A silica-modified Ce / TiO2 catalyst, its preparation method and application

Abstract

The application belongs to the field of flue gas denitration catalysts in non-electricity industry, and provides a silicon dioxide modified Ce / TiO2 catalyst, a preparation method and application thereof, the catalyst prepared by the method can effectively broaden the denitration reaction temperature window and has high denitration activity, the preparation method comprises the following steps: S1, dissolving titanium tetrachloride in concentrated hydrochloric acid, then diluting with deionized water to obtain a titanium salt solution; uniformly mixing a silicon salt solution with the titanium salt solution to obtain a mixed solution; S2, adding ammonia water to the mixed solution and stirring to gradually increase the solution pH to 8-11; then aging; filtering to obtain a co-precipitate, and washing with deionized water; S3, drying the co-precipitate, and then calcining; obtaining a carrier; S4, mixing a precursor salt of cerium metal oxide with the carrier in deionized water, and water bath heating and evaporation; S5, drying the composite material, then grinding, sieving, and calcining to obtain the catalyst.

Description

Technical Field

[0001] This invention belongs to the field of flue gas denitrification catalysts in non-electric industries, specifically relating to a silica-modified Ce / TiO2 catalyst, its preparation method, and its application. Background Technology

[0002] Currently, nitrogen oxide emissions from non-power industries such as cement, glass, petrochemicals, and metallurgy are enormous, accounting for approximately 40% of total nitrogen oxide emissions. Furthermore, the flue gas temperature in these non-power industries is generally lower; therefore, many boilers operating in these sectors still lack effective flue gas treatment and control. Existing commercial V2O5-WO3 / TiO2 catalysts are widely used for nitrogen oxide emission control in non-power flue gas. Although several zeolite-based formulations and vanadium-based catalysts exhibit high activity, they still suffer from narrow reaction temperature windows (300-400℃) and susceptibility to SO2 poisoning. Transition metal oxide catalysts such as Mn / TiO2 and Ce / TiO2 show potential in low-temperature denitrification, but face challenges such as uneven dispersion of active components, poor sulfur resistance, and insufficient hydrothermal stability. Ce / TiO2 catalysts used for low-temperature SCR flue gas denitrification in non-power sectors exhibit problems such as narrow temperature windows and low activity. CeOx exhibits poor dispersion on the TiO2 catalyst surface, resulting in less than ideal denitrification performance under low-temperature conditions. Currently, the development of low-temperature denitrification catalysts in non-electric industries mainly focuses on catalyst modification. Modified low-temperature denitrification catalysts are generally prepared by physical and chemical modifications based on TiO2 as a support and the introduction of active components such as metal oxides. Although there have been some reports on silica as a modifier, existing silica-modified catalysts still have shortcomings in terms of denitrification effect under low-temperature conditions, such as temperature window and activity. Summary of the Invention

[0003] To address at least one deficiency in existing technologies, this invention provides a silica-modified Ce / TiO2 catalyst, its preparation method, and its application. The catalyst prepared by this invention can effectively broaden the denitration reaction temperature window, has a low CeOx reduction peak temperature, high denitration activity, and high dispersion of active components on the support surface. The catalyst of this invention has excellent denitration reaction activity under low-temperature conditions, making it very suitable for SCR denitration under low-temperature conditions in non-electric industries, and the catalyst has low production cost.

[0004] To achieve its objective, the present invention provides the following technical solution: This invention provides a method for preparing a silica-modified Ce / TiO2 catalyst, wherein the catalyst comprises a support and Ce oxide supported on the support, the Ce loading being 8-12 wt% based on the total mass of the catalyst, and the support comprising TiO2 and SiO2 in a molar ratio of 1-4:1; the preparation method includes the following steps: S1. Dissolve titanium tetrachloride in concentrated hydrochloric acid with a concentration of 36-38 wt%, and then dilute with deionized water to obtain a titanium salt solution. A silicon salt solution obtained by dissolving a soluble inorganic salt of silicon in deionized water is mixed evenly with the titanium salt solution to obtain a mixed solution. S2. Add ammonia water to the mixture at a rate of 1.5-3.5 mL / min and stir to gradually raise the pH of the solution to 8-11, producing a precipitate; then age the solution; filter the resulting liquid to obtain a coprecipitate, and wash the coprecipitate with deionized water. S3. The coprecipitate obtained in step S2 is dried and then calcined in air at 450-550°C to obtain the support; S4. The precursor salt of cerium metal oxide and the carrier are mixed in deionized water and heated in a water bath at 60-90°C with stirring to evaporate excess water; thus obtaining the composite material. S5. The composite material is dried, then ground and sieved to obtain a powder; the obtained powder is calcined in air at 450-600°C to obtain the catalyst.

[0005] Preferably, in step S2, the concentration of the ammonia water is 10-30 wt%.

[0006] Preferably, in step S1, the dilution with deionized water is to dilute the solution to a titanium ion concentration of 0.3-0.7 mol / L; Alternatively, in step S1, the volume of deionized water used for dilution is 8-12 times the volume of concentrated hydrochloric acid.

[0007] Preferably, the soluble inorganic salt of silicon is one or more of sodium metasilicate, sodium silicate, potassium silicate, and their hydrates; The precursor salt of the cerium metal oxide is one or more of cerium nitrate, cerium chloride, cerium acetate, and their hydrates.

[0008] Preferably, in step S2, the aging process is carried out under stirring for 6-8 hours.

[0009] Preferably, in step S3, the drying temperature is 110-130°C, and the drying time is, for example, 11-13 hours; And / or, in step S3 or step S5, the calcination time is 1.5-2.5h; And / or, in step S5, the drying temperature is 110-130°C, and the drying time is, for example, 11-13 hours; And / or, in step S5, the sieving is performed through a 50-80 mesh sieve.

[0010] Preferably, in step S4, the ratio of the mass of the carrier to the volume of the deionized water is 1:40–1:60 g / mL.

[0011] Preferably, in step S1, the silicon salt solution is added dropwise to the titanium salt solution and stirred to mix evenly to obtain the mixture; And / or, in step S4, the evaporation is carried out until the material becomes viscous; And / or, the Ce loading is 11-12 wt%, and the support comprises TiO2 and SiO2 in a molar ratio of 3-4:1; the calcination temperature of step S3 is 500-550℃; the water bath heating temperature of step S4 is 80-90℃; and the calcination temperature of step S5 is 550-600℃.

[0012] Another aspect of the present invention provides a silica-modified Ce / TiO2 catalyst, comprising a support and Ce oxide supported on the support; the Ce loading is 8-12 wt% based on the total mass of the catalyst, and the support comprises TiO2 and SiO2 in a molar ratio of 1-4:1; Preferably, the catalyst is prepared using the preparation method described above.

[0013] In another aspect, the present invention provides the application of the catalyst prepared by the method described above or the catalyst described above in the field of SCR flue gas denitrification.

[0014] The technical solution provided by this invention has the following beneficial effects: The catalyst prepared by the method of the present invention has highly dispersed active metals on the catalyst surface and good structural stability. The catalyst exhibits strong reactivity, good reduction behavior over a wider temperature window, and has a wide denitrification reaction temperature window with better low-temperature denitrification activity. Detailed Implementation

[0015] To facilitate understanding of the present invention, the following description, in conjunction with embodiments, will further illustrate the invention. It should be understood that the following embodiments are merely for a better understanding of the invention and do not imply that the invention is limited to these embodiments.

[0016] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The term "and / or" may be used herein to include any and all combinations of one or more of the associated listed items.

[0017] This invention provides a method for preparing a silica-modified Ce / TiO2 catalyst. The catalyst comprises a support and Ce oxide supported on the support. Based on the total mass of the catalyst, the Ce loading is 8-12 wt% (e.g., 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, etc.). The support comprises TiO2 and SiO2 in a molar ratio of 1-4:1 (e.g., 1:1, 2:1, 3:1, 4:1, etc.). The preparation method includes the following steps: S1. Dissolve titanium tetrachloride in concentrated hydrochloric acid with a concentration of 36-38 wt% (e.g., 36 wt%, 37 wt%, 38 wt%, etc.), and then dilute with deionized water to obtain a titanium salt solution. A silicon salt solution obtained by dissolving a soluble inorganic salt of silicon in deionized water is mixed evenly with the titanium salt solution to obtain a mixed solution. S2. Add ammonia water to the mixture at a rate of 1.5-3.5 mL / min (e.g., 1.5 mL / min, 2.5 mL / min, 3.5 mL / min, etc.) and stir to gradually raise the pH of the solution to 8-11 (e.g., 8, 9, 10, 11, etc.) to produce a precipitate; then age the solution; filter the resulting liquid to obtain a coprecipitate, and wash the coprecipitate with deionized water until no chloride ions are present; S3. The coprecipitate obtained in step S2 is dried and then calcined in air at 450-550°C (e.g., 450°C, 500°C, 550°C, etc.) to obtain the support; S4. The precursor salt of cerium metal oxide and the carrier are mixed in deionized water and heated in a water bath at 60-90°C (e.g., 60, 70, 80, 90°C, etc.) with stirring to evaporate excess water; thus obtaining the composite material. S5. The composite material is dried, then ground and sieved to obtain a powder material; the obtained powder material is calcined in air at 450-600℃ (e.g., 450℃, 500℃, 550℃, 600℃, etc.) to obtain the catalyst.

[0018] The preparation method of this invention involves dissolving titanium tetrachloride in concentrated hydrochloric acid of a specific concentration, diluting it, and then mixing it with a silicon salt solution. Ammonia is then slowly added to the mixture at a rate of 1.5-3.5 mL / min, gradually increasing the pH to 8-11. After slow precipitation, the mixture is aged, washed to remove chloride ions, and then dried and calcined to obtain the composite support, with the molar ratio of TiO2 to SiO2 controlled at 1-4:1. Next, a Ce loading process is performed. During loading, the Ce precursor salt and the support are mixed in deionized water, and the water is slowly evaporated in a water bath at a low temperature (60-90°C) to remove moisture. The mixture is then dried again, ground, sieved, and calcined again to obtain the catalyst, with the Ce loading controlled at 8-12 wt%. The catalyst prepared using the above-mentioned specific process sequence, process, and process conditions, with the above-mentioned material composition ratio, exhibits highly dispersed active metals on the catalyst surface, a more stable structure, strong reactivity, good reduction behavior over a wider temperature window, a wider denitrification reaction temperature window, and better low-temperature denitrification activity.

[0019] In step S1, titanium tetrachloride is first dissolved in concentrated hydrochloric acid, then diluted with water, and then mixed with a silicon salt solution; wherein the concentration of concentrated hydrochloric acid is 36-38 wt%. The inventors have found that dissolving titanium tetrachloride in concentrated hydrochloric acid before subsequent operations effectively inhibits the hydrolysis and aggregation of the titanium source, facilitates uniform loading of the active metal, and helps to obtain a catalyst with better denitrification catalytic performance. Using a preferred concentration of hydrochloric acid further improves the catalyst's denitrification performance.

[0020] Preferably, in step S2, the concentration of the ammonia water is 10-30 wt%, such as 10 wt%, 20 wt%, 30 wt%, etc.

[0021] In step S2, the ammonia water is added at a rate of 1.5-3.5 mL / min, allowing the solution pH to gradually increase to 8-11, promoting slow precipitation. This improves the uniformity of the support and enhances the denitrification catalytic performance of the final catalyst. Preferably, in step S2, the aging process is carried out under stirring for 6-8 hours. This prolonged aging also helps improve the uniformity of the support, further enhancing the denitrification catalytic performance of the catalyst.

[0022] Preferably, in step S1, the dilution with deionized water is performed to dilute the solution to a titanium ion concentration of 0.3-0.7 mol / L. In some examples, the volume of deionized water used for dilution is 8-12 times the volume of concentrated hydrochloric acid used. This dilution can suppress Ti... 4+Rapid hydrolysis prevents particle agglomeration; ensures thorough and uniform mixing of titanium and silicon salts; furthermore, it helps to precisely control the ammonia co-precipitation process; this dilution operation is well-suited for industrial production and offers better economic benefits.

[0023] Preferably, the soluble inorganic salt of silicon is one or more of sodium metasilicate, sodium silicate, potassium silicate, and their hydrates. Compared with the use of organosilicon salts, the inorganic silicon salt used in this invention is not only cheaper, but also less likely to produce volatile organic compounds and potentially leave carbon residues. In addition, the use of organosilicon salts requires harsh hydrolysis and condensation conditions. This invention uses an inorganic silicon source and prepares the catalyst according to the specific process and conditions of this invention, which ensures the low-temperature denitrification activity of the catalyst while taking into account better process feasibility and economy.

[0024] The precursor salt of the cerium metal oxide is one or more of cerium nitrate, cerium chloride, cerium acetate, and their hydrates.

[0025] Preferably, in step S3, the drying temperature is 110-130°C, and the drying time is, for example, 11-13 hours; In this application, in step S3, the support is calcined in air at 450-550°C to obtain a support; then in step S5, it is calcined again in air at 450-600°C to obtain a catalyst. Performing calcination at specific temperatures in two separate stages facilitates the acquisition of a more structurally stable catalyst, and the resulting catalyst exhibits excellent denitrification catalytic performance.

[0026] Preferably, in step S3 or step S5, the calcination time is 1.5-2.5 hours. Preferably, in step S5, the drying temperature is 110-130°C, and the drying time is, for example, 11-13 hours. Preferably, in step S5, the sieving is performed through a 50-80 mesh sieve.

[0027] Preferably, in step S4, the ratio of the mass of the carrier to the volume of the deionized water is 1:40–1:60 g / mL.

[0028] Preferably, in step S1, the silicon salt solution is added dropwise to the titanium salt solution and stirred to mix evenly to obtain the mixture; In step S4, the precursor salt of cerium metal oxide and the support are mixed in deionized water and stirred in a water bath at 60-90°C to slowly evaporate excess water. The inventors have found that slow evaporation at this temperature facilitates a more uniform dispersion of the active metal in the catalyst, thus improving the catalyst's denitrification catalytic performance. Using a water bath for evaporation avoids localized overheating, boiling, localized agglomeration of cerium salts, or premature decomposition, and allows for slow evaporation while stirring, resulting in a more uniform loading. Specifically, in step S4, the evaporation continues until the material becomes viscous.

[0029] This invention first prepares a silicon-titanium composite support through co-precipitation, and then loads Ce to prepare a catalyst through a two-step method. The inventors found that if Ce is introduced in the co-precipitation step, that is, if the catalyst of this invention is prepared by a one-step co-precipitation method, it will lead to a decrease in the specific surface area of ​​the catalyst, a deterioration of the pore structure, a weakening of acidity, and a decrease in denitrification activity and resistance to sulfur and water. The low-temperature denitrification activity of the catalyst will also decrease significantly.

[0030] In a preferred embodiment, the Ce loading is 11-12 wt%, and the support comprises TiO2 and SiO2 in a molar ratio of 3-4:1; the calcination temperature in step S3 is 500-550℃; the water bath heating temperature in step S4 is 80-90℃; and the calcination temperature in step S5 is 550-600℃. The catalyst prepared in this preferred manner exhibits superior low-temperature denitrification activity, excellent dispersion of the active components, a wider temperature range within which denitrification efficiency reaches over 90%, and superior low-temperature denitrification activity.

[0031] The Ce / TiO2-SiO2 catalyst prepared in this application has a simple preparation process, the inorganic Si source is widely available and easy to obtain, and the cost is low. CeOx is highly dispersed on the surface of the titanium dioxide-silica (TiO2-SiO2) catalyst, exhibiting strong reactivity and good reduction behavior over a wider temperature window.

[0032] Another aspect of the present invention provides a silica-modified Ce / TiO2 catalyst, comprising a support and Ce oxide supported on the support; the Ce loading is 8-12 wt% based on the total mass of the catalyst, and the support comprises TiO2 and SiO2 in a molar ratio of 1-4:1; Preferably, the catalyst is prepared using the preparation method described above.

[0033] In another aspect, the present invention provides the application of the catalyst prepared by the method described above or the catalyst described above in the field of SCR flue gas denitrification.

[0034] The present invention will be further illustrated by the following embodiments, but it should not be construed as the present invention being limited to these embodiments.

[0035] Where specific experimental steps or conditions are not specified in the examples, the corresponding conventional experimental steps or conditions in this technical field can be followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0036] Example 1 Preparation of the composite support TiO2-SiO2: ① Weigh 19g of titanium tetrachloride (TiCl4), slowly add it to 20mL of concentrated hydrochloric acid (mass fraction 37%), stir to dissolve, and then dilute with deionized water to 200mL to obtain a titanium salt solution; Take another 14.2g of sodium metasilicate (Na2SiO3·9H2O), dissolve it in 100mL of deionized water to obtain a silicon salt solution; Slowly add the silicon salt solution dropwise into the titanium salt solution and stir continuously for 30 minutes until the mixture is homogeneous, thus obtaining a mixed solution. ② Add 25% ammonia solution dropwise to the above mixture at a rate of 2 mL / min, while stirring at 300 r / min, until the pH of the solution rises to 8.5, then stop adding ammonia solution; continue stirring and aging for 7 hours, then filter to obtain the coprecipitate; wash the precipitate repeatedly with deionized water until no white precipitate is produced when 0.1 mol / L silver nitrate aqueous solution is added to the washing solution (i.e., no chloride ion residue). ③ The washed precipitate was placed in a 120℃ oven and dried for 12 hours. After being removed, it was placed in a muffle furnace and heated to 500℃ in air at a heating rate of 5℃ / min. The temperature was held for 2 hours and then naturally cooled to obtain a TiO2-SiO2 composite support. The molar ratio of TiO2 to SiO2 in the composite support was 2:1. Ce-supported catalyst preparation: ①Cerium nitrate hexahydrate (Ce(NO3)3) Using 6H2O as a precursor, weigh 0.35g of the precursor and add it to a beaker containing 1.0g of the above TiO2-SiO2 composite support. Then add 50mL of deionized water and stir to completely dissolve the precursor. ② Place the beaker in a 75℃ constant temperature water bath, maintain a stirring speed of 200r / min, slowly evaporate the water until the system becomes viscous, and then stop the water bath. ③ Place the viscous substance in a 120℃ oven and bake for 12 hours. After taking it out, grind it and pass it through a 60-mesh standard sieve to obtain a uniform powder. ④ The powder was placed in a muffle furnace and heated to 500°C in air at a heating rate of 5°C / min. After calcination for 2 hours and natural cooling, Ce / TiO2-SiO2 catalyst (referred to as sample-1) was obtained. The Ce loading in the obtained catalyst was 10 wt%.

[0037] Performance testing The SCR denitrification activity of the catalyst was evaluated using a fixed-bed reactor. The reaction conditions were: simulated flue gas composition of NO 500 ppm, NH3 500 ppm, O2 6 vol%, SO2 0.03 vol%, with the balance being N2 as the equilibrium gas; and a space velocity of 30,000 h⁻¹. - ¹, The reaction temperature range is 150-400℃. Test results: Sample-1 exhibited a denitrification efficiency ≥90% within the temperature range of 200-350℃, and a denitrification efficiency exceeding 95% at 250-300℃. H2-TPR testing showed that the CeOx reduction peak temperature was 280℃, which is 40℃ lower than that of conventional Ce / TiO2 catalysts (reduction peak temperature 320℃), demonstrating stronger reduction activity. The CeOx dispersion on the support surface was 83%.

[0038] Example 2 Preparation of the composite support TiO2-SiO2: ① Weigh 9.5g TiCl4, dissolve it in 15mL concentrated hydrochloric acid (37wt%), and then dilute it with deionized water to 150mL to obtain a titanium salt solution; Weigh out 14.2g of Na2SiO3 9H2O is dissolved in 100mL of deionized water to obtain a silicon salt solution; The silica salt solution was slowly added dropwise to the titanium salt solution, and the mixture was stirred for 30 minutes to obtain a mixed solution. ② Add 25wt% ammonia solution dropwise to the above mixture at a rate of 1.5 mL / min until the solution pH = 8.0, then stop adding ammonia solution; continue stirring and aging at 300 r / min for 6 hours, filter, and wash with deionized water until no Cl is found in the washing solution. - Residue. ③ The washed precipitate was dried at 110℃ for 13 hours, and then heated to 450℃ in air at a heating rate of 5℃ / min in a muffle furnace, held for 2.5 hours, and naturally cooled to obtain a TiO2-SiO2 composite support with a molar ratio of TiO2 to SiO2 of 1:1. Ce-supported catalyst preparation: ① Weigh out 0.22g Ce(NO3)3 Add 0.8g of composite carrier to 6H2O, add 40mL of deionized water, stir to dissolve, and obtain the solution. ②Then the above liquid is slowly evaporated in a 60°C water bath with stirring at a stirring rate of 200 r / min until the system becomes viscous. ③ Bake the viscous material at 110℃ for 13 hours, then grind it and pass it through a 50-mesh sieve to obtain a uniform powder. ④ The powder was placed in a muffle furnace and heated to 450°C in air at a heating rate of 5°C / min. The mixture was calcined for 2.5 hours and then allowed to cool naturally to obtain the Ce / TiO2-SiO2 catalyst (referred to as sample-2). The Ce loading in the obtained catalyst was 8 wt%.

[0039] Performance testing The test conditions were the same as in Example 1. Test results: Sample-2 had a denitrification efficiency of ≥90% in the temperature range of 220-360℃ and a denitrification efficiency of ≥94% in the temperature range of 280-320℃; the CeOx reduction peak temperature was 295℃, and the dispersibility test showed that the CeOx dispersion on the carrier surface was 82% (calculated by XRD extrapolation). Example 3 Preparation of the composite support TiO2-SiO2: ① Weigh 38g of TiCl4, dissolve it in 30mL of concentrated hydrochloric acid (37wt%), and dilute it with deionized water to 250mL to obtain a titanium salt solution; Weigh out 14.2g of Na2SiO3 9H2O is dissolved in 50 mL of deionized water to obtain a silicon salt solution; The silica salt solution was slowly added dropwise to the titanium salt solution, and the mixture was stirred for 30 minutes to obtain a mixed solution. ② Add 25wt% ammonia solution dropwise to the above mixture at a rate of 2.5 mL / min until the solution pH = 9.0. Stop adding ammonia solution, maintain stirring at 300 r / min for aging for 8 hours, filter, and wash with deionized water until no Cl is visible. - Residue. ③ The washed precipitate was dried at 130℃ for 11 hours, then placed in a muffle furnace and heated to 550℃ in air at a rate of 5℃ / min. The calcination was maintained at this temperature for 1.5 hours, and after natural cooling, the TiO2-SiO2 composite support was obtained. The molar ratio of TiO2 to SiO2 in the composite support was 4:1.

[0040] Ce-supported catalyst preparation ① Weigh out 0.5g of Ce(NO3)3 Add 1.2g of composite carrier to 6H2O, add 60mL of deionized water and stir to dissolve, thus obtaining the solution. ②Then the above liquid is slowly evaporated in a 90°C water bath with stirring at a rate of 200 r / min until the system becomes viscous. ③ Bake the viscous material at 130℃ for 11 hours, then grind it and pass it through an 80-mesh sieve to obtain a uniform powder. ④ The powder was placed in a muffle furnace and heated to 600°C in air at a heating rate of 5°C / min, calcined for 1.5 hours, and then naturally cooled to obtain Ce / TiO2-SiO2 catalyst sample-3. The Ce loading in the obtained catalyst was 12 wt%.

[0041] Performance testing The test conditions were the same as in Example 1. Test results: Sample-3 showed a denitrification efficiency of ≥90% in the temperature range of 180-340℃ and a denitrification efficiency of ≥96% in the temperature range of 240-290℃; the CeOx reduction peak temperature was 270℃ and the dispersion was 85%, showing a wider active temperature window and stronger reduction performance. Comparative Example 1 (Ce / TiO2 catalyst prepared by conventional method, denoted as Ref-Cat) Conventional TiO2 support preparation: TiCl4 is directly dissolved in deionized water, and 25% ammonia solution is rapidly added dropwise until the pH reaches 8.5. After aging for 2 hours, the solution is washed with deionized water and then calcined at 500℃ for 2 hours to obtain the TiO2 support. Conventional Ce loading: 0.35g Ce(NO3)3 6H₂O was dissolved in 50 ml of water, and then 1.0 g of TiO₂ support was added. The mixture was then dried directly at 80 °C and calcined at 500 °C for 2 hours to obtain the Ce / TiO₂ catalyst (denoted as sample-4). The Ce loading in this catalyst was 10 wt%. Performance comparison: Sample-4 has a denitrification efficiency of ≥90% in the temperature range of 250-330℃ (only 80℃ wide), with a maximum denitrification efficiency of 92%; the CeOx reduction peak temperature is 320℃, and the CeOx dispersion on the carrier surface is 65%.

[0042] Comparative Example 2 The procedure was carried out in accordance with Example 1, except that the molar ratio of TiO2 to SiO2 in the obtained composite carrier was 5:1.

[0043] Performance testing: Test conditions were the same as in Example 1. Test results: The obtained catalyst achieved a denitrification efficiency of ≥90% in the temperature range of 240-330℃, with a maximum denitrification efficiency of 91%; the CeOx reduction peak temperature was 310℃, and the dispersibility test showed that the CeOx dispersion on the support surface was 70%.

[0044] Comparative Example 3 The procedure was carried out in accordance with Example 1, except that in step ① of preparing the composite carrier, the concentration of the concentrated hydrochloric acid used was 10 wt%.

[0045] Performance testing: Test conditions were the same as in Example 1. Test results: The obtained catalyst achieved a denitrification efficiency of ≥90% in the temperature range of 230-320℃, with a maximum denitrification efficiency of 90%; the CeOx reduction peak temperature was 315℃, and the dispersibility test showed that the CeOx dispersion on the support surface was 68%.

[0046] Comparative Example 4 The procedure was carried out in accordance with Example 1, except that in step ② of preparing the composite carrier, the drop rate of ammonia was 5 ml / min.

[0047] Performance testing: Test conditions were the same as in Example 1. Test results: The obtained catalyst achieved a denitrification efficiency of ≥90% in the temperature range of 235–325℃, with a maximum denitrification efficiency of 90.5%; the CeOx reduction peak temperature was 305℃, and the dispersibility test showed that the CeOx dispersion on the support surface was 72%.

[0048] Comparative Example 5 The procedure was carried out in accordance with Example 1, except that in step ② of preparing the catalyst on Ce support, evaporation was performed at 100°C.

[0049] Performance testing: Test conditions were the same as in Example 1. Test results: The obtained catalyst achieved a denitrification efficiency of ≥90% in the temperature range of 225–315℃, with a maximum denitrification efficiency of 91.5%; the CeOx reduction peak temperature was 300℃, and the dispersibility test showed that the CeOx dispersion on the support surface was 75%. Summary of the effects of the examples The Ce / TiO2-SiO2 catalysts prepared in Examples 1-3 of this invention have the following advantages compared with Ref-Cat prepared by conventional methods: It has a wider active temperature window (the temperature range for ≥90% denitrification efficiency reaches 140-180℃), which is suitable for the complex operating conditions of SCR flue gas denitrification. CeOx dispersion increased by 26%-31%, and reduction activity was significantly enhanced (reduction peak temperature decreased by 30-50℃). The SiO2 source in the preparation process is common sodium metasilicate, which costs only 1 / 3 of the conventional titanium-based carrier raw materials. Moreover, the process steps are simple and the parameters are controllable, making it suitable for industrial-scale production.

[0051] Compared with the comparative example, the temperature window for denitrification efficiency ≥90% of the present invention is significantly wider, with a temperature range spanning more than 140℃, and the highest denitrification efficiency is higher than 92%. The CeOx reduction peak temperature is significantly lower, and the CeOx dispersion on the carrier surface is high.

[0052] The physicochemical properties of the catalysts obtained in the examples and comparative examples were characterized as follows: The catalyst was characterized using BET (Body Surface Area and Porosity Analyzer), XRD (X-ray Diffractometer), and XPS (X-ray Photoelectron Spectrometer). The results of the examples and some comparative examples are shown in the table below:

[0053] Long-term stability testing: Long-term stability tests were conducted on catalyst sample-3 prepared in Example 3. The reaction conditions were basically the same as those for the performance test in Example 1, except that the reaction temperature was set at 280°C and the space velocity at 30,000 h⁻¹. - ¹ After running continuously for 100 hours, the denitrification efficiency was tested, and the results are shown in the table below:

[0054] Stability conclusion: After 100 hours of continuous operation, the denitrification efficiency of Sample-3 decreased by only 1.7%, which is far lower than that of conventional Ce / TiO2 catalysts (4-6% decrease after 100 hours under the same conditions), indicating that the catalyst has excellent structural stability and anti-sintering ability. The stability test results of other embodiments are similar to those of Example 3, and will not be repeated.

[0055] It is readily understood that the above embodiments are merely illustrative examples for clear explanation and do not imply that the invention is limited thereto. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a silica-modified Ce / TiO2 catalyst, characterized in that, The catalyst comprises a support and Ce oxide supported on the support. Based on the total mass of the catalyst, the Ce loading is 8-12 wt%. The support comprises TiO2 and SiO2 in a molar ratio of 1-4:

1. The preparation method includes the following steps: S1. Dissolve titanium tetrachloride in concentrated hydrochloric acid with a concentration of 36-38 wt%, and then dilute with deionized water to obtain a titanium salt solution. A silicon salt solution obtained by dissolving a soluble inorganic salt of silicon in deionized water is mixed evenly with the titanium salt solution to obtain a mixed solution. S2. Add ammonia water to the mixture at a rate of 1.5-3.5 mL / min and stir to gradually raise the pH of the solution to 8-11, producing a precipitate; then age the solution; filter the resulting liquid to obtain a coprecipitate, and wash the coprecipitate with deionized water. S3. The coprecipitate obtained in step S2 is dried and then calcined in air at 450-550°C to obtain the support; S4. The precursor salt of cerium metal oxide and the carrier are mixed in deionized water and heated in a water bath at 60-90°C with stirring to evaporate excess water. To obtain composite materials; S5. The composite material is dried, then ground and sieved to obtain a powder; the obtained powder is calcined in air at 450-600°C to obtain the catalyst.

2. The preparation method according to claim 1, characterized in that, In step S2, the concentration of the ammonia water is 10-30 wt%.

3. The preparation method according to any one of claims 1-2, characterized in that, In step S1, the dilution with deionized water is to dilute the solution to a titanium ion concentration of 0.3-0.7 mol / L; Alternatively, in step S1, the volume of deionized water used for dilution is 8-12 times the volume of concentrated hydrochloric acid.

4. The preparation method according to any one of claims 1-3, characterized in that, The soluble inorganic salt of silicon is one or more of sodium metasilicate, sodium silicate, potassium silicate and their hydrates; The precursor salt of the cerium metal oxide is one or more of cerium nitrate, cerium chloride, cerium acetate, and their hydrates.

5. The preparation method according to any one of claims 1-4, characterized in that, In step S2, the aging process involves aging for 6-8 hours under stirring.

6. The preparation method according to any one of claims 1-5, characterized in that, In step S3, the drying temperature is 110-130℃, and the drying time is, for example, 11-13 hours. And / or, in step S3 or step S5, the calcination time is 1.5-2.5h; And / or, in step S5, the drying temperature is 110-130°C, and the drying time is, for example, 11-13 hours; And / or, in step S5, the sieving is performed through a 50-80 mesh sieve.

7. The preparation method according to any one of claims 1-6, characterized in that, In step S4, the ratio of the mass of the carrier to the volume of the deionized water is 1:40–1:60 g / mL.

8. The preparation method according to any one of claims 1-7, characterized in that, In step S1, the silicon salt solution is added dropwise to the titanium salt solution and stirred to mix evenly to obtain the mixture. And / or, in step S4, the evaporation is carried out until the material becomes viscous; And / or, the Ce loading is 11-12 wt%, and the support comprises TiO2 and SiO2 in a molar ratio of 3-4:1; the calcination temperature of step S3 is 500-550℃; the water bath heating temperature of step S4 is 80-90℃; and the calcination temperature of step S5 is 550-600℃.

9. A silica-modified Ce / TiO2 catalyst, characterized in that, The catalyst includes a support and Ce oxide supported on the support; the Ce loading is 8-12 wt% based on the total mass of the catalyst, and the support comprises TiO2 and SiO2 in a molar ratio of 1-4:

1. Preferably, the catalyst is prepared by the preparation method according to any one of claims 1-8.

10. The application of the catalyst prepared by the method according to any one of claims 1-8 or the catalyst according to claim 9 in the field of SCR flue gas denitrification.

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