Modified molecular sieve catalyst and preparation method thereof

Abstract

The invention relates to the technical field of molecular sieve preparation, and particularly discloses a modified molecular sieve catalyst and a preparation method thereof. The modified molecular sieve catalyst comprises the following raw materials: 8-12 g of a modified NaY molecular sieve and 1-5 ml of a lanthanum nitrate solution, the modified NaY molecular sieve contains a nitrogen element, and the nitrogen element is modified melamine; the preparation method comprises the following steps: uniformly mixing 8-12g of modified NaY molecular sieve and 1-5ml of lanthanum nitrate solution, and stirring at 75-85 DEG C for 7-9 hours at the rotating speed of 450-550r / min; after stirring is completed, the mixture is transferred to a centrifugal machine, the rotating speed ranges from 4000 r / min to 4400 r / min, the primary centrifugation time ranges from 1 min to 3 min, washing is conducted till the solution conductivity ranges from 450 microseconds to 500 microseconds, the mixture is put into a drying oven to be dried for 7 h to 9 h at the temperature of 100 DEG C to 140 DEG C, then roasting is conducted at the temperature of 550 DEG C to 650 DEG C, and the modified molecular sieve catalyst is obtained. The modified molecular sieve catalyst has the advantage that the defect that the activity of the molecular sieve catalyst is still insufficient can be overcome.

Description

Technical Field

[0001] This application relates to the field of molecular sieve preparation technology, and more specifically, to a modified molecular sieve catalyst and its preparation method. Background Technology

[0002] In industry, porous inorganic materials are widely used as catalysts and catalyst supports. Porous materials have relatively high specific surface areas and unobstructed pore structures, making them excellent catalytic materials or catalyst supports. Porous materials can be broadly categorized as: amorphous porous materials, crystalline molecular sieves, and modified layered materials. The subtle differences in the structures of these materials indicate significant differences in their catalytic and adsorption properties, as well as differences in various observable properties used to characterize them, such as their morphology, specific surface area, pore size, and the variability of these dimensions.

[0003] Y-type molecular sieves are octahedral zeolites with excellent thermal stability and catalytic activity, mainly used as catalysts in catalytic cracking processes. The unit cell of NaY molecular sieve consists of eight sodium cages, which are composed of 192 silicon-oxygen tetrahedra and aluminum-oxygen tetrahedra. Because NaY molecular sieves contain a large amount of sodium ions, the molecular sieve structure is easily destroyed at high temperatures. Lanthanum nitrate is usually used to exchange sodium ions with ions. However, excess lanthanum ions will deposit on the surface of the molecular sieve in the form of oxides, which can easily cause blockage of the molecular sieve channels, reduce the diffusion and adsorption of the molecular sieve, and thus affect the activity of the molecular sieve catalyst. Summary of the Invention

[0004] To address the shortcomings in the activity of molecular sieve catalysts, this application provides a modified molecular sieve catalyst and its preparation method.

[0005] Firstly, this application provides a modified molecular sieve catalyst, which adopts the following technical solution: A modified molecular sieve catalyst comprises the following raw materials: 8-12g of modified NaY molecular sieve and 1-5ml of lanthanum nitrate solution, wherein the modified NaY molecular sieve contains nitrogen element, and the nitrogen element is modified melamine.

[0006] When lanthanum nitrate and NaY molecular sieve undergo ion exchange, the rate of ion exchange accelerates when there is an excess of lanthanum ions. A large number of lanthanum ions rapidly exchange with sodium ions on the surface of the molecular sieve. Due to the rapid ion exchange, some lanthanum ions do not have enough time to enter the internal channels of the molecular sieve and instead accumulate on the surface. These surface-accumulated lanthanum ions undergo hydrolysis and eventually deposit as oxides on the surface of the molecular sieve. Melamine has a high nitrogen content, and nitrogen can increase the porosity of NaY molecular sieves, thus improving the defect of lanthanum ions depositing as oxides on the surface of the molecular sieve.

[0007] Preferably, the modified melamine comprises the following raw materials: melamine, formaldehyde, sodium hydroxide solution, and aminosulfonic acid.

[0008] Since aminosulfonic acid contains sulfonic acid groups, which are strong acidic functional groups, introducing sulfonic acid groups into melamine is beneficial for providing more acidic sites for molecular sieve catalysts. Catalytic reactions such as cracking require acidic sites to promote the reaction. These acidic sites can participate in the proton transfer process in the catalytic reaction, which is beneficial for enhancing the activity of the catalyst.

[0009] Preferably, the modified melamine comprises the following raw materials in the following amounts: 1-3g melamine, 3-7ml formaldehyde, 26-34ml sodium hydroxide solution, and 2.5-4.3g aminosulfonic acid.

[0010] Since aminosulfonic acid is a key reagent for introducing acidic functional groups onto melamine, an appropriate amount of aminosulfonic acid can ensure that enough sulfonic acid groups are introduced into the melamine molecule during the sulfonation reaction, thereby endowing the modified melamine with acidic properties. The presence of acidic functional groups can enhance the interaction between melamine and NaY molecular sieve, optimize the pore structure of the molecular sieve, and thus improve the activity of the catalyst.

[0011] Preferably, the modified melamine is prepared by adding 1-3g of melamine and 3-7ml of formaldehyde to a flask, adjusting the pH value with 8-12ml of sodium hydroxide solution, then heating to 65-75℃ and reacting for 1-2 hours to obtain a precursor solution. 2.5-4.3g of aminosulfonic acid is added to the precursor solution, the pH value is adjusted with 18-22ml of sodium hydroxide solution, then heating to 85-95℃ and sulfonating for 2-4 hours to obtain the modified melamine solution.

[0012] Preferably, the modified NaY molecular sieve comprises the following raw materials: NaY molecular sieve, potassium hydroxide, and modified melamine.

[0013] Because potassium hydroxide, as an activator, can undergo an etching reaction with the framework of NaY molecular sieves, the resulting small molecules such as water and carbon dioxide can act as oxidants to physically activate and further expand the size of the original pores of the NaY molecular sieves or form new pores. This is beneficial for improving the porosity and specific surface area of ​​the NaY molecular sieves, increasing the contact opportunities between reactant molecules and active sites. Potassium hydroxide can also promote the doping of nitrogen elements from melamine into the NaY molecular sieves, forming a nitrogen-doped molecular sieve structure, thereby improving the activity of the molecular sieve catalyst.

[0014] Preferably, the modified NaY molecular sieve comprises the following raw materials in parts by weight: 3.5-7.3 parts NaY molecular sieve, 20-23 parts potassium hydroxide, and 4-6.8 parts modified melamine.

[0015] Preferably, the modified NaY molecular sieve is prepared by: weighing 3.5-7.3 parts of NaY molecular sieve and mixing it with 4-6.8 parts of modified melamine, pyrolyzing the mixture at 450-550℃ for 1-3 hours under nitrogen protection to obtain a precursor, adding 20-23 parts of potassium hydroxide for activation at 500-600℃ to obtain the modified NaY molecular sieve.

[0016] Because melamine has a high nitrogen content, it undergoes a thermal decomposition reaction at high temperatures, gradually decomposing and releasing gases such as ammonia. These gases create pressure inside the molecular sieve, requiring it to find a way to escape. During this escape process, the pores of the molecular sieve are scourted and expanded, causing the originally small pores or gaps to become larger, thereby increasing the porosity of the molecular sieve.

[0017] Secondly, this application provides a method for preparing a modified molecular sieve catalyst, employing the following technical solution: A method for preparing a modified molecular sieve catalyst includes the following steps: S1: Take 8-12g of modified NaY molecular sieve and mix it evenly with 1-5ml of lanthanum nitrate solution. Stir at 75-85℃ for 7-9h at a speed of 450-550r / min. S2: After stirring, transfer to a centrifuge at a speed of 4000-4400 r / min for 1-3 min. Wash with water until the conductivity of the solution is 450-500 μs. Place in an oven and dry at 100-140℃ for 7-9 h. Then calcine at 550-650℃ to obtain the modified molecular sieve catalyst.

[0018] In summary, this application has the following beneficial effects: 1. When there is an excess of lanthanum ions during the ion exchange between lanthanum nitrate and NaY molecular sieve, the ion exchange rate will accelerate. A large number of lanthanum ions will rapidly exchange with sodium ions on the surface of the molecular sieve. Due to the rapid ion exchange, some lanthanum ions do not have enough time to enter the internal channels of the molecular sieve and instead accumulate on the surface. These lanthanum ions that accumulate on the surface will undergo hydrolysis and eventually be deposited on the surface of the molecular sieve in the form of oxides. Melamine has a high nitrogen content, and nitrogen can increase the porosity of NaY molecular sieves. Therefore, it can improve the defect of lanthanum ions being deposited on the surface of the molecular sieve in the form of oxides.

[0019] 2. Since aminosulfonic acid contains sulfonic acid groups, which are strong acidic functional groups, introducing sulfonic acid groups into melamine is beneficial to providing more acidic sites for molecular sieve catalysts. Catalytic reactions such as cracking require acidic sites to promote the reaction. These acidic sites can participate in the proton transfer process in the catalytic reaction, which is beneficial to enhancing the activity of the catalyst.

[0020] 3. Since aminosulfonic acid is a key reagent for introducing acidic functional groups onto melamine, an appropriate amount of aminosulfonic acid can ensure that enough sulfonic acid groups are introduced into the melamine molecule during the sulfonation reaction, thereby endowing the modified melamine with acidic properties. The presence of acidic functional groups can enhance the interaction between melamine and NaY molecular sieve, optimize the pore structure of the molecular sieve, and thus improve the activity of the catalyst. Detailed Implementation

[0021] The present application will be further described in detail below with reference to Examples 1-8 and Comparative Examples 1-2.

[0022] raw material Lanthanum nitrate Aladdin Biochemical Technology Co., Ltd.; Melamine CAS: 108-78-1; Formaldehyde CAS: 50-00-0; Sodium hydroxide CAS: 1310-73-2; Aminosulfonic acid CAS: 5329-14-6; NaY molecular sieve Zibo Jiulong Chemical Technology Co., Ltd.; Potassium hydroxide CAS: 1310-58-3.

[0023] Example 1 A modified molecular sieve catalyst comprises the following raw materials: 10g of modified NaY molecular sieve and 3ml of lanthanum nitrate solution.

[0024] Specifically, the preparation method of modified molecular sieve catalysts includes the following steps: S1: Add 2g of melamine and 5ml of 38% formaldehyde solution to a flask, adjust the pH to 8.5 with 10ml of sodium hydroxide solution, then heat to 70℃ and react for 1.5h to obtain a precursor solution. Add 3.4g of aminosulfonic acid to the precursor solution, adjust the pH to 12 with 20ml of sodium hydroxide solution, then heat to 90℃ and sulfonate for 3h to obtain a modified melamine solution. S2: Weigh 5.4g of NaY molecular sieve and 5.4g of modified melamine and mix them. Pyrolyze the mixture at 500℃ for 2h under nitrogen protection to obtain the precursor. Add 21.5g of potassium hydroxide for activation at 550℃ to obtain the modified NaY molecular sieve. S3: Take 10g of modified NaY molecular sieve and mix it evenly with 3ml of lanthanum nitrate solution, stir at 80℃ for 8h, and the speed is 500r / min; S4: After stirring, transfer to a centrifuge at 4200 r / min for 2 min. Wash with water until the solution conductivity is 475 μs. Place in an oven and dry at 120℃ for 8 h. Then calcine at 600℃ to obtain the modified molecular sieve catalyst.

[0025] Example 2-Example 3 The difference from Example 1 is that the amount of each component added to the modified molecular sieve catalyst is different, as shown in Table 1.

[0026] Table 1. Amounts of each component added to the modified molecular sieve catalysts in Examples 1-3 Example 1 Example 2 Example 3 Modified NaY molecular sieve 10g 8g 12g Lanthanum nitrate 3ml 5ml 1ml Example 4-Example 5 The difference from Example 1 is that the amount of each component added to the modified NaY molecular sieve is different, as shown in Table 2.

[0027] Table 2. Amounts (g) of each component added to the modified NaY molecular sieve in Examples 1 and 4-5. Example 1 Example 4 Example 5 NaY molecular sieve 5.4 7.3 3.5 potassium hydroxide 21.5 20 23 Modified melamine 5.4 4 6.8 Example 6 The difference from Example 1 is that modified melamine is used instead of an equal amount of melamine.

[0028] Examples 7-8 The difference from Example 1 is that the amount of each component added in the modified melamine is different, as shown in Table 3.

[0029] Table 3. Amounts of each component added in the modified melamine in Examples 1 and 7-8. Example 1 Example 7 Example 8 melamine 2g 1g 3g formaldehyde 5ml 7ml 3ml Sodium hydroxide solution 30ml 26ml 34ml Aminosulfonic acid 3.4g 2.5g 4.3g Comparative Example 1 The difference from Example 1 is that modified melamine is no longer added.

[0030] Comparative Example 2 The difference from Example 1 is that the modified NaY molecular sieve is replaced with an equal amount of NaY molecular sieve.

[0031] Performance testing I. Activity Performance Testing Three samples, each containing 80 mg, were taken from Examples 1-8 and Comparative Examples 1-2. The reaction was carried out in a quartz tube reactor with an inner diameter of 4 mm. The catalyst was heated to 500 °C and pretreated for 30 min in an atmosphere of 10% O2 / 5% H2O / N2 at a flow rate of 250 mL / min. After the pretreatment, the reactor was allowed to cool naturally to the adsorption temperature. The reactor was then switched to the bypass path and 200 ppm NO and 400 ppm CO were added. After the atmosphere stabilized, the reactor was switched back to the catalyst path. After the catalyst adsorption was saturated, the catalyst was desorbed at a rate of 10 °C / min.

[0032] The test data is shown in Table 4.

[0033] Table 4. Activity performance test table for Examples 1-8 and Comparative Examples 1-2 NO adsorption capacity (μmol / gcat) CO oxidation temperature (°C) Example 1 65.5 185 Example 2 64.7 190 Example 3 64.3 195 Example 4 63.0 205 Example 5 63.2 200 Example 6 61.8 215 Example 7 62.9 210 Example 8 62.4 215 Comparative Example 1 58.7 245 Comparative Example 2 55.6 260 As can be seen from Example 1 and Comparative Example 1, and Table 4, compared with Example 1, the NO adsorption capacity of Comparative Example 1 decreased significantly and the CO oxidation temperature increased significantly. This indicates that, compared with not adding modified melamine, adding modified melamine can effectively increase the NO adsorption capacity and effectively reduce the CO oxidation temperature, which is beneficial to improving the activity of the molecular sieve catalyst.

[0034] The reason for this is that aminosulfonic acid contains sulfonic acid groups, which are strong acidic functional groups. Introducing sulfonic acid groups into melamine helps to provide more acidic sites for molecular sieve catalysts. Catalytic reactions such as cracking require acidic sites to promote the reaction. These acidic sites can participate in the proton transfer process in the catalytic reaction, which helps to enhance the activity of the catalyst.

[0035] Combining Example 1 and Comparative Example 2 with Table 4, it can be seen that, compared with Example 1, the NO adsorption capacity of Comparative Example 2 is significantly reduced and the CO oxidation temperature is significantly increased. This indicates that, compared with the addition of conventional NaY molecular sieve, the addition of modified NaY molecular sieve can effectively increase the NO adsorption capacity and effectively reduce the CO oxidation temperature, thereby improving the activity of the molecular sieve catalyst.

[0036] The reason for this is that melamine has a high nitrogen content, and nitrogen can increase the porosity of NaY molecular sieves. Therefore, it can improve the defect that lanthanum ions will deposit on the surface of molecular sieves in the form of oxides. Potassium hydroxide, as an activator, can undergo an etching reaction with the framework of NaY molecular sieves. The small molecules such as water and carbon dioxide produced can act as oxidants to physically activate and further expand the size of the original pores of NaY molecular sieves or form new pores. This is beneficial to improving the porosity and specific surface area of ​​NaY molecular sieves, increasing the contact opportunities between reactant molecules and active sites. Potassium hydroxide can also promote the doping of nitrogen from melamine into NaY molecular sieves to form nitrogen-doped molecular sieve structures, thereby improving the activity of molecular sieve catalysts.

[0037] Combining Examples 1 and 2-3 with Table 4, it can be seen that compared with Example 1, the NO adsorption capacity of Examples 2 and 3 both decreased, and the CO oxidation temperature both increased. This indicates that the amount of each component added to the modified molecular sieve catalyst affects the NO adsorption capacity and CO oxidation temperature of the molecular sieve catalyst, thereby affecting the activity of the molecular sieve catalyst. The amount of each component added to the modified molecular sieve catalyst in Example 1 is optimal.

[0038] Combining Examples 1 and 4-5 with Table 4, it can be seen that, compared with Example 1, the NO adsorption capacity of Examples 4 and 5 decreased and the CO oxidation temperature increased. This indicates that the amount of each component added to the modified NaY molecular sieve affects the NO adsorption capacity and CO oxidation temperature of the molecular sieve catalyst, thereby affecting the activity of the molecular sieve catalyst. The amount of each component added to the modified NaY molecular sieve in Example 1 is optimal.

[0039] Combining Examples 1 and 6 with Table 4, it can be seen that, compared with Example 1, the NO adsorption capacity of Example 6 is significantly reduced, and the CO oxidation temperature is significantly increased. This indicates that, compared with adding conventional melamine, adding modified melamine can effectively increase the NO adsorption capacity and effectively reduce the CO oxidation temperature, thereby improving the activity of the molecular sieve catalyst.

[0040] Combining Examples 1 and 7-8 with Table 4, it can be seen that, compared with Example 1, the NO adsorption capacity of Examples 7 and 8 decreased and the CO oxidation temperature increased. This indicates that the amount of each component added to the modified melamine affects the NO adsorption capacity and CO oxidation temperature of the molecular sieve catalyst, thereby affecting the activity of the molecular sieve catalyst. The amount of each component added to the modified melamine in Example 1 is optimal.

[0041] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A modified molecular sieve catalyst characterized by, The modified NaY molecular sieve comprises the following raw materials: 8-12 g of modified NaY molecular sieve containing nitrogen element, the nitrogen element being modified melamine and 1-5 ml of lanthanum nitrate solution.

2. The modified molecular sieve catalyst of claim 1, wherein, The modified melamine comprises the following raw materials: melamine, formaldehyde, sodium hydroxide solution and sulfamic acid.

3. The modified molecular sieve catalyst of claim 2, wherein: The modified melamine comprises the following raw materials by weight: 1-3 g of melamine, 3-7 ml of formaldehyde, 26-34 ml of sodium hydroxide solution and 2.5-4.3 g of sulfamic acid.

4. The modified molecular sieve catalyst of claim 3, wherein, The preparation method of the modified melamine comprises the following steps: adding 1-3 g of melamine and 3-7 ml of formaldehyde into a flask, adjusting the pH value by using 8-12 ml of sodium hydroxide solution, then heating to 65-75 DEG C, reacting for 1-2 h to obtain a precursor solution, adding 2.5-4.3 g of sulfamic acid into the precursor solution, adjusting the pH value by using 18-22 ml of sodium hydroxide solution, then heating to 85-95 DEG C, and sulfonating for 2-4 h to obtain the modified melamine solution.

5. The modified molecular sieve catalyst of claim 1, wherein The modified NaY molecular sieve comprises the following raw materials: NaY molecular sieve, potassium hydroxide and modified melamine.

6. The modified molecular sieve catalyst of claim 5, wherein, The modified NaY molecular sieve comprises the following raw materials by weight: 3.5-7.3 parts of NaY molecular sieve, 20-23 parts of potassium hydroxide and 4-6.8 parts of modified melamine.

7. The modified molecular sieve catalyst of claim 6, wherein, The preparation method of the modified NaY molecular sieve comprises the following steps: mixing 3.5-7.3 parts of NaY molecular sieve with 4-6.8 parts of modified melamine, pyrolyzing the mixture under nitrogen protection at 450-550 DEG C for 1-3 h to obtain a precursor, adding 20-23 parts of potassium hydroxide for activation, and heating at an activation temperature of 500-600 DEG C to obtain the modified NaY molecular sieve.

8. A process for preparing a modified molecular sieve catalyst according to any one of claims 1 to 7, characterized in that, The method comprises the following steps: S1: uniformly mixing 8-12 g of modified NaY molecular sieve with 1-5 ml of lanthanum nitrate solution, stirring at 75-85 DEG C for 7-9 h at a rotating speed of 450-550 r / min; S2: transferring the mixture to a centrifuge after the stirring is completed, centrifuging once at a rotating speed of 4000-4400 r / min for 1-3 min, washing with water until the conductivity of the solution is 450-500 mu s, placing the mixture into an oven for drying at 100-140 DEG C for 7-9 h, and then calcining at 550-650 DEG C to obtain the modified molecular sieve catalyst.