CN109772455B

CN109772455B - Preparation and application of porous polyamine composite material wrapping fine high-dispersion palladium nanoparticles

Info

Publication number: CN109772455B
Application number: CN201910195148.8A
Authority: CN
Inventors: 李留义; 杨鑫怡; 于岩
Original assignee: Fuzhou University
Current assignee: Fuzhou University
Priority date: 2019-03-14
Filing date: 2019-03-14
Publication date: 2021-07-27
Anticipated expiration: 2039-03-14
Also published as: CN109772455A

Abstract

The invention provides preparation and application of a porous polyamine composite material wrapping fine and highly dispersed palladium nanoparticles, which is synthesized by using a covalent organic framework material as a precursor, is used for catalyzing ammonia borane to decompose and produce hydrogen and is helpful for solving the problem of lack of clean energy at present. The porous polyamine compound coordinates with palladium ions to stabilize the palladium ions, and the stabilized palladium ions are reduced to fine palladium nanoparticles by one-step reduction while generating polyamine linkers. The porous polyamine composite material can effectively stabilize and protect the palladium nano particles from agglomerating in the catalytic reaction, the whole preparation process is simple, the catalytic effect is excellent, and the porous polyamine composite material has a very positive effect on the catalytic reaction.

Description

Preparation and application of porous polyamine composite material wrapping fine high-dispersion palladium nanoparticles

Technical Field

The invention belongs to the field of nano material preparation and catalysis, and relates to synthesis and application of a porous polyamine composite material wrapping fine highly dispersed palladium nano particles.

Background

In recent years, solving the energy problem is a great challenge for human beings, and the development of new clean energy becomes one of the popular research directions today. Hydrogen gas, due to its high energy density and renewability, makes it the most promising green clean energy source, but it remains a challenge for the storage and release of hydrogen gas. Ammonia borane is the most potential hydrogen storage material due to its advantages of high hydrogen content and excellent stability. It is known that metal nanoparticles have a very large promotion effect on catalytic hydrogen production of ammonia borane, but the metal nanoparticles are easy to agglomerate due to high surface energy in the catalytic reaction process, so that the catalytic cycle performance is reduced. Therefore, the synthesis of metal nanoparticle-based composite catalysts having high stability and activity remains a challenge to be solved.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and synthesize a porous polyamine composite material wrapping fine and highly dispersed palladium nanoparticles and hydrogen production by catalyzing ammonia borane decomposition. The known covalent organic framework material is adopted to coordinate with metal ions, then a reducing agent is introduced, and fine and highly dispersed palladium nano particles coated in the shell layer of the porous polyamine are synthesized through simple heating and stirring processes.

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

a preparation method of a porous polyamine composite material wrapping fine highly dispersed palladium nanoparticles comprises the following steps:

(1) dispersing palladium acetate and COF-LZU1 in dichloromethane, realizing imine bond and divalent palladium complexation by stirring, filtering, collecting, and freeze-drying;

(2) dispersing the obtained solid in a mixed solution of tetrahydrofuran and deionized water according to a certain proportion, stirring at 70 ℃, adding excessive sodium borohydride solid into the mixed solution for reduction, continuously heating and stirring for 24 hours, collecting the solid, washing the solid with tetrahydrofuran and deionized water for three times respectively, and drying at 70 ℃ overnight to obtain a porous polyamine composite material Pd @ H-PPA wrapping fine highly dispersed palladium nanoparticles;

the volume ratio of the tetrahydrofuran to the deionized water is 4: 1.

The palladium nanoparticles are wrapped on the porous polyamine shell by heating and stirring.

The obtained palladium nanoparticles have an average size of 2.6 nm, are small in size, and are highly dispersed in the shell layer of the porous polyamine material.

The application comprises the following steps: the Pd @ H-PPA catalyst is used for catalyzing ammonia borane to generate hydrogen, the synthesized catalyst is put into an ammonia borane aqueous solution, the reaction temperature is 25-45 ℃, and the high-efficiency stable recyclable excellent performance is shown.

The invention has the advantages that:

divalent palladium ions coordinated with an imine bond in COF-LZU1 are reduced into fine palladium nanoparticles in situ by adopting a one-step method, and the imine bond is reduced into a secondary amine bond. The operation is simple and convenient, and the preparation flow is simple; and the prepared composite material has excellent catalytic performance.

Drawings

FIG. 1 is an X-ray powder diffraction pattern of Pd @ H-PPA synthesized in example 1;

FIG. 2 is a Fourier transform infrared spectrum of Pd @ H-PPA synthesized in example 1;

FIG. 3 is a solid NMR carbon spectrum of Pd @ H-PPA synthesized in example 1;

FIG. 4 is a transmission electron micrograph of Pd @ H-PPA synthesized in example 1;

FIG. 5 is a graph of the cycle efficiency of the Pd @ H-PPA synthesized in example 1;

FIG. 6 is a transmission electron micrograph of the Pd @ H-PPA synthesized in example 1 after 8 catalytic reactions.

Detailed Description

In order to make the present invention more comprehensible, the technical solutions of the present invention are further described below with reference to specific embodiments, but the present invention is not limited thereto.

Example 1

COF-LZU1 was synthesized by a known method, COF-LZU1 (80 mg) was dispersed in dichloromethane (18 mL) and sonicated for 20 minutes, palladium acetate (77.5 mg) was dispersed in 2 mL dichloromethane, then a dichloromethane solution of palladium acetate was added to a dichloromethane solution of COF-LZU1, stirred for 24 hours, the resulting solid was filtered and washed with dichloromethane several times and then placed in a soxhlet extraction apparatus, washed with dichloromethane as a washing solvent for 24 hours, and freeze-dried. Dispersing the solid (40 mg) obtained in the step of reaction in tetrahydrofuran and deionized water (20 mL 4:1 v/v), stirring and heating to 70 ℃, adding 715 mg of excessive sodium borohydride solid in small batches for multiple times, continuously heating and stirring for 24 hours, filtering, washing with tetrahydrofuran and water, and drying at 70 ℃ to collect the catalyst Pd @ H-PPA.

Comparative example 1

COF-LZU1 (50 mg) was dispersed in a mixed solution of tetrahydrofuran and deionized water (4: 1 v/v) at a certain ratio (70: 1 v/v)^oStirring under C, adding a small amount of NaBH in the stirring process₄Stirring was continued for 12 h after the solid (200 mg). Filtering and collecting with tetrahydrofuranPyran and deionized water washes. 100 times more^oAnd C, vacuum drying for 5 hours. The resulting solid (40 mg) was dispersed in 10 mL of dichloromethane, a solution of palladium acetate in dichloromethane was added, stirring was continued for 12 hours, collected and washed with dichloromethane using Soxhlet extraction for 24 hours, 60^oAnd C, drying in vacuum overnight. Finally, the solid obtained above (40 mg) was dispersed in 20 mL of a mixture of tetrahydrofuran and deionized water (70 mL)^oAnd C, stirring. During stirring, NaBH was added₄Stirring was continued for 24 hours after the solid. Finally 70 in vacuum^oAnd C is dried overnight to obtain Pd/H-PPA.

The one-step synthesis method adopted in example 1 is simpler in synthesis steps, and comparative example 1 is to synthesize the porous polyamine material, then carry palladium ions and further reduce the porous polyamine material into palladium nanoparticles; however, the nano particles obtained by the method of the comparative example 1 are large, the average size is about 4 nm, and the dispersion is very uneven, so that the composite material prepared by the comparative example 1 has poor catalytic performance.

Applications of

The synthesized catalyst Pd @ H-PPA (20 mg) was dispersed in 9 mL of methanol and water mixture (v/v = 4: 5) and carefully poured into a two-necked flask. After stirring the mixture to reach air equilibrium, 1.0 mL of an aqueous solution containing ammonia borane (1 mmol) was added to the flask; catalytic activity of Pd @ H-PPA in the dehydrogenation of ammonia borane the rate of hydrogen generation was calculated by observing the water level change in the burette and completing the dehydrogenation process when the water level no longer changed.

FIG. 1 is an X-ray powder diffraction pattern of the polymer catalyst, wherein positions 39.4, 45.2 and 67.3 correspond to crystal faces of palladium nanoparticles (111), (200) and (220). 1320 cm in FIG. 2^-1This corresponds to the characteristic peak of the secondary amine bond, which also corresponds to the solid state nuclear magnetic data of FIG. 3, and the characteristic peak position of the secondary amine bond also appears at 47 ppm. It is clear from the transmission electron microscope (FIG. 4) that fine uniform nanoparticles (average 2.6 nm) are dispersed in the shell of the porous polyamine material. FIG. 5 shows the high stability of the Pd @ H-PPA catalyst, the reaction rate did not significantly decrease after 8 cycles, and the reacted catalyst was collected fromThe observation of the transmission electron microscope shows that the nanoparticles do not have serious agglomeration phenomenon (figure 6).

Table 1 shows the hydrogen production performance of the catalysts obtained in example 1 and comparative example 1

The above description is only exemplary of the present invention, and all modifications and variations that fall within the scope of the claims should be considered as falling within the scope of the present invention.

Claims

1. A preparation method of a porous polyamine composite material wrapping palladium nanoparticles is characterized by comprising the following steps: introducing a palladium acetate solution into COF-LZU1, coordinating with imine bonds in COF-LZU1, adding sodium borohydride solid to reduce bivalent palladium to zero valence and reduce imine bonds in COF-LZU1 to secondary amine bonds to obtain the porous polyamine composite material Pd @ H-PPA wrapping fine highly dispersed palladium nanoparticles;

the method specifically comprises the following steps:

(2) putting the collected solid into a mixed solution of tetrahydrofuran and deionized water according to a certain proportion, stirring at 70 ℃, adding excessive sodium borohydride solid into the mixed solution for reduction, continuously heating and stirring for 24 hours,

(3) filtering, washing with tetrahydrofuran and deionized water, and drying at 70 ℃ overnight to obtain the porous polyamine composite material Pd @ H-PPA wrapping the fine highly dispersed palladium nanoparticles.

2. The method of claim 1, wherein: the mass ratio of the COF-LZU1 to the palladium acetate is 1: 1.

3. The method of claim 1, wherein: in the step (2), the volume ratio of tetrahydrofuran to deionized water is 4: 1.

4. The method of claim 1, wherein: the obtained palladium nanoparticles have an average size of 2.6 nm, are small in size, and are highly dispersed in the shell layer of the porous polyamine material.