阅读说明：本技术 一种分子筛基单原子催化剂及其制备方法 (Molecular sieve based monatomic catalyst and preparation method thereof ) 是由 张华新 张丽丽 王洪林 杨红梅 李立威 于 2021-01-15 设计创作，主要内容包括：本发明公开了一种分子筛基单原子催化剂及其制备方法。该方法以分子筛作为基质,首先在其外表面组装一层蛋白质,然后利用蛋白质络合少量的金属离子,过滤,洗涤,干燥后,在非氧化性气体氛围下热解即可制得氮杂碳材料固定的分子筛基单原子催化剂。本发明首次利用蛋白质作为配位剂和稀释剂,将金属离子均匀固定在分子筛外表面,热解得到活性位点高度暴露的单原子催化剂。该方法不需要复杂的大型仪器设备,制备工艺简单易行,制备的单原子催化剂具有较大的比表面积和孔容,稳定性良好,并且金属活性位点充分暴露于分子筛材料的外表面,便于其与底物的充分接触,因而具有较高的催化效率,可以作为有机化合物加氢反应的催化剂。(The invention discloses a molecular sieve based monatomic catalyst and a preparation method thereof. The method comprises the steps of using a molecular sieve as a matrix, firstly assembling a layer of protein on the outer surface of the molecular sieve, complexing a small amount of metal ions by using the protein, filtering, washing, drying, and pyrolyzing in a non-oxidizing gas atmosphere to obtain the molecular sieve based monatomic catalyst fixed by the aza-carbon material. According to the invention, protein is used as a coordination agent and a diluent for the first time, metal ions are uniformly fixed on the outer surface of the molecular sieve, and the monatomic catalyst with highly exposed active sites is obtained through pyrolysis. The method does not need complex large-scale instruments and equipment, the preparation process is simple and easy to implement, the prepared monatomic catalyst has larger specific surface area and pore volume and good stability, and the metal active sites are fully exposed on the outer surface of the molecular sieve material, so that the monatomic catalyst is convenient to fully contact with a substrate, has higher catalytic efficiency and can be used as a catalyst for hydrogenation reaction of organic compounds.)

1. A molecular sieve based monatomic catalyst is characterized in that metal atoms are coated on the outer surface of a molecular sieve by a nitrogen heterocyclic carbon material to form the molecular sieve based monatomic catalyst.

2. The molecular sieve based monatomic catalyst of claim 1, wherein the metal atoms include any one or more of Co, Ni, Fe, Cu, Au, Ag, Ru, Rh, Pd, Os, Ir, Pt.

3. The molecular sieve based monatomic catalyst of claim 1, wherein the aza-carbon material is derived from protein pyrolysis.

4. The molecular sieve-based monatomic catalyst of claim 1, wherein the molecular sieve includes a microporous molecular sieve, a mesoporous molecular sieve, a macroporous molecular sieve, and a hierarchical molecular sieve.

5. The molecular sieve based monatomic catalyst of claim 1, wherein the metal atoms are dispersed on the outer surface of the molecular sieve.

6. A preparation method of a molecular sieve based monatomic catalyst is characterized by comprising the following steps:

s1, dispersing the molecular sieve material into water, and stirring at room temperature until a uniform mixed solution is formed;

s2, adding a protein solution into the mixed solution, and stirring at room temperature until the assembly reaches the balance;

s3, adding the metal ion solution into the mixed solution, stirring at room temperature until the solution is balanced, performing suction filtration, washing with deionized water, and freeze-drying;

and S4, putting the freeze-dried sample into a tubular furnace, and pyrolyzing the sample under the protection of non-oxidizing gas to obtain the molecular sieve based monatomic catalyst.

7. The method of claim 6, wherein the protein in the protein solution of step S2 is a combination of one or more natural or synthetic or modified proteins.

8. The method of claim 6, wherein the molar ratio of the protein in the protein solution to the metal in the metal ion solution is 1: 0.5-0.01.

9. The method according to claim 6, wherein the metal ions in the solution of metal ions in step S3 are soluble metal salts or metal complexes.

10. The method according to claim 6, wherein the non-oxidizing gas in the step S4 is N₂、He、Ar、H₂Any one of them.

Technical Field

The invention belongs to the technical field of preparation of catalyst materials, and relates to a molecular sieve based monatomic catalyst and a preparation method thereof.

Background

Metals and their complexes are the most widely used heterogeneous catalysts in industrial processes. Since the low coordinated metal atoms generally act as catalytically active centers, the specific activity per metal atom generally increases as the size of the metal particle decreases. However, as the particle size decreases, the free energy of the metal surface increases significantly and agglomeration tends to occur. The use of suitable support materials that strongly interact with the metal species to prevent such agglomeration and form highly dispersed metal sites with high catalytic activity has long been a method employed by the industry. In recent years, a monatomic catalyst (SAC) in which a metal is dispersed at an atomic level has been produced in order to maximize the efficiency of metal atom utilization. The research on the spatial arrangement and electronic properties of single atoms and the interaction between the single atoms and a carrier is gradually and deeply carried out, and the optimization of the activity, selectivity and stability of the heterogeneous catalyst is possible by adjusting the active center through the single metal atom, and the heterogeneous catalyst has shown application prospects in various industrial chemical reactions, thereby receiving great attention of people.

At present, the methods for preparing monatomic catalysts are mainly Mass Selective Soft Landing (MSSL) method, Atomic Layer Deposition (ALD) method, vapor phase transport method, and wet chemical synthesis method. The first three of themThe method needs expensive special equipment and has low yield, so that large-scale production is difficult to realize. Wet chemical synthesis is the most focused technology currently studied, and mainly has defects of engineering strategies, space limitation strategies, coordination design strategies and the like, and the core idea of the technology is to control the aggregation of single atoms in precursors. Therefore, the choice of matrix material or support material is crucial. The matrix materials that have been reported so far include metals, metal oxides, carbon materials, MOFs, molecular sieves, and the like. Among them, molecular sieves are considered as one of the most desirable substrates for monatomic catalysts because of their own porous structure and excellent stability. However, at present, the reports of the single-atom catalyst taking the molecular sieve as the matrix are rare. For example, Diuranyl et al add palladium or rhodium complexes to the gel from which the ZSM-5 molecular sieve is prepared, crystallize, and then calcine in a fixed atmosphere of oxygen or hydrogen, etc., to form a monoatomic dispersion of the metal within the molecular sieve (CN 107983401B, CN 107890881B); sun et al rhodium-ethylenediamine complex ion [ Rh (en)₃ ³⁺]Encapsulated in silicalite-1 and ZSM-5 in H₂After direct reduction of the precursors, they obtained monatomic catalysts in which Rh atoms are embedded in the 5-membered ring of the MFI topology and are stabilized by framework oxygen atoms (Q. Sun, et al, Angew. chem. int. Ed., 58 (2019) 18570-18576).

The methods limit the metal in the micropore pore canal of the molecular sieve, which is not favorable for the full contact of the substrate, especially the macromolecular substrate, and limits the catalytic efficiency to a certain extent.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention provides a method for preparing a monatomic catalyst with active sites distributed on the outer surface of a molecular sieve by using protein as an auxiliary reagent. The method overcomes the limitation that the prior molecular sieve based monatomic catalyst has an active center positioned in the micropore and insufficient accessibility, and improves the catalytic efficiency of the molecular sieve based monatomic catalyst.

The technical problem to be solved by the invention is realized by the following technical scheme.

A molecular sieve based monatomic catalyst is formed by coating metal atoms on the outer surface of a molecular sieve by a nitrogen-nitrogen carbon material.

Preferably, the metal atoms include any one or more of Co, Ni, Fe, Cu, Au, Ag, Ru, Rh, Pd, Os, Ir, Pt.

Preferably, the aza-carbon material is derived from protein pyrolysis.

Preferably, the molecular sieve includes known or newly synthesized or modified microporous molecular sieves, mesoporous molecular sieves, large pore molecular sieves, and hierarchical pore molecular sieves.

Preferably, the metal atoms are dispersed on the outer surface of the molecular sieve.

A preparation method of a molecular sieve based monatomic catalyst comprises the following steps:

s1, dispersing the molecular sieve material into water, and stirring at room temperature until a uniform mixed solution is formed;

s2, adding a protein solution into the mixed solution, and stirring at room temperature until the assembly reaches the balance;

s3, adding the metal ion solution into the mixed solution, stirring at room temperature until the solution is balanced, performing suction filtration, washing with deionized water, and freeze-drying;

and S4, putting the freeze-dried sample into a tubular furnace, and pyrolyzing the sample under the protection of non-oxidizing gas to obtain the molecular sieve based monatomic catalyst.

Preferably, the protein in the protein solution in step S2 is a combination of one or more natural or synthetic or modified proteins.

Preferably, the molar ratio of the protein in the protein solution to the metal in the metal ion solution is 1: 0.5-0.01.

Preferably, the metal ions in the metal ion solution in step S3 are soluble metal salts or metal complexes.

Preferably, the non-oxidizing gas in the step S4 is N₂、He、Ar、H₂Any one of them.

The invention has the beneficial effects that:

1. the method has the advantages of few synthesis steps, simple and convenient operation, no need of expensive large-scale equipment, contribution to large-scale production and wide application range.

2. The monatomic catalyst prepared by the method has a novel structure, and the nitrogen-doped carbon nano particles wrapped by metal atoms are anchored on a molecular sieve substrate; both the nitrogen heterocyclic carbon and the molecular sieve are typical porous materials, so that the diffusion mass transfer of a catalytic reaction system is facilitated.

3. The monatomic catalyst prepared by the method has the advantages that metal atoms are fully exposed on the outer surface of the molecular sieve, so that the monatomic catalyst is conveniently and fully contacted with a substrate, and the catalytic efficiency is favorably improved.

4. According to the monatomic catalyst prepared by the method, metal atoms are anchored on the surface of the molecular sieve through a carbon-nitrogen structure formed by pyrolysis of protein and an organic template agent in a pore channel, the stability is good, and the monatomic catalyst can be recycled.

Drawings

Fig. 1 is a TEM image of a cobalt single-atom catalyst supported on multi-stage pore molecular sieve microspheres prepared in example 1.

Fig. 2 is an XRD pattern of the cobalt-single-atom catalyst supported on the hierarchical pore molecular sieve microspheres prepared in example 1.

FIG. 3 is a spectrum of Co K-edge FT-EXAFS of the mesoporous molecular sieve microsphere-supported cobalt monatomic catalyst prepared in example 1.

Detailed Description

The present invention will be described in detail with reference to examples, which are only preferred embodiments of the present invention and are not intended to limit the present invention.

< example 1>

A preparation method of a hierarchical pore molecular sieve microsphere supported cobalt monoatomic catalyst comprises the following steps:

s1, preparing uniform gel of water, piperidine, diboron trioxide, aluminum isopropoxide and silicon dioxide with the molar ratio of 40: 1.5: 0.67: 0.02: 1 in a 100 mL beaker, transferring the uniform gel into a stainless steel reaction kettle provided with 120 mL of polytetrafluoroethylene lining, placing the reaction kettle into a homogeneous reactor, turning over the reaction kettle at 130 ℃ for 12 hours at the rotating speed of 60 rpm, crystallizing the reaction kettle at 170 ℃ for 72 hours, quenching the uniform gel with water to room temperature, performing suction filtration, washing the uniform gel with deionized water to be neutral, and placing the uniform gel in an oven at 80 ℃ for drying overnight to obtain the porous molecular sieve microspheres;

s2, adding 1.2 g of molecular sieve microspheres and 50 mL of deionized water into a 100 mL flask, and stirring until a uniform mixed solution is formed;

s3, adding 10 mL of aqueous solution containing 0.6 g of bovine serum albumin into the mixed solution, and stirring at room temperature for 4 hours until the adsorption reaches the balance;

s4, adding an aqueous solution containing 0.2 g of cobalt acetate tetrahydrate into the mixed solution, continuously stirring at room temperature for 1 hour, carrying out suction filtration, washing with deionized water, and carrying out freeze drying to obtain a precursor;

s5, spreading 250 mg of the precursor at the bottom of the porcelain boat, putting the porcelain boat into a tube furnace, and putting the porcelain boat into the tube furnace in a N state₂And carrying out pyrolysis for 2 hours at 600 ℃ under protection to obtain a target product.

The cobalt monoatomic catalyst loaded by the hierarchical pore molecular sieve microspheres prepared in the embodiment is used for the reaction of preparing aniline through selective hydrogenation of nitrobenzene. The reaction is carried out in a high-pressure reaction kettle, and the specific reaction conditions are as follows: 0.5 mmol of nitrobenzene, 70 mg of catalyst, 6 mL of H₂O, 2 MPa H₂The reaction product and the product are detected by gas chromatography by an internal standard method at 100 ℃ for 4 h, the nitrobenzene conversion rate reaches 99.3 percent, and the selectivity of the aniline is 100 percent. And after 8 times of catalyst circulation, 87.6 percent of initial activity can still be maintained.

The TEM photograph (fig. 1) shows that the catalyst presents the same spherical morphology as the molecular sieve matrix, and the nanoparticles generated by protein pyrolysis can be observed on the surface of the molecular sieve, and are relatively uniformly divided into the outer surface of the molecular sieve, and the metal atoms are wrapped in the outer surface. Meanwhile, the catalyst has an XRD diffraction peak (figure 2) completely consistent with the molecular sieve matrix, which shows that the catalyst completely retains the crystal structure of the molecular sieve. Further, the catalyst did not show characteristic diffraction peaks of the crystal planes of simple cobalt 111, 200, and 220 at 2 θ = 44.2 °, 51.5 °, and 44.2 °, indicating that there was almost no aggregation of Co atoms in the catalyst.

The EXAFS spectra show that the Co-Co bond signal is located near 2.2 a in cobalt foil paper, while the catalyst has almost no signal near 2.2 a (fig. 3), indicating that no Co-Co bonds are present in the catalyst prepared in this example and that metallic Co is in a monoatomic dispersion state. While its peak near 1.4 a demonstrates the interaction between Co atoms and light atoms such as N, explaining the stability of the catalyst.

< example 2>

A preparation method of a mesoporous molecular sieve nanorod supported palladium monatomic catalyst comprises the following steps:

s1, 1.05 g of cetyltrimethylammonium bromide (CTAB) and 262.5g of ultrapure water were added to a 500 mL two-necked flask at room temperature, and the mixture was dissolved sufficiently by sonication, followed by magnetic stirring at 400 rpm for 30 minutes. Adding 7.5 mL of 25% ammonia water, continuing stirring for 30 minutes, heating the water bath to 40 ℃, when the system is stable, dropwise adding 4.6 mL of Tetraethoxysilane (TEOS) under the condition of vigorous stirring, continuing stirring at the temperature for reaction for 5 hours, after the reaction is finished, performing suction filtration to collect the obtained sample, alternately washing the sample for three times respectively by water and absolute ethyl alcohol, and drying the sample overnight at 80 ℃ in a vacuum drying oven to obtain the mesoporous molecular sieve nanorod.

S2, adding 1.0 g of mesoporous molecular sieve nanorod and 50 mL of deionized water into a 100 mL flask, and stirring until a uniform mixed solution is formed;

s3, adding 10 mL of aqueous solution containing 0.4 g of bovine serum albumin into the mixed solution, and stirring at room temperature for 4 hours until the adsorption reaches the balance;

s4, adding an aqueous solution containing 0.1 g of palladium nitrate dihydrate into the mixed solution, continuously stirring for 1 hour at room temperature, performing suction filtration, washing with deionized water, and performing freeze drying to obtain a precursor;

s5, spreading 250 mg of the precursor at the bottom of the porcelain boat, putting the porcelain boat into a tube furnace, and putting the porcelain boat into the tube furnace in a N state₂And carrying out pyrolysis for 2 hours at 600 ℃ under protection to obtain a target product.

The mesoporous molecular sieve nanorod supported palladium monatomic catalyst prepared in the embodiment is used for the reaction of preparing aniline through selective hydrogenation of nitrobenzene. The reaction is carried out in a high-pressure reaction kettle, and the specific reaction conditions are as follows: 0.5 mmol of nitrobenzene, 70 mg of catalyst, 6 mL of H₂O, 2 MPa H₂The reaction product and the product are detected by gas chromatography by an internal standard method at 100 ℃ for 4 h, the conversion rate reaches 99.8 percent, and the aniline selectivity reaches 100 percent. And after the catalyst is circulated for 6 times, the initial activity of the catalyst can still be maintained by more than 90 percent.

< example 3>

A preparation method of a commercial MOR molecular sieve loaded nickel monatomic catalyst comprises the following steps:

s1, to a 100 mL flask, add 1.0 g MOR molecular sieve (Si/Al = 6) and 50 mL deionized water, stir until a homogeneous mixture is formed;

s2, adding 10 mL of aqueous solution containing 0.2 g of bovine serum albumin into the mixed solution, and stirring at room temperature for 4 hours until the adsorption reaches the balance;

s3, adding an aqueous solution containing 0.05g of nickel nitrate hexahydrate into the mixed solution, continuously stirring for 1 hour at room temperature, carrying out suction filtration, washing with deionized water, and carrying out freeze drying to obtain a precursor;

s4, spreading 250 mg of the precursor at the bottom of the porcelain boat, putting the porcelain boat into a tube furnace, and putting the porcelain boat into the tube furnace in a N state₂And carrying out pyrolysis for 2 hours at 600 ℃ under protection to obtain a target product.

The commercial MOR molecular sieve supported nickel monatomic catalyst prepared in the embodiment is used for the reaction of preparing 1,2,3, 4-tetrahydroquinoline by selectively hydrogenating quinoline. The reaction is carried out in a high-pressure reaction kettle, and the specific reaction conditions are as follows: 0.5 mmol of quinoline, 50 mg of catalyst, 5 mL of H₂O, 3 MPa H₂The reactants and the products are detected by gas chromatography by adopting an internal standard method, the conversion rate of quinoline reaches 100 percent, and the selectivity of 1,2,3, 4-tetrahydroquinoline is more than 99.9 percent. And after the catalyst is circulated for 10 times, the initial activity of the catalyst can still be maintained by more than 90 percent.

The above embodiments are merely illustrative of the technical solutions and features of the present invention, and the purpose thereof is to better enable those skilled in the art to practice the invention, and it is not intended to limit the scope of the invention, and all equivalent changes and modifications made according to the spirit of the present invention are within the scope of the present invention, wherein the prior art is not described in detail.