Selective hydrogenation process and catalyst therefor

Abstract

The application provides a selective hydrogenation method, comprising the following steps: providing a hydrogenation catalyst, which is a carbon-coated nickel nanocomposite with sulfur-containing urea on the surface; contacting a hydrogenation substrate, hydrogen and the catalyst, and catalyzing the reaction under the condition of liquid-phase hydrogenation; the benzene ring of the hydrogenation substrate contains a nitro group and a carbon-carbon unsaturated bond simultaneously. When the benzene ring of the hydrogenation substrate contains a nitro group and a carbon-carbon unsaturated bond simultaneously, the hydrogenation method and the catalyst can hydrogenate the nitro group with high activity and high selectivity.

Description

Technical Field

[0001] This invention relates to a selective hydrogenation method and its catalyst, specifically to a method and catalyst for highly selective hydrogenation of nitro groups when both nitro groups and carbon-carbon unsaturated bonds are present on the benzene ring of the hydrogenation substrate. Background Technology

[0002] Catalytic hydrogenation is a crucial reaction in chemistry, referring to the addition of hydrogen molecules to unsaturated groups of organic compounds under the action of a catalyst. When the substrate contains two or more unsaturated groups, selectively adding specific unsaturated groups has always been a research challenge in catalytic hydrogenation.

[0003] Commonly used hydrogenation catalysts in industry include platinum-carbon, palladium-carbon, and Raney nickel. The metals in these catalysts are exposed in the reaction environment, making them prone to aggregation and poisoning. Carbon-coated metal nanocomposites are a newly emerging catalytic hydrogenation material. Their metals are tightly coated with a graphene carbon shell, typically less than 10 nm thick. Adsorption of the hydrogenated substrate occurs on the carbon shell during the hydrogenation reaction, giving them both the stability of carbon nanomaterials and the high activity of metal nanomaterials.

[0004] Methods for adjusting the selectivity of hydrogenation reactions can be divided into two categories: one is to modify the properties of the metal center during catalyst manufacturing; the other is to add a selectivity modifier during the hydrogenation reaction. Regardless of the method, the goal is to directly alter the properties of the active metal center. Existing methods are all aimed at reactions directly catalyzed by metals, and there is a scarcity of literature on adjusting the selectivity of hydrogenation reactions catalyzed by carbon-coated metal materials. CN114425341A and CN114426506A were among the first to disclose the anti-sulfur poisoning properties of graphene-coated nickel nanoparticles, showing that the presence of sulfur-containing compounds did not significantly affect the hydrogenation activity of the catalyst.

[0005] Selectivity modifiers are typically nitrogen, sulfur, and phosphorus-containing compounds. These heteroatoms selectively poison highly reactive metal centers by binding to the metal surface, thereby inhibiting side reactions. However, their drawback is that the interactions between these heteroatoms and the metal are strong, generally forming chemisorption bonds or reacting directly with the active center. Therefore, their type and dosage are crucial; improper selection can severely reduce catalyst activity or even cause complete loss of catalytic ability. Current technologies usually only allow the addition of selectivity modifiers during the reaction process. These toxic compounds often remain in the reaction product components, making complete removal difficult.

[0006] Aminostyrene is an important chemical raw material, industrially synthesized through the selective hydrogenation of nitro compounds. The main challenge in manufacturing these compounds is the selective reduction of the nitro group, which contains both nitro groups and easily reducible carbon-carbon unsaturated bonds. Liu et al. (Journal of Catalysis, 2017, 350: 218–225) prepared a carbon-coated nickel catalyst using glucose as a carbon source and applied it to the selective hydrogenation of 3-nitrostyrene. When the conversion was >95%, the selectivity was approximately 80%.

[0007] The foregoing information is only intended to enhance the understanding of the background of the present invention, and may include information unknown to those skilled in the art. Summary of the Invention

[0008] The first objective of this invention is to provide a method for highly selective hydrogenation of nitro groups when both nitro groups and carbon-carbon unsaturated bonds coexist on the benzene ring of the hydrogenation substrate, wherein the catalyst used in this method is a carbon-coated nickel nanoparticle composite material. The second objective of this invention is to improve the catalytic hydrogenation activity while achieving the aforementioned objectives. The third objective of this invention is to reduce or avoid the contamination of hydrogenated products with toxic additives while achieving the aforementioned objectives. The fourth objective of this invention is to provide a catalyst for achieving the aforementioned objectives.

[0009] To achieve the above objectives, the present invention provides the following technical solution.

[0010] 1. A selective hydrogenation method, comprising:

[0011] S1 provides a selective hydrogenation catalyst, which is a composite material of carbon-coated nickel nanoparticles with an effective amount of thiourea on the surface. The composite material contains a core-shell structure with a shell and a core, wherein the shell is a graphitized carbon layer and the core is nickel nanoparticles; the mass fraction of nickel is 20% to 85% based on the mass of the catalyst.

[0012] S2 involves contacting the hydrogenated substrate and hydrogen with the catalyst to react under liquid-phase catalytic hydrogenation conditions; the hydrogenated substrate has both nitro groups and carbon-carbon unsaturated bonds on its benzene ring.

[0013] 2. According to the method of 1, wherein the catalyst in S1 has a thiourea mass fraction of 0.05% to 1%, preferably 0.1% to 0.6%, based on the mass of the catalyst.

[0014] 3. According to any of the foregoing methods, wherein the mass fraction of nickel is 30% to 80%, preferably 40% to 70%, based on the mass of the catalyst.

[0015] 4. According to any of the foregoing methods, wherein the acid pickling loss rate of the carbon-coated nickel nanoparticle composite material is ≤30%, preferably ≤10%.

[0016] 5. According to any of the foregoing methods, wherein the composite material of carbon-coated nickel nanoparticles is a mesoporous and / or macroporous material.

[0017] 6. According to any of the foregoing methods, wherein the thickness of the graphitized carbon layer is 0.3 nm to 6 nm, preferably 1 nm to 3 nm.

[0018] 7. According to any of the foregoing methods, wherein, as observed under a transmission electron microscope, the particle size of the nickel nanoparticles is 2 nm to 48 nm, preferably 4 nm to 28 nm.

[0019] 8. According to any of the foregoing methods, wherein the hydrogenated substrate is nitrostyrene.

[0020] 9. According to any of the preceding methods, wherein the mass ratio of the catalyst to the hydrogenated substrate is 1:1 to 1:50, preferably 1:2 to 1:40.

[0021] 10. According to any of the preceding methods, wherein the concentration of the hydrogenated substrate in the solvent is 5 g / L to 600 g / L, preferably 8 g / L to 500 g / L.

[0022] 11. According to any of the preceding methods, wherein the liquid-phase catalytic hydrogenation reaction is carried out in the presence of a solvent, wherein the solvent is isopropanol and water in a volume ratio of 1:1 to 50:1.

[0023] 12. According to any of the preceding methods, wherein the catalytic hydrogenation reaction conditions include: a reaction temperature of 50°C to 70°C; and a hydrogen pressure of 0.7 MPa to 2.5 MPa.

[0024] 13. According to any of the preceding methods, wherein the concentration of thiourea in the liquid phase of S2 is less than 50 mg / L, preferably less than 35 mg / L.

[0025] 14. According to any of the preceding methods, wherein the catalyst in S1 is washed with a thiourea-soluble or soluble solvent.

[0026] 15. A selective hydrogenation catalyst, wherein the catalyst is a composite material of carbon-coated nickel nanoparticles with an effective amount of thiourea on the surface, the composite material having a core-shell structure having a shell and a core, the shell being a graphitized carbon layer and the core being nickel nanoparticles; the mass fraction of nickel is 20% to 85% based on the mass of the catalyst.

[0027] 16. The catalyst according to 15, wherein the thiourea mass fraction, calculated as sulfur, is 0.05% to 1%, preferably 0.1% to 0.6%, based on the mass of the catalyst.

[0028] 17. According to any of the aforementioned catalysts, wherein the acid washing loss rate of the composite material of carbon-coated nickel nanoparticles is ≤30%, preferably ≤10%.

[0029] 18. According to any of the aforementioned catalysts, wherein the mass fraction of nickel is 30% to 80%, preferably 40% to 70%, based on the mass of the catalyst.

[0030] 19. The catalyst according to any of the foregoing, wherein the catalyst is washed with a thiourea-soluble or soluble solvent.

[0031] Compared with the prior art, the present invention has the following beneficial technical effects.

[0032] This invention provides a highly selective hydrogenation method that can selectively hydrogenate nitro groups when both nitro and carbon-carbon unsaturated bonds are present on the benzene ring of the hydrogenation substrate. The catalyst used in this method is simple to prepare, easy to control, and the product is non-flammable, can be stored in air for extended periods, and exhibits high activity, long lifespan, and is easier to separate from the reaction system. These characteristics give this invention unique advantages in industrial production and application.

[0033] This invention improves the selectivity of hydrogenation reactions by modifying the properties of the carbon layer coating the metal. The correlation between hydrogenation activity and selectivity is reduced, making both catalyst manufacturing and application easier. Through optimization, this invention achieves higher hydrogenation activity while maintaining selectivity.

[0034] Thiourea is a serious catalyst poison, and the product of this invention will be used as an organic intermediate, where thiourea content is highly detrimental to subsequent applications. This invention, through further optimization, can minimize the concentration of thiourea in the liquid phase, thereby minimizing the introduction of thiourea into the hydrogenated product.

[0035] Using the hydrogenation method and catalyst of the present invention, the conversion rate is close to or reaches 100% and the selectivity is about 95% to 100% when catalytically hydrogenating nitrostyrene.

[0036] Other features and advantages of the present invention will be described in detail in the Detailed Description section. Attached Figure Description

[0037] Figure 1 The image shows the X-ray diffraction pattern of the catalyst prepared according to the method in Example 2. Detailed Implementation

[0038] The present invention is described in detail below with reference to specific embodiments. However, it should be noted that the scope of protection of the present invention is not limited by these specific embodiments and principle explanations, but is determined by the claims.

[0039] In this invention, except where expressly stated, any matters or issues not mentioned herein are directly applicable to what is known in the art without any changes. Furthermore, any implementation described herein can be freely combined with one or more other implementations described herein, and the resulting technical solutions or concepts are considered part of the original disclosure or record of this invention, and should not be regarded as new content not disclosed or anticipated herein, unless those skilled in the art consider the combination clearly unreasonable.

[0040] All features disclosed in this invention can be combined arbitrarily, and such combinations should be understood as the content disclosed or recorded in this invention. Unless those skilled in the art consider such combinations to be obviously unreasonable, they should all be regarded as specifically disclosed and recorded in this invention. The numerical points disclosed in this specification, unless otherwise specified, include not only the numerical points specifically disclosed in the embodiments, but also the endpoints of each numerical range in the specification. Any combination of these numerical points should be regarded as the range disclosed or recorded in this invention.

[0041] In this invention, the technical and scientific terms that are directly defined herein shall be used as such; those not defined herein shall be understood according to the definitions in the references introduced herein; and the rest shall be understood according to their common meaning in the art.

[0042] The term "macroporous material" is defined as a porous material containing macroporous distribution peaks.

[0043] The term "mesoporous material" is defined as a porous material containing mesoporous distribution peaks.

[0044] The term "macroporous and mesoporous materials" is defined as porous materials containing both macroporous and mesoporous distribution peaks.

[0045] The term "inert gas" is defined as a gas that does not have a perceptible effect on the catalytic hydrogenation performance of composite materials.

[0046] The term "soluble" means that 1g to 10g can be dissolved in 100% solvent at the operating temperature.

[0047] The term "easily soluble" means that more than 10g can be dissolved in 100% solvent at the operating temperature.

[0048] The term "optional" means that something can be either present or absent. For example, A and optional B means "A is present but B is absent" or "both A and B are present".

[0049] The term "acid treatment" refers to the process of washing the product generated after the high-temperature pyrolysis step with a non-oxidizing strong acid at close to 100°C for an extended period of time during the preparation of carbon-coated nickel nanoparticle composite materials.

[0050] The contents of CN109304475A, CN109304476A, CN109304194A, CN202211348441.1 and CN202211347510.7 are incorporated herein by reference in their entirety.

[0051] A first aspect of the present invention provides a selective hydrogenation method, comprising:

[0052] S1 provides a selective hydrogenation catalyst, which is a composite material of carbon-coated nickel nanoparticles with an effective amount of thiourea on the surface. The composite material contains a core-shell structure with a shell and a core, wherein the shell is a graphitized carbon layer and the core is nickel nanoparticles; the mass fraction of nickel is 20% to 85% based on the mass of the catalyst.

[0053] S2 involves contacting the hydrogenated substrate and hydrogen with the catalyst to react under liquid-phase catalytic hydrogenation conditions; the hydrogenated substrate has both nitro groups and carbon-carbon unsaturated bonds on its benzene ring.

[0054] The homogenization of the stereostructure and electronic configuration of the active center is key to improving the selectivity of hydrogenation reactions. From this perspective, homogeneous catalysts with single active centers exhibit higher selectivity, but this also brings insurmountable problems in catalyst separation and reuse. Therefore, from an industrial perspective, heterogeneous catalysts are still necessary. Heterogeneous catalysts possess multiple metal active sites. Existing methods for improving the selectivity of hydrogenation reactions directly modify their metal components by covering or poisoning some metal active sites to achieve a certain degree of "homogenization," thereby improving reaction selectivity, generally at the cost of permanently sacrificing some activity. This invention has discovered that using a carbon-coated nickel nanoparticle composite material with a thiourea-containing surface as a hydrogenation catalyst, when both nitro groups and carbon-carbon unsaturated bonds exist on the benzene ring of the hydrogenation substrate, it can selectively hydrogenate the nitro groups on the benzene ring, thus achieving the objective of this invention.

[0055] According to the selective hydrogenation method of the first aspect of the present invention, the catalyst in S1 is a composite material of carbon-coated nickel nanoparticles with an effective amount of thiourea on its surface. The "effective amount" refers to the enhanced hydrogenation selectivity for nitro groups when both nitro groups and carbon-carbon unsaturated bonds are present on the benzene ring of the catalytic hydrogenation substrate, compared to a catalyst without thiourea and under otherwise identical conditions.

[0056] According to the selective hydrogenation method of the first aspect of the present invention, in the catalyst of S1, the mass fraction of thiourea, calculated as sulfur, is 0.05% to 1%, preferably 0.1% to 0.8%, based on the mass of the catalyst.

[0057] According to the selective hydrogenation method of the first aspect of the present invention, there are no particular limitations on the manner in which thiourea is introduced onto the surface of the composite material containing carbon-coated nickel nanoparticles; any existing and known suitable method may be used by those skilled in the art, such as impregnation.

[0058] This invention provides a method for manufacturing the catalyst in S1, comprising the steps of mixing and impregnating a composite material of carbon-coated nickel nanoparticles with a thiourea solution. The mixing temperature can be 60°C to 100°C; the mixing method can be ultrasonic or stirring; the mass ratio of the carbon-coated nickel nanoparticle composite material to thiourea is 2:1 to 100:1, preferably 4:1 to 80:1. The method further includes optional post-treatment steps, such as separation, washing, and drying. The separation can be performed by filtration or centrifugation; the washing is preferably done with water; the drying generally does not exceed 80°C.

[0059] According to the selective hydrogenation method of the first aspect of the present invention, the carbon-coated nickel nanoparticle composite material is basically composed of nickel, carbon, oxygen, and optionally nitrogen. It should be understood that the carbon-coated nickel nanoparticle composite material is mainly composed of zero-valent nickel and carbon; since the carbon source in the synthetic raw materials contains oxygen, a small amount of oxygen will inevitably be present in the surface carbon of the composite material; if the carbon source contains nitrogen, a small amount of nitrogen will also be present in the surface carbon of the composite material; oxygen will also be adsorbed on the surface of the composite material when it is stored in the air; a small or trace amount of nickel may exist in an oxidized state; impurities in the synthetic raw materials may also lead to the presence of small or trace amounts of other elements, but no significant effect has been found on the catalytic hydrogenation performance of the composite material in the present invention; the present invention considers it unnecessary to specifically address these factors.

[0060] According to the selective hydrogenation method of the first aspect of the present invention, the carbon-coated nickel nanoparticle composite material mainly consists of a core-shell structure having a shell and a core, wherein the shell is a graphitized carbon layer and the core is nickel nanoparticles. It should be understood that a small amount of carbon matrix is ​​generated during the manufacturing process of the carbon-coated nickel nanoparticle composite material, which has no significant impact on the catalytic hydrogenation performance of the composite material in the present invention. The present invention also considers it unnecessary to specify the amount of carbon matrix.

[0061] The structure, composition, and preparation method of carbon-coated nickel nanoparticle composite materials are well known in the art. This invention does not impose any particular limitation on the carbon-coated nickel nanoparticle composite material used; any existing known materials can be used, preferably those disclosed in CN109304475A, CN109304476A, CN109304194A, CN202211348441.1, and CN202211347510.7.

[0062] The pores in the aforementioned composite materials are mainly mesoporous. Mesoporous and macroporous materials can also be obtained using specific methods, such as the method in CN 111185211A. This invention preferably uses a carbon-coated nickel nanoparticle composite material as a mesoporous and / or macroporous material, and more preferably, the volume of mesoporous and / or macroporous pores accounts for more than 80% of the total pore volume. The terms mesoporous and macroporous refer to the macroscopic properties of the tested catalytic material and are unrelated to the tightness of the graphitized carbon layer coating the nickel nanoparticles.

[0063] According to the selective hydrogenation method of the first aspect of the present invention, the acid washing loss rate of the carbon-coated nickel nanocomposite material is ≤30%, preferably ≤10%. It is known in the art that poorly coated nickel can be removed by acid treatment to obtain a more tightly coated carbon-coated nickel nanoparticle composite material. Generally, under essentially the same conditions, the tightly coated composite material is more stable and exhibits higher selectivity in the catalytic reaction. Acid treatment can generally use sulfuric acid or hydrochloric acid, with an acid concentration of 0.1 mol / L to 3 mol / L, and a treatment time of 24 h to 48 h.

[0064] According to the selective hydrogenation method of the first aspect of the present invention, the thickness of the graphitized carbon layer is less than 10 nm, generally 0.3 nm to 6.0 nm, preferably 1 nm to 3 nm.

[0065] According to the selective hydrogenation method of the first aspect of the present invention, the particle size of the nickel nanoparticles observed under a transmission electron microscope is 2 nm to 48 nm, preferably 4 nm to 28 nm.

[0066] According to the selective hydrogenation method of the first aspect of the present invention, the nickel nanoparticles have a face-centered cubic lattice structure and / or a close-packed hexagonal lattice structure.

[0067] According to the selective hydrogenation method of the first aspect of the present invention, the hydrogenation substrate is nitrostyrene and its derivatives, wherein the nitro group may be located at the ortho, para, or meta position of the alkenyl group. The product is the corresponding aminostyrene and its derivatives.

[0068] Further, the hydrogenation substrate may be selected from at least one of 2-nitrostyrene, 3-nitrostyrene, 4-nitrostyrene, and their derivatives. The corresponding product is at least one of 2-vinylaniline, 3-vinylaniline, 4-vinylaniline, and their derivatives.

[0069] According to the selective hydrogenation method of the first aspect of the present invention, in S2, the mass ratio of the catalyst to the hydrogenation substrate can be 1:1 to 1:50, preferably 1:2 to 1:40, for example 1:2, 1:5, 1:10, 1:15, 1:20, 1:25, 1:30, 1:35, 1:40, or any range between the two.

[0070] According to the selective hydrogenation method of the first aspect of the present invention, the reaction in S2 is preferably carried out in the presence of a solvent. The present invention does not particularly limit the specific choice of solvent, and those skilled in the art can choose any known suitable solvent. The solvent is preferably isopropanol and water, with a volume ratio preferably between 1:1 and 50:1.

[0071] According to the selective hydrogenation method of the first aspect of the present invention, the amount of solvent used is selected over a wide range, based on the environmental conditions required for the reaction. The concentration of the hydrogenation substrate in the solvent can be from 5 g / L to 600 g / L, typically from 8 g / L to 300 g / L.

[0072] According to the selective hydrogenation method of the first aspect of the present invention, the time of the catalytic hydrogenation reaction can be appropriately selected according to the temperature and hydrogen pressure. Preferably, the time of the catalytic hydrogenation reaction is 20 min to 400 min, more preferably 40 min to 360 min, for example 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, 120 min, 130 min, 140 min, 150 min, 160 min, 200 min, 250 min, 300 min, 320 min, 360 min, or any range between the two.

[0073] According to the selective hydrogenation method of the first aspect of the present invention, the preferred conditions for the catalytic hydrogenation reaction are: a reaction temperature of 50°C to 70°C; and a hydrogen pressure of 0.7 MPa to 2.5 MPa.

[0074] According to the selective hydrogenation method of the first aspect of the present invention, the concentration of thiourea in the liquid phase of S2 is less than 50 mg / L, preferably less than 35 mg / L. Thiourea in the catalyst may enter the liquid phase of the reaction system; this portion of thiourea is detrimental to hydrogenation activity. Controlling the concentration of thiourea in the liquid phase within the above-mentioned range can result in higher hydrogenation activity.

[0075] According to the selective hydrogenation method of the first aspect of the present invention, the catalyst in S1 is washed with a readily soluble or soluble solvent of thiourea. Thiourea is a severe poison for metal catalysts and readily undergoes chemical adsorption or reaction on metal surfaces; direct contact with nickel, for example, usually renders it inactive. The interaction of thiourea with carbon surfaces is significantly different from the former; thiourea impregnated on the carbon surface can partially enter the reaction solvent. The present invention preferably washes away this portion of thiourea with a readily soluble or soluble solvent, thereby preventing thiourea from contaminating the hydrogenated product, which is generally used as an intermediate in organic synthesis, and the presence of thiourea is extremely detrimental to subsequent applications. Thiourea-induced poisoning of hydrogenation catalysts is generally permanent; however, the present invention has discovered that when the hydrogenation activity of a catalyst is reduced by treating it with large amounts of thiourea, washing with a readily soluble or soluble solvent of thiourea can restore its high hydrogenation activity, a feature not found in the prior art.

[0076] A second aspect of the present invention provides a selective hydrogenation catalyst, wherein the catalyst is a composite material of carbon-coated nickel nanoparticles with an effective amount of thiourea on the surface, the composite material having a core-shell structure having a shell and a core, the shell being a graphitized carbon layer and the core being nickel nanoparticles; the mass fraction of nickel is 20% to 85% based on the mass of the catalyst.

[0077] According to the catalyst of the second aspect of the present invention, the mass fraction of thiourea, calculated as sulfur, is 0.05% to 1%, preferably 0.1% to 0.6%, based on the mass of the catalyst.

[0078] According to the catalyst of the second aspect of the present invention, the acid washing loss rate of the composite material of the carbon-coated nickel nanoparticles is ≤30%, preferably ≤10%.

[0079] According to the catalyst of the second aspect of the present invention, the mass fraction of nickel is 30% to 80%, preferably 40% to 70%, based on the mass of the catalyst.

[0080] According to a second aspect of the present invention, the catalyst is washed with a solvent readily soluble or soluble in thiourea.

[0081] The present invention will be described in detail below through embodiments.

[0082] The surface morphology of the material was characterized by transmission electron microscopy (TEM). The TEM used was a JEM-2100 (Nippon Electron Ltd.), and the TEM testing conditions were: accelerating voltage of 200 kV.

[0083] Analysis of five elements—carbon (C), hydrogen (H), oxygen (O), nitrogen (N), and sulfur (S)—was performed on an Elementar Micro Cube elemental analyzer. The specific operating methods and conditions were as follows: the sample was combusted at high temperature in the presence of oxygen, converting C, H, N, and S in the sample into CO2, H2O, N2, and SO2, respectively. After removing interfering factors, the reaction gases were carried by the carrier gas into the chromatographic column for separation, and finally detected by a thermal conductivity detector. Oxygen analysis utilized high-temperature decomposition; under the action of a carbon catalyst, oxygen in the sample was converted into CO, which was then detected using a thermal conductivity detector. The metal element content was the normalized result after subtracting the contents of carbon, hydrogen, oxygen, nitrogen, and sulfur from the material.

[0084] The XRD diffractometer used was an X'Pert Pro model purchased from PA Nalytical in the Netherlands. The test conditions were: Cu target, Kα rays, tube voltage of 40kV, tube current of 40mA, and 2θ scanning range of 5° to 80°.

[0085] The specific surface area and pore distribution of the material were determined using the Brunauer-Emmett-Taller method (BET, Quantachrome AS-6B analyzer).

[0086] The following preparation examples illustrate the preparation of the catalyst (sulfur-modified carbon-coated nickel nanocomposite material). Preparation Example 1

[0087] S1. Weigh 21.01g of citric acid monohydrate and 14.55g of basic nickel carbonate (the molar ratio of basic nickel carbonate based on nickel element to citric acid monohydrate based on carboxylate ion is 1:3) and add them to 150mL of deionized water. Stir at 100℃ to obtain a homogeneous solution, and continue to heat to dryness. Grind the obtained solid to obtain the precursor.

[0088] S2. The obtained precursor is placed in a ceramic boat, and then the ceramic boat is placed in the constant temperature zone of a tube furnace. Nitrogen gas is introduced at a flow rate of 100 mL / min, and the temperature is increased to 600℃ at a rate of 10℃ / min. After holding at the temperature for 120 min, the heating is stopped, and the mixture is cooled to room temperature under a nitrogen atmosphere to obtain carbon-coated nickel nanocomposite material.

[0089] S3. Take 4g of the obtained carbon-coated nickel nanocomposite material and 0.8g of thiourea, add them to 20mL of deionized water, stir at 85℃ for 90min, filter, and wash several times with deionized water. Transfer the obtained filter cake to an oven and dry at 80℃ to obtain the sulfur-modified carbon-coated nickel nanocomposite material.

[0090] The elemental analysis showed that the mass fraction of sulfur (S) in the sulfur-modified carbon-coated nickel nanocomposite was 0.38%, and the mass fraction of nickel (Ni) after normalization was 73.80%.

[0091] Preparation Example 2

[0092] S1. Weigh 4.38 g (15 mmol) of ethylenediaminetetraacetic acid and 1.85 g (20 mmol) of nickel hydroxide (the molar ratio of nickel hydroxide based on nickel element to ethylenediaminetetraacetic acid based on carboxyl group is 1:3) and add them to 150 mL of deionized water. Stir at 75 °C to obtain a homogeneous solution, and continue to heat to dryness. Grind the solid to obtain the precursor.

[0093] S2. Place the precursor obtained in step S1 into a ceramic boat, then place the ceramic boat in the constant temperature zone of a tube furnace, introduce nitrogen gas at a flow rate of 80 mL / min, and heat it to 600℃ at a rate of 3℃ / min. After holding the temperature for 3 hours, stop heating and cool it to room temperature under a nitrogen atmosphere.

[0094] S3. Add the product obtained in step S2 to 60 mL of 0.5 mol / L H2SO4 solution, stir and reflux at 80 °C for 6 h, filter the solution, wash with deionized water until neutral, and then dry the powder in an oven at 100 °C for 2 h to obtain carbon-coated nickel nanocomposite material.

[0095] S4. Take 3g of the obtained carbon-coated nickel nanocomposite material and 0.15g of thiourea, add them to 30mL of deionized water, stir at 100℃ for 90min, filter, and wash several times with deionized water. Transfer the obtained filter cake to an oven and dry at 100℃ to obtain the sulfur-modified carbon-coated nickel nanocomposite material.

[0096] Figure 1 The image shows the X-ray diffraction pattern of the sulfur-modified carbon-coated nickel nanocomposite material prepared according to the method in Example 2. As can be seen from the image, diffraction peaks corresponding to fcc-Ni and hcp-Ni are present, along with diffraction peaks for the carbon material. Using the Scherrer equation, the average particle size of the nickel nanoparticles is calculated to be 13.9 nm.

[0097] Elemental analysis revealed that the sulfur content in the sulfur-modified carbon-coated nickel nanocomposite was 0.38%, and the normalized Ni content was 56.49%.

[0098] The following test examples illustrate the application of sulfur-modified carbon-coated nickel nanocomposites as catalysts in catalytic hydrogenation reactions.

[0099] Test Example 1

[0100] 50 mg of the sulfur-modified carbon-coated nickel nanocomposite material prepared in Example 1, 298 mg of 4-nitrostyrene, 27 mL of isopropanol, and 3 mL of water were added to a reaction vessel. H2 was bubbled into the vessel four times to replace the precipitate. H2 was then bubbled again to bring the pressure inside the vessel to 1.0 MPa. The temperature was raised to the predetermined reaction temperature of 60°C, and the reaction was continued for 90 min. Heating was then stopped, and the vessel was allowed to cool to room temperature before depressurization. The product was then removed from the reaction vessel for chromatographic analysis. The conversion rate of the reactants and the selectivity of the target product were calculated using the following formula:

[0101] Conversion rate (%) = (Mass of reactants reacted / Amount of reactants added) × 100%

[0102] Selectivity (%) = (Mass of target product / Mass of reaction product) × 100%

[0103] Analysis revealed that the conversion rate of 4-nitrostyrene was 99.6%, and the selectivity of 4-vinylaniline was 95.8%.

[0104] Test Example 2

[0105] 50 mg of the sulfur-modified carbon-coated nickel nanocomposite material prepared in Example 2, 298 mg of 4-nitrostyrene, 27 mL of isopropanol, and 3 mL of water were added to a reaction vessel. H2 was bubbled into the vessel four times to replace the precipitate. H2 was then bubbled again to bring the pressure inside the vessel to 1.0 MPa. The temperature was raised to the predetermined reaction temperature of 60°C, and the reaction was continued for 90 min. Heating was then stopped, and the vessel was cooled to room temperature before depressurization. The product was then removed from the reaction vessel for chromatographic analysis. The conversion rate of the reactants and the selectivity of the target product were calculated using the following formula:

[0106] Conversion rate (%) = (Mass of reactants reacted / Amount of reactants added) × 100%

[0107] Selectivity (%) = (Mass of target product / Mass of reaction product) × 100%

[0108] Analysis revealed that the conversion rate of 4-nitrostyrene was 99.8%, and the selectivity of 4-vinylaniline was 94.5%.

[0109] As can be seen from Test Example 2, using the hydrogenation method and catalyst of the present invention, the reaction conversion rate is approximately 100% and the selectivity is approximately 95% at 60°C and 1 MPa hydrogen pressure. Meanwhile, when the catalyst without thiourea and under the same conditions catalyzes the hydrogenation reaction, the yield of 4-aminophenylethane reaches 8.60%.

[0110] As can be seen from test examples 1 and 2, using the hydrogenation method and catalyst of the present invention, the reaction conversion rate is approximately 100% and the selectivity is approximately 95% at 60°C and 1 MPa hydrogen pressure. However, when using a catalyst without thiourea and with all other conditions being the same, the reaction temperature needs to be increased by 20°C to 40°C to achieve similar results when thiourea is added to the reaction system for hydrogenation.

[0111] As can be seen from test examples 1 and 2, whether or not acid washing is performed has no significant effect on the hydrogenation method and catalyst of the present invention.

[0112] As can be seen from test examples 1 and 2, the hydrogenation method and catalyst of the present invention can be used without adding thiourea to the hydrogenation reaction system.

Claims

1. A selective hydrogenation method, comprising: S1 provides a selective hydrogenation catalyst, which is a composite material of carbon-coated nickel nanoparticles with an effective amount of thiourea on the surface. The composite material contains a core-shell structure with a shell and a core, wherein the shell is a graphitized carbon layer and the core is nickel nanoparticles. Based on the mass of the catalyst, the mass fraction of nickel is 20% to 85%; based on the mass of the catalyst, the mass fraction of thiourea (calculated as sulfur) is 0.05% to 1%; the catalyst is washed with a readily soluble or soluble solvent of thiourea. S2 involves contacting the hydrogenated substrate and hydrogen with the catalyst to react under liquid-phase catalytic hydrogenation conditions; the benzene ring of the hydrogenated substrate simultaneously contains nitro groups and carbon-carbon unsaturated bonds.

2. The method according to claim 1, characterized in that, In the catalyst of S1, the mass fraction of thiourea, calculated as sulfur, is 0.1% to 0.6% based on the mass of the catalyst.

3. The method according to claim 1, characterized in that, Based on the mass of the catalyst, the mass fraction of nickel is 40% to 70%.

4. The method according to claim 1, characterized in that, The nickel nanoparticles were observed to have a particle size of 4 nm to 28 nm under a transmission electron microscope.

5. The method according to claim 1, characterized in that, The hydrogenated substrate is nitrostyrene.

6. The method according to claim 1, characterized in that, The mass ratio of the catalyst to the hydrogenated substrate is 1:1 to 1:50; the concentration of the hydrogenated substrate in the solvent is 5 g / L to 600 g / L.

7. The method according to claim 1, characterized in that, The liquid-phase catalytic hydrogenation reaction is carried out in the presence of a solvent, namely isopropanol and water, in a volume ratio of 1:1 to 50:

1.

8. The method according to claim 1, characterized in that, The catalytic hydrogenation reaction conditions include: a reaction temperature of 50℃~70℃; and a hydrogen pressure of 0.7MPa~2.5MPa.

9. The method according to claim 1, characterized in that, The concentration of thiourea in the liquid phase of S2 is less than 50 mg / L.

10. The method according to claim 9, characterized in that, The concentration of thiourea in the liquid phase of S2 is less than 35 mg / L.

11. A selective hydrogenation catalyst, wherein, The catalyst is a composite material of carbon-coated nickel nanoparticles with an effective amount of thiourea on the surface. The composite material contains a core-shell structure with a shell and a core. The shell is a graphitized carbon layer and the core is nickel nanoparticles. Based on the mass of the catalyst, the mass fraction of nickel is 20% to 85%; based on the mass of the catalyst, the mass fraction of thiourea, calculated as sulfur, is 0.05% to 1%; the catalyst is washed with an easily soluble or soluble solvent of thiourea.

12. The catalyst according to claim 11, characterized in that, Based on the mass of the catalyst, the thiourea mass fraction, expressed as sulfur, is 0.1% to 0.6%.

13. The catalyst according to claim 11, characterized in that, Based on the mass of the catalyst, the mass fraction of nickel is 40% to 70%.

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