Preparation method and application of propane dehydrogenation catalyst

Abstract

The invention discloses a preparation method and application of a propane dehydrogenation catalyst, and the preparation method comprises the following steps: dissolving hexadecyl trimethyl ammonium bromide and triethanolamine in deionized water to obtain a system A: successively adding tetraethyl orthosilicate and an aqueous solution containing Anderson type polyoxometallate into the system A, reacting at 60-80 DEG C, washing, drying, and calcining to obtain a system B; according to the method, tetraethyl orthosilicate and the aqueous solution containing Anderson type polyoxometallate (NH4) 3 [CrMo6O24H4] are sequentially added into the system A containing the template agent, and the propane dehydrogenation catalyst is generated through reaction at 60-80 DEG C. The initial conversion rate of the catalyst in CO2-ODP at a temperature interval close to 580 DEG C reaches up to 53.5%, the initial selectivity reaches up to 91%, and the catalyst has the advantages of high selectivity, high selectivity, high selectivity and the like. In a 12-hour life test, the propylene selectivity is always higher than 80%, and the catalyst has the characteristic of 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 propane non-oxidative (PDH) dehydrogenation and propane oxidative (ODP) dehydrogenation. 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 CO 2 to participate in the propane dehydrogenation reaction (CO 2 -ODP) to promote the reaction to proceed in the direction of generating propylene. However, RWGS and CO 2 -ODP usually need to be carried out under high temperature and high pressure environments, and it is extremely easy to produce other by-products due to propane cracking, and the catalyst is easily deactivated due to carbon deposition, which poses 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 mainly 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 obtained by in-situ synthesizing a titanium oxide layer on the surface of alumina as the support, and multiple metal components are used in combination as electron promoters 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 adding tetraethyl orthosilicate and an aqueous solution containing Anderson-type polyoxometalate (NH 4 ) 3 [CrMo 6 O 24 H 4 to system A containing a template agent successively, and reacting at 60 - 80 °C to produce a propane dehydrogenation catalyst. In the propane dehydrogenation reaction in the vicinity of 580 °C, the initial conversion rate of propane over 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 (NH 4 ) 3 [CrMo 6 O 24 H 4 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 rate and propylene selectivity in the catalytic propane dehydrogenation reaction.

[0008] 2. Preferably, the present invention prepares the propane dehydrogenation catalyst CrMo 6 @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 CrMo 6 @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] The following further describes the technical solutions of the present invention in detail with reference to the drawings and examples. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 For the Anderson-type polyoxometalate (NH 4 ) 3 [CrMo 6 O 24 H 4Infrared spectrum diagram;

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

[0013] Figure 3 Propylene selectivities of the catalysts in Example 1 and the comparative example in the CO 2 -ODP reaction;

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

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

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

[0017] Figure 7 Nitrogen adsorption-desorption isotherms of mesoporous silica spheres MSS and CrMo 6 @MSS before and after the reaction;

[0018] Figure 8 XRD spectra of mesoporous silica spheres MSS, Cr@MSS, and CrMo 6 @MSS;

[0019] Figure 9 For (NH 4 ) 3 [CrMo 6 O 24 H 4 and the XANES spectra of the catalyst CrMo 6 @MSS;

[0020] Figure 10 For (NH 4 ) 3 [CrMo 6 O 24 H 4 and the Fourier transform spectra of the k 6 -weighted EXAFS of the catalyst CrMo 2 @MSS;

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

[0022] Figure 12 For Cr 2 O 3Wavelet transform EXAFS spectra;

[0023] Figure 13 is CoO 3 Wavelet transform EXAFS spectra of the standard sample;

[0024] Figure 14 is CrMo 6 Wavelet transform EXAFS spectra of @MSS;

[0025] Figure 15 is the CO of the propane dehydrogenation catalyst of Examples 1 to 5 2 -ODP reaction results. Detailed implementation manners

[0026] The technical solutions will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are 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 creative efforts belong to 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 three relationships may exist. For example, A and / or B may represent: the case of A alone, the case of B alone, and the case of both A and B existing simultaneously. Wherein A and B may be singular or plural.

[0028] In the following description, the terms "comprising", "including", "having" and "containing" are all open-ended terms, that is, they are intended to include 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 mean the order of execution, and some or all of the steps can be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation to the implementation process of the embodiments of the present application.

[0030] Those skilled in the art should understand that the numerical ranges 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 may 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 this application pertains. Although this 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 this application. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the said 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 a kind of discrete nano-polyoxometalate compounds, rich in transition metal components. The general formula of the Anderson structure polyoxometalate anion is [XM 6 O 24 n- or [X(OH) 6 M 6 O 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 having a relatively large specific surface area and stable mechanical properties, mesoporous silica spheres also have the characteristics of relatively weak acidity and alkalinity and small damage to active centers. Using polyoxometalates to bind the catalytic propane dehydrogenation active components to the mesoporous silica sphere carrier to form a propane dehydrogenation catalyst CrMo 6 @MSS.

[0033] In some embodiments, a method for preparing a propane dehydrogenation catalyst is provided, including:

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

[0035] Add tetraethyl orthosilicate and an aqueous solution containing Anderson-type polyoxometalates to the said system A successively, react at 60~80°C, wash, dry, and calcine the reaction product to obtain a propane dehydrogenation catalyst; the composition of the Anderson-type polyoxometalate is (NH 4 ) 3 [CrMo 6 O 24 H 4 .

[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 the fields of electrochemistry, battery materials, etc. The present invention creatively introduces polyoxometalate into the preparation of propane dehydrogenation catalyst. By utilizing its unique structural characteristics, the active components are combined into the mesoporous silica sphere carrier. Further, the polyoxometalate is Anderson-type polyoxometalate (NH 4 ) 3 [CrMo 6 O 24 H 4 . During the preparation of the catalyst, the ammonium component volatilizes, which has no effect on the acid-base balance of the catalyst surface. 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, which has lower chemical reactivity under the electrostatic action and the confinement of the mesopores. The surface α-Cr 6 content is lower, which can effectively reduce the probability of side reactions occurring in the catalytic propane dehydrogenation reaction and has robust catalytic activity. 2 O 3

[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 amount of tetraethyl orthosilicate affects the structure and morphology of the silica spheres. It is found in the experimental process 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 spheres 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, and the pores are blocked.

[0039] In some specific embodiments, the sequential addition of tetraethyl orthosilicate and the aqueous solution containing Anderson-type polyoxometalate is specifically as follows: After adding 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 aqueous solution containing Anderson-type polyoxometalate is added immediately after tetraethyl orthosilicate is uniformly dispersed in system A, CrMo 6 ​It is uniformly dispersed in the mesoporous channels as the silica spheres grow. After calcination to remove CTAB, the polyoxoacid is distributed in the channels in the form of derivatives, and the resulting catalyst has more excellent catalytic performance. During the experiment, it was found 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 tetraethyl orthosilicate is added to system A, it will approach the surface of the CTAB micelle, induce the formation of a silica core, and then the silica spheres grow and gradually form a silica wall. After adding Anderson-type polyoxometalate, CrMo 6 will be dispersed in the mesoporous channels as the silica spheres grow. The growth of silica spheres, the formation of silica walls, and CrMo 6 occur synchronously. If the addition of Anderson-type polyoxometalate is too late, the silica walls of the mesoporous channels have already formed, and the distribution of the active components is affected.

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

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

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

[0044] After cooling, stand for aging 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 after adding to system A at 60 - 80°C 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 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, and the pores are blocked. 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, there is provided an application of the above propane dehydrogenation catalyst in CO 2 -ODP.

[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 detailed descriptions will be given below in combination 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 (NH 4 ) 3 [CrMo 6 O 24 H 4 , specifically including:

[0055] Step 101: Dissolve 5 g of (NH 4 ) 6 Mo 7 O 24 ·4H 2 O in 80 mL of deionized water, heat to boiling, then add an aqueous solution of Cr(NO 3 ) 3 •9H 2 O, mix well, filter while hot, cool to room temperature, and let stand for aging for 2 days to obtain Anderson-type polyoxometalate (NH 4 ) 3 [CrMo 6 O 24 H 4 ; the aqueous solution of Cr(NO 3 ) 3 •9H 2 O is an aqueous solution obtained by dissolving 1.24 g of Cr(NO 3 ) 3 •9H 2 O in 20 g of water; the infrared spectrum of Anderson-type polyoxometalate (NH 3 ) 3 •9H 2 O in this example is as shown in 4 ) 3 [CrMo 6 O 24 H 4 , and the vibration peaks below 450 cm Figure 1 are attributed to the vibration of the central heteroatom Cr-O, and the vibration peaks at 950 - 900 cm -1 -1 ​and 650~550 cm -1 The vibration peak at -1 belongs to the vibration of Anderson-type polyoxometalate. Based on Figure 1 As can be seen, Anderson-type polyoxometalate (NH 4 ) 3 [CrMo 6 O 24 H 4 was 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 the stirring condition at 80 °C, add 3.1 g of tetraethyl orthosilicate (TEOS) to System A, continue stirring until it is mixed evenly, 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 g of the polyoxometalate (NH 4 ) 3 [CrMo 6 O 24 H 4 obtained in Step 1 in 8 g of deionized water;

[0059] Step 203: Filter the gray-green solution, wash the filtrate with deionized water and absolute ethanol alternately three times, dry the washed product in an oven at 100 °C for 24 h, and heat the dried material to 600 °C at a heating rate of 2 °C / minute in an air atmosphere and hold for 4 h to remove the template agent, obtaining a spherical propane dehydrogenation catalyst named CrMo 6 @MSS.

[0060] In this example, a method for preparing mesoporous silica spheres is also included, 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 the stirring condition at 80 °C, add 3.1 g of tetraethyl orthosilicate to System A, continue stirring until no more precipitate is formed, 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, which specifically includes:

[0065] Step 1: Dissolve 2.238 g of (NH 4 ) 3 [CrMo 6 O 24 H 6 •7H 2 O in 80 mL of deionized water to obtain an active component source solution; the (NH 4 ) 3 [CrMo 6 O 24 H 6 •7H 2 O 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 centrifuge; the neutral alumina is spherical alumina and is purchased from Shanghai Macklin;

[0067] Step 3: Dry the solid phase obtained by centrifugation overnight at 80 °C, and heat the dried material in an air atmosphere to 600 °C at a heating rate of 2 °C / minute and hold for 1 h to obtain a propane dehydrogenation catalyst, named CrMo 6 / Al 2 O 3 .

[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 microns, purchased from Tianjin Nanhua Catalyst Co., Ltd., and the obtained catalyst is named CrMo 6 / 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 CeO 2 , spherical, purchased from Shanghai Macklin, and the obtained catalyst is named CrMo 6 / CeO 2 .

[0072] Comparative Example 4

[0073] This comparative example is the same as Comparative Example 1, except that in Step 2, the carrier is ZrO 2 , powdery, purchased from Shanghai Macklin, and the obtained catalyst is named CrMo 6 / ZrO2 .

[0074] Comparative Example 5

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

[0076] Step 1: Mix 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 a 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, obtaining 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(NO 3 ) 3 •9H 2 O 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 (NH 4 ) 3 [CrMo 6 O 24 H 4 , specifically including:

[0081] Step 101: Dissolve 5 g of (NH 4 ) 6 Mo 7 O 24 ·4H 2 O in 80 mL of deionized water, heat to boiling, add an aqueous solution of Cr(NO 3 ) 3 •9H 2 O, mix evenly, filter while hot, cool to room temperature, and let stand for aging for 1 day to obtain Anderson-type polyoxometalate (NH 4 ) 3 [CrMo 6 O 24 H 4 ; the Cr(NO 3) 3 • 9H 2 An aqueous solution of O is obtained by dissolving 1.24 g of Cr(NO 3 ) 3 • 9H 2 O in 20 g of water to obtain an aqueous solution of Cr(NO 3 ) 3 • 9H 2 O;

[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 evenly mixed, immediately add a 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 (NH 4 ) 3 [CrMo 6 O 24 H 4 in 8 g of deionized water;

[0085] Step 203: Filter the gray-green solution, wash the filtrate with deionized water and absolute ethanol alternately 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 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 an Anderson-type polyoxometalate (NH 4 ) 3 [CrMo 6 O 24 H 4 , specifically including:

[0089] Step 101: Dissolve 5 g of (NH 4 ) 6 Mo 7 O 24 ·4H 2 O in 80 mL of deionized water, heat to boiling, and then add Cr(NO3 ) 3 •9H 2 An aqueous solution of O is mixed well and filtered while hot, cooled to room temperature, and allowed to stand and age for 2 days to obtain an Anderson-type polyoxometalate (NH 4 ) 3 [CrMo 6 O 24 H 4 ; The aqueous solution of Cr(NO 3 ) 3 •9H 2 O is the aqueous solution of Cr(NO 3 ) 3 •9H 2 O obtained by dissolving 1.24 g of Cr(NO 3 ) 3 •9H 2 O 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 stirring conditions at 60 °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 60 °C for 4 h to obtain a gray-green solution; the polyoxometalate solution is the polyoxometalate solution obtained by dissolving 0.8 g of the polyoxometalate (NH 4 ) 3 [CrMo 6 O 24 H 4 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 / 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 an Anderson-type polyoxometalate (NH 4 ) 3 [CrMo6 O 24 H 4 , specifically including:

[0097] Step 101: Dissolve 5 g of (NH 4 ) 6 Mo 7 O 24 ·4H 2 O in 80 mL of deionized water, heat to boiling, then add an aqueous solution of Cr(NO 3 ) 3 •9H 2 O. After mixing evenly, filter while it is hot, cool to room temperature, and let it stand for aging for 3 days to obtain Anderson-type polyoxometalate (NH 4 ) 3 [CrMo 6 O 24 H 4 ; The aqueous solution of Cr(NO 3 ) 3 •9H 2 O is an aqueous solution obtained by dissolving 1.24 g of Cr(NO 3 ) 3 •9H 2 O in 20 g of water to obtain an aqueous solution of Cr(NO 3 ) 3 •9H 2 O;

[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 (NH 4 ) 3 [CrMo 6 O 24 H 4 in 8 g of deionized water;

[0101] Step 203: Filter the grayish-green solution, wash the filtrate three times alternately 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 to 550 °C at a heating rate of 2 °C / minute 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 (NH 4 ) 3 [CrMo 6 O 24 H 4 , specifically including:

[0105] Step 101: Dissolve 5 g of (NH 4 ) 6 Mo 7 O 24 ·4H 2 O in 80 mL of deionized water, heat to boiling, add an aqueous solution of Cr(NO 3 ) 3 •9H 2 O, mix well, filter while hot, cool to room temperature, and stand for aging for 2 days to obtain Anderson-type polyoxometalate (NH 4 ) 3 [CrMo 6 O 24 H 4 ; The aqueous solution of Cr(NO 3 ) 3 •9H 2 O is an aqueous solution of Cr(NO 3 ) 3 •9H 2 O obtained by dissolving 1.24 g of Cr(NO 3 ) 3 •9H 2 O 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 system A, continue stirring until it is well 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 1.4 g of the polyoxometalate (NH 4 ) 3 [CrMo 6 O 24 H 4 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 to 600 °C at a heating rate of 2 °C / min in an air atmosphere and hold for 4 h to remove the template agent, obtaining a spherical propane dehydrogenation catalyst.

[0110] Performance evaluation

[0111] The catalytic performance of the catalysts in Example 1 and Comparative Examples 1 to 4 was evaluated by the CO 2 -ODP reaction, and the method is 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 filled with the catalyst to 580 °C within 1 h and hold it. Pass Ar for purging for 0.5 h, then pass a gas mixture into the purged reactor. The product is analyzed by an on-line gas chromatograph GC2060. Start chromatographic sampling analysis 10 min after passing 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 C 3 H 8 , CO 2 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 for the propane dehydrogenation catalyst CrMo in Example 1 6 @MSS, both the initial propane conversion rate and the initial propylene selectivity 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 near temperature of 580°C and under atmospheric pressure, during the 3h 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 of 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 CO 2 -OPD activity of the propane dehydrogenation catalyst.

[0119] According to the above evaluation method, a 12h 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 performance testing, 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 10mL•min -1 for calcination for 1h, then Ar was introduced and cooled to room temperature, and then hydrogen was introduced at 20mL•min -1 and uniformly heated to 580°C within 1h 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 long service life.

[0121] Figure 6 a in Figure 6 is the transmission electron microscope image of the mesoporous silica spheres of Example 1 at a scale of 50nm, Figure 6 and b in Figure 6Obvious mesoporous channels can be observed in b, indicating that mesoporous silica spheres are successfully prepared by the method of the present invention.

[0122] Figure 6 c of is the spherical propane dehydrogenation catalyst CrMo of Example 1 6 TEM image of @MSS, Figure 6 d of is the spherical propane dehydrogenation catalyst CrMo of Example 1 6 SEM image of @MSS, Figure 6 e~j of are element surface scan maps. According to Figure 6 c of and Figure 6 d of, it can be known that the CrMo of the present invention 6 @MSS catalyst is spherical, with uniform size. The surface of the silica spheres is not smooth, and there is partial adhesion and agglomeration between the silica spheres. Combining with the mapping diagram, 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 is for MSS and CrMo before and after the reaction 6 Nitrogen adsorption-desorption isotherm (BET) of @MSS, among which CrMo after the reaction 6 @MSS is CrMo after the life test 6 @MSS, Table 1 is for MSS and CrMo before and after the reaction 6 @MSS specific surface area and pore size distribution. It can be seen that MSS and CrMo before and after the reaction 6 @MSS are all mesoporous structures. The pore diameter D of MSS, CrMo before and after the reaction 6 @MSS p changes little, indicating that the introduction of CrMo 6 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 CrMo before and after the reaction 6 @MSS

[0125] Figure 8 is for MSS, Cr@MSS and CrMo of Example 1 6 XRD patterns of @MSS, among which the peak positions at 24.6°, 33.7°, 36.4°, 50.2° and 54.9° belong to the standard characteristic peaks of α-Cr 2 O 3 Based on Figure 8 It can be seen that the α-Cr of CrMo 6 @MSS 2 O3 The peak height of the characteristic peak is significantly lower than that of Cr@MSS, indicating that the preparation method of the present invention can effectively inhibit α-Cr 2 O 3 phase formation on the catalyst surface.

[0126] Figure 9 For (NH 4 ) 3 [CrMo 6 O 24 H 4 and the XANES spectra of the catalyst CrMo 6 @MSS. Based on Figure 9 It can be seen that a positively charged Cr species is formed in CrMo 6 @MSS. Comparing the spectra of (NH 4 ) 3 [CrMo 6 O 24 H 4 and CrMo 6 @MSS, it can be seen that the intensity of CrMo 6 @MSS increases and the covalency of Cr-O enhances, indicating that the method of the present invention changes the coordination environment of Cr.

[0127] Table 2 Information on Cr species in CrMo 6 @MSS obtained by FT-EXAFS fitting

[0128] Table 3 Data after linear fitting

[0129] Figure 10 For (NH 4 ) 3 [CrMo 6 O 24 H 4 and the Fourier transform spectra of k 6 -weighted EXAFS of the catalyst CrMo 2 @MSS. Comparing with the Cr-Cr coordination reference substances Co 2 O 3 , CoO 3 and Co foil, it can be seen that the CrMo 6 @MSS spectrum shows a prominent Cr-O peak, indicating that the Cr species are mainly dispersed in the catalyst sample in the form of Cr oxides. Figure 11 is the wavelet transform EXAFS spectrum of Cr foil, Figure 12 is the wavelet transform EXAFS spectrum of Cr 2 O 3 andFigure 13 is CoO 3 The wavelet transform EXAFS spectra of the standard sample Figure 14 is CrMo 6 The wavelet transform EXAFS spectra of @MSS. The Cr species information obtained by FT-EXAFS fitting of the above samples is shown in Tables 2 and 3. Based on Figures 10 - 14 and as seen in Tables 2 - 3, different from long-range ordered metallic chromium, CrMo 6 @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 CrMo 6 @MSS prepared by the method of the present invention has changed, and contains high-valent chromium components.

[0130] The reaction results of the propane dehydrogenation catalysts of Examples 1 - 5 in the CO 2 -ODP reaction are as Figure 15 shown. Based on Figure 15 as seen, during the 3h catalytic reaction process, the propane conversion rates of the catalysts of Examples 1 - 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 - 1.4):3, with the increase of the addition amount of Anderson-type polyoxometalate, both the conversion rate and the yield show a trend of first increasing and then decreasing. Among them, the highest conversion rate and yield are both for the catalyst of 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: include: Dissolve hexadecyltrimethylammonium 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, reacted at 60-80° C., and the reacted materials are washed, dried, and calcined to obtain a propane dehydrogenation catalyst.

2. The method for preparing a propane dehydrogenation catalyst according to claim 1, characterized in that: The Anderson type polyoxometalate composition is (NH4)3[CrMo6O 24 H4].

3. The method for preparing a propane dehydrogenation catalyst according to claim 1, characterized in that: The mass ratio of the Anderson-type polyoxometalate to tetraethyl orthosilicate is (0.6-1.4):

3.

4. The method for preparing a propane dehydrogenation catalyst according to claim 3, characterized in that: The mass ratio of the Anderson type polyoxometalate to tetraethyl orthosilicate is 1:

3.

5. The method for preparing a propane dehydrogenation catalyst according to claim 1, characterized in that: The tetraethyl orthosilicate and the aqueous solution containing Anderson type polyoxometalate are added successively as follows: after the tetraethyl orthosilicate is added to the system A and stirred evenly, the aqueous solution containing Anderson type polyoxometalate is immediately added.

6. The method for preparing a propane dehydrogenation catalyst according to claim 1, characterized in that: The preparation method of the Anderson type polyoxometalate comprises: heating an ammonium molybdate aqueous solution to boiling, adding a chromium nitrate aqueous solution, mixing, filtering while hot, cooling, and standing for aging for 1 to 3 days to obtain the Anderson type polyoxometalate.

7. The method for preparing a propane dehydrogenation catalyst according to claim 1, characterized in that: After adding into system A, the reaction time at 60~80°C is 3~4h.

8. The method for preparing a propane dehydrogenation catalyst according to claim 1, characterized in that: Dissolve hexadecyltrimethylammonium bromide and triethanolamine in deionized water to obtain system A. Dissolve hexadecyltrimethylammonium bromide and triethanolamine in deionized water, stir and mix at 60-80° C. to obtain system A.

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

10. Use of a propane dehydrogenation catalyst prepared by the method for preparing a propane dehydrogenation catalyst according to any one of claims 1 to 9, characterized in that: Including applications in CO2-ODP.

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