Modified Palladium-based Catalyst Supported on Carbon Nitride for Hydrogen Production from Formic Acid, Its Preparation Method and Application

Abstract

The present invention discloses a carbon nitride-supported modified palladium-based formic acid hydrogen production catalyst, its preparation method and application. The method includes: (1) dissolving urea and amino acid in water, and then performing calcination to obtain carbon nitride; (2) mixing carbon nitride, soluble palladium salt and water uniformly to obtain a suspension; then adding a reducing agent to the suspension for reaction; after the reaction is completed, centrifugal separation, washing and drying are carried out to obtain a carbon nitride-supported modified palladium-based formic acid hydrogen production catalyst. The present invention uses urea as a nitrogen source and amino acid as a dopant, and utilizes the interaction between the carboxyl group in the amino acid and urea to synthesize a high-nitrogen-doped carbon nitride-supported palladium catalyst, significantly increasing the nitrogen doping content, especially pyridine nitrogen species, enhancing the interaction between the carbon nitride support and metal Pd, reducing the metal Pd particle size, dispersing metallic palladium in the form of nanoparticles on the surface of the carbon nitride support and improving its dispersibility, and greatly improving the catalytic performance of formic acid hydrogen production.

Description

Technical Field

[0001] The present invention relates to the technical field of formic acid hydrogen production catalysts, and specifically to a carbon nitride-supported modified palladium-based formic acid hydrogen production catalyst, its preparation method and application. Background Art

[0002] In order to replace traditional fossil fuels, finding a clean energy source is a key challenge. Hydrogen is a promising energy carrier and has been widely used in fuel cell-based technologies. However, its widespread use is restricted by safe storage and transportation. Formic acid is a safe and convenient chemical hydrogen storage carrier and is widely used in renewable energy storage due to its high hydrogen content (4.4 wt%), non-toxicity, liquid state, easy availability and high stability.

[0003] Currently, the catalysts for formic acid decomposition to hydrogen mainly include homogeneous catalysts and heterogeneous catalysts. Homogeneous catalysts have high catalytic activity but are difficult to separate and recycle; although heterogeneous catalysts are easy to recycle, their catalytic performance needs to be improved. In the heterogeneous catalyst system, highly dispersed supported palladium catalysts exhibit good catalytic performance for formic acid decomposition to hydrogen. Selecting a suitable support is particularly important for improving its catalytic performance.

[0004] Commonly used supports include amino-modified silica, metal-organic framework materials, carbon materials, carbon nitride, etc. Carbon nitride is beneficial to the reduction and stabilization of palladium nanoparticles and promotes the dispersion of palladium nanoparticles on the support surface due to its high nitrogen content and abundant nitrogen-containing groups. In order to further enhance the catalytic activity of single-component palladium nanoparticles, methods mainly include adding metal elements to form bimetallic or trimetallic catalysts, or modifying the original catalyst to adjust the electronic state of palladium nanoparticles and improve the catalytic performance of the catalyst. The literature with the application number 202310561654.0 discloses a nitrogen-doped oxide-supported metal catalyst, its preparation method and application, and the turnover frequency of formic acid hydrogen production at 80 °C is only 1467-2150 h -1 .

[0005] Currently reported support-supported palladium-based catalysts or support-supported palladium-based alloy catalysts still have the problem that their catalytic efficiency needs to be further improved. Summary of the Invention

[0006] Aiming at the deficiencies of the prior art, the technical problem to be solved by the present invention is to provide a carbon nitride-supported modified palladium-based formic acid hydrogen production catalyst, its preparation method and application.

[0007] The technical solution for the present invention to solve the above technical problem is to provide a preparation method for a carbon nitride-supported modified palladium-based formic acid hydrogen production catalyst, which is characterized in that the method includes the following steps:

[0008] (1) Preparation of carbon nitride support: Dissolve urea and amino acid in water, and then perform calcination to obtain carbon nitride;

[0009] (2) Preparation of carbon nitride supported modified palladium-based formic acid hydrogen production catalyst: Mix carbon nitride, soluble palladium salt and water evenly to obtain a suspension; then add a reducing agent to the suspension for reaction; after the reaction is completed, after centrifugal separation, washing and drying, a carbon nitride supported modified palladium-based formic acid hydrogen production catalyst is obtained.

[0010] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0011] (1) The present invention uses urea as a nitrogen source and amino acid as a dopant, and utilizes the interaction between the carboxyl group in the amino acid and urea to synthesize a high-nitrogen-doped carbon nitride supported palladium catalyst. Compared with conventional nitrogen-doped carbon nitride, the present invention significantly increases the nitrogen doping content, especially pyridine nitrogen species, enhances the interaction between the carbon nitride support and metal Pd, reduces the metal Pd particle size, and the metal palladium is dispersed on the surface of the carbon nitride support in the form of nanoparticles and improves the dispersion of the metal palladium on the surface of the carbon nitride support, greatly improving the catalytic performance of formic acid hydrogen production.

[0012] (2) The present invention introduces cerium-containing species, utilizes the oxygen storage characteristics of cerium dioxide to introduce oxygen-containing species, and utilizes the pyridine nitrogen species on the carrier surface to anchor Pd ions and CeO 2 Promote the electron transfer on the catalyst surface, realize the redistribution of surface electrons, synergistically regulate the electronic properties of Pd species on the catalyst surface, enhance the interaction between the carrier and the metal, solve the problem of low activity of the catalyst active component during the reaction process, further improve the formic acid conversion rate and cycle stability of the catalyst, and improve the anti-carbon monoxide poisoning ability.

[0013] (3) The present invention is based on the strategy of synergistically regulating the structure of metal palladium on the carrier surface by the carrier structure and CeO 2 doping, and adjusts the structure of carbon nitride by adjusting the types of precursors for synthesizing carbon nitride, the types and amounts of amino acids used. Description of the Drawings

[0014] Figure 1 It is the TEM image of the catalyst prepared in Example 1 of the present invention;

[0015] Figure 2 It is the XPS image of the catalyst prepared in Example 1 of the present invention;

[0016] Figure 3 It is the formic acid hydrogen production catalytic performance image of the catalysts prepared in Example 1 and Example 8 of the present invention;

[0017] Figure 4Catalytic performance graph of the catalysts prepared in Example 1, Comparative Example 1 and Comparative Example 2 of the present invention for hydrogen production from formic acid;

[0018] Figure 5 XRD graph of the catalysts prepared in Example 1 and Comparative Example 3 of the present invention. Detailed implementation manners

[0019] The following are specific examples of the present invention. The specific examples are only used for further detailed description of the present invention and do not limit the protection scope of the present invention.

[0020] The present invention provides a preparation method of a modified palladium-based formic acid hydrogen production catalyst supported on carbon nitride (abbreviated as method), which is characterized in that the method comprises the following steps:

[0021] (1) Preparation of the carbon nitride support: Dissolve urea and amino acid in water, and then carry out calcination to obtain carbon nitride;

[0022] Preferably, in step (1), the mass ratio of urea to the volume of water is 1 g:4 - 6 mL, and the mass ratio of urea to amino acid is 10:0.05 - 0.1.

[0023] Preferably, in step (1), the amino acid includes arginine (Arg), glutamic acid (GLu), aspartic acid (Asp), phenylalanine (Phe), lysine (Lys) and histidine (His), more preferably arginine, phenylalanine, lysine and histidine, and further preferably arginine.

[0024] Preferably, in step (1), the dissolution process is: dissolution at room temperature.

[0025] Preferably, in step (1), the calcination temperature is 550 - 580 °C, the time is 2 - 4 h, and the atmosphere is any atmosphere (preferably air atmosphere).

[0026] (2) Preparation of the modified palladium-based formic acid hydrogen production catalyst supported on carbon nitride: Mix carbon nitride, soluble palladium salt and water evenly to obtain a suspension; then add a reducing agent to the suspension for reaction; after the reaction is completed, after centrifugal separation, washing and drying, a modified palladium-based formic acid hydrogen production catalyst supported on carbon nitride (abbreviated as catalyst) is obtained.

[0027] Preferably, in step (2), the molar ratio of palladium in the soluble palladium salt to the mass of carbon nitride is 0.136 - 0.645 mmol:0.27 g, and the mass ratio of carbon nitride to the volume of water is 0.27 g:40 - 60 mL; the reducing agent is in excess to ensure complete reduction of palladium.

[0028] Preferably, in step (2), the soluble palladium salt includes at least one of palladium acetate, palladium nitrate and potassium chloropalladite.

[0029] Preferably, in step (2), the process of mixing evenly is: stirring at a rotation speed of 200 - 350 rpm for 1 - 2 h at room temperature.

[0030] Preferably, in step (2), sodium borohydride (NaBH 4 ) is used as the reducing agent.

[0031] Preferably, in step (2), the reaction process is: stirring and reacting at a rotation speed of 200 - 350 rpm for 2 - 4 h at room temperature.

[0032] Preferably, in step (2), the reducing agent is added dropwise into the suspension.

[0033] Preferably, in step (2), a tetravalent soluble cerium salt is further added to the suspension; the molar ratio of cerium in the tetravalent soluble cerium salt to palladium in the soluble palladium salt is 0.5 - 2:1; the tetravalent soluble cerium salts are cerium(IV) nitrate and cerium(IV) sulfate.

[0034] Preferably, in step (2), the process of centrifugal separation is: centrifuging at a rotation speed of 6000 - 7000 r / min for 3 - 8 min at room temperature to separate the reaction product from water.

[0035] Preferably, in step (2), the process of washing is: washing with water 2 - 5 times at room temperature to remove the residual sodium ions on the surface of the reaction product.

[0036] Preferably, in step (2), the process of drying is: drying at a temperature of 80 - 100 °C for 8 - 16 h to remove water.

[0037] Preferably, in steps (1) - (2), the water is deionized water.

[0038] The present invention also provides a carbon nitride - supported modified palladium - based formic acid hydrogen - production catalyst prepared by the preparation method of the carbon nitride - supported modified palladium - based formic acid hydrogen - production catalyst.

[0039] The present invention also provides an application of the carbon nitride - supported modified palladium - based formic acid hydrogen - production catalyst in formic acid hydrogen production.

[0040] In the example, the process of testing the catalytic performance of the catalyst for formic acid hydrogen production is: weighing 0.05 g of the catalyst and adding it to a round - bottom flask containing 10 mL of deionized water for stirring. Connect a burette filled with water to the reaction flask, and record the volume of the generated gas by the water - displacement method. Inject 5 mL of a mixed solution of formic acid (FA) and sodium formate (SF) (n FA = 2 mmol, c FA :c SFWhen the ratio was 1:8, the reaction started, and the reaction time and the volume of the generated gas were recorded. The reaction was carried out at 75 °C. The performance of the catalyst was evaluated using the initial turnover frequency (TOF) value, and the calculation formula was as shown in Equation (1):

[0041]

[0042] In Equation (1), P atm is the atmospheric pressure (101.325 kPa); is the volume of the gas generated by the reaction, with the unit of L; R is the ideal gas constant; T is the reaction temperature, with the unit of K; n Pd is the content of palladium metal loaded in the catalyst, with the unit of mol; t is the reaction time when the formic acid conversion rate is 20%, with the unit of h.

[0043] Example 1

[0044] (1) Preparation of the carbon nitride support: At room temperature, 10 g of urea and 0.05 g of arginine were dissolved in 50 mL of water, and then calcined in an air atmosphere at 550 °C for 2 h. After cooling to room temperature, carbon nitride was obtained;

[0045] (2) Preparation of the carbon nitride-supported modified palladium-based formic acid hydrogen production catalyst: 0.27 g of carbon nitride, 0.109 g of cerium(IV) nitrate, 0.092 g of potassium chloropalladite, and 60 mL of water were stirred for 2 h until evenly mixed, and then 0.113 g of sodium borohydride was added, and the stirring reaction continued for 4 h; then, after centrifugal separation for 5 min, washing with deionized water 3 times, and drying at 80 °C for 12 h, the carbon nitride-supported modified palladium-based formic acid hydrogen production catalyst was obtained.

[0046] It can be seen from Figure 1 that the catalyst prepared in Example 1 exhibited a nanosheet structure, and there were wrinkles at the edges of the sheets. And smaller Pd nanoparticles were evenly loaded on the support. This indicates that the palladium nanoparticles were well fixed and dispersed on the carbon nitride support.

[0047] It can be seen from Figure 2 that in the catalyst prepared in Example 1, the peaks at 284 eV, 400 eV, and 532 eV corresponded to the C, N, and O elements, and the doublet peaks at 337 eV and 343 eV corresponded to the Pd element, indicating that Pd had been successfully loaded onto the surface of the carbon nitride support. The peak at 882 - 916 eV corresponded to the Ce element, indicating that Ce had been successfully loaded onto the surface of the carbon nitride support.

[0048] Example 2

[0049] The difference from Example 1 was that: in step (1), the mass ratio of urea to arginine was 10 g:0.075 g, and the remaining steps were the same as those in Example 1.

[0050] Example 3

[0051] The difference from Example 1 is that in step (1), the mass ratio of urea to arginine is 10 g:0.1 g, and the remaining steps are the same as those in Example 1.

[0052] Example 4

[0053] The difference from Example 1 is that in step (2), the molar ratio of palladium to cerium is 1:0.5, and the remaining steps are the same as those in Example 1.

[0054] Example 5

[0055] The difference from Example 1 is that in step (2), the molar ratio of palladium to cerium is 1:0.75, and the remaining steps are the same as those in Example 1.

[0056] Example 6

[0057] The difference from Example 1 is that in step (2), the molar ratio of palladium to cerium is 1:1.5, and the remaining steps are the same as those in Example 1.

[0058] Example 7

[0059] The difference from Example 1 is that in step (2), the molar ratio of palladium to cerium is 1:2, and the remaining steps are the same as those in Example 1.

[0060] Example 8

[0061] The difference from Example 1 is that in step (2), the molar ratio of palladium to cerium is 1:0, that is, cerium nitrate is not added, and the remaining steps are the same as those in Example 1. Step (2) is specifically:

[0062] (2) Preparation of carbon nitride supported modified palladium-based formic acid hydrogen production catalyst: Stir 0.27 g of carbon nitride, 0.092 g of potassium chloropalladate and 60 mL of water for 2 h until evenly mixed, then add 0.113 g of sodium borohydride and continue stirring and reacting for 4 h; then after centrifugal separation for 5 min, washing with deionized water 3 times, and drying at 80 °C for 12 h, a carbon nitride supported modified palladium-based formic acid hydrogen production catalyst is obtained.

[0063] It can be seen from Figure 3 that for the catalyst prepared in Example 1, when the reaction time is 1.25 min, the formic acid conversion rate reaches 100%, and the initial turnover frequency reaches 4098.9 h -1 . For the catalyst prepared in Example 8, when the reaction time is 1.65 min, the formic acid conversion rate reaches 100%, and the initial turnover frequency is 1930.4 h -1It can be seen by comparison that introducing cerium element during the preparation of the catalyst is beneficial to improving the performance of the formic acid hydrogen production catalyst.

[0064] Example 9

[0065] The difference from Example 1 is that: in step (1), glutamic acid is used to replace arginine, and the remaining steps are the same as those in Example 1.

[0066] Example 10

[0067] The difference from Example 1 is that: in step (1), aspartic acid is used to replace arginine, and the remaining steps are the same as those in Example 1.

[0068] Example 11

[0069] The difference from Example 1 is that: in step (1), phenylalanine is used to replace arginine, and the remaining steps are the same as those in Example 1.

[0070] Example 12

[0071] The difference from Example 1 is that: in step (1), lysine is used to replace arginine, and the remaining steps are the same as those in Example 1.

[0072] Example 13

[0073] The difference from Example 1 is that: in step (1), histidine is used to replace arginine, and the remaining steps are the same as those in Example 1.

[0074] Comparative Example 1

[0075] The difference from Example 1 is that: in step (1), dicyandiamide is used to replace urea, that is, dicyandiamide is used as the precursor, and the remaining steps are the same as those in Example 1.

[0076] Comparative Example 2

[0077] The difference from Example 1 is that: in step (1), melamine is used to replace urea, that is, melamine is used as the precursor, and the remaining steps are the same as those in Example 1.

[0078] From Figure 4 it can be seen that for the catalyst prepared in Example 1, when the reaction time is 1.25 min, the formic acid conversion rate reaches 100%, and the initial turnover frequency is 4098.9 h -1 . For the catalysts prepared in Comparative Example 1 and Comparative Example 2, when the reaction time is 15 min, the formic acid conversion rates are 76.2% and 48.8% respectively, and the initial turnover frequencies are 338.9 h -1 and 143.5 h -1 .

[0079] Comparative Example 3

[0080] The difference from Example 1 is that arginine is not added in step (1), and the remaining steps are the same as those in Example 1. Step (1) is specifically:

[0081] (1) Preparation of the carbon nitride support: Dissolve 10 g of urea in 50 mL of water at room temperature, then calcine in an air atmosphere at 550 °C for 2 h, and after cooling to room temperature, obtain carbon nitride.

[0082] From Figure 5 It can be seen that the diffraction peak of the catalyst prepared in Example 1 at 27.4° can be attributed to the (002) crystal plane of carbon nitride, corresponding to the crystal plane stacking of the π-conjugated plane of graphitic carbon nitride; the typical diffraction peak at 39.9° corresponds to the Pd(111) crystal plane. Compared with the catalyst prepared in Comparative Example 3 without adding arginine, the half-peak width of the diffraction peak corresponding to the Pd(111) crystal plane of the catalyst prepared in Example 1 is wider, indicating that adding arginine to the catalyst support is beneficial to reducing the size of Pd nanoparticles and making them more evenly distributed on the support.

[0083] The TOF values of the catalysts prepared in the present invention are shown in Table 1.

[0084] Table 1 Hydrogen production catalytic performance of different catalysts

[0085]

[0086] Matters not described in the present invention are applicable to the prior art.

Claims

1. A method for preparing a carbon nitride-supported modified palladium-based formic acid hydrogen production catalyst, characterized in that: The method comprises the following steps: (1) Preparation of carbon nitride support: urea and amino acid are dissolved in water and then calcined to obtain carbon nitride; Amino acids include arginine, phenylalanine, lysine, and histidine; (2) Preparation of carbon nitride-supported modified palladium-based formic acid hydrogen production catalyst: carbon nitride, a soluble palladium salt, a tetravalent soluble cerium salt and water are mixed uniformly to obtain a suspension; a reducing agent is then added to the suspension to carry out a reaction; after the reaction is completed, the suspension is centrifuged, washed and dried to obtain a carbon nitride-supported modified palladium-based formic acid hydrogen production catalyst.

2. The method for preparing the carbon nitride-supported modified palladium-based formic acid hydrogen production catalyst according to claim 1, characterized in that: In step (1), the mass ratio of urea to the volume of water is 1 g:4-6 mL, and the mass ratio of urea to amino acid is 10:0.05-0.

1.

3. The method for preparing the carbon nitride-supported modified palladium-based formic acid hydrogen production catalyst according to claim 1, characterized in that: In step (1), the calcination temperature is 550-580° C., the calcination time is 2-4 hours, and the calcination atmosphere is any atmosphere.

4. The method for preparing the carbon nitride-supported modified palladium-based formic acid hydrogen production catalyst according to claim 1, characterized in that: In step (2), the ratio of the amount of palladium in the soluble palladium salt to the mass of carbon nitride is 0.136-0.645 mmol:0.27 g, and the ratio of the mass of carbon nitride to the volume of water is 0.27 g:40-60 mL; and the reducing agent is in excess.

5. The method for preparing the carbon nitride-supported modified palladium-based formic acid hydrogen production catalyst according to claim 1, characterized in that: In step (2), the soluble palladium salt includes at least one of palladium acetate, palladium nitrate and potassium chloropalladate; The process for uniform mixing is: stirring at 200-350 rpm for 1-2 hours at room temperature; The reducing agent is sodium borohydride; The reaction process is: stirring the reaction at 200-350 rpm for 2-4 hours at room temperature; The reducing agent is added to the suspension dropwise.

6. The method for preparing the carbon nitride-supported modified palladium-based formic acid hydrogen production catalyst according to claim 1, characterized in that: In step (2), the ratio of the amount of cerium in the tetravalent soluble cerium salt to the amount of palladium in the soluble palladium salt is 0.5-2:1; the tetravalent soluble cerium salt is cerium nitrate and cerium sulfate.

7. The method for preparing the carbon nitride-supported modified palladium-based formic acid hydrogen production catalyst according to claim 5, characterized in that: In step (2), the centrifugal separation process is: centrifugation at a speed of 6000-7000 r / min at room temperature for 3-8 minutes to separate the reaction product from water; The washing process is: washing with deionized water 2 to 5 times at room temperature to remove residual sodium ions on the surface of the reaction product; The drying process is: drying temperature is 80~100℃, and drying time is 8~16h.

8. A carbon nitride-supported modified palladium-based formic acid hydrogen production catalyst prepared by the method for preparing the carbon nitride-supported modified palladium-based formic acid hydrogen production catalyst according to any one of claims 1 to 7.

9. Use of the carbon nitride-supported modified palladium-based formic acid hydrogen production catalyst according to claim 8 in formic acid hydrogen production.

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