Preparation method of thin c-axis copper-based mordenite nanosheet and application thereof

Abstract

The application discloses a preparation method of thin c-axis copper-based mordenite nanosheet and application thereof, and comprises the following steps: step 1, dissolving a copper source into deionized water, and adding a nitrogen-containing ligand drop by drop into the copper source dissolved in the deionized water to obtain a copper amine complex A after intense stirring; step 2, uniformly mixing an aluminum source, an alkali source, a silicon source, a template agent and water to obtain a gel B; and step 3, mixing the copper amine complex A with the gel B, performing hydrothermal crystallization, and then performing filtration, drying and calcination treatment to obtain the thin c-axis copper-based mordenite nanosheet with regular morphology. The application has the characteristics of simple technological process, low cost and safe process, and has an industrialization prospect.

Description

Technical Field

[0001] This invention belongs to the field of mordenite nanosheet preparation technology, specifically relating to a method for preparing thin c-axis copper-based mordenite nanosheets and their applications. Background Technology

[0002] Mordenite zeolite belongs to the MOR-type molecular sieve. Due to its excellent heat resistance, acid resistance, and water vapor resistance, it is widely used in industrial fields as a catalyst and adsorbent. MOR molecular sieves belong to the orthorhombic crystal system with space group Cmcm and cell parameters a=18.1 Å, b=20.5 Å, c=7.5 Å. It has a two-dimensional channel structure with 12-membered ring (12-MR) and elliptical 8-membered ring (8-MR) channels along the

[001] direction (c-axis), and 8-membered ring side pockets connected to it along the

[010] direction (b-axis). Since molecules can only enter through the 12-membered ring channels, MOR is usually considered a one-dimensional zeolite. Studies have shown that although MOR performs relatively well in reactions such as DME carbonylation, the mass transfer limitation significantly inhibits its reactivity and stability. Therefore, there is an urgent need for MOR crystals with shortened c-axis dimensions and reduced diffusion lengths.

[0003] In recent years, zeolite nanosheets with two-dimensional morphology have attracted much attention due to their unique structural and functional advantages. Compared with conventional bulk zeolites, these nanosheets, only a few nanometers thick along the c-axis, possess significantly increased specific surface area, fully exposed active sites, and more efficient mass transfer channels. The reduction in dimensionality not only alters the physicochemical properties of zeolites, including morphology, structure, porosity, and acidity, but also endows them with unique catalytic behavior, making zeolite nanosheets particularly attractive for achieving challenging catalytic conversion reactions such as methanol conversion, cracking, isomerization, alkylation, carbonylation, and catalytic oxidation.

[0004] CN115536040A discloses a nano-lotus leaf-shaped alumina-rich mordenite zeolite molecular sieve, its synthesis method, and its application. This patent involves adding an aluminum source to a NaOH solution and mixing to obtain solution A. Then, a template agent, a silicon source, an alumina-rich agent, and a crystal growth inhibitor are sequentially added to solution A and stirred until a homogeneous sol B is formed. Finally, sol B is stirred until it reaches a dry gel state, water is added, and the mixture is transferred to a reaction vessel. Under high-temperature shaking conditions, a homogeneous and stable gel is formed. After washing, filtering, drying, calcining, ammonia exchange, and calcination, nano-lotus leaf-shaped alumina-rich MOR molecular sieves with a layer thickness of 10-100 nm are obtained. However, this method involves complex gel preparation, uses expensive template agents, has high synthesis costs, cumbersome steps, and harsh preparation conditions, making it unsuitable for large-scale industrial production. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, this invention aims to provide a method for preparing thin c-axis copper-based mordenite nanosheets and their applications. This method utilizes inexpensive commercial template agents and copper-amine complexes as co-templates. The synthesized thin c-axis nanosheet structure can shorten the diffusion path of dimethyl ether and the product, improve mass transfer efficiency, and increase the accessibility of active sites on the molecular sieve. Simultaneously, the in-situ introduction of framework copper atoms during the dimethyl ether carbonylation process can promote the adsorption and activation of CO, shorten the reaction induction period, accelerate C / C bond formation, and enhance carbonylation capability. This method features a simple process flow, low cost, and process safety, and has promising industrial application prospects.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing thin c-axis copper-based mordenite nanosheets includes the following steps; Step 1: Dissolve the copper source in deionized water, add the nitrogen-containing ligand dropwise to the copper source dissolved in deionized water, and stir vigorously to obtain copper amine complex A; Step 2: Mix the aluminum source, alkali source, silicon source, template agent, and water evenly to obtain gel B; Step 3: Mix copper ammonium complex A with gel B, perform hydrothermal crystallization, and then filter, dry, and calcine to obtain thin c-axis copper-based mordenite nanosheets with regular morphology.

[0007] In the above preparation method, the copper source in step 1 is a soluble copper salt, selected from at least one of copper nitrate, copper acetate, copper sulfate, copper chloride, and copper bromide; The nitrogen-containing ligand is at least one of linear alkyl polyamines, cyclic amines, and polyethylene polyamines; Selected from straight-chain alkyl polyamines: ethylenediamine, propylenediamine, and butylenediamine; Cyclic amines: piperazine, aziridine, pyrazole; Polyethylene polyamine: at least one of diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and pentaethylenehexamine.

[0008] In the above preparation method, the molar ratio of copper source to nitrogen-containing ligand in step 1 is 1:(0.1~10). The preferred molar ratio is 1:(0.5~2) to form a structurally stable copper amine complex A.

[0009] In the above preparation method, stirring in step 1 is carried out in a water bath at 20-60°C for 0.5-4 hours, and the solution pH is maintained at 6-10. Preferably, the pH is maintained between 8 and 10 to promote copper source dissolution and inhibit precipitation.

[0010] In the above preparation method, the aluminum source in step 2 is one or more of aluminum nitrate, aluminum sulfate, boehmite, sodium aluminate, aluminum isopropoxide, and aluminum hydroxide; the amount used is calculated based on the number of moles of Al2O3 it contains. The alkali source is at least one of the hydroxides of alkali metal M, and its amount is calculated based on the number of moles of M2O it contains. The silicon source is at least one of sodium silicate, potassium silicate, fumed silica, tetraethyl orthosilicate, tetramethyl orthosilicate, silica sol, and silica fume, and the amount used is calculated based on the number of moles of SiO2 it contains. The template agent is at least one of the following: quaternary ammonium salt cationic surfactant, quaternary ammonium base compound, and nitrogen-containing heterocyclic organic compound, specifically at least one of the following: decaalkyltrimethylammonium chloride, dodecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, dodecyltrimethylammonium hydroxide, tetrapropylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium bromide, tetraethylammonium bromide, triethylamine, and morpholine, and the amount used is calculated based on its own molar number.

[0011] In step 2, the molar ratio of raw materials is SiO2:Al2O3:M2O:R1:H2O=1:(0.01~0.08):(0.05~0.5):(0.01~0.1):(5~50) to form a stable crystallized gel B.

[0012] In the above preparation method, the stirring rate in step 2 is 100~1000 r / min. The preferred stirring speed is 600~800 r / min.

[0013] In the above preparation method, the mass ratio of copper amine complex A to gel B in step 3 is (0.01~0.1):1, so as to introduce copper atoms into the mordenite framework.

[0014] In the above preparation method, the hydrothermal crystallization in step 3 is a two-stage crystallization method, with one stage being 100~140°C. o C crystallization for 2-10 hours, with the second stage at 160-220°C. o C crystallization for 18~72h promotes the synthesis of mordenite nanosheets through a two-stage crystallization process.

[0015] In the above preparation method, the calcination in step 3 is a two-stage calcination. The first stage calcination temperature is 200℃~400℃, the heating rate is 1~10℃ / min, and the calcination time is 1~4h. The second stage calcination temperature is 550℃~800℃, the heating rate is 5~15℃ / min, and the calcination time is 2~6h. By using a two-stage calcination of low temperature and high temperature, the rapid decomposition of the template agent at high temperature is avoided, which would generate a large amount of gas and cause the molecular sieve channels to burst or the framework to collapse.

[0016] Thin c-axis copper-based mordenite nanosheets are grown along the ab plane, with the c-axis thickness maintained between 20 nm and 100 nm. They are stacked and aggregated to form a three-dimensional flower-like structure through self-assembly. This structure significantly increases the specific surface area, exposes more channels and active sites, and has the advantages of nanoscale properties and easy separation from the mother liquor.

[0017] The application of the thin c-axis copper-based mordenite nanosheets obtained by the above preparation method as a catalyst in the dimethyl ether carbonylation reaction includes the following steps: A mixture of dimethyl ether (DME) and carbon monoxide (CO) was passed into a fixed-bed reactor packed with thin c-axis copper-based mordenite nanosheets as a catalyst to produce methyl acetate and acetic acid. The catalyst is obtained by ammonium ion exchange from the thin c-axis copper-based mordenite nanosheets. The molar ratio of CO to DME in the mixed gas is (0.5~10):1, and the reaction temperature is 160°C. o C~250 o C, with a reaction pressure of 1~6MPa, the carbonylation reaction of dimethyl ether is carried out; Preferably, the molar ratio of CO to DME is (5~7):1, and the reaction temperature is 190°C. o C~230 o C, reaction pressure 2~4MPa.

[0018] The beneficial effects of this invention are: The purpose of this invention is to provide a one-pot method for preparing thin c-axis copper-based mordenite nanosheets. This method uses inexpensive commercial template agents and copper amine complexes as co-template agents. The synthesized thin c-axis nanosheet structure can shorten the diffusion path of dimethyl ether and the product, improve mass transfer efficiency, and increase the accessibility of molecular sieve active sites, thereby promoting the reaction of dimethyl ether with the Brønsted acid sites on the mordenite framework to form methyl species. At the same time, the in-situ introduction of skeletal copper atoms in the carbonylation process of dimethyl ether can promote the adsorption and activation process of CO, promote the reaction of methyl species with CO to form acetyl species, and the acetyl group can then react with dimethyl ether molecules or water molecules to generate methyl acetate or acetic acid, thereby shortening the reaction induction period, accelerating C-C bond formation, and enhancing carbonylation ability.

[0019] This method features a simple process, low cost, and safe operation, making it promising for industrialization.

[0020] In the carbonylation of dimethyl ether to prepare oxygen-containing compounds, thin c-axis copper-based mordenite nanosheets significantly improved catalytic activity and stability. Attached Figure Description

[0021] Figure 1 XRD patterns of catalysts prepared for Examples 1, 2, Comparative Example 1, and Comparative Example 2.

[0022] Figure 2 SEM image of the catalyst prepared in Example 1.

[0023] Figure 3 SEM image of the catalyst prepared in Example 2.

[0024] Figure 4 SEM image of the catalyst prepared for Comparative Example 1.

[0025] Figure 5 SEM image of the catalyst prepared for Comparative Example 2.

[0026] Figure 6 The conversion rate of dimethyl ether and the selectivity of oxygen-containing compounds (MA+AA) in the dimethyl ether carbonylation reaction of the catalysts prepared in Example 1 and Comparative Example 1 are shown. Detailed Implementation

[0027] The present invention will now be described in further detail with reference to the accompanying drawings.

[0028] Example 1 Step 1: Weigh 1g of copper sulfate pentahydrate and dissolve it in 5g of deionized water. Add 0.4g of ethylenediamine to the solution while stirring vigorously, and then add the solution at 50°C. o Stirring at C for 90 minutes yields copper amine complex A. Step Two: Dissolve 3g sodium hydroxide, 2.1g sodium aluminate, and 8g tetraethylammonium hydroxide in 50g water to form a clear solution. Then, slowly add 60g silica sol dropwise at 600 rpm. After aging, gel B is obtained. Step Three: Stir 3g complex A and 120g gel B evenly and transfer to a stainless steel high-pressure hydrothermal reactor. Stir at 130°C. o Crystallization at C for 8 hours, then at 180°C o Crystallization was carried out at C for 36 hours. After crystallization, the product was filtered and dried, then heated to 350℃ at 5℃ / min and calcined for 2 hours, followed by heating to 600℃ at 10℃ / min and calcining for 4 hours to obtain thin, uniformly morphologically shaped, copper-based mordenite nanosheet catalysts. After ammonium ion exchange, these catalysts were used in a syngas relay catalytic reaction. The evaluation results are as follows: Figure 6 As shown. From the appendix Figure 6 It can be seen that the conversion rate of dimethyl ether increased from 20.7% to 45.2%, and then slowly decreased, while the selectivity of methyl acetate and acetic acid (MA+AA) remained stable at 97.6%.

[0029] Example 2 Step 1: Weigh 2g of copper nitrate and dissolve it in 8g of deionized water. Add 1.84g of piperazine to the solution while stirring vigorously, and stir for 120 minutes at room temperature to obtain copper amine complex A. Step 2: Dissolve 7g of sodium hydroxide, 4g of sodium aluminate, and 2.19g of dodecyltrimethylammonium bromide in 200g of deionized water to form a clear solution. Slowly add 80g of silica sol dropwise at 800 rpm. After aging, obtain gel B. Step 3: Mix 5g of complex A with 200g of gel B thoroughly and transfer to a stainless steel high-pressure hydrothermal reactor. Stir at 100°C. o Crystallize at C for 10 hours, then at 190°C o Crystallize at C for 24 hours. After crystallization, filter and dry the product. Then, heat the product to 400℃ at 2℃ / min and calcine for 2 hours. Next, heat the product to 600℃ at 8℃ / min and calcine for 5 hours to obtain thin c-axis copper-based mordenite nanosheet catalyst with uniform morphology. After ammonium ion exchange, the catalyst is used for syngas relay catalysis.

[0030] Example 3 Step 1: Weigh 1g of copper sulfate pentahydrate and dissolve it in 5g of deionized water. Add 0.54g of pyrazole to the solution with vigorous stirring and stir for 120 minutes at room temperature to obtain copper amine complex A. Step 2: Dissolve 3.2g of sodium hydroxide, 2g of sodium aluminate, and 2.6g of hexadecyltrimethylammonium bromide in 190g of deionized water to form a clear solution. Slowly add 70g of silica sol dropwise at 800 rpm. After aging, obtain gel B. Step 3: Mix 3g of complex A with 120g of gel B thoroughly and transfer to a stainless steel high-pressure hydrothermal reactor. Stir at 100°C. o Crystallize at C for 10 hours, then at 190°C o Crystallize at C for 24 hours. After crystallization, filter and dry the product. Then, heat the product to 400℃ at 2℃ / min and calcine for 2 hours. Next, heat the product to 600℃ at 8℃ / min and calcine for 5 hours to obtain thin c-axis copper-based mordenite nanosheet catalyst with uniform morphology. After ammonium ion exchange, the catalyst is used for syngas relay catalysis.

[0031] Comparative Example 1 The molar ratio of the raw materials for catalyst preparation is: 6Na2O:Al2O3:30SiO2:78H2O. (1) Dissolve NaOH in H2O under stirring; (2) Mix sodium aluminate with the above NaOH solution and stir until completely dissolved; (3) Dilute the above solution with H2O; (4) Add silicon source and stir for 30 min. Place the above materials in a stainless steel reactor lined with Teflon and let it stand at 170°C for 72 h to crystallize. The product is washed with water until pH < 10, dried and calcined at 100°C to obtain MOR molecular sieve. After ammonium ion exchange, it is used for syngas relay catalytic reaction. The evaluation results are as follows. Figure 6 As shown. From the appendix Figure 6It can be seen that the conversion rate of dimethyl ether increased from 8.5% to 21.7% and then began to decrease. The selectivity of methyl acetate and acetic acid (MA+AA) increased to 96.4% after 4 hours and then decreased rapidly, indicating catalyst deactivation.

[0032] Comparative Example 2 The molar ratio of the raw materials for catalyst preparation is: 6Na2O:Al2O3:30SiO2:78H2O:3TEAOH:3CTAB. Catalyst preparation method: (1) Dissolve NaOH in H2O under stirring; (2) Mix sodium aluminate with the above NaOH solution and stir until completely dissolved; (3) Dilute the above solution with H2O; (4) Add silicon source and stir for 30 min; (5) Mix tetraethylammonium hydroxide and hexadecyltrimethylammonium bromide separately, stir, and then add the solution from step 4 and stir; (6) Add 4% seed crystals; (7) Place the above materials in a stainless steel reactor lined with Teflon and let it stand at 190°C for 15 h to crystallize. The product is washed with water until pH < 10, dried and calcined at 100°C to obtain MOR molecular sieve, which is used for syngas relay catalytic reaction after ammonium ion exchange. Figure 1 As shown, the catalysts prepared in Examples 1, 2, 1, and 2 all exhibited characteristic diffraction peaks of mordenite MOR.

[0033] like Figure 2 As shown, the catalyst prepared in Example 1 has a thin c-axis nanosheet structure. like Figure 3 As shown, the catalyst prepared in Example 2 has a thin c-axis nanosheet structure; the thin c-axis copper-based mordenite nanosheets grow along the ab plane, with the c-axis thickness maintained between 20 nm and 100 nm, and form a three-dimensional flower-like structure by self-assembly stacking and aggregating with each other.

[0034] like Figure 4 As shown, the catalyst prepared in Comparative Example 1 has a large-sized blocky structure.

[0035] like Figure 5 As shown, the catalyst prepared in Comparative Example 2 has a large columnar structure.

[0036] Table 1 is a summary of the elemental composition of the catalysts prepared in Example 1 and Comparative Example 1.

[0037] Table 1 As shown in Table 1, the catalyst in Example 1 contains 42.48% silicon, 5.89% aluminum, 50.56% oxygen, and 1.07% copper. The catalyst in Example 2 contains 42.36% silicon, 4.64% aluminum, and 53.00% oxygen.

Claims

1. A method for preparing thin c-axis copper-based mordenite nanosheets, characterized in that, Includes the following steps; Step 1: Dissolve the copper source in deionized water, add the nitrogen-containing ligand dropwise to the copper source dissolved in deionized water, and stir vigorously to obtain copper amine complex A; Step 2: Mix the aluminum source, alkali source, silicon source, template agent, and water evenly to obtain gel B; Step 3: Mix copper ammonium complex A with gel B, perform hydrothermal crystallization, and then filter, dry and calcine to obtain thin c-axis copper-based mordenite nanosheets with regular morphology. The nitrogen-containing ligand is at least one of linear alkyl polyamines, cyclic amines, and polyethylene polyamines; The linear alkyl polyamine is at least one of ethylenediamine, propylenediamine, and butanediamine; The cyclic amine is at least one of piperazine, aziridine, and pyrazole; Polyethylene polyamine is at least one of diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and pentaethylenehexamine; In step 1, the molar ratio of copper source to nitrogen-containing ligand is 1:(0.1~10); In step 2, the aluminum source is one or more of aluminum nitrate, aluminum sulfate, boehmite, sodium aluminate, aluminum isopropoxide, and aluminum hydroxide; the amount used is calculated based on the number of moles of Al2O3 it contains. The alkali source is at least one of the hydroxides of alkali metal M, and the amount used is calculated based on the number of moles of M2O it contains. The silicon source is at least one of sodium silicate, potassium silicate, fumed silica, tetraethyl orthosilicate, tetramethyl orthosilicate, silica sol, and silica fume, and the amount used is calculated based on the number of moles of SiO2 it contains. The template agent is at least one of the following: quaternary ammonium salt cationic surfactant, quaternary ammonium base compound, and nitrogen-containing heterocyclic organic compound, specifically at least one of the following: decaalkyltrimethylammonium chloride, dodecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, dodecyltrimethylammonium hydroxide, tetrapropylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium bromide, tetraethylammonium bromide, triethylamine, and morpholine, and the amount used is calculated based on its own molar number; The raw material molar ratio is SiO2:Al2O3:M2O:template agent:H2O=1:(0.01~0.08):(0.05~0.5):(0.01~0.1):(5~50); In step 3, the mass ratio of copper amine complex A to gel B is (0.01~0.1):

1.

2. The method for preparing thin c-axis copper-based mordenite nanosheets according to claim 1, characterized in that, In step 1, the copper source is a soluble copper salt, selected from at least one of copper nitrate, copper acetate, copper sulfate, copper chloride, and copper bromide.

3. The method for preparing thin c-axis copper-based mordenite nanosheets according to claim 2, characterized in that, In the above preparation method, stirring in step 1 is carried out in a water bath at 20~60℃ for 0.5~4 hours, and the pH of the solution is maintained at 6~10.

4. The method for preparing thin c-axis copper-based mordenite nanosheets according to claim 1, characterized in that, In step 2, the stirring speed is 100~1000 r / min.

5. The method for preparing thin c-axis copper-based mordenite nanosheets according to claim 4, characterized in that, In step 3, the hydrothermal crystallization is a two-stage crystallization method, with the first stage being crystallization at 100℃~140℃ for 2~10 hours and the second stage being crystallization at 160℃~220℃ for 18~72 hours. In step 3, the roasting is a two-stage roasting process. The first stage roasting temperature is 200℃~400℃, the heating rate is 1~10℃ / min, and the roasting time is 1~4h. The second stage roasting temperature is 550℃~800℃, the heating rate is 5~15℃ / min, and the roasting time is 2~6h.

6. Thin c-axis copper-based mordenite nanosheets prepared by any one of claims 1-5, characterized in that, Thin c-axis copper-based mordenite nanosheets are grown along the ab plane, with the c-axis thickness maintained between 20 nm and 100 nm. They are stacked and aggregated to form a three-dimensional flower-like structure through self-assembly.

7. The application of thin c-axis copper-based mordenite nanosheets prepared by any one of claims 1-5, characterized in that, The application of thin c-axis copper-based mordenite nanosheets as a catalyst in the carbonylation reaction of dimethyl ether includes the following steps: A mixture of dimethyl ether (DME) and carbon monoxide (CO) was passed into a fixed-bed reactor packed with thin c-axis copper-based mordenite nanosheets as a catalyst to produce methyl acetate and acetic acid. The catalyst is obtained by ammonium ion exchange from the thin c-axis copper-based mordenite nanosheets. The molar ratio of CO to DME in the mixed gas is (0.5~10):1, the reaction temperature is 160℃~250℃, and the reaction pressure is 1~6MPa, so as to realize the carbonylation reaction of dimethyl ether.

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