Use of a molybdenum carbide catalyst in the production of hydrogen from formic acid

Abstract

The application relates to the technical field of formic acid hydrogen production catalysts, in particular to application of a molybdenum carbide catalyst in formic acid hydrogen production. The molybdenum carbide catalyst is prepared by mixing, drying and then pyrolyzing ammonium molybdate tetrahydrate, citric acid and water under a protective atmosphere, and the preparation method is simple, and the raw materials are cheap and easy to obtain. When the molybdenum carbide catalyst is used to catalyze the formic acid hydrogen production reaction, the required reaction temperature is low, the hydrogen production rate is excellent, the stability is good, and the hydrogen production performance is good.

Description

Application of a molybdenum carbide catalyst in hydrogen production from formic acid Technical Field

[0001] This invention relates to the field of formic acid hydrogen production catalyst technology, and in particular to the application of a molybdenum carbide catalyst in formic acid hydrogen production. Background Technology

[0002] Hydrogen energy is currently the most promising alternative energy source, with advantages such as wide availability, cleanliness, and high efficiency. However, hydrogen has a low volumetric energy density (0.0108 MJ / L) and is prone to explosion. Traditional hydrogen production methods have high requirements for storage tanks and transportation pressure, as well as high costs.

[0003] Commonly used chemical hydrogen storage agents include formic acid, methanol, and hydrazine. Among them, formic acid has a high volumetric capacity (53 g / L) and a high gravimetric hydrogen density (4.4 wt.%). When needed, it can release a large amount of hydrogen gas through appropriate reactions, making it a stable intermediate for the widespread use and safe transportation of hydrogen energy. Furthermore, formic acid can be synthesized through renewable pathways, such as the hydrogenation of carbon dioxide.

[0004] Homogeneous catalysts and noble metal catalysts exhibit excellent catalytic performance in the formic acid to hydrogen production process. However, their high cost hinders large-scale application. Therefore, there is a need in this field to find inexpensive and high-performance non-noble metal catalysts to replace noble metal catalysts and homogeneous catalysts for large-scale application. Currently, common non-noble metal catalysts used in formic acid to hydrogen production include Mo-based and Ni-based catalysts, which are significantly cheaper than noble metal catalysts, but still suffer from complex preparation processes.

[0005] There are reports on the preparation of MoC. Chinese patent (CN109999840A) discloses a method for preparing MoC catalyst, which requires first preparing Mo2C through heat treatment, and then continuing to pyrolyze to prepare MoC. Chinese patent (CN109621998A) discloses a method for preparing MoC catalyst, which involves first preparing a dry gel using molybdenum source, carbon source and template agent as raw materials, and then carbonizing and reducing the dry gel to obtain MoC catalyst. Both of these methods require multiple steps to obtain MoC catalyst. Summary of the Invention

[0006] The purpose of this invention is to provide an application of molybdenum carbide catalyst in the production of hydrogen from formic acid, simplifying the preparation process of the formic acid hydrogen production catalyst and reducing costs.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0008] An application of a molybdenum carbide catalyst in the production of hydrogen from formic acid, wherein the preparation method of the molybdenum carbide catalyst includes the following steps:

[0009] 1) Mix ammonium molybdate tetrahydrate, citric acid and water, stir evenly and dry to obtain a molybdenum-based catalyst precursor;

[0010] 2) The molybdenum-based catalyst precursor is pyrolyzed under a protective atmosphere to obtain a molybdenum carbide catalyst;

[0011] In step 1), the mass ratio of ammonium molybdate tetrahydrate, citric acid, and water is 1:2 to 4:60 to 100.

[0012] Optionally, the mixing in step 1) is carried out under stirring conditions, with a stirring rate of 500-1000 rpm and a time of 0.5-2 h.

[0013] Optionally, the protective atmosphere in step 2) includes nitrogen, helium, or argon.

[0014] Optionally, the pyrolysis temperature in step 2) is 600–800°C, and the time is 1–4 hours.

[0015] Optionally, when molybdenum carbide catalyst is used to catalyze the production of hydrogen from formic acid, the reaction temperature is 90–98°C and the reaction time is 1–4 h.

[0016] Optionally, when molybdenum carbide catalyst catalyzes the production of hydrogen from formic acid, the mass ratio of molybdenum carbide catalyst to formic acid is 1-2:60-150.

[0017] This invention provides the application of molybdenum carbide catalysts in the production of hydrogen from formic acid. Due to the unique crystal structure of interstitial carbides, carbon is inserted into the metal-metal lattice, resulting in a longer metal-metal distance than the metal matrix. This increased metal-metal distance leads to the contraction of the d-band of Mo atoms, ultimately increasing the density of states in the Mo d-band, even reaching near the Fermi level. Simultaneously, the sp orbitals of C hybridize with the d orbitals of Mo, widening the new d orbitals of Mo (rearranged with the carbon sp orbitals) and resulting in a wider energy distribution than the Mo metal matrix. This gives the Mo-based catalyst an electronic structure similar to that of the noble metal catalyst Pt, thus exhibiting similar catalytic performance in the production of hydrogen from formic acid. Based on this, we prepared a MoC catalyst using ammonium molybdate tetrahydrate and citric acid as raw materials through one-step pyrolysis and applied it to the production of hydrogen from formic acid.

[0018] This invention utilizes ammonium molybdate tetrahydrate and citric acid as raw materials to prepare a MoC catalyst via a one-step pyrolysis process, which is then applied to the formic acid-to-hydrogen production process. The preparation process of this molybdenum carbide catalyst is simple, the raw materials are inexpensive and readily available, and by controlling the pyrolysis temperature and the raw material ratio, a molybdenum carbide catalyst with excellent hydrogen production rate and good stability is obtained, exhibiting good hydrogen production performance in the catalytic formic acid-to-hydrogen process. Attached Figure Description

[0019] Figure 1 shows the XRD patterns of the molybdenum carbide catalysts prepared in Examples 1-3;

[0020] Figure 2 shows the XRD patterns of the molybdenum carbide catalysts prepared in Examples 1 and 4-5.

[0021] Figure 3 shows the XRD pattern of the sample prepared in Comparative Example 1;

[0022] Figure 4 shows the catalytic hydrogen production rate of formic acid using the catalysts prepared in Examples 1-3.

[0023] Figure 5 shows the catalytic hydrogen production rate of formic acid using the molybdenum carbide catalysts prepared in Examples 1, 4 and 5.

[0024] Figure 6 shows the hydrogen production of formic acid to hydrogen production by the molybdenum carbide catalyst prepared in Example 1 over 60 hours.

[0025] Figure 7 shows the XRD pattern of the formic acid hydrogen production reaction catalyzed by the molybdenum carbide catalyst prepared in Example 1 after 60 h. Detailed Implementation

[0026] This invention provides an application of molybdenum carbide catalyst in the production of hydrogen from formic acid, wherein the preparation method of the molybdenum carbide catalyst includes the following steps:

[0027] 1) Mix ammonium molybdate tetrahydrate, citric acid and water, stir evenly and dry to obtain a molybdenum-based catalyst precursor;

[0028] 2) The molybdenum-based catalyst precursor is pyrolyzed under a protective atmosphere to obtain a molybdenum carbide catalyst;

[0029] In step 1), the mass ratio of ammonium molybdate tetrahydrate, citric acid, and water is 1:2 to 4:60 to 100.

[0030] In this invention, the mass ratio of ammonium molybdate tetrahydrate, citric acid and water in step 1) is preferably 1:2-4:70-95, more preferably 1:2-3:75-90, and even more preferably 1:2-3:80-85;

[0031] In this invention, the mixing in step 1) is preferably carried out under stirring conditions, with a stirring rate preferably of 500-1000 rpm, more preferably of 500-800 rpm, and even more preferably of 500-600 rpm; and a time preferably of 0.5-2 h, more preferably of 0.5-1.5 h, and even more preferably of 0.5-1 h.

[0032] In this invention, after the reaction in step 1) is completed, the product is preferably dried and ground in sequence. The drying temperature is preferably 100-140°C, more preferably 100-130°C, and even more preferably 100-120°C. The drying time is preferably 6-18 hours, more preferably 8-16 hours, and even more preferably 12 hours.

[0033] In this invention, the protective atmosphere in step 2) preferably includes nitrogen, helium or argon.

[0034] In this invention, the pyrolysis temperature in step 2) is preferably 600-800℃, more preferably 650-750℃, and even more preferably 700-750℃; the time is preferably 1-4h, more preferably 1.5-3h, and even more preferably 2-2.5h.

[0035] In this invention, after the pyrolysis in step 2) is completed, the catalyst is preferably cooled naturally to room temperature.

[0036] In this invention, a molybdenum carbide catalyst is mixed with formic acid to decompose formic acid.

[0037] In this invention, when molybdenum carbide catalyst is used to catalyze the production of hydrogen from formic acid, the reaction temperature is preferably 90-98°C, more preferably 93-98°C, and even more preferably 95-98°C; the reaction time is preferably 1-4 hours, more preferably 1-3 hours, and even more preferably 1-2 hours.

[0038] In this invention, when the molybdenum carbide catalyst catalyzes the production of hydrogen from formic acid, the mass ratio of the molybdenum carbide catalyst to formic acid is preferably 1-2:60-150, more preferably 1-1.5:75-120, and even more preferably 1:90-100.

[0039] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0040] Example 1

[0041] 1g of ammonium molybdate tetrahydrate (NH4)6Mo7O 24 4H2O and 3g of citric acid C6H8O7 were dissolved in 100mL of deionized water and stirred at 800rpm for 1h. The solution was dried at 120℃ for 12h and then ground to obtain a powdered precursor. Finally, the precursor was placed in an argon atmosphere for pyrolysis at 700℃ for 2h and then naturally cooled to room temperature to obtain a molybdenum carbide catalyst.

[0042] Example 2

[0043] Based on Example 1, the difference between Example 2 and Example 1 is that 1g of ammonium molybdate tetrahydrate (NH4)6Mo7O was used. 24 • 4H2O and 2g citric acid C6H8O7.

[0044] Example 3

[0045] Based on Example 1, the difference between Example 3 and Example 1 is that 1g of ammonium molybdate tetrahydrate (NH4)6Mo7O was used. 24 • 4H2O and 4g of citric acid C6H8O7.

[0046] Example 4

[0047] Based on Example 1, the difference between Example 4 and Example 1 is that the temperature of the pyrolysis reaction is 650°C.

[0048] Example 5

[0049] Based on Example 1, the difference between Example 5 and Example 1 is that the temperature of the pyrolysis reaction is 750°C.

[0050] Comparative Example 1

[0051] Based on Example 1, the difference between Comparative Example 1 and Example 1 is that 0g of ammonium molybdate tetrahydrate (NH4)6Mo7O was used. 24 ·4H2O and 1g citric acid C6H8O7.

[0052] The catalysts prepared in Examples 1-3 were subjected to XRD analysis, and the resulting XRD patterns are shown in Figure 1.

[0053] The catalysts prepared in Examples 1 and 4-5 were subjected to XRD analysis, and the obtained XRD patterns are shown in Figure 2.

[0054] The product obtained from Comparative Example 1 was subjected to XRD analysis, and the resulting XRD pattern is shown in Figure 3.

[0055] Figure 1 shows that at the same temperature, catalysts prepared with different ratios of ammonium molybdate tetrahydrate and citric acid were all MoC, with the only difference being the intensity of the diffraction peaks. Figure 2 shows that at the same ratio, catalysts prepared at different temperatures were all MoC, with the only difference being the intensity of the diffraction peaks. Figure 3 shows that the sample prepared by pyrolysis of citric acid alone was carbon.

[0056] Application Example 1

[0057] 0.2g of the catalysts prepared in Examples 1-5 and Comparative Example 1 were respectively placed in 20g of formic acid and subjected to formic acid decomposition to produce hydrogen at 98℃ for 1h. The formic acid hydrogen production rate was detected and the results are shown in Table 1.

[0058] The catalytic hydrogen production rates of formic acid by the catalysts prepared in Examples 1-3 and Comparative Example 1 are shown in Figure 4; the catalytic hydrogen production rates of formic acid by the catalysts prepared in Examples 1, 4 and 5 are shown in Figure 5.

[0059] Table 1. Hydrogen production rates of formic acid catalyzed by the catalysts prepared in Examples 1-5 and Comparative Example 1.

[0060] Hydrogen production rate (mL / g) cat Hydrogen production rate (mL / g) / h) cat / h) Comparative Example 10 Example 326.05 Example 1134.54 Example 463.18 Example 277.33 Example 581.01 surface

[0061] Table 1 and Figure 4 show that materials that only pyrolyze citric acid have no effect on the decomposition of formic acid. The ratio of ammonium molybdate tetrahydrate to citric acid affects the catalytic hydrogen production rate of the prepared molybdenum carbide catalyst. Among them, the molybdenum carbide catalyst prepared when the mass ratio of ammonium molybdate tetrahydrate to citric acid is 1:3 has the highest catalytic hydrogen production rate. Table 1 and Figure 5 show that, under the same preparation conditions, the temperature of the pyrolysis reaction affects the catalytic performance of the prepared molybdenum carbide catalyst. Among them, the molybdenum carbide catalyst prepared at a pyrolysis temperature of 700℃ has the highest catalytic hydrogen production rate from formic acid.

[0062] Application Example 2

[0063] Take 0.2 g of the molybdenum carbide catalyst prepared in Example 1 and maintain the reaction temperature at 98 °C. Formic acid is continuously added over 60 h to decompose the formic acid. The cumulative amount of hydrogen produced is shown in Figure 6.

[0064] The molybdenum carbide catalyst after catalytic hydrogen production from formic acid for 60 h was subjected to XRD analysis, and the obtained XRD pattern is shown in Figure 7.

[0065] As shown in Figures 6 and 7, the molybdenum carbide catalyst can catalyze the stable production of hydrogen from formic acid within 60 hours. By comparing Figures 1 and 7, it can be seen that the XRD of the molybdenum carbide catalyst does not change after 60 hours of stable hydrogen production, indicating that the molybdenum carbide catalyst has good stability.

[0066] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An application of a molybdenum carbide catalyst in the production of hydrogen from formic acid, characterized in that, The preparation method of the molybdenum carbide catalyst includes the following steps: 1) mixing ammonium molybdate tetrahydrate, citric acid and water, stirring evenly and drying to obtain a molybdenum-based catalyst precursor; 2) pyrolyzing the molybdenum-based catalyst precursor under a protective atmosphere to obtain a molybdenum carbide (MoC) catalyst; the mass ratio of ammonium molybdate tetrahydrate, citric acid and water in step 1) is 1:2~4:60~100; when the molybdenum carbide catalyst catalyzes the production of hydrogen from formic acid, the reaction temperature is 90~98℃ and the reaction time is 1~4h.

2. The application according to claim 1, characterized in that, The mixing in step 1) is carried out under stirring conditions, with a stirring rate of 500~1000 rpm and a time of 0.5~2h.

3. The application according to claim 1, characterized in that, The protective atmosphere in step 2) includes nitrogen, helium, or argon.

4. The application according to claim 1 or 3, characterized in that, The pyrolysis in step 2) is performed at a temperature of 600~800℃ for 1~4 hours.

5. The application according to claim 4, characterized in that, When molybdenum carbide catalyst is used to catalyze the production of hydrogen from formic acid, the mass ratio of molybdenum carbide catalyst to formic acid is 1~2:60~150.

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