A mesoporous cerium-based composite oxide denitration catalyst with wide temperature window and a preparation method thereof

Abstract

The present application relates to a kind of wide temperature window mesoporous rare earth cerium-based composite oxide denitration catalyst and preparation method, belong to atmospheric pollution control field.The method is first constructed by inducing self-assembly method cerium-based inorganic organic hybrid material, then high-temperature heat treatment is carried out, and new mesoporous cerium-based composite oxide catalyst is obtained.The crystal form of the composite oxide catalyst is titanium ore type titanium dioxide structure, active component and catalytic component are amorphous structure, mesoporous structure can expose more defects and active site, the introduction of catalytic component can increase the surface acidity of catalyst, enhance the redox performance of catalyst, active component cerium, catalytic component tungsten and aluminum and carrier component titanium solid solution coupling, improve the structural stability of catalyst, preparation ensures that cerium-based composite oxide maintains high efficient stable denitration performance and resistance to water sulfur poisoning ability in low, medium and high wide temperature interval.

Description

Technical Field

[0001] This invention relates to a denitrification catalyst and its preparation method, and more particularly to a method for preparing a wide-temperature-window mesoporous cerium-based composite oxide denitrification catalyst, belonging to the field of air pollution control. Background Technology

[0002] Nitrogen oxides (NO) x NOx is one of the major air pollutants emitted from industrial production and daily life. Its release into the atmosphere causes serious environmental pollution problems, such as acid rain, chemical fog, and ozone generation. NOx emissions from mobile sources such as vehicles and ships... x The limits for NOx emissions are becoming increasingly stringent. Studies have shown that NOx emissions from ships... x It accounts for 14-15% of the world's total emissions. Therefore, denitrification of flue gas is of great environmental significance. Currently, natural gas / diesel dual-fuel ship engines have the advantages of low carbon emissions and environmental protection, and are an important technological development direction for carbon reduction in the shipbuilding industry. Selective catalytic reduction (SCR) of NH3 has become the mainstream denitrification technology due to its maturity and high efficiency, and its core lies in the development of high-efficiency catalysts and their adaptability to operating conditions. However, traditional commercial vanadium-based denitrification catalysts have problems such as narrow activity temperature windows and poor resistance to poisoning, making it difficult to meet the requirements of NO3-containing flue gas from current ships. x Treatment Requirements. Rare earth elements have shown promising application prospects in the field of denitrification due to their excellent oxygen storage / release and redox properties. The article in Appl. Catal. B: Environ. 2017, 203: 199–209 uses ordered mesoporous SiO2 (KIT-6) as a hard template to prepare mesoporous Ce-based composite oxides with an activity temperature window of 200-350℃. However, this method has a complex preparation process, and the stability window needs further improvement. The article in Appl. Catal. B: Environ. 2017, 201: 461–469 uses microporous molecular sieve SSZ-13 as a support, which can broaden the catalyst's activity temperature window. However, the preparation process of SSZ-13 is complex, has low hydrothermal stability, and is costly, limiting its large-scale application. Therefore, developing efficient and economical vanadium-free SCR denitrification catalysts with a wide temperature window to adapt to the operating conditions and speed characteristics of marine engines has become a top priority in the field of denitrification. Summary of the Invention

[0003] Addressing the issues of narrow activity temperature windows and low resistance to poisoning in current commercial SCR denitration catalysts, this invention provides a method for preparing a wide-temperature-window mesoporous vanadium-cerium-based composite oxide denitration catalyst. Another objective of this invention is to provide the wide-temperature-window mesoporous vanadium-cerium-based composite oxide denitration catalyst prepared by the above method. A further objective is to provide applications for the aforementioned wide-temperature-window mesoporous vanadium-cerium-based composite oxide denitration catalyst. This composite catalyst possesses a high specific surface area, large pore volume, and a three-dimensionally interconnected mesoporous structure, exposing numerous active sites and surface defects. The introduction of promoters increases the catalyst's acidity and enhances its redox capabilities. Multi-component element solid-solution coupling improves the catalyst's stability, achieving good denitration activity over a wide temperature range and excellent resistance to water and sulfur poisoning. This preparation method is low-cost, simple in process, and suitable for large-scale applications.

[0004] The technical solution of this invention is as follows: Based on the current research status of SCR denitrification, this invention provides a wide-temperature-window multi-metal cerium-based composite oxide denitrification catalyst and its preparation method. The rare-earth cerium-based organic-inorganic hybrid material is formed by the self-assembly and gelation of metal ions, long-chain organic acid ligands, and surfactants. During the organic-inorganic self-assembly process, the various metal element components are uniformly distributed, forming an ordered micelle structure, thus synthesizing the cerium-based organic-inorganic hybrid material. The long-chain organic acid ligands combine with metal ions through positive and negative ion interactions, and also act as pH adjusters to regulate the solution pH, controlling the electrostatic interactions between metal ions, long-chain organic acid ligands, and nonionic surfactants, forming an organic-inorganic hybrid material with a specific ordered structure. Then, through high-temperature thermal decomposition processes under different atmospheres, the surfactant acts as a template to generate a uniform mesoporous structure, thus preparing a mesoporous cerium-tungsten-aluminum-titanium composite oxide denitrification catalyst. The composite oxide catalyst has an anatase titanium dioxide structure. The active component, cerium dioxide, the co-catalyst components, and aluminum oxide are in an amorphous state. The mesoporous structure provides a high specific surface area and a large pore volume, exposing more defects and active sites. The multi-metal components achieve solid solution coupling during high-temperature processes to prevent the anatase titanium dioxide structure from transforming into the inactive rutile phase, thereby improving the structural stability of the catalyst. The introduction of the co-catalyst components increases the surface acidity of the catalyst and enhances its redox performance. The mesoporous cerium-based composite catalyst exhibits high efficiency in denitrification, stability, and resistance to poisoning over a wide temperature range of low, medium, and high.

[0005] The specific technical solution of this invention is as follows: a method for preparing a wide-temperature-window mesoporous cerium-based composite oxide denitration catalyst, the specific steps of which are as follows:

[0006] (1) Weigh out the long-chain organic acid ligand and surfactant and dissolve them in a solvent to obtain solution A;

[0007] (2) Add cerium source, tungsten source, aluminum source and titanium source to solution A in sequence and stir until uniform to obtain mixture B; (3) React mixture B at 50-100℃ for 1-7 days to obtain cerium-based organic-inorganic hybrid material;

[0008] (4) The cerium-based organic-inorganic hybrid material obtained in step (3) is first carbonized at 300-500℃ for 1-5 hours, and then oxidized at 500-700℃ for 1-5 hours to obtain a wide temperature window mesoporous cerium-based composite oxide denitration catalyst.

[0009] The solvent in step (1) is preferably one of water, methanol or ethanol; the long-chain organic acid ligand is polyacrylic acid (number average molecular weight: 2000-10000); and the surfactant is one of nonionic polyepoxyalkylene copolymers F108, F127 or P123.

[0010] The preferred cerium source in step (2) is one of cerium nitrate or cerium chloride; the tungsten source is one of ammonium metatungstate or tungsten chloride; the aluminum source is one of aluminum nitrate, aluminum isopropoxide or aluminum chloride; and the titanium source is one of tetrabutyl titanate, isopropyl titanate, titanium tetrachloride or metatitanic acid.

[0011] In step (2), the preferred molar ratio of surfactant, long-chain organic acid ligand, cerium, tungsten, aluminum and titanium is (0.01~0.05):(0.007~0.025):(0.1~0.5):(0.3~0.8):(0.01~0.1):1.

[0012] The preferred atmosphere for the carbonization process in step (4) is either nitrogen or hydrogen; the preferred atmosphere for the oxidation process is either oxygen or air.

[0013] This invention also provides a wide-temperature-window mesoporous cerium-based composite oxide denitration catalyst prepared by the above method, characterized in that: the catalyst has an anatase titanium dioxide crystal structure, and the active component cerium dioxide, the co-catalyst components tungsten oxide and alumina are all amorphous structures. The molar ratio of Ce, W, Al and Ti in this catalyst is (0.1–0.5):(0.3–0.8):(0.01–0.1):1. The catalyst has a high specific surface area, a large pore volume, and exposes more defects and active sites. Doping of the co-catalyst components significantly increases the surface acidity of the catalyst, enhances its redox performance, and the coupling solid solution between components improves the structural stability of the catalyst.

[0014] This invention also provides the above-mentioned wide-temperature-window cerium-based composite oxide denitration catalyst for NO x Applications in governance.

[0015] The wide-temperature-window mesoporous cerium-based composite oxide denitration catalyst prepared in this invention was tested using a fixed-bed microreactor. The denitration performance test conditions were: NO... x The initial concentrations were 1000 ppm for NH3, 1000 ppm for O2, 1% for water vapor, 50 ppm for SO2, and 30,000 h⁻¹. -1 The reaction test temperature range is 180-520℃, and the test time is 2 hours.

[0016] Beneficial effects:

[0017] This preparation method is simple and uses inexpensive raw materials. The porous cerium-based organic-inorganic hybrid material ensures that the cerium, tungsten, aluminum, and titanium elements are uniformly and stably arranged in the solid-solution composite oxide structure, enhancing the catalyst's structural stability. Simultaneously, this composite material possesses a high surface area, large pore volume, and significant surface acidity, exhibiting excellent resistance to SO2 poisoning. Furthermore, the mesoporous structure increases the catalyst's surface roughness, which is beneficial for improving its water resistance and activity. As a denitrification catalyst, this composite material demonstrates highly efficient denitrification performance under complex flue gas conditions, possessing significant practical application value. Attached Figure Description

[0018] Figure 1 This is the X-ray diffraction pattern of Example 1;

[0019] Figure 2 This is the nitrogen adsorption-desorption curve of Example 1;

[0020] Figure 3 The graph shows the denitrification efficiency of the denitrification catalysts prepared in Examples 1-5 and Comparative Example 1. Detailed Implementation

[0021] The present invention will be further described below with reference to embodiments, but the scope of protection of the present invention is not limited thereto:

[0022] The following non-limiting embodiments are intended to enable those skilled in the art to more fully understand the invention, but do not limit the invention in any way.

[0023] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; the reagents and materials described are commercially available unless otherwise specified.

[0024] Example 1

[0025] (1) Weigh 5.61g of surfactant F108 and 2.5g of polyacrylic acid (number average molecular weight of 10000) and dissolve them in methanol to obtain solution A;

[0026] (2) 2.08g of cerium nitrate hexahydrate, 5.95g of ammonium metatungstate, 0.14g of aluminum nitrate and 10.88g of tetrabutyl titanate were added to solution A in step (1) in sequence and stirred to obtain mixture B, wherein the molar ratio of F108, polyacrylic acid, cerium, tungsten, aluminum and titanium was 0.012:0.0078:0.15:0.75:0.02:1;

[0027] (3) The mixture B from step (2) was subjected to a self-assembly reaction at 100°C for 1 day to obtain cerium-based organic-inorganic hybrid material A;

[0028] (4) The cerium-based organic-inorganic hybrid material A from step (3) was first heat-treated at 350°C under a nitrogen atmosphere for 4 hours, and then treated at 550°C under an air atmosphere for 2 hours to obtain a mesoporous cerium-based composite oxide denitration catalyst A, wherein the molar ratio between CeO2, WO3, Al2O3 and TiO2 was 0.15:0.75:0.01:1. The X-ray diffraction pattern of the prepared denitration catalyst A is shown below. Figure 1 As shown, from Figure 1 As can be seen, catalyst A has an anatase titanium dioxide crystal structure, while the active component cerium dioxide and the co-catalyst components tungsten oxide and alumina have amorphous structures; the transmission electron microscope image of catalyst A is shown below. Figure 2 As shown, from Figure 2 As can be seen above, the structure of the mesoporous cerium-based composite oxide denitration catalyst A contains a large number of nanopore structures.

[0029] (5) The denitrification performance of mesoporous cerium-based composite oxide denitrification catalyst A was tested, simulating NO in flue gas. x (1000ppm), NH3 (1000ppm), O2 (10%), water vapor (1%), SO2 (50ppm), space velocity 30000h -1 The reaction time is 2 hours. The denitrification efficiency is 96-100% within the temperature range of 220-480℃. The denitrification performance of this catalyst is as follows: Figure 3 As shown.

[0030] Example 2

[0031] (1) Weigh 8.06g of surfactant F127 and 2.4g of polyacrylic acid (number average molecular weight of 5000) and dissolve them in water to obtain solution A;

[0032] (2) Add 3.55g cerium chloride, 4.76g ammonium metatungstate, 0.38g aluminum chloride and 9.09g isopropyl titanate to solution A in step (1) in sequence, and stir to obtain mixture B, wherein the molar ratio of F127, polyacrylic acid, cerium, tungsten, aluminum and titanium is 0.02:0.015:0.45:0.6:0.09:1;

[0033] (3) The mixture B from step (2) was subjected to a self-assembly reaction at 55°C for 6 days to obtain cerium-based organic-inorganic hybrid material B;

[0034] (4) The cerium-based organic-inorganic hybrid material B from step (3) is first heat-treated with hydrogen at 450°C for 3 hours, and then heat-treated with oxygen at 650°C for 1 hour to obtain mesoporous cerium-based composite oxide denitration catalyst B, wherein the molar ratio between CeO2, WO3, Al2O3 and TiO2 is 0.45:0.60:0.045:1.

[0035] (5) The denitrification performance of mesoporous cerium-based composite oxide denitrification catalyst B was tested, simulating NO in flue gas. x (1000ppm), NH3 (1000ppm), O2 (10%), water vapor (1%), SO2 (50ppm); space velocity is 30000h -1 The reaction time is 2 hours. The denitrification efficiency is 94-100% within the temperature range of 240-500℃. The denitrification performance of this catalyst is as follows: Figure 3 As shown.

[0036] Example 3

[0037] (1) Weigh 8.35g of surfactant P123 and 3.2g of polyacrylic acid (number average molecular weight of 10000) and dissolve them in water to obtain solution A;

[0038] (2) Add 2.37g cerium chloride, 3.96g ammonium metatungstate, 0.33g isopropanol and 6.08g titanium tetrachloride to the mixture A in step (1) in sequence, and stir to obtain mixture B, wherein the molar ratio of P123, polyacrylic acid, cerium, tungsten, aluminum and titanium is 0.045:0.015:0.3:0.5:0.05:1;

[0039] (3) The mixture B from step (2) was subjected to a self-assembly reaction at 90°C for 2 days to obtain cerium-based organic-inorganic hybrid material C;

[0040] (4) The cerium-based organic-inorganic hybrid material from step (3) is first carbonized at 400°C in a nitrogen atmosphere for 3 hours, and then heat-treated at 600°C in an air atmosphere for 1.5 hours to obtain mesoporous cerium-based composite oxide denitration catalyst C, wherein the molar ratio between CeO2, WO3, Al2O3 and TiO2 is 0.30:0.50:0.025:1.

[0041] (5) The denitrification performance of mesoporous cerium-based composite oxide denitrification catalyst C was tested, simulating NO in flue gas. x (1000ppm), NH3 (1000ppm), O2 (10%), water vapor (1%), SO2 (50ppm); space velocity is 30000h-1 The reaction time is 2 hours. The denitrification efficiency is 93-100% within the temperature range of 200-460℃. The denitrification performance of this catalyst is as follows: Figure 3 As shown.

[0042] Example 4

[0043] (1) Weigh 5.57g of surfactant P123 and 1.5g of polyacrylic acid (number average molecular weight of 2000) and dissolve them in methanol to obtain solution A;

[0044] (2) Add 2.78g of cerium nitrate hexahydrate, 4.44g of tungsten chloride, 0.27g of aluminum nitrate and 3.14g of metatitanic acid to solution A in step (1) in sequence, and stir to obtain mixture B, wherein the molar ratio of P123, polyacrylic acid, cerium, tungsten, aluminum and titanium is 0.03:0.023:0.2:0.35:0.04:1;

[0045] (3) The mixture B from step (2) was subjected to a self-assembly reaction at 80°C for 2.5 days to obtain cerium-based organic-inorganic hybrid material D;

[0046] (4) The cerium-based organic-inorganic hybrid material D from step (3) is first carbonized at 350°C in a hydrogen atmosphere for 2 hours, and then heat-treated at 550°C in an air atmosphere for 3 hours to obtain mesoporous cerium-based composite oxide denitrification catalyst D, wherein the molar ratio between CeO2, WO3, Al2O3 and TiO2 is 0.20:0.35:0.02:1. (5) The denitrification performance of the mesoporous cerium-based composite oxide denitrification catalyst D is tested by simulating NO in flue gas. x (1000ppm), NH3 (1000ppm), O2 (10%), water vapor (1%), SO2 (50ppm); space velocity is 30000h -1 The reaction time is 2 hours. The denitrification efficiency is 95-100% within the temperature range of 240-500℃. The denitrification performance of this catalyst is as follows: Figure 3 As shown.

[0047] Example 5

[0048] (1) Weigh 10.08g of surfactant F127 and 1.5g of polyacrylic acid (number average molecular weight of 5000) and dissolve them in ethanol to obtain solution A;

[0049] (2) 3.47g of cerium nitrate hexahydrate, 5.08g of tungsten chloride, 0.13g of aluminum chloride and 10.88g of tetrabutyl titanate were added to solution A in step (1) in sequence and stirred to obtain mixture B, wherein the molar ratio of F127, polyacrylic acid, cerium, tungsten, aluminum and titanium was 0.025:0.0094:0.25:0.4:0.03:1;

[0050] (3) The mixture B from step (2) was subjected to a self-assembly reaction at 70°C for 4 days to obtain cerium-based organic-inorganic hybrid material E;

[0051] (4) The cerium-based organic-inorganic hybrid material E from step (3) is first carbonized at 450°C under a nitrogen atmosphere for 1.5 hours, and then heat-treated at 600°C under an oxygen atmosphere for 2 hours to obtain a mesoporous cerium-based composite oxide denitration catalyst E, wherein the molar ratio between CeO2, WO3, Al2O3 and TiO2 is 0.25:0.4:0.15:1.

[0052] (5) The denitrification performance of mesoporous cerium-based composite oxide denitrification catalyst E was tested, simulating NO in flue gas. x (1000ppm), NH3 (1000ppm), O2 (10%), water vapor (1%), SO2 (50ppm); space velocity is 30000h -1 The reaction time is 2 hours. The denitrification efficiency is 96-100% within the temperature range of 220-480℃. The denitrification performance of this catalyst is as follows: Figure 3 As shown.

[0053] Comparative Example 1

[0054] (1) 2.08g of cerium nitrate hexahydrate, 5.95g of ammonium metatungstate, 0.14g of aluminum nitrate and 10.88g of tetrabutyl titanate were added to methanol in sequence and stirred to obtain mixture A, wherein the molar ratio of cerium, tungsten, aluminum and titanium was 0.15:0.75:0.02:1;

[0055] (2) The mixture A from step (1) is self-assembled at 100°C for 1 day to obtain cerium-based composite material F; (3) The cerium-based composite material F from step (2) is first heat-treated at 350°C under a nitrogen atmosphere for 4 hours, and then treated at 550°C under an air atmosphere for 2 hours to obtain cerium-based composite oxide denitration catalyst F, wherein the molar ratio between CeO2, WO3, Al2O3 and TiO2 is 0.15:0.75:0.01:1.

[0056] (4) The denitrification performance of the cerium-based composite oxide denitrification catalyst F was tested, simulating NO in flue gas. x (1000ppm), NH3 (1000ppm), O2 (10%), water vapor (1%), SO2 (50ppm); space velocity is 30000h -1 The reaction time is 2 hours. The denitrification efficiency is 96-99% within the temperature range of 300-400℃. The denitrification performance of this catalyst is as follows: Figure 3 As shown.

Claims

1. A method for preparing a wide-temperature-window mesoporous cerium-based composite oxide denitration catalyst, the specific steps of which are as follows: (1) Weigh out the long-chain organic acid ligand and the surfactant and dissolve them in the solvent to obtain solution A; wherein the long-chain organic acid ligand is polyacrylic acid; and the surfactant is one of the nonionic polyepoxyalkylene copolymers F108, F127 or P123. (2) Add the cerium source, tungsten source, aluminum source and titanium source to solution A in sequence and stir until homogeneous to obtain mixture B; wherein the molar ratio of surfactant, long-chain organic acid ligand, cerium, tungsten, aluminum and titanium is (0.01~0.05): (0.007~0.025): (0.1~0.5): (0.3~0.8): (0.01~0.1): 1; (3) React the mixture B at 50~100℃ for 1-7 days to obtain cerium-based organic-inorganic hybrid materials; (4) The cerium-based organic-inorganic hybrid material obtained in step (3) is first carbonized at 300-500℃ for 1-5 hours, and then oxidized at 500-700℃ for 1-5 hours to obtain a wide temperature window mesoporous cerium-based composite oxide denitration catalyst; wherein the catalyst crystal structure is anatase titanium dioxide structure, and the active component cerium dioxide, the co-catalyst components tungsten oxide and alumina are all amorphous structures.

2. The preparation method according to claim 1, characterized in that: The solvent mentioned in step (1) is one of water, methanol or ethanol.

3. The preparation method according to claim 1, characterized in that: The cerium source mentioned in step (2) is one of cerium nitrate or cerium chloride; the tungsten source is one of ammonium metatungstate or tungsten chloride; the aluminum source is one of aluminum nitrate, aluminum isopropoxide or aluminum chloride; and the titanium source is one of tetrabutyl titanate, isopropyl titanate, titanium tetrachloride or metatitanic acid.

4. The preparation method according to claim 1, characterized in that... The atmosphere for carbonization in step (4) is either nitrogen or hydrogen; the atmosphere for oxidation is either oxygen or air.

5. A wide-temperature-window mesoporous cerium-based composite oxide denitration catalyst obtained by the preparation method described in claim 1.

6. A cerium-based composite oxide denitration catalyst with a wide temperature window as described in claim 5 for NO x Applications in governance.

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