阅读说明：本技术 一种磷化钼催化剂及其制备方法 (Molybdenum phosphide catalyst and preparation method thereof ) 是由 赵学波 姜慧敏 吴炜 闫理停 于 2020-06-22 设计创作，主要内容包括：本发明提供了一种磷化钼催化剂的制备方法,包括以下步骤：(1)含钼的膦酸MOF前驱体的制备：分别称取膦酸有机配体和钼盐溶于一定量的去离子水或者有机溶剂中,充分搅拌得到混合溶液；随后利用水热法或者溶剂法的合成方法合成含钼的膦酸MOF前驱体；(2)取一定量的步骤(1)中的含钼的膦酸MOF前驱体放入管式炉中,在惰性气氛中匀速升温至一定温度,保温一定时间,冷却至室温后得到MoP催化剂。本发明使用含钼的膦酸MOF作为前驱体,通过一步热处理的简单反应方式,即可得到MoP催化剂,制备方法简单易行。本发明还提供了一种磷化钼催化剂,相较于传统负载型催化剂,本发明的MoP催化剂保持了MOF前驱体均一的形貌,且催化活性分布更为均匀。(The invention provides a preparation method of a molybdenum phosphide catalyst, which comprises the following steps: (1) preparation of molybdenum-containing phosphonic acid MOF precursor: respectively weighing phosphonic acid organic ligand and molybdenum salt, dissolving in a certain amount of deionized water or organic solvent, and fully stirring to obtain a mixed solution; then synthesizing a molybdenum-containing phosphonic acid MOF precursor by using a hydrothermal method or a solvent method; (2) and (2) putting a certain amount of the molybdenum-containing phosphonic acid MOF precursor in the step (1) into a tube furnace, uniformly heating to a certain temperature in an inert atmosphere, preserving heat for a certain time, and cooling to room temperature to obtain the MoP catalyst. According to the invention, the MOP catalyst can be obtained by using the molybdenum-containing phosphonic acid MOF as a precursor through a simple reaction mode of one-step heat treatment, and the preparation method is simple and feasible. Compared with the traditional supported catalyst, the MoP catalyst provided by the invention keeps the uniform morphology of the MOF precursor, and the catalytic activity distribution is more uniform.)

1. The preparation method of the molybdenum phosphide catalyst is characterized by comprising the following steps of:

(1) preparation of molybdenum-containing phosphonic acid MOF precursor: respectively weighing phosphonic acid organic ligand and molybdenum salt, dissolving in a certain amount of deionized water or organic solvent, and fully stirring to obtain a mixed solution; then synthesizing a molybdenum-containing phosphonic acid MOF precursor by using a hydrothermal method or a solvent method;

(2) and (2) putting a certain amount of the molybdenum-containing phosphonic acid MOF precursor in the step (1) into a tube furnace, uniformly heating to a certain temperature in an inert atmosphere, preserving heat for a certain time, and cooling to room temperature to obtain the MoP catalyst.

2. The preparation method of the molybdenum phosphide catalyst according to claim 1, wherein the synthesis method of the molybdenum phosphonate MOF precursor in the step (1) is a hydrothermal method.

3. The method of claim 2, wherein the phosphonic acid organic ligand in step (1) is any one of 2,4, 6-trimethylbenzene-1, 3, 5-trimethylenetriasphonic acid ligand, 2,4, 6-trimethylbenzene-1, 3-dimethylene diphosphonic acid, 2, 5-dimethylbenzene-1, 4-dimethylene diphosphonic acid, p-xylylene diphosphonic acid, 2, 5-dimethylbenzene-1, 4-diphosphonic acid, 2, 4-diphosphonic acid trimethylbenzene, methyl phosphonic acid, hydroxyethylidene diphosphonic acid, aminomethyl phosphonic acid, aminotrimethylene phosphonic acid, or zoledronic acid.

4. The method for preparing a molybdenum phosphide catalyst according to claim 2, wherein the molybdenum salt in the step (1) is any one of ammonium molybdate hydrate, sodium molybdate hydrate, potassium molybdate hydrate or zinc molybdate hydrate.

5. The method for preparing a molybdenum phosphide catalyst according to claim 2, wherein the molar ratio of the organic phosphonic acid ligand to the molybdenum salt in the step (1) is 1:5 to 5: 1.

6. The method for preparing a molybdenum phosphide catalyst according to claim 5, wherein the concentration of the organic phosphonic acid ligand in the step (1) is 0.01-1 mol/L; the concentration of the molybdenum salt in the step (1) is 0.01-1 mol/L.

7. The method for preparing a molybdenum phosphide catalyst according to claim 2, wherein the inert atmosphere in the step (2) is any one of argon, nitrogen or helium.

8. The preparation method of the molybdenum phosphide catalyst according to claim 2, wherein in the step (2), the inert atmosphere is heated from room temperature to 600-1100 ℃ at a heating rate of 1-20 ℃/min, and is kept at 600-1100 ℃ for 0.5-12 hours; the flow rate of the introduced inert atmosphere is 1-500 mL/min.

9. The preparation method of the molybdenum phosphide catalyst according to claim 2, wherein the specific preparation steps of the molybdenum-containing phosphonic acid MOF precursor in the step (1) are as follows: respectively weighing phosphonic acid organic ligand and molybdenum salt, dissolving in a certain amount of deionized water, fully stirring to obtain a mixed solution, transferring the mixed solution into a stainless steel autoclave with a polytetrafluoroethylene lining, heating at 120 ℃ for 15-25 h, cooling to room temperature, performing centrifugal separation to obtain supernatant and precipitate, collecting the precipitate, washing the precipitate with deionized water, and drying at 70-80 ℃ for 10h to obtain the molybdenum-containing phosphonic acid MOF precursor.

10. A molybdenum phosphide catalyst, characterized by being prepared by the method for preparing a molybdenum phosphide catalyst as claimed in any one of claims 1 to 9.

Technical Field

The invention relates to the field of materials, in particular to the technical field of nano catalytic materials, and particularly relates to a molybdenum phosphide catalyst and a preparation method thereof.

Background

Noble metals such as platinum and the like have a proper electronic structure and a good catalytic effect, and are widely applied to catalytic processes in the fields of petrochemical industry, organic synthesis, fuel cells, automobiles, electronic industry and the like, but the noble metals have extremely small reserves on the earth, are very expensive, have high application cost and cannot meet the requirements of sustainable development of human beings. People are always searching for new catalytic materials which can replace noble metal catalysts such as platinum and the like.

In a plurality of novel catalytic materials, the electron arrangement outside the molybdenum phosphide nucleus is very similar to that of noble metal platinum, so that the molybdenum phosphide has higher theoretical catalytic activity, is expected to replace metal platinum to be used as a high-efficiency hydrogen evolution reaction catalyst, and has wide application prospect.

Currently, molybdenum phosphide is mostly prepared by oxidizing molybdenum and phosphine (pH)₃) And phosphine or argon-hydrogen mixed atmosphere generated by thermal decomposition of phosphate is reacted and synthesized under the condition of high temperature. The danger coefficient is high in the reaction process, the needed technological parameters are more, the prepared molybdenum phosphide particles have large size and low purity, and the exertion of the catalytic activity of the molybdenum phosphide and the application of the molybdenum phosphide in actual production are greatly limited. For example, chinese patent document CN107999105A provides a method for preparing a molybdenum phosphide hydrogen evolution catalyst with a porous rod-like morphology structure, which comprises the following steps: (1) dissolving ammonium molybdate and ammonium dihydrogen phosphate in deionized water, adding absorbent cotton, and allowing the absorbent cotton to fully absorb the solution to obtain a precursor; (2) the precursor is added with 5% of H₂Keeping the temperature of 700-900 ℃ for 2h in the Ar atmosphere, and cooling to room temperature to obtain the molybdenum phosphide hydrogen evolution catalyst with the rod-shaped porous morphology structure. However, the method needs to add a template to control the morphology of the molybdenum phosphide, the obtained molybdenum phosphide has low purity, rich pore structure and large specific surface area are difficult to obtain, and hydrogen is needed to participate and react at high temperature, so that the method has great danger. Chinese patent document CN108772089A provides a method for preparing a nitrogen-doped, carbon-linked molybdenum phosphide high-performance hydrogen evolution catalyst with a network structure, which comprises the following steps: (1) dissolving ammonium molybdate, ammonium dihydrogen phosphate and urea in deionized water, stirring to obtain a solution, and aging the solution at 80 ℃ under stirring; (2) adding melamine resin foam for adsorption,drying the adsorbed melamine resin foam to obtain a molybdenum phosphide precursor; (3) and calcining the precursor in a nitrogen atmosphere, and naturally cooling to room temperature to obtain the catalyst. However, the metals in the catalyst prepared by the above method are completely dependent on the adsorption of the solution in the melamine foam, and the uniformity, uniformity and stability cannot be guaranteed, and the steps are complicated, so that the application of the catalyst in practical commercialization is greatly limited. Chinese patent document CN108311105A provides a preparation method of a molybdenum phosphide nanoparticle-doped biomass carbon material, which comprises the following steps: (1) immersing the decolored enteromorpha in an ammonium molybdate solution for a period of time, heating the immersed enteromorpha to 350 +/-10 ℃ under the protection of inert gas for pre-carbonization for a period of time, and then heating to 700 +/-10 ℃ for carbonization to obtain an oxide-doped porous carbon composite material MoOx/HPC; (2) and carrying out at least three times of phosphating treatments on MoOx/HPC and sodium hypophosphite to obtain the molybdenum phosphide carbon composite material. However, the method has complicated steps and a plurality of involved reaction processes, and is difficult to prepare the molybdenum phosphide material with uniform nanometer morphology, so that the catalytic activity of the molybdenum phosphide can not be fully exerted.

Therefore, the prior art is in need of improvement.

Disclosure of Invention

The invention aims to provide a molybdenum phosphide catalyst and a preparation method thereof aiming at overcoming the defects of the prior art. Based on the problems, the invention provides a preparation method of a molybdenum phosphide catalyst, which does not need to add a molybdenum source, a phosphorus source and a carbon source respectively, adopts a phosphonic acid metal organic framework of molybdenum as a precursor, and adopts one-step calcination in an inert atmosphere, and is simple and easy to implement; the molybdenum phosphide catalyst provided by the invention has high dispersion, high purity and regular nanometer morphology. In the present invention, the metal-organic framework is abbreviated as "MOF".

The technical scheme of the invention is realized as follows:

a preparation method of a molybdenum phosphide catalyst comprises the following steps:

(1) preparation of molybdenum-containing phosphonic acid MOF precursor: respectively weighing phosphonic acid organic ligand and molybdenum salt, dissolving in a certain amount of deionized water or organic solvent, and fully stirring to obtain a mixed solution; then synthesizing a molybdenum-containing phosphonic acid MOF precursor by using a hydrothermal method or a solvent method;

(2) and (2) putting a certain amount of the molybdenum-containing phosphonic acid MOF precursor in the step (1) into a tube furnace, uniformly heating to a certain temperature in an inert atmosphere, preserving heat for a certain time, and cooling to room temperature to obtain the molybdenum phosphide catalyst. In the present invention, molybdenum phosphide is abbreviated as "MoP".

According to the preparation method, the MOP catalyst is prepared by taking molybdenum-containing phosphonic acid MOF as a single precursor through simple heat treatment of one-step calcination, and the obtained MoP catalyst is a composite material with MoP catalytic active centers uniformly dispersed in a carbon framework. The MoP catalyst prepared by the method has uniform and controllable morphology, and inherits the advantages of rich pore structure and large specific surface area of MOF.

Preferably, the method for preparing a molybdenum phosphide catalyst as described above, wherein the method for synthesizing the molybdenum phosphonate MOF precursor in step (1) is a hydrothermal method.

Preferably, in the preparation method of the molybdenum phosphide catalyst, the phosphonic acid organic ligand in the step (1) is any one of 2,4, 6-trimethylbenzene-1, 3, 5-trimethylbenzene triphosphonic acid ligand, 2,4, 6-trimethylbenzene-1, 3-dimethylene diphosphonic acid, 2, 5-dimethylbenzene-1, 4-dimethylene diphosphonic acid, p-xylylene diphosphonic acid, 2, 5-dimethylbenzene-1, 4-diphosphonic acid, 2, 4-diphosphonic acid trimethylbenzene, methyl phosphonic acid, hydroxy ethylidene diphosphonic acid, aminomethyl phosphonic acid, amino trimethylene phosphonic acid or zoledronic acid.

Preferably, in the preparation method of the molybdenum phosphide catalyst, the molybdenum salt in the step (1) is any one of ammonium molybdate hydrate, sodium molybdate hydrate, potassium molybdate hydrate and zinc molybdate hydrate.

Preferably, the preparation method of the molybdenum phosphide catalyst is as described above, and the molar weight ratio of the organic phosphonic acid ligand to the molybdenum salt in the step (1) is 1:5 to 5: 1.

Preferably, in the preparation method of the molybdenum phosphide catalyst, the concentration of the organic phosphonic acid ligand in the step (1) is 0.01-1 mol/L; the concentration of the molybdenum salt in the step (1) is 0.01-1 mol/L.

Preferably, in the preparation method of the molybdenum phosphide catalyst, the inert atmosphere in the step (2) is any one of argon, nitrogen and helium.

Preferably, in the preparation method of the molybdenum phosphide catalyst, the inert atmosphere in the step (2) is heated from room temperature to 600-1100 ℃ at a heating rate of 1-20 ℃/min, and is kept at 600-1100 ℃ for 0.5-12 hours; the flow rate of the introduced inert atmosphere is 1-500 mL/min.

Preferably, in the preparation method of the molybdenum phosphide catalyst, the specific preparation steps of the molybdenum-containing phosphonic acid MOF precursor in step (1) are as follows: respectively weighing phosphonic acid organic ligand and molybdenum salt, dissolving in a certain amount of deionized water, fully stirring to obtain a mixed solution, transferring the mixed solution into a stainless steel autoclave with a polytetrafluoroethylene lining, heating at 120 ℃ for 15-25 h, cooling to room temperature, performing centrifugal separation to obtain supernatant and precipitate, collecting the precipitate, washing the precipitate with deionized water, and drying at 70-80 ℃ for 10h to obtain the molybdenum-containing phosphonic acid MOF precursor.

Based on the same conception, the invention also provides a molybdenum phosphide catalyst which is prepared by the preparation method of the molybdenum phosphide catalyst.

The invention has the beneficial effects that:

1. according to the invention, the MoP catalyst can be obtained by using molybdenum-containing phosphonic acid MOF as a precursor through a simple reaction mode of one-step heat treatment. Compared with the traditional supported catalyst, the MoP catalyst prepared by the invention keeps the uniform morphology of the MOF precursor, and the distribution of catalytic activity is more uniform.

2. The invention has the advantages of less related process parameters, short flow, low requirement on a reaction device, no need of using harmful or dangerous gases, uniform appearance and high purity of the prepared MoP catalyst, and greatly promotes the exertion of catalytic activity of molybdenum phosphide and application in actual production.

Drawings

FIG. 1 is an X-ray powder diffraction (PXRD) pattern of a MOF precursor of a molybdenum-containing phosphonic acid prepared in example 1;

FIG. 2 is a PXRD pattern of the molybdenum phosphide catalyst prepared in example 1;

FIG. 3 is a Scanning Electron Microscope (SEM) photograph of a molybdenum-containing phosphonic acid MOF precursor prepared in example 1;

FIG. 4 is a Scanning Electron Microscope (SEM) photograph of a molybdenum phosphide catalyst prepared in example 1;

FIG. 5 is a Transmission Electron Microscope (TEM) photograph of a molybdenum phosphide catalyst prepared in example 1;

FIG. 6 is a mapping distribution diagram of the elements of the EDS of the nitrogen-phosphorus co-doped carbon layer coated molybdenum phosphide catalyst prepared in example 1;

FIG. 7 is a plot of linear sweep voltammetry for the catalytic electrochemical Hydrogen Evolution Reaction (HER) for the molybdenum phosphide catalyst prepared in example 1;

FIG. 8 is a PXRD pattern of the molybdenum phosphide catalyst prepared in example 6.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the contents in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

The experimental procedures used in the following examples are all conventional procedures unless otherwise specified.

Materials, reagents and the like used in the following examples are commercially available unless otherwise specified.

A preparation method of a molybdenum phosphide catalyst comprises the following steps:

(1) preparation of molybdenum-containing phosphonic acid MOF precursor: respectively weighing phosphonic acid organic ligand and molybdenum salt, dissolving in a certain amount of deionized water or organic solvent, and fully stirring to obtain a mixed solution; then synthesizing a molybdenum-containing phosphonic acid MOF precursor by using a hydrothermal method or a solvent method;

(2) and (2) putting a certain amount of the molybdenum-containing phosphonic acid MOF precursor in the step (1) into a tube furnace, uniformly heating to a certain temperature in an inert atmosphere, preserving heat for a certain time, and cooling to room temperature to obtain the molybdenum phosphide catalyst.

According to the preparation method, a molybdenum-containing phosphonic acid MOF precursor is prepared under an acidic condition, the pH value is 0-2, in the preparation process of the MoP catalyst, along with the continuous rise of the temperature, coordinate bonds in a crystal structure are gradually broken, Mo and P atoms in a framework are subjected to higher energy along with the additional heat to enter an active state required by reaction, and adjacent Mo and P atoms are combined in situ to form MoP.

According to the invention, the MoP catalyst is prepared by taking molybdenum-containing phosphonic acid MOF as a single precursor through simple heat treatment of one-step calcination, the obtained MoP catalyst is a composite material in which MoP catalytic active centers are uniformly dispersed in a carbon skeleton, the carbon skeleton has good acid-base corrosion resistance, the MoP catalytic active centers can be protected from being corroded easily, and the stability of the catalyst is enhanced. The preparation method of the molybdenum phosphide catalyst provided by the invention can be used for preparing the MoP catalyst with uniform and controllable morphology, inherits the advantage that the MOF has a large specific surface area, has more uniform catalytic activity distribution, and is simple and easy to implement. In the aspect of commerce, the price of the phosphonic acid organic ligand and the molybdenum salt used in the invention is far lower than that of noble metals such as platinum and the like, so that the manufacturing cost of the catalyst is greatly reduced, and the catalyst has strong practical value and application prospect.

Preferably, the method for preparing a molybdenum phosphide catalyst as described above, wherein the method for synthesizing the molybdenum phosphonate MOF precursor in step (1) is a hydrothermal method. In the invention, the hydrothermal method can be understood as that phosphonic acid organic ligand and molybdenum salt are respectively weighed and dissolved in a certain amount of deionized water, and the mixture is fully stirred to obtain a mixed solution; then synthesizing a molybdenum-containing phosphonic acid MOF precursor by using a hydrothermal synthesis method; the solvent method can be understood as that phosphonic acid organic ligand and molybdenum salt are respectively weighed and dissolved in a certain amount of organic solvent, and the mixed solution is obtained by fully stirring; and then synthesizing a molybdenum-containing phosphonic acid MOF precursor by using a synthesis method of a solvent method. According to the invention, the hydrothermal method is simple to operate, the reaction condition is mild, the method is economical, and the particle size and morphology of the prepared MoP catalyst can be effectively regulated and controlled.

Preferably, in the preparation method of the molybdenum phosphide catalyst, the phosphonic acid organic ligand in the step (1) is any one of 2,4, 6-trimethylbenzene-1, 3, 5-trimethylbenzene triphosphonic acid ligand, 2,4, 6-trimethylbenzene-1, 3-dimethylene diphosphonic acid, 2, 5-dimethylbenzene-1, 4-dimethylene diphosphonic acid, p-xylylene diphosphonic acid, 2, 5-dimethylbenzene-1, 4-diphosphonic acid, 2, 4-diphosphonic acid trimethylbenzene, methyl phosphonic acid, hydroxy ethylidene diphosphonic acid, aminomethyl phosphonic acid, amino trimethylene phosphonic acid or zoledronic acid. More preferably, the phosphonic acid organic ligand in the step (1) is a 2, 5-dimethylbenzene-1, 4-diphosphonic acid ligand or a 2,4, 6-trimethylbenzene-1, 3, 5-trimethylenetriasphonic acid ligand; most preferably, the phosphonic acid organic ligand is a 2, 5-dimethylbenzene-1, 4-diphosphonic acid ligand.

Preferably, in the preparation method of the molybdenum phosphide catalyst, the molybdenum salt in the step (1) is any one of ammonium molybdate hydrate, sodium molybdate hydrate, potassium molybdate hydrate and zinc molybdate hydrate. Most preferably, the molybdenum salt in step (1) is sodium molybdate hydrate.

Preferably, the preparation method of the molybdenum phosphide catalyst is as described above, and the molar weight ratio of the organic phosphonic acid ligand to the molybdenum salt in the step (1) is 5:1 to 1: 5. If the molar ratio of the organic phosphonic acid ligand to the molybdenum salt in step (1) is less than 1:5, too little product is formed and separation is difficult, and if the molar ratio is more than 5:1, the excessive ligand is difficult to be sufficiently dissolved and reacted, resulting in waste of raw materials. Most preferably, the molar weight ratio of the phosphonic acid organic ligand to the molybdenum salt in step (1) is 1: 2.

Preferably, in the preparation method of the molybdenum phosphide catalyst, the concentration of the organic phosphonic acid ligand in the step (1) is 0.01-1.0 mol/L; the concentration of the molybdenum salt in the step (1) is 0.01-1.0 mol/L. Most preferably, the concentration of the phosphonic acid organic ligand in the step (1) is 0.031 mol/L; most preferably, the concentration of the molybdenum salt in the step (1) is 0.062 mol/L.

Preferably, in the preparation method of the molybdenum phosphide catalyst, the inert atmosphere in the step (2) is any one of argon, nitrogen and helium. Most preferably, the inert atmosphere in step (2) is nitrogen. Compared with the reaction which needs hydrogen to participate and prepares the catalyst at higher temperature in the prior art, the method reduces the danger.

Preferably, in the preparation method of the molybdenum phosphide catalyst, the inert atmosphere in the step (2) is heated from room temperature to 600-1100 ℃ at a heating rate of 1-20 ℃/min, and is kept at 600-1100 ℃ for 0.5-12 hours; the flow rate of the introduced inert atmosphere is 1-500 mL/min. More preferably, the temperature of the inert atmosphere in the step (2) is raised from room temperature to 800-1100 ℃ at a temperature raising rate of 1-20 ℃/min, and the inert atmosphere is kept at the temperature of 800-1100 ℃ for 2-3 hours; the flow rate of the introduced inert atmosphere is 20-100 mL/min. Most preferably, the inert atmosphere in the step (2) is heated from room temperature to 900 ℃ at a heating rate of 20 ℃/min, and is kept at 900 ℃ for 2 hours; the flow rate of the inert gas atmosphere introduced was 30 mL/min.

Preferably, in the preparation method of the molybdenum phosphide catalyst, the specific preparation steps of the molybdenum-containing phosphonic acid MOF precursor in step (1) are as follows: respectively weighing phosphonic acid organic ligand and molybdenum salt, dissolving in a certain amount of deionized water, fully stirring to obtain a mixed solution, transferring the mixed solution into a stainless steel autoclave with a polytetrafluoroethylene lining, heating at 120 ℃ for 15-25 h, preferably at 120 ℃ for 15h, cooling to room temperature, performing centrifugal separation to obtain a supernatant and a precipitate, collecting the precipitate, washing the precipitate with deionized water, and drying at 70-80 ℃ for 10h, preferably at 80 ℃ for 10h to obtain a molybdenum-containing phosphonic acid MOF precursor.

Based on the same conception, the invention also provides a molybdenum phosphide catalyst which is prepared by the preparation method of the molybdenum phosphide catalyst.

For further understanding of the present application, the following will specifically describe a molybdenum phosphide catalyst and a preparation method thereof provided by the present invention with reference to examples.