparative Examples 1 to 5:

[0056] Test conditions: The catalysts prepared in the examples and comparative examples were respectively taken and placed in a fixed bed reactor. The raw gas composition was: 500ppm NH3, 500ppm NO, 5000ppm CO, 5vol% O2, N2 as the balance gas, the gas flow rate was 100ml / min, and the volume space velocity was 120000h -1 The test temperature window of the catalytic reaction is 150-350℃, with an interval of 25℃. The infrared flue gas analyzer (MGA6plus) is used to detect the outlet gas concentration. The test results are as follows Figure 1-9 As shown in Tables 1-4. Tables 1 and 2 show the catalysts for removing CO or NO separately. x The catalytic activity conversion rate of Mn-Cu and Mn-Cu / MS catalysts is shown in Table 3. x The CO conversion rate and NO x Conversion rate, Table 4 shows the CO conversion rate and NOx conversion rate when Mn-Cu / MS, Mn-Co / MS, Mn-Fe / MS and Mn-Ce / MS are used to remove CO and NOx simultaneously; Table 5 shows the CO and NOx conversion rate of Mn-Cu / MS catalysts at different calcination temperatures. x The CO conversion rate and NO x Conversion rate; Table 6 shows the simultaneous removal of CO and NO by Mn-Cu / MS catalyst under different calcination atmospheres x The CO conversion rate and NO x Conversion rate.

[0057] Table 1

[0058]

[0059] Table 2

[0060]

[0061] Table 3

[0062]

[0063] Table 1 and Table 2 show the removal of CO and NO by the catalysts respectively. x The catalytic activity conversion rate of Mn-Cu catalyst is shown in the table. After modification, the CO oxidation activity and NO x The catalytic activity of the catalyst was improved, with the CO conversion rate of the catalyst reaching 90% at 250°C and the NO conversion rate of the catalyst at 275°C. x The conversion rate reached 90%. Table 3 shows the simultaneous removal of CO and NO by Mn-Cu and Mn-Cu / MS catalysts. x The CO conversion rate and NO x The conversion rate is shown in the table. After modification, the CO oxidation activity and NOx The catalytic activity was improved.

[0064] Table 4

[0065]

[0066] It can be seen from the table that different metal doping can affect the catalytic activity of Mn-based catalysts, CO and NO x The order of catalytic activity is: Mn-Cu / MS>Mn-Co / MS>Mn-Fe / MS>Mn-Ce / MS, and Mn-Cu / MS shows the best activity.

[0067] Table 5

[0068]

[0069] It can be seen from Table 5 that the calcination temperature can affect the catalytic activity of the Mn-based catalyst, and the best catalytic activity is exhibited when the calcination temperature is 350°C.

[0070] Table 6

[0071]

[0072] It can be seen from Table 6 that the calcination atmosphere can affect the catalytic activity of Mn-based catalysts. The catalytic activity of Mn-Cu / MS prepared by calcining under H2 is better than that of Mn-Cu / MS prepared by calcining under N2.

[0073] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A preparation method and application of a Mn-based integral catalyst for NH3-SCR and CO oxidation synergy, the preparation method specifically comprising the following steps: (1) cutting the melamine sponge into regular shapes, placing it in a beaker, and ultrasonically cleaning it with an organic solvent, an inorganic acid, H2O, and an organic acid in sequence, drying the MS obtained by cleaning, and then cooling it to room temperature after drying under an inert atmosphere to obtain a treated melamine sponge; (2) adding KMnO4 and metal salt into deionized water, mixing and stirring to obtain an impregnation precursor solution; (3) immersing the treated melamine sponge into the impregnation precursor solution obtained in step (2) for 8-12 hours to obtain an impregnated melamine sponge, and then drying the impregnated melamine sponge to obtain a monolithic catalyst precursor; (4) The integral catalyst precursor is calcined in a H2 atmosphere to obtain a Mn-based integral catalyst.

2. The method according to claim 1, characterized in that In step (1), the regular shape is one or more of a cube, a cuboid, a cylinder, a ring, a sphere, and an octahedron; the organic solvent is one of acetone, methyl ethyl ketone, ethanol, ether, and petroleum ether; the organic acid is a carboxylic acid having 1 to 8 carbon atoms, preferably acetic acid; and the inorganic acid is one of hydrochloric acid, nitric acid, and sulfuric acid.

3. The method according to claim 1, characterized in that When using organic solvent, inorganic acid, H2O and organic acid for ultrasonic cleaning, the volume ratio of the organic solvent, inorganic acid, H2O and organic acid to the volume of the melamine sponge is 2-5:1, wherein the concentration of the inorganic acid and the organic acid is 2-5 mol / L, preferably, the concentration of the organic acid and the inorganic acid is 3-5 mol / L; the inert gas is one of nitrogen, carbon dioxide and argon.

4. The method according to claim 1, characterized in that In step (1), the vacuum drying temperature is 60-80°C, and the drying time is 3-5h, preferably, the vacuum drying time is 3-4h; in step (1), the heating temperature under N2 atmosphere is 200-350°C, and the heating time is 1-4h, preferably, the heating temperature under N2 atmosphere is 300-350°C, and the heating time is 2-3h.

5. The method according to claim 1, characterized in that In step (2), the metal salt is one or more of halides, nitrates, sulfates or soluble carboxylates of copper, iron, cobalt or cerium. Preferably, the metal salt is one or more of copper nitrate, iron nitrate, cobalt nitrate or cerium nitrate.

6. The method according to claim 1, characterized in that The molar ratio of KMnO4 to metal salt is 0.5-2:1; the molar concentration of metal salt in the impregnation precursor solution is 0.5-2 mol / L.

7. The method according to claim 1, characterized in that In step (3), the volume ratio of the treated melamine sponge to the impregnated precursor solution is 1:1.5-5, more preferably 1:2-3; the drying temperature is 60-80°C, and the drying time is 10-14h, preferably, the drying time is 60°C and the drying time is 12h.

8. The method according to claim 1, characterized in that In step (4), the calcination temperature is 300-450°C, and the calcination time is 3-6h. Preferably, the calcination temperature is 350-400°C, and the calcination time is 3-4h.

9. A Mn-based integral catalyst prepared according to the method according to any one of claims 1 to 8.

10. A method for low-temperature flue gas denitration using a Mn-based integral catalyst prepared according to any one of claims 1 to 8, characterized in that The denitration reaction temperature is 100-350° C., and the volume concentration of CO in the flue gas is above 0.5%, more preferably 0.5-2%.

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