A metal-loaded BN type catalyst for one-step conversion of methane to formaldehyde and a preparation method thereof

Abstract

The application relates to the technical field of catalyst preparation, in particular to a metal-loaded BN type catalyst for one-step conversion of methane into formaldehyde and a preparation method thereof. The preparation method comprises the following steps: S1, soaking nanometer boron nitride into a hydrogen peroxide solution by ultrasonic dispersion; S2, ultrasonically dispersing the nanometer boron nitride treated in the step S1 into a polyvinyl alcohol solution, and then adding sodium benzoate to obtain a reaction solution; S3, uniformly coating the reaction solution obtained in the step S2 on a glass substrate to obtain a glass substrate with a film; S4, treating the glass substrate with the film obtained in the step S3 under ultraviolet light in a nitrogen atmosphere; S5, dissolving the film to obtain modified nanometer boron nitride; S6, mixing the modified nanometer boron nitride with chloroauric acid, adjusting pH, and filtering and precipitating to obtain the catalyst. The catalyst prepared by the application has high formaldehyde yield, the preparation method is simple, and the catalyst is suitable for promotion.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of catalyst preparation, in particular to a metal-loaded BN type catalyst for one-step conversion of methane to formaldehyde and a preparation method thereof. BACKGROUND

[0002] Formaldehyde is a colorless organic compound with a pungent odor that has a serious impact on health. Formaldehyde is widely used in the production of various resins, such as urea-formaldehyde resin, phenol-formaldehyde resin, and polyformaldehyde, etc. In addition, it is also used to synthesize vinylon, 1,4-butanediol, pentaerythritol, and other chemical products, and as a disinfectant and preservative. Formaldehyde synthetic resins have important applications in the fields of wood processing, building materials, and textile treatment. Formaldehyde is an important industrial raw material.

[0003] Modern scientific research shows that catalysts prepared by loading noble metal particles on semiconductors can catalyze the conversion of methane to formaldehyde, and further control the further oxidation of formaldehyde by controlling the particle size of metal nanoparticles, thereby improving the selectivity of methane conversion to formaldehyde. In the prior art, to prepare such catalysts, noble metal salts are generally mixed with semiconductor nanoparticles, and then noble metal nanoparticles are deposited on the surface of the semiconductor material by deposition method. The noble metal nanoparticles prepared by this method are not uniform enough in deposition on the surface of the semiconductor, and the activity is not enough, resulting in low efficiency of conversion to formaldehyde. Therefore, in view of the problems raised in the above background art, a new type of functionalized catalyst and a preparation method thereof are proposed by those skilled in the art. SUMMARY

[0004] The present application aims to provide a metal-loaded BN type catalyst for one-step conversion of methane to formaldehyde and a preparation method thereof to solve the problems raised in the above background art.

[0005] To achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0006] A preparation method of a metal-loaded BN type catalyst for one-step conversion of methane to formaldehyde, the preparation method comprising the following steps:

[0007] S1, ultrasonic dispersion of nano boron nitride into hydrogen peroxide solution for 0.5-1.5h, then centrifugal filtration, and vacuum drying of the filtered product to constant weight at room temperature after washing with sufficient deionized water;

[0008] S2, ultrasonic dispersion of nano boron nitride treated in step S1 into polyvinyl alcohol solution, then adding sodium benzoate, continuous stirring for 0.5-1h, then adding polyethylene glycol and sodium citrate, and continuing stirring for 1-2h to obtain a reaction solution;

[0009] S3, evenly coating the reaction solution obtained in step S2 on a glass substrate, and placing the glass substrate carrying the reaction solution into an oven to bake for 0.8-1.2 h to obtain a glass substrate with a film;

[0010] S4, placing the glass substrate with the film obtained in step S3 into a sealed container filled with nitrogen, and then irradiating the glass substrate with the film with ultraviolet light;

[0011] S5, after the ultraviolet irradiation treatment in step S4, separating the glass substrate from the film thereon, and placing the film in deionized water and heating to 90-100℃ until the film is completely dissolved, and then centrifugal filtration, and drying the filtered product to constant weight at room temperature to obtain modified nanometer boron nitride;

[0012] S6, ultrasonic dispersion of the modified nanometer boron nitride obtained in step S5 into a chloroauric acid solution, dropwise addition of ammonia water to adjust the pH to 8.5-9.5, and evaporation drying to constant weight at 70-85℃ under stirring, and then heat treatment at 400-450℃ for 5-6 h to obtain a catalyst (Au nanoparticles supported on BN).

[0013] Further, the mass ratio between the nanometer boron nitride and the hydrogen peroxide in step S1 is 1:(20-30), and the concentration of the hydrogen peroxide is 15-20 wt%.

[0014] Further, the mass ratio between the nanometer silicon dioxide, polyvinyl alcohol, sodium benzoate, deionized water, polyethylene glycol, and sodium citrate in the polyvinyl alcohol solution in step S2 is (3-6):(12-15):1:(60-100):(3-5):(0.3-0.5).

[0015] Further, the temperature of the oven in step S3 is 75-90℃.

[0016] Further, the wavelength of the ultraviolet light in step S4 is 365 nm, and the irradiation time of the ultraviolet light is 0.5-1 h.

[0017] Further, the mass ratio between the film and the deionized water in step S5 is 1:(10-20).

[0018] Further, the chloroauric acid solution in step S6 contains chloroauric acid, deionized water, and ethanol, and the mass ratio between the chloroauric acid, deionized water, ethanol, and modified nanometer boron nitride is 1:(400-500):(160-200):(200-250).

[0019] Further, the noble metal salt solution in step S6 is also a platinum salt solution or a silver salt solution.

[0020] The metal-loaded BN type catalyst for one-step conversion of methane to formaldehyde is prepared by the preparation method of the metal-loaded BN type catalyst for one-step conversion of methane to formaldehyde.

[0021] Compared with the prior art, the present application has the beneficial effects that:

[0022] 1. In the present application, the surface of nano boron nitride is regulated and activated by ultraviolet light treatment, taking advantage of the photoelectrochemical effect of semiconductors, which not only enhances the interface bonding capacity, but also makes the noble metal nanoparticles on the surface of boron nitride uniformly distributed and not easy to agglomerate, thereby improving the catalytic effect of the material. The added polyethylene glycol and sodium citrate are beneficial to the uniform dispersion of nano boron nitride and the subsequent loading of gold nanoparticles.

[0023] 2. In the present application, nano boron nitride is dispersed in a polyvinyl alcohol solution, then a film layer structure is formed by coating, and then the nano boron nitride is treated by ultraviolet light irradiation in nitrogen. Compared with direct irradiation of solid powder, irradiation shadows are less likely to occur during irradiation, and the irradiation of nano boron nitride is uniform. Compared with irradiation in solution, the particles are fixed, and the irradiation control is more precise. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 XRD pattern of the catalyst prepared in Example 1 of the present application;

[0025] Figure 2 TEM pattern of the catalyst prepared in Example 1 of the present application;

[0026] Figure 3 Mapping pattern of the catalyst prepared in Example 1 of the present application;

[0027] Figure 4 Process flow chart for preparing the catalyst of the present application. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0029] Please refer to Figures 1 to 4 , the present application provides:

[0030] Example 1

[0031] A method for preparing a metal-supported BN-type catalyst for one-step conversion of methane to formaldehyde, the method comprising the following steps:

[0032] S1. 1.2g of nano boron nitride was ultrasonically dispersed in 18wt% hydrogen peroxide solution and soaked for 0.8h. The amount of hydrogen peroxide used was 26g. After centrifugation and filtration, the filtered product was washed with sufficient deionized water and then vacuum dried at room temperature to constant weight.

[0033] S2. 1.0 g of boron nanoparticles treated in step S1 were ultrasonically dispersed into a polyvinyl alcohol solution containing 3.5 g of polyvinyl alcohol and 20 g of deionized water. Then, 0.25 g of sodium benzoate was added and stirred continuously for 0.6 h. Then, 1.0 g of polyethylene glycol and 0.1 g of sodium citrate were added and stirred for another 1.2 h to obtain the reaction solution.

[0034] S3. The reaction solution obtained in step S2 is uniformly coated onto the glass substrate, and the glass substrate containing the reaction solution is placed in an oven at 80°C and baked for 1.1 hours to obtain a glass substrate with a thin film.

[0035] S4. Place the glass substrate with thin film obtained in step S3 into a sealed container filled with nitrogen gas, and then irradiate the glass substrate with thin film with ultraviolet light with a wavelength of 365nm for 0.8h.

[0036] S5. After UV irradiation treatment in step S4, the glass substrate is separated from the film on it. 3.2g of the film is placed in 36g of deionized water and heated to 95℃ until the film is completely dissolved. Then, it is centrifuged and filtered. The filtered product is washed with sufficient deionized water and dried at room temperature to constant weight to obtain modified nano boron nitride.

[0037] S6. The 0.4g modified boron nitride nanoparticles obtained in step S5 are ultrasonically dispersed in a noble metal salt solution. The noble metal solution is a chloroauric acid solution (the noble metal salt solution can also be a platinum salt solution or a silver salt solution; chloroauric acid was used for experimental verification in Examples 1-3). Ammonia water is added dropwise to adjust the pH to 9. The chloroauric acid solution contains chloroauric acid, deionized water, and ethanol. The amounts of chloroauric acid, deionized water, and ethanol are 0.0018g, 0.81g, and 0.324g, respectively. The solution is evaporated and dried to constant weight at 80°C with stirring. Then, it is heat-treated at 420°C for 5.5h to obtain the catalyst.

[0038] Example 2

[0039] A method for preparing a metal-supported BN-type catalyst for one-step conversion of methane to formaldehyde, the method comprising the following steps:

[0040] S1. 1.2g of nano boron nitride was ultrasonically dispersed in 15wt% hydrogen peroxide solution and soaked for 0.5h. The amount of hydrogen peroxide used was 24g. After centrifugation and filtration, the filtered product was washed with sufficient deionized water and then vacuum dried at room temperature to constant weight.

[0041] S2. 1.0 g of boron nanoparticles treated in step S1 were ultrasonically dispersed into a polyvinyl alcohol solution containing 3.96 g of polyvinyl alcohol and 19.8 g of deionized water. Then, 0.33 g of sodium benzoate was added and stirred continuously for 0.5 h. Then, 1.0 g of polyethylene glycol and 0.11 g of sodium citrate were added and stirred for another 1 h to obtain the reaction solution.

[0042] S3. The reaction solution obtained in step S2 is uniformly coated onto the glass substrate, and the glass substrate containing the reaction solution is placed in an oven at 75°C and baked for 0.8 hours to obtain a glass substrate with a thin film.

[0043] S4. Place the glass substrate with thin film obtained in step S3 into a sealed container filled with nitrogen gas, and then irradiate the glass substrate with thin film with ultraviolet light of wavelength 365nm for 0.5h.

[0044] S5. After UV irradiation treatment in step S4, the glass substrate is separated from the film on it. 3.2g of the film is placed in 32g of deionized water and heated to 90℃ until the film is completely dissolved. Then, it is centrifuged and filtered. The filtered product is washed with sufficient deionized water and dried at room temperature to constant weight to obtain modified nano boron nitride.

[0045] S6. The 0.4 g of modified boron nanoparticles obtained in step S5 were ultrasonically dispersed in a noble metal salt solution. The noble metal solution was a chloroauric acid solution containing chloroauric acid, deionized water, and ethanol. The amounts of chloroauric acid, deionized water, and ethanol were 0.002 g, 0.8 g, and 0.32 g, respectively. Ammonia was added dropwise to adjust the pH to 8.5. The mixture was evaporated to constant weight at 70 °C with stirring. Then, it was heat-treated at 400 °C for 5 h to obtain the catalyst.

[0046] Example 3

[0047] A method for preparing a metal-supported BN-type catalyst for one-step conversion of methane to formaldehyde, the method comprising the following steps:

[0048] S1. Disperse 1.2g of nano boron nitride in 20wt% ultrasonically into hydrogen peroxide solution and soak for 1.5h. The amount of hydrogen peroxide used is 36g. Then centrifuge and filter. The filtered product is washed with sufficient deionized water and then vacuum dried at room temperature to constant weight.

[0049] S2. 1.0 g of boron nanoparticles treated in step S1 were ultrasonically dispersed into a polyvinyl alcohol solution containing 2.55 g of polyvinyl alcohol and 12 g of deionized water. Then, 0.17 g of sodium benzoate was added and stirred continuously for 1 h. Then, 0.85 g of polyethylene glycol and 0.083 g of sodium citrate were added and stirred for another 2 h to obtain the reaction solution.

[0050] S3. The reaction solution obtained in step S2 is uniformly coated onto the glass substrate, and the glass substrate containing the reaction solution is placed in an oven at 90°C and baked for 1.2 hours to obtain a glass substrate with a thin film.

[0051] S4. Place the glass substrate with thin film obtained in step S3 into a sealed container, fill the sealed container with nitrogen gas, and then irradiate the glass substrate with thin film with ultraviolet light with a wavelength of 365nm for 1 hour.

[0052] S5. After the ultraviolet light irradiation treatment in step S4, the glass substrate is separated from the film on it. 3.2g of the film is placed in 64g of deionized water and heated to 100℃ until the film is completely dissolved. Then, it is centrifuged and filtered. The filtered product is washed with sufficient deionized water and dried at room temperature to constant weight to obtain modified nano boron nitride.

[0053] S6. The modified 0.4g of boron nitride nanoparticles obtained in step S5 are ultrasonically dispersed in a noble metal salt solution. The noble metal solution is a chloroauric acid solution containing chloroauric acid, deionized water, and ethanol. The amounts of chloroauric acid, deionized water, and ethanol are 0.0016g, 0.8g, and 0.32g, respectively. Ammonia water is added dropwise to adjust the pH to 9.5. The mixture is evaporated and dried to constant weight at 85℃ with stirring. Then, it is heat-treated at 450℃ for 6h to obtain the catalyst.

[0054] Comparative Example 1

[0055] The difference between Comparative Example 1 and Example 1 is that step S4 is completely omitted, while the remaining steps are exactly the same as in Example 1.

[0056] Comparative Example 2

[0057] The difference between Comparative Example 2 and Example 1 is that the addition of polyethylene glycol and sodium citrate in step S2 was omitted, while the remaining steps are exactly the same as in Example 1.

[0058] Comparative Example 3

[0059] The difference between Comparative Example 3 and Example 1 is that steps S2-S5 were omitted. The hydrogen peroxide containing boron nanoparticles in step S1 was directly irradiated with 365nm ultraviolet light for the same duration as in Example 1. After filtration, washing, and drying, the boron nanoparticles participated in the reaction in step S6.

[0060] Comparative Example 4

[0061] The difference between Comparative Example 4 and Example 1 is that steps S2-S5 were omitted. The boron nitride nanoparticles treated with hydrogen peroxide in step S1 were filtered, washed, and dried, and then irradiated with 365nm ultraviolet light for the same duration as in Example 1.

[0062] Catalytic conversion experiment:

[0063] The experiment was conducted in a 400 mL glass reactor (PQ-256, Beijing Pofilai Technology Co., Ltd.), equipped with a quartz window for light irradiation. A 300 W xenon lamp (full-spectrum light, 600 mW / cm²) was used. 2 A CEL-HXF300 (CEAULIGHT Technology Co., Ltd.) light source was used, and infrared components were removed using filters to reduce thermal effects. A cooling water bath was used to maintain the reaction system temperature at 60 ± 1℃ to ensure the reaction proceeded under isothermal conditions. 20 mg of catalyst prepared in Examples 1-3 and Comparative Examples 1-4 were weighed and dispersed in a certain amount of deionized water, sonicated for 30 minutes to form a uniform suspension, and then transferred to the reactor. The reactor was sealed and purged for 10 minutes with a specific gas (such as a nitrogen-oxygen mixture or pure nitrogen) to remove air impurities and ensure a controllable reaction atmosphere. The purging gas flow rate was 50 mL / min. 5 mL of high-purity methane (CH4, 99.99%) was injected, and the light source was turned on to start the reaction. During the reaction, continuous stirring (300 rpm) was maintained to ensure mass transfer efficiency. Samples were taken every 20 minutes, and the product composition was analyzed using a gas chromatograph (GC, equipped with FID and TCD detectors), the formaldehyde concentration was monitored, and the formaldehyde yield was calculated.

[0064] The specific formaldehyde yields are shown in Table 1 below:

[0065] Table 1: Formaldehyde yield of catalysts prepared in Examples 1-3 and Comparative Examples 1-4

[0066]

[0067] As can be seen from the data in Table 1 above, the catalyst prepared in this invention, nano-boron nitride, can effectively improve the formaldehyde yield of the prepared catalyst after being treated with ultraviolet light. At the same time, during the ultraviolet light irradiation process, the irradiation is carried out through a light-transmitting thin film structure, which makes the prepared catalyst more efficient than solution irradiation and direct powder irradiation.

[0068] Figure 1 The XRD pattern of the catalyst prepared in Example 1 of this invention proves that the material was successfully synthesized;

[0069] Figure 2 This is a TEM image of the catalyst prepared in Example 1 of the present invention. Figure 3 The image shows a mapping of the catalyst prepared in Example 1 of this invention, which shows that the gold nanoparticles are uniformly distributed.

[0070] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a metal-supported BN-type catalyst for one-step conversion of methane to formaldehyde, characterized in that, The preparation method includes the following steps: S1. Disperse boron nitride nanoparticles ultrasonically in hydrogen peroxide solution and soak for 0.5-1.5 h, then centrifuge and filter. Wash the filtered product with sufficient deionized water and vacuum dry at room temperature to constant weight. S2. The boron nitride nanoparticles treated in step S1 are ultrasonically dispersed into a polyvinyl alcohol solution, then sodium benzoate is added and stirred continuously for 0.5-1 h. Then polyethylene glycol and sodium citrate are added and stirred for another 1-2 h to obtain the reaction solution. S3. The reaction solution obtained in step S2 is uniformly coated onto the glass substrate, and the glass substrate containing the reaction solution is placed in an oven and baked for 0.8-1.2 hours to obtain a glass substrate with a thin film. S4. Place the glass substrate with the thin film obtained in step S3 into a sealed container, fill the sealed container with nitrogen gas, and then irradiate the glass substrate with the thin film with ultraviolet light. S5. After UV irradiation treatment in step S4, the glass substrate is separated from the film on it. The film is placed in deionized water and heated to 90-100℃ until the film is completely dissolved. Then, it is centrifuged and filtered. The filtered product is washed with sufficient deionized water and dried at room temperature to constant weight to obtain modified nano boron nitride. S6. The modified boron nanoparticles obtained in step S5 are ultrasonically dispersed in a noble metal salt solution, and ammonia is added dropwise to adjust the pH to 8.5-9.

5. The mixture is then evaporated and dried to constant weight at 70-85℃ with stirring. After that, it is heat-treated at 400-450℃ for 5-6 hours to obtain the catalyst. The noble metal salt solution in step S6 is a chloroauric acid solution.

2. The method for preparing the metal-supported BN-type catalyst for one-step conversion of methane to formaldehyde according to claim 1, characterized in that, In step S1, the mass ratio of nano-boron nitride to hydrogen peroxide is 1:(20-30), and the concentration of hydrogen peroxide is 15-20wt%.

3. The method for preparing the metal-supported BN-type catalyst for one-step conversion of methane to formaldehyde according to claim 1, characterized in that, In step S2, the mass ratio of nano-silica, polyvinyl alcohol, sodium benzoate, deionized water, polyethylene glycol, and sodium citrate in the polyvinyl alcohol solution is (3-6):(12-15):1:(60-100):(3-5):(0.3-0.5).

4. The method for preparing the metal-supported BN-type catalyst for one-step conversion of methane to formaldehyde according to claim 1, characterized in that, The temperature of the oven in step S3 is 75-90℃.

5. The method for preparing the metal-supported BN-type catalyst for one-step conversion of methane to formaldehyde according to claim 1, characterized in that, In step S4, the wavelength of the ultraviolet light is 365nm, and the irradiation time of the ultraviolet light is 0.5-1h.

6. The method for preparing the metal-supported BN-type catalyst for one-step conversion of methane to formaldehyde according to claim 1, characterized in that, In step S5, the mass ratio between the membrane and deionized water is 1:(10-20).

7. The method for preparing the metal-supported BN-type catalyst for one-step conversion of methane to formaldehyde according to claim 1, characterized in that, In step S6, the chloroauric acid solution contains chloroauric acid, deionized water, and ethanol. The mass ratio of chloroauric acid, deionized water, ethanol, and modified nano boron nitride is 1:(400-500):(160-200):(200-250).

8. The method for preparing the metal-supported BN-type catalyst for one-step conversion of methane to formaldehyde according to claim 1, characterized in that, The precious metal salt solution in step S6 is also a platinum salt solution or a silver salt solution.

9. A metal-supported BN-type catalyst for one-step conversion of methane to formaldehyde, characterized in that, It was prepared by the method for preparing the metal-supported BN-type catalyst for one-step conversion of methane to formaldehyde as described in any one of claims 1-8.

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