Composite catalyst, preparation method and application thereof

Abstract

The application discloses a composite catalyst and a preparation method and application thereof, and belongs to the technical field of hydrogen production by catalysis of liquid formic acid. The composite catalyst comprises a metal single-atom modified nitrogen-doped carbon-based carrier and noble metal nanoparticles loaded on the metal single-atom modified nitrogen-doped carbon-based carrier; and the content of the noble metal nanoparticles in the composite catalyst is 5-20 wt.%. The metal single atom is used for anchoring optimization, the surface and interface characteristics of the carbon-based carrier are modified, the electronic structure around the noble metal nanoparticles is adjusted, the interaction between the carrier and the noble metal nanoparticles is strengthened, and therefore the catalytic performance of the composite catalyst for hydrogen production by catalysis of liquid formic acid is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of catalytic hydrogen production from liquid formic acid, and particularly relates to a composite catalyst and a preparation method and application thereof. BACKGROUND

[0002] Hydrogen is one of the most promising clean and renewable energy sources. It has a very large mass energy density, and its combustion product is only water, which is green and clean, and is one of the most ideal fuels. Hydrogen-oxygen fuel cells with hydrogen as the negative electrode are expected to become the next generation of mobile energy storage devices due to their high energy density and high thermal efficiency. However, the successful application of this technology depends on the safe use and continuous supply of hydrogen. The development and use of liquid hydrogen storage technology with high energy storage density (such as catalytic hydrogen production from formic acid) is expected to solve this problem. Formic acid is the main product of biomass prepared by cellulose hydrolysis or oxidation, and has a high yield. Due to its excellent hydrogen content (4.4wt%), high volumetric hydrogen storage density (53g / L), non-toxicity, portability, regeneration by CO2 hydrogenation, good room temperature stability, and other characteristics, it has become one of the most attractive hydrogen carriers. The preparation of high-performance catalysts is an important prerequisite for realizing hydrogen production from formic acid.

[0003] At present, catalysts for hydrogen production from formic acid can be divided into homogeneous catalysts and heterogeneous catalysts. Compared with homogeneous catalysts, heterogeneous catalysts have lower reaction temperature requirements, simple preparation methods, and are easy to separate, and have better industrial application prospects. The core of hydrogen production from formic acid is the preparation of high-performance heterogeneous catalysts, especially metal nanoparticle catalysts, mainly including the design of metal nanoparticles and supports.

[0004] In heterogeneous catalysts, noble metal nanoparticles such as Pd, Au, and other single metal or alloy nanoparticles have good catalytic activity for hydrogen production from formic acid. However, noble metals have low reserves and high costs, and the catalytic active sites of metal particle catalysts only exist on the surface of the particles, and the unexposed metal components in the interior cannot participate in the catalytic reaction, resulting in low utilization of metal atoms and causing great waste of resources.

[0005] Therefore, how to improve the catalytic activity of heterogeneous catalysts while improving the atomic utilization rate and reducing the cost of heterogeneous catalysts is a major problem faced by those skilled in the art. SUMMARY

[0006] The purpose of the present application is to provide a composite catalyst and a preparation method and application thereof, so as to solve the problems of high cost, low atomic utilization rate and low activity of heterogeneous catalysts in the prior art.

[0007] To achieve the above-mentioned purpose, the present application provides the following solutions.

[0008] One of the technical solutions of the present application: a composite catalyst, comprising a metal single atom modified nitrogen-doped carbon base carrier, and a noble metal nanoparticle loaded on the metal single atom modified nitrogen-doped carbon base carrier; the content of the noble metal nanoparticle in the composite catalyst is 5-20 wt.%.

[0009] Further, the noble metal nanoparticle is a single noble metal nanoparticle formed by any one of Pd, Pt, Au, Ag, and Rh, or a noble metal alloy nanoparticle formed by any two of them; the particle size of the noble metal nanoparticle is 1-2 nm.

[0010] Further, the metal single atom modified nitrogen-doped carbon base carrier comprises a nitrogen-doped carbon base carrier, and a metal single atom anchored on the nitrogen-doped carbon base carrier.

[0011] Further, the metal single atom is one of Co, Fe, Ni, Cu, and Mn.

[0012] Further, the content of the metal single atom in the metal single atom modified nitrogen-doped carbon base carrier is 0.5-10 wt.%.

[0013] The second technical solution of the present application: a preparation method of the above composite catalyst, comprising the following steps:

[0014] Mixing a nitrogen-doped carbon base carrier or a nitrogen-doped carbon precursor with a metal salt, sintering to obtain a metal single atom modified nitrogen-doped carbon base carrier; mixing the metal single atom modified nitrogen-doped carbon base carrier with a noble metal salt solution, adding a reducing agent, and performing a reduction reaction to obtain the composite catalyst.

[0015] Mixing a nitrogen-doped carbon precursor with a metal salt, and when sintering, the nitrogen-doped carbon precursor is further decomposed to form a nitrogen-doped carbon base carrier, and a metal single atom is anchored thereon.

[0016] Further, the metal salt is one of Co salt, Fe salt, Ni salt, Cu salt, and Mn salt; the noble metal salt solution is one or two of Pd salt solution, Au salt solution, Ag salt solution, and Rh salt solution; the reducing agent is NaBH4; the sintering temperature is 600-1000℃, and the time is 1-10 h.

[0017] Further, the concentration of the noble metal salt solution is 0.05-0.5 mol / L.

[0018] Further, the molar ratio of the reducing agent to the noble metal atom contained in the noble metal salt solution is 15-40.

[0019] Further, the NaBH4 is added in the form of a solution, i.e., the NaBH4 is prepared into a solution (1-5 M) and then added to the reaction system.

[0020] Further, the reaction time of the reduction reaction is 60-120 min.

[0021] Further, the preparation method of the nitrogen-doped carbon-based carrier comprises the following steps:

[0022] The carbon material and urea are mixed and ground, and sintered at a temperature of 200-450 ℃ for 3-6 h to obtain the nitrogen-doped carbon-based carrier.

[0023] Further, the preparation method of the nitrogen-doped carbon precursor comprises the following steps:

[0024] The urea is sintered at a temperature of 450-600 ℃ for 2-4 h to obtain C3N4; the C3N4 is mixed with water and glucose, and heated to perform a hydrothermal reaction, centrifuged, and dried to obtain the nitrogen-doped carbon precursor; the temperature of the hydrothermal reaction is 180-250 ℃, and the time is 12-24 h.

[0025] Further, the mass ratio of the C3N4 to the glucose is 1:1-1:5.

[0026] Further, the specific operation of mixing the C3N4 with water and glucose is as follows: the C3N4 is added to water, and ultrasonically treated for 1-5 h, then the glucose is added, and ultrasonically treated for 2-6 h to obtain a suspension.

[0027] Further, the carbon material is porous carbon, graphene, carbon fiber, or Ketjen black.

[0028] Further, the mass ratio of the carbon material to urea is 1:1-1:5.

[0029] Further, when the nitrogen-doped carbon-based carrier or the nitrogen-doped carbon precursor is mixed with the metal salt and sintered, the amount of the metal salt is controlled so that the content of the metal monatomic atom in the metal monatomic atom-modified nitrogen-doped carbon-based carrier obtained is 0.5-10 wt.%, i.e., the amount ratio of the nitrogen-doped carbon-based carrier or the nitrogen-doped carbon precursor to the metal salt is calculated according to the content of the metal monatomic atom in the metal monatomic atom-modified nitrogen-doped carbon-based carrier to be obtained.

[0030] Further, when the metal monatomic atom-modified nitrogen-doped carbon-based carrier is mixed with the noble metal salt solution, the amount of the noble metal salt solution is controlled so that the content of the noble metal nanoparticle in the composite catalyst is 5-20 wt.% of the whole of the final composite catalyst, i.e., the amount ratio of the metal monatomic atom-modified nitrogen-doped carbon-based carrier to the noble metal salt solution is calculated according to the content of the noble metal nanoparticle in the composite catalyst to be obtained.

[0031] The third technical solution of the present application is the application of the above-mentioned composite catalyst in the catalytic hydrogen production from liquid formic acid.

[0032] The metal salt and the nitrogen-doped carbon-based carrier or nitrogen-doped carbon precursor are sintered at high temperature to prepare a metal monatomic modified nitrogen-doped carbon-based carrier, and then the noble metal nanoparticles are loaded on the metal monatomic modified nitrogen-doped carbon-based carrier by means of the wet reduction method to obtain the final composite catalyst. In the above process, the number of defects on the surface of the carbon-based carrier is first increased by nitrogen doping to provide abundant active sites for the anchoring of metal monatomic and the loading of noble metal nanoparticles; then the surface and interface properties of the carbon-based carrier are further optimized and modified by the combination of nitrogen and metal monatomic, which not only adjusts the electronic structure around the loaded noble metal nanoparticles, but also strengthens the interaction between the carrier and the noble metal nanoparticles, promotes the uniform distribution of the noble metal nanoparticles, and thus improves the catalytic performance of the composite catalyst for the catalytic hydrogen production from liquid formic acid. In addition, the particle size of the noble metal nanoparticles in the composite catalyst of the present application is 1-2 nm, which reduces the size of the noble metal nanoparticles. The highly dispersed noble metal nanoparticles with uniform size not only improve the catalytic activity of the composite catalyst, but also effectively promote the utilization rate of metal atoms.

[0033] The metal monatomic modified nitrogen-doped carbon-based carrier is mixed with a noble metal salt solution, a reducing agent is added, and the size of the noble metal nanoparticles is controlled by controlling the concentration of the noble metal salt solution at 0.05-0.5 mol / L, the molar ratio of sodium borohydride to noble metal atoms contained in the noble metal salt solution at 15-40, and the content of noble metal nanoparticles in the composite catalyst at 5-20 wt.%. The particle size of the noble metal nanoparticles is controlled at 1-2 nm. On the one hand, the reduction of the size of the noble metal nanoparticles can expose a larger contact reaction area, improve the atomic utilization rate and catalytic activity; on the other hand, the doping of nitrogen and metal monatomic in the carrier optimizes the surface electronic structure of the carrier, strengthens the interaction between the carrier and the noble metal nanoparticles, makes the noble metal nanoparticles more uniformly distributed on the nitrogen-doped carbon-based carrier, avoids agglomeration, and further improves the atomic utilization rate and the stability of the catalyst.

[0034] The present application has the following technical effects:

[0035] (1) The composite catalyst of the present application has high catalytic activity, and the turnover frequency (TOF) of the composite catalyst for the catalytic hydrogen production from liquid formic acid at low temperature is >3000 h -1 .

[0036] (2) The raw materials for preparing the nitrogen-doped carbon-based carrier of the present application are glucose and urea, or carbon materials such as Ketjen black and urea, which are low in price, and the process for preparing the nitrogen-doped carbon-based carrier is relatively simple, which has industrial prospects. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 Here is a SEM image of the composite catalyst prepared in Example 1 of this invention;

[0039] Figure 2 The XRD pattern of the composite catalyst prepared in Example 1 of this invention;

[0040] Figure 3 The time-volume curve of the composite catalyst prepared in Example 1 of this invention for the catalytic hydrogen production from liquid formic acid is shown. Detailed Implementation

[0041] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0042] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0043] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0044] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This application specification and embodiments are merely exemplary.

[0045] As used herein, the terms "comprise", "comprising", "including", "include", "contain", "containing", "have", "having" or variants thereof are open-ended, meaning that they allow also for the presence of other steps, elements or ingredients not specifically recited.

[0046] Example 1

[0047] The preparation of the composite catalyst is as follows:

[0048] (1) 20 g of urea was sintered in a muffle furnace at 550 °C for 4 h with a heating rate of 2 °C / min, and a light yellow solid C3N4 was obtained after cooling. 500 mg of C3N4 was added to 40 mL of water and ultrasonicated for 2 h to uniformly disperse it, then 2.16 g of glucose was added and ultrasonicated for another 4 h to obtain a suspension. The suspension was transferred to a 100 mL Teflon-lined autoclave and heated to 200 °C for 24 h of hydrothermal reaction. After the hydrothermal reaction, the precipitate was collected by centrifugation at 6000 r / min for 3 min, washed with water for 3 times, and dried at 60 °C to obtain a nitrogen-doped carbon precursor, denoted as C3N4@G.

[0049] (2) 9.97 mg (0.034 mmol) of Co(NO3)2·6H2O was dissolved in 0.25 mL of ethanol, and mixed with 400 mg of C3N4@G and ground for 10 min. Then it was placed in a tube furnace and sintered at 900 °C (heating rate of 5 °C / min) under N2 atmosphere for 1 h to obtain 200 mg of metal single-atom modified nitrogen-doped carbon support NC-Co 1％ (1% represents that the content of Co metal atoms in the obtained metal single-atom modified nitrogen-doped carbon support is 1 wt.%).

[0050] (3) 100 mg of NC-Co 1％ prepared in step (2) was added to a beaker with 0.5 mL of K2PdCl4 solution (0.1 M) and 40 mL of H2O, and stirred for 1 h. Then 1 mL of freshly prepared NaBH4 solution (1.25 M) was added, and the molar ratio of NaBH4 to noble metal atoms contained in the noble metal salt solution was 25:1. The reduction was carried out under stirring for 90 min, and the precipitate was collected by centrifugation at 6000 r / min for 3 min, washed with water for 3 times to obtain a composite catalyst, denoted as Pd-NC-Co 1％ (the content of Pd nanoparticles in the composite catalyst is 5 wt.% and the average particle size is 1.5 nm).

[0051] Figure 1 The SEM image of the composite catalyst prepared in this example is shown in FIG. 1. Figure 1 As can be seen from FIG. 1, the average particle size of the Pd nanoparticles is about 1.5 nm, and the Pd nanoparticles are uniformly dispersed on the nitrogen-doped carbon support without obvious agglomeration and large size particles.

[0052] Figure 2 The XRD pattern of the composite catalyst prepared for this example is shown in FIG. 1. Figure 2 It can be seen that the composite catalyst has weak diffraction peaks, indicating that the average particle size of the noble metal nanoparticles in the catalyst is small.

[0053] Example 2

[0054] The composite catalyst was prepared as follows:

[0055] (1) 20 g of urea was sintered in a muffle furnace at 550 °C for 4 h, with a heating rate of 2 °C / min. After cooling, a light yellow solid C3N4 was obtained. 500 mg of C3N4 was added to 40 mL of water and ultrasonicated for 2 h to uniformly disperse it. Then 2.16 g of glucose was added and ultrasonicated for another 4 h to obtain a suspension. The suspension was transferred to a 100 mL polytetrafluoroethylene-lined autoclave and heated to 200 °C for 24 h of hydrothermal reaction. After the hydrothermal reaction, the precipitate was collected by centrifugation at 6000 r / min for 3 min, washed with water for 3 times, and dried at 60 °C to obtain a nitrogen-doped carbon precursor, which was denoted as C3N4@G.

[0056] (2) 9.97 mg of Co(NO3)2·6H2O was dissolved in 0.25 mL of ethanol, and then mixed with 400 mg of C3N4@G and ground for 10 min. Then it was placed in a tube furnace and sintered at 900 °C (heating rate of 5 °C / min) under N2 atmosphere for 1 h to obtain 200 mg of metal monatomic atom-modified nitrogen-doped carbon-based carrier NC-Co 1％ (1% represents that the content of Co metal atoms in the obtained metal monatomic atom-modified nitrogen-doped carbon-based carrier is 1 wt.%).

[0057] (3) 100 mg of NC-Co 1％ prepared in step (2), 0.7 mL of K2PdCl4 solution (0.1 M), 0.3 mL of HAuCl4·4H2O solution (0.1 M), and 40 mL of H2O were added to a beaker and stirred for 1 h. Then 1 mL of freshly prepared NaBH4 solution (2.5 M) was added, and the molar ratio of NaBH4 to noble metal atoms contained in the noble metal salt solution was 25:1. The reduction was carried out under stirring for 90 min. The precipitate was collected by centrifugation at 6000 r / min for 3 min, washed with water for 3 times, and dried at 60 °C to obtain a composite catalyst, which was denoted as PdAu-NC-Co 1％ (the content of PdAu alloy nanoparticles in the composite catalyst was 11.8 wt.%, and the average particle size was 1.8 nm).

[0058] Example 3

[0059] The composite catalyst was prepared as follows:

[0060] (1) 1 g KB and 1 g urea were mixed and ground for 10 min, sealed with aluminum foil, sintered in a muffle furnace at 300 °C for 4 h with a heating rate of 5 °C / min, and naturally cooled to room temperature. The product was washed with ultrapure water for 3 times and dried to obtain a nitrogen-doped carbon support, denoted as N-KB.

[0061] (2) 7.21 mg (0.018 mmol) Fe(NO3)3·9H2O was dissolved in 0.25 mL ethanol, and then mixed with 100 mg N-KB and ground for 10 min. Then, the mixture was sintered in a tube furnace at 800 °C (heating rate of 5 °C / min) for 2 h under N2 atmosphere to obtain a metal single-atom decorated nitrogen-doped carbon support, denoted as N-KB-Fe. 1％ (1% represents that the content of Fe atoms in the obtained metal single-atom decorated nitrogen-doped carbon support is 1 wt.%).

[0062] (3) 30 mg N-KB-Fe prepared in step (2) 1％ , 0.5 mL K2PdCl4 solution (0.1 M), and 40 mL H2O were added into a beaker and stirred for 1 h. Then, 1 mL freshly prepared NaBH4 solution (1.25 M) was added, and the molar ratio of NaBH4 to noble metal atoms contained in the noble metal solution was 25:1. The mixture was reduced under stirring for 90 min, and then centrifuged at 6000 r / min for 3 min. The precipitate was collected and washed with water for 3 times to obtain a composite catalyst, denoted as Pd-N-KB-Fe. 1％ (the content of Pd nanoparticles in the composite catalyst was 15 wt.% and the average particle size was 2 nm).

[0063] Example 4

[0064] The composite catalyst was prepared according to the following steps:

[0065] (1) 20 g urea was sintered in a muffle furnace at 550 °C for 4 h with a heating rate of 2 °C / min, and then cooled to obtain a light yellow solid C3N4. 500 mg C3N4 was added into 40 mL water and ultrasonically dispersed for 2 h. Then, 2.16 g glucose was added and ultrasonically dispersed for another 4 h to obtain a suspension. The suspension was transferred into a 100 mL polytetrafluoroethylene-lined autoclave and heated to 200 °C for hydrothermal reaction for 24 h. After the hydrothermal reaction, the mixture was centrifuged at 6000 r / min for 3 min. The precipitate was collected, washed with water for 3 times, and dried at 60 °C to obtain a nitrogen-doped carbon precursor, denoted as C3N4@G.

[0066] (2) 19.94 mg (0.068 mmol) Co(NO3)2·6H2O was dissolved in 0.25 mL ethanol, and mixed with 400 mg C3N4@G for 10 min. Then, it was sintered in a tube furnace at 900 °C (heating rate 5 °C / min) for 1 h under N2atmosphere to obtain 202 mg of metal single-atom decorated nitrogen-doped carbon-based support NC-Co. 2％ (2% represents that the content of Co metal atoms in the obtained metal single-atom decorated nitrogen-doped carbon-based support is 2 wt.%).

[0067] (3) 100 mg of NC-Co prepared in step (2) 2％ , 0.75 mL K2PdCl4solution (0.1 M), 40 mL H2O were added into a beaker and stirred for 1 h, then 1.5 mL of freshly prepared NaBH4solution (1.25 M) was added, the molar ratio of NaBH4to noble metal atoms was 25:1, and reduction was carried out under stirring for 90 min. After centrifugation at 6000 r / min for 3 min, the precipitate was collected and washed with water for 3 times to obtain a composite catalyst, which was denoted as Pd-NC-Co. 2％ (The content of Pd nanoparticles in the composite catalyst was 7.4 wt.%, and the average particle size was 1.8 nm).

[0068] Comparative Example 1

[0069] (1) 20 g of urea was sintered in a muffle furnace at 550 °C for 4 h with a heating rate of 2 °C / min, and a light yellow solid C3N4was obtained after cooling. 500 mg of C3N4was added to 40 mL of water and ultrasonicated for 2 h to make it uniformly dispersed, then 2.16 g of glucose was added and ultrasonicated for another 4 h to obtain a suspension. The suspension was transferred into a 100 mL polytetrafluoroethylene-lined autoclave and heated to 200 °C for 24 h of hydrothermal reaction. After the hydrothermal reaction, the precipitate was collected by centrifugation at 6000 r / min for 3 min, washed with water for 3 times, and dried at 60 °C to obtain a nitrogen-doped carbon precursor, which was denoted as C3N4@G.

[0070] (2) 100 mg of C3N4@G prepared in step (1), 0.5 mL of K2PdCl4solution (0.1 M), 40 mL of H2O were added into a beaker and stirred for 1 h, then 1 mL of freshly prepared NaBH4solution (1.32 M) was added, the molar ratio of NaBH4to noble metal atoms contained in the noble metal salt solution was 26.4:1, and reduction was carried out under stirring for 90 min. After centrifugation at 6000 r / min for 3 min, the precipitate was collected and washed with water for 3 times to obtain a composite catalyst, which was denoted as Pd-NC (the content of Pd nanoparticles in the composite catalyst was 5 wt.%, and the average particle size was 1.6 nm).

[0071] Comparative Example 2

[0072] The preparation of the composite catalyst is as follows:

[0073] (1) 20 g of urea was sintered in a muffle furnace at 550 °C for 4 h with a heating rate of 2 °C / min, and a light yellow solid C3N4 was obtained after cooling. 500 mg of C3N4 was added to 40 mL of water and ultrasonicated for 2 h to uniformly disperse it, followed by the addition of 2.16 g of glucose and ultrasonication for another 4 h to obtain a suspension. The suspension was transferred to a 100 mL Teflon-lined autoclave and heated to 200 °C for 24 h of hydrothermal reaction. After the hydrothermal reaction, the precipitate was collected by centrifugation at 6000 r / min for 3 min, washed with water for 3 times, and dried at 60 °C to obtain a nitrogen-doped carbon precursor, denoted as C3N4@G.

[0074] (2) 9.97 mg of Co(NO3)2·6H2O was dissolved in 0.25 mL of ethanol, and mixed with 400 mg of C3N4@G and ground for 10 min. Then, it was placed in a tube furnace and sintered at 900 °C (heating rate of 5 °C / min) under N2 atmosphere for 1 h to obtain 200 mg of metal monatomic atom-modified nitrogen-doped carbon-based carrier NC-Co 1％ (1% represents that the content of metal Co atoms in the obtained metal monatomic atom-modified nitrogen-doped carbon-based carrier is 1 wt.%).

[0075] (3) 100 mg of NC-Co 1％ prepared in step (2), 0.5 mL of K2PdCl4 solution (0.1 M), and 40 mL of H2O were added to a beaker and stirred for 1 h, followed by the addition of 0.5 mL of freshly prepared NaBH4 solution (1.25 M), and the ratio of NaBH4 to noble metal atoms was 12.5:1. Reduction was carried out under stirring for 90 min, and the precipitate was collected by centrifugation at 6000 r / min for 3 min, washed with water for 3 times, to obtain a composite catalyst, denoted as Pd-NC-Co 1％ -1 (the content of Pd nanoparticles in the composite catalyst was 5 wt.% and the average particle size was 2.4 nm).

[0076] Effect verification

[0077] 1. Test of the catalytic performance of the catalyst

[0078] 50 mg of the composite catalyst was added to water in a two-necked flask (the total volume of the composite catalyst and water was kept at 2 mL), and the two-necked flask was fixed in a water bath. Preheating was carried out at room temperature for 80 s, 1 mL of formic acid sodium formate solution (mixed in a molar ratio of 1:2.5) was added, and the time-volume data of gas generation were recorded in a wet gas flow meter. Figure 3 The time-volume curve of the composite catalyst prepared in Example 1 for catalyzing hydrogen production from liquid formic acid, as shown in Figure 3It can be seen that 1 mmol of formic acid can be completely decomposed in 100 s to generate hydrogen and carbon dioxide under the action of the catalyst, and the total volume obtained is 144 mL, and the corresponding TOF is about 3600 h -1 .

[0079] Table 1 is a summary of the noble metal content, noble metal nanoparticle size and corresponding catalytic performance of the composite catalysts prepared in each example and comparative example. As can be seen from Table 1, within the scope of the study, the average particle size of the noble metal nanoparticles decreases as the molar ratio of the reducing agent to noble metal atoms increases, that is, the larger the molar ratio, the smaller the noble metal nanoparticle size, the higher the catalytic activity of the composite catalyst, and the larger the corresponding TOF value, that is, the higher the metal atom utilization rate. The loading of noble metal nanoparticles on the unit mass of the carrier increases (that is, the greater the noble metal content in the composite catalyst), and the size of the noble metal nanoparticles also increases.

[0080] Table 1

[0081]

[0082]

[0083] The above-described embodiments are only descriptions of the preferred modes of the present application and do not limit the scope of the present application. Without departing from the design spirit of the present application, various modifications and improvements to the technical solutions of the present application made by those of ordinary skill in the art shall fall within the protection scope determined by the claims of the present application.

Claims

1. The application of a composite catalyst in the catalytic production of hydrogen from liquid formic acid, characterized in that, The composite catalyst comprises a nitrogen-doped carbon-based support modified with a metal single atom, and noble metal nanoparticles supported on the nitrogen-doped carbon-based support modified with the metal single atom; the content of the noble metal nanoparticles in the composite catalyst is 5-20 wt.%. The noble metal nanoparticles are elemental noble metal nanoparticles formed from any one of the noble metal elements Pd, Pt, Au, Ag, and Rh, or noble metal alloy nanoparticles formed from any two of the noble metal elements; the particle size of the noble metal nanoparticles is 1 to 2 nm. The nitrogen-doped carbon-based support modified with metal single atoms includes a nitrogen-doped carbon-based support and metal single atoms anchored on the nitrogen-doped carbon-based support. The metal single atom is one of Co, Fe, Ni, Cu, and Mn; The content of metal single atoms in the nitrogen-doped carbon-based support modified with metal single atoms is 0.5–10 wt.%. The preparation steps of the composite catalyst include: Nitrogen-doped carbon-based support or nitrogen-doped carbon precursor is mixed with metal salt and sintered to obtain a nitrogen-doped carbon-based support modified with metal single atoms; the nitrogen-doped carbon-based support modified with metal single atoms is mixed with a noble metal salt solution, a reducing agent is added, and a reduction reaction is carried out to obtain the composite catalyst. The reducing agent is NaBH4; the sintering temperature is 600–1000℃, and the time is 1–10 h; The preparation steps of the nitrogen-doped carbon-based support include: Carbon materials and urea are mixed and ground, and then sintered at 200-450°C for 3-6 hours to obtain the nitrogen-doped carbon-based support. The preparation steps of the nitrogen-doped carbon precursor include: Urea is sintered at 450–600°C for 2–4 hours to obtain C3N4; the C3N4 is mixed with water and glucose, heated for a hydrothermal reaction, centrifuged, and dried to obtain the nitrogen-doped carbon precursor; the hydrothermal reaction is carried out at 180–250°C for 12–24 hours.

2. The application of the composite catalyst as described in claim 1 in the catalytic production of hydrogen from liquid formic acid, characterized in that, The metal salt is one of Co salt, Fe salt, Ni salt, Cu salt, and Mn salt; the noble metal salt solution is one or two of Pd salt solution, Pt salt solution, Au salt solution, Ag salt solution, and Rh salt solution.

Images