A propane aromatization reaction catalyst, a preparation method and application thereof

Abstract

The present invention relates to the field of catalysts, and discloses a propane aromatization catalyst and its preparation method and application. The catalyst includes (Ga / (H)ZSM‑5) formed by Ga-modified (H)ZSM‑5 molecular sieve and supported Pt nanoparticles; wherein the mass ratio of Pt nanoparticles to Ga / (H)ZSM‑5 molecular sieves in Ga / (H)ZSM‑5 is (0.4-1): 1. When the catalyst provided by the present invention is applied, propane generates olefins by dehydrogenation reaction, and olefins are used as intermediates of aromatization reaction to achieve high activity and high selectivity to synthesize target products, constituting a series catalytic reaction system of two-stage reactions before and after dehydrogenation and aromatization. The catalytic reaction system based on the catalyst is a series catalytic system that can effectively improve the production efficiency of propane aromatization and reduce the required reaction temperature.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of catalysts, and more particularly relates to a propane aromatization reaction catalyst and a preparation method and application thereof. BACKGROUND

[0002] Aromatic hydrocarbons represented by benzene, toluene and xylene are important bulk chemicals. At present, the production of aromatic hydrocarbons mainly comes from petroleum chemical industry, and propane rich in unconventional natural gas resources such as shale gas can be used as an alternative raw material for direct and efficient synthesis of aromatic hydrocarbons. Metal-modified or ion-exchanged molecular sieves are the most common catalyst types in propane aromatization reactions, and Ga / (H)ZSM-5 is the highest activity propane aromatization catalyst known at present. Since the total aromatization reaction is limited by the dehydrogenation rate-determining step, it is a great challenge to further improve the efficiency on this basis.

[0003] The Ga / (H)ZSM-5 catalysts recorded in the existing literature, such as the schemes recorded in Preparation of a Hollow HZSM-5 Zeolite Supported Molybdenum Catalyst by Desilication-Recrystallization for Enhanced Catalytic Properties in Propane Aromatization[J], Xu G, Zhang P, Cheng J, et, Journal of Solid State Chemistry, 2021, 300(6): 122238 and Effects of silylation on Ga / HZSM-5 for improved propane dehydroaromatization[J]. Xu B, Tan M, Wu X, et, Fuel, 2021, 283: 118889, the propane conversion rate and BTX (benzene, toluene and xylene) selectivity of Ga / (H)ZSM-5 catalyst at 540℃ are 49% and 55%, respectively.

[0004] In this regard, the catalysts reported in the relevant studies are mainly improved and optimized by co-impregnating other active components on the basis of Ga / (H)ZSM-5, and the improvement effect is very limited due to potential factors such as mutual coverage between sites. The aromatization reaction is carried out on the same component, for example, Ga and Cr are co-doped on HZSM-5 molecular sieve, Cr is responsible for dehydrogenation to generate olefins, and Ga is responsible for aromatization of olefins, that is, the same space is simultaneously carried out. The loading and doping of active components have certain limitations, because if Cr is doped too much on the surface of the molecular sieve, chromium oxide clusters are formed, which is not conducive to the good dispersion of the active component; but if it is doped too little, it is not conducive to the reaction. Therefore, when loading different active sites on the same component, due to the interaction and mutual influence between the two, the independence and controllability of the two are poor, which limits the improvement of catalytic activity.

[0005] Therefore, if it is desired to further improve the catalytic effect, it is necessary to reconstruct the aromatization reaction in space to provide more regulation and tailoring space for the dehydrogenation and aromatization process and the possibility of efficiency improvement. SUMMARY

[0006] In view of the above defects or improvement needs of the prior art, in order to overcome the shortcomings of the existing propane dehydrogenation aromatization technology, a propane aromatization reaction catalyst is provided, which is a composite catalyst composed of Ga / (H)ZSM-5 and supported Pt nanoparticles in a certain mass ratio. Based on the catalyst, an auxiliary dehydrogenation component is introduced into the reaction system to strengthen the dehydrogenation reaction to generate olefins, and the olefins are used as intermediates for aromatization reaction to synthesize benzene, toluene and xylene (BTX) target products with high activity and high selectivity, forming a series catalytic reaction system with dehydrogenation-aromatic two-stage reaction. The catalytic reaction system based on the catalyst is a series catalytic system that can effectively improve the production efficiency of propane aromatization and reduce the required reaction temperature.

[0007] To achieve the above-mentioned purpose, in the first aspect of the present application, a propane aromatization reaction catalyst is provided, which is composed of Ga / (H)ZSM-5 formed by Ga modified (H)ZSM-5 molecular sieve and supported Pt nanoparticles; the mass ratio of Pt nanoparticles to Ga / (H)ZSM-5 molecular sieve in the supported Pt nanoparticles is (0.4-1):1.

[0008] As a preferred embodiment of the present application, the particle size of the supported Pt nanoparticles is between 4-8 nm; the loading mass fraction of metallic platinum in the Pt nanoparticles is 0.1%-2%.

[0009] As a preferred embodiment of the present application, the carrier of the supported Pt nanoparticles is preferably one of silica, alumina, silicon-aluminum composite oxide, molecular sieve, ceria and spinel.

[0010] As a preferred embodiment of the present application, the loading mass fraction of gallium calculated by gallium trioxide in the Ga / (H)ZSM-5 is 1-3%.

[0011] As a preferred embodiment of the present application, the Ga / (H)ZSM-5 is prepared by the incipient wetness impregnation method, and the supported Pt nanoparticle component is synthesized by the flame spray pyrolysis method.

[0012] In the second aspect of the present application, a preparation method of the propane aromatization reaction catalyst according to the first aspect is provided, comprising:

[0013] (1) preparing a supported Pt nanoparticle precursor solution by mixing a metal Pt and a carrier precursor, and uniformly ultrasonic dispersing the same; and synthesizing the supported Pt nanoparticle by flame spray pyrolysis method from the supported Pt nanoparticle precursor solution;

[0014] (2) impregnating a gallium nitrate solution into (H)ZSM-5 molecular sieve until just wet, and drying for 5-8 h after standing, and calcining at a temperature of 500-600 ℃ for 2-5 h to obtain the Ga / (H)ZSM-5;

[0015] (3) uniformly mixing the Ga / (H)ZSM-5 in step (2) and the supported Pt nanoparticle in step (1) to obtain the propane aromatization reaction catalyst.

[0016] As a preferred embodiment of the present application, the flame spray pyrolysis method specifically comprises:

[0017] The flame spray pyrolysis method specifically comprises:

[0018] The supported Pt nanoparticle precursor solution is pumped from a capillary into a burner of a flame spray pyrolysis preparation system; wherein the delivery flow rate of the supported Pt nanoparticle precursor solution is 2-5 mL / min, the dispersion gas flow rate is 3-5 L / min; the premixed gas is a mixture of methane and oxygen at a volume ratio of 1:2, and the total gas velocity is 2.25-4.5 L / min; the protective gas is 5-10 L / min; and the support flame temperature formed after ignition of the premixed gas is in the range of 1800-3000 K.

[0019] As a preferred embodiment of the present application, in the step (1), the concentration of the supported Pt nanoparticle precursor solution is 0.2-0.5 mol / L.

[0020] In the third aspect of the present application, the propane aromatization reaction catalyst according to the first aspect is applied in the synthesis of aromatic hydrocarbons in propane aromatization reaction production.

[0021] As a preferred embodiment of the present application, the axial length of the reactor unit mass catalyst in the reactor is greater than 200 mm / g; the reaction temperature is 450-550 DEG C; the volume fraction of propane in the raw material gas is 25-50%; the inert gas is used as the balance gas; and the reaction space velocity is 2000-6000 mL / h / g.

[0022] Overall, compared with the prior art, the above technical scheme conceived by the present application mainly has the following technical advantages:

[0023] (1) The two components in the composite catalyst conceived by the present application are physically mixed and relatively independent in space, so that the inactivation of active sites caused by mutual covering or reaction between components in the prior art research through the introduction of modified or modified components by co-impregnation on Ga / (H)ZSM-5 can be avoided. At the same time, due to the higher degree of independence, the tailoring design of dehydrogenation or aromatization single reaction has more operability.

[0024] (2) The reaction system decouples the conventional propane dehydrogenation aromatization process in which the dehydrogenation and aromatization steps are promoted by the same catalyst and carried out in the same space into a dehydrogenation and aromatization reaction process in series catalytic reaction promoted by independent components. The auxiliary dehydrogenation catalyst is introduced on the basis of the commonly used molecular sieve catalyst to break the kinetic limitation of the total reaction by the dehydrogenation limiting step.

[0025] (3) In the present application, the dehydrogenation and aromatization reactions promoted by independent components constitute a front and rear series reaction in space, in which the auxiliary dehydrogenation catalyst (Pt nanoparticles) promotes the generation of olefins (ethylene and propylene) which are easy to be converted into aromatic hydrocarbons by the molecular sieve, and the olefins are subjected to aromatization reaction by the molecular sieve catalyst. Since the olefins produced by the front dehydrogenation reaction can be converted by the molecular sieve with high efficiency, the dehydrogenation reaction on it can be further promoted thermodynamically due to the Le Chatelier principle moving to the direction of olefin generation.

[0026] In the present application, the dehydrogenation reaction is carried out on the Pt nanoparticles, and the product is ethylene or propylene; the aromatization reaction of ethylene or propylene is carried out on the molecular sieve, i.e. the ethylene and propylene produced on the Pt nanoparticles can be quickly converted into aromatic hydrocarbons by the molecular sieve. Then, since the products of the dehydrogenation reaction can be reduced at the same time, the reaction is promoted to produce the products.

[0027] (4) The supported Pt nanoparticles of the present application, which are preferably synthesized by flame spray pyrolysis, can be used as an efficient propane dehydrogenation auxiliary catalyst to generate olefins as intermediates for aromatization reaction in a series catalytic system to break the limitation of the dehydrogenation rate-limiting step.

[0028] This is because the flame synthesis method can achieve atomic dispersion between components (precursors) during the preparation process, thereby obtaining a supported catalyst with stable high dispersion at high load. This is not an inherent atomic mixing preparation process that other processes (such as the most common impregnation method) do not have. If Pt agglomeration is too severe, it will lead to excessive dehydrogenation to form coke instead of ethylene or propylene, and the resulting coke will cover the active sites, reducing the activity of the catalyst. Therefore, the Pt nanoparticles prepared by the flame synthesis method can effectively avoid the agglomeration phenomenon that easily occurs at high temperature and high Pt load conditions, thereby improving the efficiency of generating olefins as intermediates in the aromatization reaction.

[0029] (5) The supported Pt catalyst introduced in the present application is a nanoparticle with a particle size preferably concentrated in the range of 4-8 nm, and mainly in the form of single-atom Pt structure even at a Pt loading of up to 1 wt%, and is stable in dispersion under continuous reaction conditions. For example, the supported Pt nanoparticles in Example 1 and Example 2 have atomic-scale high dispersion of Pt species at high Pt loading (1 wt%), without the formation of Pt particles or related crystal phases. Further, after uniformly dispersing a high mass fraction of single-atom Pt, not only is excessive dehydrogenation less likely to occur, but the generated coke can also be dispersed, reducing the coverage of active sites.

[0030] (6) Based on the propane aromatization reaction catalyst of the present application, the propane-dehydrogenation-aromatization tandem catalytic reaction system preferably uses a small-diameter reactor. The reaction gas has a longer travel length in the space where the catalyst is located at the same space velocity, which can promote the aromatization reaction to proceed fully and effectively reduce the generation of C4-C6 straight-chain hydrocarbon byproducts, and the selectivity of the three main aromatic hydrocarbons, benzene, toluene and xylene, is higher than 70%.

[0031] (7) The propane-dehydrogenation-aromatization tandem catalytic reaction system constructed in the present application can reduce the propane aromatization reaction temperature. At a reaction temperature of 500°C, the conversion rate is higher than that of the prior art at 550-600°C. Compared with the Ga / HZSM-5 catalyst prepared in the prior art, the propane conversion rate and the selectivity of BTX (benzene, toluene and xylene) at 540°C are about 49% and 55%, respectively. In the case of near-industrial application, i.e., when the propane concentration is as high as 50% by volume, the propane conversion rate of the catalyst of the present application can be as high as 84%. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 Schematic diagram of the propane aromatization catalytic reaction system of the present application;

[0033] Figure 2 XRD spectrum of the flame-synthesized Pt / CeO2 nanoparticle catalyst in Example 1 and Example 2 of the present application;

[0034] Figure 3 XRD pattern of the propane aromatization reaction catalyst after reacting with propane for 100 min in Example 2 of the present application;

[0035] Figure 4 High-resolution transmission electron microscopy images and particle size statistical data of the flame-synthesized Pt / CeO2 nanoparticle catalyst in Example 1 and Example 2 of the present application; wherein Figure 4 a is the high-resolution transmission electron microscopy image of the Pt / CeO2 nanoparticle catalyst, Figure 4 b is the particle size statistical data of the Pt / CeO2 nanoparticle catalyst;

[0036] Figure 5 TEM-EDS energy spectrum images of the flame-synthesized Pt / CeO2 nanoparticle catalyst in Example 1 and Example 2 of the present application; wherein Figure 5 the left image in is the TEM-EDS energy spectrum image of Ce, Figure 5 the right image in is the TEM-EDS energy spectrum image of Pt; the scale is 10 nm;

[0037] Figure 6 In-situ CO-DRIFTS spectrum of the flame-synthesized Pt / CeO2 nanoparticle catalyst in Example 1 and Example 2 of the present application. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0039] In the embodiments of the present application, the propane aromatization reaction catalyst used is a composite catalyst composed of Ga-modified (H) ZSM-5 molecular sieve Ga / (H) ZSM-5 and supported Pt nanoparticles. As shown in Figure 1 the preparation method of the propane aromatization reaction catalyst is as follows:

[0040] (1) Dissolve the metal Pt and the carrier precursor in an organic solvent capable of fully dissolving the precursor to obtain a supported Pt nanoparticle precursor solution with a total concentration of 0.2-0.5 mol / L, and disperse uniformly using ultrasonic waves. Synthesize the supported Pt nanoparticles by flame spray pyrolysis method using the above supported Pt nanoparticle precursor solution.

[0041] (2) The specific preparation method of Ga / (H)ZSM-5 is as follows: (H)ZSM-5 molecular sieve is immersed in a specified amount of gallium nitrate solution to make the loading amount of gallium trioxide 1% to 3%, and is just wetted, and is placed overnight, and is dried for 5 to 8 hours, and is calcined at a temperature of 500 to 600°C for 2 to 5 hours, to obtain the Ga / (H)ZSM-5.

[0042] (3) The Ga / (H)ZSM-5 particles in step (2) are uniformly mixed with the Pt nanoparticles in step (1) to obtain the propane aromatization reaction catalyst. The mass ratio of the Pt nanoparticles to the Ga / (H)ZSM-5 molecular sieve is (0.4 to 1):1.

[0043] In the embodiments of the present application, the supported Pt nanoparticle precursor solution is synthesized by a flame spray pyrolysis method, and specifically includes the following steps:

[0044] 1) A specified amount of metal Pt and carrier precursor is dissolved in an organic solvent capable of fully dissolving the precursors. The amount of the metal Pt and the carrier precursor is adjusted so that the mass ratio of the metal Pt to the carrier in the obtained Pt nanoparticles is 0.1:99.9 to 2:99. The two precursors are dissolved in the solvent to obtain a precursor solution with a total metal ion concentration of 0.2 to 0.5 mol / L. The solution is treated with ultrasonic waves for 1 hour.

[0045] 2) The precursor solution obtained in step 1) is pumped from a capillary into the burner of a flame spray pyrolysis preparation system by a syringe pump. The central part of the burner of the flame spray pyrolysis preparation system is a capillary port for delivering the precursor, and the surrounding part has a coaxial annular slit for releasing the dispersed gas (oxygen) therefrom; the middle part of the burner has another coaxial annular slit for releasing the premixed gas (methane and oxygen).

[0046] 3) The precursor solution undergoes breakage and atomization, high-temperature decomposition and combustion in the burner area, and forms nanoparticles after undergoing complex particle dynamics. During the formation of the nanoparticles, the flow rate of the precursor solution is 2 to 5 mL / min, the flow rate of the dispersed gas is 3 to 5 L / min, the premixed gas is methane and oxygen mixed at a volume ratio of 1:2, the total gas velocity is 2.25 to 4.5 L / min, and the supporting flame temperature formed after the premixed gas is ignited is about 1800 to 3000 K. There is also 5 to 10 L / min of protective gas (such as argon).

[0047] 4) The nanoparticles formed in step 3) are continuously driven by the vacuum pump located above and are adsorbed on the glass fiber filter paper, and finally the nanoparticles are scraped and collected to obtain the final Pt nanoparticles.

[0048] In the embodiments of the present application, as Figure 1The schematic diagram of the propane aromatization catalytic reaction system according to the embodiment of the present application is shown.

[0049] The reactor unit mass catalyst used in the propane-dehydrogenation-aromatization tandem catalytic reaction system has an axial length in the reactor of greater than 200 mm / g in a U-shaped quartz tube fixed bed reactor. The reaction temperature is 450-550°C; the propane volume fraction in the raw material gas is 25-50%, with nitrogen or argon as the balancing gas, and the reaction space velocity is 2000-6000 mL / h / g.

[0050] The specific implementation is as follows:

[0051] Example 1

[0052] The flame spray pyrolysis method is used to synthesize the supported Pt nanoparticles, i.e. Pt / CeO2 nanoparticles:

[0053] 0.087 g of platinum acetylacetonate and 28.111 g of cerium 2-ethylhexanoate (mass fraction of 49%, dissolved in ethylhexanoic acid) are weighed, and dimethylbenzene is added to the solution to a volume of 100 mL, to obtain a precursor solution with a total metal ion concentration of 0.25 mol / L. After the precursor is fully dissolved, the obtained solution is treated under ultrasonic waves for 1 h. The treated precursor solution is connected to the precursor solution pump-in pipeline of the flame spray pyrolysis nanoparticle synthesis system. The precursor solution delivery flow rate is set to 5 mL / min; the system gas path configuration is set as follows: the precursor solution delivery flow rate is 5 mL / min, the dispersing gas flow rate is 5 L / min, the premixed gas flow rate is 0.75 L / min of methane and 1.5 L / min of oxygen, and there is also protective gas (argon) of 8 L / min. A glass fiber collection filter paper is placed under the vacuum pump above the burner. Each synthesis consumes about 33 mL of precursor solution, and the synthesis is performed in three consecutive times. Finally, the Pt / CeO2 nanoparticles collected on the glass fiber filter paper are gently scraped and collected. The Pt / CeO2 nanoparticles obtained have a Pt mass fraction of 1%.

[0054] Ga / (H)ZSM-5 is prepared by the incipient wetness impregnation method:

[0055] 0.205 g of gallium nitrate is dissolved in 20 mL of deionized water, and the obtained gallium nitrate aqueous solution is added dropwise to 5 g of (H)ZSM-5 molecular sieve. After the obtained suspension is left still overnight, it is placed in a drying oven and dried at 120°C for 10 h. After grinding, it is placed in a muffle furnace and calcined at 560°C for 4 h. Finally, the obtained powder is sequentially subjected to tabletting, crushing, and sieving to obtain Ga / (H)ZSM-5 particles of 40-60 mesh.

[0056] The propane aromatization reaction catalyst is prepared:

[0057] Example 1 A propane aromatization reaction catalyst of Example 1 was prepared by physically mixing 0.2 g of Pt / CeO2nanoparticles with 0.5 g of Ga / (H)ZSM-5.

[0058] Propane aromatization reaction based on the propane aromatization reaction catalyst described above:

[0059] The propane aromatization reaction catalyst described above was packed into a 4 mm i.d. U-shaped quartz tube fixed bed reactor. Quartz wool and Al2O3particles were then added to the ends to reduce the dead space in the reactor volume. After heating to 500 °C at a rate of 10 °C / min in a 20% by volume, 50 mL / min total gas flow of oxygen / argon or air, the system was held for 20 min, then switched to argon purge for 20 min. The propane dehydroaromatization reaction was then started by switching to a 50% by volume, 25 mL / min total gas flow of propane / argon. After 20 min of reaction, the system was switched to an oxidation treatment of 20% by volume, 50 mL / min total gas flow of oxygen / argon or air for 20 min. This cycle was repeated until the system reached a steady propane aromatization performance. The reactivity data are shown in Table 1.

[0060] Example 2

[0061] Pt / CeO2nanoparticles and Ga / (H)ZSM-5 molecular sieve catalysts were prepared according to Example 1. A propane aromatization reaction catalyst of Example 2 was prepared by physically mixing 0.4 g of Pt / CeO2nanoparticles with 0.5 g of Ga / (H)ZSM-5.

[0062] Propane aromatization reaction based on the propane aromatization reaction catalyst described above:

[0063] The propane aromatization reaction catalyst of Example 2 was packed into a 4 mm i.d. U-shaped quartz tube fixed bed reactor. Quartz wool and Al2O3particles were then added to the ends to reduce the dead space in the reactor volume. After heating to 500 °C at a rate of 10 °C / min in a 20% by volume, 50 mL / min total gas flow of oxygen / argon or air, the system was held for 20 min, then switched to argon purge for 20 min. The propane dehydroaromatization reaction was then started by switching to a 50% by volume, 25 mL / min total gas flow of propane / argon. After 20 min of reaction, the system was switched to an oxidation treatment of 20% by volume, 50 mL / min total gas flow of oxygen / argon or air for 20 min. This cycle was repeated until the system reached a steady propane aromatization performance. The reactivity data are shown in Table 1.

[0064] Comparative Example 1

[0065] Ga / (H)ZSM-5 was prepared according to Example 1, 0.5 g Ga / (H)ZSM-5 was mixed with quartz sand of the same volume as 0.4 g Pt / CeO2nanoparticles, and then packed into a 4 mm inner diameter U-shaped quartz tube fixed bed reactor. Subsequently, quartz wool and Al2O3particles were added at both ends in turn to reduce the dead space in the reactor space. After heating to 500°C at a rate of 10°C / min in an oxygen / argon or air gas stream with a total gas velocity of 50 mL / min at 20% by volume, it was maintained for 20 min, and then switched to argon purge for 20 min. Then switch to a 50% by volume, total gas velocity of 25 mL / min propane / argon gas stream to start the propane dehydroaromatization reaction. When the reaction proceeds to 20 min, switch to 50 mL / min argon purge for 20 min, and then switch to 20% by volume, total gas velocity of 50 mL / min oxygen / argon or air gas stream for 20 min. This cycle is repeated until the system reaches a stable propane aromatization performance.

[0066] The reactivity data shown in Table 1 shows that,

[0067] In the case of Comparative Example 1 with only Ga / (H)ZSM-5, the propane conversion at 500°C was 62.49%, and the BTX selectivity was about 69.25%, with the main byproducts being methane and ethane, with selectivities of 10.45% and 13.00%, respectively.

[0068] In Example 1, after adding 0.2 g of Pt / CeO2catalyst, the propane conversion under the same other conditions increased to 78.26%, and the BTX selectivity was 72.73%. In Example 2, after adding Pt / CeO2nanoparticle catalyst to 0.4 g, the propane conversion under the same other conditions further increased to 84.24%, and the BTX selectivity was 73.10%. Compared with Comparative Example 1, the propane conversion increased by more than 30%, and the BTX selectivity did not decrease.

[0069] The small inner diameter U-shaped quartz tube fixed bed reactor used in the present application allows the propane to travel a longer distance in the catalyst bed under the same space velocity conditions, and the series of coupling and cyclization processes required for aromatization can be more fully carried out until the benzene ring is formed, thus greatly reducing the formation of C4-C6 straight-chain hydrocarbons, so that the BTX selectivity in all examples of the present application is at a high level.

[0070] Comparative Example 2

[0071] Pt / CeO2 nanoparticles prepared according to Example 1 were mixed with 0.4 g of quartz sand equivalent in volume to 0.5 g of Ga / (H)ZSM-5. Quartz wool and Al2O3 pellets were then added sequentially at both ends to reduce the dead space within the reactor volume. After ramping to 500 °C at 10 °C / min in a 20 vol% oxygen / argon or air gas stream at a total gas velocity of 50 mL / min, the system was held for 20 min, then switched to an argon purge for 20 min. The propane dehydroaromatization reaction was then initiated by switching to a 20 vol% propane / argon gas stream at a total gas velocity of 25 mL / min. After 10 min of reaction, the system was purged with argon at 50 mL / min for 10 min, then oxidized by switching to a 20 vol% oxygen / argon or air gas stream at a total gas velocity of 50 mL / min for 20 min. This cycle was repeated until the system reached a steady-state propane dehydroaromatization performance. Reactivity data are shown in Table 1.

[0072] Comparative Example 3

[0073] Ga / (H)ZSM-5 prepared according to Example 1 was mixed with 0.5 g of quartz sand equivalent in volume to 0.4 g of Pt / CeO2 nanoparticles, and packed into a 4 mm i.d. U-shaped quartz tube fixed bed reactor. Quartz wool and Al2O3 pellets were then added sequentially at both ends to reduce the dead space within the reactor volume. After ramping to 500 °C at 10 °C / min in a 20 vol% oxygen / argon or air gas stream at a total gas velocity of 50 mL / min, the system was held for 20 min, then switched to an argon purge for 20 min. The propylene aromatization reaction was then initiated by switching to a 10 vol% propylene / argon gas stream at a total gas velocity of 25 mL / min. After 20 min of reaction, the system was purged with argon at 50 mL / min for 20 min, then oxidized by switching to a 20 vol% oxygen / argon or air gas stream at a total gas velocity of 50 mL / min for 20 min. This cycle was repeated until the system reached a steady-state propylene aromatization performance. Reactivity data are shown in Table 1.

[0074] Comparative Example 4

[0075] Ga / (H)ZSM-5 molecular sieve catalyst was prepared according to Example 1. 0.5 g of Ga / (H)ZSM-5 molecular sieve catalyst was mixed with quartz sand equivalent in volume to 0.4 g of Pt / CeO2 catalyst and packed into a 4 mm i.d. U-shaped quartz tube fixed bed reactor. Quartz wool and Al2O3 pellets were added at both ends to reduce the dead space in the reactor space. After heating to 500 °C at a rate of 10 °C / min under a flow of 20 vol% oxygen in argon or air at a total gas velocity of 50 mL / min, the temperature was held for 20 min, followed by a 20 min purge with argon. The ethylene aromatization reaction was then started with a flow of 10 vol% ethylene in argon at a total gas velocity of 25 mL / min. After the reaction proceeded for 20 min, the system was purged with argon at a flow of 50 mL / min for 20 min, followed by an oxidation treatment with a flow of 20 vol% oxygen in argon or air at a total gas velocity of 50 mL / min for 20 min. This cycle was repeated until the system reached a steady state ethylene aromatization performance. The reactivity data are shown in Table 1.

[0076] The reactivity data shown in Table 1 show that in Comparative Example 2, the Pt / CeO2 nanoparticles have a propane conversion of 30.6% and a total olefin selectivity of 65.3% at only 500 °C, with a propylene and ethylene selectivity of 52.4% and 13.2%, respectively, with the main byproducts being methane (24.8%) and ethane (10.3%). It is noteworthy that the ethylene selectivity is even higher than that of ethane as a direct cracking byproduct, indicating that the cracking products can further undergo dehydrogenation on the Pt / CeO2 catalyst to form ethylene, which is also a potential aromatization precursor.

[0077] In Comparative Example 3, direct introduction of propylene into the Ga / (H)ZSM-5 molecular sieve catalyst produced BTX with a selectivity of about 87.88% and a propylene conversion of 89.63%. In Comparative Example 4, under the same conditions, introduction of ethylene into the reactor produced a BTX selectivity (84.7%) and conversion (79.1%) that was only slightly lower than that of propylene.

[0078] Comparative Examples 3 and 4 demonstrate that, in addition to propylene, ethylene can also be used as a precursor for the formation of BTX in the pores of Ga / (H)ZSM-5 molecular sieve catalyst. Comparative Examples 2, 3 and 4 fully demonstrate that (part of) propane is converted into propylene and ethylene on the Pt / CeO2nanoparticle catalyst and enters the pores of Ga / (H)ZSM-5 molecular sieve as an efficient intermediate for aromatization reaction, thereby further forming BTX. In addition, according to the Le Chatelier principle, the dehydrogenation reaction on the Pt / CeO2nanoparticle catalyst can also be further promoted due to the consumption of olefins by the aromatization reaction on the subsequent molecular sieve in this tandem reaction mechanism, and thus the propane conversion attributed to the Pt / CeO2nanoparticle catalyst in Examples 1 and 2 should be greater than the values obtained in Comparative Examples 3 and 4.

[0079] Table 1 Catalytic reaction performance in Examples 1-2 and Comparative Example 1

[0080]

[0081]

[0082] Figure 1 The XRD spectrum of the flame-synthesized Pt / CeO2nanoparticle catalyst in Example 1 and Example 2 is shown. The diffraction peaks shown in the spectrum are all attributed to CeO2, indicating that the Pt element on it has no obvious crystallization and has good dispersion.

[0083] Figure 2 The XRD spectrum of the composite catalyst after reacting with propane for 100 min in Example 2 is shown. The spectrum is relatively Figure 1 Only the characteristic peaks of the molecular sieve are increased, and no Pt agglomeration is observed.

[0084] Figure 3 The high-resolution transmission electron microscopy image and particle size statistical data of the flame-synthesized Pt / CeO2nanoparticle catalyst in Example 1 and Example 2 are shown, indicating that the flame-synthesized Pt / CeO2nanoparticle catalyst is a nanoparticle with a particle size of about 5-6 nm.

[0085] Figure 4 The TEM-EDS energy spectrum image of the flame-synthesized Pt / CeO2nanoparticle in Example 1 and Example 2 is shown, indicating that the Pt element has very high dispersion.

[0086] Figure 5 The in-situ CO-DRIFTS spectrum of the flame-synthesized Pt / CeO2nanoparticle catalyst in Example 1 and Example 2 is shown. The main peak at 2088 cm -1 corresponds to the bond type formed by the vertical linear combination of monatomic positively charged Pt atoms and CO.

[0087] Those skilled in the art can easily understand that the above description is only the preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A propane aromatization catalyst for use in the production of aromatic hydrocarbons by synthetic propane aromatization reaction, characterized in that: The catalyst comprises Ga / HZSM-5 formed by Ga-modified HZSM-5 molecular sieve and supported Pt nanoparticles; the mass ratio of Pt nanoparticles to Ga / HZSM-5 molecular sieve in the supported Pt nanoparticles is (0.4-1):1; The preparation method of the propane aromatization reaction catalyst comprises: (1) preparing metal Pt and a carrier precursor into a supported Pt nanoparticle precursor solution and uniformly dispersing it by ultrasonication; synthesizing the supported Pt nanoparticles by flame spray pyrolysis of the supported Pt nanoparticle precursor solution; (2) impregnating HZSM-5 molecular sieve with gallium nitrate solution until it is just wetted, standing and drying for 5 to 8 hours, calcining at a temperature of 500 to 600° C. and for a time of 2 to 5 hours to obtain the Ga / HZSM-5; and (3) uniformly mixing the Ga / HZSM-5 prepared in step (2) with the supported Pt nanoparticles prepared in step (1) to obtain the propane aromatization reaction catalyst.

2. Use of the propane aromatization catalyst according to claim 1 in producing aromatic hydrocarbons by synthetic propane aromatization reaction, characterized in that: The axial length of the catalyst per unit mass in the reactor used is greater than 200 mm / g; the reaction temperature is 450-550°C; the propane volume fraction in the feed gas is 25-50%, with an inert atmosphere as the balance gas, and the reaction space velocity is 2000-6000 mL / h / g.

3. Use of the propane aromatization catalyst according to claim 1 in producing aromatic hydrocarbons by synthetic propane aromatization reaction, characterized in that: The particle size of the supported Pt nanoparticles is between 4 and 8 nm; and the loading mass fraction of metal platinum in the supported Pt nanoparticles is between 0.1% and 2%.

4. Use of the propane aromatization catalyst according to claim 1 in producing aromatic hydrocarbons by synthetic propane aromatization reaction, characterized in that: The carrier of the supported Pt nanoparticles is one of silicon dioxide, aluminum oxide, silicon-aluminum composite oxide, molecular sieve, ceria and spinel.

5. Use of the propane aromatization catalyst according to claim 1 in producing aromatic hydrocarbons by synthetic propane aromatization reaction, characterized in that: The gallium trioxide loading mass fraction in the Ga / HZSM-5 is 1% to 3%.

6. Use of the propane aromatization catalyst according to claim 1 in producing aromatic hydrocarbons by synthetic propane aromatization reaction, characterized in that: The flame spray pyrolysis method is specifically: The supported Pt nanoparticle precursor solution is pumped from a capillary into a burner of a flame spray pyrolysis preparation system; the delivery flow rate of the supported Pt nanoparticle precursor solution is 2 to 5 mL / min, the dispersion gas flow rate is 3 to 5 L / min, the premixed gas is a mixture of methane and oxygen at a volume fraction of 1:2, and the total gas velocity is 2.25 to 4.5 L / min; the shielding gas is 5 to 10 L / min; and the supporting flame temperature formed after the premixed gas is ignited is in the range of 1800 to 3000 K.

7. Use of the propane aromatization catalyst according to claim 1 in producing aromatic hydrocarbons by synthetic propane aromatization reaction, characterized in that: In the step (1), the concentration of the supported Pt nanoparticle precursor solution is 0.2-0.5 mol / L.

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