Rare earth nanosheet heteroatom catalytic material as well as preparation method and propane aromatization application thereof

Abstract

The invention relates to the field of catalytic materials, and provides a rare earth nanosheet heteroatom catalytic material as well as a preparation method and application thereof in propane aromatization. The catalytic material carrier is s-HZSM-5, the b-axis length is 80-120nm, and the Si / Al atomic ratio is 15-80; the isolated gallium species are uniformly distributed in the s-HZSM-5 molecular sieve skeleton, and the Si / Ga atom mass ratio is 15-100; rare earth metal species are uniformly dispersed on the surface and in pore channels of the s-HZSM-5, and the rare earth loading capacity is 0.1-2wt%. The preparation method comprises the steps of synthesizing the molecular sieve by an in-situ hydrothermal crystallization method and loading rare earth species by an impregnation method. By limiting the b-axis of the molecular sieve, carbon deposition is inhibited; the rare earth metal species are highly dispersed in the s-HZSM-5 crystal through impregnation, and the rare earth element interacts with Ga atoms and Al atoms of a framework to form special active sites in a micropore confinement space of the molecular sieve, so that the aromatic hydrocarbon selectivity is improved.

Description

Technical Field

[0001] The invention relates to the field of catalytic materials, in particular to rare earth nanosheet heteroatom catalytic materials and a preparation method thereof and propane aromatization application. Background Art

[0002] Benzene, toluene, and xylene (BTX) are important bulk chemicals. The research on the reaction technology of synthesizing BTX through aromatization using low-carbon alkanes as raw materials has attracted much attention both in academic research and in the industrial field. Among them, propane is one of the main components of liquefied petroleum gas, and propane aromatization is one of the research hotspots. The propane aromatization process uses molecular sieves and other large specific surface area solid acids as catalysts. Under certain conditions of space velocity, temperature and pressure, propane can be converted into aromatics through dehydrogenation, polymerization, cyclization and other reaction processes. This process expands the chemical utilization of propane and enriches the production pathways of aromatics represented by BTX, and has broad application prospects.

[0003] Most of the aromatization catalysts studied at present are concentrated on ZSM-5 molecular sieves, which have the advantages of a three-dimensional cross-straight channel structure of a ten-membered ring, a large specific surface area, good shape-selective catalytic performance and unique surface acidity, so that it exhibits very good catalytic performance during the aromatization reaction. Since the aromatization reaction of propane mainly includes processes such as propane dehydrogenation to olefins and olefin re-aromatization, in addition, the hydrogen species produced after dehydrogenation are prone to hydrogen transfer reactions. Therefore, the catalyst requires both appropriate dehydrogenation active centers and aromatization active centers, and it is necessary to avoid the occurrence of more side reactions such as hydrogen transfer. The yield of aromatics can be effectively improved by adding metal components such as gallium and zinc. However, the common problem is that by-products such as methane and ethane have high selectivity and low yield of aromatics. Therefore, the structural improvement of the catalyst and the method of doping metal active components are particularly important. Based on ZSM-5 molecular sieves, the present invention innovates the synthesis method of molecular sieves and the method of adding metal active components, develops rare earth nanosheet heteroatom catalytic materials, and creates appropriate reaction conditions at the same time, which significantly improves the yield of propane to aromatics. Summary of the invention

[0004] The present invention provides a rare earth nanosheet heteroatom catalytic material, a preparation method thereof and an application in propane aromatization. The b axis of a nanosheet s-HZSM-5 zeolite molecular sieve is limited to 80-120 nm, so as to suppress carbon deposition and improve the performance of the catalytic material. Rare earth metal species are highly dispersed in s-HZSM-5 crystals by impregnation, and the rare earth elements interact with Ga atoms and Al atoms in the framework to form special active sites in the microporous confined space of the molecular sieve, thereby improving the selectivity of aromatics.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions: The invention discloses a rare earth nanosheet heteroatom catalytic material, wherein the carrier of the catalytic material is a hydrogen-type nanosheet ZSM-5 molecular sieve (denoted as s-HZSM-5), the b-axis length is 80-120nm, and the Si / Al atomic mass ratio is 15-80; isolated gallium species are uniformly distributed in the s-HZSM-5 molecular sieve framework, and the Si / Ga atomic mass ratio is 15-100; rare earth metal species are uniformly dispersed on the surface and in the pores of s-HZSM-5, and the rare earth loading amount is 0.1-2wt%.

[0006] Preferably, the Si / Al atomic mass ratio in the 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%.

[0007] Preferably, the rare earth metal is at least one of lanthanum, cerium, praseodymium and neodymium, and more preferably lanthanum or cerium.

[0008] The method for preparing rare earth nano-sheet heteroatom catalytic material comprises the following steps: (1) In-situ hydrothermal crystallization method for synthesizing molecular sieves The gallium compound and the raw material for preparing s-HZSM-5 are mixed, and a hydrothermal crystallization reaction is carried out at 140-200° C. for 24-96 hours. The reaction product is calcined to obtain Ga@s-HZSM-5 molecular sieve; (2) Impregnation method for loading rare earth species The Ga@s-HZSM-5 molecular sieve obtained in step (1) is placed in a rare earth solution for impregnation, and the impregnated product is calcined to obtain a rare earth nanosheet heteroatom catalytic material.

[0009] Preferably, the raw materials for preparing s-HZSM-5 are silicon source, aluminum source, template, deionized water and urea. The silicon source is at least one of tetraethyl silicate, silica sol and white carbon black, the template 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 is 0.05 to 1 times the molar amount of the silicon source, the molar amount of urea is 0.3 to 1.2 times the molar amount of the silicon source, and the molar amount of deionized water is 10 to 100 times the molar amount of the silicon source.

[0010] Preferably, the calcination temperature in step (1) is 450-650° C., and the calcination time is 3-8 hours.

[0011] The reaction product of step (1) is filtered, washed, dried and calcined to obtain Ga@s-HZSM-5 molecular sieve. The drying temperature is 80-120° C. and the drying time is 8-15 hours.

[0012] Preferably, step (2) adopts ultrasonic immersion, and the ultrasonic treatment time is 0.5 to 3 hours.

[0013] Preferably, the calcination temperature in step (2) is 450-650° C., and the calcination time is 3-8 hours.

[0014] The impregnation product in step (2) is evaporated and calcined in sequence to obtain a rare earth nano-sheet heteroatom catalytic material. The evaporation temperature is 80-140°C.

[0015] The present invention also provides application of the rare earth nanosheet heteroatom catalytic material in propane aromatization reaction.

[0016] 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°C, and the reaction mass space velocity is 0.6-3h -1 .

[0017] Preferably, the reaction is carried out in a fixed bed reactor, first pretreated with nitrogen at 450-650°C for 1-4h, and then the raw gas is introduced; the reaction pressure is 0.1-0.5MPa.

[0018] Therefore, the beneficial effects of the present invention are: (1) The catalytic material of the present invention has the advantages of good aromatization activity, easy activation of low-carbon alkanes, high selectivity for aromatics, and excellent anti-carbon deposition performance. Through in-situ synthesis technology, during the hydrothermal synthesis of s-HZSM-5 zeolite, Ga species partially replaces the framework Al, and Ga is implanted into the s-HZSM-5 framework structure, and the framework Ga sites are highly dispersed. Compared with the 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 products.

[0019] (2) The b-axis of the nanosheet s-HZSM-5 zeolite molecular sieve is limited to a short b-axis in the range of 80-120 nm, which corresponds to a shortened straight pore, reducing the accumulation of substrate molecules in the pores, which is beneficial to the diffusion of reactants and intermediates in the pores, thereby inhibiting carbon deposition and improving the performance of the catalytic material.

[0020] (3) Rare earth metal species are highly dispersed in s-HZSM-5 crystals through impregnation. Rare earth elements interact with Ga atoms and Al atoms in the framework to form special active sites in the microporous confined space of the molecular sieve. Moderate local electric field strength can stabilize olefin intermediates and facilitate aromatization. At the same time, after alkane molecules dissociate hydrogen atoms on the Ga surface, hydrogen atoms are more easily recombined to generate hydrogen desorption, reducing the generation of by-product dry gas and further improving aromatic selectivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1It is the X-ray powder diffraction spectrum 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.

[0022] Figure 2 It is a schematic diagram of the axial direction of the molecular sieve crystal.

[0023] Figure 3 is a scanning electron microscope photograph of the catalytic material; in the figure, 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 Example 1. DETAILED DESCRIPTION

[0024] The technical solution of the present invention is further described below through specific embodiments.

[0025] In the present invention, unless otherwise specified, the raw materials and equipment used can be purchased from the market or are commonly used in the art. The methods in the embodiments, unless otherwise specified, are all conventional methods in the art. Unless otherwise specified, parts are all weight parts, temperatures are expressed in ° C or at ambient temperature, and pressures are atmospheric pressure or near atmospheric pressure. There are many variations and combinations of reaction conditions (such as component concentrations, desired solvents, solvent mixtures, temperatures, pressures, and other reaction ranges) and conditions that can be used to optimize the purity and yield of the product obtained by the method, and only reasonable routine experiments will be required to optimize such method conditions.

[0026] Example 1. Rare earth nanosheet heteroatom catalytic materials Rare earth-based nano-sheet heteroatom catalytic material, the carrier of the catalytic material is hydrogen-type nano-sheet ZSM-5 molecular sieve (s-HZSM-5), the b-axis length is 80-120nm, and the Si / Al atomic ratio is 15-80 (more preferably 20-80).

[0027] 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 (more preferably 20-90).

[0028] The rare earth metal species are uniformly dispersed on the surface and in the pores of s-HZSM-5, the rare earth loading is 0.1-2wt% (more preferably 0.1-0.8wt%), and the rare earth metal is at least one of lanthanum, cerium, praseodymium, and neodymium, more preferably lanthanum or cerium.

[0029] 2. Preparation method of rare earth nanosheet heteroatom catalytic material The following steps are involved: (1) In-situ hydrothermal crystallization method for synthesizing molecular sieves The template agent is mixed with deionized water, and stirred at room temperature to obtain a template agent solution; a gallium salt hydrate is mixed with deionized water, and stirred at room temperature to obtain a gallium salt aqueous solution; the gallium salt aqueous solution is added to the template agent solution, stirred for a period of time, a silicon source is added, stirred for a period of time, an aluminum salt is added, stirred for a period of time, urea is added, stirred for a period of time, and then transferred to a hydrothermal reactor, and a hydrothermal crystallization reaction is carried out at 140-200° C. for 24-96 hours; after the reaction, the reaction product is centrifuged, washed, dried at 80-120° C. for 8-15 hours, and calcined at 450-650° C. for 3-8 hours to obtain a Ga@s-HZSM-5 molecular sieve, which is recorded as Ga@s-HZSM-5-yz, wherein y is the Si / Al atomic mass ratio, and z is the Si / Ga atomic ratio.

[0030] The silicon source is at least one of tetraethyl silicate, silica sol, and white carbon black, the template 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 is 0.05 to 1 times the molar amount of the silicon source, the molar amount of urea is 0.3 to 1.2 times the molar amount of the silicon source, and the molar amount of deionized water is 10 to 100 times the molar amount of the silicon source.

[0031] (2) Loading rare earth species by equal volume impregnation method The Ga@s-HZSM-5 molecular sieve obtained in step (1) and the rare earth aqueous solution are mixed in a centrifuge tube and ultrasonically shaken for 0.5-3 hours; after the shaking, the mixture is transferred to an evaporating dish, ground at 80-140° C. until completely evaporated, and calcined at 450-650° C. for 3-8 hours to obtain a rare earth-based nanosheet catalytic material, which is denoted as xR / Ga@s-HZSM-5-yz, wherein x is the mass percentage of the loaded rare earth and R is the rare earth.

[0032] 3. Application of rare earth nanosheet heteroatom catalytic materials in propane aromatization reaction The aromatization reaction of propane is carried out in a fixed bed reactor. First, nitrogen is introduced for pretreatment at 450-650°C for 1-4 hours, and then a propane / nitrogen mixture is introduced as the raw material gas. The volume content of propane in the mixture is 20-60%. The reaction is carried out at a temperature of 450-650°C and a pressure of 0.1-0.5 MPa. The reaction mass space velocity is 0.6-3h -1 .

[0033] Example 1 A method for preparing a rare earth nanosheet heteroatom catalytic material, comprising the following steps: (1) In-situ hydrothermal crystallization method for synthesizing molecular sieves 12g of tetrapropylammonium hydroxide (25wt.%) was mixed with 10.3g of deionized water and stirred at room temperature for 1h to obtain a tetrapropylammonium hydroxide solution; 138mg of gallium nitrate hydrate was mixed with 5g of deionized water and stirred at room temperature for 1h to obtain a gallium nitrate aqueous solution; the gallium nitrate aqueous solution was added to the tetrapropylammonium hydroxide solution and stirred for 4h, 8.4g of tetraethyl silicate was added and stirred for 8h, 285mg of aluminum isopropoxide was added and stirred for 4h, 1.695g of urea was added and stirred for 2h, and then transferred to a hydrothermal reactor for hydrothermal reaction at 180℃ for 72h, and finally the reaction product of the hydrothermal reaction was centrifuged, washed, dried at 100℃ for 12h, and calcined at 550℃ for 4h to obtain Ga@s-HZSM-5 molecular sieve. The prepared Ga@s-HZSM-5 molecular sieve has a Si / Al atomic mass ratio of 30 and a Si / Ga atomic mass ratio of 30.

[0034] (2) Loading rare earth species by equal volume impregnation method The Ga@s-HZSM-5 molecular sieve obtained in step (1) and the lanthanum nitrate aqueous solution are impregnated in equal volumes. 1g of Ga@s-HZSM-5 molecular sieve is mixed with 2mL of lanthanum nitrate aqueous solution in a centrifuge tube and ultrasonically shaken for 1h. The mass ratio of lanthanum to s-HZSM-5 in the mixed solution is 0.003:1. After the shaking, it is transferred to an evaporating dish, ground at 120°C until completely evaporated, and calcined at 550°C for 4h to obtain a rare earth-based nano-sheet catalytic material, recorded as 0.3La / Ga@s-HZSM-5-30-30.

[0035] The application of rare earth nanosheet heteroatom catalytic materials in propane aromatization reaction, the steps are: The reaction was carried out in a tubular fixed bed reactor with an inner diameter of 8 mm. 0.8 g of quartz sand (20-40 mesh) and 0.4 g of the rare earth-based nano-sheet catalytic material 0.3La / Ga@s-HZSM-5-30-30 (20-40 mesh) obtained in step (2) were uniformly mixed and placed in the constant temperature zone of the reactor. First, N2 (20 mL·min -1 ) atmosphere to 550℃, and then -1 ) atmosphere for 1 h. After the pretreatment, 15 mL min -1 40vol% C3H8 / N2 was used for the reaction, the temperature was 550℃, and the reaction mass space velocity was 1.5h -1 , the aromatization reaction lasted for 10 h.

[0036] Example 2 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 catalytic material is recorded as 0.1La / Ga@s-HZSM-5-30-30.

[0037] Example 3 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 catalytic material is recorded as 0.5La / Ga@s-HZSM-5-30-30.

[0038] Example 4 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 catalytic material is recorded as 1.0La / Ga@s-HZSM-5-30-30.

[0039] Example 5 The difference from Example 1 is that the rare earth species in step (2) is cerium, and the obtained rare earth-based nanosheet catalytic material is recorded as 0.3Ce / Ga@s-HZSM-5-30-30.

[0040] Example 6 The difference from Example 1 is that the rare earth species in step (2) is praseodymium, and the obtained rare earth-based nanosheet catalytic material is recorded as 0.3Pr / Ga@s-HZSM-5-30-30.

[0041] Example 7 The difference from Example 1 is that the rare earth species in step (2) is neodymium, and the obtained rare earth-based nanosheet catalytic material is recorded as 0.3Nd / Ga@s-HZSM-5-30-30.

[0042] Example 8 The difference from Example 1 is that the amount of aluminum isopropoxide used in step (1) is 570 mg, the Si / Al atomic mass ratio is 15, and the obtained rare earth-based nanosheet catalytic material is recorded as 0.3La / Ga@s-HZSM-5-15-30.

[0043] Example 9 The difference from Example 1 is that the amount of aluminum isopropoxide used in step (1) is 106.9 mg, the Si / Al atomic mass ratio is 80, and the obtained rare earth-based nanosheet catalytic material is recorded as 0.3La / Ga@s-HZSM-5-80-30.

[0044] Example 10 The difference from Example 1 is that the amount of gallium nitrate hydrate used in step (1) is 276 mg, the Si / Ga atomic mass ratio is 15, and the obtained rare earth-based nanosheet catalytic material is recorded as 0.3La / Ga@s-HZSM-5-30-15.

[0045] Embodiment 11 The difference from Example 1 is that the amount of gallium nitrate hydrate used in step (1) is 69 mg, the Si / Ga atomic mass ratio is 60, and the obtained rare earth-based nanosheet catalytic material is recorded as 0.3La / Ga@s-HZSM-5-30-60.

[0046] Example 12 The difference from Example 1 is that the amount of gallium nitrate hydrate used in step (1) is 46 mg, the Si / Ga atomic mass ratio is 90, and the obtained rare earth-based nanosheet catalytic material is recorded as 0.3La / Ga@s-HZSM-5-30-90.

[0047] Embodiment 13 The difference from Example 1 is that in the application step, the reaction mass space velocity is 0.75h -1 .

[0048] Embodiment 14 The difference from Example 1 is that in the application step, the reaction temperature is 600°C.

[0049] Embodiment 15 The difference from Example 1 is that in the application step, the reaction temperature is 650°C.

[0050] Example 16 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 20%, recorded as 20 vol% C3H8 / N2.

[0051] Embodiment 17 The difference from Example 1 is that in the application step, the reaction mass space velocity is 3h -1 .

[0052] Embodiment 18 The difference from Example 1 is that in the application step, the reaction mass space velocity is 0.6h -1 .

[0053] Embodiment 19 The difference from Example 1 is that in the application step, the reaction temperature is 450°C.

[0054] Embodiment 20 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%, recorded as 60 vol% C3H8 / N2.

[0055] Comparative Example 1 The difference from Example 1 is that Ga and La are loaded on the common bulk ZSM-5 molecular sieve (n-HZSM-5) by using the impregnation method.

[0056] Comparative Example 2 The difference from Example 1 is that Ga and La are loaded on the s-HZSM-5 molecular sieve by using an impregnation method.

[0057] Comparative Example 3 The difference from Example 1 is that nanosheet heteroatom catalytic material is used without loading rare earth metal.

[0058] Comparative Example 4 The difference from Example 1 is that in the application step, the reaction mass space velocity is 4h -1 .

[0059] Comparative Example 5 The difference from Example 1 is that in the application step, the reaction temperature is 700°C.

[0060] Comparative Example 6 The difference from Example 1 is that in the application step, the reaction temperature is 400°C.

[0061] Comparative Example 7 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%, which is recorded as 80 vol% C3H8 / N2.

[0062] Results Analysis 1. Morphology analysis Figure 1 The X-ray powder diffraction spectra (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 all have the characteristic diffraction peaks of the typical ZSM-5 molecular sieve, indicating that the ZSM-5 molecular sieve is successfully prepared, and there are no characteristic diffraction peaks of metal particles, indicating that the metal species are highly dispersed.

[0063] The three-dimensional molecular sieve has a, b, and c axes, similar to the length, width, and height of a cuboid, such as Figure 2 Conventional molecular sieves are block-shaped, with length, width and height being basically the same. The molecular sieve in the present invention is in the form of long nanosheets, and the b axis, i.e. the thickness of the molecular sieve, is much shorter than the length and width, thus presenting a sheet-like morphology, as shown in FIG. Figure 3A is a scanning electron microscope photo (SEM) 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, with a c-axis / a-axis ratio of >5 and a c-axis / b-axis ratio of >15. Figure 3 B is the SEM photograph 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, the c-axis / a-axis ratio is ≈1, and the c-axis / b-axis ratio is <2.

[0064] 2. Catalytic performance analysis The catalytic performance results of each embodiment and comparative example are shown in the following table.

[0065] From the above table, compared with Example 1: (1) The aromatics yield of the common block n-HZSM-5-based catalytic material in Comparative Example 1 is lower than that of the nano-sheet s-HZSM-5-based catalytic material, indicating that the larger b-axis length of the block molecular sieve will increase the diffusion distance of the substrate molecules, which is not conducive to contacting the active sites inside the molecular sieve, resulting in a decrease in conversion rate and a decrease in aromatics selectivity. The performance of the common impregnated Ga component in Comparative Example 2 is not as good as the skeleton Ga molecular sieve in Example 1, indicating that the Ga species in the Ga-impregnated sample is easily blocked in the molecular sieve pores or agglomerated on the molecular sieve surface, which is not conducive to propane conversion, and further illustrates that the special coordination environment of the skeleton Ga species in the present invention is conducive to the dehydrogenation and further aromatization of propane, thereby significantly improving the performance of the catalytic material. Comparative Example 3 does not introduce rare earth elements, and the propane conversion rate and aromatics selectivity are significantly reduced, indicating that rare earth elements can provide a unique local electric field, stabilize olefin intermediates, and are conducive to the aromatization of olefin intermediates, thereby increasing the yield of aromatic products.

[0066] (2) In Comparative Example 4, further increasing the space velocity resulted in a decrease in propane conversion and aromatics selectivity, while an increase in propylene selectivity. This is because the propane aromatization reaction undergoes a propane dehydrogenation and propylene aromatization process. The propylene generated by increasing the space velocity is desorbed before it can be further converted. This indicates that a higher space velocity is not conducive to the aromatization of propylene, and an appropriate space velocity range is required. In Comparative Examples 5 and 6, the reaction temperature is too low or too high, which is not conducive to the aromatics yield. The first step of propane dehydrogenation to propylene is an endothermic reaction. Too low a temperature is not conducive to the first step of the reaction, thereby affecting the overall catalyst conversion rate. Too high a temperature exacerbates the occurrence of side reactions such as cracking, such as C 4-6The selectivity of hydrocarbons is significantly improved, which is not conducive to the selectivity of aromatics, indicating that the catalyst can only play a 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 feed gas because the concentration of propane substrate is too high and too much propane cannot be converted in time on the unit catalyst, so the conversion rate of propane is reduced.

[0067] (3) Example 4 Rare earth element dosage increased, aromatics selectivity slightly increased, but propane conversion rate decreased, because too much rare earth elements will be enriched on the molecular sieve surface and pores, covering part of the acid sites, sacrificing part of the activity, therefore, the loading amount of rare earth elements needs to be controlled within a reasonable range. Examples 5-7 use other types of rare earth elements, and the performance is improved compared with Comparative Example 3, but the effect is not as good as lanthanum. It is speculated that the 4f electronic structure of lanthanum species has a moderate electronic effect, acting on the olefin double bond, and has the best stabilization effect on olefin intermediates, which is conducive to the further aromatization of olefin intermediates. Example 8 When the Si / Al atoms of the molecular sieve are low, the aromatics selectivity is reduced, because the lower silicon-aluminum ratio means more acid sites, resulting in the improvement of other side reaction activities. When the Si / Ga atoms are relatively low in Example 10, it means that more Ga species break the balance of propane dehydrogenation and olefin aromatization reactions, thus reducing the aromatics selectivity to a certain extent, indicating that there should be moderate Al atoms and Ga atoms in the catalyst to maximize the propane aromatization performance.

[0068] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. Rare earth nanosheet heteroatom catalytic material, characterized in that: The carrier of the catalytic material is a hydrogen-type nanosheet ZSM-5 molecular sieve, denoted as s-HZSM-5, with 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 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 0.1-2 wt%.

2. The rare earth nanosheet heteroatom catalytic material according to claim 1, characterized in that: The Si / Al atomic mass ratio in the 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 rare earth nanosheet heteroatom catalytic material according to claim 1 or 2, characterized in that: The rare earth metal is at least one of lanthanum, cerium, praseodymium and neodymium.

4. The method for preparing the rare earth nanosheet heteroatom catalytic material according to any one of claims 1 to 3, characterized in that: The following steps are involved: (1) In-situ hydrothermal crystallization method for synthesizing molecular sieves The gallium compound and the raw material for preparing s-HZSM-5 are mixed, and a hydrothermal crystallization reaction is carried out at 140-200 °C for 24-96 h. The reaction product is calcined to obtain Ga@s-HZSM-5 molecular sieve; (2) Impregnation method for loading rare earth species The Ga@s-HZSM-5 molecular sieve obtained in step (1) is placed in a rare earth solution for impregnation, and the impregnated product is calcined to obtain a rare earth nanosheet heteroatom catalytic material.

5. The method for preparing the rare earth nanosheet heteroatom catalytic material according to claim 4, characterized in that: The raw materials for preparing s-HZSM-5 are silicon source, aluminum source, template, deionized water and urea.

6. The method for preparing the rare earth nanosheet heteroatom catalytic material according to claim 4, characterized in that: The calcination temperature of step (1) is 450-650°C, and the calcination time is 3-8 h.

7. The method for preparing the rare earth nanosheet heteroatom catalytic material according to claim 4, characterized in that: The step (2) adopts ultrasonic immersion, and the ultrasonic treatment time is 0.5~3 h.

8. The method for preparing the rare earth nanosheet heteroatom catalytic material according to claim 4, 6 or 7, characterized in that: The calcination temperature of step (2) is 450-650°C, and the calcination time is 3-8 h.

9. Use of the rare earth nanosheet heteroatom catalytic material according to any one of claims 1 to 3 or the rare earth nanosheet heteroatom catalytic material prepared by any one of claims 4 to 8 in catalyzing propane aromatization reaction.

10. The use of the rare earth nanosheet heteroatom catalytic material according to claim 9, characterized in that: The raw gas is a propane / nitrogen mixture with a propane volume content of 20-60%. The reaction temperature is 450-650 °C and the reaction mass space velocity is 0.6-3 h -1 .

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