A silicon carbide confined bimetallic catalyst and its preparation method and application

Abstract

The present invention relates to the field of catalyst technology, and specifically to a bimetallic catalyst confined in silicon carbide, and a preparation method and application thereof. The preparation method comprises the following steps: dispersing and dissolving silicon carbide, an ion mediator precursor, a complexing agent, and two metal salt precursors in deionized water, and then performing a hydrothermal crystallization treatment; then centrifugally separating and drying the obtained hydrothermal crystallization product, and then calcining it in an inert atmosphere to obtain a bimetallic catalyst confined in silicon carbide. The preparation method confines two metals in defects on the surface of silicon carbide by ion-mediated complexation, and prepares a catalyst with excellent catalytic activity and target product selectivity, and the metal is not easy to sinter and agglomerate.

Description

Technical Field

[0001] The present invention relates to the field of catalyst technology, and in particular to a silicon carbide confined bimetallic catalyst and a preparation method and application thereof. Background Art

[0002] Trifluoroethylene (TrFE or HFO-1123) is a colorless gas at room temperature. It is easy to undergo polymerization and release heat at room temperature, which is explosive. A certain amount of dipentene needs to be added as a polymerization inhibitor during storage. Trifluoroethylene is an important fluorine-containing intermediate. The polycondensation of trifluoroethylene and ethanol can produce environmentally friendly cleaning agent hydrofluoroether; trifluoroethylene is added with bromine and then debrominated with hydrogen to obtain trifluoroethylene bromide. The metal organic intermediate of trifluoroethylene bromide is an important reagent for synthesizing trifluoroethylene vinyl compounds. The telomer is used as the floating liquid and damping liquid of the liquid-floating gyroscope and accelerometer of the high-precision navigation system, and is used in the aerospace industry. It is also a raw material for the manufacture of fluorobromo oil. Trifluoroethylene is also an important monomer raw material for the preparation of many fluorine-containing polymers (homopolymers or copolymers). For example, the copolymer obtained by copolymerizing trifluoroethylene with vinylidene fluoride has extraordinary piezoelectric (electrostrictive) properties, and thus has a wide range of application value in the fields of human organs, electronic appliances, and energy. Since trifluoroethylene has a low boiling point (-57°C), is prone to self-polymerization and explosion, is highly dangerous, and is difficult to transport and store for long periods of time, there is currently relatively little research on the preparation of trifluoroethylene in my country, and there is no mature production technology yet.

[0003] At present, the more mature trifluoroethylene preparation process is shown in the Chinese invention patent with application number 201910774511.1, which mainly uses trifluorochloroethylene as the initial raw material and prepares trifluoroethylene through catalytic hydrogenation and dechlorination. However, the activity and life of the catalyst in this type of process are not ideal. The main problem is that the precious metal components in the catalyst, such as Pd or Ru, will sinter and deactivate, and the selectivity of the target product trifluoroethylene is also low. Therefore, solving the sintering agglomeration deactivation of precious metals and improving the selectivity of the target product trifluorochloroethylene are the current problems that need to be solved urgently. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a silicon carbide confined bimetallic catalyst and a preparation method and application thereof, wherein the catalyst has excellent catalytic activity and target product selectivity.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for preparing a silicon carbide confined bimetallic catalyst, comprising the following steps: dispersing and dissolving silicon carbide, an ion mediator precursor, a chelating agent and two metal salt precursors in deionized water, and then performing a hydrothermal crystallization treatment; then, the obtained hydrothermal crystallization product is centrifuged and dried, and then calcined in an inert atmosphere to obtain a silicon carbide confined bimetallic catalyst.

[0006] Another technical scheme adopted by the present invention is: the silicon carbide confined bimetallic catalyst is prepared by the preparation method of the above-mentioned silicon carbide confined bimetallic catalyst.

[0007] Another technical scheme adopted by the present invention is: the application of the above-mentioned silicon carbide confined bimetallic catalyst in the reaction of preparing trifluoroethylene by hydrogenation and dechlorination of chlorotrifluoroethylene.

[0008] The beneficial effect of the present invention is that the preparation method of the present invention confines two metals in the defects on the surface of silicon carbide by ion-mediated complexation, thereby preparing a catalyst with excellent catalytic activity and target product selectivity, and the metals in the catalyst are not easy to sinter and agglomerate. 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 a silicon carbide confined bimetallic catalyst comprises the following steps: dispersing and dissolving silicon carbide, an ion mediator precursor, a complexing agent and two metal salt precursors in deionized water, and then performing a hydrothermal crystallization treatment; then centrifugally separating and drying the obtained hydrothermal crystallization product, and then calcining it in an inert atmosphere to obtain a silicon carbide confined bimetallic catalyst.

[0011] From the above description, it can be seen that the beneficial effects of the present invention are: providing a preparation method of a silicon carbide confined bimetallic catalyst and its application, and proposing its application in the field of hydrodechlorination of chlorofluorocarbons for the first time. The preparation method of the catalyst is simple, has good repeatability, and has excellent catalytic activity and target product selectivity.

[0012] The preparation method of the present invention is simple and easy to repeat. The two metals are confined at the defects on the surface of silicon carbide by ion-mediated complexation. Due to the high thermal conductivity and excellent chemical stability of silicon carbide, the catalyst maintains the maximum degree of stability during use. The two metals can greatly improve the selectivity of trifluoroethylene as the target product. At the same time, due to the confinement effect of silicon carbide on the metal, the sintering and agglomeration of the metal are effectively inhibited.

[0013] Furthermore, the ion mediator precursor is Na +or K + of nitrates.

[0014] Preferably, the ion mediator precursor is K + of nitrates.

[0015] Furthermore, the complexing agent is any one of glycine, terephthalic acid and dicyandiamide.

[0016] Preferably, the complexing agent is glycine or dicyandiamide.

[0017] Furthermore, the two metal salt precursors include a first metal salt precursor and a second metal salt precursor, the first metal salt precursor is any one of RuCl3, (NH4)2PdCl4 and (NH4)2PtCl6; the second metal salt precursor is any one of magnesium nitrate hexahydrate, barium nitrate, strontium nitrate and calcium nitrate tetrahydrate.

[0018] Preferably, the first metal salt precursor is (NH4)2PdCl4, and the second metal salt precursor is barium nitrate or strontium nitrate.

[0019] From the above description, it can be seen that the highly selective adsorption of Cl by alkaline earth metals greatly improves the selectivity of the target product trifluoroethylene. At the same time, due to the confinement effect of silicon carbide on precious metals, the sintering and agglomeration of precious metals are effectively inhibited.

[0020] Furthermore, the molar ratio of silicon carbide to the first metal salt precursor is 500:1 to 50:1.

[0021] Preferably, the molar ratio of silicon carbide to the first metal salt precursor is 200:1 to 100:1.

[0022] Furthermore, the molar ratio of silicon carbide to the second metal salt precursor is 100:1 to 30:1.

[0023] Preferably, the molar ratio of silicon carbide to the second metal salt precursor is 50:1 to 40:1.

[0024] Furthermore, the molar ratio of silicon carbide to the ion mediator precursor is 20:1 to 10:1.

[0025] Preferably, the molar ratio of silicon carbide to the ion mediator precursor is 16:1 to 12:1.

[0026] Furthermore, the molar ratio of silicon carbide to the complexing agent is 15:1 to 5:1.

[0027] Preferably, the molar ratio of silicon carbide to the complexing agent is 10:1 to 5:1.

[0028] Furthermore, the temperature of the hydrothermal crystallization treatment is 120~250 ℃, and the time is 6~24 h.

[0029] Preferably, the temperature of the hydrothermal crystallization treatment is 160-220°C and the time is 8-18 h.

[0030] Furthermore, the specific steps of centrifugal separation and drying are: after obtaining the solid product by centrifugal separation, drying it in a forced air drying oven at 120° C. for 12 h.

[0031] Furthermore, the inert atmosphere is N2.

[0032] Furthermore, the calcination temperature is 250-600°C and the calcination time is 3-12 hours.

[0033] Preferably, the calcination temperature is 350-550° C. and the calcination time is 5-8 h.

[0034] Another technical scheme adopted by the present invention is: the silicon carbide confined bimetallic catalyst is prepared by the preparation method of the above-mentioned silicon carbide confined bimetallic catalyst.

[0035] From the above description, it can be seen that the silicon carbide confined bimetallic catalyst prepared by the present invention has high catalytic activity and high selectivity for trifluoroethylene, and has excellent industrial application prospects.

[0036] Another technical scheme adopted by the present invention is: the application of the above-mentioned silicon carbide confined bimetallic catalyst in the reaction of preparing trifluoroethylene by hydrogenation and dechlorination of chlorotrifluoroethylene.

[0037] Embodiment 1 of the present invention is: a method for preparing a silicon carbide confined bimetallic catalyst, the steps are as follows: 20 g of silicon carbide powder, 3.16 g of potassium nitrate, 3.75 g of glycine, 0.71 g of (NH4)2PdCl4 and 2.61 g of barium nitrate were dissolved in 500 mL of deionized water, and then placed at 160 °C for hydrothermal crystallization for 8 h; the resulting product was then centrifuged and dried in a forced air drying oven at 120 °C for 12 h, and finally placed in a tubular furnace and calcined at 350 °C for 5 h under N2 atmosphere to obtain the silicon carbide confined bimetallic catalyst BaPd@SiC, denoted as S-1.

[0038] Embodiment 2 of the present invention is: a method for preparing a silicon carbide confined bimetallic catalyst, the steps are as follows: 20 g of silicon carbide powder, 2.12 g of sodium nitrate, 5.54 g of terephthalic acid, 0.21 g of RuCl3 and 1.28 g of magnesium nitrate hexahydrate were dissolved in 500 mL of deionized water, and then placed at 120 °C for hydrothermal crystallization for 6 h; the resulting product was then centrifuged and dried in a forced air drying oven at 120 °C for 12 h, and finally placed in a tubular furnace and calcined at 250 °C for 3 h under N2 atmosphere to obtain a silicon carbide-confined bimetallic catalyst MgRu@SiC, which was denoted as S-2.

[0039] Embodiment 3 of the present invention is: a method for preparing a silicon carbide confined bimetallic catalyst, the steps are as follows: 20 g of silicon carbide powder, 5.06 g of potassium nitrate, 8.41 g of dicyandiamide, 4.44 g of (NH4)2PtCl6 and 3.94 g of calcium nitrate tetrahydrate were dissolved in 500 mL of deionized water, and then placed at 250 °C for hydrothermal crystallization for 24 h; the resulting product was then centrifuged and dried in a forced air drying oven at 120 °C for 12 h, and finally placed in a tubular furnace and calcined at 600 °C for 12 h under N2 atmosphere to obtain a silicon carbide-confined bimetallic catalyst CaPt@SiC, denoted as S-3.

[0040] Embodiment 4 of the present invention is: a method for preparing a silicon carbide confined bimetallic catalyst, the steps are as follows: 20 g of silicon carbide powder, 4.21 g of potassium nitrate, 7.51 g of glycine, 1.42 g of (NH4)2PdCl4 and 2.65 g of strontium nitrate were dissolved in 500 mL of deionized water, and then placed at 220 °C for hydrothermal crystallization for 18 h; the product was then centrifuged and dried in a forced air drying oven at 120 °C for 12 h, and finally placed in a tubular furnace and calcined at 550 °C for 8 h under N2 atmosphere to obtain a silicon carbide-confined bimetallic catalyst SrPd@SiC, denoted as S-4.

[0041] Embodiment 5 of the present invention is: a method for preparing a silicon carbide confined bimetallic catalyst, the steps are as follows: 20 g of silicon carbide powder, 3.37 g of potassium nitrate, 5.26 g of dicyandiamide, 0.95 g of (NH4)2PdCl4 and 2.9 g of barium nitrate were dissolved in 500 mL of deionized water, and then placed at 180 °C for hydrothermal crystallization for 10 h; the resulting product was then centrifuged and dried in a forced air drying oven at 120 °C for 12 h, and finally placed in a tubular furnace and calcined at 400 °C for 6 h under N2 atmosphere to obtain a silicon carbide-confined bimetallic catalyst BaPd@SiC, denoted as S-5.

[0042] Embodiment 6 of the present invention is: a method for preparing a silicon carbide confined bimetallic catalyst, the steps are as follows: 20 g of silicon carbide powder, 3.61 g of potassium nitrate, 6.26 g of glycine, 0.79 g of (NH4)2PdCl4 and 2.65 g of strontium nitrate were dissolved in 500 mL of deionized water, and then placed at 200 °C for hydrothermal crystallization for 12 h; the product was then centrifuged and dried in a forced air drying oven at 120 °C for 12 h, and finally placed in a tubular furnace and calcined at 450 °C for 7 h in a N2 atmosphere to obtain a silicon carbide-confined bimetallic catalyst SrPd@SiC, denoted as S-6.

[0043] Embodiment 7 of the present invention is: a method for preparing a silicon carbide confined bimetallic catalyst, the steps are as follows: 20 g of silicon carbide powder, 3.89 g of potassium nitrate, 6.01 g of dicyandiamide, 0.71 g of (NH4)2PdCl4 and 3.27 g of barium nitrate were dissolved in 500 mL of deionized water, and then placed at 220 °C for hydrothermal crystallization for 16 h; the resulting product was then centrifuged and dried in a forced air drying oven at 120 °C for 12 h, and finally placed in a tubular furnace and calcined at 500 °C for 6 h under N2 atmosphere to obtain a silicon carbide-confined bimetallic catalyst BaPd@SiC, denoted as S-7.

[0044] Embodiment 8 of the present invention is: a method for preparing a silicon carbide confined bimetallic catalyst, the steps are as follows: 20 g of silicon carbide powder, 2.83 g of sodium nitrate, 7.01 g of dicyandiamide, 0.95 g of (NH4)2PdCl4 and 2.9 g of barium nitrate were dissolved in 500 mL of deionized water, and then placed at 220 °C for hydrothermal crystallization for 10 h; the resulting product was then centrifuged and dried in a forced air drying oven at 120 °C for 12 h, and finally placed in a tubular furnace and calcined at 550 °C for 6 h under N2 atmosphere to obtain a silicon carbide-confined bimetallic catalyst BaPd@SiC, denoted as S-8.

[0045] Comparative Example 1 of the present invention is: The only difference between Comparative Example 1 and Example 1 is that no barium nitrate is added, and the obtained catalyst Pd@SiC is recorded as D-1.

[0046] Example 9 of the present invention is: a silicon carbide confined bimetallic catalyst prepared by the preparation method of Example 1.

[0047] Example 10 of the present invention: Application of a bimetallic catalyst confined by silicon carbide in the hydrodechlorination of chlorotrifluoroethylene to prepare trifluoroethylene, the steps are as follows: The silicon carbide confined bimetallic catalysts synthesized in Examples 1-8 and the catalyst synthesized in Comparative Example 1 were respectively used in the hydrodechlorination reaction of chlorotrifluoroethylene, and the catalyst activity evaluation was carried out in a fixed bed reactor at atmospheric pressure.

[0048] The reaction of preparing trifluoroethylene by hydrodechlorination of trifluorochloroethylene is as follows: the reaction tube of the tubular reactor adopts a high-purity quartz tube with an inner diameter of 20 mm and a length of 1000 mm. 10 mL of catalyst particles are loaded into the fixed bed reactor, and the catalyst particle size is 20-40 mesh. After the catalyst is loaded, 100 mL / min of N2 atmosphere is introduced and heated to 300 °C, and kept warm for 1 h, and then the atmosphere is switched to a mixture of N2 / H2, with a volume ratio of N2 to H2 of 4:1 and a flow rate of 100 mL / min. The catalyst is reduced in situ for 4 h. After the reduction is completed, the atmosphere is switched to a mixture of trifluorochloroethylene and H2, with a volume ratio of trifluorochloroethylene to H2 of 1:1.5 and a gas flow rate of 75 mL / min. The tail gas generated by the reaction is washed with alkali, washed with water, and dried, and then detected online by gas chromatography.

[0049] Table 1 lists the catalysts prepared in Examples 1 to 8 and Comparative Example 1 according to the above process conditions (i.e., normal pressure, reaction temperature of 300 °C, 450 h -1 The catalyst activity test results after 50 h of reaction at 37 °C (13 °F space velocity), with the conversion rate of chlorotrifluoroethylene and the selectivity of trifluoroethylene as indicators.

[0050] Table 1

[0051] It can be seen from the activity results of the reactions in Table 1 that when the silicon carbide confined bimetallic catalyst provided by the method of the present invention is used for the hydrodechlorination of chlorotrifluoroethylene to prepare trifluoroethylene, it has a higher conversion rate and selectivity, and the catalyst life is longer.

[0052] In summary, the present invention provides a silicon carbide confined bimetallic catalyst and a preparation method thereof, and proposes for the first time the application of the catalyst in the field of hydrodechlorination of chlorofluorocarbons, which has the following advantages: 1. Alkaline earth metals and precious metals are confined to the defects on the surface of silicon carbide by ion-mediated complexation. Due to the high thermal conductivity and excellent chemical stability of silicon carbide, the catalyst remains stable to the greatest extent during use. Secondly, the highly selective adsorption of Cl by alkaline earth metals also greatly improves the selectivity of the target product trifluoroethylene. At the same time, due to the confinement effect of silicon carbide on precious metals, the sintering and agglomeration of precious metals are effectively inhibited.

[0053] 2. The preparation method is simple and easy to repeat; 3. The catalyst has high catalytic activity and high selectivity for trifluoroethylene, and has excellent industrial application prospects.

[0054] 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 specification of the present invention, 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 a silicon carbide confined bimetallic catalyst, characterized in that: The following steps are involved: Silicon carbide, an ion mediator precursor, a complexing agent and two metal salt precursors are dispersed and dissolved in deionized water, and then subjected to hydrothermal crystallization treatment; the hydrothermal crystallization product obtained is then centrifugally separated and dried, and then calcined in an inert atmosphere to obtain a silicon carbide confined bimetallic catalyst.

2. The method for preparing the silicon carbide confined bimetallic catalyst according to claim 1, characterized in that: The two metal salt precursors include a first metal salt precursor and a second metal salt precursor, wherein the first metal salt precursor is any one of RuCl3, (NH4)2PdCl4 and (NH4)2PtCl6; the second metal salt precursor is any one of magnesium nitrate hexahydrate, barium nitrate, strontium nitrate and calcium nitrate tetrahydrate.

3. The method for preparing the silicon carbide confined bimetallic catalyst according to claim 2, characterized in that: The molar ratio of the silicon carbide to the first metal salt precursor is 500:1 to 50:

1.

4. The method for preparing the silicon carbide confined bimetallic catalyst according to claim 2, characterized in that: The molar ratio of the silicon carbide to the second metal salt precursor is 100:1 to 30:

1.

5. The method for preparing the silicon carbide confined bimetallic catalyst according to claim 1, characterized in that: The molar ratio of the silicon carbide to the ion mediator precursor is 20:1 to 10:

1.

6. The method for preparing the silicon carbide confined bimetallic catalyst according to claim 1, characterized in that: The molar ratio of silicon carbide to the complexing agent is 15:1 to 5:

1.

7. The method for preparing the silicon carbide confined bimetallic catalyst according to claim 1, characterized in that: The temperature of the hydrothermal crystallization treatment is 120-250°C, and the time is 6-24 hours.

8. The method for preparing a silicon carbide confined bimetallic catalyst according to claim 1, characterized in that: The calcination process is carried out at a temperature of 250 to 600° C. and for a time of 3 to 12 hours.

9. A silicon carbide confined bimetallic catalyst prepared by the method for preparing a silicon carbide confined bimetallic catalyst according to any one of claims 1 to 8.

10. Use of the silicon carbide confined bimetallic catalyst as claimed in claim 9 in the reaction of preparing trifluoroethylene by hydrodechlorination of chlorotrifluoroethylene.

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