A method for preparing a supported highly dispersed molybdenum phosphide catalyst

Abstract

The application discloses a preparation method of a supported high-dispersion molybdenum phosphide catalyst, and comprises the following steps: S1, dissolving molybdenum acetylacetonate and ammonium hypophosphite in an aqueous solution of N,N-dimethylformamide to obtain an impregnation solution; S2, immersing a carrier in the impregnation solution, then drying and reducing to obtain a supported molybdenum phosphide catalyst. The hydrogenation activity and the hydrodesulfurization activity of the prepared molybdenum phosphide catalyst are higher than those of MoP catalysts prepared by a temperature programmed reduction method and a molybdenum trioxide reduction method with ammonium hypophosphite, and the molybdenum phosphide catalyst has very high hydrodesulfurization activity on p-benzothiophene.

Description

Technical Field

[0001] This invention belongs to the field of metal phosphide catalyst preparation technology, specifically relating to a method for preparing a supported highly dispersed molybdenum phosphide catalyst. Background Technology

[0002] Metal phosphide catalysts are widely used in catalysis, electrochemistry, photochemistry, and electromagnetics due to their unique physicochemical properties. In particular, they exhibit excellent catalytic performance in various hydrorefining reactions, such as hydrodesulfurization, hydrodenitrogenation, hydrodechlorination, and hydroisomerization. Among these phosphide catalysis reactions, molybdenum phosphide catalysts demonstrate excellent hydrogenation activity and are considered a viable alternative to traditional hydrorefining catalysts.

[0003] Temperature-programmed reduction (TPP) is the most common and widely used method for preparing molybdenum phosphide (MoP) catalysts (Ind. Eng. Chem. Res. 2019, 58, 17289-17299). It uses diammonium hydrogen phosphate and ammonium molybdate tetrahydrate as raw materials, which are dried and calcined at high temperature (500-550℃) to form a MoP precursor, which is then reduced at 650℃ to obtain the MoP catalyst. This is because the PO bond in the phosphate ion has a high bond energy, requiring high temperature to break and be reduced. This results in larger MoP catalyst particles, leading to lower activity.

[0004] Therefore, many researchers have conducted extensive research on exploring and developing a convenient, low-temperature reduction method for preparing molybdenum phosphide catalysts. Patent (200910070458.3) and literature (Journal of Catalysis 271(2010)413–415) demonstrate that reducing molybdenum oxide by thermally decomposing sodium hypophosphite in a nitrogen atmosphere to produce reducing phosphine gas can yield MoP catalysts. However, this requires an excess of hypophosphite, and the ratio of phosphorus to molybdenum atoms is 5–6:1. Furthermore, the phosphate produced by incomplete decomposition of sodium hypophosphite deposits on the catalyst surface, necessitating thorough water washing of the prepared MoP catalyst to obtain a pure molybdenum phosphide phase. Moreover, the excessive decomposition of sodium hypophosphite produces toxic phosphine gas, polluting the environment. Literature (Chem. Mater. 2014, 26, 4826-4831) reports a solvothermal-high-temperature reduction method for synthesizing molybdenum phosphide catalysts. The specific method is as follows: tri-n-octylphosphine is dissolved in isotriacontane and heated to 120°C under vacuum. Then, Mo(CO)6 is added in an argon atmosphere, and the mixture is heated to 320°C and maintained at 320°C for 2 hours. The resulting black solid can be converted into a MoP catalyst at 700°C under a hydrogen atmosphere. This preparation method requires expensive soluble molybdenum-containing organic compounds and tri-n-octylphosphine, and the operating conditions are complex with high reduction temperatures. Patent (201810453090.8) uses ammonium hypophosphite and molybdenum trioxide as raw materials to reduce the MoP catalyst under a hydrogen atmosphere. Specifically, ammonium hypophosphite and molybdenum trioxide are sequentially added to ammonia water to obtain an impregnation solution, which is then impregnated onto a support. After drying, the solution is reduced at 500–550°C to obtain the MoP catalyst. However, the MoP phase prepared by this method has large particles and low reactivity. The literature (Appl. Catal. A. 2009, 1-2, 18–25) reports the preparation of molybdenum phosphide catalysts via a citric acid complexation-high-temperature reduction method. This method involves adding citric acid during catalyst preparation, utilizing the complexation effect of citric acid with metallic molybdenum salts to improve the dispersion and reduce the grain size of molybdenum phosphide. However, this method requires high-temperature calcination and high-temperature reduction (650℃) to obtain small-particle-size molybdenum phosphide catalysts. Therefore, current MoP catalysts suffer from the following problems: ① The temperature-programmed reduction method requires high-temperature calcination and reduction, resulting in large MoP particles; ② The sodium hypophosphite decomposition method requires an excess phosphorus-molybdenum ratio, necessitating water washing of the catalyst; ③ The solvothermal-high-temperature reduction method uses expensive raw materials, is complex to operate, has high reduction temperatures, and results in large MoP particles; ④ The ammonium hypophosphite reduction of molybdenum trioxide requires reduction above 500℃, resulting in large MoP particles; ⑤ The citric acid complexation-high-temperature reduction method requires high-temperature calcination and high-temperature reduction to obtain small-particle MoP catalysts. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to provide a method for preparing a supported, highly dispersed molybdenum phosphide catalyst, which has the advantages of being free from calcination, water washing, and direct low-temperature reduction.

[0006] To achieve the above objectives, the present invention provides a method for preparing a supported highly dispersed molybdenum phosphide catalyst, comprising the following steps:

[0007] S1, Molybdenum acetylacetonate and ammonium hypophosphite are dissolved in an aqueous solution of N,N-dimethylformamide to prepare an impregnation solution;

[0008] S2, the support is placed in the impregnation solution for impregnation, then dried and reduced to obtain the supported molybdenum phosphide catalyst.

[0009] In the preparation method of the supported highly dispersed molybdenum phosphide catalyst of the present invention, the molar ratio of P to Mo in the impregnation solution is 1 to 4:1, preferably 1 to 3:1.

[0010] In the preparation method of the supported highly dispersed molybdenum phosphide catalyst of the present invention, step S1 involves preparing an impregnation solution at a temperature of 50–80°C.

[0011] The preparation method of the supported highly dispersed molybdenum phosphide catalyst of the present invention, wherein the drying conditions in step S2 are: placing at 20-35°C for 12-24 hours and then drying in an oven at 50-70°C for 12-24 hours.

[0012] In the preparation method of the supported highly dispersed molybdenum phosphide catalyst of the present invention, impregnation is carried out in step S2 with a theoretical molybdenum loading of 1 to 30 wt.%.

[0013] In the preparation method of the supported highly dispersed molybdenum phosphide catalyst of the present invention, hydrogen is used as the reducing gas during the reduction in step S2, and the reduction temperature is 450-550℃.

[0014] In the preparation method of the supported highly dispersed molybdenum phosphide catalyst of the present invention, the reduction in step S2 is a programmed temperature rise reduction.

[0015] The preparation method of the supported highly dispersed molybdenum phosphide catalyst of the present invention includes the following temperature-programmed reduction conditions: the hydrogen flow rate is 60-150 mL / min, the temperature is increased from 20-30℃ to 450-550℃ at a rate of 2-5℃ / min and maintained at this temperature for 2-4 hours, and then the temperature is reduced to 20-30℃ to obtain the supported molybdenum phosphide catalyst.

[0016] The method for preparing the supported highly dispersed molybdenum phosphide catalyst of the present invention uses a porous material as the support, which is one or more of silica, mesoporous carbon, and mesoporous molecular sieves.

[0017] The method for preparing the supported highly dispersed molybdenum phosphide catalyst of the present invention, wherein the aqueous solution of N,N-dimethylformamide has a mass fraction of 50-75 wt.%.

[0018] The impregnation method described in this invention is a conventional impregnation method in the art, such as the commonly used equal-volume impregnation method. The amount of N,N-dimethylformamide in the impregnation solution is determined by the impregnation rate of the carrier. For example, if the impregnation rate of 1g of carrier is 1g, then the amount of N,N-dimethylformamide is between 0.5g and 0.75g.

[0019] The beneficial effects of this invention are:

[0020] (1) In this invention, molybdenum acetylacetonate and ammonium hypophosphite are used as raw materials, and N,N-dimethylformamide is also used. N,N-dimethylformamide can act as a complexing agent and can also dissolve molybdenum acetylacetonate. The amino and carbonyl groups in the N,N-dimethylformamide molecule have lone pairs of electrons, which can coordinate with the molybdenum atoms in the molybdenum acetylacetonate molecule to form a complex molecule. This can inhibit the accumulation of molybdenum ions during the drying process. During the reduction process, the complex molecule gradually decomposes, and the molybdenum species released by the reduction of hydrogen gas form highly dispersed metallic molybdenum atoms. The metallic molybdenum atoms react with phosphine or zero-valent phosphorus atoms produced by the decomposition of hypophosphite to form a highly dispersed molybdenum phosphide catalyst. Under the condition of using a complexing agent, the method of this invention is conducive to the dispersion of MoP and reduces the particle size of MoP. Moreover, without high-temperature calcination, the MoP catalyst is obtained by direct low-temperature drying and reduction at 450-550℃. The calcination-free synthesis method further reduces the particle size of MoP, so that the prepared MoP catalyst has high hydrodesulfurization performance.

[0021] (2) The reduction of ammonium hypophosphite with hydrogen to prepare the MoP phase has several advantages. Firstly, ammonium hypophosphite is more conducive to the formation of phosphine or phosphorus in a low-temperature environment under a hydrogen atmosphere. Secondly, it avoids the formation of PO3 during the thermal decomposition of ammonium hypophosphite. 3- PO4 3- This improves phosphorus utilization; on the other hand, in a hydrogen atmosphere, both phosphine and H2 can reduce the molybdenum source, making it very easy to reduce the molybdenum source to metallic Mo (Mo). 0 Phosphorus or phosphine then reacts with metallic Mo (Mo) 0 The reaction generates the MoP phase without producing impurities, thus avoiding the need for subsequent water washing.

[0022] (3) The hydrogenation activity and hydrodesulfurization activity of the molybdenum phosphide catalyst prepared by the present invention are higher than those of the MoP catalyst prepared by the programmed temperature reduction method and the reduction of molybdenum trioxide by ammonium hypophosphite, especially the hydrodesulfurization activity of p-benzothiophene. Attached Figure Description

[0023] Figure 1Powder X-ray diffraction patterns of the MoP catalyst prepared in Example 1 and standard MoP.

[0024] Figure 2 Transmission electron microscopy (TEM) image of the MoP catalyst prepared in Example 1.

[0025] Figure 3 Powder X-ray diffraction patterns of the MoP catalyst prepared in Example 4 and standard MoP.

[0026] Figure 4 Powder X-ray diffraction patterns of the MoP catalyst prepared in Example 5 and standard MoP.

[0027] Figure 5 Powder X-ray diffraction patterns of the MoP catalyst prepared in Example 6 and standard MoP.

[0028] Figure 6 Powder X-ray diffraction patterns of the MoP catalyst prepared in Example 7 and standard MoP.

[0029] Figure 7 Powder X-ray diffraction patterns of the MoP catalysts prepared in Examples 1, 1, and 2, and standard MoP.

[0030] Figure 8 Powder X-ray diffraction patterns of the MoP catalyst prepared in Comparative Example 3 and standard MoP.

[0031] Figure 9 Powder X-ray diffraction patterns of the MoP catalyst prepared in Comparative Example 4 and standard MoP.

[0032] Figure 10 The conversion rates of 4,6-DMDBT on the MoP catalysts prepared in Example 1, Comparative Example 1, and Comparative Example 2 at different times are shown. Detailed Implementation

[0033] The present invention will now be described in detail through embodiments. It should be noted that the following embodiments are only for further illustration of the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above description.

[0034] Example 1

[0035] 0.3396 g of molybdenum acetylacetonate (0.001 mol) and 0.089 g of ammonium hypophosphite (0.001 mol) were weighed and placed in a glass tube. A pre-prepared 1.4 mL aqueous solution of 50 wt.% N,N-dimethylformamide was added to the glass tube. The glass tube was then placed in a water bath at 50 °C and heated to dissolve the molybdenum. A clear, dark green solution was obtained and then impregnated onto a 1 g SiO2 support. The solution was placed at 25 °C for 12 h, then dried in a 50 °C oven for 18 h. The dried solid powder was then placed in a reduction tube for reduction. The reduction procedure was to increase the temperature from 25 °C to 450 °C at a rate of 2 °C / min, maintain the temperature at 450 °C for 3 h (H2 flow rate 120 mL / min), and then reduce the temperature to 25 °C to obtain the MoP catalyst. The theoretical Mo loading in this catalyst was 10 wt.%, and the theoretical molar ratio of Mo to P was 1:1. Figure 1 The powder X-ray diffraction patterns of the prepared MoP catalyst and standard MoP are shown. The prepared catalyst exhibits the characteristic diffraction peak of MoP at 2θ of 43.1°, and the intensity of the diffraction peak is relatively weak, indicating the formation of a small-particle MoP phase. The grain size was calculated to be 4.5 nm according to the Scherrer equation. To further illustrate that a highly dispersed molybdenum phosphide catalyst can be supported according to the method of this application, TEM analysis was performed on the prepared catalyst. Figure 2 The image shows a TEM image of the prepared MoP catalyst. The interplanar spacing of the black particles is 0.28 nm, which is exactly the same as the interplanar spacing of MoP(101). This indicates that the black particles are the MoP phase, and the particle size of the MoP phase is 4-8 nm.

[0036] Example 2

[0037] 0.3396 g of molybdenum acetylacetonate (0.001 mol) and 0.26 g of ammonium hypophosphite (0.003 mol) were weighed and placed in a glass tube. A pre-prepared 1.4 mL aqueous solution of 75 wt.% N,N-dimethylformamide was added to the glass tube. The glass tube was then placed in a water bath at 50 °C and heated to dissolve the molybdenum. A clear, dark green solution was obtained and then impregnated onto a 1 g SiO2 support. The solution was placed at 25 °C for 24 h, then dried in a 50 °C oven for 12 h. The dried solid powder was then placed in a reduction tube for reduction. The reduction procedure was to increase the temperature from 25 °C to 550 °C at a rate of 5 °C / min, maintain the temperature at 550 °C for 2 h (H2 flow rate 150 mL / min), and then reduce the temperature to 25 °C to obtain a MoP catalyst. The theoretical Mo loading in this catalyst was 10 wt.%, and the theoretical molar ratio of Mo to P was 1:3.

[0038] Example 3

[0039] 0.67 g of molybdenum acetylacetonate (0.002 mol) and 0.175 g of ammonium hypophosphite (0.002 mol) were weighed and placed in a glass tube. A pre-prepared 1.4 mL aqueous solution of 75 wt.% N,N-dimethylformamide was added to the glass tube. The glass tube was then placed in a water bath at 70 °C and heated to dissolve the molybdenum. A clear, dark green solution was obtained and then impregnated onto a 1 g SiO2 support. The solution was placed at 25 °C for 15 h, then dried in a 70 °C oven for 24 h. The dried solid powder was then placed in a reduction tube for reduction. The reduction procedure was to increase the temperature from 25 °C to 500 °C at a rate of 3 °C / min, maintain the temperature at 500 °C for 2 h (H2 flow rate 100 mL / min), and then reduce the temperature to 25 °C to obtain a MoP catalyst. The theoretical Mo loading in this catalyst was 20 wt.%, and the theoretical molar ratio of Mo to P was 1:1.

[0040] Example 4

[0041] 0.3396 g of molybdenum acetylacetonate (0.001 mol) and 0.1661 g of ammonium hypophosphite (0.002 mol) were weighed and placed in a glass tube. A pre-prepared 4.0 mL aqueous solution of 50 wt.% N,N-dimethylformamide was added to the glass tube. The glass tube was then placed in an 80 °C water bath and heated to dissolve the molybdenum. A clear, dark green solution was obtained and then impregnated onto 1 g of MCM-41 support. The solution was placed at 25 °C for 20 h, then dried in an 80 °C oven for 18 h. The dried solid powder was then placed in a reduction tube for reduction. The reduction procedure was to increase the temperature from 25 °C to 450 °C at a rate of 2 °C / min, maintain the temperature at 450 °C for 2 h (H2 flow rate 80 mL / min), and then reduce the temperature to 25 °C to obtain the MoP catalyst. The theoretical Mo loading in this catalyst was 10 wt.%, and the theoretical molar ratio of Mo to P was 1:2. Figure 2 The powder X-ray diffraction patterns of the prepared MoP catalyst and standard MoP are shown. The prepared catalyst exhibits very weak characteristic diffraction peaks of MoP at 2θ of 32.2° and 43.1°, which is due to the very high BET surface area (800 m²) of MCM-41. 2 / g) and external surface area (798m²) 2 / g), which facilitates metal dispersion. A very small MoP phase is formed in the MCM-41 molecular sieve. Since the MCM-41 used is a mesoporous molecular sieve, it will only show diffraction peaks at small angle diffraction (2θ) of 2°–5°, and only envelope peaks at θ of 25°–80°.

[0042] Example 5

[0043] 0.3396 g of molybdenum acetylacetonate (0.001 mol) and 0.1661 g of ammonium hypophosphite (0.002 mol) were weighed and placed in a glass tube. A pre-prepared 1.0 mL aqueous solution of 50 wt.% N,N-dimethylformamide was added to the glass tube. The glass tube was then placed in a water bath at 60 °C and heated to dissolve the molybdenum. A clear, dark green solution was obtained and then impregnated onto a 1 g activated carbon support. The solution was placed at 25 °C for 12 h, then dried in a 70 °C oven for 12 h. The dried solid powder was then placed in a reduction tube for reduction. The reduction procedure was to increase the temperature from 25 °C to 550 °C at a rate of 2 °C / min, maintain the temperature at 550 °C for 4 h (H2 flow rate 60 mL / min), and then reduce the temperature to 25 °C to obtain the MoP catalyst. The theoretical Mo loading in this catalyst was 10 wt.%, and the theoretical molar ratio of Mo to P was 1:2. Figure 4 The powder X-ray diffraction patterns of the prepared MoP catalyst and standard MoP are shown. The prepared catalyst exhibits characteristic MoP diffraction peaks at 2θ angles of 27.9, 32.2, 43.1, and 57.4°, indicating that a supported molybdenum phosphide catalyst can be prepared according to the method of this patent application. According to the Scherrer equation, the grain size of the MoP phase is 8 nm. The activated carbon in this patent application is an amorphous material, so it exhibits peaks at diffraction angles of 5–80°. This XRD pattern confirms that the MoP catalyst is supported on activated carbon, and it is a MoP catalyst prepared by students in our research group using activated carbon as a support.

[0044] Example 6

[0045] 0.0339 g of molybdenum acetylacetonate (0.001 mol) and 0.0356 g of ammonium hypophosphite (0.004 mol) were weighed and placed in a glass tube. A pre-prepared 1.4 mL aqueous solution of 50 wt.% N,N-dimethylformamide was added to the glass tube. The glass tube was then placed in a water bath at 50 °C and heated to dissolve the molybdenum. A clear, dark green solution was obtained and then impregnated onto a 1 g SiO2 support. The solution was placed at 25 °C for 12 h, then dried in a 50 °C oven for 18 h. The dried solid powder was then placed in a reduction tube for reduction. The reduction procedure was to increase the temperature from 25 °C to 450 °C at a rate of 2 °C / min, maintain the temperature at 450 °C for 3 h (H2 flow rate 120 mL / min), and then reduce the temperature to 25 °C to obtain a MoP catalyst. The theoretical Mo loading in this catalyst was 1 wt.%, and the theoretical molar ratio of Mo to P was 1:4. Figure 5 The prepared MoP catalyst and standard MoP are shown in the powder X-ray diffraction patterns. The prepared catalyst did not show the characteristic diffraction peaks of MoP in the 2θ range of 20 to 80°, which indicates that a smaller MoP phase was formed.

[0046] Example 7

[0047] 1.0188 g of molybdenum acetylacetonate (0.003 mol) and 0.267 g of ammonium hypophosphite (0.003 mol) were weighed and placed in a glass tube. A pre-prepared 1.4 mL aqueous solution of 50 wt.% N,N-dimethylformamide was added to the glass tube. The glass tube was then placed in a 50 °C water bath and heated to dissolve the molybdenum. A clear, dark green solution was obtained and then impregnated onto a 1 g SiO2 support. The solution was placed at 25 °C for 12 h, then dried in a 50 °C oven for 18 h. The dried solid powder was then placed in a reduction tube for reduction. The reduction procedure was to increase the temperature from 25 °C to 450 °C at a rate of 2 °C / min, maintain the temperature at 450 °C for 3 h (H2 flow rate 120 mL / min), and then reduce the temperature to 25 °C to obtain a MoP catalyst. The theoretical Mo loading in this catalyst was 30 wt.%, and the theoretical molar ratio of Mo to P was 1:1. Figure 6 The prepared MoP catalyst and standard MoP are shown in the powder X-ray diffraction patterns. The prepared catalyst showed corresponding characteristic MoP diffraction peaks in the range of 2θ from 20 to 80°, and the intensity of the diffraction peaks was relatively strong, which indicates that a larger MoP phase was formed.

[0048] Comparative Example 1

[0049] Molybdenum phosphide catalyst was prepared by conventional temperature-propelled desorption: 0.3396 g of molybdenum acetylacetonate (0.001 mol) and 0.089 g of ammonium hypophosphite (0.001 mol) were added to 1.4 mL of distilled water. After obtaining a clear solution, it was impregnated onto a 1 g SiO2 support. The solution was allowed to stand at 25 °C for 12 h, then dried at 100 °C for 12 h and held at 500 °C for 3 h. The calcined sample was then placed in a reduction tube for reduction. The reduction program started at 25 °C, increased to 450 °C at a rate of 2 °C / min (H2 flow rate 120 mL / min), and held at 450 °C for 3 h. After cooling to 25 °C, a MoP catalyst with a Mo loading of 10 wt% was obtained, and the theoretical P / Mo ratio in this catalyst was 1. Figure 7 The following are powder X-ray diffraction patterns of the silica-supported MoP catalyst in Example 1, Comparative Example 1, and standard MoP. By comparing the peak intensity of the 43.1° diffraction peak, it can be seen that the MoP phase prepared in Example 1 has a smaller particle size. XRD is one of the important methods for analyzing crystal structure. When X-rays are incident on small crystals, the diffraction lines become diffuse and broadened, and the diffraction peak intensity weakens. The smaller the crystallite, the greater the broadening of the X-ray diffraction bands. Based on the broadening of the diffraction peaks, the average grain size of the sample can be determined using the Scherrer equation. β is the full width at half maximum (FWHM), D hklThe peak intensity represents the grain size along the normal direction of the crystal plane, and κ is the shape factor. According to the Scherrer equation, the weaker the peak intensity and the more severe the broadening of the full width at half maximum (FWHM), the smaller the grain size. Therefore, the grain size of the generated MoP phase can be determined based on the peak intensity of the diffraction peaks. The grain size of the MoP phase calculated using the Scherrer equation is 27 nm.

[0050] Comparative Example 2

[0051] Supported MoP catalysts were prepared according to the comparative patent (201810453090.8) using the ammonium hypophosphite reduction method for molybdenum trioxide: 0.15 g of molybdenum trioxide and 0.09 g of ammonium hypophosphite were dissolved in 1.5 mL of ammonia water. After complete dissolution, the solution was impregnated onto 1 g of SiO2. The solution was allowed to stand at 25 °C and then dried in an oven at 70 °C for 12 h. The resulting white solid was ground into powder and then placed in a reduction tube for reduction (the reduction program started at 2 °C and increased at 2 °C / min to 550 °C, and was maintained at 550 °C for 3 h). After the reduction, a MoP catalyst with a theoretical Mo loading of 10 wt.% was obtained, wherein the theoretical molar ratio of Mo to P on the catalyst was 1. Figure 7 The powder X-ray diffraction patterns are for Example 1, Comparative Example 2, and standard MoP catalysts supported on silica. By comparing the intensity of the 43.1° diffraction peak and calculating using the Scherrer equation, the grain size of the prepared MoP phase is 10 nm.

[0052] Comparison 3

[0053] 0.3396 g of molybdenum acetylacetonate and 0.089 g of ammonium hypophosphite were weighed and placed in a glass tube. 1.4 mL of pre-prepared distilled water was added to the glass tube, followed by 0.219 g of citric acid monohydrate (CA). The glass tube was then placed in a 50°C water bath and heated to dissolve the precipitate. A clear solution was not obtained. This solution was then impregnated onto a 1 g SiO2 support. The solution was placed at 25°C and then dried in a 50°C oven for 18 h. The dried solid powder was then placed in a reduction tube for reduction. The reduction procedure was to increase the temperature from 25°C to 450°C at a rate of 2°C / min, maintain the temperature at 450°C for 3 h (H2 flow rate 120 mL / min), and then reduce the temperature to 25°C to obtain the MoP catalyst. The theoretical Mo loading in this catalyst was 10 wt.%, and the theoretical molar ratio of Mo:P:CA was 1:1:1. Figure 8 Powder X-ray diffraction patterns of the prepared MoP catalyst and standard MoP. From Figure 8 It is known that MoP catalysts cannot be prepared using citric acid as a complexing agent.

[0054] Comparative Example 4

[0055] 0.3396 g of molybdenum acetylacetonate (0.001 mol) and 0.088 g of sodium hypophosphite (0.001 mol) were weighed and placed in a glass tube. A pre-prepared 1.4 mL aqueous solution of 50 wt.% N,N-dimethylformamide was added to the glass tube. The glass tube was then placed in a water bath at 50 °C and heated to dissolve the molybdenum. A clear, dark green solution was obtained and then impregnated onto a 1 g SiO2 support. The solution was placed at 25 °C for 12 h, then dried in a 50 °C oven for 18 h. The dried solid powder was then placed in a reduction tube for reduction. The reduction procedure was to increase the temperature from 25 °C to 450 °C at a rate of 2 °C / min, maintain the temperature at 450 °C for 3 h (H2 flow rate 120 mL / min), and then reduce the temperature to 25 °C to obtain a MoP catalyst. The theoretical Mo loading in this catalyst was 10 wt.%, and the theoretical molar ratio of Mo to P was 1:1. Figure 9 The prepared MoP catalyst and standard MoP are shown in the powder X-ray diffraction patterns. No characteristic diffraction peaks of MoP appeared on the prepared catalyst, indicating that MoP catalysts cannot be synthesized using sodium hypophosphite.

[0056] Catalyst applications:

[0057] The hydrodesulfurization reaction of 4,6-dimethyldibenzothiophene (4,6-DMDBT) was carried out in a fixed-bed reactor under the following conditions: 0.3 g catalyst, reaction temperature 310 °C, hydrogen pressure 5.0 MPa, and hydrogen flow rate 60 mL / min. -1 0.45 wt.% 4,6-DMDBT. Samples were taken every 1 hour and analyzed by gas chromatography. Figure 10 The figure shows the 4,6-DMDBT conversion rates at different reaction times on catalysts of Example 1, Comparative Example 1, and Comparative Example 2. As can be seen from the figure, among the MoP catalysts supported on the same SiO2 support with a theoretical Mo loading of 10 wt.%, Example 1 exhibits the highest hydrodesulfurization activity due to its smallest MoP phase grain size.

[0058] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a supported, highly dispersed molybdenum phosphide catalyst, characterized in that, It consists of the following steps: S1, Molybdenum acetylacetonate and ammonium hypophosphite are dissolved in an aqueous solution of N,N-dimethylformamide to prepare an impregnation solution; S2, the support is placed in the impregnation solution for impregnation, then dried and reduced to obtain the supported molybdenum phosphide catalyst. Hydrogen is used as the reducing gas during reduction, and the reduction temperature is 450~550 ℃. The carrier is one or more of silica, mesoporous carbon, and mesoporous molecular sieves.

2. The method for preparing the supported highly dispersed molybdenum phosphide catalyst according to claim 1, characterized in that, The molar ratio of P to Mo in the impregnation solution is 1 to 4:

1.

3. The method for preparing the supported highly dispersed molybdenum phosphide catalyst according to claim 1, characterized in that, The molar ratio of P to Mo in the impregnation solution is 1 to 3:

1.

4. The method for preparing the supported highly dispersed molybdenum phosphide catalyst according to claim 1, characterized in that, In step S1, the impregnation solution is prepared at a temperature of 50~80 ℃.

5. The method for preparing the supported highly dispersed molybdenum phosphide catalyst according to claim 1, characterized in that, The drying conditions described in step S2 are: placing the product at 20~35℃ for 12~24 h and then drying it in an oven at 50~70℃ for 12~24 h.

6. The method for preparing the supported highly dispersed molybdenum phosphide catalyst according to claim 1, characterized in that, In step S2, impregnation is carried out according to the theoretical molybdenum loading of 1~30 wt.%.

7. The method for preparing the supported highly dispersed molybdenum phosphide catalyst according to claim 1, characterized in that, The reduction in step S2 is a programmed temperature-increasing reduction.

8. The method for preparing the supported highly dispersed molybdenum phosphide catalyst according to claim 7, characterized in that, The programmed temperature reduction conditions are as follows: the hydrogen flow rate is 60 ~ 150 mL / min, the temperature is increased from 20 ~ 30℃ to 450 ~ 550℃ at a rate of 2 ~ 5℃ / min and maintained at this temperature for 2 ~ 4 h, and then cooled to room temperature of 20 ~ 30℃ to obtain the supported molybdenum phosphide catalyst.

9. The method for preparing the supported highly dispersed molybdenum phosphide catalyst according to claim 1, characterized in that, The aqueous solution of N,N-dimethylformamide has a mass fraction of 50~75 wt.%.

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