Dehydrogenation cracking bifunctional catalyst as well as preparation method and application thereof

Abstract

The invention provides a dehydrogenation cracking bifunctional catalyst and a preparation method and application thereof.The dehydrogenation cracking bifunctional catalyst comprises an HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve and transition metal nanoparticles, and the transition metal nanoparticles are loaded on the surface of the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve or in the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve. The dehydrogenation cracking bifunctional catalyst provided by the invention has the advantages of good low-temperature activity, easy activation of low-carbon alkane, high selectivity of low-carbon olefin, excellent carbon deposition resistance and the like.

Description

Technical Field

[0001] The present invention relates to a dehydrogenation cracking bifunctional catalyst, a preparation method thereof and an application thereof, belonging to the technical fields of oil refining and chemical engineering. Background Art

[0002] C4 alkanes mainly come from the catalytic cracking process in the petroleum processing process. They have strong chemical stability, are difficult to activate, have low chemical utilization rate, and are basically used as fuels with low economic added value. Light olefins such as ethylene and propylene are important organic chemical raw materials, and their market demand is increasing continuously. Improving the production of light olefins has become an urgent problem to be solved. Therefore, the catalytic cracking of n-butane into light olefins with high added value has attracted wide attention.

[0003] In the early stage, HZSM-5 catalyst was used for the catalytic cracking of n-butane. Although it has a large specific surface area and an adjustable silicon-aluminum ratio, its microporous structure limits the diffusion and mass transfer of reactants and products, making it difficult for product molecules to escape quickly. This not only affects the conversion of reactants but also easily causes carbon deposition and deactivation of the catalyst. In addition, the high acid strength of HZSM-5 causes side reactions such as polymerization-dehydrogenation-cyclization-aromatization-coking of the generated small molecule products ethylene and propylene at strong acid sites, thereby generating carbon deposition, shortening the service life of the catalyst, and reducing the selectivity of ethylene and propylene.

[0004] The development of catalysts is the key to the catalytic cracking process of light alkanes. In this regard, the applicant will briefly introduce some prior arts related to the present application.

[0005] Prior art document 1, source: Zhang Wenfang, Wang Pengzhao, Yang Chaohe, etc. High-temperature cracking reaction of n-butane on HZSM-5 zeolite [J]. Petrochemical Technology & Application, 2018, 36(06): 382-385.; related technical description: Studying the high-temperature cracking reaction of n-butane on HZSM-5 zeolite by changing the silicon-aluminum ratio; the defect of this technology or the deficiency compared with the present invention is that the reaction temperature is high, and on HZSM-5 zeolite with a low silicon-aluminum ratio, olefins are prone to hydrogen transfer reaction to generate alkanes, resulting in an increase in the selectivity of light alkanes and a decrease in the selectivity of light olefins.

[0006] Prior art document 2, source: Jiang Guiyuan, Lu Jiangyin, Duan Aijun, etc. Performance study on catalytic cracking of C4 alkanes to light olefins over transition metal Fe modified HZSM-5 zeolite [C]. Catalysis Committee of Chinese Chemical Society. Proceedings of the 11th National Youth Catalysis Academic Conference (Part I). 2007: 83-84.; related technical description: This prior art studied the performance of catalytic cracking of C4 alkanes to light olefins over transition metal Fe modified HZSM-5 zeolite; the defect of this technology or the deficiency compared with the present invention is that the reaction temperature is high and the selectivity of light olefins has not been improved.

[0007] Prior art document 3, source: Liao Zhengkun, Dilnur·Aili, Fang Yaping, etc. Influence of potassium modification on the cracking performance of n-butane over Au / ZSM-5 catalyst [J]. Journal of Molecular Catalysis, 2023, 37(02): 118-129.; Technical description: This prior art studied the influence of potassium modification on the cracking performance of n-butane over Au / ZSM-5 catalyst; Defects of this technology or deficiencies compared to the present invention: Using precious metals as catalysts is expensive.

[0008] Therefore, providing a new dehydrogenation cracking bifunctional catalyst and its preparation method and application has become an urgent technical problem in this field. Summary of the Invention

[0009] In order to solve the above-mentioned disadvantages and deficiencies, an object of the present invention is to provide a dehydrogenation cracking bifunctional catalyst. This dehydrogenation cracking bifunctional catalyst has high catalytic cracking activity and selectivity.

[0010] Another object of the present invention is also to provide a preparation method of the above-mentioned dehydrogenation cracking bifunctional catalyst.

[0011] Another object of the present invention is also to provide the application of the above-mentioned dehydrogenation cracking bifunctional catalyst in the catalytic cracking of n-butane to produce small molecule olefins.

[0012] In order to achieve the above objects, on the one hand, the present invention provides a dehydrogenation cracking bifunctional catalyst, wherein the dehydrogenation cracking bifunctional catalyst includes HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve and transition metal nanoparticles, and the transition metal nanoparticles are loaded on the surface or inside of the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve.

[0013] In the dehydrogenation cracking bifunctional catalyst provided by the present invention, most of the transition metal nanoparticles are loaded on the surface of the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve, and a small part of the transition metal nanoparticles are loaded inside the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve.

[0014] As a specific embodiment of the above-mentioned dehydrogenation cracking bifunctional catalyst of the present invention, based on the total weight of the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve being 100%, the content of the transition metal nanoparticles is 0.1%-1%.

[0015] As a specific embodiment of the above-mentioned dehydrogenation cracking bifunctional catalyst of the present invention, the transition metal includes one or a combination of several of nickel, gold, iron, etc.

[0016] On the other hand, the present invention also provides a method for preparing the dehydrogenation cracking bifunctional catalyst described above, wherein the preparation method includes:

[0017] Step (1): subject the HZSM-5 microporous molecular sieve to alkali treatment with an alkali solution to obtain an alkali-treated solution, add a template agent to the alkali-treated solution and mix evenly to obtain a mixed solution;

[0018] Step (2): perform the first hydrothermal crystallization on the mixed solution, adjust the pH value of the obtained suspension, and then continue to perform the second hydrothermal crystallization on it;

[0019] Step (3): calcine the product of the second hydrothermal crystallization to obtain a sodium-type molecular sieve;

[0020] Step (4): subject the sodium-type molecular sieve to ion exchange with an aqueous solution of an ammonium salt to obtain a hydrogen-type molecular sieve;

[0021] Step (5): calcine the hydrogen-type molecular sieve to obtain an HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve;

[0022] Step (6): uniformly drip an aqueous solution of a transition metal salt on the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve by the equal-volume impregnation method and mix evenly, and then obtain NiO-HZSM-5 / MCM-41 after drying and calcination;

[0023] Step (7): reduce NiO-HZSM-5 / MCM-41 in a hydrogen-nitrogen mixed gas atmosphere to obtain a dehydrogenation cracking bifunctional catalyst.

[0024] As a specific embodiment of the preparation method described above of the present invention, wherein the preparation method of the HZSM-5 microporous molecular sieve includes:

[0025] Step 1): weigh a certain amount of tetrapropylammonium hydroxide and add it to deionized water, stir at room temperature until it is fully dissolved; then add a quantitative alkali and stir again until it is dissolved; then add a certain amount of aluminum source to the solution and stir at room temperature; finally add a silicon source and continuously stir to make it fully hydrolyze to obtain a gel-like substance;

[0026] Step 2): put the gel-like substance into a stainless steel hydrothermal reaction kettle with a polytetrafluoroethylene inner liner, and then put the stainless steel hydrothermal reaction kettle into a rotary oven, set the reaction temperature to 80-150 °C, and perform rotary hydrothermal crystallization for 24-96 h;

[0027] Step 3): after the reaction is completed, take out the stainless steel hydrothermal reaction kettle, centrifuge, wash, and dry the obtained solution to obtain a relatively pure product, then grind the obtained product into powder, and calcine it in a muffle furnace at a temperature of 450-700 °C for 6 h;

[0028] Step 4): The product obtained after calcination in Step 3) is subjected to ion exchange with an ammonium chloride aqueous solution in an oil bath at 50 - 90°C for 1 - 3 hours each time, and this is carried out 1 - 3 times.

[0029] Step 5): The product after ion exchange is dried, and then the dried product is calcined at 450 - 700°C for 2 hours to obtain HZSM-5 microporous molecular sieve.

[0030] As a specific embodiment of the above preparation method of the present invention, in Step 1), the base includes sodium hydroxide, etc., the aluminum source includes one or a combination of several of aluminum isopropoxide, aluminum nitrate, aluminum sulfate, sodium metaaluminate, etc., and the silicon source includes tetraethyl orthosilicate and / or silicon dioxide, etc.

[0031] As a specific embodiment of the above preparation method of the present invention, in Step (1), the temperature of the base treatment is 30 - 60°C and the time is 0.5 - 3 hours.

[0032] As a specific embodiment of the above preparation method of the present invention, in Step (1), the base solution is a 0.5 - 2.0 mol / L NaOH solution. For the 0.5 - 2.0 mol / L NaOH solution, its dosage can be reasonably adjusted according to actual operation needs as long as it can achieve the purpose of base treatment. For example, in some embodiments of the present invention, the dosage of the 0.5 - 2.0 mol / L NaOH solution can be 5 - 20 mL.

[0033] As a specific embodiment of the above preparation method of the present invention, in Step (1), the mass ratio of HZSM-5 microporous molecular sieve to the template agent is 1 - 5:1 - 5.

[0034] As a specific embodiment of the above preparation method of the present invention, in Step (1), the template agent includes cetyltrimethylammonium bromide (CTAB), etc.

[0035] The present invention does not make specific requirements on the addition method of the template agent, and its addition method can be reasonably selected according to the specific substance of the template agent and actual on-site operation needs. For example, the template agent can be directly added to the base treatment solution, or the template agent can be first dissolved in deionized water to prepare a template agent solution, and then the template agent solution is added to the base treatment solution.

[0036] As a specific embodiment of the above preparation method of the present invention, in Step (1), the mixing evenly is achieved by stirring, specifically by stirring at a temperature of 30 - 80°C for 0.5 - 3 hours.

[0037] As a specific embodiment of the above-described preparation method of the present invention, in step (2), the temperatures of the first hydrothermal crystallization and the second hydrothermal crystallization are 80 - 150 °C respectively, and the times are 24 - 96 h respectively.

[0038] As a specific embodiment of the above-described preparation method of the present invention, in step (2), after adjusting the pH value of the obtained suspension to 7 - 9, the second hydrothermal crystallization is carried out on it.

[0039] As a specific embodiment of the above-described preparation method of the present invention, in step (2), the pH value of the obtained suspension is adjusted to 7 - 9 with a HCl solution having a concentration of 1 - 3 mol / L, and then the second hydrothermal crystallization is carried out on it.

[0040] The present invention prepares the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve by a secondary crystallization method and uses it as the carrier of the dehydrogenation cracking bifunctional catalyst. By the micro-mesoporous composite method, the diffusion resistance in the molecular sieve pores is reduced, carbon deposition is reduced, and the problems of large diffusion resistance, uneven distribution of strong acid sites on the surface, and easy carbon deposition of the existing HZSM-5 molecular sieve are solved.

[0041] As a specific embodiment of the above-described preparation method of the present invention, in step (3), the calcination is carried out at 450 - 700 °C for 2 - 8 h. This step of calcination in step (3) can remove the residual microporous template agent used in the preparation of the HZSM-5 microporous molecular sieve, such as tetrapropylammonium hydroxide (TPAOH), etc.

[0042] As a specific embodiment of the above-described preparation method of the present invention, in step (4), the temperature of the ion exchange is 50 - 90 °C, and it is carried out 1 - 3 times, each time for 1 - 3 h. The present invention does not make specific requirements on the ammonium salt used in step (4), and it can be reasonably selected according to the actual on-site operation needs. For example, in some embodiments of the present invention, the ammonium salt can be ammonium chloride, etc.

[0043] As a specific embodiment of the above-described preparation method of the present invention, in step (5), the calcination is carried out at 450 - 700 °C for 1 - 4 h.

[0044] For zeolite materials, the basic strategies to improve their mass transfer performance include shortening the micropore channels or enlarging the pore diameter. In this regard, the dehydrogenation cracking bifunctional catalyst provided by the present invention uses HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve as the carrier. This composite molecular sieve has a dual pore distribution of micropores and mesopores, so that the dehydrogenation cracking bifunctional catalyst has both the pore advantages of mesoporous molecular sieves and the strong acidity of microporous molecular sieves. In addition, aiming at the problem that solid acid catalysts are difficult to activate n-butane, the present invention introduces transition metals into it, which can realize the synergistic effect of metal dehydrogenation active centers and molecular sieve acidic active centers, thereby reducing the reaction temperature, improving the activation ability of the molecular sieve for alkanes, promoting the dehydrogenation reaction of alkane molecules, and the generated butene can undergo cracking reaction at the acidic sites of ZSM-5 molecular sieve, improving the catalytic cracking activity of ZSM-5 molecular sieve for alkanes, which is beneficial to improving the selectivity and yield of light olefins.

[0045] Therefore, the dehydrogenation cracking bifunctional catalyst provided by the present invention includes HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve and transition metal nanoparticles supported on its surface or inside, which can realize the multi-functional regulation of the catalyst pore structure, acid properties, and dehydrogenation activity (by metal modification), so that the catalyst has the advantages of good catalytic cracking activity for n-butane and high selectivity for light olefins such as ethylene and propylene, and solves the problems of easy deactivation and difficult activation of the current HZSM-5 molecular sieve.

[0046] As a specific embodiment of the above-mentioned preparation method of the present invention, between step (5) and step (6), it further includes:

[0047] Take a certain mass of HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve pretreated, such as by ordinary drying treatment, and place it in an eggplant-shaped flask, then slowly add deionized water drop by drop while constantly shaking; stop adding when the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve carrier reaches the critical state of adsorption saturation, weigh the mass of the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve at this time, calculate its water absorption rate according to the mass change of the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve before and after water absorption, and measure it three times and take the average as the average water absorption rate of the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve;

[0048] Calculate the volume of the impregnation solution required for the equal-volume impregnation method, that is, the aqueous solution of transition metal salt, according to the average water absorption rate, and prepare an aqueous solution of transition metal salt that meets the requirements according to the result.

[0049] As a specific embodiment of the above-described preparation method of the present invention, in step (6), the transition metal salt includes one or a combination of several of nitrates, sulfates, chlorides, etc. of transition metals. For example, when the transition metal is nickel, its salts include one or a combination of several of nickel chloride, nickel nitrate, and nickel sulfate.

[0050] As a specific embodiment of the above-described preparation method of the present invention, in step (6), an equal-volume impregnation method is used to uniformly drop an aqueous solution of a transition metal salt onto the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve, and it is continuously shaken during the process to make it mix evenly until there is no remaining impregnation solution, and then it is left standing for 12 - 48 h.

[0051] As a specific embodiment of the above-described preparation method of the present invention, in step (6), the calcination is carried out at 350 - 600 °C for 1 - 6 h.

[0052] As a specific embodiment of the above-described preparation method of the present invention, in step (7), the reduction temperature is 450 - 650 °C, the flow rate of the hydrogen-nitrogen mixed gas is 10 - 50 mL / min, and based on the total volume of the hydrogen-nitrogen mixed gas being 100%, the content of hydrogen is 1 - 50%.

[0053] On the other hand, the present invention also provides the application of the above-described dehydrogenation cracking bifunctional catalyst in the catalytic cracking of n-butane to produce light olefins.

[0054] As a specific embodiment of the above-described application of the present invention, in the catalytic cracking, the temperature is 450 - 650 °C and the pressure is 0.1 - 2.5 MPa.

[0055] The dehydrogenation cracking bifunctional catalyst provided by the present invention includes an HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve and transition metal nanoparticles, and the transition metal nanoparticles are loaded on the surface or inside of the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve. When the dehydrogenation cracking bifunctional catalyst is used for the catalytic cracking of n-butane to produce light olefins, the transition metal nanoparticles with certain alkane dehydrogenation activity loaded on the surface of the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve, such as nickel nanoparticles, change the cracking pathway of alkanes. Specifically, it first dehydrogenates to form olefin intermediates and then further cracks to form light olefins, thereby improving the activity of the catalyst for the cracking of light alkanes to form light olefins and solving the problems of low low-temperature activity of the catalyst and difficult activation of alkanes.

[0056] Compared with the prior art, the beneficial technical effects that the present invention can achieve include:

[0057] The dehydrogenation cracking bifunctional catalyst provided by the present invention uses HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve as the carrier, which has a micro-mesoporous composite structure and a large specific surface area, pore volume and Lewis acid center, significantly improving the conversion rate of n-butane, the selectivity of light olefins and the anti-coking performance of the dehydrogenation cracking bifunctional catalyst.

[0058] Compared with HZSM-5 / MCM-41, the morphology of Ni / HZSM-5 / MCM-41 has not changed significantly, with highly dispersed Ni nanoparticles and Lewis acid centers. The introduction of Ni has no obvious effect on the pore size distribution of the molecular sieve, significantly improving the conversion rate of n-butane and the selectivity of light olefins of the dehydrogenation cracking bifunctional catalyst. In addition, the dehydrogenation performance of the Ni active component and the regulation of the pore structure and acidity of the molecular sieve form a synergistic effect, further promoting the efficient conversion of n-butane and improving the selectivity of light olefins.

[0059] In summary, the dehydrogenation cracking bifunctional catalyst provided by the present invention has the advantages of good low-temperature activity, easy activation of light alkanes, high selectivity of light olefins and excellent anti-coking performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0061] Figure 1a It is the wide-angle XRD patterns of HZSM-5, HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve, 0.1% Ni-HZSM-5 / MCM-41, 0.5% Ni-HZSM-5 / MCM-41 and 1% Ni-HZSM-5 / MCM-41 in Test Example 1 of the present invention.

[0062] Figure 1b It is the small-angle XRD patterns of MCM-41, HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve, 0.1% Ni-HZSM-5 / MCM-41, 0.5% Ni-HZSM-5 / MCM-41 and 1% Ni-HZSM-5 / MCM-41 in Test Example 1 of the present invention.

[0063] Figure 2a It is the SEM image of HZSM-5 in Test Example 2 of the present invention.

[0064] Figure 2b It is the SEM image of HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve in Test Example 2 of the present invention.

[0065] Figure 2c This is the SEM image of 0.1% Ni-HZSM-5 / MCM-41 in Test Example 2 of the present invention.

[0066] Figure 2d This is the SEM image of 0.5% Ni-HZSM-5 / MCM-41 in Test Example 2 of the present invention.

[0067] Figure 2e This is the SEM image of 1% Ni-HZSM-5 / MCM-41 in Test Example 2 of the present invention.

[0068] Figure 3a This is the HRTEM image of HZSM-5 in Test Example 3 of the present invention.

[0069] Figure 3b This is the HRTEM image of MCM-41 in Test Example 3 of the present invention.

[0070] Figure 3c This is the HRTEM image of the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve in Test Example 3 of the present invention.

[0071] Figure 3d This is the HRTEM image (50 nm) of 0.5% Ni-HZSM-5 / MCM-41 in Test Example 3 of the present invention.

[0072] Figure 3e This is the HRTEM image (20 nm) of 0.5% Ni-HZSM-5 / MCM-41 in Test Example 3 of the present invention.

[0073] Figure 3f This is the Mapping image of 0.5% Ni-HZSM-5 / MCM-41 in Test Example 3 of the present invention.

[0074] Figure 4a - Figure 4f This is the n-butane cracking performance graph obtained in Evaluation Example 1 of the present invention. Detailed implementation manners

[0075] It should be noted that the term "including" and any variations thereof in the description, claims and drawings of the present invention are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device that includes a series of steps or units does not necessarily limit to those clearly listed steps or units, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0076] The "ranges" disclosed in the present invention are given in the form of a lower limit and an upper limit. There may be one or more lower limits, and one or more upper limits respectively. A given range is defined by selecting a lower limit and an upper limit. The selected lower limit and upper limit define the boundaries of a particular range. All ranges defined in this way are combinable, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 - 120 and 80 - 110 are listed for a particular parameter, ranges of 60 - 110 and 80 - 120 are also contemplated. Further, if the minimum range values listed are 1 and 2, and the maximum range values listed are 3, 4, and 5, then the following ranges are all contemplated: 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 5.

[0077] In the present invention, unless otherwise specified, the numerical range "a - b" represents an abbreviated representation of any combination of real numbers between a and b, where both a and b are real numbers. For example, the numerical range "0 - 5" means that all real numbers between "0 - 5" are fully listed in the present invention, and "0 - 5" is just an abbreviated representation of these numerical combinations.

[0078] In the present invention, if there is no special instruction, all the embodiments and preferred embodiments mentioned in the present invention can be combined with each other to form a new technical solution.

[0079] In the present invention, if there is no special instruction, all the technical features and preferred features mentioned in the present invention can be combined with each other to form a new technical solution.

[0080] In the present invention, if there is no special instruction, all the steps mentioned herein can be carried out in sequence or randomly, but preferably in sequence. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) carried out in sequence, or may also include steps (b) and (a) carried out in sequence. For example, if it is mentioned that the method may further include step (c), it means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or may also include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0081] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. The following described embodiments are some embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention. For those conditions not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments without indicating the manufacturer, they are all conventional products that can be obtained through commercial purchase. For example, tetraethyl orthosilicate used in the embodiments of the present invention is of analytical grade and is purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; aqueous solution of tetrapropylammonium hydroxide is a 25wt% aqueous solution and is purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; aluminum isopropoxide is of analytical grade and is purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; sodium hydroxide is of analytical grade and is purchased from Shanghai Macklin Biochemical Technology Co., Ltd.; cetyltrimethylammonium bromide (CTAB) is of analytical grade and is purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; nickel nitrate hexahydrate is of analytical grade and is purchased from Sinopharm Chemical Reagent Co., Ltd.; deionized water; ammonium chloride is of analytical grade and is purchased from Shanghai Macklin Biochemical Technology Co., Ltd.; the purity of n-butane is 99.9% and is purchased from Beijing Huatong Jingke Co., Ltd.; air is purchased from Zhuozhou Beiwen Industrial Gas Sales Co., Ltd.; the purity of nitrogen is 99.999% and is purchased from Zhuozhou Beiwen Industrial Gas Sales Co., Ltd.; 5v% hydrogen-nitrogen mixture gas with a purity of 99.9% is purchased from Beijing Huatong Jingke Co., Ltd.; quartz sand (40-60 mesh) is purchased from Sinopharm Chemical Reagent Co., Ltd.

[0082] Example 1

[0083] This example provides a dehydrogenation cracking bifunctional catalyst, which is prepared by a preparation method including the following specific steps:

[0084] Preparation of HZSM-5 molecular sieve:

[0085] Step 1): Weigh 18.74 g of an aqueous solution of tetrapropylammonium hydroxide with a concentration of 25wt% and add it to 13.57 g of deionized water, stir at room temperature for 0.5 h until it is fully dissolved; then add 0.13 g of sodium hydroxide pellets and stir again for 0.5 h; then add 0.13 g of aluminum isopropoxide to the solution, stir at room temperature for 1 h; finally add 13.33 g of tetraethyl orthosilicate solution and continuously stir for 12 h to make it fully hydrolyze to obtain a gel-like substance;

[0086] Step 2): Place the gel-like substance in a stainless-steel hydrothermal reaction kettle with a PTFE inner liner, then place this stainless-steel hydrothermal reaction kettle in a rotary oven, set the reaction temperature to 100 °C, and carry out rotary hydrothermal crystallization for 72 h;

[0087] Step 3): After the reaction is completed, take out this stainless-steel hydrothermal reaction kettle, centrifuge, wash, and dry the obtained solution to obtain a relatively pure product. Then grind the obtained product into powder, and then calcine it in a muffle furnace at 550 °C for 6 h;

[0088] Step 4): Carry out ion exchange of the product prepared in Step 3) with an ammonium chloride aqueous solution under the conditions of a 90 °C oil bath and stirring, 2 h each time, for a total of 3 times;

[0089] Step 5): After drying the ion-exchanged product, calcine it at 550 °C for 2 h to obtain HZSM-5 molecular sieve;

[0090] Preparation of HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve:

[0091] Step (1): Take 2 g of the above-prepared HZSM-5 molecular sieve (microporous) and add it to 13.28 mL of a NaOH solution with a concentration of 1.5 mol / L, and subject the HZSM-5 molecular sieve to alkali treatment at 40 °C for 1 h to obtain an alkali-treated solution;

[0092] Take 2.90 g of CTAB and add it to 26 mL of deionized water to dissolve, then add the obtained solution to the above alkali-treated solution and stir at 60 °C for 1 h to obtain a mixed solution;

[0093] Step (2): Subsequently, transfer the mixed solution to a stainless-steel hydrothermal reaction kettle with a PTFE inner liner, then place this stainless-steel hydrothermal reaction kettle in a rotary oven, set the reaction temperature to 110 °C, and carry out hydrothermal crystallization for 24 h;

[0094] Step (3): After the first crystallization is completed, adjust the pH value of the obtained suspension to about 8.5 with a 2 mol / L HCl solution, add water, and continue the second crystallization. The reaction conditions are the same as those in the first crystallization process;

[0095] Step (4): After the second crystallization reaction is completed, centrifuge, wash, and dry the obtained product to obtain a relatively pure product. Then grind the obtained product into powder, and calcine it in a muffle furnace at 550 °C for 6 h to remove the residual microporous template agent therein to obtain a sodium-type molecular sieve;

[0096] Step (5): Carry out ion exchange of the sodium-type molecular sieve with an ammonium chloride aqueous solution under the conditions of a 90 °C oil bath and stirring, 2 h each time, for a total of 3 times to obtain a hydrogen-type molecular sieve;

[0097] Step (6): Centrifuge and wash the hydrogen-form molecular sieve, dry it, and then calcine the dried product at 550 °C for 2 h to obtain the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve;

[0098] Preparation of the dehydrogenation and cracking bifunctional catalyst:

[0099] Step 1: Take 1 g of the dried HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve and place it in an eggplant-shaped flask. Then, gradually add deionized water dropwise while constantly shaking. Stop adding when the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve reaches the critical state of adsorption saturation. Weigh the mass of the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve at this time, and calculate its water absorption rate based on the mass change of the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve before and after water absorption. Take the average of three measurements to obtain the average water absorption rate of the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve. In this example, each gram of the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve can absorb 1.57 g of water;

[0100] Step 2: Calculate the volume of the impregnation solution required for the equal-volume impregnation method based on the average water absorption rate data, and prepare an impregnation solution that meets the requirements according to the result, that is, nickel nitrate solution. The specific preparation process is as follows:

[0101] Take 0.0049 g of nickel nitrate hexahydrate and dissolve it in 1.5682 g of deionized water to obtain a nickel nitrate solution with a mass concentration of 0.1%;

[0102] Step 3: Take 1 g of the dried HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve and place it in a flask. Using the equal-volume impregnation method, evenly drip the above-mentioned nickel nitrate solution onto the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve while constantly shaking to make it mix evenly without any remaining impregnation solution. Let it stand for 24 h;

[0103] Step 4: Take out the impregnated product obtained in Step 3 after drying, put it into a muffle furnace, and calcine it at 350 °C for 3 h to obtain an intermediate product, denoted as 0.1% NiO-HZSM-5 / MCM-41;

[0104] Step 5: Reduce 0.1% NiO-HZSM-5 / MCM-41 under the atmosphere of a hydrogen-nitrogen mixed gas (5% H 2 , volume fraction) with a flow rate of 30 mL / min at a temperature of 550 °C to obtain the dehydrogenation and cracking bifunctional catalyst, denoted as 0.1% Ni-HZSM-5 / MCM-41.

[0105] Example 2

[0106] This embodiment provides a dehydrogenation cracking bifunctional catalyst, which is prepared by a preparation method including the following specific steps:

[0107] The preparation of HZSM-5 molecular sieve and the preparation of HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve are the same as those in Example 1;

[0108] Preparation of dehydrogenation cracking bifunctional catalyst:

[0109] Step 1: Take 1 g of the dried HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve and place it in an eggplant-shaped flask. Then, gradually add deionized water dropwise while constantly shaking. Stop adding when the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve reaches the adsorption saturation critical state. Weigh the mass of the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve at this time, and calculate its water absorption rate according to the mass change of the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve before and after water absorption. Take the average of three measurements to obtain the average water absorption rate of the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve. In this embodiment, each gram of the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve can absorb 1.57 g of water;

[0110] Step 2: Calculate the volume of the impregnation solution required for the equal-volume impregnation method according to the average water absorption rate data, and prepare an impregnation solution that meets the requirements, namely nickel nitrate solution. The specific preparation process is as follows:

[0111] Take 0.0249 g of nickel nitrate hexahydrate and dissolve it in 1.5608 g of deionized water to prepare a nickel nitrate solution;

[0112] Step 3: Take 1 g of the dried HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve and place it in a flask. Using the equal-volume impregnation method, evenly drop the above-mentioned nickel nitrate solution on the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve while constantly shaking to make it mix evenly without any remaining impregnation solution, and let it stand for 24 h;

[0113] Step 4: Take out the impregnated product obtained in Step 3 after drying, put it into a muffle furnace, and calcine it at 350 °C for 3 h to obtain an intermediate product, denoted as 0.5% NiO-HZSM-5 / MCM-41;

[0114] Step 5: Under the atmosphere of a hydrogen-nitrogen mixed gas (5% H 2 , volume fraction) with a flow rate of 30 mL / min, reduce 0.5% NiO-HZSM-5 / MCM-41 at a temperature of 550 °C to obtain a dehydrogenation cracking bifunctional catalyst, denoted as 0.5% Ni-HZSM-5 / MCM-41.

[0115] Example 3

[0116] This example provides a dehydrogenation cracking bifunctional catalyst, which is prepared by a preparation method including the following specific steps:

[0117] The preparation of HZSM-5 molecular sieve and the preparation of HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve are the same as those in Example 1;

[0118] Preparation of dehydrogenation cracking bifunctional catalyst:

[0119] Step 1: Take 1 g of the dried HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve and place it in an eggplant-shaped flask. Dropwise add deionized water into it while constantly shaking. Stop adding when the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve reaches the adsorption saturation critical state. Weigh the mass of the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve at this time. Calculate its water absorption rate according to the mass change of the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve before and after water absorption. Take the average of three measurements to obtain the average water absorption rate of the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve. In this example, each gram of the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve can absorb 1.57 g of water;

[0120] Step 2: Calculate the volume of the impregnation solution required for the equal-volume impregnation method according to the average water absorption rate data, and prepare an impregnation solution that meets the requirements according to the results, that is, nickel nitrate solution. The specific preparation process is as follows:

[0121] Take 0.0494 g of nickel nitrate hexahydrate and dissolve it in 1.5517 g of deionized water to prepare a nickel nitrate solution;

[0122] Step 3: Take 1 g of the dried HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve and place it in a flask. Adopt the equal-volume impregnation method to uniformly drop the above-mentioned nickel nitrate solution on the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve while constantly shaking to make it mix evenly without remaining impregnation solution, and let it stand for 24 h;

[0123] Step 4: Take out the impregnated product obtained in Step 3 after drying, put it into a muffle furnace, and calcine it at 350 °C for 3 h to obtain an intermediate product, denoted as 1% NiO-HZSM-5 / MCM-41;

[0124] Step 5: In a hydrogen-nitrogen mixed gas with a flow rate of 30 mL / min (5% H 2, in an atmosphere of hydrogen (volume fraction) at a temperature of 550 °C, 1% NiO-HZSM-5 / MCM-41 was reduced to obtain a dehydrogenation cracking bifunctional catalyst, denoted as 1% Ni-HZSM-5 / MCM-41.

[0125] Example 4

[0126] This example provides a dehydrogenation cracking bifunctional catalyst, which is prepared by a preparation method including the following specific steps:

[0127] The preparation of HZSM-5 zeolite and the preparation of HZSM-5 / MCM-41 micro-mesoporous composite zeolite are the same as in Example 1;

[0128] Preparation of dehydrogenation cracking bifunctional catalyst:

[0129] Step 1: Take 1 g of the dried HZSM-5 / MCM-41 micro-mesoporous composite zeolite and place it in an eggplant-shaped flask. Then, add deionized water drop by drop while constantly shaking. Stop adding when the HZSM-5 / MCM-41 micro-mesoporous composite zeolite reaches the critical state of adsorption saturation. Weigh the mass of the HZSM-5 / MCM-41 micro-mesoporous composite zeolite at this time, and calculate its water absorption rate according to the mass change of the HZSM-5 / MCM-41 micro-mesoporous composite zeolite before and after water absorption. Take the average value after measuring three times to obtain the average water absorption rate of the HZSM-5 / MCM-41 micro-mesoporous composite zeolite. In this example, each gram of the HZSM-5 / MCM-41 micro-mesoporous composite zeolite can absorb 1.57 g of water;

[0130] Step 2: Calculate the volume of the impregnation solution required for the equal-volume impregnation method according to the average water absorption rate data, and prepare an impregnation solution that meets the requirements according to the result, that is, nickel chloride solution. The specific preparation process is as follows:

[0131] Take 0.0111 g of nickel chloride and dissolve it in 1.5608 g of deionized water to prepare a nickel chloride solution;

[0132] Step 3: Take 1 g of the dried HZSM-5 / MCM-41 micro-mesoporous composite zeolite and place it in a flask. Using the equal-volume impregnation method, evenly drop the above-mentioned nickel chloride solution on the HZSM-5 / MCM-41 micro-mesoporous composite zeolite while constantly shaking to make it mix evenly without any remaining impregnation solution, and let it stand for 48 h;

[0133] Step 4: Take out the impregnated product obtained in Step 3 after drying, put it into a muffle furnace, and calcine it at 350 °C for 1 h to obtain an intermediate product, denoted as 0.5% NiO-HZSM-5 / MCM-41;

[0134] Step 5: Under the atmosphere of a hydrogen-nitrogen mixed gas (5% H 2 , volume fraction) with a flow rate of 30 mL / min, the 0.5% NiO-HZSM-5 / MCM-41 is reduced at a temperature of 650 °C to obtain a dehydrogenation cracking bifunctional catalyst, denoted as C4-0.5% Ni-HZSM-5 / MCM-41.

[0135] Example 5

[0136] This example provides a dehydrogenation cracking bifunctional catalyst, which is prepared by a preparation method including the following specific steps:

[0137] The preparation of HZSM-5 molecular sieve and the preparation of HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve are the same as those in Example 1;

[0138] Preparation of dehydrogenation cracking bifunctional catalyst:

[0139] Step 1: Take 1 g of the dried HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve and place it in an eggplant-shaped flask, then add deionized water dropwise thereto, and keep shaking during the process. When the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve reaches the adsorption saturation critical state, stop dropping. Weigh the mass of the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve at this time, and calculate its water absorption rate according to the mass change of the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve before and after water absorption. Take the average value after measuring three times to obtain the average water absorption rate of the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve. In this example, each gram of the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve can absorb 1.57 g of water;

[0140] Step 2: Calculate the volume of the impregnation solution required for the equal-volume impregnation method according to the average water absorption rate data, and prepare an impregnation solution that meets the requirements according to the result, that is, nickel sulfate solution. The specific preparation process is as follows:

[0141] Take 0.0446 g of nickel sulfate hexahydrate and dissolve it in 1.5517 g of deionized water to prepare a nickel sulfate solution;

[0142] Step 3: Take 1 g of the dried HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve and place it in a flask. Using the equal-volume impregnation method, uniformly drop the above-mentioned nickel sulfate solution on the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve, and keep shaking during the process to make it mix evenly without any remaining impregnation solution, and let it stand for 12 h;

[0143] Step 4: Take out the impregnated product obtained in Step 3 after drying, put it into a muffle furnace, and calcine it at 600 °C for 6 h to obtain an intermediate product, denoted as 1% NiO-HZSM-5 / MCM-41;

[0144] Step 5: Under the atmosphere of a hydrogen-nitrogen mixed gas (5% H 2 , volume fraction) with a flow rate of 30 mL / min, reduce 1% NiO-HZSM-5 / MCM-41 at a temperature of 450 °C to obtain a dehydrogenation cracking bifunctional catalyst, denoted as C5-1% Ni-HZSM-5 / MCM-41.

[0145] Comparative Example 1

[0146] This comparative example provides a dehydrogenation cracking bifunctional catalyst, which is prepared by a preparation method including the following specific steps:

[0147] The preparation of HZSM-5 molecular sieve and the preparation of HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve are the same as those in Example 1;

[0148] Preparation of dehydrogenation cracking bifunctional catalyst:

[0149] Step 1: Take 1 g of the dried HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve and place it in an eggplant-shaped flask, then add deionized water dropwise thereto, and keep shaking during the process. When the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve reaches the adsorption saturation critical state, stop dropping. Weigh the mass of the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve at this time, and calculate its water absorption rate according to the mass change of the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve before and after water absorption. Take the average value after measuring three times to obtain the average water absorption rate of the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve. In this example, each gram of the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve can absorb 1.57 g of water;

[0150] Step 2: Calculate the volume of the impregnation solution required for the equal-volume impregnation method according to the average water absorption rate data, and prepare an impregnation solution that meets the requirements according to the result, that is, nickel nitrate solution. The specific preparation process is as follows:

[0151] Take 0.1018 g of nickel nitrate hexahydrate and dissolve it in 1.5322 g of deionized water to prepare a nickel nitrate solution;

[0152] Step 3: Take 1 g of the dried HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve and place it in a flask. Using the equal-volume impregnation method, uniformly drip the above-mentioned nickel nitrate solution onto the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve. During this process, continuously shake to make it mix evenly without any remaining impregnation solution, and let it stand for 24 h;

[0153] Step 4: Take out the impregnated product obtained in Step 3 after drying, put it into a muffle furnace, and calcine it at 350 °C for 3 h to obtain an intermediate product, denoted as 2% NiO-HZSM-5 / MCM-41;

[0154] Step 5: Under the atmosphere of a hydrogen-nitrogen mixed gas (5% H 2 , volume fraction) with a flow rate of 30 mL / min, carry out a reduction treatment on 2% NiO-HZSM-5 / MCM-41 at a temperature of 550 °C to obtain a dehydrogenation and cracking bifunctional catalyst, denoted as 2% Ni-HZSM-5 / MCM-41.

[0155] Test Example 1

[0156] In this test example, wide-angle XRD analysis was carried out on HZSM-5, HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve, 0.1% Ni-HZSM-5 / MCM-41, 0.5% Ni-HZSM-5 / MCM-41, and 1% Ni-HZSM-5 / MCM-41 respectively. The obtained wide-angle XRD patterns are as Figure 1a shown; in this test example, small-angle XRD analysis was also carried out on MCM-41, HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve, 0.1% Ni-HZSM-5 / MCM-41, 0.5% Ni-HZSM-5 / MCM-41, and 1% Ni-HZSM-5 / MCM-41 produced by Tianjin Nanhua Catalyst Co., Ltd. The obtained small-angle XRD patterns are as Figure 1b shown.

[0157] From Figure 1a the wide-angle XRD patterns shown, it can be seen that no impurity phases appear in all the samples and the crystallinity is good; all the samples show characteristic diffraction peaks (PDF#44-0003) belonging to the typical MFI structure at 7.94°, 8.80°, 23.10°, 23.42°, and 23.98°.

[0158] From Figure 1bAs can be seen from the small-angle XRD patterns shown, both the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve and the Ni-HZSM-5 / MCM-41 catalysts with different Ni loadings have the diffraction peak of the (100) crystal plane corresponding to the hexagonal mesoporous structure of MCM-41, indicating that the samples have a regular and long-range ordered six-fold symmetric structure. The above results show that in the embodiments of the present invention, mesopores were successfully introduced into the HZSM-5 molecular sieve, and the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve was prepared.

[0159] At the same time, from Figure 1a it can also be seen that compared with the pure HZSM-5 molecular sieve, after the introduction of the mesoporous structure, the characteristic diffraction peaks of MFI became weaker, indicating that the framework structure of the HZSM-5 molecular sieve was partially damaged by the NaOH solution. The catalyst samples after introducing metal Ni still had the typical crystal structure characteristics of ZSM-5, and no decrease in crystallinity was found, indicating that the Ni metal modification process did not damage the crystal structure of the molecular sieve. During the process of increasing the Ni content from 0.1% to 1%, no NiO diffraction peaks were found, indicating that the metal Ni was highly dispersed on the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve.

[0160] Test Example 2

[0161] In this test example, SEM analysis was carried out on HZSM-5, HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve, 0.1% Ni-HZSM-5 / MCM-41, 0.5% Ni-HZSM-5 / MCM-41 and 1% Ni-HZSM-5 / MCM-41 respectively, and the obtained SEM images are shown in Figure 2a - Figure 2e respectively. As can be seen from Figure 2a - Figure 2b the surface of the HZSM-5 molecular sieve particles is smooth, the morphology of the molecular sieve is in a "spherical" structure, the particle size distribution is uniform, and the average particle size is 140 nm. After the HZSM-5 molecular sieve was treated with alkali, some particles disintegrated, the size became smaller, it was damaged by the sodium hydroxide alkali solution, and the surface became rough, with slits and collapses; the alkali treatment started from the outer surface of the molecular sieve and proceeded from the outside to the inside. The nano-scale silicon-aluminum fragments removed entered the solution and assembled the mesophase through the CTAB template agent. After the surface of the crystal grains became rough, the defects and hydroxyl groups were relatively rich, which was conducive to the enrichment of the CTAB surfactant, and the MCM-41 structure grew along its periphery, evenly dispersing some dissolved zeolite crystal grains in the mesophase and assembling them. As can be seen from Figure 2a - Figure 2e after loading the Ni metal, its morphology basically did not change.

[0162] Test Example 3

[0163] This test example respectively conducts HRTEM analysis on HZSM-5, MCM-41 produced by Tianjin Nanhua Catalyst Co., Ltd., HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve, and 0.5% Ni-HZSM-5 / MCM-41, and the obtained results are as Figure 3a - Figure 3f shown below.

[0164] Among them, Figure 3a is the HRTEM image of HZSM-5. From it, the ordered lattice fringes of HZSM-5 can be clearly seen; Figure 3b is the HRTEM image of MCM-41. From it, regular and ordered mesoporous channels can be clearly observed, and the inner diameter of the channels is about 3.6 nm; Figure 3c is the HRTEM image of HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve. From it, it can be seen that the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve has a similar structure to MCM-41, that is, a large number of parallel and equidistant long stripe-like structures. These regular strip-like structures are oriented hexagonal mesoporous channels. In addition, the darker parts are some disintegrated ZSM-5 crystal grains contained in the sample. The mesoporous phase connects these small-sized zeolite fragments, that is, these zeolite nanocrystals are evenly dispersed as pore wall structural units. The channels are bent at some parallel positions, which is caused by the size effect of the zeolite fragments as pore wall units assembling the mesoporous phase. Based on the above analysis, it shows that during the preparation of the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve, the alkali treatment changed the structure of the HZSM-5 molecular sieve, and the MCM-41 mesoporous structure was successfully introduced around the HZSM-5 crystal grains, which is consistent with Figure 1a and Figure 1b the XRD characterization results shown.

[0165] Figure 3d and Figure 3e are the HRTEM images of 0.5% Ni-HZSM-5 / MCM-41. From it, it can be seen that its pore structure is similar to that of the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve, indicating that the introduction of Ni has basically no effect on the pore size of the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve, and Ni metal can be observed from Figure 3e with a larger magnification, and the Ni metal is highly dispersed on the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve, which is consistent with the XRD characterization results.

[0166] Figure 3f is the Mapping image of 0.5% Ni-HZSM-5 / MCM-41. From it, it can be seen that the Ni metal has good dispersion on the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve.

[0167] Evaluation Example 1

[0168] In this evaluation example, a fixed-bed micro-reactor was used to evaluate the performance of HZSM-5, HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve, 0.1% Ni-HZSM-5 / MCM-41, 0.5% Ni-HZSM-5 / MCM-41, and 1% Ni-HZSM-5 / MCM-41 in fixed-bed catalytic cracking (n-butane catalytic cracking), specifically including:

[0169] The catalyst dosage was 200 mg, and the quartz sand dosage was 2 g. Before the start of the reaction, it was heated from room temperature to 550 °C in an N 2 atmosphere at a flow rate of 30 mL / min to blow out all impurities. Each of the above catalysts was purged for 30 min in an air atmosphere at 30 mL / min, and then purged for 5 min in an N 2 atmosphere. Then, it was pre-reduced for 30 min in a hydrogen-nitrogen mixed gas (5 v% H 2 ) atmosphere at 30 mL / min, and finally purged for 5 min with N 2 atmosphere at 36 mL / min.

[0170] The n-butane feed flow rate was 4 mL / min, and the nitrogen feed flow rate was 36 mL / min, and they were mixed and fed into the reactor. The reactor was heated to 550 °C at a heating rate of 10 °C / min, and the system pressure was 101 kPa. The product analysis was carried out using a gas chromatograph analyzer, and on-line analysis was carried out using an Al 2 O 3 type capillary column. The injector temperature was 180 °C, the detector was a flame ionization detector (FID), the detector temperature was 120 °C, and the area normalization method was used for quantification.

[0171] The n-butane cracking performance diagram obtained in this evaluation example is as Figure 4a - Figure 4f shown. It can be seen from this that in the embodiment of the present invention, after introducing a mesoporous structure into the HZSM-5 molecular sieve, the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve is obtained. Compared with the HZSM-5 molecular sieve, the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve can significantly improve the conversion rate of n-butane, the selectivity of light olefins, and the anti-coking performance. Compared with the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve, the Ni-HZSM-5 / MCM-41 catalysts with different nickel contents can significantly improve the conversion rate of n-butane and the selectivity of light olefins. The dehydrogenation performance of the Ni active component and the pore structure and acidity regulation of the molecular sieve form a synergistic effect, promoting the efficient conversion of n-butane and improving the selectivity of light olefins.

[0172] From Figure 4a - Figure 4fIt can also be seen that with the increase of the metal Ni loading amount, the conversion rate of n-butane and the selectivity of light olefins of the Ni-HZSM-5 / MCM-41 catalyst both increase first and then decrease.

[0173] As described above, only the specific embodiments of the present invention are given, and the scope of the invention cannot be limited by them. Therefore, the replacement of equivalent components or the equivalent changes and modifications made according to the protection scope of the present invention of the patent should still fall within the scope covered by this patent. In addition, the technical features among the technical features, between the technical features and the technical invention, and between the technical inventions in the present invention can be freely combined and used.

Claims

1. A dehydrogenation cracking bifunctional catalyst, It is characterized in that The dehydrogenation cracking bifunctional catalyst comprises HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve and transition metal nanoparticles, wherein the transition metal nanoparticles are loaded on the surface or inside of the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve.

2. The dehydrogenation cracking bifunctional catalyst according to claim 1, It is characterized in that Based on the total weight of the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve being 100%, the content of the transition metal nanoparticles is 0.1%-1%.

3. The dehydrogenation cracking bifunctional catalyst according to claim 1 or 2, It is characterized in that The transition metal includes one or a combination of nickel, gold and iron.

4. A method for preparing the dehydrogenation cracking bifunctional catalyst according to any one of claims 1 to 3, It is characterized in that The preparation method comprises: Step (1): treating the HZSM-5 microporous molecular sieve with an alkali solution to obtain an alkali-treated solution, adding a template to the alkali-treated solution and mixing the mixture to obtain a mixed solution; Step (2): performing a first hydrothermal crystallization on the mixed solution, adjusting the pH value of the obtained suspension, and then performing a second hydrothermal crystallization on the obtained suspension; Step (3): calcining the second hydrothermal crystallization product to obtain a sodium molecular sieve; Step (4): performing ion exchange between the sodium molecular sieve and an aqueous solution of an ammonium salt to obtain a hydrogen molecular sieve; Step (5): calcining the hydrogen-type molecular sieve to obtain a HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve; Step (6): uniformly dropping an aqueous solution of a transition metal salt onto the HZSM-5 / MCM-41 micro-mesoporous composite molecular sieve by an equal volume impregnation method and mixing the mixture evenly, and then drying and calcining the mixture to obtain NiO-HZSM-5 / MCM-41; Step (7): reducing NiO-HZSM-5 / MCM-41 in a hydrogen-nitrogen mixed gas atmosphere to obtain a dehydrogenation cracking bifunctional catalyst.

5. The preparation method according to claim 4, It is characterized in that In step (1), the temperature of the alkali treatment is 30-60° C. and the time is 0.5-3 h.

6. The preparation method according to claim 4, It is characterized in that In step (2), the temperatures of the first hydrothermal crystallization and the second hydrothermal crystallization are 80-150° C. and the times are 24-96 h, respectively.

7. The preparation method according to claim 4 or 6, It is characterized in that In step (2), the pH value of the obtained suspension is adjusted to 7-9 and then subjected to a second hydrothermal crystallization.

8. The preparation method according to claim 4, It is characterized in that In step (3), the calcination is performed at 450-700° C. for 2-8 hours.

9. The preparation method according to claim 4, It is characterized in that In step (4), the ion exchange is carried out at a temperature of 50-90° C. for 1-3 times, each time for 1-3 hours.

10. The preparation method according to claim 4, It is characterized in that In step (5), the calcination is performed at 450-700° C. for 1-4 hours.

11. The preparation method according to claim 4, It is characterized in that In step (6), the transition metal salt includes one or a combination of nitrates, sulfates and chlorides of transition metals.

12. The preparation method according to claim 4 or 11, It is characterized in that In step (6), the calcination is performed at 350-600° C. for 1-6 hours.

13. The preparation method according to claim 4, It is characterized in that In step (7), the reduction temperature is 450-650° C., the flow rate of the hydrogen-nitrogen mixed gas is 10-50 mL / min, and the content of hydrogen is 1-50% based on the total volume of the hydrogen-nitrogen mixed gas as 100%.

14. Use of the dehydrogenation cracking bifunctional catalyst according to any one of claims 1 to 3 in catalytic cracking of n-butane to produce small molecule olefins.

15. The use according to claim 14, It is characterized in that The temperature of the catalytic cracking is 450-650°C and the pressure is 0.1-2.5MPa.

Images