Beta molecular sieve confinement type noble metal catalyst as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of catalyst preparation, and discloses a Beta molecular sieve confinement type noble metal catalyst as well as a preparation method and application thereof. The preparation method comprises the following steps: synthesizing a Beta molecular sieve (N-Beta) catalyst carrier containing auxiliary active metal N (N = Zn, Sn, Y, Co and Cu) by a hydrothermal method, and introducing main active metal M (M = Pt, Pd, Rh and Ir) into a pore channel of the N-Beta molecular sieve carrier by an ion exchange method. The M-N-Beta catalyst provided by the invention can provide stable propylene space-time yield which is more than two times higher than a literature value at the same temperature.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalyst preparation, and specifically relates to a Beta molecular sieve confined noble metal catalyst and a preparation method and application thereof. Background Art

[0002] Ethylene, propylene and butene are important raw materials for the production of a variety of high-value chemical products such as high-molecular polymers. In recent years, the global demand for these olefins has become increasingly strong. Therefore, the development of practical technologies for directly dehydrogenating these olefins from the corresponding low-carbon alkanes (ethane, propane, butane) has received increasing attention.

[0003] UOP's Oleflex process is the most commonly used process in industrial plants. This process uses a platinum-tin catalyst supported on an alumina carrier. However, the alumina carrier is highly acidic, which causes the catalyst to coke easily and requires frequent regeneration. Therefore, the development of highly active, highly selective and highly stable dehydrogenation catalysts remains the core technology in the dehydrogenation of low-carbon alkanes. In recent years, molecular sieve materials with special pore structures and shape selectivity have gradually been used in the field of dehydrogenation of low-carbon alkanes.

[0004] De Cola et al. (Appl. Catal. A, 2006, 306, 85) published a method for converting Zn into 2+ The invention discloses a method for preparing a Pt / Zn-molecular sieve propane dehydrogenation catalyst by introducing a molecular sieve to prepare a carrier, and then using a simple impregnation method to impregnate the carrier with a H2PtCl6 solution.

[0005] Cheng Kang et al. (CN116116453 A) disclosed a catalyst preparation technology in which a silicon-aluminum molecular sieve is treated with acid to dealuminate to obtain a catalyst carrier, and then a first metal (Zn, Sn, Ga, Cu, In, Na, K, Cs, Sr) and a second metal (Pt, Pd, Rh, Ir) are loaded on the carrier by an impregnation method. 0.5 @Y catalyst is used for direct dehydrogenation of propane to propylene. At a reaction temperature of 550℃, the initial space-time yield of propylene is 3.7mmol·g Pt -1 ·h -1 After 6 hours, the propylene space-time yield decreased by about 5%.

[0006] Zhu Haibo et al. (CN 117019207A) disclosed a method of first introducing a secondary active metal component (Sn, Ga or Zn) into a molecular sieve framework, and then preparing a Pt / Zn@zeolite catalyst by an impregnation method. The catalyst was used for the direct dehydrogenation of propane to propylene. The space-time yield of propylene was 21.6 mol·g at a reaction temperature of 600°C. Pt -1 ·h-1 ; In CN114570415 A, CN 117019206A and CN 117019208 A, Zhu Haibo et al. disclosed a method for synthesizing PtM@ molecular sieve (M=Cu, Ga, Zn, Sn, Ge) as a catalyst for direct dehydrogenation of propane to propylene using a one-pot process.

[0007] Xu Zhikang et al. (CN 117983279A) disclosed a method for preparing a propane dehydrogenation catalyst by introducing Pt and secondary active metals (Sn, Cu, Zn, Ga) into S-1 molecular sieve in one step (simultaneously). At a reaction temperature of 600°C, the obtained PtZnS 1.5 The initial propane conversion rate over the @S-1 catalyst was 44.7%, and after 72 hours, the propane conversion rate decreased by 12%.

[0008] Ji Hongbing et al. (CN 117482981 A) disclosed a method for preparing a Pt / Zn-S-1 propane dehydrogenation catalyst using a Zn-S-1 molecular sieve containing Na (or K) as a carrier. The Zn-S-1 molecular sieve containing Na (or K) was synthesized using dipotassium ethylenediaminetetraacetate or disodium ethylenediaminetetraacetate as a protective agent for Zn. The space-time yield of propylene on the PtZnNa3000 catalyst was 39.2 mol·g Pt -1 ·h -1 , while the PtZn3000 catalyst containing neither Na nor K was almost completely deactivated within 10 hours.

[0009] Zhang et al. (Chinese Journal of Catalysis 2023, 55, 241) published a method to prepare a PtZn@Beta propane dehydrogenation catalyst by encapsulating Zn in Beta molecular sieve with ethylenediamine and NH4F, and then impregnating the carrier with H2PtCl6 solution using a simple impregnation method. -1 Under the condition of Pt -1 ·h -1 .

[0010] The catalysts for the dehydrogenation of low carbon alkanes to olefins prepared by the above method have a low rate of propylene production or rapid deactivation per unit amount of precious metal M. In order to improve the catalytic efficiency and catalytic stability of precious metal M, a new method for preparing precious metal M-based catalysts needs to be proposed. Summary of the invention

[0011] The present invention provides a method for preparing a catalyst MN-Beta for the dehydrogenation of low-carbon alkanes to olefins with high activity and high stability. The method uses an ion exchange method to introduce a main active metal M (M = Pt, Pd, Ru, Rh, Ir) into an N-Beta carrier that does not contain alkali metal ions but is rich in secondary active metals N (N = Zn, Sn, Y, Co, Cu). The MN-Beta catalyst prepared by this method can make the space-time yield of propane dehydrogenation to propylene reach more than twice the value in existing literature at a reaction temperature of 550°C.

[0012] The preparation method of the catalyst of the present invention is achieved through the following technical scheme.

[0013] 1. Synthesis of Beta molecular sieve containing secondary active metal N (N-Beta): silicon source, strong base, secondary metal N source, tetraethylammonium hydroxide and deionized water are mixed and stirred in a molar ratio of 1SiO2: 0-0.12K2O: 0.2-0.5TEAOH: 0.002-0.08ZnO: 10-100H2O, the obtained mixture is placed in a hydrothermal kettle for hydrothermal crystallization at 105-160°C for 8-192h, and then the obtained solid is separated and dried; after calcining in air or H2 at 450-650°C for 1-8h, the N-Beta molecular sieve with the secondary metal N introduced is obtained;

[0014] 2. Introduce the main active metal M into the N-Beta molecular sieve carrier without alkali metal ions by ion exchange method: add the N-Beta molecular sieve without alkali metal ions to the salt solution containing the main active metal M at a liquid / solid ratio of 2 to 50 mL / g, treat it at 50 to 100 ° C under reflux stirring or ultrasonic conditions for more than 1 hour, then separate the solid by centrifugation or filtration, dry it, and calcine it in air at 500 to 600 ° C for 1 to 8 hours to obtain the desired MN-Beta catalyst. The ion exchange process can be completed once or multiple times. The number of exchanges required depends on the concentration of the main active metal M contained in the liquid used in the exchange process, the liquid / solid ratio used, and the M content in the MN-Beta catalyst to be prepared.

[0015] If the N-Beta molecular sieve contains alkali metal ions due to the use of a strong base in step 1, NH4 + Ion exchange removes alkali metals. The removal method is the commonly used NH4 + Ion exchange method: Add N-Beta molecular sieve containing alkali metal ions to NH4NO3 aqueous solution at a liquid / solid ratio of 2-50 mL / g, stir under reflux or ultrasonic conditions at 50-100°C for more than 1 hour, then dry the solid obtained by centrifugation and calcine at 450-600°C for 1-6 hours. +The ion exchange process can be performed once or multiple times to obtain an N-Beta molecular sieve carrier that does not contain alkali metal ions.

[0016] Furthermore, for the MN-Beta catalyst of the present invention, when it contains multiple secondary active metals N such as N1, N2, etc., the second secondary active metal (N2) can also be introduced simultaneously with the main active metal M using the same ion exchange method.

[0017] Furthermore, the side active metal N is one or more of Zn, Sn, Y, Co, and Cu, and the side active metal source is one or more of nitrates, chlorides, hydroxides, oxides, oxygen-containing acid salts, and organic acid salts of the corresponding metal.

[0018] Furthermore, the silicon source is one or more of tetraethyl orthosilicate, white carbon black, silica sol, and water glass.

[0019] Furthermore, the strong base is potassium hydroxide or sodium hydroxide.

[0020] Furthermore, when synthesizing the N-Beta molecular sieve in step 1, an organic protective agent such as ethylenediamine, sodium ethylenediaminetetraacetate or ethylenediaminetetraacetic acid may be added.

[0021] Furthermore, the main active metal M is one or more of Pt, Pd, Rh, and Ir, and the main active metal source is one or more of amino nitrates, nitrates, and chlorides of the corresponding metals.

[0022] Another object of the present invention is to claim the application of the above-mentioned MN-Beta catalyst, specifically in the dehydrogenation of low-carbon alkanes to olefins.

[0023] In the further preferred embodiment of the present invention, the low carbon alkane in the above application is ethane, propane, butane, etc., and the olefin is ethylene, propylene, butene, etc.

[0024] The method of preparing MN-Beta catalyst by introducing the main active metal M into N-Beta molecular sieve without alkali metal ions by ion exchange method proposed in the present invention can effectively avoid the adverse effects of alkali metal on catalytic performance and greatly improve the catalytic stability of the catalyst, compared with the method of preparing the catalyst by directly introducing the noble metal M into molecular sieve containing alkali metal by ion exchange method (see Table 1 for comparison of the catalytic effects of the catalysts obtained in Example 1 and Comparative Example 1, and in Example 7 and Comparative Example 5).

[0025] The method for preparing MN-Beta catalyst by introducing the main active metal M into the N-Beta molecular sieve without alkali metal ions by ion exchange method proposed by the present invention is different from the existing impregnation method in the preparation procedure in that the preparation process of the catalyst includes a separation process of the obtained solid from the liquid containing the main active metal M, while the existing impregnation method in the literature finally heats the liquid-solid mixture and directly evaporates it to dryness, so there is no such separation process. The above-mentioned catalyst preparation method for introducing M by ion exchange method proposed by the present invention can separate and recover M ions that have not entered the molecular sieve pores (adsorbed on the secondary active metal N) because the solid-liquid separation process can avoid the impregnation method heating the liquid containing the main active metal M to dry and disperse unevenly, resulting in a low generation rate of light olefins, and the impregnation method due to excessive concentration of some main active metal M sites causing excessive dehydrogenation and carbon deposition of light alkanes and rapid deactivation. Therefore, the above-mentioned catalyst preparation method of introducing M by ion exchange method proposed in the present invention can greatly improve the activity and stability of the catalyst and maximize the utilization of the precious metal M (see Table 1 for a comparison of the catalytic effects of the catalyst obtained in Example 1 and the catalyst obtained in Comparative Example 2).

[0026] The method proposed by the present invention for preparing MN-Beta catalyst by introducing the main active metal M into N-Beta molecular sieve without alkali metal ions by ion exchange method can make all the main active metal M spontaneously adsorbed on the secondary active metal N sites of N-Beta molecular sieve to obtain high dispersion and finally form MN active structure. Therefore, the catalyst prepared by the method of the present invention is far superior to any MN@zeolite catalyst prepared by one-pot method in catalytic activity and stability (see Table 1 for comparison of catalytic effect of the catalyst obtained in Example 1 with the catalysts obtained in Comparative Examples 3 and 4).

[0027] In summary, the beneficial effects of the present invention compared with the prior art are as follows: the total mass percentage of the main active metal M in the MN-Beta catalyst prepared by the technology of the present invention is between 0.02% and 0.5%, and the total mass percentage of the secondary active metal N is between 0.2% and 8%. Since the main active metal M is introduced by the ion exchange method, the main active metal M is completely adsorbed and bonded to the sites of the secondary active metal N (forming an MN active structure), so that M can be highly dispersed and stabilized, thereby giving the catalyst extremely high catalytic activity and catalytic stability. The MN-Beta catalyst prepared by the technology of the present invention can achieve a space-time yield of 100 mol·g for the dehydrogenation of propane to propylene at a reaction temperature of 550°C. Pt -1 ·h -1 , and has excellent catalytic stability, so the catalyst and the preparation method of the present invention are far superior to any existing catalyst and the preparation method thereof. DETAILED DESCRIPTION

[0028] The present invention is described in detail below by specific examples, but the protection scope of the present invention is not limited. Unless otherwise specified, the experimental methods used in the present invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used can be obtained from commercial channels.

[0029] Example 1

[0030] 1g KOH and 1.5g zinc gluconate crystals were dissolved in a mixture consisting of 40g 25wt.% TEAOH solution and 15g deionized water, and 10g white carbon black was added thereto, and stirred at 80°C for 24h. The resultant was transferred to a hydrothermal reactor and crystallized at 145°C for 96h. The obtained solid was centrifuged, dried, and calcined in air at 550°C for 6h to obtain a K-containing Zn-Beta molecular sieve.

[0031] 2 g of the above-mentioned K-containing Zn-Beta molecular sieve was added to 40 ml of 1 M NH4NO3 aqueous solution and refluxed at 80°C for 6 h, and then the solid obtained by centrifugation was dried and calcined at 550°C for 4 h. The calcined product was subjected to the exchange process again to obtain an alkali metal-free Zn-Beta molecular sieve.

[0032] Take 0.5 g of the alkali-free Zn-Beta molecular sieve, add it to 10 g of an aqueous solution containing 0.74 mg of Pt(NH3)4(NO3)2, mix it evenly with ultrasound, reflux it at 80°C for 8 hours, and then centrifuge it. The obtained solid is dried at 120°C, and calcined in air at 500°C for 2 hours to obtain a Pt-Zn-Beta catalyst.

[0033] Example 2

[0034] The Pt-Zn-Beta catalyst was synthesized by the method described in Example 1, but in the first step of synthesizing the K-containing Zn-Beta molecular sieve, 0.4 g of ethylenediamine was added to the mixed solution before adding the white carbon black.

[0035] Example 3

[0036] The Pt-Zn-Beta catalyst was synthesized by the method described in Example 1, except that 0.62 g of Zn(NO3)2 was used instead of 1.5 g of zinc gluconate when synthesizing the K-containing Zn-Beta molecular sieve in step 1. In addition, 0.4 g of ethylenediamine was added to the mixed solution before adding the white carbon black.

[0037] Example 4

[0038] The catalyst was synthesized by the method described in Example 1, but in the first step, the synthetic K-containing ZnY-Beta molecular sieve was used instead of the synthetic K-containing Zn-Beta molecular sieve, that is, 0.8 mg of Y(NO3)3 and 1.5 g of zinc gluconate crystals were dissolved in a solution containing TEAOH instead of 1.5 g of zinc gluconate crystals. The Pt-ZnY-Beta catalyst was obtained by this example.

[0039] Example 5

[0040] The catalyst was synthesized by the method described in Example 1, but Y was introduced at the same time as Pt by ion exchange, that is, when ion exchange was performed on the Zn-Beta molecular sieve without alkali metal, 10 g of a mixed aqueous solution containing 0.74 mg of Pt(NH3)4(NO3)2 and 0.8 mg of Y(NO3)3 was used instead of 10 g of an aqueous solution containing only 0.74 mg of Pt(NH3)4(NO3)2. The PtY-Zn-Beta catalyst was obtained by this example.

[0041] Example 6

[0042] 3.4 g NH4F was added to a gel composed of 1SiO2:0.02Zn(NH2CH2CH2NH2)2(NO3)2:0.54TEAOH:8.2H2O prepared from 34.7 g tetraethyl orthosilicate, and the mixture was stirred for 1 h, and then the resultant was transferred to a hydrothermal reactor and crystallized at 140°C for 96 h. The solid was filtered out, washed with water, dried, and calcined at 550°C for 6 h to obtain Zn-Beta molecular sieve.

[0043] Take 0.5g of the above Zn-Beta molecular sieve, add it to 10g of aqueous solution containing 0.74mg Pt(NH3)4(NO3)2, mix it evenly with ultrasound, reflux it at 80℃ for 8h and then centrifuge it. The obtained solid is dried at 120℃ and calcined in air at 500℃ for 2h to obtain Pt-Zn-Beta catalyst.

[0044] Example 7

[0045] The Pd-Zn-Beta catalyst was synthesized by the method described in Example 1, i.e., the introduced precious metal Pt was replaced with Pd. The Zn-Beta molecular sieve was exchanged with a PdCl2 aqueous solution having the same mass and molar concentration as the Pt(NH3)4(NO3)2 aqueous solution, and the other step conditions were the same as those in Example 1.

[0046] Example 8

[0047] The Pt-Co-Beta catalyst was synthesized by the method described in Example 2, i.e., in the first step, Co-Beta molecular sieve was synthesized, and the zinc gluconate crystals used in Example 2 were replaced by cobalt nitrate crystals with the same molar number as zinc gluconate, and the other steps and conditions were the same as in Example 2.

[0048] Comparative Example 1

[0049] The Pt-Zn-Beta catalyst was synthesized by the method described in Example 1, except that the step of removing the alkali metal was omitted. That is, the K-containing Zn-Beta molecular sieve was directly used instead of the K-free Zn-Beta molecular sieve to introduce Pt.

[0050] Comparative Example 2

[0051] The Pt-Zn-Beta catalyst was synthesized by the method described in Example 1, but the method of introducing the main active metal M was changed from the ion exchange method to the impregnation method. That is, 0.5 g of Zn-Beta molecular sieve without alkali metal was added to 0.7 g of an aqueous solution containing 0.74 mg of Pt(NH3)4(NO3)2, and then directly dried and calcined after being impregnated at room temperature for 12 hours, thereby obtaining the Pt-Zn-Beta catalyst by the impregnation method.

[0052] Comparative Example 3

[0053] The K-containing Pt-Zn-Beta catalyst was synthesized by one-pot method: 1g KOH and 1.5g zinc gluconate crystals were dissolved in a mixture of 40g 25wt.% TEAOH solution and 15g deionized water, and 10g white carbon black was added thereto, and stirred at 80°C for 24h. Then 1g of a mixed aqueous solution containing 0.4g ethylenediamine and 0.74mg Pt(NH3)4(NO3)2 was added thereto and stirred for 2h, and the resultant was transferred to a hydrothermal reactor and crystallized at 145°C for 96h. Finally, the solid was centrifuged, dried, and calcined in air at 550°C for 6h.

[0054] Comparative Example 4

[0055] The K-free Pt-Zn-Beta catalyst was synthesized by a one-pot method: 100 mg of the catalyst obtained in Comparative Example 3 was taken, 10 mL of distilled water was added thereto, and the mixture was refluxed and stirred at 80°C for 6 h. The obtained precipitate was separated by centrifugation, and 10 mL of distilled water was added thereto, and the mixture was refluxed and stirred at 80°C for 6 h. Finally, the obtained precipitate was separated by centrifugation, dried, and calcined in air at 550°C for 6 h to obtain the K-free Pt-Zn-Beta catalyst.

[0056] Comparative Example 5

[0057] The Pd-Zn-Beta catalyst was synthesized by the method described in Example 7, but the step of removing the alkali metal was omitted, that is, the K-containing Zn-Beta molecular sieve was directly used instead of the K-free Zn-Beta molecular sieve to introduce Pd by ion exchange.

[0058] Table 1 Catalytic performance of each catalyst using propane dehydrogenation as a model reaction for the dehydrogenation of light alkanes to olefins (reaction conditions: catalyst loading 25 mg, 550 ° C, C3H8:H2:N2 = 5:5:20 mL / min)

[0059]

[0060]

[0061] The above-described embodiments are only preferred embodiments of the present invention, but not all feasible embodiments of the present invention. For those skilled in the art, any obvious changes made thereto without departing from the principles and spirit of the present invention should be considered to be included in the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a Beta molecular sieve confined noble metal catalyst, characterized in that: The following steps are included: S1: Preparation of Beta molecular sieve (N-Beta) containing secondary active metal N (N = Zn, Sn, Y, Co, Cu) by hydrothermal synthesis; S2: The main active metal M (M = Pt, Pd, Ru, Rh, Ir) is introduced into the above-mentioned N-Beta molecular sieve carrier that does not contain alkali metals by ion exchange method to obtain an MN-Beta catalyst containing both the main and secondary active metals M and N.

2. The method for preparing the Beta molecular sieve confined noble metal catalyst according to claim 1, characterized in that: The step S1 is not limited to preparing N-Beta containing only one secondary active metal.

3. The method for preparing the Beta molecular sieve confined noble metal catalyst according to claim 1, characterized in that: The step S2 is not limited to being used only for introducing the main active metal, but also includes being used for simultaneously introducing the main active metal and the second secondary active metal.

4. The method for preparing the Beta molecular sieve confined noble metal catalyst according to claim 1, characterized in that: The step S1 also includes adding a step of using NH4 + The step of removing alkali metal by exchange method.

5. The method for preparing the Beta molecular sieve confined noble metal catalyst according to claim 1, characterized in that: The total mass percentage of the main active metal M in the catalyst is between 0.02% and 0.5%, and the total mass percentage of the secondary active metal N is between 0.2% and 8%.

6. The method for preparing the Beta molecular sieve confined noble metal catalyst according to claim 1, characterized in that: The step S1 is as follows: a silicon source, a strong base, a secondary metal N source, tetraethylammonium hydroxide and deionized water are mixed and stirred in a molar ratio of 1SiO2: 0.03-0.12K2O: 0.002-0.08ZnO: 0.2-0.5TEAOH: 10-100H2O, the obtained mixture is placed in a hydrothermal kettle for hydrothermal crystallization, and then the obtained solid is separated and dried; and calcined in air or H2.

7. The method for preparing the Beta molecular sieve confined noble metal catalyst according to claim 4, characterized in that: The step of removing alkali metals is to add N-Beta molecular sieve containing alkali metals to NH4NO3 aqueous solution under reflux stirring or ultrasonic conditions, and then centrifuge to obtain a solid, dry it, and then calcine it; the step of removing alkali metals includes once NH4 + Exchange or multiple NH4 + exchange.

8. The method for preparing the Beta molecular sieve confined noble metal catalyst according to claim 1, characterized in that: The step S2 is to carry out ion exchange under reflux stirring conditions or under ultrasonic conditions, and the number of times used is one or more.

9. A Beta molecular sieve confined noble metal catalyst, characterized in that: Prepared according to the method of claim 1.

10. An application of a Beta molecular sieve confined noble metal catalyst, characterized in that: Applied to the dehydrogenation of low-carbon alkanes to olefins.

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