Preparation method of flue gas denitration catalyst

Abstract

The application aims to provide a flue gas denitration catalyst preparation method, belonging to the technical field of waste gas treatment, comprising the following steps: impregnating pseudo-boehmite with cerium nitrate solution, drying the impregnated pseudo-boehmite to obtain cerium modified pseudo-boehmite, and preparing aluminum sol with the cerium modified pseudo-boehmite as raw material; immersing honeycomb cordierite in the aluminum sol, drying and calcining the coated material to obtain cordierite with an alumina coating; immersing the cordierite material with the alumina coating in organic alkali solution I for sealed pretreatment; immersing the pretreated material in organic alkali solution II again for sealed hydrothermal treatment, drying and calcining the hydrothermally treated material to obtain honeycomb cordierite carrier; impregnating the honeycomb cordierite carrier with manganese nitrate solution, and drying and calcining the impregnated material to obtain the flue gas denitration catalyst of the application. The catalyst surface morphology is curved lamellar, the lamellar particle morphology is uniform, and the catalyst surface coverage is high.

Description

Technical Field

[0001] This invention belongs to the field of waste gas treatment technology, specifically relating to a method for preparing a flue gas denitrification catalyst. Background Technology

[0002] Nitrogen oxides (NO) x NO is a major air pollutant that causes significant environmental problems such as acid rain, ozone layer depletion, and photochemical smog. Furthermore, its respiratory toxicity poses a significant threat to human health. x The sources of nitrogen oxides are divided into two categories: natural sources and anthropogenic sources. Among them, anthropogenic sources generated by human production activities are the main sources of pollutants. A series of methods for removing nitrogen oxides have been developed, among which the ammonia selective catalytic reduction (NH3-SCR) method is currently the most effective and widely used method for removing NO under oxygen-enriched conditions. x Removal technology. Specifically, by adding NH3 as a reducing agent to the reaction system, NO is removed under the action of a catalyst. x NO in the atmosphere in the presence of O2 x It is selectively reduced to non-toxic and harmless N2 and H2O. The most important component in the NH3-SCR reaction system is the NH3-SCR catalyst.

[0003] Honeycomb cordierite (2MgO·2Al2O3·5SiO2) not only possesses high mechanical strength, good heat resistance and thermal shock resistance, but also exhibits low gas flow pressure drop. Therefore, it is widely used as a catalyst support for various high-temperature processes. However, due to its high-temperature calcination and small specific surface area, it is not suitable for direct use as a catalyst support; a layer of material with a larger specific surface area must be coated onto its surface.

[0004] CN111298845A discloses a method for preparing a denitrification catalyst support. The method for preparing the support includes the following steps: (1) uniformly mixing an alumina precursor with a furfuryl alcohol solution of a certain concentration, and then adding an appropriate amount of colloidal solvent to obtain an alumina sol; (2) immersing a pretreated cordierite honeycomb ceramic substrate into the alumina sol obtained in step (1), removing it, blowing off the residual liquid, drying and calcining it to obtain the denitrification catalyst support.

[0005] CN104415780A discloses a denitrification catalyst and its preparation method. The catalyst uses pretreated cordierite honeycomb ceramic as a matrix. The matrix surface is sequentially coated with a silica-alumina coating, a composite coating, and active components. By total weight, the catalyst contains 80wt%~90wt% cordierite honeycomb ceramic, 2wt%~9wt% silica-alumina coating, 3wt%~10wt% composite coating, and 0.01wt%~15wt% active components, which are Mn and Fe. The silica-alumina coating contains 10wt%~50wt% silicon dioxide and 50wt%~90wt% alumina. The composite coating contains 40wt%~80wt% titanium dioxide, 5wt%~35wt% ZSM-5 molecular sieve, and 10wt%~40wt% additives. The additives are selected from one or more of cerium oxide, zirconium oxide, or lanthanum oxide.

[0006] Research has shown that the coating particles of cordierite matrix materials prepared by existing technologies generally have a spherical structure. The dense packing of spherical particles is not conducive to the contact between reactants and the active centers of the catalyst, thus reducing the catalytic activity and service life of the catalyst. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a method for preparing a flue gas denitrification catalyst. The catalyst prepared by this method has a curved, sheet-like structure on its surface particles, which can promote the interaction between reactant molecules and active centers, resulting in excellent denitrification performance, while also exhibiting good resistance to water vapor and SO2 poisoning.

[0008] The present invention adopts the following technical solution:

[0009] A method for preparing a flue gas denitrification catalyst includes the following steps:

[0010] The first step is to impregnate boehmite with cerium nitrate solution, and then dry the impregnated boehmite to obtain cerium-modified boehmite. Aluminum sol is prepared using cerium-modified boehmite as raw material.

[0011] The second step involves immersing honeycomb cordierite in aluminum sol, and then drying and calcining the coated material to obtain cordierite with an aluminum oxide coating.

[0012] The third step is to immerse the cordierite material with an alumina coating in organic alkali solution I for pretreatment.

[0013] The fourth step involves immersing the pretreated material from the third step in organic alkali solution II again for sealed hydrothermal treatment. After hydrothermal treatment, the material is dried and calcined to obtain a honeycomb cordierite carrier.

[0014] The fifth step involves impregnating the honeycomb cordierite carrier with manganese nitrate solution, followed by drying and calcination of the impregnated material to obtain the flue gas denitrification catalyst of this invention.

[0015] Furthermore, in the first step, the concentration of the cerium nitrate solution is 0.1-0.3M, the amount of solution used is sufficient to completely submerge the boehmite, the drying temperature is 100-160℃, and the drying time is 1-8 hours.

[0016] Furthermore, the preparation method of the aluminum sol mentioned in the first step is as follows: Cerium-modified pseudoboehmite is mixed evenly with distilled water, and then nitric acid solution is added under stirring and stirring is continued for 1-5 hours.

[0017] Furthermore, in the second step, the drying temperature is 120-180℃ and the drying time is 2-8 hours, and the calcination temperature is 450-650℃ and the calcination time is 4-10 hours.

[0018] Furthermore, the organic alkali solution I mentioned in the third step includes one of tetramethylammonium hydroxide, tetraethylaluminum hydroxide, and tetrapropylammonium hydroxide, preferably tetraethylammonium hydroxide. The organic alkali concentration in the organic alkali solution I is 0.8%-2.0%, and the amount of organic alkali solution I is such that the honeycomb cordierite material is completely submerged.

[0019] Furthermore, the sealing pretreatment described in the third step is carried out in a sealed container, preferably a high-pressure reactor, with a pretreatment temperature of 80-120°C and a pretreatment time of 1-4 hours.

[0020] Furthermore, the organic alkali solution II mentioned in step four includes one of tetramethylammonium hydroxide, tetraethylaluminum hydroxide, and tetrapropylammonium hydroxide, preferably tetraethylammonium hydroxide. Organic alkali solution II may be the same as or different from organic alkali solution I, preferably the same. The mass concentration of the organic alkali in organic alkali solution II is 3.5%-12.5%, and the amount of organic alkali solution II used is sufficient to completely submerge the honeycomb cordierite material.

[0021] Furthermore, the sealing hydrothermal treatment described in the fourth step is carried out in a sealed container, preferably a high-pressure reactor, with a hydrothermal treatment temperature of 140-180℃ and a time of 4-10 hours.

[0022] Furthermore, the drying temperature in step four is 100-160℃, and the drying time is 2-10 hours; the calcination temperature is 450-650℃, and the calcination time is 4-10 hours.

[0023] Furthermore, in step five, the concentration of the manganese nitrate solution is 0.5-1M, the amount of solution used is sufficient to completely submerge the cordierite carrier, the drying temperature is 100-160℃, the drying time is 1-8 hours, and the calcination temperature is 450-650℃, the calcination time is 4-10 hours.

[0024] The flue gas denitrification catalyst prepared by the method of the present invention comprises a honeycomb cordierite support and an active component. The honeycomb cordierite support includes a honeycomb cordierite matrix and an alumina coating, and the active component is MnO. x CeO2 and MnO on the catalyst surface x The concentration is 8.0wt%-20.0wt%, and the CeO2 concentration is 3.0wt%-7.0wt%.

[0025] The flue gas denitrification catalyst prepared by the method of the present invention has a particle morphology of curved lamellar particles with a thickness of 30-50 nm and a length of 100-600 nm. The lamellar particles are stacked to form open channels of 50-500 nm. The coverage rate of the lamellar particles on the cordierite surface is 90%-100%, wherein the coverage rate refers to the percentage of the curved lamellar alumina particles on the surface area of ​​the cordierite carrier.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] (1) The catalyst of the present invention has a curved lamellar morphology. The lamellar particles are uniform in shape and have a high coverage on the catalyst surface. The curved lamellar particles grow loosely and epitaxially on the catalyst surface, forming a large number of open channels of 50-500 nm. During the catalytic reaction, they promote the interaction between reactant molecules and the active center of the catalyst, increase the number of active sites of the catalyst, and have excellent denitrification performance. At the same time, they have good resistance to water vapor and SO2 poisoning.

[0028] (2) The active component cerium is first loaded onto the cordierite support material. During the hydrothermal treatment of the support, the active component cerium improves its interaction with the alumina support while growing alumina particles, thereby increasing the activity of the catalyst.

[0029] (3) The active components are loaded onto the cordierite support material in two steps, and the MnO is adjusted. x The structural characteristics of the -CeO2 active metal component give the catalyst high denitrification performance. Attached Figure Description

[0030] Figure 1 Scanning electron microscopy of the surface of the denitration catalyst prepared in Example 1 Figure 1 .

[0031] Figure 2 Scanning electron microscopy of the surface of the denitration catalyst prepared in Example 1 Figure 2 .

[0032] Figure 3 is a scanning electron microscope image of the surface of the denitration catalyst prepared in Comparative Example 1. Detailed Implementation

[0033] The technical solutions and effects of the present invention will be further illustrated below with reference to the embodiments, but the invention is not limited to the following embodiments.

[0034] The microstructure of the sample was characterized using scanning electron microscopy. The specific operation was as follows: accelerating voltage 8KV, accelerating current 10µA, working distance 8mm.

[0035] The content of active metals on the catalyst surface was determined by scanning electron microscopy equipped with an energy dispersive spectrometer (EDAX). During the determination, 10 micro-regions to be measured were randomly selected for composition analysis and the average value was taken. The accelerating voltage was 30 kV and the working distance was 8 mm.

[0036] Example 1

[0037] (1) Weigh 100 g of boehmite and impregnate it with a 0.13 M cerium nitrate solution. Filter the impregnated material and dry the filter cake at 120 °C for 4 hours to obtain cerium-modified boehmite. Transfer the cerium-modified boehmite to a beaker, add 200 g of distilled water, and then add 150 mL of a 30% nitric acid solution. Continue stirring for 3 hours to obtain aluminum sol.

[0038] (2) The cleaned honeycomb cordierite was immersed in the aluminum sol of step (1), and the coated material was dried at 140°C for 6 hours and calcined at 500°C for 6 hours to obtain cordierite with aluminum oxide coating.

[0039] (3) Immerse the honeycomb cordierite material with alumina coating from step (2) into a 1.5 wt% tetraethylammonium hydroxide solution, transfer the mixture into a high-pressure reactor and seal it. Then pre-treat the high-pressure reactor at 90°C for 3 hours. After treatment, the material is taken out for use.

[0040] (4) The honeycomb cordierite material pretreated in step (3) is immersed again in a 6.5 wt% tetraethylammonium hydroxide solution, and the mixture is transferred into a high pressure vessel and sealed. The high pressure vessel is then hydrothermally treated at 165°C for 6 hours. After treatment, the material is dried at 140°C for 8 hours and calcined at 500°C for 6 hours to obtain a honeycomb cordierite carrier containing the active component cerium.

[0041] (5) The honeycomb cordierite carrier containing the active component cerium from step (4) was impregnated with a 0.7M manganese nitrate solution. After impregnation, the material was dried at 140℃ for 6 hours and calcined at 500℃ for 8 hours to obtain the flue gas denitrification catalyst A-1 of this invention. The catalyst surface contains MnO. x The concentration was 8.6 wt%, the CeO2 concentration was 3.4 wt%, and the coverage of the curved lamellar particles on the catalyst surface was 96.5%. The scanning electron microscope image of the catalyst surface is shown below. Figure 1 and Figure 2 .

[0042] Example 2

[0043] Same as Example 1, except that in step (1) the concentration of cerium nitrate solution is 0.1M. In step (3) the concentration of tetraethylammonium hydroxide solution is 1.2wt%, the pretreatment temperature is 100℃, and the treatment time is 2 hours. In step (4) the concentration of tetraethylammonium hydroxide solution is 8.5wt%, the hydrothermal treatment temperature is 155℃, and the treatment time is 7 hours. In step (5) the concentration of manganese nitrate solution is 0.55M. The flue gas denitrification catalyst A-2 of this invention was obtained. The catalyst surface has MnO... x The concentration was 8.1 wt%, the CeO2 concentration was 3.1 wt%, and the coverage of the curved lamellar particles on the catalyst surface was 94.5%.

[0044] Example 3

[0045] Same as Example 1, except that in step (1) the concentration of cerium nitrate solution is 0.15M. In step (3) the concentration of tetraethylammonium hydroxide solution is 0.85wt%, the pretreatment temperature is 110℃, and the treatment time is 1 hour. In step (4) the concentration of tetraethylammonium hydroxide solution is 11wt%, the hydrothermal treatment temperature is 145℃, and the treatment time is 8 hours. In step (5) the concentration of manganese nitrate solution is 0.8M. The flue gas denitrification catalyst A-3 of this invention was obtained. The catalyst surface has MnO... x The concentration was 9.2 wt%, the CeO2 concentration was 3.6 wt%, and the coverage of the curved lamellar particles on the catalyst surface was 97.5%.

[0046] Example 4

[0047] Same as Example 1, except that in step (1) the concentration of cerium nitrate solution is 0.18M. In step (3), tetraethylammonium hydroxide is replaced with tetrapropylammonium hydroxide, the solution concentration is 1.8wt%, the pretreatment temperature is 80℃, and the treatment time is 4 hours. In step (4), tetraethylammonium hydroxide is replaced with tetrapropylammonium hydroxide, the solution concentration is 4.5wt%, the hydrothermal treatment temperature is 175℃, and the treatment time is 5 hours. In step (5), the concentration of manganese nitrate solution is 0.9M. The flue gas denitrification catalyst A-4 of the present invention is obtained. MnO on the catalyst surface x The concentration was 10.6 wt%, the CeO2 concentration was 5.2 wt%, and the coverage of the curved lamellar particles on the catalyst surface was 91.5%.

[0048] Comparative Example 1

[0049] Same as Example 1, except that in steps (3) and (4), tetraethylammonium hydroxide was replaced with ammonia water of the same concentration to prepare comparative catalyst A-5, with MnO on the catalyst surface. x The concentration was 8.7 wt%, the CeO2 concentration was 3.3 wt%, and no curved lamellar particles were observed on the catalyst surface. (Scanning electron microscopy image shown below.) Figure 3.

[0050] Comparative Example 2

[0051] Same as Example 1, except that tetraethylammonium hydroxide in steps (3) and (4) is replaced with sodium hydroxide of the same concentration to prepare comparative catalyst A-6, with MnO on the catalyst surface. x The concentration was 8.8 wt%, the CeO2 concentration was 3.5 wt%, and no curved lamellar particles were observed on the catalyst surface.

[0052] Comparative Example 3

[0053] Same as Example 1, except that step (1) is omitted, and instead, the same amount of active metal component is loaded into the catalyst in step (5) in one step to obtain comparative catalyst A-7. MnO on the catalyst surface x The concentration was 8.6 wt%, the CeO2 concentration was 3.4 wt%, and the coverage of the curved lamellar particles on the catalyst surface was 95.5%.

[0054] Example 5

[0055] Catalyst denitrification activity test:

[0056] A honeycomb catalyst was loaded into a fixed tubular reactor, and a simulated mixed reaction gas was introduced. This mixed gas consisted of NO, NH3, O2, N2, SO2, and water vapor, with NH3 concentration of 1100 ppm, NO concentration of 1100 ppm, O2 volume content of 2.5%, SO2 concentration of 240 ppm, and water vapor volume content of 12.5%. The reaction temperature was controlled at 120-255℃, and the space velocity was 5000 h⁻¹. -1 The system was operated at the reaction temperature for 500 hours, and the NO concentration at the inlet and outlet was measured by a flue gas analyzer. The denitrification effects of different catalysts at different reaction temperatures are shown in Table 1.

[0057] Denitrification activity = (C0-C) / C0×100%, where C0 is the initial NO concentration and C is the NO concentration in the treated gas.

[0058] Table 1. Denitrification effect of different catalysts at different temperatures

[0059]

[0060] As can be seen from the results in Table 1, the flue gas denitrification catalyst prepared by this method has a high denitrification efficiency in the low temperature window, and the denitrification rate is still high after 500 hours of continuous operation, indicating that the catalyst prepared by this invention has good resistance to water vapor and SO2 poisoning.

Claims

1. A method for preparing a flue gas denitrification catalyst, characterized in that: Includes the following steps: The first step is to impregnate boehmite with cerium nitrate solution, and then dry the impregnated boehmite to obtain cerium-modified boehmite. Aluminum sol is prepared using cerium-modified boehmite as raw material. The second step involves immersing honeycomb cordierite in aluminum sol, and then drying and calcining the coated material to obtain cordierite with an aluminum oxide coating. The third step involves immersing the cordierite material with an alumina coating in an organic alkaline solution I for sealing and pretreatment; the organic alkaline solution I includes one of tetramethylammonium hydroxide and tetrapropylammonium hydroxide. The fourth step involves immersing the pretreated material from the third step back into organic alkali solution II for sealed hydrothermal treatment. After hydrothermal treatment, the material is dried and calcined to obtain a honeycomb cordierite carrier. The organic alkali solution II includes one of tetramethylammonium hydroxide and tetrapropylammonium hydroxide. The fifth step involves impregnating the honeycomb cordierite carrier with manganese nitrate solution, followed by drying and calcination to obtain the flue gas denitrification catalyst.

2. The method for preparing a flue gas denitrification catalyst according to claim 1, characterized in that: The concentration of the cerium nitrate solution in the first step is 0.1-0.3M, and the amount of solution used is enough to completely immerse the boehmite. The drying temperature is 100-160℃, and the drying time is 1-8 hours.

3. The method for preparing a flue gas denitrification catalyst according to claim 1, characterized in that: The preparation method of the aluminum sol in the first step is as follows: Cerium-modified pseudoboehmite is mixed evenly with distilled water, and then nitric acid solution is added under stirring and stirring is continued for 1-5 hours.

4. The method for preparing a flue gas denitrification catalyst according to claim 1, characterized in that: The drying temperature in the second step is 120-180℃, and the drying time is 2-8 hours. The calcination temperature is 450-650℃, and the calcination time is 4-10 hours.

5. The method for preparing a flue gas denitrification catalyst according to claim 1, characterized in that: The organic alkali concentration in organic alkali solution I is 0.8%-2.0%, and the amount of organic alkali solution I used is such that the honeycomb cordierite material is completely submerged.

6. The method for preparing a flue gas denitrification catalyst according to claim 1, characterized in that: The sealing pretreatment described in the third step is carried out in a sealed container at a temperature of 80-120°C for 1-4 hours.

7. The method for preparing a flue gas denitrification catalyst according to claim 1, characterized in that: Organic alkali solution II may be the same as or different from organic alkali solution I. The organic alkali concentration in organic alkali solution II is 3.5%-12.5%, and the amount of organic alkali solution II used is to completely submerge the honeycomb cordierite material.

8. The method for preparing a flue gas denitrification catalyst according to claim 1, characterized in that: The sealing hydrothermal treatment described in step four is carried out in a sealed container at a temperature of 140-180℃ for 4-10 hours.

9. The method for preparing a flue gas denitrification catalyst according to claim 1, characterized in that: The drying temperature in step four is 100-160℃, and the drying time is 2-10 hours; the calcination temperature is 450-650℃, and the calcination time is 4-10 hours.

10. The method for preparing a flue gas denitrification catalyst according to claim 1, characterized in that: In step 5, the concentration of the manganese nitrate solution is 0.5-1M, and the amount of solution used is sufficient to completely submerge the cordierite carrier. The drying temperature is 100-160℃, and the drying time is 1-8 hours. The calcination temperature is 450-650℃, and the calcination time is 4-10 hours.

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