A nitrogen-doped carbon supported cobalt monatomic / nanocluster dual-size catalyst, a preparation method and application thereof

Abstract

The application discloses a nitrogen-doped carbon supported cobalt monatomic / nanocluster dual-size catalyst and a preparation method and application thereof, and belongs to the technical field of biomass catalytic conversion. The preparation method provided by the application comprises the following steps: A) mixing a cobalt salt, a carbon source and a nitrogen source in water, stirring at normal temperature, then high-temperature stirring and evaporating to dryness, and obtaining a mixture one after drying; grinding the mixture one and performing carbonization under an inert atmosphere to obtain a nitrogen-doped carbon supported cobalt monatomic catalyst; B) adding the nitrogen-doped carbon supported cobalt monatomic catalyst into a cobalt salt aqueous solution, stirring at normal temperature, then high-temperature stirring and evaporating to dryness, and obtaining a mixture two after drying; grinding the mixture two and performing high-temperature reduction under a reducing atmosphere, and the catalyst is obtained. The catalyst has the advantages of simple preparation process, easily available raw materials and low preparation cost. When the catalyst is applied to the preparation of 2-methoxy-4-methylphenol by vanillin hydrogenation and deoxidization, the catalyst has high catalytic activity and good cycle stability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of biomass catalytic conversion, and particularly relates to a nitrogen-doped carbon supported cobalt monatomic / nanocluster dual-size catalyst and a preparation method and application thereof. BACKGROUND

[0002] The information disclosed in the background of the present application is only intended to increase the understanding of the overall background of the present application and should not be regarded as acknowledging or implying in any form that the information constitutes prior art known to those skilled in the art.

[0003] By means of hydrodeoxygenation, the oxygen content and viscosity of lignin oil can be effectively reduced, and the lignin oil can be converted into clean and stable aromatic hydrocarbon products, so that the high-value utilization of lignin is realized. Vanillin is an organic compound derived from lignin, and 2-methoxy-4-methylphenol obtained by hydrodeoxygenation is a potential biomass fuel. At present, the hydrodeoxygenation of vanillin is mainly realized by catalytic conversion of noble metal catalysts such as Pt, Pd and Ru and transition metal catalysts such as Ni, Fe and Co.

[0004] By regulating the size of metal particles, the active components can be effectively dispersed, the active sites of the catalyst can be increased, the utilization rate of the metal can be improved, and the interaction between the active sites and the carrier can be improved. Therefore, the size of the metal particles becomes a key factor affecting the performance of the catalyst. The preparation method of the catalyst material has a decisive influence on the size of the metal particles. Therefore, it is an urgent problem to provide a hydrodeoxygenation catalyst with high catalytic activity and stability. SUMMARY

[0005] Therefore, the present application provides a preparation method and application of a nitrogen-doped carbon supported cobalt monatomic / nanocluster dual-size catalyst. The catalyst provided by the present application can more effectively promote the reaction of vanillin hydrodeoxygenation to prepare 2-methoxy-4-methylphenol through the combined action of cobalt monatomic and cobalt nanocluster, and the catalyst has strong cycle stability and can be recycled for more than 5 times while maintaining high activity, which is suitable for industrial large-scale production.

[0006] In a first aspect, the present application provides a preparation method of a nitrogen-doped carbon supported cobalt monatomic / nanocluster dual-size catalyst, which comprises the following steps:

[0007] A) mixing a cobalt salt, a carbon source and a nitrogen source in water, stirring at room temperature, then high-temperature stirring and evaporating to dryness, and drying to obtain a mixture one; grinding the mixture one and performing carbonization under an inert atmosphere to obtain a nitrogen-doped carbon supported cobalt monatomic catalyst;

[0008] B) adding the nitrogen-doped carbon supported cobalt monatomic catalyst into a cobalt salt aqueous solution, stirring at room temperature, then stirring at high temperature and evaporating to dryness, drying to obtain a mixture II; grinding the mixture II and reducing at high temperature in a reducing atmosphere to obtain the product.

[0009] Preferably, the cobalt salt in step A) and step B) is selected from cobalt acetate, cobalt nitrate or cobalt chloride; the carbon source is selected from glucose, carbon black or carbon nanotube; and the nitrogen source is selected from melamine, dicyanamide or urea.

[0010] Preferably, in the high-temperature stirring and evaporating to dryness step of step A) and step B), the stirring temperature is 60-100℃; in the stirring at room temperature step of step A), the stirring time is 1-5h; in the stirring at room temperature step of step B), the stirring time is 15-30h; in the drying step of step A), the drying time is 1-5h and the drying temperature is 60-90℃; and in the drying step of step B), the drying time is 1-5h and the drying temperature is 60-90℃.

[0011] Preferably, in step A), the mass ratio of the cobalt salt, the carbon source and the nitrogen source is (0.02-0.2):(0.8-1.2):(8-12); and in step B), the mass ratio of the nitrogen-doped carbon supported cobalt monatomic catalyst and the cobalt salt is 1:(0.04-0.08).

[0012] Preferably, the inert atmosphere is argon; and the reducing atmosphere is a mixture of hydrogen and argon.

[0013] Further, the flow rate of the inert atmosphere is 150-250mL / min, and the flow rate of the reducing atmosphere is 80-250mL / min; and in the reducing atmosphere, the volume ratio of hydrogen to argon is (5-10):(90-95).

[0014] Preferably, the carbonization step specifically comprises: increasing the temperature to 550-650℃ at a temperature increasing rate of 1-5℃ / min, and maintaining the temperature for 1-2h; and then increasing the temperature to 700-900℃, and maintaining the temperature for 1-2h.

[0015] Preferably, the high-temperature reduction step specifically comprises: increasing the temperature to 300-500℃ at a temperature increasing rate of 1-5℃ / min, and maintaining the temperature for 2-6h.

[0016] In a second aspect, the present application provides a nitrogen-doped carbon supported cobalt monatomic / nanocluster dual-size catalyst prepared by the above preparation method.

[0017] In a third aspect, the present application provides a method for preparing 2-methoxy-4-methylphenol by vanillin hydrodeoxygenation, comprising the following steps:

[0018] Vanillin, catalyst and solvent are added into a high-pressure reaction kettle, and a hydrodeoxygenation reaction is carried out under high-temperature stirring in a hydrogen atmosphere to obtain 2-methoxy-4-methylphenol; the catalyst is the above-mentioned nitrogen-doped carbon-supported cobalt monatomic / nanocluster dual-size catalyst.

[0019] Preferably, the solvent is isopropanol, and the vanillin, catalyst and solvent are used in a ratio of 0.2 g:(0.04-0.06) g:(15-25) mL; the hydrogen pressure is 1.5-2.5 MPa; the high-temperature stirring reaction is carried out at a temperature of 120-160 DEG C for 2-5 h at a stirring speed of 500-700 rpm.

[0020] Compared with the prior art, the present application has the following beneficial effects:

[0021] (1) The preparation method of the nitrogen-doped carbon-supported cobalt monatomic / nanocluster dual-size catalyst can prepare a catalyst in which a nitrogen-doped carbon carrier simultaneously supports cobalt monatomic / cobalt nanoclusters, effectively improving the atomic utilization rate and the stability of the catalyst, and the preparation process of the catalyst is simple, raw materials are easy to obtain, and the cost is low.

[0022] (2) The nitrogen-doped carbon-supported cobalt monatomic / nanocluster dual-size catalyst has high catalytic activity when applied to the preparation of 2-methoxy-4-methylphenol by hydrodeoxygenation of vanillin, the yield of 2-methoxy-4-methylphenol is maintained at more than 90%, and the catalyst has good cycle stability and can be recycled more than 5 times while still maintaining high activity, is suitable for industrial large-scale production, and has good application prospects. BRIEF DESCRIPTION OF DRAWINGS

[0023] The drawings constituting a part of the specification of the present application serve to provide a further understanding of the present application, and the schematic embodiments of the present application and the description thereof serve to explain the present application and do not constitute an improper limitation on the present application. Obviously, other drawings can be obtained by those of ordinary skill in the art without any creative effort on the basis of these drawings.

[0024] Figure 1 is a scanning electron microscope (SEM) image of the catalyst Co NP / SAC@NC prepared in Example 1 of the present application;

[0025] Figure 2 is a transmission electron microscope (TEM) image of the catalyst Co NP / SAC@NC prepared in Example 1 of the present application at different magnifications;

[0026] Figure 3 is a transmission electron microscope (TEM) image of the catalyst Co NPA high-angle annular dark-field (AC-HAADF-STEM) image of the SAC@NC;

[0027] Figure 4 A TEM image of the catalyst Co NP An X-ray diffraction (XRD) image of the SAC@NC;

[0028] Figure 5 A TEM image of the catalyst Co NP An X-ray photoelectron spectroscopy (XPS) image of the SAC@NC;

[0029] Figure 6 A TEM image of the catalyst prepared in Comparative Example 1 of the present application;

[0030] Figure 7 An AC-HAADF-STEM image of the catalyst prepared in Comparative Example 2 of the present application;

[0031] Figure 8 A TEM image of the catalyst Co NP A gas chromatogram of the product after the SAC@NC catalyzed hydrodeoxygenation of vanillin. DETAILED DESCRIPTION

[0032] It should be noted that the following detailed description is exemplary in nature and is intended to provide further description of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0033] The present application provides a preparation method of a nitrogen-doped carbon supported cobalt monatomic / nanocluster bimodal catalyst, comprising the following steps:

[0034] A) mixing a cobalt salt, a carbon source and a nitrogen source in water, stirring at room temperature, then high-temperature stirring and evaporating to dryness, and drying to obtain a mixture one; grinding the mixture one and performing carbonization under an inert atmosphere to obtain a nitrogen-doped carbon supported cobalt monatomic catalyst;

[0035] B) adding the nitrogen-doped carbon supported cobalt monatomic catalyst to an aqueous solution of the cobalt salt, stirring at room temperature, then high-temperature stirring and evaporating to dryness, and drying to obtain a mixture two; grinding the mixture two and performing high-temperature reduction under a reducing atmosphere to obtain the nitrogen-doped carbon supported cobalt monatomic / nanocluster bimodal catalyst.

[0036] The present application develops a high-efficiency and stable cobalt single atom / nanocluster dual-size catalyst through co-pyrolysis and impregnation method. The cobalt single atom is doped into the nitrogen-doped carbon skeleton through the coupling of carbon source and cobalt salt and the anchoring effect of nitrogen-doped (the nitrogen doping can anchor Co metal to form Co-N4), and then a cobalt single atom / nanocluster dual-size catalyst is constructed through impregnation method. In the hydrodeoxygenation reaction of vanillin, the cobalt single atom can more effectively activate hydrogen to form active hydrogen, and the cobalt nanocluster can effectively adsorb oxygen functional groups to promote the rupture of C-O bond in the substrate. Therefore, through the joint action of cobalt single atom and cobalt nanocluster, the reaction of vanillin hydrodeoxygenation to prepare 2-methoxy-4-methylphenol can be more effectively promoted.

[0037] In the present application, the cobalt salt of step A) and step B) is selected from cobalt acetate, cobalt nitrate or cobalt chloride; the carbon source is selected from glucose, carbon black or carbon nanotube; and the nitrogen source is selected from melamine, dicyanamide or urea.

[0038] In the high-temperature stirring and evaporation drying step of step A) and step B) of the present application, the stirring temperature is 60-100 DEG C; and the uniform Co composite carbon-nitrogen material precursor is obtained by high-temperature stirring and evaporation drying. In the normal-temperature stirring step of step A), the stirring time is 1-5 h; in the normal-temperature stirring step of step B), the stirring time is 15-30 h, and the longer normal-temperature stirring can uniformly impregnate the metal Co on the carrier. In the drying step of step A), the drying time is 1-5 h and the drying temperature is 60-90 DEG C; in the drying step of step B), the drying time is 8-15 h and the drying temperature is 60-90 DEG C.

[0039] In step A) of the present application, the mass ratio of the cobalt salt, carbon source and nitrogen source is (0.02-0.2):(0.8-1.2):(8-12); in step B), the mass ratio of the nitrogen-doped carbon supported cobalt single atom catalyst and cobalt salt is 1:(0.04-0.08), and further preferably 1:(0.06-0.07), and under this ratio, the cobalt single atom / cobalt nanocluster dual-size metal cobalt catalyst can be prepared, which is used in the hydrodeoxygenation catalytic reaction of vanillin, and the yield of 2-methoxy-4-methylphenol is above 90%. In step B), the mass ratio of the nitrogen-doped carbon supported cobalt single atom catalyst and cobalt salt has a great influence on the existing form of metal cobalt, if the addition amount of cobalt salt is too low, only the existing form of cobalt single atom can be obtained; if the addition amount of cobalt salt is too high, the catalyst of cobalt single atom / nanoparticle dual size is obtained, and when the two catalysts are used in the hydrodeoxygenation catalytic reaction of vanillin, the yield of 2-methoxy-4-methylphenol is below 90%.

[0040] In the present application, the inert atmosphere is argon or nitrogen; the reducing atmosphere is a mixture of hydrogen and argon. Further, the flow rate of the inert atmosphere is 150-250 mL / min, further preferably 180-220 mL / min; the flow rate of the reducing atmosphere is 80-250 mL / min, further preferably 90-110 mL / min; the volume ratio of hydrogen to argon in the reducing atmosphere is (5-10):(90-95).

[0041] In the present application, the carbonization step specifically comprises: heating at a heating rate of 1-5 ℃ / min to 550-650 ℃, and holding for 1-2 h; and then heating to 700-900 ℃, and holding for 1-2 h. The Co-N4 formed in the carbonization process enhances the interaction between the active sites and the support, thereby ensuring that the catalyst has good stability.

[0042] In the present application, the high-temperature reduction step specifically comprises: heating at a heating rate of 1-5 ℃ / min to 300-500 ℃, and holding for 2-6 h. In the high-temperature reduction step, the cobalt salt is reduced to cobalt nanoclusters, thereby obtaining the nitrogen-doped carbon-supported cobalt single atom / nanocluster dual-size catalyst.

[0043] The present application also provides a method for preparing 2-methoxy-4-methylphenol by vanillin hydrogenation and deoxygenation, comprising the following steps:

[0044] Vanillin, a catalyst, and a solvent are added to a high-pressure reaction kettle, and a hydrogenation and deoxygenation reaction is carried out under a hydrogen atmosphere at high temperature and stirring, to obtain 2-methoxy-4-methylphenol; the catalyst is the nitrogen-doped carbon-supported cobalt single atom / nanocluster dual-size catalyst described above.

[0045] In the present application, the solvent is isopropanol, and the use amount ratio of vanillin, the catalyst, and the solvent is 0.2 g:(0.04-0.06) g:(15-25) mL; the hydrogen pressure is 1.5-2.5 MPa; the temperature of the high-temperature stirring reaction is 120-160 ℃, the time is 2-5 h, and the stirring speed is 500-700 rpm. Under the above reaction conditions, the conversion rate of vanillin and the yield of 2-methoxy-4-methylphenol are both above 90%, and the catalyst has good cycle stability.

[0046] The technical solutions of the present application are further described below in combination with specific examples.

[0047] Example 1

[0048] The present example provides a preparation method of a nitrogen-doped carbon-supported cobalt single atom / nanocluster dual-size catalyst (Co NP / SAC@NC).

[0049] (1) 0.2 g of cobalt acetate tetrahydrate, 0.8 g of glucose, 10 g of melamine were put into 20 mL of deionized water, and after stirring for 3 h, a mixed solution was obtained. The mixed solution was transferred to an oil bath pot at 80°C and continued to be stirred. After the solution was evaporated to dryness in an oven, the mixture was cooled to obtain a mixture. The mixture was ground into powder and then carbonized. The carbonization process was as follows: heated to 600°C at a heating rate of 2.5°C / min under an argon flow of 200 mL / min and kept for 1 h, and then heated to 800°C at a heating rate of 2.5°C / min and kept for 1 h to obtain the catalyst Co / SAC.

[0050] (2) 0.063 g of cobalt acetate tetrahydrate was dissolved in 20 mL of deionized water. After the cobalt acetate tetrahydrate was completely dissolved, 1 g of the catalyst Co / SAC of step (1) was added to the solution, and stirring was continued for 24 h. After stirring, the solution was transferred to an oil bath pot at 80°C and continued to be stirred. After the solution was evaporated to dryness in an oven, the mixture was cooled to obtain a mixture. The catalyst Co / SAC@NC was obtained after reduction at 400°C for 4 h under a hydrogen-argon mixed gas atmosphere (hydrogen to argon volume ratio of 8:92) at a heating rate of 2.5°C / min. NP

[0051] Figure 1 The scanning electron microscope (SEM) image of the catalyst Co NP / SAC@NC prepared in this example, Figure 2 The transmission electron microscope (TEM) image of the catalyst Co NP / SAC@NC prepared in this example, from which it can be seen that the catalyst has a wrinkled nanosheet structure, and no obvious cobalt nanoparticles are found. Figure 3 The spherical aberration-corrected transmission electron microscope high-angle annular dark field (AC-HAADF-STEM) image of the catalyst Co NP / SAC@NC prepared in this example, it can be seen that the metal cobalt exists in the form of nanoclusters and single atoms on the nitrogen-doped carbon carrier.

[0052] Figure 4 The X-ray diffraction (XRD) pattern of the catalyst Co NP / SAC@NC prepared in this example, from which it can be seen that there is only one broad diffraction peak of carbon in the catalyst, indicating that the nitrogen doping leads to low crystallinity of carbon. And no cobalt diffraction peak is found, indicating that the particle size of the metal cobalt is small and uniformly dispersed.

[0053] Figure 5 The X-ray photoelectron spectroscopy (XPS) pattern of the catalyst Co NP / SAC@NC prepared in this example. From the figure, it can be seen that in the Co 2p XPS spectrum of the sample, a Co​0 The characteristic peak of binding energy at about 782.5 eV is attributed to Co-Nx bond, and the characteristic peak of binding energy at about 797.5 eV is attributed to Co-N bond. Figure 3 The AC-HAADF-STEM of Co / SAC@NC-1 confirms the existence of Co NP The Co single atom / nanocluster dual-size catalyst is successfully synthesized.

[0054] Example 2

[0055] The present embodiment provides a preparation method of a nitrogen-doped carbon supported cobalt single atom / nanocluster dual-size catalyst (Co NP / SAC@NC-1).

[0056] (1) 0.02 g of cobalt nitrate, 1 g of carbon black and 8 g of melamine were mixed and placed in 20 mL of deionized water and stirred for 3 h to obtain a mixed solution. The mixed solution was transferred to an 80°C oil bath and continued to be stirred. After the solution was evaporated and dried in an oven, the mixture was cooled to obtain a powder. The powder was carbonized at a heating rate of 5°C / min to 600°C under an argon flow of 200 mL / min and held for 1 h, and then heated to 850°C at a heating rate of 5°C / min and held for 1 h to obtain the catalyst Co / SAC-1.

[0057] (2) 0.040 g of cobalt nitrate was dissolved in 20 mL of deionized water. After the cobalt nitrate was completely dissolved, 1 g of the catalyst Co / SAC-1 of step (1) was added to the solution and continued to be stirred for 24 h. After stirring, the solution was transferred to an 80°C oil bath and continued to be stirred. After the solution was evaporated and dried in an oven, the mixture was cooled to obtain a powder. The powder was reduced at a heating rate of 3°C / min to 500°C under a hydrogen-argon mixed gas atmosphere (hydrogen and argon in a volume ratio of 8:92) for 3 h to obtain the catalyst Co NP / SAC@NC-1.

[0058] Example 3

[0059] The present embodiment provides a preparation method of a nitrogen-doped carbon supported cobalt single atom / nanocluster dual-size catalyst (Co NP / SAC@NC-2).

[0060] (1) 0.1 g cobalt chloride, 0.8 g carbon black, and 12 g melamine were mixed and placed in 20 mL of deionized water to stir for 3 h to obtain a mixed solution, and the mixed solution was transferred to an 80°C oil bath to continue stirring. After the solution was evaporated and dried in an oven, the mixture was cooled to obtain a mixture. The mixture was ground into powder and carbonized. The carbonization process was as follows: heated to 600°C at a heating rate of 2°C / min under an argon flow of 200 mL / min and maintained for 1 h, and then heated to 900°C at a heating rate of 2°C / min and maintained for 1 h to obtain a catalyst Co / SAC-2.

[0061] (2) 0.08 g cobalt acetate tetrahydrate was dissolved in 20 mL of deionized water, and after the cobalt acetate tetrahydrate was completely dissolved, 1 g of the catalyst Co / SAC-2 of step (1) was added to the solution and continued to stir for 24 h. After stirring, the solution was transferred to an 80°C oil bath to continue stirring. After the solution was evaporated and dried in an oven, the mixture was cooled to obtain a mixture. The catalyst Co / SAC-NC-2 was obtained after reduction at 400°C for 4 h under a hydrogen-argon mixed gas atmosphere (hydrogen and argon volume ratio of 8:92) at a heating rate of 5°C / min. NP

[0062] Example 4

[0063] This example provides a preparation method of a nitrogen-doped carbon supported cobalt monatomic / nanocluster dual-size catalyst (Co / SAC-NC-3). NP

[0064] (1) 0.05 g cobalt chloride, 1.2 g carbon black, and 10 g melamine were mixed and placed in 20 mL of deionized water to stir for 3 h to obtain a mixed solution, and the mixed solution was transferred to an 80°C oil bath to continue stirring. After the solution was evaporated and dried in an oven, the mixture was cooled to obtain a mixture. The mixture was ground into powder and carbonized. The carbonization process was as follows: heated to 550°C at a heating rate of 4°C / min under an argon flow of 150 mL / min and maintained for 1 h, and then heated to 850°C at a heating rate of 4°C / min and maintained for 1 h to obtain a catalyst Co / SAC-3.

[0065] (2) 0.04 g cobalt chloride was dissolved in 20 mL of deionized water, and after the cobalt chloride was completely dissolved, 1 g of the catalyst Co / SAC-3 of step (1) was added to the solution and continued to stir for 24 h. After stirring, the solution was transferred to an 80°C oil bath to continue stirring. After the solution was evaporated and dried in an oven, the mixture was cooled to obtain a mixture. The catalyst Co / SAC-NC-3 was obtained after reduction at 500°C for 2 h under a hydrogen-argon mixed gas atmosphere (hydrogen and argon volume ratio of 8:92) at a heating rate of 1°C / min. NP ​​Co / SAC-3.

[0066] Comparative Example 1

[0067] The present comparative example is compared with Example 1, the difference being that the mass of cobalt acetate tetrahydrate in step (2) is 0.090 g.

[0068] Figure 6 A TEM image of the catalyst prepared for Comparative Example 1 is shown in the figure. It is apparent from the figure that the Co nanoparticle size is large and unevenly dispersed, and partial agglomeration is observed, with no monodispersed Co atoms present.

[0069] Comparative Example 2

[0070] The present comparative example is compared with Example 1, the difference being that the mass of cobalt acetate tetrahydrate in step (2) is 0.01 g.

[0071] Figure 7 An AC-HAADF-STEM image of the catalyst prepared for the present comparative example 2 is shown in the figure, and it is apparent that the metal cobalt exists in the form of single atoms on the nitrogen-doped carbon support, and no nanocluster phenomenon is observed.

[0072] Comparative Example 3

[0073] The present comparative example is compared with Example 1, the difference being that the mass of cobalt acetate tetrahydrate in step (1) is 0.3 g.

[0074] Comparative Example 4

[0075] The present comparative example is compared with Example 1, the difference being that no cobalt acetate tetrahydrate is added in step (1).

[0076] Test Example

[0077] Into a 50 mL high-pressure reactor, 0.2 g of vanillin, 0.05 g of the catalyst Co / SAs-NCs of Example 1-4 NP / SAC@NC or the catalyst of Comparative Examples 1-4, 20 mL of isopropanol, and N2 was used to evacuate three times, and then 2 MPa of hydrogen was introduced, and the reaction was carried out at a temperature of 150°C and a rotation speed of 600 rpm for 180 min. After cooling to room temperature, the yield of 2-methoxy-4-methylphenol (MMP) was quantitatively detected by gas chromatography-mass spectrometry using dodecane as an internal standard.

[0078] Table 1 shows the yield of the target product MMP when the Co / SAs-NCs catalyst of Examples 1-4 or the catalyst of Comparative Examples 1-4 is used as a hydrodeoxygenation catalyst, and it can be seen that the catalyst of Example 1 has the best catalytic activity, and the gas phase detection figure of the product is shown in Figure 8 .

[0079] Table 1 Reaction conversion and target product yield of catalysts of examples 1-4 and comparative examples 1-4

[0080]

[0081]

[0082] Catalyst cycle performance determination

[0083] A 50 mL autoclave was charged with 0.2 g of vanillin, 0.05 g of the catalyst Co / SAC-NCs of example 1, 20 mL of isopropanol, and was evacuated three times with N2, and then 2 MPa of H2was introduced. The reaction was carried out at a temperature of 150°C and a rotation speed of 600 rpm for 180 min. After the reaction was completed, the temperature was lowered, and the catalyst was separated by suction filtration, washed three times with deionized water, and dried. The hydrodeoxygenation reaction was continued after adding fresh Co / SAC-NCs catalyst, and the above steps were repeated five times. The conversion of vanillin and the yield of 2-methoxy-4-methylphenol (MMP) were quantitatively detected by gas chromatography-mass spectrometry with dodecane as an internal standard, as shown in Table 2. It can be seen that the catalyst of example 1 has good recycling performance and high stability of catalytic activity.

[0084] Table 2 Reaction conversion and target product yield after 5 cycles

[0085] Cycle number Vanillin conversion (%) MMP yield (%) 1 95 94 2 95 93 3 94 92 4 93 92 5 92 90

[0086] The preferred embodiments of the present application have been described above with the purpose of illustrating the application, but not for limiting the application. The application can be variously changed and modified by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the scope of the present application.

Claims

1. A method for preparing a nitrogen-doped carbon supported cobalt monoatom / nanocluster bimodal catalyst, characterized in that, The preparation method comprises the following steps: A) mixing a cobalt salt, a carbon source and a nitrogen source in water, stirring at room temperature, then stirring at high temperature and evaporating to dryness, and obtaining a mixture one after drying; grinding the mixture one and performing carbonization under an inert atmosphere to obtain a nitrogen-doped carbon supported cobalt monatomic catalyst; B) adding the nitrogen-doped carbon supported cobalt monatomic catalyst into a cobalt salt aqueous solution, stirring at room temperature, then stirring at high temperature and evaporating to dryness, and drying to obtain a mixture two; grinding the mixture two and performing high-temperature reduction under a reducing atmosphere to obtain the nitrogen-doped carbon supported cobalt monatomic / nanocluster dual-size catalyst; In step B), the mass ratio of the nitrogen-doped carbon supported cobalt monatomic catalyst to the cobalt salt is 1:(0.04-0.08). The inert atmosphere is argon or nitrogen; and the reducing atmosphere is a mixture of hydrogen and argon. The nitrogen-doped carbon supported cobalt monatomic / nanocluster dual-size catalyst is used for a vanillin hydrodeoxygenation reaction.

2. The production method according to claim 1, wherein The cobalt salt in steps A) and B) is selected from the group consisting of cobalt acetate, cobalt nitrate and cobalt chloride; the carbon source is selected from the group consisting of glucose, carbon black and carbon nanotube; and the nitrogen source is selected from the group consisting of melamine, dicyanamide and urea.

3. The production method according to claim 1, wherein In the high-temperature stirring and evaporating to dryness steps of steps A) and B), the stirring temperature is 60-100 ℃; in the room-temperature stirring step of step A), the stirring time is 1-5 h; in the room-temperature stirring step of step B), the stirring time is 15-30 h; in the drying step of step A), the drying time is 1-5 h and the drying temperature is 60-90 ℃; and in the drying step of step B), the drying time is 8-15 h and the drying temperature is 60-90 ℃.

4. The production method according to claim 1, wherein In step A), the mass ratio of the cobalt salt, the carbon source and the nitrogen source is (0.02-0.2):(0.8-1.2):(8-12).

5. The production method according to claim 1, wherein The flow rate of the inert atmosphere is 150-250 mL / min; the volume ratio of hydrogen to argon is (5-10):(90-95); and the flow rate of the reducing atmosphere is 80-250 mL / min.

6. The production method according to claim 1, wherein The carbonization step specifically comprises: increasing the temperature to 550-650 ℃ at a temperature increasing rate of 1-5 ℃ / min, and maintaining the temperature for 1-2 h; and then increasing the temperature to 700-900 ℃, and maintaining the temperature for 1-2 h.

7. The production method according to claim 1, wherein The high-temperature reduction step specifically comprises: increasing the temperature to 300-500 ℃ at a temperature increasing rate of 1-5 ℃ / min, and maintaining the temperature for 2-6 h.

8. The nitrogen-doped carbon supported cobalt monatomic / nanocluster dual-size catalyst prepared by the preparation method in any one of claims 1-7.

9. A process for the production of 2-methoxy-4-methylphenol by hydrodeoxygenation of vanillin, characterized in that, The preparation method comprises the following steps: Vanillin, a catalyst and a solvent are added into a high-pressure reaction kettle, and a hydrodeoxygenation reaction is performed under a hydrogen atmosphere by stirring at high temperature to obtain 2-methoxy-4-methylphenol; the catalyst is the nitrogen-doped carbon supported cobalt monatomic / nanocluster dual-size catalyst in claim 8.

10. The method of claim 9, wherein, The solvent is isopropyl alcohol, the vanillin, catalyst and solvent are in a ratio of 0.2 g :(0.04~0.06) g :(15~25) mL; the hydrogen pressure is 1.5~2.5 MPa; the high-temperature stirring reaction temperature is 120~160 ℃, the time is 2~5 h, and the stirring speed is 500~700 rpm.

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