A method for preparing a metal / cerium dioxide single-atom catalyst

Abstract

The application discloses a preparation method of a metal / cerium dioxide monatomic catalyst, which comprises the following steps: mixing an inorganic alkali solution and a cerium nitrate solution to perform hydrolysis, and then performing centrifugation, washing and drying to obtain Ce(OH)3; uniformly dispersing the Ce(OH)3 in a metal salt solution, and then performing stirring, centrifugation, washing and freeze-drying to obtain a metal precursor / cerium hydroxide; and performing a decomposition reaction on the cerium hydroxide under an inert gas to obtain a metal monatomic / cerium dioxide. 3+ The Ce on the surface of the cerium dioxide in the process is subjected to electron transfer with the adsorbed metal ions, and the metal ions are reduced; and then the metal / cerium dioxide monatomic catalyst is obtained by placing in air. The cerium dioxide is used as a carrier precursor, the metal monatomic is in-situ loaded on the cerium dioxide nanostructure through the electron transfer effect between the cerium dioxide and the metal ions, and a reducing agent is not additionally added, so that the preparation process is simple and mild, and the method has good controllability and industrial application prospect.

Description

Technical Field

[0001] This invention relates to the field of catalyst preparation technology, and in particular to a method for preparing a metal / cerium dioxide single-atom catalyst. Background Technology

[0002] Cerium dioxide (CeO2) is an important rare-earth oxide material, possessing N-type semiconductor properties, a unique 4f electronic structure, and CeO2. 3+ / Ce 4+ With its reversible conversion characteristics, cerium dioxide exhibits excellent oxygen storage and release capabilities as well as charge exchange capacity, making it a promising catalyst support for industrial catalysis. Realizing the existence of metal active centers as single atoms on the cerium dioxide surface is of significant research importance for maximizing metal atom utilization and reducing catalyst costs (Chem. Rev. 2020, 120, 11986−12043). For example, Wang et al. (ACS Catal. 2018,8, 7113−7119) found that copper / cerium dioxide single-atom catalysts exhibited excellent catalytic performance in the electroreduction of carbon dioxide to methane, with a current density of 30 mA / cm². -2 The Faraday efficiency for methane was 58%. Giulia Spezzati et al. (Applied Catalysis B: Environmental 2019, 243, 36–46) prepared a palladium / cerium dioxide single-atom catalyst that showed catalytic activity for CO oxidation at room temperature, achieving 100% CO conversion at 150 °C. Chen et al. (J. Am. Chem. Soc. 2021, 143, 12074–12081) found that a ruthenium / cerium dioxide single-atom catalyst exhibited high catalytic activity in the methanol steam reforming reaction, achieving a CO2 selectivity of 99.5% at 200 °C and a hydrogen production rate of 579 mL at 350 °C. H2 g Ru -1 s -1 However, the synthesis of metal / cerium dioxide single-atom catalysts currently faces challenges such as harsh reaction conditions, difficulty in scale-up preparation, uncontrollable loading, and poor catalyst stability, all of which urgently need to be addressed. Based on this current research status, seeking a simple method to prepare metal / cerium dioxide single-atom catalysts and imparting unique catalytic properties by introducing strong metal-support interactions (SMSI) to improve catalyst stability is of great significance.

[0003] In view of this, the present invention is hereby proposed. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention aims to provide a simple method for preparing metal / cerium dioxide single-atom catalysts, thereby solving the problems of the existing preparation methods. By obtaining a reducing cerium trioxide support precursor, metal single atoms are firmly loaded onto the cerium dioxide nanostructure in situ through a redox reaction with metal ions, thus preparing a metal / cerium dioxide single-atom catalyst.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] The provided method for preparing metal / cerium dioxide single-atom catalysts includes the following steps:

[0007] 1) Under inert gas conditions, an inorganic alkaline solution and a cerium(III) salt solution in a certain molar ratio are mixed and hydrolyzed to obtain cerium(III) hydroxide;

[0008] 2) Under inert gas conditions, cerium hydroxide is uniformly dispersed in the solution of the metal precursor. After stirring, centrifugation, washing, and freeze-drying are performed to obtain the metal precursor / cerium hydroxide.

[0009] 3) Under inert gas conditions, cerium hydroxide (III) from step 2) is pyrolyzed to obtain cerium trioxide. During this process, cerium trioxide undergoes a redox reaction with the metal precursor to obtain a metal single atom / cerium trioxide composite material.

[0010] 4) Place the obtained metal single-atom / cerium trioxide composite catalyst in air to oxidize cerium trioxide to cerium dioxide, thereby obtaining a metal / cerium dioxide single-atom catalyst.

[0011] Furthermore, the inorganic base in step (1) includes one or more of sodium hydroxide, potassium hydroxide, ammonia, hexamethylenetetramine, and urea; the cerium (III) salt includes one or more of cerium (III) nitrate, cerium (III) sulfate, cerium (III) carbonate hydrate, cerium (III) oxalate hydrate, and cerium (III) acetate hydrate.

[0012] Furthermore, in step (1), the molar ratio of cerium(III) salt to inorganic base is 1:25 to 25:1.

[0013] Furthermore, the reaction temperature in step (1) is room temperature - 180°C, and the reaction time is 24-48 hours.

[0014] The metal precursor refers to a substance that can be reduced by cerium trioxide, specifically selected from any of the following metal precursors: chloroauric acid, chloroplatinic acid, ruthenium chloride, chloroiridium acid, potassium chloropalladium, hydrated rhodium chloride, copper nitrate, and silver nitrate.

[0015] Furthermore, by changing the reaction temperature, time, and molar ratio of cerium nitrate to inorganic alkali in step (1), cerium dioxide nanomaterials with different morphologies can be obtained, such as nanopolyhedra, nanorods, nanocubes, and nanoporous structures.

[0016] Furthermore, the molar ratio of cerium hydroxide to the metal precursor in step (2) is (25:2)-(100:1).

[0017] Furthermore, the dispersion process in step 2) is carried out in a solvent, the specific solvent being determined by the solubility characteristics of the metal precursor; by controlling the concentration of the metal precursor solution, controllable loading of metal single atoms on cerium dioxide material can be achieved, resulting in metal / cerium dioxide single-atom catalysts with different loading amounts.

[0018] Furthermore, to prevent cerium(III) hydroxide from being oxidized by oxygen in the air, the dispersion process after adding cerium(III) hydroxide should be carried out under inert gas protection conditions.

[0019] Furthermore, the process described in step (3) is carried out in a tube furnace at a temperature between 200-450°C, preferably 350°C, for a reaction time of 2 hours.

[0020] The present invention also provides a metal / cerium dioxide single-atom catalyst prepared using the above method.

[0021] The present invention specifically prepares a metal / cerium dioxide single-atom catalyst as follows: A certain mass (0.4 g or 1 g) of cerium nitrate is placed in a reactor to prepare a cerium nitrate aqueous solution; after deoxygenation, a certain mass (1 g or 0.12 g) of sodium hydroxide aqueous solution is added to the reactor and mixed evenly; the temperature is raised to a certain temperature (110℃-180℃) and maintained for 48 hours; after cooling, it is centrifuged, washed, and freeze-dried to obtain cerium(III) hydroxide; under nitrogen protection, cerium(III) hydroxide is dispersed in a metal precursor solution, stirred for 10 hours, centrifuged, washed, and freeze-dried; then calcined in a tube furnace at 350℃ for 2 hours under an argon atmosphere; subsequently exposed to air to obtain a metal / cerium dioxide single-atom catalyst.

[0022] The beneficial effects of this invention are as follows: This invention directly utilizes cerium(III) salt as a raw material to generate cerium trioxide nanostructures with reducing capabilities. Using these nanostructures as a carrier, metal or multi-metal single atoms are firmly loaded onto the cerium dioxide nanostructures in situ through a redox reaction via electron transfer with metal ions, thus preparing a metal / cerium dioxide single-atom catalyst. This method requires no additional reducing agent, does not introduce other impurities, and operates under mild reaction conditions. Compared to other methods, this method is simple, controllable, and conducive to industrial scale-up. Attached Figure Description

[0023] Figure 1Transmission electron microscopy (TEM) image of the silver / cerium dioxide single-atom catalyst prepared in Example 1.

[0024] Figure 2 Elemental distribution analysis of the silver / cerium dioxide single-atom catalyst prepared in Example 1.

[0025] Figure 3 The photoelectron spectrum of Ag3d in the silver / cerium dioxide single-atom catalyst prepared in Example 1.

[0026] Figure 4 Transmission electron microscopy image of the platinum / cerium dioxide single-atom catalyst prepared in Example 14.

[0027] Figure 5 Elemental distribution analysis of the platinum / cerium dioxide single-atom catalyst prepared in Example 14.

[0028] Figure 6 The photoelectron spectrum of Pt4f in the platinum / cerium dioxide single-atom catalyst prepared in Example 14.

[0029] Figure 7 Transmission electron microscopy image of the gold / cerium dioxide single-atom catalyst prepared in Example 17.

[0030] Figure 8 Transmission electron microscopy image of the ruthenium / cerium dioxide single-atom catalyst prepared in Example 18.

[0031] Figure 9 Elemental distribution analysis of the ruthenium / cerium dioxide single-atom catalyst prepared in Example 18. Detailed Implementation

[0032] The present invention will be further described below with reference to specific embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make some non-essential improvements and adjustments based on the above-described invention.

[0033] Example 1

[0034] The preparation method of the silver / cerium dioxide single-atom catalyst in this embodiment is as follows:

[0035] (1) Place 2 mL of cerium nitrate aqueous solution (containing 0.4 g of cerium nitrate, 1 mmol) in a reactor to remove oxygen. Under anaerobic conditions, add 2 mL of sodium hydroxide aqueous solution (containing 1 g of sodium hydroxide, 25 mmol) to the reactor and mix well. Heat the mixed solution to 110 °C and maintain it for 48 hours. After cooling, wash with water to remove excess sodium hydroxide and freeze-dry to obtain cerium hydroxide powder.

[0036] (2) Take 0.2 g (1 mmol) of cerium hydroxide and disperse it evenly in 20 mL of silver nitrate aqueous solution (containing 0.008 g, 0.05 mmol of silver nitrate), then remove oxygen and stir for 10 hours under anaerobic conditions; wash with water and freeze dry;

[0037] (3) The obtained powder was calcined at 350°C for 2 hours in an argon atmosphere in a tube furnace, and then exposed to air to obtain a silver / cerium dioxide single-atom catalyst with a loading of 1.85% (mass fraction). Transmission electron microscopy images are shown below. Figure 1 As shown in the figure, cerium dioxide has a rod-like structure, and no silver nanoparticles are formed. Elemental distribution (see...) Figure 2 Analysis showed that silver single atoms were uniformly distributed on the cerium dioxide nanorods. X-ray photoelectron spectroscopy (see...) Figure 3 Analysis showed that the silver single atom was positive monovalent silver.

[0038] Example 2

[0039] The preparation method of the silver / cerium dioxide single-atom catalyst in this embodiment is as follows:

[0040] (1) Place 2 mL of cerium nitrate aqueous solution (containing 0.4 g of cerium nitrate, 1 mmol) in a reactor to remove oxygen. Under anaerobic conditions, add 2 mL of sodium hydroxide aqueous solution (containing 1 g of sodium hydroxide, 25 mmol) to the reactor and mix well. Heat the mixed solution to 110 °C and maintain it for 48 hours. After cooling, wash with water to remove excess sodium hydroxide and freeze-dry to obtain cerium hydroxide powder.

[0041] (2) Take 0.2 g of cerium hydroxide (1 mmol) and disperse it evenly in 20 mL of silver nitrate aqueous solution (containing 0.004 g of silver nitrate, 0.025 mmol), then remove oxygen and stir for 10 hours under anaerobic conditions; wash with water and freeze dry;

[0042] (3) The obtained powder was calcined at 350°C for 2 hours in an argon atmosphere in a tube furnace, and then the powder was exposed to air to obtain a silver / cerium dioxide single-atom catalyst with a loading of 0.97% (mass fraction).

[0043] Example 3

[0044] The preparation method of the silver / cerium dioxide single-atom catalyst in this embodiment is as follows:

[0045] (1) Place 2 mL of cerium nitrate aqueous solution (containing 0.4 g of cerium nitrate, 1 mmol) in a reactor to remove oxygen. Under anaerobic conditions, add 2 mL of sodium hydroxide aqueous solution (containing 1 g of sodium hydroxide, 25 mmol) to the reactor and mix well. Heat the mixed solution to 110 °C and maintain it for 48 hours. After cooling, wash with water to remove excess sodium hydroxide and freeze-dry to obtain cerium hydroxide powder.

[0046] (2) Take 0.2 g of cerium hydroxide (1 mmol) and disperse it evenly in 20 mL of silver nitrate aqueous solution (containing 0.002 g of silver nitrate, 0.012 mmol), then remove oxygen and stir for 10 hours under anaerobic conditions; wash with water and freeze dry;

[0047] (3) The obtained powder was calcined at 350°C for 2 hours in an argon atmosphere in a tube furnace, and then the powder was exposed to air to obtain a silver / cerium dioxide single-atom catalyst with a loading of 0.48% (mass fraction).

[0048] Example 4

[0049] The preparation method of the silver / cerium dioxide single-atom catalyst in this embodiment is as follows:

[0050] (1) Place 2 ml of cerium nitrate aqueous solution (containing 0.4 g of cerium nitrate, 1 mmol) in a reactor to remove oxygen. Under anaerobic conditions, add 2 ml of sodium hydroxide aqueous solution (containing 1 g of sodium hydroxide, 25 mmol) to the reactor and mix well. Heat the mixed solution to 110 °C and maintain it for 48 hours. After cooling, wash with water to remove excess sodium hydroxide and freeze-dry to obtain cerium hydroxide powder.

[0051] (2) Take 0.1 g of cerium hydroxide (0.5 mmol) and disperse it evenly in 20 ml of silver nitrate aqueous solution (containing 0.008 g of silver nitrate, 0.05 mmol), then remove oxygen and stir for 10 hours under anaerobic conditions; wash with water and freeze dry;

[0052] (3) The obtained powder was calcined at 350°C for 2 hours in an argon atmosphere in a tube furnace, and then the powder was exposed to air to obtain a silver / cerium dioxide single-atom catalyst with a loading of 3.46% (mass fraction).

[0053] Example 5

[0054] The preparation method of the silver / cerium dioxide single-atom catalyst in this embodiment is as follows:

[0055] (1) Place 2 mL of cerium nitrate aqueous solution (containing 1 g of cerium nitrate, 2.3 mmol) in a reactor to remove oxygen. Under anaerobic conditions, add 2 mL of sodium hydroxide aqueous solution (containing 0.12 g of sodium hydroxide, 3 mmol) to the reactor and mix well. Heat the mixed solution to 110 °C and maintain it for 48 hours. After cooling, wash with water to remove excess sodium hydroxide and freeze-dry to obtain cerium hydroxide powder.

[0056] (2) Take 0.2 g of cerium hydroxide (1 mmol) and disperse it evenly in 20 mL of silver nitrate aqueous solution (containing 0.004 g of silver nitrate, 0.025 mmol), then remove oxygen and stir for 10 hours under anaerobic conditions; wash with water and freeze dry;

[0057] (3) The obtained powder was calcined in a tube furnace under an argon atmosphere for 2 hours, and then the powder was exposed to air to obtain a silver / cerium dioxide single-atom catalyst with a loading of 0.91% (mass fraction). The cerium dioxide has a nano-polyhedral structure.

[0058] Example 6

[0059] The preparation method of the silver / cerium dioxide single-atom catalyst in this embodiment is as follows:

[0060] (1) Place 2 mL of cerium nitrate aqueous solution (containing 0.4 g of cerium nitrate, 1 mmol) in a reactor to remove oxygen. Under anaerobic conditions, add 2 mL of sodium hydroxide aqueous solution (containing 1 g of sodium hydroxide, 25 mmol) to the reactor and mix well. Heat the mixed solution to 180 °C and maintain it for 48 hours. After cooling, wash with water to remove excess sodium hydroxide and freeze-dry to obtain cerium hydroxide powder.

[0061] (2) Take 0.2 g of cerium hydroxide (1 mmol) and disperse it evenly in 20 mL of silver nitrate aqueous solution (containing 0.004 g of silver nitrate, 0.025 mmol), then remove oxygen and stir for 10 hours under anaerobic conditions; wash with water and freeze dry;

[0062] (3) The obtained powder was calcined at 350°C for 2 hours in an argon atmosphere in a tube furnace, and then the powder was exposed to air to obtain a silver / cerium dioxide single-atom catalyst with a loading of 0.89% (mass fraction). The cerium dioxide was in a nanocubic structure.

[0063] Example 7

[0064] The preparation method of the silver / cerium dioxide single-atom catalyst in this embodiment is as follows:

[0065] (1) Place 2 mL of cerium nitrate aqueous solution (containing 0.4 g of cerium nitrate, 1 mmol) in a reactor to remove oxygen. Under anaerobic conditions, add 2 mL of sodium hydroxide aqueous solution (containing 0.5 g of sodium hydroxide, 12.5 mmol) to the reactor and mix well. Heat the mixed solution to 110 °C and maintain it for 48 hours. After cooling, wash with water to remove excess sodium hydroxide and freeze-dry to obtain cerium hydroxide powder.

[0066] (2) Take 0.2 g of cerium hydroxide (1 mmol) and disperse it evenly in 20 mL of silver nitrate aqueous solution (containing 0.004 g of silver nitrate, 0.025 mmol), then remove oxygen and stir for 10 hours under anaerobic conditions; wash with water and freeze dry;

[0067] (3) The obtained powder was calcined at 350°C for 2 hours in an argon atmosphere in a tube furnace, and then the powder was exposed to air to obtain a silver / cerium dioxide single-atom catalyst with a loading of 0.89% (mass fraction). The cerium dioxide was a mixed structure of polyhedron and nanorod.

[0068] Example 8

[0069] The preparation method of the silver / cerium dioxide single-atom catalyst in this embodiment is as follows:

[0070] (1) Place 2 mL of cerium nitrate aqueous solution (containing 0.4 g of cerium nitrate, 1 mmol) in a reactor to remove oxygen. Under anaerobic conditions, add 2 mL of sodium hydroxide aqueous solution (containing 0.0016 g of sodium hydroxide, 0.04 mmol) to the reactor and mix well. Heat the mixed solution to 110 °C and maintain it for 48 hours. After cooling, wash with water to remove excess sodium hydroxide and freeze-dry to obtain cerium hydroxide powder.

[0071] (2) Take 0.2 g of cerium hydroxide (1 mmol) and disperse it evenly in 20 mL of silver nitrate aqueous solution (containing 0.004 g of silver nitrate, 0.025 mmol), then remove oxygen and stir for 10 hours under anaerobic conditions; wash with water and freeze dry;

[0072] (3) The obtained powder was calcined at 350°C for 2 hours in an argon atmosphere in a tube furnace, and then the powder was exposed to air to obtain a silver / cerium dioxide single-atom catalyst with a loading of 0.89% (mass fraction). The cerium dioxide has a polyhedral structure.

[0073] Example 9

[0074] The preparation method of the silver / cerium dioxide single-atom catalyst in this embodiment is as follows:

[0075] (1) Place 2 mL of cerium nitrate aqueous solution (containing 0.4 g of cerium nitrate, 1 mmol) in a reactor to remove oxygen. Under anaerobic conditions, add 2 mL of hexamethylenetetramine aqueous solution (containing 1.9 g of hexamethylenetetramine, 13 mmol) to the reactor and mix evenly. Stir at room temperature and maintain for 48 hours. After cooling, wash with water to remove excess sodium hydroxide and freeze-dry to obtain cerium hydroxide powder.

[0076] (2) Take 0.2 g of cerium hydroxide (1 mmol) and disperse it evenly in 20 mL of silver nitrate aqueous solution (containing 0.004 g of silver nitrate, 0.025 mmol), then remove oxygen and stir for 10 hours under anaerobic conditions; wash with water and freeze dry;

[0077] (3) The obtained powder was calcined at 350°C for 2 hours in an argon atmosphere in a tube furnace, and then the powder was exposed to air to obtain a silver / cerium dioxide single-atom catalyst with a loading of 0.89% (mass fraction). The cerium dioxide has a polyhedral structure.

[0078] Example 10

[0079] The preparation method of the silver / cerium dioxide single-atom catalyst in this embodiment is as follows:

[0080] (1) Place 2 mL of cerium nitrate aqueous solution (containing 0.4 g of cerium nitrate, 1 mmol) in a reactor to remove oxygen. Under anaerobic conditions, add 2 mL of ammonia aqueous solution (25 mmol) to the reactor and mix evenly. Stir at room temperature and maintain for 48 hours. After cooling, wash with water to remove excess sodium hydroxide and freeze-dry to obtain cerium hydroxide powder.

[0081] (2) Take 0.2 g of cerium hydroxide (1 mmol) and disperse it evenly in 20 mL of silver nitrate aqueous solution (containing 0.004 g of silver nitrate, 0.025 mmol), then remove oxygen and stir for 10 hours under anaerobic conditions; wash with water and freeze dry;

[0082] (3) The obtained powder was calcined at 350°C for 2 hours in an argon atmosphere in a tube furnace, and then the powder was exposed to air to obtain a silver / cerium dioxide single-atom catalyst with a loading of 0.89% (mass fraction). The cerium dioxide has an irregular structure.

[0083] Example 11

[0084] The preparation method of the silver / cerium dioxide single-atom catalyst in this embodiment is as follows:

[0085] (1) Place 2 mL of cerium nitrate aqueous solution (containing 0.4 g of cerium nitrate, 1 mmol) in a reactor to remove oxygen. Under anaerobic conditions, add 2 mL of sodium hydroxide aqueous solution (containing 0.5 g of sodium hydroxide, 12.5 mmol) to the reactor and mix well. Heat the mixed solution to 110 °C and maintain it for 48 hours. After cooling, wash with water to remove excess sodium hydroxide and freeze-dry to obtain cerium hydroxide powder.

[0086] (2) Take 0.2 g of cerium hydroxide (1 mmol) and disperse it evenly in 20 mL of silver nitrate aqueous solution (containing 0.004 g of silver nitrate, 0.025 mmol), then remove oxygen and stir for 10 hours under anaerobic conditions; wash with water and freeze dry;

[0087] (3) The obtained powder was calcined at 350°C for 2 hours in an argon atmosphere in a tube furnace, and then the powder was exposed to air to obtain a silver / cerium dioxide single-atom catalyst with a loading of 0.89% (mass fraction). The cerium dioxide was a mixed structure of polyhedron and nanorod.

[0088] Example 12

[0089] The preparation method of the silver / cerium dioxide single-atom catalyst in this embodiment is as follows:

[0090] (1) Place 2 mL of cerium(III) aqueous solution (containing 0.3 g of cerium sulfate, 0.5 mmol) in a reactor to remove oxygen. Under anaerobic conditions, add 2 mL of sodium hydroxide aqueous solution (containing 1 g of sodium hydroxide, 25 mmol) to the reactor and mix well. Heat the mixed solution to 110 °C and maintain it for 48 hours. After cooling, wash with water to remove excess sodium hydroxide and freeze-dry to obtain cerium hydroxide powder.

[0091] (2) Take 0.2 g of cerium hydroxide (1 mmol) and disperse it evenly in 20 mL of silver nitrate aqueous solution (containing 0.004 g of silver nitrate, 0.025 mmol), then remove oxygen and stir for 10 hours under anaerobic conditions; wash with water and freeze dry;

[0092] (3) The obtained powder was calcined at 350°C for 2 hours in an argon atmosphere in a tube furnace, and then the powder was exposed to air to obtain a silver / cerium dioxide single-atom catalyst with a loading of 0.89% (mass fraction). The cerium dioxide was rod-shaped.

[0093] Example 13

[0094] The preparation method of the silver / cerium dioxide single-atom catalyst in this embodiment is as follows:

[0095] (1) Place 2 mL of cerium nitrate aqueous solution (containing 0.4 g of cerium nitrate, 1 mmol) in a reactor to remove oxygen. Under anaerobic conditions, add 2 mL of sodium hydroxide aqueous solution (containing 1 g of sodium hydroxide, 25 mmol) to the reactor and mix well. Heat the mixed solution to 110 °C and maintain it for 48 hours. After cooling, wash with water to remove excess sodium hydroxide and freeze-dry to obtain cerium hydroxide powder.

[0096] (2) Take 0.2 g (1 mmol) of cerium hydroxide and disperse it evenly in 20 mL of silver nitrate aqueous solution (containing 0.008 g, 0.05 mmol of silver nitrate), then remove oxygen and stir for 10 hours under anaerobic conditions; wash with water and freeze dry;

[0097] (3) The obtained powder was calcined at 450°C for 2 hours in an argon atmosphere in a tube furnace, and then exposed to air to obtain a silver / cerium dioxide single-atom catalyst with a loading of 1.85% (mass fraction). Transmission electron microscopy images are shown below. Figure 1 As shown in the figure, cerium dioxide has a rod-like structure, and no silver nanoparticles are formed. Elemental distribution (see...) Figure 2Analysis showed that silver single atoms were uniformly distributed on the cerium dioxide nanorods. X-ray photoelectron spectroscopy (see...) Figure 3 Analysis showed that the silver single atom was positive monovalent silver.

[0098] Example 14

[0099] The preparation method of the platinum / cerium dioxide single-atom catalyst in this embodiment is as follows:

[0100] (1) Place 2 mL of cerium nitrate aqueous solution (containing 0.4 g of cerium nitrate, 1 mmol) in a reactor to remove oxygen. Under anaerobic conditions, add 2 mL of sodium hydroxide aqueous solution (containing 1 g of sodium hydroxide, 25 mmol) to the reactor and mix well. Heat the mixed solution to 110 °C and maintain it for 48 hours. After cooling, wash with water to remove excess sodium hydroxide and freeze-dry to obtain cerium hydroxide powder.

[0101] (2) Take 1.025 mL of 0.01 M (0.01 mmol) chloroplatinic acid to prepare 20 mL of chloroplatinic acid aqueous solution. Disperse 0.1 g of cerium hydroxide (0.5 mmol) evenly in the chloroplatinic acid aqueous solution and remove oxygen. Stir for 10 hours under anaerobic conditions. Wash with water and freeze dry.

[0102] (3) The obtained powder was calcined at 350°C for 2 hours in an argon atmosphere in a tube furnace, and then exposed to air to obtain a platinum / cerium dioxide single-atom catalyst with a loading of 1.38% (mass fraction). Transmission electron microscopy images are shown below. Figure 4 As can be seen, no platinum nanoparticles were formed. Elemental distribution ( Figure 5 Analysis showed that platinum single atoms were uniformly distributed on the cerium dioxide nanorods. X-ray photoelectron spectroscopy (XPS) Figure 6 Analysis showed that the platinum single atom was in the divalent platinum state.

[0103] Example 15

[0104] The preparation method of the platinum / cerium dioxide single-atom catalyst in this embodiment is as follows:

[0105] (1) Place 2 mL of cerium nitrate aqueous solution (containing 0.4 g of cerium nitrate, 1 mmol) in a reactor to remove oxygen. Under anaerobic conditions, add 2 mL of sodium hydroxide aqueous solution (containing 1 g of sodium hydroxide, 25 mmol) to the reactor and mix well. Heat the mixed solution to 110 °C and maintain it for 48 hours. After cooling, wash with water to remove excess sodium hydroxide and freeze-dry to obtain cerium hydroxide powder.

[0106] (2) Take 2.05 mL of 0.01 M chloroplatinic acid (0.02 mmol) to prepare 20 mL of chloroplatinic acid aqueous solution. Disperse 0.1 g of cerium hydroxide (0.5 mmol) evenly in the chloroplatinic acid aqueous solution and remove oxygen. Stir for 10 hours under anaerobic conditions. Wash with water and freeze dry.

[0107] (3) The obtained powder was calcined at 350°C for 2 hours in an argon atmosphere in a tube furnace, and then the powder was exposed to air to obtain a platinum / cerium dioxide single-atom catalyst with a loading of 2.79% (mass fraction).

[0108] Example 16

[0109] The preparation method of the platinum / cerium dioxide single-atom catalyst in this embodiment is as follows:

[0110] (1) Place 2 mL of cerium nitrate aqueous solution (containing 0.4 g of cerium nitrate, 1 mmol) in a reactor to remove oxygen. Under anaerobic conditions, add 2 mL of sodium hydroxide aqueous solution (containing 1 g of sodium hydroxide, 25 mmol) to the reactor and mix well. Heat the mixed solution to 110 °C and maintain it for 48 hours. After cooling, wash with water to remove excess sodium hydroxide and freeze-dry to obtain cerium hydroxide powder.

[0111] (2) Take 4.1 mL of 0.01 M chloroplatinic acid (0.04 mmol) to prepare 20 mL of chloroplatinic acid aqueous solution. Disperse 0.1 g (0.5 mmol) of cerium hydroxide evenly in the chloroplatinic acid aqueous solution and remove oxygen. Stir for 10 hours under anaerobic conditions. Wash with water and freeze dry.

[0112] (3) The obtained powder was calcined at 350°C for 2 hours in an argon atmosphere in a tube furnace, and then the powder was exposed to air to obtain a platinum / cerium dioxide single-atom catalyst with a loading of 5.88% (mass fraction).

[0113] Example 17

[0114] The preparation method of the gold / cerium dioxide single-atom catalyst in this embodiment is as follows:

[0115] (1) Place 2 mL of cerium nitrate aqueous solution (containing 0.4 g of cerium nitrate, 1 mmol) in a reactor to remove oxygen. Under anaerobic conditions, add 2 mL of sodium hydroxide aqueous solution (containing 1 g of sodium hydroxide, 25 mmol) to the reactor and mix well. Heat the mixed solution to 110 °C and maintain it for 48 hours. After cooling, wash with water to remove excess sodium hydroxide and freeze-dry to obtain cerium hydroxide powder.

[0116] (2) Take 1.015 mL of 0.01 M chloroauric acid (0.01 mmol) to prepare 20 mL of chloroauric acid aqueous solution. Disperse 0.1 g of cerium hydroxide (0.5 mmol) evenly in the chloroauric acid aqueous solution and remove oxygen. Stir for 10 hours under anaerobic conditions. Wash with water and freeze dry.

[0117] (3) The obtained powder was calcined at 350°C for 2 hours in an argon atmosphere in a tube furnace, and then exposed to air to obtain a gold / cerium dioxide single-atom catalyst with a loading of 1.21% (mass fraction). Transmission electron microscopy image ( Figure 7 The results show that there are no gold nanoparticles on the cerium dioxide.

[0118] Example 18

[0119] The preparation method of the ruthenium / cerium dioxide single-atom catalyst in this embodiment is as follows:

[0120] (1) Place 2 mL of cerium nitrate aqueous solution (containing 0.4 g of cerium nitrate, 1 mmol) in a reactor to remove oxygen. Under anaerobic conditions, add 2 mL of sodium hydroxide aqueous solution (containing 1 g of sodium hydroxide, 25 mmol) to the reactor and mix well. Heat the mixed solution to 110 °C and maintain it for 48 hours. After cooling, wash with water to remove excess sodium hydroxide and freeze-dry to obtain cerium hydroxide powder.

[0121] (2) Take 0.1 g of cerium hydroxide (0.5 mmol) and disperse it evenly in 20 mL of ruthenium trichloride aqueous solution (containing 0.002 g of ruthenium trichloride, 0.01 mmol), then remove oxygen and stir for 10 hours under anaerobic conditions; wash with water and freeze dry;

[0122] (3) The obtained powder was calcined at 350°C for 2 hours in an argon atmosphere in a tube furnace, and then exposed to air to obtain a ruthenium / cerium dioxide single-atom catalyst with a loading of 0.67% (mass fraction). Transmission electron microscopy image ( Figure 8 It can be seen that no ruthenium nanoparticles were formed. Elemental distribution (see...) Figure 9 Analysis showed that ruthenium single atoms were uniformly distributed on the cerium dioxide nanorods.

[0123] Example 19

[0124] The preparation method of the copper / cerium dioxide single-atom catalyst in this embodiment is as follows:

[0125] (1) Place 2 mL of cerium nitrate aqueous solution (containing 0.4 g of cerium nitrate, 1 mmol) in a reactor to remove oxygen. Under anaerobic conditions, add 2 mL of sodium hydroxide aqueous solution (containing 1 g of sodium hydroxide, 25 mmol) to the reactor and mix well. Heat the mixed solution to 110 °C and maintain it for 48 hours. After cooling, wash with water to remove excess sodium hydroxide and freeze-dry to obtain cerium hydroxide powder.

[0126] (2) Take 0.2 g of cerium hydroxide (1 mmol) and disperse it evenly in 20 mL of copper nitrate aqueous solution (containing 0.01 g of copper nitrate, 0.05 mmol), then remove oxygen and stir for 10 hours under anaerobic conditions; wash with water and freeze dry;

[0127] (3) The obtained powder was calcined at 350°C for 2 hours in an argon atmosphere in a tube furnace, and then the powder was exposed to air to obtain a copper / cerium dioxide single-atom catalyst with a loading of 0.4% (mass fraction).

[0128] Example 20

[0129] The preparation method of the copper / cerium dioxide single-atom catalyst in this embodiment is as follows:

[0130] (1) Place 2 mL of cerium nitrate aqueous solution (containing 0.4 g of cerium nitrate, 1 mmol) in a reactor to remove oxygen. Under anaerobic conditions, add 2 mL of sodium hydroxide aqueous solution (containing 1 g of sodium hydroxide, 25 mmol) to the reactor and mix well. Heat the mixed solution to 110 °C and maintain it for 48 hours. After cooling, wash with water to remove excess sodium hydroxide and freeze-dry to obtain cerium hydroxide powder.

[0131] (2) Take 0.2 g of cerium hydroxide (1 mmol) and disperse it evenly in 20 mL of copper nitrate aqueous solution (containing 0.02 g of copper nitrate, 0.025 mmol), then remove oxygen and stir for 10 hours under anaerobic conditions; wash with water and freeze dry;

[0132] (3) The obtained powder was calcined at 350°C for 2 hours in an argon atmosphere in a tube furnace, and then the powder was exposed to air to obtain a copper / cerium dioxide single-atom catalyst with a loading of 1.02% (mass fraction).

[0133] Example 21

[0134] The preparation method of the palladium / cerium dioxide single-atom catalyst in this embodiment is as follows:

[0135] (1) Place 2 mL of cerium nitrate aqueous solution (containing 0.4 g of cerium nitrate, 1 mmol) in a reactor to remove oxygen. Under anaerobic conditions, add 2 mL of sodium hydroxide aqueous solution (containing 1 g of sodium hydroxide, 25 mmol) to the reactor and mix well. Heat the mixed solution to 110 °C and maintain it for 48 hours. After cooling, wash with water to remove excess sodium hydroxide and freeze-dry to obtain cerium hydroxide powder.

[0136] (2) Take 1.9 mL of 0.01 M potassium chloropalladium (0.019 mmol) to prepare 20 mL of potassium chloropalladium aqueous solution. Disperse 0.1 g of cerium hydroxide (0.5 mmol) evenly in the potassium chloropalladium aqueous solution and remove oxygen. Stir for 10 hours under anaerobic conditions. Wash with water and freeze dry.

[0137] (3) The obtained powder was calcined at 350°C for 2 hours in an argon atmosphere in a tube furnace, and then the powder was exposed to air to obtain a palladium / cerium dioxide single-atom catalyst with a loading of 1.13% (mass fraction).

[0138] Example 22

[0139] The preparation method of the iridium / cerium dioxide single-atom catalyst in this embodiment is as follows:

[0140] (1) Place 2 mL of cerium nitrate aqueous solution (containing 0.4 g of cerium nitrate, 1 mmol) in a reactor to remove oxygen. Under anaerobic conditions, add 2 mL of sodium hydroxide aqueous solution (containing 1 g of sodium hydroxide) to the reactor and mix evenly. Heat the mixed solution to 110 °C and maintain it for 48 hours. After cooling, wash with water to remove excess sodium hydroxide and freeze-dry to obtain cerium hydroxide powder.

[0141] (2) Take 1.04 mL of 0.01 M chloroiridic acid (0.01 mmol) to prepare 20 mL of chloroiridic acid aqueous solution. Disperse 0.1 g of cerium hydroxide (0.5 mmol) evenly in the chloroiridic acid aqueous solution and remove oxygen. Stir for 10 hours under anaerobic conditions. Wash with water and freeze dry.

[0142] (3) The obtained powder was calcined at 350°C for 2 hours in an argon atmosphere in a tube furnace, and then the powder was exposed to air to obtain an iridium / cerium dioxide single-atom catalyst with a loading of 1.17% (mass fraction).

[0143] Example 23

[0144] The preparation method of the rhodium / cerium dioxide single-atom catalyst in this embodiment is as follows:

[0145] (1) Place 2 mL of cerium nitrate aqueous solution (containing 0.4 g of cerium nitrate, 1 mmol) in a reactor to remove oxygen. Under anaerobic conditions, add 2 mL of sodium hydroxide aqueous solution (containing 1 g of sodium hydroxide, 25 mmol) to the reactor and mix well. Heat the mixed solution to 110 °C and maintain it for 48 hours. After cooling, wash with water to remove excess sodium hydroxide and freeze-dry to obtain cerium hydroxide powder.

[0146] (2) Take 1.944 mL of 0.01 M rhodium trichloride solution (0.02 mmol) to prepare 20 mL of rhodium trichloride aqueous solution. Disperse 0.1 g of cerium hydroxide (0.5 mmol) evenly in the rhodium trichloride aqueous solution and remove oxygen. Stir for 10 hours under anaerobic conditions. Wash with water and freeze dry.

[0147] (3) The obtained powder was calcined at 350°C for 2 hours in an argon atmosphere in a tube furnace, and then the powder was exposed to air to obtain a rhodium / cerium dioxide single-atom catalyst with a loading of 1.09% (mass fraction).

[0148] Example 24

[0149] The preparation method of the gold / cerium dioxide single-atom catalyst in this embodiment is as follows:

[0150] (1) Place 2 mL of cerium nitrate aqueous solution (containing 0.4 g of cerium nitrate, 1 mmol) in a reactor to remove oxygen. Under anaerobic conditions, add 2 mL of sodium hydroxide aqueous solution (containing 1 g of sodium hydroxide, 25 mmol) to the reactor and mix well. Heat the mixed solution to 110 °C and maintain it for 48 hours. After cooling, wash with water to remove excess sodium hydroxide and freeze-dry to obtain cerium hydroxide powder.

[0151] (2) Prepare a 20 mL aqueous solution of chloroauric acid by taking 1.015 mL of 0.01 M chloroauric acid (0.01 mmol) solution and 1.9 mL of 0.01 M potassium chloropalladate (0.019 mmol) solution. Disperse 0.1 g of cerium hydroxide (0.5 mmol) evenly in the aqueous solution of chloroauric acid and remove oxygen. Stir for 24 hours under anaerobic conditions. Wash with water and freeze dry.

[0152] (3) The obtained powder was calcined at 350°C for 2 hours in an argon atmosphere in a tube furnace, and then the powder was exposed to air to obtain a gold-palladium / cerium dioxide single-atom catalyst with a gold loading of 1.05% and a palladium loading of 1.13% (mass fraction).

[0153] The silver / cerium dioxide single-atom catalyst with a mass fraction of 0.48 prepared in Example 3 was applied to the electrocatalytic CO2 reduction reaction. Using BmimBF4 (1.0 M) / MeCN / H2O (0.8 M) as the cathode electrolyte and 0.5 M H2SO4 aqueous solution as the anolyte, the current density reached 403 mA cm⁻¹ in a flowing electrolytic cell. -2 The Faraday efficiency of CO reaches 97.2%.

[0154] The foregoing has shown and described the basic principles and main features of the present invention, as well as its advantages. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a metal / cerium dioxide single-atom catalyst, characterized in that... Includes the following steps: (1) Under inert gas conditions, an inorganic alkaline solution and a solution of cerium(III) salt are mixed and hydrolyzed to obtain cerium(III) hydroxide; (2) Under inert gas conditions, cerium(III) hydroxide is uniformly dispersed in the solution of the metal precursor. After stirring and reacting, the mixture is centrifuged, washed, and freeze-dried to obtain the metal precursor / cerium(III) hydroxide. (3) Under inert gas conditions, the metal precursor / cerium hydroxide (III) obtained in step (2) is placed in a tube furnace for calcination, so that cerium hydroxide (III) undergoes pyrolysis to obtain cerium trioxide. During the pyrolysis process, cerium trioxide undergoes a redox reaction with the metal precursor. (4) The composite material obtained in step (3) is placed in the air to obtain a metal / cerium dioxide single-atom catalyst; The cerium(III) salts include one or more of cerium(III) nitrate, cerium(III) sulfate, cerium(III) carbonate hydrate, cerium(III) oxalate hydrate, and cerium(III) acetate hydrate; In step (2), the molar ratio of cerium(III) hydroxide to the metal precursor is 25:2-100:1.

2.

2. The method for preparing the metal / cerium dioxide single-atom catalyst according to claim 1, characterized in that: The inorganic base in step (1) includes one or more of sodium hydroxide, potassium hydroxide, ammonia, hexamethylenetetramine, and urea.

3. The method for preparing the metal / cerium dioxide single-atom catalyst according to claim 1, characterized in that: In step (1), the molar ratio of cerium(III) salt to inorganic base is 1:25 to 25:

1.

4. The method for preparing the metal / cerium dioxide single-atom catalyst according to claim 1, characterized in that: The hydrolysis reaction in step (1) is carried out at a temperature of room temperature to 180°C and for a time of 5 to 48 hours.

5. The method for preparing the metal / cerium dioxide single-atom catalyst according to claim 1, characterized in that: In step (2), the metal precursor is one or more of the following: chloroauric acid, chloroplatinic acid, ruthenium chloride, chloroiridium acid, potassium chloropalladium, hydrated rhodium chloride, copper nitrate, or silver nitrate.

6. The method for preparing the metal / cerium dioxide single-atom catalyst according to claim 1, characterized in that: In step (2), the reaction temperature is room temperature and the stirring time is 10 hours.

7. The method for preparing the metal / cerium dioxide single-atom catalyst according to claim 1, characterized in that: In step (3), the calcination temperature is 200-450℃ and the calcination time is 2 hours.

8. The metal / cerium dioxide single-atom catalyst prepared by any one of claims 1-7.

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