Supported metal cluster and preparation method and application thereof

Abstract

The application belongs to the technical field of catalytic materials, and particularly relates to a supported metal cluster and a preparation method and application thereof. The supported metal cluster is prepared by the following method: immersing a rigid carrier in a noble metal salt solution, and obtaining a rigid carrier loaded with noble metal after drying treatment; and performing heat treatment on the rigid carrier loaded with noble metal in a reducing atmosphere to obtain the supported metal cluster. The supported metal cluster comprises a rigid carrier and a metal cluster loaded on the rigid carrier. The technical scheme can solve the technical problems that it is difficult to prepare a size-controllable and high-purity metal nanocluster by the prior art, and the catalytic performance of the metal nanocluster cannot meet the application requirements. The supported metal cluster prepared by the scheme can be used as a hydrogen oxidation catalyst and has ideal catalytic effect. The preparation process and product performance have high reproducibility, the product structure is easy to control, industrial popularization and application can be easily realized, and the supported metal cluster has a wide application prospect as a new generation of catalyst.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of catalytic materials, and particularly relates to a supported metal cluster and a preparation method and application thereof. BACKGROUND

[0002] Heterogeneous catalysis is not only of great significance in chemical industry, but also in energy conversion and environmental technology. Catalysts based on metal active species can be said to be the core of heterogeneous catalysis. In the early development of catalytic science, people chose supported metal nanoparticles as catalysts to achieve a series of important catalytic reactions. For heterogeneous metal catalysts, size effect is the most important factor in discussing the structure-property relationship. With the change of size, from single atom to cluster (generally, particles smaller than 2 nm can become clusters) to nanoparticles, their electronic structure and geometry will change. The metal utilization rate of traditional heterogeneous catalysts is generally low, because there are a large number of bulk metal atoms, and in the surface reaction dominated heterogeneous catalytic process, bulk metal atoms cannot participate in the reaction, which is unacceptable in terms of resource utilization and industrial economic benefits for metals, especially precious metals on earth. Therefore, how to improve the metal utilization rate and reduce the cost of catalysts has become an important research direction in the field of catalysis, and improving the dispersion of metal is the most intuitive and effective solution. Supported metal cluster catalysts (SMCs) load metal clusters on high specific surface carrier materials, including molecular sieves, metal oxides, carbon materials, etc., and the dispersion of metal is improved through the interaction between metal and carrier.

[0003] For single atoms, the electronic structure is very simple and can be approximated as the corresponding atomic orbital structure. The electronic structure of clusters can be regarded as a molecular orbital formed by the hybridization of multiple atoms, which is a transition state between single atoms and nanoparticles; and when the size increases to the range of nanoparticles, the "metallicity" begins to appear. Metal clusters ensure that all metal atoms participate in the adsorption and activation of reactants in catalytic reactions. At the same time, metal clusters also have physical and chemical properties different from metal single atoms and metal nanoparticles. In addition, metal single atoms are usually anchored by oxygen on the carrier and have a certain oxidation state, resulting in the loss of part of the metallicity, which reduces the activity in some catalytic reactions. Metal clusters can provide more active sites in catalytic reactions. At the same time, due to the existence of metal-metal coordination, its metallicity is stronger than that of metal single atoms. Therefore, metal clusters can not only effectively promote the activation of reactants in catalytic reactions, but also optimize the adsorption / desorption behavior of products on active sites, resulting in higher catalytic efficiency and selectivity.

[0004] In order to further accurately study the quantum size effect of nanoclusters, especially the intrinsic correlation between structure and performance, it is the basis to synthesize metal nanoclusters with high quality, high yield and size uniformity at atomic scale. However, compared with large size metal nanoparticles, it is a great challenge to prepare size-controllable and structure-determined metal clusters. Based on this, people have developed various synthesis techniques and routes and successfully applied them to the preparation of metal nanoclusters. At present, there are mainly two strategies for the synthesis of metal nanoclusters: bottom-up and top-down. The typical representative of the bottom-up synthesis strategy is the Brust-Schiffrin method (including two-phase method and single-phase method). In the two-phase method, the metal precursor salt is first dissolved in an aqueous solution, and then transferred to an organic solvent (such as toluene) through an organic phase transfer agent (such as tetraoctylammonium bromide TOAB). Subsequently, the organic protecting agent (such as mercapto compound) and the reducing agent (such as sodium borohydride) are added one by one into the above reaction solution. Finally, metal nanoclusters are obtained. This method provides a simple and effective method for the synthesis of metal nanoclusters, and is widely used in the synthesis of metal nanoclusters with different sizes and compositions. However, most of the metal nanoclusters synthesized by this method have a certain size distribution, and the yield is low. Therefore, in order to obtain monodisperse metal nanoclusters, a complex separation process (such as fractional crystallization, chromatography, solvent extraction and polyacrylamide gel electrophoresis, etc.) is often needed to purify the product to obtain monodisperse metal nanoclusters. In the top-down strategy, the representative method is the ligand etching method. This method is a method for synthesizing ultra-small nanoclusters by using the strong interaction between mercapto ligand and metal atoms. By adding excess thiol to etch large size metal nanoparticles, monodisperse metal nanoclusters are finally obtained, but the etching process of this method usually needs a long time to obtain metal nanoclusters with specific size. Although more than a dozen different synthesis techniques have been developed in recent years, there is still a lack of an effective method to prepare high-quality, high-yield and size-accurately controlled nanoclusters. Since the properties of metal nanoclusters are strongly dependent on the size of their metal core, monodispersity and high purity are the focus and difficulty of nanocluster synthesis. At present, a careful and complex post-synthesis process is needed to separate the size-mixed metal nanoclusters. Therefore, how to prepare size-controllable and high-purity metal nanoclusters is a challenging task in future synthesis work. SUMMARY

[0005] The present application aims to provide a preparation method of supported metal clusters, to solve the technical problems that it is difficult to prepare size-controllable and high-purity metal nanoclusters by the prior art, and the catalytic performance of the metal nanoclusters cannot meet the application requirements.

[0006] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0007] A preparation method of a supported metal cluster, comprising the following steps in sequence:

[0008] S1: immersing a rigid carrier in a noble metal salt solution, and obtaining a rigid carrier loaded with noble metal after drying treatment;

[0009] S2: performing heat treatment on the rigid carrier loaded with noble metal in a reducing atmosphere, and obtaining a supported metal cluster;

[0010] The supported metal cluster comprises a rigid carrier and a metal cluster loaded on the rigid carrier; the particle size of the metal cluster is 0.1-2 nm.

[0011] Further, in S1, the rigid carrier is a porous carbon material; the noble metal salt solution is a mixture of a noble metal salt and an acid solution; the noble metal salt comprises at least one of acetate, chloride or nitrate of ruthenium, rhodium, palladium, osmium, iridium, platinum, gold or silver; and the acid solution comprises a hydrochloric acid solution and / or an acetic acid solution.

[0012] Further, in S1, the solid-liquid ratio of the noble metal salt and the acid solution is 20-250 mg:0.4-5 mL; the solute concentration of the acid solution is 5-20 wt%; and the dosage ratio of the noble metal salt solution to the rigid carrier is 300-500 μL:50-300 mg.

[0013] Further, in S1, the immersion time is 5-15 min; and the drying treatment temperature is 60-100℃, and the time is 6-8 h.

[0014] Further, in S1, the rigid carrier is prepared by the following method: dissolving P123 in a hydrochloric acid solution, adding tetraethyl orthosilicate dropwise, stirring uniformly, and then placing in a hydrothermal reaction kettle for heat preservation; after suction filtration and drying, SBA-15 powder is obtained by heat preservation; dissolving sucrose and concentrated sulfuric acid in water to obtain a sucrose precursor solution; adding the sucrose precursor solution to the SBA-15 powder, drying, and then heat preservation; grinding the product, adding the sucrose precursor solution again, drying, heat preservation, high-temperature carbonization, and hydrofluoric acid solution treatment, and then after suction filtration, water washing and drying, the rigid carrier is obtained.

[0015] Further, in S2, the reducing atmosphere is composed of hydrogen and argon in a volume ratio of 10:90-30:70.

[0016] Further, in S2, the heat treatment temperature is 150-300℃, the time is 1-3 h, and the heating rate is 2-5℃ / min.

[0017] The technical scheme also provides a supported metal cluster, which comprises a rigid carrier and a metal cluster supported on the rigid carrier through chemical bonds between metals and carbon; the particle size of the metal cluster is 0.1-2nm; and the metal cluster is a metal cluster formed by at least one metal element selected from ruthenium, rhodium, palladium, osmium, iridium, platinum, gold and silver.

[0018] Further, the supported metal cluster comprises a rigid carrier and a noble metal salt solution; the noble metal salt solution is formed by mixing a noble metal salt and an acid solution at a solid-liquid ratio of 20-250mg:0.4-5mL; and the use ratio of the noble metal salt solution to the rigid carrier is 300-500μL:50-300mg.

[0019] The technical scheme also provides an application of the supported metal cluster in a hydrogen oxidation catalyst.

[0020] The principle of the technical scheme is that:

[0021] The supported metal cluster provided by the technical scheme has higher metal dispersion and more surface coordination unsaturated sites, and thus has much higher reaction performance than metal particles. An important structural feature of the metal cluster is that it has metal-metal bonds. Unlike monatomic catalysts which use a single metal atom and the surrounding coordination environment as the main catalytic active center, SMCs with adjacent metal sites promote the bonding and reaction of reactant molecules. For many catalytic reactions, the adsorption, activation and desorption processes of reactant molecules require the participation of two or more closely coordinated metal sites. In addition, due to the limitation of the carrier on the atoms themselves, the geometric structure is relatively stable and not easy to change.

[0022] In addition, in the technical scheme, the metal cluster refers to a metal particle formed by aggregation of metal atoms, and the particle size of the metal cluster is 0.1-2nm, and preferably 0.1-1nm.

[0023] Advantages of the metal cluster:

[0024] The purpose of the technical solution is to synthesize carbon material loaded with metal clusters as a hydrogen oxidation catalyst. Metal clusters have many advantages over metal single atoms and metal nanoparticles. The catalyst of the present solution belongs to a heterogeneous metal catalyst. For a heterogeneous metal catalyst, size effect is the most important factor in the structure-performance relationship. With the change of size, the electronic structure and geometric structure of the metal clusters change from single atom to cluster to nanoparticle. The utilization rate of metal in traditional nanoparticle-level heterogeneous catalysts is generally low because there are a large number of bulk metal atoms, and in the heterogeneous catalytic process dominated by surface reactions, bulk metal atoms cannot participate in the reaction. Although supported single-atom catalysts can solve the above problems, supported single-atom catalysts have other problems. For many reactions, single-atom catalysts cannot catalyze these processes well. For example, metal single atoms are usually anchored by oxygen on the support, have a certain oxidation state, and cause the loss of metallic properties, which reduces the activity in some catalytic reactions.

[0025] For the activation or generation of certain chemical bonds, specific metal aggregates can provide matching adsorption / activation sites, so they have excellent catalytic activity. For example, for the hydrogenation of most unsaturated chemical bonds, reactions involving C-C bond cleavage, and reactions involving the simultaneous activation of multiple chemical bonds, metal cluster catalysts (such as the supported metal clusters of the present solution) have better reaction activity than larger size metal nanoparticle catalysts and smaller size single-atom catalysts. This is because the group effect of these reactions determines that the adsorption of their reactants and intermediates requires multiple sites; while the cluster catalyst can provide enough adsorption sites (and is highly unsaturated) to activate the reactants, while maximizing the surface metal ratio to have the best catalytic activity. Metal clusters ensure that all metal atoms participate in the adsorption and activation of reactants in catalytic reactions. At the same time, metal clusters have different physical and chemical properties from metal single atoms and metal nanoparticles. Metal clusters can provide more active sites in catalytic reactions. At the same time, because of the coordination between metal and metal, its metallic property is stronger than that of metal single atoms. Therefore, metal clusters not only can effectively promote the activation of reactants in catalytic reactions, but also can optimize the adsorption / desorption behavior of products on active sites, resulting in higher catalytic efficiency and selectivity. Due to the above advantages of metal clusters, those skilled in the art are committed to the development of hydrogen oxidation catalysts loaded with metal clusters. According to the process of the present technical solution, a carbon carrier loaded with metal clusters can be obtained, which is also not reported in the prior art.

[0026] The difficulty of synthesizing metal clusters:

[0027] According to the description of the preparation method of metal clusters in the background art, the synthesis process of metal clusters is relatively complex. For example, the typical representative of the bottom-up synthesis strategy is the Brust-Schiffrin method. In the synthesis process, in order to obtain monodisperse metal nanoclusters, a complex separation process (such as fractional crystallization, chromatography, solvent extraction and polyacrylamide gel electrophoresis) is often required for subsequent purification treatment of the product to obtain monodisperse metal nanoclusters. The preparation method of the supported metal cluster developed in the present application only needs to prepare a solution of a metal source in a certain proportion, impregnate the solution into a rigid carrier, and dry to obtain a rigid carrier filled with metal precursors. In a reducing atmosphere, the powder is heat treated to obtain a supported metal cluster sample. The obtained supported metal cluster does not need further cleaning, screening, purification and other treatment means to obtain high-quality, high-yield, size-accurately-controlled nanoclusters.

[0028] Compared with the prior art, the present application has the following beneficial effects:

[0029] (1) The supported metal cluster of the present application, when the metal cluster is regulated by the carrier, the difference in charge transfer between the metal species and the carrier at the Fermi level occurs at the metal-carrier. Therefore, compared with large-size metal particles, SMCs exhibit cationic properties due to more metal-carrier interface site ratios. Compared with nanoparticle catalysts with metal intrinsic properties, the changing electronic structure of SMCs significantly changes the adsorption and desorption behavior of reactant, intermediate and product molecules, thereby exhibiting completely different catalytic properties. In addition, since the structure sensitivity of nanoscale metal particles in catalytic reactions is usually more closely related to the change of its geometric structure, with the structure of the metal species on the carrier changing from larger metal particles to atomically dispersed clusters, this process undoubtedly greatly changes the catalytic properties of the metal.

[0030] (2) The supported metal cluster catalyst material of the present application, the rigid carrier provides metal-carrier interface sites, provides a large specific surface area, and regulates the distribution of metal clusters and inhibits the agglomeration of metal atoms, which is of great importance to improve its catalytic activity.

[0031] (3) The supported metal cluster catalyst material of the present application, the raw material is easy to obtain; it can be prepared by impregnation method, and the preparation is simple; the heat treatment temperature is low (200 DEG C), and the energy consumption is low; high dispersibility and high purity, high quality, high yield, size uniformity on atomic scale; high performance reproducibility, easy to control product structure, easy to realize industrialization and application. As a new generation of catalyst, it has broad application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1TEM morphology of the ruthenium metal cluster loaded mesoporous carbon of Example 1.

[0033] Figure 2 Transmission EDS spectrum of the ruthenium metal cluster loaded mesoporous carbon of Example 1.

[0034] Figure 3 XRD spectrum of the ruthenium metal cluster loaded mesoporous carbon of Example 1.

[0035] Figure 4 HOR catalytic performance graph of the ruthenium metal cluster loaded mesoporous carbon of Example 1.

[0036] Figure 5 TEM morphology of the palladium metal cluster loaded carbon nanotube of Example 3.

[0037] Figure 6 Pd K-edge EXAFS spectrum of the palladium metal cluster loaded carbon nanotube of Example 3.

[0038] Figure 7 Fitting spectrum of Pd K-edge EXAFS of the palladium metal cluster loaded carbon nanotube of Example 3. DETAILED DESCRIPTION

[0039] The application will be further described in conjunction with the examples. However, the embodiments of the application are not limited to the following examples. If not specifically indicated, the technical means used in the following examples are the conventional means known to those skilled in the art; the experimental methods are conventional methods; and the materials, reagents, etc. can be obtained from commercial channels.

[0040] A supported metal cluster is prepared by the following method:

[0041] (1) immersing a rigid carrier in a noble metal salt solution, taking out and drying to obtain a rigid carrier filled with noble metal precursors; the rigid carrier filled with noble metal precursors is a rigid carrier loaded with noble metal;

[0042] (2) heat treating the rigid carrier loaded with noble metal in a reducing atmosphere to obtain the supported metal cluster.

[0043] In the present application, in step (1), the noble metal salt is at least one of acetate, chloride and nitrate of ruthenium, rhodium, palladium, osmium, iridium, platinum, gold and silver; those skilled in the art can select a mixture of noble metal salts with any mass ratio according to actual needs.

[0044] In the present application, the noble metal salt solution is obtained by mixing a noble metal salt and an acid solution, wherein the acid solution includes a hydrochloric acid solution or an acetic acid solution, preferably a hydrochloric acid solution; the concentration of the acid solution is 5-20 wt%, preferably 10 wt%.

[0045] In the present application, the solid-liquid ratio of the noble metal salt and the acid solution is 20-250 mg:0.4-5 mL, preferably 50-200 mg:1-4 mL, and further preferably 100-200 mg:2-3 mL; and the usage ratio of the noble metal salt solution to the rigid carrier is 300-500 μL:50-300 mg, preferably 350-450 μL:100-250 mg, and further preferably 400 μL:150-200 mg.

[0046] In the present application, in the step (1), the time for impregnation is 5-15 min, preferably 10 min; the drying temperature is 60-100℃, preferably 70-90℃, and further preferably 80℃; and the time for drying is 6-8 h, preferably 6.5-7.5 h, and further preferably 7 h.

[0047] In the present application, the rigid carrier is a porous carbon material rich in oxygen defects or functional groups, and preferably mesoporous carbon.

[0048] The preferred preparation method of the mesoporous carbon rigid carrier used in the present application is as follows: 4 g of P123 is dissolved in 160 g of 2M HCl, 9 mL of tetraethyl orthosilicate is slowly added thereto, and after stirring, the mixture is placed in a hydrothermal reactor at 90℃ for 24 hours. After filtration and drying, the mixture is kept at 550℃ for 8 hours to obtain SBA-15 powder. 5 g of sucrose and 0.254 mL of concentrated H2SO4 are dissolved in 16 mL of H2O, 4 mL of the precursor solution is added to 1 g of SBA-15 powder, and the obtained mixture is dried at 60℃ for 0.5 h, then heated to 100℃ and kept for 6 h. The product is ground and crushed, and 2.64 mL of the above-mentioned sucrose precursor solution is added thereto. The obtained mixture is dried at 60℃ for 0.5 h, then heated to 100℃ and kept for 6 h. The obtained mixture is carbonized at 900℃ for 3 h under an argon atmosphere. The obtained product is stirred in a hydrofluoric acid solution for 24 hours to remove the SBA-15 template. After filtration, water washing and drying, the mesoporous carbon material s-OMC is obtained.

[0049] In the present application, in the step (2), the reducing atmosphere is composed of hydrogen and argon in a volume ratio of 10:90-30:70, preferably 10:90, 20:80 or 30:70, and further preferably 10:90.

[0050] In the present application, the temperature of the reducing atmosphere heat treatment in step (2) is 150-300℃, preferably 180-280℃, and further preferably 200-250℃; the time is 1-3h, preferably 1.5-2.5h, and further preferably 2h; and the temperature increasing rate is 2-5℃ / min, preferably 3-5℃ / min, and further preferably 5℃ / min.

[0051] The supported metal cluster synthesized according to the above method comprises a rigid support and a metal cluster for modifying the rigid support; the metal cluster is a metal cluster formed by at least one metal element selected from the group consisting of ruthenium, rhodium, palladium, osmium, iridium, platinum, gold and silver. The metal cluster has adjacent metal-metal sites and a small cluster size. The supported metal cluster prepared by the above method can be applied as a hydro-oxidation catalyst.

[0052] The technical solutions provided by the present application will be described in detail below in combination with specific synthesis processes, but they should not be understood as limiting the scope of protection of the present application.

[0053] Example 1

[0054] 200mg of ruthenium chloride was dissolved in 5mL of 10wt% hydrochloric acid and treated with 100W ultrasonic for 30min to prepare a ruthenium chloride solution. 100mg of mesoporous carbon s-OMC was put into 400μL of the ruthenium chloride solution, and then taken out after 100W ultrasonic immersion for 10min and dried at 80℃ for 8h to obtain s-OMC loaded with ruthenium. Then the s-OMC loaded with ruthenium was put into a crucible and placed in a tube furnace, and heat treated in a mixed gas atmosphere of H2 and Ar with a volume ratio of 10:90, at a temperature increasing rate of 5℃ / min, and heated to 200℃ for 2h to obtain mesoporous carbon loaded with ruthenium metal clusters.

[0055] The morphology of the mesoporous carbon loaded with ruthenium metal clusters prepared in this example is shown in Figure 1 , the transmission EDS spectrum is shown in Figure 2 , and the XRD spectrum is shown in Figure 3The size of the metal cluster attached to the mesoporous carbon in the embodiment is between a metal single atom and a nanoparticle, no obvious aggregated particles are found by transmission electron microscopy, the size of the metal cluster is <1 nm (>0.1 nm, not a non-metal single atom). And by fitting the data of the synchrotron radiation, it is known that there is a metal-carbon bond in the metal cluster, and a weak metal-metal bond. If the metal single atom is monodispersed and attached to the mesoporous carbon, the metal single atom does not have metallicity, that is, no metal-metal bond is detected. If the metal nanoparticle (particle size > 3 nm) is attached to the mesoporous carbon, a strong metal-metal bond is detected. The technical solution not only ensures that the metal cluster is obtained, but also ensures that the metal cluster with ideal dispersion (monodispersed metal cluster) is obtained. Under electron microscopy observation, no obvious aggregated particles are found, and the size distribution range of the metal cluster attached to the mesoporous carbon is between 0.1-1 nm. Monodispersed metal clusters can be obtained at one time, and no additional purification step is needed to separate and remove particles with too large a particle size.

[0056] Performance verification was performed on the mesoporous carbon loaded with the ruthenium metal cluster prepared in Example 1:

[0057] HOR catalytic performance test: Electrochemical tests were all performed in a three-electrode system of a rotating disc, in which the electrolyte solution was 0.1M KOH. A glassy carbon electrode with a diameter of 5mm on which a catalyst layer was deposited was used as the working electrode. The preparation method of the catalyst layer was as follows: first, the glassy carbon electrode was polished to mirror finish using 0.05μm alumina; then, a catalyst slurry was prepared, the mesoporous carbon loaded with the ruthenium metal cluster prepared in Example 1 was weighed and dispersed in 2mL anhydrous ethanol solution, and ultrasonic treatment was performed for 30min to make it uniformly dispersed, then 10μL of Nafion solution was added thereto, and ultrasonic treatment was continued for 5min to obtain a uniform catalyst slurry; finally, a certain amount of the slurry was dropped onto the glassy carbon electrode in multiple times to obtain a uniform thin layer of the catalyst, so that the loading of the mesoporous carbon loaded with the ruthenium metal cluster on the glassy carbon electrode was 20wt%. A graphite rod was used as the counter electrode, and a saturated calomel electrode was used as the reference electrode. First, cyclic voltammetry test was performed, and the electrode was cycled at a scan rate of 20mV / s in a voltage range of-0.84 and 0.16V vs. Hg / HgO for 50 cycles to make the electrode reach a stable state, and then the HOR polarization curve was obtained at a scan rate of 5mV / s. Before the HOR test, high-purity hydrogen was used to bubble the 0.1M KOH electrolyte for at least 10min to ensure that the electrolyte was in a hydrogen-saturated state.

[0058] After testing, as Figure 4As shown in the HOR catalytic performance diagram, the mass specific activity MA of the mesoporous carbon loaded with ruthenium metal clusters prepared in Example 1 reaches 0.613 mA / μg when used as a hydrogen oxidation catalyst.

[0059] The present application can also obtain mesoporous carbon materials loaded with metal clusters of ruthenium, rhodium, palladium, osmium, iridium, platinum, gold, silver, etc. by controlling the feeding ratio.

[0060] Example 2

[0061] 100 mg of iridium chloride was dissolved in 3 mL of 20 wt% hydrochloric acid and treated with 100 W ultrasonic waves for 30 min to prepare a mixed solution of palladium chloride. 200 mg of biomass-derived carbon (coconut shell activated carbon) was put into 450 μL of the iridium chloride solution, and then taken out after 100 W ultrasonic wave immersion for 15 min, and dried at 100°C for 6 h to obtain iridium-loaded biomass-derived carbon. Then the iridium-loaded biomass-derived carbon was put into a crucible and placed in a tube furnace, and heat-treated in a mixed gas atmosphere of H2 and Ar at a volume ratio of 30:70, with a temperature rising rate of 2°C / min, and heated to 160°C for 2 h to obtain iridium metal cluster-loaded biomass-derived carbon.

[0062] The test results show that the mass specific activity MA of the iridium metal cluster-loaded biomass-derived carbon reaches 0.51 mA / μg when used as a hydrogen oxidation catalyst.

[0063] Example 3

[0064] 200 mg of palladium chloride was dissolved in 5 mL of 10 wt% hydrochloric acid and treated with 100 W ultrasonic waves for 30 min to prepare a solution of palladium chloride. 100 mg of mesoporous carbon s-OMC was put into 400 μL of the solution of palladium chloride, and then taken out after 100 W ultrasonic wave immersion for 15 min, and dried at 80°C for 8 h to obtain palladium-loaded s-OMC. Then the palladium-loaded s-OMC was put into a crucible and placed in a tube furnace, and heat-treated in a mixed gas atmosphere of H2 and Ar at a volume ratio of 10:90, with a temperature rising rate of 3°C / min, and heated to 220°C for 2 h to obtain palladium metal cluster-loaded mesoporous carbon.

[0065] The test results show that the mass specific activity MA of the palladium metal cluster-loaded mesoporous carbon reaches 0.53 mA / μg when used as a hydrogen oxidation catalyst. The morphology diagram of the palladium metal cluster-loaded mesoporous carbon is shown in Figure 5 , the Pd K-edge EXAFS spectrum and the fitting spectrum of Pd K-edge EXAFS are shown in Figure 6 and Figure 7 . According to Figure 5It can be seen that no larger loading particles are found in the carbon carrier. The size of the palladium metal cluster is less than 1 nm and greater than 0.1 nm, which indicates that the palladium is in the form of a metal cluster rather than a palladium single atom (the radius of a palladium atom is about 140 pm) or a palladium nanoparticle (the particle size of a nanoparticle is usually greater than 3 nm). Further analysis of the electronic structure and coordination characteristics of the synthesized catalyst using XAFS shows that the palladium atoms are mainly bonded to the carbon atoms of the carbon material. At the same time, a weak Pd-Pd metal bond is formed, indicating that the material does not have strong metallicity, so it is different from the strong metallicity of a nanomaterial. Palladium nanoparticles with a size greater than 2 nm have strong metallicity and form a strong Pd-Pd metal bond. The palladium atoms loaded on the carbon material are in a cluster state, with a size smaller than that of a nanoparticle and larger than that of a palladium single atom. The above experimental data prove that the palladium exists in the form of a cluster. The palladium atoms are mainly bonded to the carbon atoms of the carbon material, but there is also a weak metal-metal coordination between them, and their metallicity is stronger than that of a metal single atom. Figure 6 and 7 It can be seen that the palladium atoms are mainly bonded to the carbon atoms of the carbon material. At the same time, a weak Pd-Pd metal bond is formed, indicating that the material does not have strong metallicity, so it is different from the strong metallicity of a nanomaterial. Palladium nanoparticles with a size greater than 2 nm have strong metallicity and form a strong Pd-Pd metal bond. The palladium atoms loaded on the carbon material are in a cluster state, with a size smaller than that of a nanoparticle and larger than that of a palladium single atom. The above experimental data prove that the palladium exists in the form of a cluster. The palladium atoms are mainly bonded to the carbon atoms of the carbon material, but there is also a weak metal-metal coordination between them, and their metallicity is stronger than that of a metal single atom.

[0066] Comparative Example 1

[0067] In patent application CN115872355A (Pd-X modified X element doped mesoporous carbon hydrogen storage and hydrogen oxidation catalyst dual functional material and its preparation method and application), the inventors disclosed a preparation method of a hydrogen oxidation catalyst and a hydrogen storage material. First, mesoporous carbon is immersed in a palladium metal salt solution, and after drying, a palladium metal precursor filled mesoporous carbon is obtained. The palladium metal precursor filled mesoporous carbon is a Pd loaded mesoporous carbon. Then, in a reducing atmosphere, the Pd loaded mesoporous carbon is subjected to X element doping heat treatment, and a Pd-X modified X element doped mesoporous carbon is obtained. The prepared X element doped mesoporous carbon Pd-X modified alloy has a crystal structure with a grain size of 3-20 nm, and can be used as a hydrogen storage material and a hydrogen oxidation catalyst.

[0068] More specifically, the synthesis method is compared and illustrated as follows:

[0069] PdCl2 solution was prepared by dissolving 200 mg PdCl2 in 5 mL 10 wt% HCl under 100 W ultrasonic for 30 min. 100 mg s-OMC was put into 400 μL PdCl2 solution, and then was taken out after 100 W ultrasonic for 15 min. The Pd-loaded s-OMC was obtained by drying at 80 °C for 8 h. Then 50 mg boric acid was put into a crucible which was placed at the upwind of the tube furnace, and the Pd-loaded s-OMC was put into another crucible which was placed at the downwind of the tube furnace. The distance between the two crucibles was 1 cm. The heat treatment was carried out in the mixed gas of H2 and Ar with the volume ratio of 20:80. The heating rate was 5 °C / min, and the temperature was raised to 300 °C and kept for 3 h. The Pd3B-loaded s-OMC was obtained.

[0070] The main difference between the present comparative example and example 3 is whether boric acid is added in the preparation process. Although the technical difference is small, the obtained products show completely different properties. The Pd-B alloy nanoparticles exist on the Pd3B-loaded s-OMC, and the particle size is about 5 nm, which is a nano-level particle. Even if the parameters of the heat treatment of the present comparative example in the mixed gas are adjusted to be consistent with example 3, the particles loaded on the carbon material are still in the nano level (>2 nm), and the metal clusters formed in example 3 cannot be formed. In example 3, the particle size of the Pd metal clusters loaded on the s-OMC is below 1 nm. In the present comparative example, the addition of X element (boron element) has the following main effects: the non-metallic element X can realize the structural modification of the carbon-based material through doping at high temperature, thereby increasing the adsorption sites of overflow hydrogen atoms and the active sites of catalytic reaction; the non-metallic element X also plays a metal anchoring role to ensure the stability of the material structure; the present comparative example mainly forms a Pd-X bond, and the palladium atom is anchored on the s-OMC carrier by the non-metallic element boron. Before the present research, the person skilled in the art cannot know whether the metal atoms will be properly aggregated to form clusters if the X element is removed. Generally, in order to promote the dispersion of metal atoms and avoid the aggregation of large particles, some substances for promoting dispersion (such as ethylenediamine, diethylamine, etc.) need to be added. However, in the present scheme, the above-mentioned substances are not added, so before the actual research results are formed, the person skilled in the art may think that the metal atoms may be largely aggregated to form larger particles by using the method of the present scheme. However, the actual research results show that under appropriate condition control, even if the simple method of the present scheme is used, the formation of metal clusters can be ensured.

[0071] According to the research results of the present comparative example, it can be known that the addition of non-metallic elements is very crucial for improving the catalytic activity and ensuring the stability of the attachment of metal atoms on the porous carbon. If the non-metallic elements are removed, the performance of the catalyst can be very seriously affected. However, in the actual research process, the inventors removed the non-metallic elements and prepared a new catalyst in the manner of reference example 4. The effect of the catalyst of example 4 and the catalyst of comparative example 1 is similar, but it shows a substantial reduction in the particle size of the substance attached to the porous carbon. The present technical solution can still obtain a similar technical effect in the case of omitting the key process steps and materials, which is unexpected by the person skilled in the art before the experiment. According to the experimental phenomena, the inventors further analyzed the reasons for the above-mentioned phenomena: after omitting the addition of non-metallic elements, under the present process conditions, the palladium atoms can be aggregated into the form of clusters, which can play the advantages of metal clusters over metal single atoms and metal nanoparticles. Although the present solution lacks the activation effect of non-metallic elements, due to the formation of metal clusters, the activity of the catalyst can be maintained at a relatively ideal level.

[0072] Although the present comparative example increases the active sites by introducing non-metallic elements X, the particle size of the Pd-B alloy nanoparticles loaded on the porous carbon is mainly 3-5 nm, and there are a large number of bulk metal atoms. In the catalytic process dominated by surface reaction, bulk metal atoms cannot participate in the reaction, resulting in waste of metal elements. Therefore, the present comparative example mainly relies on the addition of non-metallic elements to activate the catalytic performance of the product and anchor the metal atoms on the carrier, but such a process method will also cause the problem of too large particle size on the carrier, which leads to the fact that the metal atoms cannot exist in the form of clusters, thereby reducing the utilization rate of the metal.

[0073] The non-metallic element-free supported metal cluster (for example, example 3) of the present solution undoubtedly realizes a lower metal usage amount while ensuring high activity of the catalyst. The innovation point of the metal cluster of example 3 relative to the present comparative example is mainly to form a Pd-C bond to anchor the metal atoms and inhibit the oxygen affinity of the metal atoms.

[0074] Comparative example 2

[0075] As can be known from comparative example 1, the addition of non-metallic elements will lead to a larger particle size of the particles loaded on the carbon material, which cannot form the mode of metal clusters. Without the addition of non-metallic elements, how to ensure the formation of metal clusters and the technical key points affecting the formation effect of metal clusters need to be further researched. After a large number of experiments, the inventors found that the temperature of the heat treatment of the rigid carrier loaded with noble metal in a reducing atmosphere is a key factor affecting the effect of the product.

[0076] The preparation method of the mesoporous carbon loaded with ruthenium metal clusters is shown in Example 1. The holding temperature (heat treatment temperature of the ruthenium-loaded s-OMC) is experimentally studied. The parameters and experimental results are shown in Table 1.

[0077] Table 1:

[0078]

[0079] As known from the patent application CN115872355A (Pd-X modified X element doped mesoporous carbon hydrogen storage and hydrogen oxidation catalyst dual functional material and preparation method and application thereof), in the case of adding non-metallic elements, the correlation between the particle size of the alloy particles loaded on the carbon material and the heat treatment temperature is not obvious. Even if the heat treatment temperature is adjusted to a lower level of 300℃, the particle size of the alloy particles is still at the nanometer level, and the cluster mode cannot be formed. However, in the present technical solution, no non-metallic elements are added, and under the action of heat treatment at 150-300℃, metal clusters (with a size of 0.1-1nm, and the range does not include the endpoints) can be formed. If the heat treatment temperature is not within the range of 150-300℃, the formation of metal clusters and the catalytic effect of the catalyst will be seriously affected.

[0080] The preparation method of the present technical solution can not only form metal nanoclusters on the carbon material, but also ensure that the particle size of the metal nanoclusters is less than 1nm, which is smaller than the cluster (particle size greater than 2nm) in the usual sense. The smaller size not only improves the metal utilization rate but also ensures the advantages of metal clusters. The temperature selection of the heat treatment step is very critical for the formation of small-size clusters. The formation of metal clusters is regulated by temperature, which was unexpected before the experiment. If the heat treatment temperature is greater than 300℃ or less than 150℃, the particle size of the formed metal clusters will exceed 1nm, which is no longer within the scope of small-size clusters of the present solution. Analysis shows that excessive heat treatment temperature will cause metal atoms to aggregate, resulting in a size exceeding the cluster range. If the heat treatment temperature is too low, the metal will exist in the form of a salt, and the particle size will also exceed the cluster range. The performance of the catalyst obtained by heat treatment at 200℃ is the best, and its mass specific activity MA is significantly better than that of the catalyst obtained by heat treatment at other temperatures.

[0081] In addition, in the present technical solution, the noble metal salt solution is a mixture of noble metal salt and acid solution. Ultrasonic treatment is performed during the mixing of the noble metal salt and the acid solution. Ultrasonic treatment is also used when the noble metal salt solution is impregnated on the rigid template. The above technical points have a significant impact on the formation of metal clusters and the performance of the catalyst. The addition of acid solution can prevent metal hydrolysis during the dissolution of the metal salt.

[0082] On the basis of Example 1, the inventors have tried to omit the two ultrasonic treatments, to dissolve the ruthenium chloride and to simply stir the mixture with hydrochloric acid for 30 min, and to not perform ultrasonic treatment during the impregnation treatment. Otherwise, the preparation of the mesoporous carbon loaded with ruthenium metal clusters was performed in the manner of Example 1. The particle size of the metal clusters in the product obtained was more than 1 nm. The inventors have analyzed the reason to be that the ultrasonic treatment ensures uniform dispersion of the solution in the pores of the carrier by capillary action, and the particle size can be controlled by the confinement effect of the mesopores, and agglomeration is not easy to occur. The ultrasonic treatment is very important for the case where the particle size of the metal clusters needs to be precisely controlled. The application scenarios and purposes of the present solution are not consistent with the case of doping X element in Comparative Example 1, and Comparative Example 1 does not have the need to precisely control the particle size of the particles, and in addition, the Pd-X particles in Comparative Example 1 are larger than the metal clusters, and the effect of the ultrasonic treatment on the particle size of the particles on the mesoporous carbon is not obvious. However, for the case where the present solution needs to form metal clusters, the ultrasonic treatment presents a significant effect on the technical effect.

[0083] The above-mentioned is only the embodiment of the present application, and the common technical solutions and / or characteristics in the solution and the like are not described in detail. It should be noted that, for those skilled in the art, without departing from the technical solutions of the present application, a number of modifications and improvements can be made, which should also be considered as the protection scope of the present application, and these will not affect the effect and practicality of the present application. The protection scope claimed in the present application should be subject to the content of its claims, and the specific embodiments and the like in the specification can be used to explain the content of the claims.

Claims

1. A method for preparing a supported metal cluster, characterized by: The method comprises the following steps in sequence: S1: immersing a rigid carrier in a noble metal salt solution, and obtaining a noble metal loaded rigid carrier after drying treatment; The rigid carrier is a porous carbon material; the noble metal salt solution is a mixture of a noble metal salt and an acid solution; the noble metal salt comprises at least one of acetate, chloride or nitrate of ruthenium, rhodium, palladium, osmium, iridium, platinum, gold or silver; and the acid solution comprises a hydrochloric acid solution and / or an acetic acid solution; The solid-liquid ratio of the noble metal salt and the acid solution is 20-250 mg:0.4-5 mL; the solute concentration of the acid solution is 5-20 wt%; and the dosage ratio of the noble metal salt solution to the rigid carrier is 300-500 μL:50-300 mg. The rigid carrier is prepared by the following method: dissolving P123 in a hydrochloric acid solution, adding tetraethyl orthosilicate dropwise, stirring uniformly, placing in a hydrothermal reaction kettle for heat preservation, and then performing suction filtration and drying to obtain SBA-15 powder; dissolving sucrose and concentrated sulfuric acid in water to obtain a sucrose precursor solution; The SBA-15 powder is added with the sucrose precursor solution, dried, and then heated and preserved; The product is ground and crushed, and then added with the sucrose precursor solution, dried, heated and preserved, and then subjected to high-temperature carbonization treatment and hydrofluoric acid solution treatment, and then subjected to suction filtration, water washing and drying to obtain the rigid carrier; In the process of mixing the noble metal salt and the acid solution, ultrasonic treatment is performed; and in the process of immersing the noble metal salt solution in the rigid template, ultrasonic treatment is performed; S2: performing heat treatment on the noble metal loaded rigid carrier in a reducing atmosphere to obtain a supported metal cluster; The heat treatment is performed at a temperature of 150-300 ℃ for 1-3 h at a temperature rising speed of 2-5 ℃ / min; The supported metal cluster comprises the rigid carrier and a metal cluster loaded on the rigid carrier; and the particle size of the metal cluster is 0.1-1 nm.

2. The method for preparing a supported metal cluster according to claim 1, characterized in that: In S1, the immersion time is 5-15 min; and the drying treatment is performed at a temperature of 60-100 ℃ for 6-8 h.

3. The method for preparing a supported metal cluster according to claim 1, characterized in that: In S2, the reducing atmosphere is composed of hydrogen and argon in a volume ratio of 10:90-30:

70.

4. A supported metal cluster obtainable by the process according to any one of claims 1 to 3, characterized in that: The supported metal cluster comprises a rigid carrier and a metal cluster loaded on the rigid carrier through chemical bonding between metal and carbon; the particle size of the metal cluster is 0.1-1 nm; and the metal cluster comprises at least one of ruthenium, rhodium, palladium, osmium, iridium, platinum, gold and silver.

5. The supported metal cluster of claim 4, wherein, The raw materials comprise a rigid carrier and a noble metal salt solution; the noble metal salt solution is obtained by mixing a noble metal salt and an acid solution in a solid-liquid ratio of 20-250 mg:0.4-5 mL; and the dosage ratio of the noble metal salt solution to the rigid carrier is 300-500 μL:50-300 mg.

6. The supported metal cluster in claim 5 in a hydrogen oxidation catalyst.

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