Low-temperature sulfur-resistant denitration catalyst for refining flue gas and preparation method thereof

Abstract

The present application relates to the technical field of industrial flue gas denitration catalyst preparation, and discloses a low-temperature sulfur-resistant denitration catalyst for refinery flue gas and a preparation method thereof, the catalyst comprising a silicon-aluminum composite modified nano TiO2 carrier, a manganese-cerium-iron-tungsten composite active component loaded on the surface of the carrier, and a phosphate sulfur-resistant modified coating. In the preparation, the silicon-aluminum modified TiO2 carrier is prepared by a sol-gel method, the manganese, cerium, iron and tungsten precursors are loaded on the surface of the carrier by ultrasonic immersion, and the composite oxide active component is formed by stepwise drying and calcination, and then the porous phosphate film is formed by ammonium hydrogen phosphate immersion and calcination. The catalyst obtained by the present application has a large specific surface area and rich pore structure, can improve the low-temperature denitration activity, inhibit the deposition of sulfates and the sulfuration of the active component, and is suitable for the denitration treatment of low-temperature, high-sulfur and high-humidity complex flue gas in the refining industry.

Description

Technical Field

[0001] This invention relates to the field of industrial flue gas denitrification catalyst preparation technology, specifically to a low-temperature sulfur-resistant denitrification catalyst for refining flue gas and its preparation method. Background Technology

[0002] The flue gas emitted from catalytic cracking units, heating furnaces, and reforming units in the petroleum refining industry is characterized by low temperature, high sulfur content, high water vapor content, and complex composition. The flue gas temperature is generally concentrated between 120 and 280°C, and it contains 200–800 ppm SO2, over 10% water vapor, and trace amounts of dust and hydrocarbon impurities, making it a typical low-temperature, high-sulfur, complex flue gas. Currently, the mainstream SCR denitrification catalysts in industry are mostly vanadium-tungsten-titanium based catalysts, with an optimal activity temperature range of 300–400°C. Below 280°C, their denitrification activity drops significantly, failing to meet the denitrification requirements of low-temperature flue gas in refining and chemical industries.

[0003] Existing low-temperature denitrification catalysts mostly use manganese and cerium oxides as the core active components, exhibiting excellent low-temperature denitrification activity. However, these catalysts have a fatal flaw: poor resistance to sulfur and water. In refining flue gas containing SO2 and water vapor, they are highly susceptible to sulfur poisoning and deactivation. On the one hand, SO2 in the flue gas oxidizes at the catalyst's active sites to form SO3, which reacts with H2O and the denitrification reducing agent NH3 in the flue gas to form ammonium sulfate and ammonium bisulfate salts, clogging catalyst pores and covering active sites. On the other hand, SO2 reacts with manganese and cerium active components to undergo sulfidation reactions, forming inert sulfides, leading to permanent catalyst deactivation, significantly shortening service life, and increasing the operation and maintenance costs of refining enterprises.

[0004] Existing low-temperature SCR catalysts mostly use manganese-based or manganese-cerium composite oxides as active components. Although they have good low-temperature denitrification performance, their resistance to sulfur and water is still insufficient. Wu et al., in their paper "The Influence of Cerium Oxide Doping on the Low-Temperature Selective Catalytic Reduction of NO by Mn / TiO2 Catalysts against SO2" (Catalysis Communications, Vol. 10, 2009, pp. 935-939), found that SO2 leads to a decrease in the activity of Mn / TiO2 catalysts, accompanied by ammonium sulfate deposition and sulfation of active components; the introduction of Ce can improve the sulfur resistance of the catalyst to a certain extent.

[0005] Existing technologies often improve the sulfur resistance of catalysts through single-metal modification or support modification. However, these methods offer limited modification effects and cannot simultaneously achieve both high activity at low temperatures and long-term sulfur resistance stability. Furthermore, the preparation processes are complex and lack repeatability, making them unsuitable for the continuous, high-load, and complex production requirements of the refining and chemical industry. Therefore, developing a denitrification catalyst that is suitable for low-temperature, high-sulfur flue gas in refining and chemical industries, exhibits excellent low-temperature activity, strong sulfur and water resistance, and is suitable for industrial-scale production is a pressing technical problem that needs to be solved in this field. Summary of the Invention

[0006] In order to overcome the shortcomings of the prior art, the present invention aims to provide a low-temperature anti-sulfur denitrification catalyst for refining flue gas and its preparation method, so as to improve the denitrification activity, anti-sulfur and water resistance and long-term operational stability of the catalyst under complex flue gas conditions of low temperature, high sulfur and high humidity.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a low-temperature anti-sulfurization and denitrification catalyst for refining flue gas, comprising a modified nano-TiO2 support, a manganese-cerium-iron-tungsten composite active component supported on the surface of the support, and a surface phosphate anti-sulfurization modified coating; based on the total mass of the catalyst (100%), the mass percentages of each component are: modified nano-TiO2 support 82%–88%, manganese-cerium-iron-tungsten composite active component 10%–15%, and phosphate anti-sulfurization modified coating 2%–3%;

[0008] In the manganese-cerium-iron-tungsten composite active component, the molar ratio of Mn, Ce, Fe, and W is 5-8:3-5:1-2:0.5-1.

[0009] The modified nano-TiO2 carrier is a silicon-aluminum composite modified nano-anatase titanium dioxide, with silicon and aluminum modification elements accounting for 2% to 4% of the total carrier mass.

[0010] The phosphate anti-sulfur modified coating is a porous phosphate film formed by in-situ sintering of ammonium hydrogen phosphate.

[0011] Furthermore, the modified nano-TiO2 support has a particle size of 20–50 nm and a specific surface area ≥180 m². 2 / g, porosity 45%–55%; the catalyst as a whole has a nanoporous powder structure with a bulk density of 0.6–0.8 g / cm³. 3 .

[0012] Furthermore, the manganese-cerium-iron-tungsten composite active components exist in the form of oxides, specifically MnO2, CeO2, Fe2O3, and WO3.

[0013] Furthermore, it includes the following steps:

[0014] S1. Modified nano-TiO2 support: Tetrabutyl titanate, anhydrous ethanol, and glacial acetic acid were mixed at a volume ratio of 1:3-5:0.8-1.2 and stirred for 30-60 min to obtain a titanium sol; tetraethyl orthosilicate and aluminum nitrate were added to the titanium sol and stirred continuously for 40-80 min; the pH of the mixture was adjusted to 3-4, and the gel was allowed to stand at room temperature for 12-24 h; the gel was dried at 80-120℃ for 6-10 h, and then calcined in stages. First, the temperature was increased to 300℃ at 2-4℃ / min and held for 2 h, and then increased to 450-500℃ at 3℃ / min and held for 3-4 h. After cooling and grinding, the nano-TiO2 support was obtained through a 200-mesh sieve.

[0015] S2. Preparation of composite active component precursor solution: Take manganese nitrate, cerium nitrate, ferric nitrate and ammonium tungstate according to the ratio, add them to deionized water, stir at room temperature, and prepare a composite precursor solution with a total molar concentration of 0.23-0.26 mol / L of total metal cations and tungsten element in tungstate.

[0016] S3. Ultrasonic impregnation of loaded active components: The modified TiO2 support prepared in step S1 is added to the precursor solution with a solid-liquid ratio of 1g:4-6mL. The mixture is ultrasonically impregnated at room temperature for 90-120min with an ultrasonic power of 300-400W. After impregnation, the mixture is allowed to stand and age for 4-6h to obtain the impregnated mixture.

[0017] S4. Segmented drying and calcination pretreatment: The impregnated mixture is pre-dried at 60-80℃ for 4-6 hours, and then heated to 100-120℃ for thorough drying for 8-12 hours; then segmented calcination is carried out, with the temperature increased at 2-3℃ / min to 250-300℃ and held for 1.5-2 hours, and then heated to 400-430℃ and held for 2.5-3.5 hours, and then naturally cooled to room temperature to obtain the active component supported intermediate;

[0018] S5. Surface Sulfur Resistance Modification Treatment: The intermediate is dispersed in an aqueous solution of ammonium hydrogen phosphate, and impregnated at a constant temperature of 50-60℃ with stirring for 30-50 minutes. The material is then removed, dried at 100℃ for 4 hours, and finally calcined at 350-380℃ for 1.5 hours. After natural cooling and grinding through a 300-mesh sieve, a low-temperature sulfur resistance denitrification catalyst is obtained. Within this temperature range, the ammonium hydrogen phosphate adhering to the catalyst surface loses some ammonia and water upon heating, undergoing a condensation reaction to generate pyrophosphate or polyphosphate eutectic, which then chemically crosslinks with the titanium hydroxyl groups or free metal oxides on the support surface, solidifying to form an amorphous porous phosphate / polyphosphate crosslinked film with a mesoporous structure.

[0019] Furthermore, in step S1, the amount of tetraethyl orthosilicate and aluminum nitrate added satisfies the following conditions: the total mass of silicon and aluminum elements is 2% to 4% of the mass of the modified TiO2 carrier, and the mass ratio of silicon to aluminum elements is 2:1.

[0020] Furthermore, in step S2, the stirring time at room temperature is 20–40 min.

[0021] Furthermore, during the ultrasonic impregnation process in step S3, the mixture is stirred once every 30 minutes, with each stirring lasting 5 minutes.

[0022] Furthermore, in step S5, the mass concentration of the ammonium hydrogen phosphate aqueous solution is 8% to 12%, and the solid-liquid ratio of the intermediate to the ammonium hydrogen phosphate aqueous solution is 1g:3 to 5mL.

[0023] Compared with the prior art, the present invention has the following beneficial technical effects:

[0024] This invention uses silicon-aluminum composite modified nano-anatase TiO2 as a support. Silicon and aluminum elements can adjust the acidity of the support surface, inhibit the excessive growth of TiO2 grains during calcination, and improve the specific surface area and pore structure stability of the support. This is beneficial for the uniform dispersion of manganese, cerium, iron and tungsten active components, reduces the agglomeration of active components, and improves the utilization rate of effective active sites of the catalyst.

[0025] This invention employs a synergistic composition of manganese, cerium, iron, and tungsten multimetal oxides to construct a composite active component, wherein the manganese oxide provides low-temperature redox activity, and the cerium oxide utilizes Ce... 3 ⁺ / Ce 4 The ⁺ cycle enhances the oxygen storage and release capacity, iron oxide promotes electron transfer and surface active oxygen generation, and tungsten oxide enhances surface acidity and structural stability, thereby broadening the low-temperature activity range of the catalyst and improving the adsorption and activation capacity of ammonia and the conversion efficiency of nitrogen oxides.

[0026] This invention forms a porous phosphate anti-sulfur modification coating in situ on the catalyst surface. While maintaining the mass transfer channels of the reactant gas, the coating can reduce the direct contact between sulfur dioxide and active components such as manganese and cerium, inhibit the sulfation of active components, and reduce the deposition of ammonium sulfate and ammonium bisulfate on the channels and active sites, thereby improving the stability of the catalyst in sulfur-containing and water-containing flue gas.

[0027] This invention employs a preparation process combining ultrasonic impregnation, segmented drying, and segmented calcination, which promotes the precursor solution to fully enter the pores of the support, reduces drying migration and local enrichment, and enables the composite oxide to form a stable bond with the support. The resulting catalyst has a uniform structure, good repeatability, and mild preparation conditions, making it suitable for the large-scale production of denitrification catalysts for low-temperature, high-sulfur flue gas in refining. Attached Figure Description

[0028] Figure 1 This is a SEM image of the catalyst from Example 1. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Tetrabutyl titanate, catalog number 244112; Tetraethyl orthosilicate, catalog number 800658; Manganese nitrate tetrahydrate, catalog number 769509; Cerium nitrate hexahydrate, catalog number 238538.

[0031] Example 1

[0032] This embodiment prepares a low-temperature anti-sulfurization and denitrification catalyst for refining flue gas. Based on a total mass of 100 parts, the catalyst includes 88 parts of silicon-aluminum composite modified nano-TiO2 support, 10 parts of manganese-cerium-iron-tungsten composite active component, and 2 parts of phosphate anti-sulfurization modified coating. The molar ratio of Mn, Ce, Fe, and W in the manganese-cerium-iron-tungsten composite active component is 5:3:1:0.5. The total mass of silicon and aluminum modifying elements is 2% of the mass of the modified nano-TiO2 support, and the mass ratio of silicon to aluminum is 2:1.

[0033] The specific preparation process is as follows:

[0034] S1. Preparation of modified nano-TiO2 support:

[0035] 100 mL of tetrabutyl titanate, 300 mL of anhydrous ethanol and 80 mL of glacial acetic acid were added to a reaction vessel and stirred at 400 r / min for 30 min at room temperature to obtain a uniform and transparent titanium sol.

[0036] Ethyl orthosilicate and aluminum nitrate were weighed out according to the following ratio: silicon and aluminum total mass accounted for 2% of the final carrier mass, and the silicon to aluminum mass ratio was 2:1. These were then added to the titanium sol, and the mixture was stirred for 40 minutes. The pH of the mixture was adjusted to 3.0 using dilute nitric acid, and the gel was allowed to stand at room temperature for 12 hours.

[0037] The obtained gel was dried in an 80℃ forced-air drying oven for 6 hours, then placed in a muffle furnace and heated to 300℃ at a heating rate of 2℃ / min and held for 2 hours. Then it was heated to 450℃ at a heating rate of 3℃ / min and held for 3 hours. After naturally cooling to room temperature, it was ground and passed through a 200-mesh sieve to obtain a silicon-aluminum composite modified nano-anatase TiO2 support.

[0038] S2. Preparation of the composite active component precursor solution:

[0039] Based on the total mass of 10 parts of the calcined manganese-cerium-iron-tungsten composite oxide, manganese nitrate, cerium nitrate, iron nitrate, and ammonium tungstate were weighed separately to make the molar ratio of Mn, Ce, Fe, and W elements 5:3:1:0.5. The above precursor was added to deionized water and stirred at room temperature for 20 min to prepare a composite precursor solution with a total molar concentration of 0.235 mol / L of total metal cations and tungstate elements.

[0040] S3, Ultrasonic impregnation loading of active components:

[0041] The modified nano-TiO2 support obtained in step S1 was added to the composite precursor solution. The solid-liquid ratio of the support to the composite precursor solution was 1g:4mL. The mixture was impregnated at room temperature with an ultrasonic power of 300W for 90min. During the ultrasonic impregnation process, mechanical stirring was performed once every 30min for 5min each time. After the ultrasonic impregnation was completed, the mixture was allowed to stand and age for 4h to obtain the impregnated mixture.

[0042] S4. Segmented drying and calcination:

[0043] The impregnated mixture was pre-dried at 60℃ for 4 hours, and then heated to 100℃ for 8 hours. The dried material was placed in a muffle furnace and heated to 250℃ at a heating rate of 2℃ / min and held for 1.5 hours, and then heated to 400℃ and held for 2.5 hours.

[0044] After calcination, the mixture is naturally cooled to room temperature, which converts manganese nitrate, cerium nitrate, ferric nitrate, and ammonium tungstate into active components containing MnO2, CeO2, Fe2O3, and WO3, respectively, thus obtaining an active component-supported intermediate.

[0045] S5. Surface sulfur-resistant modification treatment:

[0046] Prepare an 8% (w / w) aqueous solution of ammonium hydrogen phosphate. Add the intermediate loaded with the active component to the aqueous solution of ammonium hydrogen phosphate. The solid-liquid ratio of the intermediate to the aqueous solution of ammonium hydrogen phosphate is 1 g: 3 mL. Stir and impregnate at 50 °C for 30 min.

[0047] After impregnation, the material is separated, dried at 100℃ for 4 hours, and then calcined at 350℃ for 1.5 hours to allow ammonium hydrogen phosphate to sinter in situ on the catalyst surface to form a porous phosphate anti-sulfur modified coating. After natural cooling, it is ground and passed through a 300-mesh sieve to obtain a low-temperature anti-sulfur denitrification catalyst for refining flue gas.

[0048] By controlling the amount of each precursor added and the mass increment after calcination, the mass percentages of the modified nano-TiO2 support, the manganese-cerium-iron-tungsten composite active component, and the phosphate anti-sulfur modification coating in the obtained catalyst were 88%, 10%, and 2%, respectively.

[0049] Depend on Figure 1 The microstructure described above indicates that silicon-aluminum composite modification can, to a certain extent, inhibit excessive grain growth of nano-TiO2 supports during calcination, maintaining good dispersibility and porous structure. Simultaneously, ultrasonic impregnation and segmented drying and calcination processes facilitate the full entry of manganese, cerium, iron, and tungsten precursors into the support pores and their uniform loading onto the support surface, reducing the migration, enrichment, and agglomeration of active components during drying and calcination.

[0050] As shown in the figure, the catalyst surface exhibits abundant interparticle pores, which increases the contact area between the reactant gases and the catalyst's active sites, shortens the diffusion paths of NO, NH3, and O2 within the catalyst, and thus helps to improve the denitrification reaction rate under low-temperature conditions. Furthermore, the loose and porous surface structure provides a large loading interface for the phosphate anti-sulfur modification layer, allowing the phosphate coating to maintain gas mass transfer channels while providing a certain degree of isolation and protection for the active components.

[0051] Therefore, the SEM image shows that the catalyst obtained in Example 1 has a relatively uniform distribution of nanoparticles, a rich pore structure and a low degree of particle agglomeration. This structure is beneficial to improving the dispersibility of the composite active components and the utilization rate of effective active sites, and provides a structural basis for the catalyst to obtain high low-temperature denitrification activity and sulfur and water resistance stability.

[0052] Example 2

[0053] This embodiment prepares a low-temperature anti-sulfurization and denitrification catalyst for refining flue gas. Based on a total catalyst mass of 100 parts, it comprises 85 parts of silicon-aluminum composite modified nano-TiO2 support, 12.5 parts of manganese-cerium-iron-tungsten composite active component, and 2.5 parts of phosphate anti-sulfurization modified coating. The molar ratio of Mn, Ce, Fe, and W in the manganese-cerium-iron-tungsten composite active component is 6.5:4:1.5:0.75; the total mass of silicon and aluminum modifying elements is 3% of the support mass, and the mass ratio of silicon to aluminum is 2:1.

[0054] The specific preparation process is as follows:

[0055] S1. Mix 100 mL of tetrabutyl titanate, 400 mL of anhydrous ethanol and 100 mL of glacial acetic acid, and stir at 450 r / min for 45 min to obtain titanium sol.

[0056] Tetraethyl orthosilicate and aluminum nitrate were added according to the following ratio: silicon and aluminum total mass accounted for 3% of the carrier mass, and silicon to aluminum mass ratio was 2:1. The mixture was stirred for 60 min, and the pH of the mixture was adjusted to 3.5 with dilute nitric acid. The mixture was then allowed to stand at room temperature for 18 h to gel.

[0057] The gel was dried at 100℃ for 8 hours, then heated to 300℃ at 3℃ / min and held for 2 hours, followed by heating to 475℃ at 3℃ / min and holding for 3.5 hours. After cooling, grinding, and passing through a 200-mesh sieve, the silicon-aluminum composite modified nano-TiO2 support was obtained.

[0058] S2. Based on a total mass of 12.5 parts of active components in the calcined composite oxide, weigh manganese nitrate, cerium nitrate, ferric nitrate, and ammonium tungstate to achieve a molar ratio of Mn, Ce, Fe, and W of 6.5:4:1.5:0.75. Dissolve each precursor in deionized water and stir at room temperature for 30 minutes to prepare a composite precursor solution with a total molar concentration of 0.242 mol / L for the total metal cations and tungstate.

[0059] S3. Add the modified nano-TiO2 support to the composite precursor solution with a solid-liquid ratio of 1g:5mL. Impregnate at room temperature with an ultrasonic power of 350W for 105min. Stir once every 30min during ultrasonic impregnation, each stirring for 5min. Then let stand and age for 5h.

[0060] S4. Pre-dry the impregnated mixture at 70℃ for 5 hours, then raise the temperature to 110℃ and dry for 10 hours. Raise the dried material to 275℃ at 2.5℃ / min and keep it at that temperature for 1.8 hours. Then raise the temperature to 415℃ and keep it at that temperature for 3 hours. After natural cooling, the active component-supported intermediate is obtained.

[0061] S5. Prepare a 10% (w / w) aqueous solution of ammonium hydrogen phosphate. Disperse the active component-supported intermediate in the ammonium hydrogen phosphate aqueous solution at a solid-liquid ratio of 1g:4mL. Stir and impregnate at 55℃ for 40min. After impregnation, separate the material, dry at 100℃ for 4h, and then calcine at 365℃ for 1.5h. Allow to cool naturally, grind, and pass through a 300-mesh sieve to obtain a low-temperature anti-sulfurization and denitrification catalyst.

[0062] By controlling the amount of precursor added, the mass percentages of the modified nano-TiO2 support, the manganese-cerium-iron-tungsten composite active component, and the phosphate anti-sulfur modification coating in the obtained catalyst were 85%, 12.5%, and 2.5%, respectively.

[0063] Example 3

[0064] This embodiment prepares a low-temperature anti-sulfurization and denitrification catalyst for refining flue gas. Based on a total catalyst mass of 100 parts, it comprises 82 parts of a silicon-aluminum composite modified nano-TiO2 support, 15 parts of a manganese-cerium-iron-tungsten composite active component, and 3 parts of a phosphate anti-sulfurization modified coating. The molar ratio of Mn, Ce, Fe, and W in the manganese-cerium-iron-tungsten composite active component is 8:5:2:1; the total mass of silicon and aluminum modifying elements is 4% of the support mass, and the mass ratio of silicon to aluminum is 2:1.

[0065] The specific preparation process is as follows:

[0066] S1. Mix 100 mL of tetrabutyl titanate, 500 mL of anhydrous ethanol and 120 mL of glacial acetic acid, and stir at 500 r / min for 60 min to obtain titanium sol.

[0067] Tetraethyl orthosilicate and aluminum nitrate were added according to the following ratio: silicon and aluminum total mass accounted for 4% of the carrier mass, and silicon to aluminum mass ratio was 2:1. The mixture was stirred for 80 min. The pH of the mixture was adjusted to 4.0 using dilute nitric acid, and the gel was allowed to stand at room temperature for 24 h.

[0068] The gel was dried at 120℃ for 10 h, then heated to 300℃ at 4℃ / min and held for 2 h, then heated to 500℃ at 3℃ / min and held for 4 h, then cooled naturally, ground and passed through a 200-mesh sieve to obtain the silicon-aluminum composite modified nano-TiO2 carrier.

[0069] S2. Based on the total mass of 15 parts of active components of the composite oxide after calcination, weigh manganese nitrate, cerium nitrate, ferric nitrate and ammonium tungstate to make the molar ratio of Mn, Ce, Fe and W elements 8:5:2:1; add the above precursor to deionized water and stir at room temperature for 40 min to prepare a composite precursor solution with a total molar concentration of 0.250 mol / L of total metal cations and tungstate elements.

[0070] S3. Add the modified nano-TiO2 carrier to the composite precursor solution at a solid-liquid ratio of 1g:6mL, and impregnate at room temperature with an ultrasonic power of 400W for 120min. Stir once every 30min during the ultrasonic process, and stir for 5min each time. After impregnation, let stand and age for 6h.

[0071] S4. Pre-dry the impregnated mixture at 80℃ for 6 hours, then raise the temperature to 120℃ and dry for 12 hours. Raise the dried material to 300℃ at 3℃ / min and hold for 2 hours, then raise the temperature to 430℃ and hold for 3.5 hours. After natural cooling, the active component-supported intermediate is obtained.

[0072] S5. Prepare a 12% (w / w) aqueous solution of ammonium hydrogen phosphate. Disperse the active component-loaded intermediate in the ammonium hydrogen phosphate aqueous solution at a solid-liquid ratio of 1g:5mL and stir and impregnate at 60℃ for 50min.

[0073] After impregnation, the material is separated, dried at 100℃ for 4 hours, then calcined at 380℃ for 1.5 hours, naturally cooled, ground, and passed through a 300-mesh sieve to obtain a low-temperature anti-sulfurization and denitrification catalyst.

[0074] By controlling the amount of precursor added, the mass percentages of the modified nano-TiO2 support, the manganese-cerium-iron-tungsten composite active component, and the phosphate anti-sulfur modification coating in the obtained catalyst were 82%, 15%, and 3%, respectively.

[0075] Comparative Example 1

[0076] The difference between this comparative example and Example 2 is that tetraethyl orthosilicate and aluminum nitrate are not added in step S1, and tetrabutyl titanate is used directly to prepare the unmodified nano-TiO2 carrier.

[0077] Apart from the differences mentioned above, the composition, loading, ultrasonic impregnation conditions, segmented drying and calcination conditions, and phosphate anti-sulfur modification conditions of the manganese-cerium-iron-tungsten composite active component were the same as those in Example 2, resulting in a comparative catalyst.

[0078] This comparative example is used to investigate the effects of silicon-aluminum composite modification on the specific surface area, pore structure stability, and dispersibility of composite active components of TiO2 support.

[0079] Comparative Example 2

[0080] The difference between this comparative example and Example 2 is that ammonium tungstate is not added to the composite active component, and only manganese nitrate, cerium nitrate and iron nitrate are used as active component precursors. The molar ratio of Mn, Ce and Fe elements is 6.5:4:1.5. By adjusting the amount of each precursor, the total mass of the composite oxide active component after calcination is still 12.5% ​​of the total mass of the catalyst.

[0081] Apart from the differences mentioned above, the composition of the raw materials and the preparation steps are the same as in Example 2, resulting in a comparative catalyst that does not contain tungsten oxide.

[0082] This comparative example is used to investigate the effects of tungsten oxide on catalyst surface acidity, low-temperature denitrification activity, and structural stability.

[0083] Comparative Example 3

[0084] The difference between this comparative example and Example 2 is that the surface anti-sulfur modification treatment in step S5 is omitted, and the active component-loaded intermediate is not impregnated and calcined using an aqueous solution of ammonium hydrogen phosphate.

[0085] After the calcination in step S4 is completed, the active component-supported intermediate is directly cooled naturally, ground, and passed through a 300-mesh sieve to obtain a comparative catalyst without a phosphate anti-sulfur modification coating on the surface.

[0086] In this comparative catalyst, the mass percentage of the manganese-cerium-iron-tungsten composite active component is 12.5%, and the remainder is a silicon-aluminum composite modified nano-TiO2 support.

[0087] This comparative example is used to investigate the effects of phosphate anti-sulfur modified coatings on SO2 isolation, inhibition of active component sulfation, and inhibition of ammonium sulfate deposition.

[0088] Comparative Example 4

[0089] The difference between this comparative example and Example 2 is that ultrasonic impregnation is not performed in step S3. Instead, the modified nano-TiO2 carrier is added to the composite precursor solution and impregnated with mechanical stirring at 400 r / min for 105 min at room temperature, followed by standing and aging for 5 h.

[0090] Apart from the differences mentioned above, the composition of other raw materials, drying and calcination conditions, and surface sulfur-resistant modification conditions were the same as in Example 2, resulting in a comparative catalyst prepared by conventional mechanical impregnation method.

[0091] This comparative example is used to investigate the effects of ultrasound on the entry of precursors into carrier pores, uniform dispersion of composite active components, and utilization of active sites.

[0092] Comparative Example 5

[0093] The difference between this comparative example and Example 2 is that step S4 does not employ segmented drying and segmented calcination processes. Specifically, the impregnated mixture is directly dried at 110°C for 15 hours, and then directly heated to 415°C at a heating rate of 5°C / min and held at that temperature for 3 hours.

[0094] Apart from the differences mentioned above, the composition of other raw materials, ultrasonic impregnation conditions, and surface sulfur-resistant modification conditions were the same as in Example 2, resulting in a comparative catalyst prepared using a single-stage drying and calcination process.

[0095] This comparative example is used to investigate the effects of segmented drying and segmented calcination on reducing precursor migration, avoiding local enrichment of active components, and improving the pore structure of the catalyst.

[0096] Performance testing

[0097] The catalysts prepared in Examples 1-3 and Comparative Examples 1-5 were subjected to performance tests. The catalysts used for denitrification performance testing were tableted, crushed, and sieved to select particles of 20-40 mesh. Three parallel tests were set up for each test, and the average value of the results was taken.

[0098] I. Testing Methods

[0099] 1. Specific surface area and pore structure testing

[0100] The specific surface area of ​​the catalyst was determined according to the gas adsorption BET method specified in GB / T19587—2017. Approximately 0.25 g of catalyst sample was weighed and degassed at 150 °C under vacuum for 4 h. Nitrogen was used as the adsorbed gas, and the nitrogen adsorption-desorption isotherm was measured at 77 K. The specific surface area was calculated using the BET method, and the total pore volume and average pore size were calculated using the BJH method.

[0101] The porosity of the catalyst was determined by mercury intrusion porosimetry. Before the test, the sample was dried at 110°C for 2 hours.

[0102] 2. Low-temperature denitrification activity test

[0103] The low-temperature denitrification performance of the catalyst was tested using a fixed-bed reactor.

[0104] Weigh 1.00 g of catalyst particles with a particle size of 20–40 mesh and pack them into a quartz tube reactor with an inner diameter of 10 mm. Before testing, pretreat the reactor under a nitrogen atmosphere at 200 °C for 1 h.

[0105] The simulated flue gas composition is as follows:

[0106] The NO concentration is 500 ppm, the NH3 concentration is 500 ppm, the O2 volume fraction is 5%, N2 is the equilibrium gas, and the gas hourly space velocity is 30,000 h⁻¹. -1 .

[0107] Tests were conducted at 160℃, 180℃, and 200℃ respectively. After reaching the set temperature, the temperature was stabilized for 30 minutes, and the NOx concentrations at the reactor inlet and outlet were measured.

[0108] NOx conversion rate is calculated using the following formula:

[0109] η=(Cin-Cout) / Cin×100%

[0110] In the formula, η is the NOx conversion rate (%), Cin is the inlet NOx concentration (ppm), and Cout is the outlet NOx concentration (ppm).

[0111] 3. Sulfur and water resistance test

[0112] The sulfur and water resistance properties were tested at 180℃.

[0113] The simulated flue gas composition is as follows:

[0114] The concentrations of NO, NH3, and SO2 are 500 ppm, with O2 volume fraction at 5% and water vapor volume fraction at 10%. N2 is the equilibrium gas, and the gas hourly space velocity (GHSV) is 30,000 h⁻¹. -1The system was first run for 1 hour under conditions without SO2 and water vapor, and the initial NOx conversion rate was measured. Then, SO2 and water vapor were introduced, and the system was run continuously for 100 hours. The NOx conversion rate after 100 hours of operation was measured.

[0115] The activity retention rate is calculated according to the following formula:

[0116] R = η100 / η0 × 100%

[0117] In the formula, R is the activity retention rate (%), η0 is the initial NOx conversion rate (%), and η100 is the NOx conversion rate after 100 hours of continuous operation (%).

[0118] During 48 hours of operation, the outlet N2O and NH3 concentrations were simultaneously measured using a flue gas analyzer, nitrogen selectivity was calculated, and ammonia slip concentration was recorded.

[0119] Table 1: Catalyst Structure, Properties, and Low-Temperature Denitrification Performance Tests

[0120] Sample <![CDATA[Specific surface area / (m 2 / g)]]> <![CDATA[Total pore volume / (cm 3 / g)]]> Porosity / % NOx conversion rate at 160℃ / % NOx conversion rate at 180℃ / % NOx conversion rate at 200℃ / % Example 1 198.7 0.44 48.8 87.6 94.8 96.4 Example 2 205.4 0.47 51.3 88.9 95.9 97.3 Example 3 201.9 0.46 50.5 88.3 95.4 96.9 Comparative Example 1 154.6 0.33 39.2 72.8 82.7 87.9 Comparative Example 2 202.1 0.45 49.8 79.6 88.8 92.0 Comparative Example 3 209.5 0.48 52.0 88.0 95.0 96.5 Comparative Example 4 173.8 0.36 42.1 75.8 85.6 90.1 Comparative Example 5 165.7 0.34 40.6 74.2 84.0 88.7

[0121] Table 2: Catalyst's sulfur and water resistance stability and nitrogen selectivity test

[0122] Sample Initial NOx conversion rate / % <![CDATA[NOx Conversion Rate / % after 100 h of SO₂+H₂O Operation]]> Activity retention rate / % Nitrogen selectivity / % Ammonia slip concentration / ppm Example 1 94.8 89.2 94.1 96.4 6.2 Example 2 95.9 90.8 94.7 97.1 5.4 Example 3 95.4 90.2 94.5 96.8 5.7 Comparative Example 1 82.7 62.4 75.5 91.2 15.8 Comparative Example 2 88.8 70.9 79.8 92.5 13.6 Comparative Example 3 95.0 59.7 62.8 88.7 27.4 Comparative Example 4 85.6 65.9 77.0 90.8 17.9 Comparative Example 5 84.0 63.5 75.6 89.6 20.3

[0123] As shown in Table 1, in Comparative Example 1, without the use of silicon-aluminum composite modified TiO2 support, the specific surface area was reduced to 154.6 m². 2 / g, the NOx conversion rate decreased to 82.7% at 180℃, indicating that silicon-aluminum modification can improve the pore structure of the support and promote the dispersion of active components. In Comparative Example 2, without the introduction of tungsten, the NOx conversion rate decreased to 88.8% at 180℃, indicating that tungsten oxide can improve the surface acidity of the catalyst and its NH3 adsorption activation capacity. Comparative Examples 4 and 5, by omitting the ultrasonic impregnation and segmented drying and calcination processes respectively, resulted in decreased dispersion of active components and a significant reduction in low-temperature denitrification performance.

[0124] Table 2 shows that after 100 hours of continuous operation under conditions of 500 ppm SO2 and 10% water vapor, Examples 1-3 still maintained high denitrification activity, with NOx conversion rates reaching 89.2%-90.8% and activity retention rates reaching 94.1%-94.7%. Example 2 exhibited the best overall performance, indicating that a suitable ratio of active components, degree of carrier modification, and phosphate coating content can achieve a balance between low-temperature activity and sulfur resistance stability. Comparative Example 3, without phosphate sulfur resistance modification, although initially achieving a NOx conversion rate of 95.0%, only reached 59.7% after 100 hours of operation under sulfur and water conditions, with the activity retention rate decreasing to 62.8%. Simultaneously, nitrogen selectivity decreased to 88.7%, and ammonia slip increased to 27.4 ppm. This demonstrates that the phosphate sulfur resistance modification coating of this invention can effectively block the contact between SO2 and the active components Mn and Ce, reduce sulfate and ammonium sulfate deposition, and improve the long-term operational stability of the catalyst. In Examples 1-3, the nitrogen selectivity remained above 96%, and the ammonia slip concentration was below 6.2 ppm, indicating that the manganese-cerium-iron-tungsten composite oxide system can promote the selective reduction reaction of NOx and reduce the occurrence of side reactions.

[0125] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0126] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

[0127] Those skilled in the art should understand that the above descriptions are merely several specific embodiments of the present invention, and not all embodiments.

Claims

1. A low-temperature anti-sulfurization and denitrification catalyst for refining flue gas, characterized in that, It includes a modified nano-TiO2 support, a manganese-cerium-iron-tungsten composite active component loaded on the surface of the support, and a surface phosphate anti-sulfur modification coating; Based on the total mass of the catalyst (100%), the mass percentages of each component are as follows: 82%–88% for the modified nano-TiO2 support, 10%–15% for the manganese-cerium-iron-tungsten composite active component, and 2%–3% for the phosphate anti-sulfur modified coating; In the manganese-cerium-iron-tungsten composite active component, the molar ratio of Mn, Ce, Fe, and W is 5-8:3-5:1-2:0.5-1. The manganese-cerium-iron-tungsten composite active component is formed by ultrasonically impregnating a composite precursor solution containing Mn, Ce, Fe, and W onto the modified nano-TiO2 support, followed by segmented drying and segmented calcination. The ultrasonic impregnation has an ultrasonic power of 300–400 W and a time of 90–120 min. The segmented drying includes pre-drying at 60–80 °C and drying at 100–120 °C. The segmented calcination includes a first-stage calcination at 250–300 °C and a second-stage calcination at 400–430 °C. The modified nano-TiO2 carrier is a silicon-aluminum composite modified nano-anatase titanium dioxide, with silicon and aluminum modification elements accounting for 2% to 4% of the total carrier mass. The phosphate anti-sulfur modified coating is a porous phosphate film formed by in-situ sintering of ammonium hydrogen phosphate.

2. The low-temperature anti-sulfurization and denitrification catalyst for refining flue gas according to claim 1, characterized in that, The modified nano-TiO2 support has a particle size of 20–50 nm and a specific surface area ≥180 m². 2 / g, porosity 45%–55%; the catalyst as a whole has a nanoporous powder structure with a bulk density of 0.6–0.8 g / cm³. 3 .

3. The low-temperature anti-sulfurization and denitrification catalyst for refining flue gas according to claim 1, characterized in that, The manganese-cerium-iron-tungsten composite active components exist in the form of oxides, specifically MnO2, CeO2, Fe2O3, and WO3.

4. A method for preparing a low-temperature anti-sulfurization and denitrification catalyst for refining flue gas as described in any one of claims 1-3, characterized in that, Includes the following steps: S1. Modified nano-TiO2 support: Tetrabutyl titanate, anhydrous ethanol, and glacial acetic acid were mixed at a volume ratio of 1:3-5:0.8-1.2 and stirred for 30-60 min to obtain a titanium sol; tetraethyl orthosilicate and aluminum nitrate were added to the titanium sol and stirred continuously for 40-80 min; the pH of the mixture was adjusted to 3-4, and the gel was allowed to stand at room temperature for 12-24 h; the gel was dried at 80-120℃ for 6-10 h, and then calcined in stages. First, the temperature was increased to 300℃ at 2-4℃ / min and held for 2 h, and then increased to 450-500℃ at 3℃ / min and held for 3-4 h. After cooling and grinding, the nano-TiO2 support was obtained through a 200-mesh sieve. S2. Preparation of composite active component precursor solution: Take manganese nitrate, cerium nitrate, ferric nitrate and ammonium tungstate according to the ratio, add them to deionized water, stir at room temperature, and prepare a composite precursor solution with a total molar concentration of 0.23-0.26 mol / L of total metal cations and tungsten element in tungstate. S3. Ultrasonic impregnation of loaded active components: The modified TiO2 support prepared in step S1 is added to the precursor solution with a solid-liquid ratio of 1g:4-6mL. The mixture is ultrasonically impregnated at room temperature for 90-120min with an ultrasonic power of 300-400W. After impregnation, the mixture is allowed to stand and age for 4-6h to obtain the impregnated mixture. S4. Segmented drying and calcination pretreatment: The impregnated mixture is pre-dried at 60-80℃ for 4-6 hours, and then heated to 100-120℃ for thorough drying for 8-12 hours; then segmented calcination is carried out, with the temperature increased at 2-3℃ / min to 250-300℃ and held for 1.5-2 hours, and then heated to 400-430℃ and held for 2.5-3.5 hours, and then naturally cooled to room temperature to obtain the active component supported intermediate; S5. Surface anti-sulfur modification treatment: The intermediate is dispersed in an aqueous solution of ammonium hydrogen phosphate, and impregnated at a constant temperature of 50-60℃ for 30-50 minutes. Then the material is taken out, dried at 100℃ for 4 hours, and finally calcined at 350-380℃ for 1.5 hours. After natural cooling, it is ground through a 300-mesh sieve to obtain a low-temperature anti-sulfur denitrification catalyst.

5. The preparation method of the low-temperature anti-sulfurization and denitrification catalyst for refining flue gas according to claim 4, characterized in that, In step S1, the addition amounts of tetraethyl orthosilicate and aluminum nitrate satisfy the following: the total mass of silicon and aluminum elements is 2% to 4% of the mass of the modified TiO2 carrier, and the mass ratio of silicon to aluminum elements is 2:

1.

6. The preparation method of the low-temperature anti-sulfurization and denitrification catalyst for refining flue gas according to claim 4, characterized in that, In step S2, the stirring time at room temperature is 20-40 minutes.

7. The preparation method of the low-temperature anti-sulfurization and denitrification catalyst for refining flue gas according to claim 4, characterized in that, During the ultrasonic impregnation process in step S3, the mixture is stirred once every 30 minutes, with each stirring lasting 5 minutes.

8. The preparation method of the low-temperature anti-sulfurization and denitrification catalyst for refining flue gas according to claim 4, characterized in that, In step S5, the mass concentration of the ammonium hydrogen phosphate aqueous solution is 8% to 12%, and the solid-liquid ratio of the intermediate to the ammonium hydrogen phosphate aqueous solution is 1g:3 to 5mL.

Images