CN109331884B

CN109331884B - A kind of composite hydrogen production catalyst and its preparation method and application

Info

Publication number: CN109331884B
Application number: CN201811205980.3A
Authority: CN
Inventors: 臧双全; 董喜燕; 程园杰; 王锐
Original assignee: Zhengzhou University
Current assignee: Zhengzhou University
Priority date: 2018-10-17
Filing date: 2018-10-17
Publication date: 2021-07-20
Anticipated expiration: 2038-10-17
Also published as: CN109331884A

Abstract

The invention discloses a covalent organic framework package based [ Mo ]₃S₁₃]^2‑A cluster composite hydrogen production catalyst, a preparation method and an application thereof relate to the technical field of nano-catalysts and photocatalysis. The composite catalyst takes a cationic covalent organic framework EB-COF as a carrier, and anions [ Mo ] with high catalytic activity are subjected to anion-cation exchange₃S₁₃]^2‑The clusters are packaged in a COF framework to obtain the high-efficiency and stable composite catalyst. The hydrogen production rate is as high as 13215μmol h^‑1 g^‑1The composite catalyst can improve [ Mo ]₃S₁₃]^2‑The catalytic stability of the clusters is realized, and the conversion from the homogeneous catalyst to the heterogeneous catalyst is realized, and the heterogeneous catalyst can be recycled through centrifugal separation, so that the utilization rate of the catalyst is greatly improved.

Description

Composite hydrogen production catalyst and preparation method and application thereof

Technical Field

The invention relates to the technical field of nano-catalyst and photocatalysis, in particular to a covalent organic framework encapsulation based [ Mo ]₃S₁₃]^2-A cluster composite hydrogen production catalyst, a preparation method thereof and application thereof in photocatalytic hydrogen production.

Background

With the rapid development of global economy and industry, the decreasing reserves of fossil fuels and the serious environmental pollution problems caused by the heavy use of fossil fuels have stimulated a great research interest of global scientists in clean renewable energy sources. Solar energy is an inexhaustible low-cost energy source, and an effective way for converting the solar energy into chemical energy and effectively storing the chemical energy is provided.

Due to the characteristics of high energy density, no pollution of combustion products, convenience in storage and the like, hydrogen becomes one of new energy sources hopeful to replace fossil energy. The hydrogen production by utilizing solar energy can effectively convert the solar energy into hydrogen energy which can be directly utilized and is beneficial to storage. The first report of utilizing semiconductor TiO in 1972 by Fujishima project group of Japan₂The electrode decomposes water to produce hydrogen under the catalysis of ultraviolet light, and the feasibility of converting solar energy to hydrogen energy is disclosed. Therefore, the method has aroused great interest of various scientists in the technology of decomposing hydrogen in water. Water, which is a compound existing in large quantities and stable on earth, hardly achieves self-decomposition and completes conversion to hydrogen gas in a spontaneous state. Whereas the voltage required to decompose water in the cell is only 1.23eV, as calculated by the nernst equation, the thermodynamic feasibility suggests that this energy conversion process can be achieved by finding a suitable catalyst.

Bensenbacher topic group and Min topic group successively reported [ Mo ] with multiple catalytic sites in 2014 and 2018 respectively₃S₁₃]^2-The clusters have excellent catalytic performance in hydrogen production by electrocatalysis and photocatalytic water decomposition. However, since [ Mo ] is₃S₁₃]^2-The clusters participate in the reaction in a homogeneous form in the reaction of producing hydrogen by photocatalytic decomposition, and possible self-decomposition exists, so that the clusters cannot be recycled, and the utilization rate of the catalyst is greatly reduced. For this purpose, a homogeneous catalyst [ Mo ] was sought₃S₁₃]^2-The method of converting clusters into heterogeneous catalysts to recycle them has become one of the research hotspots.

Disclosure of Invention

The invention aims to provide a covalent organic framework encapsulation [ Mo ] based on recycling₃S₁₃]^2-A cluster high-efficiency composite hydrogen production catalyst; another object is to provide a process for the preparation thereofAnd applications.

In order to realize the purpose of the invention, the invention takes cationic covalent organic framework EB-COF as a carrier, and is stirred with [ Mo ] at normal temperature₃S₁₃]^2-The nano-scale composite material is obtained by the clusters through anion-cation exchange, the conversion from a homogeneous catalyst to a heterogeneous catalyst is completed, the cyclic recycling of the catalyst is realized, and the nano-scale composite material is used for catalyzing water decomposition to produce hydrogen under the irradiation of visible light.

The preparation method of the high-efficiency visible light catalytic water decomposition hydrogen production catalyst comprises the following steps:

(1) sequentially adding 2,4, 6-trihydroxy-1, 3, 5-benzene tricarboaldehyde, ethidium bromide, 1, 4-dioxane, mesitylene and glacial acetic acid into a heat-resistant glass tube, quickly freezing the tube in a 77K-80K liquid nitrogen bath, degassing through freezing-air extraction-unfreezing circulation, reacting at a constant temperature of 110-120 ℃, and naturally cooling to room temperature to obtain a suspension.

(2) And (3) filtering the suspension obtained in the step (1), washing, drying and grinding to obtain EB-COF solid powder.

(3) Ammonium heptamolybdate tetrahydrate is dissolved in water and the ammonium polysulfide solution is then added. Stirring and reacting at constant temperature of 90-96 ℃. Cooling to room temperature after the reaction is finished, standing for precipitation, filtering the obtained solid, washing, drying and grinding to obtain the [ Mo ]₃S₁₃]^2-And (3) solid powder.

(4) The obtained [ Mo ]₃S₁₃]^2-The powder was dissolved in a sodium hydrogencarbonate solution, and the EB-COF powder obtained in (2) was added thereto and the reaction was stirred at room temperature to obtain a suspension.

(5) And (4) centrifuging, carrying out ultrasonic treatment and washing the suspension obtained in the step (4). Drying and grinding to obtain Mo₃S₁₃@ EB-COF solid powder.

In the step (1), the molar ratio of the 2,4, 6-trihydroxy-1, 3, 5-benzene triformal to the ethidium bromide is 1-3: 3.

In the step (1), the volume ratio of the 1, 4-dioxane to the mesitylene is 0.5-2: 1.

The molar concentration of the glacial acetic acid added in the step (1) is 5-6 mol/L.

The composite material is used as a catalyst to be applied to a system for decomposing water into hydrogen by visible light, and after the conditions are optimized, the composite material and a proper photosensitizer and a sacrificial agent are used together to complete hydrogen production by decomposing water under the irradiation of the visible light in an N 'N' -dimethylformamide/aqueous solution system. The preferred photosensitizer in the photocatalytic hydrogen production process is ruthenium terpyridyl chloride, the preferred sacrificial agent is ascorbic acid, and the molar concentration of the ascorbic acid in an N 'N' -dimethylformamide/water solution system is preferably 300 mmol/L.

The invention has the advantages that: the composite catalyst takes a cationic covalent organic framework material EB-COF as a carrier, and anions [ Mo ] with high catalytic activity are subjected to anion-cation exchange₃S₁₃]^2-The clusters are packaged in COF, so that the high-efficiency and stable composite catalyst is obtained. The hydrogen production rate is as high as 13215 mu mol h^-1g^-1The composite catalyst can improve [ Mo ]₃S₁₃]^2-The catalytic stability of the clusters is realized, and the conversion from the homogeneous catalyst to the heterogeneous catalyst is realized, and the heterogeneous catalyst can be recycled through centrifugal separation, so that the utilization rate of the catalyst is greatly improved. At the same time improve [ Mo ]₃S₁₃]^2-Stability of the clusters in photocatalytic water splitting reactions. The catalyst has the advantages of simple synthesis method, high yield and the like. Provides a new way for preparing the novel photocatalytic hydrogen production composite catalyst and also provides a new synthesis idea for converting other homogeneous catalysts into heterogeneous catalysts.

Drawings

FIG. 1 is a comparison of powder X-ray diffraction (PXRD) patterns and simulated calculated PXRD patterns of EB-COF synthesized over a catalyst of the present invention; wherein, 1 is EB-COF synthesized in the invention, and 2 is PXRD result of simulation calculation; it can be seen that the prepared EB-COF has high purity and good crystallinity.

FIG. 2 shows the synthesis of [ Mo ] by the catalyst of the present invention₃S₁₃]^2-A powder X-ray diffraction (PXRD) pattern of the cluster and a single crystal simulated PXRD pattern contrast plot; wherein 1 is [ Mo ] synthesized by the invention₃S₁₃]^2-Cluster sample, 2 is the single crystal simulation result; it can be seen that [ Mo ] is produced₃S₁₃]^2-High cluster purityThe crystallinity is good;

FIG. 3 is a powder X-ray diffraction (PXRD) pattern of a catalyst of the present invention and a powder X-ray diffraction single crystal of EB-COF and a comparison of its simulated PXRD patterns; wherein, 1 is the catalyst of the invention, and 2 is EB-COF synthesized in the invention; the diffraction peak of the catalyst of the invention at 3.6 degrees (100 crystal planes) is sharply weakened due to the filling of the guest molecules to the COF one-dimensional pore channels;

FIG. 4a is a nitrogen adsorption isotherm at 77k for the catalyst of the invention and EB-COF synthesized in the invention, and FIG. 4b is a pore size distribution plot for the catalyst of the invention and EB-COF synthesized in the invention. Wherein, 1 is the catalyst of the invention, and 2 is EB-COF synthesized in the invention. Anion [ Mo ] can be seen₃S₁₃]^2-Filling one-dimensional pore channels occupying EB-COF;

FIG. 5 is an elemental surface scanning (mapping) electron micrograph of the catalyst of the present invention, which shows that Mo and S elements are present and uniformly distributed in the composite sample, further proving that [ Mo ] is₃S₁₃]^2-Uniformly compounding in the EB-COF material;

FIG. 6 is a comparison graph of the effect of different organic solvents on hydrogen production during the photocatalytic hydrogen production process of the catalyst of the present invention, from which it can be seen that the optimal solvent system is N 'N' -dimethylformamide and water;

FIG. 7 is a comparison graph of the effect of different volume ratios of N 'N' -dimethylformamide to water on hydrogen production in the photocatalytic hydrogen production process of the catalyst of the present invention, from which it can be seen that the optimal volume ratio of N 'N' -dimethylformamide to water is 1: 1;

FIG. 8 is a comparison graph of the effect of different amounts of the photosensitizer terpyridine ruthenium chloride added on the hydrogen production effect in the photocatalytic hydrogen production process of the catalyst of the present invention, from which it can be seen that the optimal amount of the photosensitizer added is 10 mg;

FIG. 9 is a graph comparing the effect of ascorbic acid as a sacrificial agent with different molar concentrations on hydrogen production in the photocatalytic hydrogen production process of the catalyst of the present invention, from which it can be seen that the optimal molar concentration of the sacrificial agent is 300 mmol/L;

FIG. 10 is a comparison graph of the effect of different catalyst additions on hydrogen production during photocatalytic hydrogen production by using the catalyst of the present invention, from which it can be seen that the optimum catalyst addition is 0.5 mg;

FIG. 11 is a diagram of four groups of circulation hydrogen production effect of the catalyst of the present invention, from which it can be seen that the sample is very stable, and the catalytic performance is basically not attenuated after 4 times of circulation tests.

Detailed Description

The invention is further illustrated by the following examples:

example 1: synthesis of covalent organic framework based encapsulation [ Mo ]₃S₁₃]^2-Cluster composite hydrogen production catalyst

(1) 2,4, 6-trihydroxy-1, 3, 5-benzenetricarboxylic acid, ethidium bromide, 1, 4-dioxane, mesitylene and glacial acetic acid are sequentially added into a heat-resistant glass tube, and then the tube is quickly frozen under 77K (liquid nitrogen bath) and degassed through three freezing-air extraction-unfreezing cycles. Reacting at constant temperature of 120 ℃, and naturally cooling to room temperature to obtain suspension. The molar ratio of the 2,4, 6-trihydroxy-1, 3, 5-benzene triformal to the ethidium bromide is 2: 3; the volume ratio of the 1, 4-dioxane to the mesitylene is 1: 1; the molar concentration of the glacial acetic acid added is 6 mol/L.

(2) The suspension obtained in (1) was filtered and washed three times with tetrahydrofuran to obtain a dark red solid. And (3) carrying out solvent exchange on the dark red solid in tetrahydrofuran and methanol, then carrying out vacuum drying for 12 hours at the temperature of 100 ℃, taking out and grinding to obtain dark red solid powder, namely EB-COF used for preparing the catalyst.

(3) Ammonium heptamolybdate tetrahydrate is dissolved in water and the ammonium polysulfide solution is then added. The reaction was stirred at constant temperature at 96 ℃ for 5 hours. Cooled to room temperature and settled to give a dark red solid. The solid was filtered and then washed three times each with water and ethanol. Dispersing the washed dark red solid in toluene, heating, refluxing and stirring at 80 ℃ for 3 hours, standing, removing the upper solution while the solution is hot, and repeating the steps for 3 to 4 times; then filtering the solid, drying in the air, grinding to obtain orange red solid powder, namely [ Mo ] used for preparing the catalyst₃S₁₃]^2-And (4) clustering.

(4) The [ Mo ] obtained in (3)₃S₁₃]^2-The powder (150mg) was dissolved in a sodium hydrogencarbonate solution (250mL) at a molar concentration of 0.05mol/L to give an orange-red solution, and the EB-COF powder (100mg) obtained in (2) was dispersed in the orange-red solution and stirred at room temperature for 24 hours to give a dark-red suspension. Centrifuging the suspension, washing with water for multiple times with ultrasound until the solution is colorless, vacuum drying at 100 deg.C for 12 hr, taking out, and grinding to obtain dark red solid powder as catalyst Mo₃S₁₃@ EB-COF solid powder.

Application example 1:

2mg of the composite catalyst prepared in example 1 and 10mg of ruthenium terpyridine chloride are added into a photocatalytic reactor, different organic solvents (the volume ratio of the organic solvent to water is 1:1, v/v) and ascorbic acid with the molar concentration of 50mmol/L are selected for photocatalytic hydrogen production under the irradiation of 300W visible light (a 420nm filter is added) of a xenon lamp, the hydrogen production amount of the different organic solvents is shown in the graph of FIG. 6, and the most preferable organic solvent is N 'N' dimethylformamide.

Application example 2:

2mg of the composite catalyst prepared in example 1 and 10mg of ruthenium terpyridyl chloride are added into a photocatalytic reactor, different volume ratios of N ', N' -dimethylformamide to water and ascorbic acid with the molar concentration of 50mmol/L are selected for photocatalytic hydrogen production under the irradiation of 300W visible light (a 420nm filter is added) of a xenon lamp, and the hydrogen production yield ratio of the N ', N' -dimethylformamide to water with different volume ratios is shown in figure 7, and the most preferable solvent volume ratio is 1: 1.

Application example 3:

under the condition that the volume ratio of N ', N' -dimethylformamide to water is 1:1, 2mg of the composite catalyst prepared in the example 1 and ascorbic acid with the molar concentration of 50mmol/L are added into a photocatalytic reactor, ruthenium terpyridine chloride with different adding amounts is selected, and photocatalytic hydrogen production is carried out under the irradiation of 300W visible light (a 420nm filter is added) of a xenon lamp, wherein the hydrogen production amount of the ruthenium terpyridine chloride with different amounts is shown in a graph 8, and the most preferable adding amount of the ruthenium terpyridine chloride is 10 mg.

Application example 4:

under the condition that the volume ratio of N ', N' -dimethylformamide to water is 1:1, 2mg of the composite catalyst prepared in the example 1 and 10mg of ruthenium terpyridyl chloride are added into a photocatalytic reactor, ascorbic acid with different molar concentrations is selected and subjected to photocatalytic hydrogen production under the irradiation of 300W visible light (a 420nm filter is added) of a xenon lamp, the hydrogen production amount of the ascorbic acid with different molar concentrations is shown in the graph of FIG. 9, and the most preferable molar concentration of the ascorbic acid is 300 mmol/L.

Application example 5:

under the condition that the volume ratio of N ', N' -dimethylformamide to water is 1:1, 10mg of ruthenium terpyridine chloride and ascorbic acid with the molar concentration of 300mmol/L are added into a photocatalytic reactor, the composite catalyst prepared in the example 1 with different adding amounts is selected, and photocatalytic hydrogen production is carried out under the irradiation of 300W visible light (with a 420nm filter) of a xenon lamp, and the hydrogen production amount of the composite catalyst prepared in the example 1 with different adding amounts is 0.5mg, as shown in the graph 10, and the most preferable adding amount of the composite catalyst prepared in the example 1 is 0.5 mg.

Application example 6:

after optimizing the hydrogen production conditions, 0.5mg of the composite catalyst prepared in example 1 is poured into a photocatalytic reactor, 10mg of ruthenium terpyridine chloride is added, 15mL of an N 'N' -dimethylformamide/water (1:1, v/v) solution with the molar concentration of 300mmol/L ascorbic acid is injected, nitrogen is introduced for 30 minutes to replace the air in the system so as to ensure an oxygen-free environment, a xenon lamp is used for irradiating with 300W visible light (with a 420nm optical filter), and the distance between a light source and the reactor is 10 cm. Detecting by an Agilent 7820A gas chromatography, continuously reacting for 18 hours under illumination, manually feeding a sample once every one hour for detection, and ensuring that the hydrogen peak area tends to be stable after 18 hours. The hydrogen production rate is as high as 13215 mu mol h^-1g^-1。

Application example 7:

6mg of the composite catalyst prepared in example 1 and 10mg of ruthenium terpyridine chloride were charged into a photocatalytic reactor, and 15mL of a solution of ascorbic acid in N 'N' -dimethylformamide/water (1:1, v/v) at a molar concentration of 300mmol/L was further injected. Performing a first group of photocatalytic hydrogen production under the irradiation of a xenon lamp 300W visible light (420nm filter), measuring the hydrogen production by using gas chromatography, recovering the catalyst after centrifugal separation after 5 hours of illumination, washing the centrifugally recovered sample with deionized water, drying, grinding and recovering. Then 10mg of ruthenium terpyridine chloride and 15mL of a solution of ascorbic acid in N 'N' -dimethylformamide/water (1:1, v/v) in a molar concentration of 300mmol/L were added again. And measuring the photocatalytic hydrogen production of the second group, and comparing the hydrogen production of the fourth group with that of the second group in the same way to obtain a four-group circular hydrogen production effect diagram of the catalyst shown in the figure 11. As shown in FIG. 11, the four groups of circulating hydrogen production did not decrease significantly, indicating that the catalyst has good recycling effect and high recyclability.

Claims

1. a composite hydrogen production catalyst, it is characterised in that the composite hydrogen production catalyst is a carrier with a cationic covalent organic framework EB-COF, and [Mo ₃ S ₁₃ ] ^2- cluster obtained through ion exchange Nano-scale composite material; the composite hydrogen production catalyst is prepared according to the following method:

(1) Add 2,4,6-trihydroxy-1,3,5-benzenetricarbaldehyde, ethidium bromide, 1,4-dioxane, mesitylene, and glacial acetic acid into the heat-resistant glass tube in turn , and then the tube was quickly frozen in a 77K-88K liquid nitrogen bath, and degassed through a freeze-pump-thaw cycle, a constant temperature reaction at 110°C-120°C, and the natural conditions dropped to room temperature to obtain a suspension; 2,4 The molar ratio of ,6-trihydroxy-1,3,5-benzenetricarbaldehyde and ethidium bromide is 1-3:3; the volume ratio of 1,4-dioxane and mesitylene is 0.5-2:1 ; Add molar concentration of 5-6 mol/L glacial acetic acid;

(2) The suspension obtained in (1) is filtered, washed, dried and ground to obtain EB-COF solid powder;

(3) Dissolve ammonium heptamolybdate tetrahydrate in water, then add ammonium polysulfide solution, and stir the reaction at a constant temperature of 90°C -96°C; after the reaction is completed, cool to room temperature, static precipitation, and the obtained solid is filtered, washed, and dried. , grind to obtain [Mo ₃ S ₁₃ ] ^2- solid powder;

(4) Dissolve the obtained [Mo ₃ S ₁₃ ] ^2- powder in sodium bicarbonate solution, add the EB-COF powder obtained in (2), stir and react at room temperature to obtain a suspension; centrifuge the suspension , sonicated, washed, dried and ground to obtain Mo ₃ S ₁₃ @EB-COF solid powder.

2. the application of the composite hydrogen production catalyst as claimed in claim 1 in photocatalytic hydrogen production, it is characterized in that, in the photocatalytic reactor, in the N' N'-dimethylformamide/aqueous solution of ascorbic acid, add composite product. Hydrogen catalyst and ruthenium terpyridine chloride are used for photocatalytic hydrogen production under the irradiation of 300W visible light from a xenon lamp.

3. the application of composite hydrogen production catalyst as claimed in claim 2 in photocatalytic hydrogen production, it is characterized in that, N ' N '-dimethylformamide/aqueous solution volume ratio is 1:1, ruthenium terpyridine chloride The added amount of the ascorbic acid is 10 mg, the molar concentration of ascorbic acid in the N'N'-dimethylformamide/aqueous solution system is 300 mmol/L, and the added amount of the composite hydrogen production catalyst is 0.5 mg.