Preparation method of honeycomb ultra-low temperature SCR catalyst and application thereof

Abstract

This invention relates to the technical field of SCR catalysts, and discloses a method for preparing a honeycomb-type ultra-low temperature SCR catalyst and its application, comprising the following steps: Step 1, pretreating cordierite by immersing it in an acidic solution to obtain pretreated cordierite; Step 2, adding manganese salt, cerium salt, and iron salt to water to prepare a homogeneous mixed solution; Step 3, mixing titanium sol and aluminum sol to prepare a composite sol; Step 4, slowly adding the mixed solution dropwise to the composite sol while stirring, and continuing stirring after the addition is complete to obtain a coating solution; Step 5, immersing the pretreated cordierite in the coating solution, then removing it, blowing away the liquid in the cordierite pores with compressed air, and then drying and calcining; this step can be repeated several times until a honeycomb-type ultra-low temperature SCR catalyst with a suitable loading of active components is obtained. The catalyst of this invention can achieve ultra-low temperature denitrification while avoiding problems such as uneven loading and easy peeling.

Description

Technical Field

[0001] This invention relates to the technical field of SCR catalysts, and in particular to a method for preparing a honeycomb-type ultra-low temperature SCR catalyst and its application. Background Technology

[0002] Waste-to-energy plants, as well as key processes in non-power industries such as cement, steel sintering, and coking, will face the dual challenges of high environmental standards and low energy consumption in their denitrification processes. Taking waste-to-energy plants as an example, ultra-low temperature (≤180℃) SCR denitrification is a crucial technology for addressing these challenges. Early waste-to-energy plants used only SNCR denitrification, while newly built plants generally employ a combination of SNCR and SCR processes, namely SNCR + boiler exhaust gas outlet + semi-dry + dry + baghouse dust collector + SCR process. Using SNCR technology alone, the denitrification level can generally only be controlled at 200-300 mg / m³. 3 The current emission levels have limited room for improvement and are insufficient to meet increasingly stringent emission requirements. Adding SCR denitrification after baghouse dust collection can further reduce NOx emission concentrations, but a significant problem is that the flue gas temperature after baghouse dust collection is between 120-180℃ (mainly around 150℃). Currently used commercially modified vanadium-tungsten-titanium catalysts require heat exchange to reach 220℃ before use, resulting in high equipment costs and energy consumption, increasing flue gas purification costs. Furthermore, extruded vanadium-tungsten-titanium catalysts, when immersed in high-humidity flue gas for extended periods, may soften and collapse. Researchers are focusing on developing Mn-based ultra-low temperature catalysts with lower activation temperatures and honeycomb cordierite with a more robust supporting structure.

[0003] Currently, ultra-low temperature SCR catalysts are made into granular catalysts using Mn-based catalyst powder, or by coating catalyst active powder onto a cordierite support. The former, granular denitrification catalyst bed pressure is high, making it unsuitable for applications with large flue gas volumes and high flow rates. The latter, however, has very high requirements for the particle size of the catalyst powder, requiring grinding to achieve a suitable particle size distribution during coating, which poses a significant challenge to the production of catalyst honeycomb molding. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a method for preparing a honeycomb-type ultra-low temperature SCR catalyst and its application. The method involves in-situ generation of ultra-low temperature SCR powder on a cordierite support, using a mixed solution of manganese, cerium, and iron salts as the active precursor, and a mixture of titanium sol and aluminum sol as the composite sol. This method effectively avoids problems such as uneven loading and easy peeling / detachment caused by the large particle size of ultra-low temperature SCR powder during traditional powder coating processes.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] In a first aspect, the present invention provides a method for preparing a honeycomb-type ultra-low temperature SCR catalyst, comprising the following steps:

[0007] Step 1: After pretreating cordierite by immersing it in an acidic solution, pretreated cordierite is obtained;

[0008] Step 2: Add manganese salt, cerium salt and iron salt to water to make a homogeneous mixed solution;

[0009] Step 3: Mix titanium sol and aluminum sol to prepare a composite sol;

[0010] Step 4: Slowly add the mixed solution dropwise to the composite sol while stirring. After the addition is complete, continue stirring to obtain the coating solution. Step 5: Immerse the pretreated cordierite in the coating solution, then remove it, blow away the liquid in the cordierite pores with compressed air, and then dry and calcine it. This step can be repeated several times until a honeycomb-type ultra-low temperature SCR catalyst with a suitable loading of active components is obtained.

[0011] This invention employs a method for in-situ generation of ultra-low temperature SCR powder on a cordierite support. Specifically, it uses acid-pretreated cordierite as the support, a mixed solution of manganese salt, cerium salt, and iron salt as the active precursor, and a mixture of titanium sol and aluminum sol as the composite sol. The active precursor and the composite sol are formed into a homogeneous slurry, which is then coated onto the cordierite and subsequently generated in-situ through air blowing, drying, and calcination to produce a honeycomb-type ultra-low temperature SCR catalyst.

[0012] Manganese is the main active component of the ultra-low temperature catalyst, cerium is the oxygen storage and release component, and iron is the co-catalyst, playing a role in water resistance. The synergistic effect of the three active metal salts achieves a good ultra-low temperature denitrification effect. Titanium sol and aluminum sol act as both adhesives and secondary dispersion carriers for the active component precursors, avoiding problems such as uneven loading and easy peeling and detachment caused by the large particle size of ultra-low temperature SCR powder in traditional powder coating processes.

[0013] Preferably, the cordierite has 30 to 50 pores.

[0014] Preferably, the acidic solution is one of nitric acid solution, citric acid solution, acetic acid solution, and hydrochloric acid solution; the concentration of the acidic solution is 0.1 to 0.3 mol / L.

[0015] Preferably, the molar ratio of the manganese salt, cerium salt, and iron salt is 1:0.1:0.1; and the concentration of the manganese salt in water is 0.9–1.2 mol / L.

[0016] Preferably, the manganese salt is one or both of manganese acetate and manganese nitrate; the cerium salt is cerium nitrate; and the iron salt is one or more of ferric nitrate, ferrous nitrate, and ferric acetate.

[0017] Preferably, the volume ratio of the titanium sol to the aluminum sol is 3:1; the mass fraction of the titanium sol is 30-40%; the mass fraction of the aluminum sol is 20-30%; and the pH of the composite sol is adjusted to 4-6 after mixing.

[0018] A single sol, acting as both a binder and a carrier for dispersing the three metal ions, results in a low loading capacity and easy detachment during the coating process. This invention employs a composite sol, limiting the ratio of titanium sol to aluminum sol. This allows the titanium sol to primarily act as a dispersion site for metal ions and increase surface acidity, while the aluminum sol also provides some acidic sites. Compared to a single sol, the composite sol provides a richer array of acidic sites, which is beneficial for the adsorption of SCR molecules and exhibits better dispersion for multiple metal ions, particularly for the composite solution of manganese, cerium, and iron salts used in this application. The remaining sol components also provide better adhesion to cordierite. According to experimental research based on this invention, this composite sol, compared to a single aluminum sol, aluminum sol, or composite sols in different ratios, not only has a more uniform loading capacity and is less prone to detachment, but also demonstrates superior denitrification performance.

[0019] Preferably, the volume ratio of the composite sol to the mixed solution is 1:1 to 1.2; and the stirring time is 1 to 2 hours.

[0020] Preferably, the drying is hot air drying, with a temperature of 60-70°C and a hot air flow rate of 6-8 m / s.

[0021] Preferably, the calcination is carried out at 500-600°C for 2-3 hours.

[0022] Secondly, the present invention also provides an application of a honeycomb-type ultra-low temperature SCR catalyst in denitrification reactions.

[0023] The catalyst has a robust honeycomb cordierite support structure and a denitrification temperature of 140-180℃. It can replace the current vanadium-tungsten-titanium catalysts that require heat exchange to 220℃ and soften after long-term high-humidity soaking. It can be used in ultra-low temperature denitrification fields such as waste incineration power plants, cement kilns, and coking industries.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) The composite sol effectively disperses the three metal ions on titanium oxide and makes the aluminum sol act as a binder, making it less prone to peeling and wrinkling during subsequent low-temperature rapid drying. It also modulates the acidity and alkalinity of the catalyst surface together with the aluminum sol.

[0026] (2) Low-temperature hot air is used for rapid drying, which avoids the occurrence of peeling, wrinkling and powder falling off after coating;

[0027] (3) By combining metal ions and the synergistic effect between composite sols, the acidity and alkalinity of the catalyst surface were adjusted, achieving denitrification at ultra-low temperature of 140-180℃. Moreover, it avoids the problems of uneven loading and easy peeling and falling off caused by the large particle size of ultra-low temperature SCR powder during the traditional powder coating process. Attached Figure Description

[0028] Figure 1 The diagram shows the denitrification effect of the honeycomb-type ultra-low temperature SCR catalyst in Example 1 of this invention at different denitrification temperatures. Detailed Implementation

[0029] The technical solution of the present invention is illustrated below with specific embodiments, but the scope of protection of the present invention is not limited thereto:

[0030] A method for preparing a honeycomb-type ultra-low temperature SCR catalyst includes the following steps:

[0031] Step 1: Immerse cordierite (with 30-50 pores, cross-sectional area 150mm*150mm, length 200-400mm) in an acidic solution with a concentration of 0.1-0.3mol / L for pretreatment to obtain pretreated cordierite; the acidic solution is one of nitric acid solution, citric acid solution, acetic acid solution, and hydrochloric acid solution;

[0032] Step 2: Add manganese salt, cerium salt, and iron salt in a molar ratio of 1:0.1:0.1 to water to prepare a homogeneous mixed solution, such that the concentration of manganese salt in water is 0.9–1.2 mol / L; the manganese salt is one or both of manganese acetate and manganese nitrate; the cerium salt is cerium nitrate; and the iron salt is one or more of ferric nitrate, ferrous nitrate, and ferric acetate.

[0033] Step 3: Mix titanium sol and aluminum sol in a volume ratio of 3:1, wherein the mass fraction of titanium sol is 30-40% and the mass fraction of aluminum sol is 20-30%. After mixing, adjust the pH to 4-6 with an acidic solution to prepare a composite sol.

[0034] Step 4: While stirring, slowly add the mixed solution dropwise to the composite sol. The volume ratio of the composite sol to the mixed solution is 1:1 to 1.2. After the addition is complete, continue stirring for 1 to 2 hours to obtain the coating solution.

[0035] Step 5: Immerse the pretreated cordierite in the coating solution, then remove it, blow away the liquid in the cordierite pores with compressed air, and then dry it with hot air at a temperature of 60-70℃ and a hot air flow rate of 6-8m / s. Then calcine it at 500-600℃ for 2-3 hours. This step can be repeated several times until a honeycomb-type ultra-low temperature SCR catalyst with a suitable loading of active components is obtained.

[0036] Example 1

[0037] Step 1: Take a cordierite carrier with 30 holes, a cross-sectional area of ​​150mm*150mm and a length of 200mm, immerse it in a 0.1mol / L nitric acid solution, sonicate for 30min, take it out, wash it with deionized water until neutral, and dry it at 110℃ for 12h to obtain the pretreated cordierite.

[0038] Step 2: Add 735.300g of manganese acetate (tetrahydrate), 130.266g of cerium nitrate (hexahydrate), and 121.200g of ferric nitrate (nonahydrate) to 3L of aqueous solution and stir to dissolve to obtain a mixed solution.

[0039] Step 3: Mix 2.25L of titanium sol (30% by mass) and 0.75L of aluminum sol (20% by mass), and adjust the pH to 5 with 1mol / L citric acid to obtain a composite sol.

[0040] Step 4: Add 3L of mixed solution dropwise to 3L of composite sol while stirring. After the addition is complete, continue stirring for 1 hour to obtain the coating solution.

[0041] Step 5: Immerse the pretreated cordierite in the coating solution, remove it after 20 seconds, blow away the liquid from the cordierite pores with compressed air, then dry it with a hot air blower at 70℃ and a hot air flow rate of 8m / s, and then calcine it at 500℃ for 3 hours.

[0042] Step 6: Repeat step 5 once to obtain the honeycomb-type ultra-low temperature SCR catalyst.

[0043] like Figure 1 As shown, the honeycomb-type ultra-low temperature SCR catalyst can achieve excellent denitrification effect at a denitrification temperature of 140-180℃.

[0044] Example 2

[0045] Step 1: Take a cordierite carrier with 30 holes, a cross-sectional area of ​​150mm*150mm and a length of 200mm, immerse it in a 0.1mol / L nitric acid solution, sonicate for 30min, take it out, wash it with deionized water until neutral, and dry it at 110℃ for 12h to obtain the pretreated cordierite.

[0046] Step 2: Add 753.030g of manganese nitrate (tetrahydrate), 130.266g of cerium nitrate (hexahydrate) and 86.400g of ferrous nitrate (hexahydrate) to 3L of aqueous solution and stir to dissolve to obtain a mixed solution.

[0047] Step 3: Mix 2.25L of titanium sol (30% by mass) and 0.75L of aluminum sol (20% by mass), and adjust the pH to 5 with 1mol / L citric acid to obtain a composite sol.

[0048] Step 4: Add 3L of mixed solution dropwise to 3L of composite sol while stirring. After the addition is complete, continue stirring for 1 hour to obtain the coating solution.

[0049] Step 5: Immerse the pretreated cordierite in the coating solution, remove it after 20 seconds, blow away the liquid from the cordierite pores with compressed air, then dry it with a hot air blower at 70℃ and a hot air flow rate of 8m / s, and then calcine it at 500℃ for 3 hours.

[0050] Step 6: Repeat step 5 once to obtain the honeycomb-type ultra-low temperature SCR catalyst.

[0051] Example 3

[0052] Step 1: Take a cordierite carrier with 30 holes, a cross-sectional area of ​​150mm*150mm and a length of 200mm, immerse it in a 0.1mol / L hydrochloric acid solution, sonicate for 30min, take it out, wash it with deionized water until neutral, and dry it at 110℃ for 12h to obtain the pretreated cordierite.

[0053] Step 2: Add 735.300g of manganese acetate (tetrahydrate), 130.266g of cerium nitrate (hexahydrate), and 121.200g of ferric nitrate (nonahydrate) to 3L of aqueous solution and stir to dissolve to obtain a mixed solution.

[0054] Step 3: Mix 2.25L of titanium sol (30% by mass) and 0.75L of aluminum sol (20% by mass), and adjust the pH to 6 with 1mol / L citric acid to obtain a composite sol.

[0055] Step 4: Add 3L of mixed solution dropwise to 3L of composite sol while stirring. After the addition is complete, continue stirring for 1 hour to obtain the coating solution.

[0056] Step 5: Immerse the pretreated cordierite in the coating solution, remove it after 20 seconds, blow away the liquid in the cordierite pores with compressed air, and then dry it with a hot air blower at 70℃ and a hot air flow rate of 8m / s. Then calcine it at 500℃ for 3 hours to obtain a honeycomb-type ultra-low temperature SCR catalyst.

[0057] Comparative Example 1

[0058] The difference from Example 1 is that only aluminum sol is used.

[0059] Step 1: Take a cordierite carrier with 30 holes, a cross-sectional area of ​​150mm*150mm and a length of 200mm, immerse it in a 0.1mol / L nitric acid solution, sonicate for 30min, take it out, wash it with deionized water until neutral, and dry it at 110℃ for 12h to obtain the pretreated cordierite.

[0060] Step 2: Add 735.300g of manganese acetate (tetrahydrate), 130.266g of cerium nitrate (hexahydrate), and 121.200g of ferric nitrate (nonahydrate) to 3L of aqueous solution and stir to dissolve to obtain a mixed solution.

[0061] Step 3: Adjust the pH of 3L of 20% aluminum sol to 5 with 1mol / L citric acid to obtain a single sol.

[0062] Step 4: Add 3L of mixed solution dropwise to 3L of single sol while stirring. After the addition is complete, continue stirring for 1 hour to obtain the coating solution.

[0063] Step 5: Immerse the pretreated cordierite in the coating solution, remove it after 20 seconds, blow away the liquid in the cordierite pores with compressed air, and then dry it with a hot air blower at 70℃ and a hot air flow rate of 8m / s. Then calcine it at 500℃ for 3 hours to obtain a honeycomb-type ultra-low temperature SCR catalyst.

[0064] Comparative Example 2

[0065] The difference from Example 1 is that only titanium sol is used.

[0066] Step 1: Take a cordierite carrier with 30 holes, a cross-sectional area of ​​150mm*150mm and a length of 200mm, immerse it in a 0.1mol / L nitric acid solution, sonicate for 30min, take it out, wash it with deionized water until neutral, and dry it at 110℃ for 12h to obtain the pretreated cordierite.

[0067] Step 2: Add 735.300g of manganese acetate (tetrahydrate), 130.266g of cerium nitrate (hexahydrate), and 121.200g of ferric nitrate (nonahydrate) to 3L of aqueous solution and stir to dissolve to obtain a mixed solution.

[0068] Step 3: Adjust the pH of 3L of titanium sol (30% by mass) to 5 with 1mol / L citric acid to obtain a single sol.

[0069] Step 4: Add 3L of mixed solution dropwise to 3L of single sol while stirring. After the addition is complete, continue stirring for 1 hour to obtain the coating solution.

[0070] Step 5: Immerse the pretreated cordierite in the coating solution, remove it after 20 seconds, blow away the liquid in the cordierite pores with compressed air, and then dry it with a hot air blower at 70℃ and a hot air flow rate of 8m / s. Then calcine it at 500℃ for 3 hours to obtain a honeycomb-type ultra-low temperature SCR catalyst.

[0071] Comparative Example 3

[0072] The difference from Example 1 is that the ratio of titanium sol to aluminum sol is 4:1.

[0073] Step 1: Take a cordierite carrier with 30 holes, a cross-sectional area of ​​150mm*150mm and a length of 200mm, immerse it in a 0.1mol / L nitric acid solution, sonicate for 30min, take it out, wash it with deionized water until neutral, and dry it at 110℃ for 12h to obtain the pretreated cordierite.

[0074] Step 2: Add 735.300g of manganese acetate (tetrahydrate), 130.266g of cerium nitrate (hexahydrate), and 121.200g of ferric nitrate (nonahydrate) to 3L of aqueous solution and stir to dissolve to obtain a mixed solution.

[0075] Step 3: Mix 2.4 L of titanium sol (30% by mass) and 0.6 L of aluminum sol (20% by mass), and adjust the pH to 5 with 1 mol / L citric acid to obtain a composite sol.

[0076] Step 4: Add 3L of mixed solution dropwise to 3L of composite sol while stirring. After the addition is complete, continue stirring for 1 hour to obtain the coating solution.

[0077] Step 5: Immerse the pretreated cordierite in the coating solution, remove it after 20 seconds, blow away the liquid in the cordierite pores with compressed air, and then dry it with a hot air blower at 70℃ and a hot air flow rate of 8m / s. Then calcine it at 500℃ for 3 hours to obtain a honeycomb-type ultra-low temperature SCR catalyst.

[0078] Table 1

[0079]

[0080] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made using the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing a honeycomb-type ultra-low temperature SCR catalyst, characterized in that, Includes the following steps: Step 1: After pretreating cordierite by immersing it in an acidic solution, pretreated cordierite is obtained; Step 2: Add manganese salt, cerium salt and iron salt to water to make a homogeneous mixed solution; Step 3: Mix titanium sol and aluminum sol to prepare a composite sol; the volume ratio of titanium sol to aluminum sol is 3:1; the mass fraction of titanium sol is 30-40%; and the mass fraction of aluminum sol is 20-30%. Step 4: While stirring, slowly add the mixed solution dropwise to the composite sol. After the addition is complete, continue stirring to obtain the coating solution. Step 5: Immerse the pretreated cordierite in the coating solution, then remove it, blow away the liquid in the cordierite pores with compressed air, and then dry and calcine it. This step can be repeated several times until a honeycomb-type ultra-low temperature SCR catalyst with a suitable loading of active components is obtained.

2. The preparation method of the honeycomb-type ultra-low temperature SCR catalyst as described in claim 1, characterized in that, The cordierite has 30 to 50 pores.

3. The preparation method of the honeycomb-type ultra-low temperature SCR catalyst as described in claim 1, characterized in that, The acidic solution is one of nitric acid solution, citric acid solution, acetic acid solution, and hydrochloric acid solution; the concentration of the acidic solution is 0.1~0.3 mol / L.

4. The method for preparing the honeycomb-type ultra-low temperature SCR catalyst according to any one of claims 1-3, characterized in that, The molar ratio of the manganese salt, cerium salt, and iron salt is 1:0.1:0.1; the concentration of the manganese salt in water is 0.9~1.2 mol / L.

5. The method for preparing the honeycomb-type ultra-low temperature SCR catalyst according to any one of claims 1-3, characterized in that, The manganese salt is one or both of manganese acetate and manganese nitrate; the cerium salt is cerium nitrate; and the iron salt is one or more of ferric nitrate, ferrous nitrate, and ferric acetate.

6. The method for preparing the honeycomb-type ultra-low temperature SCR catalyst as described in claim 1, characterized in that, The pH of the composite sol is adjusted to 4-6 after mixing.

7. The method for preparing the honeycomb-type ultra-low temperature SCR catalyst as described in claim 1 or 6, characterized in that, The volume ratio of the composite sol to the mixed solution is 1:1 to 1.2; the stirring time is 1 to 2 hours.

8. The method for preparing the honeycomb-type ultra-low temperature SCR catalyst as described in claim 1, characterized in that, The drying process is hot air drying, with a temperature of 60~70℃ and a hot air flow rate of 6~8 m / s.

9. The method for preparing the honeycomb-type ultra-low temperature SCR catalyst as described in claim 1 or 8, characterized in that, The calcination is carried out at 500~600℃ for 2~3 hours.

10. The application of a honeycomb-type ultra-low temperature SCR catalyst prepared by any one of claims 1-9 in a denitrification reaction.

Images