A sulfur and nitrogen co-doped carbon catalyst, a preparation method and application thereof

Abstract

The application belongs to the technical field of catalyst materials, and particularly relates to a sulfur and nitrogen co-doped carbon catalyst as well as a preparation method and application thereof. The sulfur and nitrogen co-doped carbon catalyst contains 0.18-4.4wt% of S and 0.08-7.0wt% of N. The preparation method of the sulfur and nitrogen co-doped carbon catalyst comprises the following steps: mixing a nitrogen-containing precursor, a sulfur-containing precursor and humin, and calcining to obtain the sulfur and nitrogen co-doped carbon catalyst. The sulfur and nitrogen co-doped carbon catalyst has Lewis acid-base double active centers by introducing sulfur and nitrogen into the carbon material, wherein S is an acid active center and N is an alkaline active center, and can fully activate epoxide and carbon dioxide, respectively, and has good catalytic performance and reusability.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of catalyst materials, and particularly relates to a sulfur and nitrogen co-doped carbon catalyst as well as a preparation method and application thereof. BACKGROUND

[0002] With the rapid development of global economy and the improvement of industrial productivity, a large amount of fossil resources is gradually consumed, and a large amount of carbon dioxide is also emitted. However, CO2 is also a safe, cheap and renewable C1 resource. Therefore, it is of great significance to efficiently convert CO2 into fine chemicals with high added value. In order to meet the requirements of atom economy and environmental friendliness, the reaction of CO2 and epoxide to prepare cyclic carbonate has attracted more and more attention. In addition, cyclic carbonate, as a chemical intermediate and polar solvent, plays an important role in the synthesis of fine chemicals, medicine, electrochemistry and other fields.

[0003] Among the many catalysts for the catalytic synthesis of cyclic carbonates, the currently reported heterogeneous catalysts mainly include metal oxides, molecular sieves, metal-organic framework materials, ionic liquid supported catalysts and poly-ionic liquid catalysts. However, these catalytic systems all have problems such as low catalytic efficiency, high preparation cost of catalysts, poor hydrothermal stability, harsh reaction conditions, and difficult separation of products.

[0004] Therefore, it is urgent to provide a catalyst which has good catalytic performance and reusability, and which is mild in reaction, easy to separate products, simple in preparation process and low in cost. SUMMARY

[0005] The present application aims to solve one or more technical problems in the prior art, and at least provide a beneficial alternative or create conditions. The present application provides a sulfur and nitrogen co-doped carbon catalyst which has good catalytic performance and reusability, and which is mild in reaction, easy to separate products, simple in preparation process and low in cost.

[0006] The inventive concept of the present application is that by introducing sulfur and nitrogen into carbon materials, the sulfur and nitrogen co-doped carbon catalyst has Lewis acid-base dual active centers, wherein S is an acidic active center and N is an alkaline active center, and the proportion of S and N in the catalyst is 0.18-4.4wt% and 0.08-7.0wt%, respectively. The epoxide and carbon dioxide can be fully activated, respectively, and the cycloaddition reaction of CO2 and epoxide can be efficiently catalyzed under mild conditions (reaction temperature ≤ 140℃, reaction pressure ≤ 2.0MPa, reaction time < 24h) without the aid of additives to obtain cyclic carbonate. The selectivity of cyclic carbonate can be as high as 90% or even more than 95%, and the catalytic activity does not change significantly after repeated use, which has good catalytic performance and reusability.

[0007] Therefore, the first aspect of the present application provides a sulfur and nitrogen co-doped carbon catalyst.

[0008] Specifically, the sulfur and nitrogen co-doped carbon catalyst is characterized in that, in terms of mass percentage, the proportion of S in the sulfur and nitrogen co-doped carbon catalyst is 0.18-4.4wt%, and the proportion of N is 0.08-7.0wt%.

[0009] Preferably, in terms of mass percentage, the proportion of S in the sulfur and nitrogen co-doped carbon catalyst is 0.2-4.0wt%, and the proportion of N is 0.1-6.5wt%.

[0010] Preferably, the specific surface area of the sulfur and nitrogen co-doped carbon catalyst is 20-450m 2 / g.

[0011] Further preferably, the specific surface area of the sulfur and nitrogen co-doped carbon catalyst is 20-400m 2 / g.

[0012] The second aspect of the present application provides a preparation method of a sulfur and nitrogen co-doped carbon catalyst.

[0013] Specifically, the preparation method of the sulfur and nitrogen co-doped carbon catalyst comprises the following steps:

[0014] Mixing a nitrogen-containing precursor, a sulfur-containing precursor and humin, and calcining to obtain the sulfur and nitrogen co-doped carbon catalyst.

[0015] Preferably, the nitrogen-containing precursor, the sulfur-containing precursor and the humin are first ground sufficiently and placed in a crucible, and the crucible is placed in a high-temperature tube furnace protected by N2 for calcination to obtain the sulfur and nitrogen co-doped carbon catalyst.

[0016] Specifically, the nitrogen-containing precursor, the sulfur-containing precursor and the humin provide N source, S source and C source respectively, and the three together make the prepared sulfur and nitrogen co-doped carbon catalyst have good catalytic performance and repeated use performance.

[0017] Specifically, humin is the main component of soil humus, and as a raw material for preparation, humin provides carbon source, which is equivalent to waste utilization and has great economic value.

[0018] Preferably, the nitrogen-containing precursor is selected from at least one of melamine, dicyandiamide and urea.

[0019] Preferably, the sulfur-containing precursor is thiourea.

[0020] Preferably, the ratio of the nitrogen-containing precursor, the sulfur-containing precursor and humin added by weight is (0.45-5.5):(0.45-4.5):1.

[0021] More preferably, the ratio of the nitrogen-containing precursor, the sulfur-containing precursor and the humin added, by weight, is (0.5-5):(0.5-4):1.

[0022] Preferably, the calcination temperature is 450-850℃ and the calcination time is 0.5-11h.

[0023] More preferably, the calcination temperature is 500-800℃, and the calcination time is 1-10h.

[0024] Preferably, the calcination process also includes washing and drying.

[0025] Preferably, the calcined solid is washed; deionized water is used for washing, and the number of washing cycles can vary depending on the actual situation.

[0026] Preferably, the drying is carried out in an oven; the drying temperature is 55-130℃, and the drying time is 1.5-24.5h.

[0027] More preferably, the drying temperature is 60-120℃, and the drying time is 2-24h.

[0028] More preferably, the drying temperature is 100°C and the drying time is 12 hours.

[0029] A third aspect of the present invention provides the application of a sulfur- and nitrogen-co-doped carbon catalyst in the synthesis of cyclic carbonates.

[0030] Preferably, the sulfur and nitrogen co-doped carbon catalyst is used in the catalytic synthesis of cyclic carbonates from epoxides and CO2.

[0031] Preferably, the application includes the following steps:

[0032] The cyclic carbonate is prepared by mixing epoxide, solvent, internal standard, sulfur and nitrogen co-doped carbon catalyst, introducing CO2, and reacting.

[0033] Preferably, the epoxide, solvent, internal standard, sulfur and nitrogen co-doped carbon catalyst are first added to a high-pressure reactor, sealed, and then CO2 is introduced to react and obtain the cyclic carbonate.

[0034] Preferably, the epoxide includes at least one of propylene oxide, ethylene oxide, dimethyl ethylene oxide, epichlorohydrin, cyclohexane oxide, and styrene oxide.

[0035] Preferably, the solvent includes at least one of acetonitrile, dichloromethane, and N,N-dimethylformamide.

[0036] Preferably, the internal standard includes at least one of toluene, dodecylamine, and chlorobenzene.

[0037] Preferably, the reaction temperature is 75-140℃, the reaction time is 5-24h, and the reaction pressure is 0.15-2.0MPa.

[0038] More preferably, the reaction temperature is 80-140℃, the reaction time is 6-24h, and the reaction pressure is 0.2-2.0MPa.

[0039] Specifically, the pressure of the reaction is regulated by introducing CO2.

[0040] Preferably, the reaction is followed by centrifugation; the centrifugation rate is 4500-11000 r / min, and the centrifugation time is 4-25 min.

[0041] More preferably, the centrifugation rate is 5000-10000 r / min, and the centrifugation time is 5-20 min.

[0042] Specifically, after centrifugation, the liquid product is analyzed by GC-MS (gas chromatography-mass spectrometry) to obtain the conversion rate of epoxides and the selectivity of cyclic carbonates.

[0043] Compared with the prior art, the beneficial effects of the technical solution provided by the present invention are as follows:

[0044] (1) This invention introduces sulfur and nitrogen into carbon materials, so that the sulfur and nitrogen co-doped carbon catalyst has Lewis acid-base dual active centers, where S is the acidic active center and N is the basic active center, and the proportions of S and N in the catalyst are 0.18-4.4wt% and 0.08-7.0wt%, respectively; it can fully activate epoxides and carbon dioxide, and has good catalytic performance and reusability.

[0045] (2) The sulfur and nitrogen co-doped carbon catalyst of the present invention can efficiently catalyze the cycloaddition reaction of CO2 and epoxide to obtain cyclic carbonates under mild conditions (temperature ≤140℃, pressure ≤2.0MPa, time <24h). The selectivity of the obtained cyclic carbonates can be higher than 95%, and its catalytic activity does not change significantly after repeated use.

[0046] (3) The present invention adopts a one-step high-temperature pyrolysis method, which is simple to prepare and has low catalyst raw material cost, making it easy to apply in industrial applications; in addition, humic acid is used as a raw material for preparation, which is equivalent to waste utilization and has great economic value.

[0047] (4) The present invention synthesizes cyclic carbonates without additives. The product and catalyst are easy to separate and purify, which can be achieved by solid-liquid separation. This solves the problem of difficult product separation in homogeneous systems and the need to add co-catalysts in most heterogeneous systems in traditional processes. Attached Figure Description

[0048] Fig. 1 This is a scanning electron microscope image of the sulfur and nitrogen co-doped carbon catalyst of Example 1 of the present invention;

[0049] Fig. 2 This is a scanning electron microscope image of the sulfur and nitrogen co-doped carbon catalyst of Example 3 of the present invention. Detailed Implementation

[0050] To enable those skilled in the art to more clearly understand the technical solutions described in this invention, the following embodiments are provided for illustration. It should be noted that the following embodiments do not constitute a limitation on the scope of protection claimed by this invention.

[0051] Unless otherwise specified, the raw materials, reagents or devices used in the following examples are available from conventional commercial sources or can be obtained by existing known methods.

[0052] Example 1

[0053] 1g of melamine, 1g of thiourea and 1g of humic acid were thoroughly ground and placed in a crucible. The crucible was then placed in a high-temperature tube furnace under N2 protection for calcination at 700℃ for 5 hours. After calcination, the solid was removed, washed with deionized water, and then dried in an oven at 100℃ for 12 hours to obtain a sulfur and nitrogen co-doped carbon catalyst.

[0054] Example 2

[0055] 0.5g of melamine, 1g of thiourea, and 1g of humin were thoroughly ground and placed in a crucible. The crucible was then placed in a high-temperature tube furnace under N2 protection for calcination at 650℃ for 3 hours. After calcination, the solid was removed, washed with deionized water, and then dried in an oven at 100℃ for 12 hours to obtain a sulfur and nitrogen co-doped carbon catalyst.

[0056] Example 3

[0057] 2g of melamine, 1g of thiourea, and 1g of humic acid were thoroughly ground and placed in a crucible. The crucible was then placed in a high-temperature tube furnace under N2 protection for calcination at 750℃ for 2 hours. After calcination, the solid was removed, washed with deionized water, and then dried in an oven at 100℃ for 12 hours to obtain a sulfur and nitrogen co-doped carbon catalyst.

[0058] Example 4

[0059] 1g of melamine, 0.5g of thiourea and 1g of humic acid were thoroughly ground and placed in a crucible. The crucible was then placed in a high-temperature tube furnace under N2 protection for calcination at 550℃ for 6 hours. After calcination, the solid was removed, washed with deionized water, and then dried in an oven at 100℃ for 12 hours to obtain a sulfur and nitrogen co-doped carbon catalyst.

[0060] Example 5

[0061] 1g of melamine, 2g of thiourea and 1g of humic acid were thoroughly ground and placed in a crucible. The crucible was then placed in a high-temperature tube furnace under N2 protection for calcination at 800℃ for 3 hours. After calcination, the solid was removed, washed with deionized water, and then dried in an oven at 100℃ for 12 hours to obtain a sulfur and nitrogen co-doped carbon catalyst.

[0062] Example 6

[0063] 1g of dicyandiamide, 1g of thiourea and 1g of humin were thoroughly ground and placed in a crucible. The crucible was then placed in a high-temperature tube furnace under N2 protection for calcination at 550℃ for 8 hours. After calcination, the solid was removed, washed with deionized water, and then dried in an oven at 100℃ for 12 hours to obtain a sulfur and nitrogen co-doped carbon catalyst.

[0064] Example 7

[0065] 1g of urea, 1g of thiourea and 1g of humin were thoroughly ground and placed in a crucible. The crucible was then placed in a high-temperature tube furnace under N2 protection for calcination at 700℃ for 5 hours. After calcination, the solid was removed, washed with deionized water, and then dried in an oven at 100℃ for 12 hours to obtain a sulfur and nitrogen co-doped carbon catalyst.

[0066] Comparative Example 1

[0067] The only difference between Comparative Example 1 and Example 1 is that Comparative Example 1 did not contain melamine; otherwise, they are the same as Example 1.

[0068] Comparative Example 2

[0069] The only difference between Comparative Example 2 and Example 1 is that Comparative Example 2 uses an equal amount of calcined durian peel powder to replace the humin in Example 1, while the rest is the same as Example 1.

[0070] Comparative Example 3

[0071] The only difference between Comparative Example 3 and Example 1 is that Comparative Example 3 did not contain humin, otherwise it was the same as Example 1.

[0072] Comparative Example 4

[0073] The only difference between Comparative Example 4 and Example 1 is that Comparative Example 4 uses 20 ml of dilute H2SO4 (0.05 M) instead of thiourea in Example 1, while the rest is the same as Example 1.

[0074] Performance testing

[0075] 1. Elemental analysis

[0076] Elemental analysis was performed on the sulfur and nitrogen co-doped carbon catalyst of Example 5. The elemental analysis was performed on a vario ELⅢ elemental analyzer manufactured by Elementar GmbH, Germany. The results showed that the C content was 95.96 wt%, the N content was 2.21 wt%, and the S content was 1.83 wt%.

[0077] 2. Microscopic tissue observation

[0078] Scanning electron microscopy was performed on the mesoporous nitrogen-doped carbon catalysts prepared in Examples 1 and 3, as follows: Figs. 1-2 As shown. The scanning electron microscope (SEM) images and energy dispersive spectroscopy (EDS) spectra of the samples were obtained using a NOVA NanoSEM 450 ultra-high resolution field emission scanning electron microscope from FEI (USA), with a voltage range of 1-30 kV. The samples were uniformly fixed on conductive adhesive and sputtered with gold. The magnification was 1×10⁻⁶. 4 -40×10 4 .

[0079] 3. Specific surface area test

[0080] The specific surface area of ​​the sulfur and nitrogen co-doped carbon catalysts in Examples 1-7 and Comparative Example 1 was tested. The test method was as follows: the nitrogen adsorption / desorption isotherms of the samples were measured using an Autosorb-1 physical adsorption instrument from Quantachrome, USA, at liquid nitrogen temperature (77K). The samples were degassed under vacuum for 2 hours before testing. The specific surface area of ​​the samples was calculated using the BET method, and the test results are shown in Table 1.

[0081] Table 1

[0082]

[0083] As shown in Table 1, the specific surface area of ​​the sulfur and nitrogen co-doped carbon catalysts in Examples 1-7 of the present invention is much larger than that of the sulfur and nitrogen co-doped carbon catalyst in Comparative Example 1.

[0084] 4. Catalytic performance test

[0085] The sulfur and nitrogen co-doped carbon catalysts prepared in Examples 1-7 and Comparative Examples 1-4 were used to catalyze the cycloaddition reaction of epichlorohydrin and CO2 to synthesize cyclic carbonates. The catalytic synthesis method and the catalytic performance testing method are as follows:

[0086] 0.2 g of sulfur and nitrogen co-doped carbon catalyst prepared in Examples 1-7 and Comparative Examples 1-4, 2 ml of epichlorohydrin, 22 ml of acetonitrile, and 1 ml of toluene were added to a high-pressure batch reactor. After sealing the reactor, CO2 was introduced to make the pressure in the reactor 1.0 MPa, the reaction temperature was 140 °C, and the reaction time was 20 h. After the reaction, the reactor was cooled to room temperature, excess CO2 was discharged, and the reactor was centrifuged at 6000 r / min for 5 min. The centrifuged liquid was analyzed by GC-MS, and the conversion rate of epichlorohydrin and the selectivity of cyclic carbonates were calculated. The results are shown in Table 2, serial numbers 1-11.

[0087] In addition, the sulfur and nitrogen co-doped carbon catalyst prepared in Example 5 was used to catalyze the cycloaddition reaction of propylene oxide and CO2 to synthesize cyclic carbonates. The catalytic synthesis method and catalytic performance testing method were the same as above, the only difference being the type of epoxide. The test results are shown in serial number 12 in Table 2.

[0088] The conversion rate of epoxides is calculated as follows:

[0089]

[0090] The method for calculating the selectivity of cyclic carbonates is as follows:

[0091]

[0092] 5. Reusability Performance Testing

[0093] The solid obtained after centrifugation in the first catalytic reaction of Example 3, which is the sulfur and nitrogen co-doped carbon catalyst, was washed three times with ethanol, dried at 100°C, and directly used in the next catalytic reaction. After the catalytic reaction was completed, the above operation was repeated three times. The catalytic performance results of the second, third, and fourth catalytic reactions of epichlorohydrin and CO2 to synthesize cyclic carbonates are shown in Table 2, numbers 13-15.

[0094] Table 2

[0095]

[0096]

[0097] As shown in Table 2, overall, the sulfur and nitrogen co-doped carbon catalysts of Examples 1-7 exhibited high conversion rates of epichlorohydrin and high selectivity for cyclic carbonates in the cycloaddition reaction of epichlorohydrin and CO2. Furthermore, the sulfur and nitrogen co-doped carbon catalyst of Example 5 also demonstrated high conversion rates of epichlorohydrin and high selectivity for cyclic carbonates in the cycloaddition reaction of epichlorohydrin and CO2. This indicates that the sulfur and nitrogen co-doped carbon catalyst of the present invention, containing N and S bifunctional active sites, possesses excellent catalytic activity in the cycloaddition reaction of epoxides and CO2 to synthesize cyclic carbonates.

[0098] Compared to Example 1, Comparative Example 1 differs only in that melamine was not added, resulting in a higher conversion rate of epoxides in Example 1. Compared to Example 1, Comparative Example 2 differs only in that an equal amount of calcined durian peel powder was used to replace the humin in Example 1, resulting in a higher conversion rate of epoxides in Example 1. Compared to Example 1, Comparative Example 3 differs only in that humin was not added, resulting in a higher conversion rate of epoxides and a higher selectivity for cyclic carbonates in Example 1. Compared to Example 1, Comparative Example 4 differs only in that dilute H2SO4 was used to replace the thiourea in Example 1, resulting in a higher conversion rate of epoxides and a higher selectivity for cyclic carbonates in Example 1. This indicates that melamine, thiourea, and humin are crucial to the catalytic performance of sulfur-nitrogen co-doped carbon catalysts. Nitrogen-containing precursors, sulfur-containing precursors, and humin are all indispensable, and their combined effect gives sulfur-nitrogen co-doped carbon catalysts good catalytic performance. Consequently, when applied to catalyze the cycloaddition reaction of epoxides and CO2 to synthesize cyclic carbonates, the conversion rate of epichlorohydrin and the selectivity of cyclic carbonates are both high.

[0099] Furthermore, as can be seen from serial numbers 3 and 13-15 in Table 2, during the first to fourth catalytic reactions of epichlorohydrin and CO2 to synthesize cyclic carbonates, there were no significant changes in the conversion rate of epichlorohydrin and the selectivity of cyclic carbonates. This indicates that the catalyst's catalytic activity did not change significantly after repeated use, demonstrating good reusability.

[0100] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. The application of a sulfur- and nitrogen-co-doped carbon catalyst in the catalytic synthesis of cyclic carbonates from epoxides and CO2, characterized in that, By mass percentage, the sulfur and nitrogen co-doped carbon catalyst contains 0.18-4.4 wt% S and 0.08-7.0 wt% N. The preparation method of the sulfur and nitrogen co-doped carbon catalyst includes the following steps: The sulfur-nitrogen co-doped carbon catalyst was prepared by mixing a nitrogen-containing precursor, a sulfur-containing precursor, and humin and calcining the mixture. The nitrogen-containing precursor is selected from at least one of melamine, dicyandiamide, and urea. The sulfur-containing precursor is thiourea; The ratio of the nitrogen-containing precursor, the sulfur-containing precursor and humin added by weight is (0.45-5.5):(0.45-4.5):

1.

2. The application according to claim 1, characterized in that, The specific surface area of ​​the sulfur and nitrogen co-doped carbon catalyst is 20-450 m². 2 / g.

3. The application according to claim 1, characterized in that, The calcination temperature is 450-850 ℃, and the calcination time is 0.5-11 h.

4. The application according to claim 1, characterized in that, Includes the following steps: The cyclic carbonate is prepared by mixing epoxide, solvent, internal standard, sulfur and nitrogen co-doped carbon catalyst, introducing CO2, and reacting.

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