阅读说明：本技术 一种氮掺杂碳硅复合材料负载钴铜双金属催化剂及其制备方法和应用 (Nitrogen-doped carbon-silicon composite material loaded cobalt-copper bimetallic catalyst and preparation method and application thereof ) 是由 汪学广 盛瑶 林心蕊 刘洋 邹秀晶 尚兴付 丁伟中 于 2020-06-02 设计创作，主要内容包括：本发明提供了一种氮掺杂碳硅复合材料负载钴铜双金属催化剂及其制备方法和应用,涉及催化剂技术领域。本发明提供的氮掺杂碳硅复合材料负载钴铜双金属催化剂的制备方法,包括以下步骤：将二氧化硅、水溶性钴盐、水溶性铜盐、有机碳源、有机氮源和水混合,将所得混合物加热至水蒸干,得到固体物料；将所述固体物料在保护气氛中进行焙烧,得到氮掺杂碳硅复合材料负载钴铜双金属催化剂。本发明提供的催化剂催化活性高、稳定性好、可循环使用多次,应用于硝基化合物还原制胺中具有较高的催化活性和循环稳定性。(The invention provides a nitrogen-doped carbon-silicon composite material loaded cobalt-copper bimetallic catalyst, a preparation method and application thereof, and relates to the technical field of catalysts. The preparation method of the nitrogen-doped carbon-silicon composite material loaded cobalt-copper bimetallic catalyst provided by the invention comprises the following steps of: mixing silicon dioxide, water-soluble cobalt salt, water-soluble copper salt, an organic carbon source, an organic nitrogen source and water, and heating the obtained mixture until the water is evaporated to dryness to obtain a solid material; and roasting the solid material in a protective atmosphere to obtain the nitrogen-doped carbon-silicon composite material loaded cobalt-copper bimetallic catalyst. The catalyst provided by the invention has high catalytic activity and good stability, can be recycled for multiple times, and has higher catalytic activity and cyclic stability when being applied to the preparation of amine by reduction of nitro compounds.)

1. A preparation method of a nitrogen-doped carbon-silicon composite material loaded cobalt-copper bimetallic catalyst comprises the following steps:

mixing silicon dioxide, water-soluble cobalt salt, water-soluble copper salt, an organic carbon source, an organic nitrogen source and water, and heating the obtained mixture until the water is evaporated to dryness to obtain a solid material;

and roasting the solid material in a protective atmosphere to obtain the nitrogen-doped carbon-silicon composite material loaded cobalt-copper bimetallic catalyst.

2. The method of claim 1, wherein the water-soluble cobalt salt comprises cobalt nitrate and/or cobalt acetate.

3. The method of claim 1, wherein the water-soluble copper salt comprises copper nitrate and/or copper acetate.

4. The method according to claim 1, wherein the organic carbon source comprises one or more of glucose, sucrose, glucosamine hydrochloride, and glucosamine sulfate.

5. The method according to claim 1, wherein the organic nitrogen source comprises one or more of melamine, 1, 10-phenanthroline, cyclodextrin, urea, and 2-methylimidazole.

6. The preparation method according to any one of claims 1 to 5, wherein the mass ratio of the silicon dioxide, the water-soluble cobalt salt and the water-soluble copper salt is 1:1 (0.1 to 0.4);

the mass ratio of the silicon dioxide, the organic carbon source and the organic nitrogen source is 1 (0.4-1.2) to (0.4-1.2).

7. The method according to claim 1, wherein the heating temperature is 40 to 60 ℃.

8. The preparation method according to claim 1, wherein the roasting temperature is 500-900 ℃ and the roasting time is 1-5 h.

9. The nitrogen-doped carbon-silicon composite material loaded cobalt-copper bimetallic catalyst prepared by the preparation method of any one of claims 1 to 8 comprises a silicon dioxide carrier and nitrogen-doped carbon-coated bimetallic nanoparticles loaded on the silicon dioxide carrier, wherein the bimetallic nanoparticles comprise cobalt nanoparticles and copper nanoparticles.

10. The use of the nitrogen-doped carbon-silicon composite supported cobalt-copper bimetallic catalyst of claim 9 in the selective reduction of nitro compounds to produce amines.

Technical Field

The invention relates to the technical field of catalysts, in particular to a nitrogen-doped carbon-silicon composite material loaded cobalt-copper bimetallic catalyst, and a preparation method and application thereof.

Background

Selective reduction of nitro compounds is one of the basic chemical reactions for the production of amines, aniline being an important intermediate and key precursor for the manufacture of numerous agrochemicals, pharmaceuticals, polymers and fine chemicals. The conventional non-catalytic process for reducing nitro groups uses stoichiometric amounts of reducing agents (such as Fe, Zn, Sn and metal sulfides) for reduction, but such processes cause serious problems with product separation, the reactor is susceptible to corrosion hazards, and large amounts of waste acids, bases and undesirable byproducts, such as hydroxylamine, are produced.

Efforts have therefore been focused on establishing efficient and highly selective catalytic reduction of nitro groups instead of non-catalytic processes. Since the catalysts for heterogeneously catalyzed reactions are easier to separate and recover, there is a greater tendency to use heterogeneously catalyzed reactions instead of uncatalyzed processes. The loaded noble metal-based nano-catalyst is widely applied to the reaction of selectively reducing nitroaromatic into arylamine. However, most of these catalysts do not satisfy the dual requirements of activity and selectivity. The Pt-group (Pt, Pd, Rh, Ru, etc.) catalysts have high catalytic activity, but have poor chemical selectivity when reducing nitro groups and high cost, and the supply of these noble metals has limited their widespread use in numerous industrial processes.

Non-noble metal transition metal catalysts (Fe, Co, Ni, etc.) have proven to be effective for selective hydrogenation of nitro compounds, and particularly, iron, cobalt, nickel, etc. catalysts supported on alumina, carbon materials are important novel heterogeneous catalytic materials. However, such catalysts generally have low activity and are prone to deactivation during recycling.

Disclosure of Invention

In view of the above, the present invention aims to provide a nitrogen-doped carbon-silicon composite supported cobalt-copper bimetallic catalyst and a preparation method thereof. The catalyst provided by the invention has high catalytic activity and good cycle stability, and has excellent catalytic effect when being applied to selective reduction of nitro compounds.

In order to achieve the above object, the present invention provides the following technical solutions:

a preparation method of a nitrogen-doped carbon-silicon composite material loaded cobalt-copper bimetallic catalyst comprises the following steps:

mixing silicon dioxide, water-soluble cobalt salt, water-soluble copper salt, an organic carbon source, an organic nitrogen source and water, and heating the obtained mixture until the water is evaporated to dryness to obtain a solid material;

and roasting the solid material in a protective atmosphere to obtain the nitrogen-doped carbon-silicon composite material loaded cobalt-copper bimetallic catalyst.

Preferably, the water-soluble cobalt salt comprises cobalt nitrate and/or cobalt acetate.

Preferably, the water-soluble copper salt comprises copper nitrate and/or copper acetate.

Preferably, the organic carbon source comprises one or more of glucose, sucrose, glucosamine hydrochloride and glucosamine sulfate.

Preferably, the organic nitrogen source comprises one or more of melamine, 1, 10-phenanthroline, cyclodextrin, urea and 2-methylimidazole.

Preferably, the mass ratio of the silicon dioxide to the water-soluble cobalt salt to the water-soluble copper salt is 1:1 (0.1-0.4);

the mass ratio of the silicon dioxide, the organic carbon source and the organic nitrogen source is 1 (0.4-1.2) to (0.4-1.2).

Preferably, the heating temperature is 40-60 ℃.

Preferably, the roasting temperature is 500-900 ℃, and the roasting time is 1-5 h.

The invention provides a nitrogen-doped carbon-silicon composite material loaded cobalt-copper bimetallic catalyst prepared by the preparation method in the scheme, which comprises a silicon dioxide carrier and nitrogen-doped carbon-coated bimetallic nanoparticles loaded on the silicon dioxide carrier, wherein the bimetallic nanoparticles comprise cobalt nanoparticles and copper nanoparticles.

The invention provides application of the nitrogen-doped carbon-silicon composite material loaded cobalt-copper bimetallic catalyst in preparation of amine by selectively reducing nitro compounds.

The invention provides a preparation method of a nitrogen-doped carbon-silicon composite material loaded cobalt-copper bimetallic catalyst, which comprises the following steps: mixing silicon dioxide, water-soluble cobalt salt, water-soluble copper salt, an organic carbon source, an organic nitrogen source and water, and heating the obtained mixture until the water is evaporated to dryness to obtain a solid material; and roasting the solid material in a protective atmosphere to obtain the nitrogen-doped carbon-silicon composite material loaded cobalt-copper bimetallic catalyst. The method comprises the steps of mixing water-soluble cobalt salt, water-soluble copper salt, an organic carbon source, an organic nitrogen source and silicon dioxide, evaporating to dryness to enable the water-soluble cobalt salt, the water-soluble copper salt, the organic carbon source, the organic nitrogen source and the silicon dioxide to form a complex, decomposing reductive gas, carbon and carbon nitride generated by decomposition of the organic carbon source and the organic nitrogen source into cobalt oxide and copper oxide by the water-soluble cobalt salt and the water-soluble copper salt in a roasting process, reducing the cobalt oxide and the copper oxide into a cobalt simple substance and a copper simple substance by the reductive gas and the carbon, and depositing the carbon nitride on the surface of the silicon dioxide and/or in a gap of the silicon dioxide to finally obtain the nitrogen-doped carbon-silicon composite material loaded cobalt-copper bimetallic catalyst. The cobalt simple substance and the copper simple substance in the catalyst prepared by the preparation method provided by the invention are respectively cobalt nanoparticles and copper nanoparticles, the metal particles are small, and the Co nanoparticles and the Cu nanoparticles grow adjacently and can mutually influence and interact at the particle interface to transfer electrons from cobalt to copper, so that the cobalt is in an electron-deficient state, and the catalytic performance of the catalyst for selectively reducing nitro compounds to prepare amine is improved. The preparation method provided by the invention has simple steps and easy operation, and is suitable for industrial production.

The invention provides the catalyst prepared by the preparation method in the scheme. The catalyst provided by the invention has high catalytic activity under the condition that hydrogen is used as a reducing agent, and has better catalytic activity and cycle stability compared with other Fe, Co and Ni catalysts. The results of the examples show that when the catalyst provided by the invention is applied to the selective reduction of nitrobenzene, the conversion rate of nitrobenzene can reach 81.3%, the selectivity can reach 100%, and the catalytic activity of the catalyst is basically unchanged after the catalyst is recycled for 12 times.

Drawings

FIG. 1 is an XRD pattern of catalysts prepared in example 1 and comparative examples 1-2;

FIG. 2 is a TEM image of catalysts prepared in example 1 and comparative examples 1 to 2;

FIG. 3 is a TEM image of the catalysts prepared in example 1 and comparative examples 1-2;

FIG. 4 is a graph showing the results of cyclic catalysis of the catalysts obtained in example 1 and comparative example 1.

Detailed Description

The invention provides a preparation method of a nitrogen-doped carbon-silicon composite material loaded cobalt-copper bimetallic catalyst, which comprises the following steps:

mixing silicon dioxide, water-soluble cobalt salt, water-soluble copper salt, an organic carbon source, an organic nitrogen source and water, and heating the obtained mixture until the water is evaporated to dryness to obtain a solid material;

and roasting the solid material in a protective atmosphere to obtain the nitrogen-doped carbon-silicon composite material loaded cobalt-copper bimetallic catalyst.

The method comprises the steps of mixing silicon dioxide, water-soluble cobalt salt, water-soluble copper salt, organic carbon source, organic nitrogen source and water, heating the obtained mixture until the water is evaporated to dryness, and obtaining a solid material.

In the present invention, the silica is preferably industrial silica; the particle size of the silicon dioxide is preferably 3-5 mm. The water-soluble cobalt salt preferably comprises cobalt nitrate and/or cobalt acetate, more preferably cobalt nitrate; the cobalt nitrate is preferably cobalt nitrate hexahydrate. In the present invention, the water-soluble copper salt preferably includes copper nitrate and/or copper acetate, more preferably copper nitrate; the copper nitrate is preferably copper nitrate hexahydrate. In the invention, the organic carbon source preferably comprises one or more of glucose, sucrose, glucosamine hydrochloride and glucosamine sulfate, and more preferably comprises glucose, sucrose, glucosamine hydrochloride or glucosamine sulfate; when the organic carbon source is any one of glucose, sucrose, glucosamine hydrochloride and glucosamine sulfate, the mass ratio of the organic carbon sources is not particularly limited, and any ratio can be adopted. In the invention, the organic nitrogen source preferably comprises one or more of melamine, 1, 10-phenanthroline, cyclodextrin, urea and 2-methylimidazole, and more preferably melamine, 1, 10-phenanthroline, cyclodextrin, urea or 2-methylimidazole; when the organic nitrogen source is any one of melamine, 1, 10-phenanthroline, cyclodextrin, urea and 2-methylimidazole, the mass ratio of the organic nitrogen sources is not particularly limited, and any proportion can be adopted.

In the present invention, the mass ratio of the silicon dioxide, the water-soluble cobalt salt and the water-soluble copper salt is 1:1 (0.1 to 0.4), more preferably 1:1 (0.15 to 0.35), and most preferably 1:1 (0.2 to 0.3). In the invention, the mass ratio of the silicon dioxide, the organic carbon source and the organic nitrogen source is preferably 1 (0.4-1.2): 0.4-1.2), more preferably 1 (0.5-1.1): 0.5-1.1), and most preferably 1 (0.8-1): 0.8-1.

In the present invention, the water is preferably deionized water. The amount of water used in the present invention is not particularly limited, and may be any amount known to those skilled in the art; in the embodiment of the present invention, the ratio of the volume of water to the mass of silica is preferably 12mL:1 g. In the invention, the water-soluble cobalt salt, the water-soluble copper salt, the organic carbon source and the organic nitrogen source have good solubility in water, so that the water-soluble cobalt salt, the water-soluble copper salt, the organic carbon source and the organic nitrogen source can better enter pores of silicon dioxide in the process of heating and evaporating water; and water is used as a solvent, so that the environment is protected.

In the invention, the heating temperature for heating to evaporate water to dryness is preferably 40-60 ℃, and more preferably 45-55 ℃. In the present invention, the heating to water evaporation is preferably performed under stirring conditions; the stirring speed in the present invention is not particularly limited, and a stirring speed known to those skilled in the art may be used. According to the invention, water is heated and evaporated to dryness, so that a water-soluble cobalt salt, a water-soluble copper salt, an organic carbon source and an organic nitrogen source form a complex.

After the solid material is obtained, the solid material is roasted in a protective atmosphere to obtain the nitrogen-doped carbon-silicon composite material loaded cobalt-copper bimetallic catalyst.

The protective atmosphere in the present invention is not particularly limited, and a protective atmosphere known to those skilled in the art may be used, specifically, nitrogen.

In the invention, the roasting temperature is preferably 500-900 ℃, more preferably 600-800 ℃, and the roasting time is preferably 1-5 hours, more preferably 2-4 hours. In the roasting process, reducing gas and carbon generated by decomposing an organic carbon source and an organic nitrogen source are decomposed, the organic carbon source and the organic nitrogen source generate carbon nitride in the processes of polymerization and decomposition, water-soluble cobalt salt and water-soluble copper salt are decomposed into cobalt oxide and copper oxide, the cobalt oxide and the copper oxide are reduced into cobalt simple substance and copper simple substance by the reducing gas and the carbon, the carbon nitride is deposited on the surface of silicon dioxide and/or in the gaps of the silicon dioxide, and finally the nitrogen-doped carbon-silicon composite material loaded cobalt-copper bimetallic catalyst water-soluble cobalt salt is decomposed into cobalt simple substance and cobalt oxide particles (Co simple substance and cobalt oxide particles) (Co-doped carbon-silicon composite material loaded cobalt-copper bimetallic catalyst water-soluble cobalt salt₃O₄Etc.), the water-soluble copper salt is decomposed into copper simple substance and copper oxide particles (CuO, etc.), and simultaneously the organic carbon source and the organic nitrogen source are subjected to polymerization and decomposition processes to form a nitrogen-doped carbon material; in the further roasting process, the carbon can reduce cobalt oxide into metal Co and reduce copper oxide into metal Cu, and finally the nitrogen-doped carbon-silicon composite material loaded cobalt-copper bimetallic catalyst is obtained. In addition, during firing, the organic nitrogen source polymerizes to form a layered graphitic carbon nitride (g-C)₃N₄) With organic carbon source in g-C₃N₄The interlayer polymerization forms a carbon skeleton, the cobalt nanoparticles and the copper nanoparticles are embedded in a layered structure, and the cobalt nanoparticles and the copper nanoparticles catalyze a carbon layer to generate a graphite carbon layer covering the surface of the silicon oxide as the roasting continues.

The invention provides a nitrogen-doped carbon-silicon composite material loaded cobalt-copper bimetallic catalyst prepared by the preparation method in the scheme, which comprises a silicon dioxide carrier and nitrogen-doped carbon-coated bimetallic nanoparticles loaded on the silicon dioxide carrier, wherein the bimetallic nanoparticles comprise cobalt nanoparticles and copper nanoparticles.

In the nitrogen-doped carbon-silicon composite material loaded cobalt-copper bimetallic catalyst, the content of metal cobalt nanoparticles is preferably 7-9 wt%, and more preferably 8 wt%; the content of the metal copper nanoparticles is preferably 1-3 wt%, and more preferably 2 wt%; the content of carbon is preferably 35-45 wt%, and more preferably 40 wt%; the content of nitrogen is preferably 1 to 3 wt%, more preferably 2 wt%, and the balance is silicon dioxide. In the invention, the particle size of the metal cobalt nanoparticles and the particle size of the copper nanoparticles are independently preferably 5-15 nm, more preferably 7-9 nm, and most preferably 8 nm.

In the catalyst provided by the invention, the Co nanoparticles and the Cu nanoparticles are wrapped by the nitrogen-doped carbon material to form a carbon layer, and because of the existence of the carbon layer, the metal particles are separated from each other spatially, so that the loss and agglomeration of the metal particles in the reaction process can be prevented, and the catalyst has better stability; the coated Co nanoparticles have magnetism, the whole coating structure also has magnetism, and the nitrogen-doped carbon-silicon composite material loaded cobalt-copper bimetallic catalyst is easy to recycle after the reaction is finished; in some reactions, the substrate molecule contains nitrogen, sulfur and other heteroatoms (such as quinoline, picoline and the like), the heteroatoms have strong coordination capacity with metals and easily deactivate metal catalysts, and the existence of a carbon layer can reduce or eliminate the influence; the introduction of heteroatom nitrogen improves the electronic property of the carbon layer, increases the dispersion degree of the catalyst in a polar solution, enhances the adsorption capacity of a substrate on the surface of the catalyst, and simultaneously facilitates the dispersion of Co nanoparticles and Cu nanoparticles.

The invention also provides application of the nitrogen-doped carbon-silicon composite material loaded cobalt-copper bimetallic catalyst in preparation of amine by selectively reducing nitro compounds. The present invention is not particularly limited to the specific method of application, and may be applied by methods known to those skilled in the art.

The embodiments of the present invention will be described in detail with reference to the following examples, but they should not be construed as limiting the scope of the present invention.

Example 1

Dissolving 5g of industrial silicon oxide, 5g of cobalt nitrate hexahydrate, 1.25g of copper nitrate hexahydrate, 5g of glucose and 5g of urea in 60mL of deionized water, and stirring and evaporating at 60 ℃ to dryness to obtain a solid material;

roasting the solid material at 800 ℃ for 1h in a nitrogen atmosphere to obtain the nitrogen-doped carbon-silicon composite material loaded cobalt-copper bimetallic catalyst (abbreviated as CoCu @ CN/SiO)₂)。

Example 2

Dissolving 5g of industrial silicon oxide, 5g of cobalt nitrate hexahydrate, 0.2g of copper nitrate hexahydrate, 5g of glucose and 5g of urea in 60mL of deionized water, and stirring and evaporating at 60 ℃ to dryness to obtain a solid material;

roasting the solid material at 800 ℃ for 1h in a nitrogen atmosphere to obtain the nitrogen-doped carbon-silicon composite material loaded cobalt-copper bimetallic catalyst (abbreviated as CoCu @ CN/SiO)₂)。

Example 3

Dissolving 5g of industrial silicon oxide, 5g of cobalt nitrate hexahydrate, 0.75g of copper nitrate hexahydrate, 5g of glucose and 5g of urea in 60mL of deionized water, and stirring and evaporating at 60 ℃ to dryness to obtain a solid material;

roasting the solid material at 800 ℃ for 1h in a nitrogen atmosphere to obtain the nitrogen-doped carbon-silicon composite material loaded cobalt-copper bimetallic catalyst (abbreviated as CoCu @ CN/SiO)₂)。

Example 4

Dissolving 5g of industrial silicon oxide, 5g of cobalt nitrate hexahydrate, 1.5g of copper nitrate hexahydrate, 5g of glucose and 5g of urea in 60mL of deionized water, and stirring and evaporating at 60 ℃ to dryness to obtain a solid material;

roasting the solid material at 800 ℃ for 1h in a nitrogen atmosphere to obtain the nitrogen-doped carbon-silicon composite material loaded cobalt-copper bimetallic catalyst (abbreviated as CoCu @ CN/SiO)₂)。

Comparative example 1

A catalyst was prepared according to the method of example 1, except that: no addition of copper nitrate hexahydrate was made and the catalyst obtained was reported as Co @ CN/SiO₂。

Comparative example 2

A catalyst was prepared according to the method of example 1, except that: no cobalt nitrate hexahydrate was added, and the resulting catalyst was designated as Cu @ CN/SiO₂。

The X-ray diffraction patterns of elemental copper, elemental cobalt, the catalysts prepared in example 1 and comparative examples 1-2 are shown in figure 1. A TEM image of the catalyst prepared in example 1 is shown in fig. 2. According to the figures 1-2, the grain sizes of Co and Cu in the nitrogen-doped carbon-silicon composite material loaded cobalt-copper bimetallic catalyst are smaller than those of Co or Cu in the loaded single metal catalyst, which shows that the addition of copper is beneficial to controlling the sizes of cobalt and copper metal particles and preventing the cobalt and copper metal particles from aggregating and growing.

TEM images of the catalysts prepared in example 1 and comparative examples 1-2 are shown in FIG. 3, from which FIG. 3 shows that CoCu @ CN/SiO₂Metal particles of less than Co @ CN/SiO₂And Cu @ CN/SiO₂The catalyst of small metal particles is advantageous for improving the catalytic activity, and thus, CoCu @ CN/SiO₂The catalytic activity of the catalyst is higher than that of Co @ CN/SiO₂And Cu @ CN/SiO₂。

Comparative example 3

A catalyst was prepared according to the method of example 1, except that: no cobalt nitrate hexahydrate or copper nitrate hexahydrate was added, and the resulting catalyst was designated CN/SiO₂。

Comparative example 4

A catalyst was prepared according to the method of example 1, except that: no glucose and urea were added and the resulting catalyst was reported as CoCu @ SiO₂。

Comparative example 5

A catalyst was prepared according to the method of example 1, except that: the copper nitrate hexahydrate was replaced by ferric nitrate hexahydrate and the catalyst obtained was recorded [email protected]/SiO₂。

Comparative example 6

A catalyst was prepared according to the method of example 1, except that: replacement of copper nitrate hexahydrate with nickel nitrate hexahydrate and catalyst reported as CoNi @ CN/SiO₂。

Application example

(1) The catalysts prepared in the embodiment 1 and the comparative examples 1-6 are applied to catalyze the hydrogenation reduction reaction of nitrobenzene, and the reaction conditions are as follows: 10mmol of nitrobenzene, 100mg of catalyst and 10mL of ethanol (solvent), reaction temperature of 120 ℃ and reaction pressure H₂: 2MPa and reaction time of 1 h.

The results, calculated as conversion and selectivity to nitrobenzene, are shown in table 1:

TABLE 1 catalysis results of the catalysts obtained in example 1 and comparative examples 1 to 6

Catalyst and process for preparing same	Conversion rate/%	Selectivity/%)
			Example 1	81.3	100
Comparative example 1	24.8	100
			Comparative example 2	<1	100
Comparative example 3	0	100
			Comparative example 4	<1	100
Comparative example 5	1.7	100
			Comparative example 6	6.6	100

As can be seen from comparing example 1 with comparative example 1, the conversion rate of the catalyst loaded with only cobalt nanoparticles to nitrobenzene is only 24.8%, and the catalytic activity is significantly reduced compared to the catalyst loaded with cobalt-copper bimetallic. As can be seen by comparing example 1, comparative example 2, and comparative example 4, the conversion rate of the obtained catalyst to nitrobenzene was 1% or less regardless of whether only Cu nanoparticles were supported or whether nitrogen-doped carbon modification was not performed on silica. It can be seen from the comparison of example 1 and comparative example 3 that the catalyst not supporting metal nanoparticles has no catalytic effect on the nitrobenzene hydrogenation reduction reaction. As can be seen from comparison of example 1 and comparative example 5, the conversion of nitrobenzene in the catalyst loaded with copper and cobalt nanoparticles was only 1.7%, and the catalytic activity was extremely low. As can be seen by comparing example 1 with comparative example 6, the conversion of nitrobenzene was only 6.6% and the catalytic activity was very low for the nickel and cobalt nanoparticle supported catalyst. The nitrogen-doped carbon-silicon composite material loaded cobalt-copper bimetallic catalyst prepared by the invention has high nitrobenzene conversion rate and good catalytic effect when being applied to the selective reduction of nitro compounds.

(2) And (3) testing the cycling stability: the cycle stability test was carried out according to the method of (1), and the catalysts prepared in example 1 and comparative example 1 were recycled for 12 times, wherein the catalyst was recovered by the following method: separating the catalyst from the reaction solution by a magnet, washing the catalyst by ethanol, drying the catalyst, collecting the dried catalyst, and putting the obtained catalyst into the next reaction for recycling. The catalyst recycle effect (nitrobenzene conversion) is shown in table 2 and fig. 4:

TABLE 2 Cyclic catalysis results for catalysts obtained in example 1 and comparative example 1

Catalyst and process for preparing same	Example 1 conversion/%)	Comparative example 1 conversion/%)
			Circulating for 1 time	82.5	25
Circulating for 2 times	82.2	24.9
			Circulating for 3 times	82.4	24.9
Circulating for 4 times	82.3	24.8
			Circulating for 5 times	82.5	24.2
Circulating for 6 times	82.6	20.6
			Circulating for 7 times	82.4	10.5
Circulating for 8 times	82.3	7.8
			Circulation 9 times	82.0	5.5
Circulating for 10 times	82.1	5.4
			Circulating for 11 times	81.9	4.7
Circulating for 12 times	82.0	3.6

As can be seen from the data in fig. 4 and table 2, the cycle stability of the nitrogen-doped carbon-silicon composite supported cobalt-copper bimetallic catalyst is significantly better than that of the supported cobalt monometal catalyst.

In conclusion, the preparation method provided by the invention prepares the nitrogen-doped carbon-silicon composite material loaded cobalt-copper bimetallic catalyst with high catalytic activity and good cycle stability by doping carbon and nitrogen atoms, and has wide application prospect in the preparation of amine compounds by selectively reducing nitro compounds.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.