A hydrogen production catalyst and its preparation method and application

Abstract

The present invention provides a hydrogen production catalyst by catalysis, a preparation method thereof and an application thereof, belonging to the technical field of catalysts. In the present invention, carbon nitride is prepared by mixing urea and acetone and then calcining, and then a reduction reaction is carried out by mixing the carbon nitride with a soluble palladium salt, a reducing agent and water, so that the active component palladium is loaded on the carbon nitride. The present invention utilizes the modification effect of acetone to increase the escape of small molecules during calcination, and the thermal condensation reaction of urea to form carbon nitride is more intense, thereby making the formed carbon nitride thinner. At the same time, defects are also generated in the formed carbon nitride, which is beneficial to anchoring the active component palladium particles, enabling palladium to be uniformly distributed in the carbon nitride. As a carrier, this can improve the dispersion of palladium, and further enable the catalyst to have high catalytic activity without using other noble metals for modification but only using palladium as the active component, reducing the cost of the catalyst.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, and in particular to a hydrogen production catalyst and a preparation method and application thereof. Background Art

[0002] As a clean energy source, hydrogen has received increasing attention. However, technical problems such as the safe storage and on-demand release of hydrogen are bottlenecks hindering the widespread application of hydrogen energy. Formic acid is an excellent hydrogen carrier, with the advantages of good stability, non-toxicity, and simple storage and transportation. It can be used as a hydrogen source and hydrogen carrier material to overcome the problems of safe storage and on-demand release of hydrogen.

[0003] Formic acid has two catalytic decomposition pathways: dehydrogenation decomposition into CO2 and H2, and dehydration decomposition into CO and H2O. The commonly used active component of the catalyst for catalytic dehydrogenation decomposition of formic acid to produce hydrogen is palladium metal, but its catalytic activity still cannot well meet the needs of dehydrogenation decomposition of formic acid to produce hydrogen. Currently, researchers improve the catalytic activity of the catalyst by modifying the carrier. For example, Chinese Patent CN 201810427699.8 discloses a method for catalytic hydrogen production from formic acid. Covalent triazine polymerized porous material (CTF) is synthesized by ionothermal copolymerization; precious metal Pd is loaded by precipitation deposition method to obtain the catalyst Pd / CTF; Pd / CTF is added to the formic acid solution, and hydrogen is catalytically produced from formic acid under the condition of 298 - 328K. Although this method improves the catalytic activity of formic acid to produce hydrogen to a certain extent, the activity still needs to be improved; and this method needs to first prepare CTF by ion copolymerization method, and the preparation conditions are harsh.

[0004] Therefore, there is an urgent need to provide a preparation method for a hydrogen production catalyst with simple method, mild conditions, and good catalytic activity. Summary of the Invention

[0005] The purpose of the present invention is to provide a preparation method for a hydrogen production catalyst with simple method, mild conditions, and good catalytic activity.

[0006] In order to achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0007] The present invention provides a preparation method for a hydrogen production catalyst, comprising the following steps:

[0008] (1) Mix urea and acetone and then carry out calcination to obtain carbon nitride;

[0009] (2) Mix the carbon nitride obtained in step (1) with a soluble palladium salt, a reducing agent, and water, and carry out a reduction reaction to obtain a hydrogen production catalyst.

[0010] Preferably, the method of mixing urea and acetone in step (1) is: impregnate urea in acetone for 1 - 4h.

[0011] Preferably, the mass ratio of urea to the volume of acetone in step (1) is 20 g:(7 - 40) mL.

[0012] Preferably, the calcination temperature in step (1) is 550 - 580 °C.

[0013] Preferably, the calcination time in step (1) is 2 - 4 h.

[0014] Preferably, the soluble palladium salt in step (2) includes one or more of palladium acetate, palladium nitrate, and potassium chloropalladate.

[0015] Preferably, the reducing agent in step (2) includes sodium borohydride or hydrazine hydrate.

[0016] Preferably, the molar ratio of palladium in the soluble palladium salt to the mass of carbon nitride in step (2) is (0.136 - 0.645) mmol:0.27 g.

[0017] The present invention also provides a hydrogen production catalyst prepared by the preparation method described in the above technical solution, including carbon nitride and palladium nanoparticles supported on the carbon nitride.

[0018] The present invention also provides the application of the hydrogen production catalyst described in the above technical solution in the catalytic hydrogen production from formic acid.

[0019] The present invention provides a preparation method of a hydrogen production catalyst, including the following steps: mixing urea and acetone and then performing calcination to obtain carbon nitride; mixing the carbon nitride with a soluble palladium salt, a reducing agent, and water, and performing a reduction reaction to obtain a hydrogen production catalyst. In the present invention, carbon nitride is prepared by mixing urea and acetone and then performing calcination, and then the carbon nitride is mixed with a soluble palladium salt, a reducing agent, and water to perform a reduction reaction to form the active component palladium of the catalyst and make the palladium supported on the carbon nitride; the present invention utilizes the modification effect of acetone to increase the escape of small molecules during calcination, making the thermal condensation reaction of urea to form carbon nitride more intense, and thus making the formed carbon nitride thinner; at the same time, defects are also generated in the formed carbon nitride, which is beneficial to anchoring the active component palladium particles and enabling the palladium particles to be evenly distributed in the carbon nitride, thereby improving the catalytic performance of the catalyst. The method provided by the present invention can improve the dispersion of the active component palladium by first obtaining thinner and defective carbon nitride as a carrier, and thus can make the catalyst have high catalytic activity without using other noble metal modifications but only using palladium as the active component, reducing the cost of the catalyst. The results of the examples show that when the catalyst prepared by the present invention is used for catalytic hydrogen production from formic acid, the palladium loading in the catalyst is only 10%, and the TOF value of the catalyst can reach 2710 h -1 , having excellent catalytic activity. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 XRD spectrum of Pd / CN-UA prepared in Example 1 of the present invention;

[0021] Figure 2 TEM image of Pd / CN-UA prepared in Example 1 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0022] The present invention provides a method for preparing a hydrogen production catalyst, comprising the following steps:

[0023] (1) Mix urea and acetone and then calcine to obtain carbon nitride;

[0024] (2) Mix the carbon nitride obtained in step (1) with a soluble palladium salt, a reducing agent and water, and carry out a reduction reaction to obtain a hydrogen production catalyst.

[0025] In the present invention, urea and acetone are mixed and then calcined to obtain carbon nitride. By mixing urea and acetone and then calcining, acetone can be used to modify urea, resulting in an increase in the escape of molecules during calcination, a more intense reaction of urea thermal condensation to form carbon nitride, and thus a thinner carbon nitride formed; at the same time, defects are also generated in the formed carbon nitride.

[0026] In the present invention, the urea serves as a precursor for preparing carbon nitride. Using urea as a precursor in the present invention can endow the prepared catalyst with excellent catalytic activity.

[0027] In the present invention, the acetone serves as a modifying reagent for preparing carbon nitride. Using acetone as a modifying reagent in the present invention can make the obtained carbon nitride thinner; at the same time, defects are also generated in the formed carbon nitride.

[0028] In the present invention, the mass ratio of urea to the volume of acetone is preferably 20 g:(7 - 40) mL, more preferably 20 g:(7 - 20) mL, and further preferably 20 g:(10 - 20) mL. When the mass ratio of urea to the volume of acetone is within the above range in the present invention, it is more conducive to promoting the urea thermal condensation reaction.

[0029] In the present invention, the method for mixing urea and acetone is preferably: impregnating urea in acetone for 1 - 4 h, preferably 2 - 4 h; the impregnation temperature is preferably room temperature. When the mixing of urea and acetone in the present invention adopts the above method, acetone and urea can be fully and uniformly mixed.

[0030] In the present invention, the temperature of the calcination is preferably 550 - 580 °C, more preferably 550 °C; the time of the calcination is preferably 2 - 4 h, more preferably 3 - 4 h. In the present invention, the calcination is preferably carried out in air. In the present invention, during the calcination in an air atmosphere, urea undergoes a thermal condensation reaction to form carbon nitride. Calcination in air can avoid introducing other gases as the reaction atmosphere, thereby reducing the harshness of the preparation conditions; when the temperature and time of the calcination are within the above ranges, urea can fully react to form carbon nitride. The present invention has no special limitation on the calcination device, and a calcination device well-known to those skilled in the art can be used.

[0031] The present invention preferably cools the system obtained after the calcination to room temperature to obtain carbon nitride.

[0032] After obtaining carbon nitride, in the present invention, the carbon nitride is mixed with a soluble palladium salt, a reducing agent, and water, and then a reduction reaction is carried out to obtain a hydrogen production catalyst. By mixing carbon nitride with a soluble palladium salt, a reducing agent, and water and then carrying out a reduction reaction, palladium can be formed on the surface of the carbon nitride.

[0033] In the present invention, the soluble palladium salt preferably includes one or more of palladium acetate, palladium nitrate, and potassium chloropalladate, more preferably palladium acetate. In the present invention, the soluble palladium salt is the palladium source of the hydrogen production catalyst.

[0034] In the present invention, the molar ratio of palladium in the soluble palladium salt to the mass of carbon nitride is preferably (0.136 - 0.645) mmol:0.27 g, more preferably (0.287 - 0.5) mmol:0.27 g. When the molar ratio of palladium in the soluble palladium salt to the mass of carbon nitride is within the above range, the loading amount of the active component palladium in the hydrogen production catalyst can reach 5 - 20%, thereby enabling the catalyst to have good catalytic activity.

[0035] In the present invention, the reducing agent preferably includes sodium borohydride or hydrazine hydrate. In the present invention, the reducing agent can reduce palladium ions to palladium. The present invention has no special limitation on the dosage of the reducing agent, and it can be adjusted according to the dosage of the soluble palladium salt. In the present invention, the molar ratio of the soluble palladium salt to the reducing agent is preferably 1:5 - 1:15, more preferably 1:10. When the molar ratio of the soluble palladium salt to the reducing agent is within the above range, palladium ions can be fully reduced to palladium.

[0036] In the present invention, the water serves as the solvent for the reduction reaction. There is no special limitation on the amount of the water in the present invention, and it can be adjusted according to the amount of carbon nitride. In the present invention, the mass ratio of the carbon nitride to the volume of water is preferably 0.27 g:(40 - 80) mL, more preferably 0.27 g:60 mL. When the amount of the water in the present invention is within the above range, it can form a suspension with a suitable concentration of carbon nitride, thereby facilitating the full progress of the reduction reaction.

[0037] There is no special limitation on the method for mixing the carbon nitride, soluble palladium salt, reducing agent and water in the present invention, as long as the above components can be mixed evenly. In the present invention, the method for mixing the carbon nitride, soluble palladium salt, reducing agent and water preferably includes: mixing the carbon nitride and soluble palladium salt first, and then mixing with the reducing agent.

[0038] In the present invention, the method for mixing the carbon nitride, soluble palladium salt and water is preferably stirring, the temperature of the stirring is preferably room temperature, and the time of the stirring is preferably 2 - 4 h, more preferably 3 h. When the time of the stirring in the present invention is within the above range, it can make the palladium ions fully dispersed in the carbon nitride.

[0039] In the present invention, the temperature of the reduction reaction is preferably room temperature, and the time of the reduction reaction is preferably 2 - 4 h, more preferably 3 h. In the present invention, the reduction reaction occurs during the mixing process of the carbon nitride, soluble palladium salt, reducing agent and water; the reduction reaction preferably starts when the reducing agent is added to the mixture of the carbon nitride, soluble palladium salt, reducing agent and water. When the temperature and time of the reduction reaction in the present invention are within the above range, it can fully reduce the palladium ions.

[0040] In the present invention, the reduction reaction is preferably carried out under stirring. There is no special limitation on the rotation speed of the stirring in the present invention, and it can be adjusted according to the experimental process. In the present invention, the stirring can promote mass transfer, thereby promoting the full progress of the reduction reaction, and at the same time facilitating the uniform distribution of palladium in the carbon nitride.

[0041] After the reduction reaction is completed, in the present invention, the system after the reduction reaction is preferably centrifuged, washed and dried in sequence to obtain a hydrogen production catalyst. There is no special limitation on the methods of centrifugation, washing and drying in the present invention, and the methods of centrifugation, washing and drying well-known to those skilled in the art can be used. In the present invention, the washing reagent is preferably water, and the drying temperature is preferably 80 °C.

[0042] The method provided by the present invention can obtain thinner and defective carbon nitride first, and using this as a carrier can improve the dispersion of palladium, thereby enabling the catalyst to have high catalytic activity without using other noble metal modifications and only using palladium as the active component, reducing the cost of the catalyst.

[0043] The present invention also provides a hydrogen production catalyst prepared by the preparation method described in the above technical solution, which includes carbon nitride and palladium nanoparticles supported on the carbon nitride.

[0044] In the present invention, the loading amount of palladium in the hydrogen production catalyst is preferably 5-20%, more preferably 5-10%. In the present invention, the carbon nitride in the hydrogen production catalyst has a relatively thin thickness and defects, which is beneficial to anchoring the active component palladium particles, enabling the palladium particles to be uniformly distributed in the carbon nitride, and thus enabling palladium to have excellent catalytic activity at the above loading amount.

[0045] The present invention also provides the application of the hydrogen production catalyst described in the above technical solution in the catalytic hydrogen production from formic acid. The present invention has no special limitation on the application method of the hydrogen production catalyst in the catalytic hydrogen production from formic acid, and the application method of the catalyst well-known to those skilled in the art in the catalytic hydrogen production from formic acid can be adopted.

[0046] In the present invention, the application method of the hydrogen production catalyst in the catalytic hydrogen production from formic acid preferably includes: stirring the hydrogen production catalyst, water, formic acid and sodium formate. In the present invention, due to the presence of the hydrogen production catalyst, under the above conditions, it can catalyze the decomposition of formic acid to produce hydrogen. In the present invention, the temperature of the stirring is preferably room temperature. The present invention has no special limitation on the stirring time, as long as the formic acid can be fully decomposed. The present invention has no special limitation on the dosage of the catalyst, and it can be adjusted according to needs.

[0047] The method provided by the present invention can obtain relatively thin carbon nitride with defects first. As a carrier, it can improve the dispersion of palladium, and thus enable the catalyst to have high catalytic activity without using other noble metals for modification but only using palladium as the active component. When it is used in the catalytic hydrogen production from formic acid, it shows excellent catalytic activity; at the same time, it can catalyze the hydrogenation of carbon dioxide and has excellent catalytic activity.

[0048] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the embodiments in the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0049] Example 1

[0050] The preparation method of the hydrogen production catalyst, the steps are as follows:

[0051] (1) Impregnate urea in acetone for 4 h according to the mass ratio of urea to the volume of acetone being 20 g:20 mL, then calcine it in an air atmosphere at 550 °C for 4 h. After cooling to room temperature, carbon nitride is obtained and named CN-UA;

[0052] (2) Stir 0.27 g of the carbon nitride obtained in step (1), 0.063 g of palladium acetate and 60 mL of water for 3 h, then add 0.113 g of sodium borohydride and continue stirring for 3 h for a reduction reaction. Then centrifuge, wash with water, and dry the obtained solid at 80 °C to obtain a hydrogen production catalyst, labeled as Pd / CN-UA. Among them, the molar ratio of palladium (palladium acetate) in the soluble palladium salt to the mass of carbon nitride is 0.287 mmol:0.27 g.

[0053] Example 2

[0054] The difference from Example 1 is that in step (1), the mass ratio of urea to the volume of acetone is 20 g:40 mL, and the remaining steps are the same as those in Example 1.

[0055] Example 3

[0056] The difference from Example 1 is that in step (1), the mass ratio of urea to the volume of acetone is 20 g:10 mL, and the remaining steps are the same as those in Example 1.

[0057] Example 4

[0058] The difference from Example 1 is that in step (1), the mass ratio of urea to the volume of acetone is 20 g:7 mL, and the remaining steps are the same as those in Example 1.

[0059] Comparative Example 1

[0060] The difference from Example 1 is that in step (1), water is used to replace acetone, that is, water is used as the modification reagent, and the remaining steps are the same as those in Example 1.

[0061] Comparative Example 2

[0062] The difference from Example 1 is that in step (1), methanol is used to replace acetone, that is, methanol is used as the modification reagent, and the remaining steps are the same as those in Example 1.

[0063] Comparative Example 3

[0064] The difference from Example 1 is that in step (1), ethanol is used to replace acetone, that is, ethanol is used as the modification reagent, and the remaining steps are the same as those in Example 1.

[0065] Comparative Example 4

[0066] The difference from Example 1 is that ethylene glycol is used to replace acetone in step (1), that is, ethylene glycol is used as the modification reagent, and the remaining steps are the same as those in Example 1.

[0067] Comparative Example 5

[0068] The difference from Example 1 is that ethylenediamine is used to replace acetone in step (1), that is, ethylenediamine is used as the modification reagent, and the remaining steps are the same as those in Example 1.

[0069] Comparative Example 6

[0070] The difference from Example 1 is that dicyandiamide is used to replace urea in step (1), that is, dicyandiamide is used as the precursor, and the remaining steps are the same as those in Example 1.

[0071] Comparative Example 7

[0072] The difference from Example 1 is that melamine is used to replace urea in step (1), that is, melamine is used as the precursor, and the remaining steps are the same as those in Example 1.

[0073] Comparative Example 8

[0074] The difference from Example 1 is that urea is calcined at 550 °C for 4 h in step (1), and then cooled to room temperature to obtain carbon nitride, and the remaining steps are the same as those in Example 1.

[0075] Test Example

[0076] The Pd / CN-UA prepared in Example 1 was tested by an X-ray diffractometer, and the XRD pattern of Pd / CN-UA is as Figure 1 shown. From Figure 1 it can be seen that the carbon nitride marker diffraction peak of Pd / CN-UA exists at 27.3°, which belongs to the vibration of the aromatic ring and is the (002) crystal plane marked in the figure; compared with the Pd (JCPDS: 65-2867) standard card, the diffraction peak of the XRD pattern of Pd / CN-UA appears at 39.6°, which belongs to the (111) crystal plane of Pd; due to the low metal loading and crystallinity of the catalyst, the X-ray diffraction results show a weak Pd diffraction peak.

[0077] The Pd / CN-UA prepared in Example 1 was tested by a transmission electron microscope, and the TEM image of Pd / CN-UA is as Figure 2 shown. From Figure 2 it can be seen that the CN-UA support has an ultrathin nanosheet structure with a thickness of about 2 nm to 20 nm, and the edges of the CN-UA layer are significantly wrinkled; and smaller Pd nanoparticles are uniformly loaded on the support with an average particle size of 1.9 nm. It shows that the palladium nanoparticles are well fixed and dispersed on the carbon nitride support in the Pd / CN-UA catalyst.

[0078] Application Examples 1 - 4

[0079] The hydrogen production catalysts prepared in Examples 1 - 4 were respectively applied to catalytic hydrogen production from formic acid, and the method was as follows:

[0080] Weigh 0.05 g of the prepared catalyst and add it to a round - bottom flask containing 10 mL of deionized water, stir, connect a burette filled with water to the round - bottom flask, and use the water - displacement method to record the volume of the generated gas. When 5 mL of a mixed solution of formic acid and sodium formate (SF) (FA = 2 mmol, FA:SF = 1:8) is injected into the round - bottom flask with a syringe, the reaction starts. The reaction is carried out at 75 °C, and the reaction time and the volume of the generated gas are recorded. The performance results of the catalyst are shown in Table 1.

[0081] The performance of the catalyst was evaluated using the initial turnover frequency (TOF) value, and the calculation formula is shown in Equation (I):

[0082]

[0083] Where 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 metal is the metal content 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.

[0084] Comparative Application Examples 1 - 8

[0085] The hydrogen production catalysts prepared in Comparative Examples 1 - 8 were respectively tested using the method of Application Example 1, and the performance results of the catalysts are shown in Table 1.

[0086] Table 1 Hydrogen production performance of different catalysts from formic acid

[0087]

[0088]

[0089] It can be seen from the above results that the catalyst prepared by the present invention can improve the dispersion of palladium by first obtaining a thinner and defective carbon nitride as the carrier, and then, without using other noble metal modifications but only using palladium as the active component, the catalyst has high catalytic activity and reduces the cost of the catalyst.

[0090] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of a hydrogen production catalyst by catalysis, comprising the following steps: (1) Mix urea and acetone and then carry out calcination to obtain carbon nitride; (2) Mix the carbon nitride obtained in step (1) with a soluble palladium salt, a reducing agent and water, and carry out a reduction reaction to obtain a hydrogen production catalyst by catalysis.

2. The preparation method according to claim 1, wherein, The method for mixing urea and acetone in step (1) is: impregnate urea in acetone for 1 to 4 h.

3. The preparation method according to claim 1 or 2, characterized in that, The mass ratio of urea to the volume of acetone in step (1) is 20 g:(7 to 40) mL.

4. The preparation method according to claim 1 or 2, characterized in that The calcination temperature in step (1) is 550 to 580 °C.

5. The preparation method according to claim 4, wherein The calcination time in step (1) is 2 to 4 h.

6. The preparation method according to claim 1, wherein The soluble palladium salt in step (2) includes one or more of palladium acetate, palladium nitrate and potassium chloropalladate.

7. The preparation method according to claim 1, characterized in that, The reducing agent in step (2) includes sodium borohydride or hydrazine hydrate.

8. The preparation method according to claim 1, characterized in that, The molar ratio of palladium in the soluble palladium salt to the mass of carbon nitride in step (2) is (0.136 to 0.645) mmol:0.27 g.

9. A hydrogen production catalyst by catalysis prepared by the preparation method according to any one of claims 1 to 8, comprising carbon nitride and palladium nanoparticles supported on the carbon nitride.

10. Use of the hydrogen production catalyst by catalysis according to claim 9 in the catalytic hydrogen production of formic acid.

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