A spherical Pt-based catalyst, its preparation method and application

Abstract

This invention discloses a spherical Pt-based catalyst, its preparation method, and its applications. The pore size distribution of the spherical Pt-based catalyst of this invention is as follows: pores with a diameter less than 2 nm account for 0.9% to 4.0% of the total pore volume, and pores with a diameter of 2-50 nm account for 95.0% to 99.1% of the total pore volume. The catalyst of this invention, when used in propane dehydrogenation, exhibits high propane conversion, propylene selectivity, and good stability.

Description

Technical Field

[0001] This invention relates to a spherical Pt-based catalyst, its preparation method and application, and particularly to a spherical Pt-based catalyst suitable for fluidized bed reactors, its preparation method and application. Background Technology

[0002] The shape and size of catalyst particles are generally determined according to the requirements of the reactor used in industrial production. Currently, there are four types of reactors commonly used in industry: fixed bed, fluidized bed (boiling bed), suspended bed, and moving bed. Fixed bed reactors commonly use spherical, cylindrical, cloverleaf, four-leaf, and sheet-like catalysts. Moving bed reactors often use large spherical catalyst particles. Fluidized bed reactors generally use smaller spherical or strip-shaped catalyst particles.

[0003] Spherical catalysts have advantages such as good flow properties, high filling coefficient, uniform fluid distribution, low resistance, and small pressure drop, and are widely used in the technology of dehydrogenation of low-carbon alkanes to produce olefins.

[0004] Currently, catalysts for the dehydrogenation of low-carbon alkanes to olefins are mainly prepared by supporting the active component Pt on a γ-Al₂O₃ support and other auxiliary agents, such as EP100222A and CN1185994A. However, since the dehydrogenation reaction is carried out at a high temperature of around 600℃, the high reaction temperature often leads to a large amount of coking on the catalyst. As the catalyst is used for a longer period of time, it is necessary to perform multiple high-temperature carbonization regeneration treatments. This causes the γ-Al₂O₃ support to easily undergo sintering and α-phase transformation, resulting in a significant decrease in the specific surface area of ​​the support, destruction of the pore structure, and consequently, aggregation of the active component, leading to a severe decrease in catalyst activity. Therefore, it is necessary to further modify the γ-Al₂O₃ support to give the catalyst higher thermal stability.

[0005] CN112973771A discloses a spherical catalyst support containing molecular sieves and alumina, its preparation, and its application. This catalyst support is prepared by precipitating inorganic aluminum salts with ammonia and acidifying them to obtain a sol. A mixed solution of ball-milled boehmite and molecular sieves, along with a sol-modifying agent, is added to the sol. The mixture is then drop-formed and aged in an oil-ammonia column, and finally washed, dried, and calcined to obtain high-strength, high-specific-surface-area composite microspheres. This method involves mixing a suspension slurry obtained by ball-milling boehmite and molecular sieves with a dilute sol and then re-gelling it, which results in uneven dispersion of the molecular sieves. Furthermore, the doping of solid molecular sieves also leads to a decrease in the support strength.

[0006] CN105478100A discloses a method for preparing silicon-containing γ-Al₂O₃ microspheres. The method involves stirring and slurrying pseudoboehmite dry adhesive powder and deionized water, acidifying with dilute nitric acid, adding urea and a predetermined amount of sodium silicate solution, stirring for 5 hours, adding kerosene and fatty alcohol polyoxyethylene ether, stirring for another 5 hours, forming microspheres by drop in an oil-ammonia column, curing the wet microspheres in ammonia water for 2 hours, filtering, washing with deionized water, drying, and calcining to obtain silicon-containing γ-Al₂O₃ microspheres. This method results in long curing times, difficult washing, and low production efficiency for the γ-Al₂O₃ microspheres.

[0007] CN104289220A discloses a method for preparing and using a high thermal stability low-carbon alkane dehydrogenation catalyst. The method for preparing the carrier involves adding an aluminum source to an alkaline aqueous solution, stirring, and continuing to add alkaline aqueous solution dropwise to adjust the pH of the mixed solution to 7–14. After filtration and washing with deionized water, dilute nitric acid is added to form a sol. A silicon source is then added, stirred, filtered, and aged for 10–48 hours. The mixture is then drop-formed, dried, and calcined to obtain γ-Al₂O₃ microspheres containing Si. Alternatively, the method involves adding an aluminum source to an alkaline aqueous solution, stirring, and continuing to add alkaline aqueous solution dropwise to adjust the pH of the mixed solution to 7–14. After filtration and washing with deionized water, dilute nitric acid is added to form a sol. This process is stirred, filtered, and aged for 10–48 hours. The mixture is then drop-formed, dried, and calcined to obtain γ-Al₂O₃ microspheres. These microspheres are then immersed in an aqueous or ethanolic solution of the silicon source at 60–120°C for 2–6 hours, followed by drying and calcination to obtain γ-Al₂O₃ microspheres containing Si. The disadvantages of this method are its long preparation cycle, complex process, requirement for pH control, and inability to guarantee product consistency. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a spherical Pt-based catalyst, its preparation method, and its applications. This spherical Pt-based catalyst exhibits good sphericity, high crushing strength, large pore volume and size, uniform Pt loading, and is environmentally friendly and odorless. When used in propane dehydrogenation reactions, it demonstrates high propane conversion, propylene selectivity, and good stability.

[0009] The first aspect of the present invention provides a spherical Pt-based catalyst, wherein the pore size distribution of the catalyst is as follows: the pore volume of pores with a pore size of less than 2 nm accounts for 0.9% to 4.0% of the total pore volume, and the pore volume of pores with a pore size of 2-50 nm accounts for 95.0% to 99.1% of the total pore volume, preferably 96.0% to 98.0%.

[0010] Furthermore, the specific surface area of ​​the catalyst is 70–116 m². 2 / g, with a pore volume of 0.60~0.75mL / g.

[0011] Furthermore, the average diameter of the catalyst particles is 1.6–1.8 mm.

[0012] Furthermore, the catalyst has an average pore size of 14–17 nm.

[0013] Furthermore, the crushing strength of the catalyst is 72-81 N / particle.

[0014] Furthermore, the sphericity of the catalyst is 95.6% to 99.9%.

[0015] Furthermore, in the catalyst, based on the mass of the catalyst, the content of Pt is 0.2% to 1.0% by mass fraction, the content of Sn is 0.09% to 0.9%, and the content of alumina is 98.1% to 99.8%.

[0016] A second aspect of the present invention provides a method for preparing the above-mentioned spherical Pt-based catalyst, comprising:

[0017] Aluminum hydroxide sol is mixed with a Pt-containing aqueous solution, and the resulting mixture is dripped into a four-layer oil-ammonia-oil-water mixing column to form a spherical Pt-based catalyst after drying and calcination. The four-layer oil-ammonia-oil-water mixing column consists of four layers arranged from top to bottom: the first layer is the first oil layer, the second layer is the ammonia layer, the third layer is the second oil layer, and the fourth layer is the tin-containing water layer.

[0018] Further, the tin-containing aqueous layer comprises a tin salt and hydrochloric acid, wherein the tin salt is at least one of stannous chloride or stannous tetrachloride, preferably stannous chloride. Further, in the tin-containing aqueous layer, the concentration of the tin salt is 0.5 wt% to 1.1 wt%, preferably 0.6 wt% to 0.8 wt%, and the concentration of the hydrochloric acid is 5 wt% to 8 wt%.

[0019] Furthermore, the aluminum hydroxide sol contains 15 wt% to 26 wt% aluminum oxide.

[0020] Further, the preparation method of the aluminum hydroxide sol includes: mixing aluminum hydroxide with water to obtain a slurry, adding a gelling agent, and stirring evenly to obtain aluminum hydroxide sol. Further, the gelling agent is selected from one or more inorganic acids (such as nitric acid) and organic acids (such as acetic acid and citric acid), preferably nitric acid. When the gelling agent contains an inorganic acid, the mass concentration of the inorganic acid is 30% to 50%. When the gelling agent contains an organic acid, the mass concentration of the organic acid is 30% to 50%. Further, the amount of gelling agent added, based on acid, is 1 wt% to 10 wt% of the mass of aluminum hydroxide based on alumina, preferably 2 wt% to 8 wt%. Further, the aluminum hydroxide is preferably aqueous aluminum hydroxide, such as wet aluminum hydroxide material. Preferably, the water content in the aluminum hydroxide is 17 wt% to 25 wt%. Preferably, the properties of the aluminum hydroxide after calcination are as follows: specific surface area of ​​110 to 201 m². 2 The aluminum hydroxide has a pore volume of 0.8–2.0 mL / g and an average pore size of 15–17 nm. The calcination conditions are as follows: temperature 600–850℃, time 2–12 h, and an oxygen-containing atmosphere such as air. The aluminum hydroxide can be commercially available or prepared using conventional methods. Preferably, the aluminum hydroxide is a hydrated macroporous pseudoboehmite with a water content of 19 wt%–23 wt%.

[0021] Further, the platinum-containing compound in the Pt-containing aqueous solution is one or more of platinum chloride (PtCl4) and chloroplatinic acid (H2PtCl6), preferably chloroplatinic acid. The concentration of the platinum-containing compound in the Pt-containing aqueous solution is 2 wt% to 6 wt%. The amount of the Pt-containing aqueous solution added is 8% to 40% of the aluminum hydroxide sol by mass of aluminum oxide, preferably 15% to 30%.

[0022] Furthermore, the four-layer oil-ammonia-oil-water mixture column is a straight column, preferably a cylindrical column.

[0023] Furthermore, in the four-layer oil-ammonia-oil-water mixture column, the first layer is a first oil layer, selected from one or more of white oil or diesel oil, preferably white oil, wherein the kinematic viscosity of the white oil at 40°C is 20-40 mmHg. 2 / s, preferably 25-35mm 2 / s. The height of the first layer is 30% to 50% of the height of the second layer.

[0024] Furthermore, in the four-layer oil-ammonia-oil-water mixture column, the second layer is an ammonia layer, and the concentration of the ammonia is 20wt% to 28wt%, preferably 22wt% to 26wt%.

[0025] Furthermore, in the aforementioned four-layer oil-ammonia-oil-water mixture column, the third layer is the second oil layer, i.e., the liquid-sealed oil layer, with a density between the second ammonia-water layer and the fourth tin-containing water layer, and a kinematic viscosity of 60 mmHg at 40°C. 2 The oil is one or more vegetable oils with a viscosity of less than 1 / s, preferably a mixture of castor oil and soybean oil, wherein the volume ratio of castor oil to soybean oil is preferably 1 / 4 to 1 / 6. The castor oil has a kinematic viscosity of 500 to 650 mm³ / s at 40°C. 2 / s, preferably 570–600 mm 2 / s; the kinematic viscosity of the soybean oil at 40°C is 10–25 mm. 2 / s, preferably 13-17mm 2 / s. The height of the third layer is 30% to 50% of the height of the second layer, preferably 35% to 45%.

[0026] Furthermore, in the four-layer oil-ammonia-oil-water mixed column, the fourth layer is a tin-containing aqueous layer, which is prepared by dissolving tin salt in hydrochloric acid. The height of the fourth layer is 1.0 to 2.0 times the height of the second layer, preferably 1.2 to 1.5 times. During the preparation of the spherical Pt-based catalyst, when the tin salt concentration is less than 0.5 wt%, tin salt is added via an external circulation pump to bring the concentration to the above requirement.

[0027] Furthermore, the preparation method of the oil-ammonia-oil-water four-layer mixed column includes:

[0028] (1) Pour the material required for the fourth layer into a columnar container (preferably an acrylic container) and ensure that the solution is uniform;

[0029] (2) Slowly add the material required for the third layer onto the material of the fourth layer in step (1) and stabilize for 20-35 minutes;

[0030] (3) Slowly add the required material for the second layer onto the material for the third layer in step (2);

[0031] (4) Slowly add the required material for the first layer onto the material for the second layer in step (3) to obtain a four-layer mixed column of oil-ammonia-oil-water. Preferably, during the addition of the required material for the first layer, a peristaltic pump is used to slowly circulate the material up and down above the interface between the first and second layers to reduce the surface tension at the interface between the first and second layers. Then, let it stand for 30 to 60 minutes to stabilize. This ensures that the aluminum hydroxide sol can quickly pass through the contact interface between the first and second layers, preventing stagnation and tailing, which would affect the roundness.

[0032] Furthermore, the spherical Pt-based catalyst is formed in a four-layer mixed column of oil-ammonia-oil-water, wherein a mixture of aluminum hydroxide sol and Pt-containing aqueous solution is dropped into the four-layer mixed column of oil-ammonia-oil-water, wherein the inner diameter of the dropper used is 1.0 mm to 1.6 mm.

[0033] Furthermore, the residence time of the mixture of aluminum hydroxide sol and Pt-containing aqueous solution in the four-layer oil-ammonia-oil-water mixed column is 5-18s, preferably 7-11s.

[0034] Furthermore, the drying temperature is 100℃~150℃, and the drying time is 6~10 hours; the calcination temperature is 750℃~950℃, and the calcination time is 1~4 hours.

[0035] A third aspect of the present invention provides the application of the above-mentioned catalyst in the propane dehydrogenation reaction.

[0036] Furthermore, the application includes: a propane feedstock being contacted with the catalyst to undergo a dehydrogenation reaction to obtain the product propylene.

[0037] Furthermore, the propane dehydrogenation catalyst needs to be reduced before use. The catalyst precursor is reduced under a reducing atmosphere. The preferred reducing atmosphere is H2, the reduction temperature is 450–600°C, and the reduction time is 1–3 hours.

[0038] Furthermore, the preferred conditions for the propane dehydrogenation reaction are as follows: reaction temperature of 500–600 °C, reaction pressure of 0–1 MPa, and volume hourly space velocity of 50–200 h⁻¹. -1 .

[0039] Compared with the prior art, the advantages of the present invention are as follows:

[0040] (1) This invention employs a one-step method to synthesize spherical Pt-based catalysts. A Pt-containing aqueous solution is added to the aluminum hydroxide sol, allowing the metallic Pt to be uniformly dispersed in the alumina, while also expanding the pores. The four-layer oil-ammonia-oil-water mixed column differs from a two-layer oil-ammonia column or a hot oil column by adding a third oil layer as a liquid-sealing oil layer and a fourth tin-containing water layer. This allows the sol to quickly enter the third and fourth tin-containing water layers after passing through the second ammonia layer, rapidly reducing the pH to neutral. This prevents the spheres from easily breaking or shrinking due to the evaporation of surface ammonia during drying, significantly increasing the catalyst particle size and mechanical strength. Simultaneously, it ensures sufficient contact between the metal and the support, resulting in a more uniform loading. Furthermore, the introduction of tin into the fourth water column allows for rapid adsorption of Sn as the spherical sol passes through the tin-containing water column, given the negative surface potential of the spherical sol. 2+The method involves introducing metal elements into the support in a one-step process, followed by calcination to obtain Sn-doped spherical alumina. This approach is not only simple to operate, but also avoids pore blockage due to the adsorption primarily occurring on the outer surface. Furthermore, the enhanced interaction between Sn and alumina during solidification improves the stability and dispersion of the loaded noble metal, thereby increasing catalyst activity. During preparation, the rapid decrease in pH value on the surface of the sol-gel microspheres leads to a rapid decrease in surface hydrophobicity, a significant increase in interparticle interaction forces, and a shortening of interparticle distances. This results in partial collapse of the original structure, leading to an increase in mesoporous structures within the 2–50 nm range on the support. The proportion of mesopores can be adjusted by regulating the hydrochloric acid concentration in the fourth tin-containing aqueous layer.

[0041] (2) The preparation process of the present invention is environmentally friendly. In the traditional oil-ammonia column pelletizing process, the volatilization of ammonia water causes serious environmental pollution problems and subsequent pollutant emissions. The present invention separates the second ammonia water layer and the fourth tin-containing water layer with the second oil layer, so that the ammonia water layer is sealed on the fourth water layer, which can extend the service life and avoid the product from carrying out ammonia water and causing environmental pollution. After long-term use, the tin-containing water layer can be replaced to ensure the liquid sealing effect. It is simple to operate in industry and saves costs.

[0042] (3) The spherical Pt-based catalyst obtained by the preparation method of the present invention has a high propane conversion rate and propylene selectivity in the propane dehydrogenation to propylene reaction. The large pore size and large pore volume catalyst can avoid carbon buildup after long-term operation and has good stability and good reaction performance. Detailed Implementation

[0043] The following examples further illustrate the spherical Pt-based catalyst, its preparation method, and its application effects in this invention. These examples are implemented based on the technical solution of this invention, providing detailed implementation methods and specific operating procedures. However, the scope of protection of this invention is not limited to the following examples.

[0044] Unless otherwise specified, the experimental methods used in the following examples are conventional methods in the art. Unless otherwise specified, the experimental materials used in the following examples were purchased from conventional biochemical reagent stores.

[0045] In this invention, the nitrogen adsorption-desorption curves of the samples were tested at -196℃ using a Micromeritics ASAP2020 fully automated physical adsorption instrument to determine the specific surface area, pore volume, and pore size distribution.

[0046] In this invention, the crushing strength is tested using a ZQJ-Ⅲ intelligent particle strength tester manufactured by Dalian Zhiqu Testing Machine Factory, which measures the average value of crushing ten spherical catalyst particles.

[0047] In this invention, the roundness is tested using an electron microscope from Olympus Corporation, and the average value is calculated after testing 20 samples.

[0048] Example 1

[0049] Take 250g of macroporous pseudoboehmite filter cake with a moisture content of 22wt% (calcined at 600℃ for 3h in air atmosphere, with the following properties: pore volume 0.87ml / g, specific surface area 175m²). 2 / g (average pore size 16nm), add deionized water and stir to make a uniform slurry, then add 26g of 45% nitric acid solution for gelation, and finally prepare a pseudoboehmite sol with an alumina content of 20% by mass; take 300g of the above sol (alumina content of 20wt%), add 12g of 3% chloroplatinic acid solution, stir to make a uniform sol mixture;

[0050] Using a dropper with an inner diameter of 1.2 mm (kinematic viscosity 32 mm at 40°C) 2 The above sol mixture was added dropwise to a four-layer column (cylinder) consisting of white oil, 25wt% ammonia, mixed oil, and tin-containing aqueous solution, and the residence time in the four-layer column was 8 seconds. The amount of white oil added was 35% of the volume of ammonia, the amount of mixed oil added was 38% of the volume of ammonia, and the amount of the tin-containing aqueous layer was 1.3 times the volume of ammonia. The mixed oil had a kinematic viscosity of 580 mmHg at 40°C. 2 Castor oil with a kinematic viscosity of 15 mm / s 2 The catalyst is a mixture of soybean oil and tin-containing aqueous solution, with a volume ratio of 1:5. The concentration of stannous chloride in the aqueous solution is 0.7 wt%, and the concentration of hydrochloric acid is 6 wt%. During the preparation of the tin-containing spherical alumina support, when the stannous chloride concentration is less than 0.5 wt%, an external circulation pump is used to maintain the stannous chloride concentration in the aqueous solution at the initial concentration. The catalyst is then dried at 130°C for 8 hours and calcined at 800°C for 3 hours to obtain the spherical Pt-based catalyst A of this invention. The physicochemical properties of the obtained catalyst are shown in Table 1, and the composition is shown in Table 3.

[0051] Example 2

[0052] Compared with Example 1, the difference lies in that the concentration of hydrochloric acid in the fourth layer of the four-layer mixed column is changed to 8 wt%, and the concentration of stannous chloride is changed to 0.8 wt%, thus obtaining the spherical Pt-based catalyst B of the present invention. The physicochemical properties of the obtained catalyst are shown in Table 1, and the composition is shown in Table 3.

[0053] Example 3

[0054] Compared with Example 1, the difference lies in that the concentration of chloroplatinic acid used was changed to 6%, resulting in the spherical Pt-based catalyst C of this invention. The physicochemical properties of the obtained catalyst are shown in Table 1, and the composition is shown in Table 3.

[0055] Example 4

[0056] The difference compared to Example 1 is that the white oil in the four-layer mixing column is changed to have a kinematic viscosity of 23 mmHg at 40°C. 2 The spherical Pt-based catalyst D of this invention was obtained by mixing white oil ( / s), changing the ammonia concentration to 21wt%, and changing the volume ratio of castor oil to soybean oil to 1:4. The physicochemical properties of the obtained catalyst are shown in Table 1, and the composition is shown in Table 3.

[0057] Example 5

[0058] Compared with Example 1, the difference lies in that the white oil in the four-layer mixing column is replaced with a mixture of diesel and white oil in a mixing mass ratio of 1:1, and the ammonia concentration is changed to 28 wt%, thus obtaining the spherical Pt-based catalyst E of the present invention. The physicochemical properties of the obtained catalyst are shown in Table 1, and the composition is shown in Table 3.

[0059] Example 6

[0060] The difference from Example 1 is that the concentration of chloroplatinic acid was changed to 6%, and the white oil was changed to have a kinematic viscosity of 28 mm at 40°C. 2 The white oil was mixed with ammonia concentration of 23 wt%, and the volume ratio of castor oil to soybean oil was changed to 1:4 to obtain the spherical Pt-based catalyst F of this invention. The physicochemical properties of the obtained catalyst are shown in Table 1, and the composition is shown in Table 3.

[0061] Example 7

[0062] Compared with Example 1, the difference is that the amount of white oil added is 42% of the volume of ammonia water, the amount of mixed oil added is 32% of the volume of ammonia water, and the amount of tin-containing aqueous layer added is 1.6 times the volume of ammonia water, thus obtaining the spherical Pt-based catalyst G of the present invention. The analysis results are shown in Table 1.

[0063] Comparative Example 1

[0064] The synthesis steps for the sol mixture are the same as in Example 1.

[0065] Compared with Example 1, the difference is that the four-layer oil-ammonia-oil-water mixed column is replaced with a two-layer oil-ammonia column, and the upper layer has a kinematic viscosity of 32 mmHg at 40°C. 2 The catalyst consists of a layer of white oil (approximately 0.5 g / s) and a lower layer of ammonia solution (25 wt%). The amount of white oil added is 25% of the volume of the ammonia solution. The remaining molding steps remain unchanged. After calcination, 100 g of the support is saturated and impregnated in an aqueous solution containing 0.4 g of tin tetrachloride for 30 min. It is then dried in a 90°C oven for 10 h and calcined in a muffle furnace at 600°C for 4 h to obtain the comparative spherical Pt-based catalyst H of this invention. The physicochemical properties of the obtained catalyst are shown in Table 2, and the composition is shown in Table 4.

[0066] Comparative Example 2

[0067] The method for synthesizing the sol mixture is the same as in Example 1.

[0068] Compared with Example 1, the difference is that only the first white oil column in the four-layer oil-ammonia-oil-water mixed column was removed, and a three-layer column was used to form a sphere, thus obtaining the comparative spherical Pt-based catalyst I of this invention. The physicochemical properties of the obtained catalyst are shown in Table 2, and the composition is shown in Table 4.

[0069] Comparative Example 3

[0070] The method for synthesizing the sol mixture is the same as in Example 1.

[0071] Compared with Example 1, the difference is that only the fourth tin-containing water column was removed. After calcination, 100g of the support was saturated and impregnated in an aqueous solution containing 0.4g of tin tetrachloride for 30min. Then, it was dried in a 90℃ drying oven for 10h and calcined in a muffle furnace at 600℃ for 4h to obtain the comparative spherical Pt-based catalyst J of this invention. The physicochemical properties of the obtained catalyst are shown in Table 2, and the composition is shown in Table 4.

[0072] Comparative Example 4

[0073] The method for synthesizing the sol mixture is the same as in Example 1.

[0074] Compared with Example 1, the difference is that only the third layer of castor oil and soybean oil mixture in the four-layer oil-ammonia-oil-water mixed column was removed to obtain the comparative spherical Pt-based catalyst K of this invention. The physicochemical properties of the obtained catalyst are shown in Table 2, and the composition is shown in Table 4.

[0075] Comparative Example 5

[0076] The method for synthesizing the sol mixture is the same as in Example 1.

[0077] Compared with Example 1, the difference is that the amount of white oil added is 16% of the volume of ammonia water, the amount of mixed oil added is 20% of the volume of ammonia water, and the amount of tin-containing water layer added is 0.4 times the volume of ammonia water, thus obtaining the comparative spherical Pt-based catalyst L of the present invention. The analysis results are shown in Table 1.

[0078] Table 1. Physicochemical properties of the spherical Pt-based catalysts obtained in each example.

[0079] Catalyst number A B C D E F G Average particle diameter, mm 1.79 1.76 1.77 1.79 1.73 1.76 1.74 <![CDATA[Specific surface area, m 2 / g]]> 95 92 96 97 97 98 98 Pore ​​volume, mL / g 0.671 0.675 0.670 0.661 0.660 0.670 0.658 Aperture distribution, % <2nm 2.6 2.5 2.6 2.9 2.7 2.6 2.6 2-50nm 97.1 97.3 97.2 97.0 97.1 97.3 97.3 >50nm 0.3 0.2 0.2 0.1 0.2 0.1 0.1 Average pore size, nm 16.4 16.7 16.2 15.4 15.2 16.3 15.3 Crushing strength, N / particle 79 78 76 76 75 74 75 Roundness, % 97.2 97.3 97.2 96.9 96.7 96.8 96.8

[0080] Table 2. Physicochemical properties of the spherical Pt-based catalysts obtained in each comparative example.

[0081] Catalyst number H I J K L Average particle diameter, mm 1.72 1.60 1.71 1.62 1.61 <![CDATA[Specific surface area, m 2 / g]]> 108 120 99 105 99 Pore ​​volume, mL / g 0.460 0.490 0.494 0.509 0.586 Aperture distribution, % <2nm 6.3 6.4 7.2 6.4 6.2 2-50nm 93.5 93.4 92.7 93.6 93.6 >50nm 0.2 0.2 0.1 - 0.2 Average pore size, nm 14.3 14.6 12.0 11.3 13.5 Crushing strength, N / particle 52 39 38 46 49 Roundness, % 94.4 93.7 94.6 92.5 94.5

[0082] Table 3 Composition of catalysts in each embodiment

[0083] Catalyst number A B C D E F G Alumina (wt%) 99.5 99.4 99.3 99.5 99.5 99.3 99.5 Pt (wt%) 0.3 0.3 0.5 0.3 0.3 0.5 0.3 Sn(wt%) 0.2 0.3 0.2 0.2 0.2 0.2 0.2

[0084] Table 4. Composition of catalysts in each comparative example

[0085] Catalyst number H I J K L Alumina (wt%) 99.5 99.5 99.6 99.6 99.6 Pt (wt%) 0.3 0.3 0.2 0.3 0.3 Sn(wt%) 0.2 0.2 0.2 0.1 0.1

[0086] Catalyst evaluation

[0087] Take 5g of the above catalyst and reduce it at 520℃ for 1.5h under a hydrogen atmosphere. Then, load it into a fixed-bed reactor for propane dehydrogenation activity evaluation: reaction temperature 550℃, atmospheric pressure, volume hourly space velocity 150h⁻¹. -1 The results of propane dehydrogenation are listed in Table 5-8.

[0088] Table 5 Evaluation results of the catalysts in each example for propane dehydrogenation

[0089] Catalyst number A B C D E F G Propane conversion rate (%) after 1 hour of reaction 36.5 36.4 36.2 35.2 35.4 36.3 34.7 propylene selectivity (%) after 1 hour of reaction 90.1 89.6 89.5 88.5 88.0 89.4 88.3

[0090] Table 6 Evaluation results of the comparative catalysts for propane dehydrogenation

[0091] Catalyst number H I J K L Propane conversion rate (%) after 1 hour of reaction 33.1 33.3 30.4 33.4 33.0 propylene selectivity (%) after 1 hour of reaction 87.2 86.2 84.3 86.7 85.2

[0092] Table 7. Stability evaluation results of the catalysts in each example for propane dehydrogenation.

[0093] Catalyst number A B C D E F G Propane conversion rate (%) after 5 hours of reaction 30.2 29.9 29.4 28.1 28.2 29.2 28.0 propylene selectivity (%) after 5 hours of reaction 80.2 79.5 79.6 75.9 76.4 77.7 75.2

[0094] Table 8. Stability evaluation results of each comparative catalyst for propane dehydrogenation.

[0095] Catalyst number H I J K L Propane conversion rate (%) after 5 hours of reaction 20.1 19.6 22.4 24.7 23.6 propylene selectivity (%) after 5 hours of reaction 68.4 69.7 70.1 68.5 69.2

[0096] The specific embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combining the various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A spherical Pt-based catalyst, wherein a pore size distribution of the catalyst is as follows: a pore volume of pores with a pore size less than 2 nm accounts for 0.9%-4.0% of a total pore volume, and a pore volume of pores with a pore size of 2-50 nm accounts for 95.0%-99.1% of the total pore volume; and a content of Pt is 0.2%-1.0% by mass, a content of Sn is 0.09%-0.9% by mass, and a content of alumina is 98.1%-99.8% by mass in the catalyst based on a mass of the catalyst. A preparation method of the catalyst, comprising: mixing an aluminum hydroxide sol with a Pt-containing aqueous solution, dropping the obtained mixture into an oil-ammonia water-oil-water four-layer mixed column to form a shape, drying and calcining to obtain the spherical Pt-based catalyst; and the oil-ammonia water-oil-water four-layer mixed column is sequentially provided with four layers from top to bottom, the first layer is a first oil layer, the second layer is an ammonia water layer, the third layer is a second oil layer, and the fourth layer is a tin-containing water layer. The first oil layer is selected from one or more of white oil or diesel oil; the second oil layer is a mixed oil of castor oil and soybean oil, wherein a volume ratio of the castor oil to the soybean oil is 1 / 4-1 / 6; a density of the second oil layer is between that of the second ammonia water layer and the fourth water layer; and the tin-containing water layer comprises a tin salt and hydrochloric acid. A height of the first layer is 30%-50% of a height of the second layer; a height of the third layer is 30%-50% of the height of the second layer; and a height of the fourth layer is 1.0-2.0 times the height of the second layer.

2. The catalyst of claim 1, wherein: In the catalyst, a pore volume of pores with a pore size of 2-50 nm accounts for 96%-98% of a total pore volume.

3. The catalyst of claim 1, wherein: The specific surface area of the catalyst is 70-116 m 2 / g, and the pore volume is 0.60-0.75 mL / g; And / or, an average diameter of the catalyst is 1.6-1.8 mm; And / or, an average pore size of the catalyst is 14-17 nm; And / or, a crushing strength of the catalyst is 72-81 N / particle; And / or, a true circularity of the catalyst is 95.6%-99.9%. 4.A preparation method of the catalyst according to any one of claims 1-3, comprising: mixing an aluminum hydroxide sol with a Pt-containing aqueous solution, dropping the obtained mixture into an oil-ammonia water-oil-water four-layer mixed column to form a shape, drying and calcining to obtain the spherical Pt-based catalyst; and the oil-ammonia water-oil-water four-layer mixed column is sequentially provided with four layers from top to bottom, the first layer is a first oil layer, the second layer is an ammonia water layer, the third layer is a second oil layer, and the fourth layer is a tin-containing water layer.

5. The method of claim 4, wherein: The platinum compound in the Pt-containing aqueous solution is one or more of platinum chloride and chloroplatinic acid; And / or, a concentration of the platinum compound in the Pt-containing aqueous solution is 2wt%-6wt%; And / or, an addition amount of the Pt-containing aqueous solution is 8%-40% of a mass of the aluminum hydroxide sol in terms of alumina.

6. The method of claim 5, wherein: The platinum compound in the Pt-containing aqueous solution is chloroplatinic acid; And / or, the addition amount of the Pt-containing aqueous solution is 15%-30% of the mass of the aluminum hydroxide sol in terms of alumina.

7. The method of claim 4, wherein: The oil-ammonia water-oil-water four-layer mixed column, the first oil layer is white oil; the white oil has a kinematic viscosity of 20-40 mm 2 / s at 40°C.

8. The method of claim 7, wherein: The white oil has a kinematic viscosity at 40°C of 25 to 35 mm 2 / s.

9. The method of claim 4, wherein: In the oil-ammonia water-oil-water four-layer mixed column, a concentration of the ammonia water layer is 20wt%-28wt%.

10. The method of claim 9, wherein: The concentration of the ammonia water layer is 22wt%-26wt%.

11. The method of claim 4, wherein: The oil-ammonia water-oil-water four-layer mixed column, the kinematic viscosity of the castor oil at 40℃ is 500~650mm 2 / s; the kinematic viscosity of the soybean oil at 40℃ is 10~25mm 2 / s.

12. The method of claim 11, wherein: The castor oil has a kinematic viscosity at 40°C of 570-600 mm 2 / s; and the soybean oil has a kinematic viscosity at 40°C of 13-17 mm 2 / s.

13. The method of claim 4, wherein: In the oil-ammonia water-oil-water four-layer mixed column, the tin salt in the tin-containing water layer is at least one of stannous chloride and tin tetrachloride; And / or, the tin salt concentration in the tin-containing water layer is 0.5wt%-1.1wt%, and the hydrochloric acid concentration is 5wt%-8wt%.

14. The method of claim 13, wherein: The tin salt is stannous chloride; and / or, the tin salt concentration is 0.6wt%-0.8wt%.

15. The method of claim 4, wherein: The height of the third layer is 35%-45% of the height of the second layer. And / or, the height of the fourth layer is 1.2-1.5 times of the height of the second layer.

16. The use of the catalyst according to any one of claims 1-3 in the dehydrogenation of propane.

17. Use according to claim 16, characterized in that: The catalyst needs to be reduced before use.

18. The use according to claim 17, characterized in that: The reducing atmosphere is H2, the reducing temperature is 450-600℃, and the reducing time is 1-3h.

19. The use according to claim 17, characterized in that: The reaction conditions are as follows: the reaction temperature is 500-600℃, the reaction pressure is 0-1 MPa, the space velocity is 0.5-5 h -1 , and the hydrogen / hydrocarbon molar ratio is 0.5-3.0.