A method for preparing an Au-supported MOF (Zr) catalyst, and products and uses thereof

Abstract

The application discloses a preparation method and product of an Au-loaded MOF(Zr) catalyst and application thereof, and belongs to the field of catalysts. The preparation method comprises the following steps: preparing a carrier MOF(Zr); dispersing the MOF(Zr) in a mixed solution of ethanol and deionized water, and then carrying out ultrasonic treatment; after the ultrasonic treatment, the mixed solution is placed in an ice water bath, and a HAuCl4 solution is added in the process of stirring; after sufficient stirring, a reducing agent is added, and stirring is carried out for 3-5 hours; after the reaction is completed, the precipitate is washed with deionized water for three times, and then dried, so as to obtain the MOF(Zr) catalyst loaded with Au nanoparticles. The Au nanoparticles can be efficiently utilized, and the special structure (multi-channel structure, large specific surface area, uniformly distributed active sites and the like) of the metal organic framework is favorable for the adhesion of the Au nanoparticles. The catalyst Au prepared by using NaBH4 has relatively high activity, and the catalyst prepared by using NaBH4 has the best catalytic activity.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of ammonia catalysis, and particularly relates to a preparation method and product of an Au-loaded MOF(Zr) catalyst and application thereof. BACKGROUND

[0002] Ammonia (NH3) is one of the most produced chemical products in the world, and is one of the most important chemical fertilizers and chemical raw materials. At present, a large-scale ammonia synthesis technology adopts a traditional process for synthesis. The traditional ammonia synthesis process uses a high-temperature and high-pressure Haber-Bosch method, which uses nitrogen and hydrogen as raw materials to synthesize under a relatively harsh environment, consumes a large amount of fossil energy, and emits a large amount of greenhouse gas, thereby causing pollution to the environment.

[0003] Therefore, it is particularly important to find a mild, energy-saving and environmentally friendly ammonia synthesis method.

[0004] At present, an electrochemical ammonia synthesis technology has a strong development potential. The technology uses water instead of hydrogen as a proton source, uses nitrogen to provide nitrogen atoms, and synthesizes ammonia through an electrocatalytic nitrogen reduction reaction at normal temperature and pressure. The reaction condition is mild, the raw material is easy to obtain, energy consumption is reduced, and no pollution is discharged in the synthesis process, thereby realizing sustainable development of green ammonia synthesis.

[0005] However, at the present stage, the electrochemical ammonia synthesis has problems of low ammonia generation rate and low yield, which makes it difficult to realize industrial production. SUMMARY

[0006] This section aims to summarize some aspects of the embodiments of the present application and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract and title of the specification to avoid obscuring the purpose of this section, the abstract and the title, and such simplifications or omissions cannot be used to limit the scope of the present application.

[0007] In view of the above and / or problems existing in the prior art, the present application is proposed.

[0008] Therefore, the purpose of the present application is to overcome the deficiencies in the prior art, and to provide a preparation method of an Au-loaded MOF(Zr) catalyst.

[0009] To solve the above technical problems, the present application provides the following technical scheme: a preparation method of an Au-loaded MOF(Zr) catalyst, comprising,

[0010] preparing a carrier MOF(Zr);

[0011] dispersing the MOF(Zr) in a mixture of ethanol and deionized water, and after ultrasonic treatment, placing the mixture in an ice water bath, and adding a HAuCl4 solution in the process of stirring;

[0012] After sufficient stirring, a reducing agent is added, stirred for 3-5 h, and after the reaction is completed, the precipitate is washed with deionized water three times, dried, and the Au nanoparticle-loaded MOF(Zr) catalyst is obtained;

[0013] The reducing agent includes sodium borohydride, hydrazine hydrate, sodium citrate, ascorbic acid, polyvinylpyrrolidone, and hydrogen peroxide.

[0014] As a preferred scheme of the preparation method of the Au-loaded MOF(Zr) catalyst according to the application, the reducing agent includes sodium borohydride.

[0015] As a preferred scheme of the preparation method of the Au-loaded MOF(Zr) catalyst according to the application, the preparation method of the MOF(Zr) includes,

[0016] ZrCl4 is dispersed in a mixture of N,N-dimethylformamide and acetic acid, and then terephthalic acid is added to the mixture and stirred uniformly;

[0017] The mixture is transferred to a hydrothermal reaction kettle and reacted at 120-140°C for 20-24 h, and the white precipitate that appears after the reaction is obtained by centrifugation, washing, and drying to obtain the carrier MOF(Zr).

[0018] As a preferred scheme of the preparation method of the Au-loaded MOF(Zr) catalyst according to the application, the volume ratio of N,N-dimethylformamide to acetic acid is 20:1, the mass-volume ratio of ZrCl4 to N,N-dimethylformamide is 2.53:300 (g:mL), and the mass-volume ratio of terephthalic acid to acetic acid is 2.52:15 (g:mL).

[0019] As a preferred scheme of the preparation method of the Au-loaded MOF(Zr) catalyst according to the application, the MOF(Zr) is dispersed in a mixture of ethanol and deionized water, and the volume ratio of ethanol to deionized water in the mixture is 1:1, and the mass-volume ratio of MOF(Zr) to the mixture is 0.2:40 (g:mL).

[0020] As a preferred scheme of the preparation method of the Au-loaded MOF(Zr) catalyst according to the application, the ultrasonic treatment has an ultrasonic time of 30 min and an ultrasonic power of 100 W.

[0021] As a preferred scheme of the preparation method of the Au-loaded MOF(Zr) catalyst according to the application, the concentration of the HAuCl4 solution is 30 mM, the solvent is deionized water, and the volume-mass ratio of the HAuCl4 solution to MOF(Zr) is 5:0.2 (mL:g).

[0022] As a preferred scheme of the preparation method of the Au-loaded MOF (Zr) catalyst, the molar ratio of the reducing agent to HAuCl4 is 5:3.

[0023] A further object of the present application is to provide the product prepared by the preparation method of the Au-loaded MOF (Zr) catalyst to overcome the deficiencies in the prior art.

[0024] Another object of the present application is to provide the application of the product prepared by the preparation method of the Au-loaded MOF (Zr) catalyst in electrochemical synthesis of ammonia to overcome the deficiencies in the prior art.

[0025] The present application has the following beneficial effects:

[0026] (1) The present application provides a preparation method of an Au-loaded MOF (Zr) catalyst, a product and application thereof. The Au-loaded MOF (Zr) catalyst improves the performance of electrocatalytic synthesis of ammonia. The combination of Au nanoparticles and MOF (Zr) with catalytic activity produces a synergistic effect, which promotes the performance of electrocatalytic synthesis of ammonia, and the ammonia generation rate of MOF (Zr) is increased from 7.43 ug mg -1 h -1 to 26.17 ug mg -1 h -1 , which proves that the addition of a certain amount of gold nanoparticles can optimize the catalytic activity of MOF (Zr).

[0027] (2) The present application can realize efficient utilization of Au nanoparticles. The special structure of metal organic framework (porous channel structure, large specific surface area, uniformly distributed active sites, etc.) is conducive to the attachment of Au nanoparticles. The catalyst Au prepared by NaBH4 has relatively high activity, and the catalyst prepared by NaBH4 has the best catalytic activity. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor. Among them:

[0029] Figure 1 MOF (Zr) / Au (5)-NaBH4 TEM diagram in the embodiment of the present application.

[0030] Figure 2 MOF (Zr) / Au (5)-N2H4 / TEM diagram in the embodiment of the present application.

[0031] Figure 3 TEM image of MOF (Zr) support in an embodiment of the present application.

[0032] Figure 4 Ammonia generation rate plot of MOF (Zr) / Au (x) - NaBH4 in an embodiment of the present application.

[0033] Figure 5 Ammonia generation rate plot of MOF (Zr) / Au (x) - N2H4 in an embodiment of the present application. DETAILED DESCRIPTION

[0034] In order to make the above objectives, features and advantages of the present application more apparent, the specific embodiments of the present application will be described in detail below with reference to the embodiments of the present application.

[0035] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. However, it will be apparent to one skilled in the art that the present application can be practiced without the specific details presented herein. In other instances, well-known methods have not been described in detail in order to avoid obscuring aspects of the present application.

[0036] Secondly, the "one embodiment" or "embodiment" referred to herein means that the specific features, structures or characteristics can be included in at least one implementation of the present application. The "in one embodiment" appearing in different places in the specification does not mean the same embodiment, nor is it an embodiment that is independent of or selected from other embodiments.

[0037] In the present application, the performance evaluation of electrocatalytic synthesis of ammonia is tested by an electrochemical workstation;

[0038] First, 8 mg of catalyst and 8 mg of activated carbon are weighed and added into 0.9 mL of anhydrous ethanol and 0.1 mL of NaFion solution, and then ultrasonic mixing is performed to prepare a catalyst suspension, which is dropped on a carbon paper with a size of 1.5 cm x 1.5 cm and naturally air-dried to prepare a working electrode with a catalyst loading of 0.5 mg cm -2 ;

[0039] Secondly, an H-type three-electrode electrolytic cell reaction device is used for electrochemical testing, the working electrode uses a catalyst-loaded carbon paper, the reference electrode uses an Ag / AgCl electrode, and the counter electrode uses a platinum wire, which are respectively connected to an electrochemical workstation, and the working electrode is scanned in a potential range of 0 to -1.8 V by linear sweep method (LSV), and it is determined that the optimal potential range for testing the catalyst is (-0.8 V to -1.2 V);

[0040] Finally, under the condition of the optimal potential range, select-0.8V, -0.9V, -1.0V, -1.1V and -1.2V voltage to carry out chronoamperometry (i-t) test under nitrogen, test for 3h, then take 5mL electrolyte to detect the ammonia concentration by using indigo phenol blue absorbance spectrophotometry after the reaction is completed.

[0041] The calculation formula of the ammonia generation rate is: R NH3 =(c×V) / (m×t), wherein c is the ammonia concentration in the electrolyte, V is the volume of the electrolyte, m is the mass of the catalyst on the carbon paper, and t is the electrochemical reaction time.

[0042] The ammonia generation rate calculated by the calculation is an index for evaluating the catalytic activity of the catalyst.

[0043] The preparation method of the MOF(Zr) in the application is as follows:

[0044] 2.53g of ZrCl4 is dispersed in a mixed solution of N,N-dimethylformamide and acetic acid (315mL in total, the volume ratio is 20:1), then (2.52g) of terephthalic acid is added to the mixed solution and stirred uniformly;

[0045] The mixed solution is transferred to a hydrothermal reaction kettle and reacted at 120℃ for 24h, and the white precipitate appeared after the reaction is centrifuged, washed and dried to obtain the carrier MOF(Zr), and the TEM diagram of the MOF(Zr) carrier is shown in Figure 3 .

[0046] Example 1:

[0047] Preparation and test of the MOF(Zr) / Au catalyst with NaBH4 as a reducing agent:

[0048] 0.2g of MOF(Zr) is dispersed in a mixed solution of ethanol and deionized water (40mL, the volume ratio of ethanol and deionized water is 1:1), and ultrasonic treatment is carried out for 30min (the ultrasonic treatment time is 30min, and the ultrasonic power is 100W);

[0049] The mixed solution is placed in an ice water bath, and 5mL of HAuCl4 (30mM) solution is added in the process of stirring, then 5mL of NaBH4 reducing agent (NaBH4 is dissolved in a mixed solution of ethanol and water with a volume ratio of 1:1, and the concentration is 50mM: 1.835g of sodium borohydride solid is taken, and then transferred to a 1000mL volumetric flask, and the mixed solution of ethanol and water is used to make up to the calibration line, and 50mM NaBH4 solution is obtained), and finally, the stirring is carried out for 3h for full reaction;

[0050] After the reaction is completed, the precipitate is washed with deionized water three times, and the catalyst MOF(Zr) / Au(5)-NaBH4 is obtained after drying at 80°C for 24h; the TEM diagram of MOF(Zr) / Au(5)-NaBH4 is shown in Figure 1 .

[0051] In order to regulate the loading amount of Au, the addition of HAuCl4 and NaBH4 during the reaction can be modified in proportion, and the other synthesis steps are consistent with the above. For example, x mL of HAuCl4(30mM) solution is added, followed by x mL of NaBH4 reducing agent, and the obtained catalyst is named as MOF(Zr) / Au(x)-NaBH4.

[0052] After the above catalyst is prepared into a working electrode for electrocatalytic synthesis of ammonia test, it can be seen from Figure 4 that the MOF(Zr) / Au(5)-NaBH4 catalyst has the highest electrocatalytic synthesis of ammonia performance, and the electrocatalytic synthesis of ammonia rate is 26.17ug mg -1 h -1 . The second is the MOF(Zr) / Au(4)-NaBH4 ammonia generation rate of 19.66ug mg -1 h -1 .

[0053] Example 2:

[0054] Preparation and test of MOF(Zr) / Au catalyst with N2H4 as reducing agent:

[0055] 0.2g MOF(Zr) is dispersed in a mixture of ethanol and deionized water (40mL, the volume ratio of ethanol and deionized water is 1:1), and ultrasonic treatment is performed for 30min (ultrasonic time is 30min, ultrasonic power is 100W);

[0056] The mixture is placed in an ice water bath, and 5mL of HAuCl4(30mM) solution is added during stirring, and then 5mL of N2H4 reducing agent (N2H4 aqueous solution, concentration is 50mM: 80% hydrazine hydrate is diluted to 50mM N2H4 aqueous solution, 3.125mL of 80% hydrazine hydrate is taken in a beaker, and is transferred to a 1000mL volumetric flask, and deionized water is used for constant volume) is added after sufficient stirring, and finally stirred for 3 hours for full reaction;

[0057] After the reaction is completed, the precipitate is washed with deionized water three times, and the catalyst MOF(Zr) / Au(5)-N2H4 is obtained after drying at 80°C for 24h, and the TEM diagram of MOF(Zr) / Au(5)-N2H4 is shown in Figure 2 .

[0058] To regulate the loading of Au, the addition of HAuCl4 and N2H4 during the reaction process can be modified in proportion, and other synthesis steps are consistent with the above. For example, x mL of HAuCl4 (30 mM) solution is added, followed by x mL of N2H4 reducing agent, and the obtained catalyst is named MOF(Zr) / Au(x)-N2H4.

[0059] After preparing the above catalyst into a working electrode for electrocatalytic synthesis of ammonia test, it can be seen from Figure 5 that the MOF(Zr) / Au(4)-N2H4 catalyst has the highest electrocatalytic synthesis of ammonia performance, and the electrocatalytic synthesis of ammonia rate is 26.17ug mg -1 h -1 . The second is the MOF(Zr) / Au(3)-N2H4 ammonia generation rate of 19.66ug mg -1 h -1 . The catalyst prepared using N2H4 as a reducing agent has lower electrochemical synthesis of ammonia performance than the catalyst prepared using NaBH4 as a reducing agent.

[0060] Example 3:

[0061] Preparation and testing of MOF(Zr) / Au catalyst with sodium citrate as reducing agent:

[0062] Similarly, using the same synthesis steps, the MOF(Zr) mixed solution is placed in an ice water bath, and 5 mL of HAuCl4 (30 mM) solution is added during stirring. After sufficient stirring, 5 mL of sodium citrate reducing agent (sodium citrate aqueous solution, concentration of 50 mM: weigh 6.45 g of sodium citrate solid in a beaker, add deionized water and stir to dissolve, then transfer to a 500 mL volumetric flask, use deionized water to constant volume, obtain 50 mM sodium citrate aqueous solution) is added, and finally stirred for 3 hours for full reaction; MOF(Zr) / Au(5)-C6H5Na3O7 catalyst with sodium citrate as reducing agent can be prepared.

[0063] By adding equal proportions of HAuCl4 and sodium citrate solution, catalysts with different Au loadings can be prepared, and the obtained catalyst is named MOF(Zr) / Au(x)-C6H5Na3O7.

[0064] After preparing the above catalyst into a working electrode for electrocatalytic synthesis of ammonia test, it can be seen from -1 h -1 that the MOF(Zr) / Au(4)-C6H5Na3O7 catalyst has the highest electrocatalytic synthesis of ammonia performance, and the electrocatalytic synthesis of ammonia rate is 9.14ug mg h . The ammonia generation rate of the prepared catalyst is slightly higher than that of the carrier MOF(Zr), but the catalytic activity is not as good as that of NaBH4 and N2H4.

[0065] Example 4:

[0066] Preparation of MOF(Zr) / Au catalyst with ascorbic acid as reducing agent:

[0067] Similarly, using the same synthesis procedure, the MOF(Zr) mixed solution was placed in an ice water bath, and 5 mL of HAuCl4(30 mM) solution was added during stirring. After sufficient stirring, 5 mL of ascorbic acid reducing agent (50 mM ascorbic acid aqueous solution: 4.40 g of ascorbic acid solid was weighed into a beaker, deionized water was added and stirred to dissolve, then transferred to a 500 mL volumetric flask, and deionized water was used to dilute to volume to obtain a 50 mM ascorbic acid aqueous solution) was added, and finally stirred for 3 hours for full reaction. A MOF(Zr) / Au(5)-C6H8O6 catalyst with ascorbic acid as reducing agent was prepared.

[0068] By adding equal proportions of HAuCl4and ascorbic acid solution, catalysts with different Au loadings can be prepared, and the obtained catalysts are named MOF(Zr) / Au(x)-C6H8O6.

[0069] After the above catalysts were prepared into working electrodes for electrocatalytic ammonia synthesis tests, it was found that the MOF(Zr) / Au(5)-C6H8O6 catalyst had the highest electrocatalytic ammonia synthesis performance, with an electrocatalytic ammonia synthesis rate of 10.45 ug mg -1 h -1 .

[0070] The ammonia generation rate of the prepared catalyst was similar to that with sodium citrate as reducing agent, and was slightly higher than that of the carrier MOF(Zr), but the catalytic activity was not as good as that of NaBH4and N2H4.

[0071] From Figures 1-2 It can be seen that the shape and size of Au nanoparticles produced using different reducing agents are different, and the degree of utilization of Au nanoparticles is also different. The catalyst prepared using NaBH4has smaller Au nanoparticle size, more uniform distribution, and relatively higher activity.

[0072] It should be noted that the above examples are only used to illustrate the technical solutions of the present application and are not limiting. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application, and they should be included in the scope of the claims of the present application.

Claims

1. Use of an Au-supported MOF (Zr) catalyst in the electrochemical synthesis of ammonia, characterized in that: The Au-loaded MOF(Zr) catalyst is prepared by the following method, Preparation of the carrier MOF(Zr): ZrCl4 is dispersed in a mixed solution of N,N-dimethylformamide and acetic acid, and then terephthalic acid is added to the mixed solution and stirred uniformly; the mixed solution is transferred to a hydrothermal reaction kettle and reacted at 120-140°C for 20-24 hours; the white precipitate appearing after the reaction is obtained by centrifugation, washing and drying, and the volume ratio of N,N-dimethylformamide to acetic acid is 20:1, the mass-volume ratio of ZrCl4 to N,N-dimethylformamide is 2.53:300 (g:mL), and the mass-volume ratio of terephthalic acid to acetic acid is 2.52:15 (g:mL); MOF(Zr) is dispersed in a mixed solution of ethanol and deionized water, and after ultrasonic treatment, the mixed solution is placed in an ice water bath, and HAuCl4 solution is added during stirring, wherein the volume ratio of ethanol to deionized water in the mixed solution is 1:1, the mass-volume ratio of MOF(Zr) to the mixed solution is 0.2:40 (g:mL), the concentration of the HAuCl4 solution is 30 mM, the solvent is deionized water, and the volume-mass ratio of the HAuCl4 solution to MOF(Zr) is 5:0.2 (mL:g); After sufficient stirring, a reducing agent is added, and stirring is performed for 3-5 hours; after the reaction is completed, the precipitate is washed with deionized water three times, and dried to obtain the Au nanoparticle-loaded MOF(Zr) catalyst, and the molar ratio of the reducing agent to HAuCl4 is 5:

3. The reducing agent is sodium borohydride.

2. Use according to claim 1, characterized in that: The ultrasonic treatment is performed for 30 minutes at an ultrasonic power of 100 W.

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