Molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve catalyst as well as preparation method and application thereof

Abstract

The invention discloses a molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve catalyst as well as a preparation method and application thereof, the catalyst takes an H-ZSM-5 molecular sieve as a main body framework, and molybdenum and phosphorus are co-doped into the H-ZSM-5 molecular sieve in situ; the preparation method comprises the following steps: uniformly mixing tetrapropylammonium hydroxide, tetraethoxysilane, isopropanol, urea, aluminum nitrate nonahydrate, sodium hydroxide, deionized water and phosphomolybdic acid, performing hydrothermal synthesis reaction, and sequentially performing cooling, centrifuging, washing, drying, grinding, roasting, ion exchange, grinding and roasting on a product obtained by hydrothermal synthesis. The molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve catalyst is obtained; phosphomolybdic acid is introduced in situ by using a hydrothermal synthesis method to realize atomic-scale uniform distribution of molybdenum and phosphorus elements, and high crystallinity and pore regularity of the molecular sieve are guaranteed by combining a slow heating design; the introduced molybdenum and phosphorus can accurately adjust the distribution of acidic sites and optimize the pore structure, inhibit the generation of side reactions such as deep cracking and optimize the mass transfer efficiency, and realize efficient catalysis of various long-chain hydrocarbons and mixed feeding systems.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of petrochemical catalysis technology, in particular to a molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve catalyst and a preparation method and application thereof. BACKGROUND

[0002] Fischer-Tropsch conversion with coal-based synthesis gas as raw material is an important chemical production path under the energy pattern of our country, and a large amount of long-chain hydrocarbon products are inevitably produced in the process of Fischer-Tropsch synthesis and oil processing; since these products are mainly C5+ alkane / olefin mixture, separation is difficult, and the utilization value is low, the traditional utilization path is usually limited to the production of low-end paraffin or direct combustion, resulting in low product added value and serious pollution. High-efficiency conversion of long-chain hydrocarbons into high-added-value low-carbon olefins undoubtedly opens up a new value growth path for related industries and realizes the optimized utilization of resources. However, there are problems such as severe hydrogen transfer reaction and insufficient selectivity of low-carbon olefins in the catalytic conversion of long-chain hydrocarbons. Co-feeding long-chain hydrocarbons and alcohols can produce intermolecular synergistic effect, the alkane provides hydrogen source to inhibit excessive dehydration of alcohol, and the oxygen-containing group of alcohol promotes activation of C-C bond of alkane, thereby optimizing reaction path and product distribution, which is expected to break through the bottleneck of single raw material conversion and realize efficient utilization of resources.

[0003] ZSM-5 molecular sieve has unique three-dimensional pore structure and adjustable acid strength and distribution, and has shown certain catalytic potential in methanol to olefins, alkane cracking and other reactions. The shape-selective effect of its pore can limit the diffusion of macromolecules and promote the generation of low-carbon olefins; the rich acid sites of ZSM-5 molecular sieve can effectively activate the C-C and C-O bonds in long-chain hydrocarbon and alcohol molecules. However, in the reaction of co-feeding long-chain hydrocarbons and alcohols to low-carbon olefins, the traditional ZSM-5 molecular sieve still has obvious deficiencies. On the one hand, the acid strength and distribution are not ideal, and too many strong acid centers are easy to cause the generated low-carbon olefins to further undergo polymerization, cyclization and other side reactions, causing selectivity to decrease or long-chain hydrocarbons to be excessively cracked to generate coke and other by-products, causing the catalyst surface to be deactivated by carbon deposition; on the other hand, the pore structure is limited, and the micropore size (0.55 nm) of ZSM-5 molecular sieve has large diffusion resistance to long-chain hydrocarbon molecules, which not only affects the reaction rate, but also may cause the local concentration of reactants in the pore to be too high, and the occurrence of side reactions to be intensified.

[0004] Bai (Bai Y, Liu D, Zhao L, et al. Tuning the concentrations of acid sites on ZSM 5 zeolite for improving light olefin production in catalyticpyrolysis of paraffin[J]. Industrial&Engineering Chemistry Research, 2022, 61(43): 15842-15855.) et al. proposed a method for preparing sodium-modified ZSM-5 catalyst by preliminary wet impregnation method, which adopts different concentrations of sodium hydroxide solution to treat the calcined industrial H-ZSM-5 molecular sieve, and then completes the modification through washing, drying and calcination. In the treatment process, the Si-OH-Al groups in the framework of ZSM-5 molecular sieve are destroyed, resulting in a decrease in the number of strong Brønsted acid (B acid) centers and an increase in the number of strong Lewis acid (L acid) centers. The appropriate acid center concentration is conducive to the catalytic cracking of paraffin (using n-hexane as a model component) to prepare low-carbon olefins. Under the condition of 650 ℃, the conversion rate of n-hexane can reach 61.53%, and the selectivity of low-carbon olefins can reach 64.71%. However, this method still has some shortcomings: first, the required reaction temperature is relatively high, resulting in high energy consumption of the process, which is not conducive to cost control in industrial application; second, the conversion rate of n-hexane still has room for improvement, and the utilization rate of raw materials has not reached the optimal level; third, the reaction raw material is limited to n-hexane, and the co-feeding system of multiple types of raw materials is not involved, and the range of applicable raw materials is narrow, which cannot meet the actual needs of complex raw material conversion.

[0005] Therefore, it is urgent to optimize the acidity and pore structure of ZSM-5 molecular sieve through modification means to meet the needs of efficient conversion of long-chain hydrocarbons and alcohols into low-carbon olefins. SUMMARY

[0006] In order to overcome the defects of the prior art, the purpose of the present application is to provide a molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve catalyst and its preparation method and application. The catalyst uses H-ZSM-5 molecular sieve as the main framework, co-dopes molybdenum and phosphorus in the H-ZSM-5 molecular sieve, uses hydrothermal synthesis method to introduce phosphomolybdic acid in situ to realize the atomic-level uniform distribution of molybdenum and phosphorus elements, and combines with slow heating design to ensure the high crystallinity and regularity of the molecular sieve; the introduced molybdenum and phosphorus can precisely adjust the acid site distribution and optimize the pore structure, inhibit the occurrence of deep cracking and other side reactions, and optimize the mass transfer efficiency, realizing efficient catalysis of various long-chain hydrocarbons and mixed feed systems.

[0007] In order to achieve the above purpose, the technical scheme adopted by the present application is: A molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve catalyst, taking H-ZSM-5 molecular sieve as the main framework, co-doping molybdenum and phosphorus in the H-ZSM-5 molecular sieve in situ, and taking the total mass of the molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve catalyst as the basis, the loading amount of molybdenum is 1-20 wt%, and the loading amount of phosphorus is 0.03-0.6 wt%.

[0008] A preparation method of a molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve catalyst, comprising the following steps: Step S1: uniformly mixing and stirring tetrapropylammonium hydroxide, tetraethyl orthosilicate, isopropyl alcohol, urea, aluminum nitrate nonahydrate, sodium hydroxide, deionized water and phosphomolybdic acid according to a mass ratio of 131:112:1:20:(2.5-10):1:185:(0.5-10), and then transferring to a hydrothermal kettle for hydrothermal synthesis reaction, after the reaction is completed, the mixture in the hydrothermal kettle is cooled, and centrifugation, water washing and drying are sequentially performed to obtain a molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve precursor; Step S2: sequentially performing grinding and calcination on the molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve precursor to obtain a molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve; Step S3: mixing the molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve and an ammonium chloride solution, and then performing ion exchange for not less than three times, after the ion exchange is completed, sequentially performing water washing and drying to obtain a molybdenum and phosphorus co-doped NH4-ZSM-5 molecular sieve; Step S4: sequentially performing grinding and calcination on the molybdenum and phosphorus co-doped NH4-ZSM-5 molecular sieve to obtain a molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve.

[0009] Further, in the step S1, the hydrothermal synthesis reaction is first used to raise the temperature of the hydrothermal kettle from 25-30 DEG C to 150-200 DEG C for 1200-1600 min, and then the temperature is kept at 150-200 DEG C for 2500-3000 min.

[0010] Further, in the step S1, the mixing and stirring time is 1-5 h, the mixing and stirring rate is 300-500 rpm, the mixture in the hydrothermal kettle is cooled to 25-30 DEG C, the centrifugation time is 3-5 min, the centrifugation rate is 8000-10000 rpm, the water washing time is not less than three times, the drying time is 10-15 h, and the drying temperature is 60-100 DEG C.

[0011] Further, in the step S2, the particle size distribution after grinding is 200-500 nm, the calcination is first used to raise the temperature from 25-30 DEG C to 400-700 DEG C for 100-150 min, and then the temperature is kept at 400-700 DEG C for 3-7 h, and the calcination atmosphere is air.

[0012] Further, the step S3 specifically comprises: Step S3-1: mixing the molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve and the 0.8-3 mol / L ammonium chloride solution according to a solid-liquid mass ratio of 1:(8-12), and then sequentially stirring and centrifuging to obtain a solid product one; Step S3-2: mixing the solid product one and the 0.8-3 mol / L ammonium chloride solution according to a solid-liquid mass ratio of 1:(8-12), and then repeating the operation of step S3-1 for not less than two cycles to obtain a solid product two; Step S3-3: sequentially performing water washing and drying on the solid product two to obtain the molybdenum and phosphorus co-doped NH4-ZSM-5 molecular sieve; Further, in the step S3-1, the stirring time is 6-8 h, the stirring rate is 300-500 rpm, the centrifugation time is 3-5 min, and the centrifugation rate is 8000-10000 rpm; in the step S3-3, the number of water washing times is not less than three, the drying time is 10-15 h, and the drying temperature is 60-100℃.

[0013] Further, in the step S4, the particle size distribution after grinding is 200-500 nm, and during the calcination, the temperature is first raised from 25-30℃ to 400-700℃ for 100-150 min, then maintained at 400-700℃ for 3-7 h, and the calcination atmosphere is air.

[0014] A molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve catalyst or a molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve catalyst prepared by any one of the above methods is used for converting long-chain hydrocarbons and alcohol into low-carbon olefins, the molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve is loaded into a fixed bed reactor, a mixed solution of long-chain hydrocarbons and alcohol is pumped in, nitrogen is used as a carrier gas, and low-carbon olefins are prepared under preset reaction conditions; the long-chain hydrocarbons are one of n-pentane, iso-pentane, n-hexane and n-hexene, the alcohol is one of methanol and ethanol, the volume ratio of the long-chain hydrocarbons to the alcohol is (1-5):(0-1), the mass space velocity of the molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve is 1-20 h -1 ; and the preset reaction conditions specifically include: the reaction pressure is normal pressure, the reaction temperature is 300-600℃, and the nitrogen flow rate is 10-50 mL / min.

[0015] Compared with the prior art, the present application has the following beneficial effects: 1. This invention provides a molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve catalyst. Using H-ZSM-5 molecular sieve as the main framework, its catalytic performance and hydrothermal stability are significantly improved compared to existing ZSM-5 molecular sieves. By in-situ co-doping molybdenum and phosphorus into the H-ZSM-5 molecular sieve, molybdenum partially replaces the Al / Si sites in the H-ZSM-5 molecular sieve framework. By adjusting the electronic environment and coordination state of the framework atoms, the intensity, density, and distribution characteristics of acidic sites can be controlled, providing suitable active centers for key reactions such as long-chain hydrocarbon cracking and alcohol dehydration activation. Phosphorus, on the one hand, can form stable... The invention achieves a defined chemical bonding structure, further fine-tuning the acid strength and enhancing hydrothermal stability. On the other hand, phosphorus can moderately modify the molecular sieve pore structure, improving the diffusion efficiency of reactants and products and reducing side reactions. Changes in the loading amount significantly affect the properties and distribution of acidic sites. If the molybdenum loading is too low, the acid modification of the molecular sieve pore surface is insufficient, making it difficult to form acidic sites that meet catalytic requirements. If the molybdenum loading is too high, molybdenum species are prone to agglomerate on the molecular sieve surface, clogging the pores and causing uneven surface acidity distribution. In addition, excessive phosphorus will cover the effective active sites on the molecular sieve surface, leading to a decrease in catalytic activity. This invention reasonably controls the molybdenum loading at 1~20 wt% and the phosphorus loading at 0.03~0.6 wt%, resulting in higher product selectivity and catalytic activity in the co-feeding conversion of long-chain hydrocarbons and alcohols into low-carbon olefins.

[0016] 2. In the preparation of molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve catalysts, this invention introduces phosphomolybdic acid in situ during the hydrothermal synthesis reaction. This allows Mo and P elements to be uniformly distributed at the atomic level in the framework and surface of the H-ZSM-5 molecular sieve, forming a stable chemical bond structure. This enhances its activity in cracking long-chain hydrocarbons (promoting efficient C / C bond cleavage) and its ability to dehydrate alcohols (driving directional activation of CO bonds), constructing a synergistic reaction pathway for C / C bond cleavage and CO bond activation. This improves the selectivity and catalyst stability for low-carbon olefins (especially ethylene and propylene). The addition of phosphomolybdic acid regulates the distribution of acidic sites in the H-ZSM-5 molecular sieve, reducing the number of strong acid sites and increasing the proportion of medium-strong and weak acid sites. Acid regulation inhibits the occurrence of side reactions such as deep cracking, hydrogen transfer, and aromatization, reducing the generation of byproducts such as aromatics and coke, and significantly improving the selectivity for low-carbon olefins. Compared with the traditional impregnation method, this effectively avoids the aggregation or loss of active components under high-temperature reaction conditions.

[0017] 3. In the preparation of the molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve catalyst, the hydrothermal synthesis reaction first involves heating the hydrothermal reactor from 25-30°C to 150-200°C for 1200-1600 min, and then maintaining the temperature at 150-200°C for 2500-3000 min. This slow heating design allows for uniform diffusion of the molecular sieve precursor and synchronized and orderly crystal nucleation and growth, avoiding problems such as insufficient crystallinity, small grain size, and numerous internal defects in the crystal lattice caused by rapid crystal nucleation. Simultaneously, it provides sufficient time for the reaction between phosphomolybdic acid and the molecular sieve precursor, ensuring uniform embedding of Mo and P elements and preventing element agglomeration into inactive impurities. It also guides the regular growth of the molecular sieve channels, preventing narrow and closed channels, reducing substrate retention, and minimizing side reactions such as polymerization and cyclization.

[0018] 4. The molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve catalyst of this invention exhibits excellent substrate adaptability when co-feeding long-chain hydrocarbons and alcohols to low-carbon olefins. It can be adapted not only to single long-chain hydrocarbon feedstocks such as n-pentane, isopentane, n-hexane, and n-hexene, but also maintains excellent catalytic activity and selectivity in mixed feed systems composed of n-hexane, n-hexene, and ethanol. This characteristic breaks the dependence of traditional catalysts on single substrates and provides a feasible path for the efficient conversion of complex hydrocarbon mixtures in industrial scenarios, significantly improving the flexibility and practicality of process applications.

[0019] In summary, this invention synthesizes a molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve catalyst using a one-step hydrothermal method. In-situ introduction of phosphomolybdic acid achieves atomic-level uniform distribution of Mo and P, while a slow heating design ensures high crystallinity and pore regularity of the molecular sieve. Simultaneously, the introduction of phosphomolybdic acid allows for precise regulation of acidic site distribution and optimization of pore structure, suppressing side reactions such as deep cracking while optimizing mass transfer efficiency. This overcomes the limitations of single substrates and achieves highly efficient catalysis for various long-chain hydrocarbons and mixed feed systems. Attached Figure Description

[0020] Figure 1 This is a SEM image of the H-ZSM-5 molecular sieve catalyst of the present invention.

[0021] Figure 2 This is a SEM image of the 5%Mo-0.15%PH-ZSM-5 catalyst of the present invention.

[0022] Figure 3 This is a SEM image of the 10%Mo-0.3%PH-ZSM-5 catalyst of this invention.

[0023] Figure 4 This is a flowchart of the preparation method of the molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve catalyst of the present invention. Detailed Implementation

[0024] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments: A molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve catalyst is disclosed. Using H-ZSM-5 molecular sieve as the main framework, molybdenum and phosphorus are co-doped in situ into the H-ZSM-5 molecular sieve. Molybdenum partially replaces the Al / Si sites in the H-ZSM-5 molecular sieve framework. By adjusting the electronic environment and coordination state of the framework atoms, the strength, density, and distribution characteristics of the acidic sites are controlled. Phosphorus can form stable chemical bonds with the hydroxyl groups on the molecular sieve surface and framework atoms, further fine-tuning the acidity and enhancing hydrothermal stability. Furthermore, it can moderately modify the pore structure of the molecular sieve, optimizing the pore size. Based on the total mass of the molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve catalyst, the molybdenum loading is 1–20 wt%, and the phosphorus loading is 0.03–0.6 wt%.

[0025] H-ZSM-5 molecular sieve has a typical MFI topology, consisting of a pore system composed of ten-membered rings. Figure 1 , Figure 2 and Figure 3 SEM images of H-ZSM-5 molecular sieve catalyst, 5%Mo-0.15%PH-ZSM-5 catalyst, and 10%Mo-0.3%PH-ZSM-5 catalyst are shown. SEM characterization results show that all three catalysts exhibit a uniform hexagonal plate-like structure with dimensions of approximately 200 nm to 1 μm. This regular hexagonal plate-like morphology is a direct external manifestation of the ordered growth of the MFI topology, indicating that both H-ZSM-5 molecular sieve co-doped with molybdenum and phosphorus exhibit good crystal growth, a regular crystal structure, and an ordered pore arrangement. This provides a good spatial structural basis for reactant diffusion, active site contact, and product desorption in subsequent catalytic reactions. However, while the H-ZSM-5 molecular sieve crystal surface is smooth, the addition of molybdenum and phosphorus results in a slightly rougher surface, with extremely fine granular protrusions observed in localized areas. This roughening trend slightly intensifies with increasing molybdenum and phosphorus loading. Even with differences in surface characteristics, the incorporation of molybdenum and phosphorus did not significantly damage the crystal structure of the H-ZSM-5 molecular sieve. Mo and P species were uniformly distributed at the atomic level within the framework and surface of the H-ZSM-5 molecular sieve, without causing crystal distortion or significant changes in morphology. The MFI topology of the molecular sieve was well preserved, ensuring the integrity of the pore structure. Therefore, the molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve catalyst not only maintains the original pore advantages of the molecular sieve but also constructs new active centers through the introduction of molybdenum and phosphorus species. Furthermore, surface roughening and fine protrusions may increase the exposure of active sites, creating favorable conditions for improving catalytic performance.

[0026] Example 1 See Figure 4 A method for preparing a molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve catalyst includes the following steps: Step S1: Tetrapropylammonium hydroxide (25 wt%), tetraethyl orthosilicate, isopropanol, urea, aluminum nitrate nonahydrate, sodium hydroxide, deionized water, and phosphomolybdic acid were mixed in a mass ratio of 131:112:1:20:10:1:185:0.5 and stirred at 500 rpm for 3 h. After homogenization, the mixture was transferred to a 200 mL hydrothermal reactor and sealed. The reactor was then placed in an oven for hydrothermal synthesis. The temperature of the reactor was increased from 27 °C to 170 °C in 1300 min and maintained at 170 °C for 2700 min. After the hydrothermal synthesis reaction was completed, the mixture in the reactor was cooled to 27 °C and transferred to a centrifuge tube. It was centrifuged at 9000 rpm for 4 min, then washed three times with deionized water to remove soluble residues (soluble residues refer to unreacted raw materials and amorphous soluble byproducts generated during the reaction). The mixture was then dried in a 100 °C oven for 10 minutes. h, a precursor of molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve was obtained; in this embodiment, tetrapropylammonium hydroxide, tetraethyl orthosilicate, and aluminum nitrate nonahydrate were used as template agent, silicon source, and aluminum source, respectively; urea and sodium hydroxide were used as alkali source; isopropanol and deionized water were used as solvent; and phosphomolybdic acid was used as molybdenum source and phosphorus source.

[0027] Step S2: The precursor of molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve is ground. The ground precursor of molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve with a particle size distribution of 200~500nm is transferred to a muffle furnace and sealed. It is calcined in air atmosphere. The muffle furnace is first heated from 27 ℃ to 600 ℃ in 130 min, and then held at 600 ℃ for 4 h to remove residual tetrapropylammonium hydroxide, thereby obtaining molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve. Step S3: The molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve is mixed with ammonium chloride solution and subjected to three ion exchanges. After the ion exchange is completed, it is washed with water and dried in sequence to obtain the molybdenum and phosphorus co-doped NH4-ZSM-5 molecular sieve. Step S3 specifically includes: Step S3-1: Molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve and 1.5 mol / L ammonium chloride solution were mixed at a solid-liquid mass ratio of 1:9, stirred at 500 rpm for 6 h, and then centrifuged at 9000 rpm for 4 min to obtain solid product one; Step S3-2: Mix solid product one and 1.5 mol / L ammonium chloride solution at a solid-liquid mass ratio of 1:9, and repeat step S3-1 twice to obtain solid product two. Step S3-3: Wash the solid product three times with dihydrate to remove residual ammonium chloride solution, and dry it at 100 °C for 10 h to obtain molybdenum and phosphorus co-doped NH4-ZSM-5 molecular sieve; Step S4: The molybdenum and phosphorus co-doped NH4-ZSM-5 molecular sieve was ground. The ground NH4-ZSM-5 molecular sieve with a particle size distribution of 200~500nm was transferred to a muffle furnace and sealed. It was then calcined in air. The muffle furnace temperature was first increased from 27 °C to 600 °C in 130 min, and then maintained at 600 °C for 4 h to obtain the molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve. In this embodiment, the molybdenum loading was 1 wt% and the phosphorus loading was 0.03 wt%.

[0028] The calculation process for the loading of molybdenum and phosphorus elements is as follows: The total mass of the molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve catalyst was calculated based on the mass of the H-ZSM-5 molecular sieve prepared in Comparative Example 1, combined with the theoretically generated molybdenum / phosphorus ratio from the phosphomolybdic acid used in the doping process. The specific stoichiometric relationship is: Total catalyst mass = Mass of H-ZSM-5 molecular sieve + Mass of theoretically generated molybdenum / phosphorus ratio from phosphomolybdic acid. This total catalyst mass was used as the baseline mass for subsequent loading calculations; the relevant calculation expression is: Molybdenum loading (wt%) = (mass of phosphomolybdic acid / relative molecular mass of phosphomolybdic acid) × 12 × relative atomic mass of molybdenum / total mass of catalyst × 100% Phosphorus loading (wt%) = (mass of phosphomolybdic acid / relative molecular mass of phosphomolybdic acid × relative atomic mass of phosphorus / total mass of catalyst × 100%) Example 2 A method for preparing a molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve catalyst includes the following steps: Step S1: Tetrapropylammonium hydroxide (25 wt%), tetraethyl orthosilicate, isopropanol, urea, aluminum nitrate nonahydrate, sodium hydroxide, deionized water, and phosphomolybdic acid were mixed in a mass ratio of 131:112:1:20:5:1:185:2.5 and stirred at 300 rpm for 5 h. After homogenization, the mixture was transferred to a 200 mL hydrothermal reactor and sealed. The reactor was then placed in an oven for hydrothermal synthesis. The temperature of the reactor was increased from 25 °C to 200 °C in 1600 min and maintained at 200 °C for 2500 min. After the hydrothermal synthesis reaction was completed, the mixture in the reactor was cooled to 25 °C and transferred to a centrifuge tube. The mixture was centrifuged at 8000 rpm for 5 min, washed three times with deionized water, and dried in an 80 °C oven for 13 h to obtain the precursor of molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve. Step S2: Grind the precursor of molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve. Transfer the ground precursor of molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve with a particle size distribution of 200~500nm to a muffle furnace and seal it. Calcination is carried out in an air atmosphere. First, the muffle furnace temperature is raised from 25 ℃ to 550 ℃ in 120 min, and then maintained at 550 ℃ for 5 h to obtain molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve. Step S3: The molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve is mixed with ammonium chloride solution and subjected to three ion exchanges. After the ion exchange is completed, it is washed with water and dried in sequence to obtain the molybdenum and phosphorus co-doped NH4-ZSM-5 molecular sieve. Step S3 specifically includes: Step S3-1: Molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve and 2 mol / L ammonium chloride solution were mixed at a solid-liquid mass ratio of 1:11, stirred at 300 rpm for 8 h, and then centrifuged at 8000 rpm for 5 min to obtain solid product one; Step S3-2: Mix solid product one and 2 mol / L ammonium chloride solution at a solid-liquid mass ratio of 1:11, and repeat the operation of step S3-1 twice to obtain solid product two; Step S3-3: Wash the solid product three times with dihydrate and dry it at 80 °C for 13 h to obtain molybdenum and phosphorus co-doped NH4-ZSM-5 molecular sieve.

[0029] Step S4: The molybdenum and phosphorus co-doped NH4-ZSM-5 molecular sieve was ground. The ground NH4-ZSM-5 molecular sieve with a particle size distribution of 200~500nm was transferred to a muffle furnace and sealed. It was calcined in air atmosphere. The temperature of the muffle furnace was first raised from 25 °C to 550 °C in 120 min, and then maintained at 550 °C for 5 h to obtain the molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve. In this embodiment, the molybdenum loading was 5 wt% and the phosphorus loading was 0.15 wt%.

[0030] Example 3 A method for preparing a molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve catalyst includes the following steps: Step S1: Tetrapropylammonium hydroxide (25 wt%), tetraethyl orthosilicate, isopropanol, urea, aluminum nitrate nonahydrate, sodium hydroxide, deionized water, and phosphomolybdic acid were mixed in a mass ratio of 131:112:1:20:5:1:185:5 and stirred at 500 rpm for 2 h. After homogenization, the mixture was transferred to a 200 mL hydrothermal reactor and sealed. The reactor was then placed in an oven for hydrothermal synthesis. The temperature of the reactor was increased from 30 °C to 180 °C in 1440 min and maintained at 180 °C for 2900 min. After the hydrothermal synthesis reaction was completed, the mixture in the reactor was cooled to 30 °C. The mixture was then transferred to a centrifuge tube and centrifuged at 10000 rpm for 3 min. The mixture was then washed three times with deionized water and dried in a 60 °C oven for 15 h to obtain the precursor of molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve. Step S2: Grind the precursor of molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve. Transfer the ground precursor of molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve with a particle size distribution of 200~500nm to a muffle furnace and seal it. Calcination is carried out in an air atmosphere. First, the muffle furnace temperature is raised from 30 ℃ to 700 ℃ in 150 min, and then maintained at 700 ℃ for 3 h to obtain molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve. Step S3: The molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve is mixed with ammonium chloride solution and subjected to three ion exchanges. After the ion exchange is completed, it is washed with water and dried in sequence to obtain the molybdenum and phosphorus co-doped NH4-ZSM-5 molecular sieve. Step S3 specifically includes: Step S3-1: Molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve and 1 mol / L ammonium chloride solution are mixed at a solid-liquid mass ratio of 1:10, stirred at 500 rpm for 6 h, and then centrifuged at 10000 rpm for 3 min to obtain solid product one; Step S3-2: Mix solid product one and 1 mol / L ammonium chloride solution at a solid-liquid mass ratio of 1:10, and repeat step S3-1 twice to obtain solid product two. Step S3-3: Wash the solid product three times with dihydrate and dry it at 60 °C for 15 h to obtain molybdenum and phosphorus co-doped NH4-ZSM-5 molecular sieve.

[0031] Step S4: The molybdenum and phosphorus co-doped NH4-ZSM-5 molecular sieve was ground. The ground NH4-ZSM-5 molecular sieve with a particle size distribution of 200~500nm was transferred to a muffle furnace and sealed. It was calcined in air atmosphere. The temperature of the muffle furnace was first raised from 30 ℃ to 700 ℃ in 150 min, and then maintained at 700 ℃ for 3 h to obtain the molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve. In this embodiment, the molybdenum loading was 10 wt% and the phosphorus loading was 0.3 wt%.

[0032] Example 4 A method for preparing a molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve catalyst includes the following steps: Step S1: Tetrapropylammonium hydroxide (25 wt%), tetraethyl orthosilicate, isopropanol, urea, aluminum nitrate nonahydrate, sodium hydroxide, deionized water, and phosphomolybdic acid were mixed in a mass ratio of 131:112:1:20:2.5:1:185:7.5 and stirred at 400 rpm for 3 h. After homogenization, the mixture was transferred to a 200 mL hydrothermal reactor and sealed. The reactor was then placed in an oven for hydrothermal synthesis. The temperature of the reactor was increased from 26 °C to 150 °C in 1200 min and maintained at 150 °C for 3000 min. After the hydrothermal synthesis reaction was completed, the mixture in the reactor was cooled to 26 °C and transferred to a centrifuge tube. The mixture was centrifuged at 9000 rpm for 4 min, washed three times with deionized water, and dried in a 70 °C oven for 14 h to obtain the precursor of molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve. Step S2: The precursor of molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve is ground. The ground precursor of molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve with a particle size distribution of 200~500nm is transferred to a muffle furnace and sealed. It is calcined in an air atmosphere. The muffle furnace is first heated from 26 ℃ to 400 ℃ in 100 min, and then held at 400 ℃ for 7 h to obtain molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve. Step S3: The molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve is mixed with ammonium chloride solution and subjected to three ion exchanges. After the ion exchange is completed, it is washed with water and dried in sequence to obtain the molybdenum and phosphorus co-doped NH4-ZSM-5 molecular sieve. Step S3 specifically includes: Step S3-1: Molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve and 0.8 mol / L ammonium chloride solution were mixed at a solid-liquid mass ratio of 1:12, stirred at 400 rpm for 7 h, and then centrifuged at 9000 rpm for 4 min to obtain solid product one; Step S3-2: Mix solid product one and 0.8 mol / L ammonium chloride solution at a solid-liquid mass ratio of 1:12, and repeat step S3-1 twice to obtain solid product two. Step S3-3: Wash the solid product three times with dihydrate and dry it at 70 °C for 14 h to obtain molybdenum and phosphorus co-doped NH4-ZSM-5 molecular sieve.

[0033] Step S4: The molybdenum and phosphorus co-doped NH4-ZSM-5 molecular sieve was ground. The ground NH4-ZSM-5 molecular sieve with a particle size distribution of 200~500nm was transferred to a muffle furnace and sealed. It was then calcined in air atmosphere. The muffle furnace temperature was first increased from 26 °C to 400 °C in 100 min, and then maintained at 400 °C for 7 h to obtain the molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve. In this example, the molybdenum loading was 15 wt% and the phosphorus loading was 0.45 wt%. Example 5 A method for preparing a molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve catalyst includes the following steps: Step S1: Tetrapropylammonium hydroxide (25 wt%), tetraethyl orthosilicate, isopropanol, urea, aluminum nitrate nonahydrate, sodium hydroxide, deionized water, and phosphomolybdic acid were mixed in a mass ratio of 131:112:1:20:5:1:185:10 and stirred at 500 rpm for 1 h. After homogenization, the mixture was transferred to a 200 mL hydrothermal reactor and sealed. The reactor was then placed in an oven for hydrothermal synthesis. The temperature of the reactor was increased from 28 °C to 160 °C in 1300 min and maintained at 160 °C for 2900 min. After the hydrothermal synthesis reaction was completed, the mixture in the reactor was cooled to 28 °C and transferred to a centrifuge tube. The mixture was centrifuged at 8000 rpm for 5 min, washed three times with deionized water, and dried in a 60 °C oven for 15 h to obtain the precursor of molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve. Step S2: The precursor of molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve is ground. The ground precursor of molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve with a particle size distribution of 200~500nm is transferred to a muffle furnace and sealed. It is calcined in air atmosphere. The muffle furnace is first heated from 28 ℃ to 500 ℃ in 110 min, and then kept at 500 ℃ for 6 h to obtain molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve. Step S3: The molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve is mixed with ammonium chloride solution and subjected to three ion exchanges. After the ion exchange is completed, it is washed with water and dried in sequence to obtain the molybdenum and phosphorus co-doped NH4-ZSM-5 molecular sieve. Step S3 specifically includes: Step S3-1: Molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve and 3 mol / L ammonium chloride solution were mixed at a solid-liquid mass ratio of 1:8, stirred at 300 rpm for 8 h, and then centrifuged at 8000 rpm for 5 min to obtain solid product one; Step S3-2: Mix solid product one and 3 mol / L ammonium chloride solution at a solid-liquid mass ratio of 1:8, and repeat the operation of step S3-1 twice to obtain solid product two; Step S3-3: Wash the solid product three times with dihydrate and dry it at 60 °C for 15 h to obtain molybdenum and phosphorus co-doped NH4-ZSM-5 molecular sieve.

[0034] Step S4: The molybdenum and phosphorus co-doped NH4-ZSM-5 molecular sieve was ground. The ground NH4-ZSM-5 molecular sieve with a particle size distribution of 200~500nm was transferred to a muffle furnace and sealed. It was then calcined in air atmosphere. The muffle furnace temperature was first increased from 28 °C to 500 °C in 110 min, and then maintained at 500 °C for 6 h to obtain the molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve. In this embodiment, the molybdenum loading was 20 wt% and the phosphorus loading was 0.6 wt%. Comparative Example 1 A method for preparing an H-ZSM-5 molecular sieve catalyst includes the following steps: Step S1: Tetrapropylammonium hydroxide (25 wt%), tetraethyl orthosilicate, isopropanol, urea, aluminum nitrate nonahydrate, sodium hydroxide, and deionized water were mixed in a mass ratio of 131:112:1:20:5:1:185 and stirred at 400 rpm for 4 h. After homogenization, the mixture was transferred to a 200 mL hydrothermal reactor and sealed. The reactor was then placed in an oven for hydrothermal synthesis. The temperature of the reactor was increased from 25 °C to 180 °C in 1400 min and maintained at 180 °C for 2800 min. After the hydrothermal synthesis reaction was completed, the mixture in the reactor was cooled to 25 °C and transferred to a centrifuge tube. The mixture was centrifuged at 10000 rpm for 3 min, washed three times with deionized water, and dried in an 80 °C oven for 13 h to obtain the precursor of Na-ZSM-5 molecular sieve. Step S2: Grind the precursor of Na-ZSM-5 molecular sieve. Transfer the Na-ZSM-5 molecular sieve precursor with a particle size distribution of 200~500nm into a muffle furnace and seal it. Calcine it in an air atmosphere. First, heat the muffle furnace from 25 ℃ to 550 ℃ for 120 min, and then keep it at 550 ℃ for 5 h to obtain Na-ZSM-5 molecular sieve. Step S3: Mix Na-ZSM-5 molecular sieve and ammonium chloride solution and perform three ion exchanges. After the ion exchanges are completed, wash with water and dry in sequence to obtain NH4-ZSM-5 molecular sieve. Step S3 specifically includes: Step S3-1: Mix Na-ZSM-5 molecular sieve and 1.5 mol / L ammonium chloride solution at a solid-liquid mass ratio of 1:10, stir at 400 rpm for 7 h, and then centrifuge at 10000 rpm for 3 min to obtain solid product one; Step S3-2: Mix solid product one and 1.5 mol / L ammonium chloride solution at a solid-liquid mass ratio of 1:10, and repeat the operation of step S3-1 twice to obtain solid product two; Step S3-3: Wash the solid product three times with dihydrate and dry it at 80 °C for 13 h to obtain NH4-ZSM-5 molecular sieve.

[0035] Step S4: Grind the NH4-ZSM-5 molecular sieve. Transfer the ground NH4-ZSM-5 molecular sieve with a particle size distribution of 200~500nm to a muffle furnace and seal it. Calcinate it in an air atmosphere. First, raise the temperature of the muffle furnace from 25 ℃ to 550 ℃ in 120 min, and then maintain it at 550 ℃ for 5 h to obtain H-ZSM-5 molecular sieve.

[0036] Catalyst activity test 0.3 g of each of the 5% Mo-0.15% PH-ZSM-5 molecular sieve and 10% Mo-0.3% PH-ZSM-5 molecular sieve from Examples 2-3, and the H-ZSM-5 molecular sieve from Comparative Example 1, were weighed and loaded into a fixed-bed reactor. The reactants, a mixture of hydrocarbons including n-hexane, or n-hexane and ethanol in a volume ratio of 10:1, or n-hexane, n-hexene, and ethanol in a volume ratio of 5:5:1, were transported into the fixed-bed reactor using a metering pump. The reactants were introduced into the reactor at a flow rate of 0.01 mL / min, a N2 flow rate of 10 mL / min, a reaction temperature of 550 °C, a reaction pressure of atmospheric pressure, and a catalyst mass hourly space velocity of 1.4 h⁻¹. -1 The reaction is carried out under certain conditions, and the product is a mixture of alkanes, alkenes and aromatics (mainly low-carbon olefins).

[0037] Table 1. Crack performance of H-ZSM-5 molecular sieves co-doped with molybdenum and phosphorus for co-feeding long-chain hydrocarbons and alcohols. As shown in Table 1, the H-ZSM-5 molecular sieve and the molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve involved in this invention exhibit excellent feed conversion capabilities. Except for the 5%Mo-0.15%PH-ZSM-5 catalyst, which achieves a hexane conversion rate of 98% in a hexane:ethanol (10:1) system, the hexane conversion rate reaches 99% under all other operating conditions. In feed systems containing hexene, the hexene conversion rate is also 99%, indicating that this series of catalysts can efficiently achieve deep conversion between alkane and olefin feedstocks. However, the H-ZSM-5 molecular sieve exhibits low selectivity for low-carbon olefins, only 45%-52%, while the molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve catalyst shows significantly higher selectivity for low-carbon olefins. The selectivity was significantly improved. In the hexane:ethanol (10:1) and hexane:hexene:ethanol (5:5:1) systems, the selectivity of low-carbon olefins reached 65% and 70%, respectively. The performance of 10%Mo-0.3%PH-ZSM-5 was even better, with the selectivity of low-carbon olefins further increasing to 72% in the hexane:hexene:ethanol (5:5:1) system. In summary, 10%Mo-0.3%PH-ZSM-5 has the best overall catalytic performance in the hexane:hexene:ethanol (5:5:1) system, which fully confirms the modification effect of molybdenum and phosphorus co-doping and provides a feasible technical solution for the efficient preparation of low-carbon olefins.

[0038] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve catalyst, characterized in that: Using H-ZSM-5 molecular sieve as the main framework, molybdenum and phosphorus were co-doped in situ into H-ZSM-5 molecular sieve. Based on the total mass of the H-ZSM-5 molecular sieve catalyst co-doped with molybdenum and phosphorus, the loading of molybdenum was 1~20 wt% and the loading of phosphorus was 0.03~0.6 wt%.

2. A method for preparing a molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve catalyst, characterized in that: Includes the following steps: Step S1: Tetrapropylammonium hydroxide, tetraethyl orthosilicate, isopropanol, urea, aluminum nitrate nonahydrate, sodium hydroxide, deionized water and phosphomolybdic acid are mixed and stirred evenly in a mass ratio of 131:112:1:20:(2.5~10):1:185:(0.5~10), and then transferred to a hydrothermal reactor for hydrothermal synthesis reaction. After the reaction is completed, the mixture in the hydrothermal reactor is cooled and then centrifuged, washed with water and dried in sequence to obtain the molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve precursor. Step S2: The molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve precursor is successively ground and calcined to obtain the molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve. Step S3: Mix the molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve with ammonium chloride solution and perform ion exchange at least three times. After the ion exchange is completed, wash with water and dry in sequence to obtain molybdenum and phosphorus co-doped NH4-ZSM-5 molecular sieve. Step S4: The molybdenum and phosphorus co-doped NH4-ZSM-5 molecular sieve is ground and calcined sequentially to obtain the molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve.

3. The method for preparing a molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve catalyst according to claim 2, characterized in that: In step S1, the hydrothermal synthesis reaction is first heated from 25-30°C to 150-200°C in the hydrothermal reactor over 1200-1600 min, and then maintained at 150-200°C for 2500-3000 min.

4. The method for preparing a molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve catalyst according to claim 2, characterized in that: In step S1, the mixing time is 1-5 hours, the mixing speed is 300-500 rpm, the mixture in the hydrothermal reactor is cooled to 25-30°C, the centrifugation time is 3-5 minutes, the centrifugation speed is 8000-10000 rpm, the number of water washings is no less than three times, the drying time is 10-15 hours, and the drying temperature is 60-100°C.

5. The method for preparing a molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve catalyst according to claim 2, characterized in that: In step S2, the particle size distribution after grinding is 200~500nm. During calcination, the temperature is first raised from 25~30℃ to 400~700℃ in 100~150min, and then maintained at 400~700℃ for 3~7h. The calcination atmosphere is air.

6. The method for preparing a molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve catalyst according to claim 2, characterized in that: Step S3 specifically includes: Step S3-1: Molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve and 0.8~3 mol / L ammonium chloride solution are mixed at a solid-liquid mass ratio of 1:(8~12), and then stirred and centrifuged sequentially to obtain solid product one; Step S3-2: Mix solid product one and 0.8~3 mol / L ammonium chloride solution at a solid-liquid mass ratio of 1:(8~12), and repeat the operation of step S3-1 for no less than two cycles to obtain solid product two; Step S3-3: The solid product 2 is washed with water and dried sequentially to obtain NH4-ZSM-5 molecular sieve co-doped with molybdenum and phosphorus.

7. The method for preparing a molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve catalyst according to claim 6, characterized in that: In step S3-1, the stirring time is 6-8 hours, the stirring rate is 300-500 rpm, the centrifugation time is 3-5 minutes, and the centrifugation rate is 8000-10000 rpm; in step S3-3, the number of water washings is no less than three times, the drying time is 10-15 hours, and the drying temperature is 60-100℃.

8. The method for preparing a molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve catalyst according to claim 2, characterized in that: In step S4, the particle size distribution after grinding is 200~500nm. During calcination, the temperature is first raised from 25~30℃ to 400~700℃ in 100~150min, and then maintained at 400~700℃ for 3~7h. The calcination atmosphere is air.

9. A method for preparing a molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve catalyst, characterized in that: Includes the following steps: Step S1: Tetrapropylammonium hydroxide (25 wt%), tetraethyl orthosilicate, isopropanol, urea, aluminum nitrate nonahydrate, sodium hydroxide, deionized water, and phosphomolybdic acid were mixed in a mass ratio of 131:112:1:20:5:1:185:5 and stirred at 500 rpm for 2 h. After homogenization, the mixture was transferred to a 200 mL hydrothermal reactor and sealed. The reactor was then placed in an oven for hydrothermal synthesis. The temperature of the reactor was increased from 30 °C to 180 °C in 1440 min and maintained at 180 °C for 2900 min. After the hydrothermal synthesis reaction was completed, the mixture in the reactor was cooled to 30 °C. The mixture was then transferred to a centrifuge tube and centrifuged at 10000 rpm for 3 min. The mixture was then washed three times with deionized water and dried in a 60 °C oven for 15 h to obtain the precursor of molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve. Step S2: Grind the precursor of molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve. Transfer the ground precursor of molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve with a particle size distribution of 200~500nm to a muffle furnace and seal it. Calcination is carried out in an air atmosphere. First, the muffle furnace temperature is raised from 30 ℃ to 700 ℃ in 150 min, and then maintained at 700 ℃ for 3 h to obtain molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve. Step S3: The molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve is mixed with ammonium chloride solution and subjected to three ion exchanges. After the ion exchange is completed, it is washed with water and dried in sequence to obtain the molybdenum and phosphorus co-doped NH4-ZSM-5 molecular sieve. Step S3 specifically includes: Step S3-1: Molybdenum and phosphorus co-doped Na-ZSM-5 molecular sieve and 1 mol / L ammonium chloride solution are mixed at a solid-liquid mass ratio of 1:10, stirred at 500 rpm for 6 h, and then centrifuged at 10000 rpm for 3 min to obtain solid product one; Step S3-2: Mix solid product one and 1 mol / L ammonium chloride solution at a solid-liquid mass ratio of 1:10, and repeat step S3-1 twice to obtain solid product two. Step S3-3: Wash the solid product three times with dihydrate and dry it at 60 °C for 15 h to obtain molybdenum and phosphorus co-doped NH4-ZSM-5 molecular sieve; Step S4: The molybdenum and phosphorus co-doped NH4-ZSM-5 molecular sieve is ground. The ground NH4-ZSM-5 molecular sieve with a particle size distribution of 200~500nm is transferred to a muffle furnace and sealed. It is then calcined in an air atmosphere. The muffle furnace is first heated from 30 ℃ to 700 ℃ in 150 min, and then held at 700 ℃ for 3 h to obtain the molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve. The molybdenum loading is 10 wt%, and the phosphorus loading is 0.3 wt%.

10. The application of a molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve catalyst as described in claim 1, or a molybdenum and phosphorus co-doped H-ZSM-5 molecular sieve catalyst prepared by any of claims 2-9, in the co-feeding conversion of long-chain hydrocarbons and alcohols into low-carbon olefins, characterized in that: Molybdenum and phosphorus co-doped H-ZSM-5 molecular sieves were loaded into a fixed-bed reactor, and a mixed solution of long-chain hydrocarbons and alcohols was pumped in. Nitrogen was used as the carrier gas, and low-carbon olefins were prepared under preset reaction conditions. The long-chain hydrocarbons were selected from n-pentane, isopentane, n-hexane, and n-hexene, and the alcohols were selected from methanol and ethanol. The volume ratio of the long-chain hydrocarbons to the alcohols was (1~5):(0~1), and the mass hourly space velocity (HHSV) of the molybdenum and phosphorus co-doped H-ZSM-5 molecular sieves was 1~20 h⁻¹. -1 The preset reaction conditions are as follows: the reaction pressure is atmospheric pressure, the reaction temperature is 300~600℃, and the nitrogen flow rate is 10~50 mL / min.

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