Alumina-loaded carbon confinement metal phosphide catalyst as well as preparation method and application thereof

Abstract

The invention discloses an alumina-loaded carbon confinement metal phosphide catalyst as well as a preparation method and application thereof, and belongs to the technical field of carbon-based material confinement type catalysts. The preparation method provided by the invention comprises the following steps: dispersing aluminum oxide with a high specific surface area, a phosphorus source, a nitrogen-containing carbon source and a metal salt precursor in deionized water, stirring, carrying out hydrothermal crystallization treatment, carrying out centrifugal drying on the obtained product, and finally roasting in an inert atmosphere to obtain the high-specific-surface-area aluminum oxide. The obtained alumina-loaded carbon confinement metal phosphide catalyst can be used in preparation of trifluoroethylene by hydrodechlorination of trifluorochloroethylene. According to the preparation method, expensive metal raw materials do not need to be used, the preparation steps are simple, the repeatability is good, the catalyst with excellent catalytic activity and target product selectivity can be obtained, and the production cost can be effectively reduced when the catalyst is used in a reaction for preparing trifluoroethylene through hydrodechlorination of trifluorochlor oethylene.

Description

Technical Field

[0001] The present invention belongs to the technical field of carbon-based material confined catalysts, and specifically relates to an alumina-supported carbon-confined metal phosphide catalyst and a preparation method and application thereof. Background Art

[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, the GWP100 value is only 0.005, and the environmental performance is excellent. As a new generation of low GWP (Global Warming Potential) fluorinated greenhouse gas substitute, TrFE has a wide range of applications. It can be used as a heat pump working fluid in the air-conditioning system of new energy vehicles. The refrigerant used in the heat pump is the heat pump working fluid. The mixed heat pump working fluid with TrFE as the main component has the advantages of high efficiency and environmental protection, and can solve the existing shortcomings of high GWP value (HFC-134a), low refrigeration efficiency (HFO-1234yf), and high working pressure (CO2). It can also be used as a synthetic monomer for fluorinated polymer materials. TrFE can be synthesized with other monomers through homopolymerization or copolymerization into fluorinated polymer materials with unique electrical properties, which can be used as electric card refrigeration materials and piezoelectric materials. At the same time, trifluoroethylene is also a key raw material for the synthesis of high value-added halogenated olefins. TrFE can be used as a key raw material for the synthesis of new electronic etching gas hexafluoro-1,3-butadiene (C4F6) or other fluorinated olefins (such as 2,3,3,3-tetrafluoropropylene, trifluoroethylene bromide, etc.).

[0003] At present, the more mature process for preparing trifluoroethylene mainly uses trifluorotrichloroethane as the starting material and prepares trifluoroethylene through multi-step hydrodechlorination, but the yield of trifluoroethylene is low and the catalyst is easily deactivated. Using trifluorochloroethylene as the starting material and preparing trifluoroethylene through one-step catalytic hydrodechlorination can indeed significantly improve the yield of trifluoroethylene, but the catalyst used in this process is mainly a precious metal catalyst, and the precious metal loading is large, about 2~3%, and the catalyst is expensive. Therefore, the development of a cheap base metal catalyst is an urgent problem to be solved in the process route of preparing trifluoroethylene by hydrodechlorination of trifluorochloroethylene. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a base metal catalyst which can be used for preparing trifluoroethylene by hydrogenating and dechlorinating chlorotrifluoroethylene.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for preparing an alumina-supported carbon-confined metal phosphide catalyst, wherein 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, and then hydrothermal crystallization is performed, and the obtained product is centrifugally dried and finally calcined in an inert atmosphere.

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

[0007] Another technical solution adopted by the present invention is: using the above-mentioned alumina-supported carbon-confined metal phosphide catalyst in the preparation of trifluoroethylene by hydrogenation and dechlorination of chlorotrifluoroethylene.

[0008] The beneficial effects of the present invention are as follows: the raw materials used in the preparation method provided by the present invention are easily available, the preparation steps are simple, the repeatability is good, and a catalyst with excellent catalytic activity and target product selectivity can be obtained. The catalyst can be used in the reaction of preparing trifluoroethylene by hydrogenating and dechlorinating chlorotrifluoroethylene, which can effectively reduce the production cost. DETAILED DESCRIPTION

[0009] In order to explain the technical content, achieved objectives and effects of the present invention in detail, the following is an explanation in conjunction with the implementation modes.

[0010] A method for preparing an alumina-supported carbon-confined metal phosphide catalyst comprises dispersing high specific surface area alumina, a phosphorus source, a nitrogen-containing carbon source and a metal salt precursor in deionized water, stirring the mixture, performing a hydrothermal crystallization treatment, centrifugally drying the obtained product, and finally calcining the product in an inert atmosphere to obtain the alumina-supported carbon-confined metal phosphide catalyst.

[0011] From the above description, it can be seen that the beneficial effects of the present invention are: the present invention uses high specific surface area alumina as a carrier of carbon-confined metal phosphide, which can effectively increase the surface area of ​​the catalyst, increase the dispersion of the metal phosphide, and thus improve its catalytic activity; at the same time, the metal phosphide provided by the present invention is produced by a phosphorus source and metal particles in a hydrothermal crystallization process, is confined in a nitrogen-doped carbon material, and has high catalyst stability.

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

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

[0014] Furthermore, 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] It can be seen from the above description that the raw materials used are relatively low in price and are easily available.

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

[0017] Furthermore, the stirring treatment is carried out at a temperature of 30 to 60° C., preferably 30 to 45° C., and for a time of 1 to 12 h, preferably 3 to 6 h.

[0018] Furthermore, the temperature of the hydrothermal crystallization treatment is 110-250° C., preferably 130-220° C., and the time is 4-18 hours, preferably 6-12 hours. The hydrothermal crystallization treatment is carried out in a hydrothermal kettle.

[0019] Furthermore, the centrifugal drying is to obtain a solid product by centrifugal separation, and then dry it in a forced air drying oven at 120° C. for 12 h.

[0020] Furthermore, the calcination temperature is 300-800° C., preferably 450-650° C., the calcination time is 2-12 hours, preferably 4-8 hours, and the inert atmosphere is N2 atmosphere.

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

[0022] The present invention provides an application of the above-mentioned alumina-supported carbon-confined metal phosphide catalyst in preparing trifluoroethylene by hydrogenating and dechlorinating chlorotrifluoroethylene.

[0023] Embodiment 1 of the present invention is: 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 were dissolved in 500 mL of deionized water, stirred in a water bath at 30 °C for 3 h, then transferred to a hydrothermal reactor for hydrothermal crystallization at 130 °C for 6 h, and then the obtained product was centrifuged and dried in a blast drying oven at 120 °C for 12 h, and finally placed in a tubular furnace and calcined at 450 °C for 4 h in a N2 atmosphere to obtain alumina-supported carbon-confined metal phosphide catalyst CoP. x @C / Al2O3, denoted as S-1.

[0024] Embodiment 2 of the present invention is: 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 were dissolved in 500 mL of deionized water, stirred in a water bath at 30 °C for 1 h, then transferred to a hydrothermal reactor for hydrothermal crystallization at 110 °C for 4 h, and then the obtained product was centrifuged and dried in a blast drying oven at 120 °C for 12 h, and finally placed in a tubular furnace and calcined at 300 °C for 2 h in a N2 atmosphere to obtain alumina-supported carbon-confined metal phosphide catalyst CuP x @C / Al2O3, denoted as S-2.

[0025] Embodiment 3 of the present invention is: 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 were dissolved in 500 mL of deionized water, stirred in a water bath at 60 ° C for 12 h, then transferred to a hydrothermal reactor for hydrothermal crystallization at 250 ° C for 18 h, and then the obtained product was centrifuged and dried in a blast drying oven at 120 ° C for 12 h, and then placed in a tubular furnace and calcined at 800 ° C for 12 h in a N2 atmosphere to obtain alumina-supported carbon-confined metal phosphide catalyst CuP x @C / Al2O3, denoted as S-3.

[0026] Embodiment 4 of the present invention is: 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 were dissolved in 500 mL of deionized water, stirred in a water bath at 50 °C for 8 h, then transferred to a hydrothermal reactor for hydrothermal crystallization at 120 °C for 16 h, and then the obtained product was centrifuged and dried in a blast drying oven at 120 °C for 12 h, and finally placed in a tubular furnace and calcined at 700 °C for 3 h in a N2 atmosphere to obtain alumina-supported carbon-confined metal phosphide catalyst NiP x @C / Al2O3, denoted as S-4.

[0027] Embodiment 5 of the present invention is: 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 were dissolved in 500 mL of deionized water, stirred in a water bath at 45 °C for 6 h, then transferred to a hydrothermal reactor for hydrothermal crystallization at 220 °C for 12 h, and then the obtained product was centrifuged and dried in a blast drying oven at 120 °C for 12 h, and finally placed in a tubular furnace and calcined at 650 °C for 8 h in a N2 atmosphere to obtain alumina-supported carbon-confined metal phosphide catalyst CoP. x @C / Al2O3, denoted as S-5.

[0028] Embodiment 6 of the present invention is: 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 were dissolved in 500 mL of deionized water, stirred in a water bath at 35 °C for 4 h, then transferred to a hydrothermal reactor for hydrothermal crystallization at 160 °C for 8 h, and then the obtained product was centrifuged and dried in a blast drying oven at 120 °C for 12 h, and finally placed in a tubular furnace and calcined at 550 °C for 6 h in a N2 atmosphere to obtain alumina-supported carbon-confined metal phosphide catalytic NiP x @C / Al2O3, denoted as S-6.

[0029] Embodiment 7 of the present invention is: 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 were dissolved in 500 mL of deionized water, stirred in a water bath at 40 °C for 5 h, then transferred to a hydrothermal reactor for hydrothermal crystallization at 200 °C for 10 h, and then the obtained product was centrifuged and dried in a blast drying oven at 120 °C for 12 h, and finally placed in a tubular furnace and calcined at 600 °C for 4 h in a N2 atmosphere to obtain alumina-supported carbon-confined metal phosphide catalyst CoP. x @C / Al2O3, denoted as S-7.

[0030] Embodiment 8 of the present invention is: 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 were dissolved in 500 mL of deionized water, stirred in a water bath at 45 °C for 3 h, then transferred to a hydrothermal reactor for hydrothermal crystallization at 180 °C for 6 h, and then the obtained product was centrifuged and dried in a blast drying oven at 120 °C for 12 h, and finally placed in a tubular furnace and calcined at 500 °C for 8 h in a N2 atmosphere to obtain alumina-supported carbon-confined metal phosphide catalyst CoP. x @C / Al2O3, denoted as S-8.

[0031] Embodiment 9 of the present invention is: 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 were dissolved in 500 mL of deionized water, stirred in a water bath at 35 °C for 6 h, then transferred to a hydrothermal reactor for hydrothermal crystallization at 220 °C for 6 h, and then the obtained product was centrifuged and dried in a blast drying oven at 120 °C for 12 h, and finally placed in a tubular furnace and calcined at 650 °C for 4 h in a N2 atmosphere to obtain alumina-supported carbon-confined metal phosphide catalyst NiP x @C / Al2O3, denoted as S-9.

[0032] Embodiment 10 of the present invention is: The alumina-supported carbon-confined metal phosphide catalysts S-1 to S-9 prepared in Examples 1 to 9 above were used in the hydrodechlorination reaction of chlorotrifluoroethylene, and the catalyst activity evaluation was carried out in a fixed-bed reactor at normal pressure. The reaction tube of the tubular reactor used 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 reactor, and the catalyst particle size was 20 to 40 meshes.

[0033] First, the temperature was raised to 400 °C in a 200 mL / min N2 atmosphere and kept for 1 h. Then the atmosphere was switched to a H2 atmosphere with a flow rate of 200 mL / min, and the catalyst was reduced in situ for 6 h. After the reduction was completed, the atmosphere was switched to a N2 atmosphere with a flow rate of 200 mL / min, and the temperature was raised to 450 °C in a N2 atmosphere. Then the N2 atmosphere was switched to a mixture of trifluorochloroethylene and H2, with a volume ratio of trifluorochloroethylene to hydrogen of 1:1.5 and a gas flow rate of 75 mL / min. The tail gas generated by the reaction was washed with alkali, washed with water, and dried, and then detected online by gas chromatography. The test results are shown in Table 1.

[0034] Table 1 lists the catalysts S-1 to S-9 prepared in Examples 1 to 9 according to the above process conditions, i.e., normal pressure, reaction temperature of 450 °C, 225 h- 1 The catalyst activity test results at the space velocity are the sampling results after 50 hours of reaction, with the conversion rate of chlorotrifluoroethylene and the selectivity of trifluoroethylene as indicators.

[0035] Table 1

[0036] It can be seen from Table 1 that the alumina-supported carbon-confined metal phosphide catalyst obtained by the preparation method provided by the present invention has a high conversion rate and selectivity when used for the hydrodechlorination of chlorotrifluoroethylene to prepare trifluoroethylene, and the catalyst life is long.

[0037] In summary, the raw materials of the preparation method of the present invention are easily available, no expensive precious metals are needed, and the preparation method is simple and easy to repeat. The prepared alumina-supported carbon-confined metal phosphide catalyst is a cheap base metal catalyst, which has a higher catalyst cost advantage than precious metal catalysts such as Pd and Pt, and has the characteristics of high catalytic activity, high stability, and high selectivity for trifluoroethylene, and has excellent industrial application prospects.

[0038] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent transformations made using the contents of the present invention specification, or directly or indirectly applied in related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for preparing an alumina-supported carbon-confined metal phosphide catalyst, characterized in that: The high specific surface area alumina, phosphorus source, nitrogen-containing carbon source and metal salt precursor are dispersed in deionized water and stirred, and then hydrothermal crystallization is performed, and the obtained product is centrifugally dried and finally calcined in an inert atmosphere.

2. The method for preparing 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 for preparing an alumina-supported carbon-confined metal phosphide catalyst according to claim 1, characterized in that: The nitrogen-containing carbon source is one of glycine, urea, dicyandiamide and melamine.

4. The method for preparing an alumina-supported carbon-confined metal phosphide catalyst according to claim 1, characterized in that: The metal salt precursor is one of copper nitrate trihydrate, nickel nitrate hexahydrate and cobalt nitrate hexahydrate.

5. The method for preparing an alumina-supported carbon-confined metal phosphide catalyst according to claim 1, characterized in that: 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; the molar ratio of the high specific surface area alumina to the metal salt precursor is 30:1-10:

1.

6. The method for preparing an alumina-supported carbon-confined metal phosphide catalyst according to claim 1, characterized in that: The stirring treatment is performed at a temperature of 30-60° C. and for a time of 1-12 hours.

7. The method for preparing an alumina-supported carbon-confined metal phosphide catalyst according to claim 1, characterized in that: The temperature of the hydrothermal crystallization treatment is 110-250° C., and the time is 4-18 hours.

8. The method for preparing an alumina-supported carbon-confined metal phosphide catalyst according to claim 1, characterized in that: The calcination temperature is 300-800°C and the calcination time is 2-12 hours.

9. An alumina-supported carbon-confined metal phosphide catalyst, characterized in that: The method is prepared according to any one of claims 1 to 8.

10. Use of the alumina-supported carbon-confined metal phosphide catalyst according to claim 9 in the preparation of trifluoroethylene by hydrodechlorination of chlorotrifluoroethylene.

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