A noble metal catalyst, a preparation method and application thereof

Abstract

The application relates to a noble metal catalyst and a preparation method and application thereof, and belongs to the technical field of catalysts. The catalyst comprises a carrier and an active component; wherein the active component is at least one of noble metals of ruthenium, rhodium, palladium, silver, iridium, platinum, gold and osmium; the carrier is at least one of carbon carriers, metal oxide carriers, adsorbents, semiconductors, ceramics, natural minerals and covalent organic framework compounds, and the surface area of the carrier is greater than or equal to 200 cm 2 / g. The mass percentage of the active component in the catalyst is 0.001% to 50%. The obtained noble metal catalyst shows high selectivity to single product formation, and the FE of CO2 reduction to ethanol reaches more than 90%. The noble metal catalyst has excellent oxygen evolution activity and stability. On the other hand, the preparation method of the noble metal catalyst is simple, energy consumption is low, and a single-atom catalyst with high dispersion or noble metal nanoparticles with low loading can be prepared.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, specifically relating to a noble metal catalyst, its preparation method, and its application. Background Technology

[0002] Noble metal catalysts (such as platinum, palladium, and rhodium) have become core catalytic materials in fuel cells, water electrolysis for hydrogen production, electrocatalytic carbon dioxide reduction, and fine chemical industries due to their unique d-orbital electronic structure and excellent surface adsorption-activation capabilities. However, the large-scale application of traditional noble metal catalysts faces multiple challenges: First, noble metal resources are extremely scarce, with the global annual production of platinum group metals being less than 400 tons, resulting in high catalyst costs. Reducing the noble metal loading will help alleviate resource and production pressures. Second, the atomic utilization rate of active sites dispersed in nanoparticle form is less than 20%, and agglomeration easily occurs under high-temperature sintering conditions. For example, at 800 °C, the particle size of Pt increases to more than five times its initial size, leading to a decrease in specific activity of over 70%. Therefore, catalyst preparation technologies at lower temperatures are required. Third, the strong adsorption of poisoning substances such as sulfides and CO can cause deactivation of active sites, affecting catalytic performance. Current research focuses on support optimization (such as nitrogen-doped carbon), core-shell structure design (Pt@Pd), and alloying strategies (PtNi). While these approaches have partially improved catalyst stability and atom economy, their durability under harsh conditions (such as high potential and strongly acidic environments) still falls short of industrialization requirements. Single-atom catalysts, by anchoring precious metals as isolated atoms on the support surface, can achieve near 100% atom utilization, a 3-fold increase in poisoning resistance, and a significant reduction in the amount of precious metals required. Summary of the Invention

[0003] To address the aforementioned problems in the background art, the present invention aims to provide a noble metal catalyst, its preparation method, and its application. This noble metal single-atom catalyst can achieve highly selective and efficient carbon dioxide conversion, promoting the formation of high-energy-density and high-value hydrocarbons. Furthermore, it enables the preparation and application of low-loading noble metal catalysts. Simultaneously, the catalyst of this invention can be used in low-overpotential PEM water electrolysis or oxygen reduction fuel cells, achieving long-term operation at high energy densities.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] A noble metal catalyst, comprising a support and an active component; wherein the active component is at least one of the noble metals ruthenium, rhodium, palladium, silver, iridium, platinum, gold, and osmium, which have catalytic activity; the support is at least one of carbon support, metal oxide support, adsorbent, semiconductor, ceramic, natural mineral, and covalent organic framework compound, and the surface area of ​​the support is ≥200 cm². 2 / g, preferably 1 m 2 / g to 800 m 2 / g. Further, the carbon in the carbon support is selected from at least one of carbon powder, carbon black (preferably Vulcan XC-72), Ketjen black, graphene, carbon nanotubes, and carbon supports formed by sintering metal-organic framework compounds; the metal oxide in the metal oxide support is selected from at least one of alkali metal oxides, alkaline earth metal oxides, main group metal oxides, transition metal oxides, and lanthanide metal oxides; more preferably, it is selected from at least one of Al2O3, TiO2, and CeO2.

[0006] Further, the active component accounts for 0.001% to 50% of the mass percentage of the catalyst, preferably 0.01% to 5% by mass.

[0007] A method for preparing a noble metal catalyst as described above includes the following steps:

[0008] S1: Melt alkali metals by heating under an inert atmosphere;

[0009] S2: Add the precursor of the precious metal to the molten alkali metal obtained in S1 in proportion, disperse it evenly under heat preservation and then cool it.

[0010] S3: The precious metal-alkali metal mixture obtained in S2 is placed in humidified air for more than 12 hours to convert it into alkali metal hydroxide / alkali metal salt-precious metal mixture;

[0011] S4: Mix the alkali metal hydroxide / alkali metal salt-noble metal mixture obtained in S3 with the carrier;

[0012] S5: The mixture obtained from S4 is washed with deionized water to remove alkali metal hydroxides and alkali metal salts, and then dried to obtain a noble metal catalyst.

[0013] Further, in step S1, the alkali metal is at least one of lithium, sodium, potassium, rubidium, or cesium; the inert atmosphere is at least one of argon, nitrogen, helium, or neon; and the heating temperature is 200~500℃.

[0014] Further, in step S2, the precursor of the precious metal includes at least one of elemental ruthenium, rhodium, palladium, silver, iridium, platinum, gold, and rhenium, or at least one of the following: nitrate, nitrite, hydrochloride, perchlorate, chlorate, hypochlorite, phosphate, sulfate, sulfite, carbonate, organic salt, sulfide, nitride, bromide, iodide, phosphide, fluoride, and metal oxide of ruthenium, rhodium, palladium, silver, iridium, platinum, gold, and rhenium; the method of uniform dispersion is stirring or ultrasonic dispersion. Preferably, the ultrasonic dispersion frequency is 5~100kHz, and the stirring rate is 50~800 rpm.

[0015] Further, in step S2, the mass ratio of the alkali metal to the noble metal precursor is greater than 50%, preferably, the mass ratio of the alkali metal to the noble metal precursor is greater than 90%; the heat preservation time is 1~7h.

[0016] Furthermore, in step S3, the air humidity is 10%~80%.

[0017] Further, in step S4, the mass ratio of the alkali metal hydroxide / alkali metal salt-noble metal mixture to the carrier is 0.05:1 to 10:1; the mixing method is physical mixing such as manual grinding or ball milling, until the carrier is completely and uniformly dispersed.

[0018] Further, in step S5, the drying conditions are vacuum drying or ordinary drying, and the temperature is 50~100℃. Preferably, the drying method is vacuum drying.

[0019] The application of a noble metal catalyst as described above or a noble metal catalyst prepared by the above preparation method as an electrocatalyst, wherein the catalyst is used as at least one of the following applications: electrocatalyst for CO2 electrocatalytic reduction, electrocatalyst for water electrolysis to produce hydrogen, and oxygen reduction electrocatalyst for fuel cells.

[0020] Compared with existing technologies, the beneficial effects of this invention are as follows: On the one hand, the noble metal catalyst improves the selectivity and conversion efficiency of electrocatalytic reduction of carbon dioxide to high-value hydrocarbons such as ethanol. The noble metal catalyst obtained by this invention exhibits high selectivity for the formation of a single product, with an FE of over 90% for CO2 reduction to ethanol. The noble metal catalyst also possesses excellent oxygen evolution activity and stability, maintaining a stable oxygen evolution rate at 10 mA·cm⁻¹ after 5000 cyclic voltammetry cycles. -2 The overpotential decreases by only 10 mV. On the other hand, the method for preparing noble metal catalysts provided by this invention is simple, energy-efficient, and can prepare highly dispersed single-atom catalysts or noble metal nanoparticles with low loading. Attached Figure Description

[0021] Figure 1 The image shown is a transmission electron microscope (TEM) image of the palladium single-atom catalyst prepared in Example 1 of the present invention.

[0022] Figure 2 The time-current density curve of the palladium single-atom catalyst prepared in Example 1 of the present invention is shown.

[0023] Figure 3 The distribution of electrocatalytic carbon dioxide reduction products and Faraday efficiency of the palladium single-atom catalyst prepared in Example 1 of the present invention are shown.

[0024] Figure 4 Linear sweep voltammetry (LSV) curves of the Ir / C catalyst prepared in Example 2 of this invention and commercial iridium black are shown.

[0025] Figure 5 The linear sweep voltammetry (LSV) curve of the Ir / C catalyst prepared in Example 2 of the present invention after 5000 cyclic voltammetry cycles is shown.

[0026] Figure 6 The linear sweep voltammetry (LSV) curve of the cerium oxide platinum-supported catalyst Pt / CeO2 prepared in Example 3 of the present invention is shown.

[0027] Figure 7 The electrocatalytic carbon dioxide reduction product distribution and Faraday efficiency images of the gallium nitride-supported silver single-atom catalyst prepared in Example 5 of the present invention and the commercial carbon-supported silver single-atom catalyst of Comparative Example 2 are shown. Detailed Implementation

[0028] The embodiments of the present invention will be described below with reference to the accompanying drawings and preferred embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are only for illustrating the present invention and not for limiting the scope of protection of the present invention.

[0029] Example 1:

[0030] A method for preparing a palladium single-atom catalyst, comprising the following steps:

[0031] (1) Prepare the experimental environment. The palladium single-atom catalyst was prepared in an anhydrous and oxygen-free glove box to prevent it from reacting with moisture and oxygen in the air.

[0032] (2) Melting lithium metal. The appropriate mass of lithium metal is placed in a nickel crucible and slowly heated at a certain temperature to completely melt the lithium. The mass of lithium metal is 5g and the temperature is 250℃. Since lithium has the largest range between its melting point and boiling point, it is preferred to add it to the melt as a melting medium (usually referred to as lithium melt).

[0033] (3) Weigh 200 mg of PdCl2. Immerse palladium chloride in molten lithium and wait for it to react with metallic lithium and melt completely.

[0034] (4) Homogenization treatment. The mixture of palladium metal after the displacement reaction with molten lithium and lithium chloride is kept at 250°C for 2 hours to ensure that palladium metal is completely and uniformly dispersed in lithium. Then it is poured onto a stainless steel plate and left to cool.

[0035] (5) Palladium conversion. A mixture of palladium and lithium metal / lithium chloride was placed in a humidifier to convert it into hydroxide, with the air humidity being 40%. 15g of XC-72 carbon powder was weighed and manually ground with the above mixture for 1 h. Then, the salt in the mixture was rinsed off with 500mL of deionized water and dried to obtain a Pd / C catalyst with a Pd content of 0.8 wt%.

[0036] Example 2:

[0037] A method for preparing a carbon-supported iridium Ir / C catalyst, wherein the method is as follows: the difference between this embodiment and Example 1 is that the temperature in step (2) is changed to 270℃; 200 mg PdCl2 in step (3) is replaced with 0.6 g Ir(CH3COO)3; 15 g XC-72 carbon powder in step (5) is replaced with 50 g carbon powder, wherein the iridium loading is 0.6wt%, and other conditions are consistent with Example 1.

[0038] Example 3:

[0039] A method for preparing a cerium oxide-supported platinum catalyst Pt / CeO2, wherein the method is as follows: the difference between this embodiment and Example 1 is that 200mg PdCl2 in step (3) is replaced with 1g PtCl4; 15g XC-72 carbon powder in step (5) is replaced with 25.5g CeO2; the grinding is replaced with ball milling at 500rpm for 10h, cooling for 10min every 20min, ball-to-material ratio of 20:1 (ZrO2 grinding balls), wherein the platinum loading is 1.9wt%, and other conditions are consistent with Example 1.

[0040] Example 4:

[0041] A method for preparing a ruthenium single-atom catalyst, wherein the method is as follows: the difference between this embodiment and Example 1 is that 200 mg PdCl2 in step (3) is replaced with 1 g RuBr3; 15 g XC-72 carbon powder in step (5) is replaced with 10.2 g TiO2, and other conditions are the same as in Example 1.

[0042] Example 5:

[0043] A method for preparing a gallium nitride-supported silver single-atom catalyst, wherein the method is as follows: the difference between this embodiment and embodiment 1 is that 200 mg PdCl2 in step (3) is replaced with 1 g AgCl; 15 g XC-72 carbon powder in step (5) is replaced with 23.2 g GaN, and other conditions are the same as in embodiment 1.

[0044] In Test Example 1, the palladium single-atom catalyst prepared in Example 1 was used to test its carbon dioxide reduction performance in an H-type electrolyzer with a carbon dioxide-saturated bicarbonate solution (pH 6.8) using an electrochemical workstation. The initial scan rate was 100 mV / s, and linear sweep voltammetry (LSV) was performed from 0 to -1.3 V (compared to the standard hydrogen electrode). All potentials in the test results were adjusted to the potential relative to the reversible hydrogen electrode (vs. RHE). Chronoamperometry was performed between -0.4 V and -0.8 V for 4000 s, and the product was collected afterward to ensure the stability of the catalyst and the complete formation of the resulting hydrocarbons.

[0045] Test Example 2: The carbon-supported iridium Ir / C catalyst prepared in Example 2 was selected, and the water electrolysis reaction was tested using a rotating disk electrode. A catalyst slurry was prepared using 5 mg of catalyst + 60 μL of 5‰ perfluorinated sulfonate (nafion) + 2 mL of isopropanol. The glassy carbon electrode used had an area of ​​0.07 cm². 2 Electrochemical ionization (OER) tests were performed using an electrochemical workstation. Linear sweep voltammetry (LSV) measurements were conducted in a 0.5 M H₂SO₄ electrolyte solution, with a scan range of 1.0–1.8 V and a scan rate of 5 mV / s. Mercurous sulfate, platinum wire, and glassy carbon electrodes were used as the reference, counter, and working electrodes, respectively. The catalyst current density was recorded to reach 10 mA·cm⁻¹. -2 The overpotential below.

[0046] Comparative Example 1 uses a commercially available iridium black catalyst as a comparative example. Other test conditions and methods are the same as in Test Example 2.

[0047] Test Example 3: The cerium oxide platinum-supported catalyst prepared in Example 3 was selected. The results are shown in […]. Figure 3 When evaluating the oxygen reduction reaction (ORR) performance of the catalyst using an electrochemical workstation, a rotating disk electrode with the catalyst supported was used as the working electrode, a platinum ring electrode as the counter electrode, and an Hg / HgO electrode as the reference electrode. Before starting the electrochemical tests, high-purity oxygen was bubbled into the electrolyte for 30 minutes to ensure full oxygen saturation. The electrolyte used in the experiment was a 0.1 mol / L KOH solution. Linear sweep voltammetry was used for measurements at a scan rate of 5 mV / s, with the voltage range set between 0.2 V and -0.8 V, and the scan direction was negative.

[0048] Test Example 4: The ruthenium single-atom catalyst prepared in Example 4 was used for electrochemical performance testing. Other test conditions and methods were the same as in Test Example 2. It exhibited excellent activity and stability in an acidic water oxidation environment. The catalyst performed well at a current density of 10 mA·cm⁻¹. -2 The overpotential at that time was only 215mV.

[0049] In Test Example 5, the gallium nitride-supported silver single-atom catalyst prepared in Example 5 was used for electrochemical performance testing. Other test conditions and methods were the same as in Test Example 1. The prepared silver single-atom catalyst exhibited a selectivity of 80.6% for the electrocatalytic reduction of carbon dioxide to ethanol at a low overpotential of -0.4 V.

[0050] Comparative Example 2 uses a commercial carbon-supported silver single-atom catalyst as a comparative example. Other test conditions and methods are the same as in Test Example 5.

[0051] Figure 1 This is a transmission electron microscope (TEM) image of the palladium single-atom catalyst prepared in Example 1. It can be seen that the prepared Pd is distributed in single-atom form on the amorphous carbon matrix, and no aggregated Pd is observed.

[0052] Figure 2 The time-current density curve of the palladium single-atom catalyst prepared in Example 1 of this invention is shown. The catalyst can still operate stably within 18 hours, indicating that the palladium single-atom catalyst has good stability for electrocatalytic carbon dioxide reduction.

[0053] Figure 3 The distribution of electrocatalyst carbon dioxide reduction products and Faraday efficiency of the palladium single-atom catalyst prepared in Example 1 of this invention are shown. The palladium single-atom catalyst exhibits high selectivity and high efficiency for the electrocatalytic reduction of carbon dioxide to ethanol, achieving a high selectivity of 90% for the conversion of carbon dioxide to ethanol at a low overpotential of -0.6V.

[0054] Figure 4 The Ir / C catalyst prepared in Example 2 of this invention and the catalyst in Comparative Example 1 are shown at 10 mA·cm⁻¹. -2 The overpotential of the Ir / C catalyst prepared in this invention was 272 mV, while that of commercial iridium black was 310 mV, as shown by the linear sweep voltammetry (LSV) curve.

[0055] Figure 5 The linear sweep voltammetry (LSV) curve of the Ir / C catalyst prepared in Example 2 of this invention after 5000 cyclic voltammetry cycles is shown at 10 mA·cm⁻¹. -2 The overpotential decayed by only 10mV under the given conditions, indicating that the catalyst prepared in this invention has excellent stability.

[0056] Figure 6 The linear sweep voltammetry (LSV) curve of the cerium oxide platinum-supported catalyst Pt / CeO2 prepared in Example 3 of this invention is shown. The catalyst exhibits a high half-wave potential of 0.89 V, and its catalytic activity hardly decayed after 3000 cycles, demonstrating good structural stability.

[0057] Figure 7 The images show the electrocatalytic carbon dioxide reduction product distribution and Faraday efficiency of the gallium nitride-supported silver single-atom catalyst prepared in Example 1 of this invention and the commercial carbon-supported silver single-atom catalyst in Comparative Example 2. The catalyst prepared in this invention exhibits high selectivity and high efficiency for the electrocatalytic reduction of carbon dioxide to ethanol, achieving 80% selectivity for ethanol conversion at a low overpotential of -0.4 V. In contrast, the commercial carbon-supported silver catalyst only produces carbon monoxide, indicating that the catalyst of this invention possesses a unique structural advantage for the electrocatalytic conversion of carbon dioxide to higher-value hydrocarbons.

[0058] It should be noted that the above embodiments are merely preferred embodiments for fully illustrating the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention.

[0059] While this specification contains numerous specific implementation details, it should not be construed as a limitation on the scope or declarable content of any invention, but rather as a specific description of the characteristics of a particular implementation of a particular invention. Some characteristics described in this specification in the context of a single implementation may also be implemented in combination within a single implementation. Conversely, various characteristics described in the context of a single implementation may also be implemented individually in multiple implementations or in any suitable sub-combination. Furthermore, although the aforementioned features may be described as functioning in certain combinations, or even originally required, in certain circumstances one or more features in a declared combination may be removed from that combination, and a declared combination may refer to a sub-combination or a variation of a sub-combination.

Claims

1. A method for preparing a noble metal catalyst, characterized in that: The catalyst comprises a support and an active component; wherein the active component is at least one of the noble metals ruthenium, rhodium, palladium, silver, iridium, platinum, gold, and osmium; the support is at least one of the following: carbon support, metal oxide support, adsorbent, semiconductor, ceramic, natural mineral, and covalent organic framework compound, and the surface area of ​​the support is ≥200 cm². 2 / g; The method includes the following steps: S1: The alkali metal is heated and melted under an inert atmosphere to obtain molten alkali metal; S2: Add the precursor of the noble metal to the molten alkali metal obtained in S1 in proportion, so that the non-elemental noble metal precursor and the molten alkali metal undergo an in-situ reduction / displacement reaction to generate elemental noble metal and alkali metal salt. After being uniformly dispersed under heat preservation, the mixture is cooled to obtain a mixture containing noble metal, alkali metal and alkali metal salt. The precursors of the precious metals include at least one of the following: hydrochloride, bromide, iodide, fluoride, organic salt, nitrate, sulfate, carbonate, and phosphate of ruthenium, rhodium, palladium, silver, iridium, platinum, gold, and rhenium; S3: The mixture containing noble metals, alkali metals, and alkali metal salts obtained in S2 is placed in humidified air for more than 12 hours to convert the alkali metals into alkali metal hydroxides, while retaining the alkali metal salts, resulting in a mixture containing alkali metal hydroxides, alkali metal salts, and noble metals; the humidity of the air is 10%~80%. S4: The mixture obtained in S3, which contains alkali metal hydroxide, alkali metal salt and noble metal, is mixed with the carrier to disperse the noble metal species on the surface of the carrier. S5: The mixture obtained from S4 is washed with deionized water to remove alkali metal hydroxides and alkali metal salts, and then dried to obtain a noble metal catalyst.

2. The method for preparing the noble metal catalyst according to claim 1, characterized in that: The active component accounts for 0.001% to 50% of the mass of the catalyst.

3. The method for preparing the noble metal catalyst according to claim 1, characterized in that: In step S1, the alkali metal is at least one of lithium, sodium, potassium, rubidium, or cesium; the inert atmosphere is at least one of argon, nitrogen, helium, or neon; and the heating temperature is 200~500℃.

4. The method for preparing the noble metal catalyst according to claim 1, characterized in that: In step S2, the method of achieving uniform dispersion is stirring or ultrasonic dispersion.

5. The method for preparing the noble metal catalyst according to claim 1, characterized in that: In step S2, the mass ratio of the alkali metal to the noble metal precursor is greater than 50%; the heat preservation time is 1~7h.

6. The method for preparing the noble metal catalyst according to claim 1, characterized in that: In step S4, the mass ratio of the mixture containing alkali metal hydroxide, alkali metal salt and noble metal to the carrier is 0.05:1 to 10:1; the mixing method is manual grinding or ball milling, and the mixture is mixed until the carrier is completely and uniformly dispersed.

7. The method for preparing the noble metal catalyst according to claim 1, characterized in that: In step S5, the drying conditions are vacuum drying or ordinary drying, and the temperature is 50~100℃.

8. The application of a noble metal catalyst prepared by the preparation method according to any one of claims 1 to 7 as an electrocatalyst, characterized in that: The catalyst is used in at least one of the following applications: electrocatalytic reduction of CO2, electrocatalyst for hydrogen production by water electrolysis, and oxygen reduction electrocatalyst for fuel cells.

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