Alumina-supported carbon-confined metal phosphide catalysts, methods for their preparation and use

Abstract

The application discloses an alumina-supported carbon-confined metal phosphide catalyst and a preparation method and application thereof, and belongs to the technical field of carbon-based material confined catalysts. The preparation method provided by the application comprises the following steps: dispersing high specific surface area alumina, a phosphorus source, a nitrogen-containing carbon source and a metal salt precursor in deionized water and stirring; then, performing hydrothermal crystallization treatment; then, performing centrifugal drying on the obtained product; and finally, performing calcination treatment in an inert atmosphere. The obtained alumina-supported carbon-confined metal phosphide catalyst can be used in the preparation of trifluoroethylene through the hydrogenation dechlorination of chlorotrifluoroethylene. The preparation method does not need to use expensive metal raw materials, has simple preparation steps, good repeatability, can obtain a catalyst with excellent catalytic activity and target product selectivity, and can effectively reduce production costs in the reaction of preparing trifluoroethylene through the hydrogenation dechlorination of chlorotrifluoroethylene.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of carbon-based material confined catalysts, and particularly relates to an alumina-supported carbon-confined metal phosphide catalyst as well as a preparation method and application thereof. BACKGROUND

[0002] 1,1,2-trifluoroethylene (TrFE, HFO-1123) CAS No. 359-11-5, the molecule does not contain ozone-depleting bromine and chlorine atoms, the boiling point is -51℃, the ODP is 0, and the GWP100 value is only 0.005, and the environmental performance is excellent. TrFE is widely used as a new generation of low GWP (Global Warming Potential) fluorine-containing greenhouse gas substitute. It can be used as a heat pump working medium for new energy vehicle air conditioning systems. The refrigerant used by the heat pump is the heat pump working medium. The mixed heat pump working medium mainly composed of TrFE has the advantages of high efficiency and environmental protection, and can solve the problems of high GWP (HFC-134a), low refrigeration efficiency (HFO-1234yf) and high working pressure (CO2). It can also be used as a synthetic monomer for fluorine-containing high polymer materials. TrFE can be polymerized with other monomers to synthesize fluorine-containing high polymer materials with unique electrical properties, which can be used as electrocaloric refrigeration materials and piezoelectric materials. At the same time, trifluoroethylene is also a key raw material for synthesizing high-value halogenated olefins. TrFE can be used as a key raw material for synthesizing new electronic etching gas hexafluoro-1,3-butadiene (C4F6) or other fluorine-containing olefins (such as 2,3,3,3-tetrafluoropropene, trifluorobromoethylene, etc.).

[0003] At present, the relatively mature preparation process of trifluoroethylene mainly uses trifluorotrichloroethane as the starting material, and trifluoroethylene is prepared by multi-step hydrogenation and dechlorination, but the yield of trifluoroethylene is low, and the catalyst is easy to deactivate. However, the use of trifluorochloroethylene as the initial raw material and the preparation of trifluoroethylene by one-step catalytic hydrogenation and dechlorination can significantly improve the yield of trifluoroethylene. However, the catalyst used in this process is mainly a noble metal catalyst, and the noble metal loading is relatively high, about 2-3%, and the catalyst is expensive. Therefore, developing a cheap base metal catalyst is a problem to be solved for the process of preparing trifluoroethylene by hydrogenation and dechlorination of trifluorochloroethylene. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a base metal catalyst for preparing trifluoroethylene by hydrogenation and dechlorination of trifluorochloroethylene.

[0005] In order to solve the above technical problems, the technical scheme adopted by the present application is: a preparation method of an alumina-supported carbon-confined metal phosphide catalyst, high specific surface area alumina, a phosphorus source, a nitrogen-containing carbon source and a metal salt precursor are dispersed in deionized water and stirred, then subjected to hydrothermal crystallization treatment, the obtained product is then subjected to centrifugal drying, and finally subjected to calcination treatment in an inert atmosphere.

[0006] Another technical scheme adopted by the present application is: an alumina-supported carbon-confined metal phosphide catalyst prepared by the above preparation method.

[0007] Still another technical scheme adopted by the present application is: the above alumina-supported carbon-confined metal phosphide catalyst is used in the preparation of trifluoroethylene by hydrodechlorination of chlorotrifluoroethylene.

[0008] The present application has the advantages that: the raw materials used in the preparation method provided by the present application are easy to obtain, the preparation steps are simple, the repeatability is good, and a catalyst with excellent catalytic activity and target product selectivity can be obtained, which can be used in the reaction of preparing trifluoroethylene by hydrodechlorination of chlorotrifluoroethylene, and can effectively reduce the production cost. DETAILED DESCRIPTION

[0009] In order to explain the technical content, the purposes and effects of the present application in detail, the following embodiments are described.

[0010] A preparation method of an alumina-supported carbon-confined metal phosphide catalyst, high specific surface area alumina, a phosphorus source, a nitrogen-containing carbon source and a metal salt precursor are dispersed in deionized water and stirred, then subjected to hydrothermal crystallization treatment, the obtained product is then subjected to centrifugal drying, and finally subjected to calcination treatment in an inert atmosphere, to obtain the alumina-supported carbon-confined metal phosphide catalyst.

[0011] As can be seen from the above description, the present application has the advantages that: the present application selects high specific surface area alumina as the carrier of carbon-confined metal phosphide, which can effectively increase the surface area of the catalyst, increase the dispersion degree of the metal phosphide, and thus improve its catalytic activity; at the same time, the metal phosphide provided by the present application is produced by the phosphorus source and metal particles in the hydrothermal crystallization process, and is confined in the nitrogen-doped carbon material, so that the catalyst has high stability.

[0012] Further, the phosphorus source is one of triphenylphosphine, triethyl phosphate, triethyl phosphonoacetate, ammonium hypophosphite, dihydrogen ammonium phosphate, and monohydrogen ammonium phosphate, and is preferably one of triphenylphosphine, triethyl phosphate (TEP) and ammonium hypophosphite.

[0013] Further, the nitrogen-containing carbon source is one of glycine, urea, dicyanamide and melamine, preferably glycine or dicyanamide. The carbon source used in the present application is a nitrogen-containing carbon source, and the nitrogen-doped carbon material formed can effectively rivet the metal phosphide and inhibit the sintering of the metal phosphide, thereby improving the long-term stability of the catalyst.

[0014] Further, the metal salt precursor is one of copper nitrate trihydrate, nickel nitrate hexahydrate and cobalt nitrate hexahydrate, preferably nickel nitrate hexahydrate or cobalt nitrate hexahydrate.

[0015] From the above description, it can be seen that the raw materials used are low in price and easy to obtain.

[0016] Further, the molar ratio of the high specific surface area alumina to the carbon source is 15:1 to 5:1, preferably 12:1 to 8:1; the molar ratio of the high specific surface area alumina to the phosphorus source is 20:1 to 5:1, preferably 15:1 to 10:1; and the molar ratio of the high specific surface area alumina to the metal salt precursor is 30:1 to 10:1, preferably 20:1 to 15:1.

[0017] Further, the temperature for stirring treatment is 30 to 60℃, preferably 30 to 45℃, and the time is 1 to 12h, preferably 3 to 6h.

[0018] Further, the temperature for hydrothermal crystallization treatment is 110 to 250℃, preferably 130 to 220℃, and the time is 4 to 18h, preferably 6 to 12h. The hydrothermal crystallization treatment is carried out in a hydrothermal kettle.

[0019] Further, after centrifugal separation to obtain the solid product, drying treatment is carried out in a blast drying oven at 120℃ for 12h.

[0020] Further, the temperature for calcination treatment is 300 to 800℃, preferably 450 to 650℃, and the time is 2 to 12h, preferably 4 to 8h. The inert atmosphere is N2 atmosphere.

[0021] The present application provides a preparation method of an alumina-supported carbon-confined metal phosphide catalyst prepared by any one of the above preparation methods.

[0022] The present application provides an application of the above alumina-supported carbon-confined metal phosphide catalyst in the preparation of trifluoroethylene by hydrodechlorination of chlorotrifluoroethylene.

[0023] Embodiment one of the present application is:

[0024] Take 25.5 g of high specific surface area alumina, 4.37 g of triphenylphosphine, 1.56 g of glycine and 3.64 g of cobalt nitrate hexahydrate dissolved in 500 mL of deionized water, stirring under 30 ℃ water bath for 3 h, then transferred to hydrothermal kettle for hydrothermal crystallization treatment at 130 ℃ for 6 h, then the obtained product is centrifuged and dried in a blast drying oven at 120 ℃ for 12 h, and finally dried in a tube furnace under N2 atmosphere at 450 ℃ for 4 h, to obtain an alumina-supported carbon-confined metal phosphide catalyst CoP x @C / Al2O3, denoted as S-1.

[0025] Embodiment two of the present application is:

[0026] Take 25.5 g of high specific surface area alumina, 2.8 g of triethyl phosphonoacetate, 1 g of urea and 2.01 g of copper nitrate trihydrate dissolved in 500 mL of deionized water, stirring under 30 ℃ water bath for 1 h, then transferred to hydrothermal kettle for hydrothermal crystallization treatment at 110 ℃ for 4 h, then the obtained product is centrifuged and dried in a blast drying oven at 120 ℃ for 12 h, and finally dried in a tube furnace under N2 atmosphere at 300 ℃ for 2 h, to obtain an alumina-supported carbon-confined metal phosphide catalyst CuP x @C / Al2O3, denoted as S-2.

[0027] Embodiment three of the present application is:

[0028] Take 25.5 g of high specific surface area alumina, 6.6 g of diammonium hydrogen phosphate, 6.3 g of melamine and 6.04 g of copper nitrate trihydrate dissolved in 500 mL of deionized water, stirring under 60 ℃ water bath for 12 h, then transferred to hydrothermal kettle for hydrothermal crystallization treatment at 250 ℃ for 18 h, then the obtained product is centrifuged and dried in a blast drying oven at 120 ℃ for 12 h, and finally dried in a tube furnace under N2 atmosphere at 800 ℃ for 12 h, to obtain an alumina-supported carbon-confined metal phosphide catalyst CuP x @C / Al2O3, denoted as S-3.

[0029] Embodiment four of the present application is:

[0030] Take 25.5 g of high specific surface area alumina, 3.6 g of ammonium dihydrogen phosphate, 2.5 g of urea and 2.91 g of nickel nitrate hexahydrate are dissolved in 500 mL of deionized water, stirred at 50 ℃ water bath for 8 h, then transferred to an autoclave for hydrothermal crystallization treatment at 120 ℃ for 16 h, then the obtained product is centrifuged and dried in a blast drying oven at 120 ℃ for 12 h, and finally dried in a tube furnace under N2 atmosphere at 700 ℃ for 3 h, to obtain an alumina-supported carbon-confined metal phosphide catalyst NiP x @C / Al2O3, denoted as S-4.

[0031] Embodiment five of the present application is:

[0032] Take 25.5 g of high specific surface area alumina, 4.56 g of triethyl phosphate, 2.63 g of dicyandiamide and 4.85 g of cobalt nitrate hexahydrate are dissolved in 500 mL of deionized water, stirred at 45 ℃ water bath for 6 h, then transferred to an autoclave for hydrothermal crystallization treatment at 220 ℃ for 12 h, then the obtained product is centrifuged and dried in a blast drying oven at 120 ℃ for 12 h, and finally dried in a tube furnace under N2 atmosphere at 650 ℃ for 8 h, to obtain an alumina-supported carbon-confined metal phosphide catalyst CoP x @C / Al2O3, denoted as S-5.

[0033] Embodiment six of the present application is:

[0034] Take 25.5 g of high specific surface area alumina, 1.73 g of ammonium hypophosphite, 1.88 g of glycine and 4.04 g of nickel nitrate hexahydrate are dissolved in 500 mL of deionized water, stirred at 35 ℃ water bath for 4 h, then transferred to an autoclave for hydrothermal crystallization treatment at 160 ℃ for 8 h, then the obtained product is centrifuged and dried in a blast drying oven at 120 ℃ for 12 h, and finally dried in a tube furnace under N2 atmosphere at 550 ℃ for 6 h, to obtain an alumina-supported carbon-confined metal phosphide catalyst NiP x @C / Al2O3, denoted as S-6.

[0035] Embodiment seven of the present application is:

[0036] Take 25.5 g of high specific surface area alumina, 4.68 g of triphenylphosphine, 2.34 g of dicyandiamide and 4.54 g of cobalt nitrate hexahydrate dissolved in 500 mL of deionized water, stirring under 40 ℃ water bath for 5 h, then transferred to hydrothermal kettle for hydrothermal crystallization treatment at 200 ℃ for 10 h, then the obtained product is centrifuged and dried in a blast drying oven at 120 ℃ for 12 h, and finally dried in a tube furnace under N2 atmosphere at 600 ℃ for 4 h, to obtain an alumina-supported carbon-confined metal phosphide catalyst CoP x @C / Al2O3, denoted as S-7.

[0037] Embodiment eight of the present application is:

[0038] Take 25.5 g of high specific surface area alumina, 2.08 g of ammonium hypophosphite, 1.75 g of dicyandiamide and 3.64 g of cobalt nitrate hexahydrate dissolved in 500 mL of deionized water, stirring under 45 ℃ water bath for 3 h, then transferred to hydrothermal kettle for hydrothermal crystallization treatment at 180 ℃ for 6 h, then the obtained product is centrifuged and dried in a blast drying oven at 120 ℃ for 12 h, and finally dried in a tube furnace under N2 atmosphere at 500 ℃ for 8 h, to obtain an alumina-supported carbon-confined metal phosphide catalyst CoP x @C / Al2O3, denoted as S-8.

[0039] Embodiment nine of the present application is:

[0040] Take 25.5 g of high specific surface area alumina, 3.04 g of triethyl phosphate, 2.35 g of glycine and 4.85 g of nickel nitrate hexahydrate dissolved in 500 mL of deionized water, stirring under 35 ℃ water bath for 6 h, then transferred to hydrothermal kettle for hydrothermal crystallization treatment at 220 ℃ for 6 h, then the obtained product is centrifuged and dried in a blast drying oven at 120 ℃ for 12 h, and finally dried in a tube furnace under N2 atmosphere at 650 ℃ for 4 h, to obtain an alumina-supported carbon-confined metal phosphide catalyst NiP x @C / Al2O3, denoted as S-9.

[0041] Embodiment ten of the present application is:

[0042] The alumina-supported carbon-confined metal phosphide catalysts S-1-S-9 prepared in the above Examples 1-9 were used in the hydrodechlorination reaction of chlorotrifluoroethylene, and the catalyst activity evaluation was carried out in a constant bed reaction device at normal pressure. The reaction tube of the tubular reactor was a high-purity quartz tube with an inner diameter of 20 mm and a length of 1000 mm. 20 mL of catalyst particles were loaded into the fixed bed reaction device, and the particle size of the catalyst was 20-40 mesh.

[0043] First, heating was carried out to 400 ℃ in a N2 atmosphere at a flow rate of 200 mL / min, and the temperature was kept for 1 h. Then, the atmosphere was switched to an H2 atmosphere at a flow rate of 200 mL / min, and the catalyst was reduced in situ for 6 h. After reduction, the atmosphere was switched to an N2 atmosphere at a flow rate of 200 mL / min, and the temperature was raised to 450 ℃ in the N2 atmosphere. Then, the N2 atmosphere was switched to a mixed gas of chlorotrifluoroethylene and H2, and the volume ratio of chlorotrifluoroethylene to hydrogen was 1:1.5, and the gas flow rate was 75 mL / min. The tail gas generated in the reaction was washed with alkali, washed with water, dried, and then detected on-line by gas chromatography. The detection results are shown in Table 1.

[0044] Table 1 lists the catalysts S-1-S-9 prepared in Examples 1-9, which were subjected to the above process conditions, i.e., normal pressure, a reaction temperature of 450 ℃, a space velocity of 225 h-1, and a reaction time of 50 h, and the conversion of chlorotrifluoroethylene and the selectivity of trifluoroethylene were used as indicators. 1 The catalyst activity test results under the space velocity are shown in Table 1, and the test results are the sampling results after 50 h of reaction, and the conversion of chlorotrifluoroethylene and the selectivity of trifluoroethylene are used as indicators.

[0045] Table 1

[0046]

[0047] As can be seen from Table 1, the alumina-supported carbon-confined metal phosphide catalyst prepared by the preparation method provided by the present application has high conversion rate and selectivity when used in the reaction of preparing trifluoroethylene by hydrodechlorination of chlorotrifluoroethylene, and the catalyst has a long service life.

[0048] In summary, the raw materials for the preparation method of the present application are easy to obtain, and expensive noble metals are not needed. The preparation method is simple and easy to repeat, and the alumina-supported carbon-confined metal phosphide catalyst prepared by the method is a cheap base metal catalyst, which has higher catalyst cost advantage compared to noble metal catalysts such as Pd and Pt, and has the characteristics of high catalytic activity, high stability, and high selectivity of trifluoroethylene, and has excellent industrial application prospect.

[0049] The above description is only an example of the present application, and does not limit the patent scope of the present application, and any equivalent transformation or direct or indirect application in related technical fields using the content of the present application is also included in the patent protection scope of the present application.

Claims

1. A process for the preparation of an alumina-supported carbon- confined metal phosphide catalyst, characterized in that, Disperse high specific surface area alumina, phosphorus source, nitrogen-containing carbon source and metal salt precursor in deionized water, stir and treat, then perform hydrothermal crystallization treatment, centrifugal dry the obtained product, and finally perform calcination treatment in inert atmosphere; the metal salt precursor is one of copper nitrate trihydrate, nickel nitrate hexahydrate and cobalt nitrate hexahydrate.

2. The process for the preparation of an alumina-supported carbon- confined metal phosphide catalyst according to claim 1, characterized in that, The phosphorus source is one of triphenylphosphine, triethyl phosphate, triethyl phosphonoacetate, ammonium hypophosphite, diammonium hydrogen phosphate and ammonium dihydrogen phosphate.

3. The method of making an alumina-supported carbon-encapsulated metal phosphide catalyst according to claim 1, wherein, The nitrogen-containing carbon source is one of glycine, urea, dicyandiamide and melamine.

4. The method of claim 1, wherein the method is characterized by, The molar ratio of the high specific surface area alumina to the carbon source is 15:1~5:1; the molar ratio of the high specific surface area alumina to the phosphorus source is 20:1~5:1; and the molar ratio of the high specific surface area alumina to the metal salt precursor is 30:1~10:

1.

5. The method of making an alumina-supported carbon-encapsulated metal phosphide catalyst according to claim 1, wherein, The temperature of the stirring treatment is 30~60℃, and the time is 1~12h.

6. The method of claim 1, wherein the method is characterized by, The temperature of the hydrothermal crystallization treatment is 110~250℃, and the time is 4~18h.

7. The method of making an alumina-supported carbon-encapsulated metal phosphide catalyst according to claim 1, wherein, The temperature of the calcination treatment is 300~800℃, and the time is 2~12h.

8. An alumina-supported carbon-encapsulated metal phosphide catalyst, characterized in that, Prepared by the preparation method of any one of claims 1~7.

9. Use of the alumina-supported carbon-encapsulated metal phosphide catalyst of claim 8 in the preparation of trifluoroethylene by hydrodechlorination of chlorotrifluoroethylene.

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