A catalyst, its preparation method and application

Abstract

This invention belongs to the field of catalysts, specifically disclosing a catalyst, its preparation method, and its application. In the preparation of alumina supports, this invention improves the shaping, calcination, and pore formation of the support through the synergistic effect of composite additives. This facilitates the robust loading and uniform distribution of the Cr active component, resulting in a catalyst with an ordered mesoporous structure, high specific surface area, high mechanical strength, and low wear rate. This, in turn, enhances the catalyst's catalytic activity and long-term stability.

Description

Technical Field

[0001] This invention belongs to the field of catalysts, specifically relating to a catalyst, its preparation method, and its application. Background Technology

[0002] Propylene is a common chemical raw material and a major feedstock for the production of polypropylene, propylene oxide, acrylonitrile, and other products. Domestic propylene capacity growth is primarily driven by propane dehydrogenation (PDH) processes. Currently, the main technologies are UOP's Oleflex process and Lummus's Catofin process. The former mainly uses a fluidized bed process with a Pt-Sn / Al2O3 catalyst, while the latter uses a fixed bed process with a Cr / Al2O3 catalyst. The Lummus process holds a significant market share in China due to its high online efficiency and stability.

[0003] The Cr / Al2O3 catalyst used in the Lummus process is a porous material with a certain strength, employing a porous Al2O3 support and the active material Cr. n+ Interactions affect the propylene yield and stability of the catalyst. Existing Cr / Al₂O₃ catalysts are prone to carbon deposition over long reaction periods, leading to decreased long-term stability. Studies have found that ordered mesoporous catalysts can effectively reduce the tendency of catalyst carbon deposition, while ordered mesoporous supports can improve the dispersibility of active components and enhance the overall activity of the catalyst.

[0004] However, excessively high porosity or irregular pore structure distribution in mesoporous catalysts can reduce their mechanical strength, leading to catalyst breakage during the reaction and the generation of small fragments and powder, which in turn affects the gas distribution in the reactor and thus the pressure drop in the reactor bed. Therefore, it is urgent to prepare high-porosity mesoporous catalysts while ensuring catalyst particle strength, which can effectively improve the stability of the reactor bed, as well as the catalyst's reactivity and long-term stability. Summary of the Invention

[0005] In view of the problems of low mechanical strength and poor long-term stability of Cr2O3 / Al2O3 catalysts in the prior art, the present invention will provide a catalyst, its preparation method and application.

[0006] To achieve the above objectives, the following technical solutions are specifically included: In a first aspect, the present invention provides a catalyst comprising an alumina support and a chromium active component; the catalyst having a BET specific surface area of ​​60-120 m². 2 / g, with an average pore size of 5-10nm and a pore volume of 0.1-0.25cm³. 3 / g; the average mechanical strength of the catalyst is greater than or equal to 14 N / mm.

[0007] The catalyst of the present invention has an ordered mesoporous structure and a high specific surface area, which can make the catalyst have high mechanical strength and low wear rate, thus improving the catalytic activity and long-term stability of the catalyst.

[0008] The mechanical strength test method is as follows: 30 cylindrical catalysts with an average diameter of 2.9-3.1 mm and a height of 3-6 mm are randomly selected. The height H (mm) of each catalyst is tested. Pressure is applied to the cylindrical surface of each catalyst until it breaks, and the instantaneous force value F (N) is recorded. The radial strength (N / mm) of each catalyst is calculated using the formula: F / H. The average value of the radial strength calculated for the 30 catalysts is taken as the average mechanical strength of the catalyst.

[0009] Specific surface area was tested and calculated using the BET method, while pore volume and average pore diameter were calculated using the BJH model.

[0010] Preferably, the catalyst particles have a diameter of 2.5~3.5mm and an average height of 1-10mm. The size of the catalyst particles is measured using vernier calipers, and the size of 30 particles for each catalyst sample is measured and the average value is taken.

[0011] Preferably, the catalyst particles are cylindrical in shape.

[0012] Preferably, the mass percentage of Cr element in the catalyst is 15%-50%, specifically 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, or any value within the range of the above two.

[0013] More preferably, the catalyst contains 17%-40% Cr by mass.

[0014] Secondly, the present invention provides a method for preparing a catalyst, comprising the following steps: S1. Alumina powder, composite additives, and water are mixed to obtain a mixture; the mixture is then subjected to aging, molding, and drying to obtain a carrier precursor; the composite additives include a first additive, a second additive, and a third additive; the first additive includes ascorbic acid and malonic acid; the second additive includes polyolefin; and the third additive includes amino-modified starch. S2. The carrier precursor is calcined to obtain an alumina carrier; S3. The alumina support is impregnated in a Cr-containing solution to obtain the catalyst precursor; S4. The catalyst precursor is calcined to obtain the catalyst.

[0015] In the catalyst preparation process of this invention, alumina powder is first mixed with composite additives, shaped, and dried. The composite additives improve the sol-gelation and shaping of alumina, as well as its decomposition and gas generation during calcination, enhance mechanical strength, promote sintering, and improve the pore structure and particle bonding state during calcination. This improves the mechanical strength, porosity, three-dimensional pore structure order, and abundant surface hydroxyl groups of the alumina support. Then, the Cr active component is impregnated and loaded into the alumina support. Due to the aforementioned characteristics of the support, Cr can be more uniformly and firmly adsorbed onto the alumina support. The catalyst obtained after calcination has a more uniform and firmly loaded Cr active component on the support, improving the catalyst's reactivity and stability. The catalyst also has high mechanical strength, ordered mesopores, and high specific surface area, making it less prone to breakage or significant wear, and significantly reducing carbon deposition, which is beneficial for improving the stability of the reactor bed and the catalyst therein.

[0016] In the formation of alumina support precursors, the high number of hydroxyl groups on ascorbic acid in the composite additive is beneficial for increasing the content of alumina sol formed by hydroxylation on the alumina surface. Alumina sol has a binding effect, which is beneficial for improving the mechanical strength of the catalyst after sintering. However, when ascorbic acid is used alone as the first additive, the excessive content of alumina sol will reduce the pore structure of the catalyst and cause irregular pore structures, leading to a decrease in the mechanical strength and catalytic effect of the catalyst. The inventors of this invention have discovered that the combination of ascorbic acid and malonic acid as the first additive can regulate the degree of hydroxylation on the alumina surface, resulting in an appropriate content of alumina sol in the support precursor and improving the orderliness of the pore structure, thereby enhancing the catalyst's performance. It possesses the characteristics of high mechanical strength, low wear rate, and high catalytic activity. Meanwhile, the second additive is a polyolefin, which requires prolonged high temperatures to decompose, typically above 250℃, matching the calcination temperature of the support. Its stable decomposition process results in a more uniform and stable pore structure on the support, which is beneficial for improving the catalyst's mechanical strength and catalytic effect. Furthermore, amino-modified starch acts as a binder and pore-forming agent, improving the catalyst's mechanical strength and porosity. Its low hydroxyl content allows for greater retention of surface hydroxyl groups in alumina, which is more conducive to anchoring Cr ions on the support, stabilizing the active components, and improving the catalyst's catalytic activity and stability.

[0017] Preferably, in step S1, the decomposition temperature of the polyolefin is 250-400℃, specifically 250℃, 260℃, 270℃, 280℃, 290℃, 300℃, 310℃, 320℃, 330℃, 340℃, 350℃, 360℃, 370℃, 380℃, 390℃, 400℃, or any range between the above. Thermogravimetric analysis (TGA) is used to test the decomposition temperature of the polyolefin, wherein the initial decomposition temperature corresponding to a 5% weight loss of the polyolefin under a nitrogen atmosphere is selected as the decomposition temperature of the polyolefin.

[0018] Preferably, in step S1, the polyolefin includes at least one of polypropylene, polyethylene, and oxidized polyethylene wax.

[0019] More preferably, the polypropylene is classified according to monomer composition as at least one of homopolymer polypropylene and copolymer polypropylene, the homopolymer polypropylene is classified according to the spatial arrangement of side groups on the molecular chain as at least one of isotactic homopolymer polypropylene, syndiotactic homopolymer polypropylene, and atactic homopolymer polypropylene, and the copolymer polypropylene is classified according to the arrangement of monomers as at least one of atactic copolymer polypropylene and block copolymer polypropylene.

[0020] More preferably, the polyethylene includes at least one of high-density polyethylene, low-density polyethylene, and ultra-high molecular weight polyethylene.

[0021] Preferably, in step S1, the amino-modified starch includes at least one of tertiary aminoalkyl ether modified starch, quaternary aminoalkyl ether modified starch, and aminoalkyl ether modified starch.

[0022] Preferably, the amino-modified starch contains 2% to 3% by mass, and the mass percentage of the amino component is determined by analyzing the gaseous nitrogen content through high-temperature thermal decomposition.

[0023] Preferably, in step S1, the decomposition temperature of the amino-modified starch is 170-220℃.

[0024] Preferably, in step S1, the mixing time is 1-6 hours and the aging time is 2-24 hours.

[0025] Preferably, in step S1, the drying temperature is stabilized at 70-120°C.

[0026] Preferably, in step S1, the mass ratio of alumina to water is 100:(10-30), which can specifically be 100:10, 100:12, 100:14, 100:16, 100:18, 100:20, 100:22, 100:24, 100:26, 100:28, 100:30, or any value within the range of the above two.

[0027] Preferably, in step S1, the mass ratio of alumina to the first additive is 100:(5-20), which can specifically be 100:5, 100:6, 100:7, 100:8, 100:9, 100:10, 100:11, 100:12, 100:13, 100:14, 100:15, 100:16, 100:17, 100:18, 100:19, 100:20, etc., or any value within the range of the above two.

[0028] Preferably, in step S1, the mass ratio of the alumina and the second additive is 100:(0.1-2), which can specifically be 100:0.1, 100:0.3, 100:0.5, 100:0.7, 100:0.9, 100:1.1, 100:1.3, 100:1.5, 100:1.7, 100:1.9, or any value within the range of the two mentioned above.

[0029] Preferably, in step S1, the mass ratio of alumina to the third auxiliary agent is 100:(0.1-4), specifically it can be 100:0.1, 100:0.2, 100:0.3, 100:0.4, 100:0.5, 100:0.6, 100:0.7, 100:0.8, 100:0.9, 100:1.0, 100:1.1, 100:1.2, 100:1.3, 100:1.4, 100:1.5, 100:1.6, 100:1.7, 100:1.8, 10 0:1.9, 100:2.0, 100:2.1, 100:2.2, 100:2.3, 100:2.4, 100:2.5, 100:2.6, 100:2.7, 100:2.8, 100:2.9, 100:3.0, 100:3.1, 100:3.2, 100:3.3, 100:3.4, 100:3.5, 100:3.6, 100:3.7, 100:3.8, 100:3.9, 100:4.0, etc., or any range between the two mentioned above.

[0030] More preferably, in step S1, the mass ratio of the alumina to the third auxiliary agent is 100:(0.1-2).

[0031] Preferably, in step S1, the mass ratio of ascorbic acid to malonic acid is 1:(0.7-7), which can specifically be 1:0.7, 1:0.9, 1:1.1, 1:1.3, 1:1.5, 1:1.7, 1:1.9, 1:2.1, 1:2.3, 1:2.5, 1:2.7, 1:2.9, 1:3.1, 1:3.3, 1:3.5, 1:3.7, 1:3.9, 1:4.1, 1:4.3, 1:4.5, 1:4.7, 1:4.9, 1:5.1, 1:5.3, 1:5.5, 1:5.7, 1:5.9, 1:6.1, 1:6.3, 1:6.5, 1:6.7, 1:6.9, 1:7, or any range of the above two.

[0032] Further preferred value 1: (0.7-3), which can specifically be 1:0.7, 1:0.8, 1:0.9, 1:1.0, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2.0, 1:2.1, 1:2.2, 1:2.3, 1:2.4, 1:2.5, 1:2.6, 1:2.7, 1:2.8, 1:2.9, 1:3.0, or any two of the above ranges.

[0033] In step S2, the calcination temperature is 600-900℃; the calcination time is 2-8h; the calcination atmosphere includes air; and the heating rate to the calcination temperature is 1-10℃ / min.

[0034] Preferably, in step S3, the impregnation method is equal volume impregnation.

[0035] Preferably, in step S3, the mass concentration of Cr element in the Cr-containing solution is 10wt%-60wt%; the mass ratio of the alumina support to the Cr element in the Cr-containing solution is 100:(15-30).

[0036] Preferably, in step S4, the calcination temperature is 650-800℃, the calcination time is 1-6h, the calcination atmosphere includes air, and the heating rate to the calcination temperature is 1-10℃ / min.

[0037] Preferably, the Cr-containing solution includes a chromium salt, wherein the chromium salt includes chromium nitrate.

[0038] Thirdly, the present invention provides the application of the catalyst described herein in the dehydrogenation of alkanes.

[0039] Preferably, the alkane includes at least one of propane and isobutane.

[0040] When the catalyst of the present invention is used as a catalyst for the dehydrogenation of alkanes to produce olefins, it can effectively improve the selectivity of the target product and the reaction stability, especially for the dehydrogenation of propane to propylene or the dehydrogenation of isobutane to isobutene, it has high catalytic activity and reaction selectivity.

[0041] Fourthly, the present invention provides a method for producing propylene from propane through dehydrogenation, comprising the following steps: S1. Place the catalyst in the reactor; S2. Hydrogen gas is introduced into the reactor for reduction reaction. After the reduction reaction is completed, the hydrogen gas is stopped. Then propane is introduced into the reactor for dehydrogenation reaction. After the dehydrogenation reaction is completed, the propane gas is stopped. Nitrogen gas is introduced for purging. After the purging is completed, the nitrogen gas is stopped. Then air is introduced for activation process. After the activation is completed, the air gas is stopped. S3. Repeat step S2 to obtain the catalyst after dehydrogenation reaction and the dehydrogenation reaction products.

[0042] Preferably, in step S1, the reactor includes a quartz tube with an outer diameter of 10-30 mm and a wall thickness of 1-5 mm.

[0043] Preferably, in step S2, the temperature of the reduction reaction is 500-700℃, the time of the reduction reaction is 5-30 min, and the flow rate of hydrogen is 10-80 mL / min.

[0044] Preferably, in step S2, the temperature of the dehydrogenation reaction is 500-700°C, the time of the dehydrogenation reaction is 0.5-3 h, and the space velocity of propane is 0.5-3 h⁻¹. -1 .

[0045] Preferably, in step S2, the purging temperature is 500-700℃, the purging time is 5-15 min, and the nitrogen flow rate is 10-80 mL / min.

[0046] Preferably, in step S2, the activation process is carried out at a temperature of 500-700°C for 10-40 minutes for 10 minutes and at a flow rate of 10-80 mL / min.

[0047] In step S3, the number of cycles is ≥10 times, and more preferably 15-30 times.

[0048] In the catalytic dehydrogenation of propane to propylene, the catalyst of this invention has high mechanical strength, low wear rate, ordered mesoporous structure and high specific surface area, which can improve the activity of the catalyst reaction, the number of cycles and the stability of the catalytic reaction.

[0049] Compared with the prior art, the present invention has the following beneficial effects: In the preparation of alumina support, the present invention improves the shaping, calcination and pore formation of the support by the mutual cooperation of composite additives, which is more conducive to the firm loading and uniform distribution of Cr active components, so that the catalyst has an ordered mesoporous structure, high specific surface area, high mechanical strength and low wear rate, which is beneficial to improving the catalytic activity and long-term stability of the catalyst. Detailed Implementation

[0050] To better illustrate the purpose, technical solution, and advantages of this invention, specific embodiments will be used to further explain the invention below. Unless otherwise specified, the test methods used in the embodiments and / or comparative examples are conventional methods; the materials and reagents used, unless otherwise specified, are commercially available.

[0051] PE-1: Oxidized polyethylene wax, A-C629, Honeywell; PE-2: Low-density polyethylene, DFDA-7042, Maoming Petrochemical; PE-3: Ultra-high molecular weight polyethylene, Cortena 4130, Tyco, USA; PP-1: Isotactic homopolymer polypropylene, T30S, Lanzhou Petrochemical; PP-2: Random copolymer polypropylene, F800E, Sinopec Shanghai; PP-3: Syndiotactic homopolymer polypropylene, MR 2002, Total; Amino-modified starch 1: Tertiary aminoalkyl ether modified starch; Amino-modified starch 2: Quaternary amino alkyl ether modified starch; Amino-modified starch 3: Amino alkyl ether modified starch; Polyvinyl alcohol: Inokai; Unmodified starch: corn starch, Inokai.

[0052] Example 1 (1) Preparation of carrier precursor: The second and third additives were added to 100 parts by weight of alumina powder, the first additive was added, and then 15 parts by weight of water were added. The mixture was stirred in a kneader for 3 hours and aged for 4 hours to obtain a mixture. The mixture was extruded into a cylindrical shape and dried at 80°C for 12 hours to obtain the carrier precursor. The types and amounts of the first, second, and third additives are shown in Table 1-2.

[0053] (2) Preparation of the carrier: The carrier precursor was placed in a muffle furnace and heated to 700°C at a heating rate of 5°C / min in an air atmosphere, and calcined for 6 hours. After natural cooling and sieving, the resulting particles had a diameter of 2.5~3.5 mm, thus obtaining the shaped alumina carrier.

[0054] (3) Preparation of catalyst precursor: Chromium nitrate and alumina support were weighed according to a Cr element to alumina support weight ratio of 30:100. Chromium nitrate was dissolved in deionized water to prepare a chromium-containing solution. 100 parts by weight of the shaped alumina support was added to the above solution by an equal volume impregnation method. After removing water using a rotary evaporator, the solution was dried at 120°C for 12 hours to obtain the catalyst precursor.

[0055] (4) Catalyst preparation: The catalyst precursor was placed in a muffle furnace and nitrogen gas was continuously introduced at a flow rate of 32 mL / min. The temperature was increased from room temperature to 700 °C at a rate of 5 °C / min, and calcined at this temperature for 2 h. After natural cooling, catalyst particles were obtained.

[0056] Examples 2-28 and Comparative Examples 1-6 Compared with Example 1, the difference lies in the composite additives or calcination conditions, as detailed in Table 1, while the rest are the same.

[0057] Comparative Example 7 Compared with Example 1, the difference is that ascorbic acid is replaced with citric acid in equal amounts in this comparative example, while the rest are the same.

[0058] Comparative Example 8 Compared with Example 1, the difference is that in this comparative example, oxidized polyethylene wax is replaced with polyvinyl alcohol in equal amounts, while the rest are the same.

[0059] Comparative Example 9 Compared with Example 1, the difference is that the tertiary aminoalkyl ether modified starch in this comparative example is replaced with corn starch (unmodified starch) in equal amounts, while the rest is the same.

[0060] Table 1 Application examples The catalysts prepared in the above examples and comparative examples are applied to the process of propane dehydrogenation to propylene, specifically including the following steps: 5g of sample particles were weighed and loaded into a Φ18×2mm quartz tube reactor. First, reduction was carried out at 600℃ in a hydrogen atmosphere (42mL / min) for 10 min. Then, a vacuum pump was turned on to reduce the reaction pressure to 0.5MPa, and propane feed gas was switched (space velocity 1h). -1The reaction was carried out for 1 hour, followed by purging with N2 for 1 minute and regeneration with air for 20 minutes to complete a single cycle of the reaction. During the reaction, the reactor outlet was sampled and analyzed every 5 minutes using an online gas chromatograph (GC-F80, Zhejiang Fuli Analytical Instrument Co., Ltd.). Each sample was cycled 15 times. The propane conversion (C) and propylene yield (Y) were calculated according to formulas (1) and (2), respectively: C=(M0-M1) / M0×100%(1); Y = M2 / M0 × 100% (2); Where M0 is the mass ratio of propane in a single feed, M1 is the mass ratio of propane in the effluent, and M2 is the mass ratio of propylene in the effluent. The average conversion and yield of a single cycle are calculated as the average of the data collected over 1 hour (15 times).

[0061] Characterization tests: (1) Nitrogen adsorption-desorption test: A TriStar II PLUS 3030 physical adsorption instrument from Altamira, USA was used. 0.2g of catalyst was weighed and pretreated at 300℃ under vacuum for 6-8 hours to remove surface adsorbates. Nitrogen was used as the test gas. The specific surface area was calculated using the BET method and the average pore size was calculated using the BJH model.

[0062] (2) Mechanical strength test: The YT-KD4A particle strength tester of Shandong Yuntang Intelligent Technology Co., Ltd. was used for testing. Among them, 30 cylindrical catalysts with an average diameter of 2.9-3.1 mm and a height of 3-6 mm were randomly selected. The height H (mm) of each catalyst was tested. Pressure was applied to the cylindrical surface of each catalyst until it broke, and the instantaneous force F (N) was recorded. The radial strength (N / mm) of each catalyst was calculated by the formula: F / H. The average value of the radial strength calculated from the 30 catalysts was taken as the average mechanical strength of the catalyst.

[0063] (3) The wear test was characterized by the Bruker UMT-2 friction and wear tester, and the test method complied with the HG / T3927-2020 standard.

[0064] (4) The content of Cr metal element in the catalyst was tested by X-ray fluorescence spectrometry (XRF).

[0065] The test results are shown in Table 2.

[0066] Table 2 Compared with Example 1, Examples 1-3, with the same total weight of the first additive, changed the mass ratio of ascorbic acid and malonic acid in the first additive; Examples 4-5 changed the amount of ascorbic acid; Examples 6-7 changed the amount of malonic acid; Examples 8-9 changed the oxidized polyethylene wax to low-density polyethylene and ultra-high molecular weight polyethylene, respectively; Examples 10-12 changed the oxidized polyethylene wax to homopolymer polypropylene, random copolymer polypropylene, and syndiotactic polypropylene; Examples 16-18 changed the amount of oxidized polyethylene wax; and Examples 19-20 changed the number of amino groups in the modified starch. Therefore, it can be seen that the type and amount of the second additive affect the state of the decomposition process during the calcination of the catalyst precursor, thereby affecting the Cr content, surface area, pore volume, pore size, strength, and wear rate of the catalyst, and improving the yield of propylene from the catalyst.

[0067] Compared with Example 1, Examples 21-22 changed the calcination temperature of the support precursor, and Examples 23-24 changed the calcination time of the support precursor, which affected the state of the decomposition process during the calcination of the catalyst precursor, thereby affecting the Cr content, surface area, pore volume, pore size, strength and wear rate of the catalyst, and improving the propylene yield of the catalyst.

[0068] Compared with Example 1, Examples 25-26 changed the amount of Cr source and its loading. As an active component, it significantly affected the catalytic activity. Increasing its loading was beneficial to improving the propylene yield of the catalyst.

[0069] Compared to Example 1, Examples 27-28 altered the calcination temperature of the catalyst precursor, affecting its calcination state and thus influencing the catalyst's Cr content, surface area, pore volume, pore size, strength, and attrition rate, thereby improving the propylene yield of the catalyst. Compared to Example 1, Comparative Example 1 lacked ascorbic acid, Comparative Example 2 lacked malonic acid, Comparative Example 3 lacked the first auxiliary agent, Comparative Example 4 lacked the second auxiliary agent, Comparative Example 5 lacked the third auxiliary agent, Comparative Example 6 lacked all three auxiliary agents, Comparative Example 7 replaced the first auxiliary agent with citric acid, Comparative Example 8 replaced the second auxiliary agent with polyvinyl alcohol, and Comparative Example 9 replaced the third auxiliary agent with unmodified starch. Comparative Examples 1-9 affected the state of the decomposition process during the calcination of the catalyst precursor, thereby affecting the catalyst's Cr content, surface area, pore volume, pore size, strength, and attrition rate. The three specific auxiliary agents of this invention, in combination, can significantly improve the propylene yield of the catalyst.

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A catalyst, characterized in that, The catalyst includes an alumina support and a chromium active component; the BET specific surface area of ​​the catalyst is 60-120 m². 2 / g, with an average pore size of 5-10nm and a pore volume of 0.1-0.25cm³. 3 / g; the average mechanical strength of the catalyst is greater than or equal to 14 N / mm.

2. The catalyst according to claim 1, characterized in that, The catalyst contains 15%-50% Cr by mass.

3. The method for preparing the catalyst according to claim 1 or 2, characterized in that, Includes the following steps: S1. Alumina powder, composite additives, and water are mixed to obtain a mixture; the mixture is then subjected to aging, molding, and drying to obtain a carrier precursor; the composite additives include a first additive, a second additive, and a third additive; the first additive includes ascorbic acid and malonic acid; the second additive includes polyolefin; and the third additive includes amino-modified starch. S2. The carrier precursor is calcined to obtain an alumina carrier; S3. The alumina support is impregnated in a Cr-containing solution to obtain the catalyst precursor; S4. The catalyst precursor is calcined to obtain the catalyst.

4. The method for preparing the catalyst according to claim 3, characterized in that, In step S1, the polyolefin includes at least one of polypropylene, polyethylene, and oxidized polyethylene wax; And / or, in step S1, the amino-modified starch includes at least one of tertiary aminoalkyl ether modified starch, quaternary aminoalkyl ether modified starch, and aminoalkyl ether modified starch.

5. The method for preparing the catalyst according to claim 4, characterized in that, In step S1, the mass ratio of alumina to water is 100:(10-30). And / or, in step S1, the mass ratio of the alumina to the first additive is 100:(5-20); And / or, in step S1, the mass ratio of the alumina and the second additive is 100:(0.1-2). And / or, in step S1, the mass ratio of the alumina to the third auxiliary agent is 100:(0.1-4).

6. The method for preparing the catalyst according to claim 4, characterized in that, The mass ratio of ascorbic acid to malonic acid is 1:(0.7-7).

7. The method for preparing the catalyst according to claim 3, characterized in that, In step S2, the calcination temperature is 600-900℃, the calcination time is 2-8h, the calcination atmosphere includes air, and the heating rate to the calcination temperature is 1-10℃ / min.

8. The method for preparing the catalyst according to claim 3, characterized in that, In step S4, the calcination temperature is 650-800℃, the calcination time is 1-6h, the calcination atmosphere includes air, and the heating rate to the calcination temperature is 1-10℃ / min.

9. The use of the catalyst according to claim 1 or 2 in the dehydrogenation of alkane.

10. A method for producing propylene by propane dehydrogenation, characterized in that, Includes the following steps: S1. Place the catalyst according to claim 1 or 2 in a reactor; S2. Hydrogen gas is introduced into the reactor to carry out the reduction reaction. After the reduction reaction is completed, the hydrogen gas is stopped. Then propane is introduced into the reactor to carry out the dehydrogenation reaction. After the dehydrogenation reaction is completed, the propane is stopped. Nitrogen gas is introduced for purging, and the nitrogen supply is stopped after purging; then air is introduced for regeneration and activation, and the air supply is stopped after activation. S3. Repeat step S2 to obtain the catalyst after dehydrogenation reaction and the dehydrogenation reaction products.

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