A molybdenum phosphide composite catalyst and its preparation method

Abstract

The present invention discloses a molybdenum phosphide composite catalyst and a preparation method thereof. The catalyst comprises nitrogen and phosphorus co-doped carbon nanosheets, on which molybdenum phosphide nanoparticles are loaded. The preparation method comprises the following steps: preparing a molybdenum-based metal organic framework / melamine dispersion, then adding a phytic acid solution for solvent thermal reaction and calcination. The molybdenum phosphide composite catalyst of the present invention has the advantages of strong catalytic activity and good stability, can be widely used for removing sulfur-containing organic compounds in petroleum products, can achieve efficient removal of sulfur-containing organic compounds in petroleum products under mild conditions, has high use value and good application prospects. The preparation method of the molybdenum phosphide composite catalyst of the present invention has the advantages of simple process, convenient operation, cheap and easily available raw materials, low cost, etc., can realize large-scale batch preparation, and is conducive to industrial utilization.

Description

Technical Field

[0001] The invention belongs to the field of heterogeneous catalysis technology and petrochemical technology, and relates to a molybdenum phosphide composite catalyst and a preparation method thereof. Background Art

[0002] Despite the increasing popularity of new energy applications, fuel oil still dominates global energy consumption. However, the use of high-sulfur fuel will inevitably lead to various environmental pollution. Therefore, many countries and regions have implemented stricter international fuel standards, limiting the sulfur content in fuel to below 10ppm, which has further expanded people's demand for ultra-low sulfur fuel production. Oxidative desulfurization (ODS) has been considered one of the most promising technologies for deep desulfurization of sulfur-containing fuel oil due to its mild reaction conditions, strong selectivity and high desulfurization rate. One of the key bottlenecks in the widespread application of ODS is the suboptimal catalytic activity of ODS catalysts. Therefore, the research and development of high-activity ODS catalysts has become the key to breaking through the bottleneck of ODS applications.

[0003] Among many catalysts, molybdenum phosphide is expected to stand out among many ODS catalysts due to its unique electronic properties, multi-party composition and structure. First, molybdenum phosphide easily reacts with oxidants to form electrophilic reactive intermediates, which is considered to be the driving force for efficient ODS. In addition, molybdenum phosphide has abundant free electrons, which means that it is easier to produce a large number of unsaturated metal sites, which is crucial for promoting the efficient oxidation of aromatic organosulfur compounds. Despite this, the preparation of molybdenum phosphide requires harsh conditions and the use of flammable phosphorus and highly toxic phosphine as phosphating agents, which undoubtedly hinders large-scale synthesis and application.

[0004] This invention addresses the shortcomings of molybdenum phosphide synthesis, such as harsh conditions, high costs, and the inability to synthesize on a large scale. By selecting starting molybdenum, phosphorus, and carbon precursors that strongly interact with each other, a molybdenum phosphide composite catalyst is prepared through an in-situ synthesis method. This preparation method offers advantages such as simplicity, ease of operation, readily available and inexpensive raw materials, and low cost. The resulting molybdenum phosphide composite catalyst exhibits excellent catalytic oxidative desulfurization activity and reusability, which is of great significance for effectively converting sulfur-containing organic pollutants in petroleum products and improving the availability of petroleum products. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of the existing technology and provide a molybdenum phosphide composite catalyst with strong catalytic activity and good stability for deep oxidation desulfurization of fuel. It also provides a preparation method of the molybdenum phosphide composite catalyst with simple process, low cost, easy operation, and green and pollution-free.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0007] A molybdenum phosphide composite catalyst comprises nitrogen and phosphorus co-doped carbon nanosheets, on which molybdenum phosphide nanoparticles are loaded.

[0008] 1. A molybdenum phosphide composite catalyst, characterized in that the molybdenum phosphide composite catalyst comprises nitrogen and phosphorus co-doped carbon nanosheets, and the nitrogen and phosphorus co-doped carbon nanosheets are loaded with nano-scale molybdenum phosphide particles.

[0009] The above-mentioned molybdenum phosphide composite catalyst is further improved, in which the mass ratio of nitrogen and phosphorus co-doped carbon nanosheets and molybdenum phosphide particles in the molybdenum phosphide composite catalyst is 2 to 40.

[0010] The above-mentioned molybdenum phosphide composite catalyst is further improved, wherein the mass fraction of nitrogen in the nitrogen-phosphorus co-doped carbon nanosheets is 2% to 8% of the nitrogen-phosphorus co-doped carbon nanosheets, and the mass fraction of phosphorus is 4% to 15% of the nitrogen-phosphorus co-doped carbon nanosheets.

[0011] As a general technical concept, the present invention also provides a method for preparing the above-mentioned molybdenum phosphide composite catalyst, comprising the following steps:

[0012] S1, preparing a molybdenum-based metal-organic framework into a molybdenum-based metal-organic framework dispersion, adding a melamine dispersion, and stirring to prepare a molybdenum-based metal-organic framework / melamine dispersion;

[0013] S2, mixing the molybdenum-based metal organic framework / melamine dispersion obtained in step S1 with the phytic acid solution to perform a solvothermal reaction, centrifuging, and freeze-drying to obtain a molybdenum phosphide composite catalyst precursor powder;

[0014] S3. calcining the molybdenum phosphide composite catalyst precursor powder obtained in step S2 in an argon atmosphere to obtain a molybdenum phosphide composite catalyst.

[0015] The above-mentioned method for preparing the molybdenum phosphide composite catalyst is further improved, in which in step S1, the method for preparing the molybdenum-based metal-organic framework comprises the following steps:

[0016] (1) adding molybdenum trioxide to ultrapure water, stirring to obtain a molybdenum trioxide dispersion;

[0017] (2) adding imidazole to the molybdenum trioxide dispersion obtained in step (1) to carry out a hydrothermal reaction, washing, and drying to obtain a molybdenum-based metal organic framework.

[0018] The preparation method of the molybdenum phosphide composite catalyst is further improved, wherein in step (1), the mass ratio of the molybdenum trioxide to ultrapure water is 1:70-100; the stirring time is 0.5-2h;

[0019] The preparation method of the above-mentioned molybdenum phosphide composite catalyst is further improved. In step (2), the mass ratio of imidazole to molybdenum trioxide is 0.48-0.50:1; the hydrothermal reaction is carried out at a temperature of 100-140°C; the hydrothermal reaction time is 12-24 hours; the washing is carried out by washing the filtered product 3-6 times with ultrapure water; the drying process is carried out under vacuum conditions; and the drying temperature is 40-80°C.

[0020] The above-mentioned method for preparing the molybdenum phosphide composite catalyst is further improved, wherein in step S1, the concentration of the molybdenum-based metal organic framework dispersion is 25-200 g / L; the concentration of the melamine dispersion is 30-50 g / L; and the stirring time is 0.5-2 h;

[0021] The preparation method of the molybdenum phosphide composite catalyst is further improved, in step S2, the mass fraction of the phytic acid solution is 16% to 20%; the volume ratio of the phytic acid solution to the molybdenum-based metal organic framework / melamine dispersion is 0.5 to 0.8:1; the solvent thermal reaction temperature is 60 to 80°C; the solvent thermal reaction time is 12 to 24 hours; and the freeze drying time is 12 to 24 hours;

[0022] The above-mentioned method for preparing the molybdenum phosphide composite catalyst is further improved in that, in step S3, the calcination temperature is 800-900° C.; and the calcination heating rate is 2-10° C. / min.

[0023] Compared with the prior art, the advantages of the present invention are:

[0024] (1) The present invention provides a molybdenum phosphide composite catalyst, comprising nitrogen-phosphorus co-doped carbon nanosheets, wherein the nitrogen-phosphorus co-doped carbon nanosheets are loaded with nano-scale molybdenum phosphide particles. On the one hand, the nitrogen-phosphorus co-doped carbon nanosheets have a two-dimensional layered structure, which can not only provide sufficient surface area for the attachment of active sites, but also provide sufficient space for the catalytic reaction. On the other hand, the electronic structure of molybdenum phosphide is rich and adjustable, and a large number of unsaturated metal sites are exposed on the surface, which has great application potential in the field of catalysis. On this basis, molybdenum phosphide is loaded on the nitrogen-phosphorus co-doped carbon nanosheets, and the interaction between the metal and the carrier can be effectively enhanced by regulating the interface charge. While improving the catalytic activity of molybdenum phosphide, it can effectively inhibit metal leaching and enhance the stability of the catalyst. Therefore, the molybdenum phosphide composite catalyst of the present invention has the advantages of strong catalytic activity and good stability. It is a new and efficient oxidative desulfurization catalyst that can widely remove organic sulfur compounds in oil products and has high use value and good application prospects.

[0025] (2) In the molybdenum phosphide composite catalyst of the present invention, the morphology of the molybdenum phosphide composite catalyst can be effectively regulated by optimizing the addition amount of the molybdenum-based metal-organic framework, thereby more effectively improving the catalytic activity of the catalyst. This is because the molybdenum-based metal-organic framework can effectively weaken the interaction between phytic acid and melamine molecules. If less molybdenum-based metal-organic framework is added, the strong interaction between phytic acid and melamine molecules will cause the nitrogen-phosphorus co-doped carbon to agglomerate and wrap the molybdenum phosphide particles, greatly weakening the accessibility of the active sites on the surface of molybdenum phosphide; when a sufficient amount of molybdenum-based metal-organic framework is added, the interaction between phytic acid and melamine molecules is weakened, and the nitrogen-phosphorus co-doped carbon will form a two-dimensional layered structure, providing sufficient loading sites for molybdenum phosphide, thereby improving the catalytic activity of the catalyst.

[0026] (3) The present invention uses a molybdenum-based metal organic framework as a molybdenum precursor, phytic acid as a phosphorus source, and melamine as a carbon source. The precursors are prone to strong coordination to form a cross-linked structure, and a nanostructured molybdenum phosphide anchored on nitrogen and phosphorus co-doped carbon nanosheets can be obtained by a simple one-step pyrolysis. Therefore, the method for preparing the molybdenum phosphide composite catalyst in the present invention has the advantages of simple process, operation method, low cost, green and pollution-free, and does not use flammable phosphorus and highly toxic phosphine as phosphating agents. The equipment requirements are not high, the repeatability is strong, and large-scale production can be achieved, which is conducive to industrial application.

[0027] (4) The present invention provides a method for removing sulfur-containing organic compounds from oil products using a molybdenum phosphide composite catalyst. The molybdenum phosphide composite catalyst used has the advantages of strong catalytic activity and good stability. Therefore, when the molybdenum phosphide composite catalyst is used to catalytically oxidize sulfur-containing organic compounds in oil products, it can quickly and efficiently achieve effective conversion of sulfur-containing organic compounds in fuel products, and can achieve ultra-high efficiency and ultra-deep oxidative desulfurization. It has the advantages of simple process, convenient operation, low cost, high removal efficiency, good removal effect, etc., and has excellent economic benefits and excellent application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0029] Figure 1 The present invention is a flow chart of the preparation process of the molybdenum phosphide composite catalyst in Example 1.

[0030] Figure 2 This is a scanning electron microscope image of the molybdenum phosphide composite catalyst (MoP@NPC-0.25) prepared in Example 1 of the present invention.

[0031] Figure 3This is a scanning electron microscope image of the molybdenum phosphide composite catalyst (MoP@NPC-0.10) prepared in Example 2 of the present invention.

[0032] Figure 4 This is a scanning electron microscope image of the molybdenum phosphide composite catalyst (MoP@NPC-0.15) prepared in Example 3 of the present invention.

[0033] Figure 5 This is a scanning electron microscope image of the molybdenum phosphide composite catalyst (MoP@NPC-0.20) prepared in Example 4 of the present invention.

[0034] Figure 6 This is a scanning electron microscope image of the molybdenum phosphide composite catalyst (MoP@NPC-0.30) prepared in Example 5 of the present invention.

[0035] Figure 7 Transmission electron microscopy image of the molybdenum phosphide composite catalyst (MoP@NPC-0.25) prepared in Example 1 of the present invention

[0036] Figure 8 This is a selected area electron diffraction pattern of the molybdenum phosphide composite catalyst (MoP@NPC-0.25) prepared in Example 1 of the present invention.

[0037] Figure 9 This is the X-ray diffraction pattern of the molybdenum phosphide composite catalyst (MoP@NPC-0.25) prepared in Example 1 of the present invention.

[0038] Figure 10 This is the X-ray photoelectron spectrum of the molybdenum phosphide composite catalyst (MoP@NPC-0.25) prepared in Example 1 of the present invention.

[0039] Figure 11 This is a comparison chart of the removal effects of the molybdenum phosphide composite catalysts (MoP@NPC-0.10, MoP@NPC-0.15, MoP@NPC-0.20, MoP@NPC-0.25, and MoP@NPC-0.30) in Example 6 of the present invention on dibenzothiophene sulfur in fuel.

[0040] Figure 12 This is a diagram showing the effect of repeated cyclic removal of dibenzothiophene sulfur in fuel by the molybdenum phosphide composite catalyst (MoP@NPC-0.25) in Example 7 of the present invention. DETAILED DESCRIPTION

[0041] The present invention will be further described below in conjunction with the accompanying drawings and specific preferred embodiments, but the scope of protection of the present invention is not limited thereby.

[0042] In the examples of the present invention, the raw materials and instruments used are all commercially available. Unless otherwise specified, the processes used are conventional processes, the equipment used is conventional equipment, and the data obtained are the average values of more than three repeated experiments.

[0043] Example 1

[0044] A preparation method of a molybdenum phosphide composite catalyst, the preparation process flow chart is as follows Figure 1 As shown, the following steps are included:

[0045] (1) Add 1.05 g of molybdenum trioxide to 80 mL of ultrapure water and stir for 20 min to obtain a molybdenum trioxide dispersion;

[0046] (2) adding 0.50 g of imidazole to the dispersion obtained in step (1), and then hydrothermally reacting at 120° C. for 12 h, centrifuging the solid product, and vacuum drying at 50° C. for 12 h to obtain a molybdenum-based metal-organic framework;

[0047] (3) Weighing 0.25 g of the platinum-based metal-organic framework obtained in step (2) and 1.00 g of melamine were added to 40 mL of ultrapure water and ultrasonically treated for 30 min to obtain a platinum-based metal-organic framework / melamine dispersion;

[0048] (4) adding 20 mL of a 15.3% phytic acid solution to the molybdenum-based metal organic framework / melamine dispersion obtained in step (3), stirring at 60° C. for 20 h to obtain a precursor solution;

[0049] (5) After the precursor solution obtained in step (4) is cooled to room temperature, it is centrifuged to obtain a solid product, which is freeze-dried for 12 hours and then calcined in an argon atmosphere at 800°C at a heating rate of 5°C / min for 3 hours to obtain a molybdenum phosphide composite catalyst, namely MoP@NPC-0.25, numbered A4.

[0050] Example 2

[0051] A preparation method of a molybdenum phosphide composite catalyst is basically the same as the preparation method in Example 1, except that the amount of the molybdenum-based metal-organic framework added in Example 2 is 0.10 g.

[0052] The molybdenum phosphide composite catalyst (MoP@NPC-0.10) prepared in Example 2 is numbered A1.

[0053] Example 3

[0054] A preparation method of a molybdenum phosphide composite catalyst is basically the same as the preparation method in Example 1, except that the amount of the molybdenum-based metal-organic framework added in Example 3 is 0.15 g.

[0055] The molybdenum phosphide composite catalyst (MoP@NPC-0.15) prepared in Example 2 is numbered A2.

[0056] Example 4

[0057] A preparation method of a molybdenum phosphide composite catalyst is basically the same as the preparation method in Example 1, except that the amount of the molybdenum-based metal-organic framework added in Example 4 is 0.20 g.

[0058] The molybdenum phosphide composite catalyst (MoP@NPC-0.20) prepared in Example 4 is numbered A3.

[0059] Example 5

[0060] A preparation method of a molybdenum phosphide composite catalyst is basically the same as the preparation method in Example 1, except that the amount of the molybdenum-based metal-organic framework added in Example 5 is 0.30 g.

[0061] The molybdenum phosphide composite catalyst (MoP@NPC-0.30) prepared in Example 5 is numbered A5.

[0062] Figure 2 This is a scanning electron microscope image of the molybdenum phosphide composite catalyst (MoP@NPC-0.25) prepared in Example 1 of the present invention. Figure 2 a, b are scanning electron microscopy images of MoP@NPC-0.25 at 20.0K and 100.0K magnification, respectively. Figure 3 、 4 , 5, and 6 are the scanning electron micrographs of MoP@NPC-0.10, MoP@NPC-0.15, MoP@NPC-0.20, and MoP@NPC-0.30, respectively. Figure 2 、 3 , 4, 5, and 6 show that with the increase in the addition amount of the molybdenum-based organic metal framework, the morphology of the molybdenum phosphide composite catalyst gradually changes from an agglomerated state to a two-position sheet structure, which indicates that by changing the addition amount of the molybdenum-based organic metal framework, the morphology of the molybdenum phosphide composite catalyst can be regulated to obtain higher catalytic activity.

[0063] Figure 7 Figure a is a transmission electron microscopy image of the molybdenum phosphide composite catalyst (MoP@NPC-0.25) prepared in Example 1, and Figure b is a high-resolution transmission electron microscopy image of MoP@NPC-0.25. Figure 7 The results of a show that the MoP nanoparticles and N / P co-doped carbon nanosheets are very tightly bound, and the MoP nanoparticles are firmly anchored on the carbon substrate.

[0064] Figure 8 This is the selected area electron diffraction pattern of the molybdenum phosphide composite catalyst (MoP@NPC-0.25) prepared in Example 1. Figure 8 It can be seen that the molybdenum phosphide nanoparticles anchored on the nitrogen and phosphorus co-doped carbon nanosheets present a perfect single crystal structure.

[0065] Figure 9 The X-ray diffraction pattern of the molybdenum phosphide composite catalyst (MoP@NPC-0.25) prepared in Example 1 is shown in FIG. Figure 9 It can be seen that all the diffraction peaks can be perfectly summarized as the typical monoclinic structure of molybdenum phosphide. The three high-resolution diffraction peaks are located at 32.2°, 43.1° and 57.4°, corresponding to the (100), (101) and (110) planes of molybdenum phosphide, respectively.

[0066] Figure 10 The X-ray photoelectron spectrum of the molybdenum phosphide composite catalyst (MoP@NPC-0.25) prepared in Example 1 is shown in FIG. Figure 10 It can be seen that the molybdenum phosphide composite catalyst is composed of Mo, P, N, C, and O elements.

[0067] The above results show that the molybdenum phosphide composite catalyst prepared by the preparation method provided by the present invention exhibits high purity and perfect crystalline phase, and the molybdenum phosphide nanoparticles and the nitrogen and phosphorus co-doped carbon substrate are very tightly combined, and is an oxidative desulfurization catalyst with both good catalytic activity and stability.

[0068] Example 6:

[0069] The catalytic oxidative desulfurization activity of the molybdenum phosphide composite catalyst of the present invention was investigated. Specifically, the molybdenum phosphide composite catalyst prepared in Examples 1-5 was used to remove dibenzothiophene from oil products, comprising the following steps:

[0070] 10 mg of each molybdenum phosphide composite catalyst (A1, A2, A3, A4, and A5) prepared in Examples 1-5 was accurately weighed and added to 10 mL of a 1000 ppm dibenzothiophene (DBT)-n-octane solution (i.e., a simulated petroleum containing DBT). 2 mL of a 99% by mass acetonitrile solution was then added and stirred for 10 minutes to reach extraction equilibrium. Then, 36 μL of a 30% by mass hydrogen peroxide solution (oxidant, O / S molar ratio of 6) was added, and a catalytic oxidation reaction was carried out at 60°C with magnetic stirring (600 rpm) for 60 minutes. The catalytic oxidation reaction was carried out in acetonitrile, converting DBT into dibenzothiophene sulfone, which was retained in the acetonitrile, thereby removing DBT from the oil product. After completion of the reaction, the acetonitrile phase (lower layer) was separated from the oil phase (upper layer) to obtain clean fuel oil.

[0071] In this embodiment, after the reaction is completed, the content of sulfur in dibenzothiophene in the product solution obtained by the reaction is measured by gas chromatography, and the conversion rate of sulfur in dibenzothiophene is obtained by calculation. The results are as follows: Figure 11 shown. Figure 11 This is a comparison chart of the removal effects of the molybdenum phosphide composite catalysts (MoP@NPC-0.10, MoP@NPC-0.15, MoP@NPC-0.20, MoP@NPC-0.25, MoP@NPC-0.30) on dibenzothiophene sulfur in fuel oil in Example 6 of the present invention. Figure 11 It can be seen that all molybdenum phosphide composite catalysts can effectively catalytically oxidize and remove dibenzothiophene from fuel. Among them, MoP@NPC-0.25 and MoP@NPC-0.30 can both achieve a 100% removal rate of sulfur from dibenzothiophene in oil within 60 minutes. These results show that the molybdenum phosphide composite catalysts prepared by the present invention have excellent catalytic oxidation performance. The total sulfur content in the oil treated with the molybdenum phosphide composite catalyst prepared by the present invention is less than 10ppm, meeting the Euro V fuel standard, and the total desulfurization rate is as high as 100%. In particular, the molybdenum phosphide composite catalyst (MoP@NPC-0.25) demonstrates excellent catalytic oxidation of dibenzothiophene under conditions of low metal loading, showing good economic benefits and industrial application prospects.

[0072] Example 7

[0073] To investigate the reusability of the molybdenum phosphide composite catalyst of the present invention, the molybdenum phosphide composite catalyst (MoP@NPC-0.25) prepared in Example 1 was used to catalytically oxidize and remove dibenzothiophene from oil products, comprising the following steps:

[0074] 10mg of molybdenum phosphide composite catalyst (MoP@NPC-0.25) was weighed and added to 10mL of a 1000ppm dibenzothiophene (DBT)-n-octane solution (i.e., a simulated petroleum containing DBT). 2mL of a 99% by mass acetonitrile solution was then added and stirred for 10 minutes to reach extraction equilibrium. Then, 36μL of a 30% by mass hydrogen peroxide solution (oxidant, O / S molar ratio of 6) was added. The catalytic oxidation reaction was carried out at 60°C with magnetic stirring at 600 rpm for 60 minutes. The catalytic oxidation reaction was carried out in acetonitrile, converting DBT into dibenzothiophene sulfone, which remained in the acetonitrile, completing the removal of DBT from the oil. After the reaction was complete, the upper oil phase was extracted. Then, 10 mL of 1000 ppm dibenzothiophene (DBT)-n-octane solution and 36 μL of 30% hydrogen peroxide solution were added to the reaction system for a new round of catalytic reaction without changing the reaction conditions. In addition, to meet the extraction capacity of the sulfone product, 1 mL of 99% acetonitrile solution was added to the reaction system every two cycles. This cycle was repeated 6 times, and the results were as follows: Figure 12 shown.

[0075] Figure 12 This is a diagram showing the effect of repeated cycle removal of dibenzothiophene sulfur in fuel by the molybdenum phosphide composite catalyst (MoP@NPC-0.25) in Example 7 of the present invention. Figure 12 It can be seen that the molybdenum phosphide composite catalyst of the present invention can still achieve a dibenzothiophene removal rate of 100% after being reused 5 times. Even after the sixth use, the removal rate of dibenzothiophene did not decrease significantly. After multiple cycles, it can still maintain excellent catalytic performance, which shows that the molybdenum phosphide composite catalyst of the present invention has very good reusability and stability.

[0076] The above embodiments are merely preferred embodiments of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. All technical solutions that fall within the scope of protection of the present invention are within the scope of protection of the present invention. It should be noted that improvements and modifications that can be made by a person skilled in the art without departing from the principles of the present invention are also considered to be within the scope of protection of the present invention.

Claims

1. A molybdenum phosphide composite catalyst, characterized in that The molybdenum phosphide composite catalyst comprises nitrogen and phosphorus co-doped carbon nanosheets, on which nano-scale molybdenum phosphide particles are loaded; and the preparation method of the molybdenum phosphide composite catalyst comprises the following steps: (a) preparing a molybdenum-based metal-organic framework into a molybdenum-based metal-organic framework dispersion, adding a melamine dispersion, and stirring to prepare a molybdenum-based metal-organic framework / melamine dispersion; the concentration of the molybdenum-based metal-organic framework dispersion is 25 to 200 g / L; the concentration of the melamine dispersion is 30 to 50 g / L; (b) mixing the molybdenum-based metal-organic framework / melamine dispersion obtained in step (a) with a phytic acid solution, performing a solvothermal reaction, centrifuging, and freeze-drying to obtain a molybdenum phosphide composite catalyst precursor powder; wherein the volume ratio of the phytic acid solution to the molybdenum-based metal-organic framework / melamine dispersion is 0.5 to 0.8:1; (c) calcining the molybdenum phosphide composite catalyst precursor powder obtained in step (b) in an argon atmosphere to obtain a molybdenum phosphide composite catalyst.

2. The molybdenum phosphide composite catalyst according to claim 1, wherein The mass ratio of nitrogen and phosphorus co-doped carbon nanosheets to molybdenum phosphide particles in the molybdenum phosphide composite catalyst is 2-40.

3. The molybdenum phosphide composite catalyst according to claim 1 or 2, characterized in that The mass fraction of nitrogen in the nitrogen-phosphorus co-doped carbon nanosheets is 2% to 8% of the nitrogen-phosphorus co-doped carbon nanosheets, and the mass fraction of phosphorus is 4% to 15% of the nitrogen-phosphorus co-doped carbon nanosheets.

4. A method for preparing a molybdenum phosphide composite catalyst according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1, preparing a molybdenum-based metal-organic framework into a molybdenum-based metal-organic framework dispersion, adding a melamine dispersion, and stirring to prepare a molybdenum-based metal-organic framework / melamine dispersion; S2, mixing the molybdenum-based metal organic framework / melamine dispersion obtained in step S1 with the phytic acid solution to perform a solvothermal reaction, centrifuging, and freeze-drying to obtain a molybdenum phosphide composite catalyst precursor powder; S3. calcining the molybdenum phosphide composite catalyst precursor powder obtained in step S2 in an argon atmosphere to obtain a molybdenum phosphide composite catalyst.

5. The method for preparing the molybdenum phosphide composite catalyst according to claim 4, wherein In step S1, the method for preparing the molybdenum-based metal-organic framework comprises the following steps: (1) adding molybdenum trioxide to ultrapure water and stirring to obtain a molybdenum trioxide dispersion; (2) adding imidazole to the molybdenum trioxide dispersion obtained in step (1) to carry out a hydrothermal reaction, washing, and drying to obtain a molybdenum-based metal organic framework.

6. The method for preparing the molybdenum phosphide composite catalyst according to claim 5, wherein In step (1), the mass ratio of molybdenum trioxide to ultrapure water is 1:70-100; the stirring time is 0.5-2 h; In step (2), the mass ratio of imidazole to molybdenum trioxide is 0.48-0.50:1; the hydrothermal reaction is carried out at a temperature of 100-140°C; the hydrothermal reaction time is 12-24 hours; the washing is carried out by washing the filtered product 3-6 times with ultrapure water; the drying process is carried out under vacuum conditions; and the drying temperature is 40-80°C.

7. The method for preparing the molybdenum phosphide composite catalyst according to any one of claims 4 to 6, characterized in that: In step S1, the concentration of the molybdenum-based metal-organic framework dispersion is 25 to 200 g / L; the concentration of the melamine dispersion is 30 to 50 g / L; and the stirring time is 0.5 to 2 h.

8. The method for preparing the molybdenum phosphide composite catalyst according to any one of claims 4 to 6, characterized in that: In step S2, the mass fraction of the phytic acid solution is 16% to 20%; the solvent thermal reaction temperature is 60 to 80° C.; the volume ratio of the phytic acid solution to the molybdenum-based metal organic framework / melamine dispersion is 0.5 to 0.8:1; the solvent thermal reaction time is 12 to 24 hours; and the freeze drying time is 12 to 24 hours.

9. The method for preparing a molybdenum phosphide composite catalyst according to any one of claims 4 to 6, characterized in that: In step S3, the calcination temperature is 800-900°C; and the calcination heating rate is 2-10°C / min.

Images