Rare earth-based alloy nanoparticles, methods of making and catalysts

Abstract

The application provides a rare earth-based alloy nanoparticle, a preparation method thereof and a catalyst. The preparation method comprises the following steps: mixing a metal salt, a carbon carrier and an organic solvent to form a first reaction system in a protective atmosphere, and performing first heating treatment; then adding a reducing agent to the first reaction system to form a second reaction system, and performing second heating treatment to obtain a rare earth-based alloy nanoparticle; wherein the metal salt comprises a platinum salt and a rare earth metal salt, and the molar ratio of the metal salt to the reducing agent is 0.1-1:1; the first heating treatment is performed at 120-150 DEG C for 1-2 hours, and the second heating treatment is performed at 230-260 DEG C for 2-5 hours. The application further provides the rare earth-based alloy nanoparticle obtained by the above preparation method and a catalyst comprising the rare earth-based alloy nanoparticle or made of the nanoparticle. The rare earth-based alloy nanoparticle has moderate size, uniform element distribution, is beneficial to active site exposure, and has high catalytic activity.

Description

TECHNICAL FIELD

[0001] The present application relates to a preparation method of nanoparticles, in particular to a rare earth-based alloy nanoparticle and a preparation method thereof and a catalyst. BACKGROUND

[0002] In recent years, with the rapid development of society and the large use of petroleum and chemical resources, environmental problems have become increasingly prominent, and it is urgent to find environmentally friendly and recyclable resources. The field of electrocatalysis has attracted a lot of attention from scholars; currently, commercial Pt / C is the most commonly used catalyst in electrocatalysis, but due to its high price, low storage, and rapid deactivation caused by long-term use of particle agglomeration, the commercial application of noble metal electrocatalysts has not been widely developed and utilized, so finding stable and efficient catalysts has become the main research object of scholars. Metal alloying is one of the most promising strategies for developing catalysts with high durability and enhanced activity; single metal nanocrystals often cannot meet all the requirements in practical applications, compared with single metal catalysts, the introduction of foreign metals to form multi-metal nanocrystals can change the electronic structure and spatial arrangement pattern, in addition, the electronic interaction and synergistic effect between alloy elements can significantly optimize the adsorption and desorption of reaction intermediates. Nanoscale alloy materials have very excellent and unique properties in electricity, magnetism, corrosion resistance, catalysis, etc. due to their particle size and structure different from bulk alloy materials, and have become the research focus in the field of nanomaterials in recent years.

[0003] The current preparation methods of nanomaterials can be mainly divided into physical method and chemical method. The physical method generally includes mechanical alloying method, ultrasonic method, hydrogen arc plasma method and the like. The common chemical preparation methods mainly include coprecipitation method, hydrothermal method, microemulsion method, sol-gel method and the like. Rare earth elements are collectively referred to as 17 metal elements of 15 lanthanide series elements (La-Lu) plus Sc, Y. The characteristics of the incomplete filled 4f orbit of rare earth elements, lanthanide contraction and large atomic radius make it exhibit different performance in the field of catalysis. The preparation of rare earth-based nanometer alloy material has become the research focus in the field of alloy nanomaterials. However, there are very serious challenges in the preparation of the current rare earth-based nanometer alloy material, mainly for two reasons: 1. The extremely low reduction potential of rare earth elements (-1.9 to -2.38V), the large absolute value of the reduction potential increases the difficulty of synthesis of rare earth alloy material; 2. Rare earth elements have strong oxygen affinity, and once in contact with H2O or O2, they will form stable oxides, making the reduction of RE ions more difficult, which makes the wet chemical synthesis method in water or proton solvent no longer applicable. Therefore, most of the current nanomaterial preparation methods cannot meet the synthesis of rare earth-based alloy materials; the methods suitable for rare earth-based alloy nanomaterials at present mainly include high-temperature smelting method, magnetron sputtering technology and reduction method. The high-temperature smelting method is to weigh the metal materials according to the stoichiometric ratio, put them into an induction furnace or a high-temperature furnace, and melt the materials under the protection of inert gas to obtain rare earth alloy. The magnetron sputtering method uses the high-energy particles generated by the mixture of Ar-N2 plasma under the action of electric field and alternating magnetic field to prepare alloy, but the materials obtained by the two preparation methods are mostly bulk alloy materials and do not belong to the category of nanomaterials; in addition, the strong oxygen affinity of rare earth also leads to the long-term restriction of chemical reduction method.

[0004] Therefore, with the increasing emphasis on the development of green chemistry, it is becoming more and more important to develop a new type of environmentally friendly, simple and convenient synthesis method of rare earth-based alloy nanomaterials. SUMMARY

[0005] In order to solve the above problems, the purpose of the present application is to provide a rare earth-based alloy nanoparticle and a preparation method and catalyst thereof. The preparation method can synthesize rare earth-based alloy nanoparticles at a lower temperature, and the rare earth-based alloy nanoparticles have moderate size, uniform element distribution and high catalytic activity.

[0006] In order to achieve the above object, the present application provides a preparation method of rare earth-based alloy nanoparticles, wherein the preparation method comprises: mixing a metal salt, a carbon carrier and an organic solvent to form a first reaction system in a protective atmosphere, and performing a first heating treatment; maintaining the protective atmosphere, adding a reducing agent to the first reaction system after the first heating treatment to form a second reaction system, and performing a second heating treatment on the second reaction system to obtain the rare earth-based alloy nanoparticles.

[0007] The metal salt comprises a platinum salt and a rare earth metal salt, and the molar ratio of the platinum salt and the rare earth metal salt is 1-2:1.

[0008] The temperature of the first heating treatment is 120-150 DEG C, and the time of the first heating treatment is 1-2 h; the temperature of the second heating treatment is 230-260 DEG C, and the time of the second heating treatment is 2-5 h.

[0009] In the above preparation method, the metal salt as a raw material contains two or more metal ions, and the oxidation-reduction potentials of different metal ions are different, and the reduction order is different, and the metal ion with high oxidation-reduction potential (the oxidation-reduction potential of the metal ion is negative, so the oxidation-reduction potential is high, which means that the oxidation-reduction potential is closer to 0) can be reduced preferentially. The present application can anchor the metal ion reduced preferentially by adding a carbon carrier, improve the monodispersity of metal ions to avoid agglomeration; further, the treatment temperature of the first heating treatment is relatively low, which can control the reduction speed of the metal ion and avoid the agglomeration of the metal ion caused by rapid reduction, so that the metal ion reduced preferentially is in a monodispersed state and can be regarded as a nanometer core, which can provide a template for the subsequent reduced metal ion; and the first heating treatment process can also remove the crystal water in the metal salt. When the second heating treatment is performed, the high reaction temperature and the strong reduction effect of the reducing agent can promote the reduction of the metal ion with low oxidation-reduction potential, and the metal ion (such as a rare earth metal ion) reduced in this process can be reduced to the metal particle (such as a reduced platinum particle) preferentially reduced in the first heating treatment process, and in a high-temperature environment, the metal atoms diffuse and mix, promoting the combination of different metal atoms to generate alloy nanoparticles.

[0010] For example, the platinum-cerium alloy nanoparticles, the redox potential of the rare earth element cerium (-1.9 to -2.38 V) is much lower than that of platinum (-1.18 V), and the organic solvent (such as oleylamine) itself has a certain reducing property. Therefore, in the first heating process, platinum ions are first reduced to platinum nanoparticles; the platinum nanoparticles are anchored by the carbon support to avoid aggregation and can serve as a nanometer core, and the low reduction temperature of 120°C used in the first heating process can also prevent the rapid reduction and agglomeration of platinum ions; in addition, if the cerium salt itself has crystal water (such as hydrated cerium nitrate), the crystal water can be removed at the first heating treatment temperature (120-150°C) for a period of time to prevent the formation of rare earth ion oxides. In the second heating process, the reaction temperature is further increased to 230°C-260°C, and the reducing agent sodium borohydride is present in the second reaction system, which can reduce the cerium ions with extremely low reduction potential. At this time, the anchored platinum nanometer core acts as a template, allowing cerium ions to be preferentially reduced onto the platinum nanometer core. In a high-temperature environment, metal atoms exist in a diffusion and mixing situation, and high temperature can promote the combination of platinum atoms and cerium atoms to synthesize platinum-cerium alloy nanoparticles.

[0011] According to specific embodiments of the present application, the rare earth element in the rare earth metal salt includes one or a combination of two or more of lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, scandium, and yttrium. The above-mentioned rare earth elements have similar properties and similar redox potentials.

[0012] According to specific embodiments of the present application, the molar ratio of the platinum salt to the rare earth metal salt can be controlled to be 1-2:1. In some specific embodiments, the molar ratio of the platinum salt to the rare earth metal salt can be controlled to be 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2:1, and the like, as well as ranges with any two of the above specific values as endpoints.

[0013] According to specific embodiments of the present application, the rare earth metal salt preferably includes a cerium salt and / or a praseodymium salt. The metal salt preferably includes a combination of a platinum salt and a cerium salt or a combination of a platinum salt and a praseodymium salt. The molar ratio of the platinum salt to the cerium salt and the molar ratio of the platinum salt to the praseodymium salt can be controlled to be 1-2:1.

[0014] According to specific embodiments of the present application, the anion of the metal salt can include one or a combination of two or more of nitrate, sulfate, and acetylacetone anions. In some specific embodiments, the metal salt can include a combination of chloroplatinic acid and cerium nitrate.

[0015] According to specific embodiments of the present application, the carbon carrier can anchor the metal particles generated by reduction in the first heating treatment process, avoiding agglomeration between particles. In some specific embodiments, the carbon carrier can include carbon black. Compared with other carbon materials, carbon black has good electrical conductivity, which facilitates electron transfer in the catalytic reaction when carbon black is used as a carrier; and carbon black has good durability, and the product synthesized with carbon black as a carrier can perform catalytic reactions for a long time and has a high service life.

[0016] According to specific embodiments of the present application, by using two-step heating treatment for reduction and controlling the temperature of the first heating treatment, reduction of metal salts such as platinum salts can be achieved, agglomeration of reduced metal particles can be avoided, and crystallization water in the metal salt can be removed to avoid the generation of metal oxides.

[0017] In the existing method for synthesizing alloy nanoparticles using a solvent, since a metal ion with a moderate reduction potential is generally selected, only a low reaction temperature and a weak reducing agent (such as glucose) are generally required for reduction. However, for metal elements with a low reduction potential, such as rare earth elements, the reaction conditions of the above-mentioned existing method cannot achieve the reduction of metal ions. In the present application, by controlling the temperature of the second heating treatment and adding a strong reducing agent, the energy barrier required for the reduction reaction of metal ions can be broken, and the diffusion and combination between metal atoms can be accelerated. Moreover, by controlling the heating conditions (temperature and time) of the first heating treatment and the second heating treatment, the element content and the uniformity of the morphology of the alloy nanoparticles can be controlled, which is beneficial to obtain rare earth-based alloy nanoparticles with high catalytic activity.

[0018] In some specific embodiments, the temperature of the first heating treatment can be controlled to be 120-150°C. Specifically, the temperature of the first heating treatment can be 120°C, 125°C, 130°C, 135°C, 140°C, 145°C, 150°C, and the like, and ranges with any two of the above specific values as endpoints.

[0019] In some specific embodiments, the temperature of the second heating treatment can be controlled to be 230-260°C, for example, 230°C, 235°C, 240°C, 245°C, 250°C, 255°C, 260°C, and the like, and ranges with any two of the above specific values as endpoints.

[0020] In some specific embodiments, the time of the first heating treatment can be controlled to be 1h-2h, and further controlled to be 1-1.5h, for example, 1h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 2h, and the like, and ranges with any two of the above specific values as endpoints.

[0021] In some embodiments, the second heating treatment can be controlled for a time period of 2h-5h, such as 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, or a range between any two of the above-mentioned values.

[0022] In the above-mentioned preparation method, the reducing agent added before the second heating treatment has a strong reducing effect, and in the case that the carbon carrier plays an anchoring role on the first reduced metal particles, the reducing agent can promote the reduction of the rare earth metal ions in cooperation with the high-temperature environment provided by the second heating treatment. In some embodiments, the reducing agent can include sodium borohydride or the like.

[0023] According to the embodiments of the present application, by controlling the amount of use between the reactants (such as the molar ratio of metal salt to reducing agent, the molar ratio of metal salt to carbon carrier, the molar ratio between platinum salt and rare earth metal salt), the element content and particle size of the alloy nanoparticles can be regulated.

[0024] In some embodiments, by controlling the amount of use of the reducing agent relative to the metal salt, on the one hand, the rare earth metal ions can be fully reduced, and on the other hand, the size of the generated alloy nanoparticles can be controlled to be appropriate and the morphology uniform. The molar ratio of the metal salt to the reducing agent can be controlled to be 0.1-1:1, and further controlled to be 0.2-1:1 or 0.1-0.5:1. Specifically, the molar ratio of the metal salt to the reducing agent can be 0.1:1, 0.2:1, 0.24:1, 0.25:1, 0.29:1, 0.3:1, 0.4:1, 0.49:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, or a range between any two of the above-mentioned values.

[0025] In some embodiments, the molar ratio of the metal salt to the carbon carrier can be controlled to be 1:2.5-4, such as 1:2.5, 1:2.6, 1:2.7, 1:3, 1:3.1, 1:3.5, 1:3.8, 1:3.9, 1:4, or a range between any two of the above-mentioned values.

[0026] According to the specific embodiments of the present application, the metal salt can include 7-16 parts of platinum salt (e.g. 7 parts, 7.8 parts, 11.6 parts, 15.4 parts, 16 parts, etc.), 6.5 parts of rare earth metal salt, in terms of mass parts; correspondingly, the carbon carrier can be 1.4 parts, and the reducing agent can be 2-11.2 parts (e.g. 2 parts, 2.3 parts, 4.6 parts, 5.7 parts, 7.7 parts, 9.6 parts, 11.2 parts, etc.). In some specific embodiments, the platinum salt can be 7.8-16 mg, the rare earth metal salt can be 6.5 mg, the reducing agent can be 2-11.2 mg, and the carbon carrier can be 1.4 mg.

[0027] According to the specific embodiments of the present application, at least the second heating treatment process can be carried out in a protective atmosphere, which can prevent the metal ions from being oxidized into metal oxides by oxygen or the like during the reaction process. In some specific embodiments, the protective atmosphere includes nitrogen, inert gas, or the like.

[0028] According to the specific embodiments of the present application, the organic solvent is generally an organic solvent capable of dissolving the metal salt and the reducing agent, and not reacting with the carbon carrier, and can be oleylamine or the like. In some specific embodiments, the volume-to-mass ratio of the oleylamine to the platinum salt can be 5 mL:(7-16) mg.

[0029] According to the specific embodiments of the present application, the metal salt, the carbon carrier, and the organic solvent can also be mixed by ultrasonic treatment to form the first reaction system. In some specific embodiments, the frequency of the ultrasonic treatment is 80 kHz-100 kHz, and the time of the ultrasonic treatment is 0.5 h-1.5 h.

[0030] According to the specific embodiments of the present application, the preparation method can include the operation of stirring the first reaction system while carrying out the first heating treatment. The stirring speed can be controlled to be 100-600 rpm, and further controlled to be 200 rpm-500 rpm.

[0031] According to the specific embodiments of the present application, the above preparation method further includes the operation of post-treating the product after the second heating treatment. The post-treatment generally includes the operations of cooling, washing, and centrifuging the product after the reaction, and the washing can use a mixture of ethanol and hexane.

[0032] According to the specific embodiments of the present application, the above preparation method of the rare earth-based alloy nanoparticles can specifically include:

[0033] The metal salt is at least one of a salt of a rare earth element and a platinum salt, sodium borohydride is used as a reducing agent, and carbon black is used as a carbon carrier. The metal salt, the carbon carrier, and an organic solvent (e.g., oleylamine) are mixed, and ultrasonic treatment is performed at a frequency of 80-100 kHz for 0.5-1.5 h, so that the metal salt is dissolved in the organic solution and the carbon carrier is uniformly dispersed in the organic solvent, to form a first reaction system. Then, the first reaction system is kept under stirring (at a rotation speed of 100-600 rpm), and is subjected to a first heating treatment at a temperature of 120-150 °C for 1-2 h. Then, the reducing agent is added to the first reaction system (under stirring, the reducing agent is dissolved in the solution), and the system is subjected to a second heating treatment at a temperature of 230-260 °C for 2-5 h. The reaction product obtained is cooled to room temperature, washed with a mixture of ethanol and hexane for several times (usually 6-12 times), and then subjected to centrifugation (at a speed of 8000-10000 r / min), to obtain the rare earth-based alloy nanoparticles.

[0034] The present application also provides a rare earth-based alloy nanoparticle, which is obtained by the above method. According to specific embodiments of the present application, the particle size of the rare earth-based alloy nanoparticle is 30-70 nm; further, the particle size of the rare earth-based alloy nanoparticle is 40-60 nm. In some specific embodiments, the particle size of the rare earth-based alloy nanoparticle can be 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, or the like, or a range defined by any two of the above specific values as the end points.

[0035] The present application also provides a catalyst comprising or made of the above rare earth-based alloy nanoparticle. The above rare earth-based alloy nanoparticle provided by the present application has a moderate particle size, and thus has a high specific surface area and can expose more active sites. Moreover, the elements in the rare earth-based alloy nanoparticle are uniformly distributed, the morphology is uniform, and the active sites are dispersed and not aggregated, and thus the above rare earth-based alloy nanoparticle has high catalytic activity when applied to a catalyst, such as a hydrogen production catalyst.

[0036] The present application has the following advantages. The alloy nanoparticle obtained by the preparation method provided by the present application has a moderate particle size, and the metal elements are uniformly distributed in the particle. The alloy nanoparticle has a large surface area, uniform element distribution, high catalytic activity, high purity, no aggregation, and good stability, and can be applied to a catalyst. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 Scanning transmission electron microscopy-energy dispersive spectroscopy of the platinum-cerium alloy nanoparticle of Example 1.

[0038] Figure 2 Scanning electron micrograph and particle size distribution of platinum-cerium alloy nanoparticles of Example 1.

[0039] Figure 3 Scanning electron micrograph of platinum-cerium alloy nanoparticles of Example 3.

[0040] Figure 4 Scanning electron micrograph and particle size distribution of platinum-praseodymium alloy nanoparticles of Example 14.

[0041] Figure 5 Scanning electron micrograph of platinum-cerium alloy nanoparticles of Example 9.

[0042] Figure 6 XRD spectrum of nanoparticles of Comparative Example 3.

[0043] Figure 7 XRD spectrum of platinum-cerium alloy nanoparticles of Example 1.

[0044] Figure 8 Scanning electron micrograph of nanoparticles of Comparative Example 6.

[0045] Figure 9 Scanning electron micrograph of nanoparticles of Comparative Example 7.

[0046] Figure 10 XRD spectrum of nanoparticles of Comparative Example 8.

[0047] Figure 11 Polarization curves of hydrogen evolution reaction of rare earth nanalloy obtained from Example 1 and Example 14 and commercial Pt / C under alkaline condition. DETAILED DESCRIPTION

[0048] In order to make the technical features, objectives and beneficial effects of the present application more clearly understood, the technical solutions of the present application will be described in detail below, but it should not be understood as limiting the implementable scope of the present application.

[0049] In the following experiments, chloroplatinic acid is H2PtCl6·6H2O, cerium nitrate is CeN3O9·6H2O, and praseodymium nitrate is PrN3O9·6H2O.

[0050] Example 1

[0051] The present embodiment provides a rare earth-based binary alloy nanoparticle, and a preparation method of the nanoparticle includes the following processes:

[0052] In a 25ml glass tube, 5ml of oleylamine was added, followed by 7.8mg of chloroplatinic acid, 6.5mg of cerium nitrate, and 1.4mg of carbon black. The tube was then ultrasonically cleaned at 100kHz for 1 hour to form a first reaction system (in which the metal salt was dissolved and the carbon black was evenly dispersed). The first reaction system was then placed in an oil bath, stirred at 500rpm, and heated to 120°C for a first heat treatment, which was maintained at this temperature for 1 hour. 5.7mg of sodium borohydride was then added to the first reaction system to form a second reaction system. The temperature was then raised to 250°C for a second heat treatment, which was maintained at this temperature for 3 hours. A nitrogen atmosphere was maintained throughout the reaction. The reaction product was cooled to room temperature, washed eight times with a mixture of ethanol and hexane, and centrifuged at 10,000 rpm to obtain rare earth-based binary alloy nanoparticles.

[0053] Example 2

[0054] This embodiment provides a rare earth-based binary alloy nanoparticle. The preparation method of the nanoparticle is similar to the method in Example 1, except that the amount of sodium borohydride used in this embodiment is 2.3 mg.

[0055] Example 3

[0056] This embodiment provides a rare earth-based binary alloy nanoparticle. The preparation method of the nanoparticle is similar to the method in Example 1, except that the amount of sodium borohydride used in this embodiment is 4.6 mg.

[0057] Example 4

[0058] This embodiment provides a rare earth-based binary alloy nanoparticle. The preparation method of the nanoparticle is similar to the method in Example 1, except that the amount of sodium borohydride used in this embodiment is 11.2 mg.

[0059] Example 5

[0060] This embodiment provides a rare earth-based binary alloy nanoparticle. The preparation method of the nanoparticle is similar to the method in Example 1, except that the amount of chloroplatinic acid used in this embodiment is 11.6 mg.

[0061] Example 6

[0062] This embodiment provides a rare earth-based binary alloy nanoparticle. The preparation method of the nanoparticle is similar to the method in Example 1, except that the amount of chloroplatinic acid used in this embodiment is 15.4 mg.

[0063] Example 7

[0064] This example provides a rare earth-based binary alloy nanoparticle, the preparation method of which is similar to that in Example 1, except that the reaction temperature of the second heat treatment in this example is 250°C, and the reaction time is 2h.

[0065] Example 8

[0066] This example provides a rare earth-based binary alloy nanoparticle, the preparation method of which is similar to that in Example 1, except that the reaction temperature of the second heat treatment in this example is 250°C, and the reaction time is 4h.

[0067] Example 9

[0068] This example provides a rare earth-based binary alloy nanoparticle, the preparation method of which is similar to that in Example 1, except that the reaction temperature of the second heat treatment in this example is 250°C, and the reaction time is 5h.

[0069] Example 10

[0070] This example provides a rare earth-based binary alloy nanoparticle, the preparation method of which is similar to that in Example 1, except that the reaction temperature of the second heat treatment in this example is 230°C, and the reaction time is 3h.

[0071] Example 11

[0072] This example provides a rare earth-based binary alloy nanoparticle, the preparation method of which is similar to that in Example 1, except that the reaction temperature of the second heat treatment in this example is 240°C, and the reaction time is 3h.

[0073] Example 12

[0074] This example provides a rare earth-based binary alloy nanoparticle, the preparation method of which is similar to that in Example 1, except that the reaction temperature of the second heat treatment in this example is 260°C, and the reaction time is 3h.

[0075] Example 13

[0076] This example provides a rare earth-based binary alloy nanoparticle, the preparation method of which is similar to that in Example 1, except that the reaction temperature of the first heat treatment in this example is 120°C, and the reaction time is 1.5h.

[0077] Example 14

[0078] This embodiment provides a rare earth-based binary alloy nanoparticle, the preparation method of which is similar to that in Embodiment 1, with the only difference being that praseodymium nitrate is used instead of cerium nitrate in this embodiment, and the amount of praseodymium nitrate used is 6.5 mg.

[0079] Embodiment 15

[0080] This embodiment provides a rare earth-based binary alloy nanoparticle, the preparation method of which is similar to that in Embodiment 1, with the only difference being that praseodymium nitrate is used instead of cerium nitrate in this embodiment, and the amount of praseodymium nitrate used is 6.5 mg; the amount of chloroplatinic acid used is 11.6 mg.

[0081] Embodiment 16

[0082] This embodiment provides a rare earth-based binary alloy nanoparticle, the preparation method of which is similar to that in Embodiment 1, with the only difference being that praseodymium nitrate is used instead of cerium nitrate in this embodiment, and the amount of praseodymium nitrate used is 6.5 mg; the amount of chloroplatinic acid used is 15.4 mg.

[0083] Embodiment 17

[0084] This embodiment provides a rare earth-based binary alloy nanoparticle, the preparation method of which is similar to that in Embodiment 1, with the only difference being that praseodymium nitrate is used instead of cerium nitrate in this embodiment, and the amount of praseodymium nitrate used is 6.5 mg; the reaction temperature of the first heating treatment is 120°C, and the reaction time is 1.5 h.

[0085] The main experimental parameters of Embodiments 1 to 17 above are summarized in Table 1.

[0086] Table 1

[0087]

[0088] Figure 1 The scanning transmission electron microscope-energy spectrum of the alloy nanoparticle of Embodiment 1 is shown in Figure 1. It can be seen from the figure that the size of the nanoparticle is about 45 nm; under the condition of having a particle size with a moderate size, these nanoparticles can maintain an intact structure, and the metal elements are uniformly distributed on the surface of the nanoparticles without aggregation, so that the nanoparticles have a high specific surface area and high catalytic activity. Figure 1

[0089] The morphology results of the alloy nanoparticles obtained in Embodiments 1 to 17 are as follows:

[0090] ​(1) Example 2 to Example 4 differ from Example 1 in the amount of reducing agent (sodium borohydride) used. The size of the nanoparticles obtained in Example 2 to Example 4 is similar to that of the particles of Example 1, i.e. about 45 nm to 50 nm, which shows that the size of the nanoparticles can be controlled to be 30-70 nm by controlling the molar ratio of the reducing agent to the metal salt to be 1:0.1-1.

[0091] (2) Example 5 and Example 6 differ from Example 1 in the amount of platinum salt used. Within the appropriate range of the ratio of the metal salt to the carbon carrier, the amount of platinum salt used does not cause the platinum nanoparticles obtained by the first heat treatment to agglomerate. The final nanoparticles obtained in Example 5 and Example 6 remain dispersed, and the size is still about 45 nm, which is similar to the morphology of the nanoparticles of Example 1. This shows that the dispersibility of the obtained nanoparticles can be high and the size can be kept in the range of 30-70 nm by controlling the molar ratio of the metal salt to the rare earth metal salt to be 1:2.5-4.

[0092] (3) Example 7 to Example 9 differ from Example 1 in the second heat treatment time. The size of the nanoparticles obtained in Example 7 and Example 8 is about 45 nm, while the size of the nanoparticles obtained in Example 9 is about 55 nm due to the extension of the reaction time to 5 h.

[0093] (4) Example 10 to Example 12 differ from Example 1 in the second heat treatment temperature. Since the temperature of the second heat treatment is in the range of 230-260℃, the size of the nanoparticles obtained in Example 10 to Example 12 is still the same as that of Example 1.

[0094] (5) Example 13 is based on the extension of the first heat treatment time of Example 1 by 0.5 h. Compared with the nanoparticles obtained in Example 1, the nanoparticles obtained in Example 13 do not agglomerate and the size does not change much, which is about 50 nm. This shows that the size of the nanoparticles can be controlled to be 30-70 nm and the particles do not agglomerate by controlling the first heat treatment time to be 1-2 h.

[0095] (6) Example 14 to Example 16 change the type and amount of the rare earth metal salt relative to Example 1. The obtained nanoparticles are still uniformly dispersed and the size is about 60 nm. Example 17 is based on the extension of the first heat treatment of Example 14 by 0.5 h. The extension of this time does not have a significant effect on the final morphology. The nanoparticles obtained in Example 17 do not agglomerate and the size of the nanoparticles does not change much, which is about 65 nm.

[0096] Comparing the morphology of the alloy nanoparticles obtained in Examples 1 to 17 above, the nanoparticles obtained in Example 1, Example 3 and Example 14 have more uniform and regular size and morphology than the nanoparticles obtained in other examples. It can be seen that when the amount of sodium borohydride is maintained at about 5 mg (4.6 mg to 5.7 mg, i.e. the molar ratio of metal salt to reducing agent is about 0.1 to 0.5:1), the amount of carbon carrier carbon black is about 1.4 mg (i.e. the molar ratio of carbon carrier to the total moles of metal salt is 2.5 to 4:1), the temperature of the first heating treatment is 120°C for 1 h and the temperature of the second heating treatment is 250°C for 3 h, the size of the particles is uniform, the average diameter is about 45 nm and 60 nm, and the nanoparticles have good morphology.

[0097] Figure 2 、 Figure 3 、 Figure 4 and Figure 5 show the low-magnification scanning electron microscope images of the rare earth-based binary alloy nanoparticles prepared in Example 1 and Example 3, Example 14 and Example 9. It can be seen from Figures 2 to 5 that the rare earth-based binary alloy nanoparticles provided by the present application not only have uniform size, but also have good dispersibility. The anchoring effect of the carbon carrier prevents the particles from agglomerating, has high stability and is conducive to the exertion of the catalytic performance of the alloy nanoparticles.

[0098] Comparative Example 1

[0099] The present comparative example provides a rare earth-based binary nanoparticle, and the preparation method of the nanoparticle comprises:

[0100] 5 ml of oleylamine was poured into a 25 ml glass tube, then 7.8 mg of chloroplatinic acid and 6.5 mg of cerium nitrate were added, and the mixture was placed in an ultrasonic cleaner and ultrasonically treated at 100 kHz for 1 h to form a first reaction system (metal salt dissolved in oleylamine), then the mixture was placed in an oil bath and stirred at a speed of 500 rpm and heated to 120°C for a first heating treatment, and the temperature was maintained at 120°C for 1 h; then the temperature was increased to 250°C for a second heating treatment, and the temperature was maintained at 250°C for 3 h. The reaction product was cooled to room temperature, washed with a mixture of ethanol and hexane 8 times, and centrifuged at 10,000 r / min to obtain a rare earth-based binary nanoparticle.

[0101] Comparative Example 2

[0102] The present comparative example provides a rare earth-based binary nanoparticle, and the preparation method of the nanoparticle comprises:

[0103] Into a 25ml glass tube, 5ml oleylamine was poured, then 7.8mg chloroplatinic acid and 6.5mg cerium nitrate were added, and it was placed in an ultrasonic cleaner for 1h of ultrasonic treatment at 100kHz to form a first reaction system (metal salts were dissolved in oleylamine), then it was placed in an oil bath, and was stirred at a speed of 500rpm and heated to 120°C for a first heating treatment, and was kept at this temperature for 1h; then 5.7mg of sodium borohydride was added to form a second reaction system, and was heated to 250°C for a second heating treatment, and was kept at this temperature for 3h. The reaction product was cooled to room temperature, washed with a mixture of ethanol and hexane 8 times, and centrifuged at 10000r / min to obtain the rare earth-based binary alloy nanoparticles.

[0104] Comparative Example 3

[0105] This comparative example provides a kind of nanoparticles, and the preparation method of the nanoparticles includes:

[0106] Into a 25ml glass tube, 5ml oleylamine was poured, then 7.8mg chloroplatinic acid and 6.5mg cerium nitrate were added, and it was placed in an ultrasonic cleaner for 1h of ultrasonic treatment at 100kHz to form a first reaction system (metal salts were dissolved in oleylamine), then it was placed in an oil bath, and was stirred at a speed of 500rpm and heated to 120°C for a first heating treatment, and was kept at this temperature for 1h; then 5.7mg of sodium borohydride was added to form a second reaction system, and was heated to 250°C for a second heating treatment, and was kept at this temperature for 3h. The reaction product was cooled to room temperature, washed with a mixture of ethanol and hexane 8 times, and centrifuged at 10000r / min to obtain the rare earth-based binary alloy nanoparticles. Figure 6 The XRD pattern of the nanoparticles product of this comparative example is shown in Figure 3. Figure 7 The XRD pattern of the rare earth-based binary alloy nanoparticles of Example 1 is shown in Figure 2. It can be seen that the nanoparticles generated in Example 1 are platinum-cerium alloy nanoparticles, and the nanoparticles generated in this comparative example are platinum nanoparticles, not alloy particles.

[0107] Comparative Example 4

[0108] This comparative example provides a kind of rare earth-based binary alloy nanoparticles, and the preparation method of the nanoparticles is basically the same as that in Comparative Example 3, and the only difference is that 100mg of sodium borohydride is added to participate in the second heating treatment, and the rest of the experimental steps remain unchanged.

[0109] Specifically, the preparation method includes:

[0110] In a 25ml glass tube, 5ml of oleylamine was poured, followed by 7.8mg of chloroplatinic acid, 6.5mg of cerium nitrate, and 1.4mg of carbon black. The tube was then ultrasonically cleaned at 100kHz for 1 hour to form a first reaction system (in which the metal salts were dissolved in the oleylamine and the carbon black was evenly dispersed). The reaction system was then placed in an oil bath, stirred at 500rpm, and heated to 120°C for a first heat treatment, which was maintained at this temperature for 1 hour. 100mg of sodium borohydride was added to the first reaction system to form a second reaction system, which was then heated to 250°C for a second heat treatment, which was maintained for 3 hours. The reaction product was cooled to room temperature, washed eight times with a mixture of ethanol and hexane, and centrifuged at 10,000 rpm to obtain rare earth-based binary alloy nanoparticles.

[0111] Comparative Example 5

[0112] This comparative example provides a rare earth-based binary alloy nanoparticles. The preparation method of the nanoparticles is basically the same as the method in Example 1, except that the reaction temperature of the second heat treatment is increased to 300°C, and the other experimental steps remain unchanged to obtain rare earth-based binary alloy nanoparticles.

[0113] Comparative Example 6

[0114] This comparative example provides a rare earth-based binary alloy nanoparticle, and the preparation method of the nanoparticle comprises:

[0115] In a 25ml glass tube, 5ml of oleylamine was poured, followed by 7.8mg of chloroplatinic acid, 6.5mg of cerium nitrate, and 1.4mg of carbon black. The tube was then ultrasonically cleaned at 100kHz for 1 hour to form a first reaction system (in which the metal salts were dissolved in the oleylamine and the carbon black was evenly dispersed). The reaction system was then placed in an oil bath, stirred at 500rpm, and heated to 120°C for a first heat treatment, which was maintained at this temperature for 1 hour. 5.7mg of sodium borohydride was then added to the first reaction system to form a second reaction system. The temperature was then raised to 250°C for a second heat treatment, which was maintained for 8 hours. The reaction product was cooled to room temperature, washed eight times with a mixture of ethanol and hexane, and centrifuged at 10,000 rpm to obtain rare earth-based binary alloy nanoparticles.

[0116] Figure 8 is the SEM image of the nanoparticles. Figure 8 It can be seen that the nanoparticles generated in this comparative example are larger than 100 nm.

[0117] Comparative Example 7

[0118] This comparative example provides a nanoparticle, and the preparation method of the nanoparticle comprises:

[0119] Into a 25ml glass tube, 5ml oleylamine was poured, then 7.8mg chloroplatinic acid, 6.5mg cerium nitrate and 1.4mg carbon black were added, and the first reaction system was formed by putting it into an ultrasonic cleaner for 1h at 100kHz ultrasonic, then it was placed in an oil bath, and stirred at a speed of 500rpm and heated to 120°C for the first heating treatment, and kept at this temperature for 1h; then 5.7mg of sodium borohydride was added to the first reaction system, and heated to 250°C for the second heating treatment, and kept for 0.5h. The reaction product was cooled to room temperature, washed with a mixture of ethanol and hexane for 8 times, and centrifuged at 10000r / min to obtain the nanoparticle product. Figure 9 The SEM image of the nanoparticle is shown in Fig. 1. Figure 9 It can be seen from Fig. 1 that the size and morphology of the generated nanoparticles are inconsistent.

[0120] Comparative Example 8

[0121] This comparative example provides a rare earth-based binary alloy nanoparticle, and the preparation method of the nanoparticle is basically the same as that in Example 1, the difference is that the second heating treatment environment of this comparative example is air, and the rest of the experimental steps remain unchanged, and the product is obtained. Figure 10 The XRD result of the nanoparticle product is shown in Fig. 2. Figure 10 It can be seen from Fig. 2 that the rare earth oxide is generated in the nanoparticles synthesized in this comparative example.

[0122] The main experimental parameters of Comparative Examples 1 to 8 are summarized in Table 2.

[0123] Table 2 (the conditions of the first heating treatment are all 120°C, 1h)

[0124]

[0125] The morphology observation results of the nanoparticles of Comparative Examples 1 to 8 are summarized in Table 3.

[0126] Table 3

[0127]

[0128] From Table 2 and Table 3, it can be seen that the size of the rare earth-based binary alloy nanoparticles is related to the conditions of the second heating treatment (temperature and time), the proportion of each reactant in the first reaction system, and the amount of reducing agent in the second reaction system, and the specific analysis is as follows:

[0129] (1) From Example 1 and Comparative Example 2, it can be seen that when no carbon carrier is added, whether or not a reducing agent is added, and regardless of the amount of reducing agent used, the synthesized nanoparticles are in an agglomerated state, which shows that the addition of a carbon carrier plays a good anchoring role, which can reduce the combination trend between nanoparticles, thereby inhibiting agglomeration.

[0130] (2) From Example 3 and Comparative Example 4, it can be seen that under the premise of adding a carbon carrier, without adding a strong reducing agent, only platinum nanoparticles are generated under the reduction of oleylamine, and the rare earth metal ions are not reduced; when the amount of strong reducing agent is gradually increased to 100 mg, the size of the nanoparticles becomes uneven, which is due to the influence of the concentration of the reducing agent on the reaction kinetics. The higher the concentration of the reducing agent, the stronger the driving force for the reaction process, and the growth of the obtained nanoparticles is not controlled. This comparison result shows that i) without adding a strong reducing agent, only relying on the relatively weak reduction ability of oleylamine cannot reduce the rare earth elements, and the reduction of rare earth elements requires the presence of a strong reducing agent; ii) the addition amount of the strong reducing agent relative to the metal salt has a regulating effect on the formation and size of the rare earth-based alloy nanoparticles.

[0131] (2) From Example 5 and Comparative Example 6, it can be seen that a second heating treatment at too high a temperature (Comparative Example 5) or for too long a time (Comparative Example 6) will result in the generation of nanoparticles with uneven morphology, especially in Comparative Example 6, because the second heating treatment time is extended to 8 h, the growth of the nanoparticles becomes uncontrolled, and the size of the nanoparticles increases significantly to 100 nm. This result shows that by controlling the reaction time and temperature of the second heating treatment, the formation process of the rare earth-based alloy nanoparticles can be controlled, which is beneficial to obtaining rare earth-based alloy nanoparticles with a particle size of 30-70 nm, uniform morphology, and good dispersity.

[0132] (3) From Comparative Example 7, it can be seen that the particle size is uneven when the second heating treatment is only reacted for 0.5 h. This shows that too short a reaction time causes the rare earth particles not to combine fully with the platinum particles generated by the first heating treatment.

[0133] (4) From Comparative Example 8, it can be seen that the reaction is carried out in an air environment that is not vacuum and does not remove oxygen, and rare earth oxides are obtained due to the presence of oxygen in the air. This shows that the presence of oxygen makes it easy to form rare earth oxides, and by controlling the reaction atmosphere of the second heating treatment, oxygen can be removed to avoid the oxidation of metal ions, which is beneficial to the synthesis of rare earth-based alloy nanoparticles.

[0134] Test Example

[0135] The catalytic performance of the nano-alloys obtained in Example 1 (platinum cerium, PtCe) and Example 14 (platinum praseodymium, PtPr) in generating hydrogen under alkaline conditions was investigated using a three-electrode system, and Pt / C (Pt: 20 wt %) was used as a control test. Figure 11 Polarization curves of the hydrogen evolution reaction of the Pt / Ce alloy nanoparticles obtained in Example 1, the Pt / Pr alloy nanoparticles obtained in Example 14, and commercial Pt / C (PubChem No. 23939, brand Aladdin, EC No. 231-116-1) under alkaline conditions.

[0136] like Figure 11 As shown, the rare earth alloy nanoparticles provided in Example 1 and Example 14 have a higher starting potential than commercial Pt / C as a catalyst, and at a current density of -10 mA·cm -2 The corresponding overpotential is the smallest when the catalyst is 100 nm, and the catalytic activity is higher. This indicates that the hollow nano-alloy provided by the present invention has better catalytic performance than the commercial Pt / C catalyst when used as a hydrogen production catalyst.

Claims

1. A method for preparing rare earth alloy nanoparticles, wherein: The preparation method comprises: mixing a metal salt, a carbon carrier, and an organic solvent to form a first reaction system, and performing a first heating treatment; adding a reducing agent to the first reaction system that has undergone the first heating treatment in a protective atmosphere to form a second reaction system, and performing a second heating treatment on the second reaction system to obtain the rare earth-based alloy nanoparticles; Wherein, the metal salt includes platinum salt and rare earth metal salt; The molar ratio of the metal salt to the reducing agent is 0.1-1:1; The temperature of the first heating treatment is 120-150° C., and the time of the first heating treatment is 1-2 hours; the temperature of the second heating treatment is 230-260° C., and the time of the second heating treatment is 2-5 hours.

2. The preparation method according to claim 1, wherein The molar ratio of the platinum salt to the rare earth metal salt is 1-2:

1.

3. The preparation method according to claim 1, wherein The rare earth elements in the rare earth metal salt include one or a combination of two or more of lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, scandium and yttrium.

4. The preparation method according to claim 3, wherein The rare earth metal salt includes cerium salt and / or praseodymium salt.

5. The preparation method according to claim 1, wherein The carbon support includes carbon black.

6. The preparation method according to claim 1, wherein The molar ratio of the metal salt to the carbon support is 1:2.5-4.

7. The preparation method according to claim 1, wherein The reducing agent includes sodium borohydride.

8. The preparation method according to claim 1, wherein The molar ratio of the metal salt to the reducing agent is 0.2-1:1 or 0.1-0.5:

1.

9. The preparation method according to claim 1, wherein The organic solvent includes oleylamine.

10. Rare earth-based alloy nanoparticles, which are obtained by the preparation method of rare earth-based alloy nanoparticles according to any one of claims 1 to 9.

11. The rare earth-based alloy nanoparticles according to claim 10, wherein: The particle size of the rare earth-based alloy nanoparticles is 30nm-70nm.

12. The rare earth-based alloy nanoparticles according to claim 11, wherein The particle size of the rare earth-based alloy nanoparticles is 40-60 nm.

13. A catalyst comprising the rare earth-based alloy nanoparticles according to any one of claims 10 to 12 or made from the rare earth-based alloy nanoparticles according to any one of claims 10 to 12.

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