Preparation method and application of nitrogen self-doped Ni / C catalyst based on DNT hydrogenation coupling byproduct

Abstract

The invention discloses a preparation method and application of a nitrogen self-doped Ni / C catalyst based on a DNT hydrogenation coupling byproduct, and belongs to the field of high-valued resource utilization of industrial hazardous wastes. The preparation method of the catalyst comprises the following steps: pretreating and recovering crude TDA, hydrolyzing and recovering TDA, preparing the nitrogen self-doped porous carbon material, impregnating the loaded nickel species, precipitating and aging, filtering and drying, and reducing. The catalyst can be directly reused for catalyzing a reaction for preparing TDA through DNT hydrogenation, realizes closed-loop circulation from hazardous wastes to high-value products and then to an original recycling reaction, and has the advantages of high resource utilization rate, environment friendliness and low cost.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of chemical hazardous waste treatment and resource utilization, in particular to a high-value recovery and utilization method of coupling by-products generated in the production process of TDA, and especially to a recycling method for preparing high-performance nickel-carbon (Ni / C) catalysts from the by-products and recycling them to the DNT hydrogenation reaction for preparing TDA, so as to realize a circular economy mode. BACKGROUND

[0002] Toluene diisocyanate (TDI) as a key basic raw material in modern chemical industry is the core monomer of polyurethane (PU) materials, and is known as the "sixth synthetic material". Polyurethane is prepared by the step-by-step addition polymerization of isocyanate and polyol, and its molecular structure has strong designability. By adjusting the composition and proportion of soft and hard segments, a wide performance spectrum from soft elastomer to rigid foam can be obtained. This feature makes the polyurethane product family cover many categories such as soft and hard foam, elastomer, paint, adhesive, sealant and spandex fiber, and is widely used in key fields of national economy such as building energy saving, transportation, textile and clothing, home appliances and electronic packaging due to its excellent elasticity, wear resistance, heat and sound insulation, chemical resistance and strong adhesion.

[0003] At present, the industrial synthesis of TDI mainly includes two core chemical reaction sections: one is the catalytic hydrogenation section of dinitrotoluene (DNT), which aims to convert the raw material DNT into the key intermediate toluene diamine (TDA); the other is the TDA phosgenation section, which aims to react the generated TDA with phosgene (COCl2) to ultimately synthesize the target product TDI. The crude TDI product still needs to go through a series of complex rectification and purification to obtain high-purity commercial-grade TDI.

[0004] The core bottleneck of current TDI production is that in addition to the main reaction of DNT hydrogenation to generate TDA, due to the high reactivity of amino groups, deep coupling side reactions of TDA molecules will inevitably occur, generating a large amount of polymers with high molecular weight and complex composition. These polymers form a viscous black semi-solid or solid substance in the reaction system, which is the DNT hydrogenation coupling by-product, usually accounting for 5% to 10% of the total TDA yield.

[0005] The composition of the DNT hydrogenation coupling by-product has roughly two parts: light components and heavy components. The light components are mainly TDA to ensure the fluidity of the coupling by-product slurry, accounting for about 30%; the heavy components are various heavy component derivatives formed during the reaction and separation process (i.e. secondary residual coke), accounting for about 70%. Because the by-product contains heavy metals (from the catalyst) and toxic and harmful components such as incomplete reaction of amines, it is clearly classified as hazardous solid waste.

[0006] Currently, domestic and foreign enterprises have very limited means of disposing of this part of hazardous waste, and the vast majority still adopt the simplest and most direct incineration treatment method. This "end-of-pipe" mode has multiple negative impacts: first, there is a huge waste of resources, as the coupling by-product contains a large amount of TDA product and expensive nickel catalyst, and direct incineration results in the permanent loss of these valuable resources; second, production costs are significantly increased, as more DNT raw materials need to be invested to make up for the loss of TDA yield due to the generation of coupling by-products, and the incineration disposal itself requires costs, and the continuous loss of catalyst also brings huge expenses; third, the environmental pressure is heavy, as the incineration process not only consumes energy, but also produces greenhouse gas CO2 and nitrogen oxides and other pollutants.

[0007] In the prior art, although there are explorations to convert tar into carbon materials for resource utilization (such as using biomass tar to prepare porous carbon), these schemes are difficult to directly apply to DNT hydrogenation coupling by-products. Specifically, biomass tar and other raw materials have relatively simple compositions, and can produce general-purpose porous carbon materials, but DNT coupling by-products have essential differences - they are rich in nitrogen and residual nickel, and if the existing "activation-doping" process is simply applied, not only the inherent characteristics cannot be fully utilized, but also the carbon material pore structure may be poor and the surface chemical properties may not be suitable due to component interference, making it difficult to directionally prepare high-performance special catalysts suitable for DNT hydrogenation.

[0008] Therefore, it is an urgent need in the field to develop an innovative technology that can target the characteristics of DNT hydrogenation coupling by-products and achieve full-component, high-value recycling, breaking through the bottleneck of green and sustainable development of the TDI industry. SUMMARY

[0009] The present application aims to overcome the deficiencies of the prior art, such as rough disposal of DNT hydrogenation coupling by-products, serious resource waste, great environmental pressure, and high preparation cost of special catalysts, and provides a preparation method and application of a nitrogen self-doped Ni / C catalyst based on DNT hydrogenation coupling by-products, which has reasonable process flow, high resource utilization rate, environmental friendliness, and low cost. By utilizing the characteristics of the coupling by-products, such as rich nitrogen elements and residual nickel, a high-performance nickel-carbon catalyst is prepared through template control technology, which is reused in the DNT hydrogenation process to prepare TDA, realizing a closed loop of "primary resource recycling-high level material conversion-process recycling", and providing a new technical path for the green circular economy of TDA production.

[0010] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions: In a first aspect, the present application provides a preparation method of a nitrogen self-doped Ni / C catalyst based on DNT hydrogenation coupling by-products, comprising the following steps: (1) Pretreatment and recovery of crude TDA: mixing the TDA mixture in the DNT hydrogenation process to prepare TDA with solvent a, heating under reflux at 150-200 DEG C for 1-3 h, and after cooling, performing solid-liquid separation to collect the crude TDA solid and the coupling by-product liquid respectively; (2) Hydrolysis and recovery of TDA: mixing the collected coupling by-product with solvent b, heating under reflux at 150-200 DEG C for 1-3 h again, cooling to 80-120 DEG C, and performing reflux reaction under normal pressure for 6-8 h, after the hydrolysis reaction is completed, the product is extracted, crystallized, and filtered to obtain TDA solid, and the filtrate is evaporated and concentrated, dried, and then the solvents a and b are removed to obtain secondary residual coke; (3) Preparation of nitrogen self-doped porous carbon material: grinding the collected secondary residual coke with a sulfate salt, and then placing it in a tube furnace for pyrolysis reaction under a nitrogen atmosphere; the pyrolysis product is acid washed to remove the template, then washed with deionized water until neutral, and then dried to obtain a nitrogen-doped porous carbon material; (4) Immersion and loading of nickel species: adding an appropriate amount of deionized water to the nitrogen-doped porous carbon material, dispersing and stirring, and then adding an aqueous solution of soluble nickel salt for immersion treatment; (5) Precipitation and aging: slowly adding a soluble carbonate salt solution with a concentration of 0.2-1.0 mol / L, and after the addition is completed, heating at 60-100 DEG C and stirring for 20-24 h; (6) Filtration and drying: filtering the product obtained in step (5), washing with distilled water until neutral, and vacuum drying at 60-100 DEG C overnight; (7) Reduction treatment: the material obtained in step (6) is heated to 350-650 ℃ at a temperature increasing rate of 5-20 ℃ / min in a fixed bed reactor, and reduced in a hydrogen atmosphere for 2-4 h, wherein the hydrogen flow rate is 60-100 mL / min, and the pressure is 0.05-0.5 MPa; (8) Passivation treatment: the reduced product obtained in step (7) is cooled to room temperature in a nitrogen environment, and a nitrogen-oxygen mixed gas is introduced for surface passivation. After passivation, a high-activity Ni / C catalyst is prepared.

[0011] As a preferred solution, in step (1), the solvent a is one of methanol, ethanol, n-butanol, and ethylene glycol; and the use amount ratio of TDA mixture to solvent a is 1:4-1:10.

[0012] As a preferred solution, in step (2), the solvent b is one of methanol, ethanol, n-butanol, and ethylene glycol; and the use amount ratio of coupling by-product to solvent b is 1:0.5-1:2.

[0013] As a preferred solution, in step (3), the sulfate is one of Na2SO4, MgSO4, and K2SO4; and the use amount ratio of secondary residual coke to sulfate is 1:0.1-1:2.

[0014] As a preferred solution, in step (3), the pyrolysis reaction is heated to 550-650 ℃ at a temperature increasing rate of 5-15 ℃ / min, and kept constant for 3-5 h.

[0015] As a preferred solution, in step (4), the mass ratio of the nitrogen-doped porous carbon material to deionized water is 1:30-1:40, and the aqueous solution of soluble nickel salt is prepared by mixing soluble nickel salt and deionized water at a mass ratio of 1:5-1:10. As a preferred solution, the soluble nickel salt is nickel nitrate; and the loading amount based on the mass of the nitrogen-doped porous carbon material is 30-50%.

[0016] As a preferred solution, in step (5), the soluble carbonate is sodium carbonate.

[0017] As a preferred solution, in step (6), the vacuum drying temperature is 75 ℃.

[0018] As a preferred solution, in step (7), the reduction temperature is 580 ℃.

[0019] As a preferred solution, in step (8), the oxygen content in the nitrogen-oxygen mixed gas is 0.05-5%, the nitrogen-oxygen mixed gas flow rate is 40-80 mL / min, and the passivation time is 1-3 h.

[0020] In a second aspect, the present application provides a high-activity Ni / C catalyst prepared by the above method, wherein the loading of nickel is 40-60 wt.%.

[0021] In a third aspect, the present application provides the use of the above high-activity Ni / C catalyst in catalyzing the hydrogenation of DNT to prepare TDA, wherein the catalyzing method is as follows: the high-activity Ni / C catalyst, DNT and deionized water are added into a high-pressure reactor in a ratio of (300-600 mg):(3-6 g):(200-400 mL) under a hydrogen atmosphere at a temperature of 100-130 ℃ and a pressure of 2-3 MPa, and the stirring rate is controlled at 800-1200 r / min to perform the catalytic hydrogenation reduction reaction.

[0022] Compared with the prior art, the present application has the following beneficial technical effects: (1) In the present application, the coupling by-products in the process of preparing TDA by hydrogenation of DNT are used in stages. In the first stage, the target product TDA is maximized by treating the coupling by-products, thereby improving the economy of the whole process. In the second stage, the catalyst is synthesized. The residual secondary residual coke after extraction of TDA is used as a raw material for preparing the catalyst carrier. By calcination with a template agent, the amorphous residual coke is converted into a high-performance nitrogen-doped porous carbon material, which is then used as a carrier for nickel metal to prepare a Ni / C catalyst for the original reaction. This method not only makes full use of the nitrogen elements (realizing nitrogen self-doping) and residual nickel resources in the coupling by-products, but also completely eliminates the discharge of hazardous waste, realizes the recycling and reuse of waste within the process system, significantly improves the economy and environmental benefits of the process, and fundamentally changes the inherent disadvantages of traditional "incineration disposal".

[0023] (2) In the present application, a sulfate salt is introduced in the pyrolysis process to guide the formation of regular mesoporous structures from amorphous residual coke, thereby constructing a carbon material with high specific surface area and multi-level pores. More importantly, the nitrogen elements contained in the coupling by-products are in-situ doped in the carbon skeleton during the pyrolysis process, forming nitrogen species with catalytic activity. These nitrogen species can produce strong electronic interactions with the subsequently loaded nickel, effectively anchoring the nickel particles and preventing them from sintering and growing, thereby laying a foundation for the high activity and high stability of the catalyst. Comparative experiments have confirmed that the conversion rate and selectivity of the catalyst prepared by direct pyrolysis without a template agent are significantly reduced.

[0024] (3) The nickel-based catalyst with the self-prepared nitrogen-doped porous carbon material as the carrier has better effect than the commercial activated carbon carrier catalyst in the DNT hydrogenation reaction, and the conversion rate and selectivity are both close to 100%. The NDT conversion rate can still remain >95.4% after 10 cycles, and the TDA selectivity is >97.3%, which has a wide application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 This is a complete process flow diagram of a nitrogen self-doped Ni / C catalyst based on DNT hydrogenation coupling byproducts of the present invention. Figure 2 This is the elemental distribution of DNT hydrogenation coupling byproducts; Figure 3 This is a pore size distribution diagram of the nitrogen-doped porous carbon material prepared in Example 1; Figure 4 This is the N2 physical adsorption isotherm of the nitrogen-doped porous carbon material prepared in Example 1; Figure 5 This is the XRD pattern of the highly active nickel-carbon catalyst prepared in Example 1; Figure 6 These are TEM images and particle size distribution histograms of the highly active nickel-carbon catalyst prepared in Example 1. Detailed Implementation

[0026] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Example 1 TDA recovery: 10.0 g of the TDA mixture from the DNT hydrogenation process was added to a reactor along with 50.0 g of ethylene glycol. The mixture was refluxed at 180 °C for 1.5 h. After cooling, the solid and liquid phases were separated, and the crude TDA solid and the coupling byproduct liquid were collected separately. The collected coupling byproduct was transferred to another reactor, and 10.0 g of ethylene glycol was added. The mixture was refluxed at 180 °C for 1.5 h. The reaction was then refluxed at 100 °C and atmospheric pressure for 7 h. After the hydrolysis reaction was completed, the product was extracted, crystallized, and filtered to obtain TDA solid. The filtrate was evaporated, concentrated, and dried to remove solvents a and b, yielding secondary char residue.

[0028] Preparation of nitrogen-doped porous carbon materials: Secondary coke residue was thoroughly ground with 1.0 g Na2SO4, and then placed in a tube furnace. The temperature was increased to 550 °C at a rate of 5 °C / min under a nitrogen atmosphere and maintained at this temperature for 4 h. Na2SO4 served as a template agent, enabling in-situ inheritance of nitrogen from the coupling byproducts (achieving nitrogen self-doping) while simultaneously constructing a hierarchical pore structure rich in micropores and mesopores. The pyrolysis solid product was washed with 2 mol / L hydrochloric acid, rinsed with deionized water until neutral, and dried to obtain a nitrogen-doped porous carbon material with high specific surface area (denoted as C-1).

[0029] Preparation of highly active Ni / C catalyst: In a three-necked flask, 1.05 g of the nitrogen-doped porous carbon material support (C-1) prepared above and 50 mL of deionized water (mass ratio approximately 1:48) were added and stirred for 1 h. Subsequently, a solution of 5.20 g of nickel nitrate hexahydrate (Ni(NO3)2·6H2O) prepared with 35 mL of deionized water was added, and the mixture was stirred and impregnated at 60 °C for 1 h. 100 mL of a 0.322 mol / L sodium carbonate (Na2CO3) solution was slowly added dropwise. After the addition was complete, the reaction was continued at 60 °C for 22 h with stirring. The resulting mixture was filtered, washed with distilled water until the filtrate was neutral, and dried overnight in a vacuum drying oven at 75 °C. The dried precursor was placed in a tube furnace and heated to 580 °C at a rate of 10 °C / min under a hydrogen atmosphere (flow rate 60 mL / min, pressure 0.2 MPa), and reduced at this temperature for 3 h. After reduction, the catalyst was cooled to room temperature under nitrogen protection, and then a nitrogen-oxygen mixture containing 5% oxygen (flow rate 60 mL / min) was introduced for surface passivation treatment for 3 h to obtain a highly active nickel-carbon catalyst (denoted as Cat-1).

[0030] The DNT hydrogenation reaction for TDA preparation: 500 mg of catalyst Cat-1, 5.0 g of DNT, and 300 mL of deionized water were added to a 500 mL high-pressure reactor. After purging the reactor with nitrogen and hydrogen, the catalytic hydrogenation reaction was carried out at 120 °C, 2.1 MPa hydrogen pressure, and a stirring rate of 1000 r / min. Samples were taken after 10 minutes of reaction and analyzed by gas chromatography. The results showed that the DNT conversion rate was 99.9% and the TDA selectivity was 99.5%.

[0031] Example 2 The difference from Example 1 is that 1.0 g MgSO4 was used instead of Na2SO4 in the pretreatment stage, the hydrolysis reaction temperature was increased to 120 °C, and the pyrolysis reaction temperature was adjusted to 650 °C, resulting in a nitrogen-doped porous carbon material (denoted as C-2).

[0032] The reaction conditions for the DNT hydrogenation reaction to prepare TDA were the same as in Example 1. After 14 min of reaction, the DNT conversion rate was 99.9% and the TDA selectivity was 95.7%. The catalyst prepared was designated as Cat-2.

[0033] Example 3 The difference from Example 1 is that 10.0 g of K2SO4 was used instead of Na2SO4 in the pretreatment stage, the hydrolysis reaction temperature was increased to 130 °C, and the pyrolysis reaction temperature was adjusted to 670 °C, finally obtaining nitrogen-doped porous carbon material (denoted as C-3).

[0034] The reaction conditions for the DNT hydrogenation reaction to prepare TDA were the same as in Example 1. The reaction was carried out for 20 min, with a DNT conversion rate of 99.9% and a TDA selectivity of 93.1%. The catalyst prepared was designated as Cat-3.

[0035] Comparative Example 1 The difference from Example 1 is that Na2SO4 is not added when preparing nitrogen-doped porous carbon material. Secondary coke residue is directly pyrolyzed. Using this carbon material as a carrier, a nickel-carbon catalyst (denoted as Cat-C1) is prepared using the same method as in Example 1.

[0036] The reaction conditions for the DNT hydrogenation reaction to prepare TDA were the same as in Example 1. However, with the reaction time extended to 48 min, the DNT conversion rate was 83.4%, the TDA selectivity was 89.1%, and the amount of byproducts increased, resulting in a lower catalytic effect than the catalyst of this invention.

[0037] Comparative Example 2 Unlike Example 1, biomass tar was directly pyrolyzed (under the same conditions as Example 1), and a nickel-carbon catalyst (denoted as Cat-C2) was prepared using the same method as in Example 1, with this carbon material as the carrier.

[0038] The reaction conditions for the DNT hydrogenation reaction to prepare TDA were the same as in Example 1. The reaction time was extended to 67 min, the DNT conversion rate was 78.2%, the TDA selectivity was 73.1%, and the amount of byproducts increased, resulting in a lower catalytic effect than the catalyst of this invention.

[0039] Comparative Example 3 Commercially available conventional activated carbon was used directly as the carrier. The nickel-carbon catalyst (denoted as Cat-C3) was prepared using the exact same method as in Example 1.

[0040] Under the same reaction conditions as in Example 1, the DNT hydrogenation reaction was carried out to prepare TDA. The reaction required 25 minutes to reach a conversion rate of 96.7%, and the TDA selectivity was 94.2%, which is lower than that of the catalyst of the present invention.

[0041] Comparative Example 4 A commercially available Raney nickel catalyst (denoted as Cat-C4) was used directly. The evaluation was conducted using the exact same method as in Example 1.

[0042] Under the same reaction conditions as in Example 1, DNT hydrogenation was carried out to prepare TDA. The reaction required 12 minutes to reach a conversion rate of 99.9%, and the TDA selectivity was 97.1%. The catalytic effect was basically the same as that of the catalyst of the present invention.

[0043] Comparative Example 5 A commercially available Pd / C catalyst (denoted as Cat-C5) was used directly. The evaluation was conducted using the exact same method as in Example 1.

[0044] Under the same reaction conditions as in Example 1, the DNT hydrogenation reaction was carried out to prepare TDA. The reaction took 13 minutes to reach a conversion rate of 93.1%, and the TDA selectivity was 90.2%, which is lower than that of the catalyst of the present invention.

[0045] Comparative Example 6 A commercially available Ru / C catalyst (denoted as Cat-C6) was used directly. The evaluation was conducted using the exact same method as in Example 1.

[0046] Under the same reaction conditions as in Example 1, DNT hydrogenation was carried out to prepare TDA. The reaction required 14 minutes to reach a conversion rate of 99.9%, and the TDA selectivity was 91.8%. The catalytic effect was basically the same as that of the catalyst of the present invention.

[0047] Comparative Example 7 A commercially available Pt / C catalyst (denoted as Cat-C7) was used directly. The evaluation was conducted using the exact same method as in Example 1.

[0048] Under the same reaction conditions as in Example 1, the DNT hydrogenation reaction was carried out to prepare TDA. The reaction required 12 minutes to reach a conversion rate of 90.6%, and the TDA selectivity was 89.3%, which is lower than that of the catalyst of the present invention.

[0049] Comparative Example 8 The catalyst prepared in Example 1 was evaluated using the same method as in Example 1 after 10 reuses (denoted as Cat-C8).

[0050] Under the same reaction conditions as in Example 1, DNT hydrogenation was carried out to prepare TDA. The NDT conversion rate remained at 95.4% after 10 cycles, and the TDA selectivity was 97.3%.

[0051] Comparative Example 9 The catalyst prepared in Comparative Example 3 was evaluated using the same method as in Example 1 after 10 reuses (denoted as Cat-C9).

[0052] Under the same reaction conditions as in Example 1, DNT hydrogenation was carried out to prepare TDA. The NDT conversion rate was 83.3% after 10 cycles, and the TDA selectivity was only 85.7%.

[0053] In Examples 1-3 and Comparative Examples 1-9, the testing methods used were as follows: The reaction solutions were analyzed using an Agilent 8860 gas chromatograph with an injector temperature of 250 °C, a detector temperature of 300 °C, an SE-54 column (0.32 mm × 0.5 μm × 30 m), and a flame ionization (FID) detector. The content of DNT hydrogenation coupling byproducts was determined using a Tianmei LC2030 high-performance liquid chromatograph with a UV detector at a wavelength of 280 nm, a TM.X-C18 column (4 μm, 4.6 × 250 mm), a column temperature of 35 °C, a mobile phase of methanol and water (3:2), an injection volume of 10 μL, and a flow rate of 1 mL. Specific test data are shown in Table 1.

[0054] Table 1. Performance evaluation test data results of different catalysts ; The test results in Table 1 demonstrate that this invention has successfully developed a novel method for the high-value resource utilization of coupling byproducts generated during the hydrogenation of DNT to TDA. This invention fundamentally changes the inherent drawbacks of traditional incineration disposal, transforming organic solid waste into high-value-added products, thus shifting from a "cost burden" to "green wealth." It pioneers a green circular technology path of "precise utilization of waste characteristics → targeted creation of functional materials → closed-loop recycling back to the original process" (as shown in the appendix). Figure 1 DNT hydrogenation coupling byproducts are not only waste products to be treated, but also valuable precursor materials rich in nitrogen and residual nickel. By using sulfates, coupling byproducts were successfully converted into advanced carbon materials with nitrogen self-doping, high specific surface area, and hierarchical porous structure without the addition of an additional nitrogen source.

[0055] Based on the catalyst performance shown in Table 1, the following conclusions can be drawn: Examples 1-3, using Na₂SO₄, MgSO₄, and K₂SO₄ as template agents respectively, and following a process flow of "coupling byproducts → hydrolysis → pyrolysis → loading → reduction," can stably prepare catalysts Cat-1, Cat-2, and Cat-3, indicating that the process is indeed feasible. (See attached table for details.) Figure 3 and 4It is evident that nitrogen-doped porous carbon supports (such as C-1) prepared using template agents (especially Na2SO4) through pyrolysis coupling byproducts possess high specific surface area and abundant hierarchical pore structures, providing an excellent environment for the uniform dispersion and reaction mass transfer of metallic nickel, which is the foundation of its high performance. Under the same reaction conditions, the optimal catalyst Cat-1 achieves a DNT conversion rate of 99.9% and a TDA selectivity of 99.5% in just 10 minutes, with both reaction efficiency and selectivity superior to commercial activated carbon-supported nickel catalysts (Comparative Example 3) and various noble metal catalysts (Pd / C, Pt / C, Comparative Examples 5 and 7). The activity of Cat-1 is comparable to that of commercial Raney nickel (Cat-C4) and Ru / C (Cat-C6), but it exhibits advantages in reaction time and selectivity. Compared to Comparative Example 1 without a template agent, the catalyst prepared using a template agent shows a qualitative leap in performance (conversion rate, selectivity, and reaction time), demonstrating the irreplaceable role of template agents in constructing key pore structures. After 10 cycles of application (Comparative Example 8), Cat-1 still maintained a conversion rate of 95.4% and a selectivity of 97.3%, demonstrating stability far exceeding that of commercial activated carbon-supported catalysts after application (Comparative Example 9). This proves that the support prepared from by-products has excellent structural stability and metal carrying capacity, meeting the needs of the circular economy.

[0056] Appendix Figure 1 This paper demonstrates a complete process for preparing high-performance Ni / C catalysts from DNT hydrogenation coupling byproducts and reusing them in DNT hydrogenation reactions, thus establishing a comprehensive resource recycling system. Figure 2 The byproduct is mainly composed of carbon (68.54%) and nitrogen (20.86%), totaling nearly 90%, indicating that it is a nitrogen-rich organic compound or mixture. Its structure originates from the complex framework formed by the hydrogenation coupling of benzene rings, methyl groups, and nitro groups in the DNT molecule. The high carbon content suggests that this byproduct is an excellent precursor for carbon materials, while the significant nitrogen content provides an inherent advantage for subsequent nitrogen doping. During pyrolysis, nitrogen atoms can be in situ embedded into the carbon framework, thereby controlling the electronic structure and surface properties of the material.

[0057] Appendix Figure 3 Further confirmation indicates that a hierarchical porous carbon material with a highly developed mesoporous structure and concentrated pore size distribution was successfully synthesized through the key step of "co-pyrolysis of residual char and sulfate," with the most probable pore size distribution between 2 and 3 nm. (Appendix) Figure 4 The nitrogen adsorption-desorption isotherm in the sample exhibits typical Type IV characteristics, accompanied by H... 4The presence of a hysteresis loop clearly confirms that the material has a predominantly mesoporous pore structure, while also exhibiting microporous and macroporous characteristics, forming a multi-level pore system conducive to mass transfer. This structural feature provides a favorable support environment for loading metal active centers and reactant diffusion, and is an important material basis for preparing high-performance, easily regenerable Ni / C catalysts.

[0058] Appendix Figure 5 In the XRD pattern, the sharp diffraction peaks at 44.5°, 51.8°, and 76.4° correspond to the (111), (200), and (220) crystal planes of metallic Ni, respectively. No impurity phase signals such as NiO were detected, indicating that the nickel in the catalyst exists in a crystalline, high-purity, zero-valent form, confirming the feasibility of successfully regenerating the active component by recovering nickel resources from residual coke. (Appendix) Figure 6 TEM results show that this process can produce catalysts with uniform nickel particle size and good dispersion, further confirming the controllability of the material structure and the stability of the recycling process at the microscale.

Claims

1. A method for the preparation of a nitrogen self-doped Ni / C catalyst based on DNT hydrogenative coupling by-products, characterized in that, The method comprises the following steps: (1) Pretreatment of recycled crude TDA: mixing TDA mixture in the process of hydrogenation of DNT into TDA with solvent a, heating under reflux at 150-200 ℃ for 1-3 h, and then performing solid-liquid separation after cooling to collect crude TDA solid and coupling by-product liquid respectively; (2) Hydrolysis of recycled TDA: mixing the collected coupling by-product with solvent b, heating under reflux at 150-200 ℃ again for 1-3 h, cooling to 80-120 ℃, and performing reflux reaction under normal pressure for 6-8 h, after the hydrolysis reaction is completed, the product is extracted, crystallized, filtered to obtain TDA solid, and the filtrate is concentrated by evaporation, dried and then the solvents a and b are removed to obtain secondary residual coke; (3) Preparation of nitrogen self-doped porous carbon material: grinding the collected secondary residual coke with a sulfate salt, and then placing the mixture in a tube furnace to perform pyrolysis reaction under nitrogen atmosphere; the pyrolysis product is acid washed to remove the template, then washed with deionized water until neutral, and dried to obtain a nitrogen-doped porous carbon material; (4) Immersion and loading of nickel species: adding an appropriate amount of deionized water to the nitrogen-doped porous carbon material, stirring, and then adding an aqueous solution of soluble nickel salt for immersion treatment; (5) Precipitation and aging: slowly adding a soluble carbonate salt solution with a concentration of 0.2-1.0 mol / L, and then heating and stirring at 60-100 ℃ for 20-24 h after the addition is completed; (6) Filtration and drying: filtering the product obtained in step (5), washing with distilled water until neutral, and vacuum drying at 60-100 ℃ overnight; (7) Reduction treatment: heating the product obtained in step (6) to 350-650 ℃ at a heating rate of 5-20 ℃ / min in a fixed bed reactor, reducing in a hydrogen atmosphere for 2-4 h, wherein the hydrogen flow rate is 60-100 mL / min and the pressure is 0.05-0.5 MPa; (8) Passivation treatment: reducing the reduced product obtained in step (7) to room temperature in a nitrogen environment, introducing nitrogen-oxygen mixed gas with an oxygen content of 0.05-5% and a flow rate of 40-80 mL / min, and performing surface passivation for 1-3 h to obtain a high-activity Ni / C catalyst.

2. The method for preparing a nitrogen self-doped Ni / C catalyst based on DNT hydrogenative coupling by-product according to claim 1, characterized in that: In step (1), the solvent a is one of methanol, ethanol, n-butanol and ethylene glycol; and the amount ratio of TDA mixture to solvent a is 1:4-1:

10.

3. The method for preparing a DNT hydrogenation-coupling by-product based nitrogen self-doped Ni / C catalyst according to claim 1, characterized in that: In step (2), the solvent b is one of methanol, ethanol, n-butanol and ethylene glycol; and the amount ratio of coupling by-product to solvent b is 1:0.5-1:

2.

4. The method for preparing a nitrogen self-doped Ni / C catalyst based on DNT hydrogenative coupling by-product according to claim 1, characterized in that: In step (3), the sulfate salt is one of Na2SO4, MgSO4 and K2SO4; and the amount ratio of secondary residual coke to sulfate salt is 1:0.1-1:

2.

5. The method for preparing a DNT hydrogenation-coupling by-product based nitrogen self-doped Ni / C catalyst according to claim 1, characterized in that: In step (3), the pyrolysis reaction is performed at a heating rate of 5-15 ℃ / min to 550-650 ℃, and then kept at a constant temperature for 3-5 h.

6. The method for preparing a DNT hydrogenation-coupling by-product based nitrogen self-doped Ni / C catalyst according to claim 1, characterized in that: In step (4), the mass ratio of the nitrogen-doped porous carbon material to deionized water is 1:30-1:40, and the aqueous solution of the soluble nickel salt is prepared by mixing the soluble nickel salt and deionized water at a mass ratio of 1:5-1:

10.

7. The method for preparing a DNT hydrogenation by-product based nitrogen self-doped Ni / C catalyst according to claim 1, characterized in that: The soluble nickel salt is nickel nitrate; the loading amount is 30-50% based on the mass of the nitrogen-doped porous carbon material.

8. The method for preparing a DNT hydrogenation-coupling by-product based nitrogen self-doped Ni / C catalyst according to claim 1, characterized in that: In step (5), the soluble carbonate is sodium carbonate.

9. A high-activity Ni / C catalyst prepared by the method of any one of claims 1-8, wherein the loading amount of nickel is 40-60 wt.%.

10. Use of the high-activity Ni / C catalyst of claim 9 in catalyzing the DNT hydrogenation reaction to prepare TDA, wherein the catalyzing method is as follows: the high-activity Ni / C catalyst, DNT, and deionized water are added into a high-pressure reaction kettle at a ratio of (300-600 mg):(3-6 g):(200-400 mL) under a hydrogen atmosphere at a temperature of 100-130 °C and a pressure of 2-3 MPa, and the stirring rate is controlled at 800-1200 r / min to perform the catalytic hydrogenation reduction reaction.

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