Epoxidation catalyst as well as preparation method and application thereof

Abstract

The invention provides an epoxidation catalyst as well as a preparation method and application thereof, and belongs to the technical field of catalyst preparation. A carrier in the epoxidation catalyst is a carbon nitride nanosheet, and an active component is one or more of gold, palladium, platinum, ruthenium and rhodium. The catalyst provided by the invention is good in activity, long in service life and easy to recover.

Description

Technical Field

[0001] The invention belongs to the technical field of catalyst preparation, and in particular relates to an epoxidation catalyst and a preparation method and application thereof. Background Art

[0002] Octanediol is an important diol that can be mixed with a variety of organic chemicals in any proportion and has good compatibility with formulations. As a preservative, it is mild and has good preservative effect, and is suitable for a wide pH range; as a humectant, it plays a moisturizing role by capturing water molecules through hydrophilic groups, and can moisturize and soften the skin; as a multifunctional additive, it plays a role in thickening and stabilizing foam in bath fragrance products; as a solvent, it is miscible with a variety of other chemical substances and has good compatibility; in addition, it is widely used in synthetic fragrances, lubricant additives, plasticizers, adhesives and other industries.

[0003] With the rapid development of the cosmetics industry and the rise of the concept of "additive-free" preservatives products, functional preservatives have gradually attracted attention, and compound preservatives have become inevitable. The market space for new raw materials such as 1,2-octanediol is expected to continue to grow. 1,2-octanediol not only has a good antibacterial effect, but also has the function of moisturizing and conditioning the skin. It is suitable for a wide pH range and can be used alone or in combination. It can be compounded with other components to broaden the antibacterial spectrum and improve the antibacterial activity. It is an excellent functional preservative, which has led to the rapid growth of demand for new additive-free preservatives such as 1,2-octanediol.

[0004] In the prior art, octanediol is generally prepared by an epoxidation method, in which a solid catalyst is used for catalysis. However, the existing catalysts are not stable and have a short service life. In addition, homogeneous catalysts have poor selectivity and cannot be recovered from the reaction medium, making post-processing difficult. Summary of the invention

[0005] The invention provides an epoxidation catalyst, a preparation method and an application thereof. The catalyst provided by the invention has good activity, a long service life and is easy to recycle.

[0006] In order to achieve the above object, the present invention provides an epoxidation catalyst, wherein the carrier in the catalyst is a carbon nitride nanosheet, and the active component is one or more of gold, palladium, platinum, ruthenium and rhodium.

[0007] Preferably, the active component is 0.1 wt% to 2 wt% of the carrier mass.

[0008] The present invention provides a method for preparing the epoxidation catalyst described in any one of the above, comprising the following steps:

[0009] a. thermally polymerizing a precursor of carbon nitride nanosheets to obtain a carrier;

[0010] b. The precursor of the active component is combined with a carrier to react to obtain an epoxidation catalyst; or the precursor of the active component is prepared into a sol, and the sol is combined with a carrier to obtain an epoxidation catalyst.

[0011] Preferably, the precursor of the carbon nitride nanosheets in step a comprises one or more of urea, thiourea, melamine, cyanamide and dicyandiamide.

[0012] Preferably, the temperature during thermal polymerization in step a is 200-800° C., the time is 1-5 hours, and the heating rate is 1-10° C. / min.

[0013] Preferably, the precursor of the active component in step b includes sodium chloroaurate, PdCl2, H2PtCl6·6H2O, AgNO3, RhCl3, RuCl3 and IrCl3.

[0014] The present invention provides the use of any one of the above-mentioned epoxidation catalysts in the epoxidation synthesis of 1,2-octanediol, wherein the 1,2-octanediol is synthesized by the following steps:

[0015] 1) mixing an aqueous solution of hydrogen peroxide and formic acid to carry out a synthesis reaction to obtain a mixture containing peroxyformic acid;

[0016] 2) adding a catalyst to the above mixture containing peroxyformic acid under stirring, and dropping 1-octene to carry out epoxidation reaction to obtain a reaction solution; wherein the temperature of the 1-octene is controlled at 8-10° C. during the dropping process;

[0017] 3) The reaction solution is filtered, distilled under reduced pressure and hydrolyzed in sequence to obtain 1,2-octanediol.

[0018] Preferably, the molar ratio of the hydrogen peroxide, formic acid, 1-octene and catalyst is 1.4:6:1:0.001-0.007.

[0019] Preferably, the synthesis temperature in step 1) is 25-45° C.; the epoxidation reaction temperature in step 2) is 40-60° C. and the reaction time is 6-10 h.

[0020] Preferably, in step 3), an aqueous solution of hydrogen peroxide is added dropwise to carry out a hydrolysis reaction, and after the hydrolysis reaction is completed, extraction and reduced pressure distillation are also carried out.

[0021] Compared with the prior art, the advantages and positive effects of the present invention are:

[0022] The catalyst prepared by the present invention uses carbon nitride (g-C3N4) nanosheets as carriers, not only has significant chemical and thermal stability, but also contains abundant pyridine nitrogen and amino groups, can effectively stabilize metal nanoparticles, obtain metal nano ions with small particle size and good dispersion, and at the same time, g-C3N4 has strong alkalinity, these alkaline sites can activate hydrogen peroxide, improve the utilization rate of hydrogen peroxide, and metal ions are evenly distributed in g-C3N4, providing abundant active sites, so that the catalyst exhibits excellent catalytic performance in olefin epoxidation reaction. The prepared solid catalyst can be recycled and reused by simple filtration.

[0023] At the same time, the preparation process of the present invention is simple, wherein the g-C3N4 raw material is cheap and readily available, and large-scale production can be achieved. DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] The invention provides an epoxidation catalyst, wherein the carrier in the catalyst is a carbon nitride nanosheet, and the active component is one or more of gold, palladium, platinum, ruthenium and rhodium.

[0026] In the present invention, the active component is preferably 0.1 wt% to 2 wt% of the carrier mass.

[0027] The catalyst provided by the present invention uses carbon nitride (g-C3N4) nanosheets as carriers, not only has significant chemical and thermal stability, but also contains rich pyridinic nitrogen and amino groups, can effectively stabilize metal nanoparticles, and obtain metal nano-ions with smaller particle size and better dispersion. At the same time, g-C3N4 has strong alkalinity, and these alkaline sites can activate hydrogen peroxide and improve the utilization rate of hydrogen peroxide. Metal ions are evenly distributed in g-C3N4, providing rich active sites, so that the catalyst exhibits excellent catalytic performance in olefin epoxidation reactions.

[0028] The present invention provides a method for preparing the epoxidation catalyst described in any one of the above, comprising the following steps:

[0029] a. thermally polymerizing a precursor of carbon nitride nanosheets to obtain a carrier;

[0030] b. The precursor of the active component is combined with a carrier to react to obtain an epoxidation catalyst; or the precursor of the active component is prepared into a sol, and the sol is combined with a carrier to obtain an epoxidation catalyst.

[0031] The present invention thermally polymerizes the precursor of carbon nitride nanosheets to obtain a carrier. In the present invention, the precursor of the carbon nitride nanosheets preferably includes one or more of urea, thiourea, melamine, cyanamide and dicyandiamide. In the present invention, the temperature during thermal polymerization is preferably 200-800°C, more preferably 300-650°C, and most preferably 500-600°C; the time during thermal polymerization is preferably 1-5h, more preferably 3-4h; the heating rate is preferably 1-10°C / min. The present invention adopts thermal polymerization to prepare carbon nitride nanosheets. The raw materials of this method are cheap and easy to obtain, the operation method is simple, and the obtained carbon nitride has a better shape. After obtaining the carrier, the present invention preferably grinds it so that the carrier is in powder form to facilitate the loading of the active component.

[0032] After obtaining the carrier, the present invention combines the precursor of the active component with the carrier for reaction to obtain an epoxidation catalyst; or prepares a sol from the precursor of the active component, combines the sol with the carrier, and obtains an epoxidation catalyst. In the present invention, the precursor of the active component preferably includes sodium chloroaurate, PdCl2, H2PtCl6·6H2O, AgNO3, RhCl3, RuCl3 and IrCl3.

[0033] The present invention also provides the use of any one of the above-mentioned epoxidation catalysts in the epoxidation synthesis of 1,2-octanediol, wherein the 1,2-octanediol is synthesized by the following steps:

[0034] 1) mixing an aqueous solution of hydrogen peroxide and formic acid to carry out a synthesis reaction to obtain a mixture containing peroxyformic acid;

[0035] 2) adding a catalyst to the above mixture containing peroxyformic acid under stirring, and dropping 1-octene to carry out epoxidation reaction to obtain a reaction solution; wherein the temperature of the 1-octene is controlled at 8-10° C. during the dropping process;

[0036] 3) The reaction solution is filtered, distilled under reduced pressure and hydrolyzed in sequence to obtain 1,2-octanediol.

[0037] The present invention mixes an aqueous solution of hydrogen peroxide and formic acid to carry out a synthesis reaction to obtain a mixture containing peroxyformic acid. In the present invention, the mass concentration of the aqueous solution of hydrogen peroxide is preferably 25-35%. In the present invention, the temperature during the synthesis reaction is preferably 25-45°C, more preferably 30-40°C. If the synthesis temperature is too high, the decomposition rate of H2O2 will be too fast, resulting in a reduction in the amount of epoxidation catalyst HCOOOH generated, which is not conducive to the terminal olefin epoxidation reaction. It can be understood that the present invention chooses to carry out the synthesis at 25-45°C to facilitate the synthesis reaction. If the epoxidation temperature is too high, the epoxidation reaction will become a gas-liquid two-phase reaction, resulting in insufficient reaction mixing, which is not conducive to the reaction.

[0038] After obtaining a mixture containing peroxyformic acid, the present invention adds a catalyst to the above mixture containing peroxyformic acid under stirring conditions, and drips 1-octene to carry out epoxidation reaction to obtain a reaction liquid; in the present invention, the physicochemical properties of 1-octene are highly flammable, and the storage conditions are recommended to be below 30°C. During the dripping process, it is recommended to control the temperature of 1-octene at 8-10°C, which is conducive to reaction safety and control of epoxidation reaction temperature. In the present invention, the temperature for epoxidation reaction is preferably 40-60°C, more preferably 45-55°C; the time is preferably 6-10h. If the epoxidation reaction is too high, the epoxidation reaction will become a gas-liquid two-phase reaction, resulting in insufficient reaction mixing, which is not conducive to the reaction, and if the reaction temperature is too low, it will affect the normal advancement of the reaction. It can be understood that: the present invention selects 40-60°C to facilitate the epoxidation reaction. In the present invention, the molar ratio of hydrogen peroxide, formic acid, 1-octene and catalyst is preferably 1.4:6:1:0.001-0.007.

[0039] After obtaining the reaction solution, the present invention sequentially filters, performs vacuum distillation and hydrolysis reaction on the reaction solution to obtain 1,2-octanediol. In the present invention, the catalyst in the reaction solution can be removed by filtration, so that the catalyst can be recycled. The solvent and water in the reaction solution can be removed by vacuum distillation. In the present invention, it is preferred to drip an aqueous solution of hydrogen peroxide for hydrolysis reaction. In the present invention, after the hydrolysis reaction is completed, it is preferred to perform extraction and vacuum distillation. In the present invention, the organic solvent for extraction is preferably methyl tert-butyl ether.

[0040] In order to further illustrate the present invention, the technical solutions provided by the present invention are described in detail below in conjunction with embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0041] Example 1

[0042] 50g of dicyandiamide was placed in a 100mL crucible, heated in a muffle furnace at a heating rate of 2℃ / min, heated to 550℃ and kept warm for 4h, cooled to room temperature, and the sample was ground to obtain a yellow solid powder g-C3N4 carrier. 25mL of 1.5mmol / L sodium citrate solution was ultrasonically dispersed for 20min to make it uniformly dispersed; then in a 60℃ water bath, 25mL of 0.2mmol / L sodium chloroaurate solution was dripped into the sodium citrate solution at a frequency of 5s / drop, and continued to stir in the dark for 2h. After cooling to room temperature, nano-Au sol was obtained. 0.2g of carrier g-C3N4 was placed in a small beaker and placed in a filter bottle, kept away from light throughout the process, and vacuumed to slowly absorb the above nano-Au sol. At a vacuum degree of 10 -3 Pa for two minutes, then stirred in the dark for 3 hours, filtered, and dried at 70°C to constant weight. A 0.5 wt% Au / g-C3N4 composite catalyst was obtained, which was recorded as catalyst 1.

[0043] Example 2

[0044] 50g of cyanamide was placed in a 100mL crucible, heated in a muffle furnace at a heating rate of 1℃ / min, heated to 500℃ and kept warm for 2h, cooled to room temperature, and the sample was ground to obtain a yellow solid powder g-C3N4 carrier. 25mL of 1.5mmol / L sodium citrate solution was ultrasonically dispersed for 20min to make it uniformly dispersed; then in a 60℃ water bath, 25mL of 0.12mmol / L sodium chloroaurate solution was dripped into the sodium citrate solution at a frequency of 5s / drop, and continued to stir in the dark for 2h. After cooling to room temperature, nano-Au sol was obtained. 0.2g of carrier g-C3N4 was placed in a small beaker and placed in a filter bottle, kept away from light throughout the process, and vacuumed to slowly absorb the above nano-Au sol. At a vacuum degree of 10 -3 Pa for two minutes, then stirred in the dark for 3 hours, filtered, and dried at 70°C to constant weight. A 0.3 wt% Au / g-C3N4 composite catalyst was obtained, which was recorded as catalyst 2.

[0045] Example 3

[0046] 50 g of dicyandiamide was placed in a 100 mL crucible and heated in a muffle furnace at a heating rate of 10°C / min. The temperature was raised to 550°C and kept for 4 h. The sample was cooled to room temperature and ground to obtain a yellow solid powdered g-C3N4 carrier. 1 g of the carrier g-C3N4 was dispersed in 20 mL of deionized water and ultrasonicated for 2 min. 0.033 g of PdCl2 was added and stirred for 30 min. The catalyst was reduced with 0.006 g of NaBH4. After centrifugation, washing and drying at 80°C, a dark green 2 wt% Pd / g-C3N4 composite catalyst was obtained, which was recorded as catalyst 3.

[0047] Example 4

[0048] 50g urea was placed in a 100mL crucible, heated in a muffle furnace at a heating rate of 5℃ / min, heated to 400℃ and kept for 5h, cooled to room temperature, and the sample was ground to obtain a yellow solid powder g-C3N4 carrier. 3.8g carrier g-C3N4 was dispersed in deionized water, ultrasonicated for 30min, and a uniform g-C3N4 suspension solution was obtained. 0.05g H2PtCl6·6H2O aqueous solution was added dropwise to the above suspension, and after irradiation and deposition under a xenon lamp light source for 1h, freeze-dried for 12h. Finally, a 0.5wt% Pt / g-C3N4 composite catalyst was obtained, which was recorded as catalyst 4.

[0049] Example 5

[0050] 50g of melamine was placed in a 100mL crucible, heated in a muffle furnace at a heating rate of 6℃ / min, heated to 600℃ and kept warm for 4h, cooled to room temperature, and the sample was ground to obtain a yellow solid powder g-C3N4 carrier. 25mL of 1.5mmol / L sodium citrate solution was ultrasonically dispersed for 20min to make it uniformly dispersed; then in a 60℃ water bath, 25mL of 0.4mmol / L sodium chloroaurate solution was dripped into the sodium citrate solution at a frequency of 5s / drop, and continued to stir in the dark for 2h. After cooling to room temperature, nano-Au sol was obtained. 0.2g of carrier g-C3N4 was placed in a small beaker and placed in a filter bottle, kept away from light throughout the process, and vacuumed to slowly absorb the above nano-Au sol. At a vacuum degree of 10 -3 Pa for two minutes, then stirred in the dark for 3 hours, filtered, and dried at 80°C to constant weight. A 1.0 wt% Au / g-C3N4 composite catalyst was obtained, which was recorded as catalyst 5.

[0051] Example 6

[0052] 50 g of melamine was placed in a 100 mL crucible and heated in a muffle furnace at a heating rate of 6°C / min. The temperature was raised to 600°C and kept for 4 h. The sample was cooled to room temperature and ground to obtain a yellow solid powdered g-C3N4 carrier. 0.2 g of the carrier g-C3N4 carrier was weighed and placed in a jacketed beaker. 2.04 mL of RhCl3·3H2O solution was added and stirred for 24 h. Subsequently, 4 mL of a reducing agent (a mixed solution of 0.1 mol / L NaOH and 0.53 mol / L NaBH4) was added at -3°C and the mixture was reduced at low temperature for 5 h. After centrifugal drying, a 0.4 wt% Rh / g-C3N4 composite catalyst was obtained, which was recorded as catalyst 6.

[0053] Example 7

[0054] 50g of melamine was placed in a 100mL crucible and heated in a muffle furnace at a heating rate of 6℃ / min. The temperature was raised to 600℃ and kept for 4h. The sample was cooled to room temperature and ground to obtain a yellow solid powdered g-C3N4 carrier. 0.2g of g-C3N4 was put into a cup. 0.83mL of hydrated RuCl3 solution (1g / 100mL) was measured and stirred at 60r / min for 24h. 1mL of deionized water containing 0.04g of NaOH and 0.02g of NaBH4 was added thereto at a speed of 270r / min. After reduction for 5h, the composite catalyst 2wt% Ru / g-C3N4 was obtained by centrifugation and drying, which was recorded as catalyst 7.

[0055] Example 8

[0056] H2O2 and HCOOH with a mass concentration of 30% were added to a four-necked flask to synthesize peroxyformic acid (during the synthesis process, the synthesis temperature was controlled to be 35°C), stirring was started, and after the temperature was stabilized, the catalysts of Example 1 were added respectively, and 1-octene was slowly dripped into the four-necked flask for epoxidation reaction (the molar ratio of the raw materials was n(1-octene):n(H2O2):n(HCOOH):n(catalyst)=1:1.4:6:0.005), the dropping temperature was controlled at 10°C, the epoxidation reaction temperature was 50°C, and the reaction was carried out for 8h. After completion, the catalyst is filtered and recovered for reuse, and the reaction solution is subjected to reduced pressure distillation (pressure of 0.095 MPa and distillation temperature of 80°C) to remove the formic acid aqueous solution. After distillation is completed, sodium hydroxide aqueous solution is added dropwise to the reaction solution, and the pH of the reaction solution is adjusted to 11 to hydrolyze the formate ester in the reaction solution. After the hydrolysis is completed, the oil phase is extracted with an organic solvent (methyl tert-butyl ether), and then the organic solvent is recovered by atmospheric distillation (distillation temperature of 60°C) to obtain crude 1,2-octanediol. The crude product is subjected to reduced pressure distillation (pressure of 0.095 MPa and distillation temperature of 120°C) to obtain high-purity 1,2-octanediol, and gas chromatography analysis is performed. The specific results are shown in Table 1.

[0057] Example 9

[0058] H2O2 and HCOOH with a mass concentration of 30% were added to a four-necked flask to synthesize peroxyformic acid (during the synthesis process, the synthesis temperature was controlled to be 30°C), stirring was turned on, and after the temperature was stabilized, the catalyst in Example 1 above was added, and 1-octene was slowly dripped into the four-necked flask for epoxidation reaction (the molar ratio of the raw materials was n(1-octene):n(H2O2):n(HCOOH):n(catalyst)=1:1.4:6:0.002), the dropping temperature was controlled at 10°C, the epoxidation reaction temperature was 45°C, and the reaction was carried out for 6h. After completion, the catalyst is filtered and recovered for reuse, and the reaction solution is subjected to reduced pressure distillation (pressure of 0.095 MPa and distillation temperature of 80°C) to remove the formic acid aqueous solution. After distillation is completed, sodium hydroxide aqueous solution is added dropwise to the reaction solution, and the pH of the reaction solution is adjusted to 11 to hydrolyze the formate ester in the reaction solution. After the hydrolysis is completed, the oil phase is extracted with an organic solvent (methyl tert-butyl ether), and then the organic solvent is recovered by atmospheric distillation (distillation temperature of 60°C) to obtain crude 1,2-octanediol. The crude product is subjected to reduced pressure distillation (pressure of 0.095 MPa and distillation temperature of 120°C) to obtain high-purity 1,2-octanediol, and gas chromatography analysis is performed. The specific results are shown in Table 1.

[0059] Example 10

[0060] H2O2 and HCOOH with a mass concentration of 30% were added to a four-necked flask to synthesize peroxyformic acid (during the synthesis process, the synthesis temperature was controlled to be 45°C), stirring was started, and after the temperature was stabilized, the catalyst of Example 1 was added, and 1-octene was slowly dripped into the four-necked flask for epoxidation reaction (the molar ratio of the raw materials was n(1-octene):n(H2O2):n(HCOOH):n(catalyst)=1:1.4:6:0.003), the dropping temperature was controlled to be 10°C, the epoxidation reaction temperature was 55°C, and the reaction was carried out for 10 hours. After completion, the catalyst is filtered and recovered for reuse, and the reaction solution is subjected to reduced pressure distillation (pressure of 0.095 MPa and distillation temperature of 80°C) to remove the formic acid aqueous solution. After distillation is completed, sodium hydroxide aqueous solution is added dropwise to the reaction solution, and the pH of the reaction solution is adjusted to 11 to hydrolyze the formate ester in the reaction solution. After the hydrolysis is completed, the oil phase is extracted with an organic solvent (methyl tert-butyl ether), and then the organic solvent is recovered by atmospheric distillation (distillation temperature of 60°C) to obtain crude 1,2-octanediol. The crude product is subjected to reduced pressure distillation (pressure of 0.095 MPa and distillation temperature of 120°C) to obtain high-purity 1,2-octanediol, and gas chromatography analysis is performed. The specific results are shown in Table 1.

[0061] Comparative Example 1

[0062] The difference from Example 8 is that the peroxyformic acid synthesis temperature is 60°C, the epoxidation reaction temperature is 80°C, and the other operations are exactly the same as Example 8.

[0063] H2O2 and HCOOH with a mass concentration of 30% were added to a four-necked flask to synthesize peroxyformic acid (during the synthesis process, the synthesis temperature was controlled to be 60°C), stirring was turned on, and after the temperature was stabilized, the catalysts of Example 1 were added respectively, and 1-octene was slowly dripped into the four-necked flask for epoxidation reaction (the molar ratio of the raw materials was n(1-octene):n(H2O2):n(HCOOH):n(catalyst)=1:1.4:6:0.005), the dropping temperature was controlled at 10°C, the epoxidation reaction temperature was 80°C, and the reaction was carried out for 8h. After completion, the catalyst is filtered and recovered for reuse, and the reaction solution is subjected to reduced pressure distillation (pressure of 0.095 MPa and distillation temperature of 80°C) to remove the formic acid aqueous solution. After distillation is completed, sodium hydroxide aqueous solution is added dropwise to the reaction solution, and the pH of the reaction solution is adjusted to 11 to hydrolyze the formate ester in the reaction solution. After the hydrolysis is completed, the oil phase is extracted with an organic solvent (methyl tert-butyl ether), and then the organic solvent is recovered by atmospheric distillation (distillation temperature of 60°C) to obtain crude 1,2-octanediol. The crude product is subjected to reduced pressure distillation (pressure of 0.095 MPa and distillation temperature of 120°C) to obtain high-purity 1,2-octanediol, and gas chromatography analysis is performed. The specific results are shown in Table 1.

[0064] Comparative Example 2

[0065] The difference from Example 8 is that the catalyst is g-C3N4, and no nano-metal particles are loaded. The other operations are exactly the same as those of Example 8. The specific preparation process of the catalyst is:

[0066] 50 g of dicyandiamide was placed in a 100 mL crucible and heated in a muffle furnace at a heating rate of 2°C / min. The temperature was raised to 550°C and kept for 4 h. The sample was cooled to room temperature and the yellow solid powder g-C3N4 carrier was obtained after grinding the sample, which was recorded as catalyst 8.

[0067] The obtained high-purity 1,2-octanediol was subjected to gas chromatography analysis. The specific results are shown in Table 1.

[0068] Comparative Example 3

[0069] The difference from Example 8 is that the catalyst is nano Au particles, denoted as catalyst 9, and the other operations are exactly the same as those of Example 8. The specific preparation process of the catalyst is:

[0070] Ultrasonic dispersion of 25 mL of 1.5 mmol / L sodium citrate solution was performed for 20 min to make it uniformly dispersed; then, 25 mL of 0.1 mmol / L sodium chloroaurate solution was dripped into the sodium citrate solution at a frequency of 5 s / drop in a 60°C water bath, and stirring was continued for 2 h in the dark. After cooling to room temperature, nano-Au sol was obtained.

[0071] The obtained high-purity 1,2-octanediol was subjected to gas chromatography analysis. The specific results are shown in Table 1.

[0072] Comparative Example 4

[0073] The difference from Example 8 is that no catalyst is added, the reaction time is 12 hours, and the other operations are exactly the same as Example 8. The specific operations are as follows:

[0074] Add H2O2 and HCOOH with a mass concentration of 30% into a four-necked flask to synthesize peroxyformic acid (during the synthesis process, the synthesis temperature is controlled at 35°C), start stirring, and after the temperature stabilizes, slowly drop 1-octene into the four-necked flask for epoxidation reaction (the molar ratio of the raw materials is n(1-octene):n(H2O2):n(HCOOH)=1:1.4:6), control the dropping temperature at 10°C, the epoxidation reaction temperature at 50°C, and react for 12h. After completion, the catalyst is filtered and recovered for reuse, and the reaction solution is subjected to reduced pressure distillation (pressure of 0.095 MPa and distillation temperature of 80°C) to remove the formic acid aqueous solution. After distillation is completed, sodium hydroxide aqueous solution is added dropwise to the reaction solution, and the pH of the reaction solution is adjusted to 11 to hydrolyze the formate ester in the reaction solution. After the hydrolysis is completed, the oil phase is extracted with an organic solvent (methyl tert-butyl ether), and then the organic solvent is recovered by atmospheric distillation (distillation temperature of 60°C) to obtain crude 1,2-octanediol. The crude product is subjected to reduced pressure distillation (pressure of 0.095 MPa and distillation temperature of 120°C) to obtain high-purity 1,2-octanediol, and gas chromatography analysis is performed. The specific results are shown in Table 1.

[0075] Table 1

[0076]

[0077]

[0078] As can be seen from Table 1, the addition of the composite catalyst prepared by the present invention is more conducive to the catalytic epoxidation reaction, among which 0.5wt% Au / g-C3N4 composite catalyst 1 has the best effect. During the five cycles of the catalyst, the yield of 1,2-octanediol has no significant change, indicating that the catalyst has good stability and can be recycled. For the metal ion loading, if the loading is too little, there are few active sites and the reaction is incomplete. If the loading is too much, a clustering effect will occur, thereby reducing the charge transfer rate and affecting the reaction. In Comparative Example 1, the synthesis temperature of peroxyformic acid is too high, and the decomposition rate of H2O2 is too fast, resulting in a decrease in the amount of HCOOOH, a catalyst for the epoxidation reaction, which is not conducive to the epoxidation reaction of terminal olefins. The epoxidation reaction is too high, and the epoxidation reaction will become a gas-liquid two-phase reaction, resulting in insufficient reaction mixing, which is not conducive to the reaction. In Comparative Example 2, the lack of metal ions makes the catalyst have no active sites, but g-C3N4 has strong alkalinity. These alkaline sites can activate hydrogen peroxide and improve the utilization rate of hydrogen peroxide. From this perspective, the carrier can also improve part of the reaction efficiency. In Comparative Example 3, there is no carrier, the catalyst cannot be recovered, the cost is too high, and it is not conducive to industrial investment. In Comparative Example 4, in the absence of a catalyst, the reaction time of the formic acid-hydrogen peroxide system is too long, and the excess of formic acid is too large, which is not conducive to industrialization.

[0079] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. An epoxidation catalyst, characterized in that The carrier in the catalyst is carbon nitride nanosheets, and the active component is one or more of gold, palladium, platinum, ruthenium and rhodium.

2. The epoxidation catalyst according to claim 1, characterized in that The active component accounts for 0.1 wt% to 2 wt% of the carrier mass.

3. The method for preparing the epoxidation catalyst according to claim 1 or 2, characterized in that: The steps include: a. thermally polymerizing a precursor of carbon nitride nanosheets to obtain a carrier; b. The precursor of the active component is combined with a carrier to react to obtain an epoxidation catalyst; or the precursor of the active component is prepared into a sol, and the sol is combined with a carrier to obtain an epoxidation catalyst.

4. The preparation method according to claim 3, characterized in that: The precursor of the carbon nitride nanosheets in step a includes one or more of urea, thiourea, melamine, cyanamide and dicyandiamide.

5. The preparation method according to claim 3, characterized in that: The temperature for thermal polymerization in step a is 200-800° C., the time is 1-5 hours, and the heating rate is 1-10° C. / min.

6. The preparation method according to claim 3, characterized in that: The precursors of the active components in step b include sodium chloroaurate, PdCl2, H2PtCl6·6H2O, AgNO3, RhCl3, RuCl3, and IrCl3.

7. Use of the epoxidation catalyst according to claim 1 or 2 in epoxidation synthesis of 1,2-octanediol, characterized in that: 1,2-Octanediol was synthesized using the following steps: 1) mixing an aqueous solution of hydrogen peroxide and formic acid to carry out a synthesis reaction to obtain a mixture containing peroxyformic acid; 2) adding a catalyst to the above mixture containing peroxyformic acid under stirring, and dropping 1-octene to carry out epoxidation reaction to obtain a reaction solution; wherein the temperature of the 1-octene is controlled at 8-10° C. during the dropping process; 3) The reaction solution is filtered, distilled under reduced pressure and hydrolyzed in sequence to obtain 1,2-octanediol.

8. The use according to claim 7, characterized in that: The molar ratio of the hydrogen peroxide, formic acid, 1-octene and catalyst is 1.4:6:1:0.001-0.

007.

9. The use according to claim 7, characterized in that: The synthesis temperature in step 1) is 25-45° C.; the epoxidation reaction temperature in step 2) is 40-60° C. and the reaction time is 6-10 hours.

10. The use according to claim 7, characterized in that: In step 3), an aqueous solution of hydrogen peroxide is added dropwise to carry out a hydrolysis reaction, and after the hydrolysis reaction is completed, extraction and reduced pressure distillation are carried out.

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