A method for regulating the coordination environment of single atoms and nitrogen

Abstract

The invention discloses a method for regulating the coordination environment of a single atom and nitrogen; the invention aims to provide a method for regulating the coordination environment of a single atom and nitrogen, and opens up a path for rationally designing a catalyst with high activity, high selectivity and high stability for use in certain demanding reactions; the technical scheme comprises the following steps: 1) adding different ligands to change the coordination regulation of the metal active center during the preparation process of dispersing and loading or encapsulating the metal active center on a carrier material at the atomic level, such as using ball milling, atomization and impregnation methods to achieve atomic-level dispersion of the metal active center; 2) changing the coordination number of the metal active center by adjusting the calcination temperature, calcination time, calcination atmosphere and calcination times; the invention belongs to the field of materials science and engineering technology.

Description

Technical Field

[0001] The invention belongs to the field of material science and engineering technology, and in particular relates to a method for regulating the coordination environment of a single atom and nitrogen. Background Art

[0002] Since single-atom catalysts were proposed by Academician Zhang Tao and others in 2011, they have attracted widespread attention due to their special geometric structure and electronic structure, high activity and high selectivity. Single-atom catalysts have nearly 100% atomic utilization, and the catalytic active sites and active centers are fully exposed. In addition, the active sites exposed by single-atom catalysts are highly uniform, which provides a good material model for regulating the metal coordination environment, exploring the essence of catalysis, and understanding the mechanism and structure-activity relationship of the catalytic process.

[0003] The spatial microenvironment of a single atom directly affects its activity, selectivity and stability in the catalytic process. When the single atom active sites anchored on nitrides and oxides have different coordination numbers and different coordination spaces, they will lead to completely different catalytic performance. Changes in the ligand environment will change the activation and dissociation of H2 on its surface, which will directly affect the rate of catalytic hydrogenation. In addition, changes in the coordination environment of the active center of a single atom catalyst will lead to changes in the hydrogenation energy barrier of a specific functional group on its surface, and then the hydrogenation energy barrier of a specified functional group can be reduced by adjusting the coordination, thereby achieving the effect of preferential selective hydrogenation of a specified functional group. Therefore, by regulating the single atom coordination environment, it is possible to rationally design catalysts with high activity, high selectivity and high stability. Summary of the invention

[0004] The microscopic coordination environment of a single-atom catalyst has a decisive influence on its catalytic performance. By changing the coordination environment, not only can the catalytic activity be changed, but also the path of the catalytic reaction can be changed. The purpose of the present invention is to provide a method for regulating the coordination environment of a single atom and nitrogen, so as to open up a path for the rational design of catalysts with high activity, high selectivity and high stability for certain demanding reactions.

[0005] To this end, the technical solution provided by the present invention is as follows:

[0006] A method for regulating the coordination environment of a single atom and nitrogen comprises the following steps:

[0007] 1) Spreading a nitrogen-doped carrier material on the surface of a glass plate, and dispersing a metal precursor solution on the surface of the carrier material by a precursor atomization method; mixing the carrier and the metal precursor solution and re-smoothing them every 20-40 minutes, and collecting the carrier material loaded with the metal element after accumulating for 8-12 hours;

[0008] 2) placing the collected materials in a tubular furnace, heating them to 100-1200°C at a heating rate of 1-10°C / min in an atmosphere of one or a combination of ammonia, argon, nitrogen, and hydrogen, and keeping the temperature for 1-3 hours to obtain a coordinated and stable single atom catalyst.

[0009] Furthermore, in the above method for regulating the coordination environment of a single atom and nitrogen, the metal precursor is one or a mixture of acetylacetonate, metal nitrate, metal chlorate, or metal acetate.

[0010] Furthermore, in the above-mentioned method for regulating the coordination environment of a single atom and nitrogen, the metal in the metal precursor is one or a mixture of several of the elements selected from the group consisting of nickel, cobalt, copper, palladium, iron, iridium, ruthenium, rhodium, platinum and tin.

[0011] Furthermore, in the above method for regulating the coordination environment of a single atom and nitrogen, when the carrier material does not contain nitrogen, the ligand and the carrier are heated to 400-800°C at a rate of 1-10°C / min in an ammonia atmosphere and kept warm for 1-3h to obtain a carrier material doped with nitrogen.

[0012] Furthermore, in the above method for regulating the coordination environment of a single atom and nitrogen, the carrier material doped with nitrogen is one or a mixture of carbon trinitrogen tetrakis, urea, melamine, pyridine and pyrrole.

[0013] Furthermore, in the above-mentioned method for regulating the coordination environment of a single atom and nitrogen, the ligand is one or a combination of ethylenediaminetetraacetate, 1,10-phenanthroline, dimethylimidazole, triethanolamine, and ethylenediamine; and the carrier material is one or a combination of zinc powder, copper powder, cobalt oxide, iron oxide, zinc oxide, manganese oxide, copper oxide, aluminum oxide, diamond, acetylene black, carbon balls, activated carbon, graphene and porphyrin.

[0014] Furthermore, in the above-mentioned method for regulating the coordination environment of a single atom and nitrogen, the specific operation of the precursor atomization method is: dissolving the metal precursor and the ligand in a solvent at a concentration of 0.01-2 mol / L, and uniformly depositing the dissolved solution on the surface of the carrier material through a nano-atomization device.

[0015] Furthermore, in the above-mentioned method for regulating the coordination environment of a single atom and nitrogen, the equipment parameters of the precursor atomization method are: the diameter of the sprayed droplets is 0.001-200um, and the flow rate is 1-200mL / min.

[0016] Furthermore, in the above method for regulating the coordination environment of a single atom and nitrogen, the calcination temperature is 100-1200°C, the heating rate is 1-30°C / min, and the holding time is 0.1-20h.

[0017] Furthermore, in the above method for regulating the coordination environment of a single atom and nitrogen, the calcination times are 1-5 times.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. The present invention improves the catalytic activity by regulating the coordination, and can achieve the original catalytic effect with less catalyst, which effectively saves the cost of using the catalyst. At the same time, the improvement of catalytic activity accelerates the reaction process, effectively saves time cost, and improves the production efficiency of the product.

[0020] 2. The present invention can achieve selective catalysis of different types of functional groups by regulating coordination, realize the conversion of catalytic substrates in a specified direction, reduce the generation of side reactions, reduce the complex processes such as separation and purification of products caused by side reactions, and reduce production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a spherical aberration electron microscope image of the catalyst prepared in Comparative Example 1;

[0022] Figure 2 is the fitting of the synchrotron radiation characterization of the catalyst prepared in Comparative Example 1;

[0023] Figure 3 The catalytic activity comparison results of the single-atom catalysts described in Comparative Example 1 and Example 1 when one platinum element is coordinated with five nitrogen elements and one platinum element is coordinated with three nitrogen elements for hydrogenation of nitrobenzene;

[0024] Figure 4 The catalytic results of selective hydrogenation of 3-nitrophenylacetylene when one platinum element is coordinated with four nitrogen elements and one platinum element is coordinated with three nitrogen elements in the single atom catalyst in Comparative Example 2 and Example 2 are compared. DETAILED DESCRIPTION

[0025] The present invention is described in more detail below in conjunction with embodiments, but the protection scope of the present invention is not limited to the scope represented by the embodiments.

[0026] Example 1

[0027] First, 2g of activated carbon was placed in a tube furnace, and in an ammonia atmosphere, the temperature was raised to 600℃ at a heating rate of 5℃ / min and kept warm for two hours to obtain an activated carbon carrier doped with nitrogen. 0.2g of chloroplatinic acid was dissolved in 400mL of deionized water, and 2g of activated carbon was spread on the surface of a clean glass plate. The prepared chloroplatinic acid solution was passed through a nano-atomization device, with a spray droplet diameter of 100um and a flow rate of 100mL / min, and evenly deposited on the activated carbon carrier doped with nitrogen. The carrier was mixed and re-laid every 30 minutes, and the carrier material loaded with platinum was collected after accumulating for 10 hours. The collected material was placed in a tube furnace, and in a nitrogen atmosphere, the temperature was raised to 600℃ at a heating rate of 5℃ / min and kept warm for two hours. After secondary calcination in nitrogen, a single-atom catalyst with a stable coordination of a platinum element and four nitrogen elements was obtained.

[0028] Comparative Example 1

[0029] Take 0.2g of chloroplatinic acid and dissolve it in 400mL of deionized water, take 2g of activated carbon and spread it on the surface of a clean glass plate, pass the prepared chloroplatinic acid solution through a nano-atomizer, spray droplets with a diameter of 100um and a flow rate of 100mL / min, and evenly deposit it on the surface of the activated carbon. Mix the carrier and spread it flat every 30 minutes, and collect the activated carbon loaded with platinum after accumulating for 10 hours. Place the collected material in a tubular furnace, heat it to 600℃ at a heating rate of 5℃ / min in an ammonia atmosphere, and keep it warm for two hours to obtain a single atom catalyst with a stable coordination of a platinum element and five nitrogen elements. Figure 1 The spherical aberration electron microscope image of the prepared catalyst shows that platinum metal is dispersed on the surface of the carrier material in an isolated atomic state. The catalyst prepared in Example 1 and the catalyst in Comparative Example 1 were tested for catalytic effect, and nitrobenzene was used as a catalytic model for comparison. Figure 3 The results of the test of two coordination structures catalyzing nitrobenzene hydrogenation under the same reaction conditions show that the catalytic activity of one platinum element coordinated with four nitrogen elements is about 40 times that of one platinum element coordinated with five nitrogen elements. Table 1 is the fitting results of the synchrotron radiation characterization of the catalyst prepared in Comparative Example 1;

[0030] Table 1. Synchrotron radiation fitting results

[0031]

[0032] Ptfoil: platinum foil, used as a reference for synchrotron radiation characterization fitting. Pt1 / NC: platinum (Pt) single atoms supported on the surface of nitrogen (N)-containing carbon material (C), subscript 1 represents single atom.

[0033] Example 2

[0034] Take 10g of melamine, heat it to 600℃ at a heating rate of 5℃ / min in a nitrogen atmosphere and keep it warm for two hours to obtain a carbon material doped with nitrogen. Take 0.2g of chloroplatinic acid and dissolve it in 400mL of deionized water, take the carbon material doped with nitrogen and spread it on the surface of a clean glass plate, pass the prepared chloroplatinic acid solution through a nano-atomization device, spray the droplet diameter of 100um, and the flow rate is 100mL / min, and evenly deposit it on the surface of the carrier material. Mix the carrier and re-lay it every 30 minutes, and collect the carrier material loaded with platinum after accumulating for 10 hours. The collected material is placed in a tube furnace, heated to 600℃ at a heating rate of 10℃ / min in a 10% H2 / N2 atmosphere and kept warm for two hours to obtain a stable coordination structure of platinum coordinated with three nitrogen elements. Figure 2 For the fitting of the synchrotron radiation test, Figure 2 It can be seen that the main peak has a high fitting degree, indicating that the fitting result is good and the result is highly reliable. Table 1 is the fitting result, from which it can be seen that the coordination number of Pt and N is 3, that is, one Pt is coordinated with three N.

[0035] Comparative Example 2

[0036] Take 0.2g of chloroplatinic acid and dissolve it in 400mL of deionized water, take 10g of melamine and spread it on the surface of a clean glass plate, pass the prepared chloroplatinic acid solution through a nano-atomizer, spray droplets with a diameter of 100um and a flow rate of 100mL / min, and evenly deposit it on the surface of melamine, mix the carrier and re-lay it every 30 minutes, and collect the carrier material loaded with platinum after accumulating for 10 hours. The collected material is placed in a tube furnace, heated to 600℃ at a heating rate of 10℃ / min in a 10% H2 / N2 atmosphere, and kept warm for two hours to obtain a single-atom catalyst with a stable coordination of platinum and four nitrogen elements.

[0037] The catalyst prepared in Example 2 was tested for catalytic effect with the catalyst in Comparative Example 2, and 3-nitrophenylacetylene was used as a catalytic model for comparison. Figure 4 These are the test results of the hydrogenation of 3-nitrophenylacetylene catalyzed by two coordination structures under the same reaction conditions. The results show that when a platinum element is coordinated with three nitrogen elements, it has excellent selectivity for the nitro functional group, and can achieve hydrogenation of the nitro group while keeping the alkynyl group unchanged; and when a platinum element is coordinated with four nitrogen elements, it has excellent selectivity for hydrocarbon functional groups, and can achieve the conversion of alkynes into alkanes while the nitro functional group remains almost unchanged.

[0038] Example 3

[0039] Dissolve 0.004g of cobalt nitrate in 400mL of deionized water, take 1g of alumina and spread it on the surface of a clean glass plate, pass the prepared cobalt nitrate solution through a nano-atomizer, spray droplets with a diameter of 100um and a flow rate of 100mL / min, and evenly deposit it on the surface of alumina. Mix the carrier and spread it flat every 30 minutes, and collect the carrier material loaded with cobalt after accumulating for 10 hours. Place the collected material in a tube furnace and bake it at 300℃ for 2h in a 5% H2 / N2 atmosphere to obtain a single-atom catalyst coordinated by cobalt and four oxygen elements.

[0040] Comparative Example 3

[0041] Mix 0.004g of cobalt nitrate and 0.1g of urea and dissolve them in 400mL of deionized water. Take 1g of alumina and spread it on the surface of a clean glass plate. Pass the prepared cobalt nitrate and urea mixed solution through a nano-atomizer, spray droplets with a diameter of 100um and a flow rate of 100mL / min, and evenly deposit them on the surface of alumina. Mix the carrier and spread it flat every 30 minutes. Collect the carrier material loaded with cobalt and urea after accumulating for 10 hours. Place the collected material in a tube furnace and roast it at 300℃ for 2h in a 5% H2 / N2 atmosphere to obtain a single-atom catalyst coordinated by a platinum element, three oxygen elements and one nitrogen element.

Claims

1. A method for regulating the coordination environment of a single atom and nitrogen, characterized in that: The steps include: 1) Spread the nitrogen-doped carrier material on the surface of the glass plate, and disperse the platinum precursor solution on the surface of the carrier material by precursor atomization; mix the carrier and the platinum precursor solution and spread them flat again every 20-40 minutes, and collect the carrier material loaded with platinum after accumulating for 8-12 hours; 2) placing the collected materials in a tube furnace and calcining them in an atmosphere of ammonia, argon, nitrogen, hydrogen or a combination thereof, wherein the calcination is carried out by heating the temperature to 100-1200°C at a heating rate of 1-10°C / min and keeping the temperature for 1-3 hours to obtain a coordinated stable single atom catalyst; the calcination is carried out 1-5 times; The platinum precursor is one or a mixture of platinum acetylacetonate, platinum nitrate, platinum chlorate, and platinum acetate; The nitrogen-doped carrier material is one or a mixture of carbon trinitrogen tetrakis, urea, melamine, pyridine and pyrrole; Alternatively, the nitrogen-doped carrier material is prepared by the following method: the ligand and the carrier are heated to 400-800°C at a rate of 1-10°C / min in an ammonia atmosphere, and kept warm for 1-3h to obtain the nitrogen-doped carrier material; and the ligand is one or a combination of ethylenediaminetetraacetate, 1,10-phenanthroline, dimethylimidazole, triethanolamine and ethylenediamine; the carrier material is one or a combination of diamond, acetylene black, carbon spheres, activated carbon, graphene and porphyrin; The coordination number of Pt and N is from 3 to 4.

2. A method for regulating the coordination environment of a single atom and nitrogen according to claim 1, characterized in that: The specific operation of the precursor atomization method is: dissolving the metal precursor and the ligand in a solvent at a concentration of 0.01-2 mol / L, and uniformly depositing the dissolved solution on the surface of the carrier material through a nano-atomization device.

3. A method for regulating the coordination environment of a single atom and nitrogen according to claim 1, characterized in that: The equipment parameters of the precursor atomization method are: the diameter of the sprayed droplets is 0.001-200 um, and the flow rate is 1-200 mL / min.

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