Preparation method and application of a propane dehydrogenation catalyst

Abstract

The present invention discloses a preparation method and application of a propane dehydrogenation catalyst. The preparation method includes: dissolving cetyltrimethylammonium bromide and triethanolamine in deionized water to obtain system A; successively adding tetraethyl orthosilicate and an aqueous solution containing Anderson-type polyoxometalate into system A, reacting at 60-80 °C, washing, drying, and calcining to obtain the propane dehydrogenation catalyst. By successively adding tetraethyl orthosilicate and an aqueous solution containing Anderson-type polyoxometalate (NH4)3[CrMo6O 24 H4] into system A containing a template agent, the propane dehydrogenation catalyst is generated by reacting at 60-80 °C. The initial conversion rate of this catalyst in CO2-ODP at a temperature close to 580 °C is as high as 53.5%, and the initial selectivity is as high as 91%. The propylene selectivity is always higher than 80% during the 12-hour life test, featuring stable high-temperature performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysis, and particularly relates to a preparation method and application of a propane dehydrogenation catalyst. Background Art

[0002] Propylene is a basic raw material for the production of various high-value chemicals such as polypropylene or acrylonitrile. With the consumption of fossil energy, traditional propylene production methods can no longer meet the growing demand. In recent years, the large-scale exploitation of shale gas has promoted the development of the process for direct catalytic dehydrogenation of propane to propylene. The most important routes are anaerobic (PDH) dehydrogenation of propane and aerobic (ODP) dehydrogenation of propane. To further improve the propylene yield, the prior art usually introduces hydrogen into the reaction system to utilize the reverse water-gas shift reaction (RWGS) or introduces CO2 to participate in the propane dehydrogenation reaction (CO2-ODP) to promote the reaction to proceed in the direction of generating propylene. However, RWGS and CO2-ODP usually need to be carried out under high-temperature and high-pressure environments, and it is very easy to produce other by-products due to propane cracking, and the catalyst is easily deactivated due to carbon deposition, which puts forward new requirements for the performance stability and lifespan of the propane dehydrogenation catalyst.

[0003] In the field of propane dehydrogenation catalysts, compared with Pt-based catalysts, Cr-based catalysts are widely used commercially due to their low price and high Lewis acid activity. To further improve the catalytic performance of Cr-based catalysts and their adaptability to process environments, research has focused on the adjustment and modification of the catalyst structure.

[0004] For example, patent application document 202411347515.9 discloses a chromium-based propane dehydrogenation catalyst with improved catalytic performance, its preparation method and application, which discloses a propane dehydrogenation catalyst containing a titanium oxide-aluminum oxide composite support and active components containing Cr, K, Ni, W, Co, and Zn. It uses a composite metal oxide with an in-situ synthesized titanium oxide layer on the surface of alumina as the support and multiple metal components in combination as an electron promoter to synergistically achieve the adsorption and desorption of reactants. Patent application document 202011341671.6 discloses a dual-active-center propane dehydrogenation catalyst, its preparation method and application, and discloses that it includes a support and active components supported on the support. The support uses a non-metallic carbon material, and the active components use chromium monoxide, chromium sesquioxide, chromium trioxide, or chromium dioxide. In the process of implementing the present invention, it is found that at least the following problems exist in the above technologies: easy carbon deposition during long-term reactions, poor high-temperature performance stability, complex active components or large addition amounts, and cumbersome preparation processes. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a preparation method and application of a propane dehydrogenation catalyst in view of the deficiencies of the above-mentioned prior art. This method involves sequentially adding tetraethyl orthosilicate and an aqueous solution containing Anderson-type polyoxometalate (NH4)3[CrMo6O 24 H4] to system A containing a template agent, and reacting at 60-80 °C to produce a propane dehydrogenation catalyst. In the propane dehydrogenation reaction at a temperature close to 580 °C, the initial conversion rate of propane by this catalyst is as high as 53.5%, and the initial selectivity for propylene is as high as 91%. In a 12-hour life test, the selectivity for propylene is always higher than 80%, showing the characteristic of stable high-temperature performance.

[0006] The present invention has the following advantages compared with the prior art:

[0007] 1. The present invention uses Anderson-type polyoxometalate (NH4)3[CrMo6O 24 H4] to introduce active components into mesoporous silica spheres to obtain a propane dehydrogenation catalyst. This catalyst has a low Cr content, uniform distribution of active components, and stable structure, showing high propane conversion and propylene selectivity in the catalytic propane dehydrogenation reaction.

[0008] 2. Preferably, the present invention prepares the propane dehydrogenation catalyst CrMo6@MSS by adding tetraethyl orthosilicate to system A and stirring evenly, and then immediately adding the aqueous solution containing Anderson-type polyoxometalate in its entirety, so as to achieve modular assembly of polyoxometalate and mesoporous materials, and make full use of the characteristics of high mechanical strength, good thermal stability, large specific surface area, and non-strong acid and strong base of mesoporous silica spheres as well as the structural characteristics of polyoxometalates, endowing the CrMo6@MSS catalyst with high catalytic performance and low recovery toxicity.

[0009] 3. The preparation method of the present invention is simple and the principle is reliable.

[0010] Next, in combination with the drawings and embodiments, the technical solutions of the present invention will be further described in detail. Description of the Drawings

[0011] Figure 1 Infrared spectrum of Anderson-type polyoxometalate (NH4)3[CrMo6O 24 H4] for Example 1;

[0012] Figure 2 Propane conversion rate of the catalysts in Example 1 and the comparative example in the CO2-ODP reaction;

[0013] Figure 3 Propylene selectivity of the catalysts in Example 1 and the comparative example in the CO2-ODP reaction;

[0014] Figure 4 Schematic diagram of the 12-hour life experiment results of the catalyst in Example 1;

[0015] Figure 5 Schematic diagram of the regeneration cycle test results of the catalyst in Example 1;

[0016] Figure 6 Transmission electron micrographs of the spherical propane dehydrogenation catalyst CrMo6@MSS and mesoporous silica spheres in Example 1;

[0017] Figure 7 Nitrogen adsorption-desorption isotherms of mesoporous silica spheres MSS and CrMo6@MSS before and after reaction;

[0018] Figure 8 XRD spectra of mesoporous silica spheres MSS, Cr@MSS and CrMo6@MSS;

[0019] Figure 9 For (NH4)3[CrMo6O 24 H4] and XANES spectra of the catalyst CrMo6@MSS;

[0020] Figure 10 For (NH4)3[CrMo6O 24 H4] and the k of the catalyst CrMo6@MSS 2 Weighted Fourier transform spectra of EXAFS;

[0021] Figure 11 Wavelet transform EXAFS spectra of Cr foil;

[0022] Figure 12 Wavelet transform EXAFS spectra of Cr2O3;

[0023] Figure 13 Wavelet transform EXAFS spectra of CoO3 standard sample;

[0024] Figure 14 Wavelet transform EXAFS spectra of CrMo6@MSS;

[0025] Figure 15 CO2-ODP reaction results of the propane dehydrogenation catalysts in Examples 1 to 5. Detailed implementation manners

[0026] Next, the technical solutions will be described clearly and completely in conjunction with the accompanying drawings. Obviously, the described embodiments are a part of the embodiments of the present application, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without making creative efforts shall fall within the scope of protection of the present application.

[0027] In the following description, the term "and / or" is used to describe the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent the cases of A existing alone, B existing alone, and A and B existing simultaneously. Here, A and B can be singular or plural.

[0028] In the following description, terms such as "comprise", "include", "have", and "contain" are all open-ended terms, meaning including but not limited to.

[0029] Those skilled in the art should understand that in the following description of the embodiments of the present application, the sequence numbers do not imply the sequence of execution. Some or all of the steps can be executed in parallel or sequentially, and the execution sequence of each process should be determined by its function and internal logic, without constituting any limitation to the implementation process of the embodiments of the present application.

[0030] Those skilled in the art should understand that the numerical range in the embodiments of the present application should be understood as specifically disclosing each intermediate value between the upper and lower limits of the range. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present application. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0031] Unless otherwise specified, the technical / scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present application pertains. Although the present application only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present application. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0032] The technical principle adopted by the present invention: Using polyoxometalates (POMs) and mesoporous silica spheres as the main raw materials, polyoxometalates are discrete nano-polyoxometalate compounds rich in transition metal components. The general formula of the Anderson structure polyoxometalate anion is [XM6O 24 n- or [X(OH)6M6O 18 , n- The coordination number of the central atom is 6, with an octahedral structure, stable structure, small molecular weight, and it is one of the smallest POMs. In addition to a relatively large specific surface area and stable mechanical properties, the mesoporous silica sphere also has the characteristics of weak acidity and alkalinity and small damage to the active center. The catalytic propane dehydrogenation active component is combined with the mesoporous silica sphere carrier by using polyoxometalates to form a propane dehydrogenation catalyst CrMo6@MSS with high catalytic performance.

[0033] Some embodiments provide a method for preparing a propane dehydrogenation catalyst, comprising:

[0034] Dissolve cetyltrimethylammonium bromide and triethanolamine in deionized water to obtain System A:

[0035] Add tetraethyl orthosilicate and an aqueous solution containing Anderson-type polyoxometalate to System A successively, react at 60 - 80 °C, wash, dry, and calcine the reaction product to obtain a propane dehydrogenation catalyst; the Anderson-type polyoxometalate has the composition (NH4)3[CrMo6O 24 H4].

[0036] As a discrete nano metal-oxygen cluster, polyoxometalate contains a large number of electron aggregates and can undergo rapid and reversible electron transfer without changing its structure. It is usually widely used as an ideal electron acceptor in fields such as electrochemistry and battery materials. In the present invention, polyoxometalate is creatively introduced into the preparation of a propane dehydrogenation catalyst. Utilizing its unique structural characteristics, the active component is combined into the mesoporous silica sphere support. Further, the polyoxometalate is Anderson-type polyoxometalate (NH4)3[CrMo6O 24 H4]. During the preparation of the catalyst, the ammonium component of the ammonium cation CrMo6 volatilizes, having no effect on the surface acid-base balance of the catalyst. The central atom Cr is surrounded by 6 octahedra containing Mo. After reacting with the mesoporous silica sphere, a stable polyacid derivative can be formed. Under the electrostatic action and the confinement of the mesopores, it has lower chemical reactivity and a lower content of surface α-Cr2O3, which can effectively reduce the probability of side reactions occurring in the catalytic propane dehydrogenation reaction and has robust catalytic activity.

[0037] In some embodiments, the mass ratio of the Anderson-type polyoxometalate to tetraethyl orthosilicate is (0.6 - 1.4):3. In a preferred embodiment, the mass ratio of the Anderson-type polyoxometalate to tetraethyl orthosilicate is 1:3.

[0038] The dosage of tetraethyl orthosilicate affects the structure and morphology of the silica sphere. It is found during the experiment that when the content of tetraethyl orthosilicate is too low, the mesoporous structure is incomplete, the degree of pore disorder is high, and the size of the silica sphere is too small. When the content of tetraethyl orthosilicate is too high, the product is heterogeneous or in the form of large pieces of silica gel, blocking the pores.

[0039] In some specific embodiments, the tetraethyl orthosilicate and the aqueous solution containing Anderson-type polyoxometalate are added successively as follows: after adding the tetraethyl orthosilicate to the system A and stirring evenly, the aqueous solution containing Anderson-type polyoxometalate is immediately added in its entirety; the time interval between the addition of the aqueous solution containing Anderson-type polyoxometalate and tetraethyl orthosilicate is < 1 min.

[0040] When the tetraethyl orthosilicate is uniformly dispersed in the system A and then the aqueous solution containing Anderson-type polyoxometalate is immediately added, CrMo6 is uniformly dispersed in the mesoporous channels as the silica spheres grow. After calcining to remove CTAB, the polyoxometalate is distributed in the pores in the form of derivatives, and the resulting catalyst has more excellent catalytic performance. It was found during the experiment that the time interval between the addition of Anderson-type polyoxometalate and tetraethyl orthosilicate affects the distribution of the active components and the catalytic performance of the resulting catalyst. After the tetraethyl orthosilicate is added to the system A, it will approach the surface of the CTAB micelles, induce the formation of a silica core, and then the silica spheres grow and gradually form a silica wall. After adding Anderson-type polyoxometalate, CrMo6 will be dispersed in the mesoporous channels as the silica spheres grow, and the growth of the silica spheres, the formation of the silica wall, and the dispersion of CrMo6 occur simultaneously. If the addition of Anderson-type polyoxometalate is too late, the silica wall of the mesoporous channels has already formed, affecting the distribution of the active components.

[0041] In some embodiments, the preparation method of Anderson-type polyoxometalate includes:

[0042] Heat the aqueous solution of ammonium molybdate to boiling, add the aqueous solution of chromium nitrate, mix well, filter while it is hot, cool, and let it stand and age for 1 - 3 days without recrystallization to obtain Anderson-type polyoxometalate; the heating method and specific temperature of the boiling system in the present invention are not limited as long as it can maintain the boiling state. For example, the temperature of the boiling system can be 95°C - 110°C;

[0043] Filter while it is hot to avoid crystal precipitation caused by cooling;

[0044] After cooling, let it stand and age to fully and completely precipitate the crystals, improve the yield, without recrystallization, and shorten the preparation process.

[0045] In some preferred embodiments, the reaction time at 60 - 80°C after adding to the system A is 3 - 4 h.

[0046] When the reaction time is less than 3 h, the silica spheres do not grow completely, the particle size range is wide, and the mesopores are incomplete; when the reaction time is more than 4 h, a mesoporous material with a stable structure cannot be formed.

[0047] In some embodiments, System A is obtained by dissolving cetyltrimethylammonium bromide and triethanolamine in deionized water and stirring and mixing them evenly at 60-80 °C.

[0048] In some embodiments, the calcination is carried out at 550-600 °C for 4-6 h.

[0049] When the temperature exceeds 600 °C, the grain size of chromium oxide is too large, the mesoporous structure collapses, the framework is over-condensed, the pores are blocked, and when the calcination temperature is 550-600 °C, it is beneficial to form polyoxoacid derivatives uniformly dispersed in the mesoporous channels.

[0050] On the other hand, an application of the above-mentioned propane dehydrogenation catalyst in CO2-ODP is provided.

[0051] A series of experiments were carried out before the application of the present invention. Now, some test results are listed to further describe the invention in detail, and the following is a detailed description in conjunction with the examples.

[0052] Example 1

[0053] This example provides a preparation method of a propane dehydrogenation catalyst, including:

[0054] Step 1. Provide Anderson-type polyoxometalate (NH4)3[CrMo6O 24 H4], specifically including:

[0055] Step 101. Dissolve 5 g of (NH4)6Mo7O 24 ·4H2O in 80 mL of deionized water, heat to boiling, add an aqueous solution of Cr(NO3)3•9H2O, mix evenly, filter while hot, cool to room temperature, and let stand for aging for 2 days to obtain Anderson-type polyoxometalate (NH4)3[CrMo6O 24 H4]; the aqueous solution of Cr(NO3)3•9H2O is an aqueous solution of Cr(NO3)3•9H2O obtained by dissolving 1.24 g of Cr(NO3)3•9H2O in 20 g of water; the infrared spectrum of the Anderson-type polyoxometalate (NH4)3[CrMo6O 24 H4] in this example is as shown in Figure 1 , and the vibration peaks below 450 cm -1 are attributed to the vibration of the central heteroatom Cr-O, and the vibration peaks at 950-900 cm -1 and 650-550 cm -1 belong to the vibration of Anderson-type polyoxoacid. Based on Figure 1 It can be seen that Anderson-type polyoxometalate (NH4)3[CrMo6O 24 H4] is successfully synthesized in this example;

[0056] Step 2: Provide a propane dehydrogenation catalyst, specifically including:

[0057] Step 201: Stir 0.3 g of cetyltrimethylammonium bromide (CTAB), 25.11 g of triethanolamine (TEAH3), and 50 mL of deionized water at 80 °C for 1 h to obtain System A;

[0058] Step 202: Under stirring conditions at 80 °C, add 3.1 g of tetraethyl orthosilicate (TEOS) to System A, continue stirring until evenly mixed, immediately add a polyoxometalate solution, and stir and mix at 80 °C for 3 h to obtain a gray-green solution; the polyoxometalate solution is a polyoxometalate solution obtained by dissolving 1 g of the polyoxometalate (NH4)3[CrMo6O 24 H4] in 8 g of deionized water;

[0059] Step 203: Filter the gray-green solution, wash the filtrate alternately with deionized water and absolute ethanol three times, dry the washed product in an oven at 100 °C for 24 h, and heat the dried material in an air atmosphere at a heating rate of 2 °C / minute to 600 °C and hold for 4 h to remove the template agent, obtaining a spherical propane dehydrogenation catalyst named CrMo6@MSS.

[0060] In this example, it also includes a method for preparing mesoporous silica spheres, including:

[0061] Step 1: Stir 0.3 g of cetyltrimethylammonium bromide, 25.11 g of triethanolamine, and 50 mL of deionized water at 80 °C for 1 h to obtain System A;

[0062] Step 2: Under stirring conditions at 80 °C, add 3.1 g of tetraethyl orthosilicate to System A, continue stirring until no more precipitation occurs, perform suction filtration, wash the filtrate, dry it to constant weight, and calcine it at 600 °C for 5 h to obtain mesoporous silica spheres, denoted as MSS.

[0063] Comparative Example 1

[0064] This comparative example provides a method for preparing a propane dehydrogenation catalyst. The carrier is alumina, and the preparation method is the impregnation method, specifically including:

[0065] Step 1: Dissolve 2.238 g of (NH4)3[CrMo6O 24 H6]•7H2O in 80 mL of deionized water to obtain an active component source solution; the (NH4)3[CrMo6O 24 H6]•7H2O is purchased from Shanghai Macklin;

[0066] Step 2: Add 1 g of carrier neutral alumina to the active component source solution, stir at room temperature for 4 h, let stand for 12 h, and then centrifuge. The neutral alumina is spherical alumina purchased from Shanghai Macklin;

[0067] Step 3: Dry the centrifuged solid phase overnight at 80 °C, and then heat the dried material in an air atmosphere at a heating rate of 2 °C / min to 600 °C and hold for 1 h to obtain a propane dehydrogenation catalyst named CrMo6 / Al2O3.

[0068] Comparative Example 2

[0069] This comparative example is the same as Comparative Example 1, except that in Step 2, the carrier is silica molecular sieve NKF-6(β) with a particle size of 0.5 μm, purchased from Tianjin Nanhua Catalyst Co., Ltd., and the obtained catalyst is named CrMo6 / NKF-6(β).

[0070] Comparative Example 3

[0071] This comparative example is the same as Comparative Example 1, except that in Step 2, the carrier is CeO2, spherical, purchased from Shanghai Macklin, and the obtained catalyst is named CrMo6 / CeO2.

[0072] Comparative Example 4

[0073] This comparative example is the same as Comparative Example 1, except that in Step 2, the carrier is ZrO2, powdery, purchased from Shanghai Macklin, and the obtained catalyst is named CrMo6 / ZrO2.

[0074] Comparative Example 5

[0075] This comparative example provides a preparation method of a propane dehydrogenation catalyst Cr@MSS, including:

[0076] Step 1: Stir 0.3 g of cetyltrimethylammonium bromide, 25.11 g of triethanolamine, and 50 mL of deionized water at 80 °C for 1 h to obtain System A;

[0077] Step 2: Under stirring conditions at 80 °C, add 3.1 g of tetraethyl orthosilicate to System A, continue stirring until evenly mixed, immediately add the chromium nitrate solution, stir and mix at 80 °C for 3 h, filter the mixed system, wash the filtrate alternately with deionized water and absolute ethanol three times, dry the washed product in an oven at 100 °C for 24 h, and heat the dried material in an air atmosphere at a heating rate of 2 °C / min to 600 °C and hold for 4 h to remove the template agent to obtain a spherical propane dehydrogenation catalyst named Cr@MSS; the chromium nitrate solution is a chromium nitrate solution obtained by dissolving 0.34 g of Cr(NO3)3•9H2O in 8 g of deionized water.

[0078] Example 2

[0079] This example provides a method for preparing a propane dehydrogenation catalyst, including:

[0080] Step 1: Provide Anderson-type polyoxometalate (NH4)3[CrMo6O 24 H4], specifically including:

[0081] Step 101: Dissolve 5 g of (NH4)6Mo7O 24 ·4H2O in 80 mL of deionized water, heat to boiling, add an aqueous solution of Cr(NO3)3•9H2O, mix well, filter while hot, cool to room temperature, and let stand for aging for 1 day to obtain Anderson-type polyoxometalate (NH4)3[CrMo6O 24 H4]; the aqueous solution of Cr(NO3)3•9H2O is an aqueous solution of Cr(NO3)3•9H2O obtained by dissolving 1.24 g of Cr(NO3)3•9H2O in 20 g of water;

[0082] Step 2: Provide a propane dehydrogenation catalyst, specifically including:

[0083] Step 201: Stir 0.3 g of cetyltrimethylammonium bromide, 25.11 g of triethanolamine, and 50 mL of deionized water at 70 °C for 1 h to obtain System A;

[0084] Step 202: Under stirring conditions at 70 °C, add 3.1 g of tetraethyl orthosilicate to System A, continue stirring until well mixed, immediately add the polyoxometalate solution, and stir and mix at 70 °C for 3 h to obtain a gray-green solution; the polyoxometalate solution is a polyoxometalate solution obtained by dissolving 0.6 g of the polyoxometalate (NH4)3[CrMo6O 24 H4] from Step 1 in 8 g of deionized water;

[0085] Step 203: Filter the gray-green solution, wash the filtrate alternately three times with deionized water and absolute ethanol, dry the washed product in an oven at 100 °C for 24 h, and heat the dried material in an air atmosphere at a heating rate of 2 °C / min to 550 °C and hold for 6 h to remove the template agent to obtain a spherical propane dehydrogenation catalyst.

[0086] Example 3

[0087] This example provides a method for preparing a propane dehydrogenation catalyst, including:

[0088] Step 1: Provide Anderson-type polyoxometalate (NH4)3[CrMo6O 24 H4], specifically including:

[0089] Step 101: Dissolve 5 g of (NH4)6Mo7O 24 ·4H2O in 80 mL of deionized water. After heating to boiling, add an aqueous solution of Cr(NO3)3•9H2O. After mixing evenly, filter while it is hot, cool to room temperature, and let it stand and age for 2 days to obtain the Anderson-type polyoxometalate (NH4)3[CrMo6O 24 H4]; the aqueous solution of Cr(NO3)3•9H2O is an aqueous solution of Cr(NO3)3•9H2O obtained by dissolving 1.24 g of Cr(NO3)3•9H2O in 20 g of water;

[0090] Step Two: Provide a propane dehydrogenation catalyst, specifically including:

[0091] Step 201: Stir 0.3 g of cetyltrimethylammonium bromide, 25.11 g of triethanolamine, and 50 mL of deionized water at 60 °C for 1 h to obtain System A;

[0092] Step 202: Under the stirring condition at 60 °C, add 3.1 g of tetraethyl orthosilicate to System A, continue stirring until it is mixed evenly, immediately add the polyoxometalate solution, and stir and mix at 60 °C for 4 h to obtain a gray-green solution; the polyoxometalate solution is a polyoxometalate solution obtained by dissolving 0.8 g of the polyoxometalate (NH4)3[CrMo6O 24 H4] in 8 g of deionized water;

[0093] Step 203: Filter the gray-green solution, wash the filtrate alternately with deionized water and absolute ethanol three times, dry the washed product in an oven at 100 °C for 24 h, and heat the dried material in an air atmosphere at a heating rate of 2 °C per minute to 580 °C and hold for 5 h to remove the template agent to obtain a spherical propane dehydrogenation catalyst.

[0094] Example 4

[0095] This example provides a preparation method of a propane dehydrogenation catalyst, including:

[0096] Step One: Provide the Anderson-type polyoxometalate (NH4)3[CrMo6O 24 H4], specifically including:

[0097] Step 101: Dissolve 5 g of (NH4)6Mo7O 24 ·4H2O in 80 mL of deionized water. After heating to boiling, add an aqueous solution of Cr(NO3)3•9H2O. After mixing evenly, filter while it is hot, cool to room temperature, and let it stand and age for 3 days to obtain the Anderson-type polyoxometalate (NH4)3[CrMo6O24 H4]; The aqueous solution of Cr(NO3)3•9H2O is an aqueous solution of Cr(NO3)3•9H2O obtained by dissolving 1.24 g of Cr(NO3)3•9H2O in 20 g of water;

[0098] Step 2: Provide a propane dehydrogenation catalyst, specifically including:

[0099] Step 201: Stir 0.3 g of cetyltrimethylammonium bromide, 25.11 g of triethanolamine, and 50 mL of deionized water at 80 °C for 1 h to obtain System A;

[0100] Step 202: Under stirring conditions at 80 °C, add 3.1 g of tetraethyl orthosilicate to System A, continue stirring until evenly mixed, immediately add the polyoxometalate solution, and stir and mix at 80 °C for 3 h to obtain a gray-green solution; The polyoxometalate solution is a polyoxometalate solution obtained by dissolving 1.2 g of the polyoxometalate (NH4)3[CrMo6O 24 H4] in 8 g of deionized water;

[0101] Step 203: Filter the gray-green solution, wash the filtrate alternately with deionized water and absolute ethanol three times, dry the washed product in an oven at 100 °C for 24 h, and heat the dried material in an air atmosphere at a heating rate of 2 °C per minute to 550 °C and hold for 4 h to remove the template agent, obtaining a spherical propane dehydrogenation catalyst.

[0102] Example 5

[0103] This example provides a preparation method of a propane dehydrogenation catalyst, including:

[0104] Step 1: Provide Anderson-type polyoxometalate (NH4)3[CrMo6O 24 H4], specifically including:

[0105] Step 101: Dissolve 5 g of (NH4)6Mo7O 24 ·4H2O in 80 mL of deionized water, heat to boiling, add the aqueous solution of Cr(NO3)3•9H2O, mix evenly, filter while hot, cool to room temperature, and stand for aging for 2 days to obtain Anderson-type polyoxometalate (NH4)3[CrMo6O 24 H4]; The aqueous solution of Cr(NO3)3•9H2O is an aqueous solution of Cr(NO3)3•9H2O obtained by dissolving 1.24 g of Cr(NO3)3•9H2O in 20 g of water;

[0106] Step 2: Provide a propane dehydrogenation catalyst, specifically including:

[0107] Step 201: Stir 0.3 g of cetyltrimethylammonium bromide, 25.11 g of triethanolamine, and 50 mL of deionized water at 80 °C for 1 h to obtain System A;

[0108] Step 202: Under the stirring condition at 80 °C, add 3.1 g of tetraethyl orthosilicate to the above System A, continue stirring until homogeneous, immediately add the polyoxometalate solution, and stir and mix at 80 °C for 3 h to obtain a gray-green solution; the polyoxometalate solution is a polyoxometalate solution obtained by dissolving 1.4 g of the polyoxometalate (NH4)3[CrMo6O 24 H4] in 8 g of deionized water;

[0109] Step 203: Filter the gray-green solution, wash the filtrate alternately with deionized water and absolute ethanol three times, dry the washed product in an oven at 100 °C for 24 h, and heat the dried material in an air atmosphere to 600 °C at a heating rate of 2 °C per minute and hold for 4 h to remove the template agent, obtaining a spherical propane dehydrogenation catalyst.

[0110] Performance Evaluation

[0111] The catalytic performance evaluation of the catalysts in Example 1 and Comparative Examples 1-4 was carried out by the CO2-ODP reaction, and the method was as follows:

[0112] Fill 0.1 g of the catalyst into a quartz fixed-bed reactor with an outer diameter of 10 mm and an inner diameter of 7 mm. Under atmospheric pressure, linearly heat the reactor containing the catalyst to 580 °C within 1 h and hold, purge with Ar for 0.5 h, introduce a gas mixture into the purged reactor, analyze the product by an online gas chromatograph GC2060, start chromatographic sampling analysis 10 min after introducing the gas mixture, and sample every 30 min; the flow rate of the gas mixture is 20 mL•min -1 , where the volume ratio of C3H8, CO2, and Ar is 2:8:10, and the results are as Figure 2 and Figure 3 shown.

[0113] The calculation formula for the propane conversion rate % of the reactant is as follows:

[0114]

[0115] The calculation formula for the propylene selectivity % of the product is as follows:

[0116]

[0117] Among them, is the gas flow rate at the inlet, with the unit of mL•min -1 ; is the gas flow rate at the gas outlet, with the unit of mL•min -1 ;

[0118] According to Figure 2 and Figure 3 It can be seen that both the initial propane conversion rate and the initial propylene selectivity of the propane dehydrogenation catalyst CrMo6@MSS in Example 1 are significantly higher than those of the catalysts in the comparative examples. The initial conversion rate is 53.5%, and the initial selectivity is 91%, showing good catalytic performance. At a temperature close to 580°C and under atmospheric pressure, during the 3-hour reaction process, the propane conversion rate is always higher than 35%, and the propylene selectivity is stable above 90%. Compared with the propane dehydrogenation catalysts on the remaining supports prepared by the impregnation method, that is, the catalysts in Comparative Examples 1 to 4, the catalyst of the present invention has significantly higher catalytic performance, indicating that the one-pot method of the present invention is beneficial to improving the CO2-OPD activity of the propane dehydrogenation catalyst.

[0119] According to the above evaluation method, a 12-hour life experiment was carried out, and the results are as Figure 4 shown. Based on Figure 4 It can be seen that during the continuous reaction process, the propylene selectivity is always higher than 80%, indicating that the catalyst of the present invention has good service life and stability.

[0120] After the catalyst of Example 1 was activated after the performance test, a regeneration cycle test was carried out. The test conditions were the same as those of the performance evaluation method. The number of regeneration cycle tests was 4 times. Before each regeneration cycle test, the catalyst was activated. The activation treatment specifically included: at a temperature of 580°C, oxygen was introduced at a rate of 10 mL•min -1 for 1 hour of calcination, and then Ar was introduced until the room temperature was reached. Then, hydrogen was introduced at a rate of 20 mL•min -1 and uniformly heated to 580°C within 1 hour for reduction. The results of the regeneration cycle test are as Figure 5 shown. According to Figure 5 It can be seen that the propane conversion rate and the propylene selectivity show a slow downward trend. The initial propane conversion rate in multiple cycles is above 35%. During the entire regeneration cycle test process, the propane conversion rate is stable above 30%, and the propylene selectivity exceeds 80%, indicating that the overall performance of the catalyst has not fluctuated significantly, and the catalyst of the present invention has the characteristic of a long service life.

[0121] Figure 6 The a in Figure 6 is the transmission electron microscopy image of the mesoporous silica spheres of Example 1 at a scale of 50 nm, and Figure 6 the b in Figure 6 is the transmission electron microscopy image of the mesoporous silica spheres at a scale of 200 nm. According to

[0122] Figure 6 Figure c is the transmission electron microscopy image of the spherical propane dehydrogenation catalyst CrMo6@MSS of Example 1, Figure 6 Figure d is the scanning electron microscopy image of the spherical propane dehydrogenation catalyst CrMo6@MSS of Example 1, Figure 6 Figures e - j are element surface scan images. According to Figure 6 Figure c and Figure 6 Figure d, it can be seen that the CrMo6@MSS catalyst of the present invention is spherical, with uniform size. The surface of the silica spheres is not smooth, and there is partial adhesion and aggregation between the silica spheres. Combining with the mapping images, it can be seen that Cr and a small amount of Mo appear on the surface, indicating that a small amount of POMs are loaded on the surface of the silica spheres.

[0123] Figure 7 are the nitrogen adsorption - desorption isotherms (BET) of MSS and CrMo6@MSS before and after the reaction. Among them, CrMo6@MSS after the reaction is CrMo6@MSS after the life test. Table 1 shows the specific surface area and pore size distribution of MSS and CrMo6@MSS before and after the reaction. It can be seen that both MSS and CrMo6@MSS before and after the reaction are mesoporous structures. The pore diameter D of MSS, CrMo6@MSS before and after the reaction p changes little, indicating that the introduction of CrMo6 does not significantly change the pore structure of MSS. The method of the present invention can form a high - performance propane dehydrogenation catalyst with active components embedded in the mesoporous wall on the basis of avoiding pore blockage.

[0124] Table 1 Pore structure characteristics of MSS and CrMo6@MSS before and after the reaction

[0125]

[0126] Figure 8 are the XRD spectra of MSS, Cr@MSS and CrMo6@MSS of Example 1. Among them, the peak positions at 24.6°, 33.7°, 36.4°, 50.2° and 54.9° belong to the standard characteristic peaks of α - Cr2O3. Based on Figure 8 it can be seen that the peak height of the α - Cr2O3 characteristic peak of CrMo6@MSS is significantly lower than that of Cr@MSS, indicating that the preparation method of the present invention can effectively inhibit the formation of the α - Cr2O3 phase on the surface of the catalyst.

[0127] Figure 9 is the XANES spectrum of (NH4)3[CrMo6O 24 H4] and the catalyst CrMo6@MSS. Based on Figure 9 it can be seen that positively charged Cr species are formed in CrMo6@MSS. Comparing with (NH4)3[CrMo6O 24The H4] and CrMo6@MSS spectral lines are visible. The intensity of CrMo6@MSS increases, and the covalency of Cr-O is enhanced, indicating that the method of the present invention changes the coordination environment of Cr.

[0128] Table 2 Information of Cr species in CrMo6@MSS fitted by FT-EXAFS

[0129]

[0130] Table 3 Data after linear fitting

[0131]

[0132] Figure 10 For (NH4)3[CrMo6O 24 H4] and the k of the catalyst CrMo6@MSS 2 The Fourier transform spectra of the k-weighted EXAFS of (NH4)3[CrMo6O Figure 11 The wavelet transform EXAFS spectrum of Cr foil Figure 12 The wavelet transform EXAFS spectrum of Cr2O3 Figure 13 The wavelet transform EXAFS spectrum of the CoO3 standard sample Figure 14 The wavelet transform EXAFS spectrum of CrMo6@MSS. The information of Cr species in the above samples fitted by FT-EXAFS is shown in Table 2 and Table 3. Based on Figures 10 - 14 and what is seen in Table 2-3, different from long-range ordered metallic chromium, CrMo6@MSS has a unique configuration composed of Cr-O, Cr-O-Cr, Cr-O-Si, and Cr-O-Mo bonds, and the coordination numbers CN are 6.0, 2.0, 2.0, and 2.0, indicating that the coordination structure of CrMo6@MSS prepared by the method of the present invention changes and contains high-valent chromium components.

[0133] The reaction results of the propane dehydrogenation catalysts in Examples 1-5 in the CO2-ODP reaction are as Figure 15 shown. Based on Figure 15It can be seen that during the 3h catalytic reaction process, the propane conversion rates of the catalysts in Examples 1 to 5 are all higher than 35%, the propylene selectivity is always higher than 85%, and the yield is higher than 25%, indicating that the propane dehydrogenation catalyst of the present invention has excellent catalytic performance. When the mass ratio of Anderson-type polyoxometalate to tetraethyl orthosilicate is (0.6 to 1.4):3, as the addition amount of Anderson-type polyoxometalate increases, both the conversion rate and the yield show a trend of first increasing and then decreasing. The highest conversion rate and yield are both of the catalyst in Example 1, indicating that when the mass ratio of Anderson-type polyoxometalate to tetraethyl orthosilicate is 1:3, the propane dehydrogenation catalyst has more excellent catalytic performance.

Claims

1. A method for preparing a propane dehydrogenation catalyst, characterized in that, Comprising: Dissolve cetyltrimethylammonium bromide and triethanolamine in deionized water to obtain System A: Tetraethyl orthosilicate and an aqueous solution containing Anderson-type polyoxometalate are successively added to the system A, and the reaction is carried out at 60-80 °C. The reaction product is washed, dried, and calcined to obtain a propane dehydrogenation catalyst; the mass ratio of the Anderson-type polyoxometalate to tetraethyl orthosilicate is (0.6-1.4):3; the composition of the Anderson-type polyoxometalate is (NH4)3[CrMo6O 24 H4].

2. The preparation method of the propane dehydrogenation catalyst according to claim 1, characterized in that, The mass ratio of the Anderson-type polyoxometalate to tetraethyl orthosilicate is 1:

3.

3. The preparation method of the propane dehydrogenation catalyst according to claim 1, characterized in that, The sequential addition of tetraethyl orthosilicate and the aqueous solution containing the Anderson-type polyoxometalate is specifically: after adding tetraethyl orthosilicate to System A and stirring evenly, immediately add all of the aqueous solution containing the Anderson-type polyoxometalate.

4. The preparation method of the propane dehydrogenation catalyst according to claim 1, characterized in that, The preparation method of the Anderson-type polyoxometalate includes: heating an aqueous solution of ammonium molybdate to boiling, adding an aqueous solution of chromium nitrate, mixing evenly, filtering while hot, cooling, and allowing to stand and age for 1 to 3 days to obtain the Anderson-type polyoxometalate.

5. The preparation method of the propane dehydrogenation catalyst according to claim 1, wherein, The reaction time at 60 to 80 °C after adding to System A is 3 to 4 h.

6. The preparation method of the propane dehydrogenation catalyst according to claim 1, characterized in that Dissolving cetyltrimethylammonium bromide and triethanolamine in deionized water to obtain System A means dissolving cetyltrimethylammonium bromide and triethanolamine in deionized water and stirring evenly at 60 to 80 °C to obtain System A.

7. The method for preparing a propane dehydrogenation catalyst according to claim 1, characterized in that, The temperature of the calcination is 550 to 600 °C and the time is 4 to 6 h.

8. Use of a propane dehydrogenation catalyst prepared by the preparation method of the propane dehydrogenation catalyst according to any one of claims 1 to 7, characterized in that, Including the application in CO2-ODP.

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