Rare earth nanosheet heteroatomic catalytic material, method for preparing same and application thereof in propane aromatization
By introducing rare earth nanosheet heteroatom catalytic materials into ZSM-5 molecular sieves, the problems of high byproduct selectivity and low aromatic yield in the propane aromatization process of existing catalysts were solved, and high selectivity and high efficiency of aromatic generation were achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-18
- Publication Date
- 2026-04-07
AI Technical Summary
Existing catalysts exhibit high byproduct selectivity and low aromatic yield during propane aromatization, and there is insufficient improvement in catalyst structure and metal active components.
Rare earth nanosheet heteroatom catalytic materials were used to synthesize nanosheet s-HZSM-5 molecular sieves via in-situ hydrothermal crystallization. Gallium species were uniformly distributed in its framework. Combined with the impregnation method of rare earth metal species, special active sites were formed and the reaction conditions were optimized.
It significantly improves the selectivity and catalytic performance of aromatics, inhibits carbon deposition, enhances the catalyst's ability to activate low-carbon alkanes, and reduces the formation of byproducts.
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Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the field of catalytic materials, in particular to rare earth nanosheet heteroatom catalytic materials, a preparation method thereof and propane aromatization applications. BACKGROUND
[0002] Benzene, toluene, xylene (BTX) is an important bulk chemical, and the reaction technology for synthesizing BTX from low-carbon alkanes is a research focus in both academic and industrial fields. Propane is one of the main components of liquefied petroleum gas, and propane aromatization is one of the research focuses. In the propane aromatization process, a solid acid with a large specific surface area such as a molecular sieve is used as a catalyst, and under certain space velocity, temperature and pressure conditions, propane can be converted to aromatic hydrocarbons through dehydrogenation, polymerization, cyclization and other reaction processes. This process expands the chemical utilization mode of propane and enriches the production route of aromatic hydrocarbons represented by BTX, and has a broad application prospect.
[0003] Most of the current research on aromatization catalysts is focused on ZSM-5 molecular sieves, which have a three-dimensional cross-channel structure with a ten-membered ring, a large specific surface area, good shape-selective catalytic performance and unique surface acidity, making them exhibit very good catalytic performance in the aromatization reaction process. Since the propane aromatization reaction mainly includes propane dehydrogenation to olefins, aromatization of olefins, etc., in addition, the hydrogen species produced after dehydrogenation is prone to hydrogen transfer reactions, therefore, the catalyst needs to have appropriate dehydrogenation active sites and aromatization active sites, and also needs to avoid the occurrence of many side reactions such as hydrogen transfer. The addition of gallium, zinc and other metal components can effectively improve the aromatic hydrocarbon yield, however, the common problem is that the selectivity of by-products such as methane and ethane is high, and the aromatic hydrocarbon yield is low. Therefore, the structure improvement of the catalyst and the way of adding metal active components are particularly important. Based on ZSM-5 molecular sieves, the present application innovates the synthesis method of molecular sieves and the way of adding metal active components, and develops a rare earth nanosheet heteroatom catalytic material, and at the same time creates appropriate reaction conditions, which significantly improves the yield of propane to aromatic hydrocarbons. SUMMARY
[0004] The present application provides a rare earth nanosheet heteroatom catalytic material, a preparation method thereof and propane aromatization applications, and limits the b-axis of the nanosheet-shaped s-HZSM-5 zeolite molecular sieve to 80-120 nm, inhibits carbon deposition and improves the performance of the catalytic material; the rare earth metal species is highly dispersed in the s-HZSM-5 crystal by impregnation, the rare earth element interacts with the Ga atoms and Al atoms of the framework to form special active sites in the micropore limited space of the molecular sieve, and the aromatic hydrocarbon selectivity is improved.
[0005] In order to achieve the above-mentioned purpose, the present application adopts the following technical scheme:
[0006] The rare earth nanosheet heteroatomic catalytic material has a carrier of hydrogen-type nanosheet ZSM-5 zeolite (denoted as s-HZSM-5), a b-axis length of 80-120 nm, and a Si / Al atomic mass ratio of 15-80; isolated gallium species are uniformly distributed in the s-HZSM-5 zeolite framework, and the Si / Ga atomic mass ratio is 15-100; and rare earth metal species are uniformly dispersed on the surface and in the pores of the s-HZSM-5, and the rare earth loading is 0.1-2 wt%.
[0007] Preferably, the Si / Al atomic mass ratio in the s-HZSM-5 zeolite is 20-80, the Si / Ga atomic mass ratio is 20-90, and the rare earth loading is 0.1-0.8 wt%.
[0008] Preferably, the rare earth metal is at least one of lanthanum, cerium, praseodymium, and neodymium, and further preferably lanthanum or cerium.
[0009] The method for preparing the rare earth nanosheet heteroatomic catalytic material comprises the following steps:
[0010] (1) In-situ hydrothermal crystallization method for synthesizing zeolite
[0011] The gallium compound is mixed with the raw material for preparing the s-HZSM-5, and a hydrothermal crystallization reaction is performed at 140-200℃ for 24-96 h, and the reaction product is calcined to obtain the Ga@s-HZSM-5 zeolite.
[0012] (2) Impregnation method for loading rare earth species
[0013] The Ga@s-HZSM-5 zeolite obtained in step (1) is placed in a rare earth solution for impregnation, and the impregnated product is calcined to obtain the rare earth nanosheet heteroatomic catalytic material.
[0014] Preferably, the raw material for preparing the s-HZSM-5 is a silicon source, an aluminum source, a template agent, deionized water, and urea. The silicon source is at least one of tetraethyl orthosilicate, silica sol, and white carbon black, the template agent is at least one of tetrapropylammonium hydroxide and tetrapropylammonium bromide, the aluminum source is at least one of sodium aluminate, aluminum isopropoxide, and pseudo-boehmite, the molar amount of the template agent is 0.05-1 times the molar amount of the silicon source, the molar amount of the urea is 0.3-1.2 times the molar amount of the silicon source, and the molar amount of the deionized water is 10-100 times the molar amount of the silicon source.
[0015] Preferably, the calcination temperature in step (1) is 450-650℃, and the calcination time is 3-8 h.
[0016] The reaction product in step (1) is subjected to suction filtration, washing, drying, and calcination to obtain the Ga@s-HZSM-5 zeolite. The drying temperature is 80-120℃, and the drying time is 8-15 h.
[0017] Preferably, step (2) is ultrasonic impregnation, and the ultrasonic treatment time is 0.5-3h.
[0018] Preferably, step (2) is calcination, and the calcination temperature is 450-650℃, and the calcination time is 3-8h.
[0019] The impregnated product of step (2) is subjected to evaporation and calcination in sequence to obtain the rare earth nanosheet heteroatomic catalytic material.
[0020] The application further provides application of the rare earth nanosheet heteroatomic catalytic material in a propane aromatization reaction.
[0021] Preferably, the raw gas is a propane / nitrogen mixture, the volume content of propane in the mixture is 20-60%, the reaction temperature is 450-650℃, the reaction mass space velocity is 0.6-3h -1 .
[0022] Preferably, the reaction is carried out in a fixed bed reactor, and the reactor is first pretreated with nitrogen at 450-650℃ for 1-4h, and then the raw gas is introduced; the reaction pressure is 0.1-0.5MPa.
[0023] Therefore, the application has the following beneficial effects:
[0024] (1) The catalytic material has the advantages of good aromatization activity, easy activation of low-carbon alkanes, high aromatic hydrocarbon selectivity, excellent anti-carbon deposition performance, etc. Through in-situ synthesis technology, Ga species partially replaces the framework Al during the hydrothermal synthesis of s-HZSM-5 zeolite, and Ga is implanted into the s-HZSM-5 framework structure, and the framework Ga sites are highly dispersed. Compared with framework Al, the framework Ga species has different acid properties, thereby optimizing the acid sites of the zeolite molecular sieve and improving the yield of aromatic hydrocarbon products.
[0025] (2) The b-axis of the nanosheet-shaped s-HZSM-5 zeolite molecular sieve is limited to a short b-axis in the range of 80-120nm, which corresponds to a shortened straight channel and reduces the accumulation of substrate molecules in the channel, which is beneficial to the diffusion of reactants and intermediates in the channel, thereby inhibiting carbon deposition and improving the performance of the catalytic material.
[0026] (3) The rare earth metal species is highly dispersed in the s-HZSM-5 crystal through impregnation, and the rare earth element interacts with the framework Ga atoms and Al atoms to form special active sites in the micropore limited space of the molecular sieve. The moderate local electric field strength can stabilize the olefin intermediates, which is conducive to the aromatization, and after the hydrogen atoms are dissociated from the alkane molecules on the Ga surface, the hydrogen atoms are more likely to recombine to generate hydrogen gas desorption, which reduces the generation of byproduct dry gas and further improves the aromatic hydrocarbon selectivity. BRIEF DESCRIPTION OF DRAWINGS
[0027] Figure 1 X-ray powder diffraction patterns of the 0.3La / Ga@s-HZSM-5-30-30 catalytic material of Example 1 and the 0.3Ce / Ga@s-HZSM-5-30-30 catalytic material of Example 5.
[0028] Figure 2 is an axial schematic diagram of a molecular sieve crystal.
[0029] Figure 3 are scanning electron microscope photos of catalytic materials; in the figures, A corresponds to the 0.3La / Ga@s-HZSM-5-30-30 catalytic material of Example 1, and B corresponds to the 0.3LaGa / s-HZSM-5-30-30 catalytic material of Comparative Example 1. DETAILED DESCRIPTION
[0030] The technical solutions of the present application are further described below through specific examples.
[0031] In the present application, unless specified otherwise, the raw materials and equipment used can be purchased from the market or are commonly used in the art. The methods in the examples, unless specified otherwise, are all conventional methods in the art. Unless otherwise specified, the parts are all parts by weight, the temperatures are all in °C or at ambient temperature, and the pressure is atmospheric pressure or close to atmospheric pressure. There are multiple variations and combinations of reaction conditions (such as component concentrations, required solvents, solvent mixtures, temperatures, pressures, and other reaction ranges) and conditions that can be used to optimize the purity and yield of the products obtained by the method, which will only require reasonable conventional experiments to optimize such method conditions.
[0032] EXAMPLE
[0033] I. Rare earth nanosheet heteroatomic catalytic material
[0034] The rare earth-based nanosheet heteroatomic catalytic material has a support of hydrogen-type nanosheet ZSM-5 molecular sieve (s-HZSM-5), a b-axis length of 80-120 nm, and a Si / Al atomic ratio of 15-80 (further preferably 20-80).
[0035] The isolated gallium species are uniformly distributed in the s-HZSM-5 molecular sieve framework, and the Si / Ga atomic mass ratio is 15-100 (further preferably 20-90).
[0036] The rare earth metal species are uniformly dispersed on the surface and in the pores of the s-HZSM-5, and the rare earth loading is 0.1-2 wt% (further preferably 0.1-0.8 wt%). The rare earth metal is at least one of lanthanum, cerium, praseodymium, and neodymium, and is further preferably lanthanum or cerium.
[0037] II. Preparation method of rare earth nanosheet heteroatom catalytic material
[0038] The method comprises the following steps:
[0039] (1) Synthesis of molecular sieve by in-situ hydrothermal crystallization method
[0040] The template agent is mixed with deionized water to obtain a template agent solution by stirring at room temperature; the gallium salt hydrate is mixed with deionized water to obtain a gallium salt aqueous solution by stirring at room temperature; the gallium salt aqueous solution is added to the template agent solution, stirred for a period of time, the silicon source is added, stirred for a period of time, the aluminum salt is added, stirred for a period of time, the urea is added, stirred for a period of time, and then transferred to a hydrothermal reaction kettle, and hydrothermal crystallization reaction is carried out at 140-200 ℃ for 24-96 h; after the reaction is completed, the reaction product is sequentially subjected to centrifugation, washing, drying at 80-120 ℃ for 8-15 h, and calcination at 450-650 ℃ for 3-8 h to obtain a Ga@s-HZSM-5 molecular sieve, which is denoted as Ga@s-HZSM-5-y-z, wherein y is the atomic mass ratio of Si / Al, and z is the atomic ratio of Si / Ga.
[0041] The silicon source is at least one of tetraethyl orthosilicate, silica sol, and white carbon black, the template agent is at least one of tetrapropylammonium hydroxide and tetrapropylammonium bromide, the aluminum source is at least one of sodium aluminate, aluminum isopropoxide, and pseudo-boehmite, the molar amount of the template agent is 0.05-1 times the molar amount of the silicon source, the molar amount of the urea is 0.3-1.2 times the molar amount of the silicon source, and the molar amount of the deionized water is 10-100 times the molar amount of the silicon source.
[0042] (2) Equal-volume impregnation method for loading rare earth species
[0043] The Ga@s-HZSM-5 molecular sieve obtained in step (1) and the rare earth aqueous solution are mixed in a centrifuge tube, and ultrasonic oscillation is performed for 0.5-3 h; after the oscillation is completed, the mixture is transferred to an evaporation dish, ground at 80-140 ℃ until completely evaporated, and calcined at 450-650 ℃ for 3-8 h to obtain a rare earth-based nanosheet catalytic material, which is denoted as xR / Ga@s-HZSM-5-y-z, wherein x is the mass percentage of the loaded rare earth, and R is the rare earth.
[0044] III. Application of rare earth nanosheet heteroatom catalytic material in propane aromatization reaction
[0045] The propane aromatization reaction is carried out in a fixed bed reactor. Nitrogen gas is first introduced to pretreat at 450-650 ℃ for 1-4 h, and then a raw gas mixture of propane / nitrogen is introduced, the volume content of propane in the mixture being 20-60%, and the reaction is carried out at a temperature of 450-650 ℃ and a pressure of 0.1-0.5 MPa, and the reaction mass space velocity is 0.6-3 h -1 .
[0046] Example 1
[0047] The preparation method of the rare earth nanosheet heteroatomic catalytic material comprises the following steps:
[0048] (1) Synthesizing a molecular sieve by an in-situ hydrothermal crystallization method
[0049] 12 g of tetrapropylammonium hydroxide (25 wt.%) is mixed with 10.3 g of deionized water, stirred at room temperature for 1 h to obtain a tetrapropylammonium hydroxide solution; 138 mg of gallium nitrate hydrate is mixed with 5 g of deionized water, stirred at room temperature for 1 h to obtain a gallium nitrate aqueous solution; the gallium nitrate aqueous solution is added to the tetrapropylammonium hydroxide solution, stirred for 4 h, 8.4 g of tetraethyl silicate is added, stirred for 8 h, 285 mg of aluminum isopropoxide is added, stirred for 4 h, 1.695 g of urea is added, stirred for 2 h, and then transferred to a hydrothermal reaction kettle for hydrothermal reaction at 180℃ for 72 h; finally, the reaction product of the hydrothermal reaction is sequentially subjected to centrifugation, washing, drying at 100℃ for 12 h, and calcination at 550℃ for 4 h to obtain a Ga@s-HZSM-5 molecular sieve. The Si / Al atomic mass ratio of the prepared Ga@s-HZSM-5 molecular sieve is 30, and the Si / Ga atomic mass ratio is 30.
[0050] (2) Loading a rare earth species by an equal-volume impregnation method
[0051] The Ga@s-HZSM-5 molecular sieve obtained in step (1) is subjected to equal-volume impregnation with a lanthanum nitrate aqueous solution. 1 g of the Ga@s-HZSM-5 molecular sieve is mixed with 2 mL of the lanthanum nitrate aqueous solution in a centrifuge tube, ultrasonic oscillation is performed for 1 h, the mass ratio of lanthanum to s-HZSM-5 in the mixed solution is 0.003:1, and then transferred to an evaporating dish for grinding until completely evaporated at 120℃, and calcination at 550℃ for 4 h to obtain a rare earth-based nanosheet catalytic material, which is denoted as 0.3La / Ga@s-HZSM-5-30-30.
[0052] The application of the rare earth nanosheet heteroatomic catalytic material in a propane aromatization reaction comprises the following steps:
[0053] The reaction is carried out in a tubular fixed-bed reactor with an inner diameter of 8 mm. 0.8 g of quartz sand (20-40 mesh) is uniformly mixed with 0.4 g of the rare earth-based nanosheet catalytic material 0.3La / Ga@s-HZSM-5-30-30 (20-40 mesh) obtained in step (2), and placed in the constant temperature zone of the reactor. First, the temperature is programmed to rise to 550℃ under N2 (20 mL·min -1 ) atmosphere, and then pretreated at 550℃ under N2 (20 mL·min -1 ) atmosphere for 1 h. After the pretreatment is completed, 15 mL·min -1 40 vol% C3H8 / N2 is introduced for reaction at a temperature of 550℃ and a reaction mass space velocity of 1.5 h-1 The aromatization reaction lasted for 10 h.
[0054] Example 2
[0055] The difference from Example 1 is that the mass ratio of lanthanum to s-HZSM-5 in the mixed solution of step (2) is 0.001:1, and the obtained rare earth-based nanosheet-shaped catalytic material is recorded as 0.1La / Ga@s-HZSM-5-30-30.
[0056] Example 3
[0057] The difference from Example 1 is that the mass ratio of lanthanum to s-HZSM-5 in the mixed solution of step (2) is 0.005:1, and the obtained rare earth-based nanosheet-shaped catalytic material is recorded as 0.5La / Ga@s-HZSM-5-30-30.
[0058] Example 4
[0059] The difference from Example 1 is that the mass ratio of lanthanum to s-HZSM-5 in the mixed solution of step (2) is 0.01:1, and the obtained rare earth-based nanosheet-shaped catalytic material is recorded as 1.0La / Ga@s-HZSM-5-30-30.
[0060] Example 5
[0061] The difference from Example 1 is that the rare earth species in step (2) is cerium, and the obtained rare earth-based nanosheet-shaped catalytic material is recorded as 0.3Ce / Ga@s-HZSM-5-30-30.
[0062] Example 6
[0063] The difference from Example 1 is that the rare earth species in step (2) is praseodymium, and the obtained rare earth-based nanosheet-shaped catalytic material is recorded as 0.3Pr / Ga@s-HZSM-5-30-30.
[0064] Example 7
[0065] The difference from Example 1 is that the rare earth species in step (2) is neodymium, and the obtained rare earth-based nanosheet-shaped catalytic material is recorded as 0.3Nd / Ga@s-HZSM-5-30-30.
[0066] Example 8
[0067] The difference from Example 1 is that the amount of aluminum isopropoxide in step (1) is 570 mg, the Si / Al atomic mass ratio is 15, and the obtained rare earth-based nanosheet-shaped catalytic material is recorded as 0.3La / Ga@s-HZSM-5-15-30.
[0068] Example 9
[0069] The difference from example 1 is that the amount of aluminum isopropoxide in step (1) is 106.9 mg, the atomic mass ratio of Si / Al is 80, and the obtained rare earth-based nanosheet-shaped catalytic material is recorded as 0.3La / Ga@s-HZSM-5-80-30.
[0070] Example 10
[0071] The difference from example 1 is that the amount of gallium nitrate hydrate in step (1) is 276 mg, the atomic mass ratio of Si / Ga is 15, and the obtained rare earth-based nanosheet-shaped catalytic material is recorded as 0.3La / Ga@s-HZSM-5-30-15.
[0072] Example 11
[0073] The difference from example 1 is that the amount of gallium nitrate hydrate in step (1) is 69 mg, the atomic mass ratio of Si / Ga is 60, and the obtained rare earth-based nanosheet-shaped catalytic material is recorded as 0.3La / Ga@s-HZSM-5-30-60.
[0074] Example 12
[0075] The difference from example 1 is that the amount of gallium nitrate hydrate in step (1) is 46 mg, the atomic mass ratio of Si / Ga is 90, and the obtained rare earth-based nanosheet-shaped catalytic material is recorded as 0.3La / Ga@s-HZSM-5-30-90.
[0076] Example 13
[0077] The difference from example 1 is that in the application step, the reaction mass space velocity is 0.75 h -1 .
[0078] Example 14
[0079] The difference from example 1 is that in the application step, the reaction temperature is 600℃.
[0080] Example 15
[0081] The difference from example 1 is that in the application step, the reaction temperature is 650℃.
[0082] Example 16
[0083] The difference from example 1 is that in the application step, the raw material gas is a propane / nitrogen mixture, and the volume content of propane is 20%, recorded as 20vol% C3H8 / N2.
[0084] Example 17
[0085] The difference from example 1 is that in the application step, the reaction mass space velocity is 3 h -1 .
[0086] Example 18
[0087] The difference from Example 1 is that in the application step, the reaction mass space velocity is 0.6 h -1 .
[0088] Example 19
[0089] The difference from Example 1 is that in the application step, the reaction temperature is 450℃.
[0090] Example 20
[0091] The difference from Example 1 is that in the application step, the raw gas is a propane / nitrogen mixture, and the volume content of propane is 60%, denoted as 60vol% C3H8 / N2.
[0092] Comparative Example 1
[0093] The difference from Example 1 is that Ga and La are loaded on ordinary block-shaped ZSM-5 molecular sieves (n-HZSM-5) using an impregnation method.
[0094] Comparative Example 2
[0095] The difference from Example 1 is that Ga and La are loaded on s-HZSM-5 molecular sieves using an impregnation method.
[0096] Comparative Example 3
[0097] The difference from Example 1 is that a nanosheet-shaped heteroatomic catalytic material is used, and no rare earth metal is loaded.
[0098] Comparative Example 4
[0099] The difference from Example 1 is that in the application step, the reaction mass space velocity is 4 h -1 .
[0100] Comparative Example 5
[0101] The difference from Example 1 is that in the application step, the reaction temperature is 700℃.
[0102] Comparative Example 6
[0103] The difference from Example 1 is that in the application step, the reaction temperature is 400℃.
[0104] Comparative Example 7
[0105] The difference from Example 1 is that in the application step, the raw gas is a propane / nitrogen mixture, and the volume content of propane is 80%, denoted as 80vol% C3H8 / N2.
[0106] Result Analysis
[0107] I. Morphology analysis
[0108] Figure 1 X-ray powder diffraction patterns (XRD) of the 0.3La / Ga@s-HZSM-5-30-30 catalytic material of Example 1 and the 0.3Ce / Ga@s-HZSM-5-30-30 catalytic material of Example 5. It can be seen that the catalytic materials both have characteristic diffraction peaks of ZSM-5 molecular sieve, indicating that the ZSM-5 molecular sieve is successfully prepared, and no characteristic diffraction peaks of metal particles are present, indicating that the metal species is highly dispersed.
[0109] The three-dimensional molecular sieve has a, b, and c axes, and is similar to a cuboid in length, width, and height, as shown in FIG. 1A. Figure 2 The conventional molecular sieve is blocky, and the length, width, and height are basically the same. The morphology of the molecular sieve in the present application is a long strip nanosheet, and the b axis, that is, the thickness of the molecular sieve, is much shorter than the length and width, thus presenting a sheet morphology, as shown in FIG. 1B. Figure 3 A is a scanning electron microscope (SEM) image of the 0.3La / Ga@s-HZSM-5-30-30 catalytic material of Example 1. It can be seen from the figure that the 0.3La / Ga@s-HZSM-5-30-30 catalytic material has a regular nanosheet structure, and the c axis / a axis ratio is > 5, and the c axis / b axis ratio is > 15. Figure 3 B is an SEM image of the 0.3La2Ga / n-HZSM-5-30 catalytic material of Comparative Example 1. It can be seen that the 0.3La2Ga / n-HZSM-5-30-30 catalytic material has a conventional block structure, and the c axis / a axis ratio is ≈ 1, and the c axis / b axis ratio is < 2.
[0110] II. Catalytic performance analysis
[0111] The catalytic performance results of each example and comparative example are shown in the following table.
[0112]
[0113] From the above table, compared with Example 1:
[0114] (1) The ordinary bulk n-HZSM-5-based catalytic material in Comparative Example 1 has a lower aromatic yield than the nanosheet s-HZSM-5-based catalytic material, indicating that the larger b-axis length of the bulk molecular sieve increases the diffusion distance of the substrate molecules, which is not conducive to the contact with the active sites inside the molecular sieve, resulting in a decrease in the conversion rate and a decrease in the aromatic selectivity. The performance of the ordinary impregnated Ga component in Comparative Example 2 is not as good as that of the framework Ga molecular sieve in Example 1, indicating that the Ga species in the impregnated Ga sample is easy to block in the molecular sieve channels or agglomerate on the surface of the molecular sieve, which is not conducive to the conversion of propane, further indicating that the special coordination environment of the framework Ga species in the present application is conducive to the dehydrogenation of propane and further aromatization, thus significantly improving the performance of the catalytic material. The propane conversion rate and the aromatic selectivity are both significantly reduced in Comparative Example 3 without the introduction of rare earth elements, indicating that the rare earth elements can provide a unique local electric field to stabilize the olefin intermediate, which is conducive to the aromatization of the olefin intermediate, thereby improving the yield of the aromatic product.
[0115] (2) In Comparative Example 4, the space velocity is further increased, resulting in a decrease in the propane conversion rate and the aromatic selectivity, and an increase in the propylene selectivity, because the propane aromatization reaction undergoes propane dehydrogenation and propylene aromatization processes, and the propylene generated by increasing the space velocity is desorbed before being further converted, indicating that a higher space velocity is not conducive to the aromatization of propylene, and a proper space velocity range is required. The reaction temperature is too low or too high in Comparative Examples 5 and 6, which is not conducive to the yield of aromatic hydrocarbons. The first step of propane dehydrogenation to propylene is an endothermic reaction, and a lower temperature is not conducive to the first step of the reaction, thereby affecting the conversion rate of the overall catalyst, and a higher temperature exacerbates the occurrence of side reactions such as C 4-6 The selectivity of hydrocarbons is significantly improved, which is not conducive to the selectivity of aromatic hydrocarbons, indicating that the catalyst can only exhibit good catalytic effect at a suitable reaction temperature. In Comparative Example 7, the conversion rate is reduced by increasing the content of propane in the raw material gas, because the concentration of the propane substrate is too high, and the excessive propane cannot be converted in time per unit of catalyst, therefore, the conversion rate of propane is reduced.
[0116] (3) The aromatic hydrocarbon selectivity of Example 4 slightly increased, but the propane conversion rate decreased, because too much rare earth element would be enriched on the surface and in the pores of the molecular sieve, covering a part of the acid sites and sacrificing a part of the activity. Therefore, the loading amount of the rare earth element needs to be controlled within a reasonable range. Examples 5-7 used other types of rare earth elements, and the performance was better than that of Comparative Example 3, but the effect was not as good as that of lanthanum. It is speculated that this is because the 4f electronic structure of the lanthanum species has a moderate electronic effect on the olefin double bond, which is best for the stabilization of the olefin intermediate, thereby facilitating the further aromatization of the olefin intermediate. The aromatic hydrocarbon selectivity of Example 8 decreased when the Si / Al atomic ratio of the molecular sieve was low, because a lower Si / Al ratio means more acid sites, which leads to an increase in the activity of other side reactions. When the Si / Ga atomic ratio was low in Example 10, it meant that more Ga species broke the balance between the propane dehydrogenation and olefin aromatization reactions, thus reducing the aromatic hydrocarbon selectivity to some extent. This indicates that there should be a moderate amount of Al atoms and Ga atoms in the catalyst to maximize the propane aromatization performance.
[0117] The above description is only the preferred embodiment of the present application, and does not limit the present application in any form. Although the present application has been disclosed as above with the preferred embodiment, it is not intended to limit the present application. Any person skilled in the art can make some changes or modifications to the above disclosed technical content without departing from the scope of the technical solution of the present application, and any simple modification, equivalent change and modification of the above embodiments according to the technical essence of the present application are still within the scope of the technical solution of the present application.
Claims
1. A method for preparing rare earth nanosheet heteroatom catalytic materials, characterized in that, Includes the following steps: (1) Synthesis of molecular sieve by in-situ hydrothermal crystallization: Gallium compound, silicon source, aluminum source, template agent, deionized water and urea are mixed and hydrothermally crystallized at 140~200℃ for 24~96h. The reaction product is calcined to obtain Ga@s-HZSM-5 molecular sieve. The molar amounts of template agent, urea and deionized water are 0.05~1 times, 0.3~1.2 times and 10~100 times the molar amount of silicon source, respectively. (2) Loading rare earth species by equal volume impregnation method: The Ga@s-HZSM-5 molecular sieve is placed in a rare earth solution and ultrasonically impregnated for 0.5-3h. The impregnated product is calcined to obtain rare earth nanosheet heteroatom catalytic material. The carrier of the rare earth nanosheet heteroatom catalytic material is hydrogen-type nanosheet ZSM-5 molecular sieve, denoted as s-HZSM-5, with a b-axis length of 80-120nm and a Si / Al atomic mass ratio of 15-80. Isolated gallium species are uniformly distributed in the s-HZSM-5 molecular sieve framework, with a Si / Ga atomic mass ratio of 15-100. Rare earth metal species are uniformly dispersed on the surface and in the pores of s-HZSM-5, with a rare earth loading of 0.1-2wt%. The rare earth is at least one of lanthanum, cerium, praseodymium, and neodymium.
2. The preparation method according to claim 1, characterized in that, The Si / Al atomic mass ratio in s-HZSM-5 molecular sieve is 20-80, the Si / Ga atomic mass ratio is 20-90, and the rare earth loading is 0.1-0.8 wt%.
3. The preparation method according to claim 1 or 2, characterized in that, The rare earth metals are lanthanum or cerium.
4. The preparation method according to claim 1, characterized in that, The silicon source is at least one of tetraethyl silicate, silica sol, and silica fume, and the aluminum source is at least one of sodium aluminate, aluminum isopropoxide, and boehmite.
5. The preparation method according to claim 1, characterized in that, Step (1) The roasting temperature is 450~650 ℃ and the roasting time is 3~8 h.
6. The preparation method according to claim 1, characterized in that, Step (1) The reaction product was filtered, washed, dried and calcined to obtain Ga@s-HZSM-5 molecular sieve; the drying temperature was 80~120 ℃ and the drying time was 8~15 h.
7. The preparation method according to claim 1, characterized in that, Step (2) The roasting temperature is 450~650 ℃ and the roasting time is 3~8 h.
8. The preparation method according to claim 1, characterized in that, Step (2) The impregnated product is successively evaporated and calcined to obtain rare earth nanosheet heteroatom catalytic material; the evaporation temperature is 80~140 ℃.
9. The application of the rare earth nanosheet heteroatom catalytic material prepared by any one of claims 1-8 in the catalytic aromatization reaction of propane.
10. The application according to claim 9, characterized in that, The feed gas is a propane / nitrogen mixture, with a propane volume content of 20-60%. The reaction temperature is 450-650 °C, and the mass hourly space velocity (HHSV) is 0.6-3 h⁻¹. -1 .