High-activity catalyst for treating VOCs (Volatile Organic Compounds) and preparation method thereof

Abstract

The invention provides a high-activity catalyst for treating VOCs (volatile organic compounds) and a preparation method of the high-activity catalyst. A Ce-Fe bimetal MOF material grows on a porous alumina structure in situ, so that the Ce-Fe bimetal MOF material is coupled with an interface of porous Al2O3, and a polyamine structure is directionally grafted on the surface of the Ce-Fe bimetal MOF material, so that the high-activity catalyst for treating VOCs is prepared; and by constructing a Ce-Fe bimetallic synergistic system, multiple synergistic effects of oxygen vacancy regulation, Lewis acid site enhancement and electronic structure optimization are realized, so that the obtained composite functional material shows higher adsorption efficiency, faster adsorption kinetics and more excellent structural stability under the conditions of low temperature and low-concentration VOCs (Volatile Organic Compounds).

Description

Technical Field

[0001] This invention relates to the field of air pollution control technology, and in particular to a highly active catalyst for VOCs control and its preparation method. Background Technology

[0002] Volatile organic compounds (VOCs) are widely derived from chemical production, coating, printing, electronics manufacturing, and interior decoration. Even at low concentrations, they pose significant environmental hazards and health risks, and are important precursors to ozone and fine particulate matter (PM2.5). With increasingly stringent emission standards, VOCs treatment technologies are gradually shifting from high-concentration, high-temperature treatment to high-efficiency purification under low-concentration, low-temperature, and ambient-temperature conditions.

[0003] Existing VOCs treatment technologies mainly include thermal oxidation, catalytic combustion, biological methods, and adsorption. Among these, thermal oxidation and catalytic combustion typically require high ignition temperatures, consume a lot of energy, and are unsuitable for low-concentration gases; biological methods are limited by environmental conditions and have poor stability. In contrast, adsorption methods have significant advantages in treating low-concentration VOCs due to their simple operation and low energy consumption. However, traditional adsorption materials such as activated carbon and zeolite generally suffer from the following problems: (1) Under low partial pressure conditions, the adsorption capacity is limited and the initial collection efficiency is insufficient; (2) It is sensitive to humidity, and water vapor competes for adsorption. (3) Poor surface chemical tunability makes it difficult to achieve selective adsorption of specific VOC components; (4) Structural collapse or performance degradation is likely to occur during the regeneration process.

[0004] Metal-organic frameworks (MOFs) are considered an important development direction for next-generation VOCs adsorption and treatment materials due to their advantages such as large specific surface area, tunable pore structure, and designable surface chemistry. However, existing MOFs mostly use single metals such as Cr and Al as nodes, which leads to problems such as insufficient environmental friendliness, limited low-temperature adsorption capacity, and unstable performance in humid air, thus limiting their application in practical atmospheric VOCs treatment.

[0005] Furthermore, single MOF materials generally suffer from difficulties in molding and insufficient mechanical strength in engineering applications, making them unsuitable for direct use in fixed beds or adsorption modules. Therefore, loading MOF materials onto inorganic porous supports to construct composite materials with hierarchical porous structures and interfacial synergistic effects has become a current research hotspot. However, existing composite materials mostly focus on physical loading or simple blending, failing to fully utilize the chemical activity of the support surface and lacking targeted surface functionalization designs for low-concentration, low-temperature VOCs.

[0006] In summary, there is an urgent need to develop a VOCs adsorption material that still exhibits high adsorption efficiency, good moisture resistance, and stability under low concentration and low temperature conditions, while also considering both engineering feasibility and surface chemical tunability in its structure, in order to meet the application needs of actual air pollution control. Summary of the Invention

[0007] Purpose of the invention: The purpose of this invention is to provide a composite functional material for efficient adsorption of VOCs under low concentration and low temperature conditions and its preparation method. By constructing a MOF structure with multiple metals, strengthening with an inorganic carrier, and grafting a polyamine structure on the surface, efficient capture and stable adsorption of VOCs can be achieved.

[0008] The technical solution of the present invention: In a first aspect, the present invention provides a method for preparing a composite functional material for efficiently adsorbing VOCs under low concentration and low temperature conditions, comprising the following steps: S1: Add aluminum source to deionized water, add NaCl, add ammonia to adjust pH to alkaline, stir to react and obtain slurry; then add gelling agent and pore-forming agent to slurry, stir evenly and calcine to obtain porous Al2O3 support; S2: Cerium source, iron source, ligand and porous Al2O3 support are added to deionized water, dispersed evenly and then transferred to a reactor for hydrothermal reaction. After the reaction is completed, the composite framework is obtained by washing, drying and calcining activation. S3: Disperse the composite framework in a solvent, add a polyamine compound and a catalyst, and stir to react; after the reaction is complete, centrifuge, filter, wash, dry, and calcine to obtain the composite functional material.

[0009] In some embodiments, the aluminum source is selected from one or more combinations of aluminum nitrate nonahydrate, aluminum sulfate, and aluminum chloride; further, the aluminum source is aluminum nitrate nonahydrate; in some embodiments, the concentration of the ammonia water is 25-28 wt%.

[0010] In some embodiments, the ratio of the aluminum source to deionized water and NaCl is 20-50g: 100-500ml: 1-5g.

[0011] In some embodiments, the alkalinity mentioned in S1 refers to a pH of 9.0-10.0; the stirring temperature of the stirring reaction is 25-30°C, and the stirring time is 60-120 min.

[0012] In some embodiments, the gelling agent is selected from hexamethylenetetramine (HMTA) or polyvinyl alcohol (PVA); in some embodiments, the porogen is selected from PEG-400, PEG-6000 or CTAB.

[0013] In some embodiments, the heating rate of calcination in S1 is 2-5℃ / min; the calcination temperature is 480-550℃; and the calcination time is 2-4h.

[0014] In some embodiments, the cerium source is selected from one of cerium ammonium nitrate (NH4)2Ce(NO3)3 or cerium nitrate hexahydrate Ce(NO3)3·6H2O; the iron source is selected from one of FeCl3·6H2O or Fe(NO3)3·9H2O; and the ligand is terephthalic acid.

[0015] In some embodiments, the ratio of the amount of cerium source, iron source, ligand, porous Al2O3 support and deionized water added is 1 mmol: 1-3 mmol: 3-6 mmol: 1-4 g: 100-200 ml.

[0016] In some embodiments, the hydrothermal reaction is carried out at a temperature of 150-170°C for 12-18 hours.

[0017] In some embodiments, the specific steps of calcination activation described in S2 include: vacuum drying the washed product at 70-90°C for 12-18 h, then placing it in an air atmosphere, heating it to 280-320°C, and holding it at that temperature for 2-4 h to obtain an in-situ grown composite framework.

[0018] In some embodiments, the polyamine compound S3 is selected from one or more combinations of diethylenetriamine, triethylenetetramine, tetraethylenepentamine, 1,4-diaminocyclohexane, N-(2-aminoethyl)-3-aminopropyltriethoxysilane, and polyethyleneimine (Mn 600-1800).

[0019] In some embodiments, the solvent in S3 is selected from one or more combinations of anhydrous ethanol, toluene, or DMF; and the catalyst is selected from one or more combinations of triethylamine or DMAP.

[0020] In some embodiments, the ratio of the added composite framework, polyamine compound, and catalyst is 2-5g:1-5g:0.1-0.5ml; the reaction temperature of the stirring reaction in S3 is 60-70℃, and the reaction time is 6-10h; the specific steps of calcination in S3 include: calcining the dried product in a nitrogen atmosphere at 200-220℃ for 1-3h to obtain the composite functional material.

[0021] By coupling Ce-Fe bimetallic MOF with porous Al2O3 at the interface and directionally grafting polyamine structures onto its surface, the adsorption efficiency and stability of the material for low-concentration VOCs are significantly improved without relying on high temperature conditions, making it suitable for air pollution control at room temperature or low temperature.

[0022] In a second aspect, the present invention provides a composite functional material for efficient adsorption of VOCs under low concentration and low temperature conditions, wherein the composite functional material is prepared by the above-described preparation method.

[0023] Beneficial effects: This invention constructs a Ce-Fe bimetallic MOF composite framework in situ on the surface of a porous Al2O3 support, and further grafts polyamine structures onto its surface. This enables the material to achieve efficient capture of VOCs at low concentrations and under room temperature or low temperature conditions through hydrogen bonding, dipole interaction and coordination between polyamine groups and VOCs molecules, significantly improving the adsorption efficiency in the low partial pressure region.

[0024] By introducing the oxygen vacancies and oxygen migration capabilities of Ce, along with the Lewis acidity and reversible redox properties of Fe, the composite framework possesses a certain degree of molecular activation ability while adsorbing VOCs, which is beneficial for improving adsorption capacity and rate. Furthermore, it maintains good structural stability and adsorption performance in humid air environments. Combined with an adsorption interface rich in nitrogen-containing functional groups, the material exhibits excellent adsorption responses to aldehydes, ketones, aromatic hydrocarbons, and sulfur- and nitrogen-containing VOCs, making it particularly suitable for air pollution control scenarios with complex compositions and low concentrations of VOCs.

[0025] MOF frameworks are loaded onto the surface of a support through in-situ growth, avoiding the problems of insufficient mechanical strength and easy pulverization that exist in single MOF materials in practical applications. This improves the operability and stability of the material in engineering applications such as fixed beds and adsorption modules. It is less prone to structural collapse or loss of functional groups during multiple adsorption-desorption cycles and can be regenerated through low-temperature desorption or mild heat treatment, exhibiting good recyclability. Detailed Implementation

[0026] The present invention will be described below with reference to specific embodiments. It should be noted that the following embodiments are examples of the present invention and are used only to illustrate the invention, not to limit it. Other combinations and various modifications within the scope of the present invention can be made without departing from its spirit or scope.

[0027] Unless otherwise specified, all chemical reagents used in this invention are commercially available analytical grade reagents.

[0028] Example 1 S1: Add 37.5 g of aluminum nitrate nonahydrate to 200 mL of deionized water, add 2.0 g of NaCl, stir until completely dissolved, add 25 wt% ammonia to adjust the pH to 10.0, stir to react and obtain a slurry; then add 1.5 g of HMTA and 3.0 g of PEG-400 to the slurry, stir evenly for 30 min, dry the obtained material at 100℃ for 12 h, then place it in a muffle furnace and calcine it at 550℃ at 2℃ / min under air atmosphere to obtain a porous Al2O3 support; S2: 2.5 mmol Ce(NO3)3·6H2O, 2.5 mmol FeCl3·9H2O, 5.0 mmol terephthalic acid and 2.0 g porous Al2O3 support were added to 120 mL deionized water and ultrasonically dispersed for 30 min. After uniform dispersion, the mixture was transferred to a 200 mL polytetrafluoroethylene-lined reactor and subjected to hydrothermal reaction at 150 °C for 12 h. After the reaction was completed, the product was naturally cooled and removed. It was washed three times each with water and ethanol and vacuum dried at 80 °C for 12 h. Then, the temperature was raised to 300 °C in air atmosphere and held for 2 h to obtain the composite framework. S3: 2.0 g of the composite framework was dispersed in 100 mL of toluene and sonicated for 15 min to disperse it evenly. 1.0 g of diethylenetriamine and 0.3 mL of triethylamine were added and the mixture was stirred at 60 °C for 6 h. After the reaction was completed, the mixture was centrifuged, washed three times with ethanol, dried under vacuum at 60 °C for 12 h, and calcined at 200 °C under a nitrogen atmosphere for 1 h to obtain the composite functional material.

[0029] Example 2 The preparation process is basically the same as in Example 1, except that diethylenetriamine is replaced with triethylenetetramine, and the other steps are the same to obtain the composite functional material.

[0030] Example 3 The preparation process is basically the same as in Example 1, except that diethylenetriamine is replaced with 1,4-diaminocyclohexane. The remaining steps are the same to obtain the composite functional material.

[0031] Example 4 The preparation process is basically the same as in Example 1, except that diethylenetriamine is replaced with N-(2-aminoethyl)-3-aminopropyltriethoxysilane. The remaining steps are the same to obtain the composite functional material.

[0032] Comparative Example 1 The preparation process is basically the same as in Example 1, except that diethylenetriamine is replaced with diethylene glycol. The remaining steps are the same to obtain the composite functional material.

[0033] Comparative Example 2 S1: Add 37.5 g of aluminum nitrate nonahydrate to 200 mL of deionized water, add 2.0 g of NaCl, stir until completely dissolved, add 25 wt% ammonia to adjust the pH to 10.0, stir to obtain a slurry; then add 1.5 g of HMTA and 3.0 g of PEG-400 to the slurry, stir evenly for 30 min, dry the obtained material at 100℃ for 12 h, then place it in a muffle furnace and calcine it at 550℃ at 2℃ / min under air atmosphere to obtain a porous Al2O3 support; S2: 2.0 g of porous Al2O3 support was dispersed in 100 mL of toluene and sonicated for 15 min to disperse it evenly. 1.0 g of diethylenetriamine and 0.3 mL of triethylamine were added and the mixture was stirred at 60 °C for 6 h. After the reaction was completed, the mixture was centrifuged, washed three times with ethanol, dried under vacuum at 60 °C for 12 h, and calcined at 200 °C under a nitrogen atmosphere for 1 h to obtain the composite functional material.

[0034] Comparative Example 3 S1: 2.5 mmol Ce(NO3)3·6H2O, 2.5 mmol FeCl3·9H2O, and 5.0 mmol terephthalic acid were added to 120 mL of deionized water and ultrasonically dispersed for 30 min. After uniform dispersion, the mixture was transferred to a 200 mL polytetrafluoroethylene-lined reactor and subjected to hydrothermal reaction at 150 °C for 12 h. After the reaction was completed, the product was naturally cooled and removed. It was washed three times each with water and ethanol, and then vacuum dried at 80 °C for 12 h. After that, the temperature was raised to 300 °C in air and held for 2 h to obtain the MOF framework. S2: 2.0 g of MOF framework was dispersed in 100 mL of toluene and sonicated for 15 min to disperse it evenly. 1.0 g of diethylenetriamine and 0.3 mL of triethylamine were added and the mixture was stirred at 60 °C for 6 h. After the reaction was completed, the mixture was centrifuged, washed three times with ethanol, dried under vacuum at 60 °C for 12 h, and calcined at 200 °C under a nitrogen atmosphere for 1 h to obtain the composite functional material.

[0035] Comparative Example 4 S1: Add 37.5 g of aluminum nitrate nonahydrate to 200 mL of deionized water, add 2.0 g of NaCl, stir until completely dissolved, add 25 wt% ammonia to adjust the pH to 10.0, stir to obtain a slurry; then add 1.5 g of HMTA and 3.0 g of PEG-400 to the slurry, stir evenly for 30 min, dry the obtained material at 100℃ for 12 h, then place it in a muffle furnace and calcine it at 550℃ at 2℃ / min under air atmosphere to obtain a porous Al2O3 support; S2: 2.5 mmol Ce(NO3)3·6H2O, 2.5 mmol Al(NO3)3·9H2O, 5.0 mmol terephthalic acid and 2.0 g porous Al2O3 support were added to 120 mL deionized water and ultrasonically dispersed for 30 min. After uniform dispersion, the mixture was transferred to a 200 mL polytetrafluoroethylene-lined reactor and subjected to hydrothermal reaction at 150 °C for 12 h. After the reaction was completed, the product was naturally cooled and removed. It was washed three times each with water and ethanol, and vacuum dried at 80 °C for 12 h. Then, the temperature was raised to 300 °C in air atmosphere and held for 2 h to obtain the composite framework. S3: 2.0 g of the composite framework was dispersed in 100 mL of toluene and sonicated for 15 min to disperse it evenly. 1.0 g of diethylenetriamine and 0.3 mL of triethylamine were added and the mixture was stirred at 60 °C for 6 h. After the reaction was completed, the mixture was centrifuged, washed three times with ethanol, dried under vacuum at 60 °C for 12 h, and calcined at 200 °C under a nitrogen atmosphere for 1 h to obtain the composite functional material.

[0036] Comparative Example 5 S1: Add 37.5 g of aluminum nitrate nonahydrate to 200 mL of deionized water, add 2.0 g of NaCl, stir until completely dissolved, add 25 wt% ammonia to adjust the pH to 10.0, stir to obtain a slurry; then add 1.5 g of HMTA and 3.0 g of PEG-400 to the slurry, stir evenly for 30 min, dry the obtained material at 100℃ for 12 h, then place it in a muffle furnace and calcine it at 550℃ at 2℃ / min under air atmosphere to obtain a porous Al2O3 support; S2: 2.5 mmol Cu(NO3)2•3H2O, 2.5 mmol Al(NO3)3·9H2O, 5.0 mmol terephthalic acid and 2.0 g porous Al2O3 support were added to 120 mL deionized water and ultrasonically dispersed for 30 min. After uniform dispersion, the mixture was transferred to a 200 mL polytetrafluoroethylene-lined reactor and subjected to hydrothermal reaction at 150 °C for 12 h. After the reaction was completed, the product was naturally cooled and removed. It was washed three times each with water and ethanol, and then vacuum dried at 80 °C for 12 h. After that, the temperature was raised to 300 °C in air atmosphere and held for 2 h to obtain the composite framework. S3: 2.0 g of the composite framework was dispersed in 100 mL of toluene and sonicated for 15 min to disperse it evenly. 1.0 g of diethylenetriamine and 0.3 mL of triethylamine were added and the mixture was stirred at 60 °C for 6 h. After the reaction was completed, the mixture was centrifuged, washed three times with ethanol, dried under vacuum at 60 °C for 12 h, and calcined at 200 °C under a nitrogen atmosphere for 1 h to obtain the composite functional material.

[0037] Comparative Example 6 37.5 g of aluminum nitrate nonahydrate was added to 200 mL of deionized water, followed by 2.0 g of NaCl. The mixture was stirred until completely dissolved, and 25 wt% ammonia was added to adjust the pH to 10.0. The mixture was stirred to obtain a slurry. 1.5 g of HMTA and 3.0 g of PEG-400 were then added to the slurry. After stirring for 30 min, the mixture was dried at 100 °C for 12 h. The resulting material was then placed in a muffle furnace and calcined at 550 °C at a rate of 2 °C / min in air atmosphere to obtain a porous Al2O3 support.

[0038] Performance testing 10 ppm of VOCs gas was placed in a 5 L container, and 400 mg of the above-prepared composite functional material was placed in the container beforehand. The container was placed at four temperatures: 10℃, 25℃, and 45℃. After sealing for 0 h and 24 h, 1 mL of gas was taken through a gas injection needle and the VOCs were determined by gas chromatography (Shimadzu GC-2014). The remaining VOCs were detected by an Rt-Stabilwax column (30 m × 0.53 mm × 10 μm) and an FID detector.

[0039] The obtained data is shown in the table below.

[0040] Table 1. Removal rate of VOCs adsorbed at different temperatures over 24 hours

[0041] Table 2. Removal rates of toluene at different initial concentrations after 24 hours of adsorption at 25℃.

[0042] The results showed that the composite functional material exhibited significant adsorption capacity for various typical VOCs under low temperature (≤25℃) and low concentration (≤10 ppm) conditions, with removal rates of over 95%, 96%, and 88% for toluene, acetone, and ethyl acetate, respectively. The material maintained excellent adsorption capacity even at 45℃, and its adsorption performance was largely restored after cooling, demonstrating good structural stability and application potential.

[0043] A comparison of the data from the examples and Comparative Example 1 shows that when diethylene glycol is used instead of diethylenetriamine as the surface grafting molecule, the adsorption driving force of the material for low concentration VOCs is significantly weakened due to the lack of basic nitrogen sites and metal coordination ability. Its initial adsorption efficiency and breakthrough time under low temperature conditions are significantly lower than those of the material grafted with diethylenetriamine.

[0044] Cerium has a reversible Ce³ phase. + / Ce 4+The redox properties of Ce facilitate the formation of abundant oxygen vacancies on the material surface, which enhances the polarization adsorption capacity for VOCs molecules. Iron, on the other hand, possesses strong Lewis acidity and multi-valence transition properties, enabling it to form stable coordination or electronic interactions with oxygen-containing or aromatic functional groups in VOCs molecules. When Ce and Fe coexist in the same framework structure, they can promote the formation and stabilization of oxygen vacancies through electron transfer and valence state regulation mechanisms, thereby significantly enhancing the material's adsorption and activation capacity for VOCs under low-temperature conditions.

[0045] In contrast, in the Ce-Al bimetallic system, aluminum mainly plays a role in structural support and specific surface area regulation. It lacks reversible redox capabilities and is difficult to form effective electronic cooperation with Ce, resulting in insufficient oxygen vacancy activity and limited adsorption driving force under low concentration VOCs conditions. Although the Cu-Al bimetallic system introduces some Lewis acidity of Cu, Cu is prone to agglomeration or valence instability under hydrothermal and calcination conditions, and lacks oxygen storage and migration capabilities similar to Ce, which limits its adsorption stability and persistence for VOCs at low temperatures.

[0046] Therefore, by constructing a Ce-Fe bimetallic synergistic system, this invention achieves multiple synergistic effects of oxygen vacancy regulation, Lewis acid site enhancement, and electronic structure optimization, resulting in a composite functional material that exhibits higher adsorption efficiency, faster adsorption kinetics, and superior structural stability under low temperature and low concentration VOCs conditions, significantly outperforming existing Ce-Al or Cu-Al bimetallic material systems.

[0047] This invention can also be implemented in various other ways. Without departing from the spirit and essence of this invention, those skilled in the art can make various corresponding changes and modifications according to this invention, but these corresponding changes and modifications should all fall within the protection scope of the appended claims.

Claims

1. A method for preparing a composite functional material for efficient adsorption of VOCs under low concentration and low temperature conditions, characterized in that, Includes the following steps: S1: Add aluminum source to deionized water, add NaCl, add ammonia to adjust pH to alkaline, stir to react and obtain slurry; then add gelling agent and pore-forming agent to slurry, stir evenly and calcine to obtain porous Al2O3 support; S2: Cerium source, iron source, ligand and porous Al2O3 support are added to deionized water, dispersed evenly and then transferred to a reactor for hydrothermal reaction. After the reaction is completed, the composite framework is obtained by washing, drying and calcining activation. S3: Disperse the composite framework in a solvent, add a polyamine compound and a catalyst, and stir to react; after the reaction is complete, centrifuge, filter, wash, dry, and calcine to obtain the composite functional material.

2. The method for preparing the composite functional material according to claim 1, characterized in that, The aluminum source is selected from one or more combinations of aluminum nitrate nonahydrate, aluminum sulfate, and aluminum chloride; the concentration of the ammonia water is 25-28 wt%.

3. The method for preparing the composite functional material according to claim 1, characterized in that, The ratio of the amount of aluminum source added to deionized water and NaCl is 20-50g: 100-500ml: 1-5g.

4. The method for preparing the composite functional material according to claim 1, characterized in that, The alkalinity mentioned in S1 refers to a pH of 9.0-10.0; the stirring temperature of the stirring reaction is 25-30℃, and the stirring time is 60-120 min; the heating rate of the calcination in S1 is 2-5℃ / min; the calcination temperature is 480-550℃; and the calcination time is 2-4 h.

5. The method for preparing the composite functional material according to claim 1, characterized in that, The cerium source is selected from one of cerium ammonium nitrate (NH4)2Ce(NO3)3 or cerium nitrate hexahydrate Ce(NO3)3·6H2O; the iron source is selected from one of FeCl3·6H2O or Fe(NO3)3·9H2O; and the ligand is terephthalic acid.

6. The method for preparing the composite functional material according to claim 1, characterized in that, The ratio of the amount of cerium source, iron source, ligand, porous Al2O3 carrier and deionized water added is 1 mmol: 1-3 mmol: 3-6 mmol: 1-4 g: 100-200 ml.

7. The method for preparing the composite functional material according to claim 1, characterized in that, The hydrothermal reaction is carried out at a temperature of 150-170℃ for 12-18 hours.

8. The method for preparing the composite functional material according to claim 1, characterized in that, The polyamine compound S3 is selected from one or more combinations of diethylenetriamine, triethylenetetramine, tetraethylenepentamine, 1,4-diaminocyclohexane, N-(2-aminoethyl)-3-aminopropyltriethoxysilane, and polyethyleneimine.

9. The method for preparing the composite functional material according to claim 1, characterized in that, The ratio of the added composite framework, polyamine compound, and catalyst is 2-5g: 1-5g: 0.1-0.5ml; the reaction temperature of the stirring reaction in S3 is 60-70℃, and the reaction time is 6-10h; the specific steps of calcination in S3 include: calcining the dried product in a nitrogen atmosphere at 200-220℃ for 1-3h to obtain the composite functional material.

10. The composite functional material for efficiently adsorbing VOCs prepared by the method for preparing the composite functional material according to any one of claims 1-9.

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