Metal cluster containing multilayer ligand spherical shell, preparation method of metal cluster, high-dispersion metal catalyst, preparation method of high-dispersion metal catalyst and application of high-dispersion metal catalyst

Abstract

The invention provides a metal cluster containing a multilayer ligand spherical shell, a preparation method of the metal cluster, a high-dispersion metal catalyst and a preparation method and application of the high-dispersion metal catalyst. The preparation method of the metal cluster comprises the following steps: dissolving a metal compound in a mixed solution containing water, alcohols and a ligand, and mixing to obtain a metal precursor solution; sequentially adding a solvent, a protective agent and a reducing agent into the metal precursor solution, mixing, concentrating, stirring, and supplementing the solvent; and repeating the operations of concentrating, stirring and supplementing the solvent to obtain the metal cluster containing the multilayer ligand spherical shell. According to the high-dispersion metal catalyst provided by the invention, the protective agent and the reducing agent are added into the metal precursor solution, so that a metal cluster solution which is larger in molecular size and contains multilayer ligand spherical shell protection is formed, steric hindrance exists among metal clusters, and the resistance of the clusters in the aggregation process is increased; therefore, the effect of controlling the metal dispersity is achieved, and the problems that an existing metal cluster is low in stability and difficult to use are solved.

Description

Technical Field

[0001] This invention belongs to the field of molecular sieve catalysis, specifically relating to a metal cluster containing multilayer ligand shells and its preparation method, a highly dispersed metal catalyst and its preparation method and application. Background Technology

[0002] Benzaldehyde is an important intermediate in industrial production and is widely used in food, pharmaceuticals, and pesticides. Industrially, benzaldehyde is mostly produced via the hydrolysis of benzyl chloride; however, this method is difficult to treat as wastewater, causes severe equipment corrosion, and produces a chlorine-containing product, making it unsuitable for the food and pharmaceutical industries. Although some effective homogeneous catalysts have been developed for the oxidation of benzyl alcohol, they cannot simultaneously meet the requirements for activity and selectivity. For heterogeneous catalysts, high catalytic activity and stability come with high preparation costs, while inexpensive and readily available catalysts tend to deactivate after prolonged use. Therefore, there is a need to develop green, efficient, and low-cost catalysts for the catalytic oxidation of benzyl alcohol to benzaldehyde. The active metal is typically a noble metal such as Pt or Pd, which activates and dehydrogenates benzyl alcohol. The degree of metal dispersion determines the number of effective metal sites, the metal loading, and the metal hydrogenation performance, thus influencing catalyst performance and production costs.

[0003] The latest generation of active metal phases is metal clusters. Due to their unique electronic structure and unusual physical and chemical properties, ultra-small metal nanoclusters with precise atomic arrangements have broad application prospects in many fields such as catalysis, chemical sensing, electronics, biolabeling, and biomedicine. Currently, progress has been made in the synthesis, separation, purification, characterization, and application research of metal nanoclusters. CN114082417A describes a method of preparing a noble metal precursor into an aqueous solution, adding a ligand compound, and heating and stirring to obtain a ligand-modified platinum and / or palladium impregnation solution. Using cordierite honeycomb ceramics as a support, a composite oxide containing elements such as cerium, zirconium, aluminum, and titanium is modified and prepared into a slurry, which is then coated onto the surface of the honeycomb support. The oxide honeycomb support is immersed in the above impregnation solution for 1-10 minutes, followed by purging, drying, and calcination to obtain a supported noble metal honeycomb catalyst. However, the method of immersing the support in the impregnation solution for 1-10 minutes has limited effect on improving the dispersion of the noble metal.

[0004] CN113694962A first uses a ball mill to ball mill two different types of molecular sieves, then adds oxides or metal salts containing Group VIII B metal elements and ball mills them again, finally kneading, extruding, drying, and calcining to produce the isomeric dewaxing catalyst. However, ball milling may cause the molecular sieve channels to collapse, and ball milling does not improve the metal dispersion.

[0005] CN111215053A describes a process where a noble metal precursor, consisting of chlorides, nitrates, or organic complexes of a noble metal, is dissolved in deionized water and / or an organic solvent, then impregnated onto a support and dried to obtain a supported noble metal catalyst precursor. This precursor is then reduced in an H2 atmosphere to obtain a supported nano- or sub-nano-scale noble metal catalyst. The resulting supported nano- or sub-nano-scale noble metal catalyst is then treated in one or more of the following atmospheres—CO, NO, NO2, NH3, CH3I, CH3Br, CH3Cl, C2H5I, C2H5Br, and C2H5Cl—at 150℃-400℃ for 1-600 min to obtain a supported single-atom dispersed noble metal catalyst. However, the atmosphere used in this catalyst preparation process is complex, making industrial scale-up difficult.

[0006] CN112915997A places a precious metal precursor in a quartz reaction tube of a tube furnace and heats it to more than half of the precious metal's melting point, causing the precious metal to reach a surface molten state. A carbon-containing gas is then introduced, causing it to pyrolyze and produce carbon and hydrogen. The molten atoms on the precious metal surface freely diffuse and migrate to the unsaturated sites of the newly formed carbon, forming a stable, carbon-supported, highly dispersed precious metal catalyst. However, this method for preparing highly dispersed precious metal catalysts involves a high reaction temperature, and introducing carbon-containing gases such as methane at high temperatures is dangerous.

[0007] CN113101969A describes a process where molecular sieves are mixed with a water-soluble metal salt solution in a reactor. Unreacted metal salts are removed by filtration or centrifugation to obtain a solid filter block, which is then calcined to obtain a molecular sieve-supported single-atom catalyst. However, directly reacting the metal solution with the molecular sieve can easily lead to metal ions or alcohol-based molecular sieves entering the sieve channels, causing blockage.

[0008] CN109126774B involves dissolving a metal precursor in water or ethanol, impregnating the resulting solution onto a support, and then evaporating, drying, and calcining to obtain a granular and / or powdered catalyst. The catalyst is first heated to a treatment temperature, then treated with a mixture of CO and haloalkane gases, and finally cooled to room temperature to obtain a supported single-atom noble metal catalyst. However, the atmospheric process used in the preparation of this catalyst is complex, and the CO and haloalkane gases pose certain hazards at high temperatures, making industrial production challenging.

[0009] CN111135840B describes a method where a noble metal precursor is dissolved in deionized water or a common organic solvent, and then appropriate amounts of common inorganic and organic reagents containing phosphorus (P) and sulfur (S) are added to obtain a noble metal precursor complex solution. A certain amount of support is impregnated in the noble metal precursor complex solution, stirred, filtered, and dried to obtain a noble metal catalyst precursor. A certain amount of the above catalyst precursor is then placed in an atmosphere of He, Ar, N2, H2, O2, or air and treated at 200℃-800℃ for 10-600 seconds to obtain a supported single-atom dispersed noble metal catalyst. However, the inorganic and organic reagents containing P and S added in this method do not burn completely in He, Ar, N2, or H2 atmospheres, and the residual P and S elements can easily poison and deactivate the catalyst.

[0010] As can be seen from the above-mentioned existing technologies, the current preparation process of highly dispersed metal catalysts has the following problems: incomplete removal of introduced elements such as P and S can easily reduce catalyst activity; the metal precursor is prepared at a high temperature in a molten state; complex atmospheres are used during catalyst calcination to prevent metal aggregation, which is dangerous; and operations such as ball milling and impregnation have limited effect on improving metal dispersion.

[0011] Therefore, how to configure a suitable metal precursor solution and reduce the introduction of impurity elements; how to design a suitable impregnation and dispersion process to ensure that the metal precursor is fully dispersed on the catalyst surface; and how to prevent metal aggregation through a simple and easy-to-operate calcination process are the current research priorities for improving metal dispersion and catalyst metal utilization. Summary of the Invention

[0012] To address the aforementioned technical problems, the present invention aims to provide a metal cluster containing a multilayered ligand spherical shell and a method for preparing the same.

[0013] The present invention also aims to provide a highly dispersed metal catalyst, its preparation method, and its application. By using metal clusters with multilayered ligand shells as the active component of the catalyst, the prepared catalyst can have better metal dispersion, thereby exhibiting better catalytic performance in the catalytic oxidation of benzyl alcohol.

[0014] To achieve the above objectives, the present invention provides a method for preparing metal clusters containing multilayered ligand shells, wherein the preparation method includes:

[0015] (1) Dissolve the metal compound in a mixture containing water, alcohol and ligand to obtain a metal precursor solution;

[0016] (2) Solvent, protective agent and reducing agent are added to the metal precursor solution in sequence and mixed. After concentration and stirring, solvent is added again. The concentration, stirring and solvent addition are repeated to obtain metal clusters containing multilayer ligand shells.

[0017] Wherein, the molar ratio of the ligand to the metal compound is (6-18):1, and the molar ratio of the metal compound is based on metal atoms;

[0018] The molar ratio of the metal compound to the protective agent is 1:10 to 1:100, based on the amount of substance.

[0019] The ratio of electrons lost by the metal to electrons gained by the reducing agent in the metal compound is 1:1 to 1:10, based on the number of electrons provided.

[0020] According to a specific embodiment of the present invention, preferably, the ligand comprises one or more of sorbic acid, salicylic acid, nicotinamide, and lactic acid; more preferably, it is sorbic acid. The ligand is used to dissolve and stabilize the precursor, contributing to the formation of a stable precursor solution.

[0021] According to a specific embodiment of the present invention, preferably, the metal compound includes one or a combination of two or more salts of platinum, palladium, and nickel.

[0022] According to a specific embodiment of the present invention, preferably, the metal compound includes one or more of chloroplatinic acid, tetraammineplatinum nitrate, platinum nitrate, palladium nitrate, palladium chloride, nickel chloride, and nickel nitrate; more preferably, it is chloroplatinic acid.

[0023] According to a specific embodiment of the present invention, preferably, the protective agent comprises one or a combination of two or more of the following: bis(hexadecyl)dimethylammonium halide, bis(tetradecyl)dimethylammonium halide, bis(dodecyl)dimethylammonium halide, bis(decyl)dimethylammonium halide, hexadecyltrimethylammonium halide, tetradecyltrimethylammonium halide, dodecyltrimethylammonium halide, and decadecyltrimethylammonium halide; wherein the halogen element comprises any one of bromine, iodine, and chlorine; more preferably, the protective agent comprises one or a combination of two or more of the following: bis(hexadecyl)dimethylammonium bromide, bis(tetradecyl)dimethylammonium bromide, bis(dodecyl)dimethylammonium bromide, bis(hexadecyl)dimethylammonium chloride, bis(tetradecyl)dimethylammonium chloride, and dodecyl)dimethylammonium chloride.

[0024] Unlike existing technologies, the protective agent in this invention does not undergo complete hydrolysis. Only a portion of the protective agent generates individual positive and negative ions, while the remaining protective agents maintain a tightly bound state of positive and negative ions. The bound positive and negative ion pairs are further concentrated by rotary evaporation to form a multilayered ligand shell morphology to protect the metal core. This multilayered ligand shell can serve as a second ligand. By studying the controllable loading and stacking of the second ligand (protective agent) on the metal surface, the stability of the metal cluster is improved. At the same time, the presence of the multilayered ligand shell improves the dispersion of the metal components, which is helpful for obtaining highly dispersed metal catalysts in the future.

[0025] According to a specific embodiment of the present invention, preferably, the reducing agent includes one or a combination of two or more of hydrazine hydrate, sodium borohydride, ascorbic acid, and potassium borohydride.

[0026] According to a specific embodiment of the present invention, preferably, the solvent includes one or a combination of two or more of water, acetonitrile, ethanol, propanol, isopropanol, and butanol.

[0027] In some specific embodiments, preferably, the molar ratio of the ligand to the metal compound is 12:1.

[0028] In some specific embodiments, preferably, the molar ratio of the metal compound to the protective agent is 1:15 to 1:95, more preferably 1:30 to 1:75, and even more preferably 1:40 to 1:60.

[0029] In some specific embodiments, preferably, the ratio of the number of electrons lost by the metal to the number of electrons gained by the reducing agent in the metal compound is 1:2 to 1:9.

[0030] In some specific embodiments, preferably, the alcohol includes one or more of ethanol, propanol, isopropanol, and glycerol; more preferably, it is ethanol.

[0031] In some specific implementations, preferably, in step (1), the mass ratio of water to alcohol is (1-20):1; more preferably, the mass ratio of water to alcohol is (5-20):1, and even more preferably 10:1.

[0032] In some specific embodiments, preferably, the mass ratio of the sum of the masses of the water and alcohol to the mass ratio of the metal compound is (70-290):1.

[0033] In some specific implementations, preferably, in step (1), the mixing conditions are mixing at 30-60°C for 2-6 hours.

[0034] In some specific implementations, preferably, in step (2), the concentration process is to concentrate the reaction solution to 10%-50% of its original volume, more preferably 20%-40%; this process can be carried out using a rotary evaporator.

[0035] In some specific implementations, preferably, in step (2), the stirring conditions are stirring at a speed of 100-500 rpm for 6-24 hours; more preferably, the stirring conditions are stirring at a speed of 150-450 rpm for 8-20 hours.

[0036] In some specific embodiments, preferably, in step (2), the amount of solvent added is 80%-100% of the original volume, more preferably 100%.

[0037] In some specific implementations, preferably, in step (2), the operations of concentration, stirring and adding solvent are repeated 1-10 times, more preferably 2-8 times.

[0038] The present invention also provides a metal cluster containing a multilayered ligand shell, which is prepared by the above-described preparation method.

[0039] According to a specific embodiment of the present invention, preferably, the metal cluster is an atomically precise cluster with multiple layers of ligand shells protecting its surface; the number of ligand shell layers is two or more, and the diameter of the ligand shells is 5 nm or more, giving the metal cluster ultra-high stability. The diameter refers to the overall diameter of the multiple layers of ligand shells, and the atomically precise cluster refers to a macromolecule with precise molecular weight and arrangement, completely uniform size, and possessing a metal core and surface ligands (i.e., second ligands: bound positive and negative ion pairs).

[0040] The present invention also provides a highly dispersed metal catalyst, wherein the highly dispersed metal catalyst comprises support particles and the aforementioned metal clusters containing multilayer ligand shells, the metal clusters being loaded on the support particles; wherein, based on 100% of the mass of the support particles, the amount of metal clusters added is 0.1wt%-0.6wt% (preferably 0.2wt%-0.4wt%), and the mass of the metal clusters is based on the mass of metal atoms; the metal clusters containing multilayer ligand shells can serve as the active component in the highly dispersed metal catalyst.

[0041] According to a specific embodiment of the present invention, preferably, the raw materials of the carrier particles include molecular sieves, alumina, acid solution, binder, and deionized water; wherein, the mass ratio of the molecular sieve to alumina, acid solution, binder, and deionized water is 1:(0.2-0.6):(0.3-0.6):(0.01-0.1):(0.3-1); more preferably, the mass ratio of the molecular sieve to alumina, acid solution, binder, and deionized water is 1:(0.3-0.5):(0.4-0.5):(0.05-0.1):(0.5-0.8). The acid solution is prepared by adding deionized water to concentrated acid; for example, a nitric acid solution is obtained by diluting 65% concentrated nitric acid with an appropriate amount of deionized water. The mass of the acid solution is calculated based on the total mass of the acid solution, including the deionized water used for dilution. The mass of the deionized water is calculated based on the sum of the mass of the deionized water used to dilute the acid solution and the mass of any additional deionized water added separately.

[0042] In some specific embodiments, preferably, the carrier particles are prepared by uniformly mixing molecular sieves with alumina, acid solution, binder, and deionized water, followed by kneading and extrusion molding.

[0043] In some specific embodiments, preferably, the molecular sieve includes one or more of SAPO-11 molecular sieve, SAPO-31 molecular sieve, ZSM-12 molecular sieve, ZSM-22 molecular sieve, ZSM-23 molecular sieve, and ZSM-48 molecular sieve; more preferably, it is ZSM-48 molecular sieve.

[0044] In some specific embodiments, preferably, the acid solution is a nitric acid solution and / or a phosphoric acid solution, the concentration of which is 5wt%-10wt%, and the concentration of which is adjusted by dilution with deionized water; more preferably, the acid solution is a nitric acid solution, the concentration of which is 8wt%-10wt%.

[0045] In some specific embodiments, preferably, the adhesive is one or a combination of two or more of guar gum powder, titanium dioxide, and methylcellulose; more preferably, the adhesive is a combination of guar gum powder and titanium dioxide, with a mass ratio of guar gum powder: titanium dioxide = (10-30):1, or the adhesive is a combination of methylcellulose and titanium dioxide, with a mass ratio of methylcellulose: titanium dioxide = (10-30):1; even more preferably, the adhesive is a combination of guar gum powder and titanium dioxide, with a mass ratio of guar gum powder: titanium dioxide = 20:1.

[0046] In some specific embodiments, the alumina may be conventional alumina, such as boehmite.

[0047] According to a specific embodiment of the present invention, preferably, the metal dispersion in the highly dispersed metal catalyst is 90% to 100%; the size of the metal core of the atomically precise clusters is less than 1.0 nm, indicating a highly dispersed state. According to the catalyst industry reference book *A New Compilation of Modern Catalysis Research Methods* (by Xin Qin, 2018), for metal particles on the surface of supported catalysts, the particle size d (in nm) and its dispersion D can be converted using the formula d ≈ 0.9 / D. For example, the dispersion of atomically precise clusters with a size less than or equal to 0.9 nm is 100%.

[0048] The present invention also provides a method for preparing the above-mentioned highly dispersed metal catalyst, wherein the preparation method includes: immersing support particles in a solution containing the metal clusters with multiple ligand shells, followed by ultrasonic vibration, drying, and calcination to obtain the highly dispersed metal catalyst.

[0049] According to a specific embodiment of the present invention, preferably, the calcination conditions are calcination at 450-600°C in air for 4-6 hours; more preferably, the calcination conditions are calcination at 500-550°C in air for 4-6 hours; and even more preferably, calcination at 550°C for 6 hours.

[0050] In some specific implementations, preferably, the ultrasonic oscillation is performed at 30-60°C for 2-6 hours; more preferably, the ultrasonic oscillation is performed at 50°C for 4 hours.

[0051] In some specific embodiments, preferably, the drying conditions are drying at 100-120°C for 2-4 hours; more preferably, the drying conditions are drying at 120°C for 2 hours.

[0052] This invention also provides the application of the above-mentioned highly dispersed metal catalyst in the catalytic oxidation reaction of benzyl alcohol.

[0053] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0054] (1) The highly dispersed metal catalyst provided by the present invention can be directly prepared by impregnating the support particles in a solution of metal clusters protected by a multilayer ligand spherical shell. The impregnation is carried out by ultrasonic vibration, which enables the metal clusters to be uniformly dispersed on the surface of the support particles, further preventing excessive aggregation of metal clusters during drying and calcination, thereby improving the dispersion of the metal.

[0055] (2) The highly dispersed metal catalyst provided by the present invention forms a metal cluster solution with larger molecular size and multiple ligand shell protection by adding a protective agent and a reducing agent to the metal precursor solution. This causes steric hindrance between the metal clusters, increases the resistance of the clusters in the aggregation process, thereby achieving the effect of controlling the metal dispersion, solving the problems of low stability and difficulty in utilization of metal clusters, and realizing the technical route of multi-layer ligand shell protection and soft landing of metal clusters.

[0056] (3) The highly dispersed metal catalyst provided by the present invention can be applied to the catalytic oxidation reaction of benzyl alcohol. In this reaction, atomically precise clusters containing multilayer ligand shells are used as the active component of the catalyst, which can achieve a better catalytic effect, so that the conversion rate of benzyl alcohol and the selectivity of benzaldehyde can be maintained at a high level for a long time, and it has extremely high practicality. Attached Figure Description

[0057] Figure 1 The MALDI-Tof MS mass spectrometry results for the highly dispersed metal catalyst in Example 1 are shown in the top panel, and the MALDI-Tof MS mass spectrometry results after 40 hours of use in the catalytic oxidation of benzyl alcohol are shown in the bottom panel.

[0058] Figure 2 This is a TEM image of the highly dispersed metal catalyst prepared in Example 1.

[0059] Figure 3Dark-field scanning transmission electron microscopy image of the highly dispersed metal catalyst prepared in Example 1.

[0060] Figure 4 STEM image of the metal catalyst prepared in Comparative Example 1.

[0061] Figure 5 STEM image of the metal catalyst prepared in Comparative Example 2.

[0062] Figure 6 The results show the benzyl alcohol conversion rate and benzaldehyde selectivity obtained by using the metal catalysts prepared in Example 1 and Comparative Example 1 for the catalytic oxidation of benzyl alcohol. Detailed Implementation

[0063] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0064] Example 1:

[0065] This embodiment provides a method for preparing metal clusters containing multilayered ligand shells and highly dispersed metal catalysts, specifically including the following steps:

[0066] (1) Weigh 100g ZSM-48 molecular sieve, 20g boehmite, 60g acid solution (obtained by diluting 9.23g 65wt% nitric acid with 50.77g deionized water), 4.54g guar gum powder, 0.46g titanium dioxide, and 49.23g deionized water, mix them evenly, knead and extrude them into strips to obtain catalyst support particles;

[0067] (2) Dissolve 0.21g of chloroplatinic acid in a mixed solution containing 57.14g of deionized water, 2.86g of ethanol, and 1.03g of sorbic acid, and mix at 50°C for 2 hours to prepare a metal precursor solution; then add 5mL of acetonitrile, 97mg of sodium borohydride, and 9.38g of dihexyldimethylammonium bromide and mix, then concentrate to 20% using a rotary evaporator, add acetonitrile to the original volume, and stir at 200rpm for 8 hours. Repeat this step 3 times to obtain a metal cluster containing multiple layers of ligand shells; the number of layers of the ligand shells is 2, and the diameter of the ligand shells is 5nm;

[0068] (3) The carrier particles were immersed in a solution containing metal clusters protected by multiple layers of ligand shells, ultrasonically vibrated at 30°C for 2 hours, dried at 120°C for 2 hours, and calcined at 500°C in air for 4 hours to obtain a highly dispersed metal catalyst.

[0069] The metal cluster containing multilayered ligand shells prepared in this embodiment is Pt. 32 (CTA+ ·Br - ) 20 Atom-precise clusters, comprising 32 Pt atomic cores and 20 CTA atoms. + Cation (hexadecyltrimethylammonium cation) and 20 Br - The bound ion pairs formed by anions (CTA) + ·Br - ), and was multi-layered (CTA) + ·Br - ) Ligand spherical shell protection; load Pt 32 (CTA + ·Br - ) 20 MALDI-Tof MS mass spectrometry results of metal catalysts with precise atomic clusters are as follows: Figure 1 As shown in the top image. From Figure 1 The upper side of the graph shows that the main peak is 13531 Da, indicating that all the peaks were caused by CTA. + ·Br - Pt with multilayered ligand spherical shell protection 32 (CTA + ·Br - ) 20 The atomically precise clusters have the same molecular weight, and the side peak at 13167 Da on the left differs from the main peak by one CTA. + ·Br - The mass of the bound positive and negative ion pairs; furthermore, a cluster of satellite peaks near the main peak at 13531 Da indicates that Pt 32 (CTA + ·Br - ) 20 Atomic precision clusters carry from (CTA) + ·Br - ) Br - Halogen ions.

[0070] The transmission electron microscopy (TEM) image of the densely clustered region on the highly dispersed metal catalyst prepared in this embodiment is shown below. Figure 2 As shown, from Figure 2 The image shows a multilayer (CTA) structure loaded on a carrier. + ·Br - Pt with ligand-protected spherical shells 32 (CTA + ·Br - ) 20 Atomic-precise clusters, although densely packed in this region, still maintain a certain distance from each other. Dark-field scanning transmission electron microscopy (HAADF-STEM) images of the highly dispersed metal catalyst prepared in this embodiment are shown below. Figure 3 As shown, from Figure 3 The image shows a multilayer (CTA) structure loaded on a carrier. + ·Br - Pt with ligand-protected spherical shells 32 (CTA + ·Br - ) 20 The atoms are precisely clustered, and the clusters in this region maintain a large distance from each other; therefore, Figure 2 and Figure 3 The results show that multilayer (CTA) + ·Br - The protection provided by the ligand shell can effectively prevent the fusion of metal clusters on the catalyst during use.

[0071] Example 2:

[0072] This embodiment provides a method for preparing metal clusters containing multilayered ligand shells and highly dispersed metal catalysts, specifically including the following steps:

[0073] (1) Weigh 100g ZSM-48 molecular sieve, 50g alumina, 50g acid solution (obtained by diluting 7.69g 65wt% nitric acid with 42.31g deionized water), 4.76g guar gum powder, 0.24g titanium dioxide, and 37.6g deionized water, mix them evenly, knead and extrude them into strips to obtain catalyst support particles;

[0074] (2) Dissolve 0.63g of chloroplatinic acid in a mixed solution containing 54.56g of deionized water, 5.45g of ethanol, and 2.07g of sorbic acid, and mix at 50°C for 2 hours to prepare a metal precursor solution; then add 5mL of isopropanol, 290mg of sodium borohydride, and 28g of dihexyldimethylammonium bromide and mix, then concentrate to 30% using a rotary evaporator, add isopropanol to the original volume, and stir at 250rpm for 10 hours. Repeat this step 4 times to obtain a metal cluster containing multiple layers of ligand shells; the number of layers of the ligand shells is 2, and the diameter of the ligand shells is 6nm;

[0075] (3) The carrier particles were immersed in a solution containing a metal cluster with multiple ligand shells, ultrasonically vibrated at 40°C for 4 hours, dried at 120°C for 2 hours, and calcined at 500°C in air for 4 hours to obtain a highly dispersed metal catalyst.

[0076] Example 3:

[0077] This embodiment provides a method for preparing metal clusters containing multilayered ligand shells and highly dispersed metal catalysts, specifically including the following steps:

[0078] (1) Weigh 100g ZSM-12 molecular sieve, 40g alumina, 50g acid solution (obtained by diluting 4.12g 85wt% phosphoric acid with 45.88g deionized water), 0.95g methylcellulose, 0.05g titanium dioxide, and 14.12g deionized water, mix them evenly, knead and extrude them into strips to obtain catalyst support particles;

[0079] (2) Dissolve 0.63g of chloroplatinic acid in a mixed solution containing 25g of deionized water, 25g of ethanol, and 1.27g of salicylic acid. Mix at 60°C for 2 hours. Then add 5mL of butanol, 290mg of sodium borohydride, and 28g of dihexyldimethylammonium bromide and mix. Then concentrate to 40% using a rotary evaporator. Add butanol to the original volume and stir at 350rpm for 12 hours. Repeat this step 5 times to obtain a metal cluster protected by multiple layers of ligand shells. The number of layers of the ligand shells is 3, and the diameter of the ligand shells is 7nm.

[0080] (3) The carrier particles were immersed in a solution containing a metal cluster with multiple ligand shells, ultrasonically vibrated at 60°C for 2 hours, dried at 120°C for 2 hours, and calcined at 550°C in air for 6 hours to obtain a highly dispersed metal catalyst.

[0081] Comparative Example 1:

[0082] This comparative example provides a method for preparing a metal catalyst, specifically including the following steps:

[0083] (1) Weigh 100g ZSM-48 molecular sieve, 20g boehmite, 60g acid solution (obtained by diluting 9.23g 65wt% nitric acid with 50.77g deionized water), 4.54g guar gum powder, 0.46g titanium dioxide, and 49.23g deionized water, mix them evenly, knead and extrude them into strips to form catalyst support particles;

[0084] (2) Dissolve 0.21g of chloroplatinic acid in a mixed solution containing 57.14g of deionized water and 2.86g of ethanol, mix at 50°C for 2 hours to prepare a metal precursor solution;

[0085] (3) The support particles were immersed in a metal precursor solution, ultrasonically vibrated at 30°C for 2 hours, dried at 120°C for 2 hours, and calcined at 500°C in air for 4 hours to obtain the metal catalyst.

[0086] The STEM image of the metal catalyst prepared in this comparative example is shown below. Figure 4 As shown, from Figure 4As can be seen from this, the active phase generated on the catalyst in this comparative example is not uniformly distributed, and there are periodically arranged atoms inside the particles. Therefore, the active component on the catalyst in Comparative Example 1 belongs to large nanoparticles, not to precise atomic clusters.

[0087] Comparative Example 2:

[0088] This comparative example provides a method for preparing a metal catalyst, specifically including the following steps:

[0089] (1) Weigh 100g ZSM-48 molecular sieve, 50g alumina, 50g acid solution (obtained by diluting 7.69g 65wt% nitric acid with 42.31g deionized water), 4.76g guar gum powder, 0.24g titanium dioxide, and 37.6g deionized water, mix them evenly, knead and extrude them into strips to form catalyst carrier particles.

[0090] (2) Dissolve 0.63g of chloroplatinic acid in 60g of deionized water and mix at 50°C for 2 hours to prepare a metal precursor solution.

[0091] (3) The support particles were immersed in a metal precursor solution, ultrasonically vibrated at 40°C for 4 hours, dried at 120°C for 2 hours, and calcined at 500°C in air for 4 hours to obtain the metal catalyst.

[0092] The STEM image of the metal catalyst prepared in this comparative example is shown below. Figure 5 As shown, from Figure 5 As can be seen from this, the active phase generated on the catalyst in this comparative example is not uniformly distributed, and there are periodically arranged atoms inside the particles. Therefore, the active component on the catalyst in Comparative Example 2 belongs to large nanoparticles, not to precise atomic clusters.

[0093] The catalytic performance of the metal catalysts prepared in Example 1 and Comparative Example 1 in the oxidation of benzyl alcohol to benzaldehyde is investigated below. The specific process and results are as follows:

[0094] The metal catalysts prepared in Example 1 and Comparative Example 1 were used to carry out the catalytic oxidation reaction of benzyl alcohol. The specific evaluation methods and parameters were as follows: under the conditions of a preheating furnace of 210°C, a heating pipeline of 215°C, a reaction furnace of 280°C, and high-purity nitrogen and high-purity oxygen as carrier gases with flow rates of N2 43.4 mL / min and O2 12.0 mL / min, respectively, 0.05 g of the tested metal catalyst was placed in a quartz tube reactor for reaction. After the reaction started, samples were taken at different time points to test the contents of benzyl alcohol, benzaldehyde and by-products, and the conversion rate of benzyl alcohol and the selectivity of benzaldehyde were calculated.

[0095] In Example 1 and Comparative Example 1, based on a multilayer (CTA) +·Br - Pt with ligand-protected spherical shells 32 (CTA + ·Br - ) 20 Catalysts prepared from atomically precise clusters (black, Example 1) and conventional Pt nanoparticles (red, Comparative Example 1) exhibit the following performance in the oxidation of benzyl alcohol to benzaldehyde: Figure 6 As shown; where the solid line with triangles represents the conversion rate of benzyl alcohol; and the solid line with squares represents the selectivity of benzaldehyde. From Figure 6 As can be seen from the example, the method using Example 1 contains multiple layers (CTA). + ·Br - Pt with ligand-protected spherical shells 32 (CTA + ·Br - ) 20 After the highly dispersed catalyst with precisely clustered atoms carried out the catalytic oxidation of benzyl alcohol, the conversion rate of benzyl alcohol could be maintained at over 90% for 200 hours, and the selectivity of benzaldehyde could be maintained at over 96%.

[0096] Therefore, it can be seen that highly dispersed metal catalysts prepared by loading atomically precise clusters protected by multilayered ligand shells have good catalytic effects and are highly practical.

[0097] Furthermore, the MALDI-Tof MS mass spectrometry results of the highly dispersed metal catalyst prepared in Example 1 after 40 hours of use in the catalytic oxidation reaction of benzyl alcohol are as follows: Figure 1 As shown in the lower diagram; from Figure 1 The lower side figure shows that most of the metal catalyst is supported on multiple layers (CTA). + ·Br - Pt with ligand-protected spherical shells 32 (CTA + ·Br - ) 20 The atomically precise clusters persisted after the reaction; this demonstrates that the Pt containing multilayered ligand-protected spherical shells... 32 (CTA + ·Br - ) 20 Atomically precise clusters participate as active components in the catalytic oxidation of benzyl alcohol; at the same time, the highly dispersed state of the metal formed by the protection of the multilayer ligand shell plays a positive role in improving the catalytic performance of the catalyst.

Claims

1. A method for preparing a metal cluster containing a multilayered ligand spherical shell, wherein, The preparation method includes: (1) Dissolve the metal compound in a mixture containing water, alcohol and ligand to obtain a metal precursor solution; (2) Solvent, protective agent and reducing agent are added to the metal precursor solution in sequence and mixed. After concentration and stirring, solvent is added again. The concentration, stirring and solvent addition are repeated to obtain metal clusters containing multilayer ligand shells. Wherein, the molar ratio of the ligand to the metal compound is (6-18):1, and the molar ratio of the metal compound is based on metal atoms; The molar ratio of the metal compound to the protective agent is 1:10 to 1:100 in terms of the amount of substance. In terms of the number of electrons, the ratio of the number of electrons lost by the metal to the number of electrons gained by the reducing agent in the metal compound is 1:1 to 1:

10.

2. The preparation method according to claim 1, wherein, The ligands include one or more of sorbic acid, salicylic acid, nicotinamide, and lactic acid.

3. The preparation method according to claim 1, wherein, The metal compound includes one or more salts of platinum, palladium, and nickel.

4. The preparation method according to claim 3, wherein, The metal compound includes one or more of the following: chloroplatinic acid, tetraammineplatinum nitrate, platinum nitrate, palladium nitrate, palladium chloride, nickel chloride, and nickel nitrate.

5. The preparation method according to claim 1, wherein, The protective agent includes one or more of the following: dihexadecyl dimethyl ammonium halide, ditetradecyl dimethyl ammonium halide, didodecyl dimethyl ammonium halide, didecyl dimethyl ammonium halide, hexadecyl trimethyl ammonium halide, tetradecyl trimethyl ammonium halide, dodecyl trimethyl ammonium halide, and decadecyl trimethyl ammonium halide. Halogens include any one of bromine, iodine, and chlorine.

6. The preparation method according to claim 1, wherein, The reducing agent includes one or a combination of two or more of hydrazine hydrate, sodium borohydride, ascorbic acid, and potassium borohydride.

7. The preparation method according to claim 1, wherein, The solvent includes one or more of water, acetonitrile, ethanol, propanol, isopropanol, and butanol.

8. A metal cluster containing a multilayered ligand shell, which is prepared by the preparation method according to any one of claims 1-7.

9. The metal cluster containing multiple ligand shells according to claim 8, wherein, The metal cluster is an atomically precise cluster with multiple layers of ligand shells protecting its surface; the number of ligand shells is two or more, and the diameter of the ligand shells is 5 nm or more.

10. A highly dispersed metal catalyst, wherein, The highly dispersed metal catalyst comprises support particles and metal clusters containing multilayered ligand shells as described in claim 8 or 9, wherein the metal clusters are supported on the support particles. The amount of metal clusters added is 0.1wt%-0.6wt%, with the mass of the carrier particles being 100%. The mass of the metal clusters is calculated based on the mass of metal atoms.

11. The highly dispersed metal catalyst according to claim 10, wherein, The raw materials for the carrier particles include molecular sieves, alumina, acid solution, binder, and deionized water. The mass ratio of the molecular sieve to alumina, acid solution, binder, and deionized water is 1:(0.2-0.6):(0.3-0.6):(0.01-0.1):(0.3-1).

12. The highly dispersed metal catalyst according to claim 10, wherein, The metal dispersion in this highly dispersed metal catalyst is 90% to 100%.

13. The method for preparing the highly dispersed metal catalyst according to any one of claims 10-12, wherein, The preparation method includes: immersing the carrier particles in a solution containing the metal clusters with multiple ligand shells, followed by ultrasonic vibration, drying, and calcination to obtain a highly dispersed metal catalyst.

14. The preparation method according to claim 13, wherein, The calcination conditions are as follows: calcination at 450-600°C for 4-6 hours in air.

15. The use of the highly dispersed metal catalyst according to any one of claims 10-12 in the catalytic oxidation of benzyl alcohol.

Images