Pt-based catalyst, preparation and application thereof

Abstract

The application discloses a Pt-based catalyst and a preparation and application thereof. The preparation method of the Pt-based catalyst comprises the following steps: (1) mixing an aluminum hydroxide sol with an organic Pt salt solution, dropping the obtained mixture into an oil-ammonia water-oil-water four-layer mixed column to form a spherical Pt-based catalyst precursor, and drying and calcining the spherical Pt-based catalyst precursor to obtain the Pt-based catalyst precursor; and (2) impregnating the precursor obtained in the step (1) with an impregnation solution containing Pt, and drying and calcining the impregnation solution to obtain the Pt-based catalyst. The catalyst is applied to a propane dehydrogenation reaction, and has high propane conversion rate and propylene selectivity.

Description

TECHNICAL FIELD

[0001] The present application relates to a Pt-based catalyst and its preparation and application, in particular to a Pt-based catalyst suitable for a boiling bed and its preparation and application. BACKGROUND

[0002] The shape and size of the 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. The fixed bed reactor often uses spherical, cylindrical strip, three-leaf clover, four-leaf clover and sheet-shaped catalysts. The moving bed reactor often uses large particle spherical catalysts. The fluidized bed reactor generally uses small particle spherical or strip-shaped catalysts.

[0003] Spherical catalysts have good flow performance and high packing factor, 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, the catalyst for dehydrogenation of low-carbon alkanes to produce olefins is mainly prepared by loading active components Pt and other additives on a γ-Al2O3 carrier, such as EP100222A, CN1185994A, etc. However, since the dehydrogenation reaction is carried out at a high temperature of about 600℃, the high reaction temperature often causes a large amount of carbon deposition on the catalyst. As the use time of the catalyst increases, the catalyst needs to be treated by high-temperature carbon burning and regeneration multiple times, which causes the γ-Al2O3 carrier to easily sinter and α-phase change, greatly reduces the specific surface area of the carrier, destroys the pore structure, and further causes the active components of the catalyst to aggregate, resulting in a serious decrease in the activity of the catalyst. Therefore, it is necessary to further modify the γ-Al2O3 carrier to make the catalyst have high thermal stability.

[0005] CN112973771A discloses a spherical catalyst carrier containing molecular sieve and alumina and its preparation and application. The catalyst carrier is prepared by precipitating an inorganic aluminum salt with ammonia water and acidifying to obtain a sol, adding a mixed solution of ball-milled pseudoboehmite and molecular sieve and a sol modification additive to the sol, then drop-sphere forming and aging in an oil ammonia column, and finally washing, drying and calcining to obtain a high-strength large-specific-surface-area composite pellet. This method is to mix the suspension slurry of the ball-milled pseudoboehmite and molecular sieve with the dilute sol again, which is gelatinized, and has the disadvantage of uneven dispersion of the molecular sieve. At the same time, the doping of solid molecular sieve also causes the strength of the carrier to decrease.

[0006] CN105478100A discloses a method for preparing Si-containing γ-Al2O3 pellets. The method is to stir and slurry pseudo-boehmite dry gel powder and deionized water, acidify by adding dilute nitric acid, then add urea and a predetermined amount of sodium silicate solution, stir for 5 hours, add kerosene and fatty alcohol polyoxyethylene ether and stir for 5 hours, drop ball forming in an oil-ammonia column, wet ball solidification in ammonia water for 2 hours, then filter, rinse with deionized water, dry, and calcine to obtain Si-containing γ-Al2O3 pellets. The method has long solidification time, difficult washing, and low production efficiency.

[0007] CN104289220A discloses a method for preparing and use of a high-thermal-stability low-carbon alkane dehydrogenation catalyst. The carrier preparation method is to add an aluminum source to an alkaline aqueous solution, stir, continue to add an alkaline aqueous solution to adjust the pH of the mixed solution to 7-14, filter, wash with deionized water, then add dilute nitric acid to form a sol, add a silicon source, stir, filter, age for 10-48 hours, drop ball forming, then dry and calcine to obtain Si-containing γ-Al2O3 pellets; or add an aluminum source to an alkaline aqueous solution, stir, continue to add an alkaline aqueous solution to adjust the pH of the mixed solution to 7-14, filter, wash with deionized water, then add dilute nitric acid to form a sol, stir, filter, age for 10-48 hours, drop ball forming, then dry and calcine to obtain γ-Al2O3 pellets, then immerse the γ-Al2O3 pellets in a silicon source aqueous solution or ethanol solution at 60-120℃ for 2-6 hours, then dry and calcine to obtain Si-containing γ-Al2O3 pellets. The method has long preparation period, complex process, and pH value needs to be adjusted, and cannot guarantee product consistency. SUMMARY

[0008] In view of the deficiencies of the prior art, the present application provides a Pt-based catalyst and its preparation and application. The catalyst prepared by the method has good roundness, high crushing strength, large pore volume and pore size, large Pt loading, and no odor, and has high propane conversion rate and propylene selectivity when applied to propane dehydrogenation reaction.

[0009] The first aspect of the present application provides a method for preparing a Pt-based catalyst, comprising:

[0010] (1) mixing an aluminum hydroxide sol with an organic Pt salt solution, dropping the obtained mixture into an oil-ammonia water-oil-water four-layer mixed column for forming, drying and calcining to obtain a spherical Pt-based catalyst precursor;

[0011] (2) impregnating the Pt-based catalyst precursor obtained in step (1) with a Pt-containing impregnation solution, drying and calcining to obtain a Pt-based catalyst.

[0012] Further, the alumina content of the aluminum hydroxide sol is 15wt% to 26wt%.

[0013] Further, the method for preparing the aluminum hydroxide sol comprises: mixing aluminum hydroxide with water to obtain a slurry, and adding a peptizing agent to obtain the aluminum hydroxide sol after uniform stirring. Further, the peptizing agent is selected from one or more of inorganic acids (such as nitric acid) and organic acids (such as acetic acid, citric acid), and is preferably nitric acid. When the peptizing agent contains an inorganic acid, the mass concentration of the inorganic acid is 30% to 50%. When the peptizing agent contains an organic acid, the mass concentration of the organic acid is 30% to 50%. Further, the addition amount of the peptizing agent is 1wt% to 10wt% of the mass of the aluminum hydroxide in terms of acid, and is preferably 2wt% to 8wt%. Further, the aluminum hydroxide is preferably hydrous aluminum hydroxide, such as hydrous aluminum hydroxide wet material. Preferably, the water content in the aluminum hydroxide is 17wt% to 25wt%. Preferably, the properties of the aluminum hydroxide after calcination are as follows: the specific surface area is 110 to 201m 2 / g, the pore volume is 0.8 to 2.0mL / g, and the average pore size is 15 to 17nm. The calcination conditions are as follows: the temperature is 600 to 850℃, the time is 2 to 12h, and the oxygen-containing atmosphere is air. The aluminum hydroxide can be commercially available or prepared by a conventional method. The aluminum hydroxide is preferably hydrous large-pore pseudoboehmite, and the water content is 19wt% to 23wt%.

[0014] Further, the organic Pt salt in the organic Pt salt solution is one or more of platinum acetylacetonate and platinum tetraphenylphosphine, and is preferably platinum acetylacetonate. The solvent used is preferably acetone. Further, the concentration of the organic Pt salt in the organic Pt salt solution is 1.0wt% to 1.9wt%. The addition amount of the organic Pt salt solution is 9% to 11% of the mass of the aluminum hydroxide sol in terms of alumina.

[0015] Further, the organic Pt salt solution contains stannous chloride. Preferably, the concentration of stannous chloride in the organic Pt salt solution is 0.4wt% to 11wt%.

[0016] Further, the oil-ammonia water-oil-water four-layer mixed column is a straight column, and is preferably a cylindrical column.

[0017] Further, the oil-ammonia water-oil-water four-layer mixed column is a straight column, and is preferably a cylindrical column.

[0018] Further, in the oil-ammonia water-oil-water four-layer mixed column, the first layer is a first oil layer, which is selected from one or more of white oil or diesel oil, preferably white oil, the kinematic viscosity of the white oil at 40°C is 20-40 mm 2 / s, preferably 25-35 mm 2 / s. The height of the first layer is 30%-50% of the height of the second layer.

[0019] Further, in the oil-ammonia water-oil-water four-layer mixed column, the second layer is an ammonia water layer, the concentration of the ammonia water is 20wt%-28wt%, preferably 22wt%-26wt%.

[0020] Further, in the oil-ammonia water-oil-water four-layer mixed column, the third layer is a second oil layer, i.e., a liquid seal oil layer, which is one or more of plant oil with a kinematic viscosity of 60 mm 2 / s or less at 40°C, preferably a mixed oil of castor oil and soybean oil with a volume ratio of 1 / 4-1 / 6. The kinematic viscosity of the castor oil at 40°C is 500-650 mm 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 13-17 mm 2 / s. The height of the third layer is 30%-50% of the height of the second layer, preferably 35%-45%.

[0021] Further, in the oil-ammonia water-oil-water four-layer mixed column, the fourth layer is a water layer, preferably deionized water or a dilute acid solution. The height of the fourth layer is 1.0-2.0 times the height of the second layer, preferably 1.2-1.5 times.

[0022] Further, the fourth layer preferably uses a dilute acid solution. In the dilute acid solution, the acid is selected from at least one of acetic acid and citric acid. The mass concentration of the dilute acid solution is 3%-8%.

[0023] Further, the preparation method of the oil-ammonia water-oil-water four-layer mixed column comprises:

[0024] (1) Pour the required material of the fourth layer into a columnar container (preferably an organic glass container) and ensure uniform solution;

[0025] (2) Slowly add the required material of the third layer to the fourth layer material of step (1) and stabilize for 20-35 min;

[0026] (3) Slowly add the required material of the second layer to the third layer material of step (2);

[0027] (4) Slowly add the first layer required material on the second layer material of step (3) to obtain oil-ammonia water-oil-water four layer mixed column. Preferably, during the first layer required material adding process, the surface tension on the interface between the first layer and the second layer is weakened by slow up and down circulation above the interface between the first layer and the second layer through peristaltic pump, and then stand for 30-60 min until it is stable, so as to ensure that the aluminum hydroxide sol can quickly pass through the interface between the first layer and the second layer, prevent the tailing caused by pause, and affect the roundness.

[0028] Further, the Pt-based catalyst precursor is formed in the oil-ammonia water-oil-water four layer mixed column, and the mixture of the aluminum hydroxide sol and the organic Pt salt solution is dropped into the oil-ammonia water-oil-water four layer mixed column, wherein the inner diameter of the drop head used is 1.0 mm-1.6 mm.

[0029] Further, the residence time of the mixture of the aluminum hydroxide sol and the organic Pt salt solution in the oil-ammonia water-oil-water four layer mixed column is 5-18 s, preferably 7-11 s.

[0030] Further, 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.

[0031] Further, in the Pt-based catalyst precursor obtained in step (1), Pt exists in the form of single atom.

[0032] Further, in step (2), the impregnation preferably adopts saturated impregnation method, wherein the Pt precursor used in the impregnation solution is preferably at least one of PtCl4 and H2PtCl6. The drying condition after impregnation is as follows: the drying temperature is 80-120℃, and the drying time is 8-12 h. The calcination condition after impregnation is as follows: the calcination temperature is 500-700℃, and the calcination time is 2-6 h.

[0033] The second aspect of the present application provides a Pt-based catalyst prepared by the above preparation method.

[0034] Further, the specific surface area of the catalyst is 70-115 m 2 / g, and the pore volume is 0.60-0.85 mL / g.

[0035] Further, the catalyst is spherical particle, and the average diameter of the particle is 1.6-1.9 mm.

[0036] Further, the pore size distribution of the catalyst is as follows: the pore volume of the pores with pore size less than 2 nm accounts for 1.0% to 4.5% of the total pore volume, the pore volume of the pores with pore size of 2-50 nm accounts for 95.0% to 98.9%, preferably 96.0% to 98.0% of the total pore volume.

[0037] Further, the average pore size of the catalyst is 13-17 nm.

[0038] Further, the crushing strength of the catalyst is 65-85 N / particle.

[0039] Further, the roundness of the catalyst is 96.2% to 99.9%.

[0040] Further, in the catalyst, the content of total Pt is 0.5% to 1.9% by mass, the content of Sn is 0.02% to 0.70% by mass, and the content of alumina is 97.4% to 99.48% by mass, based on the mass of the catalyst. Further, the content of Pt on the surface of the catalyst is 0.3% to 0.8%.

[0041] The third aspect of the present application provides the use of the above catalyst in a propane dehydrogenation reaction.

[0042] Further, the use includes: contacting a propane raw material with the catalyst to perform a dehydrogenation reaction to obtain a product propylene.

[0043] Further, the propane dehydrogenation catalyst needs to be reduced before use. The catalyst precursor is reduced under a reducing atmosphere. The reducing atmosphere is preferably H2, the reduction temperature is 450-600°C, and the reduction time is 1-3 h.

[0044] Further, the propane dehydrogenation reaction conditions are preferably as follows: the reaction temperature is 500-600°C, the reaction pressure is 0-1 MPa, the volume space velocity is 50-200 h -1 .

[0045] Compared with the prior art, the present application has the following advantages:

[0046] (1) In the preparation process of the Pt-based catalyst, the organic Pt salt solution is added in the aluminum hydroxide sol. Since the solubility of the organic Pt is small and the molecular weight is large, the space steric hindrance of the organic molecules connected with the Pt atom is large, and the monatomic Pt catalyst precursor is easily formed in the synthesis process. Subsequently, the catalyst precursor is impregnated with the Pt-containing impregnation solution, so that the metal Pt loading is increased, and the outer layer nanoparticle Pt site is increased. After calcination, the monatomic Pt and the nanoparticle Pt exist in the catalyst at the same time, which can play a synergistic effect. The Pt increases from the inside to the outside, which is beneficial to expose more active sites, so that the reaction is accelerated, and the carbon deposition is reduced. In the forming process, the four-layer oil-ammonia water-oil-water mixed column is different from the two-layer oil-ammonia column or the hot oil column. The third layer of oil layer is added as a liquid seal oil layer and the fourth layer of water layer, so that the sol can quickly enter the third layer and the fourth layer of water layer after passing through the second layer of ammonia water layer, and the pH value is quickly reduced to neutral. The small ball is not easy to break or shrink with the volatilization of the surface ammonia water in the drying process, so that the alumina particle size and mechanical strength are obviously increased, and the metal and the carrier are fully contacted, and the metal is not easy to agglomerate. In addition, the rapid decline of the pH value of the sol small ball surface also makes the hydrophobicity of the colloidal particle surface rapidly decrease, the interaction force between the colloidal particles obviously increases, the distance between the colloidal particles becomes shorter, and the original structure partially collapses, resulting in an increase in the mesoporous structure of the carrier in the range of 2-50 nm. By adding an appropriate amount of acidic solution into the fourth layer of water layer, the pore structure can be further optimized.

[0047] (2) The preparation process of the present application is an environmentally friendly type. In the traditional oil-ammonia column balling process, the volatilization of ammonia water causes serious environmental pollution and subsequent pollutant emission problems. The second oil layer separates the second layer of ammonia water layer and the fourth layer of water layer in the present application, so that the ammonia water layer is sealed on the fourth layer of water layer, the use time can be prolonged, the environmental pollution caused by the product taking out the ammonia water can be avoided, and the deionized water can be replaced after long-term use to ensure the liquid sealing effect. The operation is simple and cost-saving in industry.

[0048] (3) The spherical Pt-based catalyst prepared by the preparation method of the present application has high propane conversion rate and propylene selectivity in the propane to propylene reaction, fully utilizes the inner space of the catalyst, reduces the carbon deposition, and has better catalytic activity. DETAILED DESCRIPTION

[0049] The following examples further illustrate the Pt-based catalyst, its preparation method and application effect. The examples are implemented on the premise of the technical scheme of the present application, and detailed implementation modes and specific operation processes are given, but the protection scope of the present application is not limited to the following examples.

[0050] In the following examples, the experimental methods are conventional methods in the art unless otherwise specified. The experimental materials used in the following examples are purchased from conventional biochemical reagent stores unless otherwise specified.

[0051] In the present application, the nitrogen adsorption-desorption curve of the sample is tested at-196℃ by using the ASAP2020 full-automatic physical adsorption instrument of the American Micromeritics Company to determine the specific surface area, pore volume and pore size distribution.

[0052] In the present application, the crushing strength is tested by using the ZQJ-III intelligent particle strength tester manufactured by the Dalian Zixu Test Machine Factory, and the average value of crushing ten spherical catalysts is tested.

[0053] In the present application, the true roundness is tested by using the electronic microscope of the Olympus Company, and the average value is calculated after testing 20 samples.

[0054] In the present application, the metal Pt content on the surface of the catalyst is measured by using the XPS (the instrument is Kratos Axis Ultra DLD model).

[0055] Example 1

[0056] (1) 250g of the macroporous pseudo-boehmite filter cake with a water content of 22wt% (air atmosphere, 600℃ roasting for 3h, properties as follows: pore volume 0.87ml / g, specific surface area 175m 2 / g, average pore diameter 16nm) is taken, deionized water is added and stirred to be uniformly pulped, then 26g of 45wt% nitric acid solution is added for peptization, and finally the pseudo-boehmite sol with an alumina mass content of 20% is prepared; 300g of the above sol (alumina content 20wt%) is taken, 6g of the acetylacetone platinum solution with a concentration of 1.2% is added, wherein 2.4% of stannous chloride is also contained, and stirring is uniformly carried out to obtain a sol mixture;

[0057] The inner diameter of the drop head is 1.2mm, the sol is dropped into the four-layer mixed column (cylinder) of white oil (40℃ kinematic viscosity 32mm 2 / s) - ammonia water (25wt%) - mixed oil - deionized water, and the residence time in the four-layer mixed column is 8s. Among them, the addition amount of white oil is 35% of the volume of ammonia water, the addition amount of mixed oil is 38% of the volume of ammonia water, and the addition amount of deionized water is 1.3 times of the volume of ammonia water; the mixed oil is mixed by castor oil with a kinematic viscosity of 580mm 2 / s at 40℃ and soybean oil with a kinematic viscosity of 15mm 2 / s, and the volume ratio of the two is 1:5. Then it is dried at 130℃ for 8 hours, and then calcined at 800℃ for 3 hours to obtain the Pt-based catalyst precursor.

[0058] (2) Take 100 g of the Pt-based catalyst precursor obtained above, and immerse it in a saturated aqueous solution containing 2 g of chloroplatinic acid. After 30 minutes of immersion, dry the mixture in a drying oven at 90°C for 10 hours, and then calcine it in a muffle furnace at 600°C for 4 hours to obtain the Pt-based catalyst A of the present application. The analysis results are shown in Table 1.

[0059] Example 2

[0060] Compared with Example 1, the difference is that the deionized water in the fourth layer of the four-layer mixing column is replaced by a 5wt% dilute acetic acid solution to obtain the Pt-based catalyst B of the present application. The analysis results are shown in Table 1.

[0061] Example 3

[0062] Compared with Example 1, the difference is that 5.4 g of an acetylacetone platinum solution with a concentration of 1.8% acetylacetone platinum is added, and the solution also contains stannous chloride with a concentration of 0.9% to obtain the Pt-based catalyst C of the present application. The analysis results are shown in Table 1.

[0063] Example 4

[0064] Compared with Example 1, the difference is that the white oil in the four-layer mixing column is replaced by white oil with a kinematic viscosity of 23 mm 2 / s at 40°C, the concentration of ammonia water is changed to 21wt%, and the volume ratio of castor oil to soybean oil is changed to 1:4 to obtain the Pt-based catalyst D of the present application. The analysis results are shown in Table 1.

[0065] Example 5

[0066] Compared with Example 1, the difference is that the white oil in the four-layer mixing column is replaced by a mixture of diesel oil and white oil with a mixing mass ratio of 1:1, and the concentration of ammonia water is changed to 28wt% to obtain the Pt-based catalyst E of the present application. The analysis results are shown in Table 1.

[0067] Example 6

[0068] Compared with Example 1, the difference is that the concentration of acetylacetone platinum is changed to 1.8%, the white oil in the four-layer mixing column is replaced by white oil with a kinematic viscosity of 28 mm 2 / s at 40°C, the concentration of ammonia water is changed to 23wt%, and the volume ratio of castor oil to soybean oil is changed to 1:4 to obtain the Pt-based catalyst F of the present application. The analysis results are shown in Table 1.

[0069] Example 7

[0070] 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 deionized water added is 1.6 times the volume of ammonia water to obtain the Pt-based catalyst G of the present application. The analysis results are shown in Table 1.

[0071] Comparative Example 1

[0072] The synthesis procedure of the sol mixture was the same as that of Example 1.

[0073] Comparing with Example 1, the difference was that the four-layer oil-ammonia water-oil-water mixed column was changed into a two-layer oil-ammonia column, the upper layer was white oil with a kinematic viscosity of 32 mm2 / s at 40°C, and the lower layer was ammonia water with a concentration of 25 wt%, the amount of white oil added was 25% of the volume of ammonia water, and the remaining molding steps were unchanged, obtaining the comparative Pt-based catalyst H of the present application, and the analysis results are shown in Table 2. 2

[0074] Comparative Example 2

[0075] The synthesis procedure of the sol mixture was the same as that of Example 1.

[0076] Comparing with Example 1, the difference was that only the first layer of white oil column in the four-layer mixed column was removed, and the ball was formed with a three-layer column, obtaining the comparative Pt-based catalyst I of the present application, and the analysis results are shown in Table 2.

[0077] Comparative Example 3

[0078] The synthesis procedure of the sol mixture was the same as that of Example 1.

[0079] Comparing with Example 1, the difference was that only the fourth layer of water layer was removed, obtaining the comparative Pt-based catalyst J of the present application, and the analysis results are shown in Table 2.

[0080] Comparative Example 4

[0081] The synthesis procedure of the sol mixture was the same as that of Example 1.

[0082] Comparing with Example 1, the difference was that only the third layer of castor oil and soybean oil mixed layer in the four-layer mixed column was removed, obtaining the comparative Pt-based catalyst K of the present application, and the analysis results are shown in Table 2.

[0083] Comparative Example 5

[0084] The synthesis method was the same as that of Example 1, except that there was no step (2) of impregnating the catalyst precursor with a Pt-containing impregnating solution, obtaining the comparative Pt-based catalyst L of the present application, and the analysis results are shown in Table 2.

[0085] Comparative Example 6

[0086] The synthesis method of the sol mixture was the same as that of Example 1.

[0087] Comparing with Example 1, the difference was that the amount of white oil added was 16% of the volume of ammonia water, the amount of mixed oil added was 20% of the volume of ammonia water, and the amount of deionized water added was 0.4 times the volume of ammonia water, obtaining the comparative Pt-based catalyst M of the present application, and the analysis results are shown in Table 1.

[0088] ​Physical and chemical properties of Pt-based catalysts obtained in each example of Table 1

[0089] Catalyst No. A B C D E F G Particle average diameter, mm 1.83 1.82 1.81 1.82 1.80 1.82 1.81 Specific surface area, m 2 / g]] 77 81 84 82 78 80 81 Pore volume, mL / g 0.722 0.725 0.711 0.688 0.685 0.716 0.699 Pore size distribution, % < 2 nm 3.6 3.4 3.9 3.7 3.7 3.9 3.4 2-50 nm 96.2 96.4 95.5 95.4 95.5 95.7 96.5 > 50 nm 0.2 0.2 0.6 0.9 0.8 0.4 0.1 Average pore diameter, nm 15.8 16.0 15.4 14.4 14.3 15.5 14.5 Crushing strength, N / particle 79 70 75 72 74 70 72 True circularity, % 97.4 97.2 96.9 96.5 96.9 97.2 96.8

[0090] Physical and chemical properties of Pt-based catalysts obtained in each comparative example of Table 2

[0091] Catalyst No. H I J K L M Particle average diameter, mm 1.79 1.78 1.75 1.80 1.77 1.78 Specific surface area, m 2 / g]] 83 87 84 85 82 85 Pore volume, mL / g 0.594 0.591 0.472 0.563 0.725 0.583 Pore size distribution, % < 2 nm 6.8 6.3 6.1 5.7 3.4 5.1 2-50 nm 92.1 92.9 93.5 94.1 96.3 94.6 > 50 nm 1.1 0.8 0.4 0.2 0.3 0.3 Average pore diameter, nm 13.4 14.4 14.2 13.2 15.9 14.5 Crushing strength, N / particle 41 56 69 59 69 62 True circularity, % 85.2 78.4 88.2 79.4 97.7 89.5

[0092] Composition of catalysts in each example of Table 3

[0093] Catalyst No. A B C D E F G Alumina (wt%) 98.85 98.75 98.95 98.85 98.84 98.86 98.85 Total Pt (wt%) 1.0 1.1 1.0 1.0 1.0 1.1 1.0 Surface Pt (wt%) 0.69 0.69 0.67 0.67 0.69 0.70 0.69 Sn (wt%) 0.15 0.15 0.05 0.15 0.16 0.14 0.15

[0094] Composition of catalysts in each comparative example of Table 4

[0095] Catalyst No. H I J K L M Alumina (wt%) 98.84 98.94 98.95 99.05 99.78 98.85 Total Pt (wt%) 1.0 0.9 0.9 0.8 0.05 1.0 Surface Pt (wt%) 0.65 0.67 0.67 0.66 - 0.67 Sn (wt%) Catalyst No. Alumina (wt%) Total Pt (wt%) Surface Pt (wt%) Sn (wt%) 0.16 0.16 0.15 0.15 0.17 0.15

[0096] Catalyst evaluation

[0097] 5 g of each of the above catalysts were reduced under hydrogen atmosphere at 520°C for 1.5 h, and then were charged into a fixed bed reactor for evaluation of the propane dehydrogenation activity: reaction temperature 600°C, normal pressure, volume space velocity 100 h -1 The results of the propane dehydrogenation are shown in Tables 5-6.

[0098] Evaluation results of the catalysts in each example of Table 5 for propane dehydrogenation

[0099]

[0100] Evaluation results of the catalysts in each comparative example of Table 6 for propane dehydrogenation

[0101]

[0102] The specific embodiments of the present application have been described above in detail, but the present application is not limited thereto. Various simple modifications can be made to the technical solutions of the present application within the technical concept of the present application, including the combination of each technical feature in any other suitable manner, and these simple modifications and combinations should also be considered as disclosed by the present application and fall within the protection scope of the present application.

Claims

1. A method for preparing a Pt-based catalyst, comprising: (1) mixing an aluminum hydroxide sol with an organic Pt salt solution, and dropping the obtained mixture into an oil-ammonia water-oil-water four-layer mixed column to form a spherical Pt-based catalyst precursor, and drying and calcining the precursor to obtain the Pt-based catalyst; (2) impregnating the precursor obtained in step (1) with a Pt-containing impregnating solution, and drying and calcining the impregnated precursor to obtain the Pt-based catalyst; the organic Pt salt solution contains stannous chloride; the oil-ammonia water-oil-water four-layer mixed column is 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 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; the volume ratio of castor oil to soybean oil is 1 / 4 to 1 / 6; the density of the second oil layer is between that of the second ammonia water layer and the fourth water layer; the fourth water layer is deionized water or a dilute acid solution; the height of the first layer is 30% to 50% of the height of the second layer; the height of the third layer is 30% to 50% of the height of the second layer; and the height of the fourth layer is 1.0 to 2.0 times the height of the second layer.

2. The method of claim 1, wherein: the organic Pt salt in the organic Pt salt solution is one or more of platinum acetylacetonate or tetra(triphenylphosphine) platinum, and the solvent used is acetone; and / or, the concentration of the organic Pt salt in the organic Pt salt solution is 1.0 wt% to 1.9 wt%; and / or, the amount of the organic Pt salt solution added is 9% to 11% of the mass of the aluminum hydroxide sol in terms of aluminum oxide.

3. The method of claim 2, wherein: the organic Pt salt is platinum acetylacetonate.

4. The method of claim 1, wherein: the concentration of stannous chloride in the organic Pt salt solution is 0.4 wt% to 11 wt%.

5. The method of claim 1, wherein: the oil-ammonia water-oil-water four-layer mixed column is a straight column.

6. The method of claim 1, wherein: the oil-ammonia water-oil-water four-layer mixed column is a cylindrical column.

7. The method of claim 1, 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 25-35 mm 2 / s.

9. The method of claim 1, wherein: in the oil-ammonia water-oil-water four-layer mixed column, the second layer is an ammonia water layer, and the concentration is 20 wt% to 28 wt%.

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

11. The method of claim 1, 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 1, wherein: in the oil-ammonia water-oil-water four-layer mixed column, the fourth water layer is a dilute acid solution; the dilute acid in the dilute acid solution is at least one of acetic acid or citric acid; and the mass concentration of the dilute acid solution is 3% to 8%.

14. The method of claim 1, wherein: the height of the third layer is 35% to 45% of the height of the second layer; and / or, the height of the fourth layer is 1.2 to 1.5 times the height of the second layer.

15. The method of claim 1, wherein: in step (2), the impregnation is a saturation impregnation method; and / or, the Pt precursor used in the impregnating solution is at least one of PtCl4 or H2PtCl6. 16.A Pt-based catalyst prepared by the method of any one of claims 1 to 15.

17. The catalyst of claim 16, wherein: The specific surface area of the catalyst is 70 to 115 m 2 / g, and the pore volume is 0.60 to 0.85 mL / g. and / or, the average diameter of the catalyst particles is 1.6 to 1.9 mm; and / or, the average pore size of the catalyst is 13 to 17 nm; and / or, the crushing strength of the catalyst is 65 to 85 N / particle; and / or, the roundness of the catalyst is 96.2% to 99.9%.

18. The catalyst of claim 17, wherein: The pore size distribution of the catalyst is as follows: the pore volume of pores with a pore size less than 2 nm accounts for 1.0-4.5% of the total pore volume, and the pore volume of pores with a pore size of 2-50 nm accounts for 95.0-98.9% of the total pore volume.

19. The catalyst of claim 17, wherein: The pore volume of pores with a pore size of 2-50 nm accounts for 96.0-98.0% of the total pore volume.

20. The catalyst of claim 17, wherein: In the catalyst, the total content of Pt is 0.5-1.9% by mass, the content of Sn is 0.02-0.70% by mass, and the content of alumina is 97.4-99.48% by mass, based on the mass of the catalyst.

21. The catalyst of claim 20, wherein: The content of Pt on the surface of the catalyst is 0.3-0.8%.

22. Use of the catalyst of any one of claims 16-21 in a propane dehydrogenation reaction.

23. The use according to claim 22, characterized in that: The catalyst needs to be reduced before use.

24. The use according to claim 22, characterized in that: The reducing atmosphere is H2, the reducing temperature is 450-600°C, and the reducing time is 1-3 h.

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