Preparation method and application of iron-based catalyst

Abstract

The invention discloses a preparation method and application of an iron-based catalyst, and the preparation method comprises the following steps: firstly carrying out hydrothermal reaction on a mixed solution of ammonium metavanadate and an iron source aqueous solution, and then roasting at high temperature to obtain the iron-based catalyst. The iron-based non-noble metal catalyst is used for electro-catalysis propylene epoxidation of a membrane electrode system, and compared with an existing catalyst, the iron-based non-noble metal catalyst has the advantages that higher yield is obtained, and meanwhile, higher Faraday efficiency can be maintained. Through vanadium-doped modification, optimization of a preparation process of the ferrovanadate electrocatalyst and optimization of reaction conditions of using the iron-based catalyst to electrocatalyze propylene epoxidation, the current density is further improved, so that the yield of propylene oxide is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of iron-based catalysts, and particularly relates to a preparation method and application of an iron-based catalyst. Background Art

[0002] Among the currently reported catalysts for direct electrocatalytic epoxidation of olefins using water as the oxygen source, mainly noble metal catalysts such as Pt (platinum) and Ir (iridium) are used. Although some of these catalysts have shown good olefin epoxidation performance, they are rare in the earth and have too high costs, and are not suitable for future practical applications. Therefore, developing non-noble metal catalysts suitable for olefin epoxidation is more practically significant.

[0003] Iron-based non-noble metal catalysts have great development potential in the electrocatalytic epoxidation reaction of propylene, but their current density is small at high Faraday efficiency. Summary of the Invention

[0004] The purpose of this part is to outline some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments. Simplifications or omissions may be made in this part, as well as in the abstract and title of the present application, to avoid obscuring the purpose of this part, the abstract, and the title. However, such simplifications or omissions shall not be used to limit the scope of the present invention.

[0005] In view of the above and / or problems existing in the prior art, the present invention is proposed.

[0006] Therefore, the purpose of the present invention is to overcome the deficiencies in the prior art and provide a preparation method of an iron-based catalyst.

[0007] To solve the above technical problems, the present invention provides the following technical solutions:

[0008] Ammonium metavanadate and an iron source aqueous solution are stirred evenly to obtain a mixed solution;

[0009] The mixed solution is subjected to a hydrothermal reaction. After the reaction is completed, centrifugation and drying are carried out to obtain a solid powder;

[0010] The solid powder is calcined at a high temperature to obtain an iron-based catalyst;

[0011] The iron source includes one of iron nitrate and iron chloride.

[0012] As a preferred scheme of the preparation method of the iron-based catalyst of the present invention, wherein: the molar ratio of ammonium metavanadate to the iron source is 1:1 to 3.

[0013] As a preferred embodiment of the preparation method of the iron-based catalyst of the present invention, in which: in the mixed solution obtained by stirring ammonium metavanadate and an iron source solution evenly, the stirring time is 30 to 45 minutes, and the stirring temperature is 60 to 70 °C.

[0014] As a preferred embodiment of the preparation method of the iron-based catalyst of the present invention, in which: in the hydrothermal reaction of the mixed solution, the hydrothermal reaction temperature is 90 to 100 °C, and the hydrothermal reaction time is 4 to 5 hours.

[0015] As a preferred embodiment of the preparation method of the iron-based catalyst of the present invention, in which: after the reaction, centrifugation and drying are carried out to obtain solid powder, and the drying time is 12 to 18 hours.

[0016] As a preferred embodiment of the preparation method of the iron-based catalyst of the present invention, in which: in the high-temperature calcination of the solid powder, the calcination temperature is 500 to 550 °C, and the calcination time is 2 to 3 hours.

[0017] Another object of the present invention is to overcome the deficiencies in the prior art and provide an iron-based catalyst prepared by a preparation method of an iron-based catalyst.

[0018] Another object of the present invention is to overcome the deficiencies in the prior art and provide an application of an iron-based catalyst in electrocatalytic propylene epoxidation.

[0019] Another object of the present invention is to overcome the deficiencies in the prior art and provide a method for electrocatalytic propylene epoxidation.

[0020] To solve the above technical problems, the present invention provides the following technical solutions:

[0021] 1.8 to 2.2 mg of the iron-based catalyst according to claim 8, 9.8 to 10.2 μL of Nafion solution, and 0.9 to 1.1 mL of absolute ethanol are mixed evenly to obtain a slurry. Among them, the Nafion solution is composed of 5 wt% Nafion, 50 wt% ethanol, and 45 wt% water;

[0022] The slurry is coated on the surface of a carbon paper with a gas diffusion layer, and after drying, a gas diffusion electrode carrying an anode catalyst is obtained;

[0023] Using the gas diffusion electrode as the anode and nickel foam as the cathode, they are assembled together with an ion exchange membrane into a membrane electrode reactor;

[0024] Propylene gas is introduced into the anode at a flow rate of 9 to 11 mL / min, and at the same time, a 1 to 1.2 wt% NaCl solution is pumped into the cathode at a speed of 18 to 22 mL / min, and an electrochemical reaction is carried out by the potentiostatic method to obtain propylene oxide.

[0025] As a preferred embodiment of the method for electrocatalytic propylene epoxidation of the present invention, in which: during the electrochemical reaction by the potentiostatic method, the potential is 4 - 4.5 V.

[0026] Advantages of the present invention:

[0027] This iron-based non-noble metal catalyst is used for the electrocatalytic propylene epoxidation of a membrane electrode system. Compared with existing catalysts, it has achieved higher production, and at the same time, it can maintain a relatively high Faraday efficiency. By doping with vanadium, optimizing the preparation process of the iron vanadate electrocatalyst, and optimizing the reaction conditions for electrocatalytic propylene epoxidation using the iron-based catalyst of the present invention, the current density is further increased, thereby increasing the production of propylene oxide. Description of the Drawings

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings. Among them:

[0029] Figure 1 It is a flow chart for preparing the iron-based catalyst in Embodiment 1 of the present invention;

[0030] Figure 2 It is a comparison chart of the propylene oxide production and Faraday efficiency of the electrochemical reaction in Embodiments 1 - 2 of the present invention;

[0031] Figure 3 It is the (a) X-ray diffraction image, (b) infrared transmission spectrum, (c) X-ray photoelectron spectrum, and (d) V 2p high-resolution spectrum of the iron-based catalysts prepared in Embodiment 1 and Comparative Example 1 of the present invention;

[0032] Figure 4 It is the (a) current-time curve graph, (b) comparison chart of propylene oxide production and Faraday efficiency, and (c) electrochemical impedance spectroscopy (EIS) graph of the electrochemical reaction in Embodiment 1 and Comparative Example 1 of the present invention;

[0033] Figure 5 It is the (a) in-situ Raman graph of the iron-based catalyst prepared in Embodiment 1 of the present invention for electrocatalytic epoxidation and (b) in-situ Raman graph of the iron-based catalyst prepared in Comparative Example 1 for electrocatalytic epoxidation;

[0034] Figure 6 It is the in-situ infrared spectrum of the iron-based catalyst prepared in Embodiment 1 of the present invention for electrocatalytic propylene epoxidation (a) in the range of 2922 - 2848 cm -1 and (b) O2 -*Corresponding in-situ infrared spectrum;

[0035] Figure 7 It is a comparison chart of the reaction currents of the electrochemical reactions under different potential conditions in Example 1 and Comparative Example 4 of the present invention;

[0036] Figure 8 It is a comparison chart of the propylene oxide production and Faraday efficiency of the electrochemical reactions under different potential conditions in Example 1 and Comparative Example 4 of the present invention;

[0037] Figure 9 It is a comparison chart of the reaction currents of the electrochemical reactions of the iron-based catalysts prepared at different calcination temperatures in Example 1 and Comparative Examples 5-6 of the present invention;

[0038] Figure 10 It is a comparison chart of the Faraday efficiency and propylene oxide production of the electrochemical reactions in Example 1 and Comparative Example 7 of the present invention;

[0039] Figure 11 It is a comparison chart of the Faraday efficiency and propylene oxide production of the electrochemical reactions in Example 1 and Comparative Example 8 of the present invention. Detailed implementation manners

[0040] To make the above objects, features and advantages of the present invention more obvious and understandable, the following describes the detailed implementation manners of the present invention in conjunction with the embodiments of the specification.

[0041] Many specific details are set forth in the following description in order to fully understand the present invention, but the present invention may also be implemented in other ways different from those described herein. Those skilled in the art can make similar promotions without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0042] Secondly, the so-called "one embodiment" or "embodiment" herein refers to a specific feature, structure or characteristic that may be included in at least one implementation manner of the present invention. The "in one embodiment" that appears in different places in this specification does not all refer to the same embodiment, nor is it a separate or alternative embodiment that excludes other embodiments.

[0043] The carbon paper with a gas diffusion layer used in the present invention has a model of YLS-30T and an area of 4 cm 2 .

[0044] The nickel foam used in the present invention is 100 PPI and has a thickness of 1 mm.

[0045] The ion exchange membrane used in the present invention is a Fumasep FKB-PK-130 cation exchange membrane.

[0046] In the present invention, the method for determining the yield of propylene oxide is as follows: The internal standard method is used to detect the yield of propylene oxide, and the internal standard is selected as ethylene glycol dimethyl ether which is chemically inert and soluble in water. According to the relative correction factor, the amount of the product in the test solution can be calculated, and the calculation formula is as follows: f = (As / ms) / (Ar / mr); mi = f×Ai / (As / ms); where f is the relative correction factor, As and ms are respectively the added mass and the peak area of the internal standard, Ar and mr are respectively the added mass and the peak area of the product, Ai is the peak area of the product in the test solution, and mi is the mass of the product in the test solution. The steps for preparing the standard sample are as follows: Add 10 μL of PO and 10 μL of the internal standard to 20 ml of the electrolyte; Take 1 μL of the standard sample for gas chromatography detection, repeat multiple times and take the average value to calculate f. The calculation formulas for the yield and the Faraday efficiency are as follows: ni = mi / Mi; P = ni / t / S; FE = ni*z*F / It. Where ni is the amount of substance of the product in the test solution, Mi is the relative molecular mass of propylene oxide, P is the yield, FE is the Faraday efficiency, S is the anode electrode area, z is the number of reaction electrons, F is the Faraday constant, I is the reaction current, and t is the reaction time.

[0047] Example 1

[0048] This example provides a preparation method of an iron-based catalyst and its application in electrocatalytic propylene epoxidation, specifically as follows:

[0049] (1) Stir 0.176 g of ammonium metavanadate and 30 mL of ferric nitrate solution at 60 °C for 30 min to obtain a uniform mixed solution, where the concentration of the ferric nitrate solution is 0.15 mol / L, that is, the molar ratio of ammonium metavanadate to ferric nitrate is 1:3;

[0050] (2) Place the mixed solution in a hydrothermal autoclave and carry out hydrothermal reaction at 95 °C for 4 h. After the reaction, centrifuge and dry for 12 h to obtain a solid powder;

[0051] (3) Place the solid powder in a muffle furnace and calcine at a high temperature of 500 °C for 2 h by heating to 500 °C in 100 min to obtain a red-brown powder, denoted as Fe-V-O-500, which is the iron-based catalyst of this example;

[0052] (4) Ultrasonically mix 2 mg of Fe-V-O-500, 10 μL of Nafion solution, and 1 mL of absolute ethanol to obtain a slurry, where the Nafion solution is composed of 5 wt% Nafion, 50 wt% ethanol, and 45 wt% water; Coat the slurry on the surface of the carbon paper with a gas diffusion layer, and after drying, obtain a gas diffusion electrode carrying the anode catalyst; Use the gas diffusion electrode as the anode, nickel foam as the cathode, and assemble them together with an ion exchange membrane into a membrane electrode reactor;

[0053] (5)Propylene gas was introduced into the anode at a flow rate of 10 mL / min, while a 1 wt% NaCl solution was pumped into the cathode at a rate of 20 mL / min. The electrode potential was maintained at a constant 4 V for the electrochemical reaction to obtain propylene oxide.

[0054] Example 2

[0055] This example provides a preparation method of an iron-based catalyst and its application in electrocatalytic propylene epoxidation. The difference from Comparative Example 1 is that the hydrothermal reaction temperatures in step (2) were adjusted to 90 °C and 100 °C respectively to prepare the iron-based catalysts of this example, denoted as Fe-V-O-90T and Fe-V-O-100T respectively.

[0056] The products collected at the anode were analyzed by gas chromatography to determine the Faraday efficiency and the yield of propylene oxide in the electrochemical reactions of Examples 1-2. The results are as Figure 2 shown.

[0057] From Figure 2 the comparison, it was found that within the range of 90-100 °C for the hydrothermal reaction temperature, the Faraday efficiency of the electrocatalytic propylene epoxidation reaction remained at a relatively high level, and at the same time, the yield of propylene oxide was relatively high. The overall performance of the catalyst prepared at a hydrothermal reaction temperature of 95 °C was the best.

[0058] Comparative Example 1

[0059] This comparative example provides a conventional preparation method of an iron-based catalyst and its application in electrocatalytic propylene epoxidation, specifically:

[0060] (1) 30 mL of ferric chloride solution and 30 mL of sodium nitrate solution were stirred for 30 min to obtain a homogeneous mixed solution. Among them, the concentration of the ferric chloride solution was 0.15 mol / L, and the concentration of the sodium nitrate solution was 0.1 mol / L;

[0061] (2) The mixed solution was placed in a hydrothermal autoclave and subjected to a hydrothermal reaction at 95 °C for 4 h. After the reaction, it was centrifuged and dried for 12 h to obtain a solid powder;

[0062] (3) The solid powder was placed in a muffle furnace and calcined at a high temperature of 550 °C for 2 h by heating to 550 °C in 110 min to obtain a red-brown powder, denoted as Fe-O-550, which is the iron-based catalyst of this example;

[0063] (4) 2 mg of Fe-O-550, 10 μL of Nafion solution, and 1 mL of absolute ethanol were ultrasonically mixed uniformly to obtain a slurry. The Nafion solution was composed of 5 wt% Nafion, 50 wt% ethanol, and 45 wt% water. The slurry was coated on the surface of a carbon paper with a gas diffusion layer, and after drying, a gas diffusion electrode carrying an anode catalyst was obtained. Using the gas diffusion electrode as the anode and nickel foam as the cathode, they were assembled together with an ion exchange membrane into a membrane electrode reactor;

[0064] (5) Propylene gas was introduced into the anode at a flow rate of 10 mL / min, and at the same time, a 1 wt% NaCl solution was pumped into the cathode at a rate of 20 mL / min. The electrode potential was maintained at a constant 4 V for an electrochemical reaction to obtain propylene oxide.

[0065] The chemical components and structures of the iron-based catalysts prepared in Example 1 and Comparative Example 1 were analyzed, and the results are as Figure 3 shown.

[0066] Figure 3 are the (a) X-ray diffraction images, (b) infrared transmission spectra, (c) X-ray photoelectron spectra, and (d) V 2p high-resolution spectra of the iron-based catalysts prepared in Example 1 and Comparative Example 1.

[0067] From Figure 3 (a), it can be seen that the XRD peak pattern of Fe-O-550 highly coincides with the standard diffraction card of Fe2O3, indicating that Fe-O-550 is mainly composed of iron oxide, while no obvious XRD characteristic peaks appear for Fe-V-O-500. This may be due to the incorporation of vanadium, which makes the catalyst form an amorphous oxide structure.

[0068] To further clarify the internal structure of Fe-V-O-500, infrared transmission spectroscopy analysis was performed on these two catalysts, as Figure 3 (b) shown. It can be seen from it that in the region of 400 - 700 cm -1 , the infrared characteristic peaks correspond to the stretching vibration of the Fe-O bond; while in the region of 900 - 1100 cm -1 , the spectral bands are related to the stretching vibration of the V-O terminal. The spectral band located at 700 - 900 cm -1 corresponds to the stretching vibration of the V-O-Fe bridge, indicating the successful synthesis of vanadium iron oxide.

[0069] XPS was used to further study the chemical composition of the Fe-O-550 and Fe-V-O-500 catalysts, as Figure 3(c). Peaks at 285 eV, 514 eV, and 710 eV were detected for both catalysts, corresponding to the elements C, O, and Fe, respectively. The Fe-V-O-500 catalyst had an XPS characteristic peak of V2p at 516 eV, indicating the successful incorporation of V. At the same time, the comparison of the V2p spectra of the Fe-O-550 and Fe-V-O-500 catalysts is as shown in Figure 3 (d), which also indicates the successful incorporation of V. This proves the successful synthesis of the vanadium-containing iron-based catalyst.

[0070] The products collected at the anode were analyzed by gas chromatography to determine the Faraday efficiency and the production of propylene oxide in the electro-chemical reactions of Example 1 and Comparative Example 1. The results are shown in Table 1 and Figure 4 as follows.

[0071] Table 1 Production of propylene oxide and Faraday efficiency of the reaction for different iron-based catalysts

[0072]

[0073]

[0074] Figure 4 is the electro-chemical performance diagram of the iron-based catalysts prepared in Example 1 and Comparative Example 1.

[0075] Figure 4 (a) is the current-time curve diagram of the two catalysts. It can be seen that at the same potential, the reaction current of Fe-V-O-500 is significantly higher than that of Fe-O-550.

[0076] Figure 4 (b) is the production and Faraday efficiency diagram of electro-catalytically preparing propylene oxide by the two catalysts. Figure 4 (b) combined with Table 1 shows that compared with Fe-O-550, the Faraday efficiency of Fe-V-O-500 has decreased, but still remains at a relatively high level. At the same time, due to the increase in the reaction current, the production of propylene oxide by the Fe-V-O-500 catalyst has further increased. This shows that the incorporation of V has successfully increased the electro-chemical reaction current without significantly affecting the high Faraday efficiency of the Fe-O-550 catalyst, thereby achieving the effect of increasing the production of propylene oxide.

[0077] Figure 4 (c) is the electro-chemical impedance spectroscopy (EIS) diagram of the two catalysts. It can be seen that compared with Fe-O-550, Fe-V-O-500 shows an interfacial transfer impedance, indicating that Fe-V-O-500 has better electro-chemical conductivity.

[0078] In-situ Raman tests were carried out on the electro-chemical reaction processes of Example 1 and Comparative Example 1. The results are as followsFigure 5 as shown

[0079] To determine the reason for the performance improvement of Fe-O-550, in-situ Raman spectroscopy analysis was carried out on this catalyst, and the results are as Figure 5 (a) shown. It can be seen that as the reaction potential increases, a characteristic peak corresponding to Fe-O2* appears on the catalyst surface at 900-1000 cm -1 . And O2* is more favorable for the highly efficient catalytic epoxidation of propylene than OH* and O*, so this may be the main reason for the improvement of the electrochemical performance of the Fe-O-550 catalyst.

[0080] As Figure 5 (b) shows the test results of the in-situ Raman experiment for the electrocatalytic epoxidation of Fe-V-O-500. Due to the incorporation of V, new Raman peaks are introduced at 900-1000 cm -1 , which has a certain impact on the observation of Fe-O2*, but it can still be clearly found that as the potential increases, the Raman signal peak at 900-1000 cm -1 becomes stronger. This phenomenon may be related to the formation of Fe-O2*.

[0081] Electrochemical infrared characterization was carried out on the iron-based catalyst prepared in Example 1 to further determine the reaction process of the electrocatalytic epoxidation of propylene by the iron-based catalyst and the key active species favorable for epoxidation. The results are as Figure 6 shown. Among them, Figure 6 (a) is the in-situ infrared spectrum of propylene epoxidation at 2922-2848 cm -1 , and (b) is the in-situ infrared spectrum corresponding to O2 - *.

[0082] When the catalyst undergoes an electrocatalytic epoxidation reaction, the propylene on the catalyst surface participates in the reaction. Although there is always sufficient propylene supply in the electrolyte, the surface concentration of the catalyst will decrease slightly. This may be Figure 6 (a) the reason for the decrease in the methyl characteristic peak of propylene (2922-2848 cm -1 ). In addition, an infrared characteristic peak corresponding to O2 Figure 6 was observed at 1163 cm in (b) -1 . - This also shows that a peroxo structure will be formed when both the Fe-V-O-500 catalyst and the Fe-O-550 catalyst react. Therefore, it can be speculated that the peroxo ion is the key intermediate for a more efficient epoxidation reaction.

[0083] Comparative Example 2

[0084] This comparative example provides a method for preparing an iron-based catalyst and its application in electrocatalytic propylene epoxidation. The difference from Comparative Example 1 is that the temperature of high-temperature calcination in step (3) is adjusted to 450 °C, and the remaining preparation processes are the same as those in Comparative Example 1. The iron-based catalyst of this comparative example is prepared and denoted as Fe-O-450.

[0085] Comparative Example 3

[0086] This comparative example provides a method for preparing an iron-based catalyst and its application in electrocatalytic propylene epoxidation. The difference from Comparative Example 1 is that the temperature of high-temperature calcination in step (3) is adjusted to 650 °C, and the remaining preparation processes are the same as those in Comparative Example 1. The iron-based catalyst of this comparative example is prepared and denoted as Fe-O-650.

[0087] The products collected at the anode were analyzed by gas chromatography to determine the Faraday efficiency and the yield of propylene oxide in the electrochemical reactions of Comparative Examples 2 - 3. The results are shown in Table 2.

[0088] Table 2 Influence of the calcination temperature of the iron-based catalyst on the yield of propylene oxide and the Faraday efficiency

[0089]

[0090] Comparing the Fe-O catalysts prepared by calcining the precursors at different temperatures in Table 2, it can be seen that a low calcination temperature will lead to a significant decrease in the Faraday efficiency and the yield. This is because too low a temperature results in an incomplete formation of the iron oxide structure, which in turn makes the catalyst more active towards side reactions such as the oxygen evolution reaction. While too high a calcination temperature leads to catalyst sintering, which reduces the reaction active area and ultimately deteriorates the overall performance of the catalyst.

[0091] Comparative Example 4

[0092] This comparative example provides a method for preparing an iron-based catalyst and its application in electrocatalytic propylene epoxidation. The difference from Example 1 is that the potential in step (5) is increased to 4.5 V, and the remaining preparation processes are the same as those in Example 1.

[0093] The products collected at the anode were analyzed by gas chromatography to determine the Faraday efficiency, the yield of propylene oxide, and the reaction current in the electrochemical reaction of Comparative Example 4. The results are shown in Table 3 and Figures 7 - 8 as shown. Among them, Figure 7 is a comparison chart of the reaction currents after electrochemical reactions under different potential conditions; Figure 8 is a comparison chart of the Faraday efficiency and the yield of propylene oxide in the electrochemical reactions under different potential conditions.

[0094] Table 3 Influence of the calcination temperature of the iron-based catalyst on the yield of propylene oxide and the Faraday efficiency

[0095]

[0096] According to Figure 7 It can be seen that after the potential is increased from 4 V to 4.5 V, the reaction current of the electrocatalytic reaction increases. By integrating the current-time curve, it is found that the increase in current increases the number of electrons participating in the reaction. Further, the propylene oxide yield and Faraday efficiency at the two potentials were calculated. According to Table 3 and Figure 8 , it can be seen that at the reaction potential of 4.5 V, the Faraday efficiency of electrocatalytic propylene epoxidation decreases, resulting in no obvious increase in the yield of propylene oxide.

[0097] Comparative Example 5

[0098] This comparative example provides a preparation method of an iron-based catalyst and its application in electrocatalytic propylene epoxidation. The difference from Example 1 is that the temperature of high-temperature calcination in step (3) is adjusted to 400 °C, and the rest of the preparation processes are the same as those in Example 1. The iron-based catalyst of this comparative example was prepared and denoted as Fe-V-O-400.

[0099] Comparative Example 6

[0100] This comparative example provides a preparation method of an iron-based catalyst and its application in electrocatalytic propylene epoxidation. The difference from Example 1 is that the temperature of high-temperature calcination in step (3) is adjusted to 600 °C, and the iron-based catalyst of this comparative example was prepared and denoted as Fe-V-O-600.

[0101] The products collected at the anode were analyzed by gas chromatography, and the reaction currents of the electrochemical reactions in Example 1 and Comparative Examples 5-6 were measured. The results are as Figure 9 shown.

[0102] Figure 9 It is a comparison chart of the reaction currents when electrochemically reacting with iron-based catalysts prepared at different high-temperature calcination temperatures.

[0103] According to Figure 9 it can be seen that at the same potential, the reaction current of Fe-V-O-400 is the highest, but its current decay is extremely obvious and very unstable. In addition, the reaction only lasts for 40 min. After the membrane electrode reactor is disassembled after the reaction, it is found that almost all of the catalyst has fallen off. In addition, the reaction current of Fe-V-O-600 does not show an obvious increase compared with that of Fe-V-O-500.

[0104] The products collected at the anode were analyzed by gas chromatography, and the Faraday efficiency and the yield of propylene oxide of the electrochemical reactions in Example 1 and Comparative Examples 5-6 were measured. The results are shown in Table 4.

[0105] Table 4 Effects of Different High-Temperature Calcination Temperatures of Iron-Based Catalysts on the Yield and Faraday Efficiency of Propylene Oxide

[0106]

[0107] As can be seen from Table 4, when preparing the Fe-V-O catalyst, if the calcination temperature is too high or too low, the catalysts used for electrocatalytic preparation of propylene oxide will both lead to a decrease in yield and a decrease in Faraday efficiency. Compared with Fe-V-O-500, the Faraday efficiency of the electrocatalytic reaction of Fe-V-O-600 decreases instead, and the yield of propylene oxide decreases significantly.

[0108] Comparative Example 7

[0109] This comparative example provides a preparation method of an iron-based catalyst and its application in electrocatalytic propylene epoxidation. The difference from Example 1 is that the cathode electrolytes in step (5) are adjusted to HCl, PBS, and KOH respectively, and the rest of the preparation processes are the same as those in Example 1.

[0110] Perform gas chromatography analysis on the products collected at the anode, and measure the Faraday efficiency and the yield of propylene oxide of the electrochemistry reactions in Example 1 and Comparative Example 7. The results are as Figure 10 shown.

[0111] From Figure 10 it can be seen that when the electrolyte is NaCl, the yield of propylene oxide is the highest and the Faraday efficiency is the highest.

[0112] Comparative Example 8

[0113] This comparative example provides a preparation method of an iron-based catalyst and its application in electrocatalytic propylene epoxidation. The difference from Example 1 is that the flow rates of propylene gas introduced into the anode in step (5) are adjusted to 5 and 20 mL / min respectively, and the rest of the preparation processes are the same as those in Example 1.

[0114] Perform gas chromatography analysis on the products collected at the anode, and measure the Faraday efficiency and the yield of propylene oxide of the electrochemistry reactions in Example 1 and Comparative Example 8. The results are as Figure 11 shown.

[0115] According to Figure 11 it can be seen that when the flow rate of propylene gas is 10 mL / min, the yield of propylene oxide is the highest and the Faraday efficiency is the highest.

[0116] Example 3

[0117] This example provides a preparation method of an iron-based catalyst and its application in electrocatalytic propylene epoxidation, specifically as follows:

[0118] (1) 0.176 g of ammonium metavanadate and 30 mL of iron nitrate solution were stirred at 70 °C for 45 min to obtain a homogeneous mixed solution. Among them, the concentration of the iron nitrate solution was 0.15 mol / L, that is, the molar ratio of ammonium metavanadate to iron nitrate was 1:3;

[0119] (2) The mixed solution was placed in a hydrothermal reactor and subjected to hydrothermal reaction at 95 °C for 5 h. After the reaction, it was centrifuged and dried for 18 h to obtain a solid powder;

[0120] (3) The solid powder was placed in a muffle furnace and calcined at a high temperature of 500 °C for 2 h by heating to 500 °C in 100 min to obtain a red-brown powder, denoted as Fe-V-O-500, which was the iron-based catalyst of this example;

[0121] (4) 2.2 mg of Fe-V-O-500, 9.8 μL of Nafion solution, and 1.1 mL of absolute ethanol were ultrasonically mixed evenly to obtain a slurry. Among them, the Nafion solution was composed of 5 wt% Nafion, 50 wt% ethanol, and 45 wt% water; the slurry was coated on the surface of the carbon paper with a gas diffusion layer, and after drying, a gas diffusion electrode carrying the anode catalyst was obtained; using the gas diffusion electrode as the anode and nickel foam as the cathode, they were assembled together with an ion exchange membrane into a membrane electrode reactor;

[0122] (5) Propylene gas was introduced into the anode at a flow rate of 10 mL / min, and at the same time, a 1 wt% NaCl solution was pumped into the cathode at a speed of 22 mL / min. The electrode potential was maintained at a constant 4 V for an electrochemical reaction to obtain propylene oxide.

[0123] The products collected at the anode were analyzed by gas chromatography to measure the Faraday efficiency and the yield of propylene oxide in the electrochemical reaction of Example 4. The results showed that the Faraday efficiency and the yield of propylene oxide were similar to those of Example 1, and the effect of Example 1 was better.

[0124] In summary, the present invention uses ammonium metavanadate as the vanadium source, and it synthesizes an iron vanadate electrocatalyst with an iron source by the coprecipitation method for propylene epoxidation in a membrane electrode. This non-noble metal catalyst based on iron is used for electrocatalytic propylene epoxidation in a membrane electrode system. Compared with the existing catalysts, it has obtained a higher yield and can maintain a relatively high Faraday efficiency. By doping with vanadium, optimizing the preparation process of the iron vanadate electrocatalyst, and optimizing the reaction conditions for electrocatalytic propylene epoxidation using the iron-based catalyst of the present invention, the current density is further increased, thereby increasing the yield of propylene oxide.

[0125] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A preparation method of an iron-based catalyst, characterized in that: including, Ammonium metavanadate and an iron source aqueous solution are stirred evenly to obtain a mixed solution; The mixed solution is subjected to a hydrothermal reaction. After the reaction ends, centrifugation and drying are carried out to obtain a solid powder; The solid powder is calcined at a high temperature to obtain an iron-based catalyst; The iron source includes one of iron nitrate and iron chloride.

2. The preparation method of the iron-based catalyst according to claim 1, characterized in that: The molar ratio of the ammonium metavanadate to the iron source is 1:1 to 3.

3. The preparation method of the iron-based catalyst according to claim 1, characterized in that: In the process of stirring the ammonium metavanadate and the iron source solution evenly to obtain a mixed solution, the stirring time is 30 to 45 min, and the stirring temperature is 60 to 70 °C.

4. The preparation method of the iron-based catalyst according to claim 1, characterized in that: In the hydrothermal reaction of the mixed solution, the hydrothermal reaction temperature is 90 to 100 °C, and the hydrothermal reaction time is 4 to 5 h.

5. The preparation method of the iron-based catalyst according to claim 1, characterized in that: In the process of centrifuging and drying to obtain a solid powder after the reaction ends, the drying time is 12 to 18 h.

6. The preparation method of the iron-based catalyst according to claim 1, characterized in that: In the process of calcining the solid powder at a high temperature, the calcination temperature is 500 to 550 °C, and the calcination time is 2 to 3 h.

7. An iron-based catalyst prepared by the preparation method according to any one of claims 1 to 6.

8. Application of the iron-based catalyst according to claim 7 in electrocatalytic propylene epoxidation.

9. A method for electrocatalytic propylene epoxidation, characterized in that: including, 1.8 to 2.2 mg of the iron-based catalyst according to claim 8, 9.8 to 10.2 μL of Nafion solution, and 0.9 to 1.1 mL of absolute ethanol are mixed evenly to obtain a slurry. Among them, the Nafion solution is composed of 5 wt% Nafion, 50 wt% ethanol, and 45 wt% water; The slurry is coated on the surface of a carbon paper with a gas diffusion layer, and after drying, a gas diffusion electrode carrying an anode catalyst is obtained; Using the gas diffusion electrode as the anode and nickel foam as the cathode, they are assembled together with an ion exchange membrane into a membrane electrode reactor; Propylene gas is introduced into the anode at a flow rate of 9 to 11 mL / min, and at the same time, a 1 to 1.2 wt% NaCl solution is pumped into the cathode at a speed of 18 to 22 mL / min, and an electrochemical reaction is carried out by the potentiostatic method to obtain propylene oxide.

10. The method for electrocatalytic propylene epoxidation according to claim 10, wherein: In the electrochemical reaction carried out by the potentiostatic method, the potential is 4 to 4.5 V.

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