Palladium monatomic and palladium nanoparticle coexisting catalyst, preparation method and application

Abstract

The invention discloses a palladium monatomic and palladium nanoparticle coexisting catalyst, a preparation method and application. According to the method, a palladium chloride metal precursor is electrostatically adsorbed to mesoporous carbon nitride through a wet deposition method, then part of palladium species is reduced under the hydrogen and argon atmosphere, and the mesoporous carbon nitride loaded palladium monatomic and palladium nanoparticle coexisting photocatalyst is obtained. The photocatalyst in which the palladium monatomic and the palladium nanoparticles coexist promotes selective transfer hydrogenation of a hydrogen-source biomass derivative compound by taking water as a hydrogen source, and has the characteristics of stable structure, excellent catalytic performance and the like.

Description

Technical Field

[0001] The present invention relates to a catalyst coexisting palladium single atoms and palladium nanoparticles, a preparation method and an application thereof, and belongs to the technical fields of precise regulation of catalytic active sites and catalytic conversion of biomass. Background Art

[0002] Fossil fuel resources centered on coal, oil, and natural gas have long supported the progress of human society. Currently, global energy consumption still highly relies on these non-renewable fossil energies, including natural gas, coal, and oil. However, the over-exploitation and use of fossil fuels have led to the release of a large amount of greenhouse gases, which in turn has caused a significant increase in global temperatures in the past few decades. In addition to non-renewable energy sources, biofuels and waste are also important energy sources, accounting for approximately 10% of the global energy supply. Among them, biomass, as an abundant renewable organic carbon resource, shows great potential to replace fossil fuels. Compared with fossil energy, the organic compounds in biomass have higher degrees of unsaturation. Therefore, hydrogenation technology is often used to convert biomass and its derivatives into high-value-added products, making them possess properties similar to petroleum-based chemicals. However, the molecular structure and functional group diversity of biomass-derived compounds pose great challenges for the selective synthesis of target hydrogenation products. Traditional heterogeneous thermal catalytic hydrogenation is a commonly used upgrading method and is also applicable to the hydrogenation process of biomass-derived compounds. However, this method has high energy consumption and needs to be carried out under high temperature, high pressure, and hydrogen environments, presenting certain safety hazards. Thermal transfer hydrogenation is an emerging technology that uses the hydrogen protons in hydrogen-rich molecules (such as hydrazine hydrate, formic acid, silane, and ammonia borane) to combine with the unsaturated bonds of organic compounds, avoiding the use risk of high-pressure hydrogen. However, these organic compounds may still pollute surface water, soil, atmosphere, and drinking water. In addition, the overuse of oil as a non-renewable energy source has led to a series of problems such as energy shortage, greenhouse effect, and environmental pollution. Therefore, finding environmentally friendly hydrogen sources and developing new renewable energy sources to gradually replace oil resources has become an urgent task.

[0003] In industrial production, developing an eco-friendly and sustainable process has become the core goal, and water is regarded as an ideal green hydrogen source for realizing hydrogen transfer. However, due to the high thermodynamic energy barrier of water molecules (237 kJ·mol -1) Activating water molecules under mild conditions is extremely challenging. Among numerous renewable resources, solar energy has become the most important energy source on Earth due to its inexhaustible and renewable nature. The progress of photocatalytic water splitting technology has inspired the concept of "green hydrogen," a sustainable chemical energy storage, and opened up a new path to alleviate the energy crisis. Utilizing the active hydrogen intermediate (H*) generated from water splitting for hydrogenation of unsaturated bonds shows great potential. The photocatalytic transfer hydrogenation technology using water as the hydrogen source ingeniously combines photocatalytic water splitting with the hydrogenation process of biomass-derived compounds, enabling the activation of water molecules under mild conditions, avoiding the problems of hydrogen storage and transportation, and generating high-value-added organic compounds in a sustainable manner. Different from thermal catalysis, photocatalytic transfer hydrogenation using water as the hydrogen source can be carried out at room temperature and atmospheric pressure, making it possible to utilize solar energy and biomass resources simultaneously. However, this reaction process is complex and involves multiple steps, and the effects of traditional catalysts are often unsatisfactory. Therefore, the development of efficient and stable photocatalysts has become the key to promoting the development of this technology. Summary of the Invention

[0004] Object of the Invention: The first object of the present invention is to provide a photocatalyst material in which palladium single atoms and palladium nanoparticles coexist. The second object of the present invention is to provide a preparation method of a photocatalyst in which palladium single atoms and palladium nanoparticles coexist. The third object of the present invention is to provide the application of the photocatalyst in which palladium single atoms and palladium nanoparticles coexist in photocatalytic transfer hydrogenation using water as the hydrogen source. This technology can achieve the transfer hydrogenation of biomass-derived compounds under mild conditions of room temperature, atmospheric pressure, and without external hydrogen supply, effectively solving the high-risk and high-energy consumption problems existing in traditional catalytic hydrogenation technology.

[0005] Technical Solution: The present invention relates to a photocatalyst in which palladium single atoms and palladium nanoparticles coexist. The photocatalyst in which palladium single atoms and palladium nanoparticles coexist is obtained by electrostatically adsorbing a palladium chloride metal precursor onto mesoporous carbon nitride through a wet deposition method and then reducing and calcining in a hydrogen-argon atmosphere.

[0006] The preparation method of the photocatalyst in which palladium single atoms and palladium nanoparticles coexist according to the present invention is characterized by comprising the following steps:

[0007] (1) Incorporate melamine into a silica aqueous dispersion, heat and stir until the water is completely evaporated, grind, calcine, add an ammonium bifluoride solution and stir to remove the nano-silica particles, filter, wash, and dry to obtain mesoporous carbon nitride;

[0008] (2) Ultrasonically disperse the mesoporous carbon nitride in water, add the metal precursor palladium chloride, stir and react at room temperature, then heat and stir, centrifuge, wash, and dry, and reduce and calcine in a hydrogen-argon atmosphere to obtain a photocatalyst in which palladium single atoms and palladium nanoparticles coexist (Pd 1+NP -mpg-C 3 N4 )。

[0009] Further, in step (1), the concentration of the silica aqueous dispersion is 30 - 60 wt%, and the optimal concentration is 45 wt%.

[0010] Further, in step (1), the mass - volume ratio of cyanamide to the silica aqueous dispersion is 0.25 - 0.45 g / mL.

[0011] Further, in step (1), the temperature of heating and stirring is 65 - 85 °C.

[0012] Further, in step (1), the calcination conditions are as follows: in an air atmosphere, the heating rate is 2.3 - 2.8 °C / min, calcination is carried out at 480 - 600 °C for more than 4 h, preferably at 2.3 °C / min and 550 °C for 4 h.

[0013] Further, in step (1), the concentration of the ammonium hydrogen fluoride solution is 3.5 - 5 mol / L.

[0014] Further, in step (1), the drying temperature is 75 - 85 °C, and the drying time is 15 - 18 h.

[0015] Further, in step (1), the washing is carried out with deionized water and ethanol, and the ethanol is anhydrous ethanol.

[0016] Further, in step (2), the mass ratio of mesoporous carbon nitride, water and the metal precursor palladium chloride is (0.2 - 0.8):40:(0.012 - 0.018), preferably 0.5:40:0.015.

[0017] Further, in step (2), the normal - temperature stirring time is 12 - 14 h.

[0018] Further, in step (2), the heating and stirring temperature is 55 - 75 °C, and the heating and stirring time is 4 - 7 h.

[0019] Further, in step (2), the drying temperature is 75 - 85 °C, and the drying time is 15 - 18 h.

[0020] Further, in step (2), during calcination, the heating rate is 3 - 6 °C / min, calcination is carried out at 380 - 500 °C for 10 - 30 min, preferably at 5 °C / min and 380 °C for 10 min.

[0021] The application of the photocatalyst co - existing with palladium single atoms and palladium nanoparticles in the present invention in the photocatalytic selective transfer hydrogenation of biomass - derived compounds using water as the hydrogen source.

[0022] Further, the photocatalyst coexisting palladium single atoms and palladium nanoparticles of the present invention, a solvent, a hole sacrificial agent, and a biomass-derived compound are added to a photocatalytic reactor, ultrasonically treated, the reactor is purged with nitrogen, and a hydrogenation reaction is carried out under light irradiation.

[0023] Furthermore, the biomass-derived compound is one or more of chalcone, 2-furan methyl ketone, benzyl acetone, phenylacetaldehyde, 2-methyl-3-phenylpropanal, 4-ethylbenzaldehyde, methyl 3-phenylpropionate, 4-ethylphenyl acetate, 3-phenylpropanamide, phenylpropionitrile, hydrocinnamic acid, ethylbenzene, 4-methylethylbenzene, 1,2-diphenylethane, 4-ethylanisole, 1,4-butanediol, 4-ethylphenol, 4-ethyl-2-methoxyphenol, 3-phenylpropanol.

[0024] Furthermore, the solvent is a mixed solvent of water and 1,4-dioxane.

[0025] Furthermore, the volume ratio of water to 1,4-dioxane is (1 - 4):(1 - 4), preferably 2:3.

[0026] Furthermore, the hole sacrificial agent is triethylamine.

[0027] Furthermore, the solid-liquid ratio of the photocatalyst coexisting palladium single atoms and palladium nanoparticles, the solvent, the hole sacrificial agent, and the biomass-derived compound of the present invention is (5 - 15):5:0.4:(0.05 - 0.5) mg / mL / mL / mmol, preferably 10:5:0.4:0.1 mg / mL / mL / mmol.

[0028] Furthermore, the ultrasonic treatment is carried out for more than 3 min.

[0029] Furthermore, the light irradiation conditions are: a blue LED lamp, a wavelength of 390 - 450 nm, preferably 427 nm, and an output power of 40 W or more.

[0030] Furthermore, the hydrogenation reaction time is 4 h or more.

[0031] In the present invention, a palladium chloride metal precursor is electrostatically adsorbed onto mesoporous carbon nitride by a wet deposition method, and then a part of the palladium species is reduced under a hydrogen-argon atmosphere to obtain a photocatalyst coexisting palladium single atoms and palladium nanoparticles supported on mesoporous carbon nitride. The photocatalyst coexisting palladium single atoms and palladium nanoparticles of the present invention promotes the selective transfer hydrogenation of biomass-derived compounds using water as a hydrogen source, and has the characteristics of stable structure and excellent catalytic performance.

[0032] Advantageous effects: Compared with the prior art, the present invention has the following remarkable advantages:

[0033] (1) The preparation method of the catalyst coexisting palladium single atoms and palladium nanoparticles proposed by the present invention can precisely regulate the catalytic active sites, significantly improve the utilization efficiency of metal atoms and catalytic stability, and at the same time, the preparation process is simple and easy to operate.

[0034] (2) The present invention successfully prepares a photocatalyst coexisting palladium single atoms and palladium nanoparticles by wet deposition method and reduction method, and constructs a unique structure with active sites of both palladium single atoms and palladium nanoparticles. This structure enhances the synergistic effect between metal atoms and provides favorable conditions for complex reactions such as transfer hydrogenation.

[0035] (3) The catalyst coexisting palladium single atoms and palladium nanoparticles developed by the present invention exhibits excellent performance in the transfer hydrogenation reaction of catalytic biomass-derived compound chalcone. The yield of 4-ethylphenol can exceed 95%, and the selectivity is as high as over 99%. In addition, the catalyst shows excellent cyclic stability, and the activity does not decrease significantly in 5 consecutive reactions, which is suitable for industrial large-scale production and has important practical application prospects. Brief Description of the Drawings

[0036] Figure 1 STEM image of mpg-C 3 N 4 prepared in Example 1;

[0037] Figure 2 AC-HAADF-STEM image of the Pd 1+NP -mpg-C 3 N 4 catalyst prepared in Example 2;

[0038] Figure 3 AC-HAADF-STEM image of the Pd 1+NP -mpg-C 3 N 4 -1 catalyst prepared in Example 3;

[0039] Figure 4 AC-HAADF-STEM image of the Pd 1+NP -mpg-C 3 N 4 -2 catalyst prepared in Example 4;

[0040] Figure 5 AC-HAADF-STEM image of the Pd 1 -mpg-C 3 N 4 catalyst prepared in Comparative Example 1;

[0041] Figure 6 AC-HAADF-STEM image of the Pd NP-mpg-C 3 N 4 XPS spectrum of

[0042] Figure 7 Pd prepared in Comparative Example 3 1 -mpg-C 3 N 4 XRD pattern of the -1 catalyst

[0043] Figure 8 Photocatalytic performance graphs of various different catalysts in Example 5

[0044] Figure 9 Pd in Example 5 1+NP -mpg-C 3 N 4 Photocatalyst cyclic stability test graph

[0045] Figure 10 Substrate expansion performance graph in Example 6 Detailed implementation mode

[0046] The technical solution of the present invention will be further described below in conjunction with the accompanying drawings.

[0047] Example 1

[0048] 5 g of cyanamide was uniformly dispersed in 12.5 mL of silica aqueous dispersion (Sigma-Aldrich, HS-40, concentration 40 wt%), and stirred continuously at 60 °C until the water was completely evaporated. The resulting solid was ground into a powder, placed in an air atmosphere, heated to 550 °C at a heating rate of 2.3 °C / min and calcined for 4 hours. Subsequently, the calcined product was added to 150 mL of 4 mol / L ammonium bifluoride solution and stirred for 48 hours to remove the nano-silica particles. After filtration, it was washed repeatedly with deionized water and degassed ethanol, and finally dried in an oven at 80 °C for 15 - 18 hours to obtain mpg-C 3 N 4 .

[0049] Figure 1 The scanning transmission electron microscope (STEM) image of the mpg-C 3 N 4 prepared in this example, from which Figure 1 it can be seen that the mpg-C 3 N 4 sample has a rich porous structure.

[0050] Example 2

[0051] 0.5 g of the mpg-C 3 N4 Dispersed in 40 mL of deionized water, ultrasonic treatment was carried out for 1 hour, and then 15 mg of palladium chloride was added to form a suspension. The suspension was stirred for 13 hours, and then heated and stirred at 60 °C for 5 hours. After centrifugation, it was thoroughly washed with deionized water and degassed ethanol, and dried in an oven at 80 °C for 16 hours. Finally, under a hydrogen-argon mixed atmosphere (hydrogen volume fraction 10%), it was heated to 380 °C at a heating rate of 5 °C / min and calcined for 10 min to obtain Pd 1+NP -mpg-C 3 N 4 。

[0052] Figure 2 The Pd 1+NP -mpg-C 3 N 4 Spherical aberration corrected transmission electron microscopy high angle annular dark field (AC-HAADF-STEM) image of Figure 2 From which it can be observed that there are a large number of single palladium atoms around the palladium nanoparticles in Pd 1+NP -mpg-C 3 N 4 This result indicates the successful preparation of the Pd 1+NP -mpg-C 3 N 4 catalyst.

[0053] Example 3

[0054] Disperse 0.5 g of mpg-C 3 N 4 prepared in Example 1 in 40 mL of deionized water, ultrasonic treatment was carried out for 1 hour, and then 15 mg of palladium chloride was added to form a suspension. The suspension was stirred for 13 hours, and then heated and stirred at 60 °C for 5 hours. After centrifugation, it was thoroughly washed with deionized water and degassed ethanol, and dried in an oven at 80 °C for 16 hours. Finally, under a hydrogen-argon mixed atmosphere (hydrogen volume fraction 10%), it was heated to 450 °C at a heating rate of 5 °C / min and calcined for 10 min to obtain Pd 1+NP -mpg-C 3 N 4 -1.

[0055] Figure 3 The Pd 1+NP -mpg-C 3 N 4 AC-HAADF-STEM image of Figure 3 From which it can be observed that there are a large number of single palladium atoms around the palladium nanoparticles in Pd 1+NP -mpg-C 3 N 4 This result indicates that Pd1+NP -mpg-C 3 N 4 Successful preparation of the -1 catalyst.

[0056] Example 4

[0057] Disperse 0.5 g of mpg-C prepared in Example 1 3 N 4 in 40 mL of deionized water, sonicate for 1 hour, then add 15 mg of palladium chloride to form a suspension. Stir the suspension for 13 hours, then heat and stir at 60 °C for 5 hours. After centrifugation, wash thoroughly with deionized water and degassed ethanol, and dry in an oven at 80 °C for 16 hours. Finally, heat to 500 °C at a heating rate of 5 °C / min in a hydrogen-argon mixed atmosphere (hydrogen volume fraction 10%) and calcine for 10 min to obtain Pd 1+NP -mpg-C 3 N 4 -2.

[0058] Figure 4 For the Pd 1+NP -mpg-C 3 N 4 -2 prepared in this example, as can be observed from Figure 4 there are a large number of palladium single atoms around the palladium nanoparticles in Pd 1+NP -mpg-C 3 N 4 -2. This result indicates the successful preparation of the Pd 1+NP -mpg-C 3 N 4 -2 catalyst.

[0059] Comparative Example 1

[0060] The experimental procedure was the same as in Example 2, except for the different atmosphere conditions. Calcination was carried out at 380 °C for 10 min. Specifically: Disperse 0.5 g of mpg-C prepared in Example 1 3 N 4 in 40 mL of deionized water, sonicate for 1 hour, then add 15 mg of palladium chloride to form a suspension (to ensure that the loading amount is the same as that of Pd 1+NP -mpg-C 3 N 4 in Example 2). Stir the suspension for 13 hours, then heat and stir at 60 °C for 5 hours. After centrifugation, wash thoroughly with deionized water and degassed ethanol, and dry in an oven at 80 °C for 16 hours. Finally, heat to 380 °C at a heating rate of 5 °C / min in a nitrogen atmosphere and calcine for 10 min to obtain Pd 1 -mpg-C 3N 4 。

[0061] Figure 5 is Pd 1 -mpg-C 3 N 4 The AC-HAADF-STEM image of Figure 5 clearly shows that a large number of palladium single atoms are distributed on Pd 1 -mpg-C 3 N 4 and no nanoparticles are observed, confirming that Pd 1 -mpg-C 3 N 4 has been successfully prepared.

[0062] Comparative Example 2

[0063] Dissolve 15 mg of palladium chloride in 10 mL of deionized water, and then gradually add 12 mL of freshly prepared aqueous solution containing 30 mg of sodium borohydride dropwise to the above solution, and continuously stir for 48 hours. Then, add 0.5 g of mpg-C 3 N 4 prepared in Example 1 to this solution. After ultrasonic treatment for 1 hour, stir for 24 hours. Finally, centrifuge and wash thoroughly with deionized water and degassed ethanol, and dry in an oven at 80 °C for 16 hours to obtain Pd NP -mpg-C 3 N 4 。

[0064] Figure 6 is the X-ray photoelectron spectroscopy (XPS) pattern of Pd NP -mpg-C 3 N 4 It is found that only the signal of zero-valent palladium exists, indicating that only palladium nanoparticles are present, proving the successful preparation of Pd NP -mpg-C 3 N 4 。

[0065] Comparative Example 3

[0066] The experimental procedure is the same as that of Example 2, except that the final calcination temperature condition is different. Calcinate at 200 °C in a hydrogen-argon atmosphere for 10 min to obtain Pd 1 -mpg-C 3 N 4 -1.

[0067] Figure 7 is the X-ray diffraction pattern (XRD) of Pd 1 -mpg-C 3 N 4 -1. FromFigure 7 No diffraction peak of palladium nanoparticles was observed, indicating that Pd 1 -mpg-C 3 N 4 -1 does not contain palladium nanoparticles.

[0068] Example 5

[0069] The catalysts prepared in Examples 1-4 and Comparative Examples 1-3 were respectively used for the selective transfer hydrogenation of chalcone, a biomass-derived compound.

[0070] The selective transfer hydrogenation reaction of chalcone was carried out in a 12 mL Schlenk reaction tube. The specific operation is as follows: Add 10 mg of photocatalyst, 2 mL of ultrapure water, 3 mL of 1,4-dioxane, 0.4 mL of triethylamine, and 0.1 mmol of chalcone to the reaction tube and sonicate for 3 minutes. Subsequently, purge the reactor with nitrogen to form an inert atmosphere, and then irradiate the reactor with a 40 W blue LED lamp (wavelength 427 nm) for 4 hours. After the reaction, analyze the liquid product using GC-MS (model Shimadzu QP2020NX), with acetophenone as the internal standard.

[0071] In addition, Figure 8 shows a performance comparison of the catalysts prepared in Examples 1-4 and Comparative Examples 1-3. As Figure 8 can be seen, mpg-C 3 N 4 itself has no catalytic activity, indicating that palladium species play a key role in the reaction. The Pd 1+NP -mpg-C 3 N 4 prepared in Example 2 exhibits excellent catalytic performance, with a yield of 95% and a selectivity of 99%, far higher than the Pd 1 -mpg-C 3 N 4 prepared in Comparative Example 1, Comparative Example 2, and Comparative Example 3, NP -mpg-C 3 N 4 and Pd 1 -mpg-C 3 N 4 -1, which proves the high catalytic activity of Pd 1+NP -mpg-C 3 N 4 and the importance of the synergy between single atoms and palladium nanoparticles. Compared with Examples 3 and 4, the Pd 1+NP -mpg-C 3 N 4 catalyst prepared under the conditions of Example 2 exhibits the best catalytic activity. In addition, the catalyst after the reaction was recovered by centrifugation and reused.Figure 9 shows Pd 1+NP -mpg-C 3 N 4 The change in activity during five cycles shows that the catalyst has excellent stability and no obvious deactivation occurs.

[0072] Example 6

[0073] This example demonstrates a Pd 1+NP -mpg-C 3 N 4 application scheme in the substrate expansion reaction. The specific operation is as follows: Add 10 mg of Pd prepared in Example 2 1+NP -mpg-C 3 N 4 , 2 mL of ultrapure water, 3 mL of 1,4-dioxane, 0.4 mL of triethylamine, and 0.1 mmol of an organic compound containing an unsaturated bond (specific substrates are shown in Table 1) into a reaction tube and sonicate for 5 minutes. Then purge the reactor with nitrogen to form an inert atmosphere, and then irradiate the reactor with a 40 W blue LED lamp (wavelength 427 nm) for 5 hours. After the reaction is completed, analyze the liquid product using GC-MS (model Shimadzu QP2020NX) with acetophenone as the internal standard.

[0074] Table 1 Product Expansion Types

[0075]

[0076]

[0077] Figure 10 shows the results of Pd 1+NP -mpg-C 3 N 4 in the substrate expansion reaction. As can be seen from Figure 10 , for organic compounds containing different functional groups, Pd 1+NP -mpg-C 3 N 4 all exhibit excellent hydrogenation reaction performance.

[0078] The above are the preferred examples of the present invention, but the implementation manners of the present invention are not limited to the above examples. Therefore, all equivalent, modified, substituted, combined, and simplified implementations completed without departing from the spirit disclosed by the present invention are included within the protection scope of the present invention.

Claims

1. A palladium single atom and palladium nanoparticle coexistence catalyst, preparation method and application, characterized in that: The palladium single atom and palladium nanoparticle coexistence photocatalyst comprises electrostatically adsorbing a palladium chloride metal precursor onto mesoporous carbon nitride by a wet deposition method, and reducing and calcining the catalyst in a hydrogen-argon mixed atmosphere.

2. The method for preparing the palladium single atom and palladium nanoparticle coexistence photocatalyst according to claim 1, characterized in that: The steps include: (1) adding cyanamide to a silica aqueous dispersion, heating and stirring until the water is completely evaporated, grinding, calcining, adding ammonium bifluoride solution and stirring, filtering, washing, and drying to obtain mesoporous carbon nitride; (2) The mesoporous carbon nitride is dispersed in water by ultrasonication, and a metal precursor palladium chloride is added. The mixture is stirred and reacted at room temperature, and then heated and stirred, washed by centrifugation, dried, and reduced and calcined in a hydrogen and argon atmosphere to obtain a photocatalyst in which palladium single atoms and palladium nanoparticles coexist.

3. The method for preparing the coexistence photocatalyst of palladium single atoms and palladium nanoparticles according to claim 2, characterized in that: In step (1), the concentration of the silicon dioxide aqueous dispersion is 30-60wt%, and the mass volume ratio of cyanamide to the silicon dioxide aqueous dispersion is 0.25-0.45g / mL.

4. The method for preparing the coexistence photocatalyst of palladium single atoms and palladium nanoparticles according to claim 2, characterized in that: In step (1), the heating and stirring temperature is 65-85°C, the calcination conditions are: air atmosphere, the heating rate is 2.3-2.8°C / min, calcination at 480-600°C for more than 4h, the drying temperature is 75-85°C, and the drying time is 15-18h.

5. The method for preparing the coexistence photocatalyst of palladium single atoms and palladium nanoparticles according to claim 2, characterized in that: In step (2), the mass ratio of mesoporous carbon nitride, water and metal precursor palladium chloride is (0.2-0.8):40:(0.012-0.018).

6. The method for preparing the coexistence photocatalyst of palladium single atoms and palladium nanoparticles according to claim 2, characterized in that: In step (2), the stirring time at room temperature is 12-14 hours, the temperature of heating and stirring is 55-75°C, and the heating and stirring time is 4-7 hours.

7. The method for preparing the coexistence photocatalyst of palladium single atoms and palladium nanoparticles according to claim 2, characterized in that: In step (2), the drying temperature is 75-85°C, the drying time is 15-18h, and during calcination, the heating rate is 3-6°C / min, and the calcination is performed at 380-500°C for 10-30min.

8. Use of the palladium single atom and palladium nanoparticle coexistence photocatalyst as claimed in claim 1 in photocatalytic selective transfer hydrogenation of biomass-derived compounds using water as the hydrogen source.

9. The use according to claim 8, characterized in that: The palladium single atom and palladium nanoparticle coexisting photocatalyst, solvent, hole sacrificial agent, and biomass-derived compound as described in claim 1 are added into a photocatalytic reactor, ultrasonically treated, the reactor is purged with nitrogen, and a hydrogenation reaction is carried out under light.

10. The use according to claim 9, characterized in that: The solvent is a mixed solvent of water and 1,4-dioxane, the volume ratio of water to 1,4-dioxane is (1-4): (1-4), the hole sacrificial agent is triethylamine, the solid-liquid ratio of the palladium single atom and palladium nanoparticle coexisting photocatalyst according to claim 1, the solvent, the hole sacrificial agent, and the biomass-derived compound is (5-15): 5: 0.4: (0.05-0.5) mg / mL / mL / mmol; the ultrasonic treatment is for more than 3 minutes, the illumination conditions are: wavelength 390-450nm, output power above 40W, and the hydrogenation reaction time is more than 4 hours.

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