Single-atom dispersed ni-n-c catalyst, and preparation method and application thereof

Abstract

The application provides a single-atom dispersed Ni-N-C catalyst and a preparation method and application thereof, and the preparation method comprises the following steps: (1) mixing a nickel salt solution and an organic precursor solution, and then performing a crystallization reaction to obtain a catalyst precursor; (2) sequentially performing first calcination and second calcination on the catalyst precursor in step (1) to obtain the Ni-N-C catalyst; and the first calcination is performed in an ammonia atmosphere. Through the coordination anchoring effect of the organic precursor, the catalyst precursor is obtained after the crystallization reaction, and then the Ni-N-C catalyst is prepared by sequentially performing calcination in an ammonia atmosphere and calcination in an inert atmosphere, more active sites are exposed, the prepared catalyst has high dispersity, the active centers are uniformly distributed and single-atom dispersed, and the activity and stability of the catalyst are improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of catalysts, in particular to the technical field of preparation of a selective hydrogenation catalyst for maleic anhydride, and particularly relates to a monatomic dispersion Ni-N-C catalyst and a preparation method and application thereof. BACKGROUND

[0002] Succinic anhydride is an important intermediate in the chemical, pharmaceutical and food industries, and is also an important raw material for biodegradable plastic polybutylene succinate (PBS). At present, succinic anhydride production mainly uses succinic acid dehydration route and maleic anhydride direct hydrogenation route. At present, there is only one industrialization case with a production capacity of 10,000 tons.

[0003] In the succinic acid dehydration route, succinic anhydride is easy to carbonize, the product quality is poor, and the production cost is high; the maleic anhydride direct hydrogenation method is the most promising method for producing succinic anhydride at present. The key to preparing succinic anhydride by hydrogenation of maleic anhydride is to avoid the hydrogenation of C=O double bond, and to control the reaction substrate at the C=C double bond hydrogenation stage; the dispersion degree of the active center of the catalyst determines the selectivity of C=C and C=O double bond, and the aggregation of the active center is conducive to the generation of γ-butyrolactone, and good dispersion of the active center is conducive to the improvement of the selectivity of succinic anhydride. At the same time, γ-butyrolactone is generated as a byproduct, which causes succinic anhydride to react with water to generate succinic acid, which causes the loss of the active center of the catalyst in an acidic environment, which is not conducive to the stable operation of the catalyst.

[0004] Feng et al. obtained Ni single element with a wide particle size distribution (8-313 nm) by reducing nickel acetate with hydrazine hydrate, and investigated the performance of maleic anhydride hydrogenation, and found that the C=C hydrogenation rate increased with the decrease of the size of the Ni single element. CN107597159A discloses a catalyst for preparing succinic anhydride by hydrogenation of maleic anhydride and a preparation method thereof, which uses non-oxide mesoporous carbon silicon as the carrier of the Ni-based catalyst, improves the dispersion degree of the Ni center, prevents the growth and aggregation of nickel metal particles, has good activity and stability, and in the catalytic hydrogenation, the conversion rate of maleic anhydride is greater than 97%, and the selectivity of succinic anhydride is greater than 98%, but the reaction conditions of this scheme are harsh, the succinic anhydride is not completely converted, the catalyst activity is insufficient, and the stability of the catalyst is not mentioned. Therefore, it is of wide prospect to design and prepare a hydrogenation catalyst with high activity, high dispersity and stability for preparing succinic anhydride by hydrogenation of maleic anhydride.

[0005] Due to the low activity of traditional transition metal catalysts and the easy aggregation and leaching of metal nanoparticles, the active components are prone to loss, and the catalyst has a low service life. In recent years, atomically dispersed transition metal / nitrogen-doped carbon (M-N-C) materials have become a hot topic in catalysis research. Compared with heterogeneous catalysts containing metal nanoparticles, atomically dispersed M-N-C catalysts have the highest atom utilization rate, effective active sites and satisfactory catalytic activity and stability, and therefore have better catalytic performance.

[0006] Therefore, it is an urgent problem for those skilled in the art to design and prepare an atomically dispersed M-N-C catalyst with high stability and high activity, and to use it to prepare succinic anhydride by high-selectivity hydrogenation of maleic anhydride. SUMMARY

[0007] The purpose of the present application is to provide a single-atom-dispersed Ni-N-C catalyst and its preparation method and application. By the coordination anchoring effect of the organic precursor, a Ni-N-C catalyst with high dispersity, uniform active center distribution and single-molecule dispersion is prepared, and the activity and stability of the catalyst are improved.

[0008] To achieve the purpose of the present application, the following technical solutions are adopted:

[0009] In a first aspect, the present application provides a preparation method of a single-atom-dispersed Ni-N-C catalyst, which comprises the following steps:

[0010] (1) mixing a nickel salt solution and an organic precursor solution, and then performing a crystallization reaction to obtain a catalyst precursor;

[0011] (2) sequentially performing first calcination and second calcination on the catalyst precursor of step (1) to obtain the Ni-N-C catalyst;

[0012] The first calcination is performed in an ammonia atmosphere.

[0013] The preparation method of the present application uses the coordination anchoring effect of the organic precursor to obtain a catalyst precursor after a crystallization reaction, and then sequentially performs calcination in an ammonia atmosphere and calcination in an inert atmosphere to obtain a Ni-N-C catalyst with high dispersity, uniform active center distribution and single-atom dispersion. At the same time, the catalyst has high activity and excellent catalytic stability.

[0014] It is worth noting that the organic precursor selected in the present application has a strong coordination effect with the metal, can form a relatively strong framework, reduces the loss of active centers, and improves the service life of the catalyst. Subsequent calcination in an ammonia atmosphere increases the surface defects of the catalyst, exposes more active sites, and further improves the catalyst activity.

[0015] As a preferred technical solution of the present application, the molar ratio of the nickel salt to the organic precursor in step (1) is 1:(3-15), which can be 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, or 1:14, etc., but is not limited to the listed values, and other values not listed in the above range are also applicable, and the preferred value is 1:9.

[0016] It is worth noting that the present application controls the molar ratio of the nickel salt to the organic precursor in the range of 1:(3-15), taking into account the coordination number of Ni, improving the utilization rate of Ni salt, reducing the amount of free Ni in the system, and avoiding the decline of catalyst activity.

[0017] Preferably, the concentration of the nickel salt solution in step (1) is 2-8wt%, which can be 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt%, 5.5wt%, 6wt%, 6.5wt%, 7wt%, or 7.5wt%, etc., but is not limited to the listed values, and other values not listed in the above range are also applicable, and the preferred value is 3wt%.

[0018] Preferably, the concentration of the organic precursor solution in step (1) is 10-40wt%, which can be 12wt%, 15wt%, 17wt%, 20wt%, 22wt%, 25wt%, 27wt%, 30wt%, 32wt%, 35wt%, or 37wt%, etc., but is not limited to the listed values, and other values not listed in the above range are also applicable.

[0019] As a preferred technical solution of the present application, the nickel salt in the nickel salt solution in step (1) includes any one or a combination of at least two of nickel nitrate, nickel chloride, nickel bromide, nickel sulfamate, or nickel acetate, wherein a typical but non-limiting combination is a combination of nickel nitrate and nickel chloride, a combination of nickel bromide and nickel sulfamate, or a combination of nickel sulfamate and nickel acetate, etc., and the preferred one is nickel nitrate.

[0020] Preferably, the solvent in the nickel salt solution in step (1) includes any one or a combination of at least two of water, methanol, ethanol, propanol, acetone, or N,N-dimethylformamide (DMF), and the preferred one is ethanol.

[0021] Preferably, the organic precursor in the organic precursor solution in step (1) includes any one or a combination of at least two of alanine, ethylenediaminetetraacetic acid, bipyridine, 2-methylimidazole, porphyrin, cyclohexanediamine, o-phenylenediamine, hexanediamine, or dicarboxyimidazole, wherein a typical but non-limiting combination is a combination of alanine and ethylenediaminetetraacetic acid, a combination of bipyridine and 2-methylimidazole, or a combination of hexanediamine and dicarboxyimidazole, etc., and the preferred ones are 2-methylimidazole or dicarboxyimidazole.

[0022] It is worth mentioning that when the organic precursor of the present application is selected as 2-methyl imidazole or dicarboxy imidazole, it has a certain basicity due to the pyridine nitrogen, which can realize the regulation of the surface acid-base of the catalyst and help to improve the selectivity of the hydrogenation of maleic anhydride. The organic precursor of the present application is most preferably dicarboxy imidazole, because when using dicarboxy imidazole for coordination, the advantage of stronger coordination ability of O and Ni is utilized, and the prepared catalyst has the best stability.

[0023] Preferably, the solvent in the organic precursor solution of step (1) includes any one or a combination of at least two of water, methanol, ethanol, propanol, acetone or N,N-dimethylformamide, and is preferably ethanol.

[0024] As a preferred technical solution of the present application, the temperature of the crystallization reaction of step (1) is 80-140℃, for example, it can be 90℃, 100℃, 110℃, 120℃, 130℃ or 135℃, etc., but it is not limited to the listed values, and other values not listed in the above value range are also applicable, and the preferred temperature is 120℃.

[0025] It is worth mentioning that by controlling the crystallization reaction temperature in the range of 80-140℃, if the crystallization reaction temperature is too low, the crystallization is not complete, and a large amount of unreacted raw materials are contained, which leads to the decrease of the catalytic activity of the catalyst; if the crystallization reaction temperature is too high, the nucleation rate is too fast and the grain size is too small, which leads to the decrease of the catalytic activity of the catalyst.

[0026] Preferably, the crystallization reaction time of step (1) is 4-24h, for example, it can be 6h, 8h, 10h, 12h, 15h, 17h, 20h or 22h, etc., but it is not limited to the listed values, and other values not listed in the above value range are also applicable, and the preferred time is 10h.

[0027] As a preferred technical solution of the present application, after the crystallization reaction of step (1), the reaction liquid is cooled to room temperature, and then ultrasonic treatment, washing, centrifugation and drying are sequentially performed.

[0028] Preferably, the drying includes vacuum drying, and the drying temperature is 50-70℃, for example, it can be 52℃, 55℃, 57℃, 60℃, 62℃, 65℃ or 67℃, etc., but it is not limited to the listed values, and other values not listed in the above value range are also applicable, and the preferred temperature is 60℃.

[0029] Preferably, the first roasting in step (2) is performed at a temperature of 200-450℃, for example, 220℃, 240℃, 260℃, 280℃, 300℃, 320℃, 340℃, 360℃, 380℃, 400℃ or 420℃, but not limited to the listed values, and other values not listed in the above range are also applicable, and preferably 300-350℃.

[0030] Preferably, the first roasting in step (2) is performed for 1-4h, for example, 1.5h, 2h, 2.5h, 3h, 3.5h or 3.7h, but not limited to the listed values, and other values not listed in the above range are also applicable, and preferably 2h.

[0031] It is worth noting that by controlling the first roasting temperature in the range of 200-450℃, if the first roasting temperature is too low, the reaction rate is too slow, the carbon framework etching is less, and the catalytic performance of the catalyst is slightly reduced; if the first roasting temperature is too high, the ammonia etching is excessive, resulting in a decrease in the catalytic performance of the catalyst.

[0032] In the present application, the flow rate of ammonia gas introduced per gram of catalyst precursor during the first roasting process is 50-100mL / min, for example, 60mL / min, 65mL / min, 70mL / min, 75mL / min, 80mL / min, 85mL / min, 90mL / min or 95mL / min, but not limited to the listed values.

[0033] In the present application, as long as the flow rate of ammonia gas introduced during the first roasting process can meet the amount of etching the catalyst precursor, the skilled person can adjust it according to the actual situation.

[0034] Preferably, the second roasting in step (2) is performed in an inert atmosphere.

[0035] Preferably, the inert atmosphere comprises nitrogen and / or argon.

[0036] Preferably, the second roasting in step (2) is performed at a temperature of 500-800℃, for example, 550℃, 600℃, 650℃, 700℃, 750℃ or 770℃, but not limited to the listed values, and other values not listed in the above range are also applicable, and preferably 650-750℃.

[0037] Preferably, the holding time of the second calcination in step (2) is 3-9 h, for example, it can be 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, 6 h, 6.5 h, 7 h, 7.5 h, 8 h or 8.5 h, etc., but not limited to the listed values, other values not listed in the above value range are also applicable, preferably 4-6 h.

[0038] In the present application, the catalyst after the second calcination in step (2) is cooled to room temperature in the furnace.

[0039] As a preferred technical solution of the present application, the preparation method comprises the following steps:

[0040] (1) mixing a nickel salt solution with a concentration of 2-8 wt% and an organic precursor solution with a concentration of 10-40 wt%, then performing a crystallization reaction at 80-140 ℃ for 4-24 h, cooling the reaction solution to room temperature, and then sequentially performing ultrasonic treatment, washing, centrifugation and drying to obtain a catalyst precursor;

[0041] wherein the molar ratio of the nickel salt to the organic precursor is 1:(3-15); the nickel salt includes any one or a combination of at least two of nickel nitrate, nickel chloride, nickel bromide, nickel sulfamate or nickel acetate; the organic precursor includes any one or a combination of at least two of alanine, ethylenediaminetetraacetic acid, bipyridine, 2-methylimidazole, porphyrin, cyclohexanediamine, o-phenylenediamine, hexanediamine or dicarboxyimidazole;

[0042] (2) performing first calcination on the catalyst precursor in step (1) in an ammonia atmosphere at a temperature of 200-450 ℃ for 1-4 h, and then performing second calcination in an inert atmosphere at a temperature of 500-800 ℃ for 3-9 h to obtain the Ni-N-C catalyst.

[0043] In a second aspect, the present application provides a single-atom dispersed Ni-N-C catalyst, which is prepared by the preparation method of the first aspect.

[0044] The Ni in the Ni-N-C catalyst is dispersed at a single-atom level;

[0045] The mass percentage of Ni in the Ni-N-C catalyst is 4 wt%-9.5 wt%, for example, it can be 4.5 wt%, 5 wt%, 5.5 wt%, 6 wt%, 6.5 wt%, 7.5 wt%, 8 wt%, 8.5 wt% or 9 wt%, etc., but not limited to the listed values, other values not listed in the above value range are also applicable.

[0046] The prepared Ni-N-C catalyst has a single-atom dispersed active center, high activity, stability and selectivity, slow catalyst deactivation during use, can be stored in an air atmosphere, and does not need to be activated before use, and has a good application prospect.

[0047] In a third aspect, the application provides an application of the Ni-N-C catalyst of the second aspect, which is used for a hydrogenation reaction, preferably maleic anhydride hydrogenation reaction.

[0048] The prepared Ni-N-C catalyst is mainly applied to kettle type maleic anhydride hydrogenation, has excellent raw material conversion rate and product selectivity, and the molding process of the catalyst can be extended by a person skilled in the art to expand its application in fixed bed reaction.

[0049] The numerical range described in the application includes not only the point values listed above, but also any point values between the above numerical ranges that are not listed, and the specific point values included in the range are not listed in the application due to the length and the consideration of simplicity.

[0050] Compared with the prior art, the application has the following beneficial effects:

[0051] (1) The preparation method provided by the application exposes more active sites through coordination anchoring of organic precursors, crystallization reaction to obtain a catalyst precursor, and then calcination under ammonia gas atmosphere and calcination under inert gas atmosphere to obtain the Ni-N-C catalyst, and the prepared catalyst has high dispersion, uniform active center distribution and single-atom dispersion.

[0052] (2) The Ni-N-C catalyst has high activity, stability and selectivity, slow catalyst deactivation during use, can be stored in an air atmosphere, and does not need to be activated before use, and when used for maleic anhydride hydrogenation reaction, the conversion rate of maleic anhydride is above 99.9%, the selectivity of succinic anhydride product is above 99.1%, and after 12 cycles, the conversion rate of maleic anhydride is still above 98.9%, and the selectivity of succinic anhydride product is still above 99.1%. BRIEF DESCRIPTION OF DRAWINGS

[0053] Fig. 1 STEM image (200 nm) of the Ni-N-C catalyst prepared in Example 2 of the application;

[0054] Fig. 2 STEM image (2 nm) of the Ni-N-C catalyst prepared in Example 2 of the application. DETAILED DESCRIPTION

[0055] The technical solutions of the present application are further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments are only used to help understand the present application and should not be regarded as specific limitations on the present application.

[0056] Example 1

[0057] The present embodiment provides a preparation method of a single-atom dispersed Ni-N-C catalyst, which comprises the following steps:

[0058] (1) 29.1 g of nickel nitrate hexahydrate (0.1 mol) was placed in 550 g of 95% ethanol at 25°C and ultrasonically dissolved until completely dissolved to obtain a nickel salt solution A; 73.8 g of 2-methylimidazole (0.9 mol) was dissolved in 300 g of 95% ethanol at 25°C to obtain a precursor solution B; then the nickel salt solution A was added to the precursor solution B at 25°C, and after mixing, it was transferred to a reaction kettle, followed by a crystallization reaction at 120°C for 10 h, and then the reaction liquid was cooled to room temperature, followed by ultrasonic treatment, washing, centrifugation, and finally drying in a vacuum drying oven at 60°C to constant weight to obtain a catalyst precursor;

[0059] (2) The catalyst precursor of step (1) was subjected to first calcination in an ammonia atmosphere at a temperature of 300°C for 2 h, and then second calcination in a nitrogen atmosphere at a temperature of 750°C for 6 h to obtain the Ni-N-C catalyst (the Ni content was 5.9 wt% as measured by ICP quantification based on the catalyst), which was denoted as catalyst A.

[0060] Example 2

[0061] The present embodiment provides a preparation method of a single-atom dispersed Ni-N-C catalyst, which comprises the following steps:

[0062] The present embodiment obtained a Ni-N-C catalyst (the Ni content was 9.1 wt% as measured by ICP quantification based on the catalyst), which was denoted as catalyst B.

[0063] The STEM electron microscope image of the Ni-N-C catalyst prepared in the present embodiment is shown in Figs. 1-2 As can be seen from the figure, the prepared Ni-N-C catalyst is a high-dispersion Ni catalyst, and the STEM data proves the existence of single-point Ni.

[0064] Example 3

[0065] This embodiment provides a method for preparing a single-atom dispersed Ni-NC catalyst, except that step (1) is adjusted as follows: 29.1 g of nickel nitrate hexahydrate (0.1 mol) is placed in 550 g of 95% ethanol at 25 °C and sonicated until completely dissolved to obtain nickel salt solution A; 102.6 g of cyclohexanediamine (0.9 mol) is dissolved in 300 g of 95% ethanol at 25 °C to obtain precursor solution B; all other conditions are the same as in Example 1.

[0066] The Ni-NC catalyst obtained in this embodiment (based on the catalyst, the Ni content was quantitatively determined by ICP to be 5.8 wt%), denoted as catalyst C.

[0067] Example 4

[0068] This embodiment provides a method for preparing a single-atom dispersed Ni-NC catalyst, except that step (1) is adjusted as follows: 29.1 g of nickel nitrate hexahydrate (0.1 mol) is placed in 550 g of 95% ethanol at 25 °C and sonicated until completely dissolved to obtain nickel salt solution A; 140.6 g of bipyridine (0.9 mol) is dissolved in 300 g of 95% ethanol at 25 °C to obtain precursor solution B; all other conditions are the same as in Example 1.

[0069] The Ni-NC catalyst obtained in this embodiment (based on the catalyst, the Ni content was quantitatively determined by ICP to be 4.3 wt%), denoted as catalyst D.

[0070] Example 5

[0071] This embodiment provides a method for preparing a single-atom dispersed Ni-NC catalyst, except that step (1) is adjusted as follows: 17.7 g of nickel acetate (0.1 mol) is placed in 550 g of 95% ethanol at 25 °C and sonicated until completely dissolved to obtain nickel salt solution A; 73.8 g of 2-methylimidazole (0.9 mol) is dissolved in 300 g of 95% ethanol at 25 °C to obtain precursor solution B; all other conditions are the same as in Example 1.

[0072] The Ni-NC catalyst obtained in this embodiment (based on the catalyst, the Ni content was quantitatively determined by ICP to be 7.8 wt%), denoted as catalyst E.

[0073] Example 6

[0074] This embodiment provides a method for preparing a single-atom dispersed Ni-NC catalyst. Except for the molar ratio of nickel nitrate hexahydrate to 2-methylimidazole in step (1) being 1:2, all other conditions are the same as in Example 1.

[0075] The Ni-NC catalyst obtained in this embodiment (based on the catalyst, the Ni content was quantitatively determined by ICP to be 6.3 wt%), denoted as catalyst F.

[0076] Example 7

[0077] This embodiment provides a method for preparing a single-atom dispersed Ni-NC catalyst. Except for the molar ratio of nickel nitrate hexahydrate to 2-methylimidazole in step (1) being 1:18, all other conditions are the same as in Example 1.

[0078] The Ni-NC catalyst obtained in this embodiment (based on the catalyst, the Ni content was quantitatively determined by ICP to be 2.9 wt%), denoted as catalyst G.

[0079] Example 8

[0080] This embodiment provides a method for preparing a single-atom dispersed Ni-NC catalyst. Except for the crystallization reaction temperature of 60°C in step (1), all other conditions are the same as in Example 1.

[0081] The catalyst obtained in this embodiment is a Ni-NC catalyst, denoted as catalyst H.

[0082] Example 9

[0083] This embodiment provides a method for preparing a single-atom dispersed Ni-NC catalyst. Except for the crystallization reaction temperature of 180°C in step (1), all other conditions are the same as in Example 1.

[0084] The Ni-NC catalyst obtained in this embodiment is denoted as catalyst I.

[0085] Example 10

[0086] This embodiment provides a method for preparing a single-atom dispersed Ni-NC catalyst. Except for the first calcination temperature of 150°C in step (2), all other conditions are the same as in Example 1.

[0087] The Ni-NC catalyst obtained in this embodiment is denoted as catalyst J.

[0088] Example 11

[0089] This embodiment provides a method for preparing a single-atom dispersed Ni-NC catalyst. Except for the first calcination temperature of 550°C in step (2), all other conditions are the same as in Example 1.

[0090] The catalyst obtained in this embodiment is a Ni-NC catalyst, denoted as catalyst K.

[0091] Example 12

[0092] This embodiment provides a method for preparing a single-atom dispersed Ni-NC catalyst. Except for the second calcination temperature of 400°C in step (2), all other conditions are the same as in Example 1.

[0093] The catalyst obtained in this embodiment is a Ni-NC catalyst, denoted as catalyst L.

[0094] Example 13

[0095] This embodiment provides a method for preparing a single-atom dispersed Ni-NC catalyst. Except for the second calcination temperature of 900°C in step (2), all other conditions are the same as in Example 1.

[0096] The Ni-NC catalyst obtained in this embodiment is denoted as catalyst M.

[0097] Comparative Example 1

[0098] This comparative example provides a method for preparing a single-atom dispersed Ni-NC catalyst. Except for the first calcination in step (2) being carried out in a nitrogen atmosphere, all other conditions are the same as in Example 1.

[0099] The catalyst obtained in this comparative example is Ni-NC catalyst, denoted as catalyst N.

[0100] Comparative Example 2

[0101] This comparative example provides a method for preparing a single-atom dispersed Ni-NC catalyst. Except for the absence of a first calcination in step (2), all other conditions are the same as in Example 1.

[0102] The catalyst obtained in this comparative example is a Ni-NC catalyst, denoted as catalyst O.

[0103] Comparative Example 3

[0104] This comparative example provides a method for preparing a single-atom dispersed Ni-NC catalyst. Except for the absence of a first calcination in step (2), all other conditions are the same as in Example 2.

[0105] The catalyst obtained in this comparative example is a Ni-NC catalyst, denoted as catalyst P.

[0106] The Ni-NC catalysts prepared in the above examples and comparative examples are used in the hydrogenation reaction of maleic anhydride to prepare succinic anhydride. The application methods include:

[0107] 40g of maleic anhydride, 160g of tetrahydrofuran (after redistilling to remove water) and 2g of freshly prepared Ni-NC catalyst were weighed and placed in a 500mL high-pressure reactor. The reaction was stopped after 6h at a hydrogen pressure of 2MPa and 90℃. The hydrogenated reaction solution was sampled and subjected to GC analysis. The conversion rate of the raw materials and the selectivity of the products were then calculated. The evaluation results are shown in Table 1.

[0108] Table 1

[0109]

[0110]

[0111] As can be seen from Table 1:

[0112] (1) The single-atom dispersed Ni-NC catalyst prepared by the preparation method provided in Examples 1-2 of the present invention has excellent catalytic performance in the hydrogenation reaction of maleic anhydride, with a conversion rate of maleic anhydride of more than 99.9% and a selectivity of succinic anhydride of more than 99.1%.

[0113] (2) Comparing Examples 1 and 3-4, it can be seen that using 2-methylimidazolium or dicarboxyimidazole as organic precursors, because imidazolium can form stable metal imidazolium complexes, the catalyst activity is significantly improved compared to that prepared using cyclohexanediamine and bipyridine as organic precursors; Comparing Examples 1 and 5, it can be seen that when the nickel salt is changed from nickel nitrate to nickel acetate, the poor crystallinity of nickel acetate and the disordered crystallization caused by acetate ions lead to a significant decrease in the activity of the prepared catalyst;

[0114] (3) Comparing Examples 1 and 6-7, it can be seen that when the amount of 2-methylimidazole is too small, a large amount of free Ni does not enter the framework and some of it is precipitated and covers the active center, resulting in a slight decrease in the activity of the prepared catalyst; when the amount of 2-methylimidazole is too large, the Ni content of the active center is reduced, resulting in a significant decrease in the activity of the prepared catalyst.

[0115] (4) Comparing Examples 1 and 8-9, it can be seen that when the crystallization reaction temperature is below 80°C, the catalyst activity decreases due to incomplete crystallization and the presence of a large amount of unreacted raw materials; when the crystallization reaction temperature is above 140°C, the catalyst activity decreases due to excessively fast nucleation rate and small crystal size.

[0116] (5) Comparing Examples 1 and 10-11, it can be seen that when the temperature of the first calcination is below 200°C, the activity of the prepared catalyst decreases slightly due to insufficient etching; when the temperature of the first calcination is above 450°C, the activity of the prepared catalyst decreases due to excessive etching of the skeleton; comparing Examples 1 and 12-13, it can be seen that when the temperature of the second calcination is below 500°C, the activity of the prepared catalyst decreases due to the failure to form a stable carbon skeleton; when the temperature of the second calcination is above 800°C, the catalyst activity does not change significantly, but the production cost increases. Therefore, an excessively high second calcination temperature is not required.

[0117] (6) Comparison of Examples 1-2 and Comparative Examples 2-3 shows that if the first calcination is not carried out in an ammonia atmosphere, the product conversion rate of the catalyst decreases. After etching with ammonia, some of the C skeleton is etched and the active center is exposed, which significantly improves the catalytic activity of the catalyst.

[0118] Catalysts A and B prepared in Examples 1-2 were subjected to cycle performance tests to verify their cycle life. The evaluation methods included:

[0119] 40g of maleic anhydride, 160g of tetrahydrofuran (after redistilling to remove water) and 2g of reusable Ni-NC catalyst (after centrifugation) were weighed and placed in a 500mL high-pressure reactor. The reaction was stopped after 6h at a hydrogen pressure of 2MPa and 90℃. The hydrogenated reaction solution was sampled and subjected to GC analysis. The feed conversion rate and product selectivity before and after the cycle were compared. The evaluation results of catalyst A and catalyst B are shown in Table 2 and Table 3, respectively.

[0120] Table 2

[0121]

[0122] Table 3

[0123]

[0124] As can be seen from Tables 2 and 3:

[0125] (1) The catalyst prepared in this application exhibits excellent stability and cycling performance. After 12 cycles, the conversion rate of maleic anhydride is still above 98.9%, and the selectivity of succinic anhydride is above 99.1%, which still has a high feed conversion rate and product selectivity.

[0126] (2) Compared with the traditional methylimidazolium support, the catalyst B prepared by using carboxyimidazolium for coordination has better stability due to the stronger coordination ability of O and Ni.

[0127] The applicant declares that the detailed structural features of the present invention are illustrated through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the components selected in the present invention, additions of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0128] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0129] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable way without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0130] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A process for the preparation of a monolitic dispersed Ni-N-C catalyst, characterized in that, The preparation method comprises the following steps: (1) mixing a nickel salt solution and an organic precursor solution, and then performing a crystallization reaction to obtain a catalyst precursor; The nickel salt in the nickel salt solution comprises any one or a combination of at least two of nickel nitrate, nickel chloride, nickel bromide, and nickel sulfamate; The organic precursor in the organic precursor solution comprises any one or a combination of at least two of alanine, ethylenediaminetetraacetic acid, bipyridine, 2-methylimidazole, porphyrin, cyclohexanediamine, o-phenylenediamine, hexanediamine, or dicarboxyimidazole; The molar ratio of the nickel salt to the organic precursor is 1:(3-15); The temperature of the crystallization reaction is 80-140 DEG C; (2) sequentially performing first calcination and second calcination on the catalyst precursor in step (1) to obtain the Ni-N-C catalyst; The first calcination is performed in an ammonia atmosphere, the temperature is 200-450 DEG C, and the holding time is 1-4 h; The temperature of the second calcination is 500-800 DEG C, and the holding time is 3-9 h.

2. The production method according to claim 1, characterized by, The concentration of the nickel salt solution in step (1) is 2-8 wt%.

3. The preparation method according to claim 1, characterized in that, The concentration of the organic precursor solution in step (1) is 10-40 wt%.

4. The method of claim 1, wherein, The solvent in the nickel salt solution in step (1) comprises any one or a combination of at least two of water, methanol, ethanol, propanol, acetone, or N,N-dimethylformamide.

5. The preparation method according to claim 4, characterized in that, The solvent in the nickel salt solution in step (1) comprises ethanol.

6. The method of claim 1, wherein, The organic precursor in the organic precursor solution in step (1) comprises 2-methylimidazole or dicarboxyimidazole.

7. The preparation method according to claim 1, characterized in that, The solvent in the organic precursor solution in step (1) comprises any one or a combination of at least two of water, methanol, ethanol, propanol, acetone, or N,N-dimethylformamide.

8. The production method according to claim 7, characterized by, The solvent in the organic precursor solution in step (1) comprises ethanol.

9. The method of claim 1, wherein, The time of the crystallization reaction in step (1) is 4-24 h.

10. The method of claim 1, wherein, After the crystallization reaction in step (1), the reaction liquid is cooled to room temperature, and then sequentially subjected to ultrasonic treatment, washing, centrifugation, and drying.

11. The method of claim 10, wherein, The drying comprises vacuum drying, and the temperature of the drying is 50-70 DEG C.

12. The method of claim 1, wherein, The temperature of the first calcination in step (2) is 300-350 DEG C.

13. The method of claim 1, wherein, The second calcination in step (2) is performed in an inert atmosphere.

14. The method of claim 13, wherein, The inert atmosphere comprises nitrogen and / or argon.

15. The method of claim 1, wherein, The temperature of the second calcination in step (2) is 650-750 DEG C.

16. The method of claim 1, wherein, The holding time of the second calcination in step (2) is 4-6 h.

17. The method of claim 1, wherein, The preparation method comprises the following steps: (1) mixing a nickel salt solution with a concentration of 2-8 wt% and an organic precursor solution with a concentration of 10-40 wt%, and then performing a crystallization reaction at 80-140 DEG C for 4-24 h, cooling the reaction liquid to room temperature, and then sequentially performing ultrasonic treatment, washing, centrifugation, and drying to obtain a catalyst precursor; The molar ratio of the nickel salt to the organic precursor is 1:(3-15); the nickel salt comprises any one or a combination of at least two of nickel nitrate, nickel chloride, nickel bromide, and nickel sulfamate; and the organic precursor comprises any one or a combination of at least two of alanine, ethylenediaminetetraacetic acid, bipyridine, 2-methylimidazole, porphyrin, cyclohexanediamine, o-phenylenediamine, hexanediamine, or dicarboxyimidazole. (2) The catalyst precursor in step (1) is subjected to first calcination in an ammonia atmosphere at a temperature of 200-450 DEG C and isothermal for 1-4 h, and then is subjected to second calcination in an inert atmosphere at a temperature of 500-800 DEG C and isothermal for 3-9 h, to obtain the Ni-N-C catalyst.

18. A monolitically dispersed Ni-N-C catalyst characterized in that, The Ni-N-C catalyst is prepared by the method in any one of claims 1-17. In the Ni-N-C catalyst, Ni is monatomicly dispersed. In the Ni-N-C catalyst, the mass percentage of Ni is 4wt%-9.5wt%.

19. Use of the Ni-N-C catalyst of claim 18, characterized in that, The Ni-N-C catalyst is used for hydrogenation reaction.

20. Use of the Ni-N-C catalyst of claim 19, characterized in that, The Ni-N-C catalyst is used for hydrogenation reaction of dicyclohexanedicarboxylic anhydride.

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