A method for preparing microporous materials loaded with single-atom and double-atom catalysts

Abstract

The present invention relates to a method for preparing a microporous material-supported single-atom and dual-atom catalyst, belonging to the fields of nanomaterial applications and catalytic technologies. It is characterized in that: using a porous material with a size less than 2 nm as the substrate and an organometallic compound as the metal precursor, dissolving the organometallic compound in supercritical CO2 fluid and uniformly dispersing it into micropores and mesopores, and then obtaining a single-atom or dual-atom catalyst through heat treatment reduction. The catalyst of the present invention realizes the continuous preparation of a single-atom dispersed metal catalyst through a novel method. The metal single atoms are loaded on the carrier through the confinement effect, exposing more metal catalytic active sites, and having broad application prospects in the fields of fine chemistry, organic catalytic reactions, electrocatalysis, etc.

Description

Technical Field

[0001] The invention relates to a method for preparing a single-atom and double-atom catalyst, belonging to the technical field of nano material application and catalysis. Background Art

[0002] More than 80% of the world's chemical production requires catalytic processes, and efficient catalysts play an important role. Catalysts can be divided into homogeneous catalysts, heterogeneous catalysts and enzyme catalysts, of which heterogeneous catalysts account for more than 80%. Heterogeneous catalysts are catalysts in which catalytically active metal nanoparticles are dispersed on a carrier and can be activated and reused. However, compared with homogeneous catalysts, only the metal atoms exposed on the surface are active sites, so the catalytic activity and atomic utilization of heterogeneous catalysts are much lower than those of homogeneous catalysts. Reducing the size of metal particles is one of the important ways to further improve the catalytic activity of heterogeneous catalysts and reduce the cost of catalysts. When the metal in the carrier is not in the form of nanoparticles but in the form of single atoms, the catalyst is a single-atom catalyst. Single-atom catalysts have the advantages of easy separation and recycling of heterogeneous catalysts and high activity and high atomic utilization of homogeneous catalysts. Therefore, single-atom catalysts are called "tomorrow's catalysts", which significantly narrow the gap between homogeneous and heterogeneous catalysts. Single-atom catalysts have the largest metal atom utilization rate and unique structure and properties. They have shown great potential in the rational use of metal resources and the realization of atomic economy, and have become a frontier in catalytic science.

[0003] At present, a lot of research has been done on the preparation of single-atom catalysts, such as impregnation method, co-precipitation method, atomic layer deposition method, electrochemical method and chemical corrosion method. However, the single-atom catalysts obtained by these methods have problems such as low single-atom content, uneven dispersion of single atoms in the carrier, and insufficient exposure of active sites, which seriously restrict the development of single-atom catalysts. The spatial confinement method is a popular method for synthesizing single-atom catalysts in recent years. This method introduces a metal precursor with a diameter smaller than the pore size during the synthesis of the metal-organic framework, and confines the metal precursor to the pores of the carrier, thereby dispersing the metal atoms in the carrier. However, due to mass transfer problems, the accessible active centers of the catalyst are mainly concentrated on the surface, and a large number of metal sites encapsulated in the inner pores of the carrier cannot be utilized, resulting in low utilization of metal single atoms. Summary of the invention

[0004] In order to solve the above technical problems, the present invention uses a porous material mainly composed of micropores as a carrier, disperses organic metals in the micropores under the action of supercritical carbon dioxide fluid, utilizes the spatial confinement effect of the micropores and the heteroatoms of the porous material such as N, O to anchor metal atoms, obtains a single-atom catalyst, and obtains a corresponding diatomic catalyst by regulating the composition of the organic metal compound.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A method for preparing single-atom and double-atom catalysts with supercritical carbon dioxide fluid, characterized in that: a porous material with a size less than 2 nm is used as a substrate, an organic metal compound is used as a metal precursor, and the organic metal compound is dissolved in supercritical CO 2 The atoms are then uniformly dispersed into the micropores and mesopores, and then reduced by heat treatment to obtain single-atom or double-atom catalysts.

[0007] The single-atom or diatomic catalyst is one of Pt, Pd, Ru, Rh, Ir, Ag, Fe, Co, Ni, Cu and Mn dispersed in the microporous material in a single-atom state, or two of the metals are dispersed in the microporous material in a single-atom state; in the single-atom or diatomic catalyst, the single-atom content is ~0.1-1.0at%.

[0008] The method for preparing single-atom and double-atom catalysts using supercritical carbon dioxide fluid is characterized by the following steps:

[0009] (1) adding a certain amount of porous material, organic metal compound, and polar solvent into a high-pressure reactor;

[0010] (2) Pass 99.9% high-purity CO into the autoclave 2 , adjust the temperature and pressure to make CO 2 Reach a supercritical state; after stirring at 200 rpm for a certain period of time, naturally cool to 50 degrees Celsius, release the pressure, and take out the powder.

[0011] (3) Heat treating the powder in step (2) to obtain a single-atom or double-atom catalyst.

[0012] In step (1), the organic metal compound is a compound having a certain solubility in supercritical carbon dioxide, and is any one of acetylacetonate platinum, acetylacetonate palladium, acetylacetonate ruthenium, acetylacetonate ruthenium, acetylacetonate iridium, acetylacetonate platinum silver, acetylacetonate iron, acetylacetonate cobalt, acetylacetonate nickel, acetylacetonate copper, acetylacetonate manganese and acetylacetonate molybdenum, for preparing a single atom catalyst. The mass ratio of the organic metal compound to the porous material is 1:60 to 2:1, wherein the mass ratio is 1:12 as the best; and the volume of the polar solvent is 3% of the total volume of the reactor.

[0013] In step (1), the organic metal compound is a compound having a certain solubility in supercritical carbon dioxide, including: platinum acetylacetonate, palladium acetylacetonate, ruthenium acetylacetonate, ruthenium acetylacetonate, iridium acetylacetonate, platinum acetylacetonate, iron acetylacetonate, cobalt acetylacetonate, nickel acetylacetonate, copper acetylacetonate, manganese acetylacetonate, and molybdenum acetylacetonate; the organic metal compound used to prepare the diatomic catalyst is any two precious metals or any two non-precious metals, the ratio of the two organic metal compounds can be adjusted arbitrarily, the total mass ratio of the two organic metal compounds to the mass of the porous material is 1:60 to 2:15, among which the mass ratio of 1:12 is the best, and the amount of polar solvent added is 3% of the total volume of the reactor.

[0014] In step (1), the microporous material comprises one of the following groups: microporous carbon material, activated carbon, new carbon material with micropores, mesoporous silicon material, microporous silicon material and microporous metal oxide nanomaterial, and porous material with pore size distribution of ~1nm is preferred.

[0015] In step (2), the temperature of the autoclave is 50 to 100 degrees Celsius, preferably 65 degrees Celsius; the pressure is 60 to 110 atmospheres, preferably 100 atmospheres; and the supercritical fluid treatment time is 4 to 24 hours, preferably 12 hours.

[0016] In step (3), for the noble metal catalyst, the heat treatment conditions are: hydrogen / argon mixed gas, the volume ratio is 1:2, and the gas flow rate is 50-500 mL min -1 The heat treatment temperature is 160-300°C, the heating rate is 2°C, and the heat treatment time is 0.5-3 hours. The air flow rate is 50 mL min -1 The best heat treatment time is 2 hours and the heat treatment temperature is 200°C.

[0017] In step (3), for non-precious metal catalysts, the heat treatment conditions are: argon or nitrogen, the gas flow rate is 50-500 mL min -1 , heat treatment temperature 700~1100℃, heating rate 2~35℃min -1 The heat treatment time is 0.5 to 3 hours. The air flow rate is 50 ml min -1 , heating rate is 35℃min -1 The best heat treatment time is 1 hour and the heat treatment temperature is 900℃.

[0018] The single-atom and double-atom catalysts are heterogeneous catalysts used in organic chemical reactions and electrochemical reactions.

[0019] Compared with the prior art, the present invention has the following advantages: the active sites of the catalyst are more exposed, the loading amount is controllable, the loading amount is high, there is no restriction on the type of metal elements, diatomic catalysts can be prepared, the porous carrier has rich selectivity, and the metal type of the single-atom catalyst and the suitable carrier can be customized according to the needs of the catalytic reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The single-atom Pt catalyst obtained in Example 1 is shown in (a) a transmission electron microscope (TEM) image, (b) an AC-STEM image, and (c) an extended X-ray absorption fine structure spectrum (EXAFS) based on synchrotron radiation.

[0021] Figure 2 The single-atom Pd catalyst obtained in Example 2 is shown in (a) a transmission electron microscope (TEM) image, (b) an AC-STEM image, and (c) an extended X-ray absorption fine structure spectrum (EXAFS) based on synchrotron radiation.

[0022] Figure 3 The single-atom Ru catalyst obtained in Example 3 is shown in (a) a transmission electron microscope (TEM) image, (b) an AC-STEM image, and (c) an extended X-ray absorption fine structure spectrum (EXAFS) based on synchrotron radiation.

[0023] Figure 4 This is the spherical aberration scanning transmission electron microscope (AC-STEM) image of the Fe, Co diatomic catalyst obtained in Example 4.

[0024] Figure 5 This is a TEM image of the Pt catalyst prepared by conventional impregnation method obtained in Example 5. DETAILED DESCRIPTION

[0025] The present invention is further described in detail below in conjunction with the embodiments.

[0026] Example 1, using supercritical CO 2 Technology, using microporous carbon materials with a pore size of ~1nm as a carrier, to prepare single-atom Pt catalysts.

[0027] The preparation steps are as follows:

[0028] a) Preparation of Pt precursor loaded with microporous carbon materials

[0029] 1) 5 mg of Pt(acac) 2 The precursor and 60 mg of microporous carbon material were placed in a 50 ml reactor;

[0030] 2) Add 1.5 ml of tetrahydrofuran into the reaction kettle;

[0031] 3) Close the reactor and pressurize 100 atmospheres of CO 2 In a reaction kettle, the mixture was heated to 65°C and kept at this temperature for 12 hours, then naturally cooled to 50°C and the pressure was released to obtain a microporous carbon material loaded with Pt powder material;

[0032] b) Thermal reduction of the powder material in a). The precursor in a) is placed in a tube furnace under H 2 / Ar mixed atmosphere (V / V:1:2), the gas flow rate was 50 mL min -1 , the temperature was raised to 200°C at 2°C, kept at this temperature for 2h, and cooled to room temperature to obtain a single atom Pt catalyst.

[0033] Structural and morphological characterization:

[0034] The microporous carbon material loaded with single-atom Pt catalyst samples obtained in the present invention were characterized by using TEM and AC-STEM to characterize the microscopic morphology and atomic structure of the material. Figure 1 shown. Figure 1 a is a TEM image, from which it can be seen that there are no metal particles. Figure 1 b is the AC-STEM image, from which we can clearly see that many bright spots are evenly distributed on the carbon surface. The bright spots are single-atom Pt, indicating that Pt mainly exists in the catalyst in the form of single atoms. The ICP results show that the loading amount of single atoms under this condition is about 1.0at%. Figure 1 c is the EXAFS based on synchrotron radiation, located at The only bond found was Pt-N(O) bond, but no Pt-Pt bond was found, which proved that the Pt in the catalyst was a single-atom structure.

[0035] Example 2

[0036] The steps of Example 2 are the same as those of Example 1, except that the noble metal precursor Pt(acac) in step a) is 2 Replace with Pd(acac) 2 The morphology of the obtained single-atom Pd catalyst is shown in Figure 2 AC-STEM and synchrotron radiation analysis results prove that the method of the present invention successfully prepares single-atom Pd catalysts.

[0037] Example 3

[0038] The steps of Example 3 are the same as those of Example 1, except that the noble metal precursor Pt(acac) in step a) is 2 Replaced with 3 mg of Ru(acac)3. The morphology of the Ru single atom catalyst obtained is shown in Figure 3AC-STEM and synchrotron radiation analysis results prove that the method of the present invention successfully prepares single-atom Ru catalysts.

[0039] Example 4

[0040] Example 4, using supercritical CO 2 Technology, using microporous carbon materials with a pore size of ~1nm as a carrier, to prepare single-atom Pt catalysts.

[0041] The preparation steps are as follows:

[0042] a) Preparation of Pt precursor loaded on microporous carbon materials

[0043] 1) 4 mg of Fe(acac) 2 and 4mg Co(acac) 2 The precursor and 96 mg of microporous carbon material were placed in a 50 ml reactor;

[0044] 4) Add 1.5 ml of tetrahydrofuran into the reaction kettle;

[0045] 5) Close the reactor and pressurize 100 atmospheres of CO 2 In a reaction kettle, heat to 65°C, keep warm for 12 hours, naturally cool to 50°C and release the pressure to obtain a powder material;

[0046] b) Heat treatment of the powder material in a). The precursor in a) is placed in a tube furnace with an argon gas flow rate of 50 mL min -1 , heat treatment temperature 900℃, heating rate 35℃min -1 , the heat treatment time is 1 hour.

[0047] The morphology of the Fe, Co single atom catalyst obtained is shown in Figure 4 The AC-STEM image proves that the method of the present invention successfully prepares Fe and Co diatomic catalysts.

[0048] Example 5

[0049] The example is to prepare the Pt catalyst by conventional impregnation method. 60 mg of the same microporous material as in Example 1 is dispersed in 100 mL of methanol solution, and 1 mL of 5 mg of Pt(acac) is added. 2 The precursor was obtained by centrifugal washing with water after ultrasonic treatment for 30 minutes and methanol solution. The Pt catalyst was obtained by the same thermal reduction process as in Example 1. Figure 5This is a TEM image of the catalyst. From the image, it can be clearly seen that the Pt nanoparticles are dispersed in the carbon material, proving that only nano Pd catalysts can be obtained by this method, but single-atom Pt catalysts cannot be obtained, proving the superiority of the supercritical carbon dioxide fluid method of the present invention in preparing single-atom catalysts.

Claims

1. A method for preparing microporous materials loaded with single-atom and diatomic catalysts, wherein the single-atom and diatomic catalysts are heterogeneous catalysts for organic chemical reactions and electrochemical reactions. It is characterized in that The porous material with a size less than 2 nm is used as the substrate, the organometallic compound is used as the metal precursor, and the organometallic compound is dissolved in supercritical CO 2 The catalyst is then heat treated and reduced to obtain a single atom or diatomic catalyst. The specific steps are as follows: (1) adding a certain amount of porous material, organic metal compound, and polar solvent into a high-pressure reactor; (2) CO is introduced into the high pressure reactor 2 , adjust the temperature and pressure to make CO 2 Reach a supercritical state; after magnetic stirring for a certain period of time, naturally cool to 50°C, release the pressure, and take out the powder; (3) Heat treating the powder in step (2) to obtain a single-atom or double-atom catalyst. For noble metal catalysts, the heat treatment conditions are: hydrogen / argon mixed gas, the volume ratio is 1:2, and the gas flow rate is 50-500 mL min -1 The heat treatment temperature is 160-300°C, the heating rate is 2°C, and the heat treatment time is 0.5-3 hours. For non-precious metal catalysts, the heat treatment conditions are: argon or nitrogen, the gas flow rate is 50-500 mL min -1 , heat treatment temperature 700~1100℃, heating rate 2~35℃min -1 , the heat treatment time is 0.5 to 3 hours.

2. A method for preparing microporous materials loaded with single-atom and diatomic catalysts as claimed in claim 1, It is characterized in that The single-atom or diatomic catalyst is one of Pt, Pd, Ru, Rh, Ir, Ag, Fe, Co, Ni, Cu and Mn dispersed in the microporous material in a single-atom state, or two of the metals are dispersed in the microporous material in a single-atom state; in the single-atom or diatomic catalyst, the single-atom content is 0.1-1.0at%.

3. A method for preparing microporous materials loaded with single-atom and diatomic catalysts as claimed in claim 1, It is characterized in that In step (1), the organometallic compound is a compound having a certain solubility in supercritical carbon dioxide. For a single-atom catalyst, the organometallic compound is any one of acetylacetonate platinum, acetylacetonate palladium, acetylacetonate ruthenium, acetylacetonate ruthenium, acetylacetonate iridium, acetylacetonate platinum silver, acetylacetonate iron, acetylacetonate cobalt, acetylacetonate nickel, acetylacetonate copper, acetylacetonate manganese and acetylacetonate molybdenum; the mass ratio of the organometallic compound to the porous material is 1:60 to 2:1; for a diatomic catalyst, the organometallic compound is any two precious metals or any two non-precious metals among acetylacetonate platinum, acetylacetonate palladium, acetylacetonate ruthenium, acetylacetonate ruthenium, acetylacetonate iridium, acetylacetonate platinum silver, acetylacetonate iron, acetylacetonate cobalt, acetylacetonate nickel, acetylacetonate copper, acetylacetonate manganese and acetylacetonate molybdenum, the ratio of the two organometallic compounds can be adjusted arbitrarily, the total mass ratio of the two organometallic compounds to the mass ratio of the porous material is 1:60 to 2:15, and the volume of the polar solvent is 3% of the total volume of the reactor.

4. A method for preparing microporous materials loaded with single-atom and diatomic catalysts as claimed in claim 3, It is characterized in that For single-atom catalysts, the mass ratio of the organometallic compound to the porous material is 1:12; for diatomic catalysts, the mass ratio of the total mass of the two organometallic compounds to the porous material is 1:

12.

5. A method for preparing microporous materials loaded with single-atom and diatomic catalysts as claimed in claim 1, It is characterized in that In step (2), CO 2 The volume fraction is 99.9%, the temperature of the high-pressure reactor is 50 to 100° C.; the pressure is 60 to 110 atmospheres; the stirring speed is 200 rpm, and the supercritical fluid treatment time is 4 to 24 hours.

6. A method for preparing microporous materials loaded with single-atom and diatomic catalysts as claimed in claim 5, It is characterized in that The temperature of the autoclave is 65° C., the pressure is 100 atmospheres, and the supercritical fluid treatment time is 12 hours.

7. A method for preparing microporous materials loaded with single-atom and diatomic catalysts as claimed in claim 1, It is characterized in that For noble metal catalysts, the gas flow rate is 50 mL min -1 The heat treatment temperature is 200℃ and the heat treatment time is 2 hours. For non-precious metal catalysts, the air flow rate is 50ml min -1 , heating rate is 35℃min -1 The heat treatment temperature is 900°C and the heat treatment time is 1 hour.

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