CN111604081B

CN111604081B - Method for quasi-continuous synthesis of monatomic catalyst

Info

Publication number: CN111604081B
Application number: CN202010571413.0A
Authority: CN
Inventors: 纪红兵; 何晓辉; 黄丽云; 何千
Original assignee: Sun Yat Sen University
Current assignee: Sun Yat Sen University
Priority date: 2020-06-22
Filing date: 2020-06-22
Publication date: 2021-06-25
Anticipated expiration: 2040-06-22
Also published as: CN111604081A

Abstract

The invention discloses a method for quasi-continuous synthesis of a monatomic catalyst. The invention encapsulates the metal precursor in chitosan/lauryl sodium sulfate hydrogel encapsulation by a microcapsule technology, and further pyrolyzes and synthesizes the metal monatomic catalyst. The invention adopts a pendant drop method in the microcapsule technology, and the technology can continuously generate homogeneous microcapsules, thereby realizing the quasi-continuous preparation of the monatomic material. The quasi-continuous synthesis process solves the problems of poor reproducibility, amplification effect and the like caused by intermittent synthesis. In addition, the invention has good expansibility, solves the problems of less metal types, low metal content and the like in the prior art, and enriches the research of the related fields of metal monoatomic material synthesis methodology and the like.

Description

Method for quasi-continuous synthesis of monatomic catalyst

Technical Field

The invention relates to the technical field of material science and engineering, in particular to a method for quasi-continuous synthesis of a monatomic catalyst.

Background

Monatomic catalysts have attracted much attention in recent years because of their combination of "isolated active sites" of homogeneous catalysts and the ease of recycling of heterogeneous catalysts. The catalytic sites of the monatomic catalyst are highly uniform, the influence of various interference sites such as different crystal faces, vertexes, interfaces and the like in the nano particles does not exist, and the high selectivity can be obtained in the catalytic reaction. The prior monatomic catalyst is suitable for various catalytic reaction types, including oxygen reduction reaction, selective oxidation reaction, selective hydrogenation reaction, water-vapor conversion reaction and hydrogenation reaction, and shows huge industrial application prospects. The preparation of the monatomic catalyst greatly reduces the use amount of noble metal and reduces the production cost. In addition, the advent of monatomic catalysts has also allowed one to understand the nature of catalysis from an atomic perspective, enhancing understanding of catalytic reactions.

Conventional synthesis methods of metal monoatomic include a wet chemical method, a deposition method and a pyrolysis method. Wherein, the wet chemical method mainly uses noble metal single atom, and needs to accurately configure the concentration of metal salt and select proper carrier material; in the deposition method, a four-stage rod or high-temperature metal source equipment is adopted, and the conditions of deposition temperature-time and the like need to be accurately controlled; the pyrolysis method needs to synthesize a high-temperature-resistant catalytic precursor material. And the synthesis methods are intermittent and have low efficiency, which seriously hinders the industrial production of the metal monatomic catalyst.

The Chinese patent CN 105170147B prepares a Pd1/Al2O3 monatomic catalyst by utilizing atomic layer deposition, and the catalyst has good acetylene hydrogenation activity. However, this method requires strict control of deposition temperature, carrier flow rate, deposition time, and is complicated in operation and expensive in equipment.

U.S. Pat. No. 5,193,5686-A1 discloses a process for preparing a precursor of cobalt nitrate hexahydrate in silica by adjusting pH and further pyrolyzing the precursor at 500 ℃ to form a single atom of Co1/SiO 2. However, the method is complex to operate, requires precise regulation of reaction ratio, and has expensive raw materials, low reaction concentration and less product preparation amount.

Disclosure of Invention

The invention aims to provide a method for synthesizing a monatomic catalyst in a quasi-continuous manner based on the characteristics and the defects of a metal monatomic preparation method based on a wet chemical method, a deposition method and a pyrolysis method, so as to solve the problems of intermittent production, low efficiency and the like of a monatomic catalyst synthesis method

In order to achieve the purpose, the invention adopts the following technical scheme:

a method for quasi-continuous synthesis of a monatomic catalyst, comprising the steps of:

the first step is as follows: continuous synthesis of metal precursor microcapsules:

taking chitosan water solution as a continuous phase, taking metal precursor solution as a dispersion phase, dropwise adding the dispersion phase into the continuous phase solution, and carrying out high-speed shearing emulsification. The emulsion is injected into a droplet generator by a syringe pump to continuously generate droplets, and then the droplets are dropped into a coagulating bath to form microcapsules. Washing with clear water, and lyophilizing.

The second step is that: pyrolysis and acid washing of microcapsules:

microencapsulation in N₂And (3) carrying out high-temperature pyrolysis and acid washing under the atmosphere protection, and drying to obtain the metal monatomic catalyst.

Preferably, in the above-mentioned production method, the microcapsule method is an emulsion method or a suspension-drop method. The suspension drop method can efficiently generate liquid drops with uniform particle size and has the advantage of continuously producing high-quality microcapsules.

Preferably, in the above preparation method, the emulsification method is to shear at 13000 rpm for 2-5 min to complete the water-oil emulsification.

Preferably, in the above preparation method, the droplet generating device used in the pendant drop method is a glass tube with an outer diameter of 550 μm placed on a glass slide, the front end of the glass tube is connected with a dispensing needle, and finally the joint is fixed and sealed by epoxy resin glue. The pre-emulsion was injected into the droplet generation apparatus by an injection pump at a flow rate ranging from 1000-.

Preferably, in the above preparation method, the wall material of the microcapsule is chitosan with a large amount of amino groups, and the concentration is 1-5%.

Preferably, in the above preparation method, the metal precursor is iron acetylacetonate, cobalt acetylacetonate or nickel acetylacetonate, and ethyl acetate is used as a solvent.

Preferably, in the above preparation method, the coagulation bath is a solution containing 2% Sodium Dodecyl Sulfate (SDS), and the positively charged chitosan and negatively charged SDS undergo electrostatic coagulation crosslinking to form an insoluble chitosan/SDS hydrogel, and this solidification reaction can introduce a large amount of S element.

Preferably, in the above preparation method, the pyrolysis condition is 3 to 5 times under the protection of inert gas^oThe temperature rise rate of C/min is 600-^oC, pyrolyzing for 1-5 h.

Preferably, in the above-mentioned production method,the pickling conditions are 80 DEG^oUsing 0.5-1M H under C₂SO₄Washing is carried out for 8-12 hours to remove residual nanoparticles and soluble salts.

The invention utilizes microcapsule technology to continuously synthesize metal precursor microcapsules, and then carries out pyrolysis and acid washing to obtain the S and N codoped carbon monatomic catalyst. The chitosan which has a large amount of amino and is cheap is used as a wall material, can be used as a carbon source and introduces a large amount of N element. In addition, the chitosan and the lauryl sodium sulfate generate insoluble gel, so that the aggregation of the metal precursor can be prevented, and a large amount of S element is introduced. The method for continuously synthesizing the metal monatomic catalyst can avoid the problems of poor reproducibility, amplification effect and the like caused by intermittent synthesis, and lays a foundation for industrial production.

Compared with the prior art, the invention has the following beneficial effects:

the invention can realize quasi-continuous production of the monatomic, avoids the problems of poor reproducibility, amplification effect and the like caused by intermittent synthesis, and greatly improves the yield of the monatomic catalyst.

The invention prepares different metal monatomic catalysts by wrapping different metal precursors, and has good expansibility and reproducibility.

The invention has low cost in the preparation process, simple preparation method, no need of expensive precise instruments and is suitable for industrial production.

Description of the drawings:

FIG. 1 is a schematic illustration of the continuous production of metal precursor microcapsules;

FIGS. 2 (a) and (b) are the diagrams of transmission electron microscope AC HAADFSTEM for the correction of the spherical aberration of iron monoatomic atoms corresponding to the 1 h and 2 h continuous synthesis, respectively; the rings are labeled as monoatomic metals;

the specific implementation mode is as follows:

the present invention is further illustrated by the following examples, but the scope of the present invention is not limited to the scope of the examples.

Example 1:

chitosan was dissolved in 300 mL deionized water as the continuous phase, and 1 was added5 g of iron acetylacetonate are dissolved in 30 mL of ethyl acetate as a disperse phase. The dispersed phase was then added dropwise to the continuous phase solution and sheared at 13000 rpm for 5 minutes. The emulsion was injected into a quartz capillary device (outer diameter 550 μm) at a flow rate of 2000. mu.L/min using a syringe pump, and then dropped into a coagulation bath containing 2 w/v% SDS to form microcapsules. After 1 h of continuous synthesis, the microcapsules were washed with deionized water and then lyophilized with a lyophilizer. The microcapsules obtained are in N₂Under atmosphere protection 900^oC, pyrolyzing for 2 h. Then at 80^oUsing 0.5M H under C₂SO₄Washing for 12 hours, and drying to obtain the iron monatomic catalyst.

Example 2:

chitosan was dissolved in 300 mL of deionized water as a continuous phase and 1.5 g of iron acetylacetonate was dissolved in 30 mL of ethyl acetate as a dispersed phase. The dispersed phase was then added dropwise to the continuous phase solution and sheared at 13000 rpm for 5 minutes. The emulsion was injected into a quartz capillary device (outer diameter 550 μm) at a flow rate of 2000. mu.L/min using a syringe pump, and then dropped into a coagulation bath containing 2 w/v% SDS to form microcapsules. After 2 h of continuous synthesis, the microcapsules were washed with deionized water and then lyophilized with a lyophilizer. The microcapsules obtained are in N₂Under atmosphere protection 900^oC, pyrolyzing for 2 h. Then at 80^oUsing 0.5M H under C₂SO₄Washing for 12 hours, and drying to obtain the iron monatomic catalyst.

Example 3:

chitosan was dissolved in 300 mL of deionized water as a continuous phase and 0.9 g of cobalt acetylacetonate was dissolved in 30 mL of ethyl acetate as a dispersed phase. The dispersed phase was then added dropwise to the continuous phase solution and sheared at 13000 rpm for 5 minutes. The emulsion was injected into a quartz capillary device (outer diameter 550 μm) at a flow rate of 2000. mu.L/min using a syringe pump, and then dropped into a coagulation bath containing 2 w/v% SDS to form microcapsules. After 1 h of continuous synthesis, the microcapsules were washed with deionized water and then lyophilized with a lyophilizer. The microcapsules obtained are in N₂Under atmosphere protection 900^oC, pyrolyzing for 2 h. Then at 80^oUsing 0.5M H under C₂SO₄Washing 12And in the hour, drying to obtain the cobalt monoatomic catalyst.

Example 4:

chitosan was dissolved in 300 mL of deionized water as a continuous phase and 0.9 g of nickel acetylacetonate was dissolved in 30 mL of ethyl acetate as a dispersed phase. The dispersed phase was then added dropwise to the continuous phase solution and sheared at 13000 rpm for 5 minutes. The emulsion was injected into a quartz capillary device (outer diameter 550 μm) at a flow rate of 2000. mu.L/min using a syringe pump, and then dropped into a coagulation bath containing 2 w/v% SDS to form microcapsules. After 1 h of continuous synthesis, the microcapsules were washed with deionized water and then lyophilized with a lyophilizer. The microcapsules obtained are in N₂Under atmosphere protection 900^oC, pyrolyzing for 2 h. Then at 80^oUsing 0.5M H under C₂SO₄After 12 hours of washing, the nickel monatomic catalyst can be obtained after drying.

Claims

1. A method for quasi-continuous synthesis of a monatomic catalyst, characterized by comprising the steps of:

taking a chitosan aqueous solution as a continuous phase and a metal precursor solution as a dispersion phase, dropwise adding the dispersion phase into the continuous phase solution, and performing high-speed shearing emulsification; injecting the emulsion into a liquid drop generating device by using an injection pump to continuously generate liquid drops, and then dropping the liquid drops into a coagulating bath to form microcapsules; washing with clear water and freeze-drying;

the second step is that: pyrolysis and acid washing of microcapsules:

microencapsulation in N₂And (3) carrying out high-temperature pyrolysis and acid washing under the atmosphere protection, and drying to obtain the monatomic catalyst.

2. The method according to claim 1, wherein the metal precursor is iron acetylacetonate, cobalt acetylacetonate or nickel acetylacetonate, and ethyl acetate is used as a solvent.

3. The method as claimed in claim 1, wherein the pyrolysis is carried out at a temperature of 600-1000 ℃ for 1-5 h at a temperature rise rate of 3-5 ℃/min under the protection of inert gas.

4. The method according to claim 1, wherein said acid washing is carried out at 80 ℃ with a temperature of 0.5-1M H₂SO₄Washing is carried out for 8-12 hours to remove residual nanoparticles and soluble salts.