Monatomic catalyst, its preparation method and application

Abstract

The application provides a monatomic catalyst, a preparation method and application thereof. The monatomic catalyst of the application comprises a carrier and metal monatomic atoms loaded in the carrier, and overloading possibly existing in a multiatomic catalyst is avoided. Meanwhile, the distribution and properties of catalytic centers can be more accurately controlled, and more accurate catalytic effects are achieved. The application further provides a preparation method and application of the monatomic catalyst.

Description

Technical Field

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

[0002] Just as turning bulk metal materials into nanoparticles can bring about changes in the field of catalysis, further shrinking the size of metal materials to isolated single atoms and embedding them in a support can optimize catalyst design and deepen the understanding of reaction mechanisms.

[0003] Atomically dispersed metal catalysts, due to their high atom utilization, unique atomic structure, and electronic properties, hold great promise for applications in CO oxidation, hydrogenation, organic reactions, electrocatalysis, and photocatalysis. Although carbon materials are currently the most commonly used single-atom support for metals, large-scale, simple, and efficient preparation of catalysts with high-density metal single-atom sites remains extremely difficult. During high-temperature pyrolysis, metal atoms tend to aggregate or form metal carbides with the carbon support, thus reducing the dispersion sites of the single metal. Furthermore, the structural instability of the precursor during high-temperature annealing leads to uncontrollable chemical composition and structure around the metal single atoms. These factors restrict the effective construction and application of single-atom catalysts. To limit the aggregation of these isolated atoms under high-temperature conditions, it is necessary to strengthen the strong interaction between the atoms and the support.

[0004] Therefore, a new single-atom catalyst still needs to be developed. Summary of the Invention

[0005] The present invention aims to at least solve one of the aforementioned technical problems existing in the prior art. To this end, the present invention provides a single-atom catalyst that avoids the excessive packing that may occur in multi-atom catalysts. Simultaneously, it allows for more precise control of the distribution and properties of the catalytic centers, achieving a more precise catalytic effect.

[0006] The present invention also provides a method for preparing a single-atom catalyst.

[0007] This invention also provides an application of a single-atom catalyst.

[0008] A first aspect of the present invention provides a single-atom catalyst comprising a support and a metal single atom supported thereon, the metal single atom comprising at least one of Co atom, Fe atom, Ni atom, Zn atom, Cu atom, Sn atom, W atom, Ga atom, Ir atom, Pt atom, Bi atom, Cd atom, Mo atom, Zr atom, Cr atom, Mn atom, V atom, In atom, Pd atom, Ag atom, Lu atom, Rh atom, and Au atom.

[0009] One of the technical solutions of the present invention concerning single-atom catalysts has at least the following beneficial effects:

[0010] The single-atom catalyst of the present invention includes a support and a metal single atom supported on the support, which can provide high catalytic activity because each catalytic center can participate in the reaction, avoiding the excessive stacking that may exist in multi-atom catalysts. At the same time, the distribution and properties of the catalytic centers can be more precisely controlled to achieve a more precise catalytic effect.

[0011] The single-atom catalyst of this invention helps to improve reaction selectivity, reduce the generation of side reactions, and thus improve product purity. At the same time, it exhibits good catalytic stability, resisting deactivation or poisoning and extending the catalyst's lifespan.

[0012] The single-atom catalyst of the present invention includes at least one of the following metal single atoms: Co atom, Fe atom, Ni atom, Zn atom, Cu atom, Sn atom, W atom, Ga atom, Ir atom, Pt atom, Bi atom, Cd atom, Mo atom, Zr atom, Cr atom, Mn atom, V atom, In atom, Pd atom, Ag atom, Lu atom, Rh atom, and Au atom. Specific metal single atoms can be selected as needed, reducing the use of expensive metals, resulting in greater atom economy and contributing to the sustainable use of resources.

[0013] According to some embodiments of the present invention, the carrier comprises reduced graphene oxide.

[0014] Graphene is a single-layer planar crystalline material composed of carbon atoms, possessing excellent electrical and thermal conductivity, extremely high mechanical properties, and chemical stability. However, graphene also has some drawbacks, such as flammability and instability. Therefore, graphene derivatives—graphene oxide and reduced graphene—have been extensively studied and applied.

[0015] Graphene oxide is an oxidation product formed by oxidizing graphene. It possesses high chemical stability, making it suitable for applications in drug delivery, advanced energy storage, and sensing technologies. Graphene oxide can also be modified to acquire various properties and applications. For example, by combining it with polymers and biomolecules, it can be used to create strong and flexible nanomaterials.

[0016] Reduced graphene oxide, or simply reduced graphene, is a carbon material produced by reducing graphene oxide. Compared to graphene and graphene oxide, reduced graphene possesses characteristics such as bipolar charge, electron-rich properties, and high controllability, making it widely studied and applied in fields such as biosensing, energy storage, solid-state capacitors, and semiconductors. For example, through thin-film stacking technology, reduced graphene can be used in high-power energy storage devices.

[0017] The single-atom catalyst of the present invention includes a support and metal single atoms supported on the support. "Supported on the support" means that the metal single atoms are distributed on the surface of the support.

[0018] According to some embodiments of the present invention, the loading of the metal single atom is 2wt% to 25wt%.

[0019] According to some embodiments of the present invention, the loading of the metal single atom is 5 wt% to 17 wt%.

[0020] The single-atom catalyst of the present invention avoids the aggregation of metal atoms, and when the metal single atom is Co atom, the loading of the metal single atom can be as high as 16.58 wt%.

[0021] A second aspect of the present invention provides a method for preparing a single-atom catalyst, comprising the following steps:

[0022] S1: Disperse the carrier raw material in a solvent, add a pore-forming agent, an anchoring agent and a metal salt, stir and freeze dry to obtain the precursor;

[0023] S2: After subjecting the precursor to self-propagating combustion, the product is annealed in a protective atmosphere to obtain the single-atom catalyst.

[0024] One technical solution of the present invention relating to the preparation method of a single-atom catalyst has at least the following beneficial effects:

[0025] In the high-temperature pyrolysis preparation of single-atom carbon materials, precursor regulation is one of the key factors in the directional construction of pyrolysis products. Therefore, selecting single-atom material precursors with suitable structures and pre-constructing single atoms and surrounding chemical structural sites is an effective means to efficiently prepare high-density single / multi-atom carbon materials. Thus, finding suitable ligands is crucial for synthesizing highly loaded single-atom carbon materials. The preparation method of this invention is based on a self-propagating combustion reduction support raw material (such as graphene oxide), in which metal atoms are pre-anchored to the surrounding chemical structural sites, followed by annealing treatment, ultimately successfully constructing a highly loaded metal single-atom catalyst (i.e., metal single-atom reduced graphene oxide material).

[0026] The preparation method of the present invention does not require expensive equipment and complex process control, the reaction conditions are not harsh, the raw materials are readily available, the production cost is low, and it is easy to industrialize.

[0027] In step S1:

[0028] The role of pore-forming agents is to prepare porous carriers. If the carrier raw material is graphene oxide, then porous graphene refers to carbon materials with nanoscale pores on a two-dimensional surface. Porous graphene not only retains the excellent properties of graphene, but also, compared to inert graphene, the presence of pores on the surface promotes improved material transport efficiency. In particular, atomic-level pores can be used to sieve different sizes. More importantly, the introduction of pores effectively opens the band gap of graphene, promoting its application in the field of electronic devices.

[0029] Zero-valent metal single atoms are extremely unstable and tend to aggregate, eventually forming metal nanoparticles. Therefore, a solid host material (primarily reduced graphene oxide in this invention) is needed to support non-metallic atoms such as O, N, S, P, and B, enabling them to form chemical bonds with the metal single atoms and create stable metal single-atom sites. Thus, the anchoring agent in this invention is used to form stable chemical bonds with the metal atoms, resulting in uniformly dispersed and stable metal single-atom materials.

[0030] In step S2:

[0031] Self-propagation high-temperature synthesis (SHS), also known as combustion synthesis, utilizes the self-heating and self-conduction effects of the high heat of chemical reaction between reactants to synthesize materials. Once ignited, the reactants automatically propagate to unreacted areas until the reaction is complete, making it a method for preparing high-temperature inorganic compound materials. In this invention, alkali metals are used as igniters. Upon heating, graphene oxide reacts with the alkali metal surface, triggering a self-propagating reaction. Therefore, it is unnecessary to add the alkali metal to the precursor, avoiding the introduction of alkali metal impurities. The alkali metal acts only as an igniter; once the precursor is ignited, subsequent reactions can proceed.

[0032] The purpose of annealing is to further improve the graphitization degree of the material and the high-temperature stability of single atoms.

[0033] According to some embodiments of the present invention, the self-propagating combustion in step S2 can be carried out in a low-oxygen environment, such as a glove box.

[0034] The high oxygen content in the atmosphere causes the reduction reaction to be rapid and intense, resulting in the complete combustion of the graphene carbon material in the sample to produce carbon dioxide gas. Therefore, the sample needs to be ignited in a low-oxygen environment, such as a glove box. The oxygen content in the glove box is less than 0.1 ppm, which is still sufficient to ignite the precursor and ultimately cause a self-propagating reaction.

[0035] According to some embodiments of the present invention, the carrier material includes graphene oxide.

[0036] According to some embodiments of the present invention, the solvent includes water.

[0037] According to some embodiments of the present invention, the pore-forming agent includes H2O2.

[0038] According to some embodiments of the present invention, the anchoring agent includes at least one of nitrogen-containing anchoring agents, sulfur-containing anchoring agents, phosphorus-containing anchoring agents, and boron-containing anchoring agents.

[0039] According to some embodiments of the present invention, the anchoring agent includes at least one selected from urea, dicyandiamine, boric acid, ammonium thiocyanate, sodium hypophosphite, and phytic acid.

[0040] According to some embodiments of the present invention, in step S1, the mass ratio of the carrier material to the metal single atom is 1:0.5 to 0.6.

[0041] The carrier material includes graphene oxide.

[0042] According to some embodiments of the present invention, in step S1, the carrier raw material is dispersed in a solvent, and the concentration of the carrier raw material in the formed solution is 1 mg / mL to 10 mg / mL.

[0043] According to some embodiments of the present invention, in step S1, the carrier raw material is dispersed in a solvent, and the volume ratio of the solution to the pore-forming agent is 10 to 100:1.

[0044] According to some embodiments of the present invention, the molar ratio of the anchoring agent to the metal salt is 1 to 4:1.

[0045] According to some embodiments of the present invention, the metal salt includes at least one selected from nitrate, sulfate, hydrochloride, acetylacetone, acetate, and oxalate.

[0046] Metal salts are metal salts containing a corresponding single-atom element of a metal.

[0047] According to some embodiments of the present invention, the stirring time is 1 hour to 24 hours.

[0048] According to some embodiments of the present invention, the freeze-drying includes liquid nitrogen freezing and cold trap freezing.

[0049] According to some embodiments of the present invention, the freeze-drying time is 24h to 72h.

[0050] The purpose of freeze drying is to effectively separate the metal compounds and non-metal anchoring agents by these numerous cavities during the process, thereby ensuring that as many metal centers as possible are evenly distributed in the porous graphene for subsequent pre-anchoring, ultimately obtaining a uniformly dispersed single-atom catalyst.

[0051] According to some embodiments of the present invention, the ignition temperature of the self-propagating combustion is 200°C to 600°C.

[0052] According to some embodiments of the present invention, the self-propagating combustion time is 0.01s to 1.00s.

[0053] According to some embodiments of the present invention, the self-propagating combustion can be ignited by an alkali metal, such as sodium. The alkali metal serves only as a heat source, requiring only the generation of heat transfer energy; it does not need to be ignited, and therefore its combustion temperature does not need to be reached. The minimum temperature required to ignite graphene oxide is only 200°C, which is a low-temperature self-propagating combustion, effectively achieving energy conservation.

[0054] According to some embodiments of the present invention, the annealing treatment method includes: heating to 600°C to 900°C at a rate of 1°C / min to 10°C / min, holding at that temperature for 2 hours to 5 hours to further improve the graphitization degree and single-atom high-temperature stability of the material, and then naturally cooling to room temperature.

[0055] Annealing can be performed in a tube furnace.

[0056] This invention utilizes a low-temperature self-propagating combustion method, providing abundant lone pairs of electrons for capturing metal ions, forming abundant and uniform anchoring sites for metal and non-metal atoms, thereby pre-anchoring metal atoms within the carbon framework. Through the preparation method of this invention, a series of active sites with different metal-non-metal coordination can be obtained, significantly reducing the aggregation of metal atoms during high-temperature annealing, resulting in a highly loaded single-atom catalyst.

[0057] A third aspect of the invention provides the application of single-atom catalysts in fuel cell reactions, wastewater and air purification, organic synthesis, and gas conversion.

[0058] The present invention relates to a technical solution for the application of single-atom catalysts in fuel cell reactions, wastewater and air purification, organic synthesis, and gas conversion, which has at least the following beneficial effects:

[0059] The single-atom catalyst of the present invention is used to catalyze fuel cell reactions, such as the oxidation reactions of hydrogen, methanol and ethanol, and can improve energy conversion efficiency.

[0060] The single-atom catalyst of the present invention is used to treat pollutants such as nitrogen oxides (NOx) and heavy metals in wastewater and air, with higher treatment efficiency.

[0061] The single-atom catalyst of this invention, used in organic synthesis, is beneficial for optimizing reaction selectivity and improving catalytic activity.

[0062] The single-atom catalyst of the present invention can improve the efficiency of gas conversion processes, such as the conversion of methane to methanol. Attached Figure Description

[0063] Figure 1 This is the XRD pattern of the single-atom catalyst prepared in Example 1.

[0064] Figure 2 This is a SEM image of the single-atom catalyst prepared in Example 1.

[0065] Figure 3 This is a TEM image of the single-atom catalyst prepared in Example 1.

[0066] Figure 4 This is a HADDF-STEM image of the single-atom catalyst prepared in Example 1.

[0067] Figure 5 The image shows the Fourier transform (FT)-EXAFS spectra of the single-atom catalyst, Co foil, CoO, and CoPc prepared in Example 1 at the Co K-edge.

[0068] Figure 6 This is a high-rate XPS spectrum of the Co 2p of the single-atom catalyst prepared in Example 1.

[0069] Figure 7 XPS full spectrum of the single-atom catalyst prepared in Example 1.

[0070] Figure 8 This is a HADDF-STEM image of the multi-metal single-atom catalyst prepared in Example 5.

[0071] Figure 9 The images show the HADDF-STEM image and corresponding elemental distribution diagram of the multi-metal single-atom catalyst prepared in Example 5. Detailed Implementation

[0072] The following are specific embodiments of the present invention, and the technical solutions of the present invention will be further described in conjunction with the embodiments, but the present invention is not limited to these embodiments.

[0073] In some embodiments of the present invention, the present invention provides a single-atom catalyst, comprising a support and a metal single atom supported on the support, wherein the metal single atom comprises at least one selected from Co atom, Fe atom, Ni atom, Zn atom, Cu atom, Sn atom, W atom, Ga atom, Ir atom, Pt atom, Bi atom, Cd atom, Mo atom, Zr atom, Cr atom, Mn atom, V atom, In atom, Pd atom, Ag atom, Lu atom, Rh atom, and Au atom.

[0074] It is understood that the single-atom catalyst of the present invention, including the support and the metal single atom supported on the support, can provide high catalytic activity because each catalytic center can participate in the reaction, avoiding the excessive stacking that may exist in multi-atom catalysts. At the same time, the distribution and properties of the catalytic centers can be more precisely controlled to achieve a more precise catalytic effect.

[0075] Furthermore, the single-atom catalyst of this invention helps to improve reaction selectivity, reduce the generation of side reactions, and thus improve product purity. At the same time, it exhibits good catalytic stability, resisting deactivation or poisoning and extending the catalyst's lifespan.

[0076] It can also be understood that the single-atom catalyst of the present invention includes at least one of Co atoms, Fe atoms, Ni atoms, Zn atoms, Cu atoms, Sn atoms, W atoms, Ga atoms, Ir atoms, Pt atoms, Bi atoms, Cd atoms, Mo atoms, Zr atoms, Cr atoms, Mn atoms, V atoms, In atoms, Pd atoms, Ag atoms, Lu atoms, Rh atoms, and Au atoms. Specific metal single atoms can be selected as needed, reducing the use of expensive metals, resulting in greater atom economy and contributing to the sustainable use of resources.

[0077] In some embodiments of the present invention, the carrier comprises reduced graphene oxide.

[0078] It should be noted that graphene is a single-layer planar crystalline material composed of carbon atoms, possessing excellent electrical and thermal conductivity, extremely high mechanical properties, and chemical stability. However, graphene also has some drawbacks, such as flammability and instability. Therefore, graphene derivatives—graphene oxide and reduced graphene—have been widely studied and applied.

[0079] Furthermore, graphene oxide is an oxidation product formed by oxidizing graphene. It possesses high chemical stability, thus making it applicable in fields such as drug delivery, advanced energy storage, and sensing technology. Graphene oxide can also be modified through surface modification to acquire various properties and applications. For example, by combining it with polymers and biomolecules, it can be used to create strong and flexible nanomaterials.

[0080] Furthermore, reduced graphene oxide is simply called reduced graphene. Reduced graphene is a carbon material obtained by reducing graphene oxide. Compared to graphene and graphene oxide, reduced graphene possesses characteristics such as bipolar charge, electron-rich properties, and high controllability, and has been widely studied and applied in fields such as biosensing, energy storage, solid-state capacitors, and semiconductors. For example, through thin-film stacking technology, reduced graphene can be applied to high-power energy storage devices.

[0081] In some embodiments of the present invention, the loading of metal single atoms is 2wt% to 25wt%.

[0082] In some embodiments of the present invention, the loading of metal single atoms is 5 wt% to 17 wt%.

[0083] The single-atom catalyst of the present invention avoids the aggregation of metal atoms, and when the metal single atom is Co atom, the loading of the metal single atom can be as high as 16.58 wt%.

[0084] In other embodiments of the present invention, a method for preparing a single-atom catalyst is provided, comprising the following steps:

[0085] S1: Disperse the carrier raw material in a solvent, add a pore-forming agent, an anchoring agent and a metal salt, stir and freeze dry to obtain the precursor;

[0086] S2: After subjecting the precursor to self-propagating combustion, the product is annealed in a protective atmosphere to obtain the single-atom catalyst of the present invention.

[0087] It is understood that precursor regulation is one of the key factors in the directional construction of pyrolysis products in high-temperature pyrolysis preparation of single-atom carbon materials. Therefore, selecting single-atom material precursors with suitable structures and pre-constructing single atoms and surrounding chemical structural sites is an effective means of efficiently preparing high-density single / multi-atom carbon materials. Thus, finding suitable ligands is crucial for synthesizing highly loaded single-atom carbon materials. The preparation method of this invention is based on a self-propagating combustion reduction support raw material (such as graphene oxide), pre-anchoring metal atoms to surrounding chemical structural sites, and then performing annealing treatment, ultimately successfully constructing a highly loaded metal single-atom catalyst (i.e., metal single-atom reduced graphene oxide material).

[0088] The preparation method of the present invention does not require expensive equipment and complex process control, the reaction conditions are not harsh, the raw materials are readily available, the production cost is low, and it is easy to industrialize.

[0089] In step S1:

[0090] The role of pore-forming agents is to prepare porous carriers. If the carrier raw material is graphene oxide, then porous graphene refers to carbon materials with nanoscale pores on a two-dimensional surface. Porous graphene not only retains the excellent properties of graphene, but also, compared to inert graphene, the presence of pores on the surface promotes improved material transport efficiency. In particular, atomic-level pores can be used to sieve different sizes. More importantly, the introduction of pores effectively opens the band gap of graphene, promoting its application in the field of electronic devices.

[0091] Zero-valent metal single atoms are extremely unstable and tend to aggregate, eventually forming metal nanoparticles. Therefore, a solid host material (primarily reduced graphene oxide in this invention) is needed to support non-metallic atoms such as O, N, S, P, and B, enabling them to form chemical bonds with the metal single atoms and create stable metal single-atom sites. Thus, the anchoring agent in this invention is used to form stable chemical bonds with the metal atoms, resulting in uniformly dispersed and stable metal single-atom materials.

[0092] In step S2:

[0093] Self-propagation high-temperature synthesis (SHS), also known as combustion synthesis, is a technique that utilizes the self-heating and self-conduction of the high heat of chemical reaction between reactants to synthesize materials. Once ignited, the reactants automatically propagate to unreacted areas until the reaction is complete, making it a method for preparing high-temperature inorganic compound materials. In this invention, alkali metals are used as igniters. After heating, graphene oxide reacts with the alkali metal surface, resulting in a self-propagating reaction. Therefore, it is unnecessary to add the alkali metal to the precursor, avoiding the introduction of alkali metal impurities. The alkali metal acts only as an igniter; once the precursor is ignited, subsequent reactions can proceed.

[0094] The purpose of annealing is to further improve the graphitization degree of the material and the high-temperature stability of single atoms.

[0095] In some embodiments of the present invention, the self-propagating combustion in step S2 can be carried out in a low-oxygen environment, such as a glove box.

[0096] The high oxygen content in the atmosphere causes the reduction reaction to be rapid and intense, resulting in the complete combustion of the graphene carbon material in the sample to produce carbon dioxide gas. Therefore, the sample needs to be ignited in a low-oxygen environment, such as a glove box. The oxygen content in the glove box is less than 0.1 ppm, which is still sufficient to ignite the precursor and ultimately cause a self-propagating reaction.

[0097] In some embodiments of the present invention, the carrier material includes graphene oxide.

[0098] In some embodiments of the present invention, the solvent includes water.

[0099] In some embodiments of the present invention, the pore-forming agent includes H2O2.

[0100] In some embodiments of the present invention, the anchoring agent includes at least one of nitrogen-containing anchoring agents, sulfur-containing anchoring agents, phosphorus-containing anchoring agents, and boron-containing anchoring agents.

[0101] In some embodiments of the present invention, the anchoring agent includes at least one of urea, dicyandiamine, boric acid, ammonium thiocyanate, sodium hypophosphite, and phytic acid.

[0102] In some embodiments of the present invention, in step S1, the mass ratio of the carrier material to the metal single atom is 1:0.5 to 0.6.

[0103] The carrier material includes graphene oxide.

[0104] In some embodiments of the present invention, in step S1, the carrier raw material is dispersed in a solvent, and the concentration of the carrier raw material in the formed solution is 1 mg / mL to 10 mg / mL.

[0105] In some embodiments of the present invention, in step S1, the carrier raw material is dispersed in a solvent, and the volume ratio of the solution to the pore-forming agent is 10 to 100:1.

[0106] In some embodiments of the present invention, the molar ratio of anchoring agent to metal salt is 1 to 4:1.

[0107] In some embodiments of the present invention, the metal salt includes at least one selected from nitrates, sulfates, hydrochlorides, acetylacetone salts, acetates, and oxalates.

[0108] Metal salts are metal salts containing a corresponding single-atom element of a metal.

[0109] In some embodiments of the present invention, the stirring time is 1 hour to 24 hours.

[0110] In some embodiments of the present invention, freeze-drying includes liquid nitrogen freezing and cold trap freezing.

[0111] In some embodiments of the present invention, the freeze-drying time is 24h to 72h.

[0112] The purpose of freeze drying is to effectively separate the metal compounds and non-metal anchoring agents by these numerous cavities during the process, thereby ensuring that as many metal centers as possible are evenly distributed in the porous graphene for subsequent pre-anchoring, ultimately obtaining a uniformly dispersed single-atom catalyst.

[0113] In some embodiments of the present invention, the ignition temperature for self-propagating combustion is 200°C to 600°C.

[0114] In some embodiments of the present invention, the self-propagating combustion time is 0.01s to 1.00s.

[0115] In some embodiments of the present invention, ignition of self-propagating combustion can be achieved using alkali metals, such as sodium. Alkali metals serve merely as a heat source, only needing to generate heat transfer energy; ignition of the alkali metal itself is not required, and therefore, reaching its combustion temperature is unnecessary. The minimum temperature required to ignite graphene oxide is only 200°C, constituting low-temperature self-propagating combustion, which effectively achieves energy-saving effects.

[0116] In some embodiments of the present invention, the annealing process includes: heating to 600°C to 900°C at a rate of 1°C / min to 10°C / min, holding at that temperature for 2 hours to 5 hours to further improve the graphitization degree and single-atom high-temperature stability of the material, and then naturally cooling to room temperature.

[0117] Annealing can be performed in a tube furnace.

[0118] This invention utilizes a low-temperature self-propagating combustion method, providing abundant lone pairs of electrons for capturing metal ions, forming abundant and uniform anchoring sites for metal and non-metal atoms, thereby pre-anchoring metal atoms within the carbon framework. Through the preparation method of this invention, a series of active sites with different metal-non-metal coordination can be obtained, significantly reducing the aggregation of metal atoms during high-temperature annealing, resulting in a highly loaded single-atom catalyst.

[0119] In other embodiments of the present invention, the present invention provides the application of single-atom catalysts in fuel cell reactions, wastewater and air purification, organic synthesis and gas conversion.

[0120] It is understood that the single-atom catalyst of the present invention, when used to catalyze fuel cell reactions such as the oxidation reactions of hydrogen, methanol and ethanol, can improve energy conversion efficiency.

[0121] The single-atom catalyst of the present invention is used to treat pollutants such as nitrogen oxides (NOx) and heavy metals in wastewater and air, with higher treatment efficiency.

[0122] The single-atom catalyst of this invention, used in organic synthesis, is beneficial for optimizing reaction selectivity and improving catalytic activity.

[0123] The single-atom catalyst of the present invention can improve the efficiency of gas conversion processes, such as the conversion of methane to methanol.

[0124] The technical solution of the present invention will be better understood below with reference to specific embodiments.

[0125] In the examples, all raw materials were obtained from commercially available sources, and the graphene was purchased from Frontier Nanotech.

[0126] Example 1

[0127] This embodiment provides a single-atom catalyst with reduced graphene oxide as the support, and Co single atoms dispersed on the surface of the reduced graphene oxide.

[0128] The specific preparation method is as follows:

[0129] Step S1: Take 5 mL of graphene oxide aqueous solution with a mass density of 5 mg / mL, then add 15 μL H2O2, 5 mg cobalt nitrate and 3 mg dicyandiamine, which are respectively oxidant, metal source and non-metal anchoring agent. Finally, stir for 3 h to obtain a uniformly dispersed liquid, freeze with liquid nitrogen and then put it into a freeze dryer for 30 h.

[0130] Step S2: The precursor obtained in step S1 is subjected to self-propagation and ignited with sodium metal in a glove box at an ignition temperature of 260°C. After 20ms, a reduced graphene oxide precursor pre-anchored with metal Co atoms is obtained.

[0131] Step S3: The material obtained in S2 is placed in a high-temperature tube furnace and heated to 600℃ at a heating rate of 3℃ / min under an inert atmosphere and held at that temperature for 2 hours. Then it is naturally cooled to room temperature to obtain high metal single-atom Co reduced graphene oxide material.

[0132] Example 2

[0133] This embodiment provides a single-atom catalyst with reduced graphene oxide as the support, and V single atoms dispersed on the surface of the reduced graphene oxide.

[0134] The specific preparation method is as follows:

[0135] Step S1: Take 5 mL of graphene oxide aqueous solution with a mass density of 2 mg / mL, then add 8 μL of H2O2, 5 mg of vanadium chloride and 3 mg of ammonium thiocyanate, which are respectively oxidant, metal source and non-metal anchoring agent. Finally, stir for 10 h to obtain a uniformly dispersed liquid, freeze it in a cold trap and then put it into a freeze dryer to dry for 24 h.

[0136] Step S2: The precursor obtained in step S1 is subjected to self-propagation. Li metal is used for ignition in a glove box at an ignition temperature of 300°C. After 10 ms, a reduced graphene oxide precursor pre-anchored with metal V atoms is obtained.

[0137] Step S3: The material obtained in S2 was placed in a high-temperature tube furnace and heated to 700℃ at a heating rate of 5℃ / min under an inert atmosphere for 3 hours. Then it was naturally cooled to room temperature to obtain a catalyst with high single-atom V loading.

[0138] Example 3

[0139] This embodiment provides a single-atom catalyst with reduced graphene oxide as the support, and Cr single atoms dispersed on the surface of the reduced graphene oxide.

[0140] The specific preparation method is as follows:

[0141] Step S1: Take 5 mL of graphene oxide aqueous solution with a mass density of 6 mg / mL, then add 18 μL of H2O2, 10 mg of Cr(Ac)3 and 8 mg of boric acid, which are respectively oxidant, metal source and non-metal anchoring agent. Finally, stir for 8 h to obtain a uniformly dispersed liquid, freeze with liquid nitrogen and then put it into a freeze dryer for 24 h.

[0142] Step S2: The precursor obtained in step S1 is subjected to self-propagation and ignited in air with a lighter at an ignition temperature of 400°C. After 20ms, a reduced graphene oxide precursor pre-anchored with metal Cr atoms is obtained.

[0143] Step S3: The material obtained in S2 was placed in a high-temperature tube furnace and heated to 800℃ at a heating rate of 6℃ / min under an inert atmosphere for 2 hours. Then it was naturally cooled to room temperature to obtain a catalyst with high single-atom Cr loading.

[0144] Example 4

[0145] This embodiment provides a single-atom catalyst with reduced graphene oxide as the support, and V single atoms dispersed on the surface of the reduced graphene oxide.

[0146] The specific preparation method is as follows:

[0147] Step S1: Take 5 mL of graphene oxide aqueous solution with a mass density of 2 mg / mL, then add 8 μL of H2O2, 5 mg of vanadium chloride and 3 mg of ammonium thiocyanate, which are respectively oxidant, metal source and non-metal anchoring agent. Finally, stir for 10 h to obtain a uniformly dispersed liquid, freeze it in a cold trap and then put it into a freeze dryer to dry for 24 h.

[0148] Step S2: The precursor obtained in step S1 is subjected to self-propagation. Li metal is used for ignition in a glove box at an ignition temperature of 300°C. After 10 ms, a reduced graphene oxide precursor pre-anchored with metal V atoms is obtained.

[0149] Step S3: The material obtained in S2 was placed in a high-temperature tube furnace and heated to 700℃ at a heating rate of 5℃ / min under an inert atmosphere for 3 hours. Then it was naturally cooled to room temperature to obtain a catalyst with high single-atom V loading.

[0150] Example 5

[0151] This embodiment provides a single-atom catalyst with reduced graphene oxide as the support. The surface of the reduced graphene oxide is dispersed with single atoms of Cr, V, Co, Mn, Ni, Zn, Cd, Sn, Pt, and W.

[0152] The specific preparation method is as follows:

[0153] Step S1: Take 5 mL of graphene oxide aqueous solution with a mass density of 2 mg / mL, then add 20 μL of H2O2, 1 mg Cr(Ac)3, 1 mg vanadium chloride, 1 mg manganese chloride, 2 mg cobalt chloride, 1 mg nickel nitrate, 1 mg zinc chloride, 1 mg cadmium acetate, 1 mg stannous chloride, 1 mg chloroplatinic acid, 1 mg ammonium tungstate and 10 mg dicyandiamide. Finally, stir for 24 h to obtain a uniformly dispersed liquid, freeze it with liquid nitrogen and then put it into a freeze dryer for 24 h.

[0154] Step S2: The precursor obtained in step S1 is subjected to self-propagation and ignited in the air with a lighter at an ignition temperature of 400°C. After 20ms, a reduced graphene oxide precursor pre-anchored with multiple metal atoms is obtained.

[0155] Step S3: The material obtained in S2 is placed in a high-temperature tube furnace and heated to 900℃ at a heating rate of 6℃ / min under an inert atmosphere N2 for 2 hours. Then it is naturally cooled to room temperature to obtain a catalyst with a high loading of multi-atoms.

[0156] Structural characterization

[0157] The single-atom catalyst prepared in Example 1 was characterized by X-ray powder diffraction, such as... Figure 1 As shown. From Figure 1 It can be seen that, apart from the characteristic peak of C, there is no crystalline phase of metal nanoparticles.

[0158] The single-atom catalyst prepared in Example 1 was characterized by scanning electron microscopy, such as... Figure 2 As shown. From Figure 2 It can be seen that no metal atoms agglomerate into particles in the reduced graphene.

[0159] The single-atom catalyst prepared in Example 1 was characterized by transmission electron microscopy, such as... Figure 3 As shown. From Figure 3 It can be seen that there are no metal nanoparticles on the surface of reduced graphene.

[0160] The single-atom catalyst prepared in Example 1 was characterized by high-angle annular dark-field scanning transmission electron microscopy, such as... Figure 4 As shown. From Figure 4 It can be seen that a large number of metal single atoms are uniformly dispersed on the surface of the reduced graphene.

[0161] The single-atom catalyst prepared in Example 1 was characterized by X-ray absorption fine structure analysis, such as... Figure 5 As shown. From Figure 5 It can be seen that the characteristic peak of the Co-Co bond appears in In Example 1, no corresponding characteristic peaks were observed, further confirming the formation of single atoms.

[0162] Combination Figures 1 to 5 The morphology, crystal phase, and surface electronic structure characteristics of the samples jointly proved that in the catalyst prepared in Example 1, a large number of metal single atoms were uniformly dispersed on the surface of reduced graphene oxide and did not agglomerate to form metal nanoparticles.

[0163] The single-atom catalyst prepared in Example 1 was characterized by X-ray photoelectron spectroscopy, such as... Figure 6 and Figure 7 As shown. From Figure 6 It can be seen that the peaks in the high-resolution Co XPS are not attributed to elemental cobalt. From... Figure 7 It can be seen that there are no other elements besides Co, N, C, and O.

[0164] The single-atom catalyst prepared in Example 1 was analyzed according to XPS full spectrum ( Figure 7 The atomic percentage and mass percentage of different elements were quantitatively measured and are shown in Table 1.

[0165] Table 1

[0166] Element C N O Co wt.% 73.37 6.64 3.41 16.58 at.% 88.55 5.61 2.52 3.32

[0167] As can be seen from Table 1, the proportion of metallic Co is 16.58 wt%.

[0168] The single-atom catalyst prepared in Example 5 was characterized by high-angle annular dark-field scanning transmission electron microscopy, such as... Figure 8 As shown. From Figure 8 It can be seen that a large number of metal single atoms are loaded on the surface of the reduced graphene.

[0169] The elemental distribution of the multi-metal single-atom catalyst prepared in Example 5 was characterized by high-angle annular dark-field scanning transmission electron microscopy, such as... Figure 9 As shown. From Figure 9It can be seen that ten elements, namely V, Cr, Mn, Co, Ni, Zn, Cd, Sn, W, and Pt, are uniformly dispersed in the rGO high-entropy alloy. The above results show that it is experimentally feasible to use single-atom anchor points as structural units to assemble multi-metal composite SACs.

[0170] The present invention has been described in detail above with reference to the embodiments. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A process for the preparation of a single-atom catalyst, characterized in that, The single-atom catalyst comprises a support and metal single atoms supported on the support. The support is reduced graphene oxide. The metal single atoms include at least one of Co, Fe, Ni, Zn, Cu, Sn, W, Ga, Ir, Pt, Bi, Cd, Mo, Zr, Cr, Mn, V, In, Pd, Ag, Lu, Rh, and Au atoms. The loading amount of the metal single atoms is 2wt%~25wt%. The anchoring agent is selected from at least one of urea, dicyandiamine, boric acid, ammonium thiocyanate, sodium hypophosphite, and phytic acid. The preparation method of the single-atom catalyst includes the following steps: S1: Disperse the carrier raw material in a solvent, add pore-forming agent H2O2, anchoring agent and metal salt, stir and freeze dry to obtain the precursor; S2: After subjecting the precursor to self-propagating combustion, the product is annealed in a protective atmosphere to obtain the single-atom catalyst. The ignition temperature of the self-propagating combustion is 200℃~600℃.

2. The production method according to claim 1, characterized by, The molar ratio of the anchoring agent to the metal salt is 1 to 4:

1.

3. The preparation method according to claim 1, characterized in that, The annealing process includes: heating to 600℃~900℃ at a rate of 1℃ / min~10℃ / min, and holding at that temperature for 2h~5h.

4. The application of the single-atom catalyst prepared by the method described in claim 1 in fuel cell reactions, nitrogen oxide treatment, and methane to methanol conversion.

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