A nitrogen-doped carbon-supported molybdenum phosphide catalyst, its preparation method and application

Abstract

This invention provides a nitrogen-doped carbon-supported molybdenum phosphide catalyst, its preparation method, and its application, belonging to the field of catalytic hydrogen release from formic acid technology. The invention employs a one-step pyrolysis method, stirring ammonium molybdate, ammonium dihydrogen phosphate, a sugar polymer, melamine, and water to obtain a paste. After drying the paste, it is pyrolyzed under a protective gas atmosphere to obtain a nitrogen-doped carbon-supported molybdenum phosphide catalyst for hydrogen release from formic acid. The preparation process is simple, and the raw materials are readily available. The catalyst of this invention is used for hydrogen release from high-concentration formic acid at low temperatures, exhibiting high reaction efficiency, wide adaptability, and high hydrogen selectivity, comparable to the catalytic properties of noble metals. This opens up a new application field for hydrogen production from high-concentration formic acid using non-noble metal catalysts without additives.

Description

Technical Field

[0001] This invention relates to the field of catalytic hydrogen release from formic acid, and particularly to a nitrogen-doped carbon-supported molybdenum phosphide catalyst, its preparation method, and its application. Background Technology

[0002] Hydrogen is the most abundant element in the universe and the cleanest and most ideal alternative energy source. As an energy carrier, hydrogen can be re-oxidized and used to generate heat through combustion, or catalytically generate electricity in fuel cells. Hydrogen is a gas under ambient conditions, with a low volumetric energy density (0.013 MJ / L). Physical hydrogen storage technologies (compression, cryogenic liquefaction, adsorption) suffer from low hydrogen capacity, high cost, and safety issues. Among chemical hydrogen storage methods, formic acid is considered the most promising chemical hydrogen carrier due to its high hydrogen capacity (53 g / L) and high energy density (1.77 kW·h / L). Formic acid can be synthesized through renewable pathways, such as the hydrogenation reaction of carbon dioxide with "green hydrogen" or the partial oxidation synthesis of biomass. Furthermore, the decomposition of formic acid into hydrogen and carbon dioxide is thermodynamically favorable.

[0003] Currently, most catalysts for the liquid-phase formic acid hydrogen release reaction are noble metal catalysts. These studies have used a mixture of formic acid and alkali for the dehydrogenation reaction to avoid the high acidity of the reaction solution, which would deactivate the expensive catalyst. Studies have shown that reaction systems with added organic solvents as chemical additives generally exhibit lower efficiency and selectivity (EnergyEnviron.Sci.,2012,5,8171). However, in the process of using formic acid as a hydrogen storage and transport carrier, the use of additives and solvents not only reduces the overall hydrogen energy density of the reaction, but the solvent vapors in the gas mixture produced by the reaction can also damage the hydrogen fuel cell. Therefore, the use of solvents and other volatile additives should be avoided.

[0004] Under highly acidic or even pure formic acid conditions, the low solubility of many complexes limits the number of suitable catalysts for the dehydrogenation of high-concentration formic acid. The high acidity of high-concentration formic acid also leads to irreversible poisoning of many homogeneous catalysts, resulting in catalyst deactivation. David Milstein et al. (Highly efficient additive-free dehydrogenation of neatformic acid. Nature Catalysis volume 4, pages 193–201 (2021)) reported a ruthenium 9H-acridine complex catalyst for the dehydrogenation of pure formic acid, and this liquid-phase catalyst exhibited stability in formic acid for over a month. Jeff Joseph A. Celaje et al. (A prolific catalyst for dehydrogenation of neat formic acid. Nat. Commun. 7:11308) reported a system of [RuCl2(benzene)]2 and sodium formate promoting formic acid dehydrogenation under pure formic acid conditions, achieving high conversion rates under mild conditions. However, these catalysts all use expensive homogeneous noble metal catalysts, limiting their practical application prospects. Furthermore, the addition of organic solvents to the reaction system and the difficulty in controlling the start and end of the reaction in a liquid-phase reaction system limit the commercial application of formic acid hydrogen release.

[0005] Heterogeneous non-precious metal catalysts have attracted attention from industry and scientists in recent years due to their ease of separation and low cost (Adv. Energy Mater. 2022, 2200817). However, the application of heterogeneous non-precious metal catalysts in the field of formic acid hydrogen release remains very limited, mainly consisting of molybdenum-based, cobalt-based, and nickel-based catalysts. Currently, there are no reports on the use of such catalysts for hydrogen release in liquid-phase additive-free conditions under high-concentration formic acid or pure formic acid conditions.

[0006] Molybdenum phosphide (MPP) is considered one of the most promising alternatives to noble metal catalysts due to its d-band structure similar to that of noble metals and its easily tunable electronic structure (Energy Environ. Sci. 2020, 13, 4564). There are reports on the preparation and application of MPP, such as the method for preparing a porous sheet-like MPP / carbon composite material disclosed in Chinese Patent Publication No. CN110479332A. However, this patent requires freeze-drying followed by calcination and multiple cleaning processes to prepare the porous sheet-like MPP / carbon composite material, making the preparation process relatively complex. For example, existing technologies (Applied Catalysis B: Environmental 299 (2021) 120657) and (Nanoscale, 2016, 8, 17256–17261) show drastically different physicochemical properties of MPP catalysts due to the addition of different proportions of melamine. Currently, there are no reports in the prior art regarding the preparation of nitrogen-doped carbon-supported MPP catalysts by adding sugar polymers.

[0007] Therefore, it is very important to provide a nitrogen-doped carbon-supported molybdenum phosphide catalyst with high reaction efficiency, wide adaptability, and high hydrogen selectivity. Summary of the Invention

[0008] The purpose of this invention is to provide a nitrogen-doped carbon-supported molybdenum phosphide catalyst, its preparation method, and its application, in order to solve the technical problems of low reaction efficiency, narrow adaptability, and low hydrogen selectivity of supported molybdenum phosphide catalysts in the prior art.

[0009] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0010] This invention provides a method for preparing a nitrogen-doped carbon-supported molybdenum phosphide catalyst, comprising the following steps:

[0011] (1) Ammonium molybdate, melamine, saccharide polymer, ammonium dihydrogen phosphate and water are mixed and dried to obtain a precursor;

[0012] (2) The precursor was pyrolyzed in a protective atmosphere to obtain a nitrogen-doped carbon-supported molybdenum phosphide catalyst.

[0013] Furthermore, the mass ratio of ammonium molybdate, melamine, saccharide polymer, ammonium dihydrogen phosphate, and water is 1–3:1–2:4–10:2–5:20–30.

[0014] Furthermore, the carbohydrate polymer is sucrose, glucose, or starch.

[0015] Furthermore, the drying temperature is 70–150°C, and the drying time is 10–24 hours.

[0016] Furthermore, the protective atmosphere is nitrogen, argon, or helium.

[0017] Furthermore, the pyrolysis temperature is 700–850°C, and the time is 1–3 hours.

[0018] This invention provides a nitrogen-doped carbon-supported molybdenum phosphide catalyst prepared by the method described above.

[0019] The present invention also provides an application of the nitrogen-doped carbon-supported molybdenum phosphide catalyst described above in the hydrogen release of formic acid.

[0020] The beneficial effects of this invention are:

[0021] (1) Compared with the prior art, the present invention generates nitrogen-doped carbon-supported molybdenum phosphide catalyst by pyrolysis of precursor at 700-850℃, and prepares nitrogen-doped carbon-supported molybdenum phosphide catalyst by one-step pyrolysis method. The preparation process is simple and time-saving.

[0022] (2) The raw materials of the nitrogen-doped carbon-supported molybdenum phosphide catalyst prepared by the present invention are cheap and readily available, and have prospects for industrial application.

[0023] (3) The nitrogen-doped carbon-supported molybdenum phosphide catalyst of the present invention can decompose high concentrations of formic acid under mild conditions, has good activity and reaction selectivity, and has a long service life.

[0024] (4) The nitrogen-doped carbon-supported molybdenum phosphide catalyst of the present invention can adapt to hydrogen release conditions of different concentrations and temperatures, and can be applied to different industries, with a wide range of applications.

[0025] (5) The present invention prepares a nitrogen-doped carbon-supported molybdenum phosphide catalyst by using a specific ratio of melamine and sugar polymers to protect the stability of active sites under high acidity conditions. Attached Figure Description

[0026] Figure 1 The image shows the XRD pattern of the nitrogen-doped carbon-supported molybdenum phosphide catalyst prepared in Example 1.

[0027] Figure 2 The N2 adsorption-desorption curves and pore size distribution diagrams of the nitrogen-doped carbon-supported molybdenum phosphide catalyst prepared in Example 1 are shown.

[0028] Figure 3 This is a SEM scan image of the nitrogen-doped carbon-supported molybdenum phosphide catalyst prepared in Example 1.

[0029] Figure 4 The image shows the EDS-mapping scan of the nitrogen-doped carbon-supported molybdenum phosphide catalyst prepared in Example 1.

[0030] Figure 5 This is a TEM image of the nitrogen-doped carbon-supported molybdenum phosphide catalyst prepared in Example 1. Detailed Implementation

[0031] This invention provides a method for preparing a nitrogen-doped carbon-supported molybdenum phosphide catalyst, comprising the following steps:

[0032] (1) Ammonium molybdate, melamine, saccharide polymer, ammonium dihydrogen phosphate and water are mixed and dried to obtain a precursor;

[0033] (2) The precursor was pyrolyzed in a protective atmosphere to obtain a nitrogen-doped carbon-supported molybdenum phosphide catalyst.

[0034] In this invention, the mass ratio of ammonium molybdate, melamine, saccharide polymer, ammonium dihydrogen phosphate, and water is 1-3:1-2:4-10:2-5:20-30, preferably 1.5-2.5:1.2-1.8:5-9:2.5-4.5:22-28, and more preferably 2:1.5:6-8:3-4:24-26.

[0035] In this invention, the carbohydrate polymer is sucrose, glucose or starch, preferably sucrose or glucose, and more preferably sucrose.

[0036] In this invention, the drying temperature is 70-150°C, preferably 80-140°C, more preferably 90-130°C, and even more preferably 100°C; the drying time is 10-24 hours, preferably 12-20 hours, and even more preferably 14-18 hours.

[0037] In this invention, the protective atmosphere is nitrogen, argon or helium, preferably nitrogen or argon, and more preferably nitrogen.

[0038] In this invention, the pyrolysis temperature is 700–850°C, preferably 720–830°C, and more preferably 750–800°C; the time is 1–3 h, preferably 1.2–2.8 h, and more preferably 1.5–2.5 h.

[0039] This invention provides a nitrogen-doped carbon-supported molybdenum phosphide catalyst prepared by the method described above.

[0040] The present invention also provides an application of the nitrogen-doped carbon-supported molybdenum phosphide catalyst described above in the hydrogen release of formic acid.

[0041] 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.

[0042] Example 1

[0043] 2.0 g ammonium molybdate, 1.0 g melamine, 5.0 g sucrose, 2.0 g ammonium dihydrogen phosphate and 20 g deionized water were mixed to obtain a white paste. The white paste was dried at 110 °C for 12 h to obtain a precursor. The precursor was pyrolyzed at 700 °C for 2 h in a nitrogen atmosphere. After pyrolysis, it was naturally cooled to room temperature in a nitrogen atmosphere to obtain a nitrogen-doped carbon-supported molybdenum phosphide catalyst.

[0044] Figure 1 The image shows the XRD pattern of the nitrogen-doped carbon-supported molybdenum phosphide catalyst prepared in Example 1. From... Figure 1 It can be seen that the XRD diffraction peak positions of nitrogen-doped carbon-supported molybdenum phosphide correspond to the standard spectrum of molybdenum phosphide PDF#24-0771, with amorphous peaks of the carbon support at 15–25°. This proves that the product obtained in Example 1 is a well-crystallized molybdenum phosphide material, and also confirms the loading of molybdenum phosphide on carbon.

[0045] Figure 2 The images show the N2 adsorption-desorption curves and pore size distribution of the nitrogen-doped carbon-supported molybdenum phosphide catalyst prepared in Example 1. Figure 2 It can be seen that the specific surface area of ​​the catalyst is 29.89 m². 2 / g, the nitrogen-doped carbon-supported molybdenum phosphide catalyst exhibits a typical type IV adsorption isotherm, indicating that the catalyst is mainly mesoporous, and the pore size distribution diagram in the figure also confirms this conclusion.

[0046] Figure 3 This is a SEM scan image of the nitrogen-doped carbon-supported molybdenum phosphide catalyst prepared in Example 1. From... Figure 3 As can be seen, the final product prepared in Example 1 is a closely packed non-sheet molybdenum phosphide catalyst. The catalyst exhibits a three-dimensional structure, which increases the number of active sites and facilitates mass transfer in the catalytic process.

[0047] Figure 4 This is an EDS-mapping scan of the nitrogen-doped carbon-supported molybdenum phosphide catalyst prepared in Example 1. From... Figure 4 It can be seen that molybdenum and phosphorus are uniformly loaded on the carbon support, and the uniform distribution of nitrogen proves that nitrogen element has been successfully doped into the material.

[0048] Figure 5 This is a TEM image of the nitrogen-doped carbon-supported molybdenum phosphide catalyst prepared in Example 1. From... Figure 5 It can be seen that the molybdenum phosphide particles have an average size distribution of 20-30 nm and are uniformly loaded on the carbon support. At the same time, it can be seen that the prepared material has a distinct 3D structure.

[0049] The nitrogen-doped carbon-supported molybdenum phosphide catalyst prepared in Example 1 was tested with pure formic acid. Formic acid and the catalyst were placed together in a four-necked flask and heated using a water bath. The water bath temperature was raised from room temperature to 98°C. The amount of pure formic acid used was 20 mL, and the amount of catalyst used was 0.5 g. The test results showed that when the reaction temperature was 90°C, the catalyst yield was 3029 mL / g / h, and no CO byproduct was produced.

[0050] Example 2

[0051] 3.0 g ammonium molybdate, 2.0 g melamine, 6.0 g sucrose, 4.0 g ammonium dihydrogen phosphate and 20 g deionized water were mixed to obtain a white paste. The white paste was dried at 130 °C for 14 h to obtain a precursor. The precursor was pyrolyzed at 800 °C for 2 h in a nitrogen atmosphere. After pyrolysis, it was cooled to room temperature in a nitrogen atmosphere to obtain a nitrogen-doped carbon-supported molybdenum phosphide catalyst.

[0052] The nitrogen-doped carbon-supported molybdenum phosphide catalyst prepared in Example 2 was tested with a 40 vol% formic acid aqueous solution. Formic acid and the catalyst were placed together in a four-necked flask and heated in a water bath from room temperature to 88°C. The amount of 40 vol% formic acid aqueous solution was 20 mL, and the amount of catalyst was 0.5 g. The test results showed that at a reaction temperature of 80°C, the catalyst yield was 2634 mL / g / h, and no CO byproduct was produced.

[0053] Example 3

[0054] 2.0 g ammonium molybdate, 1.5 g melamine, 8.0 g glucose, 3.0 g ammonium dihydrogen phosphate and 28 g deionized water were mixed to obtain a white paste. The white paste was dried at 100 °C for 18 h to obtain a precursor. The precursor was pyrolyzed at 750 °C for 1.5 h in a nitrogen atmosphere. After pyrolysis, it was cooled to room temperature in a nitrogen atmosphere to obtain a nitrogen-doped carbon-supported molybdenum phosphide catalyst.

[0055] The nitrogen-doped carbon-supported molybdenum phosphide catalyst prepared in Example 3 was tested with an 88 vol% formic acid aqueous solution. Formic acid and the catalyst were placed together in a four-necked flask and heated in a water bath from room temperature to 98°C. The amount of 88 vol% formic acid aqueous solution was 20 mL, and the amount of catalyst was 0.5 g. The test results showed that at a reaction temperature of 90°C, the catalyst yield was 4750 mL / g / h, and no CO byproduct was produced.

[0056] Example 4

[0057] 1.0 g ammonium molybdate, 1.5 g melamine, 8.0 g glucose, 3.0 g ammonium dihydrogen phosphate and 25 g deionized water were mixed to obtain a white paste. The white paste was dried at 80 °C for 20 h to obtain a precursor. The precursor was pyrolyzed at 750 °C for 2 h in a nitrogen atmosphere. After pyrolysis, it was cooled to room temperature in a nitrogen atmosphere to obtain a nitrogen-doped carbon-supported molybdenum phosphide catalyst.

[0058] The nitrogen-doped carbon-supported molybdenum phosphide catalyst prepared in Example 4 was tested with a 60 vol% formic acid aqueous solution. Formic acid and the catalyst were placed together in a four-necked flask and heated in a water bath from room temperature to 68°C. The amount of 60 vol% formic acid aqueous solution was 20 mL, and the amount of catalyst was 0.5 g. The test results showed that at a reaction temperature of 60°C, the catalyst yield was 1872 mL / g / h, and no CO byproduct was produced.

[0059] Example 5

[0060] 2.0 g ammonium molybdate, 1.0 g melamine, 10.0 g starch, 5.0 g ammonium dihydrogen phosphate and 30 g deionized water were mixed to obtain a white paste. The white paste was dried at 100 °C for 18 h to obtain a precursor. The precursor was pyrolyzed at 750 °C for 2 h in a nitrogen atmosphere. After pyrolysis, it was cooled to room temperature in a nitrogen atmosphere to obtain a nitrogen-doped carbon-supported molybdenum phosphide catalyst.

[0061] The nitrogen-doped carbon-supported molybdenum phosphide catalyst prepared in Example 5 was tested with an 80 vol% formic acid aqueous solution. Formic acid and the catalyst were placed together in a four-necked flask and heated in a water bath from room temperature to 78°C. The volume of the 80 vol% formic acid aqueous solution was 20 mL, and the volume of the catalyst was 0.5 g. The test results showed that at a reaction temperature of 70°C, the catalyst yield was 1752 mL / g / h, and no CO byproduct was produced.

[0062] Comparative Example 1

[0063] 2.0 g ammonium molybdate, 0.5 g melamine, 10.0 g starch, 5.0 g ammonium dihydrogen phosphate and 30 g deionized water were mixed to obtain a white paste. The white paste was dried at 100 °C for 18 h to obtain a precursor. The precursor was pyrolyzed at 750 °C for 2 h in a nitrogen atmosphere. After pyrolysis, it was cooled to room temperature in a nitrogen atmosphere to obtain a nitrogen-doped carbon-supported molybdenum phosphide catalyst.

[0064] The nitrogen-doped carbon-supported molybdenum phosphide catalyst prepared in Comparative Example 1 was tested with an 80 vol% formic acid aqueous solution. Formic acid and the catalyst were placed together in a four-necked flask and heated in a water bath from room temperature to 78 °C. The volume of the 80 vol% formic acid aqueous solution was 20 mL, and the volume of the catalyst was 0.5 g. The test results showed that at a reaction temperature of 70 °C, the catalyst yield was 1321 mL / g / h, and no CO byproduct was produced.

[0065] Comparative Example 2

[0066] 2.0 g ammonium molybdate, 10.0 g starch, 5.0 g ammonium dihydrogen phosphate and 30 g deionized water were mixed to obtain a white paste. The white paste was dried at 100 °C for 18 h to obtain a precursor. The precursor was pyrolyzed at 750 °C for 2 h in a nitrogen atmosphere. After pyrolysis, it was cooled to room temperature in a nitrogen atmosphere to obtain a carbon-supported molybdenum phosphide catalyst.

[0067] The carbon-supported molybdenum phosphide catalyst prepared in Comparative Example 2 was tested in relation to an 80 vol% formic acid aqueous solution. Formic acid and the catalyst were placed together in a four-necked flask and heated in a water bath from room temperature to 78°C. The volume of the 80 vol% formic acid aqueous solution was 20 mL, and the volume of the catalyst was 0.5 g. The test results showed that at a reaction temperature of 70°C, the catalyst yield was 102 mL / g / h, and the product included 2 vol% CO as a byproduct.

[0068] Comparative Example 3

[0069] 2.0 g ammonium molybdate, 1.0 g melamine, 5.0 g ammonium dihydrogen phosphate and 30 g deionized water were mixed to obtain a white paste. The white paste was dried at 100 °C for 18 h to obtain a precursor. The precursor was pyrolyzed at 750 °C for 2 h in a nitrogen atmosphere. After pyrolysis, it was cooled to room temperature in a nitrogen atmosphere to obtain a nitrogen-doped molybdenum phosphide catalyst.

[0070] The nitrogen-doped molybdenum phosphide catalyst prepared in Comparative Example 3 was tested with an 80 vol% formic acid aqueous solution. Formic acid and the catalyst were placed together in a four-necked flask and heated in a water bath from room temperature to 78°C. The volume of the 80 vol% formic acid aqueous solution was 20 mL, and the volume of the catalyst was 0.5 g. The test results showed that at a reaction temperature of 70°C, the catalyst yield was 372 mL / g / h, and no CO byproduct was produced.

[0071] As can be seen from the above embodiments, the present invention provides a nitrogen-doped carbon-supported molybdenum phosphide catalyst, its preparation method, and its application. A one-step pyrolysis method is used to prepare the nitrogen-doped carbon-supported molybdenum phosphide catalyst by mixing ammonium molybdate, ammonium dihydrogen phosphate, a saccharide polymer, melamine, and water in a specific ratio. The preparation process is simple, and the raw materials are readily available. When the catalyst prepared by the present invention reacts with formic acid, the yield of the catalyst is tested to be 1752–4750 mL / g / h, with no CO byproducts, exhibiting good activity and reaction selectivity.

[0072] 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. The application of a nitrogen-doped carbon-supported molybdenum phosphide catalyst in the hydrogen release of formic acid, characterized in that, The preparation method of the nitrogen-doped carbon-supported molybdenum phosphide catalyst includes the following steps: (1) Ammonium molybdate, melamine, sugar compounds, ammonium dihydrogen phosphate and water are mixed and dried to obtain a precursor; The mass ratio of ammonium molybdate, melamine, carbohydrate compound, ammonium dihydrogen phosphate, and water is 1~3:1~2:4~10:2~5:20~30; The carbohydrate compound is sucrose, glucose, or starch; (2) The precursor was pyrolyzed in a protective atmosphere to obtain a nitrogen-doped carbon-supported molybdenum phosphide catalyst.

2. The application of the nitrogen-doped carbon-supported molybdenum phosphide catalyst according to claim 1 in the hydrogen release of formic acid, characterized in that, The drying temperature is 70~150℃, and the time is 10~24h.

3. The application of the nitrogen-doped carbon-supported molybdenum phosphide catalyst according to claim 2 in the hydrogen release of formic acid, characterized in that, The protective atmosphere is nitrogen, argon, or helium.

4. The application of the nitrogen-doped carbon-supported molybdenum phosphide catalyst according to claim 3 in the hydrogen release of formic acid, characterized in that, The pyrolysis temperature is 700~850℃ and the time is 1~3h.

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