A heterogeneous cobalt-based catalyst, its preparation method and application

Abstract

The present invention discloses a heterogeneous cobalt-based catalyst, a preparation method thereof and an application thereof. The cobalt-based catalyst comprises a carrier and an active component. The active component is a cobalt species, and the carrier is a carbon nitride carrier formed by calcining a zeolitic imidazolate framework material. The present invention obtains the heterogeneous cobalt-based catalyst by first synthesizing a precursor of the zeolitic imidazolate framework material and then through a calcination and reduction process. In the catalyst of the present invention, the cobalt species exist in the form of cobalt nanoparticles, which can promote the hydroformylation of ethylene oxide to highly selectively generate methyl 3-hydroxypropionate. When the catalyst is used in the heterogeneous hydroformylation of ethylene oxide, it has the advantages of mild reaction conditions, high selectivity for methyl 3-hydroxypropionate, high stability, easy separation and recovery, etc.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, and relates to a catalyst for the hydroformylation reaction of ethylene oxide, in particular to a Co-based catalyst for heterogeneous hydroformylation reaction of ethylene oxide, and its preparation method and application. Background Art

[0002] 1,3-propanediol (1,3-PDO) is an important chemical raw material, which is widely used in industries closely related to people's lives, such as food, clothing, and daily chemicals. At present, its most important use is to synthesize polytrimethylene terephthalate (PTT). PTT has a wide range of applications, and the market demand will continue to rise. It is estimated that the market demand for PTT may reach about 1.1 million tons in the next few years. At present, domestic enterprises cannot directly polymerize PTT resins with high intrinsic viscosity, and the product performance is poor. Moreover, due to the fact that 1,3-propanediol depends on imports, PTT products do not have a price advantage. Therefore, it is urgent to develop domestic PTT products and independently and efficiently synthesize 1,3-propanediol.

[0003] The reaction principle of synthesizing 1,3 - propanediol from ethylene oxide involves two key steps: the carbonylation of ethylene oxide to methyl 3 - hydroxypropionate and the hydrogenation of methyl 3 - hydroxypropionate. Among them, the hydroformylation of ethylene oxide to methyl 3 - hydroxypropionate is the key affecting the formation of 1,3 - propanediol. The hydroformylation reaction of ethylene oxide is not easy to occur thermodynamically. Researchers reduce the temperature and pressure required for the direct synthesis route and improve the selectivity and yield of 1,3 - propanediol through catalyst design and reaction mechanism research. In 2001, Shell, Samsung, and the Korea Research Institute of Chemical Technology (Patent US 0099245) completely proposed the idea of preparing 1,3 - propanediol from ethylene oxide, dividing the process into two sections. The first half is the hydroformylation of EO, and the second half is the hydrogenation of 3 - HPM. This process first proposed the use of the 3 - HPM route to achieve the conversion of EO to 1,3 - PDO, effectively avoiding the generation of unstable intermediate HPA. However, the Co2(CO)8 catalyst with 1,10 - phenanthroline as the ligand mentioned in the patent cannot efficiently catalyze the conversion of EO to 3 - HPM, and the conversion rate is only 11%, leaving much room for improvement. Currently, the catalysts for the hydroformylation of ethylene oxide are mainly homogeneous Co - based and Rh - based catalysts, especially cobalt - nitrogen complex homogeneous catalysts. In 2003, Samsung Electronics Co., Ltd. (Patent CN 1412173) proposed an improved scheme based on the Shell patent, proposing the use of imidazole, pyridine, pyrrole, pyrazine, pyrazole, pyrimidine, piperidine and their derivatives as promoters, with the molar ratio of cobalt catalyst to promoter between 1:0 - 1:100 (mol / mol), and the solvent being ether compounds, substituted aromatic compounds, acetate compounds, carbonate compounds or alcohols. At the same time, it proposed an improvement in the process of separating carbonylation products using stable gases (CO, He, N2, H2, CO2, etc.) in a back - extraction column. The temperature range of the back - extraction column is between - 30 ~ 200 °C, and it has a better effect at 10 ~ 120 °C. The conversion rate of the epoxide can reach 98%, and the selectivity is 91.9%. The main by - products are dimethyl acetal (DMA), acetaldehyde (AA), methoxyethanol (ME), etc. Although cobalt complexes can achieve the hydroformylation process of ethylene oxide, the occurrence of this reaction still requires a relatively high CO pressure, and the amount of precious metal Co catalyst used is large (≥ 4×10 -3 mol / L), and it is difficult to separate and recycle after the reaction.

[0004] Compared with homogeneous catalytic systems, heterogeneous catalysts have prominent advantages such as easy separation from products and recyclability of the catalyst. In the prior art, the activity source of Co-based heterogeneous catalysts is usually achieved through leaching, that is, by leaching Co supported on the carrier into the solvent, and then realizing the hydroformylation reaction of ethylene oxide. For example, Akiyuki Hamasaki et al. (Tetrahedron Lett. 2011, 52, 6869-6872.) synthesized carbonyl cobalt-loaded gold nanoparticles (Au / Co3O4) as a substitute for the Co2(CO)8 catalyst in the carbonylation reaction of epoxides. Au / Co3O4 is simple to prepare and continuously supplies fresh active substances during the reaction. Wang Yining et al. (Patent CN 107417527 A) developed a poly(4-vinylpyridine) (P4VP)-supported carbonyl cobalt for the hydroformylation reaction of ethylene oxide. The synthesized [P4VP][Co(CO)3] polymer catalyst was reacted for 15 h at 3 MPa for 15 h. The conversion rate of EO was 92.9%, and the selectivity was 88.5%. After 6 cycles, both the conversion rate and selectivity were above 70%. Zeng Bo et al. (Mol. Catal. 2020, 494, 111109-.) developed nitrogen-doped cobalt nanoparticles supported on a porous carrier for the hydroformylation reaction of propylene oxide in 2020. The catalyst was prepared by the pyrolysis of simple cobalt acetate, phenanthroline, and the carrier. Through XPS, XRD, and TEM characterization, it was found that the Co-N sites promoted the carbonylation activity, and the selectivity of the carbonylation product reached 93%. The good reproducibility of the catalyst was attributed to the in-situ continuous generation of active [Co(CO)4]. - of active [Co(CO)4].

[0005] The problems existing in the existing preparation methods are as follows: 1. The existing prepared catalysts rely on leaching and do not fundamentally solve the separation problem; 2. The catalytic activity effect is not good and the stability is poor. Therefore, there is a dilemma in preparing Co-based heterogeneous catalysts for the purpose of leaching to simultaneously ensure a high Co loading, good dispersion, and high stability. Therefore, it is desirable to develop a Co-based heterogeneous catalyst for the hydroformylation reaction of ethylene oxide with high ethylene oxide conversion rate, high selectivity of methyl 3-hydroxypropionate, and high stability of the reaction catalyst, achieving all three goals at the same time. Summary of the Invention

[0006] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a Co-based catalyst for heterogeneous hydroformylation reaction of ethylene oxide. The catalyst has the characteristics of mild reaction conditions, high reaction activity, high selectivity of methyl 3-hydroxypropionate, high stability, and easy separation and recovery. The preparation method has the characteristics of simple operation and high reproducibility.

[0007] The technical solution adopted by the present invention is:

[0008] A Co-based catalyst for heterogeneous ethylene oxide hydroformylation reaction, comprising a support and an active component. The support is carbon nitride formed by high-temperature calcination of zeolitic imidazolate framework material (ZIF). The active component is Co species, and the Co species exist in the form of Co nanoparticles with a size of about 4-20 nm. Zinc nitrate is used to regulate the distribution of cobalt, and the molar ratio of zinc nitrate to cobalt nitrate is between 4 and 6. Based on the total mass of the Co-C / N catalyst, the loading amount of the Co species is 6.0-15.0 wt% of the total mass of the Co-C / N catalyst, and the specific surface area of the catalyst is 500-600 m 2 / g, and the pore channels include micropores with a size of 1-2 nm and mesopores with a size of 2-4 nm.

[0009] The preparation method of the above-mentioned Co-C / N catalyst for heterogeneous ethylene oxide hydroformylation reaction comprises the following steps:

[0010] 1. Preparation of solution A: Weigh zinc nitrate and cobalt nitrate, and dissolve them in methanol solvent to obtain solution A;

[0011] 2. Preparation of solution B: Weigh 2-methylimidazole and dissolve it in methanol to obtain solution B;

[0012] Cobalt nitrate, zinc nitrate, 2-methylimidazole and the solvent methanol are all commercially available and are used directly without treatment. The molar ratio of the total amount of nitrates to 2-methylimidazole is 1:4.

[0013] Zinc nitrate is used to regulate the distribution of cobalt, and the molar ratio of zinc nitrate to cobalt nitrate is 3-9. The preferred scheme is that the molar ratio of zinc nitrate to cobalt nitrate is 4-6.

[0014] 3. Mixing: Drop solution B into solution A, and keep stirring during the dropping process. After mixing, a light purple solution is obtained, which is sealed and stored;

[0015] The stirring temperature is room temperature (20-40 °C), and the dropping rate is 1-10 mL / min.

[0016] 4. Precursor synthesis: After continuously stirring the sealed light purple solution for 10 min, let it stand for a period of time to obtain a suspension; Centrifuge the suspension to remove the solvent, and wash it three times with methanol to obtain the precursor;

[0017] The standing temperature is 20-40 °C, and the standing time is 12-72 h.

[0018] Centrifugation is carried out by a high-speed centrifuge at 8000-10000 for 10-15 min.

[0019] 5. Drying: The precursor is dried to obtain precursor powder;

[0020] Drying is carried out in an oven, and the drying method is selected from atmospheric forced-air oven drying or vacuum drying. The drying temperature is 60 °C, and the drying time is 12 - 24 h.

[0021] 6. Calcination: The catalyst precursor powder is calcined to obtain the calcined catalyst powder;

[0022] The calcination temperature is 900 - 1000 °C, the calcination atmosphere is N2 or Ar, the heating rate is 1 - 5 °C / min, and the calcination time is 2 - 3 h.

[0023] 7. Reduction: The calcined catalyst powder is placed in a reducing gas atmosphere for reduction to obtain the reduced Co-C / N catalyst powder;

[0024] The reducing atmosphere is hydrogen, the flow rate of the reducing gas is 20 - 100 mL / min, the reduction temperature is 200 - 400 °C, the heating rate is 1 - 5 °C / min, and the reduction time is 2 - 4 h.

[0025] Another object of the present invention is to provide an application of a Co-based catalyst for the heterogeneous hydroformylation of ethylene oxide. The Co-C / N catalyst is applied to the heterogeneous catalytic reaction of ethylene oxide hydroformylation to improve the stability of the catalyst for ethylene oxide hydroformylation in the ethylene oxide hydroformylation reaction. Specifically, the Co-C / N catalyst is applied to the gas-liquid-solid batch reactor for ethylene oxide hydroformylation. The reaction conditions are as follows: The reaction raw materials are a mixed solution of methanol and ethylene oxide, and CO gas. The reaction temperature is 30 - 100 °C, the pressure is 1 - 10 MPa, and the reaction time is 1 - 72 h.

[0026] The preferred scheme is: The reaction conditions are as follows: The molar ratio of the amount of cobalt in the catalyst to the molar amount of ethylene oxide is between 1:50 - 200. The reaction system also contains the solvent tetrahydrofuran. The molar ratio of the amount of methanol to the molar amount of ethylene oxide is between 2:1 - 3:1. The volume ratio of methanol to the solvent is 4:1. The pressure of CO is 6 - 8 MPa, the reaction temperature is 70 - 90 °C, and the reaction time is 20 - 40 h.

[0027] The present invention has the following beneficial effects:

[0028] 1. The present invention synthesizes a cobalt-imidazolate framework precursor and then combines high-temperature calcination and reduction methods to prepare a Co-C / N catalyst. By controlling the loading amount of the Co species, a Co-C / N catalyst can be obtained in which the Co species are composed of several Co single atoms, Co atom clusters, and Co nanoparticles. When used in the hydroformylation of ethylene oxide, it can significantly improve the stability of the hydroformylation catalyst for ethylene oxide. Compared with other previous heterogeneous Co-based catalysts, it truly achieves the dual effects of finding the most suitable loading amount and dispersion degree while ensuring catalytic stability. The present invention utilizes the unique geometric structure and electronic effect of the Co active component to promote the hydroformylation of ethylene oxide and highly selectively produce methyl 3-hydroxypropionate.

[0029] 2. The reagents used in the present invention only include cobalt salts, zinc salts, 2-methylimidazole, and methanol. The raw materials are easily obtained, and the preparation method is simple, reliable, easy to operate, and has high repeatability, suitable for large-scale production.

[0030] 3. The Co-C / N catalyst for heterogeneous catalysis of ethylene oxide hydroformylation provided by the present invention is a solid catalyst. After the gas-liquid-solid phase ethylene oxide hydroformylation reaction, the catalyst can be separated and recovered by centrifugation or filtration, greatly reducing the reaction cost.

[0031] 4. The Co-C / N catalyst for heterogeneous catalysis of ethylene oxide hydroformylation provided by the present invention uses a C / N support, which can better disperse Co. High-temperature calcination and reduction enhance the interaction between Co and the support, while modulating the electronic state of the Co active species, promoting the formation of highly efficient and stable active Co species, and significantly improving the performance of the ethylene oxide hydroformylation reaction. Under relatively mild reaction temperature and pressure conditions, among them, the 6-Co-C / N catalyst in which Co exists in the form of nanoparticles exhibits relatively excellent catalytic activity, with an ethylene oxide conversion rate of 31.9% and a methyl 3-hydroxypropionate yield of 18.8%.

[0032] 5. Compared with traditional Co-based homogeneous catalysts, the Co-C / N catalyst for heterogeneous catalysis of ethylene oxide hydroformylation provided by the present invention reduces the leaching amount of Co, has excellent cyclic stability, is easy to separate and recover, has high economic value and market prospects, and is a potential industrial catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 SEM images of ZIF precursors of Co-C / N catalysts with different Co / Zn ratios; Figure 2 Performance comparison chart of the hydroformylation of ethylene oxide of Co-C / N catalysts with different Co / Zn ratios; Figure 3 XRD patterns of Co-C / N catalysts with different Co / Zn ratios;Figure 4 Performance comparison diagram of the hydroformylation of ethylene oxide over Co-C / N catalysts under different reduction conditions; Figure 5 H2-TPR diagram of the 6-Co-C / N catalyst before reduction after calcination; Figure 6 Co 2p diagram of the Co-C / N catalyst before and after reduction of the 6-Co-C / N catalyst; Figure 7 N 1s diagram of the Co-C / N catalyst before and after reduction of the 6-Co-C / N catalyst; Figure 8 BET adsorption curve of the 6-Co-C / N catalyst; Figure 9 Pore size distribution of the 6-Co-C / N catalyst; Figure 10 SEM images of the ZIF precursors of Co-C / N catalysts prepared under different conditions; Figure 11 Performance comparison diagram of the hydroformylation of ethylene oxide over Co-C / N catalysts prepared under different conditions; Figure 12 XRD diagrams of Co-C / N catalysts prepared under different conditions. Specific implementation manners

[0034] The present invention will be described below in conjunction with specific embodiments, but the implementation manners of the present invention are not limited thereto. For the experimental methods without specific conditions noted in the embodiments, they are generally carried out according to the conventional conditions and the conditions described in the manuals, or according to the conditions recommended by the manufacturers. For the general equipment, materials, reagents, etc., unless otherwise specified, they can be obtained from commercial channels. The raw materials required in the following examples and comparative examples are all commercially available.

[0035] Examples 1-9 are for the preparation of Co-C / N catalysts with different Co / Zn ratios:

[0036] Example 1

[0037] Weigh 1.0915 g of cobalt nitrate and put it into a 100 mL beaker. Weigh 6.6936 g of zinc nitrate and add it to the beaker. Then add 60 ml of methanol and stir at room temperature for 10 min to obtain solution A. Weigh 8.6206 g of 2-methylimidazole and put it into a 100 ml beaker. Add 60 ml of methanol and stir at room temperature for 10 min to obtain solution B. Slowly add solution B to solution A at a rate of 2 mL / min. After the addition is complete, seal it with plastic wrap and let it stand at room temperature for 72 h to complete the preparation of the precursor. Subsequently, centrifuge it at 10000 rpm for 10 min using a high-speed centrifuge, wash it three times with methanol until the supernatant is clear and colorless, dry it in a forced-air drying oven at 70 °C for 12 h to obtain a dry solid. After grinding it into powder, transfer it to a tubular furnace. Under a N2 atmosphere, heat it to 900 °C at a rate of 5 °C / min and hold for 2 h, then cool it to room temperature. Switch the gas to H2, heat it to 300 °C at a rate of 5 °C / min and hold for 3 h, and then cool it to room temperature to obtain the 6-Co-C / N catalyst, which is stored under vacuum seal.

[0038] Example 2

[0039] Except for weighing 0.0000 g of zinc nitrate and 1.2315 g of 2-methylimidazole, the remaining preparation method is exactly the same as that of Example 1 to obtain the Co-C / N catalyst.

[0040] Example 3

[0041] Except for weighing 3.3467 g of zinc nitrate and 4.9259 g of 2-methylimidazole, the remaining preparation method is exactly the same as that of Example 1 to obtain the 3-Co-C / N catalyst.

[0042] Example 4

[0043] Except for weighing 4.4623 g of zinc nitrate and 6.1574 g of 2-methylimidazole, the remaining preparation method is exactly the same as that of Example 1 to obtain the 4-Co-C / N catalyst.

[0044] Example 5

[0045] Except for weighing 5.5779 g of zinc nitrate and 7.3889 g of 2-methylimidazole, the remaining preparation method is exactly the same as that of Example 1 to obtain the 5-Co-C / N catalyst.

[0046] Example 6

[0047] Except for weighing 7.8090 g of zinc nitrate and 9.8519 g of 2-methylimidazole, the remaining preparation method is exactly the same as that of Example 1 to obtain the 7-Co-C / N catalyst.

[0048] Example 7

[0049] Except for weighing 8.9246 g of zinc nitrate and 11.0834 g of 2-methylimidazole, the preparation method is exactly the same as that of Example 1, and the 8-Co-C / N catalyst is obtained.

[0050] Example 8

[0051] Except for weighing 10.0402 g of zinc nitrate and 12.3149 g of 2-methylimidazole, the preparation method is exactly the same as that of Example 1, and the 9-Co-C / N catalyst is obtained.

[0052] Example 9

[0053] Except for weighing 0.0000 g of cobalt nitrate, 1.1156 g of zinc nitrate and 1.2315 g of 2-methylimidazole, the preparation method is exactly the same as that of Example 1, and the Zn-C / N catalyst is obtained.

[0054] Examples 10-11 are for the preparation of the 6-Co-C / N catalyst with different temperature reduction of the comparative samples:

[0055] Example 10

[0056] Except that the reduction temperature is 200 °C, the preparation method is exactly the same as that of Example 1, and the 6-Co-C / N catalyst reduced at 200 °C is obtained.

[0057] Example 11

[0058] Except that the reduction temperature is 250 °C, the preparation method is exactly the same as that of Example 1, and the 6-Co-C / N catalyst reduced at 250 °C is obtained.

[0059] Examples 12-13 are for the preparation of the 6-Co-C / N catalyst with different time reduction of the comparative samples:

[0060] Example 12

[0061] Except that the reduction time is 4 h, the preparation method is exactly the same as that of Example 1, and the 6-Co-C / N catalyst reduced for 4 h is obtained.

[0062] Example 13

[0063] Except that the reduction time is 5 h, the preparation method is exactly the same as that of Example 1, and the 6-Co-C / N catalyst reduced for 5 h is obtained.

[0064] Examples 14-15 are for the preparation of the 6-Co-C / N catalyst with different Co precursors of the comparative samples:

[0065] Example 14

[0066] Except for adding 1.5347 g of zinc chloride to replace zinc nitrate, the remaining preparation method is exactly the same as that of Example 1, and a 6-Co-C / N catalyst of zinc chloride and cobalt nitrate is obtained.

[0067] Example 15

[0068] Except for adding 0.6639 g of cobalt acetate to replace cobalt nitrate and 3.9829 g of zinc acetate to replace zinc nitrate, the remaining preparation method is exactly the same as that of Example 1, and a 6-Co-C / N catalyst of zinc acetate and cobalt acetate is obtained.

[0069] Example 16 is the preparation of a 6-Co-C / N catalyst without reduction:

[0070] Example 16

[0071] Except for not undergoing the reduction process, the remaining preparation method is exactly the same as that of Example 1, and a 6-Co-C / N catalyst without reduction is obtained.

[0072] The catalysts obtained in Examples 1-16 were used in the hydroformylation of ethylene oxide, and their catalytic activities were compared. The specific catalytic reaction method is as follows:

[0073] 1. Weigh the catalyst. Weigh 0.25 g of the Co-C / N catalyst in a glove box protected by argon, put it into a centrifuge tube, and seal it for later use.

[0074] 2. Install the reactor. Weigh 16 ml of tetrahydrofuran (THF) as the solvent, 0.5 ml of toluene as the internal standard, 4 ml of methanol, and 2 ml of ethylene oxide as the reactants, add them to a 100 mL quartz inner liner, and then quickly add the Co-C / N catalyst weighed in Step 1. Immediately seal the quartz inner liner in the stainless steel autoclave body.

[0075] 3. Inflate and pressurize. Introduce 0.1 MPa of 99.999% CO gas into the autoclave, then release the pressure, and repeat the inflation and deflation 3 times to exhaust the air in the autoclave. After pressurizing to the reaction pressure of 5-10 MPa, check for leaks. After confirming no gas leakage, release the pressure to not exceed 1 / 2 of the reaction pressure value.

[0076] 4. Catalyst performance test. Start programmed heating at a heating rate of 5 °C / min. After the temperature rises to the reaction temperature of 60-80 °C, repressurize to the reaction pressure, start stirring, and start timing at the same time. After reacting for 10-40 h, stop heating and stirring, take out the product of the autoclave, and naturally cool it to room temperature.

[0077] 5. Product analysis. The analysis was carried out using Shimadzu 2030 GC and 2014 GC system chromatographs, with an FID detector, nitrogen as the carrier gas, the Shimadzu 2030 GC chromatographic column being a SH-1 (30 m × 0.32 mm × 5 μm) capillary column, the 2014 GC chromatographic column being a Plotwax (30 m × 0.32 mm × 1 μm) capillary column, and the Labsolutions software being used for data processing. The contents of the reactants and products were obtained based on the internal standard curve.

[0078] Comparing the SEM spectra of the precursors obtained in Comparative Examples 1-9, as shown in the appendix Figure 1 It can be seen that in the SEM spectra at ratios of 3 ( Figure 1 lower left corner), 5 ( Figure 1 middle right), 6 ( Figure 1 middle left), and pure Co-ZIF ( Figure 1 lower right corner), Zn-ZIF ( Figure 1 upper left corner), ZIF framework structures with sizes between 0.5 - 5 μm can be observed. The precursor of the catalyst at a ratio of 8 ( Figure 1 upper right corner) is mainly in a flake structure.

[0079] Comparing the ethylene oxide hydroformylation performance of the catalysts obtained in Comparative Examples 1-9, as shown in the appendix Figure 2 It can be seen that with the increase in the Zn / Co ratio, the selectivity of acetaldehyde increases significantly. The catalytic yield of Zn-C / N is relatively low, and a large amount of acetaldehyde is detected in the reaction products. Except for 9-Co-C / N and Zn-C / N, no acetaldehyde is detected in the catalysts with other ratios, and the main by-product of the reaction is ethylene glycol methyl ether. 6-Co-C / N exhibits relatively excellent catalytic activity, with an ethylene oxide conversion rate of 31.9% and a yield of 18.8%. The results of the activity test show that a Zn / Co molar ratio of 4 to 6 is beneficial to the improvement of the yield and selectivity of the catalyst. By regulating the Zn / Co ratio, the Co loading can be regulated, and further, the conversion rate and selectivity of the catalyst can be regulated. The Co loading of 3-Co-C / N is 14.9 w%, the loading of 6-Co-C / N is 7.0 wt%, and the loading of 8-Co-C / N is 7.5 wt%. With the increase in the Zn / Co ratio, the Co loading first increases and then decreases, and the selectivity and yield of the reaction also follow this rule. Both the Co loading and dispersion have an impact on the activity of the catalyst.

[0080] Comparing the XRD spectra of the catalysts obtained in Comparative Examples 1-9, as shown in the appendix Figure 3As shown, characteristic diffraction peaks of Co species (1 1 0), (2 0 0), and (2 2 0) were observed in the XRD pattern of Co-C / N, and no Co species were detected in the Zn-N / C species. Analyzing the Co particle size, the particle sizes of Co-C / N, 3-Co-C / N, 5-Co-C / N, and 6-Co-C / N were all around 10 nm. The particle size of Co-C / N was slightly higher, around 17.3 nm. The particle size of 8-Co-C / N was around 4.7 nm. The peaks of the catalysts generated by regulating the Zn / Co ratio were significantly weakened compared to the peaks of the catalysts without Co added, indicating that the addition of Zn improved the dispersion of Co. 8-Co-C / N had the weakest Co peak, but its catalytic effect was poor. This indicates that the catalyst agglomerated to form nanoparticles during the calcination process, and the presence of the nanoparticles was beneficial to the reaction.

[0081] Comparing the performance of 6-Co-C / N catalysts with different reduction conditions obtained in Examples 10 - 13 for the hydroformylation of ethylene oxide to methyl 3-hydroxypropionate, as shown in the appendix Figure 4 As shown. The decrease in the reduction temperature increased the selectivity of methyl 3-hydroxypropionate, but decreased its yield. The extension of the reduction time did not reduce the yield of the catalyst either. The optimal reaction conditions were to reduce at 300 °C for 3 h.

[0082] Comparing Example 16, analyzing the H2-TPR image of 6-Co-C / N before reduction, as shown in the appendix Figure 5 As shown. In an H2 environment, there was continuous reduction of the catalyst. At 300 °C, there was an obvious reduction peak. Comparing Example 16, analyzing the Co 2p XPS images of 6-Co-C / N before and after reduction, as shown in the appendix Figure 6 As shown. In the Co 2p XPS spectrum, the typical binding energies of the peaks of 2p 3 / 2 and 2p 1 / 2 of zero-valent cobalt were around 778.2 eV and 793.2 eV, those of 2p 3 / 2 and 2p 1 / 2 of +2-valent cobalt were around 782.3 eV and 797.3 eV, the satellite peaks of +2-valent cobalt were around 785.5 eV and 802.5 eV respectively, and the typical binding energies of +3-valent cobalt were around 779.7 eV and 793.2 eV. The peaks of 2p 3 / 2 and 2p 1 / 2 of Co were deconvoluted into peaks of 0, +2, and +3 valence according to the typical characteristic peaks of cobalt. After reduction, the content of +3-valent cobalt decreased, while the contents of +2-valent and zero-valent cobalt increased.

[0083] Comparing Example 16, analyzing the XPS N 1s images of 6-Co-C / N before and after reduction, as shown in the appendix Figure 7As shown in Figure 2, three different peaks were observed in the N 1s spectrum, with electron binding energies of 398.5 eV, 399.3 eV, and 401.0 eV, which were attributed to pyridinic N (N bound to Co), pyrrolic N, and graphitic N, respectively. During the reduction process, the amount of graphitic N and pyrrolic N decreased, while the amount of pyridinic N increased. During the reduction process, the interaction between Co and N was enhanced. The physical adsorption curve and pore size distribution curve of 6-Co-C / N after reduction were analyzed, as shown in the attached figure. Figure 8 , 9 As shown in Figure 2, the pore structure of 6-Co-C / N is mainly “ink bottle”, with pore sizes ranging from 1-2 nm to 2-4 nm and a surface area of ​​551.9 m 2 / g.

[0084] Comparative Examples 14-15 explore the effects of different Co and Zn precursors on the performance of 6-Co-C / N catalysts in the hydromethylation of ethylene oxide. The present invention compares the preparation methods using zinc acetate, cobalt acetate, and zinc chloride. Figure 10 The SEM images of different ZIF precursors prepared by this method. The ZIF precursor synthesized using zinc chloride and cobalt nitrate has a rough surface and unclear structure. The precursor formed using zinc acetate and cobalt acetate did not form an independent ZIF structure, but formed large particle clusters.

[0085] Comparative Examples 14-15 explore the effects of different Co and Zn precursors on the performance of 6-Co-C / N catalyst for catalytic ethylene oxide hydromethylation. The present invention compares the catalytic performance of different Co and Zn precursors. The test results are shown in the attached Figure 11 The catalyst effect obtained by the preparation method using zinc acetate, cobalt acetate, and zinc chloride is significantly worse than that of cobalt nitrate and zinc nitrate.

[0086] Comparative Examples 14-15 were used to explore the effects of Co and Zn precursors on the performance of 6-Co-C / N catalysts for the hydromethylation of ethylene oxide. XRD characterization was performed on the catalysts synthesized using zinc acetate, cobalt acetate, and zinc chloride. Figure 12 As shown, the catalyst synthesized by zinc chloride and cobalt nitrate has a similar spectrum to cobalt nitrate and zinc nitrate, and the diameter of the nanoparticles of the formed catalyst is similar. The catalyst synthesized by cobalt acetate and zinc acetate has a better dispersion effect, but the catalytic effect is poor, which shows that simply improving the dispersion without improving the structure of the catalyst has little effect on the catalyst.

[0087] To investigate the stability of the 6-Co-C / N catalyst in the heterogeneous catalytic reaction of ethylene oxide hydroformylation, in this invention, after the reaction, the 6-Co-C / N catalyst was centrifuged and washed, and after separating the solid catalyst, tests were carried out. Except that the catalyst was the catalyst separated and recovered after the reaction, the remaining steps were the same as the above catalytic method, and the results of its cyclic catalysis were poor (selectivity 16.48%). After centrifuging and washing the collected catalyst again and separating the solid catalyst, it was reduced at 300 °C for 3 h and then tested again. Its selectivity returned to 63.0%, showing no decrease but rather an increase compared with the first reaction; after the reaction, the Co content of the catalyst collected by centrifuging, washing, separating and collecting was 6.0 wt%, which was greatly reduced compared with the leaching amount of other types of heterogeneous Co-based catalysts, and the reaction stability was improved.

[0088] In this invention, the raw materials and equipment used are all common raw materials and equipment in the art without special instructions; the methods used in this invention are all conventional methods in the art without special instructions.

Claims

1. Application of a Co-based catalyst for heterogeneous oxirane hydroformylation reaction, characterized in that, The Co-based catalyst is applied to the gas-liquid-solid batch autoclave methanol hydroformylation reaction, and the reaction conditions are as follows: the reaction raw materials are a mixed solution of methanol and ethylene oxide, and CO gas; the reaction temperature is 50-100 °C, the pressure is 1-10 MPa, and the reaction time is 1-48 h; among them, the molar ratio of the catalyst cobalt to the molar amount of ethylene oxide is between 1:50 and 1:200, the reaction system also contains a solvent, the molar ratio of methanol to the molar amount of ethylene oxide is between 2:1 and 3:1, the volume ratio of methanol to the solvent is 4:1, and the solvent is tetrahydrofuran; The Co-based catalyst includes a support and an active component. The support is carbon nitride formed by high-temperature calcination of a zeolitic imidazolate framework material. The active component is a Co species, and the Co species exists in the form of Co nanoparticles with a particle size of 10 nm. Zinc nitrate is used to regulate the distribution of cobalt, and the molar ratio of zinc nitrate to cobalt nitrate is 6. Based on the total mass of the Co-based catalyst, the loading amount of the Co species is 7.0 wt% of the total mass of the Co-based catalyst, and the specific surface area is in the range of 500 - 600 m 2 / g, and the pore diameters are mainly concentrated in 1 - 2 nm micropores and 2 - 4 nm mesopores; The preparation method of the Co-based catalyst includes the following steps: Weigh 1.0915 g of cobalt nitrate and put it into a 100 mL beaker, weigh 6.6936 g of zinc nitrate and add it to the beaker, then add 60 ml of methanol, and stir at room temperature for 10 min to obtain solution A; Weigh 8.6206 g of 2-methylimidazole and put it into a 100 ml beaker, add 60 ml of methanol, and stir at room temperature for 10 min to obtain solution B; Drop solution B into solution A at a rate of 2 mL / min. After the dropping is completed, seal it with plastic wrap and let it stand at room temperature for 72 h to complete the preparation of the precursor; Subsequently, centrifuge at 10,000 revolutions for 10 min with a high-speed centrifuge, wash it three times with methanol until the supernatant is clear and colorless, dry it in a blast drying oven at 70 °C for 12 h to obtain a dry solid, grind it into powder, transfer it to a tube furnace, and under N2 atmosphere, heat it to 900 °C at a rate of 5 °C / min and hold for 2 h, then cool it to room temperature, switch the gas to H2, heat it to 300 °C at a rate of 5 °C / min and hold for 3 h, and after cooling to room temperature, obtain the 6-Co-C / N catalyst, and store it in a vacuum seal.

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