Graphite carbon layer packaged CoNi bimetallic alloy catalyst and preparation and application thereof

Abstract

The invention discloses a graphite carbon layer packaged CoNi bimetallic alloy catalyst as well as preparation and application thereof. The preparation method of the catalyst comprises the following steps: (1) dissolving a metal cobalt salt, a metal nickel salt and an organic ligand isonicotinic acid in a mixed organic solvent, then adding an aqueous solution of a deprotonation reagent, and carrying out a stirring reaction to obtain a mixed solution; (2) uniformly stirring and mixing the mixed solution with an inorganic salt aqueous solution, performing suction filtration and washing, and performing freeze drying to obtain a catalyst precursor; (3) carrying out ball milling on the catalyst precursor; and (4) putting the ball-milled catalyst precursor into a tubular furnace, heating to 500-800 DEG C in a nitrogen atmosphere, carrying out constant-temperature roasting, cooling to room temperature after roasting, and grinding to obtain the graphite carbon layer encapsulated CoNi bimetallic alloy catalyst. The invention provides the application of the obtained catalyst in synthesizing halogenated aniline through catalytic hydrogenation of halogenated nitrobenzene, and the catalyst shows excellent catalytic activity, selectivity and stability.

Description

Technical Field

[0001] The present invention belongs to the field of catalyst preparation technology and application, and relates to a graphite carbon layer encapsulated CoNi bimetallic alloy catalyst for catalytic hydrogenation of halogenated nitrobenzene to synthesize aniline, as well as the preparation and application of the catalyst. Background Art

[0002] Halogenated anilines and their derivatives are widely used in fine chemicals. They can be used as a key organic intermediate and important chemical product to synthesize various organic compounds, including pigments, dyes, agrochemicals, polymer materials, liquid crystals and drugs. Catalytic hydrogenation reduction is a method commonly used for nitro reduction, which usually involves the use of catalysts and hydrogen. This method is widely used in organic synthesis and chemical industry, conforms to the development trend of green chemistry, and has attracted widespread attention. According to the structural classification of catalysts, they can be divided into supported catalysts, single-atom catalysts and encapsulated catalysts. Among them, encapsulated catalysts are widely used in nitro hydrogenation reactions because of their advantages such as relatively easier control and implementation of the preparation process, better stability in large-scale production, and clear interactions between the encapsulation structure and the active component, which can provide a reasonable catalyst design for the target reaction.

[0003] In recent years, bimetallic catalysts have garnered widespread attention due to their typically superior catalytic hydrogenation performance compared to monometallic catalysts. Compared to monometallic catalysts, bimetallic systems possess unique active centers, and their associated physical and chemical properties can be modified by varying the bimetallic composition and morphology. Ni and Co, as the two metals with the highest catalytic graphitization activity, also serve as potential sources of activity for carbon-encapsulated catalysts. Therefore, it is essential and feasible to prepare a simple, efficient, carbon-encapsulated Co and Ni bimetallic catalyst that exhibits excellent catalytic hydrogenation performance under relatively mild reaction conditions.

[0004] This invention provides a method for preparing a graphite-carbon layer-encapsulated CoNi bimetallic alloy catalyst. By adjusting the ratio of the cobalt and nickel components, a graphite-carbon-encapsulated CoNi bimetallic catalyst with a relatively high degree of graphitization can be prepared. This catalyst exhibits excellent catalytic hydrogenation performance and stability in the selective hydrogenation of chloronitrobenzene. Summary of the Invention

[0005] The present invention aims to provide a graphite carbon layer encapsulated CoNi bimetallic alloy catalyst for catalytic hydrogenation of halonitrobenzene to synthesize halogenated aniline, as well as a preparation method and application thereof.

[0006] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a method for preparing a graphite carbon layer encapsulated CoNi bimetallic alloy catalyst for catalytic hydrogenation of halonitrobenzene to synthesize halogenated aniline, the preparation method being carried out according to the following steps:

[0008] (1) Weighing a metal cobalt salt, a metal nickel salt and an organic ligand and dissolving them in a mixed organic solvent, then adding an aqueous solution of a deprotonating agent, and stirring at 0-60° C. for 3-24 hours to obtain a mixed solution; the metal cobalt salt is at least one of cobalt nitrate hexahydrate, cobalt chloride and cobalt sulfate; the metal nickel salt is at least one of nickel nitrate hexahydrate, nickel chloride and nickel sulfate; the organic ligand is isonicotinic acid; the deprotonating agent is at least one of ammonia, triethylamine and sodium bicarbonate; the mixed organic solvent is a combination of solvent A and solvent B, the solvent A is at least one of methanol and ethanol, and the solvent B is at least one of N,N-dimethylformamide and N,N-dimethylacetamide; the ratio of the metal nickel salt to the metal cobalt salt is 6:1-4:1 in terms of the molar ratio of Ni to Co elements; the ratio of the total molar amount of metal in the metal cobalt salt and the metal nickel salt to the molar amount of the organic ligand is 1:0.70-1:0.75;

[0009] (2) The mixed solution obtained in step (1) is stirred with an inorganic salt aqueous solution at 0-60° C. for 15-45 minutes, filtered, washed, and then freeze-dried to obtain a catalyst precursor; the inorganic salt is at least one of CaCl2, NaBr, NaF, and NaI; in this step, the addition of the inorganic salt aqueous solution can interact with the organic ligand or metal salt through hydrogen bonding or electrostatic interaction, indirectly affecting the self-assembly process of the material, thereby synergistically regulating the pore structure; in addition, it can also change the ionic strength and freezing point of the solution, affect the nucleation and growth dynamics of ice crystals, and control the recrystallization process of ice crystals to obtain ice crystals of different sizes, which are embedded in the pores of the precursor. This property can be used to regulate the pore size and pore structure of the porous structure of the catalyst precursor; in this step, the ice crystals can be directly sublimated from the solid state to the gas state by using the freeze-drying treatment method, thereby avoiding the structural collapse caused by the capillary action generated by the evaporation of the solvent;

[0010] (3) ball milling the catalyst precursor obtained in step (2); in this step, the mesh size and specific surface area of the catalyst precursor can be greatly increased;

[0011] (4) placing the catalyst precursor after ball milling in step (3) in a tubular furnace, heating it to 500-800°C in a nitrogen atmosphere for constant temperature calcination, cooling it to room temperature after calcination, and grinding it to obtain a graphite carbon layer encapsulated CoNi bimetallic alloy catalyst; in this step, the catalyst precursor undergoes organic decomposition during the pyrolysis process, and the decomposition of the organic matter will produce a certain amount of reducing atmosphere. The resulting reducing atmosphere will reduce the coordinated metal ions in the precursor to obtain metal nanoparticles, and the metal nanoparticles will catalyze the graphitization of the carbon element in the precursor to generate graphite carbon and cover the surface.

[0012] In step (1) of the present invention, the choice of organic ligand will affect the elemental composition of the carbon layer in the final catalyst, thereby having an important impact on the performance of the catalyst. The inventor's research results show that the catalyst prepared using isonicotinic acid as the organic ligand has better catalytic performance in the selective hydrogenation reaction of halonitrobenzenes.

[0013] In step (1) of the present invention, the ratio of the total metal molar amount in the metal cobalt salt and the metal nickel salt to the molar amount of the organic ligand isonicotinic acid, and the molar ratio of the metal nickel salt and the metal cobalt salt have an important influence on the catalyst structure and performance. Among them, if the amount of organic ligand is too low, it is not conducive to the formation of an encapsulated structure, and if the amount of organic ligand is too high, the thickness of the encapsulated carbon layer will be too large, thereby reducing the catalyst performance. Preferably, the ratio of the total metal molar amount in the metal cobalt salt and the metal nickel salt to the molar amount of the organic ligand is 1:0.745. Among them, nickel has a high catalytic graphitization activity, which helps the catalyst to form an encapsulated structure. Although cobalt has a poor catalytic graphitization activity, its alloy with nickel is beneficial to improve the catalytic performance of the catalyst in the selective hydrogenation reaction of chloronitrobenzene. Preferably, the ratio of the metal nickel salt to the metal cobalt salt is 4:1 based on the molar ratio of Ni to Co elements. The above preferred ratio can achieve an optimal balance between the preparation efficiency and catalytic performance of the encapsulated structure catalyst.

[0014] In step (1) of the present invention, the nickel salt is preferably nickel nitrate hexahydrate. The cobalt salt is preferably cobalt nitrate hexahydrate. The molar ratio of the deprotonating agent to the carboxyl group in the organic ligand is 5 to 30:1. Preferably, the aqueous solution of the deprotonating agent is an ammonia solution, such that the amount of NH3·H2O contained in the ammonia solution is 10 to 20 times the amount of the carboxyl group in the organic ligand. In the mixed organic solvent, the volume ratio of solvent A to solvent B is 1:0.7 to 1:1.2. Preferably, the mixed organic solvent is a combination of ethanol and N,N-dimethylformamide in a volume ratio of 1:1. The mass ratio of the organic ligand to solvent A in the mixed organic solution is 1:50 to 1:1000, preferably 1:90 to 1:500, and more preferably 1:100 to 110. The stirring temperature is preferably 30 to 60°C, and the stirring time is preferably 6 to 12 hours.

[0015] In step (2) of the present invention, the concentration of the inorganic salt aqueous solution is 1 to 10 mmol / kg, preferably 2 to 5 mmol / kg, and the volume ratio of the inorganic salt solution to the mixed solution is 0.5:1 to 2:1, preferably 0.8:1 to 1.5:1. The inorganic salt aqueous solution is preferably a CaCl2 aqueous solution. The stirring conditions are: stirring at room temperature for 15 to 20 minutes. The freeze-drying conditions are: freeze-drying at -30 to -50°C and 5 to 100 Pa for 24 to 72 hours.

[0016] In step (3) of the present invention, the ball milling conditions can be: the catalyst precursor and zirconium dioxide balls (diameter 3 to 10 mm) are mixed in a grinding jar at a mass ratio of 1:40-60 (preferably 1:50), the jar is sealed and placed in a ball mill, and the ball mill is operated at a speed of 100 to 500 r / min (more preferably 150 to 250 r / min) at room temperature for 1 to 8 hours (more preferably 1 to 3 hours).

[0017] In step (4) of the present invention, the temperature setting during the calcination process will have a certain impact on the catalyst performance. The most preferred calcination temperature is 600°C. Other conditions during the calcination process can be set according to actual conditions. Generally, the nitrogen gas flow rate is 5-50 mL / min, the heating rate is 0.5-10°C / min, and after heating to the calcination temperature, the constant temperature calcination is carried out for 0.5-2 hours. Furthermore, the calcination time is 0.5-3 hours; the heating rate is 1-3°C / min; and the gas flow rate is 20-50 mL / min.

[0018] The innovation of the catalyst preparation method of the present invention lies in: (1) the preparation method of the present invention makes it possible to regulate the degree of graphitization of the carbon shell in the graphite carbon encapsulated bimetallic catalyst derived from cobalt-nickel OCPs; (2) the pore size and pore structure of the porous structure of the catalyst precursor can be regulated by regulating the inorganic salt aqueous solution; (3) by adjusting the atmosphere during the roasting process, nitrogen can be introduced, thereby changing the electronic structure of the catalyst, which helps to improve the electron transfer performance; (4) a graphene shell can be formed on the outside of the metal nanoparticles, which can effectively isolate the metal nanoparticles from the external reaction environment, ensuring that the various properties of the metal nanoparticles are not affected, and making the catalyst have excellent stability; (5) through various regulations in the preparation process, the catalyst structure of the present invention is particularly suitable for the reaction of selective hydrogenation of halogenated nitrobenzenes to synthesize halogenated anilines, so that it has excellent catalytic activity, selectivity and stability.

[0019] In a second aspect, the present invention provides a graphite carbon layer-encapsulated CoNi bimetallic alloy catalyst for catalytic hydrogenation of halonitrobenzene to synthesize halogenated aniline, prepared according to the preparation method described in the first aspect.

[0020] In a third aspect, the present invention provides the use of the graphite carbon layer encapsulated CoNi bimetallic alloy catalyst described in the second aspect in the catalytic hydrogenation of halonitrobenzenes to synthesize halogenated anilines.

[0021] Preferably, the application process comprises placing the graphite carbon layer-encapsulated CoNi bimetallic alloy catalyst, halogenated nitrobenzene, and methanol into an autoclave, sealing the autoclave, purging with H2 to remove air, then filling with 1-3 MPa of H2, and heating to the reaction temperature under magnetic stirring to carry out a hydrogenation reaction to obtain a halogenated aniline. The reaction endpoint is: reacting until no more hydrogen is consumed (i.e., the reaction pressure remains unchanged for 10 minutes), then stopping stirring, cooling to room temperature, and then releasing the pressure, and analyzing and identifying the reactants using a gas chromatograph.

[0022] As a further preference, the feed mass ratio of the graphite carbon layer encapsulated CoNi bimetallic alloy catalyst to halogenated nitrobenzene is 1:5 to 1:100.

[0023] As a further preference, the reaction temperature is 80-120° C. and the hydrogen pressure is 1-1.5 MPa.

[0024] As a further preference, the stirring rate is 1000-1500 rpm.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] (1) The catalyst preparation method of the present invention is simple to operate, the raw materials are cheap and easily available, and the production cost is low.

[0027] (2) The present invention successfully prepared a graphite carbon layer encapsulated CoNi bimetallic alloy catalyst through various adjustments during the preparation process. The structure of the catalyst is particularly suitable for the selective hydrogenation of halonitrobenzenes to synthesize halogenated anilines, which gives it excellent catalytic activity, selectivity and stability. In addition, the catalyst can be separated from the reaction system using an external magnetic field and is easy to separate and recover in the actual production process. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1The XRD patterns of the catalysts prepared in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 are used to illustrate the phase composition of the catalysts. The phase composition of the catalyst samples can be obtained from the XRD patterns, and the inset on the right depicts the diffraction peak corresponding to the (111) crystal plane. Among them, Ni@C corresponds to metal Ni with a face-centered cubic (fcc) structure (PDF#65-0380), and Co@C corresponds to metal Co with an fcc structure (PDF#15-0806). Samples Co2Ni8@C and Co8Ni2@C exhibit diffraction patterns similar to those of Ni@C and Co@C, respectively. It is worth noting that when the Co / Ni molar ratio in the sample changes from 1:4 to 4:1, the (111) diffraction peaks of Co2Ni8@C and Co8Ni2@C gradually shift from a higher angle (close to the Bragg position of fcc Ni at 44.4°) to a lower angle (close to the Bragg position of fcc Co at 44.2°). Similar trends are observed for the remaining diffraction peaks, such as (200) and (220). This phenomenon is consistent with Vegard's law, which states that the XRD diffraction peak positions systematically change with changes in the alloy ratio, indicating that the Co / Ni alloy ratio within the catalyst has been successfully regulated.

[0029] Figure 2 、 Figure 3 、 Figure 4 、 Figure 5 TEM images of the catalysts prepared in Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3 reveal the structural morphology of the catalysts. In Ni@C, the metal Ni nanoparticles and the Co / Ni alloy nanoparticles in Co2Ni8@C are evenly distributed over the entire carbon substrate. Both exhibit a typical core-shell nanostructure, consisting of an internal metal core and an external graphite carbon shell. Specifically, in Ni@C, the lattice spacing of 0.209 nm originates from the (111) crystal plane of metal Ni, and the metal Ni nanoparticles are wrapped by 1 to 3 layers of graphite carbon shells. Similarly, in Co2Ni8@C, the interplanar spacing of 0.216 nm corresponds to the (111) crystal plane of the metal Co / Ni alloy, and the outside of the metal Ni nanoparticles also has 1 to 3 layers of graphite carbon layers. In Co8Ni2@C and Co@C, no obvious graphite carbon layer structure appears on the periphery of the metal nanoparticles. Among them, the lattice spacing of 0.210nm was observed, which can be attributed to the (111) crystal plane of the metallic Co / Ni alloy in Co8Ni2@C; while the lattice spacing of 0.203nm belongs to the (111) crystal plane of metallic Co in Co@C.

[0030] Figure 6The Raman diagram of the catalysts prepared in Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3 can reflect the degree of graphitization of the carbon support of the catalyst. G / I D1 The ratios are 1.12, 1.04, 0.87 and 0.71 respectively. This data shows that as the Co / Ni ratio in the catalyst gradually increases, the degree of graphitization of the carbon material decreases.

[0031] Figure 7 This is a photograph of the catalyst prepared in Example 1 being attracted by a magnet. DETAILED DESCRIPTION

[0032] The present invention is further described below with reference to specific examples, but the protection scope of the present invention is not limited thereto.

[0033] Example 1

[0034] (1) 1.396 g of nickel nitrate hexahydrate, 0.349 g of cobalt nitrate hexahydrate, and 0.55 g of isonicotinic acid were weighed and dissolved in 150 mL of an equal volume mixed solvent of anhydrous ethanol and N,N-dimethylformamide. The molar ratio of nickel to cobalt was 4:1, the molar ratio of metal to organic ligand was 1:0.745, and the mass ratio of organic ligand to anhydrous ethanol solution was 1:107.7. The mixture was heated and stirred at 60°C until the solid in the beaker dissolved and the solution became clear. Subsequently, 4 mL of 28% ammonia solution was added and the mixture was heated and stirred at 60°C for 6 h to obtain a mixed solution.

[0035] (2) Add 100 mL of a 3.6 mmol / kg calcium chloride aqueous solution to the obtained mixed solution, stir at room temperature for 15 min to mix evenly, filter and wash it, and then freeze-dry it (-50°C, <10 Pa) for 72 h. The resulting solid is the catalyst precursor.

[0036] (3) The obtained catalyst precursor and steel balls (3 mm in diameter) were mixed in a 500 mL agate jar at a mass ratio of 1:50. The jar was sealed and placed in a ball mill. The ball mill was operated at a speed of 200 r / min at room temperature for 2 h to obtain a ground catalyst precursor.

[0037] (4) The precursor was placed in a tubular furnace and heated to 600 °C at a rate of 1 °C / min in a nitrogen atmosphere with a flow rate of 35 mL / min. It was then calcined for 0.5 h. After cooling to room temperature, the black solid, i.e., the Co2Ni8@C catalyst, was taken out.

[0038] (5) The black solid was washed in 1 mol / L hydrochloric acid solution for 4 h and its encapsulation structure was tested.

[0039] Example 2

[0040] Refer to Example 1, except that in step (1), the mass of nickel nitrate hexahydrate is adjusted to 1.495 g, and the mass of cobalt nitrate hexahydrate is adjusted to 0.249 g. The rest of the process is the same as in Example 1. Since the proportion of the added metal cobalt salt is relatively small, the resulting catalyst can still maintain its encapsulation structure, but the metal core alloy effect is weakened, resulting in reduced catalyst reactivity.

[0041] Example 3

[0042] Refer to Example 1, except that in step (1), the amount of isonicotinic acid added was changed to 0.45 g, and the rest was the same as Example 1. Due to the small amount of added organic ligand, a small amount of metal components were leached during the acid washing process, but some encapsulated catalyst remained.

[0043] Example 4

[0044] Refer to Example 1, the only difference is that in step (4), the final calcination temperature is changed to 500°C, and the rest is the same as Example 1.

[0045] Example 5

[0046] Refer to Example 1, the only difference is that in step (4), the final calcination temperature is changed to 700°C, and the rest is the same as Example 1.

[0047] Example 6

[0048] Refer to Example 1, the only difference is that in step (4), the final calcination temperature is changed to 800°C, and the rest is the same as Example 1.

[0049] Comparative Example 1

[0050] Refer to Example 1, except that in step (1), only 1.746 g of cobalt salt cobalt nitrate hexahydrate was added, and the rest was the same as Example 1. In Comparative Example 1, since only the metal cobalt salt was added, the catalytic graphitization activity of cobalt was poor, so the obtained catalyst Co@C did not have an encapsulated structure, and the metal components were leached in large quantities during the pickling process.

[0051] Comparative Example 2

[0052] Refer to Example 1, except that in step (1), 1.397 g of cobalt salt cobalt nitrate hexahydrate and 0.349 g of nickel salt nickel nitrate hexahydrate were added, and the rest were the same as in Example 1. In Comparative Example 2, since the proportion of the added metal cobalt salt was large and the proportion of the added metal nickel salt was small, the catalytic graphitization activity of the cobalt-nickel alloy with a large cobalt content was relatively poor, so the obtained catalyst Co8Ni2@C was not an encapsulated structure, and the metal components were leached out in large quantities during the pickling process.

[0053] Comparative Example 3

[0054] Refer to Example 1, except that in step (1), only 1.745 g of nickel salt nickel nitrate hexahydrate was added, and the rest was the same as Example 1. In Comparative Example 3, due to the added metal nickel salt, nickel has a higher catalytic graphitization activity, and the obtained catalyst Ni@C has an encapsulated structure, so no metal component is leached during the pickling process. However, since no alloy is formed, the performance of the obtained catalyst is poor.

[0055] Comparative Example 4

[0056] Referring to Example 1, the only difference was that in step (1), the amount of isonicotinic acid added was modified to 0.37 g, and the rest was the same as Example 1. Since the amount of added organic ligand was too small, the metal components were leached during the acid washing process, and an encapsulated catalyst could not be obtained.

[0057] Comparative Example 5

[0058] Referring to Example 1, the only difference is that in step (1), the amount of isonicotinic acid added is modified to 0.66 g, and the rest is the same as Example 1. Since the amount of added organic ligand is too large, the thickness of the carbon layer increases, which reduces the reactivity of the catalyst.

[0059] Comparative Example 6

[0060] Referring to Example 1, the only difference is that in step (1), 0.55g of isonicotinic acid is replaced by 0.53g of succinic acid. The rest is the same as in Example 1. The prepared catalyst has an encapsulated structure

[0061] Comparative Example 7

[0062] Referring to Example 1, the only difference is that in step (1), 0.55 g of isonicotinic acid is replaced by 0.49 g of pyrrole-2-carboxylic acid. The rest is the same as Example 1. The prepared catalyst has an encapsulated structure.

[0063] Example 8

[0064] Example 8 investigated the performance of the different catalysts prepared above in the catalytic hydrogenation reaction to synthesize p-chloroaniline.

[0065] In a 50 mL stainless steel reactor, add 25 mL of ethanol, 1 g of p-chloroaniline, and 0.02 g of the catalyst prepared in various Examples or Comparative Examples. The reactor was closed and purged with hydrogen 10 times to displace the air. The temperature was raised to 100°C and the hydrogen pressure to 1.2 MPa. Stirring was initiated at a rate of 1200 rpm and the reaction was continued for 45 minutes. The reaction was stopped and the temperature was allowed to cool to room temperature. The supernatant of the reaction solution was collected, filtered, and the filtrate analyzed by gas chromatography. The experimental results are shown in Table 1.

[0066] Table 1 Performance of different catalysts in the catalytic hydrogenation reaction of p-chloroaniline

[0067]

[0068]

[0069] Example 9

[0070] Example 9 investigated the performance of the graphite carbon layer-encapsulated CoNi bimetallic alloy catalyst prepared in Example 1 in the hydrogenation of p-chloronitrobenzene to prepare p-chloroaniline in Example 8. The experimental results are shown in Table 2:

[0071] Table 2 Stability of graphite carbon layer encapsulated CoNi bimetallic alloy catalyst in the hydrogenation of p-chloronitrobenzene to p-chloroaniline

[0072] Number of applications Conversion rate Selectivity 1 100 99.69 2 100 99.87 3 100 99.30 4 100 99.18 5 100 99.55 6 100 99.63 7 100 99.94 8 100 99.75 9 100 99.63 10 100 99.69

[0073] Comparative Example 6

[0074] Refer to Example 1, except that in step (2), only 100 mL of 3.6 mmol / kg calcium chloride aqueous solution is replaced by 100 mL of 3.6 mmol / kg sodium bromide aqueous solution, and the rest is the same as Example 1.

[0075] Comparative Example 7

[0076] Refer to Example 1, except that in step (2), 100 mL of 3.6 mmol / kg calcium chloride aqueous solution is replaced with 100 mL of 3.6 mmol / kg sodium fluoride aqueous solution, and the rest is the same as Example 1.

[0077] Comparative Example 8

[0078] Refer to Example 1, except that in step (2), only 100 mL of 3.6 mmol / kg calcium chloride aqueous solution is replaced with 100 mL of 3.6 mmol / kg sodium iodide aqueous solution, and the rest is the same as Example 1.

[0079] Comparative Example 9

[0080] Refer to Example 1, except that in step (2), only 100 mL of the 3.6 mmol / kg calcium chloride aqueous solution was replaced with 100 mL of deionized water. In Comparative Example 7, since no inorganic salt aqueous solution was added, the self-assembly process of the material could not be regulated, and thus the pore structure could not be coordinated and regulated. Therefore, the specific surface area of the obtained catalyst precursor was small, and the performance of the catalyst obtained after further calcination was also poor.

[0081] Example 10

[0082] Example 10 The specific surface areas of the various catalyst precursors prepared in Example 1 and Comparative Examples 6-9 were investigated using the BET method. The performance of the resulting catalysts in the catalytic hydrogenation reaction to synthesize p-chloroaniline was investigated with reference to Example 8. The experimental results are shown in Table 3.

[0083] Table 3 Specific surface areas of different catalyst precursors and the performance of the catalysts obtained after pyrolysis in the catalytic hydrogenation reaction of p-chloroaniline

[0084] Catalyst precursor <![CDATA[Specific surface area m 2 / g]]> catalyst Conversion rate Selectivity Example 1 756.12 Example 1 100 99.86 Comparative Example 6 688.24 Comparative Example 6 97.81 99.76 Comparative Example 7 705.16 Comparative Example 7 95.25 98.89 Comparative Example 8 748.08 Comparative Example 8 98.98 99.27 Comparative Example 9 120.56 Comparative Example 9 23.65 91.04

[0085] Comparative Example 10

[0086] Referring to Example 1, the only difference is that in step (4), argon with a volume fraction of 30% is mixed into the nitrogen while keeping the gas flow rate unchanged. The rest is the same as Example 1.

[0087] Comparative Example 11

[0088] Referring to Example 1, the only difference is that in step (4), argon with a volume fraction of 60% is mixed into the nitrogen while keeping the gas flow rate unchanged. The rest is the same as Example 1.

[0089] Comparative Example 12

[0090] Referring to Example 1, the only difference is that in step (4), nitrogen is replaced by argon while maintaining the same gas flow rate, and the rest is the same as in Example 1. In Comparative Example 12, since the calcination was not carried out under a nitrogen atmosphere, the nitrogen doping effect in the catalyst was reduced, and the catalytic performance was reduced.

[0091] Example 11

[0092] Example 11 XPS was used to examine the atomic content of nitrogen in the various catalysts prepared in Example 1 and Comparative Examples 10-12. The performance of the catalysts in the catalytic hydrogenation reaction to synthesize p-chloroaniline was also examined with reference to Example 2. The experimental results are shown in Table 4.

[0093] Table 4 Nitrogen content in different catalysts and their performance in the catalytic hydrogenation reaction of p-chloroaniline

[0094] catalyst Nitrogen content Conversion rate Selectivity Example 1 4.56 100 99.86 Comparative Example 10 3.11 87.51 98.96 Comparative Example 11 2.23 51.95 96.72 Comparative Example 12 0.51 18.62 93.61

Claims

1. A method for preparing a graphite carbon layer encapsulated CoNi bimetallic alloy catalyst for catalytic hydrogenation of halonitrobenzenes to halogenated anilines, characterized in that: The preparation method is carried out according to the following steps: (1) Weighing a metal cobalt salt, a metal nickel salt and an organic ligand and dissolving them in a mixed organic solvent, then adding an aqueous solution of a deprotonating agent, and stirring at 0-60° C. for 3-24 hours to obtain a mixed solution; the metal cobalt salt is at least one of cobalt nitrate hexahydrate, cobalt chloride and cobalt sulfate; the metal nickel salt is at least one of nickel nitrate hexahydrate, nickel chloride and nickel sulfate; the organic ligand is isonicotinic acid; the deprotonating agent is at least one of ammonia, triethylamine and sodium bicarbonate; the mixed organic solvent is a combination of solvent A and solvent B, the solvent A is at least one of methanol and ethanol, and the solvent B is at least one of N,N-dimethylformamide and N,N-dimethylacetamide; the ratio of the metal nickel salt to the metal cobalt salt is 6:1-4:1 in terms of the molar ratio of Ni to Co elements; the ratio of the total molar amount of metal in the metal cobalt salt and the metal nickel salt to the molar amount of the organic ligand is 1:0.70-1:0.75; (2) stirring the mixed solution obtained in step (1) with an inorganic salt aqueous solution at 0-60° C. for 15-45 minutes, filtering, washing, and freeze-drying to obtain a catalyst precursor; the inorganic salt is at least one of CaCl2, NaBr, NaF, and NaI; (3) ball milling the catalyst precursor obtained in step (2); (4) placing the catalyst precursor after ball milling in step (3) in a tubular furnace, heating it to 500-800° C. in a nitrogen atmosphere for constant temperature calcination, cooling it to room temperature after calcination, and grinding it to obtain a graphite carbon layer encapsulated CoNi bimetallic alloy catalyst.

2. The preparation method according to claim 1, wherein: The ratio of the total molar amount of metal in the metal cobalt salt and the metal nickel salt to the molar amount of the organic ligand is 1:0.

745.

3. The preparation method according to claim 1, wherein: The ratio of the metal nickel salt to the metal cobalt salt is 4:1 based on the molar ratio of Ni to Co elements.

4. The preparation method according to claim 1, wherein: In step (4), the calcination temperature is 600°C.

5. The preparation method according to claim 1, wherein: In step (1), the aqueous solution of the deprotonating agent is an ammonia solution, and the amount of NH3·H2O contained in the ammonia solution is 10 to 20 times the amount of the carboxyl substance in the organic ligand.

6. The preparation method according to claim 1, wherein: In step (2), the concentration of the inorganic salt aqueous solution is 1 to 10 mmol / kg, and the volume ratio of the inorganic salt solution to the mixed solution is 0.5:1 to 2:

1.

7. The preparation method according to claim 1 or 4, wherein: In step (4), the gas flow rate of nitrogen is 5 to 50 mL / min, the heating rate is 0.5 to 10° C. / min, and after heating to the calcination temperature, the mixture is calcined at a constant temperature for 0.5 to 2 h.

8. A graphite carbon layer encapsulated CoNi bimetallic alloy catalyst for catalytic hydrogenation of halonitrobenzenes to synthesize halogenated anilines, prepared according to the preparation method of any one of claims 1 to 7.

9. Use of the graphite carbon layer encapsulated CoNi bimetallic alloy catalyst according to claim 8 in the catalytic hydrogenation of halonitrobenzenes to synthesize halogenated anilines.

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