Oxyfluoride loaded nickel phosphide catalyst and application thereof

Abstract

The invention provides an oxyfluoride loaded nickel phosphide catalyst and application thereof. The carrier and the active phase of the oxyfluoride-loaded nickel phosphide catalyst are simultaneously prepared by adopting a'one-pot method '. The oxyfluoride-loaded nickel phosphide catalyst disclosed by the invention shows excellent reaction activity in hydrodechlorination reaction of fluorine-containing chlorohydrocarbon, and compared with a magnesium fluoride-loaded nickel phosphide catalyst obtained by a conventional impregnation method, the activity is obviously improved.

Description

Technical Field

[0001] The invention belongs to the technical field of heterogeneous catalysis, and in particular relates to an oxyfluoride-supported nickel phosphide solid catalyst for hydrogenation or hydrogenation reaction. Background Art

[0002] Hydrofluoroolefins (HFOs) are a new generation of environmentally friendly fluorine-containing specialty chemicals. The efficient synthesis of HFOs is currently a research hotspot in the field of fluorine chemicals. Gas-phase hydrodechlorination is one of the important ways to achieve green and efficient synthesis of hydrofluoroolefins due to its mild reaction conditions and controllable reaction process. However, the non-precious metal catalysts reported so far have problems such as low reaction activity and easy deactivation, which limits the promotion and application of the hydrodechlorination process for the synthesis of hydrofluoroolefins.

[0003] Metal-rich transition metal phosphides exhibit metallic properties and show good performance in the fields of hydrorefining, hydrodeoxygenation, selective hydrogenation / dehydrogenation, and photoelectrocatalysis. The method of temperature-programmed reduction of transition metal phosphate precursors under a hydrogen atmosphere is the most commonly used method for preparing transition metal phosphides. Since the PO bond of phosphates is very strong, its reduction requires a very high temperature (>500°C), which restricts the widespread application of transition metal phosphide catalysts. Changing the salt type of the precursor is one of the options to reduce the difficulty of preparation, because the phosphorus in conventional phosphates is +5 valent, while the phosphorus in phosphites is +3 valent, and the phosphorus in hypophosphites is +1 valent. They can produce PH3 through disproportionation reaction during thermal decomposition, and react with metals or metal salts to obtain phosphides, thereby reducing the reduction temperature.

[0004] CN110013867A discloses a reaction using bulk or supported nickel phosphide as a catalyst for the gas phase selective hydrodechlorination of 2-chloro-1,1,1,2-tetrafluoropropane to prepare 2,3,3,3-tetrafluoropropene. CN101037374A also discloses a supported nickel phosphide catalyst for the hydrodechlorination of chlorobenzene, dichlorobenzene or trichlorobenzene. The document (Chemical Communications, 2005, 33: 4178-4180) adopts 10 mol% PH3 / H2 atmosphere to heat treat the metal or metal oxide loaded on SiO2, and Ni2P / SiO2 catalyst can be obtained at a relatively low temperature (100-150°C); there is also a document (Journal of Catalysis, 2009, 263: 4-15) which adopts phosphorous acid as a phosphorus source to prepare a phosphorous acid precursor salt, and then obtains a Ni2P catalyst by programmed temperature reduction at a final temperature of 375°C; CN101898754A discloses a new method for preparing nickel phosphide by low-temperature reduction, which adopts sodium hypophosphite as a phosphorus source and can realize the low-temperature preparation of nickel phosphide catalyst. Summary of the invention

[0005] In view of the defects or shortcomings of the prior art, the present invention provides a fluoride oxide supported nickel phosphide catalyst.

[0006] To this end, the preparation method of the fluoride oxide supported nickel phosphide catalyst provided by the present invention comprises the following steps:

[0007] Step 1, at 20-60° C., magnesium ethoxide (Mg(OC2H5)2) is mixed with water to obtain a magnesium ethoxide suspension solution, and then ammonium bifluoride and the magnesium ethoxide suspension solution are subjected to a first mixing reaction; and then nickel acetate and the first mixed reaction solution are subjected to a second mixing reaction to obtain a reaction solution;

[0008] Step 2, placing the reaction solution at 90-110° C. for crystallization to obtain a reactant;

[0009] Step 3, calcining the reactants at 300-400° C. to obtain an intermediate product;

[0010] Step 4, mixing the intermediate product with a phosphate aqueous solution and collecting the product, and then calcining the product under an inert atmosphere at 300-400° C. to obtain a fluoride oxide-supported nickel phosphide catalyst; the phosphate is selected from ammonium hypophosphite or ammonium phosphite.

[0011] An optional scheme is that magnesium ethoxide is mixed with water for 1 hour or longer to obtain a magnesium ethoxide suspension solution; ammonium bifluoride and the magnesium ethoxide suspension solution undergo a first mixing reaction for 2 hours or longer; and nickel acetate and the first mixed reaction solution undergo a second mixing reaction for 1 hour or longer.

[0012] An optional solution is that the concentration of magnesium ethoxide in the magnesium ethoxide suspension is 5% to 20%; the molar ratio of magnesium element to fluorine element in the reaction solution is 1:3 to 1; and the molar ratio of magnesium element to nickel element in the reaction solution is 8 to 2:1.

[0013] Optionally, the crystallization time is at least 8 hours.

[0014] An optional solution is to wash, dry and then calcine the reactant obtained in step 2.

[0015] Optionally, the calcination time in step 3 is at least 2 hours.

[0016] An optional solution is that in step 4, the reaction temperature is greater than or equal to 20° C., and the reaction time is greater than or equal to 1 hour.

[0017] An optional solution is that the molar ratio of magnesium element to phosphorus element in the reaction system of step 4 is 8 to 2:1.

[0018] Optionally, step 4 is calcined for at least 2 hours.

[0019] The carrier and active phase of the catalyst of the present invention are prepared simultaneously by a "one-pot method". The preparation process of the prepared catalyst does not require a high-temperature hydrogen reduction process, and the preparation process is safe and efficient, which solves the problems of harsh preparation conditions and uncontrollable preparation process of nickel phosphide catalysts in the prior art.

[0020] The fluorine oxide supported nickel phosphide catalyst of the present invention is particularly suitable for use in the hydrodechlorination synthesis of hydrofluoroolefins. In the reaction of preparing 2,3,3,3-tetrafluoropropylene (HFO-1234yf) by gas phase hydrodechlorination of 2-chloro-1,1,1,2-tetrafluoropropane (HCFC-244bb), the catalyst is continuously operated for 200 hours, the HCFC-244bb conversion rate is maintained at more than 70%, and the HFO-1234yf selectivity is maintained at more than 90%. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is the XRD pattern of the catalyst prepared in Example 1.

[0022] Figure 2 is a SEM-element image of the catalyst prepared in Example 1. Figure 1-3 They are three randomly selected spectrum regions.

[0023] Figure 3 This is the GC-MS spectrum of the product HFO-1234yf prepared using the catalyst of Example 1. The upper figure is the test mass spectrum result, and the lower figure is the standard mass spectrum of HFO-1234yf.

[0024] Figure 4 This is the XRD pattern of the sample prepared in Comparative Example 3.

[0025] Figure 5 This is the XRD pattern of the sample prepared in Comparative Example 4.

[0026] Figure 6 This is the XRD pattern of the sample prepared in Comparative Example 5.

[0027] Figure 7 This is the XRD pattern of the sample prepared in Comparative Example 6. DETAILED DESCRIPTION

[0028] Unless otherwise specified, the terms used herein are understood according to the knowledge of ordinary technicians in the relevant fields. It should be noted that, based on the carrier preparation scheme of the present invention, those skilled in the art can optimize the methods of the present invention, including but not limited to specific reactants, ratios of reactants in each step, temperature and duration, drying temperature and calcination temperature, to achieve the relevant effects of the carrier of the present invention.

[0029] The application of the fluoride oxide supported nickel phosphide catalyst in the hydrodechlorination synthesis of hydrofluoroolefins of the present invention refers to the preparation of 2,3,3,3-tetrafluoropropene by gas phase hydrodechlorination of 2-chloro-1,1,1,2-tetrafluoropropane, and the catalyst used in the reaction is the catalyst of the present invention. Specific synthesis method example: a reasonable amount of the catalyst of the present invention is transferred to a fixed bed tubular reactor, 2-chloro-1,1,1,2-tetrafluoropropane and hydrogen are introduced after the catalyst bed temperature reaches a suitable temperature, and the contact time, H2 pressure and H2 / 2-chloro-1,1,1,2-tetrafluoropropane molar ratio are controlled; the product is collected after running for a reasonable period of time.

[0030] The catalyst performance test method in the following examples is as follows: 5 mL of the catalyst of the present invention is transferred into a fixed bed tubular reactor, and after the catalyst bed temperature reaches 240° C., 2-chloro-1,1,1,2-tetrafluoropropane and hydrogen are introduced, with a contact time of 8 s, an H2 pressure of 0.2 MPa, and an H2 / 2-chloro-1,1,1,2-tetrafluoropropane molar ratio of 2; after running for 8 hours, the product is washed with water and alkali to absorb hydrogen fluoride and hydrogen chloride, and then analyzed by a gas chromatograph, and the conversion rate of 2-chloro-1,1,1,2-tetrafluoropropane and the selectivity of 2,3,3,3-tetrafluoropropene are calculated by the area normalization method; and the life or stability of the catalyst is tested by extending the reaction time.

[0031] The following are specific examples of the present invention. It should be noted that the present invention is not limited to the following specific examples, and all equivalent changes made on the basis of the technical solution of this application fall within the protection scope of the present invention. The raw materials and reagents used in the following examples are all commercially available related products.

[0032] Embodiment 1:

[0033] Step 1, at 30±5°C, dissolve 2.86g of magnesium ethoxide in 40mL of deionized water and stir for 1 hour; then add 0.55g of ammonium bifluoride to the solution, continue stirring and reacting for 2 hours; then add 1g of nickel acetate in an aqueous solution (5mL) to the solution, continue stirring and reacting for 1 hour to obtain a reaction solution;

[0034] Step 2, after that, the reaction solution was transferred to a reactor and placed in an oven at 100±10°C for crystallization for 10 hours, and then the reactants were collected;

[0035] Step 3, washing the reactant with ethanol three times, drying it, and then calcining it in a muffle furnace at 350±10° C. for 3 hours to obtain an intermediate product;

[0036] Step 4, the intermediate product is added to an aqueous solution (10 mL) containing 2 g of ammonium hypophosphite, stirred at 50±5° C. for 2 hours, and the product is collected. After the product is dried, it is calcined in a nitrogen atmosphere at 350±10° C. for 3 hours to obtain a magnesium oxyfluoride-supported nickel phosphide catalyst, recorded as Ni-P / MgOF.

[0037] Product Characterization:

[0038] The XRD pattern of the catalyst prepared in this example is as follows: Figure 1 As shown in the SEM-element diagram Figure 2 As shown, Figure 2 The element content analysis of the three regions in Table 1 is shown in Table 1 (the mean, standard deviation, maximum and minimum values ​​in Table 1 are Figure 2 The mean, standard deviation, maximum and minimum values ​​of the content of each element in the three spectrum areas.

[0039] Table 1

[0040]

[0041]

[0042] from Figure 1 It can be seen that the main crystal phase of the obtained catalyst is Ni 12 P5 (PDF 74-1381), the diffraction peaks at 2θ around 38.42°, 41.64°, 44.42°, 46.96°, and 48.96° correspond to Ni 12 The (112), (321), (330), (420) and (312) crystal planes of P5; Figure 2 As shown in Table 1, the prepared catalyst contains four elements, Mg, F, P and Ni, with relative contents of 45.3%, 46.97%, 3.17% and 1.82% respectively. Therefore, the catalyst prepared in this example is the target catalyst to be prepared in this application.

[0043] Performance Test:

[0044] The catalyst prepared in this example was further used in the catalytic hydrodechlorination of 2-chloro-1,1,1,2-tetrafluoropropane to prepare 2,3,3,3-tetrafluoropropene (HFO-1234yf). The catalyst performance test method of the present invention was used to obtain: the feed conversion rate was 72% at 240° C., and the trifluoroethylene selectivity was 91%;

[0045] Figure 3 This is the GC-MS spectrum of the product HFO-1234yf prepared by the catalyst performance test method. The mass spectrum result has a high degree of match with the standard spectrum. Figure 3The mass spectrometry results and their peak assignments are as follows: m / z=114 is a molecular ion peak, m / z=95 is an ion peak after CF3CF=CH2 is defluorinated from HF, m / z=69 is an ion peak of a fragment trifluoromethyl, m / z=64 is an ion peak of a fragment difluorovinyl, m / z=51 is an ion peak of a fragment difluoromethyl, and m / z=31 is an ion peak of a fragment CF. Figure 3 It can be seen that the obtained product is HFO-1234yf.

[0046] Comparative Example 1:

[0047] The difference between this comparative example and Example 1 is that nickel acetate and ammonium hypophosphite are not added. That is, nickel acetate is not added in step 1; and in step 4, the intermediate product obtained in this comparative example is directly roasted under the same conditions.

[0048] The catalyst prepared in this comparative example is used in the reaction of preparing 2,3,3,3-tetrafluoropropene by catalytic hydrodechlorination of 2-chloro-1,1,1,2-tetrafluoropropane, and the catalyst performance test method of the present invention is used to obtain: without adding any other reagents, the raw material conversion rate is 27% at 240°C, and the trifluoroethylene selectivity is 62%. The results show that the catalyst has a low conversion rate for the reaction raw materials and a low selectivity for the target product, which is not conducive to further separation and purification.

[0049] Comparative Example 2:

[0050] This comparative example is different from Example 1 in that conventional magnesium fluoride is used as a carrier, and nickel acetate and ammonium hypophosphite are impregnated by an impregnation process (the ratio of magnesium fluoride, nickel acetate, and ammonium hypophosphite is the same as the molar ratio of fluorine element, nickel element, and phosphorus element in Example 1), followed by washing and drying, and calcining at 350±10°C to prepare the magnesium fluoride-supported nickel phosphide catalyst of this comparative example.

[0051] The catalyst prepared in this comparative example is used in the reaction of preparing 2,3,3,3-tetrafluoropropene by catalytic hydrodechlorination of 2-chloro-1,1,1,2-tetrafluoropropane. The catalyst performance test method of the present invention is used to obtain: without adding any other reagents, the raw material conversion rate is 37% at 240°C, and the trifluoroethylene selectivity is 80%. The results show that the catalyst has a low conversion rate for the reaction raw materials and a low selectivity for the target product, which is not conducive to further separation and purification.

[0052] Comparative Example 3:

[0053] The difference between this comparative example and Example 1 is that magnesium ethoxide, ammonium bifluoride and nickel acetate are added into water and stirred for 4 hours. The XRD result of the obtained product is as follows: Figure 4As shown, the product has diffraction peaks at about 20.53°, 39.87°, 53° and 60.92°, which correspond to the (001), (101), (102) and (110) crystal planes of Mg(OH)2(07-0239), and diffraction peaks at about 28.25°, 36.87°, 53.60° and 55.12°, which correspond to the (110), (101), (211) and (220) crystal planes of NiF2(22-0749). This indicates that the product obtained in this comparative example is completely different from the Ni-P / MgOF of Example 1.

[0054] Comparative Example 4:

[0055] The difference between this comparative example and Example 1 is that magnesium ethoxide and ammonium bifluoride are added to water and stirred for 3 hours before the subsequent operation. The XRD pattern of the obtained product sample is as follows: Figure 5 As shown, the Figure 5 The results show that the product has diffraction peaks at 20.53°, 39.87°, 53° and 60.92°, which correspond to the (001), (101), (102) and (110) crystal planes of Mg(OH)2(07-0239), respectively. This indicates that the product obtained in this comparative example is completely different from the Ni-P / MgOF in Example 1.

[0056] Comparative Example 5:

[0057] The difference between this comparative example and Example 1 is that magnesium ethoxide and nickel acetate are added to water and stirred for 2 hours, and then ammonium bifluoride is added and stirred for 2 hours before other operations are performed. The XRD pattern of the obtained product is as follows: Figure 6 As shown, Figure 6 The results show that the product has diffraction peaks at 20.53°, 39.87°, 53° and 60.92°, which correspond to the (001), (101), (102) and (110) crystal planes of Mg(OH)2(07-0239), and diffraction peaks at 40.67° and 53.81°, which correspond to the (111) and (211) crystal planes of MgF2(06-0290), respectively. This indicates that the product obtained in this comparative example is completely different from the Ni-P / MgOF in Example 1.

[0058] Comparative Example 6:

[0059] The difference between this comparative example and Example 1 is that ammonium bifluoride and nickel acetate are added to water and stirred for 3 hours, and then magnesium ethoxide is added and stirred for 1 hour before other operations are performed. The XRD analysis of the obtained product is as follows: Figure 7As shown in the figure, the result shows that the diffraction peaks of the 2θ of the prepared product are around 36.86°, 42.82° and 62.16°, which correspond to the (111), (200) and (220) crystal planes of MgO (74-1225), respectively. This shows that the product prepared in this comparative example is completely different from the Ni-P / MgOF of Example 1.

[0060] Embodiment 2:

[0061] This example gives the experimental results of evaluating the lifespan or stability of the catalyst in Example 1 and the catalyst prepared in Comparative Example 1, as shown in Table 2.

[0062] As can be seen from Table 2, the catalyst in Example 1 has stable reaction performance within 200 hours of reaction evaluation, and the catalyst activity increases with the reaction time, and the raw material conversion rate and target product selectivity are maintained in a stable numerical range; while the catalyst in Comparative Example 1 begins to deactivate 20 hours after the reaction, and the deactivation phenomenon remains unchanged as the reaction time increases. When the reaction runs for 200 hours, the catalyst activity drops to about 9.1%, and the target product selectivity is about 51.8%.

[0063] Table 2

[0064]

Claims

1. A fluoride-supported nickel phosphide catalyst, characterized in that: The preparation method of the catalyst comprises the following steps: Step 1, at 20-60° C., magnesium ethoxide is mixed with water to obtain a magnesium ethoxide suspension solution, and then ammonium bifluoride and the magnesium ethoxide suspension solution are subjected to a first mixing reaction; and then nickel acetate and the first mixed reaction solution are subjected to a second mixing reaction to obtain a reaction solution; Step 2, placing the reaction solution at 90-110° C. for crystallization to obtain a reactant; Step 3, calcining the reactants at 300-400° C. to obtain an intermediate product; Step 4, mixing the intermediate product with a phosphate aqueous solution for reaction, collecting the product, and then calcining the product under an inert atmosphere at 300-400° C. to obtain a fluoride oxide-supported nickel phosphide catalyst; the phosphate is selected from ammonium hypophosphite or ammonium phosphite.

2. The oxyfluoride-supported nickel phosphide catalyst according to claim 1, characterized in that: The mixing time of magnesium ethoxide and water is greater than or equal to 1 hour to obtain a magnesium ethoxide suspension solution; the first mixing reaction of ammonium bifluoride and the magnesium ethoxide suspension solution is greater than or equal to 2 hours; and the second mixing reaction of nickel acetate and the first mixed reaction solution is greater than or equal to 1 hour.

3. The oxyfluoride-supported nickel phosphide catalyst according to claim 1, characterized in that: The concentration of magnesium ethoxide in the magnesium ethoxide suspension is 5% to 20%; the molar ratio of magnesium element to fluorine element in the reaction solution is 1:3 to 1; and the molar ratio of magnesium element to nickel element in the reaction solution is 8 to 2:

1.

4. The fluoride oxide supported nickel phosphide catalyst according to claim 1, characterized in that The crystallization time is at least 8 hours.

5. The oxyfluoride-supported nickel phosphide catalyst according to claim 1, characterized in that: The reactant obtained in step 2 is washed, dried and then calcined.

6. The oxyfluoride-supported nickel phosphide catalyst according to claim 1, characterized in that: The roasting time in step 3 is at least 2 hours.

7. The oxyfluoride-supported nickel phosphide catalyst according to claim 1, characterized in that: In step 4, the reaction temperature is greater than or equal to 20° C., and the reaction time is greater than or equal to 1 hour.

8. The oxyfluoride-supported nickel phosphide catalyst according to claim 1, characterized in that: In step 4, the molar ratio of magnesium element to phosphorus element in the reaction system is 8 to 2:

1.

9. The oxyfluoride-supported nickel phosphide catalyst according to claim 1, characterized in that: Step 4: calcine for at least 2 hours.

10. Use of the fluoride oxide supported nickel phosphide catalyst according to claim 1 in the synthesis of hydrofluoroolefins by hydrodechlorination.

Images