Catalyst based on kl zeolite modified with sn and its preparation method and application

Abstract

The application belongs to the technical field of new materials, and relates to a catalyst based on Sn modified KL molecular sieve as well as a preparation method and application thereof. An aluminum source and a potassium source are added into water to prepare a KAlO2 solution, an ethanol solution of a divalent tin salt is added into a silicon source to uniformly mix to obtain a mixed solution, the KAlO2 solution is added into the mixed solution to fully stir to obtain an initial sol, the initial sol is subjected to crystallization treatment, and then is heated to 450-650 DEG C to perform calcination treatment to obtain Sn modified KL molecular sieve, and Pt is loaded on the Sn modified KL molecular sieve by using an atomic layer deposition method. The catalyst based on the Sn modified KL molecular sieve prepared by the application has better catalytic performance in a naphtha reforming reaction for preparing aromatic hydrocarbons.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of new materials, and relates to a catalyst based on Sn-modified KL molecular sieve as well as a preparation method and application thereof. BACKGROUND

[0002] The information disclosed in this Background section is only for the purpose of increasing an understanding of the general background of the application and does not necessarily constitute an admission or a recognition that the information forms part of the prior art that is already known in any country in the world.

[0003] Production of liquid fuel based on non-petroleum organic matter is an important means to solve the contradiction between energy demand and limited oil reserves. The oil produced by the coal-to-oil industry using indirect liquefaction process contains a large amount of naphtha, which is rich in linear alkanes and has a low market value. How to convert it into higher value chemicals is an urgent task to optimize the product structure of coal-to-oil and improve the competitiveness of the coal-to-oil industry. Although a single / multi-metallic promoter is introduced into the traditional Pt / Al2O3 catalyst, the efficiency of linear alkane reforming to aromatics is still low. The Pt / KL catalyst shows high activity and aromatics selectivity in the C6-C9 alkane reforming to aromatics reaction, but still faces the problem of carbon deposition deactivation.

[0004] According to the research and understanding of the inventors, the commonly used promoter Sn can divide Pt particles into smaller atomic clusters to improve the dispersion and inhibit Pt agglomeration sintering, and at the same time, through atomic layer deposition of active metal Pt, the dispersion of active metal Pt can be precisely controlled to improve the dispersion of active metal Pt, thereby solving the problem of carbon deposition deactivation of Pt / KL catalyst. Through further research of the inventors, it is unexpectedly found that on the basis of atomic layer deposition of active metal Pt, controlling the location of Sn on the KL molecular sieve affects the catalytic performance of the Pt / KL catalyst, and therefore the present application is proposed. SUMMARY

[0005] In order to solve the problems of the prior art, the present application aims to provide a catalyst based on Sn-modified KL molecular sieve as well as a preparation method and application thereof. The catalyst based on Sn-modified KL molecular sieve prepared by the present application has better catalytic performance in naphtha reforming reaction to prepare aromatics.

[0006] In order to achieve the above-mentioned purpose, the technical scheme of the present application is as follows:

[0007] In one aspect, a preparation method of a catalyst based on Sn-modified KL molecular sieve, an aluminum source and a potassium source are added into water to prepare a KAlO2 solution, an ethanol solution of a divalent tin salt is added into a silicon source to mix uniformly to obtain a mixed solution, the KAlO2 solution is added into the mixed solution to obtain an initial sol by stirring sufficiently, the initial sol is subjected to a crystallization treatment, and then is heated to 450-650 DEG C to perform a calcination treatment to obtain the Sn-modified KL molecular sieve, and Pt is loaded on the Sn-modified KL molecular sieve by using an atomic layer deposition method.

[0008] In the formula, the aluminum source, the potassium source, the divalent tin salt and the silicon source are calculated in terms of Al2O3, K2O, SnO and SiO2 respectively, and the molar ratio is 1:8-30:0.001-2:3.5-25.

[0009] There are various methods for loading active metal Pt, for example, in the impregnation method, the carrier is impregnated in a solution containing Pt, and then is calcined after impregnation. However, when Pt is loaded by using the impregnation method, the location of Pt cannot be controlled, the location of Pt has great randomness, and the size of the obtained Pt particles is greatly different, which is not conducive to solving the problem of carbon deposition inactivation of the Pt / KL catalyst. Among the various methods for loading active metal Pt, the atomic layer deposition has the technical advantage of self-limiting growth, can control the location of metal Pt on the KL molecular sieve at the atomic level, and can introduce the Pt source into the molecular sieve channel for location by controlling the deposition process, so that the controllable location of Pt on the KL molecular sieve can be realized, and high-dispersed Pt nanoparticles can be obtained, thereby being conducive to solving the problem of carbon deposition inactivation.

[0010] Based on the atomic layer deposition of the active metal Pt, the present application further studies the influence of Sn location on the Pt / KL catalyst. It is found that, when the Sn-modified KL molecular sieve with Sn located in the framework of the KL molecular sieve is used as the carrier by using the preparation method of the present application, and the active metal Pt is loaded by using the atomic layer deposition, the catalyst has higher catalytic activity.

[0011] Specifically, in the added ethanol solution of the divalent tin salt, ethanol can be used as a molecular sieve structure directing agent for the growth of the KL molecular sieve, and the existence of the hydroxyl group in the ethanol will have an influence on the crystallization and growth process of the molecular sieve; the ethanol solution of Sn is first combined with the silicon source to control the chemical environment of the silicon source, and then is mixed with the KAlO2 solution to have an influence on the formation of the silicon-oxygen tetrahedron and the combination with the aluminum-oxygen tetrahedron. Meanwhile, compared with the tetravalent tin, the Sn added in the present application is divalent tin, and the bonding of Sn in the framework of the KL molecular sieve is more conducive to the improvement of the catalytic performance of the finally formed catalyst.

[0012] In another aspect, a catalyst based on Sn-modified KL molecular sieve is obtained by the above preparation method.

[0013] In a third aspect, the application provides the use of the Sn-modified KL zeolite catalyst in the preparation of aromatic hydrocarbons by naphtha fraction reforming reaction.

[0014] The application has the following beneficial effects:

[0015] 1. The preparation method can regulate the positioning of Sn in the framework of the KL zeolite, and has good repeatability.

[0016] 2. The preparation method uses atomic layer deposition technology to regulate the positioning of active metal Pt on the Sn-modified KL zeolite as a carrier, which, in combination with the positioning of Sn in the framework of the KL zeolite, is more conducive to the improvement of the catalytic activity of the catalyst. BRIEF DESCRIPTION OF DRAWINGS

[0017] The accompanying drawings, which form a part of the present application, are included to provide further understanding of the application, and are incorporated in and constitute a part of the specification, illustrate embodiments of the present application and explain them, and do not constitute an inappropriate limitation on the present application.

[0018] Figure 1 XRD pattern of the conventional KL zeolite prepared for the comparative example of the present application;

[0019] Figure 2 SEM image of the Sn-modified KL zeolite in the framework of the Sn-positioned KL zeolite prepared for Example 1 of the present application;

[0020] Figure 3 XRD pattern of the Sn-modified KL zeolite in the framework of the Sn-positioned KL zeolite prepared for Example 1 of the present application;

[0021] Figure 4 SEM image of the Sn-modified KL zeolite in the framework of the Sn-positioned KL zeolite prepared for Example 1 of the present application;

[0022] Figure 5 XRD pattern of the Sn-modified KL zeolite on the surface outside the framework of the Sn-positioned KL zeolite prepared for Example 2 of the present application. DETAILED DESCRIPTION

[0023] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs.

[0024] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments in accordance with the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, steps, operations, elements, components, and / or groups thereof, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or groups thereof.

[0025] In view of the fact that the present application is based on atomic layer deposition of active metal Pt, the positioning of Sn in the KL molecular sieve affects the catalytic performance of the Pt / KL catalyst, the present application proposes a catalyst based on Sn modified KL molecular sieve and a preparation method and application thereof.

[0026] In a typical embodiment of the present application, a preparation method of a catalyst based on Sn modified KL molecular sieve is provided. An aluminum source and a potassium source are added to water to prepare a KAlO2 solution, an ethanol solution of a divalent tin salt is added to a silicon source to mix uniformly to obtain a mixed solution, the KAlO2 solution is added to the mixed solution to stir sufficiently to obtain an initial sol, the initial sol is subjected to crystallization treatment, and then heated to 450-650 DEG C for calcination treatment to obtain Sn modified KL molecular sieve, and Pt is loaded on the Sn modified KL molecular sieve by atomic layer deposition.

[0027] In the formula, the aluminum source, the potassium source, the divalent tin salt and the silicon source are respectively calculated as Al2O3, K2O, SnO and SiO2, and the molar ratio is 1:8-30:0.001-2:3.5-25.

[0028] In some embodiments, the aluminum source is aluminum sulfate, aluminum hydroxide, aluminum oxide or aluminum isopropoxide.

[0029] In some embodiments, the potassium source is potassium hydroxide.

[0030] In some embodiments, the divalent tin salt is stannous oxide, tin diiodide, tin dichloride, stannous sulfate or stannous oxalate.

[0031] In some embodiments, the KAlO2 solution is added to the mixed solution and stirred sufficiently for 60-180 min.

[0032] In some embodiments, the temperature of the crystallization treatment is 165-185 DEG C.

[0033] In some embodiments, the crystallization treatment is performed for 20-72 h.

[0034] In some embodiments, the crystallization treatment is followed by washing and drying, and then calcination treatment. Specifically, the washing is performed until the pH is 7-8. Specifically, the drying temperature is 110-130 DEG C.

[0035] In some embodiments, the time for the calcination treatment is 3-6 hours.

[0036] In some embodiments, the process for loading Pt on the Sn-modified KL zeolite by atomic layer deposition is as follows: placing the Sn-modified KL zeolite on the surface of a substrate, and performing at least one cycle of deposition using a Pt source; each cycle of deposition is performed by pulsing, depositing and purging using the Pt source, and pulsing, depositing and purging using an oxidizing agent.

[0037] In one or more embodiments, the time for pulsing, depositing and purging using the Pt source is 0.3-0.5 s, 25-35 s and 55-65 s, respectively. The Pt source is preferably trimethyl-methylcyclopentadiene platinum. The temperature for using the Pt source is 60-70 °C.

[0038] In one or more embodiments, the time for pulsing, depositing and purging using the oxidizing agent is 0.9-1.1 s, 25-35 s and 55-65 s, respectively. The oxidizing agent is preferably O3.

[0039] In one or more embodiments, the number of cycles of deposition using the Pt source is 4-6.

[0040] In one or more embodiments, the temperature of the reaction cavity in the atomic layer deposition is 180-220 °C.

[0041] In another embodiment of the present application, a catalyst based on the Sn-modified KL zeolite is provided, which is obtained by the above preparation method.

[0042] In a third embodiment of the present application, the use of the above catalyst based on the Sn-modified KL zeolite in the reforming reaction of a naphtha fraction to produce aromatic hydrocarbons is provided.

[0043] Specifically, the naphtha fraction is a C6-C 10 straight-chain alkane. Preferably, the naphtha fraction is n-heptane, and the target aromatic hydrocarbon is toluene.

[0044] Specifically, the conditions for the reforming reaction of the naphtha fraction to produce aromatic hydrocarbons are as follows: the mass hourly space velocity is 0.6-1.0 h -1 , the pressure is 0.15-0.25 MPa, the temperature is 470-490 °C, and the molar ratio of hydrogen to the naphtha fraction is 5-7:1.

[0045] In order to enable those skilled in the art to more clearly understand the technical solutions of the present application, the technical solutions of the present application will be described in detail below with reference to specific embodiments.

[0046] Comparative Example

[0047] Firstly, 22.6 g of Al(OH)3and 90.2 g of KOH were dissolved in 900 g of deionized water, and the solution was stirred uniformly and then transferred to a three-necked flask. The solution was heated to 98 ℃ under mechanical stirring, and then was cooled to room temperature after being clarified. 350 g of silica sol (SiO2content 30%) was added into 200 g of the above solution and stirred vigorously, and then was added into the above solution. After stirring for 2 h, an initial sol was obtained, which was transferred into a crystallization kettle and placed in an oven at 175 ℃ for 36 h. The product was cooled, filtered, washed with deionized water until the pH value was 7-8, and then was dried in an oven at 120 ℃ for more than 12 h. Finally, the product was calcined at 500 ℃ for 5 h in a muffle furnace to obtain a conventional KL molecular sieve carrier.

[0048] The obtained sample was subjected to X-ray powder diffraction test (XRD), and the result was as follows: Figure 1 The test result showed that the obtained product was a typical KL molecular sieve. Then, the sample was subjected to scanning electron microscope test (SEM), and the result was as follows: Figure 2 The result showed that the sample had a double-cone morphology.

[0049] The obtained molecular sieve was dispersed in an ethanol solvent, coated on a quartz sheet substrate, dried at room temperature, and then transferred into an ALD cavity. The reaction cavity temperature was controlled at 200 ℃, the nitrogen carrier gas flow was 50 sccm, the Pt source (trimethyl-methylcyclopentadiene platinum) was used at a temperature of 65 ℃, and the pulse, deposition and purge times of the Pt deposition process were controlled at 0.4 s, 30 s and 60 s, respectively. The pulse, deposition and purge times of the oxidant O3 were controlled at 1 s, 30 s and 60 s, respectively. The Pt deposition cycle number was 5, and a Pt-loaded molecular sieve catalyst was obtained.

[0050] Example 1

[0051] Firstly, 22.6 g of Al(OH)3and 90.2 g of KOH were dissolved in 900 g of deionized water, and the solution was stirred uniformly and then transferred to a three-necked flask. The solution was heated to 98 ℃ under mechanical stirring, and then was cooled to room temperature after being clarified. 350 g of silica sol (SiO2content 30%) was added into 200 g of the above solution and stirred vigorously, and then was added into the above solution. After stirring for 2 h, an initial sol was obtained, which was transferred into a crystallization kettle and placed in an oven at 175 ℃ for 24 h. The product was cooled, filtered, washed with deionized water until the pH value was 7-8, and then was dried in an oven at 120 ℃ overnight. Finally, the product was calcined at 500 ℃ for 6 h in a muffle furnace to obtain a carrier in which Sn was located in the KL molecular sieve framework.

[0052] The obtained sample was subjected to X-ray powder diffraction test (XRD), and the result was as follows: Figure 3The test results show that the obtained product is a typical KL molecular sieve. Subsequently, the sample is subjected to scanning electron microscope test (SEM), and the obtained Figure 4 The results show that the sample presents a double-elliptical cylindrical shape and the surface tends to be smooth.

[0053] The obtained molecular sieve is dispersed in an ethanol solvent, coated on a quartz sheet substrate, dried at room temperature, and then transferred to an ALD chamber. The reaction chamber temperature is controlled at 200°C, the nitrogen carrier gas flow is 50 sccm, the Pt source (trimethyl-methylcyclopentadiene platinum) is used at a temperature of 65°C, the pulse, deposition and purge times of the Pt deposition process are controlled at 0.4s, 30s and 60s respectively, the pulse, deposition and purge times of the oxidant O3 are controlled at 1s, 30s and 60s respectively, and the deposition cycle number of Pt is 5, thereby obtaining a Pt-loaded molecular sieve catalyst.

[0054] Example 2

[0055] First, 22.6g of Al(OH)3 and 90.2g of KOH are dissolved in 900g of deionized water, and after being stirred uniformly, the solution is transferred to a three-necked flask, heated to 98°C under mechanical stirring, and then cooled to room temperature for standby use. 350g of silica sol (SiO2 content 30%) is added to 200g of the above standby solution under vigorous stirring, and then the initial sol is obtained after being stirred for 2h, transferred to a crystallization kettle, and placed in a 175°C oven for 36h. The product is cooled, filtered, washed with deionized water until the pH is 7-8, dried in a 120°C oven for 12h or more, and finally calcined at 500°C for 5h in a muffle furnace, thereby obtaining a conventional KL molecular sieve carrier.

[0056] The obtained KL molecular sieve carrier is dispersed in an ethanol solvent, coated on a quartz sheet substrate, dried at room temperature, and then transferred to an ALD self-made reaction chamber. The reaction chamber temperature is controlled at 150°C, the nitrogen carrier gas flow is 50 sccm, the Sn source (tetra(dimethylamine) tin) is used at a temperature of 70°C, the pulse, deposition and purge times are controlled at 0.35s, 15s and 60s respectively, the pulse, deposition and purge times of the oxidant O3 are controlled at 1s, 15s and 60s respectively, and the deposition cycle number of Sn is controlled at 5, thereby obtaining a carrier with Sn located on the outer surface of the KL molecular sieve framework.

[0057] The obtained sample is subjected to X-ray powder diffraction test (XRD), and the obtained Figure 5 The test results show that Sn has good dispersity on the outer surface of the KL molecular sieve framework, and no particle aggregation phenomenon occurs.

[0058] The obtained molecular sieve is dispersed in an ethanol solvent, coated on a quartz sheet substrate, dried at room temperature, and then transferred to an ALD cavity, with the reaction cavity temperature controlled at 200 DEG C, the nitrogen carrier gas flow at 50 sccm, the Pt source (trimethyl-methylcyclopentadiene platinum) used at a temperature of 65 DEG C, the pulse, deposition and purge times of the Pt deposition process controlled at 0.4 s, 30 s and 60 s respectively, the pulse, deposition and purge times of the oxidant O3 controlled at 1 s, 30 s and 60 s respectively, and the Pt deposition cycle number being 5, to obtain a Pt-loaded molecular sieve catalyst.

[0059] Test Example: Reaction performance evaluation.

[0060] The catalyst prepared above is subjected to performance evaluation by taking the dehydrogenation-cyclization of n-heptane in a naphtha fraction to prepare aromatic hydrocarbons as a probe reaction, with the reaction conditions being: mass space velocity WHSV = 0.8 h-1, pressure 0.2 MPa, temperature 480 DEG C, H2 / n-Heptane = 6 (molar ratio), and all products (reaction carried out for 2 hours) analyzed by online chromatography, as shown in Table 1. -1

[0061] Table 1, catalytic performance evaluation results

[0062]

[0063]

[0064] From the data in Table 1, first, the comparison between the comparative example and each of the examples shows that the use of atomic layer deposition technology to load active metal Pt has a higher conversion rate of n-heptane, with higher selectivity of C1-C4, indicating that the secondary hydrogenolysis side reaction has higher activity, and C1-C4 is produced, which cannot continue to be reformed to prepare aromatic hydrocarbons, and is not conducive to the high-value conversion of naphtha fractions.

[0065] Secondly, the comparison between Example 1 and Example 2 shows that, on the basis of using atomic layer deposition technology to load active metal Pt, the regulation of Sn into the KL molecular sieve framework is more conducive to improving the selectivity of toluene, reducing the selectivity of benzene and heptene, and inhibiting the occurrence of secondary hydrogenolysis side reactions, effectively reducing the production of C1-C4 light hydrocarbons, and is more conducive to the high-value conversion of naphtha fractions.

[0066] The above only describes preferred embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.​

Claims

1. A method for preparing a catalyst based on Sn-modified KL molecular sieve, characterized in that, adding an ethanol solution of a divalent tin salt to a silicon source to obtain a mixed solution, adding the KAlO2 solution to the mixed solution to obtain an initial sol, performing crystallization treatment on the initial sol, and then performing calcination treatment by heating to 450-650 DEG C to obtain a Sn-modified KL molecular sieve, and loading Pt on the Sn-modified KL molecular sieve by atomic layer deposition; wherein the aluminum source, the potassium source, the divalent tin salt, and the silicon source are in terms of Al2O3, K2O, SnO, and SiO2, and the molar ratio is 1:8-30:0.001-2:3.5-25; the divalent tin salt is stannous oxide, tin diiodide, tin dichloride, stannous sulfate, or stannous oxalate.

2. The method for preparing a Sn-modified KL molecular sieve-based catalyst according to claim 1, characterized in that, the aluminum source is aluminum sulfate, aluminum hydroxide, aluminum oxide, or aluminum isopropoxide; alternatively, the potassium source is potassium hydroxide.

3. The method for preparing a Sn-modified KL molecular sieve-based catalyst according to claim 1, characterized in that, The time for stirring the KAlO2 solution in the mixed solution is 60-180 min.

4. The method for preparing a Sn-modified KL molecular sieve-based catalyst according to claim 1, characterized in that, The temperature for crystallization treatment is 165-185 DEG C. alternatively, the time for crystallization treatment is 20-72 h.

5. The method for preparing a Sn-modified KL molecular sieve-based catalyst according to claim 1, characterized in that, After crystallization treatment, washing, drying, and calcination treatment are performed.

6. The method for preparing a Sn-modified KL molecular sieve-based catalyst according to claim 5, characterized in that, The pH after washing is 7-8.

7. The method for preparing a Sn-modified KL molecular sieve-based catalyst according to claim 5, characterized in that, The drying temperature is 110-130 DEG C.

8. The method for preparing a Sn-modified KL molecular sieve-based catalyst according to claim 1, characterized in that, The time for calcination treatment is 3-6 h.

9. The method for preparing a Sn-modified KL molecular sieve-based catalyst according to claim 1, characterized in that, The process for loading Pt on the Sn-modified KL molecular sieve by atomic layer deposition is as follows: the Sn-modified KL molecular sieve is arranged on the surface of a substrate, and a Pt source is used for at least one cycle of deposition; each cycle of deposition is as follows: first, pulse, deposition, and purge are performed using the Pt source, and then pulse, deposition, and purge are performed using an oxidizing agent.

10. The method for preparing the catalyst based on Sn-modified KL molecular sieve as described in claim 9, characterized in that, The time for pulse, deposition, and purge using the Pt source is 0.3-0.5 s, 25-35 s, and 55-65 s, respectively.

11. The method for preparing a Sn-modified KL molecular sieve-based catalyst according to claim 9, characterized in that, The Pt source is trimethyl-methylcyclopentadiene platinum.

12. The method for preparing a Sn-modified KL molecular sieve-based catalyst according to claim 9, characterized in that, The use temperature of the Pt source is 60-70 DEG C.

13. The method for preparing the catalyst based on Sn-modified KL molecular sieve as described in claim 9, characterized in that, The time for pulse, deposition, and purge using the oxidizing agent is 0.9-1.1 s, 25-35 s, and 55-65 s, respectively.

14. The method for preparing the catalyst based on Sn-modified KL molecular sieve as described in claim 9, characterized in that, The oxidizing agent is O3.

15. The method for preparing the catalyst based on Sn-modified KL molecular sieve as described in claim 9, characterized in that, The number of cycles of deposition using the Pt source is 4-6.

16. The method for preparing the catalyst based on Sn-modified KL molecular sieve as described in claim 9, characterized in that, In the atomic layer deposition, the temperature of the reaction cavity is 180-220 DEG C.

17. A catalyst based on Sn-modified KL molecular sieve, characterized in that, obtained by the preparation method of any one of claims 1-16.

18. Use of the Sn-modified KL molecular sieve-based catalyst of claim 17 in the preparation of aromatic hydrocarbons by reforming of a naphtha fraction.

19. The use of claim 18, wherein the compound is ###00010### 18 The naphtha fraction is a C6-C 10 straight-chain alkane.

20. The use of claim 18, wherein the composition is administered to the subject in a single dose. The naphtha fraction is n-heptane, and the target aromatic hydrocarbon to be prepared is toluene.

21. The use of claim 18, wherein the composition is administered to the subject in a single dose. The conditions for preparing aromatic hydrocarbons by reforming naphtha fraction are as follows: mass space velocity is 0.6-1.0 h -1 -1, pressure is 0.15-0.25 MPa, temperature is 470-490 ℃, and molar ratio of hydrogen to naphtha fraction is 5-7:1.

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